A generic radio channel emulator to evaluate higher layer protocols in a CDMA system

Currently, we are involved in the standardisation process to specify the next mobile system generation. A wideband code division multiple access (WCDMA) system is considered in most of the region versions. It would be very useful to count on a radio channel emulator which allows one to evaluate higher layers protocols within this context. This paper presents a radio channel emulator developed for a code division multiple access (CDMA) based system. Its versatility and low complexity have been exposed, and the validation process to check the model accuracy has also been shown for this system as an example.Peer ReviewedPostprint (published version

A radio channel emulator for WCDMA, based on the hidden Markov model (HMM)

One of the main development and research subjects within the telecommunications area activity is the 3G mobile systems standardisation. The radio access is, of course, the main trouble in mobile systems, so it is important to investigate its implication. This paper describes a radio channel emulator for the UTRA-FDD made, based on the hidden Markov model (HMM). Since a statistical system behaviour is needed to train the HMM, off-line simulations have been made. The results between simulated and emulated statistics are presented. The use of emulation models implies a loss of accuracy with respect to simulation models, but is adequate to operate in real time. Certainly, the main advantage of using HMM in the emulator is the huge reduction in time, resources and effort with regard to a real simulation of the system. The emulator will allow in future works, for fast testing and comparison of several higher layer protocols and error control schemes.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

On soft/hard handoff for packet data services in cellular CDMA mobiles systems

Benefits of macrodiversity operation for packet data services in third generation mobile systems are not obvious. Retransmission procedures to enhance link performance and higher downlink bandwidth requirements could question macrodiversity usage. This paper describes a simple methodology to compare soft and hard handoff performance in terms of transmission delay for packet data services. The handover procedures are based exclusively on power criteria and hysteresis margins.Peer ReviewedPostprint (published version

Multiple slot allocation for voice/data transmission over PRMA++ applied to FRAMES multiple access mode 1

This paper presents some simulation results of PRMA++ for voice and data transmission over a physical air interface platform defined in the ACTS European project FRAMES. Variations on the statistics of speech sources (activity factor, petition rate) are studied and conclusions are obtained for optimal frame dimensioning. For data transmission, a multiple slot allocation scheme is presented and results are shown for different source rates and packet lengths.Peer ReviewedPostprint (published version

Credit rating agencies and unsystematic risk: Is there a linkage?

This study analyzes the effects of six different credit rating announcements on systematic and unsystematic risk in Spanish companies listed on the Electronic Continuous Stock Market from 1988 to 2010. We use an extension of the event study dummy approach that includes direct effects on beta risk and on volatility. We find effects in both kinds of risk, indicating that rating agencies provide information to the market. Rating actions that imply an improvement in credit quality cause lower systematic and unsystematic risk. Conversely, ratings announcements that imply credit quality deterioration cause a rebalance in both types of risk, with higher beta risk being joined with lower diversifiable risk. Although the event characteristics were not important to determine how the two types of risk reacted to rating actions, the 2007 economic and financial crises increase the market’s sensitivity to these characteristics

Nanoplastics: From tissue accumulation to cell translocation into Mytilus galloprovincialis hemocytes. resilience of immune cells exposed to nanoplastics and nanoplastics plus Vibrio splendidus combination

Plastic litter is an issue of global concern. In this work Mytilus galloprovincialis was used to study the distribution and effects of polystyrene nanoplastics (PS NPs) of different sizes (50 nm, 100 nm and 1 mu m) on immune cells. Internalization and translocation of NPs to hemolymph were carried out by in vivo experiments, while endocytic routes and effects of PS NPs on hemocytes were studied in vitro. The smallest PS NPs tested were detected in the digestive gland and muscle. A fast and size-dependent translocation of PS NPs to the hemolymph was recorded after 3 h of exposure. The internalization rate of 50 nm PS NPs was lower when caveolae and clathrin endocytosis pathways were inhibited. On the other hand, the internalization of larger particles decreased when phagocytosis was inhibited. The hemocytes exposed to NPs had changes in motility, apoptosis, ROS and phagocytic capacity. However, they showed resilience when were infected with bacteria after PS NP exposure being able to recover their phagocytic capacity although the expression of the antimicrobial peptide Myticin C was reduced. Our findings show for the first time the translocation of PS NPs into hemocytes and how their effects trigger the loss of its functional parameters

Emulador de canales radio para sistemas de comunicaciones móviles

Peer ReviewedPostprint (published version

On the influence of the channel impulsional response estimation on the performance of a linear interference canceller for a DS/CDMA system

In a code division multiple access (CDMA) mobile radio communication system, interference from other users is one of the most critical drawbacks due to the lack of perfect orthogonality between user access codes. So far, practical systems have used power control to overcome fading and near/far effects. Another approach which also results in an important improvement of the capacity is the use of interference cancellers. A simple linear interference cancellation scheme for coherent BPSK modulation is proposed and analyzed under Rayleigh multipath fading, and in particular, the influence of the channel impulsive response estimation on the performance of the cancellation scheme has been assessed.Peer ReviewedPostprint (published version

The use of coding and diversity combining for mitigating fading effects in a DS/CDMA system

Spatial diversity is an attractive technology to cope with the fading channel encountered in mobile communications. This paper presents novel closed analytical expressions of the bit-error rate (BER) achievable in a coherent binary phase-shift-keying (CBPSK) direct-sequence code-division multiple-access (DS/CDMA) system for any power delay profile and for either postdetection selection or maximal ratio combining (MRC). In particular, expressions for the cutoff rate Ro and for its related parameter D are also formulated in order to assess the system performance under the consideration of some channel coding schemes. Finally, an exemplary study is carried out in order to illustrate the behavior of a realistic space-diversity code-division multiple-access (CDMA) system according to the analytical expressions that have been derivedPeer Reviewe