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M ason Co mmunicat ions Ltd 2001
3 Design Elements3.1 Basic Radio Principles
WCDMA Radio Planning Course
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Where are We Now?Introduction
UMTSOverview
AccessTechnologies
WCDMAIntroduction
ModelArchitecture
UMTSStandards
Mobile Radio
Channel
NarrowbandChannel
WidebandChannel
Local MeanSignal
Path Loss
Diversity
Design
Elements
CourseOverview
Antennas andFeeders
Interference
MatchedFilters and
Rake Receivers
WCDMAPhysical Layer
Network
Design
OperatorsDesign Guides
The PlanningProcess
Polygons
Site Placement
AntennaPlacement
FrequencyPlanning
ForwardCapacityPlanning
LinkBudgets
ConventionalOptimisation
3GOptimisation
Radio ResourceManagement
Optimisation
CourseWash Up
Basic RadioPrinciples
Where are We Now?
The Course Map shows which section we are now on.
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What is in This Section?
Modulation
Radio Building Blocks
Transmitter Design
Receiver Design
Transceiver System Design
Summary
Design
Elements
Basic RadioPrinciples
Antennas andFeeders
WCDMAPhysical Layer
Interference
MatchedFilters and
Rake Receivers
What is in This Section?
This will be a high level treatment.
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Why is this Section Important to You?
This section will provide you with
an understanding of the concepts and principlesassociated with
radio design
the effect that these have on system performance
This will assist you as a network planner to
understand the reasons for rules and regulationsassociated with
your work
have a better realisation of why there are differencesbetween
theoretical and practical network coveragepredictions
Why is this Section Important to You?
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How Will You Learn?
Discussion
This section uses a number of examples and an exercise
Intermediate Frequency
How Will You Learn?
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Basic Communications Receiver
The slide shows the elements of a basic Superhet
(Superhetrodyne) communications receiver.
NJHX310D.PPT
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Basic Communications Receiver
1stoscillator
2ndoscillator
1st I.F.34.3 or
38.3 MHz
45 -49MHz
0-4kHz
2ndfrequencychanger
2nd I.F.10.7MHz
3rdfrequencychanger
3rd I.F.2.6MHz
4thfrequencychanger
Uppersideband100-106kHz
Productdetector
Lowersideband
94-100kHz
Carrier 100 kHz
Switchedbandpass
filter
0 -30dB
Widebandamplifier
0 or10dB
1stfrequencychanger
Logicunit
OverloadProtection
42.3 -46.3MHz
Frequencytranslator
Memory unit
ActivatingSignal
100 kHzreference
Frequencysynthesizer
3rdoscillator13.3 MHz
4thoscillator2.7 MHz
A. G. C.detector
A. F. C.units
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Where are We Now?
Modulation
Radio Building Blocks
Transmitter Design
Receiver Design
Transceiver System Design
Summary
Design
Elements
Basic RadioPrinciples
Antennas andFeeders
WCDMAPhysical Layer
Interference
MatchedFilters and
Rake Receivers
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What is Modulation?
Definition Process that causes a low frequency range signal to
be
shifted to a higher frequency range
Process to impress information content onto a carrier
Modulation of a signal onto a higher frequency carrier hasthe
following advantages:
Higher frequency signals are easier to radiate
Simultaneous transmission of several signals
Optimum use of available frequency spectrum Less prone to
interference effects
HF equipment tended to be large an bulky.
Cellular makes use of smaller equipment, smaller cells and hence
frequency re-use.
Over time there was a demand for higher and higher frequencies,
100+MHz, 450MHz,900MHz, 1800MHz and now 2GHz.
