CMOS for Ultra Wideband and 60 GHz Communications

BWRC OverviewBob Brodersen
http://bwrc.eecs.berkeley.edu
To show that there is increasing trend in spectrum sharing.
Details:
ISM (Industrial, Scientific and Medical bands)
902 – 928 MHz (26 MHz), 2.4 – 2.4835 GHz (85.5 MHz) and 5.725 – 5.85 GHz (125 MHz)
Cordless phones, wireless LANs and PBXs
DSS or FH modulation
Secondary access; unlicensed devices must not cause harmful interference to licensed devices, and ready to accept any interference from licensed devices as well as other unlicensed devices.
Max transmit power is 1 W.
No device diversity
UPCS (Unlicensed Personal Communications Services)
1.91 – 1.92 GHz and 2.39 – 2.4 GHz are the asynchronous subband: used for wireless LANs.
1.92 – 1.93 GHz is the isochronous subband: used for wireless PBXs.
“listen before talk” etiquette: first-come-first-serve basis
U-NII (Unlicensed National Information Infrastructure Devices)
5.15 – 5.25 GHz uses for indoor applications, wireless LANs and wireless PBXs.
5.25 – 5.35 GHz uses for short outdoor links and campus applications.
5.725 – 5.825 GHz uses for long outdoor links and point-to-point links.
Different limitations on different bands support a greater diversity of devices than the ISM bands.
Millimeter Wave band
Home networking applications
17 GHz of Unlicensed Bandwidth!
The UWB bands have some use restrictions, but FCC requirements will allow a wide variety of new applications
The 59-64 GHz band can transmit up to .5 Watt with little else constrained
How can we use these new resources?
0
10
20
UWB
UWB
UWB
Mm
Wave
Band
30
40
50
60
GHz
Comm
Vehicular
Comm
ID
Details:
No device diversity
range of application of radio technology
Carrier Frequency (GHz)
Berkeley Wireless Research Center
Lets start with UWB…
According to the FCC:
“Ultrawideband radio systems typically employ pulse modulation where extremely narrow (short) bursts of RF energy are modulated and emitted to convey information. … the emission bandwidths … often exceed one gigahertz. In some cases “impulse” transmitters are employed where the pulses do not modulate a carrier.”
-- Federal Communications Commission,
Allowed emissions from a PC
/MHz
-5db
FCC limit of -41dBm/Mhz at 10 feet severely limits range
Even using all 7.5 GHz of bandwidth the maximum power that can be transmitted is equivalent to having -2dBm (.6 mW) from an isotropic radiator (EIRP)
For short range communications this may be OK – e.g. line of sight from 10 feet for connecting a camcorder to a set-top box, “wireless Firewire”
Advantage is that it should be less expensive and lower power than a WLAN solution (since 802.11a > 100 Mbits/sec for short range)
Transmitted Signal Outdoor Rcvd Clear LoS Office Rcvd Clear LoS
200 ns
20 ns
20 ns
High Rate UWB Communications
Basically pulsed rate data transmission – sort of optical fiber without the fiber…
Key design problem, as in wireline transmission, is synchronization
New design problems that do not exist in wireline
Interference from other RF sources
Multipath (delay spreads of 10’s of ns – at least)
“1”
“0”
To Minimize Interference
Break 7.5 GHz into smaller bands (> 500MHz) and transmit in clear bands
Filter out bands that are likely to have use (e.g. 5GHz wireless LAN bands)
Directional antennas
Multipath
Equalizers (as used in SERDES), but much longer delay compensation – digital?
Directional antennas
Low Data Rate, Short Range Communications with Locationing (< 960 MHz)
Round trip time for pulse provides range information – multiple range estimates provides location
Used for asset tracking – a sophisticated RFID tag that provides location
Can be used to track people (children, firemen in buildings)
Sensor networks
Time of flight
Transmit short discrete pulses instead of modulating code onto carrier signal
Pulses last ~1-2 ns
Avoiding Interfering With Other Users
Co-existence through very low power transmission: Operate so that aggregate Interference from UWB Transmissions is “Undetectable” (or Has Minimal Impact) to Narrow-Band Receivers.
What you can do with that for communications and locationing is a research question we are looking at…
UWB
Thermal (kT) Noise Floor
Interference From other Users
Everyone is an in-band interferer… why isn’t the UWB signal swamped?
Energy in Pulse is Concentrated in Time
If Equate Energies, Find
Ratio of Amplitudes is:
For a duty cycle of 1%, this implies a pulse amplitude 7x an equivalent power sinusoid.
Ex: -77dBm (50W noise) per MHz over 1GHz is a 40mV pulse!
Time
Amplitude
*
One of the main characteristics that help us to retrieve our pulse is the nature of the pulse itself. While the frequency energy is spread thin and wide, the pulse in time has a large amplitude, which helps it stand out against the background noise. If we compare amplitudes for equal energy sines and pulses, we see the amplitude is dependent upon the duty cycle. A long duty cycle (for the same power) implies a higher amplitude, and hence more discernable pulse.
Really when we receive we are looking for a voltage, although we commonly talk about received energy. A strict comparison of energies might be misleading.
Here, the desired pulse, shown in green, is compared to an equal energy sinewave, in red.
Just to give you an idea of the amplitudes, here is an example:
Note that energy in pulse with –70dBm/5MHz over 1GHz is equivalent to a 40mV pulse (50 Ohms)
