一种新的CDMA软切换算法及其对软切换性能的改善

定义了残余容损比(RCLR)的概念,提出了一种新的基于最大RCLR的无线移动CDMA小区系统的软切换判决算法,称之为RCLR算法。区别通常的最小路径损耗(MPOL)算法,RCLR算法不仅考虑了呼叫业务的路径损耗,而且兼顾了小区负载平衡。最后,通过分别在单层小区系统和分层小区系统中进行仿真,比较了RCLR算法和MPOL算法的软切换性能,仿真结果表明RCLR算法显著地改善了呼叫业务的中断概率和分层小区系统的层间溢出概率,减少了软切换次数。     

Analysis of fade margins for soft and hard handoffs in cellular CDMA systems

The effect of handoff techniques on fade margin is investigated. We provide an accurate comparison for soft and hard handoffs in a two-cell system. An upper bound on the fade margin for hard-handoff systems is derived and an approximation formula is obtained empirically. Simulation results show that this approximation is very accurate over reasonable ranges of system parameters. Extension of our analysis to multiple-cell systems are illustrated using a three-cell system as an example.     

Handoff management without intercell hard handoffs in a multifrequency CDMA system

The paper addresses handoff management in a multifrequency code-division multiple-access system with nonuniform traffic loads over cells. We propose a new handoff scheme, adaptive handoff management (AHM), in which the intercell hard handoffs, which not only incur an equipment cost burden but also degrade call quality, are totally removed. Also strengthened in the AHM is the call-control capability of adaptively reflecting a changing traffic environment. Traffic and mobility analysis is first conducted on a single isolated cell with two concentric circle boundaries, thereby rendering two key performance measures. We then formulate a mathematical problem of finding the optimal parameters of the proposed AHM in which intracell hard handoffs are exploited most effectively. After reporting a simple solution process, computational experiments are conducted to illustrate the superiority of AHM in two key performance criteria.     

Comparing soft and hard handoffs

This paper studies the soft-handoff mechanism and compares its performance with hard handoff. Our study indicates that although a handset may potentially consume extra radio links in soft handoff, the mechanism provides better opportunity to transfer the link successfully in the handoff procedure. Thus, by carefully planning the overlay areas of cells, soft handoff can outperform hard handoff     

UWB设备对CDMA系统下行链路容量的影响

本文研究了超宽带(UWB)设备对CDMA系统下行链路容量的影响.文中首先建立了UWB设备的分布模型,针对已有的WCDMA系统模型,应用计算机仿真,得出CDMA系统中加入UWB设备后的系统容量与UWB设备发射功率、分布密度的关系.     

Fade margins for soft and hard handoffs

A particularly attractive feature of CDMA wireless systems proposed in the Telecommunication Industry Association's standard IS-95 [1] is their ability to get into what is known as soft handoff. A mobile in soft handoff maintains simultaneous radio links with multiple base-stations which enables it to make use of the best quality leg most of the time. This is believed to result in a reduction of the fade margin that is needed to provide the desired coverage in a given geographical area in the presence of log-normal shadow fading. This paper presents an analysis of fade margins for systems allowing soft handoffs (e.g. CDMA) and those where only hard handoffs are possible (e.g. FDMA, TDMA). The analysis is based on a model for hard handoffs with hysteresis and connection delay and confirms the belief that soft handoffs result in smaller fade margins.     

Effect of co-phasing diversity on CDMA downlink capacity

The impact of distributed antennas using co-phasing transmission diversity on downlink CDMA channels is examined. An expression is derived that demonstrates that uniform downlink signal-to-interference ratio across users can be achieved by appropriately weighting the distribution of transmit powers across distributed antennas. The capacity of a downlink CDMA system employing distributed antennas with optimum power allocation is then found by simulation.     

CDMA系统中的多用户检测及容量分析

利用多用户检测技术可以抑制多址干扰，从而提高CDMA系统的容量和性能。研究了CDMA系统中的多用户检测技术的原理和作用，并对连续干扰消除多用户检测器消除干扰的原理和过程进行了详细的阐述；综合考虑各种影响因素，推导出了CDMA系统容量的公式，最后利用仿真，直观地分析了多用户检测对系统容量的影响。     

Erlang capacity of ATM-based CDMA satellite system

The capacity and throughput of an ATM-based CDMA system offering flexible access rates on demand are analysed. Extending the existing analysis of traffic capacity of a power-controlled CDMA cellular system, it is shown that offering multiple access rates may result in higher throughput efficiency. An example given of a satellite system shows that the gain in capacity may be some 10%     

多业务CDMA系统上行链路容量分析

研究了多业务CDMA系统的上行链路容量,提出一种容量分析方法。在方法中考 虑了多业务的激活概率,分析了不同业务的掉话率,以系统掉话率为基准给出了系统容量。该 分析方法表明CDMA系统的容量受多业务的Eb/N0、传输速率和业务激活概率的影响。     

Improving the capacity of multi-code multimedia CDMA system

A novel method for improving the capacity of multi-code multimedia Code Division Mul- tiple Access (CDMA) systems is proposed. By factitiously improving the transmission bit rate of the call, the number of the orthogonal codes used by a user is increased which leads to the decreasing of the interference. Simulation results shows that the proposed scheme results in better throughput than traditional multi-code CDMA systems.     