Tendency now is to re-use some older bands etc. e.g. TV
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Common Modulation Techniques
Analogue
Amplitude Modulation (AM)
Frequency Modulation (FM)
Phase (or Angle) Modulation(PM)
Digital
Amplitude Shift Keying (ASK)
Frequency Shift Keying (FSK)
Phase Shift Keying(PSK)
and other derivatives
All radio communication uses a modulation scheme which is
derived from one of the
following:
Amplitude Modulation (AM)
Frequency Modulation (FM)
Phase/Angle Modulation (PM)
Each scheme has its own set of advantages and disadvantages, and
are generally best suited
for use in a set range of frequencies and for particular traffic
types. These will be detailed
later.
There are now numerous digital modulation techniques available
for the efficient transfer of
1s and 0s over-air. Each modulation technique will have been
tailored for a particular data
rate requirement, to operate over a given frequency range, and
for a given channelbandwidth.
Digital modulation schemes are generally derived from the
following:
Amplitude Shift Keying(ASK)
Frequency Shift Keying (FSK)
Phase Shift Keying (PSK)
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AM
SourceSignal
CarrierSignal
ModulatedSignal
Time
fc
Frequency
fc fc+fv
fv f
Amplitude of the RF carrier wave varies in sympathy with
thesignal to be transmitted
RF Power Output proportional to input signal level
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FM
Frequency of the RF Carrier signal varies in relation to
thesignal to be transmitted
FM derived modulation techniques provide a constantRF power
output
fc
fv f
fc f
f
SourceSignal
CarrierSignal
ModulatedSignal
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PM
Used in Digital Systems
Phase of an RF carrier is continually inverted toindicate binary
1s and 0s
Constant RF power output
Sourcev 0 1 1 0 1 0 0 1 0 0
t
v
t
v
t
SourceSignal
CarrierSignal
ModulatedSignal
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Modulation Summary
AM Signals highly efficient
best suited for audio BW signals
low BW requirements
FM Signals
constant power output
audio or low rate data input
high BW requirement
PM Signals constant power output
high data rate signals only
plethora of PM related modulation techniques available
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Where are We Now?
Modulation
Radio Building Blocks
Transmitter Design
Receiver Design
Transceiver System Design
Summary
Design
Elements
Basic RadioPrinciples
Antennas andFeeders
WCDMAPhysical Layer
Interference
MatchedFilters and
Rake Receivers
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Radio Building Blocks
Common components of radio design
RF Amplifiers
Filtering
Mixing
Local Oscillators
Intermediate Frequency (IF)
Radio Building Blocks
This subsection discusses the common components of radio
design.Care has to be taken with IF choice e.g. choosing LO of
1800MHz for microwave radios
within 1800 GSMM band!!
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RF Amplifiers
User definable gain
Element of filtering associated with RF amplifier design
Design should not distort RF signals
single stage design generates 180o phase change
RF in RF outx ndB
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Filters
Devices which attenuate a pre-selected band of frequencies
Constructed using Capacitors, Resistors and Inductors
4 Common Types:
A combination of the above can be combined to produce
morecomplex filter designs
f
gain (dB)
Low Pass Filter (LPF)
f
gain (dB)
High Pass Filter (HPF)
f
gain (dB)
Band Pass Filter (BPF)
f
gain (dB)
Band Reject Filter
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Filter Specifications
Filter designs are characterised by the followingparameters:
3dB points
Roll-off
Insertion Loss
Stop Band Attenuation
3dB plots define the bandwidth of the filter.
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Filters 3dB Points
Frequency at which amplitude of RF signal passing throughfilter
is halved (or is attenuated by 3dB)
Signal after passingthrough filter
f-1
-4
f3dB f-1
-4
f3dBf3dB
Gain (dB) Gain (dB)
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Defines the rate of change of attenuation between a filterpass
band and stop band.
