Gsm optimization

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Gsm optimization

  1. 1. 5/24/2011 Prepared by Legend Technical TeamCopy Rights © LEGEND Co. 2010Copy Rights © LEGEND Co. 2010 1
  2. 2. 5/24/2011 RF People RF people work in either RF Planning RF Optimization Responsibilities Responsibilities − Nominal Plan Design. − Maintain the Network„s Accessibility − Sites Survey. KPIs. − Validation from field. − Maintain the Network‟s Retainability − Set RF design (Structure, Azimuth, KPIs. Height, Tilt, Cables type). − Maintain the Network‟s Service − Frequency Plan. Integrity KPIs. − Neighbor Plan. − Study and Apply new features. − Sites Acceptance. − Try to think of innovative solutions to maximize the Network capacity. RF Planning KPIs: To provide coverage outdoor & indoor and to offer traffic with acceptable grade of service. They have to maintain the performance of the Network as good as possible.Copy Rights © LEGEND Co. 2010Copy Rights © LEGEND Co. 2010 2
  3. 3. 5/24/2011 Part I: Radio Network Planning Course Outlines: − Planning Process and Procedures. − Sites and Hardware Equipment. − Technical Site Survey & Validation. − Coverage and Capacity Dimensioning. − Frequency and Neighbor Planning.Copy Rights © LEGEND Co. 2010Copy Rights © LEGEND Co. 2010 3
  4. 4. 5/24/2011 Part II- Radio Network Optimization What will be our concern during this part of the course?  RF Optimization How the RF Optimization people can maintain the KPIs?  By studying the different radio network features and studying the controlling parameters of each feature and how to tune them in a smart way to achieve the target KPIs. What are we going to study during this part of the course?  Most of the Radio Network features and their controlling parameters.  KPIs monitoring and analysis.  Trouble shooting and Tuning.Copy Rights © LEGEND Co. 2010 Part II- Radio Network Optimization Course Outlines: − Idle Mode Behavior. − Handover. − HCS (Hierarchical Cell Structure). − Concentric & Multi Band Cells. − CLS ( Cell Load Sharing). − Frequency Hopping. − Intra Cell Handover. − Dynamic HR Allocation. − Power Control. − GSM to UMTS Cell Reselection and Handover. − Trouble Shooting and KPIs monitoring.Copy Rights © LEGEND Co. 2010 4
  5. 5. 5/24/2011Copy Rights © LEGEND Co. 2010Copy Rights © LEGEND Co. 2010 5
  6. 6. 5/24/2011 GSM Revision • GSM stands for “ Global System for Mobile Communication” • GSM – Second Generation for Mobile System. – Digital System. – Efficient Use of the Spectrum. – Speech privacy and security. – Better resistance to interference (Introducing the frequency Hopping) – Efficient use of the power battery (Introducing the power control) – GSM Networks are called “PLMN: Public Land Mobile Networks” i.e. the Radio Sites are located on land, not using satellites.Copy Rights © LEGEND Co. 2010 GSM Revision • GSM System can work in different bands as follows: Frequency Band-Down Link Frequency Band-Up Link GSM 800 869  894 MHz 824  849 MHz E-GSM (Extended GSM) 925  935 MHz 880  890 MHz P-GSM 900 (Primary GSM) 935  960 MHz 890  915 MHz GSM 1800 (DCS) 1805  1880 MHz 1710  1785 MHz GSM 1900 (PCS) 1930  1990 MHz 1850  1910 MHz – DCS: Digital Cellular System PCS: Personal Communication Services. • But what do we mean by frequency Band? • What is the DL and UL? • Why DL is higher than UL band?Copy Rights © LEGEND Co. 2010 6
  7. 7. 5/24/2011 GSM Revision• Frequency Band – The range of frequencies which the operator is allowed to use for transmission and reception.• Down Link and Up link bands – DL band is the range of frequencies used by the Base station when transmitting to the MS while the UL band is the range of frequencies used by the Mobile station when transmitting to the Base Station.Copy Rights © LEGEND Co. 2010 GSM Revision• Why DL band is higher than the UL band? – As freq then attenuation with air – Since Power BaseStation > Power MobileStation then it is wise to configure the higher frequencies that will be attenuated fast to the side that is using higher power (BTS).Copy Rights © LEGEND Co. 2010 7
  8. 8. 5/24/2011 Access Techniques  What do we mean by Multiple Access techniques?These are the Techniques through which many MSs can access the shared media which is the air interface. i. FDMA ( Frequency Division Multiple Access) − Each MS is assigned a dedicated frequency through which he can talk. ii. TDMA (Time Division Multiple Access) − All MSs are using the same frequency but each of them will be utilizing it only over a certain period of time called Time Slot (TS)  In GSM System we’re using TDMA over FDMA where the frequency band is divided into no. of frequencies each of which is shared among no. of MSs, where each MS will be assigned a certain TS on certain frequency.Copy Rights © LEGEND Co. 2010 GSM Revision• For P-GSM (GSM 900) – UL Band 890MHz  915MHz, DL Band 935MHz  960MHz – Each Band is 25 MHz – Guard Band between DL and UL is 20 MHz – Duplex Distance = 45 MHz – Carrier separation = 200 KHz – No. of frequencies = 124 Downlink 935 – 960 MHz Uplink 890 – 915 MHz 200 KHz 890.2 890.6 Uplink 1 2 3 4 121 122 123 124 121 890 890.4 915 F (MHz) 935.2 935.6 Downlink 1 2 3 4 121 122 123 124 121 935 935.4 960 F (MHz) GSM 900 Frequency AllocationCopy Rights © LEGEND Co. 2010 8
  9. 9. 5/24/2011 GSM Revision • For the all GSM Bands System P-GSM 900 E-GSM 900 GSM(DCS) 1800 GSM(PCS) 1900 Uplink (MS  BS) 890 – 915 MHz 880 – 915 MHz 1710 – 1785 MHz 1850 – 1910 MHz Downlink(BS MS) 935 – 960 MHz 925 - 960 MHz 1805 - 1880 MHz 1930 - 1990 MHz Wavelength  33 cm  33 cm  17 cm  16 cm Bandwidth 25 MHz 35 MHz 75 MHz 60 MHz Duplex distance 45 MHz 45 MHz 95 MHz 80 MHz Carrier separation 200 kHz 200 kHz 200 kHz 200 kHz No. of carriers 124 174 374 299 Channel rate 270.8 kbps 270.8 kbps 270.8 kbps 270.8 kbpsCopy Rights © LEGEND Co. 2010 GSM Network ArchitectureCopy Rights © LEGEND Co. 2010 9
  10. 10. 5/24/2011 Core Network (NSS: Network Switching System)  MSC (Mobile Switching Center) – Routing/Switching of calls between 2 end users within the GSM Network. – Charging & Billing. – Paging of MSs is originated from the MSC – Access to PSTN (Public Switched Telephone Network) – Act as a Gateway for other networks. – Controls no. of BSCs connected to it.Copy Rights © LEGEND Co. 2010 Core Network (NSS: Network Switching System)  HLR (Home Location Register) – Centralized Network data base stores and manages all mobile subscriptions. – Example: IMSI, MSISDN, MSRN, Services subscribed/restricted for that user. IMSI,MSISDN.ppt  VLR (Visitor Location Register) – It is co-located with the MSC. – Stored in it a copy of the user’s profile on temporary basis.  AUC (Authentication Center) – Provides the HLR with the authentication parameters and ciphering Keys used by the MSC/VLR to authenticate certain user. (Triplets: RAND, SRES, Kc) Authentication.ppt  EIR (Equipment Identification Register) – Used to authenticate the user equipment through the IMEI. IMEI = International Mobile Equipment IdentificationCopy Rights © LEGEND Co. 2010 10
  11. 11. 5/24/2011 BSS (Base Station System) BSC (Base Station Controller) – It controls the air interface, it takes the decisions based on the reports came from the MS and BTS. – Channel Allocation. – Controls the Handover Process. – Dynamic Power Control. – Frequency Hopping. BTS (Base Transceiver Station) – It is the Hardware equipment needed to provide the radio coverage. – Speech Coding/Channel Coding/Interleaving/Ciphering/Burst formatting/Modulation all these are done within the BTS (RBS=Radio Base Station) – Equipment: Cabinet, jumpers, feeders, combiners, antennas.Copy Rights © LEGEND Co. 2010 MS (Mobile Station)  Mobile Equipment – Transmit the radio waves. – Speech coding and decoding. – Call control. – Performance measurement of radio link.  SIM card (Subscriber Identification Module) – Stores user addresses (IMSI, MSISDN, TMSI). – Stores authentication key Ki, authentication algorithm A3 and ciphering algorithm A8&A5 – Stores the subscribed services.Copy Rights © LEGEND Co. 2010 11
