Michael Charles Recchione

The Enhanced Variable Rate Coder: Toll quality speech for CDMA

The Enhanced Variable Rate Coder (EVRC), standardized by the Telecommunications Industry Association (TIA) as IS-127, is intended for use with the IS-95x Rate Set 1 air interface (CDMA). This coder operates at a maximum rate of 8.5 kb/s and an average rate of about 4.1 kb/s on conversational speech. The EVRC consists of three coding modes that are all based on the Code Excited Linear Prediction (CELP) model. Selection among the three modes is based on an estimate of the input signal state, with active speech encoded primarily at 170 bits/20 msec frame (Rate 1), background noise and silence encoded at 16 bits/frame (Rate 1/8), and some active speech and essentially all transitions between speech and silence encoded at 80 bits/frame (Rate 1/2). In order to improve performance in the presence of background noise, the EVRC employs an adaptive noise-suppression filter at the input. Subjective test results are presented demonstrating that the EVRC delivers excellent quality voice in clean speech/clear channel conditions, and that its performance exceeds that of most currently standardized speech coders for wireless applications in background noise and/or impaired channel conditions.

SIP-based services architecture across wireless and wireline access

There are strong market and industry drivers to support a common set of end-user services ubiquitously across several wireline and wireless access technologies: UMTS/CDMA, 802.11 WLAN, Bluetooth∗ WLAN, DSL, and cable TV/packet cable. Currently, service providers must use different services architectures for providing the same end-user services on different access networks. A common Session Initiation Protocol (SIP)-based architecture that can support a wide range of text, voice, and video services has been developed; it is based on the 3GPP/3GPP2 IP Multimedia Subsystem (IMS) standard. With a few minor extensions, the IMS services architecture can be used to support services across wireline and wireless access networks.