(12) United States Patent
`Amalfitano et al.
`
`(10) Patent No.:
`(45) Date of Patent:
`
`US 6,545,990 B1
`Apr. 8, 2003
`
`USOO6545990B1
`
`(54) METHOD AND APPARATUS FOR A
`SPECTRALLY COMPLIANT CELLULAR
`COMMUNICATION SYSTEM
`
`(75) Inventors: Carlo Amalfitano, Melbourne Beach,
`FL (US); James A. Proctor, Jr.,
`Indialantic, FL (US)
`(73) Assignee: Tantivy Communications, Inc.,
`Melbourne, FL (US)
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`
`(*) Notice:
`
`(21) Appl. No.: 09/467,353
`(22) Filed:
`Dec. 20, 1999
`(51) Int. Cl. ................................................ H04B 71216
`(52) U.S. Cl. ........................ 370/335; 370/342; 455/450
`(58) Field of Search ................................. 370/335, 342,
`370/329, 341,441; 455/450
`
`(56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`5,319,634 A 6/1994 Bartholomew et al. ....... 370/18
`5,956,345 A * 9/1999 Allpress et al.......
`... 370/480
`6,044,073 A * 3/2000 Seshadri et al. ............ 370/342
`6,335,922 B1 *
`1/2002 Tiedemann, Jr. et al. ... 370/335
`FOREIGN PATENT DOCUMENTS
`
`EP
`
`O 701 337 A2
`
`3/1996
`
`OTHER PUBLICATIONS
`Lim, et al., “Implementation Issues on Wireless Data Ser
`vices in CDMA Cellular and PCS Networks,” Gateway to
`the Twenty First Century. International Conference on Uni
`
`versal Personal Communications. 1996 5" IEEE Interna
`tional Conference on Universal Personal Communications
`Record (Cat. No. 96th8185), Proceedings of ICUPC-5"
`International Confer, 2:582–585, XP00217205 1996, New
`York, NY, USA, IEEE, USA.
`Azad, et al., “Multirate Spread Spectrum Direct Sequence
`CDMA Techniques," IEE Colloquium on Spread Commu
`nications Systems, GB, IEE, London, XP000570787, pp.
`4-1-4–05, Apr. 15, 1994.
`Jeong, et al., “Rate-Controlled Data Transmission for IS-95
`CDMA Networks," IEEE Vehicular Technology Confer
`ence, US, New York, IEEE, vol. CONF. 47, XP000738626,
`pp. 1567–15714 May 1997.
`
`* cited by examiner
`
`Primary Examiner Edward F. Urban
`Assistant Examiner Erika A. Gary
`(74) Attorney, Agent, or Firm-Hamilton, Brook, Smith &
`Reynolds, P.C.
`ABSTRACT
`(57)
`A System for wireleSS data transmission that uses a channel
`bandwidth, channel Separation, and radio frequency power
`Spectrum which is compatible with existing deployments of
`wireleSS Voice Services. The transmitted waveforms are thus
`compatible with existing cellular networks. However, the
`time domain digital coding, modulation, and power control
`Schemes are optimized for data transmission. Existing cel
`lular network Sites can thus be used to provide a high Speed
`service optimized for wireless data traffic without the need
`for new radio frequency planning, and without interfering
`with existing voice Service deployments.
