Sdr Interference Issue Navinkumar

Software Defined Radio: Interference Issue Navin Kumar,

Wireless MIC WRAN Base Station

Public Safety Radios

TV Station

Member IEEE, IET(UK), IETE, IE(India)

WRAN Repeater

TV Station WRAN Base Station Grade B Contour of TV station

26/05/2009

TV Receiver

WRAN CPE

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 What’s the SDR ? •

Software-Defined Radio (SDR) refers to the technology wherein software modules running on a generic hardware platform consisting of DSPs and general purpose microprocessors are used to implement radio functions such as generation of transmitted signal (modulation) at transmitter and tuning/detection of received radio signal (demodulation) at receiver. 26/05/2009

Introduction .... Definition by SDR ForumSoftware defined radio is used to describe radios that provide software control of a variety of modulation techniques, wideband or narrow-band operation, communications security functions (such as hopping), and waveform requirements of current and evolving standards over a broad frequency range. 26/05/2009

Introduction .... Motivation of SDR • Commercial wireless communication industry is currently facing problems due to constant evolution of link-layer protocol standards (2.5G, 3G, and 4G) • Existence of incompatible wireless network technologies in different countries inhibiting deployment of global roaming facilities • Problems in rolling-out new services/features due to wide-spread presence of legacy subscriber handsets. 26/05/2009

Introduction .... The Key Is Configurability

ADC DAC

USER 26/05/2009

Reconfigurable Processing

DAC ADC

Reconfigurable RF Processing

NETWORK

Introduction .... • Reconfigurability –
Reconfigurability provides essential mechanisms to terminals and network segments to adapt dynamically, transparently and securely to the most appropriate 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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Introduction .... • Benifits -

Equipment manufacturers can use a common desing for multi-functional radios leading to increased market size for a single product.

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Network operators, the interoperability of different networks Is enhanced and system upgrades and bugs fixing are easier to manage and implement.

Subscribers benefit From the enhanced Funtionality of their SDR devices and The possibility to Achieve ubiquitous Connectivity.

SDR is a promising technology that has the potential to realize cost-effective, multi-band and multi-standard telematics products with reduced development cycle.

Introduction .... • Wireless providers are attracted to SDR technology because it enables remote upgrading and reconfiguration of handset and base station software with new features and patches, as well as potential interoperability across multiple networks. • SDR provides a solution for a broad range of communications and devices used in:
cellular base station and handsets
commercial and military satellites
military radios
public safety
wireless LAN/WAN
aerospace
automotive 26/05/2009

Introduction .... • What are the complexities –
It is difficult to engineer wideband, lowloss antennas and RF converters.
It is also difficult to accurately estimate processing demand of applications and processing capacity of reprogrammable DSP/CPU configurations.
In addition, sustaining required data rates across interprocessor interfaces is problematic.
The frequency bands covered may still be constrained at the front-end requiring a switch in the antenna system. .... Later on we will discuss in detail .....

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SDR: General Architecture Reconfigurable Hardware

• Connection set up • Equalization • Freqeuncy hopping • Timing recovery •26/05/2009 Correlation

Digital UP/Down Conversion

Implementation of programmable RF section is limited by the current ADC/DAC technologies – not sufficient in supporting the required digital BW, dynamic range and smpling rate.

SDR: General Architecture .... • Software architecture -

Supports link layer services to higher level protocols Handles hardware resource management, memory and interrupt management Generic Hardware platform built using programmable modules 26/05/2009

SDR: Architecture ....

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Challenges Wide band/multi band low loss Antenna

Wide Input bandwidth, High bit-rate, High bitwidth, low power

Broad band Duplexer, Broad band Freq Synthesizer

Efficient Wideband Linear Power Amplifier, Low power Linear Rxr Front End

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MFLOPS to GFLOPS DSP, Distributed Processors, Flexible DSP OS, Low power, Limited Memory and processing resources for protocols

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Source - A Abidi, ISSCC Girafe 2006

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 Interference
Multiple access interference 26/05/2009

Interference .... • Reference Interference level – • Some of the reference interference levels (for example, in GSM case is can be given as -)    

Co-Channel Interference – Adjacent Interference (200KHz)– Adjacent Interference (400KHz)Adjacent Intereference (600KHz)-

9 dB -9dB -41dB -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 performance within specifications, calls for a very advanced design, including the use of wideband tuneable filters. 26/05/2009

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 factor
Power Dynamic control
Linearizers 26/05/2009

Concern and Issues: Interference • BTS Throughput Vs Interference –

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Source -SDR ETSI Nokia / 08.02.2007

Interference .... • RF Spectrum Usage -

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Source -SDR ETSI Nokia/ 08.02.2007

Interference .... • Although spread-spectrum techniques are inherently resistant to narrow-band interference (NBI) in communication systems, Enough power spectral components of interference might pose a serious problem in providing reliable communication for many wireless systems having broadband front end. • These powerful interfering signals may push low noise amplifiers into a nonlinear region creating very severe nonlinear distortion. • When a receiver is sufficiently nonlinear, strong interference from adjacent channel can produce harmonics and intermodulation products, overpowering and 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. 26/05/2009

Interference .... • The third order intermodulation products are generally recognized 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 signal entirely. • The problem of relatively low frequency interference is still further challenging since, as can be observed in the range equation (Friis transmission formula) Pr/Pt = (GrGt) λ2 /(4π r)2 • The relative dropoff of received power for a given transmitted power and distance is more gradual at low frequencies than at high frequencies (due to the larger λ). • For example, an FRS walkie-talkie (operating at roughly 460 MHz in the U.S.) will have roughly 14.7 dB of received power advantage over an 802.11 signal (roughly 2.5 GHz) at 1 km distance from the transmitter (assuming equal transmitted power). 26/05/2009

