(19) United States
`(12) Patent Application Publication (10) Pub. No.: US 2007/0165567 A1
`
` Tan et al. (43) Pub. Date: Jul. 19, 2007
`
`
`US 20070165567Al
`
`(54) PREAMBLE SEQUENCING FOR RANDOM
`
`(22)
`
`Filed:
`
`Jan. 10,2007
`
`(75)
`
`Inventors:
`
`Jun Tan, Lake Zurich, IL (US);
`Amltava Ghosh, Buifalo GrOVe,
`
`Hoifman Estates IL (US) Fan
`’
`’
`Wang, Chicago, IL (US); Weimin
`Xiao, Barrington, IL (US)
`
`Correspondence Address:
`MOTOROLA,INC.
`1303 EAST ALGONQUIN ROAD: IL01/3RD
`SCHAUMBURG, IL 60196
`
`(73) Assignee:
`
`MOTOROLA, INC., Schaumburg,
`IL (US)
`
`(21) App]. No.:
`
`11/621,587
`
`(60) Provisional application No. 60/759,697, filed on Jan.
`17, 2006.
`
`Publication Classification
`
`(51)
`
`Int. Cl.
`
`....................................................... 370/329
`
`52 US. Cl.
`)
`(
`ABSTRACT
`(57)
`A system and method for initializing a system communica-
`tionwithoutpreViSoussreeervationsorf ranoadm
`ha-n
`nee1 (RACH)ac
`icnculdes afirst seteopoefdfincimgsat 1st
`one srepadqseuenceedcriVerdfom atlatn consatnt
`amplitude zero auotc
`realtion sequence. A neext
`setep
`includes ornibni1ng thesrpreadsqeuence W1itha WaIsheode
`to form
`extendedssrpeeasdseenqu e.nAext steep11cludes
`using the1 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 posi-
`tiVe acquisition indicator from the BTS. A next step includes
`scheduling the sending of a RACH message. A next step
`includes sending the RACH message.
`
`
`
`RADIO FRAME(lOms)
`
`RADIO FRAME CONSTRUCTED FROM t ms SUB—FRAMES
`
`
`
`
`
`%%%%77777777777%WV%V
`.\‘
`;\.\
`A
`A
`
`
`
`
`
`
`
`.\fL\1\,$1$1$1
`
`
`V
`
`/
`
`RACH SYMBOL
`
`DAT
`
`A
`
`SYMBOL
`
`HALF PILOT SYMBPL
`
`APPLE 1005
`
`APPLE 1005
`
`

`

`Patent Application Publication
`
`Jul. 19, 2007 Sheet 1 0f 13
`
`US 2007/0165567 A1
`
`RADIO FRAME n—1
`
`RADIO FRAME n
`
`RADIO FRAME n+1
`
`,
`
`
`
`
`l RADIO FRAME (10m)
`
`A
`
`RADIO FRAME CONSTRUCTED FROM t ms SUB-FRAMES
`
`»
`
`,
`
`,
`
`r
`
`v
`
`v
`
`r
`
`,
`
`,
`
`»
`
`
`r
`,
`
`I
`
`l
`
`A
`
`A
`
`1
`
`A
`
`.
`
`1
`
`.
`
`.
`
`1
`
`A
`
`A
`
`A
`
`A
`
`4
`
`A
`
`1
`
`A
`
`RACH SYMBOL
`
`DATA SYMBOL
`
`HALF PILOT SYMBPL
`
`FIG. 1
`
`

`

`Patent Application Publication
`
`Jul. 19, 2007 Sheet 2 0f 13
`
`US 2007/0165567 A1
`
`RACH PARAMETERS FOR THE TDM/FDM STRUCTURE
`
`BANDWIDTH
`RACH PARAMETERS IN
`2111111112
`2511111 mm 15111112
`12511112
`10511125511055
`______
`HE (R) n“__““
`——-__n
`# 0F SEQUENCES (FOR ALL
`SECTORS/CELLS)
`(N5)
`# 0F CYCLIC SHIFTED VERSION
`OF EACH SEQUENCE (NSH)
`
`——“-E- 640
`
`__
`
`FIG. 2
`
`