On the capacity of a cellular CDMA system

It is shown that, particularly for terrestrial cellular telephony, the interference-suppression feature of CDMA (code division multiple access) can result in a many-fold increase in capacity over analog and even over competing digital techniques. A single-cell system, such as a hubbed satellite network, is addressed, and the basic expression for capacity is developed. The corresponding expressions for a multiple-cell system are derived. and the distribution on the number of users supportable per cell is determined. It is concluded that properly augmented and power-controlled multiple-cell CDMA promises a quantum increase in current cellular capacity     

Erlang capacity of a power controlled CDMA system

This work presents an approach to the evaluation of the reverse link capacity of a code-division multiple access (CDMA) cellular voice system which employs power control and a variable rate vocoder based on voice activity. It is shown that the Erlang capacity of CDMA is many times that of conventional analog systems and several times that of other digital multiple access systems     

软切换参数对CDMA1X性能的影响及优化

分析并仿真得到了在CDMA1X系统中,不同业务负载情况下的软切换开销因子与静态和动态软切换门限,以及导频信道功率比例等参数的关系,并在此基础上提出了相应的网络优化措施。仿真采用蒙特卡罗"快照"法,并在进行传播损耗计算时加入了阴影衰落的影响。     

Effects of the BS power and soft handoff on the outage and capacity in the forward link of an SIR-based power-controlled CDMA system

In the forward link of a signal-to-interference ratio (SIR)-based fast power-controlled CDMA system, the fraction of base station (BS) power allocated to a mobile station (MS) is considered as a key factor affecting the system performance. By using our proposed macrodiversity non-orthogonality factor, we establish a unified analytical model to characterize the distribution of the fraction of BS power allocated to an MS in either the non-soft handoff mode or the soft handoff mode. By using that distribution and limiting the maximum fraction of BS power available to an MS, a closed-form expression of the capacity at a certain outage probability is obtained. The effects of system parameters, such as the available Rake fingers, the soft handoff threshold, the unbalance of the BS power, and the power control error, on the capacity are investigated from the viewpoint of the limitation on the fraction of BS power allocated to an MS. Simulation results show that soft handoff does not always improve capacity and the capacity gain may result depending on the choice of the system parameters.     

Soft handoff and uplink capacity in a two-tier CDMA system

This paper examines the effect of soft handoff on the uplink user capacity of a code division multiple access system consisting of a single macrocell in which a single hotspot microcell is embedded. The users of these two base stations operate over the same frequency band. In the soft-handoff scenario studied here, both macrocell and microcell base stations serve each system user, and the two received copies of a desired user's signal are summed using maximal ratio combining. Exact and approximate analytical methods are developed to compute uplink user capacity. Simulation results demonstrate a 20% increase in user capacity compared to hard handoff. In addition, simple approximate methods are presented for estimating soft-handoff capacity and are shown to be quite accurate.     

switched beam CDMA系统中小区容量和覆盖半径的计算

本文推导了switched beam系统中干扰因子的计算式，以及中断概率、基站接收机灵敏度、移动台最大可允许的发射功率、信干比的期望值、路径损耗与小区覆盖半径、小区容量的关系式，并以直线天线阵为例，计算了小区容量和小区的覆盖半径。     

THE CAPACITY CALCULATION FOR CDMA MOBILE SATELLITE COMMUNICATION SYSTEM

On the basis of considering downlink power flux density limit, shadowing effect frequency reuse in different systems and adjoining beams of same system, adopting voice activity and polarization isolation techniques, the capacity of CDMA mobile satellite communication system at different downlink power flux density limit modes, channel spread bandwidth and mobile user's quality factor of receiving system(G/T) are analysed and calculated, and compared with the ones of TDMA and FDMA. The conclusions are given at the end of this paper.     

Forward-link capacity of a DS/CDMA system with mixed multiratesources

Some studies have been done on capacity of a code division multiple access (CDMA) system with mixed multirate sources. However, a vast majority of these studies have concentrated on the reverse-link. This trend comes from the fact that the capacity of a CDMA system is reverse-link limited. However, the forward-link can be a limiting link because emerging data services are likely to require higher data rates in the forward-link than in the reverse-link. In this paper, we analyze and simulate the forward-link capacity of a CDMA system with mixed multirate sources in a multipath fading channel. The outage probability of the forward-link is derived for a CDMA system with mixed multirate sources. By introducing a forward-link power factor, the forward-link Erlang capacity is obtained in a closed form. The forward-link capacity is analyzed in terms of the number of multipaths, the number of RAKE fingers in a mobile station, closed-loop power control, and impact of soft handoff. The results in this paper can be applied to overall system design of a CDMA system with multimedia services in future mobile communication systems