The idea that access to information opens doors to wider economic and social development opportunities is not new. In 1984, the “Missing Link Report’’ pointed to the fact that the lack of telecommunication infrastructure in developing countries impedes economic growth, but with a scope limited to access to telephones rather than today’s wider concept of Information and Communications Technologies (ICTs) access and usage. In 1996, the International Telecommunications Union (ITU) initiated a United Nations project for the “Right to Communicate’’ aimed at providing access to basic ICTs for all, with motivation to reduce information poverty for developing countries. Thus, during the first World Summit on the Information Society (WSIS) held in Geneva in December 2003, the ‘Digital Divide’ was defined as the unequal access to ICT. Although this unequal access usually apply to differences between countries (the international digital divide) e.g. comparing developed and developing countries or regions; within countries (the domestic digital divide); and most importantly the divide between rural and urban, well educated or poorly educated populations or poor and rich citizens. Despite the various parameters and selected criteria (e.g. Internet host and/or users, fixed and mobile telephones) that can be considered or use to express an overall trend of growing ICTs disparities between and within countries, the availability and the quality of the access (i.e. the physical telecommunication infrastructure) is the key to a quick and reliable development of ICTs in the countries. Looking closer to the statistics as published by the different official bodies such as ITU or the World Bank in Figure 1, it is clear that the gap in ICTs access between developed and developing countries do exist (ITU World Telecommunications Development report 2003).
There are many reasons for the barriers why, until now, broadband ICT access was mainly deployed in developed countries and more precisely in urban areas as shown in Figure 2. However it can easily be explained that economics and existing technologies are the main drivers (and barriers in developing countries) to ICTs. Economics in the first case because, any entrepreneur in this new business, operators and service providers will naturally inclined to first serve the most populated areas (i.e. dense, rich cities and suburbs) where most of the potential customers are located instead of less populated areas such as remote and rural areas.
In the same way, while developed countries and urban areas are requiring higher and higher bit rates for multimedia applications, rural areas in developing countries are still at first favoring voice communication with a slow evolution towards ICTs. Moreover, while developed countries already have existing telecommunication infrastructure ready to evolve and the financial resources to invest and pay for new services, developing countries still suffer from the lack of basic infrastructures (not only telecommunication infrastructures, but also power supply, roads), and more crucial, have great difficulty to mobilize the necessary financial resources. This is what we call the “demand factor’’. Technologies in the second case because, until now, existing wired or wireless technologies have inherent limitations either in performances or in capacity (e.g. the 6 Km maximum distance from the exchange for digital subscriber line (DSL)) or the Line-of-Site (LOS) Customer Premise Equipment (CPE) location from the base station for wireless access. And even if such limitations can be overcome using other complementary backbones or equipments (optical fibers or microwaves links, remote switching units.etc), the extra cost of these new equipments, of their deployment and their operation directly impacts the business model. This is what we call the “cost factor’’. So, both the “Demand and Cost’’ factors are the major barriers to the broadband access as identified by (ITU World Telecommunications Development report 2003).
The paper is organized as follows. Section II defines WiMAX, the Forum and Profiles. Section III describes why and how WiMAX will be a key element in this new important worldwide objective to provide an equitable and affordable access to ICTs infrastructure and services. The various usage scenarios to illustrate the ability of WiMAX to address different applications are given in sections IV and V. And the paper ended with the conclusion.
2. What is WiMAX?
WiMAX stands for “World Interoperability for Microwave Access’’. It is a broadband wireless technology that supports fixed, nomadic, portable and mobile access. WiMAX is largely supported by the computer and the telecommunications industry, cost-effective and standard base. It is engineered to deliver the latest type of ubiquitous fixed and mobile services such as Voice 0ver Internet Protocol (VoIP), Information Technology and Video at very low cost. WiMAX systems are able to cover a large geographical area, up to 50 km and to deliver significant bandwidth to end-users up to 72 Mbps. To meet the requirements of different types of access, two versions of WiMAX have been defined. The first is based on IEEE 802.16-2004 and is optimized for fixed and nomadic access. The initial WiMAX Forum CERTIFIED products will be based on this version of WiMAX. The second version is designed to support portability and mobility, and will be based on the IEEE 802.16e amendment to the standard.
