yogesh

Power Management Schemes for NFC

YOGESH SINGH

Guide: Inderkumar Kochar

ELECTRONICS AND TELECOMMUNICATION

St. Francis Institute of Technology

• NFC

• Power Management Schemes

– Protocol Independent Method

– PTF-Determinator

– FSS and BIN

• Comparison of Methods

• Conclusion

• References

2

Contents


NFC

• NFC or Near Field Communication is a short range high frequency wireless communication technology

• Extension of Radio frequency identification

• Contactless communication between handheld devices

• It operates within the globally available and unlicensed radio frequency band of 13.56 MHz

• NFC operates in Active and Passive modes

3Power Management Schemes for NFC

Protocol Independent Detection

• In NFC, the standard method used to detect passive devices relies purely on protocol communication

• The initiator periodically sends out inquiry requests and waits for passive targets to respond

• Since the targets are passive, the initiator has to provide the energy for the target by maintaining the magnetic field for the whole communication sequence, lasting at least 5 ms.

• This approach cuts it down to 40 μs



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Fig.1: Schematic of resonant coupled RWD–tag-system [1]



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Fig.2 : f0 over M [1]



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Fig.3 : Block Diagram of Proposed Model [1]



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(a) (b)

Fig.4 : Two Excitation Frequencies (a) No Tag (b) Tag Present [1]


Results of Protocol Independent Detection

Frequency f1 ΔU ADC bits SNRmin

13.51MHz 6mV 9 57dB

13.48MHz 60mV 6 37dB

13.46MHz 120mV 5 31dB

13.44MHz 210mV 4 26dB

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TABLE 1: Results of Protocol Independent Detection [1]


PTF-Determinator

• It determines the Power transfer Function (PTF) during run-time

• NFC consumes power when integrated in devices

• Focuses on components not on the system

• In our case the component is Reader which transfers power to the Tags


• Reader can only scale the Magnetic field Strength

• A dynamic configuration of the magnetic field strength during run-time reduces this losses and this waste of energy

• With the determined PTF the field strength can be dynamically scaled

• The wireless communication channel between them can be split into two main parts,

(i) Power Transmission Path (ii) Data-Transfer Path

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PTF-Determinator


PTF-Determinator

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Fig.5 : PTF-determinator and the Integration Into the Near Field Communication System [2]


PTF-Determinator

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Fig.6: Replacement Circuit To Describe The PowerTransfer From The Reader To The Tag Without The Voltage Regulation On Tag- Side [2]


Approximation of Tag-Reader Distance

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Fig.7: Algorithm To Approximate The Distance Between The Reader And Tag [2]


Simulation Results

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Fig.8: Detection of the Tag with and without the PTF Evaluation if x < xmax [2]


Simulation Results

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Fig.9: Detection of the Tag with and without the PTF Evaluation if x > xmax [2]


FSS and BIN

• This technique does not consider multiple transponders in transmission range

• In this technique, the magnetic field strength is scaled on the reader’s side

• The scaling is based on power transmission depending on the current Physical Relation Factor, which also involves the distance between Transponders and the Reader


Magnetic Field Strength Scaling

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Fig.10: Magnetic Field Strength Scaling for Multiple Transponders in Two Possible Scenarios [3]


Magnetic Field Strength Scaling

• To prevent said issues, the field strength (shell) is dynamically scaled to consume a power of P = Pi

• In the last shell, the power consumption is equivalent to the one of the CONST algorithm, which always uses the maximum field strength

• FSS simply scales the field strength gradually until the wanted transponder can be found or the maximum output power is reached


Binary Method

• FSS strictly scales the field strength from the lowest to the highest shell, which is not optimal

• This is achieved with a quadratic binary search through the available field strengths

• The algorithm handles the field strengths as a sorted list


CONST Method

• tU ... This is an abstract time unit, which describes the smallest amount of time used in the analytic approach. The value of this time factor can be matched to the investigated system by measurement (measuring the average time of execution)

• To cover the resulting delay that influences the energy consumption, tSET is introduced which describes the amount of time required to set the field strength once. By definition one single field strength setting operation takes tU time.


