Non-uniform Subband Superposition Based Transmission Technologies

With the rapid development of the internet-of-things,cloud computing and vehicularto-vehicular(V2V),the demands for high data rate,decoding real-time transmission,flexibility and high-mobility have attracted a significant amount of research on several promising technologies.As one of the core technology for the modem,waveform design has received more attention in wireless communication systems.Orthogonal frequency division multiplexing(OFDM)is a kind of classic multi-carrier scheme,which is robust to the multipath fading channel and easy to be implemented.However,when oriented to the needs of the fifth generation/ beyond fifth generation(5G/B5G)networks,OFDM suffers from the following drawbacks: applying the time-domain rectangular pulse introduces high out-of-band emission(OOBE)and the fixed subcarrier spacing leads to poor flexibility in resource allocation,etc.To meet the diversified requirements of 5G/B5 G,it is of great importance to design a new waveform scheme.Due to the fact that the existing multi-carrier waveform schemes(including OFDM scheme)have to face many challenges,when considered for adoption in more complex networks.In this dissertation,a non-uniform subband superposed transmission system is proposed for the air interface of 5G/B5 G networks,which can accommodate single-carrier or multi-carrier according to different application scenarios.The main study contents and contributions are summarized as follows:1.Considering that the traditional 5G/B5 G waveform schemes can not obtain an effective tradeoff between the flexibility and computational complexity,the variable granularity(VG)spectrum allocation model and the non-uniform subband superposed OFDM(NSS-OFDM)scheme are respectively proposed.The VG method is exploited to divide the transmission band into a certain amount of subbands,each of which is applied to a specified application scenario through independently configuring the signaling parameters.Relying on the VG spectrum allocation model,an asynchronous transmission architecture is formulated,which meets the requirements of the flexibility for the mobile big data era.In the VG-based NSS-OFDM scheme,we also study a time-domain superposition of the filtered signals from the subband branches,which suppresses the OOBE and reduces the computational complexity while satisfying the flexibility.2.Since the NSS-OFDM system has lower OOBE,the overhead of the FGI between subbands could be reduced,thus improving the spectrum efficiency compared to the traditional OFDM system.Considering the relationship between the edge guard bands and the number of subbands,an optimal subband division scheme is acquired.Taking advantage of the optimal subband division protocol,the uniform subband OFDM(USSOFDM)system is designed,which achieves an effective balance between the bandwidth efficiency and complexity.In addition,the proposed scheme is tested in the long term evolution(LTE),digital terrestrial multimedia broadcasting(DTMB),and digital video broadcasting-terrestrial(DVB-T)standards.The results demonstrate that the spectrum efficiency of the USS-OFDM scheme is increased up to 99%.3.To adapt to the ultra-high speed mobile scenarios for the NSS-OFDM system,we analyze the performance limit of the channel estimation(CE)algorithm based on the time-frequency scattered pilot,and propose an improved interpolation algorithm in the time direction.Utilizing the minimum mean square error criterion,the interpolator is devised to estimate the coefficients,which improves the CE performance by exploiting more pilots information.In order to support the LTE-V2 V and high-speed train scenarios,a time-domain CE algorithm based on the block-type pilot is studied to further improve the CE resolution.The CE method employs the Slepian sequences-based piece-wise interpolation to reconstruct time-domain channel response for data symbols.Based on the time-domain CE,the NSS-OFDM achieves lower BER compared to the traditional CE algorithms,which supports the high-speed mobile communication system.4.Since the traditional channel equalization algorithms degrade the demodulation performance in high-speed mobile scenarios,a low complexity subband decision feedback and feedforward equalizer(SDFFE)is exploited.In the light of the subband's oversampling architecture,the proposed algorithm can harvest the diversity gains in both the Doppler and the multipath delay domains.Based on the SDFFE,the NSS-OFDM system obtains an enhanced BER performance as the normalized Doppler spreading increases,which significantly improves the demodulation performance for the subbands experiencing high-speed mobile channels.In addition,through the subband division,the bandwidth of the subband is small,which reduces the Fourier transform size and thus decreases the complexity of the SDFFE.5.To meet some low-power application scenarios,some subbands' signals utilize the single carrier modulation,named non-uniform subband superposed single carrier(NSSSC)scheme.To improve the data rate of the NSS-SC system,a splitting receiver is developed based on the power-domain information assistance.In the splitting receiver,by using a radio frequency power splitter,the received signal is divided into two streams,which jointly use coherent and non-coherent processing for the signal detection.The splitting receiver provides an additional degree of freedom in the power domain,which achieves an enhanced capacity compared to either the coherent or non-coherent receivers.In addition,the mutual information and low-complexity signal detection method are respectively studied.Our analytical and numerical results demonstrate that the splitting receiver obtains higher data rate than either the coherent receiver or the non-coherent receiver.