The potential of T2 in a WiB planned DTT scenario

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ABSTRACT

WiB (Wideband reuse-1) is a new system concept proposed for DTT (Digital Terrestrial Television), where potentially all UHF channels allocated to broadcasting services are used from all transmitter sites, thus having frequency reuse-1 (even around national borders), instead of frequency reuse 5 to 7 as adopted in “conventional” DTT plans.

In WiB, interference from co-channel neighbouring transmitters is handled by a combination of robust transmission modes, wide-band carrier aggregation, directional discrimination of the receiving antenna and, when required, sophisticated interference cancellation methods.

All of this requires new standardisation activity and new TV receivers. The paper describes a planning study that investigates the potential of reuse-1 planning for fixed DTT services, targeting current DVB-T2 receivers, i.e. using the most robust modes, but no interference cancellation techniques in the receiver, nor carrier aggregation.

Although such configuration promises, in an ideal interference-free environment, dramatic power savings and similar spectrum efficiency compared to current DTT networks, the simulations on a regular hexagonal lattice network including noise and interference produced some surprising outputs which are discussed in this article.

INTRODUCTION

Conventional planning of DTT services is based on international Plans that assign an equal portion of the spectrum to each nation in such a way that each transmitter in a MultiFrequency Network (MFN) does not cause or receive interference from the neighbouring Countries’ transmitters (a similar approach is adopted inside a MFN-planned country).

This results in a frequency reuse N, i.e. only one channel out of N channels is assigned to each transmitter or service area, with N going from 3 (theoretical minimum value for regular hexagonal lattices) to 7 (a typical figure adopted in real networks is N=5), depending on the geography of the country and the network and transmission system ruggedness against noise and interference. The effect is a N-fold reduction of the available capacity (i.e., useful bit-rate) for a given allocated spectrum.

In a traditional High Power High Tower (HPHT) DTT Multi-Frequency Network (MFN) or SingleFrequency Network (SFN) a high capacity is usually transmitted per UHF/VHF channel (8 or 7 MHz in Europe).

Table 1 indicates typical frequency reuse factors and spectral efficiency for DVB-T2 networks. These high DTT capacities (e.g. 33 - 40 Mbit/s for the Digital Video Broadcasting DVB-T2 standard) are obtained using high order modulation schemes, such as 256-QAM (256points Quadrature Amplitude Modulation) combined with LDPC (Low-Density ParityCheck) coding rate 2/3, which require large SINR (Signal-to-Interference plus Noise ratio) values and high-power transmitters.

Ideally, if conventional planning at reuse-5 is considered, with DVB-T2 256-QAM rate 2/3 the effective achievable spectral efficiency is in the order of 1 bit/s/Hz, being 5.31 the modulation and coding spectral efficiency. The corresponding required SINR is of about 18 dB on the Additive White Gaussian Noise (AWGN) channel.