January 2006 Soo-Young Chang & Jianwei Zhang, Huawei Technologies Slide 1 doc.: IEEE 802.22-05/0107r3 Submission WAVEFORM MODULATED WRAN SYSTEM IEEE P802.22 Wireless RANs Date: 2006-1-16 N am e C om pany A ddress Phone em ail Soo-Y oung Chang H uaw ei Technologies 6000 JStreet, D eptEEE, Sacram ento, CA 95819- 6019 916 278 6568 sychang@ ecs.csus. edu Jianw eiZhang H uaw ei Technologies N o. 98, Lane 91, Eshan Road, Pudong, Pudong LujiazuiSoftw are Park, Shanghai, China 200127 86-21- 68644808- 24638 zhangjianwei@ hua wei.com Authors: Notice: This document has been prepared to assist IEEE 802.22. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein. Release: The contributor grants a free, irrevocable license to the IEEE to incorporate material contained in this contribution, and any modifications thereof, in the creation of an IEEE Standards publication; to copyright in the IEEE’s name any IEEE Standards publication even though it may include portions of this contribution; and at the IEEE’s sole discretion to permit others to reproduce in whole or in part the resulting IEEE Standards publication. The contributor also acknowledges and accepts that this contribution may be made public by IEEE 802.22. Patent Policy and Procedures: The contributor is familiar with the IEEE 802 Patent Policy and Procedures http://standards.ieee.org/guides/bylaws/sb-bylaws.pdf including the statement "IEEE standards may include the known use of patent(s), including patent applications, provided the IEEE receives assurance from the patent holder or applicant with respect to patents essential for compliance with both mandatory and optional portions of the standard." Early disclosure to the Working Group of patent information that might be relevant to the standard is essential to reduce the possibility for delays in the development process and increase the likelihood that the draft publication will be approved for publication. Please notify the Chair Carl R. Stevenson as early as possible, in written or electronic form, if patented technology (or technology under patent application) might be incorporated into a draft standard being developed within the IEEE 802.22 Working Group. If you have
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Doc.: IEEE 802.22-05/0107r3 Submission January 2006 Soo-Young Chang & Jianwei Zhang, Huawei TechnologiesSlide 1 WAVEFORM MODULATED WRAN SYSTEM IEEE P802.22.
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Notice: This document has been prepared to assist IEEE 802.22. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein.
Release: The contributor grants a free, irrevocable license to the IEEE to incorporate material contained in this contribution, and any modifications thereof, in the creation of an IEEE Standards publication; to copyright in the IEEE’s name any IEEE Standards publication even though it may include portions of this contribution; and at the IEEE’s sole discretion to permit others to reproduce in whole or in part the resulting IEEE Standards publication. The contributor also acknowledges and accepts that this contribution may be made public by IEEE 802.22.
Patent Policy and Procedures: The contributor is familiar with the IEEE 802 Patent Policy and Procedures http://standards.ieee.org/guides/bylaws/sb-bylaws.pdf including the statement "IEEE standards may include the known use of patent(s), including patent applications, provided the IEEE receives assurance from the patent holder or applicant with respect to patents essential for compliance with both mandatory and optional portions of the standard." Early disclosure to the Working Group of patent information that might be relevant to the standard is essential to reduce the possibility for delays in the development process and increase the likelihood that the draft publication will be approved for publication. Please notify the Chair Carl R. Stevenson as early as possible, in written or electronic form, if patented technology (or technology under patent application) might be incorporated into a draft standard being developed within the IEEE 802.22 Working Group. If you have questions, contact the IEEE Patent Committee Administrator at [email protected].>
• In this proposal, a system concept is suggested for the IEEE802.22 WRAN standard. A set of waveforms are suggested for WRAN systems. In these systems, one TV channel frequency band is divided into 16 subbands each of which has its own waveform. In the time domain, these waveforms are added and transmitted. Multiple access schemes are suggested by applying orthogonal codes in the frequency domain.
• These waveforms are generated by utilizing full digital processing in this proposal.
• Sensing and dynamic frequency selection (DFS) schemes using FFTs are proposed.
• Use short duration waveforms: processed purely in the time domain, not in frequency domain– Simple concept: only a few components in TX and RX– Simple digital processing Low complexity Low cost– No components for processing frequency information except LNA
and wideband tuning (e.g. filter, osc., etc.)– Excellent co-existence capability due to adaptive frequency band
use – flexible to eliminate forbidden bands (e.g. active incumbent TV user bands, active microphone bands, etc.) • Dynamically frequency bands can be assigned to CPEs
• New waveforms have steep out-of-band rejection around the edges of the band.
