1. Wireless Systems: Where are we heading?

2. Outline Some definitions Current situation Near Future
4G: what we really want
What are the obstacles
Higher Layer Issues
Conclusions

3. Definitions Definition of mobility: Definition of wireless:
user mobility: users communicate anytime, anywhere, with anyone
device portability: devices can be connected anytime, anywhere to the network
Definition of wireless:
Un-tethered, no physical wire attachment
The need for mobility creates the need for integration of wireless networks into existing fixed network environments:
local area networks: standardization of IEEE
Internet: Mobile IP extension of the internet protocol IP
wide area networks: e.g., internetworking of 3G and IP

4. Current Situation Technological trends Issues in Wireless Systems
Wireless vs Fixed
Wireless LANS
Wireless PANs
Cellular

5. Technological Trends Advances in Technology
more computing power in smaller devices
flat, lightweight displays with low power consumption
user interfaces suitable for small dimensions
higher bandwidths
multiple wireless interfaces: wireless LANs, wireless WANs, home RF, wireless PANs
New Electronic Computing Devices
small, cheap, portable, replaceable and most important of all USABLE!

6. Sample Future Application: Vehicles
transmission of news, road conditions, weather
personal communication using cellular
position identification via GPS
inter vehicle communications for accident prevention
vehicle and road inter communications for traffic control, signaling, data gathering
ambulances, police, etc.: early transmission of patient data to the hospital, situation reporting
entertainment: music, video

7. An Integrated View ad hoc GSM, 3G, WLAN, Bluetooth, ...
PDA, laptop, cellular phones,
GPS, sensors

8. Constraints of Portable Devices
Power consumption
battery capacity -> limited computing power, low quality/smaller displays, smaller disks, fewer options (I/O, CD/DVD)
Device vulnerability
more rugged design required to withstand bumps, weather conditions, etc.
theft
Limited Capabilities
Small display size due to size and power
compromise between comfort/usability and portability (e.g., keyboard size)
integration of character/voice recognition, abstract symbols
memory limited by size and power

9. Wireless vs Fixed Higher loss-rates due to interference
other EM signals, objects in path (multi-path, scattering)
Limited availability of useful spectrum
frequencies have to be coordinated
lower transmission rates
local area: 2 – 11 Mbit/s, -> Mbit/s
wide area: 9.6 – 19.2 kbit/s -> Kbit/s
Higher delays, higher jitter
connection setup time for cellular in the second range, several hundred milliseconds for wireless LAN systems
Lower security, simpler active attacking
radio interface accessible for everyone
base station can be simulated, thus attracting calls from mobile phones
Always shared medium
secure access mechanisms important

10. Wireless LANs: Design Goals
global, seamless operation
low power for battery use
no special permissions or licenses needed to use the LAN
robust transmission technology
simplified spontaneous cooperation at meetings
easy to use for everyone, simple management
protection of investment in wired networks
security (no one should be able to read my data), privacy (no one should be able to collect user profiles), safety (low radiation)
transparency concerning applications and higher layer protocols, but also location awareness if necessary

11. Wireless LANs: Standards
(2M) -> b (11M) -> a (50-70M)
Wider spectrum -> Higher bitrates
Generally used with access points
Adhoc component not used, has flaws
Poor support for real-time communications
HiperLAN
European standard for high bit rate (~25M) local transmission in 5GHz range over m

12. Infrastructure vs Adhoc
infrastructure network
AP: Access Point AP AP
wired network AP
ad-hoc network

13. IEEE 802.11 MAC Traffic services
Asynchronous Data Service (mandatory)
Time-Bounded Service (optional)
Access methods: Distributed Foundation Wireless MAC (DFWMAC)
DFWMAC-DCF CSMA/CA (mandatory)
collision avoidance via randomized „back-off“ mechanism
minimum distance between consecutive packets
ACK packet for acknowledgements (not for broadcasts)
DFWMAC-DCF w/ RTS/CTS (optional)
avoids hidden terminal problem
DFWMAC- PCF (optional)
access point polls terminals according to a list

14. MAC Operation Priorities defined through different inter frame spaces
no guaranteed, hard priorities
SIFS (Short Inter Frame Spacing)
highest priority, for ACK, CTS, polling response
PIFS (PCF, Point Coordination Function IFS)
medium priority, for time-bounded service using PCF
DIFS (DCF, Distributed Coordination Function IFS)
lowest priority, for asynchronous data service

