Comparison of Convolutional and Turbo Coding for Broadband FWA Systems

It has been demonstrated that turbo codes substantially outperform other codes, e.g., convolutional codes, both in the non-fading additive white Gaussian noise (AWGN) channel as well as multiple-transmit and multiple-receive antenna fading channels. Moreover, it has also been reported that turbo codes perform very well in fast fading channels, but perform somewhat poorly on slow and block fading channels of which the broadband fixed wireless access (FWA) channel is an example. In this paper, we thoroughly compare the performance of turbo-coded and convolutional-coded broadband FWA systems both with and without antenna diversity under the condition of identical complexity for a variety of decoding algorithms. In particular, we derive mathematical expressions to characterize the complexity of turbo decoding based on state-of-the-art Log-MAP and Max-Log-MAP algorithms as well as convolutional decoding based on the Viterbi algorithm in terms of the number of equivalent addition operations. Simulation results show that turbo codes do not offer any performance advantage over convolutional codes in FWA systems without antenna diversity or FWA systems with limited antenna diversity. Indeed, turbo codes only outperform convolutional codes in FWA systems having significant antenna diversity.     

Unified approach of GOS optimization for fixed wireless access

We present analytical and simulation models that obtain the minimum number of required communication channels for subscriber units and their allocations so as to increase the level of the grade of service (GOS) per user of fixed wireless access communication systems (FWA or WACS). On the basis of the proposed analytical and simulation models, a new methodology of using user radio ports (RPs) is introduced for evaluating the optimal number of RP systems, their allocation policy, and their spatial distribution for different configurations. This methodology enables us to increase the efficiency of FWA services on the basis of GOS maximization     

Performance improvement of fixed wireless access networks by conjunction of dual polarization and time domain radio resource allocation technique

This paper considers the impact of dual polarization adoption on the performance for a fixed wireless access (FWA) network. The major limiting factor of the performance in these systems is co‐channel interference (CCI) originating from intracell and intercell concurrent transmissions. The proposed framework combines an appropriate time domain radio resource allocation technique with a dual polarization pattern to mitigate CCI and enhance the obtained signal to interference plus noise ratio (SINR). Simulation results present the performance of the proposed framework against various terrain categories and sector antenna characteristics. Copyright © 2010 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.     

一种语音业务固定无线接入方案

固定无线接入系统中语音业务的接入方法进行了研究,介绍了固定无线接入系统的结构,分析了当前广泛采用的V5接口的优缺点,提出了一种基于ISDN一次群速率接口的接入方案并给出了其具体实现方法。     

Performance analysis of single carrier and multicarrier DS‐CDMA systems over generalized fading channels

Using a recently developed moment generating function‐based approach for the performance evaluation of digital communications over fading channels, we present a unified approach for the exact performance analysis of binary direct‐sequence code division multiple access (DS‐CDMA) systems operating over generalized frequency‐selective fading channels. The results are applicable to single carrier systems employing RAKE reception as well as to multicarrier DS‐CDMA systems with frequency diversity. Aside from simplifying previous results both analytically and computationally, the proposed approach also gives a solution for many situations which heretofore defied a simple form. Copyright © 2001 John Wiley & Sons, Ltd.     

Switchable-polarisation antenna for measuring polarisation dependence of multipath in 3.5 GHz FWA systems

A previous study has shown that circular polarisation reduces multipath delay spread in indoor radio systems. However, the effect is more difficult to measure in outdoor fixed wireless access (FWA) systems. Presented is a switchable-polarisation antenna that enables accurate comparison of linear against circular polarisation in outdoor measurements. Results show that circular polarisation reduces the multipath delay spread in suburban FWA systems at 3.5 GHz.     

