Showing papers in "IEEE Communications Letters in 2015"

Cooperative Non-Orthogonal Multiple Access in 5G Systems

Abstract: Non-orthogonal multiple access (NOMA) has received considerable recent attention as a promising candidate for 5G systems. A key feature of NOMA is that users with better channel conditions have prior information about the messages of other users. This prior knowledge is fully exploited in this letter, where a cooperative NOMA scheme is proposed. The outage probability and diversity order achieved by this cooperative NOMA scheme are analyzed, and an approach based on user pairing is also proposed to reduce system complexity.

Practical Non-Linear Energy Harvesting Model and Resource Allocation for SWIPT Systems

Abstract: In this letter, we propose a practical non-linear energy harvesting model and design a resource allocation algorithm for simultaneous wireless information and power transfer (SWIPT) systems. The algorithm design is formulated as a non-convex optimization problem for the maximization of the total harvested power at energy harvesting receivers subject to minimum required signal-to-interference-plus-noise ratios (SINRs) at multiple information receivers. We transform the considered non-convex objective function from sum-of-ratios form into an equivalent objective function in subtractive form, which enables the derivation of an efficient iterative resource allocation algorithm. In each iteration, a rank-constrained semidefinite program (SDP) is solved optimally by SDP relaxation. Numerical results unveil a substantial performance gain that can be achieved if the resource allocation design is based on the proposed non-linear energy harvesting model instead of the traditional linear model.

Non-Orthogonal Multiple Access in Coordinated Direct and Relay Transmission

Abstract: In this work, non-orthogonal multiple access (NOMA) in coordinated direct and relay transmission (CDRT) is introduced, where a base station (BS) directly communicates with user equipment 1 (UE1) while communicating with user equipment 2 (UE2) only through a relay. The main challenge of non-orthogonal CDRT can be solved by using the inherent property of NOMA that allows a receiver to obtain side information such as other UE's data for interference cancellation. Analytical expressions for outage probability and ergodic sum capacity are provided. It is shown that the proposed NOMA in CDRT provides remarkable performance gain compared with NOMA in non-coordinated direct and relay transmission (nCDRT); the sum capacity scaling of the proposed scheme is $\log \rho_b$ as signal-to-noise-ratio (SNR) $\rho_b$ increases, but $\frac{1}{2_{}}\log \rho_b$ for NOMA in nCDRT. Exact and closed-form expressions for outage probability of each stream for UE1 and UE2 are respectively derived, and it is shown that the achievable diversity orders for each stream are same as one.

Capacity Analysis of Cooperative Relaying Systems Using Non-Orthogonal Multiple Access

Abstract: In this letter, we propose the cooperative relaying system using non-orthogonal multiple access (NOMA) to improve the spectral efficiency. The achievable average rate of the proposed system is analyzed for independent Rayleigh fading channels, and also its asymptotic expression is provided. In addition, a suboptimal power allocation scheme for NOMA used at the source is proposed.

Uplink Achievable Rate for Massive MIMO Systems With Low-Resolution ADC

Abstract: In this letter, we derive an approximate analytical expression for the uplink achievable rate of a massive multiinput multioutput (MIMO) antenna system when finite precision analog-digital converters (ADCs) and the common maximal-ratio combining technique are used at the receivers. To obtain this expression, we treat quantization noise as an additive quantization noise model. Considering the obtained expression, we show that low-resolution ADCs lead to a decrease in the achievable rate but the performance loss can be compensated by increasing the number of receiving antennas. In addition, we investigate the relation between the number of antennas and the ADC resolution, as well as the power-scaling law. These discussions support the feasibility of equipping highly economical ADCs with low resolution in practical massive MIMO systems.

Energy Efficient Clustering Scheme for Prolonging the Lifetime of Wireless Sensor Network With Isolated Nodes

Abstract: A suitable clustering algorithm for grouping sensor nodes can increase the energy efficiency of WSNs. However, clustering requires additional overhead, such as cluster head selection and assignment, and cluster construction. This paper proposes a new regional energy aware clustering method using isolated nodes for WSNs, called Regional Energy Aware Clustering with Isolated Nodes (REAC-IN). In REAC-IN, CHs are selected based on weight. Weight is determined according to the residual energy of each sensor and the regional average energy of all sensors in each cluster. Improperly designed distributed clustering algorithms can cause nodes to become isolated from CHs. Such isolated nodes communicate with the sink by consuming excess amount of energy. To prolong network lifetime, the regional average energy and the distance between sensors and the sink are used to determine whether the isolated node sends its data to a CH node in the previous round or to the sink. The simulation results of the current study revealed that REAC-IN outperforms other clustering algorithms.

