Application-Specific Number Representation

Reconfigurable devices, such as Field Programmable Gate Arrays (FPGAs), enable application- specific number representations. Well-known number formats include fixed-point, floating- point, logarithmic number system (LNS), and residue number system (RNS). Such different number representations lead to different arithmetic designs and error behaviours, thus produc- ing implementations with different performance, accuracy, and cost. To investigate the design options in number representations, the first part of this thesis presents a platform that enables automated exploration of the number representation design space. The second part of the thesis shows case studies that optimise the designs for area, latency or throughput from the perspective of number representations. Automated design space exploration in the first part addresses the following two major issues: ² Automation requires arithmetic unit generation. This thesis provides optimised arithmetic library generators for logarithmic and residue arithmetic units, which support a wide range of bit widths and achieve significant improvement over previous designs. ² Generation of arithmetic units requires specifying the bit widths for each variable. This thesis describes an automatic bit-width optimisation tool called R-Tool, which combines dynamic and static analysis methods, and supports different number systems (fixed-point, floating-point, and LNS numbers). Putting it all together, the second part explores the effects of application-specific number representation on practical benchmarks, such as radiative Monte Carlo simulation, and seismic imaging computations. Experimental results show that customising the number representations brings benefits to hardware implementations: by selecting a more appropriate number format, we can reduce the area cost by up to 73.5% and improve the throughput by 14.2% to 34.1%; by performing the bit-width optimisation, we can further reduce the area cost by 9.7% to 17.3%. On the performance side, hardware implementations with customised number formats achieve 5 to potentially over 40 times speedup over software implementations

Algorithms and VLSI architectures for parametric additive synthesis

A parametric additive synthesis approach to sound synthesis is advantageous as it can model sounds in a large scale manner, unlike the classical sinusoidal additive based synthesis paradigms. It is known that a large body of naturally occurring sounds are resonant in character and thus fit the concept well. This thesis is concerned with the computational optimisation of a super class of form ant synthesis which extends the sinusoidal parameters with a spread parameter known as band width. Here a modified formant algorithm is introduced which can be traced back to work done at IRCAM, Paris. When impulse driven, a filter based approach to modelling a formant limits the computational work-load. It is assumed that the filter's coefficients are fixed at initialisation, thus avoiding interpolation which can cause the filter to become chaotic. A filter which is more complex than a second order section is required. Temporal resolution of an impulse generator is achieved by using a two stage polyphase decimator which drives many filterbanks. Each filterbank describes one formant and is composed of sub-elements which allow variation of the formant’s parameters. A resource manager is discussed to overcome the possibility of all sub- banks operating in unison. All filterbanks for one voice are connected in series to the impulse generator and their outputs are summed and scaled accordingly. An explorative study of number systems for DSP algorithms and their architectures is investigated. I invented a new theoretical mechanism for multi-level logic based DSP. Its aims are to reduce the number of transistors and to increase their functionality. A review of synthesis algorithms and VLSI architectures are discussed in a case study between a filter based bit-serial and a CORDIC based sinusoidal generator. They are both of similar size, but the latter is always guaranteed to be stable

Techniques for power system simulation using multiple processors

The thesis describes development work which was undertaken to improve the speed of a real-time power system simulator used for the development and testing of control schemes. The solution of large, highly sparse matrices was targeted because this is the most time-consuming part of the current simulator. Major improvements in the speed of the matrix ordering phase of the solution were achieved through the development of a new ordering strategy. This was thoroughly investigated, and is shown to provide important additional improvements compared to standard ordering methods, in reducing path length and minimising potential pipeline stalls. Alterations were made to the remainder of the solution process which provided more flexibility in scheduling calculations. This was used to dramatically ease the run-time generation of efficient code, dedicated to the solution of one matrix structure, and also to reduce memory requirements. A survey of the available microprocessors was performed, which concluded that a special-purpose design could best implement the code generated at run-time, and a design was produced using a microprogrammable floating-point processor, which matched the code produced by the earlier work. A method of splitting the matrix solution onto parallel processors was investigated, and two methods of producing network splits were developed and their results compared. The best results from each method were found to agree well, with a predicted three-fold speed-up for the matrix solution of the C.E.G.B. transmission system from the use of six processors. This gain will increase for the whole simulator. A parallel processing topology of the partitioned network and produce the necessary structures for the remainder of the solution process

A computer-aided design for digital filter implementation

Imperial Users onl

WDM/TDM PON bidirectional networks single-fiber/wavelength RSOA-based ONUs layer 1/2 optimization

