Method and apparatus for reducing synchronization code interference in CDMA communications systems

• US 6,665,288 B1
• Filed: 11/08/1999
• Issued: 12/16/2003
• Est. Priority Date: 11/08/1999
• Status: Expired due to Term

• Current Assignee: Unwired Planet LLC (JP Morgan Chase & Co)
• Original Assignee: Ericsson, Inc. (Telefonaktiebolaget LM Ericsson)
• Inventors: Wang, Yi-Pin Eric, Ottosson, Tony
• Primary Examiner(s): Kizou, Hassan
• Assistant Examiner(s): LEVITAN, DMITRY
• Application Number:
  US09/436,788
• Time in Patent Office: 1,499 Days
• Field of Search: 370/277, 370/280, 370/294, 370/320, 370/324, 370/342, 370/350
• US Class Current: 370/342
• CPC Class Codes: H04B 1/7107 Subtractive interference cancellation
• CPC Class Codes: H04B 2201/709709 Methods of preventing interference
• CPC Class Codes: H04W 52/54 Signalisation aspects of the TPC commands, e.g. frame structure

Abstract

In a code division multiple access (CDMA) communications system, a synchronization code is transmitted on a first channel. Information is selectively communicated on a second channel, e.g., a dedicated physical channel, to limit interference attributable to the synchronization code in a signal received over the second channel. In one embodiment, a slot configuration used on the second channel reduces the likelihood of time-coincidence of the synchronization code with information transmitted on the second channel having a higher level of sensitivity to interference, such as transmit power control (TPC) commands or pilot symbols. According to another aspect, interference associated with a synchronization code is canceled from signal received on the second channel to recover information originally transmitted on the second channel. In one embodiment, an estimate of a component of the received signal associated with the synchronization code is generated from the synchronization code and a channel estimate. The estimate of the interference component is canceled from the received signal to generate an interference-canceled version of the received signal, which is then processed to recover information originally transmitted on the second channel.

Claims

1. A method of communicating in a code division multiple access (CDMA) communications system, the method comprising the steps of:

transmitting a synchronization code on a first channel; and

transmitting information of respective levels of sensitivity to interference on a second channel using a slot configuration that reduces the likelihood of time-coincidence of the synchronization code with first information transmitted on the second channel having a higher level of sensitivity to interference in comparison to second information transmitted on the second channel.

2. A method according to claim 1, wherein said step of transmitting information of respective levels of sensitivity to interference on a second channel using a slot configuration that reduces the likelihood of time-coincidence of the synchronization code with first information transmitted on the second channel having a higher level of sensitivity to interference in comparison to second information transmitted on the second channel comprises the step of transmitting on the second channel using a slot boundary offset that is selected to reduce the likelihood of time-coincidence of the synchronization code with the first information.

3. A method according to claim 1, wherein said step of transmitting on the second channel is preceded by the step of selecting the slot configuration from a plurality of possible slot configurations such that the likelihood of time-coincidence of the synchronization code with the first information is minimized.

4. A method according to claim 1, wherein the first information comprises information transmitted on the second channel with less error protection than the second information.

5. A method according to claim 1, wherein the first information comprises at least one of power control information or a pilot symbol.

6. A method according to claim 1, wherein the second channel comprises a dedicated physical channel.

7. A method according to claim 1, wherein the synchronization code comprises at least one of a primary synchronization code (PSC) and a secondary synchronization code (SSC).

8. A method of communicating in a code division multiple access (CDMA) communications system, the method comprising the steps of:

transmitting a synchronization code on a first channel; and

transmitting information on a second channel from a first entity;

receiving a signal including the second channel at a second entity; and

canceling interference associated with the synchronization code from the received signal to recover information originally transmitted on the second channel.

9. A method according to claim 8, wherein the first entity comprises a cellular base station and wherein the second entity comprises a terminal.

10. A method according to claim 8, wherein said step of canceling interference comprises the steps of:

generate an estimate of a component of the received signal associated with the synchronization code based on a channel estimate and knowledge of the synchronization code;

canceling the estimate of the component from the received signal to generate an interference-canceled version of the received signal; and

processing the interference-canceled version of the received signal to recover information originally transmitted on the second channel.

11. A method of communicating in a code division multiple access (CDMA) communications system, the method comprising the steps of:

transmitting a synchronization code on a first channel; and

encoding information according to an error correction code to produce a series of encoded symbols;

transmitting the encoded symbols on a second channel from a first station;

receiving a signal including the second channel at a second entity;

demodulating the received signal to recover a series of received symbols corresponding to the series of encoded symbols;

modifying the series of received symbols to compensate for interference from the synchronization code; and

decoding the modified series of received symbols.

