sdr interference issue navinkumar
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SoftwareDefined Radio:
Interference
Issue
Navin Kumar,Member IEEE, IET(UK), IETE, IE(India)
WRAN Repeater
TV Station
WRANBase Station
WRANBase Station
WRAN CPE
WirelessMIC
TV Station
Grade B
Contour of TV station
TV Receiver
Public SafetyRadios
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Software Defined Radio (SDR):
Outline
Introduction
Motivation, Benifits, Complexity, etc.
Architecture
Challenges and Goals
Concern and Issues
State of Art
Conclusion Further reading and references
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Introduction
Whats the SDR ?
Software-Defined Radio (SDR) refers to the
technology wherein software modules runningon a generic hardware platform consisting ofDSPs and general purpose microprocessorsare used to implement radio functions such asgeneration of transmitted signal (modulation)
at transmitter and tuning/detection of receivedradio signal (demodulation) at receiver.
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Introduction ....
Definition by SDR Forum-
Software defined radio is used to describe
radios that provide software control of avariety of modulation techniques, wide-band or narrow-band operation,
communications security functions (suchas hopping), and waveform requirementsof current and evolving standards over abroad frequency range.
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Introduction ....
Motivation of SDR Commercial wireless communication
industry is currently facing problems dueto constant evolution of link-layer protocolstandards (2.5G, 3G, and 4G)
Existence of incompatible wireless network
technologies in different countriesinhibiting deployment of global roamingfacilities
Problems in rolling-out newservices/features due to wide-spreadpresence of legacy subscriber handsets.
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Introduction ....
The Key Is Configurability
ADC
DAC
Reconfigurable
Processing
DAC
ADC
Reconfigurable
RF Processing
NETWORKNETWORK
USERUSER
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Introduction ....
Reconfigurability Reconfigurability provides essential mechanisms to
terminals and network segments to adapt
dynamically, transparently and securely to the mostappropriate radio access technology.
o via selecting pre-installed software components.
o via software downloading and installation.(Also called end-to-end reconfigurability (E2R))
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Introduction ....
End-to-End Recofigurability (E2R Vision)
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Benifits -
Equipment manufacturerscan use a common desingfor multi-functional radios
leading to increased
market size for a singleproduct.
Network operators,the interoperability
of different networksIs enhanced andsystem upgrades
and bugs fixing areeasier to manageand implement.
Subscribers benefitFrom the enhanced
Funtionality of theirSDR devices and
The possibility toAchieve ubiquitousConnectivity.
Introduction ....
SDR is a promising technology that has the
potential to realize cost-effective, multi-bandand multi-standard telematics products withreduced development cycle.
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Introduction .... Wireless providers are attracted to SDR technology because it
enables remote upgrading and reconfiguration of handset andbase station software with new features and patches, as wellas potential interoperability across multiple networks.
SDR provides a solution for a broad range of communicationsand devices used in:
cellular base station and handsets
commercial and military satellitesmilitary radios
public safety
wireless LAN/WAN
aerospace
automotive
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Introduction .... What are the complexities
It is difficult to engineer wideband, lowloss antennas andRF converters.
It is also difficult to accurately estimate processingdemand of applications and processing capacity ofreprogrammable DSP/CPU configurations.
In addition, sustaining required data rates acrossinterprocessor interfaces is problematic.
The frequency bands covered may still beconstrained at the front-end requiring a switch in theantenna system.
.... Later on we will discuss in detail .....
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SDR: General Architecture
Reconfigurable Hardware
Implementation of programmableRF section is limited by the currentADC/DAC technologies notsufficient in supporting the required
digital BW, dynamic range and
smpling rate.
DigitalUP/Down
Conversion
Connection set up Equalization Freqeuncy hopping Timing recovery
Correlation
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SDR: General Architecture ....
Software architecture -
Generic Hardwareplatform built using
programmablemodules
Handles hardwareresource management,memory and interrupt
management
Supports link layerservices to higher level
protocols
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SDR: Architecture ....
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Challenges
Wide band/multiband low loss
Antenna
Broad bandDuplexer, Broad
band Freq
Synthesizer
Efficient WidebandLinear Power Amplifier,
Low power Linear RxrFront End
MFLOPS to GFLOPS DSP,
Distributed Processors, FlexibleDSP OS, Low power, Limited
Memory and processing
resources for protocols
Wide Input bandwidth,High bit-rate, High bit-
width, low power
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Source - A Abidi, ISSCC Girafe 2006
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Concern and Issues
The interference types can be divided into:
External to the system:
Other radio system in the neighborhood
Other similar systems from different companies
Caused by the same system:Co-channel interference
Adjacent channel interference
Multi-path interference => Inter-symbol InterferenceMultiple access interference
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Interference .... Reference Interference level Some of the reference interference levels (for example, in
GSM case is can be given as -) Co-Channel Interference 9 dB
Adjacent Interference (200KHz) -9dB Adjacent Interference (400KHz)- -41dB Adjacent Intereference (600KHz)- -49dB
Co-channel Interference caused by
Nonlinear distortion Interference arising from other cells
Up and down link frequency allocations can be set in the range 100MHz to 2.6GHz.
