In the present paper, we evaluate the inter-cell interference of AS-CDMA systems. First, the cross-correlation property of AS-CDMA systems is examined by theoretical study in order to clarify the fundamental feature of the inter-cell interference. The result shows that the influence of one interference terminal in each adjacent cell is dominant regardless of whether approximate synchronization is maintained. Next, the ratio of interference signal power and desired signal power is evaluated by computer simulation. The simulation result shows that total interference power does not increase even when approximate synchronization is not maintained.

We developed an optical transceiver diode (TRAD) module for bi-directional time-compression-multiplexing (TCM) transmission systems. A wavelength-insensitive structure as a receiver and a low-capacitance configuration in the module provide a high sensitivity. Stable switching of 156 Mbit/s NRZ burst signals between the transmitter and receiver modes is achieved. In addition, it is shown that optical module cost can be further reduced by using passive alignment on a Si bench.

In the present paper, a new coding scheme for infrared ASK communication systems--Pulse Sequence Modulation (PSM)--will be proposed, which uses a combination of pulse sequences so that it canattain zero-spectrum points at specific frequencies within the main-lobe region. The interference to the other IR systems was a problem of the conventional infrared ASK communication systems. The proposed PSM coding scheme reduces the interference by decreasing the emission at specific frequencies, and helps multiple IR communication systems co-exist without deteriorating coding efficiency.

In this paper, we propose two parallel M/M/1 queueing systems with dynamic routing under a threshold-type scheduling. Arriving customer is sent to the buffer of the faster server as far as the difference of two queues does not exceed a threshold value, but it should be sent to the buffer of the slower server if and only if the difference of two queues exceeds a threshold value. It is shown that as the difference of the two service rates becomes large, the two parallel M/M/1 queueing systems with dynamic routing under the threshold-type scheduling can reduce the mean queueing time of costomers in the system compared to the conventional nonthreshold-type one. It is also found that as the asymmetry in the two service rates increases, the optimum threshold value which minimizes the mean queueing time should be large to reduce the number of queueing customer in the buffer of the slower server. On the other hand, as the traffic intensity becomes large, the optimum threshold value tends to be small in order to increase the total service rate.

By using impedance (Z) matching circuits in a low-cost transistor outline (TO) CAN package for a 10 Gb/s transmitter, we achieve a cost-effective and small bidirectional optical subassembly (BOSA) with excellent optical transmission waveforms and a > 40% mask margin over a wide temperature range (-10 to 85). We describe a design for Z matching circuits and simulation results, and discuss the advantage of the cost-effective compensation technique.

In the present paper, a new coding scheme for infrared ASK communication systems--Pulse Sequence Modulation (PSM)--will be proposed, which uses a combination of pulse sequences so that it canattain zero-spectrum points at specific frequencies within the main-lobe region. The interference to the other IR systems was a problem of the conventional infrared ASK communication systems. The proposed PSM coding scheme reduces the interference by decreasing the emission at specific frequencies, and helps multiple IR communication systems co-exist without deteriorating coding efficiency.

We developed an optical transceiver diode (TRAD) module for bi-directional time-compression-multiplexing (TCM) transmission systems. A wavelength-insensitive structure as a receiver and a low-capacitance configuration in the module provide a high sensitivity. Stable switching of 156 Mbit/s NRZ burst signals between the transmitter and receiver modes is achieved. In addition, it is shown that optical module cost can be further reduced by using passive alignment on a Si bench.

This paper describes a new timing circuit design technique for asynchronous burst-mode data transmission such as Fiber-To-The-Home (FTTH). It enables to the handling of asynchronous burst-mode data. Without an external reference clock signal, it can make a quick extraction of clock signal from received data packets using a "gating-timing circuit" and a "burst PLL." The gating-timing circuit employs bit gating for a quick phase response, and the burst PLL employs frame gating for quick frequency adjustment to differences between packets and clock extraction. This circuit has a simple configuration without any external oscillators, which reduces both cost and power. A fabricated 0.5-µm CMOS IC exhibits instantaneous response within one bit for 156 Mb/s asynchronous data packets.

The 10-gigabit Ethernet passive optical network (10G-EPON) is a promising candidate for the next generation of fiber-to-the-home access systems. In the symmetric 10G-EPON system, the gigabit Ethernet passive optical network (GE-PON) and 10G-EPON will have to co-exist on the same optical network. For this purpose, an optical triplexer (10G-transmitter, 1G-transmitter, and 10G/1G-receiver) for optical line terminal (OLT) transceivers in 10G/1G co-existing EPON systems has been developed. Reducing the size and cost of the optical triplexer has been one of the largest issues in the effort to deploy 10G-EPON systems for practical use. In this paper, we describe a novel small and low-cost dual-rate optical triplexer for use in 10G-EPON applications. By reducing the optical path length by means of a light collection system with a low-magnification long-focus coupling lens, we have successfully miniaturized the optical triplexer for use in 10G-EPON OLT 10-gigabit small form factor pluggable (XFP) transceivers and decreased the number of lenses. A low-cost design of sub-assemblies also contributes to cost reduction. The triplexer's performance complies with IEEE 802.3av specifications.

The present paper proposes a new method for constructing polyphase asymmetric zero-correlation zone (A-ZCZ) sequence sets. The proposed method can generate A-ZCZ sequence sets that cannot be obtained from methods proposed by other researchers and is a generalized version of our previously proposed method. An A-ZCZ sequence set can be regarded as a ZCZ sequence set. The newly obtained A-ZCZ sequence sets include quasi-optimal ZCZ sequence sets of which the zero-cross-correlation zone (ZCCZ) length between different sequence subsets is larger than the mathematical upper bound of conventional ZCZ sequence sets. A new method for extending the A-ZCZ sequence sets is also presented in the present paper.

