Why Link Budgets Define 5G Coverage

A link budget is the single most important calculation in radio network planning. It determines the Maximum Allowable Path Loss (MAPL) between transmitter and receiver, which directly translates to cell radius and site count. In 5G NR, link budgets are more complex than LTE because operators deploy across FR1 (sub-7 GHz) and FR2 (mmWave) with fundamentally different propagation characteristics.

3GPP defines the reference sensitivity requirements for NR UEs in TS 38.101-1 Table 7.3.1-1 (FR1) and TS 38.101-2 Table 7.3.1-1 (FR2). These values anchor the uplink budget and set the baseline for coverage dimensioning.

Link Budget Parameter Reference

Every link budget consists of gains and losses on both the transmitter and receiver sides. The following table lists the standard parameters for a 5G NR downlink budget.

For the uplink budget, UE TX power is capped at 23 dBm (Power Class 3) for FR1 and 23 dBm for FR2 per TS 38.101-1 Section 6.2.1. The uplink is almost always the limiting link in 5G coverage planning.

Worked Example 1: n78 Band at 3.5 GHz

This example calculates the downlink MAPL for an urban macro cell on n78 (3.5 GHz) with 100 MHz bandwidth, targeting outdoor coverage with 95% area reliability.

Step 1 --- Transmitter EIRP

`

TX Power (per carrier): 46.0 dBm

Cable + connector loss: -3.0 dB

gNB antenna gain (64T64R): +25.0 dBi

─────────────────────────────────────

EIRP: 68.0 dBm

`

Step 2 --- Receiver Sensitivity

The receiver sensitivity is calculated from thermal noise plus noise figure plus required SINR.

`

Thermal noise: -174.0 dBm/Hz

Channel BW (100 MHz): +80.0 dB-Hz (10 * log10(100e6))

UE noise figure: +7.0 dB

Required SINR (QPSK 1/3, 15 kHz SCS): -1.0 dB

─────────────────────────────────────

Receiver sensitivity: -88.0 dBm

`

Step 3 --- System Gains

`

UE antenna gain: +0.0 dBi

Beamforming gain: +6.0 dB (4-stream MIMO at UE)

─────────────────────────────────────

Total system gain: +6.0 dB

`

Step 4 --- Margins and Losses

`

Body loss: 3.0 dB

Shadow fading (95%): 8.3 dB

Building penetration: 20.0 dB (indoor coverage)

Interference margin: 4.0 dB

─────────────────────────────────────

Total losses: 35.3 dB

`

Step 5 --- MAPL Calculation

`

MAPL = EIRP - Receiver Sensitivity + System Gains - Total Losses

MAPL = 68.0 - (-88.0) + 6.0 - 35.3

MAPL = 126.7 dB

`

Using the 3GPP UMa NLOS model from TR 38.901 Table 7.4.1-1, with path loss exponent of 3.67 and a breakpoint distance at 4 km:

`

PL_UMa_NLOS(d) = 32.4 + 20log10(f_c) + 30log10(d_3D)

126.7 = 32.4 + 20log10(3500) + 30log10(d)

126.7 = 32.4 + 70.88 + 30*log10(d)

30*log10(d) = 23.42

d = 10^(0.781) = 604 m

` Result: Cell radius of approximately 600 m for indoor coverage at 3.5 GHz.

Worked Example 2: n258 Band at 26 GHz (mmWave)

Now the same exercise for an urban small cell on n258 (26 GHz) with 400 MHz bandwidth, targeting outdoor-only coverage.

Transmitter EIRP

`

TX Power: 35.0 dBm

Cable loss (integrated antenna): -0.5 dB

gNB antenna gain (256 elements): +30.0 dBi

─────────────────────────────────────

EIRP: 64.5 dBm

`

Receiver Sensitivity

`

Thermal noise: -174.0 dBm/Hz

Channel BW (400 MHz): +86.0 dB-Hz (10 * log10(400e6))

UE noise figure: +10.0 dB

Required SINR (QPSK 1/3): -1.0 dB

─────────────────────────────────────

Receiver sensitivity: -79.0 dBm

`

System Gains and Losses

`

UE beam gain (phased array): +10.0 dB

Total system gain: +10.0 dB

Body loss: 1.0 dB

Shadow fading (95%): 7.2 dB

Foliage loss: 10.0 dB

Interference margin: 2.0 dB

─────────────────────────────────────

Total losses: 20.2 dB

`

MAPL Calculation

`

MAPL = 64.5 - (-79.0) + 10.0 - 20.2

MAPL = 133.3 dB

`

Using the UMi Street Canyon NLOS model from TR 38.901:

`

PL_UMi_NLOS(d) = 32.4 + 20log10(f_c) + 31.9log10(d_3D)

133.3 = 32.4 + 20log10(26000) + 31.9log10(d)

133.3 = 32.4 + 88.3 + 31.9*log10(d)

31.9*log10(d) = 12.6

d = 10^(0.395) = 248 m

` Result: Cell radius of approximately 250 m for outdoor mmWave coverage.

MAPL and Cell Radius Comparison Across Bands

The low-band advantage is clear: n71 at 600 MHz achieves nearly 5x the cell radius of n78 at 3.5 GHz for indoor coverage. This is why T-Mobile's extended-range 5G on Band n71 covers over 320 million people across the US with roughly 80,000 sites, while Verizon's mmWave on n261 requires dense small cells spaced 200--300 m apart and covers select urban zones only.

Real Operator Deployment Data

Vodafone Germany deployed n78 (3.5 GHz) across urban areas with 64T64R Massive MIMO panels. Their measured cell radii average 450--650 m for outdoor coverage and 200--350 m for indoor, closely matching the MAPL predictions above. The inter-site distance (ISD) in their Frankfurt deployment is approximately 800 m. SK Telecom deployed n258 (28 GHz) mmWave in Seoul's Gangnam district using Samsung's compact radios with 256-element phased arrays on light poles. The measured ISD is 180--250 m, with consistent 1+ Gbps throughput at the cell edge for outdoor users. Indoor penetration was not viable without dedicated indoor small cells.

Uplink-Limited Coverage

In most 5G deployments, the uplink is the limiting link. The UE transmits at 23 dBm maximum compared to the gNB's 46 dBm, a 23 dB gap that antenna gains partially but never fully compensate. The uplink MAPL is typically 5--10 dB lower than the downlink MAPL, reducing cell radius by 15--25%.

To mitigate this, operators use:

1. Uplink power boosting via power class 2 UEs (26 dBm) defined in TS 38.101-1
2. SUL (Supplementary Uplink) pairing a low-band uplink carrier with a mid-band downlink carrier, per TS 38.300 Section 5.3
3. UL antenna switching between 1T2R and 2T4R configurations

Sensitivity Analysis

Small changes in link budget parameters have large effects on cell count and CAPEX:

A 3 dB improvement in MAPL translates to roughly 25% fewer cell sites---potentially saving millions in CAPEX for a nationwide deployment.

Key Takeaway: The 5G link budget directly determines cell radius and site count. At 3.5 GHz, expect 300--600 m radius depending on indoor/outdoor coverage targets, while mmWave at 26 GHz limits cells to 200--250 m. Always calculate both UL and DL budgets, as the uplink is almost always the coverage-limiting direction.