BAEK, Jong-Seob (720-24, Geonsan-riJangheung-eup, Jangheung-gun, Jeollanam-do 529-801, KR)
SEO, Jong-Soo (5-1302, Asia Seonsuchon Apt.Jamsil 7-dong, Sonpa-gu, Seoul 138-797, KR)
HWANG, Soon-Up (1 Shindong-a Apt, Dunchon-dong Gangdong-gu, Seoul 134-060, 02-1303, KR)
BAEK, Jong-Seob (720-24, Geonsan-riJangheung-eup, Jangheung-gun, Jeollanam-do 529-801, KR)
SEO, Jong-Soo (5-1302, Asia Seonsuchon Apt.Jamsil 7-dong, Sonpa-gu, Seoul 138-797, KR)
[CLAIMS]
[Claim 1 ]
An adaptive frequency-domain equalizer having a receiving unit performing
the channel equalization of a frequency-domain, the receiving unit receiving a
transmission signal, including successive transmission blocks, transmitted from a
transmitting unit, the equalizer comprising:
a first Fourier transformation unit, transforming a received signal into a
frequency-domain;
a space-time block coding (STBC)-like matrix formation unit, forming an
STBC-like matrix by using a frequency-bin from two continuous received signal blocks
transformed by the first Fourier transformation unit;
an input block matrix formation unit, forming an equalizer input block matrix
based on the STBC-like matrix having the same frequency-bin;
a channel equalization unit, performing the channel equalization of the
equalizer input block matrix according to an equalizer coefficient;
an inverse Fourier transformation unit, transforming the channel-equalized
signal into a time-domain;
a determination unit, generating a determination signal estimating the
transmission signal for the signal transformed into the time-domain;
a second Fourier transformation unit, transforming the determination signal into a frequency-domain;
an error computation unit, computing an error from the determination signal
transformed by the second Fourier transformation unit; and
a correction unit, correcting the equalizer coefficient by using the error and the
equalizer input block matrix.
[Claim 2]
The equalizer of Claim 1, wherein the first and second Fourier transformation
units perform discrete Fourier transformation, and the inverse Fourier transformation
unit performs inverse discrete Fourier transformation.
[Claim 3]
The equalizer of Claim 1 , wherein the received signal is the signal by a single
carrier system.
[Claim 4]
The equalizer of Claim 1, wherein the error computation unit computes the
error by a square root algorithm.
[Claim 5] The equalizer of Claim 1, further comprising a storage unit, storing two
continuous received signal blocks transformed into a frequency-domain by the first
Fourier transformation unit,
whereas the storage unit stores received signal blocks that are received
previously as well as a currently received signal block.
[Claim 6]
The equalizer of Claim 5, wherein the STBC-like matrix formation unit forms
the STBC-like matrix from the currently received signal block and the previously
received signal blocks, which are stored in the storage unit.
[Claim 7]
The equalizer of Claim 6, wherein the error computation unit computes the
error by applying a forgetting factor corresponding to the received time to the currently
received signal block and the previously received signal blocks.
[Claim 8]
The equalizer of Claim 6, wherein the correction unit corrects an equalizer
coefficient for the channel equalization of a signal block to be received next by using an
error computed from the determination signal of the currently received signal block. [Claim 9]
A method of allowing a receiving unit to perform the channel equalization of a
frequency-domain, the receiving unit receiving a transmission signal, including
successive transmission blocks, transmitted from a transmitting unit, the method
comprising:
(a) transforming a received signal into a frequency-domain;
(b) forming an STBC-like matrix by using a frequency-bin from the two
transformed continuous received signal blocks;
(c) forming an equalizer input block matrix based on the STBC-like matrix
having the same frequency-bin;
(d) performing the channel equalization of the equalizer input block matrix
according to an equalizer coefficient;
(e) transforming the channel-equalized signal into a time-domain; and
(f) generating a determination signal estimating the transmission signal for the
signal transformed into the time-domain,
whereas the equalizer coefficient is corrected by computing an error from the
determination signal.
[Claim 10] The method of Claim 9, wherein the step (a) performs discrete Fourier
transformation, and the step (e) performs inverse discrete Fourier transformation.