2.1. IEEE 802.16-2004 Standard
The IEEE 802.16 standard which includes Medium Access Control (MAC) and physical (PHY) layer specifications, aims at supporting Internet services over wireless metropolitan area networks (WMAN). It is also an alternative to traditional wired networks, such as Asymmetric Digital Subscriber Line (ADSL) and cable-modem. There are two modes (two different air-interfaces) defined in WiMAX networks: Point-to-Multi-Point (PMP) and Mesh modes. In PMP mode, two SSs (Subscriber Stations) can only communicate through BS (Base Station), while in Mesh mode, two SSs can communicate directly.
In the PHY layer, the IEEE 802.16 standard adopts the orthogonal frequency division multiplexing (OFDM), which is a multicarrier modulation scheme. The IEEE 802.16 standard has two OFDM-based modes: OFDM and orthogonal frequency division multiplexing access (OFDMA). Both of these technologies allow subcarriers to be adaptively modulated (e.g., QPSK, 16-QAM, and 64-QAM), depending on transmission distance and noise. Moreover, OFDMA has scalability to provide efficient use of bandwidth. The MAC layer of IEEE 802.16 standard was originally designed for the PMP mode. On the later amendments of the IEEE 802.16a and the IEEE 802.16d, the mesh mode was included. The IEEE 802.16a adopts OFDM to provide greater spectral efficiency and to mitigate interference. IEEE 802.16d covers most of the quality of service (QoS) aspects. The IEEE 802.16e introduces scalable OFDMA into the standard, and supports mobile communications. With handover mechanisms, WiMAX is thus able to support mobile communications at vehicular speeds.
2.2. IEEE 802.16e -2005 Standard
On July 2002, a study group called IEEE 802.16 Mobile WirelessMAN Task Group was initiated to produce an amendment covering the PHY and MAC layers for combined, fixed, and mobile operations in the licensed band range. The amendment was approved in December 2005 and the new standard called IEEE 802.16e-2005 was published in February 2006. The scope of this standard is to provide mobility enhancement support for SS moving at the vehicular speed, in addition to corrections to 802.16-2004 fixed operation that was developed as IEEE 802.16-2004/Cor1-2005 and published along with IEEE 802.16e-2005. 802.16e introduces many changes to PHY and MAC layer protocols owing to mobility support, which required addressing new issues that were not required in 802.16-2004, such as handoff and power management.
The mobile WiMAX PHY layer is based on OFDMA technology. The network is an IP end-to-end conventional architecture that provides high-speed broadband. With a modification from fixed WiMAX to mobile WiMAX, the PHY layer also supports BWs from 1.25 to 20 MHz. The standard is designed to accommodate either TDD or FDD (Time / Frequency Division Duplexing) deployments, allowing for both full- and half-duplex terminals in the FDD case.
The MAC layer was initially designed specifically for the point-to-point wireless access environment. It supports higher layer or transport protocols such as asynchronous transfer mode (ATM), Ethernet, or IP, and is designed to easily accommodate future protocols that have not yet been developed. MAC layer specification practices considerable departures from 802.16-2004 to provide support for mobility. It adds support for handoff and power management.
QoS Support- 802.16e defines new scheduling mechanisms: the extended real-time polling service (ErtPS), which is based on two services defined in 802.16-2004; the unsolicited grant service (UGS); and the real-time polling service (rtPS). ErtPS is similar to UGS in providing unicast grants, thus saving the delay incurred for requesting the bandwidth. However, ErtPS allocations are dynamic as rtPS while UGS allocations are fixed. The ErtPS is introduced to support real-time service flows that generate periodical variable sized data packets. Thus, ErtPS is especially important to support VoIP, since it allows for managing traffic rates and improves latency and jitter.
Handover Support- 802.16e includes new MAC-level request/grant mechanisms to achieve similar seamless mobility as that provided for cellular users. 802.16e includes fast base station switching and hard handoff mechanisms for inter-cell and inter-sector handover. In 802.16e, handoff process may be triggered for two reasons. One is due to fading of the signal, interference level, etc. within the current cell or sector. The other is due to the fact that another cell can provide a higher level of QoS for the mobile station (MS). Furthermore, 802.16e supports macro diversity handovers and inter-technology roaming. Macro-diversity handovers support handoffs between different sized cells, while inter-technology roaming addresses MS handoffs from BS to backhaul or wired network by providing roaming authentication mechanisms.
