WO2017097582A1

WO2017097582A1 - Random access enhancement for unlicensed access

Info

Publication number: WO2017097582A1
Application number: PCT/EP2016/078421
Authority: WO
Inventors: Esa Mikael Malkamaki; Juha Sakari Korhonen; Frank Frederiksen
Original assignee: Nokia Solutions And Networks Oy
Priority date: 2015-12-09
Filing date: 2016-11-22
Publication date: 2017-06-15

Abstract

Various communication systems may benefit from enhancements relating to additional ways of accessing communication. For example, unlicensed access or license-assisted access may benefit from a random access enhancement. For example, a method can include sending, by a device, a preamble or a message to an access node. The method can also include listening, by the device, for a response to the preamble or the message during a first response window segment of a multi segment response window. The method can further include continuing to listen in a second response window segment of the multi-segment response window only if the listening during the first window segment does not detect any transmission by the access node.

Description

TITLE:

RANDOM ACCESS ENHANCEMENT FOR UNLICENSED ACCESS

BACKGROUND:

Field:

[0001] Various communication systems may benefit from enhancements relating to additional ways of accessing communication. For example, unlicensed access or license-assisted access may benefit from a random access enhancement.

Description of the Related Art:

[0002] Release 13 (Rel-13) long term evolution (LTE) Licensed Assisted Access (LAA) provides licensed-assisted access to unlicensed spectrum while coexisting with other technologies and fulfilling the regulatory requirements. In Rel-13 LAA, unlicensed spectrum is utilized to improve LTE downlink (DL) throughput. In such a system, one or more LAA DL secondary cell (SCell) may be configured to a user equipment (UE) as part of DL carrier aggregation (CA) configuration, while the primary cell (PCell) needs to be on licensed spectrum.

[0003] LAA may be extended towards standalone LTE operation on unlicensed spectrum. LTE standalone operation on unlicensed spectrum means that the evolved Node B (eNB)/UE air interface relies solely on unlicensed spectrum without any anchor carrier on licensed spectrum.

[0004] All steps of random access procedure on unlicensed carrier are conventionally subject to Listen-Before-Talk (LBT). UE first sends random access preamble in the uplink (UL) and waits for Random Access Response (RAR) in downlink within the so-called RA response window. The RA response window can function as a time-out mechanism to allow the UE to assume that the eNB did not receive the random access preamble in case there is no response from the eNB within the window. Since the transmission of RAR by eNB is subject to LBT, the reception of RAR within a short RA response window cannot be guaranteed even in the situation that eNB has received the preamble. Therefore, longer RA response window sizes may be used. For example, a RA response window size of 20 ms may be considered. Even longer response windows may be considered at some point.

[0005] The UE may not be allowed to send a new random access preamble during the RA response window. Thus, a long response window may result in an overall delay of the RA procedure in case eNB has not received the RA preamble at all, and thus is not attempting to send RAR. If the RA response window size is increased from, 10 ms to 20 ms, the time required for power ramping is doubled. Power ramping means that RA preamble power is increased every time for the transmission of a new preamble if RAR is not received within RA response window.

[0006] Figure 1 illustrates preamble transmissions in legacy random access. As shown in Figure 1, a new preamble cannot be transmitted during the RA response window. Thus, if the RA response window is increased due to LBT, then preamble retransmissions and preamble power ramping is delayed.

SUMMARY:

[0007] According to certain embodiments, a method can include sending, by a device, a preamble or a message to an access node. The method can also include listening, by the device, for a response to the preamble or the message during a first response window segment of a multi segment response window. The method can further include continuing to listen in a second response window segment of the multi-segment response window only if the listening during the first window segment does not detect any transmission by the access node.

[0008] An apparatus, in certain embodiments, can include at least one processor and at least one memory including computer program code. The at least one memory and the computer program code can be configured to, with the at least one processor, cause the apparatus at least to send a preamble or a message to an access node. The at least one memory and the computer program code can also be configured to, with the at least one processor, cause the apparatus at least to listen for a response to the preamble or the message during a first response window segment of a multi segment response window. The at least one memory and the computer program code can further be configured to, with the at least one processor, cause the apparatus at least to continue to listen in a second response window segment of the multi-segment response window only if the listening during the first window segment does not detect any transmission by the access node.

