1111111111111111 IIIIII IIIII 11111 1111111111 lllll lllll lllll lllll lllll 111111111111111 11111111
`US 20030198179Al
`
`(19) United States
`(12) Patent Application Publication
`Koo et al.
`
`(10) Pub. No.: US 2003/0198179 Al
`Oct. 23, 2003
`(43) Pub. Date:
`
`(54) RANGING METHOD FOR MOBILE
`COMMUNICATION SYSTEM BASED ON
`ORTHOGONAL FREQUENCY DIVISION
`MULTIPLE ACCESS SCHEME
`
`(75)
`
`Inventors: Chang-Hoi Koo, Songnam-shi (KR);
`Dong-Seek Park, Songnam-shi (KR);
`Pan-Yuh Joo, Seoul (KR)
`
`Correspondence Address:
`Paul J. Farrell, Esq.
`DILWORTH & BARRESE, LLP
`333 Earle Ovington Blvd.
`Uniondale, NY 11553 (US)
`
`(73) Assignee: SAMSUNG ELECTRONICS CO.,
`LTD., KYUNGKI-DO (KR)
`
`(21) Appl. No.:
`
`10/413,010
`
`(22) Filed:
`
`Apr. 14, 2003
`
`(30)
`
`Foreign Application Priority Data
`
`Apr. 22, 2002
`
`(KR) .................................... P2002-22841
`
`Publication Classification
`
`Int. Cl.7
`...... ....................................... . ........ H04J 11/00
`(51)
`(52) U.S. Cl. . ............................................................. 370/208
`
`(57)
`
`ABSTRACT
`
`Disclosed herein is a ranging method for a mobile commu(cid:173)
`nication system based on an OFDMA (Orthogonal Fre(cid:173)
`quency Division Multiple Access) scheme. In the commu(cid:173)
`nication system for classifying a ranging procedure between
`a transmission side and reception sides into an initial ranging
`process, a bandwidth request ranging process, and a periodic
`ranging process, the ranging method includes the steps of
`determining the number of initial RCs(ranging codes) for the
`initial ranging process, the number of bandwidth request
`RCs for the bandwidth request ranging process, and the
`number of periodic RCs for the periodic ranging process,
`determining a backoff value of the periodic RCs according
`to the number of the periodic RCs, and sending the initial
`RCs, the bandwidth request RCs, the periodic RCs, and the
`backoff value of the periodic RCs to the reception sides.
`
`21~1 bits length PN code
`
`\-~
`
`Available RCs
`
`Ranging channel
`
`RC#l RC#2
`
`Ranging subchannel
`(53bits)
`
`L RCs for
`M RCs for
`N RCs I or
`Initial Ranging Maintenance Ranging Bandwidth ReQuest Ranging
`
`VWGoA EX1011
`U.S. Patent No. 8,467,366
`
`

`

`I·
`
`
`
`21~ 1 bits length PN code
`
`.. ,
`
`Available RCs
`
`.. ,
`
`Ranging channel
`
`RC#l RC#2
`-
`
`-
`
`-
`
`-
`
`~
`
`RC#47 RC#48
`-
`
`-
`
`I
`
`-
`-
`Ranging subchannel
`(53bits)
`
`~
`
`? "0 --· r')
`~ -· 0 =
`l O"' --· r')
`~ -· 0 =
`
`~
`
`..
`
`.. ..
`
`L RCs !or
`M RCs for
`N RCs lor
`Initial Ranging Maintenance Ranging Bandwidth ReQuest Ranging
`
`)I:..
`
`)I:
`
`FIG.1
`
`

