Electronic Design= Cognitive Radios & SDRs (long)

Wed Oct 26 16:32:46 CDT 2011

  SDR And CR Boost Wireless Communications

October 12, 2011 09:40 AM 11/10/2011 
<http://electronicdesign.com/issues/issue.aspx?issueid=11/10/2011>
Electronic Design
Louis E. Frenzel 
<http://electronicdesign.com/author/1843/LouisEFrenzel.aspx>

Software-defined radio (SDR) used to be rare and exotic. But today, most 
modern radios use SDR's architecture and techniques. Each year with 
continuing advances in ICs and other technologies, SDR becomes more 
capable and widespread. In fact, new techniques like cognitive radio 
(CR) are making SDR more useful and beneficial to wireless communications.

*SDR Defined*

SDR uses software to perform some of the signal processing in a receiver 
and transmitter. For example, a traditional receiver using the 
ubiquitous superheterodyne architecture performs all signal processing 
with basic electronic circuits (Fig. 1a 
<http://electronicdesign.com/Content/UserStorage/17928/63883-fig1.jpg>). 
The superheterodyne downconverts the input signal to an intermediate 
frequency (IF) for demodulation and other processing.

Early SDR receivers (Fig. 1b 
<http://electronicdesign.com/Content/UserStorage/17928/63883-fig1.jpg>) 
replaced the demodulator with an analog-to-digital converter (ADC) after 
the IF stage and performed the demodulation and some filtering in a 
digital signal processor (DSP). Today, because ADCs sample faster, DSPs 
can handle more functions.

To make DSPs work, the amplitude and phase of the signals both must be 
known. This has led to an architecture that divides the received signal 
into two paths, one producing an in-phase (I) signal and a 90° shifted 
quadrature (Q) signal. A basic carrier signal has the form:

V = A_c cos(2?f_c t + ?)

Where fc is the carrier frequency, ? is the phase, and A_c is the 
carrier amplitude. Any of these may be varied for modulation. For 
demodulation in the digital domain, a single signal is insufficient for 
existing algorithms. Therefore, the modulated signal is converted into 
the I and Q signals:

V = I(t) cos(2?f_c t) + Q(t) sin(2?f_c t)

With the quadrature signals, any variations in amplitude, frequency, or 
phase can be detected and used in a demodulation or other process.

Figure 2 
<http://electronicdesign.com/Content/UserStorage/17928/63883-fig2.jpg> 
shows a modern I/Q SDR receiver. A low-noise amplifier (LNA) usually 
boosts the input signal from the antenna before it is applied to the two 
mixers. The mixers develop the I and Q signals. Both receive a local 
oscillator (LO) signal from the phase-locked loop (PLL) frequency 
synthesizer. Note the 90° shift between the LO signals to the two mixers.

The LO frequency is set to the signal frequency so the difference signal 
from the mixers is zero without modulation. With modulation, the 
difference is the baseband or original modulating signal. This 
architecture is called direct conversion or zero IF.

After the baseband signals have been filtered in low pass filters to 
eliminate the sum components at the output of the mixers, the signals 
are digitized in a pair of ADCs. The digital baseband signals are then 
processed with digital downconverters (DDCs) to lower the sampling rate, 
making them more compatible with the digital signal processing circuits. 
The digital signal processing circuits then use both the I and Q signals 
to perform the demodulation, equalization, and additional filtering as 
the application demands.

In a modern SDR transmitter, the DSP modulator divides the data to be 
transmitted into I and Q signals and feeds them to digital upconverters 
(DUCs) that boost their sample rate (Fig. 3 
<http://electronicdesign.com/Content/UserStorage/17928/63883-fig3.jpg>). 
The I and Q signals are next sent to digital-to-analog converters (DACs) 
that produce the final baseband signal. The signals are then low pass 
filtered and sent to the mixers that upconvert the signal to the final 
transmitted frequency. The signal is finally sent to a power amplifier 
before being applied to the antenna.

