U.S. patent application number 14/027517 was filed with the patent office on 2014-01-09 for apparatus for transmitting and receiving data to provide high-speed data communication and method thereof.
This patent application is currently assigned to Electronics and Telecommunications Research Institute. The applicant listed for this patent is Electronics and Telecommunications Research Institute. Invention is credited to Eun-Young CHOI, Taehyun JEON, Myung-Soon KIM, Sok-kyu LEE, Deuk-Su LYU, Hee-Jung YU.
Application Number | 20140010243 14/027517 |
Document ID | / |
Family ID | 36601911 |
Filed Date | 2014-01-09 |
United States Patent
Application |
20140010243 |
Kind Code |
A1 |
YU; Hee-Jung ; et
al. |
January 9, 2014 |
APPARATUS FOR TRANSMITTING AND RECEIVING DATA TO PROVIDE HIGH-SPEED
DATA COMMUNICATION AND METHOD THEREOF
Abstract
In the present invention, data generated from a source unit are
distributed to at least one bandwidth; the data distributed to the
respective bandwidths are encoded in order to perform an error
correction; the encoded data are distributed to at least one
antenna; a subcarrier is allocated to the data distributed to the
respective antennas, and an inverse Fourier transform is performed;
a short preamble and a first long preamble corresponding to the
subcarrier are generated; a signal symbol is generated according to
a data transmit mode; and a frame is generated by adding a second
long preamble between the signal symbol and a data field for the
purpose of estimating a channel of a subcarrier which is not
used.
Inventors: |
YU; Hee-Jung; (Daejeon,
KR) ; JEON; Taehyun; (Sungnam, KR) ; KIM;
Myung-Soon; (Daejeon, KR) ; CHOI; Eun-Young;
(Daejeon, KR) ; LEE; Sok-kyu; (Daejeon, KR)
; LYU; Deuk-Su; (Daejeon, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Electronics and Telecommunications Research Institute |
Daejeon |
|
KR |
|
|
Assignee: |
Electronics and Telecommunications
Research Institute
Daejeon
KR
|
Family ID: |
36601911 |
Appl. No.: |
14/027517 |
Filed: |
September 16, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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|
13355230 |
Jan 20, 2012 |
8565346 |
|
|
14027517 |
|
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|
12805117 |
Jul 13, 2010 |
8130869 |
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13355230 |
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12401293 |
Mar 10, 2009 |
7782968 |
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12805117 |
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11767797 |
Jun 25, 2007 |
7535968 |
|
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12401293 |
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Current U.S.
Class: |
370/474 |
Current CPC
Class: |
H04L 27/2602 20130101;
H04L 1/0071 20130101; H04L 1/0059 20130101; H04L 5/003 20130101;
H04W 84/12 20130101; H04L 27/2613 20130101; H04W 28/065 20130101;
H04L 5/0044 20130101; H04L 1/0041 20130101; H04L 5/0048 20130101;
H04L 1/0618 20130101; H04L 1/0045 20130101 |
Class at
Publication: |
370/474 |
International
Class: |
H04L 27/26 20060101
H04L027/26 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 23, 2004 |
KR |
10-2004-0111065 |
Feb 11, 2005 |
KR |
PCT/KR2005/000393 |
Claims
1-9. (canceled)
10. A transmitter having plural antennas for transmitting a
two-stream signal in a wireless channel, said transmitter having
transmission circuits connected to each antenna, said transmission
circuits comprising: frame generator circuits for producing in each
stream of said two-stream signal transmission frames having a
preamble followed by data, wherein said frame generator circuits
providing signal information symbols in said preamble, said signal
information symbols indicating whether said two-stream signal is
coded using space time block coding (STBC).
11. The transmitter of claim 10, wherein said frame generator
circuits further providing: preamble symbols representing a short
preamble sequence and one or more first long preamble sequences
located in said preamble before said signal information symbols,
said short and first long preamble sequences enabling a receiver to
perform an initial frame synchronization; and additional preamble
symbols representing one or more second long preamble sequences
located in said preamble following said signal information symbols
and enabling a receiver to perform a channel estimation for each
channel defined by said two-stream signal.
12. The transmitter of claim 11, wherein the short preamble
sequence comprises a first sequence of time-domain signals, wherein
each of the time-domain signals of the first sequence has a first
duration, wherein the one or more first long preamble sequences
comprise one or more second sequences of time-domain signals,
wherein each of the time-domain signals of the one or more second
sequences has a second duration, and wherein the first duration is
shorter than the second duration.
13. The transmitter of claim 10, wherein the signal information
symbols further includes at least one of coding rate, a mapping
method, and a modulation.
14. The transmitter of claim 13, wherein said first and second long
preamble sequences are generated based on a predetermined
sequence.
15. The transmitter of claim 14, wherein said second long preamble
sequences include reference information for the receiver to form a
channel estimate that allows the receiver to demodulate said
data.
16. The transmitter of claim 15, wherein said first long preamble
sequence is preceded by a guard interval having a length of 1.6
.mu.sec, said second long preamble sequence includes two long
preambles T1, T2 wherein each of the two long preambles T1, T2 is
respectively preceded by a guard interval having a length of 0.8
.mu.sec, and said data is preceded by a guard interval having a
length of 0.8 .mu.sec.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 12/401,293, filed Mar. 10, 2009, which is a continuation of
Ser. No. 11/767,797 filed Jun. 25, 2007, and claims priority to
International Application PCT/KR2005/000393 filed Feb. 11, 2005 and
Korean Application No. 10-2004-0111065, filed on Dec. 23, 2004, the
disclosures of all which are hereby incorporated herein by
reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to an apparatus for
transmitting and receiving data in radio data communication. More
specifically, the present invention relates to an apparatus
compatible with a conventional wireless local area network
communication system, for transmitting and receiving data in
high-speed and a method thereof. In addition, the present invention
relates to a wireless communication system for increasing data
rates from 54 Mbps which has been a maximum data rate in the
conventional wireless local area network communication system, to
hundreds of Mbps.
