Note: Descriptions are shown in the official language in which they were submitted.
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Description
Method for coding a sequence of data bits, in
particular for transmission via an air interface
The invention relates to a method for coding a sequence
of data bits which have a logical on or off value.
Non-contacting identification systems operate on the
basis of non-contacting transmission techniques. This
can be achieved electromagnetically, by means of light,
infrared or ultrasound. Systems of this type are used,
for example, for identification of personnel or of
moving goods, for example of vehicles. The necessary
data is for this purpose transmitted from a
transmitter/receiver via a non-contacting data
transmission path, for example via an air interface, to
a mobile data memory, and back. In this case, the non-
contacting identification technique also allows the
recording of the data, for example while moving past
the mobile data memory, without this having to be
inserted into or passed through a reader/writer.
In order to allow the mobile data memories to be used
without any time restrictions, no chemical energy
stores, such as batteries, are integrated in them. The
required electrical energy is thus drawn in a non-
contacting manner externally, that is to say from an
electrical or magnetic field originating from the
transmitter/receiver. Suitable transmission and coding methods
are therefore required for communication of the
transmitter/receiver with such mobile data memories. On the one
hand, only specific frequency bands are in general allowed for
transmission of data, for example the ISM frequency bands
(industrial, scientific and medical) for industrial, scientific
and medical applications. In this case, the specified maximum
permissible field strength for each frequency range allows only
a maximum data rate. On the other hand, the
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transmission and coding methods must also ensure that
the electronics in the mobile data memory are supplied
with energy.
Methods of this type allow continuous energy supply to
the data memory electronics, in that the carrier
frequency which is modulated with the data to be
transmitted is switched off only for a maximum time
interval for energy transmission. Within this time
interval, an energy store which has previously been
charged in the mobile data memory must be able to
bridge the energy supply. Conversely, data is
transmitted from the mobile data memory to the
reader/writer by means of so-called load modulation. In
this case, the mobile data memory attenuates the
inducing magnetic field in a time slot pattern. In
accordance with the standards mentioned above, load
modulation may be carried out continuously or with
carrier-frequency modulation for one time slot,
depending on the chosen type of transmission.
Methods such as these are known, for example, from the
ISO/IEC Standard 15693 Part 2 "Air Interface and
Initialization", or from the Standard 14443 for
operation in an ISM frequency band.
When the reader/writer sends a transmission request to
a mobile data memory, it is now possible for two or
more mobile data memories to signal with different
subsequent data after an initially identical
synchronization sequence. The reader/writer detects
this collision in the course of an accompanying
plausibility check, but at the latest on reception of
two successive modulated time slots. The reader/writer
then waits for the ongoing data transmission sequence,
so that collision information can then be sent to the
mobile data memories. Depending on the data protocol
being used, the data transmission sequence may
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comprise from one byte to several kilobytes.
Subsequently, the collision can be resolved by the
mobile data memories by means of known collision
resolution mechanisms.
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This has the disadvantage of the need to wait for
completion of an ongoing data transmission sequence in
order, for example, that a termination command or
collision information can be sent to the mobile data
memories involved. It is thus possible for there no
longer to be sufficient time for collision resolution
and for subsequent data transmission between the
reader/writer and the individual mobile data memories
during the time for which the mobile data memories
remain in the reception area.
The invention is thus based on the object of proposing
a new coding method, which allows faster detection of a
collision, and faster termination of data transmission,
for a renewed check. The invention is based on the
further object of specifying a mobile data memory, a
reader/writer, as well as an identification system in
order to achieve the object.
The object is achieved by a method for coding a
sequence of data bits, with the data bits having a
logical on or off value, the data bits being organized
in a sequence of time slot frames, with one time slot
frame having time slots which can assume an on or off
value. In this case, the coding in a time slot frame is
carried out such that at least one time slot is
preloaded with an off value, the time slots which are
not preloaded are loaded with on or off values in order
to form the logical on or off value for a data bit, and
a time slot with an on value is followed by at least
one time slot with an off value. A preloaded time slot
in the method may be arranged at the start or end of a
time slot frame. The time slots which are not preloaded can
thus be loaded with on or off values in time slot frames, such
that the loading with a logical on value is complementary to
loading with a logical off value. Furthermore, a time slot
frame may have an odd number of time slots which are not
loaded, with a greater number of time slots being loaded with
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an on value, in particular for coding of a logical on
value, than for coding of a logical off value. In the
method, a time slot with an on value can be formed by a
pulse sequence, in which case the pulse sequence may,
in particular, have an even number of pulses and pauses
with the same duty ratio. Furthermore, a number, which
can be predetermined, of carrier oscillations may be
associated with one pulse.