`

`Patent Application Publication Oct. 23, 2003 Sheet 2 of 3
`
`US 2003/0198179 Al
`
`CHECK CELL STATUS
`
`GENERATE RCs
`
`ASSIGN RCs
`(N : initial Ranging
`L : SW-request Ranging)
`M : Maintenance Ranging)
`
`210
`
`212
`
`214
`
`YES
`
`216
`
`NO
`
`ASSIGN ~s ~I ~~NDWIDT~)
`
`REQUEST N I
`
`HERE L>
`
`218
`
`230
`
`ASSIGN RCs FOR BANDWIP TH
`RANGING (WHERE L <N
`..
`
`ASSIGN BACKOFF VALUE fvOR BANDWIDTH
`REQUEST RANGING WHERE B<A)
`
`220
`
`232
`
`ASSIGN BACmFF VALUE FOR BANDWIDTH
`REQUEST RANGING (WHERE B>A)
`
`ASSIGN RCs F~R MAINTEN~NCE
`RANGING WHERE M>N
`
`222
`
`234
`
`ASSIGN RCs FOR MAINTENANCE
`RANGING (WHERE N>M)
`
`ASSIGN BACKOFF VALUE FOR
`MAINTENANCE RANGING (WHERE C<A)
`
`224
`
`236
`
`ASSIGN BACKOFF VALUE FOR
`MAINTENANCE RANGING (WHERE C>A)
`
`ASSIGN RCs FOR INITIAL
`RANGING (WHERE N<M OR L)
`
`226
`
`238
`
`ASSIGN ~~lRi\l~I~~ ~f NGING
`
`ASSIGN BACKOFF VALUE FOR
`INITIAL RANGING (WHERE A>B OR C)
`
`22B
`
`240
`
`ASSIGN BACKOFF VALUE FOR INITIAL
`RANGING (WHERE A<B OR C)
`
`CONFIGURE ULMAP
`MESSAGE (ASSIGN RCs)
`
`CONFIGURE UCO MESSAGE
`{ASSIGN BACKOFF VALUE)
`
`242
`
`24~
`
`END
`
`FIG.2
`
`

`

`Patent Application Publication Oct. 23, 2003 Sheet 3 of 3
`
`US 2003/0198179 Al
`
`318
`
`PROCESS MESSAGE
`
`NO
`
`326
`
`SELECT INITIAL RC & YES
`ITS BACKOFF VALUE
`
`314
`
`CHECK RCs
`
`START
`
`RECEIVE MESSAGE
`312
`UUMP MESSAGE RECEIVED ?
`NO ·
`316
`UCO MESSAGE RECEIVED ?
`YE
`CHECK BACKOFF VALUE
`
`310
`
`YES
`
`320
`
`MAPPING BETWEEN RCs
`AND BACKOFF VALUES
`
`322
`
`328
`
`INITIAL PiANGING?
`NO
`ANDWIDTH REQUEST RANGING.
`NO
`SELECT BANDWIDTH RC
`AND ITS SANKOFF VALUE
`
`330
`
`YES
`
`SELECT BANDWIDTH RC
`AND ITS BACKOFF VALUE
`
`332
`
`EXECUTE UPLINK ACCESS
`
`334
`
`COLLISION GENERA.TED ?
`NO
`COMPLETE TRANSMISSION OR
`EXECUTE OTHER TPiANSMISSION
`
`E
`
`338
`
`END
`
`FIG. 3 ·
`
`