All modern SDR transceivers use some basic variation of the receiver and 
transmitter circuits shown here. Of course as ADCs and DACs get faster, 
the digital processing moves closer to the antenna. The ultimate 
receiver then becomes simply a filter at the antenna to limit the 
bandwidth and a LNA before a fast ADC (Fig. 4 
<http://electronicdesign.com/Content/UserStorage/17928/63883-fig4.jpg>). 
Then, the DSP performs all other processing like demodulation and 
filtering. Commercially available amateur radio and shortwave receivers 
covering up to 30 MHz already use this advanced architecture.

Many functions are now performed digitally:

  * Filtering (low pass, high pass, band pass, and band reject)
  * Modulation (AM, FM, PM, FSK, BPSK, QPSK, QAM, OFDM, etc.)
  * Demodulation
  * Equalization
  * Compression
  * Decompression
  * Spectrum analysis
  * Predistortion

New modulation methods and related procedures are generally known as 
waveforms. By changing waveform software, a radio for one application 
like FM voice could be reprogrammed for high-speed data on a different 
frequency with a different protocol.

The advantages of SDRs lie in the greater simplicity of the hardware. 
Standard RF circuits are reduced to a minimum, keeping the cost of ICs 
low. DSP software improves operation with functions (like filters) that 
provide better performance than equivalent analog circuits. Digital 
signal processing also can compensate for some failing of RF components.

Furthermore, the flexibility of reprogramming allows defects to be 
fixed, new features to be added, upgraded operations to be included, and 
performance to be improved. An SDR of flexible design can be quickly 
changed with software to accommodate new modulation methods, new 
protocols, and other major adjustments that would ordinarily require new 
hardware.

The downsides of SDR include software complexity, development costs and 
time, limited frequency range for some applications, and generally 
higher power consumption.

*SDR's Hardware*

SDR requires fast ADCs, DACs, and DSPs. Sampling rates of ADCs have been 
rising for years and now extend well into the gigahertz region. Many 
SDRs use a low IF architecture and an ADC boasting a range of 100 
Msamples/s to several hundred Msamples/s. Even more is possible.

National Semiconductor's (now Texas Instruments) recent ADC12Dxx00RF can 
sample at rates up to 3.6 Gsamples/s (see "ADCs Sample RF Directly 
<http://electronicdesign.com/article/analog-and-mixed-signal/ADCs-Sample-RF-Directly-.aspx>" 
at www.electronicdesign.com). This dual-channel, 12-bit ADC can be used 
with a clock phase shift that allows interleaved or alternate channel 
sampling for even faster conversion. DAC sampling speed is closely 
following this trend.

While fast conversion is essential, the DSP must be fast enough to keep 
up. That has not been a problem as most processors have easily kept 
pace. SDR is software, of course, but you still need hardware that can 
be implemented physically in several forms.

For instance, you can write code to run on a general-purpose processor 
(GPP). This may not be an optimal approach as some of the algorithms 
call for math procedures that are awkward to handle on most GPPs. 
However, an Intel or AMD dual-core processor used in most PCs today does 
a great job in some applications. Some GPPs also have special 
instructions like the multiply and accumulate (function) that are so 
commonly used in DSP algorithms.

Then you can also use a DSP designed specifically to handle signal 
processing code. It has a special architecture (usually Harvard), 
memory, and arithmetic logic unit (ALU) instruction sets that make the 
DSP fast.

Texas Instruments' popular line of DSPs has been used for years in SDR, 
such as the C5000 and C6000 series. Analog Devices and Freescale also 
have general-purpose DSPs. Like any processor, DSPs are fully 
programmable so they're very flexible in applications where changes, 
additions, and updates may be required in the future. Clock speeds to 1 
GHz are common in DSPs today.

More and more SDR designs are using FPGAs. The signal processing 
algorithms such as the fast Fourier transform (FFT) can be reduced to 
digital logic and quickly implemented in an FPGA. Since the cost of 
FPGAs has steadily declined, they have become a major alternative to 
DSPs. FPGAs are faster than some other processors with some functions 
but still have the flexibility of reprogramming. Altera and Xilinx 
support SDR on their FPGAs.