[0009] An apparatus, according to certain embodiments, can include means for sending a preamble or a message to an access node. The apparatus can also include means for listening for a response to the preamble or the message during a first response window segment of a multi segment response window. The apparatus can further include means for continuing to listen in a second response window segment of the multi- segment response window only if the listening during the first window segment does not detect any transmission by the access node.

[0010] A computer program product, in certain embodiments, can encode instructions for performing a process. The process can include sending, by a device, a preamble or a message to an access node. The process can also include listening, by the device, for a response to the preamble or the message during a first response window segment of a multi segment response window. The process can further include continuing to listen in a second response window segment of the multi-segment response window only if the listening during the first window segment does not detect any transmission by the access node.

[0011] In certain embodiments, a non-transitory computer-readable medium can be encoded with instructions that, when executed in hardware, perform a process. The process can include sending, by a device, a preamble or a message to an access node. The process can also include listening, by the device, for a response to the preamble or the message during a first response window segment of a multi segment response window. The process can further include continuing to listen in a second response window segment of the multi- segment response window only if the listening during the first window segment does not detect any transmission by the access node.

BRIEF DESCRIPTION OF THE DRAWINGS:

[0012] For proper understanding of the invention, reference should be made to the accompanying drawings, wherein:

[0013] Figure 1 illustrates preamble transmissions in legacy random access.

[0014] Figure 2 illustrates preamble transmission according to certain embodiments.

[0015] Figure 3 further illustrates preamble transmission according to certain embodiments.

[0016] Figure 4 illustrates a method according to certain embodiments.

[0017] Figure 5 illustrates a further method according to certain embodiments.

[0018] Figure 6 illustrates a system according to certain embodiments.

DETAILED DESCRIPTION:

[0019] In an LTE standalone deployment on unlicensed spectrum, there may need to be support of random access procedures within the unlicensed spectrum. In conventional LTE LAA, by contrast, this functionality is mainly supported through the licensed spectrum.

[0020] Certain embodiments permit a longer or extended random access (RA) response window. For example, certain embodiments divide an extended RA response window into two parts.

[0021] Figure 2 illustrates preamble transmission according to certain embodiments. As shown in Figure 2, during a first part of the RA response window the user equipment (UE) or other device may try to detect/decode RA response (RAR) as well as detect whether the eNB transmitted anything. If eNB transmission is detected, for example, PSS/SSS or CRS, but no RAR for the transmitted preamble is received, then the UE can assume that eNB has not received the preamble. In this case the UE can transmit a new preamble after the first part of RA response window. The preamble may be transmitted with higher power, power ramped up by one step, in order to improve the probability of preamble detection.

[0022] Figure 3 further illustrates preamble transmission according to certain embodiments. As shown in Figure 3, when no eNB transmission is detected in the first part of the RA response window, UE may assume that eNB transmission has been forbidden by LBT procedure, and then the UE can wait and try to receive RAR during the second part of RA response window. In such a case, the UE may send a new preamble only after the second part of RA Response window has expired.

[0023] It should be noted that instead of having one response window with two (or multiple) parts/segments there could also be two separate response windows. The first response window would correspond to the first segment and the second response window could correspond to the second segment. Alternatively, the second response window could cover both segments. For instance, if the first segment is assumed to be 10 ms and second segment also 10 ms, then in the alternative embodiment the first response window could be 10 ms and the second 20 ms (assuming that in this case both windows start at the same time). The response windows could be implemented, e.g., by timers. In the latter embodiment, both timers (10 ms and 20 ms) would be started at the same time whereas in the earlier implementation, first timer would be started first and the second when the first expires (without detecting any transmission from the eNB).

[0024] One advantage or benefit of certain embodiments is that the initial power ramping phase can avoid being unnecessarily extended. The UE can also avoid starting a new preamble transmission too early if the eNB has received the preamble but is not able to send RAR due to LBT failure. Too early transmissions would unnecessarily load the random access channel.

[0025] There may be various modifications of the principled outlined above. For example, if eNB transmission has not been detected in the second part of the RA response window, it may mean that LBT has prevented eNB from responding. In this case preamble power increase for retransmission could be forbidden always or depending on configuration.

