WO1998043200A1

WO1998043200A1 - Transaction system

Info

Publication number: WO1998043200A1
Application number: PCT/GB1998/000814
Authority: WO
Inventors: Neil Andrew Mcdonald
Original assignee: Marconi Communications Limited
Priority date: 1997-03-22
Filing date: 1998-03-18
Publication date: 1998-10-01
Also published as: GB9706019D0; AU6414598A; GB2323460A; EP1016025A1

Abstract

A transaction system (10) comprises a terminal (12) and a contactless card (14). The terminal (12) sends power to the card (14) by means of a carrier. Data is modulated onto a tone which is independent of the carrier, and then the carrier is modulated with the data-modulated carrier. On receiving the carrier, the card demodulates the data from the tone. The tone is used to generate a clock which is used to run the card and the data is used to carry out a transaction between the terminal (12) and the card (14).

Description

TRANSACTION SYSTEM

This invention relates to a transaction system in which a portable token, for example a

card, is used in conjunction with a device, often termed a reader or terminal, to perform

a transaction of some kind. The invention also relates to the portable token itself. The

invention is particularly, but not exclusively, related to a portable token of credit card

sized dimensions and containing electronic processor means for data storage and processing. Such a token is commonly referred to as a "smart card".

Certain portable tokens must be in physical contact with a terminal in order to operate. These are referred to as contact tokens. Other portable tokens which can operate without being in physical contact with a terminal are referred to as contactless tokens.

Contactless tokens work on, or close to, a terminal which provides power. This power is supplied via a RF (radio frequency) induction field which is referred to as a carrier. Power is transferred from an aerial in the terminal to an aerial on the token. The arrangement is akin to the terminal being a primary coil of a transformer and the token

a secondary coil. In particular embodiments both the terminal and the token each have

a single aerial each of which may comprise a coil having one or more turns.

As well as power being transmitted from the terminal to the token, data is transmitted

from the terminal to the token and vice versa. The exchange of data is used to perform

a transaction. To transmit data to the token the terminal modulates it onto the carrier. To transmit data to the terminal, the token switches an impedance to modulate the amplitude of the carrier at the terminal as the token draws extra power from the terminal

aerial due to the switching action. The term "data" refers to raw information which is

to be processed in a transaction and instructions such as commands, such as an

instruction to reset the token.

The token also requires a clock which is used in the token to provide timing information for the processor means to carry out instructions and send data. It is known in

contactless tokens for the clock to be derived either internally from a frequency source such as a crystal or ceramic resonator, or from the carrier. The latter is preferred because the clock frequency is derived from a stable frequency source in the terminal. In this case the frequency of the carrier determines the frequency of the clock. It is usual for the clock frequency to be either a divisor of the carrier frequency (for example, a high carrier frequency divided by flip flops and logic operations) or a multiple of the carrier frequency (for example, a lower carrier frequency multiplied by a phase lock loop).

A disadvantage of deriving the clock internally is that it is difficult to put a stable frequency source on a contactless token since most tokens have the dimensions of a

credit card. Furthermore, since stable frequency sources are generally made from brittle

materials such as quartz, they are liable to be damaged or broken when located in a

relatively thin and flexible card. Although frequency sources may be generated within

an integrated circuit they are not very stable and their characteristics may vary with temperature change. ~>

Deriving the clock from the carrier overcomes these problems because the frequency source is no longer on the token. However, this approach leads to other problems. The

carrier frequency is limited to be within a relatively narrow operating window in order

to limit radio frequency interference (RFI) caused by the terminal. Since the clock

frequency is determined by the carrier frequency, the clock frequency in the token is

limited to a narrow range of operation.

GB 2 207 790 B discloses a transaction system in which data is transmitted by interruption of a carrier. Since the carrier is used directly to provide a clock for a token, interruption of the carrier also interrupts the clock and so means is provided in the token to provide a clock signal which is available during times in which the carrier is being interrupted. Since the carrier is also used as a source of power to power the token, a power storage circuit is needed in the token to prevent interruption of power supply to the token.

