EP2208290A1 - Détection de la collision de préambules d'accès direct - Google Patents

Détection de la collision de préambules d'accès direct

Info

Publication number
EP2208290A1
EP2208290A1 EP08779329A EP08779329A EP2208290A1 EP 2208290 A1 EP2208290 A1 EP 2208290A1 EP 08779329 A EP08779329 A EP 08779329A EP 08779329 A EP08779329 A EP 08779329A EP 2208290 A1 EP2208290 A1 EP 2208290A1
Authority
EP
European Patent Office
Prior art keywords
value
user terminal
timing advance
thresholds
transceiver
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP08779329A
Other languages
German (de)
English (en)
Other versions
EP2208290A4 (fr
Inventor
Tobias Tynderfeldt
Magnus Lindström
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Telefonaktiebolaget LM Ericsson AB
Original Assignee
Telefonaktiebolaget LM Ericsson AB
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Telefonaktiebolaget LM Ericsson AB filed Critical Telefonaktiebolaget LM Ericsson AB
Publication of EP2208290A1 publication Critical patent/EP2208290A1/fr
Publication of EP2208290A4 publication Critical patent/EP2208290A4/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W74/00—Wireless channel access
    • H04W74/08—Non-scheduled access, e.g. ALOHA
    • H04W74/0833—Random access procedures, e.g. with 4-step access
    • H04W74/0841—Random access procedures, e.g. with 4-step access with collision treatment
    • H04W74/0858—Random access procedures, e.g. with 4-step access with collision treatment collision detection
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W56/00—Synchronisation arrangements
    • H04W56/004—Synchronisation arrangements compensating for timing error of reception due to propagation delay
    • H04W56/0045—Synchronisation arrangements compensating for timing error of reception due to propagation delay compensating for timing error by altering transmission time

