WO2007103444A1 - Procédé et appareil de communication sans fil permettant d'effectuer une élimination d'interférence basée sur les connaissances et aveugle - Google Patents

Procédé et appareil de communication sans fil permettant d'effectuer une élimination d'interférence basée sur les connaissances et aveugle Download PDF

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Publication number
WO2007103444A1
WO2007103444A1 PCT/US2007/005842 US2007005842W WO2007103444A1 WO 2007103444 A1 WO2007103444 A1 WO 2007103444A1 US 2007005842 W US2007005842 W US 2007005842W WO 2007103444 A1 WO2007103444 A1 WO 2007103444A1
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WIPO (PCT)
Prior art keywords
interference cancellation
unit
blind
interference
knowledge
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PCT/US2007/005842
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English (en)
Inventor
Prabhakar R. Chitrapu
Steven Jeffrey Goldberg
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Interdigital Technology Corporation
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
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Publication date
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Publication of WO2007103444A1 publication Critical patent/WO2007103444A1/fr

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/69—Spread spectrum techniques
    • H04B1/707—Spread spectrum techniques using direct sequence modulation
    • H04B1/7097—Interference-related aspects
    • H04B1/7103—Interference-related aspects the interference being multiple access interference
    • H04B1/7107—Subtractive interference cancellation
    • H04B1/71072—Successive interference cancellation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/69—Spread spectrum techniques
    • H04B1/707—Spread spectrum techniques using direct sequence modulation
    • H04B1/7097—Interference-related aspects
    • H04B1/7103—Interference-related aspects the interference being multiple access interference
    • H04B1/7105—Joint detection techniques, e.g. linear detectors

