Spectrum In Cellular Networks Research Articles

SOFT FREQUENCY REUSE FOR MILIGATION OF INTERCELLULER INTEREFERENCE

Background. The appearance of femtocells in LTE networks has provided indoor coverage and overcome large data flows for operators. However, strong interference occurs in neighbouring femtocell users due to the limited available spectrum in cellular networks that transmit data in the same radio range. In densely deployed environments, interference issues in single-channel femtocells cause significant performance degradation. In this study, we mitigate inter-cell interference in femtocell networks by combining femtocells as a result of common interference and soft frequency reuse in downlink and uplink by moving and exchanging interfering physical blocks.
 Objective. The purpose of the paper is to improve the efficiency of ensuring the quality of services in wireless networks by reducing any interference due to the distribution of traffic, which is able to provide uninterrupted connection to the user.
 Methods. Enabling conditions for inter-cell interference mitigation in LTE-based femtocell networks with soft frequency reuse.
 Results. Interference is a key issue in the deployment of LTE femtocells. Closely located femtocells interfere with each other if they transmit on the same frequency. Therefore, crossing femtocells and enabling them to allocate resources and reuse soft frequencies effectively reduces interference and prevents the loss of network resources. The scheme is triggered whenever the user's femto equipment experiences strong interference from neighbouring femtocells. By assigning a separate set of physical resource blocks to users at the edge of the cell, our scheme significantly reduces interference, which automatically increases cell throughput. The simulation results show the advantages of applying our scheme, in particular, the interference of the user's femto-equipment is reduced by 14% and the throughput is improved by 25%. That is, we observe a significant improvement in the performance of femtocells.
 Conclusions. A femtocell crossing scheme with soft frequency reuse is presented to reduce interference between femtocells of LTE networks, which allows effectively ensuring the quality of service transmission in wireless networks by reducing interference and increasing performance through traffic distribution.

Energy Aware Dynamic Mode Decision for Cellular D2D Communications by Using Integrated Multi-Criteria Decision Making Model

Recent developments in mobile network communication increases the usage of the cellular users and their wideband data transfer. Sometimes, network operators may get overloaded because of voice and data transmission between nodes which are under the same coverage area. Cellular device-to-device communication is one of the emerging technologies to overcome current increasing demands for spectrum in cellular networks. It reduces network traffic at centralized terminal stations by enabling direct communication link between source and destination. Mode selection is one of the steps required to fix defined configuration for transmitting data between the pairs of nodes. In this article, the mode selection problem has been considered as multi-objective decision-making problem and applied classical multi-criteria decision models such as analytic hierarchy process and technique for order preference by similarity to the ideal solution models. From simulated results, combination of these two has been proven as the most promising combination for mode selection problem in cellular device-to-device communications under three different types of data services such as text, audio, and video. A dynamically mode selection process has to be carried out with multiple factors which are affecting the performance of the system using proposed model.

Leveraging Dynamic Stackelberg Pricing Game for Multi-Mode Spectrum Sharing in 5G-VANET

5G enabled Vehicular ad hoc network (5G-VANET) plays a promising role to support diverse intelligent transportation system (ITS) applications. There are three types of communication modes in 5G-VANET: cellular mode, reuse mode and dedicated mode, i.e., vehicle users (VUEs) communicate with each other using the cellular network spectrum directly, in an underlay sharing way, and utilizing the allocated dedicated spectrum, respectively. However, how to dynamically share the multi-mode spectrum to optimize the network performance (i.e., network throughput) in 5G-VANET is a challenging task due to the high dynamic VANET environment and network resource heterogeneity. In this paper, we propose a dynamic Stackelberg pricing game enabled multi-mode spectrum sharing solution in 5G-VANET. In specific, we develop an access price strategy for different spectrum sharing modes considering the cellular BS's revenue and whole network throughput, while VUEs can select communication modes in a distributed way and dynamically change the selections through an evolutionary game. Through testing different traffic scenarios generated by SUMO, we demonstrate the effectiveness of the proposed algorithm. Specifically, the proposed algorithm can improve the total transmission rate of VANET by at least 20% compared with the random selection method.

