An Adaptive Error Correction Scheme For Synchronous Digital Hierarchy-Based Wavelength Division Multiplexed Optical Network

In optical communications there are a variety of noise and distortion sources which can cause errors. These errors become essential and more intense in the high-capacity and long-haul wavelength-division multiplexing (WDM) systems. Therefore, the development of a forward error correction (FEC) technique to mitigate errors in WDM optical networks is very relevant and important. The existing FEC techniques for optical communications are based on fixed codes, which consume unnecessary overhead bandwidth even when there are no errors. This thesis proposes an adaptive forward error correction (AFEC) scheme for synchronous digital hierarchy (SDH)-based WDM optical networks, referred to as the SDH-AFEC. The scheme supports adaptive codes because it uses a dedicated WDM channel for transmission of different sizes of FEC redundancy for the payloads. Unlike most previous adaptive FEC techniques which change to a stronger code after an error has occurred, the SDH-AFEC is able to do so before an error occurs. This is achieved by using the combination of B2 error and corrected error count as the input parameters for the algorithm. Then the algorithm is designed in such a way that it adaptively assigns a suitable value of error correction capability, t for error correction, and the number of corrected errors is maintained not exceeding t/2. The SDH-AFEC adopts Bose–Chaudhuri–Hocquenghem (BCH) and Reed–Solomon (RS) codes for correcting random and burst errors respectively. A new technique is also proposed for estimation of the error pattern so that a suitable type of code can be assigned accordingly. This technique is based on the analysis of the corrected error locations, referred to as the error location analysis (ELA). Simulation results show that the SDH-AFEC is able to use different values of t adaptively for error correction. It assigns stronger t with increasing channel bit error rate (BER) or average burst length (ABL) to maintain the output BER below the target BER of 10-9, until the strongest value of t is assigned. The SDH-AFEC uses the maximum FEC overhead for high BER or long ABL. However, the FEC overhead requirement reduces with decreasing BER or ABL. Hence, in addition to the adaptive BER performance, the SDH-AFEC also provides a way to use the FEC overhead efficiently. Lastly, the results also show that by using ELA, the performance of the SDH-AFEC is further improved that it is able to correct about three times more random errors and three times longer burst length. Meanwhile, the average FEC overhead reduction after ELA is about 38% and 36% for random and burst errors respectively

A Fast Scheduling Algorithm for WDM Optical Networks

Wavelength Division Multiplexing (WDM) is emerging as the most promising approach to exploit the huge bandwidth of optical fibre. This approach divides the optical spectrum into many different channels where each channel corresponds to a different wavelength. Single-hop WDM networks are attractive in local area environment where all the nodes can be connected to a single broadcast facility. In a single-hop WDM broadcast network, the transmitter must know when to transmit a packet and at which wavelength, while the receiver must know when to tune to the appropriate wavelength to receive the packet. This process requires some form of coordination. Many researches have focused on the scheduling algorithms that perform this kind of coordination. This thesis proposes a scheduling algorithm for the WDM broadcast networks. The algorithm employs a theory in graph, known as edge colouring of bipartite multigraph to produce the transmission schedule, which is free from collision due to the nature of the edge colouring. An optimal edge colouring of bipartite multi graph can be found in O(M log2 N) time, where M is number of packets selected for scheduling, and N is the number of the nodes. This time complexity can be improved to O(log3 N) by parallel processing using O(M) processors. Two variations of implementation of the scheduling algorithm have been proposed, namely the Variable Frame Size (VFS) and Limited Frame Size (LFS) schemes. These schemes use different criteria to select packets from the nodes for scheduling. The VFS scheme is simple, but supports only best effort transmissions. The LFS scheme ensures the frame size of the transmission schedule is bounded, thus enabling it to support bandwidth guarantee to the nodes up to a node's fair share of the network capacity. The LFS scheme is capable of supporting constant bit rate and unspecified bit rate service categories, analogous to the Asynchronous Transfer Mode (ATM) services. The results show that the LFS scheme performs better than the VFS scheme in terms of channel utilisation, packet loss probability and network throughput for all the simulated traffic patterns, especially at heavy loads. Besides, the LFS scheme respects any level of bandwidth guarantee, while the unused bandwidth can be used for best effort transmissions. The results also show that the VFS and LFS schemes are future-proof as they are able to capitalise on the increase in the number of wavelength channels

The Half-t adaptive error correction algorithm for SDH-based WDM optical networks

This paper proposes an adaptive forward error correction (FEC) algorithm, referred to as the Half-t algorithm for synchronous digital hierarchy (SDH) based wavelength division multiplexing (WDM) optical networks. Unlike most previous adaptive FEC algorithms which change to a stronger code for error correction based on either packet losses or erroneous condition, the Half-t algorithm is able to do so before an error occurs. Simulation results show that the Half-t algorithm can maintain the output bit error rate (BER) below a target BER by assigning an appropriate value of waiting delay before changing to a weaker code

