We compare the demodulation performance of an analog OTDM demultiplexing scheme and digitized OTDM demultiplexing with an ultrahigh-speed digital signal processor in a single-channel OTDM coherent Nyquist pulse transmission. We evaluated the demodulation performance for 40, 80, and 160Gbaud OTDM signals with a baseline rate of 10Gbaud. As a result, we clarified that the analog scheme performs significantly better since the bandwidth for handling the demultiplexed signal is as narrow as 10GHz regardless of the symbol rate. This enables us to use a low-speed A/D converter (ADC) with a large effective number of bits (ENOB). On the other hand, in the digital scheme, the higher the symbol rate becomes, the more bandwidth the receiver requires. Therefore, it is necessary to use an ultrahigh-speed ADC with a low ENOB for a 160Gbaud signal. We measured the ENOB of the ultrahigh-speed ADC used in the digital scheme and showed that the measured ENOB was approximately 1.5 bits lower than that of the low-speed ADC used in the analog scheme. This 1.5-bit decrease causes a large degradation in the demodulation performance obtained with the digital demultiplexing scheme.

Intelligent traffic monitoring provides information support for autonomous driving, which is widely used in intelligent transportation systems (ITSs). A method for estimating vehicle moving target parameters based on millimeter-wave radars is proposed to solve the problem of low detection accuracy due to velocity ambiguity and Doppler-angle coupling in the process of traffic monitoring. First of all, a MIMO antenna array with overlapping elements is constructed by introducing them into the typical design of MIMO radar array antennas. The motion-induced phase errors are eliminated by the phase difference among the overlapping elements. Then, the position errors among them are corrected through an iterative method, and the angle of multiple targets is estimated. Finally, velocity disambiguation is performed by adopting the error-corrected phase difference among the overlapping elements. An accurate estimation of vehicle moving target angle and velocity is achieved. Through Monte Carlo simulation experiments, the angle error is 0.1° and the velocity error is 0.1m/s. The simulation results show that the method can be used to effectively solve the problems related to velocity ambiguity and Doppler-angle coupling, meanwhile the accuracy of velocity and angle estimation can be improved. An improved algorithm is tested on the vehicle datasets that are gathered in the forward direction of ordinary public scenes of a city. The experimental results further verify the feasibility of the method, which meets the real-time and accuracy requirements of ITSs on vehicle information monitoring.

The multi-FPGA system known as, the Flow-in-Cloud (FiC) system, is composed of mid-range FPGAs that are directly interconnected by high-speed serial links. FiC is currently being developed as a server for multi-access edge computing (MEC), which is one of the core technologies of 5G. Because the applications of MEC are sometimes timing-critical, a static time division multiplexing (STDM) network has been used on FiC. However, the STDM network exhibits the disadvantage of decreasing link utilization, especially under light traffic. To solve this problem, we propose a hybrid router that combines packet switching for low-priority communication and STDM for high-priority communication. In our hybrid network, the packet switching uses slots that are unused by the STDM; therefore, best-effort communication by packet switching and QoS guarantee communication by the STDM can be used simultaneously. Furthermore, to improve each link utilization under a low network traffic load, we propose a dynamic communication switching algorithm. In our algorithm, each router monitors the network load metrics, and according to the metrics, timing-critical tasks select the STDM according to the metrics only when congestion occurs. This can achieve both QoS guarantee and efficient utilization of each link with a small resource overhead. In our evaluation, the dynamic algorithm was up to 24.6% faster on the execution time with a high network load compared to the packet switching on a real multi-FPGA system with 24 boards.

In this paper, we report an experimental and numerical analysis of ultrahigh-speed coherent Nyquist pulse transmission. First, we describe a low-nonlinearity dispersion compensator for ultrahigh-speed coherent Nyquist pulse transmission; it is composed of a chirped fiber Bragg grating (CFBG) and a liquid crystal on silicon (LCoS) device. By adopting CFBG instead of inverse dispersion fiber, the nonlinearity in a 160km transmission line was more than halved. Furthermore, by eliminating the group delay fluctuation of the CFBG with an LCoS device, the residual group delay was reduced to as low as 1.42ps over an 11nm bandwidth. Then, by using the transmission line with the newly constructed low-nonlinearity dispersion compensator, we succeeded in improving the BER performance of single-channel 15.3Tbit/s-160km transmission by one-third compared with that of a conventional dispersion-managed transmission line and obtained a spectral efficiency of 8.7bit/s/Hz. Furthermore, we numerically analyzed the BER performance of its Nyquist pulse transmission. The numerical results showed that the nonlinear impairment in the transmission line is the main factor limiting the transmission performance in a coherent Nyquist pulse transmission, which becomes more significant at higher baud rates.

