Wimax standards and Security The Wimax

QoS Scheduling

When a connection request is granted, a service flow with the QoS param- eters is created for the connection. Scheduling services is the data-handling mechanism to support the MAC scheduler for data transport on a connection. The BS controls both the UL and DL scheduling as illustrated in Figure 4.6, and this approach is similar to the QoS architecture in Ref. 10. The scheduler calculates the throughput and latency requirements of the UL and DL traffic and provides the polls and grants at the appropriate time intervals. The DL is broadcast and the scheduler fills in each burst based on the QoS parameters of the frames in the queue. The UL scheduling uses a poll/grant scheme that is more complex as it requires coordination between the BS and individual SSs.

1. 
   UGS Scheduling
   

The UGS is designed to support real-time service flow of fixed-size data packets on a fixed interval. The services provide fixed-size grants on a regular


Base station (BS)

SS₁


SS₂


SS₃




SS₄
Conn_A Conn_B Conn_C
Data
FIGURE 4.6
Base station UP and DL scheduling.

basis and eliminate the latency of SS request to assure that the real-time needs are met. The BS provides grant to the SS at a fixed interval based on the MSTR (see Table 4.1) and the size of the grants is large enough to hold the fixed-length data plus the MAC overhead. The SS receives broadcast frames from the BS at regular intervals, and the UL-MAP in the broadcast frame contains the UL channel for the SS to send the data. When an SS has the data to send, it puts the data into the assigned channel (time slot) and bursts the data to the air interface immediately. There is no bandwidth sharing of multiple connec- tions for the UGS service and each connection (service flow) is allocated with a dedicated channel (time slot) for the UL data transmission.

2.