Adaptive Pilot Allocation in Downlink OFDM

In the downlink of an Orthogonal Frequency Division Multiplexing (OFDM) system, pilot symbols are transmitted across the time-frequency plane for the receiving device to estimate the channel´s response. The density of such pilot is often designed to accommodate the devices under most extreme channel conditions. This worst case scenario design results in unnecessary overhead that could have been used for data transmission otherwise. In this paper, we propose an adaptive pilot allocation scheme that, in addition to a low-rate periodically transmitted pilot symbols, sends device associated pilot adaptively only when called for by the channel condition, thereby reducing the overall pilot overhead. Furthermore, the placement of signaling channel and reduced complexity channel estimator required to facilitate this adaptive operation are also addressed.