`

`US 2003/0198179 Al
`
`Oct. 23, 2003
`
`1
`
`RANGING METHOD FOR MOBILE
`COMMUNICATION SYSTEM BASED ON
`ORTHOGONAL FREQUENCY DIVISION
`MULTIPLE ACCESS SCHEME
`[0001] This application claims priority to an application
`entitled "RANGING METHOD FOR MOBILE COMMU(cid:173)
`NICATION SYSTEM BASED ON ORTHOGONAL FRE(cid:173)
`QUENCY DIVISION MULTIPLE ACCESS SCHEME",
`filed in the Korean Intellectual Property Office on Apr. 22,
`2002 and assigned Ser. No. 2002-22841, the contents of
`which is incorporated hereinby reference.
`
`BACKGROUND OF THE INVENTION
`[0002] 1. Field of the Invention
`[0003] The present invention relates to a ranging method
`for a BWA (Broadband Wireless Access) system, and more
`particularly to a ranging method for a mobile communica(cid:173)
`tion system using an OFDMA(Orthogonal Frequency Divi(cid:173)
`sion Multiple Access) scheme.
`[0004] 2. Description of the Related Art
`[0005] Typically, an OFDMA scheme is defined as a
`two-dimensional access scheme for combining a IDA(Time
`Division Access) scheme with a FDA (Frequency Division
`Access) scheme. In the case of transmitting data using the
`OFDMA scheme, OFDMA symbols are separately loaded
`on sub-carriers and transmitted over prescribed sub-chan(cid:173)
`nels. A communication system using the OFDMA scheme
`needs to periodically execute a ranging procedure to cor(cid:173)
`rectly establish a time offset between a transmission side,
`i.e., a Node B, and a reception side, i.e. a UE (User
`Equipment), and to adjust power between them.
`[0006] The ranging procedure is classified into an initial
`ranging process, a bandwidth request ranging process, and a
`maintenance ranging process( =periodic ranging process),
`according to its objectives.
`[0007] A RC(ranging code) for the maintenance ranging
`process corresponds to a periodic code periodically trans(cid:173)
`mitted to the Node B over the UE. The maintenance ranging
`process is also called a periodic ranging process.
`[0008] The objectives of the above three ranging processes
`have been defined in the IEEE(International Electrotechni(cid:173)
`cal Commission) 802.16.
`[0009] The ranging procedure needs ranging sub-channels
`and RCs, and the UE is assigned with a different RC
`according to the three objectives. However, the standard
`document prescribed in the IEEE 802.16 does not define a
`method for allowing the UE to assign the RC to a variety of
`ranging processes having different usages and a message
`thereof.
`[0010] The IEEE 802.16 defines a prescribed scheme
`wherein a Node B transmits a UL_MAP(Uplink Map)
`message to a UE to inform the UE of reference information
`in uplink access. The UL_MAP message informs the UE of
`various information in the uplink, for example, a UE's
`scheduling period and a physical channel configuration, etc.
`The UE receives the UL_ MAP message, and executes a
`ranging-related procedure based on information contained in
`the UL_MAP message. The UL_MAP message is transmit(cid:173)
`ted to all the UEs of a cell over broadcast data of the Node
`B.
`
`[0011] The UL_MAP message bas the following configu(cid:173)
`ration as shown in Table 1.
`
`TABLE 1
`
`Syntax
`
`UL_MAP _Message_ Format( ) {
`Management Message Type=3
`Uplink channel ID
`UCO Count
`Number of UL_ MAP elements n
`Allocation Start Time
`Begin PHY Specific Section {
`for(i=l ; i<n; i+n)
`UL_MAP _lnformation_Element {
`Connection ID
`UIUC
`Offset
`
`Size
`
`8 bits
`8 bits
`8 bits
`16 bits
`32 bits
`
`Variable
`
`[0012] As shown in Table 1, a UL_MAP _Information(cid:173)
`- Element area serving as an IE (Information Element) area
`of a UL_ MAP message includes a Connection ID(Identifier)
`area, a UIUC (Uplink Interval Usage Code) area, and an
`Offset area. The Connection ID area records information
`indicative of a transmission scheme therein. The transmis(cid:173)
`sion scheme is classified into a unicast scheme, a broadcast
`scheme, and a multicast scheme. The UIUC area records
`information indicative of the usage of offsets recorded in the
`offset area. For example, a number of 2 recorded in the
`UIUC area means that a starting offset for use in the initial
`ranging process is recorded in the offset areaa number of 3
`recorded in the UIUC area means that a starting offset for
`use in either the bandwidth request ranging or the mainte(cid:173)
`nance ranging process is recorded in the offset area. The
`offset area records a starting offset value for use in either the
`initial ranging process or the maintenance ranging process
`according to the information recorded in the UIUC area.
`
`[0013] The conventional UL_MAP message configuration
`shown in the Table 1 classifies three ranging processes
`according to the above objectives, but it does not provide RC
`allocation by which an independent process for each of the
`three ranging processes becomes available. In other words,
`although the conventional UL_ MAP message configuration
`generates a ranging mode by the use of PN (Pseudorandom
`Noise) code segmentation and also generates a RC available
`for the three objectives, the UE cannot recognize such
`information, i.e. the ranging mode and the RC. Therefore, it
`is necessary for the conventional UL_ MAP message to
`execute a RC allocation for independently performing rang(cid:173)
`ing processes having different objectives.
`
`[0014] Typically, even an OFDMAcommunication system
`makes it possible to generate all of the near and non-line(cid:173)
`of-sight conditions in the same manner as in a mobile
`communication system channel environment using other
`modulation and access schemes, and contains a partial signal
`blocking caused by wood which may affect signal attenua(cid:173)
`tion and signal multipath. Therefore, there may occur a
`signal collision in an initial transmission step, irrespective of
`the type of ranging process used in a UE, and then a random
`seed for providing the same backoff value as in an initial
`access time is adapted for a signal re-access time.
`
`

