Pablo Angueira

Layered-Division-Multiplexing: Theory and Practice

As the next generation digital TV (DTV) standard, the ATSC 3.0 system is developed to provide significant improvements on the spectrum efficiency, the service reliability, the system flexibility, and system forward compatibility. One of the top-priority requirements for the ATSC 3.0 is the capability to deliver reliable mobile TV services to a large variety of mobile and indoor devices. Layered-division-multiplexing (LDM) is a physical-layer non-orthogonal-multiplexing technology to efficiently deliver multiple services with different robustness and throughputs in one TV channel. A two-layer LDM structure is accepted by ATSC 3.0 as a baseline physical-layer technology. This LDM system is capable of delivering robust high-definition (HD) mobile TV and ultra-HDTV services in one 6 MHz channel, with a higher spectrum efficiency than the traditional time/frequency-division-multiplexing (T/FDM)-based DTV systems. This paper presents a detailed overview on the LDM technology, and its application in the ATSC 3.0 systems. First, the fundamental advantages of the LDM over the traditional TDM/FDM systems are analyzed from information theory point of view. The performance advantages of the LDM are then confirmed by extensive simulations of the ATSC 3.0 system. It is shown that, LDM can realize the potential gain offered by superposition coding over the TDM/FDM systems, by properly configuring the transmission power, channel coding, and modulation, and using different multiple antenna technologies in the multiple layers. Next, the efficient implementation of LDM in the ATSC 3.0 system is presented to show that the performance advantages of the LDM are obtained with small additional complexity. This is achieved by carefully aligning the transmission signal structure and the signal processing chains in the multiple layers. Finally, we show that the LDM can be further integrated with different multiple antenna technologies to achieve further transmission capacity.

Cloud Transmission: System Performance and Application Scenarios

Cloud transmission (Cloud Txn) is a flexible multilayer system that uses spectrum overlay technology to simultaneously deliver multiple program streams with different characteristics and robustness for different services (mobile TV, HDTV, and UHDTV) in one radio frequency channel. Cloud Txn is a multilayer transmission system like layered-division multiplexing. The transmitted signal is formed by superimposing a number of independent signals at desired power levels to form a multilayered signal. The signals of different layers can have different coding, bit rate, and robustness. The upper layer system parameters are chosen to provide very robust transmission that can be used for high-speed mobile broadcasting. The bit rate is traded for powerful coding and robustness so that the signal-to-noise ratio (SNR) threshold at the receiver is in the range of -2 to -3 dB. The top layer is designed to withstand combined noise, co-channel interference and multipath distortion power levels higher than the desired signal power. The lower-layer signal can be a DVB-T2 signal or another new system to deliver HDTV/UHDTV to fixed receivers. The system concept is open to technological advances that might come in the future: BICM/non uniform-QAM, rotated constellations, time frequency slicing or MIMO techniques can be implemented in the Cloud Txn lower (high data rate) layer. The system can have backward compatible future extensions, adding more lower layers for additional services without impact legacy services. This paper describes the performance of Cloud Txn broadcasting system.

On the Methodology for Calculating SFN Gain in Digital Broadcast Systems

For broadcast networks, the Single-Frequency Network (SFN) mode is an alternative to the well-known Multi-Frequency Network (MFN) mode, where instead of transmitters operating at different frequencies, all base stations use the same frequency. Besides the optimal frequency reuse, it is usually expected that the more homogeneous distribution of received signal strength reception in an SFN will improve the quality of service. Nevertheless, it should be noted that not all the locations within the service area will benefit from the SFN configuration. Some areas will show a degraded quality caused by the SFN echoes. In this paper, the SFN gain is defined as a parameter describing potential gain or interference. An unambiguous methodology to obtain the actual SFN gain is presented and the variation of the gain is investigated for a DVB-H network as a function of the signal strength difference received from different transmitters. This SFN gain can be used for coverage planning of future broadcast networks.

Low Complexity Layered Division Multiplexing for ATSC 3.0

In this paper, we propose novel transmitter and receiver architectures for low complexity layered division multiplexing (LDM) systems. The proposed transmitter architecture, which is adopted as a baseline technology of the Advanced Television Systems Committee 3.0, shares time and frequency interleavers, FFT, pilot patterns, guard interval, preamble, and bootstrap among different layers, so that the implementation of LDM receivers can be realized with less than 10% complexity increase compared to conventional single layer receivers. With such low complexity increment, we show simulation and laboratory test results that the proposed LDM system has significant performance advantage (3-9 dB) over traditional TDM systems, and maintains its performance up to the velocity of 260 km/h in mobile reception.

Medium wave DRM field test results in urban and rural environments

This paper presents the results of the first Spanish field trial carried out to analyze a DRM (Digital Radio Mondiale) system in the medium-wave band. A 4-kW average power omni directional ground-wave experimental DRM transmission at a frequency of 1359 kHz was surveyed by means of a measurement vehicle for fixed and mobile reception. Several radial routes starting from the transmitter site provided rural and suburban behavior features of the system. Urban reception trials were performed in several dense and open streets of Madrid, within the expected coverage area. Field strength threshold values were determined for the tested transmission configurations and compared with the AM ground-wave ITU model predictions. Reliability versus distance from the transmitter is stated in this paper for different transmission configurations and the causes of dropouts for different reception conditions are explained. This analysis took into account subjective quality features of each configuration, providing practical planning parameter values.

