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Differential amplitude phase shift keying (DAPSK) is a promising modulation technique for use in high-mobility environments, as it does not require channel estimation. In this paper, a novel reduced complexity soft demodulator for high-order DAPSK constellations is proposed. The main idea relies on a two-step approximation of the sum-log demapper. In the first step, a parallel factor analysis (PARAFAC) decomposition is used to approximate log-likelihood ratios. Next, the basis functions obtained through the first step are approximated by piecewise-linear curves. Numerical optimization techniques are employed for the PARAFAC decomposition and its piecewise-linear approximation whose parameters are then stored in a lookup table. It has been verified through computer simulations that the proposed scheme clearly outperforms the scheme proposed in the paper “Reduced-complexity noncoherent soft-decision-aided DAPSK dispensing with channel estimation,” ( IEEE Trans. Veh. Technol. , vol. 62, pp. 2633–2643, 2013.), while also having lower computational cost. Moreover, it is shown that the performance of the exact sum-log demapper and the proposed demapper is very close for ${\text{2}}\times {\text{4}}$ and ${\text{4}}\times {\text{16}}$ DAPSK constellations.

In this letter, we introduce a novel method for demodulation of general amplitude- and phase-shift keying (APSK) constellations. By noting that the max-log log-likelihood ratio (LLR) is a piecewise linear function of the received signal, we devise a scheme to determine in which linear region that the received signal falls, obtain the linear parameters from a lookup table and compute the LLR. This method is general and works for any APSK (two-dimensional) constellation. By pruning the search tree, it also provides a mechanism for performance-complexity tradeoff and we show that its complexity is much lower than a previously published scheme (which only works for regular APSK constellations).

In this letter, we derive a low-complexity method for demodulating nonuniform PAM signals. With uniform Gray-coded M-PAM constellations, the reflective symmetry can be exploited to demodulate the signals with low complexity. However with nonuniform constellations, this symmetry is lost and more complicated computations are required. We derive an analytic expression for the max-log LLR functions and show that they are piecewise linear functions. Based on this, we devise a demodulation algorithm that has complexity $\mathcal{O} \left(\log_2 M \right)$ as opposed to $\mathcal{O} \left(M \right)$ for the exhaustive search. We also present an approximation with reduced complexity and only modest performance degradation.

A fog radio access network (F-RAN) is studied, in which $K_T$ edge nodes (ENs) connected to a cloud server via orthogonal fronthaul links, serve $K_R$ users through a wireless Gaussian interference channel. Both the ENs and the users have finite-capacity cache memories, which are filled before the user demands are revealed. While a centralized placement phase is used for the ENs, which model static base stations, a decentralized placement is leveraged for the mobile users. An achievable transmission scheme is presented, which employs a combination of interference alignment, zero-forcing and interference cancellation techniques in the delivery phase, and the \textit{normalized delivery time} (NDT), which captures the worst-case latency, is analyzed., Comment: 6 pages, 7 figures

In this letter we consider array codes that are used for erasure protection in, e.g., wireless sensor networks. By treating the network as distributed storage with multiple sources, information can be exchanged between the nodes in the network allowing each node to store parity symbols relating to data from other nodes. We show how these array codes can be reconfigured to minimise the probability that some data symbols are not correctly exchanged (and therefore reducing the erasure correcting capability of the array code). We also present a suboptimal method for a class of array codes which significantly reduces the complexity of the reconfiguration while maintaining almost all of the performance.

In this paper, we introduce a lowest-density maximum-distance separable MDS array code, which is applied to a Smart Meter network to introduce reliability. By treating the network as distributed storage with multiple sources, information can be exchanged between the nodes in the network allowing each node to store parity symbols relating to data from other nodes. A lowest-density MDS array code is then applied to make the network robust against outages, ensuring low overhead and data transfers. We show the minimum amount of overhead required to be able to recover from r node erasures in an n node network and explicitly design an optimal array code with lowest density. In contrast to existing codes, this one has no restrictions on the number of nodes or erasures it can correct. Furthermore, we consider incomplete networks where all nodes are not connected to each other. This limits the exchange of data for purposes of redundancy, and we derive conditions on the minimum node degree that allow lowest-density MDS codes to exist. We also present an explicit code design for incomplete networks that is capable of correcting two node failures. Copyright © 2015 John Wiley & Sons, Ltd.

While obtaining the channel state information (CSI) required to perform Interference Alignment (IA) in a centralised MIMO network is a challenge, this is compounded in unplanned wireless networks that may be decentralised - not to mention composed of devices with varying degrees of complexity and capability. This is of particular interest to heterogeneous networks and the Internet of Things (IoT). The disparity in antenna number caused by this variation in capability can be taken advantage of, increasing the sum rate of the network providing the users are aware of the capabilities of their neighbours. This paper presents a method for estimating with a high degree of certainty the number of antennas each user possesses, endowing the receiver with the vital CSI required before channel equalisation or estimation can take place. The method is correlation based and so is not restricted to full rank channels where the receiving device has an equal or greater number of antennas than the transmitter. This permits the use of the method in situations where the rank of the channel is restricted, either by design or by nature (e.g. 'keyhole' channels).

