Space-Time Interference Alignment and Degree-of-Freedom Regions for the MISO Broadcast Channel With Periodic CSI Feedback

作者：Lee Namyoon^*; Heath Robert W Jr

来源：IEEE Transactions on Information Theory, 2014, 60(1): 515-528.

DOI：10.1109/TIT.2013.2285216

• Delayed channel state information feedback
• interference alignment
• vector broadcast channel

This paper characterizes the degree-of-freedom (DoF) regions for the multiuser 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of the result is that the achievable sum-DoF gain is improved significantly when a user sends back both current and outdated CSI compared to the case where the user sends back current CSI only.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 tradeoff between CSI feedback delay and the sum-DoF gain is characterized for the multiuser 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.

• 出版日期2014-1