US 6,661,832 B1
`(10) Patent No:
`a2) United States Patent
`Sindhushayanaetal.
`(45) Date of Patent:
`Dec. 9, 2003
`
`
`US006661832B1
`
`(54) SYSTEM AND METHOD FOR PROVIDING
`AN ACCURATEESTIMATION OF
`RECEIVED SIGNAL INTERFERENCE FOR
`USE IN WIRELESS COMMUNICATIONS
`SYSTEMS
`
`5,881,057 A *
`3/1999 Komatsu oo... 370/335
`
`5,903,554 A *
`we. 370/342
`5/1999 Saints
`..........
`6,032,026 A *
`........
`« 455/63.1
`2/2000 Seki etal.
`6,141,334 A * 10/2000 Flanaganetal.
`........... 370/342
`
`FOREIGN PATENT DOCUMENTS
`
`(75)
`
`Inventors: Nagabhushana T. Sindhushayana, San
`Diego, CA (US); Eduardo A.S.
`Esteves, Del Mar, CA (US)
`
`WO
`wo
`
`Oeeart
`9820617
`
`s/t006
`5/1998
`
`* cited by examiner
`
`(73) Assignee: Qualcomm Incorporated, San Diego,
`CA (US)
`
`(*) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`
`(21) Appl. No.: 09/310,053
`(22)
`Filed:
`May 11, 1999
`(SV) Unt. C17 eee eeeeeeceeeeeees eee eeteeeenenees HO4B 1/707
`(52) US. Ch. eee 375/144; 375/148; 375/227;
`370/342
`(58) Field of Search 0.0.00: 375/144, 147,
`375/148, 224, 227, 346, 347: 370/320
`335, 342, 441: 455/63,65, 67.1, 673, 135,
`226.1, 226.2, 226.3, 296
`
`(56)
`
`References Cited
`
`
`
`Primary Examiner—Betsy Lee Deppe
`(74) Attorney, Agent, or Firm—Philip Wadsworth; Kent D.
`Baker; Bruce W. Greenhaus
`57
`ABSTRACT
`67)
`Asystem for providing an accurate interference value signal
`received over a channel and transmitted by an external
`transceiver. The system includes a first receiver section for
`receiving the signal, which has a desired signal component
`and an interference component. A signal extracting circuit
`extracts an estimate of the desired signal component from
`the received signal. A noise estimation circuit provides the
`accurate interference value based on the estimate of the
`desired signal componentandthe received signal. A look-up
`table transforms the accurate noise and/or interference value
`to a normalization factor. A carrier signal-to interference
`ratio circuit employs the normalization factor and the
`received signal to compute an accurate carrier signal-to-
`interference ratio estimate. Path-combining circuitry gener-
`ates optimal path-combining weights based on the received
`U.S. PATENT DOCUMENTS
`signal and the normalization factor.
`In the illustrative
`4.901.307 A
`2/1990 Gilhousen et al. cece... 370/18
`embodiment,
`the system further includes a circuit for
`5,056,109 A
`10/1991 Gilhousenet al.
`............. 375/1
`employing the accurate interference value to compute a
`5,103,459 A
`4/1992 Gilhousenetal. .
`. 375/1
`carrier signal-to-interference ratio. An optimal path-
`5,109,390 A
`4/1992 Gilhousen etal. .
`» 375/1
`combining circuit computes optimal path-combining
`aoeeG A
`31008 blogata” oyos
`
`weights for multiple signal paths comprising the signalusing
`5414796 A
`................ 395/23
`5/1995 Jacobs et al.
`
`the accurate interference value and provides optimally com-
`5,416,797 A
`5/1995 Gilhousenetal. .
`.. 375/705
`bined signal paths in responsethereto. A log-likelihoodratio
`............. 375/227
`5,440,582 A *
`8/1995 Birchleret al.
`
`circuit computes a log-likelihood value based on the carrier
`........... 455/33.2
`5,548,808 A
`8/1996 Bruckertet al.
`oees A “ Loviove Ranocta easora signal-to-interference ratio and the optimallycombined sig-
`
`..........
`375/225
`5566206 A
`10/1996 Butler et al.
`nal paths. A decoder decodes the received signal using the
`5,568,483 A
`10/1996 Padovanietal. ..
`.. 370/84
`log-likelihood value. An additional circuit generates a rate
`
`.......
