# On Self-Interference Cancellation and Non-Idealities Suppression in Full-Duplex Radio Transceivers

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## Abstract

**:**

## 1. Introduction

#### 1.1. Related Work

#### 1.2. Contributions

- Three RF/analog SIC techniques, i.e., CSI, GALL filter and Kautz filter for SI cancellation to level below the receiver’s thermal noise floor or sensitivity level.
- A digital SIC technique i.e., Kalman filter for residual SI cancellation.
- Linearization techniques for the suppression of the transceiver’s component (LNA, PA, IQ mixer) non idealities, i.e.,
- ➢
- BAFF and BA algorithm for IQ mixer imbalance
- ➢
- Doherty amplifier technique with feedforward linearization technique and pre-distortion linearization technique for the linearization of PA
- ➢
- Negative feedback and feedforward linearization technique for LNA.

#### 1.3. Organization of the Paper

## 2. Proposed System Model and Techniques

#### 2.1. Transceiver’s Components Linearization

#### 2.1.1. IQ Mixer Linearization

#### Tx: Blind Adaptive Feedforward Algorithm (BAFF)

#### Rx: Blind Algorithm (BA)

#### 2.1.2. PA and LNA Linearization

#### 2.2. SI Cancellation Techniques

#### 2.2.1. Analog/RF SI Cancellation Techniques

#### Channel State Information (CSI)

#### Channel State Information at Rx (CSIR)

#### Blind Estimation

#### GALL Filter

#### Kautz Filter

#### 2.2.2. Digital SI Cancellation Techniques

#### Kalman Filter

- (i)
- Prediction stage:

- (ii)
- Updating stage:

## 3. Results and Discussion

#### 3.1. Link Budget Analysis

#### 3.2. Power Level of Different Components of SI. Signal After RF/Analog SI Cancellation

#### 3.3. SINR

#### 3.4. Linearization

## 4. Conclusions

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Conflicts of Interest

## Nomenclature

${P}_{SI}$ | Power of direct component |

${P}_{SI,im}$ | Power of image component |

${P}_{IMD}$ | Power of intermediate distortion component |

${P}_{IMD,im}$ | Power of image component of IMD |

${P}_{Ds}$ | Power of desired Signal |

${P}_{TRs}$ | Total power at the receiver input |

${P}_{Kautz}$ | Power after applying analog/RF cancellation using Kautz filter |

${P}_{GALL}$ | Power after applying analog/RF cancellation using GALL filter |

$SINRandSIN{R}_{WC}$ | SINR without any cancellation technique |

$SIN{R}_{30dB}$ | SINR with 30 dB of antenna cancellation |

$SIN{R}_{40dB}$ | SINR with 40 dB of antenna cancellation |

$SIN{R}_{CSI\_30dB}$ | SINR with CSI and 30 dB antenna cancellation |

$SIN{R}_{CSI\_40dB}$ | SINR with CSI and 40 dB antenna cancellation |

$SIN{R}_{Kautz}$ | SINR after Kautz filter implementation |

$SIN{R}_{GALL}$ | SINR after GALL filter implementation |

$SIN{R}_{Kalman\left(Kautz\right)}$ | SINR after Kautz filter with Kalman filter implementation |

$SIN{R}_{Kalman\left(GALL\right)}$ | SINR after GALL filter with Kalman filter implementation |

$SIN{R}_{Kalman\left(CSI30dB\right)}$ | SINR after CSI and 30 dB antenna cancellation with Kalman filter implementation |

$SIN{R}_{Kalman\left(CSI40dB\right)}$ | SINR after CSI and 40 dB antenna cancellation with Kalman filter implementation |

${O}_{WL}$ | The output of a non-linear amplifier |

${O}_{PD}$ | The output of PA after PD technique |

${O}_{FF}$ | The output of PA after FF technique |

${O}_{NFB}$ | The output of PA after NFB technique |

$BE{R}_{R,Im}$ | BER in the presence of receiver front end impairments |

$BE{R}_{AfterLT}$ | BER after applying linearization techniques to receiver front end components |

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**Figure 2.**IQ mixer imbalance in transceiver and IQ mixer linearization technique (BAFF and BA algorithm).