In this paper we consider the effect of varying routing probability in two parallel M/M/1 queueing systems with dynamic routing under a threshold type scheduling. We also estimate the effect of varying routing probability as well as threshold on the resequencing delay. First we obtain the general expression for state probabilities. Next we estimate the effect of varying routing probability by the numerical calculation and the computer simulation. It is shown that the mean queueing delay can be reduced by varying the routing probability appropriately. Varying the routing probability together with the threshold-type scheduling is more effective to reduce the queueing delay in the variation of the traffic intensity. And besides it is shown that the resequencing delay can be reduced in the wide region of the traffic intensity by employing the optimal threshold and routing probability.

We present a novel burst-mode transimpedance amplifier (TIA) with a gain-mode switching. The proposed TIA utilizes a regulated-cascode (RGC) input stage for broadband characteristics. To expand a dynamic range, the RGC controls a linear operating range depending on transimpedance gains by adjusting bias conditions. This TIA is implemented using the 0.18μm-CMOS technology. The experimental results show that the proposed TIA IC has a good eye-opening and can respond quickly to the burst data.

In our previous work, we have proposed a method for constructing ZCZ sequence sets. The method proposed by the previous work is based on perfect sequences and unitary matrices. This method can generate ZCZ sequence sets which possess a good feature concerning the length of zero-correlation zones. In this letter, we propose a new method for constructing ZCZ sequence sets by improving the previous method. The proposed method can generate new ZCZ sequence sets which can not be obtained from the previous method. These ZCZ sequence sets also possess the good feature concerning the length of zero-correlation zones.

An analog voice scrambling method Sample Inversion" is presented along with several experimental results. The Sample Inversion" principle is to invert the voice sample polarity according to the key code, smooth it with low pass filter and feed it to the transmission channel. Necessary techniques to utilize the principle, filtering and synchronizing are described. Key code design is examined and an error correcting code is proposed appropriate to the key code. Experimental equipment is assembled to prove the principle. Using the same equipment, spectrum variation is demonstrated and articulation by voice scrambling is measured. The Sample Inversion" method can be realized by circuits assembled with conventional parts. Sample Inversion" provides natural voice to the properly keyed-in receiver and assures that the conversation is completely unintelligible to any other receivers. Lack of voice quality sensitivity to noise is also to be emphasised.

In this paper, a Proof-of-Concept (PoC) architecture is constructed, and the effectiveness of mmWave overlay heterogeneous network (HetNet) with mesh backhaul utilizing route-multiplexing and Multi-access Edge Computing (MEC) utilizing prefetching algorithm is verified by measuring the throughput and the download time of real contents. The architecture can cope with the intensive mobile data traffic since data delivery utilizes multiple backhaul routes based on the mesh topology, i.e. route-multiplexing mechanism. On the other hand, MEC deploys the network edge contents requested in advance by nearby User Equipment (UE) based on pre-registered context information such as location, destination, demand application, etc. to the network edge, which is called prefetching algorithm. Therefore, mmWave access can be fully exploited even with capacity-limited backhaul networks by introducing the proposed algorithm. These technologies solve the problems in conventional mmWave HetNet to reduce mobile data traffic on backhaul networks to cloud networks. In addition, the proposed architecture is realized by introducing wireless Software Defined Network (SDN) and Network Function Virtualization (NFV). In our architecture, the network is dynamically controlled via wide-coverage microwave band links by which UE's context information is collected for optimizing the network resources and controlling network infrastructures to establish backhaul routes and MEC servers. In this paper, we develop the hardware equipment and middleware systems, and introduce these algorithms which are used as a driver of IEEE802.11ad and open source software. For 5G and beyond, the architecture integrated in mmWave backhaul, MEC and SDN/NFV will support some scenarios and use cases.

The total number of solar power-producing facilities whose Feed-in Tariff (FIT) Program-based ten-year contracts will expire by 2023 is expected to reach approximately 1.65 million in Japan. If the facilities that produce or consume renewable energy would increase to reach a large number, e.g., two million, blockchain would not be capable of processing all the transactions. In this work, we propose a blockchain-based electricity-tracking platform for renewable energy, called ‘ZGridBC,’ which consists of mutually cooperative two novel decentralized schemes to solve scalability, storage cost, and privacy issues at the same time. One is the electricity production resource management, which is an efficient data management scheme that manages electricity production resources (EPRs) on the blockchain by using UTXO tokens extended to two-dimension (period and electricity amount) to prevent double-spending. The other is the electricity-tracking proof, which is a massive data aggregation scheme that significantly reduces the amount of data managed on the blockchain by using zero-knowledge proof (ZKP). Thereafter, we illustrate the architecture of ZGridBC, consider its scalability, security, and privacy, and illustrate the implementation of ZGridBC. Finally, we evaluate the scalability of ZGridBC, which handles two million electricity facilities with far less cost per environmental value compared with the price of the environmental value proposed by METI (=0.3 yen/kWh).

Approximately synchronized CDMA (AS-CDMA) can reduce the inter-channel interference in a cell to zero. This property of AS-CDMA is an advantage over the conventional DS-CDMA. However, the inter-cell interference of the AS-CDMA cellular system has not been sufficiently examined previously. Therefore, the synthetic performance of AS-CDMA cellular system also has not been sufficiently clarified previously. Some factors that affect the inter-cell interference of the AS-CDMA cellular system were theoretically examined, and evaluated by using computer simulation. As the result, we found that transmission power control is effective for reducing the inter-cell interference of the AS-CDMA cellular system. In addition, the synthetic performance of AS-CDMA cellular system was clarified for the first time. Consequently, it was also found that the synthetic performance of the AS-CDMA cellular system is higher than that of the conventional DS-CDMA cellular system.