Circuit-Switched Systems

Transcription

EE 4105 Communication Engg-II
Dr. Mostafa Zaman Chowdhury
Slide # 1
Dept. of Electrical and Electronic Engineering, KUET
1
Circuit-Switched Systems
 In a circuit-switched system, each traffic channel is
dedicated to a user until its cell is terminated.
 Circuit switching is a methodology of implementing a
telecommunications network in which two network nodes
establish a dedicated communications channel (circuit)
through the network before the nodes may communicate.
 The circuit guarantees the full bandwidth of the channel
and remains connected for the duration of the
communication session. The circuit functions as if the
nodes were physically connected as with an electrical
circuit.
 Analog system
 digital system
2
Circuit-Switched Systems: Analog
 Consists of three subsystem
 a mobile unit : A mobile
telephone unit contains a
control unit, a transceiver, and
an antenna system.
 a cell site : provides interface
between the MTSO and the
mobile units. It has a control
unit, radio cabinets, antennas,
a power plant, and data
terminals.
 mobile telephone switching
office (MTSO): The switching
office, the central coordinating
element for all cell sites,
contains the cellular processor
and cellular switch.
3
Circuit-Switched Systems: Digital (e.g., GSM) (1/3)
 Consists of four
elements: mobile station,
base transceiver station
(BTS), base station
controller (BSC), and
switching subsystems,
4
GSM Architecture
 MS: consists of two parts, mobile equipment (ME) and
subscriber identify module (SIM). SIM contains all
subscriber-specific data stored on the MS side.
 BTS: Besides having the same function as the analog BTS,
it has the Transcoder/Rate Adapter Unit(TRAU), which
carries out coding and decoding as well as rate adaptation
in case data rate varies.
 BSC: A new element in digital systems that performs the
Radio Resource (RR) management for the cells under its
control. BSC also handles handovers, power management
time and frequency synchronization, and frequency
reallocation among BTSs.
6
 Switching subsystems:
 MSC: The main function of MSC is to coordinate the setup of calls between MS and
PSTN users.
 VLR (Visitor Location Register): A database of all mobiles roaming in the MSC’s
area of control.
 HLR(Home Location Register):Acentralized database of all subscribers registered
in a Public Land Mobile Network (PLMN).
 AUC (Authentication Center): Provides HLR with authentication parameters and
ciphering keys that are used for security purposes.
 EIR (Equipment Identity Register): A database for storing all registered mobile
equipment numbers.
 IWF (Interworking function): Provides the subscriber with data services that can
access data rate and protocol conversion facilities and interfaces with public and
private data networks.
 EC (Echo Canceller): Used on the PSTN side of the MSC for all voice circuits.
 XC (Transcoder): Usually installs in each BTS. But for the cost reason, it can be
installed in BSC or MSC.
 OMC(Operational and Maintenance Center): This function resided in analog MSC
but became a separated entity in digital systems.
7
Packet-Switched Systems: (2.5G+ e.g., UMTS)
 Packet switching is a digital networking communications method that
groups all transmitted data – regardless of content, type, or structure –
into suitably sized blocks, called packets
 delivery of variable bitrate data streams (sequences of packets) over a shared
network which allocates transmission resources as needed using statistical
multiplexing or dynamic bandwidth allocation techniques
8
UMTS Architecture
Mobile Station
ME
SIM
Base Station
Subsystem
BTS
BSC
Network Subsystem
MSC/
VLR
EIR
Other Networks
GMSC
PSTN
HLR
AUC
PLMN
RNS
ME
USIM
SD
+
Node
B
RNC
SGSN
GGSN
Internet
UTRAN
Note: Interfaces have been omitted for clarity purposes.
Packet-Switched Systems: (2.5G+ e.g., UMTS)
 There are six elements: MS, Node B, RNC, SGSN, GGSN, and GF
 MS: Provides the voice and packet data services. It is also called UE
(User Equipment).
 Node B: The name for base station in GSM.
 RNC (Radio Network Controller): Controls the radio resources of the
Node Bs that are connected to it. Its function is similar to BSC. A
device PCU (Packet Control Unit) converts the data stream into packet
format
 SGSN (Service GPRS Support Node): Analogous to MSC/VLR in the
circuit-switched system. This includes mobility management, security,
and access control functions. It interfaces to HLR.
 GGSN (Gateway GPRS Support Node): The point of interface with
external packet data networks such as the Internet.
 CGF (Changing Gateway Function): Mainly for billing
10
LTE Architecture
 Reff: https://sites.google.com/site/lteencyclopedia/ltenetwork-infrastructure-and-elements
Access Network
 eNode B Functionalities
 the eNodeB supports a set of legacy features, all related to physical
layer procedures for transmission and reception over the radio
interface
 Modulation and de-modulation
 Channel coding and de-coding
 Radio Resource Control: this relates to the allocation, modification
and release of resources for the transmission over the radio
interface between the user terminal and the eNodeB
 Radio Mobility management: this refers to a measurement
processing and handover decision.
12
Evolved Packet Core (EPC)
 The MME (Mobility Management Entity)
 Security procedures
 Terminal-to-network session handling
 Idle terminal location management
 The HSS (Home Subscriber Server)
is the concatenation of the HLR (Home Location Register) of GSM
User identification and addressing
User profile information
Mutual network-terminal authentication
13
Evolved Packet Core (EPC)
The Serving Gateway