D2D Enabled Cellular Network Spectrum Allocation Scheme Based on the Cooperative Bargaining Solution

In 5G cellular networks, device-to-device (D2D) communication has undoubtedly become a general trend to increase spectral efficiency while reducing communication delay. In particular, D2D technology is able to bear more and more services, which help user-centred and personalized services in future wireless networks. However, several technical issues and challenges are associated with the deployment of D2D communications. In this paper, we tackle the spectrum allocation problem of D2D enabled cellular networks. By employing the major ideas of cooperative game theory, we design a novel two-stage resource allocation protocol based on the weighted utilitarian and meta bargaining solutions. The purpose of bargaining solutions is to clarify what could be the best solution when game players share a surplus that they can jointly generate. According to the main advantages of step-by-step interactive bargaining mechanism, our proposed solution takes various benefits in a rational way. Some simulation results and numerical analysis are provided to confirm the effectiveness of our two-stage bargaining approach and validate the accuracy of the proposed spectrum allocation scheme. Finally, we address some challenges and identify research areas for the future study.

Dynamic Selection of D2D Communication for Internet of Vehicles

Vehicle communication technology, as the core technology of intelligent transportation system, is expected to pass various communication connection means, combined with artificial intelligence, situational awareness, monitoring device, and precise positioning system, to solve the demand of the intelligent transportation system in the car safety, transportation efficiency, and the information service, etc. And it has the potential to serve driverless system. Device-to-device(D2D) communication is suitable for short distance vehicle communication because of its related characteristics and advantages. D2D users multiplexing cellular network spectrum will bring the same frequency interference problems. In order to avoid interference, improve system performance, this paper proposes a vehicle networking D2D communication mode based on spectrum sensing dynamic selection method. Simulation results show that the system capacity can be maximized by changing the sensing time of spectrum. Dynamic selection model is verified through the comparison superiority, and provides the intelligent transportation system a better vehicle-to-vehicle communication method.

Spectrum allocation by wave based adaptive differential evolution algorithm

Resource allocation is very important in mobile communication. This paper studies the assignment of spectrum in cellular networks operated on orthogonal frequency division multiple access (OFDMA) system. Both network utility and fairness among all linked users are taken to measure quality of service in cellular networks. The problem is expressed as a maximization optimization model. Wave based adaptive differential evolution (WADE) algorithm is proposed to for spectrum allocation. The WADE algorithm adapts algorithmic parameters in wave propagation manner to accelerate convergence process of the algorithm. Simulation results show that WADE is more efficient than other compared algorithms. Moreover, it is effective to allocate spectrum resources in OFDMA-based cellular networks.

Security Enhancement and QoS Provisioning for NOMA-Based Cooperative D2D Networks

The characteristic of heterogeneous power utilization in device-to-device (D2D) enabled cellular networks provides a natural fit for the adoption of non-orthogonal multiple access (NOMA). It contributes to a novel D2D framework, NOMA based cooperative D2D communications, with which the heterogeneous interference among different types of nodes can be tackled well. In the framework, a D2D transmitter not only acts as a relay of a pair of cellular transceiver but also transmits its own information to the paired receiver occupying the spectrum of cellular networks with NOMA technique. Apparently, this setup makes the reliability and security of the networks more challenging, in the presence of eavesdropper. To tackle this issue, a collaborative protocol with joint power optimization is built up. Specifically, to prevent information leakage, full-duplex (FD) cellular receiver injects the artificial noise (AN) signals to deteriorate the eavesdropper's channel while performing beamforming to suppress AN in the legitimate users' directions. Meanwhile, D2D transmitter brings desirable QoS provisions for the networks by power scheduling. The joint power optimization problem is formulated by maximizing the secrecy sum rate (SSR) of the overall system, subject to the quality of service (QoS) requirements of cellular and D2D receivers. Due to the non-convexity of the problem, a double-layer optimization method is proposed and then two optimal power allocation ratios are generated. Furthermore, connection outage probability (COP) and secrecy outage probability of the system (SOPS) are respectively characterized and their closed-form expressions are derived. Finally, numerical results are employed to validate the accuracy of theoretical results and the superiority of the proposed protocol in terms of joint security enhancement and QoS provisioning.

