Friday, May 13, 2011

Excel Tips( Make an engineer perfect)

A RF engineer can get his excellence by getting not only knowledge he must be know about tool knowledge. command over Excel make perfection.




A good command on excel improve performance ........


here some good tips and command to get excellence in Excel.






Click here to download

http://www.cellular-planningoptimization.com/2010/03/excel-tips-make-engineer-perfect.html

 

Wednesday, May 11, 2011

Timing advance in GSM

Hi 

   Do you know about Timing advance in GSM??

How its work?

Which channel its use?

How it is calculated ?

All the calculations with very easy steps

 

Just click the following link

http://www.cellular-planningoptimization.com/2010/02/timing-advance-with-calculation.html

 

Do you have something to publish on the site http://www.cellular-planningoptimization.com/  Please mail me.

 

 

Br//

 

Friday, May 6, 2011

Employer's Corner

Hi 

  

Are you a  job consultant or recruiter or HR?

Searching the Telecom Professional in the following field



Cellular Planning and Optimization engineers(2G, 3G,CDMA,LTE Wimax)

 

Please go through our website  http://www.cellular-planningoptimization.com/ 



Thousands of Telecom professionals are connected with this site and many are looking for a change...

 

If you have any kind of job in the same field, Please mail on the following mail id with all details.

It will be published automatically on the site and you can get a lot of feedback from there.

 

So Please mail all types of job on

postit@cellular-planningoptimization.com

 

 

 

Regards

 

Admin

http://www.cellular-planningoptimization.com/ 

 

Wednesday, May 4, 2011

Some Question Answer of 3G

1.       If a UE is on a data call (CELL-DCH state) and there is in no activity for awhile what would you expect to see occur?

 

UE should go from CELL-DCH to CELL-FACH then if still no activity to either CELL-PCH or URA-PCH (via CELL-FACH). If they talk about inactivity timers and mention that the state goes from CELL-DCH straight to CELL-PCH or URA-PCH that is also possible. Bonus they say they would see RADIO BEARER RECONFIGURATION messages when the states are changing.

 

2.      Explain the concept of a Monte Carlo Simulation for UMTS Design.

 

This is a simulator that randomly distributes terminals/users geographically onto the network and then checks the link budget for each terminal/connection to see if they can successfully connect or not. The simulator modifies parameters such has UE Tx Power, BTS Tx Power, requested bearer (in the case that multiple bearers could support the same service) when checking if a connection can be made. In every snapshot the simulator runs through the list of terminals/connections and attempts to make them all connect successfully, it starts a new snapshot when the number of successful connections converges. The process then starts on a new snapshot.

 

3. In what cases is Open Loop Power Control used?

 

This is a simulator that randomly distributes terminals/users geographically onto the network and then checks the link budget for each terminal/connection to see if they can successfully connect or not. The simulator modifies parameters such has UE Tx Power, BTS Tx Power, requested bearer (in the case that multiple bearers could support the same service) when checking if a connection can be made. In every snapshot the simulator runs through the list of terminals/connections and attempts to make them all connect successfully, it starts a new snapshot when the number of successful connections converges. The process then starts on a new snapshot.

 

4. Explain Inner and Outer loop power control and who controls them.

 

If they start talking about Open and Closed Loop PC, tell them you want Inner/Outer Closed Loop PC. Inner loop power control is performed by the NodeB to set the transmit power of the UE and BTS to compensate for signal variations due to fading or path loss to maintain the set SIR (occurs up to 1500 times per sec). Outer loop power control is performed by the RNC to set the target SIR based on the required BER/BLER for the requested services (occurs up to 100 times per sec).

 

5. In HSDPA, how does the network manage the throughput on the Radio Interface for a user/ connection?

 

Modulation (16QAM, QPSK etc), Coding (convolution coding, fire codes etc), number of codes allocated and scheduling (it's a shared resource)

 

6. Depending on the RF conditions, what can the network do to manage call quality?

 

AMR - for good conditions use codec will low redundancy/overhead; for poor conditions use codec with lower bit rate requirement but higher overhead, stronger coding and more redundancy.