  12. 12. 5/24/2011 • Over the Air Interface – Frequency Band is divided into no. of frequencies. – Each frequency is divided into 8 Time slots (TS) – Each user will be assigned 1 TS. – One time slot duration = duration of 156.25 bits – 1 Bit duration=3.7 µsec – Time slot duration =156.25x3.69 µsec= 0.577 msec – 1 Frame = 8 TSs – Frame duration=0.577x8= 4.616 msec – Bit rate on the air interface is 270 Kbps, but for each user it is 33.8 KbpsCopy Rights © LEGEND Co. 2010 Physical Channels vs. Logical Channels  Physical channel: Time slot is called the physical channel.  Logical channel: It is the content that will be sent over the physical channel.Copy Rights © LEGEND Co. 2010 12
  13. 13. 5/24/2011 Logical Channels Logical Channels Traffic Channels Control ChannelsHalf Rate Full Rate Broadcast Dedicated Common Frequency Correction Channel Paging Channel Fast Associated Control Channel Synchronization Channel Access Grant Channel Cell Broadcast Control Channel Broadcast Control Channel Random Access Channel Slow Associated Control Channel Standalone Dedicated Control ChannelCopy Rights © LEGEND Co. 2010 Traffic Channels  Full Rate Channels (FR) – Carries user’s speech traffic or user data DL and UL. – Each user is assigned 1 TS. – Transmission rate is 13 Kbit/s.  Half Rate Channels (HR) – Carries user’s speech traffic or user data DL and UL. – 2 users will share 1 TS (physical channel), each of them will be utilizing it each frame. – Transmission rate is 6.5 Kbit/sCopy Rights © LEGEND Co. 2010 13
  14. 14. 5/24/2011 Control Channels  These are used to carry signaling or synchronization data, they’re divided into three types: – Broadcast Channels (BCH) – Common Control Channels (CCCH) – Dedicated Control Channels (DCCH)Copy Rights © LEGEND Co. 2010 BCH (Broad Cast Control Channels) i. Frequency Correction Channel (FCCH) – Pure signal is transmitted to help the MS to lock on the frequency of the BTS and synchronize to its frequency. (DL channel) ii. Synchronization Channel (SCH) – Carries the TDMA frame number. – BSIC (Base Station Identification Code) of the cell. (DL Channel) iii. BCCH (Broad Cast Control Channel) – LAI (Location Area Identity) – Cell parameters (used power, Idle mode parameters,…..etc) – List of BCCH carries of the neighbor cells i.e. “BA List” (DL Channel)Copy Rights © LEGEND Co. 2010 14
  15. 15. 5/24/2011 CCCH (Common Control Channels) i. Paging Channel (PCH) – Used to inform the MS of an incoming call or sms, where the MS’s IMSI/TMSI will be sent over it. (DL channel) ii. Random Access Channel (RACH) – Used by the MS to ask for an SDCCH to respond to the request send on the paging channel /initiate a call/location update/IMSI attach-detach. (UL Channel) iii. AGCH (Access Grant Channel) – Used by the network to assign an SDCCH sub-channel for the MS. (DL channel)Copy Rights © LEGEND Co. 2010 DCCH (Dedicated Control Channels)i. Standalone Dedicated Control Channel (SDCCH) – Used for signaling purposes: call setup, location update, IMSI attach-detach – Used to send/receive SMSs in idle mode. (DL/UL channel)ii. Slow Associated Control Channel (SACCH) – Always allocated in conjunction with traffic channel/SDCCH channel to transmit measurement reports. – DL measurement reports will include commands from the network to the MS to adjust its power level. – Information about the Time Advance. – UL measurement reports will include information about the MS own power, received SS & Quality from serving cell and SS from neighbor cells. – Used to send SMSs in active mode. (DL/UL channel)Copy Rights © LEGEND Co. 2010 15
  16. 16. 5/24/2011 DCCH (Dedicated Control Channels) iii. Fast Associated Control Channel (FACCH) – Used to send necessary Handover information. – Work in stealing Mode such that 1 TCH channel is replaced by FACCH to send the HO information. (DL/UL channel) iv. Cell Broad Cast Channel (CBCH) – It is sent point to multi point i.e. from the cell to the mobiles attached to it, this channel may carry information about the traffic, weather reports,…etc. (DL channel)Copy Rights © LEGEND Co. 2010 Mapping of Logical Channels on the Physical channelsMapping on TS0/BCCH carrier (DL) 51 consecutive control frames = 1 Control multi frame Where F:FCCH, S:SCH, B:BCCH, C:PCH/AGCHCopy Rights © LEGEND Co. 2010 16
  17. 17. 5/24/2011 Mapping of Logical Channels on the Physical channels Mapping on TS0/BCCH carrier (UL)  TS0 in UL is reserved for the RACH, for the MS to access the system.Copy Rights © LEGEND Co. 2010 Mapping of Logical Channels on the Physical channels  Mapping on TS1/BCCH carrier (DL) Where D:SDCCH, A:SACCHCopy Rights © LEGEND Co. 2010 17
  18. 18. 5/24/2011 Mapping of Logical Channels on the Physical channelsMapping on TS1/BCCH carrier (UL)Copy Rights © LEGEND Co. 2010 Mapping of Logical Channels on the Physical channels Mapping on TS2/BCCH carrier (DL/UL) if it will be used by certain MS in active mode 26 consecutive Traffic frames = 1 Traffic multi frameCopy Rights © LEGEND Co. 2010 18
  19. 19. 5/24/2011 TDMA Multi Frames Structure  Traffic Multi Frames – Traffic Multi Frame = 26 consecutive traffic frames (4.61msec x 26 =120msec)  Control Multi Frames – Control Multi Frame = 51 consecutive Control frames (4.61msec x 51 =235msec) • Super Frame  51 consecutive Traffic Multi Frames or 26 consecutive Control Multi Frames – Super Frame = 6.12 seconds • Hyper Frame  2048 consecutive super Frames – Hyper Frame = 3 hours and 29 minutes nearly.Copy Rights © LEGEND Co. 2010Copy Rights © LEGEND Co. 2010 19
  20. 20. 5/24/2011Copy Rights © LEGEND Co. 2010 IMSI : International Mobile Subscriber Identity IMSI = MCC + MNC + MSIN MCC= Mobile Country Code (3 digits) MNC= Mobile Network Code (2 digit ) MSIN= Mobile Subscriber Identification Number (10 digits) MCC MNC MSIN (3 digits) (2 digits) (10 digits) Ex: IMSI = MCC-MNC-MSIN = 602-03-1234567890 where, 602  Egypt Country Code 03 Etisalat Network Code 1234567890  Mobile Subscriber Identification NumberCopy Rights © LEGEND Co. 2010 20
  21. 21. 5/24/2011 MSISDN : Mobile Station Integrated Services Digital Network MSISDN = CC + NDC + SN CC= Country Code (2-3 digits) NDC= Network Destination Code (2-3 digit ) SN= Subscriber Number ( max 10 digits) CC NDC SN (2-3 digits) (2-3 digits) (max. 10 digits) Ex: MSISDN = CC-NDC-SN =+20-10-1234567 where, 20  Egypt Country Code 10 Vodafone Network Code 1234567  Subscriber NumberCopy Rights © LEGEND Co. 2010 LAI : Location Area Identity LAI = MCC + MNC + LAC MCC= Mobile Country Code (2-3 digits) MNC= Mobile Network Code (2-3 digit ) LAC= Location Area Code ( max 5 digits) MCC MNC LAC (2-3 digits) (2-3 digits) (max.5 digits) Ex: LAI= MCC-MNC-LAC = 602-01-12345 where, 602  Egypt Country Code 01 Mobinil Network Code 12345  Location Area CodeCopy Rights © LEGEND Co. 2010 21
  22. 22. 5/24/2011 CGI : Cell Global Identity CGI = LAI + CI = MCC + MNC + LAC + CI MCC = Mobile Country Code (2-3 digits) MNC = Mobile Network Code (2-3 digit ) LAC = Location Area Code ( max 5 digits) CI = Cell Identity ( max 5 digits) MCC MNC LAC CI (2-3 digits) (2-3 digits) (max. 5 digits) (max. 5 digits) Ex: CGI = MCC-MNC-LAC-CI = 602-01-12345-11223 where, 602  Egypt Country Code 01 Mobinil Network Code 12345  Location Area Code 11223  Cell IdentityCopy Rights © LEGEND Co. 2010 IMEI : International Mobile Equipment Identification IMEI = TAC + FAC + SNR + spare (15 digits) TAC = Type Approval Code, determined by a central GSM body(6 digits) FAC = Final Assembly Code, identified the manufacturer (2 digit ) SNR = Serial Number( 6 digits) spare = A spare bit for future use, when transmitted by MS it is always zero. ( 1 digit)Copy Rights © LEGEND Co. 2010 22
