WO2013044970A1 - Canal sur la liaison montante pour des communications sans fil - Google Patents

Canal sur la liaison montante pour des communications sans fil Download PDF

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Publication number
WO2013044970A1
WO2013044970A1 PCT/EP2011/067048 EP2011067048W WO2013044970A1 WO 2013044970 A1 WO2013044970 A1 WO 2013044970A1 EP 2011067048 W EP2011067048 W EP 2011067048W WO 2013044970 A1 WO2013044970 A1 WO 2013044970A1
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Prior art keywords
signatures
signature
wireless communication
station
transmission
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PCT/EP2011/067048
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English (en)
Inventor
Timothy Moulsley
Milos Tesanovic
Matthew Webb
Zhaojun Li
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Fujitsu Limited
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Application filed by Fujitsu Limited filed Critical Fujitsu Limited
Priority to CN201180073406.7A priority Critical patent/CN103797883A/zh
Priority to PCT/EP2011/067048 priority patent/WO2013044970A1/fr
Publication of WO2013044970A1 publication Critical patent/WO2013044970A1/fr

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    • 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
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W74/00—Wireless channel access
    • H04W74/002—Transmission of channel access control information
    • H04W74/004—Transmission of channel access control information in the uplink, i.e. towards network

Definitions

  • the present invention relates to a transmission method in a wireless communication system comprising a base station and subscriber stations for transmitting transmission data to the base station.
  • the present invention further relates to a subscriber station, to a base station and a computer program for use in said method.
  • the present invention relates to uplink communication procedures in accordance with the LTE (Long Term Evolution) and LTE-Advanced radio technology standards as, for example, described in the 3GPP TS36 series specifications, releases 9, 10 and subsequent of the 3GPP specification series.
  • LTE Long Term Evolution
  • LTE-Advanced radio technology standards as, for example, described in the 3GPP TS36 series specifications, releases 9, 10 and subsequent of the 3GPP specification series.
  • the present invention is also applicable to UMTS, WiMAX and other communication systems in which radio resource allocation requests are communicated from a subscriber station (also referred to as "user terminal”, “user equipment” or UE, “mobile terminal” etc.) to a base station.
  • BSs base stations
  • eNodeBs eNodeBs
  • UEs user equipments
  • each BS divides its available frequency and time resources in a given cell, into individual resource allocations for the user equipments which it serves.
  • the user equipments are generally mobile and therefore may move among the cells, prompting a need for handovers of radio communication links between the base stations of adjacent cells.
  • a user equipment may be in range of (i.e. able to detect signals from) several cells at the same time, but in the simplest case it communicates with one "serving" or "primary" cell.
  • a wireless communication system, and the cells within it may be operated in FDD (Frequency Division Duplex) or TDD (Time Division Duplex) mode.
  • Resources in the system have both a frequency dimension, divided in units of subcarriers, and a time dimension having units of a symbol time or "slot" (where a "slot” has typically a duration of seven symbol times), as indicated in Figure 1.
  • the UEs are allocated, by a scheduling function at the eNodeB, a specific number of subcarriers for a predetermined amount of time. Resources are allocated to UEs both for downlink and uplink transmission, although uplink transmission is of most relevance to the invention to be described.
  • the transmitted signal in each slot is described by a resource grid of sub-carriers and available OFDM symbols, as shown in the Figure.
  • Each element in the resource grid is called a resource element (RE) and each resource element corresponds to one symbol.
  • An amount of resource consisting of a set number of subcarriers and OFDM symbols is referred to as a resource block (RB) in LTE, as indicated by the bold outline in Figure 1.
  • SC-FDMA Single-Carrier FDMA
  • SC-FDMA is a linearly precoded OFDMA scheme, involving an additional DFT step before OFDMA processing.
  • Access to the uplink by multiple UEs is enabled by assigning to each UE a distinct set of non-overlapping sub- carriers.
  • 3GPP TS 36.300 providing an overall description of the radio interface protocol architecture used in LTE-based systems and in particular section 5.2 of 3GPP TS 36.300 relating to uplink transmission schemes.
  • 3GPP TS 36.300 providing an overall description of the radio interface protocol architecture used in LTE-based systems and in particular section 5.2 of 3GPP TS 36.300 relating to uplink transmission schemes.
  • several channels for data and control signalling are defined at various levels of abstraction within the system.
