14-02-2009, 11:43 PM
WIMAX: Worldwide Interoperability for Microwave access
What is WiMAX?
Think about how you access the Internet today. There are basically three different options:
* Broadband access - In your home, you have either a DSL or cable modem. At the office, your company may be using a T1 or a T3 line.
* WiFi access - In your home, you may have set up a WiFi router that lets you surf the Web while you lounge with your laptop. On the road, you can find WiFi hot spots in restaurants, hotels, coffee shops.
* Dial-up access - If you are still using dial-up, chances are that either broadband access is not available, or broadband access is too expensive.
The main problems with broadband access are that it is pretty expensive and it doesn't reach all areas and with WiFi access is that hot spots are very small, so coverage is sparse. What if there was a new technology that solved all of these problems? This new technology would provide:
* The high speed of broadband service.
* Wireless rather than wired access, so it would be a lot less expensive than cable or DSL and much easier to extend to suburban and rural areas.
* Broad coverage like the cell phone network instead of small WiFi hotspots.
This system is actually coming into being right now, and it is called WiMAX. WiMAX is short for Worldwide Interoperability for Microwave Access, and it also goes by the IEEE name 802.16.
WiMAX has the potential to do to broadband Internet access what cell phones have done to phone access. WiMAX could replace cable and DSL services, providing universal Internet access just about anywhere you go. WiMAX will also be as painless as WiFi -- turning your computer on will automatically connect you to the closest available WiMAX antenna.
WiMax Components:
The core components of a WiMax system are the subscriber station (SS) otherwise known as the CPE and the base station (BS). A BS and one or more SSs can form a cell with a point-to-multipoint (P2MP) structure. BS controls activity within the cell, including access to the medium by SS, allocations to achieve quality of service (QoS) and admission to the network based on network security mechanisms.
An 802.16-based system often uses fixed antenna at the subscriber station site. The antenna is mounted to the roof or an eave. Provisions such as adaptive-antenna systems (AAS) and sub-channelization are also supported optionally by the standard for enhanced page link budget required for in-door installation. IEEE 802.16e sub-committee is currently working on extension to the standard required for mobility and support for the power limited SS terminals.
A BS typically uses either sectored or omni-directional antennas. A fixed SS typically uses directional antenna while mobile or portable SS usually uses an omni-directional antenna. Multiple BSes can be configured to form a cellular wireless network. When OFDM is used, the cell radius can ideally reach up to 30 miles. Practical cell sizes usually have a small radius of around 5 miles or less. The 802.16 standard also can be used in a point-to-point (P2P) or mesh topology, using pairs of directional antennas. This can be used to increase the effective range of the system relative to what can be achieved in P2MP mode.
The WiMAX Scenario:
Here's what would happen if you got WiMAX. An Internet service provider sets up a WiMAX base station 10 miles from your home. You would buy a WiMAX-enabled computer (some of them should be on store shelves in 2005) or upgrade your old computer to add WiMAX capability. You would receive a special encryption code that would give you access to the base station. The base station would beam data from the Internet to your computer (at speeds potentially higher than today's cable modems), for which you would pay the provider a monthly fee. The cost for this service could be much lower than current high-speed Internet-subscription fees because the provider never had to run cables.
WIMAX ARCHITECTURE
A wireless MAN, based on the WIMAX air interface standard is configured in much the same way as a traditional cellular network with strategically located base stations using a point-to-multipoint architecture to deliver services over a radius up to several kilometers depending on frequency, transmit power and receiver sensitivity. In areas with high population densities the range will generally be capacity limited rather than range limited due to limitation in the amount of available spectrum. The base stations are typically backhauled to the core network by means of fiber or point-to-point microwave links to available fiber nodes or via leased lines from an incumbent wire-line operator. The range and non line of sight (NLOS) capability makes the technology equally attractive and cost-effective in a wide variety of environments. The technology was envisioned from the beginning as a means to provide wireless last mile broadband access in the Metropolitan Area Network (MAN) with performance and services comparable to or better than traditional DSL, Cable or T1/E1 leased line services.