[0026] The following provides some pseudo-code in terms of actions happening on the UE side:

[0027] If (RA preamble transmitted)

[0028] If ( (eNB_tx detected during the first part of RA Response window- (e.g.) either through detection of PSS/SSS or CRS) AND (RA response with corresponding preamble index not detected - no correct RA- RNTI detected on PDCCH OR correct RA-RNTI detected on PDCCH but no correct preamble index decoded inside RAR message)

[0029] Assume that RA preamble has been lost and transmit new preamble with increased tx power according to parameters

[0030] Else

[0031] Assume that RA preamble was received and do no transmission until (whole) response window has expired

[0032] Endif

[0033] Endif

[0034] Figure 4 illustrates a method according to certain embodiments. More particularly, Figure 4 shows a flow diagram with details in addition to those previously discussed.

[0035] As shown in Figure 4, at 401, an initial preamble power can be set. Then, at 403, the preamble can be transmitted. At 405, the user equipment (UE) can detect whether there as transmission by an evolved node B (eNB_TX) during a first part of a response window. If so, at 407, the UE can determine whether an RA response with corresponding preamble index (index of the preamble sent at 403) was received in the first part of the response window. If not, then at 409 the UE can update a preamble count. Then, at 411 the UE can determine whether a maximum number of preamble transmissions has been reached. If so, then at 413, the attempt at random access can end in failure. Otherwise, if the maximum number of random access attempts has not been reached, the UE can increase preamble transmission power settings at 415, and again transmit the preamble at 403.

[0036] If, at 407, an RA response with corresponding preamble index is received in the first part of the response window, then the UE can enter the second phase of an RA procedure at 417. The additional portions of the RA procedure are not discussed herein in detail for simplicity sake. Nevertheless, similar procedures to those typically used for random access, including e.g. contention resolution, may be used in accordance with certain embodiments, after an appropriate RA response has been received from an eNB or other access node. UE may, e.g., send Msg3 including e.g., UE id and then wait for Msg4 which repeats the UE id to confirm that the contention resolution was successful.

[0037] If, at 405, there is no detection of eNB_TX during the first part of the response window, then at 419 there can be detection of whether there is any eNB_TX in a second part of the response window. If so, then at 421 there can be detection of whether an RA response with the corresponding preamble index was received in the second part of the response window. If not, the method can continue at 409 by updating a preamble count. If so, the method can enter the second phase of the RA procedure at 423.

[0038] If there is no detection of eNB_TX in neither the first part of the response window nor the second part of the response window, then at 425 the UE may optionally update a preamble count. The UE can then, at 427, determine whether a maximum number of preamble transmissions has been reached. This count and maximum can be the same or different from those at 409 and 411. If the maximum has been reached, then the random access attempt can end in failure at 429. If the maximum has not been reached, at 431 the UE can optionally increase transmission power settings and then transmit the preamble again at 403. Whether UE updates the preamble count at 425 and preamble power at 431 may depend on UE specific or network broadcasted parameters or the cause or the priority of the random access.

[0039] According to a more general implementation of the same principles, a long RA response window can be divided in N sections such that after transmitting RA preamble, the UE may be allowed to retransmit a preamble if the UE detects eNB_TX in a section but does not receive RA response in the section. Retransmission may be allowed after the end of the h section if no RAR has been received before that. If the RA response window is divided into multiple segments, then the rule could also be such UE should first listen to N segments. UE is allowed to transmit a new preamble if no eNB transmission is detected during the last N-x segments. Thus a eNB transmission during the first x segment(s) but not after that may indicate that eNB transmission was stopped due to LBT after x segments and therefore, UE should still wait, e.g., y segments before transmitting a new preamble. Also if UE has not detected any transmissions from the eNB during the first N-z segments but detects transmission during the last z segments, UE could still wait some segments since the eNB may not yet have had time to send the response. These examples could be especially valid if x or z is small, e.g., 1. Alternatively, the UE could be allowed to send a new preamble if the UE has detected eNB transmission but no response for the preamble during M segments.

[0040] In addition to detecting own eNB transmission, the UE could also detect whether there is any transmission on the carrier. If there is no transmission, for example RSSI below a configurable or predetermined threshold, then the UE can assume that LBT is most likely not the reason for eNB silence and can send a new preamble with increased transmission power already after the first part of the RA response window.

