Enhanced estimation of configuration capabilities in cognitive radio [cognitive radio communications and networks]

Cognitive radio is a highly promising answer to the complexity and heterogeneity characterizing the beyond 3G wireless scenario. In this context, this article advances from the field of interference sensing to the fields of (basic) reasoning and robust reasoning. Interference sensing is concerned with the acquisition of interference related measurements for frequency bands of interest. The article describes how a cognitive radio system can reason on these measurements to obtain estimations for the capabilities of alternate configurations, especially in terms of achievable transmission capacity and coverage. Subsequently, it focuses on robust reasoning, namely, on enhancing these estimations by employing machine learning, which constitutes an important aspect of cognitive radio. Several relevant solutions are sketched and explained, with a view to providing a complete picture.     

面向高铁无线网络覆盖与容量优化的多agent模糊强化学习算法

为了提升高铁沿线LTE无线网络服务质量,提供最理想的覆盖与容量性能,在传统单agent学习算法的基础上,提出了通过多agent联合调整相邻eNodeB的天线下倾角从而实现覆盖与容量优化的模糊强化学习算法。并在LTE网络下的高速场景中进行仿真,仿真结果表明多agent学习算法与传统学习算法相比在高速环境下达到全局最优解的速率更快,特别是在应对环境突变的情况时恢复到最优解的速率有所提升。     

Wholesale Power Price Dynamics Under Transmission Line Limits: A Use of an Agent-Based Intelligent Simulator

This research proposes a use of an agent-based intelligent simulator to numerically examine the influence of a transmission line limit on the dynamics of a wholesale power market. In the proposed simulator, all agents are equipped with learning capabilities. The power market is structured by multiple zones connected by transmission lines. The following business implications are found in this study. 1) The learning speed of reinforcement learning depends upon a dynamic change of market price. 2) The marketprice and volatility of electricity is increased by a line limit. The increase is influenced by not only a capacity limit but also a zone structure and an amount of demand. 3) The average price and volatility of electricity are influenced by the number of capacity-limited links. 4) There is no major difference between day-ahead (DA) and real-time (RT) markets in terms of the influence of a line limit. 5) There is a slightly increasing trend in average DA and RT market prices along with the percentage reduction of a current line limit.     

Iterative interference cancellation and channel estimation in multibeam satellite systems

This paper deals with the use of non‐linear multiuser detection techniques to mitigate co‐channel interference on the reverse link of multibeam satellite systems. These techniques allow more capacity efficient frequency reuse strategies than classical ones, as they make possible to cope with lower C/I. The considered system takes as a starting point the DVB‐RCS standard, with the use of convolutional coding, and the use of the Ka‐band. We propose different iterative interference cancellation schemes, which operate at the beamformer outputs, and which use information from decoders. The proposed receivers assume an initial single‐user synchronization step: frame synchronization and timing recovery, and then perform channel estimation: beamformer coefficients; signal carrier phases and signal amplitudes. In a first step, these receivers are evaluated by simulation in terms of bit error rate and of channel estimation error on two interference configurations. For one of these receivers, sensitivity to imperfect timing recovery and to low‐frequency offsets from user terminals is evaluated. In a second step, since the receiver performances highly depend on the interference configuration, we propose an approach to evaluate performances on a multibeam coverage (by taking into account the variability of interference configurations on the coverage). This method is used to compare different receivers on an example based on a coverage designed on a digital focal array feed reflector antenna. Copyright © 2007 John Wiley & Sons, Ltd.     

Hybrid Amplitude Control Antenna Array System for Energy Efficient W-CDMA Network with Adaptive Coverage and Capacity

This paper introduces a novel technique and mathematical formulation of two dimensional elastic footprint variations and adaptive sector configuration variations by using a hybrid adaptive amplitude control antenna array system. The antenna array system can control the elevation beam-widths from 6.84° to 13° and the azimuth beam-widths from 33° to 93° for obtaining the adaptive capacity and coverage. The work illustrates the application of the antenna array system in the energy efficient W-CDMA network. The antenna array half-power beam width variation is achieved by using the antenna array amplitude control and co-located multiple antenna array switching. The Node-Bs can adaptively switch to three, four, five, six and non uniform sector configurations with the antenna array beam width control and adaptive neighbor relations. Sector configurations will vary according to the pre-defined specific traffic loading percentages out of Node-B’s total channel capacity to reduce the energy consumption of the entire network. The paper introduces an adaptive footprint overlaps shifting technique, where the sector with less traffic load will expand its footprint towards the sector with higher traffic load and the sector with higher traffic load will shrink its footprint by maintaining a fixed footprint overlaps to improve the coverage and the capacity of the network. The footprints overlap shifting is applicable only for the active sector antennas facing each other. The results confirm that the proposed antenna array system outperforms the automatic tilt optimization and can control coverage, capacity and improve the energy efficiency of the W-CDMA network.     

