Patent Description:
Aspects of the present disclosure relate generally to wireless communication systems, and more particularly, to discovery and synchronization channels for user-tracking zones in a cellular network.

Research and development continue to advance not only to meet the growing demand for mobile broadband access, but to advance and enhance the user experience with mobile communications.

Patent application <CIT> relates to physical layer processing and procedures for device-to-device (D2D) discovery signal generation and transmission and scheduling of D2D discovery signals. Detection and measurement of a D2D discovery signal, D2D signal identity management, and monitoring by a wireless transmit/receive unit (WTRU) of PDCCH for D2D discovery scheduling is described, as is a WTRU that may be configured with a D2D-specific transmission/reception opportunity pattern.

The detailed description set forth below, in connection with the appended drawings, is intended as a description of various possible configurations and is not intended to limit the scope of the disclosure.

This disclosure relates generally to providing or participating in authorized shared access between two or more wireless communications systems, also referred to as wireless communications networks. In various embodiments, the techniques and apparatus may be used for wireless communication networks such as code division multiple access (CDMA) networks, time division multiple access (TDMA) networks, frequency division multiple access (FDMA) networks, orthogonal FDMA (OFDMA) networks, single-carrier FDMA (SC-FDMA) networks, LTE networks, GSM networks, <NUM> networks as well as other communications networks. As described herein, the terms "networks" and "systems" may be used interchangeably.

A CDMA network may implement a radio technology such as universal terrestrial radio access (UTRA), cdma2000, and the like.

The <NUM>rd Generation Partnership Project (3GPP) defines standards for the GSM EDGE (enhanced data rates for GSM evolution) radio access network (RAN), also denoted as GERAN. GERAN is the radio component of GSM/EDGE, together with the network that joins the base stations (for example, the Ater and Abis interfaces) and the base station controllers (A interfaces, etc.). The radio access network represents a component of a GSM network, through which phone calls and packet data are routed from and to the public switched telephone network (PSTN) and Internet to and from subscriber handsets, also known as user terminals or user equipments (UEs). A mobile phone operator's network may comprise one or more GERANs, which may be coupled with the Universal Terrestrial Radio Access Network (UTRAN) that is a RAN defined as a part of the Universal Mobile Telecommunications System (UMTS), a <NUM> mobile phone technology supported by 3GPP. An operator network may also include one or more LTE networks, and/or one or more other networks. The various different network types may use different radio access technologies (RATs) and radio access networks (RANs).

UTRA, E-UTRA, and GSM are part of universal mobile telecommunication system (UMTS). 3GPP long term evolution (LTE) is a 3GPP project aimed at improving the universal mobile telecommunications system (UMTS) mobile phone standard. Certain aspects of the apparatus and techniques may be described below for LTE implementations or in an LTE-centric way, and LTE terminology may be used as illustrative examples in portions of the description below; however, the description is not intended to be limited to LTE applications. Indeed, the present disclosure is concerned with shared access to wireless spectrum between networks using different radio access technologies or radio air interfaces.

A new carrier type based on LTE/LTE-A including in unlicensed spectrum has also been suggested that can be compatible with carrier-grade WiFi, making LTE/LTE-A with unlicensed spectrum an alternative to WiFi. LTE/LTE-A, when operating in unlicensed spectrum, may leverage LTE concepts and may introduce some modifications to physical layer (PHY) and media access control (MAC) aspects of the network or network devices to provide efficient operation in the unlicensed spectrum and meet regulatory requirements. The unlicensed spectrum used may range from as low as several hundred Megahertz (MHz) to as high as tens of Gigahertz (GHz), for example. In operation, such LTE/LTE-A networks may operate with any combination of licensed or unlicensed spectrum depending on loading and availability. Accordingly, it may be apparent to one of skill in the art that the systems, apparatus and methods described herein may be applied to other communications systems and applications.

System designs may support various time-frequency reference signals for the downlink and uplink to facilitate beamforming and other functions. A reference signal is a signal generated based on known data and may also be referred to as a pilot, preamble, training signal, sounding signal, and the like. A reference signal may be used by a receiver for various purposes such as channel estimation, coherent demodulation, channel quality measurement, signal strength measurement, and the like. MIMO systems using multiple antennas generally provide for coordination of sending of reference signals between antennas; however, LTE systems do not in general provide for coordination of sending of reference signals from multiple base stations or eNBs.

In some implementations, a system may utilize time division duplexing (TDD). For TDD, the downlink and uplink share the same frequency spectrum or channel, and downlink and uplink transmissions are sent on the same frequency spectrum. The downlink channel response may thus be correlated with the uplink channel response. Reciprocity may allow a downlink channel to be estimated based on transmissions sent via the uplink. These uplink transmissions may be reference signals or uplink control channels (which may be used as reference symbols after demodulation). The uplink transmissions may allow for estimation of a space-selective channel via multiple antennas.

In LTE implementations, orthogonal frequency division multiplexing (OFDM) is used for the downlink - that is, from a base station, access point or eNodeB (eNB) to a user terminal or UE. Use of OFDM meets the LTE requirement for spectrum flexibility and enables cost-efficient solutions for very wide carriers with high peak rates, and is a well-established technology. For example, OFDM is used in standards such as IEEE <NUM>. 11a/g, <NUM>, High Performance Radio LAN-<NUM> (HIPERLAN-<NUM>, wherein LAN stands for Local Area Network) standardized by the European Telecommunications Standards Institute (ETSI), Digital Video Broadcasting (DVB) published by the Joint Technical Committee of ETSI, and other standards.

