Advanced Wireless LAN

The past two decades have witnessed starling advances in wireless LAN technologies that were stimulated by its increasing popularity in the home due to ease of installation, and in commercial complexes offering wireless access to their customers. This book presents some of the latest development status of wireless LAN, covering the topics on physical layer, MAC layer, QoS and systems. It provides an opportunity for both practitioners and researchers to explore the problems that arise in the rapidly developed technologies in wireless LAN

Application of wavelets and artificial neural network for indoor optical wireless communication systems

Abstract This study investigates the use of error control code, discrete wavelet transform (DWT) and artificial neural network (ANN) to improve the link performance of an indoor optical wireless communication in a physical channel. The key constraints that barricade the realization of unlimited bandwidth in optical wavelengths are the eye-safety issue, the ambient light interference and the multipath induced intersymbol interference (ISI). Eye-safety limits the maximum average transmitted optical power. The rational solution is to use power efficient modulation techniques. Further reduction in transmitted power can be achieved using error control coding. A mathematical analysis of retransmission scheme is investigated for variable length modulation techniques and verified using computer simulations. Though the retransmission scheme is simple to implement, the shortfall in terms of reduced throughput will limit higher code gain. Due to practical limitation, the block code cannot be applied to the variable length modulation techniques and hence the convolutional code is the only possible option. The upper bound for slot error probability of the convolutional coded dual header pulse interval modulation (DH-PIM) and digital pulse interval modulation (DPIM) schemes are calculated and verified using simulations. The power penalty due to fluorescent light interference (FL I) is very high in indoor optical channel making the optical link practically infeasible. A denoising method based on a DWT to remove the FLI from the received signal is devised. The received signal is first decomposed into different DWT levels; the FLI is then removed from the signal before reconstructing the signal. A significant reduction in the power penalty is observed using DWT. Comparative study of DWT based denoising scheme with that of the high pass filter (HPF) show that DWT not only can match the best performance obtain using a HPF, but also offers a reduced complexity and design simplicity. The high power penalty due to multipath induced ISI makes a diffuse optical link practically infeasible at higher data rates. An ANN based linear and DF architectures are investigated to compensation the ISI. Unlike the unequalized cases, the equalized schemes don‘t show infinite power penalty and a significant performance improvement is observed for all modulation schemes. The comparative studies substantiate that ANN based equalizers match the performance of the traditional equalizers for all channel conditions with a reduced training data sequence. The study of the combined effect of the FLI and ISI shows that DWT-ANN based receiver perform equally well in the present of both interference. Adaptive decoding of error control code can offer flexibility of selecting the best possible encoder in a given environment. A suboptimal ?soft‘ sliding block convolutional decoder based on the ANN and a 1/2 rate convolutional code with a constraint length is investigated. Results show that the ANN decoder can match the performance of optimal Viterbi decoder for hard decision decoding but with slightly inferior performance compared to soft decision decoding. This provides a foundation for further investigation of the ANN decoder for convolutional code with higher constraint length values. Finally, the proposed DWT-ANN receiver is practically realized in digital signal processing (DSP) board. The output from the DSP board is compared with the computer simulations and found that the difference is marginal. However, the difference in results doesn‘t affect the overall error probability and identical error probability is obtained for DSP output and computer simulations

Turbo Decoding and Detection for Wireless Applications

A historical perspective of turbo coding and turbo transceivers inspired by the generic turbo principles is provided, as it evolved from Shannon’s visionary predictions. More specifically, we commence by discussing the turbo principles, which have been shown to be capable of performing close to Shannon’s capacity limit. We continue by reviewing the classic maximum a posteriori probability decoder. These discussions are followed by studying the effect of a range of system parameters in a systematic fashion, in order to gauge their performance ramifications. In the second part of this treatise, we focus our attention on the family of iterative receivers designed for wireless communication systems, which were partly inspired by the invention of turbo codes. More specifically, the family of iteratively detected joint coding and modulation schemes, turbo equalization, concatenated spacetime and channel coding arrangements, as well as multi-user detection and three-stage multimedia systems are highlighted

Application of wavelets and artificial neural network for indoor optical wireless communication systems

