New waves for new systems [radio frequency spectrum allocation]

Everywhere changes in telecommunications, from liberalization of regulations to progress in radio technology, have increased the use of radio services to unforeseen levels, bringing in their wake a pandora's box of problems. In response, the world community has altered time-hallowed methods of spectrum management, not least the organization of the International Telecommunication Union (ITU) and the way in which radio conferences are convened and scheduled. The 1995 World Radiocommunication Conference (WRC-95) to be held in Geneva will tackle the broad challenges of managing the frequency spectrum in a rapidly changing world. WRC-95 will consider allocations of the electromagnetic spectrum and their effects on systems vital to national economies, including mobile communication services. The thrust will be more sharply on simplification of agreements governing the spectrum's use, and on just when to make broader provision for new satellite systems for mobile communications     

A simple detector for trellis-coded PSK mobile radio systems

A simple detector for a trellis-coded PSK mobile radio system is proposed. A precoder is added to the regular TC-PSK modulator before convolution coding, and a simple one-bit differential detector is used in the receiver. The decision is made symbol by symbol based on the output samples. The bit error rate of this system is evaluated in fast Rayleigh fading characterizing mobile radio channels by numerical integration.     

浅析BTS对无线电频谱的影响

随着社会的进步,人民群众的通信需求日益提高,为了提高通信质量,蜂窝无线通信基站开始日趋小型化、微型化,基站架设越来越密集,用频矛盾也开始日益显现,主要表现为通信基站之间的频率协调以及通信容量与频率资源之间的矛盾。同时,大量微蜂窝无线电通信基站发射设备的长时间高负荷工作,造成基站技     

New phase and frequency detectors for carrier recovery in PSK andQAM systems

Phase and frequency detectors (PFDs) are presented that considerably extend the acquisition range of carrier-recovery loops in digital communication systems. Based on a simple modification of conventional phase detectors (PDs), the proposed detectors are applicable to a large variety of modulation schemes, including the popular PSK and QAM signal formats. Their application to QPSK and 16- and 64-QAM is extensively discussed, and simulated frequency-detector (FD) characteristics, as well as acquisition behavior of several PFDs, are reported for QPSK and 16 QAM. The results of an experimental evaluation using a 16-QAM laboratory modem are also reported which show that the detectors increase the acquisition range achievable by conventional PDs by more than one order of magnitude. In PSK, the improved acquisition performance is obtained with no penalty in steady-state phase jitter. In combined amplitude- and phase-shift keying, it generally leads to increased jitter, but this is easily avoided by incorporating a lock indicator and switching back to the original PD after lock is acquired     

Novel spectrum sensing method based on the spatial spectrum for cognitive radio systems

Spectrum sensing is the key problem for Cognitive Radio (CR) systems. A method based on the Peak-to-Average Amplitude-Ratio (PAAR) of the Spatial Spectrum (SS) of the received signals is proposed to sense the available spectrum for the cognitive users with the help of the multiple antennas at the receiver of the cognitive users. The greatest advantage of the new method is that it requires no information of the noise power and is free of the noise power uncertainty. Both the simulation and the analytical results show that the proposed method is robust to noise uncertainty, and greatly outperform the classical Energy Detector (ED) method.     

Mobility management for D2D communication combining radio frequency and visible light communications bands

Wireless Networks - Combination of radio frequency (RF) and visible light communication (VLC) bands for device-to-device (D2D) communication is seen as a promising way to both increase the system...     

Sensing OFDM systems with timing and frequency offset for cognitive radio networks

In this paper, we consider the detection of orthogonal frequency division multiplexing with timing and frequency offset for cognitive radio over fast time‐varying multipath channels. By making different assumptions on the availability of the timing and frequency offset at the secondary user, we derive two algorithms based on likelihood ratio test and generalized likelihood ratio test, respectively and theoretically obtain the detection performances of them. The proposed algorithms jointly utilize energy of observations and correlation of the cyclic prefix (CP) data. The extensive simulations show that the two algorithms outperform the other CP‐based methods, perform well at very low signal to noise ratio (SNR) and are robust to the CP ratio. Copyright © 2012 John Wiley & Sons, Ltd.     

