1. WCDMA Introduction
2. Overview of protocols in WCDMA RAN
3. UMTS Quality Of Service
4. RRC Protocol.
5. RLC and MAC Protocols .
6. Iub Interface-NBAP Protocols
7. lur Interface-RNSAP Protocols .
8. Iu Interface-RANAP Protocol.
9. Acronyms and Abbreviations .

Download WCDMA RAN Protocols and Procedures

Basic Counters of Network Performance
Accessibility
Accessibility counter is one of the most important statistics and it is the performance expression of the network at the first glance. Accessibility is calculated by multiplying SDDCH serviceability by TCH accessibility.

Accessibility = SDCCH Serviceability * TCH Accessibility

For accessibility performance of the network, repeated short call set–ups must be performed by drive tests.
Retainability
Retainability is the clue to network continuity and targets TCH Call Success rate of the network. It takes all type of drops into consideration.

Retainability = TCH Call Access Rate = 1 – TCH Call Drop Rate

TCH Call Drop rate is calculated by dividing total number of drop calls to number of total TCH seizures and attempts. Total number of drop calls
contains all types of TCH drops including any radio related, user activated, network activated, ABIS fail, A interface, LAPD, BTS failure or BSCU
reset drops. Please note that any TCH re–establishment should be subtracted from TCH call drop rate as call is somehow able to continue.

Total number of TCH attempts and seizures will include any TCH seizures for new calls and TCH to TCH attempts during Handover and number of
intracell handovers as well.

Retainability is wanted to be as near as to 100 percent. For measuring retainability and integrity of a network, long continuous calls must be performed by drive tests.
Access Fails
Access failures are the total number of unsuccessful TCH attempts which is calculated by subtracting number of assigned TCH seizures from number of TCH attempts – including the ones during handovers.

Pilot channel failure – high downlink interference

Symptoms
From the drive test, following symptoms will be observed by using TEMS:
• Received Ec/No of the pilot channel is less than –16dB and
• Received RSCP of the pilot channel is high enough to maintain the connection, e.g. > -100dBm and
• DL RSSI is very high and
• The connection finally drops.
Reason 1 – no dominant cell

There are many overlapping cells at the problem area. The received signal strengths of these pilots are almost the same,
Solution:

The most direct and effective way to solve this problem is to increase the pilot channel power Primary CPICH power of the desired cell.
The drawbacks of this solution are:
• Due to uneven pilot power setting, some UEs might no longer be connected to the “closest” cell with respect to the pathloss.
Then they transmit with high UE powers. As a result, the uplink interference level of the carrier is consequently increased.
It means uplink is not optimized and this phenomenon is called as uplink near-far problem. It is recommended that:

–Reporting Range 1a: threshold for addition window/2 ? difference of the pilot power settings of two neighboring cells ? Reporting Range 1a: threshold for addition window/2
• In case the pilot power of a cell is increased, the required power for the downlink DPCHs in that cell also increase. Finally, the load of the cell becomes high and then cell blocking may happen.
• The downlink interference level of the carrier will be higher.
• The cell with higher pilot power will absorb more UEs from its adjacent cells. Then the load of the cell will be higher.
• Pilot power changes may lead to uplink coverage and pilot coverage imbalance problems.
Reason 2 – dominant interferer
An undesired cell with very high signal strength is found in the problem area.
Solution 1
The simplest solution to overcome this problem is to include the overshooting cell into the neighboring cell list. This means the interferer now becomes a useful radio link.
The drawbacks of the solution 1 are:
• It creates more unnecessary handovers and excessive numbers of UEs are in soft handover.
• If the overshooting cell is physically far way to the problem area, the handover sequence might be messed up after including it into the neighboring cell list.
Solution 2
An alternative solution is to change the antenna configuration of the overshooting cell, e.g. tilting down the antenna, re-directing the antenna orientation, reducing the antenna height.
With this solution, UL/DL coverage imbalance problem will not occur in the interferer because both UL/DL pathloss is modified simultaneously.
Moreover, the interferer probably will cover fewer UEs, and transmit a lower total downlink due to transmit high Tx power, they might become interferers if their coverages are not well confined.
Solution 3
The third possible solution is to decrease the pilot power Primary CPICH power of the overshooting cell.
The drawbacks of the solution 3 are:
• Reducing the pilot power, the downlink channel estimation in the UE is affected. This influences the downlink quality. In the end, the UE might request more power from base stations.
• When the pilot power is reduced, the maximum allowed DL DCH power decreases. Then, outage of the downlink DPCH will be higher if the pilot power is reduced too much.
Reason 3 – low best serving PPilot/PTot