Generalization of the Lee Method for the Analysis of the Signal Variability

The Lee method, which was recommended by the International Telecommunications Union (ITU) and the European Conference of Postal and Telecommunications Administrations (CEPT) to obtain the local mean values of the received signal along a route, was developed for a Rayleigh distribution in the ultrahigh-frequency (UHF) band. This paper describes the generalization of this method to any propagation channel and frequency band and describes the methodology to obtain the parameters involved. The Generalized Lee Method is based on field data samples, which allows estimating the mean values without the requirement of a priori knowing the distribution function that better fits the propagation channel. The accuracy in obtaining the averaging interval is also improved. The Generalized Lee Method is solved for ground-wave propagation at the medium-wave (MW) band, taking data from field trials of a Digital Radio Mondiale (DRM) transmission. The results show that the values considerably differ from those obtained for a Rayleigh channel and prove that the method allows the adequate differentiation of long-term and short-term signals. The Generalized Lee Method completes the results obtained by Lee and Parsons and makes better characterization of the spatial variability possible.

On the feasibility of unlicensed communications in the TV white space: Field measurements in the UHF band

In practical unlicensed communications in TV band, radio devices have to identify, at first, the transmission opportunities, that is, the portion of the spectrum licensed for broadcasting services unoccupied in a certain region at certain time, that is, the so-called TV white space. In this paper the outcome of field measurements in the UHF TV band (470–860 MHz) conducted in EU is presented. To obtain empirical values for the parameters upon which unlicensed radio devices are able to distinguish in a real scenario between empty and occupied TV channels, signal power measurements have been performed in Italy, Spain, and Romania on rural, suburban, and urban sites, at different heights over the ground by using different analysis bandwidths. The aim of this work is to provide a set of practical parameters upon which harmless unlicensed communication in the UHF TV white space is feasible. The results have been analyzed with respect to the hidden node margin problem, spectrum sensing bandwidth, and occupancy threshold.

LDM Core Services Performance in ATSC 3.0

Advanced Television Systems Committee (ATSC) 3.0, the new generation digital terrestrial television standard, has been designed for facing the new challenges of the future broadcasting systems. ATSC 3.0 has been built using the most recent cutting-edge technologies. Layered division multiplexing (LDM) is one of the major components of the new system baseline. LDM provides a tool to make flexible use of the spectrum for delivering simultaneous services to stationary and mobile services. This paper presents the performance evaluation of ATSC 3.0 core services in mobile scenarios using LDM. Simulation results are presented to analyze the influence of different LDM ensemble configuration modes for mobile reception. The simulation results have been also confirmed by laboratory tests under different channel models. The signal to noise ratio threshold values confirm the excellent behavior of ATSC 3.0 and LDM in mobile and portable scenarios.

Channel capacity distribution of Layer-Division-Multiplexing system for next generation digital broadcasting transmission

Cloud transmission (Cloud-Txn) with Layer-Division-Multiplexing (LDM) was proposed as a candidate Physical Layer (PHY) technology for next generation digital TV broadcasting system. This paper presents a fundamental analysis on the channel capacity allocation among the different layers of a LDM-based transmission system. The analysis reveals that, for delivering fixed and mobile TV services in the same RF channel, by controlling the power allocation among the layers, the LDM-based system provides much better efficient usage of the spectrum as compared to the single-layer Time-Division-Multiplexing (TDM) or Frequency-Division-Multiplexing (FDM)-based systems. The spectrum efficiency of LDM allows the simultaneous delivery of a high-data-rate UHDTV service and a mobile HDTV service within a single 6 MHz channel.

Co-Channel and Adjacent Channel Interference and Protection Issues for DVB-T2 and IEEE 802.22 WRAN Operation

This paper presents a study on the coexistence issue of digital terrestrial TV broadcasting and cognitive broadband access operation in the TV white spaces (TVWS). Extended measurements were performed to evaluate the protection of the existing Second generation of digital video broadcasting terrestrial standard (DVB-T2) services in the presence of IEEE 802.22 WRAN co-channel and adjacent channel interference. The absence of picture failure over 30 consecutive seconds on decoded DVB-T2 streams has been monitored to obtain the maximum tolerable level of IEEE 802.22 WRAN interference, which ensures the protection of the primary broadcast system. This paper considers practical DVB-T2 system configuration options by varying parameters of the standard, such as constellation and code rate, FFT size, pilot pattern and guard interval, and rotated constellations and compares them in terms of robustness with respect to the interference generated by IEEE 802.22 WRAN operation. The goal is to provide cognitive broadband operators in the TVWS with guidelines to optimize their network by choosing the parameters that best fit their needs in case of coexistence with DVB-T2 broadcasting services.