Anchor carrier selection in multi-carrier wireless network

Mechanism to receive control signals transmitted from a base station (210, 510, 910) to the user equipment (220, 520, 920) in a manner that minimizes power consumption on the user equipment (220, 520, 920) while still maintaining some acceptable level of performance is described. The user equipment (220, 520, 920) periodically measures the signal quality of component carriers used by the base station (210, 510, 910) and requests control signaling (anchor) carrier reselection. Either a single component carrier can be chosen if the single carrier has sufficient quality or multiple component carriers can be selected when the quality of the single quality is low. The anchor carrier reselection may also be triggered to manage the system as a whole. For fast moving user equipments (220, 520, 920), anchor carrier hopping pattern can be provided to increase robustness and reduce reselection signaling overhead.

TECHNICAL FIELD

The disclosed technology relates to selecting one or more anchor carriers for a user equipment in a wireless network.

BACKGROUND

Evolution of cellular systems promise significant data rate increase in the future, to 1 Gb/s and higher. Higher data rates typically require larger system bandwidths. For the IMT (International Mobile Telecommunications) advanced (i.e. the fourth generation mobile communication) systems, bandwidths up to 100 MHz are being discussed. Unfortunately, the radio spectrum is a limited resource and since many operators and systems need to share the same radio resource, finding a free 100 MHz contiguous spectrum is problematic.

One way to address this issue is to aggregate multiple narrow bandwidths (or component carriers) as illustrated inFIG. 1, which can be contiguous or non-contiguous to aggregately achieve the wide bandwidth. In the example ofFIG. 1, a 50 MHz bandwidth spectrum is achieved by aggregating individual narrower bandwidth component carriers, which in this instance are 20 MHz, 20 MHz, and 10 MHz wide carriers. One benefit of such a solution is that it is possible to generate sufficiently large bandwidth for supporting data rates up to and above 1 Gb/s. Furthermore, this solution also makes it possible to adapt the spectrum parts to various situations and geographical positions thus making such solution very flexible.

A straightforward evolution of current cellular systems, such as LTE (Long Term Evolution), to support contiguous and non-contiguous spectrum is to introduce multi-carriers. That is, for each spectrum “chunk” representing a “legacy LTE” system carrier, a “4G” user equipment can be made to be capable of receiving multiple number of LTE component carriers of different bandwidths transmitted at different carrier frequencies.

A user equipment needs to listen for layer 1 and 2 (L1, L2) control signals to know where (in frequency or subchannels) and/or when (in time) data packets are scheduled to the user equipment. In single bandwidth systems like the GSM and LTE, the control signals are signaled from a serving base station on a single carrier frequency of the serving cell.

The control signaling of the single bandwidth systems can be extended to the multi-carrier scenario. That is, the user equipment can listen to the entirety of the aggregated spectrum for the control signals. Although this approach seems to be straightforward, there can be a significant drawback in terms of the user equipment power consumption. The aggregated spectrum approach, especially the non-contiguous spectrum case, implies that the radio receiver architecture for the user equipment will become more complicated than for a user equipment that is capable of only receiving small and contiguous system bandwidths. The reason is that the front end radio needs to be able to suppress blocking signal in between the spectrum “chunks”. Different kind of radio architecture can be used to handle this problem. However, they typically accompany drawbacks in terms of power consumption compared to standard continuous system bandwidth receivers.

SUMMARY

One aspect of the invention is to provide a mechanism so that control signals transmitted from the base station are received by the user equipment in a manner that minimizes power consumption on the user equipment while still maintaining some acceptable level of reliability and/or performance. To achieve this balance, a minimum amount receiver capacity on the user equipment can be activated that will achieve the acceptable reliability and/or performance.

In the best scenario, a single component carrier will be sufficient for the user equipment. The user equipment can then use the single component carrier as the anchor carrier and put any remaining receiver capacity in a power conservations mode. The anchor carriers carry control signals from the base station to the user equipment.

In less than optimal conditions, the user equipment only turns on as much capacity as needed to maintain the acceptable level of performance. For example, if the user equipment includes a plurality of receivers each adapted to listen on different narrow bandwidth component carriers, multiple receivers may be turned on to listen for control signals on multiple anchor carriers. As another example, if the user equipment includes one or more adaptable bandwidth receivers, the frequency range of the receiver or receivers may be adjusted to listen on the multiple anchor carriers.

