United States Patent (19)
`Backman et al.
`
`USOO6128355A
`Patent Number:
`11
`(45) Date of Patent:
`
`6,128,355
`Oct. 3, 2000
`
`54 SELECTIVE DIVERSITY COMBINING
`75 Inventors: Johan Backman, Stockholm; Thomas
`Lindqvist, Sundsvall; Stefan
`Håkansson, Solna, all of Sweden
`73 Assignee: Telefonaktiebolget LM Ericsson,
`Stockholm, Sweden
`
`21 Appl. No.: 08/861,541
`22 Filed:
`May 21, 1997
`(51) Int. Cl." ................................. H04B 7/08; H04L 1/02
`52 U.S. Cl. ..................
`375/347; 455/133; 455/137
`58 Field of Search ..................................... 375/347, 267,
`375/224, 227; 455/65, 303, 272, 273, 278.1,
`134, 135, 137, 277.2, 140, 226.2, 226.3,
`132, 133
`
`56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`5,203,026 4/1993 Ekelund .................................. 375/347
`5,528,581
`6/1996 De Bot ......
`... 375/347
`5,553,102 9/1996 Jasper et al. ..
`... 375/347
`5,684.793 11/1997 Kiema et al. .
`... 455/135
`5,787,131
`7/1998 Bottomley ...
`... 375/347
`5,796,788 8/1998 Bottomley ...
`... 375/341
`5,848,361 12/1998 Edwards .................................. 455/562
`FOREIGN PATENT DOCUMENTS
`O 600 547 6/1994 European Pat. Off. .......... HO4B 7/08
`WO93/18593 9/1993 WIPO .............................. HO4B 7/10
`
`OTHER PUBLICATIONS
`Feeney et al., “The Performance of Various Diversity Com
`biners on Signals Received at a Base-Station Site”,
`XP-00205312 Land Mobile Radio. Third International Con
`ference (Publ. No. 65), Cambridge, UK, Dec. 10–13, 1985,
`pp. 55-62.
`Karlsson et al., “Interference Rejection Combining for
`GSM, XP002053626. Gateway to the Twenty Firrst Cen
`tury. International Conference on Universal Personal Com
`munications. 1996 5" IEEE International Conference on
`Universal Personal Communications Record (Cat. No.
`96th8185), Proceedings of ICPUC-5th International Con
`ference, New York, NY, pp. 433–437.
`Mobile Communication Design Fundamentals, by William
`C.Y. Lee (Wiley, 1993), pp. 116-132.
`Primary Examiner Stephen Chin
`Assistant Examiner Betsy L. Deppe
`Attorney, Agent, or Firm-Burns, Doane, Swecker &
`Mathis, L.L.P.
`ABSTRACT
`57
`A method and System for combining Signals in a receiver
`employing antenna diversity. If the interference exceeds a
`predetermined threshold, interference rejection combining
`(IRC) is used. If the interference does not exceed the
`predetermined threshold, maximum ratio combining (MRC)
`is used. The diversity combining technique can be Selected,
`and the Signals combined every burst, half-burst, or other
`Suitable interval.
`
`31 Claims, 6 Drawing Sheets
`
`10-12
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`
`
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`
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`18
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`ANALYZER
`
`TO DECODER
`
`COMBINER
`
`
`
`ERICSSON v. UNILOC
`Ex. 1025 / Page 1 of 11
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`

`

`U.S. Patent
`US. Patent
`
`Oct. 3, 2000
`Oct. 3, 2000
`
`Sheet 1 of 6
`Sheet 1 0f6
`
`6,128,355
`6,128,355
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`ERICSSON V. UNILOC
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`ERICSSON v. UNILOC
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`U.S. Patent
`
`Oct. 3, 2000
`
`Sheet 2 of 6
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`6,128,355
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`10
`
`FIG. 3
`
`14
`
`TO DECODER
`
`ANALYZER
`
`FIG. 4
`
`100
`
`
`
`
`
`RECEIVE
`SIGNALS
`
`INTERFERENCE
`THRESHOLD 2
`
`COMBINE
`USING IRC
`
`
`
`
`
`COMBINE
`USING MRC
`
`1
`O4
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`106
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`U.S. Patent
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`Oct. 3, 2000
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`Sheet 3 of 6
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`6,128,355
`
`FIG. 5
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`10-12
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`
`
`
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`COMBINER
`
`TO DECODER
`
`TO DECODER
`
`COMBINER
`
`ERICSSON v. UNILOC
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`U.S. Patent
`
`Oct. 3, 2000
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`Sheet 4 of 6
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`6,128,355
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`Z
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`8],
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`ÅRHOWEWN
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`ERICSSON v. UNILOC
`Ex. 1025 / Page 5 of 11
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`U.S. Patent
`
`Oct. 3, 2000
`
`Sheet S of 6
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`6,128,355
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`OZZ
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`ÅRHOVNE|WN
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`ÅRHOWEW
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`QZZ
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`0 ||
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`U.S. Patent
`
`Oct. 3, 2000
`Sheet 6 of 6
`FIG. 9
`
`6,128,355
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`--- MRC "
`i. O RC
`..........
