Marco Krondorf

GFDM - Generalized Frequency Division Multiplexing

This paper presents the GFDM system, a generalized digital multi-carrier transceiver concept. GFDM is based on traditional filter bank multi-branch multi- carrier concepts which are now implemented digitally. Our GFDM approach exhibits some attractive features which are of particular importance for scenarios exhibiting high degrees of spectrum fragmentation. Spectrum fragmentation is a typical technical challenge of digital dividend use cases, exploiting spectrum white spaces in the TV UHF bands which are located in close proximity to allocated spectrum. Specifically, the GFDM features are a lower PAPR compared to OFDM, a ultra-low out-of- band radiation due adjustable Tx-filtering and last but not least a block-based transmission using cyclic prefix insertion and efficient FFT-based equalization. GFDM enables frequency and time domain multi-user scheduling comparable to OFDM and provides an efficient alternative for white space aggregation even in heavily fragmented spectrum regions.

Symbol Error Rate of OFDM Systems with Carrier Frequency Offset and Channel Estimation Error in Frequency Selective Fading Channels

In this paper we present an analytical approach to evaluate the symbol error rate (SER) of OFDM systems subject to carrier frequency offset (CFO) and channel estimation error in Rayleigh flat fading and frequency selective fading channels. Based on correct modeling of the correlation between channel estimates and received signals with carrier frequency offset, the symbol error rate can be numerically evaluated by averaging symbol error rate on different subcarriers using an analytical expression of double integrals. The results illustrate that our analysis can approximate the simulative performance very accurately if the power delay profile of fading channels and carrier frequency offset are known.

OFDM link performance analysis under various receiver impairments

We present a methodology for OFDM link capacity and bit error rate calculation that jointly captures the aggregate effects of various real life receiver imperfections such as: carrier frequency offset, channel estimation error, outdated channel state information due to time selective channel properties and flat receiver I/Q imbalance. Since such an analytical analysis is still missing in literature, we intend to provide a numerical tool for realistic OFDM performance evaluation that takes into account mobile channel characteristics as well as multiple receiver antenna branches. In our main contribution, we derived the probability density function (PDF) of the received frequency domain signal with respect to the mentioned impairments and use this PDF to numerically calculate both bit error rate and OFDM link capacity. Finally, we illustrate which of the mentioned impairments has the most severe impact on OFDM system performance.

Numerical performance evaluation for Alamouti space time coded OFDM under receiver impairments

We present a methodology for the analysis of the capacity and symbol/bit error rate performance of Alamouti space time coded OFDM links that jointly captures the aggregate effects of real life receiver imperfections and mobile channel effects. Specifically, we investigate carrier frequency offset, channel estimation error, outdated channel state information due to time selective channel properties and flat receiver I/Q imbalance. Hence, we provide a numerical tool for realistic Alamouti space time coded (STC) OFDM performance evaluation. The main contribution of this work is the derivation of the probability density function of the received frequency domain signal with respect to the mentioned impairments. The density function is then used for numerical calculations of both the symbol and bit error rates, as well as the capacity for Alamouti STC OFDM links. Finally, we illustrate which of the mentioned impairments has the most severe impact on the overall STC OFDM system performance. The abstract goes here.

On Synchronization of Opportunistic Radio OFDM Systems

In this paper we present a study on pilot aided time and frequency synchronization for opportunistic radio (OR) OFDM systems which apply adaptive subcarrier allocation techniques to either avoid narrow band interference or to prevent licensed spectrum owners (so called primary users) from harmful disturbance. The variable subcarrier allocation of OR OFDM requires adaptive preamble designs to use state-of-the-art OFDM synchronization methods. Since these synchronization algorithms mainly require repetitive time-domain pilot structures, the novel task of providing repetitive pilot signals under arbitrary sub-carrier allocations is addressed in the paper. Furthermore we analyze the stochastic characteristics of the OR-OFDM carrier frequency offset synchronization procedure.

Numerical Performance Evaluation for OFDM Systems Affected by Phase Noise and Channel Estimation Errors

In this paper we present a numerical approach to evaluate the bit error rate (BER) and mutual information of OFDM links subject to phase noise, channel estimation error and frequency selective fading channels. Based on the analytical modeling of the correlation between channel estimates and received signals affected by phase noise, the statistical properties of the received signal can be numerically evaluated by means of a probability density function. The results illustrate that our analysis can approximate the simulative performance very accurately if the power delay profile of the fading channels and the phase noise properties are known. Hence, we present a useful numerical tool for OFDM performance analysis under the presence of phase noise that can be used for planning and design of mobile device architectures, without running extensive simulations.

Numerical Performance Evaluation of OFDM Systems Affected by Transmitter Nonlinearities, Phase Noise and Channel Estimation Errors

In this contribution we present a numerical approach to evaluate the bit error rate and mutual information of OFDM links affected by transmitter nonlinearities, phase noise, channel estimation error and frequency selective channels. The basic principle of the presented work is the correct modeling of the correlation between channel estimates and received signals. Using the statistical properties of the received signal we derive a semi-analytic expression of the received signal probability density function. The obtained PDF is a useful tool for OFDM performance analysis. For example the PDF can be used for planning and design of wireless networks, without running extensive simulations.

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.

Carrier Frequency Dependent Downlink Spectral Efficiency of Cellular LTE Deployments

This paper explains a system level evaluation framework which allows performance assessment of cellular OFDM-based systems at different carrier frequencies. In the numerical examples we model the downlink transmission of an 3GPP LTE deployment.

Symbol Error Rate Calculation for Alamouti Space Time Coded OFDM in Direct Conversion Receivers

In this paper we present an analytical approach to evaluate the M-QAM symbol error rate (SER) of Alamouti space time coded OFDM direct conversion receivers subject to carrier frequency offset (CFO), channel estimation errors, outdated channel state information and flat receiver I/Q imbalance in Rayleigh time and frequency selective fading channels. Based on correct modeling of the correlation between channel estimates and received signals with carrier frequency offset and receiver I/Q imbalance, the SER can be numerically evaluated by averaging symbol error rates on different subcarriers using an analytical expression of double integrals. The results illustrate that the analysis can approximate the simulative performance very accurately if the power delay profile of fading channels, the receiver I/Q imbalance parameters and carrier frequency offset are known.