Time frequency physical resource blocks (also denoted here in as resource blocks or "RBs" for brevity) may be defined in OFDM systems as groups of transport carriers (e.g. sub-carriers) or intervals that are assigned to transport data. The RBs are defined over a time and frequency period. Resource blocks are comprised of time-frequency resource elements (also denoted here in as resource elements or "REs" for brevity), which may be defined by indices of time and frequency in a slot. Additional details of LTE RBs and REs are described in the 3GPP specifications, such as, for example, 3GPP TS <NUM>.

UMTS LTE supports scalable carrier bandwidths from <NUM> down to <NUM>. In LTE, an RB is defined as <NUM> sub-carriers when the subcarrier bandwidth is <NUM>, or <NUM> sub-carriers when the sub-carrier bandwidth is <NUM>. In an exemplary implementation, in the time domain there is a defined radio frame that is <NUM> long and consists of <NUM> subframes of <NUM> millisecond (ms) each. Every subframe consists of <NUM> slots, where each slot is <NUM>. The subcarrier spacing in the frequency domain in this case is <NUM>. Twelve of these subcarriers together (per slot) constitute an RB, so in this implementation one resource block is <NUM>. Six Resource blocks fit in a carrier of <NUM> and <NUM> resource blocks fit in a carrier of <NUM>.

<FIG> shows a wireless network <NUM> for communication, which may be an LTE-A network. The wireless network <NUM> includes a number of evolved node Bs (eNBs) <NUM> and other network entities. An eNB may be a station that communicates with the UEs and may also be referred to as a base station, a node B, an access point, and the like. Each eNB <NUM> may provide communication coverage for a particular geographic area. In 3GPP, the term "cell" can refer to this particular geographic coverage area of an eNB and/or an eNB subsystem serving the coverage area, depending on the context in which the term is used.

An eNB may provide communication coverage for a macro cell or a small cell, such as a pico cell or a femto cell, and/or other types of cell. An eNB for a small cell may be referred to as a small cell eNB, a pico eNB, a femto eNB or a home eNB. In the example shown in <FIG>, the eNBs 105a, 105b and 105c are macro eNBs for the macro cells 110a, 110b and 110c, respectively. The eNBs 105x, 105y, and 105z are small cell eNBs, which may include pico or femto eNBs that provide service to small cells 110x, 110y, and 110z, respectively. An eNB may support one or multiple (e.g., two, three, four, and the like) cells.

For synchronous operation, the eNBs may have similar frame timing, and transmissions from different eNBs may be approximately aligned in time. For asynchronous operation, the eNBs may have different frame timing, and transmissions from different eNBs may not be aligned in time.

The UEs <NUM> are dispersed throughout the wireless network <NUM>, and each UE may be stationary or mobile. A UE may also be referred to as a terminal, a mobile station, a subscriber unit, a station, or the like. A UE may be a cellular phone, a personal digital assistant (PDA), a wireless modem, a wireless communication device, a handheld device, a tablet computer, a laptop computer, a cordless phone, a wireless local loop (WLL) station, or the like. A UE may be able to communicate with macro eNBs, pico eNBs, femto eNBs, relays, and the like. In <FIG>, a lightning bolt (e.g., communication links <NUM>) indicates desired transmissions between a UE and a serving eNB, which is an eNB designated to serve the UE on the downlink and/or uplink, or desired transmission between eNBs.

LTE/-A utilizes orthogonal frequency division multiplexing (OFDM) on the downlink and single-carrier frequency division multiplexing (SC-FDM) on the uplink. OFDM and SC-FDM partition the system bandwidth into multiple (K) orthogonal subcarriers, which are also commonly referred to as tones, bins, or the like. Each subcarrier may be modulated with data. For example, K may be equal to <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> for a corresponding system bandwidth of <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM> megahertz (MHz), respectively. The system bandwidth may also be partitioned into sub-bands. For example, a sub-band may cover <NUM>, and there may be <NUM>, <NUM>, <NUM>, <NUM> or <NUM> sub-bands for a corresponding system bandwidth of <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM>, respectively.

<FIG> shows a block diagram of a design of a base station/eNB <NUM> and a UE <NUM>, which may be one of the base stations/eNBs and one of the UEs in <FIG>. For a restricted association scenario, the eNB <NUM> may be the small cell eNB 105z in <FIG>, and the UE <NUM> may be the UE 115z, which in order to access small cell eNB 105z, would be included in a list of accessible UEs for small cell eNB 105z. The eNB <NUM> may also be a base station of some other type. The eNB <NUM> may be equipped with antennas 234a through 234t, and the UE <NUM> may be equipped with antennas 252a through 252r.

At the eNB <NUM>, a transmit processor <NUM> may receive data from a data source <NUM> and control information from a controller/processor <NUM>. The control information may be for the PBCH, PCFICH, PHICH, PDCCH, etc. The data may be for the PDSCH, etc. The transmit processor <NUM> may process (e.g., encode and symbol map) the data and control information to obtain data symbols and control symbols, respectively. The transmit processor <NUM> may also generate reference symbols, e.g., for the PSS, SSS, and cell-specific reference signal. A transmit (TX) multiple-input multiple-output (MIMO) processor <NUM> may perform spatial processing (e.g., precoding) on the data symbols, the control symbols, and/or the reference symbols, if applicable, and may provide output symbol streams to the modulators (MODs) 232a through 232t. Downlink signals from modulators 232a through 232t may be transmitted via the antennas 234a through 234t, respectively.

At the UE <NUM>, the antennas 252a through 252r may receive the downlink signals from the eNB <NUM> and may provide received signals to the demodulators (DEMODs) 254a through 254r, respectively. A MIMO detector <NUM> may obtain received symbols from all the demodulators 254a through 254r, perform MIMO detection on the received symbols if applicable, and provide detected symbols.

