Patent Application
20230171821
The present invention relates to the establishing of a wireless connection between a base station apparatus and a mobile communications device in accordance with a mobile communications standard. The invention has particular, but not exclusive, relevance to the establishing of a wireless connection between a base station apparatus and a mobile communications device in accordance with the LTE or LTE-A mobile communication standard.
According to various mobile communications standards, including long-term evolution (LTE) and long-term evolution advanced (LTE-A), a user equipment (UE) camping on a serving cell of a cellular network is required to regularly measure signal characteristics of downlink signals transmitted by base stations of the serving cell and neighbouring cells, for example received signal strength and/or signal quality. These measurements are used by the UE to decide, on the basis of a set of cell reselection criteria, whether or not a cell reselection should be performed, causing the UE to camp on one of the neighbouring cells.
Under certain circumstances, it is desired to force a UE to camp on a specific cell. For example, a dedicated base station may be deployed in association with a sports or entertainment event and it may be desired that attendees camp on that dedicated base station rather than the existing base stations in the vicinity. In another example, a dedicated base station may be deployed in or around an airport, stadium or other facility to provide limited or modified services, or to prevent access to the mobile communications network altogether, from within the facility.
In order to cause a UE to perform cell reselection to a target cell, it is necessary for the corresponding signal characteristics measured by the UE to satisfy the cell reselection criteria. This can usually be achieved by transmitting a powerful enough downlink signal in the target cell. However, if the UE measures a sufficiently high signal strength and/or signal quality for the serving cell on which the UE is currently camping, the UE may be permitted to enter a power-saving “perfect cell” mode, in which the UE only monitors the signal characteristics for the serving cell and no longer measures signal characteristics for the neighbouring cells. As a result, no reselection will be performed, irrespective of the power of the downlink signal transmitted by the base station of the target cell.
According to a first aspect of the present invention, there is provided a method of establishing a wireless connection between a base station apparatus and a mobile communications device in accordance with a mobile communication standard in which data is communicated by wireless signals using orthogonal frequency-division multiplexing. The method includes: allocating a first set of resource blocks for transmitting data from the base station apparatus to the mobile communications device via a downlink signal within a given frequency band; transmitting, by the base station apparatus, an interference signal in a second set of resource blocks within the given frequency band, the second set of resource blocks being different from the first set of resource blocks, wherein the interference signal is configured to interfere with broadcast control signals transmitted by base stations of one or more cells of a mobile communication network; and transmitting, by the base station apparatus, the downlink signal within the first set of resource blocks.
A mobile communications device camping on a serving cell may regularly check the broadcast control signals of the serving cell to determine whether there have been any changes to characteristics of the serving cell. In cases where the mobile communications device may have entered a perfect cell mode, transmitting the interference signal in resource blocks containing the broadcast control signals has been found to be an effective means of forcing the mobile communications device out of perfect cell mode, thus facilitating reselection away from the one or more cells of the mobile communication network.
In examples, the transmitted interference signal is contained within a portion of the frequency band in which the broadcast control signals are transmitted. Selectively transmitting the interference signal in the portion of the frequency band in which the broadcast control signals are transmitted provides an efficient means of forcing the mobile communications device to exit perfect cell mode, for example when it is not feasible to transmit the interference signal throughout the entire frequency band.
In examples, the interference signal is further configured to degrade measurements by the mobile communications device of reference signals transmitted by the base stations of said one or more cells of the mobile communications network in one or more portions of the frequency band in which the broadcast reference signals are not transmitted. A mobile communications device camping on a serving cell may regularly measure reference signals transmitted by the serving cell and use the measurements to determine whether to measure downlink signals transmitted in neighbouring cells, and/or whether to perform a cell reselection to a neighbouring cell. By degrading measurements of these reference signals, the effectiveness of the interference signal at forcing the mobile communications device out of perfect cell mode may be increased.