Enabling Relay-Assisted D2D Communication for Cellular Networks: Algorithm and Protocols

Recently, there is a growing emphasis on device-to-device (D2D) communication, which is the key component of the Internet-of-Things ecosystem. D2D communication can operate on the licensed spectrum of cellular networks so as to improve the spectrum utilization. In this paper, we focus on the resource allocation problem for general multihop D2D communication and introduce users’ mobility into D2D communication underlaying cellular networks. Maximizing the total end-to-end data rate involves complex tasks, such as resource allocation and routing. By leveraging on the square tessellation technique, we propose an efficient square-division-based resource allocation scheme . Furthermore, we design a relay-assisted D2D communication protocol that addresses the challenges in enabling multihop D2D communications, namely, spectrum resource allocation, users’ mobility, and relay incentive. Through extensive simulations, we show that our relay-assisted D2D communication protocol improves the system throughput up to 55% and the user access rate up to four times in typical scenarios, as compared with state-of-the-art schemes.

Efficient LTE/Wi-Fi Coexistence in Unlicensed Spectrum Using Virtual Network Entity: Optimization and Performance Analysis

Long-term evolution (LTE) operation in the unlicensed spectrum is a promising solution to address the scarcity of licensed spectrum for cellular networks. Although this approach brings higher capacity for LTE networks, the Wi-Fi performance operating in this band can be significantly degraded. To address this issue, we consider a coordinated structure, in which both networks are controlled by a higher level network entity. In such a model, LTE users can transmit in the assigned time-slots, while Wi-Fi users can compete with each other by using $p$ -persistent carrier sense multiple access (CSMA) in their exclusive time-share. In an unsaturated network, at each duty cycle, the time-division multiple access (TDMA) scheduling for LTE users and $p$ values for Wi-Fi users should be efficiently updated by the central controller. The corresponding optimization problem is formulated and an iterative algorithm is developed to find the optimal solution using complementary geometric programming and monomial approximations. Aiming to address the quality-of-service assurance for LTE users, an upper bound for average delay of these users is obtained. This analysis could be a basis for the admission control of LTE users in unlicensed bands. The simulation results reveal the performance gains of the proposed algorithm in preserving the Wi-Fi throughput requirement.

Interference-controlled D2D routing aided by knowledge extraction at cellular infrastructure towards ubiquitous CPS

Device-to-device (D2D) networks underlaying cellular networks are widely recognized as one of the major approaches for ubiquitous information acquisition and exchange, which features the future cyber-physical systems (CPSs). In this paper, we propose the interference-controlled D2D routing designs underlaying cellular networks, i.e. sharing/reusing the cellular spectrum, to support multi-hop D2D transmissions and thus enhancing the flexibility of CPS. The unique feature and challenge for this task include threefolds. First, the huge density of device nodes in future cellular networks yields huge amount of information to process. Second, as device nodes in cellular networks do not maintain the routing table, the route selection via low-complexity knowledge-extraction approach over huge amount of information needs to be performed by the base station (BS). Third, the interference generated by reusing cellular spectrum needs to be thoroughly controlled. To address these issues, we in this work consider two D2D networking scenarios that allow D2D users to share the uplink and downlink spectrum of cellular networks, respectively. Our objective for routing is hop-count minimization such that the delay and power consumptions can be decreased. In particular, we propose a maximum rate towards destination (MR-D) routing algorithm for the scenario sharing uplink spectrum and a MR-D advanced (MR-DA) routing algorithm for the scenario sharing downlink spectrum, respectively. Both algorithms have low computational complexity and thus meaningful for practical systems. Furthermore, our routing designs can avoid the violation of tolerable interferences to cellular users as well as to fulfil the rate requirement of D2D services. Also conducted are abundant simulation evaluations to demonstrate the advantages of our proposed schemes as compared to the baseline schemes including the farthest neighbour routing and closest to destination routing scheme.

