CA 02776257 2012-05-02
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DESCRIPTION
RADIO COMMUNICATION METHOD AND A BASE STATION AND USER
TERMINAL THEREOF
RELATED APPLICATION
This application is a divisional of Canadian Patent Application
Number 2,673,284 filed on December 22, 2006.
TECHNICAL FIELD
[0001]
The present invention relates to a radio communication method and a
base station and user terminal thereof, and more particularly to a radio
communication method and a base station and user terminal thereof in a radio
communication system in which each user terminal uses different data
transmission
band frequencies that are assigned from a base station to transmit data
signals to
that base station, and performs time-division multiplexing of pilot signals
onto the
data signal and transmits the resulting signal to the base station.
BACKGROUND ART
[0002]
In a radio communication system such as a cellular system, the
receiving side typically uses a known pilot signal to perform timing
synchronization
and propagation path estimation (channel estimation), and based on each of
these,
performs data demodulation. Moreover, in an adaptive modulation method that
makes it possible to improve throughput by adaptively changing the modulation
method or encoding rate according to the channel quality, the receiving side
also
uses the pilot signal when estimating the channel quality, for example the
signal to
interference ratio (SIR), in order to decide the optimal modulation method or
optimal
encoding rate.
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As a radio communication access method that is strong against
frequency selective fading due to multipaths in broadband radio communication,
is
the OFDM (Orthogonal Frequency Division Multiplexing) method. However, from
the
aspect of the power efficiency of the terminal, there is a problem that the
PAPR (Peak
to Average Power Ratio) of the transmission signal is large, so OFDM is not
suited as
a method for UP link transmission. Therefore, in the next-generation cellular
system
3GPP LTE, single-carrier transmission is performed as the uplink transmission
method,
la
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where the receiving side performs frequency equalization (refer to 3GPP
TR25814-700 Figure 9.1.1-1).
Single¨carrier transmission means that
transmission data and pilot signals are multiplexed only on the time axis,
and when compared with OFDM that multiplexes data and pilot signals on the
frequency axis, it is possible to greatly reduce the PARR.
[0003]
= Single¨Carrier Transmission
FIG. 23 is an example of the frame format of single¨carrier
transmission, and FIG. 24 is a drawing explaining frequency equalization.
A frame comprises data DATA and pilots PILOT having N number of samples
each and that are time multiplexed, where in FIG. 23 two pilot blocks are
inserted in one frame. When
performing frequency equalization, a
data/pilot separation unit 1 separates data DATA and pilots PILOT, and a
first FFT unit 2 performs FFT processing on N samples of data to generate
N number of frequency components, and inputs the result to a
channel¨compensation unit 3. A
second FFT unit 4 performs FFT processing
on N samples of pilot to generation N number of frequency components, and
a channel estimation unit 5 uses those N number of frequency components
and N number of frequency components of a known pilot to estimate the channel
characteristics for each frequency, and inputs a channel¨compensation
signal to the channel¨compensation unit 3. The
channel¨compensation unit
3 multiplies the N number of frequency components that were output from
the first FFT unit 2 by the channel¨compensation signal for each frequency
to perform channel compensation, and an IFFT unit 6 performs IFFT processing
of the N number of channel¨compensated frequency components, then converts
the signal to a time signal and outputs the result.
[0004]
= = CAZAC Sequence
In single¨carrier transmission, when the receiving side performs
frequency equalization, in order to improve the accuracy of channel
estimation in the frequency domain, it is preferred that the pilot signal
has a constant amplitude in the frequency domain, or in other words, that
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the auto correlation after an arbitrary cyclic time shift be '0'. On the
other hand, from the aspect of the PAPR, it is preferred that a pilot signal
has a constant amplitude in the time domain as well. A pilot
sequence that
makes these features possible is a CAZAC (Constant Amplitude Zero Auto
Correlation) sequence, and in the 3GPP LTE system, application of this CAZAC
sequence as the uplink pilot is decided. The CAZAC
sequence has ideal auto
correlation characteristics, so pilot signals that are obtained by
cyclically shifting the same CAZAC sequence are orthogonal to each other.
In the 3GPP LTE system, a method of using CAZAC sequences having different
amounts of cyclic shift to multiplex the pilot signals of different users,
or to multiplex pilot signals from the same user but transmitted from
different antennas is adopted and it is called CDM (Code Division
Multiplexing).
[0005]
A Zadoff¨Chu sequence, which is a typical CAZAC sequence, is expressed
by Equation (1) (refer to B.M. Popovic, "Generalized Chirp¨Like Polyphase
Sequences with Optimum Correlation Properties", IEEE Trans. Info. Theory,
Vol. 38, pp. 1406-14 09, July 1992).
ZCic(n) = expf¨ j2irk IL = (qn + n(n + L%2)/2)} (1)
Here, k and L are both prime, and express the sequence number and sequence
length, respectively. Moreover, n is the symbol number, q is an arbitrary
integer, and L%2 is the remainder when divided by 2, and may be notated
as Lmod(2). When the factorization into prime numbers of L is taken to be
L = giel x=.-x g nen (2)
(gi is a prime number), the number of CAZAC sequences can be given by the
following equation.
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cb(L)\ 1 \ /
1 )
= L 1---- x-=-x 1¨ (3)
g11 1, gn
More specifically, in the case where L = 12, L = 12 = 2' x 31, so g, = 2, .
el = 2, g2 = 3 and e2 = 1, and from Equation (3), the number of sequences
(CAZAC sequences) becomes 4. Therefore,
the number of sequences increases
the larger L is and the fewer number of prime factors there is. In other
words, in the case where L is a prime number, the number of CAZAC sequences
0 (0 becomes (L ¨ 1).
=
[0006]
ZCk(n ¨ c), for which only c in the CAZAC sequence ZCk(n) is cyclically
shifted, is expressed by the following equation.
ZCk(n ¨c) = exp {¨ j Zrric L = (q(n ¨ c) + (n ¨ c)(n ¨c + L %2) 2)} (4)
As is shown in Equation (5) below,
C
IR(T) = {01 ..................................... (5)
............................. T C
the correlation R(r) between ZCk(n) and ZCk(n ¨ c) becomes '0' at any point
except where r = c, so sequences that are obtained by applying different
amounts of cyclic shift to the main sequence ZCk(n) become orthogonal to
each other.
[0007]
When a radio base station receives a plurality of pilots that were
multiplexed by CDM (Code Division Multiplex) using the cyclic shift, by
= taking the correlation with the main sequence, it is possible to separate
the pilots based on the location where the peak occurs. The ability
to
tolerate shifting of the multipath or shifting of the reception timing
decreases the narrower the interval of the cyclic shift is, so there is
an upper limit to the number of pilots that can be multiplexed by cyclic
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shift. When the
number of pilots that are multiplexed by cyclic shifting
is taken to be P, the amount of cyclic shifting cp that is assigned to the
pth pilot can be determined, for example, by the equation given below (refer
to 3GPP R1-060374, "Text Proposal On Uplink Reference Signal Structure",
Texas Instruments).
c = (p ¨ 1)* {I, I P], where p =1õ ,P (6)
[0008]
As was described above, in a 3GPP LTE uplink, pilots and data are
multiplexed by time¨division multiplexing and transmitted by the SC¨FDMA
(Single Carrier¨Frequency Division Multiple Access) method. FIG. 25 is
a drawing
showing the construction of a SC ¨FDMA transmission unit, where
7' is a Nu sized DFT (Discrete Fourier Transformer), 8' is a subcarrier
mapping unit, 9' is a NFT sized IDFT unit, and 10 is CP (Cyclic Prefix)
insertion unit. In 3GPP
LTE, in order to suppress the amount of processing,
NFFT is an integer that is a power of 2, and the IDFT after subcarrier mapping
is replaced by IFFT.
The process of adding a cyclic shift c to the main sequence ZCk(n) can
be performed either before DFT or after IFFT. When the
process is performed
after IFFT, the cyclic shift can be an amount c x NuT/Nrx samples.
