Feedback Interference Cancellation Research Articles

ATSC DTV 방송용 중계기 궤환간섭 제거 성능 개선

본 논문에서는 ATSC DTV 시스템에서 독립적인 궤환간섭 제거기(Feedback Interference Canceller: FIC)를 가지는 등화형 디지털 동일채널 중계기(Equalization Digital On-Channel Repeater: EDOCR)의 궤환간섭 제거 성능 향상을 위한 새로운 구조의 FIC를 제안한다. FIC는 기준신호와 궤환되는 신호의 상관관계를 이용하여 궤환채널을 추정하는데, ATSC DTV 방송 신호는 신호의 상관관계 특성을 저해하는 DC 파일럿을 포함하고 있으므로 FIC로 하여금 정확한 궤환채널 추정을 수행하지 못하게 한다. 이러한 문제를 해결하기 위해, EDOCR과 FIC의 결합 구조에 기반하여 EDOCR에서 신호 재변조 시 DC 파일럿을 포함하지 않는 기준신호를 추가적으로 생성하여 궤환채널 추정에 사용하는 DC 파일럿 없는 기준신호 기반 FIC와 디지털 신호처리를 통해 입력신호들을 백색화하여 DC 파일럿을 제거한 후 궤환채널을 추정하는 백색화된 신호 영역 FIC를 제안한다. 모의실험을 통해, 제안된 두 FIC 구조 모두 기존의 상관관계 제거형 FIC에 비해 우수한 궤환간섭 제거 성능을 가짐을 보인다. We propose two feedback interference cancellers(FICs) to improve the performance of the equalization digital on-channel repeater(EDOCR) with the FIC for the ATSC DTV broadcasting system. The FIC estimates the feedback channel between Tx. and Rx. antennas of the repeater by cross-correlating the reference signal and the feedback signal. Since there is a DC pilot which ruins the white property of the ATSC DTV signals, the FIC cannot estimate the feedback channel accurately. To solve the problem, the structural method which uses an additional DC pilot free reference for feedback channel estimation and the algorithmic method based on the digital signal processing which whitens the ATSC DTV signals and performs the feedback cancellation in the whitened signal domain. Simulation results show that the proposed two FICs show better feedback cancellation performance than the conventional FIC.

Equalisation digital on‐channel repeater with a feedback interference canceller for the advanced television systems committee terrestrial digital television system

In this study, the authors propose a novel equalisation digital on-channel repeater (EDOCR) with a feedback interference canceller (FIC) for a single frequency network of the advanced television systems committee terrestrial digital television system. The proposed EDOCR with an FIC not only has high output power by the cancellation of feedback signals caused by insufficient antenna isolation through the FIC, but also shows better quality of output signals than conventional digital on-channel repeaters (DOCRs) by removing multipath signals existing between the main transmitter and DOCR, as well as residual feedback signals through an equaliser. Computer simulation results are provided to demonstrate the superior performance of the proposed EDOCR with an FIC.

Design and Simulation of Feedback Interference Cancellation Repeater

Stability and output signal quality are two important indicators to evaluate the performance of a repeater.A high gain is also the basic requirement of repeater.This paper first proposes a feedback interference cancellation repeater scheme, and then the scheme is simulated on simulink.The result shows that the proposed scheme is able to cancel the feedback interference and guarantee the stability and output signal quality of repeater. Besides, it confirms that stability and output signal quality have some relation with the repeater gain G, the order of estimated channel filter N and the introduced delay. Finally, the approach of variable gain effectively increases the repeater gain, and appropriate selection of the gain makes it possible to avoid the output signal quality deterioration.

ATSC 지상파 방송을 위한 간섭제거 동일 채널 재생 중계기 성능평가

This paper presents and analyzes laboratory test results of Interference Cancellation Digital On Channel Regenerative Repeater(IC-DOCR) to broadcast digital television signals in the Advanced Television Systems Committee(ATSC) transmission systems using single frequency networks(SFN). IC-DOCR laboratory test is classified to receiver test, transmitter test, and feedback interference cancellation test. The receiver part includes random noise, single echo, multi-path ensembles, and adjacent channel interference test. The transmitter part includes out-of channel emission, equality of transmitting signal, and phase noise test. By the laboratory test, the receiver part of the IC-DOCR eliminates 28dB of feedback signal higher than the received signal and has 17.8dB at TOV(Threshold Of Visibility) under random noise environment. Also, the transmitter part satisfies the specification of US FCC(Federal Communications Commission) as well as maintains good output signal quality for guaranteeing more than SNR 30dB.