The user equipment can periodically—rather than continuously—monitor the carriers from the base station. The periodic monitoring helps to reduce power consumption on the user equipment since the receivers for those carriers are not on continuously. When a triggering event occurs, the user equipment can request a selection (change) of anchor carrier(s) to the base station.

In an embodiment, the triggering event generally occurs when at least one of the current non-anchor carriers is better than at least one of the current anchor carriers. When the triggering event occurs, a change occurs so that the current non-anchor carrier becomes one of the new anchor carriers for the user equipment. If the current non-anchor carrier is sufficient by itself, then it can be the sole anchor carrier. This allows all other receivers of the user equipment to be put into the power conservation mode, such as being turned off a majority of time and only being turned on for periodic monitoring.

Note that minimizing the number of anchor carriers for the user equipment also has the benefit of enhancing system capacity since less resources (less number of carriers) have to be devoted to the user equipment.

These concepts can be extended to multiple base stations. For example, the user equipment can request switching of anchor carrier(s) not only to carriers from a single base station, but also to carrier(s) from another base station. That is, soft or softer handover can be requested.

In other aspects, the base station itself can initiate switching of anchor carriers for load management purposes. Also, carrier hopping can be implemented, which is a defined sequence of anchor carrier(s) changes over time for a user equipment. The carrier hopping can be especially useful for fast moving user equipments.

Advantages of the embodiments include at least the following. By introducing an anchor carrier set selection procedure as described above and detailed below, the user equipment—in many cases—can camp on a single component carrier for decoding the control signaling. This helps to reduce the current consumption considerably in the radio front end. Also, the user equipment can also select multiple component carriers for control signaling, either from a single cell or multiple cells, if that is needed for the current radio channel scenario. This provides improved control signaling robustness. Further, by implementing carrier set hopping, robust control signaling for fast moving user equipments is achieved while reducing signaling overhead. Yet further, by allowing anchor carrier set updates, load on the network can be managed efficiently.

DETAILED DESCRIPTION

In the following description, for purposes of explanation and not limitation, specific details are set forth such as particular architectures, interfaces, techniques, etc. in order to provide a thorough understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced in other embodiments that depart from these specific details. That is, those skilled in the art will be able to devise various arrangements which, although not explicitly described or shown herein, embody the principles of the invention and are included within its spirit and scope.

In some instances, detailed descriptions of well-known devices, circuits, and methods are omitted so as not to obscure the description of the present invention with unnecessary detail. All statements herein reciting principles, aspects, and embodiments of the invention, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. Additionally, it is intended that such equivalents include both currently known equivalents as well as equivalents developed in the future, i.e., any elements developed that perform the same function, regardless of structure.

The functions of the various elements including functional blocks labeled or described as “processors” or “controllers” may be provided through the use of dedicated hardware as well as hardware capable of executing software in association with appropriate software. When provided by a processor, the functions may be provided by a single dedicated processor, by a single shared processor, or by a plurality of individual processors, some of which may be shared or distributed. Moreover, explicit use of the term “processor” or “controller” should not be construed to refer exclusively to hardware capable of executing software, and may include, without limitation, digital signal processor (DSP) hardware, read only memory (ROM) for storing software, random access memory (RAM), and non-volatile storage.

In an embodiment, a L1/L2 control signaling component carrier or carriers reselection procedure is introduced. This can be accomplished in several ways. In one way, the user equipment can measure, on a regular basis (i.e., periodically), a reliability of a signal on respective component carriers of the aggregated bandwidth spectrum. The signal reliability can be measured in terms of SIR (signal-to-interference ratio), RSRP (reference signal received power), data transmission rate, error rate, repeat request rate, and so on. In general, any QoS (quality of service) measurement parameters may be used for reliability.

