CA1184249A - High capacity digital mobile radio system - Google Patents
High capacity digital mobile radio systemInfo
- Publication number
- CA1184249A CA1184249A CA000389669A CA389669A CA1184249A CA 1184249 A CA1184249 A CA 1184249A CA 000389669 A CA000389669 A CA 000389669A CA 389669 A CA389669 A CA 389669A CA 1184249 A CA1184249 A CA 1184249A
- Authority
- CA
- Canada
- Prior art keywords
- signal
- mobile
- base station
- base
- retransmission
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B7/00—Radio transmission systems, i.e. using radiation field
- H04B7/24—Radio transmission systems, i.e. using radiation field for communication between two or more posts
- H04B7/26—Radio transmission systems, i.e. using radiation field for communication between two or more posts at least one of which is mobile
- H04B7/2643—Radio transmission systems, i.e. using radiation field for communication between two or more posts at least one of which is mobile using time-division multiple access [TDMA]
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B7/00—Radio transmission systems, i.e. using radiation field
- H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
- H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B7/00—Radio transmission systems, i.e. using radiation field
- H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
- H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
- H04B7/08—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the receiving station
- H04B7/0837—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the receiving station using pre-detection combining
- H04B7/084—Equal gain combining, only phase adjustments
Abstract
A HIGH CAPACITY DIGITAL
MOBILE RADIO SYSTEM
Abstract of the Disclosure The present invention relates to a mobile radio base station capable of communicating with a large number of mobile stations by implementing space diversity and time-division retransmission techniques in a digital communication system. The digital base station contains a plurality of antenna elements and a plurality of retransmission branches associated in a one-to-one relationship. When the base station receives a digital communication signal from a mobile station, each antenna element receives the signal with a unique random phase due to the effects of the environment on signal transmission.
The signal is then processed through the plurality of retransmission branches, where each branch adapts to compensate for the random phase of the signal received by its associated antenna element. Conversely, when the base station transmits a signal back to the mobile station, each retransmission branch adds the conjugate of its associated random phase to the signal to be transmitted, allowing the environment to "undo" the effect of the conjugate random phase so that the signals transmitted by the plurality of antenna elements will arrive coherently at the mobile station.
MOBILE RADIO SYSTEM
Abstract of the Disclosure The present invention relates to a mobile radio base station capable of communicating with a large number of mobile stations by implementing space diversity and time-division retransmission techniques in a digital communication system. The digital base station contains a plurality of antenna elements and a plurality of retransmission branches associated in a one-to-one relationship. When the base station receives a digital communication signal from a mobile station, each antenna element receives the signal with a unique random phase due to the effects of the environment on signal transmission.
The signal is then processed through the plurality of retransmission branches, where each branch adapts to compensate for the random phase of the signal received by its associated antenna element. Conversely, when the base station transmits a signal back to the mobile station, each retransmission branch adds the conjugate of its associated random phase to the signal to be transmitted, allowing the environment to "undo" the effect of the conjugate random phase so that the signals transmitted by the plurality of antenna elements will arrive coherently at the mobile station.
Description
4~
A HIGH CAPACITY DIGITAL
MOBILE RADIO SYSTEM
The present invention relates to a high capacity digital mobile radio system, and more particularly, to a digital mobile radio system which employs the techniques of space diversity and time division retransmission to form a system where all the required adaptive signal processing is performed at baseband at the base station.
Radio signals are always subject to fading due to natural phenomena, but when one s~ation of a radio link is a mobile station, hereafter referred to as a mobile, and moving at variable speeds through various and unpredictable environments, the situation is seriously compounded. In such a situation there are two types of received signal level variations observed. First there is the rapid multipath Rayleigh type fading due to different path cancellations and then there is a slower variation in the mean signal level due to gross path variations from building shadowing and other terrain effects. Both types of signal level variations are functions of the speed of the mobile.
Space diversity has been found to provide one of the best solutions to mobile radio fading. One analog mobile radio system employing space diversity is disclosed in U. S. Patent 3,693,088 issued to A. J. Rustako, Jr., et al on September 19, 1972. There, diversity transmission from the base to the mobile is provided by switching between two spaced base transmitting antennas on command from the mobile. More particularly, means are provided at the mobile station for determining when the signal level then being received by the mobile from a given base sta~ion antenna falls below a level which depends upon the nature of the fade itself. ~!hen this occurs, the mobile transmits an out of message band signal back to the base whi~h causes the base to switch to a different antenna. ~ ~
A similarly operated cligital mobile radio system is disclosec1 in U. S. Patent ~,057,758 issued to T. Hattori et al on November 8, 1977. There,a plurality of receiving antenna systems are switched at a constant frequency higher than the signaling rate of the digital baseband signal but less than the frequency shift width of the frequency modulated wave or less than a product of the maximum phase shift of the phase modulated wave and the si~naling rate, so that average-power dispersion in a si~nal element oE the digital baseband signal received at the receivinq antenna system is effectively compressed~ Alternatively, the plurality of antennas may be transmitting antennas which are simultaneously switched to achieve compression of average power dispersion in the baseband signal ele~ents.
The above-described analog and digital systems, however, require the flow of feedback information to control antenna switching, necessitating the use of comple~
and expensive apparatus at the mobile. Co-phasing of the antenna elements in an analog system has been found to provide transmission from a diversity station by means of a multi-element array, as disclosed in U. S. Patent 3,717,814 issued to M. J. Gans on February 20, 1973. Phase corrected intelligence signals are transmitted from a diversity array transmitter and received in-phase at a monochannel receiver. An individual pilot associated with each diversity branch and frequency separated from the pilots of the other branches is received along with the in-phase intelligence. All of the pilots are fed back, as part of the return modulation, to the diversity transmitter where they are used to establish the proper phase correction for the modulated intelligence transmission. ~owever, the signal processing at the diversity transmitter as taught by Gans occurs at i. f., thus requiring the use of expensive RF hardware to achieve relatively accurate phase correction.
The problem remaining in the prior art is to provide a mobile radio system that does not require the excessive analog circuitry employed with analog systems and which is capable of higher capacity than the simple diversity associated with prior art digital systems.
The problem remaining in the prior art has been solved in accordance with the present invention, which relates to a high capacity digital mobile radio system, and more particularly, to a digital mobile radio system which employs the techniques of space diversity and time-divisioll retransmission to form a system where all the required adaptive signal processing is performed at baseband at a base station location.
In accordance with an aspect of the invention there is provided a mobile radio base station employing space diversity and time-division retransmission comprising a plurality of M antenna elements for operating in a space diversity mode capable of receiving a mobile-to-base communication signal from a remote station and transmitting a base-to-mobile communica~ion signal to said remote station; a plurality of M retransmission branches associated in a one-to-one relationship with said plurality of M antenna elements and capable of operating in either one of a transmitting mode or a receiving mode, each retransmission branch when operating in its receiving mode being capable of compensating for the incominq random phase associated with said mobile-to-base communication signal and subtracting said random phase therefrom, and when operating in its transmitting mode being capable of adding said random phase to said base-to~mobile communi~
cation signal; combining means coupled to the outputs of said plurality of M retransmission branches when operating in their receiving mode and capable of combining said output signals of said branches to form a coherent output siynal, and input means capable of applying an input baseband signal to said plurality of retransmission branches when operating in their transmitting mode allowing k~
said plurality of M antenna elements to transmit said base-to-mobile communication signal characterized in that the base station is capable of receiving and transmitting digital communication signals, wherein each retransmission branch includes means capable of both down-converting the mobile-to-base communication signal to a baseband representation thereof and up-converting the input baseband signal to a phased base-to-mobile communication signal.
It is an aspect of the present invention to employ digital co-phasing techniques at the base station of a digital cellular mobile radio system in conjunction with the above-mentioned space diversity and retransmission properties to overcome the mobile radio transmission-related problems of intercell interface, shadow fading and Rayleigh fadings.
Other and further aspects of the present invention will become apparent during the course of the following description and by reference to the accompanying drawings.
Referring now to the drawings in which like numerals represent like parts in several views:
FIG. 1 iLlustrates the transmission of a signal from a mobile to a base station including a plurality of antenna elements and the random phase associated with each element in accordance with the present invention;
FIG. 2 illustrates the co-phased transmission of signals from the base station back to the mobile of FIG.
