module d3 - École polytechnique fédérale de lausannemobnet.epfl.ch/slides/d3-moreoncellnw.pdf ·...

Module D3

• More on Cellular Networks– Femtocells– Frequency Management– Mobility Management

• Wireless Ad Hoc Networking– Routing

• Examples

mobnet.epfl.ch

Femtocells

2

• Home base stations for mobile networks– Licensed spectrum– Low‐power, low‐range– At user’s premises– Operated by cell. provider– Cellular access throughfixed broadband connection (ADSL,…)

• Why femtocells?– Better throughput, coverage, lower prices for users– Unload wide area cellular networks, reduce op. costs

Femtocell Deployment

3

Network ArchitecturesUMTS LTE

4

Security and Privacy Challenges• New threats

– Attacks on femtocells– Attacks on backhaul and core network (IPsectunnel)

Source: www.SafeNet-Inc.com

5

FGW:FemtocellGateway

Femtocells : Radio Measurements

Measurements carried out byCarl Hedari and Charles‐Edmond Renouardwith the contribution from Igor Bilogrevic

6

• Radiation pattern shows the performance of the antenna– The signal does not propagate equally all around the femtocell

– W‐CDMA Femtocell, ~5 MHz channel bandwidth

Femtocells – Radio Measurements

7

How to Test a Femtocell in a Femtocell‐less Country

• The femtocell should only work in its originating country, mainly because of frequency allocation issues

• Often, the femtocell uses only the IP verification and customer address to be localized

• Idea: fool the verification process using a VPN located in country X

8

AnechoicChamber at EPFL

Designed to stop reflections of RF

• Simulates a quiet space of infinite dimension

• Removes all source of exterior RF

Avoids jamming Swiss carriers and allows isolating the femtocell

9

Spectrum Analyzer – One Femtocell

Femtocell :

• Frequency : 2.137 GHz (UMTS)

• Power : ‐60.25 dBm

• Channel : 2.1351 GHz to 2.1396 GHz

10

Spectrum Analyzer

Spectrum Analyzer – Two Femtocells

• Another femtocell brought into the anechoic chamber

The femtocell listens to stations emitting on the same frequency and adapts its power output.

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Spectrum Analyzer – Two Femtocells

12

One femtocell operating normallyPower : ‐60.25 dBm

The same femtocell and another femtocell nearby. Power : ‐54.18 dBm

With two active femtocells, the received power was increased by 6 dB (4 times more power)

Radio Traces : Measures

• 1 Femtocell• 1 Mobile from Operator X• 1 Mobile from Orange CH

• An antenna was plugged into a 6 GHz capable Oscilloscope, and put inside the chamber to “listen”

• The radio traces are displayed on the screen

13

Inside the anechoic chamber

Experiment 1 : Call established from Orange CH to X

50cm 50cm ∞

Oscilloscope(not spectrumanalyzeranymore)

Fs = 5 GHz

FemtocellMobile X Orange CH

14

Femtocell & Mobile X

Experiment 2 : Call established between two Orange mobiles

2m 2.5m

Oscilloscope Orange CH Orange CH

Fs = 2.5 MHz

Note: The sampling theorem was not respected for practical issues 15

Experiment 3 : Initialization of the femto‐cell

50cm 50cm ∞

Oscilloscope FemtocellMobile X Orange CH

Note: The sampling theorem was not respected for practical issues

Fs = 2.5 MHz

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Frequency Management

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Frequency Management• In all countries of the world, the licensed spectrum ismanaged by the government and (usually) leased to private operators

• Regulation authority– In Switzerland: Federal Commission for Communications, or ComCom; assisted by BAKOM

– In the US: FCC– In the EU: each country still has its national regulationauthority

• Some political willingness (especially in the US) to reduce the role of the FCC Dynamic Spectrum Allocation (cognitive radios)See the IEEE DySpan conference (ieee‐dyspan.org)

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Procedure for Frequency Allocation

• 2 main options– Auction– Beauty contest

• Usually fixed price• Based on very detailed dossiers+ : price pre‐determined‐ : temptation/suspicion of bribery; no price discovery

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Auctioning of Frequencies• Goal of auction: best possible allocation of frequencies to operators

• Auctions are notmeant to maximize the revenue for the government

• Splitting of the frequency bands in blocks (e.g., of 2*5Mhz)

• Issue: how to combine the auctioned blocks• Caps in high‐value bands to avoid unfair behavior• Typical duration of allocation: 10 to 20 years• Minimal (or starting) price: xxx CHFrs/MHz*Year (definedby law in the case of CH)

