EC 6014 COGNITIVE RADIO UNIT I - SOFTWARE DEFINED RADIOpit.ac.in/file/jUNIT1EC6014Cognitive...

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1 | Page EC 6014 COGNITIVE RADIO UNIT I - SOFTWARE DEFINED RADIO With the rapid evolution of microelectronics, wireless transceivers are becoming more versatile, powerful, and portable. This has enabled the development of software-defined radio (SDR) technology, where the radio transceivers perform the baseband processing entirely in software: modulation/demodulation, error correction coding, and compression. Definition of SDR A software radio is a radio whose channel modulation waveforms are defined in software. All wireless telephones are controlled by this software. A software-defined radio (SDR) is a radio that can accommodate a significant range of RF bands and air interface modes through software. SDR introduced in 1991 is defined as a radio platform of which the functionality is at least partially controlled or implemented in software. Software-defined radio (SDR) is a practical reality due to convergence of two key technologies: digital radio, and computer software. Software-defined radio refers to technologies wherein these functionalities are performed by software modules running on field programmable gate arrays (FPGAs), digital signal processors (DSP), general-purpose processors (GPP), or a combination thereof. This enables programmability of both Digital Up Conversion/ Digital Down Conversion (DDC/DUC) and baseband processing blocks. Hence, operation characteristics of the radio, such as coding, modulation type, and frequency band, can be changed simply by loading a new software. Also multiple radio devices using different modulations can be replaced by a single radio device that can perform the same task. Any waveform defined in the memory of the SDR platform can be employed on any frequency. Initially it is constrained by the conversion process between analog and digital signaling domains, emergence of cheap highspeed Digital-to-Analog converters (DACs) and Analog-to-Digital converters (ADCs) have brought ideal SDR concept of an entirely software communication system implementation (including radio frequency functionality) closer to a reality. Evolution of Software-Defined Radio(SDR ) (Nov/Dec 2016, Nov/Dec 2017) Two decades ago most radios had no software at all, and those that had it didn’t do much with it.

Transcript of EC 6014 COGNITIVE RADIO UNIT I - SOFTWARE DEFINED RADIOpit.ac.in/file/jUNIT1EC6014Cognitive...

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EC 6014 – COGNITIVE RADIO

UNIT I - SOFTWARE DEFINED RADIO

With the rapid evolution of microelectronics, wireless transceivers are becoming more

versatile, powerful, and portable.

This has enabled the development of software-defined radio (SDR) technology, where the

radio transceivers perform the baseband processing entirely in software:

modulation/demodulation, error correction coding, and compression.

Definition of SDR

A software radio is a radio whose channel modulation waveforms are defined in software.

All wireless telephones are controlled by this software.

A software-defined radio (SDR) is a radio that can accommodate a significant range of RF

bands and air interface modes through software.

SDR introduced in 1991 is defined as a radio platform of which the functionality is at least

partially controlled or implemented in software.

Software-defined radio (SDR) is a practical reality due to convergence of two key

technologies: digital radio, and computer software.

Software-defined radio refers to technologies wherein these functionalities are performed

by software modules running on field programmable gate arrays (FPGAs), digital signal

processors (DSP), general-purpose processors (GPP), or a combination thereof. This

enables programmability of both Digital Up Conversion/ Digital Down Conversion

(DDC/DUC) and baseband processing blocks. Hence, operation characteristics of the

radio, such as coding, modulation type, and frequency band, can be changed simply by

loading a new software. Also multiple radio devices using different modulations can be

replaced by a single radio device that can perform the same task.

Any waveform defined in the memory of the SDR platform can be employed on any

frequency. Initially it is constrained by the conversion process between analog and digital

signaling domains, emergence of cheap highspeed Digital-to-Analog converters (DACs)

and Analog-to-Digital converters (ADCs) have brought ideal SDR concept of an entirely

software communication system implementation (including radio frequency functionality)

closer to a reality.

Evolution of Software-Defined Radio(SDR) (Nov/Dec 2016, Nov/Dec 2017)

Two decades ago most radios had no software at all, and those that had it didn’t do much

with it.

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In 1993, Joseph Mitola III envisioned a very different kind of radio: A mostly digital radio

that could be reconfigured in fundamental ways just by changing the software code

running on it. He dubbed this software-defined radio.

Mitola’s vision started to become reality and in mid-1990s military radio systems were

invented in which software controlled most of the signal processing digitally, enabling one

set of hardware to work on many different frequencies and communication protocols.

Fig. 1.1 Evolution of Software-Defined Radio (SDR)

Fig.1.1 shows evolution of software defined radio from 1G, 2G, 3G and 4G.

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Fig.1.2 Key Elements of Architecture Evolution

Fig.1.2 shows key elements of Architecture Evolution.

SDR Evolution in the United States

SDR concept started in the late 1970s with the introduction of multimode radios operating

in VHF band.

U.S. Air Force Avionics Laboratory initiated the Integrated Communication, Navigation,

Identification and Avionics (ICNIA) program in the late 1970s – Developed an

architecture to support multifunctional, multiband airborne radios in the 30 MHz -1600

MHz band – Successful flight test and final report delivery in 1992 – ICNIA radio was the

first programmable radio.

