3 g rf_optimisation_basics
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WCDMA network optimization involves four key steps: 1. Coverage optimization to ensure adequate signal levels across the network. 2. Neighbor optimization to create accurate neighbor lists and avoid dropped calls. 3. Pilot pollution optimization to reduce interference between cells by adjusting tilts and adding sites. 4. Soft handover optimization to limit the percentage of routes in soft handover through tilt and azimuth changes.
3 g rf_optimisation_basics
- 1. 3G RF Optimisation Basics
- 2. WCDMA Basics & Generic 3G Optimisation Process 1-WCDMA Basics Frequency Reuse Scrambling Codes Signal Strength/Quality Measurements in WCDMA Pilot Pollution Soft/Softer Handover Missing Neighbours 2-Generic 3G Optimisation Process Process overview RF KPIs In Call KPIs Tools for the job
- 3. Frequency Reuse •Initially operators have been launching with just a single carrier •Network will initially be FDD only e.g. Operator X will launch using only the FDD carrier (F1 =10588) All launch cells will use F1 & therefore Operator X’s 3G network will have a frequency reuse of 1
- 4. Scrambling Codes & CPICH • It carries no information and can be thought of as a “beacon” constantly transmitting the Scrambling Code of the cell • The Common Pilot Indication Channel (CPICH) is broadcast from every cell • It is this “beacon” that is used by the phone for its cell measurements for network acquisition and handover purposes (Ec, Ec/Io).
- 5. 3G Coverage Measurements The majority of 3G coverage measurements are based upon measurements of the CPICH Golden Rule: If the UE can’t see the CPICH the UE can’t see the cell. Initial 3G network optimisation will be performed purely from CPICH measurements Three key related measurements for 3G optimisation are Ec- The Received Signal Level of a particular CPICH (dBm) Io- The Total Received Power (dBm) Ec/Io - The CPICH Quality (The ratio of the above two values)
- 6. Total Received Power Io In a WCDMA network the User Equipment (UE) may receive signals from many cells whether in handover or not Io* = The sum total of all of these signals + any background noise (dBm) *Note: Sometimes Io is referred to as No, RSSI or ISSI
- 7. Received Power of a CPICH Ec Using the properties of SCs the UE is able to extract the respective CPICH levels from the sites received Ec* = The Received Power of a Particular CPICH (dBm) *Note: Sometimes Ec is referred to as RSCP
- 8. The CPICH Quality (Ec/Io) From the previous two measures we can calculate a signal quality for each CPICH (SC) received Ec/Io = Ec - Io (dB) *Note: Sometimes Ec/Io is referred to as Ec/No
- 9. Example From the above three measurements we can calculate for each pilot the Ec level for that particular pilot Ec1 = -80 - 5 = -85dBm Ec2 = -80 - 10 = -90dBm
- 10. Ec, Io and Ec/Io Measurement All commercial scanners and test UEs are capable of making Ec, Io and Ec/Io measurements It is these measurements that are used for cover analysis and basic optimisation
- 11. Handovers in WCDMA Various handover types exist in WCDMA Those between WCDMA sites (intra-system HO) Those between WCDMA and GSM (inter-system HO) Handovers in WCDMA - Softer HO ▪Softer handover occurs between sectors of the same site
- 12. Handovers in WCDMA - Soft HO Soft handover occurs between sectors of the different sites For both softer and soft it is the Ec/Io levels used to determine whether a cell should be added or removed from the active set
- 13. Handovers - Inter frequency HO Inter frequency handover occurs between two WCDMA carriers Will be used once operator deploys its second carrier, for microcell layer or capacity purposes
- 14. Handovers - Inter system HO Inter system handover occurs between 3G and 2G sites As with all handovers, accurate adjacencies will be required
- 15. Optimisation Basics 1-Coverage Optimisation 2-Neighbour Optimisation 3-Pilot Pollution Optimisation 4-SHO Optimisation