15. Interframe Spacings DIFS DIFS PIFS SIFS medium busy contention
next frame t

16. Wireless PANs
Bluetooth

17. Bluetooth Low bitrate (1M), short distances (1-10m) in 2.4GHz ISM band
Adhoc networking, cable and IrDA replacement
No mobility
Next generation higher bit rate (10M), longer distances (100m)
Scatternets: multihop environment

18. Personal Ad-hoc Networks
Usage Scenarios
Cable replacement
Adhoc PAN
Personal Ad-hoc Networks
Cable Replacement

19. Technology Low-cost, Low-power, Small-sized, Short-range,
Robust wireless technology

20. Cellular Systems: The essential elements of a cellular system are:
Low power transmitter and small coverage areas called cells
Spectrum (frequency) re-use
Handoff

21. Cells (1/2)
Space Division Multiplexing (SDM): base station covers a certain transmission area (cell)
Mobile stations communicate only via the base station
Advantages of cell structures:
higher capacity due to frequency re-use -> higher number of users
less transmission power needed
more robust, decentralized
base station deals with interference, transmission power, etc., locally

22. Cells (2/2)
Problems:
fixed network needed for the base stations
handoffs (changing from one cell to another) necessary
interference with other cells
Cell sizes range from 100 m in dense urban areas to, e.g., 35 km in rural areas
Cells sizes drop for higher frequencies as propagation loss increases

23. Multiplexing Techniques
Multiplexing techniques are used to allow many users to share a common transmission resource.
In the cellular case the users are mobile and the transmission resource is the radio spectrum.
Sharing a common resource requires an access mechanism that will control the associated multiplexing mechanism.

24. Media Access Comparison Chart

25. CDMA: Overview Each channel has a unique code
(not necessarily orthogonal)
All channels use the same spectrum at the same time
Advantages:
bandwidth efficient
no coordination and synchronization necessary
good protection against interference and tapping
Disadvantages:
lower user data rates due to high gains required to reduce interference
more complex signal regeneration

26. CDMA: Illustration k1 k2 k3 k4 k5 k6 c f t

27. CDMA C/Cs (1/2)
A CDMA system can be either code limited or interference limited.
For an interference limited system, every user has a code, but only uses it when active, this is referred to as a soft capacity system. The more users active in the system, the more codes that are used. However as more codes are used the signal to interference (S/I) ratio will drop and the bit error rate (BER) will go up for all users.
CDMA requires tight power control as it suffers from far- near effect. In other words, a user close to the base station transmitting with the same power as a user farther away will drown the latter’s signal. All signals must have more or less equal power at the receiver.

28. CDMA C/Cs (2/2)
Rake receivers can be used to improve signal reception. Time delayed versions (a chip or more delayed) of the signal (multipath signals) can be collected and used to make bit level decisions.
Soft handoffs can be used. Mobiles can switch base stations without switching carriers. Two base stations receive the mobile signal and the mobile is receiving from two base stations (one of the rake receivers is used to listen to other signals).
Burst transmission - reduces interference

29. Spread Spectrum: Basis of CDMA
Problem of radio transmission: frequency dependent fading can wipe out narrow band signals for duration of the interference
Solution: spread the narrow band signal into a broad band signal using a special code
Side effects:
coexistence of several signals without dynamic coordination
tap-proof
Techniques: Direct Sequence, Frequency Hopping

30. Operation of SS P f i) ii) sender P f iii) iv) user signal
broadband interference
narrowband interference
detection at
receiver
interference
spread signal
signal
spread f
power

31. SS and Fading narrowband channels spread spectrum channels
channel quality 2 1 5 6
narrowband channels 3 4
frequency
narrow band signal
guard space
channel quality 2 2 2
spread spectrum channels 2 2 1
frequency
spread spectrum

32. Cellular: 2G Digital wireless Low bitrate voice and data services
Circuit switched
Multiple standards: GSM, IS 136, IS 95
Global roaming within similar systems only
Messaging services: SMS
Web access: imode, wireless portals

33. Cellular: 3G
The next generation cellular, 3G, is envisioned to enable communication at any time, in any place, with any form, as such, it will:
allow global roaming
provide for wider bandwidths to accommodate different types of applications
support packet switching concepts
The ITU named this vision: IMT-2000 (International Mobile Telecommunications 2000) with the hope of having it operational by the year 2000 in the 2000MHz range.

