Introducing WiMax
"WiMAX" is an acronym that stands for Worldwide Interoperability for Microwave Access, the name actually stems from the WiMax forum, an organization of equipment and component suppliers dedicated to promoting the adoption of IEEE 802.16 and ETSI HiperMAN standards compliant equipment. In essence Wimax is a technology standard that results from coalesces of IEEE 802.16 and ETSI HiperMAN standards.
The advent of WiMAX introduces a novel approach to wireless broadband. The technology is based on the Orthogonal Frequency Division Multiplexing (OFDM,) based technology with an all-IP core network that delivers superior performance through high throughput, low latency, advanced security and QoS functionality (OFDM is a digital encoding and modulation technology that achieves high data rate and efficiency by using multiple overlapping carrier signals with the ability to deliver higher bandwidth efficiency and therefore higher data throughput even in the face of challenging deployment scenario such as NLOS links suffering from significant degradation due to multipath conditions).
IEEE 802.16 Overview
A point-to-multipoint (PMP) broadband wireless access standard for systems in the frequency ranges 10-66 GHz and sub 11 GHz has been developed by the IEEE 802.16 Working Group. The standard covers both the Media Access Control (MAC) and the physical (PHY) layers.
A number of PHY considerations were taken into account for the target environment. At higher frequencies, line of sight is very essential to reduce the effect of multipath, allowing for wide channels, typically greater than 10 MHz in bandwidth. This gives IEEE 802.16 the ability to provide very high capacity links on both the uplink and the downlink. For sub 11 GHz non line of sight capability is a requirement. The original IEEE 802.16 MAC was enhanced to accommodate different PHYs and services, which address the needs of different environments. The standard is designed to accommodate either Time Division Duplexing (TDD) or Frequency Division Duplexing (FDD) deployments, allowing for both full and half-duplex terminals in the FDD case.
The MAC was designed specifically for the PMP wireless access environment. It supports higher layer or transport protocols such as ATM, Ethernet or Internet Protocol (IP), and is designed to easily accommodate future protocols that have not yet been developed. The MAC is designed for very high bit rates (up to 268 mbps each way) of the truly broadband physical layer, while delivering ATM compatible Quality of Service (QoS); UGS, rtPS, nrtPS, and Best Effort.
The frame structure allows terminals to be dynamically assigned uplink and downlink burst profiles according to their link conditions. This allows a trade-off between capacity and robustness in real-time, and provides roughly a two times increase in capacity on average when compared to non-adaptive systems, while maintaining appropriate link availability.
The 802.16 MAC uses a variable length Protocol Data Unit (PDU) along with a number of other concepts that greatly increase the efficiency of the standard. Multiple MAC PDUs may be concatenated into a single burst to save PHY overhead. Additionally, multiple Service Data Units (SDU) for the same service may be concatenated into a single MAC PDU, saving on MAC header overhead. Fragmentation allows very large SDUs to be sent across frame boundaries to guarantee the QoS of competing services. And, payload header suppression can be used to reduce the overhead caused by the redundant portions of SDU headers.
The MAC uses a self-correcting bandwidth request/grant scheme that eliminates the overhead and delay of acknowledgements, while simultaneously allowing better QoS handling than traditional acknowledged schemes. Terminals have a variety of options available to them for requesting bandwidth depending upon the QoS and traffic parameters of their services. They can be polled individually or in groups. They can steal bandwidth already allocated to make requests for more. They can signal the need to be polled, and they can piggyback requests for bandwidth.
802.16
The first version of the WiMax standard addressed spectrum ranges above 10 GHz (specifically 10 GHz to 66 GHz). Since line-of-sight (LOS) is a primary issue in this range, multipath was addressed in this first version with orthogonal frequency division multiplexing (OFDM) techniques. Thus it supports wide channels, defined as being greater than 10 MHz in size. This first standard basically addressed licensed-only service delivery (although there is license-free spectrum in this range).
