Performance of WLAN

Wireless local Area network (Wireless Lan,wlan), as its name suggests, is a data communication system that provides wireless peer-to-peer (such as PCs to PCs, PCs to hubs or printers to hubs) and point-to-point (such as LAN to LAN) connectivity. The WLAN replaces the twisted or coaxial line or fiber used in the regular LAN to transmit and receive data through electromagnetic waves. WLAN performs traditional network communication functions such as file transfer, peripheral sharing, Web browsing, e-mail, and database access.

A WLAN includes a network interface card (NIC) (or wireless network card) for communication and an access point/bridge (such as end user to LAN and LAN to LAN). The NIC provides an interface between an end-user device, such as a desktop PC, a portable PC, or a handheld computing device, and a radio wave that passes through an antenna on an access point/bridge.

With the development of wireless communication technology and the continuous improvement of the wireless LAN communication rate, the standard of WLAN is also developing continuously, the general trend is that the data rate is higher, the security is better and the quality of service is more and more guaranteed.

And from the wireless LAN standards of the supporters and the geographical scope of use, wireless LAN can be said to have three camps: IEEE 802.11 series of standards, European hiperlan1/hiperlan2 and Japan's MMAC series standards.

802.11 series Standard

In the 802.11 series, there are 4 standards involving the physical layer: 802.11, 802.11b, 802.11a, 802.11g. According to different physical layer standards, wireless LAN devices are usually classified into different categories, as usual 802.11b wireless LAN equipment, 802.11a Wireless LAN equipment and so on.

The 802.11 standard was introduced by IEEE in 1997, and it works in the 2.4GHz band, with the physical layer using infrared, DSSS (direct sequence spread spectrum) or fsss (frequency hopping spread spectrum) technology, the highest share data rate up to 2Mbps. It is mainly used to solve the wireless access problem of the user terminal in the Office LAN and campus network. (Computer science)

802.11 of the data rate can not meet the growing business needs, so IEEE in 1999 has launched a 802.11b, 802.11a two standards. And at the end of 2001 through the 802.11G Trial hybrid scheme, which can achieve 54Mbps data rates in the 2.4GHz band, and compatible with the 802.11B standard.

802.11b work in 2.4GHz ISM (industrial, technical, medical) band, using direct series spread spectrum and complement keying, can support 5.5Mbps and 11Mbps two kinds of speed, can with the rate of 1Mbps and 2Mbps 802.11 DSSS (direct sequence spread spectrum) System interaction, but not with the 1Mbps and 2Mbps 802.11 FHSS (frequency hopping spread spectrum) system to interoperate.

802.11a work in the 5GHz band (in the United States for the u-nii band: 5.15-5.25ghz, 5.25-5.35ghz, 5.725-5.825ghz), it uses OFDM (orthogonal Frequency Division multiplexing) technology. 802.11A supports data rates up to 54Mbps.

The 802.11a rate is high, but not compatible with 802.11B, and the cost is relatively high, so in the current market 802.11b still dominate, 802.11a products are expected to be rapid development in the next few years.

802.1G is compatible with the already widely used 802.11b, which is the advantage of 802.11g compared to 802.11a.

802.11G is a high-speed physical layer extension to 802.11b, like 802.11B, 802.11g works in the 2.4GHz ISM band, but uses the OFDM technology, can achieve the highest 54Mbps data rate, It is equivalent to 802.11a and solves the interference problem of WLAN and Bluetooth well. As the 802.11G standard has not been completed, and the products in line with the 802.11A standard has appeared, I believe that 802.11a will be faster development, to a certain extent occupy the opportunity.

In the MAC (media access Control) layer, 802.11, 802.11b, 802.11a, 802.11g of these four standards are CSMA/CA (ca:collision avoidance, conflict avoidance), which is different from traditional Ethernet CSMA/CD ( Cd:collision detection, conflict detection), CSMA/CA related content defined in the 802.11 standard, 802.11b, 802.11a, 802.11g directly followed.

