LTE Coexistence & ACIR Calculator
Check whether an LTE transmitter desensitises a receiver on the adjacent channel, and how much more isolation the pair needs.
Free to use. Sign up free to save, download and print.
Worked example: adjacent 20 MHz base stations 120 dB apart
Extra isolation needed: 15.87 dB
Loading the LTE Coexistence & ACIR Calculator…
How it works
LTE coexistence calculation: desensitisation and isolation
An LTE transmitter on the next channel reaches a receiver in two ways: the power it leaks into the receiver's channel, set by its adjacent channel leakage ratio (ACLR), and the part of its carrier the receiver fails to reject, set by the receiver's adjacent channel selectivity (ACS). 3GPP TR 36.942 clause 8.1 combines the two into the ACIR. The interference at the victim is the aggressor's EIRP, less the isolation between them and the ACIR, plus the victim antenna's gain towards the aggressor. For a narrower victim, clause 5.1.1.4.1 first raises the ACLR by the bandwidth ratio, while the ACS still faces the whole carrier.
A coordination criterion limits what that interference does to the victim's noise floor. Treated as added noise, it desensitises the receiver by 10 log₁₀(1 + I/N), so 1 dB of desensitisation allows an I/N of −5.87 dB. Any I/N above that is isolation the pair still needs, decibel for decibel, from separation, antenna discrimination, filtering or a guard band.
ACIR = 1 / (1/ACLRᵥ + 1/ACS), as linear power ratios
ACLRᵥ = ACLR + 10 log₁₀(Bₐ / Bᵥ) when Bᵥ < Bₐ, otherwise ACLR
I = EIRP − L − ACIR + Gᵥ
N = −174 + 10 log₁₀(Bᵥ) + NF
D = 10 log₁₀(1 + 10^((I − N)/10))
ΔL = (I − N) − 10 log₁₀(10^(Dₚ/10) − 1)
- ACLR, ACLRᵥ
- the aggressor's adjacent channel leakage ratio, and the same referred to the victim's bandwidth, in dB
- ACS
- the victim receiver's adjacent channel selectivity, in dB
- ACIR
- adjacent channel interference ratio, in dB
- Bₐ, Bᵥ
- aggressor channel bandwidth and victim noise bandwidth; Bᵥ in Hz in the noise line
- EIRP, L, Gᵥ
- aggressor EIRP in its own channel in dBm, the path loss between the antennas in dB, and the victim antenna's gain towards the aggressor in dBi
- I, N, NF
- interference and noise floor at the victim in dBm, and its noise figure in dB; −174 dBm/Hz is the noise density of TR 36.942 Table C.1
- D, Dₚ
- desensitisation and the permitted desensitisation, in dB
- ΔL
- extra isolation needed, in dB; zero or less means the criterion is met with that much to spare
Standards
- 3GPP TR 36.942 clause 8.1: ACIR from ACLR and ACS
- 3GPP TS 36.104 and TS 36.101: base station and terminal ACLR and ACS figures
- RALI MS 47 clause 4.9.2.3: radio altimeter protection in 4200 to 4400 MHz
- Radiocommunications Licence Conditions (Fixed Licence) Determination 2025 section 36: point to multipoint emission masks
- Radiocommunications Advisory Guidelines (Managing Interference to Spectrum Licensed Receivers, 3.4 GHz Band) 2025, Schedule 2
Worked example
Worked example: adjacent 20 MHz base stations 120 dB apart
Two operators' LTE base stations, each the TR 36.942 reference base station (46 dBm, 15 dBi, a 5 dB noise figure), sit on adjacent 20 MHz channels with 120 dB of path loss between them: the aggressor radiates 61 dBm EIRP with the 45 dB ACLR of TS 36.104, and the victim has the 45 dB ACS of the notional receiver in the 3.4 GHz Advisory Guidelines 2025, 15 dBi of gain towards the aggressor and 1 dB of desensitisation permitted.
| Step | Working | Result |
|---|---|---|
| ACIR | −10 log₁₀(10^(−45/10) + 10^(−45/10)) | 41.99 dB |
| Interference, I | 61 − 120 − 41.99 + 15 | −85.99 dBm |
| Noise floor, N | −174 + 10 log₁₀(20 × 10⁶) + 5 | −95.99 dBm |
| I/N | −85.99 − (−95.99) | 10.00 dB |
| Extra isolation needed | 10.00 − (−5.87), the I/N for 1 dB | 15.87 dB |
The victim is desensitised by 10.41 dB, so the pair needs 135.87 dB of isolation in all. The ACLR and ACS are equal, so the ACIR sits 3.01 dB below both, and a filter at one end alone can win back no more than those 3.01 dB: the rest has to come from separation, antenna discrimination, filters at both ends or a guard band. Quoting the 45 dB ACLR as the isolation would have understated the shortfall by the same 3.01 dB.
How much isolation do two adjacent channel LTE systems need?
Enough to hold the interference at the I/N the desensitisation criterion allows, which is −5.87 dB for 1 dB. The calculator gives the shortfall against the isolation you enter, and the isolation needed is the two added together. Two 20 MHz base stations with 61 dBm EIRP, 45 dB ACLR, 45 dB ACS, a 5 dB noise figure and 15 dBi of victim gain towards the aggressor need 135.87 dB between the antennas. The answer is an isolation in dB rather than a distance, and the calculator links on to the tools that turn it into a separation or a filter.
Why report desensitisation rather than interference power?
An interference power means little without the noise floor it lands on. Desensitisation is 10 log₁₀ (1 + I/N), and coordination criteria are written in those terms: 1 dB of desensitisation corresponds to an I/N of about −5.9 dB, and 3 dB to an I/N of 0 dB.
How is a victim narrower than the aggressor handled?
ACLR is measured over the aggressor's channel, and a narrower receiver collects only the share of the leakage that falls in its own bandwidth, so TR 36.942 clause 5.1.1.4.1 raises the ACLR by the bandwidth ratio. Charging a 12.5 kHz receiver the leakage of a full 20 MHz channel would be about 32 dB pessimistic. The ACS is not scaled: the receiver's selectivity faces the whole aggressor carrier, which is how TR 36.942 clause 12.1.3.2 applies it. Scaling the whole power instead would be optimistic by up to the bandwidth ratio wherever the receiver limits.
Does it calculate the isolation between the antennas?
No. Isolation is an input, because coupling loss on a shared structure and path loss over a distance are measured and modelled differently. The Antenna Separation Calculator and the Co-Site Designer can work out coupling loss for co-sited antennas.
Can I use it for an LTE base station beside a UHF land mobile receiver?
Not for that pair. ACLR and ACS are defined for the first and second adjacent channels, and a receiver tens of MHz away is governed by the transmitter's spurious emissions and the receiver's blocking performance instead. That case belongs in the Co-Site Designer.
Which Australian limits does it check?
It checks the interference at the victim against the Schedule 2 spectrum licence boundary criterion from the 3.4 GHz Advisory Guidelines 2025, scaled to the victim bandwidth. It also tabulates the RALI MS 47 clause 4.9.2.3 radio altimeter figures and the Fixed Licence Determination 2025 section 36 emission masks. These checks are made on the figures you enter, and they are a guide for your own assessment rather than an ACMA decision.
Related
Related tools
Sign up free to keep your work.
Free to use. Saving, downloading and printing need a free account.