Orthogonal frequency-division multiplexing (OFDM) is an attractive transmission technique for high-bit-rate communication systems. One major drawback of OFDM is the high peak-to-average power ratio (PAPR) of the transmitter's output signal. A novel selected mapping (SLM) scheme is proposed, which employs matrix transformation, cyclically shifting, and linear combining algorithm to generate new candidates. The novel scheme requires only one IFFT and gets more candidate transmission signals throughout the entire process. The complexity analysis and simulation results show that this algorithm can dramatically reduce computational complexity comparing with the conventional SLM scheme as in Hill et al., 2000; Yang et al., 2009; Wang and Ouyang, 2005; Li et al., 2010; and Heo et al., 2007 under the similar PAPR reduction performance.

Orthogonal frequency division multiplexing is an attractive technique for wireless high-rate data transmission due to the minimizing effects over frequency-selective fading channels [

However, compared with signal carrier signals, OFDM inherits some drawbacks such as sensitivity to synchronization errors and high PAPR at the transmitter, because an OFDM signal is the sum of many narrowband signals in the time domain [

Several schemes have been proposed for reducing the PAPR of OFDM signals over the last decade. The PAPR schemes can be classified according to whether they are deterministic or probabilistic. Deterministic schemes, such as clipping [

It is well known that conventional SLM scheme is a promising PAPR reduction technique for OFDM systems, but it has its own weak points. In this paper, a novel SLM scheme is proposed to overcome its shortcomings. This paper is organized as follows: Section

In the continuous time domain, an OFDM signal

The PAPR of OFDM signal sequence

In the conventional SLM scheme,

Just as other PAPR reduction schemes, conventional SLM also has its disadvantages: firstly, the selected signal index, called

Over the last decade, various methods have been used to improve the drawbacks of conventional SLM technique. Some scholars have invented blind SLM algorithms so that no

In this section, a novel SLM scheme is proposed which is based on the matrix transformation in [

According to [

From (

According to the matrix theory, (

Let

Then, all the IFFT output signals

Idea of conversion with

In order to achieve large PAPR reduction, a large number of candidate signal sequences should be required, but it will increase computational complexity, because each alternative OFDM signal sequence should be generated by (

By simulation experiments, however, we find that if we cyclically shift

Algorithm of cyclically shifting for generating new sequences.

Let

In addition, we can improve this algorithm to increase the number of signal sequences, as shown in Figure

Algorithm of improved cyclically shifting for generate new sequences.

Furthermore, the information of the phase sequence used for the transmitted signal must be conveyed to the receiver in the SLM scheme. In the novel SLM scheme, the input symbol sequence

Finally, the number of total

The final novel SLM scheme is described in Figure

Block diagram of the novel SLM scheme.

The complexity analysis and simulation results demonstrate the effectiveness of the proposed scheme.

PAPR reduction performances of the conventional and novel SLM schemes were investigated by MATLAB simulations. The basic system parameters for the simulations are summarized in Table

Simulation parameters.

Modulation and demodulation | QPSK |

Allocated bandwidth | 8 MHz |

Channel model | i.i.d. quasi-static Rayleigh fading |

Coding rate | 1/2 |

Number of random blocks | 60,000 |

Number of subcarriers ( | 256 |

Number of signal sequences ( | 5, 7, and so forth |

Figure

PAPR reduction performance of the novel SLM scheme and the conventional SLM scheme.

Figure

PAPR reduction performance of the novel SLM scheme and the SLM schemes in [

In Figure

PAPR reduction performance of the novel SLM scheme and the SLM scheme in [

Figure

PAPR reduction performance of the novel SLM scheme and the PTS scheme in [

Figure

PAPR reduction performance of the novel SLM scheme, SLM scheme in Figure

The computational complexity reduction ratio (CCRR) of the novel SLM scheme over the conventional SLM scheme is defined as

It is well known that an

Computational complexity of the conventional SLM and the novel SLM schemes when

Conventional SLM, | Novel SLM, | CCRR | Conventional SLM, | Novel SLM, | CCRR | |

