Spread spectrum receiver for restoring received symbols with a symbol detection window adjusted in optimal and a method therefor

1. A spread spectrum receiver comprising a plurality of correlators for obtaining correlations between a received spread spectrum signal input and all of spread code sequences for the received spread spectrum signal to produce resultant correlation values, wherein said receiver compares the correlation values produced with a correlation threshold during a period in which a symbol detection window is open and which corresponds to a symbol detection period, and, when the correlation values exceed the correlation threshold, symbol data corresponding to the spread code sequence of one of said correlators which exceeds the correlation threshold is demodulated into received symbol data,

said receiver further comprising:

a correlation peak value detector for detecting a correlation peak value from the correlation values;

a symbol detection window controller operative in response to the correlation values and position information of the correlation peak value optimum window width for producing information of the symbol detection window, and generating an optimum window width symbol detection window having an optimum window width from the optimum window width information;

a comparator including a correlation threshold holding circuit for holding the correlation threshold, said comparator determining, during a predetermined period when the optimum window width symbol detection window is open, whether or not the correlation value exceeds the correlation threshold;

a symbol data selector for determining, when the correlation value exceeds the correlation threshold held in said correlation threshold holding circuit, symbol data corresponding to the spread code sequence of one of said correlators which produces the correlation value exceeding the correlation threshold as the received symbol data; and

a correlation threshold generator for generating the correlation threshold from the information of the detection window width to provide said comparator with the threshold,

said comparator updating the correlation threshold held in said correlation threshold holding circuit with the correlation threshold generated by said correlation threshold generator,

wherein said correlation threshold generator comprises:

an average correlation threshold holding circuit for holding an average correlation threshold;

a detection window width data storage for receiving from said comparator detection window width data included in the detection window width at a predetermined time interval to store the detection window width data therein;

an average detection window width data calculator for calculating an average of the stored detection window width data, and holding the average as average detection window width data;

a correlation threshold calculator for receiving from said comparator the detection window width data included in the detection window width,

said correlation threshold calculator comparing the detection window width data with the average detection window width data,

calculating a difference between the detection window width data and the average detection window width data,

subtracting, when the detection window width data is larger than the average detection window width data, a value corresponding to the difference from the average correlation threshold held in said average correlation threshold holding circuit to obtain the correlation threshold, and holding the obtained correlation threshold, and

adding, when the detection window width data is smaller than or equal to the average detection window width data, a value corresponding to the difference to the average correlation threshold held in said average correlation threshold holding circuit to obtain the correlation threshold, and holding the obtained correlation threshold; and

a transmitter for transmitting the obtained correlation threshold to said comparator.

2. A method of receiving spread spectrum wherein correlation values are obtained between an input signal and transmission spread code sequences by a plurality of correlators provided correspondingly to the transmission spread code sequences,

the correlation values obtained during a period in which a symbol detection window is open are compared with a correlation threshold, the period corresponding to a symbol detection period, and

when the correlation values exceed the correlation threshold, symbol data corresponding to the spread code sequence associated with a correlation value indicating a maximum of correlation peak values is used to demodulate received symbol data,

said method comprising:

a first step of holding the correlation threshold;

a second step of producing a correlation value between the input signal and the transmission spread code sequences;

a third step of detecting the correlation peak value from the correlation values;

a fourth step of producing from the correlation values and position information of the correlation peak values optimum window width information of the symbol detection window;

a fifth step of generating from the optimum window width information an optimum window width symbol detection window having an optimum window width;

a sixth step of determining, during a predetermined period when the optimum window width symbol detection window is open, whether or not the correlation values exceeds the correlation threshold;

a seventh step of determining, when the correlation values exceed the correlation threshold, the symbol data corresponding to the spread code sequence of one of the correlators which outputs the correlation value exceeding the correlation threshold as the received symbol data; and

an eighth step of generating the correlation threshold from the detection window width information; and

a ninth step of updating the correlation threshold held in the first step with the correlation threshold generated in said eighth step,

wherein said eighth step comprises:

a first substep of holding the average correlation threshold;

a second substep of storing, at a predetermined interval time, detection window width data included in the detection window width in said sixth step;

a third substep of calculating an average of the stored detection window width data and holding the average as average detection window width data; and

a fourth substep of comparing the detection window width data included in the detection window width in said sixth step with the average detection window width data,

said fourth substep calculating a difference between the detection window width data and the average detection window width data,

subtracting, when the detection window width data is larger than the average detection window width data, a value corresponding to the difference from the average correlation threshold held in said first substep to obtain the correlation threshold, and holding the obtained correlation threshold, and

adding, when the detection window width data is smaller than or equal to the average detection window width data, a value corresponding to the difference to the average correlation threshold held in said first substep to obtain the correlation threshold, and holding the obtained correlation threshold; and

a fifth substep of forwarding the obtained correlation threshold to said sixth step.