Uplink Interference Analysis for Two-Tier Cellular Networks With Diverse Users Under Random Spatial Patterns

Multi-tier architecture improves the spatial reuse of radio spectrum in cellular networks, but it introduces complicated heterogeneity in the spatial distribution of transmitters, which brings new challenges in interference analysis. In this work, we present a stochastic geometric model for evaluating the uplink interference in a two-tier network considering multi-type users and base stations. Each type of tier-1 users and tier-2 base stations are modeled as independent homogeneous Poisson point processes, and tier-2 users are modeled as locally non-homogeneous clustered Poisson point processes centered at tier-2 base stations. By applying a superposition-aggregation-superposition approach, we quantify the interference at both tiers. Our model is also able to capture the impact of two types of exclusion regions, where either tier-2 base stations or tier-2 users are restricted to avoid cross-tier interference. As an important application of this analytical model, an intensity planning scenario is investigated, in which we aim to maximize the total income of the network operator with respect to the intensities of tier-2 cells, under constraints on the outage probabilities of tier-1 and tier-2 users. The result of our interference analysis suggests that this maximization can be converted to a standard convex optimization problem. Finally, numerical studies further demonstrate the correctness of our analysis.

Coexistence of Wi-Fi and heterogeneous small cell networks sharing unlicensed spectrum

As two major players in terrestrial wireless communications, Wi-Fi systems and cellular networks have different origins and have largely evolved separately. Motivated by the exponentially increasing wireless data demand, cellular networks are evolving towards a heterogeneous and small cell network architecture, wherein small cells are expected to provide very high capacity. However, due to the limited licensed spectrum for cellular networks, any effort to achieve capacity growth through network densification will face the challenge of severe inter-cell interference. In view of this, recent standardization developments have started to consider the opportunities for cellular networks to use the unlicensed spectrum bands, including the 2.4 GHz and 5 GHz bands that are currently used by Wi-Fi, Zigbee and some other communication systems. In this article, we look into the coexistence of Wi-Fi and 4G cellular networks sharing the unlicensed spectrum. We introduce a network architecture where small cells use the same unlicensed spectrum that Wi-Fi systems operate in without affecting the performance of Wi-Fi systems. We present an almost blank subframe (ABS) scheme without priority to mitigate the co-channel interference from small cells to Wi-Fi systems, and propose an interference avoidance scheme based on small cells estimating the density of nearby Wi-Fi access points to facilitate their coexistence while sharing the same unlicensed spectrum. Simulation results show that the proposed network architecture and interference avoidance schemes can significantly increase the capacity of 4G heterogeneous cellular networks while maintaining the service quality of Wi-Fi systems.

Cooperative Spectrum Sharing Between Cellular and Ad-Hoc Networks

Spectrum sharing between cellular and ad-hoc networks is studied in this work. Weak signals and strong interferences at the cell-edge area usually cause severe performance degradation. To improve the cell-edge users' performance quality while keeping high spectrum efficiency, in this paper, we propose a cooperative spectrum sharing scheme. In the proposed scheme, the ad-hoc users can actively employ cooperative diversity techniques to improve the cellular network downlink throughput. As a reward, a fraction of the cellular network spectrum is released to the ad-hoc network for its own data transmission. To determine the optimal spectrum allocation, we maximize the ad-hoc transmission capacity subject to the constraints on the outage probability of the ad-hoc network and on the throughput improvement ratio of the cellular network. Both the transmission capacity of the ad-hoc network and the average throughput of the cellular network are analyzed using the stochastic geometry theory. Numerical and simulation results are provided to validate our analytical results. They demonstrate that our proposed scheme can effectively facilitate ad-hoc transmissions while moderately improving the cellular network performance.