Development History of Fixed Wireless Access Network Technology

There are many things worth learning about in the Fixed Wireless Access Network. Here we will mainly introduce the development history of the fixed wireless access network technology. In recent years, the demand for Internet access by communication users has continued to grow rapidly, while the construction progress of fixed wired network PSTN with Asymmetric Digital user line ADSL and cable modem is not fast, as a result, Fixed Wireless Access to FWA and Fixed Wireless Access are considered more in the last kilometer of the urban communication Access network ). Of course, this will be a broadband wireless access network.

The so-called multi-point multi-channel allocation Service (MMDS), Multipoint Multichannel Distribution Service) fixed wireless network is a typical example of FWA. It uses frequencies below 5 GHz, such as 3.5 GHz and GHz, to set up a fixed transceiver Base Station BTS and Base Tranceiver Station within a certain region ). In addition to the original telephone communication, many users are eager to connect to Aintemet so that they can communicate with other users through e-mails and frequently request a large amount of data information from appropriate websites, the above broadband FWA can be fully utilized to install appropriate antennas and email receiving machines on the roofs of their offices and home locations, after a base station BTS, which is close to them and several kilometers away, it connects to a fixed urban communication network to achieve the required communication purpose. This does not have to rely entirely on the traditional lead-clad copper cable access network, and does not have to wait for the construction of ADSL and modem line equipment to complete, and the wireless FWA can ensure the same satisfactory service performance, it has the advantages of Fast Construction, easy scalability, simple maintenance, and low cost, and is easy to cater to the needs of the majority of communication users. In areas that do not have a wired access network, or areas where it is difficult to create a wired access network, the fixed wireless access network can give full play to its advantages, and the construction and application are given priority. This is why such technology has been vigorously promoted internationally in recent years. However, the New Fixed Wireless Access Network must be FWA with a wide bandwidth to meet the needs of the user's development of data communication trends. As a matter of fact, the wireless cellular network of mobile communication has evolved from the current second generation to the coming third generation, and even to the far-reaching fourth generation. It also attaches great importance to the construction and development of broadband networks, meet the needs of users to increase their use of high-speed data communication and access to the Internet.

Generally, in order to enable optimal propagation of radio waves in the air, fixed wireless access to FWA lines tends to achieve "Line of Sight transmission" LOS, Line of Sight ). In this article, we mentioned that a user installs a receiving and sending antenna on the office and home roof to communicate with the base station BTS through LOS. In recent years, FWA has made significant improvements in technical design, striving to achieve "Non-line-of-sight transmission" NLOS and Non-LOS ), it is no longer required that the user's receiving and sending antennas must be installed at the high point on the roof, but to allow the antennas to be mounted on the outdoor wall or even on the indoor table. This is a major improvement and is very beneficial for the promotion and application of FWA. That is to say, in order to make the wireless FWA compete with the wired ADSL-modem, we must strive for NLOS-FWA. In this way, the client is easy to install and the performance is equivalent to that of ADSL-modem.

Difficult to popularize sight transmission

In order to be practical, FWA of the Fixed Wireless Access Network must be widely adapted to various situations on the ground. Regardless of the terrain, region, and population density, wireless communication must be smooth. In addition, compared with the wireless cellular network of mobile communication, this fixed wireless network shows its superiority in terms of data transmission speed, access reliability, and spectrum usage efficiency.

Generally, FWA is designed based on line-of-sight transmission LOS, that is, the radio wave transmission between each user and the Access Point BTS is based on line-of-sight transmission LOS. Each user is equipped with a precisely oriented, narrow, and fine-beam antenna with a high gain. Such wireless lines can be independent from neighboring routes. Generally, radio waves may have several different latencies of multi-path propagation, resulting in inter-code interference and fading. The user devices are now required to have a high targeting orientation on the roof antenna, so that they are similar to the Radio Transmission Conditions of the base station, so that they only need a small fading margin, in addition, modulation and demodulation do not require a complex equalizer. However, practical experience shows that up to 30% of FWA users are connected to their respective base stations in line with the LOS condition. In addition, if the partition and base station conditions change or adjust, the user's antenna needs to re-adjust its direction, which is quite troublesome. Therefore, FWA's comprehensive design will never allow us to rely solely on LOS transmission. Maybe FWA is divided into more small and partially covered zones, and a large number of base stations are set up to help increase the user's LOS transmission, but this makes the entire FWA network structure complex, it is not easy to use, and the cost is improved.

Non-line-of-sight transmission should be taken seriously

In order to promote the application of Fixed Wireless Access Networks and expand the frequency band width and transmission data rate of wireless access, the fixed wireless access must not be limited to LOS, instead, we should allow more users to use non-line-of-sight transmission between the base station and the actual situation. According to the latest International Journal reports: a typical NLOS-FWA requires a data transfer rate of 6 Mbit/s, the spectrum utilization efficiency should be 2 bit/s · Hz, the transmission coverage distance should reach 10 km for the roof cable, 5 km for the wall cable, and 3 km for the indoor antenna. Their transmission performance should be similar to the DSL of the wired network and the reliability should reach 0.999.

Regardless of the upstream or downstream lines, the Spectrum Utilization Efficiency refers to the BTS per base station and the bits per second per Hz: SE = rM/kB, in formula, M indicates the average transfer volume and bit number of each RF channel. r indicates the code speed of the forward Correction Code. Therefore, rM is the effective transfer volume when users access the media. This transfer volume is related to the performance of the actual wireless path, distance loss, transmission power, noise level, and other factors. B Indicates the access bandwidth, including the Protection Band. K indicates the space reuse factor, which is determined by the number of base stations. In this way, the coverage of each residential area should have its own SE. If each base station increases the number of partitions and uses different RF channels, the channel transmission volume may be increased to improve the spectrum efficiency. The uplink and downlink lines are considered more important because they are related to Internet applications. However, the uplink lines can also be calculated to meet performance requirements.

The coverage of the residential area should ensure reliable service to most users in the area. In fact, there should be two types of Reliability: Coverage reliability and channel reliability. There should be a large number of users in the whole region, such as 90% of users to obtain the minimum necessary path reliability. The so-called path Reliability refers to the maximum failure probability of a channel. For example, if the number of errors in a group exceeds the predefined value within a certain period of time, a fault may occur. For Internet applications, if they run according to the TCP/IP protocol, the path reliability can be obtained from IP group transmission statistics.

In NLOS-FWA, the performance of wireless channels is often expressed by the signal to noise and Interference Ratio SINR. This means that any receiver antenna must meet the predefined SINR requirements. This is of course closely related to the fading phenomenon of wireless channel transmission. Therefore, the diversity system is often used in wireless large-line devices to grasp and reduce the occurrence of latency difference. In general, necessary practical measures should be taken, or efforts should be made to minimize k or maximize rM to obtain the maximum spectrum utilization efficiency SE.