Definitions

  • the present invention discloses a method and a device for use in a user terminal in a cellular communications system.
  • the downlink transmissions i.e. transmission to the users in a cell
  • OFDM modulation Orthogonal Frequency Division Multiplex
  • the uplink transmissions i.e. transmission from the users in a cell
  • OFDM or OFDM-like technologies such as DFTS-OFDM
  • Transmissions to and from users in a cell are made to/from a controlling node of the cell, this node in LTE being known as the eNodeB, "evolved NodeB".
  • eNodeB evolved NodeB
  • Users in an LTE system are sometimes referred to as UEs, "User Equipment”.
  • transmissions from the UEs in a cell need to be time aligned when they arrive at the eNodeB, i.e. the transmissions from the UEs in the cell of the eNodeB need to arrive more or less simultaneously at the eNodeB.
  • the UEs in a cell may be located at different distances from the eNodeB of the cell, the UEs need to initiate their transmissions at different points in time in order for their transmissions to arrive simultaneously at the eNodeB. For example, a UE which is at the cell edge needs to start its transmissions prior to a UE which is closer to the eNodeB.
  • the issue of when to start the transmissions in the different UEs in a cell can be handled by means of a so called “timing advance", in other words an "offset" value in time at which a UE needs to start its transmissions relative to a nominal transmission time specified by the eNodeB.
  • the value of the timing advance for a UE can be determined by the eNodeB by means of measuring the arrival of uplink transmissions from the UE, and the eNodeB then transmits the timing advance value to the UE with regular updates, since the UE may move around in the cell.
  • the timing advance needed by the UE becomes uncertain, for example due to possible movement away from the eNodeB of the UE.
  • a timer in both the eNodeB and the UE which determines when a UE falls "out of synchronization" in uplink.
  • Random Access a procedure which is used in a number of cases, such as, for example:
  • Random Access procedures defined for LTE systems is a so called contention based procedure, which can be described briefly as follows: The UE starts the Random Access procedure by randomly selecting one of the preambles available for contention-based random access, and then transmits the selected random access preamble on the physical random access channel, PRACH, to the eNodeB.
  • PRACH physical random access channel
  • the eNodeB acknowledges reception of the preamble by transmitting a response message, which includes a timing advance value update to be used in future transmissions from the UE. Following this, the eNodeB transmits a second message which is in part used to trigger the establishment of radio resource control, and in part to uniquely identify the UE.
  • the eNodeB will resolve the conflict by transmitting a so called contention resolution message, which informs the UEs of which one of them has "won" the contention based procedure, and may thus communicate with the eNodeB.
  • the eNodeB is likely to arrive at an inaccurate channel estimate, particularly if the signals from the different UEs are approximately of equal strength. With an inaccurate channel estimate, the likelihood of correctly decoding the second message from the different UEs will decrease significantly, which in turn can lead to a situation in which all of the UEs involved need to restart the random access procedure with a new preamble.
  • the solution should reduce the risk of more than one UE continuing the contention based procedure after the eNodeB has transmitted the response message to the request for communication from the UEs.
  • Such a solution is offered by the present invention in that it discloses a method for use in a user terminal in a cellular communications system.
  • the user terminal applies a timing advance to its transmissions to a controlling node, and the user terminal may request communication with the controlling node by means of a special message, in response to which the terminal receives a response message which includes an updated value for the timing advance.
  • the user terminal compares the updated value for the timing advance with the value of the timing advance that the user terminal had prior to the reception of said response message. If the difference between the prior value and the updated value is greater than a first predetermined threshold or is below a second predetermined threshold, the user terminal ignores the response message and renews its request for communication.
  • the problem of multiple UEs responding to the contention response message from the eNodeB can be significantly reduced.
  • the first and the second thresholds have the same absolute value, but with different signs, so that the second threshold corresponds to the first threshold, but has a negative value.
  • the thresholds are provided to the user terminal by the controlling node in question, and in one version of this embodiment, it is provided in a system information message.
  • the thresholds are provided in a broadcast message from the controlling node.
  • the thresholds are used by all user terminals in the system, i.e. the value is a system standard value.
  • the user terminal renews its request for communication a certain predefined number of times, and if the difference between the prior value and the updated value exceeds the first threshold or falls below the second threshold during these requests, the user terminal will discard the prior value and use the updated value.
  • the invention also discloses a user terminal for use in system in which the invention is applied.
  • Fig 1 shows a schematic view of a system in which the invention may be applied
  • Figs 2 and 3 show prior art in order to illustrate a problem
  • Fig 4 shows a flow chart of a principle of the invention
  • Fig 5 shows a generalized flow chart of a method of the invention
  • Fig 6 shows a block diagram of a transceiver of the invention.
  • Fig 1 shows an overview of a system 100 in which the invention can be applied.
  • the system 100 comprises a number of cells, one of which is shown as 110 in fig 1.
  • Each cell can hold a number of users, two of which are shown in fig 1 as 120 and 130.
  • the generic term for users in an LTE system is "UE", User Equipment, a term which will also be used here, and which is used in fig 1.
  • an eNodeB 140, which controls the traffic to and from the users in the cell.
  • Traffic from the UEs to the eNodeB is known as uplink traffic, UL traffic, and traffic in the other direction is known as downlink traffic, DL traffic.
  • the UEs receive instructions from the eNodeB regarding when to make their UL transmissions, but as can be realized from fig 1, the arrival of a UL transmission at the eNodeB will depend on the distance between the eNodeB and the UE in question. For example, simultaneously made transmissions from the UEs 120 and 130 will arrive at the eNodeB 140 at different points in time, with the UL transmissions from the UE 120 arriving before those of the
