User's Manual

AN-50 System User Manual
Redline Communications …..solving the first mile challenge.
Table 9: Modulation Scheme vs. Data Rate
Modulation Coding
Rate
Over The Air
Rate (Mbps)
Coded Burst
Rate (Mbps)
Average Ethernet
Rate (Mbps)
BPSK ½ 12 6 5.7
BPSK ¾ 12 9 8.4
QPSK ½ 24 12 11.2
QPSK ¾ 24 18 16.5
16 QAM ½ 48 24 21.6
16 QAM ¾ 48 36 31.4
64 QAM ⅔ 72 48 40.5
64 QAM ¾ 72 54 44.9
As indicated in the table above, higher order modulation schemes require greater S/N to
maintain the same BER performance. The noise in this case is defined as the noise floor
of the receiver, i.e., it assumes no interference from other sources (interference from
other sources are addressed below). The main path calculation for determining range
performance is given as:
RSL = Ptx + Gtx – FSL + Grx
Where:
Ptx is the transmit power level in dBm
Gtx is the transmit antenna gain in dB
FSL is the free space loss attenuation in dB, and
Grx is the receive antenna gain in dB
The FSL value is dependent on the range between the two terminals, the type of terrain
over which the link is deployed, and whether or not the link is operating line of sight
(LOS), optical line of sight (OLOS) or non-LOS (NLOS). The LOS FSL calculation is well
understood and easy to calculate, and relies on the fact there is absolutely no obstacle
near the direct path. The precise method for determining the amount of clearance
required for LOS involves making use of a factor known as the Fresnel zone. A Fresnel
zone is defined as a path difference of λ/2 away from the direct path, as shown in Figure
36. A "cleared LOS" link assumes there are no obstacles within 60% of the first Fresnel
zone of the direct path. The diagram below illustrates OLOS conditions, where a treetop
is within the first Fresnel zone, and a clear direct path exists between the antennas.
First
Fresnel
Zone
Obstruction within
first Fresnel Zone
Figure 36: Fresnel Zone Obstruction
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