WiMAX, a wireless broadband technology, has the ability to compete with DSL and cable-modem services without the need for heav

WiMax - What I should know about it?

WiMax - Introduction

WiMax (Worldwide Interoperability for Microwave Access) is a wireless broadband technology,which supports point to multi-point (PMP) broadband wireless access over a coverage area of 3 – 5 miles. WiMax is another name for the 802.16 IEEE wireless broadband standard. The technology can support access rates up to 2+ Mbps. WiMax can solve a problem called the “last-mile” problem, by connecting individual homes and business office’s communications.

The standard has a range of up to 30 miles, and can deliver broadband at around 75 megabits per second. This is theoretically, 20 times faster than a commercially available wireless broadband. WiMax can be termed partially a successor to the Wi-Fi protocol, which is measured in feet, and works, over shorter distances. WiMax supports ATM, IPv4, Ipv6, Ethernet, and VLAN services. WiMax offers many choices.

Let us take a peek into the background of this much talked about technology, which is taking the wireless world by storm. Read More…

WiMax – Background

WiMax was a precursor to the original 802.16 standard published in December 2001. WiMax forum was formed in April 2001, an advocacy group, founded by a coalition of companies such as Intel, Nokia and Proxim. The promoters of the WiMax technology expect it to make networks with multimedia applications connect within a range of 30 miles. The forum was formed solely for promotion of devices supported by the 802.16 standard. The forum takes responsibility also to develop devices confirming to the standard and releasing it in the market. This is sometimes also termed as a wireless’ answer to advance IEEE standards for broadband wireless access (BWA) networks. The forum was reportedly planning to bring out its products based on the 802.16 technology sometime last year.

In April 2005, the WiMax promoters talked about a formal agreement with the European Telecommunications Standards Institute (ETSI). This agreement, reportedly confirmed a single global standard for all wireless metropolitan area network technology. Some prominent members of the WiMax organization are Airspan, Alvarion, Analog Devices, Aperto Networks, Ensemble Communications, Fujitsu, Intel, Nokia, OFDM Forum, Proxim and Wi-LAN.

WiMax - Standards

As discussed earlier, the 802.16, WiMax standard, which was published in March 2002, provided many, updated information on the Metropolitan Area Network (MAN) technology mentioned in the previous version. The extension given in the March publication, extended the line of sight fixed wireless Man standard, focused solely on a spectrum from 10 GHz to 60+ GHz. This extension provides for non-line of sight access in low frequency bands like 2 – 11 GHz. These bands are sometimes unlicensed. This also boosts the maximum distance from 31 to 50 miles and supports PMP and mesh technologies. Interestingly, these standards (PMP and mesh technologies) went unnoticed until the WiMax forum was formed. WiMax is the new shorthand term for IEEE Standard 802.16, which was designed to support the European standards. 802.16’s predecessors were not very accommodative of the European standards, per se. 802.11a wasn’t lucky enough to be compatible and hence lost on a global adoption. To talk of a bit of history on the 802 standards, the popular 802.11b has a range of up to 300 feet and can transmit at 11Mbits/sec. 802.11a operates at a shorter range, and 802.11g, combines the speeds of both “a” and “b”.

Lets see some more into the extensions used by the standards.

Extension b – This is especially for the quality of service features.

Extension c – This is for the interoperability and is related to protocols, test suite structures and test purposes.

Extension d – This creates system profiles for compliance testing of 802.16a devices.

Extension e – This is all about the enhancement of Wireless LAN air interface to support mobile and fixed broadband.

The base version of the 802.16 standard works in the frequency of 10 – 66 GHz. This requires line of sight towers. On the other hand, the 802.16a extension, operates in a lower frequency of 2 – 11 GHz, and also negates the need of a line of sight tower. This, however, can operate within 31 miles and offers data transfer rates of 70Mbps.

WiMax can be used for wireless networking like the popular WiFi. WiMax, a second-generation protocol, allows higher data rates over longer distances, efficient use of bandwidth, and avoids interference almost to a minimum. WiMax operates on licensed and unlicensed frequencies, provides a regulated environment and gives a feasible economic model for the users. Lets take a peek into the technology called the fixed wireless. This, fixed wireless, is also the base concept for the metropolitan area networking (MAN), given in the 802.16 standard.

Now, in fixed wireless, a backbone of base stations is connected to a public network. Each of these base stations, supports many fixed subscriber stations, either public WiFi hot spots or fire walled enterprise networks. These base stations use the media access control (MAC) layer, and allocate uplink and downlink bandwidth to subscribers as per their individual needs. This is basically on a real-time need basis.