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Fig. 1.3 SDR different types

In the late 1980s, the Air Force Research Laboratory initiated the Tactical Anti-Jam

Programmable Signal processor (TAJPSP) – a processor capable of simultaneous

waveform operations using modular approach – TAJPSP later evolved into the

SPEAKeasy program. Fig.1.3 shows SDR different types.

SPEAKeasy was a joint U.S. Government program to develop the architecture and

technology to meet future military requirements for multimedia networking operations –

The first significant military investment to integrate various existing radio families into

one family was COTS-based architecture which demonstrated multiband, multimode radio

capabilities in 1998. SPEAKeasy evolved into the Joint Tactical Radio System (JTRS).

JTRS Joint Program Office was established in 1999 – which was envisioned to be the next

generation tactical radio for future advanced military operations

Mission is to acquire a family of affordable, high-capacity tactical radios to provide

interoperable LOS/BLOS C4I capabilities to the war fighters.

SDR Forum provides expertise in software radio technology for the JTRS program. The

Object Management Group is working toward building an international commercial

standard on the Software Communications Architecture (SCA).

SPEAKeasy I and SPEAKeasy II radios

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The first (known) example of this type of radio was the U.S. military’s SPEAKeasy I and

SPEAKeasy II radios, allowed units from different branches of armed forces to

communicate for the first time. However, the technology was costly and the first design

took up racks that had to be carried around in a large vehicle.

SPEAKeasy II was a much more compact radio, the size of two stacked pizza boxes, and

was the first SDR with sufficient DSP resources to handle many different kinds of

waveforms. SPEAKeasy II subsequently made its way into the U.S. Navy’s Digital

Modulator Radio (DMR) with many waveforms and modes, able to be remotely

controlled with an Ethernet interface.

SPEAKeasy II and DMR products evolved not only to define radio waveform features in

software, but also to develop an appropriate software architecture to enable porting the

software to an arbitrary hardware platform, thus achieving independence of the waveform

software specification and design from the underlying hardware.

Companies such as Vanu, AirSpan, and Etherstack currently offer SDR products for

cellular base stations. Vanu Inc., a U.S.-based company, has been focusing on the

commercial development of SDR business since 1998.

In 2001 the 3GNewsroom reported SDR base stations as the key solution to the 3G rollout

problem. The ability of SDR base stations to reconfigure and support multiple protocols

was thought to be the safest option for rolling out 3G.

In reality, SDR didn’t play the key role that was anticipated. However, a closer look at the

operator’s infrastructure shows that programmable devices have become a key component

of current 3G base stations.

In 2005 AnywaveTM GSM base station, became the first SDR product to receive approval

under the newly established software radio regulation.

Anywave base station runs on a general-purpose processing platform and provides a

software implementation of the base transceiver station (BTS), base station controller

(BSC), and transcoder and rate adaptation unit (TRAU) modules of the base sation

subsystem (BSS). It supports GSM and can be upgraded to GPRS and Edge. The product

was first deployed in rural Texas by Mid Tex Cellular in a trial, where Vanu base station

showed successfully howit could concurrently run a time division multiple access

(TDMA) and a GSM network, as well as remotely upgrade and fix bugs on the base station

via an Internet link.

AT&T and Nextel, expressed interest in the Anywave base station.

In March 2005 Airspan released the first commercially available SDRbased IEEE 802.16

base station. The AS.MAX base station uses picoarraysTM and a reference software

implementation of the IEEE 802.16d standard. The picoarray is a reconfigurable platform

that is 10 times faster in processing power than today’s DSPs. The AS.MAX base station

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promises to be upgradeable to the next generation mobile 802.16e standard and so has the

potential to offer a future-proof route to operators looking to rolling out WiMAX services.

In addition to the preceding proprietary SDR platforms developed for the military and

commercial sectors, there is also significant progress in the SDR development in the open-

source research and university communities.

GNU Radio is an open-source architecture designed to run on general-purpose computers.

It is essentially a collection of DSP components and supports RF interface to the universal

software radio peripheral (USRP), an up- and down-convertor board coupled with ADC

and DAC capabilities, which can be coupled to a daughter RF board.

GNU Radio is extensively used as an entry-level SDR within the research community.

SDR Evolution in Europe

R&D in Advanced Communications in Europe (RACE) and Advanced Communications

Technology and Services (ACTS) programs – ACTS projects, FIRST and FRAMES, used

software radios to investigate next-generation air-interfaces.

RACE and ACTS focus on incorporating 3G and potentially 4G standards into its Global

System for Mobile (GSM) Communications network – Pave the way for more capable and

more powerful products and flexible services – Key research areas include receiver

arcchitecture, baseband DSP architecture, enabling technologies.

FIRST: Flexible Integrated Radio System and Technology FRAMES: Future Radio

Wideband Multiple Access System.

SDR Evolution in ASIA

In 1999, Japanese Institute of Electronics, Information and Communication Engineers

(IEICE) software radio group was formed with SDR Forum Radio.

