Method and apparatus for decision directed demodulation using antenna arrays and spatial processing

Claim 2

In a wireless communication system including at least one base station and at least one remote terminal of a set of remote terminals, said base station comprising an array of antennas, a method for demodulating a modulated signal transmitted by a particular remote station to produce a reference remote terminal transmission signal, said method implemented at said at least one base station, said modulated signal modulated at symbol points by a modulation scheme that has a finite symbol alphabet, each distinct antenna of the array of antennas receiving a corresponding received signal, all the received signals forming a received signal vector, each received signal comprising signals from all the remote terminals of the set that are transmitting, the method comprising: a) separating from the received signal vector a remote terminal signal corresponding to the particular remote terminal by using a spatial weight vector corresponding to the particular remote terminal, to form a particular terminal copy signal, said terminal copy signal comprising samples; and b) for each symbol point i) constructing an ideal signal from the particular terminal copy signal, the ideal signal having said modulation scheme, the amplitude and phase of the ideal signal determined from the amplitude and phase of said terminal copy signal, with the ideal signal set at the initial symbol point to be equal to said terminal copy signal at the initial symbol point; and ii) relaxing the ideal signal towards said terminal copy signal, producing a reference remote terminal transmission signal.

Claim 3

The method of claim 1 wherein the alphabet of said modulation scheme includes symbols that have different amplitudes and wherein said step of relaxing relaxes the amplitude of the ideal signal towards the amplitude of said terminal copy signal, producing the reference remote terminal transmission signal.

Claim 4

The method of claim 2 wherein said step of relaxing the amplitude |b ideal (n)| of the ideal signal b ideal (n) towards the amplitude |b N (n)| of said terminal copy signal b N (n) corresponds to computing the amplitude |b R (n)| of the reference remote terminal transmission signal b R (n) as |b.sub.R (n)|=α|b.sub.ideal (n)|+(1-α)|b.sub.N (n)| where 0<α<1.

Claim 5

The method of claim 1 wherein the alphabet of said modulation scheme includes symbols that have different phases and wherein said step of relaxing relaxes the phase of the ideal signal towards the phase of said terminal copy signal, producing the reference remote terminal transmission signal.

Claim 6

The method of claim 4, wherein the relaxing step (b)(ii) relaxes the phase ∠b ideal (n) of the ideal signal b ideal (n) towards the phase ∠b N (n) of said terminal copy signal b N (n) by an amount dependent on the difference between the ideal signal phase ∠b ideal (n) and the terminal copy signal phase ∠b N (n).

Claim 7

The method of claim 5 wherein said step of relaxing the phase ∠b ideal (n) of the ideal signal b ideal (n) towards the phase ∠b N (n) of said terminal copy signal b N (n) corresponds to computing the phase ∠b R (n) of the reference remote terminal transmission signal b R (n) as ∠b.sub.R (n)=α∠b.sub.ideal (n)+(1-α)∠b.sub.N (n) where 0<α<1.

Claim 8

The method of claim 4 wherein said modulation scheme is phase shift keying.

Claim 9

The method of claim 7, wherein the modulation scheme is differential phase shift keying, the ideal signal construction step (b)(i) constructs the ideal signal phase by advancing the phase of the reference remote terminal transmission signal at the previous symbol point of the reference remote terminal transmission signal by a modulation scheme dependent amount determined by the difference between the terminal copy signal phase and the phase of the reference remote terminal transmission signal at the previous symbol point of the reference remote terminal transmission signal, and the relaxing step (b)(ii) relaxes the phase ∠b ideal (n) of the ideal signal b ideal (n) towards the phase ∠b N (n) of said terminal copy signal b N (n) by an amount dependent on the difference between the ideal signal phase ∠b ideal (n) and the terminal copy signal phase ∠b N (n).

Claim 10

The method of claim 8 wherein said step of relaxing the phase ∠b ideal (n) of the ideal signal b ideal (n) towards the phase ∠b N (n) of said terminal copy signal b N (n) corresponds to computing the phase ∠b R (n) of the reference remote terminal transmission signal b R (n) as ∠b.sub.R (n)=α∠b.sub.ideal (n)+(1-α)∠b.sub.N (n) where 0<α<1.

Claim 11

The method of claim 4 wherein said modulation scheme is QAM and each symbol in said alphabet has a distinct phase.

Claim 12

In a wireless communication system including at least one base station and at least one remote terminal of a set of remote terminals, said base station comprising an array of antennas, a method for demodulating a modulated signal transmitted by a particular remote station to produce a demodulated remote terminal transmission signal, said method implemented at said at least one base station, said modulated signal modulated by a modulation scheme that has a finite symbol alphabet, each distinct antenna of the array of antennas receiving a corresponding received signal, all the received signals forming a received signal vector, each received signal comprising signals from all the remote terminals of the set that are transmitting, the method comprising: a) down-converting the received signal vector; b) estimating the time alignment and frequency offset of the received signal vector; c) separating from the received signal vector a remote terminal signal corresponding to the particular remote terminal by using an initial spatial weight vector corresponding to the particular remote terminal, said separating including correcting for time alignment and frequency offset using the estimated time alignment and frequency offset, said separating forming a corrected terminal copy signal; d) demodulating the corrected terminal copy signal to produce a demodulated signal; and e) performing at least once e1) synthesizing a reference signal from the demodulated signal; e2) computing a new spatial weight vector by minimizing a prescribed cost function, said cost function dependent on said reference signal; and e3) performing steps (c) and (d) using in step (c) the last determined new spatial weight vector instead of the initial spatial weight vector.

