Correlation detector for use in a spread spectrum communications receiver

• US 5,832,021 A
• Filed: 05/30/1997
• Issued: 11/03/1998
• Est. Priority Date: 05/30/1996
• Status: Expired due to Term

• Current Assignee: NEC Corporation
• Original Assignee: NEC Corporation
• Inventors: Kondo, Tadayuki
• Primary Examiner(s): Chin, Stephen
• Assistant Examiner(s): Liu, Shuwang
• Application Number:
  US08/865,658
• Time in Patent Office: 522 Days
• Field of Search: 375/1, 375/367, 375/200, 375/208, 375/365, 375/94, 375/376, 375/206, 375/343, 370/342, 370/350, 331/17, 331/25, 331/14
• US Class Current: 375/150
• CPC Class Codes: H04B 1/7085 using a code tracking loop, e.g. a delay-locked loop

Abstract

A digital delay-locked loop (DLL) circuit of high synchronous maintaining precision, which is usually affected by the quantization error of signal digitization, is provided for a spread spectrum communications receiver for mobile communications system. Three correlation sections are provided for calculating the correlation values in the peak phase, in the phase leading the peak phase and in the phase lagging behind the peak phase respectively in a delay profile on the basis of a received signal. A control section calculates the difference of the correlation values between the value in the lagging phase and the value of the advancing phase, and determines the threshold value for controlling a spread code generation section. The control section controls so as to advance the generation timing of spread code when the difference between the correlation values is greater than the positive threshold value, so as to delay the generation timing of when the difference value is smaller than the negative threshold value, and so as not to vary the generation timing when the difference value is smaller than the positive threshold value, but greater than the negative threshold value.

Claims

1. A spread spectrum communications receiver for mobile communications system, comprising:

correlation means for calculating the correlation value in the peak phase, the correlation value in the phase leading said peak phase and the correlation value in the phase lagging behind said peak phase in a delayed profile of correlation values, on the basis of a received signal;

spread code generation means;

a control section which controls said spread code generation means on the basis of the correlation values from said correlation means,

wherein said control section comprises;

means for calculating the difference between the correlation value in the Phase leading said peak phase and the correlation value in the phase lagging behind said peak phase as the difference between the correlation values;

means for determining the threshold value of a digital DLL;

means for comparing said difference between the correlation values with the threshold value of said digital DLL to control said spread code generation means and advance the phase of the shift register of the correlation means when said difference between the correlation values is greater than the positive threshold value of said digital DLL, and delay the phase of the shift register of said correlation means when said difference between the correlation values is smaller than the negative threshold value of said digital DLL, and not vary the phase of the shift register of said correlation means when said difference between the correlation values is smaller than the positive threshold value of said digital DLL, and said difference between the correlation values is greater than the negative threshold value of said digital DLL and,

means for calculating the threshold value of said digital DLL by multiplying, by a weight coefficient, the value calculated by subtracting the minimum correlation value among the correlation value in said peak phase, the correlation value in the phase lagging behind said peak phase and the correlation value in the phase leading said peak phase, from the correlation value in said peak phase.

2. A spread spectrum communications receiver for mobile communications system, comprising:

correlation means for calculating the correlation value in the peak phase, the correlation value in the phase leading said peak phase and the correlation value in the phase lagging behind said peak phase in a delayed profile of correlation values, on the basis of a received signal;

spread code generation means; and

a control section which controls said spread code generation means on the basis of the correlation values from said correlation means,

wherein said control section comprises;

means of calculating the difference between the correlation value in the phase leading said peak phase and the correlation value in the phase lagging behind said peak phase as the difference between the correlation values;

means for determining the threshold value of a digital DLL;

means for comparing said difference between the correlation values with the threshold value of said digital DLL to control said spread code generation means and advance the phase of the shift register of the correlation means when said difference between the correlation values is greater than the positive threshold value of said digital DLL, and delay the phase of the shift register of said correlation means when said difference between the correlation values is smaller than the negative threshold value of said digital DLL, and not vary the phase of the shift register of said correlation means when said difference between the correlation values is smaller than the positive threshold value of said digital DLL, and said difference between the correlation values is greater than the negative threshold value of said digital DLL;

means for determining the error rate of said received signal on the basis of the correlation values from said correlation means, and wherein said control section is designed to increase said weight coefficient when said error rate is high, and to decrease said weight coefficient when said error rate is low, and

means for calculating the threshold value of said digital DLL by multiplying, by a weight coefficient, the value calculated by subtracting the minimum correlation value among the correlation value in said peak phase, the correlation value in the phase lagging behind said peak phase and the correlation value in the phase leading said peak phase, from the correlation value in said peak phase.

3. A spread spectrum communications receiver for mobile communications system, comprising:

correlation means for calculating the correlation value in the peak phase, the correlation value in the phase leading said peak phase and the correlation value in the phase lagging behind said peak phase in a delayed profile of correlation values, on the basis of a received signal;

spread code generation means; and

a control section which controls said spread code generation means on the basis of the correlation values from said correlation means,

wherein said control section comprises;

means for calculating the difference between the correlation value in the phase leading said peak phase and the correlation value in the phase lagging behind said peak phase as the difference between the correlation values;

means for determining the threshold value of a digital DLL;

means for comparing said difference between the correlation values with the threshold value of said digital DLL to control said spread code generation means and advance the phase of the shift register of the correlation means when said difference between the correlation values is greater than the positive threshold value of said digital DLL, and delay the phase of the shift register of said correlation means when said difference between the correlation values is smaller than the negative threshold value of said digital DLL, and not vary the phase of the shift register of said correlation means when said difference between the correlation values is smaller than the positive threshold value of said digital DLL, and said difference between the correlation values is greater than the negative threshold value of said digital DLL;

means for determining the phasing cycle on the basis of the correlation values from said correlation means, referred to the received level, and wherein said control section is designed to increase said weight coefficient when the phasing cycle is long, and to decrease said weight coefficient when the phasing cycle is short.