U.S. patent application number 14/831025 was filed with the patent office on 2015-12-10 for frequency correction circuit, radio receiving apparatus, and frequency correction method.
This patent application is currently assigned to Renesas Electronics Corporation. The applicant listed for this patent is Renesas Electronics Corporation. Invention is credited to Junya TSUCHIDA.
Application Number | 20150358048 14/831025 |
Document ID | / |
Family ID | 47090236 |
Filed Date | 2015-12-10 |
United States Patent
Application |
20150358048 |
Kind Code |
A1 |
TSUCHIDA; Junya |
December 10, 2015 |
FREQUENCY CORRECTION CIRCUIT, RADIO RECEIVING APPARATUS, AND
FREQUENCY CORRECTION METHOD
Abstract
A frequency correction circuit used in a radio receiving
apparatus that receives a preamble signal through one frequency
band and also detects a periodic symbol timing in a receiving
period of a part of a symbol that composes the preamble signal, the
frequency correction circuit includes a generating unit that
generates a detection window of a predetermined time width
including each of a first symbol timing and a second symbol timing
in the receiving period of a remaining symbol that composes the
preamble signal, the first and the second symbol timing being
previously determined among periodic symbol timings, a detecting
unit that sequentially receives a correlation value between the
preamble signal and a reference signal and detects a maximum value
from the correlation value input during a period when the detection
window is opened, and a correction unit that corrects a frequency
deviation of the one frequency band.
Inventors: |
TSUCHIDA; Junya; (Tokyo,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Renesas Electronics Corporation |
Tokyo |
|
JP |
|
|
Assignee: |
Renesas Electronics
Corporation
|
Family ID: |
47090236 |
Appl. No.: |
14/831025 |
Filed: |
August 20, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13460683 |
Apr 30, 2012 |
9124451 |
|
|
14831025 |
|
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Current U.S.
Class: |
375/137 |
Current CPC
Class: |
H04L 2027/0046 20130101;
H04B 1/7156 20130101; H04L 7/0029 20130101; H04B 2201/713 20130101;
H04L 2027/003 20130101; H04L 27/2663 20130101; H04B 2001/71563
20130101; H04L 27/0014 20130101 |
International
Class: |
H04B 1/7156 20060101
H04B001/7156; H04L 27/26 20060101 H04L027/26 |
Foreign Application Data
Date |
Code |
Application Number |
May 2, 2011 |
JP |
2011-102837 |
Claims
1. A frequency correction circuit used in a radio receiving
apparatus that receives a preamble signal through one frequency
band and further detects a periodic symbol timing in a receiving
period of a part of a symbol that composes the preamble signal, the
frequency correction circuit comprising: a generating unit that
generates a detection window of a predetermined time width
including each of a first symbol timing and a second symbol timing
in the receiving period of a remaining symbol that composes the
preamble signal, the first symbol timing and the second symbol
timing being previously determined among periodic symbol timings; a
detecting unit that sequentially receives a correlation value
between the preamble signal and a reference signal, and detects a
maximum value from the correlation value input during a period when
the detection window is opened; and a correction unit that corrects
a frequency deviation of the one frequency band based on the
maximum value.
2. The frequency correction circuit according to claim 1, wherein,
when the radio receiving apparatus receives the preamble signal
through the one frequency band and another frequency band in
accordance with a predetermined hopping sequence: the generating
unit determines the first symbol timing and the second symbol
timing for each frequency band and generates the detection window;
and the correction unit corrects the frequency deviation of each
frequency band based on the maximum value detected for each
frequency band.
3. The frequency correction circuit according to claim 1, wherein
the generating unit uses as the first symbol timing and the second
symbol timing, a symbol timing that comes after the receiving
period of a predetermined number of signals has elapsed since the
receiving period of the remaining symbol started.
4. The frequency correction circuit according to claim 1, wherein
the generating unit: sets the time width depending on a period
length in which a delay wave could exist in a radio transmission
line; and opens the detection window before a time that is obtained
by multiplying the time width by a coefficient
.alpha.(0<.alpha.<1) from each of the first symbol timing and
the second symbol timing.
5. The frequency correction circuit according to claim 1, wherein
the generating unit uses an adjacent symbol timing on a time axis
as the first and the second symbol timing.
6. A radio receiving apparatus, comprising: the frequency
correction circuit according to claim 1; a circuit that receives
the preamble signal; a circuit that obtains the correlation value
from the preamble signal and the reference signal and outputs the
correlation value to the frequency correction circuit; and a
circuit that detects the symbol timing using the correlation value
and outputs the symbol timing to the frequency correction
circuit.