Channel Estimation and Interference Cancellation of Feedback Interference for DOCR in DVB-T System

This paper considers a problem of unwanted feedback interferences caused by coupling from the transmit antenna to the receive antenna in the digital video broadcasting-terrestrial (DVB-T) digital on-channel repeater (DOCR) system. We model the DVB-T DOCR system and propose a feedback interference cancellation method based on the linear minimum mean square error (LMMSE) estimation of the feedback interference channel. Since the accurate estimation of the feedback interference channel is an important factor that determines the performances of the feedback interference cancellation, the channel estimation by averaging the estimated channel and iterative decision feedback cancellation method are proposed. Simulation results of signal-to-noise ratio (SNR) relation between the reference SNR and the processed SNR are presented and the theoretical analysis is performed to verify the simulation results. The proposed methods are compared to the conventional method on the typical urban 6 channels with maximum Doppler frequencies of 0 Hz and 3 Hz in terms of SNR, bit error rate and various transmission modes in the DVB-T system. Simulation results and the theoretical results show that the proposed method outperforms the conventional method.

무선 중계기에서의 Dual NLMS 방식 궤한 간섭 제거 방법

이동 통신 시스템에서 음영 지역의 셀 커버리지를 확보하기 위하여 다양한 종류의 중계기가 사용되고 있다. 그러나 일반적인 무선 중계기는 송 수신 안테나 간의 궤환신호로 인한 발진 문제 때문에 고출력 옥외 중계기로 상용하기 어렵다. 궤환 간섭제거 중계기는 디지털 적응필터를 이용하여 송 수신 안테나 간의 궤환신호를 제거하여 발진을 방지한다. 본 논문에서는 dual NLMS(Normalized Least Mean Square) 알고리듬을 제안하며, 궤환 채널의 도플러 주파수 추정을 통하여 적응필터의 스텝 사이즈를 결정한다. 시불변 채널 및 다중 경로 페이딩 채널 환경에서 제안하는 알고리듬의 성능을 분석하고 모의 실험을 통하여 검증한다. Several repeater systems are used to enhance the cell coverage to location such as shadow and rural areas in mobile systems. But the general RF repeater solutions are not suitable for high power outdoor environment because it has the weakness such as self oscillation problem With adoption of a adaptive digital filter technology, feedback interference cancellation repeater prevents oscillation by detecting and canceling the unwanted feedback signal between transmission and receiver antenna. In this paper, dual NLMS based interference cancellation method is proposed and the step size adaptation can be implemented by the estimation of the feedback channel Doppler frequency characteristics. The performance of the proposed algorithm is quantified via analysis and simulation for the static and multipath fading feedback channels.

ATSC 지상파 DTV 시스템을 위한 궤환간섭 제거기를 가지는 EDOCR

In this paper, we propose an equalization digital on-channel repeater (EDOCR) with a feedback interference canceller (FIC) for single frequency network of the ATSC terrestrial DTV system. The proposed EDOCR with FIC does not have only high output power by cancelling feedback signals caused by insufficient antenna isolation through the FIC, but also shows better quality of output signals than the conventional on-channel repeaters (OCRs) by removing multipath signals existing between the main transmitter and the OCR, and residual feedback signals through an equalizer. In addition, computer simulations are provided to figure out the superior performance of the proposed EDOCR with FIC.

An Active Feedback Interference Cancellation Technique for Blocker Filtering in RF Receiver Front-Ends

A feedback interference cancellation circuit is presented that uses a control loop to reject blockers in wireless receivers. The concept is based on a feedback translational loop which subtracts a blocker replica from the original blocker signal. In contrast to feedforward methods loop selectivity does not depend on exact gain matching of two paths but on the open loop gain which is easier to adjust. The concept is described including the theoretical derivations of the transfer function and stability. Nonidealities like I/Q mismatch and noise mechanisms are discussed. Finally, measurements from a prototype chip in 65-nm CMOS are presented showing the feasibility of active feedback cancellation. In a desensitization scenario, gain drops by more than 12 dB for a -15 dBm blocker at 20 MHz offset without feedback interference cancellation while a gain degradation of merely 3 dB is measured with feedback interference cancellation enabled.

Novel Equalization On-Channel Repeater with Feedback Interference Canceller in Terrestrial Digital Multimedia Broadcasting System

In this paper, we propose a novel equalization on-channel repeater (OCR) with a feedback interference canceller (FIC) to relay terrestrial digital multimedia broadcasting signals in single frequency networks. The proposed OCR not only has high output power by cancelling the feedback signals caused by insufficient antenna isolation through the FIC, but also shows better output signal quality than the conventional OCR by removing multipath signals existing between the main transmitter and the OCR through an equalizer. In addition, computer simulations and laboratory test results demonstrate that the proposed OCR successfully cancels feedback signals and compensates channel distortions and provides a higher quality transmitting signal with higher output power than conventional OCRs. Keywords: T-DMB, single frequency network (SFN), on-channel repeater (OCR), equalizer, feedback interference canceller (FIC).