`

`US 2003/0198179 Al
`
`Oct. 23, 2003
`
`2
`
`[0015] A conventional Node B transmits to the UE a UCD
`(Uplink Channel Descriptor) message having information
`indicative of the backoff value in such a way that the UE
`identifies the backoff value. Such a UCD message will be
`described in Table 2.
`
`TABLE 2
`
`Syntax
`
`Size
`
`Notes
`
`UCD-Message_ Format( )
`Management Message Type=O
`Uplink Channel ID
`Configuration Change Count
`Mini-slot size
`Ranging Backoff Start
`Ranging Backoff End
`Request Backoff Start
`Request Backoff End
`TLV Encoded Information for the overall
`channel
`Begin PHY Specific Section {
`for (i=l; i<n ; i+n)
`Uplink_ BursL_ Descriplor
`
`8 bits
`8 bits
`8 bits
`8 bits
`8 bits
`8 bits
`8 bits
`8 bits
`Variable
`
`Variable
`
`[0016] As shown in Table 2, the Node B transmits to the
`UE a UCD message having information indicative of a
`backoff value available for a re-access time provided after
`the lapse of an access failure time of the UE. In other words,
`the backoff value indicates a kind of standby time being a
`duration time between the start of UE's access failure time
`and the start of UE's re-access time. The Node B transmits
`to the UE the backoff values indicating standby time infor(cid:173)
`mation for which the UE must wait for the next ranging
`process after failing to execute an initial ranging process.
`For example, for a number of 10 determined by the above
`syntaxes of the "Ranging Backoff Start" and the "Ranging
`Backoff End" shown in the Table 2, the UE must pass over
`the 2 10-times access executable chances (i.e., 1024-times
`access executable chances) and then execute the next rang(cid:173)
`ing process according to the Truncated Binary Exponential
`Backoff Algorithm. In more detail, because the UE receives
`a UL_ MAP message and its ranging access time corresponds
`to a 1025-th access time, a ranging operation can be
`executed at the 1025-th access time . However, as stated
`above, a RC is differently assigned to a UE according to the
`three ranging processes and is also dynamically assigned to
`the UE according to a cell status, such that a backoff value
`transmitted with the UCD message must be differently
`assigned to the UE according to the objectives of RCs.
`
`[0017]
`In conclusion, a communication system using an
`OFDMA scheme classifies its ranging procedure into three
`kinds of ranging processes according to its objective.
`Although a RC can be differently assigned to the three
`ranging processes, the UE is unable to identify information
`indicative of the type of ranging process and is thereby
`unable to execute an independent ranging operation. The
`conventional communication system using the OFDMA
`scheme cannot execute dynamic allocation which is variable
`with a cell status and a UE' s access characteristics because
`the UE cannot identify such ranging type information,
`thereby increasing the number of ranging access times of the
`UE's ranging procedure. As a result, the conventional com(cid:173)
`munication system using the OFDMA scheme has a disad-
`
`vantage in that it unavoidably increases the length of access
`delay time and reduces overall system performance.
`
`SUMMARY OF THE INVENTION
`
`[0018] Therefore, the present invention has been made in
`view of the above problems, and it is an object of the present
`invention to provide a method for dynamically assigning
`different RCs to a UE according to ranging objectives of the
`UE in a communication system using an OFDMA scheme.
`[0019]
`It is another object of the present invention to
`provide a method for assigning a RC to a UE for minimizing
`the length of ranging access time in a communication system
`using an OFDMA scheme.
`[0020]
`It is yet another object of the present invention to
`provide a method for dynamically assigning a backoff value
`of a RC for use in a UE according to a cell status in a
`communication system using an OFDMA scheme.
`[0021]
`It is yet another object of the present invention to
`provide a method for dynamically assigning different back(cid:173)
`off values to a UE according to the type of RC in a
`communication system using an OFDMA scheme.
`[0022]
`In accordance with one aspect of the present inven(cid:173)
`tion, the above and other objects can be accomplished by the
`provision of a method for classifying a ranging procedure
`between a transmission side and reception sides into an
`initial ranging process, a bandwidth request ranging process,
`and a periodic ranging process, and allowing the transmis(cid:173)
`sion side to send RCs and their backoff values for use in each
`ranging process to the reception sides, the method including
`the steps of determining the number of initial RCs for the
`initial ranging process, the number of bandwidth request
`RCs for the bandwidth request ranging process, and the
`number of periodic RCs for the periodic ranging process;
`determining a backoff value of the periodic RCs according
`to the number of the periodic RC; and sending the initial
`RCs, the bandwidth request RCs, the periodic RCs, and the
`backoff value of the periodic RCs to the reception sides.
`[0023]
`In accordance with another aspect of the present
`invention, there is provided a method for classifying a
`ranging procedure between a transmission side and recep(cid:173)
`tion sides into an initial ranging process, a bandwidth
`request ranging process, and a periodic ranging process, and
`allowing the transmission side to send RCs and their backoff
`values for use in each ranging process to the reception sides,
`the method including the steps of detecting a congestion
`level of a current cell, if the detected congestion level of the
`cell is over a prescribed congestion level, controlling the
`number of the initial RCs for the initial ranging process to
`be less than either the number of the bandwidth request RCs
`for the bandwidth request ranging process or the number of
`the periodic RCs for the periodic ranging process, and
`varying a backoff value of the periodic RCs; and sending the
`initial RCs, the bandwidth request RCs, and the periodic
`RCs, and the backoff value of the periodic RCs to the
`reception sides.
`[0024]
`In accordance with yet another aspect of the
`present invention, there is provided a method for classifying
`a ranging procedure between a transmission side and recep(cid:173)
`tion sides into an initial ranging process, a bandwidth
`request ranging process, and a periodic ranging process, and
`varying the number of RCs for use in each ranging process
`
`

