Introduction to various wireless WLAN Access Technologies (2)

In the previous article, "Introduction to various wireless WLAN Access Technologies", we introduced the overview of wireless WLAN Access Technologies and six Wireless Access Technologies, below we will complete up other types of wireless WLAN access technology. We are familiar with these technologies.

6. Wireless WLAN Access Technology-DBS satellite access technology

DBS is also called the digital live broadcasting satellite access technology. It uses the communication satellite in the earth synchronous orbit to send high-speed broadcast data to the user's receiving antenna. Therefore, it is also called high-orbit satellite communication. It is characterized by long communication distance, independent of cost and distance. It has a large coverage area and is not subject to geographical restrictions, bandwidth frequency, and capacity, and is suitable for multi-service transmission, it can provide users around the world with a wide range of roaming and flexible mobile communication services.

In the DBS system, a large amount of data is broadcasted using the High-Speed Uplink Channel of the satellite Main Station and the satellite forwarder after the frequency division or time division modulation, the user receives data through the satellite antenna and satellite Modem, and the receiving antenna is generally 0.53 m or m in diameter.

Because the digital satellite system has high reliability, it does not require much signal correction for analog phones using twisted pair wires in the PSTN network. Therefore, the download rate can reach 400 kbit/s, the actual DBS broadcast rate can reach 12 Mbit/s.

Currently, DBS are available in the United States and are mainly used for Internet access. The largest DBS network is the DirectPC of Hughes Network System Corporation. DirectPC data transmission is asymmetric. when connected to the Internet, the download speed is 400 kbit/s and the uplink speed is 33.6 kbit/s. Although this speed is much higher than that of common dial-up Modem, however, compared with DSL and CableModem technologies.

7. Wireless WLAN Access Technology-Bluetooth Technology

The English name of Bluetooth is "Bluetooth". In fact, it is a protocol for wireless connection between multiple devices. This Protocol enables information exchange between a large number of devices, including cellular phones, handheld computers, laptops, related peripherals, and home hubs, including home RF. Bluetooth is used to connect a mobile phone to a computer, which reduces the cost of a mobile phone and achieves data sharing, Internet access, wireless hands-free, data synchronization, and image transmission.

Although Bluetooth has great advantages in multi-direction transmission, if there are many devices, the identification method and speed may also be faulty. Bluetooth has one-to-multiple-point data exchange capability, therefore, it requires a security system to prevent unauthorized access. The basic communication speed of Bluetooth is 750 kbits/s, but now the products with 4 Mbits/sIR ports are very common, in addition, the latest 16 Mbits extension has been approved.

8. Wireless WLAN Access Technology-HomeRF Technology

HomeRF is mainly designed for home networks to reduce the cost of Speech data. To achieve efficient transmission of data packets, HomeRF adopts the CSMACA mode in the standard, which is similar to CSMACD and obtains control over the channel in a competitive manner, only one access point can transmit data over the network at a time point.

Unlike other protocols, HomeRF provides true support for StreamMedia. Because the streaming business sets a high priority and adopts a priority-based re-transmission mechanism, this ensures the bandwidth and low interference and low error codes required for Real-Time Streaming business.

HomeRF operates in the GHz band and uses the Digital Frequency Hopping Spread Spectrum Technology. The speed is 50 hops/s, and a total of 75 bandwidth 1 MHz frequency hopping channels are available. The modulation method is constant envelope of the PSK modulation, which can be divided into two types. FM modulation can effectively suppress interference and fading in wireless environments.

The maximum data transmission rate is 1 Mb/s in 2PSK mode, and 2 Mb/s in 4psk mode. In the latest HomeRF2.x version, WBFHwidebandfrequencyhopping technology is used to increase the frequency hopping bandwidth, from 1 MHz to 3 MHz and 5 MHz, and the frequency hopping rate also increases to 75 hops, its data peak value is also as high as 10 Mb/s, close. the IEEE802.11b standard is 11 Mb/s, which can basically meet the needs of home broadband communication in the future.

9. Wireless WLAN Access Technology-WCDMA access technology

The WCDMA technology can provide users with a data transmission rate of up to 2 Mbit/s. Under such conditions, any media used in computers can be easily transmitted through wireless networks. The advantage of WCDMA is that the bit rate is high, which effectively utilizes the frequency selective diversity and the space receiving and transmitting diversity.

It can solve the problem of multi-path and fading. It uses Turbo channel encoding and decoding to provide a high data transmission rate. FDD can provide full coverage for wide areas. downlink base stations use unique cell search methods, strict synchronization between base stations is not required. Uses the continuous frequency guide technology to support high-speed mobile terminals.

Compared with the second generation of mobile communication technology, WCDMA has a larger system capacity, better voice quality, higher spectrum efficiency, faster data rate, stronger anti-fading capability, better anti-multi-path performance, and can be applied to up to 500 km /h technical advantages of mobile terminals.

In addition, it can smoothly transition from the GSM system to ensure the investment of operators and provide a good technical foundation for 3G operation. Through the effective use of broadband, WCDMA not only can smoothly process sound, image data, and the Internet fast connection; in addition, WCDMA and MPEG-4 technology can also be combined to process real dynamic images.

10. Wireless WLAN Access Technology-3G Communication Technology

The technology, also known as International Mobile Phone 2000, stipulates that when a mobile terminal moves at a speed, the data transfer rate is 144 kbps, And the outdoor static or walking speed is 384 kbps, the indoor bandwidth is 2 Mbps.

However, these requirements do not mean that the user availability rate can reach 2 Mbps, because the indoor rate will also depend on the detailed frequency planning in the building and the closeness of the Organization and operator collaboration. However, since the speed of High-Speed businesses such as wireless LAN can reach 54 Mbps, it is difficult to predict what the market demand for 2 Mbps businesses will be when 3G networks are fully rolled out.

11. Wireless WLAN Access Technology-Wireless LAN

Wireless LAN WirelessLAN (WLAN) is a combination of computer networks and wireless communication technologies. It is not bound by cables and can be moved. It can solve problems caused by difficulties in wired network cabling and has the advantages of flexible networking, convenient resizing, compatibility with various network standards, and wide application. WLAN can meet the network access requirements of all types of hosts, as well as remote computer LAN access, text and fax, email, and other functions.

12. Wireless WLAN Access Technology-Wireless Optical Access System (FSO)

The wireless infrared optical transmission system is a combination of optical communication and wireless communication. It transmits optical signals through the atmosphere rather than optical fibers. This technology can provide a rate similar to optical fiber without rare resources such as spectrum. The main features are: high transmission rate, from 2 Mb/s to 622 Mb/s high-speed data transmission; the transmission distance is 200 to 6 kilometers; due to work in the infrared band, it does not interfere with other transmission systems and is highly secure. signals are transmitted and received through optical instruments without the need for a Antenna Feeder System. The devices are small in size.