Selected Mapping Based PAPR Reduction in ... - Semantic Scholar
Int. Jr. of Advanced Computer Engineering & Architecture Vol. 2 No. 2 (June-December, 2012)
Selected Mapping Based PAPR Reduction in WiMAX Without Sending the Side Information HimanshuBhusan Mishra, Madhusmita Mishra and Sarat Kumar Patra
Dept. of Electronics and Communication National Institute of Technology Rourkella-769008, India [email protected] Dept. of Electronics and Communication National Institute of Technology Rourkella-769008, India [email protected] Dept. of Electronics and Communication National Institute of Technology Rourkella-769008, India [email protected] Abstract It is well known that the orthogonal frequency division multiplexing (OFDM) is a promising technique for getting high data rate in multi path fading environment. Hence the advance technologies like LTE and WiMAX use this as its physical layer. The well-known disadvantage of OFDM is its high peak to average power ratio (PAPR). The PAPR reduction using Selected mapping (SLM) technique is being analyzed here. With following this PAPR reduction technique it requires to send extra Side Information (SI) index along with the transmitted OFDM signal and error in detecting these extra bits at the receiver leads to data rate loss.Without sending this SI index the detection of this thing will also be possible with following the sub-optimal algorithm at receiver. This paper analyses the PAPR reduction performance using complimentary cumulative distribution function (CCDF) plot and the probability of SI detection error performance as per the criteria of WiMAX(IEEE 802.16e).The BER (Bit Error Rate) performance is also being analyzed here. Keywords: Orthogonal frequency division multiplexing (OFDM); Peak to average power ratio (PAPR); selected mapping technique (SLM); complimentary cumulative distribution function (CCDF); Side Information (SI) 1INTRODUCTION IEEE.802.16 standard defines several wireless metropolitan area network (WMAN) technologies. WiMAX is a certification applied to 802.16 products tested by the WiMAX forum. IEEE 802.16d stands for fixed WiMAX and IEEE 802.16e stands for mobile WiMAX. In mobile WIMAX for downlink the modulation schemes used are QPSK, 16-QAM, 64-QAM and that for uplink are QPSK, 16-QAM, 64-QAM (optional). Here the analysis of the simulation work being described using the modulation schemes QPSK and 16-QAM. To satisfy the high data rate in frequency selective fading environment WiMAX considers the OFDM as its physical layer [7].The main disadvantage of OFDM is its high PAPR (Peak to Average Power Ratio). For the linear modulation scheme a linear power amplifier being used at the transmitter. With an increase of this PAPR at any time instant the probability of shifting the operating point of the linear power amplifier to the saturation region becomes more. This shifting of operating point leads to in-band distortion and out-of-band radiation, which can also be avoided with increasing the dynamic range of power amplifier and again it leads to the increasing of size and cost of power amplifier. Also considering the power constraint problem it is required to reduce this PAPR. There are a lot of techniques [3] like Clipping and Filtering, Coding, Partial Transmit Sequence (PTS), Selected Mapping (SLM), Tone Reservation (TR) and Tone Injection (TI) present for the reduction of PAPR and out of which SLM [1] is a promising technique. This SLM is also being known as the
179
conventional SLM. According to this technique the main data block will be divided into several independent blocks then each will be converted into OFDM symbol and finally the symbol with less PAPR will be transmitted. Here the performances like the PAPR reduction and Bit Error Rate analysis are being done with considering the baseband domain transmission. For the baseband complex signal average power for its envelope.
the PAPR is defined as the ratio between the maximum power and the |
|
| | This paper is organized as follows: In Section 2, the SLM technique is presented. In Section 3 the simulation results for the WIMAX parameters are analyzed. Finally the conclusion is being prosed in Section 4. 2
SLM TECHNIQUE
The conventional Selected Mapping (SLM) [1]is one of the promising technique for reduction of the PAPR. The aim of this method is to generate many independent OFDM blocks from a single data block and then select one having PAPR. The independent OFDM sequences can be found with finding independent phase sequences. Let us consider number of phase sequences with the sequence length of (i.e. the number of subcarriers). Then the 9 point of 9 phase sequence is given as
Where
∈
,!……….
The number of subcarriers
∈ #, … … … . .
In this classical SLM technique
$
^ Φ
.
%
(2)
%
.
