No subject

Fri Jan 29 12:04:50 UTC 2016

The BCCH is used for two types of broadcast control channel:
* BSCH (broadcast sync channel)
* Broadcast Network Chanenl (BNCH)

These channels, whcih are present only on the downlink, transmit information
about the serving base station.  The BSCH transmits the SYNC message.  This
provides physical layer synchronization information, including an
extended training sequence for synchronisation and slot alignment, frequency
correction bits to set the carrier frequency, along with MAC layer information
on frame timing (i.e. the number of the current slot, frame and multiframe) as
well as network layer information.  Due to the physical layer synchronisation,
the BSCH is transmitted on a synchronisation burst rather than a normal
downlink burst.

The BNCH either carries the ACCESS-DEFINE message or the SYSINFO message.
The SYSINFO message fives the main carrier frequency so that mobiles can tune
to it after picking up any SYSINFO message infromation on any secondary control
channels, power information and network layer information.

The broadcast control channels are normally transmitted in frame 18. Each takes
up to one block of 216 bits, leaving the other block withing the burst for the
corresponding assigned channel or for the  base station to send signalling to
other mobiles. O each slot, the sequence shon win figure 7.45 is used, and the
sequence is offset b yone for each slot in the frame, so that every frame 18
has one BSCH and one BNCH.  However, transmitting the network information takes
several half-slot BNCH instances, and it will take some time therefore for a
mobile to acquire all the information it needs.  This is not normally a concern
since mobiles will be switched on before they are used and an initial delay can
be tolerated.  The standards allow the option of transmitting the BNCH in other
physical control channels (indicated by the AACH) as neccessary.  Mobiles
continue to monitor the BCCH after they are switched on and also during
transmissions so as to ensure that they receive network information and remain

Multiframe number		1	2	3	4
DL Frame 18, first half slot		BSCH*
DL Frame 18, second half slot		*		BNCH

* = Transmitted on a Synchronisation Burst
	Figure 7.45 BSCH and BNCH transmission sequence.


- Harald Welte <laforge at> 
"Privacy in residential applications is a desirable marketing option."
                                                  (ETSI EN 300 175-7 Ch. A6)

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