Novel Research On Index Modulation In MIMO And OFDM For Future Wireless Communications

The key challenges of future wireless communication systems include improving spectral efficiency(SE),energy efficiency(EE),reducing computational complexity,and optimizing the use of resources.Multiple-input multiple-output(MIMO)systems are among the available technologies that promise to improve SE by delivering data from multiple transmit antennas simultaneously to the receiver.New wireless local-area network(WLAN)protocols that have been created in response to the growing demand for highbit-rate communications mostly employ multi-carrier orthogonal frequency division multiplexing(OFDM),which is a multi-carrier communication technique.The combination of MIMO with OFDM appears to be a promising answer to the problem of high data rates.Recently,index modulation(IM)schemes have also attracted a lot of attention.IM is an easy-to-implement digital modulation technique that uses the indices of the fundamental blocks of the associated communication systems to deliver extra information bits,thus making it a spectral and energy-efficient approach.The unprecedented growth in mobile data traffic,however,necessitates future 5G and beyond(B5G)networks to support high SE,better performance,and EE,owing to the significant growth of the information and communication technology sectors.The MIMO and OFDM systems may be insufficient to meet the difficulties in the present form.As a result,creating other efficient MIMO and OFDM based schemes which are capable of achieving high data rates while also being energy efficient and capable of overcoming the shortcomings of MIMO and OFDM with better performance is critical for future wireless networks,and the following are our contributions in this regard:1.We propose a novel precoding aided spectral efficient data transmission scheme called virtual spatial channel-number and index modulation(VS-CNIM).VS-CNIM conveys extra data by changing both the number and index of active virtual parallel channels of the MIMO system,which are obtained through the singular value decomposition(SVD)in each time slot.Unlike the conventional virtual spatial modulation(VSM),where extra data bits are transmitted only using the index of constant active virtual parallel channels,the VS-CNIM scheme transmits extra bits utilizing both the variable number and indices of active parallel channels.Therefore,VS-CNIM provides significantly superior SE compared to VSM.Considering the influence of imperfect channel estimation,a closed-form upper bound is derived on average bit error probability(ABEP).The asymptotic performance is also analyzed,which gives the coding gain and diversity order and describes the error floor under the consideration of perfect and imperfect channel estimation,respectively.2.VSM has arisen as a promising technique for improving the EE of MIMO systems.However,due to utilizing only a subset of virtual parallel channels,the SE of VSM is degraded compared to the classical MIMO system.To overcome this drawback,a new modulation technique called multiple-mode MIMO with IM(MM-MIMO-IM)is proposed,which is implemented over the virtual MIMO channel by performing indexing on Mary constellations.Compared to classical MIMO systems,the SE of MM-MIMO-IM systems is significantly higher due to the utilization of the mode permutations.Besides the development of diversity enhanced variant,we also extend the proposed scheme to an in-phase/quadrature(I/Q)dimension,creating an MM-MIMO-IM-IQ scheme,which obtains a double SE compared to MM-MIMO-IM.For the performance evaluation,a tight upper bound is also derived.3.Although in MM-MIMO-IM,the SE is enhanced by enabling more index bits,the flexibility of the system in terms of activation/deactivation of antennas and EE might be compromised.To solve this problem,we propose an index and composition VSM(IC-VSM)scheme.The IC-VSM scheme uses the indices of active/inactive codeword of virtual parallel channels and compositions of an integer to encode information,where the energy levels of the virtual parallel channels are exploited for the identification of the compositions.In IC-VSM,the information bits are mapped to the channel activation patterns(CAPs),modulation symbols,as well as energy allocation patterns(EAPs).We also propose a diversity-enhanced IC-VSM scheme,where coordinate interleaving(CI)is used to further increase the performance.Performance analysis of the proposed scheme is carried out,where an upper bound and diversity order are derived.4.A more flexible and energy-efficient composite multiple-mode VSM(C-MM-VSM)scheme is proposed to further increase the SE of VSM MIMO systems by extending the indexing to the energy and constellation domains.In C-MM-VSM,the information bits are mapped to not only the CAPs and modulation symbols,but also the EAPs and mode activation patterns(MAPs),so as to increase the SE.For generating MAPs in C-MMVSM,multiple distinguishable constellation sets are utilized.To cope with the practical situations,where the number of available constellation sets is higher than the number of distinguishable constellation sets,we propose a variant IM scheme named C-MM-VSM-II to build a new mapping rule between information bits and the increased MAPs,capable of further increasing the SE of C-MM-VSM systems.Moreover,we further propose two enhanced schemes,named generalized C-MM-VSM(GC-MM-VSM)and generalized CMM-VSM-II(GC-MM-VSM-II),which jointly considers all CAPs,EAPs,MAPs and modulated symbols.We provide a closed-form upper bound for the ABEP that takes into account the influence of imperfect channel estimation.Simulation results show that C-MM-VSM(-II)outperforms the conventional SM-related schemes i.e.VSM,especially in the high signal-to-noise ratio(SNR)region,and verify the accuracy of the theoretical analysis for the upper-bounded BER.5.MM-OFDM-IM has been proposed alternatively against OFDM-IM as a novel spectral efficient enhanced IM technique,which conveys information via the full permutation of multiple distinguishable modes and the modes itselves.OFDM-IM and MIMO have been combined to achieve high SE;however,the SE of the system is still limited because the subcarrier activation is performed combinatorially and the null mode by itself does not convey data symbols.Hence,here we propose a novel MIMO-MM-OFDM-IM scheme by combining MM-OFDM-IM and MIMO to take advantage of both techniques collectively.Maximum likelihood(ML),simple minimum mean square error(MMSE),and its variants,i.e,MMSE Viterbi-like and MMSE subcarrier-wise log-likelihood ratio(MMSE-LLR)detectors are proposed,which give tradeoffs between the detection complexity and error performance.The transceiver structure is designed and the BER analyses as well as theoretical performance are provided.Considering different system configurations,it is shown via Monte Carlo simulations that the proposed MIMO-MMOFDM-IM scheme not only achieves higher SE but also provides better error performance than the state-of-art MIMO-OFDM-IM technique.