On the uplink, at the UE <NUM>, a transmit processor <NUM> may receive and process data (e.g., for the PUSCH) from a data source <NUM> and control information (e.g., for the PUCCH) from the controller/processor <NUM>. The symbols from the transmit processor <NUM> may be precoded by a TX MIMO processor <NUM> if applicable, further processed by the modulators 254a through 254r (e.g., for SC-FDM, etc.), and transmitted to the eNB <NUM>. At the eNB <NUM>, the uplink signals from the UE <NUM> may be received by the antennas <NUM>, processed by the demodulators <NUM>, detected by a MIMO detector <NUM> if applicable, and further processed by a receive processor <NUM> to obtain decoded data and control information sent by the UE <NUM>. The processor <NUM> may provide the decoded data to a data sink <NUM> and the decoded control information to the controller/processor <NUM>.

The controllers/processors <NUM> and <NUM> may direct the operation at the eNB <NUM> and the UE <NUM>, respectively. The controller/processor <NUM> and/or other processors and modules at the eNB <NUM> may perform or direct the execution of various processes for the techniques described herein. The controllers/processor <NUM> and/or other processors and modules at the UE <NUM> may also perform or direct the execution of the functional blocks illustrated in <FIG>, <FIG>, <FIG>, and <FIG>, and/or other processes for the techniques described herein. The memories <NUM> and <NUM> may store data and program codes for the eNB <NUM> and the UE <NUM>, respectively.

Many of today's communication systems, such as third generation (<NUM>), fourth generation (<NUM>), and fifth generation (<NUM>) mobile networks provide services to mobile devices or user equipment (UEs) using a cellular or mobile network with a plurality of geographically distributed base stations or nodes. A node may include various different types of network communication entities, such as base stations, NodeBs, eNodeBs, remote radio heads (RRHs), access points, macro cells, small cells, and the like. As a UE moves in and around the nodes, it becomes important to track the location of the UE and determine which of the nodes will act as the serving node for the UE. Traditional approaches have mostly relied on the UE to take the primary responsibility for determining where the UE is topologically located in the network and to help select the serving node. These approaches typically place an expensive computational burden on the UE and often require the UE to exchange multiple messages with multiple nearby nodes before selecting the serving node. These exchanges place a significant burden on the power budget for the UE as well as the bandwidth of the network. In addition, the UE's choice of serving node may occur at the expense of overall network capability and/or efficiency. Accordingly, various aspects of the present disclosure provide for improving the tracking of UEs in a mobile network and the selection of a serving node for each UE.

In existing mobility management, a UE continually performs searches and measurements to determine the best base station to connect to for conducting wireless communications. The frequent searches and measurements consume a considerable amount of the limited power at the UE. Moreover, the network, through the base stations and access points, frequently broadcast multiple reference signals and large amounts of system information regardless of UE traffic. Accordingly, network based user-tracking can shift the burden of mobility tracking from the UE side to the network side.

One of the facilities supported by user-tracking zones in a cellular network includes large scale remote nodes that can be coordinated through a centralized node controller. <FIG> is a block diagram illustrating a user-tracking zone in a cellular network including multiple nodes <NUM>-<NUM> forming a zone <NUM> under control of a zone node controller <NUM>. Zone node controller <NUM> may be implemented by a centralized component, but may also be implemented in a distributed manner with information exchange between neighboring zone nodes. Thus, while illustrated in <FIG> as a single centralized entity, the functionality of zone node controller <NUM> may be implemented through multiple different, distributed components.

In networks configured with user-tracking zones, a zone <NUM> is considered a set of physical nodes, such as nodes <NUM>-<NUM>. Inter-working between nodes <NUM>-<NUM> is can be considered essentially seamless, including ideal backhaul, fast handover, but not necessarily coordinated multipoint (CoMP) operation. Nodes <NUM>-<NUM> are provided with individual node IDs, for example, node <NUM> is assigned node ID <NUM>, while, node <NUM> is assigned node ID <NUM>, and the like. However, over the air interface of zone <NUM>, nodes, such as nodes <NUM>-<NUM>, can send single frequency network (SFN) sync signals for discovery without revealing their assigned node ID. Each node in an SFN, such as nodes <NUM>-<NUM>, can transmit the same information simultaneously using the same resource. Thus, an accessing UE, such as UE <NUM>, would not receive the node ID of any of nodes <NUM>-<NUM>.

Nodes <NUM>-<NUM> can transmit the SFN sync signal simultaneously across zone <NUM>. The SFN sync signal may contain a reference sequence for timing acquisition. The reference signal may also be unique for each zone, which allows for inter-zone searches. In one example implementation, a multi-bit SFN sync signal may be transmitted that includes the zone ID, a time-frequency resource location, and an indication that identifies whether the system information has been updated. A time-frequency resource location may include designated frequency and slot location information. For example, the SFN sync signal transmitted by node <NUM> may include the zone ID of zone <NUM>, in addition to the bandwidth and slots designated for UE chirp signal transmissions and SFN sync signal transmissions, as well as an indicator that identifies if the SIB information has changed. If the SIB change indicator identifies that the SIB information has changed, then UE <NUM> would send a SIB transmission request. In response to the SIB transmission request, one of nodes <NUM>-<NUM> will transmit the SIB to UE <NUM>. All of the nodes in the same zone, such as nodes <NUM>-<NUM> of zone <NUM> can transmit the same SIB information. Therefore, because UE <NUM> does not obtain the node ID, intra-zone mobility is transparent to UEs, such as UE <NUM>.

