What is wireless communication?
• Transmission of information between
• Access point (AP): Base station, WiFi router, etc… • User
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• Not via wired lines
• Digital: zeros and ones
• Describes text, sound, image, …
• Wireless transmission (Electromagnetic signals) • Data rate? (Capacity/Throughput)
Base station
Uplink 50 17 Mbps
The Evolution of Mobile Communications from 1G to 6G
Capacity/ Data Rate/ Throughput/ Spectral Efficiency
Channel capacity 𝑪𝑪: The maximum rate at which information can be transmitted through a communication channel.
Capacity/ Data Rate/ Throughput/ Spectral Efficiency
Channel capacity 𝑪𝑪: The maximum rate at which information can be transmitted through a communication channel.
𝐶𝐶=log2 1+𝑆𝑆⁄𝑁𝑁 𝐶𝐶=log2 1+𝑆𝑆𝑁𝑁𝑆𝑆
• 𝐶𝐶: in [bits/sec/Hz]
• 𝑆𝑆: received signal power [W]
• 𝑁𝑁: Noise power spectral density [W/Hz]
The Shannon–Hartley theorem ( . Shannon in 1948)
Radio Propagation
• Transmitted signal power: Bluetooth 1 mW (0 dBm) Mobile phone 100 mW (20 dBm) Base station 40W (46 dBm)
https://en.wikipedia.org/wiki/Isotropic_radiator
Isotropic antenna
𝑑𝑑 • 𝐴𝐴𝑡𝑡 and 𝐴𝐴𝑟𝑟 are effective aperture areas:
• An isotropic antenna:
radiates equal power in all directions has a spherical radiation pattern
• Friis Equation:
Radio Propagation
Isotropic antenna
Multi-antenna technologies – 1948 (0G) to early 2000 (4G): Multiple-Input Multiple-Output (MIMO) to increase n Relay communications to reduce 𝒅𝒅
Multiple-Input Multiple-Output (MIMO)
Robots may have limited space!
Beamforming
Multiple-Input Multiple-Output (MIMO)
Path-loss Shadowing
Olympic Relay
+ Smooth handover + Signal processing
– Processing delay – Beamforming12
Relaying in wireless communications
WiFi Range Extenders Repeaters
Relay (R) Transmitter (Tx)
DF relay decodes, re-modulates and retransmit the received signal.
Relay is an active node/device.
Let us say that Tx-R channel and R-Rx channel have capacities 𝐶𝐶 and 𝐶𝐶 , respectively. 1 2
Receiver (Rx)
Time-slot 1
Time-slot 2
2. 0.5*(𝐶𝐶1 + 𝐶𝐶2).
3. 0.5*max(𝐶𝐶 , 𝐶𝐶 ).
12 4. 0.5*min(𝐶𝐶1 , 𝐶𝐶2).
Q. What is the effective capacity from Tx to Rx with the help of an DF relay?
1. 𝐶𝐶 + 𝐶𝐶 . 1 2
Involving to provide more data capacity
Big Picture –
Cognitive Radio Networks
Transceiver can intelligently detect channel availability Spectrum sensing
Secondary users intelligently adapt their operating parameters to access a spectrum band occupied by primary users in collaboratively.
Energy Detection
The 2010 Communication Theory Workshop
https://ctw2010.ieee-ctw.org/tues/plenary-CommTheoryDev-BestBehindOrAhead.pdf
The 2010 Communication Theory Workshop
Wireless Networks (4G to 5G and Beyond)
Current and future wireless networks (E.g., Smart cities) involve many aspects of daily life including e-businesses, intelligent transportation, telemedicine, M2M, IoT, …
Smart City
Wireless Networks (4G to 5G and Beyond)
No longer relying on cells!
Smart City
5G and Beyond
Area throughput is highly relevant performance metric
Big Picture –
MIMO + Massive MIMO + mmWave (5G)
Small Cell
Industrial robots! No coverage holes!
Big Picture – Beyond 5G
Smart Signal Propagation
Roof/wall penetration: -10, -20 dB, even more …
Smart Signal Propagation
Channels consisting of multiple paths
Smart Signal Propagation
Scatterers the incoming signal with an uncontrollable phase-shift Scattering
Reconfigurable (properties)
Intelligent (programmable/controllable) Surface (2D)
Reconfigurable (properties)
Intelligent (programmable/controllable) Surface (2D)
• Software-controlled metasurface •…
Reconfigurable Intelligent Surface (RIS)
Single n-th element Passive patch
(sub-λ sized)
Switch (Diode)
Programmable controller
Transmitter
Reconfigurable Intelligent Surface (RIS)
Single n-th element Passive patch
(sub-λ sized)
Switch (Diode)
Programmable controller
Transmitter
Smart Building IoT Solutions / Autonomous Car
Improved indoor coverage by controlling the propagation channels! 32
RIS – Communication System Model
L-Elements RIS 𝒆𝒆𝒋𝒋𝜽𝜽𝒏𝒏
𝒉𝒉𝒏𝒏 n𝒈𝒈𝒏𝒏 End-to-end channel 𝒈𝒈𝒏𝒏𝒆𝒆𝒋𝒋𝜽𝜽𝒏𝒏𝒉𝒉𝒏𝒏
General Case (𝑳𝑳 Elements) L-Elements RIS
Passive Beamforming
Large Intelligent Surface (LIS)
L-Elements RIS 𝒆𝒆𝒋𝒋𝜽𝜽𝒏𝒏
𝒉𝒉𝒏𝒏 n𝒈𝒈𝒏𝒏
BS ∝ 𝐿𝐿2 Large Intelligent Surface (LIS) End-to-end channel SNR gain
Relay vs RIS
𝑇𝑇 = 2 log2(1 + 𝑆𝑆𝑁𝑁𝑆𝑆)
+ signal amplification – pre-log penalty
𝑇𝑇=1log (1+𝑆𝑆𝑁𝑁𝑆𝑆) 2
+ no pre-log penalty
– multiplication of channel gains
Throughput (bits/sec/Hz)
In Summary …
• Wireless channel capacity
• Multi-antenna techniques (MISO/MIMO/Massive MIMO) • Small-cell/Cell-free cellular architecture
• Relay networks
• Reconfigurable Intelligent Surfaces (RIS)
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