Asia-Pacific Advanced Network

Transcription

1 Frame aggregations in the wireless LANs: A review paper Presented by: Anwar Saif Asia-Pacific Advanced Network Wireless communication 2009

2 Abstract The overhead induced by the IEEE PHY and MAC layer consumes most of the channel utilization time compared to the actual payload (figure 1). Higher data rate does not mean higher throughput! To reduce overhead, several MAC enhancements have been proposed such as block acknowledgement and frame aggregation.

3 The Problem Defer Access (NAV+DIFS) DIFS BackOf f PPDU SIFS Acknowledegmen t Channel Busy PLCP preamble PLCP Header MAC Header MSDU (Payload) FCS ACK Overhead Packet

4 Frame Aggregation Frame aggregation: Construct one large aggregation frame from multiple small Frames. Improves the throughput (Large Frames,less ACKs) Reduces transmission time ( Small Headers). Reduces the waiting time (Small Backoff,..)

5 Aggregation of 3 Frames

6 Aggregation schemes Aggregation MSDU (A-MSDU) Aggregate frames at the MAC level Aggregation MPDU ( A-MPDU) Aggregate frames at the PHY level Two level Aggregation A-MSDU aggregation followed by A- MPDU Other MAC PHY schemes

7 A-MSDU several MAC MSDUs concatenated in a single MPDU.

8 A-MPDU Several MPDUs are combined into one PPDU. PPDU

9 TWO LEVELS SF: Subframe SF HDR MSDU Padding MAC HDR MSDU SF1 MSDU SF2. MSDU SFn A-MSDU FCS MPDU Delimiter MPDU Padding PHY HDR MPDU SF 1 MPDU SF 2. MPDU SF n (PSDU) A-MPDU

10 Other schemes ( MAC Level )

11 Other schemes (PYH level)

12 Multi-Destination ( Uplink )

13 Multi-Destination ( Downlink)

14 Performance Issues Large Packet size: The Probability of The Bit Error is high.( Bad for Time-sensitive application TSA, fair For Non-TSA) Collision is low : (Good for both TSA and Non-TSA) Long construction time : (Bad for TSA) Good for Large App: FTP application Bad for VoIP application : small packet size Trade-off between robustness and efficiency Efficiency needs large packets +less delimiters!!! robustness needs small packets +more delimiters!!!

15 Open questions How to design an aggregation algorithm that supports VOIP QoS? ( packet loss, delay and jitter). How to choose the optimum packet size? How can redundant header information be compressed?

16 Conclusion Adaptive frame aggregations have to be introduced taking into account the trade-off between the robustness and efficiency, changes in the channel conations, and the type of the traffic classes.

17 Thank You

18 5. Literature reviews n proposal [1][2], introduced the A-MPDU and A- MSDU aggregations schemes for both the MAC service data unit and the MAC protocol data unit. They ensure high throughput but some issues still there regarding the channel conditions and type of traffic. Xiao & J.[4][5] Have shown that overhead is the major fundamental issue for inefficient MAC, the overhead is large either when the data rate is high or when the frame size is mall Throughput in has upper bound even the data rate goes to infinity. Xiao [6], Proposed techniques for the frame aggregations called ( Packing, concatenation, and multi-frame) Simple Techniques No adaptation no QoS Youngsoo [7] : proposed an aggregation schemes as a sub layer above the MAC layer Only error free transmission Small throughput improvement SeongKim et al [8]: Multi-user polling (MCCA) uses both MAC and physical layer aggregation Improve the non-qos traffic. No aggregation adaptation

19 Yang Xiao [9]: proposed several schemes from different aspects ( cent. vs. dist, Multi rate vs. Single rate, single Ack, Many Ack., ) Extension to what he did in [6] Cali [10], Tay & Chan[11] Propose an adaptive mechanisms for adjusting the contention window to achieve optimal throughput Based on BER. Yin et al. [12] studies the affect of packet size on the throughput in an error-prone channels. The show that an optimal packet size can be derived to maximize the throughput of the IEEE DCF under various channel conditions and network configurations. F. Zheng and J. Nelson [14] Studied different parameters that affects the throughput. They found that for low SNR, packet length optimization together with aggregation is must to achieve the desired throughput - Their analytical model assumes that no rapid change in the link conditions.

