Antennas Achieve Smart Wireless Technology

I'm sure everyone knows about the three major wireless 3G standards. Therefore, there is a unique and advanced technology in the TD wireless technology, which is different from the other two technologies-smart wireless technology, that is, smart antenna technology.

The Smart Antenna, formerly known as the Adaptive Antenna Array AAA and Adaptive Antenna Array), was initially used in Radar, sonar, and military aspects to complete spatial filtering and positioning, the familiar phase-mounted Radar is a simple adaptive wireless array. Mobile Communication Researchers give adaptive wireless arrays used in mobile communication a more attractive name: smart wireless technology, the English name is smart antenna or Intelligent antenna.

1. Basic Structure of smart Wireless

As the name suggests, an adaptive antenna array consists of multiple antenna units. Each antenna is followed by a weighting device multiplied by a certain coefficient. This coefficient is usually a plural number, which regulates both the amplitude and the phase, in the phased array radar, only the phase can be adjusted), and then merge with the adder. Smart Antennas with such structures can only process airspace, while smart antennas with airspace and time domain processing capabilities are more complex in structure, each antenna is followed by a delay-directed weighted network structure, which is the same as that of the Time-city FIR balancer ). Adaptive or intelligent means that these weighting coefficients can be adjusted properly. The above is actually the structure of the smart antenna used as the receiving antenna. When it is used for transmitting, the structure changes slightly. The weighting device or the weighted network is placed before the antenna, and there is no merging device.

2. How smart wireless technology works

Assume that the narrowband conditions for antenna transmission are met, that is ~ The response output of the Human radiation signal in each antenna unit only has a phase difference without the amplitude change. These phase differences are determined by the length difference between the human radiation signal and the route taken by each antenna. If the human radiation signal is a plane wave with only one direction), the phase difference is uniquely determined by the carrier wavelength, human radiation angle, and antenna location distribution. ~ The rough weight value indicates the intensity of a certain human shot signal. The signal intensity of different human shot angles varies depending on the phase difference in the antenna.

An image taken from the vertical coordinate of the output gain dB of the smart wireless technology corresponding to the X-coordinate of the human angle is called the pattern antenna term. The pattern of the smart antenna is different from that of the omnidirectional omni -) the antenna is ideal for a straight line), and is closer to directional) wireless pattern, that is, the main lobe, the secondary debate side lobe). However, compared with smart antennas, smart antennas usually have a narrow main valve, in terms of flexible master, sub-flap size, positional relationship, and large antenna gain wireless terms, an important indicator of the antenna is the ratio of the maximum gain to the average gain in all directions ), in addition, the biggest difference with fixed antennas is that different weights usually correspond to different patterns. We can change the weights to select the appropriate pattern. The antenna Pattern ).

Next we will explain what 10 thousand means as a proper pattern to maximize the useful signal. To suppress interference signals, the most intuitive thing is that we can align the primary debate with the human direction of the useful signal, and the lowest gain point in the pattern is called the zero trap) with the direction of the interference signal. Of course, this is only an ideal situation. The actual wireless communication environment is very complicated. There are many interference signals and there are multi-path transmission, while the number of elements of the antenna array does not have much flexibility) useful signals and interference signals may not differ much in the direction of human radiation, which makes the previous scheme not feasible. However, the pursuit of the largest signal-to-noise ratio SINR is still the final goal. The actual working principle of the smart wireless technology is more complex than described above. In particular, when performing empty and time joint processing, it is best to explain it from the perspective of signal processing, especially adaptive filtering, this requires strong theoretical and professional background knowledge, which is not described here.

3. Use of smart Wireless Technology

The communication environment of mobile communication channels is poor. ISIInter-Symbol Interference is caused by multi-path fading and delay expansion. FDMATDMA systems such as GSM) the same channel Interference CCI introduced by Frequency Multiplexing, co-ChannelInterference) and MAIMultiple Access Interference in CDMA systems all degrade the key-channel performance and system capacity. We are familiar with balanced, code matching filtering, and RAKE Receiving, channel coding techniques are designed to combat or reduce their impact. These technologies actually use time and frequency domain information. In fact, the latency sample delay version for useful signals is different from that for interference signals in the time and frequency domains. Meanwhile, there are also differences in the spatial Direction of arrival (DOA) and Direction ofArrival, diversity antenna dlversty), especially slice antenna sector antenna) can be seen as a preliminary use of this part of resources, but to make full use of it only uses smart antenna technology.

Smart antennas are good scalability technologies. In the early stages of mobile communication development, operators always wanted to cover as many areas as possible with as few base stations to save investment. This meant that users' signals were arriving at the BTS base station for sending and receiving devices) it may have gone through a long transmission path, with a large path loss). In order to make the received useful signal not lower than the threshold, either increase the transmission power of the mobile station or increase the receiving gain of the base station antenna. Because the transmission power of the mobile station, especially the mobile phone, is usually limited, what is actually feasible is to increase the antenna gain, relatively speaking, it is easier to use smart wireless technology to achieve greater gain than to use a single antenna.

In the development of mobile communication, in order to expand the system capacity and support more users, it is necessary to contract the residential area range and reduce the frequency reuse coefficient to improve the frequency utilization. The common method is to split the residential area and divide the fan area, followed by an increase in interference, the original distance actually relies on path loss) effectively reduces the CCI and MAI by a large proportion. However, with the help of the difference between the useful signal and the interference signal in the incident angle, the smart antenna selects an appropriate combination of weights to form a correct antenna receiving mode, that is, aligning the main flap with the useful signal, low-gain sub-flap is aligned with the main interference signal, which can more effectively suppress interference and reduce the Frequency Multiplexing factor in a greater proportion, for example, making multiplexing Factor 3 possible in GSM) and supports more users in CDMA ). From some point of view, we can regard a Smart Antenna as a more flexible sector antenna with a narrower main flap.

Another advantage of smart antenna is that it can reduce the multi-path effect. In CDMA, the RAKE receiver can be used to separate and merge the multi-paths with a latency difference greater than one piece of code, with the help of smart antennas, we can further separate the multi-paths with non-classified but segmented latencies, so as to effectively reduce the multi-path effect.

The main purpose of the smart antenna technology is to improve the mobile communication channel more effectively, while the channel transmission environment of the Code Division Multiple Access system is essentially the same, in addition to the differences in specific algorithms, smart antennas can be widely used in various time division and code division multiple access systems, including the commercial second generation systems.

Another possible use of smart antennas is to locate emergency calls and provide higher positioning accuracy, because it can obtain information such as latency and intensity that can be used for positioning, it can also obtain the arrival angle information.