Training Document GBSS13.0 BSC6900(V900R013C00) VAMOS Feature Description-20110512-A-1.0

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N-0
www.huawei.com
Security Level: Internal Use
Global Technical Support
N-1
Copyright © 2010 Huawei Technologies Co., Ltd. All rights reserved.
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Objectives
Upon completion of this course, you will be able to:
Know the basic principles of voice service over adaptive multi-user channels on one slot (VAMOS).
Known the design and implementation method of VAMOS.
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Contents
2. Application Scenarios
4. Data Configuration Procedure
6. Acronyms and Abbreviations
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Basic Principles of VAMOS
VAMOS is used to increase the capacity of the global system for mobile communications (GSM) network. VAMOS multiplexes two users on one full-rate or half-rate channel to increase the number of available radio channels on the Um interface.
Function description
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Left-right separation: distinguishing users based on time. Up-down separation: distinguishing users based on the TSC.
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The base transceiver station (BTS) uses the AQPSK modulation mode and orthogonal TSC in the downlink. Therefore, the mobile station (MS) must support SAIC to correctly demodulate downlink signals.
In the uplink, the MS still uses the GMSK modulation mode to modulate signals. The BTS demodulates two signals by using the interference cancellation algorithm (such as IRC and SIC) and orthogonal TSC.
GMS
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Downlink signal demodulation (SAIC algorithm)
The BTS uses the modulation mode similar to QPSK to send signals. The data of two users is mapped to different bits of the QPSK symbol. Then, π/2 phase rotation is performed for the symbol. The existing SAIC MS can directly demodulate signals from those received on the corresponding subchannel.
The SAIC receiver separates the received signals as real and imaginary parts and takes them as signal diversity tributaries so that the diversity effect is obtained by using one antenna.
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Uplink signal modulation: The MS uses the existing modulation algorithm to modulate signals.
Downlink signal demodulation (SAIC algorithm)
Successive interference cancellation (SIC) uses the interference rejection combing (IRC) algorithm to demodulate the strong-power user channels, deducts the strong-power user information from the received signals, and then uses IRC to demodulate the remaining weak-power signals.
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TSC users implement channel estimation, that is, obtain the channel characteristics. Based on the modulation and demodulation modes, third generation partnership project (3GPP) defines eight training sequences numbered 0 to 7. For example, training sequence defined by normal burst in GMSK modulation mode:
The eight TSCs defined by 3GPP are not closely related. To obtain better orthogonality, The VAMOS workgroup defines a new TSC for VAMOS multiplexing.
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To support VAMOS better, 3GPP introduces a new TSC and an advanced receiver structure. MSs are classified as follows based on whether they support the functions:
MS Classification
MS Capability
Pairing Restriction
Legacy Non-SAIC
Considering the alpha QPSK technology, a non-SAIC MS may be multiplexed on the VAMOS subchannel in the case of certain power offset.
A legacy non-SAIC MS cannot be paired with a legacy non-SAIC MS or legacy SAIC MS.
Not supported
Not supported
Low performance
Legacy SAIC
Compared with a non-SAIC MS, a legacy SAIC MS features more powerful demodulation capability but supports only the existing TSC. It supports VAMOS multiplexing well and does not require much for the MS on another subchannel.
A legacy SAIC MS cannot be paired with a legacy non-SAIC MS (the pairing is theoretically feasible, but it requires much for power offset; therefore, it is not applicable).
Supported
Not supported
Crucial for the existing MS to support VAMOS. Its capacity gain is much lower than the VAMOS MS.
The current MS penetration rate is 30% (3GPP).
VAMOS level I
None.
Supported
Supported
It is not launched to the market yet.
VAMOS level II
It supports a more advanced demodulation algorithm, supports the new TSC, and can further improve the demodulation performance based on the TSC used by the two multiplexed channels.
None.
Supported
Supported
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A legacy non-SAIC MS refers to an existing MS that does not support SAIC.
A legacy SAIC MS refers to an existing MS that supports SAIC.
The MS reports whether it supports SAIC, VAMOS level I, and VAMOS level II by using the classmark.
