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Unlike the inter-Satellite communications link (ISL) being used in current space missions, emerging scenarios require point to multi-point links with additional support for autonomous networking amongst multiple satellites. Be it for formation flying or space based wireless sensor networks, these distributed satellite systems require revised communications system design to provide for the various physical topologies, dynamic channel characteristics and user requirements. All three factors being mission specific, that is why, little literature is published, in which physical aspects of the link or the communications system design or the channel is discussed. This thesis determines channel characteristics and performance of OFDM modem for three physical topologies for a proposed mission scenario, bridging the gap in literature. The mission is used as the basis for investigating the impact of relative motion and in-orbit environment on propagating EM waves. The proposed multipoint sensing mission namely the ionosphere monitoring mission (IMM) comprises pico/nano class of satellites in a mother daughter configuration, to take finer easurement of the plasma bulk properties in LEO. Three physical topologies for ISL are identified. Relative motion is studied for (a) free flying CubeSats acting as sensor, (b) a sensor satellite with respect to a relay satellite and (c) several relay satellites in a string-of-pearl configuration. The Doppler shift is nominal tens of Hz for the first and third case, however, the Doppler shift is in kHz for case b. Thus a third order PLL is required in receiver stage. Contrary to what is assumed in literature, the communications channel is identified to exhibit fading. The dynamic fading (fast and slow) can reach up to 20 dB. To cope with the dynamic channel behaviour a reconfigurable OFDM modem is described. This channel is modelled in MATLAB as a Time Delay Line (TDL) structure, and used to evaluate the performance of OFDM modem for data rates up to 1 Mbps. The hardware-in-the-loop simulation methods, assisted in laying a much needed foundation for a testbed for evaluating ISL.

This research has focused on close-in landmine detection, which aims to identify landmines in a particular landmine area. Close-range landmine detection requires both sub-surface sensors, such as metal detectors and ground penetrating radar (GPR), and surface sensors, such as optical cameras. A new multi-focus image fusion algorithm is proposed which outperforms the existing intensity-hue-saturation (IHS) and principle components analysis (PCA) algorithms on both visual and fusion parameter analysis. In addition, the proposed algorithm can save 30.9% running time than the IHS algorithm, which is the same level as the existing PCA algorithm. A novel single GPR sensor landmine detection algorithm entropy-based region selecting algorithm is proposed which uses the entropy value of the region as the feature and continuous layers instead of a hard threshold. Two A-scan based statistics algorithms and a GPR signal oscillation feature based detection algorithm are also proposed. The results show that the proposed entropy-based algorithm outperforms the existing region selection algorithm on both detection accuracy and running time. The proposed statistics algorithms and GPR feature-based algorithm outperform the edge histogram descriptor and edge energy algorithms on both detection accuracy range, running time and memory usage. In addition, the GPR feature-based algorithm can reduce the false alarm rate (FAR) by 22% for all targets at 90% probability of detection. With regards to data fusion system design, this research overcomes the limitations of the existing Bayesian fusion approach. A new Kalman-Bayes based fusion system is developed which reduces the system uncertainty and improves the fusion process. The experimental results have shown that the proposed Kalman-Bayes fusion system and enhanced fuzzy fusion system can reach 7.8% FAR at 91.1% detection rate and 6.30% FAR at 92.4% detection rate, correspondingly, outperforming the existing Bayes and fuzzy fusion systems in terms of detection ability.

Wireless sensor networks (WSNs) have received much attention in recent years. Such networks comprise spatially distributed sensors to monitor various parameters. Space-based wireless sensor networks (SB-WSNs) consisting of tiny, low power, inexpensive satellites flying in a fleet with a close formation can offer a wide range of applications. Since communication is typically the major factor in power consumption, the activity of the transceiver should be reduced to increase the nodes’ lifetime. To understand the network power behaviour, a space-based wireless sensor network consisting of 40 nodes was designed as an experimental testbed. Several tests were undertaken to investigate the nodes’ lifetime and the packet loss with various sleep/wake up methods. The study found that the nodes with shorter paths to the sink benefit from improvement in their lifetime. In contrast, the other nodes with routes including many hops obtain less enhancement in their lifetime and high packet loss. To further reduce the power consumption, a novel sleep/wake up technique where the nodes have different sleep periods based on their locations has been proposed and tested. This modification enhanced the network operation time by 24% and increased the total delivered packets by 51% compared to when the nodes stay active all their duty cycle. Another concern was uneven power consumption due to the extra packet-relaying duties imposed on central nodes. This was addressed first by altering the connectivity of the network, and then by adding extra nodes dedicated to this task. The proposed sleep/wake up scheme was extended further through the adoption of transmission power control (TPC) and the introduction of multiple sinks. Both mechanisms were used to decrease the power budget required to deliver a packet from source to destination by reducing the number of hops in the paths. This improves the nodes’ lifetime and the total amount of collected data. Findings in this research have direct relevance to the use of commercial off the shelf (COTS) nodes in a SB-WSN and will provide an impetus for accurate estimation of the performance and design of such a network.

