WO2016161580A1

WO2016161580A1 - Randomly selecting frequency layer

Info

Publication number: WO2016161580A1
Application number: PCT/CN2015/076091
Authority: WO
Inventors: Guillaume DECARREAU; Benoist Pierre Sebire; Yan Ji ZHANG; Yang Liu
Original assignee: Nokia Solutions And Networks Oy
Priority date: 2015-04-08
Filing date: 2015-04-08
Publication date: 2016-10-13

Abstract

A method of selecting a frequency layer by a user device may include determining a primary frequency layer for communicating with a base station, randomly selecting a candidate frequency layer for communicating with the base station, determining a probability of selecting the candidate frequency layer, the probability being based on a difference between a preference for the primary frequency layer and a preference for the candidate frequency layer, determining whether to select the candidate frequency layer based on the determined probability, and if it is determined to select the candidate frequency layer, selecting the candidate frequency layer and communicating with the base station via the candidate frequency layer.

Description

RANDOMLY SELECTING FREQUENCY LAYER

TECHNICAL FIELD

This description relates to wireless networking.

BACKGROUND

Deploying multiple carrier frequencies can increase the capacity of cellular networks. If multiple user devices attempt to communicate with a base station via a same carrier frequency, collisions may occur and/or data rates may be decreased. Redirecting the user devices by the base station to other carrier frequencies may increase signaling load and handover failure rates.

SUMMARY

According to one general aspect, a method of selecting a frequency layer by a user device may include determining a primary frequency layer for communicating with a base station, randomly selecting a candidate frequency layer for communicating with the base station, determining a probability of selecting the candidate frequency layer, the probability being based on a difference between a preference for the primary frequency layer and a preference for the candidate frequency layer, determining whether to select the candidate frequency layer based on the determined probability, and if it is determined to select the candidate frequency layer, selecting the candidate frequency layer and communicating with the base station via the candidate frequency layer.

According to another general aspect, a non-transitory computer-readable storage medium may comprise instructions stored thereon. When executed by at least one processor, the instructions may be configured to cause a user device to determine a primary frequency layer for communicating with a base station, randomly select a candidate frequency layer for communicating with the base station, determine a probability of selecting the candidate frequency layer, the probability being based on a difference between a preference for the primary frequency layer and a preference for the candidate frequency layer, determine whether to select the candidate frequency layer based on the determined probability, and i f it is determined to select the candidate frequency layer, select the candidate frequency layer and communicating with the base station via the candidate frequency layer.

According to another general aspect, a user device maybe configured to determine a primary frequency layer for communicating with a base station, randomly select a candidate frequency layer for communicating with the base station, determine a probability of selecting the candidate frequency layer, the probability being based on a difference between a preference for the primary frequency layer and a preference for the candidate frequency layer, determine whether to select the candidate frequency layer based on the determined probability, and i f it is determined to select the candidate frequency layer, select the candidate frequency layer and communicating with the base station via the candidate frequency layer.

According to another general aspect, a user device may comprise a transceiver configured to send and receive signals, at least one processor controlling the transceiver, and at least one memory device comprising instructions stored thereon that, when executed by the at least one processor, are configured to cause the user device to determine a primary frequency layer for communicating with a base station, randomly select a candidate frequency layer for communicating with the base station, determine a probability of selecting the candidate frequency layer, the probability being based on a difference between a preference for the primary frequency layer and a preference for the candidate frequency layer, determine whether to select the candidate frequency layer based on the determined probability, and if it is determined to select the candidate frequency layer, select the candidate frequency layer and communicating with the base station via the candidate frequency layer.

According to another general aspect, a user device may comprise comprising means for determining a primary frequency layer for communicating with a base station, means for randomly selecting a candidate frequency layer for communicating with the base station, means for determining a probability of selecting the candidate frequency layer, the probability being based on a di fference between a preference for the primary frequency layer and a preference for the candidate frequency layer, means for determining whether to select the candidate frequency layer based on the determined probability, and if it is determined to select the candidate frequency layer, means for selecting the candidate frequency layer and communicating with the base station via the candidate frequency layer.

The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features will be apparent from the description and drawings, and from the claims.

BRIEF DESCRIPTION OF THEDRAWINGS

FIG. 1 is a diagram of a cellular network according to an example embodiment.

FIG. 2 is a timing diagram showing communication between a user device and the base station according to an example embodiment.

FIG. 3 is a flowchart showing a method for selecting a frequency layer according to an example embodiment.

FIG. 4A is a diagram showing frequency layers and cell qualities according to an example embodiment.

FIG. 4B is a diagram showing frequency layers and priorities according to an example embodiment.

FIG. 5 is a flowchart showing a method according to an example embodiment.

FIG. 6 is a diagram showing a user device according to an example embodiment.

Like reference numbers refer to like elements.

DETAILED DESCRIPTION

User devices in a network, such as a cellular network, may communicate with base stations via frequency layers, which may include carrier frequencies. A frequency layer may include, for example, one or more communication resources provided on a particular carrier frequency. The user devices may each select a frequency layer based on criteria such as priorities of the frequency layers broadcast by the base station (s) and/or quality of the associated channels, which may be based on a received signal strength and/or a signal-to-noise ratio. However, if multiple user devices are selecting frequency layers based on the same criteria, then the multiple user devices may select the same frequency layer, which may exceed the capacity of the selected frequency layer. The base station could redirect one or more of the user devices to other frequency layers, but this would increase the signaling load and handover failure rates within the network.

