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Passive RFID tags share a common channel and they use back-scattering modulation because of no self battery. It causes reader collision problems when signal from a reader interferes with signal from other readers. The evolving standards use CSMA based protocol called 'Listen Before Talk (LBT)' and FDMA based protocol called 'Frequency Hopping Spread Spectrum (FHSS)' to reduce reader collision problems...
In this paper we propose the multi-user MIMO (MU-MIMO) with the fixed relay station (RS) transmissions scheme where the base station (BS) and the fixed RS are equipped with multiple antennas and the multiple users are equipped with a single antenna. Since the MU-MIMO can improve the sum capacity significantly by transmitting the data streams to multiple users simultaneously without much link gain...
In this paper, a CDMA-based medium access control (MAC) scheme in underwater acoustic sensor networks is proposed, in which a periodic sleeping mode is jointly employed for the purpose of saving energy. A hierarchical tree-topology is considered where a staggered wakeup schedule is used across the multiple hierarchical levels from bottom-nodes to a top-node to allow long propagation delay of the underwater...
A medium access control (MAC) protocol is developed for time division multiple access (TDMA) and time division duplex (TDD)-based large wireless mesh networks (WMNs) with infrastructure support. Utilizing control time slots, the protocol operates in a fully cooperative and distributed manner: mesh routers cooperate to negotiate resource allocation, and the messages are exchanged only among one-hop...
In parallel with the proliferation of radio-frequency identification (RFID) systems, many RFID readers have been increasingly employed. In such an environment, collision among readers becomes a serious problem. Existing anticollision algorithms, depending on the information of neighboring readers, may require constant effort in order to grasp such information. Although it may be given by a server...
Mobile RFID, the technology of a cellular phone equipped with a RFID reader, allows users to read RFID tags anywhere. However, signals from more than two readers can interfere with one another, i.e., reader collision problem; reliable tag reading is necessary. This paper proposes Gentle protocol to use beacon messages and multi-channel for increasing throughput. In addition, Gentle protocol can put...
A control time slot assignment protocol is developed for time division multiple access (TDMA) and time division duplex (TDD)-based large wireless mesh networks (WMNs). Through the protocol, each wireless mesh router acquires a broadcast time slot that supports a minimum average signal-to-interference-plus-noise ratio (SINR) to all of its neighbors. The protocol employs contention-based reservation...
We propose QUEST (QUality ESTimation), a new method that accurately estimates IEEE 802.11 wireless link quality with no in-band signaling overhead. Existing link quality estimation methods either are based on hello exchanges by fixing or varying transmission rates or rely on the history (e.g., delivery ratio) of previously sent data packets in a per-rate/-neighbor manner. QUEST on the other hand,...
Broadcast protocols play a vital role in multihop wireless networks. Due to the broadcast nature of radio signals, a node's interference range can be larger than its transmission range, i.e., it can interfere with other node's reception even if the latter is not within its transmission range. To design an efficient broadcast protocol, both the collision and the interference among multiple transmissions...
In this paper, we propose a cross-layer optimization approach that exploits retransmission diversity in wireless CDMA communications. Conventionally, data packets that are not correctly detected are usually dropped. These dropped packets can be used to help data packet detection. By exploiting all the retransmitted packets, data packets can be correctly detected with higher probability. The proposed...
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