Definitions
The terms "fixed WiMAX", "mobile WiMAX", "802.16d" and "802.16e" are frequently used incorrectly. Correct definitions are the following:
* 802.16-2004 is often called 802.16d, since that was the working party that developed the standard. It is also frequently referred to as "fixed WiMAX" since it has no support for mobility.
* 802.16e-2005 is an amendment to 802.16-2004 and is often referred to in shortened form as 802.16e. It introduced support for mobility, amongst other things and is therefore also known as "mobile WiMAX".
Uses
The bandwidth and range of WiMAX make it suitable for the following potential applications:
* Connecting Wi-Fi hotspots to the Internet.
* Providing a wireless alternative to cable and DSL for "last mile" broadband access.
* Providing data and telecommunications services.
* Providing a source of Internet connectivity as part of a business continuity plan. That is, if a business has a fixed and a wireless Internet connection, especially from unrelated providers, they are unlikely to be affected by the same service outage.
* Providing portable connectivity.
Broadband access
Companies are closely examining WiMAX for last mile connectivity. The resulting competition may bring lower pricing for both home and business customers or bring broadband access to places where it has been economically unavailable.
WiMAX access was used to assist with communications in Aceh, Indonesia, after the tsunami in December 2004. All communication infrastructure in the area, other than amateur radio, was destroyed, making the survivors unable to communicate with people outside the disaster area and vice versa. WiMAX provided broadband access that helped regenerate communication to and from Aceh.
In addition, WiMAX was donated by Intel Corporation to assist the FCC and FEMA in their communications efforts in the areas affected by Hurricane Katrina. In practice, volunteers used mainly self-healing mesh, VoIP, and a satellite uplink combined with Wi-Fi on the local link.
Subscriber units (Client Units)
WiMAX subscriber units are available in both indoor and outdoor versions from several manufacturers. Self-install indoor units are convenient, but radio losses mean that the subscriber must be significantly closer to the WiMAX base station than with professionally-installed external units. As such, indoor-installed units require a much higher infrastructure investment as well as operational cost (site lease, backhaul, maintenance) due to the high number of base stations required to cover a given area. Indoor units are comparable in size to a cable modem or DSL modem. Outdoor units are roughly the size of a laptop PC, and their installation is comparable to the installation of a residential satellite dish.
With the potential of mobile WiMAX, there is an increasing focus on portable units. This includes handsets (similar to cellular smartphones), PC peripherals (PC Cards or USB dongles), and embedded devices in laptops, such as are now available for Wi-Fi. In addition, there is much emphasis from operators on consumer electronics devices (game terminals, MP3 players and the like); it is notable this is more similar to Wi-Fi than to 3G cellular technologies.
Current certified devices can be found at the WiMAX Forum web site. This is not a complete list of devices available as certified modules are embedded into laptops, MIDs (Mobile Internet Devices), and private labeled devices.
Mobile handset applications
Sprint Nextel announced in mid-2006 that it would invest about US$ 5 billion in a WiMAX technology buildout over the next few years. Since that time Sprint has been dealt setbacks that have resulted in steep quarterly losses. On May 7, 2008, Sprint, Imagine, Google, Intel, Comcast, and Time Warner announced a pooling of an average of 120 MHz of spectrum and formation of a new company which will take the name Clearwire. The new company hopes to benefit from combined services offerings and network resources as a springboard past its competitors. The cable companies will provide media services to other partners while gaining access to the wireless network as a Mobile virtual network operator. Google will contribute Android handset device development and applications and will receive revenue share for advertising and other services they provide. Clearwire Sprint and current Clearwire gain a majority stock ownership in the new venture and ability to access between the new Clearwire and Sprint 3G networks. Some details remain unclear including how soon and in what form announced multi-mode WiMAX and 3G EV-DO devices will be available. This raises questions that arise for availability of competitive chips that require licensing of Qualcomm's IPR.
Some analysts have questioned how the deal will work out: Although fixed-mobile convergence has been a recognized factor in the industry, prior attempts to form partnerships among wireless and cable companies have generally failed to lead to significant benefits to the participants. Other analysts point out that as wireless progresses to higher bandwidth, it inevitably competes more directly with cable and DSL, thrusting competitors into bed together. Also, as wireless broadband networks grow denser and usage habits shift, the need for increased back haul and media service will accelerate, therefore the opportunity to leverage cable assets is expected to increase.