This Thesis proposes the design and the optimization of a hybrid WDM/TDM PON at the L1 (PHY) and L2 (MAC) layers, in terms of minimum deployment cost and enhanced performance for Greenfield NGPON. The particular case of RSOA-based ONUs and ODN using a single-fibre/single-wavelength is deeply analysed. In this WDM/TDM PON relevant parameters are optimized. Special attention has been given at the main noise impairment in this type of networks: the Rayleigh Backscattering effect, which cannot be prevented. To understand its behaviour and mitigate its effects, a novel mathematical model for the Rayleigh Backscattering in burst mode transmission is presented for the first time, and it has been used to optimize the WDM/TDM RSOA based PON. Also, a cost-effective, simple design SCM WDM/TDM PON with rSOA-based ONU, was optimized and implemented. This prototype was successfully tested showing high performance, robustness, versatility and reliability. So, the system is able to give coverage up to 1280 users at 2.5 Gb/s / 1.25 Gb/s downstream/upstream, over 20 Km, and being compatible with the GPON ITU-T recommendation. This precedent has enabled the SARDANA network to extend the design, architecture and capabilities of a WDM/TDM PON for a long reach metro-access network (100 km). A proposal for an agile Transmission Convergence sub-layer is presented as another relevant contribution of this work. It is based on the optimization of the standards GPON and XG-PON (for compatibility), but applied to a long reach metro-access TDM/WDM PON rSOA-based network with higher client count. Finally, a proposal of physical implementation for the SARDANA layer 2 and possible configurations for SARDANA internetworking, with the metro network and core transport network, are presented

New dynamic bandwidth allocation algorithm analysis: DDSPON for ethernet passive optical networks

This project aims to present the state of the art in Dynamic Bandwidth Allocation (DBA) solutions, as well as the study and evaluation of one proposal of DBA algorithm: the Distributed Dynamic Scheduling for EPON (DDSPON), which is the UPC contribution to the research in scheduling algorithms for EPON

Physically-Adaptive Computing via Introspection and Self-Optimization in Reconfigurable Systems.

Digital electronic systems typically must compute precise and deterministic results, but in principle have flexibility in how they compute. Despite the potential flexibility, the overriding paradigm for more than 50 years has been based on fixed, non-adaptive inte-grated circuits. This one-size-fits-all approach is rapidly losing effectiveness now that technology is advancing into the nanoscale. Physical variation and uncertainty in com-ponent behavior are emerging as fundamental constraints and leading to increasingly sub-optimal fault rates, power consumption, chip costs, and lifetimes. This dissertation pro-poses methods of physically-adaptive computing (PAC), in which reconfigurable elec-tronic systems sense and learn their own physical parameters and adapt with fine granu-larity in the field, leading to higher reliability and efficiency. We formulate the PAC problem and provide a conceptual framework built around two major themes: introspection and self-optimization. We investigate how systems can efficiently acquire useful information about their physical state and related parameters, and how systems can feasibly re-implement their designs on-the-fly using the information learned. We study the role not only of self-adaptation—where the above two tasks are performed by an adaptive system itself—but also of assisted adaptation using a remote server or peer. We introduce low-cost methods for sensing regional variations in a system, including a flexible, ultra-compact sensor that can be embedded in an application and implemented on field-programmable gate arrays (FPGAs). An array of such sensors, with only 1% to-tal overhead, can be employed to gain useful information about circuit delays, voltage noise, and even leakage variations. We present complementary methods of regional self-optimization, such as finding a design alternative that best fits a given system region. We propose a novel approach to characterizing local, uncorrelated variations. Through in-system emulation of noise, previously hidden variations in transient fault sus-ceptibility are uncovered. Correspondingly, we demonstrate practical methods of self-optimization, such as local re-placement, informed by the introspection data. Forms of physically-adaptive computing are strongly needed in areas such as com-munications infrastructure, data centers, and space systems. This dissertation contributes practical methods for improving PAC costs and benefits, and promotes a vision of re-sourceful, dependable digital systems at unimaginably-fine physical scales.Ph.D.Computer Science & EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/78922/1/kzick_1.pd

