Interference signal cancelling method, receiver and communication system using the same

A receiver comprising:

• desired signal estimation means for converting a desired signal sequence candidate into an estimated received desired signal in accordance with a channel parameter and outputting said estimated received desired signal;
• interference signal estimation means for converting an interference signal sequence candidate into an estimated received interference signal in accordance with a channel parameter and outputting said estimated received interference signal;
• error estimation means connected to the outputs of said desired signal estimation means and said interference signal estimation means, for generating an estimation error signal by subtracting, from a received signal, said estimated received desired signal from said desired signal estimation means and said estimated received interference signal from said interference signal estimation means;
• state estimation means connected to the output of said error estimation means and to inputs of said desired signal estimation means and said interference signal estimation means for producing a plurality of desired signal sequence candidates and a plurality of interference signal sequence candidates respectively corresponding to a predetermined plurality of sequences of states of signal transition and for providing said plurality of desired signal sequence candidates and said plurality of interference signal sequence candidates to said desired signal estimation means and said interference signal estimation means, respectively, said state estimation means being operative to output, as the result of a sequence decision, that one of said desired signal sequence candidates that is estimated to be a desired signal sequence contained in said received signal on the basis of said estimation error signal generated by said error estimation means;
• and
• control means connected to the output of said state estimation means and to inputs of said desired signal estimation means and said interference signal estimation means, for controlling said channel parameters of said desired signal estimation means and said interference signal estimation means by an adaptation algorithm on the basis of said desired signal sequence, said interference signal sequence and said estimation error signal;
• said desired signal estimation means, said interference signal estimation means, said error estimation means and said control means constituting a first diversity branch, said receiver including a second diversity branch of the same construction as said first diversity branch, said error estimation means of said first and second diversity branches being supplied with quasi-coherently detected signal sample values obtained from received signals at different positions, respectively, and said state estimation means comprising first and second square means for calculating the squares of estimation errors from said error estimation means of said first and second diversity branches and adder means which adds the outputs from said first and second square means and outputs the added result as a likelihood signal corresponding to its likelihood, said state estimation means generating a set of a desired signal symbol sequence candidate and an interference signal symbol sequence candidate and providing said set to said desired signal estimation means, said interference signal estimation means and said control means of said first and second diversity branches.

A receiver comprising:

• desired signal estimation means for converting a desired signal sequence candidate into an estimated received desired signal in accordance with a channel parameter and outputting said estimated received desired signal;
• interference signal estimation means for converting an interference signal sequence candidate into an estimated received interference signal in accordance with a channel parameter and outputting said estimated received interference signal;
• error estimation means connected to the outputs of said desired signal estimation means and said interference signal estimation means, for generating an estimation error signal by subtracting, from a received signal, said estimated received desired signal from said desired signal estimation means and said estimated received interference signal from said interference signal estimation means;
• state estimation means connected to the output of said error estimation means and to inputs of said desired signal estimation means and said interference signal estimation means for producing a plurality of desired signal sequence candidates and a plurality of interference signal sequence candidates respectively corresponding to a predetermined plurality of sequences of states of signal transition and for providing said plurality of desired signal sequence candidates and said plurality of interference signal sequence candidates to said desired signal estimation means and said interference signal estimation means, respectively, said state estimation means being operative to output, as the result of a sequence decision, that one of said desired signal sequence candidates that is estimated to be a desired signal sequence contained in said received signal on the basis of said estimation error signal generated by said error estimation means;
• and
• control means connected to the output of said state estimation means and to inputs of said desired signal estimation means and said interference signal estimation means, for controlling said channel parameters of said desired signal estimation means and said interference signal estimation means by an adaptation algorithm on the basis of said desired signal sequence, said interference signal sequence and said estimation error signal;
• said state estimation means comprising:
• state sequence candidate generating means which generates a first transition state sequence candidate corresponding to said desired signal symbol sequence candidate and a second transition state sequence candidate corresponding to said interference signal symbol sequence candidate;
• and first and second modulated signal generating means which generate, as said desired signal sequence candidate and said interference signal sequence candidate, first and second symbol sequence candidates sequentially modulated in accordance with said first and second transition state sequence candidates, respectively.

