Soft Handover

Cell 2 Overview

The lab application includes two sectors, cell 1 and cell 2. Cell 1 is a full sector, supporting all call processing functionality available in the test set. Cell 2 is provided to allow the test set to perform a soft handover. Cell 2 alone can not be used for call processing events, such as establishing a call or handing off to a new frequency. Cell 2 can only be used in conjunction with cell 1 to test the UE's soft handover capability. The table below summarizes the features of cell 1 and cell 2, and indicates if the features are user-settable.

See How Do I Configure Cell 2? for more information about configuring cell 2 from the front panel. See Downlink Channel Codes and Levels for more information about cell 1 channelization codes and levels.

The test set's total RF output power is a combination of the power of cell 1, cell 2 and AWGN power:
Total RF Power (dBm/3.84 MHz) = [Cell 1 Power + Cell 2 Power + AWGN Power] (dBm/3.84 MHz)
(see Cell Power and AWGN Power for more information about cell power and AWGN power).

Soft Handover Overview

The soft handover functionality is accessible through the Soft Handover Information screen (select Handovers ( F5 ) on the Call Control menu, then Soft Handover Info ( F4 ).)

Generated Pilot Information

The Generated Pilot Information window reports:

• Total RF Power
• Cell 1 CPICH Power (Cell Power + CPICH Level (or Cell 1 Connected CPICH Level))
• Cell 2 CPICH Power (Cell 2 Power + Cell 2 CPICH Level)
• Delta Power (the difference between the CPICH and Total RF Power)
• Primary Scrambling Code

See Cell Power and AWGN Power , Downlink Channel Codes and Levels and CALL:STATus .

Mobile Station Reported Pilot Information

When a non-HSDPA connection is established between the test set and UE, you may request measurement results from the UE, including CPICH RSCP , CPICH Ec/No , Pathloss , OTD , OTD Type and DTCH BLER (see Cell 1/Cell 2 UE Reported Measurements ). When you request UE reported measurement results, results for CPICH RSCP, CPICH Ec/No and Pathloss are returned for both cell 1 and cell 2 (if cell 2 is set to a non-zero power level). If you have enabled soft handover (see Enabling Soft Handover ), the DTCH BLER Report result includes both cell 1 and cell 2 (there is only one DTCH in soft handover because soft combining of the two radio links in the UE occurs before the point where the DTCH is extracted and BLER is calculated).

Enabling Soft Handover

After establishing a non-HSDPA call between the test set's cell 1 and the UE, and configuring cell 2 (power, primary scrambling code, time offset, etc., see Cell 2 Overview ), you may turn soft handover on (see How Do I Perform a Soft Handover? and CALL:SHANdoff:ENABle ). This orders the UE to try to demodulate the signal from cell 2. Soft handover is not supported while on a CELL_FACH connection (see RB Test Mode RRC State Setting ) or while on an HSDPA connection.

Soft handover is supported for HSUPA connections but only to simulate a network scenario for when a UE performs a soft handover with cell 2 but the HSUPA channels remain confined to the cell 1 (serving cell). When an HSUPA call is established between the test set's cell 1 and the UE and you turn soft handover on, the DPCH is instructed to soft handover to cell 2 while the HSUPA channels remain confined to cell 1.

Soft Handover State

If the soft handover was successful (the UE responded correctly to the Active Set Update procedure), then a status of On is displayed for Soft Handover State (see CALL:STATus:SHANdoff:STATe? ).

Loopback BER and BLER Testing in Soft Handover

You can test Loopback BER and BLER while in soft handover (see How Do I Perform a Soft Handover? , Loopback Bit Error Ratio (BER) Measurement Description and Block Error Ratio (BLER) Measurement Description ). When soft handover is not enabled, as you increase cell 2 power, you will see an increase in BER/BLER (because cell 2 acts as an interferer). When you enable soft handover, the BER/BLER result should improve, as the UE is then able to soft combine the signals from both cells. (If cell 2 level is too high, the messaging to order a soft handover may not be properly received by the UE and an error will be posted. If this is the case, simply decrease cell 2 power, enable soft handover, then return cell 2 to its previous level).

Event Reporting

The soft handover functionality present in the test set also allows you to enable/disable event reporting (by turning Event State on and off), and to configure event parameters (such as Event 1a State , R 1a etc.).

When event reporting is enabled (non-HSDPA connections only), the UE reports to the test set when an event occurs (if you have enabled that event by turning its state on. For example: if you have set Event 1a State to On , then the UE will report when a 1a event occurs). You can query the most recent event reported by the UE using the CALL:STATus:SHANdoff:EVENt? query, and which cell caused the event using the CALL:STATus:SHANdoff:EVENt:CELLid? query.

When you turn Event State on (enable event reporting), the test set sends a Measurement Control message to the UE with the following user-settable event information:

• 1a (A Primary CPICH enters the Reporting Range): Event 1a State, W, R _1a , H _1a
• 1b (A Primary CPICH leaves the Reporting Range): Event 1b State, W, R _1b , H _1b
• 1c (A Non-active Primary CPICH becomes better than an active Primary CPICH): Event 1c State, H _1c
• 1d (Change of best cell): Event 1d State, H _1d
• 1e (A Primary CPICH becomes better than an absolute threshold): Event 1e State, T _1e , H _1e
• 1f (A Primary CPICH becomes worse than an absolute threshold): Event 1f State, T _1f , H _1f

(see How Do I Configure and Enable (Start) Event Reporting? and CALL:SHANdoff )