802.16a
The 802.16a update added support for spectrum ranges of 2 GHz to 11 GHz. It addressed both licensed and unlicensed ranges. It also incorporated non-line-of-sight (NLOS) capability. This version enhanced the medium access control (MAC) layer capabilities. It also improved quality of service (QOS) features. The European HiperMAN standard was supported and a total of three supported physical layers (PHY) were defined. Support for both time division duplexing (TDD) and frequency division duplexing (FDD) was incorporated -- providing for both half duplex and full duplex data transmission in cases where FDD is used. Transmission protocols such as Ethernet, ATM or IP are supported.
802.16c
This standard update dealt mostly with updates in the 10 GHz to 66 GHz range. However, it also addressed issues such as performance evaluation, testing and detailed system profiling. This last was a crucial element of the WiMax toolkit. Because there are great deals of options available with 802.16 in general, the system profile methodology evolved to define what would be mandatory features and what would be optional features. The intent was to guide vendors on mandatory elements that must be met to ensure interoperability. Optional elements such as different levels of security protocols incorporated allow vendors to differentiate their products by price, functionality and market niche.
802.16-2004(d)
All of the Fixed WiMax standards mentioned above have been rolled into 802.16-2004: it incorporates the original 802.16, 802.16a and 802.16c updates. This final standard supports numerous mandatory and optional elements. Vendors are already shipping their 802.16-2004 products to the Cetecom labs in Spain for interoperability testing.
The technology supports both TDD and FDD. Its theoretical effective data rate is around 70 Mbps, although real world performance will probably top out around 40 Mbps. It should be noted that while the technology supports at least three PHY layer Modulation schemes, the system profile chosen is OFDM 256-FFT. This is different from the OFDMA flexible FFT system used in 802.16e. Both standards, however, support the former PHY. This distinction is really a market choice. The Forum could have chosen to use OFDM 256-FFT instead of OFDMA. Market forces and in particular the WiBro standard may have precluded that.
Just some of the enhancements in this version are support for concatenation of both protocol data units (PDU) and service data units (SDU) which reduces the MAC overhead. The technology improves quality-of-service (QOS), particularly with very large SDUs. One clear improvement is support for multiple polling methodologies. The MAC facilitates polling individually or in groups. It can access allocated bandwidth to make requests, or signal that it needs polling. It can even piggyback polling requests over other traffic -- the upshot being that constant cross-talk is obviated with this system, reducing packet collisions and system overhead.
802.16e
A standard still in flux, IEEE 802.16e conserves the technical updates of Fixed WiMax while adding robust support for mobile broadband. While not completely settled, the technology will likely be based upon the OFDMA technology developed by Runcom. This OFDMA technique supports 2K-FFT, 1K-FFT, 512-FFT and 128-FFT. Interestingly, both standards do support the 256-FFT chosen for 802.16-2004. Many of the mandatory elements for this standard have been agreed upon, and a lot of the remaining work centers on the optional elements.
The OFDMA system allows signals to be divided into many lower-speed sub-channels to increase resistance to multi-path interference. For example, if a 20 MHz channel is subdivided into 1000 sub-channels, each individual user would be allowed a dynamic number of sub-channels based on their distance and needs from the cell (i.e. 4, 64, 298, 312, 346, 610 and 944). If close in, a higher modulation methodology such as 64 quadrature amplitude modulation (QAM) can be used for higher bandwidth across more channels. If the user is farther away, the number of channels can be reduced with a resultant power increase per channel. Throughput slows a bit, but distant users are not dropped.
WiBro
Koreans are always at the forefront of broadband adoption. They were ready to deploy a mobile wireless MAN and felt the standards as existed were good enough for that purpose, so WiBro was born. Product is already being shipped by several vendors in an OFDMA version using 1K-FFT in the 2.3 GHz band.
The WiMax Forum has chosen to incorporate this standard into its own testing. It is speculation but probably not far fetched that this may have influenced the Forum’s decision to choose OFDMA for its Mobile WiMax standard (early indications were that the OFDM 256-FFT was being considered.) In any event, the potential of the Korean deployments seems to have strongly influenced WiMax proponents to leverage the technology as a primary 3G competitor.
