Pre-equalization for the up-link of TDD OFDM systems

This paper investigates the possibility of using pre-equalization on the up-link of a time division duplex (TDD) OFDM system. The application of this principle is suggested to enhance the spectral efficiency by omitting the usage of training sequences on the up-link. This is desired in order to enable the efficient transmission of very short data packets, like single ATM cells. The principle proposed also keeps the complexity of synchronization low at the base station, which is accessed by many users. We describe a simple scheme to limit the transmission power on the up-link. The power is kept constant by deleting subcarriers that are severely attenuated due to fading. Parameter estimation steps for retrieving the data at the base-station are explained and evaluated. Those include the estimation of the timing-offset, the carrier phase offset, and the received magnitude. Coherent demodulation is considered.