Showing papers by "Jiandong Li published in 2014"

Zone-Based Load Balancing in LTE Self-Optimizing Networks: A Game-Theoretic Approach

Abstract: Mobility load balancing (MLB) is an important use case in long-term evaluation (LTE) self-optimizing networks (SONs). To combat the potential ping-pong load transfer and low-convergence issues, we propose a game-theoretic solution to the SON MLB to solve the asymmetry traffic distribution among multiple cells and the potential hidden-cell case. The proposed algorithm, which is referred to as zone-based mobility load balancing (ZLB), optimally redistributes the load of all cells within a zone. We model the multiple cells' ZLB as a Cournot game, where multiple cell pairs carry out load balancing (LB) simultaneously under the constraints of load distribution of hidden cells. Simulation results show that the ZLB algorithm can overcome the ping-pong LB problem and that the convergence time of LB is also dramatically reduced. Meanwhile, the load distribution of ZLB is more balancing than that of MLB, and the performance of average blocking probability and the number of unsatisfied users of ZLB are significantly improved.

Geographic routing protocol for vehicular ad hoc networks in city scenarios: a proposal and analysis

Abstract: The characteristics of vehicular ad hoc networks VANETs make the design of routing protocol a great challenge. In this paper, we propose a vehicle density and load aware routing protocol for VANETs called VDLA. VDLA adopts sequential selection of junctions to construct the route. The selection is based on the real-time vehicle density, the traffic load, and the distance to the destination. The network information is collected by a decentralized mechanism. Through factoring in these metrics, the packets are avoided being sent to roads where network is disconnected, and the network load is balanced to mitigate network congestion. The intermediate junctions are selected before the packet reaches a junction to reduce the unnecessary hops. Our study also investigates the impact of the high mobility of the nodes. An analytical framework is proposed to analyze the mobility. Based on the analysis, the traditional Hello scheme is enhanced to improve the accuracy of the neighbor table. In the simulation, we compare VDLA with greedy perimeter coordinator routing and GpsrJ+, which are geographic routings protocols proposed for VANETs. The results validate the superiority of VDLA in terms of end-to-end delay and packet delivery rate. And the superiority holds in different scenarios. Copyright © 2013 John Wiley & Sons, Ltd.

On the Capacity of Downlink Multi-Hop Heterogeneous Cellular Networks

Abstract: Multi-hop heterogeneous cellular networks (MHCNs) consist of conventional macro cellular networks overlaid with an irregular deployment of low-power base stations (BSs), where the communication between BSs and mobile users can be established through a single hop or multiple hops. By modeling different kinds of randomly located BSs as K tiers of independent homogeneous Poisson Point Processes, we first explore the capacity of downlink MHCNs and derive the expression of capacity under Rayleigh fading channels. Particularly, the capacity gain achieved by cell splitting and multi-hop relaying is quantified for the first time. We then study the effects of BS density, transmit power, and signal-to-interference-plus-noise-ratio (SINR) threshold on the capacity of MHCNs. More importantly, we obtain the spectral efficiency enhancement condition under which the increase of BS density and transmit power improve the spectral efficiency, thereby enhancing the capacity. One interesting observation is that at a given SINR threshold, the capacity increases with BS density when all the tiers have the same SINR threshold. Moreover, the capacity of some special networks (i.e., heterogeneous cellular networks, multi-hop cellular networks, and conventional cellular networks) are derived directly by specializing some system parameters in our results. Finally, numerical studies and simulations are conducted to validate our analysis.

Utility-Based Resource Allocation for Multi-Channel Decentralized Networks

Abstract: The architecture of decentralization makes future wireless networks more flexible and scalable. However, due to the lack of the central authority (e.g., BS or AP), the limitation of spectrum resource, and the coupling among different users, designing efficient resource allocation strategies for decentralized networks faces a great challenge. In this paper, we address the distributed channel selection and power control problem for a decentralized network consisting of multiple users, i.e., transmit-receiver pairs. Particularly, we first take the users' interactions into account and formulate the distributed resource allocation problem as a non-cooperative transmission control game (NTCG). Then, a utility-based transmission control algorithm (UTC) is developed based on the formulated game. Our proposed algorithm is completely distributed as there is no information exchange among different users and hence, is especially appropriate for this decentralized network. Furthermore, we prove that the global optimal solution can be asymptotically obtained with the devised algorithm, and more importantly, in contrast to existing utility-based algorithms, our method does not require that the converging point is one Nash equilibrium (NE) of the formulated game. In this light, our algorithm can be adopted to achieve efficient resource allocation in more general use cases.

