Sequential packing algorithm for channel assignment under cochanneland adjacent-channel interference constraint

Generally, the channel-assignment problem (CAP) for mobile cellular systems is solved by graph-coloring algorithms. These algorithms, though sometimes can yield an optimal solution, do not supply any information on whether an optimal solution has been found or bow far away it is from the optimum. In view of these undesirable features, two relevant results are presented. First, a lower bound for the minimum number of channels required to satisfy a given call-traffic demand is derived. This lower bound is tighter than the existing ones under certain conditions and can be used as a supplement for other approximate algorithms. Second, we propose an efficient heuristic algorithm to solve this problem. Although the CAP is nondeterministic polynomial (NP) complete in general, our algorithm provides an optimal solution for a special class of network topologies. For the general case, promising results are obtained, and numerical examples show that our algorithm has a better performance than many existing algorithms     

Performance of an in-band adjacent-channel DAB system forfrequency-selective Rayleigh and Ricean slow fading channels underanalog FM interference

In support of the 1995-1997 DAB (digital audio broadcasting) testing conducted by the NRSC (National Radio Systems Committee), an IBAC (in-band adjacent-channel) scheme was developed by AT&T. Although not for use in the United States, bit error rate (BER) system performance under both fading environments and the existing analog FM broadcasting is important to quantify. This is because there may still exist other countries and environments where an IBAC approach to DAB is feasible and economical. Given this situation, an IBAC simulation model has been developed to allow for a performance analysis study within the mobile reception environment, which is dominated by Rayleigh and Ricean fading statistics. This paper presents the simulation results for coherent quadrature phase-shift-keying (QPSK) with nonlinear equalization for both frequency-selective Rayleigh and Ricean slow fading channel environments, along with co-channel, 1st-adjacent and 2nd-adjacent analog FM interference. The results indicate that for a country where spectrum availability dictates an IBAC solution, this approach may perform well under various fading and interference environments     

Polarization-insensitive frequency-shift-keying optical heterodynereceiver using discriminator demodulation

A polarization-state-independent binary frequency-shift-keying optical heterodyne receiver, achieved by splitting the received signal between two orthogonal polarization axes and combining the signals after demodulation, is described. The authors consider various receiver configurations, using a discriminator with a limiter for applications in which received-signal-envelope fluctuations cannot be ignored, and without a limiter when the fluctuations are negligible. For applications that require the limiter, a diversity method or a variable-gain limiter that improves the performance of the limiter/discriminator receiver is proposed. Numerical results indicate that with diversity and a limiter/discriminator structure, polarization independence can be achieved with a system performance which is nearly that of an ideal receiver. Using a discriminator without a limiter, when there is no source of envelope fluctuations other than those due to Gaussian noise, the receiver performance degradation compared to the ideal baseline receiver is 0.5 dB     

Ultra-wide-band radio signal generation using optical frequency-shift-keying technique

We proposed a novel technique for generation of micro- or millimeter-wave pulses using optical frequency-shift-keying (FSK) modulation. FSK signals were obtained by an integrated four optical phase modulators. The pulses can be obtained as an optical beat of two spectral components, during transient FSK state which is shorter than 100 ps.     

Fast frequency-switching system for frequency-shift-keying pulse-code modulation

An f.s.k. pulse modulator has been developed which uses two cavity modes for the two frequency states of a Gunn oscillator. 300 megapulse operation with about 10 mW microwave output at 13.25 and 20.7 GHz for baseband pulses of about 3 V into 50 ? was obtained.     

Two-section distributed feedback lasers for incoherent frequency-shift-keying transmission systems

Fabrication and performance characteristics of two-section distributed feedback lasers operating at 1.55 mu m are presented. Using this type of laser, a 622 Mbit/s incoherent frequency-shift-keying system over a 40 km fibre has been demonstrated with a receiver sensitivity of -41 dBm at a BER of 10/sup -9/.<>     

Suppression of adjacent-channel, cochannel, and intersymbolinterference by equalizers and linear combiners

