(12) United States Patent
`Tan et al.
`
`(10) Patent No.:
`
`(45) Date of Patent:
`
`US 8,000,305 B2
`Aug. 16,2011
`
`US008000305B2
`
`......... .. 375/130
`8/2001 Bhatoolaul et a1.
`2001/0017881 A1*
`375/326
`2/2003 Min et al.
`......... ..
`2003/0031275 A1*
`370/329
`6/2003 Choi et al.
`..
`2003/0103476 A1*
`455/403
`1/2004 Lim et al.
`2004/0014452 A1*
`2004/0264550 A1* 12/2004 Dabak ......................... .. 375/142
`2005/0048920 A1
`3/2005 Liu
`.................. .. 375/267
`2005/0084030 A1*
`4/2005 Zhou et al.
`2005/0143118 A1*
`6/2005 Bernhardsson et al.
`.... .. 455/522
`2005/0202818 A1*
`9/2005 Hondo et al.
`............... .. 455/434
`2006/0050799 A1*
`3/2006 Hou et al.
`.... ..
`375/260
`2006/0126573 A1*
`6/2006 Dick et al.
`.................. .. 370/335
`
`
`
`(Continued)
`
`EP
`
`FOREIGN PATENT DOCUMENTS
`1 198 076 A1
`4/2002
`
`(Continued)
`
`OTHER PUBLICATIONS
`
`Mu1ti_Carrier_and_Spread_Spectrum_Systems, by Fazel K. and
`Kaiser S.*
`R1 -051033 Further Topics on Uplink DFT-SOFDM for E-UTRA
`Agenda Item: 8.2, 3GPP TSG RAN WG1#42 bis, San Diego, USA,
`Oct. 10-14, 2005, pp. 1-24.
`
`(Continued)
`
`Primary Examiner — Jean Gelin
`Assistant Examiner — Michael Nguyen
`
`(57)
`
`ABSTRACT
`
`A system and method for initializing a system communica-
`tion without previous reservations for random access channel
`(RACH) access includes a first step of defining at least one
`spread sequence derived from at least one constant amplitude
`zero autocorrelation sequence. A next step includes combin-
`ing the spread sequence with a Walsh code to form an
`extended spread sequence. A next step includes using the
`extended spread sequence in a preamble for a RACH. A next
`step includes sending the preamble to a BTS for acquisition.
`A next step includes monitoring for a positive acquisition
`indicator from the BTS. A next step includes scheduling the
`sending ofa RACH message. A next step includes sending the
`RACH message.
`
`13 Claims, 13 Drawing Sheets
`
`(54)
`
`(75)
`
`PREAMBLE SEQUENCING FOR RANDOM
`ACCESS CHANNEL IN A COMMUNICATION
`SYSTEM
`
`Inventors: Jun Tan, Lake Zurich, IL (US); Amitava
`Ghosh, Buffalo Grove, IL (US);
`Rapeepat Ratasuk, Hoffman Estates, IL
`(US); Fan Wang, Chicago, IL (US);
`Weimin Xiao, Barrington, IL (US)
`
`(73)
`
`Assignee: Motorola Mobility, Inc., Libertyville, IL
`(US)
`
`(*)
`
`Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. l54(b) by 621 days.
`
`(21)
`
`Appl. No.: 11/621,587
`
`(22)
`
`Filed:
`
`Jan. 10, 2007
`
`(65)
`
`(60)
`
`(51)
`
`(52)
`(58)
`
`(56)
`
`Prior Publication Data
`
`US 2007/0165567 A1
`
`Jul. 19,2007
`
`Related U.S. Application Data
`
`Provisional application No. 60/759,697, filed on Jan.
`17, 2006.
`
`Int. Cl.
`
`(2006.01)
`H04B 7/216
`U.S. Cl.
`...................................... .. 370/335; 455/434
`Field of Classification Search ................ .. 370/335;
`455/434
`
`See application file for complete search history.
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`..................... .. 375/343
`5/2003 P0p0vic'
`6,567,482 B1*
`6,804,307 B1* 10/2004 Popovic ..... ..
`.. 375/299
`5/2005 Du et al.
`........ ..
`.. 375/142
`6,901,104 B1*
`7/2005 Toskala et al.
`.. 370/335
`6,917,602 B2 *
`11/2005 Smolinske et al.
`.. 370/346
`6,967,942 B2 *
`
`
`
`..
`
`RADIO FRAME n-1
`
`RADIO FRAME n
`
`RADIO FRAME n+1
`
`
`
`RADIO FRAME (10ms)
`
`RADIO FRAME CONSTRUCTED FROM 1 ms SUB-FRAMES
`
`
`
`
`Va
`
`
`\.
`2%
`sJ
`.\
`
`
`
`
`
`
`
`
`
`V
`
`%%%%7%7
`1.42.4
`
`
`%%Z%%%%Z%
`\
`
`
`RACH SYMBOL
`
`DATA SYMBOL
`
`HALF PILOT SYMBPL
`
`ZTE 1026-0001
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`ZTE 1026-0001
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`