`
`12 Claims, 6 Drawing Sheets
`
`31 8
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`VOICE TRAFFIC PROCESSOR 310
`CHANNEL CONTROL
`...ALLOCATEBY CALL 1312
`SOFTHANDOFF
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`FWD. LINK
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`ANSMT
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`32O
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`DATA TRAFFIC PROCESSOR 330
`CHANNE CONTROL
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`e NOMADIC MOBILITY ONLY
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`
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`342 o
`
`DOWNCONVERT
`
`TUNED TO 42
`
`Ex.1017
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`U.S. Patent
`U.S. Patent
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`Apr. 8, 2003
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`Sheet 1 of 6
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`US 6,545,990 B1
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`U.S. Patent
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`U.S. Patent
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`Apr. 8, 2003
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`Apr. 8, 2003
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`US 6,545,990 B1
`
`1
`METHOD AND APPARATUS FOR A
`SPECTRALLY COMPLIANT CELLULAR
`COMMUNICATION SYSTEM
`
`BACKGROUND OF THE INVENTION
`The evolution of communication technologies continues
`to drive user preferences in the manner of access to net
`works. Wireless networks, especially for voice
`communications, now provide coverage in most areas of the
`industrialized World. Indeed, wireleSS Voice communica
`tions are becoming a preferred method in many instances
`because of their convenience. In certain situations, it may
`even be leSS expensive to use a wireleSS telephone. For
`example, wireleSS phone Service may actually be leSS expen
`Sive than bringing a Second wired telephone into a home, or
`in remote areas.
`At the same time, demand for data communication Ser
`vices and in particular demand for reliable high Speed acceSS
`to the Internet is also growing. This demand is growing So
`fast that local exchange carriers (LECs) are concerned that
`the demand will cause their networks to fall. It is expected
`that as time goes on, at least Some of this demand will
`eventually shift to the wireless side, especially with the
`popularity of laptop computers, personal digital assistants,
`and other portable computing devices increases.
`At the present time, there are difficulties integrating
`available wireleSS data Systems with existing computer
`network infrastructure. To provide coverage to an area
`requires planning of various network components, as well as
`obtaining necessary licensing to access the airwaves from
`government authorities. In particular, not only must wireleSS
`modulation Schemes be chosen from among the myriad of
`possibilities, including analog modulation Standards Such as
`AMPS, TACS and NMT, but also the emerging digital
`Standards, including Time Division Multiple Access
`(TDMA) schemes such as Global System for Module
`(GSM) communications, and Code Division Multiple
`Access (CDMA). In addition, site locations for base station
`equipment must be chosen and acquired. Additional engi
`neering is often required to determine proper tower heights,
`effective radiated power levels, and assignment of a fre
`quency plan to an area within which wireleSS Service is
`desired.
`Although it provides almost ubiquitous coverage, the
`existing cellular voice infrastructure has been very expen
`sive to build-out. Therefore, the most common method of
`using the cellular infrastructure to Send data is quite analo
`gous to how computers presently use wired telephones. In
`particular, digital data Signals are first formatted by modern
`equipment to generate audio tones in the same manner as
`used for the wireline network. The audio tones are then fed
`to cellular voice transceiving equipment which modulates
`these tones according to the interface Scheme in use. For
`example, an input data Stream Such as produced by a
`computer is first modulated to generate frequency shift
`keyed (FSK) signals at audio frequencies. The FSK audio
`signal is then modulated using, for example, the IS-95B
`standard for CDMA modulation such as is prevalent in the
`United States. This modulation Scheme impresses a pair of
`codes on a given radio frequency Signal including a pseu
`dorandom noise (PN) spreading code and a orthogonal code
`to define multiple traffic channels.
`It is also possible to use Separate networks built Specifi
`cally for data services such as so-called Cellular Packet Data
`(CDPD) networks. However, CDPD coverage is not nearly
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`as ubiquitous as the coverage presently provided for cellular
`Voice communications. This is most likely because the
`build-out of a CDPD network requires all of the costs
`asSociated with building out a separate network, including
`planning of base Station Sites, obtaining licensing, acquiring
`Such sites and engineering their tower heights and radiated
`powers and frequency planning.
`AS mentioned above, the most popular communication
`Scheme for voice cellular networks at the present time is
`based upon CDMA modulation. These standards dictate a
`radio frequency (RF) channel bandwidth of 1.2288 mega
`hertz (MHz). Therefore, RF system planning engineers and
`component industries have Standardized their products
`based upon this particular channel bandwidth, and these
`networks have been built out with radio equipment, Site
`locations, tower heights, and frequency plans that assume
`this channel Spacing.
