Volume 17, Issue 2 (9-2020)
JSDP 2020, 17(2): 32-15 |
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Abstract: (2360 Views)
Recently, orthogonal frequency division multiplexing (OFDM) has been extensively used in communications systems to resist channel impairments in frequency selective channels. OFDM is a multicarrier transmission technology in wireless environment that use a large number of orthogonal subcarriers to transmit information. OFDM is one of the most important blocks in digital video broadcast-terrestrial (DVB-T) system. The goal of this paper is comparing the methods of interpolation in OFDM system that not used channel statistics information. Therefore, we used pilots for obtaining the information of channel, and by the method of estimation without use of channel statistics information, the channel primary frequency response estimated in pilot’s frequencies. Pilots, channel estimation and interpolation methods are key roles in the OFDM block. The number of pilots are different in the OFDM symbol for different pilot patterns. In this article, we proposed three pilot patterns to improve DVB-T system performance. Our criteria for this purpose are error probability, calculation time, and the number of pilots. We have tested the performance improvement by using two-dimensional (2D) interpolation methods. Obviously, we do not obtain all of our requests and requirements via one pilot pattern. For example, the error may be decreases, but the number of pilots is increased. Therefore, we must select the pilot pattern that achieve the most important goal for us. We have applied six interpolation methods, for 2D interpolation, such as linear, nearest-neighbor, spline, cubic Hermite, cosine and low pass interpolations. We have compared three proposed pilot patterns with the conventional DVB-T pilot pattern in four different channels. In each channel, we have tested 30 interpolation methods. The applied channels are OFDM system with AWGN noise, OFDM system with AWGN noise and Rayleigh fading, DVB-T system with AWGN noise and DVB-T system with AWGN noise and Rayleigh fading. We observed that the best performance happens when we use linear interpolation in the first dimension and cosine interpolation in the second dimension of 2D interpolation. In addition, the worst performance will be happened when Nearest-neighbor interpolation is used in the second dimension of 2D interpolation. In the last step, we compared the proposed pilot patterns with the conventional DVB-T pilot pattern in 2D interpolation method that it leads to better performance in DVB-T system. We observed that the proposed pilot patterns have better performance than the conventional DVB-T pilot pattern. In the DVB-T, movement and velocity are very important and considered in this research. In the second step using DVB-T pilot pattern, we compared 2D interpolation methods in some different Doppler frequencies. Simulation results show that at 3 Doppler frequencies, i.e. 0, 30, 150Hz, the proposed schemes with a linear interpolation has better performance than the conventional method in the DVB-T systems.
Type of Study: Research |
Subject:
Paper
Received: 2017/07/30 | Accepted: 2020/06/2 | Published: 2020/09/14 | ePublished: 2020/09/14
Received: 2017/07/30 | Accepted: 2020/06/2 | Published: 2020/09/14 | ePublished: 2020/09/14
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