34. IMT-2000 Vision Common spectrum worldwide (2.8 – 2.2 GHz band)
Multiple environments, not only confined to cellular, encompasses: cellular, cordless, satellite, LANs, wireless local loop (WLL)
Wide range of telecommunications services (data, voice, multimedia, etc.)
Flexible radio bearers for increased spectrum efficiency
Data rates of: 9.6Kbps or higher for global (mega cell), 144Kbps or higher for vehicular (macro cell), 384Kbps or higher for pedestrian (micro cell) and up to 2Mbps for indoor environments (pico cell)
Global seamless roaming
Enhanced security and performance
Full integration of wireless and wireline

35. 3G Technologies
W-CDMA backward compatible with GSM (called UMTS by the ETSI)
The IS-95 standard (CDMAOne) is evolving its own vision of 3G: CDMA2000
The IS-136 standard is evolving its own migration to 3G, Universal Wireless Communications, UWC-136 or IS-136 HS

36. 3G Timeframe
The Japanese are leading the pack with their W-CDMA implementation. It is planned to be rolled out in the year 2001 (pushed back from spring to late fall).
The Koreans plan to have CDMA2000 up an running before the world cup in 2002.
The Europeans are pushing hard to UMTS up soon but the current push is for 2.5G, a middle of the road to protect current infrastructure investments.
In the US no major push yet, some service providers are following in the footsteps of the Europeans by pushing a 2.5G solution.

37. IMT 2000 Services (1/2) All of 2G plus ---> Higher Bit rates:
144Kbps or higher for vehicular (macro cell),
384Kbps or higher for pedestrian (micro cell) and
up to 2Mbps for indoor environments (pico cell)
Billing/charging/user profiles
Sharing of usage/rate information between service providers
Standardized call detail recording
Standardized user profiles

38. IMT 2000 Services (2/2)
Support of geographic position finding services
Support of multimedia services
QoS
Asymmetric links
Fixed and variable rate
Bit rates of up to 2Mpbs
Support of packet services
Internet Access (wireless cellular IP - 3GPP)

39. IMT 2000 Family Concept
The IMT 2000 family concept defines some basic interoperability capabilities between different IMT 2000 technologies to enable global roaming!
Different Radio Access Networks (RANs):
CDMA2000
W-CDMA
UWC-136
Different Core Network standards
IS 41
GSM
ISDN

40. Challenge of the Family Concept
With IMT 2000 Standard Interfaces and Capabilities:
Any Family RAN could interface with any Family Core Network for some minimum set of features.
More advanced features are possible in limited regions where the Family RAN and the Family Core Network are optimally matched
The Core Network functionality should be kept independent of the Radio technology.
By maintaining independence, each can evolve separately based on needs
User Identity Modules (UIM) Plug-In modules could be used in locally rented handsets for Global Roaming with at least the minimum feature set. (similar to GSM SIMs)

41. UIM Roaming UIM cards should allow a subscriber to obtain:
Any IMT 2000 service/capability basic feature set on
Any IMT 2000 Network family member (W-CDMA, CDMA2000 and UWC-136)
UIM Card: will be a superset of the current GSM SIM
Contains all necessary information about the user’s service subscriptions
Supports user identity separate from handset identity:
Allows a user to use different handsets, with all usage billed to the single user
Allows a user to rent a handset in a foreign country/network and obtain instant service

42. To realize the IMT 2000 Vision
Physical interfaces are being standardized:
UIM to handset interface
Radio/Air interfaces
RAN to Core Network
Network to Network Interfaces (NNI) between Core Networks
Radio independent functions are being standardized:
UIM to handset
Handset to Core Network
NNI

43. The next vision: 4G Higher bit rates (what else???):
2Mbps outdoor, high speed
20Mbps indoor, low speed
Full integration with IPv6, IP QoS and MoIP
High capacity: 5 to 10 increase
Multimode terminals: seamless switching between different systems
Cheaper infrastructure cost

44. How to realize 4G
Higher spectrum is required to accommodate higher bit rates (e.g., 2-4Mbps requires ~ 20MHz)
Problems with propagation loss, attenuation
Higher RF circuit losses
Both of these require higher output power, e.g., 2Mbps at 5GHz requires 2400 times more power than 8Kbps at 2GHz
Adaptive phased arrays are needed to achieve higher gains to counteract the losses listed above
With better antennas we get higher capacity systems as co-channel interference is reduced
These antennas are expensive but generally constitute the cheapest component of the system

45. Issues to be considered
Few studies exist that characterize the behaviour of the channel at these higher frequencies
The increased gains claimed by phased antennas are based on theoretical studies and remain to be verified in live scenarios
New space time channel codes need to be defined that work optimally in this higher frequency range
Equalization and decoding algorithms need to studied for space time coded systems
To achieve better performance 3G uses specialized circuits, 4G should use instead general purpose DSP, and implement soft radios

46. Higher Layer Issues
Network Layer
Transport Layer
Mobility Support

47. Network Layer What do cellular networks and wireless LANs provide?
Wireless connectivity
Mobility at the data link layer
What is Dynamic Host Configuration Protocol (DHCP)?
It provides local IP addresses for mobile hosts
Is not secure
Does not maintain network connectivity when moving around
What the above do not provide:
Transparent connectivity at the network layer
Mobility with local access, i.e, mobility at the data link layer
The difference between mobility and nomadicity!