CONST Method

• tREAD ... In order to demonstrate the correct behavior of all algorithms, an amount of 1 kB has to be read from the specified transponder after it was successfully reached. This process takes approximately 80 time units tREAD = 80 tU

• tFIND ... In order to communicate with a certain transponder, independently of how many targets are actually in transmission range at that time, the transmission module of the reader has to acquire its full UID (unique identifier). This process can be repeated (nTL) until either all transponders have been inspected or the wanted one was successfully found


CONST Method

• The main goal of the analytic approach is to minimize the energy consumption,

E = Pi (tSET + tFIND + tREAD) (1)

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Parameter Relation with time unit

tSET tU

tFIND 1.2*nTL*tU

tREAD 80*tU

TABLE 2: FACTORS FOR THE ANALYTIC APPROACH RELATING TO THE TIME UNIT tU BASED ON THE TIMING ANALYSIS OF THE MEASURED RFID-READER [3]


CONST Method

• Best case ... In this case the wanted transponder is the first one found by the transponder-detection procedure (nTL = 1)

tFIND = 1.2*tU (2)

t = tSET + tFIND + tREAD = 82.2*tU (3)

E = PMAX*82.2*tU (4)• Average Case ... For this case it is assumed that after listing

half of the transponders, the wanted one is found (nTL = n/2 ). tFIND = 1.2*(n/2)*tU = 0.6*n*tU (5)

t = tSET + tFIND + tREAD = (0.6*n + 81)*tU (6)

E = PMAX*(0.6*n + 81)*tU (7)


CONST Method

• Worst case ... The wanted transponder is only found after all the others have been inspected (nTL = n).

tFIND = 1.2*n tU (8)

t = tSET + tFIND + tREAD = (1.2*n + 81) tU (9)

E = PMAX*(1.2*n + 81) tU (10)


CONST Method

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Fig.11: Best Case [2]


CONST Method

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Fig.12: Average Case [2]


CONST Method

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Fig.13: Worst Case [2]


ENERGY CONSUMPTION OF CONST METHOD

Energy

Best Case PMAX*82.2*tU

Average Case PMAX*(0.6*n+81)*tU

Worst Case PMAX*(1.2*n+81)*tU

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TABLE 3: ENERGY CONSUMPTION OF THE DIFFERENT CASES OF THE CONST METHOD [3]


ENERGY CONSUMPTION OF FSS METHOD

Energy


Average Case PMAX*(0.45*n+67.33)*tU

Worst Case PMAX*(1.2*n+103.4)*tU

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TABLE 4: ENERGY CONSUMPTION OF THE DIFFERENT CASES OF THE FSS METHOD [3]


ENERGY CONSUMPTION OF BIN METHOD

Energy


Average Case PMAX*(0.49*n+69.93)*tU

Worst Case PMAX*(1.2*n+89.29)*tU

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TABLE 5: ENERGY CONSUMPTION OF THE DIFFERENT CASES OF THE BIN METHOD [3]


Comparison

Methods Energy Consumption (%)

BIN 68.13%

FSS 65.53%

Method CONST(without field strength scaling)

100%

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TABLE 6: COMPARISON OF THE ENERGY CONSUMPTIONS [3]


Conclusion

• This are the methods used to decrease the consumption of power in a NFC Device.FSS and BIN are more energy efficient than the standard approach of CONST. This scenario explains the advantage of the field strength scaling principle, as both optimized algorithms are able to successfully read from the transponder with a lower field strength, whereas CONST always operates with the maximum amount.


References[1] Richard G. Mair, “Protocol-Independent Detection of Passive Transponders for Near-Field Communication Systems.” IEEE Transactions On Instrumentation And Measurement, vol. 59, no. 4, April 2010.

[2] Manuel Menghin, Norbert Druml, Christian Steger, Reinhold Weiss, Holger Bock and Josef Haid, “The PTF-Determinator: A run-time method used to save energy in NFC-Systems.”, Fourth International EURASIP Workshop on RFID Technology,2012.

[3] Manuel Menghin, Norbert Druml, Bernhard Kipperer, Christian Steger, Reinhold Weiss,Holger Bocky and Josef Haidy “Energy Efficiency by Using Field Strength Scaling for Multi-Transponder Applications” 12th International Conference on Telecommunications - ConTEL 2013.

[4]] MLA Menghin, Manuel, et al. "NFC-DynFS: a way to realize dynamic field strength scaling during communication." Near Field Communication (NFC), 2013 5th International Workshop on. IEEE, 2013


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