Multiband Network

I. Overview

The multiband network is a network combined GSM900 and GSM1800 In the multiband network, GSM multiband MS can communicate in either GSM900 frequency band or GSM1800 frequency band. Each cell in a multiband network has frequencies from only one frequency band. The multiband network allows cell reselection, distribution and handover between GSM900 cell and GSM1800 cell. The application of multiband network is as shown in Figure 2-36.

GSM1800 Cell BSC

MSC

BSC BSC

MSC BSC

GSM900 GSM1800

GSM900 Cell

Figure 2-36 GSM900/GSM1800 multiband network

The multiband network can be used to utilize the abundant frequency resources in GSM1800 frequency band, to absorb network traffic, and to satisfy the increasing demand of network capacity.

II. Technical description

To guarantee the stable operation of multiband network, it is of utmost importance to correctly configure the parameters related with the multiband network operation at the stage of network commissioning. Given below is a description of the technical principles governing the multiband network.

1) MS Classmark

In the GSM system, MS Classmark represents the MS services, supported bands, power, and encryption capability. The Classmark of the mobile station falls into three categories: Classmark1, Classmark2 and Classmark3. The network can interrogate the Classmark of MS and realize its capabilities. In addition, the network can request the mobile station to report its Classmark3 immediately after creating a link by setting the parameter “Early Classmark Sending Control”. Since the important messages in Classmark3 are created specially for multiband applications, it is required that in the multiband network the equipment should support the processing of MS Classmark.

Huawei BSS supports ECSC, processing of MS Classmark3, etc.

2) BA list

In the GSM system, the BA (BCCH Allocation) list is a set of all the carrier channel numbers of adjacent cells of each cell.

The network carries out compatibility handling for various types of MSs through system information control. It also guides the MSs to access and handover correctly so that good services of the radio network can be guaranteed.

BA defines the absolute channel numbers used by carrier of all adjacent frequency cell BCCHs, which is used for cell selection and handover. It is the system that informs MS the BA list through system information. There are two types of BA list:

z The BA1 mainly contains the list of adjacent cells searched by the MSs in idle mode. It is transmitted periodically in the system information type 2, 2bis or 2ter, and used for cell re-selection in the idle mode.

z The BA2 mainly contains the list of adjacent cells searched by the MSs in active mode. It is transmitted in the system information 5, 5bis or 5ter, and used for handover in active mode.

When an MS is in active mode, It extracts the parameters of adjacent cells from the associated channel system information type 5, 5bis or 5ter on the SACCH, instead of from the system information type 2, 2bis and 2ter. In accordance with the actual network status, the BA list in the system information type 5, 5bis and 5ter can be either identical to or varied with that in the system information type 2, 2bis and 2ter.

The BA list shall be set in accordance with the network design requirements and the actual status of adjacent cells. Otherwise, there might be inappropriateness in handover or cell re-selection, or even handover failure. In this case, it may impact the services provided by the network.

The number of adjacent cells on each BA list shall not exceed 32.

3) Support of system Information for multiband network

The network carries out compatibility handling of MSs of various classes through system information (type 2 / 2bis / 2ter and 5 / 5bis / 5ter). The radio network controls the MSs to access and handover correctly and guarantees good services.

Huawei GSM system carries out thorough compatibility processing of Phase 1 and Phase 2 900 MSs, Phase 1 and Phase 2 1800 MSs and multiband MSs, and supports system information type 2 / 2bis / 2ter and 5 / 5bis / 5ter.

The BA1 list is sent in system information type 2 for re-selection. The BA2 list is sent in the system information type 5 for handover. In GSM900 system, the frequency channels are numbered from 1 to 124. Coding can be done on one list without 2bis / 2ter / 5bis / 5ter when the bitmap format is used. However, this should be adjusted after the multiband system is employed.

