Interferer detection and channel estimation for wireless communications networks

• US 7,218,894 B2
• Filed: 12/17/2003
• Issued: 05/15/2007
• Est. Priority Date: 05/09/2003
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Onggosanusi, Eko N., Dabak, Anand G., Schmidl, Timothy M.
• Primary Examiner(s): Nguyen; Lee
• Application Number:
  US10/738,508
• Publication Number:
  US 20040224636A1
• Time in Patent Office: 1,245 Days
• Field of Search: 455/67.11, 455/63.1, 375/341, 375/346, 375/348, 375/349
• US Class Current: 455/67.11
• CPC Class Codes: H04L 25/0228 with direct estimation from sounding signals
• CPC Class Codes: H04L 25/0244 with inversion
• CPC Class Codes: H04L 25/03006 Arrangements for removing intersymbol interference

Abstract

System and method for improving performance of digital wireless communications systems in the presence of interferers. A preferred embodiment comprises generating a list of hypotheses from a list of known interferers and timing offsets, receiving a signal transmitted over-the-air, computing an error variance for each hypothesis, and selecting the hypothesis with the lowest error variance. The hypothesis can then be used to extract data from the received signal.

Claims

1. A method for detecting interferers comprising:

generating a list of hypotheses;

receiving a signal transmitted over-the-air;

computing an error variance for each hypothesis in the list using the received signal; and

selecting the hypothesis with the lowest error variance, wherein the hypothesis contains timing offset information about interferers present in the received signal.

2. The method of claim 1, wherein a hypothesis contains information about a desired signal and any expected interferers.

3. The method of claim 2, wherein one hypothesis contains only information about the desired signal.

4. The method of claim 2, wherein the information includes a training sequence code.

5. The method of claim 1 wherein a joint least squares technique can be used to compute the error variance.

6. The method of claim 5, wherein a sum of the squared errors for a single signal can be expressed as:

E=∥

r−

S(S^HS)<sup>−

1</sup>S^Hr∥

²,

wherein I is the identity matrix, S is a circulant matrix formed from a data sequence used by the desired signal and is expressible as

$S=\left[\begin{array}{cccc}{S}_P& S_{P-1}& \mathrm{\cdots <br><br>}& S_{P-L+1}\\ S_{P+1}& S_P& \mathrm{\cdots <br><br>}& S_{P-L+2}\\ \mathrm{⋮<br><br>}& \mathrm{⋮<br><br>}& & \mathrm{⋮<br><br>}\\ S_{P+M-1}& S_{P+M-2}& \mathrm{\cdots <br><br>}& S_{P+M-L}\end{array}\right],$

S^H is a Hermitian matrix operation on S, and r is a received signal.

7. The method of claim 6, wherein (S_J^JS_H)⁻

1 can be precomputed.

8. The method of claim 1 further comprising after the selecting, using a channel estimate for the selected hypothesis to recover data from the received signal.

9. The method of claim 1, wherein the method can be turned off if no interferers are detected.

10. The method of claim 9, wherein the presence of interferers can be detected via the use of a normality test.

11. The method of claim 1, wherein the method can be used in a wireless communications system, the method further comprising before the generating:

determining an operating mode of the wireless communications system; and

stopping the method if the wireless communications system is operating in an asynchronous mode.

12. The method of claim 11, wherein a serving carrier is a carrier communicating with a device, and wherein the determining comprises:

obtaining a list of carriers detectable by the device;

determining that the wireless communications system is operating in a synchronous mode if a range of timing offsets for the carriers in the list is within a few symbols of the serving carrier; and

determining that the wireless communications system is operating in an asynchronous mode if the range of timing offsets for the carriers in the list is widely varying.

13. A method for detecting interferers comprising:

generating a list of hypotheses;

receiving a signal transmitted over-the-air;

computing an error variance for each hypothesis in the list using the received signal, wherein the error variance for the hypotheses can be scaled to place different weights on different hypotheses; and

selecting the hypothesis with the lowest error variance, wherein the hypothesis contains information about interferers present in the received signal.

14. A circuit comprising:

a hypothesis generator, the hypothesis generator containing circuitry to generate a list of hypotheses based upon known sources of interference and timing offsets; and

a channel estimator coupled to a signal input and the hypothesis generator, the channel estimator containing circuitry to compute an error variance for each hypothesis from the list of hypotheses with a received signal from the signal input.

15. The circuit of claim 14, further comprising a radio frequency circuit coupled to the signal input, the radio frequency circuit containing circuitry to filter and amplify a signal received over-the-air.

16. The circuit of claim 14, wherein the channel estimator further contains circuitry to compute a channel estimate for each hypothesis from the list of hypotheses.

17. The circuit of claim 14, wherein the channel estimator further contains circuitry to select a hypothesis resulting in a smallest error variance.

18. The circuit of claim 17, wherein the channel estimator contains circuitry to compute a channel estimate for each hypothesis from the list of hypotheses, and the circuit further comprising an equalizer coupled to the signal input and the channel estimator, the equalizer containing circuitry to recover transmitted data from the received signal using the channel estimate provided by the channel estimator.

19. A receiver comprising:

a radio frequency circuit coupled to a signal input, the radio frequency circuit containing circuitry to filter and amplify a signal provided by the signal input;

a hypothesis generator, the hypothesis generator containing circuitry to generate a list of hypotheses based upon known sources of interference and timing offsets; and

a channel estimator coupled to the radio frequency circuit and the hypothesis generator, the channel estimator containing circuitry to compute an error variance for each hypothesis from the list of hypotheses with a received signal from the signal input.

20. The receiver of claim 19, wherein the channel estimator contains circuitry to compute a channel estimate for each hypothesis from the list of hypotheses, and the circuit further comprising an equalizer coupled to the signal input and the channel estimator, the equalizer containing circuitry to recover transmitted data from the received signal using the channel estimate provided by the channel estimator.

21. The receiver of claim 19, wherein the receiver is part of a synchronous wireless communications system using a fixed set of training sequences for transmitting information.

22. The receiver of claim 21, wherein the synchronous wireless communications system is GSM compliant.