This paper proposes two space-frequency schemes with a multi-user pre-filtering technique for downlink (DL) multicarrier code division multiple access (MC-CDMA) systems. We consider the use of antenna arrays at the base station (BS) and a single antenna at the mobile terminal (MT) and derive the proposed multi-user pre-filtering technique that modulates the transmitted signal to eliminate the effects of multiple access interference (MAI) and channel distortions at the mobile terminals, while maintaining low MT complexity. Two types of detectors are considered at the MT: simple despreading and single user equalizers. The performances of the proposed schemes are compared to those of other transmit signal design approaches that have been recently proposed for DL MC-CDMA, considering both typical indoor and pedestrian scenarios, and channel coding based on UMTS specifications. © Springer Science+Business Media, LLC. 2009.

The paper considers downlink space-frequency preequalizations techniques for time division duplex (TDD) MC-CDMA. We consider the use of antenna arrays at the base station (BS) and analytically derive different preequalization schemes for two different receiver configurations at the mobile terminal: a simple despread receiver without channel equalization and an equal-gain combiner (EGC) conventional receiver. We show that the space-frequency preequalization approach proposed allows to format the transmitted signals so that the multiple access interference at mobile terminals is reduced allowing to transfer the most computational complexity from mobile terminal to the BS. Simulation results are carried out to demonstrate the effectiveness of the proposed preequalization schemes.

This paper deals with downlink space-frequency block coding with a pre-filtering technique for time division duplex MC-CDMA. We consider the use of antenna arrays at the base station (BS) and a single antenna at the mobile terminal (MT). The space-frequency block codes allow that the spatial diversity be efficiently exploited and the linear multi-user pre-filtering technique allows to format the transmitted signals so that the multiple access interference (MAI) and channel distortions at mobile terminals are completely removed. The aim of this technique is to transfer the most computational complexity from MT to the BS, keeping the first one at very low complexity. Simulations results are carried out in high data rate scenarios with the channel turbo code specified for the current UMTS system, to demonstrate the effectiveness of the proposed multi-user pre-filtering algorithm with SFBC. © 2005 IEEE.

In this communication we present a space-frequency pre-filtering technique, for downlink time division duplex (TDD) MC-CDMA systems, where the base station is equipped with an antenna array. We show that the pre-filtering approach can considerably reduce the multiple access interference at the mobile terminals allowing to transfer a significant part of the computational complexity to the base station, using a very low complex receiver at mobile. This approach relies on the availability of the channel state information at transmission, i.e., uses the time division duplex channel reciprocity between alternative uplink and downlink to obtain the channel state information. Simulation results are presented to demonstrate the effectiveness of the proposed prefiltering algorithm. Moreover, the performance of the proposed pre-filtering algorithm is assessed in two distinct scenarios: beamforming and diversity.

This communication deals with downlink time division duplex MC-CDMA system, and presents a frequency domain pre-filtering technique, where the base station is equipped with an antenna array. We show that the space-filtering approach proposed allows to format the transmitted signals so that the multiple access interference at the mobile terminals is reduced allowing to transfer a significant part of the computational burden to the base station, and therefore enabling the use of a very low complex receiver at mobile. This approach uses the time division duplex channel reciprocity between uplink and downlink to obtain the channel state information. Simulation results are presented to demonstrate the effectiveness of the proposed pre-filtering algorithm.

Channel estimation is an essential building block for UTRA-TDD high performance receivers. Once the performance of the channel estimator algorithm proposed by 3GPP is highly dependent on the time spreading between consecutive multi-path components, a Successive Multi-path channel Estimation Technique (SMET) that improves the time resolution is proposed in this paper. A SMET based maximum likelihood approach for vectorial channel estimation, to include the estimation of the direction-of-arrival, is also proposed. This algorithm solves efficiently the complex problem of DOA estimation of multiple users in a multi path propagation environment even when the number of required DOA's exceeds the number of antenna array elements. Another property of the proposed algorithm is its ability to resolve signals from different users arriving from the same direction. This is due to processing in both time and space dimensions. The performance of these algorithms is assessed by resorting to simulations in multi-path environments using the UMTS-TDD specifications, and also by comparing the rms estimation errors against the Crámer-Rao Bound. The effect of imperfect channel estimation on the performance of RAKE and Hard-Decision Parallel Interference Canceller receivers is also analysed. The results show that a good performance can be achieved with SMET, from low to high values of Eb/n0.

Agile development embodies a distancing from traditional approaches, allowing an iterative development that easily adapts and proposes solutions to changing requirements of the clients. For this reason, the industry has recently adopted the use of its practices and techniques, e.g., Test-Driven Development (TDD), Behavior-Driven Development (BDD), amongst others. These techniques promise to improve the software quality and the productivity of the programmers; therefore, several experiments, especially regarding TDD, have been carried out within the academy and in industry. These show variant results (some of them with positive effects and others not so much). The main goal of this work is to verify the impact made by the TDD and BDD techniques in software development, analyzing their main promises regarding quality and productivity. We aim to conduct the experience in the academy, with a group of students from the Systems Engineering Degree of the Universidad Técnica del Norte, Ecuador. The students will receive training and appropriate education to improve knowledge about it, and we aspire to achieve interesting results concerning both quality and productivity. The challenge that it is also desirable, is to replicate the experiment in the industry or other adequate contexts.

This paper aims to validate the use of automatic test routines in HIL to evaluate performance of PMSM drivers. Therefore, a non-sinusoidal PMSM model is implemented, driven through six-steps commutation. In addition, the conduction and commutation losses of the inverter are determined, in order to use the efficiency as a comparison parameter to generate a report for benchmarking controllers. The six-step 120°strategy is used to drive the PMSM, which determines the order of commutations of a three-phase inverter through the information of the machine rotor position obtained by Hall effect sensors. The Test Driven Design methodology was used to compare the efficiency of different controllers. Therefore, the conduction and commutation losses of the inverter were determined, taking into account the junction temperature of the IGBTs and their thermal model. From this, the power dissipated in the inverter was used to define the efficiency of the system. An automated test routine was established to benchmark six current and speed controllers in terms of efficiency and rotor speed. https://doi.org/10.53316/sepoc2022.021

The objective of this work was to use Test-Driven Development (TDD) ─ a technique employed to make the source code more intelligible and easier to maintain. The maintenance is done with the aim of altering the software structure thus guaranteeing its integrity. Nevertheless, this task may become more complex should the source code and the software internal architecture turn out being difficult to understand. As TDD suggests a step by step development style and with the behavior tests being written before each functionality, it leads the developer to build a simpler and more functional code. Such development technique is employed here on the software designing which will confer a higher maintainability level. Sofware metrics was applied over the developed code through TDD and its data were compared with those metrics data of previously existing software which hadn’t employed TDD on its designing. The results of this comparison are presented and show the improvements in relation to the expected complexity when using TDD to help build software.

There are several features, in the literature, that guide the process of building software focused at creating high quality software products. Among these features is TDD - Test-Driven Development. This study evaluates the impact of the technique at the source code by comparing software metrics proposed by the software quality standards applied in two systems, developed according to the same requirements. One of these systems was built applying the mentioned technique. The results of this comparison are presented and discussed, bringing a practical view of the impact that the technique can bring to the software product, especially on aspects related to the source code.