Fusao Nuno

Performance evaluation of QoS control scheme that uses back pressure traffic control

The spread of the Internet has given rise to strong demands for real-time services such as voice and streaming video. Since these services require guarantees that may include transmission rate, delay, and delay variance, the network, including the wireless access networks, must offer QoS (quality of service) guarantees. However, no radio access system fully supports QoS controls. IEEE 802.11e is one scheme that uses an access control mechanism for QoS support. The scheme is based on a distributed access control method, CSMA (carrier sense multiple access). Since it employs EDCA (enhanced distributed channel access) for priority differentiation, terminals with large traffic loads can throttle the throughput of priority terminals because EDCA is essentially decentralized control. This paper proposes a back pressure traffic control method that avoids this problem and supports QoS guarantees as well as describe its characteristics.

Novel coexistence scheme between wireless sensor network and wireless LAN for HEMS

The problem of coexistence between IEEE 802.11g based wireless LANs (WLANs) and IEEE 802.15.4 based wireless sensor networks (WSNs) in the 2.4GHz band is an important issue for the operation of a home energy management system (HEMS) for smart grids. This paper proposes a novel coexistence scheme which is called a distributed active channel reservation for coexistence (DACROS) scheme to solve this problem. This scheme employs a hybrid-station (H-STA) that possesses two types of network device functions. The scheme improves the data transmission quality of the WSN devices which transmit energy management information such as power consumption. The proposed DACROS scheme uses the request-to-send (RTS) and clear-to-send (CTS) frames. These WLAN control frames are used exclusively to assign WSN system traffic resources. Theoretical analysis and computer simulation results show that the DACROS scheme decreases the beacon loss rate of the WSN to less than 1% when the WLAN system consists of ten stations (STAs) under saturated traffic conditions.

Proposal of 5/25-GHz dual band OFDM-based wireless LAN for high-capacity broadband communications

We propose a new 5/25-GHz dual-band wireless LAN for high-capacity broadband communications. In Japan, the 25/27-GHz band has been allocated for nomadic wireless access systems to increase system capacity and achieve transmission rates higher than 100 Mbit/s. We will describe the application areas and regulatory requirements of 25/27-GHz band systems, and then describe the concept of 5/25-GHz dual-band OFDM-based wireless LAN systems. We will examine the transmission performance of 25-GHz OFDM-based systems on the basis of our experimental results. We will then discuss a prototype 5/25-GHz dual-band WLAN card and demonstrate the feasibility of compact mobile terminals

Wireless access system for Wide Area Ubiquitous Network

This paper introduces a wireless access system for the Wide Area Ubiquitous Network (WAUN), which is a large cell-based public sensor network, and provides feasibility study results gained through field tests. The wireless access system uses several key technologies to accommodate widely dispersed small simple terminals. First, to realize the large cell radius of several kilometers, space and site diversity technique based on digital radio over optical fiber (DROF) is developed. Second, an intelligent multiple access control scheme, a combination of demand assignment and random access, is employed to effectively accommodate tens of thousand of wireless terminals (WTs) per cell. Finally, techniques that yield low power consumption are introduced to create the long WT lifetimes needed. The system performance realized by the above-mentioned technologies is confirmed by field tests.

Performance Evaluation of Novel DSA Scheme that Combines Polling Method with Random Access Method

Ubiquitous wireless networks and wireless sensor networks, which consist of access points and a number of wireless terminals with simple functions, provide users with a wide range of applications such as environment monitoring and traffic surveillance. In these networks, even though each terminal sends only small data amounts at comparatively long transmission intervals, traffic loads are significant due to the very large number of terminals. The access point must be capable of accommodating the great many wireless terminals, while providing high throughput performance. This 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 both a polling-based method and a random access method; it improves throughput by using the feature that most terminals tend to send data periodically. In this scheme, the access point polls the terminals to decrease the random accesses made by the terminals as much as possible. Simulations verify that the proposed scheme offers better throughput performance than the conventional scheme

Throughput and QoS improvement of wireless LAN system employing radio over fiber

There are many wireless devices in our society, and new wireless communication standards are continuously appearing. It is annoying for users and also difficult for some to keep up with technology standard changes. Applying radio-over-fiber (RoF) technologies to wireless local area network (WLAN) systems is one possible solution to this problem. However, these systems contain an optical fiber cable, which has a non-negligible propagation delay for IEEE 802.11-based WLANs. This delay caused by optical transmission degrades the throughput and quality-of-service (QoS) of a WLAN system. In this paper, we describe a novel method to resolve this problem and demonstrate its effectiveness using computer simulations. We show that the proposed method provides approximately double the total throughput and provides an uplink and downlink frame-rate ratio of one regardless of the optical fiber propagation delay or the number of stations (STAs).

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.

Prototype AWA: design and implementation of a high speed ATM wireless access system using 25 GHz band

This paper describes the design and implementation of a prototype ATM Wireless Access (AWA) system that provides high speed ATM transport capability for tetherless multimedia services. The prototype AWA uses the 25 GHz band for experimental purpose because of its support of high speed transmission. This paper describes the design concept of the prototype AWA as well as key technologies that allow it to achieve high speed and high quality ATM-based transmission.