1. Handover solution for Pico-Cells
Herman Claus – based on work from Tom Van
Leeuwen
Siemens, Nokia Siemens Networks, OTN

2. Outline
 The Project and The Company
 Problem statement
 Existing solutions
 Radio over Fibre solution
 WLAN Fast Handover
 Supporting Hardware
 Future evolution
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3. The Project and the Company
 During the project, the Siemens Herentals company
went through a lot of changes
 At the start, Siemens Herentals (formerly Atea) formed the
Com Division of Siemens Belgium
 Two departments were interested in this project
 Siemens OTN department : world leader in track-side communication
for metro, also interested in trains etc.
 IP-on-trains for TGV by Siemens Services department
 The project received a GO with a dual goal
 Build up and exchange knowledge about IP-on-trains
 Good partners
 Own knowledge from Services
 Build up knowledge about communication with metro
 Experimental technology for OTN
 IBBT knowledge

4. The Project and the Company
 During the project
 Siemens Com carved out from Siemens
 Nokia Transmission Systems carved out from Nokia
 Both merged to form Nokia Siemens Networks

5. The Project and the Company
 In Herentals
 Siemens Com merged with Nokia Transmission Systems
 Corporate R&D at Herentals (with the exception of OTN) was
spun off (160 developers) and sold to Devoteam
 11 june 2008, after several months of negotiations, it was
announced that the OTN group wil carve out and is due to be
independend july 1st 2008 (GIMV -> see www.gimv.be for
press releases and other information)
 All this had its impact on the project
 But with the help of he IBBT the project could be finalised
 This presentation : only the OTN part of the project is
described
 IP-on-trains : contact Walter van Brussel, is explained in the
other WPs

6. Problem statement
 Communication with metro
 Tunnels
 Communication with trains
 No cheap global wireless coverage
 Cost of bandwidth for wireless is high
 Bandwitdh x surface should somehow be related to cost
 So : use pico-cells
 For moving vehicles : handover problem
 The faster the more problematic
 Same solution for use in tunnels
 So there is a technological problem
 Remark : there is also an economical one
 Base stations are expensive, so picocells are, too.

7. Problem statement
 Pico-cells are a problem
 Speed of access point is no problem for most technologies
 But handover between cells is
 Eg : WiFi : cell of 200 m diameter, speed 120 kmh,
 handover every 6 seconds, bad conditions at the edge
 Normally handover takes time
 Problems with VPN connections etc
 What is needed is
 Seamless handover mechanism
 Handover invisible to end-device and to network
 Part of the problem solved by other WPs
 Making handover invisible to end user and network
 Same problem as eg satellite etc.
 So : concentrate on handover mechanism

8. Existing solutions
 IST projects FIFTH and MOWGLY
 DVB-S2, DVB-RCS
 IBBT project FAMOUS
 WLAN for fast moving users
 InterAccess Point protocol modification proposed
 Several algorithms studied
 Predicting future access point
 Easily adaptable to trains and metro
 Making handover mechanism faster
 Eg SyncScan algorithm for optimising scanning

9. Existing solutions
 On the level of fast context switching
 Solutions available
 Our project
 Fast re-association of wireless connection
 Be as standard as possible
 Two solutions developed by IBBT / Ghent
 Radio over fibre based solution
 WLAN GAP filler solution

10. Radio over Fibre solution
 Not part of the project
 Idea : between antenna and electronics of the base
station there is a wire
 With fibre this wire can span hughe distances
 So :
 make many antennae, place them widely apart
 connect them to one set of electronics
 Use overlapping frequencies
 neither base station, neither moving access point is aware of
the fact that the moving access point is moving

11. Radio over Fibre solution
 Some manipulation of datastreams required
 See article feb 2007 IEEE Communications Magazine
 Problem : economical : cost of antennae-base stations

12. WLAN Fast Handover
 Handover problem : wireless layer problem
 When moving from one cell to another cell
 Old cell : communication dies
 New cell : communication starts up
 Dying and starting under bad conditions (low power budget)
 Uses lots of time because of robust modulation, broadcast messages
etc : normal communication in cell disrupted
 Idea :
 Separate the handover from normal communication in the cell
 Cell 1 uses channel1 : high speed encoding
 Cell 2 uses channel2 : high speed encoding
 Cell 1 and Cell 2 also support channel3
 Channel3 is used for handover,
 overlaps in space between cells
 Uses soft handover
 Low-speed robust encoding

13. WLAN Fast Handover
Radius
Gateway
Server
Fast Roaming WLAN Switch for Rail Systems
Data – 802.11a/g Control - 802.11h
Fast Roaming
Fast Roaming Fast Roaming Fast Roaming
WLAN AP
WLAN AP WLAN AP WLAN AP
Fast Roaming
WLAN Client
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14. WLAN Fast Handover
 Client
 1 interface
 802.11a/g data channel
 802.11h control channel
 Lightweight Access Points
 2 interfaces
 same dedicated handover frequency
 limited functionality
 handoff limited to change in WLAN channel
 Switch
 association, authentication and security

15. Handover

16. The GAP filler solution
 The problem it solves
 The system handles frequency handovers under good signal
conditions
 The handover frequency of Channel3 guarantees low speed
but continuous operation of wireless link
 The handover does not disrupt the high speed
communication
 Association with channel1, channel2 and channel3 can be
done while no data is being transmitted over this paricular
interface

17. Hardware
 OTN developed a generic supporting hardware
 Ethernet layer based data transport
 Supporting TDM separated IP channels over one fibre
 Transparant to all higher layers
 Central switch can ‘directly’ connect to access points
 Controlled delay
 All channels can be serviced individually

18. Hardware
Segment 1 Segment 2 Segment 11 Segment 12
10Mbps 25Mbps 10Mbps 30Mbps
Backplane Backplane Backplane Backplane
Logic 1 Logic 2 Logic 9 Logic 10
Ethernet programmable
Switch logic
Port1 Port2 Port9 Port10
User side

19. Hardware
Front-end FPGA
10/100Mbps 1 10 * max. 196 Mbps
10/100Mbps 2
. Backplane
. .
. .
10/100Mbps 10 .
Maximum 12 segments
10/100/1000Mbps 11
Maximum 784 Mbps
10/100/1000Mbps 12
2 * max. 784 Mbps

20. Future
 Merging of several technolgies needed
 Fast handover
 Billing and access control
 VPN structures
 The job ain’t finished yet