Showing papers in "IEEE Communications Letters in 2016"
TL;DR: The results show that, in order to mitigate interference, the altitude of the UAVs must be properly adjusted based on the beamwidth of the directional antenna as well as coverage requirements.
Abstract: In this letter, the efficient deployment of multiple unmanned aerial vehicles (UAVs) acting as wireless base stations that provide coverage for ground users is analyzed. First, the downlink coverage probability for UAVs as a function of the altitude and the antenna gain is derived. Next, using circle packing theory, the 3-D locations of the UAVs is determined in a way that the total coverage area is maximized while maximizing the coverage lifetime of the UAVs. Our results show that, in order to mitigate interference, the altitude of the UAVs must be properly adjusted based on the beamwidth of the directional antenna as well as coverage requirements. Furthermore, the minimum number of UAVs needed to guarantee a target coverage probability for a given geographical area is determined. Numerical results evaluate various tradeoffs.
982 citations
TL;DR: By simulation, it is shown that the outage performances are related to both the power backoff step and the target data rate and the proposed NOMA scheme significantly improves the achievable sum data rate.
Abstract: In order to achieve diverse arrived power in uplink nonorthogonal multiple access (NOMA), an uplink power control scheme is proposed. The proposed scheme makes evolved NodeB (eNB) distinguish the multiplexing user equipments (UEs) in power domain. The outage performance and the achievable sum data rate for the proposed scheme are theoretically analyzed, and the closed-form expressions of outage probability and achievable sum data rate are derived. By simulation, we show that the outage performances are related to both the power backoff step and the target data rate. Compared with the traditional orthogonal multiple access (OMA) scheme, the proposed NOMA scheme significantly improves the achievable sum data rate.
361 citations
TL;DR: Simulation results demonstrate that the proposed FD cooperative NOMA system attains better performance than the half-duplex cooperative N OMA system in the moderate signal-to-noise ratio regime.
Abstract: We propose a full-duplex (FD) cooperative non-orthogonal multiple access (NOMA) system with dual users, where a dedicated FD relay assists the information transmission to the user with weak channel condition. Under the realistic assumption of imperfect self-interference cancellation, the achievable outage probability of both users and ergodic sum capacity are investigated, and exact analytical expressions are derived. Simulation results demonstrate that the proposed FD cooperative NOMA system attains better performance than the half-duplex cooperative NOMA system in the moderate signal-to-noise ratio regime.
319 citations
TL;DR: This letter investigates the problem of user-demand-based UAV assignment over geographical areas subject to high traffic demands and proposes a neural-based cost function approach, in which UAVs are matched to a particular geographical area.
Abstract: Modern day wireless networks have tremendously evolved driven by a sharp increase in user demands, continuously requesting more data and services. This puts significant strain on infrastructure-based macro cellular networks due to the inefficiency in handling these traffic demands, cost effectively. A viable solution is the use of unmanned aerial vehicles (UAVs) as intermediate aerial nodes between the macro and small cell tiers for improving coverage and boosting capacity. This letter investigates the problem of user-demand-based UAV assignment over geographical areas subject to high traffic demands. A neural-based cost function approach is formulated, in which UAVs are matched to a particular geographical area. It is shown that leveraging multiple UAVs not only provides long-range connectivity but also better load balancing and traffic offload. Simulation study demonstrates that the proposed approach yields significant improvements in terms of fifth percentile spectral efficiency up to 38% and reduced delays up to 37.5% compared with a ground-based network baseline without UAVs.
319 citations
TL;DR: Numerical results are provided to show a significant SSR improvement by NOMA compared with conventional orthogonal multiple access (OMA).
Abstract: Non-orthogonal multiple access (NOMA) has been recognized as a promising technique for providing high data rates in 5G systems. This letter is to study physical layer security in a single-input single-output (SISO) NOMA system consisting of a transmitter, multiple legitimate users and an eavesdropper. The aim of this letter is to maximize the secrecy sum rate (SSR) of the NOMA system subject to the users’ quality of service (QoS) requirements. We firstly identify the feasible region of the transmit power for satisfying all users’ QoS requirements. Then we derive the closed-form expression of an optimal power allocation policy that maximizes the SSR. Numerical results are provided to show a significant SSR improvement by NOMA compared with conventional orthogonal multiple access (OMA).
