Wireless communication fundamentals form the backbone of modern connectivity. From electromagnetic wave propagation to antenna design, these principles enable seamless data transmission through the air. Understanding these concepts is crucial for tackling EMI and compatibility challenges in wireless systems.

This topic covers key aspects like modulation techniques, multiple access methods, and wireless channel characteristics. It also explores practical considerations such as link budget analysis, wireless standards, and interference mitigation strategies. These fundamentals are essential for designing robust and efficient wireless communication systems.

Electromagnetic wave propagation

• Electromagnetic wave propagation forms the foundation of wireless communication systems
• Understanding propagation mechanisms is crucial for designing effective EMI/EMC solutions
• Propagation characteristics directly impact signal integrity and interference potential in wireless systems

Free space propagation

• Describes ideal electromagnetic wave transmission through vacuum or air without obstacles
• Characterized by inverse square law, signal strength decreases proportionally to square of distance
• Free space path loss (FSPL) calculated using formula: $FSPL = (\frac{4\pi d}{\lambda})^2$
• Applies to line-of-sight communications (satellite links)
• Serves as baseline for more complex propagation models in real-world scenarios

Reflection and refraction

• Reflection occurs when electromagnetic waves encounter a boundary between two media
• Incident angle equals reflection angle according to the law of reflection
• Refraction involves change in wave direction when passing through different media
• Snell's law governs refraction: $n_1 \sin \theta_1 = n_2 \sin \theta_2$
• Reflection and refraction impact signal strength and direction in wireless environments
• Can cause multipath propagation, leading to constructive or destructive interference

Diffraction and scattering

• Diffraction allows waves to bend around obstacles or propagate through openings
• Explained by Huygens-Fresnel principle, each point on wavefront acts as a new source
• Knife-edge diffraction model used to estimate signal strength in shadowed areas
• Scattering occurs when waves encounter objects smaller than wavelength
• Rayleigh scattering affects shorter wavelengths more (explains blue sky)
• Mie scattering applies to particles comparable to wavelength (affects radar systems)

Antenna fundamentals

• Antennas serve as crucial components in wireless communication systems
• Convert electrical signals to electromagnetic waves and vice versa
• Antenna design significantly impacts EMI/EMC performance of wireless devices

Types of antennas

• Dipole antennas consist of two conductive elements, commonly used in radio applications
• Monopole antennas use a single element above a ground plane (car radio antennas)
• Patch antennas offer low-profile design for mobile devices and aircraft
• Yagi-Uda antennas provide directional gain, used in television reception
• Parabolic dish antennas offer high gain for long-distance communication (satellite dishes)
• Loop antennas used in AM radio reception and RFID systems

Antenna parameters

• Radiation pattern describes spatial distribution of radiated energy
• Gain measures antenna's ability to concentrate energy in specific directions
• Directivity quantifies antenna's ability to focus radiation in particular direction
• Bandwidth defines frequency range over which antenna operates effectively
• Polarization describes orientation of electric field in electromagnetic wave
• Input impedance affects power transfer between antenna and transmitter/receiver

Radiation patterns

• Represent three-dimensional distribution of radiated power from antenna
• Main lobe contains direction of maximum radiation
• Side lobes represent radiation in undesired directions, can contribute to interference
• Back lobe refers to radiation in opposite direction of main lobe
• Isotropic radiator serves as theoretical reference, radiates equally in all directions
• Omnidirectional antennas radiate uniformly in one plane (dipole antenna)

Modulation techniques

• Modulation enables efficient transmission of information over wireless channels
• Plays crucial role in determining spectral efficiency and interference resistance
• Proper modulation selection impacts EMI/EMC performance of wireless systems

Analog vs digital modulation

• Analog modulation varies continuous carrier signal based on analog information
• Digital modulation encodes digital data onto carrier signal
• Analog modulation techniques include AM, FM, and PM
• Digital modulation offers improved noise immunity and spectral efficiency
• Digital techniques enable advanced error correction and encryption methods
• Transition from analog to digital modulation in modern wireless systems

Amplitude and frequency modulation

• Amplitude Modulation (AM) varies carrier amplitude based on information signal
• AM susceptible to noise but simple to implement (AM radio broadcasting)
• Frequency Modulation (FM) varies carrier frequency according to information signal
• FM offers improved noise immunity compared to AM (FM radio, analog cellular systems)
• AM modulation index: $m = \frac{V_m}{V_c}$
• FM modulation index: $\beta = \frac{\Delta f}{f_m}$