`w+ 370/22
`5,577,025 A
`11/1996 Skinneretal.
`and/or powercontrol message and transmits the rate and/or
`5008 ctousen etal.
`.
`ose09
`ee A
`power control message to the external transceiver.
`
`5/1998 Bender etal. ..
`.. 370/252
`5,754,533 A
`6/1998 Butler et al. ww... 375/225
`5,774,496 A
`
`36 Claims, 6 Drawing Sheets
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`

`

`U.S. Patent
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`Dec. 9, 2003
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`Sheet 1 of 6
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`US 6,661,832 B1
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`U.S. Patent
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`Dec. 9, 2003
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`Sheet 2 of 6
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`US 6,661,832 B1
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`1a.
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`TO DECODER
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`4
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`PATH WEIGHTING/
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`C/T AND N; ESTIMATION
`CIRCUIT
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`FIG. 2
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`3
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`

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`U.S. Patent
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`Dec. 9, 2003
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`Sheet 3 of 6
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`US 6,661,832 B1
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`U.S. Patent
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`Dec. 9, 2003
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`Sheet 4 of 6
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`US 6,661,832 B1
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`U.S. Patent
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`Dec. 9, 2003
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`Sheet 5 of6
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`US 6,661,832 B1
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`DATA SIGNAL
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`FROM M-ARY
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`Nz = Nz
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`6
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`

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`U.S. Patent
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`Dec. 9, 2003
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`Sheet 6 of6
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`US 6,661,832 B1
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`
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`DATA
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`158
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`PILOT
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`7
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`

`

`US 6,661,832 B1
`
`1
`SYSTEM AND METHOD FOR PROVIDING
`AN ACCURATE ESTIMATION OF
`RECEIVED SIGNAL INTERFERENCE FOR
`USE IN WIRELESS COMMUNICATIONS
`SYSTEMS
`
`BACKGROUND OF THE INVENTION
`
`1. Field of Invention:
`
`This invention relates to communications systems.
`Specifically,
`the present invention relates to systems for
`estimating the interference spectral density of a received
`signal in wireless code division multiple access (CDMA)
`communications systems for aiding in rate and power con-
`trol and signal decoding.
`2. Description of the Related Art:
`Wireless communications systemsare used in a variety of
`demanding applications including search and rescue and
`business applications. Such applications require efficient and
`reliable communicationsthat can effectively operate in noisy
`environments.
`
`Wireless communications systems are characterized by a
`plurality of mobile stations in communication with one or
`more base stations. Signals are transmitted between a base
`station and one or more mobile stations over a channel.
`Receivers in the mobile stations and base stations must
`
`estimate noise introduced to the transmitted signal by the
`channel to effectively decode the transmitted signal.
`In a code division multiple access (CDMA) communica-
`tions system, signals are spread over a wide bandwidth via
`the use of a pseudo noise (PN) spreading sequence. When
`the spread signals are transmitted over a channel, the signals
`take multiple paths from the base station to the mobile
`station. The signals are received from the various pathsat the
`mobile station, decoded, and constructively recombined via
`path-combining circuitry such as a Rake receiver. The
`path-combining circuitry applies gain factors, called
`weights, to each decoded path to maximize throughput and
`compensate for path delays and fading.
`Often, a communications system transmission includes
`pilot interval, a power control interval, and a data interval.
`During the pilot interval, the base station transmits a pre-
`established reference signal
`to the mobile station. The
`mobile station combines information from the received
`
`reference signal, 1.e., the pilot signal, and the transmitted
`pilot signal to extract information about the channel, such as
`channel interference and signal-to-noise (SNR) ratio. The
`mobile station analyzes the characteristics of the channel
`and subsequently transmits a power control signal to the
`base station in response thereto during a subsequent power
`control interval. For example, if the base station is currently
`transmitting with excess power, given the current channel
`characteristics, the mobile station sends a control signal to
`the base station requesting that transmitted power level be
`reduced.
`
`Digital communications systems often require accurate
`log-likelihood ratios (LLRs) to accurately decode a received
`signal. An accurate signal-to-noise ratio (SNR) measure-
`mentor estimate is typically required to accurately calculate
`the LLR for a received signal. Accurate SNR estimates
`require precise knowledge of the noise characteristics of the
`channel, which may be estimated via the use of a pilot
`signal.
