1,721,213 research outputs found
Optical nonlinearity and existence conditions for quasi-steady-state photorefractive solitons
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Characterization of user mobility in low earth orbit mobile satellite systems
No full textFuture mobile communication networks will provide a global coverage by means of constellations with nongeosynchronous satellites. Multi-spot-beam antennas on satellites will allow a cellular coverage all over the Earth. Due to the unstationarity of satellites a call may require many cell changes during its lifetime. These passages will be managed by inter-beam handover procedures. This paper deals with the modeling of the user cell change process during call lifetime in Low Earth Orbit-Mobile Satellite Systems (LEO-MSSs). The analytical derivations presented in this study can be also applied to different mobility models provided that basic assumptions are fulfilled. This paper evaluates the impact of user mobility on the blocking performance of channel allocation techniques. Moreover, the handover arrival process towards a cell has been characterized by using a usual statistical parameter for stationary point processes. Finally, a performance analysis has been carried out on the basis of the classic teletraffic theory for telephone systems
Call blocking performance for dynamic channel allocation technique in future mobile satellite systems
No full textDifferent dynamic channel allocation (DCA) approaches based on the evaluation of a cost function are proposed. The scenario considered is low earth orbit and geostationary orbit mobile satellite systems. A suitable user mobility model has been defined to generate interbeam handover requests. Different alternatives to manage interbeam handovers have been investigated. Among them, the most promising solution seems to be the queuing of handover requests. The quality of service parameters that have been considered are: blocking probability for new call arrivals, handover failure probability and the probability of incompletely served call owing to the initial blocking or to the failure of a subsequent handover request. Comparisons among the proposed DCA techniques and the fixed channel allocation technique have been carried out to find a solution that represents a good trade-off between the blocking performance and the required signalling load. Indexing terms:. © IEE, 1996
Performance comparison of different dynamic channel allocation techniques for mobile satellite systems
No full textDynamic Channel Allocation (DCA) techniques permit a high resource utilization in cellular networks and are able to adapt themselves in the presence of rapid variations of traffic loads offered to the cells. Therefore, they are particularly suitable for Mobile Satellite Systems (MSSs). This paper compares the performance of several DCA solutions that are based on the evaluation of a cost function in terms of both quality of service parameters (i.e., blocking probabilities) and signaling load to be supported by the system. Both GEostationary Orbit (GEO) and Low Earth Orbit (LEO) MSSs have been considered. A particularly interesting DCA solution is proposed that tries to serve a new call attempt in a cell where no channel is available by means of a channel reconfiguration in an interfering cell. Handover requests that do not attain immediately service can be queued for a maximum time in order to enhance system performance
Handover and dynamic channel allocation techniques in mobile cellular networks
No full textThis paper deals with an efficient Dynamic Channel Allocation (DCA) technique applicable to terrestrial mobile cellular networks. A channel (or resource) is a fixed frequency bandwidth (FDMA), a specific time-slot within a frame (TDMA), or a particular code (CDMA), depending on the multiple access technique used. A cost function has been defined by which the optimum channel to be assigned on demand can be selected. In addition, a suitable mobility model has been derived to determine the effects of handovers on network performance. The performance of the proposed DCA technique has been derived by computer simulations in terms of call blocking and handover failure probabilities. Comparisons with the classical Fixed Channel Allocation (FCA) technique and other dynamic allocation algorithms recently proposed in the literature have been carried out to validate the proposed technique
Performance evaluation of different resource management strategies in mobile cellular networks
No full textThe foreseen mass diffusion of mobile communication services will require the identification of suitable resource management strategies to utilize efficiently the available spectrum. This paper refers to high-mobility cellular systems and carries out a performance evaluation for different channel assignment techniques that belong to the following classes: Fixed Channel Allocation (FCA), or Dynamic Channel Allocation (DCA). Suitable handoff prioritization techniques have been considered to obtain a high quality of service; in particular, the queueing of handoff requests and the use of guard channels have been investigated. The resource management techniques have been compared in terms of the following parameters: the call blocking probability, the call dropping probability, the probability of unsuccessful call and the average number of channel rearrangements per call. The joint use of DCA, guard channels, queueing of handoff requests and channel rearrangements has shown promising results for the management of both new call attempts and handoff requests
Handover queueing strategies with dynamic and fixed channel allocation techniques in low earth orbit mobile satellite systems
No full textThis paper deals with the performance evaluation of various resource management strategies that are suitable for low earth orbit-mobile satellite systems (LEO-MSS's). A user mobility model has been proposed and its statistical parameters have been derived. Both fixed channel allocation (FCA) and dynamic channel allocation (DCA) techniques have been considered. Moreover, in order to reduce the handover failure probability, we have assumed that interbeam handover requests which do not immediately obtain service can be queued. In particular, two different queuing disciplines have been compared: a) the first input first output (FIFO) scheme and b) a new technique called last useful instant (LUI) which is based on the knowledge of the maximum time within which the handover procedure must be accomplished. Implementation aspects for the LUI technique in a LEO-MSS have been discussed also in comparison with the measurement-based priority scheme (MBPS), previously proposed in the literature on this subject. The efficiency of the LUI queuing scheme as regards the FIFO technique has been investigated by simulations for both DCA and FCA techniques. An analytical approach has been also presented in order to allow the performance evaluation of the FCA scheme with different handover queuing disciplines
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