[0004] 2. Description of the Related Art
[0005] In the conventional IEEE 802.11a wireless local area network
(LAN) system using an orthogonal frequency division multiplexing
method, a 20 MHz bandwidth is divided into 64 subcarriers, and 52
subcarriers of the 64 subcarriers are used to transmit data and
pilot symbols. That is, the data are transmitted at a maximum speed
of 54 Mbps by using a single antenna and the 20 MHz bandwidth.
[0006] The present invention provides an apparatus for transmitting
and receiving data while being compatible with the conventional
IEEE 802.11a orthogonal frequency division multiplexing (OFDM)
method. The apparatus uses multiple antennas and a plurality of 20
MHz bandwidths to achieve a high data rate.
[0007] In response to the demand for high-speed multimedia data
transmission, various practical applications requesting more than
100 Mbps throughput have been being developed. However, even the
wireless LAN system having the greatest throughput of the current
wireless communication systems does not offer over 25 Mbps of
throughputs. Therefore the present invention suggests a system
offering a data rate which is four times as fast as the
conventional IEEE 802.11a system, or more.
[0008] In detail, the present invention suggests a configuration in
which a number of antennas and bandwidths are systematically
controlled and a maximum data rate is controlled according to
characteristics of a system. The present invention also suggests a
method for providing compatibility with the conventional
system.
[0009] FIG. 1 shows a block diagram for representing a system for
transmitting and receiving data in the conventional wireless
LAN.
[0010] In the conventional IEEE 802.11a system shown in FIG. 1, 20
MHz bandwidth is divided into 64 subcarriers. Among the 64
subcarriers, 48 subcarriers are used for data transmission 4
subcarriers are used for pilot symbol transmission, and a DC
subcarrier and the other 11 subcarriers are not used.
[0011] A convolutional code having 1/2, 2/3, and 3/4 code rates,
binary phase shift keying (BPSK) modulation, quaternary phase shift
keying (QPSK) modulation, 16 quadrature amplitude modulation (QAM)
modulation, and 64 quadrature amplitude modulation (QAM) are used
to transmit the data.
[0012] In the system shown in FIG. 1, when a source unit 101
generates binary data, the binary data are provided to a scrambler
102 for randomizing a permutation of the binary data.
[0013] A convolution encoder 103 performs channel encoding
according to a code rate and a modulation determined by a desired
data rate, and a mapper 105 performs modulation to map the previous
data permutation on a complex symbol permutation.
[0014] An interleaver 104 provided between the convolution encoder
103 and the mapper 105 interleaves the data permutation according
to a predetermined rule. The mapper 105 establishes the complex
number permutation to be a group of 48, and a subcarrier allocator
107 forms 48 data components and 4 pilot components from pilot unit
106.
[0015] A 64 inverse fast Fourier transform (64-IFFT) unit 108
performs an inverse fast Fourier transform on the 48 data and 4
pilot components to form an OFDM symbol.
[0016] A cyclic prefix adder 109 adds a cyclic prefix which is a
guard interval to the OFDM symbol.
[0017] A radio frequency (RF) transmit unit 110 transmits a
transmission frame formed by the above configuration on a carrier
frequency. An RF receive unit 112 receives the transmission signal
(the transmission frame transmitted on the carrier frequency)
through a radio channel 111. The radio channel 111 includes a
multi-path fading channel and Gaussian noise added from a receive
terminal.
[0018] The RF receive unit 112 of the receive terminal receives the
distorted signal passing through the radio channel 111, and
down-converts the signal transmitted on the carrier frequency to a
base band signal in an opposite manner executed by the RF transmit
unit 110 of the transmit terminal.
[0019] A cyclic prefix eliminator 113 eliminates the cyclic prefix
added in a transmitter. A 64 fast Fourier transform (64-FFT) unit
114 converts a received OFDM symbol into a signal of a frequency
domain by performing an FFT operation.
[0020] A subcarrier extractor 115 transmits the 48 complex symbols
corresponding to the data subcarrier among 64 outputs to an
equalizing and tracking unit 117, and transmits the 4 subcarriers
corresponding to the pilot to an equalizing and tracking parameter
estimator 116.
[0021] The equalizing and tracking parameter estimator 116
estimates a phase change caused by frequency and time errors by
using the known symbols, and transmits an estimation result to the
equalizing and tracking unit 117.
[0022] The equalizing and tracking unit 117 uses the above
estimation result to perform a tracking operation. The equalizing
and tracking unit 117 also performs a frequency domain channel
equalization operation for equalizing channel distortion in the
frequency domain in addition to the tracking process.
[0023] A demapper 118 performs a hard decision operation for
converting the output complex number after the channel equalizing
and tracking operation into the binary data, or performs a soft
decision for converting the output complex number into a real
number. A deinterleaver 119 deinterleaves the data in an inverse
process of the interleaver 104, and a Viterbi decoder 120 performs
decoding of the convolution code to correct errors and restore the
transmitted data.
[0024] A descrambler 121 randomizes the data transmitted from the
source unit in a like manner of the scrambler 102 and transmits the
received data to a sink unit 122.
[0025] The conventional wireless LAN system shown in FIG. 1 has
limits of data rate and throughput, and therefore the system is
difficult to apply to a service requiring a high data rate such as
a high quality moving picture service.
[0026] Systems using multiple bandwidths and antennas to provide a
high speed data rate have previously not been compatible with the
conventional transmitting and receiving system.
[0027] Accordingly, the present invention provides an apparatus for
transmitting and receiving for providing compatibility with the
conventional wireless communication system, and the high speed data
rate and a method thereof.
SUMMARY OF THE INVENTION
Technical Problem
[0028] The present invention provides a data transmitting and
receiving device to provide a high data rate and compatibility with
the conventional wireless communication system, and a method
thereof.
Technical Solution
[0029] The present invention provides a data transmitting and
receiving device to provide a high data rate and compatibility with
the conventional wireless communication system, and a method
thereof.
[0030] The present invention discloses a data transmitting device
including a bandwidth distributor, an encoder, a mapper, an antenna
distributor, a subcarrier allocator, an inverse Fourier transform
unit, a preamble generator, and a frame generator.