Non-Orthogonal Multiple Access for Multiple-Antenna Relaying Networks

Abstract: In this letter, we design non-orthogonal multiple access (NOMA) for multiple-antenna relaying networks. The receive antennas at the mobile users are assumed to adopt maximal ratio combining (MRC), whereas the transmit antenna that maximizes the instantaneous signal-to-noise ratio (SNR) at the relay is selected. The system outage performance is investigated and closed-form expressions for the exact outage probability are derived. Furthermore, we obtain the lower bound of the outage probability. Finally, simulation results are presented to show the correctness of the theoretical analysis and the superiority of NOMA.

Expansion Model for the Controller Placement Problem in Software Defined Networks

Abstract: In this letter, we propose a mathematical model for the controller placement problem in Software Defined Networks (SDN). More precisely, given a set of switches that must be managed by the controller(s), the model simultaneously determines the optimal number, location, and type of controller(s) as well as the interconnections between all the network elements. The goal of the model is to minimize the cost of the network while considering different constraints. The simulation results show that the model can be used to plan small scale SDN. When trying to solve larger instances of the problem, the solver is taking too much time and also running out of memory. The proposed model could be used by various enterprises and cloud-based networks to start integrating SDN or plan a new SDN.

Smart Pilot Assignment for Massive MIMO

Abstract: A massive multiple-input multiple-output (MIMO) system, which utilizes a large number of antennas at the base station (BS) to serve multiple users, suffers from pilot contamination due to inter-cell interference. A smart pilot assignment (SPA) scheme is proposed in this letter to improve the performance of users with severe pilot contamination. Specifically, by exploiting the large-scale characteristics of fading channels, the BS first measures the inter-cell interference of each pilot sequence caused by the users with the same pilot sequence in other adjacent cells. Then, in contrast to the conventional schemes which assign the pilot sequences to the users randomly, the proposed SPA method assigns the pilot sequence with the smallest inter-cell interference to the user having the worst channel quality in a sequential way to improve its performance. Simulation results verify the performance gain of the proposed scheme in typical massive MIMO systems.

Balancing Energy Consumption in Heterogeneous Wireless Sensor Networks Using Genetic Algorithm

Abstract: In a heterogeneous Wireless Sensor Network (WSN), factors such as initial energy, data processing capability, etc greatly influence the network lifespan Despite the success of various clustering strategies of WSN, the numerous possible sensor clusters make searching for an optimal network structure an open challenge In this paper, we propose a Genetic Algorithm based method that optimizes heterogeneous sensor node clustering Compared with five state-of-the-art methods, our proposed method greatly extends the network life, and the average improvement with respect to the second best performance based on the first-node-die and the last-node-die is 338% and 13%, respectively The balanced energy consumption greatly improves the network life and allows the sensor energy to deplete evenly The computational efficiency of our method is comparable to the others and the overall average time across all experiments is 06 seconds with a standard deviation of 006

Anti-Jamming Transmission Stackelberg Game With Observation Errors

Abstract: As smart jammers that can analyze the ongoing radio transmission with flexible and powerful control on jamming signals throw serious threats on cognitive radio networks, game theory provides a powerful approach to study the interactions between smart jammers and secondary users (SUs). In this work, the power control strategy of an SU against a smart jammer under power constraints is formulated as a Stackelberg game. The jammer as the follower of the game chooses the jamming power according to the observed ongoing transmission, while the SU as the leader determines its transmit power based on the estimated jamming power. The impact of the observation accuracy of the jammer regarding the transmit power of the SU is investigated. The Stackelberg equilibrium of the anti-jamming game is derived and compared with the Nash equilibrium of the game. Simulation results show that the transmission of an SU benefits from the observation error of the jammer with a higher signal-to-interference-plus-noise ratio and utility.

