Multiband RF Transceiver System
Chapter 5 Software-Defined Radio
Department of Electronic Engineering
National Taipei University of Technology
• Mobile Generations
• Traditional Hardware-Defined Radio (HDR)
• Ideal Software-Defined Radio (SDR)
• Basic SDR Architecure
• Hybrid Analog and Digital Radio Architecture
• Wideband Downconversion in the SDR
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• In the 20th century, most radios are hardware defined with
little or no software control (hardware defined radio, HDR).
Fixed in function for mostly consumer items.
A short life and are designed to be discarded and replaced.
• SDR uses programmable digital devices (DSPs or FPGAs) to
perform the signal processing necessary to transmit and
receive baseband information at radio frequency.
Offers greater flexibility and potentially longer product life.
Can be upgraded very cost effectively with software.
A major challenge is to equal the efficiencies of hardware solutions.
The developer will want to be shielded from the details hardware and
complete all development in a unified environment using a single high-
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Generation of Mobile Communications
• 1980s: 1st generation of mobile cellular
Uses analog modulation techniques to transmit and receive analog voice only
information between mobiles and base stations.
• 1990s: 2nd-generation (2G) systems
They were known as “digital” because they encoded voice into digital streams
and used digital modulation techniques for transmission.
• 2000s: IMT 2000 standard (defined 3G-compatible systems)
Support up to 2 Mbps data connections. A means to provide new services to
customers and to provide much needed capacity via better spectrum utilization.
Of the 3G standards, the 3GPP Universal Mobile Telecommunications System
(UMTS) is strongest in Europe (not universal). The 3GPP2 CDMA2000 standard
and the TDMA-based GSM-EDGE systems will be successful in North and South
America, while Japan has its own WCDMA system similar to UMTS.
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3G SDR Applications
• All of the 3G systems are potential SDR applications.
• SDR offers the potential to solve many of the problems caused
by the proliferation of new air interfaces.
• Base stations and terminals using SDR architectures can
support multiple air interfaces during periods of transition and
be easily software upgraded.
• Intelligent SDRs can detect the local air interface and adapt to
suit the need; this capability will be valuable for frequent inter-
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Traditional Hardware Radio Architecture
• Conventional dual conversion superheterodyne transceiver:
This design has been around since the 1930s. The analog superheterodyne radio
has experienced a marvelously successful history; it was used in 1G mobile phone
terminals (e.g., AMPS) and is sure to endure in lowcost broadcast radios.
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Ideal Software Defined Radio (I)
• The analog functions are restricted to those that cannot be
performed digitally. (Antenna, RF filtering, RF combination, receive pre-
amplification, transmit power amplification and reference frequency generation)
Digital processing resources
Digital signal processors
Reconfigurable communications processors
Digital subsystemAnalog subsystem
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Ideal Software Defined Radio (II)
• Analog conversion stage right up as close as possible to the
• The separation of carriers and up/down frequency conversion
to baseband, channel coding and modulation functions are
performed by the digital processing resources.
• Frameworks using an open API into the middleware will make
applications development more portable, quicker, and cheaper.
• The ideal architecture is commercially feasible for limited low
data rate HF and VHF radios but is not yet practical for any
generation of cellular mobile phone technology.
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Basic SDR Architecture
• For 3G mobile and many other multiuser radio technologies,
the ideal SDR is not yet a practical or cost-effective reality.
Direct sampling of wideband RF frequencies at high SNR (>90 dB) is not yet
• Decide where the radio stops being hardware defined and
where it starts being software defined.
• Considering normal commercial requirements (principally cost
effectiveness), it is apparent that SDR implementations of 3G
wireless need purpose-built hardware to be successful.
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2G Radio Architecture
• Compared with current generations, 1G and other equivalent
analog radio systems trade off complexity for bandwidth
That is, they are less complex and consume more bandwidth. AMPS consumes
30 kHz for a voice user.
• A major requirement of the 2G standards was to increase
bandwidth efficiency in a increase in complexity.
The 2G Groupe Speciale Mobile (GSM) standard achieved this by
implementing a digital standard that allowed for time division multiplexing,
multiple access, and other relatively sophisticated techniques to improve
system capacity. GSM occupies 200 kHz for its 8 voice users. The added
features can produce an approximately 3 to 4 times capacity improvement.
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Hybrid Radio Architecture (I)
• The analog fixed function HDR survived right through to the
1960s and 1970s, making its way into color television
transmission, private mobile radio, and even parts of 1G
cellular mobile radio.
• The complexity of a color television receiver and a 1G mobile
terminal stretched this analog technology to the absolute limit.
Analog circuits consume more space and power and are more subject to
performance variations as a result of environmental factors (e.g., temperature).
• The emergence of low-cost ADCs, DACs, and DSPs in the
1980s and the need for more efficient RF bandwidth utilization
shifted radio architecture development away from purely
analog to hybrid analog and digital systems.
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Hybrid Radio Architecture (II)
• Ppopular with early 1990s hybrid radios (e.g., 2G BTS).
IFA1, typically 140 or 70 MHz
Each filter ensures that acceptable selectivity and image
rejection are achieved.
IFA2, typically 10.7 MHz. De-interleaving and error correction (e.g., Viterbi decoder)
IFA1 IFA2 LP
Per carrier analog Rx chain Per baseband Rx channel
Per carrier analog Tx chain Per baseband Tx channel
GSM 900 BTS:
RX: 880–915 MHz
TX: 925–960 MHz.
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Hybrid Radio Architecture (III)
• The single carrier case is expanded to a multicarrier system by
adding RF carrier transmit and receive chains.
FRx IFA1 IFA2 IFA3
Tx chain 1
Tx chain 2
Tx chain N
Rx chain 1
Rx chain 2
Rx chain N
Baseband 1 Rx
Baseband 2 Rx
Baseband N Rx
Baseband 1 Tx
Baseband 2 Tx
Baseband N Tx
Multicarrier 1990s digital radio
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Basic SDR Block Diagram
Wideband capability, designed to replace many narrowband
analog receive or transmit frequency conversion chains.
FRx IFA1 IFA1
BP1 BP2 BP3
Analog Rx chain
Analog Tx chain
Wideband analog front end
Hardware defined subsystem Software defined subsystem
Digital frequency conversion and baseband processing resources
The hardware subsystem
details some lower-level
(PA, LNA, ADC…)
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• The wideband front end converts or shifts an entire segment of
spectrum to a suitable intermediate frequency—IFD, “the
digital IF”—prior to digitization.
A segment of the GSM 900-MHz band
A popular choice for IFD is 70 MHz due to the
COTS availability of satellite/ microwave
The spectrum of the required shifted to
baseband by software prior to demodulation.
N 2 1 1 2 N
N 2 1 1 2 N
~ 900 MHz0
~ 70 MHz = IF
e.g., carrier 2
~ 70 MHz
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• In this chapter, the concepts of HDR, SDR, and the hybrid
analog and digital radio architecture were introduced.
• The HDR is often fixed in function but offering higher
performance than SDR solution.
• The SDR offers greater flexibility and can be upgraded very
cost effectively with software. A major challenge is to equal
the efficiencies of hardware solutions.
• The SDR may be a good solution for wideband or multi-
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