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Application Scenarios
VAMOS is applicable to the scenario where network frequencies are loosely multiplexed and the capacity is limited. Typical scenarios are as follows:
Wide coverage in rural areas
Thin network after GSM refarming
Other scenarios
The GSM network will coexist with the 3G or even 4G network in a long term. On the one hand, the number of GSM users decreases gradually, and the GSM network undergoes continuous refarming; on the other hand, the operator needs to maintain a thin GSM network for a long time to guarantee the coverage for users. On the basis of the AHS application, VAMOS can further meet the traffic peak requirements on the thin GSM network. That is, a larger traffic capacity can be provided with a small configuration.
In the scenario of wide coverage in rural areas, the frequency multiplexing rate is low. On the basis of the AHS application, if the penetration rate of VAMOS MSs is high, satisfactory voice capacity gain can be obtained.
For some areas where the number of GSM users rapidly increases, when the user capacity requirement becomes higher, the operator can increase TRXs and improve frequency multiplexing rate to expand the capacity. This may greatly decrease the VAMOS gain. Therefore, the VAMOS technology is not applicable to the area where the number of GSM users still increases rapidly.
Rural area
Refarmed GSM
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Impacts of VAMOS on the Network (1)
After VAMOS is enabled, the number of available air interface channels increases. As a result, the number of transmission timeslots of the Abis, Ater, and A interfaces increases. Therefore, before VAMOS is enabled, transmission resources must be increased.
With the increase of transmission resources, the Abis/Ater/A interface resources must also be increased, that is, transmission interface boards in the BSC must be increased.
Along with the increase of A interface resource, TC boards must also be increased.
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The orthogonal TSC is required to enable VAMOS. Therefore, the TSCs on the network must be re-planed.
VAMOS is not used: The TSCs and BCCs are bound on the network, and the TSCs can be planned at will.
VAMOS is used: To prevent cells from using the same frequency and TSC in the case of inter-cell timeslot alignment, re-plan the TSCs on the network by using a method similar to frequency planning before enabling VAMOS. This method is meant to enlarge the multiplexing distance between the cells that use the same TSC.
After VAMOS is used, the cells need to use the second TSC, and therefore the second TSC must be planed so that the cells do not use the same TSC as peripheral cells.
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After VAMOS is enabled, more BTS destination signaling point (DSP) processing resources are required (the number of channels to be processed concurrently increases and new modulation algorithms need to be used), and the service processing capability of the BTS deteriorates. In busy hours, the EDGE rate and EDGE+ rate are decreased.
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Design and Implementation Method
After VAMOS is enabled for a cell, half-rate channels can implement VAMOS multiplexing. This can be explained as follows: one subchannel in a timeslot is equivalent to four HR subchannels instead of two HR subchannels. One full-rate channel is still indicated as one channel.
VAMOS channel management
VAMOS supports full-rate and half-rate channels but it supports only half-rate channels in GBSS13.0.
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In normal cases, when user A and user B access the network independently, each occupies one half-rate channel. If user A and user B meet the multiplexing conditions, the BSC hands user B over to the channel occupied by user A.
If user B is accessing the network and meets the multiplexing conditions, the BSC directly assigns user B to the channel occupied by user A.
VAMOS channel multiplexing
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VAMOS channel multiplexing allows two MSs to occupy the same channel and distinguishes users based on the TSC. The BSC can implement the multiplexing by means of assignment or handover. The handover-triggered multiplexing is called multiplexing handover.
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The BSC hands user B over to another half-rate channel.
VAMOS channel demultiplexing can be performed based on load or quality.
VAMOS channel demultiplexing
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VAMOS channel multiplexing allows two MSs to occupy the same channel and distinguishes the MSs based on the TSC. The BSC can implement multiplexing by means of assignment or handover. The handover-triggered multiplexing is called multiplexing handover.
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VAMOS transmission resource management
VAMOS supports TDM, IP, and high-level data link control (HDLC) transmission resources.
VAMOS supports TDM: If an office adopts TDM, the office must be configured with FlexAbis. Expand channel numbers to support VAMOS multiplexing.
VAMOS supports IP: After VAMOS is used, subchannel numbers are expanded to 0 to 3.
VAMOS supports HDLC: After VAMOS is used, subchannel numbers are expanded to 0 to 3.
