Unlike Wi-Fi, Broadband Wireless Access (BWA) technology provides a high-speed communication in a wide area. The IEEE 802.16 (WiMAX) standard of wireless mesh networks is one of the widely used BWA standards. WiMAX mesh mode achieves data transmission in conflict-free manner in multihop networks by using the control messages (three way handshake messages or MSH-DSCH messages) to reserve channel for sending data. Concurrently, the coordination of three way handshake messages depends on the mechanism named Election based Transmission Timing (EBTT). However, IEEE 802.16 mesh mode uses a static holdoff algorithm, which leads to a low performance in the majority of cases. In this paper, after analyzing the IEEE 802.16 mesh mode with coordinated distributed scheduling, we propose a novel method to improve the throughput by a dynamic holdoff algorithm. The simulation results show that our proposal gets a better throughput performance.

Sparse code multiple access (SCMA) based on the message passing algorithm (MPA) for multiuser detection is a competitive non-orthogonal multiple access technique for fifth-generation wireless communication networks Among the existing multiuser detection schemes for uplink (UP) SCMA systems, the serial MPA (S-MPA) scheme, where messages are updated sequentially, generally converges faster than the conventional MPA (C-MPA) scheme, where all messages are updated in a parallel manner. In this paper, the optimization of message scheduling in the S-MPA scheme is proposed. Firstly, some statistical results for the probability density function (PDF) of the received signal are obtained at various signal-to-noise ratios (SNR) by using the Monte Carlo method. Then, based on the non-orthogonal property of SCMA, the data mapping relationship between resource nodes and user nodes is comprehensively analyzed. A partial codeword transmission of S-MPA (PCTS-MPA) with threshold decision scheme of PDF is proposed and verified. Simulations show that the proposed PCTS-MPA not only reduces the complexity of MPA without changing the bit error ratio (BER), but also has a faster convergence than S-MPA, especially at high SNR values.

To achieve high end-to-end availability in nationwide optical transport network across thousands of office buildings, it is important to properly make each function redundant, and execute protection switching, repair failed functions and recover redundancy to prevent multiple simultaneous failures. High redundancy leads to high system cost and high power consumption, and tight conditions for recovery leads to high maintenance cost. Therefore it is important to optimize the balance between redundancy and maintenance condition based on appropriate availability indicators. We previously proposed a resource-pool control mechanism for a nationwide optical transport network that can optimize the balance. This paper proposes an end-to-end availability evaluation scheme for a nationwide optical transport network with our mechanism, by which network operators can design the pool-resource amount of each function and the maintenance conditions for each network area properly to satisfy the end-to-end availability requirement. Although the maintenance conditions are usually discussed based on failure-recovery times, they should be discussed based on cost- or load-based volumes for this design. This paper proposes a maintenance-operation-load evaluation scheme, which derives the required number of maintenance staff members from failure-recovery times. We also discuss the design of the pool-resource amount and maintenance conditions for each network area of a nationwide network based on the proposed evaluation schemes.

Digitization of analog terrestrial TV broadcasting has recently been accelerated in many countries, and the effective utilization of vacant frequencies has also been investigated for new systems in each country. In Japan, a portion of vacant frequencies in the VHF-high band was allocated to the public broadband mobile communication (PBB) system. To evaluate the current PBB system and develop future broadband communication systems in this band, it is important to analyze the propagation channel more accurately. In this study, we characterize the propagation channel for 200MHz band broadband mobile communication systems, using measured channel impulse responses (CIRs). In the characterization process, the Saleh-Valenzuela (S-V) model is utilized to extract channel model parameters statistically. When evaluating the fluctuation of path power gain, we also propose to model the fluctuation of path power gain using the generalized extreme value distribution instead of the conventional log-normal distribution. The extracted CIR model parameters are validated by cumulative distribution function of root-means-square delay spread and maximum excess delay, comparing simulation result to measurement result. From the extracted CIR model parameters, we clarified the characteristics of 200MHz band broadband mobile communication systems in non-line-of-sight environments based on S-V model with the proposed channel model.

