Unit 1 introduction to software defined radios

1. RMK College of Engineering and Technology
EC6014
Cognitive Radios
Department
of
Electronics and Communication Engineering

2. Unit 1
Introduction to
Software
Defined Radio

3. Syllabus
• Definition and Potential Benefits
• Software Radio Architecture Evolution
• Technology Trade off and Architecture Implications

4. Introduction
• Data communication networks plays a vital role in any modern society.
• They are used in numerous applications, including financial transactions, social interactions, education, national
security, and commerce.
• With the exponential growth in the ways and means by which people need to communicate - data
communications, voice communications, video communications, broadcast messaging, command and control
communications, emergency response communications, etc.
• Modifying radio devices easily and cost-effectively has become business.

5. Software Defined Radios - Concept
• The basic concept of the SDR software radio is that the radio can be totally configured
or defined by the software so that a common platform can be used across a number of
areas
• There is also the possibility that it can then be re-configured as upgrades to standards
arrive, or if it is required to meet another role, or if the scope of its operation is
changed.

6. You know what Software is….
Software, is that part of a computer system that
consists of encoded information or computer
instructions, in contrast to the
physical hardware from which the system is
built.

7. You Know What Radio is….
• Radio is the technology of using radio waves to
carry information, such as sound, by
systematically modulating some property of
electromagnetic energy waves transmitted through
space, such as their amplitude, frequency, phase, or
pulse width.

8. When Software Meets Radio……

9. Why Software Meets Radio….
• There are certain crucial drawbacks with pure radio systems.
• Least Flexibility
• Design Cost is High
• Possibility of Updating to new technologies is difficult.
• These Drawbacks are addressed by incorporating Software along with the
Hardware Radios

10. Software Defined Radios - Definition
• A number of definitions can be found to describe Software Defined Radio, also known as Software Radio or SDR.
The SDR Forum, working in collaboration with the Institute of Electrical and Electronic Engineers (IEEE) P1900.1
group, has worked to establish a definition of SDR that provides consistency and a clear overview of the technology
and its associated benefits.
• “The Radio in which some or all of the physical layer functions are software defined”
• As the name suggests, a software defined radio is a radio system where the majority of baseband processing
(Physical Layer Functions) are done in software which includes modulation, forward error correction, spreading,
filtering, frequency, timing synchronization, and so on.

11. Software Defined Radios - Applications
• One application may be for cellular base stations where standard upgrades frequently occur.
• By having a generic hardware platform, upgrades of standards can easily be incorporated.
• Any Evolution can be easily deployed just by upgrading the software.
• For example, UMTS to HSPA and on to LTE could be accommodated simply by uploading new
software and reconfiguring it without any hardware changes, despite the fact that different
modulation schemes and frequencies may be used.

12. Ideal SDR Architecture
PURELY DIGITAL Purely Analog
?

13. Solution
• The conversion process between the analog and digital signaling domains, were carried out by
Digital-to-Analog converters (DACs) and Analog-to-digital converters (ADCs).
• The concept of ideal SDR is shown in the figure.

14. Ideal SDR
• The ideal SDR architecture is more flexible such that the radio may be configured,
occasionally in real time, to adapt to various air standards and waveforms, frequency
bands, bandwidths, and modes of operation
• That is, the SDR is a multifunctional, programmable, and easy to upgrade radio that
can support a variety of services and standards while at the same time provide a low-
cost power-efficient solution

15. Ideal SDR - Working
• The received signal comes in from an antenna, is converted to the digital
domain via the analog to digital converter (ADC), and the rest of the signal
processing is done in software.
• Likewise, the transmitter performs all the signal processing in software and
sends the signal out of the antenna via the digital to analog converter

16. Ideal SDR - Limitations
• The requirements of the ADC and DAC as dictated by dynamic range, sampling rates, and
bandwidth specifications far exceed practical capabilities. Also they vary along with the
applications
• There are different types of Hardware implemented based on the application such as field
programmable gate arrays (FPGA), digital signal processors (DSP),and general purpose
processors (GPP) . Which creates the compatibility issues with the software used.

