Apparatuses and methods for CSI-RS configuration in distributed RRH systems

Apparatuses and methods for channel state information reference signal (CSI-RS) configuration in distributed remote radio head (RRH) systems are described. A transmission point selection module can receive a user equipment (UE) signal via a transmission point from a plurality of transmission points sharing a single cell identification. A downlink transmission point can be selected based on the UE signal. The UE can then be configured to report CSI-RS measurements for the selected downlink transmission point.

BACKGROUND

In wireless networks in which user equipment (e.g., a mobile phone, computer, or other wireless device), also known as UE, moves relative to transmission points (e.g., antennas, transceivers, etc.) of the wireless network, determining which transmission points will serve the user equipment is a concern for the wireless network operators. Cellular networks often organize transmission points into cells to serve the user equipment. Often, each cell is identifiable by a cell identification (ID) and transmission point performance metrics (e.g., radio signal strength, signal to noise ratio, etc.) are measured at the user equipment and reported, based on the cell ID, to the wireless network.

Coordinated multi-point (CoMP) remote radio head (RRH) (e.g., Macro+RRH scenario three) techniques logically combine different transmission points that work cooperatively to service the user equipment. Often these transmission points maintain cell IDs distinct from each other allowing user equipment reporting to remain unchanged from more traditional cellular networks.

DETAILED DESCRIPTION

CoMP scenario four Macro+RRH is a wireless network where the transmission points share a single cell ID. That is, to the user equipment, service from a single cell as opposed to multiple cells in a traditional, or CoMP scenario three Macro+RRH wireless network. For convenience, the 3GPP Long Term Evolution Advanced (LTE-A) (e.g., 3GPP Long Term Evolution release 10, 3GPP standard 36.21X vb.x.x, release 11 and beyond) family of standards are used as an example wireless network for the discussion below. However, the present subject matter is not so limited and applicable to other wireless (e.g., cellular) networks using multiple transmission points sharing the same cell ID.

Because transmission points in the CoMP scenario four Macro+RRH wireless network share a cell ID, traditional user equipment reporting mechanisms may not be effective in providing the wireless network the information to best serve the user equipment. That is, identifying transmission points to best serve the user equipment can be difficult when they appear as a single cell to the user equipment. This problem can be more complex in identifying downlink transmission points (e.g., transmission points to transmit data specifically to the user equipment).

To identify appropriate downlink transmission points the wireless network can employ alternative mechanisms to evaluate the channel metrics between the transmission points and the user equipment. For example, channel state information (CSI) between the transmission points and the user equipment can be used, although the ability of the user equipment to process and report CSI for all available transmission points can be limited.

Configuring (e.g., reconfiguring) the user equipment to report CSI for transmission points appropriate to be downlink transmission points can allow the user equipment to provide channel quality information that the wireless network can use to select a downlink transmission point. For example, a wireless infrastructure component (e.g., eNB or enhanced node B) of the wireless network can receive a user equipment signal via one or more of the transmission points. The signal can be used as a basis to select one or more appropriate downlink transmission points. The wireless infrastructure component can then configure the user equipment to report measurements on the CSI reference signal (CSI-RS) for the selected downlink transmission points. These measurements can be used to optimize downlink transmissions to the user equipment.

FIG. 1illustrates an example CoMP scenario four Macro+RRH system100. System100includes wireless infrastructure component105to perform CSI-RS configuration of the user equipment130communicatively coupled (e.g., via one or more wired or wireless networks) to transmission points120A-D sharing a single cell ID.

In an example, each of the transmission points120A-D can uniquely correspond to a CSI-RS pattern (e.g., via a mapping by the transmission point selection module110). In an example, the transmission points120A-D each have at least one radio transceiver (e.g., a transmitter, receiver, or both) and are configured to communicate with the user equipment130via its transceivers. In an example, at least one of the transmission points120A-D (e.g., transmission point120B) has a plurality of antennas.

In an example, the antennas of transmission point120B can be located at a single geographical location, or in more than one geographical location (e.g., separated by a nontrivial physical distance such as on different floors of a building). In an example, when the antennas of transmission point120B are in different geographical locations, each can be attached to different housings or transceivers. In an example, transmission point120B can be configured to communicate with the user equipment130using a multiple-input multiple-output (MIMO) radio channel. In an example, the MIMO channel can comprise up to eight spatial streams. In an example, the multi-antenna transmission capability of transmission point120B can be used for multi-user MIMO and beamforming. In an example, a CSI-RS pattern can be mapped, for example by the transmission point selection module110, a subset of the transmission point's120B antennas (one or more antennas, less than the total number of transmission point's120B antennas, can be mapped to a unique CSI-RS).

