WO2011083452A1

WO2011083452A1 - Control of contention based uplink access

Info

Publication number: WO2011083452A1
Application number: PCT/IB2011/050122
Authority: WO
Inventors: Seppo Alanara
Original assignee: Nokia Corporation
Priority date: 2010-01-11
Filing date: 2011-01-11
Publication date: 2011-07-14

Abstract

A terminal device such as a user equipment (UE) can perform contention based access only in good radio link conditions. The channel conditions can be estimated by using either downlink (DL) channel quality indicator (CQI) or a hybrid automatic repeat request (HARQ) retransmission counter in the uplink (UL) or both. Additionally or alternatively, radio link control (RLC) automatic repeat request (ARQ) in the UL can also be used to estimate channel condition. For example, contention based uplink access can be permitted only when, in recent normal UL packet transmission, no HARQ repeats are used and in addition to this the DL CQI has a value exceeding a CQI threshold. By using such techniques, it may be possible to reduce latency for uplink access.

Description

CONTROL OF CONTENTION BASED UPLINK ACCESS

BACKGROUND:

Field:

Contention based uplink access can be applied to the Long Term Evolution (LTE) Advanced (LTE-A) of the 3rd Generation Partnership Project (3GPP). Contention based uplink access can, however, affect LTE user plane packet traffic latency.

Description of the Related Art:

Contention based access is access in which multiple UEs may use the same resource simultaneously. Contention based access in LTE can lead to the case where the evolved Node B (eNB) is not able to receive the transmission due to collision of two radio frequency (RF) bursts in the receiver. The opposite of contention based access is contentionless access, of which reservation based access is one example. In reservation based access the resource has been allocated in the downlink signaling just for one user equipment (UE). Thus, in reservation based access the access can be based on uplink grant decisions by an eNB scheduler.

Contention based uplink access is not used in current cellular network radio interface protocols in the case of user plane packet transmission. Instead, the packet transmission uses dedicated radio bearers for which grants are assigned by an eNB scheduler. In LTE Release 8 (Rel8) and Release 9 (Rel9), contention based access on the control plane can be done when the uplink synchronization is lost or when the user equipment (UE) is in idle mode. In both of these cases, a random access method is used to get a dedicated uplink grant scheduled for the UE. Thus, all user plane packet transmissions are implemented through dedicated grants. Dedicated grants using scheduling request (SR) have more latency than contention based uplink packet transmission. This heightened latency is attributable to delay for SR transmission and waiting for uplink grant, which is readily available in case of contention based access. If no SR resource is available, Random Access can be used, but can cause even more latency. BRIEF DESCRIPTION OF THE DRAWINGS:

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

Figure 1 presents a block diagram of possible contention based access scenarios.

Figure 2 illustrates a method according to certain embodiments of the present invention.

Figure 3 illustrates another method according to certain embodiments of the present invention.

Figure 4 illustrates a signal flow diagram according to certain embodiments of the present invention.

Figure 5 illustrates a system according to certain embodiments of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S):

As discussed at greater length below, it is desirable for a terminal device such as a user equipment (UE) to perform contention based access in good radio link conditions. The channel conditions can be estimated by using either downlink (DL) channel quality indicator (CQI) or a hybrid automatic repeat request (HARQ) retransmission counter in the uplink (UL) or both. Additionally or alternatively, radio link control (RLC) automatic repeat request (ARQ) in the UL can also be used to estimate channel condition. For example, contention based uplink access can be permitted when, in recent normal UL packet transmission, no HARQ repeats are used, or the DL CQI has a value exceeding a CQI threshold, or when both conditions are met. By using such techniques, it may be possible to reduce latency for uplink access. Thus the uplink access can be optimized so that retransmission occur very rarely. Note that while using contention based access it may be desirable to monitor the UL retransmissions and, if there are too many, for the UE to stop using connection based UL packet access. Additionally, following the CQI of DL can be used to determine when contention based access usage is to be stopped.

