第一、三区卫星广播重新规划(上)

本文介绍了广播卫星规划的发展过程，以及２０００年无线电大会通过的卫星广播重新规划的基本原则与技术参数，重点介绍了中国卫星广播规划资源及其最新规划结果。     

Electrochromic Window Based on Conducting Poly(3,4‐ethylenedioxythiophene)–Poly(styrene sulfonate)

A short survey of technological aspects of electrochromism with various electroactive species is given. Different approaches with inorganic and organic materials have been pursued in the past. So far widespread usage of this technology for large area applications has not been achieved. Nevertheless one major technical product, self‐darkening rear‐view mirrors for cars, is already well established. This article reviews some research results on electroactive polythiophenes, especially poly(3,4‐alkylenedioxythiophenes). Some promising results with the commercially available electrically conducting polymer Baytron P (PEDT/PSS) are presented. It is demonstrated that an all solid‐state electrochromic multilayer assembly based on a polymeric electrochromic material might be close to technical realization. The coating of large area substrates with aqueous poly(3,4‐ethylenedioxythiophene)‐poly(styrenesulfonate) dispersion can be a way to an economically viable product.     

Tree‐based channel assignment schemes for multi‐channel wireless sensor networks

Many sensor node platforms used for establishing wireless sensor networks (WSNs) can support multiple radio channels for wireless communication. Therefore, rather than using a single radio channel for whole network, multiple channels can be utilized in a sensor network simultaneously to decrease overall network interference, which may help increase the aggregate network throughput and decrease packet collisions and delays. This method, however, requires appropriate schemes to be used for assigning channels to nodes for multi‐channel communication in the network. Because data generated by sensor nodes are usually delivered to the sink node using routing trees, a tree‐based channel assignment scheme is a natural approach for assigning channels in a WSN. We present two fast tree‐based channel assignment schemes (called bottom up channel assignment and neighbor count‐based channel assignment) for multi‐channel WSNs. We also propose a new interference metric that is used by our algorithms in making decisions. We validated and evaluated our proposed schemes via extensive simulation experiments. Our simulation results show that our algorithms can decrease interference in a network, thereby increasing performance, and that our algorithms are good alternatives for static channel assignment in WSNs. Copyright © 2015 John Wiley & Sons, Ltd.     

General switch‐and‐examine relaying for demodulate‐and‐forward cooperative diversity

Two new demodulate‐and‐forward schemes of multi‐relay cooperative diversity with switch‐and‐examine relaying (SER) are analyzed. To reduce relay usage and enhance bandwidth efficiency, the two new cooperative diversity schemes employ a switch‐based relay selection. The proposed schemes consume less communication resource than regular relaying schemes, such as the selection combining (SC) or maximal ratio combining (MRC) schemes that always use all relays, and also achieve better performance than distributed switch‐and‐stay schemes. In the first scheme, the decision statistic for relay usage and selection is based on the signal‐to‐noise ratio (SNR). In the second scheme, the log‐likelihood ratio (LLR) of received signals is used for the decision of relay usage and selection. With the two SER schemes, the bit error probability (BEP) of binary phase shift keying (BPSK) and the average number of used paths are derived and expressed in closed‐form for the independent and identically distributed (i.i.d.) Rayleigh fading channels. Numerical and simulation results are presented for performance illustrations. According to the numerical results, the LLR‐based SER not only achieves a lower BEP but also consumes less relay resource than the SNR‐based SER. Furthermore, the LLR‐based SER scheme even outperforms the corresponding SNR‐based SC scheme for a range of average SNR. Copyright © 2014 John Wiley & Sons, Ltd.     

Joint evolutionary spectrum and autoregressive‐based approach to modeling non‐stationary flat fading channels

Modeling of wireless channels, especially non‐stationary fading channels, is important for design and performance analysis of wireless communication systems. Recently, we proposed a new approach to modeling non‐stationary fading channels, based on the theory of evolutionary spectrum (ES). In this paper, we develop a time‐varying autoregressive (AR) model for a non‐stationary flat fading channel; specifically, we develop a method to determine the time‐varying coefficients of the AR channel model, given the ES of a non‐stationary process. Furthermore, with the ES theory, we develop a trace‐driven time‐varying AR channel simulator to generate a non‐stationary flat fading process. Simulation results show that the ES of the channel gain process produced by our joint ES‐and‐AR‐based channel model agrees well with the user‐specified ES, indicating the accuracy of our joint ES‐and‐AR‐based channel model. Copyright © 2012 John Wiley & Sons, Ltd.     

