A Differential Turbo Detection Aided Sphere Packing Modulated Space-Time Coding Scheme

A signal construction method that combines orthogonal design with sphere packing has recently shown useful performance improvements over the conventional orthogonal design. In this contribution, we extend this concept and propose a novel Sphere Packing (SP) modulated differential Space-Time Block Coded (DSTBC) scheme, referred to here as (DSTBC-SP), which shows performance advantages over conventional DSTBC schemes. We also demonstrate that the performance of DSTBC-SP systems can be further improved by concatenating sphere packing aided modulation with channel coding and performing SP-symbol-to bit demapping as well as channel decoding iteratively. We also investigate the convergence behaviour of this concatenated scheme with the aid of Extrinsic Information Transfer (EXIT) Charts. The proposed turbo-detected DSTBC-SP scheme exhibits a ’turbo-cliff’ at Eb/N0 = 6dB and provides Eb/N0 gains of 23.7dB and 1.7dB at a BER of 10?5 over an equivalent-throughput uncoded DSTBC-SP scheme and a turbo-detected QPSK modulated DSTBC scheme, respectively

A Turbo Detection and Sphere-Packing-Modulation-Aided Space-Time Coding Scheme

Arecently proposed space-time block-coding (STBC) signal-construction method that combines orthogonal design with sphere packing (SP), referred to here as STBC-SP, has shown useful performance improvements over Alamouti’s conventional orthogonal design. In this contribution, we demonstrate that the performance of STBC-SP systems can be further improved by concatenating SP-aided modulation with channel coding and performing demapping as well as channel decoding iteratively. We also investigate the convergence behavior of this concatenated scheme with the aid of extrinsic-information-transfer charts. The proposed turbo-detected STBC-SP scheme exhibits a “turbo-cliff” at Eb/N0 = 2.5 dB and provides Eb/N0 gains of approximately 20.2 and 2.0 dB at a bit error rate of 10?5 over an equivalent throughput uncoded STBC-SP scheme and a turbo-detected quadrature phase shift keying (QPSK) modulated STBC scheme, respectively, when communicating over a correlated Rayleigh fading channel. Index Terms—EXIT charts, iterative demapping, multidimensional mapping, space-time coding, sphere packing, turbo detection

Equivalent-Capacity-Based Design of Space-Time Block-Coded Sphere-Packing-Aided Multilevel Coding

A multilevel coding (MLC) scheme invoking sphere packing (SP) modulation combined with space time block coding (STBC) is designed. The coding rates of each of the MLC component codes are determined using the so-called equivalent capacity based constituent-code rate-calculation procedure invoking a 4-dimensional (4D) sphere packing bit-to-symbol mapping scheme. Four different-rate Low-Density Parity Check (LDPC) constituent-codes are used by the MLC scheme. The performance of the resultant equivalent capacity based design is characterized using simulation results. Our results demonstrate an approximately 3.5dB gain over an identical scheme dispensing with SP modulation. Furthermore although a similar performance gain is attained by both the proposed MLC scheme and its benchmarker, which uses a single-class LDPC code, the MLC scheme is preferred, since it benefits from the new classic philosophy of using low-memory, low-complexity component codes as well as providing an unequal error protection capability

A Purely Symbol-Based Precoded and LDPC-Coded Iterative-Detection Assisted Sphere-Packing Modulated Space-Time Coding Scheme

In this contribution, we propose a purely symbol-based LDPC-coded scheme based on a Space-Time Block Coding (STBC) signal construction method that combines orthogonal design with sphere packing, referred to here as (STBCSP). We demonstrate that useful performance improvements may be attained when sphere packing aided modulation is concatenated with non-binary LDPC especially, when performing purely symbol-based turbo detection by exchanging extrinsic information between the non-binary LDPC decoder and a rate-1 non-binary inner precoder. We also investigate the convergence behaviour of this symbol-based concatenated scheme with the aid of novel non-binary Extrinsic Information Transfer (EXIT) Charts. The proposed symbol-based turbo-detected STBC-SP scheme exhibits a 'turbo-cliff' at Eb/N0 = 5.0 dB and achieves an Eb/N0 gain of 19.2dB at a BER of 10-5 over Alamouti’s scheme

Iteratively Decoded Irregular Variable Length Coding and Sphere-Packing Modulation-Aided Differential Space-Time Spreading

