Comments on `Packet error probabilities in frequency-hoppedspread-spectrum packet radio networks-memoryless frequency-hoppingpatterns considered'

In the above-titled paper by M. Georgiopoulos (see ibid., vol.36, no.6, p.720-3, 1988), the packet error probability induced in a frequency-hopped spread-spectrum packet radio network is computed by using the Markovian property of the byte errors at the receiver. It is shown here that the byte errors at the receiver do not exhibit a Markovian structure. A correct analysis and numerical results are provided     

Correction to `Packet error probabilities in frequency hoppedspread-spectrum packet radio networks-memoryless frequency hoppingpatterns considered'

The author corrects the approach followed in the above-titled paper (see ibid., vol.36, no.6, p.720-3, 1988) to compute packet error probabilities in frequency-hopped spread-spectrum packet radio networks with memoryless frequency-hopping patterns. The nature of the error is that the sequence of symbol errors is not Markov, so that a formula which is instrumental for the computation of packet error probabilities, is incorrect. He obtains exact and easy to compute expressions for the evaluation of the packet error probabilities     

Comments on `Packet error probabilities in frequency-hoppedspread-spectrum packet radio networks-memoryless frequency-hoppingpatterns considered' by M. Georgiopoulos

The authors demonstrate that contrary to the claim made in the above named work (ibid., vol.36, Jun., p.720-3, 1988), the sequence of hits in an asynchronous frequency hop multiple-access system is not a Markov process. Comments of the use of a model in which the hits are independent are also given     

Bit error probabilities of NCFSK and DPSK signals in microcellular mobile radio systems

Microcellular mobile radio systems are studied where the desired signal has Rician statistics and the cochannel interferers experience Rayleigh fading. The probability density function of the signal-to-interference ratio is derived and is used to obtain the bit error probabilities of noncoherent frequency shift-keying and differential phase shift-keying signals.<>     

On the error probability of coded frequency-hopped spread-spectrummultiple-access systems

A simple, exact calculation is presented of the probability distribution of the number of hits in a block of n symbols in a frequency-hopped, spread-spectrum, multiple-access communication system. While the sequence of hits is not Markovian, there is an underlying Markovian structure that allows the probability distribution of the number of hits to be calculated in a recursive fashion. Knowing the probability distribution of the number of hits makes it possible to calculate the probability of error for a system employing error correcting codes for several different types of receivers, including receivers with both errors and erasures. The numerical results show that both the approximation obtained by assuming the actual sequence of hits is Markovian and the approximation obtained by assuming the hits are independent are very good. When the number of frequency slots is not too small (less than five), calculations show that assuming the independence of hits gives an error probability accurate to within 1% of the actual error probability. Assuming the hits are Markovian gives error probabilities which are accurate to within 0.001%     

Simple-to-evaluate error probabilities for impulse radio UWB multiple access systems with pulse-based polarity randomization

Simple-to-evaluate and accurate bit error probabilities are presented for impulse radio ultra-wideband multiple access systems that use time hopping sequences with pulse-based polarity randomization and binary phase shift keying modulation. Simplified improved Gaussian approximation is used. It is shown that despite having the same processing gain, which is the multiplication of the number of frames per bit and chips per frame, different combinations of the parameters result in different performances. The theoretical results are validated by Monte Carlo simulations.     

Spectrum efficiency of a frequency-hopped MFSK spread spectrum mobile radio system

The spectrum efficiency of a frequency-hopped multilevel frequency-shift keying (FH-MFSK) spread spectrum modulation technique proposed for use in mobile radio systems is evaluated. The analysis assumes randomly chosen address vectors, a perfect synchronization at the receiver, and noncoherent detection. With perfect transmission where the only degradation is due to mutual interference, the efficiency is 0.262, 0.295, and 0.345 at an average bit error rate of 10^-3for 1.64, 3.41, and 20 MHz bandwidth. However, with transmission impairments consisting of additive white Gaussian noise and frequency selective Rayleigh fading, which characterize the mobile radio channel, the efficiency depends on the average signal-to-noise ratio (SNR), and on the average bit error rate.     

Error probabilities of fast frequency-hopped FSK withself-normalization combining in a fading channel with partial-bandinterference

Error probability analysis is performed for a binary orthogonal frequency-shift-keying (FSK) receiver using fast frequency-hopped (FFH) spread-spectrum waveforms transmitted over a frequency-nonselective slowly fading channel with partial-band interference. Diversity is performed using multiple hops per data, bit. A nonlinear combination procedure referred to as self-normalization combining is used by the receiver to minimize partial-band interference effects. Diversity is found to completely negate degradation of the self-normalized receiver caused by partial-band interference and offers definite receiver performance improvement when the direct signal component is weak. The self-normalized receiver is sensitive to fading channels. For severe channel fading, the performance of a conventional noncoherent binary FSK receiver is generally either equivalent or superior to that of the self-normalized receiver     