2.1 The WIMAX System:
A WIMAX system consists of two parts:
A Base Station (BS) is mounted on a building or a tower that communicates on a point to multi-point basis with the Subscriber Units. It can provide coverage to a very large area - as big as 3,000 square miles (~8,000 square km). There are two likely types of base stations:
1] A Standard Base Station with:
· Basic WIMAX implementations (mandatory capabilities)
· Standard RF output power for a lower cost base station (vendor specific)
2] A Fully Featured Base Station with:
· Higher RF output power than standard base station (vendor specific)
· Sub-channeling.
· Automatic Repeat Request(ARQ)
A Subscriber Unit (SU) installed at the customer premises also called as Customer Premise Equipment, enables the customer data connection to the Access Unit (AU). CPEâ„¢s can be of different types (depending on end users):
· A modem attached to an external antenna
· A modem with an indoor antenna
· Integrated antenna.
2.2 How WIMAX Works:
A WIMAX Base Station (BS) can connect directly to the Internet using a high-bandwidth, wired connection (for example, a T3 line). It can also connect to another WIMAX BS using a line-of-sight, microwave link. This connection, often referred to as a backhaul, along with the ability of a single BS to cover up to 3,000 square miles, is what allows WIMAX to provide coverage to remote rural areas.
Fig 1: WIMAX system
WIMAX can actually provide two forms of services:
* Non Line Of Sight (NLOS): It is a WiFi sort of service where a small antenna on the CPE connects to the BS. In this mode WIMAX uses a lower frequency range (2GHz-11GHz).The signal reaches the receiver through reflections, scattering and diffractions. These lower wavelength transmissions are not easily disrupted by physical obstructions.
* Line Of Sight (LOS): In this a fixed dish antenna points straight at the WIMAX BS from the rooftop or pole. It requires most of the first Fresnel Zone to be free of any obstructions which in turn depends upon the operating frequency and the distance. LOS transmissions use high frequencies reaching a possible of 66GHZ.
LOS connection is stronger and more stable and it is able to send a lot of data with fewer errors. However there are several advantages of NLOS deployments. For large-scale contiguous cellular deployments, where frequency re-use is critical, lowering the antenna is advantageous to reduce the co channel interference between adjacent cell sites. This often forces the base stations to operate in NLOS conditions. LOS systems cannot reduce antenna heights because doing so would impact the required direct view path from the CPE to the Base Station. NLOS technology also reduces installation expenses by making under-the-eaves CPE installation a reality.
How WiMAX Works?
WiMAX transmitting tower
In practical terms, WiMAX would operate similar to WiFi but at higher speeds, over greater distances and for a greater number of users. WiMAX could potentially erase the suburban and rural blackout areas that currently have no broadband Internet access because phone and cable companies have not yet run the necessary wires to those remote locations.
A WiMAX system consists of two parts:
* A WiMAX tower, similar in concept to a cell-phone tower - A single WiMAX tower can provide coverage to a very large area -- as big as 3,000 square miles (~8,000 square km).
* A WiMAX receiver - The receiver and antenna could be a small box or PCMCIA card, or they could be built into a laptop the way WiFi access is today.
A WiMAX tower station can connect directly to the Internet using a high-bandwidth, wired connection (for example, a T3 line). It can also connect to another WiMAX tower using a line-of-sight, microwave link. This connection to a second tower (often referred to as a backhaul), along with the ability of a single tower to cover up to 3,000 square miles, is what allows WiMAX to provide coverage to remote rural areas.
Some technologies like Chipsets are currently custom-built for each broadband wireless access vendor, adding time and cost to the process. Its equivalent or competitor in Europe is HIPERMAN. But WiMax has the ability to overcome them.
What this points out is that WiMAX actually can provide two forms of wireless service:
* There is the non-line-of-sight, WiFi sort of service, where a small antenna on your computer connects to the tower. In this mode, WiMAX uses a lower frequency range -- 2 GHz to 11 GHz (similar to WiFi). Lower-wavelength transmissions are not as easily disrupted by physical obstructions -- they are better able to diffract, or bend, around obstacles.
