Performance evaluation of Wi‐Fi and WiMAX over OFDM physical layer

Orthogonal frequency division multiplexing (OFDM) is an alternative technology that is constrained to keep up with the increasingly high data transmission rate due to its robustness against selective frequency fading and its resistance to intersymbol interference (ISI). This paper aims to study and optimize its performance, namely, its probability of communication failure and signal‐to‐interference‐plus‐noise ratio (SINR) metrics. The mathematical tool used to perform OFDM evaluation and analysis is the Fourier transform and its properties. The obtained results of those equations led to the demonstration of the probability of communication outage and to notice that the cutoff time occurs after the 10th iteration for values of λ less than or equal to 1. It could also be checked that this period is small if λ exceeds 1 by considering the sensitivity factor. Moreover, for the obtained results, in terms of bit error rate (BER) and SINR, the influence of the modulation on the error vector magnitude (EVM) shows the sensitivity factor Ω presents a key role in the transmission chain.     

Modeling and performance analysis of dynamic spectrum sharing between DSRC and Wi‐Fi systems

The Notice of Proposed Rulemaking 13‐22 released by Federal Communications Commission unlocks the Dedicated Short Range Communication (DSRC) spectrum for Wi‐Fi availability, which undoubtedly brings unpredictable effects to the new‐emerging vehicular applications and services. To efficiently harmonize the spectrum operation between DSRC and Wi‐Fi networks, several dynamic spectrum‐sharing schemes are already proposed to improve the spectral efficiency over a limited bandwidth situation and as well to satisfy the ever‐increasing demand for bandwidth resource. Different from most previous literature that mainly focused on the performance analysis of cellular‐network‐centric spectrum sharing, we aim to analyze the performance of the mainstream dynamic spectrum‐sharing schemes specially designed for the coexistence of DSRC and Wi‐Fi networks against various combinations of network parameters through a hybrid network model and performance indicators. We employ the Poisson point process to model a hybrid network where DSRC vehicles and Wi‐Fi devices coexist, and introduce the performance indicators of spectrum efficiency and data rate to assess the utility of different spectrum sharing candidates. Through the presented hybrid model and performance indicators, we collect extensive numerical and simulation results to investigate four typical spectrum allocation schemes for DSRC and Wi‐Fi coexistence, that is non‐sharing scheme, original sharing scheme, and Qualcomm's and Cisco's proposals, respectively. The results show that the dynamic spectrum sharing in the 5.9‐GHz band can significantly raise the performance of Wi‐Fi network without excessively degrading the DSRC system, and especially the Cisco's proposal prefers to protect the DSRC profit while the Qualcomm's draft favors Wi‐Fi exclusively. Copyright © 2016 John Wiley & Sons, Ltd.     

Dynamic Resource Adjustment for Coexistence of LAA and Wi‐Fi in 5 GHz Unlicensed Bands

To enable the coexistence of Licensed Assisted Access (LAA) and Wi‐Fi in 5 GHz unlicensed bands, a new channel access mechanism is proposed. Accounting for the fairness between LAA and Wi‐Fi, the proposed mechanism finds the optimal transmission time ratio by adaptively adjusting the transmission durations for LAA and Wi‐Fi. In addition, we propose a new analytical model for the distributed coordination function of IEEE 802.11 through some modifications of conventional analytical models for saturation and non‐saturation loads. By computing the activity ratio of Wi‐Fi, the proposed analytical model is able to control the time ratio between LAA and Wi‐Fi, which is required for practical implementation of the proposed access mechanism. Through numerical simulations, the proposed channel access mechanism is compared with conventional methods in terms of throughput and utility.     

Heterogeneous uncoordinated deployment of WLANs: an evolving problem for current and future Wi‐Fi access

This article addresses the problem of uncoordinated heterogeneous deployment of 802.11 wireless local area networks (WLANs). It is expected that such deployments by different WLAN owners and WiFi providers will become a challenging problem that limits the network performance and quality of service of wireless users. We present results of a real case study that show a need for coordination among WLAN devices in order to avoid current and future problems. We provide potential solution directions. A special focus is given to channel assignment and coordinated channel access problems. Our results show that a new paradigm for designing WLAN devices seems to be crucial. Copyright © 2012 John Wiley & Sons, Ltd.     

