RF Fundamentals

Motorola Confidential Proprietary

RF FundamentalsRF Fundamentals


• Intro

• Part 1 - RF Concepts

• Part 2 - RF System Parameters

• Part 3 - Transceiver Architectures

•• Intro Intro

•• Part 1 - RF Concepts Part 1 - RF Concepts

•• Part 2 - RF System Parameters Part 2 - RF System Parameters

•• Part 3 - Transceiver Architectures Part 3 - Transceiver Architectures

RF FundamentalsRF Fundamentals


RF DefinedRF Defined

• Acronym used to describe a variety of systems that use Radio Frequencysignals as a means to communicate Information from point to point, orpoint to multi-point.

• Information transmitted and received may represent analog or digitalversions of the baseband signal (e.g. voice, video, data, etc.).

• This Information rides on the RF carrier.

• Acronym used to describe a variety of systems that use Radio Frequencysignals as a means to communicate Information from point to point, orpoint to multi-point.

• Information transmitted and received may represent analog or digitalversions of the baseband signal (e.g. voice, video, data, etc.).

• This Information rides on the RF carrier.


Benefits to RFBenefits to RF• Essential for mobile/portable wireless communications systems

• Efficient alternative to wireline methods that be impractical or too slow

to deploy (e.g. WLL, MMDS, LMDS).

• The physical length of the Antenna required for transmission and reception of

the info depends on signal wavelength, λ, which is inversely proportional to the

frequency, f, of the transmitted signal.

The minimum length of an antenna must be quarter-wave (λ/4) or half-wave (λ/2).

So, ……the higher the RF frequency, the smaller the antenna dimensions.

• Essential for mobile/portable wireless communications systems

• Efficient alternative to wireline methods that be impractical or too slow

to deploy (e.g. WLL, MMDS, LMDS).

• The physical length of the Antenna required for transmission and reception of

the info depends on signal wavelength, λ, λ, which is inversely proportional to the

frequency, f, of the transmitted signal.

The minimum length of an antenna must be quarter-wave (λ/4) or half-wave (λ/2).

So, ……the higher the RF frequency, the smaller the antenna dimensions.

λλ00 = = c/f c/f c = speed of light, 3x10c = speed of light, 3x1088m/sm/s

λλ00 = wavelength in free space = wavelength in free space


Basic Wireless SystemBasic Wireless System

RFin

RFout

Power ManagementPower Management

MIC

SPKR

KeypadKeypad

DisplayDisplay

MemoryMemory

BasebandDSP/MCU Processor


Data

Baseband

LO1

LO

FrequencySynthesizerFrequencySynthesizer

“Info”TransmitterTransmitter

Transceiver

Antenna“Info”ReceiverReceiver

Switch/DuplexerSwitch/

Duplexer


RF ConceptsRF Concepts


RF ConceptsRF Concepts• dB, Gain• Noise Factor and Noise Figure• Linearity and Compression• Intermodulation• Third order Intercept• C/I, Carrier to Interference• MDS, Sensitivity• Impedance Matching• Reflection Coefficient• Mismatch Loss• Frequency Conversion• Frequency Synthesis

•• dB, Gain dB, Gain•• Noise Factor and Noise Figure Noise Factor and Noise Figure•• Linearity and Compression Linearity and Compression•• Intermodulation Intermodulation•• Third order InterceptThird order Intercept•• C/I, Carrier to Interference C/I, Carrier to Interference•• MDS, Sensitivity MDS, Sensitivity•• Impedance Matching Impedance Matching•• Reflection Coefficient Reflection Coefficient•• Mismatch Loss Mismatch Loss•• Frequency Conversion Frequency Conversion•• Frequency Synthesis Frequency Synthesis


•Decibels, or dB, is a logarithmic function used to measure the ratioof two numbers, typically Power Gain or Voltage Gain.

•Decibels, or dB, is a logarithmic function used to measure the ratioof two numbers, typically Power Gain or Voltage Gain.

