User manual

Chapter 2 - Managing a Single Device/Cell Performance Parameters Page
AlvariCRAFT Device Manager 144 User Manual
 RTS Threshold (bytes)
 Number of Hardware Retries
 AVG SNR Memory Factor
 Maximum Modulation Level
 Multicast Modulation Level (AU and BU Only)
 Burst Mode Parameters
 Concatenation Parameters
 AIFS (AU and SU Only)
 Adaptive Modulation Parameters
2.23.1 Contention Window Parameters
The system uses an exponential Back-off algorithm to resolve contention between
several units that want to access the wireless medium. The method requires each
station to choose a random number N between 0 and a given number C each time
it wants to access the medium. The unit will attempt to access the medium only
after a time equal to DIFS plus N time slots, always checking if a different unit has
accessed the medium before. Each time the unit tries to transmit and a collision
occurs; the maximum number C used for the random number selection will be
increased to the next available value. The available values are 7, 15, 31, 63, 127,
255, 511 and 1023.
Minimum Contention
Window
The Minimum Contention Window parameter is the first maximum
number C used in the back-off algorithm. The higher the number of
SUs served by the same AU, the higher the Minimum Contention
Window for each SU should be. In addition, when the Wireless Link
Prioritization Option is enabled, the Minimum and Maximum
Contention Window parameters can be configured to provide certain
units with an advantage over other units.
The available values are 0, 7, 15, 31, 63, 127, 255, 511 and 1023. A
value of 0 means that the contention window algorithm is not used
and that the unit will attempt to access the medium immediately after
a time equal to DIFS. It should only be used in point-to-point
applications.