Patent Application
20130195019
poll This invention relates generally to radio frequency (RF) reception and transmission and, more specifically, relates to downlink control channels such as for example the enhanced PDCCH (E-PDCCH) in the LTE system.
This section is intended to provide a background or context to the invention that is recited in the claims. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived, implemented or described. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and claims in this application and is not admitted to be prior art by inclusion in this section.
The following abbreviations that may be found in the specification and/or the drawing figures are defined as follows:
3GPP third generation partnership project
CCE control channel element
CRS common reference signal
CSI channel state information
DL downlink (network towards UE)
DM-RS demodulation reference signal
eNB EUTRAN Node B (a BS in the LTE system)
ePDCCH enhanced PDCCH
E-UTRAN evolved UTRAN (LTE)
FDM frequency division multiplexing
LTE long term evolution
MIB master information block
MIMO multiple input multiple output
MME mobility management entity
PBCH physical broadcast channel
PDCCH physical downlink control channel
PDSCH physical downlink shared channel
PHICH physical hybrid indicator channel
PRB physical resource block
PSS/SSS primary/secondary synchronization signal
PUSCH physical uplink shared channel
RAN radio access network
RF radio frequency
RE resource element
REG resource element group
RS reference signal
SI/SIB system information/system information block
TDM time division multiplexing
UE user equipment
UL uplink (UE towards network)
UTRAN universal terrestrial radio access network
Further developments of the LTE system intend for its next release (Release 11) an enhanced downlink control channel concept referred to as ePDCCH. Early studies in the 3GPP have been carried out as part of the “Enhanced DL MIMO Study item”, and during the December 2011 radio access network RAN plenary meeting a work item in which this ePDCCH will be specified has been agreed.
One feature of this new control channel is that it shall operate with DM-RS reference symbols for the demodulation. Note that this feature has already been implemented for some configurations of the data-bearing PDSCH channel. The benefits of the ePDCCH is that it can utilize frequency domain packet scheduling (FDPS) gain and beamforming by using localized resources for the control channel. It is anticipated that for at least early adoptions the ePDCCH could use the legacy PDCCH for transmitting common control signals such as system information (SI), random access channel (RACH) response indicator and paging indicator.
It has also been discussed in the 3GPP whether the ePDCCH should contain distributed control resources for UEs for which there is no CSI available or for common control transmitted to all UEs. One of the future targets with ePDCCH is that it could also potentially be used in CRS-less cells, where the legacy PDCCH cannot operate. A decision was made in October 2011 at a 3GPP RANI meeting to specify a “new carrier type” as part of the 3GPP RAN work item concerning Carrier Aggregation Enhancements. The possible standalone operation in a CRS-less cell as a future feature requires much more refinement for the common control before such a standalone ePDCCH could be deployed in a practical wireless system.
To better appreciate the issues involved, some of the processes and signaling involved when a UE first joins a cell are now summarized. Its first task is the initial access, which in the LTE Release Aug. 9, 2010 versions includes the following steps:
After all these steps the UE is finally able to access the cell. The problem is that the above procedure does not work in a cell without a fall bandwidth CRS because the PDCCH for such cases cannot be demodulated and detected. This is because the PDCCH requires a full-bandwidth CRS, and the ePDCCH must first be configured to the UE in order for the UE to be able to decode it.
In a first exemplary aspect of the invention there is an apparatus which includes at least one processor and at least one memory including computer program code. The at least one memory and the computer program code are configured to, with the at least one processor and in response to execution of the computer program code, cause the apparatus to perform at least the following: determine frequency resources for common control regions of a control channel as a function of at least bandwidth and an identifier of a specific cell; and control a transmitter or a receiver to communicate between a wireless network and a mobile device using the defined frequency resources of the common control regions of the control channel.
In a second exemplary aspect of the invention there is a method which includes the following: determining frequency resources for common control regions of a control channel as a function of at least bandwidth and an identifier of a specific cell; and controlling a transmitter or a receiver to communicate between a wireless network and a mobile device using the defined frequency resources of the common control regions of the control channel.
In a third exemplary aspect of the invention there is a computer readable memory storing a program of instructions comprising: code for determining frequency resources for common control regions of a control channel as a function of at least bandwidth and an identifier of a specific cell; and code for controlling a transmitter or a receiver to communicate between a wireless network and a mobile device using the defined frequency resources of the common control regions of the control channel.
In a fourth exemplary aspect of the invention there is an apparatus which includes determining means and controlling means. The determining means is for determining frequency resources for common control regions of a control channel as a function of at least bandwidth and an identifier of a specific cell. The controlling means is for controlling a transmitter or a receiver to communicate between a wireless network and a mobile device using the determined frequency resources of the common control regions of the control channel. In a particular embodiment the means for determining and the means for controlling comprise at least one processor executing a program of instructions stored on a computer readable memory. Such an apparatus according to this fourth aspect may be an access node of the wireless network or the mobile device, in which case the apparatus will also include the transmitter or receiver. In other embodiments the apparatus may be only one or more components configured for use in such an access node or mobile device.
