e Gprs Explain

(E)GPRS BSS Network Planning and OptimizationMain topics
Provide information for data network dimensioning and dimensioning process
Concepts
Network Audit
Network Dimensioning and Planning
Coverage and capacity planning
Gb
SW and HW Releases
This material describes the Nokia (E)GPRS System with the following SW and HW releases:
BSS SW:
Procedures
SGSN
GGSN
Charging & statistics
Border Gateway
Enables GPRS roaming
Domain Name Server
Makes IP network configuration easier
In GPRS backbone SGSN uses DNS to get GGSN and SGSN IP addresses
Two DNS servers in the backbone to provide redundancy
Legal Interception Gateway
Chasing criminal activity
LI is required when launching the GPRS service
Mobility Management = Attach & Detach, RAU, Authentication & Ciphering, Paging, P-TMSI
Session Management = PDP context activation, deactivation and modification
Company Confidential
Signaling Interface
(E)GPRS Interfaces
Signaling Interface
Class B Packet and Speech (not at same time)
(Automatically switches between GPRS and speech modes)
Class A Packet and Speech at the same time
(DTM is subset of class A)
(E)GPRS Mobile Terminal Classes
GPRS MS CLASS
The purpose of the definition of the GPRS MS Classes is to enable the different needs of the various market segments to be satisfied by a number of MS types with distinct capabilities.
CLASS A:
CLASS B:
Simultaneous traffic shall is not supported. The mobile user can make and/or receive calls on either of the two services sequentially but not simultaneously. The selection of the appropriate service is performed automatically, i.e. an active GPRS virtual connection is put on hold, if the user accepts an incoming circuit switched call or establishes an outgoing circuit switched call.
CLASS C
Supports only non-simultaneous attach. Alternate use only. If both services (GPRS and Circuit Switched) are supported then a Class C MS can make and/or receive calls only from the manually or default selected service, i.e., either GPRS or Circuit Switched service. The status of the service which has not been selected is detached i.e., not reachable.
Multislot Classes 1-12
- Max 4 DL or 4 UL TSL (not at same time)
- Up to 5 TSL shared between UL and DL
- Minimum 1 TSL for F Change
- 2-4 TSL F Change used when idle measurements required
Multislot Classes 19-29
(not required at same time)
0-3 TSL F Change
Multislot Classes 30-45 (Rel-5)
Type 2
DL
UL
DL
UL
1 TSL for Measurement
GPRS territory is required in BTS
Packet Control Units (PCUs) need to be implemented in BSCs
Gb interface dimensioning
If CS3&CS4 will be implemented following units/items are required
PCU2 with S11.5 BSC SW
Dynamic Abis Pool (DAP)
EGPRS Implementation
Can be introduced incrementally to the network where the demand is
EGPRS capable MS
Dynamic Abis
GMSK coverage
8-PSK coverage
EDGE capable TRX,
EDGE functionality in the network elements
EDGE will provide the solution for operators wanting to offer personal multimedia services early and who need to increase the data capacity in their GSM network.
EDGE will not replace existing investments or services but will upgrade them to a highly competitive level through gradual investment.
EDGE rollout can satisfy increased data demand and produce increased revenues by first launching an EDGE service in urban and office environments for business users and then providing wider area coverage as private usage takes off.
EDGE offers data services comparable to 3rd generation prior to UMTS deployment. EDGE is especially valuable for operators that do not deploy UMTS.
Multiplexer/demultiplexer for different network layer entities onto LLC layer
Compression of protocol control information (e.g. TCP/IP header)
Compression of data content (if used)
Segmentation/de-segmentation of data to/from LLC layer
LLC
SNDCP
IP
TCP/UDP
APP
RLC
MAC
LLC
SNDCP
IP
TCP/UDP
APP
RLC
MAC
Independent of underlying radio interface protocols
Control
Address
FCS
Information
LLC Reliability – HLR QoS Profile
In practice only reliability classes 2 and 3 work today properly from the end user satisfaction perspective and can thus be commercially used.
There are some terminals in the market that can not support the usage of reliability class 2.
SDU error ratio:
RLC
Segmentation/de-segmentation of data from/to LLC layer
MAC
Flagging of PDTCH/PACCH occupancy
USF - Uplink State Flag
TFI - Temporary Flow Indicator
BSN - Block Sequence Number
FBI - Final Block Indicator
TFI - Temporary Flow Indicator = TBF ID.
BSN - Block Sequence Number = RLC block ID within TBF
TLLI - Temporary Logical Link Identifier = type of mobile ID
Countdown value - used to calculate number of RLC blocks remaining
10332.bin
LLC frames are segmented into RLC Data Blocks
In the RLC/MAC layer, a selective ARQ protocol provides retransmission of erroneous RLC Data Blocks
When a complete LLC frame is successfully transferred across the RLC layer, it is forwarded to the LLC layer.
1 TDMA frame = 4.615 ms
= BURST PERIOD
RLC/MAC Blocks
TDMA Bursts
RLC Blocks
4 x TDMA Frames = 4 Bursts = 1 Radio block = 18.46 ms = 1-2 RLC block(s)
Note: Amount of RLC blocks per radio block depends on used (modulation) coding scheme (M)CS
12 x RLC/MAC Blocks = 1 x 52 PDCH MultiFrame = 240 ms
12 RLC/MAC Blocks / 0.240 s = 50 RLC/MAC Blocks / s
7
7
7
7
0
0
0
0
Two concepts :
First the graphical description of a physical channel : timeslot 0 of the first TDMA frame and timeslot 0 of the second TDMA frame are placed one after the other to indicate that they are two consecutive elements of the same Physical Channel.
Second thing is that the timeslot lasts 0,577 (=15/26 milliseconds) which corresponds to 156,25 bits. The content of the timeslot is called BURST. There are five different types of bursts, and of these, 4 are 148 bit long and one is 88 bit long.
A tentative definition of a Physical Channel is as follows:
A physical channel is defined by a TSL number, a sequence of consecutive Frame Numbers and a function associating to each FN a frequency.
Logical Channels make use of the Physical Channels available between the MS and the BTS
DOCUMENTTYPE
_935227290.doc
CCCH
PACCH
Procedures
Mobile States
GPRS attach
GPRS detach
Routing Area
Session Management
GPRS Mobility Management - Mobile States
MS location not known, subscriber is not reachable by the GPRS nw.
IDLE
READY
STANDBY
Packet TX/RX
GPRS Attach/Detach
MS location known to Routing Area level. MS is capable to being paged for point-to-point data.
MS location known to cell level. MS is transmitting or has just been transmitting. MS is capable of receiving point-to-point data.
Ask trainees about expected durationof READY and STANDBY Timers (I.e. 44 seconds and 1-2 hours)…
STANDBY timer should be 2x > Periodic RA Update Time.
In IDLE mode no GPRS Mobility Management
In STANDBY mode Routing Area Update are performed
In READY mode a Cell Update is performed when the MS changes the cell
GPRS MM is based on States
State Transition occurs when a pre-defined transaction takes place
GPRS Attach (/Detach)
The authentication is checked and the mobile location is updated
Subscriber Information is downloaded from the HLR to the SGSN
State transition Idle to Ready
Normal procedure should occur within 5 seconds each
Mobility Management before Session Management:
GPRS attach needs to happen before PDP context activation
States controlled by timers
Timer values are configurable with SGSN Parameter Handling
Ask trainees about expected durationof READY and STANDBY Timers (I.e. 44 seconds and 1-2 hours)…
STANDBY timer should be 2x > Periodic RA Update Time.
In IDLE mode no GPRS Mobility Management
In STANDBY mode Routing Area Update are performed
In READY mode a Cell Update is performed when the MS changes the cell
READY Timer default value: 44 s
MOBILE REACHABLE Timer default value: 60 min
Attach Procedure
The GPRS Attach procedure establishes a GMM context. This procedure is used for the following two purposes:
a normal GPRS Attach, performed by the MS to attach the IMSI for GPRS services only
a combined GPRS Attach, performed by the MS to attach the IMSI for GPRS and non-GPRS services
Attach procedure description
If network accepts Attach Request it sends Attach Accept
P-TMSI, RAI
If network does not accept Attach request it sends Attach Rejected
MS responds for Attach Accept message with Attach Complete (only if P-TMSI changes)
1. Attach Request
2. Identification Request
2. Identification Response
3. Identity Request
3. Identity Response
MS
BSS
6f. Update Location Ack
7a. Location Update Request
7g. Update Location Ack
7h. Location Update Accept
GPRS Detach procedure is used for the following two purposes:
a normal GPRS Detach
MS is detached either explicitly or implicitly:
Explicit detach: The network or the MS explicitly requests detach.
Implicit detach: The network detaches the MS, without notifying the MS, a configuration-dependent time after the mobile reachable timer expired, or after an irrecoverable radio error causes disconnection of the logical link
1. Detach Request
3. IMSI Detach Indication
The Routing Area Update procedure is used for the followings:
a normal Routing Area Update
a combined Routing Area Update
a periodic Routing Area Update
an IMSI Attach for non-GPRS services when the MS is IMSI-attached for GPRS services.