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The case of Switzerland• 3 main cellular operators (cellcos)

– Swisscom (state‐controlled) has 60% of the mobile market– Failed attempt of merger of Orange and Sunrise (in 2010)

• Good quality of service, but high prices• Swiss pecularities: topography, super‐tight emissionregulations, site acquisitions (to set up base stations) often problematic, expensive manpower, high‐revenue and change‐averse population

• All licencies (800, 900, 1800, 2100 and 2600MHz) to be(re‐)allocated as of 2013 or 2016 until 2028 (auctionrun in February 2012; generated 996 MCHFrs)

non-ionizing radiation

Previous frequency allocation in CH

• GSM 900 Frequencies• Allocation until 31.12.2013• No free frequencies

• GSM 1800 Frequencies• Allocation until 31.12.2013• Some frequencies available (ex. Tele2)

• UMTS Core Band• Allocation until 31.12.2016• Some frequencies available

68MHz

Low frequencies

High frequencies

GSM900

Sunrise (50%)

Swisscom (40%)Orange (10%)

Orange (40%)

Sunrise (19%)

Swisscom (21%)

In&Phone (8%)ex. Tele2 (12%)

Sunrise (25%)

Orange (25%)

Not allocated (25%)

Swisscom (25%)

GSM1800

UMTS core band (2100 MHz)

146MHz

140MHz

Courtesy: BAKOM

Location of base stations:http://map.funksender.admin.ch/webgis/bakom.php

Frequency allocation plan:www.bakom.admin.ch/themen/frequenzen/00652/00654/index.html?lang=en

Previous frequency allocation in CHGSM 900

Company Bands Expiration

Swisscom 2 x 13.6 MHz 31.12.2013

Sunrise 2 x 17 MHz 31.12.2013

Orange 2 x 3.2 MHz 31.12.2013

GSM 1800


Swisscom 2 x 15.2 MHz 31.12.2013

Sunrise 2 x 13.6 MHz 31.12.2013

Orange 2 x 29.4 MHz 31.12.2013

Ex.Tele2 2 x 8.6 MHz free

In&Phone 2 x 5.8 MHz 31.12.2013

UMTS 2100


Swisscom 2 x 15 MHz FDD + 5 MHz TDD 31.12.2016

Sunrise 2 x 15 MHz FDD + 5 MHz TDD 31.12.2016

Orange 2 x 15 MHz FDD + 5 MHz TDD 31.12.2016

BWA (3.5 GHz)


Swisscom 2 x 21 MHz 31.12.2016

Callix (Inquam) 2 x 21 MHz 31.12.2016

Why an invitation to bid? All mobile radio frequencies auctioned together • Bidders can purchase a new, future‐proof spectrum package• A world first

Expiring licences:• GSM licences (900 + 1800 MHz): End of 2013• UMTS licences (2100 MHz): End of 2016

Many new mobile radio frequencies are available:• "Digital dividend" (in the 800 MHz band) Good propagation properties (even inside houses) Switzerland one of the first countries in Europe

• UMTS extension band (2600 MHz) Suitable for LTE technology with high bandwidths

Goals: ‐ more frequencies for more bandwidth in mobile communications‐ efficient use of spectrum with new technologies (LTE)

Note: This slide and some of the following adapted from a slideshow kindly provided by Urs von Arx and Martin Dummermuth (BAKOM)

Rapidly growing data traffic in mobile radioRapidly increasing amounts of data on mobile radio networks Doubling every 9‐12 months

More and more smartphones (iPhone, Android devices, etc): > 350 000 apps (incl. social networks such as Facebook and Twitter)mobile internet, mobile TV, YouTube... "Cloud computing" also mobile: same content present everywhere

Business Mobility: Office applications and content on all devices new, flexible forms of working

All internet applications and content anywhere, anytime on a mobile phone

Increase in network capacity essential

New mobile radio technologies are coming

HSPA+ (Evolved High Speed Packet Access "plus")• Considerable increase in transfer rates (compared with UMTS)• Market‐ready devices are already available

LTE (Long Term Evolution of UMTS; 4G)

• 3 to 4 times higher spectrum efficiency than UMTS/HSPA• Increase in data rates to up to 100 Mbit/s in the downstream• Greater capacity in the network at a relatively low cost

New generation of mobile communicationse.g. mobile HDTV, video streaming, on‐line gaming…