  • Figure 2 shows some of the uplink channels defined in LTE at each of a logical level, transport layer level and physical layer level, and the mappings between them.
  • User data and also some signalling data is carried on a Physical Uplink Shared Channel (PUSCH).
  • PUSCH Physical Uplink Shared Channel
  • the control channels include a Physical Uplink Control Channel, PUCCH, used to carry signalling from UEs including channel state information (CSI), as represented for example by channel quality indication (CQI) reports, and scheduling requests.
  • CSI channel state information
  • CQI channel quality indication
  • PRACH Physical Random Access Control Channel
  • PRACH Physical Random Access Control Channel
  • uplink resources are also allocated to reference signals, in particular a Sounding Reference Signal SRS.
  • SRS Sounding Reference Signal
  • the SRS is used by the network to estimate the quality of the uplink to the UE over a wide range of frequencies, not just on those frequencies allocated to the UE. Thus, the SRS is not necessarily transmitted together with any physical channel.
  • RRC radio resource control
  • PDSCH Physical Downlink Control Channel
  • PDCCH Physical Downlink Control Channel
  • the Physical Random Access Channel PRACH is used to carry the Random Access Channel (RACH) for accessing the network if the UE does not have any allocated uplink transmission resource.
  • RACH Random Access Channel
  • SR scheduling request
  • the SR is transmitted on a dedicated resource for this purpose. If no such resources have been allocated to the UE, the RACH procedure is initiated.
  • the transmission of SR is effectively a request for uplink radio resource on the PUSCH for data transmission.
  • RACH is provided to enable UEs to transmit signals in the uplink without having any dedicated resources available, such that more than one terminal can transmit in the same PRACH resources simultaneously.
  • the term "Random Access” is used because (except in the case of contention-free RACH, described below) the identity of the UE (or UEs) using the resources at any given time is not known in advance by the network (incidentally, in this specification the terms “system” and “network” are used interchangeably). So-called “signatures” (see below) are employed by the UEs to allow the eNodeB to distinguish between different sources of transmission.
  • RACH can be used by the UEs in either of contention-based and contention-free modes.
  • contention-based access UEs select any signature at random, at the risk of "collision" at the eNodeB if two or more UEs accidentally select the same signature.
  • Contention-free access avoids collision by the eNodeB informing each UE which signatures may be used.
  • the Physical Random Access Channel PRACH typically operates as follows (for contention based access):-
  • the UE (denoted 10 in the Figure) receives the downlink broadcast channel for the cell of interest (serving cell).
  • the network represented in Figure 3 by an eNodeB 20, indicates cell specific information including the following:
  • the UE selects a PRACH preamble signature according to those available for contention based access and the intended message size.
  • the UE 10 transmits the PRACH preamble (also called "Message 1", indicated by (1) in the Figure) on the uplink of the serving cell.
  • the network (more particularly the eNodeB of the serving cell) receives Message 1 and estimates the transmission timing of the UE.
  • the UE 10 monitors a specified downlink channel for a response from the network (in other words from the eNodeB). In response to the UE's transmission of Message 1 , the UE 10 receives a Random Access Response or RAR ("Message 2" indicated by (2) in Figure 3) from the network. This contains an UL grant for transmission on PUSCH and a Timing Advance (TA) command for the UE to adjust its transmission timing.
  • TA Timing Advance
  • the UE 10 In response to receiving Message 2 from the network, the UE 10 transmits on PUSCH ("Message 3", shown at (3) in the Figure) using the UL grant and TA information contained in Message 2.
  • a contention resolution message may be sent from the network (in this case from eNodeB 20) in the event that the eNodeB 20 received the same preamble signature simultaneously from more than one UE, and more than one of these UEs transmitted Message 3. If the UE does not receive any response from the eNodeB, the UE selects a new signature and sends a new transmission in a RACH sub-frame after a random back-off time.
  • the procedure is similar except that the UE is configured with a dedicated signature.
  • the above “signature” can be considered a generic property (or set of properties), associated with a transmission.
  • the sequence (which determines the waveform) is the most significant property for PRACH preambles.
  • a specific sequence possibly together with other characteristics of the transmission implies a particular signature.
  • the RACH procedure can be triggered in response to a PDCCH order (e.g. for DL data arrival, or positioning). Contention free RACH is only applicable for handover, DL data arrival and positioning.
  • Figure 4 illustrates the format of a PRACH preamble message in LTE.
