Multichannel Adaptive Interference Cancellation for Full-Duplex High Power AM Radios

This paper investigates the influence of the different gains of weight branches to the dynamic characteristic and interference cancellation ratio (ICR) of an analog adaptive interference cancellation system (AAICS). We solved the transient-state and steady-state characteristics of weights. And the rule of ICR varying with the different gains was studied. The difference of the gains of weight control branches leads the convergence speeds of the two weights are different. The convergence speed of the system is decided by the slower weight. Enlarging the gains will improve the average convergence speed and ICR. The analyses are in agreement with the computer simulation. For the different gains, the system is a time-variant system. The more the difference of gains is, the severer THD (Total harmonic distortion) will be. And the new interference will appear.

A time-domain model of the analog adaptive interference cancellation system (AAICS) involving both the interference and the desired signal is proposed. The stability, interference cancellation ratio, and convergence time of the AAICS are analyzed in detail. In addition, the desired signal cancellation ratio is taken into account in order to evaluate the system performance and optimize the AAICS more accurately. It is found that the parameters including the loop gain and the time constant of the negative feedback control loop need to be set reasonably so as to reduce a great distortion to the desired signal. The rules of parameter optimization are obtained for the AAICS operating in high frequency. Experiments are carried out to demonstrate the system's performance varying with parameters, and experimental results are in agreement with theoretical analysis, which is of great value for the optimization design of the AAICS.

Spurious-free Dynamic Range (SFDR) of frequency sources such as local oscillators in radio has a profound effect on the minimum signal strength that can be detected. Greater the level of unwanted spurs the more difficult it is to detect an incoming signal in the presence of existing interferers and minimum signal/noise ratio at the demodulator input. Taylor series based Direct Digital Synthesis (DDS) produces an SFDR of around 74dB. The proposed architectures in this paper attempt to improve the SFDR by using a Hartley Image suppressor and using an adaptive sinusoidal interference canceller. The resultant improvement in SFDR is around 45 dB by using the Hartley image suppressor and 40dB using the adaptive interference canceller. The two proposed spur suppression techniques are compared in terms of dynamic power, realized noise floor and hardware complexity.

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>.

The multiuser detection is a signal processing tech- nique which enhances the performance and capacity in DS- CDMA technology. Since its complexity issue was too expensive to handle, there was focus on the suboptimal detectors. In this paper we propose a hybrid method called adaptive differential interference cancellation method (ADIC) which is a hybrid of the differential interference cancellation method and which is then combined in a adaptive way to determine a weight matrix which will map the outcome of the differential interference cancellation method to come out with a better performance. This paper also looks into the computational cost of different methods using the floating point operation (flops) which is a good estimation of the comparative computational cost if not the exact one. I. INTRODUCTION The conventional DS-CDMA match filter detector fails to combat these issues due three prominent drawbacks: unrealis- tic ucorrelated code, near-far problem (even with strict power control (1)), and tough multiple access interference (MAI). Many advanced signal processing approaches have been made to improve the performances of these kinds of detectors. In this paper we will study the different approaches that were made in this field and implement these methods to reach a conclusion about the detection methods. As the name of the topic suggests the focus of our work will be study and propose cost effective better performing multiuser detection method. We will explore Multiuser Detection Techniques in Synchronous CDMA environment. Multi-user detection deals with the development and ap- plication of joint demodulation and interference cancellation cancellation techniques for improved detection of a desired set of digital signals in the presence of multiple access interfer- ence, intersymbol interference and noise. Since veterbi forward dynamic algorithm (2) is used in case of Optimum multiuser detection (3) the complexity grows in with the increase in the number of users. Hence the complexity is immense which increases exponentially with the increase in the number of users. Looking ahead for lower complexity hence lesser cost of implementation, the paper proposes the use of sub-optimal linear detectors (4). The sub-optimal detector the paper next focuses on is Decorrelator type of Detector (5) which is optimal in least squares. This detector out performs the optimal detector in many respects. Then the Minimum Mean Square Error (MMSE) linear detector is proposed which tries to minimize the squared error from the required transformation. It is one of the most popular detectors in use due to its easiness to implement and its lower complexity. But then in the above detection methods the decisions made were based on certain linear transformation criterion and there are missing efforts to check the performance in between the detection process to improvise the transformation method better detection. So then the paper proposes Adaptive multiuser detection. Then the paper focuses on Interference cancellation methods which utilize the feedback to reduce Multiple Access Interference (MAI) in the detected bits. Under the Interference Cancellation umbrella the Successive Interference Cancellation (SIC) (6), (7) method is explored and simulated to observe the results. Then the next method which performs better than SIC and more commonly used in real life, called Parallel Interference Cancellation (PIC) (6), (8) is also implemented. Before going ahead to implement the final proposed detection method, this paper implements Differential Interference Cancellation (DIC) (9) method. And then this paper finally proposes an Inter- ference Cancellation method called the Adaptive Differential Interference Cancellation Multiuser Detection method which is cost effective in comparison to other Interference Cancellation methods as we will require lesser hardware (multipliers as in the SIC or Parallel Interference Cancellation (PIC)) for that matter. More ever since we are using adaptive method the desired BER can be further reduced. This proposed method will be discussed in detail in the following section.

