1
Mobile Cellular Networks
Reference Pahlavan Chapter 6, Sect 6.3 Mobility Management in Current and Future Communications
Networks," I. Akyildiz, J. McNair, J. Ho, et. al., IEEE Network Magazine, July/August 1998, pp.39-49.
McNair, Spring 15 EEL6591 Wireless Networks 2
Outline
Review Generations (1G 4G) of wireless networks Handoff Management
Handoff Initiation Channel Assignment Radio Link Transfer
Location management in Telephone Networks Location registration Location update and paging
Location Management in the Internet (Mobile IP) Mobile IP Micro-Mobile IP
2
3
Generations of Wireless Systems: 1G
First Generation: Analog voice service Small coverage areas Low quality Examples
AMPS (North,Central,South America, etc.) TACS (Europe) NMT (Scandinavia) NTT (Japan)
McNair, Spring 15 EEL6591 Wireless Networks
4
Generations of Wireless Systems: 2G
Second Generation: Digital services (paging, messaging, fax) Larger coverage areas Cellular mobility Digital transmission and switching Personal Communication Systems (PCS) Examples
IS-54, IS-95 (North America) GSM (Europe) PDC (Japan)
McNair, Spring 15 EEL6591 Wireless Networks
Base Station Mobile Terminal
3
5
Generations of Wireless Systems: 3G
McNair, Spring 15 EEL6591 Wireless Networks
Third Generation: Higher bandwidth
multimedia digital services (email, limited internet, PCS)
Even larger coverage areas Greater mobility / roaming Heterogeneous services
(voice, video, data) Examples
IMT 2000 (USA, Korea) UMTS (Europe, China)
6
Generations of Wireless Systems: 4G Global
mobility/roaming More bandwidth,
more multimedia Internet-based
packets switching Heterogeneous
(WWAN, WMAN, WLAN, WPAN, sensors, deep space, etc.)
Example - LTE McNair, Spring 15 EEL6591 Wireless Networks
4
7
Evolution From 2G to 4G
GSM
PDC
cdmaOne
TDMA (IS-136)
GPRS EDGE
cdma2000
Wcdma
CDMA IS-95
Cdma2000 w/ EVDO
LTE
2G 2G to 2.5G 2.5G to 3G 3G 4G
McNair, Spring 15 EEL6591 Wireless Networks
2G to 4G The GSM Path
McNair, Spring 15 EEL6591 Wireless Networks 8
GSM GPRS EDGE Wcdma UMTS
FDMA/TDMA/FDD
Gaussian Minimum Shift Keying (GMSK)
Pre-3G
FDMA/TDMA/FDD
(1/8) PSK, 32QAM
DS-CDMA
2G 2.5G 3G
LTE
4G
OFDMA
Circuit and packet based Circuit-based packet-based
1 Gbps 2Mbps-100 Mbps 100Kbps 1Mbps 60-100Kbps 20Kbps
(WiMax could also have been the 4G choice)
5
2G to 4G The IS-54 Path
McNair, Spring 15 EEL6591 Wireless Networks 9
IS-54/136 digital AMPS IS-95 cdma2000
cdma2000 + EVDO
FDMA/TDMA/FDD
(Pi/4) DQPSK
3G
DS-CDMA / FDD DS-CDMA / TDMA
2G 2G 3G
LTE
4G-ish
OFDMA
Circuit and packet based Circuit-based packet-based
1 Gbps EVDO adds 2.4Mbps (fwd) /
150Kbps for Data
2Mbps 1Mbps 50Kbps
DS-CDMA
QPSK QPSK QPSK, QAM QPSK, QAM
(WiMax could also have been the 4G choice)
McNair, Spring 15 EEL6591 Wireless Networks 10
Outline
Review Generations (1G 4G) of wireless networks Handoff Management
Handoff Initiation Channel Assignment Radio Link Transfer
Location management in Telephone Networks Location registration Location update and paging
Location Management in the Internet (Mobile IP) Mobile IP Micro-Mobile IP
6
McNair, Spring 15 EEL6591 Wireless Networks 11
Mobility Management
Mobility affects the quality of service The offered load (Erlangs) in each cell changes
dynamically with aggregate user movement. Causes many dropped calls when there are not
enough channels
Mobility affects network management How do you maintain a call that is moving
