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The reconstruction of sparse signal is an active area of research. Different from a typical i.i.d. assumption, this paper considers a non-independent prior of group structure. For this more practical setup, we propose EM-aided HyGEC, a new algorithm to address the stability issue and the hyper-parameter issue facing the other algorithms. The instability problem results from the ill condition of the transform matrix, while the unavailability of the hyper-parameters is a ground truth that their values are not known beforehand. The proposed algorithm is built on the paradigm of HyGAMP (proposed by Rangan et al.) but we replace its inner engine, the GAMP, by a matrix-insensitive alternative, the GEC, so that the first issue is solved. For the second issue, we take expectation-maximization as an outer loop, and together with the inner engine HyGEC, we learn the value of the hyper-parameters. Effectiveness of the proposed algorithm is also verified by means of numerical simulations., 15 pages, 4 figures. This paper has been submitted to IEEE Signal Processing Letters

Beam selection can alleviate the requirement on the number of radio frequency (RF) chains in lens array-assisted millimeter Wave (mmWave) multiple-input multiple-output (MIMO) systems. This letter investigates the performance of joint user and beam selection in a multi-user discrete lens arrays (DLA) communication system. To reap the maximum throughput, we jointly optimize the beam selection and user selection. Specifically, two algorithms are formulated based on stable matching and greedy search in order to find a proper subset of users and beams. Simulation results show that the proposed methods can achieve almost the same performance as the exhaustive-search-based method but involve much lower complexity.

Transmit antenna selection (TAS) is an emerging technology in physical layer security. To provide new insights into the achievable secrecy performance of TAS in practical communication systems, this paper investigates the average secrecy rate (ASR) and secrecy outage probability (SOP) under practical modulation schemes in TAS aided multiple-input multiple-output multiple-antenna eavesdropper (MIMOME) wiretap channels over Rayleigh fading. Particularly, this research concentrates more on the square $M$ -ary quadrature amplitude modulation ( $M$ -QAM). Furthermore, in the considered MIMOME channel, a single antenna is selected to transmit the secret message, and selection combining (SC) or maximal-ratio combining (MRC) is utilized at the legitimate receiver and the eavesdropper. Based on this system model, novel expressions for the ASR and SOP are formulated to characterize the secrecy performance of the finite-alphabet driven MIMOME channel. Besides exact analysis, an asymptotic analysis is performed using the considered performance metrics in high signal-to-noise ratio (SNR) regime. Theoretical analyses suggest that the asymptotic ASR and SOP converge to finite constants in high SNR regime due to the discrete constellation constraint, and we find that the asymptotic behaviour of discrete inputs differs from that of Gaussian inputs. Furthermore, we derive concise expressions to characterize the rate of convergence (ROC) of the ASR and SOP, respectively. To unveil more system design insights, we discuss the relationship between the ROC and several important system parameters such as the antenna number and the modulation order.

To evaluate the performance of wireless multi-path channels with discrete inputs, this letter investigates the ergodic mutual information (EMI) of a generalized fading type named mixture gamma distribution (MGD) under $M$ -ary quadrature amplitude modulation ( $M$ -QAM) signaling. An accurate closed-form expression for the EMI is developed to approximate the exact value. The MGD fading can be specialized into several regularly used fading cases including Rayleigh fading, Nakagami- $m$ fading, $\eta -\mu $ fading, $\kappa -\mu $ fading, and ${\mathcal {K}}_{G}$ fading, and then the corresponding closed-form EMI formulas are separately derived to measure these fadings. Compared with the Gaussian source signals based research on MGD fading, this work sheds light on the performance with discrete inputs instead of Gaussian inputs, thereby being more practical. This study can be regarded as a unified tool to evaluate the EMI with discrete inputs over arbitrary wireless channels.

To analyze the achievable performance of antenna selection (AS) in practical multi-antenna systems, this paper studies the receive antenna selection (RAS) in single-input multiple-output (AS-SIMO) systems under discrete inputs. We first propose an approximate expression to evaluate the instantaneous mutual information (MI) of $M$ -ary quadrature amplitude modulation ( $M$ -QAM) signaling over additive white Gaussian noise (AWGN) channels. Then, by exploiting this approximate formula, we develop a closed-form formula for the ergodic MI in AS-SIMO systems with $M$ -QAM signaling. Additionally, we also analyze the asymptotic MI for a large number of receive antennas $N_{\mathrm{r}}$ . This asymptotic analysis suggests that the scaling rate of the MI with $N_{\mathrm{r}}$ becomes zero rate in contrast to the double logarithmic rate under Gaussian inputs. Besides, our result is also extended to discuss the mutual information of multiple-input multiple-output (MIMO) systems having discrete inputs with receive antenna selection, and an upper bound for the MI is derived. Finally, the derived result is applied to analyze several performance measures of the discrete inputs driven AS-SIMO systems. Specifically, it is first used to discuss the relationship between the ergodic MI and the number of active antennas. Our investigation shows that this relationship follows Pareto principle, i.e., 80% of the MI of full-antenna selection can be achieved via 20% of the total antennas. Then, our proposed approximation is employed to analytically study the effective MI which takes channel estimation (CE) into consideration, indicating that CE is a main limit of large-scale systems. Moreover, the energy efficiency (EE) is explored on the basis of our results, and we find there exists an optimal number of active antennas to maximize the energy efficiency. In addition to theoretical derivations, all the analytical results are validated by numerical simulations.

