Proposed Cancellation Technique Research Articles

Interference avoidance and cancellation in automotive OFDM radar networks

With increasing use of millimeter-wave radars in driving safety applications, interference between vehicles becomes a significant issue. Moreover, oscillator imperfections and relative velocity effects induce inter-carrier interference (ICI) owing to frequency offset, leading to degradation of target detection. In this paper, time-frequency resources are divided into several orthogonal logical channels according to the time-frequency division (TFD) scheme. We propose a two-stage interference mitigation method. First, an interference avoidance technique is designed for each piece of radar equipment (RE) to select logical channels with the least ICI. Then, each RE reconstructs and cancels interference according to estimated parameters based on the proposed interference cancellation technique. Computer simulations reveal that the proposed interference avoidance technique can approximately achieve the performance of ground truth, especially when the number of interferers is small. In addition, noise enhancement effects can be effectively mitigated through the proposed cancellation technique.

Adaptive Nonlinear RF Cancellation for Improved Isolation in Simultaneous Transmit–Receive Systems

This paper proposes an active radio frequency (RF) cancellation solution to suppress the transmitter (TX) passband leakage signal in radio transceivers supporting simultaneous transmission and reception. The proposed technique is based on creating an opposite-phase baseband equivalent replica of the TX leakage signal in the transceiver digital front-end through adaptive nonlinear filtering of the known transmit data, to facilitate highly accurate cancellation under a nonlinear TX power amplifier (PA). The active RF cancellation is then accomplished by employing an auxiliary transmitter chain, to generate the actual RF cancellation signal, and combining it with the received signal at the receiver (RX) low noise amplifier (LNA) input. A closed-loop parameter learning approach, based on the decorrelation principle, is also developed to efficiently estimate the coefficients of the nonlinear cancellation filter in the presence of a nonlinear TX PA with memory, finite passive isolation, and a nonlinear RX LNA. The performance of the proposed cancellation technique is evaluated through comprehensive RF measurements adopting commercial LTE-Advanced transceiver hardware components. The results show that the proposed technique can provide an additional suppression of up to 54 dB for the TX passband leakage signal at the RX LNA input, even at considerably high transmit power levels and with wide transmission bandwidths. Such novel cancellation solution can therefore substantially improve the TX-RX isolation, hence reducing the requirements on passive isolation and RF component linearity, as well as increasing the efficiency and flexibility of the RF spectrum use in the emerging 5G radio networks.

Digital Suppression of Transmitter Leakage in FDD RF Transceivers: Aliasing Elimination and Model Selection

The transmitter (TX)-induced interference due to power amplifier nonlinearities poses severe desensitization problems to the receiver chain in frequency-division duplexing transceivers. Due to nonlinear signal process involved, a high sampling rate is normally required in the existing digital suppression approaches, which can result in high cost and high power consumption in wideband systems. In this paper, a new digital suppression model is proposed to cancel the TX leakage at baseband with a low sampling rate. The cancellation model is based on the modified decomposed vector rotation model. With the addition of cross-term products, the enhanced model is capable of eliminating the aliasing effect arising from the reduced sampling rate. Theoretical analysis of aliasing elimination is presented, and the algorithm is subsequently verified by both simulation and experiment results, confirming the effectiveness and feasibility of the proposed cancellation technique for TX leakage suppression. Compared with conventional solutions, the new approach uses much less hardware resource and consumes much lower power while achieving comparable performance.

A high precision analog multiplexer for multi-channel neural recording micro-systems

This paper introduces a high precision analog multiplexer to be used in multi-channel neural recording micro-systems. In any time-division multiplexing (TDM) system, the accuracy of the analog switches within the multiplexer is a critical parameter to determine overall performance of the system. To satisfy the accuracy requirements of the switch, a novel technique to minimize the charge injection and clock feed-through errors by using a very simple structure is proposed. Moreover, an innovative approach to increase the off-resistance of the switch and consequently minimizing its leakage current is presented. In order to evaluate the performance of the proposed switch, simulations are done in a 0.18μm standard CMOS technology. Simulation results show that switch induced errors are significantly eliminated by using the proposed cancellation technique. The output error charge due to charge injection and clock feed-through over a wide range of the input signal variation is very low (less than 1.53 fC). Also Simulation results show that the proposed switch achieves signal to noise plus distortion ratio (SNDR) of 100.6 dB, effective number of bits (ENOB) of 16.42, total harmonic distortion (THD) of −100.88 dB and spurious-free dynamic range (SFDR) of 101.47 dB for a 1 kHz sinusoidal input of 800 mv peak-to-peak amplitude at 20 kHz sampling rate with a 1.8 V supply voltage. In addition to the switched induced errors, special care has to be taken with regard to the crosstalk effects while designing of the analog multiplexers. In this work, by using an appropriate analog switch with considering crosstalk requirements, using suitable buffers prior to the multiplexer input channels and designing a proper layout, the total crosstalk between adjacent channels is negligible. The post layout simulation of crosstalk shows that the total crosstalk at a sampling rate of 20 kHz per channel is less than −80 dB.

