GA-based energy-optimised relay placement in atwo-source 802.15.4 TDMA network

Abstract This paper proposes an energy-efficient communication framework for wireless systems composed of two source nodes and a common destination, assisted by a relay operating in a time-division multiple access (TDMA) scheme. The network is modeled using a nonlinear, twin-source circular topology, where the destination is placed at the centre of a circular region and the sources are symmetrically positioned on the perimeter. The relay node is flexibly located inside the circular area using polar coordinates, enabling optimised placement in terms of both angular position and radial distance. The primary objective is to minimise the energy consumption per successfully delivered bit under Rayleigh fading with Offset-QPSK (OQPSK) modulation, as defined by IEEE 802.15.4 low-rate wireless personal area network (LR-WPAN) standards. The system is assessed using various cooperative communication strategies—namely time-sharing (TS), selection combining (SC), and maximal ratio combining (MRC)—to improve both link reliability and energy efficiency. A Genetic Algorithm (GA) is applied to minimise energy consumption per bit, optimising three critical parameters: the relay’s angular position θ, its radial distance r from the destination, and the payload size. Simulation results indicate that the GA-based relay placement method substantially outperforms conventional midpoint-based approaches, achieving energy savings of up to 22.73% with SC, 18.33% with TS, and 7.14% with MRC. Additionally, an interesting observation was made in the MRC and SC configurations, where multiple relay angles resulted in identical or near-identical optimal energy consumption. These results highlight the effectiveness of geometry-aware, adaptive relay positioning in enabling energy-efficient and reliable communication in ZigBee-based low-power wireless networks. These results demonstrate the superiority of GA-optimised relay placement, relay angle, and payload in enhancing energy efficiency, making it a promising approach for sustainable cooperative communications.