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`US 8,000,305 B2
`Page 2
`
`U.S. PATENT DOCUMENTS
`2008/0253323 A1* 10/2008 Fischer
`....................... .. 370/329
`
`FOREIGN PATENT DOCUMENTS
`W0 W0 2004-102979 A2
`11/2004
`
`OTHER PUBLICATIONS
`
`IEEE 802.16 Broadband Wireless Access Working Group <http://
`ieee802.org/ 16>, Ranging Improvement for 802.16e OFDMA PHY,
`Jul. 7, 2004, IEEE C802.16e-04/143rl, pp. 1-43.
`3GPP TSG RAN WG1 Ad Hoc on LTE, San Diego, USA, Oct. 10-14,
`2005, Link Comparison of Localized vs. Distributed Pilot and Local-
`ized vs. Distributed Data, R1-0511153, pp. 1-5.
`
`3GPP TSG RAN WG1 Meeting #42bis, San Diego, USA<Oct.
`10-14, 2005, R1-051058, RACH Preamble Design, pp. 1-7.
`Fazel et al, “Multi-Carrier and Spread Spectrum Systems,” John
`Wiley & Sons, Ltd., ISBN 0-470-84899-5, entire document.
`Blaine R. Copenheaver, “Corresponding Application PCT/US2007/
`060453—PCT International Search Report and Written Opinion,”
`WIPO, ISA/US, Commissioner for Patents, Alexandria, VA, USA,
`Oct. 3, 2007, 9 pages, most relevant pp. 4, 7-9.
`Yoshiko Kuwahara, “Corresponding Application PCT/US2007/
`060453—PCT International Preliminary Report on Patentability,”
`The International Bureau of WIPO, Geneva, Switzerland, Jul. 31,
`2008, 7 pages, most relevant pp. 2, 5-7.
`
`* cited by examiner
`
`ZTE 1026-0002
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`ZTE 1026-0002
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`

`
`U.S. Patent
`
`Aug. 16,2011
`
`Sheet 1 of 13
`
`US 8,000,305 B2
`
`ZTE 1026-0003
`
`RADIO FRAME n-1
`
`RADIO FRAME n
`
`RADIO FRAME (10ms)
`
`RADIO FRAME CONSTRUCTED FRoM t ms SUB—FRAMES
`
`7%
`
`ZV
`
`SUB—FRAMES (Ag. Q5 ms)
`
`RACH SYMBOL
`
`DATA SYMBOL
`
`HALF PILOT SYMBPL
`
`FIG. 1
`
`ZTE 1026-0003
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`
`
`
`
`

`
`U.S. Patent
`
`Aug. 10, 2011
`
`Sheet 2 0113
`
`US 8,000,305 B2
`
`RACH PARAMETERS FOR THE TDM/FDM STRUCTURE
`
`RACH PARAMETERS IN
`LocALIzED MODE
`
`Immg 2.51012
`
`BANDWIDTH
`5.0 MHz
`immmmnmg 20.0 MHz
`
`f RACH OPPORTUNITIES
`
`40
`2o
`5
`# RB (N)
`—K
`# 0F SEOUENCES (FOR ALL
`SECTORS/CELLS)
`(N5)
`§ or CYCLIC SHIFTED VERSION
`or EACH SEQUENCE (NSH)
`
`ZTE 1026-0004
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`ZTE 1026-0004
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`

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`U.S. Patent
`
`Aug. 16,2011
`
`Sheet 3 of 13
`
`US 8,000,305 B2
`
`
`
`-€+-
`
`
`-£&- CIRCULAR CROSS-CORRELATION p=L2
`
`-++- CIRCULAR CROSS—CORRELATION u=17
`
`CIRCULAR AUTOCORRELATION
`
`———————— --
`
`
`
`———————— --
`
`§ 0.8
`
`0.5
`
`0.4
`
`0.2
`
`E E
`
`I E
`
`3 E
`
`53
`
`0
`
`§ §
`
`-0.2
`
`-0415
`
`-10
`
`-5
`
`0
`DELAY
`
`5
`
`10
`
`15
`
`FIG. 3
`
`cf
`.
`
`CODE gr
`
`14,;
`
`CODE g,,_30.
`I
`
`CODE g,,_50.
`
`H115
`
`CODE g,,_90.
`
`2
`
`E
`
`0
`
`30
`
`60
`
`90
`
`FIG. 4
`
`ZTE 1026-0005
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`ZTE 1026-0005
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`

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`U.S. Patent
`
`Aug. 10, 2011
`
`Sheet 4 0113
`
`US 8,000,305 B2
`
`
`
`
`
`_________________________________________________________________8
`
`
`
`
`
`
`
`
`
`___0_E,_|91_?
`
`w_
`
`_
`
`E
`
`______15_________E._._.zmf_E_1-_1.1
`
`________16..27_________________MG////¢...____1%II__|_/1-..»,|_\
`1m4./.,,_
`___Mr_I___B|_|
`
`10
`
`11
`
`12
`
`THRESHOLD 0 (dB)
`
`9
`
`FIG.
`
`6
`
`ZTE 1026-0006
`
`ZTE 1026-0006
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`
`

