Redline Communications Inc. AN30 用户手册

 

 

AN-30 System User Manual 

 

BPSK ½ 12 

6 

5.82 

BPSK ¾ 12 

9 

8.63 

QPSK ½ 24  12 

11.38 

QPSK ¾ 24  18 

16.7 

16 QAM 

½ 

48 

24 

21.77 

16 QAM 

¾ 

48 

36 

33.01 

64 QAM 

⅔ 72 

48 

44.1 

64 QAM 

¾ 

72 

54 

48.8 

 

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 
20. 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. 
 

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