`

`US 2003/0198179 Al
`
`Oct. 23, 2003
`
`3
`
`in a cell of which the number of total RCs to be used for the
`ranging processes is predetermined, the method including
`the steps of allowing the transmission side to determine the
`number of initial RCs for the initial ranging process, the
`number of bandwidth request RCs for the bandwidth request
`ranging process, and the number of periodic RCs for the
`periodic ranging process, and determining a backoff value of
`the periodic RCs according to the number of the periodic
`RCs; sending the initial RCs, the bandwidth request RCs, the
`periodic RCs, and the backoff value of the periodic RCs to
`the reception sides; and after receiving the initial RCs, the
`bandwidth request RCs, the periodic RCs, and the backoff
`value of the periodic RCs, allowing the reception sides to
`select a RC corresponding to their current target ranging
`process, and executing a ranging process corresponding to
`the selected RC.
`[0025]
`In accordance with yet another aspect of the
`present invention, there is provided a method for classifying
`a ranging procedure between a transmission side and recep(cid:173)
`tion sides into an initial ranging process, a bandwidth
`request ranging process, and a periodic ranging process, and
`varying the number of RCs for use in each ranging process
`in a cell of which the number of total RCs to be used for the
`ranging processes is predetermined, the method including
`the steps of detecting a congestion level of a current cell, if
`the detected congestion level of the cell is over a prescribed
`congestion level, controlling the number of the initial RCs
`for the initial ranging process to be less than either the
`number of the bandwidth request RCs for the bandwidth
`request ranging process or the number of the periodic RCs
`for the periodic ranging process, and varying a backoff value
`of the periodic RCs; sending the initial RCs, the bandwidth
`request RCs, and the periodic RCs, and the backoff value of
`the periodic RCs to the reception sides; and after receiving
`the initial RCs, the bandwidth request RCs, the periodic
`RCs, and the backoffvalue of the periodic RCs, allowing the
`reception sides to select a RC corresponding to their current
`target ranging process, and executing a ranging process
`corresponding to the selected RC.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`[0026] The above and other objects, features and other
`advantages of the present invention will be more clearly
`understood from the following detailed description taken in
`conjunction with the accompanying drawings, in which:
`[0027] FIG. 1 is a diagram illustrating a ranging code
`allocation procedure for a communication system based on
`an OFDMAscheme in accordance with a preferred embodi(cid:173)
`ment of the present invention;
`[0028] FIG. 2 is a flow chart illustrating a procedure for
`assigning a ranging code and a backoff value to each ranging
`process according to a ranging objective of a Node B in
`accordance with a preferred embodiment of the present
`invention; and
`[0029] FIG. 3 is a flow chart illustrating a procedure for
`assigning a ranging code and a backoff value to a UE
`according to a ranging objective of the UE in accordance
`with a preferred embodiment of the present invention.
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`[0030] Now, preferred embodiments of the present inven(cid:173)
`tion will be described in detail with reference to the annexed
`
`drawings. In the drawings, the same or similar elements are
`denoted by the same reference numerals even though they
