We consider the concept of faster-than-Nyquist rate (FTN) broadcasting, which nonorthogonally multiplexes more than one user message in the continuous-time domain for transmission over broadcast channels. Two FTN broadcasting approaches, namely, sub-FTN and full-FTN, are considered for broadcasting of K independent messages over K-user continuous time Gaussian broadcast channel. The derived achievable rate regions of the two approaches are shown to be, in general, greater than the capacity region of the optimally coded Nyquist-rate broadcasting using a same modulating pulse. The full-FTN broadcasting provides larger degrees of freedom (capacity pre-log factor) to each user of the broadcast channel while the sub-FTN improves signal-to-interference-plus-noise-ratios of the individual link. The amount of capacity gains in high SNR regime is linearly proportional to excess bandwidth in the modulating pulse used and dependent on FTN signaling rates, channel SNRs, and number of users in the broadcast channel. The simulated sub-FTN and full-FTN broadcast transceivers outperform coded Nyquist-rate systems both in BER performances and in capacity.

This work considers using faster-than-Nyquist (FTN) transmission in symbol-synchronous and symbol-asynchrounous multiple-access channels (MAC) when multi-user demodulation and decoding are used at the receiver. We derive a sum capacity expression for the FTN-MAC in the presence of user asynchronism and present numerical capacity results. This work demonstrates that the channel capacity can be improved by introducing the FTN signaling in the multiple-access channels with or without asynchronism among transmitters of various users.

This paper explores chip-asynchronous CDMA transmission when single-user demodulation and decoding are used at the receiver. First, a chip-level channel model is presented to account for chip-asynchronism between different users. Using the model, the symmetric capacity of chip-asynchronous CDMA is investigated. Numerical results indicate that a sum rate of 2 bits per channel use is achievable when chip symbols {-1, 1} are utilized in appropriate non-equiprobable fashion. This represents over a 2.5 times capacity gain over traditional uniform chip signaling in chip-synchronous CDMA. Consequently, the symmetric sum capacity is further investigated when the zero chip symbol is also utilized for CDMA transmission. The obtained capacity results indicate that nonuniform signaling with {-1,0,+1} chip symbols can lead to an energy efficient CDMA transmission scheme which could achieve energy savings of up to 3 dB over the traditional CDMA with equiprobable {-1, +1} chip symbols.

Multi-user interference (MUI) severely degrades performance in wireless CDMA transmission. Due to the central limit theorem, such interference is usually (near) Gaussian distributed (Vembu and Viterbi, 1996; and Verdu, 1998). Recently, it has been shown that for frequency/time hopping CDMA with single-user demodulation/decoding at the receiver, one can intentionally create appropriate non-Gaussian multi-user interference that allows increasing the capacity up to five times when compared to CDMA with Gaussian MUI (Garba and Bajcsy, 2006 and 2008). This paper considers the impact of direct sequence (DS) spreading on the capacity increases for CDMA with nonGaussian MUI. First, appropriate channel models are constructed for non-Gaussian DS CDMA when traditional single-user matched filter demodulator is used as well as when the optimal single-user CDMA receiver is used. The obtained numerical capacity results show that the nonGaussian CDMA capacity gains can be realized with appropriate CDMA receiver.

The faster-than-Nyquist (FTN) signaling has been of interest in the research literature due to recent advances in pre-coding and equalization techniques allowing practical removal of the intersymbol interference (ISI). Since the structure of ISI is deterministic in the FTN signaling, a data pre-coding at the transmitter to combat ISI is of practical importance. It is shown, however, that such pre-coding in FTN can significantly broaden the transmission spectrum and alter the shape of the power spectral density. In this paper, we analyze the power spectral density of convolutionally pre-coded FTN signals on linear time-invariant channels. We also identify sufficient conditions on the pre-coding coefficients for preventing the spectrum broadening. Simulation results with several pulse shapes are provided which agree with the analysis. The analysis and the simulation show that for many practically used pulses the pre-coded FTN suffers from the spectrum broadening. This suggests that pre-coding in the FTN signaling must be handled with care.