ETSI HiperMAN Overview
HiperMAN aims at providing broadband Wireless DSL, while covering a large geographic area. The standardization focuses on broadband solutions optimized for access in frequency bands below 11 GHz (mainly in the 3.5 GHz band). HiperMAN is optimized for packet switched networks, and supports fixed and nomadic applications, primarily in the residential and small business user environments.
HIPERMAN will be an interoperable broadband fixed wireless access system operating at radio frequencies between 2 GHz and 11 GHz. The HIPERMAN standard is designed for Fixed Wireless Access provisioning to SMEs and residences using the basic MAC (DLC and CLs) of the IEEE 802.16-2001 standard. It has been developed in very close cooperation with IEEE 802.16, such that the HIPERMAN standard and a subset of the IEEE 802.16a-2003 standard will interoperate seamlessly. HIPERMAN is capable of supporting ATM, though the main focus is on IP traffic. It offers various service categories, full Quality of Service, fast connection control management, strong security, fast adaptation of coding, modulation and transmit power to propagation conditions and is capable of non-line-of-sight operation. HIPERMAN enables both PMP and Mesh network configurations. HIPERMAN also supports both FDD and TDD frequency allocations and H-FDD terminals. All this is achieved with a minimum number of options to simplify implementation and interoperability.
WiMAX is a standards-based technology enabling the delivery of last mile wireless broadband access as an alternative to cable and DSL. It will provide fixed, nomadic, portable and, eventually, mobile wireless broadband connectivity without the need for direct line-of-sight with a base station. In a typical cell radius deployment of three to ten kilometers, WiMax systems deliver capacity is expected to be up to 40 Mbps per channel, for fixed and portable access applications and are expected to provide up to 15 Mbps capacity for Mobile network deployments within a typical cell radius deployment of up to three kilometers. The WiMAX technology can be deployed as embedded solution in notebook computers and PDAs. WiMax stationary platform is based on the IEEE 802.16 2004 and current ETSI HiperMAN standard and portable/mobile platforms is based on the IEEE802.16e standard
The advent of WiMAX introduces a novel approach to wireless broadband. The technology is based on the Orthogonal Frequency Division Multiplexing (OFDM,) based technology with an all-IP core network that delivers superior performance through high throughput, low latency, advanced security and QoS functionality (OFDM is a digital encoding and modulation technology that achieves high data rate and efficiency by using multiple overlapping carrier signals with the ability to deliver higher bandwidth efficiency and therefore higher data throughput even in the face of challenging deployment scenario such as NLOS links suffering from significant degradation due to multipath conditions).
IEEE 802.16 Overview
A point-to-multipoint (PMP) broadband wireless access standard for systems in the frequency ranges 10-66 GHz and sub 11 GHz has been developed by the IEEE 802.16 Working Group. The standard covers both the Media Access Control (MAC) and the physical (PHY) layers.
A number of PHY considerations were taken into account for the target environment. At higher frequencies, line of sight is very essential to reduce the effect of multipath, allowing for wide channels, typically greater than 10 MHz in bandwidth. This gives IEEE 802.16 the ability to provide very high capacity links on both the uplink and the downlink. For sub 11 GHz non line of sight capability is a requirement. The original IEEE 802.16 MAC was enhanced to accommodate different PHYs and services, which address the needs of different environments. The standard is designed to accommodate either Time Division Duplexing (TDD) or Frequency Division Duplexing (FDD) deployments, allowing for both full and half-duplex terminals in the FDD case.
The MAC was designed specifically for the PMP wireless access environment. It supports higher layer or transport protocols such as ATM, Ethernet or Internet Protocol (IP), and is designed to easily accommodate future protocols that have not yet been developed. The MAC is designed for very high bit rates (up to 268 mbps each way) of the truly broadband physical layer, while delivering ATM compatible Quality of Service (QoS); UGS, rtPS, nrtPS, and Best Effort.
