Underwater acoustic modem using OFDM

Ankara : The Department of Electrical and Electronics Engineering and the Graduate School of Engineering and Sciences of Bilkent University., 2012.Thesis (Master's) -- Bilkent University, 2012.Includes bibliographical references leaves 52-55.This thesis is about design, simulation and testing of an underwater acoustic modem using OFDM. The thesis work combines a theoretical part, whose objective is to understand the appropriate techniques to deal with the characteristics of the targeted channel, simulations and a practical part regarding the system deployment and experimental tests. There has been a great growing interest in transmitting real-time data and video. Unmanned underwater vehicles (UUVs) for military and scientific applications have become important. Building distributed and scalable underwater wireless sensor networks (UWSN) that will bring significant advantages and benefits to underwater applications, such as ocean observation for scientific exploration, commercial exploitation, coastline protection and target detection in military events has been in the scope of researchers. Based on these, designing a concrete system with high data rate will benefit many underwater acoustic (UWA) applications. The existing systems in literature use single carrier transmission and rely on linear or non-linear equalization techniques to suppress inter-symbol interference (ISI), however this requires complex equalizers and results in low data rates. Therefore we concentrate on multicarrier modulation. In this thesis ZP-OFDM (Zero Padded-Orthogonal Frequency Division Multiplexing) receiver is built, where CFO (Carrier Frequency Offset) compensation, pilot-tone based channel estimation, and data demodulation are carried out on the basis of each OFDM block. The implemented OFDM system has been developed in MATLAB. MATLAB scripts generate a data burst that contained OFDM blocks, and then they are transmitted to the hardware from a laptop by using a Data Acquisition (DAQ) Card. At the other side of the system, the receiver laptop gets the data by using a DAQ Card. As the data is received, MATLAB scripts are demodulated and data is detected. Simulations aim to provide correct implementation of all the algorithms by coupling the generated OFDM signal to a channel using Bellhop underwater channel model and noise addition algorithm, that artificially introduces some of the real channel effects into the signal. The method is tested in a shallow-water experiment at Bilkent Lake. Over a bandwidth of 12 kHz, the data rate is 13.92 kb/s with QPSK modulation, when the number of subcarriers was 1024. Bit-error-rate (BER) is less than 9x10−2 without any coding.Yüksel, Mine MerveM.S

Study of Optical OFDM System for Wireless LAN Applications

The advantages of optical fiber make it possible to extend the data rate transmission and propagation distance. Orthogonal frequency division multiplexing (OFDM) as a multicarrier technique (MC) is used in hybrid optical-wireless system designs because it has the best spectral efficiency to radio frequency (RF) interference and lower multipath distortion. In this dissertation, a study and evaluation of optical OFDM based wireless local area network (W-LAN) systems are presented. The baseband of the OFDM signal is fully transmitted and up-converted to a radio frequency signal. Also, to reduce system costs, simple base stations (BSs) are interconnected to a central office (CO) via an optical fiber. All the required operations are achieved in the CO. The directly modulated laser (DML) and continuous wave (CW) laser are used in the system simulations as optical laser sources. Identical rectangular microstrip patch antennas have been used at the transmitter and the receiver as well. The simulations were carried out for different SMF and MMF lengths, and the variable wireless distance between the transmitting and receiving antennas was in a range of 40 dB to 80 dB. The purpose of this work is to provide a framework for integrating wireless and optical technologies in one system with the presence of OFDM technology. The required microstrip patch antenna parameters for the system are analyzed and designed. The microstrip patch antenna (S-parameters) is loaded into the Optisystem communication software tool in Touchstone format. As a result, this achievement gives a greater impetus to design an integrated optical-wireless system, and simulation results validate the proposed technique. Then, the integration of the microstrip patch antenna and optical OFDM system is achieved, and the performance is intensely studied. The entire system has been presented by developing analytical models and simulations. The system performance results are obtained regarding EIRP, SNR, signal constellations and BER. The results show that this integrated optical wireless link is very robust for carrying OFDM based wireless LAN signals over an optical fiber. Moreover, using an active patch antenna in the system helps to increase the coverage service to more than 30 meters when an SMF of 80 km length is utilized

Millimeter-wave Communication and Radar Sensing — Opportunities, Challenges, and Solutions

