Kadir Turk

Experimental Ber Performance Evaluation of OFDM and Single Carrier Transmissions in Real-Time Wimax Radio

Field trails of orthogonal frequency division modulation (OFDM) and single carrier (SC) transmissions are presented in this paper which puts forward experimentally obtained BER performances ahead of simulation works submitted in the literature, instead of giving raw error performance results, experimental studies are also extended to calculate matched filter bound for both OFDM and SC systems, which matches the theoretical limit of real-time wireless medium.

Adaptive Demodulation Using Rateless Codes Based on Maximum a Posteriori Probability

Adaptive demodulation (ADM) using rateless codes has been considered as an alternative solution for rate adaptive systems. In this paper, we shall propose a maximum a posteriori probability (MAP) based ADM algorithm to select the bits to demodulate rather than using decision regions set (DRS) as in conventional ADM systems. Its main difference is that our demodulated bit selection is implemented by evaluating all bits in the data packet instead of per symbol. Therefore, the probability of discarding incorrect bits will increase, resulting in bit error rate (BER) performance improvement. In addition, our developed technique can adjust the demodulated bits rate to any rational rate and can be easily applied to any modulation scheme. Various simulations show that our proposed MAP based ADM technique significantly outperforms the conventional ADM algorithm in term of BER.

Experimental BER Performance Evolution of Equalizations and Matched Filter Bounds for Single-Carrier WiMax Radio in 3.5 GHz

This paper presents an experimental evaluation of bit-error-rate (BER) performances for adaptive training algorithms and obtaining matched filter bound in real-time WiMax (3.5 GHz) radio channels. Without involving with any modified or improved versions, two conventional adaptive equalizer training methods, the least mean squares (LMS) and recursive least squares (RLS), are implemented in a C code running over sampled received sequence and their performances are compared in different modulation techniques before and after coding. In experimental trails the obtained channel impulse responses were generally non-minimum phase and the obtained BER performance of receiver using LMS training has been quite close to whom using RLS particularly after coding, in real-time channel conditions.

Simplified Early Stopping Criterion for Belief-Propagation Polar Code Decoders

As the first theoretically proven capacity-achieving error correction code, polar codes have become a milestone in information theory field, which draw serious attention by its low complexity encoding and decoding structures. For the decoding section, studies are focused on efficient and low complex algorithms based on successive cancellation and belief-propagation (BP) decoders. To reduce computational complexity of BP-based decoders further, early stopping methods that avoid unnecessary iterations can be used. In this letter, we propose a reduced complexity early stopping method for BP-based polar code decoders. The proposed method is based on the hypothesis that observing only a small cluster of information bits polarized to the highest error probabilities is enough to detect successful decoding. Simulation results show that the proposed early stopping criterion significantly reduces the computational complexity of successful decoding detection as well as the total operation numbers of the whole decoding process compared with previous methods in the literature.

Reduced-Complexity Decoding of LT Codes

In this paper, the belief propagation (BP) based approximation methods for low-density parity-check codes are adapted to the Luby transform soft decoder structure in order to reduce its computational complexity. Moreover, the log-likelihood ratio based adaptive demodulation algorithm is combined with the BP and BP-based algorithms to further reduce the computational complexities and optimum key parameters are determined for normalized min-sum and offset min-sum algorithms. The bit error rate performances of the algorithms over the binary input additive white Gaussian noise channel are obtained by both theoretically and simulations. For theoretical analysis, the Monte-Carlo based density evolution method is used. In addition, computational complexity analyzes of methods are presented. Results show that the computational complexity can be reduced significantly by using combined methods which cost limited signal to noise ratio loss.

BP-based approximation methods for rateless codes

In this letter, belief propagation (BP) based approximation methods for low density parity check (LDPC) codes are adapted to the Luby transform (LT) soft decoder structure in order to reduce its computational complexity. The bit error rate (BER) performances of the algorithms over the binary input additive white Gaussian noise (BIAWGN) channel are obtained by both theoretically and simulations. For theoretical analysis, the Monte-Carlo density evolution (MC-DE) method is used. In addition, computational complexity analyzes of methods are presented. Results show that the computational complexity can be significantly decreased with a limited performance loss cost.

Dynamic Look-Up-Table-Based Maximum a Posterior Probability Algorithm

In this paper, a Look-Up-Table (LUT) based calculation for implementing log-likelihood ratio (LLR) of the Maximum a Posterior (MAP) decoder is introduced and analysed. In the region of low signal to noise ratio, the analysed performances of turbo coding have been found very satisfying. However, when implementing the MAP turbo decoder, the required calculation for LLR is too complex prohibiting its applications. In order to reduce the complexity a dynamic-LUT based simplification is proposed whereas a static-LUT never converge the expectations, since the limited size and resolution of LUT dramatically degrade the performance. In order to maintain simplicity for a high performance implementation, a dynamic LUT, which has partial resolutions in separate decision regions and being re-calculated for further iterations of decoding, is proposed. One of the most important results obtained is that our proposed dynamic-LUT based MAP algorithm removes “ln(·)” process, which is the natural logarithm in LLR’s calculation. Therefore, it reduces high computational complexity in the MAP algorithm with some reasonable performance degradations.

A passive acoustic based system to locate leak hole in underwater natural gas pipelines

Abstract Underwater natural gas pipelines can be punctured for a variety of reasons, but the most notable are corrosion and aging. This study proposes a novel passive acoustic based system, to detect acoustic signals, locate the leak holes, and determine the size of the leak holes remotely. The nature of acoustic signals, which are generated by leakages in underwater natural gas pipelines, is also examined. The success of this proposed localization method, which is based on the received signal strength technique, is analyzed by numerical studies and simulation works. Parameters, which are used in the numerical studies, are taken from a hypothetical pipeline whose specifications are similar to Maghreb-Europe Gas pipeline. The proposed method is examined for various measurement numbers, underwater ambient noises, the diameters of the leak holes and receiver numbers. It is shown that leakages can be located with low average position errors from several kilometers by depending on underwater ambient noise, detection method, receiver number, source strength and measurement number.

Remote leak detection for underwater natural gas pipelines

Undewater natural gas pipelines whose numbers and ages are increasing day by day can be punctured because of various reasons. In this study, nature of acoustic signals generated by leakages on pipelines is examined and a novel passive acoustic based system is proposed to detect the acoustic signals remotely, determine size of the leak hole and estimate approximate distance of the leakage. The method is examined by executing some numerical studies. In these numerical studies offshore part of Maghreb-Europe gas (MEG) pipeline which is still in use is used as an example. Obtained results revealed that the leakages can be detected from tens of kilometers. Localization of the leakage is also possible by combining proposed method with appropriate methods in literature.

Rate adaptive system for visible light communications

Visible light communications (VLC) use light emitting diodes (LEDs) for both illumination and data transmission. In this work, we propose a rate adaptive system based on Raptor codes for VLC system. We consider realistic channel by using a model room with multiple LED armatures. Chosen LEDs are commercially available (Cree Xlamp ML-C). It is assumed that LEDs simultaneously transmit same data and the VLC receiver moves around in the room. Simulation results show that proposed rate adaptive system gives seamless rate adaptation and significantly improves the spectral efficiency.