Backhaul/access network applications
WiMAX is a possible replacement candidate for cellular phone technologies such as GSM and CDMA, or can be used as a layover to increase capacity. It has also been considered as a wireless backhaul technology for 2G, 3G, and 4G networks in both developed and poor nations.
In North America, Backhaul for urban cellular operations is typically provided via one or more copper wire line T1 connections, whereas remote cellular operations are sometimes "backhauled" via satellite. In most other regions, urban and rural backhaul is usually provided by Microwave links. (The exception to this is where the network is operated by an incumbent with ready access to the copper network, in which case T1 lines may be used). WiMAX is a broadband platform and as such has much more substantial backhaul bandwidth requirements than legacy cellular applications. Therefore traditional copper wire line backhaul solutions are not appropriate. Consequently the use of wireless microwave backhaul is on the rise in North America and existing microwave backhaul links in all regions are being upgraded. Capacities of between 34 Mbit/s and 1 Gbit/s are routinely being deployed with latencies in the order of 1ms. In many cases, operators are aggregating sites using wireless technology and then presenting traffic on to fiber networks where convenient.
Deploying WiMAX in rural areas with limited or no internet backbone will be challenging as additional methods and hardware will be required to procure sufficient bandwidth from the nearest sources — the difficulty being in proportion to the distance between the end-user and the nearest sufficient internet backbone.
Technical information
WiMAX is a term coined to describe standard, interoperable implementations of IEEE 802.16 wireless networks, similar to the way the term Wi-Fi is used for interoperable implementations of the IEEE 802.11 Wireless LAN standard. However, WiMAX is very different from Wi-Fi in the way it works.
MAC layer/data link layer
In Wi-Fi the media access controller (MAC) uses contention access — all subscriber stations that wish to pass data through a wireless access point (AP) are competing for the AP's attention on a random interrupt basis. This can cause subscriber stations distant from the AP to be repeatedly interrupted[citation needed] by closer stations, greatly reducing their throughput.
In contrast, the 802.16 MAC uses a scheduling algorithm for which the subscriber station needs to compete only once (for initial entry into the network). After that it is allocated an access slot by the base station. The time slot can enlarge and contract, but remains assigned to the subscriber station, which means that other subscribers cannot use it. In addition to being stable under overload and over-subscription, the 802.16 scheduling algorithm can also be more bandwidth efficient.[citation needed] The scheduling algorithm also allows the base station to control QoS parameters by balancing the time-slot assignments among the application needs of the subscriber stations.
Physical layer
The original version of the standard on which WiMAX is based (IEEE 802.16) specified a physical layer operating in the 10 to 66 GHz range. 802.16a, updated in 2004 to 802.16-2004, added specifications for the 2 to 11 GHz range. 802.16-2004 was updated by 802.16e-2005 in 2005 and uses scalable orthogonal frequency-division multiple access (SOFDMA) as opposed to the Orthogonal frequency-division multiplexing (OFDM) version with 256 sub-carriers (of which 200 are used) in 802.16d. More advanced versions, including 802.16e, also bring Multiple Antenna Support through MIMO. See: WiMAX MIMO. This brings potential benefits in terms of coverage, self installation, power consumption, frequency re-use and bandwidth efficiency. 802.16e also adds a capability for full mobility support. The WiMAX certification allows vendors with 802.16d products to sell their equipment as WiMAX certified, thus ensuring a level of interoperability with other certified products, as long as they fit the same profile.
Most commercial interest is in the 802.16d and 802.16e standards, since the lower frequencies used in these variants suffer less from inherent signal attenuation and therefore give improved range and in-building penetration. Already today, a number of networks throughout the world are in commercial operation using certified WiMAX equipment compliant with the 802.16d standard.
Complexities of deployment
Being a standard thought to satisfy the needs of next generation data networks, nomadic and mobile (4G), it is distinguished by a dynamic burst algorithm that adapts the current physical digital modulation according to field variables that are dependent on the radio propagation conditions; the current physical mod is chosen to be spectrally more efficient (more bits per OFDM/SOFDMA symbol), that is, when the bursts have a high signal strength and a high carrier to noise plus interference ratio (CINR) and they can be easily decoded by the digital signal processing (DSP) Algorithms. In contrast, when some of those conditions are bad, then the system chooses a more robust physical mode (burst profile) which means less bits per OFDM/SOFDMA symbol, but with the advantage that power per bit is higher and therefore accurate decoding is easier. Because of this, higher order burst profiles can only be used (dynamically chosen by an algorithm) when the attenuation is not high which means only for subscriber stations located near the base station antenna and therefore the maximum distance can only be achieved by means of selecting the more robust burst profile with the MAC frame allocation inconvenience that it implies as more symbols (more portion of the MAC frame) have to be allocated for transmitting a given amount of data than if the subscriber station was close to the base station.
