United States Patent (19)
`Frodigh et al.
`
`USOO5909469A
`Patent Number:
`11
`(45) Date of Patent:
`
`5,909,469
`Jun. 1, 1999
`
`FOREIGN PATENT DOCUMENTS
`
`54) LINK ADAPTATION METHOD FOR LINKS
`USING MODULATION SCHEMES THAT
`HAVE DIFFERENT SYMBOL RATES
`75 Inventors: Carl Magnus Frodigh, Kista; Mikael
`Höök; Frank Miller, both of
`Sollentuna, all of Sweden; Peter
`Schramm, Erlangen, Germany; Johan
`Sköld, Akersberga, Sweden
`73 Assignee: Telefonaktoebolaget LM Ericsson,
`Stockholm, Sweden
`
`21 Appl. No.: 08/921,319
`
`0652680 5/1995 European Pat. Off..
`WO941 1955 5/1994 WIPO.
`WO95/28814 10/1995 WIPO.
`W: ... WE
`WO97/13388 4/1997 WIPO.
`OTHER PUBLICATIONS
`“Cellular Evolution Into Wideband Services” by Johan
`Sköld et al., VTC 1995, Jul. 3, 1997.
`“Estimation of the Performance of Link Adaption in Mobile
`Radio”, by J. Dunlap et al., 0–7803–2742-X/95, 1995 IEEE.
`“A High Speed Data Modem for Digital Cellular Radio”, by
`Jay M. Jacobsmeyer, P.E., 0–7803–4194–5/97, 1997 IEEE,
`1997 Wireless Communications Conference.
`Primary Examiner-Chi H. Pham
`Aug. 29, 1997
`22 Filed:
`ASSistant Examiner-Khai Tran
`51) Int. Cl. ................................ H03C 3700; H04J 3/16;
`Attorney, Agent, or Firm-Burns, Doane, Swecker &
`HO4B 1/38
`Mathis, L.L.P.
`52 U.S. Cl. ........................... 375/302; 370/465; 455/552
`ABSTRACT
`57
`58 Field of Search ..................................... 375/302,334,
`375/222, 223,308, 261, 279, 208; 370/465,
`468, 206, 207, 203; 455/552, 553 A communication System Supports multiple modulation
`Schemes having differing Symbol rates. The System Supports
`two modulation Schemes that have the Same Symbol rate and
`at least one modulation Scheme that does not have the same
`Symbol rate. For as long as communication can be carried
`out using the modulation Schemes with the same symbol
`rate, the System avoids using the modulation Scheme with
`different Symbol rate, even if communication can be carried
`Out using this Scheme.
`
`56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`5,363,408 11/1994 Paik et al. ............................... 375,261
`5,369,637 11/1994 Richardson et al. .
`... 370/281
`5,491,457 2/1996 Fecher ...
`... 375/302
`5,815,531
`9/1998 Dent .........
`- - - - 375/298
`5,818,827 10/1998 Usui et al. ...
`... 370/344
`5,822,315 10/1998 De Seze et al. ........................ 370/337
`
`27 Claims, 8 Drawing Sheets
`
`ASF
`
`O
`
`
`
`Qualcomm Incorporated
`Exhibit 1011
`Page 1 of 16
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`U.S. Patent
`
`Jun. 1, 1999
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`Jun. 1, 1999
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`U.S. Patent
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`Jun. 1, 1999
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`1
`LINK ADAPTATION METHOD FOR LINKS
`USING MODULATION SCHEMES THAT
`HAVE DIFFERENT SYMBOL RATES
`
`5,909,469
`
`2
`In order to provide various communication Services, a
`corresponding minimum user bit rate is required. For
`example, for voice and/or data Services, user bit rate corre
`sponds to Voice quality and/or data throughput, with a higher
`user bit rate producing better voice quality and/or higher
`data throughput. The total user bit rate is determined by a
`Selected combination of techniques for Speech coding, chan
`nel coding, modulation Scheme, and for a TDMA System, the
`number of assignable time slots per call.
