Abstract:
A method of beacon detection performed by a small cell device includes: exchanging beacon parameters with a user equipment (UE); entering a low power mode after exchanging the beacon parameters with the UE; receiving, from the UE, a beacon in a random access channel (RACH) preamble containing the beacon parameters while in the low power mode; entering a high power mode in response to receiving the beacon; and associating with the UE while in the high power mode. The method of beacon detection allows a small cell device to transition from a low power mode to a high power mode in an efficient manner. The transmission may be triggered by a user equipment that is entering a service area of the small cell device.

Description:
BACKGROUND 
     1. Field 
     The disclosure relates generally to wireless systems and methods, and, in particular, to systems and methods for beacon detection. 
     2. Background 
     Wireless communication systems are widely deployed to provide various types of communication content such as, for example, voice, data, and so on. Typical wireless communication systems may be multiple-access systems capable of supporting communication with multiple users by sharing available system resources (e.g., bandwidth, transmit power, etc.). Examples of such multiple-access systems may include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, orthogonal frequency division multiple access (OFDMA) systems, and the like. Additionally, the systems can conform to specifications such as third generation partnership project (3GPP), 3GPP long-term evolution (LTE), ultra mobile broadband (UMB), evolution data optimized (EV-DO), etc. 
     Generally, wireless multiple-access communication systems may simultaneously support communication for multiple mobile devices. Each mobile device may communicate with one or more access points via transmissions on forward and reverse links. The forward link (or downlink) refers to the communication link from access points to mobile devices, and the reverse link (or uplink) refers to the communication link from mobile devices to access points. Further, communications between mobile devices and access points may be established via single-input single-output (SISO) systems, multiple-input single-output (MISO) systems, multiple-input multiple-output (MIMO) systems, and so forth. In addition, mobile devices can communicate with other mobile devices (and/or access points with other access points) in peer-to-peer wireless network configurations. 
     To supplement conventional access points, additional restricted access points can be deployed to provide more robust wireless coverage to mobile devices. For example, wireless relay stations and low power access points (e.g., which can be commonly referred to as Home NodeBs or Home eNBs, collectively referred to as H(e)NBs, femto access points, femtocells, picocells, microcells, etc.) can be deployed for incremental capacity growth, richer user experience, in-building or other specific geographic coverage, and/or the like. In some configurations, such low power access points can be connected to the Internet via broadband connection (e.g., digital subscriber line (DSL) router, cable or other modem, etc.), which can provide the back haul link to the mobile operator&#39;s network. Thus, for example, the low power access points can be deployed in user homes or enterprise environment to provide mobile network access to one or more devices via the broadband connection. 
     In such heterogeneous networks, it is often challenging for a mobile device and a nearby access point, such as a small cell, to detect each other. One challenge lies in that there is an incentive for the small cell to remain in power-save mode for extended periods when there are no mobile devices in the coverage area of the small cell. Detection, and therefore communication, between the devices (e.g., when the mobile device returns to the coverage area) is limited while the small cell is in the power-save mode. One prior solution is for the small cell to transmit low-power beacons so that the mobile device can detect the presence of the small cell in power-save mode. 
     SUMMARY 
     A method of beacon detection performed by a small cell device includes, but is not limited to, any one or combination of: (i) exchanging beacon parameters with a user equipment (UE); (ii) entering a low power mode after exchanging the beacon parameters with the UE; (iii) receiving, from the UE, a beacon in a random access channel (RACH) preamble containing the beacon parameters while in the low power mode; (iv) entering a high power mode in response to receiving the beacon; and (v) associating with the UE while in the high power mode. 
     In various embodiments, the beacon parameters are exchanged with the user equipment while in the high power mode. 
     In various embodiments, in the low power mode, a listening component of the small cell device for receiving the beacon is activated and a transceiver of the small cell device for receiving data packets is deactivated. In the high power mode, the listening component of the small cell device is activated and the transceiver of the small cell device is activated. 
     In various embodiments, the small cell device enters the low power mode when the UE is not in coverage of the small cell device. 
     In various embodiments, the small cell device is a femtocell unit. 
     In various embodiments, the associating comprises performing a subsequent RACH procedure to complete cell reselection. 
     A method of beacon transmission performed by a user equipment includes, but is not limited to, any one or combination of: (i) exchanging beacon parameters with a small cell device; (ii) detecting presence of the small cell device; (iii) transmitting, in response to the detecting, a beacon in a random access channel (RACH) preamble containing the beacon parameters to the small cell device; and (iv) associating with the small cell device. 
     In various embodiments, the presence of the small cell device is detected while the small cell device is in a low power mode. The parameters are exchanged with the user equipment while the small cell device is a high power mode. The user equipment is associated with the small cell device while the small cell device is in the high power mode. 
     In various embodiments, the associating comprises performing a subsequent RACH procedure to complete cell reselection. 
     In various embodiments, the presence of the small cell device is detected via at least one of a neighborhood map, out-of-band signaling, and position estimation. 
