Eun-Taek Lim

Space-Time Block Coded Maximum Ratio Transmission with Imperfect Channel Estimation

We consider a multi-input-multi-output system employing space-time block codes (STBC). Different from conventional approaches, the proposed transmitter linearly combines data together with estimation of channel state information, so that no channel estimation is needed at the receiver side when phase-shift keying (PSK) modulation is employed. The employed STBC defines the number of receive antennas while the number of transmit antennas can be arbitrary. We propose a system with maximum ratio transmission for generalized orthogonal STBC with imperfect channel estimation at the transmitter. Bit-error probability of the proposed system with PSK modulated system under independent, identically distributed Rayleigh fading channels is analyzed. The result is in an explicit closed-form which shows direct dependence on the channel estimation error.

A novel threshold selection for hypotheses tests in cognitive radios

Spectrum sensing is a central part in a cognitive radio and therefore a thorough design of a spectrum sensor is of highest priority. Here, a novel implementation of a spectrum sensing technique, using a generalized version of the Neyman Pearson test, is considered. This novel implementation overcomes the usual prerequisite of the known noise power. This benefit is achieved by normalizing the signal and accurately calculated the threshold for that particular hypothesis which reflects the absence of the useful signal, usually termed hypothesis H2. It is shown by simulation results that the performance of the novel detector is promising.

Log-likelihood ratio based signal sensing strategy for cognitive radios

Cognitive radios require spectrum sensing. IEEE 802.22 defines constraints on conceivable spectrum sensing techniques. In order to fulfill theses constraints on the required detection probability and allowed false alarm probability, the signal sensing requires a certain sensing time period and an appropriately adjusted decision threshold. This manuscript presents a novel dynamic spectrum sensing scheme which is based on soft outputs. The novel scheme allows the reduction of the sensing time in order to save calculation and power effort.