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International Research Journal of Engineering and Technology (IRJET)

e-ISSN: 2395-0056

Volume: 11 Issue: 02 | Feb 2024

p-ISSN: 2395-0072

www.irjet.net

FIR filter-based Sample Rate Convertors and its use in NR PRACH Yashas R1, Ilakkiya R1, Arathi R Shankar2 1Student & BMS college of engineering Dept. of Electronics and communication Engineering, BMS college of

engineering, Karnataka, India

1Technical Leader & Nokia, Karnataka, India

2Associate Professor, Dept. of Electronics and communication Engineering, BMS college of engineering,

Karnataka, India

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Abstract - The transmission of data through the air

Random-Access Channel (PRACH) processing, where the IFFT and FFT sizes are determined based on the PRACH sequence length.

interface using both Physical Random Access channels (PRACH) and Physical Uplink Shared channels (PUSCH) in an Orthogonal Frequency Division Multiplexing (OFDM) system The data rate at instances of PRACH subcarrier frequencies is smaller than that of PUSCH subcarriers. To achieve seamless data transmission, sampling rate conversion is employed to match the varying subcarrier spacings and channel bandwidths. Sampling rate conversion involves adding or removing samples while preserving the duration and shape of the signal. This process introduces variations in the power spectral density in the frequency domain, necessitating filtering techniques to retain the original power spectral density. Specifically, in NR PRACH processing, the IFFT size at the transmitter and FFT size at the receiver are fixed based on the PRACH sequence length, requiring sampling rate conversion to align with the IFFT and FFT processing. This paper discusses and compares the characteristics and performance results of the digital Finite Impulse Response (FIR)-based sampling rate conversion filter, the Cascaded Integrator Comb (CIC) Filter, which is used with interpolation and decimation filters at the transmitter and receiver, respectively. The study provides insights into selecting the most suitable sampling rate conversion filter for OFDM systems, ensuring efficient data transmission, and optimizing spectral efficiency.

In this research paper, the Cascaded Integrator Comb (CIC) filter, recognized as a digital Finite Impulse Response (FIR) filter, is thoroughly examined for its ability to achieve precise and distortion-free sampling rate conversion in communication systems based on Orthogonal Frequency Division Multiplexing (OFDM). The CIC filter is highly favored for such applications due to its straightforward operation and minimal computational complexity. To align the sampling rate with the set IFFT FFT processing requirements in the context of OFDM systems, sampling rate conversion is required. The sampling rate is determined by subcarrier spacing and channel bandwidth; any deviation from these parameters necessitates conversion of the sampling rate to OFDM. The IFFT size at the transmitter and FFT size at the receiver are predefined based on the length of the PRACH sequence, which further emphasizes the significance of sampling rate conversion in NR PRACH processing. The proposed technique converts sampling rates using decimation filters at the receiver and interpolation filters at the transmitter. These filters effectively increase or decrease the number of samples to achieve the desired sampling rate while preserving the original signal's duration and shape. The primary goal of this paper is to evaluate the CIC Filter's capabilities and characteristics in the context of sampling rate conversion in OFDM systems.

Key Words: OFDM, PRACH, PUSCH, sampling rate conversion, interpolation, decimation, FIR filter, CIC Filter, spectral efficiency, wireless communication

1.INTRODUCTION

The paper's structure is as follows: Section 2 provides a comprehensive literature review of sampling rate conversion methods and filters utilized in OFDM systems. In Section 3, the methodology is presented, which includes an overview of digital FIR-based filters and the specific requirements for sampling rate conversion in OFDM systems and section 4 is having results. Finally, Section 5 concludes the paper by summarizing the key findings and proposing potential avenues for future research.

Sampling rate conversion is a fundamental process in signal processing that allows for the addition or removal of samples while preserving the signal's duration and shape. Its significance spans various industries, including wireless communications, where precise sampling rate conversion plays a vital role. An example is in Orthogonal Frequency Division Multiplexing (OFDM) systems, where accurate conversion ensures compatibility between the fixed Inverse Fast Fourier Transform (IFFT) at the transmitter and the Fast Fourier Transform (FFT) at the receiver. This compatibility is critical for efficient New Radio (NR) Physical

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