U.S. patent application number 15/332001 was filed with the patent office on 2017-02-09 for transmitting apparatus and method for a digital telecommunication system.
This patent application is currently assigned to Sony Deutschland GmbH. The applicant listed for this patent is Sony Deutschland GmbH. Invention is credited to Ralf Bohnke, Thomas DOLLE, Tino PUCH.
Application Number | 20170041177 15/332001 |
Document ID | / |
Family ID | 37742504 |
Filed Date | 2017-02-09 |
United States Patent
Application |
20170041177 |
Kind Code |
A1 |
Bohnke; Ralf ; et
al. |
February 9, 2017 |
TRANSMITTING APPARATUS AND METHOD FOR A DIGITAL TELECOMMUNICATION
SYSTEM
Abstract
A transmitting apparatus transmits signals in a digital
telecommunication system and a synchronising method is used for
synchronizing such signals at a receiving apparatus. The
transmitting apparatus prepares for transmission of a reference
symbol having at least two repetition patterns, whereby one of the
at least two repetition patterns is phase-shifted in relation to
the other repetition pattern, and a synchronizing mechanism in the
digital telecommunication system uses the reference symbol once
received for synchronization. The synchronizing mechanism uses a
cross-correlation mechanism to cross-correlate at least one of the
two repetition patterns within a correlation window having a
predetermined length.
Inventors: |
Bohnke; Ralf; (Esslingen,
DE) ; DOLLE; Thomas; (Munich, DE) ; PUCH;
Tino; (Bonn, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Sony Deutschland GmbH |
Stuttgart |
|
DE |
|
|
Assignee: |
Sony Deutschland GmbH
Stuttgart
DE
|
Family ID: |
37742504 |
Appl. No.: |
15/332001 |
Filed: |
October 24, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14037829 |
Sep 26, 2013 |
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15332001 |
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|
13618613 |
Sep 14, 2012 |
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14037829 |
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11429210 |
May 8, 2006 |
8861622 |
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13618613 |
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11210527 |
Aug 23, 2005 |
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11429210 |
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09510652 |
Feb 22, 2000 |
7154975 |
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11210527 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04L 7/042 20130101;
H04L 27/2663 20130101; H04B 1/16 20130101 |
International
Class: |
H04L 27/26 20060101
H04L027/26; H04L 7/04 20060101 H04L007/04 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 24, 1999 |
EP |
99103546.0 |
Claims
1. (canceled)
2. A receiver comprising: circuitry configured to receive a
reference symbol comprising at least nine synchronization
repetition patterns, wherein each repetition pattern contains a
predetermined number of samples and an end synchronization
repetition pattern in the reference symbol is phase-shifted by
180.degree..
3. The receiver of claim 2, wherein the circuitry is configured to
perform a synchronization process by detecting a timing of a
correlation peak at an end of the reference symbol.
4. A method for receiving a digital signal in a digital
telecommunication system, comprising: receiving a reference symbol
comprising at least nine synchronization repetition patterns,
wherein each repetition pattern contains a predetermined number of
samples and an end synchronization repetition pattern in the
reference symbol is phase-shifted by 180.degree..
5. The method of claim 4, further comprising: performing a
synchronization process by detecting a timing of a correlation peak
at an end of the reference symbol.
6. A receiver comprising: circuitry configured to receive a
reference symbol comprising at least nine successive
synchronization repetition patterns, wherein each repetition
pattern contains a predetermined number of samples and a last
repetition pattern of the successive repetition patterns is
phase-shifted in relation to the other repetition patterns.
7. The receiver of claim 6, wherein the last repetition pattern of
the successive repetition patterns is phase-shifted by 180.degree.
in relation to the other repetition patterns.
8. The transmitter device according to claim 6, wherein the
circuitry is configured to perform a synchronization process by
detecting a timing of a correlation peak at an end of the reference
symbol.
9. A method for receiving OFDM signals in an OFDM system,
comprising: receiving a reference symbol comprising at least nine
successive synchronization repetition patterns, wherein each
repetition pattern contains a predetermined number of samples and a
last repetition pattern of the successive repetition patterns is
phase-shifted in relation to the other repetition patterns.
10. The method according to claim 9, wherein the last repetition
pattern of the successive repetition patterns is phase-shifted by
180.degree. in relation to the other repetition patterns.
11. The method according to claim 9, further comprising: performing
a synchronization process by detecting a timing of a correlation
peak at an end of the reference symbol.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This is a continuation application of U.S. Ser. No.
14/037,829, filed Sep. 26, 2013, which is a continuation of U.S.
Ser. No. 13/618,613, filed on Sep. 14, 2012 which is a continuation
of Ser. No. 11/429,210, filed on May 8, 2006 (now U.S. Pat. No.
8,861,622), which is a continuation of U.S. Ser. No. 11/210,527,
filed on Aug. 23, 2005, which is a continuation-in-part of U.S.
Ser. No. 09/510,652, filed Feb. 22, 2000 (now U.S. Pat. No.
7,154,975), and claims priority to European Application No.
99103546.0, filed Feb. 24, 1999, the entire contents of each of
which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] Field of the Invention
[0003] The present invention relates to a transmitting apparatus
and a transmitting method, for transmitting a digital signal in a
digital telecommunication system. The present invention is hereby
particularly directed to the generation and transmission of a
reference symbol which is used on a receiver side to achieve a time
and/or frequency synchronisation.