Channel‐estimate‐based frequency‐domain equalization (CE‐FDE) for broadband single‐carrier transmission

A channel‐estimate‐based frequency‐domain equalization (CE‐FDE) scheme for wireless broadband single‐carrier communications over time‐varying frequency‐selective fading channels is proposed. Adaptive updating of the FDE coefficients are based on the timely estimate of channel impulse response (CIR) to avoid error propagation that is a major source of performance degradation in adaptive equalizers using least mean square (LMS) or recursive least square (RLS) algorithms. Various time‐domain and frequency‐domain techniques for initial channel estimation and adaptive updating are discussed and evaluated in terms of performance and complexity. Performance of uncoded and coded systems using the proposed CE‐FDE with diversity combining in different time‐varying, multi‐path fading channels is evaluated. Analytical and simulation results show the good performance of the proposed scheme suitable for broadband wireless communications. For channels with high‐Doppler frequency, diversity combining substantially improves the system performance. For channels with sparse multi‐path propagation, a tap‐selection strategy used with the CE‐FDE systems can significantly reduce the complexity without sacrificing the performance. Copyright © 2004 John Wiley & Sons, Ltd.     

A cluster‐chain‐based context transfer mechanism for fast basic service set transition in the centralized wireless LAN architecture

The emergence of centralized WLAN architectures is proposed to solve the problems of large scale deployment of WLANs. In the centralized WLAN, access point (AP) is split into two pieces: wireless termination point (WTP), and access controller (AC). An AC is the centralized controller for a large number of WTPs. A station (STA) has the demand to move from one WTP to another within the same extended service set (ESS). Such behavior is called a basic service set (BSS) transition. In this paper, we propose the cluster‐chain‐based context (C³T) mechanism with a cluster member selection (CMS) algorithm to reduce the BSS transition delay in the centralized WLAN architecture. The proposed mechanism can have lower signaling cost for context transfer and does not have the ping‐pong problem comparing with the existing context transfer schemes in terms of BSS transition, such as the proactive neighbor caching (PNC) scheme, the configuration and provisioning for wireless APs handoff protocol (CAPWAPHP), and so on. Furthermore, since the original 802.11r fast BSS transition does not specify how to work in the centralized WLAN architecture, we incorporate the C³T mechanism into IEEE 802.11r that works in the centralized WLAN architecture. Copyright © 2008 John Wiley & Sons, Ltd.     

业务支撑系统网络化体系的研究

提升业务支撑能力,在竞争激烈的市场抢占业务发展制高点,已成为目前通信业界关注的重点问题。本文针对全网一体化运营需求,结合新一代网络体系架构,研究业务支撑系统网络化部署方案,介绍了网络化体系应用模式及实施方案,为全网一体化运营提供参考。     

A multi‐access method for BPL based on orthogonal pulse division multiplexing,barker‐code‐based spectrum spreading and orthogonal frequency division multiplexing

A highly efficient multi‐access scheme of broadband power line (BPL) communication, named as OFDM‐BPS‐OPDMA, is proposed based on the Orthogonal Pulse Division Multiplexing Access (OPDMA), Barker‐code‐based Spectrum Spreading (BSS) and Orthogonal Frequency Division Multiplexing (OFDM) method. The orthogonal pulses are generated by using the eigenvectors of Hermitian matrix. At the same time, a specific pulse will be allocated to every user of the communication system. The transmitting data are first modulated by OFDM. Then, it is processed with OPDMA and BSS. Finally, the data is sent to the power line channel. On the receiving side, the data is processed with BSS demodulation, OPDMA demodulation and OFDM demodulation, and the receiving data for each user is acquired. Because of the orthogonality between these pulses, the multi‐user interference could be eliminated; when BSS is used, the waveform restoration is enhanced. Meanwhile, with the help of OFDM, the multi‐path interference is mitigated. Particularly, all users can share the resources of time and spectrum without interfering with others, and get excellent reliability in the concerned scheme. When OFDM is used, the sub‐carriers may be allocated dynamically, and the legal radio frequency band could be shunned by sharing the common bandwidth with other communication systems. Copyright © 2009 John Wiley & Sons, Ltd.     

Channel‐power profile estimation for orthogonal frequency‐division multiplexing systems

In this work, a channel‐power profile estimation for orthogonal frequency‐division multiplexing systems, based on the cyclic prefix (CP), is introduced. By knowing the delay of each path, the time‐dispersion information can be derived. The proposed method, considering long intersymbol interference (ISI) fading channels, requires only the coarse symbol timing information. More specifically, quasi‐stationary fading channels are considered. The basic contribution is to obtain the maximum‐likelihood estimation of the correlation coefficient based on the CP. Subsequently, the relationship between the correlation coefficient and the channel‐tap powers is explored. With the estimate of correlation coefficient, the least‐square solution of the channel‐tap powers can be determined. The proposed method is suitable for both short and long ISI channels. Furthermore, the Cramér–Rao lower bound of the channel‐power profile estimation is analyzed, and simulations confirm the advantages of the proposed estimator. Copyright © 2011 John Wiley & Sons, Ltd.     

