Method and system for joint timing recovery and channel estimation for DMT modems

摘要

A method and a system for acquiring data frame timing in a discrete multitone modem system in which an acquisition frame is generated having a first predetermined number of impulse signals. Each impulse signal is spaced in time by 2(P + 1)Ts, such that 1/Ts is a sample transmission rate, and P is a time length in samples of a cyclic prefix that is added to a data frame. The cyclic prefix length P is chosen such that a channel impulse response seen at a receiver effectively spans no more than P + 1 samples when a received signal is sampled at the 1/Ts rate. Data frames are generated subsequent to the acquisition frame. Each data frame includes a cyclic prefix and at least as many data samples as samples of the cyclic prefix. The acquisition and data frames are converted to an analog signal for transmission. The received acquisition frame is sampled and a summation window is advanced one sample at a time through the received acquisition frame. The sampled acquisition frame is summed over each summation window, with each summation window spanning P + 1 samples of the acquisition frame. A maximum summation value is determined as the summation window advances, and a data frame boundary is determined based on the summation window corresponding to the maximum summation value. A channel impulse response is estimated based on the P + 1 samples of the received acquisition frame corresponding to the maximum summation value, and data is coherently detected based on the estimated channel impulse response.