1, where the signals are pre-phased at the base so that they will be coherent upon reception by the mobile in accordance with the present invention;
FIG. 3 illustrates an exemplary signaling frame including two reference intervals and two message intervals for implementing time-division retransmission between a mobile and a base station as illustrated in FIGS. 1 and 2, in accordance with the present invention;
FIG. 4 contains a detailed embodiment of an exemplary diversity branch of the plurality of branches employed at the base station in association wi-th the present invention.
Mechanical constraints, cost, and main-tenance requirements all suggest that the equipment employed at the mobile stations of a mobile radio system should be kept as simple as possible. This goal has been achieved in accordance with the present invention with time-division retransmission, while retaining the advantages of space diversity processing. Instead of using a different frequency for each direction of communication, two-way communication between mobile and base station is conducted on a single time-shared channel. These basic principles of operation of the present invention may be understood by reference to FIGS. 1 and 2, which illustrate mobile-to-base and base-to-mobile communication, respectively.
In the mobile-to-base communication scheme illustrated in FIG. 1, a mobile station 10 containing a single antenna element 12 transmits a message to a base station 14 which contains a plurality of antenna elements 161, 162, .~. 16M, where the plurality of antenna elements are employed to provide for space diversity at base station 14. The detailed structure of the message transmitted from mobile station 10 to base station 14 will be explained in greater detail hereinafter in association with FIG. 3, but in general, mobile radio reception is characterized by large fluctuations in received signal power, P, at base station 14 as mobile 10 travels along a street. This variability can be modeled as the product of three factors, as shown by P(r) = ¦r¦ ~nS(r)R2(r) (1) where r is the position vector denoting the location of mobile 10 relative to base station 14. The first factor, J~
¦r¦-n, represents the general reduction in signal strength as mobile 10 recedes from base station 14. In free space, n = 2, hut in an urban environment it can be shown that _ is in the range of 3 to 4. The second factor, S(r), represents shadow fadings, which is primarily the result of blockage due to large objects such as buildings and hills.
It has been found by measurement of S in several cities that it is approximately a log-normal random variable. The third factor, R2(r), in equation (1) represents Rayleigh fading, a phenomenon caused by the random addition of signals arriving at an antenna via multiple paths. The amplitude of the received envelope, R, may be modeled as a random variable with a probability density function p(R) = (2R)e-R2 (2, Therefore, in accordance with the above-described random properties of signal strength, such as shadow fading and Rayleigh fading associated with transmission from mobile-to-base, each signal received a-t a separate antenna element 1~1 through 16M located at base station 14 will possess an independent random phase, ~1 through respectively. As will be described in greater detail hereinafter, each antenna element processes its associated received signal in its associated retransmission branch 18 through 18~, respectively, to delete the random phase so that the M received signals may be ad~ed coherently in combiner 20 at base station 14. In addition to adjusting the phases of the M received signals, each retransmission branch 181 through 18M also functions to adjust the respective ~eight of the received signal passing therethrough to achieve the optimum net signal-to-interference ratio (SIR) at base station 14. For e~ual power Gaussian interference at each retransmission branch, it can be shown that the best net SIR is achieved with a maximal-ratio combiner 20. Synchronization of reception of the plurality of antenna elements is achieved by employing a clock 31 The reverse transmisslon operation is illustrated in FIG. 2, where the message to be transmitted back to mobile 10 rom base station lq originates from a message source 21 and is applied via cloclc 31 as an input to each retransmission branch 18]-l~M. The base-to-mobile message siqnal is adapted by applying thereto the conjugate (negative) of the above-described random phases at each retransmission branch 1~ M associated with antenna elements 161 - 16M, respectively. More specifically, retransmission branch lal applied a phase shift of -~1 to the base-to-mohile message signal, retransmission branch 182 a phase shift of -~2~ and so on, with retransmission branch 18M applying a phase shift of -~M to the base-to-mobile message signal. These excitation phases -~1 through -~M exactly compensate for the different phase delays experienced by the base-to-mobile message signals so that the transmission medium "undoes" the conjugate phase shift applied at each retransmission branch, thereby allowing the M signals to be received coherently at mobile 10.
Therefore, since reception at mobile 10 will always be coherent as shown in the vector diagram of FIG~ 2 associated with mobile 10, the receiver employed by the mobi]e may be extremely simple in form and yet provide adequate reception of the signal transmitted by base station lq.
A single frame in an exemplary mobile-to-base and base-to-mobile transmission in accordance with the time-division retransmission properties of the present invention is illustrated in FIG. 3. The basic frame consists of four time intervals including two reference intervals and -two message intervals. Starting at time T = 0, and assuming that the base station and all mobiles communicating with that base station are synchronized, a carrier burst is transmitted from the mobile 10 to the base station 14 during a reference interval RIl. The carrier burst transmitted by the mobile 10 enables the base station 14 to identify the mobile and co-phase its antenna elements accordingly. The burst repetition rate is chosen to be rapid enough to ensure that the multipath conditions do not change significantly during the subsequent message transmission.
During the carrier burst transmission it is important that interference from unwanted mobiles be minimized so that the co-phasing of the antenna ele~ents can be performed accurately. This minimization of interference may be accomplished, for example, by a time-division reference transmission method or a frequency offset reference transmission method. An illustration of a particular time-division scheme is included in the expanded version of RIl included in FIG. 3. Here, the reference interval is divided into a plurality of unique time slots, labeled in this example, ~ through H, which are associated in a one--to-one relationship with eight separate pairs of communicating mobile and base stations, which are capable of interfering with each other. Therefore, if an exemplary base station is adapted to receive communication during, for example, a reference sub-interval ~, the mobile desiring to communicate with that base will transmit its reference signal during the same sub-interval B. Thus, since each base station gates its receiver "on" only during its pre-assigned time slot in the reference interval, interference from other mobiles will be minimal. In a frequency-offset reference transmission scheme, each mobile and corresponding base station in a particular area is assigned a unique offset frequency which is a multiple (n, +1, ~2, +3~ of a low frequency ~ = 2~/T, where T is the duration of reference interval RIl. During the reference interval, the transmitting frequency of a mobile and the local oscillator at the base station are shifted from the carrier frequency ~c by the offset assigned to its associated base station. The use of different reference frequencies allows the base station to select the desired reference signal and suppress the interference. The choice of ~ = 2~/T allows the various reference signals to be orthogonal; unwanted signals do not contribute to the co-phasing operation o~ the base station.
Once the base station identifies the mobile by its associated reference signal, the mobile then transmits its message to the base durin~ message interval MIl. For purposes of illustration only, to achieve, for example, a 32 kbit/sec transmission rate, which is necessary for speech transmission, 6~ bits must be sent during the message interval of, in this example, 790 ~sec, implying a baud rate of 81 kbaud/sec. This exemplary message interval of 790 ~sec was determined by assuming that the entire mobile-to-base transmission interval is 1 msec, with 210 ~sec reserved for reference interva] RIl. Depending on filtering and tolerable dB penalty, this exemplary rate would require 80-120 kHz bandwidth with binary PSK
modulation.
In a cellular mobile radio system employing the above-described space diversity properties, co--channel interference from unwanted mobiles is effectively rejected and the same frequency channel may therefore be used in cells much closer together than is the case with existing analog systems. Therefore, fewer distinct channel sets are required and each cell is able to occupy a larger share of the total system bandwidth. Thus, for the example above, the number of mobiles that can be served in ~he ~O-MHz bandwidth of the 850 M~z mobile radio band by employing the digital transmission techniques of the present inve~ltion is approximately 130. This high capacity of 130 mobiles/base illustrates the advantage of the digital system of the present invention over existing analog systems which have a much smaller capacity.
At the completion of message interval MIl the mobile transmits a second carrier burst during reference interval RI2 to update the location information of the mobile with respect to the base, where the second carrier burst may be either one of the time-division or frequency-~t~
offset forms described hereinbefore. Once the locationinformation has been updated, the message from the base to the mobile is transmitted during message interval MI2.
Like the time interval associated with RIl and MIl, the reception of location update during RI~ and base-to-mobile transmission during MI2 also occurs, in this example, during a 1 msec period. Assuming, for example, that RI2 is also 210 ~sec in duration, the same baud rate of 81 kbaud/sec is associated with transmission during MI2.
At the end of 2 msec, therefore, an entire message cycle has occurred and the entire process starts again.