* There is line-of-sight service, where a fixed dish antenna points straight at the WiMAX tower from a rooftop or pole. The line-of-sight connection is stronger and more stable, so it's able to send a lot of data with fewer errors. Line-of-sight transmissions use higher frequencies, with ranges reaching a possible 66 GHz. At higher frequencies, there is less interference and lots more bandwidth.
WiFi-style access will be limited to a 4 to 6 mile radius (perhaps 25 square miles or 65 square km of coverage, which is similar in range to a cell-phone zone). Through the stronger line-of-sight antennas, the WiMAX transmitting station would send data to WiMAX-enabled computers or routers set up within the transmitter's 30 mile radius (2,800 square miles or 9,300 square km of coverage). This is what allows WiMAX to achieve its maximum range.
WiMAX operates on the same general principles as WiFi -- it sends data from one computer to another via radio signals. A computer (either a desktop or a laptop) equipped with WiMAX would receive data from the WiMAX transmitting station, probably using encrypted data keys to prevent unauthorized users from stealing access.
The fastest WiFi connection can transmit up to 54 Mbits/sec under optimal conditions. WiMAX should be able to handle up to 70 Mbits/sec. Even once that 70 Mbits is split up between several dozen businesses or a few hundred home users, it will provide at least the equivalent of cable-modem transfer rates to each user.
The biggest difference between the WiFi and WiMax isn't speed; it's
distance. WiMAX outdistances WiFi by miles. WiFi's range is about 100 feet (30
m). WiMAX will blanket a radius of 30 miles (50 km) with wireless access. The
increased range is due to the frequencies used and the power of the transmitter. Of course, at that distance, terrain, weather and large buildings will act to reduce the maximum range in some circumstances, but the potential is there to cover
FUTURE OF WIMAX
The IEEE 802.16 standard body members are working toward incremental evolution, from fixed operation to portability and mobility. The IEEE 802.16e amendment will amend the base specification to enable not just fixed, but also portable and mobile operation. IEEE 802.16f and IEEE 802.16g task groups are addressing the management interfaces for fixed and mobile operation. Clients will be able to hand-off between 802.16 base stations, enabling users to roam between service areas. In a fully mobile scenario users may be moving while simultaneously engaging in a broadband data access or multimedia streaming session. All of these improvements will help make WIMAX an even better Internet access solution for growing economies like that of India.
Fig 7.1: Future of WIMAX
Technical advantages:
Ø WiMAX does not conflict with WiFi but actually complements it. WiMAX is a wireless metropolitan area network (MAN) technology that will connect IEEE 802.11 (WiFi) hotspots to the Internet and provide a wireless extension to cable and DSL for last mile (last km) broadband access. IEEE 802.16 provides up to 50 km (31 miles) of linear service area range and allows users connectivity without a direct line of sight to a base station.
Ø WiMAX technology theoretically supports coverage radius of 30 miles and a data rate of up to 75 Mbps, while WiFi currently supports a much shorter radius and lower data rates.
Ø WiMAX technology has the potential to enable service carriers to converge the all-IP-based network for triple-play services such as data, voice, and video.
Ø WiMAX will provide fixed, nomadic, portable and, eventually, mobile wireless broadband connectivity without the need for direct line-of-sight connection between a base station and a subscriber station.
Ø No FCC radio licensing is required.
An important aspect of the IEEE 802.16 is that it defines a MAC layer that supports multiple physical layer (PHY) specifications. This is crucial to allow equipment makers to differentiate their offerings.
Even if WiMax has the great advantages over the other technologies, it has to face some of the disadvantages.
Disadvantages:
· Line-of-sight (LOS) is required for long distance (5-30 mile) connections.
· Heavy rains can disrupt the service.
· Other wireless electronics in the vicinity can interfere with the WiMax connection and cause a reduction in data throughput or even a total disconnect. On the WiLAN side, security has been a major concern, though this has been addressed through developments in encryption technology and authentication systems. A typical access point covers an area 300 feet in diameter, but this distance can be impacted by structures within the building such as walls, furnishings etc.