`are depicted in different drawings. In the following descrip(cid:173)
`tion, a detailed description of known functions and configu(cid:173)
`rations incorporated herein will be omitted when it may
`obscure the subject matter of the present invention.
`
`[0031] FIG. 1 is a diagram illustrating a RC(Ranging
`Code) allocation procedure for a communication system
`based on an OFDMA(Orthogonal Frequency Division Mul(cid:173)
`tiple Access) scheme in accordance with a preferred embodi(cid:173)
`ment of the present invention.
`
`[0032] With reference to FIG. 1, a RC is created by
`segmenting a PN(Pseudorandom Noise) code having a pre(cid:173)
`scribed length, for example, the length of 215 -bits, in pre(cid:173)
`scribed units. Typically, one ranging channel is composed of
`two ranging sub-channels each having the length of 53 bits.
`A RC is created by such a PN code segmentation over a
`ranging channel of 106 bits. A maximum of 48 RCs
`RC(Ranging Code)#l-RC#48 can be assigned to a UE(User
`Equipment). More than two RCs for every UE are applied as
`a default value to the three ranging processes having differ(cid:173)
`ent objectives, i.e. an initial ranging process, a bandwidth
`request ranging process, and a maintenance ranging( =peri(cid:173)
`odic ranging) process. These ranging processes and their
`functions are the same as those in the aforementioned prior
`art. Particularly, a RC for use in the maintenance ranging
`process corresponds to a periodic code periodically trans(cid:173)
`mitted to the Node B over the UE, such that the maintenance
`ranging process is also called the periodic ranging process.
`Therefore, a RC is differently assigned to a UE according to
`each objective of the three ranging processes. That is,
`referring to FIG. 1, N RCs are assigned to a UE for the
`initial ranging process as denoted by a prescribed term of "N
`RCs for Initial Ranging" in FIG. 1, M RCs are assigned to
`a UE for the maintenance ranging process as denoted by a
`prescribed term of "M RCs for maintenance ranging", and L
`RCs are assigned to a UE for the bandwidth request ranging
`process as denoted by a prescribed term of "L RCs for
`Bandwidth-request ranging" . The RC for the maintenance
`ranging process is a prescribed code periodically transmitted
`from the UE to the Node B, such that it is also called a
`periodic code.
`
`[0033] The standard document prescribed in the IEEE
`(International Electrotechnical Commission) 802.16 cur(cid:173)
`rently defines the maximal number of RCs that can be
`allocated to the UE and a prescribed default value also
`allocated to the UE, but it does not describe a detailed
`method for assigning such RCs to the UE therein. Therefore,
`the UE is unable to identify reception RC information, such
`that it is unable to execute an adaptive operation in the case
`of either a signal collision between transmission RCs or
`other ranging-related procedures. In order to solve these
`problems, the present invention proposes a RC allocation
`method as well as a method for reducing a UE's access delay
`time by assigning an independent backoff value to each RC,
`and their detailed description will hereinafter be described.
`
`[0034]
`In more detail, the present invention classifies RCs
`according to the aforesaid three objectives, and informs a
`UE of the range of RCs currently available for the UE,
`resulting in a minimum access delay time. In this case, a
`message indicative of such classification and range of the
`RC is a UL(Uplink)_MAP message, and this UL_MAP
`message has the following configuration as shown in Table
`3 .
`
`