  23. 23. 5/24/2011Copy Rights © LEGEND Co. 2010 AUC : Authentication Center - In the AUC the below table is stored, such that for each user there is a unique authentication key (Ki) User# IMSI Authentication Key User1 MCC+MNC+MSIN1 Ki1 User2 MCC+MNC+MSIN2 Ki2 User3 MCC+MNC+MSIN3 Ki3 User4 MCC+MNC+MSIN4 Ki4 - On authenticating certain user, the AUC will generate the triplets: RAND,SRES,Kc - AUC generates a random no. “RAND” and send it to the MS - Both the AUC and the MS will use RAND + Ki and Algorithm A3 to produce the SRES(Signed Response) RAND1 RAND1 A3 (SRES1)_AUC A3 (SRES1)_MS Ki1 Ki1 AUC side MS Side - VLR will take the results from AUC and MS and if: (SRES1)_AUC = (SRES2)_MS  then the MS is Authenticated Copy Rights © LEGEND Co. 2010 23
  24. 24. 5/24/2011 AUC : Authentication Center - The AUC is responsible also for generating the ciphering Key (Kc) for each user. RAND1 RAND1 A8 Kc_AUC A8 Kc_MS Ki1 Ki1 AUC side MS Side - Kc_AUC should be equal Kc_MS, so the data encrypted by the network can be de-ciphered by the MS. Ciphering Process: TDMA Frame no. Kc_AUC TDMA Frame no. Kc_MS A5 A5 Ciphered Speech Speech + + Speech Network side MS sideCopy Rights © LEGEND Co. 2010Copy Rights © LEGEND Co. 2010 24
  25. 25. 5/24/2011Copy Rights © LEGEND Co. 2010 • MS in Idle Mode – Doesn’t have a dedicated channel, but able to access the Network and able to be reached by the Network. – MS will always try to camp on the best cell based on the signal strength criterion. – MS will continuously monitor the serving and neighbor BCCH carriers to decide which cell to camp on. – The purpose behind studying the Idle Mode Behavior is to always ensure that the MS is camped on the cell where it has the highest probability of successful communication.Copy Rights © LEGEND Co. 2010 25
  26. 26. 5/24/2011 • MS Tasks during Idle Mode – PLMN Selection. – Cell Selection. – Cell Reselection. – Location Updating. – Monitor the Incoming Paging.Copy Rights © LEGEND Co. 2010 • MS Tasks during Idle Mode – PLMN Selection – Cell Selection. – Cell Reselection. – Location Updating. – Monitor the Incoming Paging.Copy Rights © LEGEND Co. 2010 26
  27. 27. 5/24/2011 • PLMN Selection Criterion – PLMN identity is defined as “MCC+MNC” which is part of the LAI, where LAI=MCC+MNC+LAC. MCC: Mobile Country Code - MNC: Mobile Network Code - LAC: Location Area Code – When the MS is powered “ON”, it will check if it needs to perform a Location Update by comparing the new LAI with the old stored one. – An MS will need to make a PLMN selection only incase: 1. MS is powered “ON” for the 1st time i.e. No PLMN was registered on before (No Information on MCC&MNC is stored on SIM) 2. Old PLMN is not available any more (Out of coverage/Roaming)Copy Rights © LEGEND Co. 2010 • PLMN Selection Criterion – When the MS has to do a PLMN selection due to one of the previous cases, the selection mode will depend on the MS settings either Automatic or Manual. – Automatic PLMN Selection Mode steps: 1. Home PLMN. 2. Each PLMN stored on the SIM card in priority order. 3. Other PLMNs have Signal Strength > -85 dBm. 4. All other PLMNs in order of decreasing Signal Strength. – Manual PLMN Selection Mode: 1. Home PLMN. 2. All other available PLMNs and give the user the choice to select.Copy Rights © LEGEND Co. 2010 27
  28. 28. 5/24/2011 • PLMN Selection Criterion  National Roaming – If National Roaming is permitted then a MS can register on a PLMN in its home country other than its home PLMN. – National Roaming may be allowed on a certain location areas (LAs) of the visitor PLMN. – MS should periodically try to access back his home PLMN, but this periodic attempts will occur only on automatic selection mode.Copy Rights © LEGEND Co. 2010• MS Tasks during Idle Mode – PLMN Selection. – Cell Selection – Cell Reselection. – Location Updating. – Monitor the Incoming Paging.Copy Rights © LEGEND Co. 2010 28
  29. 29. 5/24/2011 • Cell Selection Criterion – The Cell Selection algorithm tries to find the most suitable cell in the selected PLMN and make the MS camp on. – Cell Selection is done by the MS itself. – During Idle Mode the Network doesn’t know the cell which the MS is camping on, it only knows the Location Area where the mobile registed himself in.Copy Rights © LEGEND Co. 2010• Cell Selection Criterion Scan RF Frequencies one by one and calculates the Average received signal strength over 3  5 seconds Tune to the RF Frequency with Tune to the next higher the highest average received frequency that wasn‟t tried signal strength before Check if the chosen frequency is a BCCH carrier frequency or not No Yes MS will synchronize to the BCCH frequency and read system information (LAI,BA List,…etc) Check if PLMN is desired or not No Yes Check if Cell is barred or not Yes No Check if C1 > 0 or not Yes No Camp on the CellCopy Rights © LEGEND Co. 2010 29
  30. 30. 5/24/2011 • Cell Selection Criterion – Scanning RF Frequencies may occur in 2 ways: 1. Normal Scanning: Scan all Frequencies in the band ex:124 freq. in GSM900 Band. 2. Stored List Scanning: Scan the Frequencies in the Idle BA list (BCCH Allocation) stored on the MS SIM before being switched off. (BA list can have maximum 32 frequencies)  If MS found cell belongs to the desired PLMN but not suitable, the MS will start to scan the Idle BA list of this cell.Copy Rights © LEGEND Co. 2010 • Cell Selection Criterion – Cell is said to be suitable if: 1. Cell belongs to the desired PLMN  If at least 30 strongest frequencies from GSM900 band were tried and no suitable cell was found, then the MS will try another PLMN based on PLMN criterion. 2. Cell is not Barred ( CB = NO)  Some cells can be barred for access at selection and reselection or given lower priority based on settings of parameters: CB 3. C1 > 0Copy Rights © LEGEND Co. 2010 30
  31. 31. 5/24/2011• Cell Selection Criterion – C1 is called “Cell Selection Quantity” – It is calculated at the MS based on the below equation: C1 = (Received SS – ACCMIN) – max (CCHPWR-P,0) ACCMIN  Minimum allowed DL received SS at the MS in order to access the system CCHPWR  Maximum allowed transmitting power by the MS in the UL. P  Maximum out put power of the MS according to its class. N.B: 1. ACCMIN and CCHPWR are cell parameters sent to the MS at the BCCH channel. 2. If CCHPWR > P then C1 will decrease and so the Received SS should be large enough to keep C1 > 0 (May be this cell is not designed for this MS class) 3. ACCMIN, CCHPWR, P are all measured in dBm, where C1&C2 are measured in dBsCopy Rights © LEGEND Co. 2010 • MS Tasks during Idle Mode – PLMN Selection. – Cell Selection. – Cell Reselection – Location Updating. – Monitor the Incoming Paging.Copy Rights © LEGEND Co. 2010 31
  32. 32. 5/24/2011 • Cell Reselection Criterion – After a cell has been selected, the MS will start the cell reselection measurements to know if it is better to stay on the current cell or to camp on another cell. – Cell reselection measurements: 1. Monitors the SS (Signal Strength) of the BCCH carrier of the serving cell. 2. Monitors the SS of the BCCH carrier of all defined neighbors in the Idle BA list. 3. Continuously read system information sent on the serving BCCH carrier at least every 30 seconds. 4. Continuously read system information sent on the BCCH carrier for the six strongest neighbors at least every 5 minutes. 5. Try to decode BSIC of the six strongest neighbors every 30 seconds to assure that it is still monitoring the same cells.Copy Rights © LEGEND Co. 2010 • Cell Reselection Criterion – Cell reselection measurements summary BSIC BCCH Data (System Information) Serving Cell - Every 30 Seconds Six Strongest Neighbors Every 30 Every 5 Minutes SecondsCopy Rights © LEGEND Co. 2010 32
