通信工程文献翻译——一、CDMA

CDMA是Code Division Multiple Access的英文缩写，中文翻译为码分多址。CDMA是用于数字蜂窝移动通信的一种先进的无线扩频通信技术，它能满足近年来运营者对大容量、廉价、高质量的移动通信系统的需求。CDMA中的多址可以被理解为一个滤波问题，多个用户同时使用同一频谱，然后采用不同的滤波器和处理技术，将不同用户的信号互不干扰地接收和解调出来。移动通信一般采用三种多址方式：FDMA（频分多址）、TDMA（时分多址）和CDMA（码分多址）。FDMA就是信号功率被集中在频域中一个相对的窄带中传输，不同信号被分配到不同频率的信道里，发往和来自邻近信道的干扰用带通滤波器限制，这样在规定的窄带里只能通过有用信号的能量，而任何其他频率的信号被排斥在外。模拟的FM蜂窝系统采用的就是FDMA方式。TDMA就是一个信道由一连串周期性的时隙构成，不同信号的能量被分配到不同的时隙里，利用定时选通来限制邻道的干扰，从而只让在规定时隙中有用的信号能量通过。现在使用的TDMA蜂窝系统实际上都是  FDMA和TDMA的组合。CDMA就是每一个信号被分配一个伪随机二进制序列进行扩频，不同信号的能量被分配到不同的伪随机序列里。在接收机里，信号用相关器加以分离，相关器只接收选定的二进制序列并压缩其频谱，将有用信号的信息识别和提取出来。    CDMA技术作为一种抗干扰的通信手段，很早就在军事通信中得到了应用，但是将   CDMA技术应用于民用的数字蜂窝移动通信系统，还是80年代末才由美国Qualcomm公   司实现的。QCDMA系统中采用了许多先进的技术从而保证了系统性能的优势，其标准称为IS-95系列，包含多个标准。多径衰落是移动通信系统需要克服的主要问题，CDMA系统采用了多种形式的分集，从而很好地解决了这一问题。CDMA系统采用符合交织、检错和纠错编码等方法实现了时间分集；CDMA系统的信号带宽是1.25MHz，起到了频率分集的作用；基站使用多付接收天线，基站和移动台都使用了Rake接收机技术，软切换时，移动台和基站同时联系，从中选取最好的信号送给交换机，从而起到了空间分集的作用。CDMA系统的容量主要受限于系统移动台之间的相互干扰，如果每个移动台的信号在到达基站时都保持所需的最小信噪比，系统容量将达到最大值。CDMA功率控制的目的就是使每个用户即维持高质......

CDMA Code Division Multiple Access English abbreviations, Chinese translation for code division multiple access. CDMA is for an advanced wireless spread spectrum communication technology of digital cellular mobile communication, it can meet the demand of mobile communication system operators of large capacity, low-cost, high quality in recent years. Multiple access in CDMA can be understood as a filtering problem, multiple users using the same frequency at the same time, then the filter and different processing technologies, the signals of different users do not interfere with each other to receive and demodulate. Mobile communication generally use three access methods: FDMA (frequency division multiple access), TDMA (time division multiple access) and CDMA (code division multiple access). FDMA is the signal power is concentrated transmission in the frequency domain in a relatively narrow band, different signals are assigned to different frequency channel, sent to and from the adjacent channel interference using band-pass filter restriction, so only through the useful signal energy in the narrow band signals, and any other frequencies are excluded outside. Simulation of the FM cellular system uses is FDMA. TDMA is a channel by slot a series of periodic structure, different signal energy is distributed to different time slots, the time gate to limit the interference of adjacent channel, thus only the provisions of signal energy is useful in the slot. TDMA cellular system currently in use are actually a combination of FDMA and TDMA. CDMA is that each signal is assigned a pseudo random binary sequence spread spectrum, different signal energy is distributed to different pseudo-random sequences. At the receiver, signal correlator to separation, binary sequence correlators receives only the selected and compression of the spectrum, the useful signal information recognition and extraction. CDMA technology is a kind of anti noise communication means, very early in the military communication has been applied, but the application of CDMA technology in digital cellular mobile communication system in civil, or at the end of the 80's by the American company Qualcomm implementation. QCDMA system adopts many advanced technologies so as to ensure the system performance, the standard known as IS-95 series, contains ......