Dark signalling and code division multiple access in an optical fibre LAN with a bus topology

This thesis describes an optical fibre network that uses a bus topology and Code Division Multiple Access (CDMA). Various potential configurations are analysed and compared and it is shown that a serious limitation of optical CDMA schemes using incoherent correlators is the effect of optical beating due to the presence of multiple incoherent optical signals at the receiver photodiode. The network proposed and analysed in this thesis avoids beating between multiple optical fields because it only uses a single, shared, optical source. It does this through the SLIM (Single Light-source with In-line Modulation) configuration in which there is a continuously-operating light source at the head-end of a folded bus, and modulators at the nodes to impose signals on the optical field in the form of pulses of darkness which propagate along the otherwise continuously bright bus. Optical CDMA can use optical-fibre delay-line correlators as matched filters, and these may be operated either coherently or incoherently.Coherent operation is significantly more complex than incoherent operation, but incoherent correlators introduce further beating even in a SLIM network. A new design of optical delay-line correlator, the hybrid correlator, is therefore proposed, analysed and demonstrated. It is shown to eliminate beating. A model of a complete network predicts that a SLIMbus using optical CDMA with hybrid correlators can be operated at TeraBaud rates with the number of simultaneous users limited by multiple access interference (MAI), determined only by the combinatorics of the code set

Power Control In Optical CDMA

Optical CDMA (OCDMA) is the multiplexing technique over the fiber optics medium to increase the number of users and this is a step towards all optical Passive Optical Networks (PON). Optical OFDM, WDM and Optical TDM have also been studied in this thesis which are also candidates to all optical passive optical networks. One of the main features of Optical CDMA over other multiplexing techniques is that it has smooth capacity. The capacity of OCDMA is constrained by the interference level. Hence, when some users are offline or requesting less data rates, then the capacity will be increased in the network. Same feature could be obtained in other multiplexing techniques, but they will need much more complicated online organizers. However, in OCDMA it is critical to adjust the transmission power to the right value; otherwise, near-far problem may greatly reduce the network capacity and performance. In this thesis Power control concepts are analyzed in optical CDMA star networks. It is applied so that the QoS of the network get enhanced and all users after the power control have their desired signal to interference (SIR) value. Moreover, larger number of users can be accommodated in the network. Centralized power control algorithm is considered for this thesis. In centralized algorithm noiseless case and noisy case have been studied. In this thesis several simulations have been performed which shows the QoS difference before and after power control. The simulation results are validated also by the theoretical computation.fi=Opinnäytetyö kokotekstinä PDF-muodossa.|en=Thesis fulltext in PDF format.|sv=Lärdomsprov tillgängligt som fulltext i PDF-format

Improved quality block-based low bit rate video coding.

The aim of this research is to develop algorithms for enhancing the subjective quality and coding efficiency of standard block-based video coders. In the past few years, numerous video coding standards based on motion-compensated block-transform structure have been established where block-based motion estimation is used for reducing the correlation between consecutive images and block transform is used for coding the resulting motion-compensated residual images. Due to the use of predictive differential coding and variable length coding techniques, the output data rate exhibits extreme fluctuations. A rate control algorithm is devised for achieving a stable output data rate. This rate control algorithm, which is essentially a bit-rate estimation algorithm, is then employed in a bit-allocation algorithm for improving the visual quality of the coded images, based on some prior knowledge of the images. Block-based hybrid coders achieve high compression ratio mainly due to the employment of a motion estimation and compensation stage in the coding process. The conventional bit-allocation strategy for these coders simply assigns the bits required by the motion vectors and the rest to the residual image. However, at very low bit-rates, this bit-allocation strategy is inadequate as the motion vector bits takes up a considerable portion of the total bit-rate. A rate-constrained selection algorithm is presented where an analysis-by-synthesis approach is used for choosing the best motion vectors in term of resulting bit rate and image quality. This selection algorithm is then implemented for mode selection. A simple algorithm based on the above-mentioned bit-rate estimation algorithm is developed for the latter to reduce the computational complexity. For very low bit-rate applications, it is well-known that block-based coders suffer from blocking artifacts. A coding mode is presented for reducing these annoying artifacts by coding a down-sampled version of the residual image with a smaller quantisation step size. Its applications for adaptive source/channel coding and for coding fast changing sequences are examined