If multiple UEs are using the same UL resource, collisions may possibly occur. In such circumstances, the use of ordinary HARQ may not be possible as a retransmission method, because the eNB may be unable to detect whether UL access is failed because of collision or because of a bad radio link. Thus RLC level retransmission, which are relatively inefficient, can be used assuming that User Plane traffic is using an acknowledged mode radio bearer. With RLC layer retransmission, quite long delays and packet transmission jitter can result as compared to a regular scheduling request (SR) on the physical uplink control channel (PUCCH). Thus, contention based access can be restricted to the case when the radio link quality is good enough to ensure that retransmission is very rarely needed.

Estimation in the UE of when to use Contention Based (CB) access can be employed so as to restrict CB access to the case when the radio link quality is good enough to ensure that retransmission is very rarely needed. For the estimation, conventional measurements of the channel quality can be used. For example, Channel Quality Indicator (CQI) for DL can be used. If needed the threshold level of CQI or other similar channel quality estimate value required to use contention based uplink access can be controlled by the eNB through System Information, dedicated signaling, or by specifying a fixed quality requirement in the LTE RANI and/or RAN2 specifications (that is to say, by making the threshold a standard that is consequently known in advance by the UE). One possibility for UL quality estimate is to enable CB access if, in recent normal UL packet transmission, no HARQ repeats have been used or the DL CQI has a value exceeding a CQI threshold for CB access, or both if both conditions are met.

It should be noted that more than one threshold value can be used and more than one threshold value can be signaled. The use of more than one threshold value can help to define an hysteresis, so that state changes between contention based and contentionless access are not changed in a ping-pong style. The hysteresis can be implemented either by provision of two threshold values or by providing one threshold and a hysteresis amount needed to do the state change. This means that one CQI value can be used to specify that when quality exceeds that value, then UE can use CB access if available. Then, during CB access, the UE can instead use another value, which is lower than the value to begin using CB access. Thus, in certain embodiments, only when CQI goes below the second, lower value, the UE returns to using normal reservation based UL access or some other contentionless access. In addition there may be need for enhancing the UE power consumption. CB access can be implemented by using one special contention based radio network temporary identifier (CB-RNTI) which indicates the UL grants for CB access. This extra RNTI may require additional power consumption when decoding the PDCCH. Extra power consumption can be avoided if an indication of CB access usage is indicated in the System Information. This indication of CB access usage can be additional or alternative to the indication of thresholds hysteresis. Because CB access performance gets worse when eNB UL is heavily loaded, this indication can be set whenever eNB deems that UL capacity is overloaded.

The UE may continuously check quality of the uplink by continuous logs of UL HARQ retransmissions. In addition to this, the UE can perform normal CQI measurements for the downlink. CB access can be limited to when the radio link quality exceeds the eNB-defined threshold or a threshold set in a UE firmware implementation.

If the threshold is exceeded (that is to say, when the quality is better than a threshold level), the UE can use CB access when UL synchronization is valid and the UE is in dormant state. The UL synchronization is valid when, for example, a timing advance or time alignment (TA) timer has not expired. The UE is in a dormant state when, for example, no grant for uplink is scheduled by the eNB. When the UE does employ CB access it may need to decode the PDCCH with cell radio network temporary identifier (C-RNTI) and contention based radio network temporary identifier (CB- RNTI). The UE can use normal access if C-RNTI is detected in the decoder and correspondingly can use CB access when CB-RNTI is detected in the decoder. If the eNB indicates active CB mode through System Information, some savings are possible in the UE and only C-RNTI is used in the decoder. If UL synchronization is lost, UE may need to use Random Access to gain the synchronization. In the case of CB access, the grant can be signaled using a common CB-RNTI, and in case of a regular dedicated UL grant , the C-RNTI which is unique for a single UE can be signaled.

