How Do I Choose the Best WLAN Software?

In 1990, the early wireless network products Wireless LAN appeared in the United States. In 1997, the IEEE802.11 wireless network standard was promulgated, which played an important role in promoting the development of wireless network technology and the application of wireless networks, and promoted wireless network products from different manufacturers. Interoperability. The update and improvement of the international wireless network standard in 1999 further standardized the development and application of products with different frequency points and higher network speed products.

802.11 wireless technology

1990, early

Construction of IEEE802.11

In terms of technology, the WWiSE proposal marks a major advancement in 802.11 implementation features. Key features include:

"Mandatory use of a 20MHz Wi-Fi channel width that has been approved, is now available, and is globally available, ensuring that it can be used and deployed immediately under any telecommunications regulations.

"Stronger MIMO-OFDM technology, which is the key to achieving a maximum data rate of 135 Mbps with a minimum requirement of 2 × 2 configuration and a 20 MHz channel, thereby reducing implementation costs. This technology can also greatly improve simplicity Antenna extension or channel aggregation technology.

"Using a 4 × 4 MIMO architecture and a maximum data rate of 540 Mbps achieved by a 40 MHz channel width (as long as the competent authority allows it), it can provide a blueprint for continued development of future devices and applications.

"Forced mode provides backward compatibility and interoperability with existing Wi-Fi devices in the 5 GHz and 2.4 GHz bands, ensuring that installed devices still receive strong support.

"Advanced FEC encoding capabilities help achieve maximum coverage and connection distance, and it is suitable for all MIMO configurations and channel bandwidths.

802.11n 802.11 wireless technology

2.3.1 Ins and Outs of 802.11n

In the Warring States era when various wireless local area network technologies are intertwined, WLAN, Bluetooth, HomeRF, UWB, etc. are blooming, but IEEE802.11 series WLANs are the most widely used. Since the implementation of the IEEE802.11 standard in 1997, standards such as 802.11b, 802.11a, 802.11g, 802.11e, 802.11f, 802.11h, 802.11i, and 802.11j have been formulated or brewed. "No" problems, that is, insufficient bandwidth, inconvenient roaming, weak network management, insecure system, and no killer applications. Just like VoWLAN, a brand new field in VoIP applications, although it is regarded by the industry as the most promising killer application of WLAN, it is difficult to develop further because of these four "no".

In order to achieve high-bandwidth, high-quality WLAN services, and enable wireless local area networks to reach the performance level of Ethernet, 802.11n came into being.

2.3.1, the wonderful future of 500Mbps

In terms of transmission rate, 802.11n can increase the transmission rate of WLAN from 54Mbps provided by 802.11a and 802.11g to 108Mbps, or even up to 500Mbps. This is due to the MIMO OFDM technology that combines MIMO (Multiple-In-Multiple-Out) with OFDM (Orthogonal Frequency Division Multiplexing) technology. This technology not only improves the wireless transmission quality, but also greatly improves the transmission rate.

Application prospects: 802.11n will make the WLAN transmission rate reach 10 times the transmission rate, and can support high-quality voice and video transmission, which means that people can use Wi-Fi mobile phones to make IP calls and video phones in office buildings.

In terms of coverage, 802.11n uses smart antenna technology. Through an antenna array composed of multiple independent antennas, the beam can be dynamically adjusted to ensure that WLAN users receive stable signals and reduce interference from other signals. Therefore, its coverage can be expanded to several square kilometers, which greatly improves WLAN mobility.

Application prospects: This makes it possible to use notebook computers and PDAs to move within a larger range, allowing WLAN signals to cover any corner of office buildings, hotels, and homes, allowing us to truly experience the convenience and joy of mobile office and mobile life .

In terms of compatibility, 802.11n uses a software radio technology. It is a fully programmable hardware platform, allowing base stations and terminals in different systems to communicate and be compatible through different software on this platform. This makes WLAN s Compatibility has been greatly improved. This means that WLAN will not only achieve backward and forward compatibility of 802.11n, but also the combination of WLAN and wireless wide area networks, such as 3G.

802.11 wireless technology standards debate

It is regrettable that 802.11n is now in an awkward situation of "lagging standards and premature delivery of products." The 802.11n standard has not been formally approved by the IEEE, but there are already many manufacturers using MIMO OFDM technology, including Airgo, Bermai, Broadcom, Agere Systems, Atheros, Cisco, Intel, etc. The products include wireless network cards, wireless routers, etc., and It has been widely used in PCs and laptops.

