Capacity and optimal resource allocation for fading broadcast channels .I. Ergodic capacity

TLDR

Dynamic resource allocation between users and over time significantly improves efficiency and performance in multiuser wireless systems. This paper investigates three capacity regions for fading broadcast channels—ergodic, zero‑outage, and outage with nonzero outage—and derives optimal resource allocation strategies, while also proposing a simple suboptimal policy for TD and CD without successive decoding. The authors derive the ergodic capacity region for an M‑user fading broadcast channel under CD, TD, and FD with perfect channel side information, and formulate optimal allocation policies, including a suboptimal scheme for TD and CD without successive decoding. Dynamic allocation yields identical ergodic capacity regions for TD, FD, and CD without successive decoding, whereas optimal CD achieves a larger region; the derived allocation policies are validated by numerical results across various fading broadcast channels.

Abstract

In multiuser wireless systems, dynamic resource allocation between users and over time significantly improves efficiency and performance. In this two-part paper, we study three types of capacity regions for fading broadcast channels and obtain their corresponding optimal resource allocation strategies: the ergodic (Shannon) capacity region, the zero-outage capacity region, and the outage capacity region with nonzero outage. We derive the ergodic capacity region of an M-user fading broadcast channel for code division (CD), time division (TD), and frequency division (FD), assuming that both the transmitter and the receivers have perfect channel side information (CSI). It is shown that by allowing dynamic resource allocation, TD, FD, and CD without successive decoding have the same ergodic capacity region, while optimal CD has a larger region. Optimal resource allocation policies are obtained for these different spectrum-sharing techniques. A simple suboptimal policy is also proposed for TD and CD without successive decoding that results in a rate region quite close to the ergodic capacity region. Numerical results are provided for different fading broadcast channels.