`

`Patent Application Publication
`
`Jul. 19, 2007 Sheet 3 0f 13
`
`US 2007/0165567 A1
`
`
`
`-9- CIRCULAR AUTOCORRELATION
`—EI— CIRCULAR CROSS-CORRELATION p=1.2
`
`
`-9— CIRCULAR CROSS—CORRELATION =17
`
`
`
`
`
`
`
`
`
`
`iifiifiult‘fl
`
` m
`
`
`
`
`
`NORMALIZEDCIRCULARAUTO/CROSS-CORRELATION
`
`Cr
`
`
`
`-5
`
`0
`
`5
`
`10
`
`15
`
`CODE gr
`
`CODE g,,_30 i
`
`CODE 90-50:
`
`LL? ma
`
`CODE 9n-90 .
`
`5
`
`i
`
`0
`
`30
`
`60
`
`90
`
`FIG. 4
`
`

`

`Patent Application Publication
`
`Jul. 19, 2007 Sheet 4 0f 13
`
`US 2007/0165567 A1
`
`-.__:_:::_L::_
`
`_ _ 2' DELETION ERROR RATE
`
`_ _| _ _ _ _+ _ _ _
`
`
`
`-f&-SNR=—4dB
`——I
`| —+%—SNR=-2dB
`
`
`
`
`
`
`
`
`2
`THRESHOLD 9 (dB)
`
`.jE7le71C391.
`
`455'
`
`
`
`
`
`
`
`
`
`
`
`“J
`:2
`
`E5
`
`a:
`g
`m
`3
`E
`
`
`
`-+a—SNR=-2dB
`-EI—SNR=-1dB
`—o— SNR=0dB
`—v— SNR=1dB
`+ SNR=2dB
`
`-*- SNR=3dB
`
`
`
`
`THRESHOLD 9 (dB)
`
`FIG. 6
`
`

`

`Patent Application Publication
`
`Jul. 19, 2007 Sheet 5 0f 13
`
`US 2007/0165567 A1
`
`&5 MS SUB—FRAME
`
`Q5 MS SUB—FRAME
`
` lu-IEMIIWIWIIWIWIWIWIEIWIWIW
`
`FIG- 7
`
`TIME-DOMAIN MODULATION
`
`MESSAGE
`SYME
`
`SEQUENCE
`
`gr
`FREQUENCY
`SPREADING
`
`TIME
`
`SPREADING
`
`

`

`Patent Application Publication
`
`Jul. 19, 2007 Sheet 6 0f 13
`
`US 2007/0165567 A1
`
`FREQUENCY DOMAIN MODULATION
`
`
`
`
`SPREADING
`
`GN—1
`
`FREQUENCY SPREADING SEQUENCE
`
`FIG. 9
`
`
`
`
`
`NORMALIZEDCIRCULARAUTO-lCROSS-CORRELATION
`
`
`
`-9- CIRCULAR AUTOCORRELATION
`
`"E'— CIRCULAR CROSS-CORRELATION: p
`
`
`—6— CIRCULAR CROSS-CORRELATION: p
`——— fr ———————————
`
`
`
`|
`
`1
`
`
`
`
`
`-0.2
`
`'A
`
`—300
`
`-200
`
`-100
`
`o
`
`100
`
`200
`
`300
`
`

`

`Patent Application Publication
`
`Jul. 19, 2007 Sheet 7 0f 13
`
`US 2007/0165567 A1
`
`10‘0
`
`E;
`
`E?
`
`”J
`
`10‘1
`
`10'2
`
`10'3
`
`10-4
`
`
`
`
`
`
`
`
`
`
`
`-*9-SNR=—30dB
`-+a—SNR=—28dB
`-«9—SNR=—26dB
`4-SNR=-24dB
`
`-*-SNR=-22dB
`-*-SNR=-20dB
`
`.jE711FICI;l.
`
`.2!Jl
`
`
`
`
`
`
`
`
`+SNR=-18dB
`
`
`
`
`
`ERRORRATE
`
`
`
`-E|-SNR=—24dB
`-9-SNR= -22dB
`-V-SNR= -20dB
`
`THRESHOLD 6 (dB)
`
`JE7ZZ'(ZS¥-
`
`41:2?
`
`

