摘要
一般的智能天线(SA)波束赋形都是基于移相器的载波移相波束赋形方案,其问题是工程难度大、没有充分利用基带信号处理技术。通过对SA波束赋形基本原理的研究,给出了QPSK基带信号波束赋形的数学表达式,提出了QPSK基带信号幅度加权波束赋形(BAWB)的概念,并给出了相应的电路实现框图。基于该QPSK基带幅度加权波束赋形原理,研究了CDMA系统中不同码道(用户)组合情况下QPSK调制信号对SA定向波束赋形的影响。研究发现:当采用多码道发送时,不同方向的主瓣、强的旁瓣会相互影响,影响了CDMA系统的波束空间分辨率,特别是当两个用户比较靠近或发送数据极性快速变化时,其相互干扰有所加强。于此同时,研究也表明了CDMA系统中多用户干扰(MAI)与系统性能之间的辩证关系,一方面多用户干扰使系统容量下降;而另一方面,MAI又是维持系统稳定工作的必要条件。
The carrier phase-shift directional beamforming scheme is widely employed in smart antenna （SA） system. However, the disadvantage of the phase shifter scheme is that it can not make full use of the technology of base-band signal processing and its complexity in engineering implementation. According to the study of the basic principle of SA directional beamforming, the mathematical model of SA directional beamforming realized on base-band is obtained firstly. With the mathematical model, the concept of base-band amplitude weighting beamforming （BAWB） is proposed as well as the corresponding circuit implementation unit. Based on the presented BAWB scheme, the beamforming performance analysis in CDMA system, where multiple code channels are transmitted simultaneously, is performed. The results of numerical analysis show that, due to the interaction among different code channels with different directions and the impact of strong side lobe on major lobe, the resolution of major lobe is greatly decreased. The situation is worse when the data of different code channels change lastly. At the same time, the dialectical relationship between the multi-access interference （MAI） and the system performance in CDMA is also discovered. On one hand the MAI limits the enhancement of CDMA system capacity; and on the other it is also the requirement to maintain the stability of system.
出处
《电波科学学报》
EI
CSCD
北大核心
2010年第3期505-512,共8页
Chinese Journal of Radio Science
基金
国家973项目(2007CB310607)
863关键项目(2009AA011302)
东南大学国家移动通信重点实验室开放基金(N200604)
