(12) United States Patent
`Dahlman et al.
`
`USOO6606313B1
`(10) Patent No.:
`US 6,606,313 B1
`(45) Date of Patent:
`Aug. 12, 2003
`
`(54) RANDOM ACCESS IN A MOBILE
`TELECOMMUNICATIONS SYSTEM
`(75) Inventors: Erik Dahlman, Bromma (SE); Per
`Beming, Stockholm (SE); Maria
`Gustafsson, Stockholm (SE)
`(73) Assignee: Telefonaktiebolaget LM Ericsson
`(publ), Stockholm (SE)
`-
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`
`(*) Notice:
`
`(21) Appl. No.: 09/166,679
`(22) Filed:
`Oct. 5, 1998
`H04B 71216
`(51) Int. CI.7
`(52) U.S. Cl. ....................... 370/347; 370/337; 370/344;
`455/522
`(58) Field of Search ................................. 370/329, 335
`370/336,337,346, 347, 441 32s. 321.
`327, 342 503 323 515 52s 324. 455 522.
`71 474s. 749. 750. 375,200 s 130 s 142-1 45.
`s
`s
`s
`150-152, 211, 1 40
`
`(56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`... 375/200
`5,430,760 A 7/1995 Dent ............
`5,502,721. A * 3/1996 Pohjakallio ................. 370,336
`5,544,196 A 8/1996 Tiedemann, Jr. et al. ... 375/200
`5,577.024. A * 11/1996 Malkamaki et al. .......... 370/18
`5,673.259 A 9/1997 Quick, Jr. ................... 370/342
`5,751,708 A * 5/1998 Eng et al. .............. 370/395.42
`5,850,392 A : 12/1998 Wang et al. ......
`... 370/335
`5.940,384 A 8/1999 Carney et al........
`... 370/347
`6,181,683 B1 * 1/2001 Chevillat et al. ........... 370/329
`6,320,843 B1 * 11/2001 Rydbeck et al. .....
`... 370/207
`6,381,229 B1 * 4/2002 Narvinger et al. .......... 370/328
`6,442,153 B1
`8/2002 Dahlman et al. ........... 370/342
`
`
`
`EP
`WO
`
`FOREIGN PATENT DOCUMENTS
`O 633 671 A2
`1/1995
`WO 98/1828O
`4/1998
`OTHER PUBLICATIONS
`U.S. patent application Ser. No. 08/733,501, filed Oct. 18,
`1996 6259724B1.
`U.S. patent application Ser. No. 08/847,655, filed Apr. 30,
`1997 6163533A
`Standard Search Report for RS 101856 US completed on
`Jun. 24, 1999.
`* cited by examiner
`Primary Examiner Dang Ton
`ASSistant Examiner Tri H. Phan
`(74) Attorney, Agent, or Firm Jenkens & Gilchrist, P.C.
`(57)
`ABSTRACT
`A method for processing multiple random access requests is
`disclosed in which a base Station transmits an acquisition
`indicator Signal, which indicates that the base Station has
`detected the presence of a random access transmission. The
`acquisition indicator can be generated based on the amount
`of energy received on the random access channel (e.g., as
`opposed to the correct/incorrect decoding of a random
`access message). Consequently, the delay between the
`beginning of the random access transmission and the begin
`ning of the acquisition indicator transmission is significantly
`shorter than the delay to the beginning of an acknowledg
`ment transmission based on the reception of a correctly
`decoded random access message. If a mobile Station does
`not receive a positive acquisition indicator, it should inter
`rupt the present transmission and Start to re-transmit the
`random access burst in the next time slot, while modifying
`the transmission power level accordingly between the Suc
`cessive re-transmissions
`
`56 Claims, 2 Drawing Sheets
`
`108
`
`120
`
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`110-
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`SGNATURE
`SPREADING CODE
`?.
