On the Performance of Active Analog Self-Interference Cancellation Techniques for Beyond 5G Systems

The in-band full-duplex(IBFD)mechanism is of interest in beyond 5 G systems due to its potential to enhance spectral efficiency and reduce delay.To achieve the maximum gain of IBFD systems,the significant self-interference(SI)must be efficiently suppressed.The challenges of wideband selfinterference cancellation(SIC)lie in the radio frequency(RF)domain,where the performance will be limited by the hardware.This paper reviews current RF cancellation mechanisms and investigates an efficient mechanism for future wideband systems with minimum complexity.The working principle and implementation details of multi-tap cancellers are first introduced,then an optical domain-based RF canceller is reviewed,and a novel low-cost design is proposed.To minimize the cost and complexity of the canceller,the minimum required number of taps are analyzed.Simulation results show that with the commonly used 12-bits analog-to-digital converter(ADC)at the receiver,the novel optical domain-based canceller can enable efficient SIC in the 3 GPP LTE specifications compatible system within 400 MHz bandwidth.

Adaptive digital self-interference cancellation based on fractional order LMS in LFMCW radar

Adaptive digital self-interference cancellation(ADSIC)is a significant method to suppress self-interference and improve the performance of the linear frequency modulated continuous wave(LFMCW)radar.Due to efficient implementation structure,the conventional method based on least mean square(LMS)is widely used,but its performance is not sufficient for LFMCW radar.To achieve a better self-interference cancellation(SIC)result and more optimal radar performance,we present an ADSIC method based on fractional order LMS(FOLMS),which utilizes the multi-path cancellation structure and adaptively updates the weight coefficients of the cancellation system.First,we derive the iterative expression of the weight coefficients by using the fractional order derivative and short-term memory principle.Then,to solve the problem that it is difficult to select the parameters of the proposed method due to the non-stationary characteristics of radar transmitted signals,we construct the performance evaluation model of LFMCW radar,and analyze the relationship between the mean square deviation and the parameters of FOLMS.Finally,the theoretical analysis and simulation results show that the proposed method has a better SIC performance than the conventional methods.

一种基于SIC-CDM的低复杂度混合波束赋形方案

为了平衡毫米波大规模多输入多输出系统的性能和硬件开销,降低系统功耗,以频谱效率为优化目标,在部分连接结构下提出了一种收发端联合设计的低复杂度混合波束赋形方案。首先,基于连续干扰消除将原始优化问题转化为多个子阵的速率优化问题;然后,利用坐标下降法完成模拟波束赋形矩阵设计;最后,引入等效信道矩阵大幅降低矩阵维度,再对其进行奇异值分解获得数字波束赋形矩阵。仿真结果表明,与其他算法相比,所提算法在系统功耗降低的同时保持了较优的性能,且性能逼近部分连接结构的最优方案。

Full-duplex prototype based on joint passive and digital cancellation method

Recent research shows that it is possible to achieve the full-duplex system by cancelling strong self-interference signals, which can be divided into three classes respectively, i.e., passive cancellation, active cancellation and digital cancellation. This pa- per tries to achieve the full-duplex system without using active cancellation, thus a full-duplex system using a joint mechanism based on a novel passive cancellation method and a novel digital cancellation method is proposed. Therein, a good antenna place- ment guided by the theory of the antenna electromagnetic field for the passive cancellation is presented. For the proposed digital can- cellation method, unlike previous separate mechanisms, it is de- signed by using the recursive least square （RLS） algorithm jointly with passive cancellation. The self-interference channel state in- formation （CSI） is transferred as the input of digital cancellation to balance the performance and the complexity. Experimental results show that the proposed self-interference cancellation mechanism can achieve about 85 dB which is better than the previous re- search. Meanwhile, this design provides a better performance compared with half-duplex with both line-of-sight channel and non- line-of-sight channel.