  33. 33. 5/24/2011 • Cell Reselection Criterion – When Cell Reselection will occur ? 1. Serving Cell became barred ( CB = YES ) 2. C1 serving cell falls below zero for more than 5 seconds. 3. MS tried to access the network through this cell unsuccessfully for the allowed no. of times defined by the parameter MAXRET 4. C2 neighbor cell ( one of the six strongest neighbors) became greater than C2 serving cell for more than 5 seconds. 5. MS detects Downlink Signaling Failure.Copy Rights © LEGEND Co. 2010 • Cell Reselection Criterion – What will happen when the MS needs to make cell reselection?  The MS will camp on the cell that has the highest C2 value. – C2 is called “Cell Reselection Quantity” C2 = C1 + CRO – TO * H( PT – T ) where PT ≠ 31 C2 = C1 – CRO where PT = 31 0, X<0 Where H(x) 1, X≥0 CRO  Cell Reselection Offset, unit = 2 dB, value range = 0 to 63 TO Temporary Offset, unit = 10 dB, value range = 0 to 7 PT  Penalty Time during which TO is valid T  Initiated from zero when the MS places the neighbor in the list of the Six StrongestCopy Rights © LEGEND Co. 2010 33
  34. 34. 5/24/2011 • Cell Reselection Criterion – CRO : defines a signal strength offset to encourage or discourage MSs to reselect that cell. – TO : defines a negative temporary offset for certain time according to settings of PT (Practically this is useful to prevent fast moving MS from camping on microcells) – PT: If PT is set to 31, this means that a (–ve) SS offset “CRO” will be applied to this cell and it appears less favorite for cell reselection.Copy Rights © LEGEND Co. 2010 • Cell Reselection Criterion  Down Link Signaling Failure Algorithm – The Algorithm of type “Leaky Bucket” and used a counter “D”, where D = 90/MFRMS – MFRMS is a cell parameter defines the no. of multiframes between the transmission of each paging group i.e. if MFRMS=4 then a MS attached to a certain paging group will wait in sleeping mode for 4 multiframes (4*235msec) until it is up again to listen to paging. – When the MS is up to listen to its paging group, if the message is not decoded successfully then D is decremented by 4 and if the message is decoded correctly then D is incremented by 1. – If D reaches zero, then a Down Link Signaling Failure is detected and cell reselection took place.Copy Rights © LEGEND Co. 2010 34
  35. 35. 5/24/2011 • Cell Reselection Criterion  Down Link Signaling Failure Algorithm – Ex: Assume that MFRMS = 4 Downlink signaling failure counter is initialized: D = round(90/MFRMS)=22. If the MS unsuccessfully decodes a paging message, then: D = D - 4 = 18. If the MS successfully decodes a paging message, then: D = D + 1 = 19.  If D reaches zero, then a Down Link Signaling Failure is detected and cell reselection took place. N.B: D can’t exceed the bucket size given by round(90/MFRMS)Copy Rights © LEGEND Co. 2010 • Cell Reselection Criterion  CRH ( Cell Reselection Hysteresis ) – Cell Reselection between two cells lie in two different Location Areas, will be accompanied by Location Update. – At the border between cells the Signal level may be comparable, cell reselection may occur many times accompanied by many location updating leading to huge signaling load. – To avoid this, a parameter CRH is introduced such that a cell in another location area LA2 should have C2LA2 should greater than C2LA1 of serving cell lie in LA1 by at least CRH in order to be selected. – If C2LA1 = 5 dB, CRH = 4 dB, then C2LA2 ≥ 9 dB in order to be selected.Copy Rights © LEGEND Co. 2010 35
  36. 36. 5/24/2011• MS Tasks during Idle Mode – PLMN Selection. – Cell Selection. – Cell Reselection. – Location Updating – Monitor the Incoming Paging.Copy Rights © LEGEND Co. 2010 • Location Updating – To make it possible for the mobile subscriber to receive a call and initiate a call whenever needed, the network must know where the MS is located whenever it moves that’s why Location Updating is needed. – In the Idle Mode, the Network knows the location of the MS on a Location area resolution not on a cell resolution. – There are three different types of location updating defined: 1. Normal Location Updating. 2. Periodic registration. 3. IMSI attach & IMSI detach (when the MS informs the network when it enters an inactive state)Copy Rights © LEGEND Co. 2010 36
  37. 37. 5/24/2011 • Location Updating 1. Normal Location Updating – Initiated by the MS when it enters a cell belongs to a new Location Area (LA). – The MS will compare the LAIold stored on the SIM with the LAInew broadcasted from the new cell and it will found them different so it’ll perform Location Update type normal.Copy Rights © LEGEND Co. 2010 • Location Updating 2. Periodic Registration – Regularly the MS should update the Network with its current location Area. – The Network will inform the MS how often it should report the location Area he is registering himself in. – Based on the value of the Parameter T3212 the MS will know how frequent it should make periodic registration. – T3212 take values from 1 (6min) to 255 (25.5 Hours), default = 40 (4 Hours) – MSC has a supervision time = BTDM+GTDM if it doesn’t hear from the MS during this period, the MSC will consider the MS implicitly detached. – BTDM+GTDM should > T3212 , to not consider the MS detach before periodic location update is performed.Copy Rights © LEGEND Co. 2010 37
  38. 38. 5/24/2011 • Location Updating 3. IMSI Attach/Detach – IMSI attach/detach operation is an action taken by the MS to inform the Network either it will go to inactive state (Power off) or it returned back to idle mode. – ATT is a cell parameter that will inform the MS whether IMSI attach/detach is operational or not. – If ATT=Yes, then before the MS will be switched off, it will send an IMSI detach request to the Network, so no paging messages will be sent to this MS while it is in this state. – When the MS is switched on again it will send an IMSI attach request to the Network so now paging messages can be sent normally to this MS.Copy Rights © LEGEND Co. 2010• MS Tasks during Idle Mode – PLMN Selection. – Cell Selection. – Cell Reselection. – Location Updating. – Monitor the Incoming PagingCopy Rights © LEGEND Co. 2010 38
  39. 39. 5/24/2011• Monitor the Incoming Paging Let us revise the DL logical channels and their mapping:I) BCH(Broadcast Channels): including FCCH(Frequency Correction Channel) SCH(Synchronization Channel) Always Mapped on TS0/C0 BCCH(Broadcast Control Channel)II) CCCH(Common Control Channels): including PCH(Paging Channel) Always Mapped on TS0/C0 AGCH(Access Grant Channel)III) DCCH(Dedicated Control Channels): including SDCCH(Stand Alone Dedicated Control Channel) May be Mapped on either SACCH(Slow Associated Control Channel) TS1/C0 or TS0/C0 CBCH(Cell Broadcast Channel) FACH(Fast Associated Control Channel) “ Work in Stealing mode by replacing the TCH time slot”Copy Rights © LEGEND Co. 2010 Frame 1 Frame 2 Frame 3 Frame 4 Frame 5 Frame 6 Frame 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 F S B B B B C F S B C F S C C F S C C F S C C F S C C I 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51 Default Mapping on TS0/C0 (BCH+CCCH) “Non Combined Mode” 51 TDMA Frames = 1 Control Multi-frameCopy Rights © LEGEND Co. 2010 39
  40. 40. 5/24/2011 Default Mapping on TS1/C0 (SDCCH+SACCH+CBCH(optional))Copy Rights © LEGEND Co. 2010• Monitor the Incoming Paging Combination of Control channels (Different Mapping Criteria)− Mapping on TS0/C0 is controlled by Parameter called BCCHTYPE− BCCHTYPE = NCOMB (Non Combined, BCH&CCCH)TS1/C0 will carry SDCCH+SACCH = COMB (Combined, BCH&CCCH&SDCCH/4) TS1/C0 will be free for TCH = COMBC (Combined with cell broadcast channel CBCH is in use, BCH&CCCH&SDCCH/4&CBCH)  TS1/C0 will be free for TCHCopy Rights © LEGEND Co. 2010 40
