WO2001043453A2 - Method for dynamically distributing mobile traffic capacity of a single tdma rf signal over multiple cell sites - Google Patents

Abstract

A method and apparatus for dynamically distributing the mobile traffic capacity of a single TDMA RF carrier frequency over multiple cell sites is disclosed (740). A single shared carrier frequency is assigned to a plurality of translating repeaters for the backhaul communications link (750). When a given TDMA channel is no longer needed by any one of the translating repeaters, idle TDMA channels may be reassigned to other translating repeaters (790). Translating repeaters may store repetitive control channel information in memory, freeing a portion of the control channel for separately controlling operations of each translating repeater. The translating repeater control channel may also be used by a BTS to align time slot bursts received from each of the translating repeaters.

Description

A METHOD FOR DYNAMICALLY DISTRIBUTING MOBILE TRAFFIC CAPACITY OF A SINGLE TDMA RF SIGNAL OVER MULTIPLE CELL SITES

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application

60/170,412 entitled, "A METHOD FOR DYNAMICALLY DISTRIBUTING MOBILE

TRAFFIC CAPACITY OF A SINGLE TDMA RF SIGNAL OVER MULTIPLE CELL

SITES", filed December 1 3, 1999, the entirety of which is incorporated herein

by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

This invention relates to wireless communication systems and in particular

to a method for improved carrier frequency usage whereby a single TDMA RF

carrier frequency may be shared by multiple cells.

Description of Relevant Art

The ever increasing need for wireless communication services such as

Cellular Mobile Telephone (CMT), Digital Cellular Network (DCN), Personal

Communication Services (PCS) and the like, typically require the operators of

such systems to serve an increasing number of users in a given service area. As

a result, certain types of base station equipment, including high capacity

broadband transceiver systems (BTS), have been developed which are intended to service a relatively large number of active mobile stations in each cell.

Time-division multiplexing (TDM) is a scheme in which numerous signals

are combined for transmission on a single communications line or carrier

frequency. Each signal is broken up into a plurality of segments, each having a

very short duration. Time division multiple access (TDMA) is a technology used

in digital cellular telephone communication systems which divides each carrier

frequency into multiple time slots. For example, if eight time slots are used, up

to eight separate calls can theoretically be placed on each carrier frequency,

multiplying a system's capacity by up to a factor of eight. TDMA assigns a

specific time slot for each call's use during a conversation. Code division

multiple access or CDMA is another transmission technology. Rather than

separating frequencies by time as in TDMA, CDMA separates calls by code.

When a wireless system is first installed, the demand for its use in most

cells is relatively low. Because only a few cells at high expected traffic demand

locations (such as at a freeway intersection) will justify the expense of a

build-out deploying a high capacity BTS per cell, a service provider is faced with

a dilemma. The cellular service provider can build-out the system with less

expensive narrowband equipment initially (such as equipment employing a single

RF frequency), to provide some level of coverage, and then upgrade to the more

efficient broadband BTS equipment as the number of subscribers increases in

the service area. However, the initial investment expended in narrowband

equipment may be lost. Alternatively, a larger up-front investment can be made to initially deploy a high capacity BTS per cell. As demand increases, the users

of the system can be accommodated without receiving frequent busy signals

and the like. However, this option has the disadvantage of a larger up-front

investment.

One approach for extending the service area and efficiency of a given BTS

is described in issued U.S. Patent 5,970,410 to Carney et al. ("Carney")

entitled, "Cellular System Plan Using in Band-translators to Enable Efficient

Deployment of High Capacity Base Transceiver Systems," the disclosure of

which is incorporated herein by reference. Carney discloses a wireless system

architecture whereby efficient broadband transceiver systems can be generally

deployed at an initial build out stage of a cellular system in a cost-efficient

manner. A home base station location is identified within each cluster of cells,

rather than by deployment of a complete suite of broadband base station

equipment in each cell in the cluster. A plurality of inexpensive translating

repeater units are located in the low traffic density cells and are all serviced by

the home base station. Each translating repeater is assigned at least one GSM

TDMA RF carrier frequency. A single carrier frequency permits each translating

repeater to theoretically simultaneously service up to eight cellular users, one

user per TDMA time slot. In practice, one TDMA time slot will be a dedicated

control channel leaving each translating repeater the ability to simultaneously

service up to seven cellular users. Thus, Carney generally provides a very

cost-effective solution for low traffic density installations. Although Carney describes a translating repeater, non-translating

repeaters are also used in the art. Non-translating repeaters simply receive a RF

signal directly from a base station and rebroadcast that same signal over the

same frequency.

There may be rural and highway applications where the traffic capacity

per cell required may be less than that provided by the full RF carrier provided to

each translating repeater by Carney. A full GSM TDMA RF carrier generally

provides seven traffic channels plus one control channel. Each such RF carrier

can supply 3 erlangs of traffic capacity using a TDMA protocol with 8 time slots

per carrier. For example, assume 3 erlangs of capacity is needed to support a

20-mile stretch of rural highway. Due to signal propagation limitations, it may

be necessary to deploy 3 translating repeaters to cover this same stretch of

highway, even though notwithstanding signal propagation limitations, a single

translating repeater could supply the required 3 erlangs of traffic capacity with a

single TDMA RF carrier. Use of 3 translating repeaters each using a full RF

carrier would result in 2/3 of the BTS' processing capability (6 erlangs) to be idle

and unusable by cellular users in other neighboring cells. Inefficient channel

usage raises the cost per channel to a cellular operator and is highly undesirable.

Thus, there is clearly a need for a method to dynamically distribute the time

slots of each TDMA RF carrier for use in multiple cells to maximize the

processing capability efficiency of each BTS in a given TDMA cellular system. SUMMARY OF THE INVENTION

The invention concerns a method for dynamically distributing the mobile

traffic capacity of a single TDMA RF carrier frequency over multiple cells. A

single shared carrier frequency is assigned to a plurality of translating repeaters

for the backhaul communications link. Each translating repeater is exclusively

assigned at least one time slot defining a TDMA channel for the backhaul

communications link. Backhaul communications between the base station and

the plurality of translating repeaters are performed on the shared carrier

frequency with each of the translating repeaters using their exclusively assigned

TDMA channel.