Multi-FPGA systems have gained attention because of their high performance and power efficiency. A multi-FPGA system called Flow-in-Cloud (FiC) is currently being developed as an accelerator of multi-access edge computing (MEC). FiC consists of multiple mid-range FPGAs tightly connected by high-speed serial links. Since time-critical jobs are assumed in MEC, a circuit-switched network with static time-division multiplexing (STDM) switches has been implemented on FiC. This paper investigates techniques of enhancing the interconnection performance of FiC. Unlike switching fabrics for Network on Chips or parallel machines, economical multi-FPGA systems, such as FiC, use Xilinx Aurora IP and FireFly cables with multiple lanes. We adopted the link aggregation and the slot distribution for using multiple lanes. To mitigate the bottleneck between an STDM switch and user logic, we also propose a multi-ejection STDM switch. We evaluated various combinations of our techniques by using three practical applications on an FiC prototype with 24 boards. When the number of slots is large and transferred data size is small, the slot distribution was sometimes more effective, while the link aggregation was superior for other most cases. Our multi-ejection STDM switch mitigated the bottleneck in ejection ports and successfully reduced the number of time slots. As a result, by combining the link aggregation and multi-ejection STDM switch, communication performance improved up to 7.50 times with few additional resources. Although the performance of the fast Fourier transform with the highest communication ratio could not be enhanced by using multiple boards when a lane was used, 1.99 times performance improvement was achieved by using 8 boards with four lanes and our multi-ejection switch compared with a board.

In this letter, a method for the construction of polar codes based on the mutual information approximation (MIA) is proposed for the 4Tb/in2 two-dimensional inter-symbol interference (2D-ISI) channels, such as the bit-patterned magnetic recording (BPMR) and two-dimensional magnetic recording (TDMR). The basic idea is to exploit the MIA between the input and output of a 2D detector to establish a log-likelihood ratio (LLR) distribution model based on the MIA results, which compensates the gap caused by the 2D ISI channel. Consequently, the polar codes obtained by the optimization techniques previously developed for the additive white Gaussian noise (AWGN) channels can also have satisfactory performances over 2D-ISI channels. Simulated results show that the proposed polar codes can outperform the polar codes constructed by the traditional methods over 4Tb/in2 2D-ISI channels.

Wireless networked control systems (WNCSs) are control systems whose components are connected through wireless networks. In WNCSs, a controlled object (CO) could become unstable due to bursty packet losses in addition to random packet losses and round-trip delays on wireless networks. In this paper, to reduce these network-induced effects, we propose a new design for multihop TDMA-based WNCSs with two-disjoint-path switching, where two disjoint paths are established between a controller and a CO, and they are switched if bursty packet losses are detected. In this system, we face the following two difficulties: (i) link scheduling in TDMA should be done in such a way that two paths can be switched without rescheduling, taking into account of the constraint of control systems. (ii) the conventional cross-layer design method of control systems is not directly applicable because round-trip delays may vary according to the path being used. Therefore, to overcome the difficulties raised by the two-path approach, we reformulate link scheduling in multihop TDMA and cross-layer design for control systems. Simulation results confirm that the proposed WNCS achieves better performance in terms of the 2-norm of CO's states.

When the track density of two-dimensional magnetic recording (TDMR) systems is increased, intertrack interference (ITI) inevitably grows, resulting in the extreme degradation of an overall system performance. In this work, we present coding, writing, and reading techniques which allow TDMR systems with multi-readers to overcome severe ITI. A rate-5/6 two-dimensional (2D) modulation code is adopted to protect middle-track data from ITI based on cross-track data dependence. Since the rate-5/6 2D modulation code greatly improves the reliability of the middle-track, there is a bit-error rate gap between middle-track and sidetracks. Therefore, we propose the different track width writing technique to optimize the reliability of all three data tracks. In addition, we also evaluate the TDMR system performance using an user areal density capability (UADC) as a main key parameter. Here, an areal density capability (ADC) can be measured by finding the bit-error rate of the system with sweeping track and linear densities. The UADC is then obtained by removing redundancy from the ADC. Simulation results show that a system with our proposed techniques gains the UADC of about 4.66% over the conventional TDMR systems.

With no need for Road Side Unit (RSU), multi-hop Vehicular Ad Hoc NETworks (VANETs) have drawn more and more attention recently. Considering the safety of vehicles, a Media Access Control (MAC) protocol for reliable transmission is critical for multi-hop VANETs. Most current works need RSU to handle the collisions brought by hidden-terminal problem and the mobility of vehicles. In this paper, we proposed RV-MAC, which is a reliable MAC protocol for multi-hop VANETs based on Time Division Multiple Access (TDMA). First, to address the hidden-terminal under the networks with multi-hop topology, we design a region marking scheme to divide vehicles into different regions. Then a collisions avoidance scheme is proposed to handle the collisions owing to channel competition and the mobility of vehicles. Simulation results show that compared with other protocol, RV-MAC can decrease contention collisions by 30% and encounter collisions by 50% respectively. As a result, RV-MAC achieves higher throughput and lower network delay.