Finally, hard logic is also common today. When implementing fixed 
standards like cellular radio specifications, the flexibility or 
reprogramming is not necessary. Therefore, algorithms can be implemented 
in fixed on-chip logic. It is fast, uses less chip area, and can bring 
about a major decrease in power consumption. Such blocks of logic are 
generally called accelerators.

Many cell-phone basestation ICs like TI's TMS320TC6614 system-on-a-chip 
(SoC) are examples that use accelerators. Figure 5 
<http://electronicdesign.com/Content/UserStorage/17928/63883-fig5.jpg> 
shows the 6614 with its ARM GPP and four 66x general-purpose 
floating-point DSP cores. Note the accelerator logic on the right. Most 
of the Layer 1 accelerators use DSP algorithms for the many SDR functions.

*Real SDR Transceivers*

Many SDRs have been developed for the military under the Joint Tactical 
Radio System (JTRS). This U.S. Department of Defense program aims to 
develop a complete line of SDR radios for voice, data, and video that 
can be used to form ad hoc networks on the battlefield. The program has 
been around since the late 1990s, with good progress over the years.

The whole basis of JTRS is the Software Communications Architecture 
(SCA). This open-architecture platform standard defines how the hardware 
and software work together. One of the primary objectives is to develop 
software that is fully transferrable between different hardware 
platforms, making all military radios multifunctional and interoperable.

The latest version, designated SCA 2.2.2, was recently made available to 
further improve the programmer's ability to make the software more 
flexible and scalable. Called SCA Next, the software helps make programs 
smaller and require less testing.

SCA does not have specific provisions for cognitive features. But over 
the past few years, the U.S. Defense Advanced Research Projects Agency 
(DARPA) has been testing cognitive enhancements to SCA like Dynamic 
Spectrum Access that will hopefully be available in the coming next 
generation of JTRS radios.

The Thales Communications AN/PRC-148 JTRS Enhanced Multiband (JEM) 
Inter/Intra Team Radio, which is a JTRS radio, covers all the HF, VHF, 
and UHF military frequencies from 30 to 512 MHz (Fig. 6 
<http://electronicdesign.com/Content/UserStorage/17928/63883-fig6.jpg>). 
Power output can be selected from 0.1 to 5 W. A wide range of modes and 
waveforms is available.

*Cognitive Radio*

Cognitive radio (CR) expands the definition of SDR to include features 
that make a radio intelligent. The Wireless Innovation Forum defines CR 
as "Radio in which communication systems are aware of their environment 
and internal state and can make decisions about their radio operating 
behavior based on that information and predefined objectives. The 
environmental information may or may not include location information 
related to communicant systems."

CRs are sometimes called adaptive radios that automatically adjust their 
behavior or operations to achieve specific objectives. They can sense, 
learn, and adapt. They have an internal memory that stores instructions 
for various situations. Stored knowledge about their own capabilities 
makes it possible for these radios to make their own decisions.

A CR can also access external databases for additional decision-making 
intelligence. It senses by listening to a channel assessing the presence 
of other signals, their characteristics, and the noise background. The 
CR learns from its experience as well. With all of the knowledge it has 
or can access, the CR becomes a super-intelligent radio.

The transmitter (TX) and receiver (RX) are full frequency-agile SDRs 
with a mix of applicable waveforms and all the related SDR hardware and 
software (Fig. 7 
<http://electronicdesign.com/Content/UserStorage/17928/63883-fig7.jpg>). 
A separate cognitive processor engine runs the cognitive aspects of the 
radio. It gets inputs (M) from the RX and TX to monitor their condition 
and parameters. It uses these inputs along with others to make decisions.

Other inputs can come from policy instructions stored in memory that 
define ways to operate under different conditions. External databases 
may also be accessed. Some CR units get location information by GPS. 
Decisions are then made, and controls (C) are issued to the radios to 
achieve the desired result.