The signal processing circuitry for an exernplary antenna element 16j and its associated retransmission branch 18j located at a base station formed in accordance with the present invention is illustrated in FIG. 4 and may be analyzed in conjunction with the timing sequence illustrated in FIG. 3. In the following discussion, any reference to the time-division or frequency-offset signaling schemes will be omitted for the sake of clarity, 2n however, the use of these schemes to avoid co-channel interference is an obvious extension of the principles described hereinafter.
The reference signal received at an exemplary antenna element 16j from a mobile (not shown) is of the ~5 form Rjcos(~ct ~ ~j), where ~c is the carrier frequency, R
is the Rayleigh amplitude and ~j is the previously described random phase. Although both Rj and ~j are functions of time, they vary slowly and may be considered as remaining constant during reference interval RIl.
The reference signal received by an antenna element 16j passes through a circulator 17 and into a switch 19, where switch 19 controls the transmi~ (*) and receive (R) modes of operation of retransmission branch l~j. During reference interval RIl message interval MI
and reference interval RI2, switch 19 remains in its "receive" position. After passing through switch 19 the reference signal is transmitted along two distinct signal ~t~'$~ ~
paths of retransmission branch 18j, an I-rail and a Q-rail.
The signal on the I-rail is applied as one input of a mixer 23, where the other input to mixer 23 is a local oscillator 22 which generates a cos~ct signal. The output of mixer 23 is one quadrature component of the reference signal Rjcos(~ct ~ ), specifically, Rjcos ~j. In a like manner, the signal on the Q-rail is applied to one input of a mixer 25, where the remaining input to mixer 25 is a local oscillator 29 which generates a sin~ct signal. The output of mixer 25 is, therefore, the remaining quadrature component of reference signal Rjcos(~ct + ~j), specifically, -Rjsin~j.
Phasing of antenna element 16j to receive a message signal possessing random phase ~j is accomplished by passlng the down-converted signals through separate reference coefficient generator circuits via a switch 27, the signal Rjcos~j through a reference coefficient generator circuit 26 and the signal -Rjsin~j through a reference coefficient generator circuit 28. Generators 26 and 28 produce reference coefficients ~Rjcos~j and -Rjsin~j, respectively, where for the above-described time-division scheme reference coefficient generators 26 and 28 can be sample-and-hold circuits, which samples the carrier burst transmitted from a mobile during its pre~
assigned sub-interval, as described hereinbefore. In accordance with the frequency-offset scheme, reference coefficient generators 26 and 28 may be of the form of well-known integrator circuits which integrate over the entire reference interval. Thus, reference coefficients Rjcos~j and -~Rjsin~j modify the signal received by antenna element 16j by phasing element 16j to receive a message signal with random phase ~j, where ~ is a constant generated during the reference coefficient process.
At the completion of reference interval RIl, a switch 27 is activated from a first to a second position by a clock signal from clock 31 to switch the outputs of mixers 23 and 25 ~rom the inputs of reference coef~icient generators 26 and 28 to the inputs to a pair of multipliers 30 and 32. In FIG. 4, reference coefficient generator 26 has its output coupled to an input to multiplier 30 and likewise, reference coefficient generator 28 has its output coupled to an input to multiplier 320 The message transmitted from mobile-to-base during message interval MIl comprises, for example, 64 bits, where the kth bit and accompanyinq interference may be written as IsRicos(~ct-~i)+Iccos~ccos~ct-~Issin~ct~ t3) where Ak = +l represents the transmitted bit and Ic and Is are Gaussian random variables with zero mean and variance s2. The message bit is down-converted in retransmission branch 18j through mixers 23 and 25 in a like manner as the above-described reference signal to form its quadrature components. The down-converted quadrature components of the kth bit appearing at the outputs of mixers 23 and 25 are then applied via switch 27 as inputs to multipliers 30 and 32, respectively, where the remaining inputs to the multipliers are its associated reference coefficient appearing at the outputs of reference coefficient generators 26 and 28, respectively. Specifically, the down-converted message bit on the I-rail from mixer 23 and reference coefficient ~Rjcos3j from reference coefficient generator 26 are applied as inputs to a multiplier 30, and the down-converted message bit on the Q-rail from mixer 25 and reference coefficient ~ Rjsin~j from reference coefficient generator 28 are applied as inputs to a multiplier 32. The output signals of multipliers 30 and 32 may be represented respectively byo
A HIGH CAPACITY DIGITAL
MOBILE RADIO SYSTEM
The present invention relates to a high capacity digital mobile radio system, and more particularly, to a digital mobile radio system which employs the techniques of space diversity and time division retransmission to form a system where all the required adaptive signal processing is performed at baseband at the base station.
Radio signals are always subject to fading due to natural phenomena, but when one s~ation of a radio link is a mobile station, hereafter referred to as a mobile, and moving at variable speeds through various and unpredictable environments, the situation is seriously compounded. In such a situation there are two types of received signal level variations observed. First there is the rapid multipath Rayleigh type fading due to different path cancellations and then there is a slower variation in the mean signal level due to gross path variations from building shadowing and other terrain effects. Both types of signal level variations are functions of the speed of the mobile.
Space diversity has been found to provide one of the best solutions to mobile radio fading. One analog mobile radio system employing space diversity is disclosed in U. S. Patent 3,693,088 issued to A. J. Rustako, Jr., et al on September 19, 1972. There, diversity transmission from the base to the mobile is provided by switching between two spaced base transmitting antennas on command from the mobile. More particularly, means are provided at the mobile station for determining when the signal level then being received by the mobile from a given base sta~ion antenna falls below a level which depends upon the nature of the fade itself. ~!hen this occurs, the mobile transmits an out of message band signal back to the base whi~h causes the base to switch to a different antenna. ~ ~
A similarly operated cligital mobile radio system is disclosec1 in U. S. Patent ~,057,758 issued to T. Hattori et al on November 8, 1977. There,a plurality of receiving antenna systems are switched at a constant frequency higher than the signaling rate of the digital baseband signal but less than the frequency shift width of the frequency modulated wave or less than a product of the maximum phase shift of the phase modulated wave and the si~naling rate, so that average-power dispersion in a si~nal element oE the digital baseband signal received at the receivinq antenna system is effectively compressed~ Alternatively, the plurality of antennas may be transmitting antennas which are simultaneously switched to achieve compression of average power dispersion in the baseband signal ele~ents.
The above-described analog and digital systems, however, require the flow of feedback information to control antenna switching, necessitating the use of comple~
and expensive apparatus at the mobile. Co-phasing of the antenna elements in an analog system has been found to provide transmission from a diversity station by means of a multi-element array, as disclosed in U. S. Patent 3,717,814 issued to M. J. Gans on February 20, 1973. Phase corrected intelligence signals are transmitted from a diversity array transmitter and received in-phase at a monochannel receiver. An individual pilot associated with each diversity branch and frequency separated from the pilots of the other branches is received along with the in-phase intelligence. All of the pilots are fed back, as part of the return modulation, to the diversity transmitter where they are used to establish the proper phase correction for the modulated intelligence transmission. ~owever, the signal processing at the diversity transmitter as taught by Gans occurs at i. f., thus requiring the use of expensive RF hardware to achieve relatively accurate phase correction.
The problem remaining in the prior art is to provide a mobile radio system that does not require the excessive analog circuitry employed with analog systems and which is capable of higher capacity than the simple diversity associated with prior art digital systems.
The problem remaining in the prior art has been solved in accordance with the present invention, which relates to a high capacity digital mobile radio system, and more particularly, to a digital mobile radio system which employs the techniques of space diversity and time-divisioll retransmission to form a system where all the required adaptive signal processing is performed at baseband at a base station location.
In accordance with an aspect of the invention there is provided a mobile radio base station employing space diversity and time-division retransmission comprising a plurality of M antenna elements for operating in a space diversity mode capable of receiving a mobile-to-base communication signal from a remote station and transmitting a base-to-mobile communica~ion signal to said remote station; a plurality of M retransmission branches associated in a one-to-one relationship with said plurality of M antenna elements and capable of operating in either one of a transmitting mode or a receiving mode, each retransmission branch when operating in its receiving mode being capable of compensating for the incominq random phase associated with said mobile-to-base communication signal and subtracting said random phase therefrom, and when operating in its transmitting mode being capable of adding said random phase to said base-to~mobile communi~
cation signal; combining means coupled to the outputs of said plurality of M retransmission branches when operating in their receiving mode and capable of combining said output signals of said branches to form a coherent output siynal, and input means capable of applying an input baseband signal to said plurality of retransmission branches when operating in their transmitting mode allowing k~
said plurality of M antenna elements to transmit said base-to-mobile communication signal characterized in that the base station is capable of receiving and transmitting digital communication signals, wherein each retransmission branch includes means capable of both down-converting the mobile-to-base communication signal to a baseband representation thereof and up-converting the input baseband signal to a phased base-to-mobile communication signal.