[0031] The bandwidth distributor distributes data generated in a
source unit to at least one bandwidth. The encoder performs
encoding of the distributed data in order to perform error
correction of the data. The mapper performs mapping of the encoded
data into a complex number symbol. The antenna distributor
distributes the complex number symbol to at least one antenna. The
subcarrier allocator allocates a subcarrier for orthogonal
frequency division multiplexing to the distributed complex number
symbol. The inverse Fourier transform unit performs an inverse
Fourier transform of the OFDM signal to which the subcarrier is
allocated. The preamble generator generates a short preamble, a
first long preamble, and a second long preamble of the subcarrier.
The frame generator generates frames in an order of the short
preamble, the first long preamble, a signal symbol, the second long
preamble, and a data field. At this time, one of the first long
preambles of a second antenna may be used for the second long
preamble in order to perform a channel estimation of a subcarrier
which is not used by a first antenna when two or more antennas are
used.
[0032] The signal symbol generated by the frame generator comprises
a transmit mode identifier for determining whether a transmit mode
is a single antenna transmit mode or a
multiple-input/multiple-output (MIMO) mode.
[0033] The transmit mode identifier uses an R4 bit of the signal
symbols in a frame of IEEE 802.11a.
[0034] A reserved bit of the signal symbol is used as a bit for
determining whether the transmit mode uses a spatial division
multiplexing (SDM) method or a space-time block code (STBC)
method.
[0035] The data transmitting device according to the exemplary
embodiment of the present invention further includes a scrambler,
an interleaver, a cyclic prefix adder, and an RF transmit unit.
[0036] The scrambler is coupled between the bandwidth distributor
and the encoder and performs a scrambling operation. The
interleaver is coupled between the encoder and the mapper and
performs an interleaving operation. The cyclic prefix adder adds a
cyclic prefix to an inverse-Fourier-transformed orthogonal
frequency division multiplexing (OFDM) signal. The RF transmit unit
transmits the frame through a radio channel. The antenna
distributor distributes the mapped symbols to antennas or encodes
STBC.
[0037] The present invention discloses a data receiving device
including an RF receiving unit, a channel mixer, an initial
synchronizer, a Fourier transforming unit, a signal symbol
demodulator, a channel estimator, and a detector.
[0038] The RF receiving unit receives a frame through a radio
channel. The channel mixer performs a channel mixing operation in
order to extract a 20 MHz short preamble and a 20 MHz first long
preamble from the received frame. The initial synchronizer performs
an initial synchronizing operation by using the extracted short
preamble and first long preamble. The Fourier transforming unit
performs a Fourier transforming operation of the frame. The signal
symbol demodulator demodulates a signal symbol and demodulates
information on a transmit mode. The channel estimator performs a
first channel estimation by using the first long preamble, and
performs a second channel estimation by using a second long
preamble transmitting after the signal symbol when the information
on the transmit mode is a MIMO-OFDM transmit mode. The detector
detects a complex number symbol corresponding to the data with
reference to the estimated channel and demodulated signal symbol.
We detect a transmit mode identifier established in the signal
symbol, and determine whether the transmit mode is a single antenna
transmit mode or a MIMO-OFDM transmit mode.
[0039] The channel estimator uses the second long preamble to
perform the second channel estimation of a subcarrier which is not
used by a first antenna.
[0040] The data receiving device further includes a cyclic prefix
eliminator, a subcarrier extractor, a demapper, a deinterleaver,
and an error correction decoder.
[0041] The cyclic prefix eliminator eliminates a cyclic prefix of
the signal received from the RF receiving unit. The subcarrier
extractor extracts subcarriers from the Fourier-transformed signal
and combines the subcarriers. The demapper performs demapping of
the signal demodulated to the complex number signal into a binary
data signal. The deinterleaver performs deinterleaving of the
demapped signal. The error correction decoder performs an error
correction decoding operation on the deinterleaved signal. The
detector is a SDM detector or a STBC decoder.
Advantageous Effect
[0042] According to the present invention, an increased data rate
is provided by using multiple bandwidths and antennas in a wireless
communication system.
[0043] Because of compatibility with the conventional system, the
increased data rate is provided without modifying the existing
device and design.
BRIEF DESCRIPTION OF THE DRAWINGS
[0044] FIG. 1 shows a block diagram for representing a conventional
transmitting and receiving system in the wireless LAN.
[0045] FIG. 2 shows a block diagram for representing a
configuration of a transmitter according to an exemplary embodiment
of the present invention.
[0046] FIG. 3 shows a block diagram for representing a
configuration of a receiver according to the exemplary embodiment
of the present invention.
[0047] FIG. 4 shows an OFDM subcarrier allocation method supporting
a single bandwidth and an OFDM subcarrier allocation method for
supporting multiplex bandwidths.
[0048] FIG. 5 shows a diagram for representing the IEEE 802.11a
frame configuration.
[0049] FIG. 6 shows a diagram for representing the frame
configuration according to an exemplary embodiment of the present
invention.
[0050] FIG. 7 shows a block diagram for representing a
configuration for initial synchronization of the receiver according
to an exemplary embodiment of the present invention.
[0051] FIG. 8 shows a flow chart for representing a method for
transmitting the data according to an exemplary embodiment of the
present invention.
[0052] FIG. 9 shows a flow chart for representing a method for
receiving the data according to an exemplary embodiment of the
present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0053] In the following detailed description, only the preferred
embodiment of the invention has been shown and described, simply by
way of illustration of the best mode contemplated by the
inventor(s) of carrying out the invention. As will be realized, the
invention is capable of modification in various obvious respects,
all without departing from the invention. Accordingly, the drawings
and description are to be regarded as illustrative in nature, and
not restrictive. To clarify the present invention, parts which are
not described in the specification are omitted, and parts for which
same descriptions are provided have the same reference
numerals.
[0054] While this invention is described in connection with what is
presently considered to be the most practical and preferred
embodiment, it is to be understood that the invention is not
limited to the disclosed embodiment, but on the contrary, is
intended to cover various modifications and equivalent arrangements
included within the spirit and scope of the appended claims.
[0055] FIG. 2 shows a block diagram for representing a
configuration of a transmitter according to an exemplary embodiment
of the present invention.
[0056] The transmitter includes a source unit 201, a bandwidth
distributor 202, scrambler/convolution encoders 2031 to 203L, an
interleaver 204, a mapper 205, a pilot unit 206, an antenna
distributor 207, subcarrier allocators 2081 to 208M, IFFT units
2091 to 209M, cyclic prefix adders 2101 to 210M, preamble
generators 2301 to 230M, frame generators 2311 to 231M, and RF
transmit units 2111 to 211M.