[0004] Digital telecommunication systems generally need a
synchronisation of a transmitting side and a receiving side. The
transmitting side and the receiving side can e.g. be base stations
and mobile stations of a telecommunication system, whereby the
synchronisation of the timing and the frequency of transmitted
signals is usually performed in the mobile station. To achieve a
synchronisation, it is known to transmit a special training
sequence or a reference symbol, also called synchronisation symbol.
Such a reference symbol is usually embedded in the transmission
data structure and regularly sent so that a synchronisation can be
performed regularly.
[0005] In FIG. 1, a general structure of a receiving apparatus is
shown in order to explain the synchronisation mechanism on which
the present invention is based. The receiving apparatus can e.g. be
a mobile station of a wireless digital telecommunication system.
Although the present invention essentially relates to the
transmitting part of a telecommunication terminal, it is to be
understood, that the transmitting part or transmitting apparatus of
the present invention can also be a or part of a receiving and
transmitting terminal.
[0006] The receiving apparatus 1 shown in FIG. 1 comprises an
antenna 2 for receiving signals from a transmitting side, e.g. a
base station of a wireless digital telecommunication system. The
received signals 2 are supplied to a 11F means (High Frequency
means) 3, which downconverts the received high frequency signals
into the base band. The downconverted signals are supplied to a
IQ-demodulation means, where they are demodulated and supplied to a
synchronising means 5.
[0007] The synchronising means performs time and frequency
synchronisation using a received training sequence or reference
symbol, as stated above. Using the synchronization information of
the synchronising means 5, the received user data signals are
further processed in the receiving apparatus 1, e.g. decoded by a
decoding means 6 and so on, to be made available in visible or
audible form for a user. Usually the synchronisation in the
synchronising means 5 is performed in the time domain.
[0008] Generally speaking, the synchronising means 5 performs a
time domain correlation between the reference symbol (or parts of
the reference symbol) and a delayed version of the received
reference symbol (or parts of the reference symbol) to identify the
reference symbol (or parts of the reference symbol) and thus to
determine the timing for the synchronisation. Thereby, a
correlation peak is calculated, which should correspond as accurate
as possible to the time point of the last sample of the reference
symbol.
[0009] In order to achieve a well detectable correlation peak, the
reference symbol usually consists of a plurality of synchronisation
patterns, which are repeated several times within one reference
symbol period. The synchronisation patterns usually have the same
shape or form and are thus called repetition patterns throughout
the present application. A reference symbol therefore contains
several repetition patterns, whereby each repetition pattern
consists of a plurality of samples. Each repetition pattern has the
same number of samples. Between the reference symbol and the
adjacent user data symbols, guard intervals can be inserted to
avoid intersymbol interference in a multipath environment of the
telecommunication system.
[0010] The time domain correlation of the received reference symbol
in the receiving apparatus 1 can be achieved e.g. on the basis of
an auto correlation mechanism or a cross correlation mechanism. An
auto correlation mechanism thereby does not require any knowledge
about the reference symbol on the receiver side, whereby a cross
correlation mechanism requires exact knowledge about the reference
symbol to be received on the receiver side.
[0011] A known cross correlation means 7 is shown in FIG. 2. The
cross correlation means 7 cross correlates incoming signals y(i),
e.g. coming from the IQ demodulation means 4, within a cross
correlation window of a length 16. The cross correlation window
length 16 means that the incoming digital signal y(i) is cross
correlated sample by sample on the basis of a length of 16 samples.
The cross correlation window length of 16 samples can thereby
correspond to the length of a repetition pattern of the reference
symbol. In FIG. 3, a reference symbol comprising 9 repetition
patterns is shown, whereby one repetition pattern can comprise 16
samples. The receiving apparatus 1 knows exactly the structure of
the reference symbol to be received. A complex conjugated version
of an expected repetition pattern is stored in the synchronising
means 5 and cross correlated to the received signals.
[0012] The cross correlation means 7 of FIG. 2, which has a cross
correlation window length of 16, comprises 15 delay means 8
arranged serially. The first delay means delays the incoming
complex signal y(i) by one sample, which corresponds to
multiplication with a factor z.sup.-1. The second delay means
delays the output of the first delay means again by 1 sample and so
on. Further, the cross correlation means 7 comprises 16
multiplication means 9 and a sum means 10. The delay means 8, the
multiplication means 9 and the sum means 10 are arranged so that an
incoming signal having a length of 16 samples is cross correlated
with a complex conjugated version of the samples of a repetition
pattern. The complex conjugated samples of the expected repetition
pattern are e.g. stored in the synchronising means of the receiver
and read out respectively to the multiplication means 9. E.g. a
first received sample y(0) is multiplied with a complex conjugated
version of the first sample of the expected repetition pattern,
i.e. y*(0)=s.sub.0*. The next received sample y(1) is multiplied
with y*(1)=s.sub.1* and so forth. The sum means 10 adds up all the
results from the multiplication means 9, so that an output signal
r(i) is obtained. The output signal r(i) of the sum means 10 is
supplied to an absolute value calculating means 11 which calculates
the absolute value of r(i) to detect a cross correlation peak. The
cross correlation means 7 and the absolute value calculating means
11 shown in FIG. 2 can be comprised in the synchronising means 5 of
the receiving apparatus 1 shown in FIG. 1.
