RECEIVER AND METHOD FOR PROCESSING RADIO SIGNALS USING SOFT PILOT SYMBOLS

• US 20120155574A1
• Filed: 02/23/2012
• Published: 06/21/2012
• Est. Priority Date: 06/17/2008
• Status: Active Grant

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Cairns, Douglas, Jonsson, Elias
• Granted Patent: US 8,908,781 B2
• Time in Patent Office: Days
• US Class Current: 375/320
• CPC Class Codes: H04B 2201/70701 featuring pilot assisted reception
• CPC Class Codes: H04B 2201/709727 GRAKE type RAKE receivers
• CPC Class Codes: H04L 1/0017 where the mode-switching is based on Quality of Service requirement
• CPC Class Codes: H04L 1/0041 Arrangements at the transmitter end
• CPC Class Codes: H04L 1/0068 by puncturing
• CPC Class Codes: H04L 2001/0098 Unequal error protection
• CPC Class Codes: H04L 2025/03401 PSK
• CPC Class Codes: H04L 2025/0342 QAM
• CPC Class Codes: H04L 2025/03426 transmission using multiple-input and multiple-output channels
• CPC Class Codes: H04L 2025/03509 fractionally spaced H04L2025/03515 takes precedence
• CPC Class Codes: H04L 2025/03796 Location of reference signals
• CPC Class Codes: H04L 2027/0061 remodulation
• CPC Class Codes: H04L 2027/0093 Intermittant signals
• CPC Class Codes: H04L 25/021 Estimation of channel covariance
• CPC Class Codes: H04L 25/0226 sounding signals per se
• CPC Class Codes: H04L 25/0236 using estimation of the other symbols
• CPC Class Codes: H04L 25/03044 using fractionally spaced delay lines or combinations of fractionally integrally spaced taps
• CPC Class Codes: H04L 25/03324 Provision of tentative decisions
• CPC Class Codes: H04L 25/061 providing hard decisions only; arrangements for tracking or suppressing unwanted low frequency components, e.g. removal of dc offset removal of dc offset in coupling arrangements H04L25/029, H04L25/0296
• CPC Class Codes: H04L 27/0012 arrangements for identifying the type of modulation
• CPC Class Codes: H04L 27/227 : using coherent demodulation
• CPC Class Codes: H04L 27/3455 : in order to facilitate carrier recovery at the receiver end, e.g. by transmitting a pilot or by using additional signal points to allow the detection of rotations
• CPC Class Codes: H04L 27/3818 : using coherent demodulation, i.e. using one or more nominally phase synchronous carriers H04L27/227 and H04L27/389 take precedence

Abstract

A receiver and method for receiving and processing a sequence of transmitted symbols in a digital communication system utilizing soft pilot symbols. A set of soft pilot symbols are transmitted with higher reliability than the remaining symbols in the sequence by modulating the soft pilot symbols with a lower order modulation such as BPSK or QPSK while modulating the remaining symbols with a higher order modulation such as 16 QAM or 64 QAM. The receiver knows the modulation type and location (time/frequency/code) of the soft pilot symbols, and demodulates them first. The receiver uses the demodulated soft pilot symbols as known symbols to estimate parameters of the received radio signal. Unlike traditional fixed pilots, the soft pilots still carry some data. Additionally, the soft pilots are particularly helpful in establishing the amplitude reference essential in demodulating the higher order modulation symbols.

Claims

1. A method in a radio receiver for estimating parameters of a received radio signal that includes a sequence of transmitted symbols, said method comprising the steps of:

demodulating symbols transmitted with higher reliability first to form soft pilot symbols; and

utilizing the soft pilot symbols as known symbols to estimate parameters of the received radio signal.

2. The method as recited in claim 1, wherein the soft pilot symbols have a lower order modulation than a higher order modulation utilized for the remaining symbols in the sequence.

3. The method as recited in claim 2, wherein the step of utilizing the soft pilot symbols as known symbols also includes utilizing the soft pilot symbols as known symbols to demodulate the higher order modulation symbols.

4. The method as recited in claim 3, wherein the pilot symbols are constant envelop modulation symbols, and the step of utilizing the soft pilot symbols as known symbols also includes utilizing the soft pilot symbols to establish an amplitude reference for demodulating the higher order modulation symbols.

5. The method as recited in claim 4, wherein the soft pilot symbols are modulated with Quadrature Phase Shift Keying (QPSK) or Binary Phase Shift Keying (BPSK), and the remaining symbols in the sequence are modulated with 16 Quadrature Amplitude Modulation (16 QAM) or 64 QAM.

6. The method as recited in claim 1, further comprising pre-storing in the receiver, information indicating predefined locations in the sequence for the soft pilot symbols, said locations being defined in terms of time, frequency, and code.

7. The method as recited in claim 6, further comprising pre-storing in the receiver, information indicating a modulation type for the soft pilot symbols.

8. The method as recited in claim 1, further comprising receiving signaling from the transmitter indicating locations in the sequence for the soft pilot symbols, said locations being defined in terms of time, frequency, and code.

9. The method as recited in claim 8, further comprising receiving signaling from the transmitter indicating a modulation type for the soft pilot symbols.

10. The method as recited in claim 1, further comprising extracting data from both the soft pilot symbols and the higher order modulation symbols.

11. A radio receiver for estimating parameters of a received radio signal that includes a sequence of transmitted symbols, said receiver comprising:

means for identifying a set of symbols in the sequence that is transmitted with higher reliability than the remaining symbols in the sequence;

means for demodulating the identified set of symbols first to form soft pilot symbols; and

means for utilizing the soft pilot symbols as known symbols to estimate parameters of the received radio signal.

12. The radio receiver as recited in claim 11, wherein the soft pilot symbols are modulated with Quadrature Phase Shift Keying (QPSK) or Binary Phase Shift Keying (BPSK), and the remaining symbols in the sequence are modulated with 16 Quadrature Amplitude Modulation (16 QAM) or 64 QAM.

13. The radio receiver as recited in claim 12, wherein the pilot symbols are constant envelop modulation symbols, and the means for utilizing the soft pilot symbols as known symbols includes means for utilizing the soft pilot symbols to establish an amplitude reference for demodulating the higher order modulation symbols.

14. The radio receiver as recited in claim 11, further comprising storing means for pre-storing information indicating a modulation type for the soft pilot symbols and predefined locations in the sequence for the soft pilot symbols, said locations being defined in terms of time, frequency, and code.

15. The radio receiver as recited in claim 11, further comprising means for receiving signaling from the transmitter indicating locations in the sequence for the soft pilot symbols, said locations being defined in terms of time, frequency, and code.

16. The radio receiver as recited in claim 11, further comprising means for receiving signaling from a transmitter indicating a modulation type for the soft pilot symbols and predefined locations in the sequence for the soft pilot symbols, said locations being defined in terms of time, frequency, and code.

17. The radio receiver as recited in claim 11, further comprising means for extracting data from both the soft pilot symbols and the higher order modulation symbols.

18. A system for radio communication, comprising:

a transmitter for transmitting a radio signal that includes a sequence of transmitted symbols, said transmitter comprising;

means for inserting a set of soft pilot symbols by low-level puncturing of channel coded bits and replacing with known bit patterns; and

means for modulating the sequence and transmitting the radio signal; and

a radio receiver for receiving and processing the radio signal, said receiver comprising;

means for receiving the radio signal;

means for identifying the set of soft pilot symbols;

means for demodulating the soft pilot symbols first, and

means for utilizing the soft pilot symbols as known symbols to estimate parameters of the received radio signal.