Why an auction?• A transparent procedure

• The market determines the value of frequencies

• The market decides on the scope of the licences (not the regulator): therefore: auction of small frequency blocks Operators can acquire a new spectrum package

which corresponds to their business models for the future

• Equal treatment of all candidates: All were able to take part on equal terms No unilateral preference for any new entrants

Network operators purchase spectrum corresponding to their needs

No new market entry of an other network operator

Result of the auction: CHFrs 996'268'000

Frequency band Orange Sunrise Swisscom

800 MHz 20 MHz 20 MHz 20 MHz



2.1 GHz FDD 40 MHz 20 MHz 60 MHz

2.1 GHz TDD 0 0 0

2.6 GHz FDD 40 MHz 50 MHz 40 MHz

2.6 GHz TDD 0 0 45 MHz

Adjudication price 154‘702‘000 481‘720‘000 359‘846‘000

Goals of the frequency allocation achieved

• Consumers benefit: Technological innovation continues; new broadband services. High quality and good coverage

• Technological progress supported: free choice of technology Operators can use LTE (high‐speed broadband even in peripheral regions)

• A frequency allocation with a promising future: All network operators acquire good spectrum + more spectrum

• Long‐term planning and investment security: Network operators can plan up to 2028

• Appropriate proceeds from the auction: A scarce public resource allocated appropriately Benefits the community

Reasons for the chosen form of the auction

• The participants in the auction can bid on frequency packages.

• The frequency packages correspond to their business model

• Value, for which bidders are prepared to pay

• Continuity for existing licensees:

• Consistent with the existing frequency allocation

Multi‐phase sequence of the auction

• Auction in two stages. The bidders were able:

1. to combine frequency ranges optimally;

2. bid in a second phase bid for the preferred frequencies within the individual ranges.

• The auction took place over the internet from the bidders' company headquarters

Example: Combinatorial Clock Auction

Clock rounds

Excessdemandin anyband?

Supplementaryround (fine tune expression of

wishes)

Assignment of frequencies

No

Yes

Increase price of band(s) with excess demand

Bidding restrictions

Bidding restrictions (spectrum caps)

• Maximum extent of frequencies per frequency band

• Competition

• Enabling competition during the auction

• Increasing competition as much as possible after the auction by ensuring sufficient spectrum per bidder

• No bidder may acquire the entire 900 MHz spectrum (GSM)

• No market displacement of existing operators possible

• Existing UMTS operators can purchase at least the current range of frequencies in the 2100 MHz band (UMTS)

• No single bidder can dominate the major part of the GSM spectrum (900 MHz, 1800 MHz)

Distribution of the frequency spectrum (I)

93.8

96.2

99.4

255

160

160

0 50 100 150 200 250 300

Swisscom

Sunrise

Orange

MHz

Spectrum distribution before and after the auction

purchasedat auction

to date

Distribution of the frequency spectrum (II)

255

160

160

Spectrum distributionAuction result (MHz)

SwisscomSunriseOrange

Allocation of the frequency spectrum

20

30

60

0

60

40

45

20

30

40

0

20

50

0

20

10

50

0

40

40

0

0 10 20 30 40 50 60 70

800MHz (paired)

900MHz (paired)

1800MHz (paired)

2100MHz (unpaired)

2100MHz (paired)

2600MHz (paired)

2600MHz (unpaired)

Spe

ctru

mdi

strib

utio

n

MHz

Auction result Spectrum allocation

OrangeSunriseSwisscom

Licenses (1)• Term

• Planning/investment security: early allocation and a term extending until 2028• Utilization of free frequencies from award of license onwards

• Neutrality with respect to technology• Flexible utilization of the spectrum for future developments

• Conditions relating to utilization• Gradation:

‐ 50% population coverage for frequencies < 1 GHz‐ 25% population coverage for frequencies > 1 GHz

• No frequency hoarding• Freedom with respect to configuration (coverage, quality)• Supervisory procedures in the event of non‐compliance

Licenses (2)

• Protection from immissions and spatial planning• Conditions as strict as those in existing licences• Provisions of Ordinance on Protection from Non‐Ionising Radiation (OPNIR)• Shared use of sites outside the construction zone• Informing the cantons about network planning in good time

41

References on Auctions

• Cramton, Shoham and Steinberg (eds.): Combinatorial Auctions, MIT Press, 2006

• Ausubel, Lawrence M. and Paul Milgrom (2002), “Ascending Auctions with Package Bidding,” Frontiers of Theoretical Economics, 1, 1‐45, http://www.bepress.com/bejte/frontiers/vol1/iss1/art1.

