United States Patent (19)
`Langlet et al.
`
`54
`
`(75)
`
`RADIO COMMUNICATION SYSTEM WITH
`DIVERSITY RECEPTION ON A TIME-SLOT
`BY TIME-SILOT BASIS
`
`Inventors: Carl Erik Joakim Langlet, Farentuna;
`Bo Anders Granstrom, Jarfalla, both
`of Sweden
`
`Assignee: Telefonaktiebolaget LM Ericsson,
`Stockholm, Sweden
`
`Appl. No.: 08/864,684
`Filed:
`May 28, 1997
`Int. Cl. ..................................................... H04Q 7/00
`U.S. Cl. ............................................. 370/332; 370/347
`Field of Search ..................................... 370/331, 332,
`370/333,334, 337,264, 347
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`5,542,107 5/1990 Kay ........................................ 455/33.1
`
`USOO5991282A
`Patent Number:
`11
`(45) Date of Patent:
`
`5,991,282
`Nov. 23, 1999
`
`5,577,047 11/1996 Persson et al. ........................ 370/95.3
`5,812,935 9/1998 Kay ........................................ 455/56.1
`FOREIGN PATENT DOCUMENTS
`O 454 368 A2 10/1991 European Pat. Off..
`O 501808 A2 2/1992 European Pat. Off..
`4-227136 8/1992 Japan.
`7-273705 10/1995 Japan.
`Primary Examiner-Chi H. Pham
`Assistant Examiner Kim T. Nguyen
`Attorney, Agent, or Firm-Burns, Doane, Swecker &
`Mathis, L.L.P.
`ABSTRACT
`57
`A communication System base Station improves uplink cov
`erage on a time slot by time slot basis. The coverage is
`improved by allocating diversity and non-diversity time
`Slots based on received signal quality of an RF link between
`a mobile Station and a base Station. The diversity time-slots
`are time slots during which information is received by more
`receiver branches than during the non-diversity time-slots.
`
`32 Claims, 4 Drawing Sheets
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`1
`RADIO COMMUNICATION SYSTEM WITH
`DIVERSITY RECEPTION ON A TIME-SLOT
`BY TIME-SILOT BASIS
`
`BACKGROUND
`This invention generally relates to the field of communi
`cation Systems and, more particularly, to the improvement of
`receiver Sensitivity, adjacent-channel and co-channel rejec
`tion in a communication System that Sub-divides RF chan
`nels into time slots.
`Time division multiple access (TDMA) communication
`systems, such as those based on GSM, PDC, D-AMPS
`communication Standards, Subdivide one or more radio
`frequency (RF) channels into a plurality of time slots during
`which mobile Stations within the System engage in Voice and
`data communication. By transmitting and receiving bursts of
`information during allocated time slots, the mobile Stations
`communicate through a plurality of Scattered base Stations,
`which cover corresponding communication cells. Within
`each cell, a base Station communicates with the mobile
`stations over a number of RF channels by transmitting bursts
`of downlink data to the mobile stations over downlink RF
`channels and receiving bursts of uplink data from the mobile
`stations over uplink RF channels.
`To avoid co-channel interference, neighboring cells are
`allocated different RF channels. Because of the relatively
`low power RF transmissions within a particular cell, another
`cell Spaced two or more cells apart may typically reuse the
`Same frequency. The farther the cells reusing the same
`frequencies are from each other, the lower the co-channel
`interference between them. Therefore, lowering co-channel
`interference of the uplink channels increases System capac
`ity by allowing a tighter frequency reuse cell pattern in a
`dense communication network.
`It is also very important to provide wide coverage using
`fewer number of base Stations, to reduce implementation
`cost of the network. One factor that is directly related to a
`base Station's coverage is its Sensitivity to received signals
`on the uplink channel. Some conventional Systems equip the
`base Stations with low noise amplifiers, which are positioned
`at close proximity to base Station antennas.