In the MAC Frame the subscriber stations are allocated and their individual burst profiles defined as well as the specific time allocation, but even if that is done automatically practical deployment should avoid high interference and high multipath environments as opposed to what the average radio network planning team (and executive staff from the adopting operator) could think, the reason for it lies in excessive interference and competition during the Initial Ranging (IR) process due to the usage of high transmitting power in base station (BS) and subscriber station (SS) alike, which can result in unwanted delays and ranging attempts that effectively detracts from a good user experience and can even result in wasted allocated symbols due to continuous connections/re-connections.
The system therefore is very complex to deploy as it is necessary to keep in mind not only the signal strength and CINR (as in systems like GSM) but it is also necessary to think how the spectrum is going to be dynamically assigned (resulting in dynamically changing total available bandwidth)) to the served subscriber stations (other dynamic burst systems have 2 or 3 burst profiles, WiMAX developments have showed up to 7 in use at the same time), the DSP algorithms (Decodification) are tougher than in any other wireless systems, yet they cannot reconstruct any burst in any environment; It is usually very effective though, but coupled with OFDM/SOFDMA, it can result in a double edged sword which means by having a tougher set of DSP algorithms, usually deployed on specific purpose chips, the signal could (harmfully) reach farther distances than expected due to tunnel effects (constructive interference with neighbor frequencies) resulting in highly interfered clutters and with highly reflected signals, with very high signal strength though which can fool the non experienced planning staff (usually coming from 3gpp networks).
As a result the system has to be initially deployed in conjunction with product development staff (who are usually involved in the technology development in some way) from the given vendor as opposed to service technical staff (radio planning) from the operator or vendor as is usual practice, thus raising the cost of deployment. As with all new technologies, configuration and maintenance will become easier to use as more deployments occur.
Integration with an IP based Network
The WiMAX Forum has proposed an architecture that defines how a WiMAX network can be connected with an IP based core network, which is typically chosen by operators that serve as Internet Service Providers (ISP); Nevertheless the WiMAX BS provide seamless integration capabilities with other types of architectures as with packet switched Mobile Networks.
The WiMAX forum proposal defines a number of components, plus some of the interconnections (or reference points) between these, labeled R1 to R5 and R8:
* SS/MS: the Subscriber Station/Mobile Station
* ASN: the Access Service Network
* BS: Base station, part of the ASN
* ASN-GW: the ASN Gateway, part of the ASN
* CSN: the Connectivity Service Network
* HA: Home Agent, part of the CSN
* AAA: Authentication, Authorization and Accounting Server, part of the CSN
* NAP: a Network Access Provider
* NSP: a Network Service Provider
It is important to note that the functional architecture can be designed into various hardware configurations rather than fixed configurations. For example, the architecture is flexible enough to allow remote/mobile stations of varying scale and functionality and Base Stations of varying size - e.g. femto, pico, and mini BS as well as macros.
Comparison with Wi-Fi
Comparisons and confusion between WiMAX and Wi-Fi are frequent because both are related to wireless connectivity and Internet access.
* WiMAX uses spectrum to deliver a point-to-point connection to the Internet. Different 802.16 standards provide different types of access, from portable (similar to a cordless phone) to fixed (an alternative to wired access, where the end user's wireless termination point is fixed in location.)
* Wi-Fi uses unlicensed spectrum to provide access to a network. Wi-Fi is more popular in end user devices.
* WiMAX and Wi-Fi have quite different Quality of Service (QoS) mechanisms. WiMAX uses a mechanism based on connections between the Base Station and the user device. Each connection is based on specific scheduling algorithms. Wi-Fi has a QoS mechanism similar to fixed Ethernet, where packets can receive different priorities based on their tags. For example VoIP traffic may be given priority over web browsing.
* Wi-Fi runs on the MAC's CSMA/CA protocol, which is connectionless and contention based, whereas WiMAX runs a connection-oriented MAC.
Both 802.11 and 802.16 define Peer-to-Peer (P2P) and ad hoc networks, where an end user communicates to users or servers on another Local Area Network (LAN) using its access point or base station.