Essentially, the process is the same process, so hereafter, an example will
be explained in which the cyclic shift process is performed before DFT.
[0009]
= Problems With the Related Art
In order to reduce inter¨cell interference, it is necessary to
repeatedly use CAZAC sequences having different sequence numbers as pilots
between cells. This is
because as the number of repetitions increases,
the distance between cells that use the same sequence becomes larger, so
the possibility of severe interference occurring decreases. Therefore,
it becomes necessary to maintain a lot of CAZAC sequences, and in order
to have good characteristics for the CAZAC sequences, a sequence length
L that is a large prime number is desirable. FIG. 26 is a
drawing explaining
CA 02776257 2012-05-02
inter¨cell interference, where in the case as shown in (A), in which the
number of CAZAC sequences that can be used is 2, CAZAC sequences (ZC1) having
the same sequence number are used in adjacent cells, so severe interference
occurs between the adjacent cells. Moreover,
as shown in (B), when the
number of CAZAC sequences is 3, CAZAC sequences having the same sequence
number are not used, however, the number of repetitions is 3, which is a
small number, so the distance between cells that use CAZAC sequences having
the same sequence number is short and there is a high possibility that
interference will occur between adjacent cells. In the case
shown in (C),
where the number of CAZAC sequences is 7, the number of repetitions is 7,
which is a large number, so as the distance between cells that use CAZAC
sequences having the same sequence number becomes larger, the possibility
of interference occurring gradually decreases.
Incidentally, as shown in (A) of FIG. 27, the trend of 3GPP LTE
discussion is to take the number of subcarriers that are occupied by data
a multiple of 12, and to take the subcarrier interval for pilots double
the subcarrier interval for data in order to improve the transmission
efficiency. In that
case, when the sequence length [of the CAZAC sequence
is 6, the number of sequences 0 (0 becomes 2(k=1,2), and CAZAC sequences
having the same sequence number are used, so pilot interference occurs
between adjacent cells. Moreover,
when the sequence length L is taken to
be 5, 0 (L) becomes 4(k=1,2,3,4), which is still a small number, however,
as shown in (B) of FIG. 27, there are subcarriers of data that are not covered
by a pilot, so the channel estimation accuracy decreases.
[0010]
Therefore, it is thought that by making the transmission band for pilot
signals broader than the transmission band for data and performing
transmission, a sufficient sequence length L will be maintained (refer to
3GPP R1-060925, R1-063183). FIG. 28 is
an example of the case in which
the number of multiplexed pilot signals is 2. If the
sequence length L
is taken to be 12, the number of CAZAC sequences is only 4 from the equations
(2) and (3), and the inter¨cell interference becomes large (k = 4).
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Therefore, the sequence length L is made to be the prime number 11. When L =
11,
0(0 is 10 and 10 CAZAC sequences can be used (k = 1-10), so it is possible to
reduce the inter-cell interference. The sequence length L cannot be made to be
13 or
greater. The reason for that is that when the sequence length L is 13 or
greater,
interference occurs between adjacent frequency bands.
Pilot signals from different users are multiplexed by CDM through cyclic
shifting. In other words, a CAZAC sequence ZCk(n) having a length L = 11 and
for
which cyclic shifting c1 has been performed is used as the pilot for a user 1,
and a
CAZAC sequence ZCk(n) for which cyclic shifting c2 has been performed is used
as
the pilot for a user 2.
[0011]
However, when a CAZAC sequence ZCk(n) having a length L = ibis
cyclically shifted and used for the users 1, 2, then as can be clearly seen in
FIG. 28,
the relative relationship between the transmission frequency band for the
pilots and
the transmission frequency band for data for user 1 and user 2 differs, and
thus the
channel estimation accuracy is different. In other words, subcarriers 23, 24
of the
transmission frequency band for data of user 2 deviates from the transmission
frequency band for the pilots, and the channel estimation accuracy for those
subcarriers decreases.
In FIG. 28, based on the current 3GPP LTE specifications, the
subcarrier interval for pilots is double the subcarrier interval for data,
however, the
problem described above occurs even when the ratio of the subcarrier intervals
is
changed.
[0012]
Taking the aforementioned problems into consideration, it is an object
of some embodiments to enable accurate channel estimation of data subcarriers
that
deviate from the pilot transmission frequency band.
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Another object of some embodiments is to enable accurate channel
estimation of subcarriers assigned to each user even when a specified sequence
(for
example, CAZAC sequence ZCk(n), for which different amounts of cyclic shifting
has
been performed, is used as pilots of users to be multiplexed.
Another object of some embodiments is to enable accurate channel
estimation by separating pilots for each user using a simple method, even when
a
specified CAZAC sequence, for which different amounts of cyclic shifting has
been
performed, is used as pilots of users to be multiplexed.
Another object of some embodiments is to increase the accuracy of
channel estimation of the data subcarriers of a user even when the condition
of the
propagation path of that user is poor.
DISCLOSURE OF THE INVENTION
[0013]
Some embodiments provide a radio communication method, a base
station and a user terminal in a radio communication system in which each of
user
terminals together with transmitting data signal to a base station using
different data
transmission band frequencies that are assigned by the base station, performs
time-
division multiplexing of a pilot signal with the data signal and transmits the
resulting
signal to the base station.
= Radio Communication Method
The radio communication method of some embodiments comprises: a
step of deciding pilot transmission band each user terminal so that pilot
transmission
band covers the data transmission band of the user terminal, by frequency
offset; and
a step of instructing each user terminal to transmit the pilot signal using
the
frequencies of said decided pilot transmission band.
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,
The instruction step comprises: a step of calculating an amount of
frequency offset for each user terminal, and an amount of cyclic shift of the
CAZAC
sequence corresponding to the number of multiplexed user terminals and the
amount
of the frequency offset; and a step of instructing each user terminal to
perform cyclic
shift of said CAZAC sequence used as the pilot signal by the calculated cyclic
shift
amount, and instructing the user terminal to perform frequency offset of the
pilot
transmission band by the calculated frequency offset amount.
The radio communication method further comprises: a step of adding,
when the base station received multiplexed pilot signals that were sent from a
plurality of user terminals, the frequency components of the portion of the
pilot signals
that do not overlap each other; a step of multiplying a combination of the
added result
and the received multiplexed pilot signals by a replica of the pilot signal in
a
frequency-domain; and a step of converting the replica multiplication results
to a time-
domain signal, then separating out the signal portion of a specified user
terminal from
that time-domain signal and performing channel estimation.
The radio communication method of some embodiments further
comprises: a step of acquiring the propagation path conditions of the user
terminals;
and a step of assigning preferentially a middle band of the whole data
transmission
band as the data transmission band for a user terminal having a poor
propagation
path condition, and notifying the user terminals. Alternatively, the radio
communication method of some embodiments further comprises: a step of
performing hopping control by periodically assigning a middle band and an end
band
of the whole data transmission band as the data transmission bands for the
user
terminals.
[0014]
= Base Station
The base station of some embodiments comprises a resource
management unit that decides pilot transmission band for each user terminal so
that
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the pilot transmission band covers the data transmission band of the user
terminal by
frequency offset, and instructs the user terminal to transmit the pilot signal
using the
frequencies of said decided pilot transmission band.
In the base station, the resource management unit comprises: a cyclic
shift amount calculation unit that calculates an amount of frequency offset
for each
user terminal, and an amount of cyclic shift of the CAZAC sequence that
corresponds
to the number of multiplexed user terminals and the amount of the frequency
offset;
and an instruction unit that together with instructing each user terminal to
perform a
cyclic shift of said CAZAC sequence used as the pilot signal by the calculated
cyclic
shift amount,
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instructs the user terminal to perform frequency offset of the pilot signal
by the frequency offset amount.