Translating repeaters may be exclusively assigned more than one TDMA

channel for communicating additional traffic on the backhaul communication link

upon request. When a given TDMA channel is no longer needed by any one of

the translating repeaters, idle TDMA channels may be reassigned for use by

other translating repeaters.

TDMA channels on the shared carrier frequency may be exclusively

assigned as dedicated control channels. Translating repeaters can store

repetitive control channel information in memory, freeing a portion of the

dedicated control channel on the backhaul communications link for use as a

translating repeater control sub-channel. The translating repeater control

sub-channel may also be used to align time slot bursts received from each

translating repeater. Base stations recognize the transmitted control information as originating from a specific translating repeater.

A system is disclosed for dynamically distributing the mobile traffic

capacity of a single TDMA RF carrier frequency over multiple cell sites. The

system comprises signal processing circuitry or software for assigning a single

shared carrier frequency to a plurality of translating repeaters for the backhaul

communications link, and for exclusively assigning to each translating repeater

at least one time slot defining a TDMA channel for the backhaul communications

link. The signal processing circuitry or software performs backhaul

communications between the base station and the plurality of translating

repeaters on the single shared carrier frequency with each translating repeater

using their exclusively assigned TDMA channel. The system may further

comprise signal processing circuitry or software for assigning any of the TDMA

channels to a requesting translating repeater. The system may also exclusively

assign at least one additional TDMA channel upon request to a translating

repeater. The system can also reassign TDMA channels to an unused and

available set of TDMA channels when a given channel is no longer needed by

any translating repeater.

The system may further comprise signal processing circuitry, memory or

software for assigning at least one additional TDMA channel on the single

shared carrier frequency for use exclusively as a dedicated control channel and

for storing repetitive control channel information in the memory of each

translating repeater. Storing repetitive control channel information in the memory of each translating repeater permits a portion of at least one frame of

the dedicated control channel to be made available on the downlink backhaul

communications link for use as a translating repeater control sub-channel. The

system may further include signal processing circuitry or software for using the

translating repeater control sub-channel to control TDMA channel assignments

to the group of translating repeaters. Signal processing circuitry, memory or

software for using the translating repeater control channel to align time slot

bursts received from said translating repeaters is also disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

Features and advantages of the present invention will become apparent to

those skilled in the art from the following description with reference to the

drawings, in which:

FIG. 1 is a block diagram of a wireless communications system deploying

a plurality of wireless translating repeaters and base transceiver stations.

FIG. 2 is an exemplary arrangement of the wireless communications

system of FIG. 1 , showing wireless links deployed through a translating

repeater.

FIG. 3a illustrates an uplink GSM-type TDMA frame deploying a dedicated

control channel.

FIG. 3b illustrates a downlink GSM-type TDMA frame deploying a

dedicated control channel.

FIG. 4 is a block diagram of an exemplary single omni-directional

translating repeater of the type shown in the wireless communication system of

FIG. 1 .

FIG. 5 is a block diagram of an exemplary base transceiver station of the

type shown in the wireless communication system of FIG. 1 .

FIG. 6a depicts a cellular system with a BTS using a single RF carrier

frequency serving seven translating repeaters.

FIG. 6b shows the allocation of TDMA TCHs entirely to a single

translating repeater in the prior art for the system shown in FIG. 6a. FIG. 7 is a flow chart describing the allocation and de-allocation of TDMA

TCHs using the invention applied to the system shown in FIG. 6a.

FIG. 8a shows an allocation of TDMA TCHs under the invention at a first

time.

FIG. 8b shows an allocation of TDMA TCHs under the invention at a

second time.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 is a block diagram of a conventional wireless communications

system such as a Personal Communication System ("PCS") or other similar

system 10. In this system, omni-directional translating repeaters 1 2-1 ...12-n

are deployed in peripheral cells 88-1 ... 88-n of cell clusters such as 89, each

cell cluster served by one or more broadband base transceiver stations ("BTS"),

such as 1 5-1 ...1 5-m. Several translating repeaters are generally exclusively

served or hosted by a given "host BTS." Those skilled in the art will readily

appreciate that directional or sectorized translating repeaters 12-1 ...1 2-n may

replace omni-directional translating repeaters in this system. However, for

convenience, the system 10 will first be described using omni-directional

translating repeaters 12-1 ...12-n.

The system 10 can include translator omni-directional antennas 1 1 -1 ,

1 1 -2 ...1 1 -i, ... 1 1 -n-2, 1 1 -n-1 and 1 1 -n (collectively omni-directional antennas

1 1 ), translating repeaters 1 2-1 , 12-2, . . . 1 2-i, . . . 12-n-2, 12-n-1 and 12-n

(collectively translating repeaters 12), translating repeater antennas 13-1 , 13-2,

...13-i, ... 13-n-2, 1 3-n-1 and 13-n (collectively translating repeater directional

antennas 13), BTS directional antennas 14-1 , ... 14-m (collectively BTS

antennas 14), and broadband base transceiver stations 1 5-1 , ... 1 5-m

(collectively BTS 1 5). The system 10 can further include a mobile telephone

exchange 16, one or more base station controllers 17 and a plurality of mobile

users 18-1 and 18-2. Translating repeaters 12 conventionally receive radio signals from mobile

users 18 through omni-directional antennas 1 1 and forward a frequency shifted

version of the received signal to BTS 15 through translating repeater directional

antennas 13. Likewise, radio signals transmitted from BTS 1 5 through BTS

antennas 14 are frequency shifted by translating repeater 12 and forwarded to

mobile users 18. BTS 1 5 demodulate signals received from translating repeaters

12 through BTS antennas 14 and connects these signals to the Public Switched

Telephone Network 92 ("PSTN") through mobile telephone exchange 16. In

addition, in the transmit direction, BTS 15 modulate signals received from the

PSTN 92 through mobile switching center 16 to format them for transmission

through BTS antennas 14-1 ...14-m to their respective hosted translating

repeaters 12. FIG. 2 illustrates the basic function of a translating repeater 12.