  • the message here denoted by 30
  • the message (here denoted by 30) consists of a cyclic prefix CP 31 , the preamble sequence 32 itself, and (not illustrated here) a guard interval to allow for differences in arrival timings at the eNodeB.
  • the CP has a duration T C P 33 and the sequence 32 has a duration T S EQ 34. Note that there is no room in the conventional PRACH preamble for additional information such as the UE identity.
  • FIG. 5 outlines how PRACH different preamble signatures 30A - 30D for different UEs are derived by different cyclic shifts from the same base sequence 36.
  • the CP 31 and the guard interval 35 are the same, the PRACH preambles only differing in the amount of shift, as indicated by dashed lines in each of 30A - 30D.
  • PRACH preamble sequences are derived from so-called Zadoff-Chu sequence types. This sequence type has the property that cyclically- shifted versions of the same sequence are orthogonal to each other.
  • Zadoff-Chu sequences are also involved in generating the above Sounding Reference Signals (SRS), which consequently also have signatures.
  • SRS Sounding Reference Signals
  • the UE is provided with a Zadoff-Chu sequence generator 1 1 as illustrated in Figure 6.
  • Transmission of the PRACH preamble involves, as shown in Figure 6, not only generation of the sequence but a discrete Fourier transform (DFT) stage 12 and modulation at a modulation stage 13 onto the SC-FDMA carriers used on the uplink.
  • DFT discrete Fourier transform
  • the PRACH preamble transmitted by a UE, having a certain signature results in a distinctive waveform being received by the eNodeB.
  • the eNodeB makes a decision about which signature(s) the waveform corresponds to, by correlating it with all the possible transmitted signatures. This is illustrated in Figure 7, where band 300 denotes the received signal.
  • band 300 denotes the received signal.
  • the signal is down- converted to baseband and the CP is removed.
  • the resulting signal is processed by a FFT 21 to convert the SC-FDMA symbols from the time to the frequency domain. This allows correlation in the frequency domain in a subcarrier de-mapping stage 22, to extract the RACH preamble sequences (signatures).
  • an inverse FFT back to the time domain is performed at 23.
  • an energy detection stage 24 estimates the power of the received signatures and, by comparing with a predetermined threshold, makes the above-mentioned decision.
  • the signature may be implied by the PRACH preamble sequence as already mentioned, other signals are also capable of being characterised by a signature and of being processed by the eNodeB in a similar way to that shown in Figure 7, including reference signals such as SRS as already noted.
  • the UE Given the PRACH preamble format specified in LTE as shown in Figure 4, the UE can only indicate limited control information with RACH Message 1. If it were possible to convey more information early in the RACH procedure, system performance could be improved. For example, delay could be reduced between initiation of the RACH procedure and start of data transmission with maximum data rate or spectral efficiency.
  • the signatures transmitted by the UEs are designed to be received at the network using correlation techniques as indicated in Figure 7, with typically one correlator per sequence. Directly increasing the information content of a signature by increasing the number of signatures available would impose a significant increase in complexity in the eNodeB. Therefore a different solution is needed.
  • a station performs transmission, the transmission characterised by at least one signature on an uplink to a wireless communication network, the station signifying information to the network by at least two of the following:
  • the station is primarily intended as a subscriber station, but the term “station” could also refer for example to a relay station.
  • the selection of a signature refers to the particular choice of signature.
  • the combination of transmission characteristics may include, for example, the difference between one or more characteristics.
  • the number of signatures transmitted can be one or any number more than one; this includes the case where the station is configured to be able to transmit two linked signatures, but information may be signified by sending only one signature rather than two.
  • the transmission comprises at least two signatures which are linked by at least one of: timing of or time interval between transmission of the signatures; frequency of or frequency separation between the signatures; and code domain or separation in code domain.
  • code domain refers to a set of possible codes (or sequences) which can be used to differentiate between transmissions; for example, a set of spreading codes.
  • Each signature may be associated with a distinct numerical index, the information being at least partly signified by the numerical index or, in the case of two or more signatures, by a numerical combination of (for example, the difference between) two numerical indices.
  • the signatures may differ in at least one of said resources, timing, frequency or code domain, the information may be at least partly signified by this difference.
  • the station may be a subscriber station or relay station.
  • the above- mentioned uplink transmission can be made via any one or more of: a random access channel which may be employed for a contention-based random access procedure of such stations to the network; an uplink control channel; a reference signal; and an uplink shared channel. These are referred to below as a channel or signal of interest.