17. High Level SDR Transmitter

18. High Level SDR Transmitter & Receiver

19. Difficulties in Implementation
• Things like forward error correction(FEC) and interleaving operate on bits at the bit rate.
• the decoding process at the receiver is a very complex procedure.
• The modulator converts bits into symbols in the complex plane for transmission
• Receiving process requires computationally expensive frequency, phase, and timing synchronization to properly demodulate digital signals.
• Before the symbols can be sent to the analog portion of the transmitter through the DAC, we often need some rate conversion step. The DAC
and the analog hardware will be clocked at some rate that must be at least twice as fast as the bandwidth of the signal going into the DAC to
meet the Nyquist criteria. This requires some rate conversion algorithm that up samples the signal to match the DAC’s sampling rate

20. Potential Benefits of SDR
• The usage of software defined radio offers various advantages over the hardware
radios. Few of the advantages are mentioned below
• SDR offers the greatest flexibility
• SDR provides Software Reusability
• Testing and Analysis made easy using SDR

21. 1. SDR offers the greatest flexibility
• Developing and debugging software is much easier, more practical, and more cost-effective than designing and
producing hardware like an ASIC where the turnaround time is long and expensive
• SDR offers easy upgrades and bug fixes in deployed systems
• If a new system or waveform is required, as long as there is enough processor power, software updates can be
pushed to an existing operating system
• This capability saved time and cost of design and deployment, and it lowered the costs to the service provider who
do not have to install a new system.

22. 2.SDRprovidesSoftwareReusability
• When software is modular and well-written, it can be ported between processors with
minimal rewriting.
• this is not suitable for FPGA-based SDR systems where the software language is too low
level and does not provide sufficient abstraction to be platform independent,
• Nevertheless, in systems that are GPP based, code portability is a major advantage.

23. 3. Testing and Analysis made easy using SDR
• It is easy to test individual signal processing blocks, simulate
performance, and test behavior in a closed system and then reuse the
same software for a real, over-the air system.

24. People getting benefitted from the advantages
• Radio Equipment Manufacturers and System Integrators, SDR enables:
• A family of radio “products” to be implemented using a common platform architecture, allowing new products to
be more quickly introduced into the market.
• Software to be reused across radio "products", reducing development costs dramatically.
• Over-the-air or other remote reprogramming, allowing "bug fixes" to occur while a radio is in service, thus
reducing the time and costs associated with operation and maintenance.

25. People getting benefitted from the advantages
• For Radio Service Providers, SDR Enables:
• New features and capabilities to be added to existing infrastructure without requiring major new capital
expenditures, allowing service providers to quasi-future proof their networks.
• The use of a common radio platform for multiple markets, significantly reducing logistical support and
operating expenditures.
• Remote software downloads, through which capacity can be increased, capability upgrades can be
activated and new revenue generating features can be inserted.

26. People getting benefitted from the advantages
• For End Users ,SDR technology aims to:
• Reduce costs in providing end-users with access to ubiquitous wireless
communications enabling them to communicate with whomever they need,
whenever they need to and in whatever manner is appropriate

27. Software Radio Architecture Evolution
What is Architecture?
An architecture is a framework in which a
specified class of components is used to
achieve a specified family of functions
(e.g. communications services) within
specified constraints, the design rules

28. Demographics - Method to Study the Evolution
What is Demographics?
Demographics is the science of vital and social
statistics, as of the births, deaths, diseases, marriages,
etc., of populations
Demographics identifies major trends in human history. Demographics, for example, identified the departure of
populations from villages to the cities after the turn of the century.

29. Radioarchitectureevolution

30. Understandings from the Radio Evolution
• Complexity of functions, components, and design rules increases with each subsequent generation.
• The Functionality of early analog radios was limited to transmit and receive AM or FM, with RF,
power, volume, and squelch controls.
• An antenna, analog transmitter, receiver, and hardware controls provided necessary and sufficient
Components.
• The associated Design rules consisted primarily of constraints on the RF emission template including
radiated power and out-of-band energy.

32. 1G Introduction
• 1G are the analog telecommunications standards that were introduced in the
1980s
• The main difference between the two mobile telephone systems (1G and 2G), is
that the radio signals used by 1G networks are analog, while 2G networks are
digital

33. 1st Generation Wireless Systems.
• First-generation (1G) mobile cellular radio (MCR) systems incorporated the signaling and control functions of wireline
telephony into a dedicated, digitally encoded RF signaling channel.
• This imposed rigorous structure onto the radio network, introducing the mobile wireless network hierarchy
• Voice traffic was assigned to a single narrowband (e.g., 25 kHz) analog traffic channel.
• The networks used the signaling channels to page mobiles, to accept call setup requests, and to direct mobiles to specific traffic
channels
• This centralized control transformed RF carriers into radio resources to be managed algorithmically.