Achieving such a broad range of operation, whilst maintaining radio performancewithin specifications, calls for a very advanced design, including the use of widebandtuneable filters.
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Interference ....
Adjacent Channel Interference
Frequency allocation in adjacent channels
Badly projected receiving filters
Near far effects
Spectrum regrowth nonlinear effects
Ways to minimize adjacent channel interference:Frequency allocation that do not consider adjacent
channels
Filter design with improved Q factorPower Dynamic control
Linearizers
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Concern and Issues:
Interference BTS Throughput Vs Interference
Source -SDR ETSI Nokia / 08.02.2007
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Interference .... RF Spectrum Usage -
Source -SDR ETSI Nokia/ 08.02.2007
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Interference .... Although spread-spectrum techniques are inherently
resistant to narrow-band interference (NBI) incommunication systems, Enough power spectralcomponents of interference might pose a serious problemin providing reliable communication for many wirelesssystems having broadband front end.
These powerful interfering signals may push low noiseamplifiers into a nonlinear region creating very severenonlinear distortion.
When a receiver is sufficiently nonlinear, stronginterference from adjacent channel can produceharmonics and intermodulation products, overpoweringand effectively Locking Out a weak signal of interest(generally through 3rd order intermodulation product(s)).
This is often referred to as the near-far problem.
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The third order intermodulation products are generallyrecognized to be of greatest concern. Also, if the front end in question is driven into strong distortion, it
may lock out everything except the strongest input signalentirely.
The problem of relatively low frequency interference is stillfurther challenging since, as can be observed in the rangeequation (Friis transmission formula)
Pr/Pt = (GrGt) 2/(4 r)2
The relative dropoff of received power for a given transmittedpower and distance is more gradual at low frequencies than at
high frequencies (due to the larger). For example, an FRS walkie-talkie (operating at roughly 460
MHz in the U.S.) will have roughly 14.7 dB of received poweradvantage over an 802.11 signal (roughly 2.5 GHz) at 1 kmdistance from the transmitter (assuming equal transmitted
power).
Interference ....
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Approaches For Combatting Distortion
in Wideband Front End Amplifier
Source - Ron Hickling et all, Design consideration for the front end frequency agile SDR Rxr,
Proceeding Technical Conference SDR 05
Multiplex Narrowband Amplifiers -
The total required frequency spectrumis divided into narrower band andeach band is handled by a separateamplifier. The cluster of amplifiers iscoupled together through a multiplexer.
--- Construction of widebandmultiplexer is challenging
1
Tunable Narrow BandwidthAmplifiers -
A passive LC network is tuned so
that the response is optimized topass the desired input frequency
while attenuating others
--LNA and its required matchingare affected by Fanos limit
2
Adaptive Interference Cancellation -
To cancel out the strongest few signals that arethe primary dynamic range hogs.
By adaptive filtering or by rejective NBI3
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Wideband Frequency
Combatting Frequency Tuning
Source - A Abidi, ISSCC Girafe 2006
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Effect on LNA/Mixer
Source - A Abidi, ISSCC Girafe 2006
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Wideband LNA
Source - A Abidi, ISSCC Girafe 2006
Discrete Time Receivers for
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Discrete-Time Receivers for
Software-Defined Radio* Author in this paper proposes a Discreter-Time (D-T)receiver which has already been demonstrated forBluetooth, GSM, GPRS, and WLAN.
A D-T receivers can be categorized based on their trackand hold (T/H) structures as charge sampling [1, 2] orvoltage sampling[3].
*Source- Zhiyu Ru et all, On the Suitability of Discrete-Time Receivers for Software-Defined
Radio, Circuits and Systems, 2007. ISCAS 2007. IEEE International Symposium.
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Discrete-Time Receivers for
Software-Defined Radio .... The main difference is that, charge sampling
integrates current and samples charge, whilevoltage sampling samples voltage.
Voltage sampling often seriously suffers fromnoise-and-interference aliasing, and thesuppression of the alias bands heavily relies onthe RF preselect filter.
On the other hand, due to the integration effect
of charge sampling, there is a SINC transferfunction on the input spectrum, attenuating thealiasing [4].
A CMOS 100 MH t 6 GH SDR A l
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A CMOS 100 MHz to 6 GHz SDR AnalogFront-End+
Author in a recent paper proposed a CMOS basedextensive programmable LO generator, LNA, mixers,
baseband filters and PPA, which suppors various
wireless communication standards while guaranteeing anear-optimal power/performance trade-off at any time.