7. A frequency correction method in a radio receiving apparatus
that receives a preamble signal through one frequency band and also
detects a periodic symbol timing in a receiving period of a part of
a symbol that composes the preamble signal, the frequency
correction method comprising: detecting a maximum value from a
correlation value between the preamble signal and a reference
signal obtained within a predetermined time including each of a
first symbol timing and a second symbol timing in the receiving
period of a remaining symbol that composes the preamble signal, the
first symbol timing and the second symbol timing being previously
determined among periodic symbol timings; and correcting a
frequency deviation of the one frequency band based on the maximum
value.
8. The frequency correction method according to claim 7, wherein,
when the preamble signal is received through the one frequency band
and another frequency band in accordance with a predetermined
hopping sequence, wherein the first symbol timing and the second
symbol timing are determined for each frequency band and a
detection window is generated, and wherein the frequency deviation
of each frequency band is corrected based on the maximum value
detected for each frequency band.
9. The frequency correction method according to claim 7, wherein a
symbol timing that comes after the receiving period of a
predetermined number of symbols has elapsed since the receiving
period of the remaining symbol started is used as the first and the
second symbol timing.
10. The frequency correction method according to claim 7, wherein a
time width is set depending on a period length in which a delayed
wave could exist in a radio transmission line, and wherein the
detection window is opened before a time obtained by multiplying
the time width by a coefficient .alpha.(0<.alpha.<1) from
each of the first and the second symbol timing.
11. The frequency correction method according to claim 7, wherein
an adjacent symbol timing on a time axis is used as the first
symbol timing and the second symbol timing.
Description
[0001] The present application is a Divisional application of U.S.
patent application Ser. No. 13/460,683, filed on. Apr. 30, 2012,
which is based on and claims priority from Japanese patent
application No. 2011-102837, filed on May 2, 2011, the entire
contents of which are incorporated herein by reference.
BACKGROUND
[0002] The present invention relates to a frequency correction
circuit, a radio receiving apparatus, and a frequency correction
method, and particularly to a technique for referring to a
correlation value of a preamble signal and correcting a frequency
offset (frequency deviation) between transmission and
reception.
[0003] In the field of wireless communication such as mobile phones
and wireless LAN (Local Area Network), a receiving apparatus
generally detects a periodic symbol timing by carrier sense at the
time of starting the reception and also performs subsequent
receiving operations according to the detected symbol timing. The
receiving apparatus here detects the symbol timing using a preamble
signal for synchronous acquisition transmitted in advance of a data
signal.
[0004] As an example of the communication system that adopts such a
preamble signal, Standard ECMA-368, "High Rate Ultra Wideband PHY
and MAC Standard", 3rd Edition, December, 2008 discloses the
MB-OFDM (Multiband-Orthogonal Frequency Division Multiplex) system.
In order to realize low transmission power and broadband
communication which are the characteristics of the UWB (Ultra Wide
Band) communication, the MB-OFDM system adopts frequency hopping
that performs transmission and reception while hopping among a
plurality of frequency bands. The frequency hopping is one of the
spread spectrum systems, and is a method for communication by
specifying a rule called a hopping sequence between the
transmitting side and the receiving side and switching a frequency
of a carrier by predetermined time within a certain communication
band according to the hopping sequence. In the MB-OFDM system, the
preamble signal is also transmitted by the frequency hopping.
[0005] FIG. 9 shows a transmission example of the preamble signal
in the MB-OFDM system.
[0006] The preamble signal is composed of 24 symbols S0 to S23 and
transmitted through hopping three frequency bands f1 to f3. The
receiving side synchronizes a receiving band with the frequency
hopping in accordance with the hopping sequence, and thereby
receiving and demodulating the symbols S0 to S23, which are
dispersedly transmitted to the frequency bands f1 to f3. At the
time of synchronizing, the hopping preamble signal must be surely
detected. Therefore, the receiving side fixes the receiving band to
a waiting band (the frequency band f1 in the example of FIG. 9),
establishes symbol timing synchronization in the receiving period
of a part of the symbols (the symbols S0 to S4 in the example of
FIG. 9), and thereby detecting the preamble signal (hopping
synchronization). After the preamble signal is detected, the
frequency hopping is started, and in the receiving period of the
remaining symbols (the symbols S5 to S23 in the example of FIG. 9),
initial acquisition operations such as AGC (Automatic Gain
Control), AFC (Automatic Frequency Control), and frame
synchronization, are performed.
[0007] As described above, the symbol timing synchronization fixes
the receiving band to one frequency band and is performed before
AGC. Therefore, the detected symbol timing is not necessarily
optimal for the received signal after AGC. In other words, the
symbol timing synchronization is coarse timing synchronization.
Therefore, after the symbol timing is adjusted in the operation
period of AGC, it is usually necessary to perform processes such as
AFC.
[0008] Japanese Unexamined Patent Application Publication No.
2007-19985 discloses such an adjusting method of the symbol timing.