between cells? Handoff Management How do you find a roaming user to deliver calls? Location Management
McNair, Spring 15 EEL6591 Wireless Networks 12
Intra-System, or Horizontal Handoff
Intra-cell Inter-cell (Intra-switch) Inter-switch (Intra-system)
Mobile Node changes channels at the same base station
Mobile Node changes base stations at the same switch
Mobile Node changes base stations and switches
7
Inter-System, or Vertical, Handoff
McNair, Spring 15 EEL6591 Wireless Networks 13
LAN Router
MSC
LTE
McNair, Spring 15 EEL6591 Wireless Networks 14
Handoff Considerations
Operation Initiation (Detection/Decision) New connection generation
(Channel Assignment) Data flow control (Radio Link Transfer)
Control NCHO (Network-Controlled Handoff) MAHO (Mobile-Assisted Handoff) MCHO (Mobile-Controlled Handoff)
8
McNair, Spring 15 EEL6591 Wireless Networks 15
Phase 1: Handoff Initiation
Channel Measurements Word Error Indicator (WEI)
Indicates whether the current data burst was received properly
Received Signal Strength Indication (RSSI) Measures the co-channel interference power and
noise Quality Indicator (QI).
Reflects the signal to interference (S/I) ratio plus the noise ratio
McNair, Spring 15 EEL6591 Wireless Networks 16
Relative Signal Strength Indication
BS 1 BS 2 BS 1 signal strength
BS 2 signal strength
Distance from MT to BS 1
0
1
1 dPP or =
22 d
PP or =
A
9
McNair, Spring 15 EEL6591 Wireless Networks 17
RSSI with Thresholds (QI)
BS 1 BS 2
BS 1 signal strength BS 2 signal strength
Distance from MT to BS 1
0
1
1 dPP or =
22 d
PP or =
B
T1
McNair, Spring 15 EEL6591 Wireless Networks 18
RSSI with hysteresis
1
1 dPP or =
h
BS 1 BS 2
BS 1 signal strength BS 2 signal strength
C
2
2 dPP or =
10
McNair, Spring 15 EEL6591 Wireless Networks 19
Handoff Example
Consider the handoff initiation figure, where a mobile is moving from BS1 toward BS2.
Assume Po = 6W, the distance between the base stations in 300m, and alpha=2.
Label the point where handoff would occur for RSS with a hysteresis of 0.1mW.
McNair, Spring 15 EEL6591 Wireless Networks 20
Example figure
BS 1 BS 2
BS 1 signal strength BS 2 signal strength
Distance from MT to BS 1
0
1
1 dPP or =
22 d
PP or =
11
McNair, Spring 15 EEL6591 Wireless Networks 21
Hard Handoff versus Soft Handoff
Hard Handoff The mobile node stops communicating with the former
base station before beginning communication with the target base station
Soft Handoff The mobile node communicates with several candidate
base stations simultaneously, until one is chosen.
McNair, Spring 15 EEL6591 Wireless Networks 22
Soft Handoff Active Sets using RSS
BS 1 BS 2 BS 1 signal strength BS 2 signal strength
Distance from MT to BS 1
0
1
1 dPP or =
22 d
PP or =
Tadd
Tdrop
MT communicates with both BS1 and BS2
MT drops BS1 MT drops BS2
[seconds] tdrop[seconds] tdrop
12
Example
A mobile node samples signals from four BSs as a function of time. The times and signal strengths (in dBm) are given as follows:
Show the set of candidate base stations for a mobile node using soft handoff thresholds Tadd=-60dBm and Tdrop=-70dBm
McNair, Spring 15 EEL6591 Wireless Networks 23
Time(s)
0 2.5 5 7.5 10 12.5 15
BS1 -47 -57 -55 -60 -62 -65 -64 BS2 -59 -56 -54 -52 -51 -60.5 -52 BS3 -70 -72 -70 -58 -50 -62 -75 BS4 -72 -71 -60 -55 -53 -49 -56
McNair, Spring 15 EEL6591 Wireless Networks 24
Soft Handoff Advantages
Reduces the ping-pong effect. Avoids the additional signaling delay.