  • the LTE system employs a principle known as "timing advance" of UL transmissions; the UEs are informed by the eNodeB of a “timing advance” or an “offset” which should be applied to timing instructions for UL transmissions.
  • the timing advance for an UE is determined by the eNodeB of the cell by measurements on UL transmissions received from the UE at the eNodeB.
  • timing advance is illustrated in fig 2, by means of three time lines: the top time line shows a nominal window for reception of UL transmissions from the UEs in the cell 110 at the eNodeB 140.
  • the nominal window extends between ti and X 2 .
  • the middle time line shows the timing advance for the UE 120: since the UE 120 is at a certain distance from the eNodeB, the UE 120 needs to make its transmissions between t'i and t' 2 in order for those transmissions to arrive at the eNodeB between ti and t 2 .
  • This can also be viewed as displacing the UL transmission window of UE 120 by an offset in time, shown as ⁇ i in fig 2.
  • the bottom time line in fig 2 shows the timing advance for the UE 130: since the UE 130 is quite remote from the eNodeB, the UE 130 needs to make its transmissions between t"i and t" 2 in order for those transmissions to arrive at the eNodeB between U and t 2 . This can also be viewed as displacing the UL transmission window of UE 130 by an offset in time, shown ⁇ 2 in fig 2.
  • the invention is mainly intended for the contention based Random Access (RA) procedure of E-UTRAN/LTE, which is a procedure that the UEs use in order to request/initiate communication with the eNodeB in the case that the UEs do not already have a dedicated UL resource.
  • RA contention based Random Access
  • the RA procedure is illustrated schematically in fig 3, with the messages, "MSG", being numbered as follows:
  • MSG 1 A random access preamble transmitted by a UE to the eNodeB.
  • MSG 2 A random access response from the eNodeB, including a response to detected preambles, with a timing advance update, based on a measurement of message 1.
  • MSG 3 A scheduled transmission from the UE, based on the instructions in message 2.
  • MSG 4 A contention resolution message from the eNodeB, which is transmitted in order to identify the "winning" UE. This message is always transmitted, since the eNodeB is unable to determine if more than one UE has transmitted the random access message (MSG 1) at the same time with one and the same preamble.
  • MSG 1 random access message
  • MSG 3 A problem of the RA procedure is the following: more than one UE in a cell can transmit MSG 1 at the same time, and with the same preamble. In such a case, all of those UEs will perceive MSG 2 as being addressed to them, and will thus transmit MSG 3 to the eNodeB.
  • the eNodeB will receive a plurality of MSG 3 transmissions, all of which will use the same so called UL demodulation reference signal, since the information about that signal was comprised in MSG2.
  • the eNodeB uses MSG 3 for UL channel estimates, and the fact that it may receive a plurality of MSG 3 transmissions with the same UL demodulation reference signal can lead to a poor UL channel estimate. Poor UL channel estimates may, in turn, lead to a need for all of the contending UEs to restart the RA procedure, with other preambles.
  • the invention is intended to address the problem of multiple contending UEs which reply to MSG 2 by transmitting MSG 3.
  • One thought behind the invention is that a contending UE will compare the timing advance instruction comprised in MSG 2 with the timing advance which the UE had prior to the reception of MSG 2. If the difference is too large, it can be concluded that the MSG 2 was intended for another UE in the cell, since the timing advance instruction, also referred to as the timing alignment command, which is comprised in MSG 2 is based on measurements in the eNodeB on MSG 1 , so that an overly large discrepancy between the two time advance values increases the likelihood that the value in the MSG 2 is intended for another UE.
  • Fig 4 shows a flow chart 400 of these basic steps of the invention: as shown in step 410, the UE will receive a response MSG, i.e. MSG 2, from the eNodeB, in response to an RA initiation message, i.e. MSG 1 of fig 3.
  • Step 420 shows that the UE determines the difference between the timing advance value it had prior to the reception of the response message, MSG 2, and the timing advance value comprised in MSG 2.
  • the difference, " ⁇ " is compared to a first threshold, "T1" and a second threshold T2; if the difference " ⁇ " is below the first threshold and greater than the second threshold, the UE proceeds with the RA procedure, i.e. it transmits MSG 3, step 440. Conversely, if the difference equals or exceeds the first threshold T1, or falls below the second threshold T2, the UE "restarts" the RA procedure by randomly selecting and transmitting a new RA preamble, step 450.
  • the thresholds, "TT and "T2" of the flow chart 400 can be defined by the system standard or communicated from the eNodeB to the UE. In the latter case, the thresholds could either be set by the system operator or be defined as an eNodeB internal parameter by the eNodeB vendor. Alternatively, they can be set adaptively, to fit the current system environment, i.e. the average number of UEs in the cells etc.
  • T1 and T2 could in an LTE-system typically be in the range of 1-5 ⁇ s, since 1 ⁇ s in round trip propagation delay corresponds to 150 m.
  • this is merely an example; many other values could also be used within the scope of the invention, depending on system parameters such as, for example, the typical cell size and the number of users in the system or in the cells.
  • the manner in which the thresholds are provided to the UEs in a cell can also be varied within the scope of the present invention. In one embodiment of the invention, the thresholds are provided to the UEs by their eNodeB.
  • the thresholds T are provided by the eNodeB in a system information message, such as for example a handover command message prior to handover to a new cell (110).
  • the thresholds could be either mandatory parameters, in which case the eNodeB needs to explicitly signal the value, or the thresholds could be optional parameters, in which case default values would be applied by UEs unless a value is explicitly signalled.
  • a system information message in which the thresholds "T1", “T2" are comprised can in one version of the invention be a broadcast message from an eNodeB to "its" UEs.
  • T1 and T2 are values which are specified in the system standard, so that it they are used by all of the user terminals in the system.
  • the values of T1 and T2 could be signalled indirectly from the NodeB to the UEs; the values of T1 and T2 could for example be defined by the magnitude of the so called cyclic prefix, which defines the maximum timing offset that can be tolerated in the uplink transmissions.
