17-03-2014, 02:56 PM
OFDM Training Symbol Spectral Flatness
Purpose:
To verify the orthogonal frequency division multiplexing (OFDM) transmit spectrum
of the device under test (DUT) is within conformance limits.
Resource Requirements:
• Vector Signal Analyzer (VSA), Rohde & Schwarz FSQ26 or equivalent
• Spectrum Analyzer (SA)
• OFDM PHY Station with external antenna jack
• Associated OFDM PHY AP or station with external antenna jack (optional)
• RF Power Splitter, Picosecond 5333 or equivalent
• Controlling Software (Matlab)
Last updated: April 2008
Discussion:
Reference [1] describes the orthogonal frequency division multiplexing (OFDM) physical
medium dependant (PMD) sublayer for the 2.4 GHz band. Section 17.3.9 defines OFDM
operation specifications, and subclause 17.3.9.6.2 defines the spectral flatness requirements. The
long training symbols of an OFDM frame are specified with equal power in all subcarriers for
channel estimation purposes. During this phase, the observed power should fit within the
spectral flatness limits defined in subclause 17.3.9.6.2. Training symbols which do not comply
with these limits could cause receivers to form a bad compensation filter for the channel,
resulting in interoperability issues.
Procedure:
1. For DUTs that support continuous transmission, configure the DUT to transmit 100-byte
PSDU’s continuously on channel 1 at a bit rate of 6 Mbps at maximum output power.
Otherwise, configure the DUT to associate with the AP on channel 1 at a bit rate of 6
Mbps at maximum output power; configure the AP to repeatedly transmit 100-byte ICMP
echo request packets to the DUT.
2. Configure the VSA to capture an entire packet.
3. Demodulate the long training symbols and observe the energy magnitude in each
subcarrier.
4. Repeat steps 1-3 for each channel.
Observable Results:
a. Subcarriers –26 to –17 as well as 17 to 26 should be within +2/–4dB of the average
energy.
b. Subcarriers –16 to –1 as well as 1 to 16 should be within +2/-2dB of the average energy.