Francisco Cercas
ISCTE - University Institute of Lisbon (ISCTE-IUL), DCTI, Faculty Member
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The objective of this paper is to present the estimated performance for TCH codes, in channels where errors can occur independently and in burst. Since this family of block codes is nonlinear, its performance must be determined by... more
The objective of this paper is to present the estimated performance for TCH codes, in channels where errors can occur independently and in burst. Since this family of block codes is nonlinear, its performance must be determined by simulation. The chosen technique is the interval simulation technique (IST) that is used with a two-state Markov model for the bursty channel.
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... technique; however this has the disadvantage that it is only applicable to some particular cases, and cannot be generalized for a wider range of applications (Jeruchim, Balaban & Shanmugan ... Communication Valentin Cristea,... more
... technique; however this has the disadvantage that it is only applicable to some particular cases, and cannot be generalized for a wider range of applications (Jeruchim, Balaban & Shanmugan ... Communication Valentin Cristea, Ciprian Dobre, Corina Stratan, and Florin Pop (2010 ...
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ABSTRACT With the widespread of new radio systems, it is essential that their performance is evaluated prior to auxiliary design and commercial development. Although there are many methods to model and estimate the performance of a given... more
ABSTRACT With the widespread of new radio systems, it is essential that their performance is evaluated prior to auxiliary design and commercial development. Although there are many methods to model and estimate the performance of a given radio system with some accuracy, most of these methods require high computational resources or long simulation times. In this study, the authors present a general and efficient simulation method for estimating the performance of a wireless communication systems, with particular emphasis for its forward error correction sub-system when using block channel codes, for channels affected by additive white Gaussian noise, free space attenuation, shadowing, fading and interfering sources. Both soft-decision (SD) and hard-decision (HD) decoding are considered and the overall performance takes into account modulation, coding and channel conditions. This efficient simulation is compared with the Monte Carlo simulation method and its performance is assessed for the Tomlinson, Cercas and Hughes code family. This new simulation method has an temporal efficiency of two or three orders of magnitude for SD and HD and three or four orders, considering a bit-error-ratio of 0.01 and 0.001%, respectively.
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In this article a simulation environment for digital transmission systems is presented. Its application in digital transmission experimental learning is possible by allowing key parameters influence study through a graphical interface. It... more
In this article a simulation environment for digital transmission systems is presented. Its application in digital transmission experimental learning is possible by allowing key parameters influence study through a graphical interface. It is possible to visualise some points of the system, modify structures and transmission parameters. Equivalent lowpass of BPSK and QPSK with limited Nyquist spectrum and nonlimited spectrum (finite time impulses) are considered. Fast BER curve estimation is obtained by a ...
... Only-Memories. The maximum output frequenc of the earl prototypes was limited to some kilohertz even wit\ a very edaent use of memory [4]. Nowadays fre quencies up to some hundreds of me ahertz are achievable and rea ...
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A complete characterization of direct digital frequency synthesizers; (DDFSs) is made, deducing exact expressions and general properties of these synthesizers. As an application example of the derived expression for the power spectrum... more
A complete characterization of direct digital frequency synthesizers; (DDFSs) is made, deducing exact expressions and general properties of these synthesizers. As an application example of the derived expression for the power spectrum density with phase quantization, an extremely simple algorithm is described that sequentially computes the frequency and magnitude of each component and gives exactly the, same result as an
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In LEO/MEO systems there can be significant interference between overlapping spot beams from several satellites. New codes are proposed which are interference resistant and attractive in this application. These codes, named TCH codes, are... more
In LEO/MEO systems there can be significant interference between overlapping spot beams from several satellites. New codes are proposed which are interference resistant and attractive in this application. These codes, named TCH codes, are of binary length, possess near optimum cross-correlation properties and have significant advantages from the implementation point of view. The derivation of these codes is explained. Their
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In this paper a novel multistage polyphase magnitude modulation (MPMM) scheme is proposed for efficiently controlling the envelope's peak power of single carrier band limited signals, using root-raised cosine (RRC) pulse shaping. A... more
In this paper a novel multistage polyphase magnitude modulation (MPMM) scheme is proposed for efficiently controlling the envelope's peak power of single carrier band limited signals, using root-raised cosine (RRC) pulse shaping. A new LUT-less approach of the concept of ...
