Research On Index Modulation Based Exploitation Technologies For Wireless Spatial,Temporal,Frequency,and Code Resources

Over the past fifty years,the main design idea of digital modulation scheme is to use the amplitude,the phase,or the frequency of a sinusoidal wave as the information carrier.Signals with high modulation orders,high bandwidths,and high power are often used to realize high data rate communications.However,with the rapid development of information and communication technology industries,the radio spectrum is increasingly scarce and the energy consumption is increasingly tremendous.Hence,novel wireless transmission technologies with high spectral efficiency and high energy efficiency are of great importance to future mobile communications.Index modulation recently has emerged as a spectrum-efficient and energy-efficient digital modulation technique.Index modulation utilizes the on-off state of some building block of communication systems,such as antenna,subcarrier,relay,signal constellation,and time slot,to convey information.Spatial modulation(SM)and orthogonal frequency division multiplexing with index modulation(OFDM-IM)are the two most famous representatives of index modulation,which exploit the indices of transmit antennas in multi-antenna systems and subcarriers in OFDM systems,respectively,for information embedding.In the face of the limitations of the existing studies on index modulation,this dissertation aims at maximizing the information transmission capability of the communication system by integrating index modulation with non-orthogonal multiple access,cognitive radio,spread spectrum,and pilot inseration,exploring the spatial,temporal,frequency,and code resources further.Specifically,the contributions are summarized as follows.1)We explore the spatial resource based on index modulation and propose a novel user access paradigm for multi-antenna systems–SM based cooperative non-orthogonal multiple access(SM-C-NOMA).In SM-C-NOMA,the base station embeds the information of the near and far users in constellation symbols and active antenna indices,respectively,via SM.The near user also acts as a relay to improve the performance of the far user.Unlike NOMA,SM-C-NOMA avoids superposition coding and successive interference cancellation,achieving lower system complexity.The bit error rate(BER)performance under finite constellation input(pulse amplitude modulation and quadrature amplitude modulation)and the achievable rate performance under Gaussian input are analyzed for SM-C-NOMA.The expressions for bit error probability and instantaneous achievable rate are derived for both users.Moreover,as the reference scheme,conventional C-NOMA is further re-investigated with multiple receive antennas.Besides the achievable rate,which is adopted by most of the existing NOMA works as the performance metric,the BER performance of C-NOMA is analyzed by taking into account the superposition coding and successive interference cancellation.The proposed SM-C-NOMA is shown to outperform conventional C-NOMA and SM-OMA in terms of BER as well as ergodic sum rate.2)We explore the frequency resource based on index modulation and propose a novel opportunistic spectrum sharing method for multi-carrier systems– OFDM-IM based cognitive radio(OFDM-IM-CR).In OFDM-IM-CR,the primary transmitter communicates with the primary receiver with the aid of an amplify-and-forward relay by transmitting OFDM-IM signals.Meanwhile,the secondary transmitter passively senses the spectrum and opportunistically transmits its own information over those inactive subcarriers of the primary network to the secondary receiver.In this manner,no interference occurs on each subcarrier and the spectral efficiency improves.Two different types of maximum-likelihood(ML)detectors are designed for the primary network,based on the knowledge of either the estimated channel state information or the statistical channel information of the secondary network.These two types of detectors achieve different trade-offs among error performance,detection complexity,and channel information requirement.A complexity-reducing method applicable to both types is further proposed,which achieves near optimal performance.To evaluate the performance,a tight upper bound on the BER is derived,assuming the first type of ML detection.Simulation results show that OFDMIM-CR outperforms the OFDM based spectrum sharing scheme and amplify-and-forward relaying assisted OFDM-IM in terms of BER.3)We explore the frequency and code resources based on index modulation and propose a novel multi-carrier spread spectrum model–index modulated OFDM spread spectrum(IMOFDM-SS).In IM-OFDM-SS,each data symbol is spread across several subcarriers by the spreading code whose index carries additional information.The IM-OFDM-SS scheme can obtain diversity gains,and compensate for losses of spectral efficiency to some extent.A lowcomplexity maximal ratio combining detector is designed,in which the receiver first detects the spreading codes and then de-spreads and demodulates the symbols.The BER performance in the presence of channel estimation errors is analyzed.An upper bound and approximate average bit error probability associated with the ML and maximal ratio combining detection,respectively,are derived.Subsequently,we extend IM-OFDM-SS to multi-code and multi-user scenarios,proposing generalized IM-OFDM-SS and index modulation based multi-carrier code division multiple access,respectively.The proposed(generalized)IM-OFDM-SS outperforms the existing OFDM-IM and OFDM spread spectrum schemes significantly.In addition,the index modulation based multi-carrier code division multiple access exhibits a lower BER than multi-carrier code division multiple access at the same spectral efficiency for either multi-user or single-user detection.4)We explore the temporal and frequency resources based on index modulation and propose a novel pilot aided channel track and estimation scheme–information guided pilot insertion OFDM(IGPI-OFDM).In existing OFDM systems,whether the pilots are used for phase tracking or channel estimation,the number of pilots must be greater than a certain threshold.Moreover,pilots and data occupy different subcarriers for transmission,and pilot patterns remain fixed in the communication process and do not carry any information,resulting in a great pilot overheads.By contrast,in IGPI-OFDM,the pilot positions are not fixed but selected according to information bits to be transmitted,improving the system spectral efficiency.Specifically,three different types of pilot position selection schemes,which result in equal-spaced,unequalspaced,and hybrid pilot placements,are studied,where the pilots can be used for either carrier phase tracking or channel estimation purpose.The corresponding pilot position detection methods are designed,including ML,near-ML,and expectation maximization detectors.The BER performance of the proposed scheme is better than the traditional OFDM with fixed pilots.