  • the UEs it is possible for the UEs to apply a validity timer, a so called time alignment timer, to the timing advance value which the UE has. If the timer expires before the UE received an updated value, the UE will consider the timing advance value it has to be invalid, and will consider itself to be "out of synch" with the eNodeB. In an embodiment where such a timer is used, the comparison between the timing advance values will only be carried out by a UE which has a valid timing advance value upon starting the RA procedure; if the UE has an invalid timing advance value when starting the RA procedure, the UE will accept the value comprised in MSG 2, and will proceed with the rest of the RA procedure.
  • a validity timer a so called time alignment timer
  • a UE will discard the "old" timing advance value if the difference between the new and the old value, i.e. " ⁇ ", exceeds the first threshold value T1 or falls below the second threshold T2 a predefined number of random access attempts, either consecutively or within a certain amount of time.
  • This embodiment is mainly aimed at resolving the situation where the old timing offset is inaccurate and the timing advance value from the random access response is valid, although the timer has not expired.
  • the first, T1 and the second, T2 thresholds have the same absolute value, but with different signs, so that the second threshold T2 corresponds to the first threshold T1 , but has a negative value.
  • T1 and T2 this is a design parameter, and will also depend on the specific system and the operator of the system, but an example of a suitable range of values is ⁇ 5 ⁇ s.
  • Fig 5 shows a schematic flow chart 500 of a generalized method of the invention. Steps which are options or alternatives are indicated with dashed lines in fig 5.
  • the inventive method 500 is intended for use in a user terminal in a cellular communications system, and according to the method, the user terminal applies a timing advance to its transmissions to a controlling node.
  • the user terminal may request, step 510, communication with the controlling node by means of a special message, in 0
  • a response message which includes an updated value for the timing advance.
  • the term "updated” is also used here in the sense that if a UE does not have a valid timing advance value, for example if the UE has fallen out of synch, or if the UE has its first contact with the eNodeB, the value which is received is referred to as an "updated" value.
  • the user terminal compares, step 520, the updated value for the timing advance with the value of the timing advance that the user terminal had prior to the reception of said response message, and if the difference, " ⁇ ", between the prior value and the updated value exceeds a certain first predetermined threshold or of it falls below a certain predefined second threshold T2, the user terminal ignores, step 525, the response message and renews its request for communication.
  • Step 530 shows that in one embodiment of the method 500, the thresholds T1 and T2 are provided to the user terminal by the controlling node in question.
  • the thresholds are provided in a system information message.
  • the thresholds may also be provided in a broadcast message from the controlling node in question.
  • the thresholds are used by all user terminals in the system, i.e. the value is a system standard value, suitably specified by the system standard, e.g. the E- UTRAN/LTE standard.
  • Step 546 shows that in one embodiment of the method 500, the user terminal renews its request for communication a certain predefined number of times, and if the difference between the prior value and the updated value exceeds the first threshold or falls below the second threshold during said number of times, the user terminal will discard the prior value and use the updated value.
  • the user terminal applies a timer to the timing advance value, so that the value is only valid for the duration of the timer, and the user terminal only makes the comparison between the timing advance values if the prior timing advance value is valid when the updated value is received, so that the updated value is accepted otherwise.
  • Fig 6 shows a schematic block diagram of a transceiver 600 for use as a user terminal, a UE which functions according to the invention.
  • the transceiver 600 will comprise an antenna, shown as block 610, and will also comprise a receive part 620 and a transmit part 630.
  • the transceiver 600 also comprises a control means 640 such as a micro processor, as well as a memory 650.
  • the control means 640 and the memory 650 will cooperate in order to apply a timing advance to transmissions from the transceiver 600 to a controlling node, and the control means 640 together with the transmit part 630 and the antenna 610 will be used in order to request communication with the controlling node by means of a special message.
  • the antenna 610, the receive part 620 and the control means 640 will be used in order to receive a response message to said special message, with the response message including an updated value for the timing advance.
  • the control means 640 and the memory 650 will be used in order to compare the updated value for the timing advance with the value of the timing advance that the transceiver had prior to the reception of said response message. If the difference, ⁇ , between the prior value and the updated value is greater than a first predetermined threshold, T1 , or below a second predetermined threshold, T2, the antenna 610, the transmit part 630, the memory 650 and the control means 640 will be used in order to ignore the response message, and for renewing the request for communication.
  • transceiver will use the antenna 610 and the receive part 620 in order to receive the first and second thresholds, T1 , T2, from the controlling node in question.
  • the antenna and the receiver can also be used to receive the thresholds, T1 , 12, in a system information message, or, alternatively, for receiving the thresholds, T1 , T2, in a broadcast message from the controlling node in question.
  • the transceiver 600 uses system values as the values of the thresholds, T1 , T2, in which case the threshold values may be stored in the memory 650 and accessed by the control means 640.
  • the following components may be used in order to renew the request for communication a certain predefined number of times, as well as for discarding the prior value and using the updated value if the difference between the prior value and the updated value exceeds the first threshold, T1, or falls below the second threshold, T2, during said number of times: the control means 640, the memory 650, the transmit part 630 and the antenna 610.
  • the memory 650 and the control means 640 may be used in order to apply a timer to the timing advance value so that the value is only valid for the duration of the timer, and in order to make the comparison if the prior timing advance value is valid when the updated value is received, so that the updated value is accepted otherwise.

