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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.

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.