D. Di Zenobio

Adaptive linearization of power amplifier in orthogonal multicarrier schemes

This paper describes an adaptive predistortion system to linearize a memoryless high power amplifier (HPA). The described technique is independent of the modulation format. In the present paper the behaviour of such a predistorter in the presence of orthogonal frequency division multiplexing (OFDM) modulation schemes is analysed. The predistortion scheme uses a digital signal processing microprocessor and memory look-up tables to predistort the baseband drive signal. Simulation results are given where stability of the adaptation algorithm, rate of convergence and effect of quantization are assessed.

A switching circuit scheme for a satellite site diversity system

Problems connected with a satellite site diversity system (SDS) i.e., diversity synchronization, diversity switching control, and interconnection of two diversity antenna sites are discussed, and different solutions are considered. A preliminary baseline for the SDS includes circuit solutions for the alignment and switching equipment using elastic memories, the choice of beacon signal attenuation as a quality parameter, and the adoption of an error-free optical-fiber link between the two diversity stations. As an example, the implementation of the SDS relative to the experimental Olympus satellite is presented.<<ETX>>

A closed form to predict outage of digital radio

A simplified formula for predicting the outage probability of an unprotected high capacity line-of-sight digital radio link operating under frequency-selective fading conditions is presented. First, the propagation anomaly is modeled as a linear in-band amplitude dispersion in conjunction with a transmission minimum (notch) frequency located within or outside the signal band of interest. A simplified expression for the outage probability of the radio system under these conditions is then obtained. This expression is based on the fade occurrence factor in the climatic region of interest, the bandwidth of the transmitted signal, the carrier frequency of operation, the modulation scheme employed and the length of the link under consideration. The formula is applied to predict the outage probability of 4 phase shift keying (PSK), 8-PSK, and 16 quadrature amplitude modulation (QAM) high capacity radio links with specified parameters. The results obtained compare favorably with measured data. >

An independent sharing of two 16-star QAM broadcast channels

This paper describes an example of a system, providing two-resolution equivalent digital terrestrial broadcasting, based on UHF channel frequency arrangements. In this article orthogonal frequency division multiplexing technique combined with guard-interval is used. The transmission is achieved by using 16 QAM modulation with star constellation (16 star QAM) to reduce linearization problems of the power amplifier in the transmitter, The proposed system provides 5.5 Mbit/s to portable receivers and, additionally, 5.5 Mbit/s to fixed receivers. Block codes (BCH) give burst error correction capabilities to combat the frequency selective nature of the transmission channel.

A double half-bandwidth OFDM system for digital video broadcasting

To cope with the frequency selective and time-variant channel it is a good solution to combine an orthogonal frequency division multiplexing (OFDM) technique and a coding scheme. This article presents a particular use of a coded-OFDM with guard-interval (ICOFDM) to provide transmission with one enhanced definition TV or two standard definition TV signals in a 7 MHz bandwidth. In the paper frequency arrangements of the TV channel and RF filters features are also suggested. Performance results, obtained by computer simulation, on the selective Rayleigh channel with different spread delay values, for a ICOFDM system, using 8PSK coder and BCH block code (127,106,3) are reported as an example. An experimental set-up of ICOFDM 8PSK will be tested as soon as possible. >To cope with the frequency selective and time-variant channel it is a good solution to combine an orthogonal frequency division multiplexing (OFDM) technique and a coding scheme. This article presents a particular use of a coded-OFDM with guard-interval (ICOFDM) to provide transmission with one enhanced definition TV or two standard definition TV signals in a 7 MHz bandwidth. In the paper frequency arrangements of the TV channel and RF filters features are also suggested. Performance results, obtained by computer simulation, on the selective Rayleigh channel with different spread delay values, for a ICOFDM system, using 8PSK coder and BCH block code (127,106,3) are reported as an example. An experimental set-up of ICOFDM 8PSK will be tested as soon as possible.<<ETX>>

Measurements on indoor reception of broadcast signals at 800 MHz

This paper describes measurements on indoor reception of broadcast signals. The fading characteristics in the spatial and frequency domain are studied. Furthermore, an evaluation of the building attenuation loss is given. Theoretical explanations of the observed phenomena are also provided.<<ETX>>

Measurement Setup to Evaluate BER Performance, Amplitude and Group Delay Dispersions on Digital Radio Links

Digital radio-relay systems are particularly affected by the frequency selective nature of multipath fading. To know the effects of propagation on radio-relay systems, an experimental measurement setup was realized to characterize their susceptibility to multipath distortion. The setup is basically a recorder of the frequency-selective amplitude and group delay variations. Associated to these informations, data of error presence (single error, error burst, BER, etc.) are collected to determine, by successive elaborations, relationships between error occurrence and critical values of amplitude and group delay distortions. The measured data are stored only when they exceed the prefixed reference masks. Preliminary results are reported.