wireless communication network lab. chapter 9 mobile communication systems ee of niuchih-cheng...
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Wireless Communication Network Lab.
Chapter 9Mobile Communication Systems
EE of NIU Chih-Cheng Tseng 1
Prof. Chih-Cheng Tseng
http://wcnlab.niu.edu.tw
Wireless Communication Network Lab.
MSC…HLR
VLR
EIR
AUC
Gateway MSC
MSC
…
PSTN/ISDN
BSCBTS
BTS
BTS
MS
Base Station System
BSCBTS
BTS
BTS
…
MS
Base Station System
…
Chih-Cheng Tseng 2EE of NIU
Authentication Center
Visitor Location register
Home Location register
Equipment Identity Register
Cellular System Infrastructure
Wireless Communication Network Lab.
HLR/VLR/AUC/EIR
Chih-Cheng Tseng 3EE of NIU
HLR is located at the MSC where the MS is initially registered
VLR contains information about all visiting MSs in that particular area of MSC
AUC provides authentication and encryption parameters
EIR contains identity of equipment that prevents service to unauthorized MSs
Wireless Communication Network Lab.
Post Office Cincinnati
Post Office Washington, DC
Mail from the world
Cincinnati
Washington, DC
Chih-Cheng Tseng 4EE of NIU
Classical Mail Forwarding Technique
Wireless Communication Network Lab.
PSTN
MS
HomeMobile
Switching Center
HLRHome network
Visitingarea
Caller
VisitingMobile
Switching Center
VLR
MS
1
Location update request Using Becon Signals
Update location Info. sent to HLR
2
Automatic Location Update
EE of NIU Chih-Cheng Tseng 5
Wireless Communication Network Lab.
PSTN
MS
homeMobile
Switching Center
HLR Home Network
VisitingArea
Caller
Mobile Switching
Center
VLR
1 Call sent to home location
2Home MSC checksHLR; gets current location of MSin visiting area
3
Home MSC forwards call to visiting MSC
4
MSC in visiting area sendscall to BS and connects MS
Automatic Call Forwarding using HLR-VLR
EE of NIU Chih-Cheng Tseng 6
Wireless Communication Network Lab.
BS
MS
Cell where MS is currently located
Visiting MSC
VLR
Another MSC
Through backbone
HLR
Home MSC
Call routed as per called number to MS
Home MSC
Chih-Cheng Tseng 7EE of NIU
Redirection of Call to MS at a Visiting Location
Wireless Communication Network Lab.
Chih-Cheng Tseng 8EE of NIU
Registration
Wireless system needs to know whether MS is currently located in its home area or some other area (routing of incoming calls)
This is done by periodically exchanging signals between BS and MS known as Beacons
BS periodically broadcasts beacon signal (1 signal per second) to determine and test the MSs around
Each MS listens to the beacon, if it has not heard it previously then it adds it to the active beacon kernel table
This information is used by the MS to locate the nearest BS Information carried by beacon signal: cellular network
identifier, timestamp, gateway address ID of the paging area, etc.
Wireless Communication Network Lab.
Chih-Cheng Tseng 9EE of NIU
Steps for Registration
MS listens to a new beacon, if it’s a new one, MS adds it to the active beacon kernel table
If MS decides that it has to communicate through a new BS, kernel modulation initiates handoff process.
MS locates the nearest BS via user level processing The visiting BS performs user level processing and decides:
• Who the user is?• What are its access permissions?• Keeping track of billing
Home site sends appropriate authentication response to the current serving BS
The BS approves/disapproves the user access
Wireless Communication Network Lab.
Visiting BS(Visiting MSC)
MSBeacon sig
nal exchange
1Request f
or registration
2Authentication/rejected
5
Home BS(Home MSC)
3 Authentication request
4 Authentication response
Through backbone
Chih-Cheng Tseng 10EE of NIU
Using a Mobile Phone Outside the Subscription Area
Wireless Communication Network Lab.