`
`
`
`mayor; It w a tr is a
`
`has
`
`a 8
`
`x IRC-MRC"
`
`s
`
`s ss
`
`us os s as as a
`
`us as
`
`up as
`
`so sa are is
`
`a
`
`say
`
`se is
`
`wr
`---- as
`asses or os e s are as a pose scorer a sea sna at on ea as a
`
`a ss as as is as a sas a rese or so go sers sit as a ps
`
`go 100 120 140
`to
`40
`20
`BITDELAY FOR A TWO-INTERFERER
`BURST BITS)
`
`FIG. 10
`
`
`
`: o MRC
`x IRC
`- CORR=O.7
`: --- CORR=O.3 E:
`
`10
`SNR (dB)
`
`2 14 is 18
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`ERICSSON v. UNILOC
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`6,128,355
`
`1
`SELECTIVE DIVERSITY COMBINING
`
`FIELD OF THE INVENTION
`The present invention relates generally to the processing
`of digitally modulated radio signals at a receiver having
`multiple antennas. More particularly, the present invention
`relates to the diversity combining of radio signals to reduce
`Signal impairments.
`
`2
`Alternatively, an improved method of combining received
`Signals in a System with antenna diversity is known as
`interference rejection combining (IRC). IRC assumes that
`the received signals include both white Gaussian noise and
`Signals from other transmitters (e.g., other mobile stations in
`other cells). Generally speaking, a receiver incorporating
`IRC produces received signal Samples for each antenna
`(using, e.g., log-polar signal processing), estimates channel
`taps for each antenna, estimates impairment correlation
`properties (e.g., co-channel interference), forms branch met
`rics from the received signal Samples, channel tapestimates,
`and impairment correlation estimates, and estimates the
`transmitted information Sequence using the branch metrics
`(using, e.g., the Viterbialgorithm). The receiver estimates
`impairment correlation properties by estimating the corre
`lated noise between Signal branches when a training
`Sequence (such as is contained in a typical GSM burst) is
`received. This estimated covariance is used by the receiver
`during the demodulation process. IRC is described in Sig
`nificant detail in the copending, commonly-assigned appli
`cation Ser. No. 08/284,775 entitled “Method and Apparatus
`for Interference Rejection Combining in Multi-Antenna
`Digital Cellular Communications Systems', filed on Aug. 2,
`1994 and copending, commonly assigned application Ser.
`No. 08/634,719 entitled “Method and Apparatus for Inter
`ference Rejection with Different Beams, Polarizations, and
`Phase References”, filed on Apr. 19, 1996. These applica
`tions are hereby incorporated by reference in their entirety.
`The latter patent application discloses that IRC performance
`can be improved if the impairment correlation properties are
`Scalar impairment correlation properties and the branch
`metrics are Scalar branch metrics.
`IRC is very efficient in rejecting interference from mobile
`Stations from neighboring cells which transmit at the same
`frequency as the transmitted Signal of interest (i.e.,
`co-channel interference), particularly when an interfering
`burst is Synchronized with the carrier burst (i.e., the trans
`mitted signal of interest). IRC also reduces the effects of
`adjacent channel interference. Unfortunately, IRC is com
`pleX and requires a relatively large amount of computer
`processing resources. Further, there are Some cases where
`IRC does not provide optimum performance.
