A new system concept for DTT, called "WiB", is presented, where potentially all frequencies within the Ultra High Frequency (UHF) band are used on all transmitter (TX) sites (i.e. reuse-1). The interference, especially from neighbouring transmitters operating on the same frequency while transmitting different information, is handled by a combination of a robust transmission mode, directional discrimination of the receiving antenna and interference cancellation methods. With this approach, DTT may be transmitted as a single wideband signal, covering potentially the entire UHF band, from a single wideband transmitter via the TX site. Thanks to a higher spectrum, utilisation, the approach allows for a dramatic reduction in fundamental power/cost and approximately a 37-60% capacity increase for the same coverage as with current DTT. High speed mobile reception as well as fine granularity local services would also be supported, without any loss of capacity. The paper also outlines further possible developments of WiB, e.g. doubling the capacity via cross-polar Multiple In Multiple Out (MIMO), backward-compatible with existing receiving antennas, and adding a second, WiB-mobile, Layer Division Multiplexing (LDM) layer within the same spectrum, either as a mobile broadcast or as a mobile broadband.
Rapidly time-varying channels are a major obstacle for successful data-transmission via OFDM. The resulting loss of orthogonality among neighboring subcarriers leads to intercarrier-interference, which affects channel estimation. This in turn impedes the subsequent data detection. Literature contains numerous approaches to cope with this problem working either in time-or frequency-domain. Our concern in this paper is a novel time-domain method which relies on the use of multiple directional receive antennas. Each of these antennas experiences only a fraction of the total Doppler spread of a comparable omnidirectional antenna. This not only eases channel estimation but also allows for a diversity gain due to maximum-ratio-combining. We will demonstrate that our scheme copes well with large maximum Doppler frequencies. IntroductionTransmitting data over frequency-selective channels is easily accomplished by the use of OFDM. Applying a suitable cyclic prefix not only avoids intersymbol interference between successive OFDM symbols but also performs the transformation of the linear convolution with the channel's impulse response into a circular convolution. In frequency-domain the subcarriers will then be received via flat-fading channels. However, rapidly time-varying channels with large Doppler spread will introduce intercarrier interference (ICI) in frequency domain since subcarriers loose their orthogonality. A popular approach in literature to deal with rapid channel fluctuations is the assumption of a linear model. Besides linear channel variation the authors of [1] additionally assume a block diagonal structure for the channel matrix neglecting off-diagonal elements, whose inversion demands less computional complexity but fails to capture the effect of ICI sufficiently for larger Doppler
Multi-layer broadcast systems distribute services across time and frequency domain by means of power-division multiplexing. Successive interference cancellation is required, in general, in order to extract the content of all services. For a lowcomplexity implementation, the receiver can obtain the strongest (top-layer) signal assuming underlying signals to behave like thermal noise. The thermal noise assumption may not be valid under certain conditions and a more accurate characterization of the interference could bring improved performance. This paper analyzes the validity of the noise-like assumption considering the power ratio between signals and the required Carrier-to-Noise ratio (CNR) for error-free reception. The main contribution of the paper is the proposal of a demapping algorithm that exploits the knowledge of the constellation of underlying signals. Generalized Mutual Information, performance evaluation, and complexity analysis are provided with the AWGN-like assumptions and with the proposed alternative in order to assess the potential performance improvements that can be achieved.
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