`

`Patent Application Publication
`
`Jul. 19, 2007 Sheet 8 0f 13
`
`US 2007/0165567 A1
`
`COMPARISON OF TDM/FDM AND HYBRID/CDM RACH (BW=5MHz).
`
`NUMBER OF RACH OPPORTUNITIES
`(per ms)
`
`”RDXNSXNSHXNOEDH
`"HERE ”DEDH = NUMBER OF
`OEDM SYMBOL RESERVED FOR
`RACH per ms
`e.g. 160x NOFDM FROM TABLE 1.
`
`INTERFACE GENERA TED To
`SCHEDULED USERS
`
`SNR REOUIRENENT FOR UL TALSE
`ALARN AND MISSED DETECTION
`ERROR (TU 3 KM)
`
`NONE
`
`-2 dB
`
`SMALL
`
`—17 dB
`
`NO (COLLISION LIMITED
`
`RACH OVERHEAD (per ms
`
`”OEDH “4
`
`NONE
`
`COLLISION PROBABILITY
`
`Low
`
`MEDIUM - HIGH
`
`INTER-CELL INTERFERENCE
`
`MEDIUM
`
`LOW
`
`SYSTEM INTERFERENCE LIMITED
`
`YES
`
`FIG. 13
`
`

`

`Patent Application Publication
`
`Jul. 19, 2007 Sheet 9 0f 13
`
`US 2007/0165567 A1
`
`UE
`
`SET TX POWER
`
`I408
`
`I410
`
`SEND PREAMBLE
`
`14 12
`
`
` ACK
`
`RECEIVED
`
`NO
`
`?
`
`YES
`
`CHANGE TX POWER AND/0R SEQUENCE
`
`ms
`
`SEND RACH MESSAGE
`
`1418
`
`
`
`FIG- 14
`
`

`

`Patent Application Publication
`
`Jul. 19, 2007 Sheet 10 0f 13
`
`US 2007/0165567 A1
`
` USER EQUIPMENT
`
`I500
`
`I502
`
`FIG. 15
`
`NODE-B
`
`
`
`I
`
`
`
`
`
`DETECT PREAMBLE
`
`
`
`N0
`
`YES
`
`SEND ACK
`
`1424
`
`
`
`RECEIVE RACH MESSAGE
`
`
`
`7420
`
`I426
`
`

`

`Patent Application Publication
`
`Jul. 19, 2007 Sheet 11 0f 13
`
`US 2007/0165567 A1
`
`UE
`
`ACK DETECTED
`
`NODE B
`
`ACK SENT
`
`MONITOR CONTROL CHANNEL
`
`I430
`
`I436
`
`1433
`
`SEND SCHEDULE INFO
`
`
`
`
`
`
`
`
`I432
`
`RECEIVE RACH MESSGE
`
`
`
`SCHEDULE
`
`INFO
`
`RECEIVED?
`
`1434
`
`SEND RACH MESSAGE
`
`.jEVTj!W(:§¥.
`
`.jl‘57'
`
`

`

`Patent Application Publication
`
`Jul. 19, 2007 Sheet 12 0f 13
`
`US 2007/0165567 A1
`
`UE
`
`RACH ACK DETECTED
`
`NODE B
`
`RACH ACK SENT
`
`SEND RACH MESSAGE
`
`RECEIVE RACH MESSAGE
`
`I440
`
`1446
`
`
`I442
`
`
`
`
`
`MESSAGE
`ACK
`RECEIVED?
`
` MESSAGE
`RECEIVED?
`
`I450
`
`SEND MESSAGE ACK
`
`

`

`Patent Application Publication
`
`Jul. 19, 2007 Sheet 13 0f 13
`
`US 2007/0165567 A1
`
`UE
`
`NODE B
`
`RACH ACK DETECTED
`
`RACH ACK SENT
`
`
`
`
`SEND RACH MSG ACK
`
`
`
`
`RECEIVE RACH MESSAGE
`
`1456
`
`I458
`
`
`
`1454
`
`RACKCkTSSG
`
`'ECEIVED?
`
`
`V 1452
`
`
`FIG. 19
`
`