Error probabilities of fast frequency-hopped MFSK withnoise-normalization combining in a fading channel with partial-bandinterference

An error probability analysis performed for an M-ary orthogonal frequency-shift keying (MFSK) communication system employing fast frequency-hopped (FFH) spread-spectrum waveforms transmitted over a frequency-nonselective, slowly Rician fading channel with partial band interference is discussed. Diversity is obtained using multiple hops per data bit. Noise-normalization combining is employed by the system receiver to minimize partial-band interference effects. The partial-band interference is modeled as a Gaussian process. Thermal noise is also included in the analysis. Forward error correction coding is applied using convolutional codes and Reed-Solomon codes. Diversity is found to dramatically reduce the degradation of the noise-normalization receiver caused by partial-band interference regardless of the strength of the direct signal component. Diversity offers significant performance improvement when channel fading is strong, and performance improvement is obtained for high modulation orders (M>2). Receiver performance is improved when diversity, higher modulation orders, and coding are combined     

Packet radio in a Rayleigh channel

Statistical multiple access is analysed for a number of independent transmitter-receiver pairs exchanging data packets over a shared mobile-radio channel. Rayleigh fading `softens? the channel, resulting in less packet contentions and higher traffic capacity than for the standard Aloha channel.     

软件无线电跳频电台接收机射频前端设计

基于软件无线电的基本要求和发展趋势,提出了一种应用在软件无线电跳频电台中接收机射频前端电路结构,分析了接收机射频前端的总体设计方案,包括前端各部分增益的分配、动态范围的分配、噪声系数及灵敏度的计算,讨论了对器件选择的考虑.实际测试结果表明,该射频前端性能指标满足设计要求.     

基于认知无线电的多频段跳频通信系统

为充分利用认知无线电对环境频谱的感知能力,设计了一种基于 认知无线电的多频段跳频抗干扰通信系统,通过感知单元动态控制跳频序列生成,实现了干 扰频点的避让。具体实现时,采用低频段可靠传输高频段的频谱感知信息,高频段则主要用 于具体业务传输,利用不同频段实现了频谱控制与应用业务的分离。     

Packet radio in the Amateur Satellite Service

A review of the satellite-based packet radio activities taking place in the Amateur Radio Service is presented. Five projects are discussed. The Digital Communications Experiment (DCE) on UoSAT-OSCAR-11 is a store-and-forward system that is accessed by a limited number of stations around the world designated as DCE gateways. These gateway stations retrieve and store messages forwarded to them via terrestrial packet radio networks. The Japanese FO-12 satellite is a store-and-forward system, and its user interface is much like computer bulletin boards accessed via land lines. It is available for use by all radio amateurs with the required equipment. Both UO-11 and FO-12 are in low earth orbits. The RUDAK experiment and the PACSAT project are also discussed     

超短波跳频电台跳频频率合成器的实现

跳频频率合成器是跳频电台的关键核心技术部件技术之一，它的好坏直接影响快速跳频电台的抗干扰性和稳定可靠性。现针对FH／DSDQPSK混合抗干扰电台高速跳频的频率合成器的实现做了简要介绍，实践证明该跳频频率合成器在1000跳／s的时候能清楚的实现语音通信。     

Packet access mechanisms for cellular radio

The paper reviews the findings of work completed in RACE Mobile Telecommunications Project 1043 on the suitability of packet access mechanisms for mixed services in the Universal Mobile Telecommunication System. A first order comparison of random and scheduled access is provided and conditions under which these mechanisms provide an attractive alternative to channel allocation for call duration are specified. It is concluded that packet reservation multiple access (PRMA) is an attractive candidate for mixed services over a range of cell sizes as it can accommodate fixed channel access, reserved channel access and random channel access     

ERROR-DETECTING CODES AND UNDETECTED ERROR PROBABILITIES

The definition of good codes for error-detection is given. It is proved that a (n, k) linear block code in GF(q) are the good code for error-detection, if and only if its dual code is also. A series of new results about the good codes for error-detection are derived. New lower bounds for undetected error probabilities are obtained, which are relative to n and k only, and not the weight structure of the codes.     

Calculation of error probabilities for distance-invariant nonlinear error control codes

Expressions are given for the distance distribution of some nonlinear codes which enable error probabilities to be calculated using methods commonly associated with linear error control codes.<>     

共址干扰下的车载跳频电台误码率计算与分析

针对车载HF跳频电台的共址干扰问题进行了较为全面和深入的研究.首先对共址平台和天线耦合度进行了分析,并通过建立有线实验平台和理论模型,深入研究了功率、频率、误码率等参数之间的相互关系.在此基础上,通过分析HF组网的约束条件,建立了综合共址干扰、跳频、组网等因素的误码率计算模型.实例分析表明,模型为评估系统性能和配置电台工作参数提供了理论依据.