Routing Area (RA)
RA is served by only one SGSN
For simplicity, the LA and RA can be the same
Too big LA/RA increases the paging traffic, while too small LA/RA increases the signaling for LA/RA Update
Routing Area
Bad LA/RA border design can significantly increase the TRXSIG on LA/RA border cells causing the cell-reselection outage to be longer
LA/RA border should be moved from those areas where the normal CSW and PSW traffic is very high
PAPU 1
PAPU 4
HCPAPU 5
PAPU n
PAPU 2
PAPU 3
PAPU group
From SG1 to SG3, only one Packet Processing Unit (PAPU) could serve one specific RA.
The Large RA Support feature now allows more than one PAPU to serve one RA/NSE (Network Service Entity) by making it possible to define PAPU groups with multiple PAPUs.
Together with the High Capacity PAPU, this feature offers the operators a possibility of enhancing capacity within a certain RA or NSE as the number of subscribers increases.
PAPU capacity limited and GPRS subscribers blocked if more than 20 000 subscribers
With HCPAPU (High Capacity PAPU) max. 60 000 supported subscribers in one RA.
SGSN capacity remains the same with HCPAPU - 320000 subscribers
Routing Area Update Accept
Location update request (SDDCH)
Routing Area Update complete
First System information message
Routing Area Update Request
SECURITY FUNCTIONS AS SET BY THE OPERATOR
DL TBF ASSIGNMENT
MS
BTS
BSC
MS
BTS
BSC
Packet Uplink Ack/Nack (PACCH)
Packet Downlink Ack/Nack (PACCH)
Routing Area Update Request
DL TBF ASSIGNMENT
New SGSN sends context req to old SGSN
Old SGSN sends response and starts tunneling data to new SGSN
New SGSN sends ‘Update PDP context request’ to GGSN
New SGSN informs HLR about SGSN change by sending ‘Update location’
HLR sends ‘Cancel location’ to old SGSN.
MS
BTS
BSC
Routing Area Update Complete
Packet Uplink Ack/Nack
UL TBF ASSIGNMENT
Session Management - Establishing a PDP Context
PDP Context (Packet Data Protocol): Network level information which is used to bind a mobile station (MS) to various PDP addresses and to unbind the mobile station from these addresses after use
PDP Context Activation
Initiated by the MS
Contains QoS and routing information enabling data transfer between MS and GGSN
PDP Context Activation and Deactivation should occur within 2 seconds
PDP Context Request
155.131.33.55
QoS is like type of APNs (Access Point Names) available to the user.
PDP Context Activation - 1
Access Point Name = Reference to an external packet data network the user wants to connect to
GPRS
INFRASTRUCTURE
HLR/AuC
EIR
SGSN checks against HLR
Data
network
(Internet)
Data
network
(Internet)
4.
BSC
BTS
Um
DNS (Domain Name System) = mechanism to map logical names to IP addresses
MSC
PSTN
Network
SS7
Network
GPRS
backbone
network
GPRS
INFRASTRUCTURE
HLR/AuC
EIR
Access Point Name refers to the external network the subscriber wants to use
Data
network
(Internet)
GGSN sends "Create PDP Context Response" back to SGSN
SGSN sends “Activate PDP Context Accept“ to the MS
MSC
PSTN
Network
SS7
Network
GPRS
backbone
network
Temporary Block Flow (TBF):
Physical connection where multiple mobile stations can share one or more traffic channels – each MS has own TFI
The traffic channel is dedicated to one mobile station at a time (one mobile station is transmitting or receiving at a time)
Is a one-way session for packet data transfer between MS and BSC (PCU)
Uses either uplink or downlink but not both (except for associated signaling)
Can use one or more TSLs
Comparison with circuit-switched:
normally one connection uses both the uplink and the downlink timeslot(s) for traffic
In two-way data transfer:
uplink and downlink data are sent in separate TBFs - as below
BSC
PACCH (Packet Associated Control Channel): Similar to GSM CSW SACCH
TFI - temporary flow identity,
Network starts and releases TBFs
FBI (Final Block Indicator) indicates the last block in a DL TBF
Uplink TBF
Open-ended: an arbitrary number of octets
MS may request either close-ended or open-ended TBF
NW decides the type in PACKET UPLINK ASSIGNMENT
MS can ask network to give more resources if needed
Downlink:
Uplink:
Example: Header type 1 (header for MCS-7, MCS-8 and MCS-9)
TFI Temporary Flow Identity field. In RLC data blocks, the TFI identifies the Temporary Block Flow (TBF) to which the RLC data block belongs
RRBP Relative Reserved Block Period field.
ES/P EGPRS Supplementary/Polling Field
PR Power Reduction field
SI Stall indicator bit
Paging
Packet Polling
BTS
RACH
AGCH
PDTCH
PACCH
PACCH
PACCH
PCH
AGCH
PDTCH
PACCH
PACCH
TFI2
TFI5
TFI3
TFI2
MSs
BTS
The TFI included in the Downlink RLC Block header indicates which Mobile will open the RLC Block associated with its TBF
RLC Data Block
Packet Channel Request
UL Data
Signaling + Ack/Nack
- Faster Call Setup since no SDCCH
1) Attach
Several mobiles can share one timeslot
Maximum of 7 Mobiles are queued in the Uplink
Mobile transmissions controlled by USF (Uplink State Flag) sent on DL (dynamic allocation)
TS 1
TS 2
TS 3
Mobile with correct USF will transmit in following Uplink block
Timeslot selected to give maximum throughput
New MS
7 UL because of 3 bits for USF (8 - 1 reserved = 7)
USF = 1
USF = 2
USF = 3
USF = 3
RLC Data Block
The USF included in the Downlink RLC Block header identifies which Mobile will transmit in the following Uplink RLC Block
Not like a mux but a "tolken / round robin" scheme
(E)GPRS Explain
Power Back-off
GPRS Link Adaptation
EDAP and PCU (Resource allocation)
Gb
22,5° offset to avoid zero crossing
Time
8-PSK Modulation
8-PSK (Phase Shift Keying) has been selected as the new modulation added in EGPRS
3 bits per symbol
Symbol rate and burst length identical to those of GMSK
Non-constant envelope high requirements for linearity of the power amplifier
Because of amplifier non-linearities, a 2-4 dB power decrease back-off (BO) is typically needed, Nokia guaranteed a BO of 2 DB for BTS
3/8
Phase states transitions
to avoid zero-crossing
Why avoid zero-Xing? Zero-Xing will lead to any possible interpretation of phase state from the decoder on the receiver side, so avoiding zero-Xing it’s a way to reduce the risk of misinterpretation of the right bit combination.
Any combination from star to solid dot is possible as well as from solid dot to star. All of this combinations avoid the zero-Xing.
_948803636.doc
8-PSK Modulation – Back-off Value
Since the amplitude is changing in 8-PSK the transmitter non-linearities can be seen in the transmitted signal
These non-linearities will cause e.g. errors in reception and bandwidth spreading.
In practice it is not possible to transmit 8-PSK signal with the same power as in GMSK due to the signal must remain in the linear part of the power amplifier
The back-off value is taken into account in link budget separately for UL / DL and bands: 900/850, 1800/1900)
Too high MCA (8PSK) can lead to unsuccessful TBF establishment, if the MS is on cell border with low signal level (so the back-off is taken into account) and / or low C/I
Back-off needed due to linearity requirements.
Burst Structure
Burst structure is similar with current GMSK burst, but term 'bit' is replaced by 'symbol'
Training sequence has lower envelope variations
Seamless switchover between timeslots
In case of max output power only, back-off applied to 8-PSK
1.1.1.1 Normal burst for 8PSK
Bit Number (BN)
guard period
subclause 5.2.8
where the "tail bits" are defined as modulating bits with states as follows (bits are grouped in symbols separated by ;):
(BN0, BN1 .. BN8) = (0,1,0;1,1,1;1,1,0) and
(BN435, BN436 .. BN443) = (0,1,0;1,1,1;1,1,0)
where the "training sequence bits" are defined as modulating bits with states as given in the following table according to the training sequence code, TSC. For broadcast and common control channels, the TSC must be equal to the BCC, as defined in GSM 03.03 and as described in this technical specification in subclause 3.3.2.
Training
2. Filtered to fit GSM bandwidth.
3. Constellation after filtering: error vectors introduced.
4. Constellation after receiver Edge (equalised) filtering
1
2
3
4
GPRS Coding Schemes
GPRS provides four coding schemes: CS-1, CS-2 and with PCU2 CS-3, CS-4
PCU1 and 16 kbit/s Abis links support CS-1 and CS-2, the Dynamic Abis makes it possible to use CS-3 and CS-4
Each TBF can use either a fixed coding scheme (CS-1 or CS-2), or Link Adaptation (LA) based on BLER
Retransmitted RLC data blocks must be sent with the same coding as was used initially
CS1 & CS2 – Implemented in all Nokia BTS without HW change
CS3 & CS4 – S11.5 (with PCU2) and UltraSite BTS SW CX4.1 CD1 (Talk is supporting CS1 and CS2)
Nokia GPRS
Precoded USF: 3 6 6
1/2 ~2/3 ~3/4
interleaving
57
57
57
57
57
57
57
57
CS-4
This slide is a recall of GPRS coding scheme structure for comparing GPRS and EGPRS coding schemes on the next slides.
EGPRS has nine basic coding schemes, MCS-1...9.
In general, a higher coding scheme has higher coding rate, and consequently higher peak throughput, but it also tolerates less noise or interference.
The figure shows throughput vs. C/I of EGPRS coding schemes in TU50iFH, without incremental redundancy.
The basic unit of transmission is radio block (= 4 bursts = 20 ms on average), which contains one or two RLC blocks.
