The present invention relates to an apparatus, method, system and computer program product for providing control channel coordination in heterogeneous networks.
Prior art which is related to this technical field can e.g. be found by the technical specifications TS 36.211 current version: 8.8.0), TS 36.212 (current version 8.7.0), TS 36.213 (current version: 8.8.0) and TS 36.814 (current version: 1.0.0) of the 3GPP, and by the contributions document R4-093091 and document R4-093220 of the working group 4 of the 3GPP related to radio access networks.
The following meanings for the abbreviations used in this specification apply:
3GPP: 3rd Generation Partnership Project
BLER: Block Error Rate
CCE: Control Channel Element
CDM: Code Division Multiplex
C-RNTI: Cell Radio Network Temporary Identifier
CRS: Common Reference Signal
DL: Downlink
eNB: evolved Node B (eNode B)
FD: Frequency Domain
FDD: Frequency Division Duplex
GPS: Global Positioning System
GSM: Global System for Mobile Communication
HARQ: Hybrid Automatic Repeat Request
HeNB: Home eNB
LA: Local Area
LOS: Line-of-Sight
LTE: Long Term Evolution
MBSFN: Multimedia Broadcast over Single Frequency Network
MIB: Master Information Block
OFDMA: Orthogonal Frequency Division Multiple Access
O&M: Operations and Maintenance
PBCH: Physical Broadcast Channel
PCFICH: Physical Control Format Indicator Channel
PCI: Physical Cell Identity
PDCCH: Physical Downlink Control Channel
PDSCH: Physical Downlink Shared Channel
PHICH: Physical HARQ Indicator Channel
PRB: Physical Resource Block
PUCCH: Physical Uplink Control Channel
PUSCH: Physical Uplink Shared Channel
RE: Resource Element
REG: Resource Element Group
SC-FDMA: Single Carrier Frequency Division Multiple Access
SIB: System Information Block
TD: Time Domain
TDD: Time Division Duplex
TTI: Transmission Time Interval
UE: User Equipment
UL: Uplink
UMTS: Universal Mobile Telecommunications System
UTRAN: UMTS Terrestrial Radio Access Network
WA: Wide Area
WiMAX: Worldwide Interoperability for Microwave Access
In recent years, 3GPP's LTE as the upcoming standard is under particular research. The base station of LTE is called eNodeB. LTE will be based on OFDMA in downlink and SC-FDMA in uplink. Both schemes allow the division of the uplink and downlink radio resources in frequency and time, i.e. specific frequency resources will be allocated for certain time duration to the different UE. The access to the uplink and downlink radio resources is controlled by the eNode B that controls the allocation of the frequency resources for certain time slots.
Furthermore, for mobile wireless communication systems such as those according to the 3GPP LTE low transmission power eNBs (which in the following are called Home eNodeBs or with a synonym meaning, femto or pico eNB) are proposed. These nodes can be operated at the same frequency layer, i.e. the same carrier frequency in the same frequency band, as a wide area eNB.
For example, on the field of Evolved UTRAN/Long-Term-Evolution (EUTRAN/LTE) and LTE-Advanced networks as well as in general in the field of wireless communication networks, a heterogeneous network is typically characterized by the combination of a Wide Area (WA) network (with macro base stations such as the above WA eNB) with an outdoor and/or an indoor Local Area (LA) network (with so-called pico or femto base stations such as the above HeNB) in the same geographical area.
However, the coexistence of WA and LA networks faces interference issues.
A rather simple method of solving interference issues consists of deploying the WA and the LA network in disjoint spectrum.
Though, since operators, in particular when having scarce spectrum, aim at enhancing overall capacity by offloading traffic into a LA network, the most desirable heterogeneous network deployment will be the co-channel deployment of the WA and the LA network. Moreover, many operators will require that co-channel deployment should be enabled within the existing LTE Release 8 standard definition.
To date co-channel deployment of WA and LA network relies on network planning:
For heavy traffic offloading, however, network planning options may not be sufficient. It is known already that in many cases more than 5 dB to 10 dB in-building penetration losses cannot be expected. Also, LA deployments may also be needed in quite low frequency bands (e.g. GSM, 800 MHz, U.S. 700 MHz, etc.) where in-building penetration has not been an issue to date.
For traffic offloading in lower frequency bands, the operator may want to allow for a rather wide-spread residential HeNB deployment or even for HeNB LA clusters inside an office building such that neither network planning Option 1 nor Option 2 or Option 3 are available while co-channel deployment is required by the operator.
The problem occurs in four use cases for co-channel deployment:
It is an object of the present invention to overcome at least some of the drawbacks of the prior art.
