When is the link feasible?

When received power is at least the receiver sensitivity in both directions

Client to AP received power and margin are:

−88.61 dBm, margin −8.61 dB

−83.61 dBm, margin −8.61 dB

What is the conclusion?

Not feasible; improve with higher-gain antennas, lower-loss cable, more power or shorter distance

2074 Bhadra · 12 marks

Numerical: 10 km link feasibility with Okumura

Short answer

Okumura path loss is 122.61 dB at 10 km. Received power is -83.61 dBm at the client and -88.61 dBm at the access point, both about 8.6 dB below sensitivity. The link is not feasible.

Estimate the feasibility of a 10-km wireless link in suburban area, with one access point and one client radio, using Okumura model for path loss. The median attenuation value is 20 dB and gain due to environment is 13 dB. The height of access point antenna is 100 m and that of client antenna is 10 m: a. Access point is connected to antenna with 5-dBi gain, with a transmitting power of 20-dBm and a receive sensitivity of -80-dBm b. Client is connected to antenna with 20-dBi gain, with a transmitting power of 15-dBm and a receive sensitivity of -75-dBm c. Cables in both systems are short, with a loss of 3-dB at each side at 2.4-GHz frequency of operation.

A link is feasible if the received power at each end is at least the receiver sensitivity. Path loss is found from Okumura's model and then a link budget is done for both directions.

Given: d = 10 km, f = 2.4 GHz, Amu = 20 dB, GAREA = 13 dB, hte = 100 m, hre = 10 m.

Step 1: Free space loss

λ  = 3×10⁸ / 2.4×10⁹ = 0.125 m
LF = 20 log(4πd/λ) = 20 log(4π × 10 000 / 0.125)
   = 120.05 dB

Step 2: Height gains and median path loss

G(hte) = 20 log(100/200) = −6.02 dB
G(hre) = 20 log(10/3)    = 10.46 dB

L50 = LF + Amu − G(hte) − G(hre) − GAREA
    = 120.05 + 20 + 6.02 − 10.46 − 13
    = 122.61 dB

Step 3: Link budget diagram

 Access point                          Client
 20 dBm Tx                           15 dBm Tx
 −3 dB cable                         −3 dB cable
 +5 dBi ant  <---- 122.61 dB ---->  +20 dBi ant
 Rx sens −80 dBm                    Rx sens −75 dBm

Step 4: Forward link (AP → client)

Pr = 20 − 3 + 5 − 122.61 + 20 − 3
   = −83.61 dBm
Sensitivity = −75 dBm
Margin = −83.61 − (−75) = −8.61 dB  (fails)

Step 5: Reverse link (client → AP)

Pr = 15 − 3 + 20 − 122.61 + 5 − 3
   = −88.61 dBm
Sensitivity = −80 dBm
Margin = −88.61 − (−80) = −8.61 dB  (fails)

Link	Received power	Sensitivity	Margin
AP → client	−83.61 dBm	−75 dBm	−8.61 dB
Client → AP	−88.61 dBm	−80 dBm	−8.61 dB

Answer: The 10 km link is NOT feasible; both directions fall about 8.6 dB short of the receiver sensitivity (and there is no fade margin). It could be made feasible by using higher-gain antennas (e.g. a 15 dBi or higher antenna at the AP), lower-loss cables, higher transmit power within limits, or a shorter distance.

✓ Answer checked by Claude Opus 5.5 (high effort)

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