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Method for carrier frequency offset estimation for a high bit rate OFDM WLAN

IP.com Disclosure Number: IPCOM000032568D
Publication Date: 2004-Nov-08
Document File: 7 page(s) / 391K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for carrier frequency offset (CFO) estimation for a high bit rate orthogonal frequency division multiplexing (OFDM) wireless local area network (WLAN). Benefits include improved functionality and improved performance.

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Method for carrier frequency offset estimation for a high bit rate OFDM WLAN

Disclosed is a method for carrier frequency offset (CFO) estimation for a high bit rate orthogonal frequency division multiplexing (OFDM) wireless local area network (WLAN). Benefits include improved functionality and improved performance.

Background

              Carrier frequency offset is one of the serious detriments in OFDM receivers. It is caused by the difference between the transmitter and receiver subcarrier frequencies. CFO results in the performance degradation of the receiver due to the loss of orthogonality among the subcarriers. A precise CFO compensation is required for improved OFDM receiver performance. CFO compensation can be performed in the time domain or in the frequency domain. The performance of the conventional compensation methods is not satisfactory in poor signal-to-noise ratio (SNR) conditions.

 

              In the conventional WLAN protocol, the physical layer convergence protocol (PLCP) preamble contains a short sequence, t1, with repetition for 10 times as t1, t2, …, t10. The t1 to t5 values represent the first short OFDM training symbol. The values t6 to t10 represent the second short OFDM training symbol. The short OFDM training symbol consists of 12 nonzero subcarriers, which are modulated by the elements of the sequence X as follows:

X = √(13/6) {0, 0, 1+j, 0, 0, 0, -1-j, 0, 0, 0, 1+j, 0, 0, 0, -1-j, 0, 0, 0, -1-j, 0, 0, 0, 1+j, 0, 0, 0,                         ß Negative subcarriers

                            0,                                                                                                                                                    ß DC

                        0, 0, 0, -1-j, 0, 0, 0, -1-j, 0, 0, 0, 1+j, 0, 0, 0, 1+j, 0, 0, 0, 1+j, 0, 0, 0, 1+j, 0, 0}                       ß Positive subcarriers

              The modulation results in 12 nonzero subcarriers in a total of 64 subcarriers. The sequence can be used by the receiver for estimating the CFO in the frequency domain.

 

              The received signal with CFO under noiseless conditions is represented as follows:

,                                                                                                   (1)

              The value Xk is a transmitted data symbol. The value Hk is the channel frequency response for the subcarrier k.

              The carrier frequency error normalized to the subcarrier spacing is represented as follows:

.                                                                                                                                        (2)

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