We investigate space-frequency block coding for OFDM systems with multiple transmit antennas, where coding is applied in the frequency domain (OFDM carriers) rather than in the time domain (OFDM symbols). In particular we consider Alamouti's code, which was shown to be the optimum block code for two transmit antennas and time domain coding. We show that the standard decoding algorithm results in significant performance degradation depending on the frequency-selective nature of the transmission channels, such that a low coherence bandwidth results in a huge degradation. The optimum decoding algorithm that alleviates this problem is the maximum-likelihood decoder for joint symbol detection. We present a performance analysis for the investigated space-frequency decoders in terms of the achievable BER results. Furthermore we compare space-time and spacefrequency coding and discuss the respective advantages and drawbacks of the different decoding algorithms in terms of their complexity. It should be noted that for the space-time approach we introduce the so-called matched-filter receiver, which shows significantly lower complexity compared to the maximum-likelihood decoder known from literature. The HIPERMAN system serves as an example OFDM system for quantitative comparisons.

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This paper describes an envisioned technology roadmap for the development of mobile and wireless communications until the year 2010. The roadmap description is based on a 3-years study (2001)(2002)(2003)(2004) and monitoring of the technological developments of characteristically chosen mobile and wireless communication areas. The final definition of the technology roadmap was based on selected areas of high value that the authors consider as the corner aspects of the evolution of mobile communications. Two main groups of areas were defined and analyzed from a technological and from a service perspective. From technological perspective the areas of high research interest include radio technologies with effect on spectrum use, access and radio interface technologies, and technologies related to mobile terminals. From service perspective, we considered interactive broadcasting, location technologies and location based services (LBS) and personalization of services. The paper identifies the open issues to be solved to realize the future of wireless communications and describes the enabling technologies for next generation communications. It identifies the technology and non-technology barriers to development, deployment, as well as guidelines for the use of technology. Finally, a visionary scenario is described to illustrate the necessary evolution of the value chain for the successful deployment of any new service or technology.

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