Sudeepta Mishra

Exploiting an Optimal User Association Strategy for Interference Management in HetNets

Heterogeneous Cellular Network consists of low power Pico Base Stations (PBS) overlaid in high power Macro Base Stations (MBS) coverage area. Edge User Equipments (UE) of PBS are victims of interference from MBS. Almost Blank Subframes (ABS) can provide interference free communication for these UEs. However, existing techniques perform UE-BS association before ABS determination, which is suboptimal with respect to UE-BS association.We formulate the joint optimization of UE-BS association and ABS computation as a combinatorial optimization problem, which is NP-Hard. We suggest the use of Hungarian matching algorithm and iterative exploration of candidate ABS densities to discover the ABS that can minimize system blocking.

Enhancing the performance of HetNets via linear regression estimation of Range Expansion Bias

Heterogeneous Networks (HetNets) use picocells deployed at strategic locations to fill coverage holes, improve Quality of Experience for users, and reduce blocking by supporting more users via cell splitting and spatial reuse of spectrum. Picocell Base Stations have lower transmit power compared to Macro Base Station. As a result, the observed improvements are often less than anticipated due to lower utilization and offloading. To improve picocell utilization, cell biasing attempts to offload users from macrocell by modifying cell selection/handover criteria. However, an improper bias value can increase blocking and penalize the users with higher macro interference. In this paper, we propose an efficient regression based scheme to predict a near optimal bias value that attempts to reduce blocking probability and improve load fairness index in the system. The simulation results verify that, in comparison to static bias, the proposed scheme also improves the cell edge user throughput, along with the target criteria.

Breathe to Save Energy: Assigning Downlink Transmit Power and Resource Blocks to LTE Enabled IoT Networks

Undoubtedly, the Internet of Things (IoT) is the next big revolution in the field of wireless communication networks. IoT is an invisible network, which connects the physical world to the virtual world. Seamless Internet connectivity is essential between these two worlds for IoT to become a reality. In this aspect, long-term evolution advanced (LTE-A) is a promising technology, which meets the requirements of IoT. However, an exponential increase in the number of IoT devices will increase the energy consumption at base stations in LTE-A. Therefore, in this letter, we study the downlink energy efficiency aspect of LTE-A in the IoT networks. We propose a power control and resource block allocation scheme called breathing for an IoT network. Simulation results have shown that breathing performs better than the traditional maximum power allocation scheme and greedy power reduction scheme in terms of energy efficiency, system throughput, and system blocking.

A novel spectrum reuse scheme for interference mitigation in a dense overlay D2D network

Device-to-Device (D2D) communication as an underlaying cellular network empowers direct communication between two users and helps in offloading network traffic. However, due to interference posed by the D2D transmitters to the primary cellular users, intelligent resource allocation techniques need to be incorporated for the betterment of the overall system. Overlay D2D communication eliminates the interference between cellular users and D2D users by dedicating resources for D2D users. With this approach, interference among D2D users can still pose a potential threat to the overall system performance. To handle this additional interference without significantly affecting the spectrum efficiency, smart assignment of wireless resources is necessary among D2D users. For the first time, we look into this problem and propose an efficient channel assignment scheme that mitigates the interference among D2D users. By meticulously assigning the channels with proper power control, the proposed channel assignment scheme is found to improve the spectrum reuse as well as the energy efficiency of the system. We compare our scheme with Full Reuse (FR) channel assignment scheme where every D2D pair fully shares the channel resources. Extensive simulations demonstrates that our scheme performs better than FR in terms of spectrum reuse, energy efficiency and overall system blocking.

An Analytic Hierarchy Process Based Approach for Optimal Road Side Unit Placement in Vehicular Ad Hoc Networks

Road-Side Units (RSUs) act as a backbone for Vehicular Ad hoc Networks (VANETs). The location and density of RSUs largely affect the performance of VANETs. Although, large number of RSUs guarantee better coverage and performance, it results in high capital and operational expenditure. Hence, optimal placement of RSUs is considered as an important problem in VANETs. In this paper, we propose a novel approach to solve the optimal RSU placement problem using Analytic Hierarchy Process (AHP). Our evaluations show that AHP requires lesser number of RSU deployment which eventually leads to lower overall cost. We also analyze coverage achieved by defining expected RSU-to-RSU delay as a performance metric. We find that our AHP based solution consistently outperforms in terms of delay compared to uniform and hot spot placement strategies for various vehicle densities. Obtained results are verified using extensive simulation.

