Abstract
LTE (long term evolution) is come to meet our desired high speed data communication.LTE is the last step toward the 4th generation (4G) of radio technologies designed to increase the capacity and speed of mobile telephone networks. Where the current generation of mobile telecommunication networks are collectively known as 3G (for third generation), LTE is marketed as 4G. LTE uses Orthogonal Frequency Division Multiplexing (OFDM) for the downlink - that is, from the base station to the terminal. OFDMA meets the LTE requirement for spectrum flexibility and enables cost-efficient solutions for very wide carriers with high peak rates. However, one of the main drawbacks of the OFDMA modulation technique is the large peak-to-average power ratio (PAPR) of the transmitting signals. This high PAPR causes interference when the OFDM signals are passed through an amplifier which does not have enough linear range. Several PAPR reduction techniques such as magnitude clipping, block coding, and partial transmit sequence (PTS) and pulse shaping have been proposed to reduce the PAPR. In this paper, we evaluate a clipping based PAPR reduction technique. The complementary cumulative distribution function (CCDF) of the PAPR, which can be used to evaluate the PAPR reduction performance, is derived for OFDMA signals.
Highlights
At present time the demand on high data rate is increasing in order to support broadband services
Multiple access is achieved in orthogonal frequency division multiplexing access (OFDMA) by assigning subsets of subcarriers to individual users i.e. the enter channel is divided into many narrow sub–channel, which are transmitted in a parallel, thereby increasing the symbol duration and reducing the inter symbol-interference (ISI)
In the following we describe some modifications of peak-to average power ratio (PAPR) reduction techniques for an OFDMA downlink
Summary
At present time the demand on high data rate is increasing in order to support broadband services. SCFDMA is a promising technique for high data rate transmission that utilizes single carrier modulation and frequency domain equalization. If downlink PAPR reduction is achieved by schemes designed for OFDM, each user has to process the whole data block and demodulate the assigned subcarriers extract their own information. This introduces additional processing for each user’s receiver. OFDMA (DFTS-OFDM). the main benefit of DFTS-OFDM compare to scheme is reduced variations in the instantaneous transmit power, implying the possibility for increased power –amplifier efficiency, low-complexity high quality equalization in the frequency domain and flexible bandwidth assignment [12].
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