| WiMAX, meaning Worldwide Interoperability for | | | | with an IP based core network, which is typically |
| Microwave Access, is a telecommunications | | | | chosen by operators that serve as Internet Service |
| technology that provides wireless transmission of data | | | | Providers (ISP); Nevertheless the WiMAX BS provide |
| using a variety of transmission modes, from | | | | seamless integration capabilities with other types of |
| point-to-multipoint links to portable and fully mobile | | | | architectures as with packet switched Mobile |
| internet access. The technology provides up to 10 | | | | Networks. |
| Mbps broadband speed without the need for cables. | | | | The WiMAX forum proposal defines a number of |
| The technology is based on the IEEE 802.16 standard | | | | components, plus some of the interconnections (or |
| (also called Broadband Wireless Access) that is | | | | reference points) between these, labeled R1 to R5 and |
| intended for wireless "metropolitan area networks". | | | | R8: |
| WiMAX can provide broadband wireless access | | | | · SS/MS: the Subscriber Station/Mobile Station |
| (BWA) up to 30 miles (50 km) for fixed stations, and 3 | | | | · ASN: the Access Service Network [2] |
| - 10 miles (5 -15 km) for mobile stations. In contrast, the | | | | · BS: Base station, part of the ASN |
| WiFi/802.11 wireless local area network standard is | | | | · ASN-GW: the ASN Gateway, part of the ASN |
| limited in most cases to only 100 - 300 feet (30 - | | | | · CSN: the Connectivity Service Network |
| 100m). | | | | · HA: Home Agent, part of the CSN NAP: a Network |
| With WiMAX, WiFi-like data rates are easily supported, | | | | Access Provider |
| but the issue of interference is lessened. WiMAX | | | | · NSP: a Network Service Provider |
| operates on both licensed and non-licensed | | | | It is important to note that the functional architecture |
| frequencies, providing a regulated environment and | | | | can be designed into various hardware configurations |
| viable economic model for wireless carriers. | | | | rather than fixed configurations. For example, the |
| WiMAX can be used for wireless networking in much | | | | architecture is flexible enough to allow remote/mobile |
| the same way as the more common WiFi protocol. | | | | stations of varying scale and functionality and Base |
| WiMAX is a second-generation protocol that allows | | | | Stations of varying size - e.g. femto, pico, and mini BS |
| for more efficient bandwidth use, interference | | | | as well as macros. |
| avoidance, and is intended to allow higher data rates | | | | 1.2.4 Comparison with Wi-Fi |
| over longer distances. | | | | Comparisons and confusion between WiMAX and |
| 1.1.1 Uses | | | | Wi-Fi are frequent because both are related to |
| The bandwidth and range of WiMAX make it suitable | | | | wireless connectivity and Internet access. |
| for the following potential applications: | | | | · WiMAX is a long range system, covering many |
| · Connecting Wi-Fi hotspots to the Internet. | | | | kilometers that uses licensed or unlicensed spectrum |
| · Providing a wireless alternative to cable and DSL | | | | to deliver a point-to-point connection to the Internet. |
| for "last mile" broadband access. | | | | · Different 802.16 standards provide different types |
| · Providing data, telecommunications and IPTV | | | | of access, from portable (similar to a cordless phone) |
| services (triple-play). | | | | to fixed (an alternative to wired access, where the |
| · Providing a source of Internet connectivity as part | | | | end user's wireless termination point is fixed in location.) |
| of a business continuity plan. That is, if a business has | | | | · Wi-Fi uses unlicensed spectrum to provide access |
| both a fixed and a wireless Internet connection, | | | | to a network. |
| especially from unrelated providers, they are unlikely to | | | | · Wi-Fi is more popular in end user devices. |
| be affected by the same service outage. | | | | · WiMAX and Wi-Fi have quite different quality of |
| · Providing portable connectivity. | | | | service (QoS) mechanisms: |
| 1.1.2 Subscriber Units (Client Units) | | | | · WiMAX uses a QoS mechanism based on |
| WiMAX subscriber units are available in both indoor | | | | connections between the base station and the user |
| and outdoor versions from several manufacturers. | | | | device. Each connection is based on specific |
| Self-install indoor units are convenient, but radio losses | | | | scheduling algorithms. |
| mean that the subscriber must be significantly closer to | | | | · Wi-Fi has a QoS mechanism similar to fixed |
| the WiMAX base station than with | | | | Ethernet, where packets can receive different priorities |
| professionally-installed external units. As such, | | | | based on their tags. For example VoIP traffic may be |