- 16. Coverage Optimisation As with 2G if the coverage is inadequate then the call quality will be inadequate Therefore this first stage in 3G optimisation is ensuring adequate coverage Link budgets should be used to determine both the planning targets and the drive survey level targets Note that the planning and drive survey level targets will be different
- 17. Neighbour Optimisation •Missing Neighbours was and still is the biggest cause of poor performance in most commercial 3G networks. •The majority of call drops in early cluster are due to missing neighbours. It is therefore essential that the initial neighbour list is thorough, ideally with neighbours ranked in order of importance. •In 3G the UE must be on the best cell at all times … otherwise it will drop the call – this is not the case in 2G. •3G/2G neighbour lists must also be comprehensive, incorrect 3G/2G neighbour lists will lead to dropped calls when moving from 3G to 2G and poor 3G re-selection performance when on 2G
- 18. 3G/3G Neighbour Optimisation •We declare a 3G missing neighbour as a a cell not declared as neighbour of the best active cell although it is eligible to be added in the active set. •A practical margin of 5dB is recommended as an initial window … anything bigger and the neighbour lists become too large •Solution: 3G Scanner Survey, Actix Analysis, Neighbours Added NMISSINGBESTNMISSING inMEcNoEcNo __ arg−≥
- 19. 2G/3G Neighbour Optimisation •2G/3G neighbour optimisation will require the use of both 3G and 2G drive survey equipment •Dualband scanner files can quickly be processed to pair up the best 3G cells with the best 2G cells for every sample along the drive survey.
- 20. Pilot Pollution Optimisation •As more and more 3G sites are integrated, the pilot pollution within the network will increase •With >4 pilots of a similar level it can be very difficult to establish even a voice call •The higher the data rate the more susceptible the service is to pilot pollution (bad Ec/Io). •Whilst 3G voice requires an Ec/Io of above -15dB, 384kbps will required Ec/Io levels of -9dB or higher !! •Pilot pollution should not be confused with poor coverage, where there is poor coverage, there is generally pilot pollution/bad Ec/Io
- 21. Pilot Pollution Optimisation Best server CPICH_Ec >= Ec target (dBm) And Best server CPICH EcNo < Ec/Io target (dB) ▪To avoid confusing areas of poor coverage with areas of pilot pollution we can define an area of pilot pollution as somewhere where •The Ec target is the target coverage = -100dBm •The current recommended Ec/Io target = -10dB
- 22. Pilot Pollution Optimisation There are various means of reducing pilot pollution New Sites: Additional sites may reduce pilot pollution by bringing dominance to an area (before optimising for pilot pollution, always check that a new site is not about to be brought on air in the locality) Antenna Downtilts: By adjusting tilts on the best servers, or worst interferers, pilot pollution can be removed Solution: 3G Scanner Survey, Analysis, Downtilts, New Sites?
- 23. Handover Optimisation •Softer, Soft, Inter-frequency & system HOs have all been optimised on Nokia’s trial and other customers networks •Therefore initial HO Optimisation should not require any changes to the UTRAN parameters …. •Instead initial HO optimisation will involve studying how much HO occurs in the network and where this HO occurs. •For 3G/3G HO, Actix is able to display areas where Softer & Soft HO is occurring and calculate the percentage of a drive route in SHO •Typically we should be aiming for a SHO area of less that 40% •Optimisation of SHO area should be performed using downtilt and azimuth changes •Solution: 3G Scanner Survey, Analysis, Downtilt and Azimuth changes
- 24. Optimisation Basics •Coverage Optimisation •Neighbour Optimisation •Pilot Pollution Optimisation •SHO Optimisation •Everything is based around Ec/Io, to improve this we need to • Increase Ec (improve the best server(s)) • Reduce Io (reduce pilots not eligible for the active set) • Get all neighbours optimised •In call drive runs should only take place once Radio Optimisation is complete