`Another conventional method to improve both co-channel
`interference and receiver Sensitivity uses receiver diversity
`under which two or more Spaced apart antennas that are
`coupled to corresponding receiver branches receive uplink
`Signals from the mobile Station. Based on well known
`principles that relate to combining non-coherent noise and
`desired Signals, received Signal quality is improved by
`combining received signals from the receivers. For example,
`Some conventional GSM Systems combine uplink Signals
`received by two receiver branches at the base Station, to
`improve uplink received signal quality on a continuous
`basis. Other Systems combine received Signals from two or
`more receiver branches, when the received signal Strength
`from a mobile Station at a single receiver drops below a
`predefined threshold.
`Conventional methods, however, do not improve
`co-channel interference and receiver Sensitivity on a time
`slot by time-slot basis. Because TDMA systems sub-divide
`RF channels into time slots, the received signal quality may
`be degraded during a time slot of the uplink channel that is
`assigned to a particular mobile Station. For example, the
`receiver Sensity of a signal received from a mobile Station at
`the fringes of a communication cell may be well below a
`desired level, requiring improvement during its allocated
`time-slot. Although conventional TDMA systems use
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`receiver diversity continuously when receiving uplink RF
`Signals, they do not provide for receiver diversity on a
`time-slot by time-slot basis. Therefore, there exists a need to
`improve received signal quality of an uplink RF channel that
`is Subdivided into time slots during a Selected time slot.
`SUMMARY
`The present invention that addresses this need is exem
`plified in a communication System that allocates receiver
`diversity and non-diversity time-slots based on received
`Signal quality of an uplink RF channel. In this way, the
`System of the present invention improves the uplink
`coverage, including receiver Sensitivity co-channel and
`adjacent-channel rejection, only when necessary and avoids
`waste of resources when receiver diversity is not needed.
`In one aspect, the communication System of the invention
`includes a base Station that is linked to a mobile Station via
`one or more radio frequency channels that are Subdivided
`into a plurality of time slots. The base Station includes a
`plurality of receiver branches for receiving uplink data from
`the mobile Station on diversity and non-diversity time-slots.
`The diversity time-slots are time slots during which the
`uplink data is received using more receiver branches than
`the non-diversity time-slots. The system of the invention
`also includes a controller that allocates the diversity and
`non-diversity time-slots based on a measure of received
`Signal quality of the radio frequency channels that link the
`mobile Station to the base Station.
`According to Some of the more detailed features of the
`invention, the measure of received signal quality corre
`sponds to one or a combination of measure of received
`Signal Strength, bit error rate, or frame erasure rate at the
`base Station. In another feature of the present invention, the
`base Station includes a baseband bus that allows Selective
`combination of uplink data from the receiver branches.
`According to yet another feature of the invention, the uplink
`data is combined at the base Station by an equalizer.
`Other features and advantages of the present invention
`will become apparent from the following description of the
`preferred embodiment, taken in conjunction with the accom
`panying drawings, which illustrate, by way of example, the
`principles of the invention.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. 1 is a block diagram of a communication System
`which advantageously uses the present invention.
`FIG. 2 is a diagram of a subdivided RF channel that is
`used in the communication system of FIG. 1.
`FIG. 3 is a block diagram of a radio base Station according
`to one embodiment of the invention.
`FIG. 4 is a block diagram of a radio base Station according
`to another embodiment of the invention.
`
`DETAILED DESCRIPTION
`Referring to FIG. 1, a communication system 10 accord
`ing to an exemplary embodiment of the present invention
`operates according to the GSM standard. The mode of
`operation of GSM communication systems is described in
`European Telecommunication Standard Institute (ETSI)
`documents ETS 300 573, ETS 300 574 and ETS 300 578,
`which are hereby incorporated by reference. Therefore, the
`operation of the system 10 is described to the extent nec
`essary for understanding of the present invention. Although,
`the present invention is described as embodied in a GSM
`System, those skilled in the art would appreciate that the
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`present invention could be advantageously used in a wide
`variety of other digital communication Systems, Such as
`those based on PDC or D-AMPS Standards.
