as) United States
`a2) Patent Application Publication co) Pub. No.: US 2007/0165567 Al
` Tan etal. (43) Pub. Date: Jul. 19, 2007
`
`
`
`US 20070165567A1
`
`(54) PREAMBLE SEQUENCING FOR RANDOM
`
`(22)
`
`Filed:
`
`Jan. 10, 2007
`
`(60) Provisional application No. 60/759,697,filed on Jan.
`17, 2006.
`
`(75)
`
`Inventors:
`
`Amitava Ghosh, Buffalo Gro
`
`Jun Tan, Lake Zurich, IL cen,
`Us); RapesPpatRaata
`offman
`Estates,
`;
`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) Appl. No.:
`
`11/621,587
`
`51)
`
`Int. Cl.
`
`Publication Classification
`CD H040 7/00
`(2006.01)
`(52) US. Ch. cececeecececneceesenenscnecneneens 370/329
`(57)
`ABSTRACT
`Asystem and methooir initializing a eneommunica-
`tion without previous
`rvations for random
`access chan
`nel (RACH)access inclu‘des a first step of definiing aat least
`one spread aeTieneederives rom at least one constant
`amplitude zero auto
`relatio:
`sequence. A next
`steep
`includes combining thespreead sesequence witha WaIsh code
`using the extendedspre:ad sequence in aapreamble for
`RACH.Anext step includes sendingthepreambleto a BIS
`for acquisition. A next step iincludes monitoring for a pos
`tive acquisitionindicatorfomtheBIS.net step inches
`sdhedalne thesending of a RACH message. A next step
`includes sending the RACH message.
`
`to form an extended spread sequence. A next
`
`step includes
`
`
`RADIO FRAME CONSTRUCTED FROM ¢ ms SUB-FRAMES
`
`YeepeeeranmoeismsmmeemmmenmEnaAnAAenSS
`
`
`TGA-
`
`
`
`
`SUB-FRAMES (e.g. 0.5 ms)
`
`
`
` VU ZA
`
`RACH SYMBOL
`
`DATA SYMBOL
`
`HALF PILOT SYMBPL
`
`APPLE 1005
`APPLE1005
`
`

`

`Patent Application Publication
`
`Jul. 19,2007 Sheet 1 of 13
`
`US 2007/0165567 Al
`
`RADIO FRAME n-1
`
`RADIO FRAME n
`
`RADIO FRAME n+
`
`
`
`
`|
`| RADIO FRAME (10ms)
`
`WY UYU LV VOIBo
`
`
`
`
`
`
`
`
`
`RADIO FRAME CONSTRUCTED FROM ¢ ms SUB-FRAMES
`
`DDDLaALLL
`
`RACH SYMBOL
`
`DATA SYMBOL
`
`HALF PILOT SYMBPL
`
`FIG. 1
`
`

`

`Patent Application Publication
`
`Jul. 19,2007 Sheet 2 of 13
`
`US 2007/0165567 Al
`
`RACH PARAMETERS FOR THE TDM/FDM STRUCTURE
`
`oppontunrries|40||tssett
`
`BANDWIDTH
`RACH PARAMETERS IN
`LOCALIZED WODE|425WH|2.5MHz|5.0WH|10.0Wie|15.0MH|20.0MHz_|
`min, RB_BM
`228
`PHRB(Mg)|||
`
`|fOFoccurrensupcarniers||oh|TT
`# OF SEQUENCES (FOR ALL
`SECTORS/CELLS)
`(No)
`# OF CYCLIC SHIFTED VERSION
`OF EACH SEQUENCE (Noy)
`jfRack
`
`FIG. 2
`
`

`

`Patent Application Publication
`
`Jul. 19,2007 Sheet 3 of 13
`
`US 2007/0165567 Al
`
`
`
`—e& CIRCULAR AUTOCORRELATION
`
`—E CIRCULAR CROSS-CORRELATION p=1,2
`—@— CIRCULAR CROSS-CORRELATION p=1,7
`
` NORMALIZEDCIRCULARAUTO/CROSS-CORRELATION
`
`
`
`
`
`
`“Ot
`
`-10
`
`-5
`
`0
`DELAY
`
`5
`
`10
`
`5
`
`FIG. 3
`
`C,
`!
`|
`
`0
`
`CODE gr
`
`=,
`|
`|
`|
`
`30
`
`CODE 9-30 |
`|
`|
`
`CODE 9-60 |
`|
`|
`|
`
`CODE %-90 '
`|
`|
`|
`
`'
`|
`|
`|
`
`60
`
`90
`
`FIG. 4
`
`