In an example, each of the plurality of transmission points120A-D can correspond to one of a plurality of layers. For example, transmission point120A corresponds to layer1, transmission points120B-C correspond to layer2, and120dxcorresponds to layer3as illustrated inFIG. 1. In an example, each of the plurality of layers can correspond to a transmission range. The transmission range is a desired range sought via various transmission point design dimensions, including one or more of antenna placement (e.g., height, position with respect to surrounding terrain or structures, etc.) transmit power, etc. Example layers can include macrocells, microcells, picocells, and femtocells among others. As illustrated inFIG. 1, lower numbered layers have greater transmission ranges (e.g., layer1can be a macrocell and layer3can be a femtocell). In an example, lower number layers can be considered closer to an edge of the wireless network than higher-level layers.

The wireless infrastructure component105can include a transmission point selection module110and a configuration module115, one or both communicatively coupled to the transmission points120A-D. In an example, the transmission point selection module110can be configured (e.g., include the necessary hardware and software) to receive, from the user equipment130, a UE signal via one or more of transmission points120A-D. The transmission point selection module110can also be configured to select a downlink transmission point from the transmission points120A-D based on the UE signal.

The configuration module115can be communicatively coupled to the transmission point selection module110and configured to communicate instructions to the user equipment130. The instructions can be configured to cause the user equipment130to report CSI-RS measurements for the selected downlink transmission point. Thus, the configuration module115can effectuate CSI-RS configuration of the user equipment130. In an example, the configuration module115can use LTE-A's remote resource control (RRC) protocol to configure the user equipment130. In an example, the configuration module115can also configure one or more transmission points120A-D to assign a CSI-RS pattern to a transmission point in transmission points120A-D.

In an example, the UE signal can be an uplink signal. An uplink signal can be a broadcast or data segment that is part of the wireless network's protocol communicate from the user equipment130, including measuring the quality of the uplink channel. In an example, the uplink signal relates to the uplink channel and does not include other informational data transmitted from the user equipment130to the wireless network. In an example, the uplink signal can be a sounding reference signal (SRS). In an example, the SRS can transmitted, by the user equipment130(e.g., the user equipment130is configured to transmit) at a higher power than SRS transmission power to accomplish physical uplink shared channel (PUSCH) link adaption. In an example, a different (e.g., higher) SRS transmission power can be specified in one or more SRS parameter sets communicated to the user equipment130via RRC signaling. In an example, the eNB can specify a different SRS transmission power (e.g., via a specific parameter set) to the user equipment130using downlink control signaling.

In an example, when the UE signal is an uplink signal, transmission point selection module110can be configured to measure the uplink signal at each receiving transmission point to create uplink signal measurements, rank the receiving transmission points based on the measured uplink signal measurements, and select the downlink transmission point based on the ranking (e.g., selecting a transmission point with the most favorable ranking). For example, the transmission point selection module110can measure the receiving power of SRS from multiple transmission points120and use the receiving power to estimate the absolute pathloss from multiple transmission points120to the user equipment130. In an example, the rank can be further based on a transmission metric (e.g., transmission power or range, physical location, logical network location, etc.) of the transmission points120A-D. In an example, the following can be used by the transmission point selection module110to select the best transmission point based on the SRS measurements and a transmission point transmission metric:
DLTP0=x|max{TxPower(x)+RxPowerSRS(x):xεTP}:EQ1

In Equation 1, TP is the set of receiving transmission points, TxPower and RxPowerSRS are respectively the transmission power and SRS received power of a transmission point120, and DLTP0is the optimal downlink transmission point. Thus, in this example, the SRS received power and the transmission point transmission power are a ranking bases.

In the previous example, large power difference between transmission points can result, for example, in a more distantly placed macrocell being selected (due to its powerful transmitter) with a weak SRS measurement over a picocell with a much stronger SRS measurement. The wireless network operators may wish to avoid this situation (e.g., over-selection of transmission points with greater transmission range) to achieve various purposes (e.g., load balancing, redundancy, etc.). A selection threshold can be defined and the transmission point selection module110can be configured to select a transmission point other than DLTP0as the downlink transmission point to meet the wireless network operator's purposes described above. Using TPDL0from Equation 1, any transmission point120, y in TP, can be selected if it is within the selection threshold. In an example, the following can provide the set of selectable transmission points:
Y|{TxPower(TPDL0)+RxPowerSRS(TPDL0)−TxPower(y)++RxPowerSRS(y)<ST:yεTP,y≠TPDL0}  :EQ2

In Equation 2, ST is the selection threshold (e.g., 3 dB), Y is the set of selectable transmission points, and all other terms are the same as in Equation 1.