`It would be desirable to improve the performance of a
`communication System employing antenna diversity. More
`particularly, it would be desirable to improve known meth
`ods of diversity combining.
`SUMMARY OF THE INVENTION
`The present invention overcomes the above-described
`problems, and provides additional advantages, by providing
`for a method and System for combining received signals
`from multiple antennas which employs both IRC and MRC
`(or Some other diversity combining method). According to
`exemplary embodiments of the invention, a transmitter
`generates and transmits a signal representing an Sequence of
`information Symbols. A receiver having multiple antennas
`receives the transmitted Signal on at least two antennas Such
`that there are at least two received signals. The receiver
`combines the received Signals by Selectively performing
`interference rejection combining or maximum ratio combin
`ing to maximize the receiver performance. The Signals can
`be combined every burst, half-burst, or at Some other
`suitable frequency. To select whether IRC or MRC is used,
`the receiver determines an interference indication, and a
`combining method is Selected based on the interference
`indication.
`By selectively performing IRC, a conventional diversity
`combining Scheme, or a combination of multiple Schemes,
`
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`BACKGROUND OF THE INVENTION
`In radio communications, Signals are Sometimes lost or
`impaired due to a variety of phenomena Such as multipath
`fading, time dispersion, and co-channel interference which
`exist in a typical radio communication channel. Multipath
`fading results from the interaction of the transmitted Signal
`and its reflections or echoes which arrive at the receiver at
`approximately the same time. If the number of reflections is
`relatively large, this fading exhibits a So-called Rayleigh
`distribution. Time dispersion occurs when there is a time
`delay between the reflections and the transmitted Signal.
`Interference results from the presence of Signals which are
`non-Orthogonal with respect to the transmitted Signal. Such
`non-Orthogonal Signals can originate from other radioS oper
`ating on the same frequency (co-channel interference) or
`from other radioS operating on neighboring frequency bands
`(adjacent channel interference).
`FIG. 1 shows an example of co-channel interference, in
`which a mobile station M1 communicates with a base station
`antenna A1 in a cell C1, while a mobile station M2 com
`municates with a base Station antenna A2 in a cell C2. Abase
`Station antenna A3 Serving a cell C3 may be located between
`cells C1 and C2. In this example, mobile stations M1 and
`M2 are simultaneously communicating on the Same channel
`to different antennas in different cells. AS Shown, Signals
`transmitted by mobile station M1 to antenna A1 interfere
`with the signals transmitted by mobile station M2 to antenna
`A2, causing Signal impairment.
`To reduce the effects of Such Signal impairments, it is
`known to use diversity combining, in which a receiver is
`provided with multiple Separated antennas, and the received
`Signals at each of the antennas are combined. Because the
`antennas are Separated, the Signal Strength in each antenna is
`independent. Thus, if there is a deep fading dip for one
`antenna, another antennas may have a relatively Strong
`Signal. There are many types of diversity combining meth
`ods. For example, in Mobile Communication Design
`Fundamentals, by William C. Y. Lee (Wiley, 1993), numer
`ous diversity Schemes are described at pages 116-132.
`In a typical mobile communication System, antenna diver
`sity is employed by providing base Stations with multiple
`antennas. The Signals received at the antennas are typically
`combined using maximum ratio combining (MRC). Lee,
`Supra for example, recognizes MRC as the best combining
`technique. In MRC, the received Signals are combined based
`on the assumption that the interference closely approximates
`white Gaussian noise. An exemplary MRC scheme is shown
`in FIG. 2, where each Signal branch (i.e., each received
`Signal to be combined) is weighted by a Selected weighting
`factor (C., C2), and the signal branches are combined. MRC
`60
`does not consider correlation between received signals,
`thereby enabling the received signals to be detected and
`equalized one at a time, and then combined by Summing.
`MRC, Since it assumes that the interference experienced by
`a Signal closely approximates white Gaussian noise, has
`certain performance limitations when the interference does
`not closely approximate white Gaussian noise.