Low-Complexity ML Detector and Performance Analysis for OFDM With In-Phase/Quadrature Index Modulation

Abstract: A novel variant of orthogonal frequency division multiplexing (OFDM) techniques, which carries additional information bits through the index domain including in-phase and quadrature dimensions, is recently proposed. For its nature, we refer to this technique as OFDM with in-phase/quadrature index modulation (OFDM-I/Q-IM) . In this letter, we propose a novel low-complexity detector based on the maximum-likelihood (ML) criterion for OFDM-I/Q-IM, which does not need to know the variance of the noise and the possible realizations of the active subcarrier indices. With the proposed ML detector, the asymptotic average bit error probability (ABEP) and the exact coding gain achieved by OFDM-I/Q-IM are also derived.

Full-Duplex Relay for Enhancing Physical Layer Security in Multi-Hop Relaying Systems

Abstract: In this letter, we consider secure communications in multi-hop relaying systems, where full-duplex relays (FDRs) operate to enhance wireless physical layer security. Each FDR is designed to transmit jamming signals to the eavesdropper when it receives information signals from the previous adjacent node. The achievable secrecy rate with the proposed decode-and-forward (DF) FDRs are analyzed with a total transmit power constraint. The transmit power allocation problem is solved by using the geometric programming (GP) method. Numerical results present that the proposed FDRs significantly enhance the secrecy rate compared to the conventional half-duplex relays (HDRs).

On the Performance of Multiuser Hybrid Satellite-Terrestrial Relay Networks With Opportunistic Scheduling

Abstract: In this letter, we investigate the performance of a multiuser amplify-and-forward (AF) hybrid satellite-terrestrial relay network (HSTRN) with opportunistic scheduling. Specifically, we derive the analytical approximated expression as well as the tight upper and lower bound for the ergodic capacity of the system. Moreover, we present the analytical and asymptotic formulas of the outage probability (OP), which provide practical insights on the diversity order and code gain. Finally, simulation results are given to validate the theoretical results, and show the impact of key parameters such as user numbers and shadowing severity on the performance of the considered network.

On Physical Layer Security Over Generalized Gamma Fading Channels

Abstract: In this letter, we study the secrecy performance of the classic Wyner's wiretap model over the generalized Gamma fading channels. The closed-form expressions for the probability of strictly positive secrecy capacity and the lower bound of secure outage probability are derived. Monte-Carlo simulations are performed to verify the derived analysis.

Graph Coloring Based Pilot Allocation to Mitigate Pilot Contamination for Multi-Cell Massive MIMO Systems

Abstract: A massive multiple-input multiple-output (MIMO) system, which utilizes a large number of base station (BS) antennas to serve a set of users, suffers from pilot contamination due to the inter-cell interference (ICI) In this letter, a graph coloring based pilot allocation (GC-PA) scheme is proposed to mitigate pilot contamination for multi-cell massive MIMO systems Specifically, by exploiting the large-scale characteristics of fading channels, an interference graph is firstly constructed to describe the potential ICI relationship of all users Then, with the limited pilot resource, the proposed GC-PA scheme aims to mitigate the potential ICI by efficiently allocating pilots among users in the interference graph The performance gain of the proposed scheme is verified by simulations

RUFS: RobUst Forwarder Selection in Vehicular Content-Centric Networks

Abstract: Vehicular Content-Centric Network (VCCN) has emerged as a future network technology for vehicular networks, where the focus of communication is shifted from the host to information centric However, VCCN faces several challenges, including interest/data packet(s) flooding, provider/consumer mobility, and so on In this letter, we propose a scheme named RobUst Forwarder Selection (RUFS) to mitigate the interest broadcast storm In RUFS, each vehicle shares its satisfied interest(s) statistics with neighbors All neighbors store this information in their Neighbors Satisfied List (NSL), which helps to select the potential interest forwarder Simulation results show that RUFS outperforms the recently proposed NAIF, DR based and basic interest forwarding in VCCN

Distributed Energy Efficient Fair User Association in Massive MIMO Enabled HetNets

Abstract: Massive multiple-input and multiple-output (MIMO) and heterogeneous networks (HetNets) have been recognized as key enabling technologies for future fifth generation (5G) mobile networks However, the circuit power consumption of massive MIMO scales with the tremendous number of antennas As a result, the problem of energy efficient user association in massive MIMO enabled HetNets is of vital importance We investigate the energy efficient user association problem in massive MIMO enabled HetNets, and formulate the network logarithmic utility maximization problem Based on the Lagrangian dual analysis, a low complexity distributed user association algorithm is developed for energy efficient fair user association while considering quality of service (QoS) provision for users Simulation results demonstrate the effectiveness of the proposed algorithm in improving the energy efficiency and user fairness, compared to other user association algorithms

