2g network arch v2

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O2 UK Radio Network ArchitectureJohn Button

Radio Engineering


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Overview

O2 UK Spectrum Allocation

Network Architecture

GSM Architecture, Multi-layer architecture

GSM Feature Usage

Coverage & Dimensioning Rules

O2 UK GSM Vendors

GPRS Architecture

Architecture Limitations


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O2 UK Spectrum


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Spectrum Allocation

O2 UK has spectrum within all three GSM bands

60 PGSM Channels (25 - 60 & 101 - 124)

61 available in M25 (Channel 24)

21 EGSM Channels (1000 - 1023)

28 GSM1800 Channels (512 - 539)

Definition of Licence contained in Datasheet 029

Definition of Spectrum Usage within Datasheet 030


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Spectrum Usage

PGSM Spectrum used for Primary Macrocell layer and Coverage Microcells

BCCH strategy for single interleaved structure of 16 main channels and

6 optional BCCH or TCH channels

Dedicated 6 frequency block for microcells where partitioning of

spectrum justified

GSM1800 spectrum used on Macrocell capacity layer

No defined BCCH or TCH allocation, full flexibility for AFP to optimise

EGSM spectrum used on Capacity Macrocell layer outside M25 or Microcell

Layer in M25 core

No defined BCCH or TCH allocation, full flexibility for AFP to optimise

Picocells use spectrum from all bands


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Spectrum Usage Map


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Radio Network Architecture


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GSM Network Architecture

PSPDN

HLR

MSC

A

MAP-D

VLR

BSC &

PCU

MSC - Mobile Switching CentreVLR - Visitor Location RegisterHLR - Home Location RegisterBSS - Base Station SystemPSPDN - Packet Switched Public

Data Network

PSTN/

ISDN

Gb

SGSN - Serving GPRS SupportNode

Gr

Gs

SGSN

N.B. Gc & Gs interfaces are optional

Gc

Gn Gi

GGSN

GGSN - Gateway GPRS SupportNode

Abis

BTS


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Multi-layer Networks

Mobile can be movedto upper layer

Multi-layer networks allow different spectrum utilisation within a singlenetwork.

Network attempts to place mobiles in upper layer when they are within

its coverage. O2 UK needs a multi-layer network to utilise its spectrum


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O2 UK Multi-Layer Cell Architecture

PGSM Primary

Coverage Layer

EGSM / GSM1800 Capacity Layer

Microcell Capacity/Coverage Layer

PicocellIn-building

solutions


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O2 UK Multi-Layer Traffic Movements

PGSM PrimaryCoverage Layer

Capacity Layer

Microcell Capacity/Coverage Layer

Quality HO

-ve PBGT HO

Conventional HO


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Traffic Movement Controls

Into Capacity Layers

Large negative power budget set to triggerHO request

Access into layer controlled by target cell signal strength (RxLevMinCell)

Need to ensure quality on arrival through high signal level

Out ofCapacity Layers

RxQual/RxLev triggered HO request to 900 primary coverage layer

No constraint to stop traffic moving off the capacity layer if quality is poor

900 always assumed better

Dumping ground for poor quality calls

Within Layers power budget HO is primary HO cause


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GSM Feature Usage


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Main GSM Feature Usage

PowerControl - Used on UL & DL

Frequency Hopping - Baseband Hopping on >2 TRx cells

UL DTx - Mobiles must use UL DTx

Directed Retry - SDCCH to TCHHO on originating cell TCH congestion

Traffic Reasoned HO / Congestion Relief - Pre-emptive traffic management

to reduce congestion

Dynamic SDCCH (Nokia Only) - dynamic configuration of SDCCH under load FACCHCall Setup (Nokia Only) - direct access to TCH if SDCCH congested

Dual BA Lists - separate Idle and Active BCCH Allocations used


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Main GSM features not implemented

DL DTx - Not implemented due to mobile issues with BBFH & DL DTx

IUO/Concentric Cell - Super reuse techniques not implemented

1800 layer acts as super reuse layer

Neighbour planning and management forIUO prohibitively complex

RF-SFH - Hardware issues of RTCs in Nokia kit prevent global usage

Quality of fractional reuse questionable when in poorC/I areas

Call Reestablishment - Not seen as beneficial as active BA list controlsre-establishment.

Can significantly delay ability of mobiles to retry manually


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GSM Features Future Developments

Single/Common BCCH

Removes complexity of the multi-layer architecture

One single 900 BCCH frequency can control all 900, EGSM & 1800TRxs as a single logical entity

Traffic management between Layers will not rely on HO between

cells

Drawback that all TRxs need to be synchronised

Difficult to achieve in Nokia kit where 900 & 1800 in different

racks

BCFB card not approved for use in O2 UK network

May only deploy within 900 & EGSM layers


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UK Coverage Classifications

Tier No of Post Codes UK Land Mass UK Population

Gold 4420 4.7% 54.4%

Silver 2652 18.7% 32.7%

Bronze 1327 37.9% 11.0%

Total 8399 61.2% 98.1%

QOS Level Coverage Confidence

Gold 99%

Silver 95%

Bronze 90%

UK land mass is characterised into tiers by postcodes

Coverage target confidence levels for each classification are


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Coverage Planning Thresholds