It is an aspect of the present invention to employ digital co-phasing techniques at the base station of a digital cellular mobile radio system in conjunction with the above-mentioned space diversity and retransmission properties to overcome the mobile radio transmission-related problems of intercell interface, shadow fading and Rayleigh fadings.
Other and further aspects of the present invention will become apparent during the course of the following description and by reference to the accompanying drawings.
Referring now to the drawings in which like numerals represent like parts in several views:
FIG. 1 iLlustrates the transmission of a signal from a mobile to a base station including a plurality of antenna elements and the random phase associated with each element in accordance with the present invention;
FIG. 2 illustrates the co-phased transmission of signals from the base station back to the mobile of FIG.
1, where the signals are pre-phased at the base so that they will be coherent upon reception by the mobile in accordance with the present invention;
FIG. 3 illustrates an exemplary signaling frame including two reference intervals and two message intervals for implementing time-division retransmission between a mobile and a base station as illustrated in FIGS. 1 and 2, in accordance with the present invention;
FIG. 4 contains a detailed embodiment of an exemplary diversity branch of the plurality of branches employed at the base station in association wi-th the present invention.
Mechanical constraints, cost, and main-tenance requirements all suggest that the equipment employed at the mobile stations of a mobile radio system should be kept as simple as possible. This goal has been achieved in accordance with the present invention with time-division retransmission, while retaining the advantages of space diversity processing. Instead of using a different frequency for each direction of communication, two-way communication between mobile and base station is conducted on a single time-shared channel. These basic principles of operation of the present invention may be understood by reference to FIGS. 1 and 2, which illustrate mobile-to-base and base-to-mobile communication, respectively.
In the mobile-to-base communication scheme illustrated in FIG. 1, a mobile station 10 containing a single antenna element 12 transmits a message to a base station 14 which contains a plurality of antenna elements 161, 162, .~. 16M, where the plurality of antenna elements are employed to provide for space diversity at base station 14. The detailed structure of the message transmitted from mobile station 10 to base station 14 will be explained in greater detail hereinafter in association with FIG. 3, but in general, mobile radio reception is characterized by large fluctuations in received signal power, P, at base station 14 as mobile 10 travels along a street. This variability can be modeled as the product of three factors, as shown by P(r) = ¦r¦ ~nS(r)R2(r) (1) where r is the position vector denoting the location of mobile 10 relative to base station 14. The first factor, J~
¦r¦-n, represents the general reduction in signal strength as mobile 10 recedes from base station 14. In free space, n = 2, hut in an urban environment it can be shown that _ is in the range of 3 to 4. The second factor, S(r), represents shadow fadings, which is primarily the result of blockage due to large objects such as buildings and hills.
It has been found by measurement of S in several cities that it is approximately a log-normal random variable. The third factor, R2(r), in equation (1) represents Rayleigh fading, a phenomenon caused by the random addition of signals arriving at an antenna via multiple paths. The amplitude of the received envelope, R, may be modeled as a random variable with a probability density function p(R) = (2R)e-R2 (2, Therefore, in accordance with the above-described random properties of signal strength, such as shadow fading and Rayleigh fading associated with transmission from mobile-to-base, each signal received a-t a separate antenna element 1~1 through 16M located at base station 14 will possess an independent random phase, ~1 through respectively. As will be described in greater detail hereinafter, each antenna element processes its associated received signal in its associated retransmission branch 18 through 18~, respectively, to delete the random phase so that the M received signals may be ad~ed coherently in combiner 20 at base station 14. In addition to adjusting the phases of the M received signals, each retransmission branch 181 through 18M also functions to adjust the respective ~eight of the received signal passing therethrough to achieve the optimum net signal-to-interference ratio (SIR) at base station 14. For e~ual power Gaussian interference at each retransmission branch, it can be shown that the best net SIR is achieved with a maximal-ratio combiner 20. Synchronization of reception of the plurality of antenna elements is achieved by employing a clock 31 The reverse transmisslon operation is illustrated in FIG. 2, where the message to be transmitted back to mobile 10 rom base station lq originates from a message source 21 and is applied via cloclc 31 as an input to each retransmission branch 18]-l~M. The base-to-mobile message siqnal is adapted by applying thereto the conjugate (negative) of the above-described random phases at each retransmission branch 1~ M associated with antenna elements 161 - 16M, respectively. More specifically, retransmission branch lal applied a phase shift of -~1 to the base-to-mohile message signal, retransmission branch 182 a phase shift of -~2~ and so on, with retransmission branch 18M applying a phase shift of -~M to the base-to-mobile message signal. These excitation phases -~1 through -~M exactly compensate for the different phase delays experienced by the base-to-mobile message signals so that the transmission medium "undoes" the conjugate phase shift applied at each retransmission branch, thereby allowing the M signals to be received coherently at mobile 10.
Therefore, since reception at mobile 10 will always be coherent as shown in the vector diagram of FIG~ 2 associated with mobile 10, the receiver employed by the mobi]e may be extremely simple in form and yet provide adequate reception of the signal transmitted by base station lq.
A single frame in an exemplary mobile-to-base and base-to-mobile transmission in accordance with the time-division retransmission properties of the present invention is illustrated in FIG. 3. The basic frame consists of four time intervals including two reference intervals and -two message intervals. Starting at time T = 0, and assuming that the base station and all mobiles communicating with that base station are synchronized, a carrier burst is transmitted from the mobile 10 to the base station 14 during a reference interval RIl. The carrier burst transmitted by the mobile 10 enables the base station 14 to identify the mobile and co-phase its antenna elements accordingly. The burst repetition rate is chosen to be rapid enough to ensure that the multipath conditions do not change significantly during the subsequent message transmission.
During the carrier burst transmission it is important that interference from unwanted mobiles be minimized so that the co-phasing of the antenna ele~ents can be performed accurately. This minimization of interference may be accomplished, for example, by a time-division reference transmission method or a frequency offset reference transmission method. An illustration of a particular time-division scheme is included in the expanded version of RIl included in FIG. 3. Here, the reference interval is divided into a plurality of unique time slots, labeled in this example, ~ through H, which are associated in a one--to-one relationship with eight separate pairs of communicating mobile and base stations, which are capable of interfering with each other. Therefore, if an exemplary base station is adapted to receive communication during, for example, a reference sub-interval ~, the mobile desiring to communicate with that base will transmit its reference signal during the same sub-interval B. Thus, since each base station gates its receiver "on" only during its pre-assigned time slot in the reference interval, interference from other mobiles will be minimal. In a frequency-offset reference transmission scheme, each mobile and corresponding base station in a particular area is assigned a unique offset frequency which is a multiple (n, +1, ~2, +3~ of a low frequency ~ = 2~/T, where T is the duration of reference interval RIl. During the reference interval, the transmitting frequency of a mobile and the local oscillator at the base station are shifted from the carrier frequency ~c by the offset assigned to its associated base station. The use of different reference frequencies allows the base station to select the desired reference signal and suppress the interference. The choice of ~ = 2~/T allows the various reference signals to be orthogonal; unwanted signals do not contribute to the co-phasing operation o~ the base station.
Once the base station identifies the mobile by its associated reference signal, the mobile then transmits its message to the base durin~ message interval MIl. For purposes of illustration only, to achieve, for example, a 32 kbit/sec transmission rate, which is necessary for speech transmission, 6~ bits must be sent during the message interval of, in this example, 790 ~sec, implying a baud rate of 81 kbaud/sec. This exemplary message interval of 790 ~sec was determined by assuming that the entire mobile-to-base transmission interval is 1 msec, with 210 ~sec reserved for reference interva] RIl. Depending on filtering and tolerable dB penalty, this exemplary rate would require 80-120 kHz bandwidth with binary PSK
modulation.