A UE, such as UE <NUM>, may use the SFN sync signals to synchronize with nodes <NUM>-<NUM> of zone <NUM>. If UE <NUM> has not already established a connection to zone <NUM>, the initial UE chirp would request transmission of the SIB for initial acquisition. UE <NUM> does not necessarily request the SIB from any particular node in zone <NUM>. Each of nodes <NUM>-<NUM> can transmit in the same SFN and transmit the SFN sync signals simultaneously. UE <NUM>, which has been synchronized with nodes <NUM>-<NUM> of zone <NUM> using any of the SFN sync signals received from nodes <NUM>-<NUM>, can send a SIB transmission request for initial acquisition. The network responds, in order to acknowledge the request, and then proceeds with a unicast SIB addressed to UE <NUM> in response to the transmission request.

The zone node controller (ZNC), such as ZNC <NUM>, may choose which of nodes <NUM>-<NUM> is to respond. Because the same SIB information is also being transmitted by each of nodes <NUM>-<NUM> in zone <NUM>, the responding node does not necessarily correspond to the node that detected the SIB transmission request. For example, UE <NUM> can transmit a chirp, which is detected by node <NUM>. Node <NUM> can report the chirp to ZNC <NUM>, which then can determine that node <NUM> will respond by transmitting the unicast SIB to UE <NUM>.

Alternatively, one or more nodes of a zone, such as nodes <NUM>-<NUM> of zone <NUM> may autonomously determine which node will send the unicast SIB in response to the chirp. For example, nodes <NUM>-<NUM> can each detect the chirp transmitted by UE <NUM>. However, node <NUM> may determine that it has the highest channel quality for transmissions with UE <NUM>, thus, node <NUM> can autonomously elect to transmit the unicast SIB to UE <NUM> and inform nodes <NUM>-<NUM> and <NUM>-<NUM> via the backhaul.

Moreover, in conventional systems, mobility related measurements made by the UE may contribute to UE power consumption in idle mode discontinuous reception (IDRX) and connected mode discontinuous reception (CDRX). In contrast, because the SFN is synchronized across the active set of nodes <NUM>-<NUM> in zone <NUM> of <FIG>, each SIB transmitted by any of nodes <NUM>-<NUM> will be synchronized to the same SFN in addition to including the same information. Thus, when moving across zone <NUM>, UE <NUM> may transfer from node to node transparently and without performing any mobility related measurements or searches. That is, for networks that are operating user-tracking zones as described herein, the transparent mobility management can occur without UE measurements, which covers power and complexity at the UE. Moreover, because user-tracking zones in a cellular network reduce the broadcast load of its nodes, the node operational costs (OPEX) may also be reduced.

By moving tracking responsibility from the UE to the network side, power savings may be realized from the reduced searching and measurements at the UE. Additionally, a "zero" broadcast feature of user-tracking zones in a cellular network can provide substantial network-side power savings through less broadcast signaling. With "zero" broadcast, nodes do not systematically and periodically broadcast extensive SIB data regardless of UE traffic. Instead, the network can employ an on-demand system information block (SIB), in which SIB data is only unicast to a UE in response to a signal from the UE requesting such SIB transmission.

In one embodiment, in order to track UEs, the network can monitor for chirp signals transmitted periodically by UEs. A chirp signal is a short, low payload signal that includes at least the UE identifier (ID). The UE can first synchronize with the network using single frequency network (SFN) synchronization ("sync") signals transmitted by zone nodes, and then can transmit the chirp signal. Once transmitted, the UE will then listen for some kind of response. On initial access to a network, the UE chirp signal may also request transmission of SIB information in order to obtain the system information used to establish and maintain a connection with the network. Thus, the response to an initial access chirp would be the SIB information transmitted from the network.

Once network access has been established, the network will instead respond to the chirp signals with keep alive signals. Keep alive signals may include various network information that may assist the UE to maintain the connection (e.g., power control data, load balancing information, etc.), but which do not include all of the SIB data previously transmitted. After network access has been established, the UE will only request a new SIB transmission when there is an indication that the SIB information has changed, or when the UE detects it has entered a new zone of the network.

The chirp signals allow for the network to track and monitor the location of the UEs. With this tracking information, user-tracking zones in a cellular network may use unicast paging to directly page a UE when data is available. The unicast paging facilitates a more efficient paging tracking area that reduces power consumption on the network side.

<FIG> is a block diagram illustrating a time line <NUM> that reflects communications between a zone node <NUM>, which may include the functionality and components described with respect to base station <NUM> (<FIG>), and a UE <NUM>, which may include the functionality and components described with respect to UE <NUM> (<FIG>), in a network with user-tracking zones. The network illustrated in <FIG> is further configured as having "zero" broadcast. Zone node <NUM> is one of many zone nodes supporting a zone of wireless coverage in which each node of the zone transmits in a single frequency network (SFN).

For purposes of the example illustrated in <FIG>, UE <NUM> has already established a connection to the network in the zone. Zone node <NUM> transmits SFN sync signals <NUM>, which can be a low duty cycle signal that includes at least a reference sequence configured to allow UE <NUM> to synchronize timing with zone node <NUM>. Each of the zone nodes in the zone transmits SFN sync signals simultaneously with the same SFN. UE <NUM>, synchronized with zone node <NUM>, transmits chirp signal <NUM> that includes the UE ID of UE <NUM>. After transmitting chirp signal <NUM>, UE <NUM> begins to listen for a response during listen period <NUM>. Zone node <NUM> detects chirp signal <NUM> and transmits keep alive signal <NUM> in response. Because UE <NUM> has already established a connection with the zone, keep alive signal <NUM> will include limited data that UE <NUM> may use to maintain the connection to the zone as noted above.

At time <NUM>, data arrives at zone node <NUM> for UE <NUM>. At time <NUM>, zone node <NUM> transmits a unicast page <NUM> along with additional system information for UE <NUM>. For example, the additional system information may include new resources for use in a connected mode in order to receive the data. UE <NUM> responds with a connected mode chirp <NUM> which triggers zone node <NUM> to begin delivering the data through traffic signals <NUM>. UE <NUM> will receive the data during receive period <NUM>.