Mobility Management

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2. Receive the ID of the LA3. Compare with stored ID4. If different, update

and ask for registration

User Tracking: Geographic‐based Strategy

Location area 1 (ID = 1) Location area 2 (ID = 2)

• Base stations periodically broadcast the ID of the LA• Users compare their last LA ID with the current ID, and transmits a registration message whenever the ID is different

• When there is an incoming call directed to a user, all cells within its current LA are paged

1. Change LA

5. Inform the HLRof the new LA ID

Location and Identity Privacy• Temporary Mobile Subscriber identifiers – TMSI –changed after crossing Location Area (LA) border or time‐out trigger

LA 0LA 1

LA 2

LA 3

Pseudo A

Pseudo B

Pseudo C

Pseudo D

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45

Handover

BS1 BS2

A B

t

Receivedsignal level

Level at B

Level at which handover is made(call transferred to BS2)

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MTSO:MobileTelecommunicationsSwitching Office(also called MSC:Mobile Switching Center)

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Handover Strategies• The handover power level must be carefullychosen– Too small => risk of superfluous handovers– Too high => risk of losing the call due to weak signal

• Mobile Assisted Handover (MAHO) – Mobiles measure power from surrounding base stations

– Report to the serving base station– Handover if the power received from another station exceeds the serving station power by a certain threshold for a certain amount of time

Hard/Soft Handover

Hard: Communicate with one cell at a timeSoft: Communicate with two cells simultaneously

TDMA & FDMA: Hard– Could technically use soft handover, but would be costly as it would require multiple parallel radio modules

CDMA: Soft – Needed to avoid near‐far problem (i.e., Detect weaker signal amongst strong signals)

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50

Roaming Principle

Roaming agreement

Subscriberdatabase(IDs,keys,bills,…)

Home network

Subscriberdatabase(IDs,keys,bills,…)

Visited network

User

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Roaming Architecture

Servicelogic

HomeLocationRegister

BaseStation

Servicelogic

VisitingLocationRegister

BaseStation

PSTN + Data Network

HomeNetwork

VisitedNetwork

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Mobile Ad Hoc Networks

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The classic solution for mobile networks

• 2nd generation (GSM, IS‐41), 3rd generation (UMTS), 4th generation (LTE)• Huge, expensive fixed infrastructure• License for a share of the spectrum• Operational responsibility: network operators (telcos, ISPs)

55

The new paradigm: ad hoc networks

• Terminal and node merge• Everything is potentially mobile• Initial applications: communication in the battlefield (Packet Radio

Networks, in the 70’s)• The network is self‐organized when it is run by the users themselves• Similar trend at the application layer: peer‐to‐peer

(e.g., Napster Gnutella, BitTorrent)

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Application examples of ad hoc networks

• Sensor networks• Hybrid cellular / ad hoc networks (multi‐hop cellular

networks)• Cars

– Collision avoidance– Optimization of traffic flows– …

• Crisis networks (e.g., rescue operations after major disaster)

• Military networks

• Similar concept: Delay Tolerant Networks (DTNs)

57/58

Sensor networks

• Large number of sensor nodes, a few base stations

• Sensors are usually battery powered:– Main design criteria: reduce the energy consumption

• Multi‐hop communication reduces energy consumption:– Overall energy consumption can be reduced, if packets are sent in several smaller hops instead of one long hop

– Fewer re‐transmissions are needed due to collisions

58/58

Wireless Mesh NetworksWired Access Point (WAP)

(a) A WiFi Network

• Wireless Mesh Network (WMN): Same coverage as with WiFi networks but with only one WAP (and several TAPs).

• WMNs allow a fast, easy and inexpensive network deployment.

• However, the lack of security guarantees slows down the deployment of WMNs

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What is a VANET(Vehicular Ad hoc NETwork)?

Roadside base station

Inter-vehicle communications

Vehicle-to-roadside communications

Emergency event

• Communication: typically over the Dedicated Short Range Communications (DSRC) (5.9 GHz)• Example of protocol: IEEE 802.11p• Penetration will be progressive (over 2 decades or so)

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A smart vehicle

Forward radar

Computing platform

Event data recorder (EDR)Positioning system

Rear radar

Communication facility

Display

(GPS)

Human-Machine Interface

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Vehicular communications: why?

