Uplink–downlink duality with regard to constraints imposed in practice

The uplink–downlink duality is reviewed with regard to constraints imposed on the transmission schemes in practice. In particular, the effects of non-Gaussian signaling, the use of implementable precoding schemes, and the availability of only imperfect channel state information at the central base-station are analyzed and discussed. The sources for violating the uplink–downlink duality in practical schemes are identified, and it is shown under which setting still the same (but not optimum) performance of both transmission directions can be achieved. Besides treating signal-to-interference plus noise ratios, as usually done, the duality is studied with respect to bit error rate, a parameter more relevant in practical applications.