48. Mobile IP Mobile IP provides network layer mobility
Provides seamless roaming
‘‘Extends’’ the home network over the entire Internet

49. Motivation for MoIP IP Routing Specific routes to end-systems?
based on IP destination address, network prefix (e.g ) determines physical subnet
change of physical subnet implies change of IP address to have a topologically correct address (standard IP) or needs special entries in the routing tables
Specific routes to end-systems?
requires changing all routing table entries to forward packets to the right destination
does not scale with the number of mobile hosts and frequent changes in the location, security problems
Changing the IP-address?
adjust the host IP address depending on the current location
almost impossible to find a mobile system, DNS updates slow
TCP connections break, security problems

50. Scope of MoIP Mobile IP solves the following problems:
if a node moves without changing its IP address it will be unable to receive its packets,
if a node changes its IP address it will have to terminate and restart its ongoing connections everytime it moves to a new network area (new network prefix).
Mobile IP is a routing protocol with a very specific purpose.
Mobile IP is a network layer solution to node mobility in the Internet.
Mobile IP is not a complete solution to mobility, changes to the transport protocols need to be made for a better solution (i.e., the transport layers are unaware of the mobile node’s point of attachment and it might be useful if, e.g., TCP knew that a wireless link was being used!).

51. Requirements of MoIP Transparency Compatibility Security
mobile end-systems keep their IP address
continuation of communication after interruption of link possible
point of connection to the fixed network can be changed
Compatibility
support of the same layer 2 protocols as IP
no changes to current end-systems and routers required
mobile end-systems can communicate with fixed systems
Security
authentication of all registration messages
Efficiency and scalability
only little additional messages to the mobile system required (connection typically via a low bandwidth radio link)
world-wide support of a large number of mobile systems

52. Problems with MoIP Security Firewalls QoS
authentication with FA problematic, for the FA typically belongs to another organization
no protocol for key management and key distribution has been standardized in the Internet
patent and export restrictions
Firewalls
typically mobile IP cannot be used together with firewalls, special set-ups are needed (such as reverse tunneling)
QoS
many new reservations in case of RSVP
tunneling makes it hard to give a flow of packets a special treatment needed for the QoS
Security, firewalls, QoS etc. are topics of current research and discussions!

53. Transport Layer Transport protocols typically designed for
Fixed end-systems
Fixed, wired networks
TCP congestion control
packet loss in fixed networks typically due to (temporary) overload situations
routers have to discard packets as soon as the buffers are full
TCP recognizes congestion only indirectly via missing (I.e., timed out) acknowledgements
Immediate retransmissions unwise, they would only contribute to the congestion and make it even worse
slow-start algorithm is used as a reactive action to reduce the network load

54. Influences of Mobility and Wireless
TCP assumes congestion if packets are dropped
typically wrong in wireless networks, here we often have packet loss due to transmission errors
furthermore, mobility itself can cause packet loss, if e.g. a mobile node roams from one access point (e.g. foreign agent in Mobile IP) to another while there are still packets in transit to the old access point and forwarding from old to new access point is not possible for some reason
The performance of unmodified (i.e., as is) TCP degrades severely
note that TCP cannot be changed fundamentally due to the large base of installation in the fixed network, TCP for mobility has to remain compatible
the basic TCP mechanisms keep the whole Internet together

55. Modified TCP

56. Issues with Proposed Solutions
Not one of these is a good solution
Each offers a solution to a part of the problem but not the whole

57. Mobility Support
File Systems
Databases
WWW

58. File Systems Goal Problems Solutions
efficient and transparent access to shared files within a mobile environment while maintaining data consistency
Problems
limited resources of mobile computers (memory, CPU, ...)
low bandwidth, variable bandwidth, temporary disconnection
high heterogeneity of hardware and software components (no standard PC architecture)
wireless network resources and mobile computer are not very reliable
standard file systems (e.g., NFS, network file system) are very inefficient, almost unusable
Solutions
replication of data (copying, cloning, caching)
data collection in advance (hoarding, pre-fetching)