In an example, in addition to or in place of an uplink signal, the UE signal can include a CSI-RS index (UESCI). In an example, the UESCI can be configured to carry the CSI-RS index so as to be reliable. In an example, the reliability is greater than at least one of channel quality indications (CQI) (e.g., channel quality indicators or reports thereof), precoding matrix information (PMI), and MIMO rank index (RI). In an example, the UESCI is configured to be fast enough to take advantage of one or more transmission or reporting attributes, such as enjoying a signal to noise (SINR) gain from fast fading of multiple transmission points. In an example, the UESCI can be, in whole or part, asynchronous. In an example, the UESCI can be configured to minimize impact on other user equipment130signaling (e.g., CQI reports). In an example, the UESCI can be configured to carry the CSI-RS index in the eleventh quadrature phase shift keying (QPSK) symbol of the 2b the physical uplink control channel (PUCCH) format. In an example, the UESCI can be configured to send the CSI-RS index together with the RI report. In an example, the wireless infrastructure component105(e.g., the configuration module115) can configure the user equipment130to report the CSI-RS index in one or any combination of the UESCI configurations detailed above. In an example, the wireless infrastructure component105can configure the period in which the user equipment130will report the CSI-RS index.

FIG. 2illustrates an example CSI-RS reporting period200. The reporting period can be set with respect to time or, as illustrated, with respect to other user equipment130signaling, such as RI reports205and CQI/PMI reports210. In an example, CQI is reported by the user equipment130for the user equipment's130current downlink transmission point only.

FIG. 3illustrates an example CSI-RS index300. The CSI-RS index300can include one or more slots305each corresponding to a single CSI-RS pattern (represented by CSI-RS pattern index310) and including CSI-RS based measurements315derived (e.g., by the user equipment130) from the single CSI-RS pattern. In an example, the transmission point selection module110can be configured to select the downlink transmission point based on the CSI-RS index300.

In an example, the CSI-RS index300can include fewer slots305than observable transmission points observable by the user equipment130. In this case, the transmission point selection module110can be configured to select likely transmission points based on the selected downlink transmission point (e.g., by associating transmission points to the downlink transmission point via geographical affinity, or other metric). The transmission point selection module110can then remap one or more slots305to CSI-RS patterns corresponding to the likely transmission points. In an example, when the eleventh QPSK symbol of PUCCH format 2b is used to carry the CSI-RS index300, CSI-RS index300is limited to four slots305.

In an example, the CSI-RS pattern index310can be the CSI-RS pattern. In an example, the CSI-RS pattern index310can be an abstract key associated to the CSI-RS pattern by the wireless infrastructure component105(e.g., by the configuration module115) on both the wireless infrastructure component105and the user equipment130. In an example, the wireless infrastructure component105(e.g., the configuration module115) can reconfigure the user equipment130or CSI-RS pattern mapping to CSI-RS pattern index310as the wireless network environment changes to facilitate, for example, CSI-RS reporting on the most salient transmission points when the CSI-RS index300does not have enough room to report on all user equipment130observable transmission points. In an example, the configuration module115can be configured to map CSI-RS patterns to slots305according to a sequence. In an example, the CSI-RS index300can include only one slot305to which the sequence is mapped, allowing the omission of the CSI-RS pattern index310. The following single slot sequence is an example: {CSI-RSTP-A, CSI-RSTP-B, CSI-RSTP-B, CSI-RSTP-C}

where CSI-RSTP-A, CSI-RSTP-B, and CSI-RSTP-Care the CSI-RS patterns respectively assigned to transmission points A-C. In this example, the user equipment130will report each of the CSI-RSTP-Aand CSI-RSTP-Cpatterns (or measurements derived thereof) 25% of the time and CSI-RSTP-Bthe remaining 50% of the time. In an example, the sequence can advance (i.e., the next CSI-RS pattern is mapped to a given slot305) after a predetermined period (e.g., after a time period has elapsed, after an event signals the end of the period such as a particular signal is transmitted by the user equipment130or RI reporting cycle, etc.). It will be understood that the wireless infrastructure component105can correlate the reported CSI-RS pattern based measurements by virtue of knowing the sequence used by the user equipment130. In an example, both a sequence and a non-sequenced CSI-RS index300can be used together.