`S
`12
`116
`
`118
`
`WDM
`
`--------
`
`O
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`

`

`U.S. Patent
`
`US 6,606,313 B1
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`
`
`
`
`up
`FG.2
`Random - a CCeSS burst
`Preamble
`Random - access message
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`14
`
`Aug. 12, 2003
`
`Sheet 1 of 2
`F.G. 1
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`SECTOR SPECIFIC
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`GENERATOR
`- 114
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`110-
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`ASSOCATED WITH "DATA FIELD "LONG
`SGNATURE
`SPREADING CODE
`- -
`112
`116
`
`
`
`118
`
`----
`
`------
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`U.S. Patent
`
`Aug. 12, 2003
`
`P
`eSt
`Poffset-
`Finit
`
`axe-in-a-
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`4.
`NACK
`
`US 6,606,313 B1
`
`RA burst
`
`Sheet 2 of 2
`FG.5
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`
`s
`
`4.
`NACK
`
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`NACK
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`4.
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`210
`71 208
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`(Signature 1 )
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`
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`US 6,606,313 B1
`
`1
`RANDOMACCESS IN A MOBILE
`TELECOMMUNICATIONS SYSTEM
`
`CROSS-REFERENCES TO RELATED
`APPLICATIONS
`This Application for Patent is related by subject matter to
`commonly-assigned U.S. Applications for Patent Ser. Nos.
`08/733,501, 08/847,655, and 09/148,224, filed Oct. 18,
`1996, Apr. 30, 1997, and Sep. 4, 1998, respectively, and
`Provisional Application Ser. No. 60/063,024, filed Oct. 23,
`1997. The above-cited Applications are useful for illustrat
`ing certain important premises and the State of the art for the
`present Application, and are hereby incorporated by refer
`ence herein in their entirety.
`
`15
`
`BACKGROUND OF THE INVENTION
`
`2
`does not acknowledge the access request, the IS-95 mobile
`Station re-transmits the entire access request packet at a
`higher power level. This proceSS continues until the base
`Station acknowledges the acceSS request.
`In the above-cited Applications and the IS-95 CDMA
`technical Specifications, different random access methods
`based on S-ALOHA random access Schemes have been
`described. Essentially (as illustrated in FIG. 1), using a basic
`S-ALOHA scheme, there are well-defined instants in time
`(time slots) at which random access transmissions are
`allowed to begin. Typically, a mobile Station (user) randomly
`Selects a time slot in which the transmission of a random
`access burst (e.g., U1, U2) is to begin. However, the time
`Slots are not pre-allocated to specific users. Consequently,
`collisions between the different users random access bursts
`can occur (e.g., between U3, U4).
`In a Specific mobile communications System using Such
`an S-ALOHA random access Scheme, Such as the method
`disclosed in the above-cited U.S. application Ser. No.
`08/733,501 (hereinafter, “the 501 Application”), a mobile
`Station generates and transmits a random access packet. A
`diagram that illustrates a frame Structure for Such a random
`acceSS packet is shown in FIG. 2. The transmitted random
`access packet ("access request data frame’) or "burst'
`comprises a preamble (10) and a message part (12).
`Typically, the preamble does not include user information
`and is used in the base Station receiver primarily to facilitate
`detection of the presence of the random access burst and
`derive certain timing information (e.g., different transmis
`sion path delays). Note that, as illustrated in FIG. 2, there
`can be an idle period (14) between the preamble and
`message part during which time there is no transmission.
`However, using another technique, as described in the
`above-cited U.S. Provisional Application Serial No. 60/063,
`024 (hereinafter, “the 024 Application”) and illustrated in
`FIG.3, the random access burst does not include a preamble.
`Consequently, in this case, the base Station's random access
`detection and timing estimation has to be based on the
`message part only.
`In order to reduce the risk of collisions between the
`random access bursts of two mobile Stations that have
`Selected the same time slot, the concept of burst "signatures”
`has been introduced. For example, as described in the 501
`Application (see FIG. 4), the preamble of a random access
`burst is modulated with a unique signature pattern. Also, the
`message part is spread with a code associated with the
`Signature pattern used. The Signature pattern is randomly
`Selected from a set of patterns that can be, but are not
`necessarily, orthogonal to each other. Since a collision can
`occur only between mobile Stations bursts that are using the
`Same Signature, the risk of a random acceSS collision is
`reduced in comparison with other existing Schemes. AS Such,
`the use of this unique Signature pattern feature, as described
`and claimed in the 501 Application, provides a significantly
`higher throughput efficiency than prior random access
`Schemes.
