TCS 316High Speed Information

Networks

UMTS Handover

byNasir Faruk

Email: nasirfaruk@ieee.orgMobile +234 8032428141

Week 13May, 2014

1/6021/04/23 12:50 PM

Content and rem..

• Weeks 13• Cell Search

procedure• (Skipped)• Handover

• Softer• Soft• Hard

• Sectorisation (Briefly taught last semester)

• Weeks 14 ( To be skip. You met it in industry when lucky hahaha)

• IP• IP Mobility• Mobile IP• VoIP

221/04/23 12:50 PM

Air Interface Modes

Figure 2

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UMTSCore

Network

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UMTS Terrestrial RadioAccess network (UTRAN)

User Equipment (UE)FDD Mode

User Equipment (UE)TDD Mode

CDMA

Frequency Division Duplex Mode 1Direct Sequence Mode

Time Division Duplex Mode 1TD-CDMA

21/04/23 12:50 PM 3

Handover Types• Within UTRA FDD – Intra-Mode Handover– Soft– Softer– Hard (intra- or inter-frequency)

• Inter Mode Handover– Handover to UTRA TDD – not implemented yet!

• Inter-system Handover– In R99 means only to GSM handover– In R8 & LTE (E-UTRA or E-UTRAN) means

handover to and from LTE (Long Term Evolution).

421/04/23 12:50 PM

Effect on Capacity with Contiguous Coverage

5Figure 9

Cell A in isolation10 channels

Interference

Cell B in isolation10 channels

Capacity of Cells A and Bis less than 20 because

of increased interference

Cell A Cell B

21/04/23 12:50 PM

Cell Capacity

Figure 10

Total Cell Capacity = 100 kbit/s

Total Cell Capacity = 100 kbit/s

10 users using10 kbit/s channel

2 users using50 kbit/s channel

621/04/23 12:50 PM

Power Control at Cell Boundaries

Figure 29

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Power Control

Increase ininterference here

Power Controlinstructs mobileto turn power up

Node B1

Node B2

721/04/23 12:50 PM

Necessity for Soft/Softer Handover

• Essentially to avoid interference• Mobile could penetrate far into

adjacent cell without being power controlled by that cell

• This could be overcome by the use of very fast and frequent hard handovers

• Not efficient as too much signalling involved.

821/04/23 12:50 PM

Soft Handover

Figure 30

Node B1

Node B2

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Power Control

Power Control B

9

Soft Handover – make before break21/04/23 12:50 PM

WCDMA Soft Handover• Active set - the cells participating

in the soft handover• Normally just 2 cells–Neighbour or monitored set

• Cells that the UE continuously measures

• Pilot Ec/No not strong enough to be added to the active set

1021/04/23 12:50 PM

UE Measurements

Figure 21

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Node B Micro

GSMBTS

Intra-frequency

Node B

Node B

Intra-frequencyDownlinkQuality

UE

RLCBuffer

UplinkTrafficVolume Internal TX power

RSSI

Local Measurement

Inter-frequency

Inter-system

21/04/23 12:50 PM 11

Ec/No Measurement from CPICH

• UTRA FDD intra-mode handover relies on the Ec/No measurement performed from the CPICH.

• Quantities defined that can be measured by the terminal from the CPICH are as follows:

• Received Signal Code Power (RSCP) – received power on one code after despreading defined on the pilot symbols;

• Received Signal Strength Indicator (RSSI) – wideband received power within the channel bandwidth;

• Ec/No = RSCP/RSSI, i.e. RSCP divided by the total power in the channel bandwidth.

1221/04/23 12:50 PM

WCDMA Handover Algorithm

• If a neighbour cell pilot channel signal remains better than the current best cell’s pilot minus a hysteresis value for a timeout period the neighbour cell may be added to the active set.

• If an active cell signal is worse than that of the current best cell minus a different hysteresis value for a short period it may be removed from the active set.

• If a neighbour cell signal is better than the current worst active cell plus a third different hysteresis value for the timeout period it may replace that worst active cell.

1321/04/23 12:50 PM

Soft Handover Region

Figure 31

A B

Soft handover region

Start End

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Two-Cell Case

1421/04/23 12:50 PM

Soft Handover Region

Figure 31 (continued)

Three-Cell Case

A C

B

Three-wayhandoverRequired

here

1521/04/23 12:50 PM

Example of a Soft Handover

Full specification is in 3GPP TR 25.922 V6.0.1 (2004-04)

3.Time

1. 2.

Cell C

Cell B

Cell A

Quality

Timer

MacroAdd

Threshold

MacroReplacement

Threshold

Timer

MacroRemove

Threshold

Timer

Timer

1621/04/23 12:50 PM

Soft vs Softer Handover

17

Softer Handover – also make before break21/04/23 12:50 PM

Softer Handover• Between two cells or sectors supported by the

same Node B• UE transmits & receives from both cells

simultaneously:– UE combines downlink information– Node B combines uplink information

• Only one power control loop• Both soft & softer handover may occur

simultaneously• Soft/softer handover at the UE & softer at the

Node B– Similar to multipath reception– Two separate downlink codes– RAKE fingers need to generate two codes

1821/04/23 12:50 PM

Soft Handover at the RNC

• Uplink data routed to RNC for combining

• Better frame selected– After each interleaving period 10-80 ms– Outer loop power control frame

reliability indicator utilised.

1921/04/23 12:50 PM

Serving & Drift RNC

2021/04/23 12:50 PM

Serving & Drift RNC

2121/04/23 12:50 PM

Serving & Drift RNC

2221/04/23 12:50 PM

Macro and Micro Diversity

Figure 36

RNC

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UE

Macro Diversity Combiningat RNC for Soft Handover

Node B

Node B

Micro DiversityCombining at

Node B forSofter Handover

Cell B

Cell A SoftHandover

SofterHandover

21/04/23 12:50 PM 23

UMTS Hard Handover

• Between two cells using different carrier frequencies

• Between cells whose Nodes B are• connected to different RNCs without

the Iur interface• To and from GSM

2421/04/23 12:50 PM

Handover and External Reselection Related Procedures

Figure 19

RNC BSC

UMTSCore Network

GSMCore Network

Node Bmicro

Node Bmacro

Node Bmacro BTS

Hard Handoverwithin UTRAN

Soft Handoverwithin UTRAN

Hard Handoveroutside UTRAN

Reselectionoutside UTRAN

2521/04/23 12:50 PM

UMTS Handover Types - Summary

Figure 33

A = intra-frequencyB = inter-frequencyC = inter-system

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GSM

UMTSMacro

UMTSMacro

UMTSMicro

UE

HardC

HardB

SoftA

26

Hard Handover – break before make

21/04/23 12:50 PM