Signal Processing for Communication Systems
OFDM, known as Orthogonal Frequency Division Multiplexing, is a digital modulation technique that divides a wideband signal into several narrowband signals. By doing so, it elongates the symbol duration of each narrowband signal compared to the original wideband signal, effectively minimizing the impact of time dispersion caused by multipath delay spread. OFDM is categorized as … Read more
Key focus: 5G NR resource block : a block of 14 OFDM symbols (1 slot across time domain) with the corresponding 12 subcarriers for those symbols 5G NR protocol stack In the 5G New Radio (NR), the protocol architecture can be separated into two categories: user plane protocol stack and control plane protocol stack. The … Read more
Synopsis: Cyclic prefix in OFDM, tricks a natural channel to perform circular convolution. This simplifies equalizer design at the receiver. Hands-on demo in Matlab. Cyclic Prefix-ed OFDM A cyclic-prefixed OFDM (CP-OFDM) transceiver architecture is typically implemented using inverse discrete Fourier transform (IDFT) and discrete Fourier transform (DFT) blocks (refer Figure 13.3). In an OFDM transmitter, … Read more
Goal: Simulate discrete-time cyclic-prefixed OFDM communication system. Explain role of IFFT/FFT, cyclic prefix. Simulate M-QPSK / M-QAM based cyclic prefixed OFDM over AWGN channel. Discrete-time implementation of baseband CP-OFDM The schematic diagram of a simplified cyclic-prefixed OFDM (CP-OFDM) data transmission system is shown in Figure 1. The basic parameter to describe an OFDM system is … Read more
Consider a non-ideal channel h(t)≠δ(t), that causes delay dispersion. Delay dispersion manifests itself as Inter Symbol Interference (ISI)on each subcarrier channel due to pulse overlapping. It will also cause ICC (Inter Carrier Interference ) due to the non-orthogonality of the received signal. Adding cyclic prefix to each OFDM symbol mitigates the problems of ISI and … Read more
In the previous article, the architecture of an OFDM transmitter was described using sinusoidal components. Generally, an OFDM signal can be represented as \(s(t)\) = symbols mapped to chosen constellation (BPSK/QPSK/QAM etc..,) \(f_n\) = orthogonal frequency This equation can be thought of as an IFFT process ( Inverse Fast Fourier Transform). The Fourier transform breaks a … Read more
Article moved to new pages The article has been consolidated into these following pages. Please refer these links. If you are looking for Matlab code refer this ebook : Simulation of Digital Communication Systems by Mathuranathan Viswanathan (1) Introduction to OFDM – Orthogonal Frequency Division Multiplexing (2) An OFDM Communication System – Implementation Details (3) … Read more
In modulations, information is mapped on to changes in frequency, phase or amplitude (or a combination of them) of a carrier signal. Multiplexing deals with allocation/accommodation of users in a given bandwidth (i.e. it deals with allocation of available resource).OFDM is a combination of modulation and multiplexing. In this technique, the given resource (bandwidth) is … Read more