Space-Time Interference Alignment and Degrees of Freedom Regions for the MISO Broadcast Channel with Periodic CSI Feedback
IEEE Transactions on Information Theory(2013)
摘要
This paper characterizes the degrees of freedom (DoF) regions for the multi-user vector broadcast channel with periodic channel state information (CSI) feedback. As a part of the characterization, a new transmission method called space-time interference alignment is proposed, which exploits both the current and past CSI jointly. Using the proposed alignment technique, an inner bound of the sum-DoF region is characterized as a function of a normalized CSI feedback frequency, which measures CSI feedback speed compared to the speed of user's channel variations. One consequence of the result is that the achievable sum-DoF gain is improved significantly when a user sends back both current and outdated CSI compared to the case where the user sends back current CSI only. Then, a trade-off between CSI feedback delay and the sum-DoF gain is characterized for the multi-user vector broadcast channel in terms of a normalized CSI feedback delay that measures CSI obsoleteness compared to channel coherence time. A crucial insight is that it is possible to achieve the optimal DoF gain if the feedback delay is less than a derived fraction of the channel coherence time. This precisely characterizes the intuition that a small delay should be negligible.
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关键词
space-time interference alignment,channel state information,delayed channel state information feedback,broadcast channels,sum-dof region,radiofrequency interference,interference alignment,sum-dof gain,periodic csi feedback,channel coherence time,dof regions,degree-of-freedom regions,normalized csi feedback frequency,multiuser vector broadcast channel,feedback,transmission method,csi feedback delay,vector broadcast channel,channel variations,miso broadcast channel
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