Wireless Communication Basics
With a transmit power of 20 dBm, a transmit antenna gain of 2 dBi, a receive antenna gain of 2 dBi, a propagation loss of 100 dB and cable losses on the transmit and receive sides totaling 4 dB, which is the received power?
- A−88 dBm
- B−80 dBm
- C−76 dBm
Show answer and explanation
Answer: B. −80 dBm
Received power is found by adding the antenna gains (dBi) to the transmit power in dBm and subtracting the propagation and cable losses (dB). This calculation is called a link budget: 20 + 2 + 2 − 100 − 4 = −80 dBm. If the minimum power the receiver can receive correctly (its sensitivity) is, for example, −90 dBm, there is a 10 dB margin (link margin). In practice, designs include margin for drops in received power due to fading.
- A. This subtracts the antenna gains instead of adding them. Gain acts to increase the received power.
- B. Correct. 20 + 2 + 2 − 100 − 4 = −80 dBm.
- C. This forgets to subtract the 4 dB cable loss.