A Synchronization Technique for OFDM-Based Full Duplex Relays with Frequency-Domain Feedback Interference Canceller

In a Decode and Forward (DF) type of an OFDM-based Full Duplex Relay (FDR), the frequency-domain approach is more efficient than the time-domain approach for feedback interference cancellation. However, Inter-Symbol Interference (ISI) and Inter-Carrier Interference (ICI) may occur due to timing mismatch between the feedback interference signal and the desired signal from the Base Station (BS). In this letter, the effects of a timing mismatch on synchronous types and asynchronous types of OFDM-based FDRs are investigated in uplink and downlink cases. A synchronization procedure and techniques for minimizing ISI and ICI in OFDM-based FDRs with a frequency-domain feedback interference canceller are proposed.

Analysis of Two Filtering Techniques in Differential LC VCO Design using Asymmetric Tank Structure

This paper presents two InGaP/GaAs HBT (heterojunction bipolar transistor) differential cross-coupled voltage controlled oscillators (VCO) designed with low phase noise for adaptive feedback–interference cancellation systems (AF-ICS). The main idea is to use low pass and band pass Altering technique for noise frequency. With this, the designed VCO, the first one achieved a phase noise of −130.40 dBc/Hz at 1 MHz offsets from the carrier frequency of 1.619 GHz and the second one achieved −127.93 dBc/Hz at 1 MHz offsets from the carrier frequency of 1.604 GHz. Each VCO dissipates an output power of −6.68 dBm and −10 dBm respectively by supplying 5 V. Two pairs of base-collector (BC) junction diode are used as varactor to get a broad band tuning range for both VCOs.

Iterative Transceiver Design for MIMO ARQ Retransmissions With Decision Feedback Detection

This paper investigates the problem of progressive transceiver design for integrated multi-input multioutput (MIMO) systems with automatic repeat request (ARQ) capability. We consider a generic MIMO transceiver architecture that utilizes a linear transmission precoder and a linear decoder followed by decision feedback interference cancellation at the receiver. To be consistent with ARQ, our goal is to progressively design the optimal transmission precoder and receiver feedback system to jointly minimize the mean square error (MSE) under the assumption of perfect feedback. We consider both zero-forcing and minimum MSE (MMSE) decoder as joint ARQ receivers. Unlike in single transmission design, joint ARQ receivers cannot change previous precoders. Here, we propose an approach to design the precoder and receiver which improves the system performance successively over each retransmission to achieve MSE performance close to the known lower bound.

InGaP/GaAs HBT 공정을 이용하여 향상된 탱크 구조와 LC 필터링 기술을 적용한 차동 LC 전압 제어 발진기 설계

본 논문은 InGaP/GaAs HBT 공정을 통해 제작한 적응성궤환 잡음제거시스템용 낮은 위상잡음을 갖는 LC 차동 전압제어 발진기를 제안합니다. 전압제어 발진기는 필터링 기술을 포함한 향상된 공진 탱크 구조를 갖습니다. 비대칭 인덕터 대칭 캐패시터 구조로 제안된 전압제어 발진기의 출력 가변 범위는 207 MHz입니다. 출력 전력은 balun과 케이블 손실을 포함하여 -6.68 dBm입니다. 10 kHz, 100 kHz, 1 MHz에서의 위상잡음은 각각 -102.02, -112.04 그리고 -130.4 dBc/Hz입니다. 이 전압제어 발진기는 총 <TEX>$0.9{\times}0.9mm^2$</TEX> 면적 내에 집적화되었습니다. This paper presents the InGaP/GaAs HBT differential LC VCO with low phase noise performance for adaptive feedback interference cancellation system(AF-lCS). The VCO is verified with enhanced tank structure including filtering technique. The output tuning range for proposed VCO using asymmetric inductor and symmetric capacitors withlow pass filtering technique is 207 MHz. The output powers are -6.68 including balun and cable loss. The phase noise of this VCO at 10 kHz, 100 kHz and 1 MHz are -102.02 dBc/Hz, -112.04 dBc/Hz and -130.40 dBc/Hz. The VCO is designed within total size of <TEX>$0.9{\times}0.9mm^2$</TEX>.

