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浙江大学学报(工学版)
Journal of ZheJiang University (Engineering Science)  2022, Vol. 56 Issue (10): 1977-1986    DOI: 10.3785/j.issn.1008-973X.2022.10.009
    
Digital widely linear self-interference canceller based on spread spectrum signal
Tian-qing XU1,2(),Ren-ting SONG3,Jia-jun HUANG1,2,Chao-jie ZHANG1,2,*()
1. Zhejiang Key Laboratory of Micro-Nano Satellite Research, Hangzhou 310027, China
2. Micro-satellite Research Center, Zhejiang University, Hangzhou 310027, China
3. China Xi’an Satellite Control Center, Xi’an 710043, China
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Abstract  

The effective digital domain cancellation method was designed for the self-interference in an in-band full-duplex system. The power level of each component in self-interference was analyzed. A digital LMS self-interference canceller based on widely linear model was designed aiming at the image signal caused by I/Q imbalance. Spread spectrum pseudo noise code was utilized to strengthen the non-correlation between self-interference and signal of interest for cancellation improvement. The simulation results demonstrate that the designed digital canceller possesses the ability to reconstruct and cancel the image signal for different image rejection ratios. Estimation noise caused by signal correlation in error vector of the LMS filter was reduced due to the utilization of spread spectrum pseudo noise code. A maximum cancellation gain of 7.5 dB was obtained in the simulation. The performance of the digital canceller was improved owing to the utilization of either widely linear model or pseudo noise code for different input signal-to-interference ratios.

Key words： in-band full-duplex      self-interference cancellation      widely linear model      spread spectrum      adaptive filter     
Received: 26 October 2021      Published: 25 October 2022
CLC:  TN 91  
Fund:  国家自然科学基金资助项目(62073289)
Corresponding Authors: Chao-jie ZHANG     E-mail: xutq@zju.edu.cn;zhangcj@zju.edu.cn
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Tian-qing XU
Ren-ting SONG
Jia-jun HUANG
Chao-jie ZHANG
Cite this article:

Tian-qing XU,Ren-ting SONG,Jia-jun HUANG,Chao-jie ZHANG. Digital widely linear self-interference canceller based on spread spectrum signal. Journal of ZheJiang University (Engineering Science), 2022, 56(10): 1977-1986.

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https://www.zjujournals.com/eng/10.3785/j.issn.1008-973X.2022.10.009     OR     https://www.zjujournals.com/eng/Y2022/V56/I10/1977


基于扩频信号的数字广义线性自干扰消除器

针对带内全双工系统中的自干扰信号问题，设计有效的数字域消除方案. 分析自干扰信号中各分量的功率量级，针对I/Q不平衡引起的镜像分量，设计基于广义线性模型的数字域LMS自干扰消除器. 为了提高自干扰消除性能，引入扩频伪码，以加强自干扰信号和有用信号间的非相关性. 仿真结果表明，设计的数字域消除器具备在不同镜像抑制比条件下对镜像分量的重建和抵消能力. 引入扩频伪码，能够减小滤波器误差向量中因信号相关性导致的估计噪声，仿真中最高获得了7.5 dB的消除量提升. 在不同输入信干比的条件下，采用广义线性模型和引入扩频伪码，均提升了数字域消除器的性能.