Power Allocation and Relay Selection for Two-Way Relaying Systems by Exploiting Physical-Layer Network Coding

Abstract: In this paper, we study the power allocation and relay selection strategy for two-way relaying systems using physical-layer network coding (PNC), in which two information symbols can be exchanged in two time slots. Our approach is based on maximizing the objective rate under a total power budget consumed by the transmission of the two information symbols. Two optimization objectives, namely, the minimum of the achievable rates of the two directions and the sum rate of the system, are considered here. Since the objectives are not continuously differentiable functions, we propose a method based on a suboptimal solution to solve the original problems. It is shown that the main problems have closed-form solutions, and the strategies can be implemented in a distributed manner. The numerical results verify the effectiveness of our proposal.

Achieving Bi-Channel-Connectivity with Topology Control in Cognitive Radio Networks

Abstract: In cognitive radio networks (CRNs), secondary users (SUs) must vacate the spectrum when it is reclaimed by the primary users (PUs). As such, multiple SUs transmitting on the same channel will be affected when the channel is requested by the PUs, thereby resulting in a possible network partition of CRNs. Therefore, how to maintain the connectivity of CRNs considering the activity of PUs is a critical problem. In this paper, we propose a centralized and a distributed topology control algorithm respectively to address this problem. Particularly, we combine power control and channel assignment to construct a bi-channel-connected and conflict-free topology using the minimum number of channels. In the power control phase, we tailor the topology for the channel assignment in the second phase. In the channel assignment phase, we utilize the graph coloring algorithm to achieve conflict-free transmission by assigning a channel to each SU. Theoretical analysis and simulation study show that the derived topology can maintain connectivity in the event of any single channel interruption by PUs. Simulation results also demonstrate that the proposed algorithms can efficiently reduce the average number of required channels for achieving bi-channel-connectivity and conflict-free transmission and ensure that the minimum power paths in the original network preserved in the final topology.

Interference-aware QoS multicast routing for smart grid

Abstract: In the smart grid Wide Area Control Systems (WACS), controller sends command & control message (C & C) messages to remote devices. The reliability and stability of WACS heavily depends on whether the remote devices react promptly. In other words, the end-to-end transmission delay of the C & C messages plays a significant role in ensuring the performance of WACS. Multihop wireless mesh networks are considered as suitable networking infrastructure for providing data communication in smart grid. Nevertheless, due to the interference nature of wireless networks, identifying paths with minimum end-to-end delay is not trivial. This paper deals with the issue of identifying the multicast tree with minimum end-to-end transmission delay for multicasting a C & C message from the controller to a set of remote devices. Our proposal particularly considers the specific communication requirement from smart grid. The contributions of this paper are: (1) we formulate the problem of calculating multicast tree delay as an integer linear programming; (2) we propose a delay estimation method; (3) we propose a new routing algorithm to identify a multicast tree with the minimum delay. Through extensive numerical experiments, we demonstrate that the proposed routing algorithm outperforms the existing multicast tree routing algorithm.

Correlations of Interference and Link Successes in Heterogeneous Cellular Networks

Abstract: In heterogeneous cellular networks (HCNs), the interference received at a user is correlated over time slots since it comes from the same set of randomly located base stations (BSs). This results in the correlations of link successes, thus affecting network performance. Under the assumptions of a K-tier Poisson network, strongest long-term averaged biased-received- power based BS association, and independent Rayleigh fading, we first quantify the correlation coefficients of interference. We observe that the interference correlation is independent of the number of tiers, BS density, signal-to-interference-ratio (SIR) threshold, and transmit power. Then, we study the correlations of link successes in terms of the joint success probability over multiple time slots.We show that analysis without considering the temporal interference correlation underestimates the joint success probability. Moreover, we explore the effects of BS density, transmit power and user association bias on the joint success probability. In particular, BS density and transmit power affect the joint success probability of the overall network by influencing the association probability of each tier. We also reveal that the unbiased cell association outperforms the biased cell association in terms of the joint success probability. Finally, we conduct simulations to validate our analysis.