In examples, allocating the first set of resource blocks for transmitting the data via the downlink signal includes determining timings of the broadcast control signals transmitted by the base stations of said one or more cells of the mobile communications network, and allocating the first set of resource blocks so that broadcast control signals transmitted by the base station apparatus do not interfere with the broadcast control signals transmitted by the base stations of said one or more cells of the mobile communications network. Allocating the first set of resource blocks in this way facilitates reselection to the base station apparatus when the mobile communications device has exited perfect cell mode, because the broadcast control signals of the base station apparatus do not have to compete with broadcast control signals transmitted by the cells of the mobile communications network. The broadcast control signals of the base station apparatus are therefore more readily detected and decoded by the mobile communications device, simplifying the task of error correction software in the mobile communications device in distinguishing between the broadcast control signals.
In examples, the downlink signal is a first downlink signal, and the method includes measuring a received signal strength and/or received signal quality of a second downlink signal transmitted by one of the base stations of the mobile communications network, and the transmitting of the interference signal is dependent on the measured received signal strength and/or received signal quality of the second downlink signal exceeding a threshold. This avoids unnecessary transmitting of an interference signal, for example where no neighbouring cell is a candidate perfect cell in a target operational area. Furthermore, the bandwidth of the interference signal may be dependent on the measured received signal strength and/or received signal quality of the second downlink signal. If the second downlink signal has a high received signal strength or signal quality, a relatively large bandwidth may be necessary for the interference signal to sufficiently degrade measurements of the second downlink signal by the mobile communications device. On the other hand, if the second downlink signal has a relatively low received signal strength and/or received signal quality, a smaller bandwidth, and accordingly lower transmitter power, may be sufficient.
In examples where the transmitting of the interference signal is dependent on the received signal strength and/or received signal quality of the second downlink signal exceeding a threshold, the threshold may be dependent on a parameter transmitted within the second downlink signal indicating a minimum received signal strength and/or received signal quality of the second downlink signal for mobile communications devices to refrain from performing measurements of downlink signals other than the second downlink signal. In this way, the threshold for transmitting the interference signal is responsive to the perfect cell criteria of the neighbouring cell.
According to a second aspect of the invention, there is provided apparatus for establishing a wireless connection with a mobile communications device in accordance with a mobile communication standard in which data is communicated by wireless signals using orthogonal frequency-division multiplexing. The apparatus includes a transmitter, and processing circuitry arranged to allocate a first set of resource blocks for transmitting data from the transmitter to the mobile communications device via a downlink signal within a given frequency band. The apparatus is arranged to transmit, using the transmitter, an interference signal in a second set of resource blocks within the given frequency band, the second set of resource blocks being different from the first set of resource blocks, wherein the interference signal is configured to interfere with broadcast control signals transmitted by base stations of one or more cells of a mobile communication network; and transmitting, using the transmitter, the downlink signal within the first set of resource blocks.
Further features and advantages of the invention will become apparent from the following description of preferred embodiments of the invention, given by way of example only, which is made with reference to the accompanying drawings.
In order for a cell reselection to take place, cell reselection criteria must be satisfied as specified in 3GPP TS 36.304 sections 5.2.4.5 and 5.2.4.6. The specific criteria which apply depend on whether the frequency band and radio access technology (RAT) of the target cell is the same as the frequency band and RAT of the currently serving cell, and if not, whether the frequency band and RAT of the target cell has a higher, lower, or equal reselection priority compared with the frequency band and RAT of the currently serving cell. In any case, a UE can only perform a cell reselection if the UE measures a reference signal received power (RSRP) of the target cell to be greater than a certain threshold value (which can be derived from system information transmitted by the serving cell, and may depend on the RSRP of the serving cell).
