5G NR Channel Bandwidth Calculator

Architecture of 5G NR Transmission Bandwidth Configuration

In 3GPP cellular network engineering, the air-interface channel bandwidth (BW_channel) represents the total nominal RF spectrum block allocated to a radio carrier by regulatory authorities (e.g., 20 MHz, 40 MHz, or 100 MHz). However, wireless transceivers cannot transmit active data subcarriers across 100% of this nominal bandwidth due to physical analog filter roll-off, power amplifier non-linearities, and digital-to-analog converter (DAC) reconstruction constraints. The actual spectrum occupied by modulated information is formally defined in 3GPP TS 38.101-1 and TS 38.101-2 as the Transmission Bandwidth Configuration (BW_transmission).

In legacy 4G LTE, 3GPP applied a rigid, uniform ~90% spectrum utilization rule across all channel sizes. For example, a standard 20 MHz LTE channel allocates exactly 100 Physical Resource Blocks (PRBs), each spanning 180 kHz (12 subcarriers × 15 kHz), yielding an active transmission bandwidth of exactly 18.0 MHz:

The remaining 2.0 MHz (1.0 MHz on each channel edge) served as an unmodulated guardband to satisfy Adjacent Channel Leakage Ratio (ACLR) limits. In 5G New Radio, this conservative 90% boundary was systematically dismantled. By pairing flexible subcarrier spacing with modern steep digital finite impulse response (FIR) baseband filters, windowing, and adaptive pulse-shaping, 5G NR achieves spectrum utilization efficiencies scaling up to 98.28% in wideband channels. For instance, in a 100 MHz C-Band carrier with 30 kHz SCS, 5G NR provisions 273 PRBs, occupying 98.280 MHz and leaving an edge guardband of only 845 kHz per side.

Minimum Guardband Mechanics & RF Transceiver Filtering (TS 38.101)

To maintain strict interoperability between gNodeBs and user terminals (UEs) from competing infrastructure vendors without inducing co-channel or adjacent-channel interference, 3GPP standardizes the minimum required guardband (GB_min) at each channel boundary.

The standard specifies that the actual frequency distance from the nominal RF channel edge to the center of the outermost active subcarrier must equal or exceed the minimum guardband plus half a subcarrier spacing. Mathematically, the single-edge minimum guardband is formulated as:

Where:

• BW_channel: The nominal channel bandwidth in MHz.
• N_PRB: The maximum standardized Physical Resource Block allocation per TS 38.101-1 Table 5.3.2-1 (for FR1) or TS 38.101-2 Table 5.3.2-1 (for FR2).
• Δf: The active subcarrier spacing in kHz (15, 30, 60, or 120 kHz).
• Δf / 2: The critical subtraction of half a subcarrier spacing, accounting for the physical width of the outermost subcarrier sinc-pulse lobe extending beyond its center frequency.

If the actual guardband calculated from the operator's PRB allocation is less than GB_min, the gNodeB's analog and digital filters will fail to attenuate out-of-band emissions (OOBE) sufficiently, leading to spectral mask non-compliance and adjacent-carrier desensitization.

Scalable Subcarrier Spacing (SCS) Impact on Channel Sizing

The exponential scalability of 5G NR numerology (Δf = 2^μ × 15 kHz) directly dictates which subcarrier spacings can physically operate within specific channel bandwidths:

• 15 kHz SCS (μ=0): Limited to channel bandwidths from 5 MHz up to 50 MHz in FR1. A 100 MHz channel at 15 kHz SCS would require 546 PRBs and 6,552 active subcarriers, requiring an unfeasibly large 8192-point FFT that would impose excessive computational latency and battery drain on mobile UEs.
• 30 kHz SCS (μ=1): The global workhorse for FR1 mid-band and C-Band TDD (Bands n77, n78, n41), supporting channel bandwidths from 10 MHz up to 100 MHz. At 100 MHz, 30 kHz SCS requires 273 PRBs (3,276 subcarriers), fitting inside a standard 4096-point FFT.
• 60 kHz SCS (μ=2): Supported across both FR1 (10 MHz to 100 MHz) and FR2-1 (50 MHz to 200 MHz). In FR1, it provides extreme resilience against Doppler spread in high-speed vehicular and maglev train networks (up to 500 km/h).
• 120 kHz SCS (μ=3): Exclusively deployed in FR2 millimeter-wave spectrum (Bands n257, n258, n260, n261), supporting massive contiguous channels of 50 MHz, 100 MHz, 200 MHz, and 400 MHz. The wide 120 kHz subcarrier spacing delivers essential immunity against the severe oscillator phase noise and phase jitter inherent to 28 GHz and 39 GHz local oscillators.

Carrier Aggregation & Contiguous Component Carrier Placement

When network operators aggregate multiple contiguous component carriers (intra-band contiguous CA), maintaining orthogonal subcarrier grids across carrier boundaries is essential to prevent inter-carrier interference (ICI) without requiring wide inter-carrier guardbands. 3GPP TS 38.101 defines the nominal channel spacing between two contiguous component carriers with bandwidths BW_channel,1 and BW_channel,2 as:

This quantization to multiples of 300 kHz (for FR1) or 1.44 MHz / 17.28 MHz (for FR2) ensures that the center frequencies of both aggregated carriers align precisely with the 3GPP channel raster while preserving subcarrier grid orthogonality.

3GPP TS 38.101 Transmission Bandwidth Reference Table

The table below outlines standardized 3GPP transmission bandwidth configurations, maximum allowable PRBs, total active subcarriers, single-edge minimum guardbands, and overall spectrum efficiency percentages across FR1 Sub-7 GHz and FR2 Millimeter-Wave: