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Waveform Setup - 802.11be

1. Waveform Basic

Waveform Name

Use this cell to enter a name for the waveform. The alphanumeric text entered in this cell appears in the signal generator's user interface after the configuration is downloaded to the instrument. The signal generator recognizes only waveform names that use the following characters:

A through Z

0 through 9

$ & _ # + - [ ]

If unsupported characters appear in a configuration name, the signal generator generates a "file name not found" error (Error: -256) when you download the configuration to the instrument.

The maximum allowed waveform name length depends on the connected instrument.

For N5182B/N5172B/N5166B/M9383A/M8190A/E6630A/N5106A, it is 150 characters, while for N5182A/E4438C/N8267B, it is 22 characters.

There are cases when multiple waveforms could be downloaded into a single instrument. In this case, to distinguish the waveforms, an index number will be attached at the end of the waveform name. Therefore, the allowed name length will be decremented by 2.

The software initially lets you enter a name with any length characters, but when you click outside of the cell, the software truncates the name to the maximum name length characters.

If the selected capability is the MIMO for single instrument, the max name length will be truncated to 20 characters because the name will be appended with “_*”, where * is a number representing the antenna index.

Comment

Enter an alpha-numeric comment of up to 32 characters. The comment resides in the file header and can include spaces and special characters.

Standard Version

Displays the 802.11be standard version supported by the software.

Generation Mode

Choice: EHT MU PPDU | Non-HT | EHT Trigger Based PPDU

Default: EHT MU PPDU

Coupling: Defines the type of frame to be generated and is coupled with most parameters

Select the type of frame to be generated.

The format of the EHT MU PPDU is used for transmission to one or more users that is not a response of a Trigger frame.

The format of the EHT Trigger-Based PPDU is used for a transmission that is a response to a Trigger frame.

Non-HT refers to the one defined by standard as Non-HT Duplicate Transmission, which is to repeat 802.11a signal in each 20-MHz segment.

Frame Type

Choices: Data and Control | Trigger

Default: Data and Control

Select the frame type. It could be a Data frame, a Control frame and a Trigger frame. The Trigger frame solicits and allocates resources for UL MU transmissions a SIFS after the PPDU that carries the Trigger frame. The Trigger frame also carries other information required by the responding STA to send an EHT trigger-based PPDU.

Idle Interval

Set the idle interval between frames in unit of sec.

Head Idle Interval

Set the idle interval ahead of frames in unit of seconds.

Bandwidth

Choice: 20 MHz | 40 MHz | 80 MHz | 160 MHz | 320 MHz

Default: 20 MHz

Select the bandwidth for IEEE 802.11be. The instrument must have at least the equivalent bandwidth to allow the waveform to be successfully transmitted.

Channelization

Choices: 320 MHz-1 | 320 MHz-2

Default: 320 MHz-1

Select the channelization for 320 MHz channel.

Phase Rotation Coefficients

Choices: 1:-1:1 | 1;1;-1 | 1;-1;1 | 1;-1;-1 | -1;1;1 | -1;1;-1| -1;-1;1 | -1;-1;-1

Default: 1;-1;-1

Select the Phase Rotation Coefficient Coefficients for the last 3 8-MHz subblocks in 320-MHz bandwidth.

Number of Frames

Range: 1 to 2000

Default: 1

Set the number of frames.

Total Sample Points

This is information indicating the generated waveform length in terms of sampling points.

Number of Data Symbols in One Frame

Number of OFDM Symbols in the Data portion of one frame.

RF Burst Duration in One Frame

The time duration of RF burst in one frame in unit of seconds.

Overall Waveform Duration in One Frame

The time duration of the overall waveform in one frame in unit of seconds.

2. Spectrum Control

Oversampling Ratio

Range: minimum value is 1

Default: 2

Use this cell to specify the number of times that the baseband signal is oversampled.

A higher oversampling ratio would help simplify the design of transmitting filter, but would result in a longer waveform.

Mirror Spectrum

Choice: On | Off

Default: Off

Reverse the spectrum of the waveform. This is useful for systems with external up conversion where the signal spectrum is mirrored by the up conversion process.

On: The Q channel is inverted, resulting in a mirrored spectrum.

Off: The spectrum is not inverted.