Design of NS3 VLC module and performance analysis of ad hoc network under VLC and Wi‐Fi layers

Visible light communication (VLC) is the branch of optical wireless communications that uses light‐emitting diodes for the dual purpose of illumination and very‐high‐speed data communication. The main motivation behind the current work is finding alternatives to the saturated radio frequency spectrum, radio frequency security issue, and vulnerability to interferences. The current work is aimed at developing a module for the physical layer of a VLC‐based ad hoc network in network simulation 3. The VLC physical layer module is developed by using the optical signal modules available in the network simulator. The work also includes modelling of VLC‐based transmitter, wireless optical channel, and the optical receiver. Furthermore, the implementation and evaluation of the VLC‐based physical layer is carried out over a typical ad hoc network under different performance metrics. The designed ad hoc network is also tested under Wi‐Fi module followed by its comparison with corresponding ad hoc network under VLC module. The comparison is based on bit error rate curves, system throughput, and gain in received signal‐to‐noise ratio mainly. Finally, the suitability of different modulation schemes is also investigated in the current work for both Wi‐Fi– and VLC‐based ad hoc networks.     

DISCERN: Enhanced Dynamic noISe varianCe based EneRgy sensing for cognitive radio using USRP at Wi‐Fi bands

Spectrum sensing is one of the critical tasks in a cognitive radio system that allows a secondary user to use the spectrum while the primary user does not use it. The energy detection (ED) sensing is one of the most common techniques to identify the unused portions in the spectrum bands. In ED, threshold plays a vital role in signal detection, and noise is one of the significant factors in threshold calculation. However, ED efficiency is degraded by the noise uncertainty phenomenon caused by the random changes in noise level. The adverse effects of noise uncertainty are reduced by changing its detection threshold dynamically to the noise circumstances encountered during each sensing period. In the proposed method, received random samples are arranged in M blocks, applied strong Pearson correlation to separate and estimate the variance from the noise samples. The enhanced dynamic noise variance‐based energy sensing is implemented in GNU radio processing blocks and tested on industrial, scientific, medical (ISM) 2.4 GHz frequency bands by using national instrument universal software radio peripheral (NI USRP‐2932) device. The experimental results of proposed energy detction mechanism are compared with existing sensing techniques.     

应用超分辨率方向估计实现通信卫星干扰源定位

利用卫星天线多波束特性来获取干扰信号波达方向（DOA）信息,是实现通信卫星干扰源定位的一条新思路。本文研究了在结合卫星多波束天线模型时,利用超分辨率方向估计方法实现通信卫星干扰源精确定位的可毛生,研究表明MN和LP两种算法在用于多波束天线的DOA估计时存在着方向估计模糊,而MV和MUSIC可应用于多波束天线的二维测向;文中还讨论MV、MUSIC应用于卫星干扰源定位的性能情况,并得到一些有益的结论。     

Mobile location estimation for DS‐CDMA systems using self‐organizing maps

In this paper, a self‐organizing map (SOM) scheme for mobile location estimation in a direct‐sequence code division multiple access (DS‐CDMA) system is proposed. As a feedforward neural network with unsupervised or supervised and competitive learning algorithm, the proposed scheme generates a number of virtual neurons over the area covered by the corresponding base stations (BSs) and performs non‐linear mapping between the measured pilot signal strengths from nearby BSs and the user's location. After the training is finished, the location estimation procedure searches for the virtual sensor which has the minimum distance in the signal space with the estimated mobile user. Analytical results on accuracy and measurement reliability show that the proposed scheme has the advantages of robustness and scalability, and is easy for training and implementation. In addition, the scheme exhibits superior performance in the non‐line‐of‐sight (NLOS) situation. Numerical results under various terrestrial environments are presented to demonstrate the feasibility of the proposed SOM scheme. Copyright © 2006 John Wiley & Sons, Ltd.     

Wi‐Fi‐based modeling and hybrid routing scheme for delay‐tolerant public bus network

Delay‐ or Disruption‐Tolerant Networking (DTN) is a communications approach that is utilized in easily disrupted or delayed networks. Examples of such networks are often found in heterogeneous networks, mobile or extreme terrestrial networks, and planned networks in space. In this paper, we examine the metropolitan bus network as a research target of DTN for a public transport network. We analyze the metropolitan bus network through spatial and temporal modeling using an existing Bus Information System (BIS) database. On the basis of the results of our analysis, we propose and design an appropriate DTN routing scheme called Hybrid Position‐based DTN Routing. This scheme uses position‐based routing instead of address‐based routing by soliciting infrastructural help from nearby Access Points for the real‐time BIS location service. We simulated our scheme using a WLAN for the wideband DTN communication and evaluated it by comparing it with traditional Ad hoc flooding, Epidemic routing, and strategic protocol steps in our own algorithm. The results indicate that our scheme achieves reasonably high performance in terms of packet delivery ratio, latency, and resource usage. Copyright © 2013 John Wiley & Sons, Ltd.     