Spectrum allocation issues
The 802.16 specification applies across a wide swath of the RF spectrum, and WiMAX could function on any frequency below 66 GHz, (higher frequencies would decrease the range of a Base Station to a few hundred meters in an urban environment).
There is no uniform global licensed spectrum for WiMAX, although the WiMAX Forum has published three licensed spectrum profiles: 2.3 GHz, 2.5 GHz and 3.5 GHz, in an effort to decrease cost: economies of scale dictate that the more WiMAX embedded devices (such as mobile phones and WiMAX-embedded laptops) are produced, the lower the unit cost. (The two highest cost components of producing a mobile phone are the silicon and the extra radio needed for each band.) Similar economy of scale benefits apply to the production of Base Stations.
In the unlicensed band, 5.x GHz is the approved profile. Telecommunication companies are unlikely to use this spectrum widely other than for backhaul, since they do not own and control the spectrum.
In the USA, the biggest segment available is around 2.5 GHz, and is already assigned, primarily to Sprint Nextel and Clearwire. Elsewhere in the world, the most-likely bands used will be the Forum approved ones, with 2.3 GHz probably being most important in Asia. Some countries in Asia like India and Indonesia will use a mix of 2.5 GHz, 3.3 GHz and other frequencies. Pakistan's Wateen Telecom uses 3.5 GHz.
Analog TV bands (700 MHz) may become available for WiMAX usage, but await the complete roll out of digital TV, and there will be other uses suggested for that spectrum. In the USA the FCC auction for this spectrum began in January 2008 and, as a result, the biggest share of the spectrum went to Verizon Wireless and the next biggest to AT&T. Both of these companies have stated their intention of supporting LTE, a technology which competes directly with WiMAX. EU commissioner Viviane Reding has suggested re-allocation of 500–800 MHz spectrum for wireless communication, including WiMAX.
WiMAX profiles define channel size, TDD/FDD and other necessary attributes in order to have inter-operating products. The current fixed profiles are defined for both TDD and FDD profiles. At this point, all of the mobile profiles are TDD only. The fixed profiles have channel sizes of 3.5 MHz, 5 MHz, 7 MHz and 10 MHz. The mobile profiles are 5 MHz, 8.75 MHz and 10 MHz. (Note: the 802.16 standard allows a far wider variety of channels, but only the above subsets are supported as WiMAX profiles.)
Since October 2007, the Radio communication Sector of the International Telecommunication Union (ITU-R) has decided to include WiMAX technology in the IMT-2000 set of standards. This enables spectrum owners (specifically in the 2.5-2.69 GHz band at this stage) to use Mobile WiMAX equipment in any country that recognizes the IMT-2000.
Spectral efficiency
One of the significant advantages of advanced wireless systems such as WiMAX is spectral efficiency. For example, 802.16-2004 (fixed) has a spectral efficiency of 3.7 (bit/s)/Hertz, and other 3.5–4G wireless systems offer spectral efficiencies that are similar to within a few tenths of a percent. The notable advantage of WiMAX comes from combining SOFDMA with smart antenna technologies. This multiplies the effective spectral efficiency through multiple reuse and smart network deployment topologies. The direct use of frequency domain organization simplifies designs using MIMO-AAS compared to CDMA/WCDMA methods, resulting in more effective systems.
Limitations
A commonly-held misconception is that WiMAX will deliver 70 Mbit/s over 50 kilometers (~31 miles). In reality, WiMAX can either operate at higher bitrates or over longer distances but not both: operating at the maximum range of 50 km increases bit error rate and thus results in a much lower bitrate. Conversely, reducing the range (to <1m) allows a device to operate at higher bitrates. There are no known examples of WiMAX services being delivered at bit rates over around 3 Mbit/s.
Typically, fixed WiMAX networks have a higher-gain directional antenna installed near the client (customer) which results in greatly increased range and throughput. Mobile WiMAX networks are usually made of indoor "Customer-premises equipment" (CPE) such as desktop modems, laptops with integrated Mobile WiMAX or other Mobile WiMAX devices. Mobile WiMAX devices typically have omnidirectional antennae which are of lower-gain compared to directional antennas but are more portable. In current deployments, the throughput may reach 2 Mbit/s symmetric at 10 km with fixed WiMAX and a high gain antenna. It is also important to consider that a throughput of 2 Mbit/s can mean 2 Mbit/s, symmetric simultaneously, 1 Mbit/s symmetric or some asymmetric mix (e.g. 0.5 Mbit/s downlink and 1.5 Mbit/s uplink or 1.5 Mbit/s downlink and 0.5 Mbit/s uplink), each of which required slightly different network equipment and configurations. Higher-gain directional antennas can be used with a WiMAX network with range and throughput benefits but the obvious loss of practical mobility.
