OFDM communication system

What is the achievable performance of OFDM communication system transmission over various fading and noise channels?

  1. Introduction 

Orthogonal Frequency Division Multiplexing (OFDM) is a type of signal modulation that is insensitive to frequency selectivity of transmission channels thereby achieving high transmission rate. The positive effect of utilizing Orthogonal Frequency Division Multiplexing on data transmission is attributed to the inherent behavior of this type of signal modulation to separate high data rate modulating stream by introducing them onto various slowly modulated narrowband close-spaced sub-carriers [1] [8]. However, the necessity of carrying out this project is that OFDM is an extremely popular modulation type that is used in the development of:

  • LTE (4G).
  • Link budget and link design performance.

This paper will focus on the achievable performance of OFDM communication system transmission over various fading and noise channels.

  • Background

OFDM is being one of the most populartechnologiesin communication systems fields due to the high performance that it provide without getting distortion from inter-symbol-interference (ISI). In this project, a combination of various fading and noise channel will be used in order to examine the achievable performance of OFDM transmission over them.

  1. Project Scope and Specifications 
  • Generating software for an ODFM communications system model in Matlab.
  • Using computer simulation to design and analyze the performance of OFDMover multipath propagating channels
  • Generating software for various channel models.
  • Generating software to estimate the bit error rate performance and the bit error rate performance of the OFDM system obtained by simulation.
  • Understanding techniques for the digital computer simulation of digital communication systems.
  1. Literature Review
  • OFDM principle

Generally, the high data rate of Orthogonal Frequency-Division Multiplexing is attained due to the distribution and simultaneous transmission of low signal streams into multiple sub-carriers. One distinguishing feature of OFDM is that each sub-carrier is independent to other orthogonal sub-carriers carrying a fraction of the data being transmitted. Furthermore, the spacing behavior of OFDM provides the orthogonality to the FDM technique thereby allowing the demodulators to see only its own frequencies while preventing to see other frequencies [9]. However, OFDM has several feature that distinguish it from other modulation techniques such as:

  • Decoding and de-interleaving.
  • Channel equalization.
  • Using Inverse Fast Fourier Transform (IFFT) to modulate symbols into orthogonal sub-carriers.
  • Using Fast Fourier Transform (FFT) to demodulate the received signal.
    • OFDM modulation and demodulation techniques

The two techniques that should be considered when using OFDM are the modulation and demodulation. Modulation is a technique used in order to reduce the effect of noise during the transmission of signal waves over the communication channel. According to Hirosaki [7], the three advantages of performing the modulation technique that include: excellent performance in terms of its effective bit error rate, high power and spectral efficiency. On the other hand, demodulation technique is performed at the receiver side. This technique is utilized in order to ensure the recovery of the original data transmitted from the modulated signal.

  • Fast Fourier Transform (FFT) and Inverse (FFT)

Deployment of modulation and demodulation techniques can be attained via Fast Fourier Transform (FFT) and Inverse Fast Fourier Transform (IFFT) [11]. Jung [10] conducted a study regarding the design and implementation of FFT and IFFT algorithm in order to identify the specifications covering various industrial applications for OFDM. Findings of the study indicate that the computational efficiency of OFDM has a correlation on the use of IFFT algorithm and that FFT algorithm influences the spacing behavior at the side of the recipient.

  • Performance of OFDM over fading and noise channels

Several research studies [2, 4, 5, 6] have been conducted to investigate the performance of OFDM during data transmission using fading and additive noise channels. The specific types of channels that achieved the most effective Orthogonal Frequency-Division Multiplexing transmission are Additive White Gaussian Noise (AWGN) channel, Rayleigh fading and Rician fading channel.

Additive White Gaussian Noise (AWGN) refers to a statistically random radio noise characterized by a broad range of frequency with regards to a signal in the communications channel [12]. On the other hand, Rayleigh fading is created by multipath reception that is used to normalize the properties of the channel experiencing multipath conditions. It is typically used when there is no line of sight between the transmitter and receiver [6, 12]. On the contrary, Rician fading is used when there is a line of sight between the transmitter and receiver. It usually occurs when the signal waves transmitted travel at different paths causing the partial cancellation of the signal by itself [6, 13].

  1. Approach

This is expected to be a significant section written in consultation with the supervisor detailing the method and techniques that will be used to achieve project objectives. You are encouraged to use diagrams, flowcharts, system designs, etc. for illustration.


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