P1=10 mW P2=200 mW

G = 10 log (200/10) = 13dB

V1=10mV V2=200 mV

G = 20 log (200/10) = 26dB

Decibel (dB) and Gain (G)Decibel (dB) and Gain (G)

“Power”“Power” “Voltage”“Voltage”

Gain = 10log (P2/P1) Gain = 20log(V2/V1)


Decibel (dB), RelativeDecibel (dB), Relative

Some Decibel measurements are referenced to a commonvalue, for example:

• dBm, measures the Power level referenced to 1mW, e.g.

• dBmV, measures the Voltage level referenced to 1mV, e.g

Others include…... • dBc, measures Power relative to an RF carrier• dBW, measures Power relative to 1W

Some Decibel measurements are referenced to a commonvalue, for example:

• dBm, measures the Power level referenced to 1mW, e.g.

• dBmV, measures the Voltage level referenced to 1mV, e.g

Others includeOthers include…...…... • dBc, measures Power relative to an RF carrier• dBW, measures Power relative to 1W

1W of power = 10 log (1W/1mW) = 30dBm

100mV signal = 20 log (100mV/1mV) = 40dBmV


Noise Factor (F)Noise Factor (F)

Noise Factor, F, is a measure of the amount of noise that anamplifier or other function adds to a signal.

F can be computed as the change in Signal to Noise Ratio (S/N) between the input and output of an RF function,

Noise Factor, FF, is a measure of the amount of noise that anamplifier or other function adds to a signal.

FF can be computed as the change in Signal to Noise Ratio (S/N) between the input and output of an RF function,

F = (S/N)F = (S/N)ININ /(S/N) /(S/N)OUTOUT

(S/N)IN (S/N)OUT


Noise Figure (NF)Noise Figure (NF)

Noise Figure, NF, is the Noise Factor, F expressed indecibels.

NFdB = 10log(F), …..or

NFdB = (S/N)IN, dB - (S/N)OUT, dB

Noise Figure, NF, NF, is the Noise Factor, FNoise Factor, F expressed indecibels.

NF NFdBdB = 10log(F), …..or = 10log(F), …..or

NFNFdBdB = = (S/N)(S/N)IN, dBIN, dB - (S/N) - (S/N)OUT, dBOUT, dB

(S/N)1=15dB (S/N)2=11dB

NF = 4dB


Cascaded Noise FigureCascaded Noise Figure

System Noise Figure, NFSYS can be found by cascadingthe NF of each block or function in the Receiver chain.

NFSYS = 10log(FTotal), where FTotal can be expressed as:

System Noise Figure, NFNFSYSSYS can be found by cascadingthe NF of each block or function in the Receiver chain.

NFNFSYSSYS = 10log(FTotal), where FTotal can be expressed as:

F=F1Gain =G1

F=F1Gain =G1

F=F2Gain =G2

F=F2Gain =G2

F=F3Gain =G3

F=F3Gain =G3

1st Stage 2nd Stage 3rd Stage

F=FN

Gain =GN

F=FN

Gain =GN

Nth Stage

ReceiveIN

FTotal = F1 + (F2 - 1)/G1 + (F3 - 1)/G1G2 + …… (FN -1)/G1G2G3…GN-1


LinearityLinearity

POUT

PIN

• Linearity is the ability of a device (e.g. amplifier) to maintain a constant

Gain over the range of input power levels, PIN

• Linearity is the ability of a device (e.g. amplifier) to maintain a constant

Gain over the range of input power levels, PIN

POUTPIN POUT


Gain CompressionGain Compression

Actual

IdealPOUT

PIN

∆ = 1dB

P1dB

• As input Power, Pin, increases, the device enters saturation and starts to exhibitGain Compression.

Gain compression is the reduction in Gain due saturation.

• The 1dB Compression point, P1dB, is the value of PIN where the reduction isexactly 1dB.

• As input Power, Pin, increases, the device enters saturation and starts to exhibitGain Compression.

Gain compression is the reduction in Gain due saturation.

• The 1dB Compression point, P1dB, is the value of PIN where the reduction isexactly 1dB.

POUTPIN POUT


IntermodulationIntermodulation

• With two or more signals at the input of an amplifier , non-linearities of the

device will generate unwanted harmonics and Intermodulation products inaddition to the fundamental signals at the output.