[0041] Alternatively, instead of simply waiting until the end of the second part of RA Response window, when not receiving a response to its preamble, UE could send a new preamble in any case after the first part of RA Response window but without increasing the tx power if no eNB transmission was detected. With this alternative, there would be no need to extend the RA Response window.

[0042] The same principles discussed above may be applied to a contention resolution window/timer which is started when UE sends Msg3. If a valid Msg4 is not received during the first part of the contention resolution window/timer although eNB transmission is detected, the UE may assume that the UE has lost the contention and may continue the RA procedure by returning to preamble transmission. If no eNB transmission is detected during the first part of the contention resolution window/timer, the UE can assume that eNB has not been able to transmit the Msg4 due to LBT and the UE can wait the second part of the contention resolution window/timer before continuing the RA procedure by returning to preamble transmission.

[0043] Certain embodiments may, therefore, advantageously avoid unnecessarily extending an initial power ramping phase. Furthermore, the UE can avoid starting a new preamble transmission too early if the eNB has received the preamble but is not able to send RAR due to LBT failure.

[0044] Figure 5 illustrates a further method according to certain embodiments. As shown in Figure 5, a method can include, at 510, sending, by a device, a preamble to an access node. The preamble can be configured to initiate a random access. Alternatively, the preamble may be any first message of a contention-based random access procedure. The device sending the preamble can be a user equipment. The access node can be any kind of access node, such as an access point, base station, eNB, or the like.

[0045] The method can also include, at 520, listening, by the device, during a first response window segment of a multi-segment response window. In certain embodiments, as described above, the window may be a two segment window. Alternatively, three or more segments may be employed, depending on a desired granularity of flexibility for the user equipment.

[0046] When the listening detects transmissions by the access node and does not detect a response to the preamble, the method can include, at 530, transmitting, by the device, a higher power preamble.

[0047] Alternatively, when the listening does not detect any transmissions by the access node, the method can include, at 535, continuing to listen without transmitting in a second response window segment of the multi- segment response window.

[0048] The method can additionally include, after listening a predetermined plurality of response window segments without detecting transmissions by the access node, transmitting a higher power preamble at 540.

[0049] The method can also or alternatively include, after listening a predetermined plurality of response window segments without detecting transmissions by the access node, transmitting a same power preamble at 542.

[0050] The method can also or alternatively include, after listening a predetermined plurality of response window segments without detecting any transmissions on a carrier on which the preamble was sent, transmitting a higher power preamble at 544.

[0051] The predetermined plurality of response window segments can be two or more response window segments in each of the cases described at 540, 542, and 544. In certain cases, when used in combination, the predetermined number of segments may be lower for 544 (silence on carrier) as compared with 542 or 544 (silence from access node).

[0052] Figure 6 illustrates a system according to certain embodiments of the invention. It should be understood that each block of the flowchart of Figures 4 and 5 may be implemented by various means or their combinations, such as hardware, software, firmware, one or more processors and/or circuitry. In one embodiment, a system may include several devices, such as, for example, network element 610 and user equipment (UE) or user device 620. The system may include more than one UE 620 and more than one network element 610, although only one of each is shown for the purposes of illustration. A network element can be an access point, a base station, an eNode B (eNB), or any other network element, such as a PCell base station or a SCell base station.

[0053] Each of these devices may include at least one processor or control unit or module, respectively indicated as 614 and 624. At least one memory may be provided in each device, and indicated as 615 and 625, respectively. The memory may include computer program instructions or computer code contained therein, for example for carrying out the embodiments described above. One or more transceiver 616 and 626 may be provided, and each device may also include an antenna, respectively illustrated as 617 and 627. Although only one antenna each is shown, many antennas and multiple antenna elements may be provided to each of the devices. Other configurations of these devices, for example, may be provided. For example, network element 610 and UE 620 may be additionally configured for wired communication, in addition to wireless communication, and in such a case antennas 617 and 627 may illustrate any form of communication hardware, without being limited to merely an antenna.