Roadmap of optical communications

© 2016 IOP Publishing Ltd. Lightwave communications is a necessity for the information age. Optical links provide enormous bandwidth, and the optical fiber is the only medium that can meet the modern society's needs for transporting massive amounts of data over long distances. Applications range from global high-capacity networks, which constitute the backbone of the internet, to the massively parallel interconnects that provide data connectivity inside datacenters and supercomputers. Optical communications is a diverse and rapidly changing field, where experts in photonics, communications, electronics, and signal processing work side by side to meet the ever-increasing demands for higher capacity, lower cost, and lower energy consumption, while adapting the system design to novel services and technologies. Due to the interdisciplinary nature of this rich research field, Journal of Optics has invited 16 researchers, each a world-leading expert in their respective subfields, to contribute a section to this invited review article, summarizing their views on state-of-the-art and future developments in optical communications

20 years of turbo coding and energy-aware design guidelines for energy-constrained wireless applications

During the last two decades, wireless communication has been revolutionized by near-capacity error-correcting codes (ECCs), such as turbo codes (TCs), which offer a lower bit error ratio (BER) than their predecessors, without requiring an increased transmission energy consumption (EC). Hence, TCs have found widespread employment in spectrum-constrained wireless communication applications, such as cellular telephony, wireless local area network, and broadcast systems. Recently, however, TCs have also been considered for energy-constrained wireless communication applications, such as wireless sensor networks and the `Internet of Things.' In these applications, TCs may also be employed for reducing the required transmission EC, instead of improving the BER. However, TCs have relatively high computational complexities, and hence, the associated signal-processing-related ECs are not insignificant. Therefore, when parameterizing TCs for employment in energy-constrained applications, both the processing EC and the transmission EC must be jointly considered. In this tutorial, we investigate holistic design methodologies conceived for this purpose. We commence by introducing turbo coding in detail, highlighting the various parameters of TCs and characterizing their impact on the encoded bit rate, on the radio frequency bandwidth requirement, on the transmission EC and on the BER. Following this, energy-efficient TC decoder application-specific integrated circuit (ASIC) architecture designs are exemplified, and the processing EC is characterized as a function of the TC parameters. Finally, the TC parameters are selected in order to minimize the sum of the processing EC and the transmission EC

Advances in Bosonic Quantum Error Correction with Gottesman-Kitaev-Preskill Codes: Theory, Engineering and Applications

Encoding quantum information into a set of harmonic oscillators is considered a hardware efficient approach to mitigate noise for reliable quantum information processing. Various codes have been proposed to encode a qubit into an oscillator -- including cat codes, binomial codes and Gottesman-Kitaev-Preskill (GKP) codes. These bosonic codes are among the first to reach a break-even point for quantum error correction. Furthermore, GKP states not only enable close-to-optimal quantum communication rates in bosonic channels, but also allow for error correction of an oscillator into many oscillators. This review focuses on the basic working mechanism, performance characterization, and the many applications of GKP codes, with emphasis on recent experimental progress in superconducting circuit architectures and theoretical progress in multimode GKP qubit codes and oscillators-to-oscillators (O2O) codes. We begin with a preliminary continuous-variable formalism needed for bosonic codes. We then proceed to the quantum engineering involved to physically realize GKP states. We take a deep dive into GKP stabilization and preparation in superconducting architectures and examine proposals for realizing GKP states in the optical domain (along with a concise review of GKP realization in trapped-ion platforms). Finally, we present multimode GKP qubits and GKP-O2O codes, examine code performance and discuss applications of GKP codes in quantum information processing tasks such as computing, communication, and sensing.Comment: 77+5 pages, 31 figures. Minor bugs fixed in v2. comments are welcome

Radio over multimode fiber using VCSELS

Master'sMASTER OF ENGINEERIN