Patent Description:
A communication system can be seen as a facility that enables communication sessions between two or more nodes such as fixed or mobile devices, machine-type terminals, access nodes such as base stations, servers and so on. A communication system and compatible communicating entities typically operate in accordance with a given standard or specification which sets out what the various entities associated with the system are permitted to do and how that should be achieved. For example, the standards, specifications and related protocols can define the manner how devices shall communicate, how various aspects of communications shall be implemented and how devices for use in the system shall be configured.

A user can access the communication system by means of an appropriate communication device. A communication device of a user is often referred to as user equipment (UE) or terminal. A communication device is provided with an appropriate signal receiving and transmitting arrangement for enabling communications with other parties. Typically a device such as a user equipment is used for enabling receiving and transmission of communications such as speech and content data.

Communications can be carried on wireless carriers. Examples of wireless systems include public land mobile networks (PLMN) such as cellular networks, satellite based communication systems and different wireless local networks, for example wireless local area networks (WLAN). In wireless systems a communication device provides a transceiver station that can communicate with another communication device such as e.g. a base station of an access network and/or another user equipment. The two directions of communications between a base station and communication devices of users have been conventionally referred to as downlink and uplink. Downlink (DL) can be understood as the
direction from the base station to the communication device and uplink (UL) the direction from the communication device to the base station.

<CIT> relates to wireless communications and to multi-carrier system selection. According to <CIT>, a personal base station transmits a first pilot signal to a portable access terminal operating in an idle mode in a macrocell that uses a first carrier frequency. The first pilot signal is transmitted in the first carrier frequency to allow the portable access terminal to temporarily connect to the first pilot signal. A second pilot signal is transmitted in a second frequency that is different than the first frequency. The portable access terminal is dispelled from the first pilot signal, and the portable access terminal is allowed to connect to the second pilot signal.

<CIT>, relates to wireless communications, and proposes a mechanism for transmitting a reference signal in a wireless communication system. According to <CIT>, in a wireless communication system, a first base station maps a first reference signal to a resource region and transmits the first reference signal to a user equipment. A second base station maps a second reference signal to the resource region and transmits the second reference signal to the user equipment.

"<NPL> further evaluates energy saving gain and considerations on the mobility performance impact based on the proposal to reduce the number of CRS transmissions for empty cells.

Embodiments will now be described in further detail, by way of example only, with reference to the following examples and accompanying drawings, in which:.

In the following certain exemplifying embodiments are explained with reference to a wireless or mobile communication system serving mobile communication devices. Before explaining in detail the exemplifying embodiments, certain general principles of a wireless communication system and mobile communication devices are briefly explained with reference to <FIG> to assist in understanding the technology underlying the described examples.

In a wireless communication system mobile communication devices or user equipment (UE) <NUM>, <NUM>, <NUM> are provided wireless access via at least one base station or similar wireless transmitting and/or receiving node or point. In the <FIG> example two overlapping access systems or radio service areas of a cellular system <NUM> and <NUM> and three smaller radio service areas <NUM>, <NUM> and <NUM> provided by base stations <NUM>, <NUM>, <NUM>, <NUM> and <NUM> are shown. Each mobile communication device and station may have one or more radio channels open at the same time and may send signals to and/or receive signals from more than one source. It is noted that the radio service area borders or edges are schematically shown for illustration purposes only in <FIG>. It shall also be understood that the sizes and shapes of radio service areas may vary considerably from the shapes of <FIG>. A base station site can provide one or more cells. A base station can also provide a plurality of sectors, for example three radio sectors, each sector providing a cell or a subarea of a cell. All sectors within a cell can be served by the same base station.

Base stations are typically controlled by at least one appropriate controller apparatus so as to enable operation thereof and management of mobile communication devices in communication with the base stations. In <FIG> control apparatus <NUM> and <NUM> is shown to control the respective macro level base stations <NUM> and <NUM>. The control apparatus of a base station can be interconnected with other control entities. The control apparatus is typically provided with memory capacity and at least one data processor. The control apparatus and functions may be distributed between a plurality of control units. In some systems, the control apparatus may additionally or alternatively be provided in a radio network controller.