Claim 13

In a wireless communication system including at least one base station and at least one remote terminal of a set of remote terminals, said base station comprising an array of antennas, a method for demodulating a modulated signal transmitted by a particular remote station to produce a demodulated remote terminal transmission signal, said method implemented at said at least one base station, said modulated signal modulated by a modulation scheme that has a finite symbol alphabet, each distinct antenna of the array of antennas receiving a corresponding received signal, all the received signals forming a received signal vector, each received signal comprising signals from all the remote terminals of the set that are transmitting, the method comprising: a) down-converting the received signal vector; b) estimating the time alignment and frequency offset of the received signal vector; c) separating from the received signal vector a remote terminal signal corresponding to the particular remote terminal by using an initial spatial weight vector corresponding to the particular remote terminal, said separating including correcting for time alignment and frequency offset using the estimated time alignment and frequency offset, said separating forming a corrected terminal copy signal; d) demodulating the corrected terminal copy signal to produce a demodulated signal; and e) performing at least once e1) synthesizing a reference signal from the demodulated signal; e2) computing a new spatial weight vector by minimizing a prescribed cost function, said cost function dependent on said reference signal; and e3) performing steps (c) and (d) using in step (c) the last determined new spatial weight vector instead of the initial spatial weight vector.

Claim 14

The method of claim 11 wherein step (e.3) further comprises performing step (b).

Claim 15

The method of claim 11 wherein step (c) further comprises c.1) applying the estimated time alignment and frequency offset as corrections to the received signal vector to form a corrected signal vector; and c.2) separating from the corrected signal vector the corrected terminal copy signal by using the initial spatial weight vector corresponding to the particular remote terminal.

Claim 16

The method of claim 11 wherein step (c) further comprises c1) separating from the received signal vector a particular terminal copy signal corresponding to the particular remote terminal by using the initial spatial weight vector corresponding to the particular remote terminal; and c2) applying the estimated frequency offset as corrections said particular terminal copy signal to form a frequency corrected terminal copy signal.

Claim 17

In a demodulation method implemented on a base station of a wireless system which includes one or more base stations and one or more remote terminals of a set of remote terminals, said base station comprising and array of antennas, the method demodulating a modulated signal transmitted by a particular remote terminal to produce a demodulated remote terminal transmission signal, said modulated signal modulated by a modulation scheme that has a finite symbol alphabet, each distinct antenna of the array receiving a corresponding received signal, all the received signals forming a received signal vector, each received signal receiving signals from all the remote terminals of the set transmitting, the method including an alternating projection loop which includes the steps of: a) down-converting the received signal vector; b) separating from a signal vector derived from the received signal vector a remote terminal signal corresponding to the particular remote terminal to form a particular terminal copy signal; c) determining an ideal reference signal from the particular terminal copy signal; d) determining a spatial weight vector from the ideal reference signal; and e) performing steps (b), (c) and (d) at least once, step (b) using the latest spatial weight vector determined in step (d), the improvement comprising using in step (d) a relaxed reference signal which has been relaxed from the ideal reference signal towards the particular terminal copy signal.

Claim 18

In a demodulation method implemented on a base station of a wireless system which includes one or more base stations and one or more remote terminals of a set of remote terminals, said base station comprising and array of antennas, the method demodulating a modulated signal transmitted by a particular remote terminal to produce a demodulated remote terminal transmission signal, said modulated signal modulated by a modulation scheme that has a finite symbol alphabet, each distinct antenna of the array receiving a corresponding received signal, all the received signals forming a received signal vector, each received signal receiving signals from all the remote terminals of the set transmitting, the method including an alternating projection loop which includes the steps of: a) down-converting the received signal vector; b) separating from a signal vector derived from the received signal vector a remote terminal signal corresponding to the particular remote terminal to form a particular terminal copy signal; c) determining an ideal reference signal from the particular terminal copy signal; d) determining a spatial weight vector from the ideal reference signal; and e) performing steps (b), (c) and (d) at least once, step (b) using the latest spatial weight vector determined in step (d), the improvement comprising using in step (d) a relaxed reference signal which has been relaxed from the ideal reference signal towards the particular terminal copy signal.

