Radio Network Overview Md. Mustafizur Rahman, Senior Lead Engineer,

Radio Planning & Optimization, Grameenphone Ltd.

GSM System at a Glance:

PSTN/PLMN MSC

HLR VLR X

MSC

BSC

BSC

BSC

Location Area

Home Register Visitor Register

MSC: Mobile Switching Centre BSC: Base Station Controller HLR: Home Location Register VLR: Visitor Location Register TC: Transcoder

f 2, TS 8 f2 f9

f4 f7

f1 f8

f3 f6

13 kb/s speech

S

TC speech 64 kb/s

pr speech channel

Capacity: 16 kb/s pr user

64 kb/s

Radio singnal and its behaviour (Radio signal propagation)

Path loss

Signal Fading – Multi path/Raleigh and

– Log normal/shadow fading

Penetration loss – Building loss: 15-25dBm

– In car: 5-10dBm

AIR INTERFACE Frequency Allocation

Radio Channel

DOWNLINK

935 - 960 MHz

1805-1880 MHz

UPLINK

890-915 MHz

1710-1785 MHz

Air Interface

Cell Site Mobile

GSM: TRX/TDMA Frame

25 MHZ: 890 to 915 MHz (UL)

935 to 960 MHz (DL)

Channel 1

200kHz

Channel 2

200kHz

Channel 124

200kHz

Time

Slot 0

Time

Slot 1

Time

Slot 7

TDMA Frame (4.616 ms)

57 bits(interleaved sub block)

from a 20ms Voice frame

26 bit TSC for error prediction

57 bits (interleaved sub block )

from another 20ms Voice

frame

3 tailbits

3 tail

bits1 bitflag

1 bitflag

148+8.25=156.25 bits

8.25guard

bits

Frequency band

Channels

TRX/TS

TS/bit stream

1800MHz Band : 1710-1785MHz(UL) 1805-1880MHz(DL)

Total no. of Channel is 374.

1TS=0.577ms 1bit=3.69ms

GSM Voice Transmission Block Diagram

• Speech coding - to compress speech • Channel coding – to detect and correct errors at the received

speech • Modulation - to fit bits into channel characteristics

Speech CodingConvolutional

CodingInterleaving Burst forming Modulation

Air

in

terf

ace

DemodulationDeInterleavingSpeech

decodingDecoded

Speech

Convolutional

decoding

Channel coding

Speech

High Population Density Low

GSM: Site/Cell/Sector

• Cell – A cell may be defined as an area of radio coverage for a BTS (Base

Transceiver Station) system. It is the smallest building block in a mobile network.

– Typically, cells are represented graphically by hexagons. There are two types of cell:

• Omni directional cell – An Omni-directional cell (or Omni cell) is served by a BTS with an

antenna which transmits equally in all directions (360 degrees).

• Sector cell – A sector cell is the area of coverage from an antenna, which

transmits, in a given direction only.

– One BTS can serve as two-sectored sites and more commonly, three-sectored sites.

C/I

C/A

◙ A cellular network split in to Cell.

◙ A cell is the area covered by a set of frequencies, transmitted from one radio base station antenna system.

Cell Concept – Cellular System

- What is limiting Factor in Cellular system capacity ??

- Capacity & Quality always reciprocal in Cellular

system !!

- GSM system evolve different Freq planning

technique

- Due to limitation in no. of frequency, frequency is

reused a little distant apart by 3/9 or 4/12 pattern

Cellular Concept: GSM Technology

The cellular concept solved the problem of limited spectrum by replacing a single,

high power transmitter (large cell) with many low power transmitters (small cells). Each

providing coverage to only a small portion of the service area.