If UL quality estimate is made, either using DL CQI or a HARQ retransmission counter in the UL, it is desirable that the UE use CB access only in good radio link conditions. If CB access is used in bad radio link conditions, the result may be excessive latency increase due to the use of RLC retransmissions. Figure 1 presents a block diagram of possible CB access scenarios. Figure 1 is only showing the UE activity in the active mode when UE has a radio resource control (RRC) connection and has C-RNTI as the UE's identity in the eNB. A UE that has lost UL synchronization can be using the normal random access (RA) to get time alignment for UL access. At the same time, the UE can get a grant which it can use to request a grant for uplink (SR in Figure 1 refers to a Scheduling Request). CB uplink access does not apply for UEs that have lost UL synchronization. Note that in small cells UE normally always has UL synchronization, if it is within the cell coverage. Thus, the case of losing UL synchronization may not apply to UEs in small cells. UEs which are in dormant state but still have UL synchronization are those UEs that can be candidates for CB UL access. Those UEs can then estimate if the radio link quality is sufficient. The computation of radio link quality estimate is not illustrated in Figure 1. If radio link (RL) quality exceeds the preset limit, the UE can attempt CB access. If RL quality does not exceed the preset limit or threshold, the UE can use the legacy method, for example, sending an SR and then decoding the PDCCH to get the grant for it. The UE attempting CB access can decode the PDCCH for the grant assigned for CB-RNTI, and when detected can use the given grant. The CB access may fail if another UE is simultaneously attempting to use the same grant.

An additional threshold that may be used is the number of minimum contention slots (MCS). Any MCS may work if there are no retransmissions, and consequently the HARQ count may be the main parameter to determine if some UL can be exercised under such conditions. However, UL CB usage can be based on whether the CB MCS is lower or equal to the MCS which was applied for packets that are basis for a HARQ count threshold.

Figure 2 illustrates a method according to certain embodiments of the present invention. The method of Figure 2 can be performed by, for example, a UE. The method includes estimating 210 channel quality of an uplink channel of a user equipment to provide an estimate of channel quality. The estimating 210 can include estimating using a downlink channel quality indicator. The estimating 210 can also or alternatively include estimating using a hybrid automatic repeat request retransmission counter in uplink. The estimating 210 can also or alternatively include estimating use of radio link control automatic repeat request in the uplink.

The method further includes determining 220 whether the estimate of channel quality exceeds a threshold channel quality to provide a determination of the threshold being met or exceeded. The method additionally includes performing 230 contention based uplink access contingently upon the determination of the threshold being met or exceeded being positive.

In the method illustrated in Figure 2, contention based uplink access can be performed when at least one of two criteria are met. The first criteria is if in recent normal uplink packet transmission no hybrid automatic repeat request repeats have been used. The other criterion is if a downlink channel quality indicator has a value exceeding a channel quality indicator threshold.

Figure 3 illustrates another method according to certain embodiments of the present invention. The method of Figure 3 can be performed by, for example, an eNB. The method includes providing 310 a threshold level of channel quality to a user equipment, wherein the threshold level of channel quality is configured to permit the user equipment to determine whether to use contention based uplink access depending on whether the threshold is met or exceeded. The providing 310 can include signaling the threshold level to the user equipment as system information, in dedicated signaling, or by a firmware update. The method can also include providing 320 a contention based radio network temporary identity that indicates the uplink grants for contention based access.

Figure 4 illustrates a signal flow diagram according to certain embodiments of the present invention. As illustrated in Figure 4, an eNB 420 can provide 430 a threshold level to a UE 410. The UE 410 can monitor 440 channel quality for some period of time prior to seeing uplink grant. The UE 410 can determine 450 whether or not to use contention based access based on whether the threshold level has been met, as well as additional factors. The UE can then use 460 contention based access when appropriate.