IFFTs | 34 | 5 | 70 | 7 | ||

Complex multiplications | 34,816 | 2,048 | 94.1% | 71,680 | 2,560 | 96.4% |

Complex additions | 69,632 | 15,360 | 77.9% | 143,360 | 28,160 | 80.4% |

Complex multiplications | 174,080 | 9,216 | 94.7% | 358,400 | 11,264 | 96.9% |

Complex additions | 348,160 | 63,488 | 81.8% | 716,800 | 114,688 | 84.0% |

From [

Computational complexity of the SLM schemes in [

SLM in [ | Novel SLM, | CCRR | SLM in [ | Novel SLM, | CCRR | |

IFFTs | 1 | 5 | 1 | 7 | ||

Complex multiplications | 1,024 | 2,048 | −100% | 1,024 | 2,560 | −150% |

Complex additions | 27,392 | 15,360 | 43.9% | 55,040 | 28,160 | 48.8% |

Complex multiplications | 5,120 | 9,216 | −80% | 5,120 | 11,264 | −120% |

Complex additions | 111,616 | 63,488 | 43.1% | 222,208 | 114,688 | 48.4% |

According to [

Computational complexity of the SLM schemes in [

SLM in [ | Novel SLM, | CCRR | SLM in [ | Novel SLM, | CCRR | |

IFFTs | 1 | 5 | 1 | 7 | ||

Complex multiplications | 1,024 | 2,048 | −100% | 1,024 | 2,560 | −150% |

Complex additions | 25,856 | 15,360 | 40.6% | 52,736 | 28,160 | 46.6% |

Complex multiplications | 5,120 | 9,216 | −80% | 5,120 | 11,264 | −120% |

Complex additions | 105,472 | 63,488 | 39.8% | 212,992 | 114,688 | 46.2% |

As is discussed above, using the method of cyclically shift the signal sequence and combining it with the shifting sequences to generate

Computational complexity of the SLM schemes in [

SLM in [ | Novel SLM, | CCRR | SLM in [ | Novel SLM, | CCRR | |

IFFTs | 1 | 5 | 1 | 7 | ||

Complex multiplications | 10,496 | 2,048 | 80.5% | 19,968 | 2,560 | 87.2% |

Complex additions | 11,520 | 15,360 | −33.3% | 20,992 | 28,160 | −34.1% |

Complex multiplications | 43,008 | 9,216 | 78.6% | 80,896 | 11,264 | 86.1% |

Complex additions | 48,128 | 63,488 | −32.2% | 86,016 | 114,688 | −33.3% |

From [

Computational complexity of the SLM schemes in [

PTS/CSS in [ | Novel SLM, | CCRR | PTS/CSS in [ | Novel SLM, | CCRR | |

IFFTs | 3 | 5 | 5 | 7 | ||

Complex multiplications | 8,192 | 2,048 | 75.0% | 262,144 | 2,560 | 99.0% |

Complex additions | 49,152 | 15,360 | 68.8% | 5,242,880 | 28,160 | 99.5% |

Complex multiplications | 32,768 | 9,216 | 71.9% | 1,048,576 | 11,264 | 98.9% |

Complex additions | 196,608 | 63,488 | 67.7% | 20,971,520 | 114,688 | 99.5% |

According to [

Computational complexity of the SLM schemes in [

SLM in [ | Novel SLM, | CCRR | ||||

IFFTs | 7 | 5 | ||||

Complex multiplications | 10,240 | 2,048 | 80% | |||

Complex additions | 25,088 | 15,360 | 38.8% | |||

Complex multiplications | 48,128 | 9,216 | 80.9% | |||

Complex additions | 114,688 | 63,488 | 44.6% |

From the tables listed above, we can draw a conclusion that the computation complexity of novel SLM scheme is lower than the conventional scheme and the scheme in [

In this paper, a novel SLM scheme is proposed, and its performance is numerically confirmed for the OFDM system proposed in the IEEE 802.16 standard. The results show that as compared with the conventional SLM scheme, the scheme in [