Machine learning data privacy has been improved with Federated Learning approaches. However, some obstacles to guaranteeing traceability, openness, and participant contribution incentives prevent its widespread use. In this study, Ethereum blockchain technology is integrated into the data stream Kafka-ML framework, presenting a novel asynchronous and blockchain-based Federated Learning approach. By utilising Ethereum for transparent and auditable participant tracking, this integration overcomes some shortcomings such as auditability and model sharing reliability. Furthermore, Ethereum smart contracts allow for automatic reward distribution systems, which promote equitable incentive systems and increased involvement in the Federated Learning process. To demonstrate its potential, an extensive evaluation has been carried out on a wireless net-work technology detection use case. By improving transparency, traceability, and incentive structures of Federated Learning, it is expected to strengthen the robustness of flexible machine learning collaboration with data streams.

To enable widespread use of electric vehicles (EVs), large-scale public charging stations with fast chargers are being planned in places such as shopping malls and office car parks. Operators of public charging stations need to utilize EV scheduling algorithms that can satisfy charging demands with a minimum number of simultaneous charging sessions. In this paper, we propose EV charging scheduling algorithms that meet the charging demands and deadlines of EV users while minimizing the number of simultaneous charging sessions. An uncertainty-aware deep learning (DL) framework is also used to predict EV arrivals at a charging station. The predicted EV arrivals in turn are used to help the charging operator estimate how many charging sessions to order from the grid. Our DL model not only predicts the mean EV arrival rates but also the upper limits of EV arrivals, which enhances robustness against uncertainty in EV arrivals and helps estimate the maximum charging demand for a given interval. Moreover, to overcome the challenge of insufficient EV charging data for DL models, we construct a synthetic data model that takes into account multiple factors influencing EV arrivals, such as weather, events, weekdays, and weekends. Both online and offline approaches in the design of EV scheduling algorithms are utilized. The performances of the proposed algorithms are evaluated in terms of active charging sessions used to serve EV users. We also compare their performance with a baseline algorithm which is an offline optimal algorithm based on a mixed integer linear problem formulation.

The application of hyper-wideband is required by 6G sub-THz wireless communication, to enable it provide a peak data rate of up to hundreds of Gbps. However, simultaneously achieving a large bandwidth and high signal quality at the receiver remains a challenge owing to a various hardware non-idealities; hence, additional signal processing techniques are necessary to compensate for these issues. Although conventional analog circuits for the signal compensation cause extra power consumption and hardware implementation complexity, the digital-domain signal compensation technique at the receiver modem exploits both the low power consumption per computation and side-information provided by a sub-THz communication system. In this paper, we propose a digital-domain signal compensation method comprising a compensation filter and parameter estimation, achieving both hyper-wideband and high signal quality. Numerical evaluations were conducted with hyper-wideband and high signal quality scenarios, and the performance of the proposed method was further demonstrated with the spectrum variability of sub-THz systems.

This paper comprehensively studies a content-centric mobile network based on a preference learning framework, where each mobile user is equipped with a finite-size cache. We consider a practical scenario where each user requests a content file according to its own preferences, which is motivated by the existence of heterogeneity in file preferences among different users. Under our model, we consider a single-hop-based device-to-device (D2D) content delivery protocol and characterize the average hit ratio for the following two file preference cases: the personalized file preferences and the common file preferences. By assuming that the model parameters such as user activity levels, user file preferences, and file popularity are unknown and thus need to be inferred, we present a collaborative filtering (CF)-based approach to learn these parameters. Then, we reformulate the hit ratio maximization problems into a submodular function maximization and propose two computationally efficient algorithms including a greedy approach to efficiently solve the cache allocation problems. We analyze the computational complexity of each algorithm. Moreover, we analyze the corresponding level of the approximation that our greedy algorithm can achieve compared to the optimal solution. Using a real-world dataset, we demonstrate that the proposed framework employing the personalized file preferences brings substantial gains over its counterpart for various system parameters.