• With two or more signals at the input of an amplifier , non-linearities of the

device will generate unwanted harmonics and Intermodulation products inaddition to the fundamental signals at the output.

f1

f2

desired

undesired

f1 , f2 fundamentals

2nd order intermodf2+/-f1 , f1+/-f2

n x f1 , n x f2 harmonics

3rd order intermod2f2 +/- f1 , 2f1 +/- f2


Intermodulation Intermodulation ((cont’dcont’d))

part of the resulting spectrum……...

f1 f2

fundamentals

2f2 - f12f1 - f2

3rd Order 3rd Order

f2 + f1f2 - f1

2ndOrder

2ndOrder

2f1 2f2

2nd Harmonics

• 3rd order Intermodulation products are close to the desired signalmaking them difficult to filter out.

• 3rd order Intermodulation products are close to the desired signalmaking them difficult to filter out.


Third Order Intercept PointThird Order Intercept Point

fundamental

P1POUT

PIN

3rd Order

P3

1

1

31

iip3

• 3rd order Intermodulation products increase 3x the fundamental.• For every 1dB increase in Pin, P1 increases by 1dB (linear region) butP3 increases by 3dB

• 3rd order Intermodulation products increase 3x the fundamental.• For every 1dB increase in Pin, P1 increases by 1dB (linear region) butP3 increases by 3dB

• 3rd order intercept point, iip3 is thetheoretical Pin value where P3 and P1 meet.• Saturation prevents this intersection fromoccuring.• iip3 is a measure of a device’s Linearity.

• 3rd order intercept point, iip3 is thetheoretical Pin value where P3 and P1 meet.• Saturation prevents this intersection fromoccuring.• iip3 is a measure of a device’s Linearity.

Actual P1

Actual P3


C/I, Carrier to InterferenceC/I, Carrier to Interference

carrier

Interferer

•Carrier to Interference, C/I, is a ratio between the desired signal carrier and level ofinterference.

• Noise and other sources of interference are included in the denominator.

•C/I is given as the margin required for digital wireless system to maintain through thereceiver chain to achieve a specified minimum Bit Error Rate (BER).

•Carrier to Interference, C/I, is a ratio between the desired signal carrier and level ofinterference.

• Noise and other sources of interference are included in the denominator.

•C/I is given as the margin required for digital wireless system to maintain through thereceiver chain to achieve a specified minimum Bit Error Rate (BER).

C/I

C/N

noise


MDS, SensitivityMDS, Sensitivity

•Minimum Detectable Signal, MDS, is given as the minimum signal at the inputof a receiver that causes a detectable signal at the output.

• MDS factors in the thermal noise plus the total noise contribution from the receiver orF(Total)

•Minimum Detectable Signal, MDS, is given as the minimum signal at the inputof a receiver that causes a detectable signal at the output.

• MDS factors in the thermal noise plus the total noise contribution from the receiver orF(Total)

MDS = F(total) kT0 (B)

MDS = -174dBm + NF(SYS) + 10log (B)

MDS = F(total) kT0 (B)

MDS = -174dBm + NF(SYS) + 10log (B)

k= Boltzman’s constant, B = noise bandwidth of the systemT0 is temp in Kelvin NF(SYS) is system Noise FigureF(total) is Total Noise Factor


MDS, Sensitivity (MDS, Sensitivity (cont’dcont’d))

•System Sensitivity, is the minimum signal that’s needed toprocess the received information and maintain the C/I and BERspecifications

•System Sensitivity, is the minimum signal that’s needed toprocess the received information and maintain the C/I and BERspecifications

System Sensitivity = -174dBm + NF(SYS) + 10log (B) + C/ISystem Sensitivity = -174dBm + NF(SYS) + 10log (B) + C/I

B = noise bandwidth of the system C/I is Carrier to Interference marginNF(SYS) is system Noise Figure


Impedance MatchingImpedance Matching

•Impedance Matching is the process where the output impedanceof one device is designed to match the input impedance of thefollowing device for maximum Power Transfer.

•Impedance Matching is the process where the output impedanceof one device is designed to match the input impedance of thefollowing device for maximum Power Transfer.

