Digital Signal Processing Reference
In-Depth Information
Figure 15-7.
Lost and late speech packets as a function of the bit error rate; adaptive vs. not
adaptive technique for narrowband and wideband speech, maximum number of retransmissions
set to two.
5. CONCLUSIONS
An adaptive technique to transmit speech over 802.11 wireless packet net-
works was presented. The speech coding rate of a network-driven variable bit-
rate coder, the GSM AMR, is selected to match the instantaneous wireless chan-
nel conditions: higher rates (i.e., larger packets) for low error rates, lower rates
(i.e., smaller packets) when the channel is noisy. Network simulations showed
that adaptively selecting the speech packet size consistently outperforms the
constant bit-rate approach in terms of packet loss rates and end-to-end delays.
References
[1] ISO/IEC, 8802-11 (1999). Wireless LAN Medium Access Control (MAC)
and Physical Layer (PHY) Specifications.
ANSI/IEEE Std 802.11.
