Introduction [Under WiMAX]
If you see at developments that had happened in wireless technologies till now, we can easily see a trend, sort of direction that is difficult to miss out. There is more and more independence between radio access network and core (typically wireline) network. Radio access transports are being designed in such a way that they can support multiple types of services with improving radio efficiency. Also, signaling between mobile device and core network has been made as much transparent as possible to radio access transport. On core network side, IP (over ATM/SONET or other L2/L1 technologies) has been gaining popularity due to ease in interconnection, its ability to support different types of services, availability of number of protocols (IETF RFCs) to support different services and their implementations etc.
Future end-to-end network architecture may just look like this:
One of the few challenges (and possibly most important) is to come out with "Radio Transport (and Technology)" which would provide high spectral efficiency (bits per second per Hz), high bit rates, high quality (BER), and flexible/dynamic enough to support various types of services. IEEE 802.16 standard provide one such radio access based on OFDMA. WiMAX (Worldwide Interoperability for Microwave Access) is a name given by industry to implementations of 802.16, along with its network elements for end-to-end support, certification etc. WiMAX Forum is industry wide body involved in promoting the 802.16 technology. Note that IEEE and WiMAX Forum are separate entities (check IEEE presentation on Myths and Facts about 802.16).
802 family
802.16 standard is part of IEEE 802 family of standards maintained by LMSC (LAN/MAN Standards Committee). 802 standards are meant for OSI Layer 2 and Layer 1 of LAN (Local Area Network) and MAN (Metropolitan Network).
Overall 802 architecture is shown below:
One of the popular ratified 802 technologies is 802.11 (WLAN, WiFi).
802.16 standard
802.16 standard, published in 2000/01, was meant for Wireless MAN (WMAN). It was targeted for LOS frequencies, 10- 66 GHz. WMAN was supposed to have provided backbone for connecting WLANs. WLANs typically cover a area of 10 km2 (radius of ~1.5 km). WMAN was supposed to cover a area of 100 km2 (radius of ~5.5 km). Later 802.16 amended few times and released as 802.16-2004 (or 802.16d), consolidating the amendments. It included NLOS frequencies 2-11 GHz. This resulted in three new PHY specifications to existing Single Carrier (WMAN-SC) for these added frequencies: Single Carrier (SCa), 256-point FFT OFDM, and 2048-point FFT OFDM. In addition, these new frequencies included unlicensed (open for all) frequencies. This required certain changes in both MAC and PHY layers. Overall notable PHY features were: Adaptive Antenna System (AAS) or MIMO system, Adaptive modulation schemes. Notable MAC features were: support for both TDD/FDD, full and half duplex, support for IPv4, IPv6, Ethernet, ATM etc, PKM based security, support PMP (point-to-multipoint) and optional Mesh networking operations, four scheduling mechanisms to support different types of traffic . The targeted data rates were in the range of 100 Mbps.
802.16-2004 was amended as 802.16e-2005 to include mobile enhancements for licensed bands below 6 GHz. Major PHY additions in these amendment are: use of Scalable OFDMA (FFT sizes 128, 512, 1024, 2048 subcarriers with subcarrier separation constant), additional MIMO modes. On MAC side: Handover support was added, ErtPS scheduling mechanism added, Power management procedures added for power efficient operations. The targeted data rates were in the range of 1-10 Mbps.
Industry name for 802.16e-2005 implementations is Mobile WiMAX whereas 802.16-2004(802.16d) implementations are known as Fixed WiMAX. WiMAX Forum picked up few profiles for mobile WiMAX due to interoperatability reasons, notable being 2.3 GHz/8.75Mhz (similar to WiBro in Korea), 2.5 GHz (5/7/10 Mhz), and 3.5 GHz (5/7/10 Mhz). WiBro is a mobile service available in South Korea and it is similar to WiMAX. It is required to be compliant with 802.16e-2005.
In next article, we will look at elements of 802.16. We will mainly concern ourselves with NLOS frequencies for mobility operations (Mobile WiMAX).
References: WiMAX Handbook (edited) by Ahson and Ilyas, Fundamentals of WiMAX by Andrews, Ghosh, and Muhamed, WiMAX forum web site, IEEE site for 802 standards, Overview of 802, Latest 802.16-2009 (covering amendments 802.16e-2005, 802.16-2004/Cor1-2005, 802.16f-2005 & Std 802.16g-2007 made on 802.16-2004). You can as well check Whitepapers at WiMAX.com.
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