It should be noted that various aspects of the present disclosure may provide for network-assisted zone neighbor searches based on the network-side tracking of UEs. When the network determines that the UE is close to a new or better zone, then the network may trigger a search for a new zone ID. This trigger may be included in a keep alive message, while the UE is simply chirping responses to maintain the connection.

<FIG> is a block diagram illustrating a TDD transmission stream <NUM> for communication between a UE <NUM> and nodes <NUM>-<NUM> of a user-tracking zone in cellular network. UE <NUM> may include similar functionality and components illustrated with respect to UE <NUM> (<FIG>), while nodes <NUM>-<NUM> may include similar functionality and components illustrated with respect to base station <NUM> (<FIG>). Within TDD transmission stream <NUM>, special sync/chirp subframes <NUM> are configured to accommodate sync signal <NUM> transmissions from nodes <NUM>-<NUM> and chirp signals <NUM> from UEs operating within the zone, such as UE <NUM>. Special sync/chirp subframes <NUM> are divided into sections to accommodate both the downlink and uplink transmissions of the interactions between UE <NUM> and any of nodes <NUM>-<NUM>. The first section of special sync/chirp subframe <NUM> is allocated for node transmission of sync signals <NUM>. Sync signal <NUM> occupies a short duration and only a portion of the available bandwidth available in subframes <NUM>. For purposes of the illustrated example only, sync signal <NUM> occupies <NUM> of frequency and <NUM> of bandwidth. Section <NUM> provides a gap that allows the transition from downlink to uplink. Chirp signal <NUM> also occupies only a portion of the available bandwidth of special sync/chirp subframes <NUM>. For purposes of the illustrated example only, chirp signal <NUM> occupies <NUM> of frequency and <NUM> of bandwidth. This chirp signal <NUM> is the initial UE chirp for requesting SIB transmission in a TDD operation. UE <NUM> is synchronized with nodes <NUM>-<NUM> and sends the SIB transmission request for initial acquisition through chirp signal <NUM>. Section <NUM> is a processing period of time allowed for the receiving node to process chirp signal <NUM> and transmit a response <NUM> to UE <NUM>. One of nodes <NUM>-<NUM> determines to transmit the response <NUM> in a unicast transmission to UE <NUM> in response to chirp signal <NUM>. The response <NUM> may include a portion of the SIB transmission or the SIB transmission may be scheduled for another subframe, with response <NUM> simply acknowledging that the SIB transmission request was received by the network. The transmitting node may autonomously determine to transmit SIB response <NUM> or, alternatively, a ZNC, such as ZNC <NUM> (<FIG>) may choose which of nodes <NUM>-<NUM> should transmit SIB response <NUM>.

The on-demand SIB features of user-tracking zones in a cellular network may allow for minimizing UE and zone node transmission and reception requirements when there is little or no activity. This reduction of transmission and reception requirements may also serve to reduce the overall network energy consumption, which could enable scenarios in which a UE can operate efficiently as a relay. Functionally, reduced transmission/reception requirements and energy consumption may also facilitate enabling massive multiple input, multiple output (MIMO) and other types of deployments where broadcast and multi-cast operations are not available or that may be highly inefficient. Operations within user-tracking zones in a cellular network allow for zone nodes to provide only a low-periodicity beacon for initial disclosure when no devices are around. When one or a few mobile devices enter coverage within a zone, the base stations/nodes within the zone can provide system information on demand via unicast transmissions. The base stations/nodes may revert to broadcast operations, if available, as a higher number of mobile devices are present within the coverage area or if system information changes.

<FIG> is a block diagram illustrating a time line <NUM> of transmissions between UE <NUM> and any of nodes <NUM>-<NUM> in a user-tracking zone in a cellular network. Nodes <NUM>-<NUM> broadcast periodic SFN sync signals <NUM>, <NUM>, and <NUM>, which provides enough information for a UE, such as UE <NUM>, to synchronize timing with nodes <NUM>-<NUM>, to determine if UE <NUM> has changed zones, whether system information has changed, and where to send a SIB transmission request, such as SIB transmission request <NUM>. SIB transmission request <NUM> may have a different physical (PHY) channel in some cases (e.g., for massive MIMO or mmW).

For example, UE <NUM> detects SFN sync signal <NUM> and determines either that it has entered into a new zone with nodes <NUM>-<NUM> or that system information within the zone of nodes <NUM>-<NUM> has changed. UE <NUM> transmits SIB transmission request <NUM>. In some instances, when the UE <NUM> determines that it is entering a new zone, SIB transmission request <NUM> can include a request for master system information, which may include information on various services of interest. Alternatively or in addition, SIB transmission request <NUM> may include a request for master system information when the UE <NUM> determines, through SFN sync signal <NUM>, that the system information has changed. One of nodes <NUM>-<NUM> responds with SIB transmission <NUM>, which includes the specific information requested in SIB transmission request <NUM> (e.g., master system information, information on various available services, etc.).

Nodes <NUM>-<NUM> will continue to transmit SFN sync signals <NUM>, <NUM>. However, if UE <NUM> determines that it remains in the same zone or that no system information has changed since the system information communicated in SIB transmission <NUM>, UE <NUM>, at <NUM>, will not transmit another SIB transmit request and, at <NUM>, one of nodes <NUM>-<NUM> will not transmit another SIB or other such service information.