Frequency shifted signals transmitted by translating repeaters 12 avoid

multi-path effects common in cellular systems using simple repeaters. Applied

to translating repeaters, a frequency pair or duplex frequency is used so that

BTS 15 to translating repeater 12 backhaul transmissions are at a different

frequency than translating repeater 12 to BTS backhaul transmissions 1 5. Each

backhaul signal is simply a frequency shifted version of the same signal received

by the mobile user 18 on the downlink, and a frequency shifted version of the

same signal transmitted by the mobile user 18 on the uplink.

Translating repeater 12 transmits a frequency shifted version of the

signals received from mobile users 18 to BTS 15 and receives signals from BTS

15 through backhaul channel 19. Backhaul channel 19 is comprised of uplink backhaul channel 19-1 and downlink backhaul channel 19-2. Preferably,

different carrier frequencies are used for uplink backhaul channel 19-1 and

downlink backhaul channel 19-2. Even if different carrier frequencies are used

for uplink backhaul channel 19-1 and downlink backhaul channel 19-2, backhaul

channel 19 is said to operate at a single backhaul frequency. Similarly,

translating repeater 1 2 transmits a frequency shifted version of signals received

from BTS 1 5 to mobile users 18 and receives signals from mobile users 18

through ground link channel 20. Ground link channel 20 is comprised of uplink

ground link channel 20-1 and downlink ground channel 20-2, preferably

deployed using different carrier frequencies to allow simultaneous transmission

in both directions. Even if different carrier frequencies are used for the uplink

ground link channel 20-1 and downlink ground channel 20-2, ground link

channel 20 is said to operate at a single downlink carrier frequency.

Because BTS 1 5 is generally stationary, translating repeaters 12

preferably employ directional antennas 13 pointed towards BTS 1 5 to improve

transmission and reception of signals over backhaul channel 19. In contrast,

because mobile users 18 are not stationary and the translating repeater 12 is

not sectorized, translating repeater 1 2 preferably employs one or more

omni-directional antennas 1 1 A and 1 1 B respectively to transmit and receive

signals over ground link channel 20.

Communications between mobile users, repeaters, and the base station

can be performed using a variety of multiplexing schemes that are well known in

the art. For example, a time division multiplex (TDM) scheme may be used for this purpose. FIG. 3a shows a typical uplink GSM TDMA frame 21 comprising

eight time slots, used for transmission from a translating repeater 1 2 to a BTS

1 5. The depicted GSM TDMA frame has a duration of 4.62 milliseconds,

comprising eight time slots each having a duration of 0.58 milliseconds.

Generally, for GSM-type TDMA implementations which use a single RF carrier,

one time slot is dedicated to transmitting control information, while the

remaining slots are available to transmit traffic information. Traffic channels can

carry conversations or data, as well as control information about mobile unit

itself.

Referring to FIG. 3a, slot 0 is a dedicated control channel while time slots

1 -7 support traffic. A full time slot of a given carrier frequency is commonly

referred to as a channel. Portions of a time slot, or sub-time slots, assigned

specific functions will be referred to herein as sub-channels. Typical formats for

the traffic sub-channels and control sub-channels are shown in time slot details

22 and 23, respectively. Detail 22 of time slot 4 shows typical GSM format

traffic sub-channels including tail bits 22-1 and 22-7 which are used to indicate

the beginning and end of a time slot. Data bits 22-2, 22-6 contain the digitized

call information, while training sequence bits 22-4 are used for equalization of

multi-path signals. Stealing bits 22-3, 22-5 are provided to indicate if

suppression of time slot data and replacement with priority data is requested.

Finally, guard bits 22-8 are provided to keep the individual slots from

overlapping upon receipt. The number of bits contained in a typical traffic

sub-channel is shown below the sub-channel designation in detail 22. As noted earlier, in single TDMA RF carrier implementations, one time slot

will generally be a digital control channel. As shown in detail 23 of time slot 0,

sub-channels in the uplink control time slot generally include a stand-alone

dedicated control sub-channel (SDCCH) 23-1 and a random access sub-channel

(RACH) 23-2. The SDCCH sub-channel 23-1 is used by translating repeater 1 2

to relay mobile user 1 8 information to complete call setup and for transmission

of messages for a mobile user 1 8. The RACH sub-channel 23-2 is used by

mobile users 1 8 for initial access to the network.

FIG. 3b shows a typical GSM-type eight slot TDMA frame 24 used in BTS

1 5 to translating repeater 1 2 communications. Generally, the information

format in the traffic time slots 1 -7 remains the same compared to the uplink, but

more control sub-channels are included in the control time slot 0 (compared to

the corresponding uplink control channel in detail 23), as shown in detail 26.

Specifically, downlink control time slot 0 is comprised of a frequency correction

sub-channel (FCCH) 26-1 , synchronization sub-channel (SCH) 26-2, broadcast

control sub-channel (BCCH) 26-3, paging and access grant sub-channel (PAGCH)

26-4 and SDCCH downlink sub-channel 26-5. The FCCH sub-channel 26-1

transmits frequency correction information (through translating repeater 1 2) for

a mobile user 1 8 to correct its time base, while the SCH 26-2 sub-channel

transmits (through translating repeater 1 2) synchronization information for the

mobile to synchronize to the framing structure of the network. The BCCH 26-3

sub-channel transmits (through translating repeater 1 2) information to idle

mobile users 1 8 such as local area identification and neighbor cell information. The PAGCH 26-4 sub-channel is used (through translating repeater 1 2) to page

a mobile and grant access to a mobile user 1 8 during call set up. Finally, the

SDCCH subchannel 26-5 is used (through translating repeater 1 2) to transmit

call setup information from BTS 1 5 to mobile users 1 8 to complete call setup.