[Claim 11]
The method of Claim 9, further comprising:
(g) transforming the determination signal into a frequency-domain;
(h) computing an error from the transformed determination signal; and
(i) correcting the equalizer coefficient by using the error and the equalizer input
block matrix.
[Claim 12]
The method of Claim 11, wherein the step (g) performs discrete Fourier
transformation.
[Claim 13]
The method of Claim 11 , wherein the step (h) computes the error by a square
root algorithm.
[Claim 14]
The method of Claim 11, further comprising storing the two continuous received signal blocks transformed into the frequency-domain, before the step (b),
whereas previously received signal blocks as well as the currently received
signal block are stored.
[Claim 15]
The method of Claim 14, wherein the step (b) forms the STBC-like matrix
from the currently received signal block and the previously received signal blocks,
which are stored.
[Claim 16]
The method of Claim 15, wherein the step (h) computes the error by applying a
forgetting factor corresponding to the received time to the currently received signal
block and the previously received signal blocks.
[Claim 17]
The method of Claim 15, wherein the step (i) corrects an equalizer coefficient
for the channel equalization of a signal block to be received next by using an error
computed from the determination signal of the currently received signal block. |
[DESCRIPTION]
[Invention Title]
ADAPTIVE FREQUENCY DOMAIN EQUALIZER AND ADAPTIVE
FREQUENCY DOMAIN EQUALIZATION METHOD
[Technical Field]
The present invention relates to a frequency-domain equalizer, more
specifically to an enhanced adaptive frequency-domain equalization apparatus and a
method thereof for a single-carrier space-time multiple antenna coding system.
[Background Art]
In a transmitting and receiving system, there occurs inter-symbol interference
by a multi-path channel having a limited bandwidth. This causes a transmitted signal to
be distorted and a bit error to be generated in a receiver. Accordingly, a receiving unit
uses a channel equalizer in order to recover the signal distorted by the inter-symbol
interference.
A nonlinear decision feed back equalizer, which is the most popularly-used
equalizer for a dedicated system receiver for transmitting a single-carrier such as a
present terrestrial broadcast for the foregoing purpose, is operated in a time-domain and
uses a least mean square (LMS) algorithm having a small computation amount
necessary for coefficient renewal, which has a low convergence rate but a simple
realization.
However, since the nonlinear decision feed back equalizer has a very large
distortion of channel, if an error occurs in an output of the equalizer, the re-input of the
error value causes the error propagation, which makes the output of the equalizer
deteriorated increasingly. Also, if the position of a main path is changed like a
time- varying channel, the frame-synchronization is broken.
[Disclosure]
[Technical Problem]
Accordingly, the present invention provides an adaptive frequency-domain
equalizer and a method thereof that can show outstanding features in a time-varying
channel environment by processing an inputted signal in units of blocks.
The present invention also provides an adaptive frequency-domain equalizer
and a method thereof that can minimize an excess mean square error (EMSE) through a
square root algorithm having a low complexity and a high stability.
[Technical Solution]
According to an aspect of the present invention, there can be provided an
adaptive frequency-domain equalizer having a receiving unit performing the channel
equalization of a frequency-domain, the receiving unit receiving a transmission signal,
including successive transmission blocks, transmitted from a transmitting unit, the
equalizer including a first Fourier transformation unit, transforming a received signal
into a frequency-domain; a space-time block coding (STBC)-like matrix formation unit,
forming an STBC-like matrix by using a frequency-bin from two continuous received
signal blocks transformed by the first Fourier transformation unit; an input block matrix
formation unit, forming an equalizer input block matrix based on the STBC-like matrix
having the same frequency-bin; a channel equalization unit, performing the channel
equalization of the equalizer input block matrix according to an equalizer coefficient; an
inverse Fourier transformation unit, transforming the channel-equalized signal into a
time-domain; a determination unit, generating a determination signal estimating the
transmission signal for the signal transformed into the time-domain; a second Fourier
transformation unit, transforming the determination signal into a frequency-domain; an
error computation unit, computing an error from the determination signal transformed
by the second Fourier transformation unit; and a correction unit, correcting the equalizer
coefficient by using the error and the equalizer input block matrix.
Preferably, the first and second Fourier transformation units can perform
discrete Fourier transformation, and the inverse Fourier transformation unit can perform
inverse discrete Fourier transformation.
