With the rapid development of the wireless communication industry and the rapid growth of wireless communication users, the market has put forward higher requirements for the continuous improvement and update of wireless communication technologies. How to improve the efficiency of wireless spectrum is the core problem that various new technologies are facing in recent years. Especially when China fully enters the WTO, the mobile communication industry will face new challenges as it is fully integrated with the world. At present, the input of frequency resources has become an important part of the capital input costs of operators around the world. It can be predicted that in China, the days when frequency resources are no longer used for free are not far off. Therefore, how to adopt new technologies to improve the efficiency of the use of limited frequency resources has become a topic of increasing concern. The world's first mobile phone developer, known as "the father of the world's mobile phone," Mr. Martin Cooper once said, "We are not lacking in frequency. What we lack is the efficiency of frequency use." In recent years, with With the rapid development of microelectronics technology, smart antenna technology has been successfully applied to mobile communication systems as a new technology to effectively solve this problem, and the wireless signal transmission has been greatly improved by high-speed spatio-temporal processing of wireless digital signals. It greatly increases the capacity and coverage of the system, which greatly improves the efficiency of spectrum usage. First, the principle of smart antenna Smart antennas were initially used in radar, sonar and military communications and were later introduced into mobile communication systems. Smart antennas typically include a beam-switched smart antenna (Switched BeamAntenna) and an adaptive array smart antenna (AdapTIveArrayAntenna). The adaptive array smart antenna utilizes the baseband digital signal processing technology to adaptively shape the receiving and transmitting beams of the base station through advanced algorithm processing, thereby achieving the purpose of reducing interference, increasing capacity, expanding coverage, and improving wireless data transmission rate. . At present, adaptive array smart antennas have become the mainstream of smart antenna development. The mobile communication channel transmission environment is harsh. The interference and multipath fading phenomena in the actual environment are extremely complicated, inter-symbol interference (ISI) caused by multipath fading, delay spread (ISI), and FDMATDMA system (such as GSM) due to frequency reuse (CCI, Co-Channel Interference), MAI (MulTIple Access Interference) in CDMA systems, etc. all degrade link performance and system capacity. Adaptive array antenna technology is one of the most advanced wireless technologies in the past 30 years. It uses baseband digital signal processing technology to generate spatially oriented beams, so that the main beam of the antenna, that is, the maximum gain point, is aligned with the direction of arrival of the user signal, side lobes or zero. The trap is aligned with the arrival direction of the interference signal, thereby bringing the maximum gain to the useful signal, effectively reducing the influence of the multipath effect, and at the same time achieving the purpose of deleting and suppressing the interference signal (as shown in FIG. 1). The use of adaptive array antenna technology can bring many benefits, such as expanding system coverage, increasing system capacity, increasing data transmission rate, improving spectrum utilization efficiency, reducing base station transmission power, saving system cost, reducing inter-signal interference and electromagnetic environment pollution. . The adaptive array antenna generally adopts a 4-16 antenna array structure. In the FDD, the array elements are separated by 1/2 wavelength. If the array element spacing is too large, the received signals are correlated with each other; if too small, the pattern is unnecessary. The grating lobes are generally half wavelength. In TDD, for example, the array antenna spacing of the adaptive array antenna in the PHS system of ArrayComm is 5 wavelengths. The wide spacing and narrower beam, and the TDD mode in the PHS system make it easier to perform positioning processing. Even if there are many side lobes, there are fewer adverse effects due to the small number of users and channels. The array elements are distributed in a straight line, a ring shape, and a flat type. The adaptive antenna is the main type of smart antenna, and can realize an omnidirectional antenna to complete user signal reception and transmission. The adaptive array antenna system uses digital signal processing techniques to identify the direction of arrival of the user signal and form the main beam of the antenna in this direction. The adaptive array antenna provides different spatial channels according to different spatial propagation directions of the user signals, which is equivalent to the cable for signal transmission, and effectively overcomes the influence of interference on the system. Although the antenna array is a very important device for the RF front end, the most important part of the adaptive array antenna technology is the baseband processing portion. The baseband portion weights and combines the signals received by the adaptive antenna array to maximize the signal to interference plus noise ratio. The baseband processing part uses a complex adaptive algorithm. At present, there are many algorithms for time domain and airspace. For example, the optimal weighting algorithms for obtaining antennas through time domain are: minimum mean square algorithm (LMS), direct inversion of sampling covariance matrix (DMI), recursive least mean square Error (RLS) algorithm, constant modulus (CM) algorithm, etc. Algorithms for obtaining signal arrival azimuth (DOA) estimation by analyzing the spectrum in the airspace include: multi-signal classification (MUSIC) algorithm, rotation invariant technique signal parameters Estimation method (ESPRIT) algorithm, etc. The following figure shows a simple schematic of an adaptive smart antenna implementation:
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