Phase-shift keying

• Digital modulation technique that encodes data by changing carrier phase
• Binary Phase-Shift Keying (BPSK) uses two phase states to represent binary data
• Quadrature Phase-Shift Keying (QPSK) utilizes four phase states for improved spectral efficiency
• Higher-order PSK schemes (8-PSK, 16-PSK) increase data rate at cost of noise sensitivity
• Constellation diagram visualizes phase states and decision boundaries
• PSK widely used in wireless communication systems (Wi-Fi, satellite communications)

Multiple access methods

• Enable multiple users to share common communication channel
• Critical for efficient spectrum utilization in wireless networks
• Proper access method selection impacts system capacity and interference mitigation

FDMA vs TDMA

• Frequency Division Multiple Access (FDMA) assigns unique frequency band to each user
• FDMA used in analog cellular systems and satellite communications
• Time Division Multiple Access (TDMA) allocates specific time slots to users
• TDMA employed in GSM cellular networks and satellite systems
• FDMA offers continuous transmission but requires guard bands
• TDMA provides efficient spectrum usage but requires precise timing synchronization

CDMA principles

• Code Division Multiple Access allows multiple users to share same frequency and time
• Uses spread spectrum technology to distribute signal over wide bandwidth
• Each user assigned unique spreading code to distinguish signals
• Spreading factor determines processing gain: $G_p = \frac{BW_{spread}}{BW_{info}}$
• CDMA offers improved security and resistance to narrowband interference
• Utilized in 3G cellular networks and GPS systems

OFDM basics

• Orthogonal Frequency Division Multiplexing divides channel into multiple subcarriers
• Subcarriers orthogonal to each other, minimizing interference
• OFDM efficiently handles multipath fading and offers high spectral efficiency
• Cyclic prefix added to mitigate intersymbol interference
• OFDM forms basis for 4G LTE, Wi-Fi, and digital broadcasting systems
• OFDM symbol duration: $T_{symbol} = T_{useful} + T_{guard}$

Wireless channel characteristics

• Wireless channels introduce various impairments to transmitted signals
• Understanding channel characteristics crucial for designing robust communication systems
• Channel modeling essential for predicting EMI/EMC performance in wireless environments

Path loss models

• Describe signal attenuation as function of distance between transmitter and receiver
• Free space path loss model serves as baseline for ideal conditions
• Log-distance path loss model accounts for environmental factors: $PL(d) = PL(d_0) + 10n \log(\frac{d}{d_0})$
• Okumura-Hata model used for urban and suburban environments
• COST-231 Hata model extends Okumura-Hata for higher frequencies
• Path loss exponent varies based on environment (2 for free space, 4-6 for urban areas)

Multipath fading

• Results from signal arriving at receiver via multiple paths with different delays
• Causes fluctuations in received signal strength and phase
• Rayleigh fading model applies to non-line-of-sight scenarios
• Rician fading model used when dominant line-of-sight path exists
• Delay spread quantifies time dispersion of multipath components
• Coherence bandwidth indicates frequency range over which channel response remains correlated

Doppler effect

• Occurs when transmitter or receiver in motion relative to each other
• Causes frequency shift in received signal: $f_d = \frac{v}{\lambda} \cos \theta$
• Doppler spread measures range of frequency shifts due to motion
• Coherence time indicates duration over which channel remains relatively constant
• Affects fast-moving objects (high-speed trains, aircraft)
• Doppler effect impacts performance of mobile communication systems

Link budget analysis

• Quantifies all gains and losses in wireless communication system
• Essential for predicting system performance and coverage
• Crucial tool for EMI/EMC analysis in wireless network planning

Transmit power

• Defines power level at which signal is transmitted from antenna
• Measured in watts (W) or decibel-milliwatts (dBm)
• Regulated by authorities to limit interference and ensure safety
• Higher transmit power increases coverage but may cause interference
• Effective Isotropic Radiated Power (EIRP) accounts for antenna gain: $EIRP = P_t + G_t$
• Power amplifiers used to boost transmit power in wireless systems

Receiver sensitivity

• Minimum signal power required for acceptable receiver performance
• Typically specified as signal power yielding specific bit error rate (BER)
• Depends on noise figure, bandwidth, and required signal-to-noise ratio
• Receiver sensitivity calculation: $S = -174 + 10 \log(BW) + NF + SNR_{req}$
• Improved sensitivity enables reception of weaker signals
• Low-noise amplifiers (LNAs) used to enhance receiver sensitivity

Signal-to-noise ratio

• Ratio of desired signal power to noise power at receiver
• Expressed in decibels (dB)
• Higher SNR indicates better signal quality and lower error rates
• SNR calculation: $SNR = 10 \log(\frac{P_{signal}}{P_{noise}})$
• Minimum required SNR depends on modulation scheme and error rate requirements
• SNR impacts achievable data rate in wireless systems