     A method of beacon detection performed by a small cell device includes, but is not limited to, any one or combination of: (i) exchanging beacon parameters with a user equipment (UE); (ii) transmitting the beacon parameters to a neighboring cell device; (iii) entering a low power mode after exchanging the beacon parameters with the UE; (iv) receiving a notification from the neighboring cell device in response to the neighboring cell receiving, from the UE, a beacon in a random access channel (RACH) preamble containing the beacon parameters while in the low power mode; (v) entering a high power mode in response to receiving the notification; and (vi) associating with the UE while in the high power mode. 
     In various embodiments, the neighboring cell device comprises a small cell device. 
     In various embodiments, the neighboring cell device comprises a macro cell device. 
     In various embodiments, the notification is received via a backhaul to the small cell device. 
     In various embodiments, the beacon parameters are exchanged with the UE while in the high power mode. 
     In various embodiments, in the low power mode, a listening component of the small cell device for receiving the notification is activated and a transceiver of the small cell device for receiving data packets is deactivated. In the high power mode, the listening component of the small cell device is activated and the transceiver of the small cell device is activated. 
     In various embodiments, the small cell device enters the low power mode when the UE is not in coverage of the small cell device. 
     In various embodiments, the small cell device is a femtocell unit. 
     In various embodiments, the associating comprises performing a subsequent RACH procedure to complete cell reselection. 
     A method of beacon transmission performed by a user equipment includes, but is not limited to, any one or combination of: (i) exchanging beacon parameters with a small cell device; (ii) detecting presence of the neighboring cell device associated with the small cell device; (iii) transmitting, in response to the detecting, a beacon in a random access channel (RACH) preamble containing the beacon parameters to the neighboring cell device; and (iv) associating with the small cell device. 
     In various embodiments, the presence of the neighboring cell device is detected while the small cell device is in a low power mode. The parameters are exchanged with the user equipment while the small cell device is a high power mode. The user equipment is associated with the small cell device while the small cell device is in the high power mode. 
     In various embodiments, the associating comprises performing a subsequent RACH procedure to complete cell reselection. 
     In various embodiments, the presence of the small cell device is detected via at least one of a neighborhood map, out-of-band signaling, and position estimation. 
     A method of beacon detection performed by a small cell device includes, but is not limited to, any one or combination of: exchanging beacon parameters with a user equipment (UE); transmitting the beacon parameters to a first neighboring cell device; entering a low power mode after exchanging the beacon parameters with the UE; receiving, while in the low power mode, at least one of (i) a beacon in a random access channel (RACH) message containing an identifier of the small cell, and (ii) a notification from the first neighboring cell device in response to the neighboring cell device detecting a beacon in a RACH message from the UE containing an identifier of the small cell device; entering a high power mode in response to receiving the second notification; and associating with the UE while in the high power mode. 
     In various embodiments, the RACH message includes an identifier for the small cell device. 
     In some embodiments, the identifier comprises a SRNC-ID. 
     In various embodiments, the notification is received from the neighboring cell device to which the UE transmitted the RACH message. 
     In various embodiments, the notification is received from a different neighboring cell device to which the UE transmitted the RACH message. 
     In various embodiments, the at least one of the neighboring cell devices comprises a small cell device. 
     In various embodiments, the at least one of the neighboring cell devices comprises a macro cell device. 
     In various embodiments, the notification is received via a backhaul to the small cell device. 
     In various embodiments, the high power mode uses more power than the low power mode. 
     In various embodiments, the beacon parameters are exchanged with the UE while in the high power mode. 
     A method of beacon detection transmission by a user equipment includes, but is not limited to, any one or combination of: (i) exchanging beacon parameters with a small cell device; (ii) detecting presence of a neighboring cell device; (iii) transmitting, in response to detecting the neighboring cell device, a beacon in a random access channel (RACH) message containing the beacon parameters; and (iv) associating with the small cell device. 
     In various embodiments, the RACH message is transmitted to the detected neighboring cell device. 
     In various embodiments, the RACH message includes an identifier for the small cell device. 
     In various embodiments, the identifier comprises a serving radio network control identifier (SRNC-ID). 
     In various embodiments, the presence is detected while the small cell device is in a low power mode. The parameters are exchanged with the user equipment while the small cell device is a high power mode. The user equipment is associated with the small cell device while the small cell device is in the high power mode. 
     In some embodiments, the high power mode uses more power than the low power mode. 
     In various embodiments, the associating comprises performing a subsequent RACH procedure to complete cell reselection. 
     In various embodiments, the presence of the small cell device is detected via at least one of a neighborhood map, out-of-band signaling, and position estimation. 
     An apparatus for beacon detection includes, but is not limited to, any one or combination of: means for exchanging beacon parameters with a user equipment (UE); means for entering a low power mode after exchanging the beacon parameters with the UE; means for receiving, from the UE, a beacon in a random access channel (RACH) preamble containing the beacon parameters while in the low power mode; means for entering a high power mode in response to receiving the beacon; and means for associating with the UE while in the high power mode. 
