——New interpretation of WLAN standard specification
There is still a distance from the popularization and application of WLAN, but the industry is working hard. The 802.11 standard is like a hearty feast, and it is constantly dedicated to the users who love it, stepping closer to the application.
There are 802.11b, 802.11a, and 802.11g, and recently the three latest "diners" of 802.11e, 802.11h, and 802.11n are presented to 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 experience how they are applied.
802.11e: support QoS
802.11e is a wireless universal standard introduced by IEEE. It enables enterprises, families, and public places (such as airports, restaurants, etc.) to truly communicate with each other, and at the same time has the characteristics of meeting the special needs of different industries. Different from other wireless standards, this standard adds quality of service (QoS) in the MAC physical layer and provides multimedia support for the existing 802.11b and 802.11a wireless standards, and is fully backward compatible with these standards.
QoS and multimedia support are key features of wireless networks that provide voice, video, and audio services. Broadband service providers regard QoS and multimedia support as an important part of providing users with video on demand, audio on demand, IP voice and high-speed Internet access. Therefore, before 802.11e officially came into effect, IEEE established a QoS benchmark for it and became the core component of 802.11e.
The main mechanism of the QoS benchmark is that it can better control the time-sensitive information of multimedia applications. When there is no signal to send, that is, no contention period (CFP), the QoS benchmark accepts time scheduling and polling communication, improves the effectiveness of polling, and improves channel stability and selective retransmission through forward error correction (FEC). During contention-free periods, it also improves channel access and maintains polling for backward compatibility. These mechanisms provide maximum efficiency for high-bandwidth multimedia streaming, power management, and alternate access to various rates and burst information streams.
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 within a range where they can communicate with each other without interference from wireless devices in different subnets during communication.
802.11h: remove the worry of mutual interference
Friends who love the 802.11 standard dinner may be interested in 802.11h. The reason is that it can overcome the shortcomings of other existing 802.11 standards. We know that the 802.11a wireless network works in the 5GHz frequency band, supports up to 24 non-overlapping channels, and is less sensitive to interference than 802.11g. However, due to different countries, the environment using the 5GHz frequency band will change, and the same will happen. To interfere with other systems. The mechanism defined by 802.11h in response to this problem enables wireless systems based on 802.11a to avoid interference with broadband technologies in radar and other similar systems, and to ensure smooth wireless communication.
802.11h overcomes these shortcomings and introduces two key technologies, namely dynamic frequency selection (DFS) and transmit power control (TPC).
â— DFS. DFS defines a detection mechanism, but when other devices using the same wireless channel are detected, they can switch to other channels as needed to avoid mutual interference and coordinate the use of the channel. That is, a certain wireless access point uses 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 it is necessary to switch to a new channel, the access point uses the listed channel data to determine the best channel.
â— TPC. TPC aims to reduce the mutual interference between WLAN and satellite communications by reducing the wireless transmission power of WLAN devices. 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 in accordance with the management requirements of the 5GHz band to promote the popularization and use of 802.11a wireless networks and improve the deployment and operating performance of WLAN.
802.11n: support high rate
With the rapid development of mobile communication services, the market demand for high-performance WLANs is increasing day by day. To meet this demand, IEEE formed the 802.11 TGn working group in 2003 to formulate the 802.11n standard. The main mechanism of 802.11n is to support high data rates and improve spectrum efficiency through the MAC interface, and provide ultra-high-speed data streams for wireless HDTV transmission and the dense wireless network environment where enterprises and retail users are located; running the 802.11n networking protocol will Provides 500Mbps for WLAN, which is about 10 times faster than the current WLAN, and is widely compatible with existing Wi-Fi standards, and supports devices such as PCs, consumer electronics devices, and mobile platforms.
To achieve the above functions, 802.11n also introduces two key technologies, namely multiple input multiple output (MIMO) technology and wide channel bandwidth technology.
MIMO technology: This is a wireless transmission technology that establishes multiple "air paths" to the data to be sent and increases the single-channel data throughput rate. Using multiple transmit and receive antennas, each channel can transmit different data sets on the same frequency, and increase the network capacity by increasing the transmission speed of the transmitted signal.
MIMO is actually a wireless chip technology. MIMO embedded in the chip sends signals through 2 or more antennas. At the receiving end, the information is recombined through multiple MIMO algorithms to enhance transmission performance. Therefore, MIMO technology is not only the basis for the formulation of the 802.11n standard, 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 the data transmission capacity. The 40MHz channel is composed of two 20MHz adjacent channels. Using the unused quadrant frequency band between the two channels, each transmission energy can be more than doubled from the current 54Mbps WLAN data rate, about 125Mbps.
Since the 802.11n standard is supported by two key technologies, MIMO and channel bandwidth, it brings many new applications to WLAN. At present, these applications are concentrated in three aspects: one is to work in the 5GHz band, that is, in the 5GHz band, the increase in the capacity of the 40MHz band may make 802.11n networks provide more wireless services; 11a and 11g coexist and are backward compatible, supporting the 802.11e QoS standard just completed this year; the third is the aggregation of single and multiple destination frames, that is, combining several data frames in one data packet, including IP wireless voice and multimedia content Streaming media transmission.
Perception
In fact, the development of technology and market demand have continuously produced new 802.11 standards. In addition to the above three new standards, IEEE has established a new 802.11 working group (IEEE 802.11 TGr "fast roaming" working group) at the beginning of this year at the request of SpectraLink, a major WLAN VoIP manufacturer, to formulate fast and safe roaming between access points Standard. The standard will add a new "delicious" based on the 802.11e QoS mechanism. If it is passed, it will optimize voice or multimedia services on the clear VoIP packets. When users move between secure access points while communicating with mobile WLAN phones, they can also reduce call drops and network instability , Thereby improving the performance of enterprise VoIP.
The application of new technologies needs to solve several practical problems, and the same is true of WLAN. Several new standards are smoothing the problems one by one, QoS is solved, interference is removed, the bandwidth is higher, and 802.11i has also done security. Now, Will it be far from popular applications?
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