联合SIC和QRD-M树搜索的低复杂度VBLAST检测算法

联合SIC和QRD-M树搜索,提出一种低复杂度的VBLAST检测算法:SQRM-SIC算法。该算法基于信道矩阵的排序QR分解(SQRD),首先对搜索树前几层采用QRD-M检测,然后对后续层进行SIC检测,获得了检测信号列表。在所提算法基础上,通过修改SQRD算法中的排序规则,得到MSQRM-SIC算法。复杂度分析和性能仿真表明,通过调整参数,SQRM-SIC算法和MSQRM-SIC算法都可获得较好的复杂度和性能折衷。其中,后者性能明显优于前者;且后者与QRDM算法相比,可以有效降低复杂度,而基本不损失性能。

基于SIC的单通道同频混合信号低复杂度盲分离算法

针对非协作通信中单通道同频混合信号盲分离算法复杂度高的问题,本文在连续干扰抵消(Serial Interference Cancellation,SIC)算法基础上,构建了单通道同频混合信号的信道接收模型,提出了基于SIC的低复杂度盲分离算法。并对信道重构中的信道截断影响进行了处理,避免了分离性能的损失。仿真结果表明,QPSK调制方式下分离性能与已有算法性能相当,但复杂度降低了2/3,且算法对频偏误差不敏感。

一种新的QR-SIC-MSD联合MIMO信号检测算法

针对MIMO信号检测中球形译码(Sphere decoding,SD)算法在低信噪比时接近最大似然(Maximum likelihood,ML)算法复杂度的缺点,提出了一种基于QR分解的串行干扰抵消(Successive interference cancellation,SIC)和修改的球形译码(Modified sphere decoding,MSD)联合MIMO信号检测算法,称之为QR-SIC-MSD算法。该算法在低信噪比时采用SIC算法,在高信噪比时,采用MSD算法,根据噪声方差仅选择一次初始搜索半径,若搜索失败则用SIC解代替。通过SIC算法与MSD算法的结合,大大地降低了球形译码算法的复杂性,同时保证了在中高信噪比时逼近ML算法性能,在低信噪比时接近ML算法性能。文中同时给出了完整的算法流程图及计算机仿真结果。

RF self-interference cancellation by using photonic technology [Invited]

Radio frequency(RF) self-interference is a key issue for the application of in-band full-duplex communication in beyond fifth generation and sixth generation communications.Compared with electronic technology, photonic technology has the advantages of wide bandwidth and high tuning precision, exhibiting great potential to realize high interference cancellation depth over broad band.In this paper, a comprehensive overview of photonic enabled RF self-interference cancellation(SIC)is presented.The operation principle of photonic RF SIC is introduced, and the advances in implementing photonic RF SIC according to the realization mechanism of phase reversal are summarized.For further realistic applications, the multipath RF SIC and the integrated photonic RF SIC are also surveyed.Finally, the challenges and opportunities of photonic RF SIC technology are discussed.

Polarization-based optimal detection scheme for digital self-interference cancellation in full-duplex system

In order to detect and cancel the self-interference(SI)signal from desired binary phase-shift keying(BPSK)signal,the polarization-based optimal detection(POD)scheme for cancellation of digital SI in a full-duplex(FD)system is proposed.The POD scheme exploits the polarization domain to isolate the desired signal from the SI signal and then cancel the SI to obtain the interference-free desired signal at the receiver.In FD communication,after antenna and analog cancellation,the receiver still contains residual SI due to non-linearities of hardware imperfections.In POD scheme,a likelihood ratio expression is obtained,which isolates and detects SI bits from the desired bits.After isolation of these signal points,the POD scheme cancels the residual SI.As compared to the conventional schemes,the proposed POD scheme gives significantly low bit error rate(BER),a clear constellation diagram to obtain the boundary between desired and SI signal points,and increases the receiver's SI cancellation performance in low signal to interference ratio(SIR)environment.

ON THE EQUIVALENCE OF PDA ALGORITHM AND SIC-MMSE ALGORITHM

In this letter,by employing Gaussian distribution to approximate the probability density function(pdf) of the extrinsic information at the output of the multiuser detector as a function of the pdf of the input extrinsic messages,it is concluded that the Probabilistic Data Association(PDA) algorithm is equivalent to the Soft Interference Cancellation plus Minimum Mean Square Error algo-rithm(SIC-MMSE) .