Embodiments of these teachings provide a control channel such as the ePDCCH which contains UE-specific as well as common control resources. By example the common control resources will be used for the network to send system information, for a random access channel on which UEs can first obtain a connection with the cell, and for paging UEs. Especially in PDCCH-less primary (PCell) and stand-alone carriers the system information (SI) in the common ePDCCH control resources is expected to be the only source where the initial cell specific parameters can be signaled by the network.
In current 3GPP discussions the ePDCCH is to be multiplexed with PDSCH in the frequency domain, meaning control information and data will be multiplexed together. This suggests that some of the PRB pairs will be reserved for the ePDCCH.
Additionally, it is preferable that the frequency resources for the UE-specific and for the common control will be non-overlapping, since the common control should be transmitted in a frequency distributed way in order to utilize frequency diversity and to ensure the correct reception by multiple UEs covering the entirety of a cell area. Further, it is desirable that the network have the option of providing different offsets for different cells in the system to allow for some kind of interference management between neighboring cells.
Embodiments of these teachings solve this problem by explicitly or implicitly (or a combination of both) conclude the frequency resources for the common control from the configured system bandwidth and the cell identifier. If the common control region of the ePDCCH is operational and the UE has read the SIB, the cell specific control resources are known by the UE, and further the UE-specific control parameters can in addition be signaled by the network.
The size of the resources for common control in the ePDCCH does not need to be very large in most cases. For example, in LTE Release Aug. 9, 2010 the common control region of the PDCCH is only 16 CCEs, which corresponds to 36*16=576 resource elements. For a CRS-less component carrier this would be about four physical resource blocks. One physical resource block is also known in LTE as a PRB pair. If also the physical hybrid indicator channel (PHICH, or more precisely ePHICH) is included in these common control frequency resources, the total amount of resources for common control would be correspondingly larger.
While in general there is an algorithm or function which derives the frequency resources for the common control region from the component carrier bandwidth and the cell ID, various specific embodiments also take into consideration the following non-limiting aspects. In a first embodiment the size of the resources for common control is a function of the bandwidth. In a second embodiment the PHICH resources are taken into account when defining the common control resource size. In a third embodiment the position of the common control is enforced to be in different PRBs for neighbor cells so that they do not overlap in frequency among adjacent cells, in order to mitigate interference via inter-cell coordination. In a fourth embodiment the PRB pairs used for the common control are distributed in frequency. For best performance the control resources can be interleaved on a REG basis inside the distributed resource pool (in conventional LTE there are 4 REs per REG).
In a fifth embodiment the cell is split into several transmission nodes, where each node uses different control regions even if the CellID is the same for all nodes.
In one embodiment, where the regions for control and data resources are defined by frequency division multiplexing (FDM) the common control region is defined by clusters of n consecutive PRB pairs, which are spanning all or most of the OFDM symbols in the subframe and where is n is a small number. These clusters are here referred to as stripes. In this embodiment the UE needs at least part of the following parameters to define the common control resources:
Because there are a limited number of PRBs in the smaller bandwidth of the component carriers which carry the ePDCCH (particularly stand-alone ePDCCHs), there will only be slight variations to the first two of those parameters listed above. The distance between the frequency stripes has strong variations and is very much depending on the system bandwidth, since in exemplary embodiments the frequency distributed transmission should cover the overall available bandwidth as much as possible. The frequency offset can have a larger variation and so it is also the parameter that is used to create non-overlapping common control resources in neighbor cells.
All the above embodiments are an efficient use of the spectrum because there is no waste of control resources. Namely, UE specific control can be for some downlink control information DCI format also transmitted in the common control resources, as is possible with the legacy PDCCH in current LTE specifications.
In a particular embodiment the formula or algorithm which the UE uses for determining the common control region can be a many-to-many type of mapping from the bandwidth, the cell ID, and a potential signaled shift to a small set of value candidates (such as the offset values), which the UE can blindly test with a reasonable number of blind decodings.
In one exemplary embodiment the shift value is signaled by being embedded into the eNB's transmission of the master information block MIB, which is broadcast on the synchronization and physical broadcast channel PBCH in legacy LTE systems and which is shown in
{value—1, value—2 . . . value_n }=f(BW,CellID,shift)
It is within these teachings that the above equation is deterministic for a single configuration of the common control regions of the ePDCCH from the cell or component carrier bandwidth and the cell-ID, as well as a potential signaled shift that is provided within the MIB.
