Karl Hellwig

Speech codec for the European mobile radio system

The speech coding scheme which will be used as the standard for the European mobile radio system has been selected by the CEPT Groupe Special-Mobile (GSM) as a result of formal subjective listening tests. It is based on the regular-pulse excitation linear predictive coding technique (RPE-LPC) combined with long-term prediction (LTP). The solution is called the RPE-LTP codec. The codec algorithm and the error protection scheme are presented. The net bit rate is 13.0 kb/s, and the gross bit rate, including error protection, is 22.8 kb/s. The experimental implementation based on VLSI signal processors is described. The speech quality obtained with the technique considered is far superior to that obtainable with present-day analog mobile radio systems. A duplex speech codec including error protection can be implemented with two VLSI sign processors with external data memories of about 1 K*16 b.<<ETX>>

A VR-CELP codec implementation for CDMA mobile communications

This paper focuses on the design, implementation and testing of a variable rate (VR) CELP codec aimed to be used in the testbed of one RACE-II project: CoDiT (code division testbed). The project has been conceived to demonstrate the potentiality of CDMA for the UMTS (universal mobile telecommunications system). Because of the flexibility permitted by CDMA to easily convey the information stream over a VR physical channel, the fixed-rate constraint has been removed from the speech coding algorithm design, in order to exploit the time-varying local character of speech. One major feature of the proposed algorithm is the possibility for the average rate to be either source-controlled or network-controlled. This is particularly appealing for cellular communications in order to cope with areas or cells with a high time-varying congestion.<<ETX>>

The cellular text telephone modem - the solution for supporting text telephone functionality in GSM networks

Text telephone devices are text-based terminals that allow the users to communicate by text via fixed-line telephone networks. Since cellular phone systems are sometime subject to severe radio channel impairments and the modem signals of these text telephones are therefore not always transmitted reliably, the Federal Communications Commission (FCC) has required a solution to guarantee a reliable transmission of text telephone data for emergency calls via cellular phone systems. For the North American PCS-1900 cellular phone systems the Standards Committee T1 has standardized a solution for this requirement, which is based on a new modem protocol, the cellular text telephone modem (CTM), whose signals can be reliably transmitted via the speech channel of cellular phone systems. After an introduction into text telephony, this contribution provides a description of this solution for PCS-1900 systems using CTM signals. The solution is indeed independent of the cellular system and works on de-facto all speech channels.

KISS-16V2: a one-chip ASIC DSP solution for GSM

Outlines the requirements for the various digital signal processing functions of the pan-European digital mobile cellular telephone system in terms of computational power and RAM and ROM capacities, and describes a digital signal processor (DSP) solution which is able to integrate all of these digital baseband functions for a hand-held terminal onto one VLSI chip. The KISS-16V2 processor, a low-power CMOS 16-b DSP, is optimized for digital telecommunications, especially for Groupe Speciale Mobile (GSM). A power-down mode together with the capability of memory and multiplier standby operation make this DSP well suited for handheld devices. A design strategy based on the extensive use of cell compilers and synthesis tools reduces the design of further DSP derivations to a minimum. >

A regular-pulse excited linear predictive codec

Abstract A 16 kbit/s speech codec with low complexity and low signal delay is presented which is a special version of the Regular-Pulse Excitation LPC approach (RPE-LPC). This proposal is the basis for the codec standard which will be used in the future Pan-European digital mobile telephone system. An experimental hardware model is described.

KISS-16V1: a 16 bit signal processor

The authors describe the architecture and design of the 1 6-b low-power CMOS fixed-point signal processor KISS-16V1. The 16-b data and instructions are processed in one 50-ns cycle. The KISS-16V1 is a digital-signal processor (DSP) with a multibus Harvard architecture. Its new architectural features and its sophisticated instruction set are optimized for digital telecommunications, especially for GSM. A power-down mode together with the capability of memory and multiplier standby operation make this DSP well suited for hand-held devices. A design strategy based on the extensive use of cell compilers and synthesis tools reduces the design period of further DSP derivations to a minimum. This flexible concept allows adaptation of the device for enhanced requirements of GSM as well as for other signal processing applications. This DSP is a significant step toward an all-digital-on-one-chip solution for the GSM full-rate channel.<<ETX>>