New and Emerging Wireless Technologies Beyond 3G

1
New and Emerging Wireless Technologies Beyond 3G

• Sam Samuel
• Lucent Technologies
• Swindon UK

2
TOC

• Economics and Vision
• Background to the Problem
• Future and Emerging Technologies
• MIMO
• OFDM
• Beam forming IA and Antenna Array
• Interference cancellation
• Network Time Scheduling
• IEEE Approaches
• Summary

3
Wireless Experience Curve 1985 to 1996
CEOs
Note DRAM and airtime both reduced 10x from
1985-1995
Real Estate Agents
1985
Replace Calling Cards
1986
1987
Cost per Minute
1988
1989
1990
1991
1992
Intercom
1993
1994
Elasticity 3
1995
1996
Def of Elasticity change in X/ change in y
Source G.Blonder, ATT Labs, 1977
Cumulative Minutes (B)
Note Cost excludes marketing and sales expense
and are in 1996 dollars

• Next generation systems must be spectrally
  efficient across the network (bandwidth where
  needed).
• Equipment providers will provide the compilers
  for application creation.
• Partnering will be the norm.

4
Economics and Visions
5
Information Anywhere VisionExample project EU
6FP Ambient Networks

• Ambient Networks
• Common Control Services
• Dynamic Network Composition

Services
Services

Ambient Connectivity

Community
Personal

Home
Vehicular
PAN
CAN
VAN
HAN
6
Background to the problem Motivation
7
The wireless channel

• Scattering causes local signal fading
• Delay spread dependent on environment (small for
  indoor, large for macrocell)

8
Channel Normal-modes

• Classic static multipath channel is linear.
• Normal modes are simple sinusoids. OFDM then is
  optimal in this sense.
• Information is broken into small frequency bands
  with flat fading. Great for MIMO type
  applications.
• Active research areas within Bell Labs
• OFDM, chirped pulses, MC-CDMA, OFDM-CDMA for
  legacy and practical implementation

9
Increasing the Data Rate in CDMA
Rake Receiver
Original signal
Multipath channel
Rx signal
time diversity
UMTS
10
Live Wireless Transaction Measurements

• Netscape Browser access to www.adobe.com
• blue dots are downlink packets, red dots are
  uplink packets.
• average downlink Kbps to 1 second peak
  4.31
• average uplink Kbps to 1 second peak 4.71
• MRU was 1500 bytes
• TCP Window Size was 8,192 bytes

• Traffic characteristics
• Initial download of HTTP skeleton resulted in
  GET of large objects. Many 1500 packets
  retrieved.
• Period 9 - 20 consumed by DNS accesses to
  resolve www.xxx.com addresses to IP addresses.
• End of transaction resulted in many small
  object retrievals. Large uplink payloads for
  smaller downlink payloads.
• Latency chart illustrates queuing within system
  as generated load piles up in uplink and
  downlink directions.
• This traffic profile is typical of Web accesses.

We cannot ignore delay TTI Issues
We cannot ignore uplink Symmetry Issues
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General Throughput Equation

• To optimize data performance we should combine
  rate and power control
• OFDM is convenient for water filling
• Keep number of sub-carriers manageable for uplink
  channel information

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Future and Emerging Technologies
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MIMO
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Space The Last Frontier

• Convergence of ubiquitous wireless access and
  broadband internet creates insatiable demand for
  high bit rate wireless access
• System capacity is interference limited - cannot
  be increased by increasing transmitted power
• The spectrum has become a scarce and very
  expensive resource
• For Cellular systems reducing cell size is not
  viable
• Increasing spectral efficiency with multiple
  transmit and multiple receive antennas opens a
  new dimension, space, offering exceedingly high
  bit rates without increasing transmitted power
  bandwidth allocation

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Bandwidth Efficiency Limits
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Efficiency Limits with a Single Array

• Adding a single array does provide diversity
  against fading, but it does not change the (slow
  growth) logarithmic nature of the bandwidth
  efficiency limit

17
Lifting the Limits with Dual Arrays
s1
18
Predicted outage capacities
150 100 50
SPECTRAL EFFICIENCY vs. NUMBER ANTENNAS
AT 1 OUTAGE

24dB
12dB
18 dB
SPECTRAL EFFICIENCY (bps/Hz)
6 dB
1?N Optimum Combining at 24 dB
0 dB
8
0 10
20 30
40 50 60
NUMBER OF UNCORRELATED ANTENNAS (MN)
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MIMO Capacity Increases
C/Wlog2(det(IrHHH))
Nlog2(1SNR)
Capacity grows as the number of antennas!

