In this paper, we design a new coded cooperation protocol utilizing superposition modulation together with iterative decoding/detection algorithms. The aim of the proposed system is to apply "dirty paper coding" theory in the context of half-duplex relay systems. In the proposed system, the node transmits a superposed signal which consists of its own coded information and other node's re-coded information. The destination node detects and decodes the signal using the received signals at two continuous time-slots with iterative decoding algorithm. Moreover, the destination node detects the received signal using the results of decoding, iteratively. This paper provides the outage probability of the proposed system under the assumption that the proposed system can ideally perform dirty paper coding, and it is shown from the comparison between outage probabilities and simulated results that the proposed system can get close to the dirty paper coding theory.

The impact and benefits of infrastructure support are shown by introducing an achievable throughput scaling law of a ultra-wide band (UWB) ad hoc network in which m base stations (BSs) are regularly located. The existing multi-hop scheme consisting of two variants, with and without BS help, is utilized with a slight modification. Our result indicates that the derived throughput scaling depends on the path-loss exponent due to the power-limited characteristics for all operating regimes examined. Furthermore, it is shown that the total throughput scales linearly with parameter m as m is larger than a certain level. It thus turns out the use of infrastructure is also helpful in improving the throughput scaling of UWB networks in some conditions.

Comb capacitors suitable for use in advanced complementary metal-oxide semiconductor (CMOS) technology nodes are frequently constructed from low metal layers located closely above the conductive silicon substrate. This results in high parasitic capacitances across the thin dielectric between the two layers. Therefore, a shield for reducing this parasitic capacitance is proposed in order to use the comb capacitor at high frequency. From electromagnetic (EM) simulation results using a 3D EM simulator, the quality factor (Q-factor) of the proposed shielded comb capacitor for the differential signal improved by 20% at 30-110 GHz compared to the unshielded capacitor. Consequently, a scalable model is proposed, which operates up to millimeter-wave frequencies. The results are verified by experimental data using fabricated comb capacitors from a 90 nm 1P9M CMOS process. Compared with the experimental results, the simulated common-mode and differential-mode S parameters of the model has a root-mean-square (r.m.s.) error of under 2.1%.

The non-orthogonal multiple access (NOMA) approach has been developed in the fifth-generation mobile communication systems (5G) and beyond, to improve the spectrum efficiency and accommodate a large number of IoT devices. Although power domain NOMA is a promising candidate, it is vulnerable to the nonlinearity of RF circuits and cannot achieve high-throughput transmission using high-level modulations in nonlinear environments. This study proposes a novel post-reception nonlinear compensation scheme consisting of two blind nonlinear compensators (BNLCs) and a frequency-domain equalizer (FDE) to reduce the effect of nonlinear distortion. The improvement possible with the proposed scheme is evaluated by using the error vector magnitude (EVM) of the received signal, which is obtained through computer simulations. The simulation results confirm that the proposed scheme can effectively improve the quality of the received downlink power-domain NOMA signal and enable high-throughput transmission under the transmitter (Tx) and receiver (Rx) nonlinearities via a frequency-selective fading channel.

The concept of regional diversity-multiplexing tradeoff (DMT) is introduced by extending the asymptotic outage probability expression for multiple-input multiple-output (MIMO) channels. It is shown that for both Rayleigh and Rician MIMO channels, the regional diversity gain is a linear function of the regional multiplexing gain and that the original DMT curve can be obtained from the set of regional DMT lines. As a result, vital information for capturing both finite and infinite signal-to-noise ratio characteristics in terms of DMT is provided.

Quantum dots are one of the possible building blocks for the quantum computing device. We discuss on use of carbon nanotubes for fabrication of the quantum dot, in terms of their unique physical properties and energy scales which might be advantageous for functionalities of the quantum computing device. Simple schemes of a charge qubit and a spin qubit are described, followed by the current status of the fabrication and transport measurements of the nanotube quantum dot. Based on the basic properties and the estimated energy scales of the dot, we discuss advantages and problems of the carbon nanotube for the quantum computing device. The nanotube quantum dot may have a great advantage for the spin qubit.

In this paper, we propose new radio access network (RAN) architecture for reliable millimeter-wave (mmWave) communications, which has the flexibility to meet users' diverse and fluctuating requirements in terms of communication quality. This architecture is composed of multiple radio units (RUs) connected to a common distributed unit (DU) via fronthaul links to virtually enlarge its coverage. We further present grant-free non-orthogonal multiple access (GF-NOMA) for low-latency uplink communications with a massive number of users and robust coordinated multi-point (CoMP) transmission using blockage prediction for uplink/downlink communications with a high data rate and a guaranteed minimum data rate as the technical pillars of the proposed RAN. The numerical results indicate that our proposed architecture can meet completely different user requirements and realize a user-centric design of the RAN for beyond 5G/6G.

A one-dimensional ad hoc network with a single active source–destination pair is analyzed in terms of transport capacity, where each node uses multiple antennas. The analysis is based on using a multi-hop opportunistic routing transmission in the presence of fading. Specifically, the lower and upper bounds on the transport capacity are derived and their scaling law is analyzed as the node density, λ, is assumed to be infinitely large. The lower and upper bounds are shown to have the same scaling (ln λ)1/α, where α denotes the path-loss exponent. We also show that using multiple antennas at each node does not fundamentally change the scaling law.

In order to obtain higher diversity gain, the use of additional resources such as time, frequency, and/or antennas are necessary. The aim of this study is to achieve adequate temporal diversity gain without needing additional resources beyond decoding delay and decoding complexity. If the channel state information (CSI) is not available at the transmitter side, the transmitter sends information at a given constant transmission rate while the channel capacity varies according to the channel state. If the instantaneous channel capacity is greater than the given transmission rate, the system can successfully transmit information but it does not exploit the entire available channel capacity. We focus on this extra channel capacity to transmit other information based on a joint network-channel coding in order to obtain higher diversity and coding gains. This paper provides the basic concept of the transmit diversity with the joint network-channel coding and investigates its performances in terms of outage probability, additional decoding delay and complexity, and frame-error rate (FER).

We show an improved throughput scaling law for an ultra-wide band (UWB) ad hoc network by using a modified hierarchical cooperation (HC) strategy; the n wireless nodes are assumed to be randomly sited. In a dense network of unit area, our result indicates that the derived throughput scaling depends on the path-loss exponent α for certain operating regimes due to the power-limited characteristics. It also turns out that the use of HC is helpful in improving the throughput scaling of our UWB network in some conditions. More specifically, assuming that the bandwidth scales faster than nα+1(log n)α/2, it is shown that the HC protocol outperforms nearest multi-hop routing for 2 < α < 3 while using nearest multi-hop routing leads to higher throughput for α ≥ 3.

In this paper, we introduce a distributed power allocation strategy for random access, that has the capabilities of multipacket reception (MPR) and successive interference cancellation (SIC). The proposed random access scheme is suitable for machine-to-machine (M2M) communication application in fifth-generation (5G) cellular networks. A previous study optimized the probability distribution for discrete transmission power levels, with implicit limitations on the successful decoding of at most two packets from a single collision. We formulate the optimization problem for the general case, where a base station can decode multiple packets from a single collision, and this depends only on the signal-to-interference-plus-noise ratio (SINR). We also propose a feasible suboptimal iterative per-level optimization process; we do this by introducing relationships among the different discrete power levels. Compared with the conventional power allocation scheme with MPR and SIC, our method significantly improves the system throughput; this is confirmed by computer simulations.