Interference cancellation and receive diversity for single-valued modulation receivers
View Patent ↗A combined SAIC receiver and a multiple-antenna, receive diversity receiver are employed to reduce interference in a wireless system. The real and imaginary parts of the de-rotated signal for each receive path associated with an antenna are separately filtered and a combined output signal of all receive paths is generated. The weighting coefficients are adjusted based on an error signal produced by comparing the combined output signal with a reference signal. The weighting coefficients are initially set based on an MMSE/LS type of signal processing criteria, where the reference signal is the Training Sequence Code (TSC). Subsequent adjustment/tracking can be accomplished by using known tracking algorithms, e.g. LMS or RLS, or the coefficients can be re-computed using MMSE/LS processing. The reference signal for tracking may be a combination of the TSC and estimated data symbols provided by an equalizer.
1. A method for reducing interference in a multiple antenna receiver comprising:
receiving signals in each antenna of the multiple antenna receiver;
separating each of the signals that were received at each antenna of the multiple antenna receiver into a real part and an imaginary part;
filtering each of the separated signals in separate filters to cancel interference and supplying outputs from each of the filters;
summing the filter outputs to produce a combined output signal;
initially determining filter coefficients in each of the filters utilizing an error signal determined according to a difference of the combined output signal and a reference signal, the reference signal being derived from a training sequence code portion of a communication burst; and
wherein the filter coefficients are initially determined according to a weight vector given by a product of an inverse of a time-averaged correlation matrix, Φ, of the separated signals, and a time-averaged cross-correlation vector, z, between the separated signals and the reference signal.
2. The method as recited in claim 1 wherein Φ is a matrix sized to be an rM×rM matrix where r is twice a number of antennas in the multiple antenna receiver and M is a number of filter taps.
3. The method as recited in claim 2 wherein z is an rM×1 vector.
4. The method as recited in claim 1 further comprising utilizing adaptive processing to update the filter coefficients.
5. The method as recited in claim 4 wherein the adaptive processing utilizes one of a Least Mean Square (LMS) and Recursive Least Square (RLS) tracking algorithm.
6. The method as recited in claim 1 further comprising utilizing Minimum Mean Square Error/Least Squares (MMSE/LS) processing to update the filter coefficients.
7. A method for reducing interference in a multiple antenna receiver comprising:
receiving signals in each antenna of the multiple antenna receiver;
separating each of the signals that were received at each antenna of the multiple antenna receiver into a real part and an imaginary part;
filtering each of the separated signals in separate filters to cancel interference and supplying outputs from each of the filters;
summing the filter outputs to produce a combined output signal; and
wherein the multiple antenna receiver includes a first and second antenna and the combined output signal is produced in accordance with the following equation:
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where: i is an i th signal sample; w 1k , w 2k , w 3k , w 4k are kth filter coefficients of each of the respective filters; and M is a number of taps of each filter, and u 1 is a real part and u 2 an imaginary part of a first separated signal derived from a signal received by the first antenna, and u 3 is a real part and u 4 is an imaginary part of a second separated signal derived from a signal received in the second antenna.
8. A multiple antenna receiver system, comprising:
a plurality of branches coupled to respective antennas;
two signal paths for each branch corresponding to the real and imaginary parts of each branch;
an adaptive filter/combiner coupled to the signal paths and configured to generate a combined output signal in which interference has been canceled;
wherein the adaptive filter/combiner further comprises respective filters coupled to each signal path in each branch and a summing circuit coupled to sum the signals generated by each filter and generate the combined output signal; and
wherein a series of filter coefficients contained in each filter are adjusted to cancel interference; and
wherein the filter coefficients are initially determined according to a weight vector given by the product of an inverse of a time-averaged correlation matrix, Φ, of the real and imaginary parts of each branch, and the time-averaged cross-correlation vector, z, between the real and imaginary parts of each branch and the reference signal.
9. The system as recited in claim 8 wherein Φ is a matrix sized to be an rM×rM matrix where r is twice a number of antennas in the multiple antenna receiver and M is a number of filter taps.
10. The system as recited in claim 9 wherein z is an rM×1 vector.
11. The system of claim 8 further comprising an equalizer coupled to receive the combined output signal.
12. The system of claim 8 further comprising an error signal generator coupled to receive the combined output signal and a reference signal and generate an error signal according to a difference between the combined output signal and the reference signal.
13. The system of claim 12 , wherein the reference signal is determined according to a training sequence code contained in a communication to the multiple antenna receiver system.
14. A multiple antenna receiver system, comprising:
a plurality of branches coupled to respective antennas;
two signal paths for each branch corresponding to the real and imaginary parts of each branch;
an adaptive filter/combiner coupled to the signal paths and configured to generate a combined output signal in which interference has been canceled; and
wherein the adaptive filter/combiner further comprises respective filters coupled to each signal path in each branch and a summing circuit coupled to sum the signals generated by each filter and generate the combined output signal; and
wherein the number of antennas is two and wherein the combined output signal is generated in accordance with the following equation:
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where: i is an i th signal sample; w 1k , w 2k , w 3k , w 4k are kth filter coefficients of each of the respective filters; and M is a number of taps of each filter and u 1 , u 2 , and u 3 , u 4 are the separated real and imaginary parts of respective signals received by each antenna.
15. The system of claim 14 wherein each branch further comprises a receive filter and front end processor coupled between the antenna and the two signal paths of each branch coupled to supply a real part and imaginary part of a de-rotated signal, respectively, to the two signal paths.
16. The system of claim 14 further comprising a mobile telecommunications device including the multiple antenna receiver system.
17. The system of claim 14 further comprising a base station transceiver including the multiple antenna receiver system.