Different zones may be configured using nodes of various different power classes (e.g., from 40W macro nodes to 200mW small cells) and may be arranged to be adjacent to other nodes or even embedded within larger zones. <FIG> is a block diagram illustrating network area <NUM> configured with user-tracking zones. Network area <NUM> includes multiple zones, zone <NUM><NUM>, zone <NUM><NUM>, and zone <NUM><NUM>. Zone <NUM><NUM> and zone <NUM> are adjacent to one another, while zone <NUM><NUM> is embedded within zone <NUM><NUM>. Zone <NUM><NUM> includes nodes of various power classes, including small cell nodes serving UE <NUM> in serving cluster <NUM>. In order for a UE, such as UE <NUM>, to identify and distinguish between different zones, a unique SFN sync signature may be applied to the SFN sync signals of each of zones <NUM><NUM>, <NUM><NUM>, and <NUM><NUM>. The unique SFN sync signature may include unique signaling based on time or frequency, or may also include a unique identifier in the payload associated with the particular zone. It should be noted that there is no requirement that neighboring zones are synchronized with one another.

One issue that arises with zones that are serviced by nodes of mixed power classes is the effectiveness of the power control procedure. The UE operates an open loop power control mechanism for UE chirps based on the power control information provided by the SIBs. When the identified power control is less than the power class of the node, the resulting UE chirps may undershoot the power control by providing too little power to the chirp transmissions based on the power control information. In contrast, when the identified power control is more than the power class of the node, the resulting UE chirps may overshoot the power control by providing too much power to the chirp transmission. One way to address this discrepancy is by assigning separate zone IDs to each power class with unique open loop power control mechanisms. In such aspects, all zones would have zone nodes within the same power class.

Alternatively, mixed power class nodes may reside in the same zone. However, in order to address the over/undershooting of the open loop power control for the UE chirps, additional power adjustments may be needed. For example, additional power adjustments can be included potentially in other signals, such as with the keep alive signals or secondary sync signals having a separate resource allocation, or other refinements can be used to account for the over/undershooting of the UE chirp transmit power.

It should be noted that some zones may operate as legacy regions where each node advertises its node ID through broadcast reference signals, which the UE continually receives, measures, and ranks, and may additionally report any significant changes to the tracking area. In order to inform a UE coming within coverage of a legacy region that does not operate with network based user-tracking zones after operating within such a user tracking zone, nodes of the legacy region configured according to one aspect of the present disclosure may use a special signature or legacy indicator to trigger the UE to perform a "cell" search. For example, a special signature or legacy indicator may be a predefined zone ID, such as ZoneID = <NUM>, or it may be a specific identifier, indicator, or reference signal that indicates that the zone includes legacy nodes and base stations do not actively track UE mobility. This special signature or legacy indicator will trigger the UE to perform the search. This search may also include second stage cell searching after the UE has synchronized timing with the zone.

Network assistance can reduce search complexity. The various nodes of the network already track and monitor the mobility of UEs. Therefore, when tracked UEs get near to the cell edge, the network is able to provide information that allows the UE to access the neighboring zone, similar to a neighbor list updating at the boundaries.

Various aspects of the present disclosure provide channel design for initial synchronization and discovery of user-tracking zones in a cellular network. <FIG> is a block diagram illustrating example blocks executed at a node of a zone to implement one aspect of the present disclosure. At block <NUM>, a zone node generates a reference sequence correlating to the timing of the zone node defining a zone along with one or more other zone nodes. Each of the nodes of the zone will have synchronized timing.

At block <NUM>, the zone node assembles a payload including a format for a system information transmission request for a UE, wherein the payload also includes at least a resource allocation for the UE to transmit the request. The payload also includes a zone ID, which may alternatively be embedded in the reference sequence, one or more time-frequency resource locations, which provide frequency or slots that are designated for transmission of the SFN sync signals and system information transmission requests, open loop power control information (e.g., power class, zone power class, etc.), and an update identifier which identifies when the system information for the zone has been changed or modified. The zone node can set the update identifier when changes to the system information are detected. This payload information allows the UE to discover the network. At block <NUM>, the zone node encodes the payload and, at block <NUM>, transmits a SFN synchronization channel that includes the reference sequence and the encoded payload. The SFN sync signals can be transmitted in the SFN synchronization channel accordingly.

<FIG> is a block diagram illustrating example blocks executed at a UE to implement one aspect of the present disclosure. At block <NUM>, the UE receives a SFN synchronization channel that includes a reference sequence and an encoded payload. The reference sequence allows the UE, at block <NUM>, to synchronize its timing with the zone.

At block <NUM>, the UE decodes the encoded payload to obtain at least the format for the system information transmission request and a resource allocation over which the UE can transmit the request. The UE may decode additional information in the payload, such as zone ID, which, as noted above, may also alternatively be embedded in the reference sequence, time-frequency resource locations, open loop power control information, update identifier, and the like. At block <NUM>, the UE may then transmit the system information transmission request based on information obtained in the payload and according to the resources and configuration information it may have decoded.

<FIG> is a block diagram illustrating a UE <NUM> and zone nodes <NUM>-<NUM> configured according to one aspect of the present disclosure. Zone nodes <NUM>-<NUM> operate to define a portion of the coverage area of a designated zone. UE <NUM> may operate transparently within the zone served by zone nodes <NUM>-<NUM>. UE <NUM> will periodically transmit chirp signals after synchronizing with zone nodes <NUM>-<NUM> through the SFN sync signals simultaneously transmitted by zone nodes <NUM>-<NUM>. In one example, when UE <NUM> obtains the zone ID, either decoded from the payload or extracted from the reference sequence, which indicates that UE <NUM> has entered into a new zone, UE <NUM> will transmit the SIB transmission request using the allocated resources, power control, and time-frequency resource locations indicated in the encoded payload of the SFN sync signals from zone nodes <NUM>-<NUM>.