From the above considerations, it is clear that a UE will only perform a cell reselection if the UE actively measures signal characteristics of signals transmitted within candidate cells for reselection. However, 3GPP TS 36.304 section 5.2.4.2 permits a UE to forego inter-frequency and/or intra-frequency measurements of candidate cells if the following respective measurement criteria are satisfied:
From the above criteria, it can be seen that the independent base station 110 would be able to avoid the “perfect cell” problem by operating at a frequency with a higher cell reselection priority than that of the networked base station 102a. In this case, the measurement criteria above would not be satisfied, and the cell of the networked base station 102a would therefore be forced to measure the frequency band of the independent base station 110, irrespective of the signal power/quality of the downlink signal received from the networked base station 102a. However, it is not guaranteed that a higher-priority frequency band exists, and even if such frequency bands do exist, other considerations may prevent an independent base station from operating within one of the higher-priority frequency bands.
In the example of
In order to avoid a situation where the UE 100 enters the coverage area of the independent base station 110 but does not perform a cell reselection, the independent base station 110 is configured to perform a method to help facilitate cell reselection by the UE 100. In order to do so, the independent base station 110 allocates a first set of PRBs in which to transmit data via a downlink signal within a given frequency band. The allocated PRBs include PRBs for transmitting control plane data and optionally PRBs for transmitting user plane data, depending on the specific application of the independent base station 110.
In accordance with the LTE specification, the independent base station 110 allocates PRBs in which to transmit a set of broadcast control signals. The broadcast control signals are allocated in a predetermined configuration in subframes 0 and 5 of each system frame, within a central control region of the frequency band. The broadcast control signals include a primary synchronisation (PSS), a secondary synchronisation signal (SSS), and a physical broadcast channel (PBCH).
In the present example, the subframe timing and the allocation of the first set of PRBs for the downlink signal is performed independently of any signals transmitted by eNodeBs 102 of the mobile communications network. In this way, the independent base station 110 is not required to scan for neighbouring cells in order to determine the subframe timing or to allocate the first set of PRBs. In other examples, the subframe timing can be made dependent on signals transmitted by neighbouring cells, as will be explained in more detail hereafter. Furthermore, in some examples the first set of PRBs may be allocated/scheduled in dependence on signals exchanged with eNodeBs 102 in the vicinity of the independent base station 110, for example using the X2 interface.
The independent base station 110 transmits the downlink signal in the allocated first set of PRBs, and further transmits an interference signal configured to interfere with broadcast control signals transmitted by eNodeBs 102 operating within the same frequency band in the vicinity of the independent base station 110. The interference signal is transmitted in a second set of PRBs which is different from the first set of PRBs in which the independent base station 110 transmits its downlink signal. In the present example, the second set of PRBs is disjoint from the first set of PRBs. In other words, the interference signal is not transmitted in the PRBs allocated to the downlink signal of the target cell, so the interference signal does not interfere with PRBs carrying the downlink signal of the target cell. In other examples, the interference signal may share certain PRBs with the downlink signal of the target cell. For example, the interference signal may further be transmitted in the PRBs containing the PSS, SSS and PBCH, but in resource elements that are not occupied by the PSS, SSS and PBCH.
A UE camping on a serving cell will regularly check the broadcast control signals (PSS, SSS and PBCH) of the serving cell, to determine whether there have been any changes to characteristics of the serving cell. The inventor has discovered that interfering with the broadcast control signals within the control region of the downlink signal can cause a UE to exit perfect cell mode, irrespective of the strength and quality of the CRS in other regions of the frequency band. Furthermore, interfering with the broadcast control signals transmitted by a given cell can prevent a UE from camping on that cell in the first place. Selectively transmitting the interference signal in a narrow portion of the frequency band containing the control region therefore provides an efficient means of degrading the second downlink signals, for example when it is not feasible to transmit the interference signal throughout the entire frequency band due to power limitations of the amplifier of the independent base station 110.
