U.S. patent application number 14/308997 was filed with the patent office on 2015-06-04 for method for transmitting data using variable guard interval and apparatus thereof.
The applicant listed for this patent is Electronics and Telecommunications Research Institute. Invention is credited to Dong Joon CHOI, Namho HUR, Jae-Ho LEE, Sang-Jung RA.
Application Number | 20150156045 14/308997 |
Document ID | / |
Family ID | 53266224 |
Filed Date | 2015-06-04 |
United States Patent
Application |
20150156045 |
Kind Code |
A1 |
LEE; Jae-Ho ; et
al. |
June 4, 2015 |
METHOD FOR TRANSMITTING DATA USING VARIABLE GUARD INTERVAL AND
APPARATUS THEREOF
Abstract
In an orthogonal frequency division multiplexing (OFDM) wireless
communication system, when path delay information is received from
a reception apparatus through a return path after data
transmission, a length of a cyclic prefix included in a transmitted
signal is adjusted on the basis of a delay value included in the
path delay information.
Inventors: |
LEE; Jae-Ho; (Daejeon,
KR) ; RA; Sang-Jung; (Daejeon, KR) ; CHOI;
Dong Joon; (Daejeon, KR) ; HUR; Namho;
(Daejeon, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Electronics and Telecommunications Research Institute |
Daejeon |
|
KR |
|
|
Family ID: |
53266224 |
Appl. No.: |
14/308997 |
Filed: |
June 19, 2014 |
Current U.S.
Class: |
375/260 |
Current CPC
Class: |
H04L 27/2607 20130101;
H04L 27/2646 20130101; H04L 27/2613 20130101; H04L 27/2627
20130101 |
International
Class: |
H04L 27/26 20060101
H04L027/26 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 3, 2013 |
KR |
10-2013-0149474 |
Claims
1. A method for transmitting data in an orthogonal frequency
division multiplexing (OFDM) wireless communication system, the
method comprising: receiving path delay information from a
reception apparatus through a return path, after data transmission;
adjusting a length of a cyclic prefix (CP) based on a delay value
included in the path delay information; receiving error information
from the reception apparatus through the return path; adjusting a
number of pilot symbols based on a bit error rate (BER) obtained
from the error information; and performing data transmission using
the CP having the adjusted length and the adjusted number of pilot
symbols.
2. The method of claim 1, wherein the adjusting of the length
comprises; comparing the delay value included in the path delay
information with a pre-set delay value; and when the delay value
included in the path delay information is smaller than the pre-set
delay value, adjusting the length of the CP.
3. The method of claim 2, wherein the adjusting of the length of
the CP comprises adjusting the length of the CP to be shorter than
a length thereof used for previous data transmission.
4. The method of claim 2, wherein the adjusting of the length of
the CP comprises adjusting the length of the CP to be the shortest
among all the lengths available to be used for data
transmission.
5. The method of claim 2, wherein the delay value included in the
path delay information is a maximum delay spread value.
6. (canceled)
7. The method of claim 1, wherein the adjusting of the number of
the pilot symbols comprises adjusting the number of pilot symbols
to be smaller than a number of symbols used for previous data
transmission.
8. The method of claim 1, wherein the adjusting of the number of
pilot symbols comprises adjusting the number of pilot symbols to be
the smallest among all the number of pilot symbols available to be
used for data transmission.
9. The method of claim 1, wherein the adjusting of the number of
the pilot symbols comprises: comparing the obtained BER with a
pre-set BER; and when the obtained BER is lower than the pre-set
BER, adjusting the number of pilot symbols.
10-12. (canceled)
13. An apparatus for transmitting data in an orthogonal frequency
division multiplexing (OFDM) wireless communication system, the
apparatus comprising: a path delay information receiver configured
to receive path delay information from a reception apparatus
through a return path, after data transmission; a cyclic prefix
(CP) adjusting processor configured to adjust a length of a CP
based on a delay value included in the path delay information; a CP
inserting processor configured to insert the CP having the adjusted
length into a data transmission; an error information receiver
configured to receive error information from the reception
apparatus through the return path; a symbol number adjusting
processor configured to adjust a number of pilot symbols based on a
bit error rate (BER) obtained from the error information; and a
pilot symbol inserting processor configured to insert the adjusted
number of pilot symbols into the data transmission.
