(19) United States
`(12) Patent Application Publication (10) Pub. No.: US 2006/0153282 A1
`(43) Pub. Date:
`Jul. 13, 2006
`Jung et al.
`
`US 20060153282Al
`
`(54) METHOD FOR TRANSMITTING AND
`RECEIVING PREAMBLE SEQUENCES IN AN
`ORTHOGONAL FREQUENCY DIVISION
`MULTIPLEXING COMMUNICATION
`SYSTEM USING A MULTIPLE INPUT
`MULTIPLE OUTPUT SCHEME
`
`(75) Inventors: Young-Ho Jung, Seoul (KR); Jae-Hak
`Chung, Seoul (KR); Seung-Hoon Nam,
`Seoul (KR)
`
`Correspondence Address:
`DILWORTH & BARRESE, LLP
`333 EARLE OVINGTON BLVD.
`UNIONDALE, NY 11553 (US)
`
`(73) Assignee: SAMSUNG ELECTRONICS CO.,
`LTD., SuWon-si (KR)
`
`(21) Appl. No.:
`
`11/332,531
`
`(22) Filed:
`
`Jan. 13, 2006
`
`(30)
`
`Foreign Application Priority Data
`
`Jan. 13, 2005 (KR) ....................................... .. 3464/2005
`
`Publication Classi?cation
`
`(51) Int. Cl.
`(2006.01)
`H04B 1/69
`(2006.01)
`H04B 1/707
`(52) Us. or. ............................................................ ..375/146
`
`ABSTRACT
`(57)
`In an orthogonal frequency division multiplexing (OFDM)
`communication system using multiple transmit antennas, a
`?rst base sequence With a ?rst length is segmented into a ?rst
`number of second sequences to Which different time offsets
`are applied. Subsequences of a ?rst preamble sequence
`corresponding to the number of second sequences are gen
`erated. A second base sequence With a second length is
`segmented into a second number of third sequences to Which
`different time offsets are applied. Subsequences of a second
`preamble sequence corresponding to the number of third
`sequences are generated. A subsequence is selected from the
`subsequences of the ?rst preamble sequence and is trans
`mitted through a transmit antenna in a ?rst time interval. A
`third preset number of subsequences are selected from the
`subsequences of the second preamble sequence, and are
`mapped and transmitted to the transmit antennas in a second
`time interval.
`
`;
`
`FRAME (000)
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`if 0E0M SYMBOL I‘
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`
`IPR2016-00981
`Ex. 2001 1
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`

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`Patent Application Publication Jul. 13, 2006 Sheet 1 0f 4
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`(PRIOR ART)
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`IPR2016-00981
`Ex. 2001 2
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`

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`Patent Application Publication Jul. 13, 2006 Sheet 2 0f 4
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`IPR2016-00981
`Ex. 2001 5
`
`

`
`US 2006/0153282 A1
`
`Jul. 13, 2006
`
`METHOD FOR TRANSMITTING AND RECEIVING
`PREAMBLE SEQUENCES IN AN ORTHOGONAL
`FREQUENCY DIVISION MULTIPLEXING
`COMMUNICATION SYSTEM USING A MULTIPLE
`INPUT MULTIPLE OUTPUT SCHEME
`[0001] This application claims priority under 35 U.S.C. §
`119 to an application entitled “Method for Transmitting/
`Receiving Preamble Sequences in an Orthogonal Frequency
`Division Multiplexing Communication System Using a
`Multiple Input Multiple Output Scheme” ?led in the Korean
`Intellectual Property Of?ce on Jan. 13, 2005 and assigned
`Serial No. 2005-3464, the contents of Which are incorpo
`rated herein by reference.
`
`BACKGROUND OF THE INVENTION
`
`[0002] 1. Field of the Invention
`
`[0003] The present invention generally relates to an
`orthogonal frequency division multiplexing (OFDM) com
`munication system using a multiple input multiple output
`(MIMO) scheme, and more particularly. to a method for
`transmitting and receiving preamble sequences in the
`MIMO-OFDM communication system.
`
`[0004] 2. Description of the Related Art
`
`[0005] A large amount of research is being conducted to
`provide users With services based on various qualities of
`service (QoS) at a high transmission rate in fourth-genera
`tion (4G) communication systems, Which serve as next
`generation communication systems. In the current 4G-com
`munication system, research is actively being conducted to
`support a high-speed service for ensuring mobility and QoS
`in broadband Wireless access (BWA) communication sys
`tems such as Wireless local area netWork (LAN) and Wireless
`metropolitan area netWork (MAN) communication systems.