The object is also achieved by a mobile data memory for
non-contacting interchange of a sequence of data bits
with a reader/writer, and having a first coding device
for carrying out the method according to the invention.
The mobile data memory may have checking means which
can terminate the non-contacting interchange of a
sequence of data bits on identification of an on value
in a preloaded time slot. Furthermore, the mobile data
memory can restart the non-contacting data interchange,
at least from that part of the coded sequence of data
bits which has not been interchanged, after a
termination.
The object is also achieved by a reader/writer for non-
contacting interchange of a sequence of data bits with
at least one mobile data memory, which has a second
coding device for carrying out the method according to
the invention. The second coding device may in this
case load the preloaded time slot with an on value on
reception of two successive time slots with an on
value.
Finally, the object is achieved by an identification
system for carrying out the method according to the
invention using a modulation method based on the
ISO/IEC Standard 14443 or the ISO/IEC Standard 15693
for operation in an ISM frequency band, in particular
in an ISM frequency band of 13.56 MHz. The
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identification system has at least one reader/writer
and at least one mobile data memory according to the
invention, which can interchange
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sequences of data bits via a non-contacting data
transmission path.
The advantage of the coding method according to the
invention is that the complementary coding of a data
bit in a time slot frame allows direct collision
identification, when data bits which are transmitted at
the same time and have a logical on and off value are
received.
A further advantage is that termination of the ongoing
data transmission sequence can be achieved within one
checking time slot, even within one transmitted coded
data bit. In consequence, collision information can be
sent to the mobile data memories involved, for rapid
resolution of the collision and in order to continue
with the data which has not yet been transmitted,
immediately after this.
A further advantage of the method according to the
invention is that the weighted coding of a data bit
allows correction by the reader/writer, for example in
the case of a sporadically missing modulated time slot.
This furthermore advantageously makes it possible to
improve the safety, security and reliability of the
data transmission.
The invention will be explained in more detail with
reference to the following figures, in which:
Figure 1: shows an example of an identification system,
which has a reader/writer and a mobile data
memory, each having a coding device for
carrying out the method according to the
invention for non-contacting interchange of a
sequence of data bits,
Figure 2: shows a detail of an example of a sequence of
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data bits according to the invention,
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Figure 3: shows an example which describes a collision
event during data transmission from three
mobile data memories, and
Figure 4: shows an example of an exemplary embodiment
of the method according to the invention for
carrier-frequency-modulated load modulation.
By way of example, Figure 1 shows an identification
system IS which has a reader/writer SLG and a mobile
data memory DTl, each having a coding device KE1, KE2
for carrying out the method according to the invention.
Furthermore, the mobile data memory DTl has checking
means AM for carrying out the method according to the
invention. In this case, sequences of data bits B1-B5
are transmitted via a non-contacting data transmission
path LS, for example via an air interface. The upper
part of the figure shows an example of a control
computer SR, which is connected to a reader/writer SLG
via an interface. The data is interchanged between the
control computer SR and the reader/writer SLG via this
interface, for example for data recording. The lower
part of the figure shows an object B0, for example a
vehicle, which is moving in a movement direction BW
relative to the reader/writer SLG. A mobile data memory
DT1 is fitted to the moving object B0, at the side. The
reader/writer SLG and the data storage medium DT1 are
connected via the air interface LS, which is shown by
way of example and via which the data storage medium
DTl is supplied with energy, and via which the data
transmission takes place.
The data transmission may in this case be used for
identification of the example of a vehicle BO by means
of the reader/writer SLG. A further option is to
transmit, for example, new job data for delivery of a
transporting item to the vehicle B0. Energy flow lines
EF are also shown, in order to illustrate the
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energy flow from the reader/writer SLG to the mobile
data memory DT1.
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Figure 2 shows a detail of an example of a sequence of
data bits B1-B5 according to the invention. The
sequence is in this case preceded by a synchronization
sequence SYNC which is required, inter alia, for
synchronization between a reader/writer SLG and a
mobile data memory DT1-DT3 in order to carry out the
method according to the invention. This synchronization
sequence SYNC is preferably defined as standard for the
mobile data memories D1-D3 for operation in an
identification system IS.
