Effects of correlated shadowing signals on channel reuse in mobileradio systems

The authors present a study to evaluate the cochannel interference probability for the desired and interference signals which are correlated due to shadowing. The effects of correlation on the normalized reuse distance are investigated. A generalized expression for the cochannel interference probability is derived by combining uncorrelated (fast) Rayleigh fading and correlated (slow) log-normal signals. The cochannel interference probability for sectorized cell layouts is compared with the lower bound of cochannel interference probability for omnidirectional antenna systems. It is found that omnidirectional cell layouts cause the highest level of cochannel interference probability. An omnidirectional system requires a higher cluster size than a directional system to maintain acceptable cochannel interference     

Application of narrow-beam antennas and fractional loading factorin cellular communication systems

It is well known that cellular system capacity can be increased by reducing the cell cluster size N. Reducing the cluster size, however, increases cochannel interference. In the literature, several techniques have been proposed for controlling the cochannel interference and simultaneously reducing the cluster size. In this paper, we combine two proposed capacity improvement methods and explore the effectiveness of reducing cochannel interference using narrow-beam antennas (“smart antennas”) with the fractional loading factor. As shown in this paper, it is possible to increase capacity by many times by decreasing the cluster size (i.e. increasing frequency reuse), although the proper combination of antenna specifications and fractional loading is surprisingly nonintuitive. The first cochannel mitigation technique uses base-station antennas with narrow beams in the direction of the desired mobile stations and significant side lobe attenuation in the direction of undesired users. The second technique exploits the fact that interference is related to the loading factor p_ch, which defines the probability that a given channel is in use within a cell, We show that large capacity gains with respect to a reference cellular system (N=7, three sectors per cell) can be obtained by combining these two techniques. This paper provides insight for system-level deployment of high-capacity cellular systems and can be extended to fixed wireless systems as well     

Smart cell design for high altitude platforms communication

This paper proposes a novel design technique for irregular shaped cells in the high altitude platforms (HAPs) cellular system. This technique is based on dividing the coverage area into a grid of small pixel spots and the desired cell is obtained by grouping some pixel spots to give the desired cell shape. These spots are formed with narrow and low sidelobe level beams using concentric ring array (CRA) to reduce the cochannel interference as well as improving the resolution of the design. The desired cell pattern is converted into a spatial mask that selects the desired pixel spots with a proper pre-weight smoothing function. The proposed cell design technique will optimize the cell shape according to the user distribution and behavior in the covered area and consequently is expected to reduce the frequent handoff and signaling traffic of location updating from moving users. Simulation results show that a cell with any irregular shape can be formed with as low as 40 dB sidelobe level using Gaussian CRA.     

Cochannel Interference in High-Capacity Mobile Radio Systems

The probability of cochannel interference is evaluated for a mobile radio system operating in Rayleigh fading and log-normal shadowing environment. All cochannel cells surrounding the base station are taken into consideration in this evaluation. The results obtained are used to calculate the reuse distance and the cluster size (number of cells in a group). The blocking probability, the number of channels in each cell, the protection ratio, and the standard deviation are taken as parameters in this evaluation. The results show that shadowing has a severe effect on the interference level and on the channel reuse distance ratio.     

Investigation of slotted ALOHA under Nakagami fading with synchronized and asynchronous cochannel cells

The throughput performance of slotted ALOHA (S-ALOHA) in a cellular system and Nakagami fading environment is studied. Based on the signal capture model, the effects of multiple access interference (MAI) from in-cell users and of cochannel interference (CCI) from cochannel cells are quantified analytically. Especially considered are the cases when asynchronism of cochannel cells is present, for which an approximation of the interference distribution is successfully applied to get a highly precise expression of the system throughput. Our study shows that, though the MAI level and capture effect determine the basic behavior of the S-ALOHA, CCI significantly reduces the throughput of S-ALOHA and asynchronous CCI introduces an especially severe impairment. Our analytical framework is also able to incorporate additional channel conditions and system parameters like lognormal shadowing and the cellular cluster size.     

Signal-to-interference calculations for corner-excited cellularcommunications systems

Signal-to-inference ratio calculations for corner-excited cellular communications systems are presented. Specifically, the ratio of median signal power to the sum of median interference powers is considered. The interference model includes cochannel interference, and immediately adjacent as well as nonimmediately adjacent channel interference. Related system parameters are cluster size, receiver, and transmitter filter characteristics, propagation exponent, tier coverage, and directional antenna front-to-back ratio. Both mobile-to-baseand base-to-mobile communications are considered. The method and model used for calculation are more complete than any previously reported in the technical literature. The calculated results show that the effect of adjacent channel interference compared to cochannel interference cannot be ignored in general. In mobile-to-base communications, the effect of immediately adjacent channel interference introduced by an interfering mobile which is very close to the receiving base antenna is serious     

Areas of cochannel interference and multipath created by 8-VSB modulated distributed transmitters in flat terrain

Presentation is made of the methodology for defining the area in which the signal from an auxiliary on-channel transmitter appears to the receiver as multipath, and the area where the signal from an auxiliary on-channel transmitter appears as new cochannel interference. The size and location of these areas depends on how well the contour of the receiver equalizer window can be made to overlap the cochannel interference contour. The optimum overlap requires a specific adjustment to the height, power and delay of the auxiliary transmitter.     

