To economically provide higher bit rate services to users, we previously proposed the Subcarrier Digital Modulation based Passive Optical Network (SDM-PON). We also showed the feasibility of a 16-QAM SDM-PON that constantly provides the service data rate of 1 Gbps to each user, in which ONU biases the QAM signal higher so that it is entirely positive before converting into an optical signal (bias signal sending scheme). To decrease sending optical power, this paper proposes a scheme for clipping negative components of the electrical QAM signal (clipped signal sending scheme), along with three methods for regenerating the original QAM signal at the receiving side. We show that the clipped sending signal scheme, and all three regenerating methods, are effective by simulation. The resulting SDM-PON supports 8 ONUs at different distances, 10 km to 20 km, where each ONU constantly sends 1 Gbps data to OLT using 16-QAM.

This paper proposes an indoor trace tracking algorithm with UHF-band passive RFID tags. The tags are attached to the ceiling and the user carries an RFID reader. The reader captures the RFID tags, and the user's position is estimated by the coordinates of the captured tags. The user's track is drawn by connecting estimated positions over time. To decrease the estimation errors expected with the simple approach, this paper proposes a new tracking algorithm that compensates the corner effect, and takes the movement characteristics of the user into consideration.

The sampling theorem of Whittaker, Ogura, Kotelnikov, Someya, and Shannon (WOKSS's sampling theorem) appears in most books on information theory, and is well known. WOKSS's sampling theorem must exclude periodic functions. This paper first introduces a sampling theorem for periodic functions, and gives its physical meaning; this theorem is effective for functions that can be expressed as a finite Fourier series in the same way as WOKSS's theorem deals with a band-limited signal. Since many signals such as an Orthogonal Frequency Division Multiplexing (OFDM) signal can be expressed by periodic functions, the sampling theorem can play an important role in a communications area. Extending the theorem, this paper proposes a sampling theorem for periodic functions with no minus frequency component of a finite Fourier series, and shows its example. In addition, we examine the OFDM signal generation and termination by applying sampling theorems for periodic functions including the proposed one.

It is well-known that TCP has difficulty in achieving desirable levels of performance in multi-hop ad hoc networks. TCP implements a loss-based congestion control mechanism for adjusting traffic in the networks. However, when TCP reacts to a loss event in a multi-hop ad hoc network, contentions raised in the IEEE 802.11 MAC layer among nodes usually becomes excessive. This problem eventually induces packets scheduling variation at the MAC layer. As a result, the quality of service (QoS) assurances given to multimedia traffic streams, such as UDP traffic, are violated. This paper focuses on preventing the TCP congestion window (CWND) size at the network layer from becoming excessive. We propose an interference drop scheme (IDS) at the network layer to prevent excessive increases in MAC contention by dropping over-delayed packets held by local queues. Simulations show that the proposed approach yields better a TCP performance and the assurance of QoS provision to UDP flows in multi-hop ad hoc networks.

The passive optical network (PON) shares feeder transmission facilities to provide broadband services economically. To enhance PON survivability, ITU-T Rec. G.983.5 defines some protection switching methods. These methods, however, always bring about signal loss when switching is performed. Another related problem occurs when the network operator replaces one optical fiber cable with another that takes a different route due to construction activities like social infrastructure renewal. If hitless switching is available, the operator can carry out that activity anytime without impacting users, and can also offer higher-grade broadband services. Thus a hitless protection technology for PON systems is very attractive and useful. This paper proposes hitless switching schemes for protected PON systems based on the PON's ranging functionalities. We also present a specific design example for GE-PON.

In our work, the channel estimation-oriented access control scheme has been investigated. In the system, each user estimates the channel based on the received power, and then decides whether to transmit the packet or refrain from transmission. However, each user can not estimate the channel completely because it is not practical that all users receive the signals with equal power. The purpose of this paper is to investigate the throughput performance of the scheme in consideration of free space loss. It is found that the scheme shows better performance than the conventional scheme even when free space loss occurs. It is also found that the probability of decision, which shows the best throughput, is different depending on offered load.

The performance of TCP degrades greatly in multi- hop ad hoc networks due to the fact that the traditional TCP is unable to adapt the unique properties of the IEEE 802.11 wireless technology. This paper proposes a pure rate-based TCP, Paced TCP to dynamically probe the network's bandwidth which reduces packets dropping from link layer. Paced TCP is able to alleviate the MAC channel contentions and therefore provides better performance. By alleviating packets dropping from link layer, the number of retransmissions at TCP layer can be decrease, and therefore a more efficient communication can be established. With Paced TCP, less retransmissions than TCP Reno is demonstrated in the paper. With NS-2 simulator, we show that by probing networks dynamically with pacing, packets dropped by the MAC channel contentions can be reduced, and Paced TCP is able to provide better fairness and throughput stability between competing flows.

We propose a medium access control protocol for real-time applications in wireless networks. It is a distributed mechanism that takes account of priority. At the beginning of a session, a node determines a frame of energy signals based on priority level and a random number. Nodes send energy signals or listen to the channel based on their frames. Nodes that have sent energy signals without hearing energy signals win the right to access the channel. Once a node has transmitted successfully, the frame of the node is determined by its priority class. Nodes that have been waiting longer have higher priority and can send a packet without risking collision. An analysis of the proposed protocol is provided with a mixed population of data and real-time nodes. The protocol provides stable conditions and a limit on maximum packet delay. We also evaluate the performance of the proposed protocol using simulations.

The congestion control provided by Transmission Control Protocol (TCP) plays a key role in ensuring network stability and increased Quality of Service (QoS). However, in the face of the increasing number of high-speed networks such as Multi-protocol Label Switching with band-width width reservation, conventional congestion control algorithms limit the network resource utilization efficiency since they overreact to packet loss. This paper proposes a new TCP congestion control scheme that improves the goodput by using reserved bandwidth to set the slow start threshold and the congestion window after a timeout or three duplicate acknowledgments. The advantage of this algorithm is that the TCP sender recovers faster after packet loss, especially when the connections have large round trip times; it avoids Reno's overreaction to loss.

A novel ring architecture is proposed that is suitable for asymmetric traffic and allows for protection using a single fiber ring. Existing optical ring systems provide symmetric bidirectional optical path capability for use with symmetric or asymmetric traffic. Such systems are not cost-effective for asymmetric traffic such as the Internet. The proposed optical ring system accommodates wavelengths for both directions in one fiber, and employs the 1+1 optical unidirectional path-switched ring (OUPSR) protection scheme. This architecture makes it possible to augment a unidirectional optical path and a single fiber economically.

A B-ISDN introductory scenario is described from the viewpoint of service, and a virtual-path (VP)-based access network architecture based on this scenario is discussed. In the access network each VP is dedicated to one service, such as a leased circuit, switched circuit, or video distribution. The concept and functions of a subscriber line terminal (SLT) to realize this capability are introduced. Asynchronous transfer mode (ATM) subscriber line system deployment and the main SLT functions are discussed.>

Demand for high-speed wide-band telecommunication services is rapidly growing due to the remarkable progress in office, factory, and laboratory automation. These services are expected to be first introduced in leased circuits and then extended, to high-speed switched services. This paper presents the users' demands for such high-speed services and the NTT design concepts for the high-speed digital data transmission system (HDDTS) in NTT to provide such high-speed leased circuit service. The ISDN user-network interface is adopted. The basic high-speed pointto-point transmission service started in October 1984, and enhanced leased circuit service involving multiplexed interfaces and muitipoint circuits will be introduced in the fall of 1985.