According to a first aspect of the present invention, this is accomplished by an apparatus, comprising parameter provision means configured to provide parameter indicating the availability of resources, wherein a resource is defined as an available radio frequency per time interval, and parameter indicating the configuration of a physical channel configured for downlink control, for a physical control channel configured for format indication, and for a physical channel configured for hybrid automatic repeat request indication, respectively, for use in both of two different communication cells for providing radio communication services for terminals located in said cells; and determining means configured to determine a first resource allocation set and a second resource allocation set, wherein the first resource allocation set and the second resource allocation set respectively comprise resource allocations for a physical channel configured for downlink control, for a physical control channel configured for format indication, and for a physical channel configured for hybrid automatic repeat request indication, and wherein the determining means is configured to determine the first resource allocation set and the second resource allocation set to be as mutually disjoint in resource allocation as possible in consideration of the parameters provided by the parameter provision means.
Modifications of the first aspect may be as follows.
The apparatus according to the first aspect may be configured to be suitable for providing control channel coordination in heterogeneous networks.
The two different communication cells may be selected from a group comprising a macro communication cell and a femto or pico communication cell, or comprising two or more femto or pico communication cells in a local area deployment.
The determining means may be further configured to determine the first resource allocation set and the second resource allocation set to be as mutually disjoint in resource allocation as possible by suitably selecting a physical cell identity for the second communication cell, by filling a string of control channel elements forming the physical channel configured for downlink control of the first communication cell with dummy terminal-related control channel elements where a control channel element string of the physical channel configured for downlink control of the second communication cell has its terminal-related control channel elements and vice versa, and by controlling a terminal search space on the physical channels configured for downlink control within both communication cells based on a pre-defined set of cell radio network temporary identifier for the first communication cell and a pre-defined set of cell radio network temporary identifier for the second communication cell.
According to a second aspect of the present invention, the object is accomplished by an apparatus, comprising a parameter provision processor configured to provide parameter indicating the availability of resources, wherein a resource is defined as an available radio frequency per time interval, and parameter indicating the configuration of a physical channel configured for downlink control, for a physical control channel configured for format indication, and for a physical channel configured for hybrid automatic repeat request indication, respectively, for use in both of two different communication cells for providing radio communication services for terminals located in said cells; and a determining processor configured to determine a first resource allocation set and a second resource allocation set, wherein the first resource allocation set and the second resource allocation set respectively comprise resource allocations for a physical channel configured for downlink control, for a physical control channel configured for format indication, and for a physical channel configured for hybrid automatic repeat request indication, and wherein the determining processor is configured to determine the first resource allocation set and the second resource allocation set to be as mutually disjoint in resource allocation as possible in consideration of the parameters provided by the parameter provision means.
Modifications of the second aspect of the present invention may correspond to the modifications of the first aspect.
According to a third aspect of the present invention, the object is accomplished by an apparatus, comprising detecting means configured to detect a first resource allocation set and a second resource allocation set, wherein a resource is defined as an available radio frequency per time interval, and wherein the first resource allocation set and the second resource allocation set respectively comprise resource allocations for a physical channel configured for downlink control, for a physical control channel configured for format indication, and for a physical channel configured for hybrid automatic repeat request indication; and controlling means configured to control a power of signal transmission on the physical channels reflected in the first resource allocation set in relation to the second resource allocation set such that a power of signal transmission differs in dependency on whether resource allocations in the first resource allocation set and the second resource allocation set are disjoint.
Modifications of the third aspect may be as follows.
The apparatus according to the third aspect may be configured to be suitable for providing control channel coordination in heterogeneous networks.
The controlling means may be configured to control a power of signal transmission such that a power of signal transmission is higher where resource allocations in the first resource allocation set and the second resource allocation set are disjoint, and a power of signal transmission is lower where resource allocations in the first resource allocation set and the second resource allocation set are not disjoint.
The controlling means may be configured to control a power of signal transmission such that a power of signal transmission is lower where resource allocations in the first resource allocation set and the second resource allocation set are disjoint, and a power of signal transmission is higher where resource allocations in the first resource allocation set and the second resource allocation set are not disjoint.
According to a fourth aspect of the present invention, the object is accomplished by an apparatus, comprising a detecting processor configured to detect a first resource allocation set and a second resource allocation set, wherein a resource is defined as an available radio frequency per time interval, and wherein the first resource allocation set and the second resource allocation set respectively comprise resource allocations for a physical channel configured for downlink control, for a physical control channel configured for format indication, and for a physical channel configured for hybrid automatic repeat request indication; and a controlling processor configured to control a power of signal transmission on the physical channels reflected in the first resource allocation set in relation to the second resource allocation set such that a power of signal transmission differs in dependency on whether resource allocations in the first resource allocation set and the second resource allocation set are disjoint.