34. 2G Introduction
• Second-generation 2G cellular telecom networks were commercially launched on the GSM standard in Finland by
Radiolinja
• Three primary benefits of 2G networks over their predecessors are:
• phone conversations were digitally encrypted
• more efficient on the spectrum allocation
• 2G introduced data services for mobile
• 2G technologies enabled the services such as text messages, picture messages, and MMS
• All text messages sent over 2G are digitally encrypted, allowing for the transfer of data in such a way that only the
intended receiver can receive and read it.

35. 2G Contd…
• 2G technologies can be divided into time division multiple access (TDMA)-based and code division multiple access (CDMA)-based
standards depending on the type of multiplexing used
• Few of the important standards of 2G Systems at global level are
• GSM
• IS-95 @ cdmaOne
• 2G Standards in other contries. (Least used, later migrated to GSM)
• PDC also known as JDC (Japanese Digital Cellular) (TDMA-based), used exclusively in Japan
• iDEN (TDMA-based), proprietary network used by Nextel in the United States and Telus Mobility in Canada
• IS-136 a.k.a. Digital AMPS or D-AMPS (TDMA-based, commonly referred as simply 'TDMA' in the US), was once prevalent in the Americas, but
most have migrated to GSM.

36. Evolution of 2G
• 2.5G (GPRS)
• 2.5G ("second and a half generation") is used to describe 2G-systems that have implemented a packet-switched
domain in addition to the circuit-switched domain
• Packet switching is introduced in this standard.
• This gave the way for the evolution of 2G Systems to 3 G Systems
• 2.75G (EDGE)
• GPRS networks evolved to EDGE networks with the introduction of 8PSK encoding,
• Enhanced Data rates for GSM Evolution (EDGE)
• EDGE was deployed on GSM networks beginning in 2003—initially by AT&T in the United States.

37. 2nd Generation Wireless Systems.
• The second-generation (2G) TDMA increased the complexity of commercial mobile cellular radio by an order of magnitude
over 1G
• The 2G standard employed eight-way time slicing of a single RF carrier in its TDMA air interface.
• Each RF carrier was modulated to a 270 kHz bandwidth to provide 13 kbps data rate for each of eight users
• It also incorporated digital voice coding, digital channel symbols on the traffic channels, equalization, training sequences,
precise framing, and other design rules to improve quality of service
• The GSM entered competitive deployment in the early 1990s
• Over 100 nations are now participants in the GSM Memorandum of Understanding (MoU).

38. 3G Introduction
• 3G is based on a set of standards used for mobile devices and mobile telecommunications use services and
networks that comply with the International Mobile Telecommunications-2000 (IMT-2000) specifications by the
International Telecommunication Union.
• 3G finds application in wireless voice telephony, mobile Internet access, fixed wireless Internet access, video calls
and mobile TV.
• The most widely used standards of 3 G Systems are:
• UMTS (Universal Mobile Tele communications Service)
• CDMA2000 system
• 3G Provides high levels of Security and Data rates than compared to 2 G Standards.

39. 3rd Generation Wireless Systems.
• 3G telecommunication networks support services that provide an information transfer rate of at least 200 kbit/s
• Later 3G releases, often denoted 3.5G and 3.75G, also provide mobile broadband access of several Mbit/s to
smartphones and mobile modems in laptop computers.
• The increasingly complex design rules are necessary to ensure smooth interoperation and service availability in a
heterarchical infrastructure with the many time-varying demands of voice, mobile computing, computer-telephony
integration, and ultimately multimedia.
• While deploying these more complex systems, the service providers must remain cost competitive.

40. Verdict

41. Solution…
• The ideal way for addressing this
increasing complexity is bringing in the
“Software”
• The level of software is again decided by
the level of complexity

42. Level of Software
• Low Level Calculations
• Maximum hardware, Minimum Software
• Number of lines of Codes (LOC) is less
• Medium Level Calculations
• Balanced Hardware & Software
• Number of lines of Codes (LOC) is moderate
• High Level Calculations
• Maximum Software, Minimum Hardware
• Number of lines of Codes (LOC) is High

43. ComplexityEqualsSoftware
• Based on the evolution of radios networks studied so far clearly illustrates that the complexity of the
radio system is increasing along with the technological development.
• These complexities are addressed by incorporating the software to take control over the various
parameters or to define the various radio parameters along with the radio architecture that leads us to
the development of Software Defined Radio Architecture gradually.

44. • Radio architectures may be plotted on the dimensions of network organization versus channel data rate as shown in
Figure.