+Source - M. Ingels et all, A CMOS 100 MHz to 6 GHz Software Defined Radio analog front-end with
integrated Pre-Power Amplifier, 33rd European Solid State Circuits Conference, 2007. ESSCIRC.
A CMOS 100 MH 6 GH SDR
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A CMOS 100 MHz to 6 GHz SDR
Analog Front-End .... It provides the LO through 2 wide tuning
range VCOs and integrated DMQs. The front-end also includes a versatile RX
and TX path with programmability to
address the various functionalrequirements of many different standardswhile guaranteeing an optimal powerperformance trade-off.
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Attenuation of Adjacent Channel
Signal in the adjacent channel causesinterference to the desired signal.
The most computationally intensive part of thewideband receiver of an SDR is the channelizersince it operates at the highest sampling rate.
Higher order FIR channel filters are needed in
the channelizer to meet the stringent adjacentchannel attenuation specifications of wirelesscommunications standards.
In this paper, authors presented a coefficient-
partitioning algorithm for realizing low power andhigh-speed channel filters.
Source - A. P. Vinod et all, IMPLEMENTATION OF LOW POWER AND HIGH-SPEED HIGHER ORDER CHANNELFILTERS FOR SOFTWARE RADIO RECEIVERS, 17th Annual IEEE International Symposium on Personal, Indoor and
Mobile Radio Communications (PIMRC06).
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Attenuation of Adjacent Channel....
Authors in above paper proposed a coefficient-Partitioning technique for implementing low powerchannel filters.
The key idea in this approach is to reduce the rangesofthe operands so that the adder width can be reducedwhich in turn minimizes the number of FAs.
By encoding the filter coefficients using the pseudo
floating-point (PFP) arithmetic scheme, the ranges of theoperands can be reduced considerably.
Further, a coefficient-partitioning algorithm is employed,which offers substantial reduction of FAs in implementingthe PFP coded coefficient multiplier when combined withthe Common Subexpression Elimination (CSE)[5,6]method.
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Adjacent Channel Interference ....
Author in this paper proposed an adjacentchannel interference (ACI) cancellation schemewith undersampling for multi-channel reception.
Low-IF receiver architecture is used in the multi-channel reception scheme.
The ACI cancellation scheme with analog filter
bank has been proposed to mitigate theinfluence from the adjacent channel.
Undersampling technique is applied in thissystem in order to lower the required samplingfrequency and power consumption.
Source - Anas M BOSTAMAM, Yukitoshi S, Experimental Investigation of Undersampling for Adjacent Channel
Interference Cancellation Scheme, IEICE Transactions on Communications 2006 E89-B(9):2548-2554.
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Concluding Remarks
Maintaining linearity in receivers is one of the keychallenges in light of potentially unpredictable levels ofinterference.
While inband interference is generally considered inevaluating the performance of conventional receivers,wideband receivers must also take into account theeffects of outband interference.
The development of wideband front end receivers is a
key to achieving frequency agility and realizing theultimate goal of ideal software definable radio (SDR)receivers.
In this review paper, some of the problems of
interference in SDR along with some proposed solutionare discussed. Visited state of art will provide useful information to find
out more details in this field.
F th R di d R f
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Further Reading and References...
[1] K. Muhammad et. al., A discrete-time Bluetooth receiver in a0.13um digital CMOS process, IEEE Int. Solid-State Circuits Conf.(ISSCC) Dig. Tech. Papers, pp. 268-269, Feb. 2004.
[2] K. Muhammad et. al., A discrete time quad-band GSM/GPRS
receiver in a 90nm digital CMOS process, Proc. IEEE CustomIntegrated Circuits Conf. (CICC), pp. 809-812, Sept. 2005. [3] D. Jakonis, K. Folkesson, J. Dabrowski, P. Eriksson, and C.
Svensson, A 2.4-GHz RF sampling receiver front-end in 0.18-umCMOS, IEEE J. Solid-State Circuits, vol. 40, no. 6, Jun. 2005.
[4] G. Xu and J. Yuan, Performance analysis of general chargesampling, IEEE Trans. Circuits Syst. II, vol. 52, no. 2, Feb. 2005.
[5] R. I. Hartley, Subexpression sharing in filters using canonic signeddigit multipliers, IEEE Trans. Circuits Syst. II, vol. 43, pp. 677-688,Oct. 1996.
[6] M. M. Peiro, E. I. Boemo, and L. anhammar, Design of highspeedmultiplierless filters using a nonrecursive signed commonsubexpression algorithm, IEEE Trans. Circuits Syst. II, vol. 49, no. 3,pp. 196-203, March 2002.
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Thank You !!!!
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