Modifications of the fourth aspect of the present invention may correspond to the modifications of the third aspect.
According to a fifth aspect of the present invention, the object is accomplished by an apparatus, comprising synchronization means configured to synchronize in time an internal channel transmission clock with an external channel transmission clock; and channel transmission means configured to introduce a time domain offset in downlink channel transmission of a physical channel configured for broadcast as well as of synchronization signals of a first communication cell with respect to downlink channel transmission of a physical channel configured for broadcast as well as of the synchronization signals of a second communication cell.
Modifications of the fifth aspect may be as follows.
The apparatus according to the fifth aspect may be configured to be suitable for providing control channel coordination in heterogeneous networks.
A given time structure of the first communication cell's channel transmission of the physical channel configured for broadcast comprising a periodically recurring pattern built on a frame-and-sub-frame-structure and an analogous given time structure of the second communication cell's channel transmission of the physical channel configured for broadcast may be exploited to configure a time domain offset as one frame length in time or as positive integer-multiple thereof, such that the physical channel configured for broadcast of the first and the second communication cells are interleaved and do not collide.
Each of the two or more communication cell's channel transmissions of the physical channel configured for broadcast with a time structure built on a frame structure with ten sub-frames may be configured with a mutual time domain offset which is N times the time length of one sub-frame, wherein N is a positive integer but cannot be multiples of five, and wherein in one communication cell's channel transmission a physical channel configured for shared downlink and a physical channel configured for multicast which collide in time and frequency with the other cell's channel transmission of the physical channel configured for broadcast are muted by introducing an empty multimedia broadcast over single frequency network sub-frame for each M-th frame interval time length, wherein M is a positive integer.
According to a sixth aspect of the present invention, the object is accomplished by an apparatus, comprising a synchronization processor configured to synchronize in time an internal channel transmission clock with an external channel transmission clock; and a channel transmission processor configured to introduce a time domain offset in downlink channel transmission of a physical channel configured for broadcast as well as of synchronization signals of a first communication cell with respect to downlink channel transmission of a physical channel configured for broadcast as well as of the synchronization signals of a second communication cell. Modifications of the sixth aspect of the present invention may correspond to the modifications of the fifth aspect.
According to a seventh aspect of the present invention, the object is accomplished by a method, comprising providing parameter indicating the availability of resources, wherein a resource is defined as an available radio frequency per time interval, and parameter indicating the configuration of a physical channel configured for downlink control, for a physical control channel configured for format indication, and for a physical channel configured for hybrid automatic repeat request indication, respectively, for use in both of two different communication cells for providing radio communication services for terminals located in said cells; and determining a first resource allocation set and a second resource allocation set, wherein the first resource allocation set and the second resource allocation set respectively comprise resource allocations for a physical channel configured for downlink control, for a physical control channel configured for format indication, and for a physical channel configured for hybrid automatic repeat request indication, and wherein the first resource allocation set and the second resource allocation set are determined to be as mutually disjoint in resource allocation as possible in consideration of the parameters provided by the parameter provision means.
Modifications of the seventh aspect may be as follows.
The method according to the seventh aspect may be configured to be suitable for providing control channel coordination in heterogeneous networks.
The two different communication cells may be selected from a group comprising a macro communication cell and a femto or pico communication cell, or comprising two or more femto or pico communication cells in a local area deployment.
The first resource allocation set and the second resource allocation set may be determined as mutually disjoint in resource allocation as possible by including suitably selecting a physical cell identity for the second communication cell, filling a string of control channel elements forming the physical channel configured for downlink control of the first communication cell with dummy terminal-related control channel elements where a control channel element string of the physical channel configured for downlink control of the second communication cell has its terminal-related control channel elements and vice versa, and controlling a terminal search space on the physical channels configured for downlink control within both communication cells based on a predefined set of cell radio network temporary identifier for the first communication cell and a pre-defined set of cell radio network temporary identifier for the second communication cell.
The method according to the seventh aspect or any of its modifications may be performed by the apparatus according to the first or second aspect or suitable ones of their modifications.
According to an eighth aspect of the present invention, the object is accomplished by a method, comprising detecting a first resource allocation set and a second resource allocation set, wherein a resource is defined as an available radio frequency per time interval, and wherein the first resource allocation set and the second resource allocation set respectively comprise resource allocations for a physical channel configured for downlink control, for a physical control channel configured for format indication, and for a physical channel configured for hybrid automatic repeat request indication; and controlling a power of signal transmission on the physical channels reflected in the first resource allocation set in relation to the second resource allocation set such that a power of signal transmission differs in dependency on whether resource allocations in the first resource allocation set and the second resource allocation set are disjoint.
