瑞利衰落信道中移动OFDM的Doppler Spread估计

提出了一种在瑞利衰落信道中移动多载波调制(OFDM)接收机的Doppler Spread估计方法.利用OFDM符号所固有的循环前缀,采用自相关检测方法,可以较准确地估计由于移动接收机运动所引起的Doppler Spread.在保证OFDM循环符号结构的条件下,不需要增加辅助导频和训练序列,可以直接用于普通OFDM接收机,以及采用发送分集(TD)和多输入输出(MIMO)技术的移动OFDM通信系统.理论分析和实验结果证明了方案的可行性.     

Capacity estimation of cellular mobile radio systems

A capacity estimation procedure for cellular systems is introduced under a condition of concentrated traffic distribution. Comparisons are made of systems with 12.5 kHz and 25 kHz channel spacing to clarify the difference in system capacity for uniform and concentrated traffic distribution conditions. The results show it is necessary to take actual traffic distribution conditions into account in making system capacacity estimations.     

Linear unbiased data estimation in mobile radio systems applyingCDMA

Data estimation in the uplink of a synchronous mobile radio system applying code-division multiple access (CDMA) is considered. In mobile radio systems applying CDMA, multipath propagation leads to intersymbol interference (ISI) and together with time variance, to cross interference between the signals of different users regardless of whether the user codes are chosen orthogonal or not. A linear unbiased data estimation algorithm is presented that eliminates both ISI and cross interference perfectly by jointly detecting the different user signals, leading to unbiased estimates of the transmitted data symbols. By theoretical analysis and simulation, the performance of the linear unbiased data estimation algorithm is examined under the assumption that the radio channel impulse responses are known at the receiver. The price to be paid for the interference elimination are SNR degradations, which are calculated for typical mobile radio situations in urban areas. The resulting average uncoded bit error probabilities lead to the conclusion that systems applying the linear unbiased data estimation algorithm are well suited for mobile radio applications     

一种移动环境下的信噪比估计算法及其在多普勒频移估计中的应用

利用移动信道的功率谱特性,提出了一种基于谱分析的平均信噪比估计算法,其实现可以利用FFT(fastfouriertransform),从而有效节省了运算资源。其次结合噪声环境下多普勒频移的理论偏差,提出了基于信噪比估计的改进方法。计算机仿真表明,在一般通信系统的工作信噪比范围,文章的信噪比估计方法具有较高的估计精度,而且基于信噪比估计的改进多普勒频移估计方法在各种移动速度和信噪比下都表现出较高的估计精度。     

Cramer-Rao bounds of the frequency estimation in the time selective radio channels with Doppler spread

The mobile channel is slow fading and time selective, thus the multiplicative and additive noise of the channel will smear the spectral line, or arouse Doppler spread. This spread will make the parameters estimation accuracy degrade. The goal of this paper is to analytically assess this degradation when Carrier Frequency Offset （CFO） and Doppler shift exist jointly. Then the finite-sample Cramer-Rao Lower Bound （CRLB） is derived and close-form asymptotical expression is given for large-sample CRLB. These expressions give insights into the performance room for frequency estimation. Also the variance of Doppler shift estimator is simulated to illustrate the theoretical results.     

Multiple radio zone plans in mobile radio systems

Multiple zone structure in a land mobile system seems to offer a flexibility in radio zone planning by using different interference distances conforming to the different system requirements in a system, thus improving the frequency utilization. A multiple zone structure can be formed by a tessellation of basic zone groups with an identical shape in parallel translation on a plane. To assure the possibility of the tessellation, two types of basic zone groups are investigated. One has several hexagonally shaped zones covered by an omnidirectional antenna beam from the zone center, while another is constructed as a subdivision of hexagons covered by a directive antenna beam. The former is expected to facilitate reduced interference distance between adjacent frequencies. An estimate of the latter type has shown better frequency economy than that in a conventional zone structure.     

Doppler spread measurements of indoor radio channel

The temporal variations caused by human movement or human-induced motion of the communication equipment, on the otherwise static indoor radio channel, are measured. For the reported narrowband measurements, a maximum Doppler spread of 6.1 Hz and a maximum RMS Doppler bandwidth of 0.87 Hz are observed.<>     

Land mobile radio systems in Poland

The current situation of land mobile radio (LMR) systems in Poland is described. This includes paging, dispatch, trunking, and cellular systems. Frequency plan and organization of LMR communication in Poland are presented. Finally, the plan for the future development of LMR systems in Poland, prepared by the Ministry of Telecommunications, is summarized     

Robust Doppler spread estimation in nonisotropic fading channels

A new parametric approach is proposed for the estimation of the maximum Doppler frequency, or equivalently the mobile speed, in narrowband mobile radio channels. In this work, simple and efficient Doppler-frequency estimators are formulated based on using a small number of samples of the channel autocorrelation function. Unlike previous approaches, the chosen parameterization is shown to be robust in a microcellular propagation environment, which may be characterized by nonisotropic scattering and/or a specular component of unknown strength. Simulation results are described to illustrate the effects of additive noise and the finite data-record performance.     

Outage statistics in CDMA mobile radio systems

The statistics of the outage events in the reverse link of a direct sequence code-division multiple access (DS/CDMA) wireless system are investigated taking into account the effects of correlated Rician fading. The outage probability and the average fade duration are derived by assuming a constant multipath intensity profile, which includes a direct-path component in the first path. Simulations have been carried out which validate the analytical results     

Vehicle location in cellular mobile radio systems

A tutorial discussion of vehicle location as used to control cellular mobile radio systems is presented. Early concepts and misconceptions concerning vehicle location are described, and the relation between location "accuracy" and system performance optimization is discussed. Measurement parameters commonly used for vehicle location are described, and considerations relating to the algorithm used in the location process are presented.     

