Andreas Frotzscher

Baseband analysis of Tx leakage in WCDMA Zero-IF-receivers

Frequency division duplex transceivers employing the zero-if principle suffers from Tx leakage. In this contribution a baseband representation of the Tx leakage impact in zero-if receivers is derived and the statistical properties of the involved baseband signals are analysed. Additionally requirements on the digital compensation of Tx leakage are discussed, based on measurement results of the Tx-Rx isolation of the duplexer as well as properties of the receive branch. Thus, a framework for the digital compensation of Tx leakage at the discrete baseband is presented. Simulation results are used to validate the theoretically predicted spectral shape of the Tx leakage impact and to evaluate the influence of Tx leakage on the system performance.

A Stochastic Gradient LMS Algorithm for Digital Compensation of Tx Leakage in Zero-IF-Receivers

In frequency division duplex transceivers the transmit signal is leaking through the duplexer into the receive branch. For the case of zero-IF receivers the nonlinearity of the I/Q down converter generates 2nd order intermodulation products of the transmitter leakage, causing severe interference to the desired receive signal in the baseband. In this paper we present a stochastic gradient least mean square algorithm based on a linear approximation to compensate digitally the interference caused by Tx leakage in the baseband of the receive branch. Simulation results are used to evaluate the impact of Tx leakage on the system performance. Furthermore they point out, that the least mean square compensation algorithm significantly improves the system performance and gets very close to the maximum achievable performance using this linear approximation.

Oscillator Phase Noise compensation using Kalman tracking

Phase Noise (PN) is a serious challenge in wireless transmission systems as it can cause significant degradation of the system performance. Recent publications propose iterative PN compensation algorithms for single or multicarrier systems. In this paper we will present an unscented Kalman filter PN tracking algorithm working in time domain, which is independent of the underlying system. Furthermore, we propose a reduced complexity tracking algorithm, where we perform an interpolation between the estimated PN samples. Simulation results for an OFDM setup show that by using this technique the system performance can be improved significantly.

Digital compensation of transmitter leakage in FDD zero‐IF receivers

Transmitter leakage (TxL) has a significant impact on the performance of frequency division duplex devices using zero-IF receivers and thus requires a suitable compensation. In contrast to analog approaches, digital TxL compensation approaches can easily be reconfigured and therefore are highly attractive for multiband mobile devices. In this contribution, we present a system model, describing the TxL impact on the received digital baseband signal. Furthermore, we show analytically that TxL causes an additional, irreversible signal-to-noise loss due to the quantisation in the analog-to-digital converter, which limits the applicability of a digital TxL compensation. However, this signal-to-noise ratio loss remains negligibly small as long as the TxL interference does not exceed significantly the desired received signal. For TxL to be compensated digitally, the TxL channel needs be estimated. In this work, we present two TxL channel estimation approaches suitable for frequency flat and frequency selective channels. It is shown that the usage of these approaches mitigates effectively the TxL impact on the system performance. Thus, the system designer can allow much stronger TxL, which significantly relaxes the requirements on the transmitter‐receiver isolation of the duplexer and the linearity of the analog receiver frontend. Copyright

Least Squares Estimation for the Digital Compensation of Tx Leakage in zero-IF Receivers

Transmitter Leakage has a significant impact on the system performance in mobile devices using zero-IF receivers and thus requires a suitable compensation. In contrast to analog approaches, digital Tx Leakage compensation approaches can easily be reconfigured and therefore are highly attractive for future mobile devices, using software defined radios. In this contribution we present a digital Tx Leakage compensation approach which uses a Least Squares estimator. The AD conversion of the Tx Leakage interference causes an additional SNR loss w.r.t. the desired received signal and thus limits the applicability of the digital Tx Leakage compensation. We show that the presented Least Squares approach reaches almost this upper limit and mitigates the Tx Leakage by 25 dB, considering a 8-bit uniform mid-rise ADC. Thus, using this approach, the system designer can allow much stronger Tx Leakage, which significantly relaxes the requirements on the linearity and the Tx-Rx isolation of the analog front end.

On the Time Variance of Tx Leakage in FDD Zero-IF Transceivers

Transmitter Leakage has a significant im- pact on zero-IF transceivers for mobile FDD terminals and therefore must be compensated. When Tx Leakage compensation approaches are designed, their capability to adapt to changing leakage conditions must be specified. Therefore, in this contribution we analyse the time vari- ance of Tx Leakage considering the UMTS SAW duplexer B7632 of EPCOS as an example and derive a worst case estimate of Tx Leakage coherence time. Index Terms—Tx Leakage, duplexer, time variance, FDD transceivers

On the Performance of OFDM in Zero-IF Receivers Impaired by Tx Leakage

Transmitter Leakage has a significant impact on the system performance in mobile devices using zero-IF receivers. In this contribution, the statistical properties of the Tx Leakage impact in zero-IF receivers are derived, in the context of Uplink and Downlink OFDM transmission. In order to design suitable algorithms for the digital compensation of Tx Leakage in OFDM communication systems, an accurate modeling of the corresponding performance loss is required.We therefore provide a statistical description of Tx Leakage effects on OFDM signals, which is used to compute bit error rates and mutual information.

Tx Leakage Impact on Analog-Digital Conversion in Zero-IF Receivers

Transmitter Leakage has a significant impact on the system performance in mobile devices using zero-IF receivers and thus requires a suitable compensation. In contrast to analog approaches, digital Tx Leakage compensation approaches can easily be reconfigured and therefore are highly attractive for future mobile devices, using software defined radios. In this contribution we show that Tx Leakage reduces the SNR at the ADC output. However, this SNR loss is negligibly weak in presence of moderate Tx Leakage. This proves that compensating the Tx Leakage in digital domain is a suitable approach to lower the requirements on the analog transceiver front end and to facilitate the design of software defined radios.

A Detection Algorithm for Clipped OFDM Signals Using the IDFT-Matrix

A major drawback of the orthogonal frequency division multiplex (OFDM) principle is the high dynamic range of the transmit signal. The transmit power amplifier (PA) and other elements in the signal path have to operate at high input power backoff (IBO), which decreases the efficiency of the PA and leads to higher costs. This paper presents a novel receive algorithm for OFDM signals with limited dynamic range. The received signal in the time domain (TD) is examined in order to estimate those samples which have not been distorted by the PA. In the frequency domain (FD), some of the most reliable subcarrier symbols are detected. The combination of the information from TD as well as from FD allows the computation of the remaining subcarrier symbols by using a truncated version of an inverse discrete Fourier transform (IDFT) matrix. The simulation results show that this receive algorithm significantly improves the error rate of OFDM systems impaired by clipping at the transmitter.

Project FAST - fast actuators sensors & transceivers

In this paper we give an overview of the German project cluster FAST which targets a technical breakthrough by real-time with latencies below 1 ms to enable advanced applications in the area of connectivity, traffic, manufacturing and health. FAST is based on 25 technical projects conducted by over 80 partners in industry and research. The innovations are outlined and include high frequency communication aspects such as 20 Gb/s communications at 200 GHz, real-time OFDM MIMO imaging radar, real-time GPS navigation with < 1 m accuracy, encryption using the unique air channel between nodes, time- and scenario-dependent latency measurements, the mobile edge cloud concept as well as synchronization via Ethernet with achieved measured accuracy of 1 ns. Moreover, this paper aims at stimulating potential cooperation between Latin America and Germany.