 

7. What is the typical/most common bit rate that a voice call uses?

 

They should say 12.2kbps but may be different if they start talking about AMR and the different rates then the know more. Prod them to see if they know the Spreading Factor (SF) used for the radio bearer, should be 128

 

8. In Release '99, how does the network manage the throughput on the Radio Interface for a user/connection?

 

This question is a little harder to ask, so you may need to work it differently a few times. Perhaps leading questions could be: What

parameter/configuration does the network change on the air interface What you are trying to hear from the candidate is that the network assigns a radio bearer with a channelization code with a spreading factor that matches the requested service maximum bit rate.

 

9. Name the 4 RRC Connected Modes (states) and describe the characteristics of each.

 

Cell-DCH: UE has been allocated a dedicated physical channel in uplink and downlink.

Cell-FACH: UE listens to RACH channel (DL) and is allocated a FACH channel (UL). Small amounts of UL/DL data can be transfers in this state. The RNC tracks the UE down to the cell level and cell reselections are possible with the CELL UPDATE message.

Cell-PCH: UE monitors (using discontinuous reception) a PCH channel (PCH) indicated by the PICH channel. The RNC tracks the UE down to the cell level and cell reselections are possible with the CELL UPDATE message. No data can be transferred in the UL in this state.

URA-PCH: UE monitors (using discontinuous reception) a PCH channel (PCH) indicated by the PICH channel. The RNC tracks the UE down to the URA level.

 

10. What is compressed mode, what is it's function, and what impact does it have on the network?

 

Compressed mode is when the mobile goes into a slotted transmit mode whereby it opens up an idle period (transmission gap) where it can monitor another carrier or technology (GSM). The impact is that to maintain the same bit rate, it halves the SF, and therefore increases power level causing higher interference to the network. If the SF cannot be halved then the bit rate of the bearer decreases. If they seem knowledgably, ask them if they know what messages and events trigger and configure compressed mode on/off. 2D event for on, 2F for off.  Messages would for configuration would be RADIO BEARER RECONFIGURATION, TRANSPORT CHANNEL RECONFIGFURATION or PHYSICAL CHANNEL RECONFIGURATION.

 

11. What are the general triggers for an iRAT handover?

Ec/Io of best cell below a certain threshold (usually around -16 to -18 dB) or RSCP of best cell below a certain threshold (usually around -100 dBm).

 

12. What would you define as a pilot polluter?

 

Many definitions: A cell that has high signal strength at a location but is not part of the active set. A cell that meets the criteria for addition into the Active Set but can not enter because the active set is full.

 

13. What is typically the requirements (criteria) for a cell to be added/removed/replaced to/from/in the active set?

 

For addition (Event 1a), candidate cell needs to have an Ec/Io value that is within a T_ADD threshold of the primary/reference (usually the best) cell for a specify time hysteresis. For removal (event 1b), cell needs to have Ec/Io lower than T_DROP margin for a specific time hysteresis. For replacement (event 1c), cell needs to have an Ec/Io better than the worst cell in the active set by the T_REPLACE and for a specific time hysteresis.

 

14. What is the typical maximum active set size and what needs to be considering when setting this?

 

3 to 4 cells, the larger the active set size the more likely it is that Iub link efficiency is reduced (more than one resource for a single connection due to SHO).

 

15. In the Link Budget, what is a Shadow Fade Margin for and what factors does it depend on?

 

The shadow fade margin is dependent on the target percentage area coverage, the propagation model, and the standard deviation of the lognormal shadowing (usually the same as the model's standard deviation if the fast fading effects are removed). The Shadow Fade Margin is a added margin placed in the link budget such that a guaranteed level of service can be offered "in the worst case".

