Throughput and Fairness Performance of Non-real-time Users 65

In this subsection, we evaluate the throughput and fairness performances of the non-real-time users in the practical IEEE 802.16 WMAN OFDMA environments. First, we observe the through of non-real-time users in the wireless time-varying environ-ments. From Fig. 4.9, we see that the throughput performances of FSA and RSA are almost the same. The two schemes do not take the channel state information into consideration. Nevertheless, we find that the RSA exploits the frequency to achieve better fairness performance than that of FSA from Fig. 4.10. Seeing Fig. 4.9, we

ob-serve that the DSA scheme exploits both multiuser diversity and frequency diversity to improve the throughput perfomance rather than FSA and RSA. Furthermore, the proposed CSA algorithm take advantage of the characteristics of OFDMA channel.

Real-time users do not select the best subcarriers but use the medium subcarriers instead. Hence, the non-real-time users have higher probability to utilize the sub-carriers with good conditions, which make the throughput of CSA achieve the best throughput performance among the four resource allocation policies, FSA, RSA, DSA and CSA. Moreover, the proposed CSA algorithm has the best fairness performance because it has the channel effects and characteristics comprehensively in mind.

Figures 4.11 and 4.12 show that the mean throughput and fairness perfor-mances after an amount of iteration. From Fig. 4.11, it is showed that throughput performances of FSA and RSA are almost the same. DSA improve the through-put of non-real-time users about 5% rather than FSA and RSA. The DSA scheme also improves the quality of real-time voice service but we do not care very much.

Moreover, the proposed CSA algorithm improves the throughput about 20% rather than the DSA scheme. The CSA resource management policy maintains the real-time transmission quality and utilizes the gain due to taking advantage of the specific characteristics of OFDMA systems to support the non-real-time throughput sensitive services. In Fig. 4.12, we find that the mean fairness performances of the four schemes are very good in the multicarrier systems. However, the proposed CSA algorithm is the best fair allocation approach.

4.6.5 Discussions

For radio resource scheduling, it is generally discussed that the trade-off multiuser diversity and delay [41]. In other words, throughput and fairness are not considered complete in both respects. However, frequency diversity inherently exists in the

mul-ticarrier system. Therefore, we make use of frequency diversity to support fairness requirements. Moreover, understanding the specific characteristics of OFDMA chan-nel, we try our best to enhance the throughput of non-real-time service flows with allocating subcarriers with enough good conditions. In a word, compared DSA, our proposed CSA schemes remove the diversity gain from real-time services to provide extra gain to non-real-time services.

4.7 Conclusions

In this paper, we propose an efficient QoS provisioning multicarrier allocation scheme to satisfy QoS requirements of multi-type services. By queueing analysis, we satisfy the demand of real-time users. Besides, we observe the channel characteristics of OFDMA systems and make use of it to improve the system performance. Further-more, we exploits frequency diversity and multiuser diversity to enhance throughput and maintain the fairness performance of non-real-time service with considering delay constraint of real-time service.

0 0.005 0.01 0.015 0.02 0.025 0.03 10⁻⁵

10⁻⁴ 10⁻³ 10⁻² 10⁻¹ 10⁰

arrival rate (1/sec)

Blocking probability

FSA RSA DSA CDSA CSA

Fig. 4.7: Blocking probability of real-time services when the inter-arrival rate changes.

60 80 100 120 140 160 180 0.94

0.95 0.96 0.97 0.98 0.99 1

Number of subcarriers

Minimum fairness index

FSA RSA DSA CSA

Fig. 4.8: The worst case of fairness when the number of subcarriers changes.

0 200 400 600 800 1000 1200 1400 1600 1800 70

75 80 85 90 95 100 105 110 115 120

Time

Throughput (Kbps)

FSA RSA DSA CSA

Fig. 4.9: Comparison of system throughput.

0 200 400 600 800 1000 1200 1400 1600 1800 0.94

0.95 0.96 0.97 0.98 0.99 1

Time

Minimum fairness index FSA

RSA DSA CSA

Fig. 4.10: Comparison of fairness performances.

0 5 10 15 20 25 30 80

85 90 95 100 105 110 115

Time

Throughput (Kbps)

FSA RSA DSA CSA

Fig. 4.11: Mean throughput performances

0 5 10 15 20 25 30 0.976

0.978 0.98 0.982 0.984 0.986 0.988

Time

Mean fairness index

FSA RSA DSA CSA

Fig. 4.12: Mean fairness performances

Concluding Remarks

The objective of this thesis is to exploit both frequency diversity and multiuser diver-sity with adopting dynamic resource allocation in OFDMA systems to improve the system performances. This thesis includes the following research topics:

1. Analyze the frequency diversity and multiuser diversity gains in the multicarrier OFDMA systems.

2. Demonstrate that the simple maximum carrier-to-interference (C/I) scheduling scheme can both enhance system throughput and maintain fairness performances for OFDMA systems.

3. Observe the specific characteristics of the OFDMA channel.

4. Propose a resource allocation scheme that exploits frequency diversity and mul-tiuser diversity and makes use of the specific OFDMA channel characteristics to enhance throughput of non-real-time services; while satisfying the delay constraint of real-time services

5. We provide a service-oriented water-pouring resource allocation scheme and cross-layer design.

5.1 Throughput and Fairness Enhancement for OFDMA Broadband Wireless Access

Systems Using the Maximum C/I Scheduling

In Chapter 3 and [42], we have demonstrated that the simple maximum carrier-to-interference scheduling scheme can be a fair scheduler in the OFDMA system, al-though it is viewed as an unfair scheduling scheme in the single carrier TDMA/CDMA systems. Using this simple maximum C/I scheduling algorithm in the OFDMA system can exploit multiuser diversity and frequency diversity thoroughly, thereby achieving both high throughput and good fairness performances. Moreover, using this simple maximum C/I scheduling algorithm can combat the worse channel effect and observe the good fairness performance in a multiuser OFDM system.

5.2 Channel-aware Subcarrier Allocation and QoS Provisioning for OFDMA Systems with Multi-type Traffic

In Chapter 4 and [43], we propose an efficient QoS provisioning subcarrier allocation scheme to satisfy QoS requirements of multi-type services. By queueing analysis, we satisfy the demand of real-time users. Besides, we observe the channel characteristics of OFDMA systems and make use of it to improve the system performance. Further-more, we exploits frequency diversity and multiuser diversity to enhance throughput and maintain the fairness performance of non-real-time service with considering delay constraint of real-time service.

5.3 Suggestion for Future Work

For the future research of the thesis, we provide the following suggestions to extend our work:

• Combine rate adaptation and power allocation techniques to enhance the system performances with considering channel characteristics.

• Compare the performances of scheduling schemes among CDMA and OFDMA systems. Furthermore, we can try to make use of this approach in the multi-carrier CDMA (MC-CDMA) systems.

• Considering more types of service flows, such as voice, video, data and other applications with different traffic models and QoS requirements.

• To design a criterion to describe the tradeoff between throughput and fairness.

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Vita

Wei-Jun Lin was born in Taiwan in 1979. He received the B.S. degree in Communication Engineering from National Chiao Tung University in 2002. From July 2002 to June 2004, he works his Master degree in the Wireless Network Lab of the Department of Communication Engineering at National Chiao Tung University.

His research interests are in the field of wireless communications.