Figure 5 illustrates a system according to certain embodiments of the present invention. The system includes a first apparatus 510 (which may be a UE) and a second apparatus 520 (which may be an eNB) connected by a wireless radio link 515. Each of the first apparatus 510 and the second apparatus 520 can include at least one memory 530 including computer program code 540. Additionally, each of the first apparatus 510 and the second apparatus 520 can include at least one processor 550. The memory 530 and the computer program code 540 can be configured, together with the at least one processor 550, to control the respective apparatus to perform a suitable method, such as the method illustrated in Figure 2 or the method illustrated in Figure 3. Thus, the system of Figure 5 may operate, in certain embodiments, according to the signal flow diagram shown in Figure 4.

The at least one memory 530 can be any suitable computer-readable storage medium, such as a Random Access Memory (RAM) or Read Only Memory (ROM). The computer program code 540 can be any properly configured set of instructions in a machine-readable format (for example, compiled or interpreted formats). The at least one processor 550 can be a general purpose central processing unit (CPU), an application specific integrated circuit (ASIC), or other controller, processor, or chip. The methods of Figures 2 and 3 can be implemented in hardware such as the at least one processor 550, and can be implemented using a computer-readable medium encoded with the computer instructions that, when executed in hardware, cause an apparatus (such as the first apparatus 510 or the second apparatus 520) to perform a process.

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.

A method according to certain embodiments of the present invention can include estimating channel quality of an uplink channel of a user equipment to provide an estimate of channel quality. The method can also include determining whether the estimate of channel quality exceeds a threshold channel quality to provide a determination of the threshold being met or exceeded. The method can further include performing contention based uplink access contingently upon the determination of the threshold being met or exceeded being positive.

In the method discussed above, the estimating can include estimating using a downlink channel quality indicator.

In the method discussed above, the estimating can include estimating using a 5 hybrid automatic repeat request retransmission counter in uplink.

In the method discussed above, the estimating can include estimating use of radio link control automatic repeat request in the uplink.

In the method discussed above, contention based uplink access can be performed when at least one of the following criteria is met: in recent normal uplink packet 10 transmission no hybrid automatic repeat request repeats have been used or a downlink channel quality indicator has a value exceeding a channel quality indicator threshold.

Another method according to certain embodiments of the present invention can include providing a threshold level of channel quality to a user equipment. The threshold level of channel quality can be configured to permit the user equipment to i s determine whether to use contention based uplink access depending on whether the threshold is met or exceeded.

The threshold level can be signaled to the user equipment as system information, in dedicated signaling, or by a firmware update.

The method discussed above can further include providing a contention based 20 radio network temporary identity that indicates the uplink grants for contention based access.

An apparatus can include at least one memory including computer program code and at least one processor. The at least one memory and the computer program code can be configured to, with the at least one processor, control the apparatus at least to estimate

25 channel quality of an uplink channel of a user equipment to provide an estimate of channel quality. The at least one memory and the computer program code can also be configured to, with the at least one processor, control the apparatus at least to determine whether the estimate of channel quality exceeds a threshold channel quality to provide a determination of the threshold being met or exceeded. The at least one memory and the

30 computer program code can be further configured to, with the at least one processor, control the apparatus at least to perform contention based uplink access contingently upon the determination of the threshold being met or exceeded being positive.

The at least one memory and the computer program code can also be configured to, with the at least one processor, control the apparatus at least to perform the estimation using a downlink channel quality indicator.

The at least one memory and the computer program code can further be configured to, with the at least one processor, control the apparatus at least to perform the estimation using a hybrid automatic repeat request retransmission counter in uplink.

The at least one memory and the computer program code can additionally be configured to, with the at least one processor, control the apparatus at least to perform the estimation of use of radio link control automatic repeat request in the uplink.

The at least one memory and the computer program code can also be configured to, with the at least one processor, control the apparatus at least to perform contention based uplink access when at least one of the following criteria is met: in recent normal uplink packet transmission no hybrid automatic repeat request repeats have been used or a downlink channel quality indicator has a value exceeding a channel quality indicator threshold.