To reduce the number of user devices on a same frequency layer, the user devices may randomly select a frequency layer via which to communicate with the base station. The random selection may be weighted toward selecting the frequency layer with the highest priority and/or quality. The user devices may, or example, randomly select a candidate frequency layer which is different than a primary frequency layer, the primary frequency layer having a highest priority and/or channel quality. This randomization may allow for a more efficient distribution of user devices within cells.

The user devices may then determine a probability of selecting the randomly selected candidate frequency layer instead of the current frequency layer, which, if the frequency layer has not been changed from the primary frequency layer, is the primary frequency layer. The probability may be based on a difference in preference for the primary frequency layer and the candidate frequency layer (if the frequency layer has previously been changed from the primary frequency layer, then the probability may be based on a difference in preference for the current frequency layer, to which the frequency layer was changed, and the candidate frequency layer) ； the preferences may be based on priorities of the frequency layers or measured qualities of the frequency layers, such as received power or signal strength.

If the primary frequency layer and the candidate frequency layer have a same priority, then the probability of selecting the candidate frequency layer may be based on a difference between a quality of the primary frequency layer, such as a received power measurement of the primary frequency layer, and a quality of the candidate frequency layer, such as a received power measurement of the candidate frequency layer. If the primary frequency layer and the candidate frequency layer have di fferent priorities, then the probability of selecting the candidate frequency layer may be based on a difference between a priority of the primary frequency layer and a priority of the candidate frequency layer. The probability may also be based on a “network temperature, ” according to which higher network temperatures lead to a greater likelihood of selecting a candidate frequency layer instead of the current frequency layer (which may be the primary frequency layer or may have been changed from the primary frequency layer) , and lower network temperatures lead to a lesser likelihood of selecting a candidate frequency layer instead of the current frequency layer.

After determining the probability of selecting the candidate frequency layer, the user devices may determine whether to select the candidate frequency layer based on the determined probability. The user devices may, for example, determine whether to select the candidate frequency layer by generating a random number and comparing the random number to the determined probability. If the user device does determine to select the candidate frequency layer, then the user device may select the candidate frequency layer, communicate with the base station via the candidate frequency layer, and pause for a predetermined period of time before considering whether to select a new frequency layer again. If the user device determines not to select the candidate frequency layer, then the user device may select a new candidate frequency layer, determine a probability of selecting the candidate frequency layer, and determine whether to select the candidate frequency layer based on the determined probability. According to an example embodiment, the selection of the frequency layer via which to communicate with the base station may be performed by the user device while the user device is in an idle mode.

FIG. 1 is a diagram of a cellular network according to an example embodiment. In this example, the cellular network may include

multiple cells

106A, 106B, 106C. Each

cell

106A, 106B, 106C may be served by a

base station

104A, 104B, 104C. User devices 102A, 102B, 102C may communicate with a backhaul network (not shown) via the

base stations

104A, 104B, 104C. The user devices 102A, 102B, 102C may communicate with the backhaul network via a

base station

104A, 104B, 104C serving a

cell

106A, 106B, 106C that the user device 102A, 102B, 102C is located in, or via a

nearby cell

106A, 106B, 106C, such as a neighboring

cell

106A, 106B, 106C. For ease of references, user devices will be referred to generically hereinafter as user devices 102, base stations will be referred to generically hereafter as base stations 104, and cells will be referred to generically hereinafter as cells 106.

The cellular network of FIG. 1 may be considered a wireless network. The user devices 102, which may also be referred to as mobile stations (MSs) and/or user equipments (UEs) , may be connected (and in communication) with a base station (BS) 104, which may also be referred to as an access node or an enhanced Node B (eNB) . The base stations 104 may each provide wireless coverage within their respective cell 106. Although only two user devices 102A, 102B are shown within cell 106A (connected or attached to base station 104A) , any number of user devices may be provided. The base stations 104 mays also connected to a core network and/or backhaul network, such as via a base station-core network (BS-core network) . This is merely one simple example of a wireless network, and others may be used. At least part of the functionalities of a base station or (e) Node B (eNB) may be also be carried out by any node, server or host which may be operably coupled to a transceiver, such as a remote radio head.

According to an example implementation, a user device 102 (user terminal, user equipment (UE) ) may refer to a portable computing device that includes wireless mobile communication devices operating with or without a subscriber identification module (SIM) , including, but not limited to, the following types of devices: a mobile station (MS) , a mobile phone, a cell phone, a smartphone, a personal digital assistant (PDA) , a handset, a device using a wireless modem (alarm or measurement device, etc. ) , a laptop and/or touch screen computer, a tablet, a phablet, a game console, a notebook, and/or a multimedia device, as examples. It should be appreciated that a user device may also be a nearly exclusive uplink only device, of which an example is a camera or video camera loading images or video clips to a network. While Long-term Evolution (LTE) and/or Long-term Evolution Advanced (LTE-A) may be used as an example herein, the various implementations or techniques described herein may be applied to a 5G wireless network or other wireless networks.