`The system 10 is designed as a hierarchal network with
`multiple levels for managing calls. Using an allocated Set of
`uplink and downlink RF channels, which are subdivided into
`time slots, mobile stations 12 operating within the system 10
`participate in calls using allocated time slots. At a high
`hierarchal level, a group of Mobile Service Switching Cen
`ters (MSCs) 14 are responsible for the routing of the calls
`from an originator to a destination. In particular, they are
`responsible for Setup, control and termination of the calls.
`One of the MSCs 14, known as the gateway MSC, handles
`communication with a Public Switched Telephone Network
`(PSTN) 18, or other public and private networks.
`At a lower hierarchal level, each one of the MSCs 14 are
`connected to a group of base station controllers (BSCs) 16.
`The primary function of a BSC 16 is mobility management.
`For example, based on reported received signal Strength at
`the mobile stations 12, the BSC 16 determines whether to
`initiate a hand over, the process by which the calls are
`maintained without a noticeable break. The BSC 16 com
`municates with a MSC 14 under a standard interface known
`as the A-interface, which is based on the Mobile Application
`Part of CCITT Signaling System No. 7.
`At a still lower hierarchal level each one of the BSCs 16
`controls, a group of base transceiver stations (BTSs) 20. The
`BTSs 20 primarily provide the RF links for the transmission
`and reception of data bursts to and from the mobile Stations
`12. In a preferred embodiment of the invention, a number of
`BTSs 20 are incorporated into a radio base station (RBS) 22.
`In an exemplary embodiment, the PBS 22 may be configured
`according to a family of RBS-2000 products, which is
`offered by LM EricSSon, the assignee of the present inven
`tion.
`Similar to other cellular communication Systems, the
`System 10 Subdivides a geographical area into contiguous
`communication cells that together provide communication
`coverage to a Service area, for example, an entire city. The
`communication cells are patterned according to a cell pattern
`that allows Some of the Spaced apart cells to use the same
`uplink and downlink RF channels. In this way, the cell
`pattern of the system 10 reduces the number of frequency
`channels needed to cover the service area. The system 10
`may also employs frequency hopping techniques, to avoid
`deadspots and to minimize interference in the System.
`Each BTS 20 includes a number of TRXs that use the
`uplink and downlink RF channels to Serve a particular
`common geographical area, Such as one or more communi
`cation cells. As described later in detail, the TRX includes a
`common pool of receiver branches for the reception of
`uplink Signals. Under the preferred embodiment, the
`receiver branches receive uplink Signals via a number of
`Space diversity, or polarization diversity or a combination of
`Space and polarization diversity antennas 24. This diversity
`arrangement improves the Overall co-channel and adjacent
`channel rejection and receiver Sensitivity of an RF channel
`by continuously combining received Signals at the diversity
`receivers of the TRXS.
`In order to improve co-channel interference and receiver
`Sensitivity on a time-slot by time-slot basis according to the
`present invention, the communication System 10 allocates
`Some time slots for the reception of uplink information as
`diversity time-slots. Other time slots are designated as
`non-diversity time-slots. Accordingly, the diversity time
`Slots are time slots during which uplink data is received by
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`more receiver branches than during non-diversity time-slots.
`AS a result, by Selective use of diversity reception, the
`present invention improves co-channel and adjacent-channel
`rejection and receiver Sensitivity on a time-slot by time-slot
`basis, as needed.
`The communication system 10 uses the BSC 16 for
`allocating the diversity and non-diversity time-slots. The
`BSC 16 instructs the RBS 22 to receive the information
`either via the diversity or non-diversity time-slots. The BSC
`16 instructs the RBS 22 based on a measures of received
`signal quality of the RF channels that link the mobile
`stations 12 to the RBS 22. As described later in detail, the
`received signal quality may be measured based on a number
`of parameters, including received signal Strength orbit error
`rate at the RBS 22.
