Wireless Systems: Where are we heading

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
• 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
  802.11
• 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 -gt 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, -gt 50 - 70Mbit/s
• wide area 9.6 19.2 kbit/s -gt 384 - 2000Kbit/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

• 802.11 (2M) -gt 802.11b (11M) -gt 802.11a (50-70M)
• Wider spectrum -gt 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 50-300m

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
next frame
contention
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
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 -gt 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
k2
k3
k4
k5
k6
k1
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
  latters 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
31
SS and Fading
channelquality
2
1
5
6
narrowband channels
3
4
frequency
narrow bandsignal
guard space
channelquality
2
2
spread spectrum channels
2
2
2
1
frequency
spreadspectrum
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 ---gt
• 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
  users 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
• based on IP destination address, network prefix
  (e.g. 129.13.42) 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 nodes 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
• 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
• 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
• 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
• 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 100-350 byte
• Responses avg. lt10 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
• 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
• 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
• 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
• 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 -gt 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
• Pre-fetching, caching, off-line use
• e.g. Internet Explorer
• Client Proxy
• Pre-fetching, caching, off-line use
• 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