3G SERVING CELL EVENTS
DEFINITIONS :
1.
ACTIVE SET(Serving Set)
- User information is sent from all these cells. In FDD, these are cells that are involved in Soft Handovers.
- The UE shall only consider active set cells included in the variable CELL_INFO_LIST for measurements. i.e.. Active set cells not included in the CELL_INFO_LIST shall not be considered in any event evaluation and measurement reporting.
Virtual Set - The Active Set associated with a non-used frequencyfor support of Inter-Frequency evaluation.
2.
MONITORED SET(Neighbour Set)
-
are cells which are not included in the CELL_INFO_LIST. These are cells that can be possibly become an Active set.-
The cells only measured by the UE and not part of the Active Set. The monitored set can consist of intra-frequency, Frequency and Inter-RAT cells.3.
DETECTED SET(Unmonitored Set)
- are cells detected by UE, which are neither in the Active set nor in the Monitored set. ( Missing Neighbor Definitions )
-
Reporting of measurements of detected set is only applicable to Intra-Frequency measurements made by UEs in CELL_DCH state.
The cells measured by the UE are the sum of the Active Set and the Monitored Set. The neighboring cells, which are configured, could be cells on the currently used WCDMA RAN frequency (Intra-frequency
cells) , cells on other WCDMA RAN frequencies (Inter-Frequency cells) and cells on GSM/GPRS frequencies (Inter-RAT cells). Depending on the
frequencies of the cells in the Monitored Set, intra-frequency WCDMA RAN measurements, Inter-Frequency WCDMA RAN measurements and Inter-RAT measurements are initiated in the UE.
The number of Intra-frequency cells in the Monitored Set + the Active Set cells is limited by 3GPP to 32. The number of Inter-Frequency cells in the Monitored set is limited to 32. The number of Inter-RAT cells in the
Monitored set is limited to 32.
a.
Event 1A
- Active Set Addition of cell/s from Monitored set.
Example : 2 Serving Cells will be added with one(1) cell coming frommonitored set of cells.
When a P-CPICH, not included in the Active Set, enters reportingRange1a + hysteresis1a/2, and the measured value remains in reportingRange1a + hysteresis1a/2 at least a time equal to timeToTrigger1a, event 1a occurs. The UE sends a MEASUREMENT REPORT message for event 1a to the SRNC. That a cell enters reportingRange1a + hysteresis1a /2 means that its
measured P-CPICH follows the rule:
(measured P-CPICH Ec/No) > (P-CPICH Ec/No of the Best Cell in
the Active Set) - reportingRange1a+ hysteresis1a /2
b.
Event 1B
- Deletion of Serving cell from Active set.
Example : With Existing 3 Serving Cells in the Active set, one(1) Of the 3 serving cells will be deleted or removed.
When a P-CPICH, included in the Active Set, leaves reportingRange1b - hysteresis1b /2, and the measured value is outside reportingRange1b - hysteresis1b /2 during a time at least equal to timeToTrigger1b, event 1b occurs. The UE sends a MEASUREMENT REPORT message for event 1b to the SRNC. That a cell leaves reportingRange1b - hysteresis1b /2 means that its measured P-CPICH follows the rule:
(measured P-CPICH Ec/No) < (P-CPICH Ec/No of the best cell in the
Active Set) - reportingRange1b - hysteresis1b /2
c.
Event 1C
- Replacement of Cell/s from the existing Active Set.
Example : With the existing 3 serving Cells, one(1) or two(2) will bereplaced with cell/s from the monitored set.
When a P-CPICH, not included in the Active Set, becomes stronger than the weakest P-CPICH+hysteresis1c /2 in the Active Set during a time at least equal to timeToTrigger1c,and the Active Set is full (present cells in the Active Set is equal to maxActiveSet parameter) event 1c occurs. The UE sends a MEASUREMENT REPORT message for event 1c to the SRNC.
Reporting Event 1c Concept
d. Event 1D -
When any (Active Set, Monitored set, and Detected) cell becomes stronger than the best cell+hysteresis1d /2 in the Active Set, during a time at least equal to timeToTrigger1d, event 1d occurs. The UE sends a MEASUREMENT REPORT message for event 1d to the SRNC.
Reporting Event 1d Concept
INTER – RADIO ACCESS TECHNOLOGY(
I-RAT)
COMPRESSED MODE
- It is a radio path feature that allows a single 3G UE to make
measurements from either another FDD frequency or from the GSM network.
-
This compress mode functionality halts the transmission and reception of the On-going 3G call/ data(CS/PS) to perform measurements on the other frequency or system(GSM) for a short period of time. The intention is NOT to lose any user data but to compress the data transmission in the time domain.