In some examples, the interference signal can be configured to extend into regions of the frequency band in which the broadcast reference signals are not transmitted. In this way, the interference signal can effectively degrade measurements by UEs of reference signals transmitted by eNodeBs of the mobile communications network. In LTE, measurements of RSRP and RSRQ, on which the cell reselection criteria are based, are performed using a cell-specific reference signal (CRS) which is transmitted throughout the frequency band. An effective way to degrade measurements of a given downlink signal is therefore to transmit the interference signal in resource elements containing the CRS of the given downlink signal. Transmitting the interference signal over a wider frequency range will typically result in more effective degrading of measurements of downlink signals by mobile communications devices, as the interference signal will occupy more resource elements occupied by the CRS of the downlink signals. Increasing the bandwidth and/or the power of the interference signal generally increases the size of the region in which the independent base station 110 can force a cell reselection from a candidate perfect cell to the target cell, and furthermore causes cell reselections to occur more quickly.
Since the independent base station 110 must transmit its own downlink signal within the same frequency band as the interference signal, the interference signal should be configured to avoid PRBs needed for the downlink signal of the independent base station 110, and resource elements occupied by the CRS transmitted by the independent base station 110. The independent base station 110 may, for example, transmit the interference signal in every resource element of every PRB within a given frequency range, except for:
Since the allocation of PRBs in the downlink signal can change over time, the configuration of the interference signal may need to be updated dynamically in order continue degrading measurements of the candidate perfect cell, whilst avoiding PRBs used by the target cell of the independent base station 110.
The interference signal may be any suitable form of signal suitable for interfering with downlink signals transmitted by the eNodeBs 102. The interference may comprise, for example, random or pseudo-random data bits transmitted in the appropriate PRBs or resource elements as described above, frequency-limited noise such as additive Gaussian white noise (AGWN), or a specific waveform which is arranged to interfere destructively with CRSs transmitted by the eNodeBs 102.
Although in the example above the independent base station 110 determines a subframe timing and allocates PRBs for the downlink signal and interference signal independently of any of the eNodeBs 102, in another example the system may be arranged to determine a subframe timing and PRB allocation in dependence on the eNodeBs 102, and particularly those eNodeBs 102 which are candidate perfect cells for UEs in the vicinity of the independent base station 110.
Upon detecting a downlink signal, the independent base station 110 uses the PSS of the detected downlink signal to determine, at 604, a timing of a set of broadcast control signals of the detected downlink signal. The set of broadcast control signals including the PSS, a secondary synchronisation signal (SSS), and a physical broadcast channel (PBCH). These broadcast control signals are transmitted in a predetermined configuration within a central control region of the frequency band, as described above.
In the present example, the independent base station 110 determines, at 606, whether any detected downlink signal corresponds to a candidate perfect cell. A candidate perfect cell is one that has a sufficiently high signal strength and/or signal quality in at least a portion of the target cell that a mobile communications device camped on the candidate perfect cell may be permitted not to make measurements of neighbouring cells whilst located in the target cell.
In the present example, determining whether the cell is a candidate perfect involves first determining whether the relevant measurement threshold Sintrasearch is defined in the system information (specifically, in the system information block-type 3, SIB-3). If Sintrasearch is not defined, the cell is not a candidate perfect cell, because the measurement criterion 1 cannot be satisfied. If Sintrasearch is defined, the independent base station 110 measures the RSRP of the downlink signal, and determines whether the resulting Srxlev value is greater than a threshold value Sperfectcell. If Srxlev>Sperfectcell, then the cell corresponding to the downlink signal is a candidate perfect cell. The value of Sperfectcell is set to a value such that a downlink signal satisfying the measurement criterion 1 for a UE anywhere in the coverage area of the independent base station 110 will also satisfy the candidate perfect cell criterion Srxlev>Sperfectcell at the independent base station 110 (Sperfectcell will therefore typically be set to a lower value than Sintrasearch, and may be set in dependence on the value of Sintrasearch transmitted by the serving cell). In the example of
The independent base station 110 allocates, at 608, a first set of PRBs in which to transmit data via a downlink signal. In this example, the first set of PRBs is allocated so that the broadcast control signals transmitted by the independent base station 110 are transmitted at different times to the broadcast control signals transmitted by any of the eNodeBs 102. In particular, the PSS, SSS and PBCH transmitted by the independent base station 110 do not overlap with the PSS, SSS and PBCH transmitted by the eNodeB 102a which is determined to be a candidate perfect cell. In the present example, the independent base station 110 allocates PRBs using a subframe timing which is delayed compared with that of the eNodeB 102a by a predetermined number of subframes.