FIG. 2 is a timing diagram showing communication between a user device 102 and a base station 104 according to an example embodiment. In this example, the user device 102 may receive system information 202 from the base station 104. The user device 102 may receive the system information 202 upon powering on within a cell 106 served by the base station 104, or upon entering the cell 106 served by the base station 104. The system information 202 may be broadcast to all user devices 102 within the cell 106 served by the base station 104, and/or to all user devices 102 for which a signal strength of the system information 202 is sufficient for the user devices 102 to receive and successfully decode the system information 202.

The system information 202 may include parameters such as priorities of frequency layers for communicating with the base station 104. The system information 202 may, for example, include priority levels of frequency layers such as a priority level of a primary frequency layer and a priority level of a candidate frequency layer (described below) in one or more cellReselectionPriority cell reselection parameters broadcast by the base station 104 to the user device 102 in a SystemInformation message. The priorities of the frequency layers may have been decided by an operator of the network. The frequency layers may include carrier frequencies and/or frequency bands via which the user device 102 may communicate with the base station 104. According to an example embodiment, the system information 202 may also include physical frequency layer information of the cell 106 for the user device 102 to receive further system information, information for the user device 102 to evaluate whether the user device is allowed to access a cell and may define scheduling, common and shared channel information, cell re-selection information, information about the serving frequency and intra-frequency neighboring cells relevant for cell re-selection, information about other frequencies and inter-frequency neighboring cells relevant for cell-reselection, information about frequencies and neighboring cells relevant for cell re-selection, information about frequencies relevant for cell-reselection, a home base station name, a primary notification, a secondary notification, a warning notification, multimedia broadcast multicast service-related information, information about access control, information related to mobility procedures, information related to time, information relevant for traffic steering, information related to direct communication, and/or information related to direct recovery.

Upon and/or after receiving the system information 202 from the base station 104, the user device 102 may enter the network in idle mode (204) . During the idle mode, the user device 102 may not exchange voice or other data with the base station 104,

After entering the network in idle mode (204) , the user device 102 may select a frequency layer (206) for communicating with the base station 104. The selection of the frequency layer (206) is shown and described in further detail with respect to FIG. 3.

FIG. 3 is a flowchart showing a method for selecting a frequency layer according to an example embodiment. In this example, the method may include the user device 102 determining a primary frequency layer (302) . The primary frequency layer may be a frequency layer that has a highest priority based on the system information 202 that the user device 102 received from the base station 104, according to an example embodiment. According to another example embodiment, the primary frequency layer may be determined based on a frequency layer 1 cell search procedure, such as the search procedures described in 3GPP TS 36.213: EUTRA； Physical frequency layer procedures, ” and/or 3GPP TS 36.214: “E-UTRA； Physical frequency layer； Measurements. ”

Once the primary frequency layer has been determined (302) , the user device 102 may select a candidate frequency layer (304) . The user device 102 may select the candidate frequency layer (304) randomly among available frequency layers other than the primary frequency layer. The user device 102 may, for example, make a list of available frequency layers other than the primary frequency layer, and randomly select one of the frequency layers in the list. The user device 102 may make the list periodically. The period between making lists may be the same whether the candidate frequency layer (s) has a same priority as the primary frequency layer, or may be longer or shorter depending on whether the candidate frequency layer (s) has the same priority as the primary frequency layer.

The available frequency layers included in the list may include, for example, all suitable cells which may include cells 106 on which a user device 102 may camp. In an example embodiment, these suitable cells may be those cells which meet the criteria described in subclause 4.3 of 3GPP TS 36.304 version 12.3.0 Release 12, such as those cells which are part of either a selected Public Land Mobile Network (PLMN) , a registered PLMN, or a PLMN of an equivalent PLMN list； for a closed subscriber group (CSG) , the cell is a CSG member cell for the user device 102； and/or according to the latest information provided by a non-access stratum (NAS) , the cell is not barred as indicated by the system information 202, the cell 106 is not part of a list of forbidden tracking areas for roaming, and/or the cell selection criteria of subclause 5.2.3.2 of 3GPP TS 36.304 version 12.3.0 Release 12 are ful filled. In another example embodiment, the available frequency layers included in the list may include those frequency layers for which there is a cell 106 in which a cell selection quality value (Squal) meets or exceeds a predetermined threshold, and/or a cell selection receive (RX) level value meets or exceeds a predetermined threshold value.

After selecting the candidate frequency layer (304) , the user device 102 may determine whether a priority level of the primary frequency layer is the same as a priority level of the candidate frequency layer (306) . The user device 102 may have received the priority levels of the primary frequency layer and the candidate frequency layer from the base station 104 in the system information 202.