INTRODUCTION: Barrett esophagus (BE) is a complication of gastroesophageal reflux disease. We wish to determine the effects of surgery on the histology of the esophageal mucosa and evaluate Quality of Life. MATERIALS AND METHODS: Twenty-seven patients with columnar-lined esophagus (CLE) metaplasia underwent laparoscopic Nissen-Rossetti fundoplication. Patients were submitted to close follow-up. RESULTS: One patient voluntarily left follow-up after surgery. CLE was still present in 18 patients (66.6%); no patient developed dysplasia or esophageal adenocarcinoma. Two patients with gastric metaplasia and 1 patient with intestinal metaplasia had regression at 12 and 24 months after surgery (11.1%). DeMeester and Johnson score decreased from 38.69 (SD ± 51.44) to 11.99 (SD ± 18.08) at 6 months, 12.69 (SD ± 12.91) at 12 months, and it was 11.38 (SD ± 6.43) at 24 months. Preoperative gastroesophageal reflux disease-health related quality of life was 19.90 (SD ± 18.54), 9.80 (SD ± 8.77) at 6 months, 9.57 (SD ± 9.14) at 12 months, and 11.53 (SD ± 6.48) at 24 months. Short form-36 measurement showed significant improvement. CONCLUSIONS: Management of CLE requires multidisciplinary approach. Medical therapy does not prevent biliary reflux into the esophagus. Surgical therapy is effective and long lasting. It should be performed by experienced surgical teams.

A $K_T \times K_R$ cache-aided wireless interference network, in which both the transmitters and the receivers are equipped with cache memories is studied. Each user requests one file from a library of $N$ popular files. The goal is to design the cache contents without the knowledge of the particular user demands, such that all possible demand combinations can be satisfied reliably over the interference channel. The achievable sum degrees-of-freedom ($\mathrm{sDoF}$) and the normalized delivery time (NDT) are studied for centralized and decentralized network architectures, respectively. First, using a combination of interference alignment (IA), zero-forcing (ZF) and interference cancellation (IC) techniques, a novel caching and transmission scheme for centralized networks is introduced, and it is shown to improve the $\mathrm{sDoF}$ upon the state-of-the-art. Then, the NDT is studied when the content placement at the receiver caches is carried out in a decentralized manner. Our results indicate that, for this particular network architecture, caches located at the receiver side are more effective than those at the transmitter side in order to reduce the NDT., Comment: 6 pages, 4 figures, conference

The paper focuses on the performance analysis of channel assignment algorithms for peer to peer wireless ad hoc network by means of realistic channel model. The channel assignment is modeled as an edge colouring problem and two colouring algorithms including random and greedy colouring have been studied using the realistic 3D ray tracing based path loss model and its performance is compared with the theoretical model. The simulation study shows that the algorithms perform better with the ray tracer model with around 10 dB improvement in SINR as compared to the theoretical model.

Tone reservation (TR) is a well-known and practical strategy to reduce peak-to-average power ratio (PAPR) in OFDM signals. In TR some unused or reserved subcarriers are used to accommodate a peak-cancelling signal that lowers the PAPR of the time domain OFDM signal. Several methods have been proposed to optimise the peak-cancelling signal, amongst which the so called active-set method has been shown to converge very quickly to a minimum PAPR solution for a real baseband signal with no additional power constraints. However, for a general complex baseband signal and/or when the peak-cancelling signal has to be power limited, there is no guarantee of optimality. Moreover, in the complex baseband model, the TR optimisation problem is a quadratically constrained quadratic program (QCQP), which has a prohibitive computational cost. In this paper we introduce a tree-search approach to designing the TR signal based on the sphere decoding/encoding principle. The method is proved to provide the minimum PAPR solution in the limit of fine lattice quantisation. Simulation results show a significant margin of improvement over the best known active-set method.

We study the effect on diversity of using the sphere encoder-based vector perturbation (VP) technique of Peel and the lattice reduction-aided techniques (Babai approximations) of Windpassinger on a subset of the transmitted symbols. For a system with n diversity channels, we prove that the diversity order gap between the maximum diversity of n achieved by the full-size VP and the minimum diversity of 1 provided by linear precoding can be bridged by applying VP to a group of transmitted symbols. In particular, we prove that the diversity order is n-l , where l is the number of symbols that are not vector-perturbed. We show that this result holds true for lattice-reduction with both the rounding-off and nearest plane Babai approximations. The result shows that in terms of diversity, the group of vector-perturbed users counts as a single user. In fact, in a multiple-input and multiple-output Gaussian broadcast channel with l linearly precoded users, we can add up to n-l VP users and the diversity order for all users will decrease only by one, irrespective of how many VP users are added.

Laparoscopic Nissen fundoplication is currently the gold standard for surgical treatment of gastroesophageal reflux disease. The aim of this study was to present our experience with this procedure at 1 year of follow-up. Forty patients were operated on between January 2006 and July 2007, and 30 underwent a 24-hour postoperative pH-metry study. Ninety-two percent of the patients were asymptomatic at a follow-up of 12 months. All pH-metric parameters improved. DeMeester and Johnson's score was reduced from 44.7 to 7.75; endoscopy with histologic samples revealed the healing of esophagitis in all patients; 4 (13%) patients complained of dysphagia, which resolved within 1 month after surgery. Twenty-seven (90%) patients were completely satisfied by their surgical results. One year after surgery, 24-hour ph-metric results show that laparoscopic Nissen fundoplication can completely control acid reflux with relatively few complications and a high degree of patient satisfaction.

Multiuser MIMO vector perturbation precoding facilitates multiple representations of the transmit symbols in order to improve transmit power normalisation of the transmitted signal. All the receiver needs to do is to apply a modulo operation to undo the perturbation. However existing system with multiuser MIMO support, such as LTE, employ linear precoding. This means that these legacy users will not be able to operate together with new users with vector perturbation capabilities, reducing the system throughput and flexibility in resource allocation. In this paper we present a novel precoding technique which allows the joint precoding of legacy and new users. The precoding ensures that no perturbations are made to linearly precoded users, while minimising the power normalisation using a modified sphere encoder. We also show that the diversity order of the joint precoding scheme is the difference between the number of transmit antennas and the number of legacy users, regardless of the number of new users.