Beam formation circuit and an apparatus and a method of receiving radio frequency signals ...

18 Pages·2013·1.63 MB·English

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US 20020085653A1
(19) United States
(12) Patent Application Publication (10) Pub. No.: US 2002/0085653 A1
Matsuoka et al. (43) Pub. Date: Jul. 4, 2002
(54) BEAM FORMATION CIRCUIT AND AN (30) Foreign Application Priority Data
APPARATUS AND A METHOD OF
RECEIVING RADIO FREQUENCY SIGNALS Dec. 22, 2000 (JP) .................................... .. 2000-391221
MAKING USE OF A SMART ANTENNA
Publication Classi?cation
(75) Inventors: Hidehiro Matsuoka, Bristol (GB);
Shuichi ()bayashi, Kanagawa (JP) (51) Int. Cl.7 ..................................................... .. H04L 1/02
(52) US. Cl. .......................................... .. 375/347; 375/349
Correspondence Address:
OBLON SPIVAK MCCLELLAND MAIER &
NEUSTADT PC (57) ABSTRACT
FOURTH FLOOR
1755 JEFFERSON DAVIS HIGHWAY _ _ _
ARLINGTON’ VA 22202 (Us) Abeam formation circuit and an apparatus and a method of
receiving radio frequency signals making use of a smart
(73) Assignee; KABUSHHIKI KAISH A TOSHIBA, antenna are described in Which the amount of computation
Tokyo (JP) tasks required for the Weight calculation is signi?cantly
reduced. In realizing the directivity of the smart antenna, the
(21) Appl, No,: 10/023,712 output signals corresponding to a plurality of sub-carriers
are Weighted With a common antenna Weight for each of the
(22) Filed: Dec. 21, 2001 antenna elements.
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TIMING W2
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US 2002/0085653 A1 Jul. 4, 2002
BEAM FORMATION CIRCUIT AND AN Which includes a predetermined bit sequence While all the
APPARATUS AND A METHOD OF RECEIVING sub-carriers are provided With a predetermined leading
RADIO FREQUENCY SIGNALS MAKING USE OF preamble. FIG. 4 is a graphic diagram shoWing the frequen
A SMART ANTENNA cies of the transmission signals versus time in an exemplary
con?guration of frames. In this example, there are provided
CROSS REFERENCE TO RELATED 52 sub-carriers in all each of Which has a band Width fM and
APPLICATIONS provided With leading short and long preambles. Four pilot
sub-carriers are included therein. One OFDM symbol time
[0001] This application is based upon and claims the is 4 ysec.
bene?t of priority from prior Japanese Patent Application
P2000-391221 ?led on Dec. 22, 2000; the entire contents of [0009] FIG. 2 and FIG. 3 is a schematic block diagram
Which are incorporated by reference herein. shoWing a transmitter apparatus in accordance With a con
ventional technique OFDM system. FIG. 3 is a schematic
block diagram shoWing a receiver apparatus in accordance
BACKGROUND OF THE INVENTION
With a conventional technique OFDM system. These appa
[0002] 1. Field of the Invention ratuses as illustrated respectively in FIG. 2 and FIG. 3 are
used in the Wireless LAN as described above and have been
[0003] The present invention relates generally to a Wire
described in details, for example, in “OFDM for Wireless
less communication system in accordance With Orthogonal
multimedia communications, &QUOT; (Richard Van Nee,
Frequency Division Multiplexing, and particularly to a beam
Ramjee Prasad, Artech House, 2000).
formation circuit and an apparatus and a method of receiving
radio frequency signals making use of a smart antenna a [0010] The processing of the signals by the transmitter
receiver apparatus. apparatus and the receiver apparatus Will be brie?y
explained With reference to FIG. 2 and FIG. 3. At ?rst, in
[0004] 2. Description of the Related Art
the transmitter apparatus as illustrated in FIG. 2, the data
[0005] In recent years, With the high speed advent of the sequences to be transmitted are error corrected and encoded
Wireless communication technique, Wireless terminals have by means of an encoder 601 and then interchanged by means
been used by end users for the purpose of receiving and of an interleaver 602. The output signals of the interleaver
transmitting a large amount of information such as images, 602 are converted into multi-level signals in accordance
other types of data, in addition to voices. It is inevitable for With QAM (quadrature amplitude modulation) by means of
high speed transmission of such a large amount of informa a QAM symbol relocation unit 603 folloWed by inserting
tion to treat Wide bandWidth signals and also to determine pilot signals thereto by means of a pilot signal inserting unit
the measures that could be adopted to cope With signal 604.