A scheduling algorithm for WDM optical networks

This paper proposes a scheduling algorithm for time-slotted WDM broadcast-and-select optical networks. The algorithm is free from collision and supports a particular class of quality of service (QoS), namely constant bit rate (CBR). The running time complexity of the algorithm is O(Mlog2N)1, where M and N are the number of packets used for scheduling and the number of nodes, respectively. This running time can be improved to O(log3N) by parallel processing

Experimental investigation of Reed-Solomon error correction technique for wireless sensor network

In this paper, we propose a Reed-Solomon (RS) error correction code with an error correction capability of 32 bytes for IEEE 802.15.4 wireless sensor network (WSN). This code is chosen based on our experimental investigation and the analysis of error pattern, which revealed that although there are as much as 82% of burst errors out of the total errors are present at WSN, the rate of occurrence of the burst errors decreases when the burst length increases. Experimental results show that the proposed error correction code is able to reduce the packet error rate (PER) significantly for distances shorter than 40 m. At the target PER of 10-3, the proposed technique is able to improve either the transmission distance by about 10 m or the received signal strength indication (RSSI) by about 8 dB compared to the WSN without error correction

An adaptive error correction scheme for SDH based wavelength division multiplexed optical networks

This paper proposes a synchronous digital hierarchy (SDH) based adaptive forward error correction (FEC) scheme for wavelength division multiplexing (WDM) optical networks. In this scheme, a dedicated WDM channel is used to transport the FEC redundancies. The error location analysis of the FEC correctable bits, combined with B2 bytes analysis are used to decide the suitable FEC code for the payload channels. The proposed FEC scheme is evaluated not only for the typical Poisson errors but also the burst errors. Simulation results show that the proposed FEC scheme performs significantly better than the existing FEC schemes

Does firm size matter? Evidence on the impact of the green innovation strategy on corporate financial performance in the automotive sector

In the past few years, there has been increasing awareness regarding the significance of the Green Innovation Strategy (GIS) in the academic and practical fields. Hence, it becomes important to determine the correlation between the GIS and the Corporate Financial Performance (CFP). This study attempted to determine the dynamic correlation between the GIS and the CFP, with regards to the firm size. For this purpose, this study has collected data for 163 international automotive firms, from the CSRHub database, for the period ranging between 2011 and 2017. Furthermore, we also used the dynamic panel data system, i.e., the Generalised Method of Moment (GMM) method, for estimating this relationship. The empirical results indicated that the GIS positively affected the CFP. Interestingly, we also uncovered that the firm size moderated the negative correlation between the GIS and the CFP. The small-sized firms showed higher green innovation investments return than the larger-sized firms, which indicated that these smaller firms were more prone to seek variation and visibility, for accessing better resources. Furthermore, due to the extensive scrutiny of the stakeholders, these small firms could generate higher profits. The implications for managers and the theories in this regard are then discussed

Robust estimation of bacterial cell count from optical density

Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals <1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data

Global patient outcomes after elective surgery: prospective cohort study in 27 low-, middle- and high-income countries.

BACKGROUND: As global initiatives increase patient access to surgical treatments, there remains a need to understand the adverse effects of surgery and define appropriate levels of perioperative care. METHODS: We designed a prospective international 7-day cohort study of outcomes following elective adult inpatient surgery in 27 countries. The primary outcome was in-hospital complications. Secondary outcomes were death following a complication (failure to rescue) and death in hospital. Process measures were admission to critical care immediately after surgery or to treat a complication and duration of hospital stay. A single definition of critical care was used for all countries. RESULTS: A total of 474 hospitals in 19 high-, 7 middle- and 1 low-income country were included in the primary analysis. Data included 44 814 patients with a median hospital stay of 4 (range 2-7) days. A total of 7508 patients (16.8%) developed one or more postoperative complication and 207 died (0.5%). The overall mortality among patients who developed complications was 2.8%. Mortality following complications ranged from 2.4% for pulmonary embolism to 43.9% for cardiac arrest. A total of 4360 (9.7%) patients were admitted to a critical care unit as routine immediately after surgery, of whom 2198 (50.4%) developed a complication, with 105 (2.4%) deaths. A total of 1233 patients (16.4%) were admitted to a critical care unit to treat complications, with 119 (9.7%) deaths. Despite lower baseline risk, outcomes were similar in low- and middle-income compared with high-income countries. CONCLUSIONS: Poor patient outcomes are common after inpatient surgery. Global initiatives to increase access to surgical treatments should also address the need for safe perioperative care. STUDY REGISTRATION: ISRCTN5181700