14. The apparatus of claim 13, wherein when the delay value
included in the path delay information is smaller than a pre-set
delay value, the CP adjusting processor adjusts the CP length.
15. The apparatus of claim 13, wherein the CP length adjusting
processor adjusts the length of the CP to be the shortest among all
the available lengths used for data transmission.
16. (canceled)
17. The apparatus of claim 16, wherein the symbol number adjusting
processor adjusts the number of pilot symbols to be smaller than a
number of symbols used for previous data transmission.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority to and the benefit of
Korean Patent Application No. 10-2013-0149474 filed in the Korean
Intellectual Property Office on Dec. 3, 2013, the entire contents
of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] (a) Field of the Invention
[0003] The present disclosure relates to a transmission and
reception method and an apparatus thereof, and more particularly,
to a method for transmitting and receiving data using a variable
guard interval, and a transmission apparatus and a reception
apparatus.
[0004] (b) Description of the Related Art
[0005] When high speed data is transmitted in a single carrier
using a multi-path channel, the transmission data is severely
distorted due to inter-symbol interference (ISI). To solve this
problem, orthogonal frequency division multiplexing (OFDM), a
multi-carrier scheme in which high speed data is changed into low
speed data and transmitted by using several sub-carriers, has been
spotlighted. With the OFDM scheme, limited frequency resources may
be effectively utilized, a high data transfer rate may be provided,
and ISI generated by a multi-path channel may be removed by using a
cyclic prefix (CP) as a guard interval.
[0006] Various communication standards such as digital video
broadcasting (DVB), wireless local area network (WLAN), and the
like, use a variable CP. Also, tens of pilot symbols are inserted
into every OFDM symbol to allow for simple channel estimation and
compensation, relative to a single carrier.
[0007] In a system using OFDM, a CP inserted to remove ISI
generated by a multi-path channel lowers a data rate and causes
loss of transmission power by a length thereof. Thus, in order to
enhance a data rate in a system using a variable CP, a short CP is
required to be used. However, if a CP length is short, ISI is
generated by a multi-path channel, increasing a bit error rate,
which rather lowers a data rate.
[0008] In addition, in order to estimate and compensate a
multi-path channel, a transmission apparatus inserts tens of pilot
symbols into every OFDM symbol and transmits the same, and a
reception apparatus estimates a channel of a subcarrier to which a
pilot symbol has been allocated, and in case of a subcarrier to
which a pilot symbol is not allocated, the reception apparatus
estimates a channel by using interpolation using the estimated
channel value of the subcarrier. In general, a channel may be more
accurately estimated when there are a large number of pilot symbols
than when there are less. Thus, in order to enhance performance of
the reception apparatus, it would be desirable to allocate more
pilot symbols; however, in this case, a data rate is reduced.
SUMMARY OF THE INVENTION
[0009] The present disclosure has been made in an effort to provide
a transmission and reception method and an apparatus thereof having
advantages of enhancing data transmission, while using a variable
guard interval, in an orthogonal frequency division multiplexing
(OFDM) multiplexing wireless communication system.
[0010] The present disclosure has also been made in an effort to
provide a transmission and reception method and an apparatus
thereof having advantages of enhancing a data rate by adjusting a
number of pilot symbols.
[0011] An exemplary embodiment of the present disclosure provides a
method for transmitting data in an orthogonal frequency division
multiplexing (OFDM) wireless communication system, including:
receiving path delay information from a reception apparatus through
a return path, after data transmission; adjusting a length of a
cyclic prefix (CP) included in a transmitted signal, on the basis
of a delay value included in the path delay information; and
performing data transmission using the CP having an adjusted
length.
[0012] The adjusting of the length may include: comparing the delay
value included in the path delay information with a pre-set delay
value; and when the delay value included in the path delay
information is smaller than the pre-set delay value, adjusting the
length of the CP.
[0013] The adjusting of the length of the CP may include adjusting
the length of the CP to be shorter than a length thereof used for
previous data transmission.
[0014] The adjusting of the length of the CP may include adjusting
the length of the CP to be the shortest among all the lengths
available to be used for data transmission.
