# On Optimal Spectrum Access of Cognitive Relay With Finite Packet Buffer

## TL;DR

This paper studies optimal spectrum sharing strategies for a cognitive relay system with finite buffers, aiming to maximize secondary throughput while limiting primary packet loss, using linear programming and low-complexity policies.

## Contribution

It formulates the spectrum access problem as a linear program and introduces practical sub-optimal policies for cognitive relays with finite queues.

## Key findings

- Optimal access policy derived via linear programming.
- Sub-optimal policies offer low complexity alternatives.
- Queue size impacts packet throughput significantly.

## Abstract

We investigate a cognitive radio system where secondary user (SU) relays primary user (PU) packets using two-phase relaying. SU transmits its own packets with some access probability in relaying phase using time sharing. PU and SU have queues of finite capacity which results in packet loss when the queues are full. Utilizing knowledge of relay queue state, SU aims to maximize its packet throughput while keeping packet loss probability of PU below a threshold. By exploiting structure of the problem, we formulate it as a linear program and find optimal access policy of SU. We also propose low complexity sub-optimal access policies, namely constant probability transmission and step transmission. Numerical results are presented to compare performance of proposed methods and study effect of queue sizes on packet throughput.