Though OFDM has many advantages like high spectral efficiency, robustness to channel fading, immunity to impulse interference, capacity to handle very strong echoes and less non-linear distortion it also has disadvantage of high PAPR .
Filtering after clipping can demote out of band radiation but cause peak re-growth which may exceed clip level.
A large PAPR limits the range of Linear Operation of power amplifier in transmitter this reduces the efficiency of the system. By separating large information sequence into different sub-blocks and encode these subblocks with system on programmable chips SOPC large PAPR reduction can be achieved .
This paper is organized as follows.
There are multiple transceivers at both the base station and UE in order to enhance link robustness and increase data rates for the LTE downlink. Fundamental idea behind scheme is phase rotation. The window size should be narrow otherwise it affects number of signal sample which cause increasing BER.
The main idea behind the OFDM is that since low-rate modulations are less sensitive to multipath, the better way is to send a number of low rate streams in parallel than sending one high rate waveform.
The major disadvantages of a high PAPR is increased complexity in the analog to digital and digital to analog converter. The soft information thus obtained destroys the MMS estimation. Among all above advantage it has one major flaw of peak-to-average-power ratio PAPR.
Using this technique, a serial bit is transformed into various parallel bit streams. The carriers are linearly independent i. This scheme takes an edge as no need of side information to send along with message, less complexity. The transmitter also performs a linear filtering operation referred to as pulse shaping in order to reduce out-of- band signal energy.
Suppose a bandwidth goes from frequency say a to b, then this can be subdivided into a frequency of equal spaces. The OFDM divides the frequency spectrum into sub-bands small enough so that the channel effects are constant flat over a given sub-band.
Long term evolution LTE is standardized by the third generation partnership project 3GPP and is an evolution of existing 3G technologies in order to meet projected customer needs over the next decades.
To do so, it performs the signal processing operations as shown in Figure 1. Among all above advantage it has one major flaw of peak-to-average-power ratio PAPR.
Due to this, the spectrum of each carrier has a null at the center frequency of each of the other carriers in the system. For minimizing the channel delay, a guard interval is added with each symbol.
As a result, interference is observed between sub-carriers. There is no need for additional operation and no side information to receiver. Then phase rotation is added to develop number of candidate signal and choose one with lowest PAPR .
So there should be something here.
It is also sensitive to frequency synchronization problems and having high peak-to-average-power ratio PAPR. Suppose the symbol run longer as the first choice. LTE should support several different spectrum allocation sizes as: But now the start of the symbol falls into the danger zone, and this start is the most important thing about the symbol because the slicer needs it to take a decision about the bit.
Section V describes conclusion. The subcarriers are placed close to each other so that the data can be transmitted in parallel. It also averages the interferences within the cells using allocation with cyclic permutation and offers frequency diversity by spreading the carriers all over the used spectrum.
The OFDM system transmits a large number of narrowband carriers, which are closely spaced. Here subcarriers with QPSK modulation technique are used to make sure envelope for all subcarrier are equal.
To provide adjacent channel interference protection, signals are moved further apart. The peak data rates may depend on the number of transmit and receive antennas at the User Equipment UE.
The cyclic prefix acts as a guard interval. It is also sensitive to frequency synchronization problems and having high peak-to-average-power ratio PAPR. A little bit of blank space has been added between symbols to catch the delay spread illustration not visible in this excerpt Figure 1.
This will not work for the hardware which likes to crank out signals continuously. These methods are briefly described in the following subsections There are various techniques to overcome above mentioned major problem.Selective Mapping technique for PAPR reduction in LTE-OFDM Systems - Neelam Dewangan - Master's Thesis - Engineering - Communication Technology - Publish your bachelor's or master's thesis, dissertation, term paper or essay.
OFDM PAPR REDUCTION WITH LINEAR CODING AND CODEWORD MODIFICATION SUSAR, Aylin agronumericus.com, Department of Electrical and Electronics Engineering Supervisor: Prof. Dr. Yalçın TANIK Augustpages In this thesis, reduction of the Peak-to-Average Power Ratio (PAPR) of Orthogonal Frequency Division Multiplexing (OFDM) is studied.
One drawback of an OFDM signal is its high peak-to-average power ratio (PAPR), which requires the transmitter to operate in a large dynamic range to retain all desirable information.
To reduce the PAPR,companding transform has been investigated. Low Complex PAPR Reduction Schemes for OFDM Systems by Siyu Zhang A Thesis Submitted to the Faculty of Graduate Studies through.
 Abhishek Arun Dash, “OFDM systems and papr reduction techniques in OFDM systems”, Phd Thesis, year  Komal Gupta agronumericus.com, “PAPR reduction of OFDM using a new phase sequence in SLM technique”,IEEE, vol.
2, no. 2, pp.year A New Peak Clipping Algorithm for PAPR Reduction in OFDM. Figure 1. Base-band OFDM System model with N subcarriers The paper is organized as follows.
The system model is A New Peak Clipping Algorithm for PAPR Reduction in OFDM. 9: 𝑖𝑖←𝑖𝑖+ 1 from the graphs that as the number of iteration (NOI) end while /.Download