`In the 024 Application, a mobile Station transmits a
`Signature on the Q branch within the message part of the
`burst. In preparing for the transmission, the mobile Station
`randomly Selects the Signature from a set of predetermined
`Signatures. Again, Since a collision can occur only between
`mobile Stations bursts that are using the same signature (the
`primary advantage of the novel use of Signatures in general),
`the risk of a random acceSS collision is reduced in compari
`Son with other existing Schemes.
`Notably, although the random access Systems and meth
`ods described in the above-cited Applications have numer
`
`1. Technical Field of the Invention
`The present invention relates in general to the mobile
`telecommunications field and, in particular, to a method for
`processing multiple random acceSS mobile-originated calls.
`2. Description of Related Art
`The next (so-called “third”) generation of mobile com
`munications Systems will be required to provide a broad
`25
`Selection of telecommunications Services including digital
`Voice, Video and data in packet and channel circuit-Switched
`modes. As a result, the number of calls being made is
`expected to increase significantly, which will result in much
`higher traffic density on random access channels (RACHS).
`Unfortunately, this higher traffic density will also result in
`increased collisions and acceSS failures. Consequently, the
`ability to Support faster and more efficient random access is
`a key requirement in the development of the new generation
`of mobile communications Systems. In other words, the new
`generation Systems will have to use much faster and more
`flexible random access procedures, in order to increase their
`access Success rates and reduce their acceSS request proceSS
`ing times.
`A European joint development mobile communications
`system is referred to as the “Code Division Testbed”
`(CODIT). In a CODIT-based Code Division Multiple Access
`(CDMA) system, a mobile station can gain access to a base
`station by first determining that the RACH is available for
`use. Then, the mobile Station transmits a Series of acceSS
`request preambles (e.g., single 1023 chip symbols) with
`increasing power levels, until the base Station detects the
`access request. AS Such, the mobile Station uses a “power
`ramping process that increases the power level of each
`Successive transmitted preamble symbol. AS Soon as an
`access request preamble is detected, the base Station acti
`Vates a closed loop power control circuit, which functions to
`control the mobile station's transmitted power level in order
`to keep the received signal power from the mobile Station at
`a desired level. The mobile station then transmits its specific
`access request data. The base Station's receiver despreads
`and diversity-combines the received signals using, for
`example, a RAKE receiver or Similar type of processing.
`In many mobile communication Systems, a Slotted
`ALOHA (S-ALOHA) random access scheme is used. For
`example, Systems operating in accordance with the IS-95
`standard (ANSI J-STD-008) use an S-ALOHA random
`access Scheme. The main difference between the CODIT and
`IS-95 processes is that the CODIT process does not use an
`S-ALOHA random access Scheme. Also, another difference
`is that the IS-95 mobile station transmits a complete random
`access packet instead of just the preamble. If the base Station
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`3
`ous advantages over prior random access Schemes, a number
`of problems still exist that remain to be solved. For example,
`regardless of the random access method used, a mobile
`Station has to decide just how much random access trans
`mission power to use. Ideally, a mobile Station should Select
`a transmission power level Such that the random access burst
`is received at the base Station with precisely the power
`needed for correct decoding of the random acceSS message.
`However, for numerous reasons, it is virtually impossible to
`ensure that this will be the case.
`For example, the power of the received burst as required
`at the base Station is not constant but can vary (e.g., due to
`variations in the radio channel characteristics and the Speed
`of the mobile Station). AS Such, these variations are to Some
`extent unpredictable and thus unknown to the mobile Sta
`tion. Also, there can be Significant errors in estimating the
`uplink path-loSS. Furthermore, even if a mobile Station can
`determine the “correct' transmission power level to use,
`because of existing hardware limitations, it is impossible to
`Set the actual transmission power level to precisely the
`correct value needed.