`Unfortunately, these CDMA standards also specify other
`parameters for the communication which are not optimized
`for data traffic. These include the soft hand-off processing
`needed to transfer control of a call from one base Station to
`another with the cooperation of the subscriber unit. The
`requirements reduce overall System capacity since indi
`vidual users may be communicating with two or more base
`Stations at any given time.
`Furthermore, existing CDMA protocols for wireless ser
`Vice assume that connections are to be maintained for the
`duration of a call. This is quite unlike the typical Internet
`connection which is quite irregular in its actual demand for
`information. For example, after requesting a Web page, the
`typical Internet user then expects a relatively large amount
`of data to be downloaded. However, the user then spends
`many Seconds or even minutes viewing the Web page before
`additional information needs to be transmitted.
`
`SUMMARY OF THE INVENTION
`Briefly, present invention is a System for wireleSS data
`transmission that uses a channel bandwidth, channel
`Separation, and radio frequency power spectrum which are
`compatible with existing deployments of wireleSS Voice
`networks. However, the wireleSS data protocol Specifies
`digital coding, modulation, channel use allocation, and
`power control Schemes that are optimized for data commu
`nications. Thus, the transmitted waveforms, although
`appearing to be of a different format when viewed from a
`time domain perspective are, in general, compatible from a
`frequency domain perspective with existing cellular net
`WorkS.
`AS a result, a data communication System utilizing this
`wireleSS data protocol has the Same appearance from a radio
`frequency network planning perspective as a Standard cel
`lular System. Thus, from a Service provider's point of view,
`an optimized data Service can be deployed using the same
`base Station locations, tower heights, cell Sites, and cell radii,
`as well as frequency reuse plans that were already developed
`for existing voice networkS. However, from the perspective
`of the Internet Service provider and the user, the System is
`optimized for data transmission.
`BRIEF DESCRIPTION OF THE DRAWINGS
`The foregoing and other objects, features and advantages
`of the invention will be apparent from the following more
`particular description of preferred embodiments of the
`invention, as illustrated in the accompanying drawings in
`which like reference characters refer to the same parts
`throughout the different views. The drawings are not nec
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`essarily to Scale, emphasis instead being placed upon illus
`trating the principles of the invention.
`FIG. 1 is a high level block diagram of a system for
`providing wireleSS data Service according to the invention.
`FIG. 2 is a frequency domain plot of the channel spacing
`used with the invention.
`FIG. 3 is a more detailed view of the components of a base
`Station processor.
`FIG. 4 is a detailed diagram of components of a base
`Station and Subscriber unit used to implement forward link
`communication.
`FIG. 5 is a diagram depicting how different selectable data
`rates may be Supported.
`FIG. 6 is a detailed diagram of components used to
`implement reverse link communication.
`DETAILED DESCRIPTION OF A PREFERRED
`EMBODIMENT
`FIG. 1 illustrates a cellular radio telephone communica
`tion system 10. As in the prior art, the system 10 includes
`one or more mobile users or Subscribers 12, including a
`Voice Subscriber unit 12-1 Such as associated with a moving
`vehicle, and a data Subscriber unit 12-2 Such as associated
`with a laptop computer. Base Stations 14-1, 14-2, 14-n are
`each associated with one of a number of cells 16-1,
`16-2, . . . , 16-n with each cell 16 representing portions of
`an area within which the system 10 is providing wireless
`communication. Each base Station 14 also has an associated
`base station processor BSP 18. A mobile telephone switch
`ing office 20 couples traffic and control Signaling between
`other networks 30, 36 and each of the base station processors
`18. Although only three cells 16 are shown in FIG. 1, a
`typical system 10 may include hundreds of base stations 14
`35
`and cells 16 and thousands of Subscriber units 12.
`The cellular network 10 provides a duplex radio commu
`nication link 22 between each base Station processor 18 and
`mobile Subscriber units 12 traveling within the associated
`cell 16. The function of the base station processor 18 is
`mainly to manage radio communication with the Subscriber
`unit 12. In this capacity, the base Station processors 18 Serve
`chiefly as relay Stations for both data and Voice Signals.
