WiMAX technology and application

1. Introduction to WiMAX Technology

In recent years, the IEEE802.16 series of broadband wireless access technology standards have received widespread attention in the industry. Intel and other large-scale telecommunications equipment manufacturers have established the WiMAX Forum to coordinate the interoperability of network equipment and promote the development and popularization of WiMAX. As a broadband wireless access technology WiMAX positioned for outdoor applications, it has a series of remarkable features both from a technical perspective and an application perspective. Therefore, it has great appeal for both users and telecom operators.

WiMAX is called "Worldwide Interoperability for Microwave Access" in English, and the corresponding Chinese translation is "Worldwide Interoperability for Microwave Access", which is a new air interface standard for microwave frequency bands. Among the many wireless family members, it is based on the IEEE 802.16 series of broadband wireless standards. The emergence of WiMAX technology makes up for the shortcomings of Wi-Fi transmission distance. Like Wi-Fi, it also needs to create a "hot spot", but its network coverage is unmatched by Wi-Fi, WiMAX transmission distance is up to 50 Km, the transmission speed can reach up to 75Mbps. For friends who need high-speed Internet access anytime, anywhere, WiMAX is a very good technical solution, and people are used to calling WiMAX "wireless DSL".
Currently IEEE 802.16 includes two standards: IEEE 802.16a and IEEE 802.16e. IEEE 802.16a is a revised version of the IEEE 802.16 standard in January 2003. It extends the original frequency range; IEEE 802.16e is compatible with IEEE 802.16a, which mainly enhances mobility. It can be called the mobile version of WiMAX. The Centrino suite will integrate the technology.

2. Characteristics of WiMAX broadband wireless access

However, the IEEE 802.16 series of standards only define the air wireless interface, which provides flexibility for upper-layer applications. At the same time, as a wireless metropolitan area network technology that solves the "last mile" problem, how to compete with the currently widely used cable method in the future metro network access application and give full play to the strengths of the wireless mode is also worth studying. The problem. Therefore, in this sense, it is of great value to determine its competitive application model. Here, first, the technology and application characteristics of WiMAX broadband wireless access are analyzed, and based on this, a preliminary discussion is made on its application mode.
1. Long transmission distance, fast speed, and data security. In the way of information dissemination, WiMAX technology is similar to mobile phones, and also uses wireless base stations for data transmission. When the bandwidth is 20MHz, the data transmission rate can reach up to 75Mbps, which is 30 times the broadband speed that 3G can provide. With a coverage of up to 50 kilometers, as long as a few base stations are built, the whole city can be covered. The application range of the wireless network is greatly expanded, which is unmatched by the wireless local area network. In addition to speed and transmission distance, the security of wireless networks is also the focus of users' attention. No one wants confidential files to be easily obtained by others. In order to avoid people's worries, WiMAX provides a complete encryption mechanism. It defines an encryption sublayer in the media access layer (MAC), supports 128-bit, 192-bit and 256-bit encryption systems. By using digital certificates for authentication, Ensure that the information transmitted in the wireless network is well protected.

2. Application characteristics

First of all, WiMAX as a broadband wireless access application has the characteristics of gradual investment and flexible deployment. Network operators can gradually increase investment and gradually expand capacity in place according to the needs of user capacity growth to achieve a basically flat cost curve. Secondly, the network planning can be free from the restrictions of terrain and landforms, and the ministries are flexible. At the same time, areas with low user density can still achieve coverage at a lower cost, reducing the risk of initial investment. Thirdly, the network deployment is fast, installation and capacity expansion is convenient, no complicated network planning is required, and the network structure is flexible, especially in temporary and sudden emergency communications, which can play a huge role. Finally, as a broadband wireless access technology with a cell radius of up to 50km and an access rate of up to 70Mbit / s, it can be used as both a wireless extension of the metropolitan area network and an alternative to cable. In particular, it is more competitive than cable in areas where user density or traffic is not high and the distribution is scattered.

3. Physical layer characteristics

The WiMAX working frequency band can be from 2-66GHz (for IEEE802.16 standard: 2-11GHz; for IEEE802.16a standard: 10-66GHz), the channel bandwidth can be flexibly adjusted in the range of 1.5-20MHz, which is beneficial to the allocated channel bandwidth Make full use of the spectrum resources within.

