361 research outputs found
Adaptive algorithms for improving the throughput in an indoor mobile s-aloha ds-cdma system
This paper presents a novel Adaptive DSCDMA
Slotted-ALOHA packet random access scheme
with transmitter-based spreading codes for mobiles. It
is aimed at improving the throughput and message
delay delivery when traffic load values below the
saturation point of the conventional DS-CDMA
Slotted-ALOHA system are sensed in the channel. For
this purpose, one Mobile and two Base Station assisted
algorithms are envisaged to control the change of the
transmission rate according to the traffic load. These
algorithms revealed that the optimum behavior,
obtained using a Markov Chain model, may be almost
reached at a low complexity cost.Peer ReviewedPostprint (published version
Adaptive schemes for packet data in a ds-cdma environment
This paper presents a novel adaptive DS-CDMA slotted-ALOHA packet random access scheme for improving the throughput of the conventional DS-CDMA slotted-ALOHA system. For this purpose a mobile-assisted algorithm is envisaged to control the change of the transmission rate according to the traffic load. This algorithm revealed that the optimum behavior may be almost reached at a low complexity cost. Moreover, the proposed algorithm was found to be robust to intercell interferencePeer ReviewedPostprint (published version
Dect architecture proposal for a construction site
A construction site is an specific environment where important propagation related issues
have to be considered. In particular an important problem concerns the coverage of buildings under
construction and therefore continuously changing. The deployment of a DECT system in such scenarios
can not be carried out as usually, by means of DECT base stations linked by cables. Another specific
problem is that no measures can be done prior to decide the best place for the antennas since initially
the building does not exist. In this paper a way to solve both problems is proposed through a specific
system architecture, a propagation model and a combination of software with a CAD tool.Peer ReviewedPostprint (published version
A mobile controlled algorithm for improving the throughput in a s-aloha ds-cdma system
This paper presents a novel adaptive DS-CDMA slotted-ALOHA packet random access scheme with transmitter-based spreading codes for mobiles. It is aimed at improving the throughput and message delay delivery when traffic load values below the saturation point of the conventional DS-CDMA slotted-ALOHA system are sensed in the channel. For this purpose a mobile assisted algorithm is envisaged to control the change of the transmission rate according to the traffic load. This algorithm revealed that the optimum behavior, obtained using a Markov chain model, may be almost reached at a low complexity cost. Moreover, priorities between mobiles could be easily established. Finally, a traffic model based on a realistic statistical length distribution of the messages illustrates how the delay delivery can be greatly reduced.Peer ReviewedPostprint (published version
An efficient data transmission policy in an integrated voice-data ds-cdma network
CDMA schemes appear to be promising access techniques for coping with the requirements of third-generation mobile systems, mainly because of their flexibility. This paper proposes an adaptive S-ALOHA DS-CDMA access scheme as a method for integrating non-real time (i.e. Internet applications) and real-time (i.e. voice) services, by exploiting the potentials of CDMA under time-varying conditions. The adaptive component terminals autonomously change their transmission rate according to the total (voice+data) channel occupancy, so that the minimum possible data delay is almost always achieved.Peer ReviewedPostprint (published version
Performance analysis of a second order delay-lock loop with application to a CDMA system with multipath propagation
CDMA systems require synchronization between the received sequence and the locally generated sequence. This is done by means of a delay-lock loop (DLL). The differential equation of an incoherent second-order DLL has been programmed. The mean time to lose lock (MTLL) of the DLL is a very important design parameter. The authors have obtained this parameter by computer simulation and are able to plot the MTLL as a function of the signal to noise ratio in the data bandwidth. In a narrow-band system, the simulation shows that the effect of the fast Rayleigh fading is a performance degradation even with high mean signal to noise ratio. Assuming a wide-band system, so that the receiver has enough bandwidth to resolve the different propagation paths, the authors propose a modified DLL scheme. The MTLL of the proposed DLL is evaluated using a dynamic simulation of the multipath channel. The results show an improvement with respect to the conventional DLL.Peer ReviewedPostprint (published version
Performance of a linear interference canceller for a ds/cdma synchronous system based on the ekf delay estimator
Since the conventional detector often fails to produce reliable decisions for a CDMA channel, several new multiuser detectors have previously proposed. In the present paper, the authors propose both a simple linear scheme for interference cancellation, which exhibits good performance, and a synchronism scheme based on the extended Kalman filter (EKF) to achieve synchronization among the different users at the base station, for a direct-sequence code-division multiple-access (DS/CDMA) synchronous system. The influence of the synchronism scheme on the performance of the interference canceller is analyzed under Rayleigh multipath fading.Peer ReviewedPostprint (published version
Contabilidad de sistemas de espectro ensanchado por salto de frecuencias y sistemas de banda estrecha en comunicaciones mĂłviles
En este trabajo se ha evaluado la posible compatibilidad que puede existir entre un sistema de espectro ensanchado (FH-MFSK) que utiliza saltos de frecuencia a gran velocidad y un sistema de banda estrecha en presencia de desvanecimientos tipo Rayleigh, caracterĂsticos de un entorno movil. Con 20 MHz de banda disponible y señal vocal digitalizada a 32 Kb/s un sistema FH-MFSK puede soportar unos 80 usuarios simultanees en banda estrecha. El efecto del sistema FH-MFSK sobre el sistema de banda estrecha es despreciable.Peer ReviewedPostprint (published version
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