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Providing Unlimited Wireless Capacity Bob Brodersen Berkeley Wireless Research Center Adaptrum, Inc and SiBEAM, Inc. Univ. of California, Berkeley.

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Presentation on theme: "Providing Unlimited Wireless Capacity Bob Brodersen Berkeley Wireless Research Center Adaptrum, Inc and SiBEAM, Inc. Univ. of California, Berkeley."— Presentation transcript:

1 Providing Unlimited Wireless Capacity Bob Brodersen Berkeley Wireless Research Center Adaptrum, Inc and SiBEAM, Inc. Univ. of California, Berkeley

2 More Capacity – Do we really need it ?? l Major bandwidth driver is moving from voice to video and data – a ,000 fold requirement increase l User base is moving to be a significant fraction of the 6 Billion world population l Devices (without an attached human) will communicate wirelessly »Source to HD display with uncompressed video => 4 Gbit/sec »A home will have a 1000 radios This is not going to be addressed by improving any radio system we have now

3 Looks like we need it …. l Claim: There are technological solutions to providing this capacity which is based on abandoning the property rights model of owning frequency spectrum l Assertions: »The concept of fixed frequency spectrum allocation has become fundamentally flawed »We need to exploit wireless communication strategies that exploit the time, space and frequency degrees of freedom »Exploiting these new approaches could allow essentially unlimited capacity

4 Why has Frequency Allocation become a Flawed Concept? l The applications are continually changing and allocation doesnt mean use l Frequency is only one of the 3 degrees of freedom to use to avoid interference - time and space are actually more effective

5 UWB, 60 GHz and Cognitive radios individually exploit the 3 DOF l Frequency »Separate users by using different frequency bands –traditional method using analog filtering »Exploit wide bandwidths and DSP »Exploit higher frequencies –present CMOS technology allows use up to 100GHz l Space and Angle »Reduce transmit power –decreases radius of omni-directional cells »Exploit the angular nature of the spatial channel –Multiple antennas l Time »Impulse filtering »Sense interference and avoid

6 UWB, 60 GHz and Cognitive radios individually exploit the 3 DOF l Frequency »Separate users by using different frequency bands –traditional method using analog filtering »Exploit wide bandwidths and DSP (UWB) »Exploit higher frequencies –present CMOS technology allows use up to 100GHz (60 GHz) l Space and Angle »Reduce transmit power –decreases radius of omni-directional cells (UWB) »Exploit the angular nature of the spatial channel –Multiple antennas (60 GHz) l Time »Impulse filtering (UWB) »Sense interference and avoid (Cognitive Radio)

7 Talk Organization l A discussion of the emerging techniques that are exploiting the three degrees of freedom in new ways »UWB »Cognitive Radios »60 GHz l How these can be combined to achieve unlimited capacity

8 Lets start with UWB… l Breakthrough! For the first time the regulators allowed sharing of the frequency spectrum »Underlay – Allow sharing of the spectrum if the interference is negligible »Ultrawide bandwidths were allowed l Fundamental choices remain on how to best to use the wide bandwidth »Stay with conventional frequency domain thinking »Or exploit the time degree of freedom

9 UWB Frequency and Time domain strategies Time Frequency Time UWB Impulse Frequency Time Frequency UWB OFDM (multiple sine waves) Traditional user (narrowband) Noise Power Time domain filters (block the impulse in time) can be easily made adaptive (unlike frequency domain) Time domain interference Interference in frequency domain

10 UWB is allowed in over 11 GHz of spectrum UWB GHz Comm Vehicular l Limited power allows a high level of spatial reuse l Chip sets are available for both OFDM and Impulse approaches l But ….. If this is such a good idea why has it not been commercially successful

11 What happened … l Two competing approaches were attempted which resulted in a standards battle which was waged without good technical input l The (comfortable) frequency domain approach (OFDM) had too high a complexity and too low a performance l The time domain (impulse) approach is too different and needs much more R&D in theory and implementation

12 Cognitive Radios l Basic idea »Exploit the time degree of freedom by sensing if a signal is present »Then take steps to assure there isnt interference l This is quite restricted, others use a more expanded definition

