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Recently, the radio frequency identification (RFID) technology has gained significant attention. One of the important performance issues in RFID systems is to resolve the collision among responses from RFID tags from the viewpoint of wireless media access control. We consider two kinds of smart antenna systems to enhance the RFID tag reading rate, namely the adaptive array antenna and the multipleinput multiple-output (MIMO) antenna. We consider passive tags that are operating without battery. We evaluate how much performance can be improved by employing smart antennas in the cases of the binary tree splitting algorithm and the Slotted-Aloha algorithm.

Abstract-We analyze the carrier sensing and interference relations between the two wireless links and measure the impact of these relations on link capacity in two indoor 802.11a mesh network testbeds. We show that asymmetric carrier sensing and/or interference relations happen frequently in wireless networks; these asymmetric relations affect not only the level of performance degradation, but also the fairness of channel access. We then propose a new methodology that predicts the relation of carrier sensing and interference based on radio signal strength measurements. The measurement complexity increases only linearly with the number of wireless nodes. To our knowledge, the proposed methodology is the first trial that considers physical layer capture, and detects the source of interference that is out of the communication range. We validate the prediction methodology on an 11-node wireless mesh network testbed.

Abstract. In cellular networks, the signal pattern reported by a mobile terminal has been the major source for localization. In this paper we show how the signal pattern is affected by the terminal movement such as the speed and the moving direction in CDMA/WCDMA networks. When the mobile terminal is moving, its signal pattern tends to contain more signals from base stations positioned opposite of the terminal's moving direction than signals from base stations positioned in the forward. We call this phenomenon "signal dragging". If the signal dragging prevails, it naturally provides a useful hint for figuring out the movement of a terminal, e.g., direction. We also show that the accuracy of the localization algorithm based on pattern matching varies greatly depending on the terminal movement. Based on these experimental results in commercial networks we suggest the practical data collection procedure, e.g., the war-driving, should consider the terminal movement. Otherwise the use of war-driving data can be harmful.