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`3
`the present invention allows a communication System to
`achieve the benefits of IRC when most appropriate (that is,
`when the interference is predominantly co-channel
`interference), adjacent channel interference or otherwise
`correlated between the diversity branches, and to Save
`processing resources at times when IRC is not appropriate
`(that is, when co-channel interference is relatively low and
`the interference more closely approximates white Gaussian
`noise). This selective combination Scheme greatly enhances
`the efficiency of the communication. For example, as dis
`cussed below, the present invention makes it is possible to
`achieve a 1 dB gain in performance over a System which
`uses only IRC.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`A more complete understanding of the present invention
`can be obtained upon reading the following Detailed
`Description of the Preferred Embodiments, in conjunction
`with the accompanying drawings, in which like reference
`indicia are used to designate like elements, and in which:
`FIG. 1 is a diagram showing an example of co-channel
`interference;
`FIG. 2 is a block diagram showing a diversity combining
`technique using MRC,
`FIG. 3 is a block diagram showing an implementation of
`a preferred embodiment of the present invention;
`FIG. 4 is a flow chart describing a preferred embodiment
`of the method according to the present invention;
`FIG. 5 is a block diagram showing a Second exemplary
`embodiment of the present invention;
`FIG. 6 is a block diagram of an exemplary combination of
`the embodiments of FIG. 3 and FIG. 5;
`FIG. 7 is a block diagram of another embodiment of the
`present invention;
`FIG. 8 is a block diagram of a variation of the embodi
`ment of FIG. 7;
`FIG. 9 is a graphical comparison of performance results
`for a receiver using a combination of IRC and MRC accord
`ing to the embodiment of FIG. 5; and
`FIG. 10 is a graphical comparison of performance results
`for the embodiment of FIG. 3.
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`FIG. 3 shows a block diagram of a first exemplary
`embodiment of the invention. Antennas 10 and 12, which are
`two of multiple antennas in a receiver employing antenna
`diversity, receive signals transmitted from a mobile Station
`or other transmitter (not shown). Combiner modules 14 and
`16 are each connected to receive the received Signals from
`antennas 10 and 12. Combiner modules 14 and 16 are
`capable of combining the received signals from antennas 10
`and 12 using MRC (or some other conventional diversity
`combining technique) and IRC, respectively, and outputting
`a combined signal to a decoder or other signal processing
`circuitry (not shown). The appropriate combiner module 14
`or 16 is activated by an interference analyzer 18, which
`determines whether the interference experienced by the
`received signals exceeds a predetermined threshold, and
`Selects the appropriate combiner module using a Switch 19.
`To determine whether the threshold is met or exceeded, the
`analyzer 18 can estimate a correlation between two branches
`for each received signal and compare the estimated corre
`lation to a correlation threshold. For example, an impairment
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`4
`correlation matrix can be formed, and the off-diagonal
`elements of the impairment correlation matrix can be used to
`measure the correlation and interference. A Suitable thresh
`old can then be derived from the diagonal elements of the
`matrix. Impairment correlation matrices are discussed in
`more detail in the copending, commonly-assigned applica
`tion entitled “Method and Apparatus for Interference Rejec
`tion Combining in Multi-Antenna Digital Cellular Commu
`nications Systems” and bearing Ser. No. 08/284,775, now
`issued as U.S. Pat. No. 5,680,419, the entirety of which is
`incorporated by reference. Numerous other threshold calcu
`lation and comparison Schemes can be used. If an interfering
`burst is synchronized with the carrier burst of the transmitted
`Signal of interest, the estimated correlation will be constant
`during a burst. If, as is more typical, an interfering burst is
`not Synchronized with the carrier burst, the estimated cor
`relation will not be constant during the burst. If the inter
`ference (or other Suitable impairment characteristic) meets
`or exceeds the predetermined threshold, then the interfer
`ence analyzer 18 selects the IRC combiner module 16. If the
`interference (or other Suitable impairment characteristic)
`does not meet or exceed the predetermined threshold, the
`interference analyzer 18 selects the MRC combiner module
`14. The Selected module outputs a combined signal to a
`decoder (not shown) in the receiver for further processing.
`The circuit of FIG. 3 can operate to combine the received
`Signals every burst, half-burst, or other Suitable interval.
