DESIGN OF OFDM AIDED SPACE TIME SHIFT KEYING

Abstract

The framework Space Time Shift Keying is a modulation scheme for Multiple-Input Multiple-Output (MIMO) communication systems. It uses both time and space dimensions for encoding a transmit codeword using a classic PSKIQAM modulated symbol with a dispersion matrix. A modified design has been presented here based on orthogonal matrices for both coherent and non-coherent STSK systems and for which two methods for generating dispersion matrices have been proposed; the first method is very quick compared to the second method as it only generates a unitary matrix whereas the second method uses genetic algorithm which takes little more time. The second method is proposed since the first method did not fulfil the goal for which STSK was proposed. Low complexity modified maximum likelihood detection is presented due to the modified design of codewords which renders same performance as the classic single stream based maximum likelihood detector. The performances for multiple configurations of STSK systems having same rate have been compared. The performances of PSK aided and QAM aided differential STSK schemes have been compared to show error propagation degrades the performance of QAM aided STSK - systems for having multiple amplitude levels. Moreover, performances of STSK systems concatenated with OFDM have been compared which shows similar properties as STSK systems in multipath fading scenario.