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Access Scheme (access + scheme)
Selected AbstractsA novel fair random access scheme with throughput optimization using fuzzy controller for wireless systemsINTERNATIONAL JOURNAL OF NETWORK MANAGEMENT, Issue 4 2009M. R. M. Rizk Good backoff algorithms should be able to achieve high channel throughput while maintaining fairness among active nodes. In this paper, we propose a novel backoff algorithm to improve the fairness of random access channels, while maximizing channel throughput. The mechanism of the proposed backoff algorithm uses backoff delay (retransmission delay) and channel-offered traffic to dynamically control the backoff interval, so that each active node increases its backoff interval in the case of collision by a factor which exponentially decreases as the backoff delay increases, and decreases its backoff interval in the case of successful transmission by a factor which exponentially decreases as the backoff delay of previous retransmission attempts increases. Also, the backoff interval is controlled according to the channel offered, traffic using a fuzzy controller to maximize channel throughput. Furthermore, the operation of the proposed backoff algorithm does not depend on knowledge of the number of active nodes. A computer simulation is developed using MATLAB to evaluate the performance of the proposed backoff algorithm and compare it with the binary exponential backoff (BEB) scheme, which is widely used owing to its high channel throughput, while its fairness is relatively poor. It is shown that the proposed backoff algorithm significantly outperforms the BEB scheme in terms of improving the performance of fairness, and converges to the ideal performance as the minimum backoff interval increases, while achieving high channel throughput. Copyright © 2008 John Wiley & Sons, Ltd. [source] A capture-assisted random access scheme for multi-beam LEO satellite packet data networksINTERNATIONAL JOURNAL OF SATELLITE COMMUNICATIONS AND NETWORKING, Issue 6 2004George Thomas Abstract A CDMA-based satellite switch is proposed for use in multi-beam satellites carrying random-access packet-switched data. Applications include the emerging new low-earth-orbit (LEO) satellite networks which support global wireless networking. Capture phenomenon is used to advantage in increasing the random access throughput, and the on-board switch is at once simple and specially designed to handle full loads with minimal complexity. Copyright © 2004 John Wiley & Sons, Ltd. [source] Stability analysis of an adaptive packet access scheme for mobile communication systems with high propagation delaysINTERNATIONAL JOURNAL OF SATELLITE COMMUNICATIONS AND NETWORKING, Issue 2 2003Giovanni Giambene Abstract In this paper, we investigate a packet access scheme that is able to support mixed traffics in the presence of high propagation delays. Referring to a Time-Code Division Multiple Access air interface, we propose a Medium Access Control (MAC) protocol based on a random access scheme. A successful attempt grants the use of a slot-code resource. This protocol is named Adaptive Time Code-Packet Reservation Multiple Access (ATC-PRMA), since the access parameters are changed, depending on the traffic load conditions, so as to fulfil Quality of Service requirements. Numerical examples are carried out for the Low Earth Orbit (LEO)- Mobile Satellite System (MSS) scenario, but all these considerations could be applied to High-Altitude Platform Stations (HAPSs) as well. In both cases, high propagation delays prevent an immediate feedback to users. An analytical approach is proposed to study the stability of our MAC scheme. Accordingly, we define a criterion for optimizing system performance. The predicted ATC-PRMA behaviour is supported by simulation results. Finally, we show the performance improvement of ATC-PRMA with respect to a MAC protocol not employing adaptive parameters. Copyright © 2003 John Wiley & Sons, Ltd. [source] The long term evolution towards a new 3GPP* air interface standardBELL LABS TECHNICAL JOURNAL, Issue 4 2007Rainer Bachl The performance targets for the long term evolution (LTE) of the Universal Mobile Telecommunication System (UMTS) into a 4th generation system have been chosen to be very ambitious. While all of these targets may not be achievable in practice, they have served to motivate the decisions for a particular LTE design. Specifically, we discuss the choice of the multiple access scheme for LTE, provide details on the uplink and downlink transmission formats, analyze the benefits of multiple input multiple output (MIMO), and outline approaches for intercell interference mitigation. The trade-off between usage of MIMO spatial multiplexing and beamforming is shown for a practical system. The required signaling overhead is weighed against the performance improvements available from the additional information. Finally, some examples for the achievable physical layer performance are given. © 2007 Alcatel-Lucent. [source] Broadband wireless access based on VSF-OFCDM and VSCRF-CDMA and its experimentsEUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 3 2004Hiroyuki Atarashi This paper presents broadband packet wireless access schemes based on variable spreading factor (VSF)-orthogonal frequency and code division multiplexing (OFCDM) in the downlink and variable spreading and chip repetition factors (VSCRF)-CDMA in the uplink for the systems beyond IMT-2000. In our design concept for wireless access in both links, radio parameters such as the spreading factor (SF) are optimally controlled so that the system capacity is maximized according to the cell configuration, channel load and radio channel conditions, based on the tradeoff between efficient suppression of other-cell interference and the capacity increase in the target cell by exploiting orthogonality in the time and frequency domains. We demonstrate that the peak throughput of greater than 100,Mbps and 20,Mbps is achieved by the implemented base station and mobile station transceivers using the 100-MHz and 40-MHz bandwidths in the downlink and uplink respectively. Moreover, the simulation results show the possibility of the peak throughput of approximately 1,Gbps for short-range area applications using the 100-MHz bandwidth OFCDM downlink by applying four-branch multiple input multiple output (MIMO) multiplexing with 16,QAM data modulation and punctured turbo coding. Copyright © 2004 AEI [source] Performance analysis of the IEEE 802.11 MAC protocol for wireless LANsINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 6 2005P. Chatzimisios Abstract Wireless local area networks (WLANs) are extremely popular being almost everywhere including business, office and home deployments. The IEEE 802.11 protocol is the dominating standard for WLANs. The essential medium access control (MAC) mechanism of 802.11 is called distributed co-ordination function (DCF). This paper provides a simple and accurate analysis using Markov chain modelling to compute IEEE 802.11 DCF performance, in the absence of hidden stations and transmission errors. This mathematical analysis calculates in addition to the throughput efficiency, the average packet delay, the packet drop probability and the average time to drop a packet for both basic access and RTS/CTS medium access schemes. The derived analysis, which takes into account packet retry limits, is validated by comparison with OPNET simulation results. We demonstrate that a Markov chain model presented in the literature, which also calculates throughput and packet delay by introducing an additional transition state to the Markov chain model, does not appear to model IEEE 802.11 correctly, leading to ambiguous conclusions for its performance. We also carry out an extensive and detailed study on the influence on performance of the initial contention window size (CW), maximum CW size and data rate. Performance results are presented to identify the dependence on the backoff procedure parameters and to give insights on the issues affecting IEEE 802.11 DCF performance. Copyright © 2005 John Wiley & Sons, Ltd. [source] | |||||||||||||