12. A method according to claim 11, wherein said step of decoding is preceded by the step of determining a signal to noise ratio for the received signal, and wherein said step of modifying the series of received symbols based on the determined signal to noise ratio.

13. A code division multiple access (CDMA) communications system, comprising:

a base transceiver station (BTS) operative to transmit a synchronization code on a first channel and to transmit information on a second channel using a slot configuration that reduces the likelihood of time-coincidence of the synchronization code with first information transmitted on the second channel having a higher level of sensitivity to interference in comparison to second information transmitted on the second channel.

14. A system according to claim 13, wherein the BTS is operative to transmit on a second channel using a slot boundary offset that reduces the likelihood of time-coincidence of the synchronization code with the first information.

15. A system according to claim 14, wherein the BTS is operative to transmit on the second channel using a slot configuration selected from a plurality of possible slot configurations to reduce the likelihood of time-coincidence of the synchronization code with the first information.

16. A system according to claim 13, wherein the first information comprises information that is less error-protected than the second information.

17. A system according to claim 13, wherein the information having a higher level of sensitivity to interference comprises at least one of power control information or a pilot symbol.

18. A system according to claim 13, wherein the second channel comprises a dedicated physical channel.

19. A system according to claim 13, wherein the synchronization code comprises at least one of a primary synchronization code (PSC) and a secondary synchronization code (SSC).

20. A code division multiple access (CDMA) terminal, comprising:

a synchronization code interference canceling receiver operative to cancel interference attributable to a synchronization code transmitted on a first channel in a signal received over a second channel, wherein the synchronization code interference canceling receiver comprises;

an RF-to-baseband converter operative to receive a radio frequency (RF) communications signal and operative to produce a baseband signal therefrom; and

a synchronization code interference canceling baseband processor operative to cancel a component of the baseband signal associated with the synchronization code.

21. A terminal according to claim 20, wherein the synchronization code interference canceling baseband processor comprises:

a synchronization code interference signal generator circuit that generates an estimate of a component of the baseband signal associated with the synchronization code based on the synchronization code and a channel estimate;

a summing circuit operative to subtract the estimate of the component from the baseband signal to generate an interference-canceled version of the baseband signal; and

a demodulator operative to demodulate the interference-canceled version of the baseband signal to produce estimates of symbols originally transmitted on the second channel.

22. A terminal according to claim 21, wherein the synchronization code interference canceling receiver further comprises a decoder responsive to the demodulator and operative to modify the estimates of symbols to compensate for interference from the transmitted synchronization code and to decode the modified estimates to recover information.

23. A terminal according to claim 20, wherein the second channel comprises a dedicated physical channel.

24. A terminal according to claim 20, wherein the synchronization code comprises at least one of a primary synchronization code (PSC) and a secondary synchronization code (SSC).

25. A receiver for recovering information from a received signal, comprising:

means for producing a baseband signal from the received signal;

means for generating an estimate of a component of the baseband signal associated with the synchronization code from the synchronization code and a channel estimate of a channel over which the received signal was received;

means, responsive to said means for generating an estimate of a component of the baseband signal associated with the synchronization code, for subtracting the estimate of the component from the baseband signal to generate an interference-canceled version of the baseband signal;

means, responsive to said means for subtracting, for demodulating the interference-canceled version of the baseband signal to produce estimates of symbols originally transmitted on the channel;

means, responsive to said means for demodulating, for modifying the estimates of symbols originally transmitted on the channel to compensate for interference from the synchronization code; and

means, responsive to said means for modifying, for decoding the modified estimates of symbols to recover information.

26. A receiver for recovering information from a received signal, comprising:

means for producing a baseband signal from the received signal;

means for generating an estimate of a component of the baseband signal associated with the synchronization code from the synchronization code and a channel estimate of a channel over which the received signal was received;

means, responsive to said means for generating an estimate of a component of the baseband signal associated with the synchronization code, for subtracting the estimate of the component from the baseband signal to generate an interference-canceled version of the baseband signal;

means, responsive to said means for subtracting, for demodulating the interference-canceled version of the baseband signal to produce estimates of symbols originally transmitted on the channel, wherein the synchronization code comprises at least one of a primary synchronization code (PSC) and a secondary synchronization code (SSC).

27. A receiver according to claim 26, wherein the channel comprises a dedicated physical channel.