CONTROL CHANNELSIN COMMUNICATION NETWORK SYSTEMS
On a transmitting side, control channels represented by nodes of a tree structure are allocated, each of the control channels having at least one control channel element carrying information for a respective identifier used to detect a control channel of the control channels. The allocation is performed by limiting allocation of highest level control channels of the control channels, the highest level control channels being represented by nodes of the tree structure at a highest level of the tree structure. On a receiving side, a control channel is searched for by decoding the allocated control channels, wherein the searching is limited for the highest level control channels.
This application is the U.S. national stage of International Application No. PCT/EP2008/055557, filed May 6, 2008 and claims the benefit thereof. The International Application claims the benefits of European Application No. 07107652 filed on May 7, 2007, both applications are incorporated by reference herein in their entirety.
BACKGROUNDThe method described below relates to control channels in communication network systems, and in particular to control channel allocation and decoding e.g. in 3GPP (3rd Generation Partnership Project) LTE (Long Term Evolution) network systems.
LTE technology, for example, defines a packet radio system, where all channel allocations are expected to happen in short periods of sub-frames. This is contrary to the older 3G systems, where dedicated signalling channels are necessary to be set up even for packet traffic. It is also different from WLAN (Wireless Local Area Network) type of allocations, where each IP (Internet Protocol) packet transmission contains a transport header.
According to LTE technology, all allocations are signalled in Shared Control Channels, which are present in first multi-carrier symbols of a sub-frame preceding multi-carrier symbols of data channels. The control channels are separately coded. That is, a downlink (or uplink) channel is divided into two separate parts, one for control and one for data. The data part (PDSCH) carries downlink (or uplink) data for simultaneously scheduled users, while the control part (PDCCH) carries (among others) allocation information for the scheduled users.
SUMMARYThe methods and devices described below are for reducing control channel decoding complexity. The method may be implemented as a computer program product.
Accordingly, a tree search for aggregated control channels is reduced in a systematic way, which will obtain a significant reduction of the number of decoding attempts at a UE (User Equipment) side, while still maintaining most of the scheduling flexibility in an eNB (evolved Node B), i.e. system spectral efficiency versus UE complexity trade-off is obtained.
Accordingly it is assumed that there will not be a large amount of users having the same propagation conditions being scheduled at the same time. The tree reduction is obtained by putting some limitations on the tree structure through specifications.
The UE utilizes the tree structure to reduce the decoding complexity in order to save power. According to an embodiment, power consumption in the decoding/detection of an L1/L2 control channel can be reduced.
For the purpose of the methods and devices described herein below, it should be noted that
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- a user equipment may for example be any device by which a user may access a communication network; this implies mobile as well as non-mobile devices and networks, independent of the technology platform on which they are based;
- a user equipment can act as a client entity or as a server entity, or may even have both functionalities integrated therein;
- methods likely to be implemented as software code portions and being run using a processor at one of the server/client entities are software code independent and can be specified using any known or future developed programming language;
- methods and/or devices likely to be implemented as hardware components at one of the server/client entities are hardware independent and can be implemented using any known or future developed hardware technology or any hybrids of these, such as MOS, CMOS, BiCMOS, ECL, TTL, etc, using for example ASIC components or DSP components, as an example;
- generally, any method is suitable to be implemented as software or by hardware without changing the idea of the present invention;
- devices can be implemented as individual devices, but this does not exclude that they are implemented in a distributed fashion throughout the system, as long as the functionality of the device is preserved.
The method is not limited to LTE network systems, but can be applied to any other communication systems requiring dynamic and fast channel allocation, including systems where there will be multiple code rates for the control channel.
These and other aspects and advantages will become more apparent and more readily appreciated from the following description of the exemplary embodiments, taken in conjunction with the accompanying drawings of which:
Reference will now be made in detail to the preferred embodiments, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout.