`

`Patent Application Publication
`
`Jul. 19,2007 Sheet 4 of 13
`
`US 2007/0165567 Al
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`ERRORRATE
`
`
`
`ERRORRATE
`
`
`
`
`8
`
`9
`
`10
`
`12
`1
`THRESHOLD 8 (dB)
`
`13
`
`14
`
`5
`
`
`
`
`
`
`
`
`
`
`
`
`—S— SNR=-20B
`—E& SNR=-1dB
`—o— SNR=0dB
`—7— SNR=1dB
`
`
`
`
`THRESHOLD @ (dB)
`FIG. 6
`
`

`

`Patent Application Publication
`
`Jul. 19,2007 Sheet 5 of 13
`
`US 2007/0165567 Al
`
`0.5 WS SUB-FRAME
`
`0.5 MS SUB-FRAME
`
`FIG. 7
`
`Mee FREHETEY
`
`SPREADING
`
`FIG. 8
`
`TIME-DOMAIN MODULATION
`
`SPREADING
`
`SEQUENCE
`
`

`

`Patent Application Publication
`
`Jul. 19,2007 Sheet 6 of 13
`
`US 2007/0165567 Al
`
`FREQUENCY DOMAIN MODULATION
`
`
`SPREADING
`
`Cy
`
`FREQUENCY SPREADING SEQUENCE
`
`FIG. 9
`
`
`
`
`
`NORMALIZEDCIRCULARAUTO-/CROSS-CORRELATION
`
`1
`
`
`
`—O— CIRCULAR AUTOCORRELATION
`
`
`“EE CIRCULAR CROSS-CORRELATION: p
`il=|
`
`=1,11
`] 9 CIRCULAR CROSS-CORRELATION: p
`
`
`—_—_—_—
`—- — — il lc
`
`
`
`
`
`-0.2
`-300
`
`a
`
` -200
`
`—-100
`
`0
`
`100
`
`200
`
`300
`
`

`

`Patent Application Publication
`
`Jul. 19,2007 Sheet 7 of 13
`
`US 2007/0165567 Al
`
`0°"
`
`17!
`
`
`
`
`
`
`
`
`
`
`
`—e-SNR=—300B
`=SNR=-284B
`—>-SNR=-26dB
`—7-SNR=-24dB
`
`—t-SNR=-22B
`ISNR=-200B
`
`= 07
`
`S 4
`
`975
`
`10-4
`
`FIG. 11
`
`
`
`
`
`
`
`
`—F-SNR=-20dB
`
`
`
`
`
`ERRORRATE
`
`
`
`—ESNR=-24¢B
`—0-S§NR=-22dB
`
`q
`8
`THRESHOLD @ (dB)
`
`FIG. 12
`
`

`

`Patent Application Publication
`
`Jul. 19,2007 Sheet 8 of 13
`
`US 2007/0165567 Al
`
`COMPARISON OF TDM/FDM AND HYBRID/CDM RACH (BW=5MHz).
`
`NM pp Ns Noy 18 orpy
`NuMBER OF RACH opPoRTUNTTIES|WHERE Norny = NUMBER OF
`(oer ms)
`OFDM SYMBOL RESERVED FOR
`20
`RACH per ms
`eg. 160K Noepy FROM TABLE 1
`
`NO (COLLISION LIMITED)
`
`SAR REQUIREMENT FOR 1% FALSE
`ALARM AND MISSED DETECTION
`ERROR (TU 3 Kn/t)
`RACH OVERHEAD (per ms)
`
`INTERFACE GENERATED TO
`SCHEDULED USERS
`
`NONE
`
`-2
`
`Norou 1"
`
`SMALL
`
`11 4B
`
`NONE
`
`COLLISION PROBABILITY
`
`MEDIUM - HIGH
`
`INTER-CELL_ INTERFERENCE
`
`MEDIUM
`
`SYSTEM INTERFERENCE LIMITED
`
`YES
`
`FIG. 13
`
`

`

`Patent Application Publication
`
`Jul. 19,2007 Sheet 9 of 13
`
`US 2007/0165567 Al
`
`VE
`
`
`1412 ACK
`
`?
`
`
`CHANGE TX POWER AND/OR SEQUENCEF—47g|SEND RACH MESSAGE9jasg
`
`FIG. 14
`
`No
`
`RECEIVED
`
`YES
`
`

`

`Patent Application Publication
`
`Jul. 19,2007 Sheet 10 of 13
`
`US 2007/0165567 Al
`
`

`

`Patent Application Publication
`
`Jul. 19,2007 Sheet 11 of 13.
`
`US 2007/0165567 Al
`
`UE
`
`ACK DETECTED
`
`NODE B
`
`ACK SENT
`
` SEND RACH MESSAGE
`
`FIG. 17
`
`

`

`Patent Application Publication
`
`Jul. 19,2007 Sheet 12 of 13.
`
`US 2007/0165567 Al
`
`UE
`
`NODE B
`
`RACH ACK DETECTED
`
` MESSAGE
`
`RACH ACK SENT
`
`
`RECEIVED?
`
`

