Patent ID: 9537702
Date: 2017-01-03
CPC Classifications: H04L

Claim:
1. A method for identifying a channel bandwidth and channel offset of a transmitted orthogonal frequency division multiplexing signal by a receiver having Radio Frequency (RF) bandwidth tuned to 40 MHz, comprising: receiving one or more orthogonal frequency division multiplexing signals, wherein each of the one or more orthogonal frequency division multiplexing signals have an associated center frequency index, a primary channel frequency index and a Physical Layer (PHY) protocol data unit having a training field, a signal field and a data field; identifying a location of a primary channel by comparing the center frequency index with the primary channel frequency index, and if the center frequency index is greater than the primary channel frequency index then the primary channel is located at a lower band or else if the center frequency index is lesser than the primary channel frequency index then the primary channel is located at an upper band; determining a sequence of equalized frequency domain sub-symbols of the signal field in a lower frequency band and a sequence of equalized frequency domain sub-symbols of the signal field in an upper frequency band; computing a cross-correlation between the sequence of equalized frequency domain sub-symbols of the signal field in the lower frequency band and the sequence of equalized frequency domain sub-symbols of the signal field in the upper frequency band; in case, the primary channel is located at the lower band then computing energy of the sequence of equalized frequency domain sub-symbols of the signal field in the lower frequency band; and comparing the cross-correlation between the sequence of equalized frequency domain sub-symbols of the signal field in the lower frequency band and the sequence of equalized frequency domain sub-symbols of the signal field in the upper frequency band with a product of the energy of the sequence of equalized frequency domain sub-symbols of the signal field in the lower frequency band and the predetermined threshold, if the cross-correlation between the sequence of equalized frequency domain sub-symbols of the signal field in the lower frequency band and the sequence of equalized frequency domain sub-symbols of the signal field in the upper frequency band is greater than the product, then the channel offset is identified as a first channel offset mode CH_OFF_40 or a second channel offset mode CH_OFF_40_NON_HT_DUP, else the channel offset is identified as a third channel offset mode CH_OFF_20L; in case, the primary channel is located at the upper band, then computing energy of the sequence of equalized frequency domain sub-symbols of the signal field in the upper frequency band; and comparing the cross-correlation between the sequence of equalized frequency domain sub-symbols of the signal field in the lower frequency band and the sequence of equalized frequency domain sub-symbols of the signal field in the upper frequency band with a product of the energy of the sequence of equalized frequency domain sub-symbols of the signal field in the upper frequency band and the predetermined threshold, if the cross-correlation is greater than the product then the channel offset is identified as the first channel offset mode CH_OFF_40 or the second channel offset mode CH_OFF_40_NON_HT_DUP, else the channel offset is identified as a fourth channel offset mode CH_OFF_20U; and demodulating one or more orthogonal frequency division multiplexing signals based on the identified channel bandwidth and channel offset.