[0057] When binary data generated in the source unit 201 are
transmitted to the bandwidth distributor 202, the bandwidth
distributor 202 distributes the binary data to L bandwidths
according to a number (L) of 20 MHz bandwidths to be used in the
band distributor 202.
[0058] The scrambler/convolution encoders 2031 to 203L perform
scrambling and convolutional code encoding operations for the
respective bandwidths.
[0059] The interleaver 204 receives the convolutionally encoded
data. At this time, two types of interleavers 204 are available.
One interleaver performs interleaving of each OFDM symbol of the
respective bandwidths in a like manner of the scrambler/convolution
encoders 2031 to 203L, and the other interleaver performs
interleaving of the L number of OFDM symbols in every bandwidth.
The former interleaver is simple and easy to understand, and the
latter interleaver is complex to be realized and it is expected to
obtain performance gain due to diversity gain.
[0060] The mapper 205 converts the binary data into complex
symbols. The converted complex symbols are distributed to M number
of transmit antennas by the antenna distributor 207. The subcarrier
allocators 2081 to 208M use pilot symbols from the pilot unit 206
and the distributed data complex symbols in order to allocate
subcarriers for OFDM modulation, Allocation of the subcarriers will
be described later.
[0061] Frequency domain OFDM symbols corresponding to the allocated
M number of the transmit antennas are inverse-Fourier-transformed
into time domain OFDM symbols by the (L*64)-IFFT units 2091 to
209M. The cyclic prefix adders 2101 to 210M add cyclic prefixes
corresponding to the OFDM symbols of each path.
[0062] The frame generators 2311 to 231M generate proper frames for
a system shown in FIG. 2. Similar to the conventional IEEE 802.11a
frame configuration, a frame configuration according to an
exemplary embodiment of the present invention includes a short
preamble, a first long preamble, a signal symbol, and data. In
addition, the frame configuration includes a second long preamble
in the preamble generators 2301 to 230M. The second long preamble
is a long preamble having been used in another antenna, and
multiple-input/multiple-output (MIMO) channel estimation on the
subcarriers is performed by the second long preamble.
[0063] The preamble generators 2301 to 230M generate the short
preamble, the first long preamble, and the second long preamble,
and provide the same to the frame generators 2311 to 231M.
[0064] The frame used in the exemplary embodiment of the present
invention will be described later.
[0065] FIG. 3 shows a block diagram for representing a receiver
according to the exemplary embodiment of the present invention.
[0066] The receiver shown in FIG. 3 performs an inverse operation
on the signal transmitted from the transmitter shown in FIG. 2.
[0067] The signal transmitted through the channel 212 from the
transmitter is received by N number of receive antennas in N number
of RF receive units 2131 to 213N. The received signal is restored
to a transmit signal while passing through cyclic prefix
eliminators 2141 to 214N, (L*64) FFT units 2151 to 215N, subcarrier
extractors 2161 to 216N, a channel and tracking parameter
estimation unit 217, an MIMO detector 218, a demapper 219, a
deinterleaver 220, descrambler/Viterbi decoders 2211 to 221L, and a
bandwidth combining unit 222, and data are transmitted to a sink
unit 223.
[0068] A demodulation process of the receiver shown in FIG. 3 is
similar to that of the receiver shown in FIG. 1. However, the
channel estimation unit 217 in the receiver shown in FIG. 3
estimates the MIMO channel, which is different from the system
shown in FIG. 1. In addition, the equalizing unit 117 shown in FIG.
1 is substituted to the MIMO detector 218 in the system shown in
FIG. 3. A configuration of the deinterleaver has to be changed
according to a varied configuration of the interleaver.
[0069] The bandwidth combining unit 222 added in the system shown
in FIG. 3 performs an inverse operation of the bandwidth
distributor 202 of the transmitter shown in FIG. 2.
[0070] While the (L*64) IFFT and (L*64) FFT are used in FIG. 2 and
FIG. 3, L number of 64 FFTs and 64 IFFTs may be used, and one
(L*64) IFFT and one (L*64) FFT may be also used. These
modifications are apparent to those skilled in the art.
[0071] FIG. 3 shows a receiving and demodulating configuration in
correspondence to the MIMO transmitter shown in FIG. 2, and a
configuration of the receiver for performing initial
synchronization and channel estimation will be described later.
[0072] In FIG. 2, a spatial division multiplexing (SDM) method for
increasing the data rate by using the multiple transmit/receive
antennas has been described.
[0073] The SDM method, one of the MIMO methods, increases the data
rate by transmitting independent data via the respective transmit
antennas.
[0074] When a system is designed for the purpose of broadening a
service area and increasing a signal to noise ratio (SNR) rather
than for increasing the data rate, a space-time block code (STBC)
for achieving the diversity gain may be applied to the exemplary
embodiment of the present invention.
[0075] When the STBC is applied in the exemplary embodiment of the
present invention, the antenna distributor 207 is substituted for
an STBC encoder, and the MIMO detector 218 is substituted for an
STBC decoder.
[0076] For convenience of description, a system including two
transmit antennas and two bandwidths will be exemplified to
describe the frame configuration of the exemplary embodiment of the
present invention. That is, L is 2 and M is 2 in the system shown
in FIG. 2. The conventional frame configuration and OFDM symbol
configuration are used in the exemplary embodiment of the present
invention for the purpose of providing compatibility with the
existing IEEE 802.11a system.
[0077] As to the OFDM symbol configuration, a 40 MHz bandwidth is
divided into 128 subcarriers which are generated by combining two
20 MHz bandwidths each of which is divided into 64 subcarriers in
the prior art in the exemplary embodiment of the present invention.
Accordingly, 128-IFFT is used to perform the OFDM modulation in 20
MHZ and 40 MHz bandwidths.
[0078] FIG. 4 shows an OFDM subcarrier allocation method supporting
a single bandwidth and an OFDM subcarrier allocation method for
supporting multiplex bandwidths.