`

`Patent Application Publication
`
`Jul. 19,2007 Sheet 13 of 13.
`
`US 2007/0165567 Al
`
`UE
`
`NODE B
`
`RACH ACK DETECTED
`
`RACH ACK SENT
` SEND RACH MESSAGE
`
`
`
`FIG. 19
`
`

`

`US 2007/0165567 Al
`
`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
`numberof 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 generation mobile system based on evolved Global
`System for Mobile communication (GSM) core networks
`and the radio access technologies that they support, such as
`Evolved Universal Terrestrial Radio Access
`(EUTRA)
`including both Frequency Division Duplex (FDD)and Time
`Division Duplex (TDD) modes. 3GPP’s scope was subse-
`quently amended to include the maintenance and develop-
`ment 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)).
`[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 channelis 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
`RACHresources, 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
`RACHin the context of 3GPP, or ranging in the context of
`IEEE std. 802.16e. In this invention, we use RACH inits
`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 problemsarise 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 RACHstructure;
`[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. 41s 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-RACHover
`an AWGNchannel, 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-RACHover
`an TU channelat 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
`channelat 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 Al
`
`Jul. 19, 2007
`
`typically not
`are
`embodiment
`commercially feasible
`depicted in orderto facilitate a less obstructed view ofthese
`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 is4=7.1%.
`[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
`
`& =e3M2 ,n2=0,1,...,M—-1
`
`jot prin 1)
`To minimize the performance impact to scheduled
`[0024]
`
`users, the present invention presents a hybrid approachto the
`RACH preamble in an EUTRA system. Specifically,
`the
`RACHpreambleis transmitted in a CDM manner, while the
`message is either scheduled by the Node B in the same
`manneras 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.
`
`where M=15, andp is relatively prime to M.In this case,
`p={1,2,4,7,8,11,13,14, ... }. 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 hasrela-
`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
`ACKat 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]
`CDMapproach 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 1 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 2xM out of which a total of
`twenty are used, and e) a repetition of seven is used to
`ralte-match the preamble sequence length to one millisecond.
`[0033] The Chu-sequence (complex quadratic sequence)
`or GCL sequence is given by
`
`
`
`fpS =e “Se "M2
`
`,2=0,...,M-—-1
`
`and the delayed Chu-sequence is given by
`San=8in-30dymod Ms A=0,...9
`
`Note that the Chu-sequenceis a special sequence of the GCL
`sequence class. Other GCL sequences can be applied as the
`signature sequenceas well. For example, for even M, we can
`define g,, as
`
`“pale on
`Sm = @ FM2P”
`“FMP pn =0,...,M—-1
`
`[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=1 ... 10) as shown in FIG. 1. The scheme can
`use either localized or distributed mode. In the localized
`
`mode the subcarriers are divided into Nz, resource blocks
`with each resource block using a fixed numberof contiguous
`sub-carriers. Next, for each of the Nz» resource blocks, a
`numberof signature sequence groups are pre-defined so that
`every group consists of N, signature sequences anddifferent
`groups can be assigned to different neighboring sectors.
`Each group also consists of several cyclically shifted ver-
`sions of the signature sequences (Ng). As such, the total
`number of RACH opportunities per DFT-SOFDM symbolis
`given by Ngg*No*Nozy.
`[0026] As an example for 5 MHz bandwidth, all 300
`subcarriers are divided into twenty resource blocks with
`Nzg=20. A RACHsignature sequence occupiesfifteen 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
`lowcross 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
`
`