In a cellular mobile radio system employing the above-described space diversity properties, co--channel interference from unwanted mobiles is effectively rejected and the same frequency channel may therefore be used in cells much closer together than is the case with existing analog systems. Therefore, fewer distinct channel sets are required and each cell is able to occupy a larger share of the total system bandwidth. Thus, for the example above, the number of mobiles that can be served in ~he ~O-MHz bandwidth of the 850 M~z mobile radio band by employing the digital transmission techniques of the present inve~ltion is approximately 130. This high capacity of 130 mobiles/base illustrates the advantage of the digital system of the present invention over existing analog systems which have a much smaller capacity.
At the completion of message interval MIl the mobile transmits a second carrier burst during reference interval RI2 to update the location information of the mobile with respect to the base, where the second carrier burst may be either one of the time-division or frequency-~t~
offset forms described hereinbefore. Once the locationinformation has been updated, the message from the base to the mobile is transmitted during message interval MI2.
Like the time interval associated with RIl and MIl, the reception of location update during RI~ and base-to-mobile transmission during MI2 also occurs, in this example, during a 1 msec period. Assuming, for example, that RI2 is also 210 ~sec in duration, the same baud rate of 81 kbaud/sec is associated with transmission during MI2.
At the end of 2 msec, therefore, an entire message cycle has occurred and the entire process starts again.
The signal processing circuitry for an exernplary antenna element 16j and its associated retransmission branch 18j located at a base station formed in accordance with the present invention is illustrated in FIG. 4 and may be analyzed in conjunction with the timing sequence illustrated in FIG. 3. In the following discussion, any reference to the time-division or frequency-offset signaling schemes will be omitted for the sake of clarity, 2n however, the use of these schemes to avoid co-channel interference is an obvious extension of the principles described hereinafter.
The reference signal received at an exemplary antenna element 16j from a mobile (not shown) is of the ~5 form Rjcos(~ct ~ ~j), where ~c is the carrier frequency, R
is the Rayleigh amplitude and ~j is the previously described random phase. Although both Rj and ~j are functions of time, they vary slowly and may be considered as remaining constant during reference interval RIl.
The reference signal received by an antenna element 16j passes through a circulator 17 and into a switch 19, where switch 19 controls the transmi~ (*) and receive (R) modes of operation of retransmission branch l~j. During reference interval RIl message interval MI
and reference interval RI2, switch 19 remains in its "receive" position. After passing through switch 19 the reference signal is transmitted along two distinct signal ~t~'$~ ~
paths of retransmission branch 18j, an I-rail and a Q-rail.
The signal on the I-rail is applied as one input of a mixer 23, where the other input to mixer 23 is a local oscillator 22 which generates a cos~ct signal. The output of mixer 23 is one quadrature component of the reference signal Rjcos(~ct ~ ), specifically, Rjcos ~j. In a like manner, the signal on the Q-rail is applied to one input of a mixer 25, where the remaining input to mixer 25 is a local oscillator 29 which generates a sin~ct signal. The output of mixer 25 is, therefore, the remaining quadrature component of reference signal Rjcos(~ct + ~j), specifically, -Rjsin~j.
Phasing of antenna element 16j to receive a message signal possessing random phase ~j is accomplished by passlng the down-converted signals through separate reference coefficient generator circuits via a switch 27, the signal Rjcos~j through a reference coefficient generator circuit 26 and the signal -Rjsin~j through a reference coefficient generator circuit 28. Generators 26 and 28 produce reference coefficients ~Rjcos~j and -Rjsin~j, respectively, where for the above-described time-division scheme reference coefficient generators 26 and 28 can be sample-and-hold circuits, which samples the carrier burst transmitted from a mobile during its pre~
assigned sub-interval, as described hereinbefore. In accordance with the frequency-offset scheme, reference coefficient generators 26 and 28 may be of the form of well-known integrator circuits which integrate over the entire reference interval. Thus, reference coefficients Rjcos~j and -~Rjsin~j modify the signal received by antenna element 16j by phasing element 16j to receive a message signal with random phase ~j, where ~ is a constant generated during the reference coefficient process.
At the completion of reference interval RIl, a switch 27 is activated from a first to a second position by a clock signal from clock 31 to switch the outputs of mixers 23 and 25 ~rom the inputs of reference coef~icient generators 26 and 28 to the inputs to a pair of multipliers 30 and 32. In FIG. 4, reference coefficient generator 26 has its output coupled to an input to multiplier 30 and likewise, reference coefficient generator 28 has its output coupled to an input to multiplier 320 The message transmitted from mobile-to-base during message interval MIl comprises, for example, 64 bits, where the kth bit and accompanyinq interference may be written as IsRicos(~ct-~i)+Iccos~ccos~ct-~Issin~ct~ t3) where Ak = +l represents the transmitted bit and Ic and Is are Gaussian random variables with zero mean and variance s2. The message bit is down-converted in retransmission branch 18j through mixers 23 and 25 in a like manner as the above-described reference signal to form its quadrature components. The down-converted quadrature components of the kth bit appearing at the outputs of mixers 23 and 25 are then applied via switch 27 as inputs to multipliers 30 and 32, respectively, where the remaining inputs to the multipliers are its associated reference coefficient appearing at the outputs of reference coefficient generators 26 and 28, respectively. Specifically, the down-converted message bit on the I-rail from mixer 23 and reference coefficient ~Rjcos3j from reference coefficient generator 26 are applied as inputs to a multiplier 30, and the down-converted message bit on the Q-rail from mixer 25 and reference coefficient ~ Rjsin~j from reference coefficient generator 28 are applied as inputs to a multiplier 32. The output signals of multipliers 30 and 32 may be represented respectively byo
2 2 ~AkRjcos ~j + ~IcRjcos~
for the I-rail and (4) ~AkRj2sin2~j - aIsRjsin~j for the ~-rail. These two signals are subsequently applied to an adder 3~, resulting in an output signal of aAkRj2 and a mean-square noise term Of a2Rj2s2.
Note that multiplication of the quadrature components of the message bit by their associated reference coefficients and subsequent summation thereof produces a demodulated, i.e., baseband, signal which is independent of the random phase ~j. Therefore, the demodulated signals produced by the remaining retransmission branches 181 ~ 18M
(not shown) will likewise be independent of their respective random phases Cl - ~M~ and further, each signal possesses a magnitude proportional to R2. Therefore, combiner 20 of base station 1~ may comprise only a simple adder circuit to achieve the above-mentioned optimal maximal-ratio combination of the signals produced at the base station by retransmission branches 181 - 18M.
FIG. 4 may also be used to illustrate the signal flow from the base station back to the mobile. At the completion of the mobile-to-base message during message interval MIl switch 27 is reactivated and the outputs of mixers 23 and 25 are switched back to their first positions as inputs to predictors 26 and 28, respectively. The mobile then transmits a second carrier burst durinq reference interval RI2 to update its propaqation location information with respect to the base station. In general, this reference signal will travel through slightly different propagation conditions than the signal transmitted during RIl. The up-dated random phase value stored in a like manner as the preceding ~j by reference coefficient generators 26 and 28 will enable the base station to compensate for this new value of ~j.
At the completion of reference interval RI2, switch 27j is once again activated and the outputs of mixers 23 and 25 are switched back to their alternative positions as the inputs to multipliers 30 and 32, P' - 13 ~
respectively. Also, switches 19 and 35 are activated at this time to switch retransmission branch 18j from its "receive" mode to its "transmit" mode. The base 1~ is then prepared to begin transmitting a message signal during messa~e interval MI2 back to the mobile. The message signal originates from message source 21, and the identical signal is introduced to the I- and Q-rails of each retransmission branch 181 - 18M via switch 35 and adder 34.
For transmission back to the mobile, the signal flow along the I-and Q-rails is reversed from that herelnbefore described with the reception of signals during periods RIl, MI1, and RI2, with the phase conjugation described hereinabove in association with FIG. 2 accomplished by inverting the sign of the reference coefficient produced by reference coefficient generator 28. More particularly, the input message signal is directed by adder 34 to flow along the I- and Q-rails, where on the I-rail the message signal is applied as an input to multiplier 30, the other input to multiplier 30 being the updated reference coefficient stored in reference coefficient generator 26. On the Q-rail, the message signal is applied as an input to multiplier 32, the other input to multiplier 32 being the negative of the updated reference coefficient stored in reference coefficient generator 2~ r where the use of the negative, as described hereinabove, in conjunction with the processed signal on the I-rail, will allow the signal to be received coherently by the mobile station by "undoing" the effects of the environment. The outputs of multipliers 30 and 32 are then applied as inputs to mixers 23 and 25, where local oscillators 22 and 24 are also applied as inputs to mixers 23 and 25, respectively, to upconvert the quadrature components of the message signal. The upconverted signals are then combined and passed via switch 19 through circulator 17 and transmitted by antenna element 16j. This procedure gives the same SIR at the mobile as if all the transmitted power were radiated Erom a single antenna and the mobile included the same degree of diversity (M-branch in this example) as the base station.
for the I-rail and (4) ~AkRj2sin2~j - aIsRjsin~j for the ~-rail. These two signals are subsequently applied to an adder 3~, resulting in an output signal of aAkRj2 and a mean-square noise term Of a2Rj2s2.