(3)
Fig.1 The Block diagram for SLM technique The random phasesΦ in each phase sequence will be uniformly distributed in &#, !' with satisfying the condition [4, 6] of () ∅ + #. In this way the number of alternative phase sequences can be found.According to fig.1 the number of alternative candidate vectors (i.e. , to , )can be generated with multiplying each phase sequence to the original data block. The next job is to find IDFT of the alternative candidate vectors using IFFT algorithm that leads to alternative OFDM signals. Out of all these OFDM signals transmit the signal with minimum PAPR. The information about the phase sequence required to select the minimum PAPR based OFDM signal should be sent along with this selected signal. This extra information is to be known as the Side Information (SI) index which is nothing but the set of -./0! 1number of bits. To detect the exact transmitted data at the receiver the perfect detection of this SI index should be done. There will be a chance to lose the whole transmitted data block with the erroneous detection of this SI index. With a slide modification of this classical SLM technique the transmission of the SI index can be avoided. That modification is being described in the next section.
180
2
MODIFIED SLM TECHNIQUE
The fig.1 describes concept about the classical SLM [1]. The modification can be made with designing the phase % . With following the new SLM technique [2] sequence. According to the classical SLM technique% a modified scheme can be considered for the construction of phase sequences. In this modified phase sequence at some points out of ∈ #, , … … … $ it is required to put 2 ^ Φ . Here 2 is the extension factor with satisfying the condition 2 > . With following this concept of designing the phase sequence the perfect detection of SI index at the receiver becomes easy. This detection can be done using suboptimal algorithm [2].According to the concept of sub-optimal algorithm out of number of phase sequences one sequence is being selected which satisfies the minimum energy difference between transmitted signal and received signal. This selected phase sequence should be the perfect sequence that gives the information about transmitted data block.There may be some probability of error with detecting the perfect phase sequence which is being analyzed here as the probability of SI index error with respect to different values of 2.Also the analysis of bit error rate performance being done for considering a fixed value of 2. All these above things are being analyzed here with considering the parameters of WiMAX. 3SIMULATION RESULTS To analyze different results the transmission channel is considered as a quasi-static frequency selective Rayleigh fading with equal power taps. Also the model for nonlinear solid state power amplifier (SSPA) [5] is considered at the transmitter output. The important parameters of WIMAX are to be used are given as follows: Used data subcarriers
278.98 :; ? @ B ?
Selected Mapping Based PAPR Reduction in WiMAX Without Sending the Side Information HimanshuBhusan Mishra, Madhusmita Mishra and Sarat Kumar Patra
Dept. of Electronics and Communication National Institute of Technology Rourkella-769008, India [email protected] Dept. of Electronics and Communication National Institute of Technology Rourkella-769008, India [email protected] Dept. of Electronics and Communication National Institute of Technology Rourkella-769008, India [email protected] Abstract It is well known that the orthogonal frequency division multiplexing (OFDM) is a promising technique for getting high data rate in multi path fading environment. Hence the advance technologies like LTE and WiMAX use this as its physical layer. The well-known disadvantage of OFDM is its high peak to average power ratio (PAPR). The PAPR reduction using Selected mapping (SLM) technique is being analyzed here. With following this PAPR reduction technique it requires to send extra Side Information (SI) index along with the transmitted OFDM signal and error in detecting these extra bits at the receiver leads to data rate loss.Without sending this SI index the detection of this thing will also be possible with following the sub-optimal algorithm at receiver. This paper analyses the PAPR reduction performance using complimentary cumulative distribution function (CCDF) plot and the probability of SI detection error performance as per the criteria of WiMAX(IEEE 802.16e).The BER (Bit Error Rate) performance is also being analyzed here. Keywords: Orthogonal frequency division multiplexing (OFDM); Peak to average power ratio (PAPR); selected mapping technique (SLM); complimentary cumulative distribution function (CCDF); Side Information (SI) 1INTRODUCTION IEEE.802.16 standard defines several wireless metropolitan area network (WMAN) technologies. WiMAX is a certification applied to 802.16 products tested by the WiMAX forum. IEEE 802.16d stands for fixed WiMAX and IEEE 802.16e stands for mobile WiMAX. In mobile WIMAX for downlink the modulation schemes used are QPSK, 16-QAM, 64-QAM and that for uplink are QPSK, 16-QAM, 64-QAM (optional). Here the analysis of the simulation work being described using the modulation schemes QPSK and 16-QAM. To satisfy the high data rate in frequency selective fading environment WiMAX considers the OFDM as its physical layer [7].The main disadvantage of OFDM is its high PAPR (Peak to Average Power Ratio). For the linear modulation scheme a linear power amplifier being used at the transmitter. With an increase of this PAPR at any time instant the probability of shifting the operating point of the linear power amplifier to the saturation region becomes more. This shifting of operating point leads to in-band distortion and out-of-band radiation, which can also be avoided with increasing the dynamic range of power amplifier and again it leads to the increasing of size and cost of power amplifier. Also considering the power constraint problem it is required to reduce this PAPR. There are a lot of techniques [3] like Clipping and Filtering, Coding, Partial Transmit Sequence (PTS), Selected Mapping (SLM), Tone Reservation (TR) and Tone Injection (TI) present for the reduction of PAPR and out of which SLM [1] is a promising technique. This SLM is also being known as the
179
conventional SLM. According to this technique the main data block will be divided into several independent blocks then each will be converted into OFDM symbol and finally the symbol with less PAPR will be transmitted. Here the performances like the PAPR reduction and Bit Error Rate analysis are being done with considering the baseband domain transmission. For the baseband complex signal average power for its envelope.