Definitions

  • the present invention is related to signal processing. More particularly, the present invention is related to a method and apparatus for cancelling interference from received signals by performing knowledge-based and blind interference cancellation.
  • a receiver receives signals which include both signals intended for the specific receiver and signals intended for other receivers operating within the same frequency band.
  • the signals intended for other receivers are referred to as interference.
  • Equation (2) W log 2 (l + S / N ); Equation (2) where C is capacity in bits per second, W is channel bandwidth in Hertz, S is the desired signal power and N is the power of all components not of interest which includes interference and noise.
  • SINR signal-to-interference plus noise ratio
  • OiW-Tt : — ⁇ ⁇ •
  • a conventional approach to increase the value of SINR is to exploit known characteristics of the signals by extracting them from the received signals, (i.e., non-blind technique). Training sequences are often used to allow the receiver to determine how to differentiate the signal of interest from all other signals. While the signal of interest may be the desired signal for further processing, (e.g., data extraction or location determination), the signal of interest may be one of the other signals in the received signal sum.
  • determining such a signal may facilitate its subtraction from the received signals, leading to a more robust extraction of the desired signal for utilization.
  • this type of processing is often the preferred approach to extract the desired signal, subject to other system level considerations such as computational complexity, channel variation, or the like.
  • FIG. 1 shows an exemplary conventional receiver 100 implementing SIC.
  • received baseband data 101 is stored in a buffer 102.
  • Interference is subtracted from the stored received baseband data, or the baseband data is 'orthogonally-projected' to the interference signals.
  • the processed data output of the buffer 102 is multiplied with a scrambling code conjugate by a plurality of multipliers 104A- 104L and correlated with L codes by a plurality of fast Walsh transformers (FWTs) 106A-106L.
  • FWTs fast Walsh transformers
  • the outputs from the FWTs 106A-106L are combined by a maximal ratio combiner (MRC) 108.
  • One of N outputs is selected by a decision unit 110 as an output and maximum M values selected by a selection unit 112 from N-I outputs are fed back to the buffer 102 via a signal regeneration unit 114 which cancels the M signals as interference.
  • the M signals are spread again by spreaders 116a-116M and summed by a summer 118.
  • the summed signal is multiplied with a scrambling code by a multiplier 120 and the multipath channel signal is regenerated by the signal regenerator 122.
  • the regenerated signal is subtracted from the received data 101 stored in the buffer 102 as the interference.
  • blind signal processing Another conventional approach to signal extraction is a class of signal processing referred to as blind signal processing.
  • blind refers to the fact that the signals are separated without some information required by the conventional techniques exploiting known characteristics of the signals. For example, a lack of a training sequence or inability to decode it due to excessive signal distortion does not allow comparison of a known signal to a received signal. Therefore, the channel effects on the transmitted signal can not be directly determined.
  • Blind signal separation techniques get around this lack of information by exploiting information that still exists in the various signal types.
  • One such type of information is the moment of a signal. Different communications stream sources impart different values to these moments. By maximizing a cost function based on the unique values of these parameters due to each signal, a separation matrix may be determined which will extract each signal from the mixture.
  • Independent component analysis (ICA) and principle component analysis (PCA) are examples of blind signal separation methods.
  • Both the non-blind and blind techniques have their appropriate applications. When there is knowledge concerning the signal components, a non- blind technique is usually the more robust one to utilize, although the blind technique may also work. When the knowledge is not available, the blind technique should be used.
  • FIG. 2 is a block diagram of a receiver 200 in accordance with this approach.
  • signal aggregates from different cells are separated by an ICA unit 202.
  • a separated aggregate containing the data for the receiver 200 is then selected by a selection unit 204 and the selected data alone is fed to a first Rake processing block 206 which is a non-blind approach as it exploits the spreading codes.
  • the selection unit 204 is necessary since the ICA processing can output the separated signals in an initially unknown order.
  • the selection unit 204 performs a minimal amount of processing to identify the target stream. For example, this may be performed by decoding a portion of the stream which should produce a known sequence of data, or have a specific set of signal characteristics. The stream which best satisfies the criteria is selected by the selection unit 204.
  • the received signal may be processed only by a second Rake processing block 208 via a pre-switch 210 and a post switch 212.
  • the two Rake processing blocks 206, 208 may be the same processing block.
  • the present invention is related to a method and apparatus for cancelling interference in received signals.
  • a receiver includes a knowledge- based interference cancellation unit, a blind interference cancellation unit and a trade-off management unit.
  • the knowledge-based interference cancellation unit cancels interference in the received signals based on pre-known knowledge and the blind interference cancellation unit cancels interference in the received signals without the pre-known knowledge.
  • the trade-off management unit determines a trade-off between knowledge-based interference cancellation and blind interference cancellation, whereby at least one of the knowledge-based interference cancellation and the blind interference cancellation is selectively preformed based on the trade-off.
  • the interference cancellation may be performed by implementing at least one of an SIC, a PCA and an ICA.
  • the knowledge-based and the blind interference cancellation may be performed in parallel, in series or in any combination.
  • a semi-blind interference cancellation unit may be further provided to perform a semi-blind technique for interference cancellation.
  • Figure 1 is a block diagram of a conventional receiver implementing blind and non-blind interference cancellation.
  • FIG. 2 is a block diagram of a conventional receiver implementing
