robotics

1. ZZZ DEPT. OF ELECTRICAL ENGINEERING Thursday, August 12, 2021 1
Registration Seminar
Frequency Synchronization
Carrier Frequency Offset (CFO)
• CFO cause : Mismatch of oscillator frequency
: Doppler frequency shift
• CFO Effect : Loss of orthogonality
: Inter-carrier interference (ICI) and multiple access interference (MAI)
Normalized CFO ϵ =
𝑓offset
Subcarrier Spacing
; ϵ ∈ (−0.5, 0.5)
CFO disturbs orthogonality

2. ZZZ DEPT. OF ELECTRICAL ENGINEERING Thursday, August 12, 2021 2
Registration Seminar
Effect of CFO
Constellation of received symbol with CFO : (a) 𝝐 = 0 (b) 𝝐 =0.03 (c) 𝝐 = 0.5
Table 2 : The effect of CFO on received signal (CFO)
Received Signal Effect of CFO 𝛜 on received
signal
Time-domain y[n] 𝑒
𝑗2𝜋𝑛𝜖
𝑁 𝑥[𝑛]
Frequency-domain Y[k] X[𝑘 − 𝜖]

3. ZZZ DEPT. OF ELECTRICAL ENGINEERING Thursday, August 12, 2021 3
Registration Seminar
Multiple-Input Multiple-Output OFDM
• MIMO supports high data rate through several parallel data streams.
• OFDM techniques is most favored multicarrier access technology over multipath fading channels.
• MIMO-OFDM is a combination of Multiple-Input Multiple-Output (MIMO) wireless technology with that of
OFDM, to further increase the rate in broadband multi-antenna wireless system.
• Similar to OFDM, MIMO-OFDM converts a frequency-selective MIMO channel into multiple parallel flat
fading MIMO channels.
• Hence, MIMO-OFDM significantly simplifies baseband receive processing by eliminating the need for a
complex MIMO equalizer.
MIMO system

4. ZZZ DEPT. OF ELECTRICAL ENGINEERING Thursday, August 12, 2021 4
Registration Seminar
Cont’d...
[9] R. Gupta, S. Kumar, and S. Majhi, “Blind modulation classification for asynchronous ofdm systems over unknown signal parameters and channel statistics, ”
IEEE Transactions on Vehicular Technology, vol. 69,no. 5, pp. 5281–5292, 2020.
Histogram of 𝑪𝟒𝟐𝑹
for BPSK, QPSK, OQPSK, MSK, and
16-QAM
Histogram of 𝑪𝟒𝟐𝑼
for BPSK and QPSK

5. ZZZ DEPT. OF ELECTRICAL ENGINEERING Thursday, August 12, 2021 5
Registration Seminar
Authors Features Modulations Parameter Channel Classification
Accuracy
(At 20dB SNR)
D. Shimbo [7] Amplitude Moment and
Correlation
16-QAM and 64-QAM Prior knowledge about CFO Rayleigh -
A. D. Pambudi
[8]
Mean, Variance, skewness,
kurtosis index and moment
order
QPSK, 16-QAM and
64QAM
- Rayleigh -
R. Gupta [9] Discrete Fourier transform
(DFT) and normalised fourth
order cumulant
BPSK, QPSK, OQPSK,
MSK and 16-QAM
Unknown Signal
Parameters and CSI and
imperfect synchronization
Rayleigh 97.5 %
Y. Liu [10] Gibbs sampling convergence
method
QPSK,8-PSK, 16-PSK,
and 16-QAM
Imperfect CSI and unknown
SNR
Flat fading 100 %
Table 4: Summary of features-based classifiers
Literature survey