300 citations
TL;DR: This letter derives tractable and exact approximation expressions of the uplink SE of massive MIMO with the typical maximal-ratio combining (MRC) receivers and reveals that the use of low-cost and low-resolution ADCs can still achieve satisfying SE in massive M IMO systems.
Abstract: The low-resolution analog-to-digital convertor (ADC) is a promising solution to significantly reduce the power consumption of radio frequency circuits in massive multiple-input multiple-output (MIMO) systems. In this letter, we investigate the uplink spectral efficiency (SE) of massive MIMO systems with low-resolution ADCs over Rician fading channels, where both perfect and imperfect channel state information are considered. By modeling the quantization noise of low-resolution ADCs as an additive quantization noise, we derive tractable and exact approximation expressions of the uplink SE of massive MIMO with the typical maximal-ratio combining (MRC) receivers. We also analyze the impact of the ADC resolution, the Rician $K$ -factor, and the number of antennas on the uplink SE. Our derived results reveal that the use of low-cost and low-resolution ADCs can still achieve satisfying SE in massive MIMO systems.
256 citations
TL;DR: Simulation results verify that IA beam selection can achieve the near-optimal sum-rate performance and higher energy efficiency than conventional schemes.
Abstract: The recent concept of beamspace MIMO can utilize beam selection to reduce the number of required radio-frequency (RF) chains in mmWave massive MIMO systems without obvious performance loss. However, as the same beam in the beamspace is likely to be selected for different users, conventional beam selection schemes will suffer from serious multiuser interferences, and some RF chains may be wasted since they have no contribution to the sum-rate performance. To solve these problems, in this letter, we propose an interference-aware (IA) beam selection. Specifically, by considering the potential multiuser interferences, the proposed IA beam selection first classifies all users into two user groups, i.e., the interference-users (IUs) and noninterference-users (NIUs). For NIUs, the beams with large power are selected, while for IUs, the appropriate beams are selected by a low-complexity incremental algorithm based on the criterion of sum-rate maximization. Simulation results verify that IA beam selection can achieve the near-optimal sum-rate performance and higher energy efficiency than conventional schemes.
246 citations
TL;DR: A distributed compressive sensing-based channel estimation scheme for mmWave massive MIMO over frequency selective fading (FSF) channels can solve the power leakage problem caused by the continuous angles of arrival or departure.
Abstract: This letter proposes a multi-user uplink channel estimation scheme for mmWave massive MIMO over frequency selective fading (FSF) channels. Specifically, by exploiting the angle-domain structured sparsity of mmWave FSF channels, a distributed compressive sensing-based channel estimation scheme is proposed. Moreover, by using the grid matching pursuit strategy with adaptive measurement matrix, the proposed algorithm can solve the power leakage problem caused by the continuous angles of arrival or departure. Simulation results verify the good performance of the proposed solution.
235 citations
TL;DR: By exploiting the temporal correlation of active user sets, a dynamic compressive sensing (DCS)-based multi-user detection (MUD) to realize both user activity and data detection in several continuous time slots is proposed.
Abstract: Non-orthogonal multiple access (NOMA) can support more users than OMA techniques using the same wireless resources, which is expected to support massive connectivity for Internet of Things in 5G. Furthermore, in order to reduce the transmission latency and signaling overhead, grant-free transmission is highly expected in the uplink NOMA systems, where user activity has to be detected. In this letter, by exploiting the temporal correlation of active user sets, we propose a dynamic compressive sensing (DCS)-based multi-user detection (MUD) to realize both user activity and data detection in several continuous time slots. In particular, as the temporal correlation of the active user sets between adjacent time slots exists, we can use the estimated active user set in the current time slot as the prior information to estimate the active user set in the next time slot. Simulation results show that the proposed DCS-based MUD can achieve much better performance than that of the conventional CS-based MUD in NOMA systems.
