The document discusses key tradeoffs in wireless systems between data rate, transmission power, and propagation loss. It outlines how technology progresses by improving spectral efficiency through techniques like OFDM, MIMO, and advanced coding to increase data rates under fixed power constraints. Examples of both low-end technologies for sensors and RFID, as well as high-end cellular networks like LTE-Advanced are provided to illustrate trends across different applications. The conclusion emphasizes that wireless technologies are becoming more diffuse with many low-power devices, and networks are densifying to contribute more capacity while radiating less power on a per-device basis.

1. A key parameters based vision
of trends in Wireless systemsof trends in Wireless systems
Alain Sibille
Telecom ParisTech

2. Outline
What do we speak about ?
Tradeoff between key parameters
Technology progress
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From low-end to high-end technologies
Conclusion

3. What do we speak about ?
Key parameters: data rate – power – propagation loss
• Data rate can be traded against radiated power: the energy/bit is a
KPI
• data rate ⇒⇒⇒⇒ power
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• Data rate can be traded against propagation loss: by increasing the
distance, there is less energy available/bit
• Power can be traded against propagation loss: for a given data rate,
less transmitted power reduces the correct reception distance (trivial)

4. What do we speak about ?
The data rate – power – propagation loss tradeoff
Data rate
4 GWimedia
Total data rate = user
data rate + overheads
Algorithmic
Complexity
tuning
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Power
Propagation loss
Sensors
BAN
RFID reader
Deep space
Consumed power = radiated
power + processing power
Propagation loss = free space loss
+ obstructions loss + antenna loss
Electronics
performance
tuning
Networking
tuning

5. What do we speak about ?
How do we use the resource
• Wireless signals occupy a certain spectral band. This resource is
expensive. Do we use it well ?
Concept of spectral efficiency (bits/second/Hertz)
Band width (Hz)
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• Shannon maximum capacity (bits/s)
The maximum SE is limited by the SNR (logarithmically)






+⋅=
powerNoise
P
BC received
1log 2
Max. spectral efficiency






+⋅=
0
2 1log
N
PSD
BC received
receivedreceived
PSDBP ⋅= 0NBpowerNoise ⋅=
Band width (Hz)

6. What do we speak about ?
Cell center vs. cell edge throughput
• Since the received power is small far from the base station, the
effective throughput is low !
Big lag between maximum spectral efficiency
and mean spectral efficiency !
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7. What do we speak about ?
Asymmetry
• Most often the devices at both link ends differ in their
capabilities/performance/complexity/power consumption
• Most often spectral efficiency and data rate are higher in DL than UL
• UL and DL spectral efficiency differ
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• UL and DL spectral efficiency differ
Duty cycle
• The radiated signals are often bursty:
low average power, high peak power

8. Tradeoff between key parameters
The tradeoff is a matter of specifications / constraints
• How much power is available ? (also a tradeoff vs. Battery capacity
Power Propagation loss
Data rate
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• How much power is available ? (also a tradeoff vs. Battery capacity
and required lifetime)
• What is the needed data rate ? (application dependent)

9. Tradeoff between key parameters
The tradeoff is a matter of specifications / constraints
• What is the allowed transmission power ? (regulation spectral masks)
Power Propagation loss
Data rate
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• What is the allowed transmission power ? (regulation spectral masks)
• What is the acceptable device / access points density (max. distance)

10. Technology progress
How to shift / turn around the tradeoff ?
• Improve data rate under fixed power/propagation loss: increase the
spectral efficiency (b/s/Hz) – closer to Shannon – :
- OFDM (already in many standards): efficient use of the spectrum
1bps/Hz, 2bps/Hz… 12 bps/Hz, reduced by overhead
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- Multiple antennas (MIMO): may multiply the spectral efficiency by the
number of antennas … BUT : may consume processing power

11. Technology progress
How to shift / turn around the tradeoff ?
• Improve data rate under fixed power/propagation loss: increase the
spectral efficiency (b/s/Hz) – closer to Shannon – :
- Advanced coding schemes: to reduce the energy/bit at a given error rate
– Turbo codes, LDPC… BUT : may consume processing power
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- Flexible, adaptive techniques (crosslayer, link level…)