Modifications of the eighth aspect may be as follows.
The method according to the eighth aspect may be configured to be suitable for providing control channel coordination in heterogeneous networks.
The controlling may further include controlling a power of signal transmission such that a power of signal transmission is higher where resource allocations in the first resource allocation set and the second resource allocation set are disjoint, and a power of signal transmission is lower where resource allocations in the first resource allocation set and the second resource allocation set are not disjoint.
The controlling may further include controlling a power of signal transmission such that a power of signal transmission is lower where resource allocations in the first resource allocation set and the second resource allocation set are disjoint, and a power of signal transmission is higher where resource allocations in the first resource allocation set and the second resource allocation set are not disjoint.
The method according to the eighth aspect or any of its modifications may be performed by the apparatus according to the third or fourth aspect or suitable ones of their modifications.
According to a ninth aspect of the present invention, the object is accomplished by a method, comprising synchronizing in time an internal channel transmission clock with an external channel transmission clock; and introducing a time domain offset in downlink channel transmission of a physical channel configured for broadcast as well as of synchronization signals of a first communication cell with respect to downlink channel transmission of a physical channel configured for broadcast as well as of the synchronization signals of a second communication cell.
Modifications of the ninth aspect may be as follows.
The method according to the ninth aspect may be configured to be suitable for providing control channel coordination in heterogeneous networks.
A given time structure of the first communication cell's channel transmission of the physical channel configured for broadcast comprising a periodically recurring pattern built on a frame-and-sub-frame-structure and an analogous given time structure of the second communication cell's channel transmission of the physical channel configured for broadcast may be exploited to configure a time domain offset as one frame length in time or as positive integer-multiple thereof, such that the physical channel configured for broadcast of the first and the second communication cells are interleaved and do not collide.
Each of the two or more communication cell's channel transmissions of the physical channel configured for broadcast with a time structure built on a frame structure with ten sub-frames may be configured with a mutual time domain offset which is N times the time length of one sub-frame, wherein N is a positive integer but cannot be multiples of five, and wherein in one communication cell's channel transmission a physical channel configured for shared downlink and a physical channel configured for multicast which collide in time and frequency with the other cell's channel transmission of the physical channel configured for broadcast are muted by introducing an empty multimedia broadcast over single frequency network sub-frame for each M-th frame interval time length, wherein M is a positive integer.
The method according to the ninth aspect or any of its modifications may be performed by the apparatus according to the fifth or sixth aspect or suitable ones of their modifications.
According to a tenth aspect of the present invention, the object is accomplished by an evolved Node B, comprising an apparatus according to the third to sixth aspect of the present invention or any one of their modifications.
According to an eleventh aspect of the present invention, the object is accomplished by a central network entity, comprising an apparatus according the first or second aspect of the present invention or any one of their modifications.
According to a twelfth aspect of the present invention, the object is accomplished by a computer program product comprising computer-executable components which perform, when the program is run on a computer providing parameter indicating the availability of resources, wherein a resource is defined as an available radio frequency per time interval, and parameter indicating the configuration of a physical channel configured for downlink control, for a physical control channel configured for format indication, and for a physical channel configured for hybrid automatic repeat request indication, respectively, for use in both of two different communication cells for providing radio communication services for terminals located in said cells; and determining a first resource allocation set and a second resource allocation set, wherein the first resource allocation set and the second resource allocation set respectively comprise resource allocations for a physical channel configured for downlink control, for a physical control channel configured for format indication, and for a physical channel configured for hybrid automatic repeat request indication, and wherein the first resource allocation set and the second resource allocation set are determined to be as mutually disjoint in resource allocation as possible in consideration of the parameters provided by the parameter provision means.
Modifications of the twelfth aspect may be as follows.
The computer program product according to the twelfth seventh aspect may be suitable for providing control channel coordination in heterogeneous networks.
The computer program product according to the twelfth aspect may be embodied as a computer-readable storage medium.
The determining the first resource allocation set and the second resource allocation set to be as mutually disjoint in resource allocation as possible may include suitably selecting a physical cell identity for the second communication cell, filling a string of control channel elements forming the physical channel configured for downlink control of the first communication cell with dummy terminal-related control channel elements where a control channel element string of the physical channel configured for downlink control of the second communication cell has its terminal-related control channel elements and vice versa, and controlling a terminal search space on the physical channels configured for downlink control within both communication cells based on a pre-defined set of cell radio network temporary identifier for the first communication cell and a pre-defined set of cell radio network temporary identifier for the second communication cell.
