**2.3.1 The successive scheduling scheme (SSS)**

To improve the power-saving performance, our algorithm will schedule packets into successive frames in order to reduce the number of status transitions in an MSS. The successive scheduling scheme is performed in two parts. The first part sorts all connections on the scheduling priorities of connections with tight delay requirements. The second part schedules the packets from the first priority connection into the successive frames. An MSS stays idle during sleep periods to save power, and only wakes up to transmit data packets during listen periods. Packets sent to the MSS during sleep periods are buffered at BS and are delivered to the MSS until the listen periods. In other words, the MSS only needs to receive and transmit data in listen periods and stay idle to conserve energy during sleep periods. The next paragraphs describe in detail the steps of our proposed successive scheduling scheme. Also, notations used in this chapter are summarized in Table 1.


Table 1. Notations and their descriptions.

To minimize the energy consumption of an MSS with multiple real-time connections, the successive scheduling scheme schedules the packets into their successive time slots under the radio resource and QoS requirements. Considering an MSS with *N* real-time connections, *Di* is the delay constraint in milliseconds of any two consecutive packets for connection *i*, and *I* is the average inter-packet interval time in milliseconds for connection *i*. In this chapter, these connections could be either downlinked from a BS to an MSS or uplinked from an MSS to a BS. In the scheduling of downlink packets, our proposed scheme should be implemented on a BS. However, the proposed scheme must be realized on both a BS and an MSS if the proposed scheme is to be applied to the uplink packet scheduler. A BS can know the resource requirements of an MSS through negotiations in the requests from the MSS. Thus, a BS can determine the uplink packet schedule according to the proposed algorithm and provide transmission opportunities to an MSS. When a new connection to an MSS is initiated or any existing connection is released, the proposed scheme is activated to schedule or re-schedule resources in the following frames for the MSS. First, the successive scheduling scheme sorts all connections on an MSS according to their delay constraints and schedules these connections with tight delay requirements. The reason for this is that packets of these connections with tight delay requirements need to be sent or received within a small time window. The scheduler must consider these packets first in order not to violate their QoS requirements. Conversely, for packets that could tolerate more delays, the 36 Mobile Networks

To improve the power-saving performance, our algorithm will schedule packets into successive frames in order to reduce the number of status transitions in an MSS. The successive scheduling scheme is performed in two parts. The first part sorts all connections on the scheduling priorities of connections with tight delay requirements. The second part schedules the packets from the first priority connection into the successive frames. An MSS stays idle during sleep periods to save power, and only wakes up to transmit data packets during listen periods. Packets sent to the MSS during sleep periods are buffered at BS and are delivered to the MSS until the listen periods. In other words, the MSS only needs to receive and transmit data in listen periods and stay idle to conserve energy during sleep periods. The next paragraphs describe in detail the steps of our proposed successive

scheduling scheme. Also, notations used in this chapter are summarized in Table 1.

The delay constraint for connection *i*  The interval of packet arrival The *jth* packet for connection *i* 

packets without full-filled frame

full-filled frame

Table 1. Notations and their descriptions.

packets without any available time slot

To minimize the energy consumption of an MSS with multiple real-time connections, the successive scheduling scheme schedules the packets into their successive time slots under the radio resource and QoS requirements. Considering an MSS with *N* real-time connections, *Di* is the delay constraint in milliseconds of any two consecutive packets for connection *i*, and *I* is the average inter-packet interval time in milliseconds for connection *i*. In this chapter, these connections could be either downlinked from a BS to an MSS or uplinked from an MSS to a BS. In the scheduling of downlink packets, our proposed scheme should be implemented on a BS. However, the proposed scheme must be realized on both a BS and an MSS if the proposed scheme is to be applied to the uplink packet scheduler. A BS can know the resource requirements of an MSS through negotiations in the requests from the MSS. Thus, a BS can determine the uplink packet schedule according to the proposed algorithm and provide transmission opportunities to an MSS. When a new connection to an MSS is initiated or any existing connection is released, the proposed scheme is activated to schedule or re-schedule resources in the following frames for the MSS. First, the successive scheduling scheme sorts all connections on an MSS according to their delay constraints and schedules these connections with tight delay requirements. The reason for this is that packets of these connections with tight delay requirements need to be sent or received within a small time window. The scheduler must consider these packets first in order not to violate their QoS requirements. Conversely, for packets that could tolerate more delays, the

