本論文研究非同步物理層網絡編碼(PNC) 系統。本文由兩部分構成。在第一部分中，我們提出了一個物理層網絡編碼整體框架，來處理碼元和載波相位異步問題。基於上述框架，本文證明了非同步的物理層網絡編碼可以提高系統性能。本文的第一個重要貢獻在於，不同於以往的主要理解，我們發現在採取適當的解碼方案後，非同步問題並不會降低系統性能。在第二部分中，我們通過理論和實際系統展示了物理層網絡編碼的原型機。特別是，我們採用正交頻分複用(OFDM) 系統，來解決時域的碼元非同步問題。本文的第二個重要貢獻在於，該工作是自五年前物理層網絡編碼理論提出之後，第一個真正的應用系統。 / 第一部分:在本文的第一部分里， 我們研究物理層網絡編碼系統中存在的碼元和載波相位異步問題。在物理層網絡編碼系統中，一個關鍵的問題是，接收機如何處理不同發射機發送的信號之間存在的不同步問題。也就是說，不同的發射機發送的信號達到接收機的時候，存在碼元移位的相位相對偏差。另一個關鍵的問題是，如何將信道編碼投衛和物理層網絡編碼相結合，來實現可靠的信息傳輸。本文研究上迷兩個重要問題，並且有如下四個主要貢獻1)我們提出並且分析了一個基於置信度傳遞(BP) 的物理層網絡編碼整體框架。該框架可以高效地解決碼元和相位異步問題，並且適用於有信道編碼的系統。2) 對於未經信道編碼的物理層網絡編碼系統， 在BPSK 和QPSK 調製下，我們的BP 算法可以顯著地降低非同步帶來的系統性能損失。3) 對於未經信道編碼的物理層網絡編碼系統，在相對碼元偏移為半碼元長度時，我們的BP 算法可以有效地將相位異步帶來的系統性能損失從6dB 降低到不足1dB。4) 對於經過信道編碼的物理層網絡編碼系統，在應用BP 算法後，異步系統性能優於同步系統。最後，在經過信道編碼的物理層網絡編碼系統中， 我們發現由各種碼元和相位異步組合產生的性能損失不超過ldB。上述貢獻3) 說明，如果我們可以精確地控制信號接收時間，那麼人為產生半個碼元偏移會給未經信道編碼的物理層網絡編碼系統帶來好處。上述貢獻4）說明，在採用了信道編碼後，碼元和相位非同步， 將不再是物理層網絡編碼一個主要擔憂的問題。 / 第二部分:在本文的第二部分里，我們展示了第一個物理層網絡編碼原型機的實現過程，這個原型機可以應用於雙向中繼網絡(TWRC) 。截至目前，僅有簡化的物理層網絡編碼系統，稱作模擬網絡編碼(ANC) 投街，被成功實現。模擬網絡編碼的好處在於它的簡單和容易實現;而它的缺點則是，中繼節點在放大信號的同時也放大了噪聲，因而帶來系統性能損失。在物理層網絡編碼系統中，中繼節點只有實現異或(XOR) 運算或者是去噪聲(denoising) PNC 映射，才能能顯著地提高系統性能。但是，要實現上途的XOR PNC 系統我們需要面對很多挑戰。比如， 中繼節點必須能夠處理接收信號的碼元和相位的異步問題，並且可以在解碼前實現信道估計。本文研究頻域物理曾網絡編碼實現，命名為FPNC，來解決上述問題。FPNC 基於OFDM 調製方式實現。在FPNC 系統中， XOR 映射發生在每一個OFDM 碼元的各個子載波上，而不是在時域的採樣點上。我們在通用軟件無線電設備(USRP) 平臺上實現了上述FPNC 系統。需要強調的是，我們的FPNC 實現僅需稍微修改現有的802. lla/g OFDM系統物理層前導序列。在循環前綴(CP) 的幫助下，碼元異步和多經效應都可以被相應地去除。實驗結果顯示，對於經過信道編碼的和未經信道編碼的FPNC 系統，碼元同步系統和碼元異步系統性能沒有區別。 / This thesis investigates asynchronous physical-layer network coding (PNC) systems. It consists of two parts, each part contains a major contribution within the domain of PNC research. The first part presents a theoretical framework for dealing with phase and symbol asynchronies in PNC. We show how this framework can turn asynchronies to an advantage to boost system performance. The major contribution here is the insight that, contrary to the prior belief, asynchrony is not detrimental to the performance of PNC systems with the right methods to deal with it. The second part reports the first PNC implementation prototype. In particular, we demonstrate both in theory and practice that using OFDM in the PNC system can remove the symbol asynchrony in the time domain. The major contribution here is that this is the first experimental feasibility demonstration of the PNC concept since it was conceived theoretically five years ago. / Part I: In the first part of this thesis, we study the phase and symbol asynchrony problems in PNC. A key issue in physical-layer network coding (PNC) is how to deal with the asynchrony between signals transmitted by multiple transmitters. That is, symbols transmitted by different transmitters could arrive at the receiver with symbol misalignment as well as relative carrier-phase offset. A second important issue is how to integrate channel coding with PNC to achieve reliable communication. This thesis investigates these two issues and makes the following contributions: 1) We propose and investigate a general framework for decoding at the receiver based on belief propagation (BP). The framework can effectively deal with symbol and phase asynchronies while incorporating channel coding at the same time. 2) For non-channelcoded PNC, we show that for BPSK and QPSK modulations, our BP method can significantly reduce the asynchrony penalties compared with prior methods. 