A Physical Downlink Shared Control Channel (PDSCCH) which carries (among others) allocation information for simultaneously scheduled users of a communication network system is arranged to a tree structure having of multiple control channel elements as shown in
The system bandwidth of a given number of sub-carrier resources may be divided to an integer multiple of the largest control channels. A given node of the tree, i.e., a set of sub-carriers, can be one control channel of the largest code block, of up to two control channels of the second largest code blocks or up to four control channels of the smallest code blocks.
Each control channel extends entirely over the first n OFDM symbols, which are available for the control channels. The control channels may be distributed to the sub-carriers over the system bandwidth to maximize the frequency diversity. For example, there are 4 distributed sets of sub-carrier resources allocated per each code-block. This is illustrated in
In
As each control channel has to be uniquely identified by a MAC ID, it can be combined to CRC (Cyclic Redundancy Code) by partly masking CRC bits with the MAC-ID. As the MAC ID is used for addressing both UE specific control channels and common control channels, it is reasonable to define the MAC ID in a compatible way. Thus, reception of any control channel is possible by filtering control channels with the respective MAC ID. Error detection is available from the MAC ID masked CRC. The length of the MAC ID is matched to the C-RNTI (Cell Radio Network Temporary Identifier) length.
A receiver, e.g. the UE, receives symbols of the Downlink Shared Control Channel part of the sub-frame prior to reception and processing of the symbols in the downlink and uplink Shared Data Channels. The receiver demodulates and decodes the sub-carriers of the OFDM symbols in which the receiver may search for a set of largest code blocks, e.g. CB1 of
In addition to search signalling entries with its own receiver specific c-RNTI, the UE may have to search for common signalling entries by common identifiers.
The search in the tree may happen in any other order than from the lowest level node towards the higher level nodes. Depending on the applied coding scheme, the receiver may process the nodes from the highest level of nodes to the lower level of nodes. Further on, the receiver may process the nodes in other arbitrary (or systematic) order based on some measures e.g. SINR (Signal Interference and Noise Ratio) quality of the candidate code block(s).
In the following it is assumed that only a single size of a node (i.e. control channel) at the highest level of the tree structure (level 3 in
However, the aggregation of the control channel elements may require a large number of decoding attempts from all the UEs that are listening for a possible allocation. An example of a control channel aggregation is shown in
From
In the following an embodiment will described in greater detail.
According to an embodiment, the control channel structure shown by the white and grey areas in
With the above limitation put on the tree structure, scheduling flexibility is not reduced that much, based on the following arguments:
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- If there is a lot of user equipments close to an eNB scheduling the control channels, which user equipments require only aggregation level 1, the aggregated level 2 elements with reduced power can be used to have more users due to the possibility of doing power balancing; in the example shown in
FIG. 4 , 9 favourable conditioned users can be scheduled using this approach. In other words, four control channels in aggregation level 1, two control channels in aggregation level 2, two control channels in aggregation level 4, and one control channel in aggregation level 8 can be scheduled. - If a plurality of scheduled users is present at a cell edge (aggregation level 8), additional users cannot be scheduled anyway due to limited number of available control channel elements.
- As the difference between aggregation layers is a factor of 2 and when using power balancing, to some extent there is flexibility to trade aggregation and power between each other.
- If there is a lot of user equipments close to an eNB scheduling the control channels, which user equipments require only aggregation level 1, the aggregated level 2 elements with reduced power can be used to have more users due to the possibility of doing power balancing; in the example shown in
It should be noted that although the above description is given for an allocation tree for single link direction, the method is also valid for the case where two trees, for uplink and downlink, respectively, are present.
Further, it should be noted that the number of possible control channels at each layer is not important.
According to an embodiment, using an allocation rule, usage of the smallest control channel on all control channel elements is prohibited, while at the same time the smaller control channels are allowed to be combined to aggregated control channels with better coverage.
With the above approach, the number of decoding attempts that is needed by each UE can be reduced. The limitation of the tree is possible due to the frequency diversity applied for all control channel elements, such that each CCE experiences same or similar channel conditions.
