Spectrum spread signal reception with differential demodulation of spectrum spread demodulated components at each synchronous point and at a point always one symbol period later

• US 5,612,972 A
• Filed: 12/28/1994
• Issued: 03/18/1997
• Est. Priority Date: 12/28/1993
• Status: Expired due to Term

• Current Assignee: NEC Corporation
• Original Assignee: NEC Corporation
• Inventors: Tomita, Hideho, Fukushi, Mikio
• Primary Examiner(s): Bocure, Tesfaldet
• Application Number:
  US08/364,701
• Time in Patent Office: 811 Days
• Field of Search: 375/200, 375/206, 375/208, 375/355, 375/329, 375/283, 375/343, 375/330, 375/340, 327/164
• US Class Current: 375/149
• CPC Class Codes: H04B 1/707 using direct sequence modulation

Abstract

In a spectrum spread receiver, a tracking unit tracks successive regions covering maximum correlation values, respectively, in spectrum spread demodulated components to produce a timing signal indicative of synchronous points respectively in the regions. Responsive to the timing signal, a differential demodulator unit demodulates the spectrum spread demodulated components at each synchronous point and at a time which is always one symbol period later than this synchronous point. Differential demodulation is carried out in this manner so as to be faithfully inverse relative to differential modulation in a spectrum spread transmitter.

Claims

1. A spectrum spread receiving method of receiving a spectrum spread modulated signal transmitted from a spectrum spread transmitter for differential modulation of adjacent symbol data of a transmitter input signal into differential modulated components and for individually multiplying a spectrum spread code and said differential modulated components into spectrum spread modulated components of said spectrum spread modulated signal said spectrum spread receiving method includes the steps of receiving said spectrum spread modulated signal as reception components having a common symbol period, individually multiplying said spectrum spread code and said reception components into spectrum spread demodulated components, and output demodulating said spectrum spread demodulated components into differential demodulated components of a reproduction of said transmitter input signal, wherein said output demodulating step comprises the steps of:

tracking successive regions of a greater correlation value in said spectrum spread demodulated components to produce a timing signal indicative of synchronous points in said regions, respectively; and

differential demodulating responsive to said timing signal said spectrum spread demodulated components into said differential demodulated components at each of said synchronous points and at a time which is always one symbol period later than each of said synchronous points,

said spectrum spread code includes a predetermined number of chips having a common chip period equal to said symbol period divided by said predetermined number, wherein said tracking step comprises the steps of;

leaky integrating an instantaneous amplitude, during an integral submultiple of said chip period, into integrated amplitudes produced in each of said regions and comprising maximum correlation values in said regions, respectively, wherein said instantaneous amplitude is an instantaneous amplitude which said spectrum spread demodulated components have above an amplitude threshold level as said greater correlation value, each maximum correlation value and a succeeding one of said maximum correlation values in a succeeding one of said regions having a value interval variable shorter and longer than said symbol period; and

generating responsive to said maximum correlation values said timing signal.

2. A spectrum spread receiving method of receiving a spectrum spread modulated signal transmitted from a spectrum spread transmitter for differential modulation of adjacent symbol data of a transmitter input signal into differential modulated components and for individually multiplying a spectrum spread code and said differential modulated components into spectrum spread modulated components of said spectrum spread modulated signal, said spectrum spread receiving method includes the steps of receiving said spectrum spread modulated signal as reception components having a common symbol period, individually multiplying said spectrum spread code and said reception components into spectrum spread demodulated components, and output demodulating said spectrum spread demodulated components into differential demodulated components of a reproduction of said transmitter input signal, wherein said output demodulating step comprises the steps of:

tracking successive regions of a greater correlation value in said spectrum spread demodulated components to produce a timing signal indicative of synchronous points in said regions, respectively; and

differential demodulating responsive to said timing signal said spectrum spread demodulated components into said differential demodulated components at each of said synchronous points and at a time which is always one symbol period later than each of said synchronous points,

said spectrum spread code includes a predetermined number of chips having a common chip period equal to said symbol period divided by said predetermined number, said timing signal successively defining primary through ternary periods having an integral submultiple of said chip period in common in each of said regions and including each of said synchronous points in one of said primary through said ternary periods, wherein said output demodulating step comprises the steps of;

holding responsive to said timing signal said spectrum spread demodulated components at said primary through said ternary periods as primary through ternary data;

producing responsive to said timing signal a differential demodulation control signal defining a control period lasting said integral submultiple of said chip period immediately following the ternary period of each of said regions; and

differential demodulating said primary through said ternary data at a selected one of said primary through said ternary periods that is selected in each of said regions by said differential demodulation control signal.

