1. Technical Field

The present disclosure relates to a transmitter, a receiver, a transmitting method, and a receiving method.

2. Description Of The Related Art

Multiplexing multiple signals into a compound signal is a common method in data communications to share a single medium. Traditionally, data carrying different services are multiplexed in time or frequency. These methods are called Time-Division-Multiplex (TDM) and

Frequency-Division-Multiplex (FDM). Real-world applications for TDM and FDM can be found in DVB-T2, in which multiple so-called PLPs (Physical Layer Pipes), each characterized by their own modulation and time interleaver, are sharing a certain frequency band in dedicated time slots, and the Japanese ISDB-T standard with the prominent One-Seg system, in which data is carried in banded segments which are strictly separated in frequency domain thus allowing for power-saving partial reception of individual segments.

It has been long since known that FDM and TDM are not the most efficient methods to share a medium. Their benefit lays more with the ease of implementation. From “Cooperative broadcasting” by P. P. Bergmans and T. M. Cover, IEEE Trans. Inf. Theory, vol. 20, no. 3, pp. 317-324, May 1974 (non-patent literature (NPL) 1), for instance, it is known that the superposition of different services increases the capacity over either TDM or FDM. Only recently, this form of multiplexing has found its way into a current standard, namely ATSC 3.0, where it is called Layered-Division-Multiplexing (LDM); cf. “Low Complexity Layered Division for ATSC 3.0,” by S. I. Park, et. al., IEEE Transactions on Broadcasting, vol. 62, no. 1, pp. 233-243, March 2016 (NPL 2).

Intuitively, the edge of LDM over TDM/FDM in capacity is obtained due to the simultaneous transmission of more than one service without pausing in either time domain or frequency domain. In practice, however, LDM entails higher receiver complexity as well as constraints in the transmission system design.

SUMMARY

According to an aspect of the present disclosure, a transmitter includes a mapping circuit and a framing circuit. The mapping circuit is configured to combine and map a first data sequence and a second data sequence onto orthogonal frequency division multiplexing (OFDM) subcarriers which include first subcarriers and second subcarriers. The framing circuit is configured to generate an OFDM signal from the OFDM subcarriers. The mapping circuit is configured to: map first data included in the first data sequence and second data included in the second data sequence onto the first subcarriers; and map the second data onto the second subcarriers. The first data are not mapped on the second subcarriers.