[0015] The delay value included in the path delay information may
be a maximum delay spread value.
[0016] The method may further include: receiving error information
through the return path; and when the error information is
received, adjusting a number of pilot symbols used for data
transmission.
[0017] The adjusting of the number of the pilot symbols may include
adjusting the number of pilot symbols to be smaller than a number
of symbols used for previous data transmission.
[0018] The adjusting of the number of pilot symbols may include
adjusting the number of pilot symbols to be the smallest among all
the number of pilot symbols available to be used for data
transmission.
[0019] The adjusting of the number of the pilot symbols may
include: obtaining a bit error rate (BER) from the error
information; comparing the obtained BER with a pre-set BER; and
when the obtained BER is lower than the pre-set BER, adjusting the
number of pilot symbols.
[0020] Another exemplary embodiment of the present disclosure
provides a method for transmitting data in an orthogonal frequency
division multiplexing (OFDM) wireless communication system,
including: inserting a first number of pilot symbols into every
OFDM symbol corresponding to data intended to be transmitted, and
transmitting the same; receiving error information from a reception
apparatus through a return path; when the error information is
received, adjusting the first number of pilot symbols to a second
number of pilot symbols smaller than the first number of pilot
symbols; and inserting the second number of pilot symbols into
every OFDM symbol corresponding to data intended to be transmitted,
and transmitting the same.
[0021] Yet another exemplary embodiment of the present disclosure
provides a method for receiving data in an orthogonal frequency
division multiplexing (OFDM) wireless communication system,
including: receiving signals transmitted via multi-path channels;
processing the received signals to calculate path delay
information; and transmitting the calculated path delay information
to a transmission apparatus through a return path.
[0022] The method may further include: decoding the reception
signals to obtain data; calculating a bit error rate (BER) with
respect to the obtained data; and transmitting error information
including the BER to the transmission apparatus through the return
path.
[0023] The transmitting of the error information to the
transmission apparatus through the return path may include:
comparing the calculated BER with a pre-set BER; and when the
calculated BER is lower than the pre-set BER, transmitting the
error information to the transmission apparatus through the return
path.
[0024] Still another exemplary embodiment of the present disclosure
provides an apparatus for transmitting data in an orthogonal
frequency division multiplexing (OFDM) wireless communication
system, including: a path delay information receiver configured to
receive path delay information from a reception apparatus through a
return path, after data transmission; a cyclic prefix (CP)
adjusting processer configured to adjust a length of a CP included
in a transmitted signal, on the basis of a delay value included in
the path delay information; and a CP inserting processer configured
to generate a CP on the basis of the adjusted length, and inserting
the same into data transmitted thereafter.
[0025] When the delay value included in the path delay information
is smaller than a pre-set delay value, the CP adjusting processer
may adjust the CP length. The CP length adjusting processer may
adjust the length of the CP to be the shortest among all the
available lengths used for data transmission.
[0026] The apparatus may further include: an error information
receiver configured to receive error information through the return
path; and a symbol number adjusting processer configured to adjust
a number of pilot symbols used for data transmission, when the
error information is received. The symbol number adjusting
processer may adjust the number of pilot symbols to be smaller than
a number of symbols used for previous data transmission.
[0027] Still another exemplary embodiment of the present disclosure
provides an apparatus for receiving data in an orthogonal frequency
division multiplexing (OFDM) wireless communication system,
including: a fast Fourier transform (FFT) unit configured to
receive signals transmitted through multi-path channels and perform
FFT thereon; a path delay calculator configured to calculate path
delay information including a maximum delay spread value on the
basis of the signals output from the FFT unit; and a first return
processer configured to transmit the calculated path delay
information to a transmission apparatus through a return path. The
apparatus may further include: a decoder configured to decode
reception signals output from the FFT unit to obtain data; a bit
error rate (BER) calculator configured to calculate a BER with
respect to the obtained data; and a second return processer
configured to transmit error information including the BER to the
transmission apparatus through the return path.
[0028] When the calculated BER is lower than a pre-set BER, the
second return processer may transmit the error information to the
transmission apparatus.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] FIG. 1 is a view schematically illustrating a structure of a
transmission/reception apparatus in an orthogonal frequency
division multiplexing (OFDM) system according to an exemplary
embodiment of the present disclosure.