The subscriber stations might also be mounted on rooftops of the users. The MAC layer is a common interface that makes the networks interoperable. In the future, one can look forward to 802.11 hotspots, hosted by 802.16 MANs. These would serve as wireless local area networks (LANs) and would serve the end users directly too. WiMax supporters are focusing on the broadband “last mile” in unwired areas, and on backhaul for WiFi hotspots. WiMax is expected to support mobile wireless technology too, wireless transmissions directly to mobile end users.

Impact Of WiMax

The operators, rooting for the WiMax cookie, are in for a surprise. WiMax would prove to be a double-edged sword. The initial WiMax products would operate between the frequencies of 2.5 GHz and 5.8GHz. This range includes both the licensed and unlicensed spectrum. Under the licensed spectrum, the operators can apply for franchisees for providing fixed wireless broadband. The unlicensed spectrum would have to make do with independent backhaul services for hotspots, which would create a wireless network across the nation.

The operators might be well off trying to offer parallel, integrated services for WiMax, similar to WiFi offerings. This guarantees a swifter ROI on low upfront investment. The margins would definitely be lower than cellular rates.

WiMax – Forum

As we learnt that WiMax was formed in April 2001, to promote conformance and interoperability of the standard IEEE 802.16. The Forum’s founding members were – Ensemble, CrossSpan, Harris and Nokia. In April 2002, the forum grew to accommodate another member – OFDM, and in November, added Fujitsu as its sixth member. In March 2003, after intensive lobbying for the just cause of promoting the standard by Fujitsu and Wi-LAN, many new members joined the WiMax forum. The new members were – Aperto, Alvarion, Airspan, Intel, Proxim and others. The current forum has strong presence from service providers, system manufacturers, chip vendors and eco-system vendors.

Currently the WiMax forum has 110 members, and there are no WiMax-certified products available in the market. In September 2004, Intel introduced initial samples of a WiMax chipset, named Rosedale. Intel announced plans of offering transmitters by 2005, and has plans to ship WiMax devices for use in the office and home by 2006.

Recent News from WiMax Forum

The WiMax community and its members put together a grand show in Vancouver, Canada. The main aim was to silence the skeptics and prove that the technology would sell like hot cakes, once people realize its worth.

WiMax forum discussions revolve around technology and never around operators. This is a trap that the Forum members avoid like the plague. It is very critical that the efficiency of WiMax should not be used only for competition for price and data services.

IEEE 802.16 – Impact On Wireless Broadband

The initial version of IEEE 802.16 was developed with the goal of meeting the requirements of deployment for BWA (Broadband Wireless Access) systems operating between 10 and 66 GHz. The IEEE does not provide conformance standards and test specifications. To ensure interoperability between different vendors and their equipments, the technical working group have now started working on the 11 GHz part.

The working groups develop a set of system profiles, Protocol implementation conformance statement proforma, test suite structure and test purposes, and abstract test suite specifications for the 10 - 66 GHz as well as the 11 GHz parts. This is according to the ISO / IEC 9464 series of conformance testing standards.

An Overview

The IEEE 802.16 group has been primarily developing a point-to-multipoint broadband wireless access standard for systems in a 10 - 66 G Hz and 11 GHz range. It is interesting to note that the standard covers the MAC (Media Access Control) and the PHY (Physical) layers.

While developing the target environment, many PHY considerations were noted and take into account. Line of sight becomes a must for higher frequencies. This eases the multi-path effect and allows for wider channels. Interestingly, for sub 11 GHz non line of sight capability is a requirement. Originally the IEEE 802.16 MAC was enhanced to accommodate various PHYs and services, thus taking care of different environments.

The IEEE 802.16 standard is versatile enough to accommodate time division multiplexing (TDM) or frequency division duplexing (FDD) deployments and also allows for both full and half-duplex terminals.

The MAC was developed for a point-to-multipoint wireless access environment and can accommodate futuristic products. This layer supports protocols like ATM, Ethernet and IP (Internet Protocol). The MAC frame structure dynamic uplink and downlink profiles of terminals as per the link conditions. This is to ensure a trade-off of capacity and real-time robustness.

802.16 MAC - An Overview

The MAC uses a protocol data unit of variable length, which increases the standards efficiency. Multiple MAC protocol data unit can be sent as a single PHY stream to save overload. Also, multiple Service data units (SDU) can be sent together to save on MAC header overhead. By fragmenting, you can send large volumes of data (SDUs) across frame boundaries and can guarantee a QoS (Quality of Service) of competing services. The MAC uses a self-correcting bandwidth request scheme to avoid overhead and acknowledgement delays.