Power management is a critical process for mobile applications to enable efficient operation of the MS. 802.16e defines two power management operations, sleep mode and idle mode. Idle mode operation is carried out by MS when the MS does not intend to register to a specific BS as the MS traverses a region covered by multiple BS. The advantage of idle mode for the BS is to avoid multiple handoffs and other normal operations while the SS is traversing the region, and for the BS and network is to avoid unnecessary handoffs from an inactive MS. When the MS enters the idle mode, it needs to periodically check for broadcast messages sent by the BS to see if new downlink frames have been sent to it. Sleep mode operation is a state in which MS sends a request to be unavailable to the BS. If the BS responds with approval, the MS is provided with a sleep interval time vector that determines the length of the sleep mode period. The benefit of the sleep mode operation is to minimize MS power usage and utilization of the air interface resources of the BS. While the MS is in the sleep mode, the MS scans other BSs to collect information required for handover during the sleep mode.
3. WHY WiMAX AS SOLUTION?
Compared with other wired solution such as ADSL, or any other wireless or satellite system, WiMAX based access networks will enable operators and service providers to cost-effectively reach million of new potential customers providing them with broadband ICTs access. This is even true for developing countries and rural areas for which the cost/profitability and the demand factors are essential. This obviously includes adequate coverage, reliability, performances (throughput), capacity and applications. Table 1 shows how WiMAX supports different types of access and their requirement.
The WiMAX standard has been developed with many objectives in mind. These objectives are as follows:
Flexible Architecture: WiMAX supports several system architectures, including Point-to-Point, Point-to-Multipoint and ubiquitous coverage. The WiMAX MAC (Media Access Control) supports Point-to-Multipoint and ubiquitous service by scheduling a time slot for each Subscriber Station (SS). If there is only one SS in the network, the WiMAX Base Station (BS) will communicate with the SS on a Point-to- Point basis. A BS in a Point-to-Point configuration may use a narrower beam antenna to cover longer distances. Wireless is more flexible and thus easier to deploy according to the market demand. Although most of the existing wireless technologies suffer from limited range and coverage (usually a few hundred meters around the base station) resulting in very costly combination of technologies (wired and/or wireless), WiMAX technology benefits in a wide coverage and can be deployed as a Point-to-Multipoint “last mile’’ connection but also as part of the backhaul to the private switched telephone network (PSTN) and Internet access points. The WiMAX role in an access network is illustrated in Figure 3. With potential range of 30 to 50 kilometers in line-of-site conditions, WiMAX offer a huge improvement over all existing broadband wireless technology.
Quick Deployment: Compared with the deployment of wired solutions, WiMAX requires little or no external plant construction. Ease of installation is one of the key issues to lower deployment costs in developing countries. In rural areas, the consequences of the long distances from the core network access point and the scattered location of villages, farms in the countryside makes any deployment very costly. In developing countries, the lack of main infrastructure (electricity, roads), and environmental condition (temperature, humidity) adds on the difficulty. Thanks to the non-line-of-sight (NLOS)/LOS coverage advantage, the service provider can easily plans a 95% predictability coverage ensuring high installation success rates and controls deployment costs. A quicker and simpler installation with a much greater rate of success means operators spend less money rolling out their networks. WiMAX NLOS capability also allows indoors self install CPEs within several kilometers radius.
Worldwide Standardization: Developed and supported by the WiMAX forum (more than 300 members), WiMAX will become the worldwide technology based standard for broadband and will guaranty interoperability (i.e., multivendor CPEs), reliability and evolving technology, but also will ensure equipments with very low cost. With low CPEs cost as one of the first objective, business model can easily be profitable even in developing countries.
Mobility: The IEEE 802.16e amendment has added key features in support of mobility. Improvements have been made to the Orthogonal Frequency Division Multiplexing (OFDM) and OFDMA physical layers to support devices and services in a mobile environment. These improvements, which include Scalable OFDMA, Multiple input, multiple Output (MIMO), and support for idle/sleep mode and hand-off, will allow full mobility at speeds up to 160 km/hr. The WiMAX Forum-supported standard has inherited OFDM’s superior NLOS performance and multipath-resistant operation, making it highly suitable for the mobile environment.
Wider Coverage: Even more important than the range limitation, the coverage (i.e. the capability to reach any potential customer within the base station covering area) is essential for the operator/service provider. While many currently available wireless broadband solutions can only provide line-of-site coverage, WiMAX due to its OFDM technology, has been optimized to provide excellent non-line-of-site coverage (up to 15Km around the base station) and long range transmission up to 50Km in LOS conditions. Combining both LOS and NLOS coverage, WiMAX is the ideal solution for getting the requested coverage in the most economical way.
High Capacity: Using higher modulation (64-QAM) and channel bandwidth (currently 7 MHz, with planned evolution towards the full bandwidth specified in the associated IEEE and ETSI standards), WiMAX systems can provide significant bandwidth to end-users.