The frame-in-used; the frame which had already scheduled the

The frame fully used; the frame which had already scheduled the

The unused frame that is next to the *FFU* and is more close to the next

The number of connections

**2.3.1 The successive scheduling scheme (SSS)** 

Notation Description

*N Di I Ci,j FIU* 

*FFU* 

*Fnext* 

scheduler can postpone the packets to schedule them successively without violating their delay constraints. After the scheduler decides on the scheduling priorities of connections, the packets from the first priority connection, e.g. connection *i*, are scheduled. *Ci,j* is represented the *jth* packet of connection *i* and the proposed scheme schedules *Ci,j* with following steps: (1) The frames that are within *Di* for *Ci,j* and have already scheduled the packets without full-filled frames, called *FIU*. For the various applications, the proposed scheme is based on either the shortest delay or the longest delay. For the shortest delay based, if there are two or more *FIU* for *Ci,j*, the *FIU* with shorter delay receives a higher priority for *Ci,j*. The shortest delay based is applied to the urgent applications that are very strict with delay requirements and is used to prevent packets loss. Additionally, it is done to reduce the intervals of listen periods and increase the interval of sleep periods. In other words, an MSS cannot sleep in the time slots where there are already schedule packets. Thus, *FIU* is assigned first if the time slots of *FIU* are still available to accommodate *Ci,j*. On the other hand, the *FIU* with longer delay receives a higher priority in being scheduled to *Ci,j*. The longest delay based applied to scenarios which have loose delay requirements. The BS can decide on which strategy to perform in specific applications. (2) If there is no *FIU* for *Ci,j*, the scheduler will then pick a set of frames that are within *Di* for *Ci,j* and which already have scheduled packets without any available time slot. These are called *FFU*. The frames in the set are sorted by the *Di* for *Ci,j* in ascending order. The *FFU* will be the first frame and last frame in the set with the shortest delay based and longest delay based individuals. In order to reduce the number of status transitions, the scheduler will schedule the packets in successive time slots. In the successive listen periods, the MSS will not enter the sleep periods, and the number of status transitions would be reduced. Additionally, the sleep periods will be longer after their successive listen periods. To schedule the packets successively, the scheduler will find an unused frame that is next to *FFU* and is closer to the next full-filled frame, called *Fnext*. The reason for this is that *Fnext* is closer to the next fullfilled frame has more chances to schedule the listen periods successively. In other words, packets that are scheduled to *Fnext* and that is next to *FFU* will become an *FIU*. Obviously, *FIU* gains more opportunities to serve other packets in the following connections. Therefore, *FIU* will become *FFU* after full-filled frame with packets, and this *FFU* will be successive. The listen periods will be continuously without the sleep periods and the number of status transitions would be reduced. (3) If there are no *FIU* and *FFU* within *Di* for *Ci,j*, the scheduler will schedule the packet into the last unused frame within *Di* for *Ci,j* and the unused frame will then become *FIU*. The last unused frame is selected is because once a frame is scheduled to transmit or receive packets, the frame becomes an *FIU*. As we mentioned, an *FIU* has more opportunities to serve other packets in the following connections. After the above steps, the successive scheduling scheme performs packet scheduling and achieves the power-saving for an MSS.

Fig. 1 shows the second step in the second part of the proposed algorithm. Based on the shortest delay, the scheduler chooses the first *FFU* to determine *Fnext*. Because the 4th frame is an unused frame and is closer to the next *FFU*, which is the 5th frame, the scheduler determines the 4th frame as *Fnext* and schedules the packet into the 4th frame. Once we determine the proper frame to be filled with packets, the time slots for transmission will be more successive for their following connections of scheduling. Thus, the 4th frame becomes *FIU* and has a greater chance to be filled with packets by the proposed algorithm. The status would not be switched from 3rd to 5th frame when the 4th frame is filled up with packets.

A QoS Guaranteed Energy-Efficient Scheduling for IEEE 802.16e 39

Fig. 3. Our SSS algorithm on the shortest delay based scheduling.

Fig. 4. Our SSS algorithm on the longest delay based scheduling.

