SPEECH CODECS

WLLMICRO-CELLULAR WILL

MACRO-CELLULAR WILL

32 kb/s

13.6 kb/s

DECT

GSM , CDMA, D-AMPS

BIT RATES

AUDIBLE RANGE

TELEPHONIC

PCM

VSAT

WLL

MOBILE

64 kb/s

20 Hz TO 20000Hz

300Hz to 3400Hz

16kb/s , 14.4kb/s , 9.6kb/s , 2.4 kb/s

32 kb/s , 13.6 kb/s

13.6 kb/s

REDUCING THE BIT RATE

WHY?

WHY TO REDUCE THE BIT RATE ?

TO ACCOMMODATE MORE INDIVIDUAL SPEECH CHANNELS WITHIN THE SAME TRANSMISSION CHANNEL (MEDIA BW )

THE COST TO BE PAID ?

SYSTEM CAPACITY

COST

REVENUE

LIMITED (TRANSMISSION) CHANNEL BW

HOW COME IS IT POSSIBLE?

IT IS POSSIBLE TO REDUCE THE BW WITHOUT MUCH COMPROMISE ON QUALITY

PROPERTIES OF HUMAN SPEECH &

EAR

•REDUNDANCIES IN THE SPEECH SIGNALS

•INTERMITTENT NATURE OF SPEECH

•PERCEPTUAL LIMITS OF HUMAN EAR

SPEECH REDUNDANCIES

•SPEECH ENERGY IS CONCENTRATED AT THE LOWER FREQUENCIES

•SPEECH SPECTRUM CHANGES RELATIVELY SLOWLY

(AS THE VIBRATION RATE OF THE VOCAL CORDS ALSO CHANGES RELATIVELY SLOWLY)

• SPEECH SOUNDS CAN BE MODELLED (AS PERIODIC & NOISY EXCITATIONS PASSING THROUGH THE VOCAL TRACT / FILTER)

INTERMITTENT NATURE OF SPEECH

SPEECH TRANSMISSION CHANNEL LIES INACTIVE

(3) END PARTY DELAYS 25%

FACTORS CONTRIBUTING INACTIVENESS

(1) TALK / LISTEN NATURE OF A NORMAL TWO WAY TELEPHONIC CONVERSATION

TRANSMISSION IN ONE DIRECTION IS FOR

< 50%(2) PAUSES 33%

SPEECH SPURTS 1.5 seconds

TLAF

AVERAGE FRACTION OF THE TOTAL CONNECT TIME DROPS TO AS LOW AS 25 % = Telephone Load Activity Factor

=TLAF > 0.25 ITU

THE CICUIT UTILISATION CAN BE IMPROVED BY DEMAND ASSIGNMENT OF THE CHANNEL

EAR

•STRONGER SENSITIVITY TO A SMALLER PORTION OF THE AUDIBLE FREQUENCY SPECTRUM

•LESS SENSITIVITY TO THE PHASE OF THE SIGNAL

THE DEVICE

WHAT IS THE DEVICE…..?

SPEECH CODECS

CLASSIFICATION / CATEGORIES

WAVEFORM CODECS

PCM

DPCM

ADPCM

VOCODERSLPC

HYBRID CELP

CODE EXCITED LINEAR PREDICTIVE

PERFORMANCE

PARAMETERS

• COMPLEXITY MOPS

• DELAY 30 m sec

• BIT RATE

• QUALITY

• COST

BIT RATE

DGREE OF COMPRESSION

8 BIT PCM 64 kb/s

11 BIT PCM 88 kb/s

ADPCM 32 kb/s

LPC < 4.8 kb/s

SPEECH - QUALITY

OBJECTIVE MEASURES

SUBJECTIVE MEASURES

SNR

HARMONIC DISTORTION

BW

M.O.S

MEAN OPINION SCORE

OBJECTIVE MEASURES4 QUALITY CLASSES

BROADCAST

TOLL

COMMUNICATION

SYNTHATIC

>7 kHz >30

3.1 kHz >30

2-3

2-3

HIGH QUALITY RADIO/TV

PSTN

POORER BUT STILL INTELLIGIBLE

WLL , MOBILE, MILITARY

BW SNR

HD %

< 2 kb/sRECOGNIZABILITY LOST MACHINELIKEROBOTICS

SUBJECTIVE MEASURES

M.O.S. QUALITY LISTENING EFFORTS

5 EXCELLENT NO EFFORT REQUIRED

4 GOOD ATTENTION NECESSARY BUT NO APPRICIABLE EFFORT REQUAD

3 FAIR MODERATE EFFORT REQUAD

2 POOR CONSIDERABLE EFFORT REQUAD

1 BAD NO MEANING UNDERSTOODWITH REASONABLE EFFORTS

M.O.S.

• 11 BIT PCM 4.9

• 08 BIT PCM (64 kb/s) 4.3

• ERROR FREE SPEECH

ADPCM (32 kb/s) 4.1

• MINIMUM 3.5

PARAMTERS

AT A GIVEN BIT RATE , SPEECH

QUALITY CAN BE IMPROVED BY

------------- THE COMPLEXITY OF

THE ALGORITHM & -------------THE

DELAY.