Frequency Hopping Network
In frequency hopping networks the the curves for the different MCSs are crossing each others
In non frequency hopping networks the curves are not crossing! -> Usually LA is more effective in hopping networks.
The picture is W/O IR meaning that the gain introduced by the IR is not visible here. The picture is just as an example on pattern behaviour.
Ref: TS 03.64
Code rate:
Radio block data part before coding /Radio block data part after puncturing,
e.g. for MCS-7: 468/612=0,76
Header code rate:
e.g. for MCS-9: 45/124=0,36
for MCS-4: 36/68=0,53
DOCUMENTTYPE
Family
BCS
_935227290.doc
User data
Header part, robust coding for secure transmission
Adding redundancy
Puncturing of the coded info
Header and payload is separated in EGPRS. (Those are not separated in GPRS!)
General idea of how a piece of payload information is handled when transmitted
"Additional info" consits of
Block check sequence (first step of coding procedure)
Tail bits (needed in coding)
Header part consits of
Header type
etc…
Three different up- and downlink header types for EGPRS (MCS-7, 8, 9, MCS-5, 6, MCS-1, 2, 3, 4)
coding, as shown in the figure
for MCS-9 downlink.
and tail bits.
Punctured with a selectable puncturing scheme (P1, P2 or P3).
Two separate data parts for MCS-7...9.
Header part:
Includes RLC/MAC header information and information on the coding of the data part (like used puncturing scheme).
Convolutional coding + puncturing.
FBI+E
data 1
mother code
Decreasing redundancy
Adding redundancy
Data rate:
Robust coding
for header
20 ms
USF: Uplink State Flag. Used for multiplexing several MSs on the same uplink PDCH. 3 bit field in MAC header (8 states). Coded to 12 symbols. I.e. 12 bits for GMSK, 36 bits for 8-PSK. Value '111' is for PCCCH.
FBI: Final Block Indicator (TI for uplink). Indicates that the downlink RLC data block is the last RLC data block of the downlink TBF.
E: The Extension (E) bit is used to indicate the presence of an optional octet in the RLC data block header.
HCS: Header Check Sequence. For error detection in header part, see TS 04.60 for details.
BCS: Block Check Sequence. This is added as the first step of error detection of the data part.
TB: Tail Bits. Needed for 1/3 convolutional coding.
SB: Stealing Bits. Indicates the header format. There are eight SB for 8PSK mode which allow to indicate four header formats. There are twelve SB for GMSK mode which allow to indicate two header formats: the first eight of the twelve SB indicate CS-4.
Interleaving over 2 bursts is for MCS-9 and -8. For MCS-7, these blocks are interleaved over four bursts. All the other MCSs carry one RLC block which is interleaved over four bursts. When switching to MCS-3 or MCS-6 from MCS-8, 3 or 6 padding octets, respectively, are added to the data octets.
USF
EGPRS MCS Families
The MCSs are divided into different families A, B and C
Each family has a different basic unit of payload: 37 (and 34), 28 and 22 octets respectively.
Different code rates within a family are achieved by transmitting a different number of payload units within one Radio Block.
For families A and B, 1 or 2 or 4 payload units are transmitted, for family C, only 1 or 2 payload units are transmitted
When 4 payload units are transmitted (MCS 7, MSC-8 and MCS-9), these are splitted into two separate RLC blocks (with separate sequence BSN numbers and BCS, Block Check Sequences)
The blocks are interleaved over two bursts only, for MCS-8 and MCS-9.
For MCS-7 the blocks are interleaved over four bursts
37 octets
37 octets
37 octets
37 octets
GPRS Link Adaptation (with PCU1)
The Link Adaptation (LA) algorithm selects the optimum channel coding scheme (CS-1/CS-2) for a particular RLC connection to provide the highest throughput and lowest delay available
In PCU1 the algorithm is based on detecting the occurred RLC block errors and calculating the block error rate (BLER)
The coding scheme will change based on set BLER thresholds defined in simulations and changing from hopping to non hopping networks
A new LA algorithm is introduced in BSS11.5 with PCU-2
Link Adaptation (LA)
The task of the LA algorithm is to select the optimal MCS for each radio condition to maximize RLC/MAC data rate, so the LA algorithm is used to adapt to situations where signal strength and or C/I level is low and changing slowly with time
RLC selects the data block and additionally selects the MCS depending on radio link quality and amount of available dynamic Abis channels
LA is done independently for each UL and DL TBF on RLC/MAC block level, but the LA algorithm is same for uplink and downlink
The MCS selection is not the same in case of initial transmission and retransmission (IR)
LA algorithm works differently for acknowledged mode and unacknowledged mode
RLC control blocks are transmitted with GPRS CS-1 coding
Link Adaptation
The RLC selects RLC data blocks as specified in [04.60, 9.1.3.2 Acknowledge State Array V(B) for EGPRS TBF Mode].
The following principle is used. See details from [04.60].
1) The oldest NACKED state block is selected (In BSN order)
2) If no NACKED state block exists then a new block is generated
3) If no NACKED state block exists and transmit window is stalled or there is not new data then the oldest PENDING state block is selected
Automatic Repeat reQuest (ARQ)
Forward Error Correction (FEC)
In the ARQ method the receiver detects the errors in a received RLC block and requests and receives a re-transmission of the same RLC block from the transmitter. The process continues until an uncorrupted copy reaches the destination
The FEC method adds redundant information to the re-transmitted information at the transmitter and the receiver uses the information to correct errors caused by disturbances in the radio channel
IR needs no information about link quality to in order to protect the transmitted data but can increase the throughput due to automatic adaptation to varying channel conditions and reduced sensitivity to link quality measurements
EGPRS Link Adaptation & Incremental Redundancy
Data block
Transmitter
Receiver
P2
P3
P1
P1
P1
P1
P2
P2
P3
No data recovered
Stored
The retransmission process is based on IR
LA must take into account
if IR combining is performed at the receiver
the effect of finite IR memory
EGPRS Link Adaptation & Incremental Redundancy
Modulation and Coding Schemes - MCS Selection
The link adaptation algorithm is based on Bit Error Probability (BEP) measurements performed at the MS (downlink TBF) and the BTS (uplink TBF)
In acknowledged mode, the algorithm is designed to optimize channel throughput in different radio conditions
In unacknowledged mode, the algorithm tries to keep below a specified Block Error Rate (BLER) limit
The MCS selection can be divided in four classes:
Initial MCS to be used when entering packet transfer mode
Modulation selection
MCS selection for initial transmissions of each RLC block in ACK mode
MCS to be used for re-transmissions
Modulation and Coding Schemes - MCS Selection
In DL case the MCS selection is based on EGPRS Channel Quality Report received in EGPRS PACKET DOWNLINK ACK/NACK message sent from the MS to network using PACCH to indicate the status of the downlink RLC data blocks received.
The MCS selection is based on using the BEP (Bit Error Probability) measurement data
In UL case the MCS selection is based on the respective BEP measurement values which are received within the UL PCU frames
Territory Method
Territory method is used to divide the CS and PS resources
Timeslots within a cell are dynamically divided into the CS and (E)GPRS territories
Number of consecutive traffic timeslots in (E)GPRS territory are reserved (or initially available) for (E)GPRS traffic, the remaining timeslots are available for GSM voice
The dynamic variation of the territory boundary are controlled by territory parameters
The system is able to adapt to different load levels and traffic proportions, offering an optimized performance under a variety of load conditions
The PS territory can contain dedicated, default and additional capacity
Dedicated capacity: number of timeslots are allocated to (E)GPRS on a permanent basis i.e. are always configured for (E)GPRS and cannot be used by the circuit switched traffic. This ensures that the (E)GPRS capacity is always available in a cell
Default capacity: the (E)GPRS territory is an area that always is included in the instantaneous (E)GPRS territory, provided that the current CS traffic levels permit this
Additional capacity= Additional (E)GPRS capacity means the extra time slots beyond the default capacity which are assigned due to a load demand.
Territory Method
Territory border
Cell Selection / Re-selection
The network may request measurement reports from the MS and control its cell re-selection
Depending on the NC (Network Control) mode set by the network, the MS shall behave as follows:
NC0: Normal MS control; the MS shall perform autonomous cell re-selection
NC1: MS control with measurement reports; the MS shall send measurement reports to the network and shall perform autonomous cell re-selection
NC2: Network control; the MS shall send measurement reports to the network
NC1 and NC2 only apply in MM (Mobility Management) Ready state. In MM Standby state, the MS shall always use NC0 mode independent of the ordered NC mode
A gradual introduction of EDGE capable TRXs is foreseen, which means that some BTSs will have EDGE TRXs and some others will not. The network may request measurement reports from the MS and control its cell re-selection. Depending on the NC (Network Control) mode, which is set by the network, the MS shall behave as follows:
NC0: Normal MS control. The MS shall perform autonomous cell re-selection.
NC1: MS control with measurement reports. The MS shall send measurement reports to the network. The MS shall perform autonomous cell re-selection.
NC2: Network control. The MS shall send measurement reports to the network.
NC1 and NC2 only apply in MM (Mobility Management) Ready state. In MM Standby state, the MS shall always use NC0 mode independent of the ordered NC mode.
Path loss criterion (C1)
Cell reselection criteria (C2)
These criteria are used for the cell selection for (E)GPRS in the same way as for CSW in idle mode
C31/C32 are introduced as a complement to the current GSM cell re-selection criteria
The activation requires the implementation of PBCCH
C31: Signal Strength threshold criterion
C32: Cell ranking
MS selects the cell with the highest C32 value from those having the highest priority class and fulfilling the C31 criterion (if none fulfills C31, then only C32)
The priority classes may correspond to different HCS layers
C31/C32 gives the possibility to optimise the cell re-selection for (E)GPRS without affecting the circuit switched cell re-selection behaviour. This allows more flexibility in using cell resources, allowing, for example, some cells to be packet free, should this be of interest.
The MS can make the cell re-selection also when it finds a non-serving cell that is more suitable than the serving cell. The MS selects the cell having the highest C32 value among those that have the highest priority class among those that fulfill the criterion C31 >= 0. The priority classes may correspond to different HCS layers. If none of the cells fulfills the C31>=0 criterion, the MS must select the cell having the highest C32 value.
C31 parameter
The signal strength threshold criterion (C31) for hierarchical cell structures (HCS) is used to decide whether the cell is qualified for the prioritised hierarchical cell selection. RLA - Received Link Average.
C31(s) = RLA(s) – hcsThreshold (s) (serving cell)
C31(n) = RLA(n) – hcsThreshold (n) – TO(n) * L(n) (neighbour cell)
where
TO(n) = gprsTemporaryOffset (n) * H(gprsPenaltyTime (n) – T(n))
L(n) = 0, if hcsPriorityClass (n) = PRIORITY_CLASS(s)
1, if hcsPriorityClass (n) ‡ hcsPriorityClass (s)
H(x) = 0, if x < 0
1, if x >= 0
gprsTemporaryOffset applies a negative offset to C31/C32 for the duration of gprsPenaltyTime after the timer T has started for that cell.
T is a timer implemented for each cell in the list of strongest carriers. T shall be started from zero at the time the cell is placed by the MS on the list of the strongest carriers, except when the previous serving cell is placed on the list of the strongest carriers at the cell re-selection. In this case, T shall be set to the value of PENALTY_TIME (that is, expired).
C32 parameter
The cell ranking criterion (C32) is used to select cells among those with the same priority.
C32(s) = C1(s) (serving cell)
where
gprsReselectOffset applies an offset and hysteresis value to each cell.
TO and L as in C31.
gprsReselectOffset applies an offset and hysteresis value to each cell.
NCCR (Network Controlled Cell Re-selection) (S11.5)
Enables the network to order a cell re-selection instead of the autonomous selection done by the mobile station
The network may command the MS to change cell and decides which cell is to be the target cell
Efficient allocation of EGPRS resources:
The PCU will push EGPRS capable MSs to EGPRS cells and GPRS capable MSs to non-EGPRS capable cells by power budget
Cell attractiveness can be defined neighbour cell specifically also taking into account the capabilities of each neighbour cell (e.g. CS-3/CS-4)
Can be based on the following criteria:
Power budget pushes EGPRS capable MSs to EGPRS cells and non-EGPRS capable MSs to non-EGPRS capable cells
Quality control triggers NCCR when the quality of the serving cell transmission drops even if the serving cell signal level is good
NACC (Network Assisted Cell Change) (S11.5)
Reduces service outage time when a Rel-4 capable GPRS MS moves between GSM cells in packet transfer mode
Improves both autonomous and network-controlled cell change
In a cell change the MS has to stop data transmission in the serving cell and has to acquire certain system information from the target cell
After this the MS has to restart the data transmission in the new cell
This causes a delay as the MS has to synchronise with the system information broadcast cycle and collect a consistent set of System Information and Packet System Information messages from the target cell
Outage time is reduced because the network is allowed to assist MSs before and during the cell change by
sending neighbour cell system information on the packet associated control channel (PACCH) to the MS in packet transfer mode on the serving cell
introducing the PACKET SI STATUS procedure for the cells that have no packet broadcast control channel (PBCCH)
NACC (Network Assisted Cell Change)
Neighbour cell system information messages sent to the MS contain a set of SI or PSI messages (with PBCCH) needed in performing packet access in the new cell
When all required messages are sent to the MS and PACKET SI STATUS is supported by the PCU (no PBCCH allocated) in the new cell, the MS may perform packet access and use PACKET SI STATUS procedures for the acquisition of SI messages
Without PBCCH network will send MS
SI1, SI3 and SI13 of neighbour cells
PACKET NEIGHBOUR CELL DATA (PACCH ).
With PBCCH, network will send MS
PSI TYPE 1, a consistent set of PSI TYPE 2
messages and PSI TYPE 14
In BSS 11.5 PACKET SI STATUS procedure is implemented:
This feature existed on PCCCH in S10.5 but not on CCCH
When MS is making packet access in a new cell and PACKET SI STATUS is supported in a cell, it makes the access when it has SI1, SI3 and SI13 messages.
If PACKET SI STATUS is not supported MS has to collect from the SI broadcasting cycle all the missing SI messages.
PACKET SI STATUS support information shall be broadcasted when NACC is enabled in cells, which have no PBCCH allocated and have GPRS enabled.
NACC for NC0 / NC1 - CCN Mode
A new mode, Cell Change Notification (CCN), is needed for a MS in NC0 mode in order to make use of NACC feature
MS in NC0 mode can enter CCN mode
MS must be in Transfer Mode
Both NW and the MS must support CCN
The serving and the target neighbor cell must support CCN mode
The CCN Activity support info is in:
SI13 , PSI1 and PSI14 for serving cell
SI2quater , PSI3 and PSI3bis for the neighbor cell
The support for CCN implies also that it is mandatory for the mobile station to support the Packet PSI/SI Status procedures
PSI14 is a new PSI used only for NACC feature
It is a normal PSI , but the message shall be send to MS only in PACKET NEIGHBOUR CELL DATA –message
Support of sending PSI14 message on PACCH as a plain PSI14 message, is not implemented, PBCCH in the target cell is needed.
EDAP
Abis Basic Concepts – PCM frame (E1)
One 64 kbit/s (8 bits) channel in PCM frame is called timeslot (TSL)
One 16 kbit/s (2bits) channel timeslot is Sub-TSL
PCM frame has 32 (E1) or 26 (E1) TSLs
One Radio timeslot corresponds one 16 kbit/s Sub-TSL (BCCH, TCH/F etc.) and one TRX takes two TSLs from Abis
One TRX has dedicated TRXsig of 16, 32 or 64 kbit/s
One BCF has dedicated BCFsig (16 or 64 kbit/s) for O&M
TRX1
Abis
BTS
BSC
Predefined size 1-12 PCM TSL per DAP
DAP can be shared by several TRXs in the same BCF (and same E1/T1)
Max 20 TRXs per DAP
Max 480 DAPs per BSC
DAP + TRXsig + TCHs have to be in same PCM
UL and DL EDAP use is independent
DAP schedule rounds for each active Radio Block
Different users/RTSLs can use same EDAP Sub-TSL
TRX1
TRX2
TRX3
EGPRS
pool
Master channel
Master cannel contains user data and inband signalling for TRX
Slave channel
Located in EDAP
Contains user data that does not fit in the master data frame
Dynamic Abis Pointer
DL slave frames on the same block period
UL slave frames on the next block period
EDAP
Abis PCM allocation (fixed + pool/slave)
GPRS
and
EDGE
EDGE
Higher data rates don’t fit in 16 kbit/s channels
GPRS CS-2 requires 1 slave when EDGE activated (TRX/BTS)
32, 48, 64 or 80 kbit/s Abis links per RTSL needed
Retrans.
Fixed master TSL in Abis for all EGPRS air TSL
Slave TSL’s (64 k) in EDAP pool for each air TSL
TRX and for OMU signaling fixed
TSL 0 and 31 typically used for signaling
EDAP pool dimensioning considerations
RTSL territory size
Gb link size
GPRS/EDGE traffic ratio
Packet Control Unit (PCU) - Introduction
BSC plug-in unit that controls the (E)GPRS radio resources, receives and transmits TRAU frames to the BTSs and Frame Relay packets to the SGSN
Implements both the Gb interface and RLC/MAC protocols in the BSS
Acts as the key unit in the following procedures:
(E)GPRS radio resource allocation and management
(E)GPRS radio connection establishment and management
Data transfer
PCU statistics
The first generation PCUs are optimized to meet GPRS requirements, i.e. non real time solutions (QoS classes "Background" and "Interactive“)
The second generation PCUs (PCU2) supports the real time traffic requirements and enhanced functionality (GERAN) beyond (E)GPRS
PCU types and capacity limits
The relations between PCU and BSC types as well as the connectivity limits of BTSs, TRXs, TSLs, Abis and Gb TSLs are shown below
PCU Type
BSC Types
Network elements
The 75 % utilization of the connectivity is recommended by Nokia
The number of BCSUs are limiting the max number of PCUs
Gb Interface - Introduction
The Gb interface is the interface between the BSS and the Serving GPRS Support Node (SGSN)
Allows the exchange of signaling information and user data
The following units can be found in Gb
Packet Control Unit (PCU) at the BSS side
Packet Processing Unit (PAPU) at the GPRS IP backbone side
Each PCU has its own separate Gb interface to the SGSN
BSC
PCU
BSS
SGSN
PAPU
GPRS
Gb
Gb Interface
Allow many users to be multiplexed over the same physical resource
Resources are given to a user upon activity (sending/receiving)
GPRS signaling and user data are sent in the same transmission plane and no dedicated physical resources are required to be allocated for signaling purposes
Access rates per user may vary without restriction from zero data to the maximum possible line rate (e.g., 1 984 kbit/s for the available bit rate of an E1 trunk)
BSC
PCU
BSS
SGSN
PAPU
GPRS
Gb
Gb Interface - Protocols
The Gb interface can be implemented using the Frame Relay or IP
User information transfer
L1
L2
IP
TCP/UDP
APP
Gi
Internet
Spare capacity of Ater and A interfaces is used for the Gb. The Gb timeslots are transparently through connected in the TCSM and in the MSC. If free capacity exists, it is best to multiplex all Gb traffic to the same physical link to achieve possible transmission savings. In many cases, the SGSN will be located in the MSC site, and thus the multiplexing has to take place there as well. Normal cross-connect equipment, for example, Nokia DN2 can be used for that purpose.