     An apparatus for beacon detection includes, but is not limited to, a processor configured for: exchanging beacon parameters with a user equipment (UE); entering a low power mode after exchanging the beacon parameters with the UE; receiving, from the UE, a beacon in a random access channel (RACH) preamble containing the beacon parameters while in the low power mode; entering a high power mode in response to receiving the beacon; and associating with the UE while in the high power mode. 
     A computer program product for beacon detection includes, but is not limited to, a computer-readable storage medium comprising code for: exchanging beacon parameters with a user equipment (UE); entering a low power mode after exchanging the beacon parameters with the UE; receiving, from the UE, a beacon in a random access channel (RACH) preamble containing the beacon parameters while in the low power mode; entering a high power mode in response to receiving the beacon; and associating with the UE while in the high power mode. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of an illustrative hardware configuration for an apparatus employing a processing system according to various embodiments of the disclosure. 
         FIG. 2  illustrates a wireless communication system according to various embodiments of the disclosure. 
         FIG. 3A  illustrates a communication system to enable deployment of Home Node Bs (HNBs) within a network environment according to various embodiments of the disclosure. 
         FIGS. 3B-3C  illustrate network environments according to various embodiments of the disclosure. 
         FIG. 4A-4B  are block diagrams illustrating a small cell unit and a user equipment according to according to various embodiments of the disclosure. 
         FIGS. 5A-5B  illustrate a method according to various embodiments of the disclosure. 
         FIGS. 6A-6B  illustrate a method according to various embodiments of the disclosure. 
         FIG. 7  illustrates a method according to various embodiments of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Various embodiments relate to systems and methods for detection of a beacon from a mobile device (user equipment (UE)) by a base station, such as a small cell (e.g., femtocell, picocell, etc.). In particular, systems and methods relate to detecting UE beacons that implement existing RACH preambles and messages. In some embodiments, the UE discovers its proximity to the target small cell. The UE may then transmit a RACH preamble aimed at the target small cell using previously negotiated configuration parameters. The target small cell may detect the preamble and change from a power-save mode to a high-power mode. The UE may subsequently associate with the target cell. In some embodiments, cooperation strategies between neighboring small cells (and optionally neighboring macrocells) may be implemented such that the RACH transmissions from the UE to the target cell may be detected by the neighboring cells. The target small cell may then change its power mode upon being notified by the neighboring small cells. In some embodiments, the UE is configured to send a RACH message to neighboring cells using a cell-specific ID for the target small cell to trigger the power-mode change. 
     The word “example” or “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any embodiment described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments. The techniques described herein may be used for various wireless communication networks such as Code Division Multiple Access (CDMA) networks, Time Division Multiple Access (TDMA) networks, Frequency Division Multiple Access (FDMA) networks, Orthogonal Frequency Division Multiplexing (OFDM) networks, Single-Carrier FDMA (SCFDMA) networks, etc. The terms “networks” and “systems” are often used interchangeably. A CDMA network may implement a radio technology such as Universal Terrestrial Radio Access (UTRA), cdma2000, etc. UTRA includes Wideband-CDMA (W-CDMA) and Low Chip Rate (LCR) TD-SCDMA. cdma2000 covers IS-2000, IS-95, and IS-856 standards. A TDMA network may implement a radio technology such as Global System for Mobile Communications (GSM). An OFDM network may implement a radio technology such as Evolved UTRA (E-UTRA), IEEE 802.11, IEEE 802.16, IEEE 802.20, Flash-OFDM®, etc. UTRA, E-UTRA, and GSM are part of Universal Mobile Telecommunication System (UMTS). Long Term Evolution (LTE) is an advanced release of UMTS that uses E-UTRA. UTRA, E-UTRA, GSM, UMTS, and LTE are described in documents from an organization named “3rd Generation Partnership Project” (3GPP). cdma2000 is described in documents from an organization named “3rd Generation Partnership Project 2” (3GPP2). These various radio technologies and standards are known in the art. 
       FIG. 1  is a block diagram of an illustrative hardware configuration for an apparatus  100  employing a processing system  114  according to various embodiments of the disclosure, including (but not limited to) the embodiments of  FIGS. 2-7 . In this example, the processing system  114  may be implemented with a bus architecture represented generally by bus  102 . The bus  102  may include any number of interconnecting buses and bridges depending on the specific application of the processing system  114  and the overall design constraints. The bus  102  links together various circuits including one or more processors, represented generally by the processor  104 , and computer-readable media, represented generally by the computer-readable medium  106 . The bus  102  may also link various other circuits such as timing sources, peripherals, voltage regulators, and power management circuits, which are well known in the art, and therefore, will not be described any further. A bus interface  108  provides an interface between the bus  102  and a transceiver  110 . The transceiver  110  allows for communicating with various other apparatus over a transmission medium. Depending upon the nature of the apparatus, a user interface  112  (e.g., keypad, display, speaker, microphone, joystick, etc.) may also be provided. 