Tradeoff between energy-efficiency and spectral-efficiency by cooperative rate splitting

Abstract: The trend of an increasing demand for a high-qualityuser experience, coupled with a shortage of radio resources, has necessitated more advanced wireless techniques to cooperatively achieve the required quality-of-experience enhancement. In this study, we investigate the critical problem of rate splitting in heterogeneous cellular networks, where concurrent transmission, for instance, the coordinated multipoint transmission and reception of LTE-A systems, shows promise for improvement of network-wide capacity and the user experience. Unlike most current studies, which only deal with spectral efficiency enhancement, we implement an optimal rate splitting strategy to improve both spectral efficiency and energy efficiency by exploring and exploiting cooperation diversity. First, we introduce the motivation for our proposed algorithm, and then employ the typical cooperative bargaining game to formulate the problem. Next, we derive the best response function by analyzing the dual problem of the defined primal problem. The existence and uniqueness of the proposed cooperative bargaining equilibrium are proved, and more importantly, a distributed algorithm is designed to approach the optimal unique solution under mild conditions. Finally, numerical results show a performance improvement for our proposed distributed cooperative rate splitting algorithm.

Joint Congestion Control and Scheduling in Wireless Networks with Network Coding

Abstract: This paper studies how to perform joint congestion control and scheduling with network coding in wireless networks. Under network coding, a node may need to buffer a sent packet for decoding a packet to be received later. If sent packets are not forgotten smartly, much buffer space will be taken up, leading to dropping of new incoming packets. This unexpected packet dropping harms the final throughput obtained, although optimal scheduling has been used. To solve the problem, we introduce a new node model incorporating a transmission-mode preassign- ment procedure and a scheduling procedure. The introduced transmission-mode preassignment avoids memorizing several sent packets to reduce buffer overhead. We develop a new scheduling policy based on our node model and analyze formally the stability property of a network system using the proposed policy. We finally evaluate the efficiency of our algorithm through simulations from the perspectives of throughput and packet loss ratio.

Decadal variation of East Asian radiative forcing due to anthropogenic aerosols during 1850–2100, and the role of atmospheric moisture

Abstract: An aerosol mass dataset simulated from a chemical transport model for the period 1850 to 2100 is used in an atmospheric general circulation model to investigate anthropogenic aerosol radiative forcing (RF) with a focus on East Asia. Compared to the pre-industrial era, the calculated strongest global mean direct RF (DRF) of −0.30 W m−2 at the all-sky top of the atmosphere (TOA) occurs in the 1980s and an indirect cloud albedo forcing (CAF) of −0.67 W m−2 in the 2000s; a maximum atmospheric DRF of 0.48 W m−2, mainly by black carbon absorption, is found in the 2010s. Much larger aerosol DRF and CAF values are distributed over East Asia until the 2010s, and the negative surface and positive atmospheric DRF in Eastern China is even projected to maintain a magnitude of 5.0 W m−2 until the 2030s. Increasing East Asian aerosol loading has shifted the anthropogenic aerosol RF centers to lower latitudes in the Northern Hemisphere since the 1980s, and this trend is more severe under future midand high-range emission scenarios. Further results indicate that larger DRF values over East Asia can be partly attributed to climatological summer atmospheric moisture that is higher relative to Norther American and European regions, which enhances the aerosol hygroscopic effect, then strengthens aerosol optical depth and DRF at clear-sky TOA and surface, and even influences their long-term changes. The observational comparisons reveal that present day simulated surface concentrations of key anthropogenic aerosol species and resulting optical depth are highly underestimated in Eastern China. Further research on simulated meteorology and aerosol features is therefore recommended to reduce the uncertainties in estimating aerosol RF over East Asia.

Joint Interference Alignment and Avoidance for Downlink Heterogeneous Networks

Abstract: In this letter, a two-stage interference alignment (IA) scheme and a link scheduling scheme are proposed to cooperatively address both the cross-tier and co-tier interference for downlink heterogeneous networks (HetNets). The two-stage IA enables more small cells to transmit simultaneously by exploiting the characteristics of HetNets and the sacrificed signal dimensions of conventional IA. Then we propose a link scheduling scheme to address the interference that cannot be solved by the two-stage IA. Link scheduling is responsible for choosing the small cell links that can simultaneously transmit by using the two-stage IA and scheduling interfering small cell links to different time slots to avoid interference. Link scheduling is designed with the aims to minimize the number of time slots needed to schedule all links and then maximize the number of scheduled links in these time slots. The simulation results show that the proposed scheme can significantly increase the sum rate of HetNets.

