This paper presents bandwidth-efficient speech transmission systems using rate-compatible channel coders and variable bitrate embedded source coders. Rate-compatible punctured convolutional codes (RCPC) are often used to provide unequal error protection (UEP) via progressive bit puncturing. RCPC codes are well suited for constellations for which Euclidean and Hamming distances are equivalent (BPSK and 4-PSK). This paper introduces rate-compatible punctured trellis codes (RCPT) where rate compatibility and UEP are provided via progressive puncturing of symbols in a trellis. RCPT codes constitute a special class of codes designed to maximize residual Euclidean distances (RED) after symbol puncturing. They can be designed for any constellation, allowing for higher throughput than when restricted to using 4-PSK. We apply RCPC and RCPT to two embedded source coders: a perceptual subband coder and the ITU embedded ADPCM G.727 standard. Different operating modes with distinct source/channel bit allocation and UEP are defined. Each mode is optimal for a certain range of AWGN channel SNRs. Performance results using an 8-PSK constellation clearly illustrate the wide range of channel conditions at which the adaptive scheme using RCPT can operate. For an 8-PSK constellation, RCPT codes are compared to RCPC with bit interleaved coded modulation codes (RCPC-BICM). We also compare performance to RCPC codes used with a 4-PSK constellation.

In wireless systems supporting slowly moving users, adaptive trellis-coded modulation (TCM) schemes have demonstrated large bandwidth efficiency gains over their nonadaptive counterparts. In systems with highly mobile users, the adaptive bit-interleaved coded modulation (BICM) achieves a moderate bandwidth efficiency gain over previously proposed adaptive schemes and nonadaptive schemes with similar complexity. However, adaptive BICM requires a bit interleaver, which results in long latency. In this paper, adaptive coded modulation (ACM) schemes which do not employ interleaving and do not use uncoded bits are considered for time-varying channels. Two such ACM schemes are proposed. One of the ACM schemes uses a forward trellis search algorithm (FTS) to adapt to the current channel fading. Numerical results demonstrate that the proposed FTS-ACM scheme achieves a comparable bandwidth efficiency gain to adaptive BICM. FTS-ACM is particularly attractive for low latency transmission applications.

Adaptive coded modulation is a powerful method for achieving a high spectral efficiency over fading channels. Previously proposed adaptive schemes have employed set-partitioned trellis-coded modulation (TCM) and have adapted the number of uncoded bits on a given symbol based on the corresponding channel estimate. However, these adaptive TCM schemes do not perform well in systems where channel estimates are unreliable, since uncoded bits are not protected from unexpected finding. In this paper, adaptive bit-interleaved coded modulation (BICM) is introduced. Adaptive BICM schemes remove the need for parallel branches in the trellis-even when adapting the constellation size, thus making these schemes robust to errors made in the estimation of the current channel fading value. This motivates the design of adaptive BICM schemes, which will lead to adaptive systems that can support users with higher mobility than those considered in previous work. In such systems, numerical results demonstrate that the proposed schemes achieve a moderate bandwidth efficiency gain over previously proposed adaptive schemes and conventional (nonadaptive) schemes of similar complexity.

This paper investigates optimal constellation labeling in the context of the edge profile. A constellation's edge profile lists the minimum-distance edge for each binary symbol error. The paper introduces the symmetric-ultracomposite (SU) labeling structure and shows that this structure provides undominated edge profiles for 2/sup n/-PSK, 2/sup n/-PAM, and 2/sup 2n/-point square QAM. The SU structure is a generalization of the commonly used reflected binary Gray code. With the proper choice of basis vectors, SU labeling can support either set-partition or Gray-code labeling of 2/sup n/-PSK, 2/sup n/-PAM, and 2/sup 2n/-point square QAM. Notably, there are Gray-code and set-partition labelings that do not have the SU structure. These labelings yield inferior edge profiles. The SU structure does not apply to cross constellations. However, for any standard cross constellation with 32 or more points, a quasi-SU labeling structure can approximate the SU structure. With the correct choice of basis, quasi-SU labelings produce quasi-Gray labelings. However, the quasi-SU structure cannot support set-partition labeling. In fact, the quasi-SU structure provides a better edge profile than standard set-partition labeling. Thus, for cross constellations there is a choice between edge profile optimality and the group structure provided by set-partitioning. Here, the correct choice depends on whether the encoder trellis has parallel branches.

Structurally distinct constellation labeling exists within both the Gray code and the set-partitioning paradigm. Different labeling choices within either paradigm can provide different bit error rates, especially at low SNR. This paper demonstrates that symmetric ultracomposite (SU) labeling, an extension of the binary reflected Gray code, provides undominated edge profiles for all standard PSK, PAM and square QAM constellations. (The edge profile lists the minimum distance for each binary symbol error) The SU structure can accomodate either the Gray code or the set-partitioning paradigm. It is the clear labeling choice for standard PSK, PAM and square QAM constellations. An extension of SU labeling provides quasi-SU (QSU) labeling for all 2/sup 2n+1/-cross constellations for n>1. QSU labeling satisfies the quasi-Gray property for cross constellations. For cross constellations, set-partitioning and QSU labeling structures are distinct. For 32-cross, QSU labeling has a superior edge profile and is preferred when the trellis does not have parallel branches. Despite its inferior profile, set-partitioned 32-cross is still preferred when the trellis has parallel branches.

This paper describes techniques for the design and analysis of trellis codes that provide reliable communication over every channel in a specified set of possible channels, where each channel is characterized by additive white Gaussian noise with a distinct periodic variation in signal-to-noise ratio. An important practical application for such trellis codes is the periodic erasure channel produced by partial-band interference dispersed by a block interleaver. We present trellis codes that provide reliable communication over all periodic erasure patterns of a given period for which the number of unerased coded bits per period is at least equal to the number of information bits per period.

This paper presents an embedded joint source-channel coding scheme of speech. The source coder is an embedded variable bit rate perceptually based sub-band coder producing bits with different error sensitivities. The channel encoder is a rate compatible punctured trellis code (RCPT) which permits rate variability and unequal error protection by puncturing symbols. Furthermore, RCPT code design naturally incorporates large constellations, allowing high information rate per symbol. The embedded speech coder and the rate compatible puncturing of symbols provide the embeddibility of the joint coding scheme. The coder is robust to acoustic noise and produces good quality speech for a wide range of channel conditions (AWGN or fading), allowing digital transmission of speech with analog-like graceful degradation.