双向中继载波频偏估计：最优前导码和估计器设计
Carrier Frequency Offset Estimation for Two-Way Relaying: Optimal Preamble and Estimator Design
摘要：
研究了基于放大转发协议的双向中继系统的载波频偏估计问题。我们的贡献是在设计一个最佳的前同步码，和相应的估计，密切实现最小的Cramer-Rao界（CRB）CFO。这种最优性是断言相对于新的类的块旋转的块旋转的块（BRP）。这类包括在实践中广泛使用的周期性前导，但它通过块旋转角度提供了额外的设计自由度。我们首先确定灾难性的情况下，任意大的CRB时，使用常规的周期性前导码。接下来，我们通过使用具有非零块旋转角度的BRP来解决这个问题。实际上，该角度创建了将期望的中继信号与AF协议中引入的自干扰分离的人工频率偏移。通过适当的优化，CRB在实际信道条件下只会产生来自单向中继的边际损耗。为了便于实施，一个特定的低复杂度类的估计量进行检查，并建立条件的估计，以实现优化的CRB。数值结果与理论研究结果相印证。
英文摘要：
We consider the problem of carrier frequency offset (CFO) estimation for a two-way relaying system based on the amplify-and-forward (AF) protocol. Our contributions are in designing an optimal preamble, and the corresponding estimator, to closely achieve the minimum Cramer-Rao bound (CRB) for the CFO. This optimality is asserted with respect to the novel class of preambles, referred to as the block-rotated preambles (BRPs). This class includes the periodic preamble that is used widely in practice, yet it provides an additional degree of design freedom via a block rotation angle. We first identify the catastrophic scenario of an arbitrarily large CRB when a conventional periodic preamble is used. We next resolve this problem by using a BRP with a non-zero block rotation angle. This angle creates, in effect, an artificial frequency offset that separates the desired relayed signal from the self-interference that is introduced in the AF protocol. With appropriate optimization, the CRB incurs only marginal loss from one-way relaying under practical channel conditions. To facilitate implementation, a specific low-complexity class of estimators is examined, and conditions for the estimators to achieve the optimized CRB is established. Numerical results are given which corroborate with theoretical findings.
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