Fog radio access networks (F-RANs) can effectively alleviate fronthaul loads and reduce content transmission delay by migrating cloud services to the network edge. This paper addresses a cooperative caching scenario in F-RAN, where each mobile user can acquire the requested contents from any one of its associated fog-computing-based access points (F-APs). However, caching disparate contents in different F-APs will lead to different content delivery delays, since mobile users suffer from diverse channel fadings and interferences when they download contents from different F-APs. Considering limited caching storage in each F-AP, diverse user preferences, unpredictable user mobility and time-varying channel states, an average transmission delay minimization problem is formulated. With the aid of dueling deep-Q-network framework, a delay-aware cache update policy is proposed for mobile users in F-RAN. The proposed cache update policy will decide to replace the stored contents in F-APs with the proper contents at each time slot. Compared with first in first out, least recently used and least frequently used caching policies, simulation experiments are performed to evaluate the performance of the proposed algorithm. Simulation results illustrate that the proposed caching policy yields better average hit ratio and lower average transmission delay than other traditional caching policies.

This letter considers a joint user activity, channel and data estimation problem in an uplink grant-free massive MIMO systems with low-precision analog-to-digital converters (ADCs). This joint estimation is firstly formalized as a non-overlapping group sparse problem, in which the components of compound channel follow independent conditional distribution. To address this problem, a new algorithm consists of the celebrated bilinear generalized approximate message passing (BiG-AMP) and loop belief propagation (LBP) is then proposed, where the strong connection of compound channel can be decoupled in LBP part. By exchanging the information between BiG-AMP part and LBP part, the proposed algorithm improves the performance of channel estimation compared with HyGAMP based method, in which the estimated payload data of proposed algorithm are utilized to aid channel estimation and it leads to relatively few pilot symbols to achieve equivalent channel and data estimation performances. The simulation results confirm that our proposed joint estimation algorithm improves the performance of the existing works in terms of user activity, channel and data estimation.

This letter considers the problem of a joint estimation for channel fading and user activity in an uplink grant-free massive MIMO system equipped with low-precision analog-to-digital converters (ADCs). Different from existing works, the joint estimation is formalized as a non-overlapping group problem, where the components of compound channel involving user activity indicator and channel fading are independent with condition distribution rather than independent Bernoulli-Gaussian. Based on this new formulation, a new algorithm leveraging hybrid generalized approximate passing (HyGAMP) is then developed including GAMP part (channel estimation) and loopy belief propagation (LBP) part (user activity detection), where the strong correlation among elements in each row of the channel matrix can be decoupled in LBP part. By exchanging the information between the GAMP part and the LBP part, the proposed algorithm improves the performance of channel estimation and user activity detection as compared to earlier results. In addition, the simulation results verify that the proposed algorithm develops the performance of conventional methods dramatically.

This letter investigates linear precoding scheme that maximizes the mutual information (MI) of multiple-input multiple-output (MIMO) channel with arbitrary input constellations. Since traditional precoding schemes which rely on the relationship between MI and minimum mean-square error (MMSE) are too time consuming, this letter first proposes a lower bound of MI with which the computational complexity can be significantly reduced compared with direct computation of MI, and we prove that the bound is asymptotically optimal with a constant shift. Based on this lower bound, a low-complexity precoding scheme is obtained. Numerical results verify the effectiveness and high-performance of the proposed precoding method compared with traditional precoding schemes.

To realize the high data rates with low complexity in MIMO systems, linear detections are commonly used where the received signal vector is first transformed to a new vector and then detected on per symbol basis. However, the typical linear detectors such as zero forcing detector and minimum mean-square error detector are not optimal in terms of maximizing the achievable data rate of MIMO system under linear detection constraint. In this letter, we investigate the optimal linear transformer that can maximize such rate with finite constellation inputs. By capitalizing on the relationship between mutual information and the MMSE between channel inputs and outputs, the optimal linear detector (OLD) can be expressed as a fixed-point equation and be solved iteratively. Analytical results prove the consistence between the proposed OLD and the joint maximum likelihood detector (JMLD) in the low- and high-SNR region. The further simulation results verify the consistence, and moreover, at moderate SNR, OLD can significantly improve the achievable data rate and is close to that of JMLD.

Accurate estimation of channel log-likelihood ratio (LLR) is crucial to the decoding of modern channel codes like turbo, low-density parity-check (LDPC), and polar codes. Under an additive white Gaussian noise (AWGN) channel, the calculation of LLR is relatively straightforward since the closed-form expression for the channel likelihood function can be perfectly known to the receiver. However, it would be much more complicated for heterogeneous networks where the global noise (i.e., noise plus interference) may be dominated by non-Gaussian interference with an unknown distribution. Although the LLR can still be calculated by approximating the distribution of global noise as Gaussian, it will cause performance loss due to the non-Gaussian nature of global noise. To address this problem, we propose to use bi-Gaussian (BG) distribution to approximate the unknown distribution of global noise, for which the two parameters of BG distribution can easily be estimated from the second and fourth moments of the overall received signals without any knowledge of interfering channel state information (CSI) or signaling format information. Simulation results indicate that the proposed BG approximation can effectively improve the word error rate (WER) performance. The gain of BG approximation over Gaussian approximation depends heavily on the interference structure. For the scenario of a single BSPK interferer with a 5 dB interference-to-noise ratio (INR), we observed a gain of about 0.6 dB. The improved LLR estimation can also accelerate the convergence of iterative decoding, thus involving a lower overall decoding complexity. In general, the overall decoding complexity can be reduced by 25 to 50%.

