Communication device and method for interference suppression using adaptive equalization in a spread spectrum communication system

• US 6,175,588 B1
• Filed: 12/30/1997
• Issued: 01/16/2001
• Est. Priority Date: 12/30/1997
• Status: Expired due to Term

• Current Assignee: Google Technology Holdings LLC (Alphabet Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Singh, Rahul, Visotsky, Yevgeny, Frank, Colin D., Madhow, Upamanyu
• Primary Examiner(s): Ghebretinsae, Temesghen
• Application Number:
  US09/001,248
• Time in Patent Office: 1,113 Days
• Field of Search: 375/130, 375/147, 375/232, 375/324, 375/148, 375/346
• US Class Current: 375/148
• CPC Class Codes: H04B 1/707 using direct sequence modulation
• CPC Class Codes: H04L 2025/03375 Passband transmission
• CPC Class Codes: H04L 2025/03477 not time-recursive
• CPC Class Codes: H04L 25/03038 with a non-recursive structure H04L25/03031 takes precedence

Abstract

A communication device such as a mobile station (410) for a spread spectrum communication system includes a receiver (100) having an adaptive equalizer (104) which suppresses interference on a received spread spectrum signal to produce an equalized signal (126). A pilot channel demodulator (110) demodulates the equalized signal to produce an estimate of the pilot channel (140). A summer (112) compares the pilot channel estimate and a predetermined data pattern to produce an error signal (124). A traffic channel demodulator (108) demodulates the equalized signal to produce one or more traffic channels.

Claims

1. A communication device for receiving a spread spectrum signal which includes a pilot channel and traffic channels, the pilot channel substantially orthogonal to each of the traffic channels, the communication device comprising:

an adaptive equalizer which adapts using the pilot channel, the adaptive equalizer receiving the spread spectrum signal and producing an equalized signal;

a demodulator for demodulating the equalized signal to produce a demodulated traffic channel;

a pilot channel demodulator which produces a pilot channel estimate; and

a comparator for generating an error signal in response to the pilot channel estimate, the adaptive equalizer adapting in response to the error signal.

2. A communication device as recited in claim 1 further comprising a despreader coupled to the adaptive equalizer for despreading the equalized signal in response to a predetermined spreading sequence.

3. A communication device for receiving a spread spectrum signal which includes a pilot channel and traffic channels. the communication device comprising:

an adaptive equalizer which adapts using the pilot channel, the adaptive equalizer receiving the spread spectrum signal and producing an equalized signal; and

a demodulator for demodulating the equalized signal to produce a demodulated traffic channel

wherein, when a plurality of traffic channels are assigned for communication to the communication device, the adaptive equalizer produces the equalized signal for each of the plurality of traffic channels and the demodulator selectively demodulates each of the plurality of traffic channels.

4. A communication device as recited in claim 3 wherein the demodulator comprises a despreader which despreads the equalized signal in response to a predetermined spreading sequence selected from a plurality of sequences corresponding to the plurality of traffic channels.

5. A communication device for receiving a spread spectrum signal which includes a pilot channel and traffic channels, the pilot channel and the traffic channels covered using a Hadamard code before transmission so as to be substantially mutually orthogonal, the communication device comprising:

a minimum mean-square error (MMSE) equalizer which adapts using the pilot channel, the MMSE equalizer receiving the spread spectrum signal and producing an equalized signal, the MMSE equalizer operable to adapt to minimize a mean square error of the equalized signal, the MMSE equalizer substantially the same for all traffic channels for a given channel condition; and

a demodulator for demodulating the equalized signal to produce a demodulated traffic channel.

6. A communication device as recited in claim 5 wherein, for transmission of data at high rates, a plurality of traffic channels are assigned to the communication device and wherein the MMSE equalizer is substantially the same for demodulation of all channels by the demodulator.

