Hooman Habibi

Experimental Evaluation of an Adaptive Nonlinear Interference Suppressor for Multimode Transceivers

In multimode transceivers, the transmitter for one communication standard may induce a strong interference in the receiver for another standard. Using linear filtering techniques to suppress this interference requires a receiver with a very large dynamic range, leading to an excessive power consumption. A much more power efficient approach suppresses the interference using an adaptive nonlinear interference suppressor (NIS). In previous work an ideal model was used to derive an adaptation method and study the receiver performance afforded by the NIS. In this paper, we present experimental results of a receiver that uses an implementation of the NIS, fabricated in 140 nm complementary metal-oxide-semiconductor technology. Main imperfections that limit the NIS performance are identified, simple models are developed that explain the experimental results, and for the key imperfections, low-complexity digital compensation and calibration methods are proposed. These digital methods permit the use of lower-performance analogue circuits, thus further reducing the transceiver cost and power consumption. The experimental results show that the NIS can achieve a substantial interference suppression at attractive complexity and power dissipation.

Suppression of Constant Modulus Interference in Multimode Transceivers by Closed-Loop Tuning of a Nonlinear Circuit

In multimode transceivers, the transmitter for one communication standard may induce a large interferer in the receiver for another standard. To linearly suppress this interferer, which can be several orders of magnitude larger than the desired received signal, the receiver should have a very large linear dynamic range, resulting in excessive power consumption. Many of potential interferers have a constant modulus modulation. Baier and Friederichs introduced a tuneable nonlinear circuit which can suppress a constant modulus interferer without excessive power consumption. Since an open- loop tuning method is used, the worst- case interference suppression was strongly limited by inaccuracy of circuit components. To alleviate this limitation, we propose a closed- loop tuning method that exploits the locally available interference as side information. Our analysis shows that the proposed method can strongly suppress the interferer while a symbol error rate performance close to that of an exactly linear receiver is achieved. Simulation results for a practical scenario confirm this analysis, and promise much smaller power consumption than for linear interference suppression approaches.

Suppression of constant modulus interference in multimode transceivers using an adaptive nonlinear circuit

In multimode transceivers, the transmitter for one communication standard may induce a large interference in the receiver for another standard. Using linear techniques to suppress this interference requires a receiver with a very large dynamic range, leading to an excessive power consumption. A much more power efficient approach suppresses the interference using an adaptive Nonlinear Interference Suppressor (NIS). In previous works an ideal model was used to study the receiver performance afforded by the NIS. In this paper we present experimental results of a transceiver testbed that uses an implementation of the NIS, fabricated in 140 nm CMOS technology. Main imperfections that limit the NIS performance are identified and simple models are presented that explain the experimental results. Even with these imperfections, a substantial interference suppression is achieved.

Analysis of an Adaptive Nonlinear Interference Suppressor for Wireless Multimode Transceivers

In multimode transceivers, the transmitter for one communication standard may induce strong interference in the receiver for another standard, often exceeding the desired signal by many tens of decibels. To linearly suppress this interference, the receiver requires a very large linear dynamic range, resulting in excessive power consumption. In a recent paper, a nonlinear block, which requires an adaptation signal proportional to the envelope of the received interference, has been used to strongly suppress the interference. In that work, the required adaptation signal for the nonlinear block has been determined analytically. In this paper, we quantify the required accuracy for the adaptation signal to properly suppress the interference while keeping the degradation to the receiver symbol error rate (SER) negligible. To provide the required accuracy, we propose a closed-loop method that calculates the adaptation signal based on a model, which describes the received interference in terms of the locally available baseband interference. We propose a method to adapt this model during the operation of the transceiver such that the power of the residual interference at the output of the nonlinear block is minimized. Our analysis shows that the proposed method can strongly suppress the interference while a SER close to that of an exactly linear receiver is achieved. Simulation results for a practical scenario validate this analysis.

Smart Self-interference Suppression by Exploiting a Nonlinearity

A 1.8GHz RF amplifier implemented in 0.14um CMOS with frequency-independent blocker suppression is presented. The blocker suppression functionality is obtained by the adaptation of a nonlinear input–output transfer according to the blocker amplitude. Since superposition does not apply to nonlinear transfer functions, the behavior of such a transfer for strong undesired signals is different from the behavior for weak desired signals, which is exploited here. In the presence of a 0 to +11 dBm RF blocker, a voltage gain for weak signals of respectively 7.6–9.4 dB and IIP3 >4 dBm are measured, while the blocker is suppressed by more than 35 dB. In case of no blocker present at the input, the circuit is set to amplifier mode providing 17 dB of voltage gain and an IIP3 of 6.6 dBm while consuming 3 mW. Application areas are coexistence in multi-radio devices and dealing with TX leakage in FDD systems.

Performance of a multimode LTE/WiMAX transceiver including the Nonlinear Interference Suppressor

This paper deals with the implementation of a Nonlinear Interference Suppressor (NIS) into a wireless LTE transceiver. This within the context of high energy efficient multi-standard transceivers controlled by a cognitive radio platform. In multimode transceivers, the transmitter for one communication standard may induce a large interferer in the receiver for another standard. To linearly suppress this interferer, which can be several orders of magnitude larger than the desired received signal, the receiver should have a very large linear dynamic range, resulting in excessive power consumption. For this reason, we consider the NIS, a closed-loop tuning method that exploits the locally available interference as side information. The wireless LTE transceiver model, includes all the baseband signal treatment blocks and the RF front-end of a low IF direct conversion receiver architecture. A mobile WiMAX signal is considered as the interference signal at the receiver. The obtained symbol error rate (SER) is observed for different system configurations. Matlab simulation results in this practical scenario show that the NIS can strongly suppress the interferer while a symbol error rate performance close to that of an exactly linear receiver is achieved. This results permit to identify perspective directions for the better multi-standard and high energy efficient transceivers implementation.

Digital Compensation of Cross-Modulation Distortion in Multimode Transceivers

In a multimode transceiver, the transmitter for one communication standard induces a large interference on the receiver for another one. When this large interference passes through the inherently nonlinear receiver Front-End (FE), it introduces Cross- Modulation (CM) distortion. Increasing the FE linearity to lower the CM distortion leads to unacceptable power consumption for a handheld device. Considering the continuous increase of digital computation power governed by Moores law an attractive alternative approach is to digitally compensate for the CM distortion. An existing CM compensation method is tailored to single-mode transceivers and requires an auxiliary FE. By using the locally available transmitted interference in the multimode transceiver, we propose a CM compensation method which requires no additional analog hardware. Hence the power consumption and complexity of the multimode transceiver will be reduced significantly.