Security-Aware Relaying Scheme for Cooperative Networks With Untrusted Relay Nodes

Abstract: This paper studies the problem of secure transmission in dual-hop cooperative networks with untrusted relays, where each relay acts as both a potential helper and an eavesdropper. A security-aware relaying scheme is proposed, which employs the alternate jamming and secrecy-enhanced relay selection to prevent the confidential message from being eavesdropped by the untrusted relays. To evaluate the performance of the proposed strategies, we derive the lower bound of the achievable ergodic secrecy rate (ESR), and conduct the asymptotic analysis to examine how the ESR scales as the number of relays increases.

Outage Analysis of Practical FSO/RF Hybrid System With Adaptive Combining

Abstract: Hybrid free-space optical (FSO)/radio-frequency (RF) systems have emerged as a promising solution for high-data-rate wireless transmission. We present and analyze a transmission scheme for the hybrid FSO/RF communication system based on adaptive combining. Specifically, only FSO link is active as long as the instantaneous signal-to-noise ratio (SNR) at the FSO receiver is above a certain threshold level. When it falls below this threshold level, the RF link is activated along with the FSO link and the signals from the two links are combined at the receiver using a dual-branch maximal ratio combiner. Novel analytical expression for the cumulative distribution function (CDF) of the received SNR for the proposed hybrid system is obtained. This CDF expression is used to study the system outage performance. Numerical examples are presented to compare the outage performance of the proposed hybrid FSO/RF system with that of the FSO-only and RF-only systems.

Secrecy Enhancement Analysis Against Unknown Eavesdropping in Spatial Modulation

Abstract: In multiple-input–multiple-output (MIMO) wireless communications, spatial modulation (SM) has recently emerged as a new transmission method. This letter explores the physical-layer security in typical SM systems. We present a secrecy rate analysis for multiple antenna destination and eavesdroppers receivers. Targeting against passive eavesdroppers in unknown locations, we study the efficacy of active security measure through joint signal and jamming transmission without the typical requirement of eavesdropper channel information. We demonstrate the secrecy rate and transmission power tradeoff in active source jamming by providing numerical results on achieved secrecy rate and the bit error rate (BER) at different receivers.

Cooperative Localization in NLOS Environments Using Semidefinite Programming

Abstract: In this letter, cooperative source localization using range-based measurements in severe non-line-of-sight (NLOS) environments is studied. The accuracy of localization can significantly degrade in indoor and dense environments, where the majority of connections are NLOS. Cooperative localization is highly beneficial in such environments by improving localization performance considerably. However, NLOS connections still must be handled properly. In this work, a novel cooperative localization algorithm with the ability to mitigate NLOS propagation based on semidefinite programming (SDP) is derived. It is assumed that the algorithm knows neither which connections are NLOS nor the distribution of NLOS propagation. The performance of the proposed SDP method is compared with that of the optimal maximum-likelihood estimator and several previously considered methods through computer simulations. It will be shown that the proposed SDP method substantially outperforms other methods in NLOS environments.

Code Index Modulation: A High Data Rate and Energy Efficient Communication System

Abstract: A new scheme, called code index modulation-spread spectrum (CIM-SS), is presented in this paper. This scheme is based on direct sequence-spread spectrum (DS-SS) modulation and can achieve higher data rate than the conventional DS-SS with lower energy consumption. At the transmitter, the bit stream is divided into blocks of two bits each. For each block, only the first bit is spread by one of two spreading codes while the second bit selects the code to be used. The receiver estimates both the code and the transmitted bit. The performance of the CIM-SS is analyzed and compared to the conventional DS-SS systems.

Effect of Receptor Density and Size on Signal Reception in Molecular Communication via Diffusion With an Absorbing Receiver

Abstract: The performance of molecular communication is significantly impacted by the reception process of the messenger molecules. The receptors' size and density, however, have yet to be investigated. In this letter, we analyze the effect of receptor density and size on the signal reception of an absorbing receiver with receptors. The results show that, when the total receptor area is the same, better hitting probability is achieved by using a higher number of relatively small receptors. In addition, deploying receptors, which cover a small percentage of the receiver surface, is able to create an effective communication channel that has a detectable signal level.