• Spectrum usage of TV broadcast industries– the average TV market in the United States uses approximately 7 high-
power channels of the 67 that it is allocated. This leaves an abundance of free channels that could be used for wireless access.
– With both the House and the Senate having recently passed bills requiring television broadcasts to switch from analog to digital sometime in early 2009, the 700-MHz band (channels 52 to 69) will be cleared of programming and moved to lower frequencies (channels 2 to 51). The 700-MHz band will be set aside for public-safety emergency transponders and for bidding by wireless networks.
in this proposal only channels 2 to 51 are considered.• Three possible ways suggested in one article to protect
interference with incumbent users– Listen-Before-Talk (LBT)– Geolocation/Database: GPS receivers installed in CPEs– Local beacon: locally transmitted signal used to identify incumbent users
Unused Digital TV Channels Could Increase U.S. Wireless Access, Federal action could allow unused channels at lower frequencies to be used for unlicensed wireless networks, Eric S. Crouch, Medill News Service, PC World, Saturday, November 19, 2005, http://www.washingtonpost.com/wp-dyn/content/article/2005/11/18/AR2005111800083_pf.html
• Questioned whether there will be significant channel availability for unlicensed use in major urban areas during the DTV transition.– There is likely to be substantial channel availability during transition.– The issue of channel availability during the DTV transition is likely to be
short-lived.– In rural areas, there is spectrum available now and there will be for the
foreseeable future.
• Bill Rose’s email to 22 email reflector, Wed, November 23, 2005 10:05 am – “The analysis shows that even in congested markets like Dallas/Ft. Worth,
40 percent of the TV channel spectrum will remain unused after America's DTV transition. In more rural markets like Juneau, Alaska, as much as 74 percent will be available.”
• Myth 1– ‘Digital implementation needs more complexity and is not easily realizable with existing
technologies.’ Digital implementation can be realized with less complexity and simple hardware and provide
full flexibility and adaptivity. As processing power increases and technologies advance, full digital processing is the trend.
• Myth 2– ‘Lower frequency is not easy to manage or implement.’ Unless high transmit power is not considered, digital processing method can be easily applied
for lower frequency band without using more complex algorithms. 4 W EIRP can be handled without difficulties.
• Myth 3– ‘Since this technology was not realizable yesterday, today also it is not easy to realize.’ Since technologies advance rapidly, more sophisticated and conceptual ideas should be
realized in the near future and considered for future applications. Moore’s law says that processing power increases double every 18 months: cost and
• A key property of sinusids is that they are orthogonal at different frequencies. That is, • This is true whether they are complex or real, and whatever amplitude and phase they may have. All that matters is that the frequencies be different. Note, however, that the sinusoidal durations must be infinity. • For length N sampled sinusoidal signal segments exact orthogonality holds only for the hamonics of the sampling rate-divided-by-N , i.e., only for the frequencies
• These are the only frequencies that have a whole number of periods in samples• Ex. N=100 for 4 ns pulse duration, fs=25 GHz fk=k*25*10**9/100=2.5*10**8*k=0.25*k GHz
For any integer k, fk can be determined center frequencies of each subband can be determined
• WM has strong points in– WM has almost a flat spectrum for each frequency segment while OFDM has a sync shape
spectrum if the same parameters applied WM has flatter spectra inside band and more suppression out of band WM does not use FFT/IFFT while it has to use de-emphasis at receiver de-emphasis means a different value for each sampled component which is stored in memory at receiver no burden for de-emphasis
• WM has strong points in– WM covers signals of whole TV band from 0 to the highest band while OFDM does
for one TV band WM does not need up/down conversion while OFDM needs it OFDM needs additional hardware (or another signal processing branch) to cover two bands simultaneously
f
whole target frequency band frequency band which can be covered by
• Simple design to implement– Adopt full digital implementation: ~33 Msamples/sec DACs/ADCs needed
• More radiated power efficient – Almost flat spectrum inside the assigned band
• Use almost full bands assigned to the users– Easy to meet out-of-band requirements (or frequency mask)
• Need less bits to represent samples for equal out-of-band suppression than other concepts– Achieve maximum range coverage
• More system flexibility in real time– More flexible to various applications and requirements– More dynamically adaptive to available frequency bands in real-time basis
• 6, 7, or 8 MHz BW• Single band or multiple bands which are adjacent to or depart from each other
