17-03-2014, 01:09 PM
DSSS Long Preamble and Header Format
Purpose:
To verify that the device under test (DUT) conforms to the direct sequence spread
spectrum (DSSS) Long 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
• 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. To provide interoperability with legacy
stations that use DSSS and complementary code keying (CCK) modulation, an ERP device must
support 1, 2, 5.5, and 11 Mbps data rates conforming to the Long Preamble and header format
described in 19.3.2.1, which references Figure 18-1 of 18.2.2.1. The PLCP Preamble contains
both the Synchronization (Sync) and Start Frame Delimiter (SFD). The PLCP header contains
the following fields: Signaling (SIGNAL), Service (SERVICE), length (LENGTH) and the
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.
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 long 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. Change length field such that the DUT sets the length extension bit. Observe the length
extension bit, and verify the frame fields contain valid results.
6. 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 and header should be sent at a 1 Mbps data rate.
b. The SYNC field should contain all scrambled “1”s and the scrambler should initialized to
[1101100] b.
c. The SFD field should contain [F3 A0] h.
d. In all cases, the SIGNAL field should contain the appropriate data rate used by the DUT for
PSDU transmission.
e. The LENGTH field should indicate the proper time, in microseconds, required to
transmit the PSDU.