In alternative circumstances, such as when the update indicator decoded by UE <NUM> from the SFN sync signal payload indicates that the system information, while UE <NUM> is in the same zone, has changed, UE <NUM> would transmit the SIB transmission request in order to obtain the new system information. The interaction by UE <NUM> with the zone and zone nodes <NUM>-<NUM> remains transparent as the actual node IDs are not transmitted or revealed to UE <NUM>. Moreover, each of zone nodes <NUM>-<NUM> transmits the SFN synchronization channel with SFN sync signals simultaneously. Thus, UE <NUM> transparently moves through the zone.

<FIG> is a block diagram illustrating special subframe <NUM> configured according to one aspect of the present disclosure. Special subframe <NUM> is designated as a specific TDD subframe in which SFN sync signals and SIB transmission request messages may be transmitted. A UE, such as UE <NUM>, may learn of special subframe <NUM> through payload information regarding time-frequency resource locations transmitted on the SFN synchronization channel by zones nodes, such as zone nodes <NUM>-<NUM>. Section <NUM> of special subframe <NUM> carries the SFN sync signals, which include a reference sequence for timing synchronization as well as a payload containing various other system information. Section <NUM> provides a gap or guard period to allow the communication to change from downlink to uplink. Section <NUM> of special subframe <NUM> includes the chirp signal from the UE. In situations where the UE is initially accessing a zone or when the system information of the UE's current zone changes, the chirp signal in section <NUM> will include a SIB transmission request. Section <NUM> of special subframe <NUM> allows time for the zone node to process the chirp signal. The zone node may then respond to the chirp signal at section <NUM>. In the response by the zone node, when transmitting the system information in response to a SIB transmission request, the system information may not all be transmitted during section <NUM>. Additional subframes may be used to transmit the system information.

Additional aspects of the present disclosure are directed to multiplexing the synchronization channel across zones. In a first such aspect, single-stage zone multiplexing may be implemented in which a single-stage synchronization signal is transmitted with the zone ID embedded within the SFN sync signal using, for example, a unique scrambling code or sequence or time/frequency assignment.

<FIG> is a block diagram illustrating example blocks executed by a zone node to implement one aspect of the present disclosure. At block <NUM>, a UE detects a SFN synchronization channel that includes a reference signal and encoded payload. At block <NUM>, the UE extracts a zone ID embedded in the reference signal. The zone ID may be embedded in the reference signal using a unique scrambling code or time/frequency assignment.

At block <NUM>, a determination is made whether the correct or expected zone ID has been extracted. In operation, the UE will search across each zone ID and/or time offset hypothesis to detect the zone ID embedded in the reference signal. Thus, the UE may detect a zone ID for a zone that it does not wish to access. If the correct or expected zone ID has not been extracted, then, the UE will continue extracting zone IDs, at block <NUM>. Otherwise, if the correct or expected zone ID has been extracted, at block <NUM>, the UE will synchronize its timing using the reference signal. At block <NUM>, the UE will then decode the encoded payload. The payload may include a format for a SIB transmission request that may also be scrambled using the zone ID. The UE may decode the encoded payload to obtain at least the format for the SIB transmission request and a resource allocation for the system information transmission. The format for the SIB transmission request may be descrambled from the encoded payload using the zone ID.

In another aspect of the disclosure, a two-stage signal is provided. First the SFN timing reference signal is the same for all zones, which enables initial timing synchronization to occur. <FIG> is a block diagram illustrating example blocks executed to implement one aspect of the present disclosure. At block <NUM>, the UE detects a reference signal for time synchronization and, at block <NUM>, synchronizes its timing using the reference signal. As noted, the reference signal is the same for all zones. Therefore, the UE may synchronize timing without decoding or descrambling the reference signal.

At block <NUM>, in response to the synchronizing, the UE detects a payload that includes a zone ID and an encoded payload. The UE may then extract the zone ID, at block <NUM>, and decode the payload, at block <NUM>. As with the single-stage signal, some of the information encoded into the payload may further be scrambled with the zone ID.

Additionally, the UE, whether operating with a single-stage signal, as illustrated in <FIG>, or a two-stage signal, as illustrated in <FIG>, may detect a legacy indicator within the synchronization channel. As noted above, a legacy indicator identifies zones that are not compatible with operations of user-tracking zones in a cellular network. If detected, the UE will refrain from performing the features associated with user-tracking operations and revert to legacy cell search operations.

The SFN sync signal payload may include power control information for the open loop power control procedures used by the UEs. Various aspects of the present disclosure may provide for accommodating multiple power classes. In certain aspects, multiple power classes are accommodated in a single zone, while in other aspects, each zone will include only a single power class of node.

<FIG> is a block diagram illustrating UE <NUM> and zone nodes <NUM>-<NUM> configured according to one aspect of the present disclosure. Zone nodes <NUM>-<NUM> are each within the same zone. However, the power class of zone nodes <NUM>-<NUM> is different than the power class of zone node <NUM>. Because the same SIB and sync signals are transmitted by each node in a zone, each of zone nodes <NUM>-<NUM> advertises only a single power class in the payload of the SFN sync signal. Thus, UE <NUM> will receive the same SFN sync signal from zone node <NUM> and <NUM> even though their actual power class is different. If the higher power class of zone nodes <NUM>-<NUM> is used, then when transmitting the chirp signal or a SIB transmission request to zone node <NUM>, the power used for transmitting to zone node <NUM> will overshoot the node. Overshooting the node refers to using too much power in the transmission to a particular node. Conversely, if the lower power class of zone node <NUM> is used for the entire zone, then the power used for transmissions to zone nodes <NUM>-<NUM> will undershoot those nodes. Undershooting refers to using too little power in the transmission to a particular node. Undershooting may affect the reliability of the node successfully receiving the transmitted signal, while overshooting may cause too much interference to competing signals.