Note that multiplication of the quadrature components of the message bit by their associated reference coefficients and subsequent summation thereof produces a demodulated, i.e., baseband, signal which is independent of the random phase ~j. Therefore, the demodulated signals produced by the remaining retransmission branches 181 ~ 18M
(not shown) will likewise be independent of their respective random phases Cl - ~M~ and further, each signal possesses a magnitude proportional to R2. Therefore, combiner 20 of base station 1~ may comprise only a simple adder circuit to achieve the above-mentioned optimal maximal-ratio combination of the signals produced at the base station by retransmission branches 181 - 18M.
FIG. 4 may also be used to illustrate the signal flow from the base station back to the mobile. At the completion of the mobile-to-base message during message interval MIl switch 27 is reactivated and the outputs of mixers 23 and 25 are switched back to their first positions as inputs to predictors 26 and 28, respectively. The mobile then transmits a second carrier burst durinq reference interval RI2 to update its propaqation location information with respect to the base station. In general, this reference signal will travel through slightly different propagation conditions than the signal transmitted during RIl. The up-dated random phase value stored in a like manner as the preceding ~j by reference coefficient generators 26 and 28 will enable the base station to compensate for this new value of ~j.
At the completion of reference interval RI2, switch 27j is once again activated and the outputs of mixers 23 and 25 are switched back to their alternative positions as the inputs to multipliers 30 and 32, P' - 13 ~
respectively. Also, switches 19 and 35 are activated at this time to switch retransmission branch 18j from its "receive" mode to its "transmit" mode. The base 1~ is then prepared to begin transmitting a message signal during messa~e interval MI2 back to the mobile. The message signal originates from message source 21, and the identical signal is introduced to the I- and Q-rails of each retransmission branch 181 - 18M via switch 35 and adder 34.
For transmission back to the mobile, the signal flow along the I-and Q-rails is reversed from that herelnbefore described with the reception of signals during periods RIl, MI1, and RI2, with the phase conjugation described hereinabove in association with FIG. 2 accomplished by inverting the sign of the reference coefficient produced by reference coefficient generator 28. More particularly, the input message signal is directed by adder 34 to flow along the I- and Q-rails, where on the I-rail the message signal is applied as an input to multiplier 30, the other input to multiplier 30 being the updated reference coefficient stored in reference coefficient generator 26. On the Q-rail, the message signal is applied as an input to multiplier 32, the other input to multiplier 32 being the negative of the updated reference coefficient stored in reference coefficient generator 2~ r where the use of the negative, as described hereinabove, in conjunction with the processed signal on the I-rail, will allow the signal to be received coherently by the mobile station by "undoing" the effects of the environment. The outputs of multipliers 30 and 32 are then applied as inputs to mixers 23 and 25, where local oscillators 22 and 24 are also applied as inputs to mixers 23 and 25, respectively, to upconvert the quadrature components of the message signal. The upconverted signals are then combined and passed via switch 19 through circulator 17 and transmitted by antenna element 16j. This procedure gives the same SIR at the mobile as if all the transmitted power were radiated Erom a single antenna and the mobile included the same degree of diversity (M-branch in this example) as the base station.
Claims (13)
1. A mobile radio base station employing space diversity and time-division retransmission comprising:
a plurality of M antenna elements for operating in a space diversity mode capable of receiving a mobile-to-base communication signal from a remote station and transmitting a base-to-mobile communication signal to said remote station, a plurality of M retransmission branches associated in a one-to-one relationship with said plurality of M antenna elements and capable of operating in either one of a transmitting mode or a receiving mode, each retransmission branch when operating in its receiving mode being capable of compensating for the incoming random phase associated with said mobile-to-base communication signal and subtracting said random phase therefrom, and when operating in its transmitting mode being capable of adding said random phase to said base-to-mobile communi-cation signal;
combining means coupled to the outputs of said plurality of M retransmission branches when operating in their receiving mode and capable of combining said output signals of said branches to form a coherent output signal, and input means capable of applying an input baseband signal to said plurality of retransmission branches when operating in their transmitting mode allowing said plurality of M antenna elements to transmit said base-to-mobile communication signal CHARACTERIZED IN THAT
the base station is capable of receiving and transmitting digital communication signals, wherein each retransmission branch includes means capable of both down-converting the mobile-to-base communication signal to a baseband representation thereof and up-converting the input baseband signal to a phased base-to-mobile communication signal.
a plurality of M antenna elements for operating in a space diversity mode capable of receiving a mobile-to-base communication signal from a remote station and transmitting a base-to-mobile communication signal to said remote station, a plurality of M retransmission branches associated in a one-to-one relationship with said plurality of M antenna elements and capable of operating in either one of a transmitting mode or a receiving mode, each retransmission branch when operating in its receiving mode being capable of compensating for the incoming random phase associated with said mobile-to-base communication signal and subtracting said random phase therefrom, and when operating in its transmitting mode being capable of adding said random phase to said base-to-mobile communi-cation signal;
combining means coupled to the outputs of said plurality of M retransmission branches when operating in their receiving mode and capable of combining said output signals of said branches to form a coherent output signal, and input means capable of applying an input baseband signal to said plurality of retransmission branches when operating in their transmitting mode allowing said plurality of M antenna elements to transmit said base-to-mobile communication signal CHARACTERIZED IN THAT
the base station is capable of receiving and transmitting digital communication signals, wherein each retransmission branch includes means capable of both down-converting the mobile-to-base communication signal to a baseband representation thereof and up-converting the input baseband signal to a phased base-to-mobile communication signal.
2. A mobile radio base station in accordance with claim 1 CHARACTERIZED IN THAT
each retransmission branch of the plurality of retransmission branches includes a pair of converting means capable of both (a) separating the mobile-to-base digital communication signal into a first quadrature component and a second quadrature component and transmitting said first and second quadrature components along a first and a second signal path, respectively, and (b) combining a first quadrature component of the base-to-mobile signal and a second quadrature component of said base-to-mobile signal to be transmitted by its associated antenna element.
each retransmission branch of the plurality of retransmission branches includes a pair of converting means capable of both (a) separating the mobile-to-base digital communication signal into a first quadrature component and a second quadrature component and transmitting said first and second quadrature components along a first and a second signal path, respectively, and (b) combining a first quadrature component of the base-to-mobile signal and a second quadrature component of said base-to-mobile signal to be transmitted by its associated antenna element.
3. A mobile radio base station in accordance with claim 2 CHARACTERIZED IN THAT
the received mobile-to-base communication signal comprises in sequence a first reference signal, a first message signal and a second reference signal, wherein each signal path of the first and second signal paths of each retransmission branch includes reference coefficient generating means responsive sequentially to its associated quadrature component of said first and second reference signals and capable of producing as sequential output signals a first and a second reference coefficient, said first and second reference coefficients associated with the sequential locations of the mobile station with respect to the antenna element.
the received mobile-to-base communication signal comprises in sequence a first reference signal, a first message signal and a second reference signal, wherein each signal path of the first and second signal paths of each retransmission branch includes reference coefficient generating means responsive sequentially to its associated quadrature component of said first and second reference signals and capable of producing as sequential output signals a first and a second reference coefficient, said first and second reference coefficients associated with the sequential locations of the mobile station with respect to the antenna element.
4. A mobile radio base station employing frequency-offset reference transmission in accordance with claim 3 CHARACTERIZED IN THAT
each reference coefficient generating means includes integrating means capable of integrating the first and second reference signals received during a first and a second reference interval respectively, to produce the reference coefficient output signals.
each reference coefficient generating means includes integrating means capable of integrating the first and second reference signals received during a first and a second reference interval respectively, to produce the reference coefficient output signals.
