This document describes a base station system that uses multiple carrier frequency bands and transmission diversity time delay operation between pairs of co-located control units (CUs). The CUs are connected via an antenna combiner such that even numbered CUs use one primary antenna and odd numbered CUs use a secondary antenna. Each CU pair transmits the same carrier frequency simultaneously, with the slave CU transmitting a delayed signal to provide diversity. Transmission diversity may be disabled for certain timing-sensitive signal bursts.

1. 64 A30808-X3247-L14-2-7618
Technical Description (TED:BSS)
BS-240/241
Information
Base Station System
CUs use separate antennas. A distance preferably higher than ten lambdas separates
the antennas when combining on-air transmissions.
The following example illustrates CU co-location in an extended circular cell that
provides an increased cell capacity by using several different carrier frequency bands
(e.g. GSM 850, GSM 900; GSM 1800, GSM 1900). CU pairs consisting of master and
slave CU, apply transmission diversity time delay operation. One pair of CUs transmits
on one frequency band, and the other pair of CUs transmits on another frequency band.
For example, the BTS installation uses one rack for three sectors, and antenna 0 and
antenna 1 are configured to serve the same cell sector 0. A Duplexer Amplifier
Multi-Coupler Combiner (DUAMCO 4:2) enables the master CUs of the pairs to use the
same primary antenna 0, and the slave CUs to use the same secondary antenna 1. The
CUs 0 to 3 are connected to these antennas via antenna combiner in a way that the even
CUs 0 and 2 are connected to the antenna 0, and the odd CUs 1 and 3 are connected
to the antenna 1. Then there are the CU pairs with one even and one odd number. CU
0 and CU 1 compose one CU pair, and the CU 2 and the CU 3 compose a next CU pair,
respectively. Each CU pair is suitable for transmission diversity time delay operation.
Both CUs of such a pair use the same carrier frequency, and both CUs of the same pair
transmit simultaneously. The even CU of a pair acts as a master, while the odd CU
serves as a slave. The slave CU does not read the transmitted data from its master CU,
but receives data from the system simultaneously to the master CU. The slave CU
performs the timing offset shift in order to delay the transmission signal.
Fig. 4.16 BTS Rack Cabling for Transmitter Diversity Operation
The transmission diversity time delay feature raises an additional inaccuracy caused by
the actual timing deviation of the two transmitting CUs, due to the different length of the
feeding cables and the antenna positions. The transmission diversity time delay opera-
tion can be disabled for certain burst types that are timing-sensitive, e.g., the synchro-
nization channel (SCH) for Location Services (LCS). The transmission of the slave CU
is disabled when such a burst type is going to be transmitted. The operator is allowed to