Context-Aware Uplink Resource Allocation in 4G LTE-Advanced Heterogeneous Networks

Abstract

In the Third Generation Partnership Project Long Term Evolution-Advanced (3GPP LTE-Advanced) Heterogeneous Networks (HetNets), small cells share the spectrum with the overlaid macrocell creating a multi-tier scenario, targeting to meet the day’s high data rate demands. Nevertheless, despite of the significant improvements in achieving high data rates brought by the HetNet, the design transformation from homogeneous network to HetNet also brought about several concerns. Most importantly, the co-existence of varying-range and multi-tier scalable cells has introduced several new interference scenarios (e.g. the co-channel inter-tier and cross-tier interference. Thus, it is anticipated that the presence of small cells intensifies the interference scenarios, as there are a limited number of users associated with these small cell, thereby, generating harmful interference for the rest of the users located in proximity. In this situation, if a user receives a high amount of interference from the neighboring users and receiver of the serving base station is unable to decode the control information transmitted on the Physical Uplink Control Channel, or experience excessive failures despite of the continuous re-transmission attempts; the base station declares a radio link failure and the concerned user experiences service outage. Thus, the co-existence of multi-tier cells brings about additional complexity in the interference management procedures, which if not addressed properly, have a high tendency to degrade the overall system performance. Moreover, the macrocell network infrastructure is deployed to serve macrocell users and not for small cells, hence, macrocell users entails higher priority to attain radio resources and network coverage. Therefore, it is essential to control harmful interference in order to protect macrocell users from service outage. In the current LTE-Advanced system, the adopted power control techniques are mostly developed for the conventional homogeneous network that do not consider the aforementioned new interference scenarios while allocating transmit power to the users. Further the second loophole identified in this research is the inefficient bandwidth allocation in HetNets. In LTE-Advanced system, the bandwidth allocated to the users for data transfer is represented as number of physical resource blocks (PRBs), and the more PRBs allocated to the user need more transmit power. Hence, allocating a higher number of PRBs than the user’s power can afford will reduce the power per PRB resulting in inefficient power distribution. The unbalanced allocation of PRBs either create a high interference at the evolved NodeB (eNB) or result in radio link failure and consequently the user experience outage. To this end, this research intends to develop an adaptive resource allocation algorithm that should consider the total effective received interference at the eNB (including the aforementioned interference scenario created due to HetNet deployments) while allocating resources to users with the aim of having all macrocell users reach their target signal to interference plus noise ratio (SINR) at the same system complexity and signaling overhead. Considering the above mentioned facts, we propose two power control techniques for HetNet deployment while guaranteeing the protection of macrocell users (i.e. zero-outage for the macro-cell user). In the developed power control techniques, we characterize the cross-tier/inter-tier co-channel interference as a scheduling task to allocate transmit power to the users. In the proposed technique, the transmit power of all users is updated according to the target and instantaneous SINR condition as long as the effective received interference at the serving eNB is below the given threshold. Otherwise, if the effective received interference at the eNB is greater than the threshold level, the transmit power of small cell users is gradually reduced aiming for all macrocell users to reach their target SINR. Further, in the second proposed technique, in addition to the received interference at eNB, the transmit power of all users is controlled considering the current channel condition estimated from user power headroom report (PHR) targeting to decrease outage ratio for small cell users. Furthermore, addressing the aforementioned second loophole, this work proposes balanced bandwidth allocation scheme, that is, the dynamic bandwidth allocation scheme aiming to efficiently utilize the user’s power. In order to allocate bandwidth, in the proposed scheme we exploit the user’s PHR to calculate the balanced amount of bandwidth in terms of PRBs count. To take advantage from both the proposed techniques altogether, finally, in this research we present a novel and comprehensive context-aware uplink resource allocation algorithm, specifically, for the HetNet design. Combining the aforementioned power control and bandwidth resource allocation techniques in one algorithm, we present the power efficient and interference-aware resource allocation with guaranteed cross-tier macrocell user protection (PEIARA-MP) for the uplink LTE-Advanced HetNet design with the aim to improve the overall network capacity by efficiently utilizing the scarce resources of bandwidth and power. In the proposed PEIARA algorithm, the users’ transmit power and bandwidth resources are adaptively allocated based on their SINR condition, users’ PHR report and the received interference at the serving eNB while targeting to achieve zero-outage constraint for macrocell users. The extensive system-level simulations show the significance of the proposed algorithm relative to state-of-the-art fractional power control technique by achieving higher user’s average throughput (consequently resulting in increased overall network capacity), reduced transmit power (hence achieving increased energy efficiency), lower received interference at eNB, improved SINR, and reduced outage ratio, at guaranteed macrocell user protection while compromising the throughput of small cells at extreme interference situation.