  41. 41. 5/24/2011• Monitor the Incoming Paging Combination of Control channels (Different Mapping Criteria)− SDCCH may have on of the following 4 configurations based on parameter SDCCH− SDCCH = (i) SDCCH/8 (8 SDCCH Sub-channels i.e. make call setup for 8 users) = (ii) SDCCH/8 including CBCH (7 SDCCH Sub-channels + 1 CBCH) For these two cases, the BCCHTYPE=NCOMB and the mapping of the SDCCH channel is done on TS1/C0 = (iii) SDCCH/4 (4 SDCCH Sub-channels) = (iv) SDCCH/4 including CBCH(3 SDCCH Sub-channels + 1 CBCH) For these two cases, the BCCHTYPE=COMB or COMBC and the mapping of the SDCCH channel is done on TS0/C0Copy Rights © LEGEND Co. 2010• Monitor the Incoming Paging Combination of Control channels (Different Mapping Criteria) Non Default Mapping on TS0/C0 (BCH+CCCH) 2*51 TDMA Frames = 2 Control Multi-frameCopy Rights © LEGEND Co. 2010 41
  42. 42. 5/24/2011• Monitor the Incoming Paging Combination of Control channels (Different Mapping Criteria)The Table below summarizes all the previous details Default Mapping (Non Combined) Non Default Mapping (Combined) BCH+CCCH on TS0/C0 and BCH+CCCH+SDCCH+SACCH+CBCH on TS0/C0 SDCCH+SACCH+CBCH on TS1/C0 CBCH doesnt exist CBCH exist CBCH doesnt exist CBCH exist 1 block for BCCH 1 block for BCCH 1 block for BCCH 1 block for BCCH 9 blocks for CCCH 9 blocks for CCCH 3 blocks for CCCH 3 blocks for CCCH 8 blocks for SDDCH 7 blocks for SDDCH 4 blocks for SDDCH 3 blocks for SDDCH 1 block for CBCH 1 block for CBCHCopy Rights © LEGEND Co. 2010• Monitor the Incoming Paging Paging Groups− The MS will monitor the incoming paging in only specific times, and the rest of the time it will remain in sleeping mode.− In this way we save the MS battery and we decrease the UL interference on the system.− The MS will monitor the incoming paging when the “Paging Group” assigned for this MS is transmitted only.− The CCCH block can be used by either PCH or AGCH.− When the CCCH block is used for paging it will be called “Paging Block”− The Paging Block consists of 4 consecutive Time slots lie in 4 consecutive frames.− The Paging Block can be used to page 4/3/2 users according to IMSI or TMSI is used when paging the MS ( Length IMSI = 2 TS, Length TMSI = 1 TS)− The group of users belong to the same paging block will be called “Paging Group”Copy Rights © LEGEND Co. 2010 42
  43. 43. 5/24/2011 Frame 1 Frame 2 Frame 3 Frame 4 Frame 5 Frame 6 Frame 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 F S B B B B C F S B C F S C C F S C C F S C C F S C C I 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51 Default Mapping on TS0/C0 (BCH+CCCH) “Non Combined Mode” 51 TDMA Frames = 1 Control Multi-frameCopy Rights © LEGEND Co. 2010• Monitor the Incoming Paging Paging Groups− As appeared the MS will listen to paging in only specific times.− The MS will utilize the time between the 4 TS that lie in 4 consecutive frames to make the required measurements on the neighbor cells.Copy Rights © LEGEND Co. 2010 43
  44. 44. 5/24/2011• Monitor the Incoming Paging Paging Groups− How many Paging Groups we have? This will depend on a parameter MFRMS− MFRMS is a parameter defined per cell and it defines how frequent the paging group assigned for certain MS will be transmitted.− MFRMS takes values from 1 to 9, if MFRMS=1 then the paging group assigned for certain MS will be transmitted every 1 control Multiframes=235 msec if MFRMS=9 then the paging group assigned for certain MS will be transmitted every 9 control Multiframes = 9*235msec=2.3 seconds.− If MFRMS is large:Positive Side: The MS battery life time will increase coz the MS remains in sleeping mode for longer time + paging capacity will increase.Negative Side: Call setup time will increase coz the paging won’t be sent to the MS except when the time of its paging group came.Copy Rights © LEGEND Co. 2010• Monitor the Incoming Paging Paging Strategies− Paging Strategies are controlled by parameters in the MSC.− Setting of parameters will decide whether the paging will be local paging (within the LA) or global paging (within the MSC service area).− Setting of parameters will decide also whether paging will be done via IMSI or TMSI.− Using the parameters we can decide also how the second paging will be incase the first paging failed, ex: If 1st paging was local with TMSI then we can set the 2nd paging to be global with IMSI.Copy Rights © LEGEND Co. 2010 44
  45. 45. 5/24/2011• Related Feature to the Idle Mode Behavior Adaptive Configuration of Logical Channels (ACLC)− As we know the SDCCH channel is used for signaling i.e. call setup, while the TCH channel is used to carry real user traffic (speech/data).− As per the GSM standards, the GOS for TCH=2% i.e. within 100 calls if 2 of them are blocked then this will be acceptable, for the SDCCH/8 the GOS=0.5% and for the SDCCH/4 the GOS=1%− As we know in the default settings for frequency C0, TS0 is used to carry BCH+CCCH and TS1 used to carry SDCCH+SACCH, and TS2TS7 used to carry speech/dataCopy Rights © LEGEND Co. 2010• Related Feature to the Idle Mode Behavior Adaptive Configuration of Logical Channels (ACLC)− Now if the signaling load is high, ex: many users need to make call setup, then high blocking will occur exceeding the acceptable value = 0.5%− To solve the blocking we have 2 ways:i) Static configuration of a TCH TS to be used as SDCCH forever( Now TS1&TS2 used for SDDCH+SACCH and TS3TS7 used to carry speech/data) But in this case we lost 1 TCH channel i.e. 5 users can talk simultaneously instead of 6ii) Adaptive configuration of a TCH TS to be used as SDCCH/8 when there is high SDCCH utilization only( Now TS1&TS2 used for SDDCH+SACCH and TS3TS7 used to carry speech/data, but when the utilization is back to its normal trend, TS2 will be configured back automatically as a TCH and used to carry speech/data)Copy Rights © LEGEND Co. 2010 45
  46. 46. 5/24/2011• Related Feature to the Idle Mode Behavior Adaptive Configuration of Logical Channels (ACLC) Main Controlling Parameters:ACSTATE: Activates/Deactivates the feature on cell basis, values: ON/OFFSLEVEL: No. of Idle SDCCH sub-channels below which the feature will work. The conditions that should be fulfilled for the ACLC feature to work:1) ACSTATE=ON2) No. of Idle SDCCH sub-channels ≤ SLEVEL (Indication for high utilization)3) No. of already defined SDCCH channels/8 < Max. allowed configuration of SDCCHs in the cell.4) No. of Idle TCHs > 4Copy Rights © LEGEND Co. 2010• Parameters Summary SCH Parameters Parameter Name Value Range Recommended Value Unit BSIC NCC: 0 to 7 BCC: 0 to 7 ─ ─ RACH Control Parameters Parameter Name Value Range Recommended Value Unit MAXRET 1,2,4,7 4 ─ Control Channel Parameters Parameter Name Value Range Recommended Value Unit BCCHTYPE COMB COMBC NCOMB NCOMB ─ 0 to 16 (0: No SDCCH/8 SDCCH 1 ─ configured-combined mode) IMSI Attach/Detach Parameters Parameter Name Value Range Recommended Value Unit ATT Yes, No Yes ─Copy Rights © LEGEND Co. 2010 46
  47. 47. 5/24/2011• Parameters Summary Paging Parameters and Periodic Update Parameter Value Range Recommended Value Unit Name Control Channel Multi MFRMS 2 to 9 6 frame AGBLK 0 or 1 0 ─ 0 to 255 (0: infinite-No periodic T3212 40 6 minutes registeration) Cell Selection and Reselection Parameters Parameter Value Range Recommended Value Unit Name ACCMIN − 47 dBm to −110 dBm −110 dBm dBm GSM900: 13 to 43 in steps of 2 GSM900: 33 dBm CCHPWR dBm GSM1800: 4 to 30 in steps of 2 GSM1800: 30 dBm CRO 0 to 63 0 2 dB TO 0 to 7 (7:infinite) 0 10 dB PT 0 to 31 0 CRH 0 to 14 in steps of 2 dBCopy Rights © LEGEND Co. 2010Copy Rights © LEGEND Co. 2010 47
  48. 48. 5/24/2011Copy Rights © LEGEND Co. 2010• Handover (Locating) Algorithm – The Handover (Locating) Algorithm is the basic feature to provide mobility in the Radio Network. – Aims At? i) Keep the continuity of a current call with acceptable quality. ii) Cell size control in-order to decrease total interference in the system. – Implemented where? In the BSC. – Location process initiated when? After Hand Over (HO), Assignment or Immediate Assignment. – Inputs to the Algorithm? Signal Strength, Quality measurements &TA for serving cell and Signal Strength measurements for neighbor cells. – Output from the Algorithm? List of candidates which the algorithm judges to be possible candidates for HO (List of HO candidates are ranked and sorted in descending order)Copy Rights © LEGEND Co. 2010 48