fading and interference. On the other hand, OFDM
(Orthogonal Frequency Division Multiplexing) is draWing [0011] Then, the QAM data sequences to be transmitted
are converted into N paralell data items (N: the number of
the attention as a technique of realiZing such Wide band
Width signal communications. sub-carriers) by means of a serial-to-parallel converter (S/P
converter) 605. The parallel data items are converted into
[0006] The OFDM technique is a block-oriented modula signals in the time domain on the basis of the inverse Fourier
tion scheme that maps data symbols onto a plurality of transformation by means of the inverse fast Fourier trans
orthogonal sub-carriers separated by a distance and arranged form unit (IFFT unit) 606 and then converted into serial data
Within a limited bandWidth to provide excellent resistance sequences by means of the parallel-to-serial converter (P/S
characteristics against the interference due to delay spread converter) 607.
through the multipaths. Namely, While the orthogonally
encoded data signals can be generated by means of the [0012] The output signals of the IFFT unit 606 are N
inverse Fourier transformation or the orthogonally decoded sub-carriers as modulated by the corresponding N data items
data signals can be extracted by means of the Fourier as given from the S/P converter 605. The guard interval
transformation, it is possible to provide guard intervals in inserting circuit 608 serves to put a Wave form same as the
order to remove the in?uence of the timely delay Within the tail portion of the effective symbols of the OFDM signal on
guard intervals. Because of this, tolerability of high speed the top of the effective symbols in the serial signals obtained
transmissions to frequency selective fading can be after fast Fourier transformation.
improved.
[0013] The in?uence of the timely delay Within the guard
[0007] OFDM having such features has been expected to interval can be removed by the fast Fourier transformation
be applied not only to the cellular systems and the broadcast at the receiver side. Then, the transmission signals are
services but also applied to Wireless LANs and so forth. converted into analog signals by means of the D/A converter
(DAC) 609, orthogonally modulated, frequency converted,
[0008] For example, Work is being done to formally stan
?ltered, poWer ampli?ed, treated under other necessary
dardiZe the Wireless LAN on the basis of OFDM in Japan,
processes, and then Wireless transmitted through an antenna
Europe and USA. referred to respectively as HiSWANa,
element 611.
HiperLAN and IEEE802.11a. These standards are similar to
each other in the physical layer. Particularly, in Europe, the [0014] It is necessary in this type of OFDM system to cope
standard is applicable not only to the Wireless LAN but also With the interference of delayed signals With delays exceed
to outdoor usages. In accordance With the respective three ing the guard interval length, and the interference in the
standards, there are provided, among from a set of sub same channel by any other cell and any other system making
carriers for transmission of packets, particular sub-carriers use of the same frequency band. The effective use of the
in preselected positions are used as pilot sub-carriers each of frequency resources is inevitable as a measure meant to
US 2002/0085653 A1 Jul. 4, 2002
Work out the frequency tightness problem. It is effective as transformation sections and calculate an antenna Weight of
a solution of the problem to apply the so-called smart each antenna elements corresponding to each of sub-carrier
antenna technology to the OFDM system. groups, each sub-carrier group includes a plurality of the
sub-carriers Whose center frequencies are located in the
[0015] The smart antenna technology is effective for
vicinity of the center frequency of one of pilot sub-carrier;
increasing the system capacity and the coverage area of a
a plurality of Weighting units Which are connected to said
base station and for improving the communication quality
antenna Weight calculation unit and said Fourier transfor
by making use of antenna elements Whose directivity is
mation unit and con?gured to Weight the signals of said
variable for the base station (and the mobile station). In this
sub-carrier groups respectively With the antenna Weights as
case, With a plurality of antenna elements arranged in an
calculated by means of said antenna Weight group calcula
array as illustrated in FIG. 1 rather than a single antenna
tion unit; and an adder circuit Which is connected to said
element having a variable directivity, desired directivity
Weighting units and con?gured to add together the signals of
patterns can be formed by Weighting the amplitude and the
said sub-carrier groups as Weighted With said antenna
phase for the respective antenna element. With this type of
Weights for each of said antenna elements.
such an adaptive array antenna element capable of electri
cally controlling the directivity, it is possible not only to [0019] Another aspect of the present invention provides a
receiver apparatus provided With a smart antenna capable of
direct a peak in an antenna directivity pattern to any desired
adjusting its directivity by making use of a plurality of
direction but also to direct a null to interfering Waves.