The fundamental idea behind the cellular concept is frequency reuse

B

C

A

G

D

E

F

Cluster A Cluster B Cluster C

High Population Density Low

Reuse pattern depends on the population density

Formation of Omni Directional Antenna from Dipole radiation

A single element creates the pattern like a bread ring

In order to direct the signal to the receivers close to the surface of the earth, the bread ring can be pressed flat. An array of symmetrical dipole elements radiates energy like a “flat bread ring”:

Basics of GSM Antenna : Antenna Types

Cellular Concept :Sectorization

Directional Antenna is used to divide the channels of the cell into specific areas

is using 3 sectored cellular system

3-sectored cell

120o

120

120

Omni directional cell

360o

Comm. Tower

Omni cell site Coverage

Comm. Tower

Cell B

Cell A

Cell C

3 sectored site Coverage

UL

cel

l

UL/OL cell site Coverage

Comm. Tower O

L c

ell

Cell Planning

Coverage Capacity and Quality The main Responsibility of a Radio planner is to ensure

A. Coverage

– An area is under coverage if radio signal is sufficient enough to make successful call.

• Outdoor Coverage

• In car Coverage

• Indoor Coverage

B. Capacity

– How many users can be served by the network maintaining a target Quality of Service (QoS)

C. Quality of Service (QoS)

– Accessibility of network

– Speech quality and call drop.

Coverage Coverage is a fluctuating parameter depends on lot of factors which changes from area to area and position

of user. Coverage can be classified as-

• Indoor Coverage – Indoor coverage is defined as sufficient coverage for making a successful call inside building from ground floor level.

– Very important in Urban and Dense urban Area for Home and office.

• Incar Coverage – Incar coverage is defined as sufficient coverage to make a successful call inside a car.

– Very important in Urban, Suburban and Highways

• Outdoor Coverage – Outdoor coverage is defined as sufficient coverage to make a successful call in open air.

– Important for everywhere

• Probability of Coverage(area):

GSM Capacity Evaluation Capacity of a network can be defined as follows…

• Busy hour traffic handling ability

• Calling minutes handling ability [BH traffic vs Avg traffic]

• No. of Subscriber [BH mErl per Sub]

• Unit of Traffic capacity is usually expressed as Erlang

• Capacity of the network may vary based on offered QoS

• Subscriber behavior

• Build ahead capacity (% of buffer capacity)

FR

AMRFR

AMRHR AMRHR

Quality of Service [QoS]

1. Accessibility E2E (%) – Success rate of attempted calls reaching to called party – The attempted calls have to be successful on SDCCH (signaling channel), TCH (traffic channel), BSC-

MSC routes, MSC-TSC routes to achieve the overall accessibility – (Success of Signaling x Success of traffic x Success of core network)2=(0.98 x 0.97 x 1)2 = 90%

2. Retain ability (%)

• Percentage of on-going calls that are retained by our network until disconnected intentionally by the subscribers. It is commonly expressed by Drop Call Rate (DCR)…

• Drop call rate [DCR] • It is a measure of retainability. Lower drop rates signify better QoS

• DCR=

• Minute per Drop [MPD]

• It is also a measure of retainability. Higher MPD signifies better QoS but it requires higher investment.

• MPD= DropofNoTotal

MinutesCallingTotal

.

100%xAttemptofNo

DropofNo

.

.

Quality of Service [QoS] contd…

3. Speech quality: MOS [Mean opinion score] – It is a measure of integrity of service. It is measured by

subjective or objective test.

– Subjective method: A listener panel to assess speech quality. Speech quality is expressed as a mean opinion score (MOS), which is the average speech quality perceived by the members of the panel. Speech quality is marked by 1-5 scale. 1 means worst and 5 means best.

– Objective method replace the listener panel by an algorithm to compute a MOS value from a speech sample.

ITU P 862.1

min. max.

Excellent >= 3.5 4.5

Good >= 2.7 < 3.5

Fair >= 2.1 < 2.7

Poor >= 1.5 < 2.1

Bad < 1.5

MOS:

Radio Infrastructure

Macro BTS

• Green Field

• Roof Top

-Pole

-Tower

• Mobile BTS

• Small Cell

-Pico

-Atom

-Femto

Micro Cell

Indoor BTS

Spectrum Band

• GSM900

• GSM1800

• UMTS2100

Site Type

• GSM900

• Collocated

• GSM+UMTS

Roof Top Green Field

Radio Infrastructure (Cont..)

Camouflage MC Mobile BTS

Radio Infrastructure (Cont..)