We consider differential MIMO architecture based on Cayley transform (Hassibi and Hochwald, 2002) when the channel state information is available neither at the transmitter nor the receiver. Within this framework, a low complexity iterative receiver is proposed based on a linearly complex space matched filtering signal detection, iterative probabilistic data association (PDA) and turbo equalization. Simulation results on Rayleigh faded MIMO channels illustrate good performances of the designed receiver.

The main objective of this paper is to extend EXIT charts performance analysis technique to turbo iterative decoders with practical arithmetic limitations. We first discuss the methodology for using EXIT charts in this type of a problem. Consequently, we present numerical and simulation results for a turbo compressive coding scheme using different finite precision decoders.

The main objective of this paper is to achieve high normalized spectral efficiency (in bits per OCDMA chip) in optical CDMA network transmission. We design a time-wavelength M-ary transmission scheme that uses error-control coding and trellis coded modulation (TCM), optical M-ary intensity modulation and direct detection at the receiver. We use a probabilistic wavelength-time hopping approach, in order to transmit error-control coded and TCM modulated M-ary data directly through the optical channel without using optical spreading sequences. We present simulation results showing that the proposed OCDMA scheme is robust to Poisson and thermal noise. Hundreds of active users can be supported at target BER of 10-9and achieved spectral efficiency (1.37 bits per OCDMA chip) is almost twice larger that the best result previously reported.

We consider a single "hotspot" microcell where many wireless CDMA users transmit data concurrently using power control. As opposed to traditionally considered binary CDMA transmission or conventional M-ary CDMA, we explore the potential benefits of using generalized M-ary spreading codes. We compute the symmetric sum capacity when single-user detection and decoding are used at the receiver (base station) and observe that the use of appropriate M-ary CDMA can lead to more than threefold increase in transmission rates. It turns out that even using one extra CDMA chip level (i.e., zero) can potentially improve the aggregate data throughput in a microcell by 20-50 percent. Using the insights from this analysis, we generate pseudo-random M-ary spreading codes and explore turbo coded architecture for corresponding M-ary CDMA transmission. Simulation results indicate that the proposed system can support up to 60 to 70 users at bit error rates of 10/sup -4/, with a power control error of up to 1 dB at SNR's encountered in traditional microcells.

We consider uplink multi-user MIMO transmission over slow, frequency non-selective channels affected by uncorrelated and correlated Rayleigh fading. In this paper, we generalize our design of a low complexity MIMO signal detector from the single user case (proposed in N. Mysore et al., (2004), (2005)) to the multi-user setting. We consider turbo-coded transmission where the users employ QPSK-based DS-CDMA modulation and the base-station performs iterative multi-user MIMO decoding. For various antenna configurations and five active users, performance of the proposed system is within about 3.2 dB of the corresponding ergodic capacity limits. We also present a novel performance evaluation method that accurately predicts the bit error rate (BER) for the considered coded MIMO systems. For all presented cases, the numerically evaluated BER curves are within about 0.1 to 0.5 dB of the simulated BER results in the waterfall region.

This paper considers lossless compression of black and white images using recently developed distributed turbo compression techniques. An empirical study of image pixel statistics is initially conducted in order to apply turbo compression algorithms to distributed compression of image rows. In particular, it is noted that while the entropy of the pixels throughout the image does not vary much, the distribution and conditional distributions of pixel values are nonstationary. Corresponding compression bounds are noted, appropriate coding schemes based on turbo-codes are developed and simulation results are reported.

