David Lu
Software Developer
An Introduction to Millimeter-Wave
Mobile Broadband Systems
Yung-Sheng Lu
AUG 02, 2017
@NCTU-CS
Written by Zhouyue Pi and Farooq Khan, Samsung Electronics.
Publish on IEEE Communications Magazine, JUN 2011.
Outline
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Foreword
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Introduction
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Millimeter-wave Spectrum
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Millimeter-wave Propagation
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MMB Network Architecture
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MMB Air Interface Design
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Conclusion
Foreword
Foreword
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Why should start looking at the 30-300 GHz spectrum for mobile broadband applications?
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Bandwidth
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Millimeter-wave mobile broadband (MMB) system is a candidate next-generation mobile communication system.
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MMB network architecture
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Beamforming techniques and the frame structure of the MMB air interface
Introduction
4G Systems
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Already achieves spectral efficiency close to bits per second per Hertz per cell
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Orthogonal frequency-division multiplexing (OFDM)
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Multiple-input multiple-output (MIMO)
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Multi-user diversity
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Link adaptation
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Turbo code
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Hybrid automatic repeat request (HARQ)
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4G Systems (cont.)
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Due to the limited room for further spectral efficiency imporvement, increasing capacity per geographic area is imperative.
- The capacity can only scale linearly with the number of cells.
Millimeter-wave
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A vast amount of spectrum in the 3–300 GHz range remains underutilized.
Millimeter-wave (cont.)
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Millimeter-wave communication systems can achieve point-to-point communication at multi-gigabit data rates in a few kilometers distance under some constraints.
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The 60 GHz band as unlicensed spectrum has spurred interest in gigabit-per-second short-range wireless communication.
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Several industrial standards have been developed.
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e.g., ECMA-387, IEEE 802.15.3c, IEEE 802.11ad.
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Millimeter-wave Spectrum
Unleashing the 3-300 GHz Spectrum
- The 300 MHz-3 GHz band is referred to as the sweet spot.
- The portion above 3 GHz has been explored for short-range and fixed wireless communication.
- The 28-30 GHz band - Local multipoint distribution service (LMDS)
- Up to 252 GHz can potentially be used in MMB.
LMDS and 70/80/90 GHz Bands
- Use a cellular infrastructure with multiple base stations
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The Federal Communications Commission (FCC) auctioned two LMDS licenses per market (basic trading areas).
- The A license (1.15 GHz)
- The B license (150 MHz)
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The E-band is available to ultra-high-speed data communication.
- Point-to-point wireless local area networks
- Mobile backhaul
- Broadband Internet
- Highly directional “pencilbeam” signal
LMDS and 70/80/90 GHz Bands (cont.)
Millimeter-wave Propagation
Free-space Propagation
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Misconception
Transmission loss of millimeter wave is accounted for principally by free space loss. -
Free-space propagation loss depends on frequency.
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Free-space path loss formula
- Free-space path loss in decibels
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Free-space path loss formula
L = { \left( \frac{4 \pi d}{\lambda} \right) } ^ 2 = { \left( \frac{4 \pi d f}{c} \right) }^ 2
L=(λ4πd)2=(c4πdf)2
L(dB) = 10 \log_{10} \left( {\left( \frac{4 \pi d}{\lambda} \right)} ^ 2 \right) = 20 \log_{10} \left( \frac{4 \pi d f}{c} \right)
L(dB)=10log10((λ4πd)2)=20log10(c4πdf)
= 20 \left( \log_{10}(d) + \log_{10}(f) \right) -147.55
=20(log10(d)+log10(f))−147.55
Free-space Propagation (cont.)
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An antenna with a larger aperture has larger gain than a smaller one as it captures more energy from a passing radio wave.
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Dependency of antenna aperture from antenna gain
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Dependency of antenna aperture from antenna gain
- Large numbers of antennas enable transmitter and receiver beamforming with high gains.
A = G \frac{\lambda ^ 2}{4 \pi }
A=G4πλ2
Penetration and Other Losses
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Atmosphere gaseous losses and precipitation attenuation are typically less than a few dB per kilometer in 3-300 GHz.
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The loss due to reflection and diffraction depends greatly on the material and the surface.
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non-line-of-sight (NLOS) communication
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non-line-of-sight (NLOS) communication
- While signals at lower frequencies can penetrate more easily through buildings, millimeter-wave signals do not penetrate most solid materials very well.
Penetration and Other Losses (cont.)
Doppler and Multipath
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The Doppler of a wireless channel depends on the carrier frequency and mobility.
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The narrow beams at the transmitter and receiver will significantly reduce angular spread of the incoming waves.
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The narrow beams at the transmitter and receiver will significantly reduce angular spread of the incoming waves.
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As the incoming waves are concentrated in a certain direction, there will be a non-zero bias in the Doppler spectrum.
