Spatial Modulation Concepts and Techniques

1. Spatial Modulation

2. Presented By
Abdul Qudoos
BSEE(IIUI)
MSEE(FAST-NU ISB)

3. Spectral Efficiency
Number of bits transported with in a second and with in a given
bandwidth.
Measured as bits/sec/Hz

4. Energy Efficiency
It is computed as the ratio between the channel capacity and the total
power supply that includes both the RF and the circuit power
consumption.
Energy Efficiency expressed in bits/Joule.

5. Energy Efficiency vs Spectral Efficiency
• According to this paper there has been a lot of work done to increase
spectral efficiency but no attention had been paid to energy efficiency
or a little attention had been paid.
• The pioneers of MIMO had just mentioned about the SM-MIMO
scheme which is related to improving efficiency with spectral
efficiency.
• The important thing to note that the communication systems
designed before are spectral efficient rather than energy efficient.

6. Energy Efficiency vs Spectral Efficiency
• However if any system that designed was energy efficient it must be
not spectral efficient.
• There has been a trade off between energy efficient and spectral
efficient communication system designing.
• This trade off had been removed according to this paper by using SM-
MIMO scheme instead of conventional MIMO scheme.

7. Fundamental Trade Off b/W EE AND SE

8. Fundamental Trade Off b/W EE AND SE
• Where N is the receiver noise power spectral density.
• It was clearly seen from the formulae that if we increase the spectral
efficiency it will decrease the energy efficiency.
• As spectral efficiency raised to the power base 2 will increase the
spectral efficiency will be divided by bigger number which will
decrease energy efficiency.

9. Multi Input Multi Output
• In MIMO scheme we use multiple antennas at transmitter and
receiver which are active simultaneously for the transmission of
modulated signals.
• We have to use multiple Antenna's and transmitter and receiver to
increase gain and spectral efficiency.
• The purpose of increasing spectral efficiency has been increased but
energy efficiency on the other hand is greatly neglected in this
scheme.

10. How MIMO is not Energy Efficient
• MIMO is not energy efficient because when multiple antennas will
active they will dissipate energy.
• As every antennas consist of circuit consist of RF amplifiers
,Operational amplifier and power amplifiers which required power to
run and dissipate energy.
• In case of MIMO when multiple antenna's work at a time so all the
antenna's containing circuitry inside them are in working condition
and will dissipate energy.
• More the number of antenna's more is the dissipate energy.

11. Initial Solution for EE in MIMO
• As we didn’t decrease the number of Antenna's because it will
decrease spectral efficiency.
• So the initial proposed solution to increase energy efficiency was to
decrease the number of inactive antenna's.
• This was done by monitoring the power of active antenna's which
they are receiving.
• The antenna receiving less power will be shutdown so that the power
dissipation will decreased.

12. Solution to EE Problem IN MIMO
• This solution was not so feasible to enhance the Energy efficiency. So
more advanced solution was proposed in this paper.
• SM-MIMO was proposed solution which will not only increase data
rate but also increase energy efficiency.
• SM-MIMO will remove this trade off by using only one active antenna
at one time and also doubles the data rate enhancing spectral
efficiency.
• SM-MIMO abbreviated as Special modulation multi input multi ouput.

13. HOW SM-MIMO WILL be FEASIBLE
• Minimize the number of active antenna's elements in order to
increase the energy efficiency by reducing the circuit power
consumption at the transmitter.
• Given the implementation and size constraints maximize the number
of passive elements in order to increase both the spectral efficiency
and energy efficiency by reducing the transmit power consumption.
• Passive elements are the elements which does not required any
power to work.

14. Spectral Efficiency

15. Spectral Efficiency
• As clearly seen from the formulae the data rate bits per channel will
increases in using SM.
• By applying the conventional scheme on the above formulae we will
only get 2 bpcu but from SM we will get 4 bpcu which significantly
shows the increase spectral efficiency.
• However we can go from SM to MIMO convectional scheme by
putting NT=1 which is an main advantage of using this scheme.

16. How SM-MIMO will work

17. SM-MIMO
• Given is the signal constellation for M=4 we have 2 bits to transmit so
we know the signal constellation which contains four combinations.
• Now in Special modulation we can modify the given two dimensional
constellation to three dimension where we name the third dimension
as special constellation.
• On special constellation we can map the Active antennas to their
special signal constellation.
• So for NT=4 we have four possible combinations which can mabps on
special constellation.

