Analysis of the Influence of Wireless Channel of PHS System on Radio Wave Transmission
This paper analyzes the various effects of the wireless channel of the PHS system on the transmission of radio waves, and proposes the antenna technology used in the PHS system to improve the performance of the system, and looks forward to the development of the antenna technology of the PHS system in the future. PHS is the abbreviation of Personal Handyphone System, also known as "Little Smart". It operates in the 1.9 GHz band and uses a microcellular network structure, each of which can cover a range of 100-300 meters. It has been developing in China for five years. Since the first opening of the wireless local dialect in Yuhang City, Zhejiang Province in 1998, PHS has sprung up all over the country, because it can provide mobile phones at the price of local calls. The service has attracted a large number of users. By the end of 2002, the number of users has quickly exceeded 12.5 million. In 2003, it is very likely to reach 25 million. However, as a personal communication system using wireless technology, the wireless channel of the PHS system faces various problems, such as fast fading caused by multipath transmission, co-channel interference introduced by frequency reuse, etc. These problems are solved well. Bad will directly affect the quality of PHS network calls, which will have a huge impact on the development of PHS systems. This paper analyzes the basic ideas of using diversity reception, adaptive antenna, smart antenna and other technologies in PHS system, and improves the performance of PHS system. PHS belongs to the category of low-power systems. The base station's range of action is usually in the range of tens to hundreds of meters, so the impact of small-scale fading on the base station is very obvious. Small delay fading refers to the rapid fading of a wireless signal after a short or short distance propagation. This fading is due to the same transmitted signal propagating along two or more paths, and the signals arriving at the receiver with a small time difference interfere with each other. The three main effects of the problem are: * A sharp change in signal strength after short or short-term propagation; * On different multipath signals, there is random frequency modulation caused by time-varying Doppler shift; * Extension (echo) caused by multipath propagation delay. In the PHS system, diversity reception technology is employed as an anti-fading technique. The basic idea of ​​diversity reception techniques is that if two or more independent samples of a signal are selected, the fading of these samples is irrelevant. This means that the probability that all samples are below a given level at the same time is much less than the probability that any one sample is below that value. The probability that M samples are simultaneously below a certain level is Pm, where P is the probability that a single sample is below this level. Thus, we see that the signals that are properly combined from different samples are much lighter than the fading of any single sample. The advantage of diversity technology is that it improves system performance without increasing transmitter power. The diversity technology is divided into spatial diversity, frequency diversity, polarization diversity, etc. The base station antenna used by the PHS system adopts spatial diversity. Whether the diversity reception effect is good or not depends on the correlation degree of the two signal fading, and can be expressed by the correlation coefficient. The smaller the correlation coefficient is, the better the diversity reception effect is. The larger the correlation coefficient is, the worse the diversity reception effect is. For spatial diversity, the farther the two receiving antennas are apart, the smaller the correlation coefficient is, and the smaller the probability that the two antennas are simultaneously at the fading zero point. The antenna adopting the spatial diversity method depends on the ratio H of the antenna height to the distance between the antennas, that is, H=h/d. For the horizontal diversity antenna, H is the optimal empirical value of 11, and the optimal diversity gain can be obtained. . The spacing between the two antennas should be an odd multiple of half wavelength, and the distance of the base station antenna of the existing PHS system should be greater than 5 times. The optimal empirical value of antenna height and antenna spacing is shown in Table 1: The PHS is networked using a micro-zone system, which divides the entire service area into a number of micro-areas that are organically combined to meet the needs of mobile communication throughout the wireless area. The PHS system adopts dynamic channel allocation technology in each cell, and the cell station automatically allocates the best frequency channel according to the call establishment process. However, the frequency reuse of the PHS system brings about the problem of co-channel interference. The existence of co-channel interference reduces the frequency utilization of the system, resulting in a decrease in system capacity. In the PHS system, if the adaptive antenna technology is used, the same-frequency interference can be reduced. The signals of different users in the adaptive antenna are first synthesized into one signal by the multiplexer, and then the signal is divided into D channels (D is the number of antenna elements), and these signals are weighted by coefficients W1, W2...Wn, respectively, and then sent Go to each antenna unit. The composite signal waveform on each antenna unit is the same, except that the amplitude and phase are different. The PHS base station using the adaptive array antenna technology can adjust the phase and amplitude of the transmitted signal of each antenna by adjusting the phase and amplitude of the signal transmitted by each antenna, and the antenna gain in the interference direction is maximized, and the antenna gain in the interference direction is reduced. To reduce interference and improve the carrier-to-interference ratio (C/I) by up to 10dB. After the adaptive antenna technology is adopted, the field strength between the base station and the base station is significantly different, and the interference of the mobile phone is reduced, thereby avoiding the phenomenon of repeated switching. Actual test results in Japan: The frequency utilization of the adaptive antenna base station is four times higher than that of the ordinary base station. That is to say, under the same frequency interference degree, the adaptive antenna base station can have 3 times more base station density than the ordinary type base station. The high anti-interference capability of the adaptive antenna base station makes it more effective in solving the contradiction between traffic volume and frequency conflict in the high traffic area than the ordinary base station. Since the 1990s, a new research hotspot in the field of mobile communications has emerged—smart antenna technology, which improves the communication quality of systems, alleviates the contradiction between the growing development of wireless communication and insufficient spectrum resources, and reduces the overall cost of the system and improves system management. , all have unique advantages. Japan's tests in the PHS system show that the use of smart antennas can reduce the number of base stations. Due to the limited communication distance of PHS and other systems, many base stations need to be established. If smart antenna technology is adopted, the cost can be reduced. The smart antenna first divides each user signal into D channels (D is the number of array units), and then weights each user signal separately to generate MxD signals (M is the number of users), and finally combines the corresponding M signals into All the antenna elements are sent to each antenna unit. Since the signals of the antenna elements are combined by different weighting coefficients of the M-channel signals, the waveforms of the signals of the respective antenna elements are different, and M channel patterns are formed. For each channel, when only the A point signal exists, the channel direction map of point A can be obtained by weighting W11, W12...W1D. When only the point B signal exists, W21, W22...W2D can be selected for weighting. The channel pattern of point B, when two signals exist at the same time, the superposition principle of the field can be known that the power pattern of the smart antenna is the superposition of two channel patterns, thereby ensuring that two user signals share a conventional channel, thereby realizing Space division multiplexing. In the smart antenna system, each channel beam is uncorrelated, and the tracking signals of each channel beam region can be independently adjusted. The channel beam that can be generated is independent of the number of antenna element arrays, and each user signal corresponds to one set (D). The weighting device can meet the requirements of increasing system capacity and suppressing interference. The greatest attraction of smart antennas is that they can use different signal directions to separate different signals, thus spatially multiplexing the traditional channels and multiplying the system capacity. In summary, diversity reception and adaptive antennas are two mature antenna technologies, which have been widely used in PHS systems and have achieved good results. As a new antenna technology, smart antenna is currently in the development stage. It is the biggest hope to further improve the capacity and quality of mobile communication systems. The prospects are bright, but there are many difficulties and problems. It is worthy of further research and development. Development. Fiber Optic Components,Parts Of Fiber Optic Cable,Fibre Optic Connector,Parts Of Optical Fiber Cixi Dani Plastic Products Co.,Ltd , https://www.dani-fiber-optic.com