In IEEE802.16e broadband wireless access networks, acrucial component of delay is the buffered packet delay between BS and MSS. Due to varying delays in transmission, the delays of scheduling from packet to packet may cause buffered packet delay. This

As shown in Fig. 5, we denote *Packeti* as the *ith* packet of certain connections, with the QoS requirement of delay having 7 time slots and 2 jitters. Assume *Packeti*-1 was scheduled in the first time slot, and the delay of *Packeti*-1 is 0. *Packeti* may schedule into the time slots of the 2nd time slot to the 8th time slot if we only consider the delay constraint of the QoS requirement. However, it is more realistic to consider the jitter constraint of the QoS requirement. Because the delay of *Packeti*-1 and *Packeti* cause jitter, we need to consider the delay of *Packeti* to satisfy the jitter constraint. Assume we schedule *Packeti* in the 5th time slot, the delay of *Packeti* is 3 and the jitter will also 3, and this violates the jitter constraint. Thus, under the jitter

**2.3.2 The QoS requirements for jitter** 

phenomenon is called jitter (Wu & Chen, 2004).

Fig. 1. The shortest delay based scheduling.

Therefore, we can reduce the number of the status transitions by scheduling packets successively and save energy consumption in the status transitions. The longest delay based scheduling is shown in Fig. 2.

Fig. 2. The longest delay based scheduling.

In Fig. 3, we schedule the packets of connection 1 with the QoS requirement of UGS, and connection 2 with the QoS requirement of RT-VR in an MSS. With the shortest delay based, we schedule the first packet of connection 1 which is *C*1,1. There is no *FIU* or *FFU* in the available frames under this delay constraint. In the third step of the second part in our proposed algorithm, we schedule *C*1,1 into the 5th frame with the maximum delay without violating the constraints, and the 5th frame becomes *FIU*. After that, *C*1,2 is scheduled into *FIU* which is the 5th frame according to the first step in the second part of our algorithm. *C*1,3 and *C*1,4 are also scheduled into *FIU*, which is the 5th frame by the first step in the second part of our algorithm. The 6th packet is scheduled into the 10th frame because there is no *FIU* or *FFU* within *D*1 for *C*1,6. The 10th frame becomes *FIU* after *C*1,6 is scheduled inside. The rest packets of connection 1 are scheduled in the same way as are done in previous steps. When we schedule connection 2, the first packet will be scheduled into the 6th frame because there is no *FIU*, while the 5th frame is *FFU*. By the second step in the second part of the algorithm, the *Fnext* is the 6th frame. Thus, we schedule *C*2,1 into the 6th frame and *C*2,2 is scheduled into *FIU*, which is the 6th frame. *C*2,3 and *C*2,4 are scheduled into the 9th and 14th frame, respectively. The longest delay based scheduling is shown in Fig. 4. In the result of our examples, our SSS algorithm will schedule the packets into the time slots successively and reduce the number of status transitions in an MSS and minimize the energy consumption of status transitions.

38 Mobile Networks

Therefore, we can reduce the number of the status transitions by scheduling packets successively and save energy consumption in the status transitions. The longest delay based

In Fig. 3, we schedule the packets of connection 1 with the QoS requirement of UGS, and connection 2 with the QoS requirement of RT-VR in an MSS. With the shortest delay based, we schedule the first packet of connection 1 which is *C*1,1. There is no *FIU* or *FFU* in the available frames under this delay constraint. In the third step of the second part in our proposed algorithm, we schedule *C*1,1 into the 5th frame with the maximum delay without violating the constraints, and the 5th frame becomes *FIU*. After that, *C*1,2 is scheduled into *FIU* which is the 5th frame according to the first step in the second part of our algorithm. *C*1,3 and *C*1,4 are also scheduled into *FIU*, which is the 5th frame by the first step in the second part of our algorithm. The 6th packet is scheduled into the 10th frame because there is no *FIU* or *FFU* within *D*1 for *C*1,6. The 10th frame becomes *FIU* after *C*1,6 is scheduled inside. The rest packets of connection 1 are scheduled in the same way as are done in previous steps. When we schedule connection 2, the first packet will be scheduled into the 6th frame because there is no *FIU*, while the 5th frame is *FFU*. By the second step in the second part of the algorithm, the *Fnext* is the 6th frame. Thus, we schedule *C*2,1 into the 6th frame and *C*2,2 is scheduled into *FIU*, which is the 6th frame. *C*2,3 and *C*2,4 are scheduled into the 9th and 14th frame, respectively. The longest delay based scheduling is shown in Fig. 4. In the result of our examples, our SSS algorithm will schedule the packets into the time slots successively and reduce the number of status transitions in an MSS and minimize the energy consumption of

Fig. 1. The shortest delay based scheduling.

Fig. 2. The longest delay based scheduling.

status transitions.

scheduling is shown in Fig. 2.

Fig. 3. Our SSS algorithm on the shortest delay based scheduling.

Fig. 4. Our SSS algorithm on the longest delay based scheduling.