  • the transmission is via the random access channel and comprises at least two signatures, a first of which is selected for the purpose of the random access procedure and the second of which is selected for signifying said information, either alone or in combination with the first signature.
  • the present invention is not restricted to use of random access channel. Any kind of channel or signal can be utilised for the purposes of the present invention, so long as it is capable of allowing a station to perform transmission to the network with the above- mentioned signatures.
  • Many kinds of information may be signified to the network by use of the present invention.
  • the information may be used to indicate at least one of: antennas visible to the station on at least one downlink ("visible" antennas being those the signals of which are receivable by the station); identity of the station; capability of the station; delay tolerance of the station;
  • channel conditions on a downlink of at least one cell buffer status at the station;
  • the transmission may include a first signature transmitted on a first cell and optionally a second signature transmitted on a second cell.
  • transmission of the second signature indicates channel conditions on a downlink of the secondary cell and/or a preference of the station for communication via the secondary cell.
  • one of the signatures may be randomly selected, as for example in accordance with a known RACH procedure in LTE.
  • the network, to which the method is applied may be an LTE-based network.
  • the transmission includes first and second PRACH signatures where PRACH is a Physical Random Access Channel defined in LTE, the first signature is used to request a random access response RAR in accordance with a RACH procedure defined in LTE, and the second signature is used for the purpose of signifying the information, the signatures corresponding to respective PRACH preamble sequences as defined in LTE.
  • PRACH is a Physical Random Access Channel defined in LTE
  • the first signature is used to request a random access response RAR in accordance with a RACH procedure defined in LTE
  • the second signature is used for the purpose of signifying the information, the signatures corresponding to respective PRACH preamble sequences as defined in LTE.
  • a subscriber station which is a station for use in any of the above-mentioned methods and configured to perform signature selection for signifying said information to the network.
  • the subscriber stations are mobile devices which communicate with the network via a base station, the base stations forming cells.
  • base station equipment for use in any of the above-mentioned methods and configured to extract information from said transmission by recovering the or each signature.
  • a fifth aspect of the present invention there is provided computer-readable instructions which, when executed by a processor of a transceiver device in a wireless communication system, cause the device to provide the subscriber station or the base station as defined above.
  • Such instructions may be stored on one or more computer- readable media.
  • the present invention involves signal transmissions between a station (subscriber station or relay station for example) and a network (wireless communication system).
  • the "station” referred to here may take any form suitable for transmitting and receiving such signals, such as subscriber stations and relay stations.
  • the base stations will typically take the form proposed for implementation in the 3GPP LTE and 3GPP LTE-A groups of standards, and may therefore be described as an eNodeB (eNB) (which term also embraces Home eNodeB or HeNB) as appropriate in different situations.
  • eNB eNodeB
  • some or all base stations may take any other form suitable for transmitting and receiving signals from subscriber stations and relay stations.
  • Figure 1 illustrates a resource block (RB) on the uplink of an LTE wireless communication system
  • FIG. 2 shows relationships between various uplink channels defined in LTE
  • Figure 3 shows a contention-based RACH procedure in LTE
  • Figure 4 shows the format of a PRACH preamble
  • Figure 5 illustrates generation of PRACH preamble signatures at a UE
  • Figure 6 outlines the sequence of processing in a UE for transmitting a PRACH preamble
  • Figure 7 illustrates detection of PRACH preambles at an eNodeB
  • FIG. 8 shows a contention-based RACH procedure modified in accordance with the present invention
  • Figure 9 shows steps in a method embodying the present invention performed by a subscriber station.
  • Figure 10 shows steps in a method embodying the present invention performed by a base station.
  • the wireless communication system (also referred to as the "network") operates using FDD and comprises one or more base stations (also referred to as “eNodeBs” or “eNBs”), each controlling one or more downlink cells, each downlink (DL) cell having a corresponding uplink cell.
  • Each DL cell may serve one or more subscriber stations (also referred to as "UEs”) which may receive and decode signals transmitted in that serving cell.
  • PRACH refers specifically to PRACH as this provides a convenient channel for implementing the present invention; however as already mentioned the present invention is by no means limited to PRACH.