210 citations
TL;DR: This work tackles this issue proposing the use of the self-organizing paradigm to design efficient UAV relay networks to support military operations by providing clear indications of the claimed benefits of theSelf-Organizing paradigm applied to these military systems.
Abstract: The modern battlefield scenario presents a number of challenges that highlights the importance of data gathering and information flow as crucial to the success of a military operation. In this context, network-centric warfare systems play an important role to bridge the gap between data and information sources and consumers. These systems are generally composed of different types of networks both deployed on the field and on back-end facilities. A paramount problem faced when conceiving the interconnection between the networked devices is how to provide robust and dependable connections to the devices on the field. This work tackles this issue proposing the use of the self-organizing paradigm to design efficient UAV relay networks to support military operations. As a proof of concept, realistic simulation experiments are performed providing clear indications of the claimed benefits of the self-organizing paradigm applied to these military systems.
207 citations
TL;DR: A dynamic user clustering problem from a fairness perspective is investigated, and three sub-optimal algorithms are proposed to realize the different tradeoffs of complexity and throughput of the worst user.
Abstract: In this letter, a downlink multiple-input-multiple-output non-orthogonal multiple access scenario is considered. We investigate a dynamic user clustering problem from a fairness perspective. In order to solve this optimization problem, three sub-optimal algorithms, namely, top-down A, top-down B, and bottom up, are proposed to realize the different tradeoffs of complexity and throughput of the worst user. In addition, for each given user clustering case, we optimize the power allocation coefficients for the users in each cluster by adopting a bisection search-based algorithm. Numerical results show that the proposed algorithms can lower the complexity with an acceptable degradation on the throughput compared with the exhaustive search method. It is worth noting that the top-down B algorithm can achieve a good tradeoff between the complexity and the throughput among the three proposed algorithms.
TL;DR: The merits of an HTTP/2 push-based approach to segment duration reduction, a measurement study on the available bandwidth in real 4G/LTE networks, and the induced bit-rate overhead for HEVC-encoded video segments with a sub-second duration are discussed.
Abstract: In HTTP Adaptive Streaming, video content is temporally divided into multiple segments, each encoded at several quality levels. The client can adapt the requested video quality to network changes, generally resulting in a smoother playback. Unfortunately, live streaming solutions still often suffer from playout freezes and a large end-to-end delay. By reducing the segment duration, the client can use a smaller temporal buffer and respond even faster to network changes. However, since segments are requested subsequently, this approach is susceptible to high round-trip times. In this letter, we discuss the merits of an HTTP/2 push-based approach. We present the details of a measurement study on the available bandwidth in real 4G/LTE networks, and analyze the induced bit-rate overhead for HEVC-encoded video segments with a sub-second duration. Through an extensive evaluation with the generated video content, we show that the proposed approach results in a higher video quality (+7.5%) and a lower freeze time (−50.4%), and allows to reduce the live delay compared with traditional solutions over HTTP/1.1.
TL;DR: It is shown that the PFS scheme that maximizes the minimum normalized rate can provide not only proportional fairness, but also small variation of transmission rates.
Abstract: In this letter, we consider proportional fairness scheduling (PFS) for downlink non-orthogonal multiple access (NOMA) with two users. Unlike conventional multiuser diversity systems, the power allocation plays a key role in PFS for NOMA as it can support multiple users simultaneously with positive transmission rates. With different criteria, we find optimal power allocation. Among those, it is shown that the PFS scheme that maximizes the minimum normalized rate can provide not only proportional fairness, but also small variation of transmission rates.
TL;DR: This letter is the first attempt to conflate a machine learning technique with wireless communications and provides insight into the potential of fusion of machine learning and wireless communications.
Abstract: This letter is the first attempt to conflate a machine learning technique with wireless communications. Through interpreting the antenna selection (AS) in wireless communications (i.e., an optimization-driven decision) to multiclass-classification learning (i.e., data-driven prediction), and through comparing the learning-based AS using $k$ -nearest neighbors and support vector machine algorithms with conventional optimization-driven AS methods in terms of communications performance, computational complexity, and feedback overhead, we provide insight into the potential of fusion of machine learning and wireless communications.
