80211a Transmitter

Introduction

WLAN_80211a_Tx_prj IEEE 802.11a transmitter test and verification design examples are described in this chapter.

• WLAN_80211a_Demo.dsn: WLAN signal source at 36 Mbps data rate where all data matches Annex G of IEEE 80211a.
• WLAN_80211a_SignalSource.dsn: generates IEEE 802.11a burst with different data rates.
• WLAN_80211a_Src_Glacier.dsn: generates IEEE 802.11a burst with idle, and co-simulation with VSA89600.
• WLAN_80211a_TxSpectrum.dsn: measures the transmit spectrum mask.
• WLAN_80211a_TxEVM.dsn: measures error vector magnitude and relative constellation error and tests the transmit modulation accuracy.

36 Mbps Signal Source Implementation

WLAN_80211a_Demo.dsn

Description

This design demonstrates a WLAN signal source at a data rate of 36 Mbps. The PSDU bits and all parameters settings comply with annex G of IEEE Std 802.11a-1999.

The top-level schematic for this design is shown in the following figure. Parameters that can be user-modified are contained in VAR Signal_Generation_VARs. Other parameters are set according to the specification and should not be changed.

The mapping mode is rate related; for 36 Mbps, 16-QAM mapping is used.

WLAN_80211a_Demo.dsn Schematic

Simulation Results

Simulation results displayed in WLAN_80211a_Demo.dds are the baseband burst (frame) data results in accordance with the IEEE specification (the first of the following two figures) and the transmit spectrum (the second figure).

Baseband Burst (Frame) Data Results

Transmit Spectrum

Benchmark

• Hardware platform: Pentium III 450 MHz, 512 MB memory
• Software platform: Windows NT 4.0 Workstation, ADS 2002
• Simulation time: approximately 1 minute

References

1. IEEE Std 802.11a-1999, "Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications: High-speed Physical Layer in the 5 GHz Band," 1999.

Signal Source without Idle between Two Consecutive Bursts

WLAN_80211a_SignalSource.dsn Design

Features

• Configurable signal source sub-network model
• Various data rates can be simulated by setting the Rate variable in the schematic
• Sampling rate (T, T/2, T/4, T/8 and so on) is controlled by setting the Order variable in the schematic

Description

This design is an example of WLAN signal source at various data rates without idle between two consecutive bursts.

The top-level schematic for this design is shown in the following figure. Parameters that can be user-modified are contained in VAR Signal_Generation_VARs.

WLAN_80211a_SignalSource.dsn Schematic

The modulation mode is rate related, which is controlled by the Rate variable in the schematic. The following table shows the modulation mode with various data rates.

Rate Dependent Parameters

Rate	Data Rate (Mbps)	Modulation
0	6	BPSK
1	9	BPSK
2	12	QPSK
3	18	QPSK
4	24	16-QAM
5	27	16-QAM
6	36	16-QAM
7	48	64-QAM
8	54	64-QAM

Simulation Results

Simulation results displayed in WLAN_80211a_SignalSource.dds are shown in the following two figures.

Random Burst of 802.11a

Transmit Spectrum

Benchmark

• Hardware platform: Pentium III 450 MHz, 512 MB memory
• Software platform: Windows NT 4.0 Workstation, ADS 2002
• Simulation time: approximately 1 minute

References

1. IEEE Std 802.11a-1999, "Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications: High-speed Physical Layer in the 5 GHz Band," 1999.

Signal Source with Idle between Two Consecutive Bursts

WLAN_80211a_Src_Glacier.dsn

Features

• Configurable signal source sub-network model
• Various data rates can be simulated by setting the Rate variable in the schematic
• Sampling rate (T, T/2, T/4, T/8, and so on) is controlled by setting the Order variable in the schematic
• The Idle between two consecutive bursts can be set by the Idle variable in the schematic

Description

This design is an example of WLAN signal source at various data rates with idle between two consecutive bursts and co-simulation with Agilent VSA89600.
The top-level schematic for this design is shown in the following figure. Parameters that can be user-modified are contained in VAR Signal_Generation_VARs.

WLAN_80211a_Src_Glacier.dsn Schematic

The modulation mode is rate related, which is controlled by the Rate variable. The following table shows the modulation mode with various data rates.

Rate Dependent Parameters

Rate	Data Rate (Mbps)	Modulation
0	6	BPSK
1	9	BPSK
2	12	QPSK
3	18	QPSK
4	24	16-QAM
5	27	16-QAM
6	36	16-QAM
7	48	64-QAM
8	54	64-QAM

Simulation Results

Simulation results displayed in WLAN_80211a_Src_Glacier.dds are shown in the following three figures.

Time Waveform of One Burst with Idle

Transmit Spectrum

EVM, CPE, and IQ_Offset

Benchmark

• Hardware platform: Pentium III 450 MHz, 512 MB memory
• Software platform: Windows NT 4.0 Workstation, ADS 2002
• Simulation time: approximately 1 minute

References

1. IEEE Std 802.11a-1999, "Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications: High-speed Physical Layer in the 5 GHz Band," 1999.

