Wireless transmissions such as wireless data transmissions are distorted in transit by the radio channel, i.e., distorted versions of the transmitted signals are typically received at a wireless receiver. Equalization is a term that refers to the measures taken to reduce the distortion effects in a radio channel, and this typically requires estimating the channel or its inverse. The IEEE 802.11a standard for wireless local area networks uses orthogonal frequency division multiplexing (OFDM) and data packets that each include a preamble that provides for channel estimation in a receiver. The preamble contains known symbols, including ten “short” symbols followed by two known “long” symbols. Prior art channel estimation includes averaging the two estimates of the channel obtained from the two consecutive long symbols, and then compensating for the effects of the channel using the average. Noise and other factors reduce the quality of this channel estimate, and such quality reduction lowers the quality of subsequent communication, e.g., the bit error rate (BER) and/or the packet error rate (PER). Other IEEE 802.11 OFDM standards, e.g., IEEE 802.11g are similar to the IEEE 802.11 standard. Thus there is a need for improved channel estimation, and in particular, for improved channel estimation for a receiver that uses OFDM and that conforms to the IEEE 802.11 OFDM standards.
USPTO Backgrounds
USPTO Backgrounds