Joint CSIT Acquisition Based on Low-Rank Matrix Completion for FDD Massive MIMO Systems

Abstract: Channel state information at the transmitter (CSIT) is essential for frequency-division duplexing (FDD) massive MIMO systems, but conventional solutions involve overwhelming overhead both for downlink channel training and uplink channel feedback. In this letter, we propose a joint CSIT acquisition scheme to reduce the overhead. Particularly, unlike conventional schemes where each user individually estimates its own channel and then feed it back to the base station (BS), we propose that all scheduled users directly feed back the pilot observation to the BS, and then joint CSIT recovery can be realized at the BS. We further formulate the joint CSIT recovery problem as a low-rank matrix completion problem by utilizing the low-rank property of the massive MIMO channel matrix, which is caused by the correlation among users. Finally, we propose a hybrid low-rank matrix completion algorithm based on the singular value projection to solve this problem. Simulations demonstrate that the proposed scheme can provide accurate CSIT with lower overhead than conventional schemes.

Robust NLOS Error Mitigation Method for TOA-Based Localization via Second-Order Cone Relaxation

Abstract: The existence of non-line-of-sight (NLOS) errors can significantly degrade the localization performance. In this letter, we address the time-of-arrival (TOA) based localization problem under NLOS conditions. To accurately localize a source, we propose a novel robust second-order cone relaxation (SOCR) method, which is not sensitive to NLOS errors. The proposed method does not require one to know any statistics of the NLOS errors, and instead, it only requires to know the upper bound on the magnitudes of the NLOS errors, which is relatively easy to obtain in practice. Simulation results show that the proposed robust SOCR method has good performance in various NLOS scenarios, and also it has a relatively lower computational complexity than the existing methods.

A Class of Binary Linear Codes With at Most Three Weights

Abstract: In this letter, we use Gauss sums of index 2 to construct a class of new binary linear codes with at most three weights. In special cases, they are optimal or near optimal codes. These codes can be used in authentication codes and secret sharing schemes.

Space-Constrained Massive MIMO: Hitting the Wall of Favorable Propagation

Abstract: The recent development of the massive multiple-input multiple-output (MIMO) paradigm, has been extensively based on the pursuit of favorable propagation : in the asymptotic limit, the channel vectors become nearly orthogonal and inter-user interference tends to zero [1]. In this context, previous studies have considered fixed inter-antenna distance, which implies an increasing array aperture as the number of elements increases. Here, we focus on a practical, space-constrained topology, where an increase in the number of antenna elements in a fixed total space imposes an inversely proportional decrease in the inter-antenna distance. Our analysis shows that, contrary to existing studies, inter-user interference does not vanish in the massive MIMO regime, thereby creating a saturation effect on the achievable rate.

Secret Precoding-Aided Spatial Modulation

Abstract: In this letter, the precoding-aided spatial modulation (PSM) is generalized to a secret PSM (SPSM) scheme, which has the capability to resist malicious eavesdropping from an eavesdropper that is unknown to the transmitter We design a time-varying precoder for the SPSM so that it can retain all the PSM's advantages at the desired receiver while producing time-varying interference to the eavesdropper The secrecy capacity of our proposed SPSM is studied, and the optimal power allocation between signal and interference transmission is investigated Our studies and performance results demonstrate that our SPSM can significantly improve the secrecy performance of the PSM, particularly in a high-signal-to-noise-ratio region Furthermore, the SPSM is capable of achieving a nonzero secrecy rate even when the eavesdropper has more antennas than the desired receiver

Full-Duplex MAC Protocol Design and Analysis

Abstract: The idea of in-band full-duplex (FD) communications has been revived in recent years owing to the significant progress in the self-interference cancellation and hardware design techniques, offering the potential to double spectral efficiency. The adaptations in upper layers are highly demanded in the design of FD communication systems. In this letter, we propose a novel medium access control (MAC) using FD techniques that allows transmitters to monitor the channel usage while transmitting, and backoff as soon as collision happens. Analytical saturation throughput of the FD-MAC protocol is derived with the consideration of imperfect sensing brought by residual self-interference (RSI) in the PHY layer. Both analytical and simulation results indicate that the normalized saturation throughput of the proposed FD-MAC can significantly outperforms conventional CSMA/CA under various network conditions.