[0030] FIG. 2 is a view illustrating inserting of cyclic prefixes
(CP) in the OFDM system according to an exemplary embodiment of the
present disclosure.
[0031] FIG. 3 is a view illustrating a table of system parameters
according to an exemplary embodiment of the present disclosure.
[0032] FIG. 4 is a view illustrating pilot symbols inserted into
OFDM symbols according to an exemplary embodiment of the present
disclosure.
[0033] FIG. 5 is a view illustrating parameters related to the
number of pilot symbols according to an exemplary embodiment of the
present disclosure.
[0034] FIG. 6 is a view illustrating additional elements for
enhancing a data rate of a reception apparatus according to an
exemplary embodiment of the present disclosure.
[0035] FIG. 7 is a view illustrating additional elements for
processing information received through a return path in a
transmission apparatus according to an exemplary embodiment of the
present disclosure.
[0036] FIG. 8 is a flowchart illustrating a data transmission
method according to an exemplary embodiment of the present
disclosure.
[0037] FIG. 9 is a flowchart illustrating a data reception method
according to an exemplary embodiment of the present disclosure.
DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS
[0038] In the following detailed description, only certain
exemplary embodiments of the present disclosure have been shown and
described, simply by way of illustration. As those skilled in the
art would realize, the described exemplary embodiments may be
modified in various different ways, all without departing from the
spirit or scope of the present disclosure. Accordingly, the
drawings and description are to be regarded as illustrative in
nature and not restrictive. Like reference numerals designate like
elements throughout the specification.
[0039] Throughout the specification, unless explicitly described to
the contrary, the word "comprise" and variations such as
"comprises" or "comprising" will be understood to imply the
inclusion of stated elements but not the exclusion of any other
elements.
[0040] Hereinafter, a data transmission/reception method and an
apparatus thereof according to exemplary embodiments of the present
disclosure will be described in detail.
[0041] FIG. 1 is a view schematically illustrating a structure of a
transmission/reception apparatus in an orthogonal frequency
division multiplexing (OFDM) system according to an exemplary
embodiment of the present disclosure.
[0042] As illustrated in FIG. 1, in the OFDM system, a transmission
apparatus 1 includes an encoder 11, a modulator 12, a first signal
converter 13, an inverse fast Fourier transform (IFFT) unit 14, a
cyclic prefix (CP) generater15, and a second signal converter
16.
[0043] The encoder 11 encodes data to be transmitted, and the
modulator 12 modulates the data to be transmitted to generate OFDM
symbols. For example, quadrature amplitude modulation (QAM) is
performed on bits of the transmission data.
[0044] The first signal converter 13 converts a signal including
OFDM symbols into a parallel signal and outputs the same. The first
signal converter 13 may also be referred to as a serial/parallel
(S/P) converter.
[0045] The IFFT unit 14 performs IFFT on the parallel signal
including OFDM symbols to generate a signal of a time domain.
[0046] The CP generater15 generates a CP and inserts the generated
CP into the signal of a time domain.
[0047] The second signal converter 16 converts the CP-inserted
signal into a serial signal and outputs the same. The second signal
converter 16 may also be referred to as a parallel/serial (P/S)
converter.
[0048] In this manner, the signal output from the second signal
converter 16 is processed into a radio frequency (RF) signal and
subsequently transmitted.
[0049] Meanwhile, a reception apparatus 2 includes a CP removing
processor 21, a first signal converter 22, an FFT unit 23, a second
signal converter 24, an equalizer 25, and a decoder 26.
[0050] The CP removing processor 21 removes the CP from the
reception signal. Also, the signal transmitted from the
transmission apparatus 1 may be received, converted into a baseband
signal, processed into a digital signal, and output. Thereafter,
the CP may be removed from the corresponding signal.
[0051] The first signal converter 22 converts the CP-removed
reception signal into a parallel signal and outputs the same. The
first signal converter 22 may also be referred to as an S/P
converter.
[0052] The FFT unit 23 performs FFT on the input reception signal
and outputs a signal of a frequency domain.
[0053] The second signal converter 24 converts the FFT-transformed
signal of a frequency domain into a serial signal and outputs the
same. The second signal converter 24 may also be referred to as a
P/S converter.