Any transmission network provides a point-to-point connection between the BSC and the SGSN.
Frame Relay network is used. The Gb interface allows the exchange of signalling information and user data. The Gb interface allows many users to be multiplexed over the same physical resources.
Physical layer (L1)
L1 is implemented as one or several PCM-E1 lines
Network Service (NS) layer is divided into frame relay (FR) and network service control
L1= Physical layer
NS= Provides the capability for the transmission of signals between user-network interfaces
BSSGP= Conveys routing information and QoS related information between BSS and SGSN
Gb Interface - FR
The Gb interface can be implemented using the Frame Relay or IP
The Frame Relay can be :
Point-to-point (PCU–SGSN)
any transmission network
Voice and data multiplexed
Dedicated 2 Mbit/s E1 PCM links
BSC
MSC
TC
SGSN
MUX
Gb
Gb
Gb
Voice and data multiplexed
Voice and data traffic can be multiplexed on the same transmission links that are used for GSM voice traffic on the Ater interface. At the BSC, some of the 64 kbps PCM timeslots are permanently reserved for GPRS traffic; some of them are reserved for GSM traffic. EGPRS and GSM traffic are transferred together to the digital cross-connection (for example, DN2) device residing at the MSC/SGSN site. In the digital cross-connection device, the EGPRS and GSM traffic are separated so that the EGPRS traffic is carried in dedicated E1/T1 links to the SGSN.
Voice and data separated in the transcoder
EGPRS traffic is multiplexed into the same transmission links that are used for GSM voice traffic on the Ater interface. In the transcoder, the EGPRS and GSM traffic are separated so that 64 kbps frame relay traffic timeslots are through-connected to the dedicated E1 links, which are connected to the SGSN.
Channels going through the transcoders and MSC
EGPRS traffic is multiplexed into the same transmission links that are used for GSM voice traffic on the Ater interface. In the transcoder, channels that go through the transcoder are created and the EGPRS data traffic is forwarded to the MSC switching matrix. At the MSC, the 64 kbps VCs are multiplexed into one or more ET2E cards, which are connected to the SGSN.
Traffic streams concentrated in the FR switch
To use the capacity more efficiently or cost effectively, we can concentrate the traffic streams coming from several BSCs and PCUs into one aggregate line towards the SGSN.
This concentrated traffic can be multiplexed into the same physical link that is used for GSM traffic on the Ater interface. Alternatively, it can be carried over to the SGSN site in a compatible PDN. There are several solutions that can be used to implement this method. Again, there is no single correct solution that works with each planning case. However, there are a few basic rules for the implementation and dimensioning. The data network used for transmission does not necessarily have to be a frame relay network. The frame relay traffic can be run over different kinds of networks, such as ATM. At either end of the connection, a frame relay switch or similar equipment is required for the connection to the packet data network. The switches must be able to connect to the E1/T1 link coming from the BSC with a physical interface, such as G.703, and to adapt to the PDN access point interface. In addition, the switch must be able to do the correct protocol conversion (for example, convert FR into ATM, and vice versa).
Dedicated 2 Mbit/s E1 PCM links
In this transmission option, one or more (a maximum of eight per BSC) E1/T1 PCM links per BSC are dedicated only for GPRS data traffic. If, for example, 15 or more 64 kbps Gb interfaces are required for one BSC, it is reasonable to dedicate the needed amount of 2 Mbit/s E1 interfaces only for data traffic. If, for example, 18 PCM timeslots are needed for a BSC, one E1 PCM interface of an ET2E card at the BSC and SGSN could be dedicated only for GPRS data traffic.
The increased demand for packet switched traffic transmission cost efficiency can be met by deploying IP in the transmission network
IP offers an alternative way to configure the subnetwork of the Gb interface:
the subnetwork is IP-based and the physical layer is Ethernet
The introduction of IP makes it possible to build an efficient transport network for the IP based multimedia services of the future
Both the IPv6 and IPv4 protocol versions are supported
IP transport can be used in parallel with FR under the same BSC and BCSU
Within one BCSU, separate PCUs can use different transmission media
Gb Interface - IP
Gb over IP is an application software product and requires a valid license in the BSC
The licensing is based on the number of PCUs to which IP Network Service Entities can be configured
Requires support from both BSC and SGSN
In the BSC, the capacity of the Gb interface remains the same, regardless of whether IP or FR is used as the transport technology
BTS
SGSN
Gb
IP
BTS
BSC
FR
GSM Coverage / Interference Audit
Network Audit - Introduction
Before (E)GPRS implementation a full network audit is proposed to clarify the network status
The audit helps to avoid HW, SW and feature interoperability issues
The audit should preferably contain the following areas:
BSS HW audit
(E)GPRS capability of BTSs (BTS SW support)
TALK roadmap does not have CS3-4 capability currently
Baseband unit limits in UltraSite
CS1-4 requires Ultra/Metrosite BTS SW CX4.1 CD1 or CX(M)4.1 CD1
TRX capability (mixture of GPRS and EGPRS TRXs)
TALKFAMILY TRXs are GPRS capable only.
UltraSite and MetroSite TRX capability
BSS SW/feature audit contains:
MultiBCF and Common BCCH
EPCR (EGPRS Packet Channel Request)
NACC (Network Assisted Cell Change)
NCCR (Network Controlled Cell Re-selection)
DFCA
QoS
CS3-4
PBCCH:
Advantage
Separation of CSW and PSW signaling
If the TRXSIG is overloaded, a possible way of reduction is to separate PSW signaling from CSW signaling, so the PSW signaling is not loading TRXSIG any more.
Separation of CSW and PSW users from neighboring point of view.
PSW and CSW users can have their own neighbor relations, so the PSW traffic can be pushed to the required cell
Disadvantage
The PBCCH capable terminals’ penetration might not high enough.
In case of PBCCH implementation the PSW signaling is conveyed on PBCCH only. The non PBCCH capable (E)GPRS terminals are not able to read PBCCH so they will exclude from the PSW data services.
One TCH is occupied by PBCCH
Less capacity is available for user traffic.
PBCCH is not available from S11.5 PCU2.
NMOI:
In Network Mode of Operation I the core network provides CS paging co-ordination so that CS paging requests to GPRS-attached MSs are sent to the PCU via the SGSN
MS is in packet transfer mode: the PCU provides CS paging on PACCH
MS is in packet idle mode: it is paged for CS calls on the PCH
The mobiles need to monitor only one paging channel
Disadvantage
Minimum one dedicated timeslot is a must with NMO1 to guarantee that GPRS attached subscribers can be paged and their routing updates will be received by network
If signaling and traffic channels are congested in PSW territory, no paging nor RA/LA updates will go through and mobile is “lost” by network
EPCR
EGPRS Packet Channel Request on CCCH enables to speed up the uplink TBF establishment with one phase access
The MS provides information about its EGPRS capabilities already while requesting TBF establishment from the BSC (earlier in two phases)
Always on from BSS 11 onwards and supported by MS Rel’99 onwards
NACC
Network-Assisted Cell Change minimises the service outage in cell re-selection
Target cell system information data sets are sent from the serving cell to the MS before cell re-selection is started
DFCA
Dynamic Frequency and Channel Allocation uses interference estimations derived from mobile station (MS) downlink measurements
The algorithm selects a frequency hopping radio channel for a connection based on the C/I ratio criteria
It ensures good C/I for the connection to meet the QoS requirements
(E)GPRS capable timeslots cannot be placed on DFCA capable TRXs
QoS
Priority Class Based Quality of Service functionality gives a possibility to differentiate TBFs by delay, throughput, and priority
Based on a combination of the GPRS Delay class and GPRS Precedence class values
Packets will be evenly scattered within the territory between different time slots, then packets with a higher priority are sent before packets that have a lower priority
QoS is an operating software in the BSC and always active in an active PCU
The subscriber priority is defined in the HLR once the feature is taken into use
GPRS CS3-4
CS3 and CS4 offer data rates of 14.4 and 20.0 kbps per timeslot
Requires PCU2 with Dynamic Abis
GSM Network Audit– Coverage & Interference
The coverage and interference must be analyzed because the TSL data rate is defined by coverage and interference as well
The average signal level of a cell/segment must be estimated for calculating the TSL data rate based on sensitivity
The following methods can be used in the analysis:
Planning tool plots
Drive test measurements
Coverage and Interference Planning
Dimensioning Example
Mobility Planning
Frequency Planning
The (E)GPRS coverage area depends on the GSM service area
The coverage planning aspects concern the provision of sufficient C/N ratios across the coverage area to allow for successful data transmission (UL/DL)
Each coding scheme is suited to a particular range of C/N (or Eb/No) for a given block error rate (BLER)
The higher the level of error protection, the lower required C/N
Due to the different C/N requirements the relative coverage area of the coding schemes is different:
The MCS-5 coverage is approx 50% of MCS-1, while MCS-8 coverage is approx 40% of MCS-5
In urban areas coverage is not usually the limiting factor but the interference caused by reused frequencies -> C/I requirements
(E)GPRS Coverage Relative to MCS-5 (Noise limited)
2.5
2
1.5
1
0.5
0
Receiving End
Antenna gain
Transmitting End
Output power
Tx Antenna gain
Standard deviation
SENSITIVITY
Where
T = temperature (290 K)
B = bandwidth (271 kHz)
1,1*10-15 W = -119,6 dBm
The required signal strength (sensitivity) can be calculated if Noise spectral density, Es/No requirement and receiver noise figures are known:
For MCS5 for example, where Es/No is 15 dB and if NFreceiver = 2.9 dB (900MHz):
S = -119,6 dBm + 15 dB + 2.9 dB = -101.7 dBm
For MCS5 for example, where Es/No is 15 dB and if NFreceiver = 2.4 dB (1800MHz):
S = -119,6 dBm + 15 dB + 2.4 dB = -101.2 dBm
REQUIRED SIGNAL STRENGTH
Signal-to-noise levels in digitally modulated systems are commonly expressed in terms of Eb/No, Es/No or C/N
Eb/No is the available bit energy (received power x bit duration) divided by noise spectral density (-174 dBm/Hz)
Es/No is the equivalent for the symbol case (1 bit = 1 symbol in GMSK, 3 bits = 1 symbol in 8PSK)
C/N, Carrier-to-Noise, is the received power divided by the total noise in the relevant RF bandwidth that is typically 180 kHz
C/N and Eb/No are linked by the spectral efficiency of the modulation scheme. Is spectral efficiency is 1bit/s/Hz, Eb/No is equal to C/N. In GSM (with modulating BW 271 kb/s) the spectral efficiency is 271kbit/s/200kHz =1.35 bit/s/Hz for GMSK modulation, assuming the receiver noise bandwidth is matched to the channel bandwidth:
10*log(1,35)= 1,3
C/N= Eb/No + 1.3dB
For 8PSK:
Es/No = 3*Eb/No which is 10*log(3) = 4.8 in log terms.