INCREASE IN

INCREASING

CLASSIFICATION / CATEGORIES

WAVEFORM CODECS

• SOURCE INDEPENDENT

• SUPERIOR SPEECH QUALITY

• HR BIT RATES

VOCODERS•SOURCE CODER

•VERY HIGH ECONOMY IN BIT RATE

•COMPLEX

VOCODERS

CODER

DECODER

SPEECHDIGITIZED (CODED SPEECH) SIGNALS

CODED SPEECH

SPEECH

OUTPUT

CODER

ADC

ADC

ADC

SPECTRUM ANALIZER

EXCITATION ANALIZER

M

U

X

SPEECH

VOCAL TRACT RESPONSE(FILTER)

VOICE DECISION

PITCH

DIGITIZED SPEECH

DECODER

NOISE SOURCE FILTER

SPEECH O/P

SYNTHESIZED

PITCH GENDEMUX

PITCH

VOICING DECISION

FILTER SHAPING DATA

CODED SPEECH I/P

EXAMPLES

BIT COMPLEXITY DELAY QUALITY M.O.S. RATE

kb/s MOPS ms

PCM 64 0.01 0 TOLL (High) 4.3

ADPCM 32 0.1 0 TOLL (High) 4.1

LPC 2.4 1.0 35 SYNTHETIC 2.5

MULTI PULSE 8.0 10 35 COMMUN 3.7 LPC

EXAMPLES

RELP VSAT 16kb/s RESIDUAL EXCITED

LINEAR PREDICTIVE

RPE-LTP GSM 13.6 kb/s REGULAR PULSE EXCITED LONG

TERM PREDICTIVE

TUTORIAL(1) WILL - IS IT A FACILITY TO THE SUBSCRIBER JUST LIKE CELLPHONE?

OR A TOOL FOR THE OPERATORS?

(2)DIFFERENCE BETWEEN WLL & WILL IS--

(3)GIVE THREE MAJOR DIFFERENCES BETWEEN MICRO & MACRO CELL WILL

(4) GIVE THREE EXAMPLES OF EACH

TUTORIAL(5) WHAT DO YOU MEAN BY “CELL” IN WILL?

(6) WHY CELLS ARE REQUIRED IN A WILL SYSTEM ?

(7) ON WHAT FACTORS DOES THE CELL SIZE DEPEND?

HOW TO DOUBLE THE CELL SIZE?

(8) WHY TO FURTHER DIVIDE THE CELL INTO SECTORS ?

TUTORIAL

(9) CALCULATE

HOW MANY SUBSCRIBERS CAN BE SERVED BY ONE BS/CELL ASSUMING FOLLOWING DATA

SIX SECTORS PER CELL WITH 10 RF 1.25 MHz BW CHANNELS IN EACH SECTOR

0.1 Erlg TRAFFIC PER SUBSCRIBER & 20 TO 40 ACTIVE LINES PER RF CHANNEL

TUTORIAL

(10) DRAW FUNTIONAL SCHEMATIC BLOCK DIGRAM OF

-DECT SYSTEM ARCHITECTURE

-CDMA ”””””””””””””””””

(11) IN DECT HOW DIFFERENT TONES (eg dial tone , NU tone) ARE SENT FROM CBS TO SE

TUTORIAL

(12) WHAT IS THE BANDWIDTH / BIT RATE (kbps) PER SUBSCRIBER IN CDMA AND DECT and HOW IS IT ACHIEVED ?

(13)WHAT ROLE THE SPEECH CODECS PLAY IN INCREASING THE SYSTEM CAPACITY

IN A WLL SYSTEM?

(14) SPEECH CODECS CAN BE CLASSIFIED AS ------

TUTORIAL

(15) DIFFERENTIATE BETWEEN 1G AND 2G SYSTEMS OF MOBILE SERVICES .

(16) HOW MANY BS AND SUBSCRIBERS CAN BE SERVED BY ONE DIU ?

TUTORIALFILL IN THE BLANKS

(1).MAXIMUM TRAFFIC HANDLED BY ONE CBS (DECT) IS --- AT 1%BLOCKING AND THUS 1 CBS CAN SERVE --------SUBSCRIBERS IF 0.05 Erlg / SUBS. THE INFORMATION RATE IS ------kbps ie THE RATE OF ------SPEECH CODEC

TUTORIAL(2) DECT WLL TENDER COVERS ----CITIES WITH ----LINES IN TOTAL -----SUPPLIED BY --------------(HFCL/SHYAM/LG/LUCENT) & -----------BY ------------------(HFCL/SHYAM/LG/LUCENT).

TUTORIAL

(3) IN VPT ------(CDMA/DECT) BASED WLL IS BEING INSTALLED WHICH IS OF ------(HFCL/SHYAM/LG/LUCENT) MAKE WITH ----(0/25/75/100 %)MOBILE AND ----(0/25/75/100 %)FIXED LINES ----------(68000 / 5 LAKH)LINES IN ALL

TUTORIAL

(4) FWT (LG’S CDMA FOR VPT) HAS ------------(INBUILT / SEPARATE) BATTERY WITH-----(2 / 20 HOURS) TALK TIME--------(10/20 HOURS) CHARGE TIME USES -------(SOLAR / MAINS / EITHER) CHARGING .

(5)THE DIFFERENCE BETWEEN WLL AND WILL IS THAT

TUTORIAL

(1)Vocoder with lower bit rate & the same Quality speech will be MORE / LESS Complex , MORE /LESS expensive (cost) , will add LESS/ MORE Delay(2)M.O.S. should not be less than------------

TUTORIAL

TRUE / FALSE

(1)IN CDMA THE CELL SIZE CAN BE INCREASE TO ANY LEVEL JUST BY INCREASING THE BS POWER

(2)GSM , CDMA & DAMS ARE EUROPIAN STANDARDS WHEREAS DECT , CT-2 & PHS ARE AMERICAN STANDARDS.

TUTORIAL

TRUE / FALSE

(3)GSM & DECT USE FDD WHEREAS DAMPS & CDMA USE TDD.

(4)DAMPS IS CALLED DUAL MODE BECAUSE IT CAN WORK BOTH AS A MICRO-CELLULAR AS WELL AS A MACRO-CELLULAR WLL.