`Consequently, for the above-described reasons, there is a
`Significant risk that a random access burst will be received
`at the base station with too much power. This condition
`causes excessive interference for other users and thus
`reduces the capacity of the CDMA system. For the same
`reasons, there is also a risk that a random access burst will
`be transmitted with too little power. This condition makes it
`impossible for the base Station to detect and decode the
`random access burst.
`In order to reduce the risk of transmitting with too much
`power, in the afore-mentioned IS-95 CDMA system, the
`initial random access request is transmitted with an addi
`tional negative power offset (i.e., with a lower power level
`than the required transmit power level expected), as shown
`in FIG. 5. Referring to FIG. 5, the mobile station then
`re-transmits the random access burst with a reduced negative
`power offset, until the base Station acknowledges (ACK) that
`it has correctly decoded the random access message
`("NACK" denotes no acknowledgment message
`transmitted). Typically, the base Station's acknowledgment
`is based on the calculation of a cyclic redundancy check
`(CRC) over the random access message. However, note that
`a new estimate of the required transmission power may or
`may not be calculated for each re-transmission.
`Consequently, it is only the negative offset that is reduced for
`each re-transmission.
`A significant problem that exists with the above-described
`power ramping approaches is that there is an obvious
`trade-off between the time delay incurred due to the mobile
`Station re-transmitting the random access bursts until the
`base Station's acknowledgment message is received, and the
`amount of interference caused by the random access trans
`mission. AS Such, with a larger negative initial power offset,
`on the average, more re-transmissions will be needed before
`the random access burst is received at the base Station with
`sufficient power. On the other hand, with a smaller initial
`negative power offset, there is an increased risk that the
`random access burst will be received at the base station with
`too much power. On the average, this occurrence will cause
`more interference for other users. For reasonably large
`negative power offsets, the delay until the acknowledgment
`of a correctly decoded random access message is transmitted
`can be significant, because the base Station has to receive an
`entire random access burst before it can transmit the
`acknowledgment message. AS described in detail below, the
`present invention Successfully resolves the above-described
`problems.
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`4
`SUMMARY OF THE INVENTION
`In accordance with a preferred embodiment of the present
`invention, a method for processing multiple random access
`requests is provided whereby a base Station transmits an
`acquisition indicator Signal, which indicates that the base
`Station has detected the presence of a random access trans
`mission. For this exemplary embodiment, the acquisition
`indicator is generated based on the amount of energy
`received on the random access channel (e.g., as opposed to
`the correct/incorrect decoding of a random access message).
`Consequently, the delay between the beginning of the ran
`dom access transmission and the beginning of the acquisi
`tion indicator transmission is significantly Shorter than the
`delay to the beginning of an acknowledgment transmission
`based on the reception of a correctly decoded random acceSS
`message. If a mobile Station does not receive a positive
`acquisition indicator, the mobile Station should interrupt the
`present transmission and Start to re-transmit the random
`access burst in the next time slot, while modifying the
`transmission power level accordingly between the Succes
`Sive re-transmissions.
`An important technical advantage of the present invention
`is that significantly faster power ramping can be achieved in
`an S-ALOHA random access System.
`Another important technical advantage of the present
`invention is that with an unchanged initial power offset in an
`S-ALOHA random access Scheme, the random access delay
`can be significantly reduced, which improves the System
`performance.
