WiMAX Technology Connection Based Data Transmission with Classification and QoS per Connection

The MAC layer of mobile WiMAX (802.16e) technology includes the following features which provide for high efficiency and flexibility

TheWiMAX technology provides an environment for connection-oriented services. For each service, certain classification rules are specified to define the category of traffic associated with the connection. For example, it could be Internet Protocol (IP) traffic destined for a specific IP address/port. For each connection, certain QoS parameters are defined, for example, the minimum reserved rate and maximum sustained rate. There are several types of scheduling such as real-time services that can be applied based on the application requirements. A special scheduling type (ertPS) is defined for the VoIP service with silence suppression and adaptive codecs.



Scheduled Transmissions and the Flexible Bandwidth AllocationMechanism
Bandwidth allocation mechanism is based on real time bandwidth requests transmitted by the terminals, per connection. Bandwidth requests may be transmitted using a contention based mechanism or they can be piggybacked with the data messages. The Base Station executes resources allocation based on the requests and QoS parameters of the connection.

MAC Overhead Reduction

WiMAX technology includes support of the general Purpose Header Suppression (PHS) and IP Header Compression (ROHC). PHS can be used for packets of virtually any format such as IPv4 or IPv6 over Ethernet. It is beneficial if a considerable part of the traffic has identical headers which is typical for IP or Ethernet destination addresses. The PHS mechanism replaces the repeated part of the header with a short context identifier, thus reducing the overhead associated with headers. ROHC is a highly efficient IETF standard for which WiMAX MAC has all necessary support.

Mobility Support: Handover
Handover procedures include numerous means of optimization. In particular, to reduce time expenses for the mobile to find the central frequency and acquire parameters of the neighbor base station, the mobile can apply a scanning process when the mobile is away from the serving base station to scan the wireless media for neighbor base stations. Information collected during scanning such as central frequencies of the neighbor base stations can then be used in actual handover. In some deployment scenarios, scanning can be performed
without service interruption. For this purpose, information about the central frequency and parameters of the neighbor base stations is periodically advertised by the serving base station.

To shorten the time needed for themobile to enroll into the new cell the network is capable of transferring the context associated with the mobile from the serving base station to the target base station. All of these means provide a potential for high optimization in terms of handover latency. Under ideal conditions the interval of service interruption may be as short as several 5 ms frames. The specific handover optimization scheme used in a particular handover depends on the information available to the mobile.

Power Saving: Sleep Mode
Sleep mode is the primary procedure for power saving. In sleep mode the mobile is away from the base station for certain time intervals, normally of exponentially increasing size. During these intervals the mobile remains registered at the base station but can power down certain circuits to reduce power consumption.

Power Saving: Idle Mode
If the mobile has no traffic for a long time it can switch to idle mode in which it is no longer registered at any particular base station. To resume traffic between the network and the mobile, a paging procedure may be used by the network.

Security
The security sublayer provides Extensible Authentication Protocol (EAP)-based mutual authentication between the mobile and the network. It protects against unauthorized access to the transferred data by applying strong encryption of data blocks transferred over the air. To keep the encryption keys fresh, the security sublayer employs an authenticated client/server key management protocol which allows the base station to distribute keying material to mobiles. Basic security mechanisms are strengthened by adding digital-certificate-based Subscriber Station (SS) device authentication to the key management protocol.

MAC Layer Support for the Multicast and Broadcast Service
Multicast and Broadcast Services (MBSs) allow WiMAX mobile terminals to receive multicast data even when they are in idle mode. The most popular application of this feature is TV broadcasting to mobile terminals.