5G: Opportunities and Challenges
Kate C.-J. Lin Academia Sinica
!
2015.05.29
Key Trend (2013-2025)
• Exponential traffic growth!
• Wireless traffic dominated by video multimedia!
• Expectation of ubiquitous broadband access!
• Expectation of Gbps, low latency access!
• Emerging internet of things devices
source: Intel, Sept. 2013
5G Targets
5G
High System Capacity
Reduced latency
Energy saving &
cost reduction Massive device
connectivity Higher data
rate
1000x capacity/km2
10-100x even
w/ mobility < 1ms
100x connected devices
source: NTT DoCoMo, Inc. 2014!
Disruptive Technologies
• Millimeter wave (mmWave)!
• Massive MIMO!
• Full-duplex communication!
• Device-to-device (D2D) communications!
• Heterogeneous networks
Disruptive Technologies
• Millimeter wave (mmWave)!
• Massive MIMO!
• Full-duplex communications!
• Device-to-device (D2D) communications!
• Heterogeneous networks
mmWave Scenarios
source: http://www.ece.ucsb.edu/wcsl/mmwcsresearch
Millimeter Wave
• Ranging from 3 to 300 GHz!
• e.g., license-free band at 60 GHz
mmWave Standardization
• IEEE 802.11ad!
• Short-range services!
• 60GHz!
• Beamforming antenna!
• OFDM modulation!
• Maximum data rate: 7Gbps!
• Typical distance: 1-10m
mmWave’s Properties
• Properties similar to microwave frequencies!
• Distance-dependent path loss!
• Possibility of non-light-of-sight communication!
• Properties different from microwave frequencies!
• Sensitivity to blockage!
• High power consumption of ADC/DAC
mmWave’s Key Feature
!
• Keep the antenna aperture constant!
• Eliminate the frequency dependence of path loss!
• Counter the larger thermal noise!
• Reduce the impact of interference by adaptive array with narrow beams
New random access protocols are required due to directional transmission/reception
Antenna Array
Recent work on mmWave
• Millimeter Wave (mmWave) Wireless @ NYU!
• http://faculty.poly.edu/~tsr/mmwave.php!
• Millimeter Wave Communication Systems Research @ UCSB!
• http://www.ece.ucsb.edu/wcsl/mmwcsresearch/doku.php!
• Millimeter Wave Cellular Systems @ UTAustin!
• http://www.profheath.org/research/millimeter-wave-cellular- systems/
Disruptive Technologies
• Millimeter wave (mmWave)!
• Massive MIMO!
• Full-duplex communications!
• Device-to-device (D2D) communications!
• Heterogeneous networks
http://argos.rice.edu/
Massive MIMO
• Support a much larger number of antennas, e.g., one hundred or more!
• If N grows large and all other system
parameters are assumed constant, the transmit power per user can be reduced proportionally to 1/N and 1/√N for perfect and imperfect CSI knowledge, respectively
H. Q. Ngo, E.G. Larsson, T.L. Marzetta, “Energy and Spectral Efficiency of Very Large
Multiuser MIMO Systems,” IEEE Trans. on Comm., vol. 61, no. 4, pp. 1436--1449, Apr. 2013.
Massive MIMO: Challenges
• Scalability of precoding and detection!
• Traditional zero-forcing beamforming requires non-trivial baseband processing!
• CSI estimation!
• How to efficiently collect full CSI?!
• Accurate synchronization!
• Cost, size, and power consumption
• Reading list!
• http://www.idc.lnt.de/en/forschung/massive-mimo- systems/!
• http://www.massivemimo.eu/research-library!
• http://ieeexplore.ieee.org/xpl/articleDetails.jsp?
arnumber=6798744!
• http://www.comsoc.org/best-readings/topics/
massive-mimo
Disruptive Technologies
• Millimeter wave (mmWave)!
• Massive MIMO!
• Full-duplex communications!
• Device-to-device (D2D) communications !
• Heterogeneous networks
What is Duplex?
• Simplex!
!
• Half-duplex!
!
• Full-duplex
How Half-duplex Works?
• Time-division half-duplex!
!
!
• Frequency-devision half-duplex
Co-Channel (In-band) Full-duplex
Very strong self-interference (~70dB for 802.11)
Self-Interference Elimination
• Analog interference cancellation (RF cancellation, ~25dB reduction)!
• Digital interference cancellation (baseband cancellation)!
• Antenna cancellation (~20dB reduction)!
• Separate the antennas such that the two signals become deconstructive!
• Performance degrades when the bandwidth increases
Applications
• Reducing hidden terminals!
• Multi-hop wireless networks!
• Wireless relaying (repeaters)!
• Cognitive radio (spectrum sensing)
Disruptive Technologies
• Millimeter wave (mmWave)!
• Massive MIMO!
• Full-duplex communications!
• Device-to-device (D2D) communications!
• Heterogeneous networks
D2D Communications
• Co-located devices share content directly, without going through a base station!
• Offload proximity data exchange from a congested cellular system
tx2
rx2
tx1 tx3
rx3 BS UL
rx1
Inter-link Interference in D2D
• D2D links might interfere with each other!
• D2D clients might also interfere cellular transmissions
tx2
rx2
tx1 tx3
rx3 BS UL
datainterference rx1
D2D Interference Management
• Possible solutions!
• Resource allocation (OFDMA)!
• Throughput maximization!
• Revenue maximization !
• Energy consumption!
• Incentive!
• MIMO techniques, such as interference alignment
Disruptive Technologies
• Millimeter wave (mmWave)!
• Massive MIMO!
• Full-duplex communications!
• Device-to-device (D2D) communications!
• Heterogeneous networks
Heterogeneous Networks
source: http://blog.3g4g.co.uk/
macro cell + femto cell + pico cell
Advantages and Challenges
• Reduce the cell size, and improve spatial reuse!
• larger capacity per device!
• Challenges!
• Resource allocation and interference management!
• Backhaul bandwidth management!
• Latency and QoS guarantee!
• Pricing