The received signal can be the signal by a single carrier system.
The error computation unit computes the error by a square root algorithm.
The equalizer can further include a storage unit, storing two continuous
received signal blocks transformed into a frequency-domain by the first Fourier
transformation unit, whereas the storage unit stores received signal blocks that are
received previously as well as a currently received signal block. Here, the STBC-like
matrix formation unit can form the STBC-like matrix from the currently received signal
block and the previously received signal blocks, which are stored in the storage unit.
Also, the error computation unit can compute the error by applying a forgetting factor
corresponding to the received time to the currently received signal block and the
previously received signal blocks. The correction unit corrects an equalizer coefficient
for the channel equalization of a signal block to be received next by using an error
computed from the determination signal of the currently received signal block.
According to another aspect of the present invention, there can be provided
method of allowing a receiving unit to perform the channel equalization of a
frequency-domain, the receiving unit receiving a transmission signal, including
successive transmission blocks, transmitted from a transmitting unit, the method
including (a) transforming a received signal into a frequency-domain; (b) forming an
STBC-like matrix by using a frequency-bin from the two transformed continuous
received signal blocks; (c) forming an equalizer input block matrix based on the
STBC-like matrix having the same frequency-bin; (d) performing the channel
equalization of the equalizer input block matrix according to an equalizer coefficient;
(e) transforming the channel-equalized signal into a time-domain; and (f) generating a
determination signal estimating the transmission signal for the signal transformed into
the time-domain, whereas the equalizer coefficient is corrected by computing an error
from the determination signal.
Preferably, the step (a) can perform discrete Fourier transformation, and the
step (e) can perform inverse discrete Fourier transformation.
The method can further include (g) transforming the determination signal into a
frequency-domain; (h) computing an error from the transformed determination signal;
and (i) correcting the equalizer coefficient by using the error and the equalizer input
block matrix.
Here, the step (g) can perform discrete Fourier transformation.
The step (h) can compute the error by a square root algorithm.
The method can further include storing the two continuous received signal
blocks transformed into the frequency-domain, before the step (b), whereas previously
received signal blocks as well as the currently received signal block are stored. Here, the
step (b) can form the STBC-like matrix from the currently received signal block and the
previously received signal blocks, which are stored. The step (h) can compute the error
by applying a forgetting factor corresponding to the received time to the currently
received signal block and the previously received signal blocks. Also, the step (i) can
correct an equalizer coefficient for the channel equalization of a signal block to be
received next by using an error computed from the determination signal of the currently
received signal block.
According to another aspect of the present invention, there can be provided a
recording medium tangibly embodying a program of instructions executable by a
receiving unit to perform the channel equalization of a frequency-domain, the receiving
unit receiving a transmission signal, including successive transmission blocks,
transmitted from a transmitting unit, the recording medium being readable by the
receiving unit, the program including (a) transforming a received signal into a
frequency-domain; (b) forming an STBC-like matrix by using a frequency-bin from the
two transformed continuous received signal blocks; (c) forming an equalizer input block
matrix based on the STBC-like matrix having the same frequency-bin; (d) performing
the channel equalization of the equalizer input block matrix according to an equalizer
coefficient; (e) transforming the channel-equalized signal into a time-domain; and (f)
generating a determination signal estimating the transmission signal for the signal
transformed into the time-domain, whereas the equalizer coefficient is corrected by
computing an error from the determination signal.
Other problems, certain benefits and new features of the present invention will
become more apparent through the following description with reference to the
accompanying drawings and some embodiments.
[Description of Drawings]
FIG. 1 and FIG. 2 are outline block diagrams illustrating transmitting and
receiving units of an orthogonal frequency division multiplexing system and a
single-carrier frequency-domain equalization system;
FIG. 3 is an outline block diagram illustrating a receiving unit of a
single-carrier frequency-domain equalization system in accordance with an embodiment
of the present invention;
FIG. 4 through FIG. 6 illustrate a transmission signal block format of a
transmitting unit in accordance with an embodiment of the present invention;
FIG. 7 illustrates a receiving signal block and an STBC-like matrix formed by
using the receiving signal block in accordance with an embodiment of the present
invention;
FIG. 8 through FIG. 10 illustrate a block adaptive frequency-domain
equalization of an STBC-like matrix type and a diversity combining structure;
FIG. 11 shows graphs of excess mean-square errors in an adaptive
frequency-domain equalizer in accordance with an embodiment of the present
invention;
FIG. 12 shows graphs of a bit-error-rate in an adaptive frequency-domain
equalizer in accordance with an embodiment of the present invention; and
FIG. 13 is a flow chart illustrating an adaptive frequency-domain equalization
method in accordance with an embodiment of the present invention.
