Jon Montalban

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.

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.

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.

Performance Study of Layered Division Multiplexing Based on SDR Platform

Two of the main drawbacks of the current broadcasting services are, on the one hand, the lack of flexibility to adapt to the new generation systems requirements, and on the other hand, the incapability of taking a piece of the current mobile services market. In this paper, layered division multiplexing (LDM), which grew out of the concept of Cloud Txn, is presented as a very promising technique for answering those challenges and enhancing the capacity of broadcasting systems. The major contribution of this paper is to present the first comprehensive study of the LDM performance behavior. In particular, in this paper, the theoretical considerations of the LDM implementation are completed with the first computer based simulations and laboratory tests, covering a wide range of stationary channels and the mobile TU-6 channel. The results will support LDM as a strong candidate for multiplexing different services in the next generation broadcasting systems, increasing both flexibility and performance.

Performance Characterization and Optimization of Mobile Service Delivery in LDM-Based Next Generation DTV Systems

Layered-division-multiplexing (LDM) technology is a non-orthogonal multiplexing technology to provide more efficient transmission of multiple services that have different requirements on the robustness and throughput in one TV channel. The core of LDM is to transmit multiple-layer signals, where each layer occupies the whole channel bandwidth and the whole time. To meet the different requirements on different layers, each layer is allocated a specific power level, and is configured to use a different channel coding and modulation scheme, as well as its own multiple-antenna technology. Delivering robust and high-quality mobile TV services is one of the top priorities for the next generation digital TV (NG-DTV) systems. In this paper, we first investigate the performance of the NG-DTV systems with LDM in various difficult propagation channels that are likely encountered by the large variety of mobile devices, including fast-fading channels, slow-fading channels, indoor channels, and single-frequency-network (SFN) channels. A new channel estimation technique is proposed to overcome the severe performance degradation caused by the SFN channels. We will further show that using LDM makes it possible to deliver mobile services using the efficient 32k transmission mode. Finally, receive antenna diversity is shown to provide different levels of performance improvement for different LDM configurations.

Cloud Transmission frequency domain cancellation

Cloud Transmission (Cloud Txn) is a spectrum efficient broadcasting system, which removes the co-channel interference through the use of robust forward error correction (FEC) codes. Nevertheless, the main drawback of this approach is that the system overall data rate is reduced. As a solution, the system proposes a spectrum overlay technology to increase data throughput while maintaining the robustness. The goal of this paper is to further explain and justify the spectrum overlay and corresponding frequency domain cancellation techniques.

Cloud Transmission: System simulation and performance analysis

The Cloud Transmission (Cloud Txn) is a new paradigm of broadcasting or point-to-multipoint transmission system, designed for efficient and flexible use of the spectrum, robustness against noise, multipath and co-channel interference, and capability to provide fixed or mobile reception while using low transmission power. Besides system capability, the system should meet many other challenging issues. The main purpose of this work is to demonstrate that this proposed new system is feasible and it meets today and future needs of the broadcasting industry.

Error propagation in the cancellation stage for a multi-layer signal reception

Cloud-Txn is a new broadcasting approach, which proposes the usage of the layer-division-multiplexing (LDM) to meet the requirements of the new generation digital TV services. Cloud Txn has been proposed as one of the candidate technologies for the Next Generation DTV systems. This technology is considered as an attractive alternative to the commonly used Time Division (TDM) and Frequency Division (FDM) multiplexing. Its main advantage lies in being more efficient as the RF channel is continuously used both in time and frequency, while the flexibility for each layer configuration is maintained. Nevertheless, the performance of this technique is closely related to the accuracy of the cancelation process required to decouple the multi-layered signals. The main objective of this paper is to analyze the possible error propagation due to the cancellation stage and the corresponding impact on the layers performance.