Terje Roste

Channel characterization including path loss and Doppler effects with sea reflections for mobile radio propagation over sea at 2 GHz

Maritime communication plays an important role in marine activities, but insufficient knowledge of radio channel characteristics over sea limits the development of wideband wireless communication systems for maritime applications. Therefore a land-to-ship (L2S) radio channel measurement assignment has been performed in Trondheim, Norway. In this paper we have focused open sea propagation environments, and results of the channel characterization from measurements are presented, such as path-loss, channel correlation and Doppler effects due to sea reflections, along with the reflection coefficient of the sea surface. The received signal level (RSL) has been compared to the Okumura-Hata model, the COST 231-Hata model and the ITU-R P.1546–2 model, and it has been found that the ITU-R model for open cold sea corresponding to field-strength value exceeded at 50% of the locations fits the measurement results best. By using two receiver antennas with 1.865 m spacing, partly channel correlation has been revealed when the distance between the transmitter (TX) and receiver (RX) is within 2 km, while the two channels are found to be highly correlated when the boat is further away from the shore. When the distance between the TX and RX is within the range 3 km to 12 km, a fading beat frequency is found to be 0.16 Hz, i.e. about 0.16 Hz Doppler shift caused by the sea movement. Finally, the reflection coefficient of the sea surface turns out to be about 0.11 in the same range, which does not comply with the Kirchhoff theory for effective reflection coefficient.

A Deterministic Round Earth Loss Model for Open-Sea Radio Propagation

This paper proposes a deterministic path-loss model for the open-sea environment. The model accounts for different effects including effective reflection, divergence, and diffraction due to rough sea and earth curvature. The model results show excellent agreement with experimental results from our recent measurement campaign, which investigated propagation at 2 GHz with a maximum distance of 45 km. Channel parameters like mean-square surface slope and standard deviation of surface height are evaluated, from which it can be concluded that the shadowing and scattering effects on the reflection ray will influence the fading amplitude within the distance of 0.6 First Fresnel Zone clearance.

Digital Predistortion of Power Amplifiers Based on Spline Approximations of the Amplifier Characteristics

Digital block-based predistortion (PD) is an efficient scheme to linearize power amplifiers (PA). The performance of this method highly depends on the estimation accuracy of the amplifier characteristics. In this paper, the PA characteristics are approximated by piecewise continuous polynomials in the form of splines. The approximation is based on a block of observed data at the input and output of the PA. This approach leads to a linear parametric approximation problem with moderate implementation complexity, and it also gives the best possible fit to a given set of observations. With cubic splines it is possible to get a fairly accurate estimate even with a short block of data, and hence a fast convergence of the PD algorithm. The performance of the method has been evaluated for an example selected from an application in mobile satellite communications with burst transmission. We use a model of a 2 Watts class A PA that is based on measurements, and the calculations are performed for 16-QAM modulation. The mean square approximation error, the power spectrum and the error vector magnitude (EVM) of the received signal have been analyzed by simulations. For 6 dB back-off, the adjacent channel power ratio (ACPR) level is reduced by approximately 15 dB relative to a transmitter without predistortion, after an adaptation based on only 25 transmitted symbols.

Block based predistortion for amplifier linearization in burst type mobile satellite communications

Predistortion (PD) technique has been proposed to linearize the power amplifier (PA) and improve the power efficiency for non-constant envelope modulation schemes. In this paper a new PD scheme based on block estimation suitable for burst type communications is described. Piecewise linear regression is applied to estimate the AM/AM and AM/PM distortions. The predistortion is simply the inverse of these estimated curves up to a predefined point. The PD is implemented using two cascaded uniform look-up tables (LUT) for amplitude and phase corrections. An adaptation algorithm is proposed to compensate for variations of PA characteristics due to temperature and/or shift of frequency. Simulations are carried out to find the optimum size of the LUT. Simulation results for 16-QAM modulation show significant reduction in adjacent channel interference (ACI) and considerable improvement in constellation quality for a typical class A high power amplifier. The error vector magnitude (EVM) criterion is used to measure the constellation quality. The system set-up to implement the algorithm is presented. Experimental results for 16-QAM modulated signal with the symbol rate of 151.2 kHz are presented. As shown in section V, about 10-15 dB power leakage reduction in adjacent channel and about 13 dB improvement in EVM were obtained

Experimental multipath delay profile of mobile radio channels over sea at 2 GHz

This paper is presenting measurement results characterizing radio channels at 2 GHz over open sea between a mobile single-antenna ship-borne transmitter (TX) and a fixed dual-antenna terrestrial receiver (RX). Here the measurement data are analyzed in the time domain, where the major parameters being considered are power-delay profiles (PDPs), mean excess delay and RMS delay spread. We have performed two measurement campaigns, a short range (≈ 15km) and a long range (≈ 45km). Our analysis of the short-range measurement data shows that the probability density function (PDF) of mean excess delay and RMS delay spread can be characterized by using a three-term Gaussian model, while the long-range data show that the channel can be regarded as a non frequency-selective channel.

Channel characterization of mobile radio channel over sea at 2 GHz

Maritime communication has been considered as a core issues in the marine activities. However, few wideband wireless communication systems have been carefully evaluated for maritime applications due to a.o. insufficient knowledge of radio channel characteristics over sea. Therefore, a land-to-ship (L2S) radio channel measurement assignment has been performed in Trondheim, Norway. In this paper, we have focused on the open sea propagation environments and results of the channel characterization from measurements are presented, such as path-loss, channel correlation and reflections from the sea surface. We have compared the received signal level (RSL) with the Okumura-Hata model, the COST 231-Hata model and the ITU-R P.1546–2 model, and it has been found that the ITU-R model for open cold sea corresponding to field-strength value exceeded at 50% of the locations fits the measurement results best. By using two receiver antennas with 1.85 meters spacing, partly channel correlation has been revealed when the distance between the transmitter (TX) and receiver (RX) is within 2 km, while the two channels are found to be highly correlated when the boat is far away from the shore. Finally, reflections from the sea surface are found to be rather small over the open sea and the fading mainly due to sea reflections have been observed to be maximum 2 dB with a standard deviation of 0.5 dB. Closer to land this was different.

On the Optimization of Biasing Conditions in a Digitally-Linearized Power Amplifier

Changing the class of operation in a power amplifier (PA) affects the linearity and the efficiency of the PA. In this paper, the linearization performance and the efficiency enhancement of a Digital Predistorter (DPD) in a transmitter is evaluated with different PA classes. The digital predistorter is implemented in real-time on a Digital Signal Processor (DSP). The PA under test is a 2-stage 2-watt amplifier used in mobile terminals in Inmarsat Broadband Global Area Network (BGAN) systems. The gate bias of the PA is tunable for changing the biasing conditions. It is shown that by driving the PA into class B, we increase the memory effects and therefore reduce the effectiveness of memoryless predistortion. It was also shown that using a memoryless digital predistorter and a PA biased near class AB operation, an efficiency of about 41% is achievable while the BGAN system requirements are met.