     A processor  104  is responsible for managing the bus  102  and general processing, including the execution of software stored on computer-readable storage medium  106 . The software, when executed by the processor  104 , causes the processing system  114  to perform the various functions described in the disclosure for any particular apparatus. The computer readable storage medium  106  may also be used for storing data that is manipulated by the processor  104  when executing software. 
       FIG. 2  illustrates a wireless communication system  200  configured to support a number of users according to various exemplary embodiments of the disclosure, including (but not limited to) the embodiments of  FIGS. 3A-7 . As shown in  FIG. 2 , by way of example, the system  200  provides communication for multiple cells, such as, for example, macrocells  202   a - 202   g  (referred to as macrocell(s)  202 ), with each macrocell  202  being serviced by a corresponding base station, such as base stations  204   a - 204   g  (referred to as base station(s)  204 ), also known variously as Node Bs (NBs), eNode Bs (eNBs), etc. Each of the macrocells  202  may be further divided into two or more sectors. Each of the base stations  204  may be suitably coupled to a core network (not illustrated), enabling information to be passed between the various base stations  204  and, in some examples, to the Internet. Various mobile stations, including mobile stations  206   a - 206   l  (referred to as mobile station(s)  206 ), also known variously as access terminals (AT), user equipment (UE), etc., are dispersed throughout the system  200 . Each of the mobile stations  206  may communicate with one or more base stations  204  on a downlink (DL) and/or an uplink (UL) at a given moment, depending upon whether the base station  206  is active and whether it is in soft handoff, for example. The wireless communication system  200  may provide service over a large geographic region; for example, macrocells  202  may cover a few blocks in a neighborhood. In another example, the macrocells  202  may include or be replaced by smaller cells (i.e., having a smaller geographic service area) such as microcells or picocells. In particular embodiments, the wireless communication system  200  may include femtocells with even smaller and more specific geographic coverage areas. 
     In general, when a mobile station  206  is switched on, a public land mobile network (PLMN) is selected and the mobile station  206  searches for a suitable cell of this PLMN to camp on. Criteria for cell selection and cell re-selection between radio access technologies (RATs) generally depend on various radio criteria. In addition to the RAT, the PLMN type may differ as well. The mobile station  206  searches for a suitable cell of the selected PLMN and chooses that cell to provide available services, and tunes to its control channel. This choosing is known as “camping on the cell.” The mobile station  206  will, if necessary, then register its presence in the registration area of the chosen cell and as the outcome of a successful Location Registration the selected PLMN becomes the registered PLMN. 
     If the mobile station  206  finds a more suitable cell, the mobile station  206  reselects onto that cell and camps on it. If the new cell is in a different registration area, location registration is performed. If necessary, the mobile station  206  may search for higher priority PLMNs at regular time intervals and search for a suitable cell if another PLMN has been selected. 
       FIG. 3A  illustrates a communication system  300  to enable deployment of Home Node Bs (HNBs) within a network environment according to various embodiments of the disclosure, including (but not limited to) the embodiments of  FIGS. 1, 2, and 3B-7 . As shown in  FIG. 3A , the system  300  includes a small cell device  310 , such as a femtocell unit or other small-cell unit, such as a picocell unit, microcell unit, or the like, installed in a corresponding small scale network environment  330 , such as, for example, in one or more user residences, and being configured to serve associated user equipment(s) (UE(s))  320   a ,  320   b , referred to as UE(s)  320 . The femtocell unit  310  may be coupled to Internet  340  by way of a backhaul connection  335 , for example, a cable or DSL connection. The femtocell unit  310  is further communicatively coupled to a mobile operator core network  350  via the Internet  340  utilizing suitable communication hardware and software. Further, the femtocell unit  310  may be communicatively coupled to one or more macrocell base stations  360 . In particular embodiments, the femtocell unit may utilize a network listen component  370  for sniffing an air interface broadcasted by one or more of the macrocell base stations  360 . 
     Although some of the embodiments described herein below use 3GPP terminology, it is to be understood that the embodiments may be applied to 3GPP technology, as well as 3GPP2 technology and other known and related technologies. In such embodiments described herein, the owner of the femtocell unit  310  subscribes to a mobile service, such as, for example, 3G or 4G-LTE mobile service from a provider, offered through the mobile operator core network  350 , and the UE  320  may operate both in macrocellular environment and in a residential small-scale network environment  330 . Thus, the femtocell unit  310  may be backward compatible with any existing UE  320 . 