The base station further comprises a channel estimation unit that
performs channel estimation for each user terminal; and wherein the channel
estimation unit comprises: a receiving unit that receives multiplexed pilot
signals that are transmitted from a plurality of user terminals; an addition
unit that adds the frequency components of the portion of the pilot signals
that do not overlap each other; a replica multiplication unit that
multiplies a combination of the addition results and the received
multiplexed pilot signals by a replica of the pilot signal in a
frequency¨domain; a conversion unit that converts the replica
multiplication result to a time¨domain signal; a separation unit that
separates out the signal portion of each user terminal from the time¨domain
signal; and an estimation unit that converts the separated time¨domain
signal to a frequency¨domain signal to estimate channel of each frequency.
The resource management unit acquires the propagation conditions of
the user terminals, and assigns preferentially a middle band of the whole
data transmission band as the data transmission band for a user terminal
having a poor propagation path condition, and not the user
terminal.
Alternatively, the resource management unit performs hopping control by
periodically assigning a middle band and an end band of the whole data
transmission band as the data transmission bands for the user terminals.
= User Terminal
The user terminal of the radio communication system comprises: a
receiving unit that receives uplink resource information from a base
station; and a pilot generation unit that generates a pilot according to
instructions in the uplink resource information; wherein the pilot
generation unit comprises: a CAZAC sequence generation unit that, based
on the resource information, generates a CAZAC sequence having a specified
sequence length and sequence number as a pilot signal; a first conversion
unit that converts the CAZAC sequence, which is a time¨domain pilot signal,
into a frequency¨domain pilot signal; a subcarrier mapping unit that
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,
performs mapping of the subcarrier components of the pilot signal based on
frequency offset information that is included in the resource information; a
second
conversion unit that converts the pilot signal with mapped subcarriers into a
time-
domain signal; and a cyclic shift unit that performs a cyclic shift on the
CAZAC
sequence based on a cyclic shift amount that is included in the resource
information,
either before the first conversion or after the second conversion.
According to one aspect of the present invention, there is provided a
user terminal in a radio communication system, in which each of user terminals
performs multiplexing of a data signal and a pilot signal and transmits the
multiplexed
signal to a base station using different data transmission band frequencies
that are
assigned by the base station, the user terminal comprising: a receiving unit
that
receives uplink resource information from a base station; and a pilot
generation unit
that generates a Zadoff-Chu sequence, to which a cyclic shift is applied, as a
pilot
signal based on the uplink resource information; and a transmitting unit that
transmits
the pilot signal generated by the pilot generation unit to the base station;
wherein the
pilot generation unit comprises: a subcarrier mapping unit that performs
subcarrier
mapping by copying a part of the Zadoff-Chu sequence and adding the copy to
the
Zadoff-Chu sequence in a frequency domain.
According to another aspect of the present invention, there is provided
a communication method for user terminal in a radio communication system, in
which
each of user terminals performs multiplexing of a data signal and a pilot
signal and
transmits the multiplexed signal to a base station using different data
transmission
band frequencies that are different data transmission band frequencies that
are
assigned by the base station, the communication method comprising: receiving
uplink resource information from a base station; and generating a Zadoff-Chu
sequence, to which a cyclic shift is applied, as a pilot signal based on the
uplink
resource information; performing subcarrier mapping by copying a part of the
Zadoff-
Chu sequence and adding the copy to the Zadoff-Chu sequence in a frequency
domain; and transmitting the mapped pilot signal to the base station.
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According to still another aspect of the present invention, there is
provided a radio communication system, in which each of user terminals
performs
multiplexing of a data signal and a pilot signal and transmits the multiplexed
signal to
a base station using different data transmission band frequencies that are
assigned
by the base station, the radio communication system comprising: the base
station
and the user terminals, wherein the base station includes, a first
transmitting unit that
transmits an uplink resource information to each of the user terminals; and
wherein
the each of the user terminals includes, a receiving unit that receives the
uplink
resource information from a base station; and a pilot generation unit that
generates a
Zadoff-Chu sequence, to which a cyclic shift is applied, as a pilot signal
based on the
uplink resource information; and a second transmitting unit that transmits the
pilot
signal generated by the pilot generation unit to the base station; wherein the
pilot
generation unit comprises: a subcarrier mapping unit that performs subcarrier
mapping by copying a part of the Zadoff-Chu sequence and adding the copy to
the
Zadoff-Chu sequence in a frequency domain.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015]
FIG. 1 is a drawing explaining a first principle of the present invention.
FIG. 2 is a drawing explaining a second principle of the present
invention.
FIG. 3 is a drawing explaining a third principle of the present invention.
FIG. 4 is a drawing explaining a pilot generation process on the
transmitting side that makes possible frequency offset of d subcarriers and a
cyclic
shift of (c2 ¨ s(k, d, L)).
FIG. 5 is a drawing explaining offset by the subcarrier mapping unit.
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FIG. 6 is a drawing explaining the channel estimation process on the
receiving side.
FIG. 7 is a drawing explaining a second pilot generation process.
FIG. 8 is a drawing explaining a copying method on the transmitter.
FIG. 9 is a drawing explaining a second channel estimation process on
the receiving side.
FIG. 10 is a drawing that shows frame configuration.
FIG. 11 is a drawing explaining a pilot separation method.
FIG. 12 is a drawing explaining a third channel estimation process on
the receiving side.
FIG. 13 is a drawing of the construction of a mobile station.
FIG. 14 is a drawing of the construction of a pilot generation unit.
FIG. 15 is a drawing of the construction of a base station.
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FIG. 16 is a drawing of the construction of a channel estimation unit.
FIG. 17 is a drawing of the construction of a pilot generation unit
and channel estimation unit that performs a second pilot generation process
and channel estimation process.
FIG. 18 is a drawing of the construction of a pilot generation unit
and channel estimation unit that performs a third pilot generation process
and channel estimation process.
FIG. 19 is a drawing explaining the assignment of frequencies when
the number of multiplexed pilots is 4.
FIG. 20 is a drawing explaining hopping control so that the
transmission bands that are assigned to the users are switched after each
frame, and explains assignment for an odd numbered frame.
FIG. 21 is a drawing explaining hopping control so that the
transmission bands that are assigned to the users are switched after each
frame, and explains assignment for an even numbered frame.
FIG. 22 is a drawing of the construction of the pilot generation unit
when performing hopping control.
FIG. 23 is an example of frame format for single¨carrier transmission.
FIG. 24 is a drawing for explaining frequency equalization.
FIG. 25 is a drawing of construction of a SC ¨FDMA transmission unit.
FIG. 26 is a drawing explaining inter¨cell interference.
FIG. 27 is a first drawing explaining a conventional data transmission
band and pilot transmission band.
FIG. 28 is a second drawing explaining a conventional data
transmission band and pilot transmission band.
BEST MODE FOR CARRYING OUT THE INVENTION
[0016]
(A) Principles of the Invention
As shown in (A) of FIG. 1, when a CAZAC sequence ZCk(n) to which a cyclic
shift cl has been performed is used as the pilot for a user 1, and a CAZAC
sequence ZCk(n) to which a cyclic shift c2 has been performed is used as
the pilot for a user 2, then as was explained using FIG. 28, the subcarriers
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23, 24 of the transmission frequency band for data of user 2 deviates from
the transmission frequency band for the pilot, and the channel estimation
accuracy for that subcarrier decreases. In FIG. 1,
DFT{ZCk(n ¨ c1)1 and
DFT{ZCk(n ¨ c2)} are the pilots that are obtained by performing cyclic
shifts cl, c2 of a CAZAC sequence ZCk(n) having a length L = 11, after which
OFT processing is performed on the sequences ZCk(n ¨ cl) and ZCk(n ¨ c2).
Therefore, as shown in (6) of FIG. 1, by giving a frequency offset
to the pilots of each user to correspond to the transmission band and then
multiplexing the pilots, the transmission band for the pilots will always
cover the transmission band for the data. In the
example shown in (6) of
FIG. 1, the pilot DFT{ZCk(n ¨ c2)} for user 2 can be offset the amount of
one subcarrier.
