WO2008097142A1 - Procédé d'amélioration de l'accès aléatoire dans un système d'accès sans fil cellulaire - Google Patents
Procédé d'amélioration de l'accès aléatoire dans un système d'accès sans fil cellulaire Download PDFInfo
- Publication number
- WO2008097142A1 WO2008097142A1 PCT/SE2007/050060 SE2007050060W WO2008097142A1 WO 2008097142 A1 WO2008097142 A1 WO 2008097142A1 SE 2007050060 W SE2007050060 W SE 2007050060W WO 2008097142 A1 WO2008097142 A1 WO 2008097142A1
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- Prior art keywords
- rbs
- base station
- random access
- transmissions
- interval
- Prior art date
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- 238000000034 method Methods 0.000 title claims abstract description 23
- 230000001413 cellular effect Effects 0.000 title claims abstract description 12
- 230000005540 biological transmission Effects 0.000 claims abstract description 79
- 230000000977 initiatory effect Effects 0.000 claims abstract description 7
- 230000007704 transition Effects 0.000 claims description 21
- 238000001514 detection method Methods 0.000 description 14
- 208000037918 transfusion-transmitted disease Diseases 0.000 description 9
- 230000001934 delay Effects 0.000 description 4
- 238000010586 diagram Methods 0.000 description 4
- 230000000694 effects Effects 0.000 description 3
- 235000019580 granularity Nutrition 0.000 description 3
- 125000004122 cyclic group Chemical group 0.000 description 2
- 230000003111 delayed effect Effects 0.000 description 2
- 230000030279 gene silencing Effects 0.000 description 2
- 239000013256 coordination polymer Substances 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 230000007774 longterm Effects 0.000 description 1
- 230000011664 signaling Effects 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W74/00—Wireless channel access
- H04W74/002—Transmission of channel access control information
- H04W74/006—Transmission of channel access control information in the downlink, i.e. towards the terminal
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W74/00—Wireless channel access
- H04W74/08—Non-scheduled access, e.g. ALOHA
- H04W74/0866—Non-scheduled access, e.g. ALOHA using a dedicated channel for access
-
- 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
Definitions
- a method for improved random access in a cellular wireless access system is provided.
- the present invention discloses a method for use in a cellular wireless access system in which there is at least one base station which controls the traffic to and from a cell in the system.
- the cell can accommodate a number of user terminals, and the user terminals can be scheduled for receiving traffic from the base station during a first time interval, the down link interval, and for transmitting traffic to the base station during a second time interval, the up link interval.
- the system there is a first guard period between the transition from the up link interval to the down link interval, and a second guard period between the transition from the down link interval to the up link interval, and the system also comprises a random access channel for unscheduled transmissions from the user terminal to the base station.
- TDD Time Division Duplex
- guard periods In TDD operation, pauses in the form of silent periods, so called “guard periods”, need to be inserted at the transition from downlink to uplink periods due to propagation delays and also to allow the user terminals to switch from re- ception to transmission and vice versa for the base stations.
- it is intended to create these guard periods by removing or silencing a number of down link symbols at the part of the downlink periods which immediately ad- join the uplink period. In this way, a guard time at the transition from downlink to uplink will be created.
- a guard time is also needed at the transition from uplink to downlink in order to allow the base stations to switch from reception to transmission, and to allow the user terminals to switch from transmission to reception. Since terminals have their transmission timing controlled, this second guard period may be created by advancing the terminal transmission time relative to a nominal starting time.
- the magnitude of the guard times mentioned need to take into account a number of factors, such as the cell range or size and terminal and base station switch times, as well as possible network synchronization inaccuracies.
- the transmissions of random access bursts are typically carried out in an unsynchronized fashion, i.e. the random access bursts transmitted by different user terminals are not time aligned when they arrive at the base station.
- the main reason for this is that, for an initial access to the base station, a user terminal may not know the round trip propagation delay towards the base station, which in turn means that it cannot compensate for the propagation delay when determining when to start to transmit the random access burst. Instead, the user terminal typically determines this based on the timing of the down link signals. This means that random access bursts from user terminals with a large propagation delay arrive later than random access bursts from user terminals with a short propagation delay.
- the random access detection window in the base station is sufficiently large to handle the maximum expected roundtrip propagation delay.
- the size of the random access detection window should match the length of the random access bursts transmitted by the user terminals plus the maximum expected roundtrip propagation delay in the cell.