The independent base station 110 transmits, at 210, an interference signal configured to interfere with broadcast control signals transmitted by one or more eNodeBs 102 operating within the same frequency band in the vicinity of the independent base station 110, including the broadcast control signals of the candidate perfect cell. The interference signal may be configured to occupy all PRBs in the control region which are not occupied by the broadcast control signals of the independent base station 110, or may alternatively occupy only a specific set of PRBs in the control region, for example to specifically target the broadcast control signals of the candidate perfect cell. Advantageously, the interference signal can be transmitted over a longer period than that in which the broadcast control signals are transmitted, in order to account for timing differences at different locations in the cell.
The interference signal may be of any suitable form for interfering with the broadcast control signals of the candidate perfect cell, and optionally for interfering with the CRS of the candidate perfect cell in regions of the frequency band outside of the central control region. The interference signal may be constrained to occupy specific resource elements, for example to target the CRS of the candidate perfect cell. This approach may result in an interference signal which uses less power, but will only be suitable for degrading measurements of the candidate perfect cell. In any case, the interference signal should not overlap with PRBs needed by the target cell, or the CRS transmitted by the target cell. The transmission power for the interference signal may be configured in dependence on the signal strength and/or quality of the candidate perfect cell signal, and may further depend on how many of the CRS resource elements are able to be interfered with (a higher power may be required if fewer CRS resource elements are interfered with).
The independent base station 110 transmits, at 612, the first downlink signal in the first set of PRBs allocated at 608. Since the allocation of PRBs in the downlink signal can change over time, the configuration of the interference signal may need to be updated dynamically in order continue degrading measurements of the candidate perfect cell, whilst avoiding PRBs used by the target cell of the independent base station 110.
In order for the above method to be able to degrade measurements of a candidate perfect cell without also degrading measurements of the target cell, it is advantageous for the CRS of the target cell to occupy different resource elements to the CRS of the candidate perfect cell. In this case, before transmitting the interference signal, the independent base station 110 may therefore determine a CRS configuration of the downlink signal transmitted by the candidate perfect cell. In order to do this, the independent base stations 110 may decode the PSS, SSS and PBCH of the downlink signal, which include sufficient information to allow the independent base station 110 to determine the physical cell ID, system frame number, and system bandwidth associated with the downlink signal. These parameters are sufficient for the independent base station 110 to determine the CRS configuration of the downlink signal (in accordance with 3GPP TS 36.211 section 6.10.1).
Having determined the CRS configuration of the candidate perfect cell, the independent base station 110 may select a CRS configuration for the target cell which is different to the CRS configuration of the candidate perfect cell. Selecting the CRS configuration of the target cell can be achieved by selecting a physical cell ID for the target cell that differs from the physical cell ID of the candidate perfect cell by a predetermined amount, which results in the CRS occupying resource elements on different subcarriers.