An Energy Efficient Autonomous Method for Coverage Optimization in Wireless Multimedia Sensor Networks

In this paper, a distributed method for coverage optimization of random deployed WMSNs utilizing motility and mobility capabilities of nodes, is proposed. The aims followed by the method are first, maximizing the coverage ratio by minimizing both the covered overlapping areas, and the coverage holes after random deployment, and second, enhancing energy efficiency of the coverage optimization procedure, by minimizing the needed rotations and specially movements, comparing with the previous schemes. To these aims, the most appropriate location and orientation of the nodes are calculated round by round considering all the possible nested compositions of rotation and movement. But, rotating and moving the nodes are performed after terminating the algorithm rounds and achieving the decisive results. So, the proposed method does not impose the overhead of trial and error of rotation or relocation on the network nodes. The performance of the proposed approach has been compared with the previous works for different network configurations; simulation results show that the proposed approach outperforms the previous schemes in terms of both coverage ratio and energy efficiency.     

基于深度强化学习的无人机间通信链路智能决策

由于无人机组网灵活、快速、低成本的特性,空中基站被视为在未来无线通信中有前景的技术。无人机集群可以通过相互协调和合作,完成的复杂任务,具有重大的研究和实用价值,而无人机间的高效通信是当下面临的重大挑战。为了在满足无人机间通信速率的前提下,尽可能节省发射功率,本文提出基于深度强化学习的集群方案和功率控制的智能决策算法。首先,本文设计了三种无人机集群方案,以对地面用户提供无缝的无线覆盖;然后,本文提出了基于深度Q网络（Deep Q-network）算法的集群方案和功率控制决策算法,用深度神经网络输出不同条件下联合决策的无人机集群方案和发射功率,并研究了重要性采样技术,提高训练效率。仿真结果表明,本文提出的深度强化学习算法能够正确决策无人机集群方案和发射功率,与不带强化学习的深度学习（Deep Learning Without Reinforcement Learning, DL-WO-RL）算法相比,用更低的发射功率满足无人机之间的通信速率要求,并且重要性采样技术能够缩短DQN算法的收敛时间。      

Channel capacity limits for multiple-access channels with slowRayleigh fading

The complex-valued collaborative coding multiple-access (CVCCMA) technique has been shown to offer efficient simultaneous transmission by multiple users over a common radio channel, without the use of orthorgonal codes nor subdivisions in time or frequency. The authors describe the capacity calculation for a T user CVCCMA system in a slow Rayleigh fading environment with additive white Gaussian noise (AWGN). The capacity, in terms of bits per channel use has also been derived by simulation for different values of T with MPSK modulation     

The Expanded Very Large Array

In almost 30 years of operation, the Very Large Array (VLA) has proved to be a remarkably flexible and productive radio telescope. However, the basic capabilities of the VLA have changed little since it was designed. A major expansion utilizing modern technology is currently under way to improve the capabilities of the VLA by at least an order of magnitude in both sensitivity and in frequency coverage. The primary elements of the Expanded Very Large Array (EVLA) project include new or upgraded receivers for continuous frequency coverage from 1 to 50 GHz, new local oscillator, intermediate frequency, and wide bandwidth data transmission systems to carry signals with 16 GHz total bandwidth from each antenna, and a new digital correlator with the capability to process this bandwidth with an unprecedented number of frequency channels for an imaging array. Also included are a new monitor and control system and new software that will provide telescope ease of use. Scheduled for completion in 2012, the EVLA will provide the world research community with a flexible, powerful, general-purpose telescope to address current and future astronomical issues.     

A Hybrid Adaptive Relay Technique for Cooperative Communication System

Cooperative communication will increase the channel capacity, when the communicating terminals exceed more than two. Therefore, a relay is termed, as three-terminal unit is a fundamental for user cooperation. The cooperation provides throughput enhancement, reliability, and coverage improvement for wireless communication. Relay technique plays a vital role in cooperative communication in terms of increasing coverage range as well as spectral efficiency. In existing techniques Amplify Forward increase the noise and Decode Forward increase the computational cost of the receiver. In order to overcome the above limitation, a hybrid adaptive relay technique is proposed for cooperative communication system, which will initially check the channel quality of the end user received SNR. When the receiver does not able to decode the message, then the user will choose relay signal. We derived a closed form expression to find the outage probability and channel capacity for the Rayleigh fading channel. Finally, simulation results show the performance of proposed adaptive relay technique in comparison with traditional relay technique by considering both perfect and imperfect CSI.     