`

`US 2007/0165567 A1
`
`Jul. 19, 2007
`
`PREAMBLE SEQUENCING FOR RANDOM
`ACCESS CHANNEL IN A COMMUNICATION
`SYSTEM
`
`TECHNICAL FIELD OF THE INVENTION
`
`[0001] This invention relates generally to communications
`and more particularly to use of a random access channel in
`a communication system.
`
`BACKGROUND OF THE INVENTION
`
`[0002] 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
`pat1. The original scope of 3GPP was to produce globally
`applicable technical specifications and technical reports for
`a 3rd generation mobile system based on evolved Global
`System for Mobile communication (GSM) core networks
`anc the radio access technologies that they support, such as
`Evolved Universal Terrestrial Radio Access
`(EUTRA)
`inc uding both Frequency Division Duplex (FDD) and Time
`Division Duplex (TDD) modes. 3GPP’s scope was subse-
`quently amended to include the maintenance and develop-
`me 1t of GSM technical specifications and technical reports
`inc uding evolved radio access technologies (e.g. General
`Packet Radio Service (GPRS) and Enhanced Data rates for
`GSVI Evolution (EDGE)).
`[0003]
`Presently, EUTRA calls for a random access chan-
`nel (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 information and data packets. This 3GPP UMTS
`specification permits an overall procedure that allows for
`various protocol/operational states to suit varying degrees of
`needed, anticipated, 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 of data
`transmission activity appears to underutilize these reserved
`RACH resources, thereby wasting transmission resources.
`[0004] The RACH (random access channel) is essential
`for initial access to the network, for the transmission of
`control
`information and data packets. The initial access
`channel has different names in different systems, such as
`RACH in the context of 3GPP, or ranging in the context of
`IEEE std. 802.16e. In this invention, we use RACH in its
`general sense to represent
`the initial access channel of
`communication systems.
`[0005]
`It is desired that the RACH include a contention
`channel, fast acquisition of preamble, minimization of inter-
`ference, minimum impact on other scheduled data transmis-
`sion, 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 Multiplexing (TDM), Frequency Division Multi-
`plexing (FDM), and Code Division Multiplexing (CDM).
`However, in the 3GPP system problems arise for multiplex-
`ing between RACH and scheduled-based channels using
`either TDM or FDM. In particular, TDM requires reserva-
`tion of slots for RACH access, and FDM requires a fre-
`quency (subcarrier) reservation for RACH access. In either
`case, a resource reservation is allotted even if there are few
`
`RACH requests in the system, which withholds unused
`resources that adversely affect system capacity. CDM trans-
`mission, on the other hand, will generate interference to
`other uplink users.
`[0006]
`To control interference generated by CDM trans-
`mission, a MC-CDMA (multi-carrier code division multiple
`access) technique can be applied for RACH design without
`reserving system resources. This invention uses this tech-
`nique for non-reserved RACH access of EUTRA commu-
`nication system.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`[0007] The features of the 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 reference to the following description,
`taken in
`conjunction with the accompanying drawings, in the several
`figures of which like reference numerals identify identical
`elements, wherein:
`[0008]
`FIG. 1 illustrates a TDM/FDM RACH structure;
`[0009]
`FIG. 2 is a table of RACH parameters for the
`structure of FIG. 1;
`[0010]
`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;
`[0011]
`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;
`[0012]
`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 inven-
`tion;
`FIG. 6 is a graphical representation of a detection
`[0013]
`error rate and false alarm performance of TDM-RACH over
`an TU channel at 3 kilometers/hour, in accordance with the
`present invention;
`[0014]
`FIG. 7 is a graph of an example of a RACH
`preamble, in accordance with the present invention;
`[0015]
`FIG. 8 is a block diagram of RACH preamble
`generation using time-domain modulation,
`in accordance
`with the present invention;
`[0016]
`FIG. 9 is a block diagram of RACH preamble
`generation using frequency-domain modulation, in accor-
`dance with the present invention;
`[0017]
`FIG. 10 is a graphical representation of a circular
`auto/cross correlation of a Chu-sequence with M:300, in
`accordance with the present invention;
`[0018]
`FIG. 11 is a graphical representation of RACH
`detection error and false alarm performance over an AWGN
`channel, in accordance with the present invention;
`[0019]
`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;
`[0020]
`FIG. 13 is a table showing a comparison of the
`TDM/FDM and hybrid/CDM embodiments of the present
`invention; and
`[0021]
`FIG. 14 comprises a flow diagram of a method, in
`accordance with the present invention; and
`[0022]
`FIG. 15 illustrates a block diagram of a commu-
`nication system, in accordance with the present invention.
`[0023]
`Skilled artisans will appreciate that common but
`well-understood elements that are useful or necessary in a
`
`