`With the present invention, however, the base station
`processor 18 Separately handles Voice and data traffic. In
`particular, radio channels associated with Servicing the Voice
`units 12-1 are handled differently from the radio channels
`asSociated with handling the data traffic for the data user
`12-2. Thus, these radio channels are respectively coupled to
`different circuits in the mobile telephone Switching office 20.
`For example, different radio channels are associated with
`Servicing the mobile Voice unit 12-1 than the channels
`associated with servicing the data subscriber unit 12-2. More
`Specifically, circuits 24-1 associated with Voice traffic con
`nect to a voice traffic processor 26 within the mobile
`telephone Switching office 20. Voice Signals are then routed
`through a voice Switch 27 to a voice network Such as the
`Public Switched Telephone Network (PSTN) 30 and on to a
`destination telephone 32. Voice traffic heading in the for
`ward direction from the telephone 32 to the mobile unit 127
`is handled in an analogous way, but in reverse order.
`On the other hand, data Signals associated with the data
`subscriber unit 12-2 are first coupled to a different circuit
`24-2 to a data traffic processor 28. The data Signals are in
`turn fed through a gateway 29 Such as may be a router, data
`Switch, concentrator, or other network point-of-presence to
`provide connections to a data network Such as the Internet
`
`4
`36. The data Signals are eventually coupled to and from a
`destination Such as a computer 38 which may, for example,
`be an Internet Server.
`Cellular telephone Systems have traditionally employed
`analog modulation Schemes Such as frequency division
`multiple access (FDMA) to carry signals between the Sub
`scriber units 12 and the base station 13 wherein a radio
`telephone communication channel includes one or more
`carrier frequency bands which are dedicated to each user for
`the duration of a particular call. To provide greater channel
`capacity and to more efficiently use the radio spectrum,
`however, present emerging networks now operate using
`digital modulation Schemes Such as time division multiple
`access (TDMA) or code division multiple access (CDMA).
`Communications in a TDMA System occur by assigning a
`Series of time slots on each carrier frequency band, with
`individual Subscriber units typically being allocated one or
`more time slots. Of more interest to the present invention are
`CDMA Systems, in which each user is assigned one or more
`unique channel codes. Each channel code corresponds to a
`digital modulation Sequence used for spreading the transmit
`energy of the communication Signals over a broad band
`width. A receiving Station uses the same code to despread the
`coded Signal and recover the base band information.
`One such CDMA scheme in widespread use in the United
`States is specified as Telecommunications Industry ASSocia
`tion (TIA) standard IS-95B. As shown in FIG. 2, the IS-95B
`standard specifies that an IS-95A voice channel 40-1,
`40-2, . . . , 40-n occupy a bandwidth of 1.2288 MHz, even
`though Such voice Signal may have originated only as a
`several kilohertz bandwidth signal. Thus, the affect of the
`Spreading codes is to greatly increase the required band
`width of each channel although many different Subscribers
`12 may be sharing the channel at any given time.
`In accordance with the invention, certain coded traffic
`channels 40-1, 40-2, 40-n, are associated with servicing
`mobile voice units 12-1 whereas other coded traffic channels
`42-1 are associated with Servicing data Subscribers 12-2.
`More specifically, the channel coding, channel allocation,
`power control, and handoff Schemes used for the Voice
`channels 40 may be compliant with industry standard
`IS-95B. However, the data channels 42, are also compliant
`with the voice channels 40 from a frequency bandwidth and
`power Spectrum perspective. In particular, the data channels
`42 appear as shown in FIG. 2 to be identical to the voice
`channels from a frequency domain perspective. However,
`they use a channel coding, channel allocation, handoff, and
`power control scheme which is optimized for Internet Pro
`tocol (IP)-type data access and which is different from the
`channel coding used for the voice channels. While the data
`channels may use a CDMA-type encoding, it is not the same
`as the CDMA encoding used for the voice channels.