Closed‐form expression for the BER of m‐QAM‐OFDM systems over time‐ and frequency‐selective wireless channels

The broadcast DVB‐T system is an m‐QAM‐OFDM communication system that includes pilot‐symbol‐assisted modulation (PSAM) in order to enhance channel estimation at the receiver. This characteristic makes DVB‐T suitable for a mobile reception, over time‐ and frequency‐selective wireless channels. In this work, a closed‐form expression for the BER as a function of the transmission system, channel model and the channel estimation strategy employed at the receiver is derived. In addition, adjacent channel interference due to Doppler effects is also considered. The results are focused on the DVB‐T system under different scenarios. The channel estimation at the receiver has been shown to be very critical, and the impact of channel estimation errors on the BER is analysed in detail. Copyright © 2005 John Wiley & Sons, Ltd.     

Linear time‐invariant/time‐varying equalization of MIMO channels

In this paper, the problem of equalization of linear multi‐input multi‐output (MIMO) channels is addressed. Using an algebraic approach, we propose a unifying formalism for the linear time‐invariant/time‐varying channel equalization problem. A new definition called algebraic equalization is presented. This allows us to derive the necessary and sufficient condition on the existence of equalizer. We describe the received signals in terms of Kalman model. This then provides us with a test of channel equalization, which may be performed formally in terms of ranks of some related matrices. Copyright © 2007 John Wiley & Sons, Ltd.     

Outage performance of dual‐hop relaying systems over extended generalized‐K fading channels

The outage performance of the amplify‐and‐forward relaying strategies over mutually uncorrelated extended generalized‐K fading channels is addressed in this paper. The attention is dedicated to the analyses of the noise‐limited and also interference‐limited environment. The new analytical expression for outage probability of observed relaying system in the presence of thermal noise is derived using the method for approximating equivalent signal‐to‐noise ratio. In addition, the outage performance is studied for the dual‐hop system when only the single dominant co‐channel interference is inherent at the relay and destination node. The correctness of the proposed mathematical derivations is verified by simulations. Copyright © 2014 John Wiley & Sons, Ltd.     

基于独立分量分析的正交空时分组编码盲检测方案

通过在不同天线发射的信号之间引入时域和空域信息,正交空时分组编码(OSTBC)可以获得发射分集增益,而且可以在不牺牲带宽的情况下获得更高的编码增益。但是其译码却需要精确的信道状态信息(CSI),因此,信道信息估计的准确性严重影响系统的性能。基于独立分量分析(ICA)的盲源分离(BSS)技术可以在不进行信道估计的情况下对发射信号实现有效检测。通过利用OSTBC的正交特性,提出了2种基于ICA的盲检测方案,同时,一些基于信道估计的检测算法也被用来进行性能比较。瑞利衰落信道下的仿真结果表明,2种新方案均具有较好的系统适应性和误码率性能。     

Mobile‐to‐mobile MIMO transmit–receive diversity systems: analysis and performance in three‐dimensional double‐correlated channels

Mobile‐to‐mobile (M‐to‐M) communications are expected to play a crucial role in future wireless systems and networks. In this paper, we consider M‐to‐M multiple‐input multiple‐output (MIMO) maximal ratio combining system and assess its performance in spatially correlated channels. The analysis assumes double‐correlated Rayleigh‐and‐Lognormal fading channels and is performed in terms of average symbol error probability, outage probability, and ergodic capacity. To obtain the receive and transmit spatial correlation functions needed for the performance analysis, we used a three‐dimensional (3D) M‐to‐M MIMO channel model, which takes into account the effects of fast fading and shadowing. The expressions for the considered metrics are derived as a function of the average signal‐to‐noise ratio per receive antenna in closed‐form and are further approximated using the recursive adaptive Simpson quadrature method. Numerical results are provided to show the effects of system parameters, such as distance between antenna elements, maximum elevation angle of scatterers, orientation angle of antenna array in the x–y plane, angle between the x–y plane and the antenna array orientation, and degree of scattering in the x–y plane, on the system performance. Copyright © 2011 John Wiley & Sons, Ltd.     

Co‐ordination channels for digital satellite news gathering (DSNG)

This paper presents, in Section 1, a new approach to realising co‐ordination channels for digital satellite news gathering (DSNG). The key element of the approach to the co‐ordination channels is a direct‐sequence spread‐spectrum processing of the data to be transmitted which allows for the realization of an in‐band transmission of the co‐ordination channel signals overlaying the DSNG main channel, the part of the system which is responsible for the transmission of the audio/video signal on a point‐to‐point basis. The system is analysed in theory, simulation, and measurement with respect to system performance and degradation of the DSNG main channel. It shows superior system performance combined with a maximum of operational simplicity while the degradation of the DSNG main channel remains affordably low. Section 2 describes the DVB‐DSNG system for co‐ordination channels which incorporates many elements of the system presented in the first part but is modified in some details in order to increase system flexibility. One of these details concerns the possibility to perform in‐band transmission as well as transmission in the roll‐off frequency space of the DSNG main channel. In‐band transmission has the advantage of great operational simplicity and is nearly identical to the system presented in Section 1. What characterizes the transmission in the roll‐off frequency space is the fact that it is more robust and DSNG main channel degradation is negligible, but this at the price of decreased operational simplicity. Copyright © 2000 John Wiley & Sons, Ltd.     