 

16. What would the call flow be for a Mobile Originated Call (major RRC messages)?

 

RRC Connect Request -> RRC Connection Setup -> RRC Setup Complete -> (SETUP, authentication encryption, TMSI reallocation etc) -> CALL PROCEEDING-> Radio Bearer Setup -> Radio Bearer Setup Complete -> ALERT -> CONNECT -> CONNECT ACK ->DISCONNECT -> RELEASE.

 

17. How would you find such cells from a planning tool and from a drive test tool?

 

Ignoring low signal conditions, if the best cell RSCP is greater than say -85dBm and there are cells not in the active set but are strong enough to be in the active set then they are candidate for pilot polluters. Looking at cells that have a high noise rise, high amount of traffic compared to surrounding cells, may also indicate a pilot polluter. Areas with high Signal strength for the (Active Set Size + 1) best pilot (like the 4th best pilot if AS size is 3). In DTT, areas with poor Ec/Io but good RSCP, in the monitored set contains a cell with a good Ec/Io but cannot enter the AS because it is full. Areas where scanner shows a strong signal for a far away cell.

 

18. What is the major difference in link budgets between UMTS and GSM/TDMA?

 

 In UMTS you generally have a link budget for each service (voice, data, video etc), in GSM you usually only use 1 for voice. Each service has a different Eb/No target. In UMTS you have to consider the target traffic load you will have and add a noise-rise margin, in GSM you may have a slight interference margin but not normally related to traffic. In UMTS some services (like voice) will show up as uplink limited but other services (like HSDPA, 384kbps service) will show as downlink limited. In UMTS you usually have to consider that all users use the same power from the BTS therefore the more number of users the lower the maximum power available per user (maximum power per connection) which is a starting point in the link budget.

 

19. What is an active set, monitor set and detected set?

 

Active Set: the set of cells with which the UE is currently connected/communicating with; Drive test usually show them as SC or Pilots but they are actually cells; Monitored Set: Cells that the UE has detected and is monitoring and are known to the network, they either don't meet the criteria or the active set is full; Detected Set - Cells that the UE has detected but are not known to the network as yet (missing neighbor likely).

 

20.  Explain the different Handover types in UMTS.

 

Soft(er) Handover: connected to more than one cell on the same frequency, softer occurs when 2 cells in the active set belong to same Node-B; Intra-frequency Hard Handover: Occurs when UE moves from one cell in one RNC to a cell in another RNC and the RNCs do not have an Iur link between each other; Inter-Frequency Hard Handover: when UE changes from one frequency to another frequency (usually due to traffic layer management or Quality reasons);Inter-technology (iRAT) Hard Handover: Handover from UMTS to GSM (v.v.) usually at the edge of UMTS service area but also due to quality reasons.

 

21. Explain the concept of Cell Breathing. How is the accounted for in the link Budget?

 

Io or No (the interference part of Ec/Io and Eb/No) increase as the traffic on the network increases since everyone is using the same frequency. Therefore as Io or No increases the UE or BTS needs to use more power to maintain the same Eb/No or Ec/Io. When the power required is more than the maximum power allowed, the connection cannot be made. Users at the cell edge are usually the first to lose service; hence the service area of a cell shrinks. As traffic decreases the reverse happens and the service area increases. They should say that it is accounted for in the Noise Rise Margin found in the Link Budget.

 

22. What does the scrambling code do and function?

Scrambling Code makes it possible for the UE to distinguish the transmissions from different cells/NodeBs. Bonus if he knows there are 512 primary scrambling codes and that the are broken up to 64 groups of 8 codes each.

 

23. What does channelization codes do and function?

 

Channelization codes are used for spreading and dispreading of the signals, they also create the "channels" making it possible to distinguish between users/connections/channels. Bonus if they know that they have an associated Spreading Factor and are allocated depending on the bandwidth required by the service.

 

 

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