Dimensioning and optimizing mobile networks with performance management system

Tämän diplomityön tarkoituksena oli tutkia suorituskyvyn hallintajärjestelmän käyttöä mobiiliverkkojen mitoituksen ja optimoinnin apuna. Työssä käydään suurpiirteisesti läpi tärkeimmät radioteknologiat ja niiden vaatimukset, sekä erilaiset palvelut, joita ne mahdollistavat. Käsiteltäviä radioteknologioita ovat GSM, GRPS, EDGE, UMTS, HSPA ja pintaa raapaistaan myös seuraavan sukupolven radioteknologioiden ympäriltä. Lisäksi käydään läpi tärkeimmät liityntäverkon siirtoteknologit, eli TDM, ATM, Ethernet, IP ja MPLS, ja selvitetään, miten niissä voidaan välittää palvelunlaatua sekä mitä käyttö- ja kunnossapitomenetelmiä ne mahdollistavat. Itse suorituskyvyn hallinta liittyy olennaisena osana verkonhallintaprosessiin virheen hallinnan sekä muiden OAM-menetelmien ohella. Suorituskykykyselyiden tuloksena voidaan laskea erilaisia suorituskykyindikaattoreita, joita voidaan käyttää erilaisiin verkonhallinnan tarpeisiin. Työssä tutkitaan erityisesti, millaisia suorituskykymittauksia liityntäverkoissa kannattaisi tehdä ja etenkin missä verkon osissa niistä voisi olla hyötyä. Työssä käydään läpi myös erilaisten suorituskyvyn hallintajärjestelmien integraatiota, jota monitasoisissa usean valmistajan verkoissa usein saatetaan tarvita. Itse mitoitus- ja optimointiprosessin yhteydessä selvitetään nimenomaan suorituskyvyn hallintajärjestelmän käyttöä liityntäverkoissa. Samalla selvitetään, mitkä mitoitus- ja optimointiratkaisut saattaisivat sopia liityntäverkkoihin. Valitettavasti työssä esitetään erilaisia mitoitus- ja optimointimenetelmiä varsin suppeasti. Tähän on suurimpana syynä se, ettei operaattorien keskuudessa olla menetelmiä juurikaan käytetty. Näihin päiviin asti operaattoreille on riittänyt pelkästään kapasiteetin lisääminen, mutta uusien ja nopeampien radioteknologioiden myötä se ei tule enää riittämään. Toivottavasti tulevaisuudessa tulemmekin näkemään pitkälle kehittyneitä mitoitus- ja optimointiratkaisuja pitkälle kehittyneiden verkon- ja suorituskyvynhallintajärjestelmien ohella.The purpose of this master's thesis was to investigate the dimensioning and optimizing of the mobile networks with a performance management system. The thesis discusses at the general level the most important radio technologies, their requirements and different services they provide. The radio technologies studied are GSM, GPRS, EDGE, UTMS, HSPA, and the next generation technologies. Additionally, the most important access transport technologies have been discussed; including TDM, ATM, Ethernet, IP and MPLS, and their abilities to deliver quality of service and what operation and maintenance methods they provide. Performance management system is a major component in the network management process, along with fault management and other OAM methods. Various performance indicators can be calculated from the performance queries, and they can be used for the needs of network management. The thesis examines in particular, what kind of performance measurements should be done in the access networks, focusing on what network segments receive the most benefit from it. Also, the thesis studies the implementation of different performance management systems integration, as it is often needed in multi vendor hierarchical networks. The use of performance management systems in access networks is sorted with the dimensioning and optimizing process to discover, what kind of dimensioning and optimizing solutions would fit in the access networks. Unfortunately, there are relatively few solutions in the thesis, because operators have not yet implemented any such methods. To this date, simply adding more capacity has been enough for operators. However, combined with new and faster radio technologies it will no longer be sufficient anymore. Hopefully, in the future we will see highly sophisticated dimensioning and optimizing solutions built into performance management systems