– Scalable information rate adaptive and dedicated to applications• Basic physics says (square root of coverage) x (number of simultaneous users) x (information rate/user) = constant
– High value of this constant can be achieved• Scalable with coverage, number of users, information rate
– For. Ex: wide coverage with lower information rate or vice versa
• Adaptively balancing between uplink and downlink information rates– Basically 1.5 Mbps max for downlink and 384 Kbps for uplink required– Adaptively balancing: symmetric and asymmetric according to specific applications
• Flexible enough to satisfy any frequency band given and to avoid any forbidden bands 6, 7, or 8 MHz bandwidth can be easily adopted A part of a TV channel band can be eliminated for Part 74 device services pulse waveforms can be adaptively tailored to any frequency mask or
band applied with any forbidden bands• With any given frequency band, the whole frequency band can be
used to enjoy more transmitted power and achieve higher data rates. Due to steep suppression around the edges of the band 3.8 dB more power used than Gaussian pulse’s case for the same
frequency band 3.8 dB more margin for link budget
One TV channel is divided into 16 subbands – 4 groups/channel and 4 subbands/group
FREQUENCY SUBBANDS• One TV channel frequency band is divided into 4 groups• Each group has 4 subbands
– BW of a subband = 6 MHz /16 = 0.375 MHz – Each subband has its own waveform: base waveform– If a part of a given band should be abandoned – e.g., due to active microphone
operation - one or more of corresponding subbands can be eliminated.
base waveform information is stored in ROM continuous signals of waveforms are generated by DACs at TX can be generated with relatively lower sampling rate DACs
• 180 samples/waveform used for this proposal• 2x4=8 base waveforms/group for binary representation: 8x4=32 base waveforms per TV
channel64x4=256 base waveforms/group for 64-ary representation: 256x4=1024 base waveforms per TV channel
• Max 180x1024=184,320 sample information stored in ROM per TV channel 184 Kbytes ROM per TV channel needed to store waveform information if 8 bits/sample is adopted: 184 K x 100 = 18 Mbytes ROM for 100 TV channels
• Waveforms are generated using DACs which have a sampling rate of 33.4 Msamples/sec. – 180 samples / 5.4 us = 33.4 Msamples/sec
– Each waveform is almost orthogonal to each other or perfectly orthogonal after de-emphasis at RX
• Each group has – 2**4=16 waveforms for binary base waveform modulation (BPSK) or – 4**4=256 waveforms for quaternary base waveform modulation (QPSK)– 16**4=256K waveforms for quaternary base waveform modulation (16QAM)– 64**4=16M waveforms for quaternary base waveform modulation (64QAM)– These waveforms are orthogonal to each other after de-emphasis at RX
mij,=a* wi1 +b* wi2 +c* wi3 +d* wi4
where a, b, c, and d are complex numbers determined by modulation method appliedfor BPSK a, b, c, and d are +1 or -1for QPSK a, b, c, and d are +1, +j, -j or -1for nQAM a, b, c, and d are complex numbers
where : kth sample of ith base waveform of a group for N samples/waveform
• Ratio of correlations = autocorrelation/crosscorrelation for various N values• Orthogonality holds for sinusoidal waveforms with some conditions (Orthogonality condition,
refer to next slide), but the waveforms used here are not sinusoidal with a fixed envelope– At receiver, simple de-emphasis can be used to make pure sinusoidal for a period
• mij*mij=(a* wi1 +b* wi2 +c* wi3 +d* wi4 )(a* wi1 +b* wi2 +c* wi3 +d* wi4) where mij is the waveform transmitted and mij is the waveform generated at RX after de-emphasis
• After integration for one waveform duration, only autocorrelation terms remain• Orthogonality can hold at receiver during detection for matched waveforms
– What is the best sampling frequency such that orthogonality can be achievable?• Less than 8 bits/sample will be enough for orthogonality evaluation? – needs to be verified
– “Power consumption of ADCs goes up exponentially with resolution”, EE times, Jan 17, 2005, pp 49
• A key property of sinusids is that they are orthogonal at different frequencies. That is, • This is true whether they are complex or real, and whatever amplitude and phase they may have. All that matters is that the frequencies be different. Note, however, that the sinusoidal durations must be infinity. • For length N sampled sinusoidal signal segments exact orthogonality holds only for the hamonics of the sampling rate-divided-by-N , i.e., only for the frequencies
• These are the only frequencies that have a whole number of periods in samples• Ex. N=100 for 4 ns pulse duration, fs=25 GHz fk=k*25*10**9/100=2.5*10**8*k=0.25*k GHz
For any integer k, fk can be determined center frequencies of each subband can be determined
• Frequency band: 500-506 MHz, 6 MHz Bandwidth– Whole band is divided into 16 subbands– Each subband has 0.375 MHz bandwidth– 16 Carrier frequencies: 500.1875, 500.5625, . . . , 505.8125 MHz– Frequency separation = h* fs / N = 0.375 MHz where h is an
arbitrary positive integer– fs = N / T = 0.375*N*10**6/h where T is a waveform duration
• T = h / 0.375 * 10**(-6) = h /0.375 us• For ex. for h=1, T=2.7 us, for h=3, T=8 us, for h=4, T=10.7 us, . . .