`FIG. 4 shows a flow chart describing the steps of the
`method according to the present invention. In step 100, the
`receiver receives the Signals transmitted by the mobile
`Station or other transmitter on multiple antennas. In Step 102,
`the receiver (e.g., using analyzer 18 or other Suitable means)
`analyzes the received signals to determine if the level of
`interference meets or exceeds a predetermined threshold. If
`the interference threshold used in step 102 is met or
`exceeded by the received signals, the receiver combines the
`multiple received signals using IRC in step 104, and if the
`interference threshold used in step 102 is not met or
`exceeded by the received signals, the receiver combines the
`multiple received signals using MRC (or another Suitable
`diversity combining technique) in Step 106. Regardless of
`which combining method is used, the process returns to Step
`100 after some predetermined interval to process other
`received signals. The predetermined interval can be every
`burst, half-burst, or other Suitable interval. As a result, the
`appropriate diversity combining technique can be Selected
`for each interval.
`FIG. 5 shows a block diagram of a second exemplary
`embodiment of the present invention. In this embodiment,
`both MRC and IRC are used for combining the branches,
`and then the outputs of combiner modules 14 and 16 are
`combined in combiner 20 so as to optimize the output from
`each combination algorithm. Combiner 20 can combine the
`MRC and IRC outputs each burst, half-burst, or at some
`other suitable period. The embodiment of FIG. 5 is particu
`larly beneficial when interference is present, and the carrier
`bursts and interfering bursts are unsynchronized.
`Thus, the embodiment of FIG. 3 provides improved
`performance over using only IRC when no interference is
`present, and the embodiment of FIG. 5 provides improved
`performance when interference is present and the interfering
`bursts are not synchronized with the carrier bursts. The
`embodiments of FIG. 3 and FIG. 5 can be combined to
`maximize the performance of both embodiments. One
`exemplary combination of these embodiments is shown in
`FIG. 6, in which analyzer 18 analyzes the incoming Signals
`and selects, via Switch 19, either the output of combiner 20
`or MRC combiner module 14 based on an interference
`indication.
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`FIG. 7 shows yet another embodiment of the present
`invention which includes memories 22a and 22b for Storing
`Signal bursts, analyzer 18 for analyzing the Stored bursts,
`and combiner 20 for combining the Signals in a manner
`dependent upon the output of analyzer 18. In this
`embodiment, the analyzer 18 determines a value a, based on
`the level of interference associated with the received bursts.
`The value a is a weighting factor which determines how
`much weight is assigned to differing diversity combining
`techniques. For example, an factor of 1 can be assigned by
`the analyzer 18 when the interference level is such that IRC
`would be a preferable combining technique. For an alpha
`factor of 1, the combiner 20 uses IRC. An C. factor of 0 can
`be assigned when the interference level is Such that another
`diversity combining technique (e.g., MRC) would be pref
`erable. For an O. factor of 0, the combiner 20 uses MRC. An
`C. factor of 0.5 can be assigned when the interference level
`is such that a weighted combination of 50% IRC and 50%
`MRC would be desirable. For an O. factor of 0.5, IRC and
`MRC are both performed, and the results combined equally.
`For an C. factor of 0.75, IRC and MRC are both performed,
`and the results are combined by weighting the IRC results to
`the MRC results in a ratio of 3/1. In this embodiment, a
`“Soft' or gradual shifting of combining techniques can be
`achieved. In this embodiment, the combiner 20 is imple
`mented by a programmable combiner.
`FIG. 8 shows a variation of the embodiment of FIG. 7. In
`the embodiment of FIG. 8, received bursts are stored in the
`memories 22a and 22b. Analyzer 18 determines the level of
`interference, and assigns an appropriate C. Value. Combiner
`20 combines the Stored bursts in a manner dependent upon
`the analyzer output, and the output of combiner 20 is Stored
`in a memory 22c. The analyzer 18 then resets C. to, for
`example, 0 and performs a Second combining. The output of
`this second combining is then combined with the first
`combining results Stored in memory 22c in a combiner 24.
`Numerous other variations will be readily apparent to those
`of ordinary skill in the art.
`FIG. 9 is a graphical representation comparing bit error
`rates (BERs) as a function of interferer delay for a commu
`40
`nication channel for the embodiment of FIG. 5. In the graph
`of FIG. 9, the combination of IRC and MRC (IRC-MRC) is
`implemented by combining the received signals every burst
`(i.e., on a burst-by-burst basis). Further, the signal-to-noise
`(SNR) ratio is assumed to be 25 dB, and the carrier-to
`interference ratio (C/I) is assumed to be 2 dB. As can be seen
`from the graph, the combination of IRC and MRC can
`provide a performance improvement over the case for a
`receiver using only IRC.