**Figure 3.**Linearization and efficiency improvement techniques for PA in transmitter RF front end, and linearization techniques for LNA in receiver RF front end.

**Figure 9.**Power of self-interfering signal components before and after SI cancellation techniques. SI power at receiver: (

**a**) without any SI cancellation; (

**b**) with 30 dB antenna isolation and CSI technique; (

**c**) with 40 dB antenna isolation and CSI technique; (

**d**) with the Kautz filter as an SI cancellation technique; (

**e**) with the GALL filter as an SI cancellation technique.

**Figure 10.**SINR using analog and digital cancellation techniques. (

**a**) SINR after analog SI cancellation 30 dB and 40 dB antenna isolation with CSI technique, Kautz and GALL filter; (

**b**) SINR after both analog and digital SI cancellation.

**Figure 11.**The signal trajectory and the constellation diagram of IQ mixer of transmitter chain with 25% gain and 25° phase imbalance. (

**a**–

**c**) show the signal trajectory of the ideal, imbalance, and compensated IQ mixer of the Tx chain, respectively. (

**d**–

**f**) show the constellation diagram of the ideal, imbalance, and compensated IQ mixer of the TX chain, respectively.

**Figure 13.**Doherty amplifier technique with feedforward linearization technique (

**a**); and pre-distortion linearization technique (

**b**).

**Figure 15.**Non-linear LNA with negative feedback linearization technique (

**a**); and feedforward linearization technique (

**b**).

Parameters | Values |
---|---|

Modulation Scheme | 16 QAM |

Number of Sub-carriers | 64 |

Number of Data sub-carriers | 48 |

Symbol Time | 3.2 µs |

Guard Interval or CP Duration | 25% of symbol length |

Parameters | Values |
---|---|

Bandwidth | 20 MHz |

Receiver thermal noise floor | −103.0 dBm |

Sensitivity | −88.9 dBm |

Receiver noise figure | 4.1 dB |

Noise power | −174 dBm/Hz |

Power at receiver | −88.9 dBm |

Transmit power | 5 to 40 dBm |

Antenna separation | 30 dB and 40 dB |

Carrier frequency | 2 GHz |

Component | Gain (dB) | IIP2 (dBm) | IIP3 (dBm) | NF (dB) |
---|---|---|---|---|

IQ Mixer (Tx and Rx) | 6 | 50 | 15 | 4 |

PA | 27 | - | 20 | 5 |

LNA | 25 | - | 5 | 4.1 |

VGA | 1–51 | 50 | 20 | 4 |

IQ Mixer IRR (dB) (Tx and Rx) | 13 | - | - | - |

PA memory length | 6 | - | - | - |

ADC | Bits | 12 | - | - |

P-P voltage range | 4.5 V | - | - | |

PAPR | 10 dB | - | - |

Techniques | Results | Reference Papers | ||||
---|---|---|---|---|---|---|

Analog/RF SIC | Digital SIC | Linearization Techniques (LT) | Analog/RF SIC | Digital SIC | ||

Auxiliary path (consisting of DAC, IQ, PA and RF attenuator) | Gain factor | - | 74 dB | [17] | ||

Robust algorithm known as SINC interpolation | LS algorithm | - | 60 dB | Residual linear components by 50 dB | [74] | |

Non-linear components by 20 dB. | ||||||

Hybrid model enables SI cancellation near to receiver noise floor up to 110 dB | ||||||

One tap filter depicting the delay, phase and attenuation of main coupling path | LS estimator | - | 30 dB & 20 dB | Linear Model: 25 dB | [39] | |

Widely Linear Model: 35 or 50 dB | ||||||

Passive isolation (special antenna design) | - | - | Passive isolation: 60–70 dB | - | [75] | |