If the priority levels of the primary frequency layer and the candidate frequency layer are the same, then the user device 102 may determine the probability of selecting the candidate frequency layer based on a difference in quality between the primary frequency layer and the candidate frequency layer. The user device 102 may determine the quality of the primary frequency layer and the quality of the candidate frequency layer by performing measurements in the primary frequency layer and the candidate frequency layer (308) . The measurements (308) may be performed either before or after the selecting (304) and/or determining (306) . The user device 102 may measure the primary frequency layer and the candidate frequency layer (308) by, for example, measuring a received signal strength and/or a received power at each of the primary frequency layer and the candidate frequency layer, measuring a signal-to-noise ratio at each of the primary frequency layer and the candidate frequency layer, or measuring a signal-to-interference-and-noise ratio at each of the primary frequency layer and the candidate frequency layer, any of which may be based on a best cell for the particular frequency layer as defined in subclause 5.2.4.6 of 3GPP TS 36.304 version 12.3.0 Release 12.

After measuring the frequency layers (308) , the user device 102 may determine a probability of changing frequency layers and/or selecting the candidate frequency layer based on a di fference in the measurements (310) . A greater di fference in the measurements may imply a lower probability of selecting the candidate frequency layer, and a higher network temperature may imply a higher probability of selecting the candidate frequency layer. In an example embodiment, the probability P of selecting the candidate frequency layer may be determined based on the following equation:

P＝exp (-Delta_{frequency layer}/ (K_R*T))

where Delta_{frequency layer} is equal to the difference between the quality of the primary frequency layer (or possibly the current frequency layer i f the frequency layer has previously been changed from the primary frequency layer) and the quality of the candidate frequency layer, KR may be a factor received by the user device 102 from the base station 104 such as in the system information 202, and T may be the network temperature and may be a factor received by the user device 102 from the base station 104 such as in the system information 202. The factor K_R and/or network temperature T may be determined by the base station 104 to determine how spread out the frequency layers of the user devices 102 (high network temperature T and/or low K_R) and/or how clustered the selected frequency layers will be around an optimal and/or high quality frequency layer (high K_R and/or low network temperature T) .

FIG. 4A is a diagram showing frequency layers and cell qualities according to an example embodiment. As shown in FIG. 4A, a first cell 401A may be associated with the primary frequency layer 402A, a second cell 403A may be associated with the candidate frequency layer 404A, and any other cell (s) 405A may be associated with other frequency layer (s) 408A that were not selected as the candidate frequency layer 404A. As shown in FIG. 4A, a difference 406A between the primary frequency layer 402A and the candidate frequency layer 404A may be based on their respective cell qualities, and may be used to determine the probability of selecting the candidate frequency layer, as described above.

Returning to FIG. 3, i f the priority level of the primary frequency layer is not the same as the priority level of the candidate frequency layer, then the user device 102 may determine the probability based on a difference in the priority levels of the primary frequency layer and the candidate frequency layer (312) . In an example embodiment, higher priority levels imply that a frequency layer is more likely to be selected. In another example embodiment, lower priority levels may imply that a frequency layer is more likely to be selected. A greater difference in the priority levels may imply a lower probability of selecting the candidate frequency layer, and a higher network temperature may imply a higher probability of selecting the candidate frequency layer. In an example embodiment, the probability P of selecting the candidate frequency layer may be determined based on the following equation:

P＝ exp (-Diff_{frequency layer}/ (K_P*T))

where Diff_{frequency layer} is equal to the di fference between the priority level of the primary frequency layer (or possibly the current frequency layer if the frequency layer has previously been changed from the primary frequency layer) and the priority level of the candidate frequency layer, K_P may be a factor received by the user device 102 from the base station 104 such as in the system information 202, and T may be the network temperature. The factor KP and/or network temperature T may be determined by the base station 104 to determine how spread out the frequency layers of the user devices 102 (high network temperature T and/or low K_P) and/or how clustered the selected frequency layers will be around an optimal and/or high priority frequency layer (high K_P and/or low network temperature T) .

FIG. 4B is a diagram showing frequency layers and priority levels according to an example embodiment. As shown in FIG. 4B, a first frequency layer 401B may be associated with the primary frequency layer 402B, a second frequency layer 403B may be associated with the candidate frequency layer 404B, and any other cell (s) 405B may be associated with other frequency layer (s) 408B that were not selected as the candidate frequency layer 404A. As shown in FIG. 4B, a difference 406B between the primary frequency layer 402B and the candidate frequency layer 404B may be based on their respective priority levels, and may be used to determine the probability of selecting the candidate frequency layer, as described above. While FIG. 4B shows an example in which frequency layers with higher priority values are more likely to be selected, in another example, frequency layers with lower priority values may be more likely to be selected.

Returning to FIG. 3, after the user device 102 has determined the probability of selecting the candidate frequency layer (310, 312) , the user device 102 may determine whether to select the candidate frequency layer based on the determined priority. In an example embodiment, the user device 102 may determine whether to select the candidate frequency layer by generating a random number (314) . In an example in which the determined probability must be between zero (0.0) and one (1.0) , the user device 102 may generate a random number between zero (0.0) and one (1.0) .

The user device 102 may determine whether to change frequency layer (316) and/or select the candidate frequency layer based on the generated random number. In an example embodiment, i f the generated random number is less than or equal to the determined probability, then the user device 102 may change frequency layer and/or select the candidate frequency layer, and i f the generated random number is greater than the determined probability, then the user device may not change the frequency layer and/or may not select the candidate frequency layer.

