一种用于HAPS WCDMA系统的嵌入式多波束覆盖方案

该文提出了一种用于平流层平台WCDMA系统的固定波束加可控波束天线覆盖方案。该方案根据不同用户分布,在原有固定波束中合理嵌入可控波束,并有效调整嵌入波束的位置和大小,来优化系统容量。仿真结果表明该方案能够有效地提高平流层通信系统容量,节省波束资源,并且在变化的用户分布情况下保持容量的稳定性。该方案的这种优越性尤其体现在通信热点问题的解决中。     

平流层CDMA通信的波束分集接入方案

根据平流层通信应用多波束天线的特点,提出了一种适合于平流层CDMA通信的波束分集接入方案,应用此方案,在平流层平台上可以实现各波束接收信号的最大比合并,得到高系统容量和集成的软切换性能。     

面向无人机小区覆盖的毫米波波束优化设计

为了提高无人机毫米波波束覆盖区域内的通信容量,改善覆盖区域内用户通信质量,本文结合均匀平面阵列天线,提出采用一种基于目标覆盖区域量化的波束优化设计方法。该方法首先将目标区域进行量化,根据理想波束增益得到理想混合预编码向量;其次,以实际预编码向量与理想预编码向量之间的均方误差最小化为目标获得最优波束,进一步利用改进的正交匹配跟踪算法去拟合产生适合实际系统的波束成形矢量。仿真表明该波束设计方法在收敛速度和收敛精度上均优于传统方法,并可以获得更好的波束形状和波束增益,从而提高无人机目标覆盖区域内用户的通信质量。      

多波束小基站协作通信的资源分配和位置规划

针对小基站加载多波束阵列天线后协作提供通信覆盖的资源分配与位置规划问题,建立了以最小化基站总功耗以及基站间负载均衡为目标函数的多目标混合整数非凸优化模型;给出了一种迭代优化算法,将问题分为用户关联、功率分配和位置部署3个子问题,在固定基站位置和波束功率下通过改进的鲸鱼算法求解出用户与波束的关联关系,在此基础上利用连续凸逼近法和改进差分进化算法交替优化功率分配和基站位置部署。数值仿真表明,多波束小基站与所提迭代算法可灵活适应复杂业务需求分布,降低网络功耗和均衡基站间负载。可为小基站加载阵列天线增强通信覆盖提供参考。     

分布天线系统--一种新的热点区域容量解决方案

分布天线系统是后3G系统的主要研究方向之一,具有高系统容量与系统配置灵活的特性,本文提出了采用在WCDMA宏蜂窝网络中配置分布天线系统的方式来解决热点区域容量问题,分析与仿真结果表明在WCDMA宏蜂窝网络中配置分布天线系统是解决热点区域覆盖与容量问题的理想解决方案之一.     

基于实际城区场景的TD-LTE异构网络性能研究

本文对密集城区环境下的实际TD-LTE网络部署进行了研究.通过系统级仿真对宏小区/微小区、宏小区/家庭基站小区、宏小区/微小区/家庭基站小区3种异构网络的下行系统性能进行研究,并与单一宏小区的网络部署场景进行了比较.对实际城区环境下的信号传播损耗模型和用户分布进行了三维空间建模.通过比较4种不同TD-LTE网络部署方案下,位于不同楼层高度室内用户的性能,得出异构网络中不同小区(宏小区、微小区和家庭基站小区)的覆盖和容量特性.     

LTE网络典型场景下小微基站部署方案研究

在宏微协同,分层组网的LTE网络中,布局类宏站已基本部署到位,现阶段主要问题为城区深度覆盖问题和热点区域的容量问题,小微基站作为一种有效的解决手段被提了出来.本文介绍了小微基站的定义与分类,并详细说明了在五种典型场景中小微基站的部署方案.     

微站在工程建设中的应用研究

随着4G用户的快速增长,传统室外宏站覆盖已无法满足热点区域容量需求,加上宏站站址获取难度的增加,使得采用微基站解决覆盖已经逐渐成为发展趋势.本文分析了微站的引入需求和部署场景,对比阐述了一体化微站、分布式微站等不同产品形态,评估了微站用于补盲场景的覆盖性能,并对微站用于补热场景的频率、重选、切换等参数设置进行了研究,最后给出微站应用和宏微协同组网的建议.     

