摘要
摘要
同时同频全双工（Co-time Co-frequency Full Duplex, CCFD）概念的提出，意在通过改变无线通信技术来缓解快速增长的业务需求与有限的频谱资源之间日益紧张的关系。理论上，CCFD通信模式能够在同一频率的信道上同时进行信号的发送与接收，使频谱利用率提高到目前的两倍。然而，由于CCFD系统中存在严重的自干扰问题，且具体的解决方案尚在研究优化过程中，因此CCFD技术在5G的白皮书中仅被列为潜在的关键技术。目前，关于自干扰抵消的研究主要可以分为三个方面：空域、模拟域以及数字域。其中，数字域因其极高的灵活性和强大的信号处理能力，近年来得到国内外无线通信领域的广泛关注。本论文围绕如何优化数字域的自干扰抵消技术进行展开，并且与空域、模拟域相结合，实现CCFD系统的自干扰抵消。
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已有的自干扰抵消技术虽然已经能够提供一定的自干扰抑制能力，基本保证简单CCFD系统的正常通信。但是在实际的全双工系统中，仅通过线性抵消不可能实现自干扰的完全抑制，收发链路中存在的器件损耗还会引入一些非理想因素，比如：非线性失真、相位噪声、量化噪声、高斯噪声、IQ不平衡等。
本文首先将发射链路中功率放大器（Power Amplifier, PA）的非线性效应考虑在内，分析了当输入为宽带信号时的非线性特征，对比后选择并联Hammerstein模型来近似PA的非线性失真。然后基于单发单收
全双工收发系统，根据最小二乘（Least Square, LS）准则对信道进行离线估计，实现数字域的非线性自干扰抵消。仿真结果证明，与线性自干扰抵消相比，该方案能够在数字域获取更高的干扰抵消比。
然后在此基础上，针对时变信道，又提出了基于自适应滤波的数字域非线性自干扰抵消方案。在考虑PA非线性失真的前提下，采用自适应滤波原理，根据最小均方（Least Mean Square, LMS）准则，对信道实时进行跟踪，保证信道估计的准确度，从而确保数字域的自干扰抵消能力。
最后，研究了收发链路中IQ不平衡和发射链路PA的非线性效应同时存在的情况下给CCFD系统带来的综合影响。采用广义线性模型对正交调制器进行建模，提出了一种数字域的联合抵消方案，不仅将IQ不平衡和PA非线性效应单独带来的影响考虑在内，还考虑了信号传输过程中两者产生的交叉组合项引入的不利因素。仿真结果表明，该方案能够进一步提升数字域的自干扰抑制能力，结合天线隔离和模拟域抵消，系统总的抵消比可以达到108dB左右。
关键词：同时同频全双工，数字域自干扰抵消，非线性失真，IQ不平衡，联合自干扰抵消
ABSTRACT
ABSTRACT
The concept of Co-time Co-frequency Full Duplex(CCFD) is put forward to relieve the increasingly ten relationship between the rapid growth of the business needs and the limited spectrum resources through changing the wireless communication technology. Theoretically, it can transmit and receive signals at the same time and at the same frequency, which would make the spectral efficiency of the existing communication systems be doubled. However, due to the existence of strong lf-interference(SI), and the specific solution is still in the optimization process, CCFD was only listed as a potential technique in the white paper of 5G. Currently, the rearch on SI cancellation can be mainly divided into three domains: antenna cancellation, analog cancellation and digital cancellation. And recent years, digital cancellation has been paid clo attention to becau of its high flexibility and powerful ability in signal processing. This paper focus on how to optimize the technique of digital SI cancellation, and realized the suppression of SI together with antenna attenuation and analog cancellation in CCFD system.
Though the existing SI cancellation methods can already attenuate some SI to guarantee the basic communication of simple CCFD systems, it’s impossible to realize the complete SI elimination in practical full-duplex system by only classical linear SI cancellation. This is mainly affected by the RF impairments in the transceiver chains, such as: nonlinear distortions, IQ imbalance, oscillator pha noi, quantization noi and Gaussian noi, etc.
