Improve the Usability of Polar Codes: Code Construction, Performance Enhancement and Configurable Hardware

Error-correcting codes (ECC) have been widely used for forward error correction (FEC) in modern communication systems to dramatically reduce the signal-to-noise ratio (SNR) needed to achieve a given bit error rate (BER). Newly invented polar codes have attracted much interest because of their capacity-achieving potential, efficient encoder and decoder implementation, and flexible architecture design space.This dissertation is aimed at improving the usability of polar codes by providing a practical code design method, new approaches to improve the performance of polar code, and a configurable hardware design that adapts to various specifications. State-of-the-art polar codes are used to achieve extremely low error rates. In this work, high-performance FPGA is used in prototyping polar decoders to catch rare-case errors for error-correcting performance verification and error analysis. To discover the polarization characteristics and error patterns of polar codes, an FPGA emulation platform for belief-propagation (BP) decoding is built by a semi-automated construction flow. The FPGA-based emulation achieves significant speedup in large-scale experiments involving trillions of data frames. The platform is a key enabler of this work. The frozen set selection of polar codes, known as bit selection, is critical to the error-correcting performance of polar codes. A simulation-based in-order bit selection method is developed to evaluate the error rate of each bit using Monte Carlo simulations. The frozen set is selected based on the bit reliability ranking. The resulting code construction exhibits up to 1 dB coding gain with respect to the conventional bit selection. To further improve the coding gain of BP decoder for low-error-rate applications, the decoding error mechanisms are studied and analyzed, and the errors are classified based on their distinct signatures. Error detection is enabled by low-cost CRC concatenation, and post-processing algorithms targeting at each type of the error is designed to mitigate the vast majority of the decoding errors. The post-processor incurs only a small implementation overhead, but it provides more than an order of magnitude improvement of the error-correcting performance. The regularity of the BP decoder structure offers many hardware architecture choices. Silicon area, power consumption, throughput and latency can be traded to reach the optimal design points for practical use cases. A comprehensive design space exploration reveals several practical architectures at different design points. The scalability of each architecture is also evaluated based on the implementation candidates. For dynamic communication channels, such as wireless channels in the upcoming 5G applications, multiple codes of different lengths and code rates are needed to t varying channel conditions. To minimize implementation cost, a universal decoder architecture is proposed to support multiple codes through hardware reuse. A 40nm length- and rate-configurable polar decoder ASIC is demonstrated to fit various communication environments and service requirements.PHDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/140817/1/shuangsh_1.pd

Progressive transmission of medical images

A novel adaptive source-channel coding scheme for progressive transmission of medical images with a feedback system is therefore proposed in this dissertation. The overall design includes Discrete Wavelet Transform (DWT), Embedded Zerotree Wavelet (EZW) coding, Joint Source-Channel Coding (JSCC), prioritization of region of interest (RoI), variability of parity length based on feedback, and the corresponding hardware design utilising Simulink. The JSCC can achieve an efficient transmission by incorporating unequal error projection (UEP) and rate allocation. An algorithm is also developed to estimate the number of erroneous data in the receiver. The algorithm detects the address in which the number of symbols for each subblock is indicated, and reassigns an estimated correct data according to a decision making criterion, if error data is detected. The proposed system has been designed based on Simulink which can be used to generate netlist for portable devices. A new compression method called Compressive Sensing (CS) is also revisited in this work. CS exhibits many advantages in comparison with EZW based on our experimental results. DICOM JPEG2000 is an efficient coding standard for lossy or lossless multi-component image coding. However, it does not provide any mechanism for automatic RoI definition, and is more complex compared to our proposed scheme. The proposed system significantly reduces the transmission time, lowers computation cost, and maintains an error-free state in the RoI with regards to the above provided features. A MATLAB-based TCP/IP connection is established to demonstrate the efficacy of the proposed interactive and adaptive progressive transmission system. The proposed system is simulated for both binary and symmetric channel (BSC) and Rayleigh channel. The experimental results confirm the effectiveness of the design.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Algorithms for Energy Efficiency in Wireless Sensor Networks

The recent advances in microsensor and semiconductor technology have opened a new field within computer science: the networking of small-sized sensors which are capable of sensing, processing, and communicating. Such wireless sensor networks offer new applications in the areas of habitat and environment monitoring, disaster control and operation, military and intelligence control, object tracking, video surveillance, traffic control, as well as in health care and home automation. It is likely that the deployed sensors will be battery-powered, which will limit the energy capacity significantly. Thus, energy efficiency becomes one of the main challenges that need to be taken into account, and the design of energy-efficient algorithms is a major contribution of this thesis. As the wireless communication in the network is one of the main energy consumers, we first consider in detail the characteristics of wireless communication. By using the embedded sensor board (ESB) platform recently developed by the Free University of Berlin, we analyze the means of forward error correction and propose an appropriate resync mechanism, which improves the communication between two ESB nodes substantially. Afterwards, we focus on the forwarding of data packets through the network. We present the algorithms energy-efficient forwarding (EEF), lifetime-efficient forwarding (LEF), and energy-efficient aggregation forwarding (EEAF). While EEF is designed to maximize the number of data bytes delivered per energy unit, LEF additionally takes into account the residual energy of forwarding nodes. In so doing, LEF further prolongs the lifetime of the network. Energy savings due to data aggregation and in-network processing are exploited by EEAF. Besides single-link forwarding, in which data packets are sent to only one forwarding node, we also study the impact of multi-link forwarding, which exploits the broadcast characteristics of the wireless medium by sending packets to several (potential) forwarding nodes. By actively selecting a forwarder among all nodes that received a packet successfully, retransmissions can often be avoided. In the majority of cases, multi-link forwarding is thus more efficient and able to save energy. In the last part of this thesis, we present a topology and energy control algorithm (TECA) to turn off the nodes' radio transceivers completely in order to avoid idle listening. By means of TECA, a connected backbone of active nodes is established, while all other nodes may sleep and save energy by turning off their radios. All algorithms presented in this thesis have been fully analyzed, simulated, and implemented on the ESB platform. They are suitable for several applications scenarios and can easily be adapted even to other wireless sensor platforms