Patent Publication Number: US-2018054746-A1

Title: Systems and methods for offset scheduling in wireless networks

Description:
INTRODUCTION 
     As cellular networks continue to evolve beyond Long-Term Evolution (LTE) networks, it is widely recognized that network densification (i.e., more cells per network, heterogonous wireless networks (“HetNets”) with overlaid macro-cells and small-cells) is needed to address the need for higher network throughput and to improve end-user Quality of Experience (QoE). However, excessive interference and bottlenecks in resource allocation/control processes create inefficiencies that limit the QoE for a significant number of users of user equipment (UE). 
     In a typical cellular communication network, physical channels can be broadly grouped into two categories: control channels and data channels. Control channels provide signals that include basic information necessary to establish communications between transmitters and receivers (e.g. time/frequency resources in which data transmission will occur, modulation/coding format selections, hybrid automatic repeat request feedback information etc.) while data channels mainly carry data payloads (sometimes referred to simply a “data”). 
     A typical cellular network site (i.e., a “cell”) consists of a base station for transmitting control signals (e.g. scheduling grants) to a UE over a downlink control channel. A cell that transmits control signals to a particular UE is referred to as the “serving cell” for that UE. The control signals received by the UE enable the UE to, thereafter, transmit data payloads over an uplink data channel that is established between the UE and the same serving cell. 
     One such bottleneck that occurs in existing cellular networks is due to the strict timing requirements that govern the transmission of control signals via a downlink control channel and the transmission of data payloads via an uplink data channel. Typically, there is a fixed time period or “lag” between the transmission of such control signals carrying a scheduling grant (indicating the resources and modulation/coding formats to be used) and the corresponding transmission of data payloads. This is referred to as “timing coupling.” Timing coupling creates inefficiencies that limit the QoE for a significant number of users of UEs, especially those that must rely on transmitting data payloads via the uplink of a cell in a HetNet. 
     In more detail, to adhere to existing timing coupling requirements data payloads must be transmitted via an uplink data channel from a UE to a cell (e.g., macro-cell, small-cell) in accordance with a fixed schedule/timeline after receipt of corresponding control signals via a downlink control channel from the cell. For instance, in a 3GPP-LTE network, the control signals, transmitted from a cell to a UE starting at time t, via a physical downlink control channel (PDCCH) initiates the transmission of data payloads from the UE to the cell via a physical uplink data shared channel (PUSCH) at a fixed time t+4 milliseconds (i.e., within four milliseconds of receipt of the PDCCH control signal). 
     Referring now to  FIG. 1A  there is depicted a typical, exemplary HetNet network  1 . The network  1  includes a low-power small-cell  4  deployed within the coverage area  5  of a high-power macro-cell  2 . Because macro-cell  2  typically transmits control signals via the downlink control channel  8  at a power level that is substantially higher than the control signals that are transmitted from the small-cell  4  via its downlink control channel (not shown in  FIG. 1A ), typically −16 dB higher, only those UEs (e.g., mobile devices) close to the small-cell  4  can reliably receive control signals from the small-cell  4 . In effect, this limits the coverage area  6  of the small-cell  4 . 
     To enlarge the effective coverage area of small-cells, such as small cell  4 , one suggested solution requires the use of so-called “blanked” or muted sub-frames. 
     In more detail, referring now to  FIG. 1B , in 3GPP-LTE Release 10, enhanced Inter-cell Interference Coordination (eICIC) techniques are introduced to expand the coverage area of a small-cell. One such technique requires a macro-cell, such as cell  2 , to refrain from transmitting control or data signals to a UE (e.g., UE  3 ) during certain periods of time referred to as sub-frames, effectively muting or blanking those sub-frames. Because transmissions of most control and data signals from a macro-cell are blocked during these blanked sub-frames, a UE (again, e.g., UE  3 ) associated with a small-cell (e.g., cell  4 ) can reliably receive control signals from that small cell instead, without interference from the macro-cell (e.g., cell  2 ). In the exemplary, existing network  1  in  FIGS. 1A and 1B , 35% of the frames from the macro-cell  2  are assumed to be blanked, with the cell  2  using a 9 dB association bias (i.e., UE  3  will connect to the macro-cell  2  if the strength of control signals transmitted from the cell  2  to UE  3 , as measured by UE  3 , via downlink control channel  8  is at least 9 dB higher than the strength of control signals transmitted from the small-cell  4  to UE  3  (again, as measured by UE  3 )). By allowing a UE to receive control signals from a small cell with little or no interference from a macro cell, the effective coverage area of the small cell expands from its original coverage area (e.g., area  6  in  FIG. 1B ) to an expanded coverage area (e.g., area  7  in  FIG. 1B ). 