In <FIG> stations <NUM> and <NUM> are shown as connected to a wider communications network <NUM> via gateway <NUM>.

The smaller stations <NUM>, <NUM> and <NUM> can also be connected to the network <NUM>, for example by a separate gateway function and/or via the controllers of the macro level stations. In the example, stations <NUM> and <NUM> are connected via a gateway <NUM> whilst station <NUM> connects via the controller apparatus <NUM>. In some embodiments, the smaller stations may not be provided.

A possible mobile communication device will now be described in more detail with reference to <FIG> showing a schematic, partially sectioned view of a communication device <NUM>. This may be any of the communication devices <NUM>, <NUM> and <NUM> of <FIG>. Such a communication device is often referred to as user equipment (UE) or terminal. An appropriate mobile communication device may be provided by any device capable of sending and receiving radio signals. Non-limiting examples include a mobile station (MS) such as a mobile phone or what is known as a 'smart phone', a computer provided with a wireless interface card or other wireless interface facility, personal data assistant (PDA) provided with wireless communication capabilities, or any combinations of these or the like. A mobile communication device may provide, for example, communication of data for carrying communications such as voice, electronic mail (email), text message, multimedia and so on. Users may thus be offered and provided numerous services via their communication devices. Non-limiting examples of these services include two-way or multi-way calls, data communication or multimedia services or simply an access to a data communications network system, such as the Internet. Users may also be provided broadcast or multicast data. Non-limiting examples of the content include downloads, television and radio programs, videos, advertisements, various alerts and other information.

The mobile device <NUM> may receive signals over an air interface <NUM> via appropriate apparatus for receiving and may transmit signals via appropriate apparatus for transmitting radio signals. In <FIG> transceiver apparatus is designated schematically by block <NUM>. The transceiver apparatus <NUM> may be provided for example by means of a radio part and associated antenna arrangement. The antenna arrangement may be arranged internally or externally to the mobile device.

A wireless communication device can be provided with a Multiple Input / Multiple Output (MIMO) antenna system. MIMO arrangements as such are known. MIMO systems use multiple antennas at the transmitter and receiver along with advanced digital signal processing to improve link quality and capacity. Although not shown in <FIG> and <FIG>, multiple antennas can be provided, for example at base stations and mobile stations, and the transceiver apparatus <NUM> of <FIG> can provide a plurality of antenna ports. More data can be received and/or sent where there are more antenna elements. A station may comprise an array of multiple antennas. Signalling and muting patterns can be associated with TX antenna numbers or port numbers of MIMO arrangements.

A mobile device <NUM> is typically provided with at least one data processing entity <NUM>, at least one memory <NUM> and other possible components <NUM> for use in software and hardware aided execution of tasks it is designed to perform, including control of access to and communications with access systems and other communication devices. The data processing, storage and other relevant control apparatus can be provided on an appropriate circuit board and/or in chipsets. This feature is denoted by reference <NUM>. The user may control the operation of the mobile device by means of a suitable user interface such as key pad <NUM>, voice commands, touch sensitive screen or pad, combinations thereof or the like. A display <NUM>, a speaker and a microphone can be also provided. Furthermore, a mobile communication device may comprise appropriate connectors (either wired or wireless) to other devices and/or for connecting external accessories, for example hands-free equipment, thereto.

<FIG> shows an example of a control apparatus for a communication system, for example to be coupled to and/or for controlling a station of an access system, such as a base station. In some embodiments, base stations comprise a separate control apparatus. In other embodiments, the control apparatus can be another network element such as a radio network controller. In some embodiments, each base station may have such a control apparatus as well as a control apparatus being provided in a radio network controller. The control apparatus <NUM> can be arranged to provide control on communications in the service area of the system. The control apparatus <NUM> comprises at least one memory <NUM>, at least one data processing unit <NUM>, <NUM> and an input/output interface <NUM>. Via the interface the control apparatus can be coupled to a receiver and a transmitter of the base station. The control apparatus <NUM> can be configured to execute an appropriate software code to provide the control functions.

