An overview of the IEEE 802.16e

In this section, we will focus on the PMP mode. In PMP mode, the BS will control the management of the network using the control message.

1.2.1 MAC supports of PHY

Several duplexing techniques are supported for the IEEE 802.16. Here we focus on the time division duplexing (TDD), the downlink map (DL-MAP) and the uplink map (UL-MAP).

The downlink in the 802.16 is the direction of the transmission from the BS to the MSs. And the uplink in the 802.16 is the direction of the transmission from the MSs to the BS.

In a TDD frame, the downlink and the uplink transmission start at different time.

The downlink duration and the uplink duration may be fixed or adaptive. It is controlled by the high layer. In the paper, the transmission duration is fixed. Figure 1-3 shows a TDD frame.

The DL-MAP defines the usage of the downlink intervals. And the UL-MAP defines the allocation start time of the MSs to transmit packet and the uplink allocation for a flow or a MS and the uplink intervals. These maps are generated by the BS and send to the MS at the start of every frame. Figure 1-4 shows the full frame in the IEEE 802.16.

Figure 1-3 A TDD frame

Figure 1-4 The frame in the 802.16e

1.2.2 Network entry and initialization

The IEEE 802.16 shall support a MS enter into the network. The procedure for initialize a MS shows below:

a). Scan downlink channel and establish synchronization with the BS b). Obtain transmit parameters (from the UCD messages)

c). Ranging

d). Negotiate basic capability

e). Authorize MS and perform key exchange f). Registration

g). Establish IP connectivity h). Establish time of day

i). Transfer operational parameters j). Set up connection

The phase e), g), h), i) are optional. The authorization phase shall be performed only the MS and the BS support the authorization policy.

In the ranging phase, the MS will acquire the correct time offset and adjust the

power. The ranging process shall be repeated until the ranging response contain successful notification or the BS abort. After the process, the MS will get the basic and primary management CID.

In the registration phase, the MS is allowed entry into the network and the MS receives the secondary CID. Then the MS will be the managed MS.

After the transfer operational parameters phase or the registration, the MS can start to set up the connection by the dynamic service creation process.

1.2.3 Service flow management

In the 802.16e network, the service flow is managed by the dynamic service message. The service flow may be created, changed and deleted. The dynamic service addition (DSA) message is used to create a new connection. The dynamic service change (DSC) message is used to change the connection’s parameter. And the dynamic service deletion is used to delete the existing connection. Figure 1-5 shows the management.

The dynamic service management can be initialized by the BS or by the MS. The management first will send a request message (DSx-REQ) to start the process. When

Figure 1-5 Dynamic service flow overview

receive the request, the receiver will send a response (DSx-RSP) back to the transceiver with the result. After the transceiver receive the response, the transceiver will send the acknowledge (DSx-ACK) to the receiver. Figure 1-6 and 1-7 show the BS-initiated and MS-initiated management process.

Figure 1-6 The BS-initiated dynamic service management

Figure 1-7 The MS-initiated dynamic service management

BS SS

DSx-REQ

DSx-RSP

DSx-ACK DSx-RVD

BS SS

DSx-REQ

DSx-RSP

DSx-ACK

1.2.4 Scheduling services

The scheduling services means the service that the scheduler how to handle.

Each service has a set of QoS parameters. The parameters are managed by the dynamic service process. There are five scheduling services in the 802.16e.

1.2.4.1 Unsolicited grant service (UGS)

The UGS is designed to support the real time service with fixed generation interval and packet size, such as VoIP. The character of UGS is guaranteed data rate and delay. The parameters for UGS are maximum sustained data rate, maximum latency, tolerated jitter. If present, the minimum reserved data rate will set as the maximum data rate.

1.2.4.2 Real-time polling service (rtPS)

The rtPS is designed to support the real time streaming with variable packet size, such as video. The delay is a little tolerable and the data rate is larger than the UGS.

The parameters for the rtPS are maximum sustained data rate, minimum reserved data rate, and maximum latency.

1.2.4.3 Extended real-time polling service (ertPS)

The ertPS is a new proposed scheduling service in the IEEE 802.16e std [2]. This is a scheduling scheme which builds on the efficiency of both UGS and rtPS. The BS provides grants to the MS like the UGS, but the allocation size shall be dynamic. The MS can change the allocation size by sending the control message to the BS. The parameters for the ertPS are maximum sustained data rate, minimum reserved data

rate, maximum latency.

1.2.4.4 Non-real-time polling service (nrtPS)

The nrtPS is for the delay-tolerant data flow with variable packet size. The BS shall provide request opportunity, with a larger interval than the rtPS, and the MS can use the contention request opportunity. The parameters for the nrtPS are maximum sustained data rate, minimum reserved data rate and traffic priority.

1.2.4.5 Best effort (BE)

The BE is for the data flow without the minimum service level requirement. The MS is allowed to use the contention opportunity. The parameters of this service type are maximum sustained data rate and priority.