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Mobile Radio Communication Systems (AREA)

Abstract

La présente invention concerne un procédé (500) destiné à un terminal utilisateur (12, 130) présent dans un système cellulaire (100). Le terminal utilisateur (120, 130) applique (505) une avance de synchronisation aux transmissions destinées à un noeud de commande (140). Le terminal utilisateur (120, 130) demande (510) à communiquer avec le noeud de commande (140) au moyen d'un message spécial (MSG1) en réponse auquel le terminal utilisateur (120, 130) reçoit (515) un message (MSG2) qui comprend une valeur actualisée pour l'avance de synchronisation. Le terminal utilisateur (120, 130) compare (520) la valeur actualisée à la valeur de l'avance de synchronisation que le terminal utilisateur avait avant la réception dudit message de réponse. Si la différence (Δ) entre la valeur antérieure et la valeur actualisée est supérieure à un premier seuil prédéterminé (T1) ou inférieure à un second seuil prédéterminé (T2), le terminal utilisateur (120, 130) ignore (525) le message de réponse (MG 2) et renouvelle sa demande de communication.
EP08779329.5A 2007-11-05 2008-06-02 Détection de la collision de préambules d'accès direct Withdrawn EP2208290A4 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US98533507P 2007-11-05 2007-11-05
PCT/SE2008/050647 WO2009061255A1 (fr) 2007-11-05 2008-06-02 Détection de la collision de préambules d'accès direct

Publications (2)

Publication Number Publication Date
EP2208290A1 true EP2208290A1 (fr) 2010-07-21
EP2208290A4 EP2208290A4 (fr) 2013-12-04

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EP08779329.5A Withdrawn EP2208290A4 (fr) 2007-11-05 2008-06-02 Détection de la collision de préambules d'accès direct

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JP (1) JP5091328B2 (fr)
WO (1) WO2009061255A1 (fr)

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JP2013021496A (ja) * 2011-07-11 2013-01-31 Fujitsu Ltd 移動局、及び送信制御方法
JP5770566B2 (ja) * 2011-08-24 2015-08-26 株式会社Ｎｔｔドコモ 基地局及び送信タイミング調整方法
WO2013051991A1 (fr) * 2011-10-07 2013-04-11 Telefonaktiebolaget L M Ericsson (Publ) Procédé de synchronisation de liaison montante et équipement utilisateur
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JP2011503959A (ja) 2011-01-27
JP5091328B2 (ja) 2012-12-05
WO2009061255A1 (fr) 2009-05-14
EP2208290A4 (fr) 2013-12-04

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