17-03-2014, 01:10 PM
DSSS Short Preamble and Header Format
Purpose:
To verify that the device under test (DUT) conforms to the direct sequence spread
spectrum (DSSS) Short Preamble and header format.
Resource Requirements:
• Vector Signal Analyzer (VSA), Rohde & Schwarz FSQ26 or equivalent
• ERP access point/station with external antenna jack
• Associated ERP AP or station with external antenna jack (optional)
• RF Power Splitter, Picosecond 5333 or equivalent
• Controlling Software (Matlab)
Last updated: June 2007
Discussion:
Reference [1] describes the physical layer convergence procedure (PLCP) for Extended Rate
PHYs (ERP) operating in the 2.4 GHz band. Subclause 19.3.2 requires that all ERP stations
support three different preamble and header formats. An ERP device must support 2, 5.5, and 11
Mbps data rates conforming to the DSSS Short preamble and header format discussed in
19.3.2.2, which references Figure 18-2 of 18.2.2.2. The Short preamble PPDU only differs from
18.2.2.2 in the SERVICE and SIGNAL fields, which have been modified to support the optional
modes included in the ERP.
The Short PLCP Preamble includes both a Short Synchronization (shortSync) and a Short Start
Frame Delimiter (shortSFD) field. The Short PLCP header contains a Signaling (SIGNAL), a
Service (SERVICE), a length (LENGTH), and a CCITT CRC-16 field.
Procedure:
1. For DUT’s that support continuous transmission, configure the DUT to continuously
transmit PSDUs of length ≤ 100 bytes on channel 6 at a data rate of 11 Mbps. Otherwise,
for burst mode traffic, configure the DUT to associate and generate continuous ICMP
echo request packets of length 100 bytes, and set the Beacon Interval to 100 ms. In either
case, set the modulation to CCK, and the preamble to Short.
2. Configure the trigger on the VSA to capture an entire packet and the trigger delay to
capture the entire header (i.e. delay = -20 μs). Demodulate and decode the frame.
3. Verify that the DUT is properly following the Short Preamble and Header format.
4. Calculate the CRC for the SIGNAL, SERVICE and LENGTH fields and verify that it
matches the CRC-16 field of the transmitted frame.
5. Repeat steps 1-5, however, change the data rate to 2 Mbps, and 5.5 Mbps, respectively,
and verify the results.
Observable Results:
a. The preamble should be sent at a 1 Mbps rate, while the header is sent at a 2 Mbps data rate.
b. The SYNC field should contain all scrambled “0”s and the scrambler should be
initialized to [001 1011] b.
c. The shortSFD should contain [05 CF] h and be the time reverse of the SFD in the Long
preamble (Refer to Test # 19.1.2: DSSS Long Preamble and Header Format).
d. In all cases, the SIGNAL field should indicate the data rate used by the DUT for PSDU
transmission.