Low complexity turbo equalization based on soft feedback interference cancelation

This letter presents a new soft feedback interference cancellation (SFIC) based equalizer suitable for iterative receivers applying turbo equalization. SFIC offers a very low computational complexity depending only linearly on the channel memory length. Despite its low complexity, SFIC shows a very good BER performance. Simulation results for the severely intersymbol interference distorted Proakis C channel show, that our approach performs within 0.5 dB to the powerful turbo equalization scheme based on MMSE linear filtering with time-varying coefficients and fails the mathematical optimum maximum a-posteriori (MAP) equalizer only by 1.2 dB.

Linear successive interference cancellation in DS‐CDMA systems

AbstractSuccessive interference cancellation techniques have the potential to reduce the interference and therefore increase the capacity of cellular radio systems. In this work, we analyze a linear DS‐CDMA receiver utilizing soft feedback interference cancellation. To be able to meet diverse QoS requirements, we introduce a power control scheme that takes into account heterogeneous service levels as well as the impact of imperfect interference cancellation. We address the capacity resulting from this receiver and give its user capacity region on closed‐form. We show that our results are general and provide a framework for capacity comparison for many proposed linear successive cancellation receiver models. Several receiver modifications are included, partial interference cancellation; when only part of the signal is canceled, and limited cancellation; when not every signal is canceled. We derive the minimum power solution of a single‐cell, from which convergent multicellular distributed power control algorithms that iteratively update the powers are suggested. The numerical results show that there are large gains in user capacity from interference cancellation when the Eb/I0 requirements are high. However, regardless of the required targets the maximum capacity is always achieved through partial successive interference cancellation. It is also found that the power levels are sensitive to the cancellation efficiency and worse performance than single‐user detection can occur. Copyright © 2003 John Wiley &amp; Sons, Ltd.

Inter-Carrier Interference Cancellation for OFDM Systems with Macrodiversity and Multiple Frequency Offsets

Macrodiversity provides improved coverage in wireless communications. It is used in single frequency networks (SFN), and in some cellular systems, when a mobile is in a soft handoff. The combination of OFDM and macrodiversity is very attractive for the ability of OFDM to cope with delay spread resulting from macrodiversity. However, such system is very sensitive to poor frequency synchronization among transmitters, which results in multiple frequency offsets. These cause inter-carrier interference (ICI), which severely degrades performance. In this paper we quantify the degradation, providing expressions for the receiver SINR, and find the optimum receiver frequency synchronization. Furthermore, we propose to mitigate ICI degradation using linear and decision feedback interference cancellation. In each case, we provide a solution using both the decorrelating and the MMSE criteria. Simulation results show that, for macrodiversity OFDM, our approach results in significantly improved performance and robustness to frequency offsets.

MMSE‐based groupwise successive interference cancellation scheme for multirate CDMA systems

AbstractIn this work, group‐wise successive interference cancellation (GSIC) scheme for multi‐rate CDMA systems is proposed. A multi‐rate CDMA system is a CDMA system that can support voice users together with data users which may have different data rates. In the proposed group‐wise detection, users with the same information rate are grouped and detected together. Users with the highest information rate are detected first, neglecting the presence of the other users in the system. Interference between the groups is cancelled in a successive order. The proposed scheme is based on the minimum mean square error (MMSE) criterion. We also studied the decision feedback interference cancellation for multi‐rate CDMA systems. The performance of the proposed detection scheme is compared with that of conventional detector, the decorrelating detector, and the linear MMSE detector for multi‐rate CDMA systems. The proposed scheme achieves better performance than the above‐mentioned detectors. The proposed scheme also provides significantly high spectral efficiency under certain conditions. The algorithms in the proposed scheme are suitable for both terrestrial and satellite applications of multi‐rate CDMA systems. Copyright © 2003 John Wiley &amp; Sons, Ltd.

Soft interference cancellation in multiuser communications

In this paper the performance of soft interference cancellation in synchronous multiuser channels is investigated. Two-stage detection with decorrelator in the first stage is considered. Soft first stage tentative decisions are formed by means of a multilevel quantizer or linear clipper. The asymptotic multiuser efficiency (AME) is used as a performance measured for optimization of the nonlinearity. It is shown, for the two-user case, that soft interference cancellation by means of an optimized linear clipper achieves the AME of the maximum likelihood detector if the crosscorrelation of the signature waveforms is less than $$1/\sqrt 2 $$ . For the K-user case, novel upper bounds on the AME for two-stage detectors with feedback interference cancellation, with both hard and soft tentative decisions, are obtained. The derived bounds are used to examine the performance of two-stage detectors in a cellular scenario.