A computer-readable storage medium encoded with instructions that, when executed in hardware, perform process, can be configured to perform a process. The process can include estimating channel quality of an uplink channel of a user equipment to provide an estimate of channel quality. The process can also include determining whether the estimate of channel quality exceeds a threshold channel quality to provide a determination of the threshold being met or exceeded. The process can further include performing contention based uplink access contingently upon the determination of the threshold being met or exceeded being positive.

A computer-readable storage medium encoded with instructions that, when executed in hardware, perform process, can be configured to perform a process. The process can include providing a threshold level of channel quality to a user equipment. The threshold level of channel quality can be configured to permit the user equipment to determine whether to use contention based uplink access depending on whether the threshold is met or exceeded.

Claims

WE CLAIM:

1. A method, comprising:

estimating channel quality of an uplink channel of a user equipment to provide an estimate of channel quality;

determining whether the estimate of channel quality exceeds a threshold channel quality to provide a determination of the threshold being met or exceeded; and

performing contention based uplink access contingently upon the determination of the threshold being met or exceeded being positive.

2. The method of claim 1, wherein the estimating comprises estimating using a downlink channel quality indicator.

3. The method of claim 1 or claim 2, wherein the estimating comprises estimating using a hybrid automatic repeat request retransmission count for uplink.

4. The method of any of claims 1-3, wherein the estimating comprises estimating use of radio link control automatic repeat request in the uplink.

5. The method of any of claims 1-4, wherein the contention based uplink access is performed when at least one of the following criteria is met: in recent normal uplink packet transmission no hybrid automatic repeat request repeats have been used or a downlink channel quality indicator has a value exceeding a channel quality indicator threshold.

6. A method, comprising:

providing a threshold level of channel quality to a user equipment,

wherein the threshold level of channel quality is configured to permit the user equipment to determine whether to use contention based uplink access depending on whether the threshold is met or exceeded.

7. The method of claim 6, wherein the threshold level is signaled to the user equipment as system information.

8. The method of claim 6, wherein the threshold level is signaled to the user equipment in dedicated signaling.

9. The method of claim 6, wherein the threshold level is signaled to the user equipment by a firmware update.

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

providing a contention based radio network temporary identity that indicates the uplink grants for contention based access.

11. An apparatus, comprising:

at least one memory including computer program code; and

at least one processor,

wherein the at least one memory and the computer program code are configured to, with the at least one processor, control the apparatus at least to

estimate channel quality of an uplink channel of a user equipment to provide an estimate of channel quality;

determine whether the estimate of channel quality exceeds a threshold channel quality to provide a determination of the threshold being met or exceeded; and

perform contention based uplink access contingently upon the determination of the threshold being met or exceeded being positive.

12. The apparatus of claim 11, wherein the at least one memory and the computer program code are also configured to, with the at least one processor, control the apparatus at least to perform the estimation using a downlink channel quality indicator.

13. The apparatus of claim 11 or claim 12, wherein the at least one memory and the computer program code can further be configured to, with the at least one processor, control the apparatus at least to perform the estimation using a hybrid automatic repeat request retransmission count for uplink.

14. The apparatus of any of claims 11-13, wherein the at least one memory and the computer program code can additionally be configured to, with the at least one processor, control the apparatus at least to perform the estimation of use of radio link control automatic repeat request in the uplink.

15. The apparatus of any of claims 11-14, wherein the at least one memory and the computer program code are also configured to, with the at least one processor, control the apparatus at least to perform contention based uplink access when at least one of the following criteria is met: in recent normal uplink packet transmission no hybrid automatic repeat request repeats have been used or a downlink channel quality indicator has a value exceeding a channel quality indicator threshold.

16. An apparatus, comprising:

at least one memory including computer program code; and

at least one processor,

provide a threshold level of channel quality to a user equipment,

17. The apparatus of claim 16, wherein the at least one memory and the computer program code are configured to, with the at least one processor, control the apparatus at least to signal the threshold level to the user equipment as system information.