不完全SIC下CR-NOMA系统的功率分配算法

在不完全连续干扰消除(SIC)条件下,对认知无线电-非正交多址混合系统中的次用户总传输速率进行研究,提出一种基于参数变换和KKT条件的功率分配算法。采用非正交多址方式使次用户接入授权信道,在主次用户服务质量、最大发射功率等约束条件下,通过参数变换对原约束条件进行改写设计新的优化问题,并利用KKT条件求解最优功率分配因子进而实现系统中次用户总传输速率的最大化。仿真结果表明,与CNPA算法和等功率分配算法相比,该算法可明显提高系统中次用户的总传输速率,并且对于不完全SIC具有更强的承受能力。

A Wire-Line Secure Communication System Based on CCFD Self-Interference Cancellation

This paper presents a design scheme of wire-line telephone system using self-interference(SI)cancellation technology in co-frequency co-time full-duplex(CCFD)system to realize absolute secure communication at the physical layer.This scheme can hide the target signal by skillfully releasing the high-power artificial noise to the whole link at the receiving node,and then make use of the receiver’s knowledge of the SI signal to achieve high dB SI cancellation with the help of analog domain SI cancellation technology in CCFD domain,so that the signal-to-noise ratio(SNR)received by the eavesdropper at any position of the link is far lower than that of the legitimate receiver,so as to realize the absolutely secure communication in the sense of Wyner principle.This paper not only puts forward the specific design scheme of absolutely secure communication telephone,but also analyzes the calculation of security capacity under different eavesdropping positions,different SI cancellation capability and different system parameters according to Shannon theory.

A Novel Iterative Receiver Based on Extrinsic Information Update for MIMO Systems

A novel iterative receiver for multiple input multiple output (MIMO) systems was introduced. Its basis concept is that the reliability of extrinsic information will be strengthened with continuous iterations. Extrinsic information of present iteration is added with prior information of last iteration to obtain performance gain. The simulation results show that the improved iterative receiver can approach the 5th iteration performance of conventional soft interference cancellation (SIC)-minimum mean square error (MMSE) iterative receiver after the 2nd iteration with less computational complexity. Compared with conventional iterative receiver, the improved iterative receiver has 1dB performance gain at bit error rate (BER) of 10~ -5 , with four transmit antennas and four receive antennas system.

基于干扰消除辅助稀疏连接神经网络的大规模MIMO信号检测

近年来,深度学习成为无线通信领域的关键技术之一。在基于深度学习的一系列MIMO信号检测算法中,大多未充分考虑相邻天线之间的干扰消除问题,无法彻底消除多用户干扰对误码率性能的影响。为此,该文提出一种将深度学习与串行干扰消除(SIC)算法进行结合的方法用于大规模MIMO系统上行链路信号检测。首先,通过优化传统的检测网络(DetNet)及改进ScNet检测算法,该文提出一种基于深度神经网络(DNN)的检测算法,称为ImpScNet。在此基础上,进一步将SIC思想应用到深度学习框架结构设计中,提出一种基于深度学习的大规模MIMO多用户SIC检测算法,称为ImpScNet-SIC。此算法在每个检测层上分为两级,其中,第1级由该文提出的ImpScNet算法提供初始解,再将初始解解调至相应的星座点上作为SIC的输入,由此构成该算法的第2级。此外,在SIC中也使用了ImpScNet算法估计传输符号,以便获得最优性能。仿真结果表明,与已有的各种典型代表算法相比,该文所提ImpScNet-SIC检测算法特别适合大规模MIMO信号检测,具有收敛速度快、收敛稳定及复杂度相对较低的优势,并且在10–3误码率上有至少0.5 dB以上的增益。

基于多功率电平-多前导的mMTC免授权随机接入方案

传统的免授权随机接入方案存在严重的前导碰撞,这大大限制了终端的接入性能。为了降低前导碰撞及提高免授权随机接入概率,提出一种基于多输入多输出(multiple input multiple output,MIMO)和多功率电平-多时隙联合的免授权随机接入方案。在该方案中,活跃用户从前导池中随机选择多个前导序列构成组合前导,并根据自身位置选择一个发送功率电平,将组合前导和信号以该功率电平依次发送至基站;基站采用顺序干扰抵消技术分离不同功率电平的信号,通过前导检测识别竞争用户并估计随机接入冲突。仿真结果表明,相比单一非正交多址(non-orthogonal multiple access,NOMA)方案和单一多前导方案,所提方案能够有效提高用户的接入成功概率,对大规模随机接入场景具有更好的适应性。

非完美条件下的非正交多址接入星地融合网络性能分析

随着星地融合网络(ISTNs)的快速发展,大量的传感器和无线设备都有无线服务的接入需求,从而对星地融合网络的频谱效率和服务质量提出了新的挑战。不同于传统的正交多址接入技术,非正交多址接入(NOMA)技术可在相同的频率下传输不同用户的信号,其被认作为提高星地融合网络频谱效率的有效方法,从而被广泛研究。目前,针对NOMA和星地融合网络的研究大多都是在理想条件下进行的,由此该文研究更加实际的情况,即在非完美串行干扰消除(SIC)、信道估计误差和同频干扰下,对星地融合网络的性能进行研究。该文在假设卫星端和地面端均采用多天线的前提下,推导了系统遍历容量的闭式表达式,验证了非完美条件对于系统性能的影响。同时蒙特卡罗仿真验证了理论分析和推导的正确性。