In this study, an energy-efficient self-organized framework for sub-channel allocation and power allocation is presented for ultra-dense small cell networks, which can operate in both licensed and unlicensed bands. In order to protect legacy WiFi devices (operating in unlicensed bands), we consider the Long-Term Evolution (LTE) operation in unlicensed bands based on Carrier Sense Adaptive Transmission (CSAT), in which 'ON' and 'OFF' duty cycle approach is utilized. On the other hand, there are severe interference management problems among small cells (operating in licensed and unlicensed bands) and between macro cells and small cells (operating in licensed bands) due to co-channel and ultra-dense deployment of small cells. This article proposes a self-organized optimization framework for the allocation of sub-channels and power levels by exploiting a non-cooperative game with the objective to maximize the energy efficiency of dual-access small cells without creating harmful impact on coexisting network entities including macro cell users, small cell users, and legacy WiFi devices. Simulation results show that the proposed scheme outperforms (6 and 11 percent) and (8 and 18 percent) the round-robin and the spectrum-efficient schemes, respectively, for two different small cell scenarios. In addition, it is shown that for less channel state information (CSI) estimation errors ς = 0.02, the maximum performance degradation of the proposed scheme is reasonably small (5.5 percent) as compared to the perfect CSI.

This paper presents novel ultrareliable and low-latency communication (URLLC) techniques for URLLC services, such as Tactile Internet services. Among typical use cases of URLLC services are teleoperation, immersive virtual reality, cooperative automated driving, and so on. In such URLLC services, new kinds of traffic such as haptic information including kinesthetic information and tactile information need to be delivered in addition to high-quality video and audio traffic in traditional multimedia services. Furthermore, such a variety of traffic has various characteristics in terms of packet sizes and data rates with a variety of requirements of latency and reliability. Furthermore, some traffic may occur in a sporadic manner but requires reliable delivery of packets of medium to large sizes within a low latency, which is not supported by current state-of-the-art wireless communication systems and is very challenging for future wireless communication systems. Thus, to meet such a variety of tight traffic requirements in a wireless communication system, novel technologies from the physical layer to the network layer need to be devised. In this paper, some novel physical layer technologies such as waveform multiplexing, multiple-access scheme, channel code design, synchronization, and full-duplex transmission for spectrally efficient URLLC are introduced. In addition, a novel performance evaluation approach, which combines a ray-tracing tool and system-level simulation, is suggested for evaluating the performance of the proposed schemes. Simulation results show the feasibility of the proposed schemes providing realistic URLLC services in realistic geographical environments, which encourages further efforts to substantiate the proposed work.

Heterogeneous cellular networks (HCNs) where conventional macro cells are being overlaid with low-powered small cells and the millimeter wave (mmW) frequencies are considered as a way to efficiently enhance the spectral efficiency per area with the availability of huge bandwidths. However, how to efficiently manage small cells and mmW frequencies is still an open question. In this paper, a load balancing problem for 5G HCNs is discussed with different band operation modes and a joint user association (UA) scheme using a hybrid self-organizing network (SON) is suggested for a practical clustered HCN.

In this paper, a novel accumulate-repeat-accumulate-check-accumulate (ARACA) code is proposed as a subclass of protograph-based low-density parity-check (LDPC) codes. The key feature of the proposed ARACA code is represented by the outer connection doping in the protograph. This feature can provide the linear minimum distance growth (LMDG) property at a good iterative decoding threshold while maintaining an efficient encoder structure. The effect of the outer connection doping on the typical minimum distance, the iterative decoding threshold, and the LMDG property is discussed and analyzed by comparing case examples and using the asymptotic protograph ensemble weight enumerator. Some good ARACA code protographs are provided for a wide range of code rates. In addition, an efficient and universal encoding procedure and the corresponding encoder structure are provided for them. The performance of the proposed ARACA code is evaluated and compared with well-known good LDPC codes. The simulation results confirm the superiority of the proposed ARACA codes in terms of encoding complexity and frame error rate performance, especially at low-rates in an ultra-reliable regime.

In this paper, we consider a delay and energy constrained wireless ad hoc network with node density of λn, where a packet should be delivered to the destination within D(λn) seconds using at most E(λn) energy in joules while satisfying the target outage probability. The performance metric for analyzing the network is the delay and energy constrained random access transport capacity (DE-RATC), i.e., $Cϵ(D(λn), E(λn), which quantifies the maximum end-to-end distance weighted rate per unit area of a delay and energy constrained network using a random access protocol. It is shown that a slotted ALOHA protocol is order-optimal under any delay and energy constraints if equipped with additional features such as power control, multi-hop control, interference control, and rate control, and the delay and energy constraints can be divided into three regions according to the relation between the physical quantities due to the constraints and those due to the node density and network size. The three regions are the non-constrained (NC) region, where the DE-RATC is given by Θ(√λn/logλn); the delay-constrained (DC) region, where the DE-RATC depends only on the delay constraint as Θ(D(λn); and the non-achievable (NA) region where a packet delivery under the given constraints is impossible. Also, it is shown that an arbitrary tradeoff between the rate of each source node and the number of source nodes can be achieved while keeping the optimal capacity scaling as long as λs=Ω√λn/logλn, Dλn))).