5. A mobile radio base station employing time-division reference transmission in accordance with claim 3 CHARACTERIZED IN THAT
each reference coefficient generating means includes sample-and-hold means capable of sampling and storing the first and second reference signals received by said predictor means during a first and second reference interval respectively, to produce the reference coefficient output signals.
each reference coefficient generating means includes sample-and-hold means capable of sampling and storing the first and second reference signals received by said predictor means during a first and second reference interval respectively, to produce the reference coefficient output signals.
6. A mobile radio base station in accordance with claim 3 CHARACTERIZED IN THAT
each signal path further includes a multiplier being responsive to both (a) its associated quadrature component of the first message signal and the first reference coefficient produced by its associated predictor means for producing a baseband digital output signal, and (b) the base-to-mobile baseband signal and the second reference coefficient for producing a phased base-to-mobile digital communication signal.
each signal path further includes a multiplier being responsive to both (a) its associated quadrature component of the first message signal and the first reference coefficient produced by its associated predictor means for producing a baseband digital output signal, and (b) the base-to-mobile baseband signal and the second reference coefficient for producing a phased base-to-mobile digital communication signal.
7. A mobile radio base station in accordance with claim 6 CHARACTERIZED IN THAT
the combining means includes an adder capable of combining the plurality of baseband digital output signals produced by each retransmission branch of the plurality of retransmission branches.
the combining means includes an adder capable of combining the plurality of baseband digital output signals produced by each retransmission branch of the plurality of retransmission branches.
8. A time-division retransmission method of transmitting digital communication signals between at least one base station and at least one mobile station the method comprising the steps of (a) transmitting a first carrier burst from the at least one mobile station during a first reference interval, (b) transmitting message information from said at least one mobile station to said at least one base station during a first message interval, (c) transmitting message information from said at least one base station to said at least one mobile station during a second message interval CHARACTERIZED IN THAT
the method comprises the further step of (d) prior to step (c), transmitting a second carrier burst from the at least one mobile station to the at least one base station during a second reference interval.
the method comprises the further step of (d) prior to step (c), transmitting a second carrier burst from the at least one mobile station to the at least one base station during a second reference interval.
9. The method according to claim 8 wherein the at least one base station comprises a plurality of base stations and said plurality of base stations are capable of communicating with the at least one mobile station CHARACTERIZED IN THAT
the method comprises the further steps of (e) in performing step (a) transmitting a first carrier burst from the at least one mobile station which is associated with one of the plurality of base stations during a pre-determined sub-interval of the first reference interval, each base station of said plurality of base stations being associated with a separate and distinct sub-interval of said first reference interval; and (f) in performing step (d) transmitting a second carrier burst from the at least one mobile station which is associated with one of said plurality of base stations during a predetermined sub-interval of the second reference interval, each base station of said plurality of base stations being associated with a separate and distinct sub interval of said second reference interval.
the method comprises the further steps of (e) in performing step (a) transmitting a first carrier burst from the at least one mobile station which is associated with one of the plurality of base stations during a pre-determined sub-interval of the first reference interval, each base station of said plurality of base stations being associated with a separate and distinct sub-interval of said first reference interval; and (f) in performing step (d) transmitting a second carrier burst from the at least one mobile station which is associated with one of said plurality of base stations during a predetermined sub-interval of the second reference interval, each base station of said plurality of base stations being associated with a separate and distinct sub interval of said second reference interval.
10. The method according to claim 8 wherein the at least one base station comprises a plurality of base stations and said plurality of base stations are capable of communicating with the at least one mobile station CHARACTERIZED IN THAT
the method comprises the further steps of (e) in performing step (a) transmitting a first carrier burst from the at least one mobile station to the plurality of base stations at a predetermined off-set frequency, each base station associated with a separate and distinct off-set frequency; and (f) in performing step (d) transmitting a second carrier burst from the at least one mobile station to the plurality of base stations at a predetermined off-set frequency, each base station associated with a separate and distinct off-set frequency.
the method comprises the further steps of (e) in performing step (a) transmitting a first carrier burst from the at least one mobile station to the plurality of base stations at a predetermined off-set frequency, each base station associated with a separate and distinct off-set frequency; and (f) in performing step (d) transmitting a second carrier burst from the at least one mobile station to the plurality of base stations at a predetermined off-set frequency, each base station associated with a separate and distinct off-set frequency.
11. A method of both compensating for the random phase associated with a mobile-to-base digital communication signal received at a base station and forming a baseband digital signal thereat, the method comprising the steps of:
(a) receiving at said base station a reference signal transmitted by a mobile station, (b) detecting the random phase of said reference signal, (c) receiving at said base station a message signal transmitted by said mobile station, and (d) compensating for the random phase detected in step (b) from said message signal received in step (c) CHARACTERIZED IN THAT
the method comprises the further steps of (e) in performing step (a), down-converting the reference signal into a first reference signal quadrature component and a second reference signal quadrature component, (f) in performing step (h), forming a first reference coefficient associated with the random phase of said first reference signal and a second reference coefficient associated with the random phase of said second reference signal, (g) in performing step (c), down-converting the message signal into a first message signal quadrature component and a second message signal quadrature component (h) in performing step (d), multiplying said first reference coefficient with said first message signal quadrature component to form a first baseband component, and multiplying said second reference coefficient with said second message signal quadrature component to form a second baseband component, (i) adding the first and second baseband components to form the baseband digital communication signal.
(a) receiving at said base station a reference signal transmitted by a mobile station, (b) detecting the random phase of said reference signal, (c) receiving at said base station a message signal transmitted by said mobile station, and (d) compensating for the random phase detected in step (b) from said message signal received in step (c) CHARACTERIZED IN THAT
the method comprises the further steps of (e) in performing step (a), down-converting the reference signal into a first reference signal quadrature component and a second reference signal quadrature component, (f) in performing step (h), forming a first reference coefficient associated with the random phase of said first reference signal and a second reference coefficient associated with the random phase of said second reference signal, (g) in performing step (c), down-converting the message signal into a first message signal quadrature component and a second message signal quadrature component (h) in performing step (d), multiplying said first reference coefficient with said first message signal quadrature component to form a first baseband component, and multiplying said second reference coefficient with said second message signal quadrature component to form a second baseband component, (i) adding the first and second baseband components to form the baseband digital communication signal.
12. The method according to claim 11 CHARACTERIZED IN THAT
in performing frequency-offset reference transmission the method comprises the further step of (j) in performing step (f), integrating each of the first and second reference signal quadrature components to form the first and second reference coefficients, respectively.
in performing frequency-offset reference transmission the method comprises the further step of (j) in performing step (f), integrating each of the first and second reference signal quadrature components to form the first and second reference coefficients, respectively.
13. The method according to claim 11 CHARACTERIZED IN THAT
in performing time-division reference transmission the method comprises the further step of (j) in performing step (f), sampling and holding each of the first and second reference signal quadrature components to form the first and second reference coefficients respectively.
in performing time-division reference transmission the method comprises the further step of (j) in performing step (f), sampling and holding each of the first and second reference signal quadrature components to form the first and second reference coefficients respectively.
