In Basic mode, you can select the modulation type and set the number of frames you want to generate. All the parameters are set to their nominal settings for GSM on initial entry of the modulation page (MSK modulation, 1 frame, and 6 times over sampling). In general, when using a combination of EDGE and GSM slots, it is not possible to guarantee a correct phase wrap, because the modulation type has to change between GSM and EDGE bursts. Therefore, the default number of frames is not set to 8, as it is for EDGE only modulation.

Note Oversampling Factor can only be set to values that are multiples of 3.

Creating a Frame

The Frame Config tab allows you modify the GSM frame being generated. Frame Config tab consists of 8 time slots each of which can be modified by clicking on the relevant item in the upper slot graphic.

Setting the Frame Configuration Parameters: This section describes the general settings available for frame configuration and how you can modify them.

Link Direction: Enables you to select the type of frame configuration. The default value is Up/Reverse.

Bit Encoding Method: Specifies the bit encoding method. The default value is GSM Differential.

Rise Time (Symbols): Specifies the duration of the rising edge of a burst in symbols. The valid range is between 1/Oversampling Factor and 16.0 and the resolution is 1/Oversampling Factor. The default value is 3.

Fall Time (Symbols): Specifies the duration of the falling edge of a burst in symbols. The valid range is between 1/Oversampling Factor and 16.0 and the resolution is 1/Oversampling Factor. The default value is 3.

Rise Delay (Symbols): Specifies the offset in the start of the rising edge of a burst in symbols. The valid range is between -9.0 and 9.0 and the resolution is 1/Oversampling Factor. The default value is 0.

Fall Delay (Symbols): Specifies the offset in the start of falling edge of a burst in symbols. The valid range is between -9.0 and 9.0 and the resolution is 1/Oversampling Factor. The default value is 0.

Slot Enabled: Allows you control whether the specific slot will be transmitted or not. By default, only the first slot is transmitted.

Burst Type: Specifies the type of burst that can be inserted into the frame. The default value is GSM.

Power: Specifies the power of the slot relative to the signal generator's power level. This value is expressed in dB. Valid values are 0 to – 60 dB.

Note Slot powers are readjusted such that slot with max power is generated at 0 dB. Other slots will be generated at readjusted power relative to signal generators power level.

Configuring an Uplink Slot

On this Frame Config tab, you can examine the fields that make up the slot, you can change the contents of the Sync and Data fields, and you can set the Burst Type to GSM, Access, or Edge. The Slot Enabled checkbox allows you control if the specific slot will be transmitted or not. By default, only the first slot is transmitted.

There are two 58 bits long data fields in a normal burst, which are treated as a contiguous block of data. The data source you select for either of these is automatically applied to the other and if you select a PRBS sequence the data at the start of the second field will continue in the sequence from where the first field finished. These two fields combined will generate 116 data bits of the PRBS sequence, which will restart after the total number of frames you set on the modulation page. If you want a sequence longer than 116 bits, you should increase the number of frames on the modulation page, since the PRBS sequence is continued for every frame in the set. For example, to generate a sequence of at least 5,000 bits, set the number of frames to 44, and you will get a sequence which repeats after 44 x 116 bits = 5,104 bits. The data source can be modified by clicking on the Data portion of the slot graphic, and then selecting the Source Type button.

An EDGE burst looks very similar to a normal GSM burst, except that every field has three times as many bits. The burst occupies the same number of symbols as a GSM burst, because the 8PSK modulation uses three bits per symbol.

You can change the training sequence field of a normal burst to any of the eight patterns TS0 to TS7 by selecting the sync portion of the slot graphic and then using the TSC control below. An access burst has a fixed sync field and only one data field of 36 bits.

Configuring a Downlink Slot

You can change to a downlink frame by selecting Down/Forward on the Link Direction control.

To configure a slot within the downlink frame, click the slot within the main slot graphic at the top of the tab.

Available burst types for downlink slots are GSM, Sync, Dummy, Frequency Correction, and Edge.

The following figure shows the frequency correction burst in a downlink frame. You have only two choices for the frequency correction, the fixed bits can be set to represent either + 67.7 kHz or - 67.7 kHz. To change frequency correction, Click Freq. Correction in the graphic and select the correction in the Correction control. The guard period is either long or normal, depending on the slot number, the same as uplink bursts.

A dummy burst has no user options, a synchronization burst has two data fields that you can configure, and a normal burst has two data fields and a training sequence field with options.