基于智能天线和资源预留的抗基站间干扰DCA分配算法

本文针对TD-SCDMA系统在次叉时隙间快速动态信道分配算法的不足,提出了一种基于智能天线和优级信道预留的快速动态信道分配算法。该算法在进行资源整合的基础上将信道条件较好的用户分配于交叉时隙,同时尽量分配多址干扰小的时隙给用户,从而达到减少交叉时隙干扰,提高频谱效率的目的,仿真结果表明该算法能够有效增加系统容量,改善系统性能。     

一种TD-SCDMA系统的动态信道分配策略

提出了一种适用于TD-SCDMA系统的动态信道分配算法.该算法在进行资源整合的基础上将信道条件较好的用户分配于交叉时隙,从而达到减少交叉时隙干扰,提高频谱效率的目的.仿真结果表明该算法能够有效增加系统容量,改善系统性能.     

TD-SCDMA系统中的动态时隙分配过程研究

在TD—SCDMA系统中由于上下行不对称业务的需求，使得不同小区的上下行切换点不同，出现交叉时隙，因此会产生严重的小区间干扰，需要使用动态信道分配算法以解决小区间的上下行时隙分配，小区内各种用户对时隙的选择等，使小区间干扰最小、系统容量最大，同时用户QoS最好。先介绍了TD—SCDMA系统中的资源和干扰情况，再重点介绍动态时隙分配全过程，分析了各部分所要完成的功能，并给出了慢速动态时隙分配的2种方案、快速动态时隙分配的4个过程以及各个过程的方案。     

TD-SCDMA系统动态信道分配中交叉时隙的概率分析

文章针对TD—SCDMA系统使用的信道分配算法，用马尔可夫模型对小区时隙各分配状态的稳态概率进行了分析，给出相邻小区交叉时隙的概率的计算方法，并对相邻小区交叉时隙概率以及交叉时隙对系统性能的影响进行了仿真验证。     

一种基于网络优化的动态信道分配策略

该文提出了一种在CDMA网络中基于网络优化的动态信道分配策略,它针对恒定比特率(CBR)业务建立了一种整数规划的数学模型,它不是每个时隙进行一次信道分配而是若干个时隙根据当前所有用户的状态统筹做一次调度,目的是使得用户QoS和系统性能得到折中考虑。通过仿真,相对于传统话音优先和按照优先级排队的分配算法,这种优化算法在保证业务的QoS的同时使得信道利用率得到提高。     

一种TD-HSUPA系统的动态信道分配方法

提出了一种基于智能天线测量结果的动态信道分配方法,该方法通过智能天线测量用户的方位,辅助基站给用户分配时隙资源.仿真结果表明该算法能更好地避免同频干扰,更加充分地利用码资源,对上行性能有较好的提升效果.     

一种TD-SCDMA动态信道分配的改进方案

在TD-SCDMA系统中,由于对上下行不对称业务的需求,使得不同小区间的上下行切换点不同,因此会产生严重的小区间干扰(基站和基站间干扰)。提出一种基于移动台位置的抗基站间干扰的动态信道分配(DCA)的改进方案,它通过增大交叉时隙的空间隔离度和减少交叉时隙的使用机率来改善基站间的相互干扰,同时使每个时隙的用户空间分布更加均匀,最大化提高系统容量,改善非对称业务下系统的整体性能。     

TD-SCDMA系统动态信道分配的改进方案

在时分同步码分多址(TD-SCDMA)系统中由于对上下行不对称业务的需求,不同小区间的上下行切换点不同,因此会产生严重的小区间干扰(基站和基站间干扰)。文章提出了一种基于移动台位置的抗基站间干扰的动态信道分配(DCA)的改进方案,它通过增大交叉时隙的空间隔离度和减少交叉时隙的使用机率来改善基站间的相互干扰,同时使每个时隙的用户空间分布更加均匀,最大化提高系统容量,改善非对称业务下系统的整体性能。     

TD-SCDMA系统的一种慢速动态信道分配算法

动态信道分配是TD-SCDMA的关键技术之一,根据网络负载和干扰的变化自适应地调整信道资源,使之达到合理配置。文中针对TD-SCDMA系统的帧结构,分析了双小区模型,并提出了一种采用双小区相同上下行时隙进行信道分配的方法,仿真结果表明:与传统的固定信道分配算法相比,推荐的算法大大提高了频谱利用率及系统容量。     

ATM网中图像分组的带宽分配算法

用两个节点各复用几个图像终端的ＡＴＭ网为例，研究五种图像源的带宽分配算法，静态时隙分配算法，缓冲区基础动态时隙分配算法，自适应时隙分配算法，先来先服务时隙分配算法和速度基础动态时隙分配算法，用计算机仿真和比较确定了五种算法的平均信元时延及时延偏差系数。     