`FIG. 3 is a more detailed view of how a typical base
`Station processor 18 handles Voice and data Signals differ
`ently according to the invention. The base Station processor
`18 consists of a voice traffic processor 310 including a voice
`channel controller 312, and forward link components,
`including a forward link encoder 314, and transmit modu
`lator 316, as well as reverse link components, including a
`receive demodulator 317 and reverse link decoder 318.
`Completing the circuits which process voice channels are a
`voice channel radio frequency (RF) upconverter 320 and RF
`downconverter 322.
`Also included within the base station processor 18 is a
`data traffic processor 330 which includes a data channel
`controller 332, forward link encoder 334, transmit modula
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`tor 346, reverse link decoder 348, and receive demodulator
`349. Also forming part of the data handling circuits are a
`data channel RF upconverter 340 and RF downcoverter 342.
`The voice traffic processor 310 and RF up- and down
`converter circuits 320 and 322 operate essentially as in the
`prior art. For example, these circuits are implemented in
`accordance with the IS-95B air interface standard, to provide
`duplex voice communications between the mobile Sub
`scriber unit 12 and the mobile telephone switching office 20.
`In particular, in the forward direction, that is, for voice
`signals traveling from the PSTN through the MTSO 20
`towards the Subscriber unit 12, channel Signals received over
`the network connection 24-1 are fed to the forward link
`encoder 314. The network connection 24-1 may, for
`example, use a carrier-grade multiplex circuit over digital
`transport cabling Such as T1 carrier circuits.
`The IS-95 standard specifies that the forward link encoder
`314 encodes the signal with a pseudorandom noise (PN)
`Spreading code and Orthogonal Walsh code to define the
`Voice channel. A transmit modulator then impresses the
`desired modulation Such as quadrature phase shift key
`(QPSK) modulation onto this signal, which is then for
`warded to the RF upconverter 320.
`In the reverse link direction, that is, for Signals traveling
`from the mobile unit 12 through the base station 18 towards
`the mobile telephone Switching office 20, Signals received
`from the RF downconverter 322 are passed to the receive
`demodulator 317 and reverse link decode circuits 318. The
`receive demodulator 317 removes the modulation from the
`signals, with the reverse link decoder 318 then stripping off
`the pseudorandom noise and Walsh channel coding to pro
`vide a digitized Voice Signal to the network connection 24-1.
`The voice channel RF upconverter 320 and RF downcon
`verter 322 are tuned to the channels 40 that are devoted to
`Voice traffic. Specifically, only channels devoted to voice
`traffic are allowed to be allocated by the voice channel
`controller 312 to the voice traffic processor 310. In addition,
`the voice channel controller 312 also controls the remainder
`of the circuits of the voice traffic processor 310 in accor
`dance with the IS-95B standard. For example, radio chan
`nels 40 are allocated on a per-call basis. That is, whenever
`a user of a mobile Subscriber unit 12 wishes to place a call
`by dialing a telephone number of the destination telephone
`32, the channel controller 312 opens and maintains an RF
`forward link channel and RF reverse link channel by acti
`vating encoder 314, decoder 318, modulator, and demodu
`lator circuits of the traffic processor 310, dedicating those
`channels to that call as long as the call is in progreSS.
`In addition, functions associated with mobility Such as
`call handoff, in particular the Soft handoff algorithms dic
`tated by IS-95B, are performed also by the voice channel
`controller 312.
`Turning attention now to the data traffic processor 330, it
`will now be explained how these circuits handle their
`Signaling in a different way than the Voice traffic processor
`310. In the forward link direction, signals are received from
`a data transport media 24-2 and are fed to a forward link
`encoder 334 and transmit modulator 346. However, the
`forward link encoder 334 and transmit modulator 346 oper
`ate differently than the corresponding components 314 and
`316 in the voice traffic processor 310. One such difference
`relates to the fact that (as will be described in greater detail
`in connection with FIGS. 4 and 5) forward error correction
`(FEC) coding rates are adapted for individual channels to
`allow different coding rates to be assigned to each user. In
`addition, the forward link encoder and transmit modulators
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`are only allocated on an instantaneous demand basis. Thus,
`StepS are taken to ensure that coded data radio channels are
`only allocated to data subscribers 12-2 which actually have
`data ready to be transmitted or received.