A survey on mobile satellite systems

Satellite systems represent a significant solution to provide communication services to mobile users in under‐populated regions, in emergency areas, on planes, trains, and ships. In all these cases, satellite systems have unique capabilities in terms of robustness, wide area coverage, and broadcast/multicast capabilities. This paper surveys current mobile satellite networks and services from different standpoints, encompassing research issues, recent standardization advances (e.g. mobile extension for DVB‐S2/‐RCS, DVB‐SH) and some operational systems (e.g. Globalstar, Inmarsat BGAN, Iridium, and Thuraya). The last part of this paper is devoted to qualitative and quantitative comparisons of the different mobile satellite systems to understand their characteristics in terms of services, capacity, resource utilization efficiency, and user mobility degree.Copyright © 2009 John Wiley & Sons, Ltd.     

Coverage analysis of cache-enabled small cell networks with stochastic geometry methods

Caching popular content in the storage of small cells is deemed as an efficient way to decrease latency, offload backhaul and satisfy user’s demands. In order to investigate the performance of cache-enabled small cell networks, coverage probability is studied in both single-point transmission and cooperative multipoint (CoMP) transmission scenarios. Meanwhile, the caching distribution modeled as Zipf and uniform distribution are both considered. Assuming that small base stations (SBSs) are distributed as a homogeneous Poisson point process (HPPP), the closed-form expressions of coverage probability are derived in different transmission cases. Simulation results show that CoMP transmission achieves a higher coverage probability than that of single-point transmission. Furthermore, Zipf distribution-based caching is more preferable than uniform distribution-based caching in terms of coverage probability.     

Design and optimisation for cellular access network

The service quality of a cellular-radio network is dependent on the integrity of its access network. As a cellular-radio network evolves, the challenge to the operator is to provide near ubiquitous coverage (with adequate signal-to-noise ratio and a balanced uplink and downlink for handportables) and to accommodate a high traffic density yet at the same time to ensure that the carrier-to-interference ratio remains acceptable despite a finite amount of spectrum allocation. The large number of base sites deployed for coverage and capacity must be interconnected economically and efficiently back to the switch sites without compromising on resilience and transmission capacity. To meet these challenges, better efficiency for the radio links has to be achieved through the introduction of automated planning tools and adaptive system features; improvement of the transmission network performance can be attained by the flexible use of transmission media and network topologies     

Capacity and QoS for a Scalable Ring-Based Wireless Mesh Network

The wireless mesh network (WMN) is an economical solution to support ubiquitous broadband services. This paper investigates the tradeoffs among quality-of-service (QoS), capacity, and coverage in a scalable multichannel ring-based WMN. We suggest a simple frequency planning in the proposed ring-based WMN to improve the capacity with QoS support, and to make the system more scalable in terms of coverage. We develop a physical (PHY)/medium access control (MAC) cross-layer analytical model to evaluate the delay, jitter, and throughput of the proposed WMN, by taking account of the carrier sense multiple-access (CSMA) MAC protocol, and the impact of hop distance on transmission rate in the physical layer. Furthermore, the mixed-integer nonlinear programming optimization approach is applied to determine the optimal number of rings and the associated ring widths, aiming at maximizing the capacity and coverage of a mesh cell subject to the delay requirement     

面向物联网的光载WiFi链路与波长分配协议

A novel Wireless Fidelity (WiFi) over fiber link and a wavelength assignment protocol are proposed to provide sufficient bandwidth and extensive coverage range for the various applications in the Internet of Things (IoT). The performance of the WiFi over fiber-based wireless IoT network is evaluated in terms of error vector magnitude (EVM) and data throughput for both the up and down links between the WiFi central control system and remote radio units (RRUs). The experimental results illustrate the reliability of the fiber transmission of 64 Quadrature Amplitude Modulation (64QAM) WiFi signals by direct analog modulation. In order to efficiently utilize the wavelength resources, we also demonstrated the wavelength assignment protocol by employing optical switching configurations in Central Station (CS) to realize the wavelength switching, and the simulation results indicate the queuing size and the corresponding queue delay for different numbers of available wavelengths.     

