1,721,030 research outputs found
The Effect of High-Level Acknowledgment Traffic on the Throughput of ALOHA Channels
No full textThe behavior of the throughput of an ALOHA channel is investigated, taking into account the effect of acknowledgment traffic when the acknowledgment mechanism is provided by high-level protocols. It is shown that the use of redundant ACK packets slightly increases the channel throughput
A collision resolution algorithm for random-access channels with echo
No full textn this paper random access algorithms for packet broadcast channels are considered. It is shown that utilizing channels with a central repeater as for instance a satellite channel more information is available to resolve conflicts than that utilized ..
Expressnet: A High-Performance Integrated-Services Local Area Network
No full textExpressnet is a local area communication network comprising an inbound channel and an outbound channel to which the stations are connected. Stations transmit on the outbound channel and receive on the inbound channel. The inbound channel is connected to the outbound channel so that all signals transmitted on the outbound channel are duplicated on the inbound channel, thus achieving broadcast communication among the stations. In order to transmit on the bus, the stations utilize a distributed access protocol which achieves a conflict-free round-robin scheduling. This protocol is more efficient than existing round-robin Schemes as the time required to switch control from one active user to the next in a round is minimized (on the order of a carrier detection time), and is independent of the end-to-end network propagation delay. This improvement is particularly significant when the channel data rate is so high, or the end-to-end propagation delay is so large, Or the packet size is so small as to render the end-to-end propagation delay a significant fraction of, or larger than, the transmission time of a packet. Moreover, some features of Expressnet make it particularly suitable for voice applications. In view of integrating voice and data, a simple access protocol is described which meets the bandwidth requirement and maximum packet delay constraint for voice communication at all times, while guaranteeing a minimum bandwidth requirement for data traffic. Finally, it is noted that the voice/data access protocol constitutes a highly adaptive allocation scheme of channel bandwidth, which allows data users to recover the bandwidth unused by the voice application. It can be easily extended to accommodate any number of applications, each with its specific requirements
Performance of Capture-Division Packetized Access (CDPA) with partial frequency reuse and power control
No full textPreviously, a new method for achieving spectrum reuse in cellular systems, called capture-division packetized access (CDPA), has been introduced. The method uses a single frequency in all cells but, unlike CDMA, allows each transmitter to access the full bandwidth. Practically, the CDPA's way of operation can be seen as an S-ALOHA scheme among different cells in which the mobile terminals belonging to the same cell transmit using a collision-free mechanism, which is easily obtained due to the very short intra-cell propagation delay. Parallel transmission in different cells is achieved through the “capture” capability. Packets that are not captured are almost immediately retransmitted, thus assuring that packets are eventually correctly received. In this paper we analyze an extension of the CDPA that uses partial frequency reuse. In fact, in this case, a trade-off exists between the bandwidth wasted by retransmissions and the bandwidth wasted by subdividing spectrum usage in K parts. It is shown that, depending on the capture threshold ratio b at receivers, an optimal choice exists. In all cases, the spectrum efficiency obtained almost doubles the efficiency of systems, like GSM, with K=7. The gain offered by power-control techniques is also investigate
Capture-division packetized access (CDPA) for cellular systems: performance analysis of the inbound and outbound channels
No full textThe paper presents a new cellular architecture for radio access, CDPA, that can be applied to present and future cellular systems, independently of the cell size. It poses as an appealing alternative to systems based on classical bandwidth-subdivision methods, namely TDMA, FDMA or CDMA. In these systems, parallelism of communications is achieved by subdividing the bandwidth “a priori” among cells. In CDPA no bandwidth subdivision is operated. All cells and terminals use a single frequency channel and transmit packets on a slotted channel. Parallel transmission in different cells is achieved through the “capture” capability. A dynamic polling mechanism, C-PRMA, managed by the base station, guarantees almost immediate re-transmission of packets that are not captured, thus assuring that packets are eventually correctly received. Analytical evaluations show that CDPA has the potential to provide larger capacity than the other cited systems in the case of continuous traffic sources. Furthermore, as C-PRMA is inherently apt to sustain bursty traffic, the system capacity is easily doubled in the case of packetized voice transmission using silence suppressio
Throughput and Delay Bounds for Cognitive Transmissions
No full textCognitive networks are based on agile and opportunistic use of spectrum resources. This work focuses on those network scenarios where primary or licensed users coexist with secondary or unlicensed ones. Secondary users opportunistically access the shared resources whenever vacant, with the strict constraint of being invisible to primary users. We derive here analytical bounds on throughput and transmission delay of secondary users under different assumptions on secondary and primary users traffic statistics, and we comment on the use of the proposed models to dimension secondary transmissions. © 2008 International Federation for Information Processing
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