A Survey of Enabling Technologies for 3G Wireless Systems

1
A Survey of Enabling Technologies for 3G
Wireless Systems
4G???

• Vincent Lau
• Bell Labs, Lucent Technologies
• Dec 20, 2002

2
Outline

• Background on Cellular Systems
• Evolution of Cellular Systems
• Advanced Technologies for 3G Systems
• Physical Layer Enhancement
• Multiple Antenna Processing - BLAST
• OFDM
• Utilization of Feedback
• MAC Layer Enhancement
• Adaptive Scheduling
• Architectural Enhancement
• Information Hot-spot Architecture
• Illustration with UMTS - HSDPA

3
Background of Cellular Systems

• Key Components
• Mobile station, base station, switch.
• Bottleneck is usually on the air interface due to
  the limitation on radio resource.
• Radio Resource
• Power, Bandwidth

4
Evolution of Cellular Systems

• 1G systems (AMPS, TACS)
• Analog Transmission (FM).
• Voice Applications only.
• 2G systems. (GSM, CDMA, IS54)
• Digital Transmission.
• Voice and Data applications (Circuit Switched
  only).
• Cellular and PCS.
• 2.5G systems (GPRS/EDGE, 3G1X).
• Digital Transmission,
• Circuit Switched voice and data (same as 2G
  medium speed)
• Packet switched data (medium speed, No QoS).
• Overlay Infrastructure with 2G Systems.

5
GPRS Infrastructure

• Voice Path - same infrastructure as GSM.
• Data Path - via an overlay IP-based network of
  SGSN - GGSN.

6
Evolution of Cellular Systems

• 3G systems.
• Digital transmission,
• Circuit switched voice and data (low speed)
• Packet switched data services (high speed
  2Mbps, with QoS).
• Integrated Core Network Infrastructure between
  voice and data paths.

7
Post 3G Systems

• 3G Systems??
• Based on existing 3G spectrum (not new spectrum).
• By 2010, 66 of the revenues will come from data
  services
• UMTS - Release 99/4 systems alone will not be
  capable to meet these demands. (Realistic outdoor
  data rates will be limited to 384kbps).
• Ultra high speed packet data service (10.8 Mbps)
• All-IP Core Network.

8
Advanced Technologies Physical Layer Enhancement

• Multiple Antenna (MIMO) Processing
• Traditionally, the speed of a wireless link is
  limited by the radio resource (power, bandwidth).
• When the transmitter has antennas and the
  receiver has antennas, the link speed
  increases linearly with given the same power
  and bandwidth budget.
• Multiple Antenna introduces Spatial Dimension
  into the radio resource set.
• Similar to fixed line scenario except there are
  mutual interference between the spatial channels.

9
Advanced Technologies Physical Layer Enhancement

• BLAST (Bell-Labs Layered Space-Time Architecture)
• At the transmitter, n independent data streams
  are transmitted out of the n antennas on the same
  bandwidth.
• At the receiver, each receive antenna "sees" all
  of the transmitted sub-streams superimposed, not
  separately.
• If multipath scattering is sufficient, these n
  data streams have different spatial signatures to
  each of the n receive antennas and they are
  separable.
• The processing involved is linear and could be
  (interference nulling or MMSE).
• Lucent has produced the worlds first BLAST
  receiver chip for mobile device.

10
Advanced Technologies Physical Layer Enhancement

• Block Diagram

11
Advanced Technologies Physical Layer Enhancement

• Orthogonal Frequency Division Modulation (OFDM)
• Traditionally, transmission of a wideband signal
  is more difficult than a narrowband signal.
• This is due to multi-path effects ? Inter-symbol
  interference.
• Complex equalizer is needed to overcome this
  effect.
• OFDM is an effective technique to transmit
  wideband signal.
• Serial input data is split into N parallel
  streams, each stream is fed into a frequency
  channel.
• With respect to each data stream, it is a
  narrowband signal, and could get through the
  channel easily without equalizer.
• At the receiver, the N parallel streams are
  combined.