In an example, the CSI-RS based measurements315can include reference signal received power and reference signal received quality (RSRP/RSRQ) measurements relative to the user equipment130(e.g., as observed or determined at the user equipment130). In an example, where the CSI-RS based measurements315include RSRP/RSRQ measurements, to select the downlink transmission point, the transmission point selection module110can be configured to rank the transmission points based on the RSRP/RSRQ measurements and select the downlink transmission point based on the ranking. In an example, selecting the downlink transmission point based on the ranking includes selecting a more favorably ranked transmission point120. In an example, higher observed or computed RSRP/RSRQ results in a more favorable ranking.

In an example, to prevent unproductive successive CSI-RS reconfigurations between two transmission points when the user equipment130is, for example, on the border between those two transmission points, the transmission point selection module110can be configured to favorably weight the rank (e.g., include a modifier resulting in a more favorable ranking) of the user equipment's130current downlink transmission point based on a transition threshold. In an example, the transition threshold is a received power level. In this example, the downlink transmission point will not change from the current downlink transmission point to a new downlink transmission point until the signal power level of the new downlink transmission point is the value of the threshold point greater. In an example, other transmission metrics of the transmission points can be used, the transition threshold being a value representing a difference between the transmission metrics beyond which CSI-RS reconfiguration will be unlikely to bounce between the two transmission points (e.g., the user equipment130has sufficiently moved into the new downlink transmission point's zone).

In an example, the UE signal can include a CQI corresponding to a CSI-RS pattern selected by the user equipment130to maximize a communication performance metric. In an example, the CQI can be in a CSI-RS index300slot305. In an example, the CQI can be outside the CSI-RS index300and correlated to the CSI-RS pattern via the CSI-RS index300(e.g., via CSI-RS pattern index310). In an example the performance metric is at least one of data throughput and SINR gain. In an example, where the user equipment130selects a CSI-RS pattern to report CQI for (e.g., in which the user equipment130selects its desired downlink transmission point), the transmission point selection module110can be configured to select the downlink transmission point by selecting a transmission point corresponding to the CQI. This is known as fast CSI-RS reconfiguration or selection.

In an example, where fast CSI-RS reconfiguration is employed, the transmission point selection module110can be configured to configure the user equipment130to bias CSI-RS pattern selection based on the layers (network transmission point layers discussed above, such as macrocell, etc.) corresponding to the CSI-RS pattern's transmission points. In an example, the bias can be configured to direct the user equipment's130autonomous transmission point selection behavior to prefer transmission points at particular layers to, for example load balance among the layers. This is known as CSI-RS range expansion.

FIG. 4illustrates CSI-RS pattern index310mapping (e.g., remapping) as the user equipment130moves in relation to the transmission points120A-D and transmission points425E-F. Inflection point405indicates a condition of the user equipment130movement (e.g., a physical point, or change environment affecting radio communications) on which the wireless infrastructure component105(e.g., transmission point selection module110or configuration module115) can base a decision to remap the CSI-RS pattern index310. For example, as illustrated inFIG. 4, the CSI-RS pattern index310is mapped such that CSI-RS pattern indices425A-B are respectively mapped to CSI-RS patterns corresponding to transmission points120A-D. After the user equipment130reaches, or passes, the inflection point405, the CSI-RS pattern index310is remapped such that CSI-RS index425A is now mapped to the CSI-RS pattern corresponding to transmission point E410and CSI-RS index425B is now mapped to the CSI-RS pattern corresponding to transmission point F420.

FIG. 5illustrates the transition threshold operation as the user equipment130moves in relation to the transmission points120A-B. Line505is a representation of the transmission point's120A power as perceived at the user equipment130, with the y-axis representing power and the x-axis representing position. Similarly, line510represents transmission points120B power as perceived at the user equipment130. The length of line515represents the transition threshold value and the line515's position marks the user equipment's130at which, or beyond to the right, the transmission point selection module110is configured to reconfigure the CSI-RS signaling of the user equipment130. Thus, to maximize user equipment130performance, the transition threshold can be configured to be as small as possible and still avoid successive CSI-RS reconfigurations that are likely to occur (e.g., because of signal power fluctuations) at the border between the respective ranges of transmission points120A-B (represented by the intersection of lines505-510).

