Class Notes

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path includes ECT402

2024-12-17

• Multi carrier Modulation
  if no noise$$y(t)=s(t)=\sum _i{X}_i{e}^{j2\pi f_{i}t}$$

• OFDM
• Intersymbol Interference

2024-12-31

MIMO OFDM(OFDMA)

• Combination of multiple-input multiple-output with OFDM

graph LR
A[SP Demux for transmit antennas] --> B[S/P Demux]
A --> C[S/P Demux]
B --> EM[N pt FFT]
A --> D[S/P Demux]
C--> E[N pt FFT]
D--> EE[N pt FFT]

E  --> K[MIMO Detection]
EE  --> LK[MIMO Detection]

• Complete

Effect of Freq Offset in OFDM

• Due to variations in orthogonality
• Inter Carrer Interference (ICI) in OFDM

Where $ϵ$ -> normalized freq offset

Peak to average Power Ratio (PAPR)

• Correct

Single Carrier FDMA(SC-FDMA)

• To reduce the Peak to avg power ratio

• PAPR -> $0dB$

• Picture

graph LR

AA[Symbol Stram]
A[S/P demux ]
B[N pt FFT]
C[N pt IFFT]
D[P/S Mux]
E[Add CP]

AA --> A --> B --> C --> D --> E
AA --> A --> B --> C --> D --> E
AA --> A --> B --> C --> D --> E

Hypothetical

SC_FDMA Reciever

• Sub Carrier Mapping

Sub carrier mapping in SC-FDMA

PathLoss , Shadowing , Doplar Shift

06-01-25

Path loss

• inv.prop Wavelength

Shadowing

Cause-> Scattering, reflection,and diffration -> results in signal degredation
eg: indor wifi signal cant penetrate through walls

[[#Path loss]] & [[#Shadowing]] -> Large scale fading

Multi path effect

• [ ]
• Due to reflections
• Causes: Fading , phase change

Diversity Techniques

• Used to compensate for fading channels

• implemented by using two or more receiving antenas,

• done by transmitting ultiple copies

• [[#Space Diversity]]

• [[#Freq Diversity]]

• [[#Angle Diversity]]

• [[#Time Diversity]]

Space Diversity

graph LR
Tx -- path --> Rx

• Multiple antennas are used to receive Rx

Freq Diversity

• Some freq. fading will be more
• Same info send using multiple carriers
• ie $s_1(t)$ and $s_2(t)$ will carry the same info.

Angle Diversity

Time Diversity

• Uses different timeslots ,

Polarization Diversity

• Uses antennas with different polarization

graph LR

21-02-25

802.11

• DSSS or FHSS -> 802.11(old) -> 1,2 Mbps

802.11a

• Intr OFDM
• 5Ghz Op band
• 54 Mbps

5Ghz bandwidth is devided into 3 ->

802.11b

• 2.4GHz
• upto 11Mbps
• Uses Complementary COde Keying(CCK)

802.11g

• 2.4GHz
• 1Mbps to 54Mbps
• Intr FEC(Fwd Error Correction)
• Lower DR
• High {6,9,12,18,24,36,48,54} <- By using OFDM

802.11n

• upto 100Mbps
• Introduced MIMO

802.11ac( WiFi 5)

• 5Ghz Band
• Multi User MIMO , 256 QAM

802.11 ax(WiFi 6)

• More efficient

Hyperlan

• alt
• div

Hyperlan1

• 20Mbps in 5GHz Range

2

• 54Mbps <- Infrastruycture model

Hyper access

• Used to provide remote access upto 5Km range

Hyper link

used to connect to the backbone

graph LR
node_1 --> node_2 & node_3 --> node_4 --> node_5 & node_6

• Multihub topology with ?
• Complete WiMax and Wi??? form other notes

03-03-25

802.16 WMAN (Metropolitan AN)

• 10GHz - 66Ghz
• IEEE802.16a -> WiMAX

Protocol arch

• 20Mhz , 25Mhz in US , 28 in Europe (channel BW)
• uses TDMA (Uplink)

WiMAX

WiMAX (Worldwide Interoperability for Microwave Access)

• 2-11GHz Bands

• 1.25MHz to 22MHz

• Fixe vs mobile WiMAX

Millimeter wave technology

• 10 to 1mm
• 30 - 300 GHz (EHF range)

Channel Perfomance at 60Ghz

• TODO:

=======

06-03-25

DES (Data Encryption Standard)

AES <- DES

• Block Cipher
• Block size 64 bits , KKey size 56 bits

graph LR
A[Plaintext] --> B[Initial Permutation]
B --> C[16 Rounds]
C --> D[Final Permutation]

Single Round DES

• Split the 64 bit block into two 32 bit blocks

• Key is split 28 bits each

• Keep track of permutation?

• Complete below

• [ ]

graph TD
subgraph DES Round
A[32 bit block] --> B[Expansion]
B --> C[XOR with Key]
C --> D[Substitution]
D --> E[Permutation]
end
subgraph  Key Schedule
F[56 bit key] --> G[Split]
G --> H[Shift]
H --> I[Compression]
end

Avelaanche Effect

flowchart TB
c1-->a2
subgraph one
a1-->a2
end
subgraph two
b1-->b2
end
subgraph three
c1-->c2
end