在本研究中，我們將仔細研究反向散射輔助通信系統(BCS)與傳統中繼系統的比較。反向散射系統包含一個源，多個反向散射設備(BD)與一個接收器。BD的目的是幫助提高系統的端到端吞吐量和可靠性，BD完全是在中繼模式下運行，這意味著它們不會在接收到的訊號，也就是來自訊號源的射頻訊號中添加自己的資訊。此系統的靈感來自於同步無線訊號與電源轉移(SWIPT)，BD接收環境中的RF訊號包含了來自訊號源的能量以及資訊。對於放大再傳輸（AF）模式，它會放大訊號，然後在單個時隙中將其反射到接收器；對於解碼再傳輸(DF)模式，BD在第一階段(時隙)解碼訊號。第二階段，它收集能量，然後將其用於反射在第二階段中接收器接收到的訊號。接著，本論文對AF和DF提出了優化吞吐量的問題，同時也提出了求和率的問題，並對其進行了優化。然後針對系統中不同的參數進行模擬，接著將各個模擬結果繪製成圖表，並且比較不同的指標，以了解它們之間的相互影響。最後比較傳統的中繼系統與BD輔助系統，驗證後者相較於前者是否有任何優勢。

In this study, we take a closer look at how a backscatter assisted communication system
(BCS) compares to a conventional relay system. The backscatter system consists of a
single source, multiple backscatter devices (BDs), and a single receiver. The purpose of
the BDs is to assist with the system’s end-to-end throughput and reliability. The BDs
operate in a pure relay mode, which means they do not add their own information to the
received RF signal from the source. The system is simultaneous wireless information
power transfer (SWIPT) inspired. The BD receives an ambient RF signal containing both
energy and information from the source. For amplify-and-forward (AF) mode, it amplifies
the signal and then reflects it to the receiver in a single time slot. For the decode-and-forward
(DF) mode, the BD decides to decode the signal in the first phase (time slot). In
the second phase, it harvests energy which it then uses to reflect the signal received in the
second phase to the receiver . We then formulate an optimization throughput problem for
both AF and DF. A sum-rate problem is also formulated and then optimized. Simulations
are then run for different parameters of the system. Graphs from the various simulations
are plotted and we compare different metrics to see what effect they have on each other.
Conventional relay systems are then compared to BD assisted systems to see if the latter
has any advantages over the former.

Thesis Validation Letter . . . . . . . . . . . . . . . . . . . . . . . . . . . i
Dedication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii
摘要. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iv
Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v
List of Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . viii
List of Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ix
1 Introduction......... 1
1.1 Backscatter Communications System . . . . . . . . . . . . . . . . . . . . 3
1.2 Literature Review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2 System Model ........7
2.1 System Model Under AF Mode . . . . . . . . . . . . . . . . . . . . . . . 7
2.2 System Model Under DF Mode . . . . . . . . . . . . . . . . . . . . . . . 9
3 Problem Formulation ..........12
3.1 Problem Formulation and Proposed Solution . . . . . . . . . . . . . . . . 12
3.1.1 AF Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
3.1.2 DF Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
4 Analysis and Discussion.......... 18
4.1 Simulation Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
4.2 Capacity versus Number of BDs . . . . . . . . . . . . . . . . . . . . . . 18
4.3 Capacity versus Source Power . . . . . . . . . . . . . . . . . . . . . . . 19
4.4 Pin versus Pout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
4.5 Capacity versus Source to BD distance . . . . . . . . . . . . . . . . . . . 22
4.5.1 Portion of active BDs versus Diagonal length . . . . . . . . . . . 23
4.6 Energy Efficiency versus Source Power . . . . . . . . . . . . . . . . . . 23
4.7 Benchmark: Comparison between a Conventional relay system and a
Backscatter assisted system . . . . . . . . . . . . . . . . . . . . . . . . . 24
4.7.1 AF mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
4.7.2 DF mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
4.7.3 Benchmark Results . . . . . . . . . . . . . . . . . . . . . . . . . 27
5 Conclusion....... 31
A Appendix .........32

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