`
`[0006] Research is also being conducted in an orthogonal
`frequency division multiplexing (OFDM) scheme useful to
`transmit high-speed data in a Wired/Wireless channel of the
`4G-communication system. The OFDM scheme transmits
`data using a multicarrier, and is a type of multicarrier
`modulation (MCM) scheme for converting a serially input
`symbol stream to parallel signals, modulating the parallel
`signals into a plurality of orthogonal subcarriers, and trans
`mitting the orthogonal subcarriers.
`[0007] To provide high-speed and high-quality Wireless
`multimedia services, the 4G-communication system needs
`broadband spectral resources. When the broadband spectral
`resources are used, the effect of fading due to multipath
`propagation is severe in a Wireless transmission path and
`also the effect of frequency selective fading Which occurs in
`a transmission band. When a high-speed Wireless multime
`dia service is provided, the OFDM scheme robust to the
`frequency selective fading has a higher gain than a code
`division multiple access (CDMA) scheme. Therefore, the
`OFDM scheme is becoming actively exploited in the
`4G-communication system.
`
`[0008] A Wireless communication system serving as a
`system for supporting a Wireless communication service
`includes a base station (BS) and a mobile station (MS). The
`BS and the MS support the Wireless communication service
`using a frame. Accordingly, the BS and the MS must acquire
`mutual synchronization for frame transmission and recep
`
`tion. For synchronization acquisition, the BS sends a syn
`chronization signal to the MS such that the MS can knoW the
`start of the frame sent from the BS.
`[0009] Then, the MS receives the synchronization signal
`from the BS, identi?es frame timing of the BS, and demodu
`lates a received frame on the basis of the identi?ed frame
`timing. Conventionally, the synchronization signal uses a
`speci?c preamble sequence agreed to in advance betWeen
`the BS and the MS.
`
`[0010] The preamble sequence uses a loW Peak to Average
`PoWer Ratio (PAPR) in the OFDM communication system.
`A preamble is used to perform synchronization acquisition,
`channel estimation, BS identi?cation, and so on.
`
`[0011] A preamble sequence With a loW PAPR is used in
`the OFDM communication system. The reason for this Will
`be described beloW.
`
`[0012] Because the OFDM communication system serv
`ing as the multicarrier communication system uses a plu
`rality of subcarriers, a transmitted signal is a sum of inde
`pendent signals and therefore a difference betWeen a
`maximum poWer value and a mean poWer value of time
`domain signal values is large. In the OFDM communication
`system, a PAPR value is large in a data interval and a linear
`interval of an ampli?er provided in the OFDM system is
`de?ned on the basis of a maximum PAPR value in the data
`interval. Because a preamble can be transmitted at poWer
`increased by a difference With the maximum PAPR in the
`data interval When the PAPR of the preamble is set to a loW
`value, the performance of channel estimation, synchroniza
`tion acquisition, BS identi?cation, and so on can be
`improved. Accordingly, it is important that the PAPR is
`loWered in the preamble interval.
`
`[0013] When a signal transmitted from a transmitter is
`distorted While passing through a radio channel, a receiver
`receives the distorted transmitted signal. The receiver
`acquires time/frequency synchronization using a preamble
`sequence preset betWeen the transmitter and the receiver.
`After channel estimation, the receiver demodulates a
`received signal corresponding to the distorted transmitted
`signal into frequency domain symbols through a fast Fourier
`transform (FFT). After demodulation into frequency domain
`symbols, the receiver decodes the frequency domain sym
`bols into information/data through source decoding and
`channel decoding corresponding to channel coding applied
`in the transmitter.
`
`[0014] The OFDM communication system uses a pre
`amble sequence in all of frame timing synchronization,
`frequency synchronization, and channel estimation. Of
`course, the OFDM communication system may perform the
`frame timing synchronization, frequency synchronization,
`and channel estimation using a guard interval, a pilot sub
`carrier, and so on in addition to a preamble. In the case of the
`preamble sequence, the knoWn symbols are transmitted in a
`start part of every frame or data burst. The preamble
`sequence is used to update estimated time/frequency/chan
`nel information through a guard interval and a pilot subcar
`rier of a data transmission part.
