Measure the test taker's knowledge about the principles of CDMA wireless network technology.

This article mainly introduces the principles of CDMA wireless network technology in detail, and gives you a detailed explanation. I believe this article will help you.

In fact, the CDMA technology has been used long ago. It may be that, for various reasons, the introduction of China has not been able to fully leverage its advantages. So what are the specific advantages of it? What is the principle? I will not go into detail here. Please refer to the following.

CDMA, short for Code-DivisionMultiple Access, is an advanced wireless Spread Spectrum Communication Technology in the digital mobile communication process field, this technology features high spectrum utilization, good speech quality, strong confidentiality, low disconnection rate, low electromagnetic radiation, large capacity, and wide coverage, it can meet the market's high requirements on mobile communication capacity and quality.

We may know some of the advantages of CDMA, but we may not know much about its principles. The CDMA wireless network technology is based on the Spread Spectrum Technology. The information data that needs to be transmitted with certain signal bandwidth will be modulated with a high-speed pseudo-random code with a bandwidth greater than the signal bandwidth, in this way, the bandwidth of the original data signal is extended and then modulated and sent by the carrier. The receiving end uses identical pseudo-random codes for processing with the received bandwidth signal, and converts the broadband signal into the narrowband signal of the original information data for de-expansion to realize the information communication process.

CDMA was first launched by Qualcomm in the United States and quickly developed. In China, CDMA wireless networks are a network pushed by China Unicom.

Advantages of CDMA Technology

With the rapid development of CDMA wireless networks, in addition to market factors, the advantages of CDMA wireless networks play a decisive role. Their advantages are mainly reflected in the following aspects:

(1) Spread Spectrum Communication. Because CDMA is a type of Spread-Spectrum Communication, it has strong anti-interference ability, can achieve broadband transmission, and has good anti-fading ability. In addition, the useful signal power transmitted in the channel is lower than the power of the interference signal, so the signal can be well hidden in the noise, and the confidentiality is better.

(2) Multiple diversity methods are adopted. In addition to the diversity of traditional spaces, RAKE Receiving Technology is also used in mobile stations and base stations, which is equivalent to time diversity.

(3) Speech activation and fan Partitioning technologies are used. Because the capacity of the CDMA system is directly related to the interference, using voice activation and sector technology can reduce interference and increase the capacity of the entire system.

(4) soft switchover is supported by the Mobile Station. Seamless switching ensures the continuity of calls. The mobile station in the switching area receives signals from multiple base stations by means of diversity, reducing its transmission power and thus reducing interference to the surrounding base stations.

(5) good compatibility. Due to the high bandwidth of CDMA and the wide distribution of power in the spectrum, the interference is very small for narrowband analog systems and the compatibility between the two is good.

Key CDMA Technologies

The above briefly lists some of the advantages of CDMA wireless network technology. Of course, these advantages are inseparable from the advanced technology adopted by CDMA. The key technologies include:

(1) RAKE Receiving Technology

In GSM mobile phones, the multi-path effect can only be offset by the time domain balancer, And the transmit power cannot be reduced by the superposition of the energy of multiple signals. In the CDMA wireless network mobile communication system, the RAKE receiving technology is adopted. Due to the wide signal bandwidth, the time can be used to identify relatively small multi-path signals, weighted adjustment is performed on the differentiated multi-path signals to enhance the synthesized signal, thus reducing the negative impact of the multi-path fading channel to a large extent.

(2) Smart Antenna Technology

Smart antennas have high complexity and consume a large amount of energy. They were mostly confined to applications in base stations earlier, and were gradually introduced to mobile platforms. Smart Antennas can significantly improve the performance of third-generation mobile devices. Therefore, they have become one of the hot topics in the research of third-generation mobile communication systems. The TD-SCDMA System of China's independent property rights also adopts the Intelligent antenna technology.

Smart Antenna Technology performs airspace processing on received signals to reduce the impact of multi-access interference on signals. It adopts a sector antenna with a certain direction and hollows out other interference from a certain angle, this improves system performance.

(3) multi-user detection technology

Multi-user detection technology can effectively suppress multi-access interference. It has the following advantages: Improving bandwidth utilization and inhibiting multi-path interference; eliminating or mitigating the near-far effect, and reducing the high precision of operation control, it can simplify the operation control, make up for the impact of unsatisfactory mutual correlation between spread spectrum codes, reduce the transmission power, prolong the battery time of the Mobile Station, and reduce the electromagnetic radiation of the mobile station; Improve the system performance, increase the system capacity and the coverage of the residential area. Of course, it also has some limitations, such as high complexity and system latency.

(4) Efficient code compilation technology

In the communication system, code compilation is a basic technology. In the main proposal of the third-generation mobile communication system (including WCDMA and CDMA), apart from using convolution and intertwined technologies similar to the IS-95 CDMA system, it also uses the Turbo encoding technology and RS-convolution cascade code technology. These technologies have high compilation efficiency.

(5) Power Control Technology

In a CDMA wireless network system, users use the same frequency band and interfere with each other. Any user is an interference source for other users. However, power control can eliminate this impact to some extent and has become one of the most important core technologies in the third generation communication standards. Common CDMA power control technologies can be divided into three types: Open-loop power control, closed-loop power control, and outer ring power control. In the WCDMA and CDMA 2000 systems, the downlink channel uses open-loop, closed-loop and outer-ring power control technologies, and the downlink channel uses closed-loop and outer-ring power control technologies.