WO 88/02171 discloses a transaction system in which data and clock signals sent by a

terminal are multiplexed together. Therefore, the signals are kept separate from each other and are not transmitted at the same time. As a consequence this system also

provides an interrupted power supply and power storage means is likewise needed.

Originally standards were settled involving transaction systems comprising tokens and

terminals in which the tokens were of the contact type. It was agreed that the clock in

such systems could be set to be between 1 and 5MHz (ISO 7816, part 3). It was also agreed that the token and a host with which the token communicates, such as a mainframe, a PC or a "black box", would communicate with each other at the same baud

rate, for example 9600 baud or a multiple thereof. A typical system is designed to have

a 3.5 MHz clock and to communicate at a baud rate of 9600.

Standards governing contactless tokens are currently being discussed and a carrier

frequency of 13.56MHz has been proposed as a standard because it is widely available

around the world. Therefore, transaction systems using contactless tokens are being

designed to use this carrier frequency and be configured such that they derive from the

carrier a clock which gives a non-standard processor speed of, for example, 4.52MHz

(13.56MHz-3 = 4.52MHz). Since the clock frequency is related to and fixed by the

carrier frequency using carrier frequencies other than the standard frequency agreed

upon will give other non-standard processor speeds which will result in the token

attempting to communicate with the host at a different baud rate. This would lead to

communication errors.

Another problem is caused by the need for tokens to communicate with hosts at faster

rates as the transactions carried out by such transaction systems become more complex.

For example in a system in which the token is used as a travel token in a public

transportation system, a transaction between the token and a host has to occur in less

than 100ms. However, the higher the communication rate, the wider is the spectrum of

the modulated carrier. Therefore at higher communication rates modulation of the

carrier must be small in order to restrict side bands extending beyond the permitted

operating window around the carrier frequency. This is shown schematically in Figure

1. The vertical line 2 represents the carrier frequency and its amplitude. It is centred in the operating window 4 imposed by the permitted RFI limit 6.

Terms commonly used to express an amount of modulation are "strength of modulation"

and "modulation index". Referring to Figure 2, the strength of modulation is the

absolute quantity A-B which can be expressed in units such as volts. The modulation

index is (A-B)/(A+B) which is a relative quantity and is usually expressed as a

percentage, typically 0 to 100%.

Referring back to Figure 1, modulation of the carrier causes side bands 8 which extend

beyond the operating window 4. The side bands 8 would increase in the frequency

domain as the modulation rate of the carrier is increased and increase in the amplitude

domain as the strength of modulation is increased. Therefore the strength of the

modulation which causes side bands 8 should be minimised such that they do not exceed

the RFI limit 6.

With Amplitude Shift Keying (ASK) the strength of modulation or modulation index

of the amplitude must be minimised. With Phase Shift Keying (PSK) the phase change

must be minimised. It is not possible to reduce the side bands caused by Frequency

Shift Keying (FSK) and so that there is an upper limit to the modulation rate which can

be applied to the carrier by FSK. Generally the carrier is modulated by ASK with a

relatively small modulation index to keep the side bands 8 beneath the permitted RFI

limit 6.

According to a first aspect the invention provides a transaction system comprising a terminal the terminal being capable of sending data to the token during a transaction the

terminal being capable of sending a clock signal to the token during the transaction the

clock signal being a tone on a continuous carrier in which the clock signal is

independent of the carrier.

According to a second aspect the invention provides a method of sending a clock signal

from a terminal to a contactless token in which the clock signal is sent as a tone on a

continuous carrier and the clock signal is independent of the carrier.

According to a third aspect the invention provides a transaction system for carrying out

a transaction comprising a terminal and a contactless token the system being provided

with an interface such that the token uses a plurality of clock rates during the

transaction.

Preferably the clock rates are significantly different.

The invention may provide a method according to its third aspect.

According to a fourth aspect the invention provides a contactless token for use with the

system and/or method according to the first, second and third aspects of the invention.

The term "tone" simply refers to a signal having characteristics such as amplitude,

frequency and/or phase which are independent of the characteristics of the carrier.

