Patent Application
20090279478
The present invention relates generally to wireless communication and, in particular, to facilitating dynamic cooperative interference reduction in wireless communication systems.
In evolving 4G wireless systems such as 3GPP LTE (Long Term Evolution), IEEE 802.16m and 3GPP2 UMB (Ultra Mobile Broadband), one of the key focuses is on providing superior quality VoIP service as well as high network capacity for such services. Another focus is on providing a good edge-of-cell data rate while not significantly impacting the overall sector rate. The nature of latency-sensitive traffic (VoIP-like traffic) is that capacity is primarily determined by the air-interface delay outage. Improving the post-HARQ error rate with a minimal increase in system resources (such as power, bandwidth allocation and/or amount of feedback) can provide significant improvements in coverage and outage rate, and thus, has the potential to improve capacity for these applications. Coverage improvements, even for other classes of traffic, are highly desirable in these evolving networks as are techniques for improving the cell-edge outage rate with minimal additional signaling requirements.
Some outage and coverage improvements involve semi-static partitioning of resources using fractional frequency reuse (FFR) and are described in the UMB and LTE standards. However, these methods can be wasteful since, in a given cell, the fraction of outage users can be different than what the FFR deployment targeted. Other methods to increase cell-edge rates involve interference cancellation (e.g., IDMA), but these come with the need for complex interference cancellation receivers to be implemented in the mobiles (see e.g., R1-050608, “Inter-cell Interference Mitigation based on IDMA,” RITT, 3GPP TSG RAN WG1 Ad Hoc on LTE, Sophia Antipolis, France, 20-21 Jun., 2005). Thus, new techniques able to improve coverage and/or the cell-edge outage rate that are less wasteful and/or less complex would be desirable.
Specific embodiments of the present invention are disclosed below with reference to
Simplicity and clarity in both illustration and description are sought to effectively enable a person of skill in the art to make, use, and best practice the present invention in view of what is already known in the art. One of skill in the art will appreciate that various modifications and changes may be made to the specific embodiments described below without departing from the spirit and scope of the present invention. Thus, the specification and drawings are to be regarded as illustrative and exemplary rather than restrictive or all-encompassing, and all such modifications to the specific embodiments described below are intended to be included within the scope of the present invention.
Various embodiments are described for potentially improving coverage and/or the cell-edge outage rate and thereby the system capacity. Logic flow diagrams 10 and 20, in
The disclosed embodiments can be more fully understood with reference to
Communication system 100 is depicted in a very generalized manner. For example, system 100 is shown to simply include remote unit 101, network nodes 121-123 and signaling network 131. Network nodes 121-123 are shown having interconnectivity via signaling network 131. Network node 123 is shown providing network service to remote unit 101 using wireless interface 111. The wireless interface used is in accordance with the particular access technology supported by network node 123, such as one based on IEEE 802.16. Network nodes 121-123 may all utilize the same wireless access technology, or they may utilize different access technologies. Those skilled in the art will recognize that
For example,
Thus, given a high-level description, an algorithm, a logic flow, a messaging/signaling flow, and/or a protocol specification, those skilled in the art are aware of the many design and development techniques available to implement a processing unit that performs the given logic. Therefore, devices 121-123 represent known devices that have been adapted, in accordance with the description herein, to implement multiple embodiments of the present invention. Furthermore, those skilled in the art will recognize that aspects of the present invention may be implemented in or across various physical components and none are necessarily limited to single platform implementations. For example, a network node may be implemented in or across one or more RAN components, such as a base transceiver station (BTS) and/or a base station controller (BSC), a Node-B and/or a radio network controller (RNC), or an HRPD AN and/or PCF, or implemented in or across one or more access network (AN) components, such as an access service network (ASN) gateway and/or ASN base station (BS), an access point (AP), a wideband base station (WBS), and/or a WLAN (wireless local area network) station.
Remote unit 101 and network node 123 are shown communicating via technology-dependent, wireless interface 111. Remote units, subscriber stations (SSs) and/or user equipment (UEs), may be thought of as mobile stations (MSs), mobile subscriber stations (MSSs), mobile devices or mobile nodes (MNs). In addition, remote unit platforms are known to refer to a wide variety of consumer electronic platforms such as, but not limited to, mobile stations (MSs), access terminals (ATs), terminal equipment, mobile devices, gaming devices, personal computers, and personal digital assistants (PDAs). In particular, remote unit 101 comprises a processing unit (103) and transceiver (105). Depending on the embodiment, remote unit 101 may additionally comprise a keypad (not shown), a speaker (not shown), a microphone (not shown), and a display (not shown). Processing units, transceivers, keypads, speakers, microphones, and displays as used in remote units are all well-known in the art.
