Transmission Capacity of Spectrum Sharing Ad-hoc Networks with Multiple Antennas

TL;DR

This paper analyzes how multiple antennas in secondary ad-hoc networks can be optimally used for interference nulling and cancelation to maximize transmission capacity while protecting primary network receivers.

Contribution

It derives the optimal allocation of spatial degrees of freedom for nulling and cancelation to enhance secondary network capacity under primary outage constraints.

Findings

Optimal STDOF for nulling maximizes secondary capacity.

Using a fraction of SRDOF for interference cancelation improves capacity.

Capacity scales with the number of antennas under the proposed scheme.

Abstract

Two coexisting ad-hoc networks, primary and secondary, are considered, where each node of the primary network has a single antenna, while each node of the secondary network is equipped with multiple antennas. Using multiple antennas, each secondary transmitter uses some of its spatial transmit degrees of freedom (STDOF) to null its interference towards the primary receivers, while each secondary receiver employs interference cancelation using some of its spatial receive degrees of freedom (SRDOF). This paper derives the optimal STDOF for nulling and SRDOF for interference cancelation that maximize the scaling of the transmission capacity of the secondary network with respect to the number of antennas, when the secondary network operates under an outage constraint at the primary receivers. With a single receive antenna, using a fraction of the total STDOF for nulling at each secondary transmitter maximizes the transmission capacity. With multiple transmit and receive antennas and fixing all but one STDOF for nulling, using a fraction of the total SRDOF to cancel the nearest interferers maximizes the transmission capacity of the secondary network.