Applications and Characteristics of Beacon Signals
Application Frequency band Information carried
Cellular networks824-849 MHz (AMPS/CDPD), 1,850-1,910 MHz (GSM)
Cellular IP network identifier,Gateway IP address, Paging area ID, Timestamp
Wireless LANs(discussed in Chapter 15)
902-928 MHz (industrial, scientific, and medical band for analog and mixed signals) 2.4-2.5GHz (ISM band for digital signals)
Traffic indication map
Ad hoc networks(discussed in Chapter 14)
902-928 MHz (ISM band for analog and mixed signals) 2.4-2.5 GHz (ISM band for digital signals)
Network node identify
GPS(discussed in Chapter 12)
1575.42 MHzTimestamped orbital map and astronomical information
Search and rescue 406 and 121.5 MHzRegistration country and ID of vessel or aircraft in distress
Mobile robotics 100 KHz - 1 MHz Position of pallet or payload
Location tracking 300 GHz - 810 THz (infrared)Digitally encoded signal to identify user's location
Aid to the impaired 176 MHzDigitally coded signal uniquely identifying physical locations
EE of NIU Chih-Cheng Tseng 11
Wireless Communication Network Lab.
Chih-Cheng Tseng 12EE of NIU
Handoff Parameters (1/3)
Change of radio resources from one cell to an adjacent one
Handoff depends on cell size, boundary length, signal strength, fading, reflection, etc.
Handoff can be initiated by MS or BS and could be due to• Radio link
• Network management
• Service issues
Wireless Communication Network Lab.
Chih-Cheng Tseng 13EE of NIU
Handoff Parameters (2/3)
Radio link handoff is due to mobility of MS It depends on:
• Number of MSs in the cell• Number of MSs that have left the cell• Number of calls generated in the cell• Number of calls transferred from the neighboring cells• Number and duration of calls terminated in the cell• Number of calls that were handoff to neighboring cells• Cell dwell time
Wireless Communication Network Lab.
Handoff Parameters (3/3)
Network management may cause handoff if there is drastic imbalance of traffic in adjacent cells and optimal balance of resources is required
Service related handoff is due to the degradation of QoS (quality of service)
EE of NIU Chih-Cheng Tseng 14
Wireless Communication Network Lab.
Chih-Cheng Tseng 15EE of NIU
Time for Handoff
Factors deciding right time for handoff:• Signal strength
• Signal phase
• Combination of above two
• Bit error rate (BER)
• Distance Need for handoff is determined by:
• Signal strength
• CIR (carrier to interference ratio)
Wireless Communication Network Lab.
Handoff Region (1/2)
By looking at the variation of signal strength from either base station, it is possible to decide on the optimum area where handoff can take place
EE of NIU Chih-Cheng Tseng 16
BSi
Signal strength due to BSj
E
X1
Signal strength due to BSi
X3 X5
MS
Pmin
Pi(x) Pj(x)
X4Xth X2
BSj
Wireless Communication Network Lab.
Chih-Cheng Tseng 17EE of NIU
Handoff Region (2/2)
Region X3-X4 indicates the handoff area, where depending on other factors, the handoff needs to be performed
One option is to do handoff at X5 where the two signal strengths are equal
If MS moves back and forth around X5, it will result in too frequent handoffs (ping-pong effect)
Therefore MS is allowed to continue with the existing BS till the signal strength decreases by a threshold value E
Different cellular systems follow different handoff procedure
Wireless Communication Network Lab.
Types of Handoff
Hard Handoff (break before make)• Releasing current resources from the prior BS before
acquiring resources from the next BS
• FDMA,TDMA follow this type of handoff Soft Handoff (make before break)
• In CDMA, since the same channel is used, we can use the same if orthogonal to the codes in the next BS
• Therefore, it is possible for the MS to communicate simultaneously with the prior BS as well as the new BS
EE of NIU Chih-Cheng Tseng 18
Wireless Communication Network Lab.
BS1 BS2MS
(a). Before handoff
BS1 BS2MS
(b). During handoff (No connection)
BS1 BS2MS
(c). After handoff
Chih-Cheng Tseng 19EE of NIU
Hard Handoff (FDMA and TDMA)
Wireless Communication Network Lab.