The communication devices <NUM>, <NUM>, <NUM> can access the communication system based on various access techniques, such as code division multiple access (CDMA), or wideband CDMA (WCDMA). Other examples include time division multiple access (TDMA), frequency division multiple access (FDMA) and various schemes thereof such as the interleaved frequency division multiple access (IFDMA), single carrier frequency division multiple access (SC-FDMA) and orthogonal frequency division multiple access (OFDMA), space division multiple access (SDMA) and so on.

An example of wireless communication systems are architectures standardized by the 3rd Generation Partnership Project (3GPP). A latest 3GPP based development is often referred to as the long-term evolution (LTE) of the Universal Mobile Telecommunications System (UMTS) radio-access technology. The various development stages of the 3GPP LTE specifications are referred to as releases. More recent developments of the LTE are often referred to as LTE Advanced (LTE-A). The LTE employs a mobile architecture known as the Evolved Universal Terrestrial Radio Access Network (E-UTRAN). Base stations of such systems are known as evolved or enhanced Node Bs (eNBs) and may provide E-UTRAN features such as user plane Radio Link Control/Medium Access Control/Physical layer protocol (RLC/MAC/PHY) and control plane Radio Resource Control (RRC) protocol terminations towards the communication devices. Other examples of radio access system include those provided by base stations of systems that are based on technologies such as wireless local area network (WLAN) and/or WiMax (Worldwide Interoperability for Microwave Access).

As part 3GPP Release <NUM> a work item on NCT (new carrier type) has been proposed and agreed. The carrier may be used in such a way in order to achieve one or more of the following aims: network energy-saving; overhead reduction; and enhanced support for arrangements which include one or more smaller cell at least partially overlying a larger cell. Some arrangements where one or more smaller cells overlie a larger cell (for example a macro cell) are sometimes referred to as HetNet arrangements.

To allow for network energy savings, a base station may be controlled to allow for completely blank subframes when there is no data to transmit. This means that the transmitter can be at least partially shut down.

An overhead reduction may be achieved by reducing the CRS (common reference signal) overhead in situations where the DM RS (demodulation reference signal) may be used. The overhead reduction may be particularly advantageous in beam forming MIMO (multiple input multiple output) operation with, for example four or more antennas. In situations such as the HetNet scenario outlined above, there may be reduced interference from common signals.

Some embodiments may provide base stations which support a dual dormant/active state. This may mean DTX (discontinuous transmission) like base station behaviour, with for example relatively long DTX cycles. The UE may perform procedures to take into account the state of the base station. In some embodiments there may be a reduced CRS in the active state.

Some embodiments may allow for base station energy saving, utilising the dormancy operation. Signals may be provided to allow for neighbour cell discovery and RRM (radio resource management) measurements.

In some embodiments, energy efficiency may be achieved by scheduling transmissions in as few DL subframes as possible. In this way the rest of the subframes may be kept empty ("blank") and the transmitter of the eNodeB can be shut down in those subframes to save energy.

Some embodiments relate to the use of the eNodeB (eNB) dormancy feature of a carrier for example in the context of small cells. By way of example a small cell may be a pico cell, a HetNet cell or the like.

However, even though a cell/carrier is not carrying any traffic, common signals and channels such as one or more of PDCCH (Physical Downlink Control Channel), PHICH (Physical Hybrid ARQ (Automatic Repeat-reQuest) Indicator Channel), PCFICH (Physical Control Format Indicator Channel), PSS/SSS (Primary Synchronization Signal/ Secondary Synchronization Signal), PCH (Paging Channel), PBCH (Physical Broadcast Channel), SIB (system information block), CRS (Common (cell specific) Reference Signal) and CSI-RS (Channel State Information Reference Signal) may be required, for example, in order to support mobility.

