80211b Transmitter

Introduction

WLAN_80211b_Tx_prj IEEE 802.11b transmitter test and verification design examples are described in this chapter.

WLAN_80211b_TxEVM.dsn: measures error vector magnitude and tests the transmit modulation accuracy.

Error Vector Magnitude Measurements

WLAN_80211b_TxEVM.dsn

Features

IEEE 802.11b configurable signal source, adjustable data rate
Adjustable sample rate
CCK modulation

Description

This design tests IEEE 802.11b transmit modulation accuracy by measuring the EVM. The schematic for this design is shown in the following figure.

WLAN_80211b_TxEVM.dsn Schematic

Measurements in this design are based on IEEE Standard 802.11b-1999 section 18.4.7.8. The transmit modulation accuracy requirement for the High Rate PHY is based on the difference between the actual transmitted waveform and the ideal signal waveform. Modulation accuracy is determined by measuring the peak vector error magnitude during each chip period. Worst-case vector error magnitude cannot exceed 0.35 for the normalized sampled chip data. The ideal complex I and Q constellation points associated with DQPSK modulation, (0.707,0.707), (0.707, -0.707), (-0.707, 0.707), (-0.707, -0.707), must be used as the reference. These measurements must be from baseband I and Q sampled data after recovery through a reference receiver system. The measurement example is shown in the following figure.

Modulation Accuracy Measurement Example

Simulation Results

Simulation results displayed in WLAN_80211b_TxEVM.dds are shown in the following figure. The EVM results are smaller than the specification requirements.

EVM results

Benchmark

Hardware platform: Pentium III 450 MHz, 512 MB memory
Software platform: Windows NT 4.0 Workstation, ADS 2002C
Simulation time: approximately 4 minutes

References

IEEE Standard 802.11b-1999, "Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications: High-speed Physical Layer Extension in the 2.4 GHz Band," 1999.