In parallel computing systems, the interconnection network forms the critical infrastructure which enables robust and scalable communication between hundreds of thousands of nodes. The traditional packet-switched network tends to suffer from long communication time when network congestion occurs. In this context, we explore the use of circuit switching (CS) to replace packet switches with custom hardware that supports circuit-based switching efficiently with low latency. In our target CS network, a certain amount of bandwidth is guaranteed for each communication pair so that the network latency can be predictable when a limited number of node pairs exchange messages. The number of allocated time slots in every switch is a direct factor to affect the end-to-end latency, we thereby improve the slot utilization and develop a network topology generator to minimize the number of time slots optimized to target applications whose communication patterns are predictable. By a quantitative discrete-event simulation, we illustrate that the minimum necessary number of slots can be reduced to a small number in a generated topology by our design methodology while maintaining network cost 50% less than that in standard tori topologies.

Vehicular Ad hoc Network (VANET) is an important part of the Intelligent Transportation System (ITS). VANETs can realize communication between moving vehicles, infrastructures and other intelligent mobile terminals, which can greatly improve the road safety and traffic efficiency effectively. Existing studies of vehicular ad hoc network usually consider only one data transmission model, while the increasing density of traffic data sources means that the vehicular ad hoc network is evolving into Heterogeneous Vehicular Network (HetVNET) which needs hybrid data transmission scheme. Considering the Heterogeneous Vehicular Network, this paper presents a hybrid transmission MAC protocol including vehicle to vehicle communication (V2V) and vehicle to infrastructure communication (V2I/I2V). In this protocol, the data are identified according to timeliness, on the base of the traditional V2V and V2I/I2V communication. If the time-sensitive data (V2V data) fail in transmission, the node transmits the data to the base station and let the base station cooperatively transmit the data with higher priority. This transmission scheme uses the large transmission range of base station in an effective manner. In this paper, the queueing models of the vehicles and base station are analyzed respectively by one-dimensional and two-dimensional Markov Chain, and the expressions of throughput, packet drop rate and delay are also derived. The simulation results show that this MAC protocol can improve the transmission efficiency of V2V communication and reduce the delay of V2V data without losing the system performance.

We propose a time synchronization technique for mobile base stations (BSs) by distributing the reference time information from one optical network unit (ONU) to the BSs under different ONUs over Time Division Multiplexing Passive Optical Network (TDM-PON) using common Precision Time Protocol (PTP). The time accuracy, long term time stability and time source switchover functionality for redundancy are confirmed by experimental verification. Furthermore, an interoperability test between a 10G-EPON prototype in which the proposed protocol is implemented and a commercial Time Division Long Term Evolution (TD-LTE) BS is successfully demonstrated obtaining time error within 119ns, which is much less than the criterion value of 1.5µs, for 60 hours.

IoT (Internet of Things) services are emerging and the bandwidth requirements for rich media communication services are increasing exponentially. We propose a virtual edge architecture comprising computation resource management layers and path bandwidth management layers for easy addition and reallocation of new service node functions. These functions are performed by the Virtualized Network Function (VNF), which accommodates terminals covering a corresponding access node to realize fast VNF migration. To increase network size for IoT traffic, VNF migration is limited to the VNF that contains the active terminals, which leads to a 20% reduction in the computation of VNF migration. Fast dynamic bandwidth allocation for dynamic bandwidth paths is realized by proposed Hierarchical Time Slot Allocation of Optical Layer 2 Switch Network, which attain the minimum calculation time of less than 1/100.

In this paper, we focus on two-layer wireless sensor networks (WSNs) that consist of sensor-concentrator and inter-concentrator networks. In order to collect as much data as possible from a wide area, improving of network capacity is essential because data collection applications often require to gather data within a limited period, i.e., acceptable collection delay. Therefore, we propose a two-stage scheduling method for inter-concentrator networks. The proposed method first strictly schedules time slots of links with heavy interference and congestion by exploiting the combination metric of interference and traffic demand. After that, it simply schedules time slots of the remaining sinks to mitigate complexity. Simulation-based evaluations show our proposal offers much larger capacity than conventional scheduling algorithms. In particular, our proposal improves up to 70% capacity compared with the conventional methods in situations where the proportion of one- and two-hop links is small.

To drastically increase the splitting ratio of extended-reach (40km span) time- and wavelength-division multiplexed passive optical networks (WDM/TDM-PONs), we modify the gain control scheme of our automatic gain controlled semiconductor optical amplifiers (AGC-SOAs) that were developed to support upstream transmission in long-reach systems. While the original AGC-SOAs are located outside the central office (CO) as repeaters, the new AGC-SOAs are located inside the CO and connected to each branch of an optical splitter in the CO. This arrangement has the potential to greatly reduce the costs of CO-sited equipment as they are shared by many more users if the new gain control scheme works properly even when the input optical powers are low. We develop a prototype and experimentally confirm its effectiveness in increasing the splitting ratio of extended-reach systems to 512.