[Mode for Invention]
Throughout the description of the present invention, when describing a certain
technology is determined to evade the point of the present invention, the pertinent
detailed description will be omitted. Terms (e.g. "first" and "second") used in this
description merely are identification for successively identifying identical or similar
elements.
The single-carrier frequency domain equalization (SC-FDE) method will be
described before the description related to an embodiment of the present invention.
FIG. 1 and FIG. 2 are outline block diagrams illustrating transmitting and
receiving units of an orthogonal frequency division multiplexing (hereinafter, referred
to as 'OFDM') system and a single-carrier frequency-domain equalization system.
In the OFDM system, an inverse fast Fourier transform (hereinafter, referred to
as 'IFFT') 12 is placed at a transmitting unit 10 (refer to FIG. 1). However, if a
communication system employing the SC-FDE type is compared with a communication
unit employing the OFDM type, in the SC-FDE system, an IFFT 44 is placed at a
receiving unit 40 (refer to FIG. 2). Locating the IFFT of the transmitting unit at the
receiving unit can be considered as the communication type allowing the SC-FDE
system to emphasize the channel compensation of a frequency domain. In the case of
the SC-FDE system, a transmission signal is transmitted at a time domain, and the
equalization is performed at the frequency domain.
Hereinafter, some embodiments of an adaptive frequency-domain equalization
apparatus and a method thereof will be described in detail with reference to the
accompanying drawings.
FIG. 3 is an outline block diagram illustrating a receiving unit of a
single-carrier frequency-domain equalization system in accordance with an embodiment
of the present invention, and FIG. 4 through FIG. 6 illustrate a transmission signal block
format of a transmitting unit in accordance with an embodiment of the present invention.
FIG. 7 illustrates a receiving signal block and an STBC-like matrix formed by using the
receiving signal block in accordance with an embodiment of the present invention, and
FIG. 8 through FIG. 10 illustrate a block adaptive frequency-domain equalization of an
STBC-like matrix type and a diversity combining structure.
The receiving unit 200 of the SC-FDE system includes N R receiving antennas
201(1), ... and 201(N R ), N R cyclic prefix removers 202(1), ... and 202(N R ) and a
frequency-domain equalizer 203.
The receiving antennas 201(1), ... and 201(N R ) receive signals transmitted
through a multi-path channel from the transmitting unit of the SC-FDE system.
In the present invention, the transmitting unit and the receiving unit 200 of the
SC-FDE system is assumed to be a cyclic-prefix-based multi-input multi-output single
carrier block transceiver. Also, it is assumed that the transmitting unit of the SC-FDE
system has two transmission antennas TxI and Tx2 and the receiving unit 200 has the
receiving antennas 201(1), ... and 201(N R ).
The present invention applies a space time block coding (hereinafter, referred
to as 'STBC) scheme at a block level instead of a symbol level. This leads to making it
to implement an efficient FDE by using a discrete Fourier transform (DFT) matrix later.
FIG. 4 through FIG. 6 illustrate a transmission signal block format of the
transmitting unit in the SC-FDE system.
As illustrated in FIG. 4, the transmitting unit maps a signal with regard to an
input bit stream and adds a cyclic prefix. The input bit stream is transmitted through a
first transmission antenna Tx.1 and a second transmission antenna Tx.2, respectively.
One transmission block group 300 is formed to include a first transmission
block stream 310, which is the input bit stream transmitted by the first transmission
antenna Tx.1, and a second block bit stream 320, which is the input bit stream
transmitted by the second transmission antenna Tx.2, as making a pair.
The first transmission block stream 310 includes a first transmission block 312
and a second transmission block 314, allowing each symbol duration to be Ts and a
block length to be N, and cyclic prefixes 330(1) and 330(2), added into each
transmission block.