FIG. 6illustrates fast CSI-RS selection, in contrast to the CSI-RS reconfiguration shown inFIG. 5, as the user equipment130moves in relation to the transmission points120A-B. Here, because the user equipment130selects the best transmission point between transmission points120A-B, a new downlink transmission point can be selected as near the border605. This can result in better overall performance as the user equipment130will not experience the signal quality penalty introduced by the transition threshold.

One or more operations of the method described below can be performed by one or more components (e.g., wireless infrastructure component105, transmission point selection module110, configuration module115, transmission points120A-D, and user equipment130) alone, or in any combination. It will be understood, however, that the present subject matter is not so limited and combinations including components not here described can also be used to perform the operations described below.

FIG. 7is a flowchart illustrating an example method700for CSI-RS configuration (e.g., reconfiguration) in distributed RRH (e.g., LTE-A CoMP scenario four Macro+RRH) systems. In an example, the operations of method700can be performed in whole or in part by transmission point selection module110.

At operation705the wireless infrastructure component105(e.g., transmission point selection module110) can receive a UE signal from user equipment130via one or more transmission points (e.g., receiving transmission points). The one or more transmission points are in a plurality of transmission points that share a single cell ID.

In an example, where the UE signal includes a CSI-RS index with one or more slots and each of the plurality of transmission points uniquely corresponds to a CSI-RS pattern, operation705can additionally include selecting the downlink transmission point based on the CSI-RS index.

In an example, where the CSI-RS index includes CSI-RS measurements, derived from CSI-RS patterns of the plurality of transmission points, including RSRP/RSRQ measurements relative to the user equipment130, operation705can additionally include ranking the plurality of transmission points based on the RSRP/RSRQ measurements. Operation705can continue by selecting the downlink transmission point based on the ranking. The ranking of this example can additionally include favorably weighting the rank of a current downlink transmission point based on a transition threshold (e.g., as described above).

In an example, where the UE signal further includes a CQI (e.g., CQI report) corresponding to a CSI-RS pattern selected by the UE (e.g., fast CSI-RS selection) to maximize a communication performance metric (e.g., SINR or data throughput), operation705can additionally include selection a transmission point corresponding to the CSI-RS pattern corresponding to the CQI.

At operation710the wireless infrastructure component105can select a downlink transmission point the plurality of transmission points based on the UE signal. In an example, additional transmission points (e.g., likely transmission points) can be selected based on the selected downlink transmission point. For example, the likely transmission points can be associated with the selected downlink transmission point geographically (e.g., they are located with a certain distance) or via another metric (e.g., by wireless network design to achieve a purpose such as load balancing).

In an example, where the CSI-RS index includes CSI-RS measurements, derived from CSI-RS patterns of the plurality of transmission points operation710can additionally include mapping CSI-RS patterns to slots in the CSI-RS index.

In an example, given autonomous user equipment130CSI-RS pattern selection (e.g., fast CSI-RS selection) where each of the plurality of transmission points correspond to one of a plurality of layers differentiated by transmission ranges (e.g., macrocell, microcell, etc.), operation710can optionally include configuring the user equipment130to bias CSI-RS pattern selection (as described above) based on the layer corresponding to the CSI-RS pattern's transmission point120.

In an example, where the CSI-RS index includes fewer slots than UE observable transmission points, operation710can additionally include mapping CSI-RS patterns to a slot of the CSI-RS index according to a sequence (e.g., as described above). In this example, operation710can also include configuring the user equipment130to advance the sequence after a predetermined period (e.g., as described above).

At operation715the wireless infrastructure component105(e.g., configuration module115) can configure the user equipment130to report CSI-RS measurements for the selected downlink transmission point. In an example, the user equipment130can also be configured to report CSI-RS measurements for the likely transmission points.

FIG. 8is a flowchart illustrating an example method800for selecting a downlink transmission point. In an example, the operations805-815can be performed in whole or in part by transmission point selection module110. In an example, operation820can be performed by the user equipment130. Method800operates in the context of the UE signal being an uplink signal (as described above). In an example, the uplink signal is a SRS. In an example, the uplink signal is a demodulation reference signal (DMRS).

At operation805the uplink signal can be measured at each receiving transmission point.

At operation810the receiving transmission points can be ranked based on the measured uplink signals. In an example, the ranking can be further based on a transmission metric (as described above) of the transmission point.

At operation815the downlink transmission point can be selected based on the ranking.