[0013] In FIG. 3, the cross correlation peak detection performed by
the cross correlation means 7 and the absolute value calculating
means 11 shown in FIG. 2 is explained. FIG. 3 shows three different
phases of a cross correlation calculation of an incoming signal. In
phase 1, the correlation window 13 of the cross correlation means 7
is located on received user data, which means that only user data
are cross correlated. The user data are indicated by "??? . . . ".
Thus, no cross correlation peak is detected. In phase 2, the
correlation window 13 is exactly matching with the eighth
repetition pattern S7 of the reference symbol 12, so that a
corresponding cross correlation peak is detected. In phase 3, the
cross correlation window 13 is again cross correlating user data
"??? . . . ", so that no cross correlation peak is detected.
[0014] The reference symbol 12 shown in FIG. 3 comprises 9
repetition patterns S0, S1, S8, which have identical shapes. Each
of the repetition patterns comprises e.g. 16 samples, which
corresponds to the cross correlation window length 16 of the cross
correlation means 7 in FIG. 2. Of course, the number of repetition
patterns in the reference symbol 12 and the number of samples in
each repetition pattern can be changed and adopted to the
respective application.
[0015] As stated above, the cross correlation mechanism requires
exact knowledge on the reference symbol to be received on the
receiving side. This means, that the receiving apparatus needs to
know exactly the structure and number of repetition patterns to be
able to recognise the last cross correlation peak, which serves for
a time and frequency synchronisation. On the other hand, if one of
the cross correlation peaks is not properly detected, the
synchronisation fails. In mobile communication environments, in
which multipath fading degrades the correlation peak detection
performance, the synchronisation performance in a known receiving
apparatus of the telecommunication system is thus significantly
lowered.
BRIEF SUMMARY OF THE INVENTION
[0016] The object of the present invention is to provide a
transmitting apparatus and transmitting method for transmitting a
digital signal in a digital telecommunication system which generate
a reference symbol which allows for an improved time and/or
frequency synchronisation performance and accuracy on the receiving
side.
[0017] According to a first aspect of the invention, a transmitting
apparatus for transmitting a digital signal in a digital
telecommunication system comprises means for preparing a reference
symbol comprising a sequence of a plurality of synchronisation
repetition patterns, whereby each repetition pattern contains a
predetermined number of samples, means for transmitting said
reference symbol as a part of said digital signal by using OFDM
(Orthogonal Frequency Division Multiplexing) modulation to a
receiver side apparatus, wherein an end synchronisation repetition
pattern in said reference symbol is phase-shifted by 180.degree.
and said reference symbol comprises a number of said
synchronisation repetition patterns and said phase-shifted
synchronisation repetition pattern is positioned after the sequence
of said number of synchronisation repetition patterns so that the
receiver side apparatus can exactly detect a timing of a
correlation peak at the end of said reference symbol by performing
a cross correlation of said synchronisation repetition patterns.
Advantageously, the transmitting apparatus of the present invention
further comprises adjusting means for increasing the transmission
power when transmitting the reference symbol.
[0018] According to a further aspect of the present invention, a
method for transmitting a digital signal in a digital
telecommunication system comprises the steps of preparing a
reference symbol comprising a sequence of a plurality of
synchronisation repetition patterns, wherein each repetition
pattern contains a predetermined number of samples, transmitting
said reference symbols as a part of said digital signal by using
OFDM (Orthogonal Frequency Division Multiplexing) modulation to a
receiver side apparatus, wherein an end synchronisation repetition
pattern in said reference symbol is phase-shifted by 180.degree.
and said reference symbol comprises a number of said
synchronisation repetition patterns and said phase-shifted
synchronisation repetition pattern is positioned after the sequence
of said number of synchronisation repetition patterns so that the
receiver side apparatus can exactly detect a timing of a
correlation peak at the end of said reference symbol by performing
a cross correlation of said synchronisation repetition
patterns.
[0019] Advantageously, the method according to the present
invention further comprises the step of increasing the transmission
power when transmitting the reference symbol.
[0020] According to a further aspect of the present invention, a
transmitting apparatus for transmitting a digital signal in a
digital telecommunication system comprises means for preparing a
reference symbol comprising a sequence of a plurality of
synchronisation repetition patterns, wherein each repetition
pattern contains a predetermined number of samples, means for
transmitting said reference symbol as part of said digital signal
by using OFDM (Orthogonal Frequency Division Multiplexing)
modulation to a receiver side apparatus, wherein an end
synchronisation repetition pattern in said reference symbol is 30
phase-shifted by 180.degree. and said reference symbol comprises a
number of said synchronisation repetition patterns and said
phase-shifted synchronisation repetition pattern is positioned
after the sequence of said number of synchronisation repetition
patterns so that the receiver side apparatus can perform a
synchronisation process in accordance with said synchronisation
repetition patterns and exactly detect the timing of said end of
the reference symbol by performing a cross-correlation of said
synchronisation repetition patterns.
[0021] Advantageously, the transmitting apparatus of the present
invention further comprises adjusting means for increasing the
transmission power when transmitting the reference symbol.