       FIGS. 3B and 3C  illustrate exemplary network environments. For example, in  FIG. 3B , the UE  320  is in a coverage area (network environment)  330  of the small cell device (SCD)  310 , thereby allowing communication between the devices. As another example, in  FIG. 3C , the UE  320  is outside the coverage area  330  of the small cell device  310  or is otherwise unable to communicate with the UE  320  (e.g., the small cell device  310  is in a power-save mode having reduced transmission/receiving capabilities). In such embodiments, for example, the UE  320  may communicate with one or more neighboring cell devices (e.g., NCD1, NCD2)  380 . One or more of the neighboring cell devices  380  may be a small cell device (e.g., femtocell unit, picocell unit, microcell unit, etc.). One or more of the neighboring cell devices  380  may be a macro base station (e.g., a macro base station, such as the mobile operator core network  350  in  FIG. 3A ). 
       FIG. 4A  illustrates a small cell unit, such as the femtocell unit  310  according to according to various embodiments of the disclosure, including (but not limited to) the embodiments of  FIGS. 1-3C and 4B-7 . In  FIG. 4A , a number of blocks are labeled as processors or controllers. Those skilled in the art will comprehend that each of these processors may be implemented as hardware processors such as the processor  104  (refer to  FIG. 1 ) or the processing system  114  (refer to  FIG. 1 ), or alternately, the functions performed by any number of the illustrated processors may be combined into and implemented by a single hardware processor. Further, the illustrated processors in  FIG. 4A  may represent functions to be implemented by processors, software, or the like. 
     With reference to  FIGS. 1-4A , in various embodiments, the network listen component  370  may be for neighboring cell device discovery, interference management, mobility management, and/or the like. In particular embodiments, the network listen component  370  may be for configuring the femtocell unit  310  and retrieving timing and frequency information for synchronization. The network listen component  370  may include a downlink receiver  371  and a receive processor  372  for receiving and measuring signal and interference levels on various available channels. The network listen component  370  may further utilize the receiver  371  and the receive processor  372  to acquire timing and frequency information from neighboring cells and decode broadcast messages from those cells for mobility and interference management purposes. For example, the network listen component  370  may achieve this by periodically scanning the surrounding cells. The femtocell unit  310  may further include wireless wide area network (WWAN) components including a wireless wide area network (WWAN) transceiver  311  and a WWAN processor  312 , and wireless personal area network (WPAN) components including a WPAN transceiver  313  and a WPAN processor  314 . Here, the WPAN components are optional, and may be utilized for low-power, out-of-band communication with a UE in proximity to the femtocell unit  310 . The femtocell unit  310  may further include a backhaul I/O unit  316  for facilitating communication with a modem  400 , which may be internal or external to the femtocell unit  310 , a controller/processor  315  for controlling and coordinating the various functionalities of the femtocell unit  310 , and a memory  317  for storing information for utilization by the controller/processor  315 . 
       FIG. 4B  illustrates a user equipment, such as the UE(s)  320  (according to according to various embodiments of the disclosure, including (but not limited to) the embodiments of  FIGS. 1-4A and 5-7 . In  FIG. 4B , a number of blocks are labeled as processors or controllers. Those skilled in the art will comprehend that each of these processors may be implemented as hardware processors such as the processor  104  (refer to  FIG. 1 ) or the processing system  114  (refer to  FIG. 1 ), or alternately, the functions performed by any number of the illustrated processors may be combined into and implemented by a single hardware processor. Further, the illustrated processors in  FIG. 4B  may represent functions to be implemented by processors, software, or the like. 
     With reference to  FIGS. 1-4B , the UE  320  may include a WWAN transceiver  420  and WWAN processor  430 . The UE  320  may include a WPAN transceiver  440  and a WPAN processor  450 . Accordingly, the UE  320  may be configured to establish a WWAN link and/or a WPAN link with the femtocell unit  310 . Further, the UE  320  may include an I/O  470  for accepting user input, for example, from a keypad (not illustrated) and providing output, for example, to a display (not illustrated). Further, the UE  320  may include a controller/processor  460  for controlling the various functions of the UE  320 , and a memory  480  for storing information for use by the controller/processor  460 . 
     In various embodiments, operation of the femtocell unit  310  (or other small cell device) is controlled based on a proximity indication by the UE  320 , for example, through a periodic beacon transmitted by the UE  320 . In general, the femtocell unit  310  is in a power-save mode (or low power mode) when the UE  320  is not in the coverage area of the femtocell unit  310 . When the UE  320  is in proximity of the femtocell unit  310 , the femtocell unit  310  may detect the beacon (or be notified by a neighboring cell device that the beacon has been detected), enter a high-power mode, and serve the UE  320 . By having the UE  320  transmit the beacons, the femtocell unit  310  may remain in the power-save mode until the beacons are detected. This is in contrast to conventional systems in which the femtocell unit  310  remains in the high-power mode (i.e., remains on) and transmits beacons to the UE  320  for detection by the UE  320 . 
     In particular embodiments, RACH preambles (or RACH messages) may be implemented as beacons. Such embodiments are advantageous in that existing signaling mechanisms (RACH preambles and messages) are being reused for the purpose of proximity detection (beaconing). 