the Serving GW is the termination point of the packet data interface
towards E-UTRAN
When terminals move across eNodeB in E-UTRAN, the Serving GW
serves as a local mobility anchor, meaning that packets are routed
through this point for intra E-UTRAN mobility and mobility with
other 3GPP technologies, such as 2G/GSM and 3G/UMTS.
The PDN (Packet Data Network) Gateway
anchor point for sessions towards the external Packet Data
Networks, the PDN GW also supports Policy Enforcement features
The PCRF (Policy and Charging Rules Function) Server
The Policy Decision Function (PDF)
The Charging Rules Function (CRF)
14
3G Overview
 3G is created by ITU-T and is called IMT-2000
Evolution from 2G
2G
2.5G
IS-95
GSM-
GPRS
IS-95B
HSCSD
Cdma2000-1xRTT
3G
IS-136 & PDC
EDGE
W-CDMA
EDGE
Cdma2000-1xEV,DV,DO
TD-SCDMA
Cdma2000-3xRTT
3GPP2
3GPP
17
LTE vs UMTS
 Functional changes compared to the current UMTS
architecture
The Multiple Access Problem
 The base stations need to serve many mobile terminals at
the same time (both downlink and uplink)
 All mobiles in the cell need to transmit to the base station
 Interference among different senders and receivers
 So we need multiple access scheme
 Multiple Access:
 Enable many mobile users to share simultaneously radio spectrum.
 Provide for the sharing of channel capacity between a number of
transmitters at different locations.
 Aim to share a channel between two or more signals in such way
that each signal can be received without interference from another.
20
Multiple Access Schemes
3 orthogonal Schemes:
• Frequency Division Multiple Access (FDMA)
• Time Division Multiple Access (TDMA)
• Code Division Multiple Access (CDMA)
Frequency Division Multiple Access
frequency
 Each mobile is assigned a separate frequency channel for the
duration of the call
 Sufficient guard band is required to prevent adjacent channel
interference
 Usually, mobile terminals will have one downlink frequency
band and one uplink frequency band
 Different cellular network protocols use different frequencies
 Frequency is a precious and scare resource. We are running out
of it
 Cognitive radio
FDMA
23
Features of FDMA
 If an FDMA channel is not in sue, then it sits idle and can’t
be used by other users.
 Transmit simultaneously and continuously.
 FDMA is usually implemented in narrowband systems.
 Its symbol time is large as compared to the average delay spread.
 For continuous transmission, fewer bits are needed for
overhead purposes (such as synchronization and framing
bits) as compared to TDMA.
 FDMA uses duplexers since both TX and RX operate at the
same time.
24
Time Division Multiple Access
Guard time – signal transmitted by mobile
terminals at different locations do no arrive
at the base station at the same time
• Time is divided into slots and only one mobile terminal transmits
during each slot
– Like during the lecture, only one can talk, but others may take the floor in turn
• Each user is given a specific slot. No competition in cellular network
– Unlike Carrier Sensing Multiple Access (CSMA) in WiFi
TDMA
 Transmitter share a common channel.
 Only one transmitter is allowed to transmit at a time.
 Synchronous TDMA: access to the channel is restricted to regular.
 Asynchronous TDMA: a station may transmit at any time that the
channel is free.
26
Features of TDMA
 TDMA systems divide the radio spectrum into time slots.
 Each user occupies a cyclically repeating time slot.
 Transmit data in a buffer-and-burst method, thus the
transmission for any user is not continuous.
 TDMA has TDD and FDD modes
 Share a single carrier frequency with several users.
 Data transmission is not continuous, but occurs in bursts.
 No duplexers is required since users employ different time
slots for transmission and reception.
 TDMA can allocate different numbers of time slots per
frame to different users, allowing bandwidth be supplied
on demand to different users
27
Combined used of synchronous TDMA and
FDMA
28
Code Division Multiple Access
 Use of orthogonal codes to separate different transmissions
 Each symbol of bit is transmitted as a larger number of
bits using the user specific code – Spreading
 Bandwidth occupied by the signal is much larger than the
information transmission rate
 But all users use the same frequency band together
Orthogonal among users
CDMA
30
Example of CDMA
31
Orthogonal Frequency Division
Multiplexing(OFDM
 It is a special kind of FDM
 The spacing between carriers
are such that they are
orthogonal to one another
 Therefore no need of guard
band between carriers.
 Each terminal occupies a subset
of sub-carriers
 Subset is called an OFDMA
traffic channel
 Each traffic channel is assigned
exclusively to one user at any
time
user4
user3
user2
user1
32
Advantages of OFDMA
 Multi-user Diversity
 broadband signals experience frequency selective fading
 OFDMA allows different users to transmit over different portions
of the broadband spectrum (traffic channel)
 Different users perceive different channel qualities, a deep faded
channel for one user may still be favorable to others
33
34
History of Mobile Cellular
 Chapter 1: Wireless and Cellular Telecommunication
35
Few Slides from Adv. Wireless Comm
36
1G to 5G
 1st Generation(1984)
 Analog cellular (basic voice service)
 AMPS
 2nd Generation(CDMA(1996))
 Digital cellular (enhanced voice service)
 GSM and cdmaOne(IS-95A, IS-95B(99년))
 3rd Generation(2000(cdma2000), 2002(WCDMA))
 Voice, data, and image(384Kbps)
 IMT-2000 (cdma2000 1x, EV-DO, EV-DV and WCDMA, HSDPA, HSUPA, HSPA,
3GPP LTE, LTE-Advanced)
 WiBro, WiBro Evolution
 Problems: limited mobility and up to 2Mbps~100Mbps bandwidth
 3GPP, 3GPP2, IEEE 802
 4th Generation (IMT-Advanced(2010+))