In some embodiments, to achieve energy savings, it is desirable to avoid the need to transmit common (cell specific) signals when that is not required. Instead of transmitting common channels and signals such as CRS, PDCCH, PHICH, PCFICH in every subframe, a duty cycle is provided. By way of example only the duty cycle may be <NUM>. However, in other embodiments, different duty cycles may be used. The different duty cycles may be greater or smaller than <NUM>. Where the duty cycle is <NUM>, this would result in having the common signals present in only every 5th subframe. During low network load this would allow for the eNodeB to e.g. ramp down at least some of the transmitter functionality (e.g. power amplifier) to save energy and reduce interference.

Alternatively, an eNodeB dormancy / DTX (discontinuous transmission) type operation may be provided. In this alternative, the network would suspend the transmission of all common signals and channels for a much larger period of time than say <NUM>.

It should be appreciated that in some embodiments, the eNodeB or base station dormancy operation could be applied to a carrier having all common signals present, or a carrier having reduced common signals. The carrier having all common signals present may be a so called legacy carrier. The carrier having reduced common signals may be a so called new carrier type.

Reference is made to <FIG> which shows schematically the operation of a base station which has dormant and active states. In particular, in the arrangement of <FIG>, the base station has a first dormant state <NUM>, followed by an active state <NUM> followed by another dormant state <NUM>. During the first dormant state <NUM>, there is a first DTX off period <NUM> followed by the DTX on period <NUM> followed by a second DTX off period <NUM>. When the base station is in the DTX off periods, the base station generally transmits nothing. When the base station is in the DTX on state, there will be some signals transmitted for example to allow the discovery of neighbouring cells and/ for example to allow for RRM measurements necessary for cell selection.

During the active state <NUM>, the state <NUM> is such that common signals are transmitted during this active state. In other words, the base station operates as normal, transmitting signals to user equipment. In the second dormant state <NUM>, again there is a first DTX off state <NUM> followed by a DTX on state <NUM> followed by a DTX off state <NUM>. The DTX on state may last in some embodiments for a relatively large number of sub frames and may for example last for more than <NUM> sub frames.

In some embodiments, from the UE and/or the network point of view it may be advantageous to align the DTX ON periods of neighboring cells. For a UE, having the DTX ON periods of two or more cells aligned and synchronized allows for discovering two or more cells during a relatively short period of time. This may minimize the UE energy consumption. This may alternatively or additionally impact on data throughput as the UE may not be able to transmit / receive data while performing neighbor cell measurements. Generally so called "measurement gaps" are configured.

From the perspective of the network, having the UEs measure as many neighboring cells at the same time as possible may minimize the disruptions to data transmissions due to measurement gaps. In other words, the number and/or duration of measurement gaps may be reduced.

Some embodiments may provide signaling and/or configuration options for discovery or reference signals and/or the multiplexing of such signals among different cells or transmission points during the DTX ON period of a dormant base station state.

In some embodiments, the transmission of synchronization and/or reference signals is carried out to enable a fast and/or efficient cell search.

In some embodiments, DTX ON Discovery signals (DOD) may be defined as, for example, reference signals transmitted in a given period. The DOD may be defined as the signals which are transmitted when the base station is in a dormant mode but some transmitting some basic signals. These basic signals may be reference signals. The reference signals may be a combination of PSS/SSS and CRS. The given period may be one sub frame. In other embodiments, the given period may be longer than a sub frame. A DOD signal may be provided in a single sub frame or may be provided by a burst which is transmitted over two or more sub frames. In some embodiments, the DOD signal of a given base station may be repeated in a number of sub frames. In some embodiments the sub frames in which DOD signal is transmitted are non-consecutive.

In some embodiments, the components of DOD signals may be based on the signals present already in the existing LTE standards, namely PSS/SSS and CRS. In order to provide orthogonality for the DOD signals, the PSS/SSS and CRS time and/or frequency positions within a sub frame (i.e. resource elements) can vary deterministically between the cells.

