On application of MUSIC algorithm to time delay estimation in OFDM channels

The time delays of the OFDM paths delimit the size of guard interval in OFDM symbols-important factor for system throughput. In order to apply guard interval as an adaptive parameter like in DRM system, time delays should have been evaluated in real time and in a simple way. Presented software method takes advantage of the information carried out by pilot subcarriers of the OFDM signal. It is shown that pilot subcarriers of OFDM signal in multipath channel are described by equations formally equivalent to equations of Direction-Of-Arrival (DOA) problem in antenna array processing. This analogy leads to application of the MUSIC algorithm of DOA problem to time delay estimation of the individual OFDM paths. Related condition for distribution of pilots within OFDM symbol is given. In case of time delays outside the guard interval the MUSIC algorithm is shown to produce 'shadow' and 'ghost' paths.

I. Introduction

The application of the OFDM modulated signals [1] in broadcasting and communication systems includes now DRM, DAB, DVB-T, HIPERLAN systems and is expected to be basis of future G4 system. Among them the DRM system is the first one where guard interval of the OFDM symbols is treated as an adaptive parameter. Its value is quantized into four ‘robust modes’ dependent on temporary propagation conditions. The value of guard interval is dictated by maximal time delays of different paths of the OFDM signal.