`Depending on the modulation Scheme used, link quality
`deteriorates more rapidly as C/I levels decrease. Higher level
`modulation Schemes are more Susceptible to low levels of
`C/I ratio than lower level modulation Schemes. If a HLM
`Scheme is used, the data throughput or grade of Service drops
`very rapidly with a drop in link quality. On the other hand,
`ifa LLM Scheme is used, data throughput or grade of Service
`does not drop as rapidly under the Same interference con
`ditions. Therefore, link adaptation methods, which provide
`the ability to change modulation and/or coding based on the
`channel conditions, are used to balance the user bit rate
`against link quality. Generally, these methods dynamically
`adapt a System's combination of Speech coding, channel
`coding, modulation, and number of assignable time slots to
`achieve optimum performance over a broad range of C/I
`conditions.
`One evolutionary path for next generation of cellular
`Systems is to use high-level modulation (HLM), e.g.,
`16QAM modulation scheme, to provide increased user bit
`rates compared to the existing Standards. These cellular
`Systems include enhanced GSM Systems, enhanced
`D-AMPS systems, International Mobile Telecommunication
`2000 (IMT-2000), etc. A high level linear modulation, such
`as 16QAM modulation scheme, has the potential to be more
`spectrum efficient than, for example, GMSK, which is a
`low-level modulation (LLM) scheme. Furthermore, the use
`of 16QAM modulation scheme in conjunction with a higher
`Symbol rate Significantly increase the user bit rate compared
`to the GMSK modulation scheme. In this way, the maximum
`user bit rate offered by an HLM scheme, such as 16QAM
`modulation Scheme, may be more than doubled. Because
`higher level modulation Schemes require a higher minimum
`C/I ratio for acceptable performance, their availability in the
`System becomes limited to certain coverage areas of the
`System or certain parts of the cells, where more robust links
`can be maintained. However, a System can be planned to
`provide full coverage for HLM scheme. The modulation
`Schemes provided in a cell may be a mixture of non-linear
`and linear modulation, with different symbol rates.
`Using the same Symbol rate, a conventional link adapta
`tion method uses two linear modulation Schemes with dif
`ferent modulation levels, e.g., 16QAM and QPSK modula
`tion Schemes, to decrease, for instance, transmission time by
`Switching to a higher level modulation if link quality is
`Sufficient. However, this method does not consider compli
`cations arising from using multiple modulation Schemes that
`have different symbol rates. By introduction of link adap
`tation algorithms, adaptation of coding and/or modulation
`Scheme becomes more frequent. The frequent link adapta
`tions result in an increased Signalling effort with a corre
`sponding degradation of Speech or user data performance.
`The demodulation of GMSK and 16OAM modulation
`Schemes are quite different from each other. As a result, with
`modulation Schemes having different Symbol rates, the pro
`ceSS of demodulation Switching at receivers becomes
`lengthy and complicated, causing degradation in communi
`cation quality. Therefore, there exists a need for an efficient
`and fast method of link adaptation when symbol rates of the
`modulation Schemes are different from each other.
`
`BACKGROUND
`This invention generally relates to the field of communi
`cation Systems and, more particularly, to digital communi
`cation Systems that Supports multiple modulation Schemes.
`Digital communication Systems use a variety of linear and
`non-linear modulation Schemes to communicate Voice or
`data information. These modulation Schemes include, GauS
`sian Minimum Shift Keying (GMSK), Quadrature Phase
`Shift Keying (QPSK), Quadrature Amplitude Modulation
`(QAM), etc. GMSK modulation scheme is a non-linear low
`level modulation (LLM) scheme with a symbol rate that
`Supports a specified user bit rate. In order to increase user bit
`rate, high-level modulation (HLM) schemes can be used.
