Method and apparatus for decision directed demodulation using antenna arrays and spatial processing
AssigneeArrayComm, Inc.
InventorsCraig H. Barratt, Farhad Farzaneh, David M. Parish
Life of this patent
Estimating the term…
Abstract
A method and apparatus for generating a reference signal for use in an alternating projection loop which is part of demodulation in a base station of a wireless communication system, the reference signal relaxed to minimize the effects of frequency offset and amplitude variations, the base station including an array of antennas. The alternating projection loop demodulates in the presence of co-channel interference and includes correction for time alignment and/or frequency offset.
Claims28
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.
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.
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.
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.
An apparatus for producing a reference signal in a base station for a wireless communication system, said system including at least one base station and at least one remote terminal of a set of remote terminals, the signal transmitted by a particular remote station modulated at symbol points by a modulation scheme that has a finite symbol alphabet, the base station including an array of antennas, each antenna 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, said apparatus comprising:
- a) means for separating from the received signal vector a remote terminal signal corresponding to a particular remote terminal which is transmitting, said separating means 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) a demodulator for produce a reference remote terminal transmission signal, said demodulator comprising:
- i) means for 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) means for relaxing the ideal reference signal towards said terminal copy signal, producing the reference remote terminal transmission signal.
An apparatus for demodulating a modulated signal transmitted by a particular remote station to produce a demodulated remote terminal transmission signal in a wireless communication system, said 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, said apparatus in 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 apparatus comprising:
- a) a down-converter for downconverting the received signal vector;
- b) means for estimating the time alignment and frequency offset of the received signal vector;
- c) means for separating from the received signal vector a remote terminal signal corresponding to the particular remote terminal, said separating means using an initial spatial weight vector corresponding to the particular remote terminal, said separating means comprising means for correcting for time alignment and frequency offset using the estimated time alignment and frequency offset, said separating means forming a corrected terminal copy signal;
- d) a demodulator for demodulating the corrected terminal copy signal to produce a demodulated signal;
- e) means synthesizing a reference signal from the demodulated signal;
- and
- f) means for computing a new spatial weight vector by minimizing a prescribed cost function, said cost function dependent on said reference signal.
Dependencies are inferred from the claim text.