       FIG. 5A  illustrates a method of beacon detection B 500  according to various embodiments of the disclosure. With reference to  FIGS. 1-5A , the method B 500  may be implemented by one or more of the small cell device  310  and/or the UE  320  (e.g., in the processing system  100  of the small cell device  310  and/or the UE  320 ). 
     At block B 510 , the small cell device  310  and the UE  320  exchange RACH beacon-related information (e.g., refer to  FIG. 3B ). There are several parameters transmitted from the small cell device  310  to the UE  320  in broadcast messages (e.g., in a system information block type 5 (SIB5) message in UMTS). The parameters are used by the UE  320  to send RACH preambles and RACH messages to the small cell device  310 . The parameters may include one or more of (but are not limited to) access slots, preamble scramble codes, preamble signatures, spreading factor for data part, available signatures and sub-channels for each Access Service Class (ASC), power control information, etc. 
     At block B 520 , the small cell device  310  goes into a power-save mode (or first mode or low power mode), for instance, when the UE  320  is no longer in a coverage area of the small cell device  310 . In the power-save mode, a RACH sniffing module, such as the network listening component  370 , of the small cell device  310  remains activated to receive or otherwise detect a RACH beacon (e.g., RACH preamble). In the power-save mode, other forms of reception and/or transmission may be disabled. 
     At block B 530 , upon, for example, reentering the coverage area of the small cell device  310 , the UE  320  may detect proximity to the small cell device  310  via a neighborhood map or any other suitable manner for detecting the small cell device  310  (e.g., out-of-band (OOB) signaling, position estimation, etc.). 
     At block B 540 , for instance in response to the proximity detection of the small cell device  310 , the UE  320  sends a RACH preamble (beacon) to the small cell device  310  with the beacon-related information exchanged at block B 510 . The UE  320  may send the RACH preamble designated for beaconing, for instance, without detecting a downlink pilot signal from the small cell device  310 . 
     At block B 550 , for instance in response to receiving the beacon, the small cell device  310  enters a high-power mode (or second mode), and the UE  320  associates with the small cell device  310 . After the small cell device  310  enters the high-power mode, a subsequent RACH procedure may be initiated to complete cell reselection. 
     The method B 500  described in  FIG. 5A  above may be performed by various hardware and/or software component(s) and/or module(s) corresponding to the means-plus-function blocks B 500 ′ illustrated in  FIG. 5B . In other words, blocks B 510  through B 540  illustrated in  FIG. 5A  correspond to means-plus-function blocks B 510 ′ through B 540 ′ illustrated in  FIG. 5B . 
       FIG. 6A  illustrates a method of beacon detection B 600  according to various embodiments of the disclosure. With reference to  FIGS. 1-6A , the method B 600  may be implemented by one or more of the small cell device  310  and/or the UE  320  (e.g., in the processing system  100  of the small cell device  310  and/or the UE  320 ). 
     At block B 610 , the small cell device  310  and the UE  320  exchange RACH beacon-related information (e.g., refer to  FIG. 3B ). There are several parameters transmitted from the small cell device  310  to the UE  320  in broadcast messages (e.g., in SIB5 message in UMTS). The parameters are used by the UE  320  to send RACH preambles and RACH messages to the small cell device  310 . The parameters may include (but are not limited to) access slots, preamble scramble code, preamble signatures, spreading factor for data part, available signatures and sub-channels for each Access Service Class (ASC), power control information, etc. 
     At block B 620 , the small cell device  310  exchanges the beacon-related information with one or more of the neighboring cell devices  380 . In addition, the small cell device  310  may notify the neighboring cell devices  380  that the small cell device  310  is transitioning to a power-save mode. 
     At block B 630 , the small cell device  310  goes into the power-save mode (or first mode or low power mode), for instance, when the UE  320  is no longer in a coverage area of the small cell device  310  (e.g., refer to  FIG. 3C ). In some embodiments, while in the power-save mode, the neighboring cell devices  380  may perform RACH sniffing (e.g., via respective network listening components  370 ) to detect the UE  320  identified in the beacon-related information. In some embodiments, in the power-save mode, the small cell device  310  may continue operating the network listening component  370  to receive or otherwise detect a notification from the neighboring cell devices  380 . In the power-save mode, other forms of reception and/or transmission may be disabled. In other embodiments, the small cell device  310  may receive the notification via the backhaul  335  or the like. 
     At block B 640 , upon, for example, reentering the coverage area  330  of the small cell device  310  or the coverage area of the neighboring cell devices  380  (e.g., refer to  FIG. 3C ), the UE  320  may detect proximity to the small cell device  310  and/or the neighboring cell devices  380  via a neighborhood map or any other suitable manner for detecting the small cell device  310  (e.g., out-of-band (OOB) signaling, position estimation, etc.). 
     At block B 650 , for instance in response to the proximity detection, the UE  320  transmits a RACH preamble (beacon) with the beacon-related information exchanged between the UE  320  and the small cell device  310  at block B 610 , which was also exchanged between the small cell device  310  and the neighboring cell devices  380  at block B 620 . For instance, the RACH may be for uplink data transmission, cell update, RRC connection request, and/or the like. 