Receiver window designs for radio frequency interference suppression in DMT systems

Windowing is often applied at the DMT (discrete multitone) receiver to suppress radio frequency interference (RFI). The spectral roll-off of the window determines how neighbouring tones are affected by RFI. However, the roll-off of the window is not of equal importance in all frequency range. In particular, the rolloff in high frequency will be inconsequential when the side lobes are so small that RFI is not the dominating noise. The window is designed here to minimise total interference. The frequency response of the proposed window achieves a good trade-off in spectral roll-off between high and low frequencies. As a result, fewer tones will be dominated by RFI than in the cases of commonly used Hanning and Blackman windows, in which the stopband in high frequency are often over designed. We have considered the case for informed receiver (RFI information available to the receiver) and uninformed receiver (RFI information unavailable to the receiver). In either case, the proposed window is channel-independent and can be obtained in a closed form.     

An overview of spectrum sensing techniques for cognitive LTE and LTE-A radio systems

Advanced communication systems, such as long term evolution (LTE) and LTE-advanced (LTE-A) systems, promise to increase the number of users with high-speed data exchange. However, it leads to spectrum scarcity because of the huge size of data exchange with limited spectrum resources. Cognitive radio (CR) technique is considered the best solution for this spectrum scarcity problem. Spectrum sensing (SS), one of the CR techniques is used to detect the spectrum hole of primary user (PU) without interference with PU. In this paper, several SS approaches for LTE and LTE-A systems are investigated in the CR system. These SS approaches are based on two techniques, namely energy detection and cyclostationary feature detection techniques. The first technique includes four approaches of auto-correlation based advanced energy, time domain detection, Welch periodogram and two-stage model algorithms, while the second technique contains two approaches, namely pilot induced cyclostationary and second order cyclostationary algorithms. According to the analysis, the two-stage model and the second order cyclostationary algorithms are better than the other algorithms because they produce accurate results at the expense of system complexity. Hence, in general a good SS algorithms would require some trade-off between complexity and accuracy.     

可见光混合二维CAP-DPIM调制

为了提高基于白光LED的可见光通信系统传输性能,本文围绕提高频谱效率及可靠性展开研究,提出一种兼顾功率效率和频谱效率的混合调制方案。该方案采用无载波幅度相位调制(CAP)与脉冲间隔调制(DPIM)相结合,发送端在DPIM的脉冲时隙上加载直流偏置CAP信号(DCO-CAP),生成混合调制信号,接收端采用提出的修正硬判决检测算法及最大似然检测完成混合调制信号的串行解调。考虑室内环境光的影响,推导了基于Lambertian光照模型并在高斯信道下二维DCO-CAP-DPIM方案的误比特率(BER)及误帧率(FER)解析表达式,仿真实验验证了理论解析式的准确性以及提出的修正 硬判决检测算法的有效性。对于8m×6m×3m实验场景,通过数值仿真,分析对比了DCO-CAP,以及不同混合调制在相同频带利用 率下的性能,结果表明:当频谱效率相同时,混合二维DCO-CAP-DPIM调制系统较单一调制可靠性提高2－12dB。且调制参数相同时,基于硬判决的修正算法使系统可靠性提高5dB。     

Phase and frequency estimation for PSK packets: bounds andalgorithms

New Cramer-Rao lower bounds (CRBs) are derived for the estimation of phase offset, and frequency offset, from a block of random BPSK or QPSK symbols at low signal-to-noise (SNR) ratios. These bounds are compared to existing bounds which apply to the unmodulated carrier (or to known PSK symbols), and to the performance of some estimation algorithms     

TD-LTE与LTE FDD系统间干扰分析及射频技术指标

对邻频部署1.9 GHz频段TD-LTE与1.8 GHz/2.1 GHz频段LTE FDD系统间干扰情况进行研究,分析了干扰产生的机理和干扰场景,并将重点聚焦于基站与基站之间的干扰。结合确定性分析和仿真研究两种方法的干扰计算结果,给出了TD-LTE与LTE FDD系统间共存时基站设备和终端的射频技术指标与组网要求,并通过实验室测试和外场试验,对上述指标和组网要求进行验证,同时对现网新的干扰情况展开进一步分析,为4G系统国内使用和台站协同提供依据。     

机载射频系统地面试验外场建设的新思路

介绍了国外机载射频系统的组成,分析了机载射频系统的战技指标,探讨了国外试验外场的设计和设备配备.借鉴国外经验,总结了机载射频系统测试内容,提出针对机载射频系统地面测试外场建设的新思路,为工程实施奠定基础.     