Performance analysis of multi‐input multi‐output systems with maximum likelihood detection over shadowed fading channels

Multiple‐input multiple‐output (MIMO) transmission techniques constitute an important technology in modern wireless communication. Hence, performance analysis methods for such systems are of considerable interest. This paper considers first the average pairwise error probability for uncoded MIMO systems employing maximum likelihood detection over a composite Rayleigh‐Lognormal fading channel with spatial correlation. It provides general results, applicable also to a wider class of shadowing models, concerning asymptotical diversity gains and shows that they are not changed by such shadowing. Then, analytical evaluation techniques for bit‐error‐rate (BER) over composite Rayleigh‐Lognormal fading channels, based on the truncated union bound and the transfer function, are considered. Furthermore, these techniques are modified for applications over spatially correlated channels. This paper shows that such performance evaluation techniques provide good approximations to BER of spatially uncorrelated MIMO systems and also in the presence of moderate spatial correlation, over Rayleigh‐Lognormal fading channels. Copyright © 2013 John Wiley & Sons, Ltd.     

Analysis of spectrally efficient two‐way relay assisted free space optical systems in atmospheric turbulence with path loss

In this paper, we investigate the performance of two‐way relay assisted free space optical systems over atmospheric turbulence‐induced fading channels affected by molecular absorbtion‐induced path losses. A three node, dual‐hop, bi‐directional, half‐duplex relaying system with independent but not necessarily identically distributed channels is considered. Spectral efficiency is achieved by employing network coding to complete data transmission in two‐time phases. Closed form expression for system outage performance is derived considering decode‐and‐forward protocol. Additionally, the error performance in terms of average symbol error rate for M‐ary phase shift keying is evaluated. Further, the net achievable capacity of the system is also calculated. Copyright © 2014 John Wiley & Sons, Ltd.     

Performance of block‐coded land mobile satellite systems

Although various measurements have indicated that mobile satellite channels are not memoryless, most related coded system performance analysis assumes perfect interleaving is in place so that the effect of channel memory can be completely ignored. This paper presents a systematic method to accurately and efficiently predict the performance of errors‐and‐erasures or errors‐only decoders for block‐coded systems in general mobile satellite channels. Numerical results are provided to validate our analytic results. Copyright © 2008 John Wiley & Sons, Ltd.     

An adaptive multiuser detector for DS‐CDMA systems in multipath fading channels

In this paper, we investigate the performance of an adaptive multistage detection scheme for direct‐sequence code‐division multiple‐access (DS‐CDMA) systems. The first stage consists of an adaptive multiuser detector which is based on the linear constrained minimum variance (LCMV) criterion. The interference cancellation (IC) occurs in the second stage. The performance of the iterative receiver over both flat and frequency‐selective fading channels is investigated and compared to the single‐user bound. In all cases, and under heavy system loads with near‐far problems, the iterative receiver is shown to offer substantial performance improvement and large gain in user‐capacity relative to the standard LCMV. In flat‐fading channels, our results show that the performance of the iterative detector is very close to the single‐user bound. For the frequency‐selective channel, this performance is noted to be in the order of 1 dB far from the single‐user bound. Copyright © 2007 John Wiley & Sons, Ltd.     

Secrecy outage probability of inter‐vehicular cognitive radio networks

Herein, we consider an underlay cognitive radio network (CRN) where mobile secondary user wishes to transmit a confidential information to the secondary destination in the presence of an illegitimate eavesdropper which is trying to steal the classified message signal. The proposed scenario can be viable for a secondary safety task force working with a primary regiment, which wishes to transmit the confidential information to the commander while an eavesdropper is trying to intercept the classified information. In the analysis, two novel power allocation methods are considered by assuming perfect and limited feedback channels of the primary network, and for both methods, exact and asymptotic expressions of secrecy outage probability (SOP) are derived for N*Nakagami‐m fading channels which are used to model fading channels such as mobile‐to‐mobile/vehicle‐to‐vehicle communication systems where the nodes are moving into a rich scattering environment. We further verified our analytic results through Monte‐Carlo simulations. It is shown from the numerical results that the cascading degree of the channels has a worsening effect on the secrecy outage performance of the CRN systems.     

