Genevieve Baudoin

Survey on spectrum utilization in Europe: Measurements, analyses and observations

This paper presents major results and comparisons of radio spectrum utilization measurements that have been carried out in three different locations in Europe, namely in the suburb of the city of Brno in the Czech Republic and in the suburb and the city of Paris in France during years 2008 and 2009 respectively. The analyzed radio bandwidth extends from 400 MHz to 3 GHz. The measurement method is based on the energy detection principle. Utilization performance and behaviors of major wireless communication systems and primary wireless system within different regions and different environments are investigated here. Our analyses pick out correlations between spectrum utilization within different regions and summarize common observations and physical aspects that will have to be considered in the future radio spectrum management to assure efficient spectrum utilization.

Filter Lookup Table Method for Power Amplifier Linearization

This paper presents a new method of digital adaptive predistortion for linearization of power amplifiers (PAs) exhibiting memory effects. The predistorter (PD) device consists of a lookup table (LUT) gain followed by a codebook of filters addressed by the index of the LUT. The adaptation is derived from direct learning for the LUT gains and indirect learning for the filter coefficients. We compared our results with those of two reference methods: a simple LUT system (with direct learning) and a memory polynomial system (with indirect learning). The performances of the new approach lie between those of the two reference methods in terms of adjacent channel power regrowth and error vector magnitude. The LUT is the less complex of the three methods, but it is a memoryless system, and it cannot correct the memory effects in the PA. The memory polynomial PD is more powerful, but its complexity is very high. The new technique, due to the addition of filters to the LUT, has possibilities to compensate not only for the nonlinearity but also for the memory effects in the PA, and it is one order of magnitude less complex than the memory polynomial system

From post-distortion to pre-distortion for power amplifiers linearization

This letter presents a new method of digital adaptive pre-distortion for linearization of power amplifiers (PA). The method is derived from a post-distortion approach which identifies the PA inverse function. This approach leads to the minimization of a quadratic function of the polynomial coefficients in the case of a polynomial predistorter form and a least square criterion. We have compared our solution to a method previously proposed by Ghaderi (1996) that was also based on the transformation of a post-distortion into a pre-distortion system. We have tested our predistorter (along with a baseband adaptation of Ghaderis) on OFDM Hiperlan signals. Both methods significantly reduced the signal distortion and the spectral regrowth. Our less complex approach proved to be even better for small peak back off values.

Adaptive CA-CFAR threshold for non-coherent IR-UWB energy detector receivers

In the present letter, a new adaptive threshold comparison approach for time-of-arrival (TOA) estimation in ultra wideband (UWB) signals is proposed. This approach can be used with non-coherent energy detector receivers in UWB systems. It exploits the idea of cell averaging constant false alarm rate (CA-CFAR) used in radar systems, where the threshold changes every energy block. The performance of several approaches are compared via Monte Carlo simulations using the CM1 channel model of the standard IEEE 802.15.4a. Both simulation results and comparisons are provided highlighting the effectiveness of the proposed approach.

A new low complexity NLOS identification approach based on UWB energy detection

The major problem of indoor localization is the presence of Non-line-of-sight (NLOS) channels. In order to perform the NLOS identification, this paper proposes a new NLOS identification approach. It is based on the energy statistics of the direct-path pulse (DPP) and on the statistics of the delay between the strongest-energy pulse and the DPP energy of the received signal folded version. The simplicity of the proposed approach lies in the use of the parameters of the Energy-Based time of arrival (TOA) Estimation (EBE) algorithm. The CM1 and CM2 channel models of the standard IEEE802.15.4a are used. Numerical simulations results show that the correct identification of channel models with the proposed approach is better than with the multipath channel statistics based approach.

Towards cognitive radio networks: Spectrum utilization measurements in suburb environment

This paper deals with spectrum utilization measurements in the frequency band from 100 MHz up to 3 GHz. The measurement is based on the energy detection principle using wideband logarithmically periodic antenna. The results point out the fact, that the frequency spectrum is not utilized in an optimal manner and that there do exist less or more utilized licensed frequency bands that could be possibly used by cognitive radios in an opportunistic way. Cognitive radio concept for better spectrum utilization is introduced here along with an overall approach regarding spectrum utilization in the next generation wireless networks.

Data transmission over voice dedicated channels using digital modulations

With the actual expansion in communication systems, data channels are taking more importance, especially in mobile data networks. But in some cases the transmission over data channels is not possible or not convenient, which makes the data transmission over voice channel an interesting alternative. Firstly, the operators of mobile phone networks (GSM, GPRS) tend to limit the access to the Internet in order to prevent Voice over IP (VoIP) for economical reasons. Secondly, the cross- networks bridges used in VoIP (VoIP-ISDN, VoIP-GSM, VoIP-PSTN) give an opportunity to transmit data over this voice channel without any additional data bridges. Thirdly, for security matters, transiting data dissimulated in a voice-like signal is more discrete. Lastly, some communication networks such as THURAYA are dedicated to voice communications.

Analysis of a PLL based frequency synthesizer using switched loop bandwidth for Mobile WiMAX

This paper is focused on design aspects of a fractional-N PLL (phase locked loop) based frequency synthesizer proposed for the mobile WiMAX (worldwide interoperability for mobile access) standard. Requirements in terms of phase noise, settling time, frequency resolution and frequency of operation for WiMAX frequency synthesizer are presented. Furthermore, a high-speed CP (Charge Pump) PLL based synthesizer with a switched loop bandwidth is proposed and simulated. It has a 32 MHz reference frequency and a 50 kHz loop bandwidth with frequency raster of 125 kHz and 14 mus settling time.

Analysis of a modified Polar Sigma-Delta transmitter architecture for multi-radio applications

Polar sigma delta architecture has been previously proposed as an universal architecture able to offer multi-radio transmission in a mobile system. Furthermore, it has been validated for mobile WiMax, a very exigent communication standard in terms of envelope magnitude range and channel bandwidth. This paper briefly describes polar sigma delta architecture and proposes some improvements to it, particularly the digital mixing instead of analog mixing. Simulations of the enhanced architecture have been carried out using agilent advanced design system. Results are analyzed and new architecture advantages and drawbacks are pointed out.

Data transmission over mobile voice channel based on M-FSK modulation

Voice channel in mobile communication systems has high priority and is almost always available. Its use as a bearer for data transmission allows to take advantage of this availability. But medium rate speech coders and associated VAD (Voice Activity Detector) and DTX (Discontinuous Transmission) which are well suited to voice signals, can strongly degrade other types of signals such as data modulated signals. In this paper we propose and evaluate a system for data transmission over mobile voice channel based on M-FSK modulation with optimized parameters. The parameters of the M-FSK modulation are tuned using real mobile communications voice channel in order to minimize the degradation introduced by the speech coder and by the discontinuous transmission (DTX) Our experiments show that it is possible to find a set of parameters for the M-FSK modulation which allows to achieve a moderate bit error rate (ie <; 10-2) without error-correcting code.