If the user device 102 does not change frequency layer and/or select the candidate frequency layer, then the user device 102 may continue selecting candidate frequency layers (304) until changing frequency layers. If the user device 102 does change frequency layer, then the user device 102 may pause (318) , such as by waiting Tprohibit seconds, before selecting another candidate frequency layer (304) to change frequency layers.

Returning to FIG. 2, after selecting the frequency layer (206) via which to communicate with the base station 104, the user device 102 may send a connection request 208 to the base station 104. The user device 102 may send the connection request 208 to the base station 104 via the frequency layer selected in (206) . The base station 104 may respond to the connection request message 208 by sending a connection setup message 210 to the user device 102 via the frequency layer selected in (206) . The user device 102 may respond to the connection setup message 210 by sending a setup complete message 212 to the base station 104 via the frequency layer selected in (206) . After the user device 102 has sent the setup complete message 212 to the base station 104, the user device 102 and the base station 104 may communicate (214) via the frequency layer selected in (206) . The user device 102 may, for example, leave the idle mode and/or enter an active mode when making a random access request to the base station 104.

FIG. 5 is a flowchart showing a method 500 of selecting a frequency layer by a user device according to an example embodiment. According to this example, the method 500 may comprise determining a primary frequency layer for communicating with a base station (502) . The method 500 may further comprise randomly selecting a candidate frequency layer for communicating with the base station (504) . The method 500 may further comprise determining a probability of selecting the candidate frequency layer, the probability being based on a di fference between a preference for the primary frequency layer and a preference for the candidate frequency layer (506) . The method 500 may further comprise determining whether to select the candidate frequency layer based on the determined probability (508) . The method 500 may further comprise, if it is determined to select the candidate frequency layer, selecting the candidate frequency layer and communicating with the base station via the candidate frequency layer (510) .

According to an example embodiment, the determining the primary frequency layer (502) may include determining a frequency layer currently selected by the user device as the primary frequency layer.

According to an example embodiment, the determining the primary frequency layer (502) may include determining the primary frequency layer based on receiving a priority level of the primary frequency layer from the base station.

According to an example embodiment, the determining the primary frequency layer (502) may include determining the primary frequency layer based on a best cell among one or more frequency layers with a highest priority, the priority of the one or more frequency layers being received by the user device from the base station.

According to an example embodiment, the primary frequency layer may include a first carrier frequency and the candidate frequency layer may include a second carrier frequency.

According to an example embodiment, the probability may be based on the di fference between the preference for the primary frequency layer and the preference for the candidate frequency layer, and a network temperature.

According to an example embodiment, the preference for the primary frequency layer may be based on a received power measurement performed by the user device via the primary frequency layer and the preference for the candidate frequency layer may be based on a received power measurement performed by the user device via the candidate frequency layer.

According to an example embodiment, the preference for the primary frequency layer may be based on a received power measurement performed by the user device on a best cell in the primary frequency layer, and the preference for the candidate frequency layer may be based on a received power measurement performed by the user device on a best cell in the candidate frequency layer.

According to an example embodiment, the preference for the primary frequency layer may be based on a priority level of the primary frequency layer received by the user device from the base station, and the preference for the candidate frequency layer may be based on a priority level of the candidate frequency layer received by the user device from the base station.

According to an example embodiment, the preference for the primary frequency layer may be based on a priority level of the primary frequency layer broadcast by the base station and received by the user device, and the preference for the candidate frequency layer may be based on a priority level of the candidate frequency layer broadcast by the base station and received by the user device.

According to an example embodiment, if a priority level of the primary frequency layer is the same as a priority level of the candidate frequency layer, the preference for the primary frequency layer may be based on a received power measurement performed by the user device via the primary frequency layer, and the preference for the candidate frequency layer may be based on a received power measurement performed by the user device via the candidate frequency layer. In this example, if the priority level of the primary frequency layer is different than the priority level of the candidate frequency layer, the preference for the primary frequency layer may be based on the priority level of the primary frequency layer and the preference for the candidate frequency layer may be based on the priority level of the candidate frequency layer.

According to an example embodiment, if a priority level of the primary frequency layer is the same as a priority level of the candidate frequency layer, the probability may be based on exp (-Delta_{frequency layer}/ (K_R*T)) , wherein Delta_{frequency layer} is based on a di fference between a received power measurement performed by the user device via the primary frequency layer and a received power measurement performed by the user device via the candidate frequency layer, KR is received by the user device from the base station, and T is received by the user device from the base station. In this example, if the priority level of the primary frequency layer is different than the priority level of the candidate frequency layer, the probability may be based on exp (-Diff_{frequency layer}/ (K_P*T) ) , wherein Diff_frequency _layer is based on a di fference between the priority level of the primary frequency layer and the priority level of the candidate frequency layer, KP is received by the user device from the base station, and T is received by the user device from the base station.

According to an example embodiment, the priority level of the primary frequency layer may be received by the user device from the base station and the priority level of the candidate frequency layer may be received by the user device from the base station.

According to an example embodiment, the priority level of the primary frequency layer and the priority level of the candidate frequency layer may be broadcast by the base station to the user device.

According to an example embodiment, the priority level of the primary frequency layer and the priority level of the candidate frequency layer may be included in one or more cellReselectionPriority cell reselection parameters broadcast by the base station to the user device in a SystemInformation message.