LEO卫星通信系统覆盖时间和切换次数分析

针对近地轨道(LEO)卫星移动通信系统,该文提出一种分析不同用户覆盖时间及切换次数的方法。在充分考虑地面用户随机分布特性的基础上,建立了卫星和波束对随机用户的覆盖时间统计模型,推导了星间切换及波束间切换平均次数下限值的计算方法。最后通过铱星通信系统模型(包括铱星星座参数,地面站参数和阵列天线波束模型)对该方法进行了仿真分析,结果显示该方法能很好地近似用户随机覆盖时间统计特性及平均切换次数的下限值。     

微宏协同混合组网助力LTE网络

宏微协同组网,即在传统的宏蜂窝小区基础上引入低功率基站,简称微基站,补充覆盖和吸收热点地区话务,运营商利用这种宏微协同组网方式能够以更低廉成本为更多的通信用户提供高速数据业务。宏微协同组网根据通信频段的不同可分为同频组网和异频组网两种,而具体场景下的组网方式则需要根据不同运营商所拥有的频谱资源,通信网络的负荷等综合因素决定。文章将对同频和异频组网的利弊进行分析,并结合不同场景和不同组网策略下的测试数据,给出宏微协同组网时的频率使用建议。     

HOT SPOT RELIEF WITH EMBEDDED BEAM FOR CDMA SYSTEMS IN HAPS

This paper proposes a novel micro/macro beam coverage scheme used in High Altitude Platform System （HAPS） Code Division Multiple Access （CDMA） systems. A relief of traffic burden in hot spot areas is achieved by embedding micro-beams into the macro-beams at the hot spot locations, together with appropriate power ratio control and user ratio control. The simulation results show that the hot spot problem can be relieved efficiently with the presented configuration, and a higher and more stable system capacity is expectable despite the variation of user distribution.     

Adaptive Radio Resource Allocation for a Mobile Packet Service in Multibeam Satellite Systems

In this paper, we introduce an adaptive radio resource allocation for IP‐based mobile satellite services. We also present a synchronous multibeam CDMA satellite system using an orthogonal resource sharing mechanism among downlink beams for the adaptive packet transmission. The simulation results, using a Ka‐band mobile satellite channel and various packet scheduling schemes, show that the proposed system and resource allocation scheme improves the beam throughput by more than two times over conventional systems. The simulation results also show that, in multibeam satellite systems, a system‐level adaptation to a user's channel and interference conditions according to user locations and current packet traffic is more efficient in terms of throughput improvement than a user‐level adaptation.     

平流层CDMA系统不同位置小区上行链路系统容量的研究及解决方案

分析了平流层CDMA系统位于平台下方不同位置的各小区的上行链路系统容量分布情况,仿真证明小区离平台越远,所受系统间干扰越大,系统容量越低;提出了一种平衡系统容量的方案,即在远离平台,系统容量需求大的小区采用地面基站和平流层基站协同工作的方式来降低平台基站所受的小区内干扰,从而减轻系统间干扰,增加对系统容量的影响,仿真结...     

A multimode CDMA with reduced intercell interference for broadbandwireless networks

This paper investigates the application of CDMA to broadband wireless access systems commonly known as LMDS networks. After a review of the intercell interference in the emerging LMDS networks based on TDMA, we analyze the interference in CDMA-based networks and show that, while conventional CDMA is superior to TDMA in terms of the worst-case interference on the upstream channel, it turns out to be inferior to TDMA in terms of interference on the downstream channel. Next, based on the observation that strong interference occurs only for a small range of user locations, we introduce a multimode CDMA concept that efficiently handles this interference by assigning orthogonal spreading sequences whose number and length are a function of the user position with respect to the base station. We show that in terms of worst-case SIR, the proposed technique leads to a significant improvement with respect to conventional CDMA and TDMA     

Adaptive cell sectorization for CDMA systems

Given the user distribution in a cell, we investigate the two problems of how to appropriately sectorize the cell such that we minimize the total received power and the total transmit power of all the users, while giving each user acceptable quality of service in both cases. For the received power optimization problem, we show that the optimum arrangement equalizes the number of users in each sector. The transmit power optimization is formulated as a graph partitioning problem that is polynomially solvable. We provide an algorithm that finds the best sectorization assignment as well as the optimal transmit powers for all the users. The computational complexity of the algorithm is polynomial in the number of users and sectors. For both the received power optimization and the transmit power optimization, under nonuniform traffic conditions, we show that the optimum arrangement can be quite different from uniform cell sectorization (equal width sectors). We also formulate and solve the transmit power optimization and cell sectorization problem in a multicell scenario that would improve the capacity of a hot spot in the network. We observe that, with adaptive sectorization, where the sector boundaries are determined in response to users' locations, received and transmit power savings are achieved, and the number of users served by the system (system capacity) is increased compared to uniform sectorization of the cell     