According to the invention, the example of data bits
B1-B5 is coded such that these bits are organized in a
sequence of time slot frames FR1-FR5, with the data
bits B1-B5 having a logical binary on value 1 or off
value 0. The time slot frames FR1-FR5 are subdivided
for coding purposes into time slots ZS11-ZS14, and can
assume an on value Z1, or an off value Z0. In the
example shown in the figure, four time slots ZS11-ZS14
where chosen, by way of example, for one time slot
frame FR1-FR5. In the example shown in the figure, the
coding in a time slot frame FR1-FR5 is carried out such
that a time slot AF at the location of the time slot
ZS14 is preloaded with an off value Z0. The time slots
ZS11-ZS13 which are not preloaded can be loaded with on
or off values Z1, ZO in accordance with the example
shown in the figure, so as to form the logical on or
off value l, 0 for a data bit Bl-B5. In addition, the
coding in a time slot frame FR1-FR5 is carried out such
that at least one time slot ZS11-ZS14 with an off value
ZO follows a time slot ZS11-ZS14 with an on value Z1.
A transmission protocol which is based on the method
according to the invention in this case complies with
the requirement to ensure that energy is supplied to a
mobile data memory D1-D3 in accordance with the
abovementioned ISO IEC Standards. This applies in
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particular to transmission via an air interface LS by
non-contacting inductive means. With respect to the
technical implementation of the method, a modulated
time slot in this case corresponds to a time slot ZS11-
ZS14 with an on value Zl. In the case of a
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time slot ZS11-ZS14 with an off value Z0, there is no
modulation, for example of the carrier for
transmission.
Furthermore, according to the invention, the time slots
ZS11-ZS13 which are not preloaded by way of example are
loaded with on or off values Zl, ZO such that the loading
with a logical on value 1 is complementary to a loading with
a logical off value 0.
The advantage of the coding method according to the
invention is that the complementary coding of a data bit B1-
B5 in an associated time slot frame FR1-FR5 allows immediate
collision identification when a binary on or off value 1, 0
is received. In the present example, a reader/writer SLG
would receive three time slots with an on value Z1 by
reception superimposition of the transmitted time slots
ZS11-ZS13 with an on and off value Z1, Z0. This is explained
in more detail in the example shown in Figure 3.
Furthermore, according to the invention, an odd number of
time slots ZS11-ZS13 which are not loaded is chosen. In
addition, a greater number of time slots Z11-Z14 are
loaded with an on value Z1 for coding of a logical on
value 1 than for coding of a logical off value 0. In the
example shown in Figure 2, a coded logical on value 1 has
two time slots ZS11, ZS13 with an on value Z1, in
comparison to one time slot Z12 with an off value Z0.
This is associated with the further advantage that the
weighted coding of a data bit B1-B5 in a time slot frame
FR1-FR5 allows correction by the reader/writer. Thus, for
example, a sporadically missing modulated time slot ZS11
with a coded logical on value 1 does not have any
disadvantageous effect on the transmitted data content.
Furthermore, this advantageously allows the safety,
security and reliability of the data transmission to be
increased.
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Figure 3 shows an example of a collision event C when
three mobile data memories DT1-DT3 transmit data
simultaneously. In this case, the figure shows a detail
of a coded sequence of data bits B1-B3 in the time slot
frames FR1-FR3 according to the invention. This clearly
shows that the time slots ZS11-ZS13 are loaded
differently with an on or off value Z1, ZO in the time
slot frame FR3.
According to the invention, in the present example, the
second coding device KE2 of the reader/writer SLG shown
in Figure 1 loads the preloaded time slot AF, ZS14 with
an on value Z1 on receiving at least two successive
time slots ZS11-Z13. In the example, the reader/writer
SLG receives three modulated time slots ZS11-ZS13. This
is illustrated in the figure by a lightning symbol.
Collision information S is now available to the
transmitting mobile data memories DT1-DT3 by modulation
Z1 of the preloaded time slot AF, that is to say by
loading it with an on value Z1.
According to the invention, the mobile data memories
DT1-DT3 have checking means AM, which terminate the
non-contacting interchange of a sequence of data bits
B1-B3 on identification of an on value Z1 in a
preloaded time slot AF. In the example shown in the
figure, this is done by identification of a modulated
time slot Z1 at the location of the preloaded time slot
AF in the time slot frame F3. In order to check
collision information S, the mobile data memories DT1-
DT3 change from a transmission mode to a reception mode
for a time slot AF which is, for example, short.