The repeater is a bi-directional duplex amplifier working between base station and mobile station. Based on adaptive interference cancellation technology, the scheme and algorithm of adaptive interference cancellation are studied in this paper. The comprehensive structure of adaptive interference cancellation is implemented on FPGA. The simulation and test results show that the interference problem of the traditional repeater is effectively solved by using the adaptive interference cancellation device.

Exploitation of the spatial dimension in MIMO systems enables co-channel concurrent transmissions between the nodes, thus increases the capacity of the network. A major challenge in the implementation of concurrent transmissions is the mitigation of the interference without causing excessive communication overhead in the network. In this paper, we present a low overhead Concurrent Communications scheme based on Adaptive Interference Cancellation (CC-AIC), which does not require any explicit channel estimations between the nodes in the network. By using the adaptive RLS algorithm for interference cancellation and PN sequence based preamble, we address the channel estimation and communication overhead problems of the previous Space Division-Carrier Sense Multiple Access (SD-CSMA) based protocols. Simulation results show that the proposed scheme effectively cancels the interference caused by other concurrent communications and delivers an aggregate network throughput that is 29%–78% higher than that delivered by the existing SD-CSMA based protocol. In addition, we present experimental results on the interference cancellation performance of the proposed method to prove the practicality of our method.

In this letter, we propose an adaptive step-size algorithm for the adaptive interference canceller (AIC) in the space-time coded DS-CDMA system. To improve the performance of the fixed step-size AIC (FS-AIC), the regular adaptive step-size algorithm is extended in complex domain and applied to the joint AIC and ML decoder scheme. Simulation results show that the joint adaptive step-size AIC (AS-AIC) and ML decoder scheme using the proposed algorithm has better performance than not only the conventional ML decoder but also the joint FS-AIC and ML decoder scheme without much increase of the decoding delay and complexity.

A method of interference cancellation using adaptive antenna arrays is investigated. A proposal for an adaptive antenna array is presented where the number of antenna sensors is minimized. The performance of both the proposed scheme and the ordinary one are compared through computer simulations. The effects of the number of array elements and interference to signal ratio (ISR) on the performance of the adaptive interference canceller is evaluated. It is found that the proposed scheme of the adaptive antenna array exhibits a better performance than the ordinary adaptive antenna array.