This adjusting method is to detect a difference between a peak
position of a cross-correlation value and an expected value
determined from a hopping timing while performing the frequency
hopping and adjust the hopping timing to match the peak position of
the cross-correlation value and the expected position. Since the
hopping timing can be uniquely determined when the differences
between the peak position and the expected position match in all
the frequency bands, the symbol timing is used in common among the
frequency bands. On the other hand, under the situation where the
peak positions differ among the frequency bands, processes such as
averaging and weighting are performed, and thereby compulsorily
determining one symbol timing.
[0009] Note that as a related technique, Japanese Unexamined Patent
Application Publication No. 2008-48239 discloses a technique to
detect the symbol timing more accurately. Further, Japanese
Unexamined Patent Application Publication No. 2006-74276 discloses
the technique to reduce the power consumption at the time of
detecting the symbol timing.
[0010] On the other hand, Japanese Unexamined Patent Application
Publication No. 2009-141634 (Yasukawa) discloses a radio receiving
apparatus that performs AFC. A configuration of the radio receiving
apparatus 1x disclosed by Yasukawa is shown in FIG. 10.
[0011] The radio receiving apparatus 1x includes an RF (Radio
Frequency) unit 10, an A/D (Analog to Digital) converting unit 20,
a matched filter 30, an evaluating unit 40, a frequency correction
circuit 50x, and a complex multiplier 60.
[0012] In the operation, the RF unit 10 receives a radio signal via
an antenna in the state in which the receiving band is fixed to the
waiting frequency band and converts the received signal into a
complex baseband signal (I and Q signals). The A/D converting unit
20 includes an A/D converter to convert these complex baseband
signals into digital signals. The matched filter 30 calculates a
complex correlation value 401 from the digital signal output from
the A/D converting unit 20 and the previously stored reference
signal (known preamble signal pattern), and outputs the complex
correlation value 401 to the evaluating unit 40.
[0013] The evaluating unit 40 detects a peak of the correlation
value 401 and detects a detection timing thereof as a symbol timing
402. Then, the evaluating unit 40 repeatedly outputs the symbol
timing 402 at a symbol period. In the MB-OFDM system, the symbol
period is "165T" period as shown in FIG. 9. The period of "1/165
MHz" is indicated by 1T.
[0014] Further, when the symbol timing 402 is detected, the RF unit
10 starts the frequency hopping to the receiving band.
[0015] Furthermore, the frequency correction circuit 50x generates
a frequency correction signal 403 according to the complex
correlation value 401.
[0016] Specifically, the frequency correction circuit 50x is
configured as shown in FIG. 11. The frequency correction circuit
50x includes "d" frequency offset detection circuits 310_1 to
310.sub.--d that are provided to correspond to the periods (d
sample periods) in which a delayed wave could exist in the radio
transmission line, an arctangent operator 320, an NCO (Numerically
Controlled Oscillator) 350, an averaging unit 360, and "d-1" delay
circuits 370_1 to 370.sub.--d-1.
[0017] Additionally, each of the frequency offset detection
circuits 310_1 to 310.sub.--d includes an n-symbol delay circuit
311, a complex conjugate operator 312, and a complex multiplier
313.
[0018] In the operation, the complex correlation value 401 from the
matched filter 30 is input to the frequency offset detection
circuit 310_1 as it is. On the other hand, the correlation value
401 is delayed by one sample period and input by the delay circuits
370_1 to 370.sub.--d-1 to the frequency offset detection circuits
310_2 to 310.sub.--d.
[0019] The n-symbol delay circuit 311 inside each frequency offset
detection circuit 310_1 to 310.sub.--d delays the input complex
correlation value 401 by the time equivalent to n symbols (n="3" in
the example of FIG. 9). The complex conjugate operator 312 performs
a complex conjugate operation to the correlation value delayed by
the n-symbol delay circuit 311.
[0020] The complex multiplier 313 performs complex multiplication
to the complex correlation value input from the matched filter 30
and the complex conjugate operation result output from the complex
conjugate operator 312. In other words, the complex multiplier 313
multiplies the correlation value corresponding to a current
receiving symbol and a complex conjugate of the correlation value
of n symbol before the current receiving symbol (the correlation
value corresponding to the previous receiving symbol in the same
receiving band).
[0021] Then, the averaging unit 360 calculates an average of the
complex multiplication result respectively output from the
frequency offset detection circuits 310_1 to 310.sub.--d. Further,
the arctangent operator 320 performs an arctangent operation to the
average result output from the averaging unit 360, and thereby
obtaining a frequency offset. Moreover, the NCO 350 generates the
frequency correction signal 403 for canceling the frequency offset
output from the arctangent operator 320, and the above complex
multiplier performs the complex multiplication
[0022] Accordingly, even when the symbol timing and the peak
position of the correlation value shift as a result of AGC, the
frequency offset between transmission and reception can be
corrected.
