Miranda Nafornita

Wavelet OFDM performance in frequency selective fading channels

The BER performance of a wavelet-based multi-carrier modulation scheme is investigated in this paper. The channel is considered both frequency-selective and time-variant. It is shown that the time-frequency localization of the wavelet carriers has a significant influence on the BER performance, especially at certain transmission scales.

Efficient Pulse Shaping and Robust Data Transmission Using Wavelets

Recent work has shown that the use of wavelets in a data transmission chain brings several advantages. Thus, the wavelet mothers and the associated scale functions can generate orthogonal basis that obey Nyquists first criterion and these basis can be used as pulse shaping waveforms instead of raised cosine filters. Furthermore, robust multicarrier data transmission can be performed using wavelet carriers instead of the classical sine waves proposed by OFDM. By associating these benefits, the road towards new powerful transmission techniques in data transmission systems is widely opened.

Errors per scale statistics for a wavelet OFDM transmission in flat fading channels

Wavelet-based Orthogonal Frequency Division Multiplexing (WOFDM) represents a modern orthogonal modulation technique. In WOFDM, the bits to be transmitted are split into multiple streams, which are simultaneously transmitted at different rates, using wavelet carriers. Every stream is mapped to a different transmission scale and is affected differently by the time-varying radio channel. This influence is studied in the present work by computing some errors per scale measures. These statistics show what are the best transmission scales in the flat, time-variant channel and open the path towards the coded WOFDM, where the coding rate can be adapted on a per scale basis.

The performances of interleavers used in turbo codes

A new type of interleaver, block-random interleaver, is proposed and compared with the principal types of interleavers on the basis of the BER (bit error rate) performances of the turbo code. A recursive systematic convolutional code, 1/3 rate, unpunctured turbo code was used. The convolutional code has the constraint length, K=4 with generator matrix [1, 15/13], in octal representation. The MAP algorithm, 12 iterations were used. A log likelihood ratio (LLR) stop criterion was selected. The BER and FER (frame error rate) for different interleaver lengths were obtained.

Study on inter- and intra-symbol interleaving succession in multi-binary turbo codes

Data blocks for multi-binary turbo codes are structured in the form of data arrays with R×N size, where R is the inputs number of convolutional component code and N is the block length. To achieve interleaving for these blocks are independently performed two interleavings, along the two dimensions of the block. This paper presents a practical study that answers the question: “which is the better ordering of the two interleavings that provides better performance in turbo-codes?”. The results of investigations have shown a correlation between the two interleaving, and the better ordering is: first - interleaving along the R dimension and second - interleaving along the N dimension.

Double-binary RSC convolutional codes selection based on convergence of iterative turbo-decoding process

This paper presents an analysis of the recursive systematic double-binary convolutional codes (RSDBC) and a performance criterion which can be used to establish their hierarchy. This hierarchy serves for the selection of high performance turbo-codes. The criterion already mentioned consists in the convergence of the corresponding iterative turbo decoding process. We investigated the families of codes of memory 2, 3, 4 and 5. The simulation results are presented in two manners: statistically for the entire set of codes and nominal for the best ones.

On using turbo codes over Rice flat fading channels

The turbo code performance over time-varying channels using QPSK modulation is evaluated in this paper. For this purpose we have considered a block random in line (BRL) interleaver. On the basis of this interleaver, we have further simulated the turbo code performance over Rice flat fading channel using 15 iterations. Also, we have studied the impact of the estimation error in the calculation of the channel log-likelihood ratios Lc.

Performance Comparison of Punctured Turbo Codes and Multi Binary Turbo Codes

In this paper we analyze the performance of punctured turbo codes (TCs) and punctured multi binary turbo codes (MBTCs) over additive white Gaussian noise (AWGN) channel in terms of Bit Error Rate (BER) and Frame Error Rate (FER). We consider the original TCs that consist of the parallel concatenation of two identical rate 1/2 recursive systematic convolutional (RSC) codes. We also consider MBTCs that consist of the parallel concatenation of two identical rate 2/3 RSC codes. In order to achieve high spectral efficiency, we focus on codes with higher coding rates, i.e., rates 1/2, 3/5 and 2/3 for both TCs and MBTCs by using puncturing operations. For sake of compatibility with standards IEEE 802.1 In and DVD-T, we consider only codes with moderate data block length, i.e., 1504 bits in all cases. The results are illustrated with examples based binary and duobinary 16-state TCs.

A study on turbo coding systems with /spl pi//4 shifted DQPSK modulation

In this paper some methods of using turbo coding in conjunction with /spl pi//4 shifted differential quadrature phase shift keying (/spl pi//4 shifted DQPSK) modulation are proposed. The models used in the simulation of the running turbo coded system and their BER performances are presented for each case. The turbo coding rate was R=1/3 and R=1/2. The MAP algorithm, 12 iterations were used. A log likelihood ratio (LLR) stop criterion was selected The interleaving length was N=1784 bits. The performances were obtained for AWGN and for flat Rayleigh fading channels.

Designing convolutional codes used in multi-binary turbo codes

Multi-binary turbo codes (MBTCs) have a global performance superior to the classical turbo codes. They also offer some advantages to the uni-binary turbo codes as better convergence and lower error floor. The selection criterion proposed here was the convergence of the MBTCs. We used this criterion in two steps. The first step we made was an exhaustive search over memory-3 component convolutional codes set in conjunction with a random S type interleaver. In the second step we investigated a set of interleavers used in conjunction with the best codes selected from the first step. The searching results were materialized in two MBTCs which outperform with more than 0.2 dB, for Frame Error Rate, FER=10−4, the multi-binary turbo-code with same characteristics, proposed in literature.