No hysteresis margin Avoids the additional delays and interference problems
associated with hysteresis. Reduces dropping probability.
In hard handoff, a definite choice is made to go to the new BS, according to RSSI.
In soft handoff, MTs can wait for a longer time (queued) for a channel at a new BS.
13
McNair, Spring 15 EEL6591 Wireless Networks 25
Soft Handoff Disadvantages
Reduces available network resources One MT uses up several channels.
Downlink interferers Two BSs sending to one MT, adding two
interferers to the noise floor. Must reduce soft handoff time to minimize the
impact of the added interference.
McNair, Spring 15 EEL6591 Wireless Networks 26
Soft Handoff Complexity
Selecting Optimal Parameters Add threshold Drop threshold Time to drop after drop threshold is crossed Soft handoff window: difference between the
add threshold and the drop threshold, i.e., deciding how long a soft handoff is in effect.
14
McNair, Spring 15 EEL6591 Wireless Networks 27
Phase 2: Channel Assignment
2rP
Handoff Out
Handoff In
New Call
Terminated Call
McNair, Spring 15 EEL6591 Wireless Networks 28
Channel Assignment (cont.)
Goal Need to manage a fixed number of channels, while
minimizing the dropping and blocking probability. Medium Access
Fixed channel assignment Dynamic channel assignment
Call Admission Control Guard channels Handoff request queues Priorities
15
McNair, Spring 15 EEL6591 Wireless Networks 29
Discrete Event Time Line: One Cell, 5 Channels
Time 0 1 2 3
2 new calls 2 handoff calls (in) 2 handoff calls 2 new calls
1 handoff call (out)
5 CHs Avail.
3 CHs Avail.
1 CH Avail.
0 CHs Avail.: 2 new calls blocked
4 handoff calls 1 new calls
2 handoff calls (out)
0 CHs Avail.: 1 new call blocked/ 2 handoffs dropped
McNair, Spring 15 EEL6591 Wireless Networks 30
BACKBONE TELEPHONE NETWORK
Mobile Terminal (MT)
Switch
Switch
Phase 3: Radio Link Transfer
Resource Mgmt Connection
establishment Buffering Packets
Quality of Service Some guarantees
and limited control over delay, loss, jitter, etc.
16
McNair, Spring 15 EEL6591 Wireless Networks 31
Outline
Review Generations (1G 4G) of wireless networks Handoff Management
Handoff Initiation Channel Assignment Radio Link Transfer
Location management in Telephone Networks Location registration Location update and paging
Location Management in the Internet (Mobile IP) Mobile IP Micro-Mobile IP
McNair, Spring 15 EEL6591 Wireless Networks 32
Location Management in Telephone Networks
Enables telecomm networks to Locate mobile nodes for call delivery Authenticate mobile nodes (AAA) On a limited basis, track mobile nodes as they
move through the network
17
McNair, Spring 15 EEL6591 Wireless Networks 33
Cellular Network Architecture
Location Register (Database) Mobile Switching
Center MSC
Backbone Wireline Network
Base Station Controller
Base Station
Mobile Terminal
Radio Network
Cell
McNair, Spring 15 EEL6591 Wireless Networks 34
Location Registration (GSM-MAP/IS-41)
18
McNair, Spring 15 EEL6591 Wireless Networks 35
Location Registration
MT enters a new LA, and transmits location update to new BS
BS forwards update to MSC, which queries VLR
Does the MT have an existing record?
New LA is in under same VLR. VLR updates the LA ID # for the MT.