BWRC: UWB Transceiver Chip
A single chip CMOS UWB transceiver at power levels of 1 mW/MHz for locationing and tracking applications
Flexible design for a wide range of data rates to investigate UWB transmission characteristics
For low rate applications, transmission at minimum possible signal level
Develop limits of locationing accuracy
Being Implemented by PhD students Ian O’Donnell, Mike Chen, Stanley Wang
Analog Circuits - Pulse Reception
Only Need Limited Amount of Fast Sampling
Have Rest of Time in Cycle to Process Samples
Use Parallel Sampling Blocks
Do Digital Correlation for Synchronization and Detections
Minimum of Analog Blocks Run at Full Speed to Reduce Power
Time
.
1 GHz BW
Maximum receivable Pulse ripple length (Nripple=Npulse+Nspread): < 64ns (128 samples)
Sampling rate: 2 GHz
*
This slide summarizes how flexible the digital chip will be.
PN0
PN1
Acquisition: 128-Tap Matched Filter x 128 x 11 PN Phases
Synchronization: Early/On-Time/Late PN Phases
PN sequence length requirement ( design max is 1024).
(1) Acquisition mode, ~400 chips is enough for suppressing the acquisition error below 1e-3.
(2) Data recovery mode, ~100 chips could achieve an uncoded bit error rate of 1e-3.
Chips
*
1. EbNo input = -11 dB, if you see from time domain, the peak voltage of doublet is 1 mV. Totally under the noise floor.
2. I recently run these simulation results to make sure 1024 chips is enough for our system. The simulation result is pretty close to my hand calculation!
Area = 5.3 mm2
Area ~ 55 mm2
Stay tuned at http://bwrc.eecs.berkeley.edu/Research/UWB/
17 GHz of Unlicensed Bandwidth!
The UWB bands have some use restrictions, but FCC requirements will allow a wide variety of new applications
The 59-64 GHz band can transmit up to .5 Watt with little else constrained
How can we use these new resources?
0
10
20
UWB
UWB
UWB
Mm
Wave
Band
30
40
50
60
GHz
Comm
Vehicular
Comm
ID
Details:
No device diversity
60 GHz Unlicensed Allocation (1998)
56 57 58 59 60 61 62 63 64 65 66
Frequency GHz
Space and fixed & mobile apps.
56 57 58 59 60 61 62 63 64 65 66
Frequency GHz
Exploiting the Unlicensed 60 GHz Band
5 GHz of unlicensed and pretty much unregulated bandwidth is available
Requires
New approaches for design of CMOS integrated circuits (distributed, transmission line based)
New system architectures
Oxygen absorbs RF energy at 60 GHz
The technology to process signals at 60 GHz is very expensive
The signal radiated is attenuated by the small antenna size – i.e. the power transmitted at 60 Ghz from a quarter wave dipole is 20 dB less than at 5GHz.
Oxygen attenuation
The oxygen attenuation is about 15 dB/km, so for most of the applications this is not a significant component of loss
For long range outdoor links, worst case rain conditions are actually a bigger issue
The technology to process signals at 60 GHz is very expensive
Yes, it has been expensive, but can we can do it in standard CMOS?
fmax is the important number to look at
Maximum unilateral gain
And we find that CMOS can do it!
If the device is designed correctly and enough current is used, with .13 micron fmax can easily surpass 60 GHz
Phillips reported 150 GHz fmax in .18 micron technology
However, New Kinds of CMOS Circuits are Needed
Since the device dimensions are on the order of the wavelength, distributed structures can be used
Distributed techniques allow for extremely wideband linear-phase amplification approaching fmax
This a new circuit style for CMOS
1577.psd
0.13 standard CMOS process
Calibration structures on same chip
Siemanns presented circuit in .18 micron at ISSCC 2002
Overcome the Small Antenna Problem by Using Multiple Antenna Beamformers
Wavelength is 5mm, so in a few square inches a large antenna array can be implemented
Antenna gain provides increased energy to receiver without extra noise and power
Multiple antenna implementation may actually reduce analog requirements
Single Channel
Traditional Radio vs. Microwave CMOS
Operate device far away from fT to enhance gain (cell phones at 1-2 GHz, fT ~ 50 GHz)
Many off-chip front-end components (filters, switches, matching networks, antenna)
Clear separation between lumped circuits on-chip and limited consideration of distributed effects off-chip (package and board)
Operate close or beyond fT
Integrated front-end (antenna/filter)
Use 5 GHz as an IF frequency
The open question…
What is the best way to use 5 GHz of bandwidth to implement a high datarate link?
Extremely inefficient modulation but at a very high rate? (say 2 GHz of bandwidth for 1 Gigabit/sec) – requires analog processing
Or use an efficient modulation, so lower bandwidth. e.g. OFDM – but needs digital processing and a fast A/D
Conclusions
UWB radios provide a new way to utilize the spectrum and there is a wide variety of unique applications of this technology
However, it takes a completely new kind of radio design…
At the present state of technology CMOS is able to exploit the unlicensed 60 GHz band
However, it will take a new design and modeling methodology…
There is 17 GHz of bandwidth ready to be used for those willing to try something new!
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Kevlar Sheet
MUX and Buffer
Filtering, Mod, Demod,
MUX and Buffer
Filtering, Mod, Demod,

CMOS for Ultra Wideband and 60 GHz Communications

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