What is WiMAX?
Think about how you access the Internet today. There are basically three different options:
* Broadband access - In your home, you have either a DSL or cable modem. At the office, your company may be using a T1 or a T3 line.
* WiFi access - In your home, you may have set up a WiFi router that lets you surf the Web while you lounge with your laptop. On the road, you can find WiFi hot spots in restaurants, hotels, coffee shops.
* Dial-up access - If you are still using dial-up, chances are that either broadband access is not available, or broadband access is too expensive.
The main problems with broadband access are that it is pretty expensive and it doesn't reach all areas and with WiFi access is that hot spots are very small, so coverage is sparse. What if there was a new technology that solved all of these problems? This new technology would provide:
* The high speed of broadband service.
* Wireless rather than wired access, so it would be a lot less expensive than cable or DSL and much easier to extend to suburban and rural areas.
* Broad coverage like the cell phone network instead of small WiFi hotspots.
This system is actually coming into being right now, and it is called WiMAX. WiMAX is short for Worldwide Interoperability for Microwave Access, and it also goes by the IEEE name 802.16.
WiMAX has the potential to do to broadband Internet access what cell phones have done to phone access. WiMAX could replace cable and DSL services, providing universal Internet access just about anywhere you go. WiMAX will also be as painless as WiFi -- turning your computer on will automatically connect you to the closest available WiMAX antenna.
WiMax Components:
The core components of a WiMax system are the subscriber station (SS) otherwise known as the CPE and the base station (BS). A BS and one or more SSs can form a cell with a point-to-multipoint (P2MP) structure. BS controls activity within the cell, including access to the medium by SS, allocations to achieve quality of service (QoS) and admission to the network based on network security mechanisms.
An 802.16-based system often uses fixed antenna at the subscriber station site. The antenna is mounted to the roof or an eave. Provisions such as adaptive-antenna systems (AAS) and sub-channelization are also supported optionally by the standard for enhanced page link budget required for in-door installation. IEEE 802.16e sub-committee is currently working on extension to the standard required for mobility and support for the power limited SS terminals.
A BS typically uses either sectored or omni-directional antennas. A fixed SS typically uses directional antenna while mobile or portable SS usually uses an omni-directional antenna. Multiple BSes can be configured to form a cellular wireless network. When OFDM is used, the cell radius can ideally reach up to 30 miles. Practical cell sizes usually have a small radius of around 5 miles or less. The 802.16 standard also can be used in a point-to-point (P2P) or mesh topology, using pairs of directional antennas. This can be used to increase the effective range of the system relative to what can be achieved in P2MP mode.
The WiMAX Scenario:
Here's what would happen if you got WiMAX. An Internet service provider sets up a WiMAX base station 10 miles from your home. You would buy a WiMAX-enabled computer (some of them should be on store shelves in 2005) or upgrade your old computer to add WiMAX capability. You would receive a special encryption code that would give you access to the base station. The base station would beam data from the Internet to your computer (at speeds potentially higher than today's cable modems), for which you would pay the provider a monthly fee. The cost for this service could be much lower than current high-speed Internet-subscription fees because the provider never had to run cables.
WIMAX ARCHITECTURE
A wireless MAN, based on the WIMAX air interface standard is configured in much the same way as a traditional cellular network with strategically located base stations using a point-to-multipoint architecture to deliver services over a radius up to several kilometers depending on frequency, transmit power and receiver sensitivity. In areas with high population densities the range will generally be capacity limited rather than range limited due to limitation in the amount of available spectrum. The base stations are typically backhauled to the core network by means of fiber or point-to-point microwave links to available fiber nodes or via leased lines from an incumbent wire-line operator. The range and non line of sight (NLOS) capability makes the technology equally attractive and cost-effective in a wide variety of environments. The technology was envisioned from the beginning as a means to provide wireless last mile broadband access in the Metropolitan Area Network (MAN) with performance and services comparable to or better than traditional DSL, Cable or T1/E1 leased line services.
