Receiver Sensitivity; Transmission Diversity Time Delay - Siemens BS-240 Technical Description

Technical Description (TED:BSS)
BS-240/241
4.2.2
4.3
62
The principle of On Air Combining will also be used, if TX combining beyond the Rack
borders is required. For e.g. to combine 24 carriers, belonging to the same cell, 3
FICOMs will be used, each combines 8 carriers to one antenna. Combining of the
signals from the 3 antennas takes place 'On Air'.

Receiver Sensitivity

Obtaining sensitivity better than the GSM requirements at the Rack entry is by using
DUAMCOs or DIAMCOs, and obtaining sensitivity better than the GSM requirements at
the antenna connector accomplished by using Tower Mounted Amplifiers (TMAs). The
configuration with TMA is advantageous because of highest sensitivity of the RX path.
One TMA is needed for every created RX path of DUAMCO and / or DIAMCO installed
and not cascaded.
Expansion of the RX path beyond the borders of the Rack or Shelter is possible by
cascading of the multicoupling devices (DIAMCO or RX path of a DUAMCO). With
increasing RF cable length, the noise figure rises and thus the RX sensitivity will be
degraded. The degradation is a little bit less than the additional cable loss.
In the configuration with antenna pre-amplifier, the true system RX sensitivity is guaran-
teed at the antenna connector, including the antenna feeder cable attenuation. In the
configuration without antenna pre-amplifier, the sensitivity is guaranteed only at the rack
entry.

Transmission Diversity Time Delay

General
Up to BR6.0 each BTS plus CU works on its own frequency with RF output power limited
by the maximum nominal output power of the module. To achieve higher output power,
a separated high power amplifier has to be used.
This feature "combines" the output signals of 2 standard carrier units (fed with the same
baseband signal) to increase the available output power. To allow the parallel CU oper-
ation, their transmit signal must be de-correlated.
The parallel CU operation with de-correlated signals establish a diversity down-link path.
Using down-link diversity significantly reduces the influence of signal fading.The coding
schemes CS3, CS4, MCS8, and MCS9 particularly profit from such transmission diver-
sity operation.
The mobile station (MS) receives an increased signal level. Applying downlink transmis-
sion diversity time delay enables serving large cells, e.g., in rural areas.
By using Transmission Diversity, the downlink budget of the BTS can be significantly
improved. This helps to balance the cell ranges of 850/900 MHz and 1800/1900 MHz in
co-location scenarios.
The illustration of the downlink budget in relation to the downlink capacity is shown in
the next figure, which compares several possibilities of statically allocated CU combina-
tions in one sector.
Information
Base Station System
A30808-X3247-L14-2-7618