This study investigates the use of error control code, discrete wavelet transform (DWT) and artificial neural network (ANN) to improve the link performance of an indoor optical wireless communication in a physical channel. The key constraints that barricade the realization of unlimited bandwidth in optical wavelengths are the eye-safety issue, the ambient light interference and the multipath induced intersymbol interference (ISI). Eye-safety limits the maximum average transmitted optical power. The rational solution is to use power efficient modulation techniques. Further reduction in transmitted power can be achieved using error control coding. A mathematical analysis of retransmission scheme is investigated for variable length modulation techniques and verified using computer simulations. Though the retransmission scheme is simple to implement, the shortfall in terms of reduced throughput will limit higher code gain. Due to practical limitation, the block code cannot be applied to the variable length modulation techniques and hence the convolutional code is the only possible option. The upper bound for slot error probability of the convolutional coded dual header pulse interval modulation (DH-PIM) and digital pulse interval modulation (DPIM) schemes are calculated and verified using simulations. The power penalty due to fluorescent light interference (FL I) is very high in indoor optical channel making the optical link practically infeasible. A denoising method based on a DWT to remove the FLI from the received signal is devised. The received signal is first decomposed into different DWT levels; the FLI is then removed from the signal before reconstructing the signal. A significant reduction in the power penalty is observed using DWT. Comparative study of DWT based denoising scheme with that of the high pass filter (HPF) show that DWT not only can match the best performance obtain using a HPF, but also offers a reduced complexity and design simplicity. The high power penalty due to multipath induced ISI makes a diffuse optical link practically infeasible at higher data rates. An ANN based linear and DF architectures are investigated to compensation the ISI. Unlike the unequalized cases, the equalized schemes don‘t show infinite power penalty and a significant performance improvement is observed for all modulation schemes. The comparative studies substantiate that ANN based equalizers match the performance of the traditional equalizers for all channel conditions with a reduced training data sequence. The study of the combined effect of the FLI and ISI shows that DWT-ANN based receiver perform equally well in the present of both interference. Adaptive decoding of error control code can offer flexibility of selecting the best possible encoder in a given environment. A suboptimal 'soft' sliding block convolutional decoder based on the ANN and a 1/2 rate convolutional code with a constraint length is investigated. Results show that the ANN decoder can match the performance of optimal Viterbi decoder for hard decision decoding but with slightly inferior performance compared to soft decision decoding. This provides a foundation for further investigation of the ANN decoder for convolutional code with higher constraint length values. Finally, the proposed DWT-ANN receiver is practically realized in digital signal processing (DSP) board. The output from the DSP board is compared with the computer simulations and found that the difference is marginal. However, the difference in results doesn‘t affect the overall error probability and identical error probability is obtained for DSP output and computer simulations.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Performance of Turbo Coded OFDM in Wireless Application

Orthogonal Frequency Division Multiplexing (OFDM) has become a popular modulation method in high speed wireless communications. By partitioning a wideband fading channel into flat narrowband channels, OFDM is able to mitigate the detrimental effects of multi path fading using a simple one- tap equalizer. There is a growing need to quickly transmit information wirelessly and accurately. Engineers have already combine techniques such as OFDM suitable for high data rate transmission with forward error correction (FEC) methods over wireless channels. In this thesis, we enhance the system throughput of a working OFDM system by adding turbo coding. The smart use of coding and power allocation in OFDM will be useful to the desired performance at higher data rates. Error control codes have become a vital part of modern digital wireless systems, enabling reliable transmission to be achieved over noisy channels. Over the past decade, turbo codes have been widely considered to be the most powerful error control code of practical importance. In the same time-scale, mixed voice/data networks have advanced further and the concept of global wireless networks and terrestrial links has emerged. Such networks present the challenge of optimizing error control codes for different channel types, and for the different qualities of service demanded by voice and data

Performance analysis of turbo coded OFDM in wireless application

Orthogonal Frequency Division Multiplexing (OFDM) has become a popular modulation method in high speed wireless communications. By partitioning a wideband fading channel into flat narrowband channels, OFDM is able to mitigate the detrimental effects of multi path fading using a simple one- tap equalizer. There is a growing need to quickly transmit information wirelessly and accurately.Engineers have already combine techniques such as OFDM suitable for high data rate transmission with forward error correction (FEC) methods over wireless channels. In this thesis, we enhance the system throughput of a working OFDM system by adding turbo coding. The smart use of coding and power allocation in OFDM will be useful to the desired performance at higher data rates.Error control codes have become a vital part of modern digital wireless systems,enabling reliable transmission to be achieved over noisy channels. Over the past decade,turbo codes have been widely considered to be the most powerful error control code of practical importance. In the same time-scale, mixed voice/data networks have advanced further and the concept of global wireless networks and terrestrial links has emerged. Such networks present the challenge of optimizing error control codes for different channel types,and for the different qualities of service demanded by voice and data