Mobile streaming media on subways or trains has become a typical and popular scenario in daily life. However, because of the unstable wireless network channel and fluctuations caused by movement, the constant bit rate streaming media brings low-quality service. The adaptive streaming media seems to solve the problems, but the premise is that clients can accurately estimate the network bandwidth. When the client moves at high speed, the irregular fluctuations of network channel make accurate estimation difficult, leading to the low efficiency of the adaptive streaming media. When clients move on subways or trains, the location, speed and the cell load can be known by the wireless network side. With this information, the available network bandwidth can be accurately calculated in advance. Thus, we propose an architecture called Cell-Cluster Network-Assisted Adaptive Media Streaming (CCNA) to optimize the vehicular streaming media over wireless network. We build a cell cluster to introduce the assistance of the wireless network side and estimate the network bandwidth more accurately. The architecture can help clients select the video segment with the highest QoE under the constraint of limited network bandwidth and make the best use of the network bandwidth resources. The experimental results show that compared with traditional adaptive streaming media transmission modes, our architecture improves the average playback bit rate by 32% and the utilization of network bandwidth by 34% at the same time with the least video stalls.

This paper investigates the linear precoding design for multiple-input multiple-output (MIMO) multiple access channel (MAC) with finite-alphabet inputs. Since the mutual information (MI) and its gradient-minimum mean-square error (MMSE) matrix lack closed-form solutions, traditional MI/MMSE based precoding scheme suffers from a prohibitive burden of computation. To address this problem, we first derive an asymptotically optimal lower bound of MI, which is more computationally efficient. Based on the lower bound, we derive a suboptimal precoding scheme that maximizes the weighted sum-rate (WSR) of MIMO MAC with finite-alphabet inputs. Furthermore, a low-complexity precoding algorithm is proposed to obtain the numerical results of precoding matrices. Numerical results confirm a higher efficiency of the proposed precoding scheme compared with traditional MI/MMSE based precoding strategies.

The Pattern division multiple access (PDMA) technique is proposed to meet diverse demands for the 5G system. The pattern matrix of PDMA with unequal diversity is designed to reduce error propagation, which relies on the joint design of transmission and receiver. In this paper, it forms a discrete optimization problem based on the characteristics of PDMA. We form the fitness function to maximize the average mutual information (AMI) of the PDMA system, and binary particle swarm optimization (BPSO) algorithm is introduced to design the pattern matrix of the PDMA system. It demonstrated that the optimized PDMA scheme could obtain better coding gain and diversity gain. The numerical results indicate that the optimized PDMA scheme brings about 0.5 dB-1.2 dB performance gains.

Physical layer security is investigated over mixture Gamma (MG) distributed fading channels with discrete inputs. By the Gaussian quadrature rules, closed-form expressions are derived to characterize the average secrecy rate (ASR) and secrecy outage probability (SOP), whose accuracy is validated by numerical simulations. To show more properties of the finite-alphabet signaling, we perform an asymptotic analysis on the secrecy metrics in the large limit of the average signal-to-noise ratio (SNR) of the main channel. Leveraging the Mellin transform, we find that the ASR and SOP converge to some constants as the average SNR increases and we derive novel expressions to characterize the rates of convergence. This work establishes a unified and general analytical framework for the secrecy performance achieved by discrete inputs., 8 figures 6 pages

Channel modeling is crucial to the development and evaluation of modern wireless communication systems including satellite communication system, since there might be critical safty-of-life applications. Also, the channel model is of great importance to the performance evaluation of mobile communication systems. In recent years, encouraged by the widely application of unmanned aerial vehicles, the research on channel modeling for aerial and aeronautical communications attract lots of interests. In the published articles, stationary and non-stationary channel models have been developed for air-to-ground communications based on regular shaped geometry-based stochastic model (RS-GBSM). The modeling of air-to-air or satellite-to-aircraft (S2A) communication is still quite simple or completely lacking. For obtaining more precise model of S2A channel, this paper presents an analytical non-stationary S2A channel mode based on RS-GBSM with considerations on line-of-sight path, specular reflection path, and ground scattering path. Analytical expressions of the channel impulse responses, the transfer functions, the auto-correlation functions, and the Doppler power spectrum density based on 3-path model are derived and simulated. Also, the distributions of the path antennation, the path delay, and the normalized Doppler shift based on uniform distribution of the scatterers are derived, simulated and fitted.

With the rapid growing demand for transmission rate, transmission security is becoming increasingly important. This paper proposes a novel scheme aiming at transmission security enhancement on the basis of the spatial modulation technology. In the proposed scheme, the transmitter maps the information bits to the index of a receive antenna, then a precoding vector is randomly selected in the null space of the targeted antenna. Due to the randomness of the precoding vector, it's difficult for the eavesdropper in unknown locations to detect the index of the targeted antenna using maximum-likelihood detection, hence its receiving performance can be greatly degraded compared with the legitimate receiver. Both theoretical analysis and simulation results verified the secure enhancement performance of the proposed scheme. Moreover, unlike most of the existing schemes which require that the transmitter should equip more antenna than the receiver, our scheme works well even if the transmitter has less antennas than the receiver.

