Microwave Link Budget

Faktor utama dalam link budget microwave adalah loss dari free space.

Rumus FSPL (free space loss):

Jika frekuensi 2520 MHz, dan jarak antara Tx dan Rx 100 meter, maka FSPL:

= 20 log (100) + 20 log (2520x10^6) + 20 log ((4/(22/7))/3x10^8)

= 80.47 dB

Jika Ptx = 40 dBm (note: umumnya BTS 4G Ptx 43 dBm)

maka Prx = 40 - 80.47 = -40.47 dBm

Catatan untuk beberapa device receiver minimum Prx -90 dBm (RSSI)

Lanjut...

Pertanyaannya apakah -40.47 dBm (0.00008974 miliWatt = 89.74 nanoWatt ) di sisi penerima ini cukup bagi penerima untuk bisa proses signal menjadi informasi?

Bagi penerima yang terpenting adalah berapa besar Signal tsb dibandingkan Noise.

Noise umumnya ditentukan oleh Tempratur efektif perangkat.

Noise Power at Rx = Thermal Noise * Bandwidth * Boltzman 

Dengan BW 20 MHz, dan Thermal Noise 31.65 dB, maka

Noise Power at Rx = -93.94 dBm

Dengan demikian S/N = -40.47 - (-93.94) = 53.46 dB

S/N sebesar ini sangat bagus.

Example 4G Devices:

RSRP

RSRP	Signal strength	Description
>= -80 dBm	Excellent	Strong signal with maximum data speeds
-80 dBm to -90 dBm	Good	Strong signal with good data speeds
-90 dBm to -100 dBm	Fair to poor	Reliable data speeds may be attained, but marginal data with drop-outs is possible. When this value gets close to -100, performance will drop drastically
<= -100 dBm	No signal	Disconnection

RSRQ

RSRQ	Signal quality	Description
>= -10 dB	Excellent	Strong signal with maximum data speeds
-10 dB to -15 dB	Good	Strong signal with good data speeds
-15 dB to -20 dB	Fair to poor	Reliable data speeds may be attained, but marginal data with drop-outs is possible. When this value gets close to -20, performance will drop drastically
<= -20 dB	No signal	Disconnection

SINR

SINR	Signal strength	Description
>= 20 dB	Excellent	Strong signal with maximum data speeds
13 dB to 20 dB	Good	Strong signal with good data speeds
0 dB to 13 dB	Fair to poor	Reliable data speeds may be attained, but marginal data with drop-outs is possible. When this value gets close to 0, performance will drop drastically
<= 0 dB	No signal	Disconnection

ref: https://www.everythingrf.com/rf-calculators/free-space-path-loss-calculator