A NEW PROPOSED SCHEME FOR PAPR REDUCTION OF OFDM SYSTEM
COMBINING HADAMARD TRANSFORM AND HANN PEAK WINDOWING
ABSTRACT
Orthogonal Frequency Division Multiplexing (OFDM) is a proficient modulation technique
which is used brutally both broadband wired and wireless communication. It brings many
advantages. Eliminating Inter Symbol Interference (ISI) and Inter Carrier Interference (ICI),
makes efficient use of the spectrum and dividing the channel into narrowband flat fading sub
channels are some of them. But it’s not free from disadvantages too. One major disadvantage of
OFDM is that the time domain OFDM signal which is a sum of several sinusoids leads to high
peak to average power ratio (PAPR). There are many different types of PAPR reduction
techniques. Such that Clipping, Windowing, Coding etc. In this paper a new scheme was
proposed combining Hadamard transform and Hann peak widowing technique to achieve more
novel PAPR reduction. We analyzed performance of the PAPR reduction technique calculating
BER. The PAPR reduction performances were analyzed for an OFDM system model containing
64 subcarriers and BPSK modulation technique. All simulations were performed on MATLAB
7.5 platform
PROPOSED METHOD
Figure 1: OFDM transceiver block diagram
At the starting end binary data is being inputted to the system. After that this binary data is going
through to the process of digital to analog mapping. And this mapped signal is being modulated
with proper modulation technique. This modulation signal is than converted into parallel signal
by signal to parallel converter. This parallel data is being inputted to the IFFT operation block.
This IFFT block converts the frequency domain signal to time domain signal for each subcarrier.
Cyclic prefix is being added with the time domain signal.
After that this time domain signal is being transmitted through the channel after proper
filtering and applications. This transmitted signal is received by receiver and the receiver action
is somewhat inverse of transmitter. The starting end of receiver is a synchronizer. It is being used
to equalize the received signal to prevent any channel effect and to get the proper signal. Figure 1
shows the transceiver bloc diagram of OFDM system.
ALGORITHM
The signal processing algorithm steps are given below
Step 1: The sequence of in data, X is transformed by in order Hadamard matrix
Y=HX
Here H is the Hadamard matrix
Step 2: The Hadamard transformed data sequence Y is inputted to the IFFT unit. The time
domain signal output of IFFT unit is
Y=[y (1), y (2) y (3)…..y (N)]
Step 3: Hann peak windowing is performed over this IFFT output according to following
procedure
If y(x)>threshold , then y(n)=y(n)*Hann
If y(x)≤threshold , then y(n)=y(n)
Step 4: FFT transform is performed on the received signal, r(n) that is, Yr=FFT(r)
Here,
r=[r (1), r (2) r (3)…..r (N)]
CONCLUSION
The complexity of Hadamard Transform rises with the increased number of data bit. This may
broaden the calculation time causing delay. The windowing process causes self-interference. One
major disadvantage of OFDM is that the time domain OFDM signal which is a sum of several
sinusoids leads to high peak to average power ratio (PAPR). There are many different types of
PAPR reduction techniques. Such that Clipping, Windowing, Coding etc. In this paper a new
scheme was proposed combining Hadamard transform and Hann peak widowing technique to
achieve more novel PAPR reduction.
FUTURE SCOPE
In future this work can be made more elegant by improving the signal distortion techniques
along with Hadamard transform so that a more sophisticated and prolific PAPR reduction
scheme can be obtained