# Exploiting Trust Degree for Multiple-Antenna User Cooperation

## TL;DR

This paper investigates trust-based user cooperation strategies in multi-antenna systems, optimizing power and beamforming to enhance communication rates based on trustworthiness, with solutions tailored for various antenna configurations.

## Contribution

It introduces a trust degree model for user cooperation and develops optimal and efficient strategies for power allocation and beamforming across different antenna setups.

## Key findings

- Trust degree significantly impacts cooperation performance.
- Proposed strategies achieve high achievable rates.
- Solutions are effective for SISO, MISO, SIMO, and MIMO configurations.

## Abstract

For a user cooperation system with multiple antennas, we consider a trust degree based cooperation techniques to explore the influence of the trustworthiness between users on the communication systems. For the system with two communication pairs, when one communication pair achieves its quality of service (QoS) requirement, they can help the transmission of the other communication pair according to the trust degree, which quantifies the trustworthiness between users in the cooperation. For given trust degree, we investigate the user cooperation strategies, which include the power allocation and precoder design for various antenna configurations. For SISO and MISO cases, we provide the optimal power allocation and beamformer design that maximize the expected achievable rates while guaranteeing the QoS requirement. For a SIMO case, we resort to semidefinite relaxation (SDR) technique and block coordinate update (BCU) method to solve the corresponding problem, and guarantee the rank-one solutions at each step. For a MIMO case, as MIMO is the generalization of MISO and SIMO, the similarities among their problem structures inspire us to combine the methods from MISO and SIMO together to efficiently tackle MIMO case. Simulation results show that the trust degree information has a great effect on the performance of the user cooperation in terms of the expected achievable rate, and the proposed user cooperation strategies achieve high achievable rates for given trust degree.