<FIG> is a block diagram illustrating example blocks executed by a zone node to implement one aspect of the present disclosure. At block <NUM>, a zone node generates a reference sequence correlating to a timing of the zone node and other zone nodes defining a zone. At block <NUM>, the zone node assembles a payload that includes at least a zone power class indicator, a format for a system information transmission request, and a resource allocation for transmitting the request. In certain aspects, the zone power class indicator identifies the only power class of zone nodes for the zone. In such aspects, all nodes in the same zone will have the same power class.

In additional aspects, the zone power class indicator selects a certain power class to advertise through the payload, even though zone nodes of different power classes may populate the zone. In such aspects, the payload may also include power modification instructions that instruct the UE on how to modify the power control when a power class of the particular zone node is different than the zone power class.

At block <NUM>, the zone node encodes the payload and, at block <NUM>, transmits a SFN synchronization channel that includes the reference sequence and encoded payload.

<FIG> is a block diagram illustrating example blocks executed by a UE to implement one aspect of the present disclosure. At block <NUM>, a UE receives a SFN synchronization channel that includes a reference sequence and an encoded payload. At block <NUM>, the UE uses the reference sequence to synchronize its timing to the zone node.

At block <NUM>, the UE decodes the encoded payload to obtain at least the zone power class indicator, a format for the system information transmission request, and a resource allocation for the request. Under scenarios in which the UE will send the SIB transmission request, the UE will set its transmit power according to a power associated with the zone power class indicator and then transmit, at block <NUM>, the SIB transmission request at the indicated power over the allocated resources.

In scenarios with zone nodes of multiple different power classes defining a zone, the payload will also include a power modification instruction. When the power class of the zone node does not match the zone power class, the UE will receive a power mismatch indicator. The power mismatch indicator will be a signal from the zone node that the transmitted power was either too high or too low. In response to this power mismatch indicator, the UE will use the power modification instruction to adjust the power accordingly. The zone power class may be selected to always reflect the highest or lowest power class of the nodes in the zone. Thus, the power modification instruction may be fixed in advance to adjust the power either up, in cases where the lowest power class is always advertised as the zone power class, or down, in cases where the highest power class is always advertised as the zone power class.

Additional aspects of the disclosure may provide for separate messages for different power classes. In one such example aspect, zone nodes with different power classes are simply only included in zones with other zone nodes having the same power class. In such cases, each zone will still have its own SIB and SFN synchronization channel. However, additional example aspects may provide for separate power class advertising for different power classes in the same zone, with the consideration that the SFN transmission is still maintained across power classes.

<FIG> is a block diagram illustrating example blocks executed to implement one aspect of the present disclosure. At block <NUM>, a UE receives a SFN synchronization channel that includes a reference sequence and an encoded payload. The reference sequence allows the UE, at block <NUM>, to synchronize its timing with the zone.

At block <NUM>, the UE decodes the encoded payload to obtain at least a first power class indicator, a format for the system information transmission request, and a resource allocation over which the UE can transmit the request.

At block <NUM>, the UE monitors a second resource of the SFN for a second synchronization channel that includes a second power class indicator and a second resource allocation for transmitting the system information transmission request. The second resource of the SFN may be frequency division multiplexed (FDM) from the first SFN resource that the first SFN synchronization channel was received.

At block <NUM>, a determination is made whether the UE detected such a second synchronization channel in a second resource of the SFN. If no such second sync channel is detected, then, at block <NUM>, the UE transmits the system information transmission request according to the first resource allocation at a first power associated with the first power class indicator. In other words, if the UE does not detect the secondary resource of the SFN for the zone nodes (e.g., sent from a small cell), then it will transmit according to the power class advertised in the first sync signal. Otherwise, if a second synchronization channel is detected at the second resource of the SFN, then, at block <NUM>, the UE transmits the system information transmission request according to the second resource allocation at a second power associated with the second power class indicator. In other words, if the UE detects a secondary resource (e.g., sent from a small cell), it will transmit to accommodate the second power class. The same SIB information would be provided regardless of whether the first or second power class is used, only the power and resource allocation would change.

<FIG> is a block diagram illustrating a UE <NUM> and zone nodes <NUM>-<NUM> configured according to one aspect of the present disclosure. Zone nodes <NUM>-<NUM> are a part of the same zone. However, zone nodes <NUM>-<NUM> each have the same power class, while zone node <NUM> is a small cell and has a different power class. According to the described example, while zone node <NUM> will transmit the same system information and transmit the SFN sync signals simultaneously with zone nodes <NUM>-<NUM>, zone node <NUM> also transmits a secondary SFN sync signal that is FDM with the primary SFN sync signal sent by zone nodes <NUM>-<NUM>. As UE <NUM> travels through the zone, when it detects the SFN sync signals, it will also monitor for the secondary sync signal at the secondary resource of the SFN. The detection of the secondary sync signal indicates to UE <NUM> that the zone node is at a different power class. Therefore, when transmitting, the UE <NUM> will set power according to the different power class instead of the power class advertised in the first resources of the SFN sync signal.

The functional blocks and modules in <FIG>, <FIG>, <FIG>, and <FIG> may comprise processors, electronics devices, hardware devices, electronics components, logical circuits, memories, software codes, firmware codes, etc., or any combination thereof.

Claim 1:
A method of wireless communication, comprising:
detecting a synchronization channel transmitted from at least one zone node of a plurality of zone nodes of a zone over a single frequency network, SFN, at a user equipment, UE, wherein the synchronization channel includes a reference signal and an encoded payload (<NUM>);
extracting a zone identifier, ID, embedded in the reference signal (<NUM>) wherein the extracting includes searching the synchronization channel using each of a plurality of available predefined zone IDs and available time offsets until detecting an expected zone ID; and
in response to extracting the expected zone ID:
synchronizing timing at the UE to timing of the at least one zone node using the reference signal (<NUM>); and
decoding the encoded payload (<NUM>).