M.N. Hadad

Simultaneous correlation of complementary set of sequences using a transpose generation approach

Complementary sets of sequences are currently being applied to signal coding, radar, and multi-user systems, among others. Their particular mathematical properties make them adequate for multi-emission and noisy environments. Nowadays sustained efforts are being devoted to reduce the calculations involved in the generation and/or correlation of these signals by means of recursive algorithms. Some authors have proposed efficient algorithms that are based on modular architectures made up of adders, multipliers and delays. This work introduces a new approach to correlation algorithms of complementary sets of sequences, which is based on a transposition of the generation process. This approach allows to notoriously reduce calculations, and enables the simultaneous correlation of M sequences, without adopting time multiplexing schemes or complex parallel implementations. The correlation algorithm is theoretically demonstrated and its calculation performance is evaluated in a hardware reconfigurable platform. A comparison with other algorithms is included, considering the amount of calculations as a function of the length of the sequences.

Generation and correlation algorithms for ternary complementary pairs of sequences of length 3·2n

Binary complementary pairs of sequences, which are available for certain even length values L=2ni¾?10mi¾?26p, are very interesting for applications with high noise levels and/or highly attenuated signals. To extend the range of useful lengths, some authors have defined ternary complementary pairs of sequences. These sequences have been approached from a theoretical perspective, but further research should be conducted regarding the architectures to process them. This letter describes algorithms for generating and performing the correlation of these sequences using a minimum amount of calculations. These algorithms allow to work with sequences of length 3i¾?2n, making it possible to attain a wider range of lengths, and, as a consequence, a wider range of noise immunity in some applications. The proposed approach uses a particular delay arrangement that minimizes the memory requirements in hardware applications. The procedure described could also be used in ternary complementary pairs generated from primitives of length different from 3. Copyright

Dynamic Characterization and Equalization of a Power Line Communication Channel

Power Line Communication (PLC) systems need signal processing algorithms in order to recover the transmitted signals from the high degrading medium. In the literature exist some techniques that work on the basis of a constant, known channel, but it was demonstrated that the PLC channel is time variant, therefore these techniques lose efficiency. This work presents a dynamic equalization algorithm computed in the time domain, where the channel characterization is done by a recursive least squares algorithm using the transmitted data as reference. The proposal was tested with simulations and was statistically validated using in time variant PLC channel models, obtaining a lower error rate than other methods.

Improved architecture of complementary set of sequences correlation by means of an inverse generation approach

System coding is a growing trend in all fields of engineering. Many different algorithms have been developed and studied for applications in signal processing, radar and multi-emission systems, among others. One of the most interesting algorithms, among these, is the complementary sets of sequences (CSS) given their potential and simplicity. They are characterised by a distinctive correlation and orthogonality properties. Nowadays, sustained efforts are being devoted to reducing the calculations involved in the generation and/or correlation of these sequences by means of recursive algorithms. Some authors have brought forward efficient algorithms that are based on modular architectures made up of adders, multipliers and delays. This work introduces an inverse generation approach to perform the correlation of CSS. This approach allows one to substantially reduce calculations, and enables the simultaneous correlation of M sequences, adopting neither time-multiplexing schemes nor complex parallel implementations. This is theoretically demonstrated by means of generation and correlation algorithms. An analysis of the performance and efficiency is then conducted in a reconfigurable hardware platform. The proposal represents an advance in the practical application of these sequences in the above-mentioned fields.

Broadband PLC-channel equalisation in the frequency domain based on complementary sequences

Multipath channels, like power lines, have a periodic time-variant response that impacts on data transmission. Power Line Communications (PLC) performance, in the context of a cyclic-prefix single carrier modulation scheme, can benefit from frequency domain equalisation techniques. This study proposes a frequency-domain dynamic characterisation and equalisation algorithm based on the properties of complementary sequences (CSs). This proposal takes advantage of CS properties to reduce the complexity of the algorithm by performing all the operations in the frequency domain, and without the necessity of noise/variance estimators. The proposal is compared to some well-known methods like zero forcing and minimum mean-square error (MMSE) through the transmission of data under different PLC channels. Bit error rate (BER) is also measured using Middleton Class A impulse noise (IN) model and the performance of all methods is finally evaluated under a time-variant PLC channel model showing the importance of dynamic equalisation on PLC systems. Reported computational resources and simulations show that the proposal is four time faster than MMSE and improves the BER performance by up to 4 dB. In addition, the proposed identification algorithms shows to work properly even in PLC channels with attenuations higher than 40 dB and severe IN scenarios.