WiMAX adopts macro cell mode with a maximum coverage of 50km. When the channel bandwidth is 20MHz, it supports a shared data transmission rate of up to 70Mbit / s (in this case, the maximum coverage is 3-5km). Multi-sector technology can be used to increase system capacity. One sector can simultaneously support more than 60 enterprise users using E1 / T1 or hundreds of home users.

WiMAX uses OFDM, receive / transmit diversity, adaptive modulation and other advanced technologies to achieve non-line-of-sight NLOS and blocked line-of-sight ONLOS transmission, which effectively improves the efficiency of wireless transmission in the city.

The physical layer supports two wireless duplex multiple access modes, TDD / DMTA and FDD / TDMA, to meet the requirements of telecommunication systems in different countries or regions. It supports three modulation modes: single carrier (SC), OFDM (256 points), OFDMA (2048 points), and can be flexibly selected according to needs. The physical layer can dynamically adjust the modulation method and physical layer parameters (for example: modulation parameters, FEC parameters, power levels, polarization methods, etc.) according to changes in transmission channel performance to ensure better transmission quality.

4. MAC layer features

Support QoS management to meet the requirements of different service quality. The MAC layer requests connection bandwidth or performs bandwidth adjustment in a polling manner according to service QoS requirements and service parameters to ensure low latency requirements for real-time services such as voice and video. At the same time, for the high bit error rate and packet loss rate in the wireless channel environment, ARQ based on each application stream is defined to ensure the automatic retransmission of the MAC layer service data unit MSDU to ensure the end-to-end packet transmission quality.

The MAC layer has an ATM service and packet service convergence sub-layer CS, which can easily implement network applications featuring ATM services or IP services. At the same time, the MAC layer has a security sublayer that supports the MAC layer security mechanism to implement security management such as authentication and encryption.

5. Business capability

WiMAX uses a connection-oriented approach to provide users with data, video and voice (VoIP) services with QoS performance. In the IEEE802.16 standard, the MAC layer defines a relatively complete QoS mechanism, and also defines four different services, namely: unsolicited bandwidth allocation service (UGS), real-time polling service (rtPS), non-real-time round Inquiry service (nrtPS) and best effort service (BE) can be used to provide users with high-quality video and voice services, ordinary-quality video and voice services, and services such as the Internet without quality assurance. Can dynamically allocate bandwidth according to the actual needs of the business, with greater flexibility. Therefore, WiMAX can provide different QoS for different services.

6. Network structure characteristics

Supported point-to-multipoint (PMP, PointtoMulTIpoint) architecture can build a star access network structure centered on WiMAX base stations. The newly released IEEE802.16a also supports mesh mesh architecture, which allows multiple WiMAX nodes to construct a mesh network using wireless interconnection. This means that the structure of the access network can be flexibly expanded, and WiMAX mesh network coverage can be used in areas where the backbone network cannot reach it, so as to achieve the flexible extension of the metropolitan area network.

3. Comparison between WiMax, 3G and Wi-Fi

Compared with 3G technology, WiMax has shown huge advantages in many aspects. Although the speed of the 3G network has been greatly improved compared with the current technology, the speed of the 3G network is 30 times slower than that of WiMax. In the network coverage area, the coverage of a 3G base station is only one-tenth of WiMax. And WiMAX uses free spectrum, and the cost is much lower than 3G. The core function of the 3G network is to provide mobile phone services and can also be used to transmit data; WiMax standard is high-speed data transmission, and voice quality is not a critical requirement. Therefore, the respective tasks and objectives of these two technologies are different. The focus of WiMax is to achieve broadband wireless, while 3G is more inclined to achieve wireless broadband.

Compared with Wi-Fi technology, the advantages of WiMAX technology seem to be more obvious. However, WiFi and WiMAX technologies respectively solve the "last 100 meters" and "last 1 kilometers" problems, and thus have different positioning and uses. On the contrary, Wi-Fi can be directly connected to the backbone network through the outdoor antenna and using WiMAX technology, but the current Wi-Fi network does not need to connect the wireless access point to the backbone network through the wired network, thereby greatly reducing the laying of wired The cost of the network. Therefore, for the different positioning and advantages of WiMAX and Wi-Fi technologies, the two can complement each other and develop together. Therefore, these three technologies should be more complementary than replacing.