12. Technology progress
How to shift / turn around the tradeoff ?
• Make a better use of the spectral resource: fill the gaps, opportunely
benefit of available spectrum:
- Cognitive radio and dynamic spectrum access:
future networks, cellular / local …
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- Spectral bands agregation: use of several bands simultaneously
- Use of higher frequencies: 60 GHz
enormous band width,
excellent frequency re-use

13. Technology progress
How to shift / turn around the tradeoff ?
• PHY/link/Network level advanced techniques:
- Cooperative communications
improves link robustness
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- Multi-user communications
improves agregated throughput
- Relaying, BST cooperation
reduces propagation loss

14. From low-end to high-end technologies
Some examples / trends / upcoming technologies
• « Low end »: sensors in houses, smart cities/grids, industrial
premises... very low power & data rate (kb/day), UHF down to VHF
- No battery, low processing power, low cost, green technologies…
M2M
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M2M

15. From low-end to high-end technologies
Some examples / trends / upcoming technologies
• « Low end »: RFID
- UHF(865-960 MHz, < 2W radiated): active reader, passive tag: from kbps to
~100 kbps, ~5 m detection range, EPC Gen2
- Microwave (2.4 GHz, <1 mW radiated) : active reader, passive or active tag:
from kbps to ~1000 kbps, ~10-100 m detection range, 6loPAN
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from kbps to ~1000 kbps, ~10-100 m detection range, 6loPAN
- UWB (~3-5, 6-8.5 GHz, <0.2 mW) active reader, passive or active tag: from
kbps to ~250 kbps, ~10-100 m detection range, 802.15.4a, location
enabled

16. From low-end to high-end technologies
Some examples / trends / upcoming technologies
• « Low-end »: the main target is low power (batteryless), low cost,
interference management, multipath fading, NOT spectral
efficiency as such
very low duty cycle protocols, compressed sensing, energy harvesting…
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17. From low-end to high-end technologies
Some examples / trends / upcoming technologies
• « medium-end »: GSM/GPRS/EDGE. The plain old GSM is not dead:
still many virtues (cost, coverage…) for e.g. home & industrial
automation
- Spectral efficiency 0.5 bps/Hz
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18. From low-end to high-end technologies
Some examples / trends / upcoming technologies
• « medium/high-end »: WIFI, femtocell (<100 mW): gateway to internet
+ home multimedia platform
- Spectral efficiency : 43 bps/Hz agregated SE in 160 MHz (802.11ac, MU-
MIMO) up to ~7 Gb/s !
- Cognitive WIFI in white spaces (802.11af <1 GHz)
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- Cognitive WIFI in white spaces (802.11af <1 GHz)
Major issue: how to deal with interference ?

19. From low-end to high-end technologies
Some examples / trends / upcoming technologies
• « high-end »: UMTS → HSDPA → LTE → LTE-Advanced
- Peak data rate 0.38 Mb/s → 14 Mb/s → 300 Mb/s → 1000 Mb/s
- Peak spectral efficiency 0.4 bps/Hz → 8.4 bps/Hz → 16 bps/Hz → 30
bps/Hz (8x8 MIMO)
- Future massive MIMO ?
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- Future massive MIMO ?
A lot of work ahead on terminals, network architectures, green BST…

20. Conclusion
Trends in wireless communications technologies:
• Play around the tradeoff power/data rate/propagation loss
• Depends on the applications:
- Wireless technologies become « diffuse »
- Many very low power devices, low data rate
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- Many very low power devices, low data rate
- High-end networks for interconnected media devices and internet gateway
• Densification of the network: access points, femtocells: mostly (by far)
contributes to the total b/s capacity ; lower radiated power, more
smoothly distributed
• Progress in the technologies: better use all wireless resources, less
waste of the expensive frequencies: more Mb/s for fewer Watts. Short
term & long term progress to come

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