Abstract:
This study proposes two approaches for improving the effectiveness of spatial modulation
integrated into layer division multiplexing (SM-LDM) in broadcasting systems: biased-power alloca-
tion (Bi-PA) and shared antenna selection (SAS). Even though different data rates are employed in
SM-LDM systems, Bi-PA enhances bit error rate (BER) fairness across layers. The ideal power ratios
are adaptively determined by balancing signal-to-interference plus noise ratios with a preference
for the lower layer (LL) that involves a higher modulation order. SAS alleviates the complexity of
successive interference cancellation and enhances spectral and energy efficiencies. Both the LL and
upper layer (UL) share the antenna selection decision and transmit using a single antenna. The UL
carries a space shift keying signal while the entire power is allocated for the LL. We analyze the
spectral efficiency for the SAS-based SM-LDM system with finite alphabet inputs. Numerical results
demonstrate the advantages of the proposed approaches. Compared to pre-assigned-PA (Pre-PA),
Bi-PA shows nearly identical BERs for both layers and solves the error floor problem. The sharing
property and common layer transmission of SAS-based SM-LDM yield a significant BER reduction
relative to conventional SM-LDM. It provides gains ranging from 7 to 15 dB for LL at BER equal to
10−3
, while UL performance ranges from slight gain to minor loss. Furthermore, both Bi-PA and SAS
techniques enhance the achievable LL rate and sum-rate at low and intermediate signal-to-noise ratio
values. They can achieve an improvement of up to two bits in LL rate and less than one bit in sum-rate
at a signal-to-noise ratio of −0.5 dB. These findings show that both proposed techniques have a
considerable impact on enhancing the fairness, BER performance, and feasible rates of SM-LDM
systems, making them promise for broadcast system designs.