Vs+

Rs

RLLoadSource

V1

V1 = (Vs) RL / ( Rs + RL )

setting Vs=1, Rs=1 forconvenience,

V1 = RL / ( 1 + RL )

Power delivered to RL:

P1 =V1 2 / RL

P1

RL

0.1 101.0

For Maximum Power transfer RL = RSFor Maximum Power transfer RL = RS


Reflection CoefficientReflection Coefficient

• When the Load Impedance ZL does not match the Source Impedance ZS ,part of the incident wave is reflected back to the source.

• When the Load Impedance ZL does not match the Source Impedance ZS ,part of the incident wave is reflected back to the source.

Vs

+

Zs

ZL

LoadSource

Incident

Reflected

Γ = (ZL - Zs)/(ZL + Zs)Γ = (ZL - Zs)/(ZL + Zs)

e.g. if ZL= 200Ω, and ZS = 50Ω Γ = 150/250 = 0.6

e.g. if ZL= 200Ω, and ZS = 50Ω Γ = 150/250 = 0.6

• Reflection Coefficient, Γ, is an indication of how good the match is.Γ = 0 is an ideal match. Γ = -1 (short) or +1 (open) is a perfect mismatch.


Mismatch LossMismatch Loss

•Mismatch Loss, ML is the amount of signal Power that’slost as a result of an impedance mismatch.•Mismatch Loss, ML is the amount of signal Power that’slost as a result of an impedance mismatch.

Vs+

Zs=50Ω

ZL= 200ΩLoadSource

ML = -10log(1-(Γ)2)ML = -10log(1-(Γ)2)

e.g. with Γ =0.6ML= 1.9dB losse.g. with Γ =0.6ML= 1.9dB loss


Frequency ConversionFrequency Conversion

• Frequency Conversion shifts the frequency of a signal either Down or Up.

• The device used to perform the frequency conversion is a Mixer. The Mixerproduces sum (RF+LO) and difference (RF-LO) frequency products.

• Frequency Conversion shifts the frequency of a signal either Down or Up.

• The device used to perform the frequency conversion is a Mixer. The Mixerproduces sum (RF+LO) and difference (RF-LO) frequency products.

RF IF

LO

Mixer

“Down Conversion”(Receiver)

• In Receivers, the incoming RF signal is “DownConverted” to a lower Intermediate Frequency, IF, using a Local Oscillator (LO) signal.

“Up Conversion”

RF IF

LO

Mixer

(Transmitter)

• In Transmitters, the baseband or IF signal is “Upconverted” to an RF signal.


Frequency SynthesisFrequency Synthesis

• Frequency Synthesis is performed to generate the Local Oscillator (LO)signals needed in the Downconversion and Upconversion process.

• A Frequency Synthesizer is comprised of a Phase Lock Loop (PLL), ReferenceOsc Input, Loop Filter, and a VCO.

• Frequency Synthesis is performed to generate the Local Oscillator (LO)signals needed in the Downconversion and Upconversion process.

• A Frequency Synthesizer is comprised of a Phase Lock Loop (PLL), ReferenceOsc Input, Loop Filter, and a VCO.

fRREF Osc

fV

DividerPhase

Detector

PLL

Divider

Error signal Pulses

Loop Filter

“DC Averages”V

VTuneLO

Frequency

VCO


RF System ParametersRF System Parameters


RF System ParametersRF System Parameters

• Frequency Band• ISM band• Power Level, Class, Control• Modulation• Data Rate, Bandwidth, Channelspacing• Multiple Access• Duplexing• Spread Spectrum

•• Frequency Band Frequency Band•• ISM band ISM band•• Power Level, Class, Control Power Level, Class, Control•• Modulation Modulation•• Data Rate, Bandwidth, Channel Data Rate, Bandwidth, Channelspacingspacing•• Multiple Access Multiple Access•• DuplexingDuplexing•• Spread Spectrum Spread Spectrum


•Frequency Band, refers to the allocated frequencyspectrum for a particular application.

Some wireless systems split the available spectrum intoTransmit Frequencies and Receive Frequencies.

e.g. PCS handsetsTransmit: 1850 - 1910MHz (60MHz)Receive: 1930 - 1990MHz (60MHz)

All Wireless Semiconductor solutions are optimized for aparticular frequency band.

