Abstract
Abstract Orthogonal frequency division multiplexing (OFDM) is a promising technique for high-bit-rate transmission in radio environments. Because the total bandwidth is divided into many narrowband subcarriers, the effects of multipath delay spread can be diminished. One major disadvantage associated with an OFDM system is the high peak-to-average power ratio (PAPR) of the transmitter’s output signal, where the value is proportional to the number of subcarriers used in the system. Due to the high PAPR feature, an OFDM signal may suffer from significant intermodulation distortion and undesired out-of-band radiation when it is passed through a nonlinear device, such as a transmit power amplifier. These drawbacks have motivated the search for PAPR reduction techniques. There are many schemes available for PAPR reduction, such as clipping, selective mapping, partial transmit sequence, constellation extension (CE), and so on; however, most of them require transmitting side information and thus reduce the bandwidth efficiency. The existing CE schemes do not need to transmit side information, but it usually increases the transmit power and causes bit-error-rate (BER) degradation. In this thesis, we propose three new CE schemes for PAPR reduction of OFDM signals with 16-QAM modulation, referred to as schemes A, B, and C. Each of the proposed CE schemes has four extendable constellation points, and each extendable constellation point has two possible extended constellation points. Scheme A adopts the four corners in the 16-QAM constellation as the extendable constellation points. Scheme B takes four specific points forming a square from the exterior constellation points (excluding the four corners) in the 16-QAM constellation as the extendable constellation points. Scheme C could be regarded as a hybrid from schemes A and B, where the extendable constellation points are the same as those of scheme A but the extended constellation points are the same as those of scheme B. As compared to previous related CE schemes, the proposed ones have fewer extendable constellation points with more extended constellation points each, resulting in better BER performance with almost the same PAPR reduction. Computer simulations are given to demonstrate the effectiveness of the proposed approaches.