In 2000, Korea Electromagnetic Engineering Society (KEES) monitor software radio

activities in Korea, Japan and Taiwan.

IEICE and KEES mission: – Promote R&D in SDR – Allow protocol, software, hardware

to be easily integrated for future radio system – Foster cross-organization and

collaboration among academia, industries and governments .

Digital Radio (DR)

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Fig.1.4 Block diagram of a Generic Digital Radio.

As shown in Fig.1.4 shows Block Diagram of Generic Digital Radio, it has five sections:

Antenna section, receives (or transmits) information encoded in radio waves.

RF front-end section, which is responsible for transmitting/receiving radio frequency

signals from the antenna and converting them to an intermediate frequency (IF).

ADC/DAC section, which performs analog-to-digital/digital-to-analog conversion.

Digital up-Conversion (DUC) and Digital Down-Conversion (DDC) blocks, which

essentially perform modulations of the signal on the transmitting path and demodulation of

the signal on the receiving path.

Baseband section, which performs operations such as connection setup, equalization,

frequency hopping, coding/decoding, and correlation, while also implementing the link

layer protocol.

DDC/DUC and baseband processing operations require large computing power, and in a

conventional digital radio are implemented in dedicated hardware.

In programmable digital radio (PDR) systems baseband operations and link layer protocols

are implemented in software while the DDC/DUC functionality is performed using

application-specific integrated circuits (ASICs).

If the AD/DA conversion can be pushed further into the RF block, the programmability

can be extended to the RF front end and an ideal software radio can be implemented.

Architecture

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Architecture is defined as the comprehensive, consistent set of functions, components and

design rules according to which systems of interest are organized, designed, and

constructed. A specific architecture entails partitioning of functions and components such

that functions are assigned to components and interfaces among components which

correspond to interfaces among functions.

When such functions and interfaces are defined in formal design rules via a public forum,

the resulting architectures are called open. The full economic benefits of open

architectures require the existence of a large commercial base which sometimes fails to

emerge in spite of openness. As system complexity increases, architecture becomes more

critical because of its power to either simplify and facilitate system development (a

“powerful” architecture) or to complicate development and impede progress (a “weak’

architecture).

An architecture is a framework in which a specified class of components is used to achieve

a specified family of functions (eg: communication services) within specific constraints

and design rules.

Fig 1.5 Radio architecture evolving towards a high level of complexity

Radio architectures may be plotted in the phase space of network organization versus channel data

rate, as shown in Fig. 1.5. These architectures have evolved from early point-to-point and

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relatively chaotic peer networks (e.g., citizens band and push-to-talk mobile military radio

networks) toward more hierarchical structures with improved service quality. In addition, channel

data rates continue to increase through multiplexing and spectrum spreading.

In addition, channel data rates continue to increase through multiplexing and spectrum spreading.

In a multiple-hierarchy application, a single radio unit, typically a mobile terminal, participates in

more than one network hierarchy. A software radio terminal, for example, could operate in a GSM

network, an AMPS network, and a future satellite mobile network. Multiband multimode military

radios and future Personal Communications Systems (PCS) that seamlessly integrate multimedia

services across such diverse access modes represent the high end of that evolution and the focus of

this discussion. . The components of the canonical software radio consist of a power supply, an antenna, a

multiband RF converter, and a single chip containing A/D and D/A converters with an on-chip

general purpose processor and memory that perform the ,radio functions and required interfaces

illustrated in Fig. 1.6. The canonical mobile software radio terminal interfaces directly to the user

(e.g., via voice, data, fax. and/or multimedia). The canonical base station interfaces to the public

switched telephone network (PSTN).

Fully instrumented base stations support operations and maintenance, developers and researchers

via services development workstation(s). The placement of the A/D and D/A converters as close

to the antenna as possible and the definition of radio functions in software are the hallmarks of the

software radio. lthough software radios use digital techniques, software-controlled digital radios

are generally not software radios. The key difference is the total programmability of software

radios, includingprogrammable RF bands channel access modes, and channel modulation

Contemporary radio designs mix analog hard- ware, digital hardware, and software technologies.

It is instructive to consider software radios to better understand benefits, pitfalls and relationships

to other technologies. Software radios have become practical as costs per millions of instructions

per second (MIPS) of digital signal processors (DSPs) and general purpose central processor units

(CPUs) have dropped below U.S. $10 per MIPS. The economics of software radios become

increasingly compelling as demands for flexibility increase while these costs continue to drop by a

factor of two every few years. At the same time, absolute capacities continue to climb into the

hundreds of millions of floating-point operations per second (MFLOPS) per chip, at which point

software radios are compatible with commercial TDMA and CDMA applications.

In addition, A/D/A converters available in affordable single-board open architecture

configurations offer bandwidths of tens of MHz with the dynamic range required for software

radio applications. Multimedia requirements for the desktop and palmtop continue to exert

downward pressure on parts count and on power consumption of such chip sets, pushing the

software radio technology from the base station to the mobile terminal. Although the tradeoffs

among analog devices, low-power ASICs, DSP cores and embedded microprocessors in handsets

remain fluid, cutting-edge base stations employ, software radio architectures. Finally, the

multiband, multimode flexibility of software radios appears central to the goal of seamless

integration of PCS, land mobile and satellite mobile services (including truly nomadic computing)

toward which many of us aspire.