We describe the ability of a linear equalizer/combiner or decision-feedback equalizer to suppress all received adjacent-channel, intersymbol, and cochannel interference. The emphasis is on values among transmitter bandwidth, receiver bandwidth, carrier spacing, and antenna diversity which provide the best opportunities for interference suppression. Through analyses of the number of degrees of freedom and constraints in generalized zero-forcing equalizers, and partial comparisons to calculations of equalizer minimum-mean-square performance, four results are obtained. First, with one antenna and a linear equalizer, arbitrarily large receiver bandwidths allow for marginal improvements in spectral efficiency through decreased carrier spacing, because the carrier spacing cannot be reduced to a value below the symbol rate without incurring unsuppressible interference. Second, large receiver bandwidths assist multiple antennas in improving the spectral efficiency in that carrier spacing values may go below the symbol rate, even in the presence of cochannel interference. Third, the use of equalizers and linear combiners, together with large receiver bandwidths, allows large transmitter bandwidths to be used. Fourth, for cochannel interference and intersymbol interference, the number of interferers that may be suppressible by a generalized zero-forcing linear equalizer/combiner increases linearly with the product of the number of antennas and the truncated integer ratio of the total bandwidth to the symbol rate     

Ten-to-twenty gigabit-per-second modulation performance of1.5-μm distributed feedback lasers for frequency-shift-keying systems

The frequency modulation (FM) and amplitude modulation (AM) responses of a 1.5-μm distributed feedback (DFB) laser were measured to 15 GHz. At 9-mW output power, the magnitude of the FM response was flat out to 12 GHz, and there was a 15-25-ps delay between the FM and AM responses. Computer simulation techniques indicate that the measured FM response is adequate to produce good eye patterns for frequency-shift-keying modulation at data rates up to 20 Gb/s. The high-speed frequency-shift-keying modulation capability of this 1.5-μm DFB laser was experimentally confirmed at 11 Gb/s     

GNSS干扰及抗干扰技术

全球导航卫星系统(GNSS)提供的低能级射频(RF)导航信号,易受到RF干扰的影响而导致导航精度的降低或者接收机的完全失锁.本文介绍了GNSS干扰的类型、技术手段和实施方式.针对不同干扰所采用的抗干扰技术,分析了其优缺点和适用范围.利用多种抗干扰技术初步设计了一个抗干扰方案.     

3用户MIMO干扰信道中稳健的机会干扰对齐方法

本文根据传统的干扰对齐思想,在缩小干扰空间之间弦距的同时尽量增大信号-干扰空间之间弦距,以此为目标设计用户选择准则,并在接收端采用预处理矩阵智能选取技术最大化信道容量,提出了3用户MIMO干扰信道中稳健的机会干扰对齐方法。相比文献[1]方法,所提出的方法不但具有更高的系统瞬时性能稳健性,而且还具有更高的信道容量,只是在复杂度方面略有增加。仿真结果证明了本文方法的有效性。     

Criminal interference

The article discusses the URSI Council's resolution on criminal activities using electromagnetic tools adopted at the Toronto General Assembly (August 1999). Criminal activities using electromagnetic tools are an outgrowth of more familiar disciplines: electromagnetic compatibility (EMC) and electromagnetic interference (EMI). In this case, however, the terrorist produces the offending currents or radiation intentionally. Accidental radiation can cause severe and inopportune damage to electronics, so those fields or more severe field levels can certainly also be intentionally impressed on vulnerable equipment. The EMC community must be prepared to deal with new threats as they emerge     

自适应对消在去除探地雷达信号直达波的应用

基于自适应对消和探地雷达信号中的直达波的性质,提出了一种自适应直达波滤除方法,通过对模拟实验数据和实测数据的处理,验证了这一方法的有效性.另外,还给出了其它方法对同样数据的处理结果,通过与这些方法相比较,自适应直达波滤除法是一种运算量少、信号失真小、并可实时处理的方法.     

Method of interference cancellation based on space-time code in MIMO interference channels

The authors in this article investigated how to cancel multi-user interference with low feedback amount over 3-user multiple input multiple output(MIMO) interference channel using space-time code and precoders. Space-time block code with coding rate 2 was designed, also zero vectors were introduced into each codeword. The multi-user interference is mitigated by pre-coding at the transmitters and nonlinear operation and unidirectional cooperation link at the receivers. Compared with the existing scheme for the same scene, the proposed scheme greatly reduces feedback amount and improves the sum degrees of freedom(DOF). Simulation demonstrates the validity of the proposed scheme.     

高频地波雷达电离层干扰抑制研究

高频地波雷达探测海洋状况和跟踪移动目标时,电离层干扰严重影响了雷达的工作性能.阐述了电离层干扰的来源,分析了电离层干扰的时间和空间特性,指出其在雷达相干积累时间之内在空间上具有稳定性,结合高频地波雷达OSMAR系统的阵列结构,采用分段自适应旁瓣对消的处理方法来抑制电离层干扰.对实测数据处理的结果表明该方法能够有效地抑制电离层干扰,改善海洋回波一阶峰的信噪比,从而提高了雷达对海洋的探测性能.     