There are two technical camps that dominate the 802.11n standard, namely the WWiSE (World Wide Spectrum Efficiency) Alliance and the TGn Sync Alliance. Both camps hope to take precedence in the battle for next-generation wireless LAN standards, but the technical architectures of the two camps are becoming more and more similar, for example, they are using MIMO OFDM technology, and it is reported that they have decided to ignore the former. , Jointly submitted the wireless technology version of 802.11n to the Institute of Electrical and Electronics Engineers (IEEE).

In this fierce competition, we cannot see China, and we have to feel a little regretful. This is also the consequence of our lack of core technology. The battle for standards is ultimately a battle for interests. It is very difficult for Chinese companies to achieve huge benefits in WLAN core technology. This is worthy of deep consideration.

Analysis of 802.11 wireless technology

In the previous wireless transmission technology, the development bottleneck was in coverage and transmission rate. If the coverage is wide, the transmission speed will definitely be slower; if the transmission speed goes up, then the coverage must be reduced. So how exactly does 802.11n solve these problems and how to break through this bottleneck that restricts wireless technology? What specific new technologies does it contain? We will analyze them one by one here.

2.5.1, OFDM technology

OFDM technology is a type of Multi-Carrier Modulation (MCM). The core is to divide the channel into many orthogonal sub-channels, and perform narrow-band modulation and transmission on each sub-channel, which reduces the mutual interference between the sub-channels. The signal bandwidth on each subchannel is smaller than the relevant bandwidth of the channel, so the frequency selective fading on each subchannel is flat, which greatly eliminates inter-symbol interference, as shown in Figure 1. In addition, because the carriers of the sub-channels are orthogonal to each other in the OFDM system, their spectrums overlap with each other. This not only reduces the mutual interference between the sub-carriers, but also improves the spectrum utilization.

OFDM technology analysis diagram

In addition, OFDM technology uses different numbers of subchannels to achieve different transmission rates in the uplink and downlink, which solves the problem of asymmetric transmission of wireless data services. At the same time, the OFDM system also suppresses the influence caused by narrow-band interference to some extent.

Although compared with single-carrier systems, OFDM still has some disadvantages, such as being susceptible to frequency deviation, and having a high peak-to-average power ratio (PAR). Adjacent channel interference (ICI) suppression and smart antenna technology can maximize the reliability of the physical layer. For example, combined with technologies such as adaptive modulation, adaptive coding, and dynamic subcarrier allocation and dynamic bit allocation algorithms, the performance can be further optimized.

2.5.2, MIMO technology

Multiple input multiple output (MIMO) technology is a major breakthrough in smart antenna technology in the field of wireless communications. MIMO technology can double the capacity and spectrum utilization of communication systems without increasing bandwidth.

Indoors, the electromagnetic environment is more complex. The existence of multipath effects, frequency selective fading, and other interference sources makes it difficult to achieve high-speed data transmission over wireless channels over wired channels. Multipath effects can cause fading and are considered harmful factors. However, research results show that for MIMO systems, multipath effects can be used as a favorable factor. MIMO systems use multiple antennas (or array antennas) and multiple channels at both the transmitting and receiving ends. MIMO MIMO is for multipath wireless channels, as shown in Figure 2. The transmission information stream S (k) is formed into N information sub-streams Ci (k) through space-time coding, i = 1,..., N. The N sub-streams are transmitted by N antennas, and are received by M receiving antennas after passing through the spatial channel. Multi-antenna receivers can use advanced space-time coding processing to separate and decode these data sub-streams to achieve optimal processing.

MIMO technology analysis diagram

In particular, the N sub-streams are sent to the channel at the same time, and each transmitted signal occupies the same frequency band, so the bandwidth is not increased. If the channel responses between the transmitting and receiving antennas are independent, the MIMO system can create multiple parallel spatial channels. MIMO considers multipath wireless channels, transmission, and reception as a whole to optimize, so as to achieve high communication capacity and spectrum utilization. This is a near-optimal spatial and time-domain joint diversity and interference cancellation process.

2.5.3, MIMO OFDM technology

MIMO OFDM technology is a new technology obtained by combining OFDM and MIMO through the use of array antennas in OFDM transmission systems to achieve spatial diversity and improve signal quality. It uses three diversity techniques of time, frequency, and space, which greatly increases the tolerance of the wireless system to noise, interference, and multipath. The system principle is shown in Figure 3. MIMO OFDM mainly includes the following key designs: transmit diversity, spatial multiplexing, receive diversity, interference cancellation, soft decoding, channel estimation, synchronization, adaptive modulation, and coding. The technical details are not repeated here.