[0079] A subcarrier allocation configuration (a) is formed when a
signal is transmitted by a single antenna and a single bandwidth in
the conventional IEEE 802.11a. The configuration (b) according to
the exemplary embodiment of the present invention corresponds to
that of the conventional IEEE 802.11a when a signal fills a desired
bandwidth, 0 fills other bandwidths, and the signal is transmitted
through the single antenna.
[0080] That is, the data and pilot are allocated in 52 subcarriers
between 0 and 63, and 0's are filled between -64 and -1 when one
side bandwidth having a lower frequency is used in a signal
configuration (b) using the two bandwidths of the subcarrier
allocation configuration shown in FIG. 4. Accordingly, the system
according to the exemplary embodiment of the present invention is
compatible with the conventional IEEE 802.11a system because the
conventional frame configuration is transmitted in the new
system.
[0081] The frame configuration according to the exemplary
embodiment of the present invention will be described.
[0082] FIG. 5 shows a diagram for representing the IEEE 802.11a
frame configuration.
[0083] The IEEE 802.11a frame configuration shown in FIG. 5
includes short preambles t1 to t10, long preambles T1 and T2, guard
intervals G1 and G2, a signal symbol SIGNAL, and data. The short
preamble and the long preamble are symbols for synchronization and
channel estimation in a case of demodulation. The signal symbol
includes information on data rate, length, and parity.
[0084] The short preamble is a symbol generated by
Fourier-transforming an OFDM frequency domain signal as given in
Math Formula 1, and the long preamble is a symbol generated by
Fourier-transforming an OFDM frequency domain signal as given in
Math Formula 2.
S.sub.-26,26= {square root over
((13/6))}{0,0,1+j,0,0,0,-1-j,0,0,0,1+j,0,0,0,-1-j,0,0,0,-1-j,0,0,0,1+j,0,-
0,0,0,0,0,0,-1-j,0,0,0,-1-j,0,0,0,1+j,0,0,0,1+j,0,0,0,1+j,0,0,0,1+j,0,0}
[Math Formula 1]
L.sub.-26,26={1,1,-1,-1,1,1,-1,1,-1,1,1,1,1,1,1,-1,-1,1,1,-1,1,-1,1,1,1,-
1,0,1,-1,-1,1,1,-1,1,-1,1,-1,-1,-1,-1,-1,1,1,-1,-1,1,-1,1,-1,1,1,1,1}
[Math Formula 2]
[0085] The signal symbol includes information on length of data
sections (0 to 4,095 bytes), code rates (1/2, 2/3, and 3/4), and
mapping methods (BPSK, QPSK, 16-QAM, and 64-QAM).
[0086] For the purpose of providing compatibility with the IEEE
802.11a, frame configuration shown in FIG. 5 is slightly modified
for the characteristics of the multiple antennas when signals are
transmitted according to the conventional OFDM mode (IEEE 802.11a)
in the exemplary embodiment of the present invention.
[0087] When two transmit antennas are used, 52 subcarriers of
preambles are equally divided by 26 subcarriers to be transmitted.
A second long preamble is further provided after the signal symbol
in order to estimate the channel of the subcarrier which is not
used in the first long preamble.
[0088] The MIMO channel estimation of the subcarriers is performed
by transmitting the first long preamble used as the second long
preamble by another antenna. Accordingly, the length of the long
preamble is increased by the number of the transmit antennas.
[0089] A frequency domain signal of the short preamble to be
transmitted by the two antennas is given by Math Figure 3.
S(0)-26,26 is transmitted by the antenna 0, and S(1)-26,26 is
transmitted by the antenna 1.
[0090] A frequency domain signal of the first long preamble
provided before the signal symbol is given by Math Formula 4.
L(0)-26,26 is transmitted by the antenna 0, and L(1)-26,26 is
transmitted by the antenna 1.
S.sub.26,26= {square root over
((26/6))}{0,0,1+j,0,0,0,0,0,0,0,1+j,0,0,0,0,0,0,0,-1-j,0,0,0,0,0,0,0,0,0,-
0,0,-1-j,0,0,0,0,0,0,0,1+j,0,0,0,0,0,0,0,1+j,0,0,0,0,0,0}
S.sub.26,26= {square root over
((26/6))}{0,0,0,0,0,0,-1-j,0,0,0,0,0,0,0,-1-j,0,0,0,0,0,0,0,1+j,0,0,0,0,0-
,0,0,0,0,0,0,-1-j,0,0,0,0,0,0,0,1+j,0,0,0,0,0,0,0,1+j,0,0} [Math
Formula 3]
L.sub.26,26= {square root over
(2)}{1,0,-1,0,1,0,-1,0,-1,0,1,0,1,0,1,0,-1,0,1,0,1,0,1,0,1,0,0,0,-1,0,1,0-
,-1,0,-1,0,-1,0,-1,0,-1,0,1,0,-1,0,-1,0,-1,0,1,0,1}
L.sub.26,26= {square root over
(2)}{0,1,0,-1,0,1,0,1,0,1,0,1,0,1,0,-1,0,1,0,1,0,1,0,-1,0,-1,0,1,0,-1,0,1-
,0,1,0,1,0,1,0} [Math Formula 4]
[0091] In a case of the second long preamble following the signal
symbol, a location of the first long preamble is changed so that
L(1)-26,26 is transmitted by the antenna 0 and L(0)-26,26 is
transmitted by the antenna 1.
[0092] FIG. 6 shows a diagram for representing the frame
configuration according to an exemplary embodiment of the present
invention.
[0093] As shown in FIG. 6, the frame transmitted by the first
antenna (antenna 0) uses the even subcarriers to transmit the
frame, and the frame is formed by using the first long preamble of
the odd subcarriers as the second long preamble.