`
`[0015] A preamble sequence and a preamble sequence
`generation method of the OFDM communication system
`using a multiple input multiple output (MIMO) scheme, i.e.,
`multiple transmit antennas (Tx. ANTS) (e.g., NTX transmit
`
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`US 2006/0153282 A1
`
`Jul. 13, 2006
`
`antennas) and multiple receive antennas (Rx. ANTS) (e.g.,
`NRX receive antennas) Will be described With reference to
`FIG. 1, Which schematically illustrates a preamble sequence
`mapping structure of a conventional OFDM communication
`system using the MIMO scheme.
`
`[0016] FIG. 1 illustrates the preamble sequence mapping
`structure When BSs, for example, the ?rst and second BSs
`(BS #1 and BS #2), con?guring the OFDM communication
`system use the ?rst and second transmit antennas (Tx. ANT
`#1 and Tx. ANT #2), respectively. As illustrated in FIG. 1,
`preamble sequences transmitted through the ?rst and second
`transmit antennas of BS #1 are different from each other, and
`preamble sequences transmitted through the ?rst and second
`transmit antennas of BS #2 are different from each other. The
`preamble sequences used in BS #1, i.e., the preamble
`sequences transmitted through the ?rst and second transmit
`antennas of BS #1, are different from the preamble
`sequences used in BS #2, i.e., the preamble sequences
`transmitted through the ?rst and second transmit antennas of
`BS #2.
`
`[0017] In the cellular communication system serving as
`the OFDM communication system, an MS must be able to
`distinguish a plurality of cells. Conventionally, one BS can
`cover a plurality of cells. HoWever, for convenience of
`explanation, it is assumed that one BS covers only one cell.
`As a result, the MS must be able to distinguish a plurality of
`BSs such that a target BS to Which the MS belongs can be
`identi?ed among the BSs con?guring the OFDM commu
`nication system.
`[0018] Accordingly, the OFDM communication system
`must allocate different preamble sequences betWeen the BSs
`con?guring the OFDM communication system and betWeen
`the transmit antennas of the BSs. Each BS transmits the
`allocated preamble sequences through multiple transmit
`antennas, i.e., NTX transmit antennas. Because the different
`preamble sequences are transmitted through the transmit
`antennas of each BS as described above, an MS must have
`preamble sequences based on the number of transmit anten
`nas provided in each BS. If the number of BSs con?guring
`the OFDM communication system is M and the M BSs are
`provided With the NTX transmit antennas, respectively, the
`OFDM communication system must be provided With
`M><NTX preamble sequences.
`[0019] In this case, the OFDM communication system
`must generate the M><NTX preamble sequences. When the
`preamble sequences With a preset length are generated, the
`OFDM communication system has a problem in that a
`maximum cross-correlation value betWeen the preamble
`sequences and a PAPR increase as the number of preamble
`sequences increases.
`
`[0020] Because an MS must be provided With M><NTX
`correlators to distinguish the M><NTX preamble sequences,
`the MS has a problem in that its hardWare load increases.
`There is a problem in that a computation amount for
`distinguishing betWeen BSs and synchroniZation acquisition
`using the correlators linearly increases according to the
`number of BSs and the number of transmit antennas.
`
`SUMMARY OF THE INVENTION
`
`[0021] It is, therefore, an object of the present invention to
`provide a method for transmitting and receiving preamble
`
`sequences in an orthogonal frequency division multiplexing
`(OFDM) communication system using a multiple input
`multiple output (MIMO) scheme.
`[0022] It is another object of the present invention to
`provide a method for transmitting and receiving preamble
`sequences With a minimum Peak to Average PoWer Ratio
`(PAPR) in an orthogonal frequency division multiplexing
`(OFDM) communication system using a multiple input
`multiple output (MIMO) scheme.
`[0023] It is another object of the present invention to
`provide a method for transmitting and receiving preamble
`sequences that can maximiZe the number of base stations
`(BSs) capable of being distinguished in an orthogonal fre
`quency division multiplexing (OFDM) communication sys
`tem using a multiple input multiple output (MIMO) scheme.
`[0024] It is yet another object of the present invention to
`provide a method for transmitting and receiving preamble
`sequences that can correctly perform channel estimation in
`an orthogonal frequency division multiplexing (OFDM)
`communication system using a multiple input multiple out
`put (MIMO) scheme.