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Fig.1.6 Canonical Hardware and Software Defined Radio

The software radio architecture is widely applicable to trunk radios, peer networks, air and

sea traffic management, mobile military communications and satellite mobile systems.

For simplicity, this overview in Fig.1.6 describes the software radio architecture in a

mobile cellular/PCS setting.

In an advanced application, a software radio does not just transmit: it characterizes the

available transmission channels, probes the propagation path, constructs an appropriate

channel modulation, electronically steers its transmit beam in the right direction, selects

the appropriate power level, and then transmits.

Again, in an advanced application, a software radio does not just receive: it characterizes

the energy distribution in the channel and in adjacent channels, recognizes the mode of the

incoming transmission, adaptively nulls interferers, estimates the dynamic properties of

desired-signal multipath, coherently combines desired-signal multipath. adaptively

equalizes this ensemble, trellis decodes the channel modulation, and then corrects residual

errors via forward error control (FEC) decoding to receive the signal with lowest possible

BER as shown in Fig. 1.7.

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Fig.1.7 Software Radio Functional Architecture Mobile Cellular Base Station

The Real-Time Channel Processing Stream

The canonical software radio architecture includes the channel processing stream. the

environment management stream and associated software tools illustrated in Fig. 1.7. The

real-time channel processing stream incorporates channel coding and radio access

protocols. Channel processing is char act e r i ze d by discrete time poi n t operations such

as the translation of a baseband signal to an intermediate frequency (IF) by multiplying a

discrete time-domain baseband waveform by a discrete reference carrier to yield a sampled

IF signal.

The time between samples is on the order of tens of microseconds to hundreds of

nanoseconds. Such point-operations require hundreds of MIPS and/or MFLOPS to Giga-

FLOPS with strictly isochronous performance. That is. Sampled data values must be

computationally produced and consumed within timing windows on the order of the time

between samples in order to maintain the integrity of the signals represented therein.

Input/output (I/O) data rates of this stream approach a gigabit per sec and per AID

converter.

Although these data rates are decimated through processing, it is challenging to sustain

isochronism through I/O interfaces and hard real-time embedded software in this stream.

Multiprocessing is therefore best organized as a pipeline with sequential functions of the

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stream assigned to serially interconnected processors, i.e., a multiple instruction multiple

data-stream (MIMD) multiprocessing architecture.

Environment Management Stream

The near-real-time environment management stream continuously characterizes radio

environment usage in frequency, time and space. This characterization includes channel

identification and the estimation of other parameters such as channel interference levels

(depending on the specific signaling and multiple access scheme) and subscriber locations.

The environment management stream employs block operations such as fast Fourier

transforms (FFTs), wavelet transforms, and matrix multiplies for beam forming. Channel

identification results are needed in times on the order of hundreds of microseconds to

hundreds of milliseconds, while power levels may be updated in milliseconds and

subscriber locations may be updated less frequently.

The block structure of such operations is readily accommodated by a MIMD parallel

processor. The interface between this highly parallel environment management stream and

the pipelined channel processing streams must synchronize the environment management

parameters to the channel processing streams

On-Line and Off-Line Software Tools

On-line and off-line systems analysis, signal processing, and rehosting tools illustrated in

Fig. 1.7 allow one to define incremental service enhancements. For example, an enhanced

beamformer, equalizer and trellis decoder may be needed to increase subscriber density.

These enhancements may be prototyped and linked into the channel processing stream,

allowing one to debug the algorithm(s), to experiment with parameter settings, and to

determine the service value (e.g., in improved subscriber density) and resources impact

(e.g., on processing resources, I/O bandwidth, and time delays).

Software-based enhancements may be organized around managed objects, collections of

data and associated executable procedures that work with object resource brokers and

conform to related open architecture software interface standards such as the Common

Object Resource Broker (CORBA). Enhancements may then be delivered over the air to

other software radio nodes, as contemplated in the future software-defined

telecommunications architectures being considered by ITU-T and embraced by NTT and

others.

A well integrated set of analysis and rehosting tools leads to the creation of incremental

software enhancements relatively quickly, with service upgrades provided over-the-air as

software-defined networks proliferate. Technology limitations that require hardware-based

delivery are overcome by mapping critical elements of the service enhancement to

hardware via VHDL.

Partitioning of The Channel Processing Stream

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The classical canonical model of communications concatenates source encoder, channel

encoder, channel (which adds noise, interference, and distortion channel decoder, and

source decoder. The channel encoderidecoder and related radio access functionsconstitute

the real-time stream.The canonical software radio architecture partitions classical channel

coding and decoding into the channel access segments of Fig. 1.8.

These segments are: antennas, RF conversion, IF processing, baseband processing and

bitstream processing. This canonical partitioning is useful because of the significant

differences in functionality between segments, because of the strong cohesion among

functions within a segment; because of large changes in bandwidth due to decimation

within a segment; and because of the ease with which these particular segments are

mapped to affordable open-architecture hardware. Further rationale for this partitioning is

based on set-theoretic considerations. This partitioning also structures the estimation of

first-order resource requirements so that they may be combined in ways that accurately

predict system performance.