The required Es/No is based on the required Eb/No (bit energy divided by noise spectral density) from simulation results. Typically, link budgets may consider a certain modulation and coding scheme at a certain block error rate. However, it is also possible to calculate for a given data rate. This latter case becomes more widely used as functionalities such as link adaptation (LA) and incremental redundancy (IR) tend to mask, to some extent, the actual underlying channel performance.
RECEIVING END
Sensitivity
Base station sensitivity should be checked from appropriate marketing personnel before each dimensioning (or other) exercise. UltraSite sensitivity is found to be a bit better than the previous generation's BTSs (Talk family).
Additional fast fading margin
For packet transmission, as no handover scheme is implemented, the link is based on retransmission and cell reselection. A 2 dB fast fading margin is assumed in the voice traffic case.
Cable loss + connector and Rx antenna gain
The system sensitivity is depending on cable and connector loss, antenna gain, MHA gain if applicable, additional noise, etc.
At the BS, a 16.5 dB antenna gain is assumed. However, depending on configurations lower antenna gains are found (14 dB in the GSM 900 bands). Moreover, antenna gains may vary across a network.
At the MS, the PDA type of configuration is assumed to have a 3dB advantage compared to MS near the head. Note that isotropic antenna helps in the Rx diversity schemes as the number of scatterers is increased (increased diversity and less subject to higher signal variation as well).
Body loss
As the next generation of data terminals is assumed to be hand-held in a PDA fashion, no body loss is taken into account for EDGE scenarios. This compares with an assumed loss of 3dB for a handset held near the head.
MHA Gain
If the cable loss is that high that the signal level reaches or crosses the noise floor at the input, the SNR is not enough to guarantee the quality of the reception. Therefore MHA is recommended to compensate cable losses.
However, the SNR without MHA is always be better (because the MHA generate additional noise) if the noise floor is down enough (the cable loss is still not enough to reach the noise floor). The difference between the SNR with MHA and without corresponds to the noise figure of the amplifier.
The usage of MHA is directly depending of the sensitivity and the noise floor at the input of the receiver and the loss the cable or the feeder is causing.
Diversity Gain
The diversity gain depends on the separation of receiver antennas. In case of horizontal separation, 4 meters separation generates approximately a 3 dB diversity gain.
Intelligent Uplink Diversity (IUD)
Intelligent Uplink Diversity (IUD) is a combination of Interference Rejection Combining (IRC) and up to 4-branch combing. It is part of the Nokia Smart Radio Concept.
IRC can give gain against interference on top of the current diversity gain. The actual gain/effect of IRC is, however, under study at the moment.
Intelligent Downlink Diversity (IDD)
Intelligent Downlink Diversity, which is part of the Nokia Smart Radio Concept, is based on Beam Steering and Delay Diversity (DD). See Overview of Nokia Smart Radio Concept for details.
The estimated link level gain of DD typically ranges from 4 to 5 dB. The transmitted power penalty for 8-PSK modulation can be easily counteracted by DD gain
The use of IDD can be modeled in the network planning (power budget) so that an additional 3 dB is added to the BTS transmitted power and then between 0 and 2 dB gain as BTS TX diversity (MS RX diversity). Note, however, that the diversity gain depends on the surrounding environment.
It should be noted that IDD does not improve the C/I conditions but a later version of DD called DDD (Dynamic Downlink Diversity) should provide some improvements to C/I conditions as well. The difference between IDD and DDD is that in DDD only the slots that are of a bad quality (bad performance) are duplicated instead of blindly duplicating every timeslot as in IDD.
TRANSMITTING END
Back-off for 8-PSK
In practice, BTS equipment is less likely to be in saturation than MS equipment. Therefore the back-off for the two sets of equipment may be different, and in the link budget presented a 2dB back-off is assumed for BTS and the full 4dB for MS.
Isolator+combiner+filter
Particular attention should be given to the configurations (combiner by-passed, 2:1 WBC, 4:1 WBC, RTC) as it impacts on the actual radiated power at the antenna.
Cable loss + connector and Tx antenna gain
It is the same as in the case of Receiving end.
Average gain: 3.6
Average gain: 2.3
Es/No=8.3 dB
Es/No=42.3 dB
Lower C/I can reduce the TSL data rate significantly
The figure shows that the TSL data rate is around 25 kbps if the C/I is 15 dB.
The proper frequency plan of GSM network is very important to maximize TSL data rate
C/I
Throughput
Combined interference and noise estimations needed for (E)GPRS link budget
Frequency allocation and C/I level
The existing frequency allocation has high impact on EGPRS performance
Loose re-use patterns will provide better performance for all MCSs
Data rate and network capacity
EGPRS highest data rates require high C/I, typ > 20dB for MCS-7, 8 & 9
Possibly no extra spectrum for EDGE so efficient use of the existing spectrum is very important
EGPRS traffic suited to BCCH use - typically the layer with highest C/I. But limited no. of TSLs available on BCCH; may need to use TCH layer too
Sensitivity in tighter reuse and higher load
EDGE can utilize tighter reuse schemes and this is beneficial when planning for high load with limited frequency resources
For systems with stringent spectrum constraints, EGPRS can offer good performance even with tight re-use patterns (1/3 or 3/9). Load dependent
Good quality environment
Average quality environment
Worse quality environment
Adapt the existing network configuration for (E)GPRS
Maximize the TSL data rate (RLC/MAC) and multislot usage
Minimize the impact of PSW services on CSW services (and vice versa)
Take all the hardware and software considerations into account
Controlled investment
Most of the networks can be described by few cell/segment options
The analysis of the different options can give exact picture about the network based on:
Hardware types, software releases
Coverage, quality and capacity characteristics of BSS
Deployment Plan - Cell / Segment Option Creation
The options can cover most of the cell/segment configurations of the network
These options can be analyzed in details, so the time consuming cell/segment based analysis is not needed
All the options are examples and can have different channel configuration
Layer strategy
No multiBCF/CBCCH
GPRS and EGPRS have the same territory – data rate degradation due to multiplexing
There is not any dedicated territory (CDED) – The implementation of NMO1 is not recommended, because the MS cannot paged if there is not any GPRS territory
GPRS Enabled is a must for all the cells with NMO1
Signaling strategy
TCH usage (CSW)
TRX1 has TCH/D TSLs - which can lead to heavy signaling.
The CSW calls will be allocated to FR firstly.
AMR packing – more capacity for PSW traffic
TCH usage (PSW)
CDEF is 2 TSLs only - the 4 TSL DL capable terminals require territory upgrade, which takes time
Layer strategy
The Cell / Segment Option 2 has segment configuration.
GPRS and EGPRS have the same territory possibility for GPRS-EGPRS multiplexing
The PSW territory has 4 TSLs for 4 TSL DL capable terminals.
Dedicated territory for providing PSW services even when CSW traffic high
NMO1 well supported
Layer 2 is used for CSW traffic only with as high utilization as possible (GENA = N).
Signaling
SDCCH has enough capacity for RA/LA cell-reselection (used only if NMO1 is not implemented)
The SDCCH TSL is reducing the available capacity for user traffic.
