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German Aerospace Center


Latest Content From German Aerospace Center

Whitepaper: On the Peak-to-Average Power Ratio of Pre-Equalized Multi-Carrier Code-Division Multiple-Access Transmissions

by German Aerospace CenterJan 01, 2008

Recently, pre-equalization for Multi-Carrier Code-Division Multiple-Access (MC-CDMA) systems has attained increased interest. In addition, combined-equalization has been proposed to further enhance the error rate performance of conventional MC-CDMA systems. However, an important issue, Peak-to-Average Power Ratio (PAPR), has not been addressed within such systems in the literature. The purpose of this paper is to fill this gap. In particular, the paper focuses on uplink MCCDMA with pre- or


Whitepaper: On Pilot-Symbol Aided Channel Estimation for MC-CDMA in the Presence of Cellular Interference

by German Aerospace CenterJan 01, 2008

Multi-carrier modulation, in particular Orthogonal Frequency Division Multiplexing (OFDM), has been successfully applied to various digital communications systems. OFDM can be efficiently implemented by using the Discrete Fourier Transform (DFT). Furthermore, for the transmission of high data rates its robustness in transmission through dispersive channels is a major advantage. For Multi-Carrier CDMA (MC-CDMA), spreading in frequency and/or time direction is introduced in addition to the OFDM


Whitepaper: Pre-Compensation of Fading Channels for Uplink Time Division Duplex MC-CDMA Systems

by German Aerospace CenterJan 01, 2008

Over the past several years MC-CDMA emerged as the most promising candidate for the downlink in next generation of wireless mobile radio systems. On the other hand, considering MC-CDMA for uplink transmission introduces some additional problems due to the more complex propagation conditions. Especially, channel estimation and channel compensation are more difficult and require more complex algorithms. When applying TDD mode to MC-CDMA transmission it is possible to mainly overcome these


Whitepaper: Improved MC-CDMA Reception Employing Two-Dimensional Decision-Feedback Pilot and Data Symbol Correction

by German Aerospace CenterJan 01, 2008

Many physical layer standards for modern wireless communications systems, as for example Digital Video Broadcasting (DVB) and HIPERLAN Type 2, use Orthogonal Frequency Division Multiplexing (OFDM). The data symbols in these systems are coherently modulated and pilot symbols are used to estimate the fading channel response at the receiver. This research paper explains an algorithm is presented that recovers to a large degree the performance degradation due to channel estimation and equalization


Whitepaper: Rotated Spreading Sequences for Broadband Multicarrier-CDMA

by German Aerospace CenterJan 01, 2008

The advantages of Multicarrier (MC) modulation systems and Code Division Multiple Access (CDMA) schemes are combined in MC-CDMA. Therefore MC-CDMA is a promising candidate in the downlink for the fourth generation of wireless mobile radio systems. In this paper an enhanced MC-CDM access system is presented, which exploits additional diversity more efficiently at each subcarrier. A phase shift of each spreading sequence at the transmitter offers the additional diversity gain. The phase shift can


Whitepaper: OFDM Code Division Multiplexing With Unequal Error Protection and Flexible Data Rate Adaptation

by German Aerospace CenterJan 01, 2008

OFDM (orthogonal frequency division multiplexing) and OFDM-CDM (OFDM code division multiplexing) systems have proven to be robust in time-variant multipath fading channels. This paper investigates an OFDM-CDM system which can handle parallel data streams with different data rates and error protection by flexible adapting the symbol mapping scheme individually to each data stream. The proposed scheme offers an additional degree of freedom besides adaptive channel coding with variable code rates


Whitepaper: OFDM-CDMA Versus DS-CDMA: Performance Evaluation for Fading Channels

by German Aerospace CenterJan 01, 2008

Multiple access systems based on DS-CDMA have achieved increasing signicance for mobile communications applications. OFDM-CDMA systems have been proposed lately. The aim of this study is to carry out a performance comparison between DS-CDMA and OFDM-CDMA. Both techniques are considered for the downlink base to mobile since for this application power efficient mobile receivers with low complexity are required. The analysis enables a performance comparison between the DS-CDMA system and the


Whitepaper: Countermeasures for Reducing the Influence of Frequency Offsets on Uplink MC-CDMA

by German Aerospace CenterJan 01, 2008

Over the past several years MC-CDMA emerged as the most promising candidate for the air interface of future mobile wireless downlink systems,. However, when considering MC-CDMA for uplink transmission some problems arise. In this paper, the influence of Doppler induced frequency offsets on the performance of uplink TDD/MC-CDMA is investigated and countermeasures are proposed. Sensitivity of uplink MC-CDMA systems to frequency offsets has been considered in several papers, but both, an in-depth


Whitepaper: Comparison of Space-Time Block Coding and Cyclic Delay Diversity for a Broadband Mobile Radio Air Interface

by German Aerospace CenterJan 01, 2008

Future mobile radio systems are expected to provide and serve a wide range of applications, which inherently enforces high data rates. Currently, data rates of up to 100 Mbps and a bandwidth allocation of about 100 MHz are under discussion for mobile communication systems of the 4th generation. Multicarrier (MC) based systems, are approved candidates for providing the demanded data rates in a wide range of multipath fading environments with reasonable complexity. For further increase of the


Whitepaper: MC-CDMA Versus OFDMA in Cellular Environments

by German Aerospace CenterJan 01, 2008

The studies of both transmission schemes are done in a cellular structure. To enhance the performance of OFDMA, a Radio Resource Management (RRM) is introduced. It investigates 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.