KEYWORDS: Signal to noise ratio, Transmitters, Receivers, Antennas, Error analysis, Systems modeling, Computer engineering, Signal processing, Statistical modeling, Scattering
Outdoor channels can be modelled as as a sum of array response vectors of varying gain at different Angles of Departure (AoDs) from different point sources. Based on this characteristics, we derive a hybrid of Beam-Forming (BF) and Space-Time Block Coding (STBC), where the space-time code is transmitted over the beams generated by array response vectors. This is for the practical case where the transmit array may have adequate information on the departure angles of the dominant paths between transmitter and receiver. In the case where the transmitter has knowledge on the associated complex path gains, a power loading scheme is designed when. We compute analytically the Signal-to-Noise Ratio (SNR) of the proposed hybrid for the specific case of a two-path channel model and using the orthogonal Alamouti code, and compare the result to the SNR of optimal Linear Precoding (LP) and the theoretically possible SNR of Orthogonal STBC (OSTBC). Simulation results show that the performance of the BF/STBC hybrid with and without power loading can be very close to LP-under certain conditions-or even better in the practical case where there are phase estimation errors in the path gain estimates employed at the transmitter.
Space-time transmit structures for multi-antenna systems have received considerable interest. Circulant structures were among the first space-time coding techniques ever used for multiple-input multiple-output (MIMO) systems due to their simplicity and full rate. The fact that a circulant matrix is diagonalized by the discrete Fourier transformation matrix suggests that the circulant structure can be combined with an inverse fast Fourier transform (IFFT) at the transmitter and a fast Fourier transform (FFT) at the receiver. Using this method, the spatial mixing effect of the MIMO channel is decoupled but the diversity gain is lost. To recover the diversity advantage, we propose to spread the transmitted symbols over the diagonalized channel using an invertable matrix whose entries are selected from $\{1,-1\}$. After spreading, every symbol experiences
all the components of the frequency counterpart of the channel vector which makes our scheme provide full symbolwise diversity. The proposed scheme is full rate and can be easily applied to any number of transmit antenna. Our simulation results show that the performance of our scheme is close to the performance of the ideal orthogonal space-time code and much better than the conventional circulant space-time code.
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