Broadband multimedia applications and virtual reality (VR) applications
Full mobility and higher bandwidth (100Mbps, 1Gbps )
ITU-R WP5D and ITU-T SG19
Combination of 3GPP and IEEE 802.16m or Dual Mode
 5th Generation (2020+)
 Future Internet and Networks
 Sense
37
Cellular Network Evolution
Service
System
Multiplexi
ng
1G
2G
2.5 G
3G
4G
analog
digital
PCS
IMT-2000
IMT-Advanced
FDMA
TDMA
CDMA
TDMA
CDMA
CDMA
OFDMA
2.4Kbps
(144Kbps)
Data rate
Roaming
Technolo
gy
(384Kbps~14.4Mbps)
(14.4Kbps)
No
AMPS
100Mbps(이동 시)
(mobile)
1Gbps( 정지 시)
(stationary)
Limited
Limited
Global
Global
GSM
IS-95(CDMA)
PCS-1800
(GSM)
IS-95C
cdma2000, EVDO
WCDMA, HSDPA,
LTE, LTE-Advanced,
WiBro Evolution
Mobile WiMAX,
Femtocell, VLC,..
38
4G Evolution Path
39
 Cellular communication
 Mobile communication
 Wireless communication
 Advantages
 Disadvantages
40
Why Interference Management is Required?
 Interference is one of the main obstacle for the
femtocell network deployment
 Many femtocells around a small area
 Huge interference if there is no proper planning
 Interference causes
 Reduced throughput
 Increased outage probability
 Decreased QoS/QoE
 Inefficient interference management system
 Decreased frequency utilization
 Increased cost
Interference Scenarios for Femtocells Overlaid
by Macrocells