Otherwise, modifications of the twelfth aspect may correspond to the modifications of the seventh aspect.
According to a thirteenth aspect of the present invention, the object is accomplished by a computer program product comprising computer-executable components which perform, when the program is run on a computer detecting a first resource allocation set and a second resource allocation set, wherein a resource is defined as an available radio frequency per time interval, and wherein the first resource allocation set and the second resource allocation set respectively comprise resource allocations for a physical channel configured for downlink control, for a physical control channel configured for format indication, and for a physical channel configured for hybrid automatic repeat request indication; and controlling a power of signal transmission on the physical channels reflected in the first resource allocation set in relation to the second resource allocation set such that a power of signal transmission differs in dependency on whether resource allocations in the first resource allocation set and the second resource allocation set are disjoint.
Modifications of the thirteenth aspect may be as follows.
The computer program product according to the thirteenth aspect may be suitable for providing control channel coordination in heterogeneous networks.
The computer program product according to the thirteenth aspect may be embodied as a computer-readable storage medium.
Otherwise, modifications of the thirteenth aspect may correspond to the modifications of the eighth aspect.
According to a fourteenth aspect of the present invention, the object is accomplished by a computer program product comprising computer-executable components which perform, when the program is run on a computer synchronizing in time an internal channel transmission clock with an external channel transmission clock; and introducing a time domain offset in downlink channel transmission of a physical channel configured for broadcast as well as of synchronization signals of a first communication cell with respect to downlink channel transmission of a physical channel configured for broadcast as well as of the synchronization signals of a second communication cell.
Modifications of the fourteenth aspect may be as follows.
The computer program product according to the fourteenth aspect may be suitable for providing control channel coordination in heterogeneous networks.
The computer program product according to the fourteenth aspect may be embodied as a computer-readable storage medium.
Otherwise, modifications of the fourteenth aspect may correspond to the modifications of the ninth aspect.
It is to be understood that any of the above modifications can be applied singly or in combination to the respective aspects to which they refer, unless they are explicitly stated as excluding alternatives.
The above and other objects, features, details and advantages will become more fully apparent from the following detailed description of the preferred embodiments which is to be taken in conjunction with the appended drawings, in which:
In the following, description is made to what are presently considered to be preferred embodiments of the present invention. It is to be understood, however, that the description is given by way of example only, and that the described embodiments are by no means to be understood as limiting the present invention thereto.
For example, for illustration purposes, in some of the following exemplary embodiments, interference reduction between a 3GPP LTE overlay wide area macro network and a 3GPP LTE local area network is described. However, it should be appreciated that these exemplary embodiments are not limited for use among these particular types of wireless communication systerns, and according to further exemplary embodiments, the present invention can be applied also to other types of communication systems and access networks such as e.g. to WLAN (wireless local area network) and WIMAX (worldwide interoperability for microwave access) techniques and standards.
Thus, certain embodiments of the present invention relate to mobile wireless communication systems, such as 3GPP LTE. In more detail, certain embodiments of the present invention are related to the configuration of Both LTE eNB and low transmission power eNBs which are in the following called Home eNodeBs (HeNBs), and the case where these nodes are operated at the same frequency layer, i.e. at the same carrier frequency in the same frequency band, as the wide area eNBs.
However, as indicated above, the present invention is not limited to HeNB, but other embodiments of the present invention are related to general small nodes with local services applied, and which are under an overlay wide area macro network operated on the same frequency layer.
Specifically, as shown in
Specifically, as shown in
Specifically, as shown in
and determining 53 a first resource allocation set and a second resource allocation set, wherein the first resource allocation set and the second resource allocation set respectively comprise resource allocations for a physical channel configured for downlink control, for a physical control channel configured for format indication, and for a physical channel configured for hybrid automatic repeat request indication, and wherein the first resource allocation set and the second resource allocation set are determined to be as mutually disjoint in resource allocation as possible in consideration of the parameters provided by the parameter provision means.
One option for performing the first example of a method according to certain embodiments of the present invention would be to use apparatus 1 as described above or a modification thereof which becomes apparent from the embodiments as described herein below.
One option for performing the second example of a method according to certain embodiments of the present invention would be to use apparatus 2 as described above or a modification thereof which becomes apparent from the embodiments as described herein below.
One option for performing the third example of a method according to certain embodiments of the present invention would be to use apparatus 3 as described above or a modification thereof which becomes apparent from the embodiments as described herein below.