45. Level of Software - Categories
• Based on the level of software intervention with the radio system it can be
classified into 3 categories as mentioned below:
• Radios with Minimal Software
• Moderate Software Complexity
• Toward s a million lines of Codes

46. 1. Radios with minimal Software
• Point-to-point radios included Push to Talk (PTT) and frequency division multiplexed (FDM) radios of the 1960s and 1970s
• They carried 60, 240, and 1920 voice channels or more.
• Early PTT and FDM radios included no software for physical layer and data link functions
• T-carrier digital pulse code modulation (PCM) microwave radios superseded them in the high-capacity backbone networks of the 1980s.
Current high-capacity PCM systems may employ high-order QAM [20] or multicarrier technology to achieve OC-12 (622 Mbps) and higher
data rates.
• Software complexity for such radios is generally less than 10 k LOC. Most of such code consists of hard-real-time DSP or FPGA code plus
microprocessor-based control of hybrid analog/digital functions.

47. 2. Moderate Software Complexity
• Frequency hopping radios like the slow-hopped Have Quick radio, for example, were first deployed by
the military to reduce jamming vulnerabilities. These peer networks collaboratively select one station as
the network control station.
• direct-sequence spread spectrum in addition to faster hopping and time division multiplexing to create a
robust, high-performance but relatively expensive radio however, frequency hopping reduces multipath
fading.
• A single waveform with frequency hop (FH) and other spread-spectrum features typically requires 40 k
LOC.

48. Concept of Frequency Hopping

49. Concept of Direct Sequence Spread Spectrum

50. 3. Toward s a million lines of Codes
• The RF channel modulation and hence efficiency in use of the spectrum have matured from analog FM frequency division
multiple access (FDMA) in first-generation analog systems to time division multiple access (TDMA) in 2G systems. CDMA in
3G mobile wireless
• The network organization has been that of a single hierarchy.
• That is, the mobile handset is subordinate to a Base Transceiver Station(BTS),
• BTS is subordinate to a Base Station Controller (BSC).
• The BSC is subordinate to a mobile telephone switching office (MTSO),
• MSTO is subordinate to the telecommunications management network.
• Handoff from one transceiver to another operates within one hierarchy.

51. Single Hierarchy

52. • With the emergence of satellite mobile systems which interoperate with PCS for seamless roaming, handsets may operate in two
different hierarchies:
• The terrestrial mobile hierarchy
• The satellite mobile hierarchy
• In early days the user selects the hierarchy to be followed manually. Thus there is no need of handover across the hierarchies.
• Modern 3G Systems, have become more complex, in such a way that the handset or network must pick the most appropriate band,
mode, QoS and tariff parameters autonomously.
• This leads to some kind of mode-awareness capability distributed among the handset and the hierarchies.
• These awareness are addressed by the software.
• the operating system and the air interface may comprise from 100 to 400 k LOC

53. Software Radio Architecture – Design
• To prepare for the next decade of rapid evolution of software-intensive
radios, it is mandatory to understand software radio architecture in depth.
• The architecture are presented in 3 perspectives
• Commercial Architecture
• Military Architecture
• Open Architecture.

54. To be Continued…

55. Technological Trade Off
• A trade-off (or tradeoff) is a situation that
involves losing one quality or aspect of
something in return for gaining another
quality or aspect. More colloquially, if one
thing increases, some other thing must
decrease.

56. Most Typical Example
350 cc --- 20 KmpL
150 cc --- 40 KmpL
80 cc --- 60 KmpL

57. SDR – Design Trade off
• It is very difficult to design a SDR system that provides all the required parameters at its optimum level.
• Some compromise should be done on one or the other to achieve a wide range of functionality.
• The design process of SDR is classified into 6 stages.
• Antenna design
• RF – IF Conversion Stage
• Design of ADC
• Hardware Architecture
• Software Architecture
• Evaluating the Performance

58. SDR Design Trade off

59. Antenna Trade off

60. 1. Antenna Trade off
• The antenna segment establishes the available RF bands
• The antenna determines the directional properties of the receiving system
• This tradeoff defines the structure of the antenna segment which in turn decides the RF and IF
Conversion Stage.
• Let us consider the Device with the mentioned facilities

61. Antenna tradeoffs.

62. Need for narrow band antennas
• PDA needs to operate in first-generation cellular (AMPS), and second- or third-
generation digital cellular (PCS) bands. In addition, for location-aware services,
the PDA has a GPS receiver. Finally, in order to operate on the corporate RF
LAN, it supports a LAN band.