[0054] The equalizer 25 may perform channel equalization on the
basis of a channel estimate value with respect to the reception
signal to compensate a channel.
[0055] The decoder 26 decodes data from the channel-compensated
signal.
[0056] As for the transmission apparatus 1 and the reception
apparatus 2 having the structures as described above, the
transmission apparatus 1 inserts tens of pilot symbols into every
OFDM symbol and transmits the same, and the reception apparatus 2
estimates a channel of a corresponding subcarrier on the basis of a
pilot symbol, and in case of a subcarrier to which a pilot symbol
was not allocated, the reception apparatus 2 estimates a channel by
using interpolation using the estimated channel value of the
subcarrier. The reception apparatus 2 performs channel compensation
using the estimated channel value.
[0057] The transmission apparatus 1 also generates a cyclic prefix
for reducing inter-symbol interference of the OFDM symbols.
[0058] FIG. 2 is a view illustrating inserting of cyclic prefixes
(CP) in the OFDM system according to an exemplary embodiment of the
present disclosure.
[0059] As illustrated in FIG. 2, the cyclic prefix generater15
inserts guard intervals, i.e., cyclic prefixes, in front of OFDM
symbols. The cyclic prefixes may be duplicates of predetermined (L)
number of samples in rear portions of the OFDM symbols. Here, in
general, the L number may be set such that each guard interval is
longer than a maximum delay spread (t.sub.max) of the multi-path
channel.
[0060] There are two modes with respect to a length of cyclic
prefixes.
[0061] FIG. 3 is a view illustrating a table of system parameters
according to an exemplary embodiment of the present disclosure.
[0062] As illustrated in FIG. 3, different system parameters may be
used in two types of modes, that is, first and second modes. Here,
system parameters used in a digital video broadcasting for cable 2
(DVB-C2) standard are taken as examples, and the present disclosure
is not limited thereto.
[0063] It can be seen that a CP length of the first mode and that
of the second mode are different, and a data rate loss rate D.sub.L
according to a CP length is as follows.
D L = T GI T S = T GI T FFF + T GI ( Equation 1 ) ##EQU00001##
[0064] Here, T.sub.GI indicates a CP duration, T.sub.s indicates an
OFDM symbol duration, and T.sub.FFF indicates an FFT duration. L
indicates a number of CP samples. The number of CP samples
corresponds to a CP length.
[0065] Based on Equation 1, when CP lengths are 32 samples and 64
samples, data rate loss rates DL may be calculated to be 0.77% and
1.54%, respectively. It can be seen that as the CP length is
increased, the data rate loss rate is increased.
[0066] Thus, in the exemplary embodiment of the present disclosure,
the reception apparatus calculates path delay information and
transmits the calculated path delay information to the reception
apparatus, so that the transmission apparatus may adjust a CP
length, thus preventing degradation of a data rate.
[0067] To this end, as illustrated in FIG. 1, the reception
apparatus 2 according to the exemplary embodiment of the present
disclosure calculates a path delay on the basis of a reception
signal and transmits path delay information to the transmission
apparatus 1 through a return path. Here, the reception apparatus 2
may calculate a maximum delay spread (t.sub.max), include the
calculated maximum delay spread (t.sub.max) in the path delay
information, and transmit the same.
[0068] The transmission apparatus 1 may adjust a CP length on the
basis of the received path delay information. For example, when a
path delay, that is, t.sub.max, provided from the reception
apparatus 2 through the return path, has a maximum value, e.g., 2
us, the transmission apparatus 1 may adjust the CP length to have
32 samples having a shorter length among the lengths of the two
types of mode. In this manner, the data rate may be improved by
minimizing a data rate loss rate D.sub.L, while avoiding ISI due to
a multi-path channel.
[0069] Also, the transmission apparatus 1 adjusts a number of pilot
symbols to enhance the data rate.
[0070] FIG. 4 is a view illustrating pilot symbols inserted into
OFDM symbols according to an exemplary embodiment of the present
disclosure.
