International Research Journal of Engineering and Technology (IRJET)
e-ISSN: 2395 -0056
Volume: 04 Issue: 04 | Apr -2017
p-ISSN: 2395-0072
www.irjet.net
PAPR Reduction Based Pilots Assisted Channel Estimation in OFDM Systems Abirami A1, C.Jeya suriya2 1PG
Scholar, Communication system, PET Engineering College, Vallioor 2 Assistant Professor PET Engineering College, Vallioor
---------------------------------------------------------------------***---------------------------------------------------------------------
Abstract - Channel estimation plays out an essential part in orthogonal frequency-division multiplexing (OFDM) systems. Insertion of pilot symbols is one of the required techniques for estimation of channel. However, the peak-to-average power ratio (PAPR) suffers the OFDM system. PAPR can be reduced by utilizing various accessible procedures, such as coding, active constellation extension, amplitude clipping, and selective level mapping. The coding approach produces redundant data that significantly reduce the bit rate. The active constellation extension requires higher transmission power. The clipping method and Selective Level mapping (SLM) is the best among the available methods. In this study, we combine the clipping and SLM methods, which is efficient in terms of PAPR reduction value and of spectral efficiency while the channel estimation performance is maintained. Key Words: PAPR, OFDM, SLM, Clipping, Pilots 1. INTRODUCTION Orthogonal frequency division multiplexing (OFDM) has turned out to be important in numerous applications amid the most recent decade as a result of its advantages. OFDM can give high information rates and in addition handle multipath channels without requiring confounded equalizers. Given the significance of such a framework, the channel state information(CSI) is assessed to give great quality to the conveyed information. Two important techniques are used to estimate the CSI: blind and non-blind. The visually impaired technique does not send pilots (in any event expressly), though the non-blind sends the embedded pilots to evaluate the CSI. The pilot addition based channel estimation is subdivided into two methodologies: block type channel estimation and comb type channel estimation. The look over sort is the most relevant for multipath channel estimation purposes. Be that as it may, one of the essential issues in the OFDM framework is the peak to average power ratio (PAPR). Various strategies can be utilized to diminish the PAPR values, such as the block-coding technique, active constellation extension, amplitude clipping (AC), and the selected mapping (SLM).In this paper we used AC and the SLM techniques for PAPR reduction. Another issue that emerges when the PAPR decrease strategies are connected is the contortion of the pilot tones before these are sent to the multipath channel. This issue is tended to in this paper utilizing the AC-strategy, wherein the high pinnacles are sliced off to reduce the PAPR. In a typical case, the pilot tones are embedded at high power (high peaks). All information are then subjected to the PAPR reduction to evacuate the high peaks, which brings about the incorrect estimation of CSI by the beneficiary. In the event that the SLMbased PAPR diminishment strategy is utilized rather than the AC approach, a few periods of the embedded pilots would change. Notwithstanding, this change would not influence the CSI estimation at the beneficiary. These marvels are talked about in the consequent segments of the paper. 2. OFDM SYSTEM MODEL Let A = [A0 A1 ··· AN-1] T be the input symbol vector , where Ak represents the complex data of the kth subcarrier and N is the number of subcarriers. The OFDM signal is generated by adding all the N modulated subcarriers each of which is separated by 1/NTs in the frequency domain, where Ts is the sampling period. Then, a(t) continuous time baseband OFDM signal is defined as:
a (t )
1 N
k 0 AKe N 1
j 2
k t NT
;0 t NT s
[1]
where, fk=k∆f, ∆f=1/NTs
© 2017, IRJET
|
Impact Factor value: 5.181
|
ISO 9001:2008 Certified Journal
|
Page 829