•Frequency Band, refers to the allocated frequencyspectrum for a particular application.

Some wireless systems split the available spectrum intoTransmit Frequencies and Receive Frequencies.

e.g. PCS handsetsTransmit: 1850 - 1910MHz (60MHz)Receive: 1930 - 1990MHz (60MHz)

All Wireless Semiconductor solutions are optimized for aparticular frequency band.

Frequency BandFrequency Band


ISM BandISM Band

•ISM, Industrial, Scientific and Medical - “Unlicensed “ frequencybands designated by FCC for use in Spread Spectrum systems:

• 902-928MHz• 2.400 - 2.483GHz• 5.725 - 5.850GHz

For Spread Spectrum ISM band systems, specifications given for:• output power, max

Frequency Hopping• min # of hops per sec,• channel spacing,

Direct Sequence• min spreading bandwidth

•ISM, Industrial, Scientific and Medical - “Unlicensed “ frequencybands designated by FCC for use in Spread Spectrum systems:

•• 902-928MHz 902-928MHz•• 2.400 - 2.483GHz 2.400 - 2.483GHz•• 5.725 - 5.850GHz 5.725 - 5.850GHz

For Spread Spectrum ISM band systems, specifications given for:• output power, max

Frequency Hopping• min # of hops per sec,• channel spacing,

Direct Sequence•• min spreading bandwidth


Power Level, Power Class, Power ControlPower Level, Power Class, Power Control

Power Level of a wireless system refers to the output powerradiated at the antenna.

Power Classification specifies the max level of output powerpermissible in a system. Some systems have multiple classifications.

e.g. Bluetooth Iclass 1 = 20dBm (100mW)

class 2 = 4dBm (2.5mW)

class 3 = 0dBm (1mW)

Power Control is a closed loop technique used to maintain theproper output power relationship between transmitter and receiver.

Power Level of a wireless system refers to the output powerradiated at the antenna.

Power Classification specifies the max level of output powerpermissible in a system. Some systems have multiple classifications.

e.g. Bluetooth Iclass 1 = 20dBm (100mW)

class 2 = 4dBm (2.5mW)

class 3 = 0dBm (1mW)

Power Control is a closed loop technique used to maintain theproper output power relationship between transmitter and receiver.


ModulationModulation

Modulation is the means to embed the Baseband Info into theRF carrier.

Common Forms of modulation include altering the RF carrier’sAmplitude, Frequency, or Phase, or a combination thereof, bythe Baseband Info.

Modulation is the means to embed the Baseband Info into theRF carrier.

Common Forms of modulation include altering the RF carrier’sAmplitude, Frequency, or Phase, or a combination thereof, bythe Baseband Info.


Amplitude ModulationAmplitude ModulationAmplitude Modulation is achieved when the Baseband Info signalmodulates the Amplitude of the RF carrier.

Amplitude Modulation is achieved when the Baseband Info signalmodulates the Amplitude of the RF carrier.

ASK, Amplitude Shift Keying, also On/OFF Keying (OOK) - burstsof the RF carrier are generated at a fixed amplitude and are transmittedrepresenting a logic 1 (On) and no signal is sent for logic 0 (Off).

AM, Amplitude Modulation - The envelope of the RF carrier is modulated by the Baseband info.

ASK

1 0 1

AM


Frequency ModulationFrequency Modulation

Frequency Modulation is achieved when the Baseband Info signalmodulates the Frequency of the RF carrier.

Frequency Modulation is achieved when the Baseband Info signalmodulates the Frequency of the RF carrier.

FM

FSK, Frequency Shift Keying - Frequency deviation corresponds to Digital data (1 or 0) and the rate of the frequency deviation is determined by the data rate of the info.

FM, Frequency Modulation - Frequency deviation and rate correspond to analog variation in the signal level and frequency of the info.

FSK

0 1 0


Phase ModulationPhase ModulationPhase Modulation is achieved when the Baseband Info signal modulatesthe Phase of the RF carrier.

Phase Modulation is achieved when the Baseband Info signal modulatesthe Phase of the RF carrier.