The second transmission block stream 320 includes a third transmission block
322 and a fourth transmission block 324, allowing each symbol duration to be Ts and a
block length to be N, and cyclic prefixes 330(3) and 330(4), added into each
transmission block.
Here, the first transmission block 312 and the third transmission block 322 are
transmitted together, and then the second transmission block 314 and the fourth
transmission block 324 are transmitted together. In case that the first transmission block
312 and the third transmission block 322 are the signal block transmitted in k th order in
each transmission antenna Tx.1 and Tx.2, the second transmission block 314 and the
fourth transmission block 324 is transmitted in (k+l) th order. The cyclic prefixes 330(1)
through 330(4) prevent the inter-block interference and convert the linear convolution
of symbols into the circular convolution.
An STBC block format for each symbol 340 of a transmission signal is illustrated in FIG. 5. The transmission block *» ' , transmitted to an m th transmission
antenna m i order, is represented as
block 312, 314, 322 and 324 includes symbols in a quantity of N.
In case that i = k+1, the transmission block of each transmission antenna Tx.1
and Tx.2 satisfies the same STBC rule as the following formula 1.
[Formula 1 ]
Here, n = 0, ... and N-I, and k = 0, 2, 4, .... The sign * indicates conjugate
complex numbers.
In other words, the first transmission block stream 310 is transmitted through
the first transmission antenna Tx.1, and the second transmission block stream 320 is
transmitted through the second transmission antenna Tx.2.
k is an even natural number and the same as or larger than zero. While having
the same features as the formula 1, two transmission blocks per each transmission
stream 310 and 320 are transmitted to the receiving unit 200 through a wireless channel.
The first transmission block 312 of the first transmission block stream 310 and
the fourth transmission block 324 of the second transmission block stream 320 have the
relationship of the conjugate complex numbers of Xl and *X1. The second transmission
block 314 of the first transmission block stream 310 and the third transmission block
322 of the second transmission block stream 320 have the relationship of the conjugate
complex numbers of X2 and *X2. This is for the space-time block coding.
The cyclic prefixes 330(1) through 330(4) is added into the front of each
transmission block 312, 314, 322 and 324 and has the length of N R , which is larger than
the expected maximum channel delay spread.
When the first block stream 310 and the second block stream 320 are
transmitted through each transmission antenna Tx.1 and Tx.2, the equalization
coefficient of the receiving unit 200 is allowed to be initialized and the training
sequence (TS) 350(a) is transmitted in advance in order to keep track of channel
vibration (refer to FIG. 6).
The channel between the transmitting unit and the receiving unit 200 is
assumed to be a multi input multi output frequency-selective time-varying fading
channel.
The receiving unit 200, which has received a signal including white Gaussian
noise transmitted from the transmitting unit, performs the sampling of the received
signal every 1/Ts second and then removes cyclic prefixes through the cyclic removers
202(1), ... and 202(N R ). The cyclic removers 202(1), ... and 202(N R ) are connected to
every receiving antenna.
The k th receiving signal block ^ r of the r th receiving antenna in which the
cyclic prefixes are removed is represented as
Since the receiving signal is a value of the time domain, the receiving signal is
converted into a value of the frequency-domain in order to perform the equalization.
The k th and (k+l) th receiving signal blocks of the receiving signals are set as
one receiving signal block group, and the frequency-domain equalization of the
receiving signal block group is performed. Here, k is preferably even natural numbers
including zero, hi other words, two receiving signals are paired in order to perform the
frequency-domain equalization using the STBC.
The frequency-domain equalizer 203 includes first discrete Fourier
transformation units 204(1), ... and 204(N R ), a storage unit 206, an STBC-like matrix
formation unit 208, an input block matrix formation unit 210, a channel equalization
unit 212, an inverse discrete Fourier transformation unit 214, a determination unit 216, a
second discrete Fourier transformation unit 218, an error computation unit 220 and a
correction unit 222.
The first discrete Fourier transformation units 204(1), ... and 204(N R )
(A-) transforms the receiving signal block <■ " " , removed with the cyclic prefix, into a
discrete Fourier transformation (DFT) output block r , which is the receiving
signal block of the frequency-domain, by using an N x N orthonormal DFT matrix
block can be represented as the following formula 2.