     As we noted previously, a control signal transmitted from cell  2  via downlink control channel  8  to UE  3  requires UE  3  to send data payloads via uplink data channel  9  within a fixed time period of four milliseconds. However, using the suggested eICIC technique as a solution to expand the coverage area of the small cell  4 -, certain sub-frames are muted at the macro-cell  2 . Accordingly, no control signals are transmitted from the cell  2  during these muted sub-frames. Nonetheless, the UE  3  has been pre-programmed to send data payloads via uplink data channel  9  to cell  2  after four milliseconds. However, absent a control signal (during these blanked sub-frames), the UE  3  will not be able to transmit any actual data (i.e., no payload) during the sub-frames that occur 4 milliseconds after the muted sub-frames. This is highly inefficient. 
     As discussed above, if 35% of the sub-frames are blanked to support a 9 dB admission bias, then 35% of the time allotted for the transmission of data payloads between a UE and its serving cell will be lost because the UE will not be able to transmit any data payloads during sub-frames occurring within the 4 millisecond time period after a blanked sub-frame. 
     Thus, the suggested eICIC techniques have their disadvantages and drawbacks. 
     It should be noted that the suggested eICIC techniques use sub-frames that are almost muted or blanked (not completely muted or blanked) in the sense that during such sub-frames data payloads and most control messages are not transmitted. However, during these blanked frames (time periods), basic control signals, such as cell-specific reference signals (CRS) are still transmitted. Accordingly, it has also been suggested that employing higher biases (e.g., 14 dB) with an advanced UE that employs, for instance, interference-cancelation on control channels (e.g. CRS cancelation) may allow UEs to become associated with a small-cell, instead of a macro-cell, thus increasing its effective coverage area. Unfortunately, this solution also has it drawbacks. For example, a higher bias would probably require that a higher number of sub-frames be muted at a macro-cell in order to ensure reliable reception of control signals from a small-cell by UEs within the expanded coverage area of the small cell. In other words, the use of a higher bias leads to a larger, small-cell coverage area but comes at the cost of further underutilization of uplink data channels available from a macro-cell (i.e., severe timing coupling problem). 
     Accordingly, it is desirable to provide systems and methods that address the timing coupling problems outlined above while providing a user with a high QoE, and without sacrificing the efficiency of a macro-cell. 
     SUMMARY 
     We have recognized that problems with existing techniques for improving the efficiency of cells in a wireless network can be overcome by systems and methods that provide offset scheduling grants. 
     In accordance with embodiments of the invention, the timing of the transmission of data payloads via an uplink data channel can be indicated by transmitting control signals that are offset in time from their ordinary time frames via downlink control channels. The offsets effectively break the tight timing coupling between the delivery of control signals via a downlink control channel and the responsive delivery of data payloads via uplink data channels. This, in turn, improves the utilization of uplink data channels for cells in a HetNet that employ sub-frame blanking because it allows UEs associated with a macro-cell to utilize the time periods associated with blanked sub-frames. 
     In one embodiment, rather than using a fixed offset value of 4 milliseconds, data payloads may now be sent from a UE to a macro-cell (i.e., serving cell) using a variable uplink response time value (“variable value”), denoted “A” (or t+Δ) 
     In more detail, one embodiment comprises a radio-frequency (RF) wireless system comprising: a hardware controller operable to generate an offset scheduling grant, within a downlink control signal sub-frame of a frame, that comprises a variable uplink response time value for controlling the time user equipment sends data payloads to a wireless cell via an uplink data channel. The variable value may be less than, or more than, a fixed value (less than or more than 4 milliseconds). 
     The exemplary system may further comprise a transceiver that is operable to transmit the grant to the user equipment during the downlink control signal sub-frame via a downlink control channel. 
