Locate Agent Phase (LAP): A Selected Mapping Technique without Any Side Information, to Reduce PAPR of QPSK Modulated OFDM

Locate Agent Phase (LAP): A Selected Mapping Technique without Any Side Information, to Reduce PAPR of QPSK Modulated OFDM

Md Tanvir Hossain

Faculty of Science and Technology Bangladesh University of Professionals Dhaka, Bangladesh

Md Sayfee Ahmed

Faculty of Electrical and Computer Engineering Military Institute of Science and Technology Dhaka, Bangladesh

Abstract: A standout amongst real challenges of the orthogonal frequency division multiplexing (OFDM) system is high peak to average power ratio (PAPR) which causes the execution debasement because of distortion in the high power amplifier. Diverse strategy were presented for PAPR reduction but Selected mapping (SLM) is one of the significant method to lessen the PAPR in OFDM system .However the constraint of SLM is the need of transmit side information. In this paper we have proposed a new procedure, Locate Agent Phase (LAP), that permit us to reduce the PAPR of OFDM system based on SLM procedure without transmitting any side information and creating any distortion.

Keywords: OFDM, PAPR, QPSK, SLM

1. INTRODUCTION

   OFDM is one of most demandable plans for transmission process in present day communication system. It is a multi- carrier modulation technique that has demonstrated colossal potential for rapid remote communication system. By transmitting the signal all the while over different channels, one can enhance the heartiness of the communication system. Since the individual channel transfer speed is much littler than the system data transmission, the channel attributes are for all

   SLM [8-12] might be arranged into the stage control plan to get away from the high peak. One signal of the least PAPR is chosen in an arrangement of a few signals containing the same data information. Both procedures require much framework multifaceted nature and computational weight by utilizing many IFFT block. However, this is extremely flexible scheme and has a successful execution of the PAPR diminishment without any signal distortion. Different dummy sequences are incorporated into the same input data, and, a while later IFFT, the signal has a minimum PAPR is chosen for output signal [2]. In this paper, we propose and analyze a system for reducing high PAPR, in view of part of a strategy proposed in [7] and [8].We take QPSK modulated inputs to generate OFDM signal and there is no side information required for detecting the data at the receiver. The proposed algorithm is easy to actualize and preserves the great PAPR reduction capability of the original SLM method.

2. CONVENTIONAL SCHEME

   A. Review of OFDM and SLM

   N

   N

   An OFDM signal o(n) is represented as

   intents and purposes level, despite the fact that they may not be level over the system data transmission. Unfortunately,

   o(n)

   1 M (k)e

   2 j (n1)( k 1)

   N

   ; N n 1

   (1)

   OFDM has a major issue of a high peak to average power ratio (PAPR) when various modulated subcarriers are included with the same stage. The high PAPR acquires on signal distortion in the nonlinear locale of high power amplifier (HPA) and corruption of bit error rate (BER) execution. Along these lines, it is essential to reduce the PAPR in the OFDM communication system. There are different techniques for reducing the PAPR [1].These are broadly examined and numerous diminishment procedures have been proposed for multicarrier system. These technique can be sorted into the accompanying, clipping and filtering [1], coding [2], phasing [3], scrambling[4],

   interleaving [5], and companding [6].

   Clipping method is to cut the top over a specific level. The section system can without much of a stretch diminish PAPR. Be that as it may, the BER execution turns out to be more regrettable because of numerous absconded signals [7].Block coding is another technique for PAPR decrease. This method can reduce the PAPR internal 3 dB without any signal distortion. Nonetheless, the code rate turns out to be low and in addition the transfer speed productivity [7].

   N k 1

   Where N is the number of subcarriers, M(k) the frequency domain of OFDM signal and k is the subcarrier index.

   The PAPR of the OFDM signal is expressed as

   papr

   papr

   maxo(n) o *(n)

   Eo(n) o *(n)

   (2)

   Fig.1 demonstrates the conventional SLM scheme. In the SLM technique, they make different data blocks with the same data and chooses the most good for transmission. Additionally, when they take this equation, transmitted side information is essential. This procedure cuts down the data rate and losing of side information obliterates the entire data. The proposed LAP system tackle these issues. This is one sort of blind SLM technique and has been discussed about in [11] and [12] by capitalizing on the finite alphabet nature of the information star grouping.