`Linear modulation Schemes, Such as QAM Scheme, may
`have different level of modulation. For example, 16QAM
`Scheme is used to represent the Sixteen variation of 4 bits of
`data. On the other hand, a QPSK modulation Scheme is used
`to represent the four variations of 2 bits of data. Although
`16QAM scheme provides a higher bit rate than QPSK, both
`of these modulation Schemes could have the Same Symbol
`rate. Application of modulation Schemes, however, differ in
`many aspects, for example Symbol rate and/or burst format,
`which complicates their Support in Systems that use multiple
`modulation Schemes.
`In wireleSS digital communication Systems, Standardized
`air interfaces Specify most of System parameters, including
`modulation type, burst format, communication protocol,
`Symbol rate, etc. For example, European Telecommunica
`tion Standard Institute (ETSI) has specified a Global System
`for Mobile Communications (GSM) standard that uses time
`division multiple access (TDMA) to communicate control,
`voice and data information over radio frequency (RF) physi
`cal channels or links using GMSK modulation Scheme at a
`symbol rate of 271 kSps. In the U.S., Telecommunication
`Industry Association (TIA) has published a number of
`Interim Standards, such as IS-54 and IS-136, that define
`various versions of digital advanced mobile phone Service
`(D-AMPS), a TDMA system that uses a Differential QPSK
`(DQPSK) modulation scheme for communicating data over
`RF links.
`TDMA systems subdivide the available frequency band
`into one or several RF channels. The RF channels are
`divided into a number of physical channels corresponding to
`time slots in TDMA frames. Logical channels are formed
`from one or more physical channels, where modulation and
`channel coding Schemes are specified. In these Systems, the
`mobile Stations communicate with a plurality of Scattered
`base Stations by transmitting and receiving bursts of digital
`information over uplink and downlink RF channels.
`The growing number of mobile Stations in use today has
`generated the need for more Voice and data channels within
`cellular telecommunication Systems. As a result, base Sta
`tions have become more closely Spaced, with an increase in
`interference between mobile Stations operating on the same
`frequency in neighboring or closely spaced cells. Although
`digital techniques gain more useful channels from a given
`frequency spectrum, there Still remains a need to reduce
`interference, or more specifically to increase the ratio of the
`carrier signal strength to interference, (i.e., carrier-to
`interference (C/I)) ratio. RF links that can handle lower C/I
`ratios are considered to be more robust than those that only
`can handle higher C/I ratioS.
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`SUMMARY
`The present invention that addresses this need is exem
`plified in a link adaptation method that uses a Second low
`level modulation Scheme to provide modulation Switching
`between a third modulation Scheme that has the same
`Symbol rate as the Second modulation Scheme and a first
`modulation scheme that has a symbol rate different from the
`Second and third modulation Schemes.
`The link adaptation method according to the invention
`determines whether a base Station and a mobile Station can
`communicate with each other using the first, Second, or third
`modulation Schemes. The link adaptation method uses the
`Second modulation Scheme, if the mobile Station and the
`base Station can not communicate with acceptable commu
`nication performance using the third modulation Scheme,
`even if they can communicate with each other Satisfactorily
`using the first modulation Scheme.
`According to Some of the more detailed features of the
`invention the first modulation Scheme is a non-linear modu
`lation Scheme and the Second and third modulation Schemes
`are linear modulation Schemes. For example, the first modu
`lation scheme is GMSK modulation scheme, the second
`modulation scheme is QPSK modulation scheme, and the
`third modulation scheme is higher level 16QAM modulation
`Scheme. Preferably, the Second modulation Scheme uses a
`reduced Signal Set of third modulation Scheme. The Second
`and third modulation Schemes use the same pulse shaping
`and burst format as well as an identical training Sequence.
`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.
`
`4
`Supports multiple modulation Schemes. In an exemplary
`embodiment of the invention, the system 10 Supports a first
`LLM (LLM1) scheme, which is a non-linear modulation
`Scheme, Such as GMSK modulation Scheme used in GSM
`systems. Preferably, system 10 also supports a HLM modu
`lation Scheme, which is a higher level linear modulation
`Scheme, for example, 16OAM Scheme.
