AG Kommunikationstheorie


Software Defined Radio Based Adaptive Modulation and Power Allocation for OFDM with Imperfect Channel State Feedback


This thesis discusses and evaluates the software defined radio implementation of an orthog- onal frequency-division multiplexing (OFDM) transmission system extended by adaptive resource allocation. An advantage of OFDM compared to single carrier schemes is its ability to cope more efficiently with severe channel conditions, e.g multipath induced time- and frequency-selective fading. Furthermore, it enables optimized multiuser schemes called orthogonal frequency-division multiple access (OFDMA). However, in order to exploit the full potential of the channel and achieve the channel capacity, the system has to adapt the transmitted signal to the current channel state. Given a Quality-of-Service demand it determines the most efficient power allocation and the corresponding bitloading with a waterfilling algorithm. The implementation is able to feed back the receiver channel state information to the transmitter for every OFDM frame and for each subcarrier. Although, such fine granularity implies a high overhead, it enables the exploration of the theoretical limits of the concept. The thesis provides an overview of the theoretical background of OFDM with adaptive resource allocation, subsequently explaining the design of the rele- vant parts of the implementation. Finally an evaluation and interpretation of the system performance for different scenarios and conditions is presented.

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