# What are subcarriers in OFDM?

## 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.

How many subcarriers are used in OFDM?

52 subcarriers
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 do you calculate the number of subcarriers 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 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. Intersymbol interference is eliminated almost completely by introducing a guard time in every OFDM symbol.

#### What does OFDM stand for?

Orthogonal frequency division multiplexing
Orthogonal frequency division multiplexing (OFDM) is a multicarrier modulation technique that has been chosen as the modulation scheme for several current and next generation broadband communication systems.

How is OFDM calculated?

Thus the bandwidth of the OFDM baseband signal is N/2*delta_f,delta_f is the sub-carrier frequency spacing. The sub-carrier frequency spacing delta_f =1/Ts= 1/(Td * N), Ts is the OFDM symbol duration,Td is the sampling symbol duration and equal to the smapling time interval。 Thus Td=1/fs, fs is the DAC sampling rate.

## What is difference between OFDM and Ofdma?

The main difference between an OFDM and an OFDMA (Orthogonal Frequency Division Multiple Access) system if the fact that in the OFDM the user are allocated on the time domain only while using an OFDMA system the user would be allocated by both time and frequency. For the uplink SC-FDMA will be used.

What is a symbol in OFDM?

In a digitally implemented OFDM system, the input bits are grouped and mapped to source data symbols that are a complex number representing the modulation constellation point (e.g., the BPSKBinary phase shift keying – A type of phase modulation using 2 distinct carrier phases to signal ones and zeros. or QAM symbols …

### What is OFDM and how it works?

In data communications and networking, orthogonal frequency-division multiplexing (OFDM) is a method of digital data modulation, whereby a single stream of data is divided into several separate sub-streams for transmission via multiple channels.

What is OFDM in 5G?

Orthogonal Frequency Division Multiplexing (OFDM) is an efficient modulation format used in modern wireless communication systems including 5G. OFDM combines the benefits of Quadrature Amplitude Modulation (QAM) and Frequency Division Multiplexing (FDM) to produce a high-data-rate communication system.

#### When do you use a null subcarrier in OFDM?

The only portion of the spectrum that is “occupied” or “transmitted” are the subcarriers that are actually used (i.e. 10 MHz instead of 15 MHz). The null subcarriers referenced in your question are used for two purposes:

Which is a null subcarrier in the PHY layer?

Another null subcarrier is the DC (Direct Current) subcarrier. 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. It corresponds to frequency zero (Direct Current) if the FFT signal is not modulated.

## When to use a null subcarrier at DC?

The null subcarrier at DC is used to allow the use of simple (again, cheaper) direct-conversion (zero-IF) RF receivers. One disadvantage of zero-IF receivers is that they typically encounter a strong interfering signal at DC.

How many lower frequency subcarriers are used in OFDM PHY?

For OFDM PHY, NFFT = 256, the number of lower-frequency guard subcarriers is 28 and the number of higher-frequency guard subcarriers is 27. Considering also the DC subcarrier, there remains Nused, the number of used subcarriers, excluding the null subcarriers.