Hybrid Relaying Based Cross Layer MAC Protocol Using Variable Beacon for Cooperative Vehicles

The onset of network coded cooperation (NCC) and its applications in vehicle-to-everything (V2X) scenarios have allowed vehicular networks to relish both reliability and throughput which are the key factors in an on-road scenario. However, a typical NCC based network uses a time division multiple access (TDMA) based data transmission aided by a relay employing a fixed relaying scheme. This puts a concern on the system's quality-of-service (QoS). We thus propose a dual threshold-based hybrid (DTH) relaying scheme where the relay vehicle dynamically decides the relaying scheme or asks for a re-transmission to improve the QoS. The decision to select a relaying scheme is based on the instantaneous signal-to-noise ratio (SNR). Consequently, an acknowledgement frame structure is proposed to convey the crucial information to the destinations which are required during data extraction. A variable beacon interval is also proposed where the relay vehicle dynamically changes the beacon transmission time based on the number of re-transmissions which helps new users to join the system. Metrics like outage probability, achievable rate and throughput have been considered as the QoS metrics to compare the performance of the proposed model with respect to other existing works. Extensive simulations in MATLAB show that the proposed scheme experiences a better outage performance than amplify-and-forward (AF) whereas a worse performance when compared with decode-and-forward (DF). However, the better performance in the case of DF comes with a trade-off in terms of throughput when compared to the proposed scheme.