`The mode of operation of GSM communication systems
`is described in European Telecommunication Standard Insti
`tute (ETSI) documents ETS300 573, ETS 300 574 and ETS
`300 578, which are hereby incorporated by reference.
`Therefore, the operation of the GSM system is described to
`the extent necessary for understanding of the present inven
`tion. Although, the present invention is described as embod
`ied in a GSM system, those skilled in the art would appre
`ciate that the present invention could be used in a wide
`variety of other digital communication Systems, Such as
`those based on PDC or D-AMPS standards and enhance
`ments thereof. The present invention may also be used in
`CDMA or a hybrid of CDMA and TDMA communication
`Systems.
`The communication System 10 covers a geographical area
`that is Subdivided into communication cells, which together
`provide communication coverage to a Service area, for
`example, an entire city. Preferably, 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 RF channels needed to cover the
`Service area. The System 10 may also employ frequency
`hopping techniques, for example, to avoid "deadspots.”
`According to the present invention, the System 10 Sup
`ports a second LLM (LLM2) scheme that has a symbol rate
`that is the same as the symbol rate of HLM scheme. Under
`this aspect of the invention, link adaptation is performed
`between LLM1, LLM2, and HLM schemes. In an exemplary
`embodiment, LLM2 scheme is a QPSK Scheme, which has
`the same symbol rate as the HLM 16QAM scheme.
`Referring to FIGS. 2(a) and 20b), the signal sets in
`modulation constellations of 16OAM Scheme and QPSK
`Scheme are shown, respectively. The outer signal points of
`16QAM Scheme are shown by points A, B, C, and D, and the
`signal points of QPSK Scheme are shown by points A, B',
`C, and D'. QPSKscheme can be viewed as having a reduced
`signal set relative to 16QAM scheme. If the symbol rates of
`QPSK and 16OAM Schemes are the same, a 16OAM
`demodulator can demodulate the reduced signal set of QPSK
`modulation Scheme by using exclusively the Outer Signal
`points A, B, C and D of 16QAM scheme. Consequently, the
`Same demodulator can be used to demodulate Signals that
`are modulated with QPSK and 16OAM Schemes, if the same
`pulse shaping and burst format is used for both of these
`Schemes. This arrangement significantly facilitates demodu
`lation Switching between QPSK and 16QAM Schemes dur
`ing link adaptation. One Such demodulation method is
`described in a concurrently filed patent application titled “A
`METHOD FOR DEMODULATING INFORMATION INA
`COMMUNICATION SYSTEM THAT SUPPORTS MUL
`TIPLE MODULATION SCHEMES,” which is hereby
`incorporated by reference.
`The present invention takes advantage of the ease of
`demodulation Switching with modulation Schemes that have
`the same Symbol rate, pulse Shaping, burst format, and a
`reduced Signal Set relative to each other. More specifically,
`the communication system 10 determines whether a base
`Station and a mobile Station 12 can communicate with each
`
`25
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`35
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. 1 is a block diagram of a communication System
`which advantageously uses the present invention.
`FIG. 2(a) an 2(b) are diagrams of modulation constella
`tions of a 16QAM and QPSK modulation schemes, respec
`tively.
`FIG. 3 is a diagram of a subdivided RF channel that is
`used in the communication system of FIG. 1.
`FIG. 4 is a diagram of a normal transmission burst
`transmitted on the RF channel of FIG. 2.
`FIG. 5 is a block diagram of a mobile station used in the
`communication system of FIG. 1.
`FIG. 6 is a block diagram of a radio base station used in
`the communication system of FIG. 1.
`FIG. 7 is a block diagram of a radio transceiver used in the
`base station of FIG. 6.
`FIG. 8 is a diagram of an exemplary cell arrangement.
`FIG. 9 is a flow chart of an inter-cell handover method
`used in the communication system of FIG. 1.
`FIG. 10 is a flow chart of a link adaptation method
`according to one embodiment of the invention.