Clearly, it is convenient for the tone to be cyclic. Since the tone is independent of the carrier, it is possible to reduce the absolute power level of the carrier without affecting

the level of modulation by the clock signal. In this way different power requirements

for RFI limits in different countries can be met.

Preferably the tone can be used by the token to generate a clock for itself. Preferably

in addition to the clock signal, data may also be sent by the terminal and/or the token.

The data may be information which is needed to conduct a transaction and may include

financial value, identifiers of the card and/or the user, and/or journey particulars if the

token is being used as a travel token.

Preferably the carrier undergoes a double modulation in which the carrier is modulated

by the tone which itself has previously been modulated by data.

Preferably the tone is modulated by the data to be sent in order to produce a modulated

tone. ASK, PSK or FSK may be used to modulate the tone by the data (which may be

digital). PSK is preferred. The modulated tone may then be used to modulate the carrier

in order to produce a modulated carrier. Amplitude or phase modulation may be used

to modulate the carrier. Amplitude modulation (AM) is preferred.

Conveniently the tone may be generated by a clock supplied by a host. The host clock

may be divided by a factor of N to provide the tone. Preferably the factor N is 8.

However, the host clock may be multiplied by a factor N to provide the tone. The factor

N is chosen to provide a tone and thus a clock in the token appropriate to an operation

which is to occur between the token and the host. Preferably the shape of the tone is sinusoidal. However, it could be square, triangular

or some other shape.

Preferably the carrier is continuous during a communication procedure, such as a

transaction, between the token and the terminal. That is, there may be no interruption

in the transmission of the carrier whilst a transaction is occurring. Preferably the tone

is a continuous modulation of the carrier, that is the carrier is modulated by the tone at

all times during which the carrier is transmitted.

Preferably the token has a single inductive coil aerial.

In the token, the modulated carrier may be demodulated to provide the modulated tone.

Demodulation of the modulated tone may provide the data and the tone.

The clock signal for the token may be extracted from the tone by using a phase lock loop

which multiplies the tone by the factor N to reproduce the original clock frequency of

the host. In this way the contactless token can be provided with a clock operating at the

same frequency as the host clock.

An advantage of sending a clock signal to the token which is modulated as a tone on the

carrier is that the clock is independent of the carrier and may be varied as desired.

Therefore the terminal and the token can operate and communicate at standard speeds

at any carrier frequency which allows inductive coupling between the token and the

terminal, and carrier frequencies may be chosen to take advantage of locally available operating windows determined by RFI limits.

Another advantage of having a clock which is independent of the carrier is that the host

can select one of a plurality of clock frequencies to determine one of a plurality of clock

frequencies in the token. In this way the host may drive the token at different speeds

dependent on the operation being carried out by the token. However since the terminal

and the token are operating at the same speeds error- free operation can be maintained.

Since the tone is being modulated by the data and its modulation level is low enough to meet RFI limits the data can modulate the tone either strongly or weakly without the RFI limits for the carrier being exceeded.

When two signals are modulated this is, in effect, multiplying the signals together such that one new signal is obtained. That is one of the signals effects properties of the other of the signals. The one whose properties are being altered is usually called the carrier as it contains within it the other signal. It is distinct from multiplexing two signals

which is, in effect, adding the signals together.

An embodiment of the invention will now be described by way of example only with

reference to the accompanying figures in which:

Figure 1 shows a schematic representation of a frequency spectrum generated by

modulation of a carrier;

Figure 2 shows a schematic representation of modulation;

Figure 3 shows a schematic representation of a transaction system; Figure 4 shows steps in the modulation of a carrier; and

Figure 5 shows steps in demodulation of the carrier to obtain a clock signal and a data

signal.