蓝牙技术及其使用的无线电频谱

近年来,通信领域发展最快的就是移动通信和互联网.为满足人们对通信和信息与日俱增的需求,电信业务已不仅仅局限于语音通信,诸如移动数据、移动因特网接入、移动办公等应用以及"人与机"甚至"机与机"之间的通信,也将成为无线移动通信网中的主要业务.如今,应运而生的"蓝牙"技术,可让人们在不使用电线或电缆的情况下,方便而快捷地将各种办公设备甚至家用电器、电子设备连接起来,更加轻松地进行通信和工作.面向未来,蓝芽技术有着十分诱人的应用前景.     

Joint cooperative spectrum sensing and channel selection optimization for satellite communication systems based on cognitive radio

Cognitive radio has attracted considerable attention because of its ability to make full use of the available spectrum resources for wireless terrestrial communication networks. In addition, the satellite communication scenario, which requires a transparent air interface to integrated/hybrid Satellite–Terrestrial communication systems and provides a supplement for other multimedia services, will cause frequency scarcity. Satellite communication systems based on cognitive radio are available under scenarios that involve transmission with changing communications. In this paper, a cooperative spectrum‐sensing algorithm based on a time or bandwidth‐based cooperative spectrum‐sensing model of an integrated/hybrid cooperative satellite communication system is proposed. Moreover, the concept of weighted cooperative spectrum sensing is introduced. Compared with the traditional single‐user spectrum‐sensing algorithm, the cooperative spectrum sensing is able to cope with the interference to the primary user caused by a secondary user better. In addition, multiple earth stations that use some part of the bandwidth cooperatively to perform spectrum sensing throughout the whole frame can detect the presence of primary user in time. The satellite component combines the sensing results from earth stations to reach a final decision, and the optimal combination weights to maximize the detection probability of the secondary user are obtained. Numerical results that demonstrate the performance of the proposed algorithm are presented. Copyright © 2015 John Wiley & Sons, Ltd.     

A radio frequency identification application for car theft prevention in parking lot management systems

Currently, there are many parking lot management systems in use; however, most of them are unsuited to the problem of car theft. For example, a thief can drive a jalopy into a parking lot, and because the gate does not have any mechanism to detect whether the driver is the owner of the car, the gate will be open according merely to whether the driver pays the parking fee. A thief can drive away with a luxurious car away using his own parking ticket. We propose a new scheme to prevent the car theft. We adopt radio frequency identification technology conforming to EPCglobal Class 1 Generation 2 to our scheme design. Our scheme supplies an easy, cheap and high security parking environment for customers and the parking management system. Copyright © 2012 John Wiley & Sons, Ltd.     

Outage probability and spectrum efficiency of cellular mobile radio systems with smart antennas

Relying on the distribution of noncentral multivariate F variates, we investigate the outage probability and spectrum efficiency performance of cellular systems with smart antennas. We consider interference-limited systems in which the number of interferers exceeds or is equal to the number of antenna elements, and we present closed-form expressions when the desired signal is subject to Rician-type fading and interfering signals exhibit Rayleigh-, or, more general Nakagami-type fading. When applicable, these new expressions are compared to those previously reported in the literature dealing with the performance of cellular systems without smart antenna capabilities and the performance of cellular systems with optimum combining when both the desired and interfering signals are subject to Rayleigh-type fading. Corresponding numerical results and plots are also provided and discussed.     

PAPR reduction for OFDM‐based visible light communication systems using proposed hybrid technique

Orthogonal Frequency Division Multiplexing (OFDM) is utilized with visible light communication (VLC) systems to decrease the impacts of inter‐symbol interference and to achieve communication with high speed of data transmission and huge bandwidth. In any case, the main problem in OFDM‐based VLC systems is high peak‐to‐average power ratios (PAPRs). This paper proposes a hybrid PAPR reduction technique based on signal transformation combined with clipping. The Hadamard transform is used in the proposed technique to reduce the PAPR without affecting the bit error rate (BER) of the VLC systems. The optimum clipping threshold at which the PAPR is reduced simultaneously with the improvement the BER of the VLC systems is also determined. The performance of the proposed system is assessed in terms of complementary cumulative distribution function and the BER. The obtained results demonstrate that the proposed procedure can simultaneously decrease the PAPR and achieve good BER performance compared to the OFDM‐based VLC system.