07 Mobility Management

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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

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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

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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)


Base Station Mobile Terminal

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5



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)

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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

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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


2G to 4G The GSM Path


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)

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2G to 4G The IS-54 Path


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)


Outline





6


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


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

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Inter-System, or Vertical, Handoff


LAN Router

MSC

LTE


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)

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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


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

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RSSI with Thresholds (QI)

BS 1 BS 2

BS 1 signal strength BS 2 signal strength


0

1

1 dPP or =

22 d

PP or =

B

T1


RSSI with hysteresis

1

1 dPP or =

h

BS 1 BS 2


C

2

2 dPP or =

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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.


Example figure

BS 1 BS 2



0

1

1 dPP or =

22 d

PP or =

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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.


Soft Handoff Active Sets using RSS

BS 1 BS 2 BS 1 signal strength BS 2 signal strength


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

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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


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


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.

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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.


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.

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Phase 2: Channel Assignment

2rP

Handoff Out

Handoff In

New Call

Terminated Call


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

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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


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.

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Outline






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

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Cellular Network Architecture

Location Register (Database) Mobile Switching

Center MSC

Backbone Wireline Network

Base Station Controller

Base Station

Mobile Terminal

Radio Network

Cell


Location Registration (GSM-MAP/IS-41)

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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


Call Delivery

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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


Paging Techniques

Selective Paging Stepwise Paging Paging under delay constraints

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Paging

(MSC)

VLR


Location Area Design

Tradeoff Location Updates versus Terminal Paging

Goal: Improvements to tradeoff Geographical Fixed versus Dynamic User-based versus Global definition Network-specific

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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.


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)

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Example Figure: Movement Based

A

D

C

B

H

G

F L

K P

N S

R

Q M

J

I E O


Example Figure: Distance based

A

D

C

B

H

G

F L

K P

N S

R

Q M

J

I E O

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Example Figure: Time Based

A

D

C

B

H

G

F L

K P

N S

R

Q M

J

I E O


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)

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Example Figure Paging Area for Movement-based (T=3)


Outline





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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?


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

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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


Review: IPv4 Addresses

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BACKBONE INTERNETWORK

Mobile Node (MN)

Home Agent

Foreign Agent

Mobile IP Architecture

?

Router

Router

Correspondent Node (CN)


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

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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?


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

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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



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

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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



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

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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


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07 Mobility Management