Claim 19

In a demodulation method implemented on a base station of a wireless system which includes one or more base stations and one or more remote terminals of a set of remote terminals, said base station comprising an array of antennas, the method demodulating a modulated signal transmitted by a particular remote terminal to produce a demodulated remote terminal transmission signal, said modulated signal modulated by a modulation scheme that has a finite symbol alphabet, some of said symbols having different phases, each distinct antenna of the array receiving a corresponding received signal, all the received signals forming a received signal vector, each received signal receiving signals from all the remote terminals of the set transmitting, the method including an alternating projection loop which includes the steps of: a) down converting the received signal vector; b) separating from a signal vector derived from the received signal vector a remote terminal signal corresponding to the particular remote terminal to form a particular terminal copy signal; c) determining an ideal reference signal from the particular terminal copy signal; d) determining a spatial weight vector from the ideal reference signal; and e) performing steps (b), (c) and (d) at least once, step (b) using the latest spatial weight vector determined in step (d), the improvement comprising estimating the time alignment and frequency offset of the received signals, and using in step (d) a corrected reference signal which has been corrected for frequency offset and time alignment.

Claim 20

In a demodulation method implemented on a base station of a wireless system which includes one or more base stations and one or more remote terminals of a set of remote terminals, said base station comprising an array of antennas, the method demodulating a modulated signal transmitted by a particular remote terminal to produce a demodulated remote terminal transmission signal, said modulated signal modulated by a modulation scheme that has a finite symbol alphabet, some of said symbols having different phases, each distinct antenna of the array receiving a corresponding received signal, all the received signals forming a received signal vector, each received signal receiving signals from all the remote terminals of the set transmitting, the method including an alternating projection loop which includes the steps of: a) down converting the received signal vector; b) separating from a signal vector derived from the received signal vector a remote terminal signal corresponding to the particular remote terminal to form a particular terminal copy signal; c) determining an ideal reference signal from the particular terminal copy signal; d) determining a spatial weight vector from the ideal reference signal; and e) performing steps (b), (c) and (d) at least once, step (b) using the latest spatial weight vector determined in step (d), the improvement comprising estimating the time alignment and frequency offset of the received signals, and using in step (d) a corrected reference signal which has been corrected for frequency offset and time alignment.

Claim 21

The improvement of claim 16 wherein the phase of the corrected reference signal used in step (d) has been relaxed from the phase of the ideal reference signal towards the phase of the particular terminal copy signal.

Claim 24

The apparatus of claim 18 wherein the alphabet of said modulation scheme includes symbols that have different amplitudes and wherein said relaxing means relaxes the amplitude of the ideal signal towards the amplitude of said terminal copy signal, producing the reference remote terminal transmission signal.

Claim 25

The apparatus of claim 19 wherein said means for relaxing the amplitude |b ideal (n)| of the ideal signal b ideal (n) towards the amplitude |b N (n)| of said terminal copy signal b N (n) includes means for computing the amplitude |b R (n)| of the reference remote terminal transmission signal b R (n) as |b.sub.R (n)|=α|b.sub.ideal (n)|+(1-α)|b.sub.N (n)| where <α<1.

Claim 26

The apparatus of claim 18 wherein the alphabet of said modulation scheme includes symbols that have different phases and wherein said relaxing means relaxes the phase of the ideal signal towards the phase of said terminal copy signal, producing the reference remote terminal transmission signal.

Claim 27

The apparatus of claim 21, wherein the means for relaxing relaxes the phase ∠b ideal (n) of the ideal signal b ideal (n) towards the phase ∠b N (n) of the terminal copy signal b N (n) by an amount dependent on the difference between the ideal signal phase ∠b ideal (n) and the terminal copy signal phase ∠b N (n).

Claim 28

The apparatus of claim 22 wherein said means for relaxing the phase ∠b ideal (n) of the ideal signal b ideal (n) towards the phase ∠b N (n) of said terminal copy signal b N (n) includes means for computing the phase ∠b R (n) of the reference remote terminal transmission signal b R (n) as ∠b.sub.R (n)=α∠b.sub.ideal (n)+(1-α)∠b.sub.N (n) where 0<α<1.

Claim 29

The apparatus of claim 21 wherein said modulation scheme is phase shift keying.

Claim 30

The apparatus of claim 24, wherein the modulation scheme is differential phase shift keying, the means for ideal signal constructing constructs the ideal signal phase by advancing the phase of the reference remote terminal transmission signal at the previous symbol point of the reference remote terminal transmission signal by a modulation scheme dependent amount determined by the difference between the terminal copy signal phase and the phase of the reference remote terminal transmission signal at the previous symbol point of the reference remote terminal transmission signal, and the means for relaxing relaxes the phase ∠b ideal (n) of the ideal signal b ideal (n) towards the phase ∠b N (n) of the terminal copy signal b N (n) by an amount dependent on the difference between the ideal signal phase ∠b ideal (n) and the terminal copy signal phase ∠b N (n).

Claim 31

The apparatus of claim 25 wherein said step of relaxing the phase ∠b ideal (n) of the ideal signal b ideal (n) towards the phase ∠b N (n) of said terminal copy signal b N (n) corresponds to computing the phase ∠b R (n) of the reference remote terminal transmission signal b R (n) as ∠b.sub.R (n)=α∠b.sub.ideal (n)+(1-α)∠b.sub.N (n) where 0<α<1.

Claim 32

The apparatus of claim 21 wherein said modulation scheme is QAM and each symbol in said alphabet has a distinct phase.