The growing increase in wireless communication connectivity and usage has continued to put pressure on service providers to expand coverage areas and increase data rates. In Long Term Evolution (LTE) Advanced, one way to increase data rates is to implement a multicarrier or carrier aggregation (CA) scheme. In CA operation, the wireless device is able to receive and/or transmit data to more than one serving cell, thereby increasing overall transmission/reception bandwidth. In other words, a CA capable wireless device may be configured to operate with more than one serving cells. The carrier of each serving cell is generally called as a component carrier (CC). The component carrier (CC) means an individual carrier in a multi-carrier system.
The term carrier aggregation (CA) is also called (e.g. interchangeably called) “multi-carrier system”, “multi-cell operation”, “multi-carrier operation”, “multi-carrier” transmission and/or reception. This means the CA is used for transmission of signaling and data in the uplink and downlink directions. One of the component carriers (CCs) in Carrier Aggregation (CA) is the primary component carrier (PCC), also referred to as a primary carrier or anchor carrier. The remaining CCs are called secondary component carriers (SCCs), also referred to as secondary carriers or supplementary carriers. The serving cell, as used herein, is interchangeably called a primary cell (PCell) or primary serving cell (PSC). Similarly the secondary serving cell, as used herein, is interchangeably called as secondary cell (SCell) or secondary serving cell (SSC).
Generally, the primary CC, i.e., PCC or PCell, carries the essential wireless device specific signaling. The primary CC exists in both uplink and downlink directions in CA. Where there is a single Uplink (UL) CC, the PCell is on that CC. Further, the network may assign different primary carriers to different wireless devices operating in the same sector or cell. Measurements are performed by the wireless device on the serving one or more cells (multiple serving cells may be with CA) as well as on neighbor cells over some known reference symbols or pilot sequences. These measurements are done on cells on an intra-frequency carrier, inter-frequency carrier(s) as well as on inter-Radio Access Technology (RAT) carriers(s), depending upon whether the wireless device supports that RAT.
In a CA scenario, the wireless device may perform the measurements on the cells on the primary component carrier (PCC) as well as on the cells on one or more secondary component carriers (SCCs). A CA capable wireless device may also perform inter-frequency measurements without measurement gaps since the wireless device is configured with a broadband receiver and/or multiple receivers. Examples of intra-frequency and inter-frequency measurements in LTE are Reference symbol received power (RSRP) and Reference symbol received quality (RSRQ). Examples of intra-frequency and inter-frequency measurements in High speed packet access (HSPA) are Common pilot channel received signal code power (CPICH RSCP) and CPICH Ec/No.
Measurements such as mobility measurements may also include identifying or detecting a cell in which cell detection includes identifying at least the physical cell identity (PCI), primary scrambling code (PSC) or base station identity code (BSIC), and performing the signal measurement, e.g., RSRP, RSCP or RSSI, of the identified cell. The wireless device may also have to acquire the cell global ID (CGI) of a cell.
Examples of positioning measurements in LTE are reference signal time difference (RSTD) for OTDOA positioning method, and wireless device RX-TX time difference measurement for E-CID positioning method. The wireless device RX-TX time difference measurement requires the wireless device to perform measurement on downlink reference signal as well as on uplink transmitted signals. Another example of positioning measurements is UL Relative Time Of Arrival (RTOA), which is performed in UL on radio signals (namely SRS) transmitted by the wireless device.
The radio measurements performed by the wireless device are used by the wireless device for one or more radio operational tasks. Examples of such tasks are reporting the measurements to the network, which in turn may use the measurements for various tasks. For example, in the RRC_CONNECTED state the wireless device reports radio measurements to the serving node or to another network node via the serving node. In response to the reported wireless device measurements, the network node such as the serving node makes certain decisions, e.g., it may send mobility command to the wireless device for the purpose of cell change, request more measurements, (re)configure the set of serving cell, (re)configure one or more network node parameters related to radio signal transmission and/or reception configuration, calculate a performance metric or performance statistical measure, etc. In another example the wireless device may itself use the radio measurements for performing tasks, e.g., cell reselection, etc.
Several positioning methods for determining the location of a target device such as a wireless device, mobile relay, PDA, etc., exist. Several of these well-known methods include: Satellite based methods that use A-GNSS (e.g. A-GPS) measurements; OTDOA methods that uses wireless device RSTD measurement; UTDOA, which uses measurements done at LMU; Enhanced cell ID that uses one or more of wireless device Rx-Tx time difference, BS Rx-Tx time difference, LTE P/RSRQ, HSPA CPICH measurements, angle of arrival (AoA) etc.; and hybrid methods that use measurements from more than one of these known methods. In LTE, the positioning node configures the wireless device, eNodeB or LMU to perform one or more positioning measurements. The positioning measurements are used by the wireless device or positioning node to determine the wireless device location. Once such positioning method known in the art is OTDOA that makes use of the measured timing of downlink signals received from multiple eNode Bs at the wireless device.
