IEEE® 802.11b WLAN Physical Layer

This model shows an implementation of the direct sequence spread spectrum (DSSS) system that provides 1 Mbps, 2 Mbps, 5.5 Mbps, and 11 Mbps payload data rates.

MAC sublayer protocol data units (MPDU) are converted to PHY protocol data units (PPDU) for transmission. The conversion is accomplished by adding the PLCP preamble and PLCP header to the MPDU. There are two formats that are simulated in the example:

  • Long PLCP PPDU format

  • Short PLCP PPDU format

The PLCP preamble and the PLCP header are modulated with DBPSK. The MPDU is modulated with DBPSK, or the combination of DQPSK, QPSK, and CCK, depending on the data rate used.

The root raised cosine pulse shaping filter is used at both the transmitter end and the receiver end.

An AWGN channel is used to simulate the transmission channel.

Structure of the Example

The model makes extensive use of configurable subsystems, swapping in and out the required components for your chosen parameters. The following configurable subsystems are constructed in the commwlan80211b library:

  • Modulate and spread, and demodulate and despread (4 different data rates)

  • PLCP mod and PLCP demod (Long preamble or short preamble)

  • Mix to and Mix from (With or without frequency shift)

  • Channel (AWGN or direct connection)

Set system parameters by double-clicking the "Model Parameters" block in the top left. Toggle instrumentation (scatter plot and spectrum analyzer) by double-clicking the switch. The BER subsystem contains error meters.

The received signal constellation:

The received signal spectrum

Results and Displays

The scope display includes:

  • The received signal spectrum

  • The scatter plot of the received signal

The BER meters calculate:

  • The preamble BER

  • The header BER

  • The PSDU BER

The rate detection blocks calculate:

  • The received signal rate

  • The transmitted chip rate

  • The PSDU data rate


IEEE® Std 802.11b-1999, available at:

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