The DOD configuration (i.e. combination of PSS/SSS and CRS positions) may be derived for example based on the physical cell ID and modulo operation. An example will be given later.

Presently there are <NUM> physical cell Ids (PCI) defined. Of course this may be different in different standards and different versions of this standard. As outlined below there are in some embodiments <NUM> unique (orthogonal) positions for DOD signals indexed e.g. <NUM>. The index of the positions for DOD signal is given by:
DOD index = PCI Modulo <NUM>.

It should be appreciated that the index can be generalized to one of x different options where x is the number of unique positions in the duty cycle. X will be an integer. The index can thus be generalized to DOD index =PCI Modulo x.

Alternatively or additionally, the position may be signaled. This may be signaled using for example dedicated RRC (radio resource control) signaling when the corresponding measurement object is configured (in a similar way as different measurement patterns for different cell ID groups can be configured in Rel-<NUM>). At the time when the network configures the UE to perform measurements on a given frequency carrier, the network may provide also information related to e.g. reference signal configuration. This reference signal information would indicate in which sub frame or sub frames and/or at which frequency or frequencies the UE should look for reference signals from base stations or cells which are in an inactive mode.

In some embodiments, the DOD signals for different cells can be transmitted in different predetermined sub frames.

The DOD signals for a given cell may be transmitted in burst of for example <NUM> - <NUM> sub frames. It should be appreciated in some embodiments, the number of sub frames may be one or in some cases more than <NUM>. The sub frames may be consecutive or non-consecutive sub frames or a mixture of consecutive and non-consecutive. The DOD signal may be considered to be a whole burst, consisting of CRS/PSS/SSS repeated y times in every Nth sub frame. In alternative embodiments, the DOD signal may alternatively be considered to be the reference signal or signals transmitted by a given cell in a one sub frame.

In some embodiments, the duty cycle of DOD signals within the burst may be <NUM> which means that the duty cycle is aligned with the duty cycle of the so called new carrier type. However in other embodiments the duty cycle may be more or less than <NUM>. A DOD signal may be repeated every <NUM>. The burst may alternatively or additionally be defined in terms of numbers of sub frames.

In some embodiments there is an information exchange between eNBs. This exchange of information is used to ensure that the eNBs within range of each other have coordinated their respective configurations. This information exchange may be via wired and/or wireless interfaces. One example of an interface is the X2 interface. Information may alternatively or additionally be provided through a wireless exchange where the eNBs communicates over an air interface. The information exchange may be based on an implementation of a network listen mode (NLM) where a new eNB listens for the configurations of current neighbors and adapts to those configurations to minimize any impact on their respective configurations.

Alternatively or additionally, a controller may control the base stations to ensure their respective configurations are coordinated. The signaling may be provided to one or more of the base stations by the controller. The controller may be an entity such as radio network controller or the like.

In this way, each base station will know when it is supposed to transmit its DOD and that will be a time different to another base station. In some embodiments, more than one different base station will transmit their DOD in the same sub frame using the same PRB but using for example different symbols and/or subcarriers.

The PSS/SSS for a given base station in LTE may be transmitted twice in every radio frame, in sub frames #<NUM> and #<NUM>. This may be used with the so called new carrier type. Some embodiments may follow this pattern. However, other embodiments may use different patterns.

Considering one embodiment for DOD signals, taking FDD (frequency division duplexing) and normal CP (cyclic prefix) as an example, the following orthogonal time positions within the same sub frame may be available in some embodiments:.

The symbol pairs are used to transmit the PSS/SSS signal. It should be appreciated that in other embodiments, one or more different symbol pairs may be available. It should be appreciated that alternatively, the PSS/SSS may be transmitted by non-adjacent symbols.