FIG. 4 is a detailed block diagram of a translating repeater 1 2 which can

be used in connection with the present invention. Translating repeater 1 2 can

comprise a ground sector transceiver 27 for communications with mobile user

1 8 and backhaul transceiver 28 for communications with host BTS 1 5. It will

readily be appreciated by those skilled in the art that the particular transceiver

architecture shown is not critical to the invention and the invention as described

herein is not intended to be so limited.

In a preferred embodiment, transceivers 27 and 28 are each capable of

transmitting and receiving over a broad range of carrier frequencies allocated to

a service provider for multi-carrier operation. However, the invention is not

limited in this regard and more narrowbanded transceivers can also be used for

the purposes of the present invention. Each transceiver 27, 28 is preferably

configured so that its operation can be controlled by microprocessors 46 and

47, respectively.

FIG. 4 shows a single sector omni-directional translating repeater 1 2, it

being understood that the invention is not so limited. In fact, a variety of

sectorized translation repeaters can also be used for this purpose. In the receive

direction, voice or data signals are encoded and transmitted by mobile user 1 8

using a standard wireless telephony format such as GSM and typically result in signal power received at ground sector transceiver at omni-directional antennas

1 1 A and/or 1 1 B of from between about -1 1 1 to -25 dBm. The received signal

passes through cavity filter 29A to downconverter 35A or, alternatively, 35B

where, in conjunction with synthesizer module 36A and voltage-controlled

crystal oscillator 37A, the signal is mixed down to intermediate frequency or IF.

A high-speed analog-to-digital converter 39A (or 39B) then converts the analog

IF signal into a digital signal. Once the IF signal is digitized, digital

downconverter 41 A (or 41 B) translates the signal down to a complex baseband

signal. Digital downconverter 41 preferably provides the ability to downconvert,

decimate, filter and control the power level of the signal. After conversion to

complex baseband, the signal is demodulated by digital signal processor 42A.

Digital signal processor 42A is configured for decoding the received signal data

from the standard wireless telephony format, such as GSM, to a common

format used internally within translating repeaters 1 2.

The common format data is then transferred over multi-channel buffered

serial port 32 to digital signal processor 42B in backhaul transceiver 28. The

signal is re-modulated by digital signal processor 42B. The re-modulated signal

is output as a complex baseband signal and translated to real IF by digital

upconverter 40B. After the signal is translated to real IF, digital-to-analog

converter 38C converts the signal back to an analog signal where it is mixed by

upconverter 34B in conjunction with synthesizer module 36B and

voltage-controlled crystal oscillator 37B. The signal then passes through cavity

filter 29B and is transmitted via translating repeater directional antenna 1 3 on uplink backhaul channel 19-1 to host BTS 1 5.

Transceivers 27 and 28 are preferably controlled by one or more control

circuits. The control circuits can be in the form of general purpose computers

interfaced with the transceiver, a programmable microprocessor integrated with

the transceivers with appropriate software, a hardware based controller, or any

other combination of microprocessors, electronic circuitry and programming as

may be necessary or appropriate for controlling the first and second

transceivers.

As shown in FIG. 4, the control circuits include master processor 47 and

control processor 46. Master processor 47 preferably controls the operation of

backhaul transceiver 28, including selection of transmit and receive frequencies.

Master processor 47 is also linked with PCM data and message bus 31 so that it

can communicate with control processor 46, and vice versa. Control processor

46 is preferably a slave processor controlled by master processor 47. Control

processor 46 can also preferably control the operation of ground sector

transceiver 27, including selection of transceiver receive and transmit

frequencies.

Frequency translation of signals by translating repeater 1 2 received from

the BTS 1 5 through the backhaul channel 1 9-2 is similar to the procedure

employed to translate signals received from mobile users 1 8. Specifically, a

signal, preferably at -70 dBm but typically ranging anywhere from -1 1 1 dBm to

-25 dBm, is received from a BTS 1 5 at translating repeater directional antenna

1 3 attached to backhaul transceiver 28. The signal passes through cavity filter 29B to downconverter 35C where, in conjunction with synthesizer module 36B

and voltage-controlled crystal oscillator 37B, the signal is mixed down to IF.

Analog-to-digital converter 39C converts the analog IF signal to a digital signal

where it is subsequently processed by digital downconverter 41 C to complex

baseband.

Once converted into complex baseband, the signal is demodulated by

digital signal processor 42B and transferred to digital signal processor 42A over

multi-channel buffered serial port 32. The signal is then re-modulated by digital

signal processor 42A and translated from complex baseband to real IF by digital

upconverter 40A. After the signal is translated to real IF, digital-to-analog

converter 38A converts the signal back to an analog signal. Upconverter 34A,

synthesizer 36A, and voltage-controlled crystal oscillator 37A operate together

to mix the signal for transmission. The signal is then amplified by high-power

amplifier 30, filtered by cavity filter 29A and transmitted from omni-directional

antenna 1 1 A to the mobile user 1 8 through ground link channel 20-2.

Translating repeater 1 2 may include memory, such as shared memory 75.

In addition, translating repeater 1 2 may also include external alarm surge

protection 33, which may be interfaced with master processor 47.

Referring now to FIG. 5, a broadband BTS 50 is illustrated, which

comprises a receiver section 56 and a transmitter section 55. It will be readily

appreciated by those skilled in the art that the particular transceiver architecture

shown is not critical. Accordingly, the invention disclosed herein is not intended

to be so limited. Receiver section 56 preferably includes antennas 68, 70 and a wideband receiver 51 capable of receiving a plurality of carrier frequency

channels. Signals from the received channels can include new power requests,

power adjustment requests and traffic channel data from mobile users 1 8. The

term "wideband," as used herein, is not limited to any particular spectral range,

and it should be understood to imply a spectral coverage of multiple frequency

channels within the communication range over which a wireless communication

system may operate (e.g. 1 2 MHZ). Narrowband, on the other hand, implies a

much smaller portion of the spectrum, for example, the width of an individual

channel (e.g. 30 kHz).