TL;DR: Performance of wireless powered relay with amplify-and-forward protocol is studied for Nakagami-m fading channels and an analytical expression is derived for the complementary cumulative distribution function (CCDF) of the end- to-end signal-to-noise ratio.
Abstract: Performance of wireless powered relay with amplify-and-forward protocol is studied for Nakagami- $m$ fading channels. Different from the existing literature, we consider the nonlinearity of the energy harvester. An analytical expression is derived for the complementary cumulative distribution function (CCDF) of the end-to-end signal-to-noise ratio. Using the CCDF, outage capacity is calculated.
TL;DR: The closed-form analytical results are developed to show that the cooperative transmission scheme gives better performance when more secondary users participate in relaying, which helps achieve the maximum diversity order at secondary user and a diversity order of two at primary user.
Abstract: This letter studies the application of non-orthogonal multiple access to a downlink cognitive radio (termed CR-NOMA) system. A new cooperative transmission scheme is proposed aimed at exploiting the inherent spatial diversity offered by the CR-NOMA system. The closed-form analytical results are developed to show that the cooperative transmission scheme gives better performance when more secondary users participate in relaying, which helps achieve the maximum diversity order at secondary user and a diversity order of two at primary user. The simulations are performed to validate the performance of the proposed scheme and the accuracy of the analytical results.
TL;DR: In this letter, a novel detection scheme for the cooperative relaying system using non-orthogonal multiple access (CRS-NOMA) is proposed and the advantages of the proposed scheme are revealed.
Abstract: In this letter, a novel detection scheme for the cooperative relaying system using non-orthogonal multiple access (CRS-NOMA) is proposed. For CRS-NOMA, the source simultaneously transmits two symbols by employing the superposition code, and the relay decodes and forwards the symbol with lower allocated power by employing the successive interference cancellation (SIC). In the proposed scheme, the destination jointly decodes two symbols from both the directed signal and the forwarded signal by employing the maximum-ratio combination and another SIC. The ergodic sum rate and the outage performance of the system are investigated. A suboptimal allocation strategy is also designed. Both analysis and simulations reveal the advantages of the proposed scheme.
TL;DR: A structured iterative support detection algorithm is proposed by exploiting the inherent structured sparsity of user activity naturally existing in NOMA systems to jointly detect user activity and transmitted data in several continuous time slots and can achieve better performance than conventional solutions.
Abstract: Non-orthogonal multiple access (NOMA) has been regarded as one of the promising key technologies for future 5G systems. In the uplink grant-free NOMA schemes, dynamic scheduling is not required, which can significantly reduce the signaling overhead and transmission latency. However, user activity has to be detected in grant-free NOMA systems, which is challenging in practice. In this letter, by exploiting the inherent structured sparsity of user activity naturally existing in NOMA systems, we propose a low-complexity multi-user detector based on structured compressive sensing to realize joint user activity and data detection. In particular, we propose a structured iterative support detection algorithm by exploiting such structured sparsity, which is able to jointly detect user activity and transmitted data in several continuous time slots. Simulation results show that the proposed scheme can achieve better performance than conventional solutions.
TL;DR: Simulation results show that the PCC polar codes with the heuristic construction have evident performance gains over the cyclic redundancy check-concatenated polar codes.
Abstract: In this letter, concatenation of parity-check and polar codes is proposed to improve error correction performance. In addition, a heuristic construction of the parity-check-concatenated (PCC) polar codes is proposed. Simulation results show that the PCC polar codes with the heuristic construction have evident performance gains over the cyclic redundancy check-concatenated polar codes.
TL;DR: A novel and robust DM synthesis method based on conditional minimum mean square error that is capable of substantially improving the bit error rate performance compared with the state-of-the-art methods.