Intersymbol interference in duobinary systems

An upper bound for the error probability due to intersymbol interference and Gaussian noise is calculated for duobinary signalling systems. The duobinary system with twice the binary signalling speed has an error rate in excess of that of a binary system using identical filters.     

Intercarrier interference in MIMO OFDM

In this paper, we examine multicarrier transmission over time-varying channels. We first develop a model for such a transmission scheme and focus particularly on multiple-input multiple output (MIMO) orthogonal frequency division multiplexing (OFDM). Using this method, we analyze the impact of time variation within a transmission block (time variation could arise both from Doppler spread of the channel and from synchronization errors). To mitigate the effects of such time variations, we propose a time-domain approach. We design ICI-mitigating block linear filters, and we examine how they are modified in the context of space-time block-coded transmissions. Our approach reduces to the familiar single-tap frequency-domain equalizer when the channel is block time invariant. Channel estimation in rapidly time-varying scenarios becomes critical, and we propose a scheme for estimating channel parameters varying within a transmission block. Along with the channel estimation scheme, we also examine the issue of pilot tone placement and show that in time-varying channels, it may be better to group pilot tones together into clumps that are equispaced onto the FFT grid; this placement technique is in contrast to the common wisdom for time-invariant channels. Finally, we provide numerical results illustrating the performance of these schemes, both for uncoded and space-time block-coded systems.     

Tone interference in VSAT spectrum

This paper investigates the problem of tone interference within the very small aperture terminal (VSAT) binary phase-shift keying (BPSK) signal spectrum. The degree of performance degradation of a VSAT link in the presence of a tone interference is discussed. A simple theoretical analysis is derived, and its validity is verified by experimental measurements performed using a standard commercial VSAT modem measurement setup     

Adaptive narrowband interference rejection in DS-CDMA systems: ascheme of parallel interference cancellers

In the presence of narrowband interference (NBI), the performance of the direct-sequence code-division multiple access communication system can be improved by using various interference cancellation schemes. In this paper, a scheme of parallel interference cancellers (PICs), which includes a set of NBI cancellation filters and a set of multiple access interference (MAI) cancellation filters, is developed to improve the signal-to-interference ratio (SIR) and handle the MAI effect. In order to avoid performance deterioration due to unreliable initial detection, a robust coefficient γ is introduced in our proposed design criterion. A recursive least-square algorithm is employed to update the tap coefficients of the PICs. In other words, no training or retraining period is needed in our proposed PICs. Finally, the SIR performance of the proposed detector is analyzed and compared to that of the conventional linear detector     

An analytical method for assessing interference in interference environments involving NGSO satellite networks

An Erratum has been published for this article in International Journal of Satellite Communications 2000; 18(3):219. This paper presents an analytical approach to assess interference involving NGSO satellite networks. The proposed method can be implemented through numerical techniques, and is intended to perform the analysis of interference sensitivity to system and network parameters without the reliability problems and the very excessive computer time associated, sometimes, with direct computer simulation methods. The method is based on the knowledge of the probability density function of the position of a single satellite placed in an orbit with an arbitrary inclination, which is derived in the paper. To illustrate the applicability of the proposed method to complex interference environments, results for two specific situations are presented. Comparisons of the results obtained using the proposed method and those generated by a widely used commercially available simulation software have indicated that the proposed method can generate reliable and precise results with less computer time. Copyright © 1999 John Wiley & Sons, Ltd.     

Mitigating multiple access interference and intersymbol interference in uncoded CDMA systems with chip-level interleaving

The presence of intersymbol interference (ISI), in addition to multiple access interference, severely hampers the performance of a code-division multiple-access (CDMA) communication system. In such a situation, channel coding can be used to obtain better performance, but at the cost of a reduction in rate of flow of information. In this paper, it is shown with the help of simulation results that the chip-interleaved CDMA system effectively combats ISI without requiring additional channel coding. The system differs from the conventional CDMA system in the sense that, the chip sequence resulting from the pseudo noise (PN) sequence modulation is interleaved before transmission. Two receivers are proposed, one based on the turbo equalization method which employs a maximum a posteriori equalizer of exponential complexity and the other based on minimum-mean square error-optimized iterative interference cancellation principles which is of linear complexity. Simulation results are provided which show that error rates close to the no-ISI single-user case can be obtained. The shortcomings of the coded CDMA with turbo detection system in the presence of ISI are also discussed.