In addition to the 802.11, 802.11b, 802.11a, 802.11g of these four standards involved in the physical layer, in order to promote 802.11a in Europe, and the promotion of the development of ETSI HIPERLAN/2 competition, IEEE has also proposed a 802.11h standard, on the basis of 802.11a to increase the automatic frequency selection (DFS) and send Power control (TPC) function to adapt to 802.11a in Europe to promote the development needs, in line with European regulatory requirements.

802.11 is the basis of the MAC layer standard, on this basis, in order to meet the security, QoS and other aspects of further requirements, IEEE successively put forward 802.11e, 802.11f, 802.11i and other standards.

The 802.11e enhances the 802.11 MAC layer, providing QoS support for WLAN applications. 802.11e to enhance the MAC layer and 802.11a, 802.11b in the physical layer of the improvement of the combination of enhanced performance of the entire system, expanding the application of the 802.11 system, so that WLAN can also transmit voice, video and other applications.

The 802.11f standard defines a set of protocols called IAPP (Inter-Access point Protocol) to enable interoperability between APS of access points for different vendors.

When it comes to the 802.11i standard, you cannot fail to mention the 802.1X standard. The 802.1X standard, completed in 2001, is the overall security architecture for all IEEE 802 series LANs, including wireless LANs, including authentication (EAP and RADIUS) and key management capabilities. 802.11i is a security enhancement to the 802.11 MAC layer, which, along with 802.1X, provides authentication and security mechanisms for WLANs.

In addition to the standards described above, there is also a 802.11d standard in the 802.11 series standard, which defines some physical layer requirements (such as channel, FH mode, etc.) to accommodate the special requirements of these national radio controls when 802.11 devices are applied in some countries.

HIPERLAN1/HIPERLAN2 Standard

At the same time as IEEE developed the 802.11 series WLAN standards, the European ETSI (European Communication Standards Institute) is vigorously promoting hiperlan1/hiperlan2 standards.

HiperLAN1 was released in 1996, it works in the 5GHz frequency band, adopts the modulation mode for the Gaussian filter minimum frequency shift keying (GMSK); The HiperLAN1 provides a maximum data rate of up to 25Mbps. Overall, the HiperLAN1 is equivalent to the 802.11b.

HiperLAN2 was the second-generation version of HiperLAN1 and was approved by ETSI at the end of 2000 as a standard. It corresponds to IEEE 802.11a, works in the 5GHz band, uses OFDM technology, and has dynamic frequency selection (DFS), Send power control (TPC) function, support the highest data rate of 54Mbps. In the MAC layer, HiperLAN2 uses a reserved TDMA multiple access mode, dynamic TDD duplex mode. and can support the QoS under the high throughput rate, thus provides the support for the video stream, the voice and so on real-time application.

MMAC Standard

Japan's multimedia Mobile Access Communication Facilitation Committee (multimedia Mobile Access Communication promotion Council) has been working on WLAN technology research and standard-setting. Hiswana and HISWANB standards have been developed successively. Hiswana work in the 5GHz band, HISWANB working in the 25/27ghz band, supporting the data rate of 6~54mbps, using OFDM modulation, TDMA multiple access mode, TDD duplex mode.

In the further development of WLAN technology, the current research shows such characteristics as: first, the research direction to higher data rate (>100mbps), higher frequency band development, the second is to actively study the wireless LAN and 3G or 4G Cellular mobile communication network interoperability and integration.

The IEEE launched the WLAN wng (the next Generation research group for wireless LANs) in January 2002 with the goal of studying WLANs with a peak rate of over 100Mbps. The multimedia Mobile Access Communication Promotion Committee of Japan is studying the ultra-high speed wireless local area network (Ultra high Speed Wireless LAN) working in the 60GHz band, with a speed of up to 156Mbps.

In order to promote the coordinated development of 3G and WLAN two kinds of technology, the research work of 3G and WLAN is being carried out in the International Organization for Standardization, such as 3GPP, and the work plan and target have been established, and some progress has been made. At present, the focus of the work is to study how to use the ability of 3G network to provide user access authentication and billing service to WLAN system.