   Partitioning
   Into
   Blocks And	X
   Serial to
   Parallel
   Conversion

   Partitioning
   Into
   Blocks And	X
   Serial to
   Parallel
   Conversion

   Transmitted data

   P1

   X

   X

   X(1) (2)

   IFFT

   P2

   X

   X

   X(2) (2)

   IFFT

   .

   .

   Pu .

   X

   X

   X(u) (2)

   IFFT

   Select one with Minimum PAPR

   Transmitted Signal

   Side information

   1. Transmitter

      FFT

      FFT

      Demapping

      Demapping

      Received Signal

      Received Data

      Chose phase sequence to demodulate

      Chose phase sequence to demodulate

      Side information

   2. Receiver

   Fig. 1 Conventional SLM with side information

   Transmitted Data

   1. Transmitter

      QPSK

      Chose one with lowest PAPR

      Chose one with lowest PAPR

      IFFT

      IFFT

      Phase1mod

      .

      .

      .

      Phase4mod

      Phase4mod

      Transmitted Signal

      FFT

      FFT

      Received Singnal

      Found Agent Phase?

      yes

      Match with Phase1mod?

      No

      .

      .

      .

      No

      No

      yes

      Phase1mod

      .

      .

      .

      Received data

      Phase4mod

      Phase4mod

   2. Receiver

   QPSK

   Demodulation

   QPSK

   Demodulation

   Fig. 2 Proposed SLM Model

   In [10], blind SLM was carried out in conjunction with

   pilot symbol assisted with the modulation in OFDM. Our proposed method works on any QPSK modulated sequences.

   N

   ,

   ,

   4

   4

   d

   N (7)

   It is less complexes than the strategy in [11] and [12] and beats the blind SLM algorithm proposed in [10].We change the

   Phase1de mod

   d

   d

   , 1

   2

   amplitude of the PSK modulated data which increase the signal power and LAP overcomes this issue.

   1, Otherwise

3. p>PROPOSED SCHEME

   A. Locate Agent Phase

   Fig. 2 shows the proposed Locate Agent Phase (LAP) scheme.In LAP we use most popular and important

   Phase 2

   demod

   d

   d

   d

   d

   , N

   8

   , 3N 4

   (8)

   modulation techniques QPSK, where we create different data block which represent the same information and transit the one

   1, Otherwise

   with lowest PAPR. Here each phase sequence is different from

   each other. Those Phase sequences create Agent phases. The agent phase is the phase which is not present in conventional

   3N

   ,

   ,

   8

   8

   d

   N

   (9)

   QPSK. At the receiver we detect the used phase sequence by determining the location of the Agent Phase. To make a

   Phase 3

   de mod

   ,

   d

   d

   2

   0

   0

   signals phase an agent phase we need to multiply the signal

   1, Otherwise

   with m

   e( j45 )

   For example when we have N=8 subcarriers we have our phase sequences:

   d

   d

   , 7N

   8

   ,

   ,

   N

   4

   4

   m

   (3)

   Phase 4demod d , N

   1, Otherwise

   Phase1

   mod

   , N 1

   2

   (10)

   m

   m

   1, Otherwise

   Fig. 2 shows the proposed scheme. For higher N number we just repeat this phase sequence of 8 Subcarrier.

   Phase 2

   mod

   m

   m

   m

   m

   , N

   8

   , 3N 4

   (4)

4. PERFORMANCE EVALUATION AND RESULT

   To visualize our scheme we use MATLAB simulation tool and to show our PAPR reduction capability we use complementary cumulative distribution function distribution

   1, Otherwise

   function (CCDF) graph [7] which signifies the likelihood of a data block surpasses a given threshold. We use 64 subcarriers,

   3N

   m ,

   8

   N

   (5)

   640000 data and QPSK modulation technique. We multiply it with 4 phase sequences and bring one with most minimal

   PAPR. Fig.3 demonstrates the PAPR lessening capability of

   Phase 3

   mod

   ,

   m

   m

   2

   LAP compared with the conventional OFDM.

   1, Otherwise

   m

   m

   , 7N

   8

   (6)

   Phase 4mod m , N

   1, Otherwise

   ( j450 )

   ( j450 )

   At the receiver after determining the used phase sequence for modulation, we revert the signal to its original phase by multiplying it with d e in the appropriate positions.