Based on the reliability of the component carriers, the user equipment can request an anchor carrier reselection to the base station. That is, the user equipment can request a change in the anchor carrier set—which is a set of carriers that include one or more anchor carriers for the user equipment. An anchor carrier can be viewed as the carrier that carries the control signals, such as the L1/L2 control signals, from the base station to the user equipment. The control signals inform the user equipment regarding specific downlink and uplink resources (such as identification of resource blocks of a component carrier) scheduled for the user equipment, modulation scheme to be used, transmission power level, and so on.

In the anchor carrier reselection, a single component carrier can be chosen or multiple component carriers may be selected to be included in the anchor carrier set. For example, a single component carrier may have sufficient SIR from the perspective of the user equipment and thus can be chosen to be the single anchor carrier in the set. If the single component carrier does not have the sufficient SIR, then multiple carriers can be selected to be included in the anchor carrier set to achieve the desired SIR.

The anchor carrier selection process may be initiated also for load management purposes. Typically, a base station is in communication with multiple user equipments and one component carrier can be used by the base station to transmit control signals to multiple user equipments. The same component carrier can be used to carry data signals as well. In these instances, some component carriers may be overutilized and other component carriers may be underutilized. To alleviate this problem, different anchor carriers can be selected for different user equipments to distribute the load. Also, the anchor carrier set for the different user equipments may be changed dynamically.

When the anchor carrier selection process completes, the number of anchor carriers for the user equipment will typically change, preferably to a lower number than there was before the change.

In another way, a control signaling hopping pattern, i.e. an anchor carrier hopping pattern, can be provided to the user equipment. The anchor carrier hopping pattern defines a sequence over time of anchor carrier or carriers selected for the user equipment. The sequence can be at regular intervals such as at every subframe (1 ms), at every super frame (10 ms), and so on. By introducing hopping robustness to frequency and time selective fading is introduced and the reselection signaling overhead is reduced.

FIG. 2illustrates an embodiment of a wireless network200, which includes a base station210wirelessly communicating with user equipments220-1,220-2, and220-3. The base station210is also sometimes referred to as a Node B or eNB and examples of user equipments220include a cellular phone, portable digital assistants (PDA) and mobile terminals.

The bidirectional zigzag arrowed lines from the base station210to the user equipments220each represent a component carrier of an aggregated wide bandwidth spectrum (seeFIG. 1) used as anchor carriers. InFIG. 2, a single anchor carrier is in the anchor carrier set for the user equipment220-1, two anchor carriers are included in the anchor carrier set for the user equipment220-2, and three anchor carriers are included in the anchor carrier set for the user equipment220-3.

Note that the user equipments220can share a common component carrier as the anchor carrier. For example, one of the anchor carriers for the user equipment220-2may be the same component carrier used as the anchor carrier for the user equipment220-1.

InFIG. 2, it is assumed that the base station210is capable of transmitting and the user equipments220are capable of receiving a plurality of component carriers where each component carrier is associated with a bandwidth. That is, the wireless network200can be a multi carrier system such as a multi carrier LTE or GSM, WCDMA, and so on. The plurality of carriers can be such that there is at least one gap in the aggregated frequency spectrum represented by the plurality of carriers as illustrated inFIG. 1.

FIG. 3illustrates an example method M300to select one or more anchor carriers for the user equipment220from the perspective of the user equipment220. In the method, the user equipment220receives information on the component carriers from the base station210that can potentially be selected as the anchor carriers. For example, when the user equipment220first connects to the base station210, the base station210may broadcast the information. At this point, it can be assumed that at least one component carrier is used as the anchor carrier for the user equipment220. In one example, a default carrier may be assigned as the anchor carrier for the user equipment220upon initial connection with the base station210.

Then in A320, the user equipment220monitors the signals transmitted over one or more of the plurality of component carriers from the base station210. It is preferred that the monitoring of the carriers be performed periodically, such as every 50-100 ms. In this manner, power consumption is minimized.

In A330, the user equipment220makes a determination as to whether the anchor carrier set should be changed. An anchor carrier set is defined as a set of carriers that includes one or more anchor carriers used by the user equipment220to receive control signals transmitted from the base station210. The user equipment220makes the determination based on the monitoring performed in A320, i.e., it is determined whether the triggering event has occurred.

