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Radio Technologies Basics

Radio Technologies Basics. A. f c. •. •. f. 1. T. 2. T. Radio Technologies Basics. Modulation Techniques. Symbols. Is a sinusoidal signal (carrier) with specific parameters dictated by the data bit(s), transmitted for a finite period of time

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Radio Technologies Basics

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  1. Radio Technologies Basics

  2. A fc • • f 1 T 2 T Radio Technologies Basics Modulation Techniques Symbols • Is a sinusoidal signal (carrier) with specific parameters dictated by the data bit(s), transmitted for a finite period of time • Carrier parameters do not change for the duration of the symbol • Even if the symbol itself is comprised of one single frequency (the carrier), the fact that it is transmitted over a finite period of time generates an infinite spectrum, centered on the carrier frequency Time domain Frequency domain A unmodulated carrier fc f Modulated carrier (symbols) T T = Symbol duration

  3. Radio Technologies Basics Modulation Techniques Quadrature Amplitude Modulation (QAM) • QAM is a modulation modifying the phase and the amplitude of the carrier signal • QAM symbols are represented by the carrier signal being transmitted with specific phase / amplitude (dictated by the message), for finite periods of time, symbol.

  4. Radio Technologies Basics Modulation Techniques Quadrature Amplitude Modulation (QAM) • QAM constellations (patterns) • 2 QAM (BPSK) • Two symbols are defined (1 amplitude; 2 phases) • Every symbol transmitted over the transmission channel represents(carries) 1 message bit • Baud rate = bit rate • Transmission channels limited bandwidth limits the amount of symbols per second (Baud rate) that can be transmitted • To increase the bit per sec (bps) capacity of a channel, while keeping the Baud rate at the low values imposed by the channel bandwidth, the symbols will carry (represent) more than one single bit. Symbols will represent n-bits, increasing the channel capacity by a factor of n • The price paid is the presence of multiple symbols in the channel, increasing the probability of incorrect symbol identification at the receiver

  5. Radio Technologies Basics Modulation Techniques Quadrature Amplitude Modulation (QAM) • QAM constellations (patterns) number of symbols modulation technique number of constellation generated using nr. of cosine amplitudes nr. of sine amplitudes bit rate / Baud rate number of bits per symbol amplitudes phases 2QAM (BPSK) 2 1 1/1 1 2 2 (1 bit) 0 4QAM (QPSK) 4 2 2/1 1 4 2 (1 bit) 2 (1 bit) 16QAM 16 4 4/1 3 12 4 (2 bits) 4 (2 bits) not all combinations are used

  6. Radio Technologies Basics Modulation Techniques Quadrature Amplitude Modulation (QAM) • QAM constellations (patterns) number of symbols modulation technique number of constellation generated using nr. of cosine amplitudes nr. of sine amplitudes bit rate / Baud rate number of bits per symbol amplitudes phases 64QAM 64 6 6/1 9 52 8 (3 bits) 8 (3 bits) not all combinations are used

  7. Pin Pout Radio Technologies Basics DeciBELL G=? • When trying to calculate cascade amplifiers in most cases it will be difficult using the linear way (long numbers and most of the time notround ones) • This is the reason for working in decibels G=10Log(Pout/Pin) [dB] • Power measurements units in a logarithmical world is dBm (in reference to 1mW) or dBW (in reference to 1W) • 1mW = -30dBW = 0dBm • 1W = 0dBW = 30dBm • Gain is a referenced Value without measurements units Pin Pout 1 = 0 dB 2 = 3 dB 3 = 4.7 dB 4 = 6 dB 5 = 7 dB 6 = 7.7 dB 7 = 8.5 dB 8 = 9 dB 9 = 9.5 dB 10 = 10 dB A reminder

  8. 17.5 15.5 14.5 13 sectorial Radio Technologies Basics Antenna Basics

  9. Sr [dBm] Lt [dB] Lair [dB] Lr [dB] XMT RCV Pt [dBm] Gta [dBi] Gra [dBi] Pr [dBm] For correct operation: ³ P S r r Radio Technologies Basics Power Budget Pt - Power generated by transmitter Lt - Transmit line loss Gta - Transmitter antenna gain Lair - Losses in the air Gra - Receiver antenna gain Lr - Receive line loss Pr - Power received at receiver Sr - Receiver sensitivity Pr = Pt - Lt + Gta - Lair + Gra - Lr

  10. Sr [dBm] Lt [dB] Lair [dB] Lr [dB] XMT RCV Pt [dBm] Gta [dBi] Gra [dBi] Pr [dBm] Path loss models - Clear line of sight - Free space - Dual slope - Non line of sight - Knife edge - Multiple knife edge Radio Technologies Basics Power Budget Path Loss Models

  11. Radio Technologies Basics

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