The output of the wideband receiver 51 is downconverted into a

multi-channel baseband signal that preferably contains the contents of all of the

voice/data carrier frequency channels currently operative in the communication

system or network of interest. This multi-channel baseband signal is preferably

coupled to high speed A-D converters 52-1 and 52-2 operating in parallel for

diversity receive capability. Where no diversity capability is required, a single

A-D 52-1 could be utilized. Additionally, more than one parallel leg may be

required for sectorized applications. Hence, it should readily be appreciated by

one skilled in the art that the presence of a second parallel processing leg is not

intended to be a limitation on the instant invention. The dynamic range and

sampling rate capabilities of the A-D converter are sufficiently high (e.g. the

sampling rate may be on the order of 25 Mega-samples per second (Msps)) to

enable downstream digital signal processing (DSP) components, including

Discrete Fourier Transform (DFT) channelizers 53-1 and 53-2, to process and output each of the active channels received by receiver 56.

The channelized outputs from the A-D converters are further processed to

extract the individual channel components for each of the parallel streams. FFT

channelizers 53-1 and 53-2 are preferably used to extract respective

narrowband carrier frequency channel signals from the composite digitized

multi-channel signals. These narrowband signals are representative of the

contents of each of the respective individual carrier frequency communication

channels received by the wideband receiver 51 . The respective carrier

frequency channel signals are coupled via N output links through a common data

bus 61 to respective digital signal processing receiver units 63-1 ...63-N, each of

which demodulates the received signal and performs any associated error

correction processing embedded in the modulated signal. In the case where the

received signals are destined for the PSTN, these demodulated signals derived

from the digital signal processing receiver units 63 can be sent via a common

shared bus 54 to a telephony carrier interface, for example, T1 carrier digital

interface 62, of an attendant telephony network (not shown) .

The transmitter section 55 includes a second plurality of digital signal

processing units, specifically, transmitter digital signal processing units

69-1 ...69-N, that are coupled to receive from the telephony network respective

ones of a plurality of channels containing digital voice/data communication

signals to be transmitted over respectively different individual carrier frequency

channels of the multi-channel network. Transmitter digital signal processing

units 69 modulate and perform pre-transmission error correction processing on respective incoming communication signals, and supply processed carrier

frequency channel signals over the common bus 54 to respective input ports of

an inverse FFT-based multi-channel combiner unit 58. The combiner 58 outputs

a composite multi-channel digital signal. This composite signal is representative

of the contents of a wideband signal which contains the respective narrowband

carrier frequency channel signals output from the digital signal processing

transmitter units 69. A composite signal generated from the output of the

multi-channel combiner unit 58 is then processed by the digital-to-analog (D-A)

converter 59. The output of D-A converter 59 is coupled to a wideband

(multi-channel) transmitter unit 57, which can include or have a separate

multi-channel high power amplifier (HPA) 57A. The transmitter unit 57

transmits a wideband (multi-channel) communication channel signal defined by

the composite signal output of the inverse fast Fourier transform-based

combiner unit 58. The output of the HPA 57A is then coupled to antenna 68

for transmission.

A central processing unit (CPU) controller 64 is provided for coordinating

and controlling the operation of BTS 50. For example, the CPU 64 can include a

control processing unit, memory and suitable programming for responding to

transmit power control requests received from mobile transceiver units. CPU 64

can selectively control transmit power levels for each TDMA communication

channel on a timeslot-by-timeslot basis. The CPU 64 may be a microprocessor,

DSP processor, or micro controller having firmware, software or any

combination thereof. DSPs 63 can extract encoded information from each of the narrowband

carrier frequency channel signals. Information for each of these channels can be

stored in shared memory 75 through the common control and data bus 61 . CPU

64, under firmware and/or software control, can then access the shared memory

75 through bus 61 . For example, control channel data concerning a particular

downlink or control channel can be received at antenna 70 from a repeater

station through a backhaul communication link. After the information for each

channel in the received signal is processed and separated, DSPs 63 can store

the control channel data in the shared memory 75. CPU 64 can then access

shared memory 75 to retrieve the control channel data. CPU 64, under

software and/or firmware control, can then use this data, for example, as an

input to a control algorithm. The output from the algorithm can be stored in

shared memory 75 for later use.

With this background in mind, dynamically distributing mobile traffic

capacity of a single TDMA RF carrier over multiple cell sites can now be better

understood. Referring now to FIG. 6a, a TDMA cellular system is shown

comprising a single base station 80 assigned a single RF carrier frequency and

seven surrounding translating repeaters 82-1 ...82-7. BTS 80 may only be

assigned a single RF carrier in low cellular usage zones. In prior art cellular

systems, such as Carney, BTS 80 must assign the full TDMA RF carrier for

exclusive use to a single translating repeater 82. Thus, although prior art BTS

80 supports seven traffic channels and a dedicated control channel in a typical

GSM TDMA system, all seven traffic channels must be assigned to a single translating repeater 82, such as 82-2 as shown in FIG. 6b. Thus, although

seven mobile users can be simultaneously supported in the system of FIG. 6,

each mobile user must be located within the cell associated with the translating

repeater assigned the TDMA RF carrier. The invention provides a method for

dynamically distributing the traffic capacity of a single TDMA RF carrier

frequency to multiple translating repeaters 82, thus simultaneously supporting

mobile users 1 8 located in multiple cell sites using a single RF carrier frequency.

To implement the invention, in communications between BTS 80 and its

associated translating repeaters 82-1 ...82-7, each may recognize control

signals as coming from or destined for a specific translating repeater 82.

Referring again to FIG. 3b, in the preferred embodiment of the invention, a

translating repeater control sub-channel (TRCH) may be created and positioned

within the downlink control channel to enable specific translating repeaters 82

to recognize control signals transmitted by host BTS 80, which are intended for

a particular translating repeater 82. For example, assuming the dedicated

control channel is otherwise fully utilized, a sub-time slot to create a TRCH

sub-channel may be made available by realizing that the BCCH sub-channel 26-3

generally transmits repetitive information from host BTS 80 to each translating

repeater 82. This same information is retransmitted by translating repeaters 82

to mobile users 1 8 in their cells. For example, upon a mobile user 1 8 entering a

particular cell, cell specific information such as the identity of the network,

current location area code and information on nearby cells (such as neighboring

cell lists with associated frequencies used to aid in handoffs) is generally provided to the mobile user 1 8. This cell specific information provided to the

mobile user 1 8 changes infrequently.

