A signal multiplexing apparatus, comprising: a core layer Bit-Interleaved Coded Modulation, BICM, unit configured to perform a first BICM encoding corresponding to a core layer signal; an enhanced layer BICM unit configured to perform a second BICM encoding corresponding to an enhanced layer signal; an injection level controller configured to generate a power-reduced enhanced layer signal by reducing power of the enhanced layer signal; a combiner configured to combine the core layer signal and the power-reduced enhanced layer signal to generate a multiplexed signal; a power normalizer configured to generate a power-reduced multiplexed signal by reducing power of the multiplexed signal to power corresponding to the core layer signal; and a time interleaver configured to perform interleaving applied to both the core layer signal and the power-reduced enhanced layer signal in the power-reduced multiplexed signal after combining the core layer signal and the power-reduced enhanced layer signal, wherein the time interleaver is shared for both the core layer signal and the power-reduced enhanced layer signal in the power-reduced multiplexed signal, wherein the injection level controller reduces the power of the enhanced layer signal corresponding to a scaling factor and the power normalizer reduces the power of the multiplexed signal corresponding to a normalizing factor, wherein the scaling factor is applied to the enhanced layer signal and the normalizing factor is applied to both the core layer signal and the power-reduced enhanced layer signal, wherein the scaling factor and the normalizing factor vary in opposite directions according to variation of reduction in power corresponding to the injection level controller, wherein the injection level controller changes an injection level with predetermined step sizes, the predetermined step sizes including 0.5dB. a core layer Bit-Interleaved Coded Modulation, BICM, unit configured to perform a first BICM encoding corresponding to a core layer signal; an enhanced layer BICM unit configured to perform a second BICM encoding corresponding to an enhanced layer signal; an injection level controller configured to generate a power-reduced enhanced layer signal by reducing power of the enhanced layer signal; a combiner configured to combine the core layer signal and the power-reduced enhanced layer signal to generate a multiplexed signal; a power normalizer configured to generate a power-reduced multiplexed signal by reducing power of the multiplexed signal to power corresponding to the core layer signal; and a time interleaver configured to perform interleaving applied to both the core layer signal and the power-reduced enhanced layer signal in the power-reduced multiplexed signal after combining the core layer signal and the power-reduced enhanced layer signal, wherein the time interleaver is shared for both the core layer signal and the power-reduced enhanced layer signal in the power-reduced multiplexed signal, wherein the injection level controller reduces the power of the enhanced layer signal corresponding to a scaling factor and the power normalizer reduces the power of the multiplexed signal corresponding to a normalizing factor, wherein the scaling factor is applied to the enhanced layer signal and the normalizing factor is applied to both the core layer signal and the power-reduced enhanced layer signal, wherein the scaling factor and the normalizing factor vary in opposite directions according to variation of reduction in power corresponding to the injection level controller, wherein the injection level controller changes an injection level with predetermined step sizes, the predetermined step sizes including 0.5dB.