`FIG. 10 is a graphical representation comparing bit error
`rates as a function of the signal-to-noise ratio (SNR) for the
`embodiment of FIG. 3, where the IRC algorithm is switched
`off, or not Selected, during periods where no co-channel
`interference is present. AS shown, it is possible to gain
`approximately 1 dB in Sensitivity compared to the case
`where IRC is always used.
`Thus, it should be apparent that the present invention
`provides Significant advantages over known diversity com
`bining techniques. In particular, by Selectively using IRC
`and MRC or another suitable diversity combining technique,
`receiver performance can be improved compared to a
`receiver using only one diversity combining technique. It
`will be appreciated that the principles of the present inven
`tion can be applied to Systems which use more than two
`different combining techniques.
`While the foregoing description includes numerous
`details and Specificities, it is to be understood that these are
`
`6
`for purposes of explanation only. Many modifications will
`be readily apparent to those of ordinary skill in the art which
`are clearly within the Spirit and Scope of the invention, as
`defined by the following claims and their legal equivalents.
`More than two different diversity combining techniques may
`be combined.
`What is claimed is:
`1. A method for diversity combining in a radio commu
`nication System, comprising the Steps of
`receiving a transmitted Signal on at least two antennas
`Such that at least two received signals exist;
`combining the received signals by using interference
`rejection combining together with another diversity
`combining method.
`2. The method of claim 1, wherein the step of combining
`is performed by Separately performing both interference
`rejection combining and the another diversity combining
`method to achieve Separate results, and combining the
`Separate results.
`3. The method of claim 2, wherein the another diversity
`combining method is maximum ratio combining.
`4. The method of claim 2, wherein the Separate results are
`weighted prior to combining.
`5. The method of claim 1, wherein the step of combining
`further comprises the Steps of
`producing an interference indication;
`determining a weight factor based on the interference
`indication; and
`combining the received signals using a weighted combi
`nation of interference rejection combining and the
`another diversity combining technique.
`6. A method for diversity combining in a radio commu
`nication System comprising the Steps of:
`receiving a transmitted Signal on at least two antennas
`Such that at least two received signals exist;
`producing an interference indication;
`Selecting, based on the interference indication, a combin
`ing method from a plurality of combining methods, and
`combining the Signals using the Selected combining
`method,
`wherein the Step of producing an interference indication is
`performed by estimating a covariance for each received
`Signal and comparing the estimated covariances to a
`covariance threshold.
`7. The method of claim 6, wherein the combining method
`is Selected from at least one of maximum ratio combining
`and interference rejection combining.
`8. The method of claim 7, wherein interference rejection
`combining is performed by:
`producing received signal Samples for each antenna, esti
`mating channel taps for each antenna, estimating
`impairment correlation properties among the antennas,
`forming branch metrics from the received signal
`Samples, channel tap estimates, and impairment corre
`lation estimates, and estimating the information
`Sequence using the branch metrics.
`9. The method of claim 6, wherein the received signals
`include one or more bursts, and the combining method is
`Selected for each burst.
`10. A method for diversity combining in a radio commu
`nication System comprising the Steps of:
`receiving a transmitted Signal on at least two antennas
`Such that at least two received signals exist;
`producing an interference indication;
`Selecting, based on the interference indication, a combin
`ing method from a plurality of combining methods, and
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`combining the Signals using the Selected combining
`method, wherein the received signals include one or
`more bursts, and the combining method is Selected for
`each half-burst.
`11. The method of claim 10, wherein the step of producing
`an interference indication is performed by estimating a
`covariance for each received signal and comparing the
`estimated covariances to a covariance threshold.
`12. A System for receiving communication signals, com
`prising:
`a plurality of antennas for receiving a communication
`Signal Such that multiple received signals are present;
`a plurality of Signal combiners for combining the received
`Signals, each Signal combiner associated with each of
`the plurality of antennas, and
`analyzer means for determining a level of Signal
`impairment, comparing the level of Signal impairment
`to a threshold level, and Selectively operating Said
`Signal combiners based on the comparison.
`13. The system of claim 12, wherein the plurality of signal
`combiners includes a first Signal combiner using interference
`rejection combining and a Second combiner using maximum
`ratio combining.
