Implementing Frequency Selective Fading for OPNET's Wireless LAN Modules

In OFDM-based IEEE 802.11 Wireless LANs, adapting the modulation type per sub-carrier to the frequency selectivity of the wireless channel leads to significant performance improvements. To integrate adaptive modulation into IEEE 802.11a/g networks, some minor modifications to the standard are needed in order to acquire the subcarrier gains and signalize the modulation assignments (on a per-packet basis), amongst others. However, to implement adaptive modulation in OPNET some changes have to be performed at the physical layer processing to include a frequency selective fading profile and to accurately compute packet error events based on the frequencyselective channel profile. We take an analytical approach for this and demonstrate a much more precise packet error behavior than with standard OPNET modules.