A novel analog switch for high‐precision switched‐capacitor applications

SummaryThe performance of a switched‐capacitor circuit strongly depends on its analog switches. This paper introduces a new technique to design a high‐precision analog metal‐oxide‐semiconductor switch for switched‐capacitor applications. The accuracy of analog switches is a critical parameter to determine overall performance of the discrete‐time analog systems. To satisfy the accuracy requirements of the switch, a novel technique to minimize the charge injection and clock feedthrough errors by using a very simple structure is proposed. Moreover, an innovative approach to increase the OFF resistance of the switch and consequently minimizing its leakage current is presented. To evaluate the performance of the proposed switch, simulations are done in TSMC 0.18μm standard complementary metal‐oxide‐semiconductor technology with BSIM3V3 device models. The ON and OFF resistances of the switch are one of the most important factors that should be considered while investigating analog switches. The ON resistance of the proposed switch is less than 560Ω over entire input signal range which completely satisfies the tracking bandwidth requirements. In addition, since the proposed switch provides an ultrahigh OFF resistance in the range of several GΩs, the leakage current of the proposed switch is negligible. Simulation results also show that switch‐induced errors are significantly eliminated by using the proposed cancellation technique. The output error charge due to charge injection and clock feedthrough over a wide range of input signal variation is very low (less than 1.6 fC). Moreover, simulation results show that the proposed switch achieves signal to noise plus distortion ratio of 80.55 dB, effective number of bits of 13.08, total harmonic distortion of −81.41 dB, and spurious‐free dynamic range of 87.7 dB for a 2.5‐MHz sinusoidal input of 800‐mV peak‐to‐peak amplitude at 200‐MHz sampling rate with a 1.8‐V supply voltage. Consequently, the simulation results verify that the proposed switch can significantly improve the dynamic and static performances of a switched‐capacitor circuit.

Phase-Locked Coherent Demodulator With Feedback and Sampling for Optically Phase-Modulated Microwave Links

A novel phase-locked coherent optical phase demodulator with feedback and sampling is presented and investigated for high-linearity microwave photonic links. The overall receiver concept is novel in terms that we use feedback loop for linear phase demodulation and optical sampling to achieve operation at high RF signal frequencies. The phase-locked demodulator is to be used for RF signal demodulation of optically phase-modulated analog links. We aim at operating the demodulator for short-range applications since the demodulator only recovers the phase. A new time-domain numerical model is developed and the calculated results are in good agreement with measurements. The effect of amplitude and timing jitter associated with the optical pulse source is also taken into account. Stochastic Euler scheme is used to solve stochastic differential equations associated with amplitude and timing jitter. Using the model, we investigate how loop gain, tracking phase-modulator nonlinearities and amplitude modulation influence the signal-to-intermodulation ratio (SIR) of the demodulated signal. Furthermore, in order to alleviate nonlinearities associated with the tracking phase modulator, we report on a novel cancellation technique. The proposed cancellation technique is input RF signal power and frequency independent leading to a significant increase in dynamic range of the coherent demodulator. This technique demonstrates that large values of the signal-to-intermodulation ratio of the demodulated signal can be obtained even though the tracking phase modulator is fairly nonlinear, and thereby relaxing the linearity requirements for the tracking phase modulator. The demodulator is capable of operating at high frequencies, by using optical sampling to downconvert the high-frequency input RF signal to the frequency range of the baseband loop. Using the model the effect of optical sampling on the signal demodulation is investigated. The simulation results show that the operation of the sampling demodulator resembles the operation of the baseband demodulator for very short optical pulses (<2 ps). We also investigate how signal-to-noise-ratio of the demodulator is affected by timing and amplitude jitter of the pulsed optical source. Finally, experimental demonstration of the sampling loop using the phase-locked demodulator is presented. We show that an improvement of 14.1 dB in spur-free-dynamic-range is obtained using the proposed phase-locked coherent demodulator compared to the open loop sampling.

Frequency-Domain Multi-Stage Soft Interference Cancellation for DS-CDMA Uplink Signal Transmission

SUMMARY It is well-known that, in DS-CDMA downlink signal transmission, frequency-domain equalization (FDE) based on minimum mean square error (MMSE) criterion can replace rake combining to achieve much improved bit error rate (BER) performance in severe frequencyselective fading channel. However, in uplink signal transmission, as each user’s signal goes through a different channel, a severe multi-user interference (MUI) is produced and the uplink BER performance severely degrades compared to the downlink. When a small spreading factor is used, the uplink BER performance further degrades due to inter-chip interference (ICI). In this paper, we propose a frequency-domain multi-stage soft interference cancellation scheme for the DS-CDMA uplink and the achievable BER performance is evaluated by computer simulation. The BER performance comparison of the proposed cancellation technique and the multiuser detection (MUD) is also presented.

Dynamic range enhancement of a novel phase-locked coherent optical phase demodulator

We report on a novel cancellation technique, for reducing the nonlinearity associated with the tracking phase-modulator in recently proposed phase-locked coherent demodulator for phase modulated analog optical links. The proposed cancellation technique is input RF signal power and frequency independent leading to a significant increase in dynamic range of the coherent demodulator. Furthermore, this technique demonstrates that large values of the signal-to-intermodulation ratio of the demodulated signal can be obtained even though the tracking phase modulator is fairly nonlinear, and thereby relaxing the linearity requirements for the tracking phase modulator. A new model is developed and the calculated results are in good agreement with measurements.