How is subcarrier spacing calculated in OFDM?
Choosing the first subcarrier to have a frequency such that it has an integer number of cycles in a symbol period, and setting the spacing between adjacent subcarriers (subcarrier bandwidth) to be BSC = B/L, where B is the nominal bandwidth (equal to data rate), and L is the number of subcarriers, ensures that all …
What is the major problem on OFDM?
However, OFDM communication systems have two main disadvantages. The first drawback is the high sensitivity to carrier frequency offsets (CFO) and phase noise, while the second and main aspect is the high peak-to-average power ratio (PAPR) of the transmitted signals.
What are the disadvantages of OFDM?
The main drawbacks of OFDM are its high peak to average power ratio and its sensitivity to phase noise and frequency offset.
How the reliability of OFDM modulation system will improve?
The OFDM system with multiple carriers has high spectral efficiency compared to the single carrier system. To improve the reliability of system, the easiest way is to increase transmission power.
What is subcarrier spacing in OFDM?
Subcarrier spacing is equal to the reciprocal of the symbol time. As a result of the longer symbol time, the subcarrier size and spacing decreases from 312.5 KHz to 78.125 KHz. The narrow subcarrier spacing allows better equalization and therefore enhanced channel robustness.
What is subcarrier 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. The frequency of each subcarrier is selected to form an orthogonal signal set.
How orthogonality is achieved in OFDM?
In OFDM, multiple closely spaced orthogonal subcarrier signals with overlapping spectra are transmitted to carry data in parallel. In coded orthogonal frequency-division multiplexing (COFDM), forward error correction (convolutional coding) and time/frequency interleaving are applied to the signal being transmitted.
What is the advantage of OFDM over OFDM is?
Immunity to selective fading: One of the main advantages of OFDM is that is more resistant to frequency selective fading than single carrier systems because it divides the overall channel into multiple narrowband signals that are affected individually as flat fading sub-channels.
How does OFDM subcarrier work?
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.
What is the subcarrier spacing in LTE?
15 kHz apart
In LTE, each subcarrier is spaced 15 kHz apart. These subcarriers are combined in groups of 12 to form a single resource block. Each resource block is used in an OFDMA arrangement to send data to different handsets or combined for high-speed data.
What does DC subcarrier indicate?
3. What does the DC subcarrier indicate? Explanation: All the subcarriers of an OFDM symbol do not carry useful data. In OFDM and OFDMA PHY layers, the DC subcarrier is the subcarrier whose frequency is equal to the RF centre frequency of the transmitting station.
