WCDMA网络软容量提升优化

WCDMA系统属于自干扰型系统,具有软容量特性,系统容量受外部干扰、小区间和用户间的干扰影响。对WCDMA系统下行功率分配与链路容量进行了分析,探讨了通过采取小区间干扰改善、信道功率分配优化等手段,高效利用宝贵的功率资源,提升WCDMA网络软容量的思路和方法。     

cdma2000—lx系统前向链路渐近容量的研究

CDMA系统是干扰限制系统 ,其前向链路受信噪比、发射功率、数据速率等诸多因素的影响 ,本文通过推导和数据仿真分析了前向链路导频和业务信道信噪比以及业务信道比特率等对cdma2 0 0 0 - 1x系统前向链路渐近容量的影响     

提高W-CDMA通信系统容量的技术

文章主要讨论了提高W-CDMA通信系统容量采取的技术,包括:小区间异步操作和3步快速小区搜索、引导符号辅助相干信道估计、基于信干功率比的快速发射功率控制、位置分集、前向链路的发射分集,以及干扰抵消和自适应天线阵列分集接收和发射。     

两跳中继CDMA蜂窝系统的上行链路容量分析

首先在两跳中继CDMA蜂窝系统的基础上,提出了2种使用带外信道提高传统CDMA蜂窝系统上行链路容量的中继方法;然后通过分析传统无中继CDMA蜂窝系统的干扰功率,分别得到这2种中继方法对当前小区和邻居小区总的干扰功率;最后在一种对称小区模型的基础上,通过数值计算对两跳中继CDMA蜂窝系统的上行链路容量进行分析,并讨论了2种中继方法对系统性能所产生的影响.     

卫星无线电定位通信系统用户容量模型的研究

由地球同步卫星、地面中心站和用户机组成的集中式卫星定位系统中,用户到中心站的入站链路采用码分随机多址接入信道;出站链路采用扩频/TDM广播信道。本文建立了入站信道的用户容量模型,获得用户容量、系统参数、设备要求之间的关系;为增大出站广播信道的通信容量、采用同步码分多路复用技术,推导出计算数据误码率的公式。由计算机模拟,给出一系列曲线和图表以作为系统设计依据。     

多中继协作通信系统容量分析及中继选择协作分集策略

本文针对多中继辅助通信系统,将系统建模为一个两跳通信链路,并进行了系统容量分析。针对两种特殊情况:用户端接收噪声方差远小于中继端接收噪声方差和中继端接收噪声方差远小于用户端接收噪声方差的情况,本文具体给出了系统传输容量上限与协作中继个数之间的关系。基于容量的分析,本文设计了两种中继选择策略。在第一种情况下,根据中继与用户间的信道特征值对多路数据流分别选取不同的中继子信道进行传输;在第二种情况下,选择一个信道条件最好的中继完成多路数据流的并行传输。仿真分析表明,不同的信道环境需要选择不同的中继选择策略。      

CDMA系统下行链路的干扰抵消

CDMA蜂窝移动通信系统是一种采用多址技术的通信系统，即采用不同的地址码来区分用户、基站和信道。然而由于其在多径衰落信道中的自相关和互相关特性的不理想造成了多址干扰。在扩频通信系统的下行链路中，有效地抵消多址干扰是进一步改善系统性能和提高系统容量的重要途径。本文提出一种应用于CDMA下行链路的干扰抵消算法，分析了下行链路接收机的实现原理及过程，并对其中的关键算法进行了详细地分析，仿真结果表明，所选取的下行接收算法能改善系统的性能。     

几种提高蜂窝移动通信系统容量的方法

分析了信道分配技术、功率控制技术和自适应天线技术等3种常用的改善移动通信系统容量的方法,其中信道分配主要通过采用恰当的信道分配技术实现有效的频率复用,功率控制和自适应天线技术主要从降低同频干扰角度提高系统容量。虽然单独使用这些技术可以在一定程度上提高系统容量,但频率复用会引起同频干扰,从而降低无线链路服务质量。这3种技术若彼此之间相互结合,则可以充分发挥各自特点,最大限度地提高移动通信系统容量。具体分析了上述3种技术两两结合所产生的优势和存在的局限性,并讨论分析了它们对容量改善的影响。     

基于强化学习的定向无线通信网络抗干扰资源调度算法

为了在无线网络中进行高效的链路资源调度、减小网络干扰、提高网络容量,提出了一种利用回溯天线并考虑干扰环境的链路资源分布式智能调度算法.首先,结合通信的路径损耗模型设计卷积核,对节点密度矩阵进行卷积来衡量干扰链路强度,从而避免对所有干扰链路进行信道估计产生巨大的计算代价;然后,结合强化学习的思想设计了与通信环境交互的链路调度学习模型,每个链路利用神经网络进行独立的训练,将训练所得的决策结果反馈到环境中进行状态更新,模型在不断更新的环境中迭代来学习最优的调度策略.该方法能分布式的运行,可有效衡量无线网络中的链路干扰强度,结合衡量结果进行高效的链路资源分布式调度,从而最大化网络容量.仿真结果验证了该调度算法无论是在算法迭代收敛还是网络容量性能上都能很好地逼近全局的调度算法,达到全局算法最优结果的92%~100%.     

