Admissions in india 2015

Admissions in India 2015

By:

admission.edhole.com

http://school.edhole.com/

Second Generation (2G) Cellular

Dr. A. ChockalingamAssistant Professor

Indian Institute of Science, Bangalore-12

[email protected]

http://www.ece.iisc.ernet.in/~achockal



Dr. A. Chockalingam WW'99, Dept of ECE, IISc, Bangalore 3

2G Cellular Systems

GSM GSM – European Digital Cellular StandardEuropean Digital Cellular Standard

– TDMA Access TechnologyTDMA Access Technology

IS-54/IS-136 IS-54/IS-136 – North American Digital Cellular StandardNorth American Digital Cellular Standard– TDMA Access Technology TDMA Access Technology

IS-95AIS-95A

– North American Digital Cellular StandardNorth American Digital Cellular Standard– CDMA Access TechnologyCDMA Access Technology




GSM

Global System for Mobile communications

BTS

BTS

BTS

BTS

BTS

MS

MS

BSC

BSC

MSC

PSTN

ISDN

Data Networks

OMC

HLR VLR AUC

Base Station Subsystem (BSS)

Network and Switching Subsystem (NSS)

Public Networks

MS: Mobile Station MSC: Mobile Switching CenterBTS: Base Transceiver Station HLR: Home Location RegisterBSC: Base Station Controller VLR: Visitor Location RegisterAUC: Authentication Center OMC: Operation Maintenance Centeradmission.edhole.com



GSM - Interfaces

BTS

BTS

BTS

MS

BSC MSC PSTN

SS7A Interface(standardized)

Abis Interface(standardized)

GSM Radio Air Interface (standardized)




GSM: Services & Features

Teleservices– standard mobile telephony, both mobile originated

and mobile terminated Data Services

– computer to computer traffic (e.g., Async Data)– Digital Fax

Supplementary Services– Caller ID, Short Messaging Service (SMS)

Subscriber Identity Module (SIM)– user memory device to activate service from any

GSM phoneadmission.edhole.com



GSM: Air Interface

TDMA access technology 25 MHz BW spectrum on both directions

– 890 to 915 MHz Reverse link (mobile-to-base)– 935 to 960 MHz Forward link (base-to-mobile)

200 KHz RF carriers 8 TDMA slots on each carrier (i.e., each 200

KHz carrier can support 8 simultaneous calls) (25 MHz / 200 KHz) * 8 = 1000 traffic channels 13 Kbps vocoder rate (half rate vocoder can

double capacity)admission.edhole.com



GSM: Air Interface

Slow frequency hopping to mitigate fading effects Channel data rate : 270.833 Kbps GMSK modulation with 0.3 BT product Channel types

– Traffic Channels (TCH) - carry traffic signals» Full Rate TCH, Half Rate TCH

– Control Channels (CCH) - carry call control signals» Broadcast Channel (BCH)

» Common Control Channel (CCH): Paging and Random Access Channels

» Dedicated Control Channel (DCCH)admission.edhole.com



TDMA Frame in GSM

GSM TDMA Frame

577 microseconds

(8 time slots = 4.615 milliseconds)

0 1 2 4 5 6 7

Time Slot

3




GSM: Normal Traffic Burst

0 1 2 3 4 5 6 7

DATA DATA

57 BITS 57 BITS

(e.g. encoded voice) (e.g. encoded voice)

TrainingSequence

FLAG

FLAG

TAIL

TAIL

3 BITS 1 BIT 1 BIT 3 BITS

148 BITS

26 BITS




GSM: Air Interface

Downlink Control Signaling Frequency Correction: Sends a frequency

reference. Synchronization: Sends a timing reference. Broadcasting: Broadcasts general information

about the Base Station. Paging: Notifies the mobile of incoming calls.

Assigns a traffic channel to a mobile. Uplink Signaling

Random Access Channel: used by mobiles to request a traffic channel admission.edhole.com



GSM: Channel Interaction

Mobile - Base Station Initialization Mobile identifies a Frequency Correction burst on the

Frequency Correction Channel. Mobile synchronizes timing using a synchronization

burst on the Synchronization Channel. Mobile obtains general system information over the

Broadcast channel.

