# LDM-Ex-FDM: A Novel Multi-Service Transmission Scheme for the ATSC 3.0 System
## 1 Introduction  
Digital TV programs can be broadcast via terrestrial, satellite, and cable networks, in which the digital terrestrial television broadcasting (DTTB) system is particularly important in the broadcast coverage network. In recent years, the next generation DTTB which supports ultra-high definition TV (UHDTV) has become one of the research hotspots in academia and industry [1]. On the one hand, in addition to the fixed service reception of ultra-high definition programs, with the proliferation of a large number of intelligent portable terminals, the demand for a variety of mobile services is also increasing. On the other hand, the available spectrum resources for DTTB are limited. Therefore, it is of great importance to efficiently use spectrum resources and flexibly meet the growing multi-service requirements in the future. Many terrestrial broadcasting standards have been published internationally. In September 2009, the European Telecommunications Standards Institute (ETSI) released the first version of the DVB-T2 standard [2]. In July 2015, digital terrestrial television multimedia broadcasting-advanced (DTMB-A), China's next-generation digital television broadcasting system was officially adopted by the International Telecommunication Union (ITU) as the international standard [3]. In September 2016, the Americannext-generation terrestrial broadcasting system Advanced Television System Committee (ATSC) 3.0 physical layer standard was released [4]. It is worth pointing out that DVB-T2, DTMB-A, and ATSC 3.0 all support 4K UHDTV and are suitable for multi-service transmission of both mobile and fixed services [4; 5; 6]. In the ATSC 3.0 standard, the layered division multiplexing (_LDM_) technique is used, which is a non-orthogonal multiple access (NOMA) scheme of air interface technologies. Point-to-multipoint (P2 MP) transmission mode will be supported in future networks to achieve high spectrum efficiency and high capacity [7]. Eventually, NOMA and P2 MP have been identified as key technologies for more efficient use of spectrum in 5G [8; 9; 10]. Reference [7] proves that the 5G P2 MP subsystem with _LDM_ can make use of the broadband infrastructure to provide high-quality broadcast-type services. _LDM_ enables the simultaneous delivery of different services in the same time-frequency resources. One typical scenario for an LDM-based ATSC 3.0 system is to deliver a robust high-definition TV (HDTV) service in the core layer (_CL_) for mobile reception and a 4K UHDTV service in the enhanced layer (_EL_) for fixed reception [11]. One of the technical advantages of _LDM_ is that it can achieve a lower signal-to-noise ratio (SNR) threshold under the same data throughput. Another advantage is that, compared to the traditional time-division multiplexing (TDM) and/or frequency-division multiplexing (FDM), the spectrum efficiency of _LDM_ is much higher [12; 13; 14]. So far, there have been extensive studies on the performance improvement of the _EL_ of _LDM_ in typical scenarios in the literature, where the integration of _LDM_ and TDM/FDM is an effective way to improve the performance of the multi-service transmission. Reference [15] proposes a multi-physical layer pipe (M-PLP) configuration scheme called time-layered division multiplexing (TLDM)/ layered-time division multiplexing (LTDM), which proves the advantages of the _LDM_ technology to provide hierarchical broadcasting services. However, if the new service mentioned therein is a truncated part of the _EL_ services, the improvement of the overall performance of the _EL_ in this case would be very limited. Moreover, the capacity of the _CL_ services will be decreased due to the reduced time duration caused by the combination of the TDM. Reference [16] studied the elimination method of the interference of the _CL_ signal to the _EL_, which can improve the performance of the latter. However, the _EL_ and _CL_ of the _LDM_ signal in reference [16] carries the same services in the considered scenario.