There are three modes for multiband networking: standalone MSC networking, shared MSC/standalone BSC networking, and shared BSC. In general, the former two modes are called standalone networking and shared BSC network is also known as mixed networking.
1) Standalone MSC networking
Standalone MSC networking refers to that GSM900 and GSM1800 use different MSCs for networking respectively, as shown in Figure 2-38.
M S
M S
B T S
B T S
B S C
E IR
H L R /A U C O M C
S M C
G S M 9 0 0 G S M 1 8 0 0 B T S
B T S
B S C M S C /V L R
M S C /V L R
Figure 2-38 Standalone MSC networking mode
The standalone MSC networking has the following features:
z No impact on original network
z Clear network planning, clear network data configuration, and easy to construct.
z Satisfy the requirement of long-term capacity expansion.
z Convenient to manage the whole network and develop new services.
z The initial investment of network is relative large but the investment for each subscriber is the smallest.
z Introduce competition so as to lower equipment investment and improve quality of service.
Besides the above features, the standalone MSC networking increases the inter-office handovers and position updates, thus the load of signaling link is increased. In addition, the standalone MSC networking has the problem of collaboration of equipment of different providers. In a long-term view, it is better than mixed networking.
2) Shared MSC / standalone BSC networking
MS
Figure 2-39 Shared MSC/standalone BSC networking
Shared MSC/standalone BSC networking has the following features:
z It has impact on the original network.
z It needs to plan NSS again and it is hard to be constructed.
It is hard to expand its capacity. As network develops, construction and maintenance might become difficult.
z The initial investment of network is relative small and the investment for each subscriber is small.
z Introduce competition so as to lower equipment investment and improve quality of service.
z BSC has backup function so the network security is good.
3) Shared BSC networking
Shared BSC networking refers to that BTSs of GSM900 and GSM1800 access the same BSC or multiband mixed BTS accesses BSC, as shown in Figure 2-40.
MS
Figure 2-40 Shared BSC networking mode
Shared BSC networking has the following features:
z It might impact on original network greatly, especially when BSC has a small capacity.
z It needs to plan NSS and BSS again so the construction is difficult.
z It is hard to expand its capacity. As network develops, construction and maintenance might become difficult.
z Development of new services is restricted.
z It cannot introduce competition thus it is hard to lower the cost and to improve service.
z The initial investment of network is the smallest and the investment for each subscriber is the largest.
2.2.9 Carrier Mutual-assistance
I. Overview
In case of BCCH TRX failure or baseband frequency hopping TRX failure, the cell can handle it automatically through the TRX aiding function. Thus, the cell services can not be affected before the failed TRX is replaced.
II. Technical description
TRX aiding contains BCCH TRX aiding and baseband frequency hopping TRX aiding.
For the non-baseband frequency hopping cell, only BCCH TRX aiding will occur. For the baseband frequency hopping cell, both BCCH TRX aiding and baseband frequency hopping TRX aiding may occur.
1) BCCH TRX aiding
In the idle state, MS needs to know some information about the infrastructure of the network. BSC sends the generic broadcast message to BTS, and BTS broadcasts it on BCCH. BCCH is a low-capacity channel and can send a message of 23 bytes every 0.235s. The broadcast information includes cell selection information, adjacent cell information, access control information, private channel control information, cell identification code, location, system parameters of packet service, etc.
When BCCH TRX of a cell is failed, all services of this cell will be interrupted. In order to ensure the cell services not to be affected, in case of BCCH TRX failure, another available TRX of the cell can substitute for the TRX that BCCH is originally on. Thus, the cell can continue to provide the services. After the fault of TRX that BCCH is originally on is removed, BCCH can be recovered (or, changed back) onto this TRX.
In the baseband frequency hopping cell, if a TRX participating in frequency hopping is failed, the conversations on this frequency hopping channel will lose some voice frames. Correspondingly, the communication quality will be decreased. In order to ensure the communication quality, in case of baseband frequency hopping TRX failure, BSC will start the TRX aiding function. It will automatically change the cell to the non-frequency-hopping mode. Thus, the failure of a TRX will not affect the communication quality of the entire cell. When the fault is removed, this cell can be restored to the frequency hopping mode. This is the function of baseband frequency hopping TRX aiding.
When TRX aiding or TRX aiding recovery occurs, there will be corresponding alarms reported (all are event alarms):
198: BCCH TRX aiding alarm.
199: BCCH TRX aiding recovery alarm.
200: Baseband frequency hopping TRX aiding alarm.
201: Baseband frequency hopping TRX aiding recovery alarm.
Note:
z If BCCH TRX in a baseband frequency hopping cell is failed, except for BCCH TRX aiding, baseband frequency hopping TRX aiding will also occur. That is, the cell is changed to the non-frequncy-hopping mode. In addition, only when the faults of all TRXs participating in frequency hopping and the original BCCH TRX are removed, can the baseband frequency hopping TRX aiding recovery occur. That is, the cell is restored to the frequency hopping mode.
z When TRX aiding or TRX aiding recovery occurs, the cell will be initialized again.
z In the previous BSC versions of G3BSC32.10100.06.1120A, the TRX aiding function cannot be used together with the baseband timeslot frequency hopping function. From the version of G3BSC32.10100.06.1120A, this limitation is canceled. These two functions can be used at the same time.
z If such adjustment as SDCCH dynamic adjustment, full-rate/half-rate dynamic adjustment or PDCH channel dynamic adjustment occurred in the cell, the dynamic adjustment channel on the TRXs involved in TRX aiding will be restored to the channel type configured originally. For BCCH TRX aiding, the involved TRXs contain the current BCCH TRX and TRX to be aided. For baseband frequency hopping TRX aiding, the involved TRXs are all TRXs in the entire cell.
z When inter-E1 BCCH TRX aiding occurs, the traffic channels of the current BCCH TRX can not work normally if the E1 carrying the original BCCH TRX is broken. From the version of G3BSC32.10102.06.1120A, BSC will automatically block the traffic channels of the current BCCH TRX when the E1 carrying the original BCCH TRX is broken. These channels will be unblocked when that E1 recovers.
III. Parameters
The TRX aiding function only uses a parameter for controlling. The parameter is configured in [Cell Configuration Data Table], as shown in Table 2-16.
Table 2-16 Description of parameter of Cell Configuration Date Table
Parameter Value range Description
TRX Aiding Not Allowed TRX aiding is not allowed. That is, the TRX aiding function is closed.
Allowed, Recover Forbidden
TRX aiding is allowed. However, after the fault TRX is restored, TRX recovery is forbidden.
Allowed, Recover
Immediately TRX aiding is allowed. After the fault TRX is restored, it can be recovered immediately.
TRX Aiding Function Control
Allowed, Recover When TRX aiding is allowed. After the fault TRX is restored, it will not be recovered
2.2.10 Cell Broadcast
I. Overview
Cell broadcast is a specific service of the GSM system, broadcast information to all mobile stations in a specific area periodically. The MS supporting this service can monitor this broadcast information continuously and this information can be displayed on the MS terminals. The typical examples of cell broadcast are to broadcast traffic information and weather forecast.
Short Message Service Cell Broadcast (SMSCB) allows short message to be broadcast to all mobile stations in certain areas. These areas may be one or several cells, even the entire PLMN area. The short message from Cell Broadcast Centre (CBC) is sent to BSC, and BSC will manage and dispatch the message, and send the received message to BTS, which can control the flow of short message broadcast.
The architecture of cell broadcast system is as shown in Figure 2-41.
CBC
Figure 2-41 Cell broadcast system architecture