The original smart antenna technology was mainly used for radar, sonar, and military anti-jamming communications to perform spatial filtering and positioning. In recent years, with the development of mobile communication and the deepening of research on mobile communication wave propagation, networking technology, antenna theory, etc., modern digital signal processing technology has developed rapidly, and the processing capacity of digital signal processing chips has been continuously improved, using digital technology. It is possible to form an antenna beam by the baseband, and the reliability and flexibility of the antenna system are continuously improved.
Smart antenna technology can be used in mobile communication environments with complex wave propagation. The principle of the smart antenna is to direct the radio signal to a specific direction, and generate a spatial directional beam, so that the main beam of the antenna is aligned with the DOA (DirecTIonofArrinal) of the user signal, and the side lobes or nulls are aligned with the arrival direction of the interference signal to achieve full and efficient use. Move the user signal and delete or suppress the purpose of the interference signal. At the same time, the smart antenna technology utilizes the difference in signal space characteristics between mobile users, and receives and transmits multiple mobile user signals on the same channel through array antenna technology without mutual interference, making the use of radio spectrum and signal transmission more efficient. . The use of smart antennas can meet the needs of service quality and network expansion without increasing system complexity. In fact, it extends communication resources beyond the time domain, frequency domain, or code domain to the spatial domain, and is a space division multiple access (SDMA) system. The third generation of mobile communication standards organizations have recognized the important role of smart antennas in reducing network interference. Therefore, in 3G standards such as WCDMA and cdma2000, the terms supporting smart antennas have emerged, and smart antennas have become an important part of 3G.
At present, except for a very small number of countries with formal 3G commercial networks, China and most regions are still in the trial network stage. It is expected that the GSM network will remain the main bearer network for mobile services in the next two to three years. The number of users of GSM networks in large and medium-sized cities in China has increased by about 20% per year. In some hotspots, the traffic carried per square kilometer has even reached 1500 erl. The capacity of the GSM network is completely limited by the frequency resources of the network in a fully equipped environment. In a limited bandwidth, the network capacity must be increased, and the frequency reuse distance can be reduced. The closer the frequency reuse distance is, the network is. The higher the interference.
According to the current experience of GSM network operation, under the premise of ensuring the use of appropriate cell signals, in order to maintain the network quality within the range of voice quality (clear and no noise) acceptable to the customer, the wireless network must be carried out according to the carrier-to-interference ratio of 18 dB or more. planning. Whether in accordance with the traditional 4/12 frequency reuse method or MRP or 1*3 frequency reuse mode, the frequency is planned at a maximum carrier-to-interference ratio of 12 dB under the existing bandwidth, and the remaining carrier-to-interference ratio can only be relied on. The gain of dynamic power control, frequency hopping, discontinuous transmission, etc. is compensated. Reducing the interference level of the network and increasing the carrier-to-interference ratio of the system are very important in the GSM high-speed growth period, especially after the GPRS service is officially commercialized. Therefore, many GSM manufacturers and operators are considering using the smart antenna in the 3G standard. In the GSM network, some companies, such as Ericsson and Medway, have carried out corresponding research and experiments in local areas with high traffic, and achieved satisfactory results.
Second, the principle of smart antennaSmart switching antennas with high gain, narrow beam phase array antennas are replacing traditional sector antennas. A multi-beam antenna panel consists of four 30? The beam (or 22.5?) can thus receive less interference signals than standard sector antennas when receiving signals, thus improving the quality of the received signal. According to theoretical calculations, an average C/I value including four switchable narrow beam antennas can be increased by 6 dB over a conventional 3-sector antenna system.
The smart antenna system continuously performs beam selection on a time slot basis to ensure the voice quality of the user during a call.
The smart antenna used for the test consists of two parts, a multi-beam array antenna and a dual-polarized antenna. These two parts can be packaged in one antenna plate or separately. The multi-beam array antenna is a horizontal 3dB lobe width of 22.5 formed by an antenna array of 6-8 antenna arrays. A multi-beam array antenna, generally referred to as a narrow-beam antenna, has a main function of transmitting a traffic channel signal (TCH) and receiving an uplink signal; a dual-polarized antenna comprising two horizontal 3 dB lobe widths of 90? An antenna, generally referred to as a wide beam antenna, functions as a signal that transmits a control channel (eg, BCCH, SDCCH, CBCH, etc.).
Third, the application example of smart antenna in GSM network1. Cell selection for introducing smart antennas
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