A filter design with a high rate of change of attenuation issaid
to have a high Q
High Q devices are several filters serially connected -higher
unit cost
Filters Roll-Off
Roll off = 20dB/decade
f(Hz)0
-20
10Gain
-40
-60
100 100010000
Q, Quality factor is related to the resonance of the filter and,
for a lumped constant filter,
I.e. one using resistors (R), Capacitor (C) and Inductors(L), is
given by:
Q = 0
CR = R/(0
L) where:
0 is the resonant frequency in radians per second i.e. (0
=2f)
R is in Ohms
C is in Farads
L is in Henrys
A good Filter Book:
Donald R.J. White A Handbook on Electrical Filters, Synthesis,
Design and Applications
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Insertion Loss - loss experienced by a pass band
signalpropagating through the filter
Typically 0.5-2dB
Stop-Band Attenuation - loss experienced by a stop bandsignal
propagating through the filter
Typically 50-80dB
Filters Insertion Loss & Stop Band Attenuation
Stop BandAttenuation
f(Hz)0
-20
Gain (dB)
-40
-60
Insertion Loss
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Filter Example -7-stage Butterworth Low-pass Filter
Number of stages equal tonumber of frequencysensitive filter
components
Design established fromfollowing initial spec.
3dB cut off at 10kHz
>40dB attenuation at20kHz
source and loadimpedances = 300ohm
3
10
20
30
40
50
60
0
2.5 10 20 405
Tra
nsmissionLossindB
Frequency in kHz
3dB point roll-o
ff=42d
Bperoctave
300ohmLoad0.024uF 0.096uF0.096uF 0.024uF
5.96mH 9.55mH 5.96mH
InputSignal
Note a lot of filtering can be implemented in software using
DSPs (Digital Signalling
Processors)
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Mixing
We require a process which is capable of shifting a lowfrequency
range signal to a higher range or vice-versa
Advantages of over-air transmission using higher
frequencyrange
Requirements of such a process are:
Minimal distortion of original signal
Capability of working over a range of frequencies
Majority of circuit tuning alterations to be automatic
WE NEED MIXERS!
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Mixing
Why? Up-convert or down-convert sinusoidally based signals
How?
literally mixing, or multiplying twosinusoidally basedsignals
together
When?
Between stages in a radio requiring different workingcarrier
frequencies
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Mixing - Inputs
Take two signal inputs to a mixer
Signal to be
modulated ontocarrier(e.g. voice)
Asin 1t
Bsin 2t
What is theoutput?
RF Carriersignal
(e.g. 900MHz)
Where1 = Angular frequency of input signal
A = Amplitude of input signal
2 = Angular frequency of RF carrier ( =2f)
B = Amplitude of RF carrier signal
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Mixing - Mathematical Derivation
Using trigonometricequation:
( )cos .cos cos( ) cos( )
.sin( ). sin( ) .cos( ). .cos( )
cos( ) cos( )
A B A B A B
A t B t A t B t
ABt
ABt
+ +
+ +
1
2
2 2
1 1 1 2
1 2 1 2
Upper Product
i.e. higher freq
Lower Product
i.e. lower freq
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Mixing - Graphical Representation
Amplitude
B
A
1 1-2 2 1+2
Frequency (Hz)
AB/2
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Local Oscillator (LO)
Generates pure sinusoidal reference signal for use in
mixingprocesses
Variable Frequency Output
In a radio system, all LO devices referenced from one
masteroscillator
Quartz Crystal derived clock reference, accuracy prone to:
temperature fluctuations
pressure variation
vibration & shock
LO accuracy specified as x ppm (parts per million)
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Intermediate Frequency (IF)
What ? A fixed frequency stage in the radio design
All devices in the stage operate on one frequency only
Why ?
Standardisation (set of frequencies)
Common IF modules and devices
Improved device performance
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IF = 10.7MHz
LO frequency selection dependent on desired outputsignal from
mixing process
Intermediate Frequency Question
f (Hz)IF LO RF
What is LO?
What if RF
changes?
unwantedproduct
(RF-LO)
RF
LO
SignalAmplitude
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Where are We Now?
Modulation
Radio Building Blocks
Transmitter Design
Receiver Design
Transceiver System Design
Summary
Design
Elements
Basic RadioPrinciples
Antennas andFeeders
WCDMAPhysical Layer
Interference
MatchedFilters and
Rake Receivers
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Aim of a Transmitter?
