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arXiv 0909.4983cs.ITmath.IT
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事件驱动的多天线波束形成最优反馈控制

Event-Driven Optimal Feedback Control for Multi-Antenna Beamforming

Kaibin Huang, Vincent K. N. Lau, Dongku Kim

摘要:

发射波束成形是用于增加无线通信系统的吞吐量和传输范围的简单多天线技术。所需的信道状态信息(CSI)的反馈可能潜在地导致过多的开销,特别是对于高移动性或许多天线。这项工作涉及有效的反馈传输波束形成,并建立了一个新的方法来控制反馈,最大限度地提高净吞吐量,定义为吞吐量减去平均反馈成本。使用固定策略的反馈控制器根据包括信道状态和发射波束形成器的系统状态来开启/关闭CSI反馈。假设通道各向同性和马尔可夫性,控制器的状态减少到两个标量。这允许使用动态规划有效地计算最优控制策略。考虑完美的反馈渠道没有错误,其中每个反馈即时支付固定的价格。证明了相应的最优反馈控制策略是阈值型的。无论控制器的状态空间是离散的还是连续的,这个结果都成立。在阈值型策略下,每当指示发送CSI的准确性的状态变量低于阈值时执行反馈,该阈值随信道功率而变化。还考虑了实际的有限速率反馈信道。量化反馈的最优策略也是阈值型的。CSI量化的效果被证明是相当于一个增量的反馈价格。此外,增量的上界由1减去量化误差的期望对数限定。最后,仿真表明,反馈控制增加了传统的周期性反馈的净吞吐量高达0.5位/秒/赫兹,而不需要额外的带宽或天线。

英文摘要:

Transmit beamforming is a simple multi-antenna technique for increasing throughput and the transmission range of a wireless communication system. The required feedback of channel state information (CSI) can potentially result in excessive overhead especially for high mobility or many antennas. This work concerns efficient feedback for transmit beamforming and establishes a new approach of controlling feedback for maximizing net throughput, defined as throughput minus average feedback cost. The feedback controller using a stationary policy turns CSI feedback on/off according to the system state that comprises the channel state and transmit beamformer. Assuming channel isotropy and Markovity, the controller's state reduces to two scalars. This allows the optimal control policy to be efficiently computed using dynamic programming. Consider the perfect feedback channel free of error, where each feedback instant pays a fixed price. The corresponding optimal feedback control policy is proved to be of the threshold type. This result holds regardless of whether the controller's state space is discretized or continuous. Under the threshold-type policy, feedback is performed whenever a state variable indicating the accuracy of transmit CSI is below a threshold, which varies with channel power. The practical finite-rate feedback channel is also considered. The optimal policy for quantized feedback is proved to be also of the threshold type. The effect of CSI quantization is shown to be equivalent to an increment on the feedback price. Moreover, the increment is upper bounded by the expected logarithm of one minus the quantization error. Finally, simulation shows that feedback control increases net throughput of the conventional periodic feedback by up to 0.5 bit/s/Hz without requiring additional bandwidth or antennas.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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