18. The apparatus of claim 16, wherein the at least one memory and the computer program code are configured to, with the at least one processor, control the apparatus at least to signal the threshold level to the user equipment in dedicated signaling.

19. The apparatus of claim 16, wherein the at least one memory and the computer program code are configured to, with the at least one processor, control the apparatus at least to signal the threshold level to the user equipment by a firmware update.

20. The apparatus of any of claims 16-19, wherein the at least one memory and the computer program code are also configured to, with the at least one processor, control the apparatus at least to provide a contention based radio network temporary identity that indicates the uplink grants for contention based access.

21. A computer-readable storage medium encoded with instructions that, when executed in hardware, perform process, configured to perform a process, the process comprising:

22. The computer-readable storage medium of claim 21, wherein the estimating comprises estimating using a downlink channel quality indicator.

23. The computer-readable storage medium of claim 21 or claim 22, wherein the estimating comprises estimating using a hybrid automatic repeat request retransmission count for uplink.

24. The computer-readable storage medium of any of claims 21-23, wherein the estimating comprises estimating use of radio link control automatic repeat request in the uplink.

25. The computer-readable storage medium of any of claims 21-24, wherein the contention based uplink access is performed when at least one of the following criteria is met: in recent normal uplink packet transmission no hybrid automatic repeat request repeats have been used or a downlink channel quality indicator has a value exceeding a channel quality indicator threshold.

26. A computer-readable storage medium encoded with instructions that, when executed in hardware, perform process, configured to perform a process, the process comprising:

providing a threshold level of channel quality to a user equipment,

27. The computer-readable storage medium of claim 26, wherein the threshold level is signaled to the user equipment as system information.

28. The computer-readable storage medium of claim 26, wherein the threshold level is signaled to the user equipment in dedicated signaling.

29. The computer-readable storage medium of claim 26, wherein the threshold level is signaled to the user equipment by a firmware update.

30. The computer-readable storage medium of any of claims 26-29, wherein the process further comprises providing a contention based radio network temporary identity that indicates the uplink grants for contention based access.

31. An apparatus, comprising:

estimating means for estimating channel quality of an uplink channel of a user equipment to provide an estimate of channel quality;

determining means for determining whether the estimate of channel quality exceeds a threshold channel quality to provide a determination of the threshold being met or exceeded; and

contention means for performing contention based uplink access contingently upon the determination of the threshold being met or exceeded being positive.

32. The apparatus of claim 31, wherein the estimating means is configured to estimate using a downlink channel quality indicator.

33. The apparatus of claim 31 or claim 32, wherein the estimating means is configured to estimate using a hybrid automatic repeat request retransmission count for uplink.

34. The apparatus of any of claims 31-33, wherein the estimating means is configured to estimate use of radio link control automatic repeat request in the uplink.

35. The apparatus of any of claims 31-34, wherein the contention based uplink access is performed when at least one of the following criteria is met: in recent normal uplink packet transmission no hybrid automatic repeat request repeats have been used or a downlink channel quality indicator has a value exceeding a channel quality indicator threshold.

36. An apparatus, comprising:

threshold providing means for providing a threshold level of channel quality to a user equipment; and

threshold configuring means for configuring the threshold level of channel quality to permit the user equipment to determine whether to use contention based uplink access depending on whether the threshold is met or exceeded.

37. The apparatus of claim 36, wherein the threshold level is signaled to the user equipment as system information.

38. The apparatus of claim 36, wherein the threshold level is signaled to the user equipment in dedicated signaling.

39. The apparatus of claim 36, wherein the threshold level is signaled to the user equipment by a firmware update.

40. The apparatus of any of claims 36-39, further comprising:

identity providing means for providing a contention based radio network temporary identity that indicates the uplink grants for contention based access.