– For ex., fs=698 MHz• Frequency separation=fs/N=3/8 MHz for h=1• N=698*8/3=1862 ~ 2K points/waveform 2K samples/waveform
• Energy or power efficient? joule/sec– Energy=power*time– Power limited by spectral mask and EIRP
• Pmax=PSD/MHz*BW
to use more energy, more time needed to be transmitted totally related to transmit time for WRAN, BW~6MHz short duration waveforms can be used for higher data rates one possibility to increase energy by using multiple pulses for one bit (or symbol) need to use more power under frequency mask to have higher power power constrained with frequency mask and EIRP for WRAN case new waveforms needed to fit the frequency mask to have more transmitted power
• Spectrally efficient? bit/Hz– limited bandwidth given– More complex modulation schemes have to be applied entails higher system complexity
• Time efficient? bit/sec– For higher rate, more important : needs a short duration waveform for one symbol Needs to put more information in a symbol duration Needs more sophisticated modulations
• An orthogonal set of 8 8-bit Walsh codes is used– Max autocorrelation, zero crosscorrelation each other– One code consists of 8 frequency domain bins– Minimal Hamming distance of this code set is 4 – mostly 8
• One frequency bin error can be corrected while three bin errors can be detected; works like an ECC code; increases robustness
• 64 simultaneously operated users– For one user, two Walsh codes (16 bits) are assigned– One time domain bin is occupied by two codes
• two codes represent one symbol; one time domain bin represents one symbol; one time domain bin deliver one symbol
• Hamming distances between two user codes are 4 and mostly 8.
• For each frequency bin waveform, BPSK, QPSK, 16QAM or 64QAM is applied according to signal environments – or according to the distance between a CPE and the base station.
• Use of full frequency band– Codes are spread over the full band – entails higher power efficiency
• TV band signal sensing for one channel band– Use only spectral components – not time domain components
• Less sensitive on other parameters used to design TV band tuners – for example, Phase noise, etc.
– Use FFT transform of received TV band signals at the receiver for only one TV band
• After wide band tuning and down converting or down converting and low pass filtering
• BW=F=6 MHz• Sampling interval T=1/B=1/6 us, sampling rate=BW=6 MHz• Frequency resolution (or frequency separation) F0=3 KHz• Time period T0=1/F0=1/3 ms• Number of samples needed N0=T0/T= 2 KHz• Needs 2K point FFT
• Sensing procedure for wireless microphone signals– Two types of wireless microphone systems according to frequency usage
• Single frequency systems• Frequency agile systems
– Wireless systems should NOT be operated on the same frequency as a local TV station.
• Only open (unoccupied) frequencies should be used. In the U.S., each major city has different local TV stations.
– Microphone signal detection procedure: sensing the spectral components using FFT devices
• For every 3 KHz in a 6 MHz band a spectral component is measured and compared with other components.
• If considerable components in a 200 KHz band exist, a wireless microphone is considered to be operated in that band: if consecutive six components have considerable amount of energy, a microphone signal is detected.
• After DTV transition in the U.S.,– VHF low band: Chs 2-6 54-88 MHz– VHF high band: Chs 7-13 174-216 MHz– UHF band: Chs 14-51 470-698 MHz *
• n consecutive bands in VHF High or UHF band selected for WRAN services
– The whole band of n bands is divided into n*l subbands• Each band has l subbands; each subband has 6000/l KHz bandwidth
– At receiver, the received signal after down conversion is inputted to a l*n point FFT• By comparing FFT output signals, currently operated incumbent users can be identified and
categorized – NTSC, DTV, or Part 74 devices
• With method all incumbent signal throughout the whole band (n TV bands) can be detected simultaneously – Periodically all CPEs and BSs can do this sensing to update the list of
• Select k consecutive bands out of n bands– Each band is divided into l subbands.– Each subband in selected bands carries information.