A method for cancelling an interference signal from a received signal in a receiver which comprises error estimation means, state estimation means, desired signal estimation means, interference signal estimation means and channel estimation means, said method comprising:

• A. a step wherein upon each input of a quasi-coherently detected signal sample value into said error estimation means, said state estimation means sequentially generates a plurality of first symbol sequence candidates and a plurality of second symbol sequence candidates corresponding to a plurality of transition state sequence candidates for received signals of desired and interference waves;
• B. a step wherein said desired signal estimation means and said interference signal estimation means respectively perform convolutional operations of said first and second symbol sequence candidates and channel impulse response estimated values for said desired and interference waves from said channel estimation means to generate an estimated received interference signal;
• C. a step wherein said error estimation means subtracts said estimated received desired signal and said estimated received interference signal from said sample value to generate an estimation error signal;
• and
• D. a step wherein said state estimation means calculates the likelihood corresponding to said estimation error signal for said set of first and second symbol sequence candidates to decide a desired signal sequence candidate of the maximum likelihood and outputs the result of said decision;
• said method including an interference wave training signal period during which a symbol sequence corresponding to an interference wave training signal is provided, as a substitute for said second symbol sequence candidate, to said interference signal estimation means and said channel estimation means, and said channel estimation means outputs said channel impulse response estimated value corresponding to said symbol sequence candidate of said desired signal which provides the maximum likelihood.

A method for cancelling an interference signal from a received signal in a receiver which comprises error estimation means, state estimation means, desired signal estimation means, interference signal estimation means and channel estimation means, said method comprising:

• A. a step wherein upon each input of a quasi-coherently detected signal sample value into said error estimation means, said state estimation means sequentially generates a plurality of first symbol sequence candidates and a plurality of second symbol sequence candidates corresponding to a plurality of transition state sequence candidates for received signals of desired and interference waves;
• B. a step wherein said desired signal estimation means and said interference signal estimation means respectively perform convolutional operations of said first and second symbol sequence candidates and channel impulse response estimated values for said desired and interference waves from said channel estimation means to generate an estimated received interference signal;
• C. a step wherein said error estimation means subtracts said estimated received desired signal and said estimated received interference signal from said sample value to generate an estimation error signal;
• and
• D. a step wherein said state estimation means calculates the likelihood corresponding to said estimation error signal for said set of first and second symbol sequence candidates to decide a desired signal sequence candidate of the maximum likelihood and outputs the result of said decision;
• said step A being a step wherein, in a predetermined period of a received signal, said channel estimation means sets the number of states to a value larger than the numbers of possible transition states for desired and interference waves and increases the numbers of said first and second symbol sequence candidates accordingly and said channel estimation means outputs said channel impulse response estimated values corresponding to said first and second symbol sequence candidates of said desired and interference waves which provide the maximum likelihood in said predetermined period.

A method for cancelling an interference signal from a received signal in a receiver which comprises error estimation means, state estimation means, desired signal estimation means, interference signal estimation means and channel estimation means, said method comprising:

• A. a step wherein upon each input of a quasi-coherently detected signal sample value into said error estimation means, said state estimation means sequentially generates a plurality of first symbol sequence candidates and a plurality of second symbol sequence candidates corresponding to a plurality of transition state sequence candidates for received signals of desired and interference waves;
• B. a step wherein said desired signal estimation means and said interference signal estimation means respectively perform convolutional operations of said first and second symbol sequence candidates and channel impulse response estimated values for said desired and interference waves from said channel estimation means to generate an estimated received interference signal;
• C. a step wherein said error estimation means subtracts said estimated received desired signal and said estimated received interference signal from said sample value to generate an estimation error signal;
• D. a step wherein said state estimation means calculates the likelihood corresponding to said estimation error signal for said set of first and second symbol sequence candidates to decide a desired signal sequence candidate of the maximum likelihood and outputs the result of said decision;
• and
• E. a step wherein in desired and interference wave training signal periods, training signal symbol sequences respectively corresponding to desired and interference wave training signals are provided to said desired signal estimation means and said interference signal estimation means, as substitutes for said first and second symbol sequence candidates, said training symbol sequences being provided to said channel estimation means as well, and said channel impulse response estimated values to be provided to said desired signal estimation means and said interference signal estimation means are determined so that said estimation error signal of said error estimation means is minimized in said training signal periods.