Figures 1 and 2 have already been discussed in the foregoing. Figure 3 shows a

transaction system 10 comprising a terminal 12 and a contactless card 14. The operation

of Figure 3 will be described with reference to Figures 4 and 5 which show a number

of waveforms. A host supplies the terminal 12 with a clock signal 16 which is sent to

a divider 18. The clock signal 16 is divided by N, which is typically eight, to produce

a tone signal 20. This step, referred to as tone generation, is shown in Figure 4(a). The

tone signal 20 is supplied to a first modulator 22 where it is modulated by data 24 to

produce a data modulated tone 26. This step, referred to as tone modulation, is shown

in Figure 4(b). It should be noted that the tone signals in figures 4(a) and 4(b) are

identical but shown with different scales. The data is modulated as phase shifts of +90°

and -90° shown at points 70 and 72. Although Figure 4(b) shows the use of PSK

modulation, ASK or FSK may be used. The data modulated tone 26 is used to modulate

a carrier signal 28 in a second modulator 30 to produce a modulated carrier signal 32.

This step, referred to as carrier modulation, is shown in Figure 4(c). Phase shifts

representing the data can be seen in the modulated carrier signal 32. Amplitude

modulation is typically used to modulate the carrier although angular modulation

(including phase modulation) may be used. Therefore the carrier is modulated by the

tone which itself is modulated by the data.

The modulated carrier signal 32 is amplified by an amplifier 34 and then used to drive an induction coil 36 which generates the RF induction field of the terminal 12.

The RF induction field induces in an induction coil 42 in the card 14 a signal 40

representing the modulated carrier signal 32. Part of the signal 40 is fed into power

recovery means 44 to provide power to drive the card and part is fed into a demodulator

46 to extract the modulated tone 26 from the carrier to leave a signal 48 comprising the

tone modulated by the data. This step, referred to as carrier demodulation, is shown in

Figure 5(a). In one embodiment extraction of power and tone from the modulated

carrier signal occurs in separate parts of the card with a rectifier being used to extract

the power and a demodulator being used to extract the tone. However, in an

embodiment in which the tone is modulated on the carrier using AM, the rectifier and

the demodulator may be combined because the circuitry which serves as the rectifier

would also AM demodulate the received tone signal.

Data 50 and clock 52 information can then be extracted from signal 48 by known

techniques. For example, as PSK was used to modulate the original tone, data 50 and

clock 52 may be extracted by using a phase locked loop (PLL) arrangement 54. This

arrangement 54 extracts the data and also multiplies the tone by N to provide a

reproduction of the original clock frequency of the terminal 12. This step, referred to

as tone demodulation, is shown in Figure 5(b). In this way the card 14 can receive the

same clock as is used in the terminal 12 irrespective of the carrier frequency which is

used by the system.

The PLL arrangement 54 may be configured such that it can extract both the data and the clock thus removing the need for a further step such as multiplication. In the PLL

arrangement a phase detector receives an incoming signal (the data modulated tone) and

a feedback signal. The phase detector outputs a signal which is sent to a low pass filter.

After the filter, a signal may be produced which has a trace signal representative of data.

This trace signal may be detected and used to generate the data.

Since the token clock depends on the host clock, the host can modify its clock and so

determine the processor speed on the token. If a slower clock is used the token will

operate at a slower speed, will consume less power and will be able to operate further

away from the terminal than if a faster clock was used. Some operations which are

relatively simple, such as reading data off the card do not need to occur at a high speed.

Other operations such as those using encryption algorithms do need to occur at a higher

speed in order not to take an undue length of time. This means that the host may

calculate a reasonable clock rate at which to carry out an operation, estimate the power

required by the token to perform the operation and hence estimate the distance from the

terminal at which the token will work. If necessary the terminal may adjust its power

output to ensure that for a specific operation, the token will be able to operate at a

predetermined distance.

A clock of 1 MHz is supplied to the token so that the token operates at a relatively low

level of power thus allowing operation long range, typically 10cm. A relatively low

clock speed allows non-demanding transactions to take place such as hand-shake or

decrement of value on the card. As the token approaches the terminal and more power

becomes available, the clock can be switched to a relatively higher rate of about 5MHz to allow more complex operations such as a full challenge response encryption

transaction, to be executed in a reasonable time period.

Communication from the card 14 to the terminal 12 will occur at a rate determined by

the clock of the card 14. Since the clock of the card 14 is deteπnined by the clock of the

terminal 12, this communication will occur at a determined rate and conventional

techniques may be used.