[0022] According to a further aspect of the present invention, a
method for transmitting a digital signal in a digital
telecommunication system comprises the steps of preparing a
reference symbol comprising a sequence of a plurality of
synchronisation repetition patterns, wherein each repetition
pattern contains a predetermined number of samples, transmitting
said reference symbol as a part of said digital signal by using
OFDM (Orthogonal Frequency Division Multiplexing) modulation to a
receiver side, wherein an end synchronisation repetition pattern in
said reference symbol is phase-shifted by 180.degree.) and said
reference symbol comprises a number of said synchronisation
repetition patterns and said phase-shifted synchronisation
repetition pattern is positioned after the sequence of said number
of synchronisation repetition patterns so that the receiver side
can perform a synchronisation process in accordance with said
synchronisation repetition patterns and exactly detect a timing of
said end of said reference symbol by performing a cross-correlation
of said synchronisation repetition pattern.
[0023] Advantageously, the method according to the present
invention further comprises the step of increasing the transmission
power when transmitting the reference symbol.
[0024] According to a further aspect of the present invention, a
transmitter device for transmitting OFDM (Orthogonal Frequency
Division Multiplexing) signals to a receiver in an OFDM system
comprises means for preparing a reference symbol comprising a
sequence of a plurality of synchronisation repetition patterns,
wherein each repetition pattern contains a predetermined number of
samples, means for transmitting said reference symbol as part of
said digital signal by using OFDM modulation to a receiver side
apparatus in said OFDM system, means for preparing a reference
symbol comprising a plurality of successive repetition patterns,
whereby said reference symbol is transmitted from said transmitter
device by using multicarriers of said OFDM system and a last
repetition pattern of said successive repetition patterns is
phase-shifted in relation to the other repetition patterns, and
wherein each of said successive repetition patterns generated by
said generating means is composed of the same number of samples, so
that said synchronisation repetition patterns transmitted to said
receiver side device are cross-correlated in said receiver side
device in order to perform time and frequency synchronisation in
said receiver side device.
[0025] Advantageously, in the transmitter device according to the
present invention, the last repetition pattern of said successive
repetition pattern is phase-shifted by 180.degree. in rotation to
the other repetition patterns. Further advantageously, the
transmitter device according to the present invention further
comprises adjusting means for increasing the transmission power
when transmitting the reference symbol.
[0026] According to a further aspect of the present invention, a
method for transmitting OFDM (Orthogonal Frequency Division
Multiplexing) signals to a receiver side in an OFDM system
comprises the steps of preparing a reference symbol comprising a
sequence of a plurality of synchronisation repetition patterns,
wherein each repetition pattern contains a predetermined number of
samples, transmitting said reference symbol as part of said digital
signal by using OFDM modulation to a receiver side in said OFDM
system, preparing a reference symbol comprising a plurality of
successive repetition patterns, whereby said reference symbol is
transmitted from a transmitter side by using multicarriers of said
OFDM system and a last repetition pattern of said successive
repetition pattern is phase-shifted in relation to the other
repetition patterns, and wherein each of said generated successive
repetition patterns is composed of the same number of samples, so
that said synchronisation repetition patterns transmitted to said
receiver side are cross-correlated on said receiver side in order
to perform time and frequency synchronisation on said receiver
side.
[0027] Advantageously, in the method according to the present
invention, the last repetition pattern of said successive
repetition patterns is phase-shifted by 180.degree. in relation to
the other repetition patterns. Further advantageously, the method
according to the present invention further comprises the step of
increasing the transmission power when transmitting the reference
symbol.
[0028] According to a further aspect of the present invention, a
transmitter device for transmitting OFDM (Orthogonal Frequency
Division Multiplexing) signals in an OFDM telecommunication system
comprises means for generating said OFDM signals having a reference
symbol comprising a plurality of successive repetition patterns,
wherein a last repetition pattern of said plurality of successive
repetition patterns is phase-shifted in relation to the other
repetition patterns, and means for transmitting said generated OFDM
signals including said reference symbol and transmitting data to a
receiver side device, wherein each of said plurality of successive
repetition patterns generated by said generating means is composed
of the same number of samples, respectively, so that said
repetition patterns transmitted to said receiver side device are
cross-correlated in said receiver side device in order to perform
time and frequency synchronisation in said receiver side.
[0029] Advantageously, in the transmitter device according to the
present invention, the last repetition pattern of said plurality of
successive repetition patterns is phase-shifted by 180.degree. in
relation to the other repetition patterns. Further advantageously,
the transmitter device according to the present invention further
comprises adjusting means for increasing the transmission power
when transmitting the reference symbol.
[0030] According to a further aspect of the present invention, a
method for transmitting OFDM (Orthogonal Frequency Division
Multiplexing) signals in an OFDM telecommunication system comprises
the steps of generating said OFDM signals having a reference symbol
comprising a plurality of successive repetition patterns, wherein a
last repetition pattern of said plurality of successive repetition
patterns is phase-shifted in relation to the other repetition
patterns, and transmitting said generated OFDM signals including
said reference symbol and transmitting data to a receiver side,
wherein each of said generated successive repetition patterns is
composed of the same number of samples so that said repetition
patterns transmitted to said receiver side are cross-correlated on
said receiver side in order to perform time and frequency
synchronisation on said receiver side.
[0031] Advantageously, in the method according to the present
invention, the last repetition pattern of said successive
repetition patterns is phase-shifted by 180.degree. in relation to
the other repetition patterns. Further advantageously, the method
according to the present invention further comprises the step of
increasing the transmission power when transmitting the reference
symbol.