TCH (CSW)
TRX1 has TCH/D TSLs, which can lead to heavy signaling – TRXsig size
AMR packing
More time slots available for (E)GPRS traffic without more hardware
Bad C/I - AMR HR quality might suffer
TCH (PSW)
GPRS and EGPRS multiplexing likely – impact depends on the penetration of GPRS and EGPRS users and CSW traffic
There is dedicated territory provides minimum PSW capacity for cell
Layer strategy
GPRS and EGPRS have separated territory GPRS-EGPRS multiplexing less likely
EGPRS has 4 TSLs territory for 4 TSL DL capable terminals.
There is dedicated territory for providing PSW services even in high CSW traffic, too.
NMO1 well supported
Signaling
SDCCH/8 SDCCH has probably enough capacity for RA/LA cell-reselection (if NMO1 is not implemented)
The SDCCH TSL is reducing the available capacity for user traffic.
TCH (CSW)
TRX1 has TCH/D TSLs, which can lead to heavy signaling – TRXsig size
AMR packing
TCH (PSW)
Layer1 has GPRS territory only (EGENA = N) with three TSLs.
Layer2 has the EGPRS territory with 4 TSLs, support for 4 RTSL MSs
Less GPRS - EGPRS multiplexing
Layer strategy
GPRS and EGPRS have separated territory GPRS-EGPRS multiplexing less likely
Both layers have 4 TSLs territory for 4 TSL DL capable terminals.
There is dedicated territory for providing PSW services even in high CSW traffic, too.
NMO1 well supported
EGPRS territory is allocated to TRX1. It is useful if BCCH frequency has good C/I
Signaling
The SDCCH has enough capacity for RA/LA cell-reselection if NMO1 is not implemented.
The CSW traffic should be moved from TRX1, because the limited resources for CSW.
AMR packing
TCH (CSW)
TCH (PSW)
Layer1 has EGPRS territory (EGENA = Y) with 4 TSLs.
Layer2 has GPRS territory with 4 TSLs support for 4 RTSL MS
Multiplexing is still possible in case of high PSW and CSW traffic, but the possibility is reduced.
Both layers have dedicated territory for minimum PSW capacity
Capacity Calculations
After the network audit the following need to be completed:
Air Interface Capacity Calculations
Capacity Planning – Introduction
The accuracy of BTS dimensioning depends on the accuracy of the input values
The capacity of the radio interface has a significant role in defining the capacity of the rest of the network elements (BSC, SGSN and transmission interfaces between the different network elements)
Changes in the BTS configurations have direct impact on the BSC and SGSN configuration
The BSC can handle a limited number of BTSs, TRXs and timeslots and the PCUs have maximum data traffic limitations and restrictions for the number of PAPU units in the SGSN
The following information should be available to define the available/required capacity:
BSC
Available capacity:
Calculation determines how much traffic is available through the current system
The calculation input is a pre-defined system configuration
The calculation output is the available traffic capacity with a defined performance level
Alternatively, the available capacities for different alternative configurations can be calculated
Required capacity:
It is calculated to design a network that supports the defined amount of traffic and targeted performance level
The inputs are additional traffic volume, type, and performance requirements
The output is the needed amount of traffic dependent hardware and associated software configurations
Air interface Capacity Calculations – Available Capacity
The air interface capacity planning is based on deployment scenarios (PCU-1)
All the HW, SW and feature interworking are audited by the different cell/segment options
The next step is to calculate the capacity of the air interface related to the different cell / segment options analyzed above
The air interface capacity calculation contains the following items:
TSL data rate estimation
PSW Multislot usage (with CSW traffic volume and free TSLs)
The TSL data rate calculations and the territory figures together for all the cells/segments can give the calculation results of available air interface capacity
Air Interface Capacity Planning – Required Capacity
The needed capacity is usually estimated based on assumptions on the number of data users and on the average user traffic during busy hour considering also different types of user profiles
Voice traffic capacity:
Half/dual rate usage
maximum allowed blocking
Data volume per cell can be calculated/estimated as the total data volume per cell (MB/BH/Cell, avg throughput/TSL)
Using subscriber information is more complicated, data user penetration must be known and user data amount per busy hour must be estimated
The required capacity can be defined with dedicated time slots (Guaranteed Bit Rate) when the data volume has been calculated
Air Interface Capacity Planning – Required Capacity
The required capacity calculation is the calculation of number of TSLs needed for both circuit switched traffic and packet switched traffic in each cell in order to achieve a given blocking probability for circuit switched traffic and required throughput for packet switched traffic.
User profile for BH (example)
PSW BH traffic in kbps and in MB
CSW BH traffic in Erlang
Service Mix: e.g. 45 % Voice, 10 % Video Streaming, 20 % PoC, etc
Traffic distribution
Traffic density
GPRS/EGPRS multiplexing
Connectivity Capacity Planning (MS-Gb)
The aim of connectivity capacity planning is to calculate the amount of required PCUs and allocate the sites (BCFs) among these PCUs (BSCs) for avoiding connectivity limits and maximizing QoS
The view here is on the chain between MS and Gb, so all the network elements and interfaces are planned for enough connectivity capacity
The number of required PCUs are CDEF and DAP size dependent from physical layer point of view, while the amount of Gb links used by PCUs is PAPU limiting factor (or the limited number of PAPUs can limit the number of PCUs, because of Gb link limits in PAPU).
Connectivity Planning
The connectivity planning for maximum capacity is based on the proper set of CDEF and DAP size
To provide enough capacity for territory upgrade the 75 % utilization in the connectivity limits is recommended by Nokia
(*PCU & PCU-S only handle 128 radio TSLs with S11.5, PBCCH not implemented)
The CDEF is allocated to the cells (BTSs in segment), so the too big CDEF territory will need more PCUs.
The Dynamic Abis Pool (DAP) is allocated to the sites (BCFs). Higher DAP size provides more MCS9 capable TSLs on air interfaces, but on the other side, higher DAP size needs more capacity on E1s and more PCUs as well.
So the proper value of CDEF on cell (BTS) level and DAP on BCF level can help to be below the 192 (96*) radio TSL limit with 75 % utilization to avoid connectivity bottlenecks even in case of territory upgrades
*It is important to know that the PCU and PCU-S have 128 radio TSL limit with S11.5, which can cause limitations in GPRS only networks.
**Recommended number of EDAPs per PCU1 is 1,2,4 or 8
Outputs
256
75%
192
TSLs
EDAPs*
16
100%
16
Pcs
The following limits must be taken into account:
1024 PCUs can be connected to SGSN (with 16 PAPU)
64 PCUs can be connected to PAPU
3072 Gb links can be connected to SGSN (with 16 PAPU)
192 Gb links can be connected to PAPU
120 E1s can be connected to SGSN (with 16 PAPU)
3 BTSs per BCF
BCF voice traffic
2+2+2 site on average has traffic of 8 Erl per BTS
4+4+4 site on average has traffic of 18 Erl per BTS
Blocking criteria 2%
Average data throughput per BTS (by operator)
“Central area” - 200 kbit/s
“Surrounding area” – 100 kbit/s
Dimensioning Inputs
TRX configurations
2+2+2 configuration
4+4+4 configuration
TRX and Abis configurations are examples and not binding recommendations. Presented configurations are just example used here.
Abis configurations
Rf-environment
Average RxLevel = -85 dBm
35 kbit/s (BCCH layer)
Typically best C/I TRX preferred for maximum throughput
Depending on frequency plan this can be either BCCH or TCH TRX
Features impacting location selection:
DR RTSL location needs to be considered with 2+2+2 configuration
DR RTSLs should not be allocated close to GPRS territory boundary.
Dimensioning Inputs – Free timeslots on Air IF
Free RTSLs between CS and PS territory required in order to serve incoming CS calls without blocking
Table above gives free RTSLs with default parameters
CS downgrade – if less RTSLs free in CS territory, PS territory downgrade triggered
CS upgrade – PS territory upgrade can be triggered if at least that amount of RTSLs free
Free TSLs for up and downgrade can be controlled by BSC parameters
free TSL for CS downgrade
free TSL for CS upgrade
Mean free RTSLs for 2 TRXs: 1.5; Mean free RTSLs for 4 TRXs: 2.5
free TSL for CS downgrade (CSD) – MML default: 95 %
free TSL for CS upgrade (CSU) – MML default: 4
14 RTSLs for CS traffic
CS BH traffic 8 Erl per BTS – all BTSs have same BH traffic
Erlang B table – 1.7% CS blocking @ BH
Mean free RTSLs = 1.5
Amount_of_TRXs*8 - signaling_RTSLs – CS_BH_traffic-free_RTSLs =
2*8-2-8-1.5 =4.5 RTSLs
4.5*35 kbit/s = 157.5 kbit/s (> 100 kbit/s)
4+4+4 configuration
29 RTSLs for CS traffic
CS BH traffic 18 Erl per BTS – all BTSs have same BH traffic
Erlang B table – 0.4% CS blocking @ BH
Mean free RTSLs = 2.5
Amount_of_TRXs*8 - signaling_RTSLs – CS_BH_traffic-free_RTSLs =
4*8-3-18-2.5 = 8.5 RTSLs
8.5*35 kbit/s = 297.5 kbit/s (> 200 kbit/s)
Average PS traffic maximum during CS BH. If all average available PS RTSLs used during CS BH, TRX RTSL utilization 100%.