[0023] In the MB-OFDM system in recent years, along with the
expansion of the available carrier frequency bands, communication
in high frequency bands in 6 GHz to 10 GHz is required in addition
to the conventional 3 GHz to 4 GHz frequency bands. When the
carrier frequency is increased, there is a problem that the
propagation loss of the radio wave increases and the communication
distance is reduced. Therefore, an improvement in the minimum
receiving sensitivity in the radio receiving apparatus is
desired.
[0024] On the other hand, with the cost-cutting demand in the
market by the widespread use of mobile communication devices, cost
reduction for LSI (Large Scale Integration) mounted on the radio
receiving apparatus is also desired.
SUMMARY
[0025] However, the present inventor has found a problem in the
technique disclosed by Yasukawa that while the frequency offset can
be corrected when the symbol timing and the peak position of the
correlation value differ, the size of the frequency correction
circuit (in other words, the development cost) increases. The
reason is because it is necessary to mount the abovementioned
frequency offset detection circuit for the number corresponding to
the period when the delayed wave could exist. Note that this
problem is generated regardless of whether or not the frequency
hopping is adopted.
[0026] An embodiment of the present invention is a radio receiving
apparatus that receives a preamble signal through one frequency
band and also detects a periodic symbol timing in a receiving
period of a part of a symbol that composes the preamble signal. A
frequency correction circuit includes a generating unit, a
detecting unit, and a correction unit. The generating unit
generates a detection window of a predetermined time width
including each of a first and a second symbol timing that are
previously determined among the periodic symbol timings in the
receiving period of a remaining symbol that composes the preamble
signal. The detecting unit sequentially receives a correlation
value between the preamble signal and a reference signal and
detects a maximum value from the correlation value input during a
period when the detection window is opened. The correction unit
corrects a frequency deviation of the one frequency band based on
the maximum value.
[0027] Accordingly, in the present invention, a simple
configuration using a detection window surely detects the
correlation peak value that can appear in the certain period before
and after the symbol timing and contributes to the correction of
the frequency offset. Therefore, the frequency offset can be
corrected even when the symbol timing and the peak position of the
correlation value differ.
[0028] The present invention can improve the correction accuracy of
the frequency offset while suppressing the increase in the circuit
size.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] The above and other aspects, advantages and features will be
more apparent from the following description of certain embodiments
taken in conjunction with the accompanying drawings, in which:
[0030] FIG. 1 is a block diagram showing a configuration example of
a frequency correction circuit and a radio receiving apparatus
according to an embodiment of the present invention;
[0031] FIG. 2 is a block diagram showing a configuration example of
a detection window generating unit used in the frequency correction
circuit according to the embodiment of the present invention;
[0032] FIG. 3 is a block diagram showing a configuration example of
a frequency correction unit used in the frequency correction
circuit according to the embodiment of the present invention;
[0033] FIG. 4 is a time chart showing an overall operation example
of the frequency correction circuit and the radio receiving
apparatus according to the embodiment of the present invention;
[0034] FIG. 5 is a flowchart showing an overall operation example
of a controlling unit used in the frequency correction circuit
according to the embodiment of the present invention;
[0035] FIG. 6 is a flowchart showing an operation example of a
timing counter used in the frequency correction circuit according
to the embodiment of the present invention;
[0036] FIG. 7 is a flowchart showing an operation example of a
symbol counter used in the frequency correction circuit according
to the embodiment of the present invention;
[0037] FIG. 8 is a flowchart showing a generation process example
of a detection window in the controlling unit used in the frequency
correction circuit according to the embodiment of the present
invention;
[0038] FIG. 9 is a time chart showing a transmission example of a
preamble signal in the MB-OFDM system;
[0039] FIG. 10 is a block diagram showing a configuration example
of a general radio receiving apparatus; and
[0040] FIG. 11 is a block diagram showing a configuration example
of a general frequency correction circuit.
DETAILED DESCRIPTION
[0041] Hereinafter, an embodiment of the present invention of a
frequency correction circuit, and a radio receiving apparatus and a
communication apparatus to which the frequency correction circuit
is applied, is explained with reference to FIGS. 1 to 8. Note that
the same components are denoted by the same reference numeral in
each drawing, and the duplicate explanation is omitted as necessary
for the clarity of the explanation.
[0042] Note that in this embodiment, the case in which the MB-OFDM
system (in other words, the frequency hopping) is adopted as a
communication system is explained as an example. However, the
present invention can also be applied to other communication
systems that do not perform the frequency hopping.