`By taking into account the received signal quality, the
`communication System 10 improves uplink coverage by
`efficiently allocating diversity and non-diversity communi
`cation resources. The BSC 16 dynamically increases the
`number of time slots allocated for diversity reception, if the
`received signal quality of the linking RF channels So require.
`For example, when a large number of mobile Stations 12 are
`positioned at the fringes of a communication cell with
`degraded RF links on the non-diversity time slots, the BSC
`16 can designate Some of the non-diversity channels as
`diversity channels, to improve the uplink coverage.
`Similarly, the BSC 16 could reallocate the diversity time
`Slots as non-diversity time-slots, if the propagation proper
`ties of the RF channels are such that diversity reception is
`not necessary, thereby increasing System capacity.
`As a result, the BSC 16 regularly adjusts the size of the
`pools of time slots used for diversity or non-diversity
`reception. In this way, by using more receiver resources, the
`System 10 improves the received signal quality during a
`Selected time slot, thereby reducing capacity. Conversely,
`the capacity of the System 10 may be increases at the
`expense of reduced Signal quality from the mobile Stations.
`Therefore, the invention uses the common pool of receiver
`branches to balance the need for better reception of uplink
`Signals with the need for capacity. AS described later in
`detail, the BSC 16 also dynamically reallocates the diversity
`and non-diversity resources based on operating require
`ments of the System, for example, based on fault conditions
`reported by the RBS 22.
`With reference to FIG. 2, an RF channel 26 (uplink or
`downlink) is divided into repetitive time frames 27 during
`which information are transmitted. Each frame is further
`divided into time slots 28 that carry packets of information.
`The system 10 carries out the transmission of information
`during the time slots in bursts that contain a predefined
`number of encrypted bits. Speech data is transmitted during
`time slots designated as traffic channels (TC,..., TC). All
`Signaling functions pertaining to call management in the
`System, including initiations, hand overs, and termination
`are handled via control information transmitted over Signal
`ing channels.
`The Signaling channels may be transmitted during dedi
`cated time slots or they may be transmitted in association
`with a number of traffic channels. For each cell, the BSC 16
`allocates certain time slots on an RF channel as the dedicated
`Signaling channels. For example, a dedicated control
`channel, known as Broadcast Control Channel (BCCH), is
`transmitted at the first time slot of the frame 27, to provide
`the mobile stations with general information about a BTS.
`The mobile Stations 12 use the associated channels to
`transmit associated control Signals, Such as an RX-LEV
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`Signal, which corresponds to the received signal Strength at
`the mobile station and RX-QUAL signal, which is a measure
`of various levels of bit error rate at the mobile station 12, as
`defined by the GSM standard.
`Preferably, the BSC 16 designates all dedicated uplink
`Signaling channels as diversity time-slots, to insure the
`reception of important signaling information from all the
`mobile Stations 12 within a communication cell, including
`those far away from the RBS. On the other hand, associated
`Signaling channels are allocated as diversity time-slots, if
`their corresponding traffic channels are allocated as diversity
`time-slots.
`Referring to FIG. 3, the block diagram of the RBS 22
`according to one embodiment of the invention is shown to
`include a plurality of BTSS 20 that serve different geographi
`cal areas. The RBS 22 includes a base station common
`function (BCF) block 68 that controls the operation and
`maintenance of the RBS 22. The BSC 16 interfaces with the
`BCF 68 through an A-bis interface on line 70. The BCF 68
`controls the operation and maintenance (O & M) functions
`associated with the RBS 22. Through a timing bus 72, the
`BTSs 20 are synchronized with each other. Voice and data
`information are provided to and from the RBS 22 through a
`traffic bus 74 that may be coupled, through the A-bis
`interface, to a public or private Voice and data transmission
`line, Such as a T1 line (not shown).