`FIG. 11 is a diagram of another exemplary cell arrange
`ment.
`FIG. 12 is a flow chart of a link adaptation method
`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
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`other using LLM1, LLM2, or HLM schemes. The commu
`nication system 10 uses LLM2 scheme, if the mobile station
`12 and the base Station can not communicate with each other
`with acceptable communication performance using HLM
`Scheme, even if they can communicate with each other using
`LLM1 Scheme with acceptable communication perfor
`mance. In this way, the communication System communi
`cates with the mobile stations 12 using HLM scheme within
`a first coverage area that may Support LLM1, LLM2, and
`HLM Schemes and communicates with the mobile stations
`12 using LLM2 Scheme within a Second coverage that
`supports both LLM1 and LLM2 schemes but not HLM
`scheme. It will be understood by one skilled in the art that
`the present invention is not limited to the described exem
`plary modulation schemes of LLM1, LLM2 and HLM.
`Several modulation Schemes can be applied to Systems with
`different channel coding Schemes.
`The system 10 is designed as a hierarchical network with
`multiple levels for managing calls. Using an allocated Set of
`uplink and downlink RF links, 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 Centers (MSCs) 14 are responsible for the routing
`of calls from an originator to a destination. In particular, they
`are responsible for Setup, control and termination of 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. The
`communication System 10 uses the present invention to
`provide for link adaptation, when mobile stations 12 within
`a cell move within coverage areas that Support one or more
`of LLM1, LLM2, HLM schemes.
`At a lower hierarchical level, each one of the MSCs 14 are
`connected to a group of base station controllers (BSCs) 16.
`35
`The primary function of a BSC 16 is radio resource man
`agement. For example, based on reported received signal
`strength at the mobile stations 12, the BSC 16 determines
`whether to initiate a hand over. Under the GSM standard, the
`BSC 16 communicates 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 hierarchical level each one of the BSCs 16
`controls, a group of base transceiver stations (BTSs) 20.
`Each BTS 20 includes a number of TRXs that use the uplink
`and downlink RF channels to Serve a particular common
`geographical area. The BTSS 20 primarily provide the RF
`links for the transmission and reception of data bursts to and
`from the mobile stations 12 within their designated cell. In
`an exemplary embodiment, a number of BTSs 20 are incor
`porated into a radio base station (RBS) 22. The RBS 22 may
`be configured according to a family of RBS-2000 products,
`which is offered by EricSSon, the assignee of the present
`invention.
`With reference to FIG. 3, an RF channel 26 (uplink or
`downlink) is divided into repetitive time frames 27 during
`which information are communicated. Each frame 27 is
`further divided into time slots 28 that carry packets of
`information. Speech or data is transmitted during time slots
`designated as traffic channels (TCH, . . . , TCH). All
`Signaling functions pertaining to call management in the
`System, including initiations, hand overs, and termination
`are handled via control information transmitted over control
`channels.
`The mobile Stations 12 use Slow associated control chan
`nels (SACCHS) to transmit associated control signals, Such
`as an RX-LEV signal, which corresponds to the received
`
`6
`signal strength at the mobile station 12 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.
`Fast associated control channels (FACCHs) perform control
`functions, Such as hand-overs, by Stealing bursts for the
`allocated TCHs.
`The BSC 16 instructs the RBS 22 based on measures of
`channel characteristics of RF links between mobile stations
`12 to the RBS 22. As described later in detail, the channel
`characteristics may be measured based on a number of
`parameters, including received signal Strength at the mobile
`station 12, bit error rate at the mobile station 12, the
`multipath propagation property of the uplink RF channel, for
`example, time dispersion, or a combination of them.
`The system 10 carries out the transmission of information
`during a time slot in a burst that contain a predefined number
`of coded bits. The GSM specification defines various types
`of bursts: normal burst (NB), frequency correction burst
`(FB), synchronization burst (SB), access burst (AB), and
`dummy burst. The normal burst, which has a duration of 576
`tus, is used both during the traffic and Some control Signalling
`channels. The remaining bursts are primarily used for access
`and maintaining Signal and frequency Synchronization
`within the system.
