Niranjan Shetty
ABSTRACT
The communication of voice over wireless local area networks (WLANs) is influenced by the choice of speech codec, packetization interval and PHY layer bit rates. These choices affect the number of voice users that can be supported on the WLAN as well as the speech quality experienced by each user. We investigate the effect of different combinations of these parameters for a 802.11a WLAN in different channel conditions with the objective of maximizing the number of voice users supported on the WLAN subject to a quality constraint. We use an indicator for assessing the speech quality experienced by a single user in a WLAN, based on a Perceptual Evaluation of Speech Quality (PESQ) Mean Opinion Score (MOS) constraint and the probability of a voice user achieving this constraint. The contributions of this paper are three-fold. First, a PHY layer rate adaptation scheme is proposed, in which the operating rate for each Signal to Noise Ratio (SNR) is chosen as the one that maximizes the capacity given a quality constraint. Second, based on the PHY layer rate adaptation scheme, we evaluate the effect of the choice of codec and voice payload size on the capacity values obtainable at different SNRs. Finally, we show the effect of channel conditions and the tightening of quality constraints on the capacity values at different SNRs.
- ITU-T Recommendation G.711. Pulse Code Modulation for voice frequencies, Nov. 1988.Google Scholar
- ITU-T Recommendation G.729. Coding of speech at 8 kbit/s using conjugate-structure algebraic-code-excited linear-prediction (CS-ACELP), Mar. 1996.Google Scholar
- A. Doufexi, S. Armour, M. Butler, A. Nix, D. Bull and J. McGeehan. A Comparison of the HIPERLAN/2 and IEEE 802.11a Wireless LAN Standards. IEEE Communications Magazine, May 2002. Google ScholarDigital Library
- N. Chayat. Tentative Criteria for Comparison of Modulation Methods. IEEE P802.11-97/96, Sept. 1997.Google Scholar
- D. P. Hole and F. A. Tobagi. Capacity of an IEEE 802.11b wireless LAN supporting VoIP. IEEE Intl. Conf. on Communications, 2004.Google ScholarCross Ref
- J. Heiskala and J. Terry. OFDM Wireless LANs: A Theoretical and Practical Guide. Sams, December 2001. Google ScholarDigital Library
- IEEE 802.11a WG. Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specification: High-Speed Physical Layer in the 5 GHz Band. 1999.Google Scholar
- ITU-T Recommendation G.107. The E-model: A computational model for use in transmission planning. Feb. 2001.Google Scholar
- ITU-T Recommendation G.114. One-Way Transmission Time. May 2000.Google Scholar
- ITU-T Recommendation G.711 Appendix I. A high quality low-complexity algorithm for packet loss concealment with g.711. Oct. 1999.Google Scholar
- ITU-T Recommendation P.862. PESQ: An objective method for end-to-end speech quality assessment of narrowband telephone networks and speech codecs. Feb. 2001.Google Scholar
- K. Madepalli and P. Gopalakrishnan and D. Famolari and T. Kodama. Voice Capacity of IEEE 802.11b, 802.11a and 802.11g Wireless LANs. GLOBECOM, 2004.Google ScholarCross Ref
- K. Madepalli and P. Gopalakrishnan and D. Famolari and T. Kodama. Voice Capacity of IEEE 802.11b and 802.11a Wireless LANs in the Presence of Channel Errors and Different User Data Rates. VTC, 2004.Google ScholarCross Ref
- O. Awoniyi and F. A. Tobagi. Effect of Fading on the performance of VoIP in IEEE 802.11a. IEEE Intl. Conf. on Communications, 2004.Google Scholar
Index Terms
- Voice capacity under quality constraints for IEEE 802.11a based WLANs
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