`
`U.S. Patent
`
`Aug. 16,2011
`
`Sheet 5 of 13
`
`US 8,000,305 B2
`
`05 MS SUB—FRAME
`
`05 MS SUB—FRAME
`
` IIIEMIEMIEMIIEMIIEMIIIEMIEMIEM
`
`FIG. 7
`
` TIME-DOMAIN MODULATION
`
`MESSAGE
`
`ZTE 1026-0007
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`ZTE 1026-0007
`
`

`
`U.S. Patent
`
`Aug. 16,2011
`
`Sheet 6 of 13
`
`US 8,000,305 B2
`
`FREQUENCY DOMAIN MODULATION
`
`TIME
`SPREADING
`
`
`
`GN—1
`
`FREQUENCY SPREADING SEQUENCE
`
`FIG. 9
`
`_0 ' 2
`
`9‘
`
`4
`
`-300
`
`-200
`
`-100
`
`0
`
`100
`
`200
`
`300
`
`ZTE 1026-0008
`
`NORMALIZEDCIRCULARAUTO-/CROSS-CORRELATION
`
`
`
`
`
`
`
`ZTE 1026-0008
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`

`
`U.S. Patent
`
`Aug. 16,2011
`
`Sheet 7 of 13
`
`US 8,000,305 B2
`
`=E:_=E__§:::=E:_=E__§:::_E1+4EJLJ§:1I:
`
`§:Zf:_:E__:
`
`=:__M:E___
`
`=E:_=E__§:::=E:_=E__§:::__=E_§:::_4=3
`_§1Z:Z_E__:Z:_::f:_M:__
`
`-w_
`
`:EV\\,
`
`V — — DETECTION ERROR RATE-
`
`THRESHOLD e (dB)
`
`9
`
`10
`
`11
`
`12
`
`JE7T1T¢C3¥. 11
`
`_EE_=
`
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`
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`
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`
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`
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`
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`
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`
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`
`THRESHOLD 9 (dB)
`
`9
`
`1o
`
`11
`
`1l7iZ'(C5¥.
`
`12
`
`ZTE 1026-0009
`
`ZTE 1026-0009
`
`
`
`
`
`

`
`U.S. Patent
`
`Aug. 16,2011
`
`Sheet 8 of 13
`
`US 8,000,305 B2
`
`COMPARISON OF TDM/FDM AND HYBRID/CDM RACH (BW=5MHz).
`
`- mm W
`
`HYBRID/CDM mu
`
`NUMBER OF RACH OPPORTUNITIES
`(per ms)
`
`”MD”s“’sM”oEDM
`"HERE "0/‘W = "Um °F
`DEDM SYMBOL RESERVED FOR
`RACH per ms
`e.g. 160X No,-M FROM TABLE 1.
`
`INTERFACE GENERA TED T0
`SCHEDULED USERS
`
`SNR REDUIREMEMI FOR 1% FALSE
`ALARM AND MIssED DETECTION
`ERROR (TU 3 Km/h)
`
`"°”E
`
`-2 dB
`
`5”“
`
`-17 dB
`
`”oEDM /14
`
`RACH OVERHEAD (per ms)
`COLLISION PROBABILITY
`MEDIUM
`INTER—CELL INTERFERENCE
`SYSTEM INTERFERENCE LIMIIEDN0 (COLLISION LIMITED)
`
`NONE
`MEDIUM - HIGH
`
`FIG. 13
`
`ZTE 1026-0010
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`ZTE 1026-0010
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`

`
`U.S. Patent
`
`Aug. 16,2011
`
`Sheet 9 of 13
`
`US 8,000,305 B2
`
`UE
`
`NO
`
`YES
`
`FIG. 14
`
`
`
`CHANGE TX POWER AND/OR SEQUENCE
`
`I416
`
`SEND “Ac” “ESSAGE
`
`ma
`
`ZTE 1026-0011
`
`ZTE 1026-0011
`
`

`
`U.S. Patent
`
`Aug. 16, 2011
`
`Sheet 10 of 13
`
`US 8,000,305 B2
`
` USER EQUIPMENT
`
`I500
`
`1502
`
`FIG. 15
`
`NODE-B
`
`I420
`
`1426
`
`
`
`YES
`
`DETECT PREAMBLE
`
`
`
`
`I
`
`
`
`N0
`
`
`
`SEND ACK
`
`I424
`
`RECEIVE RACH MESSAGE
`
`
`
`FIG. 16
`
`ZTE 1026-0012
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`ZTE 1026-0012
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`

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`U.S. Patent
`
`Aug. 16, 2011
`
`Sheet 11 of 13
`
`US 8,000,305 B2
`
`NODE B
`
`ACK SENT
`
`
`SEND SCHEDULE INFO
`
`
`RECEIVE RACH MESSCE
`
`
`
`
`
`UE
`
`ACK DETECTED
`
`I430
`
`MONITOR CONTROL CHANNEL
`
`SEND RACH MESSAGE
`
`
`
`FIG. 17
`
`I436
`
`14.38
`
`ZTE 1026-0013
`
`ZTE 1026-0013
`
`