However, when the pilot DFT{ZCk(n ¨ c2)} is offset, on the receiving
side the correlation between the received pilot and replica ZCk(n) of a
known pilot does not reach a peak at t = c2, and the location of the peak
shifts, so it is not possible to correctly restore the pilot, and as a result
channel estimation is not possible. The reason
that the location of the
correlation peak shifts will be explained below.
[0017]
= Relationship between the Frequency Offset and Cyclic Shift in the Time
Domain
First, the relationship between the frequency offset and cyclic shift
in the time domain will be explained. Taking the
result of performing OFT
conversion on the CAZAC sequence ZCk(n) to be F(m), F(m) can be expressed =
by the equation below.
L-1
F(m) =;ZC(n)- expf¨ j2mnnIL} (7)
Using Equation (7) and Equation 4, the equation can be transformed to obtain
the equation below.
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L
exp{- jek,, F(m -d) = ZC(n - c) = exp{- j2Rmn L}
(8)
where kc = d (mod L), O = jik IL (c2 2qc - c = L%2)
Here, d(mod 0 means that kc and d have the same remainder after dividing
by the modulus L.
As can be seen from Equation (8), in the time domain, applying a cyclic
shift c to a CAZAC sequence is equivalent to applying a cyclic shift having
an amount of d subcarriers and phase rotation Q in
the frequency domain.
Here, k and L are both prime each other, so c(<a) is uniquely decided
according to k and d. In order to
more easily understand that c is decided
according to k, d and L, then c will newly be taken to be c = s(k,d, L).
Table 1 shows values of c that correspond to various combinations of
s(k,d,L) and k for the case in which L
= 11. For example, when k = 1, d
= 1, L = 11 and c = 1; and when k = 2, d = 1, L = 11 and c = 6.
[Table 1]
s(k,d,L) when L = 11
s(k,1,11) s(k,2,11) s(k,3,11)
1 1 2 3
2 6 1 7
3 4 8 1
4 3 6 9
9 7 5
6 2 4 6
7 8 5 2
8 7 3 10
9 5 10 4
10 9 8
[0018]
From the above, applying frequency offset of one subcarrier portion
to the pilot 2 as shown in (A) of FIG. 2 corresponds to moving the component
pll in subcarrier I to subcarrier 12 after a one subcarrier cyclic shift
has been added in the frequency domain as shown in (B) of FIG. 2. As a
result, from Equation (8), the correlation peak position (see Equation (5))
of the pilot 2 shifts only s(k,d,L) (r=c2 + s(k,d,L)). The
correlation
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peak position of pilot 1 (r=c1) does not shift, so the correlation peak
of pilot 2 and pilot 1 changes relatively only s(k, d=1, L=11), and on the
receiving side it is not possible to restore the pilot correctly, thus as
a result it becomes impossible to perform channel estimation.
To obtain the conventional correlation peak position, the amount of
cyclic shift can be changed from c2 to (c2 ¨ s(k,d,L). In other
words, as
shown in (A) of FIG. 3, by applying both a d¨subcarriers frequency offset
(d = 1 in the figure), and a (c2 ¨ s(k,d,L) cyclic shift, the relationship
between pilot 1 and pilot 2 becomes as shown in (B) of FIG. 3. By doing
as described above, the correlation peak positions of pilots 1 and 2 do
not shift, and on the receiving side it is possible to correctly restore
the pilots, and thus it is possible to improve the channel estimation
accuracy. That is, it
is possible to separate pilot 1 and pilot 2 by the
correlation peak value positions (t =cl, r =c2) as the case where the
frequency offset is not applied.
[0019]
(a) First Pilot Generation Process and Channel Estimation Process
FIG. 4 is a drawing for explaining the pilot generation process on
the transmission side that makes possible the d subcarrier frequency offset
and (c2 ¨ s(k,d,L) cyclic shift that were explained using FIG. 3.
A CAZAC sequence generation unit 11 generates a CAZAC sequence Zck(n)
as a pilot where L = 11, and a cyclic shift unit 12 cyclically shifts the
CAZAC sequence ZCk(n) only c2 ¨ s(k,d,L) to generate ZCk(n ¨ c2 + s(k,d,L))
and inputs the result to a OFT unit 13. An Wu sized
(Nu = L = 11) OFT unit
13 performs a OFT calculation process on ZCk(n ¨ c2 + s(k,d,L)) to generate
the pilot DFT {ZCk(n ¨c2 +s(k,d,L))1. A
subcarriermapping unit 14 offsets
11 pilot components pl to pll of the frequency domain an amount of d
subcarriers (d = 1 in the figure), and inputs the result to an IFFT unit
15.
FIG. 5 is a drawing explaining the offset by the subcarrier mapping
unit 14, where (A) shows the case where there is no offset (d = 0), and
the subcarrier mapping unit 14 inputs 11 pilot components p1 to pll to the
CA 02776257 2012-05-02
frequency terminals f, frno of the
IFFT unit 15, and inputs
0 to the other terminals. In the
figure, (B) shows the case where there
is offset (d = 1), and the subcarrier mapping unit 14 inputs 11 pilot
components pl to pll to the frequency terminals fm, fi+2, fiu , , and
inputs 0 to the other terminals. .An Nru
sized (for example NFFT = 128) IFFT
unit 15 performs 1DFT calculation processing on the input subcarrier
components to convert the signal to a time¨domain signal, and a CP (Cyclic
Prefix) insertion unit 16 adds a cyclic prefix for preventing interference
and outputs the result. In FIG. 5,
(C) shows another example of the case
of when there is offset (d = 1). In this
case, the cyclic shift unit 12
cyclically shifts the CAZAC sequence ZCk(n) only c2 to generate ZCk(n ¨ c2)
and inputs the result to the OFT unit 13. The DFT
unit 13 performs DFT
calculation processing on ZCk(n ¨ c2) to generate a pilot DFT {ZCk(n ¨ c2)}.
The subcarrier mapping unit 14 inputs pilot components p2 to pll to the
terminals f, fino of the
IFFT unit 15, and inputs pilot
component pl to the terminal frm of the IFFT unit 15.
[0020]
FIG. 6 is a drawing explaining the channel estimation process on the
receiving side.
A pilot 1 and pilot 2 that are respectively transmitted from a user
1 and user 2 (see FIG. 3) are multiplexed in air to become the subcarrier
components (p1 to p12) of the subcarrier frequencies f, f,n,
fini and input to the channel estimation unit. A
subcarrier addition unit
52 adds the subcarrier components p12 and pl that do not overlap each other,
and takes the added result to be the new subcarrier component pl of
subcarrier frequency fl.
A replica signal multiplication unit 53 multiplies a replica signal
of a pilot qi and received pilot signal pi for each subcarrier, an IDFT
unit 54 performs an IDFT calculation processing on the replica
multiplication results and outputs a delay profile in the time domain. The
replica signal of the pilot is obtained by performing DFT calculation
processing on a known CAZAC sequence ZCk(n) for a cyclic shift of zero.
16
CA 02776257 2012-05-02
The time¨domain delay profile has a length of L samples with correlation
peaks at t = cl, t = c2, so a profile extraction unit 55 separates out the
correlation peaks by t = (cl + c2)/2, to generate profiles PRF1, PRF2 having
a length of L/2 samples for user 1 and user 2. An L sized
DFT unit 56a
inserts L/4 number of zeros on both sides of the L/2 long profile PRF1 to
make the length L, and performs DFT calculation. By doing
so, the channel
estimation values hl to hll for user 1 are obtained from the DFT unit 56a
at the subcarrier frequencies fõ f i+37 " = 7 f 1+10' Similarly,
an
L sized DFT unit 56b inserts L/4 number of zeros on both sides of the L/2
sample length profile PRF2 to make the length L, and performs DFT
calculation. By doing
so, the channel estimation values h2 to h12 for user
2 are obtained from the DFT unit 56b at the subcarrier frequencies f,fl, f0.2,
fin,. However,
since the subcarrier adding unit 52 adds pl and
p12 to become the subcarrier component of the subcarrier frequency f, the
channel estimation value of the subcarrier frequency f, that is output from
the DFT unit 56b is taken to be the channel estimation value h12 of the
subcarrier frequency fi.m.
