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    Evolution of STBC-based OFDM-IM for wireless vehicular communication
    (2026-01-01)
    Mata, Tanairat
    ;
    Boonsrimuang, Pisit
    This paper studies wireless vehicular communication (VehCom) in intelligent transportation systems using an orthogonal frequency division multiplexing with index modulation (OFDM-IM). In the concept of IM, data is transmitted not only through the modulated symbols but also via the indices of the active subcarriers. In contrast to the original OFDM, OFDM-IM activates only non-zero subcarriers, increasing energy efficiency. However, the pilot-assisted channel estimation (CE) method is a significant challenge in OFDM-IM, where the desired pilot subcarrier interval is related to the OFDM-IM subblock length. This paper proposes a walsh-scattered pilot-assisted CE for OFDM-IM VehCom. The optimum walsh-scattered pilot assignment is proposed to improve the transmission efficiency. Furthermore, a space-time block code with a high transmit diversity gain is employed for OFDM-IM VehCom to enhance VehCom's signal quality. The results show that the proposed method performs higher CE accuracy and better bit-error rate with significant spectral and energy efficiencies than conventional methods.
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    Channel Estimation for Enhanced Subcarrier Index Modulation OFDM Using Zadoff-Chu Sequence Pilot in Nonlinear Channel
    (2022-01-01)
    Mi, Si Sar
    ;
    Siriwanitpong, Aphichaya
    ;
    Boonsrimuang, Pornpawit
    ;
    Boonsrimuang, Pisit
    Orthogonal Frequency Division Multiplexing with Index Modulation (OFDM-IM) is a digital modulation scheme that conveys additional information bits by using the index of subcarriers. OFDM with enhanced subcarrier index modulation (OFDM-SIM) has been recently proposed to improve the bit error rate (BER) performance of multicarrier communication systems. It is challenging to estimate channel variation of the OFDM-SIM system in wireless communication systems for coherent detection at the receiver side. This paper proposes a new pilot data information Zadoff-Chu sequence for the channel estimation OFDM-SIM system. And OFDM-SIM channel estimation will be done by using the conventional OFDM-SIM symbol pilot and the proposed Zadoff-Chu sequence pilot in the multipath Rician fading channel. And evaluate the simulation results by using BER performance. BER results of channel estimation OFDM-SIM with proposed Zadoff-Chu sequence pilot decreased than BER results of channel estimation OFDM-SIM using conventional OFDM-SIM symbol pilot. And we evaluate the proposed Zadoff-Chu sequence channel estimation OFDM-SIM in a nonlinear multipath Rician fading channel. We can see that the proposed Zadoff-Chu sequence pilot outperformed than conventional OFDM-SIM symbol pilot in every input back off (IBO)=0 dB,-2dB,-4dB, and-6dB. Our proposed channel estimation method is evaluated by using computer simulation.