Method And Apparatus To Track Gain Variation In Orthogonal Frequency Division Multiplexing (OFDM) Systems

Abstract

Gain variations during a packet can lead to significant performance degradation in communications systems that use high order quadrature amplitude modulation (QAM). A method and the associated apparatus track such variations in an OFDM system and completely eliminate any performance degradation. Gain estimation and compensation is employed with the use of pilot subcarriers in the payload of an OFDM data packet. Estimated pilot magnitude ratios are averaged, throughout the processing life of a packet, to yield accurate gain estimations. A gain compensation factor is used to adjust data carriers. An exclusion method is also employed to eliminate pilot carriers which contribute to noise.

What is claimed is: 
     
         1 . A method for mid-packet gain compensation of a packet in an orthogonal frequency division multiplexing (OFDM) system comprising:
 establishing an initial magnitude estimate for a packet;   determining a variation in magnitude of the packet over the packet's length, the determining further comprising obtaining a variation over the packet's length of a pilot magnitude ratio estimate for each of a plurality of pilots within a plurality of payload symbols within the packet; and   applying to the packet a gain based on the initial magnitude estimate and the variation in magnitude.