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VAMOS processing capability adaptation
For the MRFU/MRRU V1&V2, service restrictions coexist with VAMOS, EDGE, and EDGE+. Based on the DSP computing capability of the supported carrier group, the BSC determines the VAMOS channel of the timeslot in the carrier group.
After VAMOS is used, the DSP decreases the uplink rate of EDGE and EDGE+ services based on GMSK modulation if the DSP processing capability is low.
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MS compatibility
Due to MS compatibility, MS type database is not available on the BSC. This database records the VAMOS capability of MSs of different types. The MSs are classified as follows:
MSs in the white list: This type of MSs can completely support VAMOS multiplexing.
MSs in the gray list: The performance of this type of MSs varies with the TSC combination. The hop-Alpha QPSK modulation mode, however, can be used to upgrade the MS performance.
If MS compatibility is not considered, the BSC implements multiplexing based on the VAMOS support capability reported by the MS by using the classmark. If MS compatibility is considered, the BSC obtains the MS type and then implements multiplexing based on the MS compatibility stored in the MS type database.
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MS compatibility
You can run ADD GMSSAICCAP to set the MS type database on the BSC, that is, add MSs in the white list and gray list manually.
You can configure up to 20,000 records in the white list and gray list in total.
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Mute-SAIC MS identification
Mute-SAIC MS: An MS that supports SAIC but does not report the SAIC support capability. This type of MSs affects the VAMOS multiplexing rate.
If the CONNECTACK message is received during a call and the channel quality of the call meets the condition, a detection request is initiated to instruct the BTS to implement automatic mute-SAIC identification.
After the BTS receives the automatic mute-SAIC identification request, the BTS starts automatic mute-SAIC identification.
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Procedure for identifying Mute-SAIC MSs by the BTS:
The BSC records the MS type (TAC in the IMEI) based on the BTS test result and periodically exports the records to the OMU.
The BTS forcibly changes the modulation mode of downlink data to alpha-QPSK, and sends dummy frames on another channel.
The BTS determines whether the MS supports VAMOS based on the downlink quality changes.
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Mute-SAIC MS identification
You can run EXP MSSAICCAPMML to convert the BSC detection result into a man-machine language (MML) script and save it in \bam\version_x\ftp \ms_saic_cap on the OMU. Here, x refers to the specific version number.
You can use the file manager on the Web LMT to export the generated MML script to a local path. Then, run the MML script to import the automatic detection result into the MS database.
Mute-SAIC MS identification causes network key performance indicators (KPIs) to degrade.
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Automatic problem MS identification
Problem MS: An MS that supports SAIC and causes call drops during multiplexing. This type of MSs requires to be identified.
The procedure for identifying a problem MS is the same as that for identifying a mute-SAIC MS.
Automatic problem MS identification causes KPIs to degrade.
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Run SET FHO to force calls to implement VAMOS multiplexing.
VAMOS is mutually exclusive with the following functions:
IBCA and Flex-MAIO
External DXX connection in TDM transmission
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Data Configuration Procedure
VAMOS configuration procedure
Step 1: If the BTS transmission mode is TDM, when you run ADD BTS to add a BTS, set Flex Abis Mode to FLEX_ABIS. For an existing BTS, you can run MOD BTS to set Flex Abis Mode to FLEX_ABIS. If the BTS transmission mode is IP or HDLC, skip this step.
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Step 2: Run SET GCELLPWRBASIC to set Power Control Switch to PWR3.
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Step 3: Run SET GCELLPWR3 to set III Power Control to YES.
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Step 4: Run SET GCELLVAMOS to set VAMOS to ON.
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Step 5: Run SET GCELLVAMOSPWR to set Allow alpha-QPSK Power Control and Allow SIC Power Control to ON.
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Configuration procedure for mute-SAIC MS identification (optional)
Step 6: Run SET GCELLVAMOS to set Mute SAIC Terminal Processing Switch and Auto Mute SAIC Identification Switch to ON.
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Configuration procedure for problem MS identification (optional)
Step 7: Run SET GCELLVAMOS to set Problem SAIC Terminal Processing Switch and Problem SAIC Terminal Identify Switch to ON.