CRs are also a good example of artificial intelligence (AI) in action. 
AI is a collection of software that is used to store and use knowledge 
to solve problems. It can use standard algorithms but it can also draw 
on several AI techniques such as expert systems, natural language 
processing, neural networks, fuzzy logic, and search techniques. AI/CR 
emulates the human user by assessing the situation and making decisions 
based on existing knowledge and taking actions to achieve the desired 
best result.

One important aspect of CR is dynamic spectrum access (DSA), which 
allows the CR to tune to a channel in the frequency spectrum for its 
operation after it decides that the channel is unused. A DSA radio uses 
unused spectrum, producing greater efficiency of limited spectrum space.

A cognitive transceiver essentially tells the SDR what to do in the way 
of frequency of operation, modulation, power level, protocol, and other 
factors and makes corresponding adjustments automatically. A CR is 
software that monitors the SDR and delivers commands and control 
instructions as needed.

CRs primarily seek to solve two major wireless problems: limited 
spectrum and interoperability between different radios or wireless 
systems. A CR can find open spectrum and use it. It also can change its 
waveforms or protocols to adapt to radios of a different nature, making 
communications possible or more reliable.

There are also several different classifications of CRs. For example, a 
policy-based radio is programmed with a predefined set of capabilities 
like waveforms and procedures. The radio is used by selecting one of 
several different preprogrammed fixed functions. The fixed functions are 
loaded during manufacturing, selected by the user, or downloaded over 
the air.

Another CR form is a fully reconfigurable radio. This fully generic 
transceiver can operate over a wide frequency and power range. This type 
of radio can be fully reconfigured on the fly for new applications or 
communications conditions.

*CR Examples*

The xG Technology xMax carrier-class CR system for mobile communications 
uses the unlicensed industrial, scientific, and medical (ISM) band 
spectrum in the 902- to 928-MHz range. In its first iteration, it was 
deployed as a trial garrison and battlefield cellular radio system for 
the U.S. Army.

The system was tested earlier this year at Fort Bliss and the White 
Sands Missile Range as part of a military Network Integration Evaluation 
(NIE) process used to validate and test systems for the field. The 
system did well based on written media accounts and quotes from Army 
personnel.

The prototype xMax system used a compact mobile basestation and its own 
TX70 handset. It also used a 900-MHz time division duplex (TDD) digital 
radio with cognitive technology in the handsets themselves. The system 
supported Voice over Internet Protocol (VoIP) calls and texting (SMS) as 
well. The handset included a full Wi-Fi radio.

The xMax system adheres to the Federal Communications Commission's part 
15 rules for the 902- to 928-MHz spectrum. Radios can radiate up to 4 W 
(EIRP), and that goes for the basestations too. The system divides the 
spectrum into 18 1.44-MHz channels and uses robust binary phase-shift 
keying (BPSK) modulation. Access is time division multiple access 
(TDMA), and each channel can handle up to 12 voice calls.

The cognitive feature of the radio listens to the band in use to 
determine where any interference is and then switches to a frequency 
with the lowest noise levels. The xG handsets scan the band 33 times per 
second looking for the interference and identifying the clear spots 
where a good link can be formed. It then notifies the basestation, 
causing the frequency to change as needed to keep a clean connection.

Now xG Technology is moving into its second-generation xMax design. This 
new xMax system drops the special handsets and uses standard smart 
phones. This is something that the military wants as soldiers can use 
standard off-the-shelf smart phones, laptops, or tablets to save money.

In this new system, the smart phones talk to a bridging device called 
the xMod (Fig. 8 
<http://electronicdesign.com/Content/UserStorage/17928/63883-fig8.jpg>). 
This device resembles the Novatel MiFi devices that let multiple laptops 
use Wi-Fi connections to talk to it and then backhauls these connections 
back to the Internet via a connection to the cellular network. The xMod 
works in a similar fashion supporting a Wi-Fi (or a direct USB wire) 
connection to commercial smart phones or computers and using the 
cognitive xMax network to connect back into the Internet or military 
network.

