Apparatus and Method for Tracking Symbol Timing of OFDM Modulation in a Multi-Path Channel

• US 20100239053A1
• Filed: 06/04/2010
• Published: 09/23/2010
• Est. Priority Date: 09/07/2005
• Status: Active Grant

• Current Assignee: CSR Technology Incorporated (Qualcomm, Inc.)
• Original Assignee: CSR Technology Incorporated (Qualcomm, Inc.)
• Inventors: Cahn, Charles Robert, Ananth, Sharath
• Granted Patent: US 8,290,075 B2
• Time in Patent Office: Days
• US Class Current: 375/342
• CPC Class Codes: H04L 27/2662 Symbol synchronisation
• CPC Class Codes: H04L 27/2676 Blind, i.e. without using known symbols
• CPC Class Codes: H04L 27/2678 using cyclostationarities, e.g. cyclic prefix or postfix
• CPC Class Codes: H04L 27/2688 Resistance to perturbation, e.g. noise, interference or fading

Abstract

Methods and Systems for tracking symbol timing of an OFDM signal are disclosed. In one embodiment, a wireless receiver includes signal tracking and timing logic to facilitate the timing of a demodulation operation such that the demodulation operation occurs on the proper symbol boundary, particularly when the OFDM signal has multipath components and the second component has greater power than the first.

Claims

1. A wireless signal receiver to demodulate an OFDM signal with our without multipath components, said receiver comprising:

power monitoring logic to determine the average power in a predetermined number of samples from the OFDM signal; and

edge detection logic to detect rising edges of average power measured, wherein each rising edge determines the location of a multipath component, and the location of the first rising edge indicates the first received multipath component which is used to control the timing of a Fourier Transformation operation by Fast Fourier Transform (FFT) logic.

2. The wireless signal receiver of claim 1 further comprising firmware to determine the predetermined number of samples from the OFDM signal to evaluate.

3. The wireless signal receiver of claim 1, wherein each change in average energy level in a null carrier represents effects of inter-symbol interference (ISI) due to different multipath components.

4. The wireless signal receiver of claim 1, wherein the power monitoring logic includes a sliding DFT logic to perform a sliding DFT operation on the predetermined number of samples.

5. In a wireless signal receiver, a method of tracking symbol timing in a received signal having multipath components, comprising:

monitoring the power within a null carrier portion of the received signal to detect a first increase in power caused by a time delayed null carrier of a multipath component; and

driving a Fast Fourier Transorm (FFT) operation on the signal based on the detection of the first increase in power.

6. The method of claim 5 wherein the first increase in power caused by the time delayed null carrier of a multipath component creates ISI in the null carrier portion of the received signal.

7. The method of claim 5 wherein the first increase in power is identified by locating the first positive edge occurring after a negative edge in a waveform representing the power within a null carrier portion of the received signal.

8. The method of claim 5 wherein a Sliding DFT is used to efficiently monitor the power in every individual null carrier of interest over every input sample.