PSK, Phase Shift Keying - The phase of the RF carrier is shifted depending on digital data being transmitted.

BPSK, Binary Phase Shift Keying - The phase of the RF carrier is shiftedto 1 of 2 possible phases corresponding to a 1 or 0.

BPSK

0 1 0


QPSKQPSK

QPSK Modulation, Quadrature Phase Shift Keying - the phase of theRF carrier can be modulated by 1 of 4 different phases.

• Each possible phase represents a “Symbol” that corresponds to 2bits of data.

• Π/4 QPSK shifts the Constellation by 45Deg to minimize Linearityrequirements.

QPSK Modulation, Quadrature Phase Shift Keying - the phase of theRF carrier can be modulated by 1 of 4 different phases.

• Each possible phase represents a “Symbol” that corresponds to 2bits of data.

• Π/4 QPSK shifts the Constellation by 45Deg to minimize Linearityrequirements.

QPSK

I, Inphase

Q, Quadratureconstellation

SymvbolΠ/4QPSK

I, Inphase

Q, Quadrature

45


M-QAMM-QAM

QAM Modulation, Quadrature Amplitude Modulation - the phase andamplitude of the RF carrier is modulated by the baseband Info.

QAM Modulation, Quadrature Amplitude Modulation - the phase andamplitude of the RF carrier is modulated by the baseband Info.

16-QAM

I, Inphase

Q, Quadrature16 point

constellation

Symbols Bits16 QAM 16 4256 QAM 256 8

Symbols Bits16 QAM 16 4256 QAM 256 8

e.g.

• Each “Symbol” represents a unique combination of phase and amplitude of the carrier.

• There are M total symbols in the constellation where M =2N, N = Bits/Symbol.


Data Rate, Bandwidth, Channel SpacingData Rate, Bandwidth, Channel Spacing

Data Rate, refers to the “Gross” data rate in a single channel. It includesthe data rate of the Baseband Info plus overhead (encoding, interleaving,etc).

Bandwidth is the required spectrum determined by the Gross Data Rate,spectral efficiency of the modulation scheme (bits/symbol) and anyspreading performed on the signal.

Channel Spacing is the frequency boundary set to accommodate thebandwidth needed for each channel.

Data Rate, refers to the “Gross” data rate in a single channel. It includesthe data rate of the Baseband Info plus overhead (encoding, interleaving,etc).

Bandwidth is the required spectrum determined by the Gross Data Rate,spectral efficiency of the modulation scheme (bits/symbol) and anyspreading performed on the signal.

Channel Spacing is the frequency boundary set to accommodate thebandwidth needed for each channel.


Multiple AccessingMultiple Accessing

Multiple Accessing is a technique commonly used in wirelesscommunications to increase the # of users per channel (channel capacity).

MA schemes used today include…..

• TDMA - Time Division Multiple Access

• CDMA - Code Division Multiple Access

• FDMA - Frequency Division Multiple Access

• SDMA - Spatial Division Multiple Access

Multiple Accessing is a technique commonly used in wirelesscommunications to increase the # of users per channel (channel capacity).

MA schemes used today include…..

• TDMA - Time Division Multiple Access

• CDMA - Code Division Multiple Access

• FDMA - Frequency Division Multiple Access

• SDMA - Spatial Division Multiple Access


TDMATDMA

In TDMA systems, the channel is divided into time slots that areassigned to multiple users.

In TDMA systems, the channel is divided into time slots that areassigned to multiple users.

Transmit 6 7 0 1 2 3 4 5 6 7 0 1

User1 Transmit

Receive 6 7 0 1 2 3 4 5 6 7 0 1

User1 Transmit


CDMACDMA

In CDMA systems, channel capacity is increased by a technique called

Direct Sequence spread spectrum.

• Each user’s signal is multiplied by a unique “spreading code”resulting in an increase in the overall bandwidth.

• The spreading signal is an orthogonal pseudo random or pseudo noise(PN) code word that helps distinguish one user from another.

• Multiple uses occupy the same channel which is now widened due tothe spreading.

• At the receiver, the signal is time correlated (“de-spread”) using a copy of thePN code. Due to orthogonality, all other signals appear as noise.