`[0025] In accordance With an aspect of the present inven
`tion, there is provided a method for transmitting preamble
`sequences from a transmitter in an orthogonal frequency
`division multiplexing (OFDM) communication system
`using multiple transmit antennas, including segmenting a
`?rst base sequence With a ?rst preset length into a ?rst preset
`number of second sequences; applying different time offsets
`to the second sequences and generating subsequences of a
`?rst preamble sequence corresponding to the number of
`second sequences; segmenting a second base sequence With
`a second preset length into a second preset number of third
`sequences; applying different time offsets to the third
`sequences and generating subsequences of a second pre
`amble sequence corresponding to the number of third
`sequences; selecting a speci?c subsequence from the sub
`sequences of the ?rst preamble sequence and transmitting
`the speci?c subsequence through a speci?c transmit antenna
`of the multiple transmit antennas in a ?rst preset time
`interval; and selecting a third preset number of subsequences
`from the subsequences of the second preamble sequence and
`mapping and transmitting the selected subsequences of the
`second preamble sequence to the multiple transmit antennas
`in a second preset time interval.
`
`[0026] In accordance With another aspect of the present
`invention, there is provided a method for receiving preamble
`sequences in a receiver of an orthogonal frequency division
`multiplexing (OFDM) communication system, the OFDM
`communication system including at least one transmitter
`using multiple transmit antennas and the receiver using at
`least one receive antenna, the method including receiving a
`signal and correlating the received signal and a ?rst preset
`number of subsequences of a ?rst preamble sequence;
`acquiring synchroniZation With a transmitter to Which the
`receiver belongs on a basis of a subsequence of the ?rst
`preamble sequence With a maximum correlation value of
`correlation values betWeen the received signal and the
`subsequences of the ?rst preamble sequence; correlating the
`received signal and a second preset number of subsequences
`of a second preamble sequence; detecting a third preset
`number of correlation values from a maximum correlation
`value of correlation values betWeen the received signal and
`
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`
`the subsequences of the second preamble sequence; and
`identifying a transmitter to Which the receiver belongs on a
`basis of subsequences of the second preamble sequence
`mapped to the detected correlation values.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`[0027] The above and other objects and advantages of the
`present invention Will be more clearly understood from the
`folloWing detailed description taken in conjunction With the
`accompanying draWings, in Which:
`[0028] FIG. 1 schematically illustrates a preamble
`sequence mapping structure of a conventional orthogonal
`frequency division multiplexing (OFDM) communication
`system using a multiple input multiple output (MIMO)
`scheme;
`[0029] FIG. 2 schematically illustrates a preamble
`sequence structure of a MIMO-OFDM communication sys
`tem in accordance With an embodiment of the present
`invention;
`[0030] FIG. 3 schematically illustrates a ?rst preamble
`sequence structure of the MIMO-OFDM communication
`system in accordance With an embodiment of the present
`invention; and
`[0031] FIG. 4 schematically illustrates a second preamble
`sequence structure of the MIMO-OFDM communication
`system in accordance With an embodiment of the present
`invention.
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`
`[0032] Preferred embodiments of the present invention
`Will be described in detail herein beloW With reference to the
`accompanying draWings. In the folloWing description, only
`parts needed to understand the operation of the present
`invention Will be described, and other parts are omitted for
`clarity and conciseness.
`
`[0033] The present invention provides a method for trans
`mitting and receiving preamble sequences in an orthogonal
`frequency division multiplexing (OFDM) communication
`system using a multiple input multiple output (MIMO)
`scheme. Speci?cally, the present invention provides the
`method for transmitting and receiving preamble sequences
`in the OFDM communication system using the MIMO
`scheme, i.e., multiple transmit antennas (TX. ANTS) (e.g.,
`NTX transmit antennas) and multiple receive antennas (RX.
`ANTS) (e.g., NRX receive antennas). In the OFDM commu
`nication system, a preamble sequence to be transmitted
`through the ?rst transmit antenna (TX. ANT #1) is set to be
`different from a preamble sequence to be transmitted
`through other transmit antennas, i.e., the second to NTX-th
`transmit antennas (TX. ANT #2 to TX. ANT # NTX), eXcept
`the ?rst transmit antenna.
`[0034] The OFDM communication system using the
`MIMO scheme (hereinafter, referred to as the MIMO
`OFDM communication system) must generate a preamble
`sequence used for synchronization acquisition, channel esti
`mation, and BS identi?cation While considering the folloW
`ing points.
`[0035] (l) Orthogonality must be maintained betWeen
`multipath components of preamble sequences transmitted
`
`from transmit antennas of the MIMO-OFDM communica
`tion system such that the performance of channel estimation
`can be optimized.