The frame structure allows terminals to be dynamically assigned uplink and downlink burst profiles according to their link conditions. This allows a trade-off between capacity and robustness in real-time, and provides roughly a two times increase in capacity on average when compared to non-adaptive systems, while maintaining appropriate link availability.
The 802.16 MAC uses a variable length Protocol Data Unit (PDU) along with a number of other concepts that greatly increase the efficiency of the standard. Multiple MAC PDUs may be concatenated into a single burst to save PHY overhead. Additionally, multiple Service Data Units (SDU) for the same service may be concatenated into a single MAC PDU, saving on MAC header overhead. Fragmentation allows very large SDUs to be sent across frame boundaries to guarantee the QoS of competing services. And, payload header suppression can be used to reduce the overhead caused by the redundant portions of SDU headers.
The MAC uses a self-correcting bandwidth request/grant scheme that eliminates the overhead and delay of acknowledgements, while simultaneously allowing better QoS handling than traditional acknowledged schemes. Terminals have a variety of options available to them for requesting bandwidth depending upon the QoS and traffic parameters of their services. They can be polled individually or in groups. They can steal bandwidth already allocated to make requests for more. They can signal the need to be polled, and they can piggyback requests for bandwidth.
802.16
The first version of the WiMax standard addressed spectrum ranges above 10 GHz (specifically 10 GHz to 66 GHz). Since line-of-sight (LOS) is a primary issue in this range, multipath was addressed in this first version with orthogonal frequency division multiplexing (OFDM) techniques. Thus it supports wide channels, defined as being greater than 10 MHz in size. This first standard basically addressed licensed-only service delivery (although there is license-free spectrum in this range).
802.16a
The 802.16a update added support for spectrum ranges of 2 GHz to 11 GHz. It addressed both licensed and unlicensed ranges. It also incorporated non-line-of-sight (NLOS) capability. This version enhanced the medium access control (MAC) layer capabilities. It also improved quality of service (QOS) features. The European HiperMAN standard was supported and a total of three supported physical layers (PHY) were defined. Support for both time division duplexing (TDD) and frequency division duplexing (FDD) was incorporated -- providing for both half duplex and full duplex data transmission in cases where FDD is used. Transmission protocols such as Ethernet, ATM or IP are supported.
802.16c
This standard update dealt mostly with updates in the 10 GHz to 66 GHz range. However, it also addressed issues such as performance evaluation, testing and detailed system profiling. This last was a crucial element of the WiMax toolkit. Because there are great deals of options available with 802.16 in general, the system profile methodology evolved to define what would be mandatory features and what would be optional features. The intent was to guide vendors on mandatory elements that must be met to ensure interoperability. Optional elements such as different levels of security protocols incorporated allow vendors to differentiate their products by price, functionality and market niche.
802.16-2004(d)
All of the Fixed WiMax standards mentioned above have been rolled into 802.16-2004: it incorporates the original 802.16, 802.16a and 802.16c updates. This final standard supports numerous mandatory and optional elements. Vendors are already shipping their 802.16-2004 products to the Cetecom labs in Spain for interoperability testing.
The technology supports both TDD and FDD. Its theoretical effective data rate is around 70 Mbps, although real world performance will probably top out around 40 Mbps. It should be noted that while the technology supports at least three PHY layer Modulation schemes, the system profile chosen is OFDM 256-FFT. This is different from the OFDMA flexible FFT system used in 802.16e. Both standards, however, support the former PHY. This distinction is really a market choice. The Forum could have chosen to use OFDM 256-FFT instead of OFDMA. Market forces and in particular the WiBro standard may have precluded that.
Just some of the enhancements in this version are support for concatenation of both protocol data units (PDU) and service data units (SDU) which reduces the MAC overhead. The technology improves quality-of-service (QOS), particularly with very large SDUs. One clear improvement is support for multiple polling methodologies. The MAC facilitates polling individually or in groups. It can access allocated bandwidth to make requests, or signal that it needs polling. It can even piggyback polling requests over other traffic -- the upshot being that constant cross-talk is obviated with this system, reducing packet collisions and system overhead.