     In embodiments of the invention, the controller may be part of a serving cell, non-serving cell or a network management system (NMS). 
     In addition to a controller and transceiver located at a cell or NMS, an inventive system may further comprise user equipment. Such user equipment may be operable to receive a scheduling grant during the downlink control signal sub-frame via a downlink control channel from a cell and to transmit the data payloads via the uplink data channel at a time indicated by the grant to the cell. 
     In addition to generating variable offset scheduling grants, controllers provided by the present invention may also generate one or more blanking sub-frames during a frame. Thereafter, a transceiver may be operable to transmit the grants to the user equipment during one or more downlink control signal sub-frames of the frame that are not blanking sub-frames via a broadcast channel. 
     In yet a further embodiment, before transmitting a grant to user equipment, the controller may be further operable to identify the highest quality available uplink data channel for transmitting the data payloads from the user equipment to a cell (either one where the controller is located, or another cell) based on channel quality measurements (e.g., signal strength measurements, and time-averaged instantaneous interference statistics). 
     In addition to the systems described above, the present invention also provides methods for improving the efficiency of wireless cells. On such method comprises generating, by a hardware controller, an offset scheduling grant, within a downlink control signal sub-frame of a frame, that comprises a variable uplink response time value for controlling the time user equipment sends data payloads to a wireless cell via an uplink data channel. The controller may be part of a serving cell, non-serving cell or an NMS 
     The variable value may be less than, or more than, a fixed value (e.g., 4 milliseconds). 
     The method may further comprise (1) transmitting, from a transceiver, the grant to the user equipment during the downlink control signal sub-frame via a downlink control channel; (2) receiving, at the user equipment, the grant during the downlink control signal sub-frame via a downlink control channel and transmitting, from the user equipment, the data payloads via the uplink data channel at a time indicated by the grant; (3) generating, by the controller one or more blanking sub-frames during the frame, and transmitting the grant from a transceiver to the user equipment during one or more downlink control signal sub-frames of the frame that are not blanking sub-frames via a broadcast channel; and (4) receiving the grant at the user equipment during the downlink control signal sub-frame via a downlink control channel and transmitting the data payloads from the user equipment via the uplink data channel at a time indicated by the grant. 
     As before, prior to generating and transmitting a grant, the method may additional comprise identifying, by the controller, the highest quality available uplink data channel for transmitting the data payloads from the user equipment to a cell based on channel quality measurements (e.g., signal strength measurements, and time-averaged instantaneous interference statistics). 
     Additional systems and methods will be apparent from the following detailed description and appended drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A and 1B  depict an existing wireless network. 
         FIG. 2A  depicts a wireless network that utilizes inventive offsets according to embodiments of the invention. 
         FIG. 2B  depicts an exemplary base station of a macro-cell according to an embodiment of the invention. 
         FIG. 2C  depicts exemplary user equipment according to an embodiment of the invention. 
         FIG. 3  depicts a simplified flowchart of exemplary methods according to embodiments of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     Exemplary embodiments of systems and methods for providing offset scheduling in RF wireless networks are described herein and are shown by way of example in the drawings. Throughout the following description and drawings, like reference numbers/characters refer to like elements. 
     It should be understood that, although specific exemplary embodiments are discussed herein, there is no intent to limit the scope of the present invention to such embodiments. To the contrary, it should be understood that the exemplary embodiments discussed herein are for illustrative purposes, and that modified and alternative embodiments may be implemented without departing from the scope of the present invention. 
     It should also be noted that one or more exemplary embodiments may be described as a process or method. Although a process/method may be described as sequential, it should be understood that such a process/method may be performed in parallel, concurrently or simultaneously. In addition, the order of each step within a process/method may be re-arranged. A process/method may be terminated when completed, and may also include additional steps not included in a description of the process/method. 
     As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. As used herein, the singular forms “a,” “an” and “the” are intended to include the plural form, unless the context and/or common sense indicates otherwise. 
     It should be understood that when a component or element of an inventive system is referred to, or shown in a figure, as being “connected” to (or other tenses of connected) another component or element such components or elements can be directly connected, or may use intervening components or elements to aid a connection. In the latter case, if the intervening components and elements are well known to those in the art they may not be described herein. 