Mobile - Base Station Communication Mobile and Base communicate over Random Access

and Paging channels when not involved in a call. Mobile and Base communicate over Traffic channels

while involved in a call.admission.edhole.com



IS-54

IS-54 – also known as “Digital AMPS” (D-AMPS)– upgrade AMPS analog technology to a digital

technology– same spectrum and frequency spacing (30 KHz)

like AMPS– supports 3 or 6 users on a single single 30 KHz

carrier using TDMA scheme with 6 slots– control channels are identical to analog AMPS

control channels, but twice as many control channels as AMPS




IS-54 Radio Interface

Parameters IS-54 Specifications

Multiple Access TDMA/FDDModulation Pi/4 DQPSKChannel bandwidth 30 KHzRev Channel band 824 – 849 MHzFvd channel band 869 – 894 MHzFvd & Rev channel data rates 48.6 Kbps

Spectrum efficiency 1.62 bps/Hz

Channel Coding 7 bit CRC and rate ½ convol.coding of K=6

Users per channel 3 (full-rate speech coder of 7.95kbps/user)6 (with half-rate speech coder of3.975 kbps/user)




IS-54 vs IS-136

IS-54 vs IS-136– IS-54 uses 10 Kbps FSK modulated control channels – IS-136 uses 48.6 Kbps digital modulated control

channels» IS-136 does not support 10 Kbps FSK control channel. » So IS-136 user terminals are not compatible with IS-54

– IS-136 provides a host of new features and services, including

» short messaging capabilities» private user group features (suited for wireless PBX and

paging applications)» “Sleep Mode” to conserve battery power




GSM / IS-54 Summary

G S M IS -5 4Y e a r o f in tro d u c tio n 1 9 9 0 1 9 9 1M u ltip le A cc e ss T D M A /F D M A /F D D T D M A /F D M A /F D D

F re q u e n c ie s 8 9 0 - 9 1 5 M H z (R )9 3 5 – 9 6 0 M H z (F )

8 2 4 – 8 4 9 M H z (R )8 6 9 – 8 9 4 M H z (F )

M o d u la tio n G M S K (B T = 0 .3 ) 4/ - D Q P S KC a rrie r s e p a ra tio n 2 0 0 K H z 3 0 K H z

C h a n n e l d a ta ra te 2 7 0 .8 3 3 K b ps 4 8 .6 K b ps

N o . o f vo ic e c h a n n e ls 1 0 0 0 2 5 0 0

S p e c trum e ffic ie nc y 1 .3 5 b p s /H z 1 .6 2 b p s /H z

S p e e c h c o d in g R E L P -L T P @ 1 3 K b p s V S E L P @ 7 .9 5 K b ps

C h a n n e l c o d in g C R C w ith r= 1 /2 ; K = 5C o n v.

7 b it C R C w ith r= 1 /2 ; L = 6C o n v

E q u a lize rs A d a p tive A d a p tive




IS-95 CDMA

Direct sequence spread spectrum signaling on reverse & forward links

Each channel occupies 1.25 MHz Fixed chip rate 1.2288 Mcps Variable user data rate - depends on voice activity Universal frequency reuse fast power control to overcome near-far problem RAKE receiver to take advantage of multipath Soft handoffs




CDMA Channels & Frequencies

CDMA frequencies assigned through a 11-bit CDMA Channel number, N

At Mobile

MHz

MHz

At Base Station

MHz

MHz

825)1023(030.0

825030.0

10231013

7771

N

N

N

N

870)1023(030.0

870030.0

10231013

7771

N

N

N

N




CDMA Channel & Frequency

1.25MHz1.25MHz 1.25MHz1.25MHz

ReverseReverseCDMA ChannelCDMA Channel

ForwardForwardCDMA ChannelCDMA Channel

45 MHz45 MHz

FrequencyFrequencyCDMACDMAChannelChannelFrequencyFrequency 847.74 MHz847.74 MHz

892.74 MHz892.74 MHz




Frequency Reuse CDMA

DDEE

FF

GG BBCC

DDEE

FF

BBCC

GG

DDEE

FFCC

DD

EE

BBCC

GGAABB

CC

FF

BB

AAAA

7 cell Freq Reuse Plan Freq Reuse Plan in CDMA

AAAA

AAAA

AA

AAAA

AA

AAAA

AAAA

AAAA

AAAA

AA

AA

AA

AA

AA

AA

AA

AAAA

AA

AA

AA




Spreading Codes in IS-95 CDMA

Two types of spreading codes are used in IS-95– Walsh codes of length 64 are used on the

forward link (base-to-mobile link)e.g., c1 = 0 0 0 0

c2 = 0 1 0 1

c3 = 0 0 1 1

c4 = 0 1 1 0

» used to separate one user from another

– PN codes are used on both forward and reverse (mobile-to-base) links

jikckc ji ,0)()(




IS-95 CDMA Forward Link

Pilot Channel (Code Channel 0)

– provides phase reference for coherent demodulation – pilot strength measurement for handoffs