`

`US 2003/0198179 Al
`
`Oct. 23, 2003
`
`4
`
`TABLE 3
`
`TABLE 4-continued
`
`Syntax
`
`Size
`
`Syntax
`
`UL_MAP _Message_ Format( ) {
`Management Message Type=3
`Uplink channel ID
`UCO Count
`Number of UL_ MAP elements n
`Allocation Start Time
`Begin PHY Specific Section {
`for(i=l ; i<n; i+n)
`UL_MAP _Information_ Element {
`Connection ID
`UIUC
`Offset
`Initial Ranging code
`Bandwidth request Ranging code
`Maintenance Ranging code
`
`8 bits
`8 bits
`8 bits
`16 bits
`32 bits
`
`Variable
`
`Initial Ranging Backoff Start
`Initial Ranging Backoff End
`Bandwidth-reques t Ranging Backoff Start
`Bandwidth-reques t Ranging Backoff End
`Maintenance Ranging Backoff Start
`Maintenance Ranging Backoff Endt
`Request Backoff Start
`Request Backoff End
`Request Backoff Start
`TLV Encoded Information for the overall
`channel
`Begin PHY Specific Section {
`for (i=l; i<n ; i+n)
`Uplink__Burst_ Descriptor
`
`Notes
`
`Size
`
`8 bits
`8 bits
`8 bits
`8 bits
`8 bits
`8 bits
`
`8 bits
`8 bits
`Variable
`
`Variable
`
`[0035] As shown in Table 3, one UE is assigned with 48
`RCs as a maximum RC number. Provided that at least two
`RCs from among the 48 RCs are assigned to the UE as a
`specific RC for each of the three ranging objectives, the UE
`is assigned with 6 RCs in total. Such RCs are differently
`assigned for every ranging objective, one UE is assigned
`more than two RCs corresponding to each RC for the three
`ranging objectives, and the maximal number of 48 RCs is
`available for the one UE. In other words, the UL_MAP
`message shown in Table 3 contains an initial RC for the
`initial ranging process, and a periodic RC such as a band(cid:173)
`width-request RC and a maintenance RC, which is trans(cid:173)
`mitted to the UE. Therefore, the UE receiving the UL_ MAP
`message is able to use a proper RC in response to its own
`current ranging objective. Also, the Node B dynamically
`assigns RCs to the UE according to a current cell status. For
`example, provided that a small number of UEs are inter(cid:173)
`connected (hereinafter referred to as the connected-state
`UEs) within a cell, the Node B may assign many RCs (i.e.
`initial RCs) for use in the initial ranging process to the UEs
`during an initialization time. Provided that a large number of
`connected-state UEs are contained in a cell, the Node B may
`reduce the number of RCs assigned the initial RCs. In brief,
`the Node B dynamically assigns RCs to each UE according
`to a congestion state within a cell. Such a dynamic RC
`allocation may be adapted to control the cell's congestion
`state and cell priority. The RC allocation is variable with a
`cell status, resulting in reduction of a UE's access delay
`time.
`[0036] A UCD (Uplink Channel Descriptor) message for
`differently setting up a backoff value according to the type
`of RCs will be hereinafter described with reference to Table
`4.
`
`TABLE 4
`
`Syntax
`
`Size
`
`Notes
`
`UCD-Message_ Format( )
`Management M essage Type=0
`Uplink Channel ID
`Configuration Change Count
`Mini-slot size
`
`8 bits
`8 bits
`8 bits
`8 bits
`
`[0037] As shown in Table 4, the UCD message provides
`UEs with different backoff values in response to the number
`of RCs dynamically assigned to the UEs according to the
`number of connected-state UEs within a cell and the number
`of UEs attempting to execute an initial access. That is, if R Cs
`having different objectives are assigned with different back(cid:173)
`off values, access to UEs contained in the cell is controlled
`according to a cell status. In this way, access to the UEs is
`controlled by assigning different backoff values to the UEs,
`resulting in a minimal access delay time. For example, in the
`case where 10 RCs are assigned with an initial ranging
`process over a UL_MAP message and the remaining RCs
`other than the 10 RCs are assigned with a bandwidth request
`ranging process and a maintenance ranging process, the
`probability of a code collision caused by UEs respectively
`selecting the same RCs as their initial RCs is ½o. Therefore,
`in order to further reduce the probability of such collisions
`caused by the UEs selecting the same RCs, if a re-access
`time for which each UE re-accesses RCs for the initial
`ranging process is divided into a plurality of access time
`segments, that is, if the UEs each are assigned a high initial
`ranging backoff value, the probability of access collisions
`from among the UEs in the initial ranging process can be
`significantly reduced. Even in the case where the bandwidth
`request ranging process typically assigned many more RCs
`than the initial ranging process is assigned a relatively low
`backoff value lower than the initial ranging backoff value,
`the probability of UEs collisions in the bandwidth request
`ranging process can also be reduced because the number of
`RCs assigned to the bandwidth request ranging process is
`much more than the number of other RCs assigned to the
`initial ranging process. In this way, an access time of each
`UE is shortened by reducing a backoff value for use in the
`bandwidth request ranging process.
`
`[0038] The Node B for executing a RC allocation and a
`backoff value allocation according to a ranging objective
`will hereinafter be described with reference to FIG. 2.
`[0039] FIG. 2 is a flow chart illustrating a procedure for
`assigning a RC and a backoff value to each ranging process
`according to a ranging objective of a Node B in accordance
`with a preferred embodiment of the present invention.
`
`[0040] Referring to FIG. 2, the Node B checks its own cell
`status at step 210. In more detail, the Node B checks a
`
`

