80211a Transmitter System Test Using Instrument Links

Introduction

WLAN_80211a_ESGc_prj project for IEEE 802.11a transmitter test and verification design example is described in this chapter.

WLAN_80211a_ESGc.dsn for generating 11a OFDM signal and Sending the signal to ESG4438C to test WLAN OFDM Transmitter components.

Specification Requirements

Receiver performance requirements are listed in the following table.

Receiver Requirements

Data Rate	Modulation Accuracy - EVM
36 Mbps	11.2%
54 Mbps	5.6

Transmitter System Test Using ADS-ESGc Link

WLAN_80211a_ESGc.dsn

Signal Parameters

Data rate is 54 Mbps
OFDM modulation
PSDU length is 512 octets
Carrier is 5.8 GHz

Description

This example demonstrates how to use the ADS-ESGc link to test an OFDM transmitter system. Hardware and software requirements and setup information are provided.

Hardware Requirements

Agilent E4438C signal generator with 100 MHz clock rate and 6 GHz carrier frequency.
Agilent 89641A Vector Signal Analyzer (VSA) with 6 GHz carrier frequency or 89640A with 2.7 GHz carrier frequency plus PSA E4440A as a down-converter.

Software Requirements

Advanced Design System (ADS) version 2003A or later with WLAN option
- To run complex designs of WLAN systems, 500 MB RAM and 500 MB virtual space is required.
Agilent Instrument Library version 2003A with GPIB and/or LAN interface component model.

PC Setup and Software Installation

Install ADS version 2003A or later version on your PC (Win2000, XP).
Install WLAN library.
Install ADS instruments library and set up the IO library using VISA layer for communicating to instruments.

WLAN-ESGC Link Setup

Connect ADS, ESGC, the device under test (DUT), and Agilent 89641A as shown in the following figure. With this setup users can bring waveforms captured from VSA back to ADS for performing BER/PER or other performances in ADS.

Test Setup
Switch on all instruments and the PC.
Start ADS and load schematic design WLAN_80211a_ESGc.dsn for signal generation as shown in the following figure.

WLAN Transmitter Test Using ADS-ESGc Link

In the design, the model WLAN 802.11a OFDM signal source with hierarchical structure can generate an RF WLAN OFDM signal with specific data rate, burst length, symbol clock, carrier frequency, and power. All signal parameters can be easily modified in the top level of the design. Var blocks Signal Generation and RF_Measurement are designed for ease of setting key parameters. The data rate is set to 54 Mbps. The signal sent to ESG4438CSink E1, the ADS-ESGc interface for driving the Arb signal generator in ESGc.
Key parameters for ESG4438Csink E1 must be set properly.

Interface is the HPIB/GPIB interface or IP address. In this example we set Interface=141.121.237.165 (IP address).
Address is the instrument address. We set it to 20 (the ESGc address).
Start and Stop define the signal sequence length sent to ESGc that must be carefully set to keep the signal sequence contents an integer number of burst. In the example projects for transmitter and receiver tests, Start is set to 0 and Stop is automatically set by an equation in the RF_Measurement block. For understanding the way to calculate the Stop , steps are described as below:
- Calculate the number of OFDM symbols per burst for WLAN data:
  
  NSyPB = ceiling [(16 + 8 × Length + 6) /NDBPS]
  where NDBPS is the number of data bits per OFDM Symbols, and Length is the octet number of PSDU (physical layer convergence procedure service data units). NDBPS depends on data rate as shown in the following table.

WLAN Signal Parameters Specified by IEEE 802.11a Standard

Data Rate (Mbps)	Modulation	Coding Rate (R)	Coded Bits per Subcarrier (NBPSC)	Coded Bits per OFDM Symbol (NCBPS)	Data Bits per OFDM Symbol (NDBPS)
6	BPSK	1/2	1	48	24
9	BPSK	3/4	1	48	36
12	QPSK	1/2	2	96	48
18	QPSK	3/4	2	96	72
24	16-QAM	1/2	4	192	96
27	16-QAM	9/16	4	192	108
36	16-QAM	3/4	4	192	144
48	64-QAM	2/3	6	288	192
54	64-QAM	3/4	6	288	216

In this example, WLAN signal Length =512 and data rate=54 Mbps. Based on the table, NDBPS=216. From the equation for number of OFDM symbols, NSyPS=20.

Total number of samples per burst:

NSaPB = (preamble (short and long) time
+ signal time + idle time + NSyPS × 4) / tstep
For this example, preamble time =16 µ, signal plus GI=4 µ, and the idle time set to 4 µ
NSaPB = (20 + 4 + 4 × 20) × 1000/12.5 = 8320

ESGc Settings

The ARB generator in ESGc is driven by the WLAN RF signal source in ADS through HPIB/LAN. Follow the ESGc setup sequence:

ARB Settings

Press panel button Mode > Dual ARB
Press ARB on/off to ARB off
Press ARB set up
Set the ARB sample clock to 80 MHz for this example
Set the ARB Reference to Int
Set the Reconstruction Filter to Through
Press Select/Waveform and select the name of the file defined in the model ESG4438CSink, for example wlan_24
Press panel button Mod On/Off to ensure Mod On
Press panel button RF On/Off to ensure RF On
Press Frequency and set to 5.8 GHz
Press Amplitude and set to -5dBm
Press ARB On/Off to ensure ARB On

Set up the design under test.

The DUT can be any component in a transmitter. As an example, we test a power amplifier called TT-64 as the DUT. The expected performances are: output power 17 dBm for carrier 5.8 GHz.
Connect the input to the ESGc and Output to VSA89641A.
Make sure the power supply is set properly and turned on.

VSA 89641A Settings

The VSA 89641A must be connected to a PC that has an IEEE 1394 card and VSA software with WLAN flavor (option B7R) installed. When installing the VSA software, the IEEE 1374 option must be turned on.
To set up the measurement settings:

Click MeasSetUp and set the demodulator type by clicking Modulator , then select Wireless Networking > DSSS/OFDM/PBCC
Click Frequency , then enter the correct center frequency and frequency span (you can use the full span button).

To set up the input settings: click Input , then set data format to hardware .

The VSA software settings for transmission test can now be saved as a set file; for example, 11a.set . The saved set file can then be called and will use the above settings. A set file has been made that can be found in the data directory under this project: make sure you use the correct set file.

Under this setting, the EVM is measured to see if the power amplifier can be used as a transmitter power amplifier based on IEEE 802.11a std. Simulation results are compared to the standard.

Simulation Results

EVM = 1.2%, which is less than the standard value 11.2%. So, the EVM passes the test.

Benchmark

Hardware platform: Pentium IV 1.8GHz, 512 MB memory
Software platform: Windows 2000, ADS 2002C
Simulation time: approximately 10 minutes

References

IEEE Standard 802.11a-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.