The PHY and MAC parameters in our simulations are shown in Table 7.1. Note that the sizes of QoS ACK and QoS-Poll in the table only include the sizes of MAC header and CRC overhead. We assume the minimum physical rate is 2Mbps and tPLCP is reduced to 96us. All related information is presented in Table 7.2.
Same as in [6], the bit rate of ordinary streaming video is chosen from 300kbps to 1Mbps. In our simulations, we consider three kinds of data rate: 300kbps, 600kbps and 1Mbps. As for nominal MSDU size, 750bytes, 1000bytes and 1250bytes are studied for each data rate. The behavior of packet arrival is modeled by Poisson process. For constant packet size, the video source is assumed to havethe fixed packet size equal to nominal MSDU size. For variable packet size, the packet length varies according to exponential distribution with mean packet size equal to nominal MSDU size. All related parameters are summarized in Table 7.3. Simulations are performed for 100,000 SIs.
We assume the traffic is delivered from QSTAs to AP and the contention free period occupies half of service interval, i.e., 50ms. The TXOP duration (TD) of the reference scheduler is calculated by plugging in the simulation parameters to equations (2) and (3) shown in Chapter 2. The TXOP duration for the scheme of [3] is
borrowed from the data given in [3] and the TXOP duration of our proposed scheme is calculated by the method shown in Chapter 4.
SIFS 10 us
MAC Header size 32 bytes
CRC size 4 bytes
QoS-ACK frame size 16 bytes
QoS CF-Poll frame size 36 bytes
PLCP Header Length 4 bytes
PLCP Preamble length 20 bytes
PHY rate(R) 11 Mbps
Minimum PHY rate (Rmin) 2 Mbps
Table 6.1: PHY and MAC parameters
PLCP Preamble and Header (tPLCP) 96us
Data MAC Header (tHDR) 23.2727us
Data CRC (tCRC) 2.90909us
ACK frame (tACK) 107.63636us
QoS-CFPoll (tPOLL) 122.1818us
Per-packet overhead (O) 249.81818us
Table 6.2: Transmission time for different header and per-packet overhead
Chapter6 Simulation Results
Mean Data Rate (ρ) 300k, 600k ,1M (bps) Nominal MSDU Size (L) 750, 1000,1250 (bytes)
Maximum Service Interval (SImax) 100ms
Packet Loss Rate Requirement (PLreq) 0.01 Table 6.3: QoS parameter of different traffic
The numerical results for constant and variable packet size are shown in Table 7.4 and Table 7.5, respectively. In these tables, N means the average number of packets that can be sent during one SI while n means the number of VBR flows that can be accommodated. It is clear that the packet loss probability (PL) increases as the allocated TXOP duration decreases. On the other hand, the medium waste rate (PW), which is defined as the ratio of the wasted transmission time over the allocated TXOP duration, increases as the allocated TXOP duration increases. A good algorithm should allocate TXOP duration as small as possible without violating the predefined packet loss probability. One can see from Table 7.4 and Table 7.5 that, for the single flow case, the TXOP durations allocated by our proposed algorithm is close to (only slightly greater than) those allocated by the algorithm of [3], which uses exact probability distribution functions in calculation. Moreover, both our proposed algorithm and the algorithm of [3] yield packet loss probability under the expected level, 0.01.
Table 6.4: Simulation result for constant packet size
Chapter6 Simulation Results
Table 6.5: Simulation result for variable packet size
Table 7.6 shows the result when one QSTA requests multiple VBR flows. For M
= 2 (i.e., two flows), the allocated aggregate TXOP is about 20% less than two times the TXOP allocated to an individual flow. The percentage of reduction increases as the number of concurrent flows increases, as illustrated in Figure 7.1. Table 7.6 and Figure 7.1 are both for VBR traffic with following characteristics: variable packet size, mean data rate = 300kbps, and nominal MSDU size = 1250 bytes.
Table 6.6: Simulation result for variable packet size on multiplexing gain
0 1 2 3 4 5
0 10 20 30 40 50 60
Data Rate = 300kbps & Nominal MSDU=1250 bytes
Number of VBR flows
TXOP Du
Reference
Our Scheme Without Multiplexing Our Scheme With Multiplexing
ration
Figure 6.1: TXOP duration vs. Number of VBR connections
Chapter7 Conclusions
Chapter 7 Conclusions
In this paper, we present a simple admission control algorithm for IEEE 802.11e WLANs which uses Gaussian distribution to approximate the behavior of VBR traffic.
Both constant packet size and variable packet size VBR traffic are studied. The effect of multiplexing gain is also investigated. As verified with computer simulations, our proposed algorithm is effective in the sense of guaranteeing packet loss probability under a predefined threshold. Moreover, it is efficient because the allocated TXOP durations are close to those allocated by an algorithm which uses exact probability distribution functions. An important advantage of our proposed algorithm is its simplicity which makes it suitable for implementation in a real system. An interesting further research topic which is currently under study is to allow packets to stay in buffer for more than one service interval to reduce the packet loss probability.
Bibliographies
[1] IEEE 802.11 WG: IEEE Standard 802.11-1999, Part 11: Wireless LAN MAC and Physical Layer Specifications. Reference number ISO/IEC 8802-11:1999(E), 1999.
[2] IEEE 802.11 WG: IEEE 802.11e/D8.0, Wireless MAC and Physical Layer Specifications: MAC QoS Enhancements.
[3] W.F.Fan et al., ”Admission Control for Variable Bit Rate Traffic in IEEE802.11e WLANs”, Proc. IEEE LANMAN ’04, Mill Valley,CA 2004, pp.61-6.
[4] A.Leon-Garcia,” Probability and Random Process for Electrical Engieering,”
Addison Wesley 1994.
[5] R.Nelson,” Probability, Stochastic and Queueing Theory - The Mathematics of Computer Performance Modeling.” Springer Verlag, 1995.
[6] F.Kozamernik, “Media Streaming over the Internet – an overview of delivery technologies,” EBU TECHNICAL REVIEW, Oct. 2002.
[7] D.Gao,” Admission control in IEEE 802.11e wireless LANs,” IEEE Network, vol.19, issue 4, Jul./Aug. 2005, pp. 6-13
Bibliography
[8] P. Ansel, Q. Ni, and T. Turletti, "FHCF: A Fair Scheduling Scheme for IEEE 802.11e WLAN", INRIA Research Report No 4883, July 2003.
[9] S. Mangold, S. Choi, G. R. Hiertz, et al, “Analysis of IEEE 802.11e for QoS Support in Wireless LANs”, IEEE Wireless Communications, Volume 10, Issue 6, Dec, 2003.
[10] William Stallings,” Data and Computer Communications,” Prentice Hall 2004.
[11] Arthur W. Berger, Ward Whitt, “Extending the Effective Bandwidth Concept to Networks with Priority Classes”, IEEE communication August 1998.
[12] P.O.Borjession and C.E.W. Sundberg, ＂Simple Approximation of the Error Function Q(x) for Communication Applications, ＂ IEEE transaction on Communications, March,1979
一、 個人資料
姓名 黃郁文
性別 男
出生地 高雄縣岡山鎮
生日 1982/05/19
血型 A
生肖 狗
星座 金牛座
E-mail [email protected]
興趣 打球、攝影
實驗室 交大電信所 網路技術實驗室 (工程四館 823 室)
二、 學歷
國小 高雄縣立岡山國民小學
國中 高雄縣立岡山國民中學
高中 國立台南第一高級中學
大學 國立交通大學電信工程學系
研究所 國立交通大學電信工程研究所 碩士班 系統組