     When used herein the phrase “hardware controller” means an electronic device such as a microchip, expansion card, or a stand-alone device that interfaces with memory and uses stored electronic instructions to control and manage the operation of a larger device or system, such as a base station. 
     When the words “first” or “second” or other similar words denoting a number are used it should be understood that the use of these words does not denote a level of importance or priority. Rather, such words are used to merely distinguish one element or component from another. Relatedly, it should be understood that one or more of these elements or components may be combined to form fewer elements/components, or, may be further divided to form additional elements/components. 
     As used herein the term “macro-cell” means a system that transmits and receives radio frequency (RF) signals and data payloads at (relatively) high power levels. It should be understood that a macro-cell may comprise a fixed (by location) transceiver that is a part of a base station. Typically, the coverage area of a macro-cell is between 500 meters to several kilometers. 
     As used herein the phrase “small-cell” means a system that transmits and receives RF signals and data payloads using low-power levels. Typically, a small cell has a coverage area of 10 meters to a few hundred meters. 
     As used herein the term “cell” means a macro-cell or a small cell. 
     Connected together, macro-cells and small-cells make up a wireless network. 
     When used herein the phrase “user equipment” or UE includes all types of mobile devices, such as phones, laptop computers, desktop computers, tablets, phablets or any other device that can be used by a user that is moving from one location to another and that is equipped with the necessary electronics to send and receive signals and data payloads over a wireless RF network. 
     As used herein, the term “embodiment” refers to an example of the present invention. 
     Referring now to  FIG. 2A  there is depicted a system  100  according to one embodiment. System  100  comprises an RF wireless serving cell  20 , UE  30 , and RF wireless non-serving cell  40 , the latter two components within the coverage area  50  of the serving cell  20 . In an embodiment, the serving cell  20  may be a macro-cell while the non-serving cell  40  may be a small-cell. The components of system  100  may be part of a 5G wireless network, for example. 
     In one embodiment, the inventive serving cell  20  may be operable to generate a plurality of downlink control signals, and send these signals during set time frames in accordance with a generated time schedule. For example, in a Long-Term Evolution (LTE) based system a frame has duration of 10 milliseconds, and one frame may comprise 10 sub-frames. Further, typically each sub-frame has a duration of 1 millisecond. In more detail, within a particular frame the serving cell  20  may be operable to transmit a full set of control signals during certain sub-frames of the frame, or may only transmit basic control signals during other sub-frames (the latter being blanked or muted sub-frames) to the UE  30 . In one embodiment, the cell  20  may be operable to send an indication (e.g., values) of those sub-frames that will be blanked during a particular frame to the UE  30  via a broadcast channel (not shown in  FIG. 2A ), not via its downlink control channel  80 . 
     More particularly, the serving cell  20  may be operable to generate a downlink control signal frame that includes a plurality of sub-frames where one or more of the sub-frames include a full set of control signals, including an offset scheduling grant (i.e., those sub-frames where downlink transmissions are not blanked), where the grant comprises a variable uplink response time value, A, (variable value) for controlling the time that the UE  30  transmits data payloads to the cell  20 . The so generated grant may be transmitted to the UE  30  from the cell  20  via downlink control channel  80 . 
     Upon receiving the offset scheduling grant, the UE  30  is operable to transmit data payloads, via an uplink data channel  90  established between the UE  30  and cell  20 , at a time indicated by the offset time indicator, i.e., the variable value, instead of after a fixed offset (i.e., four milliseconds after a blanked sub-frame is received). By transmitting data payloads in accordance with the variable value, the time period within which the UE  30  must transmit its data payload(s) to cell  20  may be effectively varied. For example, the UE  30  may transmit data payloads before, or after, the  4  millisecond time period associated with the typical fixed offset. The net result is that the UE  30  may now transmit data using uplink data channels provided by the cell  20  during any sub-frame, notwithstanding the fact that the cell  20  is not transmitting control signals during blanked sub-frames. The inventors believe this will lead to more efficient use of the uplink channels provided by the cell  20 . 
     In embodiments of the invention, the variable value may be more or less than four milliseconds. 
