On the Improved Memory Utilization in HARQ Pooling

We consider a novel mechanism to pool HARQ (Hybrid Automatic Repeat Request) memory at the UE (User Equipment). In legacy systems, each carrier is allocated a separate section of the total HARQ memory. By pooling this memory and allocating as HARQ requests arrive, we significantly improve the memory utilization. Moreover, we can accommodate a larger fraction of arriving HARQ requests thus increasing HARQ throughput without increasing buffer requirement at the UE. In this work, we model the HARQ memory system as a multiserver queue, and obtain expressions for dropping probability and memory occupancy. We compare the pooling system to the legacy technology in an asymptotic regime, which is a good approximation in cases where the ratio of the largest to smallest packet size is large. This regime holds for scenarios with large Transport Block sizes, such as 5G New Radio. In this regime, under large load factor, we show that blocking probability reduces under the pooling mechanism and uses less resources.