A wireless communication system such as the cellular system illustrated in FIG. 1 typically includes a collection of base stations 100, 102, 104 positioned at known locations in their respective service areas 106, 108, 110 and connected to a common radio access network hub 118. These base stations provide wireless communication services to a set of mobile transceivers such as cellular telephone handsets 112, 114, 116 which may wander throughout service areas 106, 108, 110. Typically, at any given time, a mobile transceiver is served by one or more of the base stations. Wireless signals, such as signal 120, propagating through the environment between a mobile and a base station experience various types of environmental distortions due to noise, interference, attenuation, reflection, refraction, and diffraction. In particular, reflections from scattering objects in the environment results in multipath effects, i.e., the splitting of the original signal into multiple signals following different paths and, consequently, arriving at the receiver with distinct delays, phases, angles-of-arrival and amplitudes. The overall effect of multipath and other signal distortions is described in terms of channel characteristics. FIG. 2 illustrates schematically how a signal sk transmitted from a transmitter 200 as transmitted signal xk is distorted as it propagates through channel 202 characterized by a channel impulse response h. The distorted signal, plus noise nk, is received at a receiver 204 as received signal yk. The task of the receiver is to recover original signal sk from the received signal yk. Normally, however, the noise nk and channel impulse response h are not known a priori, resulting in the problem at the receiver of recovering the original signal. Thus, a well-known challenge of wireless communication systems is to estimate the channel characteristics, and thereby improve the ability of the receiver to accurately recover the original signal.
Known techniques for channel estimation include the use of training symbols and/or blind/joint estimation techniques. In a mobile communications system, however, channel characteristics vary due to changes in the environment and changes in the location of the mobile transceiver. These changes in the channel characteristics make it difficult to obtain up-to-date and accurate estimates of the current channel characteristics, thereby limiting the performance and capacity of the communication system. There is a need, therefore, for improved techniques for channel estimation in wireless communication systems.