MIMO系统中的交叉优化调度算法

多入多出（MIMO）系统中在多用户环境下可以在链路级利用空间复用或者在系统级利用多用户调度来提高系统容量。但是仅仅是分别优化MIMO系统链路级性能或是仅仅单纯在系统级进行调度是不够的,将两者联合起来进行优化可以获得更大的系统容量。为此,该文提出了一种新的交叉优化调度算法（Cross Optimization Scheduling Algorithm,COSA）,将系统级的调度策略和链路级的物理层优化相结合,并且采用注水算法动态调整各天线的功率分配。仿真结果表明COSA算法不但在系统级为每个用户提供了公平的接入信道机会,而且在链路级中充分利用MIMO系统的空间复用特点以及动态的功率分配,提高了系统的容量。     

Performance Comparison of Downlink Capacity Improvement Schemes: Orthogonal Code-Hopping Multiplexing Versus Multiple Scrambling Codes

In this paper, we compare the performance of two downlink capacity-improvement schemes based on orthogonal code-hopping multiplexing (OCHM) and multiple scrambling codes (MSCs). Both OCHM and MSC systems have been proposed to overcome a code-limitation problem in a code division multiple access (CDMA) downlink. We mathematically analyze the user capacity in a general form, considering various factors such as user activity, spreading factor, amount of transmission symbol energy that is allocated to common control channels, amount of outer-cell interference, orthogonality factor, and sectorization factor. Numerical examples show that the capacity gain of the OCHM-based system increases as the other-cell interference decreases and the channel activity decreases. Thus, the OCHM-based system is a more effective scheme than the MSC-based system, considering that a code-limited situation more frequently occurs in the case of low other-cell interference and low channel activity. However, the OCHM-based system is more sensitive to the orthogonality factor.      

Orthogonal time-frequency signaling over doubly dispersive channels

This paper develops a general framework for communication over doubly dispersive fading channels via an orthogonal short-time Fourier (STF) basis. The STF basis is generated from a prototype pulse via time-frequency shifts. In general, the orthogonality between basis functions is destroyed at the receiver due to channel dispersion. The starting point of this work is a pulse scale adaptation rule first proposed by Kozek to minimize the interference between the basis functions. We show that the average signal-to-interference-and-noise (SINR) ratio associated with different basis functions is identical and is maximized by the scale adaptation rule. The results in this paper highlight the critical impact of the channel spread factor, the product of multipath and Doppler spreads, on system performance. Smaller spread factors result in lesser interference such that a scale-adapted STF basis serves as an approximate eigenbasis for the channel. A highly effective iterative interference cancellation technique is proposed for mitigating the residual interference for larger spread factors. The approximate eigendecomposition leads to an intuitively appealing block-fading interpretation of the channel in terms of time-frequency coherence subspaces: the channel is highly correlated within each coherence subspace whereas it is approximately independent across different subspaces. The block-fading model also yields an approximate expression for the coherent channel capacity in terms of parallel flat-fading channels. The deviation of the capacity of doubly dispersive channels from that of flat-fading channels is quantified by studying the moments of the channel eigenvalue distribution. In particular, the difference between the moments of doubly dispersive and flat-fading channels is proportional to channel spread factor. The results in this paper indicate that the proposed STF signaling framework is applicable for spread factors as large as 0.01.     

Implementing interference cancellation to increase the EV-DO Rev A reverse link capacity

This article provides the principles and practice of how interference cancellation can be implemented on the EV-DO Rev A reverse link. It is shown that applying interference cancellation to CDMA achieves the multiple access channel sum rate capacity for either frame synchronous or asynchronous users. The per user SINR gain from space-time interference cancellation translates directly into a CDMA capacity gain of the same factor, allowing EV-DO Rev A to support more users with higher data rates. We demonstrate how interference cancellation can be added to base station processing without modifying user terminals, EV-DO standards, or network coverage. We present commercially viable receiver architectures for implementing interference cancellation with the asynchronism and H-ARQ of EV-DO RevA, and explain why closed loop power control can operate the same way it does today. Network level simulations over a wide range of channels confirm that interference cancellation offers significant capacity gains for all users, while maintaining the same link budget and system stability.     