We investigate the joint source-channel coding problem of transmitting nonuniform memoryless sources over binary phase-shift keying-modulated additive white Gaussian noise and Rayleigh fading channels via turbo codes. In contrast to previous work, recursive nonsystematic convolutional encoders are proposed as the constituent encoders for heavily biased sources. We prove that under certain conditions, and when the length of the input source sequence tends to infinity, the encoder state distribution and the marginal output distribution of each constituent recursive convolutional encoder become asymptotically uniform, regardless of the degree of source nonuniformity. We also give a conjecture (which is empirically validated) on the condition for the higher order distribution of the encoder output to be asymptotically uniform, irrespective of the source distribution. Consequently, these conditions serve as design criteria for the choice of good encoder structures. As a result, the outputs of our selected nonsystematic turbo codes are suitably matched to the channel input, since a uniformly distributed input maximizes the channel mutual information, and hence, achieves capacity. Simulation results show substantial gains by the nonsystematic codes over previously designed systematic turbo codes; furthermore, their performance is within 0.74-1.17 dB from the Shannon limit. Finally, we compare our joint source-channel coding system with two tandem schemes which employ a fourth-order Huffman code (performing near-optimal data compression) and a turbo code that either gives excellent waterfall bit-error rate (BER) performance or good error-floor performance. At the same overall transmission rate, our system offers robust and superior performance at low BERs (< 10/sup -4/), while its complexity is lower.

The paper presents a data compression scheme based on serial turbo coding using finite state machine (FSM) encoders and iterative decoding. The scheme is applied to the fixed length to fixed length compression of a single memoryless source, the Slepian-Wolf problem of separate encoding of correlated sources, and joint source-channel coding. Simulation results are presented to document its efficiency.

Summary form only given. All traditional data compression techniques, such as Huffman coding, the Lempel-Ziv algorithm, run-length limited coding, Tunstall coding and arithmetic coding are highly susceptible to residual channel errors and noise. We have previously proposed the use of parallel concatenated codes and iterative decoding for fixed-length to fixed-length source coding, i.e., turbo coding for data compression purposes. The work presented here extends these results and also considers the case when decompression must be done from compressed data corrupted by additive white Gaussian noise (AWGN).

This paper proposes a practical space-time coded architecture that is based on concatenated codes and iterative decoding. Performance results of several systems are presented on MIMO (multi-input, multi-output) wireless channels with flat Rayleigh fading when the receiver has perfect channel state information. Significant performance gains are observed by increasing the number of transmit/receive antennas from two to four as well as by utilizing improved interleaving strategies.

This paper proposes a practical coding scheme for the Slepian-Wolf problem of separate encoding of correlated sources. Finite-state machine (FSM) encoders, concatenated in parallel, are used at the transmit side and an iterative turbo decoder is applied at the receiver. Simulation results of system performance are presented for binary sources with different amounts of correlation. Obtained results show that the proposed technique outperforms by far both an equivalent uncoded system and a system coded with traditional (non-concatenated) FSM coding.

Iterative decoding is used to achieve backward compatible performance improvement in several existing systems. Concatenated coding and iterative decoding are first set up using composite mappings, so that various applications in digital communication and recording can be described in a concise and uniform manner. An ambiguity zone detection (AZD) based iterative decoder, operating on generalized erasures, is described as an alternative for concatenated systems where turbo decoding cannot be performed. The described iterative decoding techniques are then applied to selected wireless communication and digital recording systems. Simulation results and utilization of decoding gains are discussed.

We attempt to improve the performance of an existing wireless packet transmission system that uses coding and transmitter diversity. We view it as a concatenated system, system constructed by "concatenation" of encoding blocks and interleavers at the transmitter. The transmitter structure is improved using a better interleaving scheme, the receiver architecture by applying an iterative decoder with AZD (ambiguity zone detection) structure. This receiver uses generalized erasures, which are resolved in an iterative process. Using this framework, overall encoding and decoding gain of almost 9 dB is achieved with small increase in complexity and decoding delay.

We study error correcting which are constructed by using permutation and in conjunction with concatenation. These include concatenated codes, product codes and turbo codes as special cases. We then extend our approach to a continuous channel, by adopting AZD (ambiguity zone detection) at the receiver, which introduces generalized erasures. Iterative decoding can significantly improve the performance of a coded system that contains a channel with memory (e.g., spectral shaping, ISI, multipath delay), modulation with memory (e.g., trellis coded modulation, continuous phase modulation) and/or diversity. Moreover, it is implementable with low decoding complexity and requires a small decoding delay. Using this framework, we propose two architectures for iterative receivers in an existing wireless packet transmission system. These receivers are fully backward compatible with the existing transmitter, have low decoding complexity and delay, and offer a decoding improvement of several dBs.