`

`US 2003/0198179 Al
`
`Oct. 23, 2003
`
`5
`
`congestion state of its own cell on the basis of the number
`of UEs currently in a traffic state at step 210. The Node B
`generates RCs at step 2U. In more detail, as previously
`stated in FIG. l, the Node B generates a plurality of RCs by
`segmenting a PN code having the length of 215
`- 1 bits in
`predetermined units at step 212. The Node B assigns RCs to
`be used for three ranging processes having different objec(cid:173)
`tives, i.e. the initial ranging process, the bandwidth request
`ranging process, and the maintenance ranging process, to the
`three ranging processes, respectively, at step 214. In more
`detail, as previously stated in FIG. 1, the Node B assigns N
`number of RCs to the initial ranging process, assigns L
`number of RCs to the bandwidth request ranging process,
`and assigns M number of RCs to the maintenance ranging
`process at step 214. In case of assigning the RCs to each
`ranging process at step 214, the Node B varies the number
`of RCs to be used for the initial ranging process, the
`bandwidth request ranging process, and the maintenance
`ranging process, according to the cell status checked at step
`210. In the case where it is determined at step 216 that the
`cell is in a heavy load state over a prescribed congestion
`state, the Node B goes to step 218.
`[0041] The Node B controls the number L of RCs for the
`bandwidth request ranging process to exceed the number N
`of RCs for the initial ranging process and executes RC
`allocation for the bandwidth request ranging process at step
`218 because the cell is in such a heavy load state at step 216,
`and goes to step 220. That is, the Node B executes RC
`allocation for the bandwidth request ranging process in a
`prescribed condition of L>N at step 218. The reason why the
`Node B provides such a prescribed condition of L>N at step
`218 is to minimize the number of collisions caused by the
`UEs' initial ranging operation, as previously stated above. In
`more detail, provided that any cell is in a high congestion
`state, this means that this cell has too much traffic. There(cid:173)
`fore, in case of assigning RCs to each ranging process, the
`Node B controls the number L of RCs to be used for the
`bandwidth request ranging process to exceed the number N
`of RCs to be used for the initial ranging process, thereby
`minimizing the number of uplink access collisions of UEs at
`step 218. The Node B executes backoff-value allocation for
`the bandwidth request ranging process at step 220. In this
`case, provided that a backoff value for the initial ranging
`code is denoted by a reference character ' A', a backoff value
`for the bandwidth request ranging code is denoted by a
`reference character 'B ', and a backoff value for the main(cid:173)
`tenance ranging code is denoted by a reference character
`'C', the Node B controls the backoff value of B to be less
`than the backoff value of A at step 220, that is, provides a
`prescribed condition of B<A at step 220, and then goes to
`step 222. The backoff value reduces the length of re-access
`time caused by access collisions among several UEs in
`inverse proportion to the