45 research outputs found
Binary Turbo Coding with Interblock Memory
[[abstract]]We investigate the performance of binary codes T constructed from turbo coding with interblock memory. The encoding of T is implemented by serially concatenating a multiplexer, a multilevel delay processor, and a signal mapper to the encoder of a conventional binary turbo code C. With such a construction, in T, there is some irregularity for the code bits in C. To provide more variety of irregularity, we can construct TC which is obtained by passing only a fraction of C through a multilevel delay processor and a signal mapper. We propose iterative decoding between adjacent codewords (IDAC), which provides error performance much better than the iterative decoding within a single codeword (IDSC). Simulation shows that T can have a lower error floor than C for either short or long code length. In some cases, TC can provide better error floors and waterfall regions than C.[[fileno]]2030133030003[[department]]電機工程å¸
A turbo FDE technique for reduced-CP SC-based block transmission systems
For conventional cyclic-prefix (CP)-assisted block transmission systems, the CP length is selected on the basis of the expected maximum delay spread. With regard to single-carrier (SC)-based block transmission implementations, a full-length CP
is recommendable, since it allows good performances through the
use of simple frequency-domain equalization (FDE) techniques.
In this letter, a soft-decision-directed correction (SDDC)-aided
turbo FDE technique is presented for reduced-CP SC-based block
transmission systems using conventional frame structures. The
relations with some already known iterative FDE techniques are
established, and a set of performance results is reported and discussed.
The advantages of the proposed approach are emphasized,
namely, the possibility of approximately achieving (besides the
obvious bandwidth efficiency gain) the maximum power efficiency
gain that a strong CP reduction allows.Fundação para a Ciencia e Tecnologia (FCT), Centro de Análise e processamento de Sinais (CAPS
Estimation and detection techniques for doubly-selective channels in wireless communications
A fundamental problem in communications is the estimation of the channel.
The signal transmitted through a communications channel undergoes distortions
so that it is often received in an unrecognizable form at the receiver.
The receiver must expend significant signal processing effort in order to be
able to decode the transmit signal from this received signal. This signal processing
requires knowledge of how the channel distorts the transmit signal,
i.e. channel knowledge. To maintain a reliable link, the channel must be
estimated and tracked by the receiver.
The estimation of the channel at the receiver often proceeds by transmission
of a signal called the 'pilot' which is known a priori to the receiver.
The receiver forms its estimate of the transmitted signal based on how this
known signal is distorted by the channel, i.e. it estimates the channel from
the received signal and the pilot. This design of the pilot is a function of the
modulation, the type of training and the channel. [Continues.
Wavelet-based distributed source coding of video
Publication in the conference proceedings of EUSIPCO, Antalya, Turkey, 200
A reduced-CP approach to SC/FDE block transmission for broadband wireless communications
For conventional cyclic prefix (CP)-assisted single-carrier/frequency-domain equalization (SC/FDE) implementations, as well as for orthogonal frequency-division multiplexing (OFDM) implementations, the CP length is known to be selected on the basis of the expected maximum delay spread. Next, the data block size can be chosen to be large enough to minimize the CP overhead, yet small enough to make the channel variation over the block negligible. This paper considers the possibility of reducing the overall CP assistance, when transmitting sequences of SC blocks, while avoiding an excessively long fast Fourier transform window for FDE purposes and keeping good FDE performances through low-complexity, noniterative receiver techniques. These techniques, which take advantage of specially designed frame structures, rely on a basic algorithm for decision-directed correction (DDC) of the FDE inputs when the CP is not long enough to cope with the time-dispersive channel effects. More specifically, we present and evaluate a novel class of reduced-CP SC/FDE schemes, which takes advantage of a special frame structure for replacing "useless" CP redundancy by fully useful channel coding redundancy, with the help of the DDC algorithm. When using the DDC-FDE technique with these especially designed frame structures, the impact of previous decisions, which are not error-free, is shown to be rather small, thereby allowing a power-efficiency advantage (in addition to the obvious bandwidth-efficiency advantage) over conventional block transmission implementations under full-length CP. Additionally, the DDC algorithm is also shown to be useful to improve the power efficiency of these conventional implementations.Fundação para a Ciencia e Tecnologia (FCT), Centro de Análise e processamento de Sinais (CAPS
Factor graph based detection approach for high-mobility OFDM systems with large FFT modes
In this article, a novel detector design is proposed for orthogonal frequency division multiplexing (OFDM) systems over frequency selective and time varying channels. Namely, we focus on systems with large OFDM symbol lengths where design and complexity constraints have to be taken into account and many of the existing ICI reduction techniques can not be applied. We propose a factor graph (FG) based approach for maximum a posteriori (MAP) symbol detection which exploits the frequency diversity introduced by the ICI in the OFDM symbol. The proposed algorithm provides high diversity orders allowing to outperform the free-ICI performance in high-mobility scenarios with an inherent parallel structure suitable for large OFDM block sizes. The performance of the mentioned near-optimal detection strategy is analyzed over a general bit-interleaved coded modulation (BICM) system applying low-density parity-check (LDPC) codes. The inclusion of pilot symbols is also considered in order to analyze how they assist the detection process
Neural Network Equalizers and Successive Interference Cancellation for Bandlimited Channels with a Nonlinearity
Neural networks (NNs) inspired by the forward-backward algorithm (FBA) are
used as equalizers for bandlimited channels with a memoryless nonlinearity. The
NN-equalizers are combined with successive interference cancellation (SIC) to
approach the information rates of joint detection and decoding (JDD) with
considerably less complexity than JDD and other existing equalizers.
Simulations for short-haul optical fiber links with square-law detection
illustrate the gains of NNs as compared to the complexity-limited FBA and Gibbs
sampling.Comment: Submitted to IEEE Trans. Commun. on January 11, 2024
Symbol by Symbol Soft-Input Soft-Output Multiuser Detection for Frequency Selective Mimo Channels
We introduce a symbol by symbol, soft-input soft-output (SISO) multiuser detector for frequency selective multiple-input multiple-output (MIMO) channels. The basic principle of this algorithm is to extract a posteriori probabilities (APPs) of all interfering symbols at each symbol interval and then feed these updated APPs as a priori probabilities (apPs) for joint APP extraction in the next symbol interval. Unlike nearoptimal block oriented sphere decoding (SD) and soft decision equalization (SDE), the computational complexity of this updating APP (UA) algorithm is linear in the number of symbols but the exponential computational load of optimal joint APP extraction makes the basic UA impractical. To decrease computations we replace the optimal joint APP extractor by a groupwise SISO multiuser detector with a soft sphere decoding core. The resulting reduced complexity updating APP (RCUA) equalizer is flexible in different situations and outperforms the traditional sub-optimal MMSE-DFE without increasing the computational costs substantially