An efficient location aware distributed physical resource block assignment for dense closed access femtocell networks

The demand for higher data-rate in the indoor environment is unrelenting, and has triggered a huge deployment of Femto Base Stations (FBSs) in such environments. A large portion of these FBSs are privately owned and operate in closed access mode. However, due to aggressive spectrum reuse among these FBSs, co-tier interference is very high. Techniques relying on Fractional Frequency Reuse (FFR) will not scale in these dense FBS networks as the effective available spectrum per FBSs will be a little to support any meaningful data-rate at any FBS. Moreover, the techniques that use both power control and sub-channel allocation usually operate in a centralized fashion. Hence, these are a huge burden to the entire system. To handle this additional interference without significantly affecting spectrum efficiency, efficient location aware Physical Resource Block (PRB) assignment among interfering FBSs is necessary. In this paper, we formulate the PRB assignment problem as a Mixed Integer Non-Linear Program (MINLP) that exploits User Equipment (UE) location with respect to its interfering FBSs. Since the optimization problem is NP-hard, we propose a twofold solution which can efficiently reuse the PRBs while maintaining the interference below a threshold. First, an iterative elimination algorithm for PRB allocation and second, an adaptive PRB power control to find the required transmission power which minimizes interference. The proposed technique operates in a distributed manner and improves per FBS PRB reuse, energy efficiency, system blocking. Obtained results are verified using extensive simulations.

Efficient coverage management of pico cells in HetNets via spectrum slicing, cell biasing, and transmit power spreading

AbstractCell biasing is an effective solution for mobile user offloading in Heterogeneous Cellular Network (HetNet). Cell biasing modifies the user association criteria by incorporating Range Expansion Bias (REB) in traditional reference signal based user association technique. For sparse user distribution, REB for picocells does not offload users located outside RSRP Threshold Coverage Area. This is because the actual Reference Signal Received Power (RSRP) value for such users is lesser than the threshold RSRP value for successful communication. On the other hand, using a negative REB value for dense user distribution around picocells is not desirable because it leads to higher interference at users and high energy consumption at macrocells. In this paper, we suggest a unified framework for coverage optimization using spectrum slicing and transmit power spreading. Our proposed framework considers a combination of subchannel transmit power and REB which is based on the user distribution around picocells. Additionally, in order to protect the signal quality of macrocell users located close to picocells, we suggest location aware subchannel allocation technique. This technique maximizes the number of Interference Free subchannels for macrocell users. Obtained results show that our proposed framework can significantly improve the coverage and system blocking for HetNet.

An Efficient Physical Resource Block Assignment for Dense Femtocell Networks

Femtocells have proved to be an effective solution for handling the ever increasing demands for wireless data without incurring additional deployment costs. Deployment of these low cost, miniature base stations not only improves network robustness but also facilitates efficient location specific services for mobile users. However, dense deployment of femtocells comes with the cost of increased interference. To handle this additional interference without significantly affecting spectrum efficiency, smart assignment of wireless resources is necessary among femtocells. In this paper, we suggest a technique to intelligently reuse the available wireless resources among interfering femtocells so as to improve spectrum reuse and energy efficiency. Additionally, the suggested technique also shows improvement in system blocking for all possible deployment scenarios. Obtained results are verified using extensive simulations.

A multi-tier cooperative resource partitioning technique for interference mitigation in heterogeneous cellular networks

In Heterogeneous cellular networks (HetNets), co-channel interference is a major concern due to the co-existence of multiple base stations with overlaid regions. Edge users are typically the victims because of high interference exposure. To counter this high interference, picocells communicate with the edge users in protected subframes (PSF). The severity of the problem intensifies in case of hotspot deployment, where picocells cannot provide coverage to the entire hotspot, thus forming a dense ring of macrocell users around picocells. We argue that these macrocell users are also victims, constituting a significant victim user population in hotspot deployment. We propose that, along with the macrocell muting during PSF, picocells should also be operated in cooperative manner with macrocell, and be barred from transmission during some of the subframes for protection of these macrocell victim users. We define a utility function to find the optimal values of PSF density for both macrocell and picocells, which would increase victim user throughput thereby enhancing system fairness. Exhaustive simulations illustrate that the proposed scheme improves victim user throughput significantly, while maintaining the overall system capacity.

Increasing Energy Efficiency via Transmit Power Spreading in Dense Femto Cell Networks

Adding Femto Base Stations (FBSs) has become a common approach toward capacity and coverage enhancements in the current cellular networks. Moreover, rapidly growing demand for capacity results in ultradense deployments of FBS and these skyrocket the energy consumption of the cellular networks. Thus, increasing Energy Efficiency (EE) has gained great importance in small cell research to minimize the impact on the environment. In this paper, we first model a problem to maximize the EE of an FBS network. Then, we suggest a heuristic approach to calculate the transmission power of FBSs in terms of spreading factors that maximize the EE of the network while protecting User Equipments’ (UEs’) signal to interference plus noise ratio threshold and quality of service requirements. Moreover, transmit power spreading decreases energy consumption and co-tier interference among neighboring FBSs. The proposed approach does not require any feedback from neighboring FBSs but depends on the channel quality indicator from its associated UEs. The study is carried out in two different scenarios: outdoor with open access mode FBSs and indoor with closed access mode FBSs. The simulation results indicate increase in FBS network EE and energy saving without any loss in throughput. The results depict up to