A method for cancelling an interference signal from a received signal in a receiver which comprises error estimation means, state estimation means, desired signal estimation means, interference signal estimation means and channel estimation means, said method comprising:

• A. a step wherein upon each input of a quasi-coherently detected signal sample value into said error estimation means, said state estimation means sequentially generates a plurality of first symbol sequence candidates and a plurality of second symbol sequence candidates corresponding to a plurality of transition state sequence candidates for received signals of desired and interference waves;
• B. a step wherein said desired signal estimation means and said interference signal estimation means respectively perform convolutional operations of said first and second symbol sequence candidates and channel impulse response estimated values for said desired and interference waves from said channel estimation means to generate an estimated received interference signal;
• C. a step wherein said error estimation means subtracts said estimated received desired signal and said estimated received interference signal from said sample value to generate an estimation error signal;
• D. a step wherein said state estimation means calculates the likelihood corresponding to said estimation error signal for said set of first and second symbol sequence candidates to decide a desired signal sequence candidate of the maximum likelihood and outputs the result of said decision;
• and
• E. a step of selecting a path which provides the maximum state transition path metric, by use of the Viterbi algorithm, for each of all predetermined possible transition states of a combination of said desired and interference signals and, upon each selection of said path for each state at each point in time, updating channel parameters for said desired and interference signals on the basis of said first and second symbol sequence candidates corresponding to said selected path.

A method for cancelling an interference signal from a received signal in a receiver which comprises error estimation means, state estimation means, desired signal estimation means, interference signal estimation means and channel estimation means, said method comprising:

• A. a step wherein upon each input of a quasi-coherently detected signal sample value into said error estimation means, said state estimation means sequentially generates a plurality of first symbol sequence candidates and a plurality of second symbol sequence candidates corresponding to a plurality of transition state sequence candidates for received signals of desired and interference waves;
• B. a step wherein said desired signal estimation means and said interference signal estimation means respectively perform convolutional operations of said first and second symbol sequence candidates and channel impulse response estimated values for said desired and interference waves from said channel estimation means to generate an estimated received interference signal;
• C. a step wherein said error estimation means subtracts said estimated received desired signal and said estimated received interference signal from said sample value to generate an estimation error signal;
• D. a step wherein said state estimation means calculates the likelihood corresponding to said estimation error signal for said set of first and second symbol sequence candidates to decide a desired signal sequence candidate of the maximum likelihood and outputs the result of said decision;
• and
• E. a step wherein states groups composed of combinations of possible transition states of said desired signal and possible transition states of said interference signal are defined;
• the state transition between adjacent points in time is limited to one path which provides the maximum path metric between respective state groups;
• and upon each selection of one path on the basis of said path metric, channel impulse responses for said desired and interference signals are updated in accordance with said first and second symbol sequence candidates of said desired and interference signals corresponding to the selected state transition.

A communication system which uses a receiver to receive a desired signal in signals transmitted from a plurality of transmitting stations, said plurality of transmitting stations each including random generating means for generating a pseudo-random number and phase shift means for shifting the phase of the signal to be transmitted, by an amount corresponding to said pseudo-random number;