• Increases the spectral efficiency
• Compact antenna arrays
• Low-cost receivers

20
MIMO
MIMO Increase data rates by exploiting multiple
antennas at both Tx and Rx.
Channel
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The Wireless Channel in MIMO Processing

• Multiple antenna techniques rely on the
• characteristics of the spatial signature
• Diversity techniques rely on the assumption that
  distinct spatial signatures correspond to
  different pairs of transmit-receive antennas.
• Intelligent antenna techniques rely on the
  efficient adaptation of the array pattern
  according to the spatial distribution of the
  desirable user and interferers.

22
Open-Loop Transmit Diversity

• Time-Switched Transmit Diversity (TSTD)

x1
Data
Mobile
time
x1 , x2
x2
time

• Space-Time Block Code Transmit Diversity (STC)

x1
x2
Space-Time Block Code
Data
Mobile
time
x1 , x2
x1
x2
time
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MIMO Research Trends
Advanced MIMO receivers can be costly on the
downlink due to limitations in mobile form-factor
and complexity.

• High-performance, low-complexity detection
  algorithms for MIMO. Algorithms based on
  joint-detection or serial/parallel interference
  cancellation techniques following space-time
  equalization.

• High-performance, low-complexity receiver
  architectures for MIMO based on multiple
  iterations between a low-complexity detector and
  a error-correcting decoder.

• Transmitter encoding for High-Order Modulations
  in MIMO, allowing reduced complexity at the
  receiver.

• Dynamic packet scheduling across multiple
  antennas.

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Propagation Modeling Measurements
Indoor propagation measurements consistently show
high BLAST gains. Recent outdoor measurements
demonstrate similar results.
Mobile Measurements
theory
omni ant.
BLAST/1x1 capacity
120 ft
antenna in laptop
time (sec)

• narrowband channel capacity in mobile suburban
  80 of theory
• narrowband channel capacity of laptop in van is
  65 of theory
• Capacity improvements are real

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OFDM
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Orthogonal Frequency Division Duplexing

• Breaks high-speed data into low-rate parallel
  streams
• Longer symbol period reduces ISI ICI for spread
  OFDM
• fnfcnDf, where for orthogonality DfTs1
• Simple DFT implementation

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Beam Forming Intelligent Antenna
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Performance Enhancements

• Transmit Diversity achieves
• Improved call quality on the downlink by
  combating multipath fading.
• Reduced BTS transmit power, thereby reducing
  downlink inter-cell interference.
• Intelligent Antennas achieve
• Higher antenna gain - by maximising received
  energy or transmitting more effective power.
• Reduction of Interference by maximising Signal
  to - Interference Ratio

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Intelligent Antennas

• An antenna-array transceiver system.
• Combined with a base station architecture and
  signal processing techniques designed to
  dynamically select or form the optimum beam
  pattern per user.

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Adaptive Antenna Principle
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Closed-Loop Transmit Diversity
w1
Mobile
Data
w2
Feedback on Uplink
Closed-loop TxAA
Quantised Weights

• Weights are computed by the mobile as a function
  of the downlink channel estimates to maximise the
  received signal energy.
• Weights are then quantised in amplitude/phase and
  sent back on the uplink control channel.
  

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Multi-Antenna Solutions
Pathloss (dB)
dB
antenna separation
time

• Signal fades in time and space. Include both
  space and time diversity

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Base and terminal Smart Antenna Prototypes
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Basestation Antenna Configurations

• two beam lobes
• polarization and spacial diversity configurations
• 2-6 dB improvement
• high gain for low-speed users
• 4-fold diversity on the uplink

polarization beams

• 16 element tower top electronics
• 9o beamwidth with -35 dB side lobes
• Space-division multiple access

35
Polarization Antennas at Mobile
Without scattering polarization perpendicular to
k-vector
Tripole antenna

• Three omni-antennas co-located at feed point
• Key feature to obtain MIMO gains
• achieving the separation between Antennas on the
  end device
• Ceramic Antenna, Tripole Antenna

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Interference Cancellation
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Interference Mitigation (1)Cellular Downlink
Intra- and inter-cell interference mitigation
algorithms at the mobile.

