Exploiting transport-block constraints in LTE improves downlink performance

Efficient resource allocation is necessary to provide the users with the quality of service promised in modern cellular networks, such as LTE. Traditional allocation methods make use of the smallest granularity available, the physical resource block (PRB), to assign resources to each user. The selected resources assigned to a user form a transport block (TB). However, the standard constrains the use of only one modulation and coding rate per TB. This forces the channel quality of the resources to be averaged across the TB, in order to determine the best modulation and coding scheme. In state-of-the-art systems, a non-linear heuristic is used in order to perform this averaging. Unfortunately, when bad PRBs are present next to good ones, this strategy is not optimal. We show that dropping the worst PRBs can improve the performance while remaining standard-compliant. We propose a simple algorithm that can be overlaid to any existing solution and we analyse its effect on multiple state-of-the-art schedulers. A gain is obtained both in throughput (up to 8% increase) and in power consumption (up to 23% reduction).