无线接入系统及其应用

本文讨论了固定无线接入系统 (FWA)在公众电话网中的应用 ,分析了它的技术特点和系统性能优势以及与公众电话网的网络关系。最后 ,通过三个不同用户环境下的规划范例 ,讨论固定无线接入系统在上海市的应用前景。     

Performance evaluation of OFDM and single‐carrier systems using frequency domain equalization and phase modulation

In this paper, we study the performance of the continuous phase modulation (CPM)‐based orthogonal frequency division multiplexing (CPM‐OFDM) system. Also, we propose a CPM‐based single‐carrier frequency domain equalization (CPM‐SC‐FDE) structure for broadband wireless communication systems. The proposed structure combines the advantages of the low complexity of SC‐FDE, in addition to exploiting the channel frequency diversity and the power efficiency of CPM. Both the CPM‐OFDM system and the proposed system are implemented with FDE to avoid the complexity of the equalization. Two types of frequency domain equalizers are considered and compared for performance evaluation of both systems; the zero forcing (ZF) equalizer and the minimum mean square error (MMSE) equalizer. Simulation experiments are performed for a variety of multipath fading channels. Simulation results show that the performance of the CPM‐based systems with multipath fading is better than their performance with single path fading. The performance over a multipath channel is at least 5 and 12 dB better than the performance over a single path channel, for the CPM‐OFDM system and the proposed CPM‐SC‐FDE system, respectively. The results also show that, when CPM is utilized in SC‐FDE systems, they can outperform CPM‐OFDM systems by about 5 dB. Copyright © 2010 John Wiley & Sons, Ltd.     

Minimal Euclidean distance‐inspired optimal and suboptimal modulation schemes for vector OFDM system

In single‐input and single‐output (SISO) systems, the vector orthogonal frequency division multiplexing (VOFDM) has been proposed to reduce the cyclic prefix length, whereas the precoded OFDM has been proposed to overcome spectral‐null channels. However, VOFDM does not show robustness to spectral‐null channels, and the precoded OFDM system has expanded data rate. This work proposes the optimal and suboptimal modulation schemes in vector OFDM systems with knowledge of the channel impulse response (CIR) in order to reduce the bit error rate (BER). As the BER performance is determined by the diversity of the received vector symbols, the proposed modulation scheme mainly concerns the minimal Euclidean distance of all the possible received vector symbols. Through the analysis of the vector input and output equations, we derive the Euclidean distance of the received vector symbols. Then, we propose optimal and suboptimal modulation schemes in VOFDM system to overcome spectral‐null channels by improving the minimal Euclidean distance. Both theoretical performance analysis and simulation results are presented to show the robustness of our system. Finally, we conduct a compared performance analysis of the proposed VOFDM system, the conventional precoded OFDM system, and the conventional VOFDM system. Copyright © 2010 John Wiley & Sons, Ltd.     

ICI reduction scheme for OFDM system with phase noise over time‐varying channels

For mobile orthogonal frequency division multiplexing (OFDM) systems, time‐varying channels and random phase noise introduced by the oscillator result in severe intercarrier interference (ICI), respectively, and degrade the overall OFDM system performance. However, the existing ICI reduction methods only aim at a single interference source, i.e. either time‐varying channels or phase noise. Therefore, these methods are not suitable for the actual situation. In this paper, we analyze the spectral property of the transfer function composed of time‐varying channels and phase noise, and propose that the transfer function can be approximated by a finite parameter complex exponential basis expansion model (CE‐BEM). Then, a pilot‐aided minimum mean square error estimation is adopted to estimate the CE‐BEM coefficients in order to reconstruct the transfer function and reduce ICI. Finally, our simulation results show how the proposed scheme would improve the system performance in a time‐varying environment with phase noise. Copyright © 2008 John Wiley & Sons, Ltd.     

