TIA TIA/EIA-136-210-A

Abstract

This document defines the minimum performance specifications for non-bit-exact implementations of TIA/EIA-136-410 speech codecs operating in CTX (DTX-high) and CNG (DTX-low) operation under channel error free conditions. This speech codec is the Algebraic Codebook Excited Linear Predictive coding (ACELP) system described in TIA/EIA-136-410 document, i.e., <em>TDMA Cellular/PCS - Radio Interface - Enhanced Full-Rate Voice Codec</em>, which is accompanied by a soft copy consisting of fixed point ANSI C code and a number of test sequences. The ACELP speech codec is used to digitally encode the speech signal for transmission at a data rate of 7400 bps or 148 bits every 20 ms. <br>The TIA/EIA-136-410 standard includes a bit-exact specification of the ACELP speech codec using a fixed point ANSI C code. Six sets of test sequences are provided along with this standard. These test sequences are designed to provide for maximum coverage of the fixed point ANSI C code. There are separate test sequences for testing the encoder and for testing the decoder portions of the TIA/EIA-136-410 standard speech codec. A bit-exact implementation of this standard on a fixed point device would have to pass all six test sequences for the encoder and the six test sequences for the decoder in order to comply with the TIA/EIA-136-410 standard. These test sequences are described in Annex A of TIA/EIA-136-410 standard. As mentioned before, implementations of the TIA/EIA-136-410 standard at the Mobile Stations must pass all these test sequences since they are required to be bit-exact. <br>At the Base Station end, non-bit-exact implementations of the TIA/EIA-136-410 standard are permitted. For such implementations, it may not be possible to generate test vectors that can guarantee compatibility with the standard by using them as input to the speech encoder or decoder and by examining their output for exact replication of the corresponding reference vector. This document describes a series of tests which are used to test conformance to the specification. These tests do not necessarily ensure that the codec operates satisfactorily under all possible input signals and it is still a requirement of the manufacturer to ensure that his implementation operates in a consistent manner. The purpose of these tests is to test for minimum performance levels and the manufacturer should attempt to provide the highest performance possible. <br>The testing of any non-bit-exact implementation of the codec operating in CTX or DTX-high is based upon two classes of procedures: <br>Objective tests, which are based upon actual measurements of the speech codec function. <br>Subjective tests, which are based upon listening tests to judge overall speech quality. <br>Minimum performance specification for CNG is based on objective tests. These tests are defined by the test database, a method for generating individual test data files, the test requirements on candidate CNGs, a method to collect performance metrics, and the means to test those metrics so as to validate conformance to the specification. <br>The main purpose of the testing is to ensure adequate performance between any Base Station's encoder and any Mobile Station's decoder and vice-versa. Since the Mobile Station is restricted to have bit-exact implementations of the TIA/EIA-136-410 standard only, it suffices to demonstrate that minimum performance standards have been met when inter-operating with any bit-exact implementation. For this purpose, the fixed point ANSI C code provided as a part of the TIA/EIA-136-410 standard can be treated as the reference or master coder. <br>The restriction that Mobile Stations can only have bit-exact implementations of the TIA/EIA-136-410 standard is the primary reason that allows this standard to ensure minimum performance standards between any pairing of Base Stations and Mobile Stations; otherwise, we can guarantee this only by testing all combinations of encoder/decoder pairings in both Base Stations and Mobile Stations. With the number of equipment manufacturers expected to supply equipment this could easily become a prohibitive task. <br>By convention in this document, the Courier font is used to indicate C language and other software constructs such as file and variable names. The diacritical mark, &#167;, is used to indicate section numbers.