According to an example embodiment, the determining whether to select the candidate frequency layer (508) may include generating a random number and comparing the random number to the determined probability.

According to an example embodiment, the randomly selecting the candidate frequency layer (504) , determining the probability (506) , and determining whether to select the candidate frequency layer (508) may be performed repeatedly until it is determined to select the candidate frequency layer (510) .

According to an example embodiment, the method 500 may further include pausing after selecting the candidate frequency layer, and continuing to perform the randomly selecting the candidate frequency layer (504) , determining the probability (506) , and determining whether to select the candidate frequency layer (508) repeatedly until it is again determined to select the candidate frequency layer (510) .

According to an example embodiment, if it is determined not to select the candidate frequency layer, the method may further include communicating with the base station via the primary frequency layer.

According to an example embodiment, the method 500 may be performed while the user device is in an idle mode.

FIG. 6 is a diagram showing a user device 102 according to an example embodiment. The user device 102 may include, for example, two RF (radio frequency) or

wireless transceivers

602A, 602B, where each wireless transceiver includes a transmitter to transmit signals and a receiver to receive signals. The user device 102 also includes a processor or control unit/entity (controller) 604 to execute instructions or software and control transmission and receptions of signals, and a memory 606 to store data and/or instructions.

Processor 604 may also make decisions or determinations, generate frames, packets or messages for transmission, decode received frames or messages for further processing, and other tasks or functions described herein. Processor 604, which may be a baseband processor, for example, may generate messages, packets, frames or other signals for transmission via wireless transceiver 602 (602A or 602B) . Processor 604 may control transmission of signals or messages over a wireless network, and may control the reception of signals or messages, etc. , via a wireless network (e.g., after being down-converted by wireless transceiver 602, for example) . Processor 604 may be programmable and capable of executing software or other instructions stored in memory 606 or on other computer media to perform the various tasks and functions described above, such as one or more of the tasks or methods described above. Processor 604 may be (or may include) , for example, hardware, programmable logic, a programmable processor that executes software or firmware, and/or any combination of these. Using other terminology, processor 604 and transceiver 602 together may be considered as a wireless transmitter/receiver system, for example.

In addition, referring to FIG. 6, a controller (or processor) 608 may execute software and instructions, and may provide overall control for the user device 102, and may provide control for other systems not shown in FIG. 6, such as controlling input/output devices (e.g., display, keypad) , and/or may execute software for one or more applications that may be provided on user device 102, such as, for example, an email program, audio/video applications, a word processor, a Voice over IP application, or other application or software.

In addition, a storage medium may be provided that includes stored instructions, which when executed by a controller or processor may result in the processor 604, or other controller or processor, performing one or more of the functions or tasks described above.

According to another example implementation, RF or wireless transceiver (s) 602A/602B may receive signals or data and/or transmit or send signals or data. Processor 604 (and possibly transceivers 602A/602B) may control the RF or

wireless transceiver

602A or 602B to receive, send, broadcast or transmit signals or data.

According to an example embodiment, the user device 102 may include means for (602A, 602B, 604, 606, 608) determining a primary frequency layer for communicating with a base station, means for (602A, 602B, 604, 606, 608) randomly selecting a candidate frequency layer for communicating with the base station, means for (602A, 602B, 604, 606, 608) determining a probability of selecting the candidate frequency layer, the probability being based on a di fference between a preference for the primary frequency layer and a preference for the candidate frequency layer, means for (602A, 602B, 604, 606, 608) determining whether to select the candidate frequency layer based on the determined probability, and, if it is determined to select the candidate frequency layer, means for (602A, 602B, 604, 606, 608) selecting the candidate frequency layer and communicating with the base station via the candidate frequency layer.

According to an example embodiment, the means for (602A, 602B, 604, 606, 608) determining the primary frequency layer may include means for (602A, 602B, 604, 606, 608) determining a frequency layer currently selected by the user device as the primary frequency layer.

According to an example embodiment, the means for (602A, 602B, 604, 606, 608) determining the primary frequency layer may include means for (602A, 602B, 604, 606, 608) determining the primary frequency layer based on receiving a priority level of the primary frequency layer from the base station.

According to an example embodiment, the means for (602A, 602B, 604, 606, 608) determining the primary frequency layer may include means for (602A, 602B, 604, 606, 608) determining the primary frequency layer based on a best cell among one or more frequency layers with a highest priority, the priority of the one or more frequency layers being received by the user device from the base station.

According to an example embodiment, i f a priority level of the primary frequency layer is the same as a priority level of the candidate frequency layer, the preference for the primary frequency layer may be based on a received power measurement performed by the user device via the primary frequency layer, and the preference for the candidate frequency layer may be based on a received power measurement performed by the user device via the candidate frequency layer. In this example, if the priority level of the primary frequency layer is different than the priority level of the candidate frequency layer, the preference for the primary frequency layer may be based on the priority level of the primary frequency layer and the preference for the candidate frequency layer may be based on the priority level of the candidate frequency layer.

