roberto verdone · 2020-03-04 · prof. roberto verdone time latency rb= bit rate = number of bits...

Prof. Roberto Verdonewww.robertoverdone.org

TelecomunicazioniRoberto Verdone

[email protected]

https://www.linkedin.com/in/roberto-verdone/

Radio NetworksDEI, University of Bologna


Fundamentals of Digital Comms


T R

bitsbits

source destination

signal signal

coding

modulationamplification

detection

demodulationamplification

filtering

decoding

... plus all protocol functionalities

... plus all protocol functionalities

transmitter receiver

Digital Communications à Protocols

Fundamentals of Digital Communications

transmission medium


T R

source destinationtransmitter receiver

signal signal

APPLICATION

NETWORK

TRANSPORT

DATA LINK

PHYSICAL

APPLICATION

NETWORK

TRANSPORT

DATA LINK

PHYSICAL

data chunk

data bursts

bits bits

source destination

protocolsL5

L4

L3

L2L1T R

L0



transmission medium


T R

source destination

signal signal

APPLICATION

NETWORK

TRANSPORT

DATA LINK

PHYSICAL

APPLICATION

NETWORK

TRANSPORT

DATA LINK

PHYSICAL

data chunk

data bursts

bits bits

source destination

protocolsL5

L4

L3

L2L1T R

L0

fragmentation assembling




transmission medium


T R

source destination

signal signal

APPLICATION

NETWORK

TRANSPORT

DATA LINK

PHYSICAL

APPLICATION

NETWORK

TRANSPORT

DATA LINK

PHYSICAL

bits bits

data blocks




transmission medium


* Sometimes erroneously denoted as Packet. Packets are L3 entities.

time

Data Block*

Data Burst

T R

source destination

signal signalbits bits

Protocol Headers

transmitter receivertransmission medium




Control Plane

UserPlane

“out-of-band”or

“in-band”signalling

control messages

T R

user data




time

Latency

Rb = Bit Rate = number of bits per second transmitted on the channel.U = User Throughput = number of information bits per second

successfully received by the destination.W = Latency = time to transfer a data chunk from source to destination.

i-th data chunkdata bursts

User Plane

transmitter side receiver side




Digital Communications à Application Requirements



T R

time

W = Latency


BER

U = User Throughput = Number of information bits per second receivedBER = Bit Error Rate = Percentage of erroneous bits

i-th data chunk i-th data chunk

data bursts

User Plane



T R

timedata burstdata block


protocol headers

User Plane


data block

Three main options:

1. All bits are correct2. Errors are correctable3. To be discarded

4. Only partially discarded

data block


T R


BLER

BLER = BLock Error Rate = Percentage of erroneous data blocks

User Plane


data blockdata block

timedata burstdata block

protocol headers


T R


EE = Energy Efficiency = Number of information bits per joule received

Both Planes


data blockdata block

Energy consumed (Joule)


T R

user throughput 10 Kbit/s 100 Kbit/s n. a. n. a.

latency 300 ms 500 ms n. a. 0.1-10 ms

BLER 0.05 0.01 zero 0.0001

Interactive audio Interactive video web browsing control

Some examples




T R



Latency

User Throughput

Energy Efficiency

BLER

… with different levels of reliability (BLER).


Digital Communications à Protocol Efficiency



T R

APPLICATION

NETWORK

TRANSPORT

DATA LINK

PHYSICAL

APPLICATION

NETWORK

TRANSPORT

DATA LINK

PHYSICALbit rate

User Throughput

throughputnetwork throughput

channel bandwidth


data burst

protocol headersBit Rate Rb

data block



T R

APPLICATION

NETWORK

TRANSPORT

DATA LINK

PHYSICAL

APPLICATION

NETWORK

TRANSPORT

DATA LINK

PHYSICALbit rate

U < Rb

throughputnetwork throughput

channel bandwidth


data burst

protocol headersBit Rate Rb

data block



time

Transmission Time Interval (TTI)


Data Burst Transmission Time (DBTT)


protocol headers

control message

Duration D

User Throughput = Rb * hp < Rb (ideal channel conditions)Protocol Efficiency = hp = DBTT / TTI < 1

U < Rb for three reasons:

1. protocol headers (redundancy)2. control messages (overhead)3. silent intervals (overhead)


time



Data Burst Transmission Time (DBTT)


protocol headers

control message

Redundancy Factor = hr = DBTT / D < 1Overhead Factor = ho = D / TTI < 1

Duration D





Protocol Efficiency = hp = DBTT / TTI = hr ho


time


Data Burst Transmission Time (DBTT)protocol headers

control message

Duration D





e.g. CSMA with RTS/CTS

Rx

Txtime

time

R

P C

DS

t

Transmission Time Interval

P

t Z


Protocol Efficiency = hp = Z / [ Z + (S+R+C+(D-Z)+2P+2t) ] E.g. in WiFi hp ≅ 1 / [ 1 + (S+2t)/Z] ≅ 0.5 with large data bursts (1 KB)



e.g. TDMA

time

D


Z


1 2 … P

Protocol Efficiency = hp = Z / P D = ha * Z / D = ha * hrE.g. in 2G hp ≅ 0.04 when using only one slot over eight

slot

Tx

Frame



e.g. TDD

time


Z


1 2

Protocol Efficiency = hp = Z / 2 D = hd * Z / D = hd * hrE.g. in Bluetooth hp ≅ 0.25 when only one slave is connected to a master

slot

Tx

D

1 2



hr Redundancy Factorho Overhead Factor

T R

hp = hr * ho



T R


Higher user throughputs require:

u Larger bit ratesu More efficient protocolsu Reliable channels

data blocks BLER

U = Rb * hp * ( 1 – BLER )


roberto verdone · 2020-03-04 · prof. roberto verdone time latency rb= bit rate = number of bits...

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