1

Approaches For Combatting Distortion in Wideband Front End Amplifier •

2 Multiplex Narrowband Amplifiers The total required frequency spectrum is divided into narrower “band” and each band is handled by a separate amplifier. The cluster of amplifiers is coupled together through a multiplexer. --- Construction of wideband multiplexer is challenging

3

Tunable Narrow Bandwidth Amplifiers A passive LC network is tuned so that the response is optimized to pass the desired input frequency while attenuating others --LNA and its required matching are affected by Fano´s limit

Adaptive Interference Cancellation To cancel out the strongest few signals that are the primary dynamic range “hogs”. By adaptive filtering or by rejective NBI Source - Ron Hickling et all, “Design consideration for the front end frequency agile SDR Rxr”, Proceeding Technical Conference SDR 05 26/05/2009

Wideband Frequency Combatting Frequency Tuning

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Source - A Abidi, ISSCC Girafe 2006

Effect on LNA/Mixer

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Source - A Abidi, ISSCC Girafe 2006

Wideband LNA

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Source - A Abidi, ISSCC Girafe 2006

Discrete-Time Receivers for Software-Defined Radio* • Author in this paper proposes a Discreter-Time (D-T) receiver which has already been demonstrated for Bluetooth, GSM, GPRS, and WLAN.

• A D-T receivers can be categorized based on their track and hold (T/H) structures as charge sampling [1, 2] or voltage 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. 26/05/2009

Discrete-Time Receivers for Software-Defined Radio .... • The main difference is that, charge sampling integrates current and samples charge, while voltage sampling samples voltage. • Voltage sampling often seriously suffers from noise-and-interference aliasing, and the suppression of the alias bands heavily relies on the RF preselect filter. • On the other hand, due to the integration effect of charge sampling, there is a SINC transfer function on the input spectrum, attenuating the aliasing [4]. 26/05/2009

A CMOS 100 MHz to 6 GHz SDR Analog Front-End+ • Author in a recent paper proposed a CMOS based extensive programmable LO generator, LNA, mixers, baseband filters and PPA, which suppors various wireless communication standards while guaranteeing a near-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. 26/05/2009

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 functional requirements of many different standards while guaranteeing an optimal power performance trade-off. 26/05/2009

Attenuation of Adjacent Channel • Signal in the adjacent channel causes interference to the desired signal. • The most computationally intensive part of the wideband receiver of an SDR is the channelizer since it operates at the highest sampling rate. • Higher order FIR channel filters are needed in the channelizer to meet the stringent adjacent channel attenuation specifications of wireless communications standards. • In this paper, authors presented a coefficientpartitioning algorithm for realizing low power and high-speed channel filters. Source - A. P. Vinod et all, “IMPLEMENTATION OF LOW POWER AND HIGH-SPEED HIGHER ORDER CHANNEL FILTERS FOR SOFTWARE RADIO RECEIVERS”, 17th Annual IEEE International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC’06).

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Attenuation of Adjacent Channel.... • Authors in above paper proposed a coefficientPartitioning technique for implementing low power channel filters. • The key idea in this approach is to reduce the ranges of the operands so that the adder width can be reduced which in turn minimizes the number of FAs. • By encoding the filter coefficients using the pseudo floating-point (PFP) arithmetic scheme, the ranges of the operands can be reduced considerably. • Further, a coefficient-partitioning algorithm is employed, which offers substantial reduction of FAs in implementing the PFP coded coefficient multiplier when combined with the Common Subexpression Elimination (CSE)[5,6] method. 26/05/2009

Adjacent Channel Interference .... • Author in this paper proposed an adjacent channel interference (ACI) cancellation scheme with undersampling for multi-channel reception. • Low-IF receiver architecture is used in the multichannel reception scheme. • The ACI cancellation scheme with analog filter bank has been proposed to mitigate the influence from the adjacent channel. • Undersampling technique is applied in this system in order to lower the required sampling frequency 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. 26/05/2009

Concluding Remarks • Maintaining linearity in receivers is one of the key challenges in light of potentially unpredictable levels of interference. • While inband interference is generally considered in evaluating the performance of conventional receivers, wideband receivers must also take into account the effects of outband interference. • The development of wideband front end receivers is a key to achieving frequency agility and realizing the ultimate goal of ideal software definable radio (SDR) receivers. • In this review paper, some of the problems of interference in SDR along with some proposed solution are discussed. • Visited state of art will provide useful information to find out more details in this field. 26/05/2009

Further Reading and References... • [1] K. Muhammad et. al., “A discrete-time Bluetooth receiver in a 0.13um 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 Custom Integrated 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-um CMOS”, IEEE J. Solid-State Circuits, vol. 40, no. 6, Jun. 2005. • [4] G. Xu and J. Yuan, “Performance analysis of general charge sampling”, IEEE Trans. Circuits Syst. II, vol. 52, no. 2, Feb. 2005. • [5] R. I. Hartley, “Subexpression sharing in filters using canonic signed digit 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 highspeed multiplierless filters using a nonrecursive signed common subexpression algorithm,” IEEE Trans. Circuits Syst. II, vol. 49, no. 3, pp. 196-203, March 2002. 26/05/2009

Thank You !!!! ?

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