The above exemplary embodiments are summarized with reference to
The shading which is centered on and which includes the center frequency fc of the ePDCCH is used for the PSS/SSS and PBCH on which the UE's seeking initial access to the cell may obtain the MIB. From decoding that MIB the UE will learn the bandwidth of the cell and the cellID. In some deployments of LTE Release 11 it may be adopted that when the cell bandwidth is below a certain threshold that cell will utilize an ePDCCH but no PDCCH, and so from the bandwidth information the UE will know to use the algorithm/function it has stored in its local memory in order to define where are the frequency resources for the common control in the ePDCCH. In one embodiment there are a number of such algorithms/functions (or different adaptations to some base algorithm) that are pre-configured for the UE, and the eNB indicates to the UE (such as in the MIB) which one to use in a given situation. In any case both the eNB and the UE have a common understanding of how to define the common regions of the ePDCCH. The bandwidth & CellID could define number of frequency stripes, offset etc. by such algorithms/functions so with proper network planning, choosing the CellID should in most cases be enough to avoid having that additional signaling above in the In other embodiments the MIB will indicate directly that the carrier is using ePDCCH without any PDCCH since the MIB and the PBCH are assumed to be always available. In another embodiment, the MIB content will indicate the combined resources for common control in ePDCCH. Any of these mentioned embodiments implies the carrier does not use CRSs.
Block 202 of
Block 204 of
Further portions of
Block 212 details an embodiment above in which the frequency resources for common control regions 112 of the control channel 110 are defined or determined further as a function of frequency resources allocated for a physical hybrid indicator channel PHICH.
Block 214 details another specific embodiment in which the frequency resources comprise frequency stripes which are distributed in frequency across the bandwidth, as shown for each ePDCCH 110, 120 at
For the case in which the process of
For the case in which the process of
The logic flow diagram of
The various blocks shown at
Certain of the exemplary embodiments of these teachings provide the following technical effects and advantages. They enable CRS-less initial cell access by a UE, and can be adopted using only existing channels for future advances of the LTE system. There is no additional signaling overhead in some embodiments as the offset may be implicitly defined as a function of the bandwidth and the CellID rather than signaled in the MIB directly, and the function used to define the common control regions is adaptable to different bandwidths. These teachings assure a robust operation because the common control resources 112 are in a known position. Adoption of these teachings will not adversely affect enhanced inter-cell interference coordination. And finally there is no waste of radio resources because the UE-specific control can, for at least some DCI formats, be transmitted in the common control resources in a manner that is already done for legacy PDCCH.
Reference is now made to
The UE 20 includes processing means such as at least one data processor (DP) 20A, storing means such as at least one computer-readable memory (MEM) 20B storing at least one computer program (PROG) 20C or other set of executable instructions, communicating means such as a transmitter TX 20D and a receiver RX 20E for bidirectional wireless communications with the eNB 22 via one or more antennas 20F. Also stored in the MEM 20B at reference number 20G is the UE's algorithm or function for defining the common control regions of the control channel/ePDCCH as detailed further above. From knowing these control regions the DP 20A can then know the tuning command with which to control the receiver 10E to tune to the correct frequency.
The eNB 22 also includes processing means such as at least one data processor (DP) 22A, storing means such as at least one computer-readable memory (MEM) 22B storing at least one computer program (PROG) 22C or other set of executable instructions, and communicating means such as a transmitter TX 22D and a receiver RX 22E for bidirectional wireless communications with the UE 20 (or UEs) via one or more antennas 22F. The eNB 22 stores at block 22G the algorithm or function for defining the common control regions of the control channel/ePDCCH as detailed in the various embodiments above. From knowing these control regions the DP 20A can then know the tuning command with which to control the transmitter 22D to tune to the correct frequency and send the common control information cell-wide.
At least one of the PROGs 22C/22G in the eNB 22 is assumed to include a set of program instructions that, when executed by the associated DP 22A, enable the device to operate in accordance with the exemplary embodiments of this invention, as detailed above. The UE 20 also stores software 20C/20G in its MEM 20B to implement certain aspects of these teachings. In these regards the exemplary embodiments of this invention may be implemented at least in part by computer software stored on the MEM 20B, 22B which is executable by the DP 20A of the UE 20 and/or by the DP 22A of the eNB 22, or by hardware, or by a combination of tangibly stored software and hardware (and tangibly stored firmware). Electronic devices implementing these aspects of the invention need not be the entire devices as depicted at
In general, the various embodiments of the UE 20 can include, but are not limited to personal portable digital devices having wireless communication capabilities, including but not limited to cellular telephones, navigation devices, laptop/palmtop/tablet computers, digital cameras and music devices, and Internet appliances.
Various embodiments of the computer readable MEMs 20B, 22B include any data storage technology type which is suitable to the local technical environment, including but not limited to semiconductor based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed memory, removable memory, disc memory, flash memory, DRAM, SRAM, EEPROM and the like. Various embodiments of the DPs 20A, 22A include but are not limited to general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs) and multi-core processors.
Various modifications and adaptations to the foregoing exemplary embodiments of this invention may become apparent to those skilled in the relevant arts in view of the foregoing description. While the exemplary embodiments have been described above in the context of the LTE and LTE-A system, as noted above the exemplary embodiments of this invention may be used with various other types of wireless communication systems.
Further, some of the various features of the above non-limiting embodiments may be used to advantage without the corresponding use of other described features. The foregoing description should therefore be considered as merely illustrative of the principles, teachings and exemplary embodiments of this invention, and not in limitation thereof.