     At block B 660 , for instance in response to detection of the beacon from the UE  320 , one or more of the neighboring cell devices  380  notifies the small cell device  310 . 
     At block B 670 , for instance in response to receiving the notification, the small cell device  310  enters a high-power mode (or second mode), and the UE  320  associates with the small cell device  310 . After the small cell device  310  enters the high-power mode, a subsequent RACH procedure may be initiated to complete cell reselection. 
     Because such embodiments include multiple small cell devices performing RACH sniffing, probability of detecting presence of the UE  320  increases. In addition, an area over which the presence of the UE  320  can be detected is increased. As a result, the presence of the UE  320  can be detected earlier, allowing the small cell device  310  to enter the high-power mode earlier. Accordingly, by the time the UE  320  enters the coverage of the small cell device  310 , the small cell device  310  may have entered the high-power mode and started transmitting overhead channels for detection and reselection by the UE, thus lowering handover latency. 
     The method B 600  described in  FIG. 6A  above may be performed by various hardware and/or software component(s) and/or module(s) corresponding to the means-plus-function blocks B 600 ′ illustrated in  FIG. 6B . In other words, blocks B 610  through B 640  illustrated in  FIG. 6A  correspond to means-plus-function blocks B 610 ′ through B 640 ′ illustrated in  FIG. 6B . 
     With reference to  FIGS. 1-7 , in various embodiments, a beacon-detection method may include the UE  320  transmitting a RACH message as a beacon. The RACH message may be received by one or more of the neighboring cell devices  380 .  FIG. 7  illustrates such a method of beacon detection B 700  according to various embodiments of the disclosure. With reference to  FIGS. 1-7 , the method B 700  may be implemented by one or more of the small cell device  310  and/or the UE  320  (e.g., in the processing system  100  of the small cell device  310  and/or the UE  320 ). 
     At block B 710 , the small cell device  310  and the UE  320  exchange RACH beacon-related information (e.g., refer to  FIG. 3B ). There are several parameters transmitted from the small cell device  310  to the UE  320  in broadcast messages (e.g., in SIB5 message in UMTS). The parameters are used by the UE  320  to send RACH preambles and RACH messages to the small cell device  310 . The parameters may include (but are not limited to) access slots, preamble scramble code, preamble signatures, spreading factor for data part, available signatures and sub-channels for each Access Service Class (ASC), power control information, etc. 
     At block B 720 , the small cell device  310  exchanges the beacon-related information with one or more of the neighboring cell devices  380 . In addition, the small cell device  310  may notify the neighboring cell devices  380  that the small cell device  310  is transitioning to a power-save mode. The neighboring cell devices  380 , for example, may include a first neighboring cell device  381 . In some embodiments, at least one of the neighboring cell devices  380  may include a second neighboring cell device  382  that did not exchange the beacon-related information with the small cell device  310  or is otherwise not implementing the cooperative method B 700 . 
     The small cell device  310  may share this information with the neighboring cell devices  380  during neighbor discovery. For instance, in some embodiments, the small cell device  310  may inform the neighboring cell devices  380  that the small cell device  310  of its intent to participate in the method of B 700  (or the like) via a pre-defined field in its cell broadcast information. In another embodiment, the small cell device  310 , before going into the power-save mode, may send inquiries to all or a subset of the neighboring cell devices  380  about their intent to participate in such a method. 
     At block B 730 , the small cell device  310  goes into a power-save mode (or first mode), for instance, when the UE  320  is no longer in the coverage area  330  of the small cell device  310 . In some embodiments, while in the power-save mode, one or more of the neighboring cell devices  380  may perform RACH sniffing (e.g., via respective network listening components  370 ) to detect the UE  320 . In some embodiments, in the power-save mode, the small cell device  310  may continue operating the network listening component  370  to receive or otherwise detect a RACH beacon (e.g., RACH message) and/or a notification from the other small cell devices. In the power-save mode, other forms of reception and/or transmission may be disabled. In other embodiments, the small cell device  310  may receive the notification via the backhaul  335  or the like. 
     At block B 740 , upon, for example, reentering the coverage area of the small cell device  310  or the coverage area of the neighboring cell devices  380 , the UE  320  may detect proximity to the small cell device  310  and/or the neighboring cell devices  380  via a neighborhood map or any other suitable manner for detecting the small cell device  310  (e.g., out-of-band (OOB) signaling, position estimation, etc.). 
     At block B 750 , for instance in response to the proximity detection, the UE  320  sends a RACH message to at least one of the neighboring cell devices  380 , such as the first neighboring cell device  381 . For example, the UE  320  may send the RACH message to the neighboring cell device  380  with which the UE  320  is currently associated (e.g., the first neighboring cell device  381 ). 
     The RACH message may be a cell update message with a unique identifier of the small cell device  310  or the like. For example, the unique identifier may be a serving radio network control identifier (SRNC-ID) in UTRAN Radio Network Temporary Identifier (U-RNTI). 