Partial relay selection for a roadside-based two-way amplify-and-forward relaying system in mixed nakagami-m and 'double' nakagami-m fading

Abstract: This study analyses the performance of a roadside two-way relaying system in which a roadside access point (AP) and a vehicle exchange messages with the aid of amplify-and-forward mobile relay (MR) based on partial relay selection. It has been shown that AP-MR-vehicle communications may experience severer channel fading than conventional cellular communications. Mixed Nakagami-m and ‘double’ Nakagami-m fading is adopted to provide a realistic description of the involved AP-MR-vehicle channels. In this scenario, a tight closed-form lower bound and high signal-to-noise ratio approximate expression for the system outage probability are derived. By applying these results, the authors obtain the diversity and the coding gains and the average symbol error rate for the considered system. In particular, the optimum number of relays is provided, providing valuable guidelines for practical system design. It is shown that when the number of relays is greater than the optimum number, no performance gain would be further achieved. The simulation results highlight the authors theoretical analysis.

Network selection policy based on effective capacity in heterogeneous wireless communication systems

Abstract: A great deal of previous research was based on the concept of Shannon theory without considering the delay characteristic. However, in reality, different services have different delay constraints. In this paper, two new network selection policies are proposed for heterogeneous wireless communication systems using effective capacity, which incorporate delay in the transmission rate. Users can access the proper network after considering the delay demands of different services. Our proposed policies aim to maximize the entire throughput with different delay constraints. Both the mathematical analysis and simulations show that the proposed network selection policies can improve network throughput while providing quality-of-service guarantees.

Strategic bargaining in wireless networks: basics, opportunities and challenges

Abstract: Strategic bargaining cooperative games have found extensive applications to resource management in wireless networks. In this survey, basics of a strategic bargaining game and solution concepts are firstly presented. Geometrical interpretations are introduced to better understand real meanings of them. Then, the authors survey the applications of various strategic bargaining games for the emerging wireless networks, where the authors concentrate on several interesting problems based on their previous systematic studies: (i) distributed resource management design for cognitive radio networks based on geometrical interpretation of the cooperative solution; (ii) asymmetric bargaining modelling for green communications; (iii) a unified utility tradeoff design between spectral and energy efficiency in heterogeneous cellular networks; (iv) the cooperative rate splitting game for Long Term Evolution-coordinated multi-point system; and (v) a general bargaining formulation with different tradeoffs between efficiency and fairness. In addition, the authors survey the applications of strategic bargaining games to cooperation incentive mechanism, bargaining game on capacity region of interference channel and multiuser and multimedia applications. Finally, challenges and potential research direction are summarised in this work.

Robust power allocation in two-tier heterogeneous networks

Abstract: This paper focuses on a robust distributed power allocation scheme for downlink two-tier heterogeneous networks (HetNets). The objective is to maximize the network aggregate utility of femtocell users (FUEs) which factors the fairness between users under the constraint of not causing serious interference to existing macrocell users (MUEs). Being impractical for different nodes to cooperate in HetNets to obtain precise estimated values of the channel gains between them, it is a challenge to guarantee the performance of the power allocation algorithm by using existing methods. This work makes a step forward in the direction of conquering this challenge by taking into account channel uncertainty, and the robust counterpart of nominal problem, without channel uncertainty, is framed by using worst-case robust optimization theory. To make the robust counterpart computationally tractable, we exploit its convexity and derive that the channel uncertainties between a FUE and nearby femtocell base stations (FBSs) fall into water-filling form being related to the received power from interference sources. Based on the inherent relationship between channel uncertainty and received power, we design a distributed algorithm which merely needs to solve a deterministic problem. The algorithm is devised based on alternating direction method of multipliers (ADMM) with a fast convergence speed. The simulation results demonstrate the robustness of our proposed approach, and the corresponding cost of robustness is investigated.

Antenna selection and transmit beamforming optimisation with partial channel state information in distributed antenna systems

Abstract: This study studies the joint antenna selection and transmit beamforming optimisation in the downlink of a single-cell multi-user distributed antenna system, assuming that all users are delay sensitive and only partial channel state information is available at the transmitter side. Under the constraint of the maximum transmit power of each distributed antenna unit, the authors formulate an optimisation problem to minimise the total power consumption while maintaining the rate outage ratio of each user below a threshold. To mitigate the signalling overhead, they firstly propose an adaptive antenna selection strategy based on the received pilot signal power strength. Then, considering that the remaining transmit beamforming problem may be infeasible and non-convex, a series of relaxation and convex approximation are applied. Finally, they propose a transmit beamforming algorithm based on successive convex approximation and user admission control. Simulation results show that the authors proposed algorithm can achieve a near optimal system performance in both the satisfied user ratio and total power consumption.

