Introduction
"[WiMAX] could potentially be the biggest thing since the Internet itself," as Sriram Viswanathan,
general manager of Intel's Worldwide Interoperability for Microwave Access (WiMAX) program office,
once stated. That is quite a bold statement and underscores the sentiment of many WiMAX proponents.
But as the WiMAX industry has grown, so has WiMAX hype and confusion.
This article is the first in a five-part WiMAX tutorial series. The series begins by introducing WiMAX technology, applications and terminology. Further articles will discuss WiMAX services, performance, security and devices.
Fixed WiMAX
The
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IEEE originally formed the IEEE
802.16 working group in 1998 to provide a standard for wireless metropolitan area networks. The
primary application was for high-speed fiber access solutions using high-frequency line-of-sight
(LOS) fixed wireless connections. The original standard was referred to as 802.16 and
evolved to support fixed broadband wireless access over lower-frequency non-line-of-sight (NLOS)
wireless connections. The evolved standard, 802.16-2004, is often referred to as fixed
WiMAX.
Mobile WiMAX
Once the 802.16-2004 standard was complete, the IEEE committee began work to further evolve the
standard to support mobile applications. Mobile communication is more complex than fixed
communication. The technology must be able to hand off a wireless connection from one base station
to another while the user is moving, without dropping the connection. The new 802.16e-2005 standard
was completed in December 2005 and not only supports mobile applications but also nomadic and fixed
applications. 802.16e-2005 is often referred to as mobile WiMAX.
Physical layer
The fixed/mobile WiMAX PHY layer
uses a technology called orthogonal
frequency division multiplexing (OFDM). OFDM techniques have been around for decades. The
technology is now commonplace in wireless systems such as Wi-Fi. OFDM evolved from earlier
single-carrier modulation systems and frequency division multiplexing systems. OFDM is a type of
frequency division multiplexing system that provides better channel throughput because all of the
underlying sub-carriers are orthogonal to one another.
Media access control layer
The primary job of the MAC layer
is to provide an interface between the PHY layer and upper layer protocols. Each instance of the
MAC layer in a fixed/mobile WiMAX station has a 48-bit address as defined by the IEEE Std
802. Unlike the distributed and connectionless 802.11 MAC, the WiMAX MAC is centralized and
connection-oriented. A 16-bit connection identifier (CID) identifies each WiMAX connection. Each
WiMAX MAC layer protocol data unit uses the CID, instead of the MAC address, to identify source and
destination. WiMAX has a rich quality of service mechanism that is based on the Data Over Cable
Service Interface Specifications (DOCSIS).
WiMAX applications
At the most basic level, WiMAX supports mobile, fixed and nomadic wireless applications. A mobile
application provides communication while the user is in transit. A good example is a business
traveler who communicates while on a train. The Sprint Xohm service -- to be launched in spring 2008 --
will provide Internet access while moving at high speeds using WiMAX technology. It will compete
with 3G technologies like EV-DO
and HSDPA
.
Fixed wireless applications often provide last-mile connections in rural or underdeveloped areas that do not have DSL, Hybrid Fiber-Coax (HFC), or other last-mile wired infrastructure. Enterprises can either purchase fixed WiMAX technology for use in their own private network (e.g., a point-to-point wireless connection between two buildings) or can purchase fixed WiMAX service from a wireless Internet service provider (WISP).
Finally, a nomadic application is one where a user moves from location to location but communicates only while stationary. A good example is a repairman who needs high-speed network access while parked at a customer location but not while driving. .
Summary
Table 1 summarizes how WiMAX technology relates to WiMAX applications. Over time, 802.16e-2005 is
likely to become the dominant standard for fixed, nomadic and mobile applications, thus limiting
the use of 802.16-2004.
Table 1: WiMAX applications and technologies
As we can see from this article, terminology is important. Therefore, throughout the rest of this WiMAX tutorial series, we will use the following terminology to ensure clarity.
- Fixed WiMAX will refer to technology that adheres to the 802.16-2004 standard.
- Mobile WiMAX will refer to technology that adheres to the 802.16e-2005 standard.
- Fixed WiMAX application will refer to a last-mile wireless application irrespective of the underlying technology standard.
Looking ahead
In the next story in this series, we look at WiMAX services. We will discuss which services will be
offered, who will offer them, and when they will be generally available.