From the above, as long as the distortion due to the propagation
conditions is small, it is possible to separate pilot 1 and pilot 2 in a
completely orthogonal form in a time¨domain delay profile after the
components that do not overlap each other on the receiving side have been
added and multiplied by a replica as shown in FIG. 6. When the
distortion
due to the propagation conditions is large, it is possible to omit the
subcarrier addition, and separate pilot 1 and pilot 2 in a time¨domain delay
profile after direct replica multiplication.
[0021]
(b) Second Pilot Generation Process and Channel Estimation Process
In the first-channel estimation process described above, subcarrier
components p12 and pl that do not overlap each other are added together
and the added result is taken to be the component of subcarrier frequency
fõ However, when the subcarrier component for subcarrier frequency f, of
the received signal is already the value obtained by adding p12 and pl,
17
CA 02776257 2012-05-02
it is not necessary to add subcarriers on the receiving side.
FIG. 7 is a drawing explaining a second pilot generation process, where
(A) shows the data subcarriers for a user 1 and user 2.
As shown in (B) of FIG. 7, the transmitting side (user 1) copies the
subcarrier component pl of the subcarrier frequency f, of pilot 1 so that
it becomes the subcarrier component of subcarrier frequency f,,, and
performs transmission, and as shown in (C) of FIG. 7, user 2 copies the
subcarrier component p12 of subcarrier frequency fin, of pilot 2 so that
it becomes the subcarrier component of subcarrier frequency f, and performs
transmission. By doing
so, as shown in (D) of FIG. 7, these pilots are
multiplexed in air and received by the receiving side, and the subcarrier
component of the subcarrier frequency f, becomes the sum of pl and p2, so
there is no need to add subcarriers on the receiving side.
[0022]
FIG. 8 is a drawing explaining the copying method on the transmitting
side, where (A) is the copying method for pilot 1 by user 1, and in this
method, the subcarrier mapping unit 14 inputs the subcarrier component pl
of the subcarrier frequency fi of pilot 1 to the terminal of frequency fin,
of the IFFT unit 15 as well so that it is also the subcarrier component
of the subcarrier frequency f,11. In the
figure, (B) is the copying method
for pilot 2 by user 2, and in this method, the subcarrier mapping unit 14
inputs the subcarrier component p12 of the subcarrier frequency fim of
pilot 12 to the terminal of frequency fi of the IFFT unit 15 as well so that
it is also the subcarrier component of the subcarrier frequency fõ In the
figure, (C) is an example of implementing the copying method for pilot 2
by user 2, and corresponds to (C) of FIG. 5.
[0023]
FIG. 9 is a drawing explaining the channel estimation process by the
receiving side. Pilot 1 and
pilot 2 (see (B) and (C) of FIG. 7) that are
respectively transmitted from user 1 and user 2 are multiplexed in air to
become the subcarrier components (p1 to p12) of the subcarrier frequencies
fm, f and input to
the channel estimation unit (see
118
CA 02776257 2012-05-02
(0) of FIG. 7).
The replica signal multiplication unit 53 for user 1 multiplies the
replica signals qi (ql to q11) of the pilot by the received pilot signals
pi (pl to p11) for each subcarrier, and after that, the IDFT unit 54,
correlation separation unit 55, and DFT unit 56 perform processing in the
same way as shown in FIG. 6 to generate channel estimation values hl to
hll for user 1.
On the other hand, the replica signal multiplication unit 53' for user
2 multiplies the replica signals qi (ql to 01) of the pilot with the
received pilot signals pi (p2 to p12) for each subcarrier, and after that,
the IDFT unit 54', correlation separation unit 55' and DFT unit 56' perform
the same processing as was performed for user 1 to generate channel
estimation values h2 to h12 for user 2.
[0024]
(c) Third Pilot Generation Process and Channel estimation Process
In the first channel estimation process described above, the
correlation separation unit 55 separates the pilot components for user 1
and the pilot components for user 2, however, as shown in FIG. 10, when
two pilot blocks are included in one frame, for example, they can be
separated as explained below. FIG. 11 is
a drawing explaining the pilot
separation method, where (A) shows the data subcarriers for user 1 and user
2.
As shown in (B) and (C) of FIG. 11, each of the subcarrier components
of the first pilot 1 (= DFT {ZCk(n ¨ 0)}) and pilot 2 (= DFT {ZCk(n ¨ c2
+ s(k,d,L))1), of user 1 and user 2 are multiplied by +1 and transmitted,
then as shown in (D) and (E), and each of the subcarrier components of the
next pilot 1 and pilot 2 are multiplied by +1 and ¨1, respectively and
transmitted.
By doing this, the receiving side first receives the following
multiplexed pilot signal
DFT{ZCk(n ¨ c1)} x (+1) + DFT{ZCk(n ¨ c2 + s(k,d,L)} x (+1),
then next receives the multiplexed pilot signal
19
CA 02776257 2012-05-02
DFT{ZCk(n ¨ x (+1) +
DFT{ZCk(n ¨ c2 + s(k,d,L)1 x (-1).
Therefore, in order for the receiving side to generate the pilots for
user 1, the next multiplexed pilot signal can be added to the first
multiplexed pilot signal. In other
words, the polarities of pilots 2 are
different, so by adding the signals, pilots 2 are negated, and only pilot
1 remains. Moreover,
in order for the receiving side to generate the pilots
for user 2, the next multiplexed pilot signal can be subtracted from the
first multiplexed pilot signal. In other
words, the polarities of pilots
1 are the same, so by subtracting the signals, pilots 1 are negated and
only pilot 2 remains.
[0025]
FIG. 12 is a drawing explaining the channel estimation process on the
receiving side. Pilot 1 and
pilot 2 that are transmitted from user 1 and
user 2, respectively (see (B), (0, (0) and (E) of FIG. 11) are multiplexed
in air to becomes the subcarrier components (p1 to p12) of the subcarrier
frequencies fi, f fi+2, fifli and
input to the channel estimation
unit.
An inter¨block subcarrier addition unit 61 receives and saves the
first received pilot signal. Then, when
generating the pilots for user
1, the inter¨block subcarrier addition unit 61, after receiving the second
received pilot signal, adds the first and second received pilot signals
for each subcarrier to generate the subcarrier components pl to pll for
the subcarrier frequencies f, f, i+2, fi,,...,
fino of pilot 1. The
replica signal multiplication unit 53 for user 1 multiplies the replica
signals qi (ql to 01) of the pilot by the received pilot signals pi (p1
to p11) for each subcarrier, and after that, the IOFT unit 54, correlation
separation unit 55 and OFT unit 56 perform the same processing as shown
in FIG. 6 to generate the channel estimation values hl to hll for user 1.
On the other hand, when generating the pilots for user 2, the
inter¨block subcarrier addition unit 61 subtracts the first and second
pilot signals for each subcarrier, to generate the subcarrier components
P2 to p12 of the subcarrier frequencies fin, fil2, fin, of
pilot 2.
CA 02776257 2012-05-02
The replica signal multiplication unit 53' for user 2 multiplies the replica
signals qi (q1 to q11) of the pilot by the received pilot signals pi (p2
to p12) for each subcarrier, and after that, the IDFT unit 54', correlation
separation unit 55' and DFT unit 56' perform the same processing as was
performed for user 1 to generate the channel estimation values h2 to h12
for user 2.
The case in which the number of pilot blocks is two was explained above,
however, this third pilot generation process and channel estimation process
can also be applied in the case in which there is an even number of pilot
blocks. In that
case, the base station instructs a certain user terminal
to multiply the pilot signals of all of the blocks by +1, and instructs
other user terminals to multiply half of the pilot signals by +1 and to
multiply the remaining half of the pilot signals by ¨1. Also, when
the
base station receives multiplexed pilot signals that have been transmitted
from each of the user terminals, the base station performs an addition or
subtraction calculation process on the pilot signals for all of the blocks
so that only the pilot signal from a specified user terminal (user terminal
1 or 2) remains, then multiplies the calculation result by the replica of
the pilot signal, converts the replica multiplication result to a
time¨domain signal, after which it separates out the signal portion of the
user terminal from that time¨domain signal and performs channel estimation.