Operation of embodiments in accordance with the present invention occurs substantially as follows, first with reference to
Processing unit 103 then transmits signaling 112, via transceiver 105, indicating that remote unit 101 is requesting an interfering communication device to reduce transmissions that may be interfering with signaling from network node 123. Depending on the embodiment, signaling 112 may indicate a resource block, a sub-channel, a beam and/or a duration for which reduced transmission is requested. Processing unit 126 receives signaling 112, via transceiver 125, and based at least in part on what was indicated by signaling 112, it reduces transmissions. Again depending on the embodiment, reducing transmissions may involve muting transmit power, reducing transmit power or reducing transmit power spectral density (PSD) for an indicated resource block, for an indicated sub-channel, for an indicated beam and/or for an indicated duration.
In addition to network node 121, network node 122 may also receive signaling 112 and reduce transmissions accordingly. (That is, unless signaling 112 is specifically directed to node 121.) Also, depending on the embodiment, node 121 may not receive signaling 112 via transceiver 125. Rather, another network node, such as node 123, may receive signaling 112 from remote unit 101 and forward the indications of signaling 112 to node 121 via signaling network 131 and network interface 127.
A brief summary that focuses on certain more detailed embodiments appears below to provide some additional and more particular examples. They are intended to further the reader's understanding of the variety of possible embodiments rather than to limit the scope of the invention.
Three components of dynamic interference relief are proposed to improve coverage and outage rates. Depending on the embodiment, these components may be incorporated individually, in part or in combination:
Static interference avoidance schemes like fractional frequency reuse rely on knowing in advance a good split of types of users (e.g., good/bad geometry, different traffic mixes) within a cell. This is not necessarily the best way to improve a cell-edge data rate or a voice outage rate. In H-NAK embodiments, minimal signaling is proposed over-the-air so that users are able to tell other base-stations to reduce their transmission power dynamically. Since this is done per-packet and is not sent very often, it has a small impact on scheduler resources, while having the potential to improve outage and cell-edge rate.
A second approach enhances the interference relief ideas for multiple antenna systems. Typically, multiple antenna systems are deployed to work without any inter-BS coordination. But because of the spatial dimensions available, it is desirable to have cooperative interference reduction with multi-antenna base-stations and terminals. This is achieved in the proposed scheme with low overhead and over-the-air signaling (on an “as-needed” basis).
In H-NAK embodiments, users that are about to abort on a packet (e.g., having reached the last transmission), send a special signal (perhaps a one bit signal), called the Help NAK to its nearest (or a set of strongest) interfering base-stations. The idea is for users that are about to experience an outage to get interference relief from their nearest interfering cells.
The H-NAK signal may be modulated with a sequence that conveys the resource blocks that are used for its transmission. Thus, the other base-stations can detect this signal and know that a given user needs interference relief on a particular resource block. There could be more than one user sending the same H-NAK signal from different cells. These will all be combined implicitly by a given base-station, using the idea of single-frequency-reuse. The strength of this combined signal gives an indication to the base-station as to how much to reduce its power in the next transmission on that particular resource block.
As depicted in
By the same token, for UL transmissions, a base-station can broadcast an H-NAK signal corresponding the resource blocks where packets are likely to be aborted. Cell-edge users in other cells can detect this broadcast signal, and decide to autonomously power down their next transmission if they are using those indicated resource blocks.
Thus, a given receiver provides feedback in the form of a “Help NAK” (H-NAK) to reach users (for UL transmissions) or base-stations (for DL transmissions) of other cells. By doing so, dynamic cooperative interference reduction is enabled when a user's packet is close to being in outage.
For DL service, users transmit an H-NAK to reach other cells when the packet is about to fail. Depending on the embodiment, these other cells know the resource block allocation by the position/modulation of the H-NAK. If possible, other cells then mute or reduce transmit power spectral density on those requested resource blocks for the remaining duration of that packet's transmission. Depending on the embodiment, the power of an H-NAK signal may be boosted to reach the strongest interfering cell.
In H-NAK embodiments that apply these techniques to UL service, users in other cells monitor H-NAK signaling from a candidate set of cells. If they use the same sub-channel in which an H-NAK is observed, they will reduce the transmit PSD of their subsequent transmissions autonomously and to the extent possible. The transmit power of a broadcast H-NAK on the DL may need to be adapted to achieve a moderate penetration into the other cells.
A detailed description of some of the Other-cell Beamformed Interference Suppression (OBIS) embodiments follows. In some of these embodiments, when a base-station is equipped with multiple antennas, a user that needs interference relief will measure the optimal beam from a set of the strongest interfering cells and feed these beam weights back to the interfering base-stations along with the H-NAK. Knowing the beam that causes the maximum power to be directed to that user, the base can decide to allocate smaller power in the direction of that beam on the requested resource blocks. This allows the interfering base-station to not have to reduce the power unilaterally on that resource block, but rather, only over the spatial beam that results in maximum interference to the user that needs interference relief.