- With narrow transmitter and receiver beams, the multipath components of millimeter waves are limited.
MMB Network Architecture
A Standalone MMB Network
- In order to ensure good coverage, MMB base stations need to be deployed with higher density than macrocellular base stations.
A Standalone MMB Network (cont.)
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The transmission and/or reception in an MMB system are based on narrow beams.
- Suppress the interference from neighboring MMB base stations
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Extend the range of an MMB link
- Allows significant overlap of coverage among neighboring base stations
A Standalone MMB Network (cont.)
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With the high density of MMB base stations, the cost to connect every MMB base station via a wired network can be significant.
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Allow some MMB base stations to connect to the backhaul via other MMB base stations.
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Allow some MMB base stations to connect to the backhaul via other MMB base stations.
- Due to large beamforming gains, the MMB inter-BS backhaul link can be deployed in the same frequency as the MMB access link without causing much interference.
A Standalone MMB Network (cont.)
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The low efficiency of RF devices such as power amplifiers and multi-antenna arrays with current technology.
- Use fixed beams or sectors with horn antennas.
- The mobile station receiver needs to use a multi-antenna array to form a beamforming pattern toward the base station.
Hybrid MMB + 4G Systems
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Improves coverage and ensure seamless user experience
- Make the entire millimeter-wave spectrum available for data communication.
MMB Air Interface Design
Beamforming
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Beamforming is a signal processing technique used for directional signal transmission or reception.
- Spatial selectivity/directionality is achieved by using adaptive transmit/receive beam patterns.
Beamforming (cont.)
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Beamforming is a key enabling technology of MMB.
- For MMB transceivers, the small size ( dipoles) and separation (also around ) of millimeter-wave antennas allow a large number of antennas and thus achieve high beamforming gain in a relative small area.
- Spatial-division multiple access (SDMA)
\lambda / 2
λ/2
\lambda / 2
λ/2
Beamforming (cont.)
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Challenges
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The cost of implementing one RF chain per antenna
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Battery power consumption
- Reduce the cost and complexity of mobile stations
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The cost of implementing one RF chain per antenna
Frame Structure
- MMB uses OFDM and single-carrier waveform for largely the same reasons between multiplexing schemes of 4G systems.
Frame Structure (cont.)
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The OFDM/single-carrier numerology is carefully chosen according to a number of engineering considerations.
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The sampling rate is chosen to be a multiple of 30.72 MHz.
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The cyclic prefix (CP) is chosen to be 520 ns
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The subcarrier spacing is chosen to be 480 kHz.
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Frame Structure (cont.)
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MMB supports transmission with single-carrier waveform.
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Single-carrier waveform has lower peak-to-average-power(PAPR) than OFDM.
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A lower PAPR allows the receiver to use a low-resolution analog-to-digital converter (ADC).
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註：峰值因數 (Peak-to-average ratio; PAR)
和波形有關的無因次量，為波形的振幅再除以波形 RMS (time-averaged) 所得到的值。
R_{peak\ to\ avg} = \frac { |x|_{peak} } { x_{rms} }
Rpeak to avg=xrms∣x∣peak
註：峰均功率比 (Peak-to-average power ratio; PAPR)
為振幅平方 (表示峰值功率) 除以 RMS 平方 (表示平均功率) 的比值。
R_{peak\ to\ avg\ power} = \left( \frac{ {|x|_{peak}} }{ {x_{rms}} } \right) ^ 2 = C ^ 2
Rpeak to avg power=(xrms∣x∣peak)2=C2
Link Budget
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Determine the downlink link budget of an MMB system
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Base station transmission power
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Transmitter and receiver beamforming gains
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Path loss
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Conclusion
Conclusion
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Millimeter-wave spectrum can potentially provide the bandwidth required for mobile broadband applications for the next few decades and beyond.
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The narrow beam width of MMB transmissions
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The MMB base stations form a grid.
- The inter-BS backhaul link can be used to mitigate the cost of backhauling (and to expedite deployment).
Conclusion (cont.)
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In order to operate in an urban mobile environment while keeping a low overhead, we chose the MMB subcarrier spacing to be 480 kHz and the CP to be 520 ns.
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Design the frame structure to facilitate hybrid MMB + 4G operation.
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In the link budget analysis, a 2 Gb/s data rate is achievable at 1 km distance with millimeter waves in an urban mobile environment.
References
References
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An Introduction to Millimeter-Wave Mobile Broadband Systems
-
Written by Zhouyue Pi and Farooq Khan, Samsung Electronics.
-
Publish on IEEE Communications Magazine, JUN 2011.
-
An Introduction to Millimeter-Wave Mobile Broadband Systems Yung-Sheng Lu AUG 02, 2017 @NCTU-CS Written by Zhouyue Pi and Farooq Khan, Samsung Electronics . Publish on IEEE Communications Magazine, JUN 2011 .
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