IEEE 802.16-2009

The IEEE 802.16 standard describes several modes of operation, each of which fits a specific deployment objective. In the amalgamated standard document, IEEE 802.16-2009, two modes are described: a mandatory Point-to-Multi-Point (PMP) and an optional Multihop Relay (MR). While both modes describe regular downlink communication, that is, from gateway or base station to mobile terminal, the MR mode utilizes intermediate RSs between a cell's BS and the MT. This latter is described in the amendment IEEE 802.16j. An example of an IEEE 802.16-2009 deployment is shown in Figure 3.1.

Figure 3.1 A schematic of a IEEE 802.16-2009 deployment, including a base station and different types of mobile terminals.

In a PMP deployment, BSs provide a continuous coverage through a cellular configuration, with the BSs interconnected through a network management infrastructure that oversees the overall management of network operations. Through the BSs, Subscriber Stations (SSs) and Mobile Subscribers (MSs) connect to the network and, when applicable, to the Internet. In the standard, the generic term SS describes user equipment capable of using different RITs operating under both, Line of Sight (LOS) and Non LOS (NLOS) circumstances. On the other hand, MSs are equipment sets whose connected mobility is supported in the NLOS network. As will be described below, mobility is supported only under one IEEE 802.16 interface type, namely OFDMA, and does not require LOS with the BS for communication. More importantly, mobility support is enabled through employing handover mechanisms both within IEEE 802.16 networks and between IEEE 802.16 and other Radio Access Technologies (RAT).

In the IEEE 802.16j amendment, a BS that supports MR is called a MR-BS. In MR, an MR-BS communicates with MSs either directly or through RSs. As was discussed in the previous chapter, a RS is a dedicated, fixed or mobile, relay unit that is connected to the BS through a wireless link. Two types of RS are defined: transparent and non-transparent. Transparent RSs (tRSs) share the carrier frequency with their superordinate station (either an MR-BS or an ntRS) and subordinate stations (only MS), and are mostly deployed within an MR-BS's coverage to improve throughput. Non-transparent RSs (ntRS) are mainly aimed at extending the coverage of an MR-BS cell (MR-cell), and operates either in the same or in a different carrier frequency. When different carrier frequencies are utilized within an MR-cell or an MR network, the amendment advises the use of interference mitigation mechanisms for both access links (between an MR-BS or RS and an MS) and relay links (between MR-BS and RS or in between RSs). An example MR deployment is shown in Figure 3.2.

Figure 3.2 Example deployments of IEEE 802.16-2009 relay networks (i.e., amendment j), with (a) showing tRS and (b) showing ntRS.

Management of the air interface in MR networks can be either centralized or distributed. In centralized operation, all management functionalities are overseen by the MR-BS while in distributed operation, some autonomy is provided for RSs. tRSs always operate in a centralized mode, while ntRSs can operate in both modes. In distributed scheduling, for example, bandwidth allocations for an ntRS's subordinates are made by the ntRS in cooperation with the MR-BS. An autonomous ntRS in distributed scheduling can be also called a scheduling RS.

The IEEE 802.16j amendment is an extension for OFDMA mobility in IEEE 802.16-2009. A salient feature of the IEEE 802.16j is that an MS is not aware of the underlying operating mode of the network, that is, whether PMP or MR. Accordingly, the procedures and signaling made and processed by an MS in both PMP and MR operation are exactly the same. The amendment also describes how MR infrastructure components, that is, MR-BSs and RSs, should handle a MS's requests and traffic in a manner that achieves this seamlessness.

IEEE 802.16-2009 Air Interfaces

The IEEE 802.16 standard describes different air interfaces for different deployment scenarios. For example, the Wireless Metropolitan Area Networks—Single Carrier (WirelessMAN-SC) interface aims at creating wireless backhaul between dedicated stations that rely on LOS connectivity. Meanwhile, the WirelessMAN-OFDMA, which is our focus in this book, aims at cellular mobile communications.

The following air interfaces are defined in IEEE 802.16-2009:

• WirelessMAN-SC, operates in the 10–66 GHz band with either Time Division Duplex (TDD) or Frequency Division Duplex (FDD) schemes. Moreover, it supports only PMP LOS communications with fixed SSs.
• WirelessMAN-OFDM, operates in the licensed bands below 11 GHz with TDD or FDD duplexing. Supports near-LOS and NLOS communications with fixed SSs but only with provisions for power management, interference mitigation and multiple antennas.
• WirelessMAN-OFDMA, operates in licensed bands below 11 GHz with TDD or FDD duplexing. It supports both, PMP and MR¹ operation. It also supports near-LOS and NLOS communications with either fixed or mobile SSs. In addition, it requires provisions for power management, interference mitigation and multiple antennas.
• WirelessHUMAN, operates in license-exempt bands below 11 GHz (primarily 5–6 GHz) with TDD duplexing. Complies with either the OFDM or OFDMA description. Supports coexistence mechanisms such dynamic frequency selection.

In this book, all descriptions are mainly aimed at OFDM and OFDMA operations. However, exclusive considerations for SC operation will be noted where applicable. No descriptions for WirelessHUMAN will be provided.

Protocol Reference Model

Figure 3.3 shows the protocol reference model for IEEE 802.16-2009. The scope of the IEEE 802.16 standard comprises two planes: Data plane and Management/Control plane. In the Data plane, the standard provides descriptions for both the Medium Access Control (MAC) and the PHY layers. Descriptions for the Management/Control plane include abstractions to be used by Network Control and Management Systems (NCMS). Details of the NCMS are beyond the standard's scope. The described abstractions, however, include descriptions for Service Access Points (SAPs) for both management and control functionalities.

The MAC layer is divided into three sublayers: a Service Specific Convergence Sublayer, abbreviated CS, a Common Part Sublayer (CPS), and a Security Sublayer. Different CSs provide SAPs for upper layers such as ATM, IPv4, IPv6, etc. It also enables classification and processing of higher Protocol Data Units (PDUs) before admitting them to the IEEE 802.16 network infrastructure.

Figure 3.3 The IEEE 802.16-2009 Protocol Reference Model. Reproduced by permission of © 2009 IEEE.

The CPS provides the core MAC functionalities for IEEE 802.16 networks. It receives PDUs from various CSs and applies appropriate classification and Quality of Service (QoS) handling. It also provides a SAP for the different CSs. The CPS also contains a Security Sublayer to provide for communication privacy and integrity.

Descriptions for the PHY layer span the different air interfaces described above. The PHY also offers SAPs for the CPS.