[0094] The configuration of the preamble and the signal symbol are
repeatedly connected to support multiple bandwidths. For example,
the short preamble and long preamble for the conventional mode
(dual band IEEE 802.11a) using two bandwidths are represented by
Math FIG. 5 and Math Formula 6 when the two bandwidths are
used,
S.sub.58,58= {square root over
((13/6))}{0,0,1+j,0,0,0-1-j,0,0,0,1+j,0,0,0,-1-j,0,0,0,-1-j,0,0,0,1+j,0,0-
,0,0,0,0,0,-1-j,0,0,0,-1-j,0,0,0,1+j,0,0,0,1+j,0,0,0,1+j,0,0,0,1+j,0,0,0,0-
,0,0,0,0,0,0,0,0,0,0,0,1+j,0,0,0,-1-j,0,0,0,1+j,0,0,0,-1-j,0,0,0,-1-j,0,0,-
0,1+j,0,0,0,0,0,0,0,-1-j,0,0,0,-1-j,0,0,0,1+j,0,0,0,1+j,0,0,0,0,1+j,0,0,0,-
1+j,0,0} [Math Formula 5]
L.sub.58,58={1,1,-1,-1,1,1,-1,1,-1,1,1,1,1,1,1,-1,-1,1,1,-1,1,-1,1,1,1,1-
,0,1,-1,-1,1,1,-1,1,-1,1,-1,-1,-1,-1,-1,1,1,-1,-1,1,-1,1,-1,1,1,1,1,0,0,0,-
0,0,0,0,0,0,0,0,1,1,-1,-1,1,1,-1,1,-1,1,1,1,1,1,1,-1,-1,1,1,-1,1,-1,1,1,1,-
1,0,1,-1,-1,1,1,-1,1,-1,1,-1,-1,-1,-1,-1,1,1,-1,-1,1,-1,1,-1,1,1,1,}
[Math Formula 6]
[0095] When the two bandwidths and two antennas are used, the short
preamble and the long preamble transmitted by the respective
antennas are given by Math Formula 7 and Math Formula 8.
S.sub.58,58= {square root over
((13/6))}{0,0,1+j,0,0,0,0,0,0,0,1+j,0,0,0,0,0,0,0,-1-j,0,0,0,0,0,0,0,0,0,-
0,0,-1-j,0,0,0,0,0,0,0,1+j,0,0,0,0,0,0,0,1+j,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0-
,0,0,0,1+j,0,0,0,0,0,0,0,1+j,0,0,0,0,0,0,0,-1-j,0,0,0,0,0,0,0,0,0,0,0,-1-j-
,0,0,0,0,0,0,0,1+j,0,0,0,0,0,0,0,1+j,0,0,0,0,0,0}
S.sub.58,58= {square root over
((26/6))}{0,0,0,0,0,0,-1-j,0,0,0,0,0,0,0,-1-j,0,0,0,0,0,0,0,1+j,0,0,0,0,0-
,0,0,0,0,0,0,-1-j,0,0,0,0,0,0,0,1+j,0,0,0,0,0,0,0,1+j,0,0,0,0,0,0,0,0,0,0,-
0,0,0,0,0,0,0,0,0,-1-j,0,0,0,0,0,0,0,-1-j,0,0,0,0,0,0,0,1+j,0,0,0,0,0,0,0,-
0,0,0,0,-1-j,0,0,0,0,0,0,0,1+j,0,0,0,0,0,0,0,1+j,0,0} [Math Formula
7]
L.sub.58,58.sup.(0)= {square root over
(2)}{1,0,-1,0,1,0,-1,0,-1,0,1,0,1,0,1,0,-1,0,1,0,1,0,1,0,1,0,0,0,-1,0,1,0-
,-1,0,-1,0,-1,0,-1,0,-1,0,1,0,-1,0,-1,0,-1,0,1,0,1,0,0,0,0,0,0,0,0,0,0,0,1-
,0,-1,0,1,0,-1,0,-1,0,1,0,1,0,1,0,-1,0,1,0,1,0,1,0,1,0,0,0,-1,0,1,0,-1,0,--
1,0,-1,0,-1,0,-1,0,1,0,-1,0,-1,0,1,0,1,0,1}
L.sub.58,58.sup.(1)= {square root over
(2)}{0,1,0,-1,0,1,0,1,0,1,0,1,0,1,0,-1,0,1,0,-1,0,-1,0,1,0,1,0,1,0,-1,0,1-
,0,1,0,1,0,-1,0,-1,0,1,0,-1,0,1,0,1,0,1,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,1,0,-
-1,0,1,0,1,0,1,0,1,0,1,0,-1,0,1,0,-1,0,-1,0,1,0,1,0,1,0,-1,0,1,0,1,0,1,0,--
1,0,-1,0,1,0,-1,0,1,0,1,0,1,0,1,0} [Math Formula 8]
[0096] As described above, S(0)-58,58 is transmitted by the antenna
0 and S(1)-58,58 is transmitted by the antenna 1. L(0)-58,58 is
transmitted by the antenna 0, and L(1)-58,58 is transmitted by the
antenna 1. However, the second long preamble following the signal
symbol is transmitted in an inverse order.
[0097] According to the above-described configuration, the receive
terminal performs the channel estimation of the subcarriers by
further performing the channel estimation using the second long
preamble without determining which antenna transmits the signal in
the system using the multiple bandwidths and the multiple
antennas.
[0098] Accordingly, the long preamble is generated in the like
manner of generating the long preamble by the preamble generators
2301 to 230M shown in FIG. 2, and the preamble generators 2301 to
230M additionally inserts the second long preamble after the signal
symbol to generate the frame.
[0099] The frame generator modifies the signal symbol in order to
provide compatibility with the conventional system.
[0100] A bit which has not been used as a reserved bit in the
conventional symbol configuration is redefined as an antenna bit A,
and the bit is used for discerning between the SDM and the
STBC.
[0101] An R4 bit of four RATE bits is used for distinguishing
between the conventional IEEE 802.11a mode and the multiple antenna
OFDM mode. Accordingly, the frame generator allocates the RATE bits
R1 to R4 and the antenna bit A as shown in Table 1.