The user equipment 10 includes a receiving/transmitting section 11 and a decoding section 12. The receiving/transmitting section 11 receives symbols from the network device 20, which includes a receiving transmitting section 21 transmitting the symbols and an allocation section 22.
The allocation section 22 allocates control channels represented by nodes of a tree structure, each of the control channels having at least one control channel element carrying information for a respective identifier used to detect a control channel of the control channels, wherein the allocation is performed by limiting allocation of highest level control channels of the control channels, the highest level control channels being represented by nodes of the tree structure at a highest level of the tree structure. For example, in
The allocation section 22 may increase allocation of lower level control channels of the control channels, the lower level control channels being represented by nodes of the tree structure at lower levels of the tree structure. For example, in
The receiving/transmitting section 21 may transmit the allocated control channels as symbols to user equipments including the user equipment 10, by distributing the allocated control channels to sub-carriers over a system bandwidth.
The higher level control channels may be combined to the lower level control channels. In other words, smaller control channels are allowed to be combined to aggregated control channels with better coverage.
The allocation section 22 may increase allocation more the lower the level of the tree structure.
The searching section 12 of the user equipment 10 searches for a control channel by decoding control channels represented by nodes of a tree structure, by using an identifier such as an MAC ID, CRC or c-RNTI, each of the control channels having at least one control channel element carrying information for a respective identifier used to detect a control channel of the control channels, wherein the searching section 12 limits the searching for highest level control channels of the control channels, the highest level control channels being represented by nodes of the tree structure at a highest level of the tree structure.
The searching section 12 may increase the searching for lower level control channels of the control channels, the lower level control channels being represented by nodes of the tree structure at lower levels of the tree structure.
The receiving/transmitting section 11 may receive the control channels as symbols from the network device 20.
The searching section 11 may begin the searching with lowest level control channels represented by nodes of the tree structure at a lowest level of the tree structure. For example, in
It is to be noted that the network device 20 and user equipment 10 shown in
According to an embodiment, on a transmitting side, control channels represented by nodes of a tree structure are allocated, each of the control channels having at least one control channel element carrying information for a respective identifier used to detect a control channel of the control channels. The allocation is performed by limiting allocation of highest level control channels of the control channels, the highest level control channels being represented by nodes of the tree structure at a highest level of the tree structure. On a receiving side, a control channel is searched for by decoding the allocated control channels, wherein the searching is limited for the highest level control channels.
The system also includes permanent or removable storage, such as magnetic and optical discs, RAM, ROM, etc. on which the process and data structures of the present invention can be stored and distributed. The processes can also be distributed via, for example, downloading over a network such as the Internet. The system can output the results to a display device, printer, readily accessible memory or another computer on a network.
It is to be understood that the above description is illustrative of the invention and is not to be construed as limiting the invention. Various modifications and applications may occur to those skilled in the art without departing from the scope of the invention as defined by the appended claims which may include the phrase “at least one of A, B and C” as an alternative expression that means one or more of A, B and C may be used, contrary to the holding in Superguide v. DIRECTV, 358 F3d 870, 69 USPQ2d 1865 (Fed. Cir. 2004).
Claims
1-20. (canceled)
21. A method, comprising:
- allocating control channels represented by nodes of a tree structure with highest level nodes of the tree structure representing control channel elements and lower level nodes of the tree structure representing lower level control channels, each of the control channels having at least one of the control channel elements carrying information for a respective identifier used to detect a control channel among the control channels,
- said allocating limiting allocation of highest level control channels and thereby allowing allocation of the lower level control channels among the control channels.
22. The method of claim 21, further comprising transmitting the control channels after said allocating to user equipment by distributing the allocated control channels to sub-carriers over a system bandwidth.
23. The method of claim 21, wherein the higher level control channels are combined with the lower level control channels.