`Each BTS 20 includes two TRXS 75 and 76 that com
`municate with the mobile station 12 via antennas 24, which
`cover Separate geographical areas 77 and 78. In an exem
`plary embodiment of the invention, the antennas 24 are dual
`polarized antennas that receive electromagnetic radio fre
`quency waves on a horizontal and vertical field. Preferably,
`the antennas are spaced apart from each other, for example
`by 10 meters, to provide for un-correlated reception of
`35
`uplink Signals. AS shown, two antennas designated as 24A
`and 24B are Spaced accordingly to cover the coverage area
`78. The TRXs 75 and 76 include pairs of receivers 80 and
`81 that are coupled to the antennas 24A and 24B via RF
`amplifiers 83. The receiver pairs 80 and 81 apply the
`received uplink Signals to corresponding TRX Modulator/
`Demodulator and combiner blocks 82 via Switch pairs 84
`and 85, which are incorporated into the TRXs 75 and 76,
`respectively.
`The system 10 uses at least two receiver branches to
`provide diversity reception of all uplink Signals received
`during diversity and non-diversity time slots. Each receiver
`branch is a reception path for the uplink Signals through each
`one of the receivers 80 or 81 which are tuned by corre
`sponding control signals on lines 77 from blocks 82. Under
`the control of Switch control signals, on lines 87, the Switch
`pairs 84 or 85 connect the uplink received signals from two
`or more receiver branches to the blocks 82 for diversity
`combination.
`According to the present invention, the uplink received
`Signal quality is improved by providing diversity reception
`on a slot by slot basis. Consequently, the Switch pairS 84 and
`85 are switched so that the TRX's 75 and 76 can dynami
`cally receive the uplink Signals either via a two-receiver
`branch diversity or a four-receiver-branch-diversity
`arrangement, with each receiver branch being an indepen
`dent path for receiving the uplink Signals. In other words,
`during non-diversity time-slots leSS receiver branches are
`used than during diversity time-slots. Under this
`arrangement, the BSC 16 allocates certain time slots as
`diversity time slots during which four receiver branches are
`used for combining the received uplink Signals. Other time
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`Slots are allocated as non-diversity time slots during which
`two receiver branches are used for combining the received
`signals. In this way, the BSC 16 makes an Intra-BTS hand
`over to move degraded communication from a non-diversity
`time slot to a diversity time-slot, to improve uplink Signal
`quality. The antenna connection configurations for all anten
`nas of the RBS 22 are stored in the BCF 68. Via the A-bis
`interface, the BSC 16 can access the antenna connection
`configuration information, when allocating diversity and
`non-diversity time slots.
`In this embodiment of the invention, the block 82 includes
`a combiner for combining the uplink data from the receiver
`branches. The combiner may combine Soft information (per
`bit or burst) provided at the output of a GSM equalizer (not
`shown). Alternatively, the combining of the uplink data may
`be performed by the equalizer within the block 82 using a
`Suitable algorithm. The combining may also be done by
`Selecting the receiver branch that provides the best quality
`and disregarding the rest. A combination of above described
`combining techniques may also be used.
`Referring to FIG. 4, a block diagram of a BTS 20
`according to another embodiment of the invention is shown.
`The BTS 20 includes a pair of identical TRXs 93. Each TRX
`93 includes a transmitter section 86, two receiver Sections
`95, a baseband processor 88 and a TRX controller 90. When
`transmitting downlink baseband data, the baseband proces
`Sor 88 receives properly coded digitized speech from the
`BSC 16 over the traffic bus 74 and applies it to a channel
`coder 102 that codes and multiplexes the Speech according
`to a GSM specified protocol. The transmitter section 86,
`which is coupled to the channel coder 102, transmits the
`down link baseband data via the antennas 24.
`The receiversections 95 down convert the uplink signals
`from the mobile Station 12, Via corresponding down con
`version blocks 91 (only one block is shown). The down
`conversion blocks 91 are controlled by the TRX controller
`90 for setting the receiver frequencies of the uplink RF
`channels. The TRX controller 90 sets the receiver frequen
`cies based on instructions from the BSC 16 over the traffic
`buS 74. After down converting the received Signals, the
`receiver Sections 87 Sample the Signal (e.g., the phase and
`magnitude) via sampler blocks 92 (only one block is shown),
`to provide Sampled Signal data to the baseband processor 88.