2+2+2 – territory considerations
MS multislot capability (4 RTSLs)
Data throughput 100 kbit/s
Air interface – 35 kbit/RTSL
Default territory size
Data throughput 200 kbit/s
Air interface – 35 kbit/RTSL
Default territory size
2+2+2 configuration
14 – 2 (CDED) = 12 RTSLs
Traffic per BTS = 8 Erl
Erlang B (8Erl, 12 TSLs) = 5.1% CS blocking
5.1% > 2% - NOK
Erlang B (8Erl,2%) = 14 channels
Either 2 more RTSLs (DR/HR) are needed or one new TRX
Capacity increase done with DR RTSLs
Streaming user support required per BTS (one streaming user)
Streaming requires 50 kbit/s
=> (50kbit/s)/(35 kbit/s/RTSL) = 2 RTSLs needs to be dedicated (CDED) per BTS in order to support streaming
4+4+4 configuration
29-2 (CDED) = 27 RTSLs
Erlang B (18Erl, 27 TSLs) = 1.1% CS blocking
1.1% < 2% - OK
Amount of needed DR RTSLs depends on HR/AMR HR capable phone penetration. If HR/AMR HR capable MS penetration is 100% 2 RTSLs could be enough.
2 RTSL dedicated territory to support streaming
4 RTSL default territory for 2+2+2 configuration
2 additional DR RTSLs needed to get blocking less than 2%
4+4+4 configurations
2 RTSL dedicated territory per BTS for streaming support
6 RTSL default territory for 4+4+4 configuration
No additional DR RTSLs or TRXs needed
Max(4, 2.9) => 4
4+4+4 configuration
Max(4, 5.7) => 6
The CDEF parameter set is 6 RTSLs
The results of default territory size calculations (refer to slide 8) determines the CDEF parameter value.
Connectivity Capacity - EDAP Size
General EDAP size considerations:
If support for MCS-9 at least with one MS in one BTS of BCF is required. (Needed if MS multislot capability not taken into account with default territory calculations)
Min_EDAP_1 = MS_Multislot capability (= 4 TSLs)
If support for MCS-9 in all GPRS territory timeslots of BTSs is required
Min_EDAP_2 = Max_Default_Territory_size_of one_BTS
Min_EDAP_size = Max(Min_EDAP_1, Min_EDAP_2)
If EDAP has more than one BTS attached, BTS multiplexing factor can be taken into account if
EDAP peak load is estimated to exceed one BTSs territory size
BTS multiplexing factor can be estimated e.g. by
k = 2/(1+1/x), where
EDAP size can be estimated by
EDAP_size = k * Min_EDAP_size
2+2+2 configuration
Default territory size per BTS = 4 RTSLs
=> Min_EDAP_size = Max(4,4) = 4
Default territory size per BTS = 6 RTSLs
=> Min_EDAP_size = Max(4,6) = 6
Capacity for EDAPs in E1 for 2+2+2 is 16 and for 4+4+4 configuration 2 TSLs
2+2+2 configuration fits easily into existing E1
4+4+4 configuration does not fit into existing E1
Abis TSL allocation of 4+4+4 configuration needs redesign
Two options for Abis TSL allocation
TRXs are grouped by function so that all EDGE TRXs and EDAP are allocated to one E1 while the non-EDGE resources are mapped to other E1 frame. One EDAP is enough to serve all cells (BTS objects)
TRXs are grouped by cell so that two cells are allocated to one E1 and the third one to the second E1. In this case EDAP is created for both groups.
Pros and cons.
TRXs grouped by function (the 1st E1: 2+2+2 & EDAP, the 2nd E1 2+2+2 non-EDGE)
+ maximum trunking gain of the EDAP can be achieved less total Abis capacity is required (#TSLs for EDAP = 9)
+ smaller number of EDAPs saves PCU resources
- Special care needed to maintain and upgrade the configuration to keep the original slit.
TRXs grouped by cell (the 1st E1: 4+4 & EDAP1, the 2nd E1 4 & EDAP2)
+ Straightforward to maintain and upgrade
- trunking gain of the EDAPs is smaller or non more total Abis capacity is required (#TSLs for EDAP = 8+6 = 14)
- bigger number of EDAPs eats more PCU resources
TRXs grouped by cells
TRXs grouped by function
4+4+4 configuration
EDAP size 9 TSLs
EDGE TRXs grouped for same E1
A new E1 needed for each 4+4+4 BCF -> need for 15 new E1s
Connectivity Capacity - PCU Planning Considerations
Target is to calculate the optimal number of PCUs to serve the given network.
PCU utilization 75% (25% connectivity for territory upgrdaes)
Recommended number of EDAPs per PCU is 1,2,4 or 8
The optimal number of EDAPs and associated default RTSL is calculated for each PCU configuration.
E.g. up to 5 EDAPs of size 6 TSL serving three cells each having default territory size 4 RTSL can be allocated to PCU without exceeding the 75%.
To full fill the 1,2,4 and 8 recommendation the number of EDAPs would be 4
Connectivity Capacity - PCU Configurations and Requirements
Table below lists possible PCU combinations
4+4+4 configurations -> 3 sites per PCU has too low load, 4 too low
2+2+2 configuration -> 5 sites per PCU provides reasonable load
When considering total network, 15 (4+4+4) and 25 (2+2+2) configurations one possibility is to have
5 PCUs with 1 (2+2+2) and 3 (4+4+4) configurations
4 PCUs with 5 (2+2+2) configurations
Gb over FR
Gb link size can be calculated from maximum EDAP size of PCU
Gb_link_size=5/4*Max_EDAP_size as minimum
Inputs from PCU planning
5 PCUs with 1 EDAP of 6 TSLs and 3 EDAPs of 9 TSLs
4 PCUs with EDAP of 6 TSLs
Gb link sizes / PCU
Connectivity Capacity - Gb Links
When Gb links are combined into E1s maximum 31 TSLs can be used
Table above shows that 1 E1 can fit well either
2 Gb links of 11 TSLs and one link of 8 TSL
1 Gb link of 11 TSL and two links of 8 TSLs
9 PCUs can therefore be fitted into 3 E1 links
LA/RA Design
Mobility Planning
The aim of mobility planning is to reduce the cell outage time during cell re-selection.
Cell outage can be reduced by
Providing enough signaling capacity for cell re-selection (the RACH, PCH, AGCH and SDCCH channel are not limiting the signaling flow)
Allocating BCFs to PCUs properly (the important neighbors are allocated to the same PCU)
Allocating LA/RA borders properly
Outage measurements
Cell Outage (MS - PCU) is measured between the first BCCH observation and Packet Uplink Assignment
Data Outage (MS - SGSN) is measured between the first BCCH observation and Packet Downlink Assignment
Test cases
Layer 3 Downlink
full cell-outage (ms)
Outage measurements
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PCU Allocation Plan
The proper allocation of the cells among PCUs can help to maximize the number of intra PCU cell re-selections, which is the most stable cell re-selection event.
RLC/MAC layer: The intra PCU cell re-selection takes less time compared with inter PCU cell reselection
LLC layer: In case of intra PCU cell re-selection the untransferred data is moved to new cell (BVCI) and the transfer can be continued on new cell without packet loss on higher layer, while in case of inter PCU cell re-selection the untransferred data is not moved to new cell (BVCI).
The following rules can be followed:
The cells of a BCF should be connected to the same PCU
The neighbor relations with high re-selection traffic should be connected to the same PCU
The neighbor relations in very bad signal and quality environment should be connected to the same PCU
NACC and NCCR can be used if there is not any possibility to connect the neighbor cells to the same PCU (NACC is working inside BSCs only)
LA/RA Design – Radio Aspects
Important to avoid LA/RA border allocation between cell with high neighboring traffic
Usage of NMO I, where the combined RA reduces the cell re-selection time
Radio Aspect of LA/RA Design
The too big LA/RA will increase the paging, while the too small LA/RA will increase the LA/RA Update. So the balance should be found between too big and too small LA/RAs.
The not so appropriate LA/RA border design can significantly increase the signaling on air interface signaling channels and TRXSIG on LA/RA border cells, so the cell-reselection outage can be longer in this case because of congestion on signaling.
The LA/RA border should be moved from those areas where the normal CSW and PSW traffic is very high.
The combined RAU (NMO I with Gs) is shorter compared to NMO II
In S11 backwards the GPRS resume always can cause a lot of RAs if GPRS MS has high CS call activity, but this behavior cannot be avoided by proper LA/RA design
In S11.5 the Resume is working without LA/RA update
(E)GPRS Explain
GSM Network Optimization
(E)GPRS Network Optimization
Data Rate
E2E data rate (applications)
GSM Network Optimization
The optimal GSM network from PSW services point of view has:
As high signal level as possible
It means that even the indoor signal level should be high enough to have MCS9 for getting the highest data rate on RLC/MAC layer.
As low interference as possible
The aim of having high C/I is to avoid throughput reduction based on interference.
Enough capacity
Enough BSS hardware capacity (interface and connectivity) is needed to provide the required capacity for PSW services in time. Both CSW and PSW traffic management should be harmonized with the layer structure and long term plans.
As few cell-reselection as possible
The dominant cell coverage is important to avoid unnecessary cell-reselections in mobility. The prudent PCU allocation can help to reduce the inter PCU cell reselections.
Dominant cell structure can help to maximize the signal level and reduce the interference, too.
Features
All the features should be used which can improve the PSW service coverage, capacity and quality in general.
Before any (E)GPRS optimization related act

e Gprs Explain

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