[0054] Transceivers 616 and 626 may each, independently, be a transmitter, a receiver, or both a transmitter and a receiver, or a unit or device that may be configured both for transmission and reception. The transmitter and/or receiver (as far as radio parts are concerned) may also be implemented as a remote radio head which is not located in the device itself, but in a mast, for example. It should also be appreciated that according to the "liquid" or flexible radio concept, the operations and functionalities may be performed in different entities, such as nodes, hosts or servers, in a flexible manner. In other words, division of labor may vary case by case. One possible use is to make a network element to deliver local content. One or more functionalities may also be implemented as a virtual application that is provided as software that can run on a server. [0055] A user device or user equipment 620 may be a mobile station (MS) such as a mobile phone or smart phone or multimedia device, a computer, such as a tablet, provided with wireless communication capabilities, personal data or digital assistant (PDA) provided with wireless communication capabilities, portable media player, digital camera, pocket video camera, navigation unit provided with wireless communication capabilities or any combinations thereof. The user device or user equipment 620 may be a sensor or smart meter, or other device that may usually be configured for a single location.

[0056] In an exemplifying embodiment, an apparatus, such as a node or user device, may include means for carrying out embodiments described above in relation to Figures 2 through 5.

[0057] Processors 614 and 624 may be embodied by any computational or data processing device, such as a central processing unit (CPU), digital signal processor (DSP), application specific integrated circuit (ASIC), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), digitally enhanced circuits, or comparable device or a combination thereof. The processors may be implemented as a single controller, or a plurality of controllers or processors. Additionally, the processors may be implemented as a pool of processors in a local configuration, in a cloud configuration, or in a combination thereof.

[0058] For firmware or software, the implementation may include modules or unit of at least one chip set (e.g., procedures, functions, and so on). Memories 615 and 625 may independently be any suitable storage device, such as a non-transitory computer-readable medium. A hard disk drive (HDD), random access memory (RAM), flash memory, or other suitable memory may be used. The memories may be combined on a single integrated circuit as the processor, or may be separate therefrom. Furthermore, the computer program instructions may be stored in the memory and which may be processed by the processors can be any suitable form of computer program code, for example, a compiled or interpreted computer program written in any suitable programming language. The memory or data storage entity is typically internal but may also be external or a combination thereof, such as in the case when additional memory capacity is obtained from a service provider. The memory may be fixed or removable.

[0059] The memory and the computer program instructions may be configured, with the processor for the particular device, to cause a hardware apparatus such as network element 610 and/or UE 620, to perform any of the processes described above (see, for example, Figures 4 and 5). Therefore, in certain embodiments, a non-transitory computer-readable medium may be encoded with computer instructions or one or more computer program (such as added or updated software routine, applet or macro) that, when executed in hardware, may perform a process such as one of the processes described herein. Computer programs may be coded by a programming language, which may be a high-level programming language, such as objective-C, C, C++, C#, Java, etc., or a low-level programming language, such as a machine language, or assembler. Alternatively, certain embodiments of the invention may be performed entirely in hardware.

[0060] Furthermore, although Figure 6 illustrates a system including a network element 610 and a UE 620, embodiments of the invention may be applicable to other configurations, and configurations involving additional elements, as illustrated and discussed herein. For example, multiple user equipment devices and multiple network elements may be present, or other nodes providing similar functionality, such as nodes that combine the functionality of a user equipment and an access point, such as a relay node.

[0061] One having ordinary skill in the art will readily understand that the invention as discussed above may be practiced with steps in a different order, and/or with hardware elements in configurations which are different than those which are disclosed. Therefore, although the invention has been described based upon these preferred embodiments, it would be apparent to those of skill in the art that certain modifications, variations, and alternative constructions would be apparent, while remaining within the spirit and scope of the invention.

Claims

WE CLAIM:

1. A method, comprising

sending, by a device, a preamble or a message to an access node;

listening, by the device, for a response to the preamble or the message during a first response window segment of a multi segment response window; continuing to listen in a second response window segment of the multi- segment response window only if the listening during the first window segment does not detect any transmission by the access node.

2. The method of claim 1, further comprising:

when the listening during the first access window detects transmissions by the access node and does not detect a response to the preamble, transmitting, by the device, a new preamble.