Abstract: Directional modulation (DM) is a secure transmission technology that is able to retain the original constellation of transmitted signals along the desired direction, while distort the constellation in the undesired directions at the same time. In this letter, we develop novel and robust DM synthesis methods for enhancing the transmission performance. Specifically, we first propose a low-complexity dynamic DM synthesis method. In this method, we derive a closed-form expression for the null space of conjugate transpose of the steering vector in the desired direction. Based on the expression derived, we construct a projection matrix in order to form artificial noises to those undesired directions. Then, we focus our attention on more practical scenarios, where there is uncertainty in the estimated direction angle. This uncertainty will cause estimation errors and seriously jeopardize the receiving performance in the desired direction. To mitigate the uncertainty effect, we further propose a robust DM synthesis method based on conditional minimum mean square error. The proposed method aims to minimize the distortion of the constellation points along the desired direction. Simulation results show that our proposed robust DM method is capable of substantially improving the bit error rate performance compared with the state-of-the-art methods.
TL;DR: The proposed mathematical framework finds the optimal contention window size of cellular base stations, which maximizes the total throughput of both networks while satisfying the required throughput of each network.
Abstract: In this letter, we analyze the coexistence performance of Wi-Fi and cellular networks with different listen-before-talk (LBT) procedures in the unlicensed spectrum. For this analysis, the behavior of a cellular base station is modeled as a Markov chain that is combined with Bianchi’s Markov model depicting the behavior of a Wi-Fi access point. The proposed mathematical framework finds the optimal contention window size of cellular base stations, which maximizes the total throughput of both networks while satisfying the required throughput of each network. Numerical results show the validity of adjustment in the parameter of LBT.
TL;DR: This work considers a hybrid satellite-terrestrial relay system that employs a multiantenna satellite to communicate with multiple users via multiple amplify-and-forward relays and employs a max-max user-relay selection scheme to minimize the outage probability.
Abstract: We consider a hybrid satellite-terrestrial relay system that employs a multiantenna satellite to communicate with multiple users via multiple amplify-and-forward relays. We employ a max-max user-relay selection scheme to minimize the outage probability of the system. Considering both variable and fixed gain relaying protocols, we derive exact closed-form expressions of outage probability and their asymptotic behavior over independent and identically distributed fading channels for each hop. Numerical and simulation results validate our analysis and highlight the performance gains of the proposed scheme.
TL;DR: This letter shows that Willie can often limit Alice to the same performance scaling as when he knows his channel statistics, and observes T(n) length-n codeword slots, where some number may be used by Alice to attempt covert transmission.
Abstract: If the warden Willie attempting to detect the transmission knows the statistics of his receiver noise, Alice can transmit no more than O(√n) covert bits reliably to Bob in n channel uses of an AWGN channel. However, if Willie does not know his noise statistics exactly, Alice can covertly transmit O(n) bits. In this letter, Willie lacks knowledge of his channel statistics but observes T(n) length-n codeword slots, where some number may be used by Alice to attempt covert transmission. We show that Willie can often limit Alice to the same performance scaling as when he knows his channel statistics.
TL;DR: This letter considers simultaneous wireless information and power transfer (SWIPT) in multirelay-assisted two-hop relay system, where multiple relay nodes simultaneously assist the transmission from source to destination using the concept of distributed space-time coding.
Abstract: In this letter, we consider simultaneous wireless information and power transfer (SWIPT) in multirelay-assisted two-hop relay system, where multiple relay nodes simultaneously assist the transmission from source to destination using the concept of distributed space-time coding. Each relay applies power splitting protocol to coordinate the received signal energy for information decoding and energy harvesting. The optimization problems of power splitting ratios at the relays are formulated for both decode-and-forward (DF) and amplify-and-forward (AF) relaying protocols. Efficient algorithms are proposed to find the optimal solutions. Simulations verify the effectiveness of the proposed schemes.
TL;DR: Simulation results show that the proposed method outperforms Neumann Series, Richardson method, and conjugate gradient based methods, while achieving the near-optimal performance of linear detectors with a small number of iterations.
Abstract: A new approach based on joint steepest descent algorithm and Jacobi iteration is proposed to iteratively realize linear detections for uplink massive multiple-input multiple-output (MIMO) systems. Steepest descent algorithm is employed to obtain an efficient searching direction for the following Jacobi iteration to speed up convergence. Moreover, promising initial estimation and hybrid iteration are utilized to further accelerate the convergence rate and reduce the complexity. Simulation results show that the proposed method outperforms Neumann Series, Richardson method, and conjugate gradient based methods, while achieving the near-optimal performance of linear detectors with a small number of iterations. Meanwhile, the FPGA implementation results demonstrate that our proposed method can achieve high throughput owing to its high parallelism.