2.1 The WIMAX System:
A WIMAX system consists of two parts:
A Base Station (BS) is mounted on a building or a tower that communicates on a point to multi-point basis with the Subscriber Units. It can provide coverage to a very large area - as big as 3,000 square miles (~8,000 square km). There are two likely types of base stations:
1] A Standard Base Station with:
· Basic WIMAX implementations (mandatory capabilities)
· Standard RF output power for a lower cost base station (vendor specific)
2] A Fully Featured Base Station with:
· Higher RF output power than standard base station (vendor specific)
· Sub-channeling.
· Automatic Repeat Request(ARQ)
A Subscriber Unit (SU) installed at the customer premises also called as Customer Premise Equipment, enables the customer data connection to the Access Unit (AU). CPEâ„¢s can be of different types (depending on end users):
· A modem attached to an external antenna
· A modem with an indoor antenna
· Integrated antenna.
2.2 How WIMAX Works:
A WIMAX Base Station (BS) can connect directly to the Internet using a high-bandwidth, wired connection (for example, a T3 line). It can also connect to another WIMAX BS using a line-of-sight, microwave link. This connection, often referred to as a backhaul, along with the ability of a single BS to cover up to 3,000 square miles, is what allows WIMAX to provide coverage to remote rural areas.
Fig 1: WIMAX system
WIMAX can actually provide two forms of services:
* Non Line Of Sight (NLOS): It is a WiFi sort of service where a small antenna on the CPE connects to the BS. In this mode WIMAX uses a lower frequency range (2GHz-11GHz).The signal reaches the receiver through reflections, scattering and diffractions. These lower wavelength transmissions are not easily disrupted by physical obstructions.
* Line Of Sight (LOS): In this a fixed dish antenna points straight at the WIMAX BS from the rooftop or pole. It requires most of the first Fresnel Zone to be free of any obstructions which in turn depends upon the operating frequency and the distance. LOS transmissions use high frequencies reaching a possible of 66GHZ.
LOS connection is stronger and more stable and it is able to send a lot of data with fewer errors. However there are several advantages of NLOS deployments. For large-scale contiguous cellular deployments, where frequency re-use is critical, lowering the antenna is advantageous to reduce the co channel interference between adjacent cell sites. This often forces the base stations to operate in NLOS conditions. LOS systems cannot reduce antenna heights because doing so would impact the required direct view path from the CPE to the Base Station. NLOS technology also reduces installation expenses by making under-the-eaves CPE installation a reality.
How WiMAX Works?
WiMAX transmitting tower
In practical terms, WiMAX would operate similar to WiFi but at higher speeds, over greater distances and for a greater number of users. WiMAX could potentially erase the suburban and rural blackout areas that currently have no broadband Internet access because phone and cable companies have not yet run the necessary wires to those remote locations.
A WiMAX system consists of two parts:
* A WiMAX tower, similar in concept to a cell-phone tower - A single WiMAX tower can provide coverage to a very large area -- as big as 3,000 square miles (~8,000 square km).
* A WiMAX receiver - The receiver and antenna could be a small box or PCMCIA card, or they could be built into a laptop the way WiFi access is today.
A WiMAX tower station can connect directly to the Internet using a high-bandwidth, wired connection (for example, a T3 line). It can also connect to another WiMAX tower using a line-of-sight, microwave link. This connection to a second tower (often referred to as a backhaul), along with the ability of a single tower to cover up to 3,000 square miles, is what allows WiMAX to provide coverage to remote rural areas.
Some technologies like Chipsets are currently custom-built for each broadband wireless access vendor, adding time and cost to the process. Its equivalent or competitor in Europe is HIPERMAN. But WiMax has the ability to overcome them.
What this points out is that WiMAX actually can provide two forms of wireless service:
* There is the non-line-of-sight, WiFi sort of service, where a small antenna on your computer connects to the tower. In this mode, WiMAX uses a lower frequency range -- 2 GHz to 11 GHz (similar to WiFi). Lower-wavelength transmissions are not as easily disrupted by physical obstructions -- they are better able to diffract, or bend, around obstacles.
