LANWLAN Demand for Bandwidth

1
LAN/WLAN Demand for Bandwidth
10GbT
10G
1000bT
1G
802.15.3a
100bT
100M
Throughput (bps)
802.11a/g
1Gbps The next wireless challenge!
10bT
802.11b
10M
802.11
LAN
1M
WLAN
88
90
92
94
96
98
00
02
04
06
Year
2
The 60GHz Opportunity
57 dBm
40 dBm
7 GHz

• Unprecedented amount of unlicensed spectrum
• Few regulatory specifications
• Small wavelength allows for multi-antenna
  approach in reasonable form factors

3
60GHz High-speed Link Key Channel and Circuit
Challenges

• Friis Transmission equation Loss increases with
  fc
• Additional 22dB loss relative to 5GHz system for
  fixed G
• Multipath channel issues
• Specular, (moderately) reflective channel
• Baseband analog interface bottleneck
• High-speed link ? high-speed, high-resolution
  ADC/DAC?
• Power-handling, linearity, and noise performance
  of CMOS circuits at 60GHz
• Limited RF performance constrains baseband design

4
Research Proposal

• Problem
• Given 60GHz circuit and channel limitations, how
  do we design the baseband system and architecture
  for a power-efficient, high-data rate 60GHz
  wireless link?
• Approaches
• Utilize beam-forming to combat channel loss and
  multipath
• Identify modulation format most amenable to 60GHz
  RF circuits
• Identify baseband architectures that allow for
  power-efficient, high data-rate baseband circuits
• Goals
• Ease performance requirements on 60GHz RF
  circuits
• Enable a low-complexity baseband architecture

5
60 GHz Channel Spatial Properties

• Specular, moderately reflective channel
• Building materials poor reflectors at 60GHz
• Typical 60GHz indoor channel properties 1
• Omni-antenna w/ LOS TRMS 25ns, KRician
  0-5dB
• 30 horn w/ LOS TRMS 5ns, KRician 10-15dB
• KRician PLOS/SPMultipath

Antenna directivity reduces multipath fading
problem to constrained ISI problem

• 1 M. Williamson, et al, "Investigating the
  effects of antenna directivity on wireless indoor
  communication at 6O GHz," PIMRC 1997

6
Modulation Scheme Comparisons
Beamforming to combat multipath. Simple
modulation (MSK) for feasible CMOS RF circuits.
7
Baseband Architecture Considerations

• Targeting 1 Gbps with simple modulation scheme
• Must use low-order constellation, high baud rate
• Fast baud rate (1Gsym/s) ? high-speed ADCs, VGAs
• Desire baseband architectures that
• Minimize ADC resolution
• Minimize required ADC oversampling ratio
• Incurs minimal SNR loss from above
  simplifications
• Adaptable, robust to channel variations

Re-think traditional partitioning of analog and
digital subsystems!
8
Comparison Digital vs. Mixed-signal DFE

• Mixed-signal equalizer requires 2 fewer ADC bits
• PAR reduction
• Quantization effects in digital equalizer and
  CORDIC

9
Hybrid-Analog Receiver Architecture
Proposed Baseband Architecture
Clk
Clock Rec
BBI
Timing, DFE Carrier Phase, Estimators
BBI
IF
Complex DFE
ejq
BBQ
BBQ
LOIF

• Synchronization in hybrid-analog architecture
• ESTIMATE parameter error in digital domain
• CORRECT for parameter error in analog domain
• Greatly simplifies requirements on power-hungry
  interface ckts (i.e. ADC, VGA)
• Additional analog hardware is relatively simple

10
Analog-to-Digital Converters

• 6-bit ADC requires extra analog processing, power
• 6-bit 2Gs/s ADC consumes 300mW (ISSCC 03)
• 4-bit ADC consumes much less power
• 4x less power from 2-bit resolution reduction
• Pure flash architecture reduces power
  additional 2x-3x
• 30mW power consumption ? 270mW savings per ADC

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Analog Phase ShifterVGA

• Phase shifter VGA requirements
• Linear gain programmability
• Output summation
• Digital control
• Novel analog phase shifter architecture

Replica VGA tuning circuit
Primary VGA
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Analog DFECurrent-switching pairs

• Weighted subtraction of past decisions
• Diff pair fully switches current
• Each tap current is digitally controlled by
  DAC/mirror

Input V/I converter
DFE switching pairs