Paging Channel (up to 7 channels - Code Channels 1 to 7)

– sends control messages and page messages – Walsh Code Channels 1 through 7

Sync Channel (Code Channel 32)

– broadcasts system timing messages

Traffic Channel (up to 63 channels - remaining code channels)

– supports variable data rates at 9600, 4800, 2400, or 1200 bps




Forward Link Channel Structure

Forward CDMA Channel(1.25 MHz Chl. Tx by Base Stn

PilotChl

W0

SyncChl

W32

PagingChl. 1

W1

PagingChl. 7

W7 W8 W9 W63

TrafficChl. 1

TrafficChl. 2

TrafficChl. 55

Traffic dataPower ControlSub channel




FL Modulation Structure

W0

W32

Pilot Chl: all 0’s

Convol. Encoder/Repetition

Block Interleaver

1.2288 Mcps

1.2288 Mcps

Sync Chl1200 bps 4800 bps

Convol. Encoder/Repetition

Block Interleaver9600 bps

4800 bps2400 bps

19.2 Kbps1.2288 Mcps

Wp

Paging Chl

Paging Chl pLong code Mask

Long CodeGenerator

Decimator

1.2288 Mcps19.2 Kbps

To QuadratureSpreading






FL Modulation Structure

Convolutional Encoder

and Repetitionr=1/2, K = 9

User dataBlock

Interleaver

Long Code generator Decimator Decimator

MUX

Basebandfilter

Basebandfilter

Long code for nth user

1.2288 Mcps

1.2288 Mcps19.2 k

Power ControlBit

800 Hz

Walsh Code

Symbolcover

Scrambling

I-Chl Pilot PN Seq

Q-Chl Pilot PN Seq

Forward CDMA Traffic Channel Structure

9600 bps4800 bps2400 bps1200 bps

Quadrature Spreader

Note: Pilot PN Offset identifies the base stationadmission.edhole.com



FL Modulation Parameters

Parameter Data Rate (bps)

User Data Rate 1200

Coding rate 1/2

Repetition 2

Coded data rate 4800

PN Chips/coded data bit 256

PN chip rate (Mcps) 1.2288

PN Chips/bit 1024

Sync Channel






User Data Rate 9600 4800 2400

Coding rate 1/2 1/2 1/2

Repetition 1 2 4

Coded data rate 19,200 19,200 19,200

PN Chips/coded data bit 64 64 64

PN chip rate (Mcps) 1.2288 1.2288 1.2288

PN Chips/bit 128 256 512

Paging Channel





User Data Rate 9600 4800 2400 1200

Coding rate 1/2 1/2 1/2 1/2

Repetition 1 2 4 8

Coded data rate 19,200 19,200 19,200 19,200PN Chips/coded data bit 64 64 64 64

PN chip rate (Mcps) 1.2288 1.2288 1.2288 1.2288

PN Chips/bit 128 256 512 1024

Forward Traffic Channel



IS-95 CDMA Reverse Link

Reverse CDMA Channel(1.25 MHz Chl. Rx by Base Stn

AccessChl. 1

AccessChl. 2

AccessChl. n

TrafficChl. 1

TrafficChl. 2

TrafficChl. m

TrafficChl. 3

Addressed by long code PNs



IS-95 CDMA Reverse Link

Access Channels– enables mobile to communicate non-traffic information (e.g.,

call request) in random access mode

– fixed data rate at 4.8 kbps – identified by a distinct access channel long code sequence

offset– a paging channel number is associated with access channel

Traffic Channels– identified by long distinct user code offset

– data rate 9.6, 4.8, 2.4, 1.2 Kbps– data is convolutionally encoded, block interleaved, 64-ary

orthogonal modulated, and direct sequence spread before transmission



RL Modulation Structure

Convolutional Encoder

and Repetitionr=1/3, K = 9

Informationbit

Block Interleaver

Long Code generator

Basebandfilter

Basebandfilter

Long code Mask for user n 1.2288 Mcps

Zero offsetPilot PN Seq I Chl

Reverse CDMA Traffic Channel Structure

9600 bps4800 bps2400 bps1200 bps

Code symbol

28.8 Ksps

64-1ryOrthogonalModulator

Zero offsetPilot PN Seq Q Chl

Data burst

randomizer

Code symbol

Walshchip

307.2 Kcps

PN chip

D

1/2 PN chiipdelay=406.9 ns



RL Modulation Parameters


User Data Rate 9600 4800 2400 1200

Coding rate 1/3 1/3 1/3 1/3

Tx Duty Cycle (%) 100 50 25 12.5

Coded data rate (sps) 28,800 28,800 28,800 28,800

Bits per Walsh symbol 6 6 6 6

Walsh symbol rate 4800 4800 4800 4800

Walsh chip rate (Kcps) 307.2 307.2 307.2 307.2

Walsh symbol duration(microsec)