Space weather phenomena have a significant impact on satellite communications but are not well understood. In-situ measurements of the ionospheric environment would significantly improve the understanding of the origins and progressions of these phenomena. Whilst previous scientific satellites have measured the ionospheric plasma, they only provide a limited view due to their small number. It has previously been suggested that a swarm of femto-satellites (PCBsats) could be used to collect high quality temporal and spatial measurements, whilst being financially effective. To give the measurements any scientific value, the location and time of each measurement needs to be accurately recorded. The PCBsat prototype used a solution that, due to export requirements and fundamental limitations with the device, would not be capable of working in space. Several location and timing solutions have been investigated, with none matching the precision, accuracy, power consumption and physical size of a GNSS receiver (i.e. a receiver of GPS, GLONASS, Galileo etc. signals). To further reduce the power consumption, a novel distributed GNSS receiver has been designed and built, where the largest computational burden (calculating the receivers position) is offloaded to a relaying node. This use of distributed computing has been shown to reduce the power consumption of the receiver by between 5:6% and 13:3% - which is equivalent to between 2 and 5 times the power consumption of the PCBsat’s main processor. In addition to this, this novel approach has the additional benefit of being used in a hybrid scheme. Where information required to calculate a receiver’s position is stored so that it can be used with higher precision ephemerides that are publicly available but are delayed by up to three weeks. This has many applications as it can increase the utility of collected data, at a reduced cost. As the intended femto-satellite application relies on a link to relaying satellites, the dynamics, in particular the dispersion, of the intended constellation needs to be known. This has been modelled using a novel orbit simulator. The orbit simulator is the first of its kind to model multidimensional free molecular drag to simulate the effects of the low density atmosphere on a satellite. This allows the dispersion of a constellation of satellites to be investigated with maximum separations for the PCBsat being presented.

Current and future space missions demand highly reliable, High Performance Embedded Computing (HPEC). The review of the literature has shown that no single solution could meet both issues efficiently at present addressing HPEC as well as reliability. Furthermore, there is no suitable method of assessing performance for such a scheme. In this thesis a novel cooperative task-oriented fault-tolerant distributed computing (FTDC) architecture is proposed, which caters for high performance and reliability in systems on board spacecraft. In a nut shell, the architecture comprises two types of nodes, a computing node and an input-output node, interfaced together through a high-speed network with bus topology. To detect faults in the nodes, a fault management scheme specifically designed to support the cooperative task-oriented distributed computing concept is proposed and employed, which is referred to as Adaptive Middleware for Fault-Tolerance (AMFT). AMFT is implemented as a separate hardware block and operates in parallel with the processing unit within the computing node. A set of metrics is designed and mathematical models of availability and reliability are developed, which are used to evaluate the proposed distributed computing architecture and fault management scheme. As a new development, extending the current state of the art, the proposed fault-tolerant distributed architecture has been subjected to a rigorous assessment through hardware implementation. Implementation approaches at two levels were adopted to provide a proof of concept: a board level and a Multiprocessor System-on-Chip (MPSoC) level. Both distributed computing system implementations were evaluated for functional validity and performance. To examine the FTDC architecture performance under a realistic space related distributed computing scenario a case-study application, representing a satellite Attitude and Orbit Control System (AOCS), was developed. The AOCS application was selected because it features a time critical task execution, in which system failure and reconfiguration time must be kept minimal. Based on the case-study application, it was demonstrated that the FTDC architecture is capable of fully meeting the desired requirements by timely migrating tasks to functional nodes and keeping rollback of task states minimal, which proves the advantages of the adopted cooperative distributed approach for use on board spacecraft.

This research contributes to a better understanding of how reconfigurable Field Programmable Gate Array (FPGA) devices can safely be used as part of satellite payload data processing systems that are exposed to the harsh radiation environment in space. Despite a growing number of publications about low-level mitigation techniques, only few studies are concerned with high-level Fault Detection, Isolation and Recovery (FDIR) methods, which are applied to FPGAs in a similar way as they are applied to other systems on board spacecraft. This PhD thesis contains several original contributions to knowledge in this field. First, a novel Distributed Failure Detection method is proposed, which applies FDIR techniques to multi-FPGA systems by shifting failure detection mechanisms to a higher intercommunication network level. By doing so, the proposed approach scales better than other approaches with larger and complex systems since data processing hardware blocks, to which FDIR is applied, can easily be distributed over the intercommunication network. Secondly, an innovative Availability Analysis method is proposed that allows a comparison of these FDIR techniques in terms of their reliability performance. Furthermore, it can be used to predict the reliability of a specific hardware block in a particular radiation environment. Finally, the proposed methods were implemented as part of a proof of concept system: On the one hand, this system enabled a fair comparison of different FDIR configurations in terms of power, area and performance overhead. On the other hand, the proposed methods were all successfully validated by conducting an accelerated proton irradiation test campaign, in which parts of this system were exposed to the proton beam while the proof of concept application was actively running.