Like most wireless systems, available bandwidth is shared between users in a given radio sector, so performance could deteriorate in the case of many active users in a single sector. In practice, most users will have a range of 2-3 Mbit/s services and additional radio cards will be added to the base station to increase the number of users that may be served as required.
Because of these limitations, the general consensus is that WiMAX requires various granular and distributed network architectures to be incorporated within the IEEE 802.16 task groups. This includes wireless mesh, grids, network remote station repeaters which can extend networks and connect to backhaul.
Silicon implementations
A critical requirement for the success of a new technology is the availability of low-cost chipsets and silicon implementations.
Intel Corporation is a leader in promoting WiMAX, and has developed its own chipset. However, it is notable that most of the major semiconductor companies have not and most of the products come from specialist smaller or start-up suppliers. For the client-side these include Sequans, whose chips are in more than half of the WiMAX Forum Certified(tm) MIMO-based Mobile WiMAX client devices, GCT Semiconductor, ApaceWave, Altair Semiconductor, Beceem, Comsys, Runcom, Motorola with TI, NextWave Wireless, Wavesat, Coresonic and SySDSoft. Both Sequans and Wavesat manufacture products for both clients and network while Texas Instruments, DesignArt, and picoChip are focused on WiMAX chip sets for base stations. Kaben Wireless Silicon is a provider of RF front-end and semiconductor IP for WiMAX applications.
Standards
The current WiMAX incarnation, Mobile WiMAX, is based upon IEEE Std 802.16e-2005, approved in December 2005. It is a supplement to the IEEE Std 802.16-2004, and so the actual standard is 802.16-2004 as amended by 802.16e-2005 — the specifications need to be read together to understand them.
IEEE Std 802.16-2004 addresses only fixed systems. It replaced IEEE Standards 802.16-2001, 802.16c-2002, and 802.16a-2003.
IEEE 802.16e-2005 improves upon IEEE 802.16-2004 by:
* Adding support for mobility (soft and hard handover between base stations). This is seen as one of the most important aspects of 802.16e-2005, and is the very basis of 'Mobile WiMAX' (though this has yet to be demonstrated in any installed systems).
* Scaling of the Fast Fourier transform (FFT) to the channel bandwidth in order to keep the carrier spacing constant across different channel bandwidths (typically 1.25 MHz, 5 MHz, 10 MHz or 20 MHz). Constant carrier spacing results in a higher spectrum efficiency in wide channels, and a cost reduction in narrow channels. Also known as Scalable OFDMA (SOFDMA). Other bands not multiples of 1.25 MHz are defined in the standard, but because the allowed FFT subcarrier numbers are only 128, 512, 1024 and 2048, other frequency bands will not have exactly the same carrier spacing, which might not be optimal for implementations.
* Advanced antenna diversity schemes, and hybrid automatic repeat-request (HARQ)
* Adaptive Antenna Systems (AAS) and MIMO technology
* Denser sub-channelization, thereby improving indoor penetration
* Introducing Turbo Coding and Low-Density Parity Check (LDPC)
* Introducing downlink sub-channelization, allowing administrators to trade coverage for capacity or vice versa
* Fast Fourier transform algorithm
* Adding an extra QoS class for VoIP applications.
802.16d vendors point out that fixed WiMAX offers the benefit of available commercial products and implementations optimized for fixed access. It is a popular standard among alternative service providers and operators in developing areas due to its low cost of deployment and advanced performance in a fixed environment. Fixed WiMAX is also seen as a potential standard for backhaul of wireless base stations such as cellular, or Wi-Fi.
SOFDMA (used in 802.16e-2005) and OFDM256 (802.16d) are not compatible thus most equipment will have to be replaced if an operator wants or needs to move to the later standard. However, some manufacturers are planning to provide a migration path for older equipment to SOFDMA compatibility which would ease the transition for those networks which have already made the OFDM256 investment. Intel provides a dual-mode 802.16-2004 802.16-2005 chipset for subscriber units.
Source from : http://en.wikipedia.org/wiki/WiMAX