Improvement of conventional networks with an incremental approach is an important design method for the development of the future internet. For this approach, we are developing a future aggregation network based on passive optical network (PON) technology to achieve both cost-effectiveness and high reliability. In this paper, we propose a timeslot (TS) synchronization method for sharing a TS from an optical burst mode transceiver between any route of arbitrary fiber length by changing both the route of the TS transmission and the TS control timing on the optical burst mode transceiver. We show the effectiveness of the proposed method for exchanging TSs in bidirectional bufferless wavelength division multiplexing (WDM) and time division multiplexing (TDM) multi-ring networks under the condition of the occurrence of a link failure through prototype systems. Also, we evaluate the reduction of the required number of optical interfaces in a multi-ring network by applying the proposed method.

The λ-tunable WDM/TDM-PON is a promising candidate for next-generation optical access networks since it can provide load balancing between optical subscriber units, power savings, high reliability, and pay-as-you-grow capability. In a λ-tunable WDM/TDM-PON system, the degradation of communication quality caused by wavelength switching should be minimized. The system should also preferably be able to change wavelengths of multi ONUs simultaneously to make wavelength reallocation speed high. The system should also be able to accommodate ONUs whose wavelength tuning times are different. The challenge to meet all three requirements is to suppress latency degradation and frame loss when wavelengths of multi-type ONU are switched simultaneously in WDM/TDM-PON systems. We proposed an OLT architecture and a wavelength switching method that cooperates with traffic control to suppress frame loss and latency degradation by multi-ONU wavelength switching. However, there have been no reports on the impact on latency of downstream and upstream traffic when wavelengths of multi-ONU are simultaneously switched in λ-tunable WDM/TDM-PON. In this paper, we evaluate and analyze the impact of wavelength switching on latency in 40 Gbps WDM/TDM-PON systems. An experiment results show that latency degradation and frame loss are suppressed. Dynamic wavelength allocation operation with 8-ONUs-simulateous wavelength switching in 512-ONUs WDM/TDM-PON system is demonstrated.

We propose a QoS scheme for ad hoc networks by combining TDMA and IEEE 802.11 DCF, and present performance evaluation results of the scheme. In the proposed scheme, the channel time is composed of two different periods, specifically TDMA period and DCF period. The TDMA period provides contention free transmission opportunities for QoS flows, and the DCF period provides contention-based access for best effort or low priority flows. We evaluate the proposed scheme for various numbers of TCP flows and different CBR data rates with QualNet simulator. Simulation results show that the protocol is able to provide an efficient solution for QoS control in ad hoc networks.

A virtual network edge using live migration of virtualized network functions (VNFs) can be expected to reduce computation time and save resources instead of conventional network edge routers that have complex functions. Wavelength-division-multiplexing/time-division-multiplexing (WDM/TDM) photonic switching technology for metro ring networks is proposed to provide fast bandwidth resource allocation for rapidly changing service-flow demand. However, there are no reports on the coexistence of high-speed path switching for live migration with fast bandwidth resource allocation, as far as we know. We propose an architecture that achieves both high-speed path switching and fast dynamic bandwidth allocation control for service flows with in-service live migration. The feature of this architecture is that the VNF for the virtual edge corresponds to each 10-gigabit Ethernet-passive optical network (10G-EPON) and fast route change can be achieved with a simple point-to-point path between VNFs and optical line terminals (OLTs). The second feature is that the live migration of a VNF is limited to a part of it that contains a larger number of subscribers. Owing to the reduction in the number of total paths, fast resource allocation can be provided.

Multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) combined with time division multiplexing (OFDM/TDM) based on frequency domain equalization (FDE) has been proposed to reduce the high peak-to-average power ratio (PAPR) of OFDM and improve the bit error rate (BER) performance in comparison to the conventional OFDM. However, due to the nonlinearity of the high-power amplifier (HPA) at the transmitter and the fact that the PAPR problem is not completely eliminated, the nonlinear noise due to HPA saturation still degrades the BER performance. In this paper, we theoretically evaluate the effect of nonlinear HPA on the performance of MIMO-OFDM/TDM using a minimum-mean square-error frequency-domain equalizer (MMSE-FDE). We determine the equalization weights while taking into account the negative effect of HPA saturation and then evaluate the system performance in terms of average BER and ergodic capacity by way of both, numerical and computer simulation. Our simulation results have shown that appropriate system design can make MIMO-OFDM/TDM more robust against nonlinear degradation due to HPA saturation in comparison to MIMO-OFDM while reducing required signal-to-noise ratio (SNR) for the given target BER.