As explained above, although in the example of
In the examples described above, the independent base station 110 operates in the same frequency band as the eNodeB 102a, and therefore the corresponding cell reselection from the eNodeB 102a to independent base station 110 is an intra-frequency cell reselection, and measurement criterion 1 above is relevant for whether the UE 100 performs measurements of the downlink signal of the independent base station 110. Alternatively, if the independent base station 110 were to operate in a different frequency band to the eNodeB 102a, the cell reselection would be an inter-frequency cell reselection, and measurement criterion 2 above would be relevant. In this case, the UE 100 would only be permitted to refrain from measuring the downlink signal of the independent base station 110 if the cell reselection priority of the eNodeB 102a were higher than the reselection priority of the independent base station 110. The independent base station 110 can therefore avoid the “perfect cell” problem by operating at a frequency with a higher cell reselection priority than that of the independent base station 110. In cases where it is not possible for the independent base station 110 to operate at a higher priority frequency, the independent base station 110 may be tuned to the same frequency band as the candidate perfect cell, as described above, or a different frequency with the same or a lower priority. If a different frequency is used, a further antenna, either integral to, or communicatively coupled with, the independent base station 110, may be tuned to the frequency of the candidate perfect cell and used to transmit the interference signal.
It is feasible that more than one candidate perfect cell may exist at the location of the target cell, for example at different frequencies. In this case, multiple antennas may be required to transmit appropriately-configured interference signals for each of the candidate perfect cells. In any case, one or more dedicated antennas may be provided for transmitting interference signals, as an alternative to transmitting the interference signal using the same antenna that transmits the downlink signal. In an example where the present invention is used to degrade measurements of multiple neighbouring cells in the same frequency band, the target cell may advantageously transmit a downlink signal with a timing such that the PSS, SSS and PBCH of the target cell do not interfere with the PSS, SSS and PBCH of any of the neighbouring cells.
The method described facilitates cell reselection by the UE 100 from a candidate perfect cell to the target cell of the independent base station 110. In order to prevent the UE 100 from subsequently reselecting a different cell whilst still in the coverage area of the independent base station 110, the independent base station 110 can specify values of various parameters which makes such a reselection unlikely or impossible. For example, the independent base station 110 can set very low values for the thresholds Sintrasearch and/or Snonintrasearch, such that UEs camping on the independent base station 110 are permitted to stop measuring neighbouring cells, even when the Srxlev measured for the independent base station 110 is relatively low.
In the example of
Whilst the methods above have been described in the context of cell reselection for UEs in idle mode, the same methods can also be used to trigger events as defined in 3GPP TS 36.331 for a UE in connected mode, facilitating handover to a target cell.
The methods described above may be performed using processing circuitry integral to a base station. The processing circuitry may include any suitable form or forms of processing unit, for example a central processing unit (CPU), an application-specific integrated circuit (ASIC), and/or a digital signal processor (DSP). The method is generally implemented through the execution of machine-readable code stored on a non-transient storage medium at the base station.
Although in the illustrative example described above, the functionality of each of the networked base stations is incorporated into an eNodeB, it will be appreciated that for other RATs, the functionality of a base station may be performed by other network entities, for example a Next Generation NodeB (gNB) in 5G, a nodeB in 3G, a base station controller (BSC) and base transceiver station (BTS) in GSM.
A person skilled in the art would appreciate that, although the example described above involves a separately introduced base station, the methods described herein could equally be performed by an existing base station connected to a core network, in order to provide access to the core network via that base station.
The above embodiments are to be understood as illustrative examples of the invention. Further embodiments of the invention are envisaged. In particular, the present invention can be applied for any RAT which uses orthogonal frequency-division multiplexing, and which permits a UE to stop measuring neighbouring cells under certain conditions, including LTE-A and 5G. It is to be understood that any feature described in relation to any one embodiment may be used alone, or in combination with other features described, and may also be used in combination with one or more features of any other of the embodiments, or any combination of any other of the embodiments. Furthermore, equivalents and modifications not described above may also be employed without departing from the scope of the invention, which is defined in the accompanying claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2012046.5 | Aug 2020 | GB | national |
This application is a continuation under 35 U.S.C. § 120 of International Application No. PCT/EP2021/071697, filed Aug. 3, 2021, which claims priority to GB Application No. 2012046.5, filed Aug. 3, 2020, under 35 U.S.C. § 119(a). Each of the above-referenced patent applications is incorporated by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/EP2021/071697 | Aug 2021 | US |
| Child | 18101360 | US |
