Use this cell to set the capability for WLAN 802.11n to either Basic or Advanced.
Basic Capability supports configuration of all of the WLAN 802.11n signal parameters except the channel coding function, and so is suitable for component testing.
Parameters under Basic capability are a subset of the Advanced capability.
Advanced capability supports generation of fully channel-coded waveforms and is suitable for both receiver testing and component testing.
The following parameters are supported only by the Advanced capability
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 length for file names is 22 characters.
Enter an alpha-numeric comment of up to 32 characters. The comment resides in the file header and can include spaces and special characters.
This cell displays the number of samples (or data points) in the waveform. The number of sample points varies with the Oversampling Ratio and is related to the number of packets, the frame mode, the data rate, and the length of the user data. The maximum number of samples a waveform can have depends on the ARB memory capacity of the signal generator's baseband generator. You cannot edit cells in this column. This total samples value also appears in the status bar at the bottom of the main window.
Use this cell to select framed or unframed mode to generate a signal. A framed signal is needed in receiver tests, and an unframed signal is useful in component tests or in other instances where continuous, non-bursted modulation of unframed data is desired.
Use this cell to select the signal generation format
Legacy- The legacy mode is applicable only for 802.11n MxN (1SG) setup application. In legacy mode, you can select either 40 MHz or 20 MHz bandwidth. When 20 MHz bandwidth is selected, data packets are transmitted in the legacy 802.11a/g format. When 40 MHz bandwidth is selected, the device operates in a 40 MHz channel composed of two adjacent 20 MHz channels. The packets to be sent are in the legacy 802.11a format in each of the 20 MHz channels. To reduce the PAPR, the upper channel (higher frequency) is rotated by 90° relative to the lower channel.
HT (High Throughput) - In HT mode, the device operates in either 40 MHz bandwidth or 20 MHz bandwidth and with one to four spatial streams. This mode includes the HT-duplicate mode.
Use this cell to set the length (in microseconds) of the idle time between frames. This is relevant only in framed mode.
No signal is transmitted during the idle interval, but the MAC layer operates as if a signal is being transmitted.
Set the idle interval ahead of frames in unit of seconds.
Choice: Data and Control | Beacon
Default: Data and Control
Coupling: When Capability is set to Basic or Generation Mode is set to Unframed, this parameter becomes read-only and is set to Data and Control.
Select the frame type. When you select Beacon, an additional node appears in the 
tree view under Signal Configuration, giving you access to additional parameters for configuring the Beacon frame type.
This feature requires Option H or Option R (802.11n Advanced).
Use this cell to set the occupied bandwidth for 802.11n to either 20 MHz or 40 MHz.
Displays the number of OFDM symbols in the data portion of one frame.
Displays the time duration (in seconds) of the burst in one frame. The burst duration is equal to the preamble portion plus the data portion.
Displays the time duration (in seconds) of the overall waveform in one frame. The overall waveform duration is equal to the RF burst duration plus the idle interval.
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:
None - No filter.
The Gaussian filter does not have zero Inter-Symbol Interference (ISI). Wireless system architects must decide just how much of the ISI can be tolerated in a system and combine that with noise and interference. The Gaussian filter is Gaussian shaped in both the time and frequency domains, and it does not ring like the root cosine filters do. The effects of this filter in the time domain are relatively short and each symbol interacts significantly (or causes ISI) with only the preceding and succeeding symbols. This reduces the tendency for particular sequences of symbols to interact, which makes amplifiers easier to build and more efficient.
Root cosine, also referred to as square root raised cosine, filters have the property that their impulse response rings at the symbol rate. Adjacent symbols do not interfere with each other at the symbol times because the response equals zero at all symbol times except the center (desired) one. Root cosine filters heavily filter the signal without blurring the symbols together at the symbol times. This is important for transmitting information without errors caused by ISI. Note that ISI does exist at all times, only at the symbol (decision) times.
In the frequency domain, this filter appears as a low-pass, rectangular filter with very steep cut-off characteristics. The pass band is set to equal the symbol rate of the signal. Due to a finite number of coefficients, the filter has a predefined length and is not truly "ideal." The resulting ripple in the cut-off band is effectively minimized with a Hamming window. This filter is recommended for achieving optimal ACP. A symbol length of 32 or greater is recommended for this filter.
Allows you 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.
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.
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.
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.
This is valid only for user-defined filters.
When you select
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.
Set the effective bandwidth for Ideal Lowpass filter.
Use this cell to specify the number of times that the baseband signal is oversampled.
The minimum value of this cell is 1.
For 802.11n with 20 MHz bandwidth, the maximum value is 5.
For 802.11n with 40 MHz bandwidth, the maximum value is 2.
Use this cell to set the mirror spectrum to ON or OFF.
As a signal propagates normally through the different functional blocks of a receiver (for example, the mixer block), the signal spectrum may be inverted. Enabling this cell facilitates realistic testing of receiver functional blocks that would normally be presented with a mirrored spectrum signal. The default setting is OFF.
ON: When turned ON, the Q channel is inverted, resulting in a mirrored spectrum
OFF: When turned OFF, the spectrum is not inverted.
Use this cell to set the length of the OFDM raised cosine window. The maximum value of this cell is related to the guard interval.
For short guard interval (400 ns), the maximum value is 16 samples
For normal guard interval (800 ns), the maximum value is 32 samples
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.
TVWS spectrum is attractive due to long range and better indoor penetration for signal propagation at the lower frequencies. Downclocking Ratio enables 802.11n signal to operate at the TVWS spectrum with a narrow bandwidth. It downclocks the oversampled 802.11n signal with a specified factor. Therefore, the final sample clock employed by the signal generator is equal to Bandwidth x Oversampling Ratio / Downclocking Ratio.