`
`U.S. Patent
`
`Aug. 16, 2011
`
`Sheet 12 of 13
`
`US 8,000,305 B2
`
`UE
`
`RACH ACK DETECTED
`
`1440
`
`NODE B
`
`RACH ACK SENT
`
`SEND RACH MESSAGE
`
`RECEIVE RACH MESSAGE
`
`
`
`FIG- 18
`
`ZTE 1026-0014
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`ZTE 1026-0014
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`

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`U.S. Patent
`
`Aug. 16, 2011
`
`Sheet 13 of 13
`
`US 8,000,305 B2
`
`UE
`
`NODE B
`
`RACH ACK DETECTED
`
`RACH ACK SENT
`
`1456
`
`I458
`
`ZTE 1026-0015
`
`
`SEND RACH MSG ACK
`
`
`
`
`RECEIVE RACH MESSAGE
`
`
`
`V 1452
`
`RACH MSSG
`ACK
`ECEIVED?
`
`SEND RACH MESSAGE
`
`FIG. 19
`
`ZTE 1026-0015
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`

`
`US 8,000,305 B2
`
`1
`PREAMBLE SEQUENCING FOR RANDOM
`ACCESS CHANNEL IN A COMMUNICATION
`SYSTEM
`
`Applicant hereby claims domestic priority benefits of
`Application No. 60/759,697 filed on Jan. 17, 2006, and the
`contents of which are incorporated by reference herein.
`
`TECHNICAL FIELD OF THE INVENTION
`
`This invention relates generally to communications and
`more particularly to use of a random access charmel in a
`communication system.
`
`BACKGROUND OF THE INVENTION
`
`Various communications protocols are known in the art.
`For example,
`the Third Generation Partnership Project
`(3GPP) has been working towards developing a number of
`protocols for use with a wireless communication path. The
`original scope of 3GPP was to produce globally applicable
`technical specifications and technical reports for a 3rd gen-
`eration mobile system based on evolved Global System for
`Mobile communication (GSM) core networks and the radio
`access technologies that they support, such as Evolved Um-
`versal Terrestrial Radio Access (EUTRA) including both Fre-
`quency Division Duplex (FDD) and Time Division Duplex
`(TDD) modes. 3GPP’s scope was subsequently amended to
`include the maintenance and development of GSM technical
`specifications and technical reports including evolved radio
`access technologies (e.g. General Packet Radio Service
`(GPRS) and Enhanced Data rates for GSM Evolution
`(EDGE)).
`Presently, EUTRA calls for a random access channel
`(RACH) protocol and in particular a physical random access
`procedure requiring reserved resources for RACH access.
`The RACH channel is used for initial access to the network as
`well as to transmit small to medium amount of control infor-
`
`mation and data packets. This 3GPP UMTS specification
`permits an overall procedure that allows for various protocol/
`operational states to suit varying degrees of needed, antici-
`pated, and/or desired operational activity for transmission of
`data packets. Unfortunately, for some desired applications
`using small of medium amounts of control information and
`data packets, the amount ofdata transmission activity appears
`to underutilize these reserved RACH resources, thereby wast-
`ing transmission resources.
`The RACH (random access channel) is essential for initial
`access to the network, for the transmission of control infor-
`mation and data packets. The initial access channel has dif-
`ferent names in different systems, such as RACH in the con-
`text of 3GPP, or ranging in the context of IEEE std. 802.16e.
`In this invention, we use RACH in its general sense to repre-
`sent the initial access charmel of communication systems.
`It is desired that the RACH include a contention channel,
`fast acquisition of preamble, minimization of interference,
`minimum impact on other scheduled data transmission, and
`low data rate transmission for short data/control messages.
`Several options are available for multiplexing between the
`RACH and scheduled-based channels; Time Division Multi-
`plexing (TDM), Frequency Division Multiplexing (FDM),