  49. 49. 5/24/2011• Handover (Locating) Algorithm – What types of Handover (locating) algorithm we have? i) SS & Path Loss based Algorithm: Follows the GSM specifications. HO decision is taken based on both Signal Strength (SS) and Path Loss. ii) SS based Algorithm: HO decision is taken based on Signal Strength only and this leads to better performance. It is less complex, uses less parameters and easy to be maintained in the Radio Network.Copy Rights © LEGEND Co. 2010• Handover (Locating) Algorithm – The main Flow of the Handover (locating) Algorithm goes as follow: Initiations Filtering Basic Urgency Conditions Ranking Handling Auxiliary Radio Network Features Evaluation Organizing the List Sending the List & Allocation ReplyCopy Rights © LEGEND Co. 2010 49
  50. 50. 5/24/2011 • Handover (Locating) Algorithm – Initiation – Filtering. – Basic Ranking. – Urgency Conditions Handling. – Auxiliary Radio Network Features Evaluation. – Organizing the List. – Sending the List & Allocation ReplyCopy Rights © LEGEND Co. 2010• Initiation of the Handover (Locating) Process/Algorithm  The Locating Process is initiated when one of the following occurs: 1. Handover: Normal, Intra Cell HO (IHO), Sub-cell change (OLUL or ULOL) 2. Assignment: Allocation of TCH channel after completing call setup on SDCCH. 3. Immediate assignment: You are assigned SDCCH to make call setup, or a TCH to make call setup on when no free SDCCH channels exist.Copy Rights © LEGEND Co. 2010 50
  51. 51. 5/24/2011• Handover (Locating) Algorithm – Initiation – Filtering – Basic Ranking. – Urgency Conditions Handling. – Auxiliary Radio Network Features Evaluation. – Organizing the List. – Sending the List & Allocation ReplyCopy Rights © LEGEND Co. 2010• Filtering − Simply it is the process of collecting the required data on Signal Strength (SS), Quality and Time Advance (TA) for serving and neighbor cells and average these consecutive measurements over a specified period to rank these cells. − This is accomplished in two steps: 1. Measurements preparation 2. SS, Quality and TA filteringCopy Rights © LEGEND Co. 2010 51
  52. 52. 5/24/2011• Filtering1. Measurements preparation− Data that is measured: Cell on which measurements Who makes the Measured Quantity are reported measurements? SS DL MS Quality DL (rxqual_DL) MS Serving Cell Quality UL (rxqual_UL) BTS TA BTS 6 Strongest neighbor cells SS DL MS− The MS can measure the SS of up to 32 neighbor frequencies but only the six strongest neighbors (which it succeeded to decode its BSIC over the last 10 seconds) are reported and considered candidates for HO.Copy Rights © LEGEND Co. 2010• Filtering1. Measurements Preparation− SS measurements are delivered as integer values 0  63 corresponds to real SS from -110 dBm  - 47 dBm− Quality is measured based on the BER and it may be represented in two forms:i) Integers 0 (Best)  7 (Worst)ii) Decitransformed Quality units (dtqu) from 0 (Best)  70 (Worst)− Time Advance (TA) is reported as values between 0  63 bit period.N.B: If TA=1 then the MS is at nearly 0.5 km from the cellCopy Rights © LEGEND Co. 2010 52
  53. 53. 5/24/2011• Filtering2. SS, Quality and TA filtering:− The consecutive measurements for SS, Quality and TA are averaged in some way based on the equation of the filter used.− We’ve 5 Types of Filters that may be used, each one has its own equation or its way to produce output results from the collected consecutive measurements:A. General FIR filters (Finite Impulse response)B. Recursive Straight Average filterC. Recursive exponential filterD. Recursive 1st order Butterworth filterE. Median filterCopy Rights © LEGEND Co. 2010• Filtering2. SS, Quality and TA filtering:− In addition to the way each filter use to produce output results from the consecutive measurements, each filter has what we call filter length which is the period over which measurements are considered.− We have controlling parameters on cell basis to select the type of filter used and the length of the filter.− Also the type of the filter used in signaling (call setup) and dedicated phases may be configured separately as we’ll see.Copy Rights © LEGEND Co. 2010 53
  54. 54. 5/24/2011• Handover (Locating) Algorithm – Initiation – Filtering – Basic Ranking – Urgency Conditions Handling. – Auxiliary Radio Network Features Evaluation. – Organizing the List. – Sending the List & Allocation ReplyCopy Rights © LEGEND Co. 2010• Basic Ranking− It is called “Basic” coz in this stage ranking is done before handling the urgency conditions and evaluation of the auxiliary radio network features.− As mentioned earlier, two algorithms are available for basic ranking (SS&Path loss based Algorithm and SS based Algorithm) and they’re selected according to the parameter EVALTYPE− EVALTYPE=1, SS & Path loss based Algorithm is used for basic ranking taking into consideration both Signal Strength measurements and the path loss.− EVALTYPE=3, SS based Algorithm is used for basic ranking taking into consideration Signal Strength measurements only.Copy Rights © LEGEND Co. 2010 54
  55. 55. 5/24/2011• Basic RankingBasic Ranking Algorithm following the SS based Algorithm will be done on four steps:A. Correction of Base Station output power. Common forB. Evaluation of the minimum signal strength condition for neighbors. BothC. Subtraction of signal strength penalties. AlgorithmsD. Rank the Candidates after applying Offsets and Hysteresis.Copy Rights © LEGEND Co. 2010• Basic RankingBasic Ranking Algorithm following the SS based AlgorithmA. Correction of Base Station output power The location algorithm aims at making the Pure traffic frequencies to control the cell borders and not the BCCH frequencies, coz most of the time the seized TCH Time slot will be located on a TCH frequency. BSPWR is a parameter to set the output power of the BCCH carrier and BSTXPWR is a parameter to set the output power of the TCH frequencies. Correction for the output power will done for both:(A-i) Correction for Neighbor Cells.(A-ii) Correction for Serving Cell.Copy Rights © LEGEND Co. 2010 55
  56. 56. 5/24/2011 • Basic Ranking Basic Ranking Algorithm following the SS based Algorithm A. Correction of Base Station output power (A-i) Correction for Neighbor Cells − The MS is informed by the BCCH frequencies of the neighbors cells on which he has to perform his measurements via the Active BA list. − SS_corrected_DLneighbor = SS_measured_DLneighbor - ( BSPWR - BSTXPWR )Copy Rights © LEGEND Co. 2010• Basic RankingBasic Ranking Algorithm following the SS based AlgorithmA. Correction of Base Station output power(A-ii) Correction for Serving Cell1) TCH Time Slot (TS) is on the BCCH frequencySS_corrected_DLservingcell = SS_measured_DLservingcell - ( BSPWR - BSTXPWR )2) TCH TS is hopping between a BCCH frequency and a TCH frequency:SS_corrected_DLservingcell = SS_measured_DLservingcell - ( BSPWR - BSTXPWR )/N ,Where N is the no. of the hopping frequencies3) TCH TS is on the OL (Over Laid sub cell)SS_corrected_DLUnderLaid = SS_measured_DLOverLaid+ ( BSTXPWR Under Laid – BSTXPWROverLaid )Copy Rights © LEGEND Co. 2010 56