59. Databases Request processing Replication management
power conserving, location dependent, cost efficient
example: find the fastest way to a hospital
Replication management
similar to file systems
Location management
tracking of mobile users to provide replicated or location dependent data in time at the right place (minimize access delays)
example: with the help of the HLR (Home Location Register) in GSM a mobile user can find a local towing service
Transaction processing
“mobile” transactions cannot necessarily rely on the same models as transactions over fixed networks (ACID: atomicity, consistency, isolation, durability)

60. WWW 1/3
Protocol (HTTP, Hypertext Transfer Protocol) and language (HTML, Hypertext Markup Language) of the Web have not been designed for mobile applications and mobile devices, thus creating many problems!
Typical transfer sizes
HTTP request: byte
Responses avg. <10 Kbyte, header 160 byte, GIF 4.1Kbyte, JPEG 12.8 Kbyte, HTML 5.6 kbyte
And many large files
The Web is no file system
Web pages are not simple files to download
static and dynamic content, interaction with servers via forms, content transformation, push technologies etc.
many hyperlinks, automatic loading and reloading, redirecting
a single click might have big consequences!

61. WWW 2/3 Characteristics Problems
stateless, client/server, request/response
needs a connection oriented protocol (TCP), one connection per request (some enhancements in HTTP 1.1)
primitive caching and security
Problems
designed for large bandwidth (compared to wireless access) and low delay
large and redundant protocol headers (readable for humans, stateless, therefore large headers in ASCII)
uncompressed content transfer
using TCP
DNS lookup by client causes additional traffic and delays

62. WWW 3/3 Caching POSTing (i.e., sending to a server)
quite often disabled by information providers to be able to create user profiles, usage statistics etc.
dynamic objects cannot be cached
numerous counters, time, date, personalization, ...
mobility quite often inhibits caches
security problems
caches cannot work with authentication mechanisms that are contracts between client and server and not the cache
today: many user customized pages, dynamically generated on request via CGI, ASP, ...
POSTing (i.e., sending to a server)
can typically not be buffered, very problematic if currently disconnected
Many unsolved problems!

63. HTML and Mobility HTML Mobile devices Additional “features”
designed for computers with “high” performance, color high-resolution display, mouse, hard disk
typically, web pages optimized for design, not for communication
Mobile devices
often only small, low-resolution displays, very limited input interfaces (small touch-pads, soft-keyboards)
Additional “features”
animated GIF, Frames, ActiveX Controls, Shockwave, movie clips,
many web pages assume true color, multimedia support, high-resolution and many plug-ins
Web pages ignore the heterogeneity of end-systems!
e.g., without additional mechanisms, large high-resolution pictures would be transferred to a mobile phone with a low-resolution display causing high costs

64. WWW and Mobility Application gateways, enhanced servers Examples
simple clients, pre-calculations in the fixed network
Compression, transcoding, filtering, content extraction
automatic adaptation to network characteristics
Examples
picture scaling, color reduction, transformation of document format
Present only parts of the image: detail studies, clipping, zooming
headline extraction, automatic abstract generation
HDML (handheld device markup language): simple language similar to HTML requiring a special browser
HDTP (handheld device transport protocol for HDML
Problems
proprietary approaches, require special enhancements for browsers
heterogeneous devices make approaches more complicated

65. What is happening 1/2 HTTP/1.1
client/server use the same connection for several request/response transactions
multiple requests at beginning of session, several responses in same order
enhanced caching of responses (useful if equivalent responses!)
semantic transparency not always achievable: disconnected, performance, availability -> most up-to-date version...
several more tags and options for controlling caching (public/private, max-age, no-cache, etc.)
encoding/compression mechanism, integrity check, security of proxies, authentication, authorization...

66. What is Happening 2/2 Enhanced browsers Client Proxy
Pre-fetching, caching, off-line use
e.g. Internet Explorer
Client Proxy
e.g., Caubweb, TeleWeb, Weblicator, WebWhacker, WebEx
Client and network proxy
combination of benefits plus simplified protocols
e.g., MobiScape, WebExpress
Special network subsystem
adaptive content transformation for bad connections, pre-fetching, caching
e.g., Mowgli

67. Conclusions
The problems with 3G are mostly infrastructure cost related
The problems facing 4G are much more fundamental
It is absolutely imperative that we start to think about what the future will be like so that we can direct our energies to solving these problems
Wireless systems will become pervasive and will exist in a multitude of flavors (sensors, satellites, LANs, PANs, cellular, access, etc,).
We need to be able to provide a seamless integration of all these systems
Still need work at higher layers for true nomadicity, not just wireless and mobility