  • Figure 3 is a block diagram of a receiver for cancelling interference in accordance with one embodiment of the present invention.
  • Figures 4 and 5 are block diagrams of a receiver configured to selectively implement interference cancellation in accordance with another embodiment of the present invention.
  • Figure 6 is a block diagram of a receiver configured to perform knowledge-based and blind interference cancellation selectively in accordance with another embodiment of the present invention.
  • Figure 7 is a block diagram of a receiver for selective interference cancellation in accordance with another embodiment of the present invention.
  • Figure 8 is a block diagram of a receiver which is a generalized version of the receiver in Figure 7.
  • the present invention may be implemented in any type of wireless communication system, as desired.
  • the present invention may be implemented in any type of IEEE 802 system, wideband code division multiple access (WCDMA), universal mobile telecommunication system (UMTS)- frequency division duplex (FDD), UMTS-time division duplex (TDD), time division synchronous code division multiple access (TDSCDMA), CDMA2000, orthogonal frequency division multiplex (OFDM)-multiple-input multiple-output (MIMO) or any other type of wireless communication system.
  • WCDMA wideband code division multiple access
  • UMTS universal mobile telecommunication system
  • FDD frequency division duplex
  • TDD time division synchronous code division multiple access
  • CDMA2000 CDMA2000
  • OFDM orthogonal frequency division multiplex
  • MIMO multiple-input multiple-output
  • the present invention may also be implemented as a digital signal processor (DSP), or on an integrated circuit (IC), such as an application specific integrated circuit (ASIC), multiple ICs, logical programmable gate array (LPGA), discrete components, or a combination of DSP, ICs, LPGAs, and discrete components.
  • DSP digital signal processor
  • IC integrated circuit
  • ASIC application specific integrated circuit
  • LPGA logical programmable gate array
  • the present invention may be implemented as a wireless transmit/receive unit (WTRU) or a base station.
  • WTRU includes but is not limited to a user equipment (UE), a mobile station, a fixed or mobile subscriber unit, a pager, or any other type of device capable of operating in a wireless environment.
  • base station includes but is not limited to a Node-B, a site controller, an access point (AP) or any other type of interfacing device in a wireless environment.
  • FIG. 3 is a block diagram of a receiver 300 for cancelling interference in accordance with one embodiment of the present invention.
  • the receiver 300 includes an SIC unit 302, a PCA unit 304, an ICA unit 306, a signal selection unit 308 and a demodulator 310, where SIC, PCA and ICA are performed in series.
  • the received signals 301 are first processed by the SIC unit 302 to cancel interference using an SIC technique.
  • SIC is an iterative process for cancelling interference from received signals and may be terminated upon one of the following conditions:
  • the third condition means that there is no need to perform additional interference cancellation and therefore a subsequent blind interference cancellation, (i.e., PCA and ICA), may not be performed.
  • a subsequent blind interference cancellation i.e., PCA and ICA
  • the PCA unit 304 processes the output of the SIC unit 302 and the ICA unit 306 may further process the output from the PCA unit 304 to further improve the SINR of the received signals 301.
  • the signal selection unit 308 selects one of a plurality of signals from the output of the ICA unit 306 and forwards the selected signal to the demodulator 310 for further processing.
  • a blind interference cancellation method (such as PCA or ICA), separates unknown signals based on iterative decorrelation (first and second moments in the case of PCA and third and fourth moments in the case of ICA) to a cost function.
  • the ICA has the additional benefit of being able to remove a Gaussian signal. If the number of signals is sufficient in number and mixing, they often appear as a single Gaussian signal as indicated by the central limit theorem. In such a case, the signal aggregate will actually be separable.
  • the SIC is provided as an example and any other knowledge- based interference cancellation means may be implemented.
  • Figure 4 is a block diagram of a receiver 400 configured to selectively implement interference cancellation in accordance with another embodiment of the present invention.
  • the receiver 400 includes an SIC unit 402, a PCA unit 404, an ICA unit 406, a signal selection unit 408, a demodulator 410, a first analysis unit 412, a second analysis unit 414 and a third analysis unit 416.
  • Certain functions may be advantageous to avoid under certain circumstances.
  • PCA which is a whitening technique, tries to maximally decorrelate the signal vectors making up the sum from the noise signals. However, the whitening often increases the noise level. Therefore, in some cases, it is favorable to skip the PCA process.
  • the first analysis unit 412 determines whether it is advantageous to perform PCA. If the determination is positive, the interference cancelled signal 403 by the SIC unit 402 is sent to the PCA unit 404. After the signal 403 is processed by the PCA unit 404, the second analysis unit 414 determines whether it is advantageous to further perform ICA. If the determination is positive, the output 405 of the PCA unit 404 is forwarded to the ICA unit 406. The ICA unit 406 separates the components of the output 405 of the PCA unit 404 and one of the components is selected by the signal selection unit 408. The selected signal 409 is then sent to the demodulator 410 for demodulation.
  • the third analysis unit 416 further determines whether it is advantageous to process ICA on the output 403 of the SIC 402. If the determination is positive, the output 403 of the SIC unit 402 is sent to the ICA unit 406 for signal cancellation using ICA.
  • the determination by the analysis units 412, 414, 416 may be based on the remaining signal sum, (i.e., output from the previous processing units). Alternatively, as shown in Figure 5, the determination may be based on feedback from subsequent processing units and demodulated signals 411 made by the demodulator 410. As shown in Figure 5, the first analysis unit 412 compares the output 403, the output 405 from the PCA unit 404 and the demodulated signals 411.
  • the second analysis unit 414 compares the output 405 from the PCA unit 404, the output 407 from the ICA unit 406 and demodulated signals 411.
  • the third analysis unit 416 compares the output 405 from the PCA unit 404, the output 407 from the ICA unit 406 and the demodulated signals 411.
