Multi-Carrier and Spread Spectrum Systems: From OFDM and MC ...

WiMAX 247Radio ResourceControlInitializationControlConnection ControlRadio Link ControlSegmentation and Re-assembling, SARMedium Access ControlFigure 5-25IEEE 802.16 common MAC layer functions– Radio resource control. Its main goal is to supervise the QoS assigned for a givenservice. This function has a very close relation with the MAC (see below).– Initialization control. It covers all protocol processes for any initialization, i.e. newregistration, new link set-up, link recovery after link down, etc.– Connection control. It deals with all functions related to set-up and release of a givenconnection.– Radio link control. The microwave link below 11 GHz suffers from multi-path propagation,attenuation, and interferences. Control and monitoring of the link quality byautomatic transmit power control (ATPC), adaptive modulation and coding (AMC),and ARQ are covered here.– Segmentation and re-assembling. To be in line with the MAC packet format the longmessages emanating from the control plane protocol functions will be segmented atthe transmitter side and re-assembled at the reception side.– Medium access control. This is the most important protocol function, which requiressome real-time implementation. Its main goal is to share the available capacity ofthe radio resources in an efficient manner, where the required QoS for every servicewill be guaranteed.Quality of Service (QoS) in IEEE 802.16 and HIPERMANThe 802.16x/HIPERMAN MAC protocol is connection oriented; i.e. first a radioconnection is established before starting any data transmission. The QoS of each connectioncan be managed through the so-called ‘service-flow’ control. The QoS parametersassociated with the service flow define the radio transmission ordering and schedulingon the air interface. Note that a connection-oriented QoS control strategy ensures anaccurate control over the air interface, being the main capacity bottleneck due to its limitedradio bandwidth. The service flow parameters can be dynamically managed throughMAC messages to accommodate the dynamic service demand. This service flow basedQoS mechanism is applied to both the downlink and uplink. The supported data serviceand its application with varied QoS requirements are listed in Table 5-17.