Translating repeaters 1 2 are generally installed stationary and thus only

need to receive updated BCCH 26-3 information when something changes in the

system that affects the served cell (such as a neighbor cell list). Thus,

appropriately equipped translating repeaters 82 having memory may receive this

information from BTS 80 and store it in memory for retransmission to mobile

users 1 8 at later times. Once stored in memory, translating repeaters 82 may

use this stored information for transmitting the same to the mobile user 1 8,

rather than receiving and re-broadcasting the repetitive BCCH 26-3 information

otherwise continually sent by BTS 80. Using this method, the BCCH

sub-channel 26-3 over the backhaul link may be made available for other uses.

The sub-time slot occupied by the former BCCH sub-channel 26-3 may be used

for a TRCH sub-channel.

Although the invention describes use of the BCCH sub-channel 26-3 for

the TRCH sub-channel, sub-time slots normally allocated for other purposes may

also be used. For example, FCCH 26-1 and SCH 26-2 sub-channels may also be

reallocated for use as a TRCH to independently control translating repeaters 82

associated with a given BTS 80. In addition, it will readily be appreciated by

those skilled in the art that the particular method of adding a TRCH is not critical

to the invention and the invention as described herein is not intended to be so

limited.

In the preferred embodiment, the invention utilizes the digital translating repeater 82 as shown in FIG. 4 and uses shared memory 75 to store repetitive

information received from BTS 80 for later transmission to mobile users 18.

However, the invention may also be used with non-translating repeaters,

provided that the non-translating repeaters have appropriate memory.

To implement the invention, signals sent to translating repeaters 82 from

BTS 80 and received by BTS 80 from translating repeaters 82 may include a

methodology for identifying specific translating repeaters 82. Three example

methods are described for identifying translating repeaters 82 served by a BTS

80, for downlink communications. However, analogous methods may also be

used in the uplink direction. A first method comprises adding distinct addresses

which may be identified with specific translating repeater 82. For example, in a

system having seven translating repeaters, three bits (permitting seven distinct

digital addresses 001 to 1 1 1 ) may be used to uniquely identify each of seven

translating repeater 82-1 ...82-7. These address bits may be positioned in the

sub-timeslot normally allocated to the BCCH sub-channel 26-3 to control signals

sent by BTS 80 to translating repeaters 82-1 ...82-7 as well as signals sent by

each translating repeater 82-1 ...82-7 to BTS 80. The addressing technique can

also be modeled after common Internet protocol (IP) addressing. Alternatively,

the dedicated control channel can be further divided into subdivided sub-time

slots, specific times which may be identified with a specific translating repeater

82. For example, for a cellular system comprising a host BTS 80 and seven

translating repeaters 82, the sub-time slot represented by the first 1 /7 of the

sub-time slot normally allocated to the BCCH sub-channel 26-3 in each control time slot may be identified with translating repeater 82-1 . Similarly, the second

1 /7 of each control time slot may be identified within the system with

translating repeater 82-2, and so on.

As a further alternative, a given sub-time slot in the control channel on

periodically spaced frames may be identified with a specific translating repeater

82. Thus, if translating repeater 82-1 is assigned the control channel in frames

1 , 9, 1 7, 25, etc., control signals sent by BTS 80 on such frames may be

identified with translating repeater 82-1 . The methods disclosed above are not

exhaustive. Other methods for identifying and enabling specific translating

repeaters 82 will be apparent to those skilled in the art.

Referring to FIGS. 3a, 3b, and 7, in step 710, a mobile user 1 8 may send

a RACH signal 23-2 requesting access to a traffic channel (collectively TCH 90)

to the translating repeater 82 located in his or her cell. Slots 1 -7 in FIG. 3a on

the uplink and slots 1 -7 FIG. 3b on the downlink represent TCHs (90). In step

720, translating repeater 82 decodes the RACH signal 23-2 received from the

mobile user 1 8. In step 730, translating repeater 82 informs host BTS 80 of the

mobile's 1 8 attempt to access a TCH 90 in the cell served by the translating

repeater 82 over the RACH 23-2 with a modified RACH signal 23-2 that

uniquely identifies the requesting translating repeater 1 2 as well as the mobile

user 1 8 requesting system access. The RACH signal 23-2 from the translating

repeater 82 to host BTS 80 adds information that identifies the specific

requesting translating repeater 82-1 ...82-7 to the RACH signal 23-2 received

from the mobile user 18. The method used to identify a specific requesting translating repeater may

be analogous to the techniques discussed relating to downlink communications

between BTS 80 and translating repeaters 82-1 ...82-7. In step 740, BTS 80

receives and decodes the translating repeater's 82 RACH signal 23-2. If the

mobile user 1 8 is authenticated, BTS 80 responds by allocating an available and

unused TDMA traffic channel to the requesting translating repeater 82 (at the

backhaul frequency) and the mobile user 1 8 for use in the translating repeater's

82 cell. In step 750, BTS 80 sends a control signal over the TRCH containing

the time slot of the allocated TDMA channel and the identity of the requesting

translating repeater 82. In step 760, translating repeater and the mobile user 1 8

begin transmissions on the assigned TDMA traffic channel. In step 770, BTS

80 determines that transmissions on the allocated TDMA channel are completed

or that the call has been handed off to a neighboring cell. In step 780, BTS 80

disables the TDMA traffic channel assigned in step 740 through an appropriate

TRCH signal. In step 790, the TDMA traffic channel assigned in step 740 is

returned to an unused and available set of TDMA traffic channels.