In the following, for illustration purposes, certain embodiments of the present invention are described by referring to control channel coordination in heterogeneous networks.
If cells compete in co-channel deployment and none of the network planning options as described in the introductory part is sufficient, in a first approach the following two types of solutions can be considered:
However, the first group (Group 1) of solutions does not solve the macro to macro cell or macro to femto cell interference problem, and is therefore only partly applicable.
The second group (Group 2) of solutions supports all four use cases (see above), but none of the prior work has provided a full set of coordination measures and schemes.
According to certain embodiments of the present invention, co-channel deployment coordination based on groups or pairs of allocation sets is proposed. Two allocation sets are perfect if they are 100% mutually disjoint in frequency and/or time. Two allocation sets are imperfect if they are as mutually disjoint as possible in frequency and/or time. This allocation set based method is compliant to LTE Release 8 and allows for mitigating all kinds of wide area (WA) and local area (LA) interference cases as described in the above use cases 1 to 4.
According to certain embodiments of the present invention, a coordination of PDCCH, PCFICH, and PHICH is based on pairs or groups of imperfect (close to perfect) allocation sets. Furthermore, a combination of PBCH synchronization and time shift in the femto cell and provision of empty MBSFN sub-frames in the macro cell to protect the femto synchronization phase is provided.
Such a (offline) coordination based on pairs (or groups) of allocation sets (which are as mutually disjoint in frequency and time as possible) supporting in particular the above use case 2 and use case 3 (and thus also the hybrid use case 4).
According to such embodiments, a concept of a femto friendly macro cell “hosting” can be implemented with a femto cell deployment without additional or dynamic coordination actions needed in the macro cell.
The co-channel control channel coordination of use case 4 can be established by defining
According to certain embodiments of the present invention, the introduction of perfect (imperfect) groups or pairs of allocation sets is based on:
It is assumed that a residential HeNB or a femto cluster adapts to the time of the macro cell, and that frequency channel assignment in the residential HeNB and the femto cluster are within the 3GPP specifications.
In the following Table 1, control channel coordination schemes for creating a complete resolution mechanism in order to overcome interference issues between macro cells and femto cells are summarized, representing certain embodiments of the present invention.
Herein below, the embodiments depicted in Table 1 are described in further detail. It is to be noted that each section or subsection may represent an independent embodiment or even a plurality of independent embodiments. However, more than one of these embodiments may be advantageously combined or brought into interaction with each other, in particular where indicated.
1. PDSCH Scheduling Constraints
The macro eNB's scheduler as well as the femto scheduler(s) all get “reserved” PDSCH areas for frequency-selective scheduling. An alignment of the resource allocation types may be needed for this purpose. Alignment and reservation are configured semi-statically in order to be able to react on traffic imbalance between macro cell and femto network.
In case of relative side system bandwidths available for LTE operation, one could define three frequency bands for “free to use”, “can be used for additional traffic”, and “do not use”, which is coordinated between the eNBs and HeNBs. This configuration allows for relative controlled interference patterns on the PDSCH while allowing for a certain amount of guaranteed traffic in each cell. The “can be used for additional traffic”-frequency bands could potentially also be combined with a restriction on the maximum transmit power.
2.1 TTI Level Synchronization, PCFICH Static
In order to further resolve collisions in the PDCCH/PHICH/PCFICH TTI area, PCFICH is fixed to a semistatically configured number of OFDM symbols.
2.2 Interference Mitigation for PDCCH/PCFICH/PHICH Interfering with PDCCH/PCFICH/PHICH Based on (Partially) Frequency and Time Disjoint Allocation Sets
The encoded contents of Physical Downlink Control Channels (PDCCH) of UEs scheduled in the present TTI are assembled, interleaved, and mapped to resources in such a way that the PDCCH of a UE is spread over the channel bandwidth in pieces of mini Control Channel Elements (mini-CCEs) or Resource Element Groups (REGs). For details, reference is made to TS 36.211 and TS 36.213.