By offloading storage and computing resources to the edge of networks, mobile edge computing (MEC) is emerged as a promising architecture to reduce the transmission delay and bandwidth waste for mobile multimedia services. This paper focuses on a multi-service scenario in the MEC systems, where the MEC server can provide three multimedia services including live streaming, buffered streaming and low latency enhanced mobile broadband applications for edge users at the same time. In order to satisfy various quality of service (QoS) requirements for different multimedia applications, the 5G QoS model is applied. Notably, the packets from the multimedia applications with the same or similar requirements are mapped into the same QoS flow, and each QoS flow is processed individually. Therefore, how to effectively schedule the limited radio resource for QoS flows is an intractable problem. To address the problem above, a QoS evaluation model is designed, and a QoS maximization problem is formulated. Furthermore, a deep reinforcement learning method, deep-Q-network, is adopted to make decisions to allocate radio resource dynamically. Compared with round-robin and priority-based scheduling algorithms, the simulation results validate that the proposed algorithm outperforms other resource scheduling algorithms for multi-service scenario.

In this paper, we studied the secure transmission of a hybrid automatic repeat request with chase combining (HARQ-CC) system, under the existence of multiple eavesdroppers and limited latency. First, we analyzed some critical performance metrics, including connection outage probability (COP), secrecy outage probability (SOP) and effective secrecy throughput (EST). Then, to maximize the EST, three optimization problems of rate adaption were discussed: (i) optimizing the code rate with a given secrecy redundancy rate by a parameterized closed-form solution, (ii) optimizing the secrecy redundancy rate with a given code rate by a fixed-point method, (iii) optimizing both code rate and secrecy redundancy rate by an iterative optimization algorithm. We also considered COP and SOP constraints among the problems while corresponding solutions were deduced. Finally, numerical and simulated results verified our conclusions that the approximated SOP matches well with Monte&ndash, Carlo simulation for a strict reliable constraint, and that the optimized transmitting rate enhances EST efficiently with multiple eavesdroppers and retransmissions. Moreover, the influence of the number of eavesdroppers on secrecy performance was analyzed. Briefly, secrecy performance inevitably deteriorates with increasing number of eavesdroppers due to raised information leakage.

This letter proposes a novel joint decoding scheme for correlated sources using systematic polar codes. In the proposed scheme, each source independently encodes its message into a systematic polar code word and sends the codeword via a binary-input additive white Gaussian noise channel to the common destination, where adaptive cyclic redundancy check-aided successive cancellation list (CA-SCL) decoders are employed. During the iterative decoding process, the log likelihood ratios (LLRs) fed to each adaptive CA-SCL decoder are iteratively combined with the extrinsic LLRs from other decoders. The correlation among the sources is exploited to improve the decoding performance. Simulation results show that, in comparison with independent decoding, the proposed scheme can achieve significantly improved decoding performance without increased complexity.

As an extension of source polarization and channel polarization, this paper considers joint source-channel polarization, which results in a joint source-channel coding (JSCC) scheme using a quasi-uniform systematic polar code (SPC). In this JSCC scheme, the source with side information is encoded as a systematic polar codeword and only parity bits are transmitted through the channel. The indices of systematic bits are quasi-uniform, which enable the source and the channel to be jointly polarized to either a high entropy part or a low entropy part. The analysis reveals that the quasi-uniform SPC cannot be constructed via original polar coding. To solve this problem, additional bit-swap coding is introduced to modify original polar coding and construct this kind of SPCs. The proposed JSCC scheme can asymptotically approach the information-theoretical limit. For the noiseless channel, the proposed scheme is degraded into classic Slepain-Wolf coding or lossless source coding based on parity approach.

In this letter, we develop a recurrence formula for the capacity of Nakagami- $m$ fading channel with BPSK/QPSK modulations when channel state information is available at the receiver. For each fading parameter $m$ , a simply constructed series representation with a fast-convergence rate can be obtained through the recurrence formula. The series expansion provides a numerically efficient way to calculate the capacity for both Rayleigh and Nakagami- $m$ fading channels. The simulation results show that the recurrence formula is a good alternative for estimating the capacity of Nakagami fading channel.

In a hybrid automatic repeat request with chase combining (HARQ-CC) system,we analyze physical layer secure performance and determine the secrecy redundancy rateby proposed quasi-concave optimization methods with effective secrecy throughput (EST) criteria.First, key performance metrics, including connection outage probability (COP),secrecy outage probability (SOP), EST, and delay, are discussed.Then, under the constraint of COP, we optimize the secrecy redundancy rate to maximize the EST,which is a quasi-concave function, by both the bisection and fixed-point methods.Furthermore, under the simultaneous constraints of COP and SOP,the bisection and Lagrangian multiplier methods are applied to optimize the secrecy redundancy rate.From the comparison of the numerical and simulated results,it is concluded that EST demonstrates practical secure performance of HARQ-CC,and the proposed optimization methods adjust the secrecy redundancy rate for improved security.

