Juan J. Alcaraz

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TCP, the dominant transport protocol for Internet applications, suffers severe performance degradation due to packet losses when a wireless link is present in the end-to-end path. For this reason, the 3G specification entity, 3GPP, has defined a reliable link layer protocol, RLC, to support packet switched services over UMTS. RLC provides error recovery in(More)
This paper is focused on data transmission scheduling in V2I communications, where a central station, the roadside beacon, decides how to allocate system resources among the vehicles under coverage. We consider non-safety applications, whose commercial appeal is expected to accelerate the deployment of VANETs. In this case, the main objective is to deliver(More)
—In Cooperative Automatic Repeat reQuest (C-ARQ) protocols, the retransmission process between a pair of nodes can be assisted by a relay node. We investigate the performance of C-ARQ algorithms in cellular access networks, where the use of relays is a promising strategy for future evolutions. By means of Markov analysis and simulation we show that the(More)
—Automatic identification based on radio frequency identification (RFID) is progressively being introduced into industrial environments, enabling new applications and processes. In the context of communications, RFID rely mostly on Frame Slotted Aloha (FSA) anticollision protocols. Their goal is to reduce the time required to detect all the tags within(More)
Keywords: Radio frequency identification Frame slotted ALOHA Equilibrium point analysis Stability Discrete time system Tag loss ratio a b s t r a c t In many practical RFID applications tags are attached to items that pass through the read-er's field moving at a constant speed, following a fixed path. The time-constrained presence of the tags in the(More)
— Transport channel synchronization in 3G access networks is currently based on a simple algorithm that tries to track the delay of the link by adding or subtracting a constant step. We propose an algorithm that improves the responsiveness of the system under abrupt delay changes, reducing frame losses. Our proposal is faster than the proportional tracking(More)
—We consider a spectrum leasing system in which secondary networks offer offload services to a primary network (PN) in exchange for temporary access to the PN's spectrum. When the coverage areas of several secondary access nodes (SANs) overlap, they compete for primary users (PUs), which benefits the PN, except when the SANs collude and coordinate their(More)
—RFID systems implementing Dynamic Frame Slotted Aloha (DFSA) can adjust the number of identification rounds (slots) within an inventory cycle (frame). The usual approach to reduce the identification time of the tag population is to select the frame size attaining the highest throughput in the frame. However, it is more accurate to minimize the(More)
TCP performance over 3G links can be enhanced by means of Active Queue Management (AQM) techniques at the downlink buffer of the mobile network link layer (RLC). In this paper we describe Slope Based Discard (SBD), a novel deterministic buffer management technique whose discarding policy is based on the observation of the filling rate of the buffer. By(More)