In this paper, partial feedback schemes for a multiple input multiple output orthogonal frequency division multiple access system using a random beamforming are analyzed and optimized. For partial feedback schemes, the partial channel quality indicator feedback schemes and the partial channel quality rank indicator feedback schemes are considered. For these schemes, we first derive the effective downlink spectral efficiencies by considering the required uplink resource for feedback together over block fading channels. Then, by using the analysis, the amount of feedback overhead per user is optimized to maximize the effective downlink spectral efficiency according to the system and channel parameters. From the analysis and numerical examples, we show that the partial channel quality rank indicator feedback scheme provides better performance than the partial channel quality indicator feedback scheme unless the channel rapidly varies owing to its feedback efficiency, and the proposed adaptive control of the feedback overhead can improve the performance of practical systems, such as the 3rd generation partnership project 3GPP long term evolution, in practical scenarios. Copyright © 2012 John Wiley & Sons, Ltd.

In this paper, we consider delay-constrained wireless multi-hop ad hoc networks where a packet should be delivered to the destination within the maximum allowed delay while satisfying the target outage probability. The proposed performance metric for analyzing networks is the delay-constrained random access transport capacity (D-RATC), which quantifies the maximum end-to-end (e2e) link achievable rate per unit area of a delay-constrained network using a random access protocol. The scaling of the D-RATC is obtained for various slotted ALOHA (SA) protocols and it is shown that the SA protocol is order-optimal for delay-constrained random networks when interference control is used with an additional feature such as rate control or admission control. If interference control is not used, the SA protocol suffers from the negatively infinite scaling exponent except the case of using rate control where a finite but suboptimal scaling exponent may be achieved. Also, it is shown that multi-hop control does not affect the scaling exponent but just improves the D-RATC pre-constant.

We study joint feedback design for multiple access channel (MAC) over fading Gaussian Channel. The transmitters use partial channel-state information (CSI), which is obtained via an optimized feedback link. We develop a simple iterative algorithm for the design of CSI quantization to maximize the expected rate. Also, we show the performance by simulation result.

In this paper, we propose a 6-step scheme for efficient CoMP scheme selection and radio resource management. Simulations show that the proposed 6-step scheme can greatly improve user average throughput compared to a conventional 4-step scheme.

In this paper, detailed cross-correlation properties for Chu sequences are investigated. All possible values of the cross-correlation function of Chu sequences are derived for any given sequence length and lag, and the maximum magnitude distribution function$\rho _{N}(x)$, which is defined as the number of all Chu sequence pairs with length-$N$whose maximum magnitude of the cross-correlation function is${\sqrt {Nx}}$, is obtained. Also, good lower and upper bounds on the maximum number of available Chu sequences and a construction algorithm for the corresponding partial Chu sequence set are proposed when the maximum magnitude of the cross-correlation among the sequences is constrained. Numerical examples show that the proposed bounds are quite tight and the proposed construction algorithm is near-optimal up to fairly large value of$N$.

In this paper, optimal pilot sequence designs for MIMO-OFDM systems in multi-cell environments are provided. The proposed multi-cell optimality criterion is to minimize the worst-case MSE of an LS-based channel estimator. To satisfy the multi-cell optimality, it is found that the pilot sequence set, having the perfect auto-correlation property, should meet the Welch bound and the maximum magnitude of the cross-correlation function should be further minimized. Multi-cell optimal pilot sequence designs for various pilot types and their DFT representations are proposed by adopting Chu sequences and a tight upper-bound on the maximum size of the pilot sequence set is derived for a given pilot sequence length and the maximum allowed cross-correlation value. Simulation results show that the proposed pilot sequences can improve both the MSE performance and the system performance in multi-cell environments.