BS1 BS2MS
(b). During handoff
BS1 BS2MS
BS1 BS2MS
(c). After handoff(a). Before handoff
Chih-Cheng Tseng 20EE of NIU
Soft Handoff (CDMA only)
Wireless Communication Network Lab.
Chih-Cheng Tseng 21EE of NIU
Roaming Support (1/2)
To move from a cell controlled by one MSC area to a cell connected to another MSC
Beacon signals and the use of HLR-VLR allow the MS to roam anywhere provided the same service provider using that particular frequency band, is there in that region
Wireless Communication Network Lab.
BS1 BS2MS
Home MSC
Visiting MSC
BS1 BS2MS
Home MSC
Visiting MSC
MS moves
Chih-Cheng Tseng 22EE of NIU
Roaming Support (2/2)
Wireless Communication Network Lab.
PSTN
Paging Area 1
MSC2
c
MSC4
Paging Area 2
e
MS
MSC1
a b
Handoff Scenarios with Different Degree of Mobility
EE of NIU Chih-Cheng Tseng 23
MSC3
d
Wireless Communication Network Lab.
Chih-Cheng Tseng 24EE of NIU
Possible Handoff Situations
Assume MSC1 to be the home of the MS for registration, billing, authentication, etc.
When handoff is from position “a” to “b”, the routing can be done by MSC1 itself
When handoff is from position “b” to “c” , then bi-directional pointers are set up to link the HLR of MSC1 to VLR of MSC2
When handoff occurs at “d” or “e”, routing of information using HLR-VLR may not be adequate (“d” is in a different paging area)
Concept of Backbone network
Wireless Communication Network Lab.
Connection Path after handoff
MSC1 HLR
MSC2 VLR
a b c
Information to MS being sent
Initial path of information transfer
MS
Information Transmission Path when MS Hands Off from “b” to “c”
EE of NIU Chih-Cheng Tseng 25
Wireless Communication Network Lab.
MSC
Router
Paging area 1 (PA1) Paging area 2 (PA2)
MSC1
(a,b)MSC2 (c) MSC3 (d)
MSC4 (e)
(a,b,c,d,e)
(a,b)
(a,b,c)
(d)R3
R4 R6
R2
R5
R9
R1
R7
R10
R12
R8
R11 R13
From rest of the backbone
(c) (e)
R: Routers
EE of NIU Chih-Cheng Tseng 26
MSC Connections to Backbone Network & Routing/ Rerouting
Wireless Communication Network Lab.
Chih-Cheng Tseng 27EE of NIU
Backbone Network
Routing done according to the topology and connectivity of the backbone network
The dotted lines show the possible paths for a call headed for different MS locations
One option is to find a router along the original path, from where a new path needs to start to reach the MSC along the shortest path
Wireless Communication Network Lab.
Chih-Cheng Tseng 28EE of NIU
Home Agents (HA), Foreign Agents (FA) and Mobile IP
Two important software modules are associated with routers, home agent (HA) and foreign agent (FA)
MS is registered with a router, mostly a router closest to the home MSC can be used to maintain its HA
A router other than closest one could also serve as an HA Once a MS moves from the home network, a software module
in the new network FA assists MS by forwarding packets for the MS
This functionality is somewhat similar to HLR-VLR
Wireless Communication Network Lab.
Home MSC MSC1 MSC2 MSC3 MSC4
Selected router for maintaining its
home agentR3 R4 R6 R9
Home MSC and Home Agent (HA) for the Previous Network
EE of NIU Chih-Cheng Tseng 29
Wireless Communication Network Lab.
Chih-Cheng Tseng 30EE of NIU
Call Establishment using HA-FA (1/2)
Whenever a MS moves to a new network, it still retains its initial HA
The MS detects the FA of the new network, by sensing the periodic beacon signals which FA transmits
MS can also itself send agent solicitation messages to which FA responds
When FA detects a new MS, it allocates a CoA (care of address) to the MS, using dynamic host configuration protocol (DHCP)
Once MS receives CoA, it registers its CoA with its HA and the time limit binding for its validity
Such registration is initiated either directly by MS to the HA of the home router or indirectly through FA
Wireless Communication Network Lab.
