roberto verdone · 2020-03-04 · prof. roberto verdone time latency rb= bit rate = number of bits...
TRANSCRIPT
Prof. Roberto Verdonewww.robertoverdone.org
TelecomunicazioniRoberto Verdone
https://www.linkedin.com/in/roberto-verdone/
Radio NetworksDEI, University of Bologna
Prof. Roberto Verdonewww.robertoverdone.org
Fundamentals of Digital Comms
Prof. Roberto Verdonewww.robertoverdone.org
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
Prof. Roberto Verdonewww.robertoverdone.org
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
Digital Communications à Protocols
Fundamentals of Digital Communications
transmission medium
Prof. Roberto Verdonewww.robertoverdone.org
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
transmitter receiver
Digital Communications à Protocols
Fundamentals of Digital Communications
transmission medium
Prof. Roberto Verdonewww.robertoverdone.org
T R
source destination
signal signal
APPLICATION
NETWORK
TRANSPORT
DATA LINK
PHYSICAL
APPLICATION
NETWORK
TRANSPORT
DATA LINK
PHYSICAL
bits bits
data blocks
transmitter receiver
Digital Communications à Protocols
Fundamentals of Digital Communications
transmission medium
Prof. Roberto Verdonewww.robertoverdone.org
* 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
Digital Communications à Protocols
Fundamentals of Digital Communications
Prof. Roberto Verdonewww.robertoverdone.org
Control Plane
UserPlane
“out-of-band”or
“in-band”signalling
control messages
T R
user data
Digital Communications à Protocols
Fundamentals of Digital Communications
Prof. Roberto Verdonewww.robertoverdone.org
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 Protocols
Fundamentals of Digital Communications
Prof. Roberto Verdonewww.robertoverdone.org
Digital Communications à Application Requirements
Fundamentals of Digital Communications
Prof. Roberto Verdonewww.robertoverdone.org
T R
time
W = Latency
Digital Communications à Application Requirements
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
Fundamentals of Digital Communications
Prof. Roberto Verdonewww.robertoverdone.org
T R
timedata burstdata block
Digital Communications à Application Requirements
protocol headers
User Plane
Fundamentals of Digital Communications
data block
Three main options:
1. All bits are correct2. Errors are correctable3. To be discarded
4. Only partially discarded
data block
Prof. Roberto Verdonewww.robertoverdone.org
T R
Digital Communications à Application Requirements
BLER
BLER = BLock Error Rate = Percentage of erroneous data blocks
User Plane
Fundamentals of Digital Communications
data blockdata block
timedata burstdata block
protocol headers
Prof. Roberto Verdonewww.robertoverdone.org
T R
Digital Communications à Application Requirements
EE = Energy Efficiency = Number of information bits per joule received
Both Planes
Fundamentals of Digital Communications
data blockdata block
Energy consumed (Joule)
Prof. Roberto Verdonewww.robertoverdone.org
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
Digital Communications à Application Requirements
Fundamentals of Digital Communications
Prof. Roberto Verdonewww.robertoverdone.org
T R
Digital Communications à Application Requirements
Fundamentals of Digital Communications
Latency
User Throughput
Energy Efficiency
BLER
… with different levels of reliability (BLER).
Prof. Roberto Verdonewww.robertoverdone.org
Digital Communications à Protocol Efficiency
Fundamentals of Digital Communications
Prof. Roberto Verdonewww.robertoverdone.org
T R
APPLICATION
NETWORK
TRANSPORT
DATA LINK
PHYSICAL
APPLICATION
NETWORK
TRANSPORT
DATA LINK
PHYSICALbit rate
User Throughput
throughputnetwork throughput
channel bandwidth
Digital Communications à Protocol Efficiency
data burst
protocol headersBit Rate Rb
data block
Fundamentals of Digital Communications
Prof. Roberto Verdonewww.robertoverdone.org
T R
APPLICATION
NETWORK
TRANSPORT
DATA LINK
PHYSICAL
APPLICATION
NETWORK
TRANSPORT
DATA LINK
PHYSICALbit rate
U < Rb
throughputnetwork throughput
channel bandwidth
Digital Communications à Protocol Efficiency
data burst
protocol headersBit Rate Rb
data block
Fundamentals of Digital Communications
Prof. Roberto Verdonewww.robertoverdone.org
time
Transmission Time Interval (TTI)
Digital Communications à Protocol Efficiency
Data Burst Transmission Time (DBTT)
Fundamentals of Digital Communications
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)
Prof. Roberto Verdonewww.robertoverdone.org
time
Transmission Time Interval (TTI)
Digital Communications à Protocol Efficiency
Data Burst Transmission Time (DBTT)
Fundamentals of Digital Communications
protocol headers
control message
Redundancy Factor = hr = DBTT / D < 1Overhead Factor = ho = D / TTI < 1
Duration D
U < Rb for three reasons:
1. protocol headers (redundancy)2. control messages (overhead)3. silent intervals (overhead)
Prof. Roberto Verdonewww.robertoverdone.org
Digital Communications à Protocol Efficiency
Protocol Efficiency = hp = DBTT / TTI = hr ho
Fundamentals of Digital Communications
time
Transmission Time Interval (TTI)
Data Burst Transmission Time (DBTT)protocol headers
control message
Duration D
U < Rb for three reasons:
1. protocol headers (redundancy)2. control messages (overhead)3. silent intervals (overhead)
Prof. Roberto Verdonewww.robertoverdone.org
Digital Communications à Protocol Efficiency
e.g. CSMA with RTS/CTS
Rx
Txtime
time
R
P C
DS
t
Transmission Time Interval
P
t Z
Fundamentals of Digital Communications
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)
Prof. Roberto Verdonewww.robertoverdone.org
Digital Communications à Protocol Efficiency
e.g. TDMA
time
D
Transmission Time Interval
Z
Fundamentals of Digital Communications
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
Prof. Roberto Verdonewww.robertoverdone.org
Digital Communications à Protocol Efficiency
e.g. TDD
time
Transmission Time Interval
Z
Fundamentals of Digital Communications
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
Prof. Roberto Verdonewww.robertoverdone.org
Digital Communications à Protocol Efficiency
hr Redundancy Factorho Overhead Factor
T R
hp = hr * ho
Fundamentals of Digital Communications
Prof. Roberto Verdonewww.robertoverdone.org
T R
Digital Communications à Protocol Efficiency
Higher user throughputs require:
u Larger bit ratesu More efficient protocolsu Reliable channels
data blocks BLER
U = Rb * hp * ( 1 – BLER )
Fundamentals of Digital Communications