`Yet another important technical advantage of the present
`invention is that for the Same delay constraints involved, a
`larger initial power offset can be used for one user in an
`S-ALOHA random access system, which reduces the risk of
`excessive interference for other users.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`A more complete understanding of the method and appa
`ratus of the present invention may be had by reference to the
`following detailed description when taken in conjunction
`with the accompanying drawings wherein:
`FIG. 1 is a diagram that illustrates how collisions between
`different users random access bursts can occur in an
`S-ALOHA random access Scheme;
`FIG. 2 is a diagram that illustrates a frame Structure for a
`random access packet in an S-ALOHA random access
`Scheme,
`FIG. 3 is a diagram that illustrates a random access burst
`that does not include a preamble;
`FIG. 4 is a diagram that illustrates a preamble of a random
`access burst modulated with a unique Signature pattern, and
`a message part spread with a code associated with the
`Signature pattern used;
`FIG. 5 is a diagram that illustrates a random access
`transmission with an initial negative power offset;
`FIG. 6 is a block diagram of an exemplary detection
`Section (for one antenna) that can be used in a base stations
`receiver to detect the presence of a random acceSS transmis
`Sion from a mobile Station, in accordance with a preferred
`embodiment of the present invention;
`FIG. 7 is a diagram that illustrates a mobile station
`receiving an acquisition indicator Signal during an idle
`period in a random access burst, in accordance with the
`preferred embodiment of the present invention; and
`FIG. 8 is a diagram that illustrates a mobile station
`receiving an acquisition indicator Signal in a System where
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`S
`a random access burst has been transmitted without a
`preamble, in accordance with the preferred embodiment of
`the present invention.
`DETAILED DESCRIPTION OF THE DRAWINGS
`The preferred embodiment of the present invention and its
`advantages are best understood by referring to FIGS. 1-8 of
`the drawings, like numerals being used for like and corre
`sponding parts of the various drawings.
`Essentially, in accordance with a preferred embodiment of
`the present invention, a method for processing multiple
`random access requests is provided whereby a base Station
`transmits an acquisition indicator Signal, which indicates
`that the base Station has detected the presence of a random
`access transmission. For this exemplary embodiment, the
`acquisition indicator is generated based on the amount of
`energy received (or, possibly, also the interference energy)
`on the random access channel (e.g., as opposed to the
`correct/incorrect decoding of a random access message).
`Consequently, the delay between the beginning of the ran
`dom access transmission and the beginning of the acquisi
`tion indicator transmission is significantly Shorter than the
`delay to the beginning of an acknowledgment Signal trans
`mission based on the reception of a correctly decoded
`random access message. If a mobile Station does not receive
`a positive acquisition indicator, the mobile Station should
`interrupt the present transmission and Start to re-transmit the
`random access burst in the next time slot, while modifying
`the transmission power level accordingly between the Suc
`cessive re-transmissions.
`FIG. 6 is a block diagram of an exemplary detection
`Section (for one antenna) that can be used in a base stations
`(204) receiver to detect the presence of a random access
`transmission from a mobile Station (202), in accordance with
`a preferred embodiment of the present invention. The exem
`plary detection section 200 includes a matched filter 206
`(e.g., used during the preamble period) which is tuned
`(matched) to a preamble's spreading code. For this example,
`the matched filter is used to detect the presence of the
`random access burst, despread the preamble part, and feed
`the despread signal to an appropriate Section of an accumu
`lator 208. Since each received preamble can include a
`unique Signature pattern, the accumulator 208 includes one
`unit tuned to one of the possible signature patterns (1-1) that
`can be received. The output of each accumulator unit
`208(1-1) is coupled to a respective threshold detection unit
`210(1-1). The accumulator unit 208 accumulates the energy
`received over the duration of the preamble.
`During the preamble period, if a threshold detection unit
`210(1-1) detects an input signal that exceeds a predeter
`mined detection threshold, that threshold detection unit
`outputs a signal. This output signal (indicating detection of
`Sufficient energy from a received random access burst) is
`coupled to a respective acquisition indicator generator cir
`cuit 212(1-1), which outputs an acquisition indicator signal
`(A) for transmission by the base station.
`For the case where a burst is transmitted without a
`preamble, the matched filter 206 in FIG. 6 is matched to the
`spreading code used on the control part of the burst (i.e.,
`where a signature is located). However, in this case, the
`accumulation performed by the accumulator 208(1-1)
`occurs for a specified period of time (e.g., just enough time
`to provide a good estimate, whether or not the base Station
`has received a random access burst).