- the "additional" time in the random access detection window, corresponding to the roundtrip propagation delay, may be viewed as a guard period for random access bursts.
- the guard period at the transition from down link to up link may be increased by adding more idle symbols at the end of the down link period, the cell range may still be limited by the guard period of the random access burst.
- the cell mentioned is able to accommodate at least a number of user terminals, and in the system a user terminal can be scheduled for receiving traffic from the base station during a down link interval, and a user terminal can be scheduled for transmitting traffic to its base station during an up link interval, with a first guard period between the transition from the up link interval to the down link interval, and a second guard period between the transition from the down link interval to the up link interval.
- the base station determines and transmits information to user terminals in the cell of the base station which allows the user terminals to calculate an offset time for initiating random access transmissions relative to a nominal starting time for random access transmissions.
- the offset time is also used by the base station to initiate reception of said random access transmissions.
- said information is transmitted explicitly, i.e. the base station transmits a time interval to the user terminals in the cell, with the interval being the offset from the nominal starting time for random access transmissions.
- said information is transmitted from the base station as information relative to an amount of idle, i.e. "silent", symbols which are comprised in the down link and/or the up link transmissions.
- silent an amount of idle
- the user terminals calculate the offset.
- the invention also makes it possible to effectively, in terms of overhead, support variable cell ranges for TDD with a rather fine resolution or granular- ity.
- the invention also comprises a radio base station and a user terminal for use in a system which functions as explained above.
- Fig 1 shows a system in which the invention may be applied
- Fig 2 shows a random access structure in a known system
- Fig 3 shows a problem which may be addressed by the invention
- Fig 4 shows examples of solutions according to the invention
- Fig 5 shows a flowchart of some steps of the invention
- Fig 6 shows a block diagram of a base station of the invention
- Fig 7 shows a block diagram of a user terminal of the invention.
- Fig 1 schematically shows a system 100 in which the invention may be applied.
- the system 100 is a cellular wireless access system, and as such comprises a number of cells, one of which is shown in fig 1 with the reference number 110.
- the cell 110 comprises at least one radio base station, an RBS, shown as 120 in fig 1.
- the RBS 120 serves, inter alia, to control the traffic to and from users in the cell 110.
- the cell 110 can accommodate at least one user termi- nal, with two user terminals being shown in fig 1 , with the reference numbers 130 and 140.
- the system 100 is shown as a cellular telephony system, and the invention will be described with reference to such a system, but it should be pointed out that this is by way of example only, the invention may be applied to a number of different wireless access systems.
- the terminology used when describing the invention with reference to the system 100 is merely intended to facilitate the reader's understanding of the invention, and is not intended to restrict the scope of protection sought by this application.
- the term base station or radio base station, RBS should be interpreted as meaning a node in the system with the function of an RBS.
- a function essentially corresponding to that of the RBS is performed by a node called Node B.
- Such systems are naturally also encompassed by the invention.
- the term user terminal or UE is merely an example intended to facilitate the reader's understanding of the invention.
- the terms UT, User Terminal, or MS, Mobile Station are used. Naturally, such systems are also encompassed by the scope of the present invention.
- the UEs 130, 140 are shown as cellular telephones in fig 1 , it should be realized that this is merely to facilitate the understanding of the invention, the UEs may be many other kinds of devices, portable or stationary, such as, for example, computers.
- the system 100 for which the invention is intended is one in which communication to the UEs 130, 140, from the RBS 120 can be scheduled to take place during a first interval in time, usually referred to as the down link interval.
- DL and the traffic from the UEs 130, 140, to the RBS 110 can be sched- uled to take place during a second interval in time, the up link interval, UL.
- a scheduler in the RBS 120 controls when the different UEs in the cell will transmit and receive data.
- the time unit that the scheduler works with will in the following be referred to as Transmission Time Interval, TTI.
- TTI Transmission Time Interval
- the invention is especially suitable for a so called TDD system, "Time Division Duplex", in which the UL and the DL transmit on the same frequency but are divided in time.
- the invention can also be applied to FDD systems, Frequency Division Duplex.
- guard periods In the system 100, there are silent or idle periods, so called 'guard periods" inserted at the transitions from down link to up link, as well as at the transitions from up link to down link. These guard periods are inserted in order to account for a number of factors, as will be explained in the following.
- guard periods need to be inserted between downlink and uplink periods due to propagation delays between the RBS and the UEs, and also to allow the UEs and the RBS to switch from receive to transmit and vice versa.