Phase-only synthesis of minimum peak sidelobe patterns for linearand planar arrays

Minimization of the maximum sidelobe level for a given array geometry by phase-only adjustment of the element excitations is considered. Optimum phases are obtained by using a numerical search procedure to minimize the expression for the pattern sidelobe level with respect to the element phases. Results for both linear and planar arrays of equispaced elements are presented. The data suggests that optimum sidelobe level is a logarithmic function of array size, and optimum patterns have relative efficiencies that are typically somewhat greater than for comparable-amplitude tapered arrays. An analytic synthesis algorithm is presented for use on very large arrays for which the numerical search technique for the minimization of the sidelobe level is computationally impractical. This method produces patterns with characteristics similar to arrays synthesized using the numerical search method, i.e. relatively uniform angular distribution of energy in the sidelobe region, and generally decreasing maximum sidelobe level as the array size is increased     

Sharp cutoff radiation patterns

A method is described for estimating the available slope (dB/ deg) for the design of a sharp cutoff radiation pattern with a given aperture size, sidelobe level, and ripple factor. Curves are presented which relate slope factor (dB/deg/wavelength of aperture), sidelobe level, and ripple factor. These curves are obtained by defining and evaluating a Chebyshev integral pattern function which is representative of a sharp cutoff radiation pattern.     

Sidelobe suppression of planar array antennas by the multistage decision method

The sidelobe level of a planar array antenna with equal amplitude excitation can be suppressed by element thinning. The method of element thinning employed here is a kind of multistage decision procedure or steepest descent approach. Although this method gives the local optimum results, the reduced sidelobe level is assured to be within the obtained level over the whole radiation region. The sidelobe level, for example, can be suppressed -29.7 dB where the array contains 3120 elements arranged within a circular aperture capable of 5815 elements if fully filled. The computation time is also discussed, and it is shown that the computation time decreases drastically by the use of the design method.     

Performance Analysis of the Spectral Correlation Discriminator Array

Mobile communications suffer from cochannel interference, adjacent channel interference and fading. The cell capacity or the number of users per cell is limited by the interference. In this paper we analyze a new blind adaptive array structure called the spectral correlation discriminator array (SCDA), designed to reject cochannel interference for advanced mobile phone service (AMPS) signals. The blind adaptive array exploits the spectral redundancy in the AMPS signals which arises due to the presence of the supervisory audio tone (SAT). SCDA is shown to provide an improvement of 25–30 dB in signal-to-interference plus noise ratio (SINR) in static multipath channels and 10–15 dB improvement of SINR in Rayleigh fading channels. The SCDA is compared to the least squares constant modulus array (LSCMA) and is shown to have better signal selectivity properties. The reduction in interference power can significantly reduce the frequency reuse factor.     

基于遗传算法的相控阵天线口径激励的多阶振幅量化

本文利用二进制编码的遗传算法实现天线阵口径激励的振幅量化。该方法考虑了互耦的影响和大扫描角的情况,计算实例为98单元偶极子线阵,它安装在理想反射面上,单元距离反射面λ0／4,采用7阶振幅量化。在不扫描情况下可达到峰值副瓣-35dB,在60°扫描角情况下可达-30dB。     

Effects of Rician faded and log-normal shadowed signals on spectrumefficiency in microcellular radio

An assessment of spectrum efficiency for a microcellular land mobile radio system is presented by considering the desired signal as (fast) Rician fading with (slow) log-normal shadowing and cochannel interfering signals as uncorrelated (fast) Rayleigh fading superimposed over (slow) log-normal shadowing. Spectrum efficiency is defined in terms of reuse distance, i.e., cluster size, traffic intensity, bandwidth of the system, and area of a cell by considering cochannel interference probability. The expression for cochannel interference probability is derived using appropriate path-loss law for microcells for four different cases: Rician plus log-normal desired signal and Rayleigh plus log-normal interfering signals; Rician desired signal and Rayleigh fading plus log-normal shadowing interfering signals; Rician desired signal and Rayleigh interfering signals; and both desired and interfering signals as Rician fading. The performance of a microcellular system is compared with that of a conventional macrocellular system     

Measurement distance effects on low sidelobe patterns

Because of the current strong emphasis on low sidelobe antennas, the effects of measurement distance in distorting patterns are reexamined. Previous calculations have used obsolete or suboptimum aperture distributions. The Taylorbar{n}linear distribution is a versatile highly efficient and robust optimum distribution; its use here allows a single curve of sidelobe measurement error versus measurement distance (normalized to far field distance2D^{2}/lambda) for a given sidelobe level. The calculations give data from a uniform distribution to a 60 dB Taylor. For example, the first sidelobe of a 40 dB Taylor pattern is in error 1 dB at a distance of6 D^{2}/lambda.     