To superimpose an input signal onto an RF carrier, such thatthe
modulated output signal can be successfully transmittedand
subsequently received at a remote station
A transmitter requires:
an appropriate modulation technique
suppression of locally generated interference signals
linear RF power output
user frequency selection
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Basic Transmitter Design
BPFIF Stage
InputSignal
Mixer 1
LO1
Mixer 2
Low pass filter
Bandpass filter
Mixer
Local oscillator
Amplifier
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Basic Transmitter Design
BPFIF Stage
InputSignal
Mixer 1
LO1
Mixer 2
BPF permits only the wanted signal to enter the first mixing
stage
Unwanted signals filtered off
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Basic Transmitter Design
BPFIF Stage
InputSignal
Mixer 1
LO1
Mixer 2
Input signal and 1st LO frequency mixed to produce 1st IFstage
frequency
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Basic Transmitter Design
High Q filters and precision amplifiers produce a clean IF
signal
What is IF?
Signal
Amplitude
IF Frequency (Hz)
unwanted signal,filtered off in IF stage
LO
IN
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Basic Transmitter Design
BPFIF Stage
InputSignal
Mixer 1
LO1
Mixer 2
Finely tuned filters and amplifiers clean the signal in
preparationfor the next stage
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Basic Transmitter Design
BPFIF Stage
InputSignal
Mixer 1
LO1
Mixer 2
Up-convert to the required RF carrier frequency
User selectable Tx frequency has impact on LO frequency andfinal
stage filter performance
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What is LO?
What if RF
changes?
Basic Transmitter Design
Signal
Amplitude
Frequency (Hz)
unwanted signal,filtered off in final RF stage
IF
LO
RF
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Basic Transmitter Design
BPFIF Stage
InputSignal
Mixer 1
LO1
Mixer 2
Amplify to user selectable RF power output level
Minimisation of harmonics and spurious RF signals
Good RF loading to external device (e.g. external PA,
antenna,external filtering, combiners)
ganged
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Harmonic Suppression
Multiples of the wanted signal
Interference signals affect other radio systems in the local
vicinity
fc 2fc 3fc 4fc 5fc
Amplitude (dB)
Frequency (Hz)
Note odd harmonics have the highest power.
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Harmonics Derivation
Amplifier has non-linearities in its amplitude transfer
characteristic Consider input signal with single frequency
present:
v V tin = c o s
Non-linearities result in output signal: v a v a v a vout in in
in= + + +1 2 3
2 3 .. .
v A V t B aV
t aV
tou t = + + + +cos cos cos .. . 2
2
3
3
22
43
Looking at the first 3 components:
Linear output DC Shift 2nd HarmonicDistortion
3rd HarmonicDistortion
Non-linear distortion introduces harmonic components
whosefrequencies are integer multiples of the fundamental frequency
()
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Spurious Signals
Generated by inadvertent mixing between two or moreof the
following sources:
LO outputs
Inadequate filtering outputs
Internal clocks
Digital Signals (data rates)
Minimised by:
Good screening practices
Careful circuit layout
Decoupling & Choking
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Final Stage BPF
Band-pass, or notch, varies with selected RF output
frequency
Attenuates unwanted spurious and harmonic signals
gain (dB)
Filter Characteristics:
Frequency (Hz)
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Where are We Now?
Modulation
Radio Building Blocks
Transmitter Design
Receiver Design
Transceiver System Design
Summary
Design
Elements
Basic RadioPrinciples
Antennas andFeeders
WCDMAPhysical Layer
Interference
MatchedFilters and
Rake Receivers
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Aims of a Receiver?