Joint user scheduling and power allocation with quality of service guarantees in downlink distributed antennas system

Abstract: In this study, the authors study the downlink joint user scheduling and power allocation in a single-cell distributed antennas system. Considering that all users are delay sensitive and without any assumption on the feasibility of the system, they formulate an optimisation problem to minimise the total power consumption while maximising the number of satisfied users. Given a user scheduling result, a deflation-based joint user removal and power allocation algorithm and a conservative power allocation algorithm are proposed. Owing to the complexity in full enumeration of all user scheduling results, they further propose a joint heuristic user scheduling and power allocation algorithm, in which a priority parameter is defined to determine the user scheduling order and the conservative power allocation algorithm is applied to execute the power allocation. The user with the worst quality of experience is iteratively removed away from the active user set until all the remaining users are guaranteed with their quality of service requirements. Simulation results show that the authors proposed heuristic algorithm obtains a near optimal system performance in both user outage ratio and total power consumption.

Cooperative Spectrum Leasing to Femtocells with Interference Compensation

Abstract: Spectrum leasing is a novel promising technique to improve the spectrum efficiency (SE) through the spectrum owner leasing its free or under-utilization spectrum to unlicensed users for superfluous spectrum revenue, while the unlicensed users should pay for spectrum renting. Recently, spectrum leasing is used between femtocell service provider (FSP) and the coexisting macrocell service provider (MSP) in heterogeneous networks (HetNets). However, the energy efficiency (EE), a critical performance metric in HetNets, especially when multiple FSPs are densely overlaid on the coverage of MSP, has been largely neglected in available SE-oriented spectrum leasing. In this paper, a cooperative spectrum leasing framework is proposed to both mitigate interference and save energy, where a Stackelberg coordination game is formulated to analyze a joint spectrum leasing, pricing and interference coordination process between FSPs and MSP with the novel energy-aware utility functions for the players of FSPs and MSP. We rigorously derive the optimal closed-form solutions of spectrum leasing, pricing, and power coordination solutions for the FSP and the MSP. We propose a multi-stage distributed algorithm to approach these solutions. Finally, simulation results are provided to clarify effects of multiple parameters in the gaming process and verify the final improved performance.

On minimizing delay with probabilistic splitting of traffic flow in heterogeneous wireless networks

Abstract: In the paper, we propose a framework to investigate how to effectively perform traffic flow splitting in heterogeneous wireless networks from a queue point. The average packet delay in heterogeneous wireless networks is derived in a probabilistic manner. The basic idea can be understood via treating the integrated heterogeneous wireless networks as different coupled and parallel queuing systems. The integrated network performance can approach that of one queue with maximal the multiplexing gain. For the purpose of illustrating the effectively of our proposed model, the Cellular/WLAN interworking is exploited. To minimize the average delay, a heuristic search algorithm is used to get the optimal probability of splitting traffic flow. Further, a Markov process is applied to evaluate the performance of the proposed scheme and compare with that of selecting the best network to access in terms of packet mean delay and blocking probability. Numerical results illustrate our proposed framework is effective and the flow splitting transmission can obtain more performance gain in heterogeneous wireless networks.

Joint subcarrier, code, and power allocation for parallel multi-radio access in heterogeneous wireless networks

Abstract: In the heterogeneous wireless networks, it has been proved that the joint spectrum and power allocation can achieve network diversity gains for parallel multi-radio access in theory. This article aims to develop an effective and practical algorithm of joint subcarrier, code, and power allocation for parallel multi-radio access of the downlink in heterogeneous wireless networks (e.g., CDMA and OFDMA). Firstly, we propose a unified framework to formulate the subcarrier, code, and power allocation as an optimization problem. Secondly, we propose a resource element (subcarrier and code) scheme based on the threshold type. Simulation results show that the proposed scheme outperforms the existing algorithm for considered wireless scenarios.