In CDMA systems, channel capacity is increased by a technique called

Direct Sequence spread spectrum.

• Each user’s signal is multiplied by a unique “spreading code”resulting in an increase in the overall bandwidth.

• The spreading signal is an orthogonal pseudo random or pseudo noise(PN) code word that helps distinguish one user from another.

• Multiple uses occupy the same channel which is now widened due tothe spreading.

• At the receiver, the signal is time correlated (“de-spread”) using a copy of thePN code. Due to orthogonality, all other signals appear as noise.


CDMA (CDMA (Cont’dCont’d))

Baseband Processor

Interleave Conv Encode Speech Encoder

28.8kHz

Transmit

1.23MHz

“Spreading”

PN Code Generator

1.23Mcps

Modulator

Gspread = Bspread / R

Gspread = Spreading GainBspread = Spreading BandwidthR = incoming data rate

Gspread = Spreading GainBspread = Spreading BandwidthR = incoming data rate


FDMA, SDMAFDMA, SDMA

In FDMA, Frequency Division Multiple Access, systems, each channel(user) is assigned a specific frequency from the available spectrum.

• Most portable wireless communications systems use a form of FDMA.

In SDMA, Spatial Division Multiple Access, systems increase channelcapacity via the use of directional antenna which divides a region intospatial channels.

In FDMA, Frequency Division Multiple Access, systems, each channel(user) is assigned a specific frequency from the available spectrum.

• Most portable wireless communications systems use a form of FDMA.

In SDMA, Spatial Division Multiple Access, systems increase channelcapacity via the use of directional antenna which divides a region intospatial channels.


OFDMOFDM

Orthogonal Frequency Division Multiplexing is commonlyused in wireless broadband communications systems which demand highdata rate throughput, (e.g. WLAN 802.11a, HyperLan2).

In OFDM systems, the Transmit data stream is split into parallel paths,modulated onto an orthogonal set of frequencies, multiplexed and thentransmitted.

Orthogonal Frequency Division Multiplexing is commonlyused in wireless broadband communications systems which demand highdata rate throughput, (e.g. WLAN 802.11a, HyperLan2).

In OFDM systems, the Transmit data stream is split into parallel paths,modulated onto an orthogonal set of frequencies, multiplexed and thentransmitted.

Transmit Mux Mod S/PTransmit Data


DuplexingDuplexing

Duplexing is the technique that specifies how Transmit and Receive signalflow is handled at the Antenna…..

TDD, Time Division Duplex• Transmit and Receive are done in separate, non-overlapping timeslots, e.g GSM systems.

• T/R antenna switch is used in TDD systems.

FDD, Frequency Division Duplex• Transmit and Receive are done simultaneously using different

frequency assignments and a duplexer e.g, AMPS (analog) cellular.

• Ceramic Duplexer is used to separate Tx and Rx paths.

Duplexing is the technique that specifies how Transmit and Receive signalflow is handled at the Antenna…..

TDD, Time Division Duplex• Transmit and Receive are done in separate, non-overlapping timeslots, e.g GSM systems.

• T/R antenna switch is used in TDD systems.

FDD, Frequency Division Duplex• Transmit and Receive are done simultaneously using different

frequency assignments and a duplexer e.g, AMPS (analog) cellular.

• Ceramic Duplexer is used to separate Tx and Rx paths.


Spread SpectrumSpread Spectrum

• Spread Spectrum is an “anti-jamming” concept originallyemployed for use in military communication systems.• Spread Spectrum is an “anti-jamming” concept originallyemployed for use in military communication systems.

• Designed to “Spread” the Information signal over a wider bandwidth to make it more immune to interference.

• Two widely used spread spectrum techniques include “Frequency Hopping” and “Direct Sequence” (e.g. CDMA).


Frequency HoppingFrequency Hopping

Frequency Hopping divides the baseband Info into small packetsof data and transmits each packet over a different frequency.

• FH systems uses a unique “hopping” algorithm that determines thesequence of frequencies that are used.

• The Receiver uses the same algorithm and hops to the specificfrequency locations to receive the data.

Frequency Hopping divides the baseband Info into small packetsof data and transmits each packet over a different frequency.