Whilst some of the pairs are mutually exclusive, four unique pairs can be easily found (e.g. {<NUM>, <NUM>}, {<NUM>, <NUM>}, {<NUM>, <NUM>}, {<NUM>, <NUM>}). With a duty cycle of <NUM> sub frames, it is possible to multiplex altogether <NUM> x <NUM> = <NUM> PSS/SSS fully orthogonal sequences into a single radio frame. In other words up to <NUM> different base stations can be supported. Put another way, each frame of the <NUM> sub frames could support four different base stations in a dormant DTX ON mode. After that, the pattern may be repeated. Further multiplexing capacity may be obtained by utilizing different frequency resources (i.e. PRB (physical resource blocks) for PSS/SSS transmission. In other words, if additional physical resource blocks are used for the PSS/SSS transmission, then each sub frame of each PRB could support four different base stations.

The CRS-component of DOD-signal may be for frequency and/or time tracking purposes. The component may be a single CRS port transmitted with a <NUM> duty cycle. Orthogonality may be obtained in one or more of the following ways:
Different CRS frequency shifts can be utilized: LTE Rel-<NUM> for example supports six different subcarrier positions for CRS.

Different CRS ports can be utilized: the Res (resource elements) corresponding to CRS ports <NUM> or <NUM> can be used. However, if all <NUM> frequency shifts are in use, this may not provide further orthogonality.

Shifting CRS positions in time: similarly as with PSS/SSS assuming <NUM> sub frame duty cycle for CRS, interleaving the transmissions of CRS corresponding to different cells' DODs. In combination with CRS frequency shifting this provides altogether <NUM> x <NUM> = <NUM> unique time-frequency resources for DOD signal. Each sub frame is able to support <NUM> different base stations. A duty cycle of <NUM> sub frames would mean that <NUM> base stations could be supported. Of course, only <NUM> base stations need to be supported in one sub frame in some embodiments as the PSS/SSS requirements mean only four base stations may be supported in one sub frame.

It should be appreciated that in some embodiments, the PSS/SSS and CRS for a given base station will be provided in the same sub frame.

Reference is now made to <FIG> shows the multiplexing principle according to one embodiment. <FIG> illustrates a signal which might be received by a UE. Here only one PRB pair is shown. In for example 3GPP, a PRB pair has a duration of <NUM>, and has <NUM> subcarriers. A PRB consists of two <NUM> slots, and technically a PRB is <NUM> subcarriers * <NUM>,<NUM>. The physical resource block pair is made up of <NUM> symbols. Each symbol is made up of <NUM> resource elements, each resource element of a symbol is associated with a different subcarrier. As discussed above, it is possible to provide four fully orthogonal time-frequency resources for a DOD signal consisting of PSS/SSS and CRS. Furthermore, adding e.g. <NUM> sub frame level duty cycle on top, the capacity is further increased. In the arrangement of <FIG>, four symbol pairs provide a respective PSS/SSS signal referenced SS1, SS2, SS3 and SS4. Each of the symbol pairs is provided for each of the <NUM> subcarriers. Each symbol pair provides the PSS/SSS signal for a respective different base station. The CRS signals are provided in symbols <NUM>, <NUM>, <NUM> and <NUM>. Each of these symbols provides part of the CRS signal for up to <NUM> different base stations. Different ones of the subcarriers of a symbol are used for the CRS signal from different base stations. For example, subcarrier <NUM> and <NUM> in symbol <NUM> and <NUM>, and subcarrier <NUM> and <NUM> in symbol <NUM> and <NUM> provide the CRS signal for a first base station. Subcarrier <NUM> and <NUM> in symbol <NUM> and <NUM>, and subcarrier <NUM> and <NUM> in symbol <NUM> and <NUM> provide the CRS signal for a second base station and so on.

In some embodiments, by combining PSS/SSS and CRS such as previously described, some embodiments may have one or more of the following advantages: A plurality of fully orthogonal discovery signals may be constructed (up to <NUM> without including PSS/SSS frequency offset in some embodiments);.