Technologies and performance for non-line-of-sight broadbandwireless access networks

This article presents emerging technologies for upcoming non-line-of-sight fixed or stationary broadband wireless access systems. We describe design trade-offs for overall maximization of the radio capacity and coverage of fixed wireless access (FWA) in multicell interference- and fading-prone environments. We characterize quantitatively the impact of key emerging radio technologies on the overall performance     

Queuing analysis of shared‐buffer ATM switches with grouped output channels

Shared buffering and channel grouping are powerful techniques with great benefits in terms of both performance and implementation. Shared‐buffer switches are known to have better performance and better utilization than input or output queued switches. With channel grouping, a cell is routed to a group of channels instead of a specific output channel. In this way, congestion due to output contention can be minimized and the switch performance can therefore be greatly improved. Although each technique is well known by itself in the traditional study of queuing systems, their combined use in ATM networks has not been much explored previously. In this paper, we develop an analytical model for a shared‐buffer ATM switch with grouped output channels. The model is then used to study the switch performance in terms of cell loss probability, cell delay and throughput. In particular, we study the impact of the channel grouping factor on the buffer requirements. Our results show that grouping the output channels in a shared‐buffer ATM switch leads to considerable savings in buffer space. Copyright © 2001 John Wiley & Sons, Ltd.     

Second‐order statistics of system with N‐branch microdiversity and L‐branch macrodiversity operating over gamma shadowed Nakagami‐m fading channels

The problem concerning short‐term fading and long‐term fading (shadowing) and their deleterious effects on wireless systems performance has been in focus for a long time. In this paper, motivated by the results of propagation measurements in land‐mobile and indoor‐mobile systems, and by the fact that gamma distribution can describe shadowing reliably, Nakagami‐m distribution is used to model the signal envelope and gamma distribution is used to model the average signal power. Receive diversity with maximal‐ratio combining and selection combining is implemented at the microlevel and macrolevel, respectively. The general case is explored, which assumes that microdiversity and macrodiversity are provided through arbitrary number of channels. Because shadowing has larger correlation distance than short‐term fading, correlated macrodiversity channels are studied. This paper investigates the dynamics of the received signal. A novel rapidly converging infinite‐series expression for average level crossing rate and average fade duration are obtained. Numerical results are graphically presented to examine the impact of fading severity, shadowing severity, number of diversity branches at the microlevel, number of base stations and correlation between base stations to the system's performance. Computer simulations are also performed to verify the validity and the accuracy of proposed theoretical analysis. Copyright © 2012 John Wiley & Sons, Ltd.     

Differential space–time modulation for DS‐CDMA systems

Differential space–time modulation (DSTM) schemes were recently proposed to fully exploit the transmit and receive antenna diversities without the need for channel state information. DSTM is attractive in fast flat fading channels since accurate channel estimation is difficult to achieve. In this paper, we propose a new modulation scheme to improve the performance of DS‐CDMA systems in fast time‐dispersive fading channels. This scheme is referred to as the differential space–time modulation for DS‐CDMA (DST‐CDMA) systems. The new modulation and demodulation schemes are especially studied for the fast fading down‐link transmission in DS‐CDMA systems employing multiple transmit antennas and one receive antenna. We present three demodulation schemes, referred to as the differential space–time Rake (DSTR) receiver, differential space–time deterministic (DSTD) receiver, and differential space–time deterministic de‐prefix (DSTDD) receiver, respectively. The DSTD receiver exploits the known information of the spreading sequences and their delayed paths deterministically besides the Rake‐type combination; consequently, it can outperform the DSTR receiver, which employs the Rake‐type combination only, especially for moderate‐to‐high SNR. The DSTDD receiver avoids the effect of intersymbol interference and hence can offer better performance than the DSTD receiver. Copyright © 2001 John Wiley & Sons, Ltd.