20 Lin, Y. and W.S. Wong [16]: They proposed an optimal frame size adaptation algorithm uner error channels. They did investigate the throughput and delay for the QoS flows. Li, Q. Ni et al [17][18] :They proposed aggregation scheme with partial acknowledgment AFR, in which only the defected sub frame form the aggregated frame will be acknowledged and then retransmitted. Good for large frame, not small ones Long processing time F. Sabrina and J. Valin [19] : They proposed an adaptive multi-rate encoding for VoIP based on the channel conditions and speech characteristics Parthasarathy S, and Q.-A. Zeng[20] :Adaptive scheme that change the number of antennas in n based on the channel conditions and traffic flows. T. Kawata and H [25] Proposed an adaptive multi-rate VoIP. They adapt the VoiP encoding rate and packetization interval according to the transmission rate

21 References [1] IEEE n TGn Sync, TGn Sync proposal technical specification, May [2] IEEE n WWiSE, WWiSE proposal: High throughput extension to the standard, Jan [3] Enhanced Wireless Consortium, HT MAC specification, Jan [4] Y. Xiao and J. Rosdahl, Performance Analysis and Enhancement for the Current and Future IEEE MAC Protocols, ACM SIGMOBILE Mobile Computing and Communications Review (MC2R), special issue on Wireless Home Networks, Vol. 7, No. 2, Apr. 2003, pp [5] Y. Xiao and J. Rosdahl, Throughput and Delay Limits of IEEE ," IEEE Communications Letters, Vol. 6, No. 8, Aug. 2002, pp [6] Y. Xiao, Packing Mechanisms for the IEEE n Wireless LANs, IEEE Communication Society, Globecom 2004, pp [7] Y. Kim, S. Choi, K. Jang, H. Hwang, Throughput Enhancement of IEEE WLAN via Frame Aggregation, Vehicular Technology Conference., vol. 4, Sept. 2004, pp [8] S. Kim, Y. Kim, S. Choi, K. Jang and J. Chang, A High-Throughput MAC Strategy for Next-Generation WLANs", IEEE WoWMoM [9] X. Yang, IEEE n: Enhancements for Higher Throughput in Wireless LANs in IEEE Wireless Communications, Vol. 12, pp , Dec [10] F. Cali, M. Conti, and E. Gregori, Dynamic tuning of the IEEE protocol to achieve a theoretical throughput limit, IEEE/ACM Trans. Networking, vol. 8, no. 6, pp , Dec

22 [11] Y. Tay and K. Chua, A capacity analysis for the IEEE MAC protocol, Wireless Networks, vol. 7, no. 2, pp , Mar channel for IEEE distributed coordination function, in Proc. Of IEEE WCNC, Mar. 2004, pp [12] J. Yin, X. Wang, and D. P. Agrawal, Optimal packet size in error-prone channel for IEEE distributed coordination function, in Proc. Of IEEE WCNC, Mar. 2004, pp [14] F. Zheng and J. Nelson: Adaptive Design for the Packet Length of IEEE n Networks, 2008 IEEE Intern. Conf. Communications (ICC 2008), May [15] D. Skordoulis, Qiang Ni, H. Chen, A. Stephens, C. Liu, and A. Jamalipour. "IEEE n MAC Frame Aggregation Mechanisms for Next-Generation High-Throughput WLANs". IEEE Wireless Communications Magazine, Volume 15, Issue 1, February [16] Lin, Y. and W.S. Wong, V. Frame Aggregation and Optimal Frame Size Adaptation for IEEE n WLANs. in Proceedings of IEEE Global Telecommunications Conference San Francisco, CA [17] T. Li, Q. Ni, D. Malone, D. Leith, T. Turletti, and Y. Xiao, Aggregation with Fragment Retransmission in Very High-Speed WLANs, IEEE/ACM Transactions on Networking (ToN), [18] T. Li, Q. Ni, D. Malone, D.Leith Y. Xiao, T. Turletti, A new MAC Scheme for very highspeed WLANs, Proceedings of the 2006 International Symposium on a World of Wireless, Mobile and Multimedia Networks (WoWMoM'06), 2006 [19] F. Sabrina and J. Valin, Adaptive Rate control for Aggregated VoIP Traffic [20]S. S. Parthasarathy and Q.-A. Zeng, A Novel Adaptive Scheme to Improve the Performance of the IEEE n WLANs in Proc. of 21st Int'l Conference on Advanced Information Networking and Applications Workshops (AINAW 2007), Vol. 2, pp , May 2007

23 [21 Sean Lawrence, Ashim Biswas, Anees A. Sahib: A comparative analysis of VoIP support for HT transmission mechanisms in WLAN. 27th International Conference on Distributed Computing Systems Workshops (ICDCSW'07), 2007 [22] Wireless Networks, The Definitive Guide by Matthew Gast, O'Reilly, 2005 [23] Peter Dely Adaptive Aggregation of Voice over IP in Wireless Mesh Networks, MSc thesis, Karlstad University,2007. [24] A. Schmitter, A. Schwarzbacher, T. Smith, Analysis of network conformity with voice over IP specifications, Irish Systems and Signals Conference (2003) [25] T. Kawata and H. Yamada, Adaptive multi-rate VoIP for IEEE wireless networks with link adaptation function, in Proc. IEEE GLOBECOM, San Francisco, CA, 2006.