To extract the wanted signal from a received modulated RFcarrier
without distortion
A receiver shall:
provide Rx frequency selectivity
filter off interfering signals
minimise distortion of the wanted signal
Note that we are trying to receive signals around 100dBm,which
can be a factor of 10 15 less than that coming from thetransmitter
antenna
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S
Superheterodyne Receiver
Basis for all modern day receivers
Superheterodyne - advanced mixing
Rf Pre-Amp
Antenna
BPF Amplifier Filter
IF StageFront End
90O
LPF
Quadrature Detector
Mixer
I
Q
hetrodyne means mixing
Super refers to that fact that there a number of mixer
stages.
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S
Superheterodyne Receiver
Basic Front End (FE) Stage - Why ? What ?
Rf Pre-Amp
Antenna
BPF Amplifier Filter90O
LPF
Quadrature Detector
Mixer
I
Q
IF StageFront End
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FE Stage
Why ? To maximise the receive sensitivity of the radio, by:
coupling the antenna signal to the receiverefficiently
attenuating interfering signals
amplifying selected RF signal
What ?
The above is performed using a series of:
RF Pre-amplifiers
Tunable Filters
Remember - If sensitivity is maximised, the greater theeffective
range of the radio system
A good example of improving sensitivity is at GSM1800 when LNAs
were used.
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S
Superheterodyne Receiver
Mixing
To down-convert received RF signal to the 1st IF frequency
Variable output LO to track selected Rx frequency
Rf Pre-Amp
Antenna
BPF Amplifier Filter90O
LPF
Quadrature Detector
Mixer
I
Q
IF StageFront End
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What is LO?
What if RF changes?
1ST Mixer Stage
SignalLevel
Frequency (Hz)
F
LO
RF
lower product higher product
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S
Superheterodyne Receiver
IF Stage
High Q filters and precision amplifiers produce a clean IF
signal
Rf Pre-Amp
Antenna
BPF Amplifier Filter90O
LPF
Quadrature Detector
Mixer
I
Q
IF StageFront End
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S
Superheterodyne Receiver
Quadrature Detector
Commonly used demodulator to extract two wantedsignals from a
single RF carrier
Rf Pre-Amp
Antenna
BPF Amplifier Filter90O
LPF
Quadrature Detector
Mixer
I
Q
IF StageFront End
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Quadrature Detector
Two signals modulated onto a single RF carrier
Each signal modulated onto carrier in different 90o phases
Signals demodulated using LO inputs which are phase related
towanted signal (phase difference between LOs is 90o)
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QAM contd...
S
m1(t)
m2(t)
2 cos wct
2 sin wct
s(t)
-90o
cos ct
sin ct
m1(t)
m2(t)
x1(t)
x2(t)
s(t) = m 1 (t)cos ct + m 2(t)sin ct
x1(t) = s(t).2.cos ct
= m 1(t) + m 1(t)cos 2 ct + m 2(t)sin 2 ct
x2(t) = s(t).2.sin c t
= m 2(t) + m 1(t)cos 2 ct + m 2(t)sin 2 ct
-90o
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Double Superheterodyne Receiver
Extra IF stage to improve adjacent channel
selectivityperformance
Rf Pre-Amp
Antenna
BPF Amplifier Filter
2nd IF Stage
Mixer
Amplifier Filter
Front End
MixerTo quad.detector
1st IF Stage
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Receiver Design Summary
An RF signal has been inputted to the receiver design
anddown-converted, in stages, to the wanted signal
All receiver designs are based on the
superheterodyneprinciples
Modern receivers provide more digital control (DSP)
Note we have dealt largely with old world technology to
introduce the concepts.
Nowadays Direct conversion is often used together with receiver
on a chip concept.
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Where are We Now?
Modulation
Radio Building Blocks
Transmitter Design
Receiver Design
Transceiver System Design
Summary
Design
Elements
Basic RadioPrinciples
Antennas andFeeders
WCDMAPhysical Layer
Interference
MatchedFilters and
Rake Receivers
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Transceiver?
