Showing papers by "Stefan Kaiser published in 2005"

MC-CDMA versus OFDMA in cellular environments

Abstract: In this paper, two candidates for a next generation (4G) downlink system in a multi-cell environment are studied in respect to their error performance. We investigate on the one hand, an orthogonal frequency division multiplexing (OFDM) based multiple access scheme (OFDMA), and on the other hand, a multi-carrier code division multiple access (MC-CDMA) scheme. The studies of both transmission schemes are done in a cellular structure. The cellular environment model takes into account path loss and shadowing depending on the position of the mobile terminal. To enhance the performance of OFDMA, we introduce a radio resource management (RRM). Error performances are given to compare the two multiple access proposals. The results show that OFDMA outperforms MC-CDMA at the edge of the cell for low resource loads by using the RRM. In the inner part of the cell, OFDMA can gain up to 0.5 dB at a target bit error rate of 10−3 in a fully-loaded system. For a not fully-loaded system, MC-CDMA surpasses the OFDMA performance by utilizing its whole diversity of used sub-carriers. In this scenario, MC-CDMA can even gain 2 dB compared to OFDMA.

Method for transmission of digital information signals with a plurality of antennas

Abstract: In einem Ubertragungssystem fur digitale Nachrichtensignale werden zum Reduzieren der negativen Auswirkungen des Signalschwunds in einem Mehrwegeausbreitungskanal sendeseitig durch zeitdispersive diskontinuierliche Verschiebung die Sendesignale an mehreren Antennen (5) oder Antennengruppen verschieden modifiziert, so dass man empfangsseitig in der Lage ist, das Signal auf Grund der zusatzlichen Diversitat korrekt zu detektieren. Anwendung bei Funkubertragungssystemen und bei anderen, von zeitlicher Selektivitat profitierenden Ubertragungssystemen

Exploitation of Diversity in MC-CDMA Systems

Abstract: MC-CDMA has an additional degree of freedom to exploit diversity compared to OFDMA or MC-TDMA due to spreading. This paper analyzes the achievable BER lower bounds for different MC-CDMA schemes exploiting channel state information (CSI) at the transmitter, the receiver, or both. Using channel knowledge at both sides is referred to as combined-equalization. Different design criteria for single-user combined-equalization are investigated and the corresponding lower bounds are derived. It is shown that the new lower bounds for combined-equalization outperform the known lower bounds for MC-CDMA systems, which exploit CSI only at the transmitter or receiver.