Broadcast Channels with Delayed Finite-Rate Feedback: Predict or Observe?

Most multiuser precoding techniques require accurate transmitter channel state information (CSIT) to maintain orthogonality between the users. Such techniques have proven quite fragile in time-varying channels because the CSIT is inherently imperfect due to estimation and feedback delay, as well quantization noise. An alternative approach recently proposed by Maddah-Ali and Tse (MAT) allows for significant multiplexing gain in the multi-input single-output (MISO) broadcast channel (BC) even with transmit CSIT that is completely stale, i.e. uncorrelated with the current channel state. With K users, their scheme claims to lose only a log(K) factor relative to the full K degrees of freedom (DoF) attainable in the MISO BC with perfect CSIT for large K. However, their result does not consider the cost of the feedback, which is potentially very large in high mobility (short channel coherence time). In this paper, we more closely examine the MAT scheme and compare its DoF gain to single use...

• Type: Journal
• Year: 2011
• Where: CORR
• Authors: Jiaming Xu, Jeffrey G. Andrews, Syed Ali Jafar
• Keywords: Channel Coherence Time, Coherence Times, CORR 2011, Education, Single User Transmission