13 A Cognitive Radio using Time and Frequency l Sense the spectral environment over a wide bandwidth l Transmit in White Space l Detect if primary user appears l Move to new white space l Adapt bandwidth and power levels to meet QOS requirements Power Frequency PU 1 PU 2 PU 3 PU 4

14 Cognitive Radio system level view Network coordination Medium Access Sensing Signal Processing Sensing radio Resource Allocation Wideband signaling Wideband radio Physical Layer Network Link Layers Spectrum sensing is the key enabling functionality and must be very sensitive to limit unwanted interference

15 Sensing Weak Signals A new radio functionality – requires new algorithms and understanding High SNR Low SNR Spectrum density Energy Detector Spectral correlation Cyclostationary Feature Detector

16 Sensing Performance (Danijela Cabric) l Incoherent sensing time goes as 1/(SNR 2 ) l Coherent sensing time goes as 1/SNR Log Time (Cyclostationary) Incoherent processing Coherent sensing Cyclostationary

17 Coherent sensing - ATSC signal l Correlation of fixed header is used by Adaptrum in FCC trials being held now – highest performing results

18 Adaptrum TV-band CR prototype CR Transceiver CR Baseband/MAC FPGA (Altera) Bowtie wideband UHF antenna

19 ATSC sensitivity measurement result

20 Planned Bay Area Cognitive Radio MHz experimental testbed

21 Using the Space Degree of Freedom to improve sensing l Spatially separated sensing radios can make independent measurements l Single radio sensitivity can be improved by the use of multiple antennas using beamforming

22 Spatially separated sensing radios Expected result for independent measurements: Primary System Tx Rx Decoding SNR Exploit spatial diversity in Sensing SNRs P d, network =1-(1-P d, radio ) N

23 Experimental Setup Location (11,9) Location (16,3) Central combining and processing Fiber provides 1/3 mile separation between radios and platform controlled PHY and MAC integration Sensing radio Sensing PHY/MAC processors

24 Network Spectrum Sensing Results Prob. of false alarm Prob. of detection 1 radio 5 radios If spacing >> λ/2 a few cooperative radios give big improvements Danijela Cabric, Mubaraq Mishra and Anant Sahai

25 Dynamic range problem in wideband sensing PSD Freq. A/D LNA AGC Fixed LO Band of interest l Wideband sensing is required to quickly sense the open bands »Small signals need to be sensed in the presence of strong interference and then processed digitally »Places difficult requirements on RF front end and A/D l Multi-antenna spatial processing provides two solutions

26 Multi-antenna spatial processing to improve sensing Primary user f 1 Phased antenna array l Improvements with N antennas »allow suppression of up to N-1 large signals »provide up to an N times increase in sensitivity l Well find more uses for these arrays Primary user f 2

27 One possible implementation Time Domain Interference Cancellation to address the dynamic range problem (Jing Yang) Yields N+M equivalent bits of dynamic range

28 Simulated interference attenuation l Attenuate the strong interference and reduce the dynamic range to the Residue ADC by 35dB l Extending the effective number of bits for this system by nearly 6 bits Strong FSK modulated interfering signal Moderate sinusoidal interfering signal Before After Attenuated strong interfering signal CR signal

29 The opportunity of higher frequencies GHz l Effectively no use above 5 GHz l Antenna arrays require only a small area l Absolutely necessary to get to gigabit/sec rates 0-3 GHz >> 99% of all wireless transmission 7 GHz of unused and unlicensed spectra

30 Use of Higher Frequencies (e.g. 60 GHz) Conventional wisdom is that lower frequencies are better »Only line of sight operation is possible and cant penetrate materials »The technology to process signals is expensive »As you go up in frequency there is an inherent path loss that reduces range Not True!!!

31 Material Penetration – actually not so bad 60 GHz2.5 GHz Pine board – ¾ 8 db1.5dB Clay Brick9 dB2 dB Glass with wire mesh10.2 dB7.7 dB Asphalt Shingle1.7 dB1.5 dB Plywood – ¾ 7 dB1.5 dB Clear Glass6.4 dB3.6 dB Atmosphere per 100m 1.5 dB0 dB What about Oxygen absorption?