`As shown in FIG. 4, a normal burst 29 includes two
`Separate data portions 30 during which digital data bits are
`communicated. The normal burst also includes tail and
`guard Sections 31 and 32 as shown. Among other things, the
`guard Section 32 is used to allow for up-ramping of the burst
`and for down-ramping of the bursts. The tail section 31 is
`used for demodulation purposes. All burst transmissions,
`except dummy burst transmissions, include training
`Sequences. The training Sequences are patterned with pre
`defined autocorrelation characteristics. During demodula
`tion process, the auto correlation characteristic of the train
`ing Sequence helps in the Synchronization of the received bit
`sequences over an RF channel. In the normal burst 29, a
`training Sequence 33 is positioned in the middle of the burst
`between its data portions.
`In order to compensate for propagation delays, the com
`munication System 10 uses a time alignment process by
`which the mobile stations 12 align their burst transmissions
`to arrive at the BTSs 20 in proper time relationship relative
`to other bursts transmissions. AS described later, the mobile
`station 12 and the RBS 22 incorporate equalizers, which
`correlate received baseband bit Sequences over the uplink or
`downlink RF channels with the training Sequences, to pro
`vide correlator responses that correspond to the properties of
`multipath propagation. Based on the correlator responses,
`the receiver section of the BTS 20 generates a timing
`advance (TA) parameter, which corresponds to a propaga
`tion delay over the uplink RF channel. The mobile station 12
`uses the TA parameter, which is transmitted from the RBS
`22, for advancing or retarding its burst transmissions relative
`to a time reference.
`With reference to FIG. 5, the block diagram of a mobile
`station 12 is shown. The mobile station 12 includes a
`receiver section 34 and a transmitter section 36, which are
`coupled to an antenna 38 through a duplexer 39. The antenna
`38 is used for receiving and transmitting RF signals to and
`from the BTS 20 over allocated uplink and downlink RF
`channels. The receiver section 34 includes an RF receiver
`40, which includes a local oscillator 41, a mixer 42, and
`Selectivity filters 43 arranged in a well known manner, for
`down-converting and demodulating received signals to a
`baseband level. The RF receiver 40, which is tuned by the
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`7
`local oscillator 41 to the downlink channel, also provides an
`RX-LEV signal on line 44 that corresponds to the received
`Signal Strength at the mobile Station 12.
`The RF receiver provides a baseband signal to a demodu
`lator 46 that demodulates coded data bits representing the
`received speech, data and Signaling information. Depending
`on the type of mobile station 12, the demodulator 46 can
`Support one or more demodulation Schemes corresponding
`to LLM1, LLM2, and HLM schemes. For example, the
`demodulator of a mobile station 12 Subscribed to an operator
`that supports LLM1 scheme may be capable of demodulat
`ing LLM1 modulated signals only. On the other hand, the
`demodulator of a mobile station 12 Subscribed to an operator
`that Supports all of the three modulation Schemes is prefer
`ably capable of demodulating LLM1, LLM2, and HLM
`15
`Schemes.
`AS described above, the demodulator 46 includes an
`equalizer (not shown) that processes the coded bit pattern
`disposed on the training Sequences, to provide correlator
`response that are used for predictive demodulation of the
`baseband Signal. The equalizer uses the correlator responses
`to determine the most probable bit Sequence for demodula
`tion. As defined by the GSM specification, a channel
`decoder/interleaver 50 also provides an RX-QUAL signal on
`line 48, which is a measure of various levels of bit error rate
`at the mobile station 12. The mobile station 12 reports the
`RX-QUAL signal and the RX-LEV signal to the BSC 16 on
`a SACCH channel.
`Preferably, bursts modulated according to LLM2 and
`HLM Scheme, i.e., 16OAM and QPSK Schemes, use the
`Same pulse shaping, Symbol rate and burst format, and use
`the same training Sequences. Both modulation Schemes use
`the Same signal points to modulate the training Sequence.