At operation820, where the uplink signal is a SRS, the SRS can be transmitted (e.g., by the user equipment130) at a higher power than SRS transmission power for PUSCH link adaption.

Examples, as described herein, can include, or can operate on, logic or a number of components, modules, or mechanisms. Modules are tangible entities capable of performing specified operations and can be configured or arranged in a certain manner. In an example, circuits can be arranged (e.g., internally or with respect to external entities such as other circuits) in a specified manner as a module. In an example, the whole or part of one or more computer systems (e.g., a standalone, client or server computer system) or one or more hardware processors can be configured by firmware or software (e.g., instructions, an application portion, or an application) as a module that operates to perform specified operations. In an example, the software can reside (1) on a non-transitory machine-readable medium or (2) in a transmission signal. In an example, the software, when executed by the underlying hardware of the module, causes the hardware to perform the specified operations.

Machine (e.g., computer system)900can include a hardware processor902(e.g., a central processing unit (CPU), a graphics processing unit (GPU), a hardware processor core, or any combination thereof), a main memory904and a static memory906, some or all of which can communicate with each other via a bus908. The machine900can further include a display unit910, an alphanumeric input device912(e.g., a keyboard), and a user interface (UI) navigation device911(e.g., a mouse). In an example, the display unit910, input device917and UI navigation device914can be a touch screen display. The machine900can additionally include a storage device (e.g., drive unit)916, a signal generation device918(e.g., a speaker), a network interface device920, and one or more sensors921, such as a global positioning system (GPS) sensor, compass, accelerometer, or other sensor. The machine900can include an output controller928, such as a serial (e.g., universal serial bus (USB), parallel, or other wired or wireless (e.g., infrared (IR)) connection to communicate or control one or more peripheral devices (e.g., a printer, card reader, etc.).

The storage device916can include a machine-readable medium922on which is stored one or more sets of data structures or instructions924(e.g., software) embodying or utilized by any one or more of the techniques or functions described herein. The instructions924can also reside, completely or at least partially, within the main memory904, within static memory906, or within the hardware processor902during execution thereof by the machine900. In an example, one or any combination of the hardware processor902, the main memory904, the static memory906, or the storage device916can constitute machine readable media.

While the machine-readable medium922is illustrated as a single medium, the term “machine readable medium” can include a single medium or multiple media (e.g., a centralized or distributed database, and/or associated caches and servers) that configured to store the one or more instructions924.

The term “machine-readable medium” can include any tangible medium that is capable of storing, encoding, or carrying instructions for execution by the machine900and that cause the machine900to perform any one or more of the techniques of the present disclosure, or that is capable of storing, encoding or carrying data structures used by or associated with such instructions. Non-limiting machine-readable medium examples can include solid-state memories, and optical and magnetic media. Specific examples of machine-readable media can include: non-volatile memory, such as semiconductor memory devices (e.g., Electrically Programmable Read-Only Memory (EPROM), Electrically Erasable Programmable Read-Only Memory (EEPROM)) and flash memory devices; magnetic disks, such as internal hard disks and removable disks; magneto-optical disks; and CD-ROM and DVD-ROM disks.

Additional Notes & Examples

Example 1 includes subject matter (such as a system, an apparatus, a device, etc.) comprising transmission points sharing a single cell identification (ID). Each transmission point comprises at least one radio transceiver. Example 1 further comprises a transmission point selection module (TPSM) communicatively coupled to the transmission points. The transmission point selection module is configured to receive, from a user equipment device (UE), a UE signal via one or more of the transmission points, and select a downlink transmission point from the transmission points based on the UE signal. Example 1 further comprises a configuration module communicatively coupled to the TPSM and configured to communicate instructions to the UE, the instructions configured to cause the UE to report channel state information reference signal (CSI-RS) measurements for the selected downlink transmission point.

In Example 2, the subject matter of Example 1 can optionally include wherein the UE signal is an uplink signal, and wherein to select the downlink transmission point based on the UE signal includes the TPSM further configured to measure the uplink signal at each receiving transmission point, rank the receiving transmission points based on the measured uplink signals, and select the downlink transmission point based on the ranking.

In Example 3, the subject matter of Example 2 can optionally include wherein the rank is further based on a transmission metric of the transmission point.

In Example 4, the subject matter of one or any combination of Examples 2-3 can optionally include wherein the uplink signal is a sounding reference signal (SRS).

In Example 5, the subject matter of Example 4 can optionally include wherein the SRS is transmitted, by the UE, at a higher power than SRS transmission power for physical uplink shared channel (PUSCH) link adaption.