In the preferred embodiment of the above method, the TRCH is used bi-

directionally. In addition to commanding the translating repeater 82 over the

downlink to activate, deactivate, or perform other control functions, a TRCH

could be allocated on the uplink backhaul control channel. This uplink TRCH

could be used by the translating repeater 82 for purposes such as sending

status and alarms detected at the translating repeater 82 to the BTS 80. The

BTS 80 can forward such messages to the cellular operator. Alternatively, traffic channels from a single RF carrier can be dynamically

distributed over multiple cell cites without the use of a control channel between

BTS 80 and translating repeater 82. In this method, translating repeaters 82

simply monitor messages received from BTS 80 and act as switches between

BTS 80 and mobile users 1 8, in response to activation or deallocation of TCHs

90 commanded by BTS 80. A mobile user 1 8 accesses the translating repeater

82 in its cell using a RACH. The translating repeater 82 can decode the RACH

received to determine a random value included in the RACH to determine the

mobile user's 1 8 identity and the type of access requested (answer to page,

originating call, location update, etc.) . The RACH information received by the

translating repeater 82 can be passed by the translating repeater 82 to the BTS

80 unaltered. The translating repeater 82 then can await the BTS 80 to respond

on a downlink control subchannel, such as an AGCH, with an allocated SDCCH

and the random value transmitted by the mobile user 1 8.

If the random value is received by translating repeater 82, the translating

repeater 82 can enable the allocated SDCCH to be passed through from BTS 80

to the mobile user 1 8. The translating repeater 82 can then monitor the

allocated SDCCH looking for a TCH 90 assignment to the mobile user 1 8 by the

BTS 80. When the BTS 80 TCH 90 assignment included on the allocated

SDCCH is detected by the translating repeater 82, the translating repeater 82

can allow the TCH 90 assignment received from BTS 80 to be passed through

unaltered to the requesting mobile user 1 8. The translating repeater 82 can also

monitor the TCH 90 assigned to a mobile user 1 8 in its cell for BTS 80 deactivation messages. Upon receipt of a deactivation message from BTS 80,

translating repeater 82 can respond by deactivating the TCH 90 to the mobile

user 18 in its cell.

Using the invention, all translating repeaters 82-1 ...82-7 may use any of

the TCHs 90 on the backhaul as well as locally. After a call is terminated or

handed off to a neighboring cell, a disabled TCH 90 may be re-used at a later

time by any translating repeater 82 served by host BTS 80. FIG. 8 applies the

invention to the cellular system shown in FIG. 6a having a BTS with a single

TDMA RF carrier and seven translating repeaters 82-1 ...82-7. Referring now to

FIG. 8a, assignments of seven TDMA TCHs 90 are shown at a first time. Note

that some translating repeaters, such as 82-3, are not assigned any traffic

channels 90, while some translating repeaters 82 may be assigned more than

one TCH 90. FIG. 8b shows the assignments of seven traffic channels at a

second time, a time after the first time. During the interval between the first

and second time, calls were terminated in cells 1 , 4 and 6 and initiated in cells 2

and 7.

The ability to uniquely identify signals as coming from specific translating

repeaters 82 may be used when transmitting certain information to BTS 80

requiring unique translating repeater 82 identification. To perform this function,

the frames normally used for RACH 23-2 may be made available for such uses.

For example, since translating repeaters 82 are generally at different distances

from host BTS 80, for TDMA implementations, the uplink signals received from

each translating repeater 82-1 ...82-7 served by a given BTS 80 must be adjusted to synchronize the transmitted signals into specific time slots (bursts)

upon arrival at host BTS 80 for proper time division multiplexing. To assure

synchronization, signals from each translating repeater 82-1 ...82-7 must be

measured by host BTS 80. Based on these measurements, translating repeaters

82 may be separately commanded by BTS 80 to adjust their time slot (burst)

timing to align with a predetermined time base. The predetermined time base is

typically generated by a master clock incorporated into BTS 80. This operation

may be performed as follows:

1 . During system initialization, each translating repeater 82 transmits

a special access burst over the control channel during the sub-time slot normally

allocated for the RACH sub-channel.

2. Host BTS 80 recognizes the access burst as one from a specific

translating repeater 82. Any available methodologies for identifying a specific

translating repeater 82 may be used, such as specific addressing, use of

assigned sub-time slots, or specific control channel frames numbers

assignments.

3. Host BTS 80 measures the timing of each translating repeater 82-1

...82-7 access burst. BTS 80 then separately commands specified translating

repeaters 82-1 ...82-7 over the TRCH to adjust their timing. Timing is adjusted

such that transmitted signals from translating repeaters 82-1 ...82-7 fit precisely

into specific time slots upon arrival at host BTS 80.

Besides communications to host BTS 80 required for time slot alignment,

each translating repeater 82-1 ...82-7 may need to transmit other information to host BTS 80, such as alarm formation. This information may be communicated

from translating repeaters 82-1 ...82-7 to host BTS 80 also using control

channel sub-time slots normally used for the RACH sub-channel 23-2, as

follows:

1 . Requesting translating repeater 82 signals its need to transmit this

type of information with transmission of a special RACH 23-2 burst, which is

identifiable as coming from a specific translating repeater 82- 1 ...82-7.

2. Host BTS 80 may allocate an SDCCH 23-1 channel for

communication with the requesting translating repeater 82.

3. Requesting repeater 82 is then commanded by BTS 80 over the

TRCH to transmit its information over the specified SDCCH 23-1 .

4. Once the transmission is completed, the SDCCH 23-1 is

deallocated by BTS 80.

In addition, since the backhaul, and thus the RACH 23-2 transmitted by

translating repeaters 82 to host BTS 80, is shared among several translating

repeaters 82 on a common control channel, there is a chance that more than

one translating repeater 82 may try to access host BTS 80 on the same channel

at the same instant. Simultaneous requests for access may arrive at host BTS

80, thereby creating a corrupted signal. In this event, host BTS 80 may treat

this situation as if two mobile users 1 8 tried to access BTS 80 simultaneously,

basically ignoring the corrupted composite RACH signal caused by the

combination of individual RACH signals 23-2 from more than one translating

repeater 82. If the originating signals were from mobile users 1 8 and two or more RACH signals 23-2 arrived at a translating repeater 82 at the same instant

on the same channel, the translating repeater 82 would wait until the mobiles

tried again to gain access. In either above situation, the requester would simply

repeat the request after a random period of time.