A Novel Detection Algorithm Efficient for Turbo Coded CDMA Signals in Detect and Forward Cooperative Channels

In this paper, a new detection algorithm is proposed for turbo coded Code Division Multiple Access (CDMA) signals in detect and forward cooperative channels. Use of user cooperation makes much improvement in the performance of CDMA systems. Due to the special structure of CDMA systems, cooperative schemes increase the sum and cutoff capacities of CDMA based wireless systems and improve the quality of user-partner link which enhances the overall performance of the system. In this paper, a new combining scheme is proposed that makes the receiver more robust against the decision errors in the partner link. This structure is simulated for punctured 1/2 rate 4 states turbo code in a channel with first order Markov time variation and different Rice factor variances. Through various simulations, it is shown when the channel estimates are available in the partner and receiver, the cooperation between users provides much diversity gain especially while using the new proposed combining algorithm.     

Hot-spot traffic relief with a tilted antenna in CDMA cellularnetworks

Direct-sequence code division multiple-access (DS-CDMA) cellular networks are highly promising in terms of their potential to provide more capacity than an advanced mobile phone system (AMPS). However, heterogeneous traffic loading causes traffic congestion in a CDMA hot-spot. This paper presents a tilted antenna mechanism for sectored cells in CDMA cellular networks to relieve the congestion in a hot-spot sector. The fixed antenna-tilted mechanism, which only tilts the hot-spot antenna, can provide the merit of traffic balancing. Besides, we design a dynamic antenna-tilted mechanism in which tilting the antennas of the hot spot and its adjacent cell sectors is based on varying the signal-to-noise ratio (SNR). The dynamic mechanism can automatically tilt the antenna corresponding to the variation of traffic. Consequently, more capacity can be provided than in a fixed tilting mechanism, which only tilts the hot-spot antenna. Another benefit is the traffic-balancing effect with a tilted-antenna mechanism that reduces the transceivers of a hot-spot base station. Therefore, extra facilities are unnecessary for the hot spot than for a normal or light traffic sector     

Optimising CDMA Cell Planning with Soft Handover

Soft handover (SHO) is one of the fundamental features of code division multiple access (CDMA) systems such as universal mobile telecommunication system (UMTS), and it is affected by the placement and density of cells. Inclusion of soft handover in optimization models for UMTS and CDMA cell site selection and configuration has previously been very limited but it is important for coverage because it can provide gain to the user. Some authors have excluded SHO on the basis of tractability while others have found that omitting SHO in planning gives adequate solutions. As such the incorporation of SHO remains an important component for definitive investigation in optimisation models for cell planning. In this paper we focus on the problem and effect of including SHO in cell planning optimisation. We introduce a new cell planning optimisation model that explicitly incorporates SHO and reduces computational complexity. Exact results can be obtained when the orthogonality factor is zero, while a conservative approximation of interference is used to generate lower bounds on coverage in the general case. We demonstrate the tractability of this model and show that it leads to improved lower bounds for coverage maximisation in network planning.     

Adaptive interference suppression for CDMA overlay systems

It has been proposed that CDMA systems can be assigned to spectral bands which are presently occupied by narrowband users to further increase spectral capacity. Such CDMA overlay systems could provide new options for efficient utilization of the spectrum with minimal disruption to existing narrowband users, especially if adaptive interference suppression techniques are utilized in the spread spectrum receiver. Previous studies have defined the SNR improvement ratio which can be achieved for tone interferers and for narrowband interferers for which the center frequency of the interference is at the carrier frequency of the CDMA signal. In this paper the bit-error-rate (BER) performance of the mobile-to-base link of a CDMA system for a single narrowband user which occupies a significant portion of the CDMA bandwidth is evaluated. It is shown that the narrowband model used in previous studies does not apply in this case, especially for the large, effective, bandwidths which are characteristic of the interferers in the overlay system. The dependence of the BER on the filter order, the bandwidth of the interference, and its center frequency relative to the CDMA carrier frequency are defined. Additionally the increase in BER for a digital implementation of the adaptive suppression filter relative to the optimal Wiener filter is characterized with respect to the adaptive time constant and the quantization errors due to finite wordlength. It is shown that these implementation errors can be made negligible compared to the errors which are characteristic of the optimal Wiener filter. Analytic results are validated by simulation for typical system parameters