[Formula 2]
Here,
antenna and the r th receiving antenna.
The first discrete Fourier transformation unit generates a receiving signal block
of the frequency-domain having each of the N symbols from receiving signals
corresponding the k th DFT output block and the (k+l) th DFT output block through the
discrete Fourier transformation.
The storage unit 206 stores the receiving signal blocks of the
frequency-domain outputted from the first discrete Fourier transformation units 204(1),
... and 204(N R ), connected to each receiving antennas. In addition to the k th and (k+l) th
DFT output blocks that are received at the present time, the storage unit 206 stores B-I
receiving block groups(i.e. 2x(B-l) DFT output blocks), which were previously
received and discrete-Fourier-transformed.
The STBC-like matrix formation unit 208 forms a STBC-like matrix having a
similar type to the transmission block group 300 of the transmitting unit, illustrated in
FIG. 4, from the DFT output block, stored in FIG. storage unit 206. The STBC-like
matrix formation unit 208 has the similar type to the matrix by the structure of the
space-time block coding.
The below description is based on the DFT output block, which is received by
the first receiving antenna 201(1) and Fourier-transmitted. The first receiving antenna
201(1) receives the receiving block group 400(0) having the similar type to the
transmission block group 300, illustrated in FIG. 4 (refer to FIG. 7). Before the
presently received block group 400(0), B-I receiving block groups 400(1) through
400(B-I) has already been received and stored in the storage unit 206.
The receiving block group 400(0) includes a first receiving block 410 and a
second receiving block 420. The first receiving block 410 includes an Y 1 signal, and the
second receiving block 420 includes an Y 2 signal. The cyclic prefix has already bean
removed by the cyclic prefix remover 202(1).
Each receiving block 410 and 420 include N symbols.
The STBC-like matrix formation unit 208 forms an STBC-like matrix by using
a frequency-bin from each receiving clock 410 and 420 of the present receiving block
group 400(0).
The STBC-like matrixes 450(0) through 450(N-I) are formed by extracting the
symbols, having the same frequency-bin, of the symbols in each receiving block 410
and 420 and re-arranging the symbols to have the similar arrangement to the STBC
matrix.
For example, in the case of one matrix 450(1) of the STBC-like matrixes, the
STBC-like matrix formation unit 208 extracts a symbol y t (l) corresponding to a first
frequency-bin of the first receiving block 410 and a symbol y 2 (l) corresponding to a
first frequency-bin of the second receiving block 420. The STBC-like matrix 450(1) can
be newly formed by using the extracted symbols and the conjugate complex numbers of
the extracted symbols.
The same operations of all symbols of the receiving block result in the
formation of a total of N STBC-like matrixes. The N STBC-like matrixes are formed
from the receiving block group 400(0), which is received at a present time. Identically,
N STBC-like matrixes are formed from each of the B-I receiving block groups, which
were previously received.
It is preferable that the STBC-like matrixes of the receiving block groups
400(1) through 400(B-I), which were previously received, have yet been formed when
the frequency-domain equalization of the previously received block group are
performed.
Also, the formation of the foregoing STBC-like matrix is described for the
signal received from the first receiving antenna 201(1). The formation of the foregoing
STBC-like matrix is performed for each of N R receiving antennas by the foresaid
methods.
Accordingly, a total of N R X B X N STBC-like matrixes are generated. The
input block matrix formation unit 210 forms an input block matrix by using the
STBC-like matrixes, having the same frequency-bins, of the STBC-like matrixes
formed corresponding to each receiving antenna by the STBC-like matrix formation
unit 208.
The input block matrix formation unit 210 receives the STBC-like matrixes,
which are classified according to the frequency-bin and formed from the presently
received block group 400(0) per each receiving antenna corresponding to each
frequency-bin, and the STBC-like matrixes formed from B-I receiving block group
400(1) through 400(B-I), which were previously received. In other words, since the
STBC-like matrixes having the same frequency-bins are placed at each receiving block
group of each receiving antenna one by one, the input block matrix for the channel
equalization is formed by using a total of N R x B STBC-like matrixes.
The formed input block matrix is defined as the following formula 3.