To provide system design insights for practical communication systems equipped with the frequency diverse array (FDA), this letter investigates the secrecy performance of FDA systems exploiting finite-alphabet inputs over fluctuating two-ray (FTR) fading channels. More specifically, closed-form expressions for the average secrecy rate (ASR) and the secrecy outage probability (SOP) are derived, while their correctness is confirmed by numerical simulations. In addition, we perform asymptotic analysis to quantify the secrecy performance gap between Gaussian and finite-alphabet inputs, for a sufficiently large average signal-to-noise ratio (SNR) of the main channel. Compared with Gaussian inputs-based research, this letter focuses on practical scenarios which sheds lights on properties of FDA systems.

Mutual information (MI) between channel inputs and outputs plays a critical role in communication systems. However, with finite-alphabet inputs, no closed-form solution exists to the MI of multiple-input multiple-output (MIMO) channel. Although numerical integration methods can be used to estimate MI, it can be quite slow, especially for larger input-output dimensions. This paper presents a new way to approximately evaluate the MI of MIMO channel with equiprobable M-ary inputs. With the aid of entropy power Gaussian approximation, a MIMO channel can be approximately decomposed into parallel independent single-input multiple-output (SIMO) channels which are, in terms of MI, equivalent to single-input single-output (SISO) channels. Thus the MI of MIMO channel can be approximately evaluated with that of multiple SISO channels. With this result, the computational complexity can be reduced to linear complexity. Furthermore, we proof that the proposed approximation gives the true MI with massive receiver antennas. Simulation results verify the accuracy and effectiveness of the proposed method.

This paper studies the secrecy performance of multiple-input multiple-output (MIMO) wiretap channels, also termed as multiple-input multiple-output multiple-eavesdropper (MIMOME) channels, under transmit antenna selection (TAS) and BPSK/QPSK modulations. In the main channel between the transmitter and the legitimate receiver, a single transmit antenna is selected to maximize the instantaneous Signal to Noise Ratio (SNR) at the receiver. At the receiver and the eavesdropper, selection combining (SC) is utilized. Additionally, suppose that the transmitted message is modulated by BPSK/QPSK modes. We first derive the closed-form approximated expression for the ergodic secrecy rate under Rayleigh fading, assuming that the channel state information of the eavesdropper (CSIE) is available at the transmitter. Next, analytical formulas for the approximated and asymptotic secrecy outage probability are also developed when CSIE is unavailable (NCSIE). Simulation results are provided to demonstrate the approximation precision of the derived results above. Furthermore, the asymptotic results reveal that the secrecy diversity order degrades into 0 due to the finite-alphabet inputs, which is totally different from that driven by the Gaussian inputs.

Unmanned aerial vehicle (UAV) communication system equipped with multiple input and multiple output (MIMO) antennas has been recognized as an efficient technique for obtaining high spectral efficiency. To improve the system capacity in UAV communication scenario, this paper investigates the user clustering and downlink user scheduling strategy. We first develop a channel correlation based K-means algorithm for user clustering. Furthermore, to diminish intergroup interference, a greedy user scheduling algorithm driven by the K-means clustering strategy, is devised to appropriately select the users with low-correlated channels to schedule at the same time slot. Simulation results are provided to demonstrate the superior performance of the proposed scheduling algorithm over conventional method. It is observed that the presented K-means aided algorithm can achieve near maximum average sum rate with much lower computational complexity.

This paper studies the ergodic mutual information of hybrid selection/maximal-ratio combining (H-S/MRC) diversity system under BPSK/QPSK modulations. We consider a simple single-input multiple-output (SIMO) channel, where a subset of branches are selected and combined using maximal-ratio combining (MRC) to maximize the instantaneous Signal to Noise Ratio (SNR) at the receiver. For independent and identically distributed (i.i.d.) Rayleigh flat fading, a general recursive expression is developed to estimate the ergodic input-output mutual information of the whole system. Besides analytical derivations, simulations are provided to demonstrate the feasibility and validity of the derived results., 5 pages. arXiv admin note: text overlap with arXiv:1903.03032

This paper studies the transmit antenna selection in massive multiple-input multiple-output (MIMO) wiretap channels, also termed as multiple-input multiple-output multiple-eavesdropper (MIMOME) channels. The transmitter, equipped with a large-scale antenna array whose size is much larger than that of the legitimate receiver and eavesdropper, selects a subset of antennas to transmit messages. A branch-and-bound (BAB) search based algorithm for antenna selection in independent and identical distributed Rayleigh flat fading channel is proposed to maximize the secrecy capacity between the transmitter and the legitimate receiver when the transmit power is equally allocated into the selected antennas. Furthermore, the proposed algorithm is separately applied to two scenarios which is based on whether the channel side information of the eavesdropper (CSIE) is available at the transmitter. Simulation results show that the proposed algorithm has the same performance as the exhaustive search under both scenarios but with much lower complexity.