`
`[0036] (2) A cross-correlation must be minimized betWeen
`preamble sequences allocated to BSs con?guring the
`MIMO-OFDM communication system such that the perfor
`mance of BS identi?cation, i.e., BS detection, can be opti
`mized.
`
`[0037] (3) Auto-correlation characteristics of the preamble
`sequence itself must be eXcellent such that the performance
`of synchronization acquisition can be optimized.
`
`[0038] (4) A loW Peak to Average PoWer Ratio (PAPR)
`must be provided.
`
`[0039] A linear interval of a poWer ampli?er (PA) pro
`vided in the transmitter of the MIMO-OFDM communica
`tion system is designed on the basis of a maXimum PAPR
`value in a data interval. Because a preamble can be trans
`mitted at poWer increased by a difference With the maXimum
`PAPR in the data interval When the PAPR of the preamble
`is set to a loW value, the performance of channel estimation,
`synchronization acquisition, BS identi?cation, and so on can
`be improved. Accordingly, it is important that the PAPR is
`loWered in the preamble interval.
`
`[0040] (5) The number of preamble sequences must be
`minimized such that not only the synchronization acquisi
`tion performance can be optimized, but also an amount of
`computation of the receiver can be minimized.
`
`[0041] In the present invention considering the above
`described points, preamble sequences are transmitted and
`received in Which the preamble sequence to be transmitted
`through the ?rst transmit antenna is set to be different from
`the preamble sequence to be transmitted through other
`transmit antennas, i.e., the second to NTX-th transmit anten
`nas. Here, the preamble sequence transmitted through the
`?rst transmit antenna is referred to as the ?rst preamble
`sequence (Preamble Sequence #1) and the preamble
`sequence transmitted through the ?rst to NTX-th transmit
`antennas is referred to as the second preamble sequence
`(Preamble Sequence #2).
`[0042] A preamble sequence structure of the MIMO
`OFDM communication system in accordance With the
`present invention Will be described With reference to FIG. 2.
`
`[0043] Referring to FIG. 2, the preamble sequence struc
`ture of the present invention is a structure in Which the ?rst
`and second preamble sequences are combined as described
`above. The ?rst preamble sequence is transmitted through
`the ?rst transmit antenna, and the second preamble sequence
`is transmitted through the ?rst to NTX-th transmit antennas.
`The ?rst preamble sequence is used to estimate a frequency
`o?fset, acquire frame synchronization, send cell-speci?c
`information of an associated BS or cell, and estimate a
`sequence set used in a transmission interval of the second
`preamble sequence. The cell-speci?c information Will be
`described beloW.
`
`[0044] NoW, the ?rst preamble sequence Will be described
`as folloWs.
`
`[0045] The MIMO-OFDM communication system is pro
`vided With Ngroup ?rst base sequences to generate ?rst
`preamble sequences. Here, the ?rst base sequences use a
`
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`US 2006/0153282 A1
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`sequence With excellent auto-correlation characteristics, for
`example, a Constant Amplitude Zero Auto-Correlation
`(CAZAC) sequence or a Zero Auto-Correlation (ZAC)
`sequence. The reason Why the ?rst base sequences use the
`sequence With the excellent auto-correlation characteristics
`is as follows.
`
`[0046] A PAPR ofthe CAZAC sequence is 0 [dB] because
`the amplitude of the CAZAC sequence is constant, and a
`PAPR of the ZAC sequence is less than 3 [dB]. That is, the
`CAZAC sequence is an optimal sequence in terms of the
`PAPR. When a time difference betWeen an associated
`CAZAC sequence and an arbitrary CAZAC sequence is 0,
`that is, the associated CAZAC sequence correctly matches
`the arbitrary CAZAC sequence Without the time difference,
`an auto-correlation value becomes a peak value. As a result,
`the sequence detection performance is optimal because the
`auto-correlation value becomes 0 When the CAZAC
`sequence is incorrectly synchronized. Multiple (i.e., Ngmup)
`?rst base sequences use multiple (i.e., Ngmup) sequences
`With a minimum cross-correlation value retrieved from
`CAZAC sequences With an associated length. Neighbor BSs
`allocate different ?rst base sequences and therefore cross
`interference is minimiZed.