3) For non-channel-coded PNC, with half symbol offset between the transmitters, our BP method can drastically reduce the performance penalty due to phase asynchrony, from more than 6 dB to no more than 1 dB. 4) For channel-coded PNC, with our BP method, both symbol and phase asynchronies actually improve the system performance compared with the perfectly synchronous case. Furthermore, the performance spread due to different combinations of symbol and phase offsets between the transmitters in channel-coded PNC is only around 1 dB. The implication of 3) is that if we could control the symbol arrival times at the receiver, it would be advantageous to deliberately introduce a half symbol offset in non-channel-coded PNC. The implication of 4) is that when channel coding is used, symbol and phase asynchronies are not major performance concerns in PNC. / Part II: In the second part of this thesis, we present the first implementaii tion of a two-way relay network based on the principle of physical-layer network coding. To date, only a simplified version of physical-layer network coding (PNC) method, called analog network coding (ANC), has been successfully implemented. The advantage of ANC is that it is simple to implement; the disadvantage, on the other hand, is that the relay amplifies the noise along with the signal before forwarding the signal. PNC systems in which the relay performs XOR or other denoising PNC mappings of the received signal have the potential for significantly better performance. However, the implementation of such PNC systems poses many challenges. For example, the relay must be able to deal with symbol and carrier-phase asynchronies of the simultaneous signals received from the two end nodes, and the relay must perform channel estimation before detecting the signals. We investigate a PNC implementation in the frequency domain, referred to as FPNC, to tackle these challenges. FPNC is based on OFDM. In FPNC, XOR mapping is performed on the OFDM samples in each subcarrier rather than on the samples in the time domain. We implement FPNC on the universal soft radio peripheral (USRP) platform. Our implementation requires only moderate modifications of the packet preamble design of 802.11a/g OFDM PHY. With the help of the cyclic prefix (CP) in OFDM, symbol asynchrony and the multi-path fading effects can be dealt with in a similar fashion. Our experimental results show that symbol-synchronous and symbol-asynchronous FPNC have essentially the same BER performance, for both channel-coded and non-channelcoded FPNC. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Lu, Lu. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2012. / Includes bibliographical references (leaves 123-128). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese. / Abstract --- p.i / Acknowledgement --- p.viii / Publications --- p.x / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Asynchrony Problems in Physical-Layer Network Coding --- p.3 / Chapter 1.2 --- Implementation of Physical-Layer Network Coding --- p.4 / Chapter 1.3 --- Outline of the Thesis --- p.5 / Chapter 2 --- Asynchronous PNC --- p.7 / Chapter 2.1 --- Introduction --- p.7 / Chapter 2.2 --- Related Work --- p.10 / Chapter 2.2.1 --- Classification --- p.11 / Chapter 2.2.2 --- Non-channel-coded PNC --- p.11 / Chapter 2.2.3 --- Channel-coded PNC --- p.12 / Chapter 2.3 --- System Model --- p.14 / Chapter 2.4 --- Non-channel-coded PNC --- p.19 / Chapter 2.4.1 --- Synchronous Non-channel-coded PNC --- p.19 / Chapter 2.4.2 --- BP-UPNC: A Belief Propagation based Non-channelcoded PNC Scheme --- p.20 / Chapter 2.4.3 --- Numerical Results --- p.27 / Chapter 2.4.4 --- Diversity and Certainty Propagation --- p.29 / Chapter 2.5 --- Channel-coded PNC --- p.33 / Chapter 2.5.1 --- Channel-decoding and Network-Coding (CNC) Process --- p.34 / Chapter 2.5.2 --- Jt-CNC: A Joint Channel-decoding and Network-Coding Scheme --- p.36 / Chapter 2.5.3 --- XOR-CD: A Disjoint Channel-decoding and Network-Coding Scheme --- p.40 / Chapter 2.5.4 --- Numerical Results --- p.43 / Chapter 2.5.5 --- Shannon Limits for Gaussian Channel --- p.48 / Chapter 2.5.6 --- Diversity and Certainty Propagation in Jt-CNC --- p.50 / Chapter 2.6 --- Conclusions --- p.51 / Chapter 3 --- Implementation of Asynchronous PNC --- p.54 / Chapter 3.1 --- Introduction --- p.54 / Chapter 3.1.1 --- Challenges --- p.56 / Chapter 3.2 --- Effect of Delay Asynchrony in Frequency Domain --- p.60 / Chapter 3.2.1 --- Effective Discrete-time Channel Gains --- p.60 / Chapter 3.2.2 --- Delay-Spread-Within-CP Requirement --- p.63 / Chapter 3.3 --- FPNC Frame Format --- p.66 / Chapter 3.3.1 --- FPNC Short Training Symbol --- p.68 / Chapter 3.3.2 --- FPNC Long Training Symbol --- p.69 / Chapter 3.3.3 --- FPNC Pilot --- p.70 / Chapter 3.4 --- Addressing Key Implementation Challenges in FPNC --- p.71 / Chapter 3.4.1 --- FPNC Carrier Frequency Offset (CFO) Compensation --- p.71 / Chapter 3.4.2 --- FPNC Channel Estimation --- p.75 / Chapter 3.4.3 --- FPNC Mapping --- p.76 / Chapter 3.5 --- Experimental Results --- p.80 / Chapter 3.5.1 --- FPNC Implementation over Software Radio Platform --- p.80 / Chapter 3.5.2 --- Experimental Results --- p.81 / Chapter 3.6 --- Conclusions --- p.88 / Chapter 4 --- Conclusions and Future Work --- p.90 / Chapter 4.1 --- Conclusions --- p.90 / Chapter 4.2 --- Future Work --- p.92 / Chapter 4.2.1 --- Asynchronous PNC --- p.93 / Chapter 4.2.2 --- Implementation of PNC --- p.94 / Chapter A --- Message Update Steps of Jt-CNC --- p.97 / Chapter A.1 --- Step 1. Updates of messages below code nodes X: --- p.98 / Chapter A.2 --- Step 2. Updates of upward messages into check nodes C: --- p.98 / Chapter A.3 --- Step 3. Update of upward messages into the source nodes S: --- p.99 / Chapter A.4 --- Step 4. Update of downward messages into the check nodes C: --- p.100 / Chapter A.5 --- Step 5. Updates of downward messages into code nodes X: --- p.100 / Chapter B --- Channel-coded Collision Resolution --- p.101 / Chapter B.1 --- Introduction --- p.101 / Chapter B.2 --- System Model --- p.103 / Chapter B.3 --- C-CRESM --- p.105 / Chapter B.3.1 --- Review of RA code --- p.106 / Chapter B.3.2 --- Virtual Tanner Graph for RA coded CRESM --- p.107 / Chapter B.3.3 --- Definitions --- p.108 / Chapter B.3.4 --- Message Update Rules --- p.109 / Chapter B.4 --- Comparison of Different Methods --- p.115 / Chapter B.4.1 --- Independent Multiuser Detection and Channel Decoding (Independent MU-CD) --- p.116 / Chapter B.4.2 --- Turbo-SIC --- p.117 / Chapter B.4.3 --- Channel-coded CRESM (C-CRESM) --- p.118 / Chapter B.5 --- Simulation Results --- p.119 / Chapter B.6 --- Conclusion --- p.121 / Bibliography --- p.123
| Identifer | oai:union.ndltd.org:cuhk.edu.hk/oai:cuhk-dr:cuhk_328013 |
| Date | January 2012 |
| Contributors | Lu, Lu, Chinese University of Hong Kong Graduate School. Division of Information Engineering. |
| Source Sets | The Chinese University of Hong Kong |
| Language | English, Chinese |
| Detected Language | English |
| Type | Text, bibliography |
| Format | electronic resource, electronic resource, remote, 1 online resource (xxiii, 128 leaves) : ill. (some col.) |
| Rights | Use of this resource is governed by the terms and conditions of the Creative Commons “Attribution-NonCommercial-NoDerivatives 4.0 International” License (http://creativecommons.org/licenses/by-nc-nd/4.0/) |
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