  57. 57. 5/24/2011• Basic RankingBasic Ranking Algorithm following the SS based AlgorithmB. Evaluation of the minimum Signal Strength condition for Neighbors− Not all the neighbors are allowed to be ranked!!− The neighbor should pass the minimum signal strength condition in order to be ranked.− SS_corrected_DLneighbor will be compared with respect to parameter called MSRXMIN,If SS_corrected_DLneighbor ≥ MSRXMIN  this neighbor will be included in rankingIf SS_corrected_DLneighbor < MSRXMIN  this neighbor will be excluded from ranking− If UL measurements are included then SS_corrected_ULneighbor will be compared with respect to parameter called BSRXMIN,If SS_corrected_ULneighbor ≥ BSRXMIN  this neighbor will be included in rankingIf SS_corrected_ULneighbor < BSRXMIN  this neighbor will be excluded from rankingCopy Rights © LEGEND Co. 2010• Basic RankingBasic Ranking Algorithm following the SS based AlgorithmB. Evaluation of the minimum Signal Strength condition for Neighbors− Example: Assume that a MS is connected to cell A that has five neighbors B,C,D,E&F, the MSRXMIN for all the cells is -104 dBm and the SS_corrected_DLneighbor for each cell after correcting the BTS o/p power is given in the below Table Neighbors SS_corrected_DLneighbor B -85 dBm C -110 dBm  Cell C will be excluded from ranking and won‟t be D -87 dBm considered in the next stage E -70 dBm and the MS will never HO to it F -100 dBmCopy Rights © LEGEND Co. 2010 57
  58. 58. 5/24/2011 • Basic Ranking Basic Ranking Algorithm following the SS based Algorithm C. Subtraction of signal strength penalties − Penalties or Punishments will be applied on cells that are for some reasons temporarily undesirable. − A Penalty value will decrease the rank of some cells for certain penalty time. − SS_punished_DL = SS_corrected_DL – Locating Penalties – HCS Penalties − In the coming slides we’ll talk about the two types of penalties: (C-i) Locating Penalties (C-ii) HCS PenaltiesCopy Rights © LEGEND Co. 2010• Basic RankingBasic Ranking Algorithm following the SS based AlgorithmC. Subtraction of signal strength penalties(C-i) Locating Penalties1) Due to HO failure: If HO to a neighbor cell failed then we’ve to apply a penalty value for some time on this neighbor so when basic ranking is done again we don’t go back to this cell. Penalty value will be configured using parameter PSSHF (default 63 dB) Penalty time will be configured using parameter PTIMHF (default 5 sec)Copy Rights © LEGEND Co. 2010 58
  59. 59. 5/24/2011• Basic RankingBasic Ranking Algorithm following the SS based AlgorithmC. Subtraction of signal strength penalties(C-i) Locating Penalties2) Due to Bad Quality (BQ) Urgency HO: If a cell was abandon due to BQ, then it should have been the best cell from SS point of view so without penalties using the basic ranking we’ll be back to this cell. Penalty value will be configured using parameter PSSBQ (default 7 dB) Penalty time will be configured using parameter PTIMBQ (default 5 seconds)3) Due to Excessive TA Urgency HO: Handled in the same manner like the BQ case. Penalty value will be configured using parameter PSSTA (default 63 dB) Penalty time will be configured using parameter PTIMTA (default 30 seconds)Copy Rights © LEGEND Co. 2010• Basic RankingBasic Ranking Algorithm following the SS based AlgorithmC. Subtraction of signal strength penalties(C-ii) HCS Penalties− It is related to the HCS (Hierarchical Cell Structure) feature when a MS is detected as a fast moving mobile (If fast moving mobile feature is activated)− A penalty will be applied on lower layer cells so in ranking we will prioritize cells in the same layer of the serving cell and cells in higher layers and in this way unnecessary HO’s are prevented ( ex: layer2 cells will be prioritized than layer1 cells)Copy Rights © LEGEND Co. 2010 59
  60. 60. 5/24/2011• Basic RankingBasic Ranking Algorithm following the SS based AlgorithmD. Rank the Candidates after applying Offsets and Hysteresis− Ranking for neighbor cells will be done afterapplying Offsets and Hysteresis.– Offset: Displace the cell border as compared to The border strictly given by SS.Controlling parameter: OFFSET (default: zero dB)– Hysteresis: To reduce the risk of ping pong HO a region for Hysteresis is applied around the cell border.Copy Rights © LEGEND Co. 2010• Basic RankingBasic Ranking Algorithm following the SS based AlgorithmD. Rank the Candidates after applying Offsets and Hysteresis− If the Hysteresis value is too high there will be a risk that the MS will be connected to the cell of low SS for long time and if the Hysteresis is too low then there will be a risk that ping pong HO’s occur.− So the applied value of Hysteresis will be variable based on the received SS of the serving cell.− SS_corrected_DLservingcell will be compared to value HYSTSEP (default -90 dBm), If SS_corrected_DLservingcell > HYSTSEP, then the serving cell is strong enough and high value of Hysteresis will be applied such that Hysteresis value=HIHYST (default 5 dB) If SS_corrected_DLservingcell < HYSTSEP, then the serving cell is not strong enough and low value of Hysteresis will be applied such that Hysteresis value=LOHYST (default 3 dB)Copy Rights © LEGEND Co. 2010 60
  61. 61. 5/24/2011• Basic RankingBasic Ranking Algorithm following the SS based AlgorithmD. Rank the Candidates after applying Offsets and Hysteresis N SS_corrected_DLservingcell > HYSTSEPo HYST=LOHY ST Yes HYST=HIHYST Output from Basic RankingNow, Rankservingcell = SS_corrected_DLservingcell Rankneighbor= SS_punished_DLneighbor – OFFSETneighbor – HYSTneighborCopy Rights © LEGEND Co. 2010 • Handover (Locating) Algorithm – Initiation – Filtering – Basic Ranking – Urgency Conditions Handling – Auxiliary Radio Network Features Evaluation. – Organizing the List. – Sending the List & Allocation ReplyCopy Rights © LEGEND Co. 2010 61
  62. 62. 5/24/2011 • Urgency Conditions Handling − After the Basic Ranking stage a check is made on the serving cell to know if Urgency conditions are detected or not. − We have two types of Urgency HO: 1. Bad Quality (BQ) Urgency HO 2. Excessive Time Advance (TA) Urgency HO − If Urgency conditions are detected then the serving cell should be abandon as fast as possible, but some of the neighbors will be removed from the candidate list and the MS will not be able to HO to them as we will see later. − As seen before, cells that were abandon due to Urgency HO will be subjected to punishment/penalty.Copy Rights © LEGEND Co. 2010• Urgency Conditions Handling1. Bad Quality (BQ) Urgency HO− The Quality measured at the DL and UL for the serving cell will be compared with two parameters QLIMDL & QLIMUL (default 50 dtqu) and if: Or  Urgency HO due to BQ should be rxqual_DL > QLIMDLperformed rxqual_UL > QLIMUL− The Quality may drop like that as a result of Co-Channel Interference or when the SS became very low.− When Urgency condition is detected the MS has to leave the cell and make HO to other cell, but in this case the serving cell is the one that has the highest SS so the MS has to HO to a cell of worse SS, but is the MS allowed to HO to any worse cell?Copy Rights © LEGEND Co. 2010 62
  63. 63. 5/24/2011• Urgency Conditions Handling1. Bad Quality (BQ) Urgency HO− Is the MS allowed to HO to any worse cell? No, this will be based on a parameter called BQOFFSET which will ensure that far neighbors won’t be selected.− If Rankservingcell – Rankneighbor ≤ BQOFFSET+HYST, then this neighbor is near to the serving cell and it is not much worse than the serving cell and it can be candidate for HO.− If Rankservingcell – Rankneighbor > BQOFFSET+HYST, then this neighbor is far from the serving cell and it will be removed from the candidate list.− Ex: If Urgency condition is detected where Rankservingcell = -75 dBm and the neighbors: RankB = -79 dBm ,RankC = -90 dBm ,RankD = -87 dBm and BQOFFSET=5dB,HYST=0 dBRankservingcell – RankB =4dB<BQOFFSET= 5dB Cell B is kept in the candidate listRankservingcell –RankC=15dB>BQOFFSET= 5dB Cell C is removed from the candidate listRankservingcell – RankD = 8dB > BQOFFSET=5dB  Cell D is removed from the candidate listCopy Rights © LEGEND Co. 2010• Urgency Conditions Handling2. Excessive Time Advance (TA) Urgency HO− TA can be used as a measure for the distance between the BTS and the MS.− If TA > TALIM (63 bit period)  Urgency HO due to TA is initiated.Copy Rights © LEGEND Co. 2010 63