Particularly, it is possible to effectively use the frequency antenna elements, said receiver apparatus comprising: a
resources by forming a plurality of antenna directivity plurality of Fourier transformation sections Which are con
nected to said plurality of antenna elements and con?gured
patterns orthogonal to each other (i.e, the null of one pattern
to the peak of another) and assigning the same time slot and to output signals carried on sub-carriers orthogonal to each
other from signals received by each of said antenna ele
the same frequency channel to the respective beams corre
sponding thereto to accomplish the so-called SDMA (Space ments; a plurality of parallel-to-serial conversion sections
Division Multiple Access). Which are connected respectively to said Fourier transfor
mation sections and con?gured to perform parallel-to-serial
[0016] A plurality of tapped-delay-lines (TDL) and a conversion of the signals carried on said sub-carriers as
plurality of Weighting units for the respective antenna ele Fourier transformed in a time division manner; a pilot signal
ments have to be provided for the smart antenna in order to extraction unit Which intermittently extracts signals carried
form appropriate beams carrying Wide bandWidth signals. on pilot sub-carriers having a predetermined center frequen
Also, in the case of the OFDM system capable of separating cies from the output signals of said parallel-to-serial con
signals in the frequency domain, Weighting units provided version section; an antenna Weight calculation unit Which is
for each sub-carrier can be used for implementing an equiva connected to said Fourier transformation sections and said
lent function. In this case, hoWever, a large amount of pilot signal extraction unit and con?gured to calculate an
computation tasks are necessarily required to obtain the antenna Weight of each antenna elements corresponding to
Weights of all the sub-carriers of the OFDM system. For this each of sub-carrier groups by the use of the signals carried
reason, the excessive amounts of processing poWer and on said pilot sub-carriers as extracted by said pilot signal
computation time become obstacles to the operation of the extraction unit, each sub-carrier group includes a plurality of
system, for example, in the case Where voice signal pro the sub-carriers Whose center frequencies are located in the
cessing is required in real time. It becomes in this case vicinity of the center frequency of one of pilot sub-carrier;
therefore necessary to increase the system in circuit siZe or a plurality of Weighting units Which are connected to said
to make use of a high speed DSP or CPU for removing the parallel-to-serial conversion section and said antenna Weight
obstacles. group calculation unit and con?gured to multiply the output
signals of said parallel-to-serial conversion section With said
[0017] Furthermore, since all the sub-carriers are provided
antenna Weights as calculated by said antenna Weight group
With a predetermined bit sequence having a suf?cient length,
calculation unit for each of the sub-carrier groups; and an
the packet ef?ciency tends to be reduced (While this is no the
adder circuit Which is connected to said Weighting units and
case When a blind algorithm is employed). In the case of the
con?gured to add together the signals of said sub-carrier
Wireless communication system as described above making
groups as Weighted With said antenna Weights for each of
use of a short preamble, it is very dif?cult to obtain optimal
said antenna elements.
solutions on the basis of knoWn algorithms.
[0020] A further aspect of the present invention provides
a receiver apparatus provided With a smart antenna capable
BRIEF SUMMARY OF THE INVENTION
of adjusting its directivity by making use of a plurality of
[0018] An aspect of the present invention provides a antenna elements, said receiver apparatus comprising: a
receiver apparatus provided With a smart antenna capable of plurality of Weighting units Which are connected to said
adjusting its directivity by making use of a plurality of antenna Weight calculation unit and said antenna elements
antenna elements, said receiver apparatus comprising: a respectively and con?gured to Weight the signals received
plurality of Fourier transformation sections Which are con by said antenna elements respectively With predetermined
nected to said plurality of antenna elements and con?gured antenna Weights; an adder circuit Which is connected to said
to output signals carried on sub-carriers orthogonal to each Weighting units and con?gured to add together the output
other from signals received by each of said antenna ele signals of said Weighting units; a Fourier transformation
ments; an antenna Weight calculation unit Which is con section Which is connected to said adder circuit and con?g
nected to said Fourier transformation sections and con?g ured to output signals carried on sub-carriers orthogonal to
ured to extract the said signals carried on pilot sub-carriers each other; a pilot signal extraction unit Which is connected
of said sub-carriers from the output signal of said Fourier to said Fourier transformation section and con?gured inter