• Combat the awful side‐effects of road traffic– In the EU, around 40’000 people die yearly on the roads; more

than 1.5 millions are injured– Traffic jams generate a tremendous waste of time and of fuel

• Most of these problems can be solved by providing appropriate information to the driver or to the vehicle

• More information: ACM VANET Workshop; ivc.epfl.ch

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Upper bound for the throughput of ad hoc networksIf we have:

- identical randomly located nodes- each capable of transmitting bits/sThen the throughput ( ) obtainable by each node for a destination is

( )log

nW

nrandomly chosen

Wnn n

Ref: P. Gupta, P. Kumar, The Capacity of Wireless NetworksIEEE Transactions on Information Theory, March 2000

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Intuition behind the upper bound

N nodes (users)

O(N) users O(N) users

Cut set ~ N

O(N) transmissions from left to right

over

O( ) transmission links

mean

O( ) capacity per attempted transmission

N

1N

Ways to improve scalability:• Directional antennas• Locality of the traffic• Hybrid system

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Routing in ad hoc networks• Peculiarities

– Node mobility– High rate of link failure Traditional routing approaches are not well suited

• Assumptions– Multihop communication– Symmetric links (in most cases)– Omnidirectional antennas (in most cases)– All nodes have equal capabilities and responsibilities

• Figures of merit– Latency of route discovery– Overhead (bandwidth, energy, processing power)– Security

• Current status of research: – Many, many proposals– Optimal solution depends on deployment scenario: mobility patterns,

radio model, traffic characteristics,…

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Brief reminder : Link‐state protocols

• Example: OSPF• May consume a lot of resources to update the routes

• Techniques to alleviate the problem : limit the propagation of information

• Does not seem to be well suited to cope with mobility

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Distance vector routing (1/2)

0 1 5 ¥

1 0 1 3

5 1 0 7

¥ 3 7 0

A

B

D

C

13

1

5 7

A

B

C

D

A B C D

1 0 1 3

Distancevector

Distancevector of B

2 1 2 4

+ Distance from A to B =

Cost to dest.via B

nTake the min

0 1 2,B 4,B

(1 row stored in each node)

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Distance vector routing (2/2)

• Even if the updates are asynchronous, the routing tables converge

• The algorithm is often called Bellman‐Ford• Problem: undesirable behaviour when links go up and down (e.g., count to infinity problem)

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Routing protocols for wireless ad hoc networks

Response time,bandwidth Energy

Mobile ad hoc networks Sensor networks

Proactiveprotocols

Reactiveprotocols

Destination-SequencedDistance-Vector (DSDV)

Optimized Link-State Routing(OLSR)

Ad Hoc On-DemandDistance-Vector(AODV)

DynamicSourceRouting(DSR)

Geography-based routing

Cluster-based(or hierarchical)routing

Geodesic packetforwarding

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Dynamic source routing (DSR)

• Reactive routing protocol• 2 phases, operating both on demand:

– Route discovery• Used only when source S attempts to to send a packet to destination D• Based on flooding of Route Requests (RREQ)

– Route maintenance• makes S able to detect, while using a source route to D, if it can no longer use its route (because a link along that route no longer works)

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DSR: Route discovery (1)

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(S,A)

(S,E)

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(S,E,G)

(S,B,C)

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(S,A,F,H)

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(S,A,F,H,K,P)

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RREP(S,E,G,J,D)

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DSR: Route Discovery (9)

• Route reply by reversing the route (as illustrated) works only if all the links along the route are bidirectional

• If unidirectional links are allowed, then RREP may need a route discovery from D to S

• Note: IEEE 802.11 assumes that links are bidirectional

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DSR: Data delivery

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DATA(S,E,G,J,D)

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DSR: Route maintenance (1)

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DATA(S,E,G,J,D)

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DSR: Route maintenance (2)

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XRERR(G-J)

When receiving the Route Error message (RERR), S removes the broken link from its cache.It then tries another route stored in its cache; if none,it initializes a new route discovery

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DSR: Optimization of route discovery: route caching

• Principle: each node caches a new route it learns by any means

• Examples– When node S finds route (S, E, G, J, D) to D, it also learns route (S, E, G) to node G

– In the same way, node E learns the route to D– Same phenomenon when transmitting route replies

• Moreover, routes can be overheard by nodes in the neighbourhood

• However, route caching has its downside: stale caches can severely hamper the performance of the network

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DSR: Strengths

• Routes are set up and maintained only between nodes who need to communicate

• Route caching can further reduce the effort of route discovery

• A single route discovery may provide several routes to the destination

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DSR: Weaknesses• Route requests tend to flood the network and generally reach all the nodes of the network