In one embodiment, the user equipment220determines that the anchor carrier set should be changed when a reliability of a non-anchor component carrier (a carrier currently not in the anchor carrier set) is greater than a reliability of an anchor carrier (a carrier currently in the anchor carrier set). Note that the reliability comparison is made from the perspective of the user equipment220.

Reliability may be determined based on signal-to-interference ratio (SIR), reference signal received power (RSRP), a data transmission rate, an error rate, a repeat request rate, etc. of each carrier. That is, between a first carrier currently not in the anchor carrier set and a second carrier current in the anchor carrier set, the first carrier can be determined to be more reliable than the second carrier when the SIR of the first carrier is higher than the second carrier, the RSRP of the first carrier is higher than the second carrier, the data transmission rate of the first carrier is greater than the second carrier, and the error rate of the first carrier is lower than that of the second carrier. Also, the repeat request rate of the first carrier could be lower than that of the second carrier, for example, the HARQ (hybrid automatic repeat request) rate of the first carrier can be lower than that of the second carrier. In general, QoS (quality of service) parameters can be used for the reliability measurement.

If the user equipment220determines that the anchor carrier set should be changed in A330, then the user equipment220can make a request to the base station210to change the anchor carrier set in A340. Otherwise, the user equipment220can go back to monitor the carriers in A320.

FIG. 4illustrates an example method to perform A340ofFIG. 3. InFIG. 4, the user equipment220determines whether the first carrier, i.e., the current non-anchor carrier, meets a predetermined minimum reliability threshold in A410. That is, the user equipment220determines whether the first carrier is sufficient on its own to serve as the sole anchor carrier. If the first carrier meets the predetermined minimum reliability threshold, then in A420, the user equipment220makes a request to the base station210to include only the first carrier in the anchor carrier set. This allows the receivers of the user equipment220configured to listen on other component carriers to be put into a power conservation mode. Examples of power conservation modes include turning off the receiver, turning on a DRX (discontinuous reception) mode for the receiver, narrowing the frequency of the receiver (in case of adaptable bandwidth receiver), and so on.

On the other hand, if the first carrier does not meet the predetermined minimum reliability threshold in A410, then the user equipment220makes a request to the base station210to include multiple carriers into the anchor carrier set in A430which can include the first carrier. Here, the multiple carriers can be chosen from the plurality of carriers to which the user equipment220is capable of listening so as to minimize the number of anchor carriers in the anchor carrier set necessary to meet the predetermined minimum reliability threshold. The predetermined reliability threshold may be based on the reliability parameters such as the parameters discussed above.

InFIG. 2, the user equipment220receives control signals from a single base station210. That is, the anchor carriers are all from the same base station210. However, it is possible to include multiple base stations. In an embodiment illustrated inFIG. 5, the anchor carrier set for the user equipment520can include component carriers from different base stations510-1and510-2. In this instance, the user equipment520can monitor the signals carried on component carriers used by both base stations510. InFIG. 5, one of the base stations510, such as the base station510-1, is assumed to be the serving base station510for the user equipment520.

FIG. 6illustrates an example method M600to select anchor carriers for the user equipment when there are multiple base stations. In the method, the user equipment520can receive information of component carriers that can be used as anchor carriers in A610. In this situation, the user equipment520receives information on component carriers of multiple base stations510.

In A620, the user equipment520monitors the component carriers of the respective base stations510. Based on the monitoring, the user equipment520makes a determination on whether the anchor carrier set should be changed in A630, i.e., determines whether the triggering event has occurred. If the user equipment520makes such determination, then the user equipment520makes a request to switch the anchor carrier set in A640. Otherwise, the user equipment520goes back to monitoring the carriers in A620. Note that A610, A620, and A630inFIG. 6are similar to A310, A320and A330inFIG. 3, respectively. The difference is that component carriers of multiple base stations510are considered inFIG. 6.

FIG. 7illustrates an example method to perform A640ofFIG. 6. InFIG. 7, the user equipment520determines whether the first carrier meets the predetermined minimum reliability threshold in A710. If so, then the user equipment520makes a request to include only the first carrier in the anchor carrier set in A720. Otherwise, in A730, the user equipment520makes a request to include multiple carriers in the anchor carrier set. Again, the multiple carriers are chosen to minimize the number of carriers to meet the predetermined minimum reliability threshold. Note that the multiple carriers need not be all from a single base station. Carriers from multiple base stations510can be selected to meet the predetermined minimum reliability threshold while minimizing the number of carriers selected.