`The data channel controller 332 responsible for allocating
`radio channels to the data Subscriber 12-2 also handles
`mobility and handoff of data calls in a way which is different
`from the channel controller 312 associated with the voice
`traffic processing 310. In particular, the data channel con
`troller 332 in the preferred embodiment supports nomadic
`type mobility only. That is, the data users 12-2 are not
`expected to cross a boundary between two cells 16-1 and
`16-2, for example, during the duration of an active connec
`tion. However, the system 10 does provide service if, for
`example, a data user 12-2 disconnects, at least the radio
`connection, moves to a different cell, and then reestablishes
`a radio connection.
`The data traffic processor 330 will be described in greater
`detail now in connection with FIG. 4. This figure illustrates
`a detailed View of the forward link processing used to
`transmit data Signals from the base Station 18 to the data
`Subscriber units 12-2. In the base station 18, these include a
`forward link transmit controller 450 and signal processing
`circuits which generate the various signals making up the
`forward link transmitted Signals. These include circuits for
`implementing functions Such as a pilot channel 432, paging
`channel 434, and one or more traffic channels 436. As it is
`known in the art, the pilot channel 432 is responsible for
`generating known continuous pilot Signals that permit
`receiver circuits in the Subscriber unit 12 to properly Syn
`chronize to signals transmitted by the base station 18. The
`paging channel 434 Sends control Signals to the Subscriber
`unit 12 to, for example, allocate traffic channel capacity over
`the forward link 416. For example, the paging channel 434
`is used to Send messages to the Subscriber unit 12 when it is
`necessary to allocate a traffic channel on the forward link to
`Send messages.
`The traffic channel 436 provides a physical layer structure
`for Sending payload data over the forward link. In a pre
`ferred embodiment, CDMA encoding is used to define the
`pilot channels 432, paging channels 434, as well as the traffic
`channels 436. More specifically, the traffic channel circuitry
`436 includes symbol framing function 440, forward error
`correction logic 442, a multiplexer 444, a Summer 450, and
`radio frequency (RF) upconverters 452.
`Data which is to be sent over the forward link 416 is first
`fed to the framing function 440. The framing function 440
`packages input payload data into conveniently sized groups
`referred to as frames. The size of these pre-encoded frames
`will vary depending upon the particular forward error cor
`rection (FEC) coding Scheme Selected at any given time by
`the FEC encoder 442. What is important is that the combi
`nation of the framers 440 and FEC encoder 442 produce a
`fixed number of output FEC symbols in each given trans
`mitted frame.
`FIG. 5 is a diagram showing how the framers 440 and
`FEC encoders 442 are selected in pairs to accomplish this
`end result. The fixed output FEC frame size in the illustrated
`embodiment is 4096 symbols. This embodiment uses four
`different FEC symbol encoders 442-1, 442-2, 443-3 and
`442-4 providing, respectively, a 1/4, 1/3, 1/2, and 7/8 rate
`encoding. The coding rate of each FEC symbol encoder 442
`indicates the ratio of the number of input bits to the number
`of output bits. The actual codes used by the FEC encoders
`442 may be any of a number of different types of error
`correction codes Such as R, thus, a higher information rate
`is obtained with higher rate FEC code.
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`Ex.1017
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`This embodiment also uses four framer circuits 440-1,
`440-2, 440-3, 440-4 corresponding to the four FEC encoders
`442-1, 442-2, 443-3 and 442-4. For example, the 1/4 rate
`encoder 442-1 requires a 1/4 rate framing circuit 440-1
`which groups incoming bits into pre-coded FEC groups of
`1024 bits, producing the desired 4096 output symbols.
`Similarly, the 1/3 rate encoder 442-2 requires a 1/3 rate
`framer 440-2 to group incoming bits into pre-encoded Sets of
`1331 bits. The 1/4 rate encoder 442-3 uses a framer 440-3
`with a pre-encoded set size of 2048, and 7/8 encoder 442-4
`uses a framing circuit 440-4 with the pre-encoded size of
`3584 bits.