According to the invention, the mobile data memories
DT1-DT3 can restart the non-contacting interchange, at
least from that part of the sequence of data bits B1-B5
which has not been interchanged, after a termination.
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On reception of the collision information S, the mobile
data memories DT1-DT3 which are involved can, for
example, make use of known collision mechanisms in the
first
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coding device KE1. These may, for example, also be
stored in the first coding device KE1. It is thus, for
example, possible to use the serial number to determine
which of the mobile data memories DT1-DT3 involved
should be the first to restart the transmission of the
sequence of data bits Bl-B5.
This is associated with the advantage that the ongoing
data transmission sequence can still be terminated
within a transmitted coded data bit B1-B5, that is to
say within the associated time slot frame FR1-FRS. It
is thus advantageously possible, immediately after
this, to send collision information S to the mobile
data memories DT1-DT3 involved in order to rapidly
resolve the collision S and continue with the data B1-
B5 which has not yet been transmitted.
Figure 4 shows an example of an exemplary embodiment of
the method according to the invention for carrier-
frequency-modulated load modulation. In this case,
according to the invention, a time slot ZS11-ZS14 with
an on value 21 is formed by a pulse sequence PF for
modulation. In the example shown in the figure, these
are the time slots ZS11 and ZS13 in the time slot frame
FR1. The pulse sequence PF may have an even number of
pulses PL and pauses PS with the same duty ratio, as is
illustrated by way of example in Figure 4. Furthermore,
according to the invention, a number, which can be
predetermined, of carrier oscillations fo can be
associated with each pulse PL. The number 8 was chosen
in the example shown in Figure 4.
This is associated with the advantage that the Type B
modulation methods, which are standardized in the
abovementioned ISO IEC Standards, can also be used by
masking out the carrier frequency fo in the pauses PS.
According to the invention, the identification system
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IS can be operated with the reader/writer SLG and with
at least one mobile data memory DT1-DT3 in order to
carry out the method according to the invention using a
modulation method based on the ISO/IEC 14443 Standard
or the ISO/IEC 15693 Standard in an
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ISM frequency band, in particular in an ISM frequency
band of 13.56 MHz, for non-contacting data transmission
on inductively coupled paths.
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Description
Method for coding a sequence of data bits, in particular
for transmission via an air interface
The invention relates to a method for coding a sequence
of data bits which have a logical on or off value.
A continuity monitoring system which operates using coded
identification marks is known from US 4,471,345. An
associated monitoring station has means for transmission
of a checking signal with a specific code pattern.
A system in which a test sequence is coded on the basis
of return-to-zero modulation is known from the document
"QUICK BIT ERROR RATE ESTIMATOR FOR INFRARED DATA
ASSOCIATION" IBM TECHNICAL DISCLOSURE BULLETIN, IBM CORP.
NEW YORK, US, Vol. 39, No. 12, December 1, 1996 (1996-12-
01), pages 61-63, XP000686019 ISSN: 0018-8689.
Signal codings in baseband, which are normally used for
RFID systems, for example NRZ, Manchester and Unipolar RZ
coding, are described on pages 190 and 191 of the
textbook by Klaus Finkenzeller titled "RFID Handbuch"
[RFID Manual], 3rd Edition, Carl Hanser Verlag, Munich
2002.
Non-contacting identification systems operate on the
basis of non-contacting transmission techniques. This
can be achieved electromagnetically, by means of
light, infrared or ultrasound. Systems of this type
are used, for example, for identification of
personnel or of moving goods, for example of
vehicles. The necessary data is for this purpose
transmitted from a transmitter/receiver via a non-
AMENDED SHEET
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contacting data transmission path, for example via an
air interface, to a mobile data memory, and back. In
this case, the non-contacting identification technique
also allows the recording of the data, for example
while moving past the mobile data memory, without this
having to be inserted into or passed through a
reader/writer.
In order to allow the mobile data memories to be used
without any time restrictions, no chemical energy
stores, such as batteries, are integrated in them. The
required electrical energy is thus drawn in a non-
contacting manner externally, that is to say from an
electrical or magnetic field originating from the
transmitter/receiver. Suitable transmission and coding
methods are therefore required for communication of the
transmitter/receiver with such mobile data memories. On
the one hand, only specific frequency bands are in
general allowed for transmission of data, for example
the ISM frequency bands (industrial, scientific and
medical) for industrial, scientific and medical
applications. In this case, the specified maximum
permissible field strength for each frequency range
allows only a maximum data rate. On the other hand, the
AMENDED SHEET