`The rate or power at which a base station or mobilestation
`broadcasts a signal is dependant on the noise characteristics
`
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`2
`of the channel. For maximum capacity, transceivers in the
`base stations and mobile stations control
`the power of
`transmitted signals in accordance with an estimate of the
`noise introduced by the channel. If the estimate of the noise,
`1e., the interference spectral density of different multipath
`components of the transmitted signal
`is inaccurate,
`the
`transceivers may broadcast with too much or too little
`power. Broadcasting with too much power may result in
`inefficient use of network resources, resulting in a reduction
`of network capacity and a possible reduction in mobile
`station battery life. Broadcasting with too little power may
`result in reduced throughput, dropped calls, reduced service
`quality, and disgruntled customers.
`Accurate estimates of the noise introduced by the channel
`are also required to determine optimal path-combining
`weights. Currently, many CDMAtelecommunications sys-
`tems calculate SNR ratios as a function of the carrier signal
`energy to the total spectral density of the received signal.
`This calculation is suitable at small SNRs, but becomes
`inaccurate at larger SNRs, resulting in degraded communi-
`cations system performance.
`In addition, many wireless CDMA communications sys-
`tems fail to accurately account for the fact that some base
`stations that broadcast during the pilot
`interval do not
`broadcast during the data interval. As a result, noise mea-
`surements based on the pilot signal may become inaccurate
`during the data interval, thereby reducing system perfor-
`mance.
`
`Hence, a need exists in the art for a system and method for
`accurately determining the interference spectral density of a
`received signal, calculating an accurate SNR or carrier
`signal-to-interference ratio, and determining optimal path-
`combining weights. There is a further need for a system that
`accounts for base stations that broadcast pilot signals during
`the pilot interval, but that do not broadcast during the data
`interval.
`
`SUMMARYOF THE INVENTION
`
`The need in the art for the system for providing an
`accurate interference value for a signal received over a
`channel and transmitted by an external transceiver of the
`present
`invention is now addressed.
`In the illustrative
`embodiment, the inventive system is adapted for use with a
`wireless code division multiple access (CDMA) communi-
`cations system and includes a first receiver section for
`receiving the signal, which has a desired signal component
`and an interference and/or noise component. A signal-
`extracting circuit extracts an estimate of the desired signal
`component from the received signal. A noise estimation
`circuit provides the accurate interference value based on the
`estimate of the desired signal component and the received
`signal. A look-up table transforms the accurate noise and/or
`interference value to a normalization factor. A carrier signal-
`to-interference ratio circuit employs the normalization factor
`and the received signal
`to compute an accurate carrier
`signal-to-interference ratio estimate. Path-combining cir-
`cuitry generates optimal path-combining weights based on
`the received signal and the normalization factor.
`In the illustrative embodiment,
`the system further
`includes a circuit for employing the accurate interference
`value to compute a carrier signal-to-interference ratio (C/1).
`The system further includes a circuit for computing optimal
`path-combining weights for multiple signal paths compris-
`ing the signal using the accurate interference value and
`providing optimally combined signal paths in response
`thereto. The system also includes a circuit for computing a
`
`8
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`

`

`US 6,661,832 B1
`
`3
`log-likelihood value based on the carrier signal-to-
`interference ratio and the optimally combined signal paths.
`The system also includes a circuit for decoding the received
`signal using the log-likelihood value. An additional circuit
`generates a rate and/or powercontrol message and transmits
`the rate and/or power control message to the external
`transceiver.
`
`the first receiver section
`In a specific embodiment,
`includes downconversion and mixing circuitry for providing
`in-phase and quadrature signal samples from the received
`signal. The signal extracting circuit includes a pseudo noise
`despreader that provides despread in-phase and quadrature
`signal samples from the in-phase and quadrature signal
`samples. The signal extracting circuit further includes a
`decovering circuit that separates data signals and a pilot
`signal from the despread in-phase and quadrature signal
`samples and provides a data channel output and a pilot
`channel output in response thereto. The signal extracting
`circuit further includes an averaging circuit for reducing
`noise in the pilot channel output and providing the estimate
`of the desired signal component as output
`in response
`thereto. The noise estimation circuit includes a circuit for
`computing a desired signal energy value associated with the
`estimate, multiplying the desired signal energy value by a
`predetermined constant
`to yield a scaled desired signal
`energy value, and subtracting the scaled desired signal
`energy value from an estimate of the total energy associated
`with the received signal to yield the accurate interference
`value.
