马尔可夫衰落信道下的渐近最优导频分配
Asymptotically optimal pilot allocation over Markovian fading channels
摘要：
研究了马尔可夫衰落信道下无线网络中的导频分配问题。在无线系统中，信道状态信息（CSI）是在基站（BS）处收集的，特别地，本文考虑了一种导频辅助的信道估计方法（TDD模式）。通常，可用的导频比用户少，因此在每个时隙，调度器需要以最大化长期平均吞吐量为目标来决定向用户分配导频。在如何使用有限的导频方面存在固有的权衡：将导频分配给具有最新CSI和良好信道条件的用户以供利用，或者将导频分配给具有过时CSI的用户以供探索。正如我们所示，所产生的导频分配问题是一个不安分的强盗问题，因此其最优解是遥不可及的。在本文中，我们提出了一个近似，通过拉格朗日松弛方法，提供了一个低复杂性的启发式，惠特尔指数政策。我们证明了这一政策是渐近最优的许多用户制度（当系统中的用户数量和可用的导频信道感测增长大）。我们评估的性能惠特尔的指数政策在各种情况下，并说明其显着良好的性能。
英文摘要：
We investigate a pilot allocation problem in wireless networks over Markovian fading channels. In wireless systems, the Channel State Information (CSI) is collected at the Base Station (BS), in particular, this paper considers a pilot-aided channel estimation method (TDD mode). Typically, there are less available pilots than users, hence at each slot the scheduler needs to decide an allocation of pilots to users with the goal of maximizing the long-term average throughput. There is an inherent tradeoff in how the limited pilots are used: assign a pilot to a user with up-to-date CSI and good channel condition for exploitation, or assign a pilot to a user with outdated CSI for exploration. As we show, the arising pilot allocation problem is a restless bandit problem and thus its optimal solution is out of reach. In this paper, we propose an approximation that, through the Lagrangian relaxation approach, provides a low-complexity heuristic, the Whittle index policy. We prove this policy to be asymptotically optimal in the many users regime (when the number of users in the system and the available pilots for channel sensing grow large). We evaluate the performance of Whittle's index policy in various scenarios and illustrate its remarkably good performance.
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