For the GSM900 cells, the GSM1800 frequency channels on its adjacent cell list are for multiband MSs. They are transmitted via the system information type 2ter / 5ter. Only a multiband MS supports the system information type 2ter / 5ter. Whereas the frequency channels of its GSM900 adjacent cells are placed in the system information type 2 / 5 and can be coded in the bitmap format. The Phase 1 MS recognizes the bitmap format

For the GSM1800 cells, they are handled in a similar way. The 900M frequency channels on the list of its adjacent cells are for multiband MSs, transmitted through the system information type 2ter / 5ter. Whereas the frequency channels of its GSM1800 adjacent cells are placed in the system information type 2/5. As they cannot be coded on one list, the BA list needs to be split into two parts, transmitted respectively in the system information type 2 (or 5) and 2bis (or 5bis). The system information type 2bis (5bis) is for single-band M1800 MSs and multiband MSs only.

For the multiband network, it is required that the equipment should support the system information type 2ter/5ter.

4) ECSC (Early Classmark Sending Control)

ECSC indicates whether MS is required to report the MS Classmark3 voluntarily and early. For further details refer to the protocol 0408. On receipt of the Classmark change message, MS will send the additional Classmark message to the network as early as possible. Classmark3 information includes the power messages of various frequency bands of multi-frequency MS. In the handover between different frequency bands, power level should be correctly described. It is essential to know the Classmark3 message when making a paging call or sending the BA2 list in different bands.

The sampling range of the ECSC is as follows:

ECSC=1, transmission required.

ECSC=0, transmission not required.

This function comes into beings for the multiband-networking situation. And the information in Classmark3 is for multiband application.

In case of single-band networking, it is advisable to set this parameter to 0. In case of multiband networking, the recommended value of ECSC is 1 so that signaling flow can be reduced.

The parameter ECSC is transmitted in system information type 3.

5) MBR (Multi-Band Report)

MBR serves to help the network to notify the MS that the 6 adjacent cells reported must cover multiple bands.

In the single-band GSM system, when the MS reports the adjacent cell measurement results to the network, it need only report the 6 adjacent cells with strongest signals in a band. When there is a multi-band network, the operator will usually expect the MS to have the priority to enter a band in time of handover depending on the actual status of the network. Therefore, the MS is expected to report the measurement results based not only on the level of the signals but also on the band of the signals. The system parameter “Multi-band Report”, therefore, serves to notify the mobile station to report the multi-band adjacent messages.

In the multiband network, the following situation often occurs because the propagation loss in the 1800 MHz band is larger than that of the 900MHz band: among the 6 adjacent cells with strongest signals as reported by MSs, none of them is a GSM 1800 cell. This will affect the absorption of traffic by the GSM1800 network. In this case, the network can request the multiband MSs to send the MR about the adjacent 1800MHz cells by setting the MBR value. By setting different values for MBR, the MSs can report the messages of the adjacent cells of different bands as required when submitting the MRs of 6 best adjacent cells.

MBR is represented in decimal digits, with the ranges from 0 to 3. Its implication is shown in Table 2-14.

Table 2-14 MBR implication

MBR Implication

0 MS shall report the measurement results of 6 adjacent cells with strongest signals known and allowed by NCC depending on the signal level of the cells, regardless of which band the cells are in.

1

MS shall report the measurement results of an adjacent cell in each band with strongest signals, which are known and allowed by NCC on the adjacent cell list. Then it shall report the adjacent cells in the band used by the current service area in the remaining space of the report. If there is still space left, it shall report the status of the other adjacent cells, regardless of which band they are in.

2

The MS shall report the measurement results of two adjacent cells in each band with strongest signals known and allowed by NCC on the adjacent cell list. Then it shall report the adjacent cells in the band used by the current service area in the remaining space of the report. If there is still space left, it shall report the status of the other adjacent cells, regardless of which band they are in.

3

The mobile station shall report the measurement results of three adjacent cells in each band with strongest signals known and allowed by NCC on the adjacent cell list. Then it shall report the adjacent cells in the band used by the current service area in the remaining space of the report. If there is still space left, it shall report the status of the other adjacent cells, regardless of which band they are in.

6) PI (Cell Reselection Parameter Index)

PI is used to notify MS whether to adopt C2 as cell reselection parameter and to calculate whether the parameter of C2 exist.

Value range of PI: Y or N.

Y indicates that MS should extract parameters from broadcasting of system information in cell to work out C2 value and use the value to serve as the standard of cell reselection; N indicates that MS should use C1 to serve as cell reselection standard (i.

e. C2 = C1). Generally, PI is set as Y in multiband network.