Elements of cellular mobile radio systems

A major concern in a cellular mobile radio system is the co-channel interference. Therefore, the reduction of co-channel interference becomes a main thrust for the system design engineers. We use the co-channel interference reduction factor as a design criterion and predict the signal-to-interference (S/I) ratios in different system configurations. The handoff mechanism and algorithmic considerations, the traffic capacity and procedure for splitting cells, and the near-end-to-far-end ratio interference and reduction are the elements described.     

Capacity of cellular mobile radio systems

A lower bound to the Shannon capacity of the uplink channel of a cellular system, with perfect channel state information (CSI) at the receiver, is evaluated against the reuse distance and the level of shadowing affecting the interfering signals. Capacity is normalised to the covered area and expressed in bit/s/Hz/unit area     

Iterative receiver for joint detection and channel estimation in OFDM systems under mobile radio channels

In this paper, an iterative receiver for a joint data-detection and channel-estimation scheme is presented for orthogonal frequency-division multiplexing systems, which incorporates iterative decoding in the receiver. In the proposed scheme, a maximum a posteriori-based decoder and a channel estimator provide more reliable information on the coded bits for each other in an iterative manner. We first consider a practical implementation issue for the optimal minimum mean squared error two-dimensional (2-D) channel estimator as an essential element in the iterative receiver. To reduce the complexity of the 2-D estimator as suited to the iterative receiver, we focus on rigorously investigating how a separable estimator must be designed so that its structure may become asymptotically equivalent to that of the optimal 2-D estimator. Furthermore, we derive an analytical expression of the iterative process to evaluate a convergence performance as a function of the number of iterations and discuss its convergence property. Our simulation results demonstrate that the proposed iterative receiver achieves a near-ideal performance with only a few iterations under time-variant multipath fading channels.     

Outage possibilities in mobile radio systems suffering cochannelinterference

Mobile radio systems are usually designed on the basis of providing adequate reception quality to a specified area. The outage probability equations are used to determine the quality of radio reception when that quality is limited by a minimum required signal level, interference from a cochannel transmitter, and variability in the received signal levels. Considering Rayleigh fading and lognormal shadowing as joint causes of signal variation, average outage probability expressions are derived for mobile radio systems of a uniform nature. These expressions are used to investigate the influence of various system and propagation characteristics on reception quality     

Channel estimation joint DOAs and time delay correlation in TD‐SCDMA mobile radio systems

An improved channel estimation technique based on the Steiner low‐cost channel estimator is proposed, which is widely used in TD‐SCDMA (Time Division‐Synchronous Code Division Multiple Access) cellular mobile radio systems. TD‐SCDMA is also known as third‐generation mobile systems where adaptive antennas are employed. As additive noise has a great adverse effect on the performance of the Steiner estimator, the proposed method employs time‐correlated post‐processing with a threshold filter to reduce channel noise and compensate channel variations. Furthermore, channel estimation combining direction‐of‐arrivals (DOAs) is performed, which can reduce channel interferences without adding computational complexity, for the information of DOAs has been obtained by the inherent adaptive antenna system. The performance of the improved channel estimator is compared with conventional channel estimation approaches, and numerical results show that the new approach can lead to considerable performance enhancement even in high‐speed vehicle propagation environments. Copyright © 2008 John Wiley & Sons, Ltd.     

Security services for protecting radio mobile systems

The development of radio networks has brought the problem of security specifically related to mobility of terminals sharply into focus, and has created the need for radio network operators to implement new security functionalities. The security level of the analog radio mobile systems (the so-called “first generation ” systems was very low, and these systems were often exposed to massive fraud. The development of digital radio mobile systems (the so-called “second generation” systems: GSM, DECT,. allowed the systematic introduction of cryptology based protection mechanisms. Hence, for gsm networks for instance, the main fraud and confidentiality problems were taken into account at the design stage and a security architecture was implemented to provide security services to users and network operators. The third generation mobile telecommunication systems belonging to the imt- 2000 family (which are still under specification within standardisation bodies in particular within the 3gpp worldwide third generation partnership project) will, in the forthcoming years, provide a wide variety of services on a single terminal in a multi-environment (domestic, public, business), multi-operator, and multi-service provider context. Security will be based on second generation systems security functions that have proved to be needed and reliable, and shall be adapted and improved to resolve security threats underlying to new services supplied by third generation radio systems. This document presents examples of security solutions currently implemented for protecting second generation radio mobile systems against frauds and attacks and gives an overview of potential solutions for protecting future third generation radio mobile telecommunication systems.     

Network planning for third-generation mobile radio systems

The success of UMTS relies not only on the development of a flexible air interface, efficient coding techniques, and handset technology; it is equally important to design a system that can support the underlying technology and to interface with other networks     

移动通信中一种不受功率控制影响的多普勒频偏估计方法

分析了时变多径信道均方相位差分的统计特性，进而利用接收机有效到达径上信道参数的估计值，统计其相位差分的均方值，据此估计出时变多径信道的多普勒频偏。同时针对噪声环境下平方相位差分法的估计偏差，本文给出了改进方法，使得通信系统在各种移动速度和信噪比下都具有较高的估计精度。