3. A spectrum spread receiver for receiving a spectrum spread modulated signal transmitted from a spectrum spread transmitter for differential modulating adjacent symbol-data of a transmitter input signal into differential modulated components and for individually multiplying a spectrum spread code and said differential modulated components into spectrum spread modulated components of said spectrum spread modulated signal, said spectrum spread receiver includes receiver means for receiving said spectrum spread modulated signal as reception components having a common symbol period, spectrum spread demodulating means for individually multiplying said spectrum spread code and said reception components into spectrum spread demodulated components, and output demodulator means for demodulating said spectrum spread demodulated components into differential demodulated components of a reproduction of said transmitter input signal, wherein said output demodulator means comprises:

tracking means for tracking successive regions of a greater correlation value in said spectrum spread demodulated components to produce a timing signal indicative of synchronous points in said regions, respectively; and

differential demodulator means responsive to said timing signal for differential demodulating said spectrum spread demodulated components into said differential demodulated components at each of said synchronous points and at a time which is always one symbol period later than each of said synchronous points,

said spectrum spread code includes a predetermined number of chips having a common chip period equal to said symbol period divided by said predetermined number, wherein said tracking means comprises;

leaky integrator means for integrating an instantaneous amplitude, during an integral submultiple of said chip period, into integrated amplitudes produced in each of said regions and comprising maximum correlation values in said regions, respectively, wherein said instantaneous amplitude is an instantaneous amplitude which said spectrum spread demodulated components have above an amplitude threshold level as said greater correlation value, each maximum correlation value and a succeeding one of said maximum correlation values in a succeeding one of said regions having a value interval variable shorter and longer than said symbol period; and

timing signal generator means responsive to said integrated amplitudes and timing signal.

4. A spectrum spread receiver as claimed in claim 3, wherein said leaky integrator means comprises:

an amplitude detector for detecting an amplitude of said spectrum spread demodulated components as said instantaneous amplitude; and

a leaky integrator for integrating during said integral submultiple of the chip period said instantaneous amplitude into said integrated amplitudes with said instantaneous amplitude reduced by a leak value serving as said amplitude threshold level in each of said regions to provide said greater amplitude value.

5. A spectrum spread receiver as claimed in claim 4, wherein said leaky integrator comprises:

an adder for adding said instantaneous amplitude and an addend into an amplitude sum;

a shift register for shifting at said submultiple of the chip period said amplitude sum supplied from said adder as an input correlation value to produce an output correlation value one symbol period later;

a leak value generator responsive to said output correlation value for generating said leak value; and

an integrator circuit substracter for subtracting said leak value from said output correlation value to provide said addend for feedback to said adder;

said adder thereby producing said amplitude sum as each of said integrated amplitudes.

6. A spectrum spread receiver as claimed in claim 4, wherein said timing signal generator means comprises:

correlation threshold level generator means responsive to said integrated amplitudes for generating a correlation threshold level;

a comparator for comparing with said correlation threshold level the integrated amplitudes supplied from said leaky integrator means as a comparator input correlation value at said symbol period to produce a trigger signal when said comparator input correlation value exceeds said correlation threshold level; and

a timer defining a region interval in each symbol period and triggered by said trigger signal to produce said timing signal with said timing signal made to indicate each of said regions during said region interval.

7. A spectrum spread receiver as claimed in claim 6, wherein said correlation threshold level generator means comprises:

a latch circuit for latching said integrated amplitudes as latched amplitudes;

a bit shift circuit for bit shifting said latched amplitudes to produce bit shifted amplitudes as reduced amplitudes;

an on-off switch responsive to said timing signal for producing said reduced amplitudes as subtrahend amplitudes during said region interval; and

a threshold subtracter for substracting said subtahend amplitudes from said latched amplitudes to produce said correlation threshold level.

8. A spectrum spread receiver as claimed in claim 4, said timing signal successively indicating primary through ternary periods having said integral submultiple of the chip period in common in each of said regions, wherein said output demodulator means comprises:

data holding means responsive to said timing signal for holding said spectrum spread demodulated components at said primary through said ternary periods as primary through ternary data;

differential demodulation control means responsive to said timing signal for producing a differential demodulation control signal defining a control period lasting said integral submultiple of the chip period immediately following said ternary period; and

differential demodulator means for differential demodulating said primary through said ternary data at a selected one of said primary through said ternary periods that is selected in each of said regions by said differential demodulation control signal.