  • PRACH Physical Downlink Control
  • additional control information such as the following would be beneficial: o UE ID (identity) (or shortened version of UE ID)
  • UE capability e.g. capable of transmitting/receiving using MIMO
  • o Buffer status i.e. amount of data ready for transmission by the UE
  • Antenna ports at eNodeB(s) visible to the UE e.g. in case of distributed antennas
  • Use of a modified version of the RACH procedure e.g. without a subsequent TA (Timing Advance) message, where time alignment is already established, or not needed
  • TA Timing Advance
  • Events log or some information derived therefrom
  • Radio link failure e.g. for the case of radio link failure
  • Past history such as indication of interference or other channel conditions observed recently by the UE.
  • the present invention conveys additional information compared with (for example) the known RACH scheme for LTE, by means of two linked signals transmitted by the UE.
  • these signals can comprise two instances of PRACH signatures where the first signature is transmitted according to the current RACH procedure and the second conveys additional information.
  • first does not necessarily mean earlier in time.
  • conveys means that, rather than the second message explicitly containing the information, the choice of second message (possibly in combination with the first message) has a pre-arranged meaning which allows the network to infer some information.
  • the principle is illustrated in Figure 8 for the case of using RACH as an example.
  • Figure 8 can be compared with Figure 3 showing the conventional contention-based RACH access procedure.
  • Initial access to the system by a UE 10 is a carried out using the RACH procedure as already outlined with respect to Figure 3, where the UE transmits a PRACH preamble using one of the available signatures chosen at random. This is indicated at (1) in the Figure.
  • this form of the present invention involves the UE 10 transmitting an additional RACH message to the eNodeB 20.
  • This may be referred to for convenience as a Message V, and is denoted by (1') in the Figure.
  • the remainder of the RACH procedure proceeds in the conventional manner with Message 2, 3 and 4 being transmitted as usual.
  • Figure 8 shows Message V following Message 1 , this is only schematic.
  • the two RACH preambles may be transmitted in any order, or simultaneously.
  • the two signals may be linked by one or more of the following principles:- ⁇ Using the same resources (e.g. in time/frequency/code domains)
  • the time difference between two PRACH messages from the same UE should be exactly an integer number of subframes.
  • the time difference between PRACH messages from different UEs will typically have an additional small offset, (e.g. due to different propagation paths) which can be detected.
  • the different possible waveforms for each of the signals may be considered to be different signatures (e.g. in the case of PRACH, different signatures correspond to different preamble sequences). With 64 different signatures available in the case of PRACH, selection of one signature among the 64 can be considered equivalent to sending up to 6 bits of information.
  • the additional information may be indicated directly by a numerical index corresponding to one of a set of possible signatures transmitted as one of the signals.
  • the information may be indicated by some numerical combination of the indices, for example the difference in indices between the signatures transmitted by each of the two signals, or the sum thereof.
  • the respective indices are denoted by n1 and n2
  • the difference would simply be the arithmetic value n1-n2, and this value would have some pre-arranged meaning.
  • the information may be at least partly conveyed by some combination of (e.g. difference between) the resources used.
  • the network can typically confirm that two signals are transmitted by the same UEs, and therefore intended to be linked, since they will have identical transmission timing and propagation delay and so be received with no significant relative timing difference.
  • the same two signals might happen to transmitted by different UEs. In this case they would be likely to have slightly different transmission timings and propagation delays and so be received with slightly different relative timings.
  • the timing difference can be identified by the network, which would then not consider the signals to be linked. This does not prevent the network from identifying, as linked, first and second signatures having a specific timing difference such as an integer number of subframes.
  • Figures 9 and 10 outline the procedure carried out at each of the UE 10 and eNodeB 20 respectively, in this form of the invention. As already mentioned, the present invention is not restricted to use with PRACH and consequently Figures 9 and 10 illustrate a more generic process than Figure 8.
  • the process begins with the UE receiving notification of the resources to be used for the channel/signal of interest (PRACH for example), in step S1 10.
  • PRACH the resource to be used for the channel/signal of interest
  • the UE listens to a downlink broadcast signal to obtain the transmission timing. It is also informed of the available signatures, frequency bands and time slots for random access.
  • the UE selects a first message to transmit to the network, such as the Message 1 in the modified PRACH procedure of Figure 8. This may involve selection at random from at least one set of predefined messages, such as PRACH signatures.
  • step S130 the UE decides whether it is needed to convey additional information to the network at this stage by use of the present invention. If not (N at S130) the UE simply transmits the first message as indicated at S140, using the resources notified in S1 10.
  • the UE If, on the other hand, the UE wishes (or is required by the network) to indicate additional information, the UE selects a second, linked message such as the Message V described with respect to Figure 8. It then transmits both messages to the network using resources notified in S1 10.
