What frequency bands are allocated for 5G NR millimeter wave and how do they differ globally?
5G mmWave Spectrum
The allocation of millimeter wave spectrum for 5G varies significantly across regions, creating challenges for global device compatibility and economies of scale.
FR2 Band Details
(1) n257 (26.5-29.5 GHz, 3 GHz bandwidth): the largest contiguous mmWave band available. Up to 400 MHz per carrier, with carrier aggregation up to 1.6 GHz total bandwidth. Subcarrier spacing: 120 kHz (most common) or 240 kHz. Maximum channel bandwidth: 400 MHz (SCS = 120 kHz: 264 resource blocks). Peak theoretical throughput per carrier: approximately 2.5 Gbps with 256-QAM, 4×4 MIMO. (2) n261 (27.5-28.35 GHz, 850 MHz bandwidth): a subset of n257, used in the US. FCC auctioned this spectrum in Auction 101 (2019). Total of 850 MHz per geographic area, divided among operators. Typical operator allocation: 200-400 MHz. (3) n260 (37-40 GHz, 3 GHz bandwidth): higher frequency means: smaller antenna elements (lambda/2 = 4 mm), allowing denser phased arrays. More path loss (approximately 3 dB more than 28 GHz for the same distance). More atmospheric absorption (but still < 0.5 dB/km, not significant for small cells). FCC allocated via Auction 103 (2020). (4) FR2-2 extension (52.6-71 GHz): defined in 3GPP Release 17. n263: 57-71 GHz (14 GHz bandwidth). This overlaps with the 60 GHz unlicensed band (WiGig). The vast bandwidth enables multi-Gbps throughput for short-range, high-capacity scenarios (indoor hot spots, fixed wireless access). Challenges: very high path loss, oxygen absorption peak at 60 GHz (15 dB/km), and limited penetration through walls.
Channel Bandwidth and Throughput
(1) Maximum channel bandwidth: 400 MHz per component carrier (for SCS = 120 kHz). With 8 component carriers (carrier aggregation): up to 3.2 GHz total bandwidth (theoretical maximum for FR2). (2) Data rate calculation: R = N_layers × Q_m × f × R_max × N_RB × 12 × (1/T_symbol). For 400 MHz BW, 264 RBs, SCS = 120 kHz: T_symbol = 8.33 us. 14 OFDM symbols per slot. Slot duration = 125 us. R = 2 × 8 × 264 × 12 × 14 / 125e-6 × 0.948 = approximately 2.4 Gbps per carrier per layer. With 2 layers (typical mmWave MIMO): 4.8 Gbps per carrier. With dual carrier (800 MHz total): 9.6 Gbps. (3) Practical throughput: 1-4 Gbps typical in good conditions (LOS, close range, single user). Factors reducing throughput: NLOS propagation (beam misalignment, multipath), hand/body blockage (10-30 dB attenuation), sharing among multiple users, control channel overhead (10-20%), and hybrid beamforming constraints.
Device Design Implications
(1) Multi-band support: a 5G mmWave device for global roaming must support n257, n258, n260, and n261. This requires: wideband antenna arrays covering 24.25-40 GHz (very challenging; typically handled with two arrays: one for 26-30 GHz and one for 37-40 GHz). Wideband transceiver ICs with tunable frequency synthesizers. Power amplifiers with bandwidth covering each band (multi-band or switchable-band PAs). (2) Multiple antenna modules: a smartphone typically has 3-4 mmWave antenna modules placed on different edges of the phone to provide spatial diversity (one module is always facing the base station regardless of how the phone is held). Each module contains a small phased array (4-8 elements) with integrated PA, LNA, and phase shifters. (3) Thermal management: mmWave PAs dissipate significant power (0.5-2 W per module). With 3-4 modules active: total dissipation can reach 3-8 W. This requires careful thermal design in the phone (heat spreading layers, throttling algorithms).
n258: 24.25-27.5 GHz (3250 MHz)
n260: 37-40 GHz (3000 MHz)
n261: 27.5-28.35 GHz (850 MHz)
Max BW per CC: 400 MHz (SCS 120 kHz)
Frequently Asked Questions
Why is mmWave 5G not deployed as widely as sub-6 GHz?
Several factors limit mmWave deployment: (1) Coverage: mmWave cells have much smaller coverage radius (100-300 m) than sub-6 GHz cells (1-5 km). Covering the same area requires 10-100× more base stations. (2) Cost: each small cell costs $10K-50K (hardware + installation + backhaul). Deploying thousands of small cells per city is expensive. (3) Propagation: mmWave signals do not penetrate buildings well (15-40 dB through exterior walls). Indoor coverage requires dedicated indoor small cells or repeaters. (4) Device cost: mmWave front-end modules add $10-30 per device. Most mid-range and budget phones do not include mmWave. (5) Use cases: the primary motivation (multi-Gbps throughput) is not yet critical for most users. Sub-6 GHz provides 100 MHz - 1 Gbps, sufficient for current applications. mmWave deployment is focused on: dense urban areas (stadiums, transit hubs), fixed wireless access (last-mile broadband), and enterprise/industrial (factories, campuses).
What is the difference between n257 and n261?
n261 (27.5-28.35 GHz) is a subset of n257 (26.5-29.5 GHz). n261 was defined specifically for the US FCC allocation (the LMDS band at 28 GHz). A device that supports n257 automatically covers the n261 frequency range. However: a device designed only for n261 covers only 850 MHz of the 3 GHz n257 band, and would miss the 26.5-27.5 GHz and 28.35-29.5 GHz portions used in other countries. For global compatibility: support n257 (the superset). Most mmWave chipsets (Qualcomm SDX55/60/65) support both n257 and n261 with the same hardware.
Will mmWave spectrum expand beyond 52.6 GHz?
3GPP Release 17 extended FR2 to 71 GHz (FR2-2). Release 18 and beyond are studying extensions to: 90-100 GHz (W-band). 100-300 GHz (sub-THz). The ITU World Radiocommunication Conference (WRC) will consider additional mmWave allocations in future sessions. The 60 GHz band (57-71 GHz): already available as unlicensed spectrum in most countries (used by WiGig). 5G NR can operate here for short-range, very high throughput scenarios. Above 100 GHz: research-stage (6G). THz communications promise > 100 Gbps throughput for short-range links (< 10 m). Significant technical challenges remain (semiconductor technology, antenna design, atmospheric absorption).