`

`US 2007/0165567 A1
`
`Jul. 19, 2007
`
`typically not
`are
`embodiment
`commercially feasible
`depicted in order to facilitate a less obstructed view of these
`various embodiments of the present invention.
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENT
`
`example, if the RACH access is reserved every 1 millisec-
`ond, the RACH overhead is 1/14:7.l%.
`[0030]
`Specific RACH preamble sequencing can be
`defined. Since the sequence length equals to fifteen, a
`Chu-sequence can be selected which is defined as
`
`To minimize the performance impact to scheduled
`[0024]
`users, the present invention presents a hybrid approach to the
`RACH preamble in an EUTRA system. Specifically,
`the
`RACH preamble 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 trans-
`mitted, or ACK based transmitted. With proper configuration
`of the preamble sequence, the amount of interference gen-
`erated can be minimized. In addition, the message portion is
`scheduled, whereby variable data rates can be supported
`with no impact to other uplink users. Moreover, both TDM/
`FDM and Hybrid/CDM techniques can be utilized as can-
`didate RACH methods for EUTRA, as will be detailed
`below.
`
`[0025] 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-carriers. 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 ver-
`sions of the signature sequences (NEH). As such, the total
`number of RACH opportunities per DFT—SOFDM symbol is
`given by NRB*NS*NSH.
`[0026] 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 sub-
`carriers corresponding to 225 kHz bandwidth,
`thus the
`length of a 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.
`
`[0027] Dividing the RACH opportunities into resource
`blocks provides the opportunity to take advantage of channel
`frequency selective characteristics to further improve the
`performance. The user equipment (UE) chooses the best
`available resource blocks for RACH preamble transmission
`based on information of the current frequency selective
`nature of the channel.
`
`In general, the signature sequences are obtained
`[0028]
`from a constant amplitude zero autocorreleation (CAZAC)
`sequence, which include different “classes” of generalized
`chirp like (GCL) or Chu-sequences which are complex
`valued 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.
`[0029] The numbers of RACH groups for different band-
`widths are summarized in FIG. 2. The total RACH overhead
`
`is dependent on the reserved RACH access rate. For
`
`*Jgflpmml)
`gnze M2
`
`,n:0,l,...,M—l
`
`where M:15, and p is relatively prime to M. In this case,
`p:{l,2,4,7,8,ll,l3,l4, .
`.
`. }. Fora fixed p, the Chu-sequence
`is orthogonal
`to its time-shift. For a different p, Chu-
`sequences 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
`autocorrelation property, while its cross-correlation has rela-
`tively small value for different delays.
`the
`[0031]
`If the preamble is detected at the Node-B,
`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/
`[0032]
`CDM approach is used for the RACH preamble configura-
`tion. To minimize uplink interference, the RACH preamble
`is designed to use time-frequency spreading with a long
`spreading factor. With this approach, no reservation of
`symbols and sub-carriers are required and uplink interfer-
`ence 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 milli-
`second 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) component, 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 repetition of seven is used to
`rate-match the preamble sequence length to one millisecond.
`[0033] The Chu-sequence (complex quadratic sequence)
`or GCL sequence is given by
`
`,JE ,fiflnz
`gnze Se M2
`
`,n:0,...,M—l
`
`and the delayed Chu-sequence is given by
`gd,n:g(nr30d)modZ‘/Il “7:0, -
`-
`- 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
`
`,2”; "2,2,” n
`gnze’MZ”
`’Mpq,n=O,... ,M—l
`
`

`

`US 2007/0165567 A1
`
`Jul. 19, 2007
`
`[0037] The RACH preamble detection is similar to the
`detection algorithm of TDM/FDM-based RACH at a Node-
`B. The block-by-block detection utilizes frequency-domain
`correlation, which is suitable for Frequency Domain Equal-
`ization (FDE). There is no time-domain correlation needed,
`which makes calculations less complex. For example,
`assume an UE randomly selects a RACH preamble sequence
`with sequence identifier number s. The 2M length RACH
`sequence is
`
`Fifi/“(0%," Wk(1)gd,n+Z\/L/I ”:0----- M-1
`
`where s:2><d+k. At the receiver side of Node-B, the received
`signal can be represented as
`y,1 :96" 0 h +znna
`
`where ® indicates circular convolution, h" is channel
`impulse response, Z" is the channel noise, and x" is either
`Wk(0)gd,n 0r Wk(1)gd,n~
`[0038] At the receiver the circular (periodic) correlation of
`sequence g" and y" is computed. This yields
`
`1 M71
`Cm=— yng?7)odM
`
`The correlation can be performed either in time or frequency
`domain. Through some simple manipulations, the following
`is obtained
`
`a
`
`0 1
`
`k k
`
`cm 2
`
`{ V M hm730d +3,“
`— V M hm730d +Z;n
`
`where the term Zm' is the equivalent channel noise. Usually
`the channel maximum delay is assumed to be less than the
`length of cyclic prefix. Here, it is assumed that the maximum
`channel 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.
`[0039]
`Since there are two Walsh sequence for k:0 and
`k:l, one can combine the nearby two blocks for both Walsh
`sequences. There are a total of fourteen blocks of which one
`2M RACH 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 correlation 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.
`[0040] 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 illus-
`trated in FIG. 4. The figure shows two RACH requests with
`sequence delay 0 and sequence delay 2. The correlation
`sequence cm indicates corresponding channel
`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)
`[0041]
`optimal detection of the RACH request
`if the channel
`impulse response is known. However, usually such channel
`information is not available to the receiver at the Node-B. A
`
`simple detection algorithm is the maximum power detection.
`
`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}
`
`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
`
`PS:[wk(0)gdfl Wk(l)gdfl+M], n:0..... M—l
`
`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 chan-
`[0034]
`nel, different Chu-sequences or GCL sequences can be used
`for different sectors/cells. A generalized Chu-sequence is
`given by:
`
`,Jz'flpn
`gnze m ,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 {1,7,1l,l3,l7,l9,23,29,3l,37,
`.
`.
`. }.
`Given a fixed p, the corresponding Chu-sequence is orthogo-
`nal 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.
`[0035] RACH preamble generation can be accomplished
`using either time-domain modulation (FIG. 8) or frequency-
`domain generation (FIG. 9). In time-domain modulation, a
`message 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 fre-
`quency-domain modulation 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 fre-
`quency-spreading sequence as described herein in accor-
`dance 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.
`[0036] The circular autocorrelation and cross correlation
`properties 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 gener-
`ated by the RACH preamble is expected to be insignificant
`for lightly loaded system.
`
`

`

`US 2007/0165567 A1
`
`Jul. 19, 2007
`
`When the maximum power in a certain region is greater than
`a power threshold, a RACH request corresponding to that
`region is assumed.
`[0042] The detection algorithm has three steps. First,
`calculate average power of correlation sequence. This yields
`
`’= — Icmlz-
`Mm:0
`
`The second step is to find the maximum power in all regions
`to obtain
`
`[0043]
`
`yd = — max 0
`l 30d+29|
`Pm30d m
`
`I2-
`
`The final step is to check whether the maximum power is
`greater than a pre-defined power threshold yTH. Thus,
`[0044]
`
`74 27TH RACH request with delay d is present
`yd <y7-H RACH request with delay d is absent-
`
`[0045] With the detected d, and its corresponding Walsh
`code index k, the RACH sequence identifier number s, can
`be obtained through s:2d+k.
`[0046] 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 pre-
`amble is detected. Naturally, the choice of threshold deter-
`mines detection performance. FIGS. 5 and 6 illustrate detec-
`tion performance of the TDM/FDM RACH preamble under
`AWGN and TU (typical 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.
`[0047]
`To maximize capacity utilization in the uplink,
`there are three approaches for RACH message transmission.
`At first, RACH message transmission can be 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 of these RACH
`messages regions will depend on system design and deploy-
`ment 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 successfillly received, a four-bit acknowledge-
`ment 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 monitors the downlink control
`channel for a period of time for scheduling information in
`order to transmit the RACH message. Due to the use of
`
`micro-sleep mode, power consumption from monitoring the
`downlink control channel is not expected to be an issue. In
`addition, the UE may already need to monitor the downlink
`control channel for possible downlink data transmission.
`[0048] The second RACH message transmission approach
`can be contention based. Once UE receives ACK from
`
`Node—B for RACH access, UE sends the RACH message in
`the predefined channel. Then UE can further monitor down-
`link control channel for further ACK information for the
`
`transmitted RACH message.
`[0049] The third RACH message transmission approach is
`ACK based. With this approach, a resource block for mes-
`sage 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.
`[0050]
`FIG. 13 compares the RACH features between the
`TDM/FDM technique and the Hybrid/CDM embodiments
`of the present invention.
`[0051] Referring to FIG. 14, the present invention also
`provides a method for random channel access between a
`user equipment (UE) and a Node-B of a EUTRA commu-
`nication system, as shown in FIG. 15, wherein the UE 1500
`reserves and transmits information on the RACH channel
`1516, and the Node-B 1502 receives the information on the
`RACH channel. However 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 station’, and that ‘base station’, ‘BTS’ and ‘node-B’
`
`can be used interchangeably, as are known in the art. The U3
`1500 includes a transmitter 1504, receiver 1506, and pro-
`cessor 1508 coupled thereto. The node-B 1502 also includes
`a transmitter 1510,
`receiver 1512, and processor 1514
`coupled thereto.
`[0052]
`In a first step, the UE 1500 defines 1400 a plurality
`of spread sequences derived from a plurality of constant
`amplitude zero autocorrelation (CAZAC) sequences. Spe-
`cifically,
`the sequences can be Chu-sequences or GCL
`sequences. In addition, the sequence may be delayed. The
`UE then combines 1402 the spread sequences with an
`orthogonal code (e.g. Walsh code) to form extended spread
`sequences (signature sequences). In a next step, the U3
`selects 1404 one of the signature sequences, whichis used
`1406 in a preamble for a RACH. Preferably, the selection 's
`randomly selected. However, the select sequence could be
`predefined or selected to reduce the possibility of interfe‘-
`ence.
`
`
`
`[0053] The UE then determines an available RACH access
`slot and other transmission parameters. In a next step, the
`
`UE sets 1408 a transmission power. In a next step, the U3
`transmits 1410 the RACH preamble using the selected slot,
`signature sequence, and power, and then monitors 1412 for
`a positive acquisition indicator (ACKnowledgement) from
`the node-B 1502. If no positive acquisition indicator is
`detected, in a next step, the UE may wait 1414 for a period
`of time or the UE changes 1416 transmission power with a
`new access slot and a new randomly selected signature until
`the maximum number of transmissions or maximum power
`is reached. If positive acquisition indicator is detected, in a
`next step, the UE sends 1418 RACH message to Node-B.
`FIG. 16 illustrates the procedure of preamble detection in
`Node-B 1502. Node-B detects 1420 preamble until
`the
`
`