The optimal pre-coder or beam-former weights change dynamically for diversity antennas and thus should be fed back dynamically. For correlated antennas, the beam can be known at BS 512 using long-term updates of the preferred beam index by MS 501 as the spatial beam pattern does not change very fast. This “most interfering beam” information may be sent along with the H-NAK feedback, or possibly in separate signaling. BS 512 then can use other spatial dimensions available to transmit to its users using SDMA (Spatial-Division Multiple Access).
In some of the embodiments that apply OBIS techniques to UL service, if the base uses correlated antennas, then it transmits the H-NAK using the best beam used for uplink reception of the user in outage. The other-cell users that receive this H-NAK are automatically the ones that cause the most interference on the uplink in that spatial direction. These users can then mute (or reduce) their transmit PSD (as described before). By using beamformed H-NAKs, a smaller fraction of users will need to reduce their PSD in comparison to the single-base-antenna H-NAK case, thus leading to spatial interference suppression. Further, users with multiple transmit antennas can, in time division duplex (TDD) systems, use the H-NAK based channel estimates to spatially null their uplink transmissions in the beam direction of the base transmitting the H-NAK. Thus, the OBIS approach enables spatial interference reduction per-beam in conjunction with “Help NAK” signaling and allows for spatial interference suppression both at the transmit and the receive ends.
In the above discussion, the general approach was to reduce the power spectral density of transmissions based on an H-NAK signal that receivers feed back in cases when they are about to experience an outage. This leads to a user-specific and packet-specific interference nulling/suppression scheme. Another approach is to devise an average spatial interference suppression that would be applicable for all users in all cells in order for cells to come up with non-uniform spatial power loading. The idea here is to feed back a signal like the H-NAK, but on a very slow basis, to indicate spatial interference conditions. Such an approach could enable dynamic fractional spatial reuse (FSR).
For example, for the DL, there could be an H-NAK signaling slot where all users that need interference relief would send an H-NAK signal, not specific to any resource allocation, but indicating the spatial beam (from a finite set of spatial beams that are pre-defined, e.g.) that each is seeing the most interference from. The base-station could then collect the H-NAK energies corresponding to each of these finite spatial beams and decide how to reduce the transmit power on those spatial beams. This approach may lead to a slow-adaptation of spatial interference patterns based on the actual interference experienced by the cell-edge users in other cells. The base-station could then transmit a smaller PSD on the beams that cause the most interference to users in neighboring cells, thereby possibly improving cell-edge data rates.
One of skill in the art will appreciate that various modifications and changes may be made to the specific embodiments described above with respect to
Benefits, other advantages, and solutions to problems have been described above with regard to specific embodiments of the present invention. However, the benefits, advantages, solutions to problems, and any element(s) that may cause or result in such benefits, advantages, or solutions, or cause such benefits, advantages, or solutions to become more pronounced are not to be construed as a critical, required, or essential feature or element of any or all the claims.
As used herein and in the appended claims, the term “comprises,” “comprising,” or any other variation thereof is intended to refer to a non-exclusive inclusion, such that a process, method, article of manufacture, or apparatus that comprises a list of elements does not include only those elements in the list, but may include other elements not expressly listed or inherent to such process, method, article of manufacture, or apparatus. The terms a or an, as used herein, are defined as one or more than one. The term plurality, as used herein, is defined as two or more than two. The term another, as used herein, is defined as at least a second or more. Unless otherwise indicated herein, the use of relational terms, if any, such as first and second, and the like, are used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions.
The terms including and/or having, as used herein, are defined as comprising (i.e., open language). The term coupled, as used herein, is defined as connected, although not necessarily directly, and not necessarily mechanically. Terminology derived from the word “indicating” (e.g., “indicates” and “indication”) is intended to encompass all the various techniques available for communicating or referencing the information or object being indicated. Some, but not all examples of techniques available for communicating or referencing the information or object being indicated include the conveyance of the information or object being indicated, the conveyance of an identifier of the information or object being indicated, the conveyance of information used to generate the information or object being indicated, the conveyance of some part or portion of the information or object being indicated, the conveyance of some derivation of the information or object being indicated, the conveyance of some symbol representing the information or object being indicated, and the manner of, form of, type of, location of, relative location of, placement of, timing of or other characteristic or attribute of the conveyance itself. The terms program, computer program, and computer instructions, as used herein, are defined as a sequence of instructions designed for execution on a computer system. This sequence of instructions may include, but is not limited to, a subroutine, a function, a procedure, an object method, an object implementation, an executable application, an applet, a servlet, a shared library/dynamic load library, a source code, an object code and/or an assembly code.
The present application claims priority from a provisional application Ser. No. 61/050,768, entitled “METHOD AND APPARATUS FOR FACILITATING DYNAMIC COOPERATIVE INTERFERENCE REDUCTION,” filed May 6, 2008, which is commonly owned and incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61050768 | May 2008 | US |
