Advanced Wireless Communications lecture notes: section 4
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Advanced Wireless Communications lecture notes: section 4 Andrea M. Tonello Double Master Degree in Electrical Engineering ‐ University of Udine, Italy and Information and Communication Engineering ‐ University of Klagenfurt, Austria Note: these lecture notes have been prepared as part of the material for the joint class “Advanced wireless communications” and “Comunicazioni Wireless” by A. Tonello. The class has been offered in the Spring 2015 term, by means of video conferencing in time sharing between two locations.
Transcript of Advanced Wireless Communications lecture notes: section 4
Advanced Wireless Communications
lecture notes: section 4
Andrea M. Tonello
Double Master Degree in Electrical Engineering ‐ University of Udine, Italy
and Information and Communication Engineering ‐ University of Klagenfurt, Austria
Note: these lecture notes have been prepared as part of the material for the joint class “Advanced wireless communications” and “Comunicazioni Wireless” by A. Tonello. The class has been offered in the Spring 2015 term, by
means of video conferencing in time sharing between two locations.
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Section content Topics
oMulticarrier modulation
oDiscrete time system representation
oOrthogonality principle: DMT and FMT
oOFDM with cyclic prefix
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System model
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System model
ADSL : advanced digital subscriber line
DAB : digital audio broadcast
DVB : digital video broadcast
IEEE 802.11 and Hiperlan II : wireless LAN
proposed although killed for 3rd generation cellular
Adopted in LTE
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General architecture
( )t
10( )a lT
0( )ka lT
kf
0( )My nT
10( )y nT 1
0ˆ ( )a lT
0ˆ ( )Ma lT
1f
Mf
1f
0( )Ma lT
Mf
0( )ky nT 0ˆ ( )ka lT
kf
Two efficient digital implementations
DMT (Discrete Multitone): well known OFDM (orthogonal frequency division multiplexing)
scheme. Prototype filter with rectangular impulse response
FMT (Filtered Multitone): prototype pulse with frequency concentrated response
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System model
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System model
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Discrete time realization
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Discrete time realization
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Discrete time realization
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Receiver
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Receiver
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Receiver output signal
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Bidimensional Nyquist criterion
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Bidimensional Nyquist criterion
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Orthogonal solutions
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Orthogonal solutions (DMT‐OFDM‐FMT)
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Comparison of SNR in SC and MRC
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OFDM
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OFDM
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Efficient realization of an FMT system
Complexity: M/N log2M + Lg,h /N operations/sample
M point IDFT and cyclic extension to 2 1 2. . .( , )M l c m M N L M L N( )( ) ( ) 0,..., 1ig nN g i nN i N Pulses: PP components of order N, i.e.,
2L Sample with period
Synthesis
Dual operations Analysis
(Lg,h: pulse length)
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OFDM with Cyclic Prefix
M tones (sub‐channels)
Rectangular sub‐channel pulse (window) of duration N > M samples
Cyclic prefix (CP) of length µ=N‐M samples (longer than the channel duration)
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OFDM with cyclic prefix
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OFDM with cyclic prefix
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OFDM with cylic prefix
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OFDM with cylic prefix
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OFDM with cylic prefix
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OFDM design
Knowing the channel duration NpT and the total signal bandwidth
W=1/T, we choose CP of length μ samples larger than Np
Then, we set the number of sub‐channels M so that the rate penalty
is not too high:
R = M / ((M+ μ)T)
Transmission rate in CP‐OFDM
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Main advantages of multicarrire modulation
MC modulation allows to simplify the equalization task
CP‐OFDM is orthogonal is a multipath channel
The power can be optimally allocated over the sub‐channels
Spectrum notching can be easily applied
FDMA can be easily implemented to multiple in the frequency
domain multiple users
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Optimal power allocation in OFDM
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