The encoding on the PDCCH-carrying OFDM symbols can be done as follows: all encoded PDCCH are assembled and mapped to a string of mini-CCEs while tree aggregation rules apply that a PDCCH must start in a repetitive pattern of L*9 mini-CCEs (where L can be 1, 2, 4, or 8 and corresponds to the aggregtion or robustness level of the PDCCH encoding). The start position of the UE in the mini-CCE string depends on its
After assembly of the mini-CCE string, it is mapped to REGs. The mapping depends on
The mini-CCE chain mapping onto REGs is “floating” around the fixed positions of the PCFICH and PHICH, while the resource mappings of the PCFICH and the PHICH again depend on
Coordinating the PDCCH/PCFICH/PHICH of the femto deployment with the PDCCH/PCFICH/PHICH of the macro cell is done as follows: The mini-CCE string created in the macro cell as well as the mini-CCE strings in the femto deployment shall follow semi-statically pre-defined allocation patterns that are mutually as disjoint in frequency and time as possible. This allows for avoiding mutual interference by avoiding collisions of macro cell REGs with femto cell REGs. Albeit 100% collision-free allocation patterns are rare and rather improbable, but
Hence, assuming a macro to femto split of the overall level of mutual macro-to-femto interference on PDCCH/PCFICH/PHICH can be reduced by 70% to 80%, the remaining known 30% down to 20% collision positions can be mitigated by profiling the macro cell's DL power mask accordingly (low power transmission by macro cell base station, i.e. eNB). Vice versa, the DL power mask of the femto cell may be profiled in a complementary manner. It is to be noted that in the femto-to-macro interference direction, it is estimated that the overall interference level on PDCCH/PCFICH/PHICH can be reduced by more than 90%.
Ultimately, the macro cell does not need to adhere to the pre-defined allocation pattern (i.e. the macro cell may allocate all mini-CCEs), but the Macro cell can exploit its knowledge about the femto deployment allocation patterns to profile its DL power mask to help the femto deployment.
In the following, it is explained how the pre-defined allocation patterns can be created. This can be done in advance in an O&M center after macro cell network planning was done and when the operator has decided which macro cells must “host” massive femto deployment (use case 2, use case 3, and use case 4) based on LTE Rel-8 backward compatible control channel coordination.
Specifically, the mechanisms to create pre-defined allocation patterns can be as follows, wherein
1 Same fixed number of PDCCH symbols: Assume a fixed number of (most likely 3) OFDM symbols for PDCCH in the macro cell as well as in the femto deployment, hence the contents of PCFICHs are the same both in the macro cell and in the femto deployment.
2 Fixed number of PHICH: Assume a fixed number of PHICH mini-CCEs in macro and in femto deployment (not necessarily the same amount).
3 Mutually reserved fixed number of mini-CCEs for macro and femto deployment: It is assumed that the femto PDCCH will not be thinly populated. Thus, a fixed number of mini-CCEs is reserved for the femto deployment, potentially filled with DUMMY mini-CCEs. For example, in 3 MHz there are (120-4 -3* PHICH-mini-CCEs) mini-CCEs available for PDCCH. For example, as little as 36 mini-CCEs (L=8 times 9 mini-CCEs) could be reserved for the femto deployment in use case 2. For use cases 3 and 4, at least more mini-CCEs should be reserved. The fixed remainder of mini-CCEs, potentially filled with DUMMY mini-CCEs, can be given to the macro cell. In a 3 MHz implementation the macro cell then has (120 - 36-2* (4 - 3* PHICH-mini-CCEs)) mini-CCEs for its use. For use case 3, the femto resources could take up to 50%, for use case 2 the femto resources should not exceed 33%.
4 Very limited pre-defined and reserved C-RNTIs for femto deployment: In the femto deployment, a very limited predefined set of C-RNTI's is used and the C-RNTI's are chosen in such a way that the set is aligned, or in a similar manner, for a given macro cell to femto deployment a sub-frame alignment or time shift in the UE PDCCH search space creation can be effected. This may not be 100% collision-free, but can be optimized to be collision-free for as many TTIs as possible. For connection setup the UE will use its temporary C-RNTI. In this case, the network may not be able to control the position of the temporary C-RNTI in the PDCCH mini-CCE string such that collisions between macro cell and femto cell occur on random resources. In this case, the femto DL power profiling and a high aggregation level can be used to compensate the macro to femto PDCCH interference. As soon as the C-RNTI is provided by the eNB, the level of collisions is under control and the femto PDCCH can be optimized thanks to this coordination.
5 Creating complementary PDCCH mini-CCE strings both in macro and in femto: The macro mini-CCE string is created in a pre-defined way by using non-transmitted dummy UEs/mini-CCEs where the femto mini-CCEs are reserved.
6 Limited set of femto PCIs “compliant” to macro PCIs: The femto PCI set is pre-calculated in the O&M center in such a way that an as small as possible level of collisions between the macro cell's PDCCH/PCFICH/PHICH and the femto cell's PDCCH/PCFICH/PHICH is generated when combining one out of this set of PCIs with the macro cell's PCI.
2.3 Avoiding CRS Collisions by PCI Selection
PCIs can be selected in a network for squeezing active downlink bandwidth. The PCI selection can be controlled in such a way that collision scenarios are controlled. It is assumed that a direct overlap of PCIs of the macro cell and the femto cell should be avoided.