• said receiver comprising:
• desired signal estimation means for converting a desired signal sequence candidate into an estimated received desired signal in accordance with a channel parameter and outputting said estimated received desired signal;
• interference signal estimation means for converting an interference signal sequence candidate into an estimated received interference signal in accordance with a channel parameter and outputting said estimated received interference signal;
• error estimation means connected to the outputs of said desired signal estimation means and said interference signal estimation means, for generating an estimation error signal by subtracting, from a received signal, said estimated received desired signal from said desired signal estimation means and said estimated received interference signal from said interference signal estimation means;
• state estimation means connected to the output of said error estimation means and to inputs of said desired signal estimation means and said interference signal estimation means for producing a plurality of desired signal sequence candidates and a plurality of interference signal sequence candidates respectively corresponding to a predetermined plurality of sequences of states of signal transition and for providing said plurality of desired signal sequence candidates and said plurality of interference signal sequence candidates to said desired signal estimation means and said interference signal estimation means, respectively, said state estimation means being operative to output, as the result of a sequence decision, that one of said desired signal sequence candidates that is estimated to be a desired signal sequence contained in said received signal on the basis of said estimation error signal generated by said error estimation means;
• and
• control means connected to the output of said state estimation means and to inputs of said desired signal estimation means and said interference signal estimation means, for controlling said channel parameters of said desired signal estimation means and said interference signal estimation means by an adaptation algorithm on the basis of said desired signal sequence, said interference signal sequence and said estimation error signal.

A communication system which uses receiver to receive a desired signal in signals transmitted from a plurality of transmitting stations, each transmitting station including random generating means for generating a pseudo-random number and power control means for changing the amplitude of the signal to be transmitted in accordance with said pseudeo-random number;

• said receiver comprising:
• desired signal estimation means for converting a desired signal sequence candidate into an estimated received desired signal in accordance with a channel parameter and outputting said estimated received desired signal;
• interference signal estimation means for converting an interference signal sequence candidate into an estimated received interference signal in accordance with a channel parameter and outputting said estimated received interference signal;
• error estimation mean connected to the outputs of said desired signal estimation means and said interference signal estimation means, for generating an estimation error signal by subtracting, from a received signal, said estimated received desired signal from said desired signal estimation means and said estimated received interference signal from said interference signal estimation means;
• state estimation means connected to the output of said error estimation means and to inputs of said desired signal estimation means and said interference signal estimation means for producing a plurality of desired signal sequence candidates and a plurality of interference signal sequence candidates respectively corresponding to predetermined plurality of sequence of states of signal transition and for providing said plurality of desired signal sequence candidates and said plurality of interference signal sequence candidates to said desired signal estimation means and said interference signal estimation means, respectively, said state estimation means being operative to output, as the result of a sequence decision, that one of said desired signal sequence candidates that is estimated to be a desired signal sequence contained in said received signal on the basis of said estimation error signal generated by said error estimation means, and
• control mean connected to the output of said state estimation means and to inputs of said desired signal estimation means and said interference signal estimation means, for controlling said channel parameters of said parameters of said desired signal estimation means and said interference signal estimation means by an adaptation algorithm on the basis of said desired signal sequence, said interference signal sequence and said estimation error signal.

A method for cancelling an interference signal from a received signal in a receiver which comprises error estimation means, state estimation means, desired signal estimation means, interference signal estimation means and channel estimation means, said method comprising:

• A. a step wherein upon each input of a quasi-coherently detected signal sample value into said error estimation means, said state estimation means sequentially generates a plurality of first symbol sequence candidates and a plurality of second symbol sequence candidates corresponding to a plurality of transition state sequence candidates for received signals of desired and interference waves;
• B. a step wherein said desired signal estimation means and said interference signal estimation means respectively perform convolutional operations of said first and second symbol sequence candidates and channel impulse response estimated values for said desired and interference waves from said channel estimation means to generate an estimated received desired signal and an estimated received interference signal;
• C. a step wherein said error estimation means subtracts said estimated received desired signal and said estimated received interference signal from said sample value to generate an estimation error signal;
• and
• D. a step wherein said state estimation means calculates the likelihood corresponding to said estimation error signal for said set of first and second symbol sequence candidates to decide a desired signal sequence candidate of the maximum likelihood and outputs the result of said decision;
• said method including a desired wave training signal period during which a symbol sequence corresponding to a desired wave training signal is provided, as a substitute for said first symbol sequence candidate, to said desired signal estimation means and said channel estimation means, and said channel estimation means outputs said channel impulse response estimated value corresponding to said symbol sequence candidate of said interference wave which provides the maximum likelihood.