Kazuji Watanabe

Digitized Radio-over-Fiber (DROF) System for Wide-Area Ubiquitous Wireless Network

Site diversity techniques using a distributed wireless access point for a large cell are important to achieve wide-area ubiquitous wireless networks that support embedded ubiquitous services. We propose a digitized radio-over-fiber (DROF) system for ubiquitous wireless network. The DROF system uses standard IP networks as the transmission lines of radio signals for distributed access points and can establish site diversity techniques at low cost. We also propose a network time protocol based reference frequency and time distribution scheme to synchronize distributed access points. Experiment results show that the DROF prototype achieves precise frequency and time distribution over IP based networks

Diversity Technique Employing Digitized Radio over Fiber Technology for Wide-Area Ubiquitous Network

Wide area ubiquitous networks should have the capability to handle more than 10,000 wireless terminals in a large wireless cell with the radius of several kilometers. However, the functions of wireless terminal are severely limited due to low power consumption and low cost requirements. Therefore, there is a need for a sophisticated wireless access system that employs smart wireless signal processing such as the site diversity technique with maximal-ratio-combining at the wireless access point. This paper presents the site diversity technique that employs digitized radio over fiber technology and field test that confirms the effect of site diversity.

Centralized Multiple Random Access Protocol with Contention Window Adjustment

In this paper, we propose a new multiple access protocol for the ubiquitous network and analyze its performance in the nonsaturated condition. Based on the concept of equilibrium analysis, we analyze its throughput and the contention window size that maximizes its throughput by constructing a Markov model of terminal state. From this work we introduce an index that uniquely decides throughput regardless of the number of terminals or the offered traffic and propose a contention window adjustment algorithm based on the index. Computer simulations that compare the proposed protocol to conventional protocols clarify that the former has superior throughput.

DSA-II: using Traffic Characteristics to Enhance Throughput Performance of Wide Area Ubiquitous Wireless Networks

Wide area ubiquitous wireless networks, which consist of access points (APs) connected to the fixed network and a great many wireless terminals (WTs), can offer a wide range of applications everywhere. In order to enhance network performance, we need to collect different kinds of data from as many WTs as possible; each AP must be capable of accommodating more than 103 WTs. To satisfy this requirement, we proposed DSA-I; it adds request-polling to random access. We showed that DSA-I increases throughput. However, in DSA-I, a request and its acknowledgement must be exchanged before sending data by request-polling even if the data size is known or can be predicted accurately, which increases the overhead. This paper proposes DSA-II; it adds data-polling to DSA-I to reduce the overhead. In DSA-II, the AP decides the polled data size according to the latest distribution of data size and polls the WT for the data directly. If the data-polling size cannot be determined with confidence, the AP uses request-polling instead of data-polling. Simulations verify that DSA-II offers better transmission performance than DSA-I and existing schemes.

A New Qos Control Scheme Using Dynamic Window Size Control for Wide Area Wireless Networks

In the wide area wireless network, most wireless terminals will send small amounts of data with very long transmission intervals. Therefore, each access point must accommodate a large number of wireless terminal and devices. Moreover, the network is required to accommodate a variety of wireless terminals, so quality of service (QoS) needs to be guaranteed. In this paper, we propose a new QoS control scheme for the wide area wireless network. The proposed scheme observes the delay time of the higher priority class and, according to the delay, it amends the back-off parameters of the lower priority class. This guarantees the throughput and delay performance of the higher priority class. This paper also clarifies the problems of the conventional scheme and reveals the throughput and delay performance of the conventional and proposed scheme by computer simulation.

A Burst Modulation/Demodulation Method for Narrowband Ubiquitous Communication Systems

This paper presents a wireless burst modulation/demodulation method for narrowband ubiquitous communication systems. This method especially suits those systems, whose traffic is especially dominated by short frame bursts. The proposed modulation method provides a preamble-less frame structure with training symbols, which improves both transmission efficiency and burst synchronization performance. Moreover, the proposed demodulation method achieves superior burst synchronization performance in low carrier-to-noise power ratio (CNR) environments by applying a synchronization method that includes symbol timing recovery, slot synchronization, carrier frequency correction and channel tracking. In addition, this paper presents the result of experiments on hardware prototypes of the proposed modulator and demodulator. The basic operation and practical performance of the proposed method is confirmed through testbed studies.

A slot timing detection method with multiple-symbol differential detection for MDPSK burst signals

This paper presents a slot timing detection method with multiple-symbol differential detection (MSDD) that offers improved transmission efficiency and mitigates the performance deterioration caused by carrier frequency offset. The method is applicable for burst wireless systems with short burst M-differential phase shift keying (MDPSK) signals and low symbol rates, which suits radio-frequency identifications (RF-IDs) or other ubiquitous wireless applications. Computer simulations show that the proposed method improves slot timing detection and error rate performances and yields robust demodulation of data symbols against carrier frequency offset.

A Novel Prioritized Control Scheme Using Random Access Period Control for Wide Area Ubiquitous Wireless Networks

In wide area ubiquitous wireless networks, most wireless terminals (WTs) will transmit small amounts of data at comparatively long intervals. Therefore, each AP must be capable of accommodating a great many WTs. Moreover, this network is required to accommodate a variety of services; some services need to be prioritized. In this paper, we propose a novel prioritized control scheme that applies random access to wide area ubiquitous wireless networks. Two kinds of priority classes are considered; high priority (HP) class and low priority (LP) class. The transmission performance of HP class must be guaranteed regardless of LP class traffic situation. To meet this requirement, the proposed scheme isolates the random access (RA) periods of the two classes and controls the RA period for HP class according to the HP class traffic situation, which is predicted from the HP event notification history (event here means that a WT has HP traffic to send). This paper also clarifies the problems of the conventional scheme and reveals the transmission performance of the conventional and proposed scheme by computer simulation.

Novel DSA Scheme that Uses Traffic Characteristics to Enhance Throughput Performance of Wide Area Ubiquitous Wireless Networks

Wide area ubiquitous wireless networks, which consist of access points (APs) connected to the fixed network and a great many wireless terminals (WTs), can offer a wide range of applications everywhere. In order to enhance network performance, we need to collect different kinds of data from as many WTs as possible; each AP must be capable of accommodating more than 103 WTs. This requirement can be achieved by employing DSA, a typical centralized media access control scheme, since it has high resource utilization efficiency. In this paper, we propose a novel DSA scheme that employs three new techniques to enhance throughput performance; (1) considering that most terminals tend to send data periodically, it employs both polling-based schemes, i.e. request-polling and data-polling, and a random access scheme. (2) In order to enhance bandwidth utilization effectiveness by polling, the polling timing is decided according to the data generation timing. (3) The AP decides the polled data size according to the latest distribution of data size and polls the WT for the data directly. If the data-polling size can not be determined with confidence, the AP uses request-polling instead of data-polling. Simulations verify that the proposed scheme offers better transmission performance than the existing schemes.