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 world’s 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 --> hot spot access points. (e.g. Wireless LAN Access Point). • Medium speed, high mobility, macro-coverage --> 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. HSDPA Release 5 HSDPA Release 6 Release 99/4 HS-DSCH HS-DSCH DCH/DSCH Enhanced Channel Structure Adaptive Modulation & Coding MIMO Fast Cell Selection Hybrid ARQ Dynamic Scheduling 2 Mbps Packet 2.4Mbps Packet 10.8 Mbps Packet (2x2) 20 Mbps Packet (4x4) R99 R4 Dec 00 Mar 00 June 02 ‘03 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