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The IUP Journal of Telecommunications
Distributed Resource Allocation for Two-Tier Heterogeneous Cellular Networks
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Heterogeneous cellular Network (HetNet) is a promising technology for 5th generation (5G) mobile networks that can potentially improve spatial resource reuse and extend coverage, therefore allowing it to achieve significantly higher data rates than single-tier networks. However, the performance of HetNet is limited by co-channel (inter-UE, inter-cell) interference. Hence, resource allocation is carefully done in this paper to ensure that the loss in achievable data rate due to interference does not diminish the gain in the achievable data rate due to higher spatial reuse. The resources considered are the spatial resource (unit-beamformer) and the power resource. Distributed spatial resource allocation problem is formulated as a quadratic optimization problem with non-convex quadratic constraints and solved by exploiting Karush-Kuhn-Tucker (KKT) conditions. The proposed hybrid power resource allocation scheme involves a three-step process, starting with two power optimization procedures. These two power optimization procedures are formulated as convex optimization problems and solved by exploiting KKT conditions and CVX (a Matlab software for discipline convex programming), respectively, while the third step involves utilizing results from the aforementioned power optimization procedures to compute average powers allocated to UEs. The simulation results of the proposed method, when compared with other existing methods showed significant improvement.

 
 

Resource Allocation (RA) is all about how the best radio resources such as frequency, time, transmit powers, spatial directions (unit norm beamformers), etc. can be properly allocated to User Equipments (UEs) in a system in order to maximize the system Spectral Efficiency (SE). RA is especially important in system such as Heterogeneous Network (HetNet) (Damnjanovic et al., 2011) which is limited by co-channel interference rather than noise (Nam et al., 2014). The basic problem facing RA is the issue of coupling among UEs. UEs are coupled due to interference (inter-UE, inter-cell) and power constraints. This paper is focused on the optimal distributed RA procedure in two-tier HetNet such that UEs in the Cell Range Expansion (CRE) (Kenta et al., 2011; and RI-100701) area of the picocells will experience minimized loss in throughput due to the higher level of interference received from the Macro Base Station (MBS). By distributed RA, we mean that the RA algorithm is computed at each BS without exchanging or sharing control variables or channel state information, unlike in a centralized system. In homogeneous cellular network, UE is usually served and connected to the strongest BS in downlink, hence interference from other signals are received with a lower power than the desired signal. In contrast and in order to enable cell splitting gain, some UEs in HetNet may be served and connected to the strongest BS in uplink (i.e., low powered BS), even though the received power from an MBS could be higher (Lopez et al., 2011). This method of cell selection in HetNet always causes high level of interference from the MBS to such UEs which are usually located at the CRE of the low powered BS. Apart from this, they also suffer from enormous signal attenuation from their home (serving) BS. These problems therefore cause them to exhibit poorer performance than the interior UEs, thereby degrading the system aggregate sum-rate.

 
 

Telecommunications Journal, Heterogeneous cellular Networks (HetNet), Interference leakage, Lagrange, Optimization, Resource allocation.