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With Digital Terrestrial Television (DTT) it is possible to transmit different digital contents together with the video signal, ie datacasting. This has become possible due to the coding and compression technologies used to process the... more
With Digital Terrestrial Television (DTT) it is possible to transmit different digital contents together with the video signal, ie datacasting. This has become possible due to the coding and compression technologies used to process the signal, not available with analogue technology. This ...
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An efficient multistage polyphase magnitude modulation (MPMM) scheme was recently proposed to solve the problem of controlling the envelope's power peak of single carrier modulated signals, band limited by root-raised cosine (RRC)... more
An efficient multistage polyphase magnitude modulation (MPMM) scheme was recently proposed to solve the problem of controlling the envelope's power peak of single carrier modulated signals, band limited by root-raised cosine (RRC) pulse shaping filters, in order to maximize the efficiency of the transmitter's high power amplifier (HPA). This paper addresses the statistical analysis of MPMM coefficients and performs an
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ABSTRACT We consider communication between a legitimate transmitter and a legitimate receiver in the presence of an eavesdropper in the conventional Gaussian wiretap channel setting. Based on Wyner's coding scheme, we show that a... more
ABSTRACT We consider communication between a legitimate transmitter and a legitimate receiver in the presence of an eavesdropper in the conventional Gaussian wiretap channel setting. Based on Wyner's coding scheme, we show that a code construction using orthogonal codewords can achieve the secrecy capacity of the Gaussian wiretap channel in the wideband regime. This is illustrated through analysis of the error probability between the legitimate parties and the eavesdropper equivocation rate, as well as various simulation results.
Page 1. Mobile Network Monitoring Information System Rodrigo MS Gonçalves(1), Bruno MG Miranda(1) and Francisco AB Cercas(1) (2) (1)Instituto Superior das Ciências do Trabalho e da Empresa, DCTI Avenida das Forças ...
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Abstract QAM and APSK are used to meet the ever growing demand for higher data rates in bandwidth limited satellite channels whose main constraint to communication capacity is a non-linear transmitting High Power Amplifier (HPA). The... more
Abstract QAM and APSK are used to meet the ever growing demand for higher data rates in bandwidth limited satellite channels whose main constraint to communication capacity is a non-linear transmitting High Power Amplifier (HPA). The inherent APSK robustness ...
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Abstract Magnitude Modulation is a technique proposed with success for QPSK and OQPSK in order to maximize power and bandwidth of small satellite earth stations, by reducing PAPR of the modulated signal at the HPA input. To meet the ever... more
Abstract Magnitude Modulation is a technique proposed with success for QPSK and OQPSK in order to maximize power and bandwidth of small satellite earth stations, by reducing PAPR of the modulated signal at the HPA input. To meet the ever growing demand for higher ...
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ABSTRACT This paper addresses the problem of controlling the envelope's power peak of single carrier modulated signals, band limited by root-raised cosine (RRC) pulse shaping filters, in order to reduce power amplifier back-off... more
ABSTRACT This paper addresses the problem of controlling the envelope's power peak of single carrier modulated signals, band limited by root-raised cosine (RRC) pulse shaping filters, in order to reduce power amplifier back-off for very small aperture terminals ground stations. Magnitude modulation (MM) is presented as a very efficient solution to the peak-to-average power ratio problem. This paper gives a detailed description of the MM concept and its recent evolutions. It starts by extending the look-up-table (LUT) based approach of the MM concept to M-ary constellations with M ≤ 16. The constellation and RRC symmetries are explored, allowing considerable reduction on LUT computation complexity and storage requirements. An effective multistage polyphase (MPMM) approach for the MM concept is then proposed. As opposed to traditional LUT-MM solutions, MM coefficients are computed in real-time by a low complexity multirate filter system. The back-off from high-power amplifier saturation is almost eliminated (reduction is greater than 95%) with just a 2-stage MPMM system even for very demanding roll-off cases (e.g., α = 0.1). Also, the MPMM is independent of modulation in use, allowing its easy application to constellations with M > 16.