`and Code Division Multiplexing (CDM). However, in the
`3GPP system problems arise for multiplexing between
`RACH and scheduled-based channels using either TDM or
`FDM. In particular, TDM requires reservation of slots for
`RACH access, and FDM requires a frequency (subcarrier)
`reservation for RACH access. In either case, a resource res-
`
`2
`
`ervation is allotted even ifthere are few RACH requests in the
`system, which withholds unused resources that adversely
`affect system capacity. CDM transmission, on the other hand,
`will generate interference to other uplink users.
`To control interference generated by CDM transmission, a
`MC-CDMA (multi-carrier code division multiple access)
`technique can be applied for RACH design without reserving
`system resources. This invention uses this technique for non-
`reserved RACH access of EUTRA communication system.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`The features ofthe present invention, which are believed to
`be novel, are set forth with particularity in the appended
`claims. The invention,
`together with further objects and
`advantages thereof, may best be understood by making ref-
`erence to the following description, taken in conjunction with
`the accompanying drawings, in the several figures of which
`like reference numerals identify identical elements, wherein:
`FIG. 1 illustrates a TDM/FDM RACH structure;
`FIG. 2 is a table of RACH parameters for the structure of
`FIG. 1;
`FIG. 3 is a graphical representation of a circular auto/cross
`correlation of a Chu-sequence with M:15, in accordance
`with the present invention;
`FIG. 4 is a graphical representation of a correlation
`sequence in the presence of two RACH requests with delays
`of 0 and 2, in accordance with the present invention;
`FIG. 5 is a graphical representation of a detection error rate
`and false alarm performance of TDM-RACH over an AWGN
`channel, in accordance with the present invention;
`FIG. 6 is a graphical representation of a detection error rate
`and false alarm performance of TDM-RACH over an TU
`channel at 3 kilometers/hour, in accordance with the present
`invention;
`FIG. 7 is a graph of an example of a RACH preamble, in
`accordance with the present invention;
`FIG. 8 is a block diagram of RACH preamble generation
`using time-domain modulation,
`in accordance with the
`present invention;
`FIG. 9 is a block diagram of RACH preamble generation
`using frequency-domain modulation, in accordance with the
`present invention;
`FIG. 10 is a graphical representation of a circular auto/
`cross correlation of a Chu-sequence with M:300, in accor-
`dance with the present invention;
`FIG. 11 is a graphical representation of RACH detection
`error and false alarm performance over an AWGN channel, in
`accordance with the present invention;
`FIG. 12 is a graphical representation of RACH detection
`error and false alarm performance over an TU channel at 3
`kilometers/hour, in accordance with the present invention;
`FIG. 13 is a table showing a comparison ofthe TDM/FDM
`and hybrid/CDM embodiments of the present invention; and
`FIG. 14 comprises a flow diagram of a method, in accor-
`dance with the present invention; and
`FIG. 15 illustrates a block diagram of a communication
`system, in accordance with the present invention.
`FIG. 16 illustrates the procedure of preamble detection in
`Node-B.
`
`FIG. 17 is the method of schedule-based RACH message
`transmission.
`
`5
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`FIG. 18 is the method of contention-based RACH message
`transmission.
`
`FIG. 19 is ACK-based RACH message transmission
`approach.
`
`ZTE 1026-0016
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`ZTE 1026-0016
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`

