Uplink-Downlink Transformation of the Channel Transfer Function for OFDM Systems

Abstract:
In this paper we consider the uplink-downlink transformation of the channel transfer function for a frequency division duplex system in a frequency-selective channel. A directional channel model is used to model the frequency-selective channel. Two uplink-downlink transformation algorithms, based on the directional channel model, are proposed. The first uplink-downlink transformation algorithm, a parametric algorithm, exploits the radio propagation paths. Whereas, the second algorithm, based on the fact that the uplink-downlink transformation problem can be considered as a linear estimation problem, uses the Wiener filter to perform the uplink-downlink transformation. We consider three scenarios for the parametric uplinkdownlink transformation algorithm. For the first scenario, the instantaneous uplink channel transfer function samples are used to perform the uplink-downlink transformation. Whereas, for the second scenario, the present and past estimates of the uplink channel transfer function samples are used for the uplink-downlink transformation. For the third scenario, besides the present and past estimates of the uplink channel transfer function, the estimated but outdated downlink channel transfer function samples are fed back to perform the uplink-downlink transformation. The performance of the proposed algorithms is assessed based on channel measurements carried out in an indoor scenario. It is shown that the proposed algorithms result in a satisfactory performance for different uplink and downlink frequency bandwidths and gap bands.