[0032] It is to be noted that the use of a sequence of a plurality
of synchronisation repetition patterns in the reference symbol
significantly enhances the time and frequency synchronisation
performance and accuracy as compared to the provision of only a few
repetition patterns. Further, by phase-shifting the last
synchronisation repetition pattern in the reference symbol by
180.degree. in relation to all other synchronisation repetition
patterns in the reference symbol, a very accurate and reliable
phase detection on the receiver side and thus an accurate time
and/or frequency synchronisation is possible.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0033] The present invention is explained in detail in the
following description by means of preferred embodiments relating to
the enclosed drawings, in which
[0034] FIG. 1 shows the general structure of a receiving apparatus
of a digital telecommunication system,
[0035] FIG. 2 shows a known cross correlation means and absolute
value calculation means for detecting a cross correlation peak,
[0036] FIG. 3 shows the cross correlation peak detection performed
by the cross correlation structure of FIG. 2,
[0037] FIG. 4 shows the structure of a reference symbol used for
synchronisation according to the present invention,
[0038] FIG. 5 shows the cross correlation peak detection using the
reference symbol shown in FIG. 4,
[0039] FIG. 6 shows a transmitter structure according to the
present invention,
[0040] FIG. 7 shows a cross correlation means and a detection means
for detecting cross correlation peaks and respective phase
information on the basis of a reference symbol as shown in FIG.
4,
[0041] FIG. 8 shows a cross correlation means and another detection
means for detecting a single cross correlation peak on the basis of
a reference symbol as shown in FIG. 4,
[0042] FIG. 9 shows a synchronisation result of the cross
correlation means and tilt detection means of FIG. 8,
[0043] FIG. 10 shows a further embodiment of the detection means of
FIG. 6,
[0044] FIG. 11 shows a simulation result of the cross correlation
means and the detection means of FIG. 10,
[0045] FIG. 12 shows a further embodiment of a cross correlation
means according to the present invention together with an absolute
value calculation means,
[0046] FIG. 13 shows a simulation result of the cross correlation
means and the absolute value calculation means shown in FIG. 12 for
detecting a cross correlation peak,
[0047] FIG. 14 shows a further embodiment of a synchronising
structure according to the present invention comprising a cross
correlation means according to the present invention and a peak
threshold detection means and a gap detection means, and
[0048] FIG. 15 shows an alternative structure to the embodiment
shown in FIG. 14.
DETAILED DESCRIPTION OF THE INVENTION
[0049] FIG. 4 shows the structure of a reference symbol 14 as
example for a reference symbol structure to be used according to
the present invention. The reference symbol 14 of FIG. 4 comprises
9 synchronisation repetition patterns S0, S1, . . . S8. Each
repetition pattern has a length of 16 samples s.sub.0, s.sub.1, . .
. s.sub.15. Thereby, the last repetition pattern S8 is
phase-shifted by 180 degrees in relation to the other repetition
patterns, which means a multiplication by (-1). Thus, the last
repetition pattern S8 comprises 15 samples -s.sub.0, -s.sub.1, . .
. -s.sub.15. All synchronisation repetition patterns of the
reference symbol 14 have the same shape, i.e. identical content,
whereby the last repetition pattern S8 is phase-inverted by 180
degrees in relation to the other repetition patterns of the
reference symbol. All other (preceding) synchronisation repetition
patterns have the same phase. It is to be noted, that the reference
symbol 14 can have more or less than 9 repetition patterns and that
each repetition pattern can have more or less than 16 samples.
[0050] In FIG. 5, the reference symbol 14 is shown to be embedded
in a user data sequence. The reference symbol 14 can hereby be
inserted in any wanted or advantageous location within a sequence
of data symbols. Between the reference symbol and the data symbols
before and after the reference symbols, a so-called guard interval
can be inserted in order to avoid inter-symbol interference (ISI)
in a multipath environment. In the time domain the reference symbol
14 has a length N and each synchronisation repetition pattern has a
length of N.sub.sp, so that the reference symbol 14 consists of
(N/N.sub.sp) copies of the synchronisation repetition pattern. A
very efficient way of generating reference symbols of the desired
structure, e.g. in an OFDM (Orthogonal Frequency Division
Multiplexing) transmission system, is the application of an IFFT
(Inverse Fast Fourier Transformation) exploiting the properties of
the DFT (Discrete Fourier Transformation) algorithm. Consequently,
in order to generate a reference symbol of length T.sub.s with
(N/N.sub.sp) synchronisation repetition patterns of length
THN.sub.sp/N only every (N/N.sub.sp)-th DFT coefficient (every
N/N.sub.sp-th subcarrier in the frequency domain) has to be
modulated. At the beginning and/or at the end of a reference symbol
14, a guard interval may be inserted in order to avoid inter-symbol
interference (ISI). Hereby, the guard interval can be formed by a
cyclic extension of each symbol by copying the last few
synchronisation repetition patterns.
