Last updated: December 2, 2008
This section is only applicable to the lab applications.
Frequency hopping is the technique of improving the signal to noise ratio in a link by adding frequency diversity. The base station commands the mobile station to activate frequency hopping as the mobile station moves toward the edge of a cell or into an area of high interference. When frequency hopping is activated in the mobile station, the base station assigns the mobile station a set of RF channels, rather than a single RF channel. A frequency hopping algorithm is also assigned to the mobile and is used to inform the mobile of the pattern of the available frequencies it is to use. In a GSM/GPRS/EGPRS network, frequency hopping is specified in individual cells based on the number of frequencies offered by a specific cell. The advantages that frequency hopping offers are:
The test set offers two basic forms of frequency hopping algorithms: cyclic and pseudo random. When set to the cyclic form, the test set and the mobile station are cycled through a fixed repeated pattern of frequencies. There are a total of 64 different frequency patterns that the test set can generate and use. The hopping sequence the mobile station uses depends on the Hopping Sequence Number (HSN) specified in the test set. An HSN of zero corresponds to the cyclic hopping sequence, and values 1 through 63 correspond to the pseudo random patterns. The ARFCNs used in the hopping sequence pattern are determined by the contents of the test set's Mobile Allocation (MA) Table. The entry of the MA Table at which the hopping sequence begins is called the Mobile Allocation Index Offset (MAIO). Note that an MAIO of zero corresponds to the first entry of the MA Table.
An MA Table is a list of the ARFCNs present in the Cell Allocation (CA) Table that share the same frequency band. There is a separate MA Table for each frequency band. The ARFCNs in the MA Table must be chosen from the test set's Cell Allocation (CA) Table because the CA Table contains all the ARFCNs available for use in the cell. If a handoff to another band occurs, the test set uses the MA Table for the band that it was instructed to handoff to.
The following table shows which ARFCNs represent each frequency band in the test set's default CA Table. The default CA Table contains all the ARFCNs listed in the third column. There is a separate MA Table for each frequency band. The values in each row of the third column show the MA Tables for each corresponding frequency band. For example, when the test set's selected frequency band is PCS, the default values contained in MA Table for the PCS band are: 520, 661,810. Note that there the default MA Table for the T-GSM810 band is empty.
| Frequency Band | ARFCN Range | Default ARFCN |
|---|---|---|
| DCS | 512 to 885 | 520, 661, 810, 885 |
| EGSM | 0 to 124 and 975 to 1023 | 1, 124, 975 |
| GSM450 | 259 to 293 | 259, 293 |
| GSM480 | 306 to 340 | 306, 340 |
| GSM750 | 438 to 511 | 438, 511 |
| GSM850 | 128 to 251 | 128, 251 |
| PCS | 512 to 810 | 520, 661, 810 |
| PGSM | 1 to 124 | 1, 124 |
| RGSM | 0 to 124 and 955 to 1023 | 1, 124, 955, 975 |
The MA Tables and the CA Table can be manually or automatically configured. Sixteen is the maximum number of entries for an MA Table.
When the MA Table is configured automatically, any changes to the CA Table are populated in the MA Table of the appropriate frequency band. The state of each entry in an MA Table can be manually set.
To maintain measurement accuracy, the measurement down converter is set to an ARFCN in the selected MA Table. This ARFCN is called the Measurement ARFCN.
| NOTE |
| GPIB Commands | |
|---|---|
| Cell Allocation (CA) Table | |
| Mobile Allocation (MA) Table Configuration Mode | |
| Mobile Allocation (MA) Table Automatic Configuration | |
| Mobile Allocation (MA) Table Manual Configuration | |
| Mobile Allocation (MA) Table Points Manual Configuration | |
| Mobile Allocation (MA) Table Points Automatic Configuration | |
| Measurement ARFCN |
Frequency hopping can only occur when the Operating Mode is set to one of the following: Active Cell (with GSM, GPRS or EGPRS as the Serving Cell ), GSM TCH, GPRS BCH+PDTCH, or EGPRS BCH+PDTCH. Frequency Hopping parameters can be changed in any Operating Mode, but the test set's operation is not effected until it is set to a valid Operating Mode.
The Cell Allocation (CA) table is transmitted on the BCCH whenever there is a presence of a BCH.
Frequency Hopping in applicable to the following Connection Types: ETSI Type A, ETSI Type B (Unack), ETSI Type B (Ack), BLER, Auto, SRB Looback.
The Operating Mode must be set to Cell Off before the CA Table can be changed. The maximum number of entries the CA table and MA table can contain is sixteen, and the MA values can only be chosen from the CA Table values.
If frequency hopping is enabled, the adjacent burst power implies the burst power before and after the traffic channel bursts. The Adjacent Burst Power can be set using the GPBI command: CALL:TCHannel:PREDuction:ADJacent or CALL:(PDTCH|PDTChannel):PREDuction:ADJacent .
The RF Amplitude Offset applied to the Test Set's RF signal generator output (for mobile station receiver measurements) is the middle frequency/offset pair in the RF In/Out Amplitude Offset table. This single offset value is applied to the RF output for all hopped channels. (Note: If there is an even number of frequency/offset pairs in the RF In/Out Amplitude Offset table, the offset used is the higher of the two middle pairs. For example, if there are 4 frequency / offset pairs, the offset of pair 3 is used).
When the
BCH Type
is set to
Combined
, Frequency Hopping cannot take place on the SDCCH.