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					    A Survey of Enabling Technologies for 3G+
                Wireless Systems

                                  Vincent Lau
                        Bell Labs, Lucent Technologies

                                Dec 20, 2002

                                               Lucent Technologies
1                                                   Bell Labs Innovations
 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:
                                               Lucent Technologies
 2                                                  Bell Labs Innovations
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

                                                           Lucent Technologies
 3                                                              Bell Labs Innovations
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.

                                                    Lucent Technologies
 4                                                       Bell Labs Innovations
GPRS Infrastructure
                       Voice Path - same
                        infrastructure as GSM.
                       Data Path - via an
                        overlay IP-based network
                        of SGSN - GGSN.

                                  Lucent Technologies
 5                                     Bell Labs Innovations
 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

                                                        Lucent Technologies
   6                                                         Bell Labs Innovations
Post 3G Systems
                   3G+ Systems??
                    – Based on existing 3G
                      spectrum (not new
                    – 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
                    – Ultra high speed packet
                      data service (10.8
                    – All-IP Core Network.

                     Lucent Technologies
 7                        Bell Labs Innovations
Advanced Technologies – Physical Layer
     – Multiple Antenna (MIMO) Processing:
       » Traditionally, the speed of a wireless link is limited by the
         radio resource (power, bandwidth).
       » When the transmitter has nT antennas and the receiver
         has n R antennas, the link speed increases linearly with
         min  nT , nR   given the same power and bandwidth
       » Multiple Antenna introduces Spatial Dimension into the
         radio resource set.
       » Similar to fixed line scenario except there are mutual
         interference between the spatial channels.

                                                        Lucent Technologies
 8                                                           Bell Labs Innovations
Advanced Technologies – Physical Layer
 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 world’s first BLAST receiver chip
     for mobile device.
                                                      Lucent Technologies
  9                                                        Bell Labs Innovations
Advanced Technologies – Physical Layer
 Block Diagram

                                    Lucent Technologies
10                                       Bell Labs Innovations
Advanced Technologies – Physical Layer
 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.

                                                     Lucent Technologies
11                                                        Bell Labs Innovations
Advanced Technologies – Physical Layer
 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.

                                                    Lucent Technologies
12                                                       Bell Labs Innovations
  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
   – Priority is given to users with good channel conditions. (because
   13 they could use the radio resource more effectively).
                                                          Lucent Technologies
                                                                Bell Labs Innovations
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.

                                  Lucent Technologies
14                                     Bell Labs Innovations
Advanced Technologies – MAC layer Enhancement

           %UEs with PCT < abscissa
                                       30                    Proportional Fair
                                       20                    Normalized Max C/I
                                       10                    Max C/I
                                            0   500   1000     1500               2000

 Proportional fair is another common objective of scheduling.

                                                                                 Lucent Technologies
15                                                                                    Bell Labs Innovations
Advanced Technologies – Architectural
 Information Hot-spot Architecture (Wireless LAN vs Cellular Systems):
   – High speed, low mobility, localized-coverage wireless multimedia
     access --> hot spot access points. (e.g. Wireless LAN Access
   – Medium speed, high mobility, macro-coverage --> cellular wireless.
     (e.g UMTS)
   – Mobility between localized hot-spots and cellular wireless through
 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.
                                                       Lucent Technologies
16                                                          Bell Labs Innovations
Information Hot-spot Architecture (Tight Integration)

                                        Lucent Technologies
17                                           Bell Labs Innovations
Information Hot-spot Architecture (Loose

                                      Lucent Technologies
18                                         Bell Labs Innovations
Mobile-IP Operation




• 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                                                      Lucent Technologies
 19                                                                 Bell Labs Innovations
  Wireless Virtual Private Network
               Corporate  NavisRadius
                Network Home AAA Server
                     Xedia                                 Local AAA
                    AP1000                                   Server
 Mobile-IP            HA                                                Lucent
  tunnel                                                                 PCF              WSP
             NavisRadius                               PDSN
              Local AAA                                                           BSC
                Server                               Springtide
                         Xedia                          (FA)
                          FA            End-to-end
               Ethernet                   IPSec
                                          tunnel                                 BS

                  802.11 Access
 W-LAN                Points
Hot Spot
                                                      Dual-mode terminal w/
                                                         MobileIP client

                                                                                  Lucent Technologies
    20                                                                                  Bell Labs Innovations
An Example of 3G+ Evolution - UMTS HSDPA (High
Speed Downlink Packet Access)

    Release 99/4     HSDPA Release 5            HSDPA Release 6
                           HS-DSCH                    HS-DSCH

        DCH/DSCH      Enhanced      Adaptive                      Fast Cell
                      Channel      Modulation      MIMO           Selection
                      Structure     & Coding

                      Hybrid ARQ

                                                10.8 Mbps Packet (2x2)
   2 Mbps Packet      2.4Mbps Packet             20 Mbps Packet (4x4)

  R99         R4

                                                            Lucent Technologies
            Dec 00
                                                                 Bell Labs Innovations
Mar 00                       June 02                      ‘03
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


      Antennas used in MIMO
      channel measurements
                                                    Lucent Technologies
22                                                       Bell Labs Innovations