Analysis diagram of MIMO OFDM technology

2.5.4, MAC layer optimization technology

From the perspective of network logical structure, 802.11 only defines the physical layer and the media access control (MAC) sublayer. The MAC layer provides competitive and non-competitive use of shared wireless media, with functions such as wireless media access, network connection, data verification, and confidentiality. In order to improve the throughput of the entire network, the 802.11n standards team has also optimized the MAC layer protocol, changed the data frame structure, increased the proportion of the net load, reduced the number of bytes occupied by management error detection, and greatly improved the network. Throughput.

2.5.5 Smart Antenna Technology

Smart antenna is an antenna array system composed of multiple independent antennas. The output of the array is combined with multiple inputs of the transceiver to provide a comprehensive space-time signal. Different from a single antenna, the antenna array system can dynamically adjust the beam direction so that each user gets the largest main lobe and reduces sidelobe interference. This not only improves the SINR (Signal-to-Interference and Noise Ratio), but also increases the system capacity, expands the maximum coverage area of the cell, and reduces the mobile station's transmit power. The basic structure of a smart antenna is shown in Figure 4.

Smart antenna technology analysis diagram

Smart antenna technology guarantees communication at a transmission rate of not less than 108 Mbps, and can also be used as a broadband access part of cellular mobile communications, which is more closely integrated with wireless wide area networks. On the one hand, 802.11n can provide users with high data rate communication services (such as video-on-demand VOD and online viewing of HDTV); on the other hand, wireless wide area networks provide users with better mobility.

2.5.6 Software-defined radio technology solves mobile problems

Multiple standards of WLAN coexist. Different standards use different operating frequency bands and different modulation methods, which makes it difficult for systems to communicate with each other and poor mobility. Software-defined radio is the most promising technology to solve these problems.

Software defined radio refers to the development of a fully programmable hardware platform. All applications are realized through software programming on this platform. In other words, the base stations and mobile terminals of different systems can all be implemented by different software based on the same hardware. This technology will ensure seamless integration between various mobile stations and various mobile communication devices, and greatly reduce construction costs.

Software radio-based mobile communication has the following characteristics:

(1) Compatible with different systems on the same hardware platform

(2) With automatic roaming capability, can intelligently switch between different systems

(3) You can download public software and upgrade yourself

(4) Supports multiple services such as voice, data, image, and fax, and can automatically select the appropriate transmission channel based on business traffic, channel quality, etc.

(5) Automatically select the communication mode, and use the appropriate communication protocol and signal format to realize remote communication.

The application of software radio in 802.11n will fundamentally change its network structure, realize the integration of wireless local area network and wireless wide area network and can accommodate various standards and protocols, provide a more open interface, and ultimately greatly increase the flexibility of the network.

As a new standard, IEEE802.11n wireless LAN has two advantages over the previous 802.11 protocol. The first is the short-term advantage. It has a high transmission rate and the data transmission rate is above 100Mbps, which enables the wireless LAN to be smoothly integrated with the wired network, and comprehensively improves the network throughput. Dual-frequency mode, that is, based on the MIMO + OFDM modulation technology in the 2.4GHz and 5.8GHz frequency bands, improves the data transmission rate. At the same time, the transmission distance of 802.11n is longer, and it is easy to integrate with wireless WAN.

802.11 wireless technology editorial point of view

802.11n can definitely bring a real killer application to WLAN. Think about the fact that we can no longer use mobile phones and desktop phones in the office, but use Wi-Fi phones, or we can make laptops without interrupting the network connection. Mobile office in various offices and conference rooms. In the home, we can enjoy a variety of broadband wireless applications, from IPTV to video phones can be achieved through WLAN, more importantly, all kinds of smart home appliances can be connected through WLAN, connected to the communication system can be more intelligent control.

802.11n is like a beacon in the mist, it is getting closer and closer to us.

802.11 wireless technology open source project

Using the open source software radio GNU Radio, BBN Technologies Internetwork Research BBN -BBN Technologies Internetwork Research ADROIT Project writes 802.11 code under the auspices of DARPA. GNU Radio is a free software development tool suite. It provides signal operation and processing modules that can be used to implement software-defined radios on easy-to-manufacture, low-cost radio frequency (RF) hardware and general-purpose microprocessors. This kit is widely used by amateurs, academic institutions and commercial institutions to research and build wireless communication systems. GNU Radio applications are mainly written in the Python programming language. But its core signal processing module is C ++ built on a microprocessor with floating point arithmetic. Therefore, developers can simply and quickly build a real-time, high-capacity wireless communication system. Although its main function is not an emulator, GNU Radio supports the study of algorithms for signal processing of pre-stored and (signal generator) generated data without RF RF hardware components.