In this paper we consider serially concatenated and iteratively decoded Irregular Variable Length Coding (IrVLC) combined with precoded Differential Space-Time Spreading (DSTS) aided multidimensional Sphere Packing (SP) modulation designed for near-capacity joint source and channel coding. The IrVLC scheme comprises a number of component Variable Length Coding (VLC) codebooks having different coding rates for the sake of encoding particular fractions of the input source symbol stream. The relative length of these source-stream fractions can be chosen with the aid of EXtrinsic Information Transfer (EXIT) charts in order to shape the EXIT curve of the IrVLC codec, so that an open EXIT chart tunnel may be created even at low Eb/N0 values that are close to the capacity bound of the channel. These schemes are shown to be capable of operating within 0.9 dB of the DSTS-SP channel’s capacity bound using an average interleaver length of 113, 100 bits and an effective bandwidth efficiency of 1 bit/s/Hz, assuming ideal Nyquist filtering. By contrast, the equivalent-rate regular VLC-based benchmarker scheme was found to be capable of operating at 1.4 dB from the capacity bound, which is about 1.56 times the corresponding discrepancy of the proposed IrVLC-aided scheme

Analysing service level agreements with multiple customers.

Within numerous production and distribution environments, maintenance of effective customer service is central to securing competitive benefits. Globalised industries are becoming more commonplace as well, further increasing the competitive pressure. Companies, as a result, are forced to expand product availability and deliver to the demand on schedule. As part of a supply chain, service levels are an important measure of performance in operations management and are widely used to evaluate and manage supplier performance. This thesis examines the SLA for the supplier under two types of contracts to guarantee the agreed customer service level. Specifically, this dissertation will shed light on the two most important (SLA) measurements for inventory systems: fill rate and ready rate. Both SLA measurements are commonly used as performance measures in SLAs between customers and suppliers. Throughout this thesis, we examine performance-based contracts in which the supplier has either: a single customer with a large demand, or multiple customers with a smaller demand. Our experiments were designed so that the demand distribution for the single customer case was similar to the aggregated demand distribution in the multiple customer case. The thesis primarily focused on four main questions, with each question being examined in its own chapter. The first research problem is addressed in Chapter 3. Earlier studies of finite horizon fill rate only consider the situation in which there is a single customer in the supply chain. In Chapter 3, we develop a model to analyse the fill rate distributions for a supplier that has multiple customers, each with its own SLA. In particular, we examine the impacts of performance review period length and the correlation between customer demands on the average fill rate and the probability of overreaching the target fill rate when a supplier has multiple customers. Under the multiple customer contracts, two service policies for demand fulfilment. In the first policy, First-Come-First-Served (FCFS), demand is filled with no prioritization (e.g., in the case of two customers, there is a 50% chance that the first customer is served first). In the second policy, Prioritized Lowest Fill Rate (PLFR), customers are prioritized so that the customer with the highest negative deviation from its target fill rate in the current performance review period is served first. The results and findings in Chapter 3 provide insights that can assist suppliers in the design and negotiation of SLAs. The second research problem is addressed in Chapter 4. Previous studies on the finite horizon fill rate are limited and assume a zero lead time for the supplier. We create a model to examine the impact of different supplier lead times on the finite horizon fill rate, considering either single customer or multiple customers. As lead time exists in reallife supply chains, we explore the effect of various lead times on the fill rate distribution and required base stock over finite horizons with a variety of review period lengths. The results revealed that to fix the long-run fill rate, as the lead time increases, more stock is required; however, the probability of exceeding the target fill rate (the probability of success) increases as the lead time increases. The results indicate that the increase in the probability of success as the lead time increases is higher when the review period is shorter. For the third research problem Chapter 5 presents further results related to the fill rate, an important measure of supply chain performance, specifically ensuring that a customer’s service need is met with maximum reliability. These results mainly concentrate on variability, an aspect that is largely ignored in the literature on fill rate. Related results concerning consistency and asymptotic normality extend the range of application of the fill rate in evaluating reliability and determining the optimal stock level of a supply chain. Chapter 6 explores the fourth research problem which considers the ready rate, a widely used performance measure in SLAs. The ready rate considered in this study is defined as the long-run fraction of periods in which all customer demand is filled immediately from on-hand stock. Previous studies of SLAs have been solely concerned with one supplier serving one customer, whereas in practice, a supplier usually deals with more than one customer. In multiple customer cases, the supplier has an SLA with each customer, and a penalty is incurred whenever the agreement is violated. In this chapter, we create a model to examine the impacts of various factors such as the base-stock level, the type of penalty (lump-sum and linear penalty), and the review period duration on the supplier’s cost function when the supplier deals with multiple customers. The results show that dealing with more customers is preferable for a supplier (assuming the overall demand is the same) and that under a lump-sum penalty contract, a longer performance review is beneficial. Finally, Chapter 7 closes with a brief review, discussion on the models constructed and suggests areas for future studies

Corrigendum to “The Current Practice of Screening, Prevention, and Treatment of Androgen-Deprivation-Therapy Induced Osteoporosis in Patients with Prostate Cancer”

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