[Formula 3]
In the formula 3, the 2B χ
2N R
matri
received from each receiving antenna at a i ■ th time, is defined as the following formula 4.
[Formula 4]
Here,
receiving signal blocks of the r Jh receiving antenna 201(r), is represented as the
following formula 5.
[Formula 5]
The channel equalization unit 212 performs the channel equalization of the N
input block matrixes (N frequency-bins), formed by the input block matrix formation 210, by using an equalizer coefficien
equalizer coefficient is defined as the following formula 6.
[Formula 6]
In the formula 6,
receiving antenna. The output signal of the block adaptive frequency-domain
equalization and the diversity combining structure by using the formulas 3 and 6 is
represented as follows.
[Formula 7]
riere,
Then, an algorithm renewing the block adaptive frequency-domain
equalization and the diversity combining structure is described. The typical adaptive
algorithm is defined as follows.
[Formula 8]
In the formula 8, is the correction term of
error
dimension of 2B x 1 , in order to optimize the
[Formula 9]
[Formula 10]
In the formulas 9 and 10,
[Formula 11 ]
The posteriori error
terms of
[Formula 12]
As a result,
the following formula 13.
[Formula 13]
Here, the 2B*2B matrix -^ is defined as the following formula with a
forgetting factor
[Formula 14]
Accordingly,
substituting the formula 12 for the formula 13 and then differentiating with respect to the
[Formula 15]
In the formula 15, it can be recognized that
is recursively updated through the formulas 3 and 4 as follows.
[Formula 16]
In particular, an inverse correlation matrix
be represented as the following formula 17 by using "matrix inversion lemma."
[Formula 17]
Here, a gain matri
[Formula 18]
Accordingly, the algorithm for renewing the block adaptive frequency-domain
equalization and the diversity combining structure can be represented as the following
formula 19 by applying the formulas 15 though 18 to the formula 8.
[Formula 19]
However, the formula 19 has yet provided the algorithm having the low
stability. To solve the problem, the present invention attempts to solve the formulas 17
and 18 through a square root algorithm. Firstly, a factor influencing the renewal of the
formulas 17 and 18 is represented as the same matrix as the following formula 20 in
order to realize an adaptive square root algorithm.
[Formula 20]
Here, the dimension of π(A J (0 is represented as 2 ^ i¥ft + 1 ^ X 2( iV/ϊ + 1 ^ .
Referring to the formula 20, " ■ J consists of κ ' . Since the formula 20 is the
determinant consisting of a nonnegative-define matrix, the formula 20 can be
represented as the following formula 21 through Cholesky factorization.
[Formula 21]
Here, the determinant denotes the null matrix having the magnitude of
R
. The relationship between a prearra , which can be seen in the
factorization theories is represented as the following formula 22.
[Formula 22]
The relationship of the formula 22, which is the relationship between the
prearray n be represented as the following
[Formula 23]
Here, an unitary matrix " ^ ' having the magnitude of
*n^ ' rt + ) x ( - ■ ,R ' , which can be evaluated by using a sequence of Givens
rotations, operates on the
annihilating its elements one by one, so as to produce a block zero entry of the first row of the postarrray β . In case that l ' used in the formula 19 is defined from
the formula 23 as
postarray ^ K Also, the
prearray
coefficient updating the block adaptive frequency-domain equalization and the diversity
combining structure can be recursively evaluated by the same method as the formula 19.
The inverse discrete Fourier transformation unit 214 transforms the
transmission signal estimated by using the formulas 19 and 23, which is the signal
channel-equalized by the channel equalization unit 212, into the time-domain. It is
preferable that the inverse discrete Fourier transformation unit 214 transforms the signal
of the present receiving block group 400(0) of the signals, outputted through the
channel equalization unit 212, into the time-domain.
The diversity combining structure by discrete Fourier transformation 510,
STBC-like matrix formation 520, input block matrix formation 530, channel
equalization 540 and inverse discrete Fourier transformation 550 operations per each
receiving antenna is illustrated in FIG. 8 through FIG. 10.
The determination unit 216 determines a presently received signal by using a
signal transformed into a time-domain by the inverse discrete Fourier transformation
unit 214.
The second discrete Fourier transformation unit 218 transforms the determined
signal, into the frequency-domain in order to compute an error of the signal determined
by the determination unit 216.