12
Advanced Technologies Physical Layer Enhancement

• Utilization of Feedback
• Wireless channel is time varying. Good ? ? Bad
• Adaptive transmission is possible to exploit the
  time varying nature of the channel.
• High throughput transmission mode is employed
  when channel is good,
• When channel is bad, low throughput transmission
  mode is employed for better protection.
• Need the feedback of channel condition to the
  transmitter.

13
Advanced Technologies MAC Layer Enhancement

• Jointly Adaptive MAC Scheduling
• For voice service, data source is quite steady.
  Optimal strategy is to power control users so as
  to act against fading ? maintain a steady
  channel throughput.
• For packet data service, data source is in burst.
  Optimal strategy is to act in line with fading.
  Increase power when channel is good. Decrease
  power when channel is bad.
• For multi-user network, MAC layer is used to
  coordinate resource allocation among different
  users.
• Between a user and a base station, the link
  throughput (speed) is adaptive based on the link
  condition.
• The key is to have a jointly adaptive MAC layer
  and physical layer.
• Priority is given to users with good channel
  conditions. (because they could use the radio
  resource more effectively).

14
Advanced Technologies MAC Layer Enhancement

• Since users are independent with each other, we
  could always find users with good channel
  condition at any given time (if the total number
  of user is large) ? Multiuser Diversity.
• In addition to maximum network capacity, fairness
  is also an important attribute.

15
Advanced Technologies MAC layer Enhancement

• Proportional fair is another common objective of
  scheduling.

16
Advanced Technologies Architectural Enhancement

• Information Hot-spot Architecture (Wireless LAN
  vs Cellular Systems)
• High speed, low mobility, localized-coverage
  wireless multimedia access --gt hot spot access
  points. (e.g. Wireless LAN Access Point).
• Medium speed, high mobility, macro-coverage --gt
  cellular wireless. (e.g UMTS)
• Mobility between localized hot-spots and cellular
  wireless through mobile-IP.
• The WLAN advantages
• Order of magnitude higher data rates than 3G
• Rapidly falling price (available from retail)
• HW embedded in laptops (Dell, IBM, Toshiba,
  Fujitsu, Acer). SW supported in Window XP
• 50 of USA laptops and PDAs are expected to be
  WLAN-enabled by 2004.

17
Information Hot-spot Architecture (Tight
Integration)
18
Information Hot-spot Architecture (Loose
Integration)
19
Mobile-IP Operation
Home Agent
Foreign Agent
Mobile Node

• Traffic is sent as usual to the home subnet
• The home agent intercepts (Proxy ARP) the traffic
  while the mobile node is registered as away
• Traffic is tunneled to its current location
• Traffic from the mobile node can go directly to
  the correspondent host

20
Wireless Virtual Private Network
Corporate Network
NavisRadius Home AAA Server
NavisRadius Local AAA Server
Xedia AP1000 HA
Lucent PCF
WSP
Mobile-IP tunnel
Internet
NavisRadius Local AAA Server
PDSN Springtide (FA)
BSC
Xedia FA
End-to-end IPSec tunnel
Ethernet
BS
BS
802.11 Access Points
W-LAN Hot Spot
Dual-mode terminal w/ MobileIP client
21
An Example of 3G Evolution - UMTS HSDPA (High
Speed Downlink Packet Access)
22
Practical considerations at the terminal

• For uncorrelated fading, 1/2 lambda spacing is
  sufficient because of local scatterers.
• Each antenna requires RF/IF chain. Significant
  cost savings using direct conversion (homodyne)
  solutions.
• 20 and 70 of baseband processing used by VBLAST
  detector and turbo decoder, respectively, for
  (4,4) receiver. Overall processing is within
  range of existing hardware technologies.

Antennas used in MIMO channel measurements