• Iterative detectors based on space-time
  filtering. Filter weights trained via transmitted
  pilots of the desired signal using Least squares
  and semi-blind (e.g. constant modulus)
  optimisation criteria.

38
Interference Mitigation (2)WLAN
Inter-system Interference due to co-existing
technologies in unlicensed bands.

• Space-time filtering at the receiver in
  conjunction with enhanced MAC algorithms to cope
  with inter-system interference.

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Interference Mitigation Advances
K4, M2, Nt20, Nd80, SIR0dB, 500 trials
0
10
Known parameters
LR with outliers selection
LS
Conventional solutions
LSB
SB (delta0.1)
Proposed semi-blind solution
-1
10
MSE
Finite data ML benchmark
Optimal solution Full a priori info
-2
10
10
11
12
13
14
15
16
17
18
19
20
SNR, dB
Techniques advancing to point where they
approaching theoretical limits
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Network Time Scheduling
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Short Delay vs. Long Delay Services
link loss
Tx power
Delay constraints force user to power control
through fades
delay jitter
Tx power
Schedule transmission around fades. Transmit at
full power maximum rate. Higher latency.
42
Data scheduling

• Partition low and high latency services in power

43
Coordinated Cell Scheduling

• MESH Network
• 802.16a
• Other relay techniques
• being proposed in 4G
• research
• Considered a key
• Future Emerging
• Technology by EU

possible 3X improvement

• High priority packets are sent with neighbors
  quiet.
• Coordination is local between nearest neighbour

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IEEE Approaches
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Impact of 802.20, 802.16 , 802.11

• IEEE approach is largely OFDM based
• Even IEEE 802.15.3 is OFDM based
• Actively adding mobility to the standards
• 802.16e and 802.20
• 802.11 considering management plane that would
  allow mobility
• Differences
• 802.20 wide scale mobility (vehicular)
• frequency band 500Mhz to 3.5GHz
• 802.16e pedestrian
• Based on 802.16a frequency band 2GHz to 6 GHz
• Appears there is an overlap between two

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Efficiency Targets for 802.20
Source IEEE 802.20
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802.11 Indoor Wireless LAN Migration
IEEE 802.11 Fourth-Generation of Wireless
Communications
First Generation Wireless LANs

• Peer/Peer and Client/Server
• Small User Population
• Isolated "Cells" and User Groups
• Non-Contiguous Coverage
• Indoor Operation
• Limited Mobility
• Mostly Asynchronous Traffic
• Slower than Ethernet

• Larger User Population
• Managed Services
• Full Roaming/Handoff Capability
• Contiguous Coverage in Dense Areas
• Wider Area Coverage for Community LANs
• Mobility (Follow-Me Service)
• Mix of Async and Isochronous Traffic
• Higher System Utilization
• Enhanced Security

Merge of 3G and 4G services (WLAN WAN)
Source ATT proposal to IEEE 802.11
48
802.11 Device Management
Process of Managed 802.11 devices in the Standards
(Small steps to make good progress)
Inter-Access Port Protocol
Inter-Communications between APs (Now a Standard)
Radio Resource Measurements
Ability to obtain MAC and PHY measurements by
Upper Layers (Now a Task Group)
Enable external entities to manage Devices (APs
and Clients) (Proposed Next Logical
Step)
Remote Managed Device
Source ATT proposal to IEEE 802.11
49
IEEE impact on 4G

• Mobility
• Higher layer approach to mobility
• MIP and enhancements e.g. Dynamic Home Agents
• Considering proposals to Link layer mobility
• That all 802.xx standards adhere to MAC and VLAN
  bridging
• Conclusion
• Aim is for improved spectral efficiency
• Incorporating ideas of
• PAN - 802.15.x
• VAN 802.20, 802.16e
• HAN 802.11(a-g)
• CAN 802.16a
• Potential High Impact on 4G

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Summary
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• In this talk we have
• Looked at the motivation and vision for the
  emergence of new technologies
• Looked at which technologies are likely to
  succeed
• Noticed that the IEEE approach to 4G
  standardisation may succeed before others
• Thank You!!