A New Waveform based on Linear Precoded Multicarrier Modulation for Future Digital Video Broadcasting Systems

Abstract

Orthogonal Frequency Division Multiplexing (OFDM) has been perceived as one of the most effective transmission schemes for multipath propagation channels. It has been widely adopted in most of the digital video broadcasting (DVB) standards such as DVB-T in Europe, DMB-T in China, FLO in North America, ISDB-T in Japan. The major reason for this success lies in the capability of OFDM to split the single channel into multiple parallel intersymbol interference (ISI) free subchannels. It is easily carried out by implementing Inverse Fast Fourier Transform (IFFT) at the transmitter and Fast Fourier Transform (FFT) at the receiver [1]. Therefore, the distortion associated to each subchannel, also called subcarrier, can be easily compensated for by one coefficient equalization. For that purpose, the receiver needs to estimate the channel frequency response (CFR) for each subcarrier. In the DVB-T standard [2], one subcarrier over twelve is used as pilot for CFR estimation as illustrated in Fig. 1, i.e. symbols known by the receiver are transmitted on these subcarriers. Thus, the receiver is able to estimate the CFR on these pilot subcarriers and to obtain the CFR for any subcarrier using interpolating filtering techniques [3]. Nevertheless, OFDM systems are very sensitive to synchronization error such as carrier frequency offset (CFO) or sampling frequency offset (SFO) [4]. Indeed, when the carrier frequency or the sampling frequency of the transmitter and the receiver are not equal, the orthogonality between the different subcarriers is lost which can lead to strong intercarrier interference (ICI) effects [4]. This is why in addition to the scattered pilot subcarriers used for CFR estimation, continuous pilot subcarriers have been defined in the DVB-T standard [2] to estimate the CFO and the SFO [5]. Fig. 1 depicts the locations of the data subcarriers and the pilot subcarriers over the time and frequency grid as defined in the DVB-T standard. The originality of this work is to reduce the overhead part resulting from pilot insertion by using a joint CFR, CFO and SFO estimation approach based on a linear precoding function. Eventually, these pilots dramatically reduce the spectral efficiency and the useful bit rate of the system. The basic idea consists in using a two-dimensional (2D) linear Source: Digital Video, Book edited by: Floriano De Rango, ISBN 978-953-7619-70-1, pp. 500, February 2010, INTECH, Croatia, downloaded from SCIYO.COM