7. A spread spectrum communication system comprising:

a plurality of stationary transmitters which transmit respective spread spectrum signals including two or more signals, a first signal being substantially orthogonal to a second signal, wherein each stationary transmitter transmits a pilot channel and substantially orthogonal traffic channels;

a receiver which receives spread spectrum signals, the receiver including

an adaptive equalizer which adapts using the first signal, and

a demodulator for demodulating the second signal; and

a plurality of mobile receivers including the receiver, the receiver producing an error signal in response to the pilot channel, the adaptive equalizer adapting using the error signal to produce an equalized signal.

8. A spread spectrum communication system as recited in claim 7 wherein each mobile receiver is assigned a predetermined spreading sequence for detecting a traffic channel and wherein the demodulator comprises a despreader for despreading the equalized signal in response to the predetermined spreading sequence.

9. A spread spectrum communication system as recited in claim 8 wherein the receiver further comprises a plurality of adaptive equalizers and an associated plurality of despeaders which are assignable to individual spread spectrum signals transmitted by different transmitters for handing off communication between one transmitter and another transmitter.

10. A receiver for receiving a spread spectrum signal, the spread spectrum signal including a pilot channel and a plurality of traffic channels, all channels being substantially orthogonal, the receiver comprising:

an adaptive equalizer for receiving the spread spectrum signal and an error signal, the adaptive equalizer suppressing interference on the spread spectrum signal to produce an equalized signal;

a traffic channel demodulator for demodulating the equalized signal and producing one or more traffic channels;

a pilot channel demodulator for demodulating the equalized signal to produce a pilot channel estimate; and

an error signal generator for producing the error signal in response to the pilot channel estimate.

11. A receiver as recited in claim 10 wherein the pilot channel comprises a predetermined data sequence and wherein the error signal generator comprises a comparator which compares the pilot channel estimate and the predetermined data sequence to produce the error signal.

12. A receiver as recited in claim 11 wherein the predetermined data sequence comprises an unchanging sequence of data.

13. A receiver as recited in claim 10 wherein the adaptive equalizer adapts independently of the one or more traffic channels being demodulated.

14. A receiver as recited in claim 13 wherein the adaptive equalizer is substantially the same for each of the plurality of traffic channels for a given channel condition.

15. A receiver as recited in claim 13 wherein the adaptive equalizer adapts using the pilot channel to yield a solution which is independent of the plurality of traffic channels.

16. A communication device for a spread spectrum communication system including a plurality of remote transceivers, the communication device comprising:

a first receiver circuit, including;

a first adaptive equalizer for receiving first spread spectrum signals from a first base transmitter, suppressing interference and producing a first equalized signal in response to a first error signal,

a first demodulator for demodulating the first equalized signal to produce traffic signals, and

a first pilot channel estimator for producing a first pilot channel estimate for the first spread spectrum signals;

a second receiver circuit, including;

a second adaptive equalizer for receiving second spread spectrum signals from a second base transmitter, suppressing interference and producing a second equalized signal in response to a second error signal,

a second demodulator for demodulating the second equalized signal to produce traffic signals, and

a second pilot channel estimator for producing a second pilot channel estimate for the second spread spectrum signals; and

an error signal generator which produces the first error signal and the second error signal in response to the first pilot channel estimate and the second pilot channel estimate.

17. A communication device as recited in claim 16 wherein the error signal generator comprises:

a combiner for combining the first pilot channel estimate and the second pilot channel estimate to form a combined estimate; and

a comparator for comparing the combined estimate with a predetermined data sequence and producing the first error signal and the second error signal.

18. A communication device as recited in claim 17 wherein the first error signal and the second error signal are the same error signal.

19. A communication device as recited in claim 16 wherein the error signal generator comprises:

a first comparator for comparing the first pilot channel estimate with a first predetermined data pattern and producing the first error signal; and

a second comparator for comparing the second pilot channel estimate with a second predetermined data pattern and producing the second error signal.