`
`US 8,000,305 B2
`
`3
`Skilled artisans will appreciate that common but well-
`understood elements that are useful or necessary in a com-
`mercially feasible embodiment are typically not depicted in
`order to facilitate a less obstructed View of these various
`
`embodiments of the present invention.
`
`DETAILED DESCRIPTION OF THE PREFERRED
`EMBODIMENT
`
`To minimize the performance impact to scheduled users,
`the present invention presents a hybrid approach to the RACH
`preamble in an EUTRA system. Specifically, the RACH pre-
`amble is transmitted in a CDM manner, while the message is
`either scheduled by the Node B in the same manner as regular
`data transmission, contention based transmitted, or ACK
`based transmitted. With proper configuration ofthe preamble
`sequence, the amount of interference generated can be mini-
`mized.
`In addition,
`the message portion is scheduled,
`whereby variable data rates can be supported with no impact
`to other uplink users. Moreover, both TDl\/I/FDM and Hybrid/
`CDM techniques can be utilized as candidate RACH methods
`for EUTRA, as will be detailed below.
`A RACH preamble can be sequenced using TDM/FDM. In
`this scheme a dedicated or special symbol is used for RACH.
`The RACH symbol can be reserved every x frames
`(e.g. x:l .
`.
`. 10) as shown in FIG. 1. The scheme can use
`either localized or distributed mode. In the localized mode the
`
`subcarriers are divided into NR3 resource blocks with each
`resource block using a fixed number of contiguous sub-car-
`riers. Next, for each of the NR3 resource blocks, a number of
`signature sequence groups are pre-defined so that every group
`consists of NS signature sequences and different groups can
`be assigned to different neighboring sectors. Each group also
`consists of several cyclically shifted versions of the signature
`sequences (NSH). As such, the total number of RACH oppor-
`tunities per DFT-SOFDM symbol is given by NRB*NS*NSH.
`As an example for 5 MHz bandwidth, all 300 subcarriers
`are divided into twenty resource blocks with NRB:20. A
`RACH signature sequence occupies fifteen subcarriers corre-
`sponding to 225 kHz bandwidth, thus the length ofa signature
`sequence is fifteen. For the scalable bandwidth structure, the
`length of a signature sequence is fixed to fifteen. The number
`of RACH opportunities thus varies according to different
`bandwidth deployments. Detailed numerology is shown in
`FIG. 2 for a set of scalable bandwidth.
`
`Dividing the RACH opportunities into resource blocks
`provides the opportunity to take advantage of channel fre-
`quency selective characteristics to further improve the per-
`formance. The user equipment (UE) chooses the best avail-
`able resource blocks for RACH preamble transmission based
`on information ofthe current frequency selective nature ofthe
`channel.
`
`In general, the signature sequences are obtained from a
`constant
`amplitude
`zero
`autocorreleation
`(CAZAC)
`sequence, which include different “classes” of generalized
`chirp like (GCL) or Chu-sequences which are complex val-
`ued and have unit amplitude. The GCL/Chu sequence has low
`cross correlation at all time lags which improves the detection
`performance. As used herein, the CAZAC, Chu and GCL
`sequences can be used interchangeably.
`The numbers of RACH groups for different bandwidths are
`summarized in FIG. 2. The total RACH overhead is depen-
`dent on the reserved RACH access rate. For example, if the
`RACH access is reserved every 1 millisecond, the RACH
`overhead is 1/14:7.l%.
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`4
`
`Specific RACH preamble sequencing can be defined. Since
`the sequence length equals to fifteen, a Chu-sequence can be
`selected which is defined as
`
`.27rl
`gn = eT"IVl7”"("+1), n: 0, l,
`
`, M —l
`
`where M:l5, and p is relatively prime to M. In this case,
`p:{l,2,4,7,8,l l,l3,l4, .
`.
`.
`For a fixed p, the Chu-sequence
`is orthogonal to its time-shift. For a different p, Chu-se-
`quences are not orthogonal. The circular autocorrelation and
`cross-correlation properties of a Chu sequence is shown in
`FIG. 3. FIG. 3 shows that Chu sequence has optimal autocor-
`relation property, while its cross-correlation has relatively
`small value for different delays.
`If the preamble is detected at the Node-B, the Node-B
`sends an ACKnowledge. Upon detection of the ACK at the
`UE, the UE sends the message part in the next slot using the
`same resource block (RB) location which was used to send
`the preamble. As an alternative, if the system is lightly loaded
`the message can be scheduled as outlined below.
`In accordance with the present invention, a hybrid/CDM
`approach is used for the RACH preamble configuration. To
`minimize uplink interference,
`the RACH preamble is
`designed to use time-frequency spreading with a long spread-
`ing factor. With this approach, no reservation of symbols and
`sub -carriers are required and uplink interference generated is
`minimal (e.g. 27.8 dB reduction with a spreading gain of
`600). In addition, a simple receiver structure with frequency
`domain processing can be used to process the preamble. The
`RACH preamble structure is summarized as follows: a) the
`preamble length is l millisecond using two 0.5 millisecond
`sub-frames; a total of 4200 chips excluding Cyclic Prefix
`length, b) frequency spreading with spreading factor M using
`a Chu-sequence (complex quadratic sequence), where M is
`the occupied sub-carriers excluding DC (direct current) com-
`ponent, c) time spreading with a Walsh sequence of length
`two, d) signature sequences with combined spreading factor
`2><M out of which a total of twenty are used, and e) a repeti-
`tion of seven is used to rate-match the preamble sequence
`length to one millisecond.
`The Chu-sequence (complex quadratic sequence) or GCL
`sequence is given by
`
`.7{
`.27rl
`g,,=e’8e ‘M2
`
`,l’L=0,... ,M—l
`
`and the delayed Chu-sequence is given by
`
`gd,n:g(n—30d)modZ\/I: 11:0, -
`
`-
`
`- 9
`
`Note that the Chu-sequence is a special sequence of the GCL
`sequence class. Other GCL sequences can be applied as the
`signature sequence as well. For example, for even M, we can
`define g” as
`
`.27r
`2
`.27rl
`gn = e”'IW7”" ”'IW”‘7", n = 0,, M —l
`
`where p is an integer relatively prime to M, and q is any
`integer. To provide temporal spreading, a Walsh sequence of
`length two is used; w:0, l. The sequence is given by
`
`w°:{+1,+1}, w1:{+1,—1}
`
`ZTE 1026-0017
`
`ZTE 1026-0017
`
`