By using a tone placed on the carrier, the clock and the carrier frequencies are

independent of each other. Consequently to obtain a clock of a specific frequency any

carrier frequency may be used. Therefore, a carrier may be chosen having a frequency

optimised for RFI limits and power transfer.

Although the foregoing discusses one terminal talking to one card there may be a

number of cards in communication with the terminal at the same time. In this case all

of the cards would be receiving the same tone signal and therefore the same clock. One

reason why it would be necessary for a terminal to talk to several cards at the same time

would be to carry out an anti-collision method thus enabling individual cards to conduct

individual transactions sequentially with the host.

It is required by the invention that a tone is present on the carrier. If the tone is removed

this can act as a signal to cause a warm reset of one or more cards. This is opposed to

a cold reset in which the carrier, and thus the transfer of power, is removed.

Claims

1. A transaction system comprising a terminal and a contactless token the terminal

being capable of sending data to the token during a transaction the terminal

being capable of sending a clock signal to the token during the transaction the

clock signal being a tone on a continuous carrier in which the clock signal is

independent of the carrier.

2. A transaction system according to claim 1 in which the token uses a common inductive loop to receive the clock signal and the data from the terminal.

3. A transaction system according to claim 1 or claim 2 in which the clock signal and the data are both sent on the same carrier.

4. A transaction system according to any preceding claim in which the clock signal and the data are transmitted substantially at the same time.

5. A transaction system according to any preceding claim in which the token has

processing means for processing the data.

6. A transaction system according to any preceding claim in which the clock signal

and the data are separate signals.

7. A transaction system according to any preceding claim in which the clock signal and the data are independent signals.

8. A transaction system according to any preceding claim in which the tone is used

by the token to generate a clock for itself.

9. A transaction system according to any preceding claim in which the carrier

undergoes a double modulation in which the carrier is modulated by a first signal

which itself has previously been modulated by a second signal one of the signals

being the clock signal and the other of the signals being the data.

10. A transaction system according to claim 9 in which one of ASK, PSK and FSK

is used to modulate the first signal with the second signal.

11. A transaction system according to claim 9 or claim 10 in which one of amplitude

modulation and phase modulation is used to modulate the carrier.

12. A transaction system according to any of claims 9 to 11 in which the modulated

carrier is demodulated in the token to provide the modulated tone.

13. A transaction system according to claim 12 in which demodulation of the

modulated tone provides the data and the tone.

14. A transaction system according to any preceding claim in which a clock

provided by a host is divided by a factor of N to provide the tone.

15. A transaction system according to claim 14 in which the clock signal for the token is extracted from the tone by using a phase lock loop which multiplies the

tone by the factor N to reproduce the original clock frequency of the host.

16. A transaction system according to any preceding claim in which one of a

plurality of clock signals having different frequencies is chosen to be modulated

onto the carrier to determine one of a plurality of clock frequencies in the token.

17. A transaction system according to claim 16 in which the token operates at different speeds dependent on the operation which it is carrying out.

18. A transaction system according to any preceding claim in which the data sent to the token includes commands which instruct the token to carry out a particular processing step such as storing the data or resetting the token.

19. A transaction system substantially as described herein with reference to Figures

3, 4 and 5 of the accompanying drawings.

20. A token for use with a transaction system according to any preceding claim.

21. A token substantially as described herein with reference to Figures 3, 4 and 5 of

the accompanying drawings.

22. A method of sending data and a clock signal from a terminal to a contactless token during a transaction in which the clock signal is sent as a tone on a

continuous carrier and the clock signal is independent of the carrier.

23. A method according the claim 22 in which the token uses a common inductive

loop to receive the clock signal and the data.

24. A method substantially as described herein with reference to Figures 3, 4 and 5

of the accompanying drawings.

25. A transaction system for carrying out a transaction comprising a terminal and a

contactless token the system being provided with an interface such that the token

uses a plurality of clock frequencies during the transaction.

26. A transaction system according to claim 25 in which at least one of the clock

frequencies is significantly different to at least one other of the clock

frequencies.