[0026]
(6) Mobile Station
FIG. 13 is a drawing showing the construction of a mobile station.
In the case in which uplink transmission data is generated, the mobile
station (user terminal) sends a request to the base station to assign
resources, and according to that request the base station assigns resources
based on the condition of the propagation path of the mobile station and
notifies the mobile station of the resource assignment information. A
radio communication unit 21 of the mobile station converts a radio signal
that is received from the base station to a baseband signal and inputs the
baseband signal to a baseband processing unit 22. The
baseband processing
21
CA 02776257 2012-05-02
unit 22 separates out the data and other control information from that
received signal, as well as separates out the resource assignment
information and inputs that resource assignment information to a
transmission resource management unit 23. In addition
to the transmission
frequency band, timing, modulation method and the like of the data, the
resource assignment information includes the transmission frequency band
of the pilot, the sequence number k and sequence length L of the CAZAC
sequence that is used as the pilot, the amount of cyclic shift, the amount
of frequency offset d, etc.
The transmission resource management unit 23 inputs the information
necessary for transmission of control information to a data processing unit
24, and inputs the information necessary for generating and transmitting
a pilot to a pilot generation unit 25. Based on
the input information,
the data processing unit 24 performs data modulation and single¨carrier
transmission processing on the data and control information and outputs
the result, and according to an instruction from the transmission resource
management unit 23, the pilot generation unit 25 performs processing such
as the generation of a CAZAC sequence, cyclic shift, frequency offset and
the like to generate a pilot, after which a frame generation unit 26, as
shown in FIG. 10 for example, performs time¨division multiplexing of six
data blocks and two pilot blocks to generate a frame, and the radio
communication unit 21 transmits that frame to the base station.
[0027]
FIG. 14 is a drawing showing the construction of the pilot generation
unit 25, and shows the construction in the case where pilots are generated
according to the first pilot generation process explained using FIG. 3,
where (A) shows the case in which a cyclic shift is performed before DFT,
=
=
and (B) shows the case in which a cyclic shift is performed after IFFT.
In (A) of FIG. 14, the transmission resource management unit 23 inputs
the parameters (CAZAC sequence number, sequence length, amount of cyclic
shift, and frequency offset) that are included in the resource assignment
information received from the base station and that are necessary for
22
CA 02776257 2012-05-02
generating and transmitting pilots to the respective units.
The CAZAC sequence generation unit 11 generates a CAZAC sequence ZCk(n)
having the instructed sequence length Land sequence number k as a pilot,
and the cyclic shift unit 12 performs a cyclic shift of the CAZAC sequence
ZCk(n) by the instructed c sample amount and inputs the obtained sequence
ZCk(n ¨ c) to the DFT unit 13. For
example, for pilot 1 shown in (B) of
FIG. 3, the cyclic shift unit 12 shifts ZCk(n) by just the amount cl to
generate ZCk(n ¨ cl), and for pilot 2, shifts ZCk(n) by just the amount c2
¨ s(k,d,L) to generate ZCk(n ¨ c2 + s(k,d,L)) and inputs the results to the
DFT unit 13. The Nu sized (Nu = DFT unit 13
performs DFT processing
on the input pilot ZCk(n ¨ c) to generate a frequency¨domain pilot DFT{ZCk(n
¨c)}. Based on
the instructed amount of frequency offset, the subcarrier
mapping unit 14 controls the mapping position of the pilot and performs
frequency offset, and the NFFT sized (NFFT = 128) IFFT unit 15 performs IFFT
processing on the input subcarrier components and converts the signal to
a time¨domain signal, then inputs that signal to the frame generation unit
26.
In FIG. 14, (B) shows the construction of a pilot generation unit 25
for the case in which cyclic shift is performed after IFFT, where by
performing cyclic shift an amount of c x NFFT/Nu samples, the cyclic shift
unit 12 is able to obtain the same result as in the case shown in (A) of
FIG. 14.
[0028]
(C) Base Station
FIG. 15 is a drawing showing the construction of a base station.
When uplink transmission data is generated, a mobile station (user
terminal) executes a procedure for establishing a communication link with
the base station, and in this procedure transmits the condition of the
propagation path to the base station. In other
words, the mobile station
receives a common pilot that was transmitted from the base station and
performs radio measurement (SIR or SNR measurement), then reports the
results of that radio measurement to the base station as the condition of
23
CA 02776257 2012-05-02
the propagation path. For
example, the base station divides the
transmission band into a plurality of transmission frequency bands, and
transmits common pilots for each transmission frequency band, then the
mobile station performs radio measurement for each transmission frequency
band and sends the measurement result to the base station. After
receiving
a resource assignment request, together with obtaining the condition of
the propagation path from the mobile station, the base station assigns
resources based on the propagation path condition from the mobile station,
and sends resource assignment information to the mobile station.
The radio communication unit 31 converts a radio signal that is
received from the mobile station to a baseband signal, a separation unit
32 separates out the data/control information and the pilots, then inputs
the data/control information to the data processing unit 33, and inputs
the pilots to the channel estimation unit 34. The data
processing unit
33 and channel estimation unit 34 comprise the frequency equalization
construction shown in FIG. 24.
The data processing unit 33 demodulates the propagation path condition
information that was transmitted from the mobile station at the time the
communication link was established, and inputs that information to the
uplink resource management unit 35. The uplink
resource management unit
35 assigns resources based on the propagation path condition, then creates
resource assignment information and inputs that information to the downlink
signal baseband processing unit 36. In addition
to the transmission
frequency band, timing, modulation method and the like of the data, the
resource assignment information includes the sequence number k and sequence
length L of the CAZAC sequence that is used as a pilot, the amount of cyclic
shift, the amount of frequency offset d, etc. The
downlink signal baseband
processing unit 36 performs time¨division multiplexing of the data, control
information and resource assignment information, and transmits the
resulting signal from the radio communication unit 31.
After receiving the resource assignment information, the mobile
station performs processing as explained in FIG. 13 and FIG. 14, and
24
CA 02776257 2012-05-02
transmits a frame comprising data and pilots.
The channel estimation unit 34 uses the pilots that were separated
out and input by the separation unit 32 to perform a first channel estimation
process as was explained using FIG. 6, then inputs the channel estimation
values to the data processing unit 33. The data
processing unit 33 performs
channel compensation based on the channel estimation values, and based on
the channel compensation results, demodulates the data. The uplink
resource management unit 35 comprises a cyclic shift amount calculation
unit 35a and a link assignment information instruction unit 35b.
[0029]
FIG. 16 is a drawing showing the construction of the channel estimation
unit 34, where the same reference numbers are given to parts that are the
same as those shown in FIG. 6.
The OFT unit 51 performs DFT processing on a pilot signal that is input
from the separation unit and converts the signal to a frequency¨domain pilot
signal (subcarrier components pl to p12). The
subcarrier addition unit
52 adds subcarrier components p12 and pl that do not overlap each other,
and designates the addition result as the new subcarrier component pl of
subcarrier frequency fl.
The replica signal multiplication unit 53 multiplies the replica
signals qi of the pilot with the received pilot signals pi for each
subcarrier, and the IOFT unit 54 performs IDFT processing on the replica
multiplication result to output a time¨domain pilot signal. The profile
extraction unit 55 separates out the IOFT output signal at t = (cl + c2)/2,
and when the signal is a signal received from user 1, selects profile PRF1
(see FIG. 6), then the OFT unit 56 performs OFT processing on that profile
=
PRF1 and outputs channel estimation values hl to h11. On the other hand,
when the signal is a'signal received from user 2, the profile extraction
unit 55 selects profile PRF2, then the OFT unit 56 performs OFT processing
on that profile PRF2 and outputs channel estimation values h2 to h12.