`For example, a 16 QAM modulator modulates the training
`Sequence using outer signal points A, B, C, and D, (shown
`in FIG. 2(a)). Similarly, a QPSK modulated signal, which
`has a reduced signal set relative to 16QAM modulated
`Signal, uses signal points A, B, C, and D" (shown in FIG.
`2(b)) for transmitting the training sequence. In this way, the
`mobile Station 12 can use the same demodulator, i.e., a
`16OAM demodulator, to demodulate the training Sequence.
`This arrangement significantly facilitates decoding of the
`training sequence of both HLM and LLM2 modulated
`Signals.
`The channel decoder/de-interleaver 50 decodes and
`de-interleaves the demodulated Signal. The Speech data bits
`are applied to a speech decoder 52 that decodes the Speech
`pattern using one of a variety of speech decoding algorithms.
`After decoding, the Speech decoder 52 applies an analog
`Speech Signal to a output device 53, e.g., a Speaker, via an
`audio amplifier 54. The channel decoder 50 provides the
`decoded data and Signalling information to a microprocessor
`56 for further processing, for example, displaying the data to
`a SC.
`The transmitter section 36 includes an input device 57,
`e.g., a microphone and/or keypad, for inputting Voice or data
`information. According to a Specified Speech/data coding
`techniques, a speech coder 58 digitizes and codes the Voice
`Signals according to a variety of Supported Speech coding
`Schemes. A channel coder/interleaver 62 codes the uplink
`data according to a specified coding/interleaving algorithms,
`which improves error detection and correction at the BTS
`20. The channel coder/interleaver 62 provides an uplink
`baseband signal to a modulator 64. The modulator 64
`modulates the uplink baseband Signal according to one or
`more of Supported modulation Schemes. Similar to the
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`demodulator 46, the modulator 64 of the mobile station 12
`may support one or more of LLM1, LLM2, and HLM
`Schemes.
`The modulator 64 applies the coded Signal to an
`up-converter 67, which receives a carrier Signal from the
`up-converted signal local oscillator 41. An RF amplifier 65
`amplifies the up-converted Signal for transmission trough the
`antenna 38. A well known frequency synthesizer 66, under
`the control of the microprocessor 56, Supplies the operating
`frequency information to the local oscillator 41. The micro
`processor 56 causes the mobile station 12 to transmit the
`RX-QUAL and RX-LEV parameters to the RBS 22 over the
`SACCH.
`Referring to FIG. 6, an exemplary block diagram of the
`RBS 22 is shown to include a plurality of BTSS 20 that serve
`different geographical areas. 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
`TRXS 75 and 76 that communicate with the mobile station
`12. AS shown, two antennas designated as 24A and 24B are
`spaced accordingly to cover cells 77 and 78. The TRXs 76
`are coupled to the antennas 24 through combiner/duplexers
`80 that combine downlink transmission signals from the
`TRXS 76 and distribute the uplink received signals from the
`mobile station 12. The RBS 22 also includes a base station
`common function (BCF) block 68 that controls the operation
`and maintenance of the RBS 22.
`Referring to FIG. 7, a block diagram of a TRX 76 is
`shown. The TRX 76 includes a transmitter section 86, a
`receiver section 87, a baseband processor 88 and a TRX
`controller 90. Through a corresponding antenna 24 (shown
`in FIG. 6), the receiver section 87 receives uplink signals
`from the mobile station 12. A down-conversion block 91
`down-converts the received signal. After down-converting
`the received Signals, the receiver Section 87 Samples its
`phase and magnitude, via a Sampler block 92, to provide
`received bit sequence to the baseband processor 88. An RSSI
`estimator 94 provides an RSSI signal on line 95, which is a
`measure of the received signal strength. The RSSI estimator
`94 may also measure noise disturbance levels during idle
`channels. 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 baseband