Transmit Spectrum Mask Measurement

WLAN_80211a_TxSpectrum.dsn

Features

• IEEE 802.11a configurable signal source, adjustable data rate
• Adjustable sample rate
• Spectrum analysis
• Integrated RF section

Description

This design demonstrates the IEEE 802.11a transmitter signal spectrum due to modulation and wideband noise.
The schematic for this design is shown in the following figure.

WLAN_80211a_TxSpectrum.dsn Schematic

Measurements in this design are based on IEEE Standard 802.11a-1999 section 17.3.9.2. The transmitted spectrum must have a 0 dBr (dB relative to the maximum spectral density of the signal) bandwidth not exceeding 18 MHz, -20 dBr at 11 MHz frequency offset, -28 dBr at 20 MHz frequency offset, and -40 dBr at 30 MHz frequency offset and above. The transmitted spectral density of the transmitted signal must fall within the spectral mask, as shown in the following figure.

Transmit Spectrum Mask

Simulation Results

Simulation results displayed in WLAN_80211a_TxSpectrum.dds are shown in the following three figures for 5180 MHz (36 operating channels), 5280 MHz (56 operating channels), and 5805 MHz (161 operating channels) frequencies.

Transmit RF Spectrum, 5180 MHz

Transmit RF Spectrum, 5280 MHz

Transmit RF Spectrum, 5805 MHz

Benchmark

• Hardware platform: Pentium III 450 MHz, 512 MB memory
• Software platform: Windows NT 4.0 Workstation, ADS 2002
• Simulation time: approximately 1 minute

References

1. IEEE Standard 802.11a-1999, "Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications: High-speed Physical Layer in the 5 GHz Band," 1999.

Error Vector Magnitude and Relative Constellation Error Measurements

WLAN_80211a_TxEVM.dsn

Features

• IEEE 802.11a configurable signal source, adjustable data rate
• Adjustable sample rate
• Constellation display
• Integrated RF section

Description

This design tests IEEE 802.11a transmit modulation accuracy and transmitter constellation error by measuring the EVM. The schematic for this design is shown in the following figure.

WLAN_80211a_TxEVM.dsn Schematic

Measurements in this design are based on IEEE Standard 802.11a-1999 section 17.3.9.6. The transmit modulation accuracy test must be performed by instrumentation capable of converting the transmitted signal into a stream of complex samples at 20 Msamples per second or more, with sufficient accuracy in terms of I/Q arm amplitude and phase balance, dc offsets, phase noise, and so on. A possible embodiment of such a setup is converting the signal to a low IF frequency with a microwave synthesizer, sampling the signal with a digital oscilloscope and decomposing it digitally into quadrature components.
The sampled signal must be processed in a manner similar to an actual receiver, according to the following, or equivalent steps:

• Start of frame must be detected.
• Transition from short sequences to channel estimation sequences must be detected, and fine timing (with one sample resolution) must be established.
• Coarse and fine frequency offsets must be estimated.
• The packet must be de-rotated according to estimated frequency offset.
• The complex channel response coefficients must be estimated for each subcarrier.
• For each data OFDM symbol: transform the symbol into subcarrier received values, estimate the phase from the pilot subcarriers, de-rotate the subcarrier values according to estimated phase, and divide each subcarrier value with a complex estimated channel response coefficient.
• For each data-carrying subcarrier, find the closest constellation point and calculate the Euclidean distance from it.
• Calculate the RMS average of all errors in a packet:
  
  where
  L _P is the length of the packet
  N _f is the number of frames for the measurement
  ( I ₀ ( i, j, k ), Q ₀ ( i, j, k )) denotes the ideal symbol point of the i th frame, j th OFDM symbol of the frame, k th subcarrier of the OFDM symbol in the complex plane
  ( I ( i, j, k ), Q ( i, j, k )) denotes the observed point of the ith frame, jth OFDM symbol of the frame, k th subcarrier of the OFDM symbol in the complex plane (see the following figure)
  P ₀ is the average power of the constellation.

The vector error on a phase plane is shown in the following figure.

The test must be performed over at least 20 frames ( N _f ) and the RMS average must be taken. The packets under test must be at least 16 OFDM symbols long. Random data must be used for the symbols.

Constellation Error

The EVM and relative constellation RMS error, averaged over subcarriers, OFDM frames, and packets, cannot exceed a data-rate dependent value according to the following table.

Allowed EVM and Relative Constellation Error

Data Rate (Mbps)	Relative Constellation Error (dB)	EVM (% RMS)
6	-5	56.2
9	-8	39.8
12	-10	31.6
18	-13	22.3
24	-16	15.8
36	-19	11.2
48	-22	7.9
54	-25	5.6

Simulation Results

Simulation results displayed in WLAN_80211a_TxEVM.dds are shown in the following figure for EVM and relative constellation error of 54 Mbps. The EVM is less than 0.6%; the constellation error is approximately -45dB which is much smaller than the specification requirements given in the preceding table.

EVM and Relative Constellation Error of 54 Mbps

Benchmark

• Hardware platform: Pentium III 450 MHz, 512 MB memory
• Software platform: Windows NT 4.0 Workstation, ADS 2001
• Simulation time: approximately 30 minutes

References

1. IEEE Standard 802.11a-1999, "Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications: High-speed Physical Layer in the 5 GHz Band," 1999.