9. A spectrum spread receiver as claimed in claim 3, wherein said timing signal generator comprises:

a correlation threshold level generator means responsive to said integrated amplitudes for generating a correlation threshold level;

a comparator for comparing with said correlation threshold level the integrated amplitudes supplied from said leaky integrator means as an input correlation value at said symbol period to produce a trigger signal when said input correlation value exceeds said correlation threshold level; and

a timer defining a region interval in each symbol period and triggered by said trigger signal to produce said timing signal with said timing signal made to indicate each of said regions during said region interval.

10. A spectrum spread receiver as claimed in claim 9, wherein said correlation threshold level generator means comprises:

a latch circuit for latching said integrated amplitudes as latched amplitudes;

a bit shift circuit for bit shifting said latched amplitudes to produce bit shifted amplitudes as reduced amplitudes;

an on-off switch responsive to said timing signal for producing said reduced amplitudes as subtrahend amplitudes during said region interval; and

a threshold subtracter for subtracting said subtrahend amplitudes from said latched amplitudes to produce said correlation threshold level.

11. A spectrum spread receiver as claimed in claim 9, wherein said leaky integrator means comprises:

an amplitude detector for detecting an amplitude of said spectrum spread demodulated components as said instantaneous amplitude; and

a leaky integrator for integrating during said integral submultiple of the chip period said instantaneous amplitude into said integrated amplitudes with said instantaneous amplitude reduced by a leak value serving as said amplitude threshold level in each of said regions to provide said greater correlation value.

12. A spectrum spread receiver as claimed in claim 11, wherein said leaky integrator comprises:

an adder for adding said instantaneous amplitude and an addend into an amplitude sum;

a shift register for shifting at said submultiple of the chip period said amplitude sum supplied from said adder as a shift register input correlation value to produce an output correlation value one symbol period later;

a leak value generator responsive to said output correlation value for generating said leak value; and

an integrator circuit subtracter for subtracting said leak value from said output correlation value to provide said addend for feedback to said adder;

said adder thereby producing said amplitude sum as each of said integrated amplitudes.

13. A spectrum spread receiver as claimed in claim 9, said timing signal successively indicating primary through ternary periods having said integral submultiple of the chip period in common in each of said regions, wherein said output demodulating means comprises:

data holding means responsive to said timing signal for holding said spectrum spread demodulated components at said primary through said ternary periods as primary through ternary data;

differential demodulation control means responsive to said timing signal for producing a differential demodulation control signal defining a control period lasting said integral submultiple of the chip period immediately following said ternary period; and

differential demodulator means for differential demodulating said primary through said ternary data at a selected one of said primary through said ternary periods that is selected in each of said regions by said differential demodulation control signal.

14. A spectrum spread receiver for receiving a spectrum spread modulated for receiving a spectrum spread modulated signal transmitted from a spectrum spread transmitter for differential modulating adjacent symbol-data of a transmitter input signal into differential modulated components and for individually multiplying a spectrum spread code and said differential modulated components into spectrum spread modulated components of said spectrum spread modulated signal, said spectrum spread receiver includes receiver means for receiving said spectrum spread modulated signal as reception components having a common symbol period, spectrum spread demodulating means for individually multiplying said spectrum spread code and said reception components into spectrum spread demodulated components, and output demodulator means for demodulating said spectrum spread demodulated components into differential demodulated components of a reproduction of said transmitter input signal, wherein said output demodulator means comprises:

tracking means for tracking successive regions of a greater correlation value in said spectrum spread demodulated components to produce a timing signal indicative of synchronous points in said regions, respectively; and

differential demodulator means responsive to said timing signal for differential demodulating said spectrum spread demodulated components into said differential demodulated components at each of said synchronous points and at a time which is always one symbol period later than each of said synchronous points

said spectrum spread code includes a predetermined number of chips having a common chip period equal to said symbol period divided by said predetermined number, said timing signal successively indicating primary through ternary periods having an integral submultiple of said chip period in common in each of said regions, wherein said output demodulator means comprises;

data holding means responsive to said timing signal for holding said spectrum spread demodulated components at said primary through said ternary periods as primary through ternary data;

differential demodulation control means responsive to said timing signal for producing a differential demodulation control signal defining a control period lasting said integral submultiple of the chip period immediately following said ternary period; and

differential demodulator means for differential demodulating said primary through said ternary data at a selected one of said primary through said ternary periods that is selected in each of said regions by said differential demodulation control signal.