Transmitter/Receiver
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Aims of a Transceiver
To provide both receive and transmit capabilities in one
unit,with ancillary circuitry to control switching between the
twostates
Require
user definability of Tx and Rx frequencies
suppression of interference between two stages
cost and size reductions due to duplication (sharing
ofoscillators, mixers stages, etc.....)
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Conceptual Transceiver Block Diagram
Note: * = Tx / Rx switch or duplex filter
Quad.Mod
Quad.Demod
FrequencySynthesis
*
FRONT ENDIF STAGE
IF STAGE RF STAGE
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RF Switching
Tx/Rx Switch transceiver cannot
transmit and receivesimultaneously
switch is usuallycontrolled by user PTT(press-to-talk)
orexternal Tx controlsignal
maintain impedance
loading
Duplex Filter transceiver can
transmit and receivesimultaneously
essentially two BPFsbolted together
common antenna input
used in Repeatersystems
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System Filtering
At a site, several receivers and transmitters may co-exist
Methods of ensuring RF signals (Rx and Tx) are routed to
theappropriate antenna/transceiver without interference from
otherRF signals
One antenna may be connected to several transceivers
Require the use of:
Combiners
Splitters
Directional Couplers
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Combiners
Passive device which has anoutput equal to the vector sumof its
multiple RF inputs
Insertion loss increases withnumber of inputs
High isolation between inputports
RF in_2 RF out
PowerCombiner
RF in_3
RF in_1
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Splitters
Passive device which accepts aninput signal and delivers
multipleoutput signals
Output signals are equal inamplitude and phase ifterminated into
identical loads
Insertion loss increases withnumber of output ports
High isolation between eachoutput signal
RF out_2RF in
PowerSplitter
RF out_3
RF out_1
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Directional Couplers
Device which couples an RF signalonto a Transmission Line
(TL)
Sometimes termed RF sniffer
Coupled RF signal is attenuated
Extent of coupling dependent onRF frequency
Range of devices availabledependent on attenuation
requirements and signal to becoupled onto
TL outRF in DirectionalCoupler
RF Signal in
RF Signal out(optional)
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Node B
Internal base station
Capacity: 2+2+2
Note that it appears morecard oriented than a GSMBTS
Note in 3G the amplifier needs to be highly linear.
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Where are We Now?
Modulation
Radio Building Blocks
Transmitter Design
Receiver Design
Transceiver System Design
Summary
Design
Elements
Basic RadioPrinciples
Antennas andFeeders
WCDMAPhysical Layer
Interference
MatchedFilters and
Rake Receivers
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Summary
In this section on Basic Radio Principles you have learnt
about
Modulation
Radio building blocks
Transmitter and receiver design
Transceiver system design
This section is important to you because you will
understand the reasons for rules and regulations associatedwith
your work
have a better realisation of why there are differencesbetween
theoretical and practical network coveragepredictions
Summary
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The End of Basic Radio PrinciplesIntroduction Network
Design
Design
Elements
CourseOverview
Mobile Radio
Channel
Optimisation
NarrowbandChannel
WidebandChannel
Local MeanSignal
Path Loss
Diversity
Basic RadioPrinciples
UMTSOverview
AccessTechnologies
ModelArchitecture
UMTSStandards
WCDMAIntroduction
OperatorsDesign Guides
The PlanningProcess
Polygons
Site Placement
AntennaPlacement
FrequencyPlanning
ForwardCapacityPlanning
LinkBudgets
Radio ResourceManagement
Antennas andFeeders
WCDMAPhysical Layer
Interference
MatchedFilters and
Rake ReceiversConventionalOptimisation
CourseWash Up
3GOptimisation
Any MoreQuestions?
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Presentation
Title
Date
Tel:+44(0)1618777808
Fax:+44(0)1618777810
Client
MasonCommunicationsLtd
5ExchangeQuay
ManchesterM53EF
England
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providedonconditionthatitwillnotbereproduced,
copied,lentordisclosed,
directlyorindirectly,orusedforanypurposeotherth
anthatforwhichitwas
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