With the development of communication and radar sensing technology, people are able to seek for a more convenient life and better experiences. The fifth generation (5G) mobile network provides high speed communication and internet services with a data rate up to several gigabit per second (Gbps). In addition, 5G offers great opportunities of emerging applications, for example, manufacture automation with the help of precise wireless sensing. For future communication and sensing systems, increasing capacity and accuracy is desired, which can be realized at millimeter-wave spectrum from 30 GHz to 300 GHz with several tens of GHz available bandwidth. Wavelength reduces at higher frequency, this implies more compact transceivers and antennas, and high sensing accuracy and imaging resolution. Challenges arise with these application opportunities when it comes to realizing prototype or demonstrators in practice. This thesis proposes some of the solutions addressing such challenges in a laboratory environment.High data rate millimeter-wave transmission experiments have been demonstrated with the help of advanced instrumentations. These demonstrations show the potential of transceiver chipsets. On the other hand, the real-time communication demonstrations are limited to either low modulation order signals or low symbol rate transmissions. The reason for that is the lack of commercially available high-speed analog-to-digital converters (ADCs); therefore, conventional digital synchronization methods are difficult to implement in real-time systems at very high data rates. In this thesis, two synchronous baseband receivers are proposed with carrier recovery subsystems which only require low-speed ADCs [A][B].Besides synchronization, high-frequency signal generation is also a challenge in millimeter-wave communications. The frequency divider is a critical component of a millimeter-wave frequency synthesizer. Having both wide locking range and high working frequencies is a challenge. In this thesis, a tunable delay gated ring oscillator topology is proposed for dual-mode operation and bandwidth extension [C]. Millimeter-wave radar offers advantages for high accuracy sensing. Traditional millimeter-wave radar with frequency-modulated continuous-wave (FMCW), or continuous-wave (CW), all have their disadvantages. Typically, the FMCW radar cannot share the spectrum with other FMCW radars.\ua0 With limited bandwidth, the number of FMCW radars that could coexist in the same area is limited. CW radars have a limited ambiguous distance of a wavelength. In this thesis, a phase-modulated radar with micrometer accuracy is presented [D]. It is applicable in a multi-radar scenario without occupying more bandwidth, and its ambiguous distance is also much larger than the CW radar. Orthogonal frequency-division multiplexing (OFDM) radar has similar properties. However, its traditional fast calculation method, fast Fourier transform (FFT), limits its measurement accuracy. In this thesis, an accuracy enhancement technique is introduced to increase the measurement accuracy up to the micrometer level [E]

Improved Ultra Wideband Communication System through Adaptive Modulation and Spatial Diversity

PhDAdvances in Multimedia communications have shown the need for high data rate wireless links over short distances. This is to enhance flexibility, accessibility, portability and mobility of devices in home and enterprise environment thereby making users more productive. In 2004, the WiMedia group proposed the Multiband Orthogonal Frequency Division Multiplex Ultra Wideband (MB-OFDM UWB) system with a target of delivering data rate of 480Mbps over 3 metres. However, by now no existing commercial UWB product can meet this proposed specification. The project aims to investigate the reason why UWB technology has failed to realise its potential by carrying out detailed analysis and to seek ways of solving the technical problems. Detailed system analyses were carried out on the UWB technology using a commercial UWB product and a MB-OFDM UWB Evaluation kit. UWB channel measurements of different scenarios were carried out in order to characterise both time varying and time invariant channels. The scenarios are the realistic environments where UWB devices are operating with human subjects in various movement patterns. It gives insight into the effects of human object blocking on the MB-OFDM system performance and estimates an acceptable feedback rate in a UWB time varying channel when implementing an adaptive modulation. The adaptive modulation was proposed and implemented in the MB-OFDM system model to demonstrate the improved Bit Error Rate (BER) performance. Modulating bits are varied across the sub-channels depending on the signal to noise ratio (SNR). Sub-channels experiencing severe fading employ lower or no bit-loading while sub-channels with little or no fading utilise higher bit-loading to maintain a constant system data rate. Spatial diversity was employed to exploit different properties of the radio channel to improve performance. Good diversity gain of two receiving diversity systems using maximal ratio combining and antenna selection techniques is demonstrated in the measurements with the different antenna orientations. An antenna selection circuit is designed and implemented working together with AT90CAP9 UWB Evaluation kit, verifying an improved performance of the UWB system in an indoor environment. The maximal ratio combining technique is also implemented and demonstrated to give a better system performance on a test bed after post-processing

Implementation of an OFDM based underwater acoustic modem

Ankara : The Department of Electrical and Electronics Engineering and the Graduate School of Engineering and Sciences of Bilkent University, 2011.Thesis (Master's) -- Bilkent University, 2011.Includes bibliographical references leaves 52-55.In this thesis we designed and implemented an underwater acoustic (UWA) communication system employing multicarrier modulation in the form of orthogonal frequency division multiplexing (OFDM). UWA communication became more popular as there has been a growing interest in transmitting real-time data, such as video and sonar images. There are many applications where these transmissions are used. These applications are underwater wireless sensor networks(UWSN) and unmanned underwater vehicles (UUVs) for military and scientific purposes. Therefore, building an efficient UWA communication system which has a high data rate can improve these applications’ performance signifi- cantly. Currently, many underwater communication systems use single carrier modulation which have limited data rate due to complexity of their receivers, as frequency selectivity of the channel increases when the symbol rate increases, so we preferred to use multicarrier modulation in UWA communication in order to increase data rate of our system. In this thesis, we considered a system that uses zero-padded (ZP) OFDM modulation. Based on ZP-OFDM, we used a receiver model that performs pilot-tone based channel estimation, carrier frequency offset compensation based on least squares (LS) fitting error or null subcarriers if they occur and data demodulation for each OFDM block individually. We used MATLAB environment for implementing our system. The MATLAB scripts generate a data burst that contains OFDM blocks, and then it is transmitted to the hardware from a laptop by using a Data Acquisition (DAQ) Card. At the other side of the system, the receiver laptop gets the data by using a DAQ Card. As the data is received, MATLAB scripts are used for demodulating it. As we built our system, we performed underwater experiments at Bilkent Lake Facility to investigate its performance in a real UWA channel. In our test, a data rate of 13.92 kbps has been achieved with quadrature phase shift keying (QPSK) modulation while the bit-error-rate (BER) was less then 9x10−2 without using any coding.Demirörs, EmrecanM.S