the PAPR is defined as the ratio between the maximum power and the |
|
| | This paper is organized as follows: In Section 2, the SLM technique is presented. In Section 3 the simulation results for the WIMAX parameters are analyzed. Finally the conclusion is being prosed in Section 4. 2
SLM TECHNIQUE
The conventional Selected Mapping (SLM) [1]is one of the promising technique for reduction of the PAPR. The aim of this method is to generate many independent OFDM blocks from a single data block and then select one having PAPR. The independent OFDM sequences can be found with finding independent phase sequences. Let us consider number of phase sequences with the sequence length of (i.e. the number of subcarriers). Then the 9 point of 9 phase sequence is given as
Where
∈
,!……….
The number of subcarriers
∈ #, … … … . .
In this classical SLM technique
$
^ Φ
.
%
(2)
%
.
(3)
Fig.1 The Block diagram for SLM technique The random phasesΦ in each phase sequence will be uniformly distributed in &#, !' with satisfying the condition [4, 6] of () ∅ + #. In this way the number of alternative phase sequences can be found.According to fig.1 the number of alternative candidate vectors (i.e. , to , )can be generated with multiplying each phase sequence to the original data block. The next job is to find IDFT of the alternative candidate vectors using IFFT algorithm that leads to alternative OFDM signals. Out of all these OFDM signals transmit the signal with minimum PAPR. The information about the phase sequence required to select the minimum PAPR based OFDM signal should be sent along with this selected signal. This extra information is to be known as the Side Information (SI) index which is nothing but the set of -./0! 1number of bits. To detect the exact transmitted data at the receiver the perfect detection of this SI index should be done. There will be a chance to lose the whole transmitted data block with the erroneous detection of this SI index. With a slide modification of this classical SLM technique the transmission of the SI index can be avoided. That modification is being described in the next section.
180
2
MODIFIED SLM TECHNIQUE
The fig.1 describes concept about the classical SLM [1]. The modification can be made with designing the phase % . With following the new SLM technique [2] sequence. According to the classical SLM technique% a modified scheme can be considered for the construction of phase sequences. In this modified phase sequence at some points out of ∈ #, , … … … $ it is required to put 2 ^ Φ . Here 2 is the extension factor with satisfying the condition 2 > . With following this concept of designing the phase sequence the perfect detection of SI index at the receiver becomes easy. This detection can be done using suboptimal algorithm [2].According to the concept of sub-optimal algorithm out of number of phase sequences one sequence is being selected which satisfies the minimum energy difference between transmitted signal and received signal. This selected phase sequence should be the perfect sequence that gives the information about transmitted data block.There may be some probability of error with detecting the perfect phase sequence which is being analyzed here as the probability of SI index error with respect to different values of 2.Also the analysis of bit error rate performance being done for considering a fixed value of 2. All these above things are being analyzed here with considering the parameters of WiMAX. 3SIMULATION RESULTS To analyze different results the transmission channel is considered as a quasi-static frequency selective Rayleigh fading with equal power taps. Also the model for nonlinear solid state power amplifier (SSPA) [5] is considered at the transmitter output. The important parameters of WIMAX are to be used are given as follows: Used data subcarriers
278.98 :; ? @ B ?
