Alessio Filippi

Key technologies for next-generation terrestrial digital television standard DVB-T2

A new platform for HDTV transmissions, in the form of a new-generation terrestrial digital video broadcasting standard (DVB-T2), has been developed by the DVB Project and will be published by the European Telecommunications Standards Institute. A number of technical innovations have been included in DVB-T2 to boost throughput and ruggedness, enhance single-frequency network coverage, and ease both transmitter and receiver implementation. This article starts from the motivations that led the DVB project to create the new standard and then surveys the key technologies behind DVB-T2, including the LDPC/BCH forward error correction scheme, transmission scheduling, orthogonal frequency-division multiplexing with huge block size, multiple-antenna transmissions, and synchronization techniques. A comparison with the current DVB-T standard is also provided, showing that DVB-T2 is able to increase the payload throughput and allows HDTV transmission with current network planning.

OFDM symbol synchronization using frequency domain pilots in time domain

In this paper, we describe and evaluate a novel time synchronization algorithm for OFDM systems robust to channels with long echoes. Most of the OFDM based standards provide known pilots in the frequency domain for channel estimation purposes. The basic idea of our contribution consists of interpreting the frequency domain pilots in the time domain and using them to obtain a rough channel estimation prior to the receiver discrete Fourier transform (DFT). The rough channel estimation is then used to perform the fine time synchronization.

ML Period Estimation With Application to Vital Sign Monitoring

The real time estimation of the period of signals that are periodic over short time intervals requires fast algorithms. In this letter, the maximum likelihood (ML) period estimator is derived for a periodic signal with additive white Gaussian noise. A low complexity approximation is then proposed, and compared with the state of the art of the estimation techniques in a practical scenario for the remote estimation of human heart rate using an ultra wide band radar.

OFDM Symbol Synchronization Using Frequency Domain Pilots in Time Domain

In this paper, we describe and evaluate a novel symbol synchronization algorithm for orthogonal frequency division multiplexing (OFDM) systems especially suited for channels with very long echoes. Most of the OFDM based standards provide known pilots in the frequency domain for channel estimation purposes. The basic idea of our contribution consists of interpreting the frequency domain pilots in the time domain to obtain a rough channel estimate before performing the discrete Fourier transform (DFT) and use it to properly position the DFT window. The proposed method aims to maximize the signal-to-inter-block-interference ratio after the DFT windowing. In short channels, where the channel length is shorter than the cyclic prefix length, the proposed method looks for an interblock-interference free windowing of the OFDM symbol. In long channels, where the channel length is longer than the cyclic prefix of the OFDM symbol, the proposed method search for the minimum inter-block-interference power windowing of the OFDM symbol.

Low-Complexity Interleaved Subcarrier Allocation in Multicarrier Multiple-Access Systems

We propose a new method to efficiently carry out an interleaved subcarrier assignment in multicarrier (MC) multiple-access (MA) systems. According to the conventional approach, the assignment of the subcarriers to the different users is accomplished prior to the MC modulation that is performed over the whole set of subcarriers within the transmission bandwidth. The proposed method enables the MC modulation/demodulation of only the subcarriers assigned to a specific user, thus being much simpler to implement than the conventional approach

Compressive Sampling for Non-Intrusive Appliance Load Monitoring (NALM) using Current Waveforms

We propose a NALM technique by exploiting the compressive sampling and sparse reconstruction framework. We estimate the contribution of the individual appliances by measuring the current of the total load. We further assume to know the steady-state current waveform of each appliance. We exploit the sparsity of the current signal to compress the measurement via random sampling, which lowers significantly the processing complexity, the storage and the communication burden. Using the proposed sparse reconstruction approach, we can still identify the on/off status of each appliance from the compressed measurement as if the original non-compressed measurement is used.

Multi-appliance power disaggregation: An approach to energy monitoring

Consumers increasingly want to make informed and proactive decisions based on an understanding of their energy consumption. However, current energy monitoring solutions are either too limited in the information they provide or are too intrusive. We consider a solution for disaggregating the electrical power consumption of individual appliances connected in a residential electricity network, with a single point of measurement. We pose the power disaggregation problem in the framework of multi-user detection. Two linear detection algorithms are then provided to determine which appliances are active in the network and in turn to determine their individual power consumptions. An experimental setup is described that was used to evaluate the performance of the algorithms along with simulation results.

Blind Estimation of Maximum Delay Spread in OFDM Systems

We present a new method of estimating the maximum delay spread of a channel in an OFDM system. The method differs from other approaches because it uses all active OFDM subcarriers (pilot and data) and therefore avoids the aliasing problem arising from the exclusive usage of pilot subcarriers. The method considers the transmitted data as a random probe signal for obtaining characteristics of a channel. Although the data content is not known at the receiver, it turns out that useful second order statistics can be extracted, from which the maximum delay spread is estimated. The method is shown to be robust to noise and Doppler spread.

Effects of Time Synchronization on OFDM Systems Over Time-Varying Channels

In this paper we refine a previously proposed model of time-varying OFDM systems, by taking into account the effects of non-ideal time synchronization. The considered non-ideal time synchronization includes the positioning of the receiver discrete Fourier transform (DFT) window and a cyclic shift of the input data. In OFDM systems with time-invariant channel, these two operations are equivalent. However, in the presence of a time-varying channel, OFDM suffers from intercarrier interference (ICI) which is differently affected by the positioning and the cyclic shift. We investigate the different effects and propose a refinement of the ICI modelling so that it holds also in the presence of non-ideal time synchronization. We verify the proposed refinement by testing a previously proposed ICI cancellation algorithm in the presence of non-ideal time synchronization

Channel estimation pilots for Single Frequency Networks

In this work, we introduce a new approach for channel estimation in single frequency networks (SFN). The intention is to exploit the a-priori knowledge of the SFN scenario. Conventional pilot schemes for SFN design the pilot scheme to deal with the aggregate channel. In this paper, we show that by being aware of how this long channel is generated, we can design a more efficient pilot scheme. The core idea consists in assigning orthogonal pilot sequences to the transmitters belonging to the same SFN. This allows the receivers for a separate estimate of each of the propagation channels. We have proposed a new pilot scheme for the DVB-T standard in which we assign orthogonal pilot sequences to the different transmitters in the SFN.