`In an exemplary embodiment, an RSSI estimator 94
`provides an RSSI signal on line 95, which is a measure of
`propagation properties of the uplink RF channel. The RSSI
`estimator 94 measures noise disturbance levels during idle
`channels and received signal Strength during active chan
`nels. The TRX controller 90, which is coupled to the traffic
`bus 74, processes the commands received from the BSC 16
`and transmits TRX related information, Such as various TRX
`measurements, to the BSC 16. Under this arrangement, the
`TRX 76 periodically reports the RSSI signal and noise
`disturbance levels to the BSC 16. The BSC 16 Selects the
`diversity time-slots and non-diversity time-slots based on
`the quality of the RF channels. Using its receiverS Sections
`95, the TRXs 93 detect channel activity by continuously
`measuring and averaging the noise disturbance levels on the
`RF channels. Based on Such measurements, the TRX's 93
`can inform the BSC 16 as to the quality of RF channels. By
`comparing a measurement from a particular channel to an
`average disturbance level measurement, the BSCS can assess
`the quality of a particular channel. The lower the disturbance
`level, the better the reception quality would be on that
`channel.
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`The present invention uses one or a combination of uplink
`Signal quality parameters that are continuously measured for
`allocating diversity and non-diversity time-slots. These
`parameters include Bit Error Rate (PER), Frame Erasure
`Rate (FER), or received signal strength level (RX-LEV)
`parameters, which are measures of received signal quality of
`the uplink RF channel. In a well known way, the RX-LEV
`is measured by the RSSI block 94, and BER and FER are
`measured by a channel decoder in the BTSs 20. The BSC 16
`receives the RSSI signal from the BTS 20 and compares
`them to a corresponding threshold. Preferably, the corre
`sponding thresholds against which one or a combination of
`propagation path parameters BER, FER or, RX-LEV are
`compared are Selected to indicate a condition warranting the
`use of either diversity or non-diversity time-slots. For
`example, an RX-LEV value below a low threshold would
`warrant the use of diversity reception and an RX-LEV value
`above an upper threshold would indicate suitability of
`non-diversity reception. Of course, the upper and lower
`threshold are Selected to introduce hysteresis. Once a con
`dition warranting the use of diversity is indicated, the BSC
`allocates a diversity time-slot for communicating with a
`mobile station. The BSC 16 then makes the intra-BTS hand
`over to Switch from a non-diversity time-slot to a diversity
`time-slot. If Suitability of non-diversity reception indicated,
`then the BSC 16 could switch from a diversity time-slot to
`a non-diversity time-slot.
`During an initial selection phase, the BSC 16 determines
`the idle channel quality for each RF channel. Based on a
`predefined criteria associated with received signal quality on
`the RF channels, the BSC 16 allocates certain RF channels
`for diversity reception and others for non-diversity recep
`tion. For example, all time slots of RF channels having an
`idle channel quality that exceeds a predefined threshold may
`be allocated as non-diversity time-slots, because the uplink
`reception quality provided by Such channels may not require
`the use of diversity reception. Conversely, all time slots of
`RF channels having a channel quality below the threshold
`may be allocated as diversity time-slots, to improve uplink
`coverage on Such channels.
`AS described before, the present invention combines the
`received uplink Signals from the receiver branches to
`improve uplink received Signal quality on a time slot by time
`slot basis. Preferably, uplink baseband data received from
`different receiver branches are combined dynamically using
`a baseband bus 79 which interconnects the TRXS 93 to each
`other. Each RBS 22 within the system 10 also includes the
`baseband bus 79. The baseband bus 79, which is a TDMA
`bus, supports a protocol that allows the RBS 22 to selec
`tively address the TRXs 93 for receiving and transmitting
`information during designated time slots. The baseband bus
`protocol uses Separate packets of data to transfer baseband
`data, as well as address and control information among the
`TRXs 93. The packets, which are assembled by each TRX
`93, carry baseband data and their TRX address over the
`55
`baseband bus 79. This way, the uplink baseband data packets
`assembled by the baseband processors 88 can be associated
`with the address of the TRXs 93 selected by the BSC 16 for
`diversity reception.