   The phase sequences used for this process are:

   Fig. 3 CCDF curve of conventional OFDM vs. OFDM using LAP

   100

   101

   102

   Symbol error rate

   Symbol error rate

   103

   104

   105

   106

   0 2 4 6 8 10 12 14

   SNR, dB

   or rate

   or rate

   Fig. 4 Symbol err Same Symbol error rate

   REFERENCES

   1. X. Li and L. J. Cimini Jr., Effects of clipping and filtering on the performance of OFDM, IEEE Communication Letters, pp. 131-133, May 1998.

   2. A. E. Jones, T. A. Wilkinson and S. K. Barton,Block coding scheme for reduction of peak to mean envelope power ratio of multicarrier transmission schemes,ElectronicLetters,pp.20982099, Dec.1994.

   3. A. E. Jones, T. A. Wilkinson and S. K. Barton,Block coding scheme for reduction of peak to mean envelope power ratio of multicarrier transmission schemes,ElectronicLetters,pp.20982099, Dec.1994.

   4. V. Tarokh and H. Jafakhani, On the computation and reduction of peak to average power ratio in multicarriercommunications, Proc. IEEE 53rd Vehicular Technology Conference, vol.2, pp. 37-44, Jan 2000.

   5. P. Van Eetvelt, G. Wade and M. Tomlinson, Peak to average power reduction for OFDM schemes by selective scrambling, Electronic letters, vol. 32, pp.1963-1994, Jan 2000.

   6. A. D. S. Jayalath and C. Tellambura The use of interleaving to reduce the peak to average power ratio of an OFDM signal, Global Telecommunication Conference, 2000, GLOBECOM 00. IEEE, vol. 1, pp. 82-86, Nov.-1 Dec. 2000.

      Here we can see that the PAPR probability curve of

      conventional OFDM reaches 10.7dB whereas OFDM using LAP techniques highest PAPR is 8dB. From the above graph we can conclude that our scheme have 2.7dB less PAPR than the conventional OFDM but symbol error rate are same in Fig.4.

5. CONCLUSION

In this paper we recommended a method to decrease PAPR modified from those past SLM strategy. It is indicated that PAPR diminishment utilizing our method requiring low intricacy for an expansive number for subcarriers same time it supports the comparable PAPR diminishment execution compared with the tantamount customary SLM plan. Finally, our computer simulation demonstrates that recommended plan accomplishes an excellent execution to PAPR diminishment.

1. Xiao Huang, Jianhua Lu, Justin Chuang, and Junli Zheng, Companding transform for the reduction of peak to average power ratio of OFDM signal, IEEE Trans. On Commun. vol. 48, pp. 835-839, May 2001.

2. Seung Hee Han, Stamford University, Jae Hong Le, Seoul National University An overview of peak to average power ratio reduction techniques for multicarrier transmission IEEE Wireless Communications April 2005.

3. Heung-Gyoon Ryu, Jae-Eun Lee, and Jin-Soo Park,"Dummy sequence insertion (DSI) for PAPR reduction in the OFDM communication system," IEEE Transactions on Consumer Electronics, vol. 50, pp.89-94, Feb. 2004.

4. Heung-Gyoon Ryu, Jae-Eun Lee, and Jin-Soo Park,"Dummy sequence insertion (DSI) for PAPR reduction in the OFDM communication system," IEEE Transactions on Consumer Electronics, vol. 50, pp.89-94, Feb. 2004.

5. [Dov Wulich Definition of Efficient PAPR in OFDM IEEE communication letters, vol. 9, no. 9, Sep.

6. G. Tong Zhou, Peak-to-average power ratio reduction in OFDM:Blind selective mapping for psk inputs School of Electrical and Computer Engineering, Georgia Tech, Atlanta, GA 30332-0250, USA.

7. A. D. S. Jayalath and C. Tellambura, A blind SLM receiver for PAR- reduced OFDM, Proc. IEEE Vehicular Technology Conference, pp. 219-222, Sept. 2002.

8. R. J. Baxley and G. T. Zhou, MAP metric for blind phase sequence detection in selected mapping, IEEE Trans. on Broadcasting, vol. 5, no. 4, pp. 565-570, Dec. 2005.Science, 1989.