20. A method for controlling soft handoff in a spread spectrum communication system, the method comprising the steps of:

receiving first spread spectrum signals from a first remote transmitter;

receiving second spread spectrum signals from a second remote transmitter;

producing an error signal in response to at least one of the first spread spectrum signals and the second spread spectrum signals;

adaptively equalizing the first spread spectrum signals and the second spread spectrum signals in response to the error signal to produce a first equalized signal and a second equalized signal;

demodulating a first traffic channel from the first equalized signal;

demodulating a second traffic channel from the second equalized signal; and

combining the first traffic channel and the second traffic channel as received data.

21. A method as recited in claim 20 further comprising the steps of:

detecting a plurality of spread spectrum signals, including the first spread spectrum signals and the second spread spectrum signals, transmitted by respective transceivers;

selecting the first spread spectrum signals and the second spread spectrum signals as signals for soft handoff; and

assigning a first adaptive equalizer to the first spread spectrum signal and a second adaptive equalizer to the second spread spectrum signal.

22. A method as recited in claim 21 further comprising the steps of:

providing a plurality of adaptive equalizers;

initiating soft handoff with a plurality of sectors greater in number than the plurality of adaptive equalizers;

selecting sectors having best signal quality and entering soft handoff with those sectors; and

assigning adaptive equalizers to those sectors.

23. A method as recited in claim 22 wherein the method further comprises the steps of:

when a signal quality estimate of a sector in soft handoff with no assigned adaptive equalizer exceeds a signal quality estimate of a sector which has been assigned an adaptive equalizer, reassigning the adaptive equalizer to the sector with no assigned adaptive equalizer.

24. A method as recited in claim 20 wherein adaptively equalizing comprises the steps of:

adapting a first equalizer in response to a first error signal, equalizing the first spread spectrum signals; and

adapting a second equalizer in response to a second error signal, equalizing the second spread spectrum signals.

25. A method as recited in claim 20 wherein producing an error signal comprises the steps of:

producing a first pilot signal estimate in response to the first equalized signal and a second pilot signal estimate in response to the second equalized signal;

combining the first pilot signal estimate and the second pilot signal estimate, producing a combined signal; and

comparing the combined signal and a predetermined data sequence, producing the error signal.

26. A method for receiving radio frequency (RF) signals at a receiver, the method comprising the steps of:

in an adaptive equalizer, equalizing the RF signals, producing an equalized signal;

demodulating the equalized signal, producing demodulated data;

producing an error signal by comparing a pilot channel of the equalized signal with a predetermined data sequence; and

adapting the adaptive equalizer in response to the error signal.

27. A method as recited in claim 26 further comprising the steps of:

producing an estimate of signal to noise ratio (SNR) for the RF signals; and

scaling the demodulated data in response to the estimate of SNR.

28. A method as recited in claim 27 further comprising the steps of decoding the scaled demodulated data according to a maximum likelihood coding algorithm.

29. A method as recited in claim 26 further comprising the steps of:

receiving pilot symbols during first time intervals;

receiving data symbols during second time intervals interspersed with the first time intervals; and

adapting the adaptive equalizer only during the first time intervals.

30. A method as recited in claim 29 further comprising the step of providing the demodulated data only during the second time intervals.

31. A method as recited in claim 26 further comprising the steps of:

receiving pilot symbols during first time intervals;

receiving data symbols during second time intervals interspersed with the first time intervals;

adapting the adaptive equalizer during the first time intervals, producing a first equalized signal;

interpolating an interpolated equalizer during the second time intervals using coefficients from the adaptive equalizer, producing a second equalized signal.

32. A method as recited in claim 31 further comprising the steps of:

producing the error signal in response to the first equalized signal; and

demodulating the second equalized signal to produce the demodulated data.

33. A method as recited in claim 26 further comprising the steps of:

detecting a pilot channel and one or more synchronization channels of the RF signals; and

producing the error signal in response to the pilot channel and the one or more synchronization channels.