Bounds on the Maximum Number of Concurrent Links in MIMO Ad Hoc Networks with QoS Constraints

TL;DR

This paper derives a theoretical bound on the maximum number of concurrent links in MIMO ad hoc networks with QoS guarantees, incorporating realistic PHY layer models and optimal power/link strategies.

Contribution

It provides the first theoretical formulation for the maximum concurrent links in MIMO MANETs considering practical channel effects and QoS constraints.

Findings

Up to 3x more concurrent links with 4 antennas compared to SISO.

Diminishing returns beyond 4 antennas and 10 dBm transmit power.

Optimal power control and link selection improve network capacity.

Abstract

Multiple-Input Multiple-Output (MIMO) based Medium Access Control (MAC) protocols have received a good deal of attention as researchers look to enhance overall performance of Ad Hoc networks by leveraging multi antenna enabled nodes. To date such MAC protocols have been evaluated through comparative simulation based studies that report on the number of concurrent links the protocol can support. However, a bound on the maximum number of concurrent links (MNCL) that a MIMO based MAC protocol should strive to achieve has hitherto been unavailable. In this paper we present a theoretical formulation for calculating the bound on the MNCL in a Mobile Ad Hoc Network (MANET) where the nodes have multiple antenna capability, while guaranteeing a minimum Quality of Service (QoS). In an attempt to make our findings as practical and realistic as possible, the study incorporates models for the following PHY layer and channel dependent elements: (a) path loss and fast fading effects, in order to accurately model adjacent link interference; (b) a Minimum Mean Squared Error (MMSE) based detector in the receiver which provides a balance between completely nulling of neighboring interference and hardware complexity. In calculating the bound on the MNCL our work also delivers the optimal power control solution for the network as well as the optimal link selection. The results are readily applicable to MIMO systems using Receive Diversity, Space Time Block Coding (STBC), and Transmit Beamforming and show that with a 4 element antenna system, as much as 3x improvement in the total number of concurrent links can be achieved relative to a SISO based network. The results also show diminishing improvement as the number of antennas is increased beyond 4, and the maximum allowable transmit power is increased beyond 10 dBm (for the simulated parameters).