Spectrum Flexibility: In line with the objective to become the worldwide standard based technology for broadband, WiMAX use single radio covering all licensed and unlicensed frequency bands allocated by the ITU for such services. These are:
In addition to the flexibility offered to address all national spectrum situations, this single radio, will makes base stations and customer premises equipment costs very attractive.
Multi-application Technology: Following the normal trend of digitalization and packet transmission and switching, WiMAX uses the Internet protocol and thus supports all multimedia services from Voice over IP to high speed internet and video transmission. WiMAX allows service providers to offer all the latest generation of services and beyond, thanks to a throughput up to tens of Mbps. With regard to the potential users, this means that WiMAX have the capacity to deliver services from households to small and medium enterprises (SMEs), small office home office (SOHO), Cybercafés, Multimedia Telecentres, Schools and Hospitals. See Table 2 for more WiMAX range of applications.
4. WiMAX Applications
WiMAX was developed to become a last mile access technology comparable to DSL, cable and E1/T1 technologies. It is a rapidly growing technology that is most viable for backhauling the rapidly increasing volumes of traffic being generated by Wi-Fi hotspots. WiMAX is a MAN technology that fits between wireless LANs, such as 802.11, and wireless wide-area networks (WANs), such as the cellular networks. WiMAX can serve in applications such as cellular backhaul systems, in which microwave technologies dominate, backhaul systems for Wi-Fi hot spots and most prominently as residential and business broadband services. WiMAX is billed to support many types of wireless broadband connections including but not limited to the following: high-bandwidth MANs, cellular backhaul, clustered Wi-Fi hotspot backhaul, last-mile broadband, cell phone replacements and other miscellaneous applications such as automatic teller machines (ATMs), vehicular data and voice, security applications and wireless VoIP.
Today, wherever available, these applications use expensive, proprietary methods for broadband access. WiMAX was developed to provide low-cost, high-quality, flexible, BWA using certified, compatible and interoperable equipments from multiple vendors. As WiMAX is based on interoperability-tested systems that were built using the IEEE 802.16 standard-based silicon solutions, WiMAX will reduce costs. WiMAX is well placed to address challenges associated with traditional wired access deployment types such as:
Large area coverage access, covering a large area (also referred to as hot zones) around the base station and providing access to 802.16 clients using point-to-multipoint topology;
Last-mile access, connecting residential or business subscribers to the base station using point-to-multipoint topology;
Backhaul, connecting aggregate subscriber sites to each other and to base stations across long distances using point-to-point topology.
In summary, the WiMAX standard has been developed to address a wide range of applications as shown in Table 2.
Some more disruptive applications of WiMAX can be:
Remote monitoring of patients’ vital signs in health-care facilities to provide continuous information and immediate response in the event of a patient crisis.
Mobile transmission of maps, floor layouts and architectural drawings to assist fire-fighters and other response personnel in the rescue of individuals involved in emergency situations.
Real-time monitoring, alerting and control in situations involving handling of hazardous materials.
Wireless transmission of fingerprints, photographs, warrants and other images to and from law-enforcement field personnel.
5. Usage Scenarios
Based on its technical attributes and service classes, WiMAX is suited to supporting a large number of usage scenarios. WiMAX technology will revolutionize the way we communicate. It will provide total freedom to people who are highly mobile, allowing them to stay connected with voice, data and video services. It will allow people to go from their homes to their cars, and then travel to their offices or anywhere in the world, all seamlessly. To illustrate the ability of WiMAX to address the applications outlined in Table 2, several representative usage scenarios are outlined in Table 3.
5.1. Cellular Backhaul
Majority of backhaul is done by leasing E1 services from incumbent wire-line operators. With the WiMAX technology, cellular operators will have the opportunity to lessen their independence on backhaul facilities leased from their competitors. Outside the United States, the use of point-to-point microwave is more prevalent for mobile backhaul, but WiMAX can still play a role in enabling mobile operators to cost-effectively increase backhaul capacity using WiMAX as an overlay network as depicted in Figure 5. This overlay approach will enable mobile operators to add the capacity required to support the wide range of new mobile services they plan to offer without the risk of disrupting existing services.
Some salient points about WiMAX use as cellular backhaul are:
multiple cell sites are served;
there is capacity to expand for future mobile services;
It is a lower cost solution than traditional landline backhaul.
