CrossPwr (802.11n/ac/ax/be)
The values in the is the measure of the crosstalk between transmit channels and is calculated for each VSA measurement channel as the average of the power level of the indirect paths (non-diagonal terms in the channel response matrix) received on that measurement channel.
When performing a MIMO Multiple Input, Multiple Output: A physical layer (PHY) configuration in which both transmitter and receiver use multiple antennas. measurement, there can be 2 to 8 data streams. The VSA supports only square MIMO configurations (NxN) so the number of analysis channels used will also match the number of streams. The simplest case is the Direct Map case and has stream 1 connected to measurement channel 1, stream 2 connected to measurement channel 2, etc. In this case, the ideal channel response matrix at each subcarrier is an NxN identity matrix.
[ 1 0 0 ]
[ 0 1 0 ]
[ 0 0 1 ]
Example: ideal (no crosstalk) channel response matrix for the 3x3 Direct Map case
However, in a real transmitter there will be leakage of stream1 into transmitter2, stream2 into transmitter1, etc. resulting in a channel response matrix that looks more like:
[ ~1 e12 e13 ]
[ e21 ~1 e23 ]
[ e31 e32 ~1 ]
Example: non-ideal channel response matrix for the 3x3 Direct Map case
The eXY term represent the leakage from transmitter Y to transmitter X (or in other words, the power received on VSA measurement channel X from transmitter Y). There is a matrix like this for each subcarrier in the system.
For example, the received on VSA measurement channel 1 is calculated in the Direct Map case by averaging the power level of the e1Y terms (power from the other Tx channels) for all subcarriers/symbols in the measurement interval. Then the average cross power is normalized by the power from Tx Channel 1 received on measurement channel 1, and the resulting value is shown in the metric for Ch1.
For a transmitter in Direct Map mode, the ideal value for the is 0 (-780dB). The actual value provides a useful measure of how much crosstalk is present between the two RF Radio Frequency: A generic term for radio-based technologies, operating between the Low Frequency range (30k Hz) and the Extra High Frequency range (300 GHz). chains of the transmitter. If the transmitter is not in Direct Map mode, then the ideal values for the will no longer be zero but will instead depend on how the transmitter is mixing the two data streams.
An example of a non-Direct Map case is where there are two Tx channels and Tx Ch1 = stream1 + stream2 and Tx Ch2 = stream1 - stream2. In this case, the non-diagonal terms in the channel matrix have the same power as the diagonal power terms and the ideal value for the in this case is 1 (0dB). The amount by which deviates from 0dB is a useful indication of the crosstalk between the two RF chains, but the value no longer reflects the actual crosstalk power.
See Also
