Extending Constellation Shaping by Shell Mapping Method to Reduce the Peak and Average Power of Space-Time Block Coded OFDM Systems

Abstract:
We extend our constellation shaping by shell mapping method of reducing the peak and average power of orthogonal frequency division multiplexing (OFDM) signals using quadrature-amplitude modulation (QAM) on all subcarriers from single transmit antenna systems to multiple transmit antennas systems. We consider space-time block codes that are designed for maximum antenna diversity and start from the observation that all the columns of the transmit matrix have the same power. The constellation shaping by shell mapping first groups the two-dimensional (2D) QAM symbols into rings; our main point is that we group length-L rings into a super-ring, where L is the number of rows of the transmit matrix. An OFDM frame has length N = L·Q. The super-rings are further grouped into shells, each shell being an ordered set of length-Q super-rings. To support the validity of our approach, we give illustrative examples for L = 2 and L = 4. Index Terms—MIMO wireless systems, mobile communications, orthogonal frequency division multiplexing, rectangular signal constellations, reducing the peak and average power of OFDM signals.