EECS 4215 Wireless Transmission

• Course: EECS 4215 Mobile Communications
• Semester: W2025, Section Z
• Topic: Wireless Transmission

Evaluation Scheme

• Assignments: 2 or 3 assignments contribute 18% to the final grade.
• Quizzes: 2 quizzes account for 17% of the final grade.
• Midterm Test: A single midterm test is worth 25%
• Final Exam: The final exam constitutes 40% of the final grade.
• Grading: Letter grades are computed using the standard YorkU mapping.
• Missed Work: There are no makeups for missed assignments or tests. Consult the Course Syllabus for details.
• Accommodation: Students needing accommodations for tests/exams should make arrangements as soon as possible.

Physical Layer Overview

• Focus is on signals, channels, and systems.
• Key signal aspects: baseband signal, modulation, bandwidth, and transmission/reception.
• Channel considerations: bandwidth, noise, attenuation, and loss.

Types of Signals

• Analog signals have continuous time and continuous values.
• Digital signals have discrete time and discrete values.
• Periodic signal: analog or digital signal that repeats over time according to the formula s(t + T) = s(t) where -∞ < t < +∞, and T is the period.
• Parameters of periodic signals include: amplitude (A), period (T), frequency (f = 1/T), and phase shift (φ).
• Sine wave: a special periodic signal typically used for a carrier, represented as s(t) = A sin(2πft + φ).

Additional Key Concepts

• Bandwidth considerations for both a signal and a channel.
• Some math for Fourier representation of periodic signals, where an ideal periodic signal can turn into a real composition
• Signals can be represented by amplitude, frequency spectrum, or constellation diagram.
• Fundamental frequency: When all frequency components of a signal are integer multiples of one frequency.
• Spectrum: Range of frequencies contained within a signal.
• Absolute bandwidth: Width of the spectrum of a signal.
• Effective bandwidth: Narrow band of frequencies containing most of the signal's energy.
• Rectangular signals have infinite bandwidth.
• Transmission systems limit the bandwidth is transmittable, and high bandwidth increases cost.
• Limiting bandwidth can cause distortions.
• Impairments like noise limit achievable data rates.
• Channel Capacity: The maximum rate at which data is transmittable over a communication channel under specified conditions.

Formulas For Bandwidth

• Nyquist Bandwidth for binary signals: C = 2B, where C is the channel capacity and B is the bandwidth.
• Nyquist Bandwidth with multilevel signaling: C = 2B log2 M, where M is the number of discrete signal levels.
• Signal-to-noise ratio (SNR): Ratio of signal power to noise power.
• (SNR)dB = 10 log10 (signal power / noise power) is used to calculate the signal-to-noise ratio in decibels.
• High SNR indicates a high-quality channel and sets an upper bound on achievable data rate.
• Shannon Capacity Formula: C = B log2(1 + SNR) defines the theoretical maximum channel capacity. This assumes white noise and does not account for impulse noise, attenuation, or delay distortion

Example Calculations

• A channel with a spectrum between 3 MHz and 4 MHz, and an SNRdB of 24 dB, has a bandwidth B = 1 MHz and SNR = 251.
• Using Shannon's formula results in a capacity C ≈ 8 Mbps. As a general guide, about 1 Mbps per 3 dB of SNR.
• The number of signalling levels that are required may be found using the following formula M = √1 + (S/N)

Modulation and Frequencies

• Frequency Bands:
• VLF: Very Low Frequency
• LF: Low Frequency
• MF: Medium Frequency
• HF: High Frequency
• VHF: Very High Frequency
• UHF: Ultra High Frequency
• SHF: Super High Frequency
• EHF: Extra High Frequency
• UV: Ultraviolet Light
• Wavelength formula is λ = c / f, with c equaling 3x10^8 m/s
• VHF/UHF are well-established and inexpensive and SHF/EHF has heavy absorption, therefore short range

Antennas

• Isotropic radiator: Equal radiation in all directions (theoretical).
• Real antennas have directive effects.
• Radiation Pattern: Measurement of radiation around an antenna.
• Gain: Maximum power in the direction of the main lobe compared to the power of an isotropic radiator.
• Simple dipoles have a shape proportional to wavelength.
• Directed and sectorized antennas are used for microwave connections or base stations.
• MIMO: use of several antennas at receiver and transmitter

Signal Propagation Range

• Normal range means that the transmission can be sent and received
• Beyond normal the signal can be detected but not communicated
• Even further the signal will only add to background EM noise
• signal Power is proportional to 1/d^2 in a vacuum, but d^3 and d^4 in the real world
• Atmospheric absorption occurs above 15 GHz

Types of Propagation

• Ground wave is typically up to 2MHz
• Sky wave of 3-30Mhz includes Ionosphere reflections
• Satellite Communication can occur above 30 Mhz

Equations for Line-of-sight

d=3.57√h for the optical line of sight d = 3.57√Kh: effective, or radio, line of sight

• d is distance between antenna and horizon (km)
• h is antenna height (m)
• K is the adjustment factor

Free Space Loss

• Free space loss is described in the following formula
• Pt / Pr= (4πd)² / λ² = (4πfd)² / c²
• Where Pt= signal power at transmitting antenna
• Pr = signal power at receiving antenna
• λ = carrier wavelength
• d = propagation distance between antennas
• c = speed of light (≈ 3 × 108 m/s)
• As an alternative FSPL(dB) = 20 log10(dkm) + 20 log10(f (GHz)) + 92.45
• Distant obstacles cause slow fading

Multiplexing

• Dimensions: space, time, frequency, and code.
• Space-division multiplexing (SDM)
• Frequency multiplexing (FDM): A channel gets a certain frequency band of the spectrum for the whole time
• Time division multiplexing (TDM): A channel gets the whole spectrum for a certain amount of time
• Time Frequency Multiplex is a combination of both and provides better protection against frequencies
• Code-division multiplexing (CDM): All channels use the same spectrum at the same time
• Polarization-division multiplexing (PDM): Each channel has a unique polarization

Modulation types

• Digital Modulation is where data converts into an analog signal
• Analog Modulation shifts the center frequency of baseband to the radio carrier

Digital Modulation

• Digital Modulation uses the shiftkey approach, which includes
• Amplitude Shift Keying (ASK)
• Frequency Shift Keying (FSK)
• Phase Shift Keying (PSK)
• Advanced Frequency Shift Keying depends on the the carries frequency.
• MSK and GMSK are equivalent to offset QPSK

Phase shift keying

• BPSK
• QPSK
• Can often transmit relativity compared to absolute
• QAM, combines amplitude and phase modulation

Hierarchical Modulation

• DVB-T modulates two separate data streams onto a single DVB-T stream

Spread Spectrum

• Technology is useful to solve the problem radio transmissions through using
• Direct Sequence (DSSS
• Frequency Hopping (FHSS

DSSS

• (DSSS)Each bit in original signal is represented by multiple bits
• One technique combines digital information stream with the spreading code bit stream using exclusive-OR

FHSS

• (FHSS)Signal broadcasts over a seemingly random set of frequencies
• Two approaches may be used
• Fast Hopping
• Slow Hopping

CDMA

• Uses different codes for receivers/ transmitters
• Relies on synchronization to minimize the incorrect noise channels

Overview of wireless transmission for EECS 4215 Mobile Communications, W2025, Section Z. Focuses on signals, channels, and systems. Key aspects include signal types, channel considerations, and the evaluation scheme for the course.