3. The method of claim 2, wherein the new preamble is transmitted with higher power than the previous preamble.

4. The method of any of claims 1-3, wherein the device refrains from transmitting while listening in the first response window segment or in the second response window segment, or both.

5. The method of any of claims 1-4, wherein the preamble is configured to initiate a random access.

6. The method of any of claims 1-5, wherein the device comprises a user equipment.

7. The method of any of claims 1-6, further comprising:

after listening a predetermined plurality of response window segments without detecting transmissions by the access node, transmitting a higher power preamble.

8. The method of any of claims 1-6, further comprising:

after listening a predetermined plurality of response window segments without detecting transmissions by the access node, transmitting a same power preamble.

9. The method of any of claims 1-6, further comprising:

after listening a predetermined plurality of response window segments without detecting any transmissions on a carrier on which the preamble was sent, transmitting a higher power preamble.

10. The method of any of claims 7-9, wherein the predetermined plurality of response window segments is two response window segments.

11. An apparatus, comprising

at least one processor; and

at least one memory including computer program code,

wherein the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus at least to send a preamble or a message to an access node;

listen for a response to the preamble or the message during a first response window segment of a multi segment response window;

continue to listen in a second response window segment of the multi- segment response window only if the listening during the first window segment does not detect any transmission by the access node.

12. The apparatus of claim 11, wherein the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus at least to transmit a new preamble when the listening during the first access window detects transmissions by the access node but does not detect a response to the preamble.

13. The apparatus of claim 12, wherein the new preamble is transmitted with higher power than the previous preamble.

14. The method of any of claims 1-3, wherein the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus at least to refrain from transmitting while listening in the first response window segment or in the second response window segment, or both.

15. The apparatus of any of claims 11-14, wherein the preamble is configured to initiate a random access.

16. The apparatus of any of claims 11-15, wherein the apparatus comprises a user equipment.

17. The apparatus of any of claims 11-16, wherein the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus at least to, after listening a predetermined plurality of response window segments without detecting transmissions by the access node, transmit a higher power preamble.

18. The apparatus of any of claims 11-16, wherein the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus at least to, after listening a predetermined plurality of response window segments without detecting transmissions by the access node, transmit a same power preamble.

19. The apparatus of any of claims 11-16, wherein the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus at least to, after listening a predetermined plurality of response window segments without detecting any transmissions on a carrier on which the preamble was sent, transmit a higher power preamble.

20. The apparatus of any of claim 17-19, wherein the predetermined plurality of response window segments is two response window segments.

21. An apparatus, comprising:

means for sending a preamble or a message to an access node;

means for listening for a response to the preamble or the message during a first response window segment of a multi segment response window; means for continuing to listen in a second response window segment of the multi- segment response window only if the listening during the first window segment does not detect any transmission by the access node.

22. The apparatus of claim 21, further comprising:

means for, when the listening during the first access window detects transmissions by the access node and does not detect a response to the preamble, transmitting a new preamble.

23. The apparatus of claim 22, wherein the new preamble is transmitted with higher power than the previous preamble.

24. The apparatus of any of claims 21-23, wherein the apparatus refrains from transmitting while listening in the first response window segment or in the second response window segment, or both.

25. The apparatus of any of claims 21-24, wherein the preamble is configured to initiate a random access.

26. The apparatus of any of claims 21-25, wherein the apparatus comprises a user equipment.

27. The apparatus of any of claims 21-26, further comprising:

means for, after listening a predetermined plurality of response window segments without detecting transmissions by the access node, transmitting a higher power preamble.

28. The apparatus of any of claims 21-26, further comprising:

means for, after listening a predetermined plurality of response window segments without detecting transmissions by the access node, transmitting a same power preamble.

29. The apparatus of any of claims 21-26, further comprising:

means for, after listening a predetermined plurality of response window segments without detecting any transmissions on a carrier on which the preamble was sent, transmitting a higher power preamble.

30. The apparatus of any of claims 27-29, wherein the predetermined plurality of response window segments is two response window segments.

31. A computer program product encoding instructions for performing a process, the process comprising the method according to any of claims 1-10.

32. A non-transitory computer-readable medium encoded with instructions that, when executed in hardware, perform a process, the process comprising the method according to any of claims 1-10.