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Interference suppression in CDMA systems

  • US 6,975,666 B2
  • Filed: 12/22/2000
  • Issued: 12/13/2005
  • Est. Priority Date: 12/23/1999
  • Status: Active Grant
First Claim
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1. A receiver suitable for a base station of a CDMA communications system comprising at least one base station (11) having a transmitter and a said receiver and a multiplicity (U) of user stations (101, . . . , 10U) including a plurality (U′

  • ) of user stations served by said at least one base station, each user station having a transmitter and a receiver for communicating with said at least one base station via a corresponding one of a plurality of channels (141, . . . , 14U), the base station receiver for receiving a signal (X(t)) comprising components corresponding to spread signals transmitted by the transmitters of the plurality of user stations, each of said spread signals comprising a series of symbols spread using a spreading code unique to the corresponding user station, said base station receiver comprising;

    a plurality (U′

    ) of receiver modules (201, . . . , 20NI, 20d) each for deriving from successive frames of the received signal (X(t)) estimates of said series of symbols of a corresponding one of the user stations, preprocessing means (18) for deriving from the received signal (X(t)) a series of observation matrices (Yn) each for use by each of the receiver modules (20) in a said frame to derive an estimate of a symbol of a respective one of said series of symbols, and means (19,44;

    44/1,44/2) for deriving from each observation matrix a plurality of observation vectors (Yn;

    Yn−

    1
    ;

    Zn1 . . . ZnNI;

    Znd) and applying each of the observation vectors to a respective one of the plurality of receiver modules (201, . . . , 20NI, 20d);

    each receiver module comprising;

    channel identification means (28) for deriving from one of the observation vectors a channel vector estimate (Ĥ

    n1, . . . , Ĥ

    nNI;

    Ŷ

    0,nd;

    {circumflex over (Y)}0,n−

    1
    i) based upon parameter estimates of the channel between the base station receiver and the corresponding user station transmitter;

    beamformer means (271, . . . , 27NI, 27d;

    47d) having coefficient tuning means (50) for producing a set of weighting coefficients in dependence upon the channel vector estimate, and combining means (51,52) for using the weighting coefficients to weight respective ones of the elements of a respective one of the observation vectors and combining the weighted elements to provide a signal component estimate (ŝ

    n1, . . . , ŝ

    nU); and

    symbol estimating means (291, . . . , 29U, 301, . . . , 30U) for deriving from the signal component estimate an estimate ({circumflex over (b)}n1, . . . , {circumflex over (b)}nU) of a symbol (bn1, . . . , bnU) transmitted by a corresponding one of the user stations (101, . . . , 10U), wherein said receiver further comprises means (42,43) responsive to symbol estimates ({circumflex over (b)}n1, . . . , {circumflex over (b)}nNI;

    g1, g2, g3;

    gl

    1,n
    ) and to channel estimates (custom charactern1 . . . custom characternNI;

    custom charactern−

    1
    i) comprising at least said channel vector estimates (Ĥ

    n1, . . . , Ĥ

    nNI) for channels (141, . . . , 14NI) of a first group (I) of said plurality of user stations (101, . . . , 10NI) to provide at least one constraint matrix (Ĉ

    n) representing interference subspace of components of the received signal corresponding to said predetermined group, and in each of one or more receiver modules (20Ad) of a second group (D) of said plurality of receiver modules, the coefficient tuning means (50Ad) produces said set of weighting coefficients in dependence upon both the constraint matrix (Ĉ

    n) and the channel vector estimates (Ĥ

    nd) so as to tune said one or more receiver modules (20Ad) each towards a substantially null response to that portion of the received signal (X(t)) corresponding to said interference subspace.

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