Receiver and method for processing radio signals using soft pilot symbols

• US 8,908,781 B2
• Filed: 02/23/2012
• Issued: 12/09/2014
• Est. Priority Date: 06/17/2008
• Status: Active Grant

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Cairns, Douglas, Jonsson, Elias
• Primary Examiner(s): PATEL, DHAVAL V
• Application Number:
  US13/403,369
• Publication Number:
  US 20120155574A1
• Time in Patent Office: 1,020 Days
• Field of Search: 375/259, 375/320, 375/340
• US Class Current: 375/259
• 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:

receiving a sequence of unknown data symbols comprising first unknown data symbols modulated with a lower order modulation and second unknown data symbols modulated with a higher order modulation, said lower order modulation having a higher reliability than the higher order modulation;

demodulating the first unknown data symbols first, before demodulating the second unknown data symbols, to form soft pilot symbols; and

utilizing the soft pilot symbols as known symbols to estimate parameters of the received radio signal to facilitate the extraction of data from the soft pilot symbols and the second unknown data symbols.

2. The method as recited in claim 1, 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 second unknown data symbols modulated with the higher order modulation.

3. The method as recited in claim 2, wherein the soft 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 second unknown data symbols modulated with the higher order modulation.

4. The method as recited in claim 3, wherein the soft pilot symbols are modulated with Quadrature Phase Shift Keying (QPSK) or Binary Phase Shift Keying (BPSK), and the second unknown data symbols in the sequence are modulated with 16 Quadrature Amplitude Modulation (16 QAM) or 64 QAM.

5. 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.

6. The method as recited in claim 5, further comprising pre-storing in the receiver, information indicating a modulation type for the soft pilot symbols.

7. 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.

8. The method as recited in claim 7, further comprising receiving signaling from the transmitter indicating a modulation type for the soft pilot symbols.

9. The method as recited in claim 1, further comprising extracting data from both the soft pilot symbols and the second unknown data symbols.

10. A radio receiver for estimating parameters of a received radio signal that includes a sequence of transmitted symbols, said receiver configured to:

receive a sequence of unknown data symbols comprising first unknown data symbols modulated with a lower order modulation and second unknown data symbols modulated with a higher order modulation, said lower order modulation having a higher reliability than the higher order modulation;

demodulate the first unknown data symbols first, before demodulating the second unknown data symbols, to form soft pilot symbols; and

utilize the soft pilot symbols as known symbols to estimate parameters of the received radio signal to facilitate the extraction of data from the soft pilot symbols and the second unknown data symbols.

11. The radio receiver as recited in claim 10, wherein the soft pilot symbols are modulated with Quadrature Phase Shift Keying (QPSK) or Binary Phase Shift Keying (BPSK), and the second unknown data symbols in the sequence are modulated with 16 Quadrature Amplitude Modulation (16 QAM) or 64 QAM.

12. The radio receiver as recited in claim 11, wherein the soft pilot symbols are constant envelop modulation symbols, and the receiver utilizes the soft pilot symbols to establish an amplitude reference for demodulating the second unknown data symbols modulated with the higher order modulation.

13. The radio receiver as recited in claim 10, wherein the receiver is further configured to pre-store 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.

14. The radio receiver as recited in claim 10, wherein the receiver is further configured to receive 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.

15. The radio receiver as recited in claim 10, wherein the receiver is further configured to receive 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.

16. The radio receiver as recited in claim 10, wherein the receiver is further configured to extract data from both the soft pilot symbols and the second unknown data symbols.