ARFCN

Absolute Radio Frequency Channel Number (ARFCN) is a term commonly used in mobile communication systems to uniquely identify a specific carrier frequency or within a frequency band. It is important for frequency planning, channel allocation, and communication between mobile devices and base stations. Term ARFCN started from the GSM and evolved with the new technologies like UARFCN for UMTS/WCDMA, named EARFCN for E-UTRA/LTE and now renamed as NR-ARFCN for 5G/NR.

ARFCNs are like numbered parking spots. The center frequency of a carrier is like the parking lot, and the frequency grid spacing is the distance between spots. In the context of Frequency Division Duplexing (FDD), distinct ARFCN values are allocated for the downlink and uplink directions due to their differing frequencies. Equivalently, the offset with respect to the downlink ARFCN could be used to identify the uplink ARFCN. By default, the UL ARFCN is exactly lower than the DL ARFCN by the value of the bandwidth. However, in the Time Division Duplexing (TDD) system, a singular ARFCN value is sufficient as the downlink and uplink frequencies coincide.

To convert the ARFCN and frequency values in MHz to each other, the equations below are used, where $N$ is the ARFCN value, $f$ is the frequency in MHz, $f_\text{off}$ is the frequency offset in MHz, $N_\text{off}$ is the ARFCN offset, and $\Delta$ is the frequency grid spacing in kHz. The values of $f_\text{off}$, $N_\text{off}$, and $\Delta$ depend on the frequency range as given in the table below.

$$f = f_\text{off} + \Delta (N - N_\text{off}) N = N_\text{off} + \frac{f - f_\text{off}}{\Delta}$$

Frequency range	$\Delta$	$f_\text{off}$	$N_\text{off}$	Range of $N$
0 – 3000 MHz	5 kHz	0 MHz	0	0 – 599999
3000 – 24250 MHz	15 kHz	3000 MHz	600000	600000 – 2016666
24250 – 100000 MHz	60 kHz	24250 MHz	2016667	2016667 – 3279167

While choosing the frequencies for the next lab exercises, you have to make sure that the chosen frequencies are divisible by the frequency grid spacing $\Delta$ and the subcarrier spacing used.