Fig. 4.15 Capacity Downlink Improvements For Tx Diversity; Functionality - Siemens BS-240 Technical Description

Information
Base Station System
Fig. 4.15 Capacity Downlink Improvements for TX Diversity

4.3.1Functionality

A30808-X3247-L14-2-7618
The fully equipped BTS site with combined CU pairs to apply transmission diversity
keeps up with later capacity requirements and helps operate the BTS sites in temporarily
adjustable modes of operation. The Transmission Diversity mode provides the BTS sites
with double power and half capacity, and it performs using a CU pair of master and slave.
Later, in case additional BTS sites get installed, the BTS sites of combined CU pairs can
switch over to normal capacity and normal power mode and release their slave CUs from
no longer needed pair-halves to make them the single CU of an additional BTS site.
Fixed TX Time Shift
The method adds a distinct timing offset to the GSM bursts of one of the two CUs. The
method introduces an assigned GSM timer to control the CU timing for offset shift
purposes, and the GSM timer processes an offset control input. The GSM timer oper-
ates at a stable 52MHz clock signal, and the generated GSM burst signal can be delayed
by an appointed amount of 52MHz clocks. The operator is able to adjust the delay value,
which is proportionate to a step size of 0.25 symbols between minus 5 and plus 5
symbols.
The CUs transmit the two signals, and the mobile station resolves them by using the
built-in equalizer. The equalizer performs pulse response computation for each trans-
mitted burst, and handles the two signals according to multi-path propagation. In
contrast to the vector addition of the two transmitted signals, the equalizer performs the
signal addition using the bit energy value.
Parallel CU Operation
A parallel operation of two CUs required for the parallel transmission of de-correlated
signals is feasible and compatible with baseband hopping. The CU processes data simi-
larly to baseband hopping. With difference to baseband hopping, not a single CU but a
pair of CUs is defined to transmit data. The CU pair operates at the same carrier
frequency. Both CUs of the pair are assigned to the same cell antenna sector, and the
Technical Description (TED:BSS)
BS-240/241
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