Berkeley Wireless Research Center Why Theorists and Implementers Should Work Together Bob Brodersen Dept. of EECS Univ. of Calif. Berkeley

Berkeley Wireless Research Center The trend towards more flexibility, more sharing… ISM (1986) UPCS (1994) U-NII (1997) Millimeter Wave (1998) Ultra Wideband (2002) Cognitive Radio (2005?) Link Control Modulation Total Transmit Power Power Spectral Density Antenna Gain Out of Band Emission More Sharing U-NIIISMUPCS ISMU-NII ISM Millimeter Wave Band Frequency (MHz) Ultra Wideband/CR??? 3100 UWB/CR

Berkeley Wireless Research Center In particular 17 GHz of New Unlicensed Bandwidth… l The UWB bands have some use restrictions, but FCC requirements will allow a wide variety of new applications l The GHz band can transmit up to.5 Watt with little else constrained l Cognitive Radio allocations in the regulatory process ( MHz band to start with) – maybe also in 3-10 like UWB? l How can we use these new resources? UWB/CR? UWB/ CR UWB Mm Wave Band GHz Comm Vehicular Comm ID

Berkeley Wireless Research Center New radio technologies- UWB, 60 GHz and Cognitive Carrier Frequency (GHz) Peak Data Rate (bps) 1 G 100 M 10 M 1 M 100 k 10 k HDTV motion picture, Pt.-to-Pt. links NTSC video; rapid file transfer MPEG video; PC file transfer Voice, Data Cellular 3G b 60 GHz Pt.-to-Pt. 60 GHz WLAN Bluetooth a ZigBee UWB Cognitive Radios

Berkeley Wireless Research Center New Challenges l Interference channel is the one of interest »How do we model this channel »What is its capacity »How do we best use this channel l Non-sinusoidal radios »How to analyze and design with impulses l Microwave Radios »The path to Gbit/sec links »Requires optimal antenna systems l Cognitive Radios »How do we sense signals »How do we design radios with large in-band interferers

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, ET Docket , First Report and Order, Feb. 2002

Berkeley Wireless Research Center Two basically different signaling approaches Sinusoidal, Narrowband Frequency Time Frequency Impulse, Ultra-Wideband

Berkeley Wireless Research Center First Major Application Area High Speed, Inexpensive Short Range Communications ( GHz) »FCC limit of -41dBm/Mhz at 10 feet severely limits range –Power level roughly 1 mW –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 a > 100 Mbits/sec for short range)

Berkeley Wireless Research Center Status of High Rate, Short Range UWB Major standards battle in IEEE Two competing approaches »Frequency hopping OFDM –Exploits the wide bandwidth to provide higher rates with lower precision hardware (e.g. reduced A/D accuracy, linearity requirements) –Uses a well understood technique (802.11a/g) » Impulse radios – New approach, so somewhat unknown ultimate performance and efficiency

Berkeley Wireless Research Center OFDM or Impulse? l OFDM strategy makes sense from a theoretical standpoint (deals with multipath) l But what about the implementation ??

Berkeley Wireless Research Center Lets compare to an a chip l What can we eliminate? ADC/DAC Viterbi Decoder MAC Core Time/Freq Synch FFT DMA PCI AGCFSM

Berkeley Wireless Research Center How about using Impulses? l Basically pulsed rate data transmission – sort of optical fiber without the fiber… l Key design problem, as in wireline transmission, is synchronization “1” “0” Biphase signalling

Berkeley Wireless Research Center Front-end is very simple l Mostly Digital Radio Architecture: - Wideband antenna - Wideband amplifier / matching network - RF bandpass filtering (low Q filter) - High bandwidth sample and track - High-speed and low resolution ADC - Sampling Clock generator - DSP

Berkeley Wireless Research Center Receive match filter l Basic approach is to create a match filter for the above received pulse shape l This collects all the energy associated with the waveform

Berkeley Wireless Research Center Sampling Offset Effects l Unfortunately a small timing offset results in a very different waveform so the match filter output is very dependent on the timing

Berkeley Wireless Research Center A solution to this… (Mike Chen) l Convert the single baseband pulse into an analytic signal (real and imaginary parts) via a Hilbert transformation. l The analogy is the use of the I and Q channel for sinusoidal systems Pulse in (real) Imag Real

Berkeley Wireless Research Center UWB impulse signal processing Research into the signal processing for impulse detection is just beginning – so lots of opportunities Analytic impulse signal processing also achieves a timing resolution below the sampling period, what can this be used for?