`
`US 8,000,305 B2
`
`6
`randomly selects a RACH preamble sequence with sequence
`identifier number s. The 2M length RACH sequence is
`
`Ps:[Wk(0)gd,n Wk(1)gd,n+Z\/L/271:0: .
`
`.
`
`. ,M—1
`
`where s:2><d+k. At the receiver side of Node-B, the received
`signal can be represented as
`
`y.:x. Q) h.+z.,
`
`where (9 indicates circular convolution, h" is channel
`impulse response, z" is the charmel noise, and x" is either
`Wk(0)gd,n Or Wk(1)gd,n~
`At
`the receiver the circular (periodic) correlation of
`sequence g" and y" is computed. This yields
`
`,
`1”’
`C=T yg(—)odM
`.. _M;....,.
`
`The correlation can be performed either in time or frequency
`domain. Through some simple manipulations, the following
`is obtained
`
`,
`
`O 1
`
`k k
`
`-{
`
`V M hm-304 + Z;,,
`— V M hm—30d +z,’,,
`
`where the term zm' is the equivalent charmel noise. Usually the
`channel maximum delay is assumed to be less than the length
`of cyclic prefix. Here, it is assumed that the maximum chan-
`nel delay is less than thirty signal chips. For 5 MHz bandwidth
`deployment, the length of thirty chips using current E-UTRA
`numerology equals to 6.67 microseconds.
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`Since there are two Walsh sequence for k:0 and k:l, one
`can combine the nearby two blocks forboth Walsh sequences.
`There are a total of fourteen blocks of which one 2M RACH
`
`45
`
`50
`
`55
`
`60
`
`65
`
`sequence uses two blocks. Two neighbor cm are added to yield
`seven correlation sequences for k:0. For k:l, two neighbor
`cm are subtracted accordingly to yield another seven correla-
`tion sequences for k:l. In the next step, we detect the delay
`index d, so that the RACH sequence identifier number s
`(s:2><d+k) can be obtained.
`
`From the correlation sequence cm, when a RACH request
`with delay index d is present, the channel impulse response
`will appear in the frame {30d, 30d+30}, as illustrated in FIG.
`4. The figure shows two RACH requests with sequence delay
`0 and sequence delay 2. The correlation sequence cm indicates
`corresponding charmel impulse response at {0-30} and {60-
`90} regions. By detecting power in different regions, one can
`thus detect the RACH preamble at the Node-B.
`
`It is possible to have a ML (maximum likelihood) optimal
`detection of the RACH request
`if the channel
`impulse
`response is known. However, usually such charmel informa-
`tion is not available to the receiver at the Node-B. A simple
`detection algorithm is the maximum power detection. When
`the maximum power in a certain region is greater than a power
`threshold, a RACH request corresponding to that region is
`assumed.
`
`The detection algorithm has three steps. First, calculate
`average power of correlation sequence. This yields
`
`5
`To generate the twenty unique signature sequences, a
`sequence identifier s is first computed via s:2><d+k where
`d:0, .
`.
`. 9 corresponds to the delay of the Chu-sequence and
`k:0,l is the index of the Walsh sequence. The resulting s-th
`RACH preamble signature sequence (with length 2M) is then
`given by
`
`P,:M<o>gd,. Wk(1)gd,n+Z\/L/I n:0, .
`
`.
`
`. ,M—1
`
`An example of the RACH preamble sequence is shown in
`FIG. 7. In this case, d:5, and k:l with a resulting sequence
`index number of eleven. The sequence P11, made up of g5,"
`and —g5,n (i.e. Walsh code {l,—l}) is then repeated seven
`times in order to cover 1 millisecond.
`
`To mitigate inter-cell interference of RACH channel, dif-
`ferent Chu-sequences or GCL sequences can be used for
`different sectors/cells. A generalized Chu-sequence is given
`by:
`
`.27rl
`gn =e”'IWT2”",n= l,
`
`, M—l
`
`where p is chosen such that the greatest common divisor of p
`and M is 1. For example, when M:300, and p represents the
`prime numbers {l,7,l l,l3,l7,l9,23,29,3l,37, .
`.
`. Given a
`fixed p, the corresponding Chu-sequence is orthogonal when
`it
`is shifted circularly. However,
`the sequences are not
`orthogonal for different p and behave as random sequences.
`Thus, by assigning different p to different sector/cell, inter-
`cell interference can be mitigated.
`RACH preamble generation can be accomplished using
`either time-domain modulation (FIG. 8) or frequency-do-
`main generation (FIG. 9). In time-domain modulation, a mes-
`sage symbol is mixed with a frequency-spreading sequence as
`described herein in accordance with the present invention.
`The combined signal is then processed using time-spreading,
`followed by a Discrete Fourier Transform (DFT), mapping,
`Inverse Fast Fourier Transform (IFFT), and Cyclic Prefix
`(CP), as are known in the art. In frequency-domain modula-
`tion is first processed using time-spreading, which is copied
`to multiple paths, as are known in the art. These different
`paths are then mixed with frequency-spreading sequence as
`described herein in accordance with the present invention.
`The combined signals are then processed by an Inverse Fast
`Fourier Transform (IFFT), and Cyclic Prefix (CP), as are
`known in the art.
`
`The circular autocorrelation and cross correlation proper-
`ties for M:300 is shown in FIG. 10. This figure illustrates an
`optimal property of circular autocorrelation and good cross
`correlation performance of Chu-sequence with length 300.
`FIGS. 11 and 12 show the RACH preamble detection error
`rate and false alarm rate for AWGN and TU (typical urban)
`channel. The RACH preamble detection is outlined above. In
`this case, BW:5 MHz, corresponding to a Chu-sequence of
`length 300. Compared to the power requirement for data
`transmission, it is seen that the transmit power of the CDM
`RACH preamble is significantly less (20-30 dB lower) per
`user. As a result, interference generated by the RACH pre-
`amble is expected to be insignificant for lightly loaded sys-
`tem.
`
`The RACH preamble detection is similar to the detection
`algorithm of TDl\/I/FDM-based RACH at a Node-B. The
`block-by-block detection utilizes frequency-domain correla-
`tion, which is suitable for Frequency Domain Equalization
`(FDE). There is no time-domain correlation needed, which
`makes calculations less complex. For example, assume an UE
`
`ZTE 1026-0018
`
`ZTE 1026-0018
`
`

