Adaptive Pilot Signaling in the Uplink of OFDM- Based Wireless Systems

has been considered as one of key transmission technologies for high-speed wireless communication systems. For channel-adaptive transmission of OFDM signal, base stations transmit a common pilot signal in the downlink, but mobile stations transmit individual pilot signal in the uplink. As a consequence, the uplink may suffer from poorer channel estimation accuracy than the downlink. This problem can be alleviated by increasing the pilot signal density. But this reduces the time and frequency resources for the data transmission, deteriorating the actual transmission throughput. In this paper, we propose an adaptive pilot signaling scheme that adjusts the pilot density in response to the change of channel characteristics. Simulation results show that the proposed scheme can remarkably reduce the pilot overhead without performance degradation, compared to conventional schemes. I