The error computation unit 220 computes an error by using the determination
signal transformed into the frequency-domain through the second discrete Fourier
transformation unit 218.
The correction unit 222 corrects the equalizer coefficient of the channel
equalization unit 212 by using the error, computed by the error computation unit 220,
and an input block matrix, formed by the input block matrix formation unit 210, and a
square root algorithm.
FIG. 11 shows graphs of excess mean-square errors (EMSE) in an adaptive
frequency-domain equalizer in accordance with an embodiment of the present invention,
and FIG. 12 shows graphs of a bit-error-rate in an adaptive frequency-domain equalizer
in accordance with an embodiment of the present invention.
FIG. 11 shows the excess mean-square error according to the number of the
previous time blocks when a frequency-domain equalizer. The larger the number of
blocks is than the case of one block (refer to 610(a) and 620(a) in the conventional art),
the less the excess mean-square error is.
Also, the cases of two transmission antennas and two receiving antennas (610)
and two transmission antennas and three receiving antennas (620) are taken as examples.
Any one of the two cases also show that the increase of blocks results in the decrease of
the excess mean-square errors.
FIG. 12 shows the bit error rate (BER) according to the number of blocks.
When the frequency-domain equalizer performs the channel equalization, the case of
using a lot of the previous time block has smaller bit error rate than the case of using no
previous time block (refer to 700(a) in the conventional art).
FIG. 13 is a flow chart illustrating an adaptive frequency-domain equalization
method in accordance with an embodiment of the present invention.
In a step represented by S810, the first Fourier transformation unit 204
transmits a receiving signal into the frequency-domain, hi a step represented by S 820,
the STBC-like matrix formation unit 208 forms an STBC-like matrix by using a
frequency-bin from the two continuous receiving signal blocks, transformed in the
foregoing step. In a step represented by S830, the input block matrix formation unit 210
forms an equalizer input block matrix based on the STBC-like matrix having the
frequency-domain. In a step represented by S840, the channel equalization unit 212
performs the channel equalization of the equalizer input block matrix according to an
equalizer coefficient. In a step represented by S850, the inverse Fourier transformation
unit 214 transforms the channel-equalized signal into a time-domain. In a step
represented by S860, the determination unit 216 generates a determination signal
estimating the transmission signal for the signal transformed into the time-domain.
Here, each receiving signal transformed into the frequency-domain before the
step represented by S820 can be stored in the storage unit 206.
In a step represented by S870, the second Fourier transformation unit 218
transforms the determination signal into the frequency-domain. In a step represented by
S 880, the error computation unit 220 computes an error from the transformed
determination signal. In a step represented by S890, the correction unit 222 corrects the
equalizer efficient by using the error and the equalizer input block matrix.
The channel equalization technologies of this description can be realized by
various means. For example, these technologies can be realized as hardware, software
or their combination, hi the case of being realized as the hardware, a processing unit,
which is used by the receiving unit to perform the frequency-domain equalization, can
be realized as at least one application specific integrated circuit (ASIC), a digital signal
processor (DSP), a digital signal processing devices (DSPD), a programmable logic
device (PLD), a field programmable gate array (FPGA), a processor, a controller, a
micro-controller, a micro-processor, other electronic units, designed to perform
functions of the description or their combinations.
In the case of being realized as the software, the frequency-domain channel
equalization by the receiving unit can be realized as a module performing the function
of the description (e.g. a procedure's function). A software code can be stored in a
memory unit or can be processed by a processor. The memory unit can be realized
inside or outside the processor. In the case of being realized outside the processor, the
memory unit can be communicatively coupled to another processor through various
means, which is known in the related art.
Hitherto, although some embodiments of the present invention have been
shown and described for the above-described objects, it will be appreciated by any
person of ordinary skill in the art that a large number of modifications, permutations and
additions are possible within the principles and spirit of the invention, the scope of
which shall be defined by the appended claims and their equivalents
[industrial Applicability]
As described above, the adaptive frequency-domain equalizer and a method
thereof in accordance with the present invention show the outstanding features in a
time-varying channel environment by processing an inputted signal in units of blocks.
The present invention can also minimize an excess mean square error (EMSE)
through a square root algorithm having a low complexity and a high stability.
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