100 dB of overall self-interference suppression | ||||||

Presents a novel RF circuit architecture | - | - | 100 MHz waveform bandwidth: 41 dB total cancellation | - | [76] | |

20 MHz carrier bandwidth: 60 dB total cancellation | ||||||

Digitally controlled RF self-interference canceller structure | - | - | More than 40 dBs of active RF cancellation gain up to 80 MHz instantaneous waveform bandwidths | - | [77] | |

Used a shared antenna and a circulator, an adjustable impedance mismatch terminal (IMT) circuit at the antenna interface is added for cancellation of SI | - | - | 40 dB | - | [78] | |

Block-adaptive Learning algorithm through decorrelation for RF cancellation | - | - | 54 dB | - | [79] | |

Assumed 15 dB circulator isolation with variable RF cancellation | Orthogonalization of the design matrix using QR decomposition | - | As low as 50 dB | [80] | ||

Hybrid multi-stage cancellation system, consisting of an analog cancellation setup at RF frequencies following the so-called Stanford architecture | Base-band digital cancellation i. LMS (Least Mean Square) ii. APA (Affine Projection Algorithm) methods | - | Up to 80 dB of power interference cancellation can be achieved with a full-duplex OFDM scheme | [81] | ||

Nonlinear signal reconstruction and cancellation with post-distortion, least-squares method for channel estimation | - | Iteratively estimation of coefficients (IQ Imbalance, PA and LNA) using Newton’s method & discrete Fourier transform | Approximately 50 dB | [46] | ||

Antenna cancellation, self-reflector and develop custom Arduino code for updating the weights for RF cancellation | Develop custom Arduino code for updating the weights in in-house chip using SPI | - | 58 dB | 26 dB | [82] | |

Total of 84 dB | ||||||

Assumed 30 dB and 40 dB antenna isolation | Extended Kalman Filter (EKF) | - | - | 40–45 dB | Ourprevious work [69] | |

- i
- CSI using LS and MMSE
- ii
- GALL Filter
- iii
- Kautz Filter
| KALMAN Filter | - i
- IQ mixer LT (BAFF & BA)
- ii
- PA LT (Doherty + pre-distortion & Feedforward)
- iii
- LNA LT (Negative & Feedforward)
| - i
- 60–70 dB
- ii
- 75–85 dB
- iii
- 75–85 dB
| 40–45 dB | PROPOSED WORK | |

Proposed model results. (Assumed antenna isolation of 30 dB & 40 dB) | - i
- CSI + KALMAN Filter + LT
- ii
- GALL Filter + KALMAN Filter + LT
- iii
- Kautz Filter + KALMAN Filter + LT
| - i
- 100–120 dB
- ii
- 115–130 dB
- iii
- 115–130 dB
* If EKF (our own previous work) is used for digital SIC, SIC of 115–130 dB. |

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## Share and Cite

**MDPI and ACS Style**

Ayesha, A.; Rahman, M.; Haider, A.; Majeed Chaudhry, S.
On Self-Interference Cancellation and Non-Idealities Suppression in Full-Duplex Radio Transceivers. *Mathematics* **2021**, *9*, 1434.
https://doi.org/10.3390/math9121434

**AMA Style**

Ayesha A, Rahman M, Haider A, Majeed Chaudhry S.
On Self-Interference Cancellation and Non-Idealities Suppression in Full-Duplex Radio Transceivers. *Mathematics*. 2021; 9(12):1434.
https://doi.org/10.3390/math9121434

**Chicago/Turabian Style**

Ayesha, Areeba, MuhibUr Rahman, Amir Haider, and Shabbir Majeed Chaudhry.
2021. "On Self-Interference Cancellation and Non-Idealities Suppression in Full-Duplex Radio Transceivers" *Mathematics* 9, no. 12: 1434.
https://doi.org/10.3390/math9121434