Monopole Site Hybrid Tower

Radio Infrastructure (Small Cell)

TG sync cable

Combination of RBS 2216 w/ 24 TRX

Combination of RBS 2216 w/ BBS

RBS 2111 RBS2216

Radio Cabinet

RBS 2308

GSM Basic RF Features

– Hopping – Power control – DTX – AMR – Handover – Frequency Reuse

Data service: RS/ERS:

Backbone

Network

Corporate

Network

ISP

Network

BTS

SGSN GGSN

BSC MSC/VLR

MS Gi (IP)

Gi (IP)

Gn

Gr (MAP)

Gs Gb

Gn

A A’’

SMS-G/IW MSC

Gd

(BSSAP+)

(MAP)

Additional HW

Additional SW

BGw

SOG

AUC

Traffic & Signalling

Signalling

HLR

P

C

U

Evolution of Data Service

Class A The MS is attached to both RS and other GSM services and the MS supports simultaneous

operation of RS and other GSM services.

Operational requirements of this class include an additional receiver in the mobile phone for neighbor cell measurements

Class B The MS is attached on RS network and GSM network simultaneously but not enabling circuit

switching and packet switching services at the same time.

Simultaneous CS/PS paging.

Services are selected automatically.

Class C The MS is attached to either RS or other GSM services. Alternate use only.

Simultaneous CS/PS paging not possible.

Services are selected manually or default selected service.

Multislot Class

Maximum Number of Slots Minimum Number of Slots

Type

Rx Tx Sum Tta Ttb Tra Trb

1 1 1 2 3 2 4 2 1

2 2 1 3 3 2 3 1 1

3 2 2 3 3 2 3 1 1

4 3 1 4 3 1 3 1 1

5 2 2 4 3 1 3 1 1

6 3 2 4 3 1 3 1 1

7 3 3 4 3 1 3 1 1

8 4 1 5 3 1 2 1 1

9 3 2 5 3 1 2 1 1

10 4 2 5 3 1 2 1 1

11 4 3 5 3 1 2 1 1

12 4 4 5 2 1 2 1 1

Access Techniques

WCDMA Process Diagram

Page 38

Comparison Between GSM and WCDMA Network Interfaces

RNS

RNC

RNS

RNC

WCDMA Core Network

Node B Node B Node B Node B

Iu－CS Iu

Iur

Iub Iub Iub Iub

Iu－PS

BSS

BSC

GSM NSS

BTS BTS

A

Abis Abis

Gb

Sector = Cell. One cell can include multiple carriers.

One sector can include multiple cells. Cell = Carrier

Page 39

Major Differences Between WCDMA and GSM Air Interfaces

GSM WCDMA

Carrier spacing 200 kHz 5 MHz

Frequency reuse coefficient 1-18 1

Method for differentiating

cells Frequency + BSIC Frequency + Scrambling code

Power control frequency 2 Hz or lower 1500 Hz

QoS control Network planning (frequency

planning)

Algorithm of radio resource

management

Frequency diversity Frequency hopping

The 3.84-MHz bandwidth enables

the network to use the rake receiver

for multipath diversity

Packet data Timeslot-based scheduling in the RS Packet scheduling based on loads

Downlink transmit diversity Not supported by the standards but

applicable

Supported for increasing the capacity

of downlinks

Page 40

Multipath Environment

Time

Rx signals

Tx signals

Intensity

15 Code

Shared

transmission

16QAM

Modulation

TTI = 2 ms Hybrid ARQ

with incr. redundancy

Fast Link

Adaptation

Advanced

Scheduling

Benefit

Higher Downlink Peak rates: 14 Mbps

Higher Capacity: +100-200%

Reduced Latency: ~75 ms

• Hybrid ARQ introduces IR method of retransmission

• Shorter TTI ensures larger bit rate and 16QAM also ensures larger bit rate

• Active scheduing is done in NodeB whereas in R99 it is done in RNC.

HSDPA Overview

Comparison of UTRAN & E-UTRAN Network

Access Techniques OFDMA

Worldwide LTE Network

Difference Between UMTS and LTE

Thank You