[0051] The user data are indicated by "??? . . . " FIG. 5 shows
three different phases of cross correlating a received signal
having a reference symbol 14, in which the last repetition pattern
S8 is phase-inverted by 180.degree.. Relating to the receiving
apparatus 1 shown in FIG. 1, the data sequence of the three phases
shown in FIG. 5 are for example supplied from the IQ demodulation
means 4 to the synchronising means 5, whereby the synchronising
means 5 is e.g. constructed as shown in FIG. 6. In phase 1, the
cross correlation window 15 cross correlates only user data, so
that no cross correlation peak is detected. In phase 2, the 8th
repetition pattern S7 of the reference symbol 14 is matched by the
correlation window 15, so that a cross correlation peak is
detected. The relative phase of the cross correlation peak of the
8th repetition pattern S7 is also detected to be "+". Since the 9th
repetition pattern S8 is phase-inverted by 180.degree. in relation
to the 8th repetition pattern S7, the cross correlation peak
detected for the 9th repetition pattern S8 has the relative phase
"-" in relation to the phase of the 8th repetition pattern S7. The
repetition patterns S0, S1 . . . S6 preceding the two last
repetition patterns S7 and S8 have a relative phase "+".
[0052] In phase 3 of FIG. 5, only user data are cross correlated in
the cross correlation window 15, so that no cross correlation peak
is detected. As can be seen in FIG. 5, by using a reference symbol
structure like the one shown in FIG. 4, in which one of the
repetition patterns is phase-inverted in relation to at least one
of the other repetition patterns in the reference symbol, a
relative phase information can be obtained additional to the cross
correlation peak information. This phase information provides
additional information on the position of the last correlation peak
in the reference symbol and thus a more accurate and reliable
synchronisation information.
[0053] FIG. 6 shows a transmitting apparatus or transmitting device
60 according to the present invention. To be precise, FIG. 6 shows
important elements of a transmitting apparatus 60 according to the
present invention which are necessary to explain and to understand
the present invention. Data to be transmitted are supplied to a
channel encoder 61. The output of the channel encoder 61 is
supplied to a reference symbol insertion circuit 62. In the
reference symbol insertion circuit 62, the reference symbols from a
memory 64, where they are stored, are multiplexed by a multiplexer
63 with the data to be transmitted. The output from the reference
symbol insertion circuit 62 is supplied to an OFDM (Orthogonal
Frequency Division Multiplexing) burst mode controller 15. The
output from the OFDM burst mode controller 65 is given to an
inverse FFT circuit 66. The output from the inverse FFT circuit 66
is supplied to a power adjustment circuit 67. In the power
adjustment circuit 67, the transmitting power is increased when a
reference symbol is transmitted. The output from the power
adjustment circuit 67 is supplied to a synchronisation repetition
pattern rotation (inverting) circuit 68. The synchronisation
repetition pattern rotation circuit 68 contains a circuit 69 for
extracting the last synchronisation repetition pattern of a
reference symbol, a phase shifter 70 and a combining circuit 71
combining the phase shifted last synchronisation repetition pattern
of a reference symbol with the other synchronisation repetition
patterns in the same reference symbol. The output of the
synchronisation repetition pattern rotation circuit 68 is supplied
to a circuit 72 which inserts a cyclic extension into the reference
symbol. Then the data stream containing the data to be transmitted
as well as the reference symbols is modulated by a modulator 73 on
a radio frequency (RF). After filtering the data to be transmitted
in a filter 74 the filter data are given to an RF-front-end stage
75. The reference symbols are inserted into the data in the
frequency domain to avoid the generally large implementation effort
when inserting the reference symbols of the data in the time
domain.
[0054] The average power of the reference symbol upon transmission
is lower than the average power of other OFDM-symbols due to the
lower number of modulated subcarriers. Therefore, the adjustment
circuit 67 is provided in order to increase the transmitting power
to match the average transmission power of the OFDM-data symbols.
This can be achieved by a multiplication of each sample of the
reference symbol with a power adjustment factor which calculates to
F.sub.power= {square root over (N/N.sub.sp)}. After the power
adjustment the last synchronisation repetition pattern is rotated
by 180.degree., which is realised through a multiplication by -1 in
the synchronisation repetition pattern rotation circuit 68. After
the complex signal is converted into a real signal by the
IQ-modulator 73, it is passed to the transmission RF-front-end
stage 75 in order to be transmitted through an antenna over a
wireless link to a receiving device, which is e.g. disclosed in the
following figures.
[0055] In FIG. 7, a cross correlation means 16 and a detection
means 19 are shown, which can be implemented in a first embodiment
of a synchronising means 5 of a receiving apparatus 1 of the
present invention, the general structure of which is shown in FIG.
1. The structure of the cross correlation means 16 is identical to
the structure of the cross correlation means 7 shown in FIG. 2, so
that a detailed explanation is omitted. The cross correlation means
16 comprises 15 delay means 17 and 16 multiplication means 18 as
well as a sum means for adding the outputs of the multiplication
means 18. The cross correlation window length of the cross
correlation means 16 corresponds to the length of one repetition
pattern, which is e.g. 16 samples. A received data stream of 16
samples is cross correlated with complex conjugated samples of an
expected repetition pattern stored in the receiving apparatus 1.
The output signal r(i) of the sum means, i.e. the output signal of
the .phi. cross correlation means 16 is supplied to a detection
means 19 for detecting the magnitude and the phase of the signal
r(i) and therefore the exact position of the cross correlation peak
of the last repetition pattern S8 of the reference symbol 14 can be
detected (cf. FIG. 5).
[0056] FIG. 8 shows another arrangement of the detection means. The
cross correlation means 16 of FIG. 8 corresponds to the cross
correlation means 16 of FIG. 7. In the example shown in FIG. 8, the
detection means comprises a delay means 20 for delaying the output
signal r(i) of the cross correlation means 16 by one repetition
pattern length, which is e.g. 16 samples. The detection means 19
further comprises a subtraction means 21 for subtracting the output
signal s(i) of the delay means 20 from the output signal r(i) of
the cross correlation means 16. The output signal z(i)=r(i)-s(i) of
the subtraction means 21 is supplied to an absolute value
calculation means 22, which calculates the absolute value of z(i).