`Notably, the present invention provides a Solution that is
`applicable for those cases where the random access burst
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`6
`both does or does not include a preamble. Specifically, as
`illustrated by the uplink and downlink transmission diagram
`shown in the embodiment of FIG. 7, in those cases where a
`preamble is used, if the idle period in the burst between the
`preamble (P) and message part is Sufficiently large, a mobile
`Station can receive an acquisition indicator (A) transmitted
`by the base station during that idle period. However, in
`accordance with an underlying principle of this exemplary
`embodiment, the mobile station will not transmit the mes
`Sage part (M) of the random access burst until an acquisi
`tion indicator (A) is received (no acquisition indicator
`transmission is denoted by “NA'). Instead of transmitting
`the message part of the burst if no acquisition indicator is
`received (e.g., NA, NA), the mobile station will continue
`to transmit a new preamble (e.g., P., P.) As illustrated by the
`uplink and downlink transmission diagram shown in FIG. 8,
`in those cases where a preamble is not used in a random
`access burst (or, for example, the idle period between the
`preamble and message part is too short in duration), a mobile
`Station will receive the base Station's transmitted acquisition
`indicator (A) during the mobile station's transmission of a
`message part (M) of the burst. However, in accordance with
`the principles of this exemplary embodiment, if no acqui
`Sition indicator is received (e.g., NA, NA) at a predeter
`mined instant of time, the mobile station will interrupt its
`transmission of the message part (M1, M) of the random
`access burst, and re-transmit the random access burst in the
`next time slot until an acquisition indicator (A) is received.
`In a different aspect of the present invention, for those
`cases where signatures are used in the random access
`Scheme, each acquisition indicator transmitted by a base
`Station can indicate reception of a corresponding Signature
`(transmitted from a mobile Station). Alternatively, a plurality
`of Signatures can share one acquisition indicator. In this
`case, the base Station's transmission of the acquisition
`indicator indicates that at least one of the corresponding
`Signatures (transmitted from a mobile Station) has been
`received. In another aspect of the present invention, a mobile
`Station can also select (randomly or non-randomly) a new
`Signature and/or a new RACH for each burst re-transmission
`(until an acquisition indicator is received).
`Abase Station can transmit an acquisition indicator Signal
`on a downlink physical channel. Such a physical channel can
`be dedicated and used only for transmissions of acquisition
`indicator Signals or, for example, the acquisition indicator
`Signals can be time-multiplexed with other signals on one
`physical channel or on a plurality of different physical
`channels. AS Such, a physical channel used for transmission
`of an acquisition indicator Signal can be either orthogonal or
`non-Orthogonal to other downlink physical channels used by
`the mobile communication System.
`In another aspect of the present invention, a base Station
`can transmit an acquisition indicator as a type of “on-off
`Signal. In other words, the base Station transmits the Signal
`only if the base Station has detected a random access burst,
`and does not transmit the Signal if a random access burst has
`not been detected. For example, the base Station can transmit
`acquisition indicator Signals as different orthogonal code
`words for different Signatures. In that case, the base Station's
`transmission of a specific code word would indicate the base
`Station's acquisition of a random access Signal with the
`corresponding Signature. Alternatively, a plurality of Signa
`tures can share one acquisition indicator. In this case, the
`base Station's transmission of the acquisition indicator indi
`cates that at least one of the corresponding Signatures has
`been received.
`Although a preferred embodiment of the method and
`apparatus of the present invention has been illustrated in the
`
`IPR2020-00038
`MM EX1009, Page 6
`
`ERICSSON v. UNILOC
`Ex. 1038 / Page 6 of 8
`
`

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`accompanying Drawings and described in the foregoing
`Detailed Description, it will be understood that the invention
`is not limited to the embodiment disclosed, but is capable of
`numerous rearrangements, modifications and Substitutions
`without departing from the Spirit of the invention as Set forth
`and defined by the following claims.