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VAMOS Configuration Procedure
Step 1: If the BTS service mode is set to TDM, set Flex Abis Mode to Flex Abis when adding BTSs with the wizard, and run the MOD BTS command to set Flex Abis Mode to Flex Abis. If the BTS service mode is set to IP or HDLC, ignore this step.
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Step 1: If the BTS already exists, right-click the BTS, and choose Modify Multiplexing Mode or Flex Abis Mode… from the shortcut menu, and set Flex Abis mode to Flex Abis in the displayed dialog box. If the service mode of the BTS is set to IP or HDLC, ignore this step.
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Step 2: Set Power Control Switch to Power controlIII in the Basic Parameters for Power Control of Cell table.
The procedure for navigating to the Basic Parameters for Power Control of Cell table is as follows: On the Main View tab, right-click a cell, and choose Cell Configuration Express from the shortcut menu. On the Properties tab, click Basic Parameters for Power Control of Cell. The Basic Parameters for Power Control of Cell table is displayed in the right pane.
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Step 3: Set III Power Control Optimized Enable to Yes in the Parameters for Power Control III of Cell table.
The procedure for navigating to the Parameters for Power Control III of Cell table is as follows: On the Main View tab, right-click a cell, and choose Cell Configuration Express from the shortcut menu. On the Properties tab, click Parameters for Power Control III of Cell. The Parameters for Power Control III of Cell table is displayed in the right pane.
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Step 4: Set VAMOS Switch to On in the VAMOS Channel Multiplex Parameters of Cell table.
The procedure for navigating to the VAMOS Channel Multiplex Parameters of Cell table is as follows: On the Main View tab, right-click a cell, and choose Cell Configuration Express from the shortcut menu. On the Properties tab, click VAMOS Channel Multiplex Parameters of Cell. The VAMOS Channel Multiplex Parameters of Cell table is displayed in the right pane.
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Step 5: Set Allow alpha QPSK Power Control to On and Allow SIC Power Control to On in the Power Control Parameters for VAMOS Call of Cell table.
The procedure for navigating to the Power Control Parameters for VAMOS Call of Cell table is as follows: On the Main View tab, right-click a cell, and choose Cell Configuration Express from the shortcut menu. On the Properties tab, click Power Control Parameters for VAMOS Call of Cell. The Power Control Parameters for VAMOS Call of Cell table is displayed in the right pane.
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Configuration Procedure on the CME
Setting Mute SAIC Identification (Optional)
Step 6: Set Mute SAIC Terminal Processing Switch to On and Auto Mute SAIC Identification Switch to On in the VAMOS Channel Multiplex Parameters of Cell table.
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Configuration Procedure on the CME
Setting Faulty Terminal Detection (Optional)
Step 7: Set Problem SAIC Terminal Identify Switch to On and Problem SAIC TRMNL Identify Manual Start to On in the VAMOS Channel Multiplex Parameters of Cell table.
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VAMOS verification procedure
Step 1: Assume that VAMOS is enabled for a cell and two MSs supporting VAMOS are used in the cell to initiate calls, configure parameters so that the two calls occupy half-rate channels.
Step 2: Run SET FHO to forcibly multiplex one half-rate call on the other channel.
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Parameter Name
Parameter Description
Specifies whether to enable VAMOS on the network.
VAMOS sacrifices quality to increase capacity. Therefore, if VAMOS is enabled in a cell, the network capacity increases and the congestion rate decreases, but the network-quality KPIs are affected to a certain extent.
Primary TSC in VAMOS
Specifies the primary TSC used on the network when VAMOS is enabled in a cell. Before any call enters the VAMOS mode, the primary TSC is allocated preferentially. After VAMOS pairing succeeds, the primary and secondary TSCs are determined based on the TSC that is used by the first call connected to the timeslot.
TSC selection affects MSs.
Secondary TSC in VAMOS
Specifies the secondary TSC used on the network when VAMOS is enabled in a cell. Before any call enters the VAMOS mode, the primary TSC is allocated preferentially. After VAMOS pairing succeeds, the primary and secondary TSCs are determined based on the TSC that is used by the first call connected to the timeslot.
TSC selection affects MSs.