[0043] As shown in FIG. 1, a radio receiving apparatus 1 according
to this embodiment composes a part of a communication apparatus,
and includes an RF unit 10, an A/D converter 20, a matched filter
30, an evaluating unit 40, and a complex multiplier 60, which are
similar to those in FIG. 10. Further, the radio receiving apparatus
1 includes a frequency correction circuit 50 according to this
embodiment in place of the frequency correction circuit 50x shown
in FIGS. 10 and 11. Although not illustrated, the radio receiving
apparatus 1 includes a circuit and the like for performing AGC.
[0044] The frequency correction circuit 50 includes a detection
window generating unit 100, a maximum value detecting unit 200, and
a frequency correction unit 300.
[0045] Among these units, a first input of the symbol timing 402
from the evaluating unit 40 triggers the detection window
generating unit 100 to operate and generate the detection window
411. The detection window 411 here is opened for predetermined time
in the period including each of the two symbol timings determined
for the frequency band.
[0046] Specifically, as shown in FIG. 2, the detection window
generating unit 100 includes a timing counter 110, a symbol counter
120, and a controlling unit 130. The symbol timing 402 is input in
common to these timing counter 110, the symbol counter 120, and the
controlling unit 130.
[0047] The timing counter 110 operates according to an enable
signal 421 from the controlling unit 130 and outputs a timing count
value 422 to the controlling unit 130. The timing count value 422
here is used to count the abovementioned symbol period "165T" by 1T
and repeatedly presents values of 0T to 164T.
[0048] The symbol counter 120 operates according to the enable
signal 421 from the controlling unit 130 and outputs the symbol
count value 423 to the controlling unit 130. The symbol count value
425 here is incremented every time the symbol timing 402 is
input.
[0049] A first input of the symbol timing 402 triggers the
controlling unit 130 to generate the enable signal 421, so as to
operate the timing counter 110 and the symbol counter 120.
Moreover, the controlling unit 130 monitors the timing count value
422 and the symbol count value 423, and executes the generation
process of the detection window 411 as described later.
[0050] Turning back to FIG. 1, the complex correlation values 401
from the matched filter 30 are sequentially input to the maximum
value detecting unit 200. The maximum value detecting unit 200
detects a maximum value 412 (hereinafter may be referred to as a
maximum correlation value) from the correlation values input during
the period when the detection window 411 is opened.
[0051] Further, the frequency correction unit 300 recognizes the
receiving band in the RF unit 10 according to a receiving band
indication signal 404 output from the RF unit 10. Furthermore, the
frequency correction unit 300 generates the frequency correction
signal 403 according to the maximum correlation value 412, and the
complex multiplier 60 performs complex multiplication of the
received signal and the frequency correction signal 403.
[0052] Specifically, as shown in FIG. 3, the frequency correction
unit 300 includes one frequency offset detection circuit 310, an
arctangent operator 320, three holding units 330_1 to 330_3, a
selecting unit 340, and an NCO 350.
[0053] The frequency offset detection circuit 310 includes a set of
an n-symbol delay circuit 311, a complex conjugate operator 312,
and a complex multiplier 313, which are similar to the those in
FIG. 11. Accordingly, the maximum correlation value corresponding
to the current receiving symbol output from the maximum value
detecting unit 200 and the complex conjugate of the maximum
correlation value corresponding to the previous receiving symbol in
the same receiving band are input to the complex multiplier
313.
[0054] The arctangent operator 320 performs the arctangent
operation and the like to the complex multiplication result output
from the complex multiplier 313, and thereby obtaining a frequency
offset if. More specifically, the arctangent operator 320
calculates the frequency offset .DELTA.f by the following formula
(1).
.DELTA.f=arg(A/B)/(C*165)[rad/T] formula (1)
[0055] In the above formula (1), A is the maximum correlation value
corresponding to the current receiving symbol, and B is the maximum
correlation value corresponding to the previous receiving symbol in
the same receiving band. Further, C differs depending on the value
of TFC (Time Frequency Code, a code for specifying the hopping
order). In the case of TFC1 (the receiving bands are switched in
the order of f1.fwdarw.f2.fwdarw.f3.fwdarw.f1.fwdarw. . . . as
shown in FIG. 9) or TFC2 (the receiving bands are switched in the
order of f1.fwdarw.f3.fwdarw.f2.fwdarw.f1.fwdarw. . . . ), C is set
to "3", and in other cases, C is set to "1". Further
arg(z)=arctan(Im(z)/Re(z)). Im(z) is a function to retrieve an
imaginary part of an arbitrary complex number z, and Re(z) is a
function to retrieve a real part of the complex number z.
[0056] Each holding unit 330_1 to 330_3 performs an operation to
hold the frequency offset .DELTA.f according to the receiving band
indication signal 404. More specifically, when the receiving band
indication signal 404 indicates the frequency band f1, the holding
unit 330_1 holds the frequency offset if as a frequency offset
.DELTA.f1 for the frequency band f1. Similarly, the holding unit
330_2 holds the frequency offset .DELTA.f2 for the frequency band
f2, and the holding unit 330_3 holds the frequency offset .DELTA.f3
for the frequency band f3.