2.4a PBCH Offset/Sync Offset between Femto and Macro Allocation Sets in 10 ms Granularity
The Physical Broadcast Channel (PBCH) is transmitted within a 10 ms pattern. The MIB and SIB1 information periodicity of this information can be configured and is typically 40 ms.
Hence, the PBCH channel can be time-multiplexed by establishing a 10-ms-granular offset between the femto cell and the macro cell. With a periodicity of 40 ms, 4 different PBCH time schemes could run in parallel.
This will lead to colliding primary and secondary synchronization signals between the femto and the macro allocation set which corresponds to potential collisions at the cell edge for a frequency reuse 1 network. Due to the unique scrambling sequences a separation of the synchronization signals is possible, while on the other hand a significant interference must be accepted.
One alternative option here is to have 3 of the 4 PBCH reserved for macro operation, while the last is reserved for pico/femto operation. Given that there is a relative low code rate on the PBCH, this could also be a valid approach, but can require a per-10-ms coordination between eNBs and HeNBs.
The advantage of this approach is that none of the shared channels will be affected.
2.4b PBCH Offset/Sync Offset between Femto and Macro Allocation Sets in 1 ms Granularity (not 5 ms)
Such a time-disjoint pattern will completely resolve the collision of the PBCH and synchronization signals, while both shared channels would have to be punctured whenever a full band allocation is aimed at. If not, PDSCH allocation may avoid as often as possible the six center PRBs for allocation. Again, one could consider reserving a set of time offsets within the new set of 40 possibilities for creating a separation between macro operation and HeNB operation.
2.4c Protection of Femto PBCH/Sync from Macro PBCH/Sync and Macro PDSCH at the same Time by Empty PMCH Sub-Frame(s) in the Macro Cell for Offsets in 1 ms Granularity (not Multiple of 5 ms)
This kind of coordination extends the coordination measure of 2.4b and allows for protecting the femto PBCH/sync from macro PBCH/sync interference and macro PDSCH interference at the same time.
The following PMCH rules are considered:
Any time domain offset other than multiples of 5 ms avoids collisions of the femto PBCH/sync with the macro PBCH/sync.
The macro cell is configured to send empty MBSFN sub-frames e.g. for its sub-frames #1 and #6, while femto deployment aligns its sub-frames #0 and #5 with the macro cell's #1 and #6. In doing this, the femto cell UEs are not interfered when listening to the femto cell's PBCH/sync.
Some of the various embodiments according to the present sub-section 2.4 are illustrated in
3. Femto Cell Adapts to Macro Cell Set-Up for Hosting Femto Deployments
Despite the fact that there is a coordination scheme based on the combination of different methods into imperfect pairs or groups of allocation sets (in particular between the macro cell and the femto cell in use case 2) it is not desirable that the macro cell must permanently interact with the femto deployment for resource management.
According to certain embodiments, the presented approach provides for the macro cell:
According to certain embodiments, the presented approach provides for the femto cell:
While the femto cell synchronizes with the macro cell and seeks to create (when applicable) a sub-frame time shift, there is no need that the macro cell interacts with the femto cells.
Similarly, femto cells in an office environment interfering with each other can be coordinated semi-statically after having been set-up, if it is assumed that an O&M system knows (successively via a self organized network) about the neighbor relationships of the femto cells in the office environment (use case 3).
As indicated above, implementations examples for certain embodiments of the present invention include base station equipment for WA and LA cells such as LTE eNB and HeNB, but are not limited thereto.
According to the above description, it should thus be apparent that exemplary embodiments of the present invention provide, for example from the perspective of a network element such as an evolved Node B (eNB), a Home evolved Node B, and/or a network planning element such as a O&M entity, or a component thereof, an apparatus embodying the same, a method for controlling and/or operating the same, and computer program(s) controlling and/or operating the same as well as mediums carrying such computer program(s) and forming computer program product(s).
For example, described above are apparatuses, methods and computer program products capable of providing control channel coordination in heterogeneous networks.
Implementations of any of the above described blocks, apparatuses, systems, techniques or methods include, as non limiting examples, implementations as hardware, software, for example in connection with a digital signal processor, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof.
What is described above is what is presently considered to be preferred embodiments of the present invention. However, as is apparent to the skilled reader, these are provided for illustrative purposes only and are in no way intended that the present invention is restricted thereto. Rather, it is the intention that all variations and modifications be included which fall within the spirit and scope of the appended claims.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/EP2009/063556 | 10/16/2009 | WO | 00 | 6/19/2012 |