  • the linked messages do not require to be transmitted in any specific order. They may be transmitted in any particular order or simultaneously, but in some cases transmission is made with a defined time delay between the two messages, the amount of the time delay (e.g. , number of subframes) conveying part of the information.
  • the UE monitors a specified downlink channel for some form of response from the network, such as the RAR (Message 2) of Figure 8, as shown at step S170.
  • RAR Message 2 of Figure 8
  • the UE continues the procedure as required, for example (in the case of PRACH) by transmitting Message 3.
  • the procedure on the network side begins at a step S210 with the network notifying subscriber stations of resources to be used for the channel/signal of interest, e.g. PRACH.
  • step S220 the eNodeB waits to receive a message on the channel of interest, or to receive the signal of interest. If no such message is received (S220, N), the eNodeB will periodically (e.g. after every frame) repeat S210.
  • the eNodeB checks at S230 whether a second message, linked to the first in accordance with the present invention, has been received. If the UE has been configured to send the first and second messages with different timings, the eNodeB waits for a suitable time to elapse before checking at S230.
  • the flow proceeds to sending a response as described shortly, but if a linked second message has been received (S230, Y) then the eNodeB uses both messages in step S240 to derive additional information.
  • the eNodeB may associate each signature with a numerical index n1 and n2, and based on a pre-arranged combination of the indices (such as their difference n1 -n2 or sum n1 +n2) infer some information.
  • the eNodeB may detect that the signatures were received an integer number of subframes apart, in which case this integer number will signify some information. The nature of this information is explained with respect to various embodiments below.
  • the eNodeB sends (S250) some response to the UE, for example a RAR sent via PDSCH in the case of the PRACH procedure of Figure 8.
  • the procedure then continues (S260) for example to complete the conventional processing associated with the channel/signal of interest.
  • first and second linked messages are transmitted, this is not essential, and the absence of a second message may in itself be used (so long as the UE is configured to send multiple linked messages in general) as an indication of information to the network.
  • the embodiments described below are based on LTE, where the network operates using FDD and comprises one or more eNodeBs, each controlling one or more downlink cells, each downlink cell having a corresponding uplink cell.
  • Each DL cell may serve one or more terminals (U Es) which may receive and decode signals transmitted in that serving cell.
  • U Es terminals
  • the eNodeB sends control channel messages (PDCCH) to the UEs.
  • PDCCH control channel messages
  • a PDCCH message typically indicates whether the data transmission will be in the uplink (using PUSCH) or downlink (using PDSCH), it also indicates the transmission resources, and other information such as transmission mode, number of antenna ports, data rate, and number of codewords enabled.
  • PDCCH may indicate which reference signals may be used to derive phase reference(s) for demodulation of a DL transmission. Reference signals for different antenna ports, but occupying the same locations, are distinguished by different spreading codes.
  • each UE provides feedback on the DL channel state for one, two or more serving cells to the eNodeB controlling the serving cell(s) for that UE.
  • each U E may be configured to have two or more serving cells at the same carrier frequency is not excluded.
  • two sets of PRACH resources would be defined.
  • Some co-ordination may be involved (e.g. if the cells are controlled by different eNodeBs, they should ideally be made aware of the PRACH resources in the other cell).
  • the antennas supporting the cell being accessed or used by the U E are distributed in the sense that the physical antennas are placed at various different locations within the coverage area of the cell.
  • Each antenna (or more correctly each virtual antenna or antenna port) is associated with one of a small set of reference signals.
  • the U E can identify the reference signals of those antennas with sufficiently strong signals (i.e. low enough path loss) but may not be able to receive reference signals from all the antennas in the cell. Therefore, in order that the network can easily identify which antennas should be used to transmit to the UE, it is desirable that the network can establish from which antennas the U E can best receive signals.
  • PRACH resources are defined and signalled by the network according to LTE Release 8.
  • additional PRACH resources are defined and signalled by the network.
  • the UE transmits a first signature using PRACH in the Release 8 resources (according to Release 8) and a second signature using PRACH in the additional resources.
  • the second signature indicates from which antenna ports the UE is currently receiving reference signals (or could receive - this can be determined by comparison of amplitude of different reference signals).
  • This indication can be done by means of a bit map, where each bit corresponds to an antenna port with sufficient received signal strength.