[0030]
(D) Second Pilot Generation Unit and Channel estimation Unit
CA 02776257 2012-05-02
(A) of FIG. 17 is a drawing showing the construction of a pilot
generation unit that performs the second pilot generation process that was
explained using FIG. 7, where the same reference numbers are given to parts
that are the same as those of the pilot generation unit shown in (A) of
FIG. 14. This pilot
generation unit differs in that two operations,
subcarrier mapping performed by the subcarrier mapping unit 14 based on
the amount of frequency offset d, and copying of pilot components of
specified subcarriers, are performed; the other operation is the same.
The CAZAC sequence generation unit 11 generates a CAZAC sequence ZCk(n)
having an instructed sequence length L and sequence number k as a pilot,
and the cyclic shift unit 12 performs a cyclic shift of the CAZAC sequence
ZCk(n) a specified amount of c samples, then inputs the obtained sequence
ZCk(n ¨ c) to the DFT unit 13. .For example, in the case of pilot 1 for user
1 as shown in (13) of FIG. 7, the cyclic shift unit 12 shifts ZCk(n) by the
amount cl to generate ZCk(n ¨ cl), and in the case of pilot 2 for user 2,
the cyclic shift unit 12 shifts ZCk(n) by the amount c2 ¨ s(k,d,L) to generate
ZCk(n ¨ c2 s(k,d,L)), and inputs the results to the DFT unit 13. The Nu
sized (Nn = DFT unit 13
performs DFT processing on the pilot ZCk(n ¨ c)
to generate a frequency¨domain pilot DFT{ZCk(n ¨ c)}.
The subcarrier mapping unit 14 performs subcarrier mapping based on
copy information and frequency offset information that was specified from
the transmission resource management unit 23. For
example, for pilot 1
of user 1 shown in (6) of FIG. 7, the subcarrier mapping unit 14 performs
the subcarrier mapping process shown in (A) of FIG. 8, and for pilot 2 of
user 2 shown in (C) of FIG. 7, the subcarrier mapping unit 14 performs the
subcarrier mapping shown in (6) of FIG. 8. The NuT
sized (for example, NuT
= 128) 1FFT unit 15 performs IFFT processing on the subcarrier components
that are input to convert the signal to a time¨domain pilot signal, and
inputs the result to the frame generation unit 26.
[0031]
(B) of FIG. 17 is a drawing showing the construction of a channel
estimation unit 34 that performs the second channel estimation process that
26
CA 02776257 2012-05-02
was explained using FIG. 9, where the same reference numbers are given to
parts that are the same as those of the channel estimation unit shown in
FIG. 16. This
channel estimation unit 34 differs in that the subcarrier
addition unit 52 has been eliminated, and there is a predetermined
multiplication process that is performed by a replica signal multiplication
unit 53.
In addition to performing DFT processing on the pilot signal input
from the separation unit 32, the DFT unit 51 converts the signal to a
frequency¨domain pilot signal (subcarrier components pl to p12). In the
case of pilot 1 from user 1, the replica signal multiplication unit 53
multiplies the components pl to pll of the subcarriers f, f,,
f010 of the received pilot that is output from the DFT unit 51 with the
replica signals ql to qll, and in the case of pilot 2 from user 2, multiplies
the components p2 to p12 of the subcarriers f1, "., of the
received pilot that is output from the DFT unit 51 with the replica signals.
After that, the IDFT unit 54 performs IDFT processing on the replica
multiplication result and outputs a time¨domain delay profile. The
profile extraction unit 55 separates out the IDFT output signal at t = (cl
+ c2)/2, and in the case of a pilot signal from user 1, selects profile
PRF1 (see FIG. 6), then the DFT unit 56 performs DFT processing on that
profile PRF1 and outputs the channel estimation values hl to hll. On the
other hand, in the case of a received signal from user 2, the profile
extraction unit 55 selects profile PRF2, then the DFT unit 56 performs DFT
processing on profile PRF2 and outputs the channel estimation values h2
to h12.
[0032]
(E) Third Pilot Generation Unit and Channel Estimation Unit
(A) of FIG. 18 is a drawing showing the construction of a pilot
=
generation unit that performs the third pilot generation process that was
explained using FIG. 11, where the same reference numbers are given to parts
that are the same as those of the pilot generation unit shown in (A) of
FIG. 14. This pilot generation unit differs in that a polarity assignment
27
CA 02776257 2012-05-02
unit 61 has been added; the other operation is the same.
The CAZAC sequence generation unit 11 generates a CAZAC sequence ZCk(n)
having a specified sequence length L and sequence number k as a pilot, and
the cyclic shift unit 12 performs a cyclic shift of the CAZAC sequence ZCk(n)
by a specified amount of c samples, then inputs the obtained sequence ZCk(n
¨ c) to the DFT unit 13. For
example, in the case of pilot 1 for user 1
shown in (B) and (D) of FIG. 11, the cyclic shift unit 12 shifts ZCk(n) by
just the amount cl to generate ZCk(n ¨ cl), and in the case of pilot 2 for
user 2, the cyclic shift unit 12 shifts ZCk(n) by just the amount c2 ¨
s(k,d,L) to generate ZCk(n ¨ c2 + s(k, d, 0), and inputs the result to the
DFT unit 13. An Nn sized
(N-rx = L) DFT unit 13 performs DFT processing on
the input pilot ZCk(n ¨ c) to generate a frequency¨domain pilot DFT {ZCk(n
¨c)}.
The subcarrier mapping unit 14 performs subcarrier mapping based on
frequency offset information specified from the transmission resource
management unit 23. The
polarity attachment unit 61 attaches polarity that
was specified from the transmission resource management unit 23 to the
output from the subcarrier mapping unit 14, and inputs the result to the
IFFT unit 15. For
example, in the case of pilot 1 for user 1, a polarity
of +1 is specified for the first and second pilot blocks (see (B) and (D)
of FIG. 11), and the polarity attachment unit 61 multiplies all of the
carrier components that are output from the subcarrier mapping unit 14 by
+1 and inputs the result to the IFFT unit 15. Also, in
the case of pilot
=
2 for user 2, the polarity of +1 is specified for the first pilot block,
and ¨1 is specified for the second pilot block (see (C) and (E) of FIG.
11), so the polarity attachment unit 61 multiplies all of the carrier
components that are output from the subcarrier mapping unit 14 by +1 for
the first pilot block, and inputs the result to the IFFT unit 15, and by
¨1 for the second pilot block, and inputs the result to the IFFT unit 15.
The NuT sized (NFT= 128) IFFT unit 15 performs IFFT processing on the
input subcarrier components to convert the signal to a time¨domain pilot
signal, then inputs the result to the frame generation unit 26.
28
CA 02776257 2012-05-02
[0033]
(B) of FIG. 18 is a drawing showing the construction of a channel
estimation unit 34 that performs the third channel estimation process that
was explained using FIG. 12, where the same reference numbers are given
to parts that are the same as those of the channel estimation unit shown
in FIG. 16. This
channel estimation unit differs in that an inter¨block
subcarrier addition unit 62 is provided instead of a subcarrier addition
unit 52.
In addition to performing OFT processing on the pilot signal of the
first pilot block that is input from the separation unit 32, the OFT unit
51 converts the signal to a frequency¨domain pilot signal (subcarrier
components pl to p12), and the inter¨block subcarrier addition unit 62 saves
that pilot signal (subcarrier components pl to p12) in an internal memory.
After that, in addition to performing OFT processing on the pilot signal
of the second pilot block that is input from the separation unit 32, the
OFT unit 51 converts the signal to a frequency¨domain pilot signal
(subcarrier components p1 to p12), and inputs that signal to the inter¨block
subcarrier addition unit 62.