32 Millimeter wave radios l Misconception: Implementing millimeter wave radios requires exotic materials »Conventional state-of-the-art digital CMOS can be used to implement integrated radios up to 100 GHz »Future technology scaling will allow even higher frequency operation (research is beginning into Terahertz operation)

33 60-GHz CMOS operation (130 nm) 1 mm 1.3 mm l Use of transmission line interconnect allows control of electrical and magnetic fields l Better control than at lower frequencies! 11-dB 60 GHz

34 60-GHz CMOS Receiver front-end CMOS integration means even a 60 GHz receiver will eventually cost about the same as a WiFi

35 Millimeter wave radios l Misconception: As you go up in frequency there is an inherent path loss that reduces range »This comes from only considering omnidirectional antennas which have a size that is inverse with carrier frequency »Solution is to keep area constant using directional antennas - then the received signal increases with frequency

36 Tx Rx Low Gain Tx Antenna Area of sphere = 4 r 2 Captured energy Antenna fundamentals: Receive Antenna Energy A r = Area of receive antenna Fraction of power received from an omnidirectional transmission =

37 Effective transmit antenna power l Maximum increase in power in direction of beam = ( wavelength of carrier) l Effective maximum power as if it came from an omnidirectinal antenna = P t G t Rx P t G t Tx A t = Area of transmitter

38 The link budget with directional antennas Receive power improves with frequency!! Rx Captured energy In Area A r Wasted energy Tx 22 dB more gain at 60 GHz over 5 GHz if antenna size is kept constant (Compare to Friis path loss formula )

39 Millimeter wave radios l Misconception: Only line of sight transmission is possible »millimeter waves reflect like lower frequency waves, so adaptive directional antenna arrays can choose strongest signal »millimeter waves have higher material penetration loss, but this can be compensated for with the higher power and antenna gain

40 Non line of sight transmission Transmitter in Source l Phased Array Antennas » Power used more efficiently for better reception, longer distance, higher bandwidth » Dynamically steers beam to specific receiving station SiBEAM Module

41 Phased array circuitry l N antennas allow N power amps to transmit in parallel l Phase accuracy requirement is very low as the number of antennas go up (2 bits for 16 antennas)

42 Algorithms for adaptive beamforming l Separate the multipath into separate channels through an SVD l Choose the strongest one and put all the energy into it σ1σ1 σ2σ2 σ3σ3 σ4σ4 Blind tracking Array Processing Array Processing 1 st path, σ 1 =10 2 nd path, σ 2 =6

43 As beams get narrow the capacity increases (Ada Poon) Capacity 2 A -2 W T log SNR Carrier frequency Cumulative scattering solid angle Transmit Array area Polarization The old (Shannon) Formula: Capacity W T log SNR With spatial processing: Transmission interval Bandwidth New spatial degrees of freedom provide multiplicative increases The time frequency degrees of freedom

44 How do we get to unlimited capacity? Two ways – probably more »Angular isolation of beamformed signals requires not only co-location but the same angle –This essentially eliminates interference –Add in UWB-like spectrum sharing and cognitive techniques to achieve essentially unlimited »Increasing the number of users with multiple antennas provides an unlimited increase if frequency or antenna area is increased

45 Angular isolation l A transmits towards B with phased array l B only receives in direction of A l Transmitter C doesnt interfere with B C A B

46 Angular isolation Interference between beamformed signals has to not only be in the same space, but also have the same angle C A B

47 Another solution to aligned receivers l Start with link AB l Add aligned link CD l What do we do now…. D C A B

48 Use a reflection l Usually at least 2-3 reflections l This is requiring more resolution in the phase shifters to control sidelobes

49 Capacity increases with number of RX&TX=N Scheme No.of Antennas Capacity Increase Frequency/Time Subdivision N1 Packet Multihop N N 1/2 Cooperative Diversity (Tse) NN MIMO at each user (Chung) N2N2 N2N2 MIMO with reflections N A/ 2 (N A/ 2 ) 2

50 Back to our Frequency Allocation Chart If we use all 3 degrees of freedom then a chart like this really is meaningless

51 A future allocation chart… Now how do we get to this!! Shared Spectrum


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