`
`An alternative implementation of the noise estimation
`circuit includes a subtractor that subtracts the desired signal
`component from the pilot channel output and provides an
`interference signal in response thereto. The noise estimation
`circuit includes an energy computation circuit for providing
`the accurate interference value from the interference signal.
`The accurate interference value is applied to a look-up
`table (LUT), which computes the reciprocal of the interfer-
`ence powerspectral density, which correspondsto the accu-
`rate interference value. The reciprocal is then multiplied by
`the scaled desired signal energy value to yield a carrier
`signal-to-interference ratio (C/l) estimate that
`is subse-
`quently averaged by an averaging circuit and input to a log
`likelihood ratio (LLR) circuit. The reciprocal is also multi-
`plied by path-combining weights derived from the pilot
`channel output to yield normalized optimal path-combining
`weight estimates, which are subsequently scaled by a con-
`stant factor, averaged, and input to the LLR circuit, which
`computes the LLR of the received signal.
`The circuit for computing optimal path-combining
`weights for each multiple signal path comprising the
`received signal includes a circuit for providing a scaled
`estimate of the complex amplitude of the desired signal
`component from an output of a pilot filter and a constant
`providing circuit. The scaled estimate is normalized by the
`accurate interference value. A conjugation circuit provides a
`conjugate of the scaled estimate, which is representative of
`the optimal path-combining weights.
`The novel design of the present inventionis facilitated by
`the noise estimation circuit that provides an accurate esti-
`mate of an interference component of the received signal.
`The accurate estimate of the interference componentresults
`in a precise estimate of carrier signal-to-interference ratio,
`which facilitates optimal decoding of the received signal.
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a diagram of a telecommunications system of the
`present invention having an accurate interference energy
`computation circuit.
`
`4
`FIG. 2 is a more detailed diagram of the accurate inter-
`ference energy computation circuit,
`log-likelihood ratio
`(LLR)circuit, and the path-combining circuit of FIG. 1
`adapted for use with forward link transmissions.
`FIG. 3 is a diagram of an accurate interference energy
`computation circuit optimized for reverse link transmission
`and including the path weighting and combining circuit and
`the LLR circuit of FIG. 2.
`
`FIG. 4 is a diagram showing alternative embodiments of
`the accurate interference energy estimation circuit and the
`maximal ratio path-combining circuit of FIG. 2.
`FIG. 5 is a block diagram of a frame activity control
`circuit for improving estimates of interference energy and
`which is adapted for use with the accurate interference
`energy computation circuit of FIG. 2.
`FIG. 6 is an exemplary timing diagram showing an active
`slot and idle slot.
`
`FIG. 7 is an exemplary timing diagram showinga traffic
`channel signal, a pilot channelsignal, a frame activity signal
`(FAC) (also knownas a reverse power control channel), and
`idle channel skirts of the slots of FIG. 6.
`
`DESCRIPTION OF THE INVENTION
`
`invention is described herein with
`While the present
`reference to illustrative embodiments for particular
`applications, it should be understoodthat the invention is not
`limited thereto. Those having ordinary skill in the art and
`access to the teachings provided herein will recognize
`additional modifications, applications, and embodiments
`within the scope thereof and additional fields in which the
`present invention would be of significant utility.
`FIG. 1 is a diagram of a telecommunications transceiver
`system 10, hereinafter referred to as transceiver system 10,
`of the present invention having an accurate carrier signal-
`to-interference (C/I) and interference energy (N,) estimation
`circuit 12. The transceiver system 10 is adapted for use with
`a CDMAmobile station. In the present specific embodiment,
`signals received by the transceiver system 10 are received
`over a forward communications link between a base station
`(not shown) and the transceiver system 10. Signals trans-
`mitted by the transceiver system 10 are transmitted over a
`reverse communications link from the transceiver system 10
`to the associated base station.
`
`Forclarity, many details of the transceiver system 10 have
`been omitted, such as clocking circuitry, microphones,
`speakers, and so on. Those skilled in the art can easily
`implement the additional circuitry without undue experi-
`mentation.
