主题：Wi-MAX -- octane99

Abstract

In this essay, we examine an emerging wireless broadband technology – WiMax – in a perspective of technical characteristics, marketing prospects and challenges. We also compare the WiMax technology with other contemporary wireless technologies, such as Wi-Fi and 3G. As the result of our research, we conclude that, as an effective and alternative access technology, WinMax will compete and coexist with other wireless technologies in the near future.

Key words: WiMax, wireless broadband access

1. Introduction

It is widely recognized that wireless, broadband, and technologies combining them are major trends in the future of telecommunication. Wireless broadband access is not a new technology, but it is infused new vigor along with emerging WiMax, Worldwide Interoperability for Microwave Access. WiMax, the industry consortium associated with IEEE 802.16 standard, is promising to deliver high speed data rates over MAN (Metropolitan Access Network), which is attractive for both carriers and the customers.

WiMax will provide fixed, nomadic, portable and mobile wireless broadband connection. For fixed and portable application, which is suitable for notebook computers and PDAs, WiMax provides up to 40Mbps per channel capacity. For mobile application, it provides up to 15Mbps of capability. WiMax working group has developed two version of standard to address different access demands. 802.16-2004 WiMAX supports fixed and nomadic access, whereas 802.16e WiMAX supports portable and mobile access as well as fixed access.

In table 1, we illustrate the types of access to a WiMax network according to IEEE 802.16 specification.

Table 1. Types of access to a WiMax network

(WiMAX Forum)

Besides IEEE 802.16, there is another equivalent standard in Europe, ETSI HiperMAN, and in South Korea, WiBro. WiMax is working on interoperating with HiperMAN seamlessly.

In following sections, we will give details on WiMax’s technical specifications, market prospects and the challenges it will face.

2. Technical specifications

1. Spectrum and modulation

WiMax has the advantage of using multiple broad frequency ranges, which maximizes the transmission ability and avoids interference. WiMax use both licensed and non-licensed frequencies, including the frequency bands from 10 to 66 GHz and sub 11GHz. Initial WiMAX 802.16-2004 profiles are in the 3.5 GHz and 5.8 GHz frequency bands. The frequency bands for the 802.16e profiles have not yet been announced, but 2.3 GHz and 2.5 GHz are the most likely initial candidates.

IEEE 802.16-2004 profiles use OFDM( Orthogonal Frequency Division Multiplexing) with 256 carriers. OFDM increases bandwidth and data capacity by splitting broad channels into multiple narrowband channels—each using a different frequency—that can then carry different parts of a message simultaneously.

IEEE 802.16e profiles are most likely using SOFDMA (Scalable Orthogonal Frequency Division Multiplexing Access) with 2048 carriers. SOFDMA is a multi-carrier modulation technique that uses sub-channelization, and it is designed to minimize the interference on user devices with omnidirectional antennae. IEEE 802.16e offers improved support for MIMO (Multiple Input Multiple Output) and AAS (Adaptive Antenna Systems).

The initial profiles of channel bandwidth are limited to 3.5 MHz and 7 MHz in the licensed spectrum as these are the prevalent spectrum channels allocated in the 3.5 GHz band.

2. Transmission rate

WiMAX should be able to handle up to 70 megabits per second. Even that bandwidth is split up between several dozen businesses or a few hundred home users, it will provide at least the equivalent transfer rates of cable-modem to each user.

3. Media access layer

IEEE 802.16 defines its MAC (media-accessc ontrol) layer into sublayers that support different physical layers, including IPv4, IPv6, Ethernet, and ATM. This gives equipment manufactures flexibilities to offer different devices. The MAC layer of Ethernet, which is used by Wi-Fi, is deployed by contention access—subscribers are competing with each other to get the access. On the contrary, the WiMax MAC layer is a scheduling MAC where the subscriber station only has to compete for initial entry into the network. The subscribers are assigned a time slot by the base station. This scheduling algorithm is stable and much more bandwidth efficient. At the same time, base station can control Quality of Service by this algorithm.

4. Transmission distance

WiMax can operate at high power rates and use directional antennas; therefore, its transmission distance is up to 30 miles. Even in the case of keeping (????) user’s bandwidth, which needs to reduce the number of customers it serves, the base station still serves an area of 10-mile radius.

