Search

Cyclic delay diversity (CDDx) is a simple multiple antenna technologyxs which provides additional diversity in Rayleigh fading channels, and therefore, improves the system performance. We recall the principles of CDD and discuss the properties and impact of this transmit (TX) antenna diversity technology. Different applications motivate variations of the CDD principle. This variants are briefly introduced and discussed. We show the application to several types of wireless systems, in particular terrestrial digital video broadcasting, cellular mobile radio communications systems and a wireless communications system using adaptive bit loading (ABL). Simulation results highlight the benefits of CDD for these kind of systems.

This paper investigates the potential of orthogonal frequency division multiplexing-code division multiplexing (OFDM-CDM) for its application in future broadband mobile radio systems. The focus is on the performance analysis of OFDM-CDM with spatial pre-coding and its comparison with OFDM. Code division multiplexing (CDM) is an efficient coding scheme without rate loss. The investigations take into account the spatial diversity and pre-coding schemes cyclic delay diversity (CDD), spatial phase coding (SPC), equal gain transmission (EGT) and maximum ratio transmission (MRT). SPC can closely approach the performance of optimum pre-coding schemes, whereas SPC requires less complexity and overhead with respect to channel estimation and feedback information. Imperfections due to channel estimation are taken into account in the analysis. It can be shown that OFDM-CDM with spatial pre-coding applying single symbol detection as well as multi-symbol detection outperforms OFDM with spatial pre-coding. Copyright © 2008 John Wiley & Sons, Ltd.

Cyclic delay diversity (CDD) was introduced in 2001 to obtain spatial diversity in an orthogonal frequency division multiplexing (OFDM) based transmission system. In contrast to space-time codes, CDD introduces no additional effort at the receiver side, since CDD changes only the channel impulse response seen by the receiver by increasing the frequency selectivity. Furthermore, CDD has the advantage that there is no rate loss even for more than two transmit antennas. In this paper, we analyse CDD for an orthogonal frequency division multiple access (OFDMA) based transmission system. To increase not only the frequency selectivity but also the time selectivity, we introduce time-varying cyclic delay diversity (TV-CDD), which changes the cyclic shift with each OFDM symbol. Especially in systems, where each user can only allocate a few subcarriers for data transmission, TV-CDD improves the performance of the OFDMA-based transmission system significantly. Copyright © 2006 AEIT

We present a space-frequency coding scheme using cyclic delay diversity (CDD) for an orthogonal frequency division multiplexing (OFDM)-based transmission system. CDD is a simple multiple transmit antenna approach for increasing the frequency selectivity of the channel seen at a single antenna receiver. This is due to the insertion of virtual echoes caused by antenna specific cyclic delays in the time domain at the transmitter. On each antenna a shifted version of the signal is sent, with these shifts being performed in the frequency domain. This allows the receiver to apply optimum demodulation, and thus exploit the diversity introduced by CDD. We optimize the selection of the time domain cyclic delays in the CDD so as to get full spatial diversity with the proposed space-frequency codes with CDD (SFC-CDDs) scheme. Moreover, we show simulation results for SFC-CDD, which confirm theoretical results with respect to the achieved spatial diversity, and present a comparison with the well-known Alamouti scheme implemented as SFC.

Orthogonal frequency division multiplexing signals with cyclic delay diversity (CDD) exhibit distinguishable cyclostationarity that can be used to design cyclostationary signatures for cognitive radio networks. However, such cyclostationary signatures are