Τρίτη, 9 Ιουλίου 2013

The IEEE 802.16 WG Standardization of WiMax

The standardization of WiMax began with the WirelessMAN developed by IEEE 802.16 WG, which includes detailed specifications and  both mandatory and many optional functionalities in order to achieve more flexibility and possible performance enhancement for various operating scenarios. As any other IEEE standard, IEEE 802.16 fulfills the five-criteria: broad market potential, technical and economic feasibility, distinct identity and compatibility [7]. It consists of three main parts, starting from top to bottom:
·         the convergence sublayer (CS), that interfaces higher-layer protocols such as IPv4 and IPv6to the IEEE 802.16 media access control service data unit (MAC SDU)
·         the MAC common part sublayer (CPS), which conducts the fragmentation or the packing of of the MAC SDU’s in order to make them fit into MAC protocol data units (PDUs), which have a suitable format for handling by the physical layer
·         the physical layer, which defines the physical frame format, forward error correction (FEC) and modulation schemes.
These three parts are shown in Figure 8,with the physical layer at the bottom and the MAC CPS and the CS on top of it.
Figure 8: IEEE 802.16 WG standardization coverage
The IEEE standardization of WiMax has a long history, starting from 2001, with 802.16. The ancestor of it lies on the IEEE 802 Study Group on Broadband Wireless Access (BWA) in November of 1998 [7]. The first final draft document of the complete standard was 802.16 in December 2001, a huge milestone of the WiMax standardization. It was published in April of 2002 with the title “IEEE standard for local and metropolitan area networks part 16: air interface for fixed broadband wireless access systems” and it described a fixed wireless access scenario at 10-66 GHz with line-of-sight and point-to-point for a cell radius not bigger than 5 kilometers [4].
 In May 2002 802.16c introduced a number of profiles including a set of predetermined parameter values for interoperability support. 802.16c (or 802.16c-2002) is “Amendment 1: detailed system profiles for 10-66 Ghz”. In January 2003 802.16a-2003 was approved under the name “Amendment 2: medium access control modifications and additional physical layer specifications for 2-11 GHz”. As it is obvious from its name, it included frequencies lower than 11 GHz (down to 2 GHz) and it also described non-light-of-sight links. The next major update was 802.16-2004 in September 2004 , called “IEEE Standard for local and metropolitan area networks part 16: air interface for fixed broadband wireless access systems” [4].
Table 1: main initial WiMax standardization milestones
Figure 9: illustration of the 802.16-2001 development until 2005
After that, 802.16e was published in December 2005 which was “Amendment 2: physical and medium access control layers for combined fixed and mobile operation in licensed bands” and introduced mobility (at speeds less than 120 kilometers per hour) for WiMax as well as handovers, with the cell radius being 5 kilometers or less. These WiMax milestones are summarized in table 1, along with their achievable bitrates and modulation formats. The progress of the 802.16-2001 is illustrated in Figure 9 [7].
The next important update was 802.16j, which was published in June 2009. It features relay support for 802.16m network architecture. As a result, the “16jm” Ad Hoc Group was established in order to study the issues. The final report of the group was delivered in July 2008 and was approved in May 2009.It was an amendment to IEEE 802.16-2009, which was called “Amendment 1: Multihop Relay Specification” . The IEEE 802.16-2009 was “IEEE standard for local and metropolitan area networks part 16: air interface for broadband wireless access systems”. Finally, the IEEE 802.16m-2011 doubles both the user and sector throughput and supports speeds up to 350 kilometers per hour, for ultra-fast train travelers. These improvements are illustrated in Figure 10 [4].
Figure 10: 802.16j and 802.16m new characteristics
As of July 2013, two new standards are under development: 802.16n and 802.16p [12]. The first one is an amendment aiming towards higher reliability networks and the second one towards enhancements to support machine-to-machine applications. Many features of the WiMax standard are still open and under discussion and there is always a constant willing for further improvements and upgrades.
A detailed presentation of the 802.16-2001 from 2002 to 2007 standard is shown in Figure 11. “PAR” stands for Project Authorization Request, “TG” for task group and “SG” for Study Group. PARs are the means by which standards projects are started in the IEEE Standards Association [7].
IEEE 802.16 holds a plenary meeting every March July and November and 802.16 WG holds an interim meeting every January, May and September, resulting into 6 annual meetings in total, concerning the WiMax. The participants in those meetings were a few tens at the beginning (1999-2000), but exceeded the 400 in 2007 [4].

Figure 11: IEEE 802.16-2001 and its amendments until 2007

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