  • the signal comparisons may be performed by a number of different techniques. For example, the signals may be compared to determine if they have essentially changed before and after the processing units. A lack of significant change indicates the processing unit is likely unnecessary. Alternatively, the signal may be fed back along the processing chain. For instance, the demodulated data has usually been processed by error correction techniques. The number of errors encountered may be the feed back data. By monitoring the data error rate in conjunction with the usage of a particular processing unit, it may be determined if the processing unit should be used or not.
  • 414, 416 may not be implemented and subsequent steps, (e.g., PCA and/or ICA), may be automatically performed without such comparisons. This is because the overhead involved with making the decision may be excessive; the decision may not be reasonably made under specific conditions; the logic to perform the decision may not be an effective trade-off of implementation requirements versus anticipated results; or due to timing restrictions it is desirable to perform the subsequent processing whether or not it is beneficial.
  • subsequent steps e.g., PCA and/or ICA
  • FIG. 6 is block diagram of a receiver 600 configured to perform knowledge-based interference cancellation and blind interference cancellation selectively in accordance with another embodiment of the present invention.
  • the receiver 600 includes a knowledge-based interference cancellation unit 602, a blind interference cancellation unit 604, a demodulator 606 and a trade-off management unit 608.
  • the knowledge-based interference cancellation unit 602 cancels interference based on "pre-known" knowledge and the blind interference cancellation unit 604 cancels interference without the pre-known knowledge.
  • the knowledge-based interference cancellation unit 602 and the blind interference cancellation unit 604 are selectively turned on and off under the control of the trade-off management unit 608.
  • the trade-off management unit 608 considers a plurality of trade-off factors and determines which interference cancellation be performed.
  • FIG. 7 is a block diagram of a receiver 700 for selective interference cancellation in accordance with another embodiment of the present invention.
  • the receiver 700 includes a switch matrix 702, an SIC unit 704, a PCA unit 706, an ICA unit 708 and a combiner 710.
  • Received signals 701 are fed to the switch matrix 702 and forwarded to at least one of the SIC unit 704, the PCA unit 706 and the ICA 708 via the switch matrix 702.
  • the received signals 701 are then processed by at least one interference cancellation unit 704, 706, 708 and the interference cancelled signal 704a, 706a, 708a is forwarded to the combiner 710.
  • the interference cancelled signal 704a, 706a, 708a may be fed back to the switch matrix 702 to be forwarded to another interference cancellation unit.
  • any combination of interference cancellation is possible.
  • the switch matrix 702 may forward the received signals 701 to the SIC unit 704, the PCA unit 706 and the ICA unit 708 at the same time such that the interference cancellation, (i.e., SIC, PCA, and/or ICA) is performed in parallel on the same data.
  • the interference- cancelled signals 704a, 706a, 708a are then examined to determine which ones are usable and combinable, or whether feedback is required to perform another interference cancellation.
  • the interference- cancelled signals 704a, 706a, 708a may be combined by the combiner 710 or fed back to the switch matrix 702.
  • the interference cancellation may be performed dynamically. For example, if the power levels of the signal components are not strictly in decreasing order, the interference cancellation may be performed dynamically.
  • SIC processing may optimally identify and remove a signal if it is the dominant one remaining in the signal sum. However, if two or more signals are not sufficiently different to be separable, the blind signal separation should be applied. For example, if the order of the signal components is as follows in decreasing significance: si, s ⁇ ⁇ S3, S4, ss, the signal si would be removed by the SIC unit 704. However, the signals S2 and S3 would require blind separation either by the PCA unit 706 or the ICA unit 708 due to neither being dominant.
  • FIG. 8 is a block diagram of a receiver 800 which is a generalized version of the receiver 700 in Figure 7.
  • the receiver 800 includes a switch matrix 802, a knowledge-based interference cancellation unit 804, a blind interference cancellation unit 806, a semi-blind interference cancellation unit 808 (optional), a combiner 810 and a trade-off management unit 812.
  • the semi-blind interference cancellation unit 808 exploits both knowledge-based and blind techniques as appropriate. For instance, when a synchronization pattern is available, the most robust processing approach is to use it to determine the signal extraction matrix. However, if the synchronization pattern can not be identified, or is not available during particular sequence of data, a blind technique may be employed. The semi-blind interference cancellation unit 808 may therefore change from one means to another, or employ both means as appropriate.
  • FIG. 8 Another example of semi-blind interference cancellation is when the receiver knows that the interference is one of M known signals, but does not know which one it is.
  • the specific processing units in Figure 7 are replaced by classes of processors, indicating that depending on the specific applications and future approaches, other means and combinations may be supported.
  • the trade-off management unit 812 determines how the processing should proceed based on various factors, such as the signal sum state being adequate for demodulation, latency constraints, power consumption, likelihood of further processing being beneficial, or the like.
  • An interference cancellation apparatus for canceling interference signals from received signals.
  • the apparatus of embodiment 11 comprising a knowledge- based interference cancellation unit configured to cancel interference in the received signals based on pre-known knowledge.
  • the apparatus as in any one of embodiments 11-12, comprising a bund interference cancellation unit configured to cancel interference in the received signals without the pre-known knowledge.
  • the apparatus of embodiment 13 comprising a trade-off management unit configured to determine a trade-off between knowledge-based interference cancellation and blind interference cancellation, whereby interference cancellation is performed by at least one of the knowledge-based v interference cancellation unit and the blind interference cancellation unit based on the trade-off.
  • blind interference cancellation unit implements one of a PCA and an ICA.