Efficient resource allocation scheme for multi-service based on interference mitigation in LTE-Advanced networks

Abstract: The exponential growth of various services demands the increased capacity of the next-generation broadband wireless access networks, which is toward the deployment of femtocell in macrocell network based on orthogonal frequency division multiple access. However, serious time-varying interference obstructs this macro/femto overlaid network to realize its true potential. In this article, we present a macro services guaranteed resource allocation scheme, which can mitigate various dominant interferences and provide multiple services in macro/femto overlaid Third-Generation Partnership Project Long Term Evolution-Advanced networks. We model our multiple services resource allocation scheme into a multiobjective optimization problem, which is a non-deterministic polynomial-time (NP)-hard problem. Then, we give a low-complexity algorithm consisting of two layers based on chordal graph. Simulation results verify that the proposed scheme can achieve better efficiency than the previous works and raise the satisfaction ratio of Guaranteed Bit Rate (GBR) services while improving the average performance of non-GBR services.

Power allocation and relay selection for AF two-path successive relaying networks

Abstract: Two-path or successive relaying, which aims to establish two relay links transmitting different information symbols in adjacent time slots, has recently emerged as an attractive wireless communication protocol to improve the spectral efficiency in half-duplex cooperative systems. In this paper, we investigate power allocation and relay selection techniques for amplify-and-forward two-path successive relaying networks. Our approach is based on the maximization of the received SNR subject to a total power budget consumed by the source and the relay assisting this specific transmission. Two scenarios including with and without direct link are considered here. We show that the main problem has a closed-form solution and only requires a few amounts of feedback bits to be broadcasted. Numerical results reveal that the proposed approaches are more insensitive to the inter-relay interference and robust to channel estimation errors; meanwhile, they perform better than the existing schemes. Copyright © 2013 John Wiley & Sons, Ltd.

Interference Mitigation and Energy Management in Heterogeneous Networks: A Cognitive Radio Perspective

Abstract: In Long Term Evolution (LTE) 4G systems, coexistence of multiple in-band smallcells defines what is called heterogeneous cellular networks. There is no doubt that the development of heterogeneous networks and the popularization of intelligent terminals facilitate subscribers with great convenience, better Quality of Experience (QoE) guarantee, and much higher traffic rate. However, interference management will be indispensable in heterogeneous networks. Meanwhile, with emerging various energy-hungry services of subscribers, energy-aware design attracts a wide attention. Motivated by interference mitigation and energy-saving challenges of the heterogeneous networks and the promising cognitive radio techniques, more advanced energy-saving and interference control techniques based on cognitive radio should be developed for better QoE. In this chapter, the authors first review cognitive radios, multiple types of smallcells, and introduce the benefits of cognitive radio-enabled heterogeneous networks. Then, focusing on the scheme design of cognitive interference management and energy management, finally, simulation results are provided to show the improved performance of these proposed cognitive schemes. INTRODUCTION AND MOTIVATION Next generation (xG) wireless networks will contain a number of radio access networks (RANs). Different RANs employ different radio access technologies (RATs). Meanwhile, subscribers who are equipped with smart terminals are pursuing much better user experience with multi-mode, reconfigurable and cognitive equipments. In long term evolution (LTE) 4G systems, coexistence of multiple in-band smallcells defines what is called heterogeneous cellular networks. Since Chungang Yang Xidian University, China Jiandong Li Xidian University, China DOI: 10.4018/978-1-4666-5978-0.ch006

Access point selection in heterogeneous wireless networks using belief propagation

Abstract: The next generation wireless network will be composed by various heterogenous wireless access networks, such as cellular network, worldwide interoperability for microwave access (WiMAX), wireless local area network (WLAN), etc. Different access networks cooperatively provide high-bandwidth connectivity with bandwidth guarantees. This paper proposes a utility-based access point selection scheme, which selects an accessible point for each user, such that the bandwidth requirement of each user is satisfied, and also the defined utility function is maximized. Due to the NP-complete nature of the problem, the existing proposals apply the greedy method to find a solution. We find that belief propagation is an efficient tool to solve this problem, and thus, we derive the same optimization objective in a new way, and then draw a factor graph representation which describes our combinatorial optimization problem. Afterwards, we develop the belief propagation algorithm, and show that our algorithm converges. Finally, we conduct numerical experiments to evaluate the convergency and accuracy of the belief propagation in load balancing problem.

