Patent Abstract:
The present invention is directed to systems and methods which accommodate OTA delays exceeding the delay associated with a 100 km transmission (more than approximately 0.667 ms) while still affording the full processing time required by both the UE and the eNode B equipment.

Full Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. Provisional Application No. 61/639707, filed Apr. 27, 2012, the entire contents of which is specifically incorporated herein by reference without disclaimer. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates generally to wireless communications and, more particularly, to apparatuses, systems, and methods for cell range expansion in wireless communications. 
       BACKGROUND OF THE INVENTION 
       [0003]    Fast retransmission requirements have been included in wireless communications standards such as LTE, WiMAX, and HSPA to improve system performance. For example, in LTE, the retransmission latency requirement is 8 ms. This means that the total processing time, on both the transmitter side and the receiver side, plus the over-the-air (“OTA”) delay should be less than 8 ms in LTE systems. The LTE standard states that a cell range of up to 100 km is supported, which translates to a maximum 2-way OTA delay of about 0.667 ms. For certain applications, such as using LTE as backhaul access for in-flight Wi-Fi service, the distance between the LTE User Equipment (“UE”) and the base station (“eNode B”) can be 200 km or more. Thus, traditional LTE systems cannot be used for such applications, because the OTA delay would be more than the allotted 0.667 ms, which would limit the available processing time for the UE and eNode B equipment. Additional limitations include the design of LTE preamble signals as defined in the LTE standard, and maximum Uplink Advanced Time supported in UE implementations as defined under the LTE standard. 
         [0004]    In certain systems, uplink signals from different UEs arrive at eNode B at roubly the same time. This may be usefull to maintain the orthogonality between signals from different UEs, and to simplify eNode B design through, e.g., sharing of the same Fast Fourier Transform (“FFT”) engine. In common LTE systems, the initial uplink synchronization is achieved using Preamble Random Access Channel (“PRACH”) procedures. Even when the uplink synchronization is established, it may eventually be lost for various reasons, including movement of the UE or inaccuracy of local oscillators in the UEs or eNode B. Therefore, uplink timing maintenance is required, and mechanisms for uplink timing maintenance are described in some communication standards, such as the LTE standard. 
         [0005]    In general, the timing synchronization and maintenance process begins when a UE receives a signal from eNode B. The signal may include timing information, which UE uses to determine downlink timing. UE may then return a Preamble signal aligned with its downlink receiving timing. eNode B then detects the preamble, estimates the latency, and then instructs UE to advance its subsequent uplink transmission time by twice the one-way latency. With the timing advancement, the UE&#39;s subsequent uplink transmission is synchronized. The synchronization may be lost if the UE moves to a location where the latency is different. Thus, eNode B is generally configured to detect timing drift and send periodic timing updates to UE. 
         [0006]    Fast Retransmission is used in many packet-based wireless communication standards, such as CDMA EVDO, HSPA, and LTE to improve performance. In these systems, if the receiver can decode the packet, it sends back an ACK signal. Otherwise, the receiver replies with a NACK signal. If a NACK is received by the transmitter, it will retransmit the packet. In order to support delay-sensitive applications, the retransmission interval is usually very small. For example, LTE systems only use a retransmission of eight subframes (8 ms). A certain minimum amount of time is required by both UE and eNode B for processing uplink and downlink signals. Any over-the-air (“OTA”) delay uses up a portion of that processing time. Thus in many systems, an OTA limit is set, which effectively limits the possible range of communication between eNode B and UEs. For example, in LTE, the typical OTA limit is 68 ms, which is roughly equivalent to a 100 km radius from eNode B. 
       BRIEF SUMMARY OF THE INVENTION 
       [0007]    The present invention is directed to systems and methods which accommodate OTA delays exceeding the delay associated with a transmission across a 100 km distance (more than approximately 0.667 ms) while still affording the full processing time required by both the UE and the eNode B equipment. In one embodiment, a plurality of transmission states are defined by the range of a UE from eNode B. For example, states may include a “Regular State,” a “Transition State,” and an “Extended State.” Such embodiments may eliminate or significantly reduce collisions of signals received by eNode B from UEs located within the 100 km transmission zone (Regular State) and those received from UEs located outside of the 100 km transmission zone (transition state and/or extended state). Additionally, the present embodiments may reduce misdetection of transmission zones. 
         [0008]    In one embodiment, a method for cell range expansion is wireless communications includes receiving a communication from a base station in a wireless communication network. For example, a wireless receiver in e.g., a mobile smartphone may receive the communication. Additionally, the method may include determining a distance from the base station in response to the communication. The distance may be determined using a data processing device loaded with executable code which comprises instructions for causing the processing device to determine the distance. Additionally, the method may include setting a communication timing state according an estimated distance from the base station and internal transmission timing advance capability. Setting may also be accomplished by the processing device. Finally, the method may include sending a response to the base station according to a timing scheme defined according to communication timing state. 