This new arrangement adds high-speed data connectivity to the system. 
Furthermore, it adds a managed VoIP capability via a smart-phone app. 
Normal 3G and 4G cellular smart phones use the cellular systems' 
standard voice service via 2G or 3G cellular links, which currently 
isn't of the VoIP kind. The xMax system puts a special app on the smart 
phone that permits it to identify and prioritize the voice packets. The 
xMax system then can provide landline quality voice, even though it is a 
100% complete IP-based system.

The new system modifies the xMax waveform by leveraging orthogonal 
frequency division multiplexing (OFDM). Each of the previously defined 
18 1.44-MHz channels is further subdivided into 128 subcarriers. Radio 
access is TDD. Another key addition, multiple input multiple output 
(MIMO), greatly improves the range, reliability, and data rate. The xMod 
devices use a 2x4 MIMO system with four receiver chains and two transmit 
chains.

The cognitive capabilities as well as the radio itself are primarily 
implemented in software, commonly called SDR. The system's mix of CR 
techniques, MIMO, and advanced signal processing maximizes range, 
reliability, and throughput. The substantial processing complexity 
required leverages a new generation processor capable of supporting 50 
GOPS in both the xMod and basestation. This kind of processing power is 
brand new and now available in a size and at a power consumption level 
suitable for battery powered devices like the xMod.

Rick Rotondo of xG explained that the cognitive capabilities and 
interference mitigation algorithms allow the xMax to operate reliably in 
"white spaces" as well as "gray spaces." White space is defined as the 
unused TV channels that have been blessed by the FCC for unlicensed use. 
It's used to mean a 6-MHz channel free of any interference from TV 
broadcasters.

However, white spaces can rapidly become gray spaces due to wireless 
microphones that operate in these channels as well as other white space 
devices operating nearby. In fact, the 900-MHz band that xG cut its 
teeth on is heavily used and "dark gray" with interference from cordless 
phones, wireless security systems, telemetry radios, and other devices.

So, the system had to operate reliability in the presence of high 
interference from day one. The result is that the xG cognitive system 
lets you maximize the capacity of gray spaces by reliably letting you 
operate where other radio systems may not be able to operate.

As for applications, xG Technology will soon offer an advanced system 
suitable for the military, rural broadband, and the enterprise. The new 
system will include the 902- to 928-MHz band and the 5.8-GHz ISM band. 
Future systems may also use the 700-MHz spectrum.

In addition, xG is evaluating its options in the TV white space arena 
both here in the U.S. as well as in the U.K., where the system would be 
a good fit. Imagine a powerful mobile voice and data cellular system 
that could leverage the free white space 6-MHz TV channels and offer the 
same services and better economics than commercial 3G and 4G cellular 
systems.

Speaking of white spaces, this is another excellent application for CR. 
White spaces comprise the unused 6-MHz TV channels that were abandoned 
in 2009 with the switch from analog to digital TV. TV stations still use 
channels 2 through 51 (54 to 698 MHz), though many of them are unused. 
The open channels vary widely by region but represent a huge waste of 
valuable spectrum.

The FCC has approved the use of these channels in a license-free 
service. The guidelines call for low power and knowledge of the 
available local channels. The FCC and a number of other organizations 
like Spectrum Bridge and Telcordia have developed comprehensive 
databases logging the TV stations and other wireless devices and 
services using these channels in most U.S. locations. To use the 
channels, a white space radio must access the database to see if it is 
being used. If it is, another channel is selected, preventing interference.

White space radios fall into two categories: basestations and customer 
premise equipment (CPE) terminals. The CPE terminals may be mobile. If 
they want to transmit, they send their location based on GPS coordinates 
to the basestation that accesses the database to see if the desired 
channel is open. If it is, the CPE is notified that it can transmit.

In some systems, the CPE actually listens to the desired channel to 
assess the presence of other signals. In any case, both the basestation 
and CPE radios use forms of cognitive radio to make intelligent 
decisions on what channel to use and when.

White space radios promise to make more efficient use of the unused TV 
spectrum, but CR methods make it practical to do so without 
interference. One key application for white space is wireless broadband 
in rural areas. There are still many places where good, high-speed 
Internet connections are not available. White space is well suited to 
this use.