  • LTE currently supports 64 different signatures (i.e. 6 bits) which would be sufficient to indicate any combination of up to 6 antennas or antenna ports.
  • a more limited set of combinations can be indicated for up to 8 antenna ports (e.g. any one antenna + any two antennas + all eight antennas + a few more combinations ).
  • the network would preferably make at least some subsequent transmissions to the UE using the indicated antennas only.
  • the advantage of this scheme is that it would reduce interference and wasted transmission power by not using antennas for which the transmitted power would not reach the UE.
  • the antennas are grouped together (e.g. provided by a remote radio head (RRH) at each location, each RRH with one or more antennas), and the visibility of each group is indicated by the UE.
  • RRH remote radio head
  • a conventional PRACH preamble message does not contain the identity of the UE.
  • the choice of second signature indicates the UE identity (or a shortened version of the identity, or part of the identity, such as the LSBs of the identity, the result of a hash function applied to the identity, or an additional short identity). If the second signature is carried by LTE PRACH, this choice can convey up to 6 bits of I D information since there are 64 (2 to the power 6) possible signatures. If the second signature is carried by another means (e.g. on PUSCH) more bits can be conveyed.
  • This I D information may allow the network to confirm the UE identity more quickly, for example avoiding the need to repeat configuration information and proceeding to establish high data rate communications with the UE with minimum delay. Note that a suitable UE identity may only be available when the UE has already established a connection with the network.
  • the I D is normally communicated after the PRACH preamble, for example in Message 3 referred to above.
  • the UE capability (indicated by a performance category) can be conveyed by the second signature.
  • the second signature can indicate whether the UE is delay tolerant or not (e.g. with respect to the current application requirements). This would allow the network to prioritize processing RACH requests from different UEs, or prioritize allocation of UL/DL resources.
  • the second signature indicates information about the radio channel conditions.
  • This could be in the form of some or all of the channel state information (CSI) already defined for the LTE downlink, where a CSI report may comprise Rank Indicator (Rl), preferred precoder (PMI) and channel quality (CQI).
  • Rl Rank Indicator
  • PMI preferred precoder
  • CQI channel quality
  • the third embodiment can be combined with the second embodiment to provide the ID in addition to the information about radio channel conditions.
  • the second signature could indicate measured interference conditions at the UE (e.g. mean interference level, or history of interference).
  • the second signature could indicate channel quality for different DL carriers than the one paired with the carrier with the PRACH resources.
  • the pairing here is between an UL carrier and a DL carrier, assuming FDD. In many FDD cases the carriers come in pairs, but there may be exceptions: e.g. in CA, there may be different numbers of UL and DL carriers. This embodiment allows the network to determine quickly whether additional carrier(s) should be activated.
  • the Buffer Status reporting procedure is used to provide the serving eNodeB with information about the amount of data available for transmission in the uplink buffer(s) of the UE.
  • the second signature indicates buffer status at the UE (i.e. the amount of information waiting for uplink transmission).
  • LTE defines a buffer status report (BSR) for transmission by the media access control layer MAC.
  • BSR buffer status report
  • a subset of this information can be provided using the invention. This allows the network to quickly assign suitable resources for UL data transmission.
  • the second signature indicates whether the UE is synchronised with the network or not (e.g. whether the UE has established suitable timing for UL transmissions other than via PRACH).
  • the second signature indicates information relating to a previous radio link failure, such as a statistical metric of error rate observed on the PDSCH and/or PUSCH.
  • the communication between UE and network may simultaneously use more than one cell at different carrier frequencies (i.e. carrier aggregation).
  • carrier aggregation i.e. carrier aggregation
  • the first signature is transmitted on a first or primary cell (Pcell) and the second signature is transmitted on a second or secondary cell (Scell).
  • Pcell primary cell
  • Scell secondary cell
  • the transmission of the second signature on an Scell indicates a preference by the UE for using that cell (e.g. because channel conditions in DL and/or UL are judged to be better)
  • first signature or second signature may be transmitted using any one of the following uplink channels:
  • the "signature” can be considered a generic property (or set of properties), associated with a transmission.
  • the sequence (which determines the waveform) is the most significant property for PRACH preambles.
  • Other properties can also be considered, such as time/frequency of transmission.
  • PUCCH where different signatures would correspond to different PUCCH resources. Up to 36 combinations of 12 cyclic shifts and 3 spreading codes per PUCCH RB (Resource Block) are available.