The research presented in this thesis is concerned with lossless hyperspectral image compression of satellite imagery using the Integer Karhunen-Loève Transform (KLT). The Integer KLT is addressed because it shows superior performance in decorrelating the spectral component in hyperspectral images compared to other algorithms, such as, Discrete Cosine Transform (DCT), Discrete Wavelet Transform (DWT) as well as the Lossless Multispectral and Hyperspectral Image Compression algorithm proposed by the Consultative Committee for Space Data Systems (CCSDS-MHC). The aim of the research is to develop a reliable low complexity implementation of the computationally intensive Integer KLT, which is suitable for use on board remote sensing satellites. The performance of the algorithm in terms of compression ratio (CR) and execution time was investigated for different levels of clustering and tiling of hyperspectral images using airborne and spaceborne test datasets. It was established that the clustering technique could improve the CR, which is a completely new finding. To speed up the algorithm the Integer KLT was parallelised based on the clustering concept and was implemented using a multi-processor environment. The core part of the Integer KLT algorithm, i.e. the PLUS factorisation, has proven to be the most vulnerable part to single-bit errors that could cause a large loss to the encoded image. An error detection algorithm was proposed which was incorporated in the Integer KLT to overcome that. Based on extensive testing it was shown that it is capable of detecting errors with a sufficiently low error tolerance threshold of 1e-11 featuring a low execution time depending on the extent of clustering and tiling. A new fixed sampling method for the covariance matrix calculation was proposed, which could avoid variation in the data volume of the encoded image that would be beneficial for remote debugging. Analysis of the overhead information generated by the Integer KLT was carried out for the first time and a compaction method which is crucial to clustering and tiling was also suggested. The full range of the proposed enhanced Integer KLT schemes was implemented and evaluated on a desktop computer and two DSP platforms, OMAP-L137 EVM and TMDSEVM6678L EVM in terms of execution time and average power consumption. A new method for estimating the best clustering level, at which the compression ratio is maximised for each tiling level involved, was also proposed. The estimation method could achieve 87.1% accuracy in determining the best clustering level based on a test set of 62 different hyperspectral images. The best average compression ratio, recorded for Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) and Hyperion (spaceborne) images is 3.31 and 2.39, respectively. The fully optimised KLT system, achieving a maximum CR, could compress an AVIRIS image in 3.6 to 8.5 seconds, depending on the tiling level, while a Hyperion image - in less than 1 second on a desktop computer. On the multi-core DSP, an AVIRIS image could be compressed in 18.7 seconds to 1.3 minutes, depending on the tiling level, whereas a Hyperion image - in around 3.4 seconds. On the low power DSP platform OMAP-L137 the compression of an AVIRIS image takes 5.4 minutes and of a Hyperion image - 44 seconds to 2.1 minutes, depending on the tiling level.

Solid State Devices (SSDs) are becoming ubiquitous in many embedded devices due to their features such as no moving parts, shock/temperature resistance and low power consumption. The reliability, performance, lifespan, and verification of these devices is an increasing issue in many application domains. Redundant Array of Independent Disk (RAID) architectures have previously been used to increase reliability of magnetic disk devices. Recent works have proposed re-use of RAID architectures to address these issues in SSDs, however these have an inherent problem as all flash memory chips wear out at the same rate due to even distribution of write operations. Existing solutions partly solve this problem using uneven parity distribution across the array, but suffer age-variation problems under random and sequential writes thereby decreasing the reliability of the array as well as increasing the cost. The aim of this thesis is to enhance the use of RAID mechanisms in SSD storage systems, and to do so in a reliable, and efficient manner. In this thesis the two novel mechanisms are explored that enhance data reliability in a SSD array regardless of I/O workload characteristics. The first mechanism solves the age convergence problem in RAID systems and quickly achieves steady-state age convergence. The second mechanism reduces page writes, thereby increasing the lifespan of each element in the array. The SSD controller ( ANFS ) architecture and the associated RAID architecture (flash-RAID) are presented. The embedded Flash Translation Layer (FTL), RAID controller, SSD low level controller, and specialized host interface are developed on an FPGA in synthesizable Verilog. In these architectures the concept of a forced random write is introduced which is used to solving the age distribution problem of pure sequential writes. It further employs a log-structured approach to control on-chip wear-levelling, and a power-fail reliability mechanism. In addition to this a new flash management framework is presented that increases the performance of SSD storage systems in the exploitation of both multi-chip parallelism and out-of-order execution. The contribution of this thesis can be summarised as follows: the presentation of new algorithms that successfully enable the efficient and reliable RAID techniques in SSD devices, the development of a number of techniques that enhance the performance and reliability of flash-based file systems, the implementation of a controller in synthesizable Verilog that employs these techniques, and the provision of a complete test bed supporting the experiments.