– One complex number of information is assigned to each subband • For k selected bands, one complex number is assigned to each subband
– A complex number is determined by the constellation which depends on modulation adopted for the system:
• BPSK: two points: can deliver only one bit per symbol duration
• QPSK: four points: can deliver two bits per symbol duration• 2m QAM: 2m points: can deliver m bits per symbol duration
• For (n-k) not-selected bands, zero is assigned to each subband: – By assigning zero to each subband and applying OOK, no signal is transmitted
– Dynamic frequency selection can be achieved: by changing the assigned values for subbands of a unused band dynamically, WRAN service band(s) can be selected.
• At receiver, data receiving and incumbent signal sensing are executed simultaneously.– Without having separate receiving and processing branches– Using sensing method 2– If more precise sensing is needed, sensing method 1 may be applied with
an additional signal processing block – needs one more ADC and FFT.
receive antenna
LNAcos2fptwhere fp: left edge freq. of the channel (or whole target band)
• For n=32, k=4, l=60 – Four bands of 6 MHz BW each selected out of thirty three bands assigned
for WRAN– Each band is divided into 60 subbands
• each subband has 100 KHz bandwidth
– FFT parameters• Frequency separation F0=100 KHz• Symbol duration T0=1/100 KHz=10 us• Sampling rate F=6x32=192 MHz• Sampling interval T=1/F=1/192 us• No. of samples in a symbol duration N=T0/T=1920• 2048 point FFT/IFFT can be used
– Dynamically the system can select any four consecutive bands out of 32 bands or easily expand the operating band in these four bands.
• n: total number of TV channel bands observed– Total target frequency band for which incumbent signals can be sensed– In this band, some TV channel bands can be occupied to send information for
WRAN services– As n increases, total band increases and number of samples of FFT increases:
number of points of FFT?IFFT increases– Sampling interval is inversely proportional to n: sampling interval is inversely
proportional to n)• k: number of bands used to deliver information
– k determines symbol rates: for a 6 MHz channel, its symbol rate is 6 Msymbols/sec determines data rates which depends on modulation
– As k increases, bandwidth used for information delivery increases and the number of inputs and outputs of FFT used for information delivery increases.
• l: number of subbands in a TV channel band– l determines one FFT symbol duration– As l increases, frequency separation decreases and one symbol duration increases
• The number of points of FFT/IFFF is proportional to n*l
• With 6 MHz bandwidth– One band is divided into 16 subbands– Each subband has its waveform: all 16 waveforms are nearly orthogonal to each other– Modulations: BPSK, QPSK, 16QAM, and 64QAM– Sectorization can be implemented with directional antennas for BSs and omni directional
antennas for CPEs to increase data rates• Exactly same hardware for CPEs as that without sectorization• Three receiving blocks needed for a base station with derectional antenna
– Multiple access: coded MA in frequency domain• 64 users at one instant
– Aggregated data rates: min 11.85 Mbps, max 71.11 Mbps– Data rates per subscriber: min 0.19 Mbps, max 1.08 Mbps– Spectral efficiency : min 1.98 bits/sec/Hz, Max 11.85 bits/sec/Hz
• Advantages over other OFDM concepts– Simpler concept: much simpler implementation/lower complexity than other competing
technologies– Pure digital implementation– More flexibility in scalability, up/down balancing– Realized with lower sampling rate DACs and ADCs
• Very simple concepts / architecture– Directly generated pulse waveforms using ROMs– Processing in digital methods
• No need to have analog devices (e.g., mixer, LO, integrator, etc) except LNAs low complexity / low cost / low power consumption
• High out-of-band rejection with equal complexity– More transmit power and more bandwidth efficient high data rates can be achieved
• High adaptability to frequency, data rate, transmit power requirements high scalability in frequency band, data rate, system configuration, uplink/downlink balancing, waveform, etc.
• More transmit power used under frequency mask– More margin in link budget: 3.8 dB more by using full power under any frequency-
power constraints with waveforms adaptive to frequency mask Spectrally efficient / more received signal power More chance to intercept signals