208.33 208.33 208.33 208.33

PN chips per code symbol 42.67 42.67 42.67 42.6

PN chips per Walsh symbol 256 256 256 256

PN Chips per Walsh chip 4 4 4 4

PN chip rate (Mcps) 1.2288 1.2288 1.2288 1.2288

Reverse Traffic Channel



Power Control

To combat the effect of fading, shadowing and distance losses

Transmit only the minimum required power to achieve a target link performance (e..g, FER)– Minimizes interference– Increases battery life

FL Power Control– To send enough power to reach users at cell edge

RL Power Control– To overcome “near-far” problem in DS-CDMA



Power Control

Types of Power Control– Open Loop Power Control– Closed loop Power Control

Open Loop Power Control (on FL)– Channel state on the FL is estimated by mobile

– RL Transmit power made proportional to FL channel Loss

– Works well if FL and RL are highly correlated» which is generally true for slowly varying distance and

shadow losses» but not true with fast multipath Rayleigh fading

– So open loop power control can effectively compensate for

distance and shadow losses, and not for multipath fading admission.edhole.com


Power Control

Closed Loop Power Control (on RL)

– Base station measures the received power– Compares it with the desired received power (target

Eb/No) – Sends up or down command to mobile asking it to

increase or decrease the transmit power– Must be performed fast enough a rate (approx. 10

times the max. Doppler BW) to track multipath fading

– Propagation and processing delays are critical to loop performance



Power Control in IS-95

At 900 MHz Carrier frequency and 120 km/h mobile speed, Doppler = 100 Hz

In IS-95A, closed loop power control is operated at 800 Hz update rate

Power control bits are punctured into the traffic data stream Closed loop power control step size is +/- 1 dB Power control bit errors do not affect performance much Coding and interleaving has effect on CLPC performance Both open (outer) and closed (inner) loops drive the

transmit power to ensure a target FER of 1%admission.edhole.com


RAKE Receiver

4 RAKE fingers are used in the Mobile Receiver

– 3 fingers for tracking and demodulating multipath components of the FL CDMA channel

– 1 finger is used for searching and estimating the signal strength on different pilots

» used to select the desired (strongest) base station in idle mode

» for generating pilot strength information messages

during traffic mode to enable Handoff



Handoffs in IS-95 CDMA

Types of Handoff

– Soft Handoff» Mobile commences commun with a new base station without

interrupting commun with old base station» same freq assignment between old and new base station» provides different site selection diversity

– Softer handoff» Handoffs between sectors in a cell

– CDMA-to-CDMA Hard Handoff» Mobile transmits between two base stations with different

frequency assignmentadmission.edhole.com


Soft Handoff Architecture

Mobile

BSC BSC

BTS BTSBTSBTS

New LinkOld Link

RR

MSCTo other switch

R

R - Handoff request sent to the old cell on the degrading link Energy measurements are made at

the mobile

Switch Diversity:MSC selects the bit stream with lower error rate



Handoff Procedure

Pilot Sets– Active Set

» Pilot associated with FL traffic channels assigned to the mobile

– Candidate Set» Pilots that are not in Active Set but are received by the mobile

with sufficient strength

– Neighbor Set» Pilots not in Active or Candidate Set but are likely candidates

for handoff

– Remaining Set» Set in the current system on current freq assignment, excluding

the above 3 sets



Handoff Example

Time

PilotStrength

(1)

T_ADD

T_DROP

(2) (3) (4) (5) (6) (7)

NeighborSet

CandidateSet Active Set

T_TDROP

NeighborSet



Handoff Example (..contd)

(1) Pilot strength exceeds T_ADD. Mobile sends a Pilot Strength Measurement Message (PSMM) to base station and transfers pilot to the Candidate Set

(2) Base station sends a Handoff Direction Message (HDM)

(3) Mobile transfers pilot to Active Set and sends s Handoff Completion Message (HCM)

(4) Pilot strength drops below T_DROP. Mobile starts handoff drop timer

(5) Handoff drop timer expires. Mobile sends a PSMM

(6) Base station sends a HDM

(7) Mobile moves pilot from Active Set to Neighbor Set and sends a HCM


Admissions in india 2015

Education

dept of ece

chockalingam ww99

mobile station msc

reverse link mobile

computer traffic

traffic signals

rate tch control channels

mobile switching centerbts