`

`US 2007/0165567 Al
`
`Jul. 19, 2007
`
`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, 1. The sequence is given by
`w={41 41), wl={41,-1}
`
`To generate the twenty unique signature sequences, a
`sequence identifier s is first computed via s=2xd+k where
`d=0, .. . 9 correspondsto the delay of the Chu-sequence and
`k=0,1 is the index of the Walsh sequence. Theresulting s-th
`RACH preamble signature sequence (with length 2M) is
`then given by
`
`P.=[WO)an WSapneaN=0,-.-, M-1
`
`An example of the RACH preamble sequence is shown in
`FIG.7. In this case, d=5, and k=1 with a resulting sequence
`index numberof eleven. The sequence P,,, made up ofg,,,,
`and -g,,, (i.e. Walsh code {1,-1}) is then repeated seven
`times in order to cover 1 millisecond.
`[0034]
`To mitigate inter-cell interference of RACH chan-
`nel, different Chu-sequences or GCL sequences can be used
`for different sectors/cells. A generalized Chu-sequence is
`given by:
`
`ee
`gn =e M2" n=l,...,M—-1
`
`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 {1,7,11,13,17,19,23,29,31,37, ... }.
`Givena fixed p, the corresponding Chu-sequenceis orthogo-
`nal whenit is shifted circularly. However, the sequencesare
`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 combinedsignals are
`then processed by an Inverse Fast Fourier Transform (IFFT),
`and Cyclic Prefix (CP), as are knownin theart.
`[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
`requirementfor 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.
`
`[0037] The RACH preamble detection is similar to the
`detection algorithm of TDM/FDM-based RACHat 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 randomlyselects a RACH preamble sequence
`with sequence identifier number s. The 2M length RACH
`sequence is
`
`PH[WOGan WBansad 2=0,---, M1
`
`where s=2xd+k. At the receiver side of Node-B, the received
`signal can be represented as
`y,=%,, 0h, +zntéy
`
`is channel
`indicates circular convolution, h,,
`where (X)
`impulse response, z,, is the channel noise, and x,, is either
`w(O)gz,, oF WD) Sa-
`[0038] At the receiver thecircular (periodic) correlation of
`sequence g,, and y,, is computed. This yields
`
`Cm
`
`1
`
`M-1
`» Yn&(n-m)modM
`VM n=0
`
`The correlation can be performedeitherin time or frequency
`domain. Through some simple manipulations, the following
`is obtained
`
`Cm =
`
`{ VM Im30a +2,
`
`-VM Iysoa tz, k=l
`
`k=0
`
`where the term z,,' is the equivalent channel noise. Usually
`the channel maximum delay is assumedto 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=1, one can combinethe nearby two blocks for both Walsh
`sequences. There are a total of fourteen blocks of which one
`2M RACHsequence uses two blocks. Two neighborc,,, are
`addedto yield seven correlation sequences for k=0. For k=1,
`two neighborc,, are subtracted accordingly to yield another
`seven correlation sequences for k=1. In the next step, we
`detect
`the delay index d, so that
`the RACH sequence
`identifier number s (s=2xd+k) can be obtained.
`[0040] From the correlation sequence c,,, 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 RACHrequests with
`sequence delay 0 and sequence delay 2. The correlation
`sequence c,,
`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 1s not available to the receiver at the Node-B. A
`
`simple detection algorithm is the maximum powerdetection.
`
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`US 2007/0165567 Al
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`When the maximum powerin 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 powerof correlation sequence. This yields
`
`1 M-1
`P= > lenl?-
`m=0
`
`The secondstep is to find the maximum powerin all regions
`to obtain
`
`[0043]
`
`= — max |e,
`1 30d+29,
`Biman, len
`
`é
`
`5
`
`Yd
`
`The final step is to check whether the maximum poweris
`greater than a pre-defined power threshold y,,,. Thus,
`[0044]
`
`Ya = y¥1H RACH request with delay d is present
`Ya <YrH RACH request with delay d is absent”
`
`[0045] With the detected d, and its corresponding Walsh
`code index k, the RACH sequenceidentifier numbers, 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 and6 illustrate detec-
`tion performance of the TDM/FDM RACHpreamble 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.
`Atfirst, 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 successfully received, a four-bit acknowledge-
`ment corresponding to the sequence numberis transmitted to
`the UE. This is done even when the UE may not be
`scheduled for sometimeto 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 messagetransmission approachis
`ACKbased. 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 UEreceives this ACK information,
`the RACH messageis 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 knownin the art. The UE
`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]
`Ina 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 UE
`selects 1404 one ofthe signature sequences, which is used
`1406 in a preamble for a RACH. Preferably, the selection is
`randomly selected. However, the select sequence could be
`predefined or selected to reduce the possibility of interfer
`ence.
`
`
`
`[0053] The UE then determines an available RACH access
`slot and other transmission parameters. In a next step, the
`
`UEsets 1408 a transmission power. In a next step, the UE
`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 numberoftransmissions 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
`
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`

`US 2007/0165567 Al
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`Jul. 19, 2007
`
`preamble is detected 1422. Then the RACH ACKis sent
`1424 to UE. The next step will be the RACH message
`transmission.
`
`meansfor 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
`RACHmessage 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 ACKis 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 messageafter the
`RACH ACKis 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 ACKandreceive 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 invention provides the advantage of
`enhancing capacity of the E-UTRA system pursuant to the
`above embodiments.
`In particular, providing the RACH
`preamble sequencing without the need for reserved RACH
`access resources enhancesthe peak rate of data transmission
`and can reduce latency issues for data transmissions. One
`can also expect to achieve higher sector and user packet call
`throughput. Notwithstanding these benefits, these embodi-
`ments can be realized with only minimal changes to the
`relevant 3GPP, 3GPP, and 802.16 standards.
`[0060]
`It will be appreciated that the above description for
`clarity has described embodiments of the invention with
`reference to different functional units and processors. How-
`ever,
`it will be apparent that any suitable distribution of
`functionality between different functional units or proces-
`sors may be used without detracting from the invention. For
`example, fu