`The baseband processor 88 includes an equalizer 100 that
`receives the uplink Sampled Signal data from both receivers
`branches of a TRX 93. The equalizer 100 generates soft
`information per bit or burst (baseband data) for each receiver
`branch or combined soft information for the receiver
`branches by the equalizer 100. The equalizer 100 places the
`uplink baseband data over the baseband bus 79. The uplink
`baseband data on the baseband bus 79 is applied to a channel
`
`45
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`50
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`60
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`65
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`8
`decoder 97 that combines baseband data from receiver
`branches and decodes the baseband Signal according to the
`GSM specified protocol. The channel decoder 97 places the
`decoded baseband signal on the traffic bus 74, for further
`processing by the BSC 16. Over the traffic bus 74, the BSC
`16 is kept informed of various operating conditions includ
`ing antenna connection configuration within the RBS 22 and
`supplies address and timing information to the TRXs 93.
`The BSC provides address information to the TRX control
`ler 90 on TRXs participating in the diversity reception. The
`TRX controller 90 then instructs the channel decoder 97 to
`combine the uplink baseband data from the addressed TRXs.
`In this way, the use of the baseband bus 79 significantly
`facilitates Selective diversity reception of the invention on a
`time slot by time slot basis, as the BSC can specify the TRX
`addresses used for diversity reception.
`Based on the information provided over the traffic bus, the
`BCF 68 determines the fault conditions associated with each
`one of the TRXs. The BCF 68 reports the fault conditions to
`the BSC 16 via the A-bis bus. According to yet another
`feature of the present invention, the BSC 16 reconfigures
`and reallocate the RBS resources used for diversity or
`non-diversity reception based on RBS fault reports. For
`example, if the RBS 22 reports a fault condition on one of
`its receiver sections, the BSC 16 would not allocate the
`faulty TRX 93 for diversity reception. If the fault is devel
`oped during the RBS operation, a TRX 93 allocated for
`diversity reception would be de-allocated, even eliminated,
`as a resource until the fault condition is cured. Once cured,
`the TRX 93 may be allocated for diversity reception by the
`BSC 16.
`It is well known that the noise generated in each one of the
`receiver branches is independent of each other and, thus,
`un-correlated. Therefore, the Sensitivity increases in accor
`dance with that of an Additive White Gaussian Noise
`(AWGN) channel by:
`10 log 10 (N) dB,
`where N is the number of receiver branches having
`un-correlated noise Sources. Therefore, the co-channel and
`adjacent-channel rejection is improved by insuring the
`received signals by the receiver branches are Substantially
`un-correlated. AS described before, the antennas 24 are
`Sufficiently Spaced apart from each other to provide Substan
`tially un-correlated uplink received signals.
`From the foregoing description, it will be appreciated that
`the communication System 10 according to the present
`invention Substantially improves the uplink received signal
`quality, while providing an efficient allocation of diversity
`and non-diversity resources. It has been determined that the
`present invention improves the uplink coverage of the
`system by up to 5 dB. The present invention allocates the
`diversity and non-diversity resources based on individual RF
`links between the mobile stations 12 and the BTSS 20 as well
`as based on the operating conditions of the System 10. AS
`described above, the improved coverage is traded for capac
`ity in a dynamic manner. The allocation of resources accord
`ing to the present invention increases communication
`throughput within the system 10, which would allow more
`calls to go through, especially in heavily congested com
`munication cells.
`Although the invention has been described in detail with
`reference only to a preferred embodiment, those skilled in
`the art will appreciate that various modifications can be
`made without departing from the invention. Accordingly, the
`invention is defined only by the following claims which are
`intended to embrace all equivalents thereof.
`
`ERICSSON v. UNILOC
`Ex. 1024 / Page 9 of 11
`
`

`

`What is