24. The method of claim 21, wherein said allocating is increased more in at least one lower level of the tree structure.
25. A method, comprising:
- searching for a control channel by using an identifier and decoding control channels represented by nodes of a tree structure with highest level nodes of the tree structure representing control channel elements and lower level nodes of the tree structure representing lower level control channels, each of the control channels having at least one of the control channel elements carrying information for a respective identifier used to detect a control channel among the control channels,
- said searching being limited for highest level control channels, thereby allowing searching for the lower level control channels.
26. The method of claim 25, further comprising receiving the control channels from a network device.
27. The method of claim 26, wherein said searching is performed beginning with a lowest level control channel represented by nodes of the tree structure at a lowest level of the tree structure.
28. A device, comprising:
- an allocation unit allocating control channels represented by nodes of a tree structure with highest level nodes of the tree structure representing control channel elements and lower level nodes of the tree structure representing lower level control channels, each of the control channels having at least one of the control channel elements carrying information for a respective identifier used to detect a control channel among the control channels,
- said allocation unit limiting allocation of highest level control channels and thereby allowing allocation of the lower level control channels among the control channels.
29. The device of claim 28, further comprising a transmitting unit transmitting the allocated control channels to user equipment by distributing the allocated control channels to sub-carriers over a system bandwidth.
30. The device of claim 29, wherein the device is an evolved node B.
31. A device, comprising:
- a decoding unit searching for a control channel by using an identifier and decoding control channels represented by nodes of a tree structure with highest level nodes of the tree structure representing control channel elements and lower level nodes of the tree structure representing lower level control channels, each of the control channels having at least one of the control channel elements carrying information for a respective identifier used to detect a control channel among the control channels,
- said decoding unit limiting searching for highest level control channels, thereby allowing searching for the lower level control channels.
32. The device of claim 31, further comprising a receiving unit receiving the control channels from a network device.
33. The device of any one of claim 32, wherein the device is user equipment.
34. A tangible computer readable medium embodying a computer program that when executed by a processing device causes the processing device to perform a method comprising:
- allocating control channels represented by nodes of a tree structure with highest level nodes of the tree structure representing control channel elements and lower level nodes of the tree structure representing lower level control channels, each of the control channels having at least one of the control channel elements carrying information for a respective identifier used to detect a control channel among the control channels,
- said allocating limiting allocation of highest level control channels and thereby allowing allocation of the lower level control channels among the control channels.
35. The tangible computer readable medium according to claim 34, wherein the computer program is directly loadable into an internal memory of the processing device.
36. The tangible computer readable medium of claim 34, further comprising transmitting the control channels after said allocating to user equipment by distributing the allocated control channels to sub-carriers over a system bandwidth.
37. The tangible computer readable medium of claim 34, wherein the higher level control channels are combined with the lower level control channels.
38. The tangible computer readable medium of claim 34, wherein said allocating is increased more in at least one lower level of the tree structure.
39. A tangible computer readable medium embodying a computer program that when executed by a processing device causes the processing device to perform a method comprising:
- searching for a control channel by using an identifier and decoding control channels represented by nodes of a tree structure with highest level nodes of the tree structure representing control channel elements and lower level nodes of the tree structure representing lower level control channels, each of the control channels having at least one of the control channel elements carrying information for a respective identifier used to detect a control channel among the control channels,
- said searching being limited for highest level control channels, thereby allowing searching for the lower level control channels.
40. The tangible computer readable medium of claim 39, further comprising receiving the control channels from a network device.
41. The tangible computer readable medium of claim 40, wherein said searching is performed beginning with a lowest level control channel represented by nodes of the tree structure at a lowest level of the tree structure.
Type: Application
Filed: May 6, 2008
Publication Date: Aug 19, 2010
Patent Grant number: 9271266
Inventors: Frank Frederiksen (Klarup), Troels Emil Kolding (Klarup)
Application Number: 12/451,350
International Classification: H04W 72/04 (20090101); H04L 12/28 (20060101);