18. SM-MIMO
• So only one antenna was active at one time. So if we consider T3 on
the above figure so we can transmit 4 bits at a time. The shifting from
one sequence to another is called switching frequency.
• So as we can see that only one antenna was active at one time which
can achieve energy efficiency and we can transmit more that two bits
for M=2 which can achieve spectral efficiency .
• So by using SM-MIMO instead of conventional MIMO we had achieve
both energy efficiency and power efficiency.

19. Transmission/Encoding Techniques
Encoding technique has been given above where 10 has been
mapped to antenna selection and other bit 1 is mapped to
bpsk.

20. Channel Impulse Response/Finger Print
• As active antenna's are placed at different spatial locations so the
signals omitted by the antenna's may face different propagation
conditions due to different environment objects.
• As the signals travel through the transmission/communication
channel which introduces finger print or channel response specifically
channel impulse response.
• Due to different special locations of TA’s signals omitted may face
different impulse response of transmission channel.

21. Transmission/Encoding Techniques

22. Demodulation of Signals at Receiver
• As the signals transmitted have different impulse responses so they can be
demodulated ow receiver get information of signals from their channel
impulse response.
• Receiver had saved all the impulse responses and after receiving channel
impulse response it can test all the impulse responses and calculate
Euclidean distances.
• The received channel impulse response have lowest Euclidian distance with
given impulse response will be selected as the correct received signal.
• The more the distance between the spatial locations of active antenna's
the more easy for the receiver to retrieved transmitted signal.

23. Euclidian distance calculation

24. MIMO Schemes(OSTBC)
• Space-time block codes are used for MIMO systems to enable the
transmission of multiple copies of a data stream across a number of
antennas and to exploit the various received versions of the data to
improve the reliability of data-transfer. Space-time coding combines
all the copies of the received signal in an optimal way to extract as
much information from each of them as possible.
• The columns represent transmit antenna's and the rows represent the
time slots.
• Moreover any two pair of column's are orthogonal to each other.

25. MIMO Schemes(OSTBC)

26. Comparison of different MIMO schemes
• Comparison of bit error rate vs SNR of MIMO scheme with R=6bpcu
and NR=4.

27. Comparison of different MIMO schemes
• Comparison of bit error rate vs SNR of MIMO scheme with R=6bpcu
and NR=2.

28. Comparison of SM-MIMO WITH Conventional
MIMO
• So we can plot the energy efficiency vs bit rate by comparing the SM-
MIMO with conventional MIMO which show 70% or above energy
efficiency achieved in case of SM-MIMO.
• It has been seen that it has an intercept point at one stage when we
increase the throughput which means that the energy efficiency of SM-
MIMO becomes equal to conventional MIMO.
• This intercept point can be avoided by using large number of transmit
antenna's.
• This is the case where transmit antenna NT=4. which may not be energy
efficient when throughput is higher because of large data may increase
complexity iin signal process algorithms which make its less energy
sufficient.

29. Comparison of SM-MIMO WITH Conventional
MIMO

30. What are Femto Cells and why we need it
• As we all know that the conventional base stations are directly
connected to the grid station which are called on grid base stations
and some on remote areas are off grid base station but they require
genertars which also consume great amount of power.
• So to avoid this power consumption femto cells was introduced.
• a femtocell is a small, low-power cellular base station, typically
designed for use in a home or small business. A broader term which is
more widespread in the industry is small cell, withfemtocell as a
subset. It is also called femtoAccessPoint(AP).

31. What are Femto Cells and why we need it

32. Experimental Evaluation
• In experimental evaluation two transmitter and two receivers are
used and they are placed at a short distance following strong line of
sight.
• As due to short distance and line of sight the channel is modeled by
Rician distribution. So 10000 information has been divided to 50
frames each containing 200 bits.
• The experimental result is very much close to the therotical one.
• However a gap at low SNR is due to timing recovery Sycronization
problems and some other similar factors.

33. Experimental Evaluation

34. Conclusion /Future work
• SM-MIMO has proved to be more efficient energy scheme than
conventional MIMO.
• However there is an need to be considered large scale anteena’s
array’s so that the transmitter and receiver are designed with low
complexity and more energy will be reduced at the transmitter end.
• There is an need to reduce more RF chains to reduce energy usage
and make the system more power efficient.

35. Comparison of different schemes using GUI
SNR=0:25db,Channel:AWGN