The increasing adoption of the Internet of Things has led to the need for systems with higher spectral and energy efficiency (EE) in order to enable communication. Larger data rate demands had led researchers to look at millimeter wave (mmWave) bands to boost network rates. This paper investigates the downlink performance of a three-tier heterogeneous network that consists of sub-6 GHz macrocells overlaid with small cells operating on both the mmWave and sub-6 GHz bands. A model is developed using tools from stochastic geometry to analyze the coverage, rate, area spectral efficiency, and EE of such a network. Various deployment strategies and their impacts on the considered metrics are studied. Simulation results are used to verify the validity of the proposed model.

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Multiobjective Optimization in 5G Hybrid Networks

Hybrid networks consisting of both millimeter wave (mmWave) and microwave $(\mu W)$ capabilities are strongly contested for next-generation cellular communications. A similar avenue of current research is device-to-device (D2D) communications, where users establish direct links with each other rather than using central base stations. However, a hybrid network, where D2D transmissions coexist, requires special attention in terms of efficient resource allocation. This paper investigates dynamic resource sharing between network entities in a downlink transmission scheme to maximize energy efficiency (EE) of the cellular users (CUs) served by either $(\mu W)$ macrocells or mmWave small cells while maintaining a minimum quality-of-service (QoS) for the D2D users. To address this problem, first, a self-adaptive power control mechanism for the D2D pairs is formulated, subject to an interference threshold for the CUs while satisfying their minimum QoS level. Subsequently, an EE optimization problem, which is aimed at maximizing the EE for both CUs and D2D pairs, has been solved. Simulation results demonstrate the effectiveness of our proposed algorithm, which studies the inherent tradeoffs between system EE, system sum rate, and outage probability for various QoS levels and varying densities of D2D pairs and CUs.

Energy-Aware Radio Resource Management in D2D-Enabled Multi-Tier HetNets

Analytical evaluation of heterogeneous cellular networks under flexible user association and frequency reuse

In fifth generation (5G) networks, the densification of small base stations in the coverage region of macro base station (MBS) leads to significant inter-cell interference (ICI). Similarly, drones (a.k.a. unmanned aerial vehicles) have a diverse scope in multifarious 5G assisted applications and, therefore, cause considerable drones interference (DI) as a result of excessive drone usage. This paper investigates the bottleneck uplink (UL) coverage performance of the MBS edge users in the presence of ICI and DI. To mitigate both ICI and DI, we use an efficient resource allocation scheme known as reverse frequency allocation (RFA). Moreover, we use decoupled association (DeCA) in place of coupled association to further improve UL signal-to-interference ratio. The results depict that RFA in conjunction with DeCA overpass all other techniques in terms of improved UL coverage performance because of effective DI and ICI mitigation.

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Interference Management in Ultra-Dense 5G Networks With Excessive Drone Usage

Coverage analysis of cell‐edge users in heterogeneous wireless networks using Stienen's model and RFA scheme

The deployment of heterogeneous networks (HetNets) inevitably demands the design of interference management techniques to elevate the overall network performance. This paper presents a novel interference mitigation technique known as reverse frequency allocation (RFA), which provides an efficient resource allocation compared with the other state-of-the-art techniques. RFA reverses the transmission direction of interferers, thereby minimizing the cross-tier interference. Eventually, better coverage as well as increased data rates are achieved by providing complementary spectrum to the macro and pico users. In this paper, we present a tractable approach for modeling HetNets under the proposed RFA scheme. Specifically, we employ well known tools from stochastic geometry to derive closed-form expressions for the coverage probability and rate coverage in two-tier cellular network employing RFA and its variants. The modeling is performed using two approaches; first, where the base stations and users are modeled as independent Poisson point processes (PPPs) and second, the interference is approximated using the fluid model. It is shown that the results obtained from the PPP model are accurate for higher values of path loss exponents, while the results from fluid model are useful for smaller values of path loss exponents. The plausibility of model is validated through the Monte-Carlo simulations and the network performance is evaluated in terms of coverage probability, coverage rate, and outage capacity. The results demonstrate that 2-RFA yields outage capacity gains of 13% as compared with the soft fractional frequency reuse scheme, whereas, the performance gains can be further improved by 14% by employing the proposed variants of RFA.

Syed Mohammad Hassan Zaidi

Papers

Coverage and Rate Analysis for Downlink HetNets Using Modified Reverse Frequency Allocation Scheme