• FH systems uses a unique “hopping” algorithm that determines thesequence of frequencies that are used.

• The Receiver uses the same algorithm and hops to the specificfrequency locations to receive the data.

Transmit

Baseband Processor

Hop Algorithm

Tx Data

f4 f2 f6 f3f5f1

+

Frequency Gen


RF Transceiver RF Transceiver ArchitecturesArchitectures


RF Transceiver ArchitecturesRF Transceiver Architectures

•• RF Detector RF Detector•• SuperheterodyneSuperheterodyne•• Direct Conversion ReceiverDirect Conversion Receiver•• Very Low IF Very Low IF•• Superheterodyne Superheterodyne Blocks Blocks


• An RF Detector architecture is commonly used for AM/ASKbased modulation systems.

• The Detector uncovers the envelope of the waveform which carriesthe Information signal.

•The Motorola 2.4GHz ISMLink solution is based on ASK modulation,hence it uses an RF Detector architecture.

• An RF Detector architecture is commonly used for AM/ASKbased modulation systems.

• The Detector uncovers the envelope of the waveform which carriesthe Information signal.

•The Motorola 2.4GHz ISMLink solution is based on ASK modulation,hence it uses an RF Detector architecture.

RF DetectorRF Detector

Detector Filter


SuperheterodyneSuperheterodyne

In Superheterodyne Architectures, the incoming RF signal is“DownConverted” to an Intermediate Frequency, IF, using a Local Oscillator(LO) signal.

In Superheterodyne Architectures, the incoming RF signal is“DownConverted” to an Intermediate Frequency, IF, using a Local Oscillator(LO) signal.

IF

IF Filter

RFIN

LO

LNA Mixer

Filter1

Front End Receiver

The IF signal is then demodulated in a backend IF/Demodulator function to recover the Baseband Info.

IF/Demodulator

DemodulatorBaseband

Info


Direct Conversion Receiver (DCR)Direct Conversion Receiver (DCR)

In Direct Conversion Architectures, the incoming RF signal is“DownConverted” directly to the Baseband Frequency in the demodulator.

Direct Conversion eliminates many external components including the IFfilter.

Direct Conversion architectures, however, do face problems with LOleakage, DC output component and the need for linear components in thedemodulator.

In Direct Conversion Architectures, the incoming RF signal is“DownConverted” directly to the Baseband Frequency in the demodulator.

Direct Conversion eliminates many external components including the IFfilter.

Direct Conversion architectures, however, do face problems with LOleakage, DC output component and the need for linear components in thedemodulator.

RFIN

LO

LNA

Filter1

Front End Receiver

Baseband Info

Demodulator


Very Low IFVery Low IF• Very Low IF, VLIF, Architectures offer a compromise between Superhet andDCR designs.

• VLIF receivers “downconvert” the RF to a low IF which is then processed in theIF/Demodulator.

• The Low IF frequency enables integration of the IF Filter onboard theIF/Demodulator block.

• VLIF’s avoid the DC component and LO Leakage problems faced in DCR design

• Very Low IF, VLIF, Architectures offer a compromise between Superhet andDCR designs.

• VLIF receivers “downconvert” the RF to a low IF which is then processed in theIF/Demodulator.

• The Low IF frequency enables integration of the IF Filter onboard theIF/Demodulator block.

• VLIF’s avoid the DC component and LO Leakage problems faced in DCR design

VLIFRFIN

LO

LNA Mixer

Filter1

Front End ReceiverIF/Demodulator

Baseband Info

Demodulator

IF Filter


RFin

RFout

Power ManagementPower Management

Superheterodyne Superheterodyne BlocksBlocks

MIC

SPKR

KeypadKeypad

DisplayDisplay

MemoryMemory



Data

Baseband

PLL

LoopFilterVCO

LO1

LO

Frequency Synthesizer

LO

AGC

Modulator DAC

Upconverter “Info”

Modulator/Upconverter

PowerControl

Power Amplifier (PA)

Transceiver

Antenna

LNA Mixer

Front End Receiver

Switch/DuplexerSwitch/

Duplexer

“Info”

LO2

IF Demodulator

IFDemodulator ADC

RF Fundamentals

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