According to an example embodiment, if a priority level of the primary frequency layer is the same as a priority level of the candidate frequency layer, the probability may be based on exp (-Delta_{frequency layer}/ (K_R*T)) , wherein Delta_{frequency layer} is based on a di fference between a received power measurement performed by the user device via the primary frequency layer and a received power measurement performed by the user device via the candidate frequency layer, KR is received by the user device from the base station, and T is received by the user device from the base station. In this example, i f the priority level of the primary frequency layer is di fferent than the priority level of the candidate frequency layer, the probability may be based on exp (-Diff_{frequency layer}/ (K_P*T) ) , wherein Diff_frequency _layer is based on a di fference between the priority level of the primary frequency layer and the priority level of the candidate frequency layer, K_P is received by the user device from the base station, and T is received by the user device from the base station.

According to an example embodiment, the means for (602A, 602B, 604, 606, 608) determining whether to select the candidate frequency layer may include means for (602A, 602B, 604, 606, 608) generating a random number and comparing the random number to the determined probability.

According to an example embodiment, the user device 102 may include means for (602A, 602B, 604, 606, 608) randomly selecting the candidate frequency layer, determining the probability, and determining whether to select the candidate frequency layer repeatedly until it is determined to select the candidate frequency layer.

According to an example embodiment, the user device 102 may include means for (602A, 602B, 604, 606, 608) pausing after selecting the candidate frequency layer, and continuing to perform the randomly selecting the candidate frequency layer, determining the probability, and determining whether to select the candidate frequency layer repeatedly until it is again determined to select the candidate frequency layer.

According to an example embodiment, i f it is determined not to select the candidate frequency layer, the user device 102 may include means for (602A, 602B, 604, 606, 608) communicating with the base station via the primary frequency layer.

According to an example embodiment, the user device 102 may include means for (602A, 602B, 604, 606, 608) performing the above functions, processes, and/or methods while the user device 102 is in an idle mode.

Implementations of the various techniques described herein may be implemented in digital electronic circuitry, or in computer hardware, firmware, software, or in combinations of them. Implementations may implemented as a computer program product, i.e., a computer program tangibly embodied in an information carrier, e.g., in a machine-readable storage device, for execution by, or to control the operation of, data processing apparatus, e.g., a programmable processor, a computer, or multiple computers. A computer program, such as the computer program (s) described above, can be written in any form of programming language, including compiled or interpreted languages, and can be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. A computer program can be deployed to be executed on one computer or on multiple computers at one site or distributed across multiple sites and interconnected by a communication network.

Method steps may be performed by one or more programmable processors executing a computer program to perform functions by operating on input data and generating output. Method steps also may be performed by, and an apparatus may be implemented as, special purpose logic circuitry, e.g., an FPGA (field programmable gate array) or an ASIC (application-speci fic integrated circuit) .

Processors suitable for the execution of a computer program include, by way of example, both general and special purpose microprocessors, and any one or more processors of any kind of digital computer. Generally, a processor will receive instructions and data from a read-only memory or a random access memory or both. Elements of a computer may include at least one processor for executing instructions and one or more memory devices for storing instructions and data. Generally, a computer also may include, or be operatively coupled to receive data from or trans fer data to, or both, one or more mass storage devices for storing data, e.g., magnetic, magneto-optical disks, or optical disks. Information carriers suitable for embodying computer program instructions and data include all forms of non-volatile memory, including by way of example semiconductor memory devices, e.g., EPROM, EEPROM, and flash memory devices； magnetic disks, e.g., internal hard disks or removable disks； magneto-optical disks； and CD-ROM and DVD-ROM disks. The processor and the memory may be supplemented by, or incorporated in special purpose logic circuitry.

To provide for interaction with a user, implementations may be implemented on a computer having a display device, e.g., a cathode ray tube (CRT) or liquid crystal display (LCD) monitor, for displaying information to the user and a keyboard and a pointing device, e.g., a mouse or a trackball, by which the user can provide input to the computer. Other kinds of devices can be used to provide for interaction with a user as well； for example, feedback provided to the user can be any form of sensory feedback, e.g., visual feedback, auditory feedback, or tactile feedback； and input from the user can be received in any form, including acoustic, speech, or tactile input.

Implementations may be implemented in a computing system that includes a back-end component, e.g., as a data server, or that includes a middleware component, e.g., an application server, or that includes a front-end component, e.g., a client computer having a graphical user interface or a Web browser through which a user can interact with an implementation, or any combination of such back-end, middleware, or front-end components. Components may be interconnected by any form or medium of digital data communication, e.g., a communication network. Examples of communication networks include a local area network (LAN) and a wide area network (WAN) , e.g., the Internet.

While certain features of the described implementations have been illustrated as described herein, many modifications, substitutions, changes and equivalents will now occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modi fications and changes as fall within the true spirit of the embodiments of the invention.

