Resource Allocation in Uplink Downlink Decoupled Heterogeneous Networks

Abstract

Optimal utilization of resources like base station (BS) selection, power and spectrum allocation are ambitious targets of future 5th generation (5G) heterogeneous network (HetNet). User association in downlink (DL) and uplink (UL) to a particular base station will have remarkable effect on energy efficiency (EE) and throughput of the network. In traditional 3rd generation (3G) single-tier homogeneous network and 4th generation (4G) HetNet, user association with a BS was based on strongest received signal power (SRSP) in DL only in an asymmetric data traffic environment, i.e., high data rate in DL and low data rate in UL etc. Here, DL and UL are coupled and user is associated to same BS, i.e., macro base station (MBS), small base station (SBS) etc, based on SRSP in DL only in 3G and 4G network. This strategy is known as coupled cell association strategy. This strategy dictates that majority of mobile station (MS), in the near vicinity and remote location, will associate with a remote MBS due to high transmit power compare to nearby SBS with low transmit power in 4G HetNet. Moreover, remote MS associated to MBS will interfere nearby SBS during UL transmission. This results into MSs traffic imbalances among MBS and SBS and interference challenges in 4G HetNet. As a result of coupled cell association strategy, challenges emerged that require novel strategies for cell association in DL and UL for optimal and economical resource utilization in upcoming 5G HetNet. Hence, a novel cell association strategy is defined where the DL and UL of HetNet nodes are considered different entities and the MS is free to associate to different BSs, i.e., MBS and SBS etc, in DL and UL based on strongest signal to interference plus noise ratio (SINR) in DL and UL in HetNet. This novel cell association strategy is known as decoupled cell association in HetNet. As a result of this strategy, MS will associate based on strongest SINR from MBS or SBS in DL and UL in HetNet. Therefore, a MS in the near vicinity may associate to the same MBS in the DL and UL but a MS, far away from MBS and in the near vicinity of the SBS, will associate to MBS in DL but will associate to SBS in UL in HetNet. Thus, interference is mitigated in UL and MS traffic imbalances observed among MBS and SBS in the DL are addressed effectively in the UL. Moreover, decoupled cell association strategy will ensure sub-optimal and economical utilization of resources, i.e., infrastructure, power, frequency etc, in 5G HetNet. In first part of thesis, we investigate coupled and decoupled cell association strategies and formulate a sum-rate maximization problem in terms of admission control, cell association and power allocation based on coupled and decoupled HetNets. Formulated optimization problem falls into class of mixed integer non linear programming (MINLP) problem and an outer approximation algorithm (OAA) is proposed as a solution to find the near optimal solution with less computation complexity. In the second part of thesis, performance analysis of 4G HetNet with coupled cell association strategy verses 5G HetNet with decoupled cell association strategy is done employing outer approximation and heuristic algorithms. In third part of thesis, performance analysis of 4G HetNet with coupled cell association strategy vs 5G HetNet with decoupled cell association strategy is done for effective resource allocation to ensure EE maximization in HetNet. Results show effectiveness of decoupled cell association strategy over coupled cell association strategy in term of number of users attached, addressing traffic imbalances, sum-rate and EE in 5G HetNets.