Distributed cross‐layer optimization for wireless regional area network‐based cognitive radio networks

This paper presents a study of a cross‐layer design through joint optimization of spectrum allocation and power control for cognitive radio networks (CRNs). The spectrum of interest is divided into independent channels licensed to a set of primary users (PUs). The secondary users are activated only if the transmissions do not cause excessive interference to PUs. In particular, this paper studies the downlink channel assignment and power control in a CRN with the coexistence of PUs and secondary users. The objective was to maximize the total throughput of a CRN. A mathematical model is presented and subsequently formulated as a binary integer programming problem, which belongs to the class of non‐deterministic polynomial‐time hard problems. Subsequently, we develop a distributed algorithm to obtain sub‐optimal results with lower computational complexity. The distributed algorithm iteratively improves the network throughput, which consists of several modules including maximum power calculation, excluded channel sets recording, base station throughput estimation, base station sorting, and channel usage implementation. Through investigating the impacts of the different parameters, simulation results demonstrates that the distributed algorithm can achieve a better performance than two other schemes. Copyright © 2011 John Wiley & Sons, Ltd.     

Frequency shift filter‐based multi‐carrier transceiver

It is well known that orthogonal frequency division multiplexing (OFDM) is sensitive to carrier frequency offset (CFO) and suffers from a high peak‐to‐average ratio. In addition, the performance of OFDM is severely affected by strong co‐channel interference and strong narrowband interference. To mitigate the limitations of OFDM, we propose a new multi‐carrier transceiver based on frequency‐shift filter. A frequency‐shift filter can separate spectrally overlapping sub‐carrier signals by exploiting the spectral correlation inherent in the cyclostationary modulated signals. To increase spectral efficiency, we increase the percentage of spectral overlap between two adjacent sub‐channels. We derive an upper bound and a lower bound on the bit error rate performance of the proposed multi‐carrier transceiver in additive white Gaussian noise channel and frequency‐nonselective Rayleigh fading channel, respectively. Compared with OFDM, our simulation results show that the proposed multi‐carrier transceiver is much less sensitive to CFO and has a lower peak‐to‐average ratio; moreover, without any additional interference suppression technique, the proposed transceiver has the advantage of being able to mitigate strong co‐channel interference with CFO from the intended multi‐carrier signal and mitigate strong narrowband interference in additive white Gaussian noise channel and in Rayleigh fading channel in which a large CFO between the transmitted signal and the received signal often occurs. Copyright © 2011 John Wiley & Sons, Ltd.     

An end‐to‐end channel allocation scheme for a wireless mesh network

Co‐channel interference seriously influences the throughput of a wireless mesh network. This study proposes an end‐to‐end channel allocation scheme (EECAS) that extends the radio‐frequency‐slot method to minimize co‐channel interference. The EECAS first separates the transmission and reception of packets into two channels. This scheme can then classify the state of each radio‐frequency‐slot as transmitting, receiving, interfered, free, or parity. A node that initiates a communication session with a quality of service requirement can propagate a channel allocation request along the communication path to the destination. By checking the channel state, the EECAS can determine feasible radio‐frequency‐slot allocations for the end‐to‐end path. The simulation results in this study demonstrate that the proposed approach performs well in intra‐mesh and inter‐mesh communications, and it outperforms previous channel allocation schemes in end‐to‐end throughput. Copyright © 2013 John Wiley & Sons, Ltd.     

Combined orthogonal physical‐layer network coding over fading two‐way relay channels

This paper proposes a new physical‐layer network coding (PNC) scheme, named combined orthogonal PNC (COPNC), for fading two‐way relay channels. The scheme is based on orthogonal PNC (OPNC). In the scheme, the two source nodes employ orthogonal carriers, and the relay node makes an orthogonal combining of the two information bits rather than exclusive or (XOR), which is employed in most PNC schemes. The paper also analyzes the bit error rate (BER) performance of PNC, OPNC, and COPNC for Rayleigh fading model. Simulation results for Rayleigh and Nakagami‐m fading channels show that COPNC can provide outstanding BER performance compared with PNC and OPNC, especially when the uplink channel conditions are asymmetric. The results in Nakagami‐m channels also imply that COPNC will provide higher BER gain with more severe fading depth. Potential works about COPNC are also presented in this paper. Copyright © 2013 John Wiley & Sons, Ltd.