Modulation Design and Optimization for RIS-Assisted Symbiotic Radios.
CoRR(2023)
摘要
In reconfigurable intelligent surface (RIS)-assisted symbiotic radio (SR),
the RIS acts as a secondary transmitter by modulating its information bits over
the incident primary signal and simultaneously assists the primary
transmission, then a cooperative receiver is used to jointly decode the primary
and secondary signals. Most existing works of SR focus on using RIS to enhance
the reflecting link while ignoring the ambiguity problem for the joint
detection caused by the multiplication relationship of the primary and
secondary signals. Particularly, in case of a blocked direct link, joint
detection will suffer from severe performance loss due to the ambiguity, when
using the conventional on-off keying and binary phase shift keying modulation
schemes for RIS. To address this issue, we propose a novel modulation scheme
for RIS-assisted SR that divides the phase-shift matrix into two components:
the symbol-invariant and symbol-varying components, which are used to assist
the primary transmission and carry the secondary signal, respectively. To
design these two components, we focus on the detection of the composite signal
formed by the primary and secondary signals, through which a problem of
minimizing the bit error rate (BER) of the composite signal is formulated to
improve both the BER performance of the primary and secondary ones. By solving
the problem, we derive the closed-form solution of the optimal symbol-invariant
and symbol-varying components, which is related to the channel strength ratio
of the direct link to the reflecting link. Moreover, theoretical BER
performance is analyzed. Finally, simulation results show the superiority of
the proposed modulation scheme over its conventional counterpart.
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关键词
modulation,ris-assisted
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