Adaptive MIMO-OFDM combining space-time block codes and spatial multiplexing

The increase in demand for higher capacity and data rates over wireless channels has fueled researchers to explore the time, frequency and spatial dimensions of signal transmission. Thus, dynamic signal transmission with a multiple dimensions approach emerged as a powerful paradigm in meeting with these demands. Multiple-input multiple-output (MIMO) communication systems offer significant capacity gain compared to conventional single-input single-output (SISO) systems by exploiting the spatial dimension. Many MIMO techniques have been proposed including space-time coding (STC) and spatial multiplexing (SM). STC is used to provide more reliable communication, whereas the SM technique delivers faster communication. Combining STC and SM offers the best trade-off between transmission reliability and capacity. Using adaptive power and bit loading schemes, time-varying channel characteristics are exploited to improve data rate, reliability and power optimization. Spectrum efficiency is increased using orthogonal frequency division multiplexing (OFDM), a powerful method that utilizes the orthogonality of signals in the frequency domain to combat intersymbol interference (ISI). The paper proposes an adaptive MIMO-OFDM system model that combines both STC and SM over space. This model exploits all three dimensions of signal transmission to provide high data rates and robust signal transmission.