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FCC PART 15, SUBPART C, SEC. 15.247 - DIRECT SEQUENCE SPREAD SPECTRUM TRANSMITTERS
PCMCIA Wireless LAN Card, Model WL-211F
8.6.
PROCESSING GAIN OF A DIRECT SEQUENCE SPREAD SPECTRUM
The processing gain may be measured using the CW jamming margin method. Figure 1 shows the test configuration. The
test consists of stepping a signal generator in 50 KHz increments across the passband of the system. At each point, the
generator level required to produce the recommended Bit Error Rate (BER) is recorded. This level is jammer level. The
output power of the transmitting unit is measured at the same point. The Jammer to Signal (J/S) ratio is then calculated.
Discard the worst 20% of the J/S data points. The lowest remaining J/S ratio is used when calculating the Process Gain.
The signal to noise ratio for an ideal differentially coherent detection of a differentially encoded BPSK receiver can be
derived from the Bit Error Probability (Pb) versus Signal-to-Noise ratio. See attached plot for detailed information.
For measurement of the (S/N)
Ref.:
Viterbi, A.J. Principles of Coherent Communications (New York: McGraw-HILL 1966), Pg. 207
Using equation (1) shown above, calculate the signal to noise ratio required for your chosen BER. This value and the
measured J/S ratio are used in the following equation to calculate the Process Gain (Gp) of the system.
Where:
(S/N)o:
Theoretical signal to noise ratio required to maintain the normal operation just before the BER
appears. In real measurements the maximum error of 0.001 is allowed in an ideal system using
their modulation scheme with all codes turned off (i.e. no spreading or processing gain).
Mj:
Maximum jammer to Signal Ratio that recorded at the detected BER.
Lsys:
System losses such as non-ideal synchronization, tracking circuitry, non-optimal baseband receiver
filtering and etc... These losses can be in excess of 3 dB for each transmitter and receiver pair. For
the purpose of this processing gain calculation we assume a Lsys at its minimum value of 2 dB.
Ref.: Dixon, R, Spread Spectrum Systems. (New York: Wiley, 1984), Chapter 1.
•
(S/N)o: Refer to attached curves, BER versus (S/N)o for Differential Coherent Detection of Differentially Encoded
BPSK
•
Processing gain Gp = (S/N)o + Lsys + Mj = (S/N)o + 2 + Mj
ULTRATECH GROUP OF LABS
3000 Bristol Circle, Oakville, Ontario, Canada L6H 6G4
Tel. #: 905-829-1570, Fax. #: 905-829-8050, Email: vhk.ultratech@sympatico.ca, Website: http://www.ultratech-labs.com
•
Assessed by ITI (UK) Competent Body, NVLAP (USA) Accreditation Body & ACA/AUSTEL (Australia)
•
Accredited by Industry Canada (Canada) under ACC-LAB (Europe/Canada MRA)
•
Recognized/Listed by FCC (USA )
•
All test results contained in this engineering test report are traceable to National Institute of Standards and Technology (NIST)
-5
we use the Pb of 1.0x10
o
Gp = (S/N)o+Mj+Lsys
minimum.
Page 72
FCC ID: MXF-WL211F
File #: GTT-013FTX
March 17, 2000
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