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Noise Elimination (AREA)

Abstract

L'invention a trait à un procédé et à un appareil permettant d'éliminer l'interférence présente dans des signaux reçus. Un récepteur comprend une unité d'élimination d'interférence basée sur les connaissances, une unité d'élimination d'interférence aveugle et une unité de gestion de compromis. L'unité d'élimination d'interférence basée sur les connaissances élimine l'interférence présente dans les signaux reçus sur la base de connaissances préalables, et l'unité d'élimination d'interférence aveugle élimine l'interférence présente dans les signaux reçus sans lesdites connaissances préalables. L'unité de gestion de compromis détermine un compromis entre l'élimination d'interférence basée sur les connaissances et l'élimination d'interférence aveugle, ce qui permet de procéder soit à l'élimination d'interférence basée sur les connaissances soit à l'élimination d'interférence aveugle soit aux deux, sur la base du compromis. L'élimination d'interférence peut être réalisée par l'exécution d'une élimination d'interférence successive (SIC), d'une analyse en composantes principales (PCA) et/ou d'une analyse en composantes indépendantes (ICA). L'élimination d'interférence basée sur les connaissances et l'élimination d'interférence aveugle peuvent être réalisées en parallèle, en série ou selon n'importe quelle combinaison.
PCT/US2007/005842 2006-03-09 2007-03-06 Procédé et appareil de communication sans fil permettant d'effectuer une élimination d'interférence basée sur les connaissances et aveugle WO2007103444A1 (fr)

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US78071106P 2006-03-09 2006-03-09
US60/780,711 2006-03-09
US82550806P 2006-09-13 2006-09-13
US60/825,508 2006-09-13

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WO2013051974A1 (fr) * 2011-10-07 2013-04-11 Telefonaktiebolaget L M Ericsson (Publ) Annulation de brouillage
US9319151B2 (en) 2009-07-29 2016-04-19 Qualcomm Incorporated Methods and apparatus for blind interference decrease/cancellation techniques
WO2020169196A1 (fr) * 2019-02-20 2020-08-27 Telefonaktiebolaget Lm Ericsson (Publ) Compensation de distorsion aveugle pour systèmes sans fil
CN116015345A (zh) * 2022-12-27 2023-04-25 中国人民解放军军事科学院系统工程研究院 一种基于独立分量分析的卫星通信扩频信号盲分析方法

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Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US9319151B2 (en) 2009-07-29 2016-04-19 Qualcomm Incorporated Methods and apparatus for blind interference decrease/cancellation techniques
WO2013051974A1 (fr) * 2011-10-07 2013-04-11 Telefonaktiebolaget L M Ericsson (Publ) Annulation de brouillage
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CN116015345B (zh) * 2022-12-27 2023-09-12 中国人民解放军军事科学院系统工程研究院 一种基于独立分量分析的卫星通信扩频信号盲分析方法

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