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
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US209,146 | 1980-11-21 | ||
US06/209,146 US4383332A (en) | 1980-11-21 | 1980-11-21 | High capacity digital mobile radio system |
Publications (1)
Publication Number | Publication Date |
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CA1184249A true CA1184249A (en) | 1985-03-19 |
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ID=22777540
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
CA000389669A Expired CA1184249A (en) | 1980-11-21 | 1981-11-09 | High capacity digital mobile radio system |
Country Status (5)
Country | Link |
---|---|
US (1) | US4383332A (en) |
JP (1) | JPS57115039A (en) |
CA (1) | CA1184249A (en) |
DE (1) | DE3145992A1 (en) |
GB (1) | GB2090105B (en) |
Families Citing this family (44)
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US4513412A (en) * | 1983-04-25 | 1985-04-23 | At&T Bell Laboratories | Time division adaptive retransmission technique for portable radio telephones |
US4510595A (en) * | 1983-10-03 | 1985-04-09 | At&T Bell Laboratories | Modified time-division transmission technique for digital mobile radio systems |
ATE47948T1 (en) * | 1984-07-13 | 1989-11-15 | Motorola Inc | CELLULAR VOICE AND DATA RADIO TRANSMISSION SYSTEM. |
US4639914A (en) * | 1984-12-06 | 1987-01-27 | At&T Bell Laboratories | Wireless PBX/LAN system with optimum combining |
US4675880A (en) * | 1985-05-02 | 1987-06-23 | The United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration | Antimultipath communication by injecting tone into null in signal spectrum |
JPS62185415A (en) * | 1986-02-10 | 1987-08-13 | Nec Corp | Operating method for counter type radio line |
SE460449B (en) * | 1988-02-29 | 1989-10-09 | Ericsson Telefon Ab L M | CELL DIVIDED DIGITAL MOBILE RADIO SYSTEM AND PROCEDURE TO TRANSFER INFORMATION IN A DIGITAL CELL DIVIDED MOBILE RADIO SYSTEM |
USRE37754E1 (en) * | 1988-02-29 | 2002-06-18 | Telefonaktiebolaget Lm Ericsson (Publ) | Cellular digital mobile radio system and method of transmitting information in a digital cellular mobile radio system |
SE8802229D0 (en) | 1988-06-14 | 1988-06-14 | Ericsson Telefon Ab L M | MOBILE RADIO STATION PROCEDURE |
JPH0744497B2 (en) * | 1988-06-14 | 1995-05-15 | 国際電気株式会社 | Signal combining method for multiple receivers |
US5097484A (en) * | 1988-10-12 | 1992-03-17 | Sumitomo Electric Industries, Ltd. | Diversity transmission and reception method and equipment |
US4953197A (en) * | 1988-12-08 | 1990-08-28 | International Mobile Machines Corporation | Combination spatial diversity system |
US5231407A (en) * | 1989-04-18 | 1993-07-27 | Novatel Communications, Ltd. | Duplexing antenna for portable radio transceiver |
JPH0338932A (en) * | 1989-07-06 | 1991-02-20 | Oki Electric Ind Co Ltd | Space diversity system |
SE465198B (en) * | 1990-02-02 | 1991-08-05 | Televerket | PROCEDURE AND DEVICE TO PROVIDE CAPACITY IN A MOBILE PHONE SYSTEM |
GB2244189A (en) * | 1990-05-17 | 1991-11-20 | Orbitel Mobile Communications | Space diversity receiver for mobile telephones |
US5384826A (en) * | 1990-10-01 | 1995-01-24 | At&T Bell Laboratories | Distributed packetized switching cellular radio telephone communication system with handoff |
US5371780A (en) * | 1990-10-01 | 1994-12-06 | At&T Corp. | Communications resource assignment in a wireless telecommunications system |
US5479448A (en) * | 1992-03-31 | 1995-12-26 | At&T Corp. | Method and apparatus for providing antenna diversity |
US5274844A (en) * | 1992-05-11 | 1993-12-28 | Motorola, Inc. | Beam pattern equalization method for an adaptive array |
DE4303355A1 (en) * | 1993-02-05 | 1994-08-11 | Philips Patentverwaltung | Radio system |
EP0622910B1 (en) * | 1993-04-29 | 2003-06-25 | Ericsson Inc. | Time diversity transmission system for the reduction of adjacent channel interference in mobile telephone systems |
DE4322863C2 (en) * | 1993-07-09 | 1995-05-18 | Ant Nachrichtentech | Cellular antenna system |
CA2118355C (en) * | 1993-11-30 | 2002-12-10 | Michael James Gans | Orthogonal polarization and time varying offsetting of signals for digital data transmission or reception |
DE4410174A1 (en) * | 1994-03-24 | 1995-09-28 | Sel Alcatel Ag | Hand-held mobile radio telephone |
DE4415282A1 (en) * | 1994-04-30 | 1995-11-02 | Sel Alcatel Ag | Multipath reception radio receiver |
DE4421573A1 (en) * | 1994-06-21 | 1996-01-11 | Ant Nachrichtentech | Arrangement for receiving signals which emit moving objects in a predetermined area |
DE4427755A1 (en) * | 1994-08-05 | 1996-02-08 | Sel Alcatel Ag | Fixed or mobile radio station for an SDMA mobile radio system |
DE4445850A1 (en) * | 1994-12-22 | 1996-06-27 | Alcatel Mobile Comm Deutsch | Receiving device for mobile radio, in particular for rail mobile radio |
US5579341A (en) * | 1994-12-29 | 1996-11-26 | Motorola, Inc. | Multi-channel digital transceiver and method |
DE19511751C2 (en) * | 1995-03-30 | 1998-07-09 | Siemens Ag | Process for the reconstruction of signals disturbed by multipath propagation |
US5857144A (en) * | 1996-08-09 | 1999-01-05 | Ericsson, Inc. | In-band vehicular repeater for trunked radio system |
US6047160A (en) * | 1996-08-29 | 2000-04-04 | Ericsson Inc. | Transportable base station for a trunked radio communication system |
US6169880B1 (en) | 1996-10-16 | 2001-01-02 | Ericsson Inc. | Method and system of load sharing and prioritization of radio repeaters |
BR9713298A (en) * | 1996-11-26 | 1999-10-26 | Sanyo Electric Co | Base station for mobile communications systems |
US5933421A (en) | 1997-02-06 | 1999-08-03 | At&T Wireless Services Inc. | Method for frequency division duplex communications |
US6501771B2 (en) | 1997-02-11 | 2002-12-31 | At&T Wireless Services, Inc. | Delay compensation |
US6359923B1 (en) | 1997-12-18 | 2002-03-19 | At&T Wireless Services, Inc. | Highly bandwidth efficient communications |
US6408016B1 (en) * | 1997-02-24 | 2002-06-18 | At&T Wireless Services, Inc. | Adaptive weight update method and system for a discrete multitone spread spectrum communications system |
US6128276A (en) * | 1997-02-24 | 2000-10-03 | Radix Wireless, Inc. | Stacked-carrier discrete multiple tone communication technology and combinations with code nulling, interference cancellation, retrodirective communication and adaptive antenna arrays |
US6584144B2 (en) | 1997-02-24 | 2003-06-24 | At&T Wireless Services, Inc. | Vertical adaptive antenna array for a discrete multitone spread spectrum communications system |
US7720458B2 (en) * | 2002-05-30 | 2010-05-18 | Lockheed Martin Corporation | Rapidly deployable emergency communications system and method |
US7327811B2 (en) * | 2003-04-01 | 2008-02-05 | Telefonaktiebolaget L M Ericsson | Method and apparatus for facilitating signal discrimination in a wireless network by applying known frequency offsets |
IL196146A (en) | 2008-12-23 | 2014-01-30 | Elta Systems Ltd | System and method of transmitting a signal back towards a transmitting source |
Family Cites Families (9)
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US3566274A (en) * | 1966-05-31 | 1971-02-23 | Cardion Electronics Inc | Multipath wave-signal receiving apparatus |
US3696421A (en) * | 1969-06-06 | 1972-10-03 | Bell Telephone Labor Inc | Space diversity phased array retransmission system using time division |
US3631494A (en) * | 1969-08-08 | 1971-12-28 | Bell Telephone Labor Inc | Retransmission system |
FR2076193A5 (en) * | 1970-01-06 | 1971-10-15 | Commissariat Energie Atomique | |
US3662268A (en) * | 1970-11-17 | 1972-05-09 | Bell Telephone Labor Inc | Diversity communication system using distinct spectral arrangements for each branch |
US3693088A (en) * | 1970-12-29 | 1972-09-19 | Bell Telephone Labor Inc | Diversity system for mobile radio using fade rate switching |
US3717814A (en) * | 1971-09-23 | 1973-02-20 | Bell Telephone Labor Inc | Cophasing diversity communication system with pilot feedback |
JPS5147313A (en) * | 1974-10-21 | 1976-04-22 | Nippon Telegraph & Telephone | |
US4054753A (en) * | 1975-10-20 | 1977-10-18 | Digital Communications Corporation | Double sync burst TDMA system |
-
1980
- 1980-11-21 US US06/209,146 patent/US4383332A/en not_active Expired - Lifetime
-
1981
- 1981-11-09 CA CA000389669A patent/CA1184249A/en not_active Expired
- 1981-11-20 DE DE19813145992 patent/DE3145992A1/en not_active Ceased
- 1981-11-21 JP JP56187664A patent/JPS57115039A/en active Pending
- 1981-11-23 GB GB8135211A patent/GB2090105B/en not_active Expired
Also Published As
Publication number | Publication date |
---|---|
GB2090105B (en) | 1985-09-25 |
JPS57115039A (en) | 1982-07-17 |
GB2090105A (en) | 1982-06-30 |
US4383332A (en) | 1983-05-10 |
DE3145992A1 (en) | 1982-06-24 |
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