`
`[0047] For convenience of explanation, an example of
`generating the ?rst base sequence using the CAZAC
`sequence Will be described herein. A ?rst preamble sequence
`structure of the MlMO-OFDM communication system in
`accordance With the present invention Will be described With
`reference to FIG. 3.
`
`[0048] A set of ?rst preamble sequences in accordance
`With the present invention is con?gured by cyclic shift
`transpose sequences With different time o?fsets in the ?rst
`base sequence of the length N, i.e., a CAZAC sequence
`c=[clc2 .
`.
`. cN_lcN]T. That is, the CAZAC sequence c=[clc2
`.
`.
`. cN_lcN]T is segmented into Nlprel CAZAC subsequences,
`i.e., subsequences of the ?rst preamble sequence. The arbi
`trary i-th CAZAC subsequence ci, i.e., the i-th preamble
`subsequence of the ?rst preamble sequence, among the N1pm l
`CAZAC subsequences, is de?ned as shoWn in Equation (1).
`
`T
`
`Equation (1)
`
`[0049] The Nlprel CAZAC subsequences are shifted in the
`form of having different time offsets, such that Nlprel pre
`amble subsequences of the ?rst preamble sequence are
`generated. Here, the length of the i-th CAZAC subsequence
`ci, i.e., the i-th preamble subsequence of the ?rst preamble
`sequence, is N/Nprel, and is set to be greater than or equal
`to the number of maximum delay samples, i.e., the maxi
`mum length of channel delay spread, Lmax, such that a
`cross-correlation betWeen preamble sequences is prevented.
`
`[0050] In an embodiment of the present invention, it is
`assumed that the length N of the ?rst preamble sequence
`corresponds to 512 samples and Nlprel is 4. As described
`above, Ngroup BSs can generate Nlprel subsequences of the
`?rst preamble sequence using a different ?rst base sequence,
`respectively. A subsequence of the ?rst preamble sequence
`is selected from the Nlprel generated sub sequences of the ?rst
`
`preamble sequence and the selected subsequence of the ?rst
`preamble sequence is transmitted through the ?rst transmit
`antenna.
`
`[0051] When a subsequence of the ?rst preamble sequence
`is selected from the generated N1M6 1 subsequences of the ?rst
`preamble sequence and the selected subsequence of the ?rst
`preamble sequence is transmitted through the ?rst transmit
`antenna, each BS can map cell-speci?c information to a
`subsequence index of the ?rst preamble sequence to be
`transmitted through the ?rst transmit antenna. The cell
`speci?c information is speci?c information managed in an
`associated cell or BS. That is, the speci?c information may
`be a ratio betWeen an uplink and doWnlink per frame When
`the BS uses a Time Division Duplex (TDD) scheme. The
`speci?c information is shoWn in Table 1.
`
`TABLE 1
`
`Preamble sequence #l-
`subsequence index
`
`Number of uplink
`symbols
`
`Number of doWnlink
`symbols
`
`1
`2
`3
`4
`
`2
`4
`6
`8
`
`8
`6
`4
`2
`
`[0052] When a subsequence index of the ?rst preamble
`sequence is l and the number of symbols con?guring the
`frame is 10, the number of uplink symbols is 2 and the
`number of doWnlink symbols is 8. Table 1 shows the number
`of uplink symbols and the number of doWnlink symbols
`mapped to a subsequence index of the ?rst preamble
`sequence. Of course, other cell-speci?c information can be
`indicated.
`
`[0053] The ?rst preamble sequence structure of the
`MlMO-OFDM communication system in accordance With
`the present invention has been described With reference to
`FIG. 3. Next, a second preamble sequence structure of the
`MlMO-OFDM communication system in accordance With
`an embodiment of the present invention Will be described
`With reference to FIG. 4.
`
`[0054] A set of second preamble sequences in accordance
`With the present invention is con?gured by cyclic shift
`transpose sequences With different time o?fsets in the second
`base sequence of the length N, i.e., a CAZAC sequence
`c=[clc2 .
`.
`. cN_lcN]T. That is, the CAZAC sequence c=[c1c2
`.
`.
`. cN_lcN]T is segmented into N1Dre2 CAZAC subsequences,
`i.e., subsequences of the second preamble sequence. The
`arbitrary i-th CAZAC subsequence ci, i.e., the i-th preamble
`subsequence of the second preamble sequence, among the
`N 62 CAZAC subsequences, is de?ned as shoWn in Equation
`(23.