In Example 6, the subject matter of one or any combination of Examples 1-5 can optionally include wherein the TPSM is a part of an eNB, wherein the eNB is configured as a 3GPP LTE Advanced eNB, and wherein the system is a coordinated multi-point (CoMP) remote radio head (RRH) scenario 4 system.

In Example 7, the subject matter of one or any combination of Examples 1-6 can optionally include wherein at least one of the transmission points includes a plurality of antennas and is configured to communicate with the UE using a multiple-input and multiple-output (MIMO) radio channel.

In Example 8, the subject matter of one or any combination of Examples 1-7 can optionally include wherein the UE signal includes a CSI-RS index including one or more slots, wherein each slot of the CSI-RS index corresponds with a single CSI-RS pattern and includes CSI-RS measurements derived from the single CSI-RS pattern, wherein each of the transmission points uniquely corresponds to a CSI-RS pattern, wherein to select the downlink transmission points based on the UE signal includes the TPSM further configured to select the downlink transmission point based on the CSI-RS index, and wherein the instructions configured to cause the UE to report channel state information reference signal (CSI-RS) measurements for the selected downlink transmission point include instructions to map CSI-RS patterns to slots in the CSI-RS index.

In Example 9, the subject matter of Example 8 can optionally include wherein the UE signal further includes a channel quality indicator (CQI) corresponding to a CSI-RS pattern selected by the UE to maximize a communication performance metric, the CQI correlated to the CSI-RS pattern via the CSI-RS index, and wherein to select the downlink transmission point includes selecting a transmission point corresponding to the CQI.

In Example 10, the subject matter of Example 9 can optionally include wherein each of the transmission points correspond to one of a plurality of layers, wherein a layer in the plurality of layers corresponds to a transmission range; and the TPSM is further configured to configure the UE to bias CSI-RS pattern selection based on a layer corresponding to the CSI-RS pattern's transmission point.

In Example 11, the subject matter of one or any combination of Examples 8-10 can optionally include wherein the CSI-RS measurements include reference signal received power and reference signal received quality (RSRP/RSRQ) measurements, wherein the RSRP/RSRQ measurements are relative to the UE; and

wherein to select the downlink transmission point based on the CSI-RS index includes the TPSM configured to rank the transmission points based on the RSRP/RSRP measurements and select the downlink transmission point based on the ranking.

In Example 12, the subject matter of one or any combination of Examples 8-11 can optionally include wherein to rank the transmission points based on the RSRP/RSRQ measurements includes the TPSM further configured to favorably weight the rank of a current downlink transmission point based on a transition threshold.

In Example 13, the subject matter of one or any combination of Examples 8-12 can optionally include wherein the CSI-RS index includes fewer slots than UE observable transmission points, and wherein the instructions to map CSI-RS patterns to slots in the CSI-RS index include instructions to map CSI-RS patterns to a slot of the CSI-RS index according to a sequence, wherein the sequence advances after a predetermined period.

Example 14 can include, or can optionally be combined with the subject matter of one or any combination of Examples 1-13 to include, subject matter (such as a method, means for performing acts, or a machine readable medium including instructions that, when performed by the machine cause the machine to perform acts) comprising receiving, at a transmission point selection module (TPSM) from a user equipment device (UE), a UE signal via a transmission point, wherein the transmission point is one of a plurality of transmission points sharing a single cell identification (ID), selecting a downlink transmission point from the transmission points based on the UE signal, and configuring the UE to report channel state information reference signal (CSI-RS) measurements for the selected downlink transmission point.

In Example 15, the subject matter of Example 14 can optionally include wherein the UE signal is an uplink signal, and wherein selecting the downlink transmission point based on the UE signal includes measuring the uplink signal at each receiving transmission point, ranking the receiving transmission points based on the measured uplink signals, and selecting the downlink transmission point based on the ranking.

In Example 16, the subject matter of Example 15 can optionally include wherein the ranking is further based on a transmission metric of the transmission point.

In Example 17, the subject matter of one or any combination of Examples 15-16 can optionally include wherein the uplink signal is a sounding reference signal (SRS).

In Example 18, the subject matter of Example 17 can optionally include further comprising transmitting, by the UE, the SRS at a higher power than SRS transmission power for physical uplink shared channel (PUSCH) link adaption.

