Fabrice Belveze

Impact of RF impairments on a DS-CDMA receiver

This letter provides an analysis of the impact of classical radio frequency (RF) front-end impairments (RF mismatch and direct current (dc) offset) on the performance of direct-sequence code-division multiple-access (DS-CDMA) receivers; such issues are of particular importance in the case of zero intermediate-frequency (Zero-IF) receivers. Using a standard expression of the baseband signals as well as basic properties of spreading codes used in DS-CDMA communications, we show that the consequence of such RF mismatch and dc offset is essentially a degradation of the wanted signals level and an increase of the noise power. We give closed-form expressions (in E/sub b//N/sub 0/ form) for both. The results are then shown to be in accordance with numerical simulations utilizing the codes of the universal terrestrial radio access in the frequency-division duplex mode downlink standard.

Performance of a digital transmitter leakage LMS-based cancellation algorithm for multi-standard radio-frequency transceivers

This paper deals with a joint estimation algorithm that is dedicated to digital compensation of transmitter leakage pollution in frequency division duplexing transceivers. These transceivers are affected by transmitter to receiver signal leakage. Combined with the nonlinearity of amplifying components in the receiver path, the baseband signal received can be severely polluted by a baseband polluting term. This term is based on the square modulus of the transmitted signal, and it depends on the equivalent transmitter leakage channel which models leakages and the receiver path. Here, we consider a nonconvolutive, time-varying channel that is modeled by a time-varying complex gain and the presence of a fractional delay, modeling the propagation effects into the receiver. The complex gain is a sum of two components, a constant term that models static effects, and a first-order autoregressive model that approximates the time variation of the transmitter leakage channel. We focus here on a fully digital approach, using digital signal processing techniques and knowledge of the transmitted samples to mitigate the pollution. We first express the asymptotic performance of a transmitter leakage gain estimator piloted by a reference-based least-mean-square (LMS) approach in the synchronized case, and then we derive the influence of the fractional delay. We show that, in practice, the fractional delay cannot be neglected, and we propose a joint estimation of the fractional delay and the transmitter leakage gain to perform digital compensation. The proposed method is adaptive, recursive and online, and it has low complexity. This algorithm, that is developed for a flat transmitter leakage channel case, is seen to be robust in a typical selective channel simulation case, and more suitable than a classic multi-tap LMS scheme proposed in the literature. We study the performance of a Tx Leakage compensation algorithm.The baseband model is parametrized by a complex gain and a fractional delay.A recursive online joint estimation (complex gain, fractional delay) is proposed.All theoretical asymptotic performance and optimal step formulae are derived.

Joint estimation of complex gain and fractional delay for Tx leakage compensation in FDD transceivers

This paper deals with a joint estimation algorithm dedicated to the digital compensation of the Tx leakage in FDD transceivers. Such transceivers are affected from transmitter-receiver signal leakage. Combined with non linearity of components in the received path, it leads to a pollution in the baseband signal. The baseband polluting term depends on the equivalent Tx leakage channel, modeling leakages and the received path. In this paper we consider a first-order autoregressive model to approximate Tx-Leakage channel gain variations, and the presence of a fractional delay, modeling propagation effects. We first express asymptotic performance of a gain estimator based on a least-mean-square (LMS) approach in the synchronized case and then derive the influence of the fractional delay. We show that in practice, the fractional delay can not be neglected and we propose a joint estimation of the fractional delay and the cross-channel gain to perform the digital compensation. The proposed method is recursive, online and exhibits low complexity.

On the performance of digital adaptive spur cancellation for multi-standard radio frequency transceivers

This study deals with the asymptotic performance of a multiple-spur cancellation scheme. Radio frequency transceivers are now multi-standard and specific impairment can occur. The clock harmonics, called spurs, can leak into the signal band of the reception stage, and thus degrade the performance. The performance of a fully digital approach is presented here. A one-spur cancellation scheme is first described, for which we exploit the a priori knowledge of the spur frequency to create a reference of the polluting tone with the same frequency. A least-mean-square (LMS) algorithm block that uses this reference to mitigate the polluter is designed. However, due to imperfections in the physical components, there is a shift between the a priori frequency and the actual frequency of the spur, and the spur is affected by Brownian phase noise. Under these circumstances, we study the asymptotic and transient performance of the algorithm. We next improve the transient performance by adding a previously proposed adaptive-step-size process. In a second part of this paper, we present a multiple-spur parallel approach that is based on the one-spur cancellation scheme, for which we provide a closed-form expression of the asymptotic signal-plus-noise interference ratio in the presence of frequency shifts and phase noise.

Specifying receiver IP2 and IP3 based on tolerance to modulated blockers

This paper provides an analysis of the impact of amplitude modulated blocking signals on receiver performance due to device nonlinearity. Using a standard polynomial model of nonlinearity, we derive limitations on the receiver SNR capabilities, depending on the blocking signal modulation statistical properties. The phenomena that we focus on are cross-modulation due to odd-order nonlinearity and amplitude demodulation due to even-order nonlinearity. The results are then detailed for two types of blocking signal modulations: GSM/EDGE modified 8PSK and UTRA/FDD uplink HPSK.

Performance of Fractional Delay Estimation in Joint Estimation Algorithm Dedicated to Digital Tx Leakage Compensation in FDD Transceivers

This paper deals with the performance of the fractional delay estimator in the joint complex amplitude / delay estimation algorithm dedicated to digital Tx leakage compensation in FDD transceivers. Such transceivers are affected from transmitter-receiver signal leakage. Combined with non linearity of components in the received path, it leads to a pollution in the baseband signal. The baseband polluting term depends on the equivalent Tx leakage channel, modeling leakages and the received path. We have proposed in [7, 8] a joint estimation of the complex gain and the fractional delay and derived asymptotic performance of the complex gain estimator, that showed the necessity of the fractional delay estimation. In this paper, we propose a comprehensive study of the fractional delay estimation algorithm and its analytic performance. The study is based on the analysis of the S-curve and loop noise variance of the timing error detector, from which an approximation of the asymptotic performance of the joint estimation algorithm is derived.