         [0009]    In one embodiment, the method may also include setting a first communication timing state when the desistance from the base station is within a first predetermined threshold distance. The timing scheme does not modify the timing of the response to the base station when the first communication timing state is set. Additionally, the method may include setting a second communication timing state when the distance is greater than the first predetermined threshold distance. The timing scheme shortens the timing of the response to the base station by one subframe length and then adds a transition compensation delay when the second communication timing state is set. 
         [0010]    In an embodiment, the method may also include setting a third communication timing state when the distance is greater than a second predetermined threshold distance, the second predetermined threshold distance being greater than the first predetermined threshold distance. In such an embodiment, the timing scheme shortens the timing of the response to the base station by one subframe length. 
         [0011]    The method may also include holding the response to the base station until a second communication is received from the base station, and then responding to the base station according to the timing scheme. In PDSCH systems, the method may include automatically sending a NACK in response to a first PDSCH communication received from the base station, and waiting for the base station to respond with a second PDSCH communication before sending a response to the base station. Similarly, in PUSCH systems, the method may include automatically setting the transmitter to mute in response to a first command from the base station, and waiting for the base station to retransmit the command before sending a PUSCH response to the base station. 
         [0012]    The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    For a more complete understanding of the present invention, reference is now made to the following descriptions taken in conjunction with the accompanying drawing, in which: 
           [0014]      FIG. 1  is a schematic diagram illustrating one embodiment of a system for cell range expansion in wireless communications; 
           [0015]      FIG. 2  is a schematic block diagram of one embodiment of an apparatus for cell range expansion in wireless communications; 
           [0016]      FIG. 3  is a graphical timing diagram of two-way wireless communication in three ranges of distance between a UE device and an eNode B device; 
           [0017]      FIG. 4  is a graphical timing diagram illustrating a timing of two-way wireless communications according to a method for cell range expansion in wireless communications; 
           [0018]      FIG. 5  is a graphical representation of a modified method for uplink data channel PUSCH configured for cell range expansion in wireless communications; 
           [0019]      FIG. 6  is a graphical representation of a modified method for downlink PDSCH transmission configured for cell range expansion in wireless communications; and 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0020]      FIG. 1  is a schematic diagram illustrating one embodiment of system  100  for cell range expansion in wireless communications. In the depicted embodiment, system  100  includes base station (eNode B)  102  configured for wireless communications with one or more User Equipment (UE) devices  104 - 108 . In one embodiment, first UE device  104  may be located within a normal range of eNode B  102 . As described above, in LTE systems, the normal range  110  from eNode B  102  is 100 km as defined by LTE standards. In other communication systems, such as WiMAX, the normal range  110  may be different than in LTE standards. As illustrated in  FIG. 1 , UE  104  may determine that it is within the normal range  110  of eNode B  102  and set a regular state setting in its communication circuitry. 
         [0021]    Additionally, system  100  includes two UE devices  106 ,  108  that are located outside of the normal range  110 . For example, UE  108  may be located in extended range region  114  and UE  106  may be located in transition region  112 . One of ordinary skill in the art will recognize that a variety of ranges or regions may be defined according to the present embodiments. In the embodiment of  FIG. 1 , UE  106  sets a transition state setting in its communication circuitry and UE  108  sets an extended state setting in its communication circuitry. 
         [0022]      FIG. 2  is a schematic block diagram of one embodiment of an apparatus for cell range expansion in wireless communications. In one embodiment,  FIG. 2  represents at least a portion of the communication circuitry of UE devices  104 - 108 . In one embodiment, the apparatus includes UE system-on-chip (SoC) device  202 . In various embodiments, SoC  202  may be a programmable data processor, Field Programmable Gate Array (FPGA), Digital Signal Processor (DSP), Programmable Logic Chip (PLC), or the like. UE SoC  202  may produce an output  204  which is coupled to delay logic device  206  and to multiplexer (“MUX”)  210 . Additionally, a control line  212  may be coupled between UE SoC  202  to MUX  210  for controlling whether MUX  210  used output  204  from UE SoC  202  or output  208  from Delay Logic  206 . MUX  210  then generates an output for which is converted by Digital to Analog Converter (“DAC”) device  214  for communication to eNode B  102 . 
         [0023]    Additionally, UE SoC  202  may be coupled to Analog to Digital Converter (“ADC”)  216  to receive data and commands from eNode B  102  on input line  218 . In one embodiment, UE SoC  202  may use information derived from the data and commands received on input line  218  to determine whether UE  104 - 108  is located in normal range  110 , transition range  112 , extended range, or some other range from eNode B  102 . Then, UE SoC  202  may use such information to set a state setting within UE SoC  202  to one of a plurality of states. For example, the states may include “Regular” state, “Transition” state, and “Extended” state. In one embodiment, the state of UE SoC  202  may determine the timing of communications sent back to eNode B  102 . For example, in regular state, UE  104  may send communications to eNode B  102  according to the conventional timing as defined. In extended state, UE SoC  202  may adjust the timing for the response to a  1 -subframe-sooner timing advance. In a particular embodiment, UE SoC  202  may cause the UE  108  to respond to eNode B  102  1 ms sooner than it would in regular state. In the transition state, UE SoC  202  of UE  106  may also set a 1-subframe timing advance, but in addition may add some delay using either internal delay or delay logic  206 , so that the timing of the response is greater than possible in normal state, but less than the timing advance in extended state. 