Berkeley Wireless Research Center Second Major Application Area 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

Berkeley Wireless Research Center Location Determination Using UWB l UWB provides »Indoor measurements »Relative location »Insensitivity to multipath »Material penetration (0-1 GHz band) Time of flight Transmit short discrete pulses instead of modulating code onto carrier signal –Pulses last ~1-2 ns –Resolution of inches

Berkeley Wireless Research Center Signal processing for ranging The problem is to determine the leading edge of the response l Simple averaging… l “Clean” algorithm (iterative best fit of time delayed waveforms)

Berkeley Wireless Research Center Many new questions… l What are the limits on locationing accuracy and what are the dependences l What algorithms can be used to achieve these limits l How do we coordinate networks of devices and what advantages can we obtain

Berkeley Wireless Research Center Next lets look at the 60 GHz band… UWB/CR UWB CR UWB Mm Wave Band GHz Comm Vehicular Comm ID Microwave communications

Berkeley Wireless Research Center Why is operation at 60 GHz interesting? Lots of Bandwidth!!! »7 GHz of unlicensed bandwidth in the U.S. and Japan »Europe CEPT “there is an urgent need to identify and harmonize civil requirements in the frequency range 54–66GHz.” 57 dBm 40 dBm

Berkeley Wireless Research Center Why isn’t 60 GHz in widespread use? l The technology to process signals at 60 GHz is expensive l Misconceptions about path loss and propagation at 60 GHz

Berkeley Wireless Research Center Why isn’t 60 GHz in widespread use? l The technology to process signals at 60 GHz is expensive l Misconceptions about path loss and propagation at 60 GHz

Berkeley Wireless Research Center V GS = 0.65 V V DS = 1.2 V I DS = 30 mA W/L = 100x1u/0.13u CMOS can do it nm CMOS has a gain of 7dB at 60 GHz

Berkeley Wireless Research Center 40-GHz and 60-GHz CMOS Amplifiers l Design and modeling can be incredibly accurate…. l Power consumption: 36 mW (40 GHz), 54 mW (60 GHz) 18-dB 40 GHz 11.5-dB 60 GHz

Berkeley Wireless Research Center A Leap Forward for CMOS CMOS offers two orders of magnitude cost reduction while providing higher integration and reliability Each new process generation moves it 20-40% higher X Where we are now with 130 nm

Berkeley Wireless Research Center Why isn’t 60 GHz in widespread use? l The technology to process signals at 60 GHz is expensive l Misconceptions about path loss and propagation at 60 GHz

Berkeley Wireless Research Center  Typical path loss (Friis) formula is a function of antenna gain G r and G t :  But maximum antenna gain increases with frequency for the same antenna area, A Path loss of line-of-sight transmission – is that a major problem?

Berkeley Wireless Research Center Using the same effective area then…  There is an improvement by the frequency squared  It is better to be at higher frequencies!

Berkeley Wireless Research Center Material penetration l Not that much worse for most materials »Compensated for by larger receive antenna (> 5 cm 2 ) »Exploit wider available bandwidths as need through stronger coding (trade data rate for range) (from Bob Scholtz)

Berkeley Wireless Research Center The future will need GBit/sec wireless links l What technology will get us there? l Lets compare 3 systems links »UWB – (OFDM) »802.11n – (MIMO) »60 GHz

Berkeley Wireless Research Center n (TgnSync an Wwise proposals) ConfigurationRate ½, 16-QAM Rate ¾, 16-QAM Rate 2/3, 64-QAM Rate ¾, 64-QAM Rate 5/6, 64- QAM 1 Tx, 40 MHz Tx, 40 MHz Tx, 40 MHz Tx, 40 MHz TgnSync Wwise

Berkeley Wireless Research Center Comparison l Lets take an antenna that has an effective area of 5 cm 2 FrequencyAntenna Gain UWB (7 band mode)5.092 GHz2.4 dB n (highest range) 5 GHz2.4 dB 60 GHz 24 dB l We can have 24 dB of gain on both antennas – or even more on the receive side

Berkeley Wireless Research Center Power limitations l In all three cases near limit of FCC regulation (much higher in Japan) l An advantage of from 17 to 43 dB How about bandwidth? PowerAnt. GainTx power UWB-6.6 dBm2.4 dB-4.2 dBm n20 dBm2.4 dB22.4 dBm 60 GHz15 dBm24 dB39 dBm

Berkeley Wireless Research Center Bandwidth efficiency requirement for a Gbit/sec l The efficiencies required to meet the Gbit/sec goals are unrealistic for any approach but at 60 GHz BandwidthEfficiency needed Actual Maximum Design Goal UWB480 MHz2 Bits/Hz1 Bit/Hz (480 Mbits/sec) n40 MHz25 Bits/Hz17 Bits/Hz (680 Mbits/sec) 60 GHz2 GHz.5 Bits/Hz.5 Bit/Hz (1 Gbits/sec)