5.2. Education Networks
School boards can use WiMAX networks to connect schools and school board offices within a district, as shown Figure 6. Some of the key requirements for a school system are NLOS, high bandwidth (>15 Mbps), Point-to-Point and Point-to-Multipoint capability, and a large coverage footprint. WiMAX-based education networks, using QoS, can deliver the full range of communication requirements, including telephony voice, operating data (such as student records), email, Internet and intranet access (data), and distance education (video) between the school board office and all of the schools in the school district, and between the schools themselves. The WiMAX solution provides broad coverage, making it very cost-effective, particularly for rural schools, which may have little or no communications infrastructure, and which are widely dispersed. When school boards own and operate their own network, they can be responsive to changes in the location and layout of their facilities. This will significantly reduce the annual operating cost of leased lines. Wired solutions cannot offer a quickly deployable, low-cost solution, and most versions of DSL and cable technology do not have the throughput required by these education networks.
5.3. Campus Connectivity
Government agencies, large enterprises, universities, and colleges, can use WiMAX networks to connect multiple locations, sites and offices within their campus, as shown in Figure 7. Campus systems require high data capacity, low latency, a large coverage footprint, and high security. Campus networks carry a mix of voice, data, and video, which the WiMAX QoS helps prioritize and optimize. It takes less time and resources to interconnect a campus through a WiMAX network, since excavation and external construction are not required. Some campuses have been around for a long time, and digging trenches for cable may not be permitted. In such cases, WiMAX solutions may be one of the most effective ways to interconnect campus buildings. Even if wired installations are permitted, the lead-time to deploy a wired solution is much longer than the lead-time to deploy a WiMAX solution, without offering any accompanying benefits.
5.4. Rural Connectivity
Service providers use WiMAX networks to deliver service to underserved markets in rural areas and the suburban outskirts of cities as shown in Figure 8. The delivery of rural connectivity is critical in many developing countries and underserved areas of developed countries, where little or no infrastructure is available. Rural connectivity delivers much-needed voice telephony and Internet service. Since the WiMAX solution provides extended coverage, it is a much more cost-effective solution than wired technology in areas with lower population densities. It solutions can be deployed quickly, providing communication links to these underserved areas, providing a more secure environment, and helping to improve their local economies.
5.5. Wireless Service Provider Access Network
Wireless Service Providers (WSPs) use WiMAX networks to provide connectivity to both residential (voice, data and video) and business customers (primarily voice and Internet), as illustrated in Figure 9. The WSP could be a CLEC (Competitive Local Exchange Carriers) that is starting its business with little or no installed infrastructure. Since WiMAX is easy to deploy, the CLEC can quickly install its network and be in position to compete with the ILEC (Incumbent Local Exchange Carrier). A common network platform, offering voice, data and video, is highly attractive to end customers, because it presents a one-stop shop and a single monthly bill. Support for multiple service types allows for different revenue streams, yet it reduces customer acquisition cost, and increases ARPU (Average Revenue Per User). The WSP needs only one billing system and one customer database. Cellular operators may also be interested in applying WiMAX in their networks. These operators already have towers, billing infrastructure and a customer base in place, but the deployment of a WiMAX solution will expand their market presence in their service area.
5.6. Theme Parks
Theme park operators can use WiMAX to deliver a broad range of communication services for their amusement parks, expositions, hospitality and operation centers, and buses and service vehicles, as shown Figure 10. The network can support a wide range of communications traffic, including two-way dispatch from a control center, video surveillance throughout the park, reservation data, inventory database access and update, site status monitoring, video on demand, and voice telephony. Some of the key requirements for a system like this are support for fixed and mobile operations, high security, scalable architecture and low latency. The broad coverage range of WiMAX means an entire park can be covered from only a few numbers of Base Stations, scalable upwards as capacity requirements increase.
Re-deployment of the network, in response to changes in theme park facilities, is straightforward and simple, unlike the changes that would be required had the park been served by wired facilities, such as DSL or cable. WiMAX mobility capability will support two-way voice and data communications to the theme park’s tour buses and service vehicles. Real-time video can be broadcast to tour buses, providing tourist information, promotions, and weather to passengers.
Demand for wireless broadband access is growing fast and embracing an ever-widening range of applications that encompass fixed, nomadic, portable and mobile data access as well as fixed and mobile voice services, and content streaming. Looking back to the barriers as summarized by ITU in Figure 2 and section 3, WiMAX appears clearly as the solution to favor the broadband ICTs access in developing countries. Undoubtedly, WiMAX is a new powerful broadband wireless technology aiming at providing a universal ubiquitous and equitable and affordable access to ICTs infrastructure and services, and thus highly contributing to bridge the “Digital Divide”.