Macrocell downlink
Macrocell uplink
Femtocell downlink
Femtocell uplink
QoS
 What is QoS?
 Ability of a network to provide a service at an assured service level
 QoS management
 Network planning
− Network dimensioning
• Number of radio, transmission element and core network
− Details network planning
• Requirement of coverage, capacity and QoS
 QoS provisioning
− A process that deploys QoS in networks and MT
− Radio, core and transport QoS
 QoS monitoring
− Measure QoS and improve it further
 QoS optimization
− A process to improve the overall network quality
− Performance measurements, analysis of measurement results and
update of network quality
QoS Requirements for HSDPA Networks
▣ QoS Requirements target for audio and video services
Medium
Application
Key performance parameters and target values
E2E delay
Audio
Conversational
voice
< 150 ms (
preferred)
Jitter
Loss
< 1 ms
< 3% PLR
< 1 ms
< 3% PLR
<<1ms
< 3% PLR
< 400 ms limit
< 1 s for play back
Audio
Voice messaging
< 2 s for record
Audio
High quality
streaming audio
< 10 s
< 150 ms
(preferred)
Video
Videophone
< 1% PLR
< 400 ms limit
Lip-synch:<100 ms
Video
One-way video
<10 s
< 1% PLR
QoS Requirements for HSDPA Networks
▣ QoS requirement target for data services
Medium
Application
Key performance parameters and target values
E2E one-way delay
Data
Web-browsing
HTML
Jitter
Information loss
<2 s /page (preferred)
< 4 s/page (acceptable)
N.A
0
Data
Bulk data
Transfer /retrieval
< 15 s (preferred)
< 60s acceptable)
N.A
0
Data
High priority
Transaction/services
< 2 s (preferred)
< 4 s (acceptable)
N.A
0
Data
Command/control
< 250 ms
N.A
0
Data
Still image
< 15 s (preferred)
<60 s acceptable)
N.A
0
Data
Interactive games
< 200 ms
N.A
0
Data
Telnet
< 250 ms
N.A
0
Data
E-mail (server
access)
< 2 s (preferred)
< 4s (acceptable)
N.A
0
Data
E-mail (server to
server transfer)
Can be several
minutes
N.A
0
Why Mobility Management is Needed?
 Moving entity?
 Mobile terminal
 Mobile user
 Mobile network
 Moving scope?
 Intra/Inter-domain, Micro/Macro-mobility
 Horizontal, Vertical
 Active session?
 Location management (for Paging)
 Handoff (Session mobility)
 More network coverage in same area
 Cost
 QoS
 Reliability
Handoff Management Requirements
 Reduction of signaling and processing overhead
 Minimize packet loss and delay (seamless HO)
 QoS guarantees during the process and transfer of
context
 Use of any “triggers” or metrics available to decide when
and where (planned HO)
 Efficient use of network and MT resources
 Enhanced scalability, reliability and robustness
 Allow inter-technology handoff (VHO)
Soft Handoff Process
 MS continually scan for pilot signals from neighbor cells
 When a pilot from a neighbor cell crosses a threshold, MS requests a
handoff
 BS commands MS to perform handoff
Handover Steps
 System Discovery





MT must know which wireless networks are reachable
Periodic beacons from AP
Signal measurements
Gathering handoff metrics : bandwidth, cost, delay, SNR, power, etc.
Periodic network scanning
 Handoff Decision




MT evaluates the reachable wireless networks to make a decision
Price
Power consumption
Bandwidth availability
 Handoff Execution
 If MT decides to perform a HO, it executes the HO procedure required to be
associated with the new wireless network
Wireless Networks & Communications Lab.
50

Circuit-Switched Systems

Transcription

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