`
`The transceiver system 10 is a dual conversion telecom-
`munications transceiver and includes an antenna 14 con-
`
`nected to a duplexer 16. The duplexer 16 is connected to a
`receive path that
`includes, from left
`to right, a receive
`amplifier 18, a radio frequency (RF) to intermediate fre-
`quency (IF) mixer 20, a receive bandpassfilter 22, a receive
`automatic gain control circuit (AGC) 24, and an IF-to-
`baseband circuit 26. The IF-to-baseband circuit 26 is con-
`nected to a baseband computer 28 at the C/I and N,estima-
`tion circuit 12.
`
`The duplexer 16 is also connected to a transmit path 66
`that includes a transmit amplifier 30, an IF-to-RF mixer 32,
`a transmit bandpass filter 34, a transmit AGC 36, and a
`baseband-to-IF circuit 38. The transmit baseband-to-IF cir-
`
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`cuit 38 is connected to the baseband computer 28 at an
`encoder 40.
`
`65
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`The Cf and N,estimation circuit 12 in the baseband
`computer 28 is connected to a path weighting and combining
`
`9
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`

`US 6,661,832 B1
`
`5
`circuit 42, a rate/power request generation circuit 44, and a
`log-likelihood ratio (LLR) circuit 46. The LLR circuit 46 is
`also connected to the path-weighting and combining circuit
`42 and a decoder 48. The decoder 48 is connected to a
`software/circuitry controller 50, hereinafter referred to as the
`controller 50 that is also connected to the rate/power request
`generation circuit 44 and the encoder 40.
`The antenna 14 receives and transmits RF signals. A
`duplexer 16, connected to the antenna 14, facilitates the
`separation of receive RF signals 52 from transmit RF signals
`54.
`
`RF signals 52 received by the antenna 14 are directed to
`the receive path 64 where they are amplified by the receive
`amplifier 18, mixed to intermediate frequencies via the
`RF-to-IF mixer 20, filtered by the receive bandpassfilter 22,
`gain-adjusted by the receive AGC 24,and then converted to
`digital basebandsignals 56 via the IF-to-basebandcircuit 26.
`The digital baseband signals 56 are then input to a digital
`baseband computer 28.
`In the present embodiment, the transceiver system 10 is
`adapted for use with quadrature phase shift-keying (QPSK)
`modulation and demodulation techniques, and the digital
`baseband signals 56 are quadrature amplitude modulation
`(QAM)signals that include both in-phase (I) and quadrature
`(Q) signal components. The I and Q baseband signals 56
`represent both pilot signals and data signals transmitted from
`a CDMAtelecommunications transceiver such as a trans-
`
`ceiver employed in a basestation.
`In the transmit path 66, digital baseband computer output
`signals 58 are converted to analog signals via the baseband-
`to-IF circuit 38, mixed to IF signals, filtered by the transmit
`bandpassfilter 34, mixed up to RF by the IF-to-RF mixer32,
`amplified by the transmit amplifier 30 and then transmitted
`via the duplexer 16 and the antenna 14.
`Both the receive and transmit paths 64 and 66,
`respectively, are connected to the digital baseband computer
`28. The digital baseband computer 28 processes the received
`baseband digital signals 56 and outputs the digital baseband
`computer output signals 58. The baseband computer 28 may
`include such functions as signal-to-voice conversions and/or
`vise versa.
`
`The baseband-to-IF circuit 38 includes various compo-
`nents (not shown) such as digital-to-analog converters
`(DACs), mixers, adders,filters, shifters, and local oscilla-
`tors. The baseband computer output signals 58 include both
`in-phase (I) and quadrature (Q) signal components that are
`90° out of phase. The output signals 58 are input to digital-
`to-analog converters (DACs) in the analog baseband-to-IF
`circuit 38, where they are converted to analog signals that
`are thenfiltered by lowpassfilters in preparation for mixing.
`The phasesof the output signals 58 are adjusted, mixed, and
`summed via a 90° shifter (not shown), baseband-to-IF
`mixers (not shown), and an adder (not shown), respectively,
`included in the baseband-to-IF circuit 38.
`
`The adder outputs IF signals to the transmit AGC circuit
`36 where the gain of the mixed IF signals is adjusted in
`preparation for filtering via the transmit bandpassfilter 34,
`mixing up to RF via the IF-to-transmit mixer 32, amplifying
`via the transmit amplifier 30, and eventually,
`the radio
`transmission via the duplexer 16 and the antenna 14.