Fig.1.8 Canonical Software Radio Functional Architecture

Challenges of SDR

There are a number of challenges in the transition from hardware radio to software (-

defined) radio.

First, transition from hardware to software processing results in a substantial increase in

computation, which in turn results in increased power consumption.

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This reduces battery life and is one of the key reasons why software-defined radios have

not been deployed yet in end-user.

Issues relating to SDR

The main issue with introducing SDR into portable devices is that it requires the use of

programmable platforms, which are generally power hungry and hence lead to reduced

battery life and large devices.

Advantages of SDR-Potential Benefits of SDR (Nov/Dec 2016)

SDR provides the ability to support multiple waveforms on a single device, and so

ultimately could give an end user increased choice of services if incorporated into a

portable device, such as a handset.

SDR also assist seamless roaming at the national and international levels.

In late 1990s SDR started to spread from the military domain to the commercial sector,

with the pace of penetration into this market considerably accelerating in the new

millennium. Cellular networks are considered potentially most lucrative market for SDR

could penetrate.

Interoperability through the ability to support multiple standards.

Benefits for industry include a general-purpose and economic hardware platform, future-

proofing and easier bug fixes through software upgrades, increased functionality.

SDR can provide potential benefits for aviation community.

Accommodate multiple air-interface standards

Facilitate transition by bridging legacy and future technologies

Allow multiple services – incentives for equipage

Implement future-proof concept

Capable for insertions of future technologies and allow easy upgrades

Implement open-architecture to allow multiple vendors to supply or participate, offer

declining prices

Reduce product development time

Enable other advanced commercial technologies to be adapted to offer user’s services and

benefits

Drawbacks of SDR

Due to its high demand on computation and processing, SDR technology works only in

devices that have less constraint in size and power consumption, such as base stations and

moving vehicles.

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SDR Applications

SDR is currently used mostly in military applications, where cost is less of a constraint.

SDR is used in commercial sector.

SDR is currently used to build radios that support multiple interface technologies (e.g.,

CDMA, GSM, and WiFi) with a single modem by reconfiguring it in software.

However, SDR modems are expensive, since they typically entail programmable devices

like FPGAs, as opposed to the mass-produced, single-purpose Application Specific

Integrated Circuit (ASIC)s used in most consumer devices today (and are key enablers for

low-cost handsets). Today’s multimode devices tend to just have multiple ASICs (or

multiple cores on a single ASIC).

SDR is a modem technology and it ignores RF design issues. In particular, the RF design

of a wireless device is typically closely coupled with the underlying access technology and

modem design. For example, different air interface technologies have different spectral

mask requirements and different degrees of vulnerability to cochannel interference and

strong adjacent channel power. A device that must work over a wide bandwidth or over a

wide range of RF signal scenarios (i.e., what other devices are operating in the nearby

spectrum neighborhood) will be more complex and expensive than a single-purpose

device.

But there is an increasing demand for SDR to enter portable and handheld devices

in the future.

However, as new processing platforms emerge that overcome power and size

constraints, it is very likely that SDR will make its way into portable devices.

Technology Tradeoff’s (Nov/Dec 2016, April/May 2017, Nov/Dec 2017)

Segment Design Tradeoffs

Segment design tradeoff’s are Antenna Tradeoffs, RF and IF Processing Tradeoffs, ADC

Tradeoffs, Digital Architecture Tradeoffs, Software Architecture Tradeoffs, Performance

Management Tradeoffs, End-to-End Tradeoffs.

Antenna Tradeoff’s

The antennas of the software radio span multiple bands, up to multiple octaves per band

with uniform shape and low losses to provide access to available service bands. In military

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applications, for example, a mobile terminal may need to employ VHF/UHF line of sight

frequencies, UHF satellite communications, and HF as a backup mode.

As a result, the competing demands for directional selectivity, multipath compensation and

interference suppression versus wideband low-loss antennas versus affordability define the

tradeoffs of the antenna segment

Antenna architecture determines the number and bandwidth of RF channels. This

constrains the number and bandwidth of Analog to Digital to Converters (ADC). Some

waveforms require dedicated Application Specific Integrated Circuits(ASIC) instead of

ADC. Digital streams connect FPGAs, DSPs and general purpose process yielding a multi-

threaded, multi-tasking, multi-processing operating environment.

Flexible antennas, RF hardware and IF processing is a major technology challenge for

software radio. Optimum analog performance requires resonant narrowband antennas.

Fig.1.9 shows results in multiple parallel antenna/RF-conversion channels. In the example

A Personal Digital Assistant(PDA) access 1G cellular AMPS, 2G digital cellular Personal

Communication Systems (PCS) or 3G waveforms in the 1G or 2G bands. For location

aware services it has a GPS receiver. It also uses corporate wireless LAN (WLAN).