| indoor-installed units require a much higher | | | | given priority over web browsing. |
| infrastructure investment as well as operational cost | | | | · Wi-Fi runs on the Media Access Control's CSMA |
| (site lease, backhaul, maintenance) due to the high | | | | CA protocol, which is connectionless and contention |
| number of base stations required to cover a given | | | | based, whereas WiMAX runs a connection-oriented |
| area. Indoor units are comparable in size to a cable | | | | MAC. |
| modem or DSL modem. Outdoor units are roughly the | | | | · Both 802.11 and 802.16 define Peer-to-Peer (P2P) |
| size of a laptop PC, and their installation is comparable | | | | and ad hoc networks, where an end user |
| to the installation of a residential satellite dish. | | | | communicates to users or servers on another Local |
| With the potential of mobile WiMAX, there is an | | | | Area Network (LAN) using its access point or base |
| increasing focus on portable units. This includes | | | | station. |
| handsets (similar to cellular smartphones), PC | | | | 1.2.5 Spectrum Allocation Issues |
| peripherals (PC Cards or USB dongles), and | | | | There is no uniform global licensed spectrum for |
| embedded devices in laptops, which are now available | | | | WiMAX, although the WiMAX Forum has published |
| for Wi-Fi services. In addition, there is much emphasis | | | | three licensed spectrum profiles: 2.3 GHz, 2.5 GHz and |
| from operators on consumer electronics devices such | | | | 3.5 GHz, in an effort to decrease cost. Economies of |
| as Gaming consoles, MP3 players and similar devices. | | | | scale dictate that the more WiMAX embedded |
| It is notable that WiMAX is more similar to Wi-Fi than | | | | devices such as mobile phones and |
| to 3G cellular technologies. | | | | WiMAX-embedded laptops are produced, the lower |
| Current certified devices can be found at the WiMAX | | | | the unit cost (The two highest cost components of |
| Forum web site. This is not a complete list of devices | | | | producing a mobile phone are the silicon and the extra |
| available as certified modules are embedded into | | | | radio needed for each band). |
| laptops, MIDs (Mobile internet devices), and private | | | | WiMAX profiles define channel size, TDD/FDD and |
| labeled devices. | | | | other necessary attributes in order to have |
| 1.1.3 Backhaul/Access Network Applications | | | | inter-operating products. The current fixed profiles are |
| WiMAX is a possible replacement candidate for | | | | defined for both TDD and FDD profiles. At this point, all |
| cellular phone technologies such as GSM and CDMA, | | | | of the mobile profiles are TDD only. The fixed profiles |
| or can be used as an overlay to increase capacity. It | | | | have channel sizes of 3.5 MHz, 5 MHz, 7 MHz and 10 |
| has also been considered as a wireless backhaul | | | | MHz. The mobile profiles are 5 MHz, 8.75 MHz and 10 |
| technology for 2G, 3G, and 4G networks in both | | | | MHz. (Note: the 802.16 standard allows a far wider |
| developed and poor nations [1]. | | | | variety of channels, but only the above subsets are |
| WiMAX is a broadband platform and as such has | | | | supported as WiMAX profiles). |
| much more substantial backhaul bandwidth | | | | 1.2.6 Spectral Efficiency |
| requirements than legacy cellular applications. | | | | One of the significant advantages of advanced |
| Therefore traditional copper wire line backhaul solutions | | | | wireless systems such as WiMAX is spectral |
| are not appropriate. Capacities of between 34 Mbps | | | | efficiency. For example, 802.16-2004 (fixed) has a |
| and 1 Gbps are routinely being deployed with latencies | | | | spectral efficiency of 3.7 (bit/s)/Hertz, and other 3.5-4G |
| in the order of 1ms. In many cases, operators are | | | | wireless systems offer spectral efficiencies that are |
| aggregating sites using wireless technology and then | | | | similar to within a few tenths of a percent. The notable |
| presenting traffic on to fiber networks where | | | | advantage of WiMAX comes from combining |
| convenient. | | | | SOFDMA with smart antenna technologies. This |
| 1.2 Technical Information | | | | multiplies the effective spectral efficiency through |
| WiMAX refers to interoperable implementations of the | | | | multiple reuse and smart network deployment |
| IEEE 802.16 wireless-networks standard, in similarity | | | | topologies. The direct use of frequency domain |
| with Wi-Fi, which refers to interoperable | | | | organization simplifies designs using MIMO-AAS |
| implementations of the IEEE 802.11 Wireless LAN | | | | compared to CDMA/WCDMA methods, resulting in |
| standard. | | | | more effective systems. |
| 1.2.1 Physical Layer | | | | 1.2.7 Limitations |