[0071] As illustrated in FIG. 4, for channel estimation and
compensation, pilot symbols are inserted in every OFDM symbol, and
in this case, the pilot symbols are inserted at every pilot symbol
interval S.sub.f. When pilot symbols instead of data symbols are
transmitted, the data rate is much reduced. The data rate loss rate
D.sub.L according to pilot symbols may be expressed as follows.
D L = N p N ( Equation 2 ) ##EQU00002##
[0072] Here, N indicates a size of IFFT, and N.sub.p indicates a
number of pilot symbols inserted per OFDM symbol
[0073] The number of pilot symbols may vary according to a
mode.
[0074] FIG. 5 is a view illustrating parameters related to the
number of pilot symbols according to an exemplary embodiment of the
present disclosure. In FIG. 5, system parameters used in DVB-C2
standard are taken as an example, and the present disclosure is not
limited thereto.
[0075] As illustrated in FIG. 5, when a pilot symbol interval
S.sub.f is 48, one pilot symbol is inserted for every 48
subcarriers, and in this case, the number of pilot symbols is 84.
When a pilot symbol interval S.sub.f is 96, one pilot symbol is
inserted for every 96 subcarriers, and in this case, the number of
pilot symbols is 42.
[0076] On the basis of Equation 2, when the numbers of pilot
symbols are 84 and 42, data rate loss rates D.sub.L are calculated
as 2.05% and 1.025%, respectively. That is, as the pilot symbol
interval S.sub.f is shorter, the data rate loss rate D.sub.L is
increased, and accordingly, the data rate is reduced.
[0077] In general, as the pilot symbol interval Sf is shorter, the
number of inserted pilot symbols is increased. Thus, a smaller
amount of errors are generated in channel estimation, reducing the
bit error rate (BER) of the reception apparatus. Meanwhile, as the
pilot symbol interval Sf is longer, the number of inserted pilot
symbols is reduced. Thus, a larger amount of errors are generated
in channel estimation, increasing the BER of the reception
apparatus. Thus, in order to reduce the BER of the reception
apparatus, a larger amount of pilot symbols is required, and it can
be recognized that the BER indicating performance of the reception
apparatus and a data rate are traded off. That is, when the number
of pilot symbols is increased to increase the BER, the data rate is
relatively reduced, and when the number of pilot symbols is reduced
to increase the data rate, the BER is relatively reduced.
[0078] In the exemplary embodiment of the present disclosure, in
order to enhance the data rate in consideration of the trade-off
characteristics between a BER and the data rate, the transmission
apparatus 1 adjusts the number of pilot symbols on the basis of the
BER measured by the reception apparatus 2. To this end, the
reception apparatus 2 calculates a BER on the basis of a reception
signal, and transmits the calculated BER to the transmission
apparatus 1 through a return path. The transmission apparatus 1
adjusts the number of pilot symbols to an appropriate number on the
basis of the BER received through the return path. For example, in
a case in which a BER permitted in the reception apparatus is equal
to or less than 10.sup.-6, when a BER calculated from a reception
signal is lower than the pre-set BER, e.g., when it is 10.sup.-7,
the reception apparatus transmits information including the
calculated BER to the transmission apparatus through the return
path. Accordingly, the transmission apparatus determines that the
BER does not satisfy the permitted pre-set BER, and adjusts the
number of pilot symbols inserted into OFDM symbols such that it is
reduced. Therefore, the data rate may be enhanced by minimizing the
data rate loss rate DL, while increasing the BER of the reception
apparatus to a level that meets a requested BER.
[0079] In order to enhance the data rate, the reception apparatus 2
may further include elements as follows.
[0080] FIG. 6 is a view illustrating additional elements for
enhancing a data rate of a reception apparatus according to an
exemplary embodiment of the present disclosure.
[0081] As illustrated in FIG. 6, the reception apparatus 2 include
a delay calculator 210 that calculates a path delay value from a
reception signal, a first return processer 220 that transmits path
delay information including the path delay value, a BER calculator
230 that calculates a BER on the basis of a signal decoded from the
reception signal, a determining processer 240 that determines
whether to inform about the calculated BER, and a second return
processer 250 that transmits error information including the BER
calculated according to determination of the determining processer
240 through a return path.