Hybrid precoding is widely studied in millimetre-wave (mmWave) massive MIMO systems due to low cost as well as low power consumption. In general, there are two kinds of hybrid precoding structures: one is fully connected structure (FCS), where each radio frequency (RF) chain is connected to all antennas, and the other is partially connected structure (PCS), where each RF chain is connected to a sub-array. In this paper, we investigate the optimal hybrid precoder design problem for mmWave massive MIMO systems based on PCS, since this kind of structure is more practical for antenna deployment. We first focus on the optimization of analog precoder (AP) and propose two AP design schemes for high signal-to-noise ratio (SNR) condition and low SNR condition, respectively. For each of the schemes, the original optimization problem is reformulated to single-stream optimal transmitter beamforming problem with per-antenna power constraint, which has an optimal solution. Then, the optimal digital precoder is obtained by water-filling algorithm after AP is determined. Moreover, upper bounds of the achievable data rate for the proposed schemes with closed-form expression are derived.

In this letter, the physical layer security of hybrid automatic repeat request with chase combining (HARQ-CC) scheme is investigated from the viewpoint of information theory. Different from the literature which used Wyner code, our analysis focuses on the general scenario without specific code. We firstly obtain the outage probability of both main channel and wiretap channel. Since retransmissions are completely determined by main channel, we then prove that its achievable diversity order equals to maximum transmission number (K) while this order of wiretap channel is only one. Furthermore, we evaluate the metric of secure gap which demonstrates the difference between main channel and wiretap channel with reliable and secure constraints. As K increases, the secure gap decreases monotonously. When K is large enough, the security can be guaranteed even if wiretap channel is better than main channel.

Fluctuations in wireless channel conditions have a negative impact on naked-eye three-dimensional (3D) video streaming. While offering free stereo perception, it poses a challenge to wireless networks for the large volumes of video traffic. To obtain better viewing experiences, a trade-off between stereo perception improvement and freeze avoidance is necessary. Though adaptive streaming seems to work well, traditional bandwidth estimation methods are at risk of overestimation which may lead to stall or underestimation which may cause resource waste. To improve the quality of experience (QoE), a novel scheme named QoE-driven and Network-assisted Naked-eye 3D Adaptive Video Streaming over Wireless Network (QNANA) is proposed to transmit naked-eye 3D video streaming over wireless networks adaptively with network assistance. In view of the constraint of bandwidth capacity, the scheme can select the video of the highest QoE under the current bandwidth conditions, so as to achieve the highest QoE overall. Besides, the clients can follow the fluctuating channel conditions timely and accurately. Results show that the scheme can realize the lowest prediction error and the best resource utility with up to 54% reduction in total stall durations compared to traditional bandwidth estimation methods.

Since the performance of Turbo and Low Density Parity Check Code (LDPC) codes are very close to Shannon limit, a great deal of attention has been placed on the capacity of additive white Gaussian noise (AWGN) and fading channels with arbitrary channel inputs. However, no closed-form solution has been developed due to the complicated Gaussian integrations. In this paper, we investigate the capacities of AWGN and Rayleigh fading channels with $M$ -ary inputs, e.g. phase shift keying (PSK) and quadrature amplitude modulation (QAM). By firstly adopting successive interference cancellation (SIC) and the entropy power Gaussian approximation, the capacity of an AWGN channel with $M$ -QAM and $M$ -PSK modulations can be approximated as the superposition of the capacity of an AWGN channel with BPSK modulation. Furthermore, the ergodic capacity of a Rayleigh fading channel can be derived directly by averaging the instantaneous capacity of an AWGN channel with respect to the probability density function (PDF) of the fading channel gain. Simulation results verify the effectiveness of the proposed method for estimating the capacity of AWGN and Rayleigh fading channels of all SNR ranges.

A novel no-reference method based on machine learning algorithm for SWB (Super Wideband) speech quality measurement is proposed in this paper. For this, a SWB audio database including 28786 degraded signal samples acquired from actual network is built. With this database, a multidimensional waveform feature description is built up for the degraded signal. Gradient Boosting Decision Tree (GBDT) algorithm is used to design the model, establishing the relationship between the feature description and the perceptual mean opinion score (MOS). The results predicted by the proposed method coincide with the perceptual quality and demonstrate more effective performances than the current P.563 algorithms, in terms of Pearson coefficient, root mean square error and mean absolute percent error.

The millimeter wave (mmWave) communications have gained increasing attention to satisfy the high data-rate requirements in the fifth generation (5G) cellular systems. To overcome the severe path loss, multiple narrow beamforming vectors are configured at both the next generation NodeB (gNB) and the user equipment (UE), thus it is critical to select the best beam pair for maximum beamforming gain. This paper focuses on the beam selection problem for beam refinement procedure, where selection occurs between each UE with its serving gNB. A hybrid approach is proposed where the beam pair is selected either with the max-signal-to-noise (Max-SNR) criteria or with the max-signal-to-interference-plus-noise ratio (Max-SINR) criteria, depends on the highest reference signal received power (RSRP) measured by UE. Simulation results indicate that the proposed hybrid approach can achieve a good tradeoff between the beam selection delay and the SINR performance

Virtual reality (VR) and augmented reality (AR) applications with interactions are usually delaysensitive. Fast delivery of three-dimensional (3-D) models in VR/AR over wireless networks has been a crucial task due to limited bandwidth and packet error. In this paper we propose an application layer content-aware joint source-channel coding scheme based on forward error correction (FEC). A 3D model is progressively encoded to a base mesh and several refinement layers consisting of connectivity and geometric data. A new design of LT code with a special coding graph has been proposed to provide unequal error protection (UEP) to these two kinds of data. Then a statistical measure is used to optimize the rate allocation for each refinement layer, which is scalable to both network bandwidth and packet loss rate (PLR). Experimental results show that the proposed streaming scheme can achieve the objectives of low transmission delay and small distortion under serious loss.

