SDR Interference Issue NavinKumar

8/14/2019 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



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Effect on LNA/Mixer



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Wideband LNA


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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SDR Interference Issue NavinKumar