INTER-RAT HANDOVER EVENTS
a. Event 3A
- Triggers Hard Handover from 3G to 2G (Inter-System)
b. Event 2D
- Start Compressed Mode
c. Event 2F
- Stop Compressed Mode
During inter-frequency handover the UE’s must be given time to make the necessary measurements on the different WCDMA carrier frequency. 1 to 7 slots per frame can be allocated for the UE to perform this intra frequency (hard handover). These slots can either be in the middle of the single frame or spread over two frames.
This compressed mode operation can be achieved in three different methods:
Decreasing the spreading factor by 2:1. This will increase the data rate so bits will
get sent twice as fast.
Puncturing bits. This will remove various bits from the original data and hence
reduce the amount of information that needs to be transmitted.
The higher layer scheduling could also be changed to use less timeslots for user
traffic.
•
From the 3GPP TS 25.212:In compressed frames, Transmission Gap Length slots from Nfirst to Nlast are not used for transmission of data. As illustrated below, the instantaneous transmit power is increased in the compressed frame in order to keep the quality (BER, FER, etc.) unaffected by the reduced processing gain. The amount of power increase depends on the transmission time reduction method. What frames are compressed, are decided by the network. When in compressed
mode, compressed frames can occur periodically, or requested on demand. The rate and type of compressed frames is variable and depends on the
environment and the measurement requirements.
The frame structure for uplink compressed frames is illustrated below.
There are two different types of frame structures defined for downlink compressed frames. Type A maximizes the transmission gap length and type B is optimized for power control. The frame structure type A or B is set by higher layers independent from the downlink slot format type A or B.
• With frame structure of type A, the pilot field of the last slot in the transmission gap is transmitted. Transmission is turned off during the rest of the transmission gap (below).
• With frame structure of type B, the TPC field of the first slot in the transmission gap and the pilot field of the last slot in the transmission gap is transmitted. Transmission is turned off during the rest of the transmission gap (below).
•
Compressed Mode
Control - is a mechanism whereby certain idle periods
are created in radio frames during which the UE can perform measurements on other frequencies. The UE can carry out measurements in the neighboring cell, such as GSM cell and FDD cell on another frequency.
Compressed Mode is not used for HS-DSCH or for EUL.
Compressed Mode Control handles UL and DL independently, thus compressed mode can be used in DL only, UL only, or both UL and DL depending on the UE capabilities.
Compressed Mode is used as soon as the UE requires Compressed Mode for any of the GSM bands that it supports to avoid having to check and possibly
start/stop Compressed Mode at Active Set updates.
Two different methods, HLS or SF/2, are used to create these idle periods depending on the radio bearer combination.
In case of HLS, the idle periods are created by higher layers (that is, layer 2) that set restrictions so that only a subset of the allowed TFCs are used in the compressed radio frames, thus reducing the user data throughput.
In case of SF/2, the idle periods are created by using a channelization code from the alternate code tree, corresponding to a spreading factor equal to half the one that is normally used and thus using more radio resources, that is, power and code to transmit the normal amount of user data
The Inter-RAT Handover Evaluation algorithm performs the Inter-RAT (WCDMA RAN to GSM/GPRS) handover evaluation based on the UE GSM/GPRS
measurement reports. At event reports, a GSM/GPRS cell is proposed to make handover to, based on the reported measurements.
The Inter-RAT Handover and Cell Change provide the ability to maintain
connection with a UE when moving to other radio access systems and WCDMA RAN. Inter-RAT Handover is used when the UE is using a Circuit-Switched service and is moving out from WCDMA RAN coverage area to a GSM/GPRS coverage area and vice versa. Inter-RAT Cell Change is used when the UE is using a Packet-Switched service.
Inter-RAT Handover for CS services is a type of hard handover where the UE is ordered by the network to tune to another RAT, establish contact with it and then continue the traffic using resources from the new contacted system. This means that there will be small interruptions in the data flow to and from the UE.
Inter-RAT Cell Change is similar to Inter-RAT Handover. Inter-RAT Cell Change is also used when the UE is in connected mode, CELL_DCH state. The major
difference between Inter-RAT Handover and Inter-RAT Cell Change is that in the Inter-RAT Cell Change case there are no resources reserved in the target cell before the Inter-RAT Cell Change is executed. If the Inter-RAT Cell Change is evaluated and executed by the UE in Idle mode or connected mode on common channels it is denoted Cell Reselection or Inter-RAT Cell Reselection, see Idle Mode and Common Channel Behavior for more details.