  64. 64. 5/24/2011 • After Basic Ranking and Evaluation of the Urgency Conditions, the Serving cell and Neighbor cells will be divided into 3 Groups Better Cell Categorization #1 Serving Cell Worse CellCopy Rights © LEGEND Co. 2010• Handover (Locating) Algorithm – Initiation – Filtering – Basic Ranking – Urgency Conditions Handling – Auxiliary Radio Network Features Evaluation – Organizing the List. – Sending the List & Allocation ReplyCopy Rights © LEGEND Co. 2010 64
  65. 65. 5/24/2011• Auxiliary Radio Network Features Evaluation1. Assignment to Another Cell Evaluation2. Cell Load Sharing Evaluation3. Over Laid/Under Laid sub-cell Evaluation4. IHO Evaluation5. HCS Evaluation After these Evaluations, some candidates will be removed from the HO candidate list and Categorization#2 will be performed.Copy Rights © LEGEND Co. 2010• Auxiliary Radio Network Features Evaluation1. Assignment to Another Cell Evaluation− The Locating Algorithm may be initiated after immediate assignment to know whether it is better for the MS to take a TCH time slot on the current cell or not.− If during the signaling phase a better cell was found after ranking, then “Assignment to Better Cell” will be initiated.− If during the signaling phase no better cell was found, then the MS will normally be assigned a TCH time slot on the current cell.− If the Better/Serving cells were congested then “Assignment to Worse Cell” will be initiated if possible.Copy Rights © LEGEND Co. 2010 65
  66. 66. 5/24/2011• Auxiliary Radio Network Features Evaluation1. Assignment to Another Cell Evaluation− Is the MS allowed to take TCH time slot on any worse cell? No, this will be based on a parameter called AWOFFSET which will ensure that far neighbors won’t be selected.− Only if Rankservingcell – Rankneighbor ≤ AWOFFSET+HYST, then this neighbor is near to the serving cell and it is not much worse than the serving cell and assignment to it can be done.− If Rankservingcell – Rankneighbor > AWOFFSET+HYST, then this neighbor is far from the serving cell and it will be removed from the candidate list. Copy Rights © LEGEND Co. 2010• Auxiliary Radio Network Features Evaluation2. Cell Load Sharing (CLS) Evaluation− This feature is used to reduce congestion on the serving cell.− When CLS is activated and the load on the serving cell becomes higher than certain threshold then:i) Valid CLS HO candidates are definedii) Re-calculation of their ranking values will be performed. Copy Rights © LEGEND Co. 2010 66
  67. 67. 5/24/2011• Auxiliary Radio Network Features Evaluation2. Cell Load Sharing (CLS) Evaluationi) Valid CLS HO candidates are defined as follow:− Load on neighbor cells < CLS load threshold− Internal cells: lies in the same BSC− Same Layerii. Re-calculation of their ranking values will be performed− We’re going to recalculate the Ranking values of the valid CLS neighbors with reduced Hysteresis so these worse neighbors will appear with higher SS than they really are and the MS can make HO to them and relief the congestion on the current cell. This feature will be discussed in details afterwards. Copy Rights © LEGEND Co. 2010• Auxiliary Radio Network Features Evaluation3. OL/UL Sub-Cell Evaluation− The OL/UL feature provides a way of increasing the traffic capacity in a cellular network without building new sites.− Since OL subcell serves smaller area than the corresponding UL subcell a smaller reuse distance can be used in in the OL subcell than in the under laid.− The OL/UL evaluation may result in a recommendation to change the subcell from the one currently in use, this evaluation is based on: DL SS, TA serving Cell, Distance to cell border, Traffic Load in the cell This feature will be discussed in details afterwards. Copy Rights © LEGEND Co. 2010 67
  68. 68. 5/24/2011• Auxiliary Radio Network Features Evaluation4. Intra Cell HO (IHO) Evaluation− The IHO feature provides a way to improve the speech quality during the conservation when bad quality is detected while the SS is high.− This is can be accomplished by changing the channel the connection is currently using within the same cell. This feature will be discussed in details afterwards.Copy Rights © LEGEND Co. 2010• Auxiliary Radio Network Features Evaluation5. Hierarchical Cell Structure (HCS) Evaluation− The HCS feature provides the possibility to give priority to cells that are not strongest but provide sufficient SS.− The priority of a cell is given by associating a layer to the cell.− We have 8 layers from layer 1 (Highly prioritized) to layer 8 (least prioritized).− Micro cells are prioritized than Macro cells for capacity purposes.− Cells of lower layers will be ranked higher than cells of higher layers in the HO candidate list. This feature will be discussed in details afterwards.Copy Rights © LEGEND Co. 2010 68
  69. 69. 5/24/2011 • After the Auxiliary Radio Network features evaluation some candidates may be prioritized and the order of the candidate list will be modified. The Serving cell and Neighbor cells will be divided into 3 Groups Above S Serving Cell Categorization #2 (SC) Below SCopy Rights © LEGEND Co. 2010• Handover (Locating) Algorithm – Initiation – Filtering – Basic Ranking – Urgency Conditions Handling – Auxiliary Radio Network Features Evaluation – Organizing the List – Sending the List & Allocation ReplyCopy Rights © LEGEND Co. 2010 69
  70. 70. 5/24/2011• Organizing the List− The final list will contain maximum up to six neighbors + the serving cell and categorized as follows: Serving Cell (SC), Above S, Below S− To reach the final form before sending the list the following steps will be done:A. Removal of CandidatesB. Ordering the Candidate list based on the Current Conditions.Copy Rights © LEGEND Co. 2010• Organizing the ListA. Removal of Candidates Some Candidates may be removed coz:− Some Controlling timers are active and preventing HO to certain cell:TALLOC: This timer prevents HO on a target cell for some time after assignment/HO failure due to congestion on target cell. (N.B: No penalties are applied on this cell)TURGEN: This timer prevents HO on a target cell for some time after urgency HO failure due to congestion on target cell. (N.B: No penalties are applied on this cell)N.B: TALLOC and TURGEN are BSC parameters (Default Values= 2 SACCH periodsCopy Rights © LEGEND Co. 2010 70
  71. 71. 5/24/2011• Organizing the ListB. Ordering the Candidate list based on the Current Conditions− Means what? Means in what order the 3 categories (Above S, S, Below S) will be arranged before sending the candidate list. This will be based on some condition flags.− Condition flags: 1  Assignment Request Arrived 2  Assignment to Worst Cell is in use 3  Excessive TA detected 4  BQ Urgency HO 5  OL/UL Subcell load change or IHOCopy Rights © LEGEND Co. 2010• Organizing the ListB. Ordering the Candidate list based on the Current ConditionsCondition flags: 1  Assignment Request Arrived 2  Assignment to Worse Cell is in use 3  Excessive TA detected 4  BQ Urgency HO 5  OL/UL Subcell load change or IHO Condition Flags Case Ordering Comment 1 2 3 4 5 1 0 x 0 0 0 Above S Normal Case Serving Cell has BQ so it should be abandon 2 0 x 0 1 0 Above S Below S either to the Above S or Below S cell An Assignment request came and the AW flag is 3 1 0 0 0 0 Above S S not raised An Assignment request came and the AW flag is 4 1 1 0 0 0 Above S S Below S raised Serving Cell has BQ so it should be abandon but coz the OL/UL subcell change flag is raised, then 5 0 x 0 1 1 Above S S Below S the serving cell is included coz this subcell change may solve the issue with no need to go for a below worse cellCopy Rights © LEGEND Co. 2010 71

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