`Framing circuit 440 and FEC encoder 442 thus only
`utilize one of the specific framers 440-1, 440-2, 440-3, or
`440-4, and one of the specific encoders 442-1, 442-2, 443-3
`and 442-4 at any given point in time. Which particular
`framing circuit 440 and FEC encoder 442 is activated is
`controlled by coding rate control signal 456 input to each of
`the framing circuits 440 and encoder 442. The code rate
`select signal 456 is generated by the forward link transmit
`controller 450.
`A given connection may require multiple traffic channels
`to be allocated to at a particular time. For example, the
`demultiplexer 444 accepts the signal produced by the FEC
`encoder 442 being to multiple spreading circuits 436-1 and
`channel modulators 438-1 which impress not only the
`quadrature phase shift keyed (QPSK) modulation, but also
`the appropriate pseudorandom noise (PN) and/or Walsh
`orthogonal coding in order to produce multiple CDMA
`channel signals 439-1,..., 439-n. As mentioned previously,
`the QPSK spreaders 436 and modulators 438 ensure that the
`modulated bandwidth and power spectrum of the forward
`link signal produced by the data traffic processor 330 is the
`Same as the modulated bandwidth and power spectrum of
`the modulated Voice Signals produced by the Voice traffic
`processor. These multiple CDMA traffic signals are then
`Summed by the Summer 440, together with the pilot channel
`Signal produced by the channel pilot circuits 432 and the
`paging Signal produced by the paging channel circuit 434
`before is fed to the RF upconverter 442.
`The forward link transmit controller 450, which may be
`any convenient Suitable microcontroller or microprocessor,
`has among its Software programs a process referred to as the
`capacity manager 455. The capacity manager 455 not only
`allocates one or more of the channel modulators 448 to a
`Specific forward link traffic channel, but also sets the value
`for the code rate Select Signals 456. In addition, the capacity
`manager 455 sets power levels for a particular forward link
`Signals 416.
`A Single capacity manager 455 in a base Station processor
`12 may manage multiple traffic channel circuits, Setting their
`respective code rate Select Signal 456 according to observed
`conditions in a corresponding traffic channel. These adjust
`ments to the channel physical layer characteristics are made
`preferably in response to determining a Signal Strength
`value, Such as by measuring a ration of the energy per data
`bit divided by a normalized noise power level (Eb/No) at the
`receiver.
`Thus, in addition to changing the power level of the
`individual modulated Signals generated by the modulators
`448, it is also possible with a System according to the
`invention to control the Eb/No at the receiver by adjusting
`the value of code rate select signal 456 in order to select
`different code rates under different conditions.
`For example, if a remote access unit 12 located deep
`inside of building is experiencing particularly adverse mul
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`tipath or other distortion conditions, in the past it would have
`been thought to be necessary to increase the power level of
`the forward link 16-n in order to obtain an appropriate
`received signal level at the acceSS unit 12. However, with the
`invention, if a full maximum data rate is not needed, then the
`coding rate implemented by the FEC encoder 442 can be
`lowered.
`And in other environments where multipath distortion is
`minimal, Such as in a direct line of Sight Situation, the
`highest code rate generate 442-4 can be Selected while at the
`Same time reducing the radiated power level on forward link
`for that particular channel. This, therefore, maximizes the
`available data rate for given user while also minimizing
`interference generated to other users of the same radio
`channel.
`Thus, in environments where propagation is good, the
`System 10 can increase the data rate to a given user without
`introducing additional interference to other users. However,
`in a bad Signaling environment, an advantage is also
`obtained since each particular user channel can be made
`more robust without increasing its power level.
`Continuing to pay attention to FIG. 4, various components
`of the receiver portion of the access unit 12 will be discussed
`in more detail. These consist of an RF downconverter 460,
`equalizer 462, multiple rake receivers 464-1, . . . , 464-n,
`multiple ch