Joseph Camp
ABSTRACT
Accurately selecting modulation rates for time-varying channel conditions is critical for avoiding performance degradations due to rate overselection when channel conditions degrade or underselection when channel conditions improve. In this paper, we design a custom cross-layer framework that enables (i) implementation of multiple and previously unimplemented rate adaptation mechanisms, (ii) experimental evaluation and comparison of rate adaptation protocols on controlled, repeatable channels as well as residential urban and downtown vehicular and non-mobile environments in which we accurately measure channel conditions with 100-μs granularity, and (iii) comparison of performance on a per-packet basis with the ideal modulation rate obtained via exhaustive experimental search. Our evaluation reveals that SNR-triggered protocols are susceptible to overselection from the ideal rate when the coherence time is low (a scenario that we show occurs in practice even in a nonmobile topology), and that "in-situ" training can produce large gains to overcome this sensitivity. Another key finding is that a mechanism effective in differentiating between collision and fading losses for hidden terminals has severely imbalanced throughput sharing when competing links are even slightly heterogeneous. In general, we find trained SNR-based protocols outperform loss-based protocols in terms of the ability to track vehicular clients, accuracy within outdoor environments, and balanced sharing with heterogeneous links (even with physical layer capture).
- Technical report on RF channel characterization and system deployment modeling. Technical Report JTC(AIR)/94.09.23-065R6, JTC (Air) Standards Contribution, September 1994.Google Scholar
- MadWifi Project. http://madwifi.org, September 2005.Google Scholar
- D Aguayo, J. Bicket, S. Biswas, G. Judd, and R. Morris. Link-level measurements from an 802.11 mesh network. In ACM SIGCOMM, Portland, OR, 2004. Google ScholarDigital Library
- J. C. Bicket. Bit-rate selection in wireless networks. M.S. Thesis, MIT, February 2005.Google Scholar
- J. Camp, V. Mancuso, O. Gurewitz, and E. Knightly. A measurement study of multiplicative overhead effects in wireless networks. In IEEE INFOCOM, 2008.Google ScholarCross Ref
- J. Camp, J. Robinson, C. Steger, and E. Knightly. Measurement driven deployment of a two-tier urban mesh access network. In ACM MobiSys, Uppsala, Sweden, June 2006. Google ScholarDigital Library
- P. Chevillat, J. Jelitto, A. Noll Barreto, and H. L. Truong. A dynamic link adaptation algorithm for IEEE 802.11a wireless LANs. In IEEE International Conference on Communications, Anchorage, Alaska, May 2003.Google Scholar
- M. Heusse, F. Rousseau, G. Berger-Sabbatel, and A. Duda. Performance anomaly of 802.11b. In IEEE INFOCOM, San Francisco, CA, April 2003.Google ScholarCross Ref
- G. Holland, N. Vaidya, and P. Bahl. A rate-adaptive MAC protocol for multi-hop wireless networks. In ACM MobiCom, Rome, Italy, July 2001. Google ScholarDigital Library
- G. Judd, X. Wang, and P. Steenkiste. Efficient channel-aware rate adaptation in dynamic environments. In ACM MobiSys, Boulder, Colorado, June 2008. Google ScholarDigital Library
- A. Kamerman and L. Monteban. WaveLAN II: A high-performance wireless LAN for the unlicensed band. Bell Labs Technical Journal, pages 118--133, Summer 1997.Google ScholarCross Ref
- A. Khattab, J. Camp, C. Hunter, P. Murphy, A. Sabharwal, and E. Knightly. WARP: A flexible platform for clean-slate wireless medium access protocol design. SIGMOBILE Mob. Comput. Commun. Rev., 12(1):56--58, 2008. Google ScholarDigital Library
- J. Kim, S. Kim, S. Choi, and D. Qiao. CARA: Collision-aware rate adaptation for IEEE 802.11 WLANs. In IEEE INFOCOM, 2006.Google ScholarCross Ref
- A. Kochut, A. Vasan, A. U. Shankar, and A. Agrawala. Sniffing out the correct physical layer capture model in 802.11b. In IEEE ICNP, Berlin, Germany, October 2004. Google ScholarDigital Library
- M. Lacage, M. Hossein, and T. Turletti. IEEE 802.11 rate adaptation: A practical approach. In MSWiM, October 2004. Google ScholarDigital Library
- K. Mandke, S.-H. Choi, G. Kim, R. Grant, R. Daniels, W. Kim, R. Heath, and S. Nettles. Early results on Hydra: A flexible MAC/PHY multihop testbed. In IEEE Vehicular Technology Conference, Dublin, Ireland, April 2007.Google Scholar
- B. Sadeghi, V. Kanodia, A. Sabharwal, and E. Knightly. Opportunistic media access for multirate ad hoc networks. In ACM MobiCom, Atlanta, GA, September 2002. Google ScholarDigital Library
- S. Wong, S. Lu, H. Yang, and V. Bharghavan. Robust rate adaptation for 802.11 wireless networks. In ACM MobiCom, 2006. Google ScholarDigital Library
Index Terms
- Modulation rate adaptation in urban and vehicular environments: cross-layer implementation and experimental evaluation
Recommendations
Cross-layer wireless bit rate adaptation
SIGCOMM '09: Proceedings of the ACM SIGCOMM 2009 conference on Data communicationThis paper presents SoftRate, a wireless bit rate adaptation protocol that is responsive to rapidly varying channel conditions. Unlike previous work that uses either frame receptions or signal-to-noise ratio (SNR) estimates to select bit rates, SoftRate ...
Modulation rate adaptation in urban and vehicular environments: cross-layer implementation and experimental evaluation
Accurately selecting modulation rates for time-varying channel conditions is critical for avoiding performance degradations due to rate overselection when channel conditions degrade or underselection when channel conditions improve. In this paper, we ...
Rate Adaptation for 802.11 Multiuser MIMO Networks
In multiuser MIMO (MU-MIMO) networks, the optimal bit rate of a user is highly dynamic and changes from one packet to the next. This breaks traditional bit rate adaptation algorithms, which rely on recent history to predict the best bit rate for the ...
Comments