• Because of source routing, the packet header size grows with the route lengh

• Risk of many collisions between route requests by neighboring nodes need for random delays before forwarding RREQ

• Similar problem for the RREP (Route Reply stormproblem), in case links are not bidirectional

Note: Location‐aided routingmay help reducing the number of useless control messages

85

Ad Hoc On‐Demand Distance Vector Routing (AODV)

• As it is based on source routing, DSR includes source routes in data packet headers

• Large packet headers in DSR risk of poor performance if the number of hops is high

• AODV uses a route discovery mechanism similar to DSR, but it maintains routing tables at the nodes

• AODV ages the routes and maintains a hop count • AODV assumes that all links are bi‐directional

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AODV : Route discovery (1)

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Note: if one of the intermediate nodes (e.g., A)knows a route to D, it responds immediately to S

: Route Request (RREQ)

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: represents a link on the reverse path

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AODV : Route reply and setup of the forward path

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: Link over which the RREP is transmitted: Forward path

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Route reply in AODV

• In case it knows a path more recent than the one previously known to sender S, an intermediate nodemay also send a route reply (RREP)

• The freshness of a path is assessed by means of destination sequence numbers

• Both reverse and forward paths are purged at the expiration of appropriately chosen timeout intervals

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AODV : Data delivery

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The route is not included in the packet header

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AODV : Route maintenance (1)

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AODV : Route maintenance (2)

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XRERR(G-J)

When receiving the Route Error message (RERR), S removes the broken link from its cache.It then initializes a new route discovery.

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AODV: Destination sequence numbers

• If the destination responds to RREP, it places its current sequence number in the packet

• If an intermediate node responds, it places its record of the destination’s sequence number in the packet

• Purpose of sequence numbers:– Avoid using stale information about routes– Avoid loops (no source routing!)

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AODV : Avoiding the usage of stale routing tables

S DA

B

DSN(D) = 5

: Forward path

S

D

A

B

DSN(D) = 5

… …

DSN(D) = 8

1. 2.

S

D

A

B

DSN(D) = 5

…

DSN(D) = 8

3.

RREQS

D

A

B

DSN(D) = 5

…

DSN(D) = 8

RREP

4.

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AODV : Avoiding loops

A B S D

C

: Forward path

• Assume there is a route between A and D; link S-D breaks; assume A is not aware of this, e.g. becauseRERR sent by S is lost

• Assume now S wants to send to D. It performs a RREQ, which can be received by A via path S-C-A• Node A will reply since it knows a route to D via node B• This would result in a loop (S-C-A-B-S)• The presence of sequence numbers will let S discover that the routing information from A is outdated• Principle: when S discovers that link S-D is broken, it increments its local value of DSN(D). In this way,

the new local value will be greater than the one stored by A.

X

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AODV (unicast) : Conclusion

• Nodes maintain routing information only for routes that are in active use

• Unused routes expire even when the topology does not change

• Each node maintains at most one next‐hop per destination

• Many comparisons with DSR (via simulation) have been performed no clear conclusion so far

FlashLinQ (Qualcomm)

• Vision: extend users’ sensing capabilities• Operates in licensed spectrum• All devices globally synchronized to a commonexternal timing source (e.g., GPS or cellular base stations)

• All devices operate in OFDMA (Orthogonal Frequency‐Division Multiple Access)

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Conclusion on wireless ad hoc networks

• Extensive research activity over the last decade

• Scalability is still an open issue• NIC and FlashLinQ show that vendors are considering this seriously

Next week, 15:00 – 15:45Special session on career management

‐ How to choose my first job?‐ Should I do an MBA? A PhD?‐ Should I go to the US?‐ How about joining a start‐up company? Or even create a

new one?‐ How do I get the «big picture» of the job market?‐ I want to stay in Switzerland, are there interesting

companies here?

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References on wireless ad hoc networks

Overview of ad hoc network routing protocols: seethe references mentioned at:http://en.wikipedia.org/wiki/Ad_hoc_networking

Research conference: ACM MobiHoc (especially for the theoretical aspects)

For FlashLinQ (Qualcomm):M. Scorson et al., Toward Proximity‐AwareInternetwoking, IEEE Wireless Comm., Dec. 2010

module d3 - École polytechnique fédérale de lausannemobnet.epfl.ch/slides/d3-moreoncellnw.pdf ·...

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