TH预编码的超奈奎斯特系统残余干扰消除算法

超奈奎斯特(Faster-Than-Nyquist,FTN)技术能够有效提高传输系统的频谱效率,然而代价是引入了严重的码间串扰(Inter-Symbol Interference,ISI)。在基于Ungerboeck模型的FTN系统中的发送端使用TH预编码(Tomlinson-Harashima Precoding,THP)并不能完全有效消除FTN系统所引入的ISI,会存在残余ISI。对此,针对FTN系统中的残余干扰提出了两种接收端检测算法,分别是基于后向串行干扰消除(Backward Serial Interference Cancellation,BSIC)的无迭代检测算法和基于连续干扰消除(Successive Interference Cancellation,SIC)的Turbo迭代均衡改进算法,并通过蒙特卡洛方法寻找最优的扩展取模间隔。计算机数值仿真结果表明,在选定的扩展取模间隔下,两种接收端检测算法在FTN系统的加速因子为0.8和0.9时均能有效消除FTN技术所引入的ISI,其误码率趋近于奈奎斯特正交传输性能。

带内全双工水声通信残余自干扰实时抵消技术研究

带内全双工水声通信(In-Band Full Duplex Underwater Acoustic Communication,IBFD-UWAC)因其频谱利用率可达传统半双工模式的两倍,已成为水声通信领域的研究热点之一。由于本地发射强功率自干扰信号会导致通信系统误码率性能无法达到正常需求,因此自干扰抵消(Self-interference Cancellation,SIC)技术成为IBFD-UWAC中的核心问题。针对经过模拟SIC或空间自干扰抑制后的残余干扰信号问题,文章利用硬件在环(Hardware In-Loop,HIL)仿真,基于Simulink^(■)Desktop Real-time平台,实现了实时SIC,并利用瞬时状态误差判断期望信号到达情况,提出一种基于期望信号到达阈值的改进Sigmoid函数可变步长最小均方(Improved Sigmoid function based Variable Step Size,LMS,ISVS-LMS)算法,该算法大大降低了期望信号对SIC过程带来的影响。分析、仿真及实验表明:该方法可实现实时带内全双工水声通信的自干扰抵消,且算法的收敛速度以及稳态效果均有显著提升。

Intelligent reflecting surface-assisted cognitive radio-inspired rate-splitting multiple access systems

Intelligent reflecting surface(IRS)has been widely regarded as a promising technology for configuring wireless propagation environments.In this paper,we utilize IRS to assist transmission of a secondary user(SU)in a cognitive radio-inspired rate-splitting multiple access(CR-RSMA)system in which a primary user's(PU's)quality of service(QoS)requirements must be guaranteed.Without introducing intolerable interference to deteriorate the PU's outage performance,the SU conducts rate-splitting to transmit its signal to the base-station through the direct link and IRS reflecting channels.For the IRS-assisted CR-RSMA(IRS-CR-RSMA)scheme,we derive the optimal transmit power allocation,target rate allocation,and successive interference cancellation decoding order to enhance the outage performance of the SU.The closed-form expression for the SU's outage probability achieved by the IRS-CR-RSMA scheme is derived.Various simulation results are presented to clarify the enhanced outage performance achieved by the proposed IRS-CR-RSMA scheme over the CR-RSMA scheme.

Successive interference cancellation (SIC) in V-BLAST systems with asynchronous transmission mode

The V-BLAST system with asynchronous transmission mode first proposed by Shao can achieve full diversity only by using a simple linear detection scheme under zero forcing （ZF） criterion; therefore it gives a reasonable tradeoff between complexity and performance. In this paper, we propose two types of successive interference cancellation （SIC） detection schemes for the asynchronous V-BLAST system, one is characterized by applying Mr successive interference cancellators before a maximal ratio combiner （where Mr is the number of receive antennas）, and the other has a maximal ratio combiner before a successive interference cancellator. Since Type Ⅰ consumes more energy of the previously detected signals to recover a signal, Type Ⅱ can offer a better performance and simulations demonstrate its validity.