TL;DR: The closed-form expressions for the average secrecy capacity, secure outage probability, and the probability of strictly positive secrecy capacity are derived and provide a unified form, which can handle several of the well-known composite fading environments as special or limiting cases.
Abstract: In this letter, the secrecy performance of the classic Wyner's wiretap model over generalized-K fading channels is studied. The closed-form expressions for the average secrecy capacity, secure outage probability, and the probability of strictly positive secrecy capacity are derived. The new expressions provide a unified form, which can handle several of the well-known composite fading environments as special or limiting cases. Monte-Carlo simulations are performed to verify the proposed analysis models.
TL;DR: The simulation results indicate that the proposed algorithms can reuse the deployed VNFs efficiently and arrange the spectrum utilization in a much more load-balanced manner.
Abstract: We study how to allocate spectrum and IT resources jointly for realizing efficient virtual network function (VNF) service chaining in inter-datacenter elastic optical networks. We first formulate an integer linear programming model to solve the problem exactly, and then a longest common subsequence-based heuristic is proposed. The simulation results indicate that the proposed algorithms can reuse the deployed VNFs efficiently and arrange the spectrum utilization in a much more load-balanced manner.
TL;DR: This letter proposes a novel HBF algorithm for the uplink multiuser scenario, which has low computational complexity and its robustness is verified by comparisons with other existing algorithms under two different channel assumptions.
Abstract: In a millimeter-wave (mmWave) multiple-input multiple-output (MIMO) system, a large number of antennas can be placed into a very limited space. It is not practical to equip each antenna with one independent radio frequency (RF) chain. Fortunately, the hybrid analog/digital beamforming (HBF) can be utilized to greatly reduce the number of RF chains, while providing an acceptable performance. However, the conventional multiuser MIMO beamforming algorithms cannot be directly applied to the mmWave system with HBF structure. In this letter, based on the idea that interuser interference reduction should be done for both analog beamforming and digital beamforming, we propose a novel HBF algorithm for the uplink multiuser scenario, which has low computational complexity. Simulations indicate that the proposed algorithm performs very close to the full digital algorithm, and its robustness is verified by comparisons with other existing algorithms under two different channel assumptions.
TL;DR: A set of rules are proposed based on repeatability of chaotic behavior and enormous growth in the ratio of number of packets to number of source IP addresses during attack times to classify normal and attack traffics from each other.
Abstract: This letter deals with the problem of detecting DoS and DDoS attacks. First of all, two features including number of packets and number of source IP addresses are extracted from network traffics as detection metrics in every minute. Hence, a time series based on the number of packets is built and normalized using a Box-Cox transformation. An ARIMA model is also employed to predict the number of packets in every following minute. Then, the chaotic behavior of prediction error time series is examined by computing the maximum Lyapunov exponent. The local Lyapunov exponent is also calculated as a suitable indicator for chaotic and nonchaotic errors. Finally, a set of rules are proposed based on repeatability of chaotic behavior and enormous growth in the ratio of number of packets to number of source IP addresses during attack times to classify normal and attack traffics from each other. Simulation results show that the proposed algorithm can accurately classify 99.5% of traffic states.
TL;DR: It is figured out that the proposed NOMA scheme can approach nearly the same performance as optimal dirty paper coding, as verified by computer simulations.
Abstract: In this letter, based on the non-orthogonal multiple access (NOMA) concept, a quality-of-service optimization problem for two-user multiple-input-single-output broadcast systems is considered, given a pair of target interference levels. The minimal power and the optimal precoding vectors are obtained by considering its Lagrange dual problem and via Newton’s iterative algorithm, respectively. Moreover, the closed-form expressions of the minimal transmission power for some special cases are also derived. One of these cases is termed quasi-degraded, which is the key point and will be discussed in detail in this letter. Our analysis further figures out that the proposed NOMA scheme can approach nearly the same performance as optimal dirty paper coding, as verified by computer simulations.