Femtocell is a small base station with low power which can be installed by users to get better data rate in the indoor environment. The power control scheme of the femtocell BS is the most important issue in the femtocell implementation but there still exist deadzones if macrocell users are located very close to the femtocell. In this paper, we have proposed a new frame structure for the IEEE 802.16e based femtocell. Self-initialized segements selection and preamble allocation scheme are also proposed. Using the proposed preamble structure and self-initialization scheme, macrocell users can detect a macrocell BS even though they are located very close to the femtocell. The simulation results show that macrocell users can survive and communicate with the macrocell BS even though they are in the femtocell coverage. Additionally, it is shown that the proposed system provides the highest throughput of the macrocell and the femtocell inside the femtocell coverage.

We consider multiuser multicarrier systems, where each non-symmetrically distributed user reports only partial indices of subcarriers whose normalized SNRs exceed the predetermined threshold so that only partial feedback information is available at the base station. To accommodate both efficiency and fairness, the base station is assumed to perform the normalized SNR based proportional fair scheduling (PFS). Using the simple and quite well matched approximation of the ordered channel capacity, the approximated ergodic capacity of the full SNR feedback scheme is derived as well as the exact expression of the ergodic capacity of the partial index feedback scheme. Their asymptotic behaviors as the number of users and average SNR increase are also derived. An important finding through the performance analysis and numerical examples in this paper is that, also in the non-symmetrical multiuser distributed multicarrier system performing the PFS with limited feedback, the ergodic capacity of the optimal asymptotic growth rate can be achieved, keeping the average feedback overhead bounded regardless of the number of users.

A simple design method using trellis search is proposed for good low-density parity-check (LDPC) codes with relatively low code rates. By applying a trellis search technique to the design of a pre-assigned part of the parity-check matrix that allows a simple encoding, we improve the distribution of cycles formed by the entries contained in the parity-check part of the parity-check matrix. In addition, we extend the proposed algorithm to a class of structured LDPC codes, which have been recently preferred in many practical applications. Simulation results show that the codes designed by the proposed method outperform those constructed by conventionally used greedy design algorithms.

This paper presents variable power and rate allocation (PRA) for a multiuser orthogonal frequency division multiple access code division multiplexing (OFDMA-CDM) system which exploits both orthogonality among users and symbol-level diversity. To predict the link performance, we analyze the postprocessing SNR as the transmit power (TP) varies when the minimum mean square error combiner (MMSEC) is employed. It is shown from analysis that the MMSEC SNR is nonlinear in TP, but is bounded by the harmonic and the arithmetic means of the subcarrier SNRs. From the observation, we propose two variable PRA methods using a simple channel quality indication and a required TP estimation method. Simulation results show that the proposed methods not only guarantee the target performance but also increase the throughput at the same or slightly increased feedback overhead compared with the fixed TP allocation case.

In this letter, a novel time-domain recursive algorithm is proposed for a minimum-mean-squared error (MMSE) with successive interference cancellation (SIC) scheme. This algorithm allows us to reduce the complexity of classical MMSE-SIC equalizer for suppressing intercarrier interference (ICI) caused by time-varying multipath channels in orthogonal frequency division multiplexing (OFDM) systems, and it can provide almost the same performance as that of the optimal MMSE-SIC equalizer. It is shown in complexity analysis that the proposed scheme shows better complexity reduction than previously reported low-complexity MMSE-SIC schemes when applied to a channel equalizer for an OFDM system.

In this paper, we propose a generalized formula for generating puncturing patterns for block-type low-density parity check (B-LDPC) codes with dual-diagonal parity structure. The proposed formula distributes punctured bits uniformly in the zigzag edge connections, as well as maximizes the minimum recovery speed and the reliability of each punctured node. Also, the proposed puncturing can be applied to any B-LDPC code with dual-diagonal parity structure and can provide efficient bitwise puncturing patterns even when the number of puncturing bits is not equal to an integer multiple of the block size. Simulation results show that the proposed punctured B-LDPC codes are better than existing punctured B-LDPC codes and even dedicated B-LDPC codes used in commercial standards.

In this paper, we propose an efficient puncturing method for LDPC codes. The proposed algorithm provides the order of variable nodes for puncturing based on the proposed cost function. The proposed cost function tries to maximize the minimum reliability among those provided from all check nodes. Also, it tries to allocate survived check nodes evenly to all punctured variable nodes. Furthermore, the proposed algorithm prevents the formation of a stopping set from the punctured variable nodes even when the amount of puncturing is quite large. Simulation results show that the proposed punctured LDPC codes perform better than existing punctured LDPC codes.