[0057] The selecting unit 340 selects any one of the frequency
offsets .DELTA.f1 to .DELTA.f3 output from the holding units 330_1
to 330_3 according to the receiving band indication signal 404, and
outputs the selected frequency offset to the NCO 350. More
specifically, when the receiving band indication signal 404
indicates the frequency band f1, the selecting unit 340 selects the
frequency offset .DELTA.f1. Similarly, the selecting unit 340
selects the frequency offset .DELTA.f2 when the receiving band
indication signal 404 indicates the frequency band f2, and selects
the frequency offset .DELTA.f3 when the receiving band indication
signal 404 indicates the frequency band f3.
[0058] Then, the frequency correction signal 403 according to the
switched receiving band is generated in the NCO 350. Note that when
the communication system that does not perform the frequency
hopping is adopted, it is not necessary to install the holding
units 330_1 to 330_3 and the selecting unit 340. In this case, the
NCO 350 generates a unique frequency correction signal 403 using
the frequency offset .DELTA.f output from the arctangent operator
320.
[0059] Next, the operation of this embodiment is explained in
detail with reference to FIGS. 4 to 8. Note that in the following
explanation, an example is explained with a case of TFC3 (the
receiving bands are switched in the order of
f1.fwdarw.f1.fwdarw.f2.fwdarw.f2.fwdarw.f3.fwdarw.f3.fwdarw.f1.fwdarw.f1.-
fwdarw. . . . ).
[0060] In FIG. 4, a parameter N indicates a symbol count value to
start detecting the frequency offset .DELTA.f. A parameter P
indicates the number of symbols for detecting the frequency offset
.DELTA.f. WIN indicates the time width of the detection window 411.
The value of N differs depending on TFC. In the case of TFC1 or
TFC2, N is "14". In the case of TFC3 or TFC4 (the receiving bands
are switched in the order of
f1.fwdarw.f1.fwdarw.f3.fwdarw.f3.fwdarw.f2.fwdarw.f2.fwdarw.f1.fwdarw.f1.-
fwdarw. . . . ), N is "17". In the case of TFC5 to TFC7 (the
receiving bands are respectively fixed to f1 to f3), N is "20". The
value of P differs depending on TFC, and in the case of TFC1 to
TFC4, the value of P is "6" and in the case of TFC5 to TFC7, the
value of P is "2". Note that the operation in the case of adopting
the communication system that does not perform the frequency
hopping is same as the case of TFC5 to TFC7.
[0061] As shown in FIG. 4, in a carrier sensing period, the RF unit
10 fixes the receiving band to the waiting frequency band (f1 in
the example of FIG. 4). Therefore, the complex correlation value
401 output from the matched filter 30 presents a correlation peak
P0 at the boundary of the receiving symbol S0, and presents a
correlation peak P1 at the boundary of the receiving symbol S1. In
response to these correlation peaks P0 and P1, the evaluating unit
40 detects the symbol timing 402 and repeatedly outputs the symbol
timing 402 at the symbol period "165T". Further, the RF unit 10
starts the frequency hopping to the receiving band.
[0062] At this time, the controlling unit 130 in the detection
window generating unit 100 operates as shown in FIG. 5.
Specifically, the controlling unit 130 maintains the enable signal
421 to "0" until the symbol timing 402 is input from the evaluating
unit 40 (steps S11 and S12).
[0063] When the symbol timing 402 is input, the controlling unit
130 outputs the enable signal 421="1" to operate the timing counter
110 and the symbol counter 120 (step S13).
[0064] Then, the controlling unit 130 starts monitoring the timing
count value 422 and the symbol count value 423, and moves to the
generation process of the detection window 411 (step S14).
[0065] On the other hand, the timing counter 110 operates as shown
in FIG. 6. Specifically, the timing counter 110 maintains the
timing count value 422 to "0" until the enable signal 421="1" is
input (steps S21 and S22).
[0066] When the enable signal 421="1" is input, the timing counter
110 repeatedly executes the processes shown in the steps S24 to S25
while the enable signal 421="1" is satisfied (step S23).
[0067] More specifically, the timing counter 110 increments the
timing count value 422 by one every time "1T" elapses until the
symbol timing 402 is input from the evaluating unit 40 (steps S24
and S25).
[0068] When the symbol timing 402 is input, the timing counter 110
resets the timing count value 422 to "0" (step S26).
[0069] Then, the timing count value 422 repeatedly presents the
values of 0T to 164T as shown in FIG. 4.
[0070] Moreover, the symbol counter 120 operates as shown in FIG.