Reverberation chambers (RCs) are used widely in the electromagnetic measurement area. An RC is designed to have a long reverberation time, generate numerous modes, and provide good field uniformity within the chamber. The purpose of this paper is to describe the design process and measurement of the KRISS Reverberation Chamber (KRC). KRC models with 4.5m × 3.4m × 2.8m dimensions are simulated by 3D numerical simulation software. The field uniformity and correlation coefficient are then analyzed at 200MHz to obtain the optimized model. The simulation results show good performance in terms of field uniformity and are confirmed by measurement from 200MHz to 1GHz. The lowest usable frequency (LUF) of KRC was confirmed by field uniformity to be 200MHz. However, the stirrer correlation coefficient results show good performance above 300MHz.

By exploiting the inherent sparsity of wireless channels, the channel estimation in an orthogonal frequency division multiplexing (OFDM) system can be cast as a compressed sensing (CS) problem to estimate the channel more accurately. Practically, matching pursuit algorithms such as orthogonal matching pursuit (OMP) are used, where path delays of the channel is guessed based on correlation values for every quantized delay with residual. This full search approach requires a predefined grid of delays with high resolution, which induces the high computational complexity because correlation values with residual at a huge number of grid points should be calculated. Meanwhile, the correlation values with high resolution can be obtained by interpolation between the correlation values at a low resolution grid. Also, the interpolation can be implemented with a low pass filter (LPF). By using this fact, in this paper we substantially reduce the computational complexity to calculate the correlation values in channel estimation using CS.

A novel secure spatial modulation (SM) scheme based on dynamic multi-parameter weighted-type fractional Fourier transform (WFRFT), abbreviated as SMW, is proposed. Each legitimate transmitter runs WFRFT on the spatially modulated super symbols before transmit antennas, the parameters of which are dynamically updated using the transmitting bits. Each legitimate receiver runs inverse WFRFT to demodulate the received signals, the parameters of which are also dynamically generated using the recovered bits with the same updating strategies as the transmitter. The dynamic update strategies of WFRFT parameters are designed. As a passive eavesdropper is ignorant of the initial WFRFT parameters and the dynamic update strategies, which are indicated by the transmitted bits, it cannot recover the original information, thereby guaranteeing the communication security between legitimate transmitter and receiver. Besides, we formulate the maximum likelihood (ML) detector and analyze the secrecy capacity and the upper bound of BER. Simulations demonstrate that the proposed SMW scheme can achieve a high level of secrecy capacity and maintain legitimate receiver's low BER performance while deteriorating the eavesdropper's BER.

The 1-bit digital radio frequency (DRF) transmitter using a band-pass delta-sigma modulator (BP-DSM) can output a radio frequency (RF) signal carrying a binary data stream with a constant data rate regardless of the carrier frequency, which makes it possible to transmit RF signals over digital optical links with a constant bit rate. However, the optical link requires a line coding, such as 8B10B or 64B66B, to constrain runlength and disparity, and the line coding corrupts the DRF power spectrum owing to additional or encoded data. This paper proposes a new line coding for BP-DSM, which is able to control the runlength and the disparity of the 1-bit data stream by adding a notch filter to the BP-DSM that suppresses the low frequency components. The notch filter stimulates the data change and balances the direct current (DC) components. It is demonstrated that the proposed line coding shortens the runlength from 50 bits to less than 8 bits and reduces the disparity from several thousand bits to 5 bits when the 1-bit DRF transmitter outputs an LTE signal with 5 MHz bandwidth, when using carrier frequencies from 0.5GHz to 2GHz and an output power variation of 60dB.

When trying to estimate time-varying multipath channels by applying a basis expansion model (BEM) in orthogonal frequency division multiplexing (OFDM) systems, pilot clusters are contaminated by inter-carrier interference (ICI). The pilot cluster ICI (PC-ICI) degrades the estimation accuracy of BEM coefficients, which degrades system performance. In this paper, a PC-ICI suppression scheme is proposed, in which two coded symbols defined as weighted sums of data symbols are inserted on both sides of each pilot cluster. Under the assumption that the channel has Flat Doppler spectrum, the optimized weight coefficients are obtained by an alternating iterative optimization algorithm, so that the sum of the PC-ICI generated by the encoded symbols and the data symbols is minimized. By approximating the optimized weight coefficients, they are independent of the channel tap power. Furthermore, it is verified that the proposed scheme is robust to the estimation error of the normalized Doppler frequency offset and can be applied to channels with other types of Doppler spectra. Numerical simulation results show that, compared with the conventional schemes, the proposed scheme achieves significant improvements in the performance of PC-ICI suppression, channel estimation and system bit-error-ratio (BER).

