^{1}

^{*}

^{2}

FPGA implementation used of Rotating phase shift (RPS) for peak-to-average power ratio (PAPR) reduction in Multi Carrier Code Division Multiple Access (MC-CDMA) signals. Because, MC-CDMA is still suffering from PAPR which is a major drawback in most of the multi carrier communication systems. In addition, the implementation of the system in an FPGA becomes more flexible and scalable. It eliminates the search for optimum phase factors from a given set, which manifests improved PAPR at reduced computational complexity as compared to conventional PTS and SLM. The amplitude of the signal is reduced by rotating each of the partially transmitted sequence anticlockwise by a π/2 degree and the peak power is reduced by circularly shifting the quadrature component of the partially transmitted sequence after phase rotation. A brief description of PTS, SLM is compared with the RPS, which best reduces PAPR from PTS and SLM. It is also presented that VHDL code of the RPS is designed by Xilinx ISE 14.1 implements of FPGA. The peak-to-average power ratio performance of the proposed method has been investigated.

The 4G wireless technology has approved MC-CDMA transmission supporting high data rate communications [

In [

In this present paper, the use of phase factors is eliminated, which is originally employed in SLM and PTS, by introducing the method of rotating each time domain sub-block symbol by a predetermined degree and circular shifting of partially transmitted quadrature phase components. Moreover, the Very High Speed Integrated Circuits Hardware Description Language (VHDL) implementation of Rotating Phase shifted technique is achieved where parallel processing of symbols is carried out instead of serial processing. Furthermore, the multiplicative complexity is reduced by shift-and-add algorithm. VHDL implementation of PAPR calculation is also performed which provides the PAPR of the respective symbol transmitted.

This paper is organized as: Section 2 discussed a brief review of PAPR in MC-CDMA system. It proposed method Rotating Phase Shift display in Section 3. In Section 4, RPS-PAPR is implemented in Xilinx ISE 14.1 using VHDL. Finally, results of simulation performed are provided in Section 5. Section 6 presents the concluding remarks.

The MC-CDMA is a multi-carrier transmission, which has a high data rate and greater flexibility for voice, data, and video and internet services for future wireless systems. This is multiplied by the first of the original data load, with the spreading code and then the chips of spread data are modulated onto orthogonal subcarriers [^{h} is first multiplied with the user specific spread code by = ^{h} obtained after spreading can be given in vector scheme as:

The c^{h} is converted to parallel

where

Formerly, the PAPR [

where N is the number of sub-carriers and

As one of the characteristics of the PAPR, which bears stochastic characteristics in MC-CDMA systems, often can be expressed in terms of Complementary Cumulative Distribution Function (CCDF). Which is described as the probability of the PAPR exceeding a certain level w [

where, N total number of sub-carrier and w is the level of exceed.

RPS takes away the use of phase factors and reduces PAPR. After multiple data by spreading code, then modulation, the data symbols are partitioned into sub-blocks which generate the frequency domain symbols [

On the other hand, the support sets of

then multiplied by a valid phase shift

where,

The PAPR of

The receiver must know the index information to recover the original input vector. The PAPR reduction performance and the computational complexity of the RPS structure depend on the method of sub-block separating. Furthermore, a search is a strategy that works well on optimization problems with the minimize PAPR show in Algorithm. 1 the search algorithm For algorithm, let

Algorithm 1: GVS Search

v Let:

v Require:

v Inialize:

v For

v

・ For m=1:M do

・ IF

・ Else empty

・ End

v End

v Return

In addition, to define the effect of each factor is compared to the performance of the RPS algorithm by selecting one of the factors are constant and change the rest of the factors in order to measure the effectiveness of that factor in the reduction of PAPR and then change with all cases the same method and each parameter triple

where

Implement the RPS-MC transmitter system and its peak to average power ratio calculation in VHDL. The archi-

π/2 | π | 3π/2 | 2π | |

1 | π | 2π | π | 2π |

2 | π/4 | π/2 | 3π/4 | π |

3 | 2π/3 | 4π/3 | 2π | π/3 |

4 | 3π/8 | 3π/4 | 9π/8 | 3π/2 |

π/4 | 3π/4 | 5π/4 | 7π/4 | |

1 | π/2 | 3π/2 | π/4 | 3π/2 |

2 | π/8 | 3π/8 | 5π/8 | 7π/8 |

3 | π/3 | π | 5π/3 | π/3 |

4 | 3π/16 | 9π/16 | 15π/16 | 21π/16 |

tecture proposed in this paper was coded in VHDL and then simulated and synthesized in Xilinx ISE 14.1. The computational complexity which arises due to IFFT operation is reduced by its VHDL implementation [_{ps} the rotate a range of possible phase shifts shown in

Simulations were performed to compare the performance of PAPR reduction in MC-CDMA system SLM, PTS and RPS at phases 3π/2 and 3π/8, with N = 64 subcarriers. The CCDF plots of the PAPR of the MC-CDMA signals in

RPS-PAPR calculation of the MC-CDMA system is calculated and the symbol with minimum peak-to average power ratio is transmitted.

RPS technique is achieved, which verifies the best PAPR reduction as compared to traditional SLM and PTS techniques. Additionally, the application is parallel processing and pipeline of symbols by implementation in

R_{ph} | R_{ps} With shift π/4 | Register Value |
---|---|---|

π/2 | π/4 | 01 |

π | 3π/4 | 10 |

3π/2 | 5π/4 | 11 |

2π | 7π/4 | 00 |

Parameters | Value |
---|---|

Number of transmitting bits | 2000 |

No. Subcarriers N | 64 |

No. of Users H | 4 |

Modulation | 32-QAM |

IFFT&FFT size | 128 |

Additive noises | 20dB |

Spading code type | Gold code |

No. Partitions P | 4 |

Predetermined codes | 16, 32 |

VHDL, which reduces the complexity by eliminating the difficult multiplication. Matlab simulations are done for 1000 samples of the MC-CDMA system with N = 64 subcarriers to plot the CCDF, which shows that RPS is the best method compared with the ways in various cases. The same idea is implemented in VHDL to calculate PAPR, and it can also be a simulation of subcarriers equal to 16 and 32 using the same process. This system eliminates the phase combined factor with lower PAPR better.

Ali KareemNahar,Kamarul H. BinGazali, (2015) PAPR Reduction Based on Proposed Rotating Phase Shift Technique in MC-CDMA Using FPGA. International Journal of Communications, Network and System Sciences,08,249-259. doi: 10.4236/ijcns.2015.87025