TABLE-US-00001 TABLE 1 RATE ANTENNA bit allocation Date Mapping
Code (R1-R4, A) rate method rate Transmit mode 1101X 6 BPSK 1/2
IEEE 802.11a 1111X 9 BPSK 3/4 IEEE 802.11a 0101X 12 QPSK 1/2 IEEE
802.11a 0111X 18 QPSK 3/4 IEEE 802.11a 1001X 24 16QAM 1/2 IEEE
802.11a 1011X 36 16QAM 3/4 IEEE 802.11a 0001X 48 64QAM 2/3 IEEE
802.11a 0011X 54 64QAM 3/4 IEEE 802.11a 11000 6 BPSK 1/2 STBC-OFDM
11100 9 BPSK 3/4 STBC-OFDM 01000 12 QPSK 1/2 STBC-OFDM 01100 18
QPSK 3/4 STBC-OFDM 10000 24 16QAM 1/2 STBC-OFDM 10100 36 16QAM 3/4
STBC-OFDM 00000 48 64QAM 2/3 STBC-OFDM 00100 54 64QAM 3/4 STBC-OFDM
11001 12 BPSK 1/2 SDM-OFDM 11101 18 BPSK 3/4 SDM-OFDM 01001 24 QPSK
1/2 SDM-OFDM 01101 36 QPSK 3/4 SDM-OFDM 10001 48 16QAM 1/2 SDM-OFDM
10101 72 16QAM 3/4 SDM-OFDM 00001 96 64QAM 2/3 SDM-OFDM 00101 108
64QAM 3/4 SDM-OFDM
[0102] As shown in Table 1, when the R4 bit is established to be 1,
the data is received in the IEEE 802.11a method. Because the
transmission mode is the IEEE 802.11a mode when the R4 bit is 1, a
value of the antenna bit A has no effect, and the configuration of
the signal symbol corresponds to that of the IEEE 802.11a.
[0103] However, when the R4 bit is established to be 0, the system
is the MIMO system. At this time, it is determined whether the
transmit mode is the SDM mode or the STBC mode with reference to
the antenna bit A.
[0104] The R1 to R3 bits respectively correspond to information on
eight data rates, mapping methods, and code rates.
[0105] Accordingly, the signal symbol is configured by combining 24
bits in a like manner of the conventional signal symbol. The 24
bits include length of 12 bits, parity of 1 bit, and tail of 6
bits. The data is transmitted on the 64 or repeated 128 (64+64)
subcarriers in the conventional IEEE 802.11a mode, and the data is
separately transmitted on the even subcarriers and the odd
subcarriers in the multiple antenna mode as shown in Math Figure 4
and Math Figure 8.
[0106] In terms of the output of the transmit antenna,
predetermined preamble and signal symbol configurations are formed
regardless of the number of the transmit antennas and
bandwidths.
[0107] In the above frame configuration, a process for maintaining
the compatibility by the conventional system and the system
according to the exemplary embodiment in the receive terminal will
be described.
[0108] When the data is transmitted in the conventional IEEE
802.11a system, the conventional receiver may perform a
demodulation of the short preamble, the first long preamble, and
the signal symbol field. However, when the signal symbol is
interpreted, the data following the signal symbol is demodulated
because the frame corresponds to the conventional frame when the R4
bit of the RATE bits is 1, the data demodulation is not performed
until the frame ends because the frame is not demodulated by the
conventional demodulator when the R4 bit is 0. Accordingly, the
compatibility is provided in a, network formed by combing the
conventional system and the system according to the exemplary
embodiment of the present invention.
[0109] The receiver of the system according to the exemplary
embodiment of the present invention starts to perform demodulating
of the data following the signal symbol after the receiver
acknowledges that the frame is the IEEE 802.11a frame when R4 of
the signal symbols is 1. When the R4 is 0, however, the receiver
performs the channel estimation by using the second long preamble
following the signal symbol, searches the antenna bit A, determines
whether the transmit mode is the SDM-OFDM or the STBC-OFDM, and
restores the transmit data after a proper demodulation process
according to the determined mode.
[0110] Accordingly, the system according to the exemplary
embodiment of the present invention is allowed to be compatible
with the conventional IEEE 802.11a system.
[0111] FIG. 7 shows a block diagram for representing a
configuration for an initial synchronization of the receiver
according to the exemplary embodiment of the present invention.
[0112] In FIG. 7, the receiver includes DC-offset compensators 300a
and 300b, and inphase and quadrature (I/Q) compensators 310a and
310b for compensating 1/Q mismatch, for a path of the respective
antennas. The DC-offset compensators 300a and 300b eliminate a
DC-offset on the path of the respective antennas which may be
generated in an analog and RF circuits. The I/Q compensators 310a
and 310b compensate the 1/0 mismatch which may be generated in the
analog and RF circuits.
[0113] The data before the signal symbol, which are the short
preamble part and the first long preamble part, is input to a
channel mixer 400. In the channel mixer 400, the frequency is
shifted by +10 MHz and by -10 MHz in order to respectively divide
two bandwidth 40 MHz signals into channel 0 of 20 MHZ and channel 1
of 20 MHz. Accordingly, two outputs are generated from the
respective antenna paths. The signals pass through a low pass
filter (LPF) 410 and the signals are decimated by 1/2 in order to
convert the signals to 20 MHz bandwidth signals. The initial
synchronization is performed by using the short preamble and first
long preamble of 20 MHz.
[0114] A carrier frequency offset (CFO) estimator 430 estimates a
carrier frequency offset by using an auto-correlation of the short
preamble and the first long preamble. A carrier offset (CFO)
compensator 320a, 320b compensates the carrier frequency offset
based on the estimated value output from the CFO estimator 430.
[0115] A frame synchronizer 420 performs frame synchronization by
using a cross correlation of the short preamble and the first long
preamble. A bandwidth detector 440 performs bandwidth detection for
determining the operational bandwidth by using the auto correlation
of the first long preamble.
[0116] The signal symbol including the first long preamble and the
data part are input to FFT units 330a and 330b after the initial
synchronization is performed. At this time, the channel is
estimated and the signal symbol is demodulated by using an FFT
output of the first long preamble.
[0117] The signal symbol is demodulated without having information
on the transmit mode because a method for transmitting the signal
symbol is always the same. After the signal symbol is demodulated,
the information on the transmit mode, operational bandwidth, frame
length, demodulation method, and code rate is provided.
[0118] As described above, when the R4 is 1 (that is, when the
transmit mode is the MIMO-OFDM mode), a channel estimator 450
further performs the channel estimation by using the second long
preamble.
[0119] The data field is demodulated with reference to the
information established in the signal symbol when the channel
estimation is performed.
[0120] Phase compensators 340a and 340b estimate and compensate
residual frequency and phase offsets by using the pilot
subcarrier.