When receiving a pilot 1 from user 1, the inter¨block subcarrier
addition unit 62 adds the pilot signal (subcarrier components pl to p12)
of the saved first pilot block and pilot signal (subcarrier components pl
to p12) of second pilot block for each subcarrier. By doing
so, the
multiplexed pilot signal components from another user (for example, user
2) are removed. Moreover,
when receiving a pilot 2 from user 2, the
inter¨block subcarrier addition unit 62 subtracts the pilot signal
(subcarrier components pl to p12) of the second pilot block from the pilot
signal (subcarrier components pl to p12) of the saved first pilot block
for each subcarrier. By doing
so, multiplexed pilot signal components from
another user (for example, user 1) are removed.
When receiving a pilot 1 from user 1, the replica signal multiplication
unit 53 multiplies the components pl to pll of the subcarriers f f
fi+2,
..., fwo of the received pilot that is output from the inter¨block
29
CA 02776257 2012-05-02
subcarrier addition unit 62 with the replica signals ql to q11, and when
receiving a pilot 2 from user 2, multiplies the components p2 to 1312 of
the subcarriers fin, of the
received pilot that is output
from the inter¨block subcarrier addition unit 62 with the replica signals
ql to qll.
After that, the IDFT unit 54 performs IOFT processing on the replica
multiplication results, and outputs a time¨domain pilot signal. The
profile extraction unit 55 separates out the 1DFT output signal at t = (cl
+ c2)/2, and in the case of a pilot signal from user 1, selects profile
PRF1 (see FIG. 6), then the DFT unit 56 performs OFT processing on that
profile PRF1 and outputs the channel estimation values hl to h11. On the
other hand, when the received signal is from user 2, the profile extraction
unit 55 selects profile PRF2, then the DFT unit 56 performs DFT processing
on that profile PRF2 and outputs the channel estimation values h2 to h12.
[0034]
(F) Adaptive Control
As described above the uplink resource management unit 35 of the base
station (see FIG. 15) decides the transmission frequency band for pilots,
the CAZAC sequence number and sequence length L, cyclic shift amount,
frequency offset d, and the like based on the propagation path condition
of the mobile station, and notifies the mobile station. Moreover,
the
uplink resource management unit 35 of the base station also decides the
multiplexing number in a transmission frequency band based on the
propagation path condition of each mobile station.
FIG. 19 is a drawing explaining the frequency assignments when the
multiplexing number is 4, where the first 12 subcarriers are assigned to
user 1, the second 12 subcarriers are assigned to user 2, the third 12
subcarriers are assigned to user 3, and the last 12.subcarriers are assigned
to user 4, and a CAZAC sequence ZC,(n) having a sequence length L = 19 is
used as the pilot for each user by changing the amount of cyclic shift.
[0035]
The frequency offset of a pilot is decided such that the data
CA 02776257 2012-05-02
transmission band for each user is covered by the pilot transmission band
as much as possible. The cyclic
shift unit 35a (see FIG. 15) calculates
the amount of cyclic shift for each user according to the following
equation.
c, = c ¨ s(k,d,L) (9)
Here, i and p express the data transmission band number and user number,
respectively. Also,
s(k,d,L) is the amount of cyclic shift for a sequence
number k, sequence length Land frequency offset d, having the relationship
given by the following equation.
k = s(k,d,L) d(modL) (10)
Here, cp for the pth user can be calculated by the following equation, for
example.
cp = (p ¨1) x[L I Pi p=1,2õP (11)
P expresses the number of pilots (number of users) that are multiplexed
by cyclic shift. In the case
shown in FIG. 19, the amounts of cyclic shift
cl to c4 for user 1 to user 4 become as shown below.
ci = 0
c2 = [L/4]
c3 = [2 = L/4] ¨ s (k, d,
c4 = [3 - L/4] ¨ s(k,d,L)
[0036]
Incidentally, depending on the reception method for receiving pilot
signals, the channel estimation characteristics on both ends of the pilot
transmission band may be poor, and the channel estimation characteristics
=
of the middle portion may be good. In other
words, in the transmission =
band for subcarriers 1 to 12 and 37 to 48 in FIG. 19, the channel estimation
accuracy may be poor, and in the transmission band for subcarriers 13 to
24 and 25 to 36, the channel estimation accuracy may be good.
Therefore, the middle of the transmission band for subcarriers 13 to
31
CA 02776257 2012-05-02
24 and 25 to 36 is assigned for users having a poor propagation path
condition, and both ends of the transmission band for the subcarriers 1
to 12 and 37 to 48 are assigned to users having a good propagation path
condition. By doing
so, there are no users for which the channel estimation
accuracy is extremely poor. FIG. 19
shows an example of assigning user
2 and user 3 to the middle transmission band.
Moreover, as shown in FIG. 20 and FIG. 21, it is possible to perform
control (hopping control) so that the transmission band assigned to the
users changes for each frame. FIG. 20 is
a drawing explaining the
assignment for an odd number frame, and FIG. 21 is a drawing explaining
the assignment for an even number frame.
As shown in FIG. 20, for an odd number frame, the subcarriers 1 to
12 and 37 to 48 on both ends are assigned to user 1 and user 4, and the
middle subcarriers 13 to 24 and 25 to 36 are assigned to user 2 and user
3. Also, as
shown in FIG. 21, for an even number frame, the middle
subcarriers 13 to 24 and 25 to 36 are assigned to user 4 and user 1, and
the subcarriers 1 to 12 and 37 to 48 on both ends are assigned to user 3
and user 2. A frequency
offset is applied to the pilots of user 3 and user
4 for an odd number frame, and a frequency offset is applied to the pilots
of user 1 and user 2 for an even number frame. By doing
so, there are no
users for which the channel estimation accuracy is extremely poor.
[0037]
FIG. 22 is a drawing showing the construction of a pilot generation
unit when hopping control is performed, where the same reference numbers
are given to parts that are the same as those of the pilot generation unit
shown in (A) of FIG. 14. This pilot generation unit differs in that a
frequency offset switching control unit 71 has been added; the other
operation is the same.
The CAZAC sequence generation unit 11 generates a CAZAC sequence ZCk(n)
having a specified sequence length L and sequence number k as a pilot, and
a cyclic shift unit 12 performs a cyclic shift of the CAZAC sequence ZCk(n)
by a specified amount of c samples, then inputs the obtained sequence ZCk(n
CA 02776257 2012-05-02
- 0 to the DFT unit 13. The Nu sized (Nu = DFT unit 13
performs DFT
processing on the input pilot ZCk(n ¨ c) to generate a frequency¨domain pilot
DFT{ZCk(n ¨ c)}. The
frequency offset switching control unit 71 decides
whether or not to perform frequency offset based on the amount of frequency
offset d and the hopping pattern specified from the transmission resource
management unit 23. The
subcarrier mapping unit 14 performs subcarrier
mapping according to whether or not frequency offset is performed. The
NuT sized (NFFT = 128) IFFT unit 15 performs IDFT processing on the input
subcarrier components to convert the signal to a time¨domain pilot signal,
and inputs the result to the frame generation unit 26.
[0038]
-Effect of the Invention
With the present invention described above, it is possible to perform
channel estimation of data transmission subcarriers that deviate from the
pilot transmission frequency band with good accuracy.
In addition, with the present invention, it is possible to perform
channel estimation of data transmission subcarriers that are assigned to
users even when cyclic shifting of differing amounts is performed on a
specified sequence (for example the CAZAC sequence ZCk(n)) as the pilot for
users that will be multiplexed.
Moreover, with the present invention, it is possible to perform
channel estimation by separating out the pilots of each user by a simple
method, even when cyclic shifting of differing amounts is performed on a
specified sequence as the pilot for users that will be multiplexed.
Furthermore, with the present invention, by assigning the middle
portion of the pilot transmission band to users whose propagation path
condition is poor, it is possible to improve the accuracy of channel
estimation of data transmission subcarriers of a user, even though the
propagation path condition of that user is poor.
Also, with the present invention, by performing hopping of the data
transmission bands assigned to users between the middle portion and end
portions of the pilot transmission band, it is possible to improve the
33
CA 02776257 2012-05-02
accuracy of channel estimation of data transmission subcarriers of a user,
even though the propagation path condition of that user is poor.
34
