Sunday, May 6, 2007

[WiMAX] Fundamentals of WiMAX - (1)

WiMAX (Worldwide Interoperability for Microwave Access) is one kind of wirless broadband access technology. In my country, China, WiMAX is going to be deployed for the 2008 Olypmic games. Actually, in China there is another technology called McWill (Multicarrier Wireless internet Local Loop), which is a synchronous CDMA system using Smart Antenna , SWAP signaling , synchronous CDMA and Software Radio. This McWill is developed by a Chinese company. I remembered in the end of 2006, the news said McWill would be used for 2008 Olympic games. However, just after several months, the latest news says that WiMAX is authorized by the committe of the Olympic games and China Mobile is goint to deploy it in 2008. It looks like McWill lost the game. It is really a pity.

Ok, let us go back to our topic and concentrate on techniques. From today, I'm going to give a series of introduction of WiMAX, mainly focuses on its fundamental issues, such as overview, history, technicall challeges, physical layer, MAC layer etc. I think it also helps me consolidate my knowledge on WiMAX.

History of WiMAX

Before WiMAX, there already exist many wireline broadband access techniques, such as DSL(Digital Subscriber Line), cable modem, FTTP(Fiber to the premises ) and VDSL. This market grows quickly. When I came to the US in 2001, the rate of Verizon's is about 768Kbps. Now I'm using Comcast's cable modem with rate 5Mbps. Recently, Verizon is promoting its FIOS system which is said to support rate at 15-40Mbps.

Later, people found it is necessary to provide broadband access service in wireless, because it offers additional benifits and convenience. For example, it may be easier to install than wire-line access, the cost may be lower, it can be portable and mobile.

Generally speaking, wireless broadband access can be categorized into two types:
1) Fixed wireless broadband,
2) Mobile broadband.

As for WiMAX, it has evolved through four stages. [1]
1) Narrowband WLL (Wireless Local Loop) system
2) First generation LOS (Line of Sight) broadband system
3) Second generation NLOS (Non Line of Sight) broadband system
4) Standard-based broadbank system.

Next, let us take a quick look of those four stages.

1) Narrowband WLL

It is mainly based on DECT or CDMA. As I know, WLL on CDMA at 450MHz has been using in China for a long while.

2) LOS

In 1990s, LMDS(Local Multipoint Distribution System), works on 2.5 or 3.5GHz. Operator: Nextlink. Now it is almost dead. [2]

In late 1990s, MMDS(Multichannel Multipoint Distribution System), works on 2.5GHz. Operators: MCI, Sprint.

Starting in 2006, MMDS frequencies in the 2110-2155 MHz range are being re-allocated for the Advanced Wireless Services (AWS-1). [3]


It is proposed to overcome the LOS issue, and improve link performance under multipath conditions. It may use OFDM, CDMA or multiantenna techniques.

4) Standard-based

It is the well-known IEEE 802.16x [4], a seriers of standards for Wireless Metropolitan Area Network (WMAN).

  • December 2001, IEEE 802.16 standards completed for > 11GHz.
    Wireless WAN-SC, uses single carrier modulation techniques. MAC layer is with TDM.
  • January 2003, IEEE 802.16a standard completed.
    Works in the 2GHz to 11GHz range, enables NLOS deployments by using OFDM. MAC is using OFDMA.
  • June 2004, IEEE 802.16-2004 standard completed and approved.
    It replaces 802.16, 802.16a, 802.16c with a single standard. It is also called Fixed WiMAX.
  • December 2005, IEEE802.16e-2005 approved.
    Supports vehicular mobility applications. It is also referred to as Mobile WiMAX.

Similar to 802.11x, IEEE established the specifications for WiMAX but left to the industry the task of converting them into an interoperable standard and the task of certification. WiMAX Forum (analogous as Wi-Fi Alliance) was formed to do those tasks.

[1] J.G.Andrews, Arunabha Ghosh and Rias Muhamed, "Fundamentals of WiMAX-understanding Broadband Wireless Networking", Prentice Hall, Feb, 2007





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