[0121] The signal is detected according to the transmit mode by the
detector 300, and the receiver combines the data passed through the
demapper, the deinterleaver, the Viterbi decoder, and the
descrambler and transmits the combined data to a media access
control (MAC) layer.
[0122] Therefore, the system supporting the multiple antennas
facilitates the channel estimation and provides the compatibility
with the conventional system.
[0123] FIG. 8 shows a flow chart for representing a method for
transmitting the data according to an exemplary embodiment of the
present invention.
[0124] The binary data generated in the source unit are distributed
to the plurality of bandwidths in step S100. The data rate may be
increased as the binary data are distributed to the plurality of
bandwidths.
[0125] The data distributed to the respective bandwidths are
respectively encoded in step S110 by exemplarily using the
convolution code for increasing error correction of data. The
scrambling operation may be further performed before the encoding
operation.
[0126] The interleaving operation for preventing a burst transmit
error is performed, and the binary data are mapped into a plurality
of complex symbols in step S120 when the data are encoded. The
mapping method includes the BPSK, QPSK, =AM, and 84QAM
modulations.
[0127] The data mapped into the complex number symbols are
distributed to the antennas, and the subcarriers allocated to the
respective antennas are allocated to the distributed complex
symbols in step S140. The OFDM signals formed by allocating the
subcarriers respectively perform the Inverse fast Fourier
transform, to transform the frequency domain signal to the time
domain signal.
[0128] When the subcarriers are allocated, the signal fills the
desired bandwidths, and 0 fills other bandwidths. The subcarriers
may be also allocated such that a subcarrier used by an antenna may
not be used by another antenna.
[0129] Not only the multiple bandwidths and antennas but also a
single bandwidth and a single antenna may be also used in steps
S100 and S130.
[0130] When the single bandwidth and antenna are used, the data
modulation process corresponds to that of the conventional IEEE
802.11a.
[0131] Accordingly, it is determined whether the OFDM signal is to
be transmitted according to the MIMO transmit method using the
multiple bandwidths and antennas in step S150. The information for
determining the MIMO state is determined by searching the
configuration and previous operation of the transmitter.
[0132] When the OFDM signal is to be transmitted according to the
MIMO transmit method using the multiple antennas, the preambles for
the respective subcarriers are generated in step S160. The preamble
includes the long preamble of the operational antennas and
subcarriers. The long preamble includes the first long preamble for
the channel estimation of the operational subcarriers of the
antenna and the second long preamble for the channel estimation of
the subcarriers which are not used.
[0133] At this time, the first long preamble which has been used
for a subcarrier by an antenna may be used for the second long
preamble.
[0134] The signal symbol having information on the data
demodulation is generated in step S161. The signal symbol is
generated by mapping the information on the transmit mode, the data
rate, the mapping method, and the code rate on the bits R1 to R4
and the antenna bit as shown in Table 1.
[0135] The data field and the frame for the MIMO antenna are
generated by using the generated short preamble, the first tong
preamble, and the second long preamble in step S162. The frame is
configured in an order of the short preamble, the first long
preamble, the signal symbol, the second long preamble, and the data
field.
[0136] When it is determined that the OFDM signal is not to be
transmitted according to the MIMO transmit method, the frame for
the single antenna is generated in step S170 in a like manner of
the conventional system. The frame for the single antenna also
includes a short preamble, a long preamble, a signal symbol, and a
data field. A description of the generation of the frame for the
single antenna which has been described above will be omitted.
[0137] The frame generated by the above configuration is
transmitted to the receiver through the RF transmit unit in step
S180.
[0138] FIG. 9 shows a flowchart for representing a method for
receiving the data according to an exemplary embodiment of the
present invention.
[0139] In the method for receiving the data, the OFDM signal
received through the radio channel is initially synchronized in
step S210. In addition, the DC offset is eliminated by using a
filter, and the I/O discordance is compensated in step S210. The
short preamble and the first long preamble before the signal symbol
are used to perform the initial synchronization of the compensated
signal.
[0140] The subcarrier frequency offset is estimated by using the
auto-correlation of the short preamble and the first long preamble,
and the frame synchronization is performed by using the
cross-correlation of the short preamble and the first long preamble
in step S220.
[0141] The bandwidth detection is performed for determining the
operational bandwidth by using the auto correlation of the first
long preamble in step S230.
[0142] A first channel estimation is performed by the fast Fourier
transform of the first long preamble in step S240. Methods for the
initial timing synchronization, frequency synchronization, and
channel estimation are easily selected by those skilled in the art
because a physical layer convergence procedure (PLCP) preamble
which is a train signal for the synchronization has been defined in
the IEEE 802.11a.
[0143] The receiver demodulates the signal symbol and determines
the information on the signal symbol in step S250. The signal
symbol includes information on transmit mode, data rate, mapping
method, and code rate.
[0144] The receiver determines whether the demodulated signal
symbol is transmitted from the MIMO system with reference to the
transmit mode information in step S260. The transmit mode
information is given based on an establishment value of the R4 bit
among the signal symbols.
[0145] When the transmit mode is the MIMO-OFDM mode, the channel
estimation is performed by using the second long preamble
transmitted after the signal symbol. The first long preamble of a
subcarrier which is not used by another antenna is substituted for
the second long preamble. Accordingly, the channel estimation on
the MIMO-OFDM signal is finished when the second estimation is
performed 8270.
[0146] The phase offset is compensated by using the pilot
subcarrier, and the data demodulation is performed according to the
data rate, mapping method, and code rate in the signal symbol S280.
The data demodulation has been described with reference to FIG.
3.
[0147] When the transmit mode is not the MIMO-OFDM mode in the
previous step S260, the phase compensation and the data
demodulation are performed without performing another channel
estimation.
[0148] According to the exemplary embodiment of the present
invention, the high-speed data rate is provided by the MIMO-OFDM
system, and the compatibility with the conventional system is also
provided because most of the frame configuration of the
conventional single antenna OFDM system is maintained in the
exemplary embodiment of the present invention.
[0149] While the present invention has been described in detail
with reference to the preferred embodiments, those skilled in the
art will appreciate that various modifications and substitutions
can be made thereto without departing from the spirit and scope of
the present invention as set forth in the appended claims.
* * * * *