Wireless information and power transfer technology is a promising means of supplying power for remote terminals in future communication systems. This paper investigates time-splitting (TS) recource allocation schemes for multi-cell massive MIMO systems with downlink (DL) wireless power transfer and uplink (UL) user information transmission under a harvest-then-transmit protocol. In order to jointly optimize the power and time allocation, two power minimization problems are formulated under different constraints on the minimal quality-of-service (QoS) requirement. Then, these original non-convex problems are transformed into their convex approximated ones which can be solved iteratively by successive convex approximation. Simulation results show that by exploiting the diversity effect of large-scale antenna arrays, the complexity-reduced asymptotic recourse allocation scheme almost match the power efficiency of the nonasymptotic scheme.

In this paper, we devise low-complexity uplink detection algorithms for Massive MIMO systems. We treat the uplink detection as an ill-posed problem and adopt the Landweber Method to solve it. In order to reduce the computational complexity and increase the convergence rate, we propose improved Landweber Method with optimal relax factor (ILM-O) algorithm. In addition, to reduce the order of Landweber Method by introducing a set of coefficients, we propose reduced order Landweber Method (ROLM) algorithm. An analysis on the convergence and the complexity is provided. Numerical results demonstrate that the proposed algorithms outperform the existing algorithm.

In this paper, we propose a novel primary user detection scheme for spectrum sensing in cognitive radio. Inspired by the conventional signal classification approach, the spectrum sensing is translated into a classification problem. On the basis of feature-based classification, the spectral correlation of a second-order cyclostationary analysis is applied as the feature extraction method, whereas a stacked denoising autoencoders network is applied as the classifier. Two training methods for signal detection, interception-based detection and simulation-based detection, are considered, for different prior information and implementation conditions. In an interception-based detection method, inspired by the two-step sensing, we obtain training data from the interception of actual signals after a sophisticated sensing procedure, to achieve detection without priori information. In addition, benefiting from practical training data, this interception-based detection is superior under actual transmission environment conditions. The alternative, a simulation-based detection method utilizes some undisguised parameters of the primary user in the spectrum of interest. Owing to the diversified predetermined training data, simulation-based detection exhibits transcendental robustness against harsh noise environments, although it demands a more complicated classifier network structure. Additionally, for the above-described training methods, we discuss the classifier complexity over implementation conditions and the trade-off between robustness and detection performance. The simulation results show the advantages of the proposed method over conventional spectrum-sensing schemes.

Smallcells have recently emerged as a potential approach for local area deployments that can satisfy high data rate requirements, reduce energy consumption and enhance network coverage. In this paper, we work on maximizing the weighted sum energy efficiency (WS-EE) for densely deployed smallcell networks. Due to the combinatorial and the general fractional program nature of the resource allocation problem, WS-EE maximization is non-convex and the optimal joint resource blocks (RBs) and power allocation is NP-hard. To solve this complex problem, we propose to decompose the primal problem into two subproblems (referred as RBs allocation and power control) and solve the subproblems sequentially. For the RBs allocation subproblem given any feasible network power profile, the optimal solution can be solved by maximizing throughput locally. For the power control subproblem, we propose to solve it locally based on a new defined pricing factor. Then, a distributed power control algorithm with guaranteed convergence is designed to achieve a Karush-Kuhn-Tucker (KKT) point of the primal problem. Simulation results verify the performance improvement of our proposed resource allocation scheme in terms of WS-EE. Besides, the performance evaluation shows the tradeoff between the WS-EE and the sum rate of the smallcell networks.

Video streaming over HTTP/2 is a new trend in multimedia delivery. Compared to the pull-based HTTP/1.1 protocol, the new HTTP/2 protocol's Server Push feature is very effective in reducing the overheads (e.g., in terms of energy, processing, bandwidth) for clients, servers, and network nodes. This paper presents an HTTP/2 push-based adaptation method for on-demand video streaming that reduces the number of requests and provides high video quality. In our method, for each client request, the server sends video segments continuously until it receives another client request with a new quality. Since a request is sent only if the client wants to update the video bitrate, our method can significantly reduce the request related overhead. For this context, a buffer based algorithm is proposed to provide high and smooth video quality while avoiding buffer underflows. Experiments show that the proposed method can provide a lower number of requests, higher average quality and better quality smoothness than existing methods.