         [0024]    UE SoC  202  may then set controls on MUX  210  over control line  212  according to the state of SoC  202  to determine whether delay will be used or not. In a further embodiment, UE SoC  202  may include a further control line (not shown) for setting a delay time in delay logic  206 . Alternatively, delay logic  206  may be preset to a predetermined delay period. 
         [0025]      FIG. 3  is a graphical timing diagram of two-way wireless communication between UE device  104 - 108  and an eNode B  102 . In particular,  FIG. 3  illustrates one embodiment of a LTE timing diagram. In such an embodiment, the total round-trip communication turnaround time is completed within an 8 ms time period. The 8 ms time period may be broken into eight equal Subframe Lengths (SFL), where each SFL is 1 ms. 
         [0026]    On the first row, eNode B  102  may transmit a command at interval K to UE  104 . The OTA delay for the transmission between eNode B  102  and UE  104  is represented by “d”. Thus, d ms later, UE  104  receives the command and starts processing the command. Ordinarily, UE  104  should have three SFLs to process the command, but that time is shortened by the total round trip OTA delay of 2d ms. Previous UE devices in LTE systems were configured to handle processing times where the total OTA delay of 2d is less than or equal to 0.667 ms. In one embodiment, this time delay corresponds to total distance of 100 km between eNode B  102  and UE  104 . 
         [0027]    Thus, UE  104  transmits a response at K+4−2d ms in order to get the timing for eNode B  102  processing times correct and allow for synchronization of communications between UE  104  and eNode B  102 . It can be appreciated that as the distance between eNode B  102  and UE  106 ,  108  exceeds normal range  110 , the OTA delay 2d may be so long that the processing time is insufficient for UE  106 ,  108  to process the command and prepare a response. 
         [0028]      FIG. 4  is a graphical timing diagram illustrating a timing of two-way wireless communications according to a method for cell range expansion in wireless communications. In this embodiment, UE SoC  202  may be configured to set a “1-subframe-earlier” flag when it determines that the UE  106 ,  108  is outside of normal range  110 . As described further in  FIGS. 5A -5B , on the uplink data channel UE  106 ,  108  may hold a PUSCH packet transmission until eNode B  102  sends a retransmit command. On the downlink, as described in  FIGS. 6A-6B , UE  106 ,  108  may be configured to always transmit a NACK in response to a first received PDSCH packet from eNodeB  104 , thus causing eNode B  102  to retransmit the PDSCH packet. This allows UE  106 ,  108  to have a full 3 ms time period to process the response, and then communicate a timely response to the second command from eNode B  102 . Although this may cause some delay because eNode B must retransmit the command, it enables the UE to effectively increase the transmission range to twice the normal range  110  or more, because it allows UE  106 ,  108  to synchronize communications with eNode B  102  even though the OTA delay is so long that UE  106 ,  108  would ordinarily not have sufficient processing time. 
         [0029]      FIGS. 5A-B  is a graphical representation of a modified method for uplink data channel PUSCH configured for cell range expansion in wireless communications. In  FIG. 5A  illustrates a normal uplink data channel PUSCH command and response schedule. This schedule may be used for UE  104 , which is within normal range  110 . In one embodiment, eNode B  102  sends a command for a new packet transmission to UE  104 . In response, UE  104  may process the command and generate a PUSCH packet within a predetermined time frame. If eNode B  102  fails to decode a packet, it may send a NACK command to UE  104  for retransmission of the packet. In response, UE  104  may retransmit the PUSCH packet. ENode B  102  will continue to send a NACK command until a packet is decoded correctly, at which time eNode B  102  may either: send an ACK command and set UE  104  to mute, or send another command for a new packet. 
         [0030]      FIG. 5B  illustrates a modified scheme for cell range expansion in wireless communications. In this embodiment, UE SoC  202  may set UE  106 ,  108  to mute when receiving commands for new packet transmissions due to insufficient time to prepare the PUSCH new transmission. Thus, UE  106 ,  108  holds it&#39;s the PUSCH transmission until it receives a retransmit command from eNode B  102 . Having the PUSCH packet prepared in response to the new packet command, UE  106 ,  108  immediately transmits the PUSCH packet at the prescribed time in response to the retransmit command from eNode B  102 . If the PUSCH packet is decoded correctly , eNode B  102  may either: send an ACK command and set UE  104  to mute, or send another command for a new packet. If the PUSCH packet is not decoded correctly, eNode B  102  may send a NACK retransmit command to UE  106 ,  108  until a correct PUSCH packet is decoded. 
         [0031]      FIGS. 6A-6B  