The IEEE 802.16e MAC

In our module, there are two timers for every connection that the scheduling will check these timers when it makes the schedule. The first timer is the minimum requirement timer. It is used to satisfy the minimum requirement of all flows. By the dynamic service message, the BS can get the minimum reserved rate and the packet size, then the BS can calculate a maximum packet inter arrival time, T_i,min−req. If the connection is with variable packet size, the scheduling will use a fixed size to calculate the time, and when the connection receive the opportunity, the connection can fragment or pack the packet in the queue to satisfy the opportunity length L.

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min(

min

, L rate i

T_{i −req}+= (1) By using the time to give the transmit opportunity to the connection, the connection must be satisfied with the minimum requirement. The minimum requirement timer will set the value to the T_i,min−req at first and start to count down. When the value of the timer is less than zero, it means that the connection needs to get opportunity. And the scheduling will schedule the connection into the UL-MAP and the timer is reset to the T_i,min−req value.

The other timer is the advanced allocation timer. When the minimum requirement of every connection has been satisfied, the residual resource BW_R will be shared to the connections that the maximum requirement has not been satisfied.

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minimum reserved rate of the flow. Because UGS only has one data requirement, UGS will not share the residual resource. The ratio of rtPS, ertPS, nrtPS is as below.

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rate_max(i) is the maximum sustained rate of the connection i. In the same type of the scheduling service, the connection i can get the advance resource is:

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BWex is the advance allocation of the connection in the scheduling service type video.

Then the time interval Ti,ex that is used to get the advance opportunity is as bellow.

ex

i,ex L BW

T += (7) And the advanced allocation timer will set the value to Ti,ex at first and start to count down as the minimum requirement timer. While the timer is less than zero, the scheduling will schedule the advance opportunity for the connection and reset the timer.

The scheduling may not schedule all the connections that need the opportunity.

The scheduling will schedule all the connections that need to allocate opportunity to transmit data until the frame is full and schedule the not satisfied connections at the next frame.

2.2.2 CAC and dynamic service process

The CAC and the dynamic service process has describe before. The main purpose of CAC is used to guarantee the QoS requirements of the admitted services, and we introduce this to help the scheduling. In our module, we introduce the CAC in [8] and do a little modification. Our CAC is performed by the formula below. If the new connection’s rate can satisfy the formula, the CAC will accept the new connection.

After the exchange of the service flow message and the response is with success information, the CAC will inform the scheduling to re-calculate the new time interval value for the advance allocation timer.

If the traffic load is heavy, the BS may still have a little resource and a new connection wants to be set up, but the resource is not enough to satisfy the minimum requirement, the connection will be rejected by the BS. At this time, we hope the new connection can reduce its requirement and the reject probability can reduce a little. So we propose a message exchange process to achieve the intent. If a new connection’s request send to the BS, and the CAC find there is no sufficient resource to satisfy the connection and the connection is not a voice flow, the CAC will send the response message with success message to the MH, then send a DSC request (DSC-REQ) to request the SS to reduce the new flow’s minimum requirement. If the SS accept the request, then the BS records the original minimum requirement, and uses the temporary requirement to do the scheduling process. Else if the MH rejects the request, than the BS will send the DSD-REQ to the MH to delete the service flow.

After other connections are end and have advance resource, the BS will send a

DSC-REQ to ask the SS to change the minimum requirement to the original requirement first and re-calculate the new time interval value will be done after the message exchange process.

2.2.3 The queue and scheduler in the MS

The MSs need the queue module in IEEE 802.16e is because every flow will get the grant individually, every flow need a independent queue to store the packets.

When a new flow wants to be set up, the queue module will receive the message from the up layer and inform the scheduler in the MS to execute the dynamic service process. After the success dynamic service addition process, the queue module will create a new queue for the new flow.

The scheduler in the MS has another function. When receiving a UL-MAP, the scheduler need to check the map that whether there is a grant for the flow in the MS or not. If there are grants for flows, the scheduler will wait to the assignment of the start time and transmit the packet from the queue module.