`
`US 8,000,305 B2
`
`The second step is to find the maximum power in all regions
`to obtain
`
`1 30d+29
`: max |cm|
`yd = P m—30d
`
`2
`
`.
`
`10
`
`The final step is to check whether the maximum power is
`greater than a pre-defined power threshold YTH. Thus,
`
`15
`
`yd z7’TI~1 RACH request with delay d is present
`yd <7’TI~1 RACH request with delay d is absent-
`
`With the detected d, and its corresponding Walsh code
`index k, the RACH sequence identifier number s, can be
`obtained through s:2d+k.
`The above technique detects the received power based on
`correlation of the received sequence to all
`the possible
`sequences. The correlation can be carried out either in time or
`frequency domain. Once the detected power is greater than a
`pre-defined power threshold, a RACH preamble is detected.
`Naturally, the choice of threshold determines detection per-
`formance. FIGS. 5 and 6 illustrate detection performance of
`the TDl\/I/FDM RACH preamble under AWGN and TU (typi-
`cal urban) propagation channels, respectively. The following
`definitions were used in the performance evaluation: a) false
`alarm refers to a scenario where a particular code was
`detected when nothing or a different code was transmitted,
`and b) detection error refers to when a particular code was
`transmitted but not detected.
`
`To maximize capacity utilization in the uplink, there are
`three approaches for RACH message transmission. At first,
`RACH message transmission canbe scheduled by the Node B
`on a time-frequency region reserved specifically for RACH
`message transmissions. These regions are fixed and known
`beforehand so as to minimize control message overhead. The
`frequency, size, and number ofthese RACH messages regions
`will depend on system design and deployment scenarios.
`Naturally, when there is no RACH message transmission, the
`Node B can schedule other users in these time-frequency
`regions. At the Node B, once the RACH preamble is success-
`fully received, a four-bit acknowledgement corresponding to
`the sequence number is transmitted to the UE. This is done
`even when the UE may not be scheduled for some time to
`prevent the UE from transmitting the RACH preamble again.
`Subsequent to receiving an acknowledgement, the UE moni-
`tors the downlink control channel for a period of time for
`scheduling information in order to transmit the RACH mes-
`sage. Due to the use of micro-sleep mode, power consump-
`tion from monitoring the downlink control charmel is not
`expected to be an issue. In addition, the UE may already need
`to monitor the downlink control charmel for possible down-
`link data transmission.
`
`The second RACH message transmission approach can be
`contention based. Once UE receives ACK from Node-B for
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`RACH access, UE sends the RACH message in the pre-
`defined charmel. Then UE can further monitor downlink con-
`trol charmel for further ACK information for the transmitted
`
`65
`
`RACH message.
`
`8
`The third RACH message transmission approach is ACK
`based. With this approach, a resource block for message
`transmission is reserved by Node-B once needed. The RACH
`ACK information indicates the readiness of the reserved
`channel. Once UE receives this ACK information, the RACH
`message is sent in the reserved channel.
`FIG. 13 compares the RACH features between the TDl\/I/
`FDM technique and the Hybrid/CDM embodiments of the
`present invention.
`Referring to FIG. 14, the present invention also provides a
`method for random channel access between a user equipment
`CUE) and a Node-B of a EUTRA communication system, as
`shown in FIG. 15, wherein the UE 1500 reserves and trans-
`mits information on the RACH channel 1516, and the Node-B
`1502 receives the information on the RACH channel. How-
`
`ever it should be recognized that the present invention is
`applicable to other systems including 3GPP, 3GPP2, and
`802.16 communication systems, and that the terms ‘user
`equipment’ can be used interchangeably with ‘mobile sta-
`tion’, and that ‘base station’, ‘BTS’ and ‘node-B’ can be used
`interchangeably, as are known in the art. The UE 1500
`includes a transmitter 1504, receiver 1506, and processor
`1508 coupled thereto. The node-B 1502 also includes a trans-
`mitter 1510, receiver 1512, and processor 1514 coupled
`thereto.
`
`In a first step, the UE 1500 defines 1400 a plurality of
`spread sequences derived from a plurality of constant ampli-
`tude zero autocorrelation (CAZAC) sequences. Specifically,
`the sequences can be Chu-sequences or GCL sequences. In
`addition, the sequence may be delayed. The UE then com-
`bines 1402 the spread sequences with an orthogonal code
`(e.g. Walsh code) to form extended spread sequences (signa-
`ture sequences). In a next step, the UE selects 1404 one ofthe
`signature sequences, which is used 1406 in a preamble for a
`RACH. Preferably, the selection is randomly selected. How-
`ever, the select sequence could be predefined or selected to
`reduce the possibility of interference.
`The UE then determines an available RACH access slot
`
`and other transmission parameters. In a next step, the UE sets
`1408 a