Yes No
VLR determines address of HLR, and sends location registration message
HLR authenticates and registers MT by updating the VLR ID # for the MT. Then, HLR cancels former VLR.
Start
McNair, Spring 15 EEL6591 Wireless Networks 36
Call Delivery
19
McNair, Spring 15 EEL6591 Wireless Networks 37
Call Delivery
Incoming call for roaming MT reaches an MSC
The calling MSC determines the address of the MTs HLR, and sends a location request message to the HLR.
The HLR sends a route request message to the VLR, which forwards the message to its MSC
The MSC gives the MT a temporary local directory number (TLDN), and forwards the TLDN back to the HLR
The HLR forwards this message to the calling MSC, which sets up a route to the MT at its current MSC.
Finally, the current MSC tells all of the BSs in the MTs LA to send a polling signal to page the MT. When the MT responds, the call is connected.
Start
McNair, Spring 15 EEL6591 Wireless Networks 38
Paging Techniques
Selective Paging Stepwise Paging Paging under delay constraints
20
McNair, Spring 15 EEL6591 Wireless Networks 39
Paging
(MSC)
VLR
McNair, Spring 15 EEL6591 Wireless Networks 40
Location Area Design
Tradeoff Location Updates versus Terminal Paging
Goal: Improvements to tradeoff Geographical Fixed versus Dynamic User-based versus Global definition Network-specific
21
McNair, Spring 15 EEL6591 Wireless Networks 41
Dynamic Location Update Schemes
Movement-based The MT performs an update each time it crosses a
certain movement threshold, where one movement is made by crossing a cell boundary.
Distance-based The MT performs an update when its distance from
the cell where it performed its last update surpasses a certain distance threshold.
Time-based The MT performs an update at a constant time
threshold, deltaT.
McNair, Spring 15 EEL6591 Wireless Networks 42
Example
A MT is moving through the cellular network (R= km) as shown in the figure at a rate of 30km/hour.
Label the cell IDs where the MT will perform its updates for: Movement-based (T=3) Distance-based (T=6km) Time-based (30 minutes)
3
22
McNair, Spring 15 EEL6591 Wireless Networks 43
Example Figure: Movement Based
A
D
C
B
H
G
F L
K P
N S
R
Q M
J
I E O
McNair, Spring 15 EEL6591 Wireless Networks 44
Example Figure: Distance based
A
D
C
B
H
G
F L
K P
N S
R
Q M
J
I E O
23
McNair, Spring 15 EEL6591 Wireless Networks 45
Example Figure: Time Based
A
D
C
B
H
G
F L
K P
N S
R
Q M
J
I E O
McNair, Spring 15 EEL6591 Wireless Networks 46
Example
A MT is moving through the cellular network (R= km) as shown in the figure at a rate of 30km/hour.
Show the paging area, i.e., how many cells will the network page to find the MT for: Movement-based updates (T=3) Distance-based updates (T=6km) Time-based updates (30 minutes)
3
24
McNair, Spring 15 EEL6591 Wireless Networks 47
Example Figure Paging Area for Movement-based (T=3)
McNair, Spring 15 EEL6591 Wireless Networks 48
Outline
Review Generations (1G 4G) of wireless networks Handoff Management
Handoff Initiation Channel Assignment Radio Link Transfer
Location management in Telephone Networks Location registration Location update and paging
Location Management in the Internet (Mobile IP) Mobile IP Micro-Mobile IP
25
McNair, Spring 15 EEL6591 Wireless Networks 49
Location Management in Internet
The Telephone network is no longer the basis for most forms of communication.
The Internet is Commercially viable Available worldwide Designed for a multi-network environment
What are the implications for a seamless global network based on the Internet?