6. ZZZ DEPT. OF ELECTRICAL ENGINEERING Thursday, August 12, 2021 6
Registration Seminar
Author(s) Features extraction Algorithm Modulation(s) Parameter(s) Channel Classification
Accuracy
(At 20dB
SNR)
S. E. El-Khamy
[11]
Higher order moments and
cumulants, Fuzzy K-Means
and Fuzzy C-means
BPSK, QPSK, 8-PSK, 16-
QAM, 32-QAM and 64-QAM.
- AWGN and
Rayleigh
100 %
X. Yuan [12] Higher-order cumulants,
random forest based
AMC algorithm
BPSK, QPSK, 8-PSK, 16-
QAM, and 64-QAM.
Imperfect time
synchronization
Frequency
Selective
100 %
Y. Zhang [13] Higher order cumulants and Decision
Tree Classifier
OFDM, BPSK, QPSK,
GFSK, 16-QAM, and 64-
QAM
Presence of
timing offset
Flat fading 99.5 %
Y. Zhang [14] K-Nearest Neighbors (KNN), Support
Vector Machine (SVM), Decision Theory
(DT), Back Propagation Neural Network
(BPNN)
OFDM, BPSK, QPSK, GFSK,
16-QAM, 64-QAM
Presence of
CFO
and Imperfect
CSI
Rayleigh 99.2 %
Table 5: Summary of machine learning based classifiers
Machine Learning based AMC

7. ZZZ DEPT. OF ELECTRICAL ENGINEERING Thursday, August 12, 2021 7
Registration Seminar
Cont’d...
The discrete baseband OFDM samples 𝑑𝑚[𝑛] of 𝑚𝑡ℎ
OFDM symbol, generated by 𝑁-point inverse discrete
Fourier Transform (IDFT), can be written as
𝑑𝑚 𝑛 = 𝑘=0
𝑁−1
𝐷𝑚 𝑘 𝑒𝑗2𝜋𝑘𝑛/𝑁 , 0 ≤ 𝑛 ≤ 𝑁 − 1 ,
where 𝑁 = 𝜌𝑆 × 𝑁0, 𝜌𝑆 is the oversampling factor, 𝑁0 is the number of data subcarriers, 𝐷𝑚 𝑘 is the baseband
modulated oversampled data obtained by zero padding the baseband modulated information 𝐷𝑚 𝑘 . Thus, 𝐷𝑚 𝑘
is given by
𝐷𝑚 𝑘 =
𝐷𝑚 𝑘 0 ≤ 𝑘 ≤
𝑁0
2 − 1
𝑍0
𝑁0
2 ≤ 𝑘 ≤ 𝑁0( 𝜌𝑆−1/2)−1
𝐷𝑚 𝑘 𝑁0( 𝜌𝑆−1/2) ≤ 𝑘 ≤ N−1,
where 𝑍0 is a vector of zeros of length 𝑁0 𝜌𝑆−1

8. ZZZ DEPT. OF ELECTRICAL ENGINEERING Thursday, August 12, 2021 8
Registration Seminar
Cont’d...
The transmitted baseband OFDM symbol 𝑑𝑚 𝑛 of length 𝑁 + 𝑁𝑐𝑝, with CP is then given by
𝑑𝑚 𝑛 =
𝑑𝑚 𝑛 + 𝑁 −𝑁𝑐𝑝 ≤ 𝑛 ≤ −1
𝑑𝑚 𝑛 0 ≤ 𝑛 ≤ 𝑁 − 1 ,
After passing through a frequency-selective fading channel with impulse response g[𝑙] of length 𝐿, the received
baseband OFDM samples of the 𝑚𝑡ℎ
OFDM symbol is given by
𝑥𝑚 𝑛 = 𝑒(
𝑗2𝜋𝜖𝑛
𝑁
+𝜙)
𝑙=0
𝐿−1
𝑔 𝑙 𝑑𝑚 𝑛 − 𝑙 − 𝜏 + 𝜔(𝑛), 0 ≤ 𝑛 ≤ 𝑁𝑠 − 1 .
where 𝜖 is the normalized carrier frequency offset (CFO), 𝜙 is the phase offset, 𝜏 is the symbol timing offset
(STO), 𝑁𝑠 length of the OFDM symbol with CP, 𝑁𝑠 =𝑁 + 𝑁𝑐𝑝 and 𝑁𝑐𝑝≥ 𝐿 and 𝜔 𝑛 is the additive white
Gaussian noise (AWGN) with zero mean and variance 𝜎𝜔
2
.