Windowing Length

Range:

For short guard intervals (400 ns): 0 to 16 samples

For normal guard intervals (800 ns): 0 to 32 samples

Default: 2

Set the duration of the transition time (Ttr) in the windowing function. Ttr creates a small overlap between consecutive subsections in order to smooth the transitions between them. Smoothing the transition is required in order to reduce the spectral sidelobes of the transmitted waveform.

Entering 0 samples means no windowing will be applied. A raised cosine time domain window is applied to the baseband signal to reduce out-of-band power.

Increasing the window length is a good way to decrease the adjacent channel power with a fairly small degradation in EVM performance.

Filter

A baseband filter is applied to reduce the transmitted bandwidth, increasing spectral efficiency.

For signals generated with digital signal processing, baseband filters are often finite impulse response (FIR) filters with coefficients that represent the sampled impulse response of the desired filter. FIR filters are used to limit the bandwidth of the input to the I and Q modulators.

Five options for baseband filtering can be selected in the Filter Type menu:

Length (symbol)

The symbol length of the filter determines how many symbol periods will be used in the calculation of the symbol. The filter selection influences the symbol length value.

The Gaussian filter has a rapidly decaying impulse response. A symbol length of 6 is recommended. Greater lengths have negligible effects on the accuracy of the signal.

The root cosine filter has a slowly decaying impulse response. It is recommended that a long symbol length, around 32, be used. Beyond this, the ringing has negligible effects on the accuracy of the signal.

The ideal low pass filter also has a very slow decaying impulse response. It is recommended that a long symbol length, 32 or greater, be used.

For both root cosine and ideal low pass filters, the greater the symbol length, the greater the accuracy of the signal. Try changing the symbol length, and plotting the spectrum to view the effect the symbol length of the filter has on the spectrum.

BT

This cell sets the filter's bandwidth-time product (BT) coefficient. It is valid only for a Gaussian filter.

B is the 3 dB bandwidth of the filter and T is the duration of the symbol period. BT determines the extent of the filtering of the signal. Occupied bandwidth cannot be stated in terms of BT because a Gaussian filter's frequency response does not go to zero, as does a root cosine filter. Common values for BT are 0.3 to 0.5. As the BT product is decreased, the ISI increases.  

Alpha

This cell sets the filter's alpha coefficient. It is valid only for root cosine filters.

The sharpness of a root cosine filter is described by the filter coefficient, which is called alpha. Alpha gives a direct measure of the occupied bandwidth of the system and is calculated as: occupied bandwidth = symbol rate X (1 + alpha). If the filter had a perfect (brick wall) characteristic with sharp transitions and an alpha of zero, the occupied bandwidth would be: symbol rate X (1 + 0) = symbol rate. An alpha of zero is impossible to implement. Alpha is sometimes called the "excess bandwidth factor" as it indicates the amount of occupied bandwidth that will be required in excess of the ideal occupied bandwidth (which would be the same as the symbol rate).

At the other extreme, take a broader filter with an alpha of one, which is easier to implement. The occupied bandwidth for alpha = 1 will be: occupied bandwidth = symbol rate X (1 + 1) = 2 X symbol rate. An alpha of one uses twice as much bandwidth as an alpha of zero. In practice, it is possible to implement an alpha below 0.2 and make good, compact, practical radios. Typical values range from 0.35 to 0.5, though some video systems use an alpha as low as 0.11.

Bandwidth

This cell sets the effctive bandwidth for the ideal low pass filter. It is valid only for low pass filters.

Filter Coefficient

This is valid only for user-defined filters.

When you select User Defined as the filter type, click the button in this cell to select a simple unformatted text file (*.txt) of coefficient values, characterizing a user-defined filter. Each line in the file contains one coefficient value. The number of coefficients listed must be a multiple of the selected oversampling ratio. Each coefficient applies to both I and Q components.

3. Marker

Marker 1 Source

Frame Start - It indicates the beginning of each frame. It starts at the beginning of the Head Idle Interval.

Marker 2 Source

RF Blanking - It controls On/Off of the RF signal. There is a 500 ns pre-blanking before the Preamble part and a 335 ns latency after the Data part for Marker2.

Marker 3 Source

Frames - It indicates the period of each frame. The Head Idle Interval is included in the frame, and the Idle Interval is excluded.

Marker 4 Source

Preamble Blanking - It indicates the Preamble part of each frame.