63. Problem
• The physical integration of the different RF devices creates
implementation difficulties.

64. Solution – Broad Band Approach
• The broadband approach illustrated in Figure 6-2b simplifies the antenna and RF
design to only two parallel channels. Finally, Figure 6-2c illustrates the spectral
coverage of a single wideband antenna
• Note that the antenna response is not uniform across such a broad range.
• This can be an effective approach if cost is not a major consideration.

65. Trade offs
• interface between the antenna and the RF conversion stage determines VSWR, insertion loss,
and other miscellaneous losses.
• Transmission efficiency and matching voltage standing wave ratios (VSWR) are more
challenging as bandwidth increases.
• As frequency increases, wavelengths approach the physical dimensions of the RF devices,
making it more difficult to fabricate.

66. Parameters that contributes to antenna trade-off
• The various parameters that contribute to the antenna trade off are as
mentioned below:
• Antenna selection
• Parameter control
• Packaging installation and operation

67. 1. Antenna Selection
• Each antenna will have their own merits and demerits.
• Every antenna varies with the Bandwidth, Efficiency, Directivity , VSWR, Etc.,
• Narrowband antennas have only a few percent relative bandwidth
• Wideband antennas such as log periodic and equiangular spirals require a large number of
resonant elements and therefore have a relatively high cost compared to narrowband resonant
antennas

68. AvailabilityofDifferentAntennas

69. For the ideal software radio, one needs a single antenna element
that spans all bands. Requirements of the JTRS program are
illustrated in Figure 7-2a.

70. 2.ParameterControl
• The use of wideband antennas that enable SDR levels of performance
complicates the control of SNR, timing, and phase parameters
• Linearity and Phase Noise
• Parameters for Emitter Locations

71. • Linearity and Phase Noise:
• As the antenna bandwidth is increased, the thermal noise power increases linearly. Thus, the antenna
channels must be filtered to select only those subsets of the band required to service subscriber signals. This
is accomplished in the RF conversion and digital IF processing segments.
• Parameters for Emitter Locations
• To provide the effective SDR Services it is important to estimate the exact location of the node in the
network. Network-based emitter location techniques include time-difference of arrival (TDOA) and angle
of arrival (AOA) estimation using phase interferometry

72. 3. Packaging of Antennas:
• The final stage of the antenna design is that it should be fabricated properly
so as to accommodate within the stipulated space and direction constraints.
• The various parameters that are affected due to these limitations are:
• Gain of the antenna,
• Bandwidth of the antenna and
• Calibration of antenna

73. Gain of the antenna
• The Gain of the antenna will be at its optimum level only in certain directions.
• Approximately, the high gain is available only within about 20 degrees of the direction
in which the antenna is pointing.
• As the SDR engineer increases coverage to satisfy the need for agile RF access, it in
turn demands the antenna to point in more than one direction.

74. Bandwidthoftheantenna
• The micro strip patch antenna provides a much more convenient physical structure, but with only moderate
relative bandwidth.
• Several such antennas could be combined using an analog received signal strength indicator (RSSI) circuit to
yield reasonable gain in most directions.
• Using a lower gain antenna reduces the link margin and therefore increases the outage probability
proportionally.
• However, the SDR design process must entertain the use of such suboptimum antennas. That is, the SDR
antenna may be suboptimal for a specific band, but may be optimal in terms of aggregate cost and quality of
information services across the combination of bands and modes over which the radio operates.

75. Calibrationofantenna
• Proper care should be taken in calibrating the antenna since the antennas involved in SDR have to deal with
multiple channels which are separated with minute band gaps.
• Any misinterpretation in the received signal leads to a major problem in the entire system.
• Recalibration process should generally be undertaken when the antenna subsystem undergoes configuration
changes.
• Movement of a large antenna to a new site may necessitate recalibration using portable test equipment.
• Structural changes to a vehicle on which the antenna(s) are mounted may also necessitate recalibration.

