Method of estimating the frequency response of multipath channels

A method of estimating a multipath channel's frequency response in a digital communication system;

• said digital communication system comprising:
• a transmitter, a receiver, and a transmission channel, which could be wired or wireless and may distort a transmitted signal;
• the transmitted signal having the following characteristics:
• a bandwidth and spectral shape known to both the transmitter and the receiver;
• a test sequence embedded within the transmitted signal;
• a content of the test sequence being known in advance by both the transmitter and the receiver;
• a location of the test sequence both in time and frequency being known by both the transmitter and the receiver;
• wherein a transmission channel is a multipath channel, comprising a plurality of channel paths, including a dominant channel path;
• and wherein the method comprises
• at the receiver:
• downconverting the transmitted signal at the receiver to baseband;
• locating and extracting a received version of the test sequence from the transmitted signal;
• executing a signal processing algorithm upon the received version of the test sequence in order to estimate the multipath channel's frequency response;
• the signal processing algorithm comprising the steps of:
• modeling the multipath channel as a series of L multipath components, each having an associated delay and gain factor which are to be estimated;
• calculating an initial rough approximation of the multipath channel's impulse response using the received version of the test sequence;
• iteratively estimating the associated delay and gain factor of each multipath component by:
• a) performing peak detection on absolute values of the approximation of the multipath channel's impulse response to estimate a gain factor and delay of the dominant channel path;
• b) modulating the gain factor and delay of the dominant channel path with a modeling function to obtain an estimate of the effect of the dominant channel path upon the approximation of the multipath channel's impulse response, where the modeling function is determined based upon the bandwidth and spectral shape of the transmitted signal;
• c) subtracting the estimate of the effect of the dominant channel path from the approximation of the multipath channel's impulse response, such that the next largest channel path in terms of gain factor's magnitude becomes the dominant channel path in the remaining approximation of the multipath channel's impulse response;
• d) repeating L−1 times, said delay and gain factor estimation steps a) to c) to obtain associated delays and gain factors of the plurality of channel paths;
• e) iteratively performing steps a) to d) one or more times in order to further refine the estimate of the associated delay and gain factor of each multipath component until a desired level of accuracy is reached;
• and
• f) using the associated delay and gain factors of each multipath component obtained at the last iteration to obtain the frequency response of the multipath channel by applying a discrete Fourier transformation.