- guard periods While maintaining a high degree of commonality with FDD systems is by silencing or in effect "removing" a number of DL symbols at the end of the DL period, i.e. DL symbols which immediately precede the uplink period. In that way, a guard time T D u at the transi- tion from downlink to uplink is created. These "removed" symbols are also called idle symbols.
- a guard time TUD is needed at the transition from uplink to downlink to allow the RBS to switch from reception to transmission and to allow the UE to switch from transmission to reception.
- the guard period TUD may be created by advancing the terminal transmission time, i.e. by moving it forward in time relative to a nominal starting time for the UL, which is done within the "slack" created by idle DL symbols.
- the sum of both guard periods, T D u and TUD matches the time of the idle DL symbols.
- the guard period between downlink and uplink, T D u should be chosen taking into account the maximum expected roundtrip propagation delay from the RBS to a cell edge UE 1 in addition to which there should also be time allocated to allow cell edge terminals to switch from reception to transmission.
- the length of the guard period may be varied and made greater in a larger cell. This can be done by increasing the number of silent or "idle" DL symbols.
- the system 100 also comprises a so called random access channel, i.e. a channel where the UEs may initiate unscheduled transmissions to the RBS.
- the random access detection window in the RBS is intended to comprise a guard period which is sufficiently large to cover the uncertainty in arrival time of random access bursts at the RBS. This guard period should therefore cover the maximum roundtrip propagation de- lay for a cell of a certain size.
- the same random access burst is expected to be used both in FDD and TDD systems, and the burst is depicted in fig 2.
- the RACH (random access channel) burst comprises a Cyclic Prefix, CP, and the pre- amble as such.
- the difference in length between the random access detection window (T C P + TPRE) in the RBS and the random access bursts transmitted by UEs is also shown in fig 2 as a random access guard period TGT- It should be pointed out that the random access burst could contain some information instead of / in addition to the preamble.
- guard periods TDU and TU D these may be increased by, inter alia, adding more idle DL symbols.
- TUD is intended to be created by using a time offset for the scheduled UL signals. Since this time offset will not be known by UEs transmitting RACH bursts, the actual random access detection window will be reduced by TUD. i.e., the time required to switch from UL reception to DL transmission in the RBS. Thus, the cell range may become limited by the random access detection window.
- the random access burst format is typically designed so that the random access window in the RBS conforms to the TTI length of the other (i.e. scheduled) UL and DL channels.
- the random access detection window in the RBS should be 1 ms.
- the random access detection window will be 1 ms - TUD-
- a further option, which has been considered, is to not schedule users in the UL TTI immediately following the RACH, and to thereby increase the random access guard period by one TTI.
- this method would provide a very coarse granularity in the random access window size.
- Another problem with the RACH burst in a TDD system is that in a multi-cell network, there may be RBS-RBS interference due to transmissions from distant base stations that are still "on the air" at the DL to UL transition, and also due to transmissions from nearby base stations that have started to transmit too early due to synchronization errors at the UL to DL switch. This may significantly interfere with parts of the random access detection window, effectively making initial access e.g. at handover degrade.
- This is depicted in fig 3, which shows an UL period flanked by two DL periods, and also shows the interference RBS-RBS / in an RBS of the system as a function of time
- the problem of varying the transmission timing of the RACH burst according to cell size will be addressed by letting the RBS determine and transmit information to user terminals in the cell of the base station which allows the user terminals to calculate an offset time for initiating random access transmissions, i.e. the RACH "bursts".
- the offset is relative to a nominal starting time for random access transmissions, and will allow the UEs to adjust their RACH transmission timing so that the RACH burst, in particular the random access preamble, is received at the RBS within the actual detection "window" used at the RBS for the RACH.
- This window is also ex- tended by the same offset. It should be noted that it would in principle be possible to set the window size so that the cyclic prefix is not included.
- the information about time offset for the RACH transmitted from the RBS to the UEs in the cell can be sent in a number of different ways.
- One such way is to transmit the offset explicitly, i.e. that the RBS transmits a time interval to the UEs in the cell, said interval being the offset. This could e.g. be done as an exact time offset, or as an index in a predefined look up table. In the case that a look up table is used, this look up table will be known by the UE.
- the RBS can transmit the information as being relative to the amount of idle symbols which are comprised in the down link transmissions.
- some of the effects as well as the purpose of the timing advance offset TT A is illustrated.
- varying cell ranges may be supported by letting the random access detection window (RACH slot) in the RBS increase and by shifting it in time to start earlier at the UEs as well.