Wireless standards

• Define protocols and specifications for wireless communication systems
• Ensure interoperability between devices from different manufacturers
• Crucial for managing EMI/EMC issues in complex wireless environments

Wi-Fi protocols

• IEEE 802.11 family of standards for wireless local area networks (WLANs)
• 802.11a/b/g/n/ac/ax define different generations of Wi-Fi technology
• Operate in 2.4 GHz and 5 GHz unlicensed bands
• Employ various modulation schemes (OFDM, MIMO) for improved performance
• Implement carrier sense multiple access with collision avoidance (CSMA/CA)
• Wi-Fi 6 (802.11ax) introduces OFDMA for improved efficiency in dense environments

Cellular networks

• Global System for Mobile Communications (GSM) established 2G cellular standard
• UMTS and CDMA2000 formed basis for 3G networks
• Long-Term Evolution (LTE) defines 4G cellular technology
• 5G New Radio (NR) enables high-speed, low-latency communications
• Cellular networks utilize licensed frequency bands to minimize interference
• Employ various multiple access techniques (TDMA, CDMA, OFDMA)

Bluetooth technology

• Short-range wireless communication standard for personal area networks (PANs)
• Operates in 2.4 GHz ISM band using frequency hopping spread spectrum (FHSS)
• Bluetooth Low Energy (BLE) designed for low-power applications
• Utilizes adaptive frequency hopping to mitigate interference
• Supports various profiles for different applications (audio, file transfer, health devices)
• Bluetooth 5.0 introduces longer range and higher data rates

Interference in wireless systems

• Interference poses significant challenge to wireless communication reliability
• Understanding interference mechanisms crucial for effective EMI/EMC management
• Proper interference mitigation techniques essential for optimal system performance

Co-channel interference

• Occurs when multiple transmitters use same frequency channel simultaneously
• Common in cellular networks with frequency reuse
• Signal-to-interference ratio (SIR) quantifies impact of co-channel interference
• Frequency reuse factor determines trade-off between capacity and interference
• Beamforming and MIMO techniques help mitigate co-channel interference
• Power control algorithms adjust transmit power to minimize interference

Adjacent channel interference

• Results from imperfect filtering allowing signal energy to leak into nearby channels
• Adjacent Channel Power Ratio (ACPR) measures amount of signal leakage
• Proper channel spacing and guard bands help reduce adjacent channel interference
• Spectral mask defines allowable out-of-band emissions
• Digital modulation techniques with better spectral efficiency reduce ACI
• Adaptive filtering techniques employed to suppress adjacent channel interference

Intersymbol interference

• Occurs when symbols overlap due to multipath propagation or bandwidth limitations
• Causes distortion and increased error rates in digital communication systems
• Nyquist criterion defines minimum bandwidth for ISI-free transmission
• Raised cosine filtering used to shape pulses and minimize ISI
• Equalization techniques compensate for channel-induced ISI
• OFDM with cyclic prefix effectively combats ISI in multipath environments

Error correction techniques

• Enable reliable communication over noisy wireless channels
• Critical for maintaining data integrity in presence of interference
• Proper error correction selection impacts system performance and EMI/EMC robustness

Forward error correction

• Adds redundancy to transmitted data to detect and correct errors at receiver
• Block codes (Reed-Solomon, BCH) operate on fixed-size blocks of data
• Convolutional codes process continuous stream of data
• Turbo codes and Low-Density Parity-Check (LDPC) codes offer near-Shannon limit performance
• Coding gain measures improvement in SNR due to error correction
• FEC widely used in wireless standards (Wi-Fi, cellular networks, satellite communications)

Interleaving

• Rearranges data bits or symbols to spread burst errors over multiple codewords
• Block interleaving operates on fixed-size blocks of data
• Convolutional interleaving provides continuous interleaving process
• Interleaving depth determines effectiveness against burst errors
• Often used in conjunction with FEC to improve overall error correction capability
• Particularly effective in combating fading channels and impulse noise

Diversity techniques

• Exploit multiple uncorrelated signal paths to improve reliability
• Spatial diversity uses multiple antennas at transmitter or receiver
• Frequency diversity transmits information over multiple frequency channels
• Time diversity repeats information at different time intervals
• Polarization diversity utilizes different signal polarizations
• Maximal Ratio Combining (MRC) optimally combines diversity branches
• MIMO systems leverage spatial diversity to increase capacity and reliability