4. Application scenarios Compared with other access methods, WiMAX broadband wireless access has the advantages of faster deployment speed, stronger expansion capabilities and higher flexibility. Its typical application scenarios are:

1. Internet access

For communities and buildings with integrated wiring, install the outdoor unit ODU of the WiMAX client on the top of the building, and install the user-side indoor unit and Ethernet switch in the building or community. Use the existing integrated wiring to access users through the wireless air interface Provide broadband Internet service.
WiMAX has truly achieved broadband wireless, which has freed the Internet from the constraints of wires. At the same time, WiMAX can provide high bandwidth according to user needs, so that end users can truly experience the speed experience brought by high technology.
2. Internet cafes and talk cafes mainly use soft-switched VoIP (VOICE OVER IP), which is a new generation of network communication technology for commercial operations of telephone supermarkets. At present, VoIP communication technology has been widely used in voice operation business, especially in the application of telephone supermarket business, the revenue is the most significant, and the voice quality has been comparable to traditional circuits.
Internet cafes mainly need high-speed Internet access, operating Internet access, online online games, voice chat (QQ, MSN, etc.), online video on demand movies and other services.

3. Village to Village Project

For low-end users in rural and remote areas, communication services are mainly focused on cheap voice calls and small data traffic data services. Rural communication services require large system coverage, do not depend on the laying of cables, and have fast access speeds and low costs. WiMAX (802.16-2004) technology is very suitable for this market, improves the quality of universal service in China's rural areas, and narrows the "digital divide" with cities in a shorter period of time.

4. Real-time video monitoring Most of the traditional video monitoring systems can only be simulated and monitored on site. The transmitted monitoring information is simple, the real-time image of large flow cannot be transmitted clearly, and the actual situation on the spot cannot be understood in time and accurately. The efficiency of the monitoring system is relatively low .
The WiMAX network makes it possible to transmit large amounts of video, allowing traditional video surveillance to be extended over WiMAX technology â€™s wireless broadband. Real-time surveillance business applications are very wide and can cover most industries. Common applications can be hotel lobby , Banking business hall, insurance company monitoring, traffic flow monitoring of traffic roads, it can also be derived from kindergarten monitoring, family anti-theft monitoring, coal mine underground working surface monitoring and so on.
On the other hand, WiMAX eliminates the need to lay pipelines, avoiding time-consuming and labor-intensive construction of pipeline lines, and provides convenient and fast access to real-time monitoring services through wireless transmission.

5. LAN LAN interconnection For large enterprises, if there are multiple enterprise branches in the region, the WiMAX broadband fixed wireless access system can easily achieve the LAN connection between the headquarters and each branch.

6. Narrowband service or base station interconnection provides the E1 interface through the WiMAX broadband fixed wireless access system, which can meet the access of GSM mobile base stations and support 3G network base station interconnection in the future.

V. Current status and development trend Currently, WiMAX has been widely used abroad, especially the commercialization of 16d WiMAX chips has accelerated the pace of the equipment market. There are already many companies that can provide 16d equipment, and there are many fixed and mobile operators worldwide. WiMAX trials have been conducted. There are 130 deployment cases in more than 30 countries around the world, of which more than 30 are commercial networks. At present, the frequency band of their work is mainly 3.5GHz.

The 3.5GHz frequency is the frequency band recommended by the ITU for fixed wireless access (Fixed Wireless Access). The 3.5GHz fixed wireless access system uses point-to-multipoint microwave technology and mainly provides large-capacity voice and data. Services can also provide backhaul connections for narrowband wireless systems and mobile base stations. For users who are inconvenient to lay optical cables, users who are relatively uneconomical to lay optical cables, and users who have a strong urgency to open the network, the introduction of a fast and economical fixed wireless access system can provide users with much-needed access services. The bottleneck of the access network has played a powerful complementary role. Therefore, it has broad commercial application prospects.
Compared with the traditional 3.5GHz point-to-multipoint fixed wireless access system, the 3.5GHz WiMAX wireless access system using the IEEE 802.16 technology standard has the combined advantages of WiMAX and 3.5GHz, and has standardization, mature technology, fast transmission speed, and coverage The advantages of wide range, good rain attenuation resistance, strong capacity expansion, and flexible networking have become the ideal wireless access method for the current operator's "last mile" construction of broadband metropolitan area networks. Through the use of this technology, operators can provide customers with various value-added services. With less initial investment, operators can quickly achieve large-scale user coverage, quickly occupy the market, and attract customers; With continuous development and expansion, the smoothness of system expansion meets its rolling development needs.

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