76. Verdict
• The antenna characteristics determine not only the gain, but also several critical
characteristics of the SDR, including:
• The number of antenna channels required to support multiband multimode operation
• Usually, the number of parallel RF conversion chains
• Often, the number of ADCs and DACs required

77. RF to IF Trade off

78. RfandIfProcessingTradeoffs
• The second tradeoff concerns RF and IF conversion.
• When the antenna receives the RF signals then the next step is to convert them to IF
for further processing at the receiver.
• The main focus of this trade off is about the Noise added during the RF to IF
Conversion.
• The various noise that are added is as follows:
• Spurious Noise
• Local Oscillator Leakage
• Thermal Noise

79. RfandIfProcessingTradeoffs

80. Two ways of RF to IF Conversion
• RF to IF Conversion can be done in two familiar methods, they are:
• Direct Conversion Method
• Super heterodyne Method
• Here the super heterodyne receiver used in base station applications, as it has the capability to
handle multiple channels at the same time.
• The direct conversion receiver used in handsets, as they are well suited for single channel
operations

81. SuperHeterodyneReceiver
• Each conversion stage includes one LO and additional filtering and amplification.
• . The modulator that converts the RF into the initial IF generates sum and difference frequencies in addition to the desired
frequency.
• Each and every stage of conversion produces an unwanted noise which are amplified in the subsequent stages.
• After a particular point this noise signal becomes dominant to the original message signal.
• In addition to the desired sideband, the conversion process introduces thermal noise, and undesired sidebands into the IF
signals.

82. SuperHeterodyneReceiver

83. DirectConversionReceiver
• The homodyne receiver translates RF to baseband, with the center frequency tuned to zero Hz in one
step.
• LO leakage and DC bias can be significant problems with such an approach.
• Local-oscillator energy can leak through the mixer stage to the antenna input and then reflect back into
the mixer stage.
• The overall effect is that the local oscillator energy will self-mix and create a DC offset signal. The offset
may be large enough to overload the baseband amplifiers and prevent receiving the wanted signal.

84. DirectConversionReceiver

85. ADC
Trade off

86. ADC Trade Off
• The third trade-off is the design of the ADC segment
• The wideband ADC is one of the fundamental components of the software radio, the analog signal to be
converted must be compatible with the capabilities of the ADC or DAC.
• We know that the signal can be effectively reconstructed by satisfying the Nyquist Rate.
• The minimum rate at which a signal can be sampled without introducing errors, which is twice the
highest frequency present in the signal is called as the Nyquist Rate

87. Problem..
• If the wideband analog signal extends beyond the Nyquist frequency, then there is a chance of “Aliasing”
as shown in the figure.
• Although some aliasing is unavoidable, an ADC designed for software-radios must keep the total power in
the aliased components below the minimum level that will not unacceptably distort the weakest subscriber
signal.

88. Alternative for Nyquist ADC
• An alternative for the Nyquist ADC referred to as Oversampling ADC.
Real oversampling with digital quadrature provides a lower-complexity.
• oversampling is the process of sampling a signal with a sampling
frequency significantly higher than the Nyquist rate.

89. Methods for Implementing ADC
• There are several methods for implementing the ADC, they are:
• Sigma – Delta ADC
• Quadrature Techniques
• Band Pass Sampling ADC

90. Sigma Delta ADC
• Sigma Delta ADCs are now ideal for converting analog signals over a wide range of
frequencies, from DC to several megahertz.
• Basically, these converters consist of an oversampling modulator followed by a digital/
decimation filter that together produce a high-resolution data-stream output.

92. • A modulator converts the input analog signal into digital bit streams (1s and
0s).
• The decimation filter receives the input bit streams and, depending on the over
sampling ratio (OSR) value, it gives one N-bit digital output per OSR clock
edge. (Averaging)

93. Working of a Modulator
X1
X2 X3 X4
X5

94. X2 = X1-X5
X3 = X2 + X3(n-
1)
IF X3 > 0 IF X3 < 0
X4 = 1 X4 = 0
X5 = +1 X5 = -1
X1
• Density of ones is
more when the input
is more positive.
• Density of zeros is
more when input is
more negative.

95. Working of Decimation Filter
A sinc filter is an idealized filter that removes all frequency components above a
given cutoff frequency, without affecting lower frequencies,

96. Functioning of Decimation Filter
SIGMA – DELTA
BLOCK
DECIMATION
FILTER
Analog input 1100000110000011 Avg.= (6/16 )= 0.375
0110
16 - one bit stream
One 4 - bit representation
16:1 Decimation
Over sampled
at 16 times

97. Advantages of Over Sampling
• The various advantages of oversampling are as follows:
• The usage of sample and hold circuit are minimized.
• The oversampling minimizes the Aperture Jitter by integrating the over samples
signals.
• The requirement of Anti-Aliasing filters of sigma-delta ADC are not as severe as for
Nyquist ADC