Other control sub-channels remain unchanged under the invention. The

PAGCH 26-4, FCCH 26-1 , SCH 26-2 and SDCCH 26-5 control sub-channels

transmitted by host BTS 80 may each be passed through the translating

repeater 82 to mobile users 1 8 its cell unaltered, other than frequency shifted.

Likewise, TCH 90 would be passed through when enabled. Translating

repeaters 82 can request access on the RACH 23-2 to access host BTS 80 the

same as mobile users 1 8. The SDCCH sub-channel 26-5 could be assigned to

any translating repeater 82 in a similar manner as mobiles are assigned to

SDCCHs.

The invention described uses a GSM air-interface. However, this

invention could also apply to other TDMA structures such as IS-1 36 and IS-54.

Additionally, the invention may be practiced with either a broadband BTS or a

narrowband BTS. It should be understood that the examples and embodiments

described herein are for illustrative purposes only and that various modifications

or changes in light thereof will be suggested to persons skilled in the art and are

to be included within the spirit and purview of this application. The invention

can take other specific forms without departing from the spirit or essential

attributes thereof for an indication of the scope of the invention.

Claims

CLAIMSWhat is claimed is:

1 . In a wireless cellular communications system having a plurality of

translating repeaters communicating with mobile subscribers and communicating

with a base station via a backhaul communications link, a method for improved

carrier frequency usage comprising the steps of:

assigning a single shared carrier frequency to said plurality of translating

repeaters for said backhaul communications link;

exclusively assigning to each of said plurality of translating repeaters at least

one time slot defining a TDMA channel for said backhaul communications link;

and

performing backhaul communications between said base station and said

plurality of translating repeaters on said single shared carrier frequency with

each of said translating repeaters using said exclusively assigned TDMA

channel.

2. The method according to claim 1 , wherein each of said TDMA

channels is assigned to a requesting one of said translating repeaters responsive

to a request received at said base station from said requesting one of said

translating repeaters.

3. The method according to claim 2, further comprising the step of

exclusively assigning to said requesting one of said translating repeaters at least one additional TDMA channel for communicating additional traffic on said

backhaul communication link upon request.

4. The method according to claim 2, further comprising the step of

re-assigning at least one of said TDMA channels to an unused and available set

of TDMA channels when said TDMA channel is no longer needed by any one of

said translating repeaters.

5. The method according to claim 1 , wherein at least one additional

TDMA channel on said single shared carrier frequency is exclusively assigned as

a dedicated control channel.

6. The method according to claim 5, further comprising the step of

storing repetitive control channel information in memory of said translating

repeaters, whereby a portion of at least one frame of said dedicated control

channel is made available on said backhaul communications link for controlling

operation of said plurality of translating repeaters.

7. The method according to claim 6, further comprising the step of

using said made available portion of said at least one frame of said dedicated

control channel for TDMA channel assignments to said plurality of translating

repeaters.

8. The method according to claim 7, further comprising the step of

using said translating repeater control channel to align time slot bursts received

from said translating repeaters.

9. The method according to claim 5, further comprising the step of

transmitting control information from one or more said translating repeaters to

said base station, whereby upon receipt, said base station recognizes said

transmitted control information as originating from one of said translating

repeaters.

10. The method according to claim 5, further comprising the steps of:

transmitting control information from at least one of said plurality

of translating repeaters to said base station, said control information requesting

one of said TDMA channels for a requesting mobile user, said transmission

including information identifying said requesting mobile user;

monitoring control information transmitted by said base station,

said base station control information including a TDMA channel assignment and

said identifying information;

retransmitting said TDMA channel assignment to said requesting

mobile user if said identifying information is detected.

1 1 . The method according to claim 5, further comprising the step of deallocating said assigned TDMA channel by said translating repeater responsive

to a deallocation message transmitted by said base station, if said deallocation

message includes said identifying information.

1 2. In a wireless cellular communications system having a plurality of

translating repeaters communicating with mobile subscribers and communicating

with a base station via a backhaul communications link, a system for improved

carrier frequency usage comprising:

a means for assigning a single shared carrier frequency to said

plurality of translating repeaters for said backhaul communications link;

a means for exclusively assigning to each of said plurality of

translating repeaters at least one time slot defining a TDMA channel for said

backhaul communications link, and

a means for performing backhaul communications between said

base station and said plurality of translating repeaters on said single shared

carrier frequency with each of said translating repeaters using said exclusively

assigned TDMA channel.

1 3. The system according to claim 1 2, further comprising a means for

assigning each of said TDMA channels requesting one of said translating

repeaters in response to a request received at said base station from said

requesting one of said translating repeaters.

14. The system according to claim 1 3, further comprising a means for

exclusively assigning to said requesting one of said translating repeaters at least

one additional TDMA channel for communicating additional traffic on said

backhaul communication link upon request.

1 5. The system according to claim 1 3, further comprising a means for

re-assigning at least one of said TDMA channels to an unused and available set

of TDMA channels when said TDMA channel is no longer needed by any one of

said translating repeaters.

1 6. The system according to claim 1 2, further comprising a means for

assigning at least one additional TDMA channel on said single shared carrier

frequency exclusively as a dedicated control channel.

1 7. The system according to claim 1 6, further comprising a means for

storing repetitive control channel information in memory of said translating

repeaters, whereby a portion of at least one frame of said dedicated control

channel is made available on said backhaul communications link for controlling

operation of said plurality of translating repeaters.

1 8. The system according to claim 1 7, further comprising a means for

using said made available portion of said at least one frame of said dedicated control channel for TDMA channel assignments to said plurality of translating

repeaters.

1 9. The system according to claim 1 8, further comprising a means for

using said translating repeater control channel to align time slot bursts received

from said translating repeaters.

20. The system according to claim 1 6, further comprising a means for

transmitting control information from one or more said translating repeaters to

said base station, whereby upon receipt, said base station recognizes said

transmitted control information as originating from one of said translating

repeater