关键词： 带内全双工,  自干扰消除,  广义线性模型,  扩频,  自适应滤波器 
Fig.1 Architecture of IBFD zero-IF transceiver based on spread spectrum signal
Fig.2 Power level of signal components in IBFD system
参数 含义 参数 含义
$ {P}_{{\rm{T}}} $ 发射功率 $ {{\rm{SIC}}}_{{\rm{P}}} $ 传播域自干扰消除量
$ {P}_{{\rm{SI}}} $ SI信号功率 ${ {\rm{SIC}}}_{{\rm{A}}} $ 模拟域自干扰消除量
$ {P}_{{\rm{SI}},{\rm{ADC}}} $ ADC输入SI信号功率 $ {\rm{SIC}}_{{\rm{D}}} $ 数字域自干扰消除量
$ {P}_{{\rm{SI}},{\rm{Res}}} $ 残余SI信号功率 $ {{\rm{SNR}}}_{{\rm{HD}}} $ 半双工系统信噪比
$ {P}_{{\rm{SOI}}} $ 有用信号功率 ${ {\rm{NF}}}_{{\rm{R}}} $ 接收机噪声系数
$ \mathrm{Q}\mathrm{N}\mathrm{F} $ 量化噪底 $ {\rm{BW}} $ 接收机带宽
Tab.1 Parameters of IBFD system
Fig.3 Simplified self-interference channel
信号分量 中间信号中各分量功率/dBm
$ {x}_{{\rm{Mixer}}}\left(t\right) $ $ {x}_{{\rm{PA}}}\left(t\right) $ $ {y}_{{\rm{RF}}}\left(t\right) $ $ {y}_{{\rm{Mixer}}}\left(t\right) $
$ {P}_{{{\rm{SI}}}_{{\rm{base}}}} $ $ {P}_{{\rm{in}}} $ $ {P}_{{\rm{out}}} $ $ {P}_{{\rm{out}}}-{{\rm{SIC}}}_{{\rm{P}}+{\rm{A}}} $ ${P}_{ {\rm{out} } }-{ {\rm{SIC} } }_{ {\rm{P} }+{\rm{A} } } ,$
$ {P}_{{\rm{out}}}-{{\rm{IRR}}}_{{\rm{TX}}}-{{\rm{SIC}}}_{{\rm{P}}+{\rm{A}}}-{{\rm{IRR}}}_{{\rm{RX}}} $
$ {P}_{{{\rm{SI}}}_{{\rm{im}}}} $ $ {P}_{{\rm{in}}}-{{\rm{IRR}}}_{{\rm{TX}}} $ $ {P}_{{\rm{out}}}-{{\rm{IRR}}}_{{\rm{TX}}} $ $ {P}_{{\rm{out}}}-{{\rm{IRR}}}_{{\rm{TX}}}-{{\rm{SIC}}}_{{\rm{P}}+{\rm{A}}} $ ${P}_{ {\rm{out} } }-{ {\rm{IRR} } }_{ {\rm{TX} } }-{ {\rm{SIC} } }_{ {\rm{P} }+{\rm{A} } } ,$
$ {P}_{{\rm{out}}}-{{\rm{SIC}}}_{{\rm{P}}+{\rm{A}}}-{{\rm{IRR}}}_{{\rm{RX}}} $
$ {P}_{{\rm{IMD}}} $ ? $ 3{P}_{{\rm{out}}}-2{{\rm{IIP}}}_{3}-2{G}_{{\rm{PA}}} $ $3{P}_{ {\rm{out} } }-2{{\rm{IIP}}}_{3}-2{G}_{ {\rm{PA} } }-{ {\rm{SIC} } }_{ {\rm{P} }+{\rm{A} } }$ $3{P}_{ {\rm{out} } }-2{{\rm{IIP}}}_{3}-2{G}_{ {\rm{PA} } }-{ {\rm{SIC} } }_{ {\rm{P} }+{\rm{A} } }$
${P}_{ { {\rm{IMD} } }_{{\rm{im}}} }$ ? ? ? $3{P}_{ {\rm{out} } }-2{{\rm{IIP}}}_{3}-2{G}_{ {\rm{PA} } }-{ {\rm{SIC} } }_{ {\rm{P} }+{\rm{A} } }-{ {\rm{IRR} } }_{ {\rm{RX} } }$
Tab.2 Power of signal components in self-interference
Fig.4 Power level of signal components in self-interference after cancellation in propagation and analog domain
Fig.5 Diagram of LMS adaptive filter
Fig.6 LMS canceller based on widely linear model
参数 数值
信号带宽 10.23 MHz
接收机噪声系数 4 dB
接收机输入噪声功率 ?103.9 dBm
发射信号功率 20 dBm
有用信号功率 ?80.0 dBm
PA增益 27 dB
PA IIP3 20 dBm
低噪声放大器增益 15 dB
IRR（TX和RX） 可变
ADC位数 14 bit
伪随机码 Gold码
码长 1023
${ {\rm{SIR} } }_{{\rm{in}}}$ ?50 ~ ?15 dB
$ {M}_{{\rm{pre}}} $ 45
$ {M}_{{\rm{post}}} $ 15
LMS滤波器步长初值 0.01（ $ {{\rm{SI}}}_{{\rm{base}}} $分量）
0.0005（ $ {{\rm{SI}}}_{{\rm{im}}} $分量）
Tab.3 Parameters of IBFD transceiver
Fig.7 Cancellation for different image injection ratios
Fig.8 Cancellation for different input SIR levels
Fig.9 Comparison between LMS filter output and ideal signal of interest with or without spread spectrum signal
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