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Parameter Name
Parameter Description
Impact on the Network
Allow alpha-QPSK Power Control
Specifies whether to enable the alpha-QPSK power control sub-algorithm of the VAMOS technology (one timeslot multiplexed by voice services of multiple users).
If the alpha-QPSK downlink power control algorithm is enabled, the BTS power consumption decreases, the network interference decreases, and the downlink network drive test (DT) quality is improved.
Allow SIC Power Control
Specifies whether to enable the uplink SIC power control sub-algorithm of the VAMOS technology.
If the SIC uplink power control algorithm is enabled, the MS power consumption decreases, the network interference decreases, and the uplink network DT quality is improved.
Mute SAIC Terminal Processing Switch
Specifies whether to enable the mute-SAIC MS processing function of a cell. ON: enable the mute-SAIC MS processing function; Off: disable the mute-SAIC MS processing function. Mute-SAIC MS processing includes mute-SAIC matching and identification based on the database and automatic mute-SAIC identification.
If this switch is on, IMEI identification is performed for a call before TCH assignment. As a result, call connection is delayed.
Auto Mute SAIC Identification Switch
Specifies whether to enable the automatic mute-SAIC identification function of a cell. Mute-SAIC MS: An MS that supports SAIC but is reported as incapable of SAIC. ON: enable the automatic mute-SAIC identification function of a cell; Off: disable the automatic mute-SAIC identification function of a cell.
If this switch is on, uplink and downlink DTX must be disabled during mute-SAIC identification, and this influences the network interference. Alpha-QPSK modulation is used in the downlink, and the downlink receiving quality is degraded in a call.
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Counter Name
Short Name
Counter Description
A3100J
This counter measures the total number of new calls that meet the VAMOS candidate user conditions during assigned channel multiplexing determination. If the value of this counter is low, it indicates that the SD channel quality is low or the number of new calls that meet the VAMOS candidate user conditions is small because the VAMOS candidate user conditions set for new calls are strict (excessively higher requirements for quality and ATCB).
Number of VAMOS Channel Multiplexing Attempts (Assignment)
A3100L
This counter measures the total number of times that a new call during assignment and an established call can be paired (the paring is determined in assignment mode) in a cell. It is used to calculate the assigned channel multiplexing success rate and the ratio of the number of assigned channel multiplexing attempts to the total number of channel multiplexing attempts. If the value of this counter is far smaller than the value of Number of Successful VAMOS Candidate Call Decisions (Assignment) , you can loosen the path loss offset threshold and VAMOS overload threshold involved in assigned channel multiplexing determination to allow more users to be paired.
Number of VAMOS Channel Multiplexing Commands (Assignment)
A3100M
This counter measures the total number of VAMOS channel assignment commands for VAMOS channel multiplexing (VAMOS channel multiplexing is triggered by assignment) in a cell. If the value of this counter is far smaller than the value of Number of VAMOS Channel Multiplexing Attempts (Assignment), it indicates that lower-layer connection fails or the Abis interface resources are insufficient.
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Counter Name
Short Name
Counter Description
A3100N
This counter measures the number of times that access to the specified VAMOS channel fails after the VAMOS channel assignment command is delivered after VAMOS channel multiplexing is triggered by assignment in a cell. This counter reflects the air interface quality during user access. If the value of this counter is large, it indicates that the VAMOS candidate user selected for pairing is improper. You can set strict multiplexing candidate user determination conditions for new calls to guarantee the performance during VAMOS channel access by users.
Number of Successful VAMOS Candidate Call Decisions (Intra-Cell Handover)
H3050
This counter measures the total number of established calls that meet the VAMOS candidate user conditions. If the value of this counter is low, it indicates that the quality of the channel for non-VAMOS calls is low or the VAMOS candidate user conditions set for established calls are strict (excessively higher requirements for quality and ATCB). You can adjust the power control parameters or loosen the VAMOS candidate user conditions for new calls to allow more established VAMOS candidate users.