3GPP LTE‐Assisted Wi‐Fi‐Direct: Trial Implementation of Live D2D Technology

This paper is a first‐hand summary on our comprehensive live trial of cellular‐assisted device‐to‐device (D2D) communications currently being ratified by the standards community for next‐generation mobile broadband networks. In our test implementation, we employ a full‐featured 3GPP LTE network deployment and augment it with all necessary support to provide real‐time D2D connectivity over emerging Wi‐Fi‐Direct (WFD) technology. As a result, our LTE‐assisted WFD D2D system enjoys the required flexibility while meeting the existing standards in every feasible detail. Further, this paper provides an account on the extensive measurement campaign conducted with our implementation. The resulting real‐world measurements from this campaign quantify the numerical effects of D2D functionality on the resultant system performance. Consequently, they shed light on the general applicability of LTE‐assisted WFD solutions and associated operational ranges.     

Position‐based adaptive quantization for target location estimation in wireless sensor networks using one‐bit data

The problem of target location estimation in a wireless sensor network is considered, where due to the bandwidth and power constraints, each sensor only transmits one‐bit information to its fusion center. To improve the performance of estimation, a position‐based adaptive quantization scheme for target location estimation in wireless sensor networks is proposed to make a good choice of quantizer' thresholds. By the proposed scheme, each sensor node dynamically adjusts its quantization threshold according to a kind of position‐based information sequences and then sends its one‐bit quantized version of the original observation to a fusion center. The signal intensity received at local sensors is modeled as an isotropic signal intensity attenuation model. The position‐based maximum likelihood estimator as well as its corresponding position‐based Cramér–Rao lower bound are derived. Numerical results show that the position‐based maximum likelihood estimator is more accurate than the classical fixed‐quantization maximum likelihood estimator and the position‐based Cramér–Rao lower bound is less than its fixed‐quantization Cramér‐Rao lower bound. Copyright © 2015 John Wiley & Sons, Ltd.     

Small‐cell intensities for cellular network affected by cell‐edge and hotspot

At present, every network operator is looking for a cost‐effective and spectrally efficient solution not only for better coverage but also to offer higher data rates. Stochastic‐based heterogeneous cellular networks have taken over the thoroughly planned traditional hexagonal grid networks. Heterogeneous networks typically include multiple tiers of base stations and small cells. This paper presents an analysis of a cellular network with cell‐edge, uncovered, and hotspot (HS) users based on spatial bivariate Poisson Point Process. The work compares the relationship between small cell intensity for cell‐edge and HS user's intensity within macrocell area. The variations in small cell intensity for uncovered and HS users outside macrocells are also presented. The simulation results depict higher small cell intensity in cell‐edge areas as compared with HS areas within the macrocells, while for outside of macrocells, small cell intensity in HS areas is much higher than that for uncovered areas. The expected numbers of small cell inside and outside macrocells are obtained along with the total new cells required for the proposed model.     

Hybrid TOA/AOA estimation error test and non‐line of sight identification in wireless location

In this paper, a modified time‐of‐arrival (TOA) estimation error test and a hybrid time‐of‐arrival/angle‐of‐arrival (TOA/AOA) estimation error test for identification of line of sight (LOS) base stations (BSs) are proposed. The proposed schemes aim to improve the location accuracy of wireless location systems suffering from the non‐line of sight (NLOS) propagation errors. The modified TOA‐based estimation error test is considered a straightforward approach in identifying the LOS‐BS set when the number of LOS BSs is greater than or equal to three. When both TOA and AOA metrics are available, hybrid TOA/AOA squares of normalized estimation errors are formulated by adopting the approximate maximum likelihood (AML) estimation. The proposed hybrid estimation error test scheme is capable of identifying the LOS/NLOS status of each BS, and performing location estimation in the situation where only two LOS BSs exist. Simulation results show that the proposed schemes are capable of correctly identifying the LOS BSs and improving the overall location accuracy. Copyright © 2009 John Wiley & Sons, Ltd.     