干扰长度对WDM光网络阻塞性能的影响

引入WDM光网络中静态业务下一种适合于计算各种网络阻塞概率的分析模型,计算出波长连续网络和波长可转换网络的阻塞概率,采用波长转换增益定性分析了干扰长度对这两种网络阻塞性能的影响,并提出关于干扰长度的相对波长转换增益系数和相对通道长度系数的概念.Matlab仿真的结果表明,波长转换增益最大值大约为相对通道长度系数的一半;当干扰长度较大时,波长连续网络中的波长利用率较高,波长转换增益不明显.应用到网络拓扑设计时,可考虑相对通道长度系数,适当减小通道长度而增大干扰长度,从而减少波长转换器的数目,降低网络的硬件花费,提高网络的使用效率.     

Evaluation of bistatic intersystem interference due to scattering by hydrometeors on tropical paths

Evaluation of bistatic transmission loss cumulative distribution is very useful in assessing the effect of interference due to hydrometeor scatter between the communication links operating at the same frequency. Out of the many factors that could be responsible for the intersystem interference between the microwave communication systems, this paper presents the result of computation of intersystem interference resulting from the hydrometeor scatter on tropical paths. Interference is computed in terms of the cumulative distribution of transmission loss. The effect of varying common volume formed by the intersection of the antenna beams on the transmission loss is investigated. Results show that at frequencies higher than 10 GHz, for antenna separation longer than 100 km, common volume will be in the ice region, leading to a higher interference level at the interfered terminal. Also, results obtained show that because total path attenuation at 30 GHz is lower than at 20 GHz (this is due to the decrease in water vapour attenuation in the 22·2–30 GHz window), transmission loss tends to be higher at 20 GHz than at 30 GHz. In addition, increasing the antenna gain of the interfering station will result in the increasing interference level at the interfered station. Evaluation of the effective transmission loss shows that this parameter gives a better assessment of interference on the tropical propagation paths noted for high-intensity convective precipitation. In this case, the effective transmission loss has been evaluated in terms of the joint occurrence of additional rain attenuation on the wanted path, and the cumulative distribution of transmission loss on the intersecting paths. Copyright © 1999 John Wiley & Sons, Ltd.     

外辐射源雷达抗直达波干扰技术研究

外辐射源雷达系统中,直达波干扰严重影响了雷达对目标的探测性能.文中针对直达波干扰问题,通过对LMS、NLMS、改进的NLMS算法的收敛速度、时变系统跟踪能力、失调量等的分析,将改进的归一化LMS(NLMS)自适应滤波算法应用于直达波干扰抑制,取得了较好的处理效果,其对消得益可达40 dB;分析了滤波器阶数、参数选择对对消性能和信噪比损失的影响,给出了典型参数值.最后,真实数据的处理结果验证了该方法的有效性.     

一种新的认知无线电非合作功率控制博弈算法

当认知无线电网络以"衬底式"(Underlay)的方式与主用户网络共享频谱时,需要对认知用户进行功率控制,以确保认知用户在不干扰主用户的前提下,公平地共享认知频谱资源。利用博弈分析的方法,设计了一个基于链路增益因子的代价函数,并据此提出了一种新的非合作功率控制博弈算法。仿真结果表明,该算法的均衡结果既改善了用户的帕累托(Pareto)性能,又提高了链路增益较差的用户的吞吐量,实现了网络资源的平等共享。     

Error propagation analysis for underwater cooperative multi-hop communications

The potential gains of cooperative communication and multi-hopping in underwater acoustic communication channels is examined. In particular, performance of such systems is compared to a comparable single hop system (direct transmission) with a common transmission distance. The effects of error propagation with decode and forward at each relay are explicitly treated and it is shown that strong gains can be achieved by multi-hopping (an effective SNR gain) as well as cooperation, which contributes to a diversity gain. We observe that cooperative diversity gains are retained even when considering error propagation. The analysis is done via a Markov chain analysis for both regular linear and grid networks. Our initial analysis is for single path channels; the effects of inter-symbol interference as well as multi-user interference are examined. It is found that due to the strong decay of signal power as a function of transmission distance, multi-user interference is not as significant as inter-symbol interference. In both cases, cooperative and multi-hopping gains are observed.     