Claims

A method of selecting a frequency layer by a user device, the method comprising:

determining a primary frequency layer for communicating with a base station；

randomly selecting a candidate frequency layer for communicating with the base station；

determining a probability of selecting the candidate frequency layer, the probability being based on a difference between a preference for the primary frequency layer and a preference for the candidate frequency layer；

determining whether to select the candidate frequency layer based on the determined probability； and

if it is determined to select the candidate frequency layer, selecting the candidate frequency layer and communicating with the base station via the candidate frequency layer.
The method of claim 1, wherein the determining the primary frequency layer includes determining a frequency layer currently selected by the user device as the primary frequency layer.
The method of claim 1 or 2, wherein the determining the primary frequency layer includes determining the primary frequency layer based on receiving a priority level of the primary frequency layer from the base station.
The method of claim 1, 2, or 3, wherein the determining the primary frequency layer includes determining the primary frequency layer based on a best cell among one or more frequency layers with a highest priority, the priority of the one or more frequency layers being received by the user device from the base station.
The method of any of claims 1 through 4, wherein the primary frequency layer includes a first carrier frequency and the candidate frequency layer includes a second carrier frequency.
The method of any of claims 1 through 5, wherein the probability is based on:

the difference between the preference for the primary frequency layer and the preference for the candidate frequency layer； and

a network temperature.
The method of any of claims 1 through 6, wherein:

the preference for the primary frequency layer is based on a received power measurement performed by the user device via the primary frequency layer； and

the preference for the candidate frequency layer is based on a received power measurement performed by the user device via the candidate frequency layer.
The method of any of claims 1 through 6, wherein:

the preference for the primary frequency layer is based on a received power measurement performed by the user device on a best cell in the primary frequency layer； and

the preference for the candidate frequency layer is based on a received power measurement performed by the user device on a best cell in the candidate frequency layer.
The method of any of claims 1 through 6, wherein:

the preference for the primary frequency layer is based on a priority level of the primary frequency layer received by the user device from the base station； and

the preference for the candidate frequency layer is based on a priority level of the candidate frequency layer received by the user device from the base station.
The method of any of claims 1 through 6, wherein:

the preference for the primary frequency layer is based on a priority level of the primary frequency layer broadcast by the base station and received by the user device； and

the preference for the candidate frequency layer is based on a priority level of the candidate frequency layer broadcast by the base station and received by the user device.
The method of any of claims 1 through 6, wherein: if a priority level of the primary frequency layer is the same as a priority level of the candidate frequency layer:

the preference for the primary frequency layer is based on a received power measurement performed by the user device via the primary frequency layer； and

the preference for the candidate frequency layer is based on a received power measurement performed by the user device via the candidate frequency layer； and

if the priority level of the primary frequency layer is different than the priority level of the candidate frequency layer, the preference for the primary frequency layer is based on the priority level of the primary frequency layer and the preference for the candidate frequency layer is based on the priority level of the candidate frequency layer.
The method of any of claims 1 through 6, wherein:

if a priority level of the primary frequency layer is the same as a priority level of the candidate frequency layer, the probability is based on exp (-Delta_{frequency layer}/ (K_R*T)) , wherein Delta_{frequency layer} is based on a difference between a received power measurement performed by the user device via the primary frequency layer and a received power measurement performed by the user device via the candidate frequency layer, K_R is received by the user device from the base station, and T is received by the user device from the base station； and

if the priority level of the primary frequency layer is different than the priority level of the candidate frequency layer, the probability is based on exp (-Di ff_{frequency layer}/ (K_P *T)) , wherein Diff_{frequency layer} is based on a difference between the priority level of the primary frequency layer and the priority level of the candidate frequency layer, K_P is received by the user device from the base station, and T is received by the user device from the base station.
The method of any of claims 11 or 12, wherein the priority level of the primary frequency layer is received by the user device from the base station and the priority level of the candidate frequency layer is received by the user device from the base station.
The method of either of claims 11 or 12, wherein the priority level of the primary frequency layer and the priority level of the candidate frequency layer are broadcast by the base station to the user device.
The method of either of claims 11 or 12, wherein the priority level of the primary frequency layer and the priority level of the candidate frequency layer are included in one or more cellReselectionPriority cell reselection parameters broadcast by the base station to the user device in a SystemInformation message.
The method of any of claims 1 through 15, wherein the determining whether to select the candidate frequency layer includes generating a random number and comparing the random number to the determined probability.
The method of any of claims 1 through 16, wherein the randomly selecting the candidate frequency layer, determining the probability, and determining whether to select the candidate frequency layer are performed repeatedly until it is determined to select the candidate frequency layer.
The method of claim 17, wherein the method further comprises:

pausing after selecting the candidate frequency layer； and continuing to perform the randomly selecting the candidate frequency layer, determining the probability, and determining whether to select the candidate frequency layer are performed repeatedly until it is again determined to select the candidate frequency layer.
The method of any of claims 1 through 18, wherein if it is determined not to select the candidate frequency layer, the method further comprises communicating with the base station via the primary frequency layer.
The method of any of claims 1 through 19, wherein the method is performed while the user device is in an idle mode.
A non-transitory computer-readable storage medium comprising instructions stored thereon that, when executed by at least one processor, are configured to cause a user device to perform the method of any of claims 1 through 20.
A user device configured to perform the method of any of claims 1 through 20.
A user device comprising:

a transceiver configured to send and receive signals；

at least one processor controlling the transceiver； and

at least one memory device comprising instructions stored thereon that, when executed by the at least one processor, are configured to cause the user device to perform the method of any of claims 1 through 20.
A user device comprising means for performing the method of any of claims 1 through 20.