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AbstractA multistage polyphase magnitude modulation (MPMM) technique is proposed for single carrier (SC) mod-ulations, to efficiently reduce the peak-to-average power ratio (PAPR) of the bandwidth limited signal resulting from... more
AbstractA multistage polyphase magnitude modulation (MPMM) technique is proposed for single carrier (SC) mod-ulations, to efficiently reduce the peak-to-average power ratio (PAPR) of the bandwidth limited signal resulting from root-raised cosine (RRC) filtering. ...
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O processo de Bolonha revela-se hoje como o maior desafio proposto à sociedade académica, dado que obriga a um repensar de estratégias e opções tomadas no passado. O objectivo é tornar possível a mobilidade entre instituições, quer dentro... more
O processo de Bolonha revela-se hoje como o maior desafio proposto à sociedade académica, dado que obriga a um repensar de estratégias e opções tomadas no passado. O objectivo é tornar possível a mobilidade entre instituições, quer dentro do nosso País, ...
This paper addresses the problem of controlling the enve-lope's power peak of single carrier modulated signals, band limited by root-raised cosine (RRC) pulse shaping filters, in order to maximize the efficiency of the... more
This paper addresses the problem of controlling the enve-lope's power peak of single carrier modulated signals, band limited by root-raised cosine (RRC) pulse shaping filters, in order to maximize the efficiency of the transmitter's high power amplifier (HPA). A ...
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Google, Inc. (search). ...
This paper focuses on the use of an equalization-based receiver for WCDMA (Wideband Code-Division Multiple Access) in an inter-cellular environment, for handover studies. The receiver is based on the MMSE (Minimum Mean Square Error)... more
This paper focuses on the use of an equalization-based receiver for WCDMA (Wideband Code-Division Multiple Access) in an inter-cellular environment, for handover studies. The receiver is based on the MMSE (Minimum Mean Square Error) algorithm and uses the UMTS (Universal Mobile Telecommunications System) HSDPA (High Speed Downlink Packet Access) standard as a basis, alongside the reference UMTS environments
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The LMMSE (Linear Minimum Mean Square Error) algorithm is one of the best linear receivers for DS- CDMA (Direct Sequence-Code Division Multiple Access). However, for the case of MIMO/BLAST (Multiple Input, Multiple Output / Bell... more
The LMMSE (Linear Minimum Mean Square Error) algorithm is one of the best linear receivers for DS- CDMA (Direct Sequence-Code Division Multiple Access). However, for the case of MIMO/BLAST (Multiple Input, Multiple Output / Bell Laboratories Layered Space Time), the perceived complexity of the LMMSE receiver is taken as too big, and thus other types of receivers are employed, yielding
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Frederico Varela, Pedro Sebastião, Américo Correia, Member, IEEE, Francisco Cercas, Member, IEEE ISCTE-LUI/Instituto de Telecomunicações Av.ª das Forças Armadas 1649-026 Lisboa, Portugal fredericovarela@gmail.com,... more
Frederico Varela, Pedro Sebastião, Américo Correia, Member, IEEE, Francisco Cercas, Member, IEEE ISCTE-LUI/Instituto de Telecomunicações Av.ª das Forças Armadas 1649-026 Lisboa, Portugal fredericovarela@gmail.com, pedro.sebastiao@lx.it.pt, ...
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This paper addresses the performance of the downlink High Speed Data Packet Access (HSDPA) in multipath fading channels using several enhancement schemes applied both at the transmitter and at the receiver. 3GPP specifications define... more
This paper addresses the performance of the downlink High Speed Data Packet Access (HSDPA) in multipath fading channels using several enhancement schemes applied both at the transmitter and at the receiver. 3GPP specifications define several transmit diversity schemes for two antennas, namely the standardized closed loop modes 1 and 2 and the open loop Space Time Transmit Diversity (STTD). This paper studies these techniques but also other transmitting schemes such as open loop modes using space time block codes (STBC’s) for 4 and 8 transmitting antennas, Selective Transmit Diversity (STD) and hybrid modes combining space time block codes and STD. It is shown that the multipath interference introduced by the channel induces a severe performance loss, which is especially relevant for the CQIs with 16-QAM modulation, using several simultaneous physical channels. A Multipath Interference Canceller (MPIC) using clipped soft decision (CSD) is proposed for suppressing this multipath inter...