`Similarly, the IF-to-basebandcircuit 26 in the receive path
`64 includes circuitry (not shown) such as analog-to-digital
`(ADC) converters, oscillators, and mixers. A received gain-
`adjusted signals output from the receive AGCcircuit 24 is
`transferred to the IF-to-basebandcircuit 26 where it is mixed
`to baseband via mixing circuitry and then converted to
`digital signals via analog-to-digital converters (ADCs).
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`Both the baseband-to-IF circuit 38 and the IF-to-baseband
`circuit 26 employ an oscillator signal provided via a first
`oscillator 60 to facilitate mixing functions. The receive
`RF-to-IF mixer 20 and the transmit IF-to-RF mixer 32
`employ an oscillator signal input from a second oscillator
`62. The first and second oscillators 60 and 62, respectively,
`may be implemented as phase-locked loops that derive
`output signals from a master reference oscillator signal.
`Those skilled in the art will appreciate that other types of
`receive and transmit paths 64 and 66 may be employed
`instead without departing from the scope of the present
`invention. The various components such as amplifiers 18
`and 30, mixers 20 and 32, filters 22 and 34, AGC circuits 24
`and 36, and frequency conversion circuits 26 and 38 are
`standard components and mayeasily be constructed by those
`having ordinary skill in the art and access to the present
`teachings.
`In the baseband computer 28, the received I and Q signals
`56 are input to the C/I and N,estimation circuit 12. The C/I
`and N, estimation circuit 12 accurately determines the
`interference energy of the I and Q signals 56 based on the
`pilot! signal and determines a carrier signal-to-interference
`ratio in response thereto. The carrier signal-to-interference
`ratio (C/I) is similar to the signal-to-noise ratio (SNR) and
`is the ratio of the energy of the received I and Q signals 56
`less interference and noise components to the interference
`energy of the received I and Q signals 56. Conventional C/I
`estimation circuits often fail
`to accurately estimate the
`multipath interference energy.
`The C/I and N,estimation circuit 12 outputs a C/I signal
`to the rate/power request generation circuit 44 and the LLR
`circuit 46. The C/I and N,estimation circuit 12 also outputs
`the reciprocal of the interference energy (1/N,), a despread
`and decovered data channel signal, and a despread and
`decovered pilot channel signal to the path weighting and
`combining circuit 42. The despread and decovered data
`channel signalis also provided to the decoder 48 whereit is
`decoded and forwardedto the controller 50. At the controller
`
`50, the decoded signal is processed to output voice or data,
`or to generate a reverse link signal for transfer to the
`associated base station (not shown).
`The path-weighting and combining circuit 42 computes
`optimal ratio path-combining weights for multipath compo-
`nents of the received data signal corresponding to the data
`channel signal, weights the appropriate paths, combines the
`multiple paths, and provides the summed and weighted
`paths as a metric to the LLR circuit 46.
`The LLR circuit 46 employs metrics from the path-
`weighting and combining circuit 42 with the C/I estimation
`provided by the C/I and N,estimation circuit 12 to generate
`an optimal LLR and soft decoder decision values. The
`optimal LLR and soft decoder decision values are provided
`to the decoder 48 to facilitate decoding of the received data
`channel signals. The controller 50 then processes the
`decoded data channel signals to output voice or data via a
`speaker or other device (not shown). The controller 50 also
`controls the sending of speech signals and data signals from
`an input device (not shown)to the encoder 40 in preparation
`for transmission.
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`The rate/power request generation circuit 44 generates a
`rate control or powerfraction request message based on the
`C/I signal input from the C/I and N,estimation circuit 12.
`The rate/power request generation circuit 44 compares the
`C/I with a set of predetermined thresholds. The rate/power
`request generation circuit 44 generates a rate request or
`powercontrol message based on the relative magnitude of
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`US 6,661,832 B1
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`7
`the C/I signal with respect to the various thresholds. The
`exact details of the rate/power request generation circuit 44
`are application-specific and easily determined and imple-
`mented by those ordinarily skilled in the art to suit the needs
`of a given application.
`The resulting rate control or powerfraction request mes-
`sage is then transferred to the controller 50. The controller
`50 prepares the powerfraction request message for encoding
`via the encoder 40 and eventual transmission to the associ-
`ated base station (not shown) over a data rate request
`channel (DRC) via the transmit path 66, duplexer 16 and
`antenna 14. Whenthe base station receives the rate control
`
`or power fraction request message, the base station adjusts
`the rate and/or powerof the transmitted signals accordingly.