`14. The system of claim 13, wherein the level of signal
`impairment is interference.
`15. The system of claim 13, wherein the first combiner
`produces received signal Samples for each antenna, esti
`mates channel taps for each antenna, estimates impairment
`correlation properties among the antennas, forms branch
`metrics from the received signal Samples, channel tap
`estimates, and impairment correlation estimates, and esti
`mates the information Sequence using the branch metrics.
`16. The system of claim 12, wherein the received signals
`include one or more bursts, and the Selection of combiners
`is performed every burst.
`17. The system of claim 12, wherein the received signals
`include one or more bursts, and the Selection of combiners
`is performed every half-burst.
`18. A System for receiving communication signals, com
`prising:
`a plurality of antennas for receiving a communication
`Signal Such that multiple received signals are present,
`wherein each received signal is a Substantially identical
`copy of the communication signal;
`a plurality of Signal combiners, each Signal combiner
`combining received signals using a different one of a
`plurality of Signal combining techniques,
`a combiner for combining outputs of at least Selected ones
`of the Signal combiners, and
`means for determining a level of Signal impairment,
`comparing the level of Signal impairment to a threshold
`level, and Selecting one of either the combined signal
`combiner output or an output of one of the plurality of
`Signal combiners as a System output.
`19. The system of claim 18, wherein one of the plurality
`of Signal combining techniques is interference rejection
`combining.
`20. The system of claim 18, wherein the level of signal
`impairment is interference.
`21. A System for receiving communication signals, com
`60
`prising:
`a plurality of antennas for receiving a communication
`Signal Such that multiple received signals exist;
`an analyzer for determining an interference indicator
`asSociated with the received signals, and for Selecting
`a weighting factor based on the interference indicator;
`and
`
`45
`
`50
`
`55
`
`65
`
`8
`a first Signal combiner for performing a weighted com
`bination of at least two Signal combining techniques
`based on the weighting factor.
`22. The System of claim 21, wherein one of the Signal
`combining techniques is interference rejection combining.
`23. The System of claim 22, wherein another Signal
`combining technique is maximum ratio combining.
`24. The System of claim 21, further comprising one or
`more memories for Storing the received signals for analysis
`by the analyzer.
`25. The system of claim 24, further comprising:
`a combiner output memory for Storing a first output of the
`first signal combiner; and
`a Second Signal combiner for combining the Stored first
`output with a Second output of the first signal combiner.
`26. A method for diversity combining in a radio commu
`nication System, comprising the Steps of
`receiving a transmitted Signal on at least two antennas
`Such that at least two received signals exist; and
`combining received Signals by Selecting, based on a signal
`impairment, between at least a first combining method
`and a Second combining method.
`27. The method of claim 26, wherein at least one of the
`first combining method and the Second combining method is
`a combination of at least two combining methods.
`28. The method of claim 26, wherein the first combining
`method is maximum ratio combining and the Second com
`bining method is interference rejection combining.
`29. A method for diversity combining in a radio commu
`nication System, comprising the Steps of
`receiving a transmitted Signal on at least two antennas
`Such that at least two received signals exist;
`combining received Signals using a plurality of combining
`methods wherein each combining method produces a
`Separate result, and
`combining the Separate results, wherein each Separate
`result is assigned a weight factor before the Separate
`results are combined.
`30. The method of claim 29, wherein the weight factor of
`at least one separate result is dependent on an interference
`indication.
`31. A method of receiving communication Signals, com
`prising the Steps of
`receiving a communication Signal Such that multiple
`received signals are produced;
`combining a plurality of the multiple received signals,
`thereby producing a plurality of combinations, by per
`forming at least the Steps of:
`combining at least two of the multiple received signals
`according to a first signal combining technique,
`thereby producing a first combination; and
`combining at least two of the multiple received signals
`according to a Second signal combining technique,
`thereby producing a Second combination;
`combining Selected combinations,
`determining a level of Signal impairment;
`comparing the level of Signal impairment to a threshold
`level; and
`based on the comparing Step, Selecting either a combina
`tion or the combined Selected combinations as an
`Output signal.
`
`ERICSSON v. UNILOC
`Ex. 1025 / Page 11 of 11
`
`