98. 2. Quadrature Sampling Techniques
• Quadrature sampling uses complex numbers to double the bandwidth accessible with a given sampling
rate.
• Consider a band pass signal g(t) (limited to the frequency band [Fc - W, Fc +W])
• Let gi(t) denote the in phase component of the bandpass signal g(t) and gq(t) denote its quadrature
component.
• Then we may express g(t) in terms of gi(t) and gq(t) as follows
g(t) = gi(t) cos(2∏ Fct) - gq(t) sin(2∏ Fct)

99. • We know that the two signals gI (t), gQ (t) are low pass and limited to a frequency band of [-
W, W].
• This means that we can represent each of these two signals using 2W samples per second.
• This results in a total of 4W samples per second for the band pass signal g(t) which has a
band width of 2W.
• To reconstruct the original band pass signal from its quadrature sampled version we first
reconstruct gI (t), gQ (t) and then combine them.

101. Block Diagram for Quadrature Sampling

102. Implementation Difficulties
• The modulators, signal paths, and low-pass filters in each I&Q path must be
matched exactly in order for the resulting complex digital stream to be a faithful
representation of the input signal.
• Any mismatches in the amplitude or group delay of the filters yields distortion
of complex signal.

103. 3. Band Pass Sampling
• They are also called as Digital Down Conversion Techniques
• Band pass sampling or under sampling is a technique where one samples a band pass-filtered signal
at a sample rate below its Nyquist rate
• The principle of band pass sampling is to sample a passband of bandwidth WNyquist centred at
frequency k fs (k >= 2, k is even), at the Nyquist rate fs. The high-frequency components are
translated to baseband by the frequency translation property of subsampling.

105. Hardware
Trade off

106. Hardware Trade Off
• As we all know that a software cannot work on its own.
• It has to be installed on a hardware to process the information acquired by the
software.
• This brings in the need for processors which process the information based on the
instructions given by the software.
• It is important to choose the processor so as to get the optimum output from the
software defined radios.

107. Metrics
• The processing capacity of the SDR is defined by the processor.
• There are several “Metrics” to measure the capacity of the processor.
• Metric should be chosen properly because, Based on these metrics the designer should be able to
• Predict the performance of an unimplemented software suite on an unimplemented hardware platform.
• Manage the computational demands of the software against the benchmarked capacities of the hardware as the
product is implemented. Finally,
• Determine whether an existing software personality is compatible with an existing hardware suite.

108. Processing Metrics

109. Instruction Vs Operation
• An operation (OP) is a logical transformation of the data in a designated element of hardware in one
clock cycle.
• An instruction is a command given to the processor which involves multiple operations.
• ADD A,B  Instruction
• Get A
• Store in Memory
• Get B
• Store in Memory
• Perform Addition
• Store Result in Memory
Operations

110. Relation Between MIPS and MOPS
• Processor architectures typically include hardware elements such as arithmetic
and logic units (ALUs), multipliers, address generators, data caches, instruction
caches, all operating in parallel at a synchronous clock rate.
• α = Number of parallel hardware elements.
MIPS = α MOPS, α < 1

111. Demand for Memory Unit
• Based on the number of instructions and number of
operations going to be handled by the hardware there comes
for the demand of the Memory Unit.
• The memory is to be decided accordingly to handle as many instructions needed by the processor
• The demand for memory increases or the memory unit becomes an important parameter when there are more
instructions to be fetched from cache.
• The performance may get degraded if there is no enough memory

112. Processor Memory Interplay
• Processors that are more complex may fill a
pipeline with instructions to be executed
concurrently. Pipelines produce no results
until the pipeline is full.

113. Processor Memory Interplay
• The solution is that the memory should be provided with most advanced pipelining techniques.
• Eg: Set-associative cache.
• This technique helps in loading the necessary instructions in the memory rather dumping all available
information.
• This increases the processing capacity of the processors.

114. Interconnecting processor and memory
• The physical packaging of these functions may be organized in point-to-point
connections, buses, pipelines, or meshes.

115. 3 types of interconnect
• Dedicated Interconnect: They are well suited for the applications with relatively small
numbers of IF channels, it represents a solid engineering approach.
• Wideband Bus: These type of bus are suited for higher speed channels and also
multichannel support such as 8X140 MBps channels
• Shared Memory: Shared memory can deliver the ultimate interconnect bandwidth.
Clock rates of 25 to 250 MHz are within reach.