It is to be noted, that y(i), r(i), s(i), z(i) are complex values
so that the magnitude and the phase information is contained in
z(i). If it is assumed, that r(i) is in the part of the reference
symbol, in which the phase of the repetition patterns is not
phase-shifted, for example in the part S0, . . . S7 of the
reference symbol 14 shown in FIG. 4, then s(i)
r(i-16)=r(i)e.sup.i.phi..psi.
z.sub.1(i)=r(i)-s(i)=r(i)(1-e.sup.i.phi.).
[0057] If it is assumed, that r(i) matches with the phase-inverted
repetition pattern S8 of the reference symbol 14, then
s(i)=r(i-16)==r(i)e.sup.i.phi..psi.
z.sub.2(i)=r(i)-s(i)=r(i)(1+e.sup.i.phi.).
[0058] It can be seen that the absolute value of z(i) is enhanced
if r(i) matches with the phase-shifted repetition pattern S8. The
phase value cp has nothing to do with the phase shift between the
repetition pattern S7 and S8, but results from a possible frequency
offset between the transmitter side and the receiver side.
Considering the detection range of the phase change introduced by
the reference symbol structure according to the present invention
under the influence of a frequency offset between the transmitter
and the receiver, the following result is obtained:
z.sub.i(i)/z.sub.2(i)=-j cot(.sub..phi./2). Thus, for a
non-ambiguous detection the absolute value of .phi. has to be
smaller than .pi. whereby the phase value c is the product between
the frequency offset and the duration T.sub.P of one repetition
pattern, .phi.=2.pi.f.sub.offsetT.sub.P.
[0059] In FIG. 9, a simulation result for the absolute value of
z(i) as the output signal of the structure shown in FIG. 8 is
shown. For the reference symbol 14 comprising 9 repetition
patterns, whereby each repetition pattern consists of 16 samples,
and whereby the phase of the last repetition pattern S8 is inverted
in relation to the phase of the other repetition patterns, the
cross correlation peak is expected to be at the last sample, i.e.
the time point corresponding to the last sample, of the last
repetition pattern S8. As can be seen in FIG. 9, the cross
correlation peak is located at sample 144, which is the correct
value. Thus, the cross correlation means 16 and the detection means
19 shown in FIG. 9 and in FIG. 8 enable a correct and efficient
detection of the cross correlation peak.
[0060] In FIG. 10, the cross correlation means 16 and another
embodiment of the detection means of FIG. 8 are shown. Thereby, the
structure shown in FIG. 109 corresponds to the structure shown in
FIG. 8, whereby the output of the absolute value calculating means
22 is supplied to an averaging means 23 for smoothening the
absolute value of z(i) output from the means 22. The structure
shown in FIG. 9 is particularly advantageous in severe noise and
fading environments. The averaging means 23 advantageously is a
moving average filter having a filter length corresponding to the
length of one repetition pattern, which is for example 16 samples
as shown in FIG. 4. The cross correlation structures shown in FIGS.
8 and 10 can e.g. be implemented in the synchronising means 5 of
the receiving apparatus 1 shown in FIG. 1.
[0061] FIG. 11 shows a simulation result for the averaged absolute
value of z(i) as the output signal of the structure shown in FIG.
10. The detection of the last repetition pattern having an inverted
phase as shown in FIG. 4 can be seen in the transition between
sample 128 and sample 144.
[0062] In FIG. 12, a second embodiment of a cross correlation means
24 is shown, which CM be implemented in a synchronising means 5 of
a receiving apparatus 1 of the present invention, a general
structure of which is e.g. shown in FIG. 1.
[0063] The cross correlation means 24 essentially has the same
structure as the cross correlation means 16 shown in FIG. 7 and the
cross correlation means 7 shown in FIG. 2. The main difference is,
that the cross correlation means 24 shown in FIG. 12 has a cross
correlation window length of two repetition patterns, which in the
shown example corresponds to 32 samples, when the structure of the
reference symbol shown in FIG. 4 is assumed. Thereby, the cross
correlation means 24 comprises 31 delay means 25, which are
arranged serially and respectively cause a delay of one sample.
Further, the cross correlation means 24 comprises 32 multiplication
means, which multiply the respective (delayed) samples of the
received signal y(i) with stored positive and negative complex
conjugated values of the samples of the expected repetition
pattern. Thereby, e.g. the first sample entering the cross
correlation means 24 is multiplied with the first complex
conjugated sample s.sub.0* of the expected repetition pattern. The
same is true for the rest of the samples entering the cross
correlation means 24, which are respectively multiplied with the
rest of the stored (positive) complex conjugated samples s.sub.1*
to s.sub.15*. The second 16 samples entering the cross correlation
means 24 are respectively multiplied will the stored negative
complex conjugated samples -s.sub.0* to -s.sub.15* of the expected
repetition pattern. Hereby, e.g. the first sample entering the
means 24 is multiplied with the negative value of the complex
conjugated first sample of the expected repetition pattern
-s.sub.0*. The same is true for the rest of the second 16 samples
entering the means 24 which are respectively multiplied with the
negative values of the complex conjugated values, namely -s.sub.1*
to -s.sub.15*. It is to be noted, that the values s.sub.0, s.sub.1,
s.sub.15 of the repetition patterns S0, S1, . . . , S8, of the
reference symbol 14 shown in FIG. 4 are respectively the same. In
other words, all the repetition patterns S0, S1, . . . , S8 of the
reference symbol 14 of FIG. 4 have the same shape, except that the
last repetition pattern S8 has an inverted phase.