The received Ec/No of the best serving pilot channel is very low (near or less than –16dB) even though there is no other cell. It means the pilot power setting is not large enough to fulfill existing downlink load.
Solution 1
The best solution is to add a new site with “good coverage control” at the problematic area.
Solution 2
The direct but ineffective solution is to increase the pilot channel power Primary CPICH power of the problematic cell. With high pilot power, the common channel powers and the required power for the downlink DPCHs will be increased. At the end, the ratio of the PPilot/PTot does not increase much.

RF optimization includes the following aspects:

? Pilot signal coverage optimization It includes the following two parts:

• ? Weak coverage optimization for ensuring seamless coverage by pilot signals in the network
• ? Primary pilot cell optimization for ensuring proper coverage areas by each primary pilot cell, clear edge of primary pilot cells, and that alternation of primary pilot cells is reduced as possible.

? Pilot pollution optimization

Pilot pollution refers to that excessive pilots of approximately equivalent strength cover an area without a primary pilot. Pilot pollution might cause increasing of downlink interference, call drop due to frequent handover, low network capacity. The problems must be solved by adjusting engineering parameters.

? Handover optimization It consists of two parts:

• ? Checking missing neighbor cells, verifying and perfecting list of neighbor cells, solving handover, call drop, and downlink interference problems.
• ? Ensuring proper SHO Factor based on DT by adjusting engineering parameters properly.

The URA_PCH state is similar to the CELL_PCH state.

The difference is that the UE does not execute Cell Update after cell reselection, but instead it reads the UTRAN Registration Area (URA) identities from the broadcast channel and only when URA changes, the UE performs a URA update.

The UE is known on a cell level in the SRNC for CELL_PCH, but it can only be reached via the Paging Channel (PCH). Therefore is the battery consumption of the UE very low because the Paging Channel includes Discontinuous Reception (DRX) functionality.

The UE also listens to system information on the BCH. A UE supporting the Cell Broadcast Service (CBS) is also capable of receiving BMC messages.

If the network wants to initiate any activity, it first needs to page the UE. When the UE receives the paging it changes to the CELL_FACH substate, and performs a Cell Update.

Whenever the UE wants to initiate any activity it triggers a switch to the CELL_FACH substate by performing a Cell Update.

In this substate, the UE has no dedicated channel allocated.

Instead the UE uses the common channels, the RACH and FACH to communicate, both for signaling messages and small amounts of data (best effort), with the network. A dedicated control channel (DCCH) or common control channel (CCCH) is used for control signaling.

A dedicated traffic channel is used for user data transmission. CCCH, DCCH and DTCH are mapped onto a common transport channel (RACH and FACH).

The UE performs cell reselections and sends periodically Cell Update messages to RNC and is therefore known on cell level in the RNC. In this state the UE is also capable of listening to the broadcast channel (mapped on FACH) to require system information.

UE is known by its serving RNC (SRNC), on cell level or active set level. UE has been allocated a dedicated channel. Dedicated control channels (DCCH) are used for control signaling and a dedicated traffic channel (DTCH) is used for user data transmission.

DCCH and DTCH are mapped onto dedicated transport channels (DCH).

The UE performs measurements and sends reports to the RNC accordingly to the measurement control information it received from the RNC.

For multimode terminals (WCDMA – GSM/GPRS) it is possible to perform Inter Radio Access Technology handover (IRATHO) (WCDMA to GSM) and Inter Radio Access Technology Cell Change (IRATCC) (WCDMA to GPRS).