Zheng Zhang

Capacity-approaching turbo coding and iterative decoding for relay channels

In this paper, we design turbo-based coding schemes for relay systems together with iterative decoding algorithms. In the proposed schemes, the source node sends coded information bits to both the relay and the destination nodes, while the relay simultaneously forwards its estimate for the previous coded block to the destination after decoding and re-encoding. The destination observes a superposition of the codewords and uses an iterative decoding algorithm to estimate the transmitted messages. Different from the block-by-block decoding techniques used in the literature, this decoding scheme operates over all the transmitted blocks jointly. Various encoding and decoding approaches are proposed for both single-input single-output and multi-input multi-output systems over several different channel models. Capacity bounds and information-rate bounds with binary inputs are also provided, and it is shown that the performance of the proposed practical scheme is typically about 1.0-1.5 dB away from the theoretical limits, and a remarkable advantage can be achieved over the direct and multihop transmission alternatives.

Capacity Approaching Turbo Coding For Half-Duplex Relaying

In this paper, we develop capacity-approaching turbo-coding schemes for half-duplex relay systems as an extension of our previous work on coding for full-duplex relays. We consider the use of specific signal constellations (e.g., binary phase-shift keying) in transmission, develop practical coding schemes to be used at the source and the relay nodes, and describe a suitable information combining technique at the destination node. Unlike the full-duplex relay systems, the destination node does not perform joint decoding of multiple consecutive blocks; instead, it works with one frame at a time. Furthermore, for the half-duplex relaying scheme, the optimization of the length of the listening period for the relay node is an issue. By utilizing information theoretical tools, we perform this optimization and use it in the development of our capacity-approaching coding/decoding schemes. Specifically, when the fraction of time turns out to be less than the transmission rate, the relay node is unable to decode all the information bits transmitted, and a partial decoding approach has to be used. Through a comprehensive set of examples, we observe that the proposed scheme is promising to approach the corresponding information theoretical limits (bounds). In particular, for all the cases studied, we have obtained bit error rates of 10-5 or lower within 1--1.5 dB (in most cases, almost within 1.2 dB) of the constrained capacity under a variety of channel conditions. Extensions of the proposed scheme to coded modulation and to multiple-input multiple-output systems are also described.

Achievable information rates and coding for MIMO systems over ISI channels and frequency-selective fading channels

We propose a simulation-based method to compute the achievable information rates for general multiple-input multiple-output (MIMO) intersymbol interference (ISI) channels with inputs chosen from a finite alphabet. This method is applicable to both deterministic and stochastic channels. As an example of the stochastic MIMO ISI channels, we consider the multiantenna systems over frequency-selective fading channels, and quantify the improvement in the achievable information rates provided by the additional frequency diversity (for both ergodic and nonergodic cases). In addition, we consider the multiaccess multiantenna system and present some results on the achievable information-rate region. As for the deterministic MIMO ISI channels, we use the binary-input multitrack magnetic recording system as an example, which employs multiple write and read heads for data storage. Our results show that the multitrack recording channels have significant advantages over the single-track channels, in terms of the achievable information rates when the intertrack interference is considered. We further consider practical coding schemes over both stochastic and deterministic MIMO ISI channels, and compare their performance with the information-theoretical limits. Specifically, we demonstrate that the performance of the turbo coding/decoding scheme is only about 1.0 dB away from the information-theoretical limits at a bit-error rate of 10/sup -5/ for large interleaver lengths.

Capacity approaching turbo coding for half duplex relaying

In this paper, we develop capacity approaching turbo coding schemes for half-duplex relay systems as an extension of our previous work on the full-duplex relay systems. We design the codes to be used at the source and the relay nodes, and develop an information combining technique at the destination node. In addition, by utilizing information theoretical results, we compute the optimal fraction of time during which the relay node should listen, and use it in the design of capacity approaching coding/decoding schemes. We observe that the performance of the practical coding schemes proposed is about 1.2 dB away from the theoretical limits (for a variety of channel models)

Capacity approaching codes for relay channels

In this paper, turbo-based coding scheme for relay systems together with iterative decoding algorithms is designed. The performance of the proposed schemes is about 1.0-1.5 dB away from the information theoretical limits for various channel models.

Information rates of binary-input intersymbol interference channels with signal-dependent media noise

We introduce a simulation-based method to compute the information rates of intersymbol interference (ISI) channels with additive colored Gaussian noise and/or signal-dependent Gaussian noise when the inputs are binary and independent identically distributed. The method extends the idea advanced by Arnold and Loeliger (2001), which focuses on the ISI channels with additive white Gaussian noise (AWGN). With the new method, we can compute the information rates of the Lorentzian channel with media noise that represents a suitable model for practical magnetic recording channels. We illustrate the use of the technique via several examples and show that media noise is preferable to AWGN in terms of the achievable information rates, at low signal-to-noise ratios, in particular. We also present examples of turbo codes for Lorentzian channels with media noise and compare the performance with the achievable information rates. The results demonstrate, not surprisingly, that improved detectors are necessary to achieve the channel capacity for magnetic recording channels when the media noise is dominant.

Information rates and coding for wireless MIMO relay channels

In this paper, we design turbo-based coding/decoding schemes for relay systems with multiple transmit/receive antennas at the respective terminals. In the proposed scheme, the source node sends coded information bits to both the relay and the destination nodes, while the relay forwards simultaneously its estimate for the previous coded block to the destination after decoding and re-encoding. Then, the destination observes a superposition of the codewords and uses an iterative decoding algorithm to estimate the transmitted messages. We also provide the capacity bounds and information rate bounds with binary inputs. It is shown that the performance is typically about 1.0-1.5 dB away from the theoretical limits, and a remarkable advantage can be achieved over the direct and multihop transmission schemes.

On information rates of single-track and multi-track magnetic recording channels with intertrack interference

We compute the achievable information rates for multi-track magnetic recording channels under the binary i.i.d. input constraint using a method based on Monte-Carlo simulations.

Achievable information rates of multi-antenna systems over frequency-selective fading channels with constrained inputs

Information rates of multiple-input multiple-output (MIMO) systems over frequency-selective fading channels are computed under the constraint of independent identically distributed inputs chosen from a finite alphabet. The method uses a simulation based approach that employs the sum-product algorithm. The setting includes as special cases the single-input single-output systems over frequency-selective fading channels and the MIMO systems over flat fading channels. Both ergodic and nonergodic channels are considered, and examples are provided for the case of binary signaling.

Intersymbol interference channels with signal-dependent non-Gaussian noise: estimation of achievable information rates

In this letter, we calculate the achievable information rates for the intersymbol interference channels with general signal-dependent correlated noise under the constraint that the inputs are chosen from a finite alphabet. The proposed method employs canonical multivariate density estimation techniques. This method is important in that it can be used for accurate estimation of the achievable information rates for magnetic recording channels with media noise, where higher order media noise models can be taken into account instead of the first-order model.