Table of Contents
What are subcarriers in OFDM?
Both OFDM and OFDMA divided a channel into subcarriers through a mathematical function known as an inverse fast Fourier transform (IFFT). The spacing of the subcarriers is orthogonal, so they will not interfere with one another despite the lack of guard bands between them. Each OFDM subcarrier is 312.5 KHz.
What is basic principle of OFDM?
The basic principle of OFDM is to split a high-rate datastream into a number of lower rate streams that are transmitted simultaneously over a number of subcarriers.
What is the encoding scheme used in OFDM?
In telecommunications, orthogonal frequency-division multiplexing (OFDM) is a type of digital transmission and a method of encoding digital data on multiple carrier frequencies. OFDM is a frequency-division multiplexing (FDM) scheme that was introduced by Robert W.
What is cyclic prefix in OFDM?
A cyclic prefix is created to prevent intersymbol interference (ISI) when an OFDM signal is transmitted in a dispersive channel. As shown in Figure 13.5, the cyclic prefix (CP) is essentially an identical copy of the last portion of the OFDM symbol appended before the OFDM symbol.
How many subcarriers are in OFDM?
A single OFDM symbol contains 52 subcarriers; 48 are data subcarriers and 4 are pilot subcarriers. The center, “DC” or “Null”, zero subcarrier is not used.
How orthogonality is maintained in OFDM?
In this simple OFDM system there are N sinusoidal input signals. Each subcarrier transmits one bit of information (N bits total) as indicated by its presence or absence in the output spectrum. To maintain orthogonality, T must be the reciprocal of the subcarrier spacing.
What is the use of cyclic prefix in OFDM?
The purpose of the cyclic prefix is to combat ISI and intra-symbol interference. The cyclic prefix is a guard time made up of a replica of the time-domain OFDM waveform. The basic premise is to replicate part of the back of the OFDM signal to the front to create the guard period, as shown in Figure 3.31.
What are pilot symbols in OFDM?
Training OFDM symbols or equivalently OFDM preambles are transmitted at the beginning of the transmission record, while pilot symbols (complex exponentials in time) are embedded in each OFDM symbol, and they are separated from information symbols in the frequency-domain [1–3].
What is guard interval in OFDM?
The standard symbol guard interval used in IEEE 802.11 OFDM is 0.8 μs. The shorter guard interval results in a higher packet error rate when the delay spread of the channel exceed the guard interval and/or if timing synchronization between the transmitter and receiver is not precise.
How does cyclic prefix work in OFDM?
Use of cyclic prefix is a key element of enabling the OFDM signal to operate reliably. The cyclic prefix acts as a buffer region or guard interval to protect the OFDM signals from intersymbol interference.