Firstly, the nonlinear effect of Power Amplifier(PA) is taken into consideration, and the nonlinear characteristics with wideband input signals is analyzed, then the Parallel Hammerstein model is chon to approximate PA. Afterwards, the unknown channel respon is estimated off-line according to the Least Square(LS) criterion bad on the Single-input Single-output(SISO) CCFD system. The simulation results show that compared with linear SI cancellation, the propod scheme can obtain higher interference cancellation ratio(ICR) in digital domain.
Secondly, a new digital adaptive cancellation scheme is propod for the scenario where the channel is variable. Considering the PA non-linearity, it ensured the accuracy of the channel estimation by tracking the channel variety in real time. And during the estimation period, the
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Least Mean Square(LMS) algorithm is adopted. The performance of this cancellation method is also varied and analyzed at last.
Finally, the detrimental effects introduced by both the IQ imbalance and the transmitter non-linearity in CCFD system is rearched. On the basis of the, a joint digital cancellation scheme is propod, in which not only the effect of IQ imbalance and PA non-linearity individually, but also the c
omprehensive function of them are taken into account. And a widely linear model is ud to simulate the non-ideal quadrature modulator in transceiver chains. The results show that the propod canceller can eliminate more compared with other cancellation schemes, and the overall SI attenuation can reach 108dB together with antenna paration and analog cancellation.
Keywords: Co-time Co-frequency Full Duplex, Digital Self-interference Cancellation, Nonlinear Distortion, IQ Imbalance, Joint Self-interference Cancellation
插图索引
插图索引
图1.1 FDD系统中灵活双工模式原理图 (2)
图2.1 CCFD系统信道配置示意图 (7)
图2.2 双节点CCFD无线通信系统框图 (8)
图2.3 简易中继系统 (9)
图2.4 无线网络拓扑结构 (10)
图2.5 自干扰抵消技术分类图 (11)
图2.6 CCFD系统中环形器结构示意图 (12)
图2.7 天线对消原理图 (13)
图2.8 基于幅相控制的自适应抵消原理框图 (14)
图2.9 基于正交矢量合成的自适应抵消原理框图 (15)
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图2.10 基于多路延迟线的自适应抵消原理框图 (16)
图2.11 时域/频域数字自干扰抵消原理框图 (17)
图3.1 功率放大器AM/AM和AM/PM转化特性曲线图 (22)
图3.2 双音信号输出频率成分示意图 (23)
图3.3 并联Hammerstein模型结构图 (25)
图3.4 带有自干扰抵消模块的CCFD收发链路结构示意图 (26)
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图3.5 基于干扰重构的数字非线性自干扰抵消原理框图 (27)
图3.6 全双工收发链路频率对照图 (29)
图3.7 射频域功率谱对比图 (30)
图3.8 数字域功率谱对比图 (31)
图3.9 数字抵消性能与信号带宽之间的关系 (32)
图3.10 自适应滤波器原理图 (33)hereby
图3.11 时变横向FIR结构示意图 (34)
图3.12 自适应干扰抵消原理图 (34)
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图3.14 自适应数字非线性自干扰抵消效果图 (37)
图3.15 自适应数字干扰抵消算法收敛效果图 (38)
安娜与国王主题曲图4.1 理想正交调制器的结构示意图 (42)
图4.2 带有IQ不平衡的正交调制器 (43)
椭圆公式图4.3 直接变频的全双工收发系统基带等效模型框图 (44)
图4.4 数字域联合干扰抵消结构示意图 (47)
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图4.5 数字域联合干扰抵消性能与数值k的曲线关系图 (50)
图4.6 数字域干扰抵消性能对比图 (51)
图4.7 不同IRR时，系统ICR与SNR之间的曲线关系图 (52)
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