The lower-frequency and non-line-of-sight (NLOS) characteristics of the 
white space channels make long-range connections of several miles not 
only possible but also reliable. In one potential business model, 
wireless Internet service providers (WISPs) would help fulfill the 
federal government's National Broadband Initiative.

Remote monitoring and control is another potential use for white spaces. 
Machine-to-machine (M2M) applications like Smart Grid connections, video 
surveillance cameras, medical patient monitoring, and sensor networks 
all would benefit from access to white spaces.

Designed specifically for white space use, the RuralConnect IP Version 
II (RCIP VII) SDR/CR creates point-to-point and point-to-multipoint 
networks with priority routing for voice, data, and video (Fig. 9 
<http://electronicdesign.com/Content/UserStorage/17928/63883-fig9.jpg>). 
The target application is rural broadband access but it can be used in 
IP video surveillance, well and pipeline monitoring, smart metering, and 
traffic signal communications.

The RCIP VII operates in the 470- to 786-MHz range. It uses TDD and can 
achieve data rates of 4, 6, 8, 12, or 16 Mbits/s in a 6-MHz channel 
using quadrature phase-shift keying (QPSK) or 16-phase quadrature 
amplitude modulation (16QAM). Its transmit power is +30 dBm, and its 
receive sensitivity is in the --86- to --89-dBm range. Security is by 
AES-128 with a shared secret key. The units are designed to use the 
Telcordia database and operate under the FCC's Part 15 rules as well as 
the Ofcom regulations in the U.K.

The Neul NeulNET white space radio system is designed for M2M and rural 
broadband in the white spaces as well (see "First Commercial White Space 
Radios Target M2M And Broadband Applications 
<http://electronicdesign.com/article/communications/First-Commercial-White-Space-Radios-Target-M2M-And-Broadband-Applications.aspx>" 
at www.electronicdesign.com).

*Developing SDR/CR*

An SDR transceiver is mainly a software project. Once you get a firm RF 
platform, the DSP processing choice is next. It could be a standard DSP, 
an FPGA, or some GPP. For first projects, a reference design with vendor 
development tools really speeds and simplifies things. Other than that 
there are few choices beyond going it alone.

One approach is to use GNU Radio, which is an open-source development 
platform for SDR. It includes a set of signal processing routines 
including modulation for Gaussian minimum shift keying (GMSK), 
phase-shift keying (PSK), QAM, OFDM, and a few others. The software also 
includes error correcting codes like Reed-Solomon, Viterbi, and turbo 
codes. There are routines for optimized filters, FFT, equalizers and 
timers. And, it allows coding in C++ or Python. The software runs under 
Windows, Linux, or MacOS.

The GNU Radio software relies on a basic RF platform called the 
Universal Software Radio Peripheral (USRP). It consists of several 
choices of RF boards covering frequency ranges up to 5.9 GHz. Also 
included is a complete data acquisition system of fast ADCs and DACs and 
related support circuitry. A USB port provides basic I/O.

Ettus Research, a good source for USRP, makes a line of RF boards 
covering different frequency ranges that use a basic I/Q architecture 
and are full duplex capable. Transmit/receive switching is provided. 
Transmitter power and receiver gain are controllable. Typical bandwidth 
capability is 30 MHz. You can use either a standard DSP like the TI 
OMAP3 that combines an ARM GPP and a TI C64xx DSP or a Xilinx Spartan 3A 
DSP1800 or Altera Cyclone FPGA for the software.

As for the ADC and DAC, some models of the Ettus USRP use 100-Msample/s, 
14-bit ADCs and 400-Msample/s, 16-bit DACs. Other models use 
64-Msample/s, 12-bit ADCs and 128-Msample/s, 14-bit DACs.

If you're just beginning with SDR/CR or if you want to teach it, a great 
new choice is National Instruments' USRP product (Fig. 10 
<http://electronicdesign.com/Content/UserStorage/17928/63883-fig10.jpg>). National 
Instruments owns Ettus and uses its basic hardware in two products, the 
NI USRP 2120 with a frequency range of 50 MHz to 2.2 GHz and the NI USRP 
2921 with a frequency range of 2.4 to 5.5 GHz.