A search algorithm for stopping sets in a Tanner graph is proposed for designing good low-density parity-check (LDPC) codes. By applying the belief-propagation algorithm with messages containing the information of originated variable nodes and their connected edges, the stopping sets can be detected. Furthermore, a code design method using the algorithm is presented and the performances of the designed code over several channels are shown

In this paper, we propose an LDPC-coded OFDMA system with a resource allocation method suitable for the uplink of mobile cellular environments. At the receiver of the proposed system, an iterative channel estimation and decoding (IED) method with a Wiener filter adapting to the channel variation rate is employed to support high mobility without boosting the pilot power. For practical applications, the channel variation rate is also estimated with pilot symbols to select Wiener filter coefficients for every received packet dynamically allocated. It is shown that the proposed system supports the mobility up to 250 km/h and exhibits more than 1 dB performance gain over the system with conventional non-iterative receiver.

For pt.I see ibid., vol.50, p.2018-31 (2002). In part I, we proposed and investigated a hybrid pulse position modulation/ultrashort light pulse code-division multiple-access (PPM/ULP-CDMA) system for ultrafast optical communication networks. In this scheme, the large bandwidth of a ULP is efficiently utilized by virtue of the very high time resolution of a time-space processor. More detailed analysis and discussion on the receiver scheme using the time-space processor is now presented; nonideal performance of the time-space processor, including the reference pulse realization problem, as well as amplifier and detector noise, are taken into account. Discussions on physically achievable ranges of the system parameters that determine the performance of the proposed PPM/ULP-CDMA system are also made based upon current, state of the art technology. As remedies to overcome the physical limitations on the system parameters, two modified modulation/demodulation schemes are proposed and investigated to enhance the performance of the hybrid PPM/ULP-CDMA system.

We propose a hybrid pulse position modulation/ultrashort light pulse code-division multiple-access (PPM/ULP-CDMA) system for ultrafast optical communications. The proposed system employs spectral CDMA encoding/decoding and PPM with very short pulse separation. The statistical properties of the encoded ULP are investigated with a general pulse model, and the performance of the proposed PPM/ULP-CDMA system is investigated. It is shown that we can improve upon the performance of other ULP-CDMA systems, such as those using on-off keying, by employing PPM. It is also shown that we can improve the performance of the proposed system by increasing the effective number of chips, by increasing the number of PPM symbols, and by reducing the ULP duration. The performance analysis shows that the aggregate throughput of the proposed PPM/ULP-CDMA system could be over 1 Tb/s.

We consider the quasi-maximum-likelihood (quasi-ML) detectors of the reverse link system that uses antenna arrays in asynchronous channels when the channel vector is time-invariant and time-varying. A channel vector estimation method based on eigendecomposition for time-invariant channels and its adaptive version suitable for the time-varying channels are also proposed. It is shown that the proposed quasi-ML detector can be regarded as a beamformer followed by a decorrelating filter and that the proposed system performs better than the conventional decorrelator scheme. It is also observed that the performance gain of the proposed scheme over the conventional decorrelator system increases as the numbers of active users and antenna arrays increase.

A vector channel model is proposed and some statistical properties of the asymptotic efficiency of the decorrelating detector with base-station antenna arrays are investigated. It is shown that we can get gain over the conventional decorrelator by employing antenna arrays and the gain increases as the number of antennas increases and the angle dispersion decreases. It is also shown that we can increase the asymptotic efficiency of the decorrelating detector with base-station antenna arrays up to unity if we use an infinite number of antennas when the channel is angle-nondispersive: we cannot, however, increase the asymptotic efficiency of the decorrelating detector by employing base-station antenna arrays if the dispersion is infinite.

A new sequence generation method and a method for reconstructing information symbols for a modulated orthogonal sequence are suggested: the sequence is generated by only integer sums and modular techniques. The autocorrelation and cross-correlation characteristics of the sequence are investigated via a new procedure. A modified sequence also having the orthogonality and satisfying the mathematical lower bound of the cross-correlation is proposed, and the symbol error probability of the sequence is investigated.

Detection of the existence of a desired user is considered in this paper. We assume that the signal to noise ratio is high enough to ignore the effects of noise compared with those of the interference by other users. The inter-user interference and user signals are modeled by the Nakagami model. The observation model for this situation is proposed, the locally optimum test statistic is derived under the model, and the asymptotic performance of the test statistic is compared with that of the envelope detector. We show that the locally optimum detector has performance better than the conventional envelope detector.