Transmit Diversity
The software provides a downlink transmit diversity feature that incorporates both STTD and TSTD encoding. During transmit diversity operation, the software does not incorporate any DTX periods.
Transmit diversity diminishes the effects of fading by transmitting the same information from two different antennas. For this software, the two different antennas means one carrier set as antenna one and another carrier set as antenna two. STTD and TSTD encoding is what lets a UE distinguish whether a signal is from antenna one or antenna two. The data from the second antenna (second carrier—Open Loop Antenna 2) is encoded differently to distinguish it from the primary antenna (Open Loop Antenna 1). The user equipment (UE) must be able to recognize that the information is coming from two different locations (in this case different carriers) and properly decode the data.
There are a few different ways to configure transmit diversity. If the requirement is to look at the data from a single transmit diversity antenna, you can configure an individual carrier as either antenna one or as antenna two. If the test requires a signal from both antennas, then you need to configure a minimum of two carriers, one as antenna one and the other as antenna two. Since this software is a multicarrier product capable of transmitting 16 different carriers, the flexibility of the software also lets you configure each carrier as a transmit diversity antenna, meaning that you can have several as antenna one, as antenna two, or a mixture of both.
The software applies STTD encoding to the following channels:
|
DPCH |
E-AGCH |
|
E-HICH |
E-RGCH |
|
HS-PDSCH |
HS-SCCH |
|
OCNS |
PICH |
|
P-CCPCH |
S-CCPCH |
The CPICH is not STTD encoded, but it is affected by transmit diversity. Even though it is transmitted from both antennas, its predefined bit sequence differs between antenna one and antenna two per the 3GPP specifications. The SCH uses TSTD encoding and is phase inverted:
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Open Loop Antenna 1 – sets up the carrier as antenna one, and broadcasts the SCH during even numbered slots.
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Open Loop Antenna 2 – sets up the carrier as antenna two, broadcasts the SCH during odd numbered slots, modifies the DPCCH pilot bits, and encodes the data to distinguish it from antenna one.
To configure a carrier for transmit diversity, use the Carrier Setup node located in the tree view.