Adaptive modulation schemes for optical wireless communication systems

High-speed wireless optical communication links have become more popular for personal mobile applications. This is a consequence of the increasing demand from the personal information service boom. Compared to the radio frequency domain, optical wireless communication offers much higher speeds and bit rates per unit power consumption. As stated by the official infrared standard IrDA optical communication enjoys much lower power consumption than Bluetooth, with an inherent security feature while in Line of Sight (LOS) applications. There are also drawbacks such as the infrared radiation cannot penetrate walls as radio frequencies do and interference from the background contribute to the channel dispersions. Focus on the modulation aspects of the optical wireless communication, this thesis try to improve the channel immunity by utilising optimised modulation to the channel. Modulation schemes such as on off keying (OOK), pulse amplitude modulation (PAM) and pulse position modulation (PPM) and pulse position and amplitude modulation PAPM schemes have been validated. The combined power and bandwidth requirements suggest that the adaptive modulation schemes can provide reliability when deployed in a real time channel, resulting in improved system performance. As a result, an adaptive modulation technique is proposed. Extensive simulations of severe noise distraction have been carried out to validate the new scheme. The simulation results indicate that the new scheme can provide increased immunity against channel noise fluctuation at a relatively low complexity. The scheme obtained formed a basis to support reliable mobile optical wireless communication applications. The adaptive scheme also takes the real time channel conditions into account, which is different from existing schemes. Guaranteed system performance can be secured without compromising power and bandwidth efficiency. This is also a new approach to realise reliable optical wireless links. Fuzzy logic control module has been developed to match the adaptive pattern

Adaptive modulation schemes for optical wireless communication systems

High-speed wireless optical communication links have become more popular for personal mobile applications. This is a consequence of the increasing demand from the personal information service boom. Compared to the radio frequency domain, optical wireless communication offers much higher speeds and bit rates per unit power consumption. As stated by the official infrared standard IrDA optical communication enjoys much lower power consumption than Bluetooth, with an inherent security feature while in Line of Sight (LOS) applications. There are also drawbacks such as the infrared radiation cannot penetrate walls as radio frequencies do and interference from the background contribute to the channel dispersions. Focus on the modulation aspects of the optical wireless communication, this thesis try to improve the channel immunity by utilising optimised modulation to the channel. Modulation schemes such as on off keying (OOK), pulse amplitude modulation (PAM) and pulse position modulation (PPM) and pulse position and amplitude modulation PAPM schemes have been validated. The combined power and bandwidth requirements suggest that the adaptive modulation schemes can provide reliability when deployed in a real time channel, resulting in improved system performance. As a result, an adaptive modulation technique is proposed. Extensive simulations of severe noise distraction have been carried out to validate the new scheme. The simulation results indicate that the new scheme can provide increased immunity against channel noise fluctuation at a relatively low complexity. The scheme obtained formed a basis to support reliable mobile optical wireless communication applications. The adaptive scheme also takes the real time channel conditions into account, which is different from existing schemes. Guaranteed system performance can be secured without compromising power and bandwidth efficiency. This is also a new approach to realise reliable optical wireless links. Fuzzy logic control module has been developed to match the adaptive pattern.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Channel Coding in Molecular Communication

This dissertation establishes and analyzes a complete molecular transmission system from a communication engineering perspective. Its focus is on diffusion-based molecular communication in an unbounded three-dimensional fluid medium. As a basis for the investigation of transmission algorithms, an equivalent discrete-time channel model (EDTCM) is developed and the characterization of the channel is described by an analytical derivation, a random walk based simulation, a trained artificial neural network (ANN), and a proof of concept testbed setup. The investigated transmission algorithms cover modulation schemes at the transmitter side, as well as channel equalizers and detectors at the receiver side. In addition to the evaluation of state-of-the-art techniques and the introduction of orthogonal frequency-division multiplexing (OFDM), the novel variable concentration shift keying (VCSK) modulation adapted to the diffusion-based transmission channel, the lowcomplex adaptive threshold detector (ATD) working without explicit channel knowledge, the low-complex soft-output piecewise linear detector (PLD), and the optimal a posteriori probability (APP) detector are of particular importance and treated. To improve the error-prone information transmission, block codes, convolutional codes, line codes, spreading codes and spatial codes are investigated. The analysis is carried out under various approaches of normalization and gains or losses compared to the uncoded transmission are highlighted. In addition to state-of-the-art forward error correction (FEC) codes, novel line codes adapted to the error statistics of the diffusion-based channel are proposed. Moreover, the turbo principle is introduced into the field of molecular communication, where extrinsic information is exchanged iteratively between detector and decoder. By means of an extrinsic information transfer (EXIT) chart analysis, the potential of the iterative processing is shown and the communication channel capacity is computed, which represents the theoretical performance limit for the system under investigation. In addition, the construction of an irregular convolutional code (IRCC) using the EXIT chart is presented and its performance capability is demonstrated. For the evaluation of all considered transmission algorithms the bit error rate (BER) performance is chosen. The BER is determined by means of Monte Carlo simulations and for some algorithms by theoretical derivation