Berkeley Wireless Research Center We now need adaptive beamforming algorithms l Very closely related to MIMO algorithms – similar problem, need to spatially localize transmission l Need to rapidly adapt to varying conditions Array Processing Array Processing 1 st path,  1 = 1 2 nd path,  2 = 0.6

Berkeley Wireless Research Center Multiple antenna beamforming hardware is straight-forward l Wavelength is 5mm, so in a few square inches a large antenna array can be implemented l The challenge is how to determine the coefficients of this beamformer to maximize range while minimizing interference a1a1 b1b1 a0a0 b0b0 a2a2 b2b2 PA Single Channel Transceiver

Berkeley Wireless Research Center The open questions… l How best to implement a flexible, adaptive antenna system l What is the best way to use 7 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

Berkeley Wireless Research Center Last topic – Cognitive Radios According to the FCC: “We recognize the importance of new cognitive radio technologies, which are likely to become more prevalent over the next few years and which hold tremendous promise in helping to facilitate more effective and efficient access to spectrum” - Federal Communications Commission, ET Docket No , Dec 30 th 2003

Berkeley Wireless Research Center The spectrum shortage…. l All frequency bands up to 60 GHz (and beyond) have FCC allocations for multiple users l The allocation from 3-6 GHz is typical - seems very crowded… GHz

Berkeley Wireless Research Center The reality… l Even though the spectra is allocated it is almost unused l Cognitive radios would allow unlicensed users to share the spectrum with primary users l The TV band is interesting, but higher frequencies are even more attractive GHz The TV band

Berkeley Wireless Research Center What is a Cognitive Radio? l Cognitive radio requirements » co-exists with legacy wireless systems » uses their spectrum resources » does not interfere with them l Cognitive radio properties »RF technology that "listens" to huge swaths of spectrum »Knowledge of primary users’ spectrum usage as a function of location and time »Rules of sharing the available resources (time, frequency, space) »Embedded database to determine optimal transmission (bandwidth, latency, QoS) based on primary users’ behavior

Berkeley Wireless Research Center Cognitive Radio Functions D/A PA LNA A/D IFFT FFT ADAPTIVE LOADING INTERFERENCE MEAS/CANCEL MAE/ POWER CTRL CHANNEL SEL/EST TIME, FREQ, SPACE SEL LEARN ENVIRONMENT QoS vs. RATE FEEDBACK TO CRs l Sensing Radio Wideband Antenna, PA and LNA High speed A/D & D/A, moderate resolution Simultaneous Tx & Rx Scalable for MIMO Physical Layer OFDM transmission Spectrum monitoring Dynamic frequency selection, modulation, power control Analog impairments compensation MAC Layer Optimize transmission parameters Adapt rates through feedback Negotiate or opportunistically use resources RF/Analog Front-endDigital BasebandMAC Layer

Berkeley Wireless Research Center Spectrum Sensing Key challenge: detecting weak Primary user signals Analog Processing Digital Processing Networking A/D Approach: Spectrum Sensing is a cross-layer functionality

Berkeley Wireless Research Center Wideband Sensing Front-end GHz wideband antenna A/D RF Filter LNA Huge dynamic range High speed A/D converter Wideband Receiver Nyquist sampling -> Multi-GHz A/D Large dynamic range signal Limitation: number of bits in A/D E.g. 70dB dynamic range needs 12 bits A/D figure of merit f s *2 n Need dynamic range reduction Possible solutions Tunable notch filters Active cancellation Spatial filtering using multiple antennas AGC

Berkeley Wireless Research Center Sensing Radio Function l Subdivide the spectrum into sub- channels (say 1 MHz) l Detect primary user occupancy in each location/direction l Continually monitor for appearance of primary user l Provide information to MAC layer x Frequency (Hz) Signal Strength (dB) TV bands Cell PCS Spectrum usage in (0, 2.5) GHz

Berkeley Wireless Research Center Spectrum Allocation and Access l What access scheme can assign ANY sub-channel  ANY CR user l If we restrict one user per sub-channel: »Orthogonal Frequency Division Multiple Access (OFDMA) l More general solution: »One user to multiple non-contiguous subchannels (how?) CR 1 CR 2 CR 3 CR 4 Spectrum Allocation Spectrum pool f1f1 fNfN PU present PU absent Interference

Berkeley Wireless Research Center Summary l UWB – Need a new approach which yields high data rates with low complexity or new algorithms for positioning l 60 GHz – Requires sophisticated adaptive antenna systems and modulation techniques which have reduced analog complexity l Cognitive radios – Requires sensing and highly adaptive transmission

Berkeley Wireless Research Center Conclusion Lots of New Opportunities That Require Close Cooperation between Theorists and Implementers!!!