`The accurate C/I and N,estimates from the C/I and N,
`estimation circuit 12 improve the performance of the rate/
`power request generation circuit 44 and improve the per-
`formanceof the decoder 48, thereby improving the through-
`put and efficiency of the transceiver system 10 and
`associated telecommunications system.
`FIG. 2 is a more detailed diagram of the accurate C/I and
`N, estimation circuit 12, LLR circuit 46, and path-weighting
`and combining circuit 42 of FIG. 1 adapted for use with
`forward link transmissions.
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`terminal of the fourth multiplier 96 is connected to the
`second constant generation circuit 98. An output of the
`fourth multiplier 96 is connected to a second input of the
`third multiplier 94. The output of the third multiplier 94
`provides input to the complex conjugate circuit 100. The
`output of the complex conjugate circuit 100 is connected to
`a first input of the fifth multiplier 102. An output of the
`constant divider circuit 78 is connected to a second input of
`the fifth multiplier 102. An output of the fifth multiplier 102
`is connected to an input of the path accumulatorcircuit 104.
`The output of the path accumulator circuit 104 is connected
`to a second input of the LLR circuit 46. The output of the
`LLRcircuit is connected to an input of a decoder (see 48 of
`FIG. 1).
`In operation, the PN despreader 70 receives the I and Q
`signals and despreads L fingers,
`i.e., paths (1). The PN
`despreader 70 despreadsthe I and Q signals using an inverse
`of the pseudo noise sequence used to spread the I and Q
`signals before transmission over the channel. The construc-
`tion and operation of the PN despreader 70 is also well
`knownin theart.
`
`Despread signals are output from the PN despreader 70
`and input to the M-ary Walsh decover 72 and the I, com-
`putation circuit 74. The I, computation circuit 74 computes
`the total received energy (I,) per chip, which includes both
`a desired signal component and an interference and noise
`component. The I, computation circuit provides an estimate
`(°) of I, in accordance with the following equation:
`
`i, = in,wal
`
`1]
`
`The C/I and N,estimation circuit 12 includes, from left to
`right and top to bottom, a pseudo noise (PN) despreader 70,
`an M-ary Walsh decover circuit 72, a total received signal
`energy (I,) computation circuit 74, a first constantcircuit 84,
`a pilot filter 76, a subtractor 80, a first multiplier 82,a pilot
`energy calculation circuit 86, a look-up table (LUT) 88, a
`second multiplier 90, and a C/I accumulation circuit 92. In
`the C/I and N,estimation circuit 12, the pseudo noise (PN)
`despreader 70 receives the I and Q signals 56 from the
`where N is the numberof chips per pilot burst and is 64 in
`IF-to-basebandcircuit 26 of FIG. 1. The PN despreader 70
`the present specific embodiment and °*
`represents the
`provides input,
`in parallel,
`to the M-ary Walsh decover
`received despread signal output from the PN despreader 70.
`circuit 72 and the I, computation circuit 74. The M-ary
`Walsh decovercircuit 72 provides input to the pilot filter 76
`Those skilled in the art will appreciate that the I, may be
`computed before despreading by the PN despreader 70
`and to a constant divider circuit 78 in the path weighting and
`without departing from the scope of the present invention.
`combining circuit 42.
`For example,
`the I, computation circuit 74 may receive
`The output of the energy computation circuit 74 is con-
`direct input from the I and Q signals 56 instead of input
`nected to a positive terminal of the subtractor circuit 80. A
`provided by the PN despreader 70, in which case an equiva-
`negative terminal of the subtractor circuit 80 is connected to
`lent estimate of I, will be provided at the output of the I,
`an output terminalof a first multiplier 82. A first input of the
`computation circuit 74.
`first multiplier 82 is connected to an output of the first
`The M-ary Walsh decover circuit 72 decovers orthogonal
`constant circuit 84. A second input of the first multiplier 82
`data signals, called data channels, and pilot signals, called
`is connected to an output of the pilot energy calculation
`the pilot channel, in accordance with methods knownin the
`circuit 86. The pilot filter 76 provides input to the pilot
`art. In the present specific embodiment, the orthogonal data
`energy calculation circuit 86.
`signals correspond to one data channel(s) that is represented
`An output of the subtractor 80 is connected to the look-up
`by the following equation:
`table (