Parallel programming using functional languages

It has been argued for many years that functional programs are well suited to parallel evaluation. This thesis investigates this claim from a programming perspective; that is, it investigates parallel programming using functional languages. The approach taken has been to determine the minimum programming which is necessary in order to write efficient parallel programs. This has been attempted without the aid of clever compile-time analyses. It is argued that parallel evaluation should be explicitly expressed, by the programmer, in programs. To do achieve this a lazy functional language is extended with parallel and sequential combinators. The mathematical nature of functional languages means that programs can be formally derived by program transformation. To date, most work on program derivation has concerned sequential programs. In this thesis Squigol has been used to derive three parallel algorithms. Squigol is a functional calculus from program derivation, which is becoming increasingly popular. It is shown that some aspects of Squigol are suitable for parallel program derivation, while others aspects are specifically orientated towards sequential algorithm derivation. In order to write efficient parallel programs, parallelism must be controlled. Parallelism must be controlled in order to limit storage usage, the number of tasks and the minimum size of tasks. In particular over-eager evaluation or generating excessive numbers of tasks can consume too much storage. Also, tasks can be too small to be worth evaluating in parallel. Several program techniques for parallelism control were tried. These were compared with a run-time system heuristic for parallelism control. It was discovered that the best control was effected by a combination of run-time system and programmer control of parallelism. One of the problems with parallel programming using functional languages is that non-deterministic algorithms cannot be expressed. A bag (multiset) data type is proposed to allow a limited form of non-determinism to be expressed. Bags can be given a non-deterministic parallel implementation. However, providing the operations used to combine bag elements are associative and commutative, the result of bag operations will be deterministic. The onus is on the programmer to prove this, but usually this is not difficult. Also bags' insensitivity to ordering means that more transformations are directly applicable than if, say, lists were used instead. It is necessary to be able to reason about and measure the performance of parallel programs. For example, sometimes algorithms which seem intuitively to be good parallel ones, are not. For some higher order functions it is posible to devise parameterised formulae describing their performance. This is done for divide and conquer functions, which enables constraints to be formulated which guarantee that they have a good performance. Pipelined parallelism is difficult to analyse. Therefore a formal semantics for calculating the performance of pipelined programs is devised. This is used to analyse the performance of a pipelined Quicksort. By treating the performance semantics as a set of transformation rules, the simulation of parallel programs may be achieved by transforming programs. Some parallel programs perform poorly due to programming errors. A pragmatic method of debugging such programming errors is illustrated by some examples

Residue number system coded differential space-time-frequency coding.

Thesis (Ph.D.)-University of KwaZulu-Natal, Durban, 2007.The rapidly growing need for fast and reliable transmission over a wireless channel motivates the development of communication systems that can support high data rates at low complexity. Achieving reliable communication over a wireless channel is a challenging task largely due to the possibility of multipaths which may lead to intersymbol interference (ISI). Diversity techniques such as time, frequency and space are commonly used to combat multipath fading. Classical diversity techniques use repetition codes such that the information is replicated and transmitted over several channels that are sufficiently spaced. In fading channels, the performance across some diversity branches may be excessively attenuated, making throughput unacceptably small. In principle, more powerful coding techniques can be used to maximize the diversity order. This leads to bandwidth expansion or increased transmission power to accommodate the redundant bits. Hence there is need for coding and modulation schemes that provide low error rate performance in a bandwidth efficient manner. If diversity schemes are combined, more independent dimensions become available for information transfer. The first part of the thesis addresses achieving temporal diversity through employing error correcting coding schemes combined with interleaving. Noncoherent differential modulation does not require explicit knowledge or estimate of the channel, instead the information is encoded in the transitions. This lends itself to the possibility of turbo-like serial concatenation of a standard outer channel encoder with an inner modulation code amenable to noncoherent detection through an interleaver. An iterative approach to joint decoding and demodulation can be realized by exchanging soft information between the decoder and the demodulator. This has been shown to be effective and hold hope for approaching capacity over fast fading channels. However most of these schemes employ low rate convolutional codes as their channel encoders. In this thesis we propose the use of redundant residue number system codes. It is shown that these codes can achieve comparable performance at minimal complexity and high data rates. The second part deals with the possibility of combining several diversity dimensions into a reliable bandwidth efficient communication scheme. Orthogonal frequency division multiplexing (OFDM) has been used to combat multipaths. Combining OFDM with multiple-input multiple-output (MIMO) systems to form MIMO-OFDM not only reduces the complexity by eliminating the need for equalization but also provides large channel capacity and a high diversity potential. Space-time coded OFDM was proposed and shown to be an effective transmission technique for MIMO systems. Spacefrequency coding and space-time-frequency coding were developed out of the need to exploit the frequency diversity due to multipaths. Most of the proposed schemes in the literature maximize frequency diversity predominantly from the frequency-selective nature of the fading channel. In this thesis we propose the use of residue number system as the frequency encoder. It is shown that the proposed space-time-frequency coding scheme can maximize the diversity gains over space, time and frequency domains. The gain of MIMO-OFDM comes at the expense of increased receiver complexity. Furthermore, most of the proposed space-time-frequency coding schemes assume frequency selective block fading channels which is not an ideal assumption for broadband wireless communications. Relatively high mobility in broadband wireless communications systems may result in high Doppler frequency, hence time-selective (rapid) fading. Rapidly changing channel characteristics impedes the channel estimation process and may result in incorrect estimates of the channel coefficients. The last part of the thesis deals with the performance of differential space-time-frequency coding in fast fading channels