[0082] The path delay calculator 210 calculates a path delay value
with respect to a signal received through a multi-path on the basis
of a signal output through the second signal converter 24 of the
reception apparatus 2. In particular, the path delay calculator 210
calculates a maximum delay spread t.sub.max on the basis of signals
by respective paths.
[0083] The BER calculator 230 calculates a BER on the basis of
decoded data output from the decoder 26. The determining processer
240 compares the calculated BER with a pre-set BER allowable in the
reception apparatus, and when the calculated BER is greater than
the pre-set BER, the determining processer 240 determines to
provide corresponding information to the transmission
apparatus.
[0084] The transmission apparatus 1 that receives the information
through the return path from the reception device 2 and processes
the same may further include elements as follows.
[0085] FIG. 7 is a view illustrating additional elements for
processing information received through a return path, in a
transmission apparatus according to an exemplary embodiment of the
present disclosure.
[0086] As illustrated in FIG. 7, the transmission apparatus 1
includes a path delay information receiver 110 that receives path
delay information transmitted through the return path, a CP length
adjusting processer 120 that draws a delay value (e.g., a maximum
delay spread t.sub.max value) from the path delay information and
sets a CP length on the basis of the delay value, an error
information receiver 130 that receives error information
transmitted through the return path, a symbol number adjusting
processer 140 that draws a BER from the error information and sets
the number of pilot symbols on the basis of the BER, and a pilot
symbol inserting processer 150 that inserts a pilot symbol into an
OFDM symbol.
[0087] The CP length adjusting processer 120 compares the delay
value, e.g., the maximum delay spread value transmitted from the
reception apparatus 2 with a pre-set delay value, and when the
delay value is smaller than the pre-set delay value, the CP length
adjusting processer 120 selects a CP length shorter than a CP
length which was selected in a previous transmission, from among
available CP lengths. In a case in which different CP lengths are
set for the two types of mode as mentioned above, the CP length
adjusting processer 120 selects a shorter length. In a case in
which three or more lengths exist, the CP length adjusting
processer 120 may select the shortest length or a length shorter
than that selected in a previous transmission.
[0088] The CP length adjusting processer 120 provides information
regarding the selected length to the CP generater15 such that a CP
having the corresponding length may be generated for data
transmission.
[0089] Meanwhile, the symbol number adjusting processer 140 draws
the BER from the error information received through the return
path, and sets the number of pilot symbols on the basis of the BER.
The pilot symbol inserting processer 150 inserts pilot symbols
equal to the number of symbols set in every transmitted OFDM symbol
on the basis of the set symbol number. The pilot symbol inserting
processer 150 may generate pilot symbol signals with respect to the
OFDM symbols output from the modulator 12 and provide the same to
the IFFT unit 14 such that the pilot symbol signals may be disposed
in corresponding positions in the OFDM symbols. In this case, as
illustrated in FIG. 1, the pilot symbol signals may be converted
into parallel signals through the first signal converter 13 and
subsequently input to the IFFT unit 14 so as to be inserted into
the OFDM symbols.
[0090] Hereinafter, a method for transmitting and receiving data
according to an exemplary embodiment of the present disclosure will
be described.
[0091] FIG. 8 is a flowchart illustrating a data transmission
method according to an exemplary embodiment of the present
disclosure.
[0092] As illustrated in FIG. 8, the transmission apparatus 1
encodes data to be transmitted, modulates the coded data to
generate an OFDM symbol, and performs IFFT on the OFDM symbol
signal, while inserting a predetermined number of pilot symbols
into the OFDM symbol, to convert the OFDM symbol signal into a
signal of a time domain (S100 and S110).
[0093] Thereafter, the transmission apparatus 1 inserts a CP having
a certain length into the IFFT-transformed signal, processes the
corresponding signal into a transmission-available signal, and
transmits the same (S120 and S130).
[0094] Thereafter, when predetermined information is received from
the reception apparatus 2 through the return path (S140) and the
received information is path delay information, the transmission
apparatus 1 obtains a delay value (e.g., a maximum delay spread
t.sub.max from the path delay information (S150). The transmission
apparatus 1 compares the obtained delay value with a pre-set delay
value, and when the obtained delay value is smaller than the
pre-set delay value, the transmission apparatus 1 adjusts a CP
length (S160 and S170). For example, when the obtained delay value
is smaller than the pre-set delay value, the transmission apparatus
1 changes the CP length into a shorter length than a CP length
which was used in previously data transmission or changes the CP
length into the shortest one among available lengths. Thereafter,
the transmission apparatus 1 inserts the changed CP length into a
signal desired to transmit a CP in subsequent data
transmission.
