Jen-Chu Liu

TAMMAC: An Adaptive Multi-Channel MAC Protocol for MANETs

The use of multiple channels in wireless networks could provide performance advantages in reducing collisions and enabling more concurrent transmissions. So et al. proposed a multi-channel MAC protocol, which uses a single transceiver and divides the beacon interval into two parts: channel negotiation and data transmission. However, the fixed length of channel negotiation interval limits the channel utilization. We propose a new single transceiver MAC protocol, named traffic aware multichannel medium access control (TAMMAC), that can exploit multiple channels with smart window increase and decrease rules to adjust the contention window size dynamically and properly. The simulation results show that the proposed protocol achieves higher aggregate network throughput than other schemes under various traffic loads.

WASP: An innovative sensor observation service with web-/GIS-based architecture

Geographic Information System (GIS) can locate, manages, and presents data or location by coordinate information. GIS-based applications are tools that allow users to create interactive queries, analyze and show the spatial information on maps. On the other hand, Wireless Sensor Network (WSN) is widely used. There are huge amount of data retrieved by sensors sent to the server for query by users. The raw data are usually hard to be understood by users. If the raw data can be transferred into add-on valued data and shown on the web pages, the user can obtain more useful and realizable information. This paper proposed an innovated sensor observation service with web-based and GIS-based architecture, which is named WSN Application Service Platform (WASP). WASP is a data management center, which designed with the concept of Services Oriented Application (SOA) as a Cloud Service. WASP is the combination of Internet/Web-based services and components, database systems, users, and WSN communities. The main goal of WASP is providing an easy and straightforward mechanism of data presentation for users. Users can query and obtain the valuable information and realize the meanings of these data through webbased interfaces, which is defined in Sensor Web Enablement (SWE) by Open Geospatial Consortium (OGC). In WASP, all sensors provide their location information to data center and form a community. WASP provides remote control functions for WSN to increase the data retrieval efficiency based on OGC SWE Sensor Observation Service (SOS), Sensor Planning Service (SPS), and Sensor Alert Service (SAS). We demonstrated two applications using WASP in Taiwan. The WASP architecture is a helpful and efficient tool for user to construct a sensor observation service.

An Adaptive Multi-channel MAC protocol for Wireless Ad Hoc Networks

Employing multiple channels is an effective way to improve the performance of wireless networks [2-10]. Some previous works on multiple channels [2-4] assume at least two transceivers and result in a higher cost on hardware requirements. The protocol in [5] uses a single transceiver and divides the beacon interval into two parts: channel negotiation and data transmission. However, the fixed length of channel negotiation interval limits the channel utilization. This paper proposed a new single transceiver MAC protocol that can exploit multiple channels effectively and dynamically adjust the length of negotiation interval to better utilize the wireless channel resources. The simulation results show that the proposed protocol achieves higher aggregate network throughput than the fixed schemes on various traffic loads.

An efficient QoS guaranteed MAC protocol in wireless ATM networks

In order to provide QoS guarantees in the wireless networks, wireless ATM (WATM) is suitable to be the framework. With an appropriate medium access control (MAC) protocol, WATM can support multimedia service efficiently and guarantee their QoS requirements. Due to limitation of wireless bandwidth available, an efficient wireless ATM MAC protocol is needed. A new MAC protocol, named CRPMA/DS (combination of reservation and polling multiple access with distributed scheduling), is proposed to support various ATM services, such as CBR, VBR, ABR and UBR. CRPMA/DS is based on a distributed scheduling architecture to access the shared wireless bandwidth. Each mobile terminal (MT) can handle its connections more efficiently according to its requirements. CRPMA/DS also uses a scheme with the proposed contention resolution algorithm to solve the request collision and VBR bursty problems. We simulate our proposed MAC protocol and compare its performance with DTDMA/PR and PRMA/DA. The simulation results show that CRPMA/DS has higher throughput of data traffic (ABR and UBR traffic) and still guarantees the QoS of CBR and VBR traffic. With the contention resolution algorithm, CRPMA/DS also provides a low collision probability when the MTs send their requests in the reservation period.

An Efficient Wireless Internet Access Scheme

We propose and describe an efficient wireless local access system for high-speed Internet users at home, school or business. This system takes advantage of the asymmetric traffic characteristic of popular Internet services (such as Web search and FTP) to realize very high system capacity and very low delay response time to users due to effective statistical multiplexing. Specifically, the system provides subscribers with 10-Mb/s downlink (base-to-user) and 2-Mb/s uplink (user-to-base) speeds by using a three-cell frequency reuse plan with packet-mode sectorized base-station antennas. Using the 2-GHz band as an example, the cell radius can be up to 5 miles, and the total number of active users in each cell can be in excess of 15000 with delay bounds commensurate with todays typical Web services. Our design discussions include considerations for radio propagation, link budget, inter-cell interference, signal-to-interference ratio, high-speed modem, base-station gateway and capacity estimates.