Performance evaluation of non‐Gaussian channel estimation techniques on ultrawideband impulse radio channels

We study the problem of adaptive channel estimation for a multipath channel on an ultrawideband (UWB) impulse radio (IR) system. The purpose of the work is to demonstrate that the statistical characteristics of the UWB‐IR environment are strongly non‐Gaussian and that as a result, non‐Gaussian signal processing techniques are both efficient and powerful in a UWB‐IR environment. The multipath channel estimation problem has been chosen as an illustrative example because UWB‐IR systems often operate in complex multipath environments. We study both blind and training‐based estimation techniques and demonstrate that even simple non‐Gaussian strategies can achieve significant performance improvement when compared to more common second‐order estimation techniques. Copyright © 2006 John Wiley & Sons, Ltd.     

Object location and centroiding techniques with CMOS active pixel sensors

A system based on a pixel-parallel CMOS active pixel sensor architecture is demonstrated for capturing the location and approximate size of an object. The object is distinguished from the background by a global threshold. Three prototype sensors are implemented in standard CMOS technologies. In the first, a high fill factor three-transistor pixel with integral comparator is demonstrated. It is shown that performance of this sensor is limited by device nonuniformities, so a novel in-pixel fixed-pattern noise correction circuit using a single capacitor is demonstrated in the second sensor. The system concept is further enhanced by a cumulative cross section readout architecture which provides additional information regarding the object with little reduction in speed. The application of these systems to centroid determination using multiple thresholds is discussed.     

Optimal and suboptimal broad-band source location estimation

Two maximum-likelihood (ML) estimators are considered for direction-of-arrival (DOA) estimation of broadband sources with unknown spectral parameters. One is based on the assumption that the sources radiate stochastic-Gaussian signals and therefore is called the stochastic-Gaussian ML (SGML) estimator; the other, using estimates of the actual signals (not their assumed distribution), is called the conditional ML (CML) estimator. Neither is efficient if the source spectral parameters are completely arbitrary and unknown, but the problem can be avoided for a version of the SGML estimation if the signal and noise spectra are known to satisfy certain smoothness conditions. While this version of the SGML is formally superior to the CML, it is demonstrated that the performance difference is small with underconditions not infrequently encountered in practice. When these are satisfied, the computationally simpler CML can be used without significant loss. The required conditions become more stringent as the source separation decreases or correlation between sources increases. A closed-form analytic expression is obtained for the small-error variance of the CML estimator of the DOA of the nth source in the presence of N-1 other sources     

无线VoIP与移动电话

由于当前的Wi-Fi技术多是基于LAN的,因此限制了Wi-Fi电话的应用。无线VoIP是VoIP与无线技术相结合的一种技术,具有价格便宜、应用范围广等优点,因此具有很大的发展潜力。通过对无线VoIP、普通VoIP和移动电话的比较分析,分别从他们的优缺点、安全性、呼叫质量、传输标准、用户群和价格等方面,探讨了目前人们比较关注的两种通信方式。     

航空互联网客舱WiFi发展现状及接入技术探究

虽然互联网+时代,互联网得以快速普及,但是对于航空领域模块,航空客舱WiFi发展仍然滞后,其接入技术也是航空客舱局域网变互联网的一大考验。文章结合移动互联网和航空产业,深入探讨航空互联网客舱WiFi发展现状及接入技术,以期促进其进一步发展。     

Binary‐offset‐carrier modulation techniques with applications in satellite navigation systems

An important aspect in designing the modulation scheme for various satellite systems, such as the modernized GPS and Galileo, is to obtain good spectral properties and suitable spectral shaping. For example, in the future satellite navigation systems, some of the main goals are: low interference with the existing GPS signals, good root‐mean‐square (RMS) bandwidth, good time resolution (in order to allow the separation between channel paths and to decrease the synchronization errors) etc. Starting from the recently proposed cosine‐ and sine‐BOC modulation families for GPS and Galileo systems, we introduce a new, generalized family, denoted here by double‐BOC (DBOC) modulation. We derive and analyze the properties of the power spectral densities (PSD) and autocorrelation functions (ACF) of the DBOC modulation with various orders, we show its relationship with BPSK, sine‐ and cosine‐BOC modulations, and we illustrate via several examples how to choose optimally the parameters of this new modulation family, according to different optimization criteria. The examples are targeting at applications such as the design of suitable modulations for Galileo open service (OS) and public regulated service (PRS) signals, but the authors believe that the DBOC concept might be useful to other satellite‐based applications, when the available bandwidth is large enough. Copyright © 2006 John Wiley & Sons, Ltd.