7. Specifically, the symbol counter 120 maintains the symbol count
value 423 to "0" until the enable signal 421="1" is input (steps
S31 and S32).
[0071] When the enable signal 421="1" is input, the symbol counter
120 repeatedly executes the processes shown in the steps S34 and
S35 while the enable signal 421="1" is satisfied (step S33).
[0072] More specifically, the symbol counter 120 waits for the
input of the symbol timing 402 from the evaluating unit 40 (step
S34). When the symbol timing 402 is input, the symbol counter 120
increments the symbol count value 423 by one (step S35).
[0073] Then, the symbol count value 423 synchronizes with the
symbol timing 402 and counted up as shown in FIG. 4.
[0074] Hereinafter, an example of the generation process of the
detection window 411 in the controlling unit 130 is explained in
detail with reference to FIG. 8. In FIG. 8, a parameter WIN
indicates the time width of the detection window 411 and previously
set according to a period length d in which the delayed wave could
exist in the radio transmission line. For example, when the period
length d is "5T", WIN is set to "11T" 2d+1), which is twice the
period length d. A coefficient .alpha.(0<.alpha.<1) is used
to determine a center phase of the detection window 411 (in other
words, a timing to open the detection window 411). INT is a
function to integerize an argument value.
[0075] As shown in FIG. 8, the controlling unit 130 waits for the
symbol count value 423 to reach N ("17" in the example of FIG. 4)
(step S41).
[0076] When the symbol count value 423 reaches N, the controlling
unit 130 repeatedly executes the process shown in the steps S43 to
S48 while the symbol count value 423 is N+P ("23" (17+6) in the
example of FIG. 4) (step S42).
[0077] More specifically, firstly the controlling unit 130
evaluates whether or not the timing count value 422 is greater than
"165T-{WIN-INT(WIN.times..alpha.)}" (in other words, whether or not
the timing to open the detection window 411 has come) (step S43).
When "165T-{WIN-INT(WIN.times..alpha.)}"<the timing count value
422 is satisfied, the controlling unit 130 evaluates that the
timing to open the detection window 411 has come. However, when the
symbol count value 423="N+P" (in other words, the current symbol
timing is the last symbol timing to be detected by the frequency
offset Of) (step S44), the controlling unit 130 evaluates that it
is not the timing to exceptionally open the detection window
411.
[0078] When it is evaluated that the timing to open the detection
window 411 has come in the above steps S43 and S44, the controlling
unit 130 sets the detection window 411 to "1" (high) to open the
detection window 411 (step S45).
[0079] Then, the controlling unit 130 continues to monitor the
timing count value 422 and maintains the detection window 411 to
"1" (opened state) while
"165T-{WIN-INT(WINx.times..alpha.)}"<the timing count value 422
is satisfied. After that, the controlling unit 130 evaluates
whether or not the timing count value 422 is smaller than
"INT(WIN.times..alpha.)" (in other words, whether or not to
maintain the detection window 411 in the opened state when the
timing count value 422 is once reset and counting up is resumed)
(step S46). When "INT(WIN.times..alpha.)">the timing count value
422 is satisfied, the controlling unit 130 evaluates that the
detection window 411 should be maintained in the opened state.
However, when the symbol count value 423="N" (in other words, when
the current symbol timing is the first symbol timing to be detected
by the frequency offset .DELTA.f and the detection window 411 is
not opened yet) (step S47), the controlling unit 130 evaluates that
the detection window 411 should not be exceptionally maintained in
the opened state.
[0080] When it is evaluated that the detection window 411 should be
maintained in the opened state in the abovementioned steps S46 and
S47, the controlling unit 130 proceeds to the above step S45 and
maintains the detection window 411 to "1".
[0081] On the other hand, when it is evaluated that the detection
window 411 should not be maintained in the opened state in the
above step S46 or S47 or it is not the timing to open the detection
window 411 in the above step S44, the controlling unit 130 sets the
detection window 411 to "0" (low) to close the detection window 411
(step S48).
[0082] Note that when the symbol count value 423>"N+P" is
satisfied in the above step S42, the controlling unit 130 outputs
the enable signal 421="0" to stop the operations of the timing
counter 110 and the symbol counter 120 (step S49).
[0083] Then, as shown in FIG. 4, the detection window 411 is opened
for the time equivalent to INT(WIN.times..alpha.) from the symbol
timing corresponding to each of the receiving symbols S18 to S23
and closed after the time equivalent to WIN elapses.
[0084] The maximum value detecting unit 200 detects a correlation
peak from the correlation values input during the period when the
detection window 411 is opened and outputs the correlation peak to
the frequency correction unit 300 as the maximum correlation value
412.