802.16e
A standard still in flux, IEEE 802.16e conserves the technical updates of Fixed WiMax while adding robust support for mobile broadband. While not completely settled, the technology will likely be based upon the OFDMA technology developed by Runcom. This OFDMA technique supports 2K-FFT, 1K-FFT, 512-FFT and 128-FFT. Interestingly, both standards do support the 256-FFT chosen for 802.16-2004. Many of the mandatory elements for this standard have been agreed upon, and a lot of the remaining work centers on the optional elements.
The OFDMA system allows signals to be divided into many lower-speed sub-channels to increase resistance to multi-path interference. For example, if a 20 MHz channel is subdivided into 1000 sub-channels, each individual user would be allowed a dynamic number of sub-channels based on their distance and needs from the cell (i.e. 4, 64, 298, 312, 346, 610 and 944). If close in, a higher modulation methodology such as 64 quadrature amplitude modulation (QAM) can be used for higher bandwidth across more channels. If the user is farther away, the number of channels can be reduced with a resultant power increase per channel. Throughput slows a bit, but distant users are not dropped.
WiBro
Koreans are always at the forefront of broadband adoption. They were ready to deploy a mobile wireless MAN and felt the standards as existed were good enough for that purpose, so WiBro was born. Product is already being shipped by several vendors in an OFDMA version using 1K-FFT in the 2.3 GHz band.
The WiMax Forum has chosen to incorporate this standard into its own testing. It is speculation but probably not far fetched that this may have influenced the Forum’s decision to choose OFDMA for its Mobile WiMax standard (early indications were that the OFDM 256-FFT was being considered.) In any event, the potential of the Korean deployments seems to have strongly influenced WiMax proponents to leverage the technology as a primary 3G competitor.
ETSI HiperMAN Overview
HiperMAN aims at providing broadband Wireless DSL, while covering a large geographic area. The standardization focuses on broadband solutions optimized for access in frequency bands below 11 GHz (mainly in the 3.5 GHz band). HiperMAN is optimized for packet switched networks, and supports fixed and nomadic applications, primarily in the residential and small business user environments.
HIPERMAN will be an interoperable broadband fixed wireless access system operating at radio frequencies between 2 GHz and 11 GHz. The HIPERMAN standard is designed for Fixed Wireless Access provisioning to SMEs and residences using the basic MAC (DLC and CLs) of the IEEE 802.16-2001 standard. It has been developed in very close cooperation with IEEE 802.16, such that the HIPERMAN standard and a subset of the IEEE 802.16a-2003 standard will interoperate seamlessly. HIPERMAN is capable of supporting ATM, though the main focus is on IP traffic. It offers various service categories, full Quality of Service, fast connection control management, strong security, fast adaptation of coding, modulation and transmit power to propagation conditions and is capable of non-line-of-sight operation. HIPERMAN enables both PMP and Mesh network configurations. HIPERMAN also supports both FDD and TDD frequency allocations and H-FDD terminals. All this is achieved with a minimum number of options to simplify implementation and interoperability.
WiMAX is a standards-based technology enabling the delivery of last mile wireless broadband access as an alternative to cable and DSL. It will provide fixed, nomadic, portable and, eventually, mobile wireless broadband connectivity without the need for direct line-of-sight with a base station. In a typical cell radius deployment of three to ten kilometers, WiMax systems deliver capacity is expected to be up to 40 Mbps per channel, for fixed and portable access applications and are expected to provide up to 15 Mbps capacity for Mobile network deployments within a typical cell radius deployment of up to three kilometers. The WiMAX technology can be deployed as embedded solution in notebook computers and PDAs. WiMax stationary platform is based on the IEEE 802.16 2004 and current ETSI HiperMAN standard and portable/mobile platforms is based on the IEEE802.16e standard
posted by iddy @ 10:54 PM
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