To a telecommunication system using code division multiple access (CDMA)

• US 6,301,289 B1
• Filed: 05/20/1999
• Issued: 10/09/2001
• Est. Priority Date: 03/25/1999
• Status: Expired due to Fees

• Current Assignee: Alcatel SA (Nokia Corporation)
• Original Assignee: Alcatel SA (Nokia Corporation)
• Inventors: Bejjani, Elie, Bouquier, Jean-Francois, de Cacqueray, Benoi ;t
• Primary Examiner(s): Chin, Stephen
• Assistant Examiner(s): Ha, Dac V.
• Application Number:
  US09/315,066
• Time in Patent Office: 873 Days
• Field of Search: 375/144, 375/145, 375/148, 375/149, 375/354, 375/356, 375/358, 455/295, 455/296, 455/304
• US Class Current: 375/144
• CPC Class Codes: H04B 7/2668 Arrangements for Wireless Code-Division Multiple Access [CDMA] System Synchronisation, for code acquisition H04B1/7075, for code tracking H04B1/7085
• CPC Class Codes: H04W 56/0005 synchronizing of arrival of multiple uplinks
• CPC Class Codes: Y02D 30/70 in wireless communication networks

Abstract

The invention relates to a telecommunication method, wherein: terminals communicate through a central station, uplink and downlink communications are coded with a spread spectrum sequence, and terminals have different powers. At the central station, interference cancellation is performed in order to reduce the interfering effect of the highest power signals on the detected lowest power signals. In this method, at least for some of the most powerful interfering signals, groups of symbols (TS₁, TS₃) of different interfering signals are time aligned when they reach the central station. Preferably, the synchronized groups of symbols are synchronously detected at the central station and are processed jointly prior to be subtracted from the signal to be detected.

Claims

1. A telecommunication method, comprising the steps of:

a plurality of terminals communicating through a central station;

coding uplink and downlink communications with a spread spectrum sequence;

performing interference cancellation at the central station on particular signals transmitted from said plurality of terminals with different powers, in order to reduce the interfering effect of the detected highest power signals on the detected lowest power signals; and

controlling the transmission of at least for some of the most powerful interfering signals such that groups of symbols of the different interfering signals are time aligned when they reach the central station.

2. A method according to claim 1, wherein:

the synchronized groups of symbols are synchronously detected at the central station and are processed jointly prior to being subtracted from the signal to be detected.

3. A method according to claim 1, wherein:

the control of time alignment of groups of symbols of different interfering signals is performed from the central station.

4. A method according to claim 1, wherein:

said time alignment of said groups of signals is performed between frames of said interfering signals.

5. A method according to claim 1, wherein:

time alignment of said groups of signals is performed between time slots of said interfering signals.

6. A method according to claim 1, wherein:

time alignment of said groups of signals is performed between integer fractions of time slots of said interfering signals.

7. A method according to claim 1, wherein:

the accuracy of time alignment is of several chip intervals of the spread spectrum sequence.

8. A method according to claim 1, wherein:

the highest power signals have the highest data rates, and the transmission power of said terminals is centrally controlled.

9. A method according to claim 1, wherein said controlling step is performed in response to detected interference at said central station.

10. A central station for a telecommunication system wherein terminals communicate through said central station, the digital data received by the central station and transmitted by said central station being coded by Hadamard and scrambling sequences, and wherein the communications received from the terminals have different powers, and wherein said central station performs interference cancellation in order to subtract the most powerful interference signals from the received least powerful signals, characterized in that said central station comprises control apparatus for controlling transmission by said terminals such that groups of symbols of the most powerful received communications are time aligned at reception by said central station.

11. A central station according to claim 10, wherein the time-aligned signals are jointly detected and processed during interference cancellation.

12. A central station according to claim 10, wherein the highest power signals have the highest data rates, and the transmission power of said terminals is controlled by said central station.

13. A central station according to claim 10, wherein said control apparatus controls transmission by said stations in response to detected interference.

14. A method of reducing interference in a cellular telecommunication system wherein a plurality of terminals located within a cell communicate through a central station by transmitting and receiving signals coded with a spread spectrum sequence, said method comprising the steps of:

detecting at said central station the signals transmitted by said plurality of terminals, the detected signals having different respective powers;

determining at said central station which detected signals are interfering signals; and

controlling the transmission of at least some of the interfering signals in response to said determination such that the interfering signals are coarsely synchronized upon reaching said central station.