1. 802.16 for WAN (WiMax)

2. What is WiMax? Acronym for Worldwide Interoperability for Microwave Access It’s the IEEE standard, first introduced in 2001, for wireless communications systems that cover an area larger than WiFi does. Use a tall antenna to cover a relatively large area to provide two-way wideband (high speed) connections wirelessly. The initial 802.16 was designed to provide a wireless alternative to cable and DSL for the last mile (last km) broadband access. The new 802.16e amendment can also serve mobile users (see below for detail).

3. Versions 802.16-2004 (also known as 802.16d) WiMAX. It uses Orthogonal Frequency Division Multiplexing (OFDM) and supports fixed users. 802.16e WiMAX. This amendment was ratified in December 2005 and supports both fixed and mobile users. It uses Scalable Orthogonal Frequency Division Multiple Access (SOFDMA). 802.16m, the newest version.

4. Advantages of WiMax over wired networks –Lower cost. Equipment may be more expensive, but it does not require laying cables. –Faster installation, if spectrum and base station locations can be obtained. –Will be installed only for users that need the service. To lay cables one has to consider the potential users.

5. Compared with other wireless services One can get high speed connection using telephone lines (DSL), but the phone line may not be good enough, or may be too far from the central office. 3G is slower for data transmission. Wi-Fi has smaller coverage range and designed for fewer users (it lacks sophisticated resource allocation, etc.).

6. Basic features Point – multiple point communications (the earlier version of WiMax) to replace fiber optic backbones Can use a large range of frequencies (2-66 GHz). In the US, 15 bands between 2-40 GHz can be used for WiMax. (It doesn’t mean a service provider can use all those bands. One can only get a band, usually small, that is auctioned by FCC.) Range: a few miles to 30 miles (see below) Data rate: up to tens of Mbps (see below)

7. Longer range It provides up to 50 km (31 miles) of linear service area range and allows connectivity between users without a direct line of sight (at lower frequency bands). This should not be taken to mean that users 50 km (31 miles) away without line of sight will always have connectivity. Practical limits from real world tests seem to be around 3 to 5 miles. If the density of users and thus the demand for resource (bandwidth) are high, the range will be determined by the demand for resource. (The bandwidth will be shared by many users, thus the number of users will be limited, and thus the range of service, too.)

8. Performance The technology has been claimed to provide downlink data rates up to 70 Mbit/s (even 128 Mbit/s with MIMO), which, according to WiMAX proponents, is enough bandwidth to simultaneously support more than 60 businesses with T1-type connectivity and well over a thousand homes at 1Mbit/s DSL-level connectivity. Real world tests, however, show practical maximum data rates between 500kbit/s and 2 Mbit/s, depending on conditions at a given site. New 802.16m can reach 1 Gbit/s fixed speeds and 100 Mbit/s for mobile users.

9. 802.16e It is designed to support mobile users. It uses OFDMA (Orthogonal Frequency Division Multiple Access), which gives 802.16e more flexibility when managing different user devices with a variety of antenna types and form factors. It brings a reduction in interference for user devices with omnidirectional antennas and improved Non-line-of-sight (NLOS) capabilities that are essential when supporting mobile subscribers.

10. Subchannilization in 802.16e Subchannelization defines subchannels that can be allocated to different subscribers depending on the channel conditions and their data requirements. This gives the operator more flexibility in managing the bandwidth and transmit power, and leads to a more efficient use of resources. For instance, within the same time slot more transmit power can be allocated to a user with less favorable channel conditions, while lowering the power for users in better locations. Improved in-building coverage can be achieved by allocating higher power to sub-channels assigned to indoor user devices.

11. Resource allocation 802.16-2004 uses OFDM. A user device transmits using the entire spectrum. Users are separated by time division (different users are assigned different time slots). 802.16e uses SOFDMA (Scalable Orthogonal Frequency Division Multiple Access). Users can be allocated partial spectrum as well as various time slots.

12. Assigning sub-channels

13. Handoff 802.16e supports different types of handoff, ranging from hard to soft. Hard handoffs use a break-before-make approach. The user device is connected to only one base station at any given time which is less complex than soft-handoffs but has a high latency. Soft handoffs allow the user device to retain the connection to a base station until it is associated with a new one (make-before-break approach), thus reducing latency. While applications like mobile Voice over Internet Protocol (VoIP) or gaming greatly benefit from low- latency soft handoffs, hard handoffs typically suffice for data services.

14. Version Selection Fixed and mobile deployments have very different requirements and target substantially different market segments, with different usage patterns and locations, throughput needs, user device form factors, and SLAs. In a fixed deployment, 802.16-2004 and 802.126e offer similar performance. Single sector maximum throughput for both versions of WiMAX is about 15 Mbps for a 5 MHz channel, or 35 Mbps for a 10 MHz channel. Base station range in densely populated areas can go up to a few kilometers depending on the actual conditions. In networks that are capacity constrained, the number of base stations installed depends on throughput demand, rather than range.

15. Advantage of 802.16-2004 Less complex modulation. OFDM is a simpler modulation technique. Use of License-exempt bands. Fixed deployments have successfully used license-exempt bands in areas where interference levels are acceptable. Mobile services require licensed spectrum to provide coverage in wide areas. Higher data rates. Higher spectrum bands selected for the 802.16-2004 profiles result in higher data rates. This is a clear advantage, especially when targeting enterprise users requiring higher data rates. Better time to market, because 802.16-2004 products will be available earlier.

16. Advantages of 802.16e Support for mobility. 802.16e supports handoffs. Support for power-saving and sleep modes will extend the battery life of mobile user devices. Better indoor coverage achieved through subchannelization and channel power control or Adaptive Antenna System (AAS). This is especially important for mobile applications. Greater flexibility in managing spectrum resources. Sub- channelization allows the network to allocate resources to user devices as needed. This results in a more efficient use of spectrum, thus higher throughput and better indoor coverage. Wider range of form factors for user devices. Laptop PCMCIA cards, mini cards, indoor modems, PDAs, and phones will be available among 802.16e user devices. This variety allows operators to extend their services to new market segments and to give more freedom to their subscribers.