     In an alternative embodiment before the cell  20  transmits the grant to the UE  30 , the cell  20  may be operable to identify the highest quality available uplink data channel for transmitting data payloads from the UE  30  to the cell  20 . In an embodiment, the cell  20  may be operable to identify such a channel based on channel quality measurements (e.g. CQI reports). Further, because data payloads may be transmitted before or after the traditional four millisecond time period, in accordance with another embodiment the cell  20  may be further operable to verify that the uplink data channel previously selected as the highest quality channel based on CQI measurements is, in fact, still the highest quality channel at the time the data payloads will be transmitted (i.e., at time t+Δ) 
     In more detail, the cell  20  may be operable to select the uplink data channel that is expected to be the highest quality uplink data channel during the sub-frame in which data payloads will actually be transmitted based on the variable value and based on signal strength measurements, and time-averaged instantaneous interference statistics used to compute CQI information. This capability addresses the need to accommodate potential backhaul delays and changes in the CQI. 
     By using the inventive variable offset scheduling grants, sub-frames in an uplink data channel that would normally be empty due to the use of blanked or muted downlink sub-frames can now be filled with data payloads. This may be particularly important in high-bias scenarios where a large number of sub-frames may need to be muted at the macro-cell (e.g. half of the frames may need to be muted with 14 dB bias). 
     Referring now to  FIG. 2B , macro-cell  20  may comprise a base station  200 . In one embodiment, base station  200  may include a transceiver  201  (e.g., combination of a transmitter  201   a  and receiver  201   b ) for exchanging control signals with the UE  30  as well as a hardware controller  202  that may comprise one or more processors  202   a,  and associated memory  202   b.  The processor  202   a  may be operable to generate the control signals that are sent to the UE  30  based on executing instructions stored in memory  202   b  and process responsive signals received from the UE  30 . When the macro-cell  20  is referred to herein as being “operable to” perform a specified feature, function or process, it should be understood that this means the components of its base station  200  are completing the feature, function or process. 
     In more detail, the hardware controller  202  may be operable to generate the offset scheduling grants, and variable values based on estimates of channel quality measurements (at the time the data payloads from the UE  30  may be transmitted), signal strength measurements, and time-averaged instantaneous interference statistics that it measures (using instructions stored in its memory  202   b ). The controller  202  may also generate the sub-frames to be blanked for a given frame. Alternatively, the cell  20  may receive all or some of the above (e.g., offset scheduling grants, variable values, channel quality measurements, signal strength measurements, time-averaged instantaneous interference statistics, and information indicating the sub-frames to be blanked) based on information received from a network management system (NMS) that need not be co-located (i.e., is separate from) with the cell  20 . 
     In the latter case, the NMS may be operable to generate the offset scheduling grants, and variable values, information indicating the sub-frames to be blanked, as well as generate the channel quality measurements, signal strength measurements, and time-averaged instantaneous interference statistics using its components, such as its own hardware controller (e.g., controller  202 ), for example, and then send them to the cell  20  using its own transceiver. 
     Referring to  FIG. 2C , UE  30  may include a transceiver  301  (transmitter  301   a  and receiver  301   b ) for receiving and exchanging control signals, including the offset scheduling grants, and variable values, with the cell  20 , and transmitting data payloads to the cell  20  (or cell  40 ). The UE  30  may further include a controller  302  that may comprise one or more processors  302   a  and associated memory  302   b.  The processor  302   a  may be operable to generate the necessary internal signals for receiving the control signals and for transmitting the data payloads via uplink data channel  90  in accordance with the offset scheduling grants, and variable values included in the signals the UE  30  receives form the cell  20  via downlink control channel  80 . 
     The processor  302   a  may rely upon instructions stored in memory  302   b  to complete these functions, for example. When the UE  30  is referred to herein as being “operable to” perform a specified feature, function or process, it should be understood that this means its transceiver  301 , processor  302   a  and/or memory  302   b,  or some combination of the above components complete the feature, function and process. 
       FIG. 3  depicts an exemplary method for improving the efficiency of wireless cells that makes use of the systems described above and elsewhere herein. 
     The foregoing description only describes a few of the many possible embodiments of the invention. Numerous changes and modifications to the embodiments disclosed herein may be made without departing from the spirit and scope of the invention. For example, while only two cells are utilized in the examples described herein, it should be understood that more cells may be utilized in the inventive systems and methods. The metes and bounds of the scope of the present invention are best defined by the claims that follow.