[0095] Meanwhile, in a case in which the information received
through the return path is error information, the transmission
apparatus 1 obtains a BER from the received error information
(S180) and compares the obtained BER with a pre-set allowable BER.
When the obtained BER is lower than the pre-set allowable BER, the
transmission apparatus 1 adjusts the number of pilot symbols
inserted into the OFDM symbol such that it is reduced to be smaller
than the present number of pilot symbols (S190 and S200). For
example, the transmission apparatus 1 changes the number of pilot
symbols inserted into the OFDM symbol such that it is smaller than
the number of symbols used for previous data transmission.
Thereafter, in case of subsequent data transmission, the
transmission apparatus 1 inserts the pilot symbols corresponding to
the changed number of symbols into the OFDM symbol and transmits
the same.
[0096] When the received information is error information, the
transmission apparatus 1 may adjust the number of pilot symbols to
be inserted into the OFDM symbol such that it is reduced to be
smaller than the present number of symbols, according to the
received error information.
[0097] FIG. 9 is a flowchart illustrating a data reception method
according to an exemplary embodiment of the present disclosure.
[0098] As illustrated in FIG. 9, the reception apparatus 2 receives
a signal transmitted through a multi-path, removes a CP from the
received signal, performs FFT on the CP-removed signal, and outputs
a signal of a frequency domain (S300 and S310). The reception
apparatus 2 performs channel equalization on the basis of a channel
estimate value with respect to the FFT-transformed signal to
compensate for a channel thereof. Also, the reception apparatus 2
calculates a delay value (e.g., a maximum delay spread t.sub.max on
the basis of the FFT-transformed signal (S320). Thereafter, the
reception apparatus 2 decodes the channel-compensated signal to
obtain data (S330).
[0099] In particular, the reception apparatus 2 transmits path
delay information including the calculated delay value to the
transmission apparatus 1 through the return path in order to
enhance the data rate (S340).
[0100] The reception apparatus 2 calculates a BER with respect to
the obtained data in consideration of tradeoff between a data rate
and the BER (S350), and transmits error information including the
calculated BER to the transmission apparatus 1 through the return
path. In this case, the reception apparatus 2 compares the
calculated BER with a pre-set allowable BER, and when the
calculated BER is lower than the pre-set BER, the reception
apparatus 2 may transmit error information including the calculated
BER through the return path (S350).
[0101] Thereafter, the transmission apparatus 1 adjusts the CP
length according to the path delay information transmitted through
the return path, and adjusts the number of pilot symbols to be
inserted into the OFDM symbol according to the error information to
thus enhance the data rate.
[0102] According to exemplary embodiments of the present
disclosure, in an OFDM wireless communication system, by informing
a transmission apparatus about a channel delay value obtained from
a reception signal, inter-symbol interference (ISI) generated by a
multi-path channel may be avoided, and since the shortest cyclic
prefix (CP) among several CPs is used, data transmission may be
maximized.
[0103] Since a reception apparatus informs a transmission apparatus
about a bit error rate (BER) calculated over a received signal, the
transmission apparatus may adjust the number of pilot symbols on
the basis of the BER, thus enhancing a data rate.
[0104] Therefore, the transmission apparatus may enhance the data
rate while minimizing the BER due to a channel by using an optimal
system parameter for data transmission on the basis of information
provided from the reception apparatus.
[0105] The exemplary embodiments of the present disclosure may not
necessarily be implemented only through the foregoing apparatuses
and methods, but may also be implemented through a program for
realizing functions corresponding to the configurations of the
exemplary embodiments of the present disclosure, a recording medium
including the program, or the like.
[0106] While this invention has been described in connection with
what is presently considered to be practical exemplary embodiments,
it is to be understood that the invention is not limited to the
disclosed exemplary embodiments, but, on the contrary, is intended
to cover various modifications and equivalent arrangements included
within the spirit and scope of the appended claims.
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