392 Chapter 14
Real Time TDMA Formats
Enhanced Observed Time Difference (E-OTD)
Non-combined Broadcast Channel
The broadcast channel can be used in two different modes. The first is called non-combined mode where a
51 frame multiframe is used. The basic components of the non-combined broadcast channel are the
frequency control channel (FCCH) which provides a mobile station with a frequency reference for the base
station and allow the mobile station to lock on to the beacon frequency, the synchronization channel (SCH)
which allows the mobile station to synchronize in the time domain, the broadcast control channel (BCCH)
which contains more information needed for the mobile station to connect to the base station, and the
common control channel (CCCH) which contains the information to provide the channel setups and can
originate from the base station or the mobile. Refer to Figure 14-3 on page 392.
Figure 14-3 GSM Multiframe Structure
Combined Broadcast Channel
Two separate 51-frame multiframes are used to form a repeating 102 frame sequence. The main difference
between the combined broadcast channel and the non-combined broadcast channel is that some of the
CCCH channels are replaced with standalone dedicated control channels (SDCCH/4) and slow associated
control channels (SACCH/4). Standalone dedicated control channels are intended for the transfer of
signaling information between a mobile and a base station. The purpose of the slow associated control
channel is to provide channel maintenance. The combined broadcast channel on the ESG simulates the
situation when no data is required to be transmitted to the mobile station but the logical channels are made
available. When this situation occurs a real base station would send dummy bursts, the ESG will therefore
also use dummy bursts. Refer to Figure 14-3 on page 392.
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