Number of VAMOS Channel Multiplexing Attempts (Intra-Cell Handover)
H3051
This counter measures the total number of times that two established calls can be paired (the pairing is determined in intra-cell handover mode) in a cell. It is used to calculate the success rate of VAMOS channel multiplexing handovers. If the value of this counter is small, it indicates that the number of non-VAMOS that can be paired on the network is small. You can adjust the power control parameters for common calls to improve the common call quality or loosen the VAMOS multiplexing determination conditions for established calls to increase the number of VAMOS candidate users on the network; in addition, you can loosen the path loss threshold during intra-cell channel multiplexing determination to allow more users to be paired.
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Counter Name
Short Name
Counter Description
H3052
This counter measures the number of handover commands of all the calls that are handed over due to VAMOS channel multiplexing triggered by intra-cell handover in a cell. If the value of this counter is far smaller than the value of Number of VAMOS Channel Multiplexing Commands (Intra-Cell Handover), it indicates that lower-layer connection fails or the Abis interface resources are insufficient.
Number of VAMOS Channel Multiplexing Commands (Intra-Cell Handover)
H3053
This counter measures the number of times that access the specified VAMOS channel fails after the handover commands are delivered (the commands correspond to all the calls that are handed over due to VAMOS channel multiplexing triggered by intra-cell handover) in a cell. This counter reflects the air interface quality during user access. If the value of this counter is large, it indicates that the VAMOS candidate user selected for pairing is improper. You can set strict multiplexing candidate user determination conditions for new calls to guarantee the performance during user handover.
Number of VAMOS Call Handover Attempts (Others)
H3054
This counter measures the total number of handovers that trigger VAMOS channel demultiplexing in a cell. If the value of this counter is large, it indicates that VAMOS demultiplexing is triggered frequently because the VAMOS call power control parameters are improper or the demultiplexing conditions are strict (high load threshold, low quality threshold, and high ATCB threshold).
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Counter Name
Short Name
Counter Description
H3058
This counter measures the total number of handovers initiated for VAMOS calls due to other reasons in a cell. All the handovers except for VAMOS demultiplexing handovers are included. If the value of this counter is large, modify the handover (of other types) determination parameters to decrease handovers of other types.
Number of VAMOS Call Handover Commands (Others)
H3059
This counter measures the number of handover commands of all the VAMOS calls that are handed over due to other reasons in a cell. All the handovers except for VAMOS demultiplexing handovers are included. If the value of this counter is far smaller than the value of Number of VAMOS Call Handover Attempts (Others), it indicates that congestion occurs, lower-layer connection fails, or Abis transmission resource allocation fails.
Number of Failed VAMOS Call Handover Attempts (Others)
H3060
This counter measures the number of failed handovers after handover commands are delivered (the handover commands correspond to all the VAMOS calls that are handed over due to other reasons) in a cell. This counter reflects the air interface quality during user access. If the value of this counter is large, it indicates that the channel allocated to the selected demultiplexing user is improper. Optimize the channel allocation parameters.
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Counter Name
Short Name
Counter Description
H3061
This counter measures the number of VAMOS call drops caused by handovers that are triggered by VAMOS demultiplexing in a cell. If the value of this counter is large, it indicates that the quality of the channel newly allocated to the user is low or calls are dropped before handovers because VAMOS demultiplexing is not performed in time. If VAMOS demultiplexing is not performed in time, you can adjust the demultiplexing parameters so that demultiplexing is triggered earlier.
Number of VAMOS Call Drops (Other Handover)
H3062
This counter measures the number of VAMOS call drops caused by the handovers except for the handovers that are triggered by VAMOS demultiplexing in a cell. If the value of this counter is large, it indicates that the quality of the channel newly allocated to the user is low or calls are dropped before handovers because handover is not performed in time due to other reasons. If handover is not performed in time due to other reasons, you can adjust the handover algorithm parameters so that handover is triggered earlier.
Number of VAMOS Call Drops (Stable State)
H3063
This counter measures the number of VAMOS call drops in the stable state in a cell. If the value of this counter is large, it indicates that the call quality is low after the user enters the VAMOS stable state. You can adjust the VAMOS power control parameters to improve VAMOS call quality and prevent call drops.
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GERAN
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Thank you
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Left-right separation: distinguishing
IMEI
15
digits
TAC
8
digits
SNR
6
digits
CD

Training Document GBSS13.0 BSC6900(V900R013C00) VAMOS Feature Description-20110512-A-1.0

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