`What is claimed is:
`1. A method for improving the performance of a random
`access mobile communications System, comprising the Steps
`of:
`a mobile Station transmitting a random acceSS request,
`Said random acceSS request comprising a preamble,
`Said preamble being modulated with a Signature pattern
`randomly Selected from a set of patterns, and
`a base Station detecting a presence of Said random acceSS
`request, generating an indicator Signal indicating Said
`presence of Said random acceSS request, and transmit
`ting Said indicator Signal to the mobile Station prior to
`decoding of the random access request, wherein Said
`indicator Signal is associated with the Selected Signa
`ture.
`2. The method of claim 1, wherein Said transmitting Step
`comprises transmitting Said indicator Signal at a predeter
`mined instant of time.
`3. The method of claim 1, wherein said indicator signal
`comprises an ON portion of an ON-OFF signal.
`4. The method of claim 1, further comprising the steps of:
`if Said mobile Station receives Said indicator Signal, Said
`mobile Station continuing Said transmitting of Said
`random acceSS request, and
`if Said mobile Station does not receive Said indicator
`Signal by a predetermined instant of time, Said mobile
`Station discontinuing Said transmitting of Said random
`acceSS request.
`5. The method of claim 1, wherein said step of detecting
`a presence of Said random access request comprises detect
`ing a power level equal to or exceeding a predetermined
`threshold level.
`6. The method of claim 1, wherein said random access
`mobile communications System comprises a spread Spec
`trum mobile communications System.
`7. The method of claim 1, wherein said random access
`mobile communications System comprises a wideband
`CDMA system.
`8. The method of claim 1, wherein said indicator signal
`comprises an acquisition indicator Signal.
`9. The method of claim 1, wherein said indicator signal is
`transmitted on a physical channel.
`10. The method of claim 4, wherein said step of discon
`tinuing Said transmitting of Said random access request
`further comprises the Step of re-transmitting Said random
`access request in a Subsequent time slot.
`11. The method of claim 10, wherein the step of
`re-transmitting Said random access request includes
`re-transmitting the preamble.
`12. The method of claim 11, wherein the step of
`re-transmitting comprises re-transmitting Said preamble
`with a different spreading code.
`13. The method of claim 11, wherein the step of
`re-transmitting comprises re-transmitting Said preamble
`with a different Signature.
`14. The method of claim 12, further comprising the step
`of Said mobile Station reducing a negative power offset for
`Said random access request prior to Said re-transmitting Step.
`15. The method of claim 9, wherein said physical channel
`is a downlink channel that is orthogonal to other downlink
`physical channels.
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`16. The method of claim 9, wherein said physical channel
`is a downlink physical channel that is non-Orthogonal to
`other downlink physical channels.
`17. The method of claim 1, wherein said indicator signal
`is associated with a unique Signature.
`18. The method of claim 1, wherein said indicator signal
`is associated with a set of unique signatures.
`19. The method of claim 17, wherein said indicator signal
`comprises an Orthogonal code word associated with Said
`unique signature.
`20. The method of claim 17 or 18, wherein said indicator
`signal comprises an ON part of an ON-OFF signal.
`21. A random access communications System, compris
`ing:
`a mobile Station, Said mobile Station including a trans
`mitter for transmitting a random acceSS request, Said
`random acceSS request comprising a preamble, Said
`preamble being modulated with a signature pattern
`randomly Selected from a set of patterns, and
`a base Station coupled to Said mobile Station via an air
`interface, Said base Station configured to detect a pres
`ence of Said random acceSS request, generate an indi
`cator Signal indicating Said presence of Said random
`acceSS request, and transmit Said indicator Signal to the
`mobile Station prior to decoding of the random access
`request, wherein Said indicator Signal is associated with
`the Selected Signature.
`22. The system of claim 21, wherein said means for
`transmitting comprises means for transmitting Said indicator
`Signal at a predetermined instant of time.
`23. The system of claim 21, further comprising:
`Said mobile Station including means for receiving Said
`indicator Signal, and determining if Said mobile Station
`has received said indicator Signal, and if So, Said mobile
`Station continuing Said transmitting of Said random
`access request; and
`if Said mobile Station does not receive said indicator
`Signal by a predetermined instant of time, Said mobile
`Station discontinuing Said