Design, Analysis And Implementation Of Orthogonal Frequency Coding In Saw Devices Used For Spread Spectrum Tags And Sensors

SAW based sensors can offer wireless, passive operation in numerous environments and various device embodiments are employed for retrieval of the sensed data information. Single sensor systems can typically use a single carrier frequency and a simple device embodiment, since tagging is not required. In a multi-sensor environment, it is necessary to both identify the sensor and retrieve the sensed information. This dissertation presents the concept of orthogonal frequency coding (OFC) for applications to SAW sensor technology. OFC offers all advantages inherent to spread spectrum communications including enhanced processing gain and lower interrogation power spectral density (PSD). It is shown that the time ambiguity in the OFC compressed pulse is significantly reduced as compared with a single frequency tag having the same code length and additional coding can be added using a pseudo-noise (PN) sequence. The OFC approach is general and should be applicable to many differing SAW sensors for temperature, pressure, liquid, gases, etc. Device embodiments are shown and a potential transceiver is described. Measured device results are presented and compared with COM model predictions to demonstrate performance. Devices are then used in computer simulations of the proposed transceiver design and the results of an OFC sensor system are discussed

Optical techniques for broadband in-building networks

Optical fibres, which can easily handle any bandwidth demand, have been rolled out to more than 32 million consumer’s homes and professional buildings worldwide up to 2010. The basic technological and economical challenges of fibre-to-the-home (FTTH) has been solved. The current FTTH technology can now providing baseband Gbit Ethernet and high definition TV services to the gates of homes. Thus, the bottleneck for delivery of broadband services to the end users is shifting from the access network to the in-building network. In the meantime, the need for high-capacity transmission between devices inside the building, e.g. between desktop PC and data services, are also rapidly increase. How to bring high bandwidth to the mobile terminals such as laptops, PDAs or cell phones as well as to the fixed terminals such as desktop PCs and HDTV equipment in an all-in-one network infrastructure is a challenge we are facing. Building on the flexibility of the wireless access networks and the latent vast bandwidth of a fibre infrastructure, radio-over-fibre (RoF) techniques have been proposed as a cost-effective solution to the future integrated broadband services in in-building networks. This thesis investigates techniques to deliver high data rate wireless services via in-building networks: high capacity RoF links employing optical frequency multiplication (OFM) and sub-carrier multiplexing (SCM) techniques, with single- or multi-carrier signal formats. The orthogonal frequency division multiplexing (OFDM) format is investigated for the RoF transmission system, particularly with regard to the optical system nonlinearity. For low-cost short-range optical backbone networks, RoF transmission over large-core diameter plastic optical fibre (POF) links has been studied, including the transmission of the WiMedia-compliant multiband OFDM UWB signal over bandwidth-limited large-core POF as well as a full-duplex bi-directional UWB transmission over POF. In order to improve the functionalities for delivery of wireless services of in-building networks, techniques to introduce flexibility into the network architecture and to create dynamic capacity allocation have been investigated. By employing optical switching techniques based on optical semiconductor amplifiers (SOA), an optically routed RoF system has been studied. The dynamic capacity allocation is addressed by investigating one-dimensional and two-dimensional routing using electrical SCM and optical wavelengths. In addition, next to RoF networking, this thesis explores techniques for wired delivery of baseband high capacity services over POF links by employing a multi-level signal modulation format, in particular discrete multi-tone (DMT) modulation. Transmission of 10 Gbit/s data over 1 mm core diameter PMMA POF links is demonstrated, as a competitor to more expensive fibre solutions such as silica single and multimode fibre. A record transmission rate of more than 40 Gbit/s is presented for POF whose core diameter is comparable with silica multimode fibre. Finally, from the network perspective, the convergence of wired and wireless multi-standard services into a single fibre-based infrastructure has been studied. Techniques have been designed and demonstrated for in-building networks, which can convey both high capacity baseband services and broadband radio frequency (RF) services over a POF backbone link. The multi-standard RoF signals carry different wireless services at different radio frequencies and with different bandwidths, including WiFi, WiMax, UMTS and UWB. System setups to carry them together over the same multimode optical fibre based network have been designed and experimentally shown. All the concepts, designs and system experiments presented in this thesis underline the strong potential of multimode (silica and plastic) optical fibre techniques for the delivery of broadband services to wired and wireless devices in in-building networks, in order to extend to the end user the benefits of the broadband FTTH networks which are being installed and deployed worldwide