A multi-carrier SCell setup herein refers to a procedure which enables the network node to at least temporarily setup or release the use of a SCell, in DL and/or UL by the CA capable wireless device. The SCell setup or release procedure or command can perform any one or more of: configuration of SCell(s), de-configuration of SCell(s), activation of SCell(s), and deactivation of SCell(s). The configuration procedure (i.e. addition/release of SCell is used by the serving radio network node, e.g., eNode B, to configure a CA capable wireless device with one or more SCells. On the other hand, the de-configuration procedure is used by the eNode B to de-configure or remove one or more already configured SCells (DL SCell, UL SCell or both). The configuration or de-configuration procedure can also be used to change the current multi-carrier configuration e.g. for increasing or decreasing the number of SCells or for swapping the existing SCell(s) with new one(s). Further, the serving radio network node can activate one or more deactivated SCells or deactivate one or more SCells on the corresponding configured secondary carriers. The PCell is always activated. The configured SCells are initially deactivated upon addition and after a cell change, e.g., handover. The deactivation of SCell saves wireless device battery power.
The wireless device may perform measurements even on a deactivated SCell or other cells on the SCC with a deactivated SCell. In this case, the measurements are performed in measurement cycles configured by protocol(s) for higher network layers. It is expected that the measurements of deactivated SCells or other cells on the SCC with a deactivated SCell are made without network provided measurement gaps. The PRS configuration for an RSTD and the SCell measurement cycle used for mobility measurements, e.g., RSRP and RSRQ, are examples of measurement cycles. The SCell measurement cycles may have periodicity of 160 ms, 320 ms, 640 ms or 1024 ms. The maximum time of a measurement within each measurement cycle is currently not restricted by Third Generation Partnership Project (3GPP) standard, but in practice is likely to be up to 6 subframes in each cycle.
However, SCell setup or release, i.e., when SCell is configured, de-configured, activated or deactivated, may cause a glitch or interruption of operation on the PCell or any other activated SCell. Similarly, a glitch or interruption of operation of the PCell or any other activated SCell may occur when the radio for receiving the deactivated SCell is enabled or disabled to make measurements of cells on the deactivated SCC. The term “operation” as used herein means reception and/or transmission of signals. The glitch in UL and/or DL typically occurs when the wireless device has a single radio chain to receive and/or transmit more than one CC. In some situations, the glitch may even occur when the wireless device has independent radio chains on the same chip.
The glitch may occur when the carrier aggregation (CA) capable wireless device changes its reception and/or transmission bandwidth (BW) from single-carrier to multiple-carrier operation or vice versa. In order to change the BW, the wireless device has to reconfigure its RF components in the RF chain, e.g., RF filter, power amplifier (PA), etc. For example, the interruption may be caused due to several factors including RF tuning to reconfigure BW, i.e., shorten or extend, setting or adjusting of radio parameter such as an AGC setting, etc. This interruption caused by the reconfiguration of RF components can vary between 2-5 ms. The glitch may also occur even for interband CA, where separate RF receiver paths are typically used to receive signals on each of the component carriers. In this case, glitches may occur when a single radio frequency (RF) integrated circuit (IC) is used to implement the receive paths. Transient effects may be caused by starting or stopping a local oscillator (LO) circuit which impacts another local oscillator circuit that is active.
During the interruption period the wireless device cannot transmit and/or receive any signal or information to/from the network. Further, during the interruption, the wireless device cannot perform measurements due the wireless device's inability to transmit and/or receive signals to/from the network. This interruption period leads to the loss or dropping of packets transmitted between the wireless device and the wireless device's serving cell(s). It should be noted that the interruption may impact several or all active carriers, and may affect both the uplink and downlink.
When performing measurement on cells of the SCC with deactivated SCell(s) without gaps the wireless device typically retunes the bandwidth of the wireless device receiver or activates another RF path. The cells may be an SCell and/or one or more neighbor cells of the SCC. Therefore, the interruption in DL and/or UL of serving cell occurs before and after each measurement sample, i.e., when the bandwidth is extended, e.g., from 20 MHz to 40 MHz, and also when it is reverted back to the BW of the serving carriers, e.g., from 40 MHz to 20 MHz. The interruption may also occur when the serving carrier and SCC are on the same chip. The interruption in each direction in this case can be between 2-5 ms, since the wireless device has to retune the center frequency and bandwidth of the downlink. The wireless device performs measurements on cells of SCC with deactivated SCell(s) on a regular basis according to the Scell measurement cycle configured by the eNB.
In an existing solution to managing these interruptions, the interruption on the PCell of up to five subframes is allowed for intra-band CA when any of the SCell setup or release procedures are executed by the wireless device. However, the interruption on the PCell of up to one subframe is allowed for inter-band CA when any of the SCell setup or release procedures are executed by the wireless device. Further, in existing solutions to managing these interruptions, the SCell activation and deactivation delay requirements are defined for the wireless device which supports only one SCell in at least the DL. Therefore, when the wireless device is configured with the SCell activates or deactivates, the SCell is not affected by any other serving cell, and the activating or deactivating does not affect any other SCell since there is only one SCell.
However, for a wireless device capable of being configured with two or more SCells, at least two SCells can also be deactivated and configured with SCell measurement cycles for doing measurements on SCCs with deactivated SCells. In this configuration, the wireless device behavior with respect to the impact on the serving cell performance, e.g., PCell interruption, is undefined in the 3GPP standards. This undefined wireless device behavior may result in the wireless device being unable to be served by the serving cell and/or may degrade the measurement performance of measurements on SCCs. In method for avoiding such a situation requires that all SCells be kept in an activated state, even though all of them are not needed all the time. However, this method is not efficient as keeping all SCells in an activated state will degrade wireless device battery life and may also require more processing resources in the network node.