`

`US 2007/0165567 A1
`
`Jul. 19, 2007
`
`preamble is detected 1422. Then the RACH ACK is sent
`1424 to UE. The next step will be the RACH message
`transmission.
`
`means for providing the described functionality rather than
`indicative of a strict logical or physical structure or organi-
`zation.
`
`[0054] There are three approaches for RACH message
`transmission. The details of message transmitting 1418 in
`UE and message receiving 1426 in Node-B will be illus-
`trated in FIGS. 17, 18, and 19.
`[0055]
`FIG. 17 is the method of schedule-based RACH
`message transmission. UE monitors 1430 the downlink
`control channel for a fixed amount of time to obtain 1432
`
`scheduling information for the RACH message. The Node-B
`can be signaled for RACH message transmission, and the
`RACH message can then be sent 1434 as scheduled. Node-B
`schedules 1436 RACH message transmission after the
`RACH ACK is sent. Node-B will receive 1438 RACH
`
`message at its scheduled time and frequency.
`[0056]
`FIG. 18 is the method of contention-based RACH
`message transmission. UE sends 1440 the RACH message
`upon RACH ACK is received. In the next step, UE listens
`1442 the downlink control channel for RACH message ACK
`to determine 1444 whether the message is received by
`Node-B. Node-B will receive 1446 RACH message after the
`RACH ACK is sent. When the message is received 1448, a
`RACH message ACK should be sent 1450.
`[0057]
`FIG. 19 is ACK-based RACH message transmis-
`sion approach. A RACH message channel is reserved. UE
`will wait 1452 for RACH MSG (message) ACK from
`Node-B for clear of RACH message channel. Once the
`channel
`is available,
`the RACH message is sent 1454.
`Node-B monitors the availability of the RACH message
`channel. It will send 1456 MSG ACK and receive 1458
`
`RACH message in the next step.
`[0058] Advantageously, the present invention provides a
`CDM type of RACH with a MC-CDMA approach in the
`EUTRA system. There is no reservation of time slots or
`sub-carriers involved, which results in zero RACH over-
`head. The present invention has the capability of working at
`very low transmitting power (L:600 spreading gain), and
`any interference introduced in minimal
`(spreading gain
`L:600 results in 27.8 dB reduction). In addition, a simple
`receiver configuration can be used with frequency domain
`processing.
`[0059] The present