FIG. 8illustrates a method to perform A720ofFIG. 7in the multiple base station environment. Here, the user equipment520has determined that the first carrier is sufficient on its own. Thus, if the first carrier is not from the current serving base station510-1, then a handoff is required.

In A810, the user equipment520determines whether a handoff is necessary. That is, it is determined whether the first carrier is from a base station that is not the current serving base station. If such determination is made, then in A820, the user equipment520makes a request to the current serving base station510-1to be handed off to the new serving base station510-2. Once the handoff is completed, then in A830, the user equipment520makes a request to the new serving base station510-2to include only the first carrier in the anchor carrier set. If the handoff is not required, then in A840, the user equipment520makes a request to include only first carrier to be in the anchor carrier set to the current serving base station510-1.

As noted previously, one advantage of minimizing the number of anchor carriers is that power of the user equipment may be conserved. For example, the user equipment may include a plurality of fixed narrow bandwidth receivers each configured to receive signals on particular component carriers. By minimizing the number of anchor carriers, the receivers that do not correspond to the anchor carriers can be put in power conservation mode. The power conservation mode can include any one or more of turning off the receiver, putting the receiver in a periodic monitoring mode, enabling a DRX (discontinuous reception) mode, and so on.

In another example, the user equipment may include one or more adaptable bandwidth receivers where the frequency range of each receiver can be dynamically adapted. Here, a receiving frequency range of the receivers can be narrowed to exclude non-anchor carriers for power conservation. Of course, the user equipment can include both fixed and adaptable bandwidth receivers.

The embodiments illustrated inFIGS. 1-8can work very well for a user equipment that is either stationary or slow moving. In the slow moving situation, the quality/reliability of the component carriers are unlikely to change from the perspective of the user equipment. However, for a fast moving user equipment, the situation can be very different, as illustrated inFIG. 9. As illustrated, the user equipment920is at significantly different positions at time t1and at time t2. The anchor carrier set that was sufficient at time t1may not be sufficient at time t2, and the anchor carrier set would need to be changed for the user equipment920at time t2. If the user equipment920is very fast moving, the anchor carrier set would be changed frequently.

Even under the fast moving user equipment scenario, the methods outlined inFIGS. 2-8can be used with good results. However, it may be more resource efficient to anticipate the need for frequent anchor carrier set changes and to provide the information to the user equipment920in advance. In one embodiment, an anchor hopping pattern provided to the user equipment920. The anchor hopping pattern specifies a sequence over time of one or more anchor carriers to be used by the user equipment920to receive the control signals transmitted by the base station910.

The hopping pattern can be user equipment specific and be based on the identification of the user equipment920. The hopping pattern can also be cell specific based on some cell specific hopping pattern. The hopping pattern could be such that the user equipment listens on a control channel on a particular component carrier for a superframe (10 ms long in LTE) and then jump to another component carrier or carriers. Then the user equipment920can receive the message and detect the control signals on the component carrier(s) according to the hopping pattern. An advantage of applying the anchor carrier hopping pattern is that it introduces robustness to the frequency and/or time selective fading, and at the same time, reduces the anchor carrier reselection signaling overhead associated with the methods illustrated inFIGS. 2-8.

FIG. 10illustrates an example method M1000to implement the carrier hopping process described above. In A1010, the user equipment920receives information regarding the component carriers from the base station910.

The hopping pattern may be provided because the base station910determines that there is a need for the hopping pattern. For example, the base station910can determine that the hopping pattern is needed in A1020because the user equipment920is moving at a speed greater than a predetermined minimum rate. In one embodiment, a strength of the uplink transmission from the user equipment920can be measured by the base station910over time to determine the speed of movement of the user equipment920.

The hopping pattern may also be provided because the user equipment920determines the need. In A1030, the user equipment920itself can determine that it is moving at a rate greater than the predetermined minimum rate, and thus, makes a request for the hopping pattern. For example, the user equipment920may include a location detection unit such a GPS unit.

