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