The PSS/SSS sequences define the physical cell id (one of <NUM> alternatives). Additionally, modulo operation binds the physical Cell ID to the DOD signal positions. In this way the UE will know which reference signals are associated with which base stations or cells. It should be appreciated that the CRS position may be tied to the associated position of the PSS/SSS sequences.

Reference is made to <FIG> which shows a method of an embodiment. In step S1, a cell goes into a less active or dormant mode. This may be controlled by the cell itself and/or by a controller such as a radio network controller.

In step S2, the cell determines the timing for the reference signals. In particular, the cell determines when and on which resources to send the reference signals. In one embodiment, the timing for the reference signal will be based on the cell ID.

In step S3, the cell transmits the reference signals. The timing of the reference signals will be controlled by the cell in dependence on for example the cell ID.

In step S4, a user equipment receives the reference signals and processes the signals. In practice, the user equipment may receive reference signals from more than one base station. The reference signals may be orthogonal. In some embodiments, this may mean that the reference signals received at different times. In some embodiments, the reference signals from two different base stations may be received within the same sub frame. In alternative embodiments, reference signals from different cells may be received in different sub frames. Of course, in some embodiments, a user equipment may receive reference signals from three or more base stations. It is possible that some reference signals from different base stations may be in different sub frames and/or different reference signals from different base stations may be received in the same sub frame.

In step S5, based on the position of the reference signals, the user equipment is able to determine from which cell the signal has been transmitted. These reference signals are used by the user equipment for discovery purposes.

Reference is made to <FIG> which schematically shows an apparatus of a cell. The apparatus comprises an activity mode controller <NUM>. The activity mode controller will control whether the cell is in an active or dormant mode. This may be in response to information determined by the cell itself and/or information received for example from a radio network controller. The activity mode controller <NUM> is configured to provide information to a reference signal timing controller <NUM>. They reference signal timing controller <NUM> is arranged so that in a dormant mode, the cell ID is used to control the timing of the reference signals, that is when and on which resources a reference signal is to be transmitted. The cell ID may be stored in memory <NUM>.

The reference signal timing controller <NUM> is configured to provide timing information to a reference signal block <NUM>. This provides the reference signal with timing information to a transmitter <NUM> which transmits the reference signal with the required timing.

Reference is now made to <FIG> which schematically shows an apparatus of a user equipment. The apparatus comprises a receiver <NUM> which is arranged to receive reference signals from one or more cells. A processor <NUM> is configured to process the reference signals and may determine from which cell a respective reference signal has been received. This may be determined from the cell ID. This information may be provided to a cell selection block <NUM> which may use information in making cell selection and handover decisions.

It should be appreciated that one or more of the blocks shown in <FIG> or <FIG> may be provided by at least one processor and/or at least one memory. Different functions may be provided by the same or different processors and/or memories. It should be appreciated that in alternative embodiments, one or more of the blocks shown in <FIG> or <FIG> of may be provided by suitable circuitry and/ or hardware arrangement.

DTX mode is one example of an inactive or lower activity mode. Alternative embodiments may be used with any other suitable inactive or lower activity mode. The dormant state may be a state where one or more components of a base station may be turned off, put into a standby state or not used. In one embodiment, a dormant state may be one where no signals are transmitted other than one or more reference signals. The dormant state may consume less power than an active state.

It should be appreciated that where a base station supports more than one carrier option, one or more of the carrier options may be put into a dormant state. In this alternative, one or more carrier options may be in an active state while one or more carrier options is in a dormant state.

The active state may in some embodiments be considered to a normal operation mode of a base station.

Reference has been made to cells, in some embodiments. In some embodiments, the teachings may alternatively applied by a network node. The network node may be a base station or the like.

In some embodiments, the user equipment may receive mode information indicating when a cell is in the less active or dormant mode. This information may be provided directly or indirectly. For example, the mode information may be provided when the state of the first cell changes to the less active mode. However, in some embodiments, the user equipment will assume that the cell is in the less active mode unless the user equipment receives information indicating that the use the cell is in the active mode. Of course, in some embodiments, the user equipment may receive information which indicates when the active mode starts and when the active mode ends.

