Station Performance Evaluation on Location of Relay

To evaluate the impact of the RS location, we compare the performances for three RS locations: one is at two thirds of the cell radius, another is at three fourths of the cell radius, and the other is at the seven eighths of the cell radius. Also, if the desired site is not located also an intersection, the RS is placed on the nearest intersection from the desired site location. Both QoS_GTE and LMP+TC are used in the

simulation. SO_based resource allocation algorithm is adopted as the scheduling for LMP+TC.

Figure depicts the system throughput for three distinct RSs locations in QoS_GTE and in LMP+TC, respectively. At the light traffic load, the performance order of three cases has no regularity. When the traffic load is at 0.3, the case of 2/3 is the best.

When the traffic load is 0.45, the case of 7/8 is the best. This is because there is enough resource for low traffic load; therefore, the location of RS does not affect the system performance. On the contrary, as the traffic load increases, the throughput performance from best to worst is the case of 3/4, the case of 2/3 and the case of 7/8, which is clearer in LMP+TC scheme. For the case of 2/3 radius, RSs are so close to each other that each RS coverage is overlapped and this results in reducing the service area of RSs in the cell. Besides, RSs are too close to BS to replace the transmission from BS to MSs and the probability of using relay is low. On the contrary, when RSs is at the 7/8 radius, there may be a gap between any two RSs where no RS can serves this area. Further, half of the RS service area is almost out of the cell when RSs are on 7/8 radius which also make the RS service area decrease. As the RS coverage decreasing, the probability of replacing direct path is attenuating. As a result, RSs are idle and the relay-assisted system acts like without RS system. As to the case of RSs at 3/4 radius, it can get the largest RS service area and relay path replaces the direct transmission as efficiently as it can hence its QoS_guaranteed and system throughput enhancement are both done in the best way.

0

(b) System Throughput of LMP+TC

Figure 4.7. System Throughput of Tow Relay Schemes

Figure is the voice packet dropping rate in QoS_GTE and also in LMP+TC. The voice packet dropping rate is all zero for each case of RS location. Nevertheless, video packet dropping rates for different RS locations in QoS_GTE and LMP+TC are obviously distinguished in Figure. The case of 3/4 radiuses has the lowest video packet dropping rate and the case of 7/8 radius is the worst. Also, Figure reveals the non-guaranteed ratio of HTTP users in QoS_GTE and LMP+TC respectively. The case of 7/8 radiuses has the largest HTTP non-guaranteed rate of all undoubtedly.

From Figure to Figure, we can summarize that the system performance is affected severely by the location of RSs. A proper RS location makes the RS service coverage maxima and makes RSs supply BS as long as the direct path is not good enough. The location too near or too far from BS leads the advantage of setting RSs in vain.

0 0.01 0.02 0.03 0.04 0.05

0.15 0.3 0.45 0.6 0.75 0.9

Traffic Load 2/3 radius

3/4 radius 7/8 radius

Packet Dropping Rate

Figure 4.8. Voice Packet Dropping Rate in QoS_GTE and LMP+TC

0

(a) Video Packet Dropping Rate of QoS_GTE

0

(b) Video Packet Dropping Rate of LMP+TC Figure 4.9. Video Packet Dropping Rate

0

(a) HTTP traffic Non-guaranteed Ratio of QoS_GTE

0

(b) HTTP traffic Non-guaranteed Ratio of LMP+TC Figure 4.10. Non-guaranteed Ratio of HTTP traffic

Chapter 5

Conclusions

In the thesis, a downlink centralized QoS guaranteed and throughput enhancement (QoS_GTE) scheduling scheme for WiMAX relay-assisted network is proposed, where two hop relay system is considered. The QoS_GTE scheduling scheme consists of a transmission time based (TT_based) path selection algorithm, a service order based (SO_based) resource allocation algorithm and a transmission concurrency (TC) decision algorithm.

The TT_based path selection algorithm takes the overall path of path-loss, shadow fading, and interference into consideration in terms of transmission time. It chooses the path with the minimal total transmission time as the transmission path. It not only considers the link quality but also the transmission efficiency, which react directly upon the transmission time. The TT_based algorithm helps to find a path by which the link quality is better than that of the algorithm without relay. Also, the system efficiency is improved compared with other path selection algorithms in relay network. This is because the conventional scheme (LMP) selects the path only based on the bottleneck path loss, which can improve the link quality but the system throughput.

The SO_based resource allocation algorithm gives high priority to the urgent users

according to service order Sm at the current frame and dynamically adjusts the Sm of users frame by frame. The goals of the SO_based resource allocation algorithm are for QoS satisfaction and throughput maximization. In addition, multiple service classes, which include real time, non real time, and best effort services, are considered.

Since using relay may cause resource consuming, The TC decision algorithm carries out resource reuse by deciding which RSs can transmit concurrently using the same frequency and time slots.

Simulation results show that the QoS_GTE is compared with LMP+TC and without relay case. From the results, we can conclude that QoS_GTE outperforms LMP+ TC and without relay case in terms of system throughput and the satisfaction extent of QoS requirements. The TT_based path selection algorithm is better than LMP scheme both in link quality and system performance. The SO_based resource allocation algorithm can make sure that voice packets will be satisfied with the requirement all the time. The video packet cans also be satisfied until the traffic load is high. The TC decision algorithm indeed raises the throughput pretty much. Besides, the location of RS plays an important effect on the system performance. It is concluded that the proper location of RS in our scenario is at three fourth cell radius.

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Vita

Chia-Shueng Chuang was born on 1983 in T aitong, Taiwan. She received the B.E.

degree in electrical engineering from National Cheng-Kung University, Tainan, Taiwan, in 2005, and the M.E. degree in the department of communication engineering, college of electrical and computer engineering from National Chiao Tung University, Hsinchu, Taiwan, in 2007. Her research interests include radio resource management and wireless communication.