Deployment of Long Term Evolution (LTE) in unlicensed spectrum has been a candidate feature to meet the explosive growth of traffic demand since 3GPP release 13. To further explore the advantage of unlicensed bands, in this context the operation of both uplink and downlink has been supported and studied in the subsequent releases. However, it has been identified that scheduled uplink transmission performance in unlicensed spectrum is significantly degraded due to the double listen-before-talk (LBT) requirements at both eNB when sending the uplink grant, and at the scheduled UEs before transmission. In this paper, in order to overcome this issue, a novel uplink transmission scheme, which does not require any grant, is proposed, and the details regarding the system design are provided. By modeling the dynamics in time of the LBT for both a system that employs a conventional uplink scheme, as well as the proposed scheme, it is verified through analytical evaluation that the double LBT scheme for uplink transmission greatly reduces the channel access probability for the UE, and leads consequently to performance loss, while the proposed scheme is able to alleviate this issue. System level simulation results, compliant with the LTE standard, show that the proposed scheme can achieve a significant performance gain in terms of throughput with negligible performance loss for the downlink, and other technologies operating in the same spectrum., Comment: 6 pages, 6 figures - in IEEE International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC) 2017

For 5G systems operating in the millimeter-wave range, the impact of the phase noise in oscillators can get higher than that in low band. In 3GPP TSG RAN1 Meeting# 86bis, agreement is achieved that the reference signal for phase tracking is supported for both 5G downlink and uplink. The preliminary design of tracking reference signal (TRS) for orthogonal frequency division multiplexing (OFDM) waveform has been done. But when the same method applies to single carrier frequency division multiple access (SC-FDMA) waveform, the peak-to-average power ratio (PAPR) of transmit signal gets huge growth. Therefore how to design the TRS for SC-FDMA waveform becomes one issue. In this paper, we propose some TRS patterns to track and compensate the phase noise based on SC-FDMA waveform, which fits for practical 5G system. The TRS and data can be mapped in a frequency division multiplexing (FDM) manner, similar as simultaneously physical uplink control channel (PUCCH) and physical uplink shared channel (PUSCH) transmission in LTE. Further the link level performance for different TRS design patterns and generation sequences are discussed, which indicate that using new patterns, the impact of phase noise can be effectively improved with little PAPR growth.

This paper presents an improved congestion control algorithm of Transmission Control Protocol (TCP), TCP WDL (Westwood LTE). Traditional TCP will decrease congestion window regardless the reason of packet loss in wireless links. The primary purpose of TCP WDL is to enhance TCP performance in Long Term Evolution (LTE) networks by being able to distinguish the random packet losses from the congestion packet losses. TCP WDL combines Bandwidth Estimation (BE) strategy with Rate Estimation (RE) strategy to calculate available bandwidth. In congestion avoidance phase, WDL divides the network congestion grades to estimate congestion degree based on throughput. This paper compares its performance with NewReno and Westwood by network simulator ns-3.24. The simulation results show that TCP WDL achieves higher throughput and fairness is comparable to NewReno and Westwood in LTE networks.

This paper investigates the sum capacity of a single-cell multi-user system under the constraint that the transmitted signal is adopted from M-ary two-dimensional constellation with equal probability for both uplink, i.e., multiple access channel (MAC), and downlink, i.e., broadcast channel (BC) scenarios. Based on the successive interference cancellation (SIC) and the entropy power Gaussian approximation, it is shown that both the multi-user MAC and BC can be approximated to a bank of parallel channels with the channel gains being modified by an extra attenuate factor that equals to the negative exponential of the capacity of interfering users. With this result, the capacity of MAC and BC with arbitrary number of users and arbitrary constellations can be easily calculated which in sharp contrast with using traditional Monte Carlo simulation that the calculating amount increases exponentially with the increase of the number of users. Further, the sum capacity of multi-user under different power allocation strategies including equal power allocation, equal capacity power allocation and maximum capacity power allocation is also investigated. For the equal capacity power allocation, a recursive relation for the solution of power allocation is derived. For the maximum capacity power allocation, the necessary condition for optimal power allocation is obtained and an optimal algorithm for the power allocation optimization problem is proposed based on the necessary condition.

创新点 针对无线衰落信道中物理层传输的安全问题, 提出了一种基于随机线性码的解决方案。 所提方案中, 发送方 (A) 使用的编码生成多项式由接收方 (B) 产生并发送给A。 生成多项式的产生满足一定的规则, 使得窃听方 (E) 如果漏掉A、 B双方数据包中的任何一个, 则无法解出任意一个信源数据包, 从而可以显著降低窃听方截获信息的概率。

It is widely recognized that different antenna layouts have different effect on the ergodic capacity of Multiple- input-Multiple- output (MIMO) system. However, the multidimensional optimization problem involved in the optimization of antenna layout is mathematically intractable due to the exponential computation complexity. Therefore, in this paper a suboptimal iterative algorithm is presented for optimization of antenna layout in terms of ergodic capacity. In the proposed algorithm, the multi-dimensional optimization problem is reduced to one-dimensional problems within each iteration, hence the computation complexity is reduced greatly. The numerical results show that the ergodic capacity obtained with the proposed algorithm is very close to that obtained with simulated annealing.

