802.11 new standard consolidates WLAN applications

——New solution to WLAN standard specification

There is still a distance from the popularization of WLAN, but the industry is working hard, the 802.11 standard is like a sumptuous meal, constantly dedicated to the users who love it, step by step to close the application distance.

There are 802.11b, 802.11a and 802.11g. Recently, the three latest "big meals" of 802.11e, 802.11h and 802.11n are on the table. For 802.11b, 802.11a and 802.11g, we have reported a lot. Now let's taste the deliciousness of 802.11e, 802.11h and 802.11n and see how they are applied.

802.11e: Support QoS

802.11e is a wireless universal standard introduced by IEEE. It enables real interoperability between enterprises, homes and public places (such as airports, restaurants, etc.) while at the same time having characteristics that meet the special needs of different industries. Unlike other wireless standards, the standard adds quality of service (QoS) at the MAC physical layer and multimedia support for existing 802.11b and 802.11a wireless standards, while being fully backward compatible with these standards.

QoS and supporting multimedia are key features of wireless networks that provide voice, video and audio services. Broadband service providers view QoS and multimedia support as an important part of providing video on demand, audio on demand, IP voice and high speed Internet access to users. Therefore, before the 802.11e came into effect, the IEEE established a QoS benchmark and became the core component of 802.11e.

The primary mechanism of the QoS benchmark is to better control the time-sensitive information of multimedia applications. When there is no signal transmission, ie, no contention period (CFP), QoS benchmarks receive time scheduling and polling communications, improve polling performance, and improve channel stability and selective retransmission through forward error correction (FEC). Channelless access is also improved during contention-free periods, and polling for backward compatibility is maintained. These mechanisms provide maximum performance for high-bandwidth multimedia streaming, power management, and round-robin access to various rates and bursts of information.

Even in dense deployments of wireless networks, such as enterprise wireless environments, the 802.11e standard can enhance QoS support. In such an environment, multiple 802.11e subnets can be configured to communicate with each other without interference that may be generated by wireless devices in different subnets during communication.

802.11h: remove the interference from mutual interference

Friends who love the 802.11 standard meal may be interested in 802.11h. The reason is that it can overcome the shortcomings of other existing 802.11 standards. We know that 802.11a wireless networks work in the 5GHz band and support up to 24 non-overlapping channels. The sensitivity to interference is lower than that of 802.11g. However, depending on the country, the environment using the 5GHz band will change. To problems that interfere with other systems. The mechanism defined by 802.11h for this problem enables 802.11a-based wireless systems to avoid interference with broadband technologies in radars and other similar systems, and to ensure the smooth flow of wireless communications.

802.11h overcomes the above shortcomings and introduces two key technologies, Dynamic Frequency Selection (DFS) and Transmit Power Control (TPC).

● DFS. DFS defines a detection mechanism, but when it detects the presence of other devices using the same wireless channel, it can switch to other channels as needed to avoid mutual interference and coordinate the utilization of the channel. That is, a wireless access point uses the DFS of the WLAN device to find other access points. When a WLAN device is connected to an access point, the wireless device lists the channels it can support. When a transition to a new channel is required, the access point uses the listed channel data to determine the best channel.

● TPC. TPC aims to reduce mutual interference between WLAN and satellite communications by reducing the wireless transmit power of WLAN devices. The TPC can also be used to manage the power consumption of the wireless device and the distance between the access point and the wireless device.

The novelty of the DFS and TPC mechanisms defined by 802.11h is to ensure the implementation of standard communication methods according to the management requirements of the 5 GHz band, to promote the promotion and use of 802.11a wireless networks, and to improve the deployment and operation performance of WLANs.

802.11n: Support for high rates

With the rapid development of mobile communication services, the market demand for high-performance WLAN is increasing. To meet this demand, the IEEE formed the 802.11 TGn working group in 2003 to develop the 802.11n standard. The main mechanism of 802.11n is to support high data rates and improve spectrum efficiency through the MAC interface, providing ultra-high-speed data streams for wireless HDTV transmissions and dense wireless network environments where enterprise and retail users are located; running 802.11n networking protocols will It provides 500Mbps for WLANs, which is about 10 times faster than current WLANs, and is widely compatible with existing Wi-Fi standards and supports devices such as PCs, consumer electronics and mobile platforms.

To achieve these capabilities, 802.11n also introduces two key technologies, Multiple Input Multiple Output (MIMO) technology and wide channel bandwidth technology.

MIMO technology: This is a wireless transmission technology that establishes multiple "air paths" for data to be transmitted and increases single channel data throughput. Using multiple transmit and receive antennas, each channel can transmit different data sets on the same frequency and increase network capacity by increasing the transmission speed of the transmitted signal.

MIMO is actually a wireless chip technology embedded in a chip where MIMO transmits signals through two or more antennas. At the receiving end, the information is recombined by a multi-MIMO algorithm to enhance transmission performance. Therefore, MIMO technology is not only the basis for the development of the 802.11n standard, but the 3G communication standards body is also evaluating the possibility of using this technology for cellular communication networks.

20/40MHz channel bandwidth: The 802.11n standard supports 20/40MHz channel bandwidth, which makes it possible to achieve a high rate of 500Mbps worldwide and increase data transmission capacity. The 40MHz channel consists of two 20MHz adjacent channels. By utilizing the unused quadrant bands between the two channels, each transmission can be more than doubled to the current 54Mbps WLAN data rate, which is about 125Mbps.

Because the 802.11n standard is based on two key technologies, MIMO and channel bandwidth, it brings many new applications to WLAN. Currently, these applications are concentrated in three aspects: First, working in the 5 GHz band, that is, in the 5 GHz band, the increase in capacity in the 40 MHz band may make 802.11n networks provide more wireless services; second, with 802.11b, 11a and 11g coexist and are backward compatible, supporting the 802.11e QoS standard just completed this year; third, single and multiple destination frame aggregation, that is, combining several data frames into one data packet, including IP wireless voice and multimedia content Streaming media transfer.

Feeling

In fact, the development of technology and market demand continue to give birth to the new 802.11 standard. In addition to the above three new standards, the IEEE has set up a new 802.11 working group (IEEE 802.11 TGr "fast roaming" working group) at the beginning of this year to develop fast and secure roaming between access points. Standard. The standard will add a new "delicious" to the 802.11e QoS mechanism. If passed, it will optimize voice or multimedia services on clear VoIP packets, and reduce call drop and network instability when users move between secure access points while communicating via mobile WLAN phones. , thereby improving the performance of enterprise VoIP.

The application of new technologies needs to solve a number of practical problems. The WLAN is also the same. Several new standards are putting the problem flat, QoS is solved, interference is removed, bandwidth is higher, and 802.11i also secures it. Now, Will it be far from universal application?