Chih-Cheng Tseng 31EE of NIU
Call Establishment using HA-FA (2/2)
HA confirms its binding through a reply to the MS A message sent from an arbitrary source to the MS at the home
address is received by the HA Binding is checked, the CoA of the MS is encapsulated in the
packet and forwarded to the network If CoA of the FA is used, then packet reaches FA, it
decapsulates packet and passes to MS at the link layer In an internet environment, it is called Mobile IP After binding time, if MS still wants to have packets
forwarded through HA, it needs to renew its registration When MS returns to its home network, it intimates its HA
Wireless Communication Network Lab.
FA
3 CoA or C-CoA created
MSHA
Here is my HA and binding information
2
OK, send information
1
1”
1’
Beacon Signal
I am new here
(Any one new)
Acknowledge Registration + binding
4
4’ Same as step
Here is CoA or co-located CoA (C-CoA) for this MS
4
4” Same as step 4
EE of NIU Chih-Cheng Tseng 32
Registration Process Btw FA, MS, and HA When the MS Moves to a Paging area
Wireless Communication Network Lab.
Source To MS Payload DataIncoming message for MS
HA
HA CoA/C-CoA Source To MS Payload Data
Encapsulation
FA
Forwarding through intermediate router if CoA used Forwarding through
intermediate router if C-CoA used
Source To MS Payload Data
Decapsulation done at MSMS
Message Forwarding using HA-FA Pair
EE of NIU Chih-Cheng Tseng 33
Wireless Communication Network Lab.
Chih-Cheng Tseng 34EE of NIU
Routing in Backbone Routers
How FA finds HA of the MS? One approach is to have a global table at each router
of each MSC so that the route from FA to HA for that MS can be determined
Disadvantages: Information too large, one network might not like to give out information about all its routers to any external network (only gateways information is provided)
Use of Distributed Routing Scheme
Wireless Communication Network Lab.
PA1 PA2
PA3
PA4
PA5
Router X
Router W
Router Z
Network 1
Network 2
MS moves
PA1 PA2
PA3
PA4
PA5
Router Y
Network 1
Network 2
Illustration of Paging Areas (PAs) and Backbone Router Interconnect
EE of NIU Chih-Cheng Tseng 35
Wireless Communication Network Lab.
Route to PA
Next hop
Route to PA
Next hop
Route to PA
Next hop
Route to PA
Next hop
1 X 1 - 1 X 1 Y
2 X 2 - 2 X 2 Y
3 X 3 Y 3 Z 3 -
4 X 4 Y 4 Z 4 -
5 X 5 Y 5 Z 5 -
Table at routerW
Table at router X
Table at router Y
Table at routerZ
Distributed Routing Table and Location PAs
EE of NIU Chih-Cheng Tseng 36
Wireless Communication Network Lab. Process of transmitting messages from a source to
multiple recipients by using a group address for all hosts that wish to be the members of the group
Reduces number of messages to be transmitted as compared to multiple unicasting
Useful in video/audio conferencing, multi party games Multicasting can be performed either by building a
source based tree or core based tree
Chih-Cheng Tseng 37EE of NIU
Multicasting
Wireless Communication Network Lab.
Chih-Cheng Tseng 38EE of NIU
Source-Based Tree Multicasting
In source based tree, for each source of the group a shortest path is maintained, encompassing all the members of the group, with the source being the root of the tree
Source0
1
1
1
1
22
2
2
3
3
3Nodes not a part of Multicast group
Wireless Communication Network Lab.
Core-Based Tree Multicasting
In core based tree, a particular router is chosen as a core and a tree is maintained with the core being the root.
Every source forwards the packet to a core router, which then forwards it on the tree to reach all members of the multicast group
EE of NIU Chih-Cheng Tseng 39
Tree
Core
Wireless Communication Network Lab.
