Wireless communications is often subject to channel fading. Various
statistical models have been proposed to capture the inherent randomness in
fading, and conventional model-based receiver designs rely on accurate
knowledge of this underlying distribution, which, in practice, may be complex
and intractable. In this work, we propose a neural network-based symbol
detection technique for downlink fading channels, which is based on the maximum
a-posteriori probability (MAP) detector. To enable training on a diverse
ensemble of fading realizations, we propose a federated training scheme, in
which multiple users collaborate to jointly learn a universal data-driven
detector, hence the name FedRec. The performance of the resulting receiver is
shown to approach the MAP performance in diverse channel conditions without
requiring knowledge of the fading statistics, while inducing a substantially
reduced communication overhead in its training procedure compared to
centralized training.

本研究提出一种使用神经网络进行符号检测的技术，名为 FedRec，其采用联邦学习的训练方案，可以在不需要了解衰落信道统计信息的情况下，在多样化的信道条件下接近 MAP 检测器的性能，并显著降低了其训练过程中的通信开销。

FedRec: 在衰落信道上进行通用接收机联邦学习

FedRec: Federated Learning of Universal Receivers over Fading Channels

In this paper, we study the power control problem for Over-the-air
computation (AirComp) over fading channels. Our objective is to minimize the
computation error by jointly optimizing the transmit power at the
power-constrained devices and a signal scaling factor (called denoising factor)
at the fusion center (FC). The problem is generally non-convex due to the
coupling of the transmit power over devices and denoising factor at the FC. To
tackle the challenge, we first consider the special case with static channels,
for which we derive the optimal solution in closed form. The optimal power
control exhibits a threshold-based structure. Specifically, for each device, if
the product of the channel quality and power budget, called quality indicator,
exceeds an optimized threshold, this device applies channel-inversion power
control; otherwise, it performs full power transmission. Building on the
results, we proceed to consider the general case with time-varying channels. To
solve the more challenging non-convex power control problem, we use the
Lagrange-duality method via exploiting its "time-sharing" property. The derived
optimal power control exhibits a regularized channel inversion structure, where
the regularization has the function of balancing the tradeoff between the
signal-magnitude alignment and noise suppression. Moreover, for the special
case with only one device being power limited, we show that the optimal power
control for the power-limited device has an interesting channel-inversion
water-filling structure, while those for other devices (with sufficient power
budgets) reduce to channel-inversion power control over all fading states.

该论文研究了在衰落信道上 Over-the-air computation（空中计算）的功率控制问题。通过优化无线设备的发送功率和协作中心的信号缩放因子，实现最小化计算误差的目标。通过推导出闭合形式的最优解，并设计规则化的通道倒置结构，通过平衡信号幅度对齐和噪声抑制之间的权衡，以获得更好的计算性能。

在衰落信道中为无线计算优化功率控制

Optimized Power Control for Over-the-Air Computation in Fading Channels

This paper investigates the maximal achievable rate for a given blocklength
and error probability over quasi-static multiple-input multiple-output (MIMO)
fading channels, with and without channel state information (CSI) at the
transmitter and/or the receiver. The principal finding is that outage capacity,
despite being an asymptotic quantity, is a sharp proxy for the
finite-blocklength fundamental limits of slow-fading channels. Specifically,
the channel dispersion is shown to be zero regardless of whether the fading
realizations are available at both transmitter and receiver, at only one of
them, or at neither of them. These results follow from analytically tractable
converse and achievability bounds. Numerical evaluation of these bounds
verifies that zero dispersion may indeed imply fast convergence to the outage
capacity as the blocklength increases. In the example of a particular $1 \times
2$ single-input multiple-output (SIMO) Rician fading channel, the blocklength
required to achieve $90\%$ of capacity is about an order of magnitude smaller
compared to the blocklength required for an AWGN channel with the same
capacity. For this specific scenario, the coding/decoding schemes adopted in
the LTE-Advanced standard are benchmarked against the finite-blocklength
achievability and converse bounds.

本文探索了在具有和不具有在发射机和 / 或接收机处的信道状态信息（CSI）的情况下，给定块长度和误码率的准静态多输入多输出（MIMO）衰落信道的最大可实现速率。主要发现是，尽管失效容量是一个渐进量，但它是慢衰落信道有限块长度基本极限的尖锐代理。特别是，在分析可行性的边界和实现边界的基础上，显示了通道色散为零，不管衰落实现是否在发射机和接收器上都可用，还是在其中之一或两者都不可用。