Code division multiple access mobile communication system

• US 6,456,609 B2
• Filed: 08/07/2001
• Issued: 09/24/2002
• Est. Priority Date: 09/11/1995
• Status: Expired due to Term

• Current Assignee: Hitachi, Ltd.
• Original Assignee: Hitachi, Ltd.
• Inventors: Doi, Nobukazu, Yano, Takashi, Ohgoshi, Yasuo
• Primary Examiner(s): Olms, Douglas
• Assistant Examiner(s): VANDERPUYE, KENNETH N
• Application Number:
  US09/922,803
• Publication Number:
  US 20020003788A1
• Time in Patent Office: 413 Days
• Field of Search: 370/335, 370/320, 370/342, 370/491, 370/206, 370/503, 370/479, 370/350, 370/468, 375/200, 375/206, 375/362, 375/344, 375/130
• US Class Current: 370/335
• CPC Class Codes: H04B 1/707 using direct sequence modulation
• CPC Class Codes: H04B 7/2628 using code-division multiple access [CDMA] or spread spectrum multiple access [SSMA] H04B7/2618 takes precedence

Abstract

A code division multiple access (CDMA) mobile communication system with improvements to permit stable reception with a minimum of bit error. The system comprises a voltage-controlled oscillator for supplying a carrier to a radio frequency quadrature demodulator, and a frequency controller for detecting a frequency error from a phase correction signal of the first step to generate a control signal that controls the oscillator. The frequency controller includes an extracting circuit and an integrating circuit. The extracting circuit extracts a phase change based on the frequency error derived from the phase correction signal of the first step and from a signal preceding that signal by a predetermined delay time. The integrating circuit integrates the phase change and outputs the integrated result as the control signal. The predetermined delay time is preferably set within a range not exceeding the delay time needed for averaging by an averaging circuit that receives the phase correction signal of the first step and outputs a phase correction signal. The carrier to a radio frequency quadrature modulator is preferably supplied from the voltage-controlled oscillator.

Claims

1. A mobile station for use with a mobile communication system multiplexing a plurality of communication channels using spread spectrum codes comprising:

an oscillator;

a radio frequency demodulator demodulating a radio frequency band signal transmitted from a base station by use of a signal from the oscillator; and

a despreading circuit extracting a pilot signal by despreading the demodulated radio frequency band signal using the spread spectrum code assigned to the pilot signal;

wherein an oscillation frequency of the oscillator is controlled by use of a change of a phase shift detected using a signal representing a phase shift detected from the extracted pilot signal.

2. A mobile station according to claim 1, further comprising:

an accumulator converting the extracted pilot signal with a chip rate by the despreading circuit into a pilot signal with a symbol rate;

wherein a phase shift detected from the pilot signal is a phase shift with a symbol rate outputted by the accumulator.

3. A mobile station according to claim 2, wherein the oscillation frequency of the oscillator is controlled by use of the phase shift detected with a symbol rate.

4. A mobile station according to claim 2, wherein the oscillation frequency of the oscillator is controlled by use of an average of the phase shift detected with a symbol rate during a set period.

5. A mobile station according to claim 1, wherein the oscillator is a voltage-controlled oscillator.

6. A base station for use with a mobile communication system multiplexing a plurality of communication channels using spread spectrum codes comprising;

a spreading circuit spreading a pilot signal using the spread spectrum code assigned to the pilot signal;

an oscillator;

a radio frequency modulator modulating the spread pilot signal into a radio frequency band signal by use of an oscillation frequency of the oscillator; and

a radio frequency demodulator demodulating a radio frequency band signal transmitted from a mobile station by use of an oscillation frequency of the oscillator;

wherein the radio frequency band signal transmitted from a mobile station is a signal modulated with a carrier controlled by use of a phase shift detected from the pilot signal.

7. A base station according to claim 6, wherein the phase shift is detected with a symbol rate.

8. A mobile station for use with a mobile communication system multiplexing a plurality of communication channels using spread spectrum codes comprising:

an oscillator;

a radio frequency demodulator demodulating a radio frequency band signal transmitted from a base station by use of a signal form the oscillator;

a first despreading circuit extracting a data signal by despreading the demodulated radio frequency band signal using the spread spectrum code assigned to the data signal;

a second despreading circuit extracting a pilot signal by despreading the demodulated radio frequency band signal using the spread spectrum code assigned to the pilot signal; and

a phase correction circuit performing phase correction for the data signal by use of a phase shift detected from the extracted pilot signal;

wherein an oscillation frequency of the oscillator is controlled by use of a signal representing the phase shift.

9. A mobile station according to claim 8, further comprising:

an accumulator converting the extracted pilot signal with a chip rate by the second despreading circuit into a pilot signal with a symbol rate;

wherein a phase shift detected from the pilot signal is a phase shift with a symbol rate outputted by the accumulator.

10. A mobile station according to claim 9, further comprising:

an averaging circuit averaging the phase shift with a symbol rate during a first period;

wherein the phase correction circuit performs phase correction for the data signal by use of the averaged phase shift.

11. A mobile station according to claim 9, wherein the oscillation frequency of the oscillator is controlled by use of the phase of the phase shift detected with a symbol rate.

12. A mobile station according to claim 10, wherein the oscillation frequency of the oscillator is controlled by use of an average of the phase of the phase shift detected with a symbol rate during a second period that does not exceed the first period.

13. A mobile station according to claim 8, wherein the oscillator is a voltage-controlled oscillator.