In this paper we present an autonomous wide band adaptive interference canceller solution that alleviates the problem of performance degradation of an electronic support system (ESS) operating in a high interference RF environment. The interference canceller improves the sensitivity and dynamic range of a complex receiver to allow the detection of signals of interest that are dominated by local high power interfering signals. It is demonstrated through simulation and prototype system testing that the interference canceller can enhance capability of a state of the art ESS in the presence of both saturating and non-saturating interfering signals, independent of modulation scheme. The results show a 15 – 25 dB cancellation improvement and a detection range improvement of up 16 times when compared with a system without cancellation within the radar horizon.

It is well-known that the capacity of a direct sequence CDMA system is multiple access interference limited. Adaptive antenna arrays and interference cancellation can significantly reduce the multiple access interference and can greatly enhance the system performance. This paper investigates the performance improvement that can be achieved by integrating adaptive antenna array processing and interference cancellation, where the receiver steers the beams of the adaptive antenna towards not only the desired user but the interferers as well to facilitate the interference cancellation process. We analyze how the use of an FFT beamformer preceding the 2-D RAKE receiver reduces the complexity of the receiver without severe degradation in the overall system performance.

In this paper, we propose an adaptive multistage parallel interference cancellation (PIC) structure for multipath fading channels. Similarly to the previous partial interference cancellation (IC) approach suggested in Divsalar et al. (1998), only part of the multiaccess interference (MAI) estimate is canceled at each stage. However, the weights employed in this proposed scheme are derived from an LMS algorithm which tries to minimize the mean-square error between the actual signal received and its replica. The complexity of the proposed adaptive multistage PIC scheme is much lower than that of linear multiuser detectors. Performance of the proposed structure in single-path Rician and multipath Rayleigh fading channels is evaluated by simulations. Our results show that the proposed technique outperforms the existing interference cancellation methods in multipath fading channels.

The performance of the SAGE algorithm in channel parameter estimation could be severely degraded by the error accumulated from the interference cancellation (IC) stage as each path in the channel is estimated sequentially. This is a direct result of removing inaccurate estimate of the interfering paths, and errors occurring at the IC stage for the first few paths will be accumulated and influence the process of the paths later on. Adaptive interference cancellation suggested by Xue [1] employs a set of weights to control the the amount of interferences removed from each interferer. We extend this idea to the SAGE algorithm, where the weights are obtained by minimising the mean square error between the received signal and its estimate through a least mean square (LMS) algorithm. Simulation results show the proposed scheme can outperform the standard SAGE algorithm in non-LOS environments.

Dual Polarization Frequency Reuse (DPFR) effectively doubles the available frequency spectrum by simultaneously transmitting two independent signals over the same frequency band by using orthogonal polarizations. The result is a communication link whose capacity is essentially doubled. Such system gain does not come without its potential impairments. At higher frequencies, depolarization can occur due to several factors such as rain or poor antenna axial ratio thereby inducing interference and reducing link availability. For satellite-to-ground links, Adaptive Cross-Polarization Interference Cancellation (AXPIC) can be employed to mitigate the effects of depolarization and maximize link availability. Using the framework of a modem to be employed in a satellite downlink, AXPIC design trades and their system impacts are discussed. Laboratory tests producing cross-polarization channels are described along with performance test results for a minimum mean-square error (MMSE) AXPIC. As a benchmark with respect to un-restricted system complexity, modulation constrained information rate analysis for DPFR with cross-polarization interference is derived. Information theoretic analysis for a MMSE AXPIC is also presented with laboratory test results showing performance gains consistent with analysis.

We investigate the performance of adaptive interference cancellation receivers for the wideband code division multiple access (WCDMA) uplink physical data channel. For the WCDMA uplink waveform, we derive a blind adaptive receiver (BAR) based an the constant modulus algorithm (CMA), and an multistage adaptive parallel interference cancellation (APIC) receiver. In order to improve the performance of the APIC receiver, we propose a hybrid APIC (H-APIC) receiver structure which uses the CMA based BAR as the first stage of the APIC. We evaluate and compare the performance of the above receivers in a near-far scenario and show that the proposed H-APIC receiver performs better than the APIC receiver.