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

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 basis theorem for the degenerate affine oriented Brauer-Clifford supercategory

We introduce the oriented Brauer-Clifford and degenerate affine oriented Brauer-Clifford supercategories. These are diagrammatically defined monoidal supercategories which provide combinatorial models for certain natural monoidal supercategories of supermodules and endosuperfunctors, respectively, for the Lie superalgebras of type Q. Our main results are basis theorems for these diagram supercategories. We also discuss connections and applications to the representation theory of the Lie superalgebra of type Q.Comment: 37 pages, many figures. Version 3 replaces the partial results from the previous versions with a proof by the first author of a basis theorem for cyclotomic quotients at all levels. Various other minor corrections and revisions were mad

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