Fig. 1.9 Antenna Tradeoff

Broadband approach of above Fig.1.9 simplifies antenna and RF to two parallel channels,

reducing parts count. Next Fig.1.10 shows a unitary wideband channel. The antenna

response is not uniform across such a broad RF range. High performance in multiple RF

bands drives towards parallel narrowband channels. This can be an effective approach if

cost is not an issue. Transmission efficiency and impedance matching are more

challenging as bandwidth increases. Since antennas, RF conversion, IF Processing and the

ADC can account for over 60% of the manufacturing cost of an SDR, reducing the number

of RF channels is a significant design goal.

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Fig.1.10 Antenna Tradeoff

Anticipating the Joint Tactical Radio System (JTRS) program of the US Department of

Defense (DoD), SPEAKeasy RF range extended from 2 MHz and 2 GHz, a ratio of

through, since the maximum relative-bandwidths of well-established designs are atmost

10:1, one decade. Through in-depth technology tradeoffs it was determined that atleast 3

bands are needed. SPEAKeasy bands were 1)2-30 MHz 2) 30-400 MHz and 3) 0.4 to 2

GHz. Band 2 was implemented in SPEAKeasy I. Bands 1 and 2 are implemented in

SPEAKeasy II. Currently affordable RF access is limited to less than one decade per

channel.

It includes the following parameters RF Access, Parameter Control, Linearity and Phase

Noise, Parameters for Emitter Locations, Packaging, Installation, and Operational

Challenges, Gain versus Packaging, Bandwidth versus Packaging, Antenna Calibration,

Antenna Separation, Human Body Interactions, Antenna Diversity, Spatial Coherence

Analysis Potential Benefits of Spatial Diversity, Spatial and Spectral Diversity, Diversity

Architecture Tradeoffs, Programmable Antennas, Cost Tradeoffs

RF and IF Processing Tradeoffs

RF/IF Conversion Segment Tradeoffs includes

RF Conversion Architectures

Receiver Architectures

The Superheterodyne Receiver

Direct Conversion Receiver

Digital-RF Receivers

Interference Suppression

RF Component Technology

RF MEMS

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Superconducting Filters

Dual-Mode Amplifiers

Electronically Programmable Analog

Components

RF Subsystem Performance

RF/IF Conversion Issues

The second tradeoff concerns RF and IF conversion. The transmitter requires both linear

operation (eg: for QAM waveforms) and non-linear operation (eg:class-C amplifier for

high power efficiency with FSK or PSK waveforms). Fig. 1.11 shows IF Tradeoff where

desired response is obtained after 70 MHz and spurious response is obtained at 37 MHz in

IF spectrum. Also thermal noise and LO leakage are other side effects of IF processing.

Fig.1.11 IF processing tradeoff

Single channel receivers may non-linearly distort the waveform eg: in a direct conversion

architecture ever, must provide linear response for the strongest and weakest subscriber

signals(near-far ratio, typically 90 dB). The RF and IF conversion linearity and dynamic

range must match the ADC and Automatic Gain Control (AGC) and support digital

filtering and signal enhancement algorithms. The goal of this tradeoff is to balance the

noise, spurious components, intermodulation products and artifacts. The noise floor is

determined by the total bandwidth or by the low noise amplifier (LNA) eg: microwave

bands. Spurious responses and Local Oscillator (LO) leakage sometimes can mask

subscriber signals. LO leakage is problematic in homodyne receivers. A conservative

design keeps the peak energy of all noise, spurs and artifacts at about half of the least

significant bit (LSB) of the wideband ADC.

RF conversion includes output power generation, preamplification, and conversion of RF

signals to and from standard intermediate frequencies (IFS) suitable for wideband AIDIA

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conversion. In most radio bands, RF conversion will be analog. Certain critical RF

problems are exacerbated in the software radio. These include the need for amplifier,

linearity and efficiency across the access band. Fig.1.12 shows the diagram for RF

conversion and tradeoff

Fig.1.12 RF processing tradeoff with interference suppression

RF shielding of processors may also be necessary to avoid the introduction of processor

clock harmonics into the analog RF,’IF circuits. Consisting of multiple transmitters also

creates electromagnetic interference (EMI) problems. but these are about the same for

software radios as for cosite collections of multiple discrete hardware radios.

The IF processing segment maps the transmit and receive signals between modulated

baseband and IF. The IF receiver processing segment including wideband digital filtering

to select a service band from among those available. Furthermore. IF filtering recovers

medium band channels (e.g.. J 700 kHz TDMA channel in GSM) and/or wideband

subscriber channels (e.g., a 2 MHz CDMA channel) and converts the signal to baseband.

The complexity of frequency conversion and filtering is the first order determinant of the

processing demand of the IF segment.

In a typical application, a 12.5 MHz mobile cellular band is sampled at 30.72 MHz (M

samples per second). Frequency translation, filtering and decimation requiring I/O

operations per sample equates to more than 3000 MIPS of processing demand. Although

such microprocessors are on the horizon, contemporary implementations offload this

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computationally intensive demand to dedicated chips such as the Harris Decimating Down

Converter (DDC) or Gray digital receiver chip. Spreading and de-spreading of CDMA, is

also an IF processing function and creates demand that is proportional to the bandwidth of

the spreading waveform (typically the chip rate) times the baseband signal bandwidth.