* There is line-of-sight service, where a fixed dish antenna points straight at the WiMAX tower from a rooftop or pole. The line-of-sight connection is stronger and more stable, so it's able to send a lot of data with fewer errors. Line-of-sight transmissions use higher frequencies, with ranges reaching a possible 66 GHz. At higher frequencies, there is less interference and lots more bandwidth.
WiFi-style access will be limited to a 4 to 6 mile radius (perhaps 25 square miles or 65 square km of coverage, which is similar in range to a cell-phone zone). Through the stronger line-of-sight antennas, the WiMAX transmitting station would send data to WiMAX-enabled computers or routers set up within the transmitter's 30 mile radius (2,800 square miles or 9,300 square km of coverage). This is what allows WiMAX to achieve its maximum range.
WiMAX operates on the same general principles as WiFi -- it sends data from one computer to another via radio signals. A computer (either a desktop or a laptop) equipped with WiMAX would receive data from the WiMAX transmitting station, probably using encrypted data keys to prevent unauthorized users from stealing access.
The fastest WiFi connection can transmit up to 54 Mbits/sec under optimal conditions. WiMAX should be able to handle up to 70 Mbits/sec. Even once that 70 Mbits is split up between several dozen businesses or a few hundred home users, it will provide at least the equivalent of cable-modem transfer rates to each user.
The biggest difference between the WiFi and WiMax isn't speed; it's
distance. WiMAX outdistances WiFi by miles. WiFi's range is about 100 feet (30
m). WiMAX will blanket a radius of 30 miles (50 km) with wireless access. The
increased range is due to the frequencies used and the power of the transmitter. Of course, at that distance, terrain, weather and large buildings will act to reduce the maximum range in some circumstances, but the potential is there to cover
FUTURE OF WIMAX
The IEEE 802.16 standard body members are working toward incremental evolution, from fixed operation to portability and mobility. The IEEE 802.16e amendment will amend the base specification to enable not just fixed, but also portable and mobile operation. IEEE 802.16f and IEEE 802.16g task groups are addressing the management interfaces for fixed and mobile operation. Clients will be able to hand-off between 802.16 base stations, enabling users to roam between service areas. In a fully mobile scenario users may be moving while simultaneously engaging in a broadband data access or multimedia streaming session. All of these improvements will help make WIMAX an even better Internet access solution for growing economies like that of India.
Fig 7.1: Future of WIMAX
Technical advantages:
Ø WiMAX does not conflict with WiFi but actually complements it. WiMAX is a wireless metropolitan area network (MAN) technology that will connect IEEE 802.11 (WiFi) hotspots to the Internet and provide a wireless extension to cable and DSL for last mile (last km) broadband access. IEEE 802.16 provides up to 50 km (31 miles) of linear service area range and allows users connectivity without a direct line of sight to a base station.
Ø WiMAX technology theoretically supports coverage radius of 30 miles and a data rate of up to 75 Mbps, while WiFi currently supports a much shorter radius and lower data rates.
Ø WiMAX technology has the potential to enable service carriers to converge the all-IP-based network for triple-play services such as data, voice, and video.
Ø WiMAX will provide fixed, nomadic, portable and, eventually, mobile wireless broadband connectivity without the need for direct line-of-sight connection between a base station and a subscriber station.
Ø No FCC radio licensing is required.
An important aspect of the IEEE 802.16 is that it defines a MAC layer that supports multiple physical layer (PHY) specifications. This is crucial to allow equipment makers to differentiate their offerings.
Even if WiMax has the great advantages over the other technologies, it has to face some of the disadvantages.
Disadvantages:
· Line-of-sight (LOS) is required for long distance (5-30 mile) connections.
· Heavy rains can disrupt the service.
· Other wireless electronics in the vicinity can interfere with the WiMax connection and cause a reduction in data throughput or even a total disconnect. On the WiLAN side, security has been a major concern, though this has been addressed through developments in encryption technology and authentication systems. A typical access point covers an area 300 feet in diameter, but this distance can be impacted by structures within the building such as walls, furnishings etc.