With the increasing usage of wireless devices, the power consumption and energy efficiency of cellular networks have been receiving much attention in wireless network in recent years. One way of saving energy is to switch off some underutilized small cells in light traffic conditions. In existing researches, the number of the base stations (BSs) that can be switched off in a network is take as the the optimization object. However, under many circumstances, it would be acceptable if the energy efficiency increases with less cells switched off. In this paper, we take the energy efficiency as the optimization object and suppose that each user equipment (UE) has a minimum rate requirement and the bandwith is uniformly shared by UEs in a cell. Under this assumption, the problem of optimizing cell switch-off for maximum energy efficiency is still NP-hard. We present an artificial neural network based small cell switch-off algorithm followed by flip-over method in omnidirectional cell deployment which offers a good result with linear complexity in on-line system and the Quality of Service (QoS) of the UEs can be met. Numerical results are presented through system level simulations.

In 5G communication system, the application of massive Multiple Input and Multiple Output (MIMO) technology makes it possible to transmit a plurality of narrow Transmitting (Tx) beams at eNodeB side. Each Tx beam may be applied to each Beam Reference Signal (BRS), which can be used by the User Equipment (UE) to accomplish beam tracking. In addition, a UE could also contain massive antennas and maintain several Receiving (Rx) beams, and it should measure all possible Tx beams or Tx-Rx beam pairs to determine the best one. The beam tracking process could result in an unacceptable delay, which is determined by the number of Tx and Rx beams. In this paper, an improved method is proposed which could reduce search delay further at the cost of energy loss. In addition, an optimized method for Tx beam pattern design is presented to reduce the performance loss with fast search. Simulation results show that with the help of the optimized Tx beam pattern, the performance of fast beam search method could be improved significantly.

It is of vital importance to make audiovisual quality assessment, as the growing demand on video telephone services. Users are more enjoying higher quality of video telephone, and their perceptions on video telephone service will directly influence the service provider's performance. So it is significant to study end users' subjective perception, named as Quality of Experience (QoE), on video telephone. In this paper, subjective tests have been conducted with participation from laboratories with ages ranging from 20 to 40, and we analyze the collected data and build a QoE model for evaluating video telephone services, considering different video telephone content types. The QoE model, named as Video-Telephone-Mean Opinion Score model, directly focuses on end-users' feeling. The key performance indicators (KPIs) are mapped to QoE score. The performance of model for QoE evaluation on video telephone quality has been verified via plenty subjective Mean Opinion Score (MOS) test, which includes 120 video telephone samples with 2760 valid votes. The Pearson Correlation Coefficient between VT MOS and MOS is 0.90, which indicates that this model can be used to evaluate users' perception on video telephone quality.

HTTP Adaptive Streaming(HAS) has become widely deployed in multimedia services for its ability for providing the best Quality of Experience(QoE) for viewers with limited resource, especially in fluctuating wireless networkings. With its client-driven rate adaptation mechanism, HAS is able to adapt to fluctuating network condition and various terminals dynamically. The rate adaptation algorithm is crucial in HAS for its direct impact on the QoE. Most of researches focus on optimizing objective indicators, such as elevating mean bit-rate, lessening playout interruption, and avoiding quality switches, etc. However, the promotion in objective indicators doesn't indicate better experience of end users directly. In this paper, a novel QoE-Optimal Rate Adaptation(QORA) algorithm is proposed to achieve the best QoE. Firstly, a QoE model with iterative form is deduced for on-line evaluation. According to this model, the QORA is able to predict the possible QoE of each bit-rate level in candidate, then greedily choose the one with the highest QoE. The perceptual quality of HAS is optimized by the QORA directly and quantitatively. The simulation result shows that the proposed QORA is able to provide the optimal QoE compared with other rate adaptation schemes, although some of them have better performance in a single objective indicator.

In recent years, data traffic over cellular networks has experienced an exponential rise, primarily due to the explosion of smartphones, tablets and laptops. This increase in data traffic on cellular networks has caused an immediate need for offloading traffic for optimum performance of both voice and data services. The paper focuses on the coverage improvements of high floor users by offloading these users to picos. Four antenna patters with different vertical half power beam width are applied in both outband and inband pico scenarios. The simulation results indicate that both outband and inband picos can offload the same amount of high floor users but the outband picos can provide a much better coverage than macros while inband pico cannot significantly improve the coverage performance.

With the rapid increase of traffic in cellular networks, low power nodes overlaid within a macro network is considered to be a cost-effective way to significantly enhance the capacity of cellular networks. In this paper, the impact of the pico cell antenna pattern and tilt on the performance of TD-LTE networks is analyzed in 3D Scenario. The optimal values of antenna tilts and the choice of antenna pattern are given under certain restriction. Besides, the simulation results show that the pico antenna pattern and tilt can significantly affect the key performance indices of the network, namely, the SINR, the capacity, the pico connected user ratio and others. In addition, the simulation results show that picos equipped with uptilt antennas can provide good coverage for high floor users.