Reference has been made to particular configurations. Some embodiments may be applied to other configurations.

Reference has been made to various channels. It should be appreciated that other embodiments may be used with other channels.

Reference has been made to the so called new carrier type. It should be appreciated that this may be referred to by alternative nomenclature in the future. It should be appreciated that other embodiments may alternatively or additionally be used with any other carriers.

It is noted that whilst embodiments have been described in relation to LTE, similar principles can be applied to any other communication system or to further developments with LTE. Therefore, although certain embodiments were described above by way of example with reference to certain exemplifying architectures for wireless networks, technologies and standards, embodiments may be applied to any other suitable forms of communication systems than those illustrated and described herein.

In the previously described embodiments, reference has been made to the reference signals PSS, SSS and CSR. One or more of these signals may be omitted. It should be appreciated that alternatively or additionally any other suitable reference signal may be used.

In some embodiments only one reference signal may be required. In other embodiments more than one reference signal may be required.

In the above, reference has been made to the reference signals of base stations. In some embodiments the reference signals may be provided by a cell, In some embodiments, a base station can provide one or more cells. In some embodiments, the resource elements of the PSS/SSS may be determined by the physical cell ID as previously described.

In some embodiments an association is provided between a) cell (cell ID), and b) resource elements on which the three reference signals (PSS/SSS/CRS) are transmitted.

In some embodiments, in addition to the resource elements within a PRB, the sub frame in which the reference signals are transmitted is associated.

In some embodiments PSS/SSS and CRS signals consisting of a burst (a predefined number of repetitions with a given duty cycle) is used for neighbour-cell discovery to achieve fast and efficient cell search during eNB's dormant state. If in the DTX ON mode, (where the eNB is in a sleep mode but is only transmitting PSS/SSS/CRS) a dormant type of downlink DL time period is defined for DL LTE. In this period only CRS and PSS/SSS are transmitted on the downlink to support a UE e.g. synchronization and network cell selection features during the dormant state.

In some embodiments, different cells transmit their PSS/SSS signals at different OFDM-symbols within a sub frame, thus guaranteeing the orthogonality of discovery between different cells. Moreover, further orthogonality is provided by introducing additional dependency between the cell ID and the timing of the PSS/SSS within the burst (both within sub frame as well as among different sub frames) and/or frequency shift of the CRS.

The required data processing apparatus and functions of a base station apparatus, a communication device and any other appropriate apparatus may be provided by means of one or more data processors. The described functions at each end may be provided by separate processors or by an integrated processor. The data processors may be of any type suitable to the local technical environment, and may include one or more of general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASIC), gate level circuits and processors based on multi core processor architecture, as non limiting examples. The data processing may be distributed across several data processing modules. A data processor may be provided by means of, for example, at least one chip. Appropriate memory capacity can also be provided in the relevant devices. The memory or memories may be of any type suitable to the local technical environment and may be implemented using any suitable data storage technology, such as semiconductor based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory.

In general, the various embodiments may be implemented in hardware or special purpose circuits, software, logic or any combination thereof. Some aspects of the invention may be implemented in hardware, while other aspects may be implemented in firmware or software which may be executed by a controller, microprocessor or other computing device, although the invention is not limited thereto.

Claim 1:
A method comprising;
receiving (S4) at least one reference signal from a first cell in a dormant state and at least one reference signal from a second cell in a dormant state within a same or different sub frames of a set of sub frames, wherein said at least one reference signal from the first cell is associated with different resource elements of said set of sub frames to those associated with the at least one reference signal from the second cell, the reference signals from each cell comprising a primary synchronisation signal and/or a secondary synchronisation signal, wherein the primary synchronisation signal and/or the secondary synchronisation signal are transmitted using four unique symbol pairs.