McNair, Spring 15 EEL6591 Wireless Networks 50
Circuit-switched Network Packet Network
PATH ROUTE Determined and fixed at time of call set up
Determined for each packet at transmission time
Call Setup Required
Not needed
PATH Dedicated Shared
BANDWIDTH ALLOCATION
Fixed Dynamic
QUALITY Guaranteed Best Effort
Circuit Switching to Packet Routing
Internet Mobility = Changing IP Address
26
McNair, Spring 15 EEL6591 Wireless Networks 51
Review: IP v4 Packet
Version IHL Type of Service Total Length
Identification Flags Fragment Offset
Time to Live Protocol Header Checksum
Source Address
Destination Address
Options + Padding
0 4 8 16 19 31 bits
Data Field
McNair, Spring 15 EEL6591 Wireless Networks 52
Review: IPv4 Addresses
27
McNair, Spring 15 EEL6591 Wireless Networks 53
BACKBONE INTERNETWORK
Mobile Node (MN)
Home Agent
Foreign Agent
Mobile IP Architecture
?
Router
Router
Correspondent Node (CN)
McNair, Spring 15 EEL6591 Wireless Networks 54
When the mobile moves from its home location to a new location, it must maintain two addresses: A Home address, an IP address with the home agent A Care-of-Address, which is an IP address from its new location
(foreign agent). Location Update:
Binding updates are sent to the home agent to notify it of each new Care-of-Address.
Call delivery: All incoming packets are sent to the mobile node at its home (IP)
address. Then the home agent tunnels all incoming packets to the mobile
node at the foreign agent using its Care-of-Address.
Mobile IP Location Management
28
McNair, Spring 15 EEL6591 Wireless Networks 55
Mobile IP Example (1)
A mobile node has a home address of 136.142.117.21 and a Care-of-Address of 130.216.16.5. It listens to agent advertisements periodically. The agent advertisement indicates that the
Care-of-Address is 130.220.45.3. What happens? Why?
McNair, Spring 15 EEL6591 Wireless Networks 56
Subnet Mask Routing
Outside networks forward all packets with Network IP address 192.228.17.x
Router applies subnet mask 255.255.255.224 to determine which LAN should receive the packet.
LAN X (Subnet 1) 192.228.17.32
LAN Y (Subnet 2) 192.228.17.64
LAN Z (Subnet 3) 192.228.17.96
Local Router on LAN recognizes IP address and delivers packet to host.
Host 1 192.228.17.33
Host 25 192.228.17.57
Host 1 192.228.17.97
Host 2 192.228.17.98
29
McNair, Spring 15 EEL6591 Wireless Networks 57
Mobile IP Example (2)
A mobile node has a home address of 136.142.117.21 and a Care-of-Address of 130.216.16.5. The new network has the following subnet mask: 255.255.240.0.
It listens to agent advertisements periodically. The agent advertisement indicates that the
Care-of-Address is 130.216.45.3. What happens? Why?
McNair, Spring 15 EEL6591 Wireless Networks 58
Mobile IP Shortcomings
Resource Mgmt? Triangle Routing Waste of Bandwidth
Quality of Service? What kind of
guarantees? Security
Firewalls? Authentication?
BACKBONE INTERNETWORK
Home Agent
?
Router
Router
Mobile Terminal
(MT)
Foreign Agent
30
Improvements to Mobile IP
Route Optimization Rerouting the connection between the CN
and the MN Fast Mobile IP
Predicting/Anticipating next access router Micro-mobility
Reducing the need for signaling to the home agent
McNair, Spring 15 EEL6591 Wireless Networks 59
McNair, Spring 15 EEL6591 Wireless Networks 60
Mobile IP - Micromobility
Distinguishes between Change in network ID Change in subnet ID
Micro-mobile IP attempts to Reduce delay and packet loss Achieve fast, seamless, scalable handoff
Current protocols Cellular IP, Hawaii, Hierarchical Mobile IP
31
McNair, Spring 15 EEL6591 Wireless Networks 61
Micro-Mobile IP Example
In a micro-Mobile IP network, a mobile node has a home address of 136.142.117.21 and a Care-of-Address of 130.216.16.5. It listens to agent advertisements periodically. The agent advertisement indicates that the
Care-of-Address is 130.216.45.3. What happens? Why?