| The original version of the standard on which WiMAX | | | | A commonly-held misconception is that WiMAX will |
| is based (IEEE 802.16) specified a physical layer | | | | deliver 70 Mbit/s over 50 kilometers (30 miles). In reality, |
| operating in the 10 to 66 GHz range. 802.16a updated in | | | | WiMAX can either operate at higher bitrates or over |
| 2004 to 802.16-2004, added specifications for the 2 to | | | | longer distances but not both: operating at the |
| 11 GHz range. 802.16-2004 was updated by | | | | maximum range of 50 km increases bit error rate and |
| 802.16e-2005 in 2005 and uses scalable orthogonal | | | | thus results in a much lower bitrates. Conversely, |
| frequency-division multiple access (SOFDMA) as | | | | reducing the range (to less than 1 km) allows a device |
| opposed to the orthogonal frequency-division | | | | to operate at higher bitrates. There are no known |
| multiplexing (OFDM) version with 256 sub-carriers (of | | | | examples of WiMAX services being delivered at bit |
| which 200 are used) in 802.16d. More advanced | | | | rates over around 40 Mbit/s. |
| versions, including 802.16e, also bring multiple antenna | | | | Typically, fixed WiMAX networks have a higher-gain |
| support through MIMO. This brings potential benefits in | | | | directional antenna installed near the client (customer) |
| terms of coverage, self installation, power consumption, | | | | which results in greatly increased range and |
| frequency re-use and bandwidth efficiency. 802.16e | | | | throughput. Mobile WiMAX networks are usually made |
| also adds a capability for full mobility support. The | | | | of indoor "customer-premises equipment" (CPE) such |
| WiMAX certification allows vendors with 802.16d | | | | as desktop modems, laptops with integrated Mobile |
| products to sell their equipment as WiMAX certified, | | | | WiMAX or other Mobile WiMAX devices. Mobile |
| thus ensuring a level of interoperability with other | | | | WiMAX devices typically have omnidirectional antenna |
| certified products, as long as they fit the same profile. | | | | which are of lower-gain compared to directional |
| 1.2.2 MAC (Data Link) Layer | | | | antennas but are more portable. In current |
| In Wi-Fi the media access controller (MAC) uses | | | | deployments, the throughput may reach 2 Mbit/s |
| contention access - all subscriber stations that wish to | | | | symmetric at 10 km with fixed WiMAX and a high gain |
| pass data through a wireless access point (AP) are | | | | antenna. It is also important to consider that a |
| competing for the AP's attention on a random interrupt | | | | throughput of 2 Mbit/s can mean 2 Mbit/s symmetric |
| basis. This can cause subscriber stations distant from | | | | simultaneously, 1 Mbit/s symmetric or some |
| the AP to be repeatedly interrupted by closer stations, | | | | asymmetric mix (e.g. 0.5 Mbit/s downlink and 1.5 Mbit/s |
| greatly reducing their throughput. | | | | uplink or 1.5 Mbit/s downlink and 0.5 Mbit/s uplink), each |
| In contrast, the 802.16 MAC uses a scheduling | | | | of which required slightly different network equipment |
| algorithm for which the subscriber station needs to | | | | and configurations. Higher-gain directional antennas can |
| compete only once (for initial entry into the network). | | | | be used with a WiMAX network with range and |
| After that it is allocated an access slot by the base | | | | throughput benefits but the obvious loss of practical |
| station. The time slot can enlarge and contract, but | | | | mobility. Like most wireless systems, available |
| remains assigned to the subscriber station, which | | | | bandwidth is shared between users in a given radio |
| means that other subscribers cannot use it. In addition | | | | sector, so performance could deteriorate in the case |
| to being stable under overload and over-subscription, | | | | of many active users in a single sector. In practice, |
| the 802.16 scheduling algorithm can also be more | | | | most users will have a range of 2-3 Mbit/s services |
| bandwidth efficient. The scheduling algorithm also | | | | and additional radio cards will be added to the base |
| allows the base station to control QoS parameters by | | | | station to increase the number of users that may be |
| balancing the time-slot assignments among the | | | | served as required. |
| application needs of the subscriber stations. | | | | Because of these limitations, the general consensus is |
| 1.2.3 Integration with an IP-based Network | | | | that WiMAX requires various granular and distributed |
| The WiMAX Forum has proposed an architecture that | | | | network architectures to be incorporated within the |
| defines how a WiMAX network can be connected | | | | IEEE 802.16 task groups. |