Interference Cancellation System for Satellite Communication Earth Station

A new interference cancellation system was devised to suppress the mutual interference between satellite and terrestrial communication systems and to expand the number of potential earth station locations for effective frequency reuse. This system basically adopts the sidelobe canceller concept and has main and auxiliary antennas. The originality of this system lies in that the auxiliary channel signal to be combined with the main channel signal is modulated by a low frequency signal, and the amplitude and phase controlling voltages are obtained by means of envelope detection, to get the envelope of the residue, and then by phase detection, using the envelope signal and the low frequency signal. As a result of experiments, more than 40 dB cancellation was achieved over a 50 MHz range for CW, FM(TP, TV) and PSK signals, even if the desired and interference signals are in the cochannel. In the field test on a 45 km path, sufficient cancellation performance and response were obtained even during fading periods.     

一种低旁瓣非均匀圆形活塞换能器的设计

针对水声换能器的指向性旁瓣级问题,该文提出了一种低旁瓣非均匀圆形活塞平面水声换能器。该换能器在均匀圆形活塞换能器的基础上,采取去双环分布方法去除均匀圆形活塞换能器部分压电相体积,改变换能器结构,实现了抑制旁瓣的效果。以均匀连续平面活塞阵为基础,该文推导了去双环圆形平面活塞阵指向性函数,并采用Matlab对该指向性函数求解,分析两个环的位置和宽度随换能器指向性最大旁瓣级的变化规律,根据优化结果确定了换能器的最优尺寸。通过有限元仿真分析表明,该去双环圆形活塞换能器指向性最大旁瓣级为-25.3 dB,与均匀圆形活塞换能器相比,最大旁瓣级降低了8.3 dB,实现了旁瓣抑制,有效降低了最大旁瓣级。     

基于子带滤波器组的宽带自适应天线旁瓣相消技术

文[6]提出在数字移动通信中子带滤波器组处理可以提高不同阵元信号的相关性,从而能改善自适应阵列抑制码间干扰(ISI)和共信道干扰(CCI)的能力.在文[6]的基础上,本文研究了子带滤波器组在宽带自适应天线旁瓣相消中的应用,对其原理进行了理论分析,提出了有效的子带处理方法.经研究表明,子带滤波器组处理能有效增加主、辅助天线信号的相关性,从而提高系统干扰相消比.而且适当的过采样能使系统干扰相消比进一步提高.计算机仿真结果和实测雷达数据处理结果证实了子带处理方法的有效性和理论分析的正确性.     

A low sidelobe asymmetric beam antenna for high altitude platform communications

In a communications network served by a high altitude platform, the antenna beams illuminating each cell require minimized sidelobe powers. Asymmetric beams are advantageous so that cell footprints remain circular. At millimeter wavelengths a lens antenna can have the desired properties. We have chosen a 6 km diameter cell at 32/spl deg/ elevation angle and shown how the required beam asymmetry can be implemented using an optimized polynomial for describing the lens profile. The measured average sidelobe level is below -42 dB.     

Trellis-coded cochannel interference canceller for microcellularradio

Cochannel interference is a major impairment that limits the capacity of microcellular radio systems. This paper proposes a trellis-coded cochannel interference canceller, which uses trellis-coded modulation with maximum likelihood sequence estimation of both the desired signal and cochannel interference. This technique permits operation even when the signal-to-interference ratio is 0 dB. Computer simulation results show that this technique significantly reduces the bit-error rate in microcellular systems with Nakagami-Rice fading, particularly when the average signal-to-interference ratio is 0 dB. However, the technique requires: (1) synchronization of the interference and the desired signal and (2) higher computational complexity than standard techniques     

新型桅杆材料对舰载雷达副瓣性能影响的研究

设计了一种工作于C/S 波段的带通滤波性能良好的透波材料。该透波材料的周期单元尺寸为10 mm,结构的厚度为20 mm,在2.5~5 GHz 的频带内都有良好的透波性能。基于这种透波材料的舰船顶桅能够大大减小顶桅对舰载雷达天线电性能的影响,特别是对天线方向图副瓣电平抬升的影响。与理想导体相比,采用这种透波材料后,顶桅对舰载雷达天线的副瓣电平抬升作用显著降低,进而降低了雷达产生虚警的概率。天线最大副瓣降幅分别为18.2 dB(C 波段)与7.8 dB(S 波段)。