`
`C; = C min/v Wii +
`pre 2
`
`cgll?+2
`Npre 2
`
`C [N
`
`C’ [N
`
`T
`
`Equation (2)
`
`[0055] The Npm2 CAZAC subsequences are shifted in the
`form of having different time offsets, such that N1Dre2 pre
`amble subsequences of the second preamble sequence are
`generated. Here, the length of the i-th CAZAC subsequence
`ci, i.e., the i-th preamble subsequence of the second pre
`
`IPR2016-00981
`Ex. 2001 9
`
`

`
`US 2006/0153282 A1
`
`Jul. 13, 2006
`
`amble sequence, is N/Nprez, and is set to be greater than or
`equal to the number of maximum delay samples, i.e., the
`maximum length of channel delay spread, Lmax, such that a
`cross-correlation betWeen preamble sequences is prevented.
`
`[0056] In an embodiment of the present invention, it is
`assumed that the length of the second preamble sequence
`corresponds to 1,024 samples and N1Dre2 is 10. As described
`above, Ngroup BSs can generate Nlm2 subsequences of the
`second preamble sequence using a different second base
`sequence, respectively. NTX subsequences of the second
`preamble sequence corresponding to the number of transmit
`antennas are selected from the N1Dre2 generated subsequences
`of the second preamble sequence and are transmitted
`through the ?rst to NTX-th transmit antennas.
`[0057] When each BS selects the NTX subsequences of the
`second preamble sequence from the N1Dre2 generated subse
`quences of the second preamble sequence and transmits
`through the ?rst to NTX-th transmit antennas as described
`above, a BS identi?er (ID) is de?ned by a combination of
`subsequence indices of the second preamble sequence to be
`transmitted through the second to NTX -th transmit antennas.
`[0058] The NTX subsequences of the second preamble
`sequence are selected from the N1Dre2 generated subse
`quences of the second preamble sequence and are transmit
`ted through the ?rst to NTX-th transmit antennas. Alterna
`tively, the NTX subsequences of the second preamble
`sequence may be transmitted through some transmit anten
`nas of the NTX transmit antennas. This case Will be described
`beloW.
`
`[0059] Preamble sequences, i.e., subsequences of the sec
`ond preamble sequence, selected to indicate BS IDs in the
`BSs con?guring the MIMO-OFDM communication system
`are different from each other. That is, the BSs con?guring
`the MIMO-OFDM communication system use subse
`quences of the second preambles sequences differently from
`each other, such that orthogonality can be maintained
`betWeen the transmit antennas and also betWeen the BSs.
`Because the preamble sequence uses the CAZAC sequence,
`PAPR characteristics are excellent.
`
`[0060] Next, there Will be described in more detail the case
`Where the NTX subsequences of the second preamble
`sequence are selected from the N1Dre2 generated subse
`quences of the second preamble sequence and are transmit
`ted using only some transmit antennas of the NTX transmit
`antennas Without using all the ?rst to NTX-th transmit
`antennas.
`
`[0061] It is assumed that ?xed subsequences of the second
`preamble sequence are transmitted through In transmit
`antennas of the NTX transmit antennas used in an arbitrary
`BS of the MIMO-OFDM communication system, Where
`NTX is 4, m is 2, andN 2 is 10.
`pre
`[0062] The ?xed subsequences of the second preamble
`sequence are transmitted through the third and fourth trans
`mit antennas of the ?rst to fourth transmit antennas. The
`ninth subsequence of the second preamble sequence is
`transmitted through the third transmit antenna. The tenth
`subsequence of the second preamble sequence is transmitted
`through the fourth transmit antenna. Different subsequences
`of the second preamble sequence are transmitted through the
`remaining transmit antennas, i.e., the ?rst and second trans
`mit antennas, except the third and fourth transmit antennas.
`
`NgmulwnCNTXm subsequence combinations of the second
`preamble sequence are generated in total. Here, a combina
`tion of subsequences of the second preamble sequence to be
`transmitted through the ?rst and second transmit antennas
`indicates a BS ID and is referred to as IDpre. Next, an
`operation for allocating ID1pm corresponding to the BS ID
`Will be described With reference to Table 2.
`
`TABLE 2
`
`IDPre
`
`TX. ANT #1
`
`TX. ANT #2
`
`1
`
`2
`
`3
`
`4
`
`5
`
`6
`
`Preamble
`sequence #2
`subsequence #1
`Preamble
`sequence #2
`subsequence #1
`Preamble
`s