     In some embodiments, at block B 760 , for instance in response to receiving the RACH message (beacon) from the UE  320 , the first neighboring cell device  381  notifies the small cell device  310  (based on the unique identifier in the RACH message) of the presence of the UE  320 . This may occur, for example, if the neighboring cell device (e.g., the first neighboring cell device  381 ) to which to UE  320  sends the RACH message (e.g., as in block B 750 ) is implementing the cooperative method B 700  (e.g., as in block B 720 ). Accordingly, the first neighboring cell device  381 , for example, may request the small cell device  310  to enter a high-power mode. 
     In other embodiments, at block B 770 , for instance in response to sniffing the RACH message (beacon) from the UE  320 , the first neighboring cell device  381  notifies the small cell device  310  (based on the unique identifier in the RACH message) of the presence of the UE  320 . This may occur, for example, if the neighboring cell device (e.g., the second neighboring cell device  382 ) to which to UE  320  sends the RACH message (e.g., as in block B 750 ) is not is implementing the cooperative method B 700  (e.g., as in block B 720 ). The second neighboring cell device  382  may reject the RACH message from the UE  320 , but the first neighboring cell device  381  may sniff the RACH message. Accordingly, the first neighboring cell device  382 , for example, may request the small cell device  310  to enter a high-power mode. 
     In yet other embodiments, at block B 780 , the small cell device  310  may sniff the RACH message, for example via the network listening component  370 , and detect its unique identifier, such as the SRNC-ID or the like. This may occur, for example, if the neighboring cell device (e.g., the second neighboring cell device  382 ) to which to UE  320  sends the RACH message (e.g., as in block B 750 ) is not is implementing the cooperative method B 700  (e.g., as in block B 720 ). The second neighboring cell device  382  may reject the RACH message from the UE  320 , but the small cell device  310  may sniff the RACH message. 
     At block B 790 , for instance in response to receiving the notification (e.g., block B 760  or block B 770 ) or sniffing the RACH message (e.g., block B 780 ), the small cell device  310  enters the high-power mode. Accordingly, the UE  320  may associate with the small cell device  310 . 
     Because such embodiments include multiple small cell devices performing RACH sniffing, probability of detecting presence of the UE  320  increases. In addition, an area over which the presence of the UE  320  can be detected is increased. As a result, the presence of the UE  320  can be detected earlier, allowing the small cell device  310  to enter the high-power mode earlier. Accordingly, by the time the UE  320  enters the coverage of the small cell device  310 , the small cell device  310  may have entered the high-power mode and started transmitting overhead channels for detection and reselection by the UE, thus lowering system latency. 
     In various embodiments, the small cell device  310  and the UE  320  may select a subset of the parameters to use as part of the beaconing method (e.g., B 500 , B 600 , B 700 , etc.). For instance, in particular embodiments, the small cell device  310  and the UE  320  may select a subset of preamble signatures for use as beaconing. Typically, in UMTS, a UE may choose one of sixteen preamble signatures during preamble transmission. However, in some embodiments, the UE may choose from fifteen preamble signatures and select one (or other number of) preamble signature for beaconing purposes only. Accordingly, when in a power-save mode (as discussed in the disclosure), the small cell device  310  need only search for the selected preamble signature and not the other fifteen preamble signatures. 
     In various embodiments, the small cell device  310  and/or one or more of the neighboring cell devices  380  are configured to coordinate a schedule for allowing the cell devices to enter power-save mode. 
     It is understood that the specific order or hierarchy of steps in the processes disclosed is an example of exemplary approaches. Based upon design preferences, it is understood that the specific order or hierarchy of steps in the processes may be rearranged while remaining within the scope of the present disclosure. The accompanying method claims present elements of the various steps in a sample order, and are not meant to be limited to the specific order or hierarchy presented. 
     Those of skill in the art would understand that information and signals may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof. 
     Those of skill would further appreciate that the various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present disclosure. 
     The various illustrative logical blocks, modules, and circuits described in connection with the embodiments disclosed herein may be implemented or performed with a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general-purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration. 
     The steps of a method or algorithm described in connection with the embodiments disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. An exemplary storage medium is coupled to the processor such the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor. The processor and the storage medium may reside in an ASIC. The ASIC may reside in a user terminal. In the alternative, the processor and the storage medium may reside as discrete components in a user terminal. 
     In one or more exemplary embodiments, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium. Computer-readable media includes both computer storage media and communication media including any medium that facilitates transfer of a computer program from one place to another. A storage media may be any available media that can be accessed by a computer. By way of example, and not limitation, such computer-readable media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to carry or store desired program code in the form of instructions or data structures and that can be accessed by a computer. In addition, any connection is properly termed a computer-readable medium. For example, if the software is transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of medium. Disk and disc, as used herein, includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk and blu-ray disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media. 
     The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present disclosure. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the disclosure. Thus, the present disclosure is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.