[0064] The outputs of the multiplication means 26 of the cross
correlation means 24 are added up in a sum means 27, which generate
an output signal z(i). The output signal z(i) of the sum means 27
is supplied to an absolute value calculation means 28, which
calculates the absolute value of z(i). The output signal of the
absolute value calculation means 28 therefore provides information
on the magnitude as well as on the phase of the data signals, which
are cross correlated by the cross correlation means 24.
[0065] A simulation result for the output of the absolute value
calculation means 28 of the structure shown in FIG. 12 is shown in
FIG. 13. In this case, a reference symbol similar to the reference
symbol 14 shown in FIG. 4 had been used, but only with 6 repetition
patterns, whereby each repetition pattern consists of 16 samples.
The phase of the last repetition pattern is shifted by 180.degree.
in relation to the other preceding repetition patterns. Thus, the
position of the last sample of the last repetition pattern is
expected to be at sample position number 96, which is clearly
visible in the simulation result shown in FIG. 13. FIG. 13 shows
clearly, that the output signal has a maximum exactly when a
correct overlapping between the two repetition patterns processed
in the cross correlation means 24 is achieved.
[0066] FIG. 14 shows an extended structure for increasing the
reliability and accuracy of the output signal of the absolute value
calculation means 22 of the structure shown in FIG. 8, the
averaging means 23 of the structure shown in FIG. 10 or the
absolute value calculation means 28 of the structure shown in FIG.
12. In the improved structure shown in FIG. 13, the respective
output signal of the cross correlation means 24 or the detection
means 19, which is the absolute value of z(i), is supplied to a
peak threshold detection means 29 and a gap detection means 30. The
peak threshold detection means 29 detects if the absolute value of
z(i) exceeds a predetermined cross correlation peak threshold. The
gap detection means 30 detects if the absolute value of z(i) has
been below a predetermined gap threshold before said detected cross
correlation peak. In FIG. 13 it can be seen, that the absolute
value of z(i) is zero or close to zero as long as the data signals
entering the cross correlation means are in the part of the
reference symbol, where the phase of the repetition patterns is not
inverted in relation to each other. Hereby, a presynchronisation
can be achieved, since the detected correlation peak is only
confirmed when the gap in front of the correlation peak is
detected.
[0067] In other words, the gap in front of the correlation peak can
be used to identify the (range for the possible position of the
cross correlation peak. Only when the peak threshold detection
means 29 detects that the absolute value of z(i) exceeds the
predetermined cross correlation threshold and the gap detection
means detects that the absolute value of z(i) has been below a
predetermined gap threshold before the detective cross correlation
peak, the cross correlation peak is confirmed. In this case, the
peak threshold detection means 29 and the gap detection means 30
send respectively a positive information to a determination means
33, which can for example be an AND gate, which outputs the
position of the detected cross correlation peak only in case of a
positive signal from both of the means 29 and 30. In front of the
gap detection means 30, an averaging means 31 and/or a delay means
32 can be located. The averaging means 31 can for example be a
moving average filter to smoothen the absolute value of z(i). The
filter length preferably corresponds to the length of one
repetition pattern of the reference symbol. The delay means 32
preferably provides a delay corresponding to the length of one
repetition pattern of the reference symbol. The averaging means 31
as well as the delay means 32 can be provided or not depending on
the application.
[0068] FIG. 154 shows an alternative structure to FIG. 14. In FIG.
15, the absolute value of z(i) is supplied to a peak threshold
detection means 29 identical to the peak threshold detection means
29 of FIG. 14. The gap detection means 34 shown in FIG. 15 detects
if the absolute value of z(i) has been below a predetermined gap
threshold before the detected cross correlation peak and
additionally detects if it has been below the predetermined gap
threshold during a predetermined gap time. In the contrary to the
gap detection means 30 of FIG. 14, which only checks one time point
before the detected cross correlation peak, the gap detection means
34 of FIG. 15 checks a time period before the detected cross
correlation peak. Identically to FIG. 14, a determination means 33,
which can for example be an AND gate, determines if the output
signals from the peak threshold detection means 29 and the gap
detection means 34 are both positive and confirms the detected
correlation peak to be the required correlation peak for that case.
Both structures shown in FIGS. 14 and 15 provide an increased
detection accuracy and reduce the false alarm possibility by
combined detection of a presynchronisation and a correlation peak
detection. The presynchronisation, i.e. the detection of the gap in
front of a detected cross correlation peak enables to detect the
range of possible synchronisation peak positions, what can be used
to reduce the number of computations needed for the succeeding
synchronisation.
[0069] It has to be noted, that although the cross correlation and
synchronisation structures shown in FIGS. 7, 8, 10, 12, 14 and 15
can be implemented in the synchronising means 5 of the receiving
apparatus 1 shown in FIG. 1, these inventive structures can be
implemented or used in any other receiving apparatus as long as the
scope of the present invention as defined in the enclosed claims is
met.
* * * * *