Flexible platform for coding evaluation in narrowband power line communication

Power line communications (PLC) represent a key part of smart grid techonologies. PLC provides a bidirectional, secure, decentralized and cost-effective communication infrastructure to interconnect and control the grid, and also, devices connected to it. Moreover, it is fairly well known that power lines were not designed to transmit information. PLC signals coexist in the medium with different kind of colored and impulsive noises, so, the complexity to achieve high bit rates and low error transmissions are really important. In this paper it is proposed the use of Complementary Sequences to encode transmited data in order to improve the quality and accuracy of the communication. This is done through the implementation of a bidirectional narrowband PLC system designed to transmit encoded information over low voltage networks. Experimental results are conformed by transmissions along more than 100 meters of a university laboratory network, which clearly demonstrates the benefits of the codification process. The main control of the system is carried out by two independent Spartan 6 FPGAs.

Hardware optimization of Generalized Pairwise Complementary sequences generation

Generalized Pairwise Complementary (GPC) sequences are increasingly being used in many applications due to their properties, which allow uncorrelated sequences generation from a base pair. The generation of these sequences is conducted by iterative algorithms developed to be implemented in hardware platforms. However, in order to reduce even further the amount of resources required for the implementation, these algorithms can be improved with digital synthesis as the final goal. This work proposes an improved GPC sequences generator developed for FPGA platforms, which notoriously reduces resources requirements by applying some concepts developed for Golay sequences generation. FPGA implementation is performed with generic parameters to evaluate and compare it with the straightforward approach.

Channel estimation and equalization of broadband PLC systems - Part 1: Complementary Sequences based channel estimation in OFDM

In the context of broadband Power Line Communications (PLC), this work proposes an estimation and equalization method for block-pilot OFDM systems. The proposal is based on the correlation properties of Complementary Sequences (CS), performing all the operations in the frequency domain, which allows to reduce communication errors and the overall computational effort. The performance of the method is compared with other approaches, as the Least-Squares (LS) and Linear Minimum Mean-Square Error (LMMSE). Simulations were performed by using two realistic PLC channels, as well as additive white Gaussian noise (AWGN) and diverse configurations of impulse noise (IN) modeled by Middleton Class A distribution (MCA). Results are reported as Bit Error-Rate (BER) graphs, showing that the proposal produces better results than LS, approaching to the good performance of LMMSE but with lower computational requirements.

Channel estimation and equalization of broadband PLC systems - Part 2: Comparison between Single Carrier and OFDM approaches

High-speed broadband power line communications (BB-PLC) have become a good option for all residential subscribers. Today regulations imply the use of multi-carrier (MC) systems, like orthogonal frequency-division multiplexing (OFDM) or, as an alternative, the use of single-carrier (SC) technologies as main modulation scheme. In this work, it is proposed a complementary sequences (CS) based frequency domain equalization (FDE) scheme for use in SC systems, and it is compared with zero forcing (ZF) and minimum mean-square error (MMSE) techniques. Finally, the present proposal and previously proposed OFDM PLC scheme (Part 1) will be discussed and compared through realistic simulations carried out by using different Middleton Class A (MCA) impulse noise model and by using two PLC channel models available in the literature.

Simultaneous generation and correlation of complete sets of generalized pairwise complementary sequences

Summary New coding schemes are increasingly being developed to adapt multisensor and communication systems to the requirements of the current technological environment. In some cases, the practical implementation of these schemes involves a great amount of signal processing operations. In order to achieve and make suitable their use in different platforms, efficient algorithms are required to process coding. In the last years, a new kind of complementary sequences, known as Generalized Pairwise Complementary sequences, has been proposed. These sequences provide high noise immunity when they are applied to multiuser systems, as well as a low cross-correlation, which is convenient in those applications. The aim of this paper is to propose optimized generation and correlation architectures for Generalized Pairwise Complementary sequences that would allow to process a complete set using a reduced amount of operations. An analytical demonstration is provided, with a final comparison to evaluate the reduction with regard to other algorithms. Copyright