5. Service types

WiMAX can provide two forms of wireless service: non-line-of-sight and line-of-sight.

Non-line-of-sight service is implemented by a small antenna on the computer, using 2 GHz to 11 GHz frequency range. The lower wavelength allows the transmissions get through physical obstructions. Non-line-of-sight service is aimed to portable and mobile customers.

Line-of-sight service uses a fixed dish antenna and higher frequencies up to 66 GHz. At higher frequencies, there is less interference and lots more bandwidth. This service is used by fixed customers.

6. Comparison with Wi-Fi and 3G

WiMax Wi-Fi 3G

Coverage Wide area

(city) Local area

(campus,building,home) Wide area

(city)

Spectrum 10G-66G & sub 11G

Licensed and unlicensed 2.4G

Unlicensed 800M ~2.4G

Licensed

modulation OFDM & SOFDMA CCK GMSK

Data rate Up to 70 Mbps Up to 54 Mbps Up to 2 Mbps

Standard IEEE802.16

ETSI HiperMAN IEEE 802.11 IMT2000

Equipment WiMax tower

& receiver

Access point

& Wi-Fi card Cellular tower

& cellular phone

Application Line-of-sight

& Non-line-of-sight Non-line-of-sight Non-line-of-sight

Mobility IEEE802.16e supports handoff and roaming no Support handoff and roaming

Table 2. Comparison with other wireless technologies

3. Market prospect

WiMax has its potential to be widely used for different Internet access, such as video, VoIP, and son on. We list the market opportunities for WiMax as following:

1. Both cable and telephone companies are examining it as an alternative to DSL, cable, and T1 for the last mile access.

2. Cellular companies use WiMax to increase bandwidth for data-intensive applications in addition to their traditional cellular services.

3. For developing countries without optical fiber or copper infrastructure, WiMax provides an opportunity of affordable high speed access.

So far, a lot of major cities in USA, China are planning to launch WiMax services for their customers. Recently, KT Launches Commercial WiBro Services in Korea, which is the first commercial application of WiMax. It is estimated that the early products are going to provide fixed access for network service providers and business customers, and expand to mobile access for end consumers.

4. Challenges

1. Spectrum

Some of the WiMax spectrum has been used for other purposes; this is an obstacle for achieving its initiative of high speed access. Moreover, the higher the frequencies, the more it will cost to deploy wireless technology. This will increase the cost of WiMax implementation since the many of lower frequencies have been licensed for other uses.

2. Competition

WiMax will face furious competitions from other wireless technologies, such as 3G and IEEE 802.20. The mobile version of WiMax, IEEE 802.16e, are providing mobile broadband connection for similar users as 3G. The giants in the industry, Intel, Nokia, Motorola are collaborating to promote WiMax , whereas Qualcomm, the advocator of 3G and beyond wireless system, is finding the way to compete with WiMax.

3. Chipsets

Although WiMax is a standard-based technology, its chipsets are still custom-built for each manufacturer. This will increase the expense of commercialization for WiMax since it can’t overcome this disadvantage.

4. Conclusion

WiMax, an alternative technology of traditional last-mile accesses, promises high speed wireless connection for a variety of customer groups. With its diversity service ability, network service providers can benefit from its high capacity fixed application; individual customers can benefit from its mobile broadband access application. There are still some limitations to deploy WiMax in the competitive market. WiMax will coexist with other wireless technologies; it could connect Wi-Fi hotpots and complement cellular system in data-intensive applications.

Reference

S. J. Vaughan-Nichols, “Achieving Wireless Broadband with WiMax”. June 2004.

http://ieeexplore.ieee.org/iel5/2/28995/01306375.pdf

Wikipedia, “WiMAX, From Wikipedia, the free encyclopedia”.

http://en.wikipedia.org/wiki/Wimax

WIMAX Forum, “Fixed, nomadic, portable and mobile applications for 802.16-2004 and 802.16e WiMAX networks ”, White Paper. November 2005.

http://www.wimaxforum.org/news/downloads/Applications_for_802.16 2004_and_802.16e_WiMAX_networks_final.pdf

WIMAX Forum, “Telephony’s “Complete Guide to WiMAX””, White Paper.May 2004.

http://www.wimaxforum.org/news/press_releases/Telephony_WiMAX.pdf

WiMax.com

http://wimax.com/education/index_html/view