This is so computationally intensive that with current technology limitations, it is typically

assigned to dedicated chips.Fig.1.12 shows Interference Suppression Tradeoff where RF

input is passed into a band of preselectors which selects the predefined frequency and

further passed into a low pass filter for removing the high frequency components. The

output of the filter is passed into step attenuator and the mixer and local oscillator

generates the IF signal with suppression for passing into the subsequent stages.Fig.1.13

shows the roofing filter response for suppressing the interference before use of roof and

after roofing filter.

Fig. 1.13 Interference Suppression Tradeoff

The Baseband Processing Segment

The baseband segment imparts the first level of channel modulation onto the signal (and

conversely demodulates the signal in the receiver). Predistortion for nonlinear channels

would be included in baseband processing. Trellis coding and soft decision parameter

estimation also occur in the baseband processing segment. The complexity of this segment

therefore depends on the bandwidth at baseband wb, the complexity of the channel

waveform, and the complexity of related processing (e.g., soft decision support). For

typical digitally encoded baseband waveforms such as binary phase shift keying (BPSK),

quadrature phase shift keying (QPSK), Gaussian minimal shift keying (GMSK).

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In the transmission side of the baseband segment, such waveforms are generated one

sample at a time (a “point operation”). If three samples are generated for the highest

frequency component, demand falls between Rb and 6*Rb. Greater oversampling

decreases the transmitted power of spectral artifacts, but also increases transmit power and

processing demand. In the receiver, digital baseband modulations require timing recovery

which typically includes the integration of baud intervals over time. If baud interval is

measured in transitions of a high-speed clock, some timing-sensitive signal structures (e.g.,

TDMA) and some synchronization algorithms require up to 96 b precision integer

arithmetic in the clock recovery loop(s), and such extended precision arithmetic may not

be readily available, particularly on newer chips.

Bitstream Segment

The bitstream segment digitally multiplexes sourcecoded bitstreamsfrom multiple users

(and, conversely, frames and demultiplexes them). The bitstream segment imparts forward

error control (FEC) onto the bitstream, including bit interleaving and block and/or

convolutional coding and/or automatic repeat request (ARQ) detection and response.

Frame alignment, bit-stuffing, and radio link encryption occur in the bitstream segment.

Encryption requires the isolationof encrypted bits from clearbits, resulting in the

requirement to partition and isolate bitstream hardware accordingly.

Source Segment

The source segment differs between the mobile terminal and the base station. In the mobile

terminal, the source segment consists of the user and the source encoders and decoders.

Here, the relatively narrowband voice and fax A/D/A converters are typically located in

the handset, palmtop, or workstation. In the base station, on the other hand, the source

segment consists of the interface to the PSTN for access to remote source coding.

Conversion of protocols required for interoperabilitywith the PSTN creates processing

demand in the base station’s source segment. Conversion of DSO 64 kb/s PCM to RPE-

LTP (GSM [ll])f,o r example, would create 1 to 2 MIPS of demand per subscriber.

End-to-End Timing Budgets

Time delays are introduced in the IF, baseband, bitstream and source segments due to

finite I/0 and processing resources that empty and fill buffers in finite but sometimes

random amounts of time. The end-to-end accumulation of these delays must be kept within

bounds of isochronism at each segment-to-segment interface. These bounds depend on

signal type and the larger network architecture. Thus, for example, end-to-end voice delay

should be less than 150 ms, but the external network may consume 100 ms of this timing

budget, leaving only 50 ms for the software radio. Maintaining such budgets in software

radios is complicated (compared to digital radios) by queuing delays internal to and

between processors.

Interference Suppression

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Antenna separation, frequency separation, programmable analog notch filters and active

cancellation suppress the interference at the RF stage. A programmable interference

suppression filter is called a roofing filter due to fact that the interference sets the

maximum linearly processable signal level(“roof”) while the dynamic range sets the

minimum floor.

Without roofing filter, the roof of the dynamic range is so high that weak signals fall

below the floor resulting in the dropped calls.

Active cancellation is the process of introducing a replica of the transmitted signal into the

receiver so that it may be coherently subtracted from the input signal.

Wideband antennas and RF exacerbate interference. SDR algorithms contribute to

interference suppression. SDR monitors mutual constraint satisfaction to minimize self-

generated interference.

RF MEMS

• Most RF integrated circuits require off-chip resonators, inductors and capacitors. Each

discrete device increases the cost of production manufacturing which is nearly a linear

function of the number of parts. RF MEMS replaces these with on-chip 3D structures.

MEMS RF switches are an electromechanical alternative to PIN diode switching circuits

substantially reducing size, weight and power while improving performance. MEMS switches

and tunable capacitors operate upto 40 GHZ. Fig.1.14 and Fig. 1.15 shows RF MEMS and its

fabric.