Propagation model prediction error standard deviation is 8.4 dB

Based on required confidence levels, target coverage levels for each tier

can be derived

Target level depends on clutter classification of individual bins

Planning Tool Thresholds dBm

old ilver Bronze

On-street - 8 -84 -88In-car - 2 -80 -84

In-building (suburban) - 8 - -81

In building (dense urban) - 0 - - 0

In-train (open line) - - -81

In-train (cutting) - 4 - 3 - 8


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Radio Dimensioning Rules

Traffic modelling using Poisson, not Erlang B, fits mobile networks best

Radio resource dimensioning is performed to 1% TCH congestion

probability for Gold areas and 2% TCH congestion for other areas

This is the aggregate of capacity for dual band cells

Dual band carrier configurations added after4 TRx limit reached

Microcell capacity added depending on local traffic conditions

SDCCH congestion target is 0.5%

Additional SDCCH capacity is added on location area boundaries

GPRS dedicated timeslots exist on PGSM cells

1 TS on macrocells and single Tx microcells

2 TS on >1 Tx microcells


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Radio Dimensioning Table

Number of GSM Carriers Number of Voice

Channels

Max. TCH Traffic

(1% Poisson)

SDCCH

Configuration

Max. SDCCH

Traffic1

(0.5% Blocking)

1 1 - 6 2.1 D /8 2.15

2 7 - 14 7.42 D /8 2.15

3 15 - 22 13.50 D /8 2.15

3 Boundary 15 - 21 12.72 D /16 7.37

4 23 - 29 19.03 D /16 7.37

5 30 - 37 25.61 D /16 7.37

5 Boundary + high 30 - 36 24.76 D /24 13.41

6 38 - 44 31.47 D /24 13.41

Excludes effect of GPRS Dedicated TSs


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O2 UK GSM BSS Vendors


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Vendors

O2 UK uses Nokia as single BSS vendor

Core network vendor is Ericsson

Vendor inter-working prevents some key features working correctly overBSC / MSC boundaries.


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Nokia Hardware Types (DS002)

Nokia kit has three generation variants

2nd Gen. (DE21)

Macrocells up to 4+4+4 configuration

3rd Gen. (DE34/DF34)

Macrocell up to 6+6+6 (P/EGSM) and 2+2+2 1800

2 TRx Microcell (DE34 mini)

4th Gen. (Ultrasite / Metrosite / Insite)

Very high capacity Macrocell up to 12+12+12 (Ultrasite)

4 TRx microcells (Metrosite)

4+4+4 Street Furniture (3 Metrosite in SF box)

single carrier picocell (Insite)


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GPRS Architecture


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GPRS Architecture

BTSBTS

BTS

BTS

GGSN

PCU

SGSN

PCU

SGSN

BSC

BSC

Intra-PLMNIP Backbone

FrameRelay

FrameRelay

BTS BTS

PCUBSC

Corporate

GGSN

WAP

GGSN

Inter-PLMNNetwork

BG NS

BTS

MSC MSC

Internet PSTNPSTN

AXE10 AXE10IWF


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Circuit Switched only (normal GSM)

GPRS Capacity on Demand

Enables Latent Capacity to be exploited.

CS calls have priority - GPRS sessions terminated ifCS needs

timeslot

Possible TS Configurations:

0 1 2 3 4 7 07 65

Permanent dedicated GPRS data channel

Switchable between CS and GPRS (Dynamic)


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GPRS Radio Configuration

Dedicated Timeslots

1 Dedicated Timeslot on all GSM900 Macrocells

1 Dedicated Timeslot on all 1 carrier Microcells

2 Dedicated Timeslots on all 2 carrier Microcells

Default GPRS Timeslots

6 timeslots are configured a default on all cells

Additional Territory

Under high GPRS load, additional TS can be configured into the GPRS

territory

GPRS territory limited by PCU resource

Possible to use all timeslots on a cell, but unlikely due to CS load

preventing territory expansion


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GPRS Key Features

GPRS mobiles currently work autonomously for mobility management

No network control of HO during data transfer

GPRS currently shares CCCH with CS services

Limited by CS optimised idle mode cell reselection

Paging and access grant capacity limited

PBCCH feature will not be utilised

Problems with UE implementation make PBCCH usage problematical


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GPRS Future Developments

Gs interface between SGSN and MSC

Prerequisite for PBCCH

Network Controlled cell re-selection Will give ability for network to control when mobiles re-select

Improved GPRS throughput while on the move


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Spectrum Allocation

3 band of spectrum make architecture complex

Forced into multi-layer operation that inherently requires a highnumber of handovers

Each HO adds risk of failure and dropped calls

Exceptional Traffic Densities

Dense urban areas lead to microcell requirements to support trafficlevels

Desire to drive microcells hard to recoup high deployment costs

again leads to excessive HO usage


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Architecture Limitations (2)

GSM limitations prevent Quality on HO target being evaluated prior to

HO command

Need to be conservative on how hard capacity layers are driven to

prevent excessive ping-pong

Varied mobile base and legacy phase 1 single band mobiles limit

architecture

Need to ensure equal coverage for single band and multi-band

mobiles restricts dual band architecture options

prohibits use of 1800 only or EGSM only cells to simplify

architecture

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