Chih-Cheng Tseng 40EE of NIU
Multicasting over Mobile IP (1/3)
Bi-directional Tunneling (BT) and Remote Subscription approaches have been proposed by IETF for providing multicast over Mobile IP
In BT approach, whenever a MS moves to a foreign network, HA is responsible for forwarding the multicast packets to the MS via FA
In Remote Subscription protocol, whenever a MS moves to a foreign network, the FA (if not already a member of multicast group) sends a tree join request
Wireless Communication Network Lab.
Chih-Cheng Tseng 41EE of NIU
Multicasting over Mobile IP (2/3)
Remote Subscription based approach is simple and prevents packet duplication and non optimal path delivery
It can cause data interruption till the FA is connected to the tree
It results in a number of tree join and tree leave requests when MS are in continuous motion
In contrast, in the BT approach, the HA creates a bi-directional tunnel to FA and encapsulates the packets for MS
FA then forwards the packets to the MS
Wireless Communication Network Lab.
Chih-Cheng Tseng 42EE of NIU
Multicasting over Mobile IP (3/3)
BT approach prevents data disruption due to the movement of MS
But causes packet duplication if several MSs of the same HA, that have subscribed to the same multicast group move to same FA
Also causes Tunnel Convergence Problem, where one FA may have several MSs subscribed to the same group, belonging to different HAs and each HA may forward a packet for its MSs to the same FA
Wireless Communication Network Lab.
HA
Multicast packets from the multicast tree MS1
MS2
MS3
FA
MS 1
MS 2
MS 3
Packet Duplication in BT Tunnel Approach
EE of NIU Chih-Cheng Tseng 43
Wireless Communication Network Lab.
Multicast packets from the multicast tree
HA 1
HA 2
HA 3
CoA (MS1)
CoA (MS2)
CoA (MS3)
CoA (MS4)
MS 1
MS 2
MS 3
MS 4
FA
Tunnel Convergence Problem
EE of NIU Chih-Cheng Tseng 44
Wireless Communication Network Lab.
Chih-Cheng Tseng 45EE of NIU
MoM Protocol
To overcome Tunnel Convergence Problem, MoM protocol is proposed wherein the FA selects one of the HAs, called the Designated Multicast Service Provider (DMSP), from the HA List for a particular group
The remaining HAs do not forward packets to FA
Wireless Communication Network Lab.
Multicast packets from the multicast tree
HA 1
HA 2
HA 3
CoA (MS1)
CoA (MS2)
CoA (MS3)
MS 1
MS 2
MS 3
MS 4
Stop
Stop
Forward
DMSP Selection
FA
CoA (MS4)
Illustration of MoM Protocol
EE of NIU Chih-Cheng Tseng 46
Wireless Communication Network Lab.
Ultra-Wideband Technology (UWB)
UWB Radio: Radio System having large bandwidth.
• Bandwidth > 25% of center frequency or > 1 GHz.
Wide bandwidth makes it possible to share spectrum with other users with certain co-coverage sense.
Wide band signals are naturally suited for location determination applications.
EE of NIU Chih-Cheng Tseng 47
Wireless Communication Network Lab.
UWB Basics - TM-UWB
Basic element: Ultra short monocycle wavelet• Wavelet pulse width between 0.2 and 1.5 nsecs• Center frequency between 5 GHz and 600 MHz• Pulse-to-pulse interval between 25 and 1000 nsecs
System uses pulse position modulation No Intermediate frequency stage
• Reduces complexity Single bit of information is spread over multiple
monocycels
EE of NIU Chih-Cheng Tseng 48
Wireless Communication Network Lab.
TM-UWB Modulation and DSC-UWB
Pulse position modulation• Positions signal one quarter cycle early or late
relative to the nominal PN coded location or pulse polarity
• Modulation further smoothes the spectrum of the signal, thus making the system less detectable
DSC-UWB• Wavelet pulse trains at duty cycles approaching
that of a sine wave carrier are direct sequence modulated to spread the signal. A PN sequence provides spectrum spreading, channelization and modulation
EE of NIU Chih-Cheng Tseng 49
Wireless Communication Network Lab.
