| Summary: | 博士 === 國立臺灣大學 === 電信工程學研究所 === 105 === The ongoing evolution of wireless techniques gains great progress in improving the spectrum efficiency and data rate. However, enhancing the achievable data rate to accommodate the explosive growing of data traffic is not the only goal in the next generation communication system. Besides the mobile broadband data service, numbers of brand-new applications are developed based on a varieties of new-type devices, such as Internet of Things (IoT), proximate services, and wireless front/backhaul, and they are supposed to also play important roles in the near future. To realize these emerging applications with diverse requirements, several new essential technologies gain attentions in recent years. In this thesis, we aim to solve the critical challenges of three of the representative ones, namely, massive machine-to-machine networks, device-to-device (D2D) communication, and full-duplex radio (FDR) systems.
To enable an M2M network supporting massive number (e.g. more than one thousands) of devices, efficient description and conveying method of the scheduling information to scheduled users is essential to avoid the tremendous increasing of signaling overhead. To do this, we proposed a new efficient description approach, namely, Sorted-Rectangular Description (SRD), to describe the time/frequency resource allocations in an OFDMA frame. SRD first partitions a frame into rectangular polygons, namely rectangular bursts (RB), in which each RB contains the resource units belongs to the same assignment. We showed that an RB-partitioned frame is sufficient to be reconstructed by the top-left coordinates of each RB in a specific sorted order. Moreover, the sorting and reconstruction algorithms with linear time complexity in the total number of RBs was also proposed. Simulation results showed that, when it was compared with existing methods for conveying the scheduling information, SRD could provide dramatic improvement of the capacity in a system with large number of users.
Concerning the deployment of cellular overlaying D2D networks, we found that mitigating the timing misalignment (TM) among nearby D2D devices is critical to allow more than one D2D source devices to convey data to their D2D sink devices simultaneously. Otherwise, severe interference problems including inter-block interference (IBI) and inter-carrier interference (ICI) might occur and make acceptable reception quality impossible. To cope with this problem, we proposed a new approach to avoid the interferences at the receiver side via shifting the Discrete Fourier Transform (DFT) window by a number of sample durations, namely, jumping value. We proved the sufficient condition for the existence of a proper jumping value which could ideally mitigate the interferences. An algorithm for estimating the proper jumping value via the existing reference signal structure of LTE-A D2D data channel is also developed. Simulation results shown that our proposed JDWM (Jumping DFT Window Method) approach could provide much more effective interference mitigation than that of traditional end-to-end timing synchronization methods and achieve a packet error rate quite close to that under perfect global timing synchronization.
In the study of the final topic, we aim to solve the problem of mitigating the strong self-interference (SI) for full-duplex radio (FDR) devices. In general, achieving SI cancellation at the digital domain in the initial stage is very difficult since the transmitted signal from the transmit chain of an FDR device could be dramatically stronger (e.g. larger than 100 dB) than that of the received desired signal. Thus, we proposed a new algorithm, called, probe-and-update method (PUM), to tune the gains of a multi-tap analog SI cancellation filter. PUM performs a novel gain updating procedure based on the comparison of two consecutive measurements of the residual SI power. Via sufficient number of updates, it can be proved that PUM could approach the minimum average residual SI power. Moreover, PUM is applicable in multipath environment and no channel knowledge is needed in advance, which considerably facilitate the implementation. Simulation results showed that PUM could achieve a reasonably low residual SI power down to 5.5 dB of the noise floor in a 20-MHz system. The remained SI is sufficiently low to be measured and canceled in the digital domain.
In summary, several new methods are developed to provide solutions for some of the essential problems known in the next generation device based communication system in this thesis. By our analysis and simulations, we believe the proposed methods are both effective and practical, and can be the possible solutions for overcoming these critical challenges.
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