  • the sounding reference signal provides uplink channel quality information as a basis for scheduling decisions in the base station.
  • the UE sends a sounding reference signal in different parts of the bandwidths where no uplink data transmission is available.
  • the sounding reference signal is transmitted in the last symbol of the subframe. Up to 16 combinations of 2 RPF (repetition factor) and 8 cyclic shifts are available. In addition, different bandwidths and frequency domain positions can be configured.
  • PUSCH where different signatures could correspond to different data contents. To be useful for random access, this variation is preferably limited to small PUSCH resource sizes (e.g. 1 or 2 RBs). Preferably details such as packet size and modulation and coding scheme are pre-configured.
  • the second signature carries all the additional information.
  • the choice of first signature may also be used to indicate additional information (which would reduce the number of signatures among which to make a random selection).
  • the first signature is used by the eNodeB as a "normal" signature, but may have been chosen deliberately by the UE .
  • either or both of the first and second signatures may be configured or randomly selected, for example depending on the requirements of the applications.
  • transmission of the second signature is optional, which means that information can be conveyed according to whether the second signature is transmitted or not.
  • further signatures may be added in order to transmit more information.
  • the above behaviour would be configured by UE-specific RRC signalling, broadcast signalling (to enable the feature) or defined behaviour in the system specification. Not all UEs need be configured to behave in the ways described. As an example, only
  • preconfigured UEs would transmit an indication of the type envisaged. For other UEs the eNodeB would conclude that nothing was transmitted.
  • information may be included in broadcast information, e.g. SIBs, for suitable UEs to make use of, since a capable UE could find itself in a legacy network. Then the assumption above would apply.
  • the invention has been described with reference to LTE FDD, but could also be applied for LTE TDD, and to other communications systems such as UMTS and WiMAX.
  • the various features may be implemented in hardware, or as software modules running on one or more processors. Features of one embodiment may be applied to any of the other embodiments.
  • the invention also provides a computer program or a computer program product for carrying out any of the methods described herein, and a computer readable medium having stored thereon a program for carrying out any of the methods described herein.
  • a computer program embodying the invention may be stored on a computer-readable medium, or it may, for example, be in the form of a signal such as a downloadable data signal provided from an Internet website, or it may be in any other form.
  • embodiments of the present invention allow the random access process in an LTE UE to transmit more useful information earlier in the procedure. This is typically achieved by transmitting two linked signals, for example two simultaneously transmitted PRACH signatures.
  • the additional information (such as UE identity or buffer status) is indicated, in other words inferred by the network, by the choice of the second signal/signature.
  • This allows an LTE network to reach a state of transmitting and/or receiving higher data rates more quickly than the current RACH procedure, thus reducing latency and improving the user experience. This is achieved without requiring significant additional complexity in the network (as would be needed to indicate more information simply by increasing the number of signatures, for example).

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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 a pour objectif de proposer un scénario qui permette à la procédure d'accès aléatoire (par exemple) d'un UE dans un réseau LTE de transmettre plus d'informations utiles plus tôt dans la procédure. Cet objectif peut être atteint en transmettant deux signaux liés, qui peuvent être deux signatures PRACH transmises simultanément. Les informations supplémentaires (telles que l'identité de l'UE ou le statut du tampon) sont indiquées par le choix du second signal/de la seconde signature et/ou par une combinaison de caractéristiques de transmission des signaux liés. Ceci permet à un réseau LTE d'atteindre un état dans lequel il peut transmettre et/ou recevoir des données à des débits plus élevés et plus rapidement qu'avec la procédure RACH actuelle. Par voie de conséquence, ceci permet de réduire le temps d'attente et d'améliorer l'expérience de l'utilisateur. En outre, ce résultat peut être atteint sans ajouter de façon significative à la complexité du réseau.
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US9913237B2 (en) 2012-03-27 2018-03-06 Fujitsu Limited Presence indication in a wireless communication system
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JP6018685B1 (ja) * 2015-07-15 2016-11-02 タタ コンサルタンシー サービシズ リミテッドＴＡＴＡ Ｃｏｎｓｕｌｔａｎｃｙ Ｓｅｒｖｉｃｅｓ Ｌｉｍｉｔｅｄ ロングタームエボリューション通信システムにおける物理ランダムアクセスチャネルのプリアンブルの検出
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US11425720B2 (en) 2017-06-14 2022-08-23 Qualcomm Incorporated System and method for transmitting beam failure recovery request

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