Architectures and performance of AWG-based optical switching nodes for IP networks

In order to support the continuous growth of transmission capacity demand, optical packet switching technology is emerging as a strong candidate, promising to allow fast dynamic allocation of wavelength-division multiplexing (channels, combined with a high degree of statistical resource sharing). This work addresses the design of optical switch architectures, based on previous proposals available in the technical literature that use an arrayed waveguide grating (AWG) device to route packets. Since the port number of currently available AWGs is a limiting factor, we propose two new modified structures which better exploit the switching capability of this component in the wavelength domain. Since a limited hardware complexity is a key requirement for all-optical switches, due to the high cost of optical components, these different node configurations are compared in terms of complexity. Traffic performance of these new structures in a full optical packet switching scenario is also examined.     

一种基于UDP电子政务消息传输的新技术

为了提高小消息、大并发、高吞吐量、高实时消息传输的高效性和可靠性,提出了一种基于UDP（User Datagram Protocol,用户数据报协议）的电子政务消息传输的新技术.该技术采用了一种消息刚好满足使用（Just meet）的思想,通过可靠UDP技术、低延迟处理协议等信息处理技术,尽量剔除数据传输中没有用的多余信息,来保证信息传输处理的低延迟和可靠性.应用结果表明,该技术提高了消息传输效率和可靠性,消息的处理能力可以高达每秒百万（条）级,处理延迟可控制在50ms左右.     

Use of Asymptotic Waveform Evaluation Technique in the Analysis of Multilayer Structures With Doubly Periodic Dielectric Gratings

The reflection and dispersion characteristics of multilayer structures that involve periodically implanted material blocks are obtained by using the MoM solution of the volume integral equation. The asymptotic waveform evaluation (AWE) technique is utilized to obtain a Pade approximation of the solution in terms of a parameter such as frequency or incident angle. The use of AWE technique enables a fast sweep with respect to the approximation parameter. Moreover, a robust method for extracting the dispersion characteristics of periodic structures via Pade approximation is proposed. The AWE procedure requires the calculation of high order derivatives of the complicated kernel function that consists of Green's functions for stratified medium. These derivatives are calculated by employing the automatic differentiation theory. The reflection coefficient, propagation constant and band diagram of the structure are obtained both via point-by-point simulations and through the use of AWE technique. It is observed that AWE technique increases the computational efficiency without losing accuracy.     

Antenna subset selection at multi‐antenna relay with adaptive modulation

In this paper, we proposed several antenna selection schemes for cooperative diversity systems with adaptive transmission. The proposed schemes were based on dual‐hop relaying where a relay with multiple‐antenna capabilities at reception and transmission is deployed between the source and the destination nodes. We analyzed the performance of the proposed schemes by quantifying the average spectral efficiency and the outage probability. We also investigated the trade‐off of performance and complexity by comparing the average number of active antennas, path estimations, and signal‐to‐noise ratio comparisons of the different proposed schemes. Copyright © 2011 John Wiley & Sons, Ltd.     

Exploiting Macrodiversity with Distributed Antennas in Micro-Cellular CDMA Systems

We consider the use of distributed antennas to increase the capacity and peak data rate achievable in a microcellular CDMA system with limited bandwidth. In additon to the diversity against Rayleigh fading achievable by use of microdiversity among nearly co-located transmit or receive antennas, we exploit macrodiversity against shadow fading that more widely separated antennas permit. We report on antenna configurations for both directional and omni-directional antennas that provide the most uniform signal-to-interference ratio coverage, averaged over a large number of position vectors drawn from a spatially uniform distribution of mobiles. Call capacities and peak transmission rates are determined for an integrated system carrying traffic at different constant rates, where processing gain and the transmission rate are selected to satisfy a common chip rate. For the downlink a 5.5 dB capacity gain can be achieved for 64 kb/s calls using four antennas located on the diagonals of each square cell. A bandwidth of 5 MHz allows two or more calls to be simultaneously supported at data rates up to 512 kb/s, as opposed to only 128 kb/s for three co-located antennas. On the uplink we distinguish between the computationally simpler equal-gain combining of the antenna signals and the possibly more complex maximum-ratio combining. With equal gain combining we achieve a peak data rate of 128 kb/s and a capacity gain of 2.5 dB relative to equal gain combining of three nearly co-located antenna signals. With maximum ratio combining the peak uplink rate can be as high as 512 kb/s and the capacity is increased by 2.0 dB relative to the maximum-ratio combining of three co-located antennas.