116. Types of Hardwares
• There are 3 main types of hardware that are mostly used in SDR.
• Field Programmable Gate Array – FPGA
• Application Specific Integrated Circuits – ASIC
• Digital Signal Processors - DSP

117. Applications-SpecificIntegratedCircuits
(ASIC’s)
• An application-specific integrated circuit (ASIC), is an integrated circuit (IC)
customized for a particular use, rather than intended for general-purpose use.
• ASICs particularly suited for software radios include 3 important modules:
• Digital Filters,
• Forward Error Correction,
• RF-transceiver.

118. Digital Filter ASIC
• Base station architectures need digital frequency translation and filtering for hundreds of
simultaneous users.
• The computational complexity in filtering and translating hundreds of user’s frequency is very
high at the base station.
• Frequency translation, filtering, and decimation requiring 200 operations per sample equates to
over 6000 MIPS of processing demand.

119. ForwardErrorControl(FEC)ASICs
• the FEC decoder synchronizes the input bit stream, reverses symbols into
message bits and computes the majority logic best-estimate of the transmitted
bits using a Viterbi decoder.
• It then differentially decodes the stream and descrambles the resulting bit
stream by adding the scrambling bit stream synchronously to the output
stream.

120. FEC ASIC architecture.

121. TransceiverASICs
• These are the ASIC’s which is similar to that of the digital Filter ASIC, in
addition to that it also has a transceiver functions along with it.
• The best example of such ASIC’s are STEL-2000 A

122. STEL-2000Ablock diagram

123. Inbuilt Functions…
• The numerically controlled oscillator (NCO) and clock feed the CPSK modulator
• The architecture also consists of Differential encoding and decoding pairs.
• The receiver clock generator, PN code generator, matched filter, power detector, and
symbol tracking processor may function as a de spreader.
• Control and interface logic permit to integrate this ASIC into a spread-spectrum class
SDR.

124. 2. Field-Programmable Gate Arrays (FPGAS)
• FPGAs are high-speed configurable logic circuits packaged as high-density commodity chips
• The physical and logical layout is designed for rapid implementation of state machines and
sequential logic.
• Combinatorial logic such as buffer registers, decoders, and multiplexers may be implemented
efficiently in FPGAs
• Most commercial chips also include timer circuits FPGAs may be used for complex processes
such as convolution, correlation and filtering

125. Digital Signal Processors
• A digital signal processor (DSP) is a specialized microprocessor with its architecture optimized for the
operational needs of digital signal processing.
• The goal of DSPs is usually to measure, filter and/or compress continuous real-world analog signals.
• DSPs often use special memory architectures that are able to fetch multiple data and/or instructions at the
same time.
• DSP chips are designed for efficient execution of computationally intense functions like filtering and fast
Fourier transforms (FFTs).
• The best example is : TMS320C30

126. Software
Trade off

127. • This section deals with the design of Software for SDR.
• Based on the capability of the software they are given as the function of
level of abstraction as mentioned in the figure.

128. Overview of software architecture tradeoffs

129. Communication Services Layer
• This is the highest level,
• Defining interfaces among applications and services is the main function of this
layer
• Such interfaces need to be radio-aware so that the radio’s low data rates, high
variability in data transfer times, and occasional outages do not severely reduce
user satisfaction with the services.

130. Radio Applications Layer
• Partitioning the radio software into reusable objects and defining the radio level
interfaces are the main functions of this layer.
• In the radio applications layer, object-oriented design techniques help group related
data structures with appropriate algorithm methods.
• This simplifies detailed design, development, testing, deployment, and evolution of the
software architecture.

131. Radio Infrastructure
• This layer defines an architecture for the software.
• There are 2 types of architectures
• Open architecture
• Closed architecture
• Open-architecture approaches now favour the use of the industry-standard CORBA in radio
infrastructure middleware.
• Such architecture reduces the coupling between radio functions and distributed processor hardware.
• This adds flexibility but requires processing capacity above that which is needed for a closed
architecture.

132. Hardware Platforms
• This layer deals with the real-time interface to the hardware platform.
• Defining the Operating system profile and tuning it for performance is the
main function of this layer.
• This includes not just the processors, but the many computer-controlled
features of the analog radio platform.

133. Performance
Trade off

134. • The final major trade off concerns the management of processing demand offered by the
software against the resources provided by the hardware platform.
• A sustained measurement and instrumentation campaign to monitor performance
implications of development decisions reduces development risk.
• Performance prediction and management steps add cost to a software radio development
program.

135. Architectural
Implications

136. End
of
UNIT 1