Adaptive HARQ (A-HARQ) for ultra-reliable communication in 5G

This thesis addresses the need for motivating applications, such as mission critical industrial control and medical applications, to operate under Ultra-Reliable Communication (URC) mode in future 5th generation (5G) cellular wireless networks, while also under strict Quality of Service (QoS) constraints such as ultra-low latency. Reliability has been shown to improve through the use of Hybrid Automatic Repeat reQuest (HARQ) for the retransmission (RTX) of erroneous packets during poor channel conditions. However, this can increase the delay to unacceptable levels if more than 1 RTX is required. Thus, an adaptive HARQ (A-HARQ) scheme is proposed, where RTX are implemented on of better quality sub-bands with resources dynamically allocated based on Channel Quality Indicator (CQI) reports. A-HARQ also increases the number of RTX within a 4 ms time period, by utilising Transmission Time Interval (TTI) bundling to decrease the delay incurred from many RTX. Performance analysis is conducted, by comparing A-HARQ and the legacy HARQ in terms of delay, where A-HARQ was shown to have about 35% lower delay than the legacy HARQ, with a slight decrease in throughput. Planned future work involves the field testing of A-HARQ and dynamic resource allocation for URC and A-HARQ, and optimising the balance between reliability, latency and energy-efficiency.