In Example 19, the subject matter of one or any combination of Examples 14-18 can optionally include wherein the TPSM is part of an eNB, wherein the eNB is configured as a 3GPP LTE Advanced eNB, and wherein the eNB and the plurality of transmission points comprise a coordinated multi-point (CoMP) remote radio head (RRH) scenario 4 system.

In Example 20, the subject matter of one or any combination of Examples 14-19 can optionally include wherein at least one of the transmission points includes a plurality of antennas and is configured to communicate with the UE using a multiple-input and multiple-output (MIMO) radio channel.

In Example 21, the subject matter of one or any combination of Examples 14-20 can optionally include wherein the UE signal includes a CSI-RS index including one or more slots, wherein each of the plurality of transmission points uniquely corresponds to a CSI-RS pattern, wherein selecting the downlink transmission points based on the UE signal includes selecting the downlink transmission point based on the CSI-RS index, and wherein configuring the UE to report channel state information reference signal (CSI-RS) measurements for the selected downlink transmission point includes mapping CSI-RS patterns to slots in the CSI-RS index.

In Example 22, the subject matter of Example 21 can optionally include wherein the UE signal further includes a channel quality indicator (CQI) corresponding to a CSI-RS pattern selected by the UE to maximize a communication performance metric, the CQI correlated to the CSI-RS pattern via the CSI-RS index, and wherein selecting the downlink transmission point includes selecting a transmission point corresponding to one of the CSI-RS patterns.

In Example 23, the subject matter of Example 22 can optionally include wherein each of the plurality of transmission points correspond to one of a plurality of layers, wherein a layer in the plurality of layers corresponds to a transmission range, and wherein configuring the UE to report channel state information reference signal (CSI-RS) measurements for the selected downlink transmission point includes configuring the UE to bias CSI-RS pattern selection based on a layer corresponding to the CSI-RS pattern's transmission point.

In Example 24, the subject matter of one or any combination of Examples 21-23 can optionally include wherein the CSI-RS measurements include reference signal received power and reference signal received quality (RSRP/RSRQ) measurements, wherein the RSRP/RSRQ measurements are relative to the UE, and

wherein selecting the downlink transmission point based on the CSI-RS index includes ranking the transmission points based on the RSRP/RSRP measurements, and selecting the downlink transmission point based on the ranking.

In Example 25, the subject matter of one or any combination of Examples 21-24 can optionally include wherein ranking the transmission points based on the RSRP/RSRQ measurements includes favorably weighting the rank of a current downlink transmission point based on a transition threshold.

In Example 26, the subject matter of one or any combination of Examples 21-25 can optionally include wherein the CSI-RS index includes fewer slots than UE observable transmission points, and wherein mapping CSI-RS patterns to slots in the CSI-RS index includes mapping CSI-RS patterns to a slot of the CSI-RS index according to a sequence, wherein the sequence advances after a predetermined period.

Example 27 can include, or can optionally be combined with the subject matter of one or any combination of Examples 1-26 to include, subject matter (such as a method, means for performing acts, or a machine readable medium including instruction that, when performed by the machine cause the machine to perform acts) comprising receiving, at a transmission point selection module (TPSM) from a user equipment device (UE), a UE signal via a transmission point, wherein the transmission point is one of a plurality of transmission points sharing a single cell identification (ID), selecting a downlink transmission point from the transmission points based on the UE signal, and configuring the UE to report channel state information reference signal (CSI-RS) measurements for the selected downlink transmission point.

In Example 28, the subject matter of Example 27 can optionally include wherein configuring the UE to report CSI for the selected downlink transmission point includes configuring a CSI-RS index using remote radio control (RRC), and

wherein the CSI-RS index includes one or more slots, each slot mapped to a CSI-RS pattern and including CSI-RS measurements derived from the CSI-RS pattern, each transmission point of the plurality of transmission points uniquely corresponding to a CSI-RS pattern, the CSI-RS index having fewer slots than observable CSI-RS patterns.

In Example 29, the subject matter of Example 28 can optionally include wherein configuring the CSI-RS index includes remapping the one or more slots to candidate CSI-RS patterns in response to selecting a downlink transmission point different from a current downlink transmission point of the UE, the candidate CSI-RS patterns corresponding to likely transmission points from the plurality of transmission points based on the downlink transmission point.

In Example 30, the subject matter of one or any combination of Examples 28-29 can optionally include wherein the CSI-RS index is carried on the eleventh quadrature phase-shift keying (QPSK) symbol according to a 3GPP LTE-A family of standards physical uplink control channel (PUCCH) 2b.