This also allows better QoS handling than the traditional acknowledged schemes. The terminals have a variety of options to request for bandwidth depending on the QoS and other parameters. The signal requirement can be polled or a request can be piggybacked. More to come…

WiMax – Architecture

WiMax has two main topologies – namely Point to Point for backhaul and Point to Multi Point Base station to Subscriber station. In each of these situations, multiple input multiple output antennas would be used. In the Subscriber station WiMax architecture, the wireline connections would link to WiFi access points, servers, phones, VoIP gateways and optical fiber connections to the Internet.

The IEEE approved the 802.16 standards in June 2004, and three working groups were formed to evaluate and rate the standards. The initial development was of a point to multi point broadband wireless access standards operating in the range of 10 – 66 GHz. The 802.16 standard includes the media access control (MAC) and the physical (PHY) layers. WiMax has been designed basically to complement the existing WiFi and Bluetooth technologies.

The protocol structure of IEEE 802.16 – Broadband wireless MAN standard is shown below:

Source: www.javvin.com

The above picture shows four layers – Convergence, MAC, Transmission and Physical. These layers map to two of the lowest layers – physical and data link layers of the OSI model. The ISO model is given below for your reference.

Source: http://www.tutorial-reports.com/wireless/wlanwifi/

The 802.11 is based on a distributed architecture, whereas, WiMax is based on a centrally controlled architecture. In this the scheduler residing in the Base station (BS) has the complete control of the wireless media access. WiMax can support multiple connections conforming to a set of QoS parameters and provides the packet classifier ability to map the connections to many user applications and interfaces. Read more on this...

These interfaces may range from Ethernet, TDM, ATM, IP, and VLAN etc. The flexibility provided by WiMax also increases the complexity in service deployment and provisioning of fixed and mobile broadband wireless access (BWA) networks.

It would be better to explain the differences in the QoS mechanisms in the 802.11 and 802.16. This helps in finding out the challenges associated with large-scale WiMax deployment.

WiFi network is characterized by its simplicity. A Subscriber Station (SS) can very easily travel through a hotspot or an Access Point (AP). This does not require any user intervention. 802.11 is based on a distributed architecture. Here, MAC is coordinated among AP s and SS’. On the other hand, WiMax is based on centralized control architecture. Here, the scheduler in the BS has complete control of the wireless media access among all SS’. WiMax can support multiple connections having complete QoS readiness.

WiMax provides many user application and interfaces like Ethernet, TDM, ATM, IP, and VLAN.

WiMax offers a rich feature set and flexibility, which also increases the complexity of service deployment and provisioning for fixed and mobile networks. Let us take a look at the WiMax Management Information Base (MIB).

WiMax Management Information Base

Source: http://www.intel.com

The above figure shows the management reference model for BWA networks. This consists of a Network Management System (NMS), some nodes, and a database. BS and SS managed nodes collect and store the managed objects in an 802.16 MIB format. Managed objects are made available to NMS’ using the Simple Network Management Protocol (SNMP).

The database shows the service flow and its associated QoS information. The information is then directs the BS and SS to create transport connections.

WiMax – How It Works

It is imperative that customer intervention and truck roll is minimized so that WiMax can be deployed properly. When a customer subscribes to the WiMax service, the service provider asks the customer for the service flow information. This would include number of UL / DL connections with the data rates and QoS parameters. The customer also needs to tell the kind of applications that he proposes to run.

The service provider then proceeds to pre-provision the services and enters the information in the Service Flow Database.

WiMax – Competing Technologies

As we learnt in the previous pages, that WiMax was formed to complement Bluetooth and WiFi technologies, let us look at the differences in each of these:

Table I – Difference between WiMax, WLAN and Bluetooth

Parameters	WiMax	WLAN	Bluetooth
Frequency	2 – 11 GHz	2.4 GHz	Varies
Range	~31 miles	~100 metres	~10 metres
Data Transfer Rate	70mbps	11 – 55mbps	20 – 55mbps
Users	1000s	> 10	> 10

Source: www.javvin.com

WiMax Implementation Challenges

The 802.16 MAC protocol performs mainly two tasks – Periodic and Aperiodic activities. Fast activities (periodic) like scheduling, packing, fragmentation and ARQ are hard-pressed for time and have hard deadlines. They must be performed within a single frame.

The slow activities, on the other hand, typically execute as per pre-fixed timers, but are not associated with any timers. They also do not have specific time frame or deadline.

Subscriber station and Base station and their association occur through an exchange of messages and create many connections. There is an associated state between the SS and the BS. These connections sometime include the state to be tracked in the fast category. The connections may include fragmentation status, ARQ retransmissions and packing. The QoS and MAC challenges described above are not the only ones faced by WiMax. There are some virtualization challenges faced by the 802.16 MAC implementers.

Conclusion

WiMax may very well be the happening technology of the future, but the community is keeping its fingers crossed!