Interference management for rate-constrained moving relay node in a heterogeneous network

Abstract: Cooperative communication via a moving relay node (MRN) helps resolve both the poor quality of service (QoS) and limited battery-capacity problems of cell-edge vehicle user equipment (VUE). This paper investigates the performance of MRNs in a heterogeneous network (HetNet). MRNs as well as other small cells are expected to coexist in a complex manner. In such a HetNet, the inter-cell interference may degrade the expected improvement of MRNs, especially at the cell-edge. In this paper, we investigate the impact of intercell interference on the performance of MRNs. To alleviate this impact, we first formulated a general optimization problem for which it is intractable to find a global optimal solution. To have a practical solution with low computational complexity, we used a practical interference management algorithm that aimed to ensure that every MRN achieved its required minimum-rate while maximizing total network throughput. In the simulations, the proposed algorithm was observed to improve both the QoS and fairness of MRNs. Numerical results demonstrate that the proposed algorithm can offer an efficient trade-off between the performance of both the victim MRNs and aggressing femtocells.

Geometric-Mean-Decomposition-Based Optimal Transceiver for a Class of Two-Hop MIMO-Aided Amplify-and-Forward Relay Channels

Abstract: A geometric mean decomposition (GMD)-based joint transceiver is investigated in the context of a multiple-input-multiple-output (MIMO)-aided relay-assisted two-hop amplify-and-forward relaying system. The canonical form of the optimal weighting matrix is derived, which is capable of achieving the maximum received signal-to-noise ratio (SNR) at the destination. Furthermore, the optimal power allocation is formulated as a geometric programming problem. The proposed optimal design of the linear weighting matrix achieves an approximately 5-dB SNR gain over the naive weighting matrix at the bit error rate (BER) of 10-3 as a benefit of efficiently exploiting the low-complexity linear signal processing capability of the relay.

Interference Alignment for VFDM Based Uplink Transmission in Two-Tiered Networks

Abstract: In this work, we study the problem of interference in a two-tiered uplink network which contains a macro-cell and multiple small-cells. We null the interference from small-cells to macro-cell by using Vandermonde-subspace frequency division multiplexing (VFDM). VFDM can exploit frequency selectivity and null space generated by the cyclic prefixes (CP) used by the macro-cell communication. We use an interference alignment (IA) scheme with an extension of a grouping method to align the interference between multiple small-cells into a lower dimensional-subspace, by using this grouping method we reduce the number of receive antennas required to null interference. Finally, we derive the achievable degrees of freedom (DoF).

Delay Performance Optimization of Multiaccess for Uplink in Heterogeneous Networks

Abstract: Heterogeneous networks are an attractive means of improving the network capacity. Heterogeneous network are typically composed of multiple radio access points (macro, pico and femto) where the base stations are transmitting with variable power. In this study, we consider the uplink of heterogeneous networks, where each terminal can simultaneously connected to multiple radio access points and requests delay-sensitive traffic (e.g., real-time video). We adopt the framework of Hou, Borkar,and Kumar, and study the delay in heterogeneous networks and analyze the multiaccess transmission delay by considering three extreme scheduling schemes. Moreover, a parallel-aggregation multiple radio access points (PA-MRA) algorithm for packet scheduling is presented to improve the transmission delay in heterogeneous networks. Analysis and numerical results show that the proposed algorithm obtains the optimal and robust transmission delay gain compared with the three extreme scheduling policies.

3D Polarization Projection for WINNER Channel Simulations

Abstract: Wireless world initiative new radio (WINNER) delivers a 3D cross-polarized channel model for B3G/4G system designs. Comprehensive radiation characteristics of polarized antenna are crucial in generating channel coefficients. Being currently supported within WINNER channel model, field patterns are technically obtained by chamber measurement. However, in some channel related performance analysis scenarios, design insight can be crystallized better by starting the derivations with theoretical co-pol and cross-pol components. Specifically, these two components are mathematically linked with field patterns through the proposed polarization projection algorithm. In this paper, we focus on revealing the physical significance of polarization transform between the antenna plane and the propagation plane. In practice, it makes retrieving the field patterns by electromagnetic computation possible. Meanwhile, the impact imposed by distinct antenna orientations is geometrically illustrated and consequently incorporated into the proposed algorithm. The result is analytically verified by the closed-form expression of the dipole field pattern and we find that its 2D degenerative case is aligned with that defined in 3GPP TR 25.996. The benefit is to significantly reduce the cost on generating channel coefficients in WINNER channel simulations.