Rana Ahmed

Wireless Communications:

Mobile reception of OFDM based broadcasting signals

Blind Diversity Combining and Equalization for Multiple Antenna Systems:

Wireless transmission signals arrive at the receiver over different paths with unknown delay, amplitude and phase variation. Typically, the impulse response (IR) of a wireless channel is time-variant due to relative movements between transmitter, receiver and objects which are involved in the signal propagation. Signals of different transmission paths may add up destructively at the receiver antenna, such that the received total signal is very small compared to the additive noise of the receive amplifier circuits.

The probability of such a destructive superposition can be reduced by means of constructively combining the signals of multiple spatially separated receive antennas. A generally good performance can be achieved with maximum ratio combining (MRC) provided that the channel IR is known for each receive antenna. In the literature, many references for receive antenna diversity combining schemes. Such schemes make use of knowledge of channel state information (CSI) at the receiver side using pilot assisted channel estimation, which depends on the structure of the transmitted communication signal.

It is advantageous, in some applications, to have the combining stage as a “standard independent” stage. In this case, the communication channel coefficients have to be estimated blindly (without any knowledge of the sent signal structure, training data etc.) hence the name “Blind Diversity Combining“. Blind channel estimation can be achieved using second (SOS) or higher order statistics (HOS). For our purposes, we use second order statistics, such as cross relations (CR) because of the relatively faster convergence in comparison to HOS.