On the Convexity of Feasible QoS Regions

The feasible quality-of-service (QoS) region is the set of all QoS vectors that can be provided to the users by means of power control, with interference treated as noise. In an interference-limited scenario, this set is determined by the Perron root of some QoS-dependent nonnegative matrix. In a previous work, we showed that if the signal-to-interference ratio (SIR) is a log-convex function of the QoS, then the Perron root is a log-convex function. This implies convexity of the feasible QoS region. In this correspondence, we prove that the log-convexity property is also necessary for the Perron root to be convex for any choice of the (path) gain matrix. Interestingly, a significantly less restrictive property is sufficient when the gain matrix is confined to be symmetric positive semidefinite     

On the diversity gain region of the dynamic decode-and-forward relay-assisted Z-channel

In an interference-limited system, the interference forwarding by a relay enhances the interference level and thereby enables the cancellation of the interference. In this work, interference forwarding by a half-duplex dynamic decode-and-forward (HD DDF) relay in a two-user Z-channel is considered. In the two-user Z-channel, one user is interference-limited while the other user is interference-free. The diversity gain region (DGR), which characterizes the tradeoff between the achievable diversity orders between the two users, is an appropriate performance metric for the Z-channel. Closed-form expression for the achievable DGR with the interference forwarding by the HD DDF relay is presented. The multiplexing gain regions (MGRs) where the HD DDF protocol achieves better DGR over the direct transmission scheme, full-duplex decode-and-forward (FD DF) and FD partial DF relay assisted Z- channel are identified. The HD DDF protocol is shown to achieve better DGR than the FD DF and FD PDF relay for a large range of MGR. The achievable DGRs for the HD DDF, FD DF, and FD PDF relay-assisted Z-channel and direct transmission scheme are presented for various interference levels and multiplexing gain pairs.     

Resource allocation for multiple classes of DS-CDMA traffic

We consider a packet data direct-sequence code-division multiple-access (DS-CDMA) system which supports integrated services. The services are partitioned into different traffic classes according to information rate (bandwidth) and quality of service (QoS) requirements. Given sufficient bandwidth, QoS requirements can be satisfied by an appropriate assignment of transmitted power and processing gain to users in each class. The effect of this assignment is analyzed for both a single class of data users and two classes of voice and data users. For a single class of data users, we examine the relationship between average delay and processing gain, assuming that ARQ with forward error correction is used to guarantee reliability. The only channel impairment considered is interference, which is modeled as Gaussian noise. A fixed user population is assumed and two models for generation of data packets are considered: (1) each user generates a new packet as soon as the preceding packet is successfully delivered and (2) each user generates packets according to a Poisson process. In each case, the packets enter a buffer which is emptied at the symbol rate. For the second traffic model, lowering the processing gain below a threshold can produce multiple operating points, one of which corresponds to infinite delay. The choice of processing gain which minimizes average delay in that case is the smallest processing gain at which multiple operating points are avoided. Two classes of users (voice/data and two data classes) are then considered. Numerical examples are presented which illustrate, the increase in the two-dimensional (2-D) capacity region achievable by optimizing the assignment of powers and processing gains to each class     

A multiuser interference cancellation technique utilizingconvolutional codes and orthogonal multicarrier modulation for wirelessindoor communications

This paper suggests that multicarrier modulation reduces the complexity and the delay caused by the multiuser interference cancellation process utilizing convolutional codes. For spread spectrum multiple access, multiuser interference (interference due to signals from other users) limits the performance of the communication link. To remove this interference, a multiuser interference cancellation technique which utilizes orthogonal convolutional codes has been proposed for the uplink (mobiles to a base station) of the cellular code-division multiple-access (CDMA) systems. However, this technique requires large interleavers and huge memory, or artificial multipath diversity and a RAKE system to achieve sufficient coding gain if it is applied to wireless indoor communications and fading is slow compared to the data rate. To reduce the complexity of the canceller, multicarrier modulation is employed as it provides frequency diversity gain and coding gain without the interleavers or a RAKE system. This paper shows that multicarrier modulation reduces the complexity of the canceller and still provides sufficient coding gain in order to cancel the multiuser interference. A canceller with decoding in the initial decision and multicarrier modulation improves the capacity by a factor of 1.4 as compared with a canceller without decoding     

Effects of antenna height, antenna gain, and pattern downtiltingfor cellular mobile radio

Results of wideband path loss and delay spread measurements using high gain, high and low antenna heights with pattern tilting are presented. The measurements were done in the frequency range 905-915 MHz, at two existing cellular mobile radio (CMR) sites. Also presented are potential approaches for analyzing data from high gain antennas. It is shown that, to a large extent, existing models can be used to predict path loss for high gain antennas with downtilting. The results further support the notion that high sites together with high gain antennas and suitably selected pattern tilting can result in a significant reduction in path loss and delay spread, as well as reduction in power transmitted from the cell site and reduction in system interference