Frequency offset tracking

Details Frequency offset tracking Frequency offset tracking

2005-10-31

2010-02-23

Ahn, Sam K (Department: 2611)

Pulse or digital communications

Systems using alternating or pulsating current

Plural channels for transmission of a single pulse train

Reexamination Certificate

active

07668252

ABSTRACT:
The present invention relates to estimating and correcting for frequency offset errors in wireless receivers, and is particularly but not exclusively related to MIMO WLAN applications. The present invention provides an improved method of tracking receiver frequency offsets in a receiver for MIMO systems. These receiver based frequency offset components are caused by errors or inaccuracies in various receiver sub-systems such as phase lock loops or carrier frequency oscillator error, and sampling clock rate errors. The frequency offsets due to each of a number of receiver sub-systems are estimated by monitoring frequency offsets on a number of channels or subcarriers (such as OFDM pilot channels) on different frequencies. These channel frequency offsets are preferably estimated by detecting the phase rotation between adjacent pilot symbols on each respective channel. They are then weighted according to a quality parameter of the estimates, which corresponds to their accuracy. An example of a quality parameter is the effective SNR of the respective channels, or preferably the error variance of the phase rotation. In an embodiment the quality parameter is or is proportional to ∥Hx∥2. The weighted channel frequency offsets are then used to determine one or more receiver sub-system frequency offset components. For example a least squares line fit analysis can be performed.

REFERENCES:
patent: 7058002 (2006-06-01), Kumagai et al.
patent: 2002/0065047 (2002-05-01), Moose
patent: 2004/0001563 (2004-01-01), Scarpa
patent: 2004/0190637 (2004-09-01), Maltsev et al.
patent: 1 363 435 (2003-11-01), None
Jianhua Liu, et al., “A Mimo System with Backward Compatibility for OFDM Based WLANS”, 4THIEEE Workshop on Signal Processing Advances in Wireless Communications, 2003, pp. 130-134.
V. S. Abhayawardhana, et al., “Residual Frequency Offset Correction for Coherently Modulated OFDM Systems in Wireless Communication”, VTC, 2002, pp. 777-781.
Christian Oberli, et al., “Maximum Likelihood Tracking Algorithms for MIMO-OFDM”, IEEE Communications Society, 2004, pp. 2468-2472.

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