Fig.1.14 RF MEMS

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Fig. 1.15 RF MEMS SWITCH FABRIC

Architecture Tradeoffs

Software radios ideally place all IF, baseband, bitstream and source processing in a single

processor. The assessment of the feasibility of the software radio centers on comparing

estimated demand to the capacities of the available processors. Implementations back off

from the ideal single- CPU implementation where driven to do so by processor, memory,

or interconnect technology limitations, or to achieve cost advantages (e.g., of off-loading

filtering to a Harris chip so that the DSP is less expensive). Software tasks are then

structured into managed objects designed to run on any DSP or CPU with access to the

data and sufficient processing capacity

ADC and DAC Tradeoffs

It includes the following parameters

Dynamic Range (DNR) Budget

Anti-aliasing Filters

Clipping Distortion

Aperture Jitter

Quantization and Dynamic Range

Technology Limits

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Quadrature Techniques

Bandpass Sampling (Digital Down Conversion) DAC Tradeoffs

Conversion Rate, Dynamic Range

Applications

ADC Product Evolution

Low-Power Wireless Applications

Digital RF

ADC Design Rules

Linearity

Measuring SNR

Noise Floor Matching

Figure of Merit

Technology Insertion

Wa th e bandwidth of the IF to be digitized, determines what kinds of AID techniques are

feasible. According to the Nyquist criterion for band limited signals f 5 , the sampling rate

of the AID converter, must be at least twice Wa. Practical systems typically require modest

oversampling: f, > 2.5 Wa .

Wideband A/D and D/Aconverters access broad instantaneous segments of spectrum.

typically IO to 50 MHz. Such wide access may also be achieved in parallel subbands of

more modest 1 to 10 MHz bandwidths each. The dynamic range of each parallel subband

depends on the dynamic range of the ND/A converters. Since the product of dynamic

range times sampling rate is approximately constant for a given NDIA technology.

narrower subbands generally increase the useful dynamic range, albeit at the cost of

increased system complexity.

The placement of wideband A/D/A conversion before the final IF and channel isolation

filters achieves three key architectural objectives: It enables digital signal processing

before detcction

I t reduces the cost of mixed channel access modes by consolidating IF and baseband

processing into programmable hardware. It focuses the component tradeoffs to a single

central issue: providing the computational resources bandwidth, memory. and processing

capacity) critical toeach architecture segment, power and cost constraints of the application

subject to the size. weight.

Digital Processing Tradeoffs

Metrics

Heterogeneous Multiprocessing Hardware

Hardware Classes

Digital Interconnect

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Applications-Specific Integrated Circuits (ASICs)

Digital Filter ASICs

Forward Error Control (FEC) ASICs

Transceiver ASICs

Field-Programmable Gate Arrays (FPGAs)

Reconfigurable Hardware Platforms

FPGA-DSP Architecture Tradeoffs

Table-Driven Signal Generation

Evolutionary Design of FPGA Functions

DSP Architectures

DSP Cores for Wireless Basic DSP: The TMS320C30

Increasing Interconnect Capacity: The C40 and SHARC

Size–Power Tradeoffs: The C54x, and Motorola Chips

Toward Greater Parallelism: The C80 and

C6xx

Chips

Potential Technology Limits

INFOSEC Processor Architectures

The Clipper Chip—Key Escrow Approach

Programmable INFOSEC Modules

Host Processors

Software Architecture Tradeoffs

Software Design Process

Top-Down, Object-Oriented Design

Object-Oriented Design for SDR

Defining Software Objects

Software Architecture Analysis

SDR Software Architecture

SPEAKeasy I Software Architecture

Characteristics of Top-Level Objects

Specialized Tasks

SPEAKeasy II Code

Architecture Implications (Nov/Dec 2017)

Signal Digitization Extensive development of A/D capability in recent years by the

semiconductor industry has been stimulated by the prospects of digital wireless

applications. This has resulted in improvements in accuracy, linearity, sampling rates, and

resolution; however, the trade-off between A/D performance and sampling rate continues

to be a limitation. While the use of multiple A/D channels may be a short-term solution,

power consumption limits this approach to base station products.

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Hardware Architectures European research into software radio architectures and

technology, as it relates to handset terminals and base stations, was recently reviewed.

Such work is focused mainly on 3G standards. Table 1 summarizes the relevant

collaborative projects, mainly undertaken within the European ACTS and ESPRIT

research programs, and gives sources for additional information.

The main issues explored within these public domain research projects include:

• RF hardware architecture innovation and RF semiconductor process technology evolution

• Baseband DSP architecture evolution, including specific accelerators and software-

programmable hardware reconfigurability

• Architectural and algorithmic implications of software radio, including combinations with other

advanced processing concepts (e.g., beamforming and multiple signal extraction)

• Network implications of software radio — developing a nonconstraining, open evolutionary

route from where we are today In addition, work is beginning on the development of tools,

libraries, and environments to support product development and software portability.

In practice, reflecting the wide gulf between the purist view of the software radio ideal and the

pragmatic reality of commercially available technology today, some handset manufacturers

choose to adopt an understandably cautious and pragmatic approach to the implementation of

software-defined handsets, evolving from today’s products. Fig.1.15 shows architecture

implications at a transceiver sections of software radio architecture (SRA).

Fig. 1.15 Architure Implications

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