1,721,075 research outputs found
Euclidean Distance for Combinations of Some Hamming Codes and Binary CPFSK Modulation
No full textThe integration of channel coding and modulation in a communication system to increase the Euclidean distance between modulated signals is analyzed. Systems using binary continuous-phase frequency-shift keying modulation and some block codes, such as Hamming codes and shortened Hamming codes, are considered. It is shown that the minimum Euclidean distance depends on the configuration of the parity-check matrix H of the code. For the examined codes the optimum configurations of H , which give the maximum values of the minimum Euclidean distance, are determined
An Efficient Two-tier MAC Scheme for Satellite Machine-to-Machine Communications
No full textThe use of satellite communications to support the Internet of Things paradigm is of paramount importance for application scenarios where machines are spread in remote and wide areas. In such context, this paper proposes an efficient hierarchical radio access scheme. Ground machines randomly access the radio channel to communicate with their cluster heads, which in turn relay the cluster's aggregated traffic toward the satellite. The aim is optimizing the resource allocation to different communication stages, allowing resource reuse among clusters, in order to minimize the packet drop probability, and hence, to maximize the system throughput. First, the optimal solution is derived for the single cluster, then it is extended to the multi-cluster scenario. Numerical results show the effectiveness of the proposed method, also in comparison with benchmark approaches
WiMAX Network Security
No full textThe possible usage scenarios of a WiMAX service network are extremely various. The network can support static and mobile users roaming in a metropolitan area, the kind of traffic can be the typical Internet browsing or real-time traffic with stringent QoS constraints. The components of a WiMAX network must assure that all these needs are fulfilled. To reach this goal, all the layers of the OSI stack are required to co-operate in order to guarantee security, session establishment, fast handover and correct quality levels
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
Efficient Spectrum Spatial Reuse Approach Based on Gibbs Sampling for Ultra Dense Networks
No full textThe ultra dense deployment of small cells is consid- ered a key technology to achieve the requested capacity in future cellular networks. However, the interference pattern becomes more unpredictable and challenging in these networks. Therefore, a suitable trade-off between spectrum spatial reuse and interfer- ence level has to be pursued to achieve good performance in terms of provided throughput. This paper proposes a new method to maximize the achievable throughput of an UDN with a suitable level of spatial spectrum reuse. In particular, the focus is on the small cells tier where the available spectrum is divided into sub-bands and each cell can use some of these to communicate with its associated users. The goal is to find the sub-bands allocation among cells that maximizes the system throughput. However, to limit complexity and signaling overhead that could result unaffordable in an UDN, a new metric to approximate the cell throughput to be optimized is defined. Moreover, the newly defined problem is solved using the Gibbs Sampling approach. The method effectiveness is proven by comparing the achieved results with those of the maximization of the effective system throughput and the optimal solution
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
A modified PRMA protocol for voice and data transmissions in low earth orbit mobile satellite systems
No full textFuture mobile communication systems will provide multimedia services to users in every environment through uniform access procedures, In this scenario, it is essential to define efficient medium access control (MAC) protocols that are suitable for both terrestrial and satellite systems (integrated networks). This paper envisages packet reservation multiple access (PRMA) for supporting voice and data transmissions in low earth orbit (LEO) mobile satellite systems. In particular, a modified PRMA (MPRMA) protocol is proposed and analyzed, Simulation results are also presented in order to validate the analytical approach. A parameter optimization has been carried out to improve the protocol performance. Finally, a comparison with PRMA has permitted to highlight the advantages of the new MPRMA scheme
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
Analysis of a MAC protocol for a time-code air interface in LEO mobile satellite systems
Full text linkThis paper deals with Low Earth Orbit - Mobile Satellite Systems (LEO-MSSs) and proposes a novel Medium Access Control (MAC) scheme for a hybrid time-code wideband air interface. This is a reservation scheme where each mobile terminal that needs to transmit makes random accesses (on available time-code resources) until it receives a positive acknowledgment from the satellite. Our protocol is named Code Division-Packet Reservation Multiple Access scheme with Hindering States. This work has been carried out within the “Multimedialità” Project of the Italian National Consortium for Telecommunications. © Springer-Verlag Berlin Heidelberg 2002
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