Both transceivers use the standard direct conversion architecture and 
output their I/Q signals via a 1-Gigabit Ethernet port to a PC. Signals 
up to 25 Msamples/s baseband may be steamed this way. The bandwidth is 
50 MHz. The units cost about $4000 each.

The digital signal processing and other procedures run on the PC. 
National Instruments' LabVIEW software with the Modulation Tool Kit is 
used for development. Advanced software can be downloaded to NI's Flex 
RIO PXI module with its Xilinx FPGA.

The NI USRP was developed primarily for university instruction and 
research, though it makes a good learning platform for anyone just 
beginning with SDR/CR. When you purchase a two-unit bundle, you get the 
full set of instructional materials developed at the University of Texas 
and Stanford University. The bundle costs about $6000. For initial 
exploration and prototyping, including projects with OFDM and MIMO, the 
NI USRP appears to be a good place to start

Fig 10. The National Instruments' Universal Software Radio Peripheral 
(USRP) uses standard I/Q architecture radios with 100-Msample/s 
sampling. Designed for SDR and CR development, the USRP uses NI's 
LabVIEW software with Modulation Tool Kit. The DSP runs on an external 
PC. 
<http://electronicdesign.com/Content/UserStorage/17928/63883-fig10.jpg>Fig 
9. The Carlson RuralConnect IP basestation mounts near the antenna. The 
contour map shows coverage of three basestations in rural areas. 
<http://electronicdesign.com/Content/UserStorage/17928/63883-fig9.jpg>Fig 8. 
The xG Technology xMod wireless bridge links multiple standard smart 
phones (and laptops) via Wi-Fi to the xMax wireless network. 
<http://electronicdesign.com/Content/UserStorage/17928/63883-fig8.jpg>Fig 7. 
The transmitter and receiver in a typical CR are frequency-agile SDR 
units. The cognitive processor manages the cognitive processes with 
inputs from a policy memory, external data bases, and in some cases GPS 
location information. 
<http://electronicdesign.com/Content/UserStorage/17928/63883-fig7.jpg>Fig 6. 
The Thales AN/PRC-148 JEM military radio uses the JTRS SCA software 
platform to ensure military radio interoperability. 
<http://electronicdesign.com/Content/UserStorage/17928/63883-fig6.jpg>Fig 5. 
The Texas Instruments TMS320TC6614 is a basestation-on-a-chip IC used 
for implementing pico, micro, metro, and other small basestations. All 
baseband functions are performed here. The RF circuitry is external. 
Note the hardware accelerators on the right that use hardwired logic to 
speed up the many DSP SDR functions. 
<http://electronicdesign.com/Content/UserStorage/17928/63883-fig5.jpg>Fig 4. 
The ultimate SDR receiver uses only an input bandpass filter, an ADC, 
and a DSP. All demodulation, filtering, and other functions are 
performed in the DSP. 
<http://electronicdesign.com/Content/UserStorage/17928/63883-fig4.jpg>Fig 3. 
In an SDR transmitter, modulation is performed in the DSP. Then, the I/Q 
architecture creates two orthogonal signals that are combined and 
upconverted to the final frequency for transmission. 
<http://electronicdesign.com/Content/UserStorage/17928/63883-fig3.jpg>Fig 2. 
A modern software-defined receiver uses the I/Q architecture to divide 
the signal into two orthogonal paths. The I and Q channels are needed to 
recover any type of modulation by digital signal processing algorithms. 
<http://electronicdesign.com/Content/UserStorage/17928/63883-fig2.jpg>Fig 1. 
A conventional legacy radio receiver (a) uses the standard analog 
superheterodyne architecture with analog circuitry performing all 
functions. A more advanced superheterodyne receiver (b) uses digital 
demodulation with DSP. 
<http://electronicdesign.com/Content/UserStorage/17928/63883-fig1.jpg>

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