- Fig 4 shows some versions of the timing advance offset, with the offset being shown as T A .
- Three examples are shown in fig 4:
- RACH transmissions relative to which the offset is employed to advance the RACH transmission.
- TTA TUD-
- the RACH transmission from the UE has been advanced in time by an offset corresponding to the guard period TUD-
- the RBS has also extended the window for RACH transmissions by
- TTA TUD + TDU-
- the RACH transmission from the UE has been advanced in time by an offset corresponding to both of the guard period T UD and T D u-
- the RBS has also extended the window for
- a negative TTA could either be combined with a shorter random access burst, so that the RACH burst doesn't interfere with the TTI which would follow the RACH window, or with no scheduled data in one or more TTI immediately following the RACH.
- the random access detection window would thus be allowed to extend into the un- scheduled TTI, which could be useful if there is significant interference at the beginning of the scheduled UL transmission period.
- the offset can be transmitted to the UEs as, for example, the number of si- lent or idle DL symbols which constitute the total sum of T D u + T U D, and the UEs will then calculate how much earlier the RACH transmissions should start, based on a standardized rule which is programmed in the UEs, for example when the system is set up, or when the UE is manufactured.
- the offset TTA can be calculated by RBS as, or based on, the guard period, TUD between the UL and the DL.
- TTA can be determined by the RBS based on cell range or size, which will tell the RBS how much timing advance is necessary for the RACH, since the propagation delay can be calculated from this.
- T T A can be determined by the RBS based on the interference in the cell, suitably the interference in the up link period.
- the interference in the UL is measured by measuring means in the RBS or calculated in the RBS based upon such parameters as BER, BLER, signal throughput, received power etc.
- the interference level will allow the RBS to calculate how much the RACH transmissions need to be "moved in time" to avoid interference.
- T DU and/or the number of idle DL symbols (which determines TDU+TUD) based on the T TA value selected by the RBS. This would be done if it is determined that the system needs a T TA value that is close to the total number of DL idle symbols, or perhaps even larger than this number, in which case it might be desirable to increase the number of DL idle symbols.
- the scheduled UEs transmitting in UL will be delayed by Tis - TUD, where Tis corresponds to the time of the idle symbols.
- the RACH time offset should be advanced by TTA - Tis from the nominal starting point.
- the scheduled UEs transmitting in UL will be delayed by T
- step 510 the base station determines the offset time TT A , i.e. information which will allow the UEs in the cell to calculate an offset time for initiating the RACH bursts.
- the offset can be either negative or positive.
- the time TT A can be determined in a number of ways, e.g. based on the first guard period, TU D , or based on the cell range or size, as an alternative to which it can be based on the interference in the cell, suitably but not necessarily the interference in the up link period.
- the information regarding the time TJA is transmitted to the UEs in the cell, either explicitly, step 530, as a time interval, or "implicitly", step 540.
- “Implicitly” here means that the information about the time TJA is transmitted as information relative (540) to an amount of idle symbols which are comprised in the down link transmissions.
- Step 550 shows that regardless of how the time T T A is transmitted to the UEs, the RBS uses the time TJA to intitate reception of the random access transmissions from the UEs in the cell.
- Fig 6 shows a schematic block diagram of an RBS 600 according to the in- vention.
- the RBS 600 comprises scheduling means 610, which serve to schedule a user terminal for receiving traffic from the RBS 600 during the down link interval and for scheduling a user terminal to transmit traffic to the RBS 600 during the up link interval.
- the scheduling means 610 of the RBS 600 also serve to schedule the guard period, TUD. between the transition from the up link interval to the down link interval and the guard period, TDU > between the transition from the down link interval to the up link interval,
- the RBS 600 comprises means 620 for determining and means 630 for transmitting to the UEs in the cell the information which allows the user terminals to calculate the offset time TTA-
- the offset time T ⁇ A is used by reception means 640 in the RBS 600 to initiate reception of the RACH bursts.
- a block diagram of some of the components of a user terminal, UE, 700 are shown.
- the UE 700 comprises means 710 for being scheduled by an RBS for the DL 1 the UL and the guard periods T D u and TUD-
- the UE 700 comprises means 720 for receiving informa- tion from an RBS which allows calculating means 730 in the UE 700 to calculate the time offset TJA-
- the information regarding the idle symbols by means of which the offset time is created are comprised in the down link transmissions.
- they may also be comprised in the up link transmissions.