UWB Signal Propagation
Generally follow a free space propagation law Millions of coded pulses transmitted per second Emissions below conventional receiver noise floor
and across an ultra wide bandwidth Very low extant RF signature , providing intrinsically
secure transmissions Low probability of detection and interception
EE of NIU Chih-Cheng Tseng 50
Wireless Communication Network Lab.
UWB Applications
Communications:• Noise like spectral characteristics of UWB signals
enables secure communication with less detection
• Suitable for robust in-building communications Advanced Radar Sensing:
• Through the wall radar, terrain mapping radar, ground penetrating radar
Precision Location and Tracking:• Remote, secure and real time tracking system
EE of NIU Chih-Cheng Tseng 51
Wireless Communication Network Lab.
Difference Between UWB and Spread Spectrum Techniques
UWB uses an extremely wide band of RF spectrum to transmit more data in a given period of time, which is a time-domain concept
Spread spectrum technique, including direct sequence spread spectrum or frequency hopping spread spectrum, is a transforming technique in frequency domain
EE of NIU Chih-Cheng Tseng 52
Wireless Communication Network Lab.
UWB Advantages & Limitations
UWB radio systems have large bandwidth (>1 GHz). UWB has potential to address today’s “spectrum
drought” Emissions below conventional level Single technology with 3 distinct capabilities Secure transmission, low probability of interception
or detection and anti-jam immunity Not appropriate for a WAN (Wide Area Network)
deployment such as wireless broadband access UWB devices are power limited
EE of NIU Chih-Cheng Tseng 53
Wireless Communication Network Lab.
Need for Femtocell
Advanced cellular standards such as 3GPP’s UMTS and LTE; 3GPP2’s CDMA2000, 1x, EVDO and WiMAX
High data rate and seamless coverage important objective Signal strength is weak inside buildings More than 50% voice call and more than 70% data traffic start
from an indoor environment Easier solution is to deploy some indoor devices serving only
the indoor users Femtocell Network is an effective way to remedy coverage
holes
EE of NIU Chih-Cheng Tseng 54
Wireless Communication Network Lab.
F-BS
F-BS
F-BS
FGW
MS
MS
MS
MS
MS
MS
Internet
Wired Connection Wireless
Connection
F-BS: Femtocell Base StationFGW: Femtocell GatewayM-BS: Macrocell Base StationMS: User Mobile Station
M-BS
Telephony Core Network
Femtocell
EE of NIU Chih-Cheng Tseng 55
Wireless Communication Network Lab.
Femtocell Characteristics (1/2)
Femtocell Base Station (F-BS)• Wireless Interface• Internet Interface
Internet Link Femtocell Gateway (FGW) Benefits of Femtocell Network
• Better and seamless coverage• Enhanced capacity• Lower transmit power• Prolong handset battery life• Higher signal-to-interference-noise ratio (SINR)
Hand off Synchronization Self-Configuration, Self-Operation and Location Tracking Security Issues
EE of NIU Chih-Cheng Tseng 56
Wireless Communication Network Lab.
Femtocell Characteristics (2/2)
EE of NIU Chih-Cheng Tseng 57
Characteristics Femtocell Macrocell
Air interface Telecommunication standard
Telecommunication standard
Backhaul Broadband Internet Telephony network
Cost $200/year $60,000/year
UE Power consumption low high
Radio Range 10-50 meters 300-2000 meters
Wireless Communication Network Lab.
Comparing F-BS with AP
EE of NIU Chih-Cheng Tseng 58
Characteristics F-BS APSpectrum Licensed Unlicensed
Wireless MAC Connection-based
Contention-based
Backhaul Broadband Internet
Broadband Internet
Power 100mW ~1.5 WAir interface Telecommunicat
ion standard802.11a/b/g/n
Range 10-50m 35-70mService Primarily voice Primarily data
Current cost $200-$250 $50-$100
Wireless Communication Network Lab.
Handoff
Three hand off categories:• Hand-Out: user handset handoff from a Femtocell to a
macrocell
• Hand-In: user handset handoff from a Femtocell to a macrocell
• Hand off: user handset handoff from a Femtocell to close-by another Femtocell
EE of NIU Chih-Cheng Tseng 59