On Capacity Under Receive and Spatial Spectrum-Sharing Constraints

TLDR

Capacity is traditionally studied under input‑signal constraints, but recent spectrum‑sharing questions motivate examining output‑based constraints when independent networks occupy the same band spatially disjointly. The study investigates capacity when output‑signal constraints are imposed, posing and partially answering the resulting capacity question. Coexistence is enabled by imposing spatial interference‑power restrictions at the network level instead of device level. While point‑to‑point capacity remains essentially unchanged, output‑constraint scenarios alter the structure and conclusions for network settings such as many‑user Gaussian MACs with dependent sources, cooperation, or feedback, and nondegraded Gaussian relay networks, where new capacity results are derived.

Abstract

Capacity is often studied under constraints on the channel input signals. This paper investigates the behavior of capacity when constraints are placed on the channel output signal (as well as generalizations thereof). While such a change in perspective leaves the point-to-point problem (essentially) unchanged, the main conclusion is that in certain network scenarios, including multiple-access and relay situations, both the structure of the problem and the conclusions change. For example, capacity results are found for the many-user Gaussian multiple-access channel (MAC) with arbitrarily dependent sources, cooperation, or feedback, and for the nondegraded Gaussian relay network. The investigations are motivated by recent questions arising in spectrum sharing and dynamic spectrum allocation: Multiple independent networks share the same frequency band, but are spatially mostly disjoint. One approach to grant coexistence is via spatial interference power restrictions, imposed at the network level, rather than at the device level. The corresponding capacity question is posed and partially answered in this paper