When the need for the hopping pattern is determined in A1020or the request for hopping pattern is made by the user equipment in A1030, then the base station920provides the hopping pattern to the user equipment910in A1040. Then in A1050, the user equipment920adapts the receivers to receive the control signals transmitted from the base station910by sequencing through the anchor carriers according to the anchor carrier hopping pattern.

In the example methods and embodiments discussed above, the selection of the anchor carriers in the anchor carrier set is based on considerations regarding the user equipment. However, the composition of the anchor carrier set for a user equipment may also be based on the consideration of the network as a whole. For example, there may be a capacity issue in the network. Over time, some component carriers may be overutilized and other component carriers may be underutilized. The overutilization can stem from not only transmitting control signals to the user equipments, but also from using the carrier to carry data between the base stations and the user equipments.

FIG. 11illustrates a method to redistribute anchor carriers, i.e., update anchor carrier sets, for load management. InFIG. 11, the base station monitors, in A1110, the load on each of the plurality of component carriers it uses for communication with the user equipments. Based on the monitoring, the base station determines whether anchor carrier sets should be updated to the user equipments in A1120. If such determination is made, then in A1130, the base station notifies one or more user equipments to switch anchor carriers, i.e., to update the anchor carrier set. That is, the base station informs the user equipments on which component carrier or carriers the control signals for that particular user equipment will be transmitted on. Afterwards, the base station transmits the control signals accordingly.

There can be a host of reasons to initiate updates of the anchor carrier sets. For example, the SIR of an anchor carrier used by one of the user equipments may fall below the predetermined minimum SIR threshold. Other reasons include: an error rate of data carried over an anchor carrier passes over a predetermined error rate threshold; a repeat request rate of data transmitted over an anchor carrier falls below a predetermined repeat request rate threshold; a number of user equipments being served by the base station over one carrier is greater than a number of user equipments being served by the base station over another carrier by at least a predetermined number; an amount of data transmitted over one carrier is greater than an amount of data transmitted over another carrier by at least a predetermined amount; and so on.

FIG. 12illustrates an embodiment of the user equipment220,520and920, which includes a processing unit1210, a monitoring unit1220, a communication unit1230and a location detection unit1240. The monitoring unit1220can, e.g., monitor the quality of the signals on carriers transmitted by the base stations210,510,910and the location unit1240, such as the GPS unit, can determine the present location of the user equipment220,520,920as well as determining the rate of movement.

The communication unit1230is arranged to communicate with the base stations210,510,910and can include any combination of fixed bandwidth receivers and adaptable bandwidth receivers. If only fixed bandwidth receivers are considered, then the communications unit1230is preferred to include a plurality of receivers, where each receiver is configured to listen on one of the plurality of component carriers. If only adaptable bandwidth receivers are considered, then there can be one or more of these receivers. If a combination is considered, then there can be one or more fixed bandwidth receivers and one or more adaptable bandwidth receivers.

The processing unit1210is arranged to control the operations of the components of the user equipment220,520,920including the monitoring unit1220, the communication unit1230and the location unit1240to perform the methods described above.

FIG. 13illustrates an embodiment of a base station210,510,910as illustrated inFIGS. 2,5and9. The base station210,510,910includes a processing unit1310, a monitoring unit1320and a communication unit1330. The monitoring unit1320is arranged to monitor, e.g., the load on the component carriers used by the base station210,510,910. The communication unit1330is arranged to communicate with the user equipments220,520,920in the network. The processing unit1310is arranged to control the operations of the components of the base station210,510,910including the monitoring unit1320and the communication unit1330to perform the methods as described above.

Although the description above contains many specificities, these should not be construed as limiting the scope of the invention but as merely providing illustrations of some of the presently preferred embodiments of this invention. Therefore, it will be appreciated that the scope of the present invention fully encompasses other embodiments which may become obvious to those skilled in the art, and that the scope of the present invention is accordingly not to be limited. All structural, and functional equivalents to the elements of the above-described preferred embodiment that are known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed hereby. Moreover, it is not necessary for a device or method to address each and every problem described herein or sought to be solved by the present technology, for it to be encompassed hereby. Furthermore, no element, component, or method act in the present disclosure is intended to be dedicated to the public.