Improved cochannel interference cancellation for MFSK/FH-SSMAsystems

There has been much interest in the application of frequency hopping-spread spectrum multiple access (FH-SSMA) to wireless systems because of its frequency diversity and resistance to the near-far problem. In FH-SSMA systems, cochannel interference (CCI) is the dominant factor limiting the user capacity. Various techniques used to resolve the CCI problem have been extensively investigated. We propose several multiuser detection schemes based on canceling CCI to increase user capacity in a multilevel frequency shift keying (MFSK)/FH-SSMA system. The performance of systems with the proposed interference cancellers over a Rayleigh fading channel are analyzed and compared with those of the conventional and other interference cancellers. Our results show that the proposed schemes have the best performance in both nonfading and fading channels     

Performance Study for Two-Tier CDMA Cellular Systems with Multi-Channel Access

The CDMA cellular system can provide more capacity than AMPS systems and the hierarchical layer of cells is required for system design. However, system performance and capacity is degraded due to the cochannel interference between microcell and macrocell if a single frequency channel is shared. This paper proposes three multi-channel access schemes where various frequency channels are assigned for microcell and macrocell. Performances of channel capacity, blocking probability and blocking ratio in uplink and downlink are evaluated. Due to channel segregation and thus the cochannel interference among macrocell and microcell are minimized, the proposed scheme 3 where all channels are accessible sequentially in macrocell and microcell performs the best in system capacity and blocking probability than the other schemes.     

Outer bounds on the capacity of interference channels (Corresp.)

New outer bounds are demonstrated for the capacity regions of discrete memoryless interference channels and Gaussian interference channels. The bound for discrete channels coincides with the capacity region in special cases. The bound for Gaussian channels improves previous knowledge when the interference is of medium strength.     

On the Multiuser Capacity of WDM in a Nonlinear Optical Fiber: Coherent Communication

Previous results suggest that the crosstalk produced by the fiber nonlinearity in a WDM system imposes a severe limit to the capacity of optical fiber channels, since the interference power increases faster than the signal power, thereby limiting the maximum achievable signal-to-interference-plus-noise ratio (SINR). We study this system in the weakly nonlinear regime as a multiple-access channel, and show that by optimally using the information from all the channels for detection, the change in the capacity region due to the nonlinear effect is minimal. On the other hand, if the receiver uses the output of only one wavelength channel, the capacity is significantly reduced due to the nonlinearity, and saturates as the interference power becomes comparable to the noise, which is consistent with earlier results. The results hold in channels with or without memory. Every point in the capacity region can be achieved without knowledge of the nonlinearity parameters at the transmitters. The structures of optimal/suboptimal receivers are briefly discussed     

Interference-based channel assignment for DS-CDMA cellular systems

Link capacity is defined as the number of channels available in a link. In direct-sequence code-division multiple-access (DS-CDMA) cellular systems, this is limited by the interference present in the link. The interference is affected by many environmental factors, and, thus, the link capacity of the systems varies with the environment. Due to the varying link capacity, static channel assignment (SCA) based on fixed link capacity is not fully using the link capacity. This paper proposes a more efficient channel assignment based on the interference received at the base station (BS). In the proposed algorithm, a channel is assigned if the corresponding interference margin is less than the allowed interference, and, thus, channels are assigned adaptively to dynamically varying link capacity. Using the proposed algorithm yields more channels than using SCA in such an environment changes with nonhomogeneous traffic load or varying radio path loss. The algorithm also improves service grade by reserving channels for handoff calls     

Variable bit allocation for FH-CDMA wireless communication systems

In the wireless indoor environment, the channel may vary slowly as users and the interferers may move at slow speeds. A frequency-hopped code-division multiple-access system can adapt to the different interference levels in hopping patterns and assign the slots different bit rates to increase the system capacity. We show that the maximum throughput bit-rate/channel-assignment problem is NP-hard. Several practical ad hoc bit-allocation algorithms are designed based on the insights derived from exhaustive searches. The algorithms that achieve the most system capacity perform interference avoidance. Users concentrate their throughput in a small fraction of the slots with low interference by transmitting large signal constellations, while avoiding the channels with large interference. Simulations show that the flexibility of users to adjust their bit rates to the interference environment can significantly increase the system capacity.     

Method for evaluating W-CDMA system capacity considering adjacentchannel interference

An evaluation method is developed for calculating the loss in W-CDMA system capacity due to adjacent-channel interference. It is shown that the capacity loss is effectively characterised by two parameters: one depends on the cell structures and propagation environments and the other represents the interference coupling between two adjacent channels. The simulation results strongly support the validity of this expression