- the idle symbols are comprised in the down link transmissions, they are inserted at the end of the down link transmission period, and if they are comprised in the up link transmissions, they are suitably inserted at the start of the up link period.
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- Computer Networks & Wireless Communication (AREA)
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- Mobile Radio Communication Systems (AREA)
Abstract
Procédé destiné à être utilisé dans un système sans fil cellulaire (100) ayant une station de base (120) qui contrôle le trafic vers et depuis une cellule (110) et un certain nombre de terminaux utilisateur (130) qui peuvent recevoir le trafic provenant de la station de base pendant un intervalle de liaison descendante et transmettre le trafic à la station de base pendant un intervalle de liaison montante. Il existe des périodes de réserve entre les intervalles de liaison montante et de liaison descendante, et entre les intervalles de liaison descendante et de liaison montante. Le système comprend un canal d'accès aléatoire destiné aux transmissions non planifiées par le terminal utilisateur, et le procédé comprend le fait de laisser la station de base déterminer et transmettre des informations aux terminaux utilisateur afin de calculer un moment de décalage de façon à déclencher des transmissions d'accès aléatoire par rapport à un moment de démarrage nominal pour les transmissions d'accès aléatoire, ledit moment de décalage étant également utilisé par la station de base afin de déclencher (530) la réception desdites transmissions d'accès aléatoire.
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Application Number | Priority Date | Filing Date | Title |
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PCT/SE2007/050060 WO2008097142A1 (fr) | 2007-02-05 | 2007-02-05 | Procédé d'amélioration de l'accès aléatoire dans un système d'accès sans fil cellulaire |
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PCT/SE2007/050060 WO2008097142A1 (fr) | 2007-02-05 | 2007-02-05 | Procédé d'amélioration de l'accès aléatoire dans un système d'accès sans fil cellulaire |
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WO2008097142A1 true WO2008097142A1 (fr) | 2008-08-14 |
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PCT/SE2007/050060 WO2008097142A1 (fr) | 2007-02-05 | 2007-02-05 | Procédé d'amélioration de l'accès aléatoire dans un système d'accès sans fil cellulaire |
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Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO2018001471A1 (fr) * | 2016-06-29 | 2018-01-04 | Huawei Technologies Co., Ltd. | Transmission de messages par l'intermédiaire d'un système d'accès aléatoire |
EP3328134A1 (fr) * | 2016-11-28 | 2018-05-30 | Sequans Communications S.A. | Extension de plage de cellules lte |
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WO2001011907A1 (fr) * | 1999-08-11 | 2001-02-15 | Ericsson Inc | Augmentation de la portee d'une station de base au moyen de structures de trames amont decalees, et appareil et procedes a cet effet |
US6388997B1 (en) * | 1995-06-05 | 2002-05-14 | Xircom Wireless, Inc. | Timing adjustment control for efficient time division duplex communication |
US20030169722A1 (en) * | 2000-09-29 | 2003-09-11 | Paul Petrus | Frame structure for radio communications system |
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2007
- 2007-02-05 WO PCT/SE2007/050060 patent/WO2008097142A1/fr active Application Filing
Patent Citations (4)
Publication number | Priority date | Publication date | Assignee | Title |
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US6388997B1 (en) * | 1995-06-05 | 2002-05-14 | Xircom Wireless, Inc. | Timing adjustment control for efficient time division duplex communication |
CA2190539A1 (fr) * | 1995-12-15 | 1997-06-16 | Seppo Alanara | Terminal mobile et systeme utilisant un format d'intervalle de temps abrege de longueur variable pour voie de retour a commande numerique |
WO2001011907A1 (fr) * | 1999-08-11 | 2001-02-15 | Ericsson Inc | Augmentation de la portee d'une station de base au moyen de structures de trames amont decalees, et appareil et procedes a cet effet |
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Cited By (4)
Publication number | Priority date | Publication date | Assignee | Title |
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WO2018001471A1 (fr) * | 2016-06-29 | 2018-01-04 | Huawei Technologies Co., Ltd. | Transmission de messages par l'intermédiaire d'un système d'accès aléatoire |
US10764930B2 (en) | 2016-06-29 | 2020-09-01 | Huawei Technologies Co., Ltd. | Message transmission through a random access scheme |
EP3328134A1 (fr) * | 2016-11-28 | 2018-05-30 | Sequans Communications S.A. | Extension de plage de cellules lte |
US10531416B2 (en) | 2016-11-28 | 2020-01-07 | Sequans Communications S.A. | Range extension of LTE cells |
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