[0085] FIG. 4 shows the case in which as a result of AGC and the
like, in the receiving band f1, the symbol timing 402 and the
positions of the correlation peaks P18 and P19 corresponding to the
receiving symbols 818 and S19 match. As shown in FIG. 4, the
correlation peaks P18 and P19 appear within the period when the
detection window 411 is opened. Therefore, the maximum value
detecting unit 200 can detect the correlation peaks P18 and P19 as
the maximum correlation value 412 corresponding to the receiving
band f1.
[0086] On the other hand, in the receiving band f2, the case is
shown in which the correlation peaks P20 and P21 corresponding to
the receiving symbols S20 and S21 appear after the symbol timing
402. However, as shown in FIG. 4, the correlation peaks P20 and P21
appear within the period when the detection window 411 is opened.
Therefore, the maximum value detecting unit 200 does not miss but
can detect the correlation peaks P20 and P21 as the maximum
correlation value 412 corresponding to the receiving band f2.
[0087] Further, in the receiving band f3, the case is shown in
which the correlation peaks P22 and P23 corresponding to the
receiving symbols S22 and S23 appear before the symbol timing 402.
However, as shown in FIG. 4, the correlation peaks P22 and P23
appear within the period when the detection window 411 is opened.
Therefore, the maximum value detecting unit 200 does not miss but
can detect the correlation peaks P22 and P23 as the maximum
correlation value 412 corresponding to the reception band f3.
[0088] The frequency correction unit 300 detects and holds the
frequency offsets .DELTA.f1 to .DELTA.f3 for the receiving bands f1
to f3 by the above formula (1). Then, the frequency correction unit
300 generates the frequency correction signal 403 according to the
switched receiving band using one of the frequency offsets
.DELTA.f1 to .DELTA.f3 according to the receiving band indication
signal 404.
[0089] As explained above, in this embodiment, it is possible to
surely detect the correlation peak that could appear within the
certain period before and after the symbol timing and to contribute
to the frequency offset correction. Therefore, the frequency offset
can be corrected even when the symbol timing and the peak position
of the correlation value differ. Further, as shown in FIG. 3, only
one frequency offset detection circuit should be mounted while
Japanese Unexamined Patent Application Publication No. 2009-141634
(Yasukawa) requires the frequency offset detection circuits for the
number corresponding to the period in which the delayed wave could
exist. Accordingly, the size of the frequency correction circuit
can be largely reduced as compared to the technique disclosed by
Yasukawa. Thus, this embodiment can achieve both the advantages to
suppress the increase in the circuit size and improve the
correction accuracy of the frequency offset. In addition, as only
one frequency offset detection circuit should be mounted, the
advantage is achieved that the power consumption for the detection
of the frequency offset can be reduced.
[0090] Moreover, this embodiment uses the symbol timing that comes
after a predetermined period has elapsed since when the symbol
timing 402 is detected (specifically, after performing AGC) as the
symbol timing to be detected by the frequency offset .DELTA.f.
Therefore, optimal frequency correction can be performed to the
received signal.
[0091] Additionally, in this embodiment, the time width WIN of the
detection window 411 is set according to the period length d in
which the delayed wave could exist, and the center phase of the
detection window 411 is determined using the coefficient .alpha..
Therefore, the correction accuracy of the frequency offset can be
dynamically changed conforming to the delay characteristics in the
operational environment of the radio receiving apparatus.
[0092] In this embodiment, the adjacent symbol timing on the time
axis in the same receiving band is used as the symbol timing to be
detected by the frequency offset .English Pound.f. In this case, it
is not necessary to provide excessive amount of delay to the above
n-symbol delay circuit 311 and the increase in the size of the
frequency correction circuit can further be suppressed.
[0093] Note that it is clear that the present invention is not
limited by the abovementioned embodiment and various modifications
can be made by those skilled in the art based on the description of
the claims.
[0094] For example, the above maximum correlation value 412 can
contribute to the correction of a phase deviation in each frequency
band (a phase difference between the symbol timing and the
correlation peak). In the example of FIG. 4, in the receiving band
f2, the phase of the symbol timing 402 is proceeded to match the
phase of the correlation peak P20 or P21 detected in the detection
window 411. On the other hand, in the receiving band f3, the phase
of the symbol timing 402 is delayed to match the phase of the
correlation peak P22 or P23 detected in the detection window 411.
As described so far, the present invention can correct the phase
deviation by a simple configuration using the detection window.
[0095] While the invention has been described in terms of several
embodiments, those skilled in the art will recognize that the
invention can be practiced with various modifications within the
spirit and scope of the appended claims and the invention is not
limited to the examples described above.
[0096] Further, the scope of the claims is not limited by the
embodiments described above.
[0097] Furthermore, it is noted that, Applicant's intent is to
encompass equivalents of all claim elements, even if amended later
during prosecution.
* * * * *