Space-Time Coded OFDM with Low PAPR

Abstract

Recently the use of multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems has been proposed for signaling over frequency-selective fading channels. Although various aspects of these systems have been considered in the literature, the problem of the inherent high peak-to-average power ratio (PAPR) is not examined. In this paper, we consider PAPR reduction for MIMO-OFDM systems and propose alternate low-complexity algorithms that can be used in conjunction with the trellis shaping method. We show that a PAPR reduction in the order of 4-5 dB can be achieved at the cost of a slight reduction in the spectral efficiency. Furthermore, we compare the trellis shaping technique with other PAPR reduction techniques such as tone reservation and partial transmit sequences.

Peak-to-Average Power Ratio Reduction in MIMO-OFDM with Trellis Exploration Algorithm

“…1 which is similar to the model considered in [5]. The system is assumed to have M t transmit antennas and M r receive antennas.…”

“…For the entire system, the PAPR is defined as the maximum of PAPRs among all transmit antennas [5], i.e.,…”

“…However, peak-to-average power ratio (PAPR) is a significant drawback in multi-carrier systems such as OFDM. In [3], [4] and [5], the PAPR problem in MIMO-OFDM has been addressed. However, in precoded MIMO-OFDM, the PAPR performance is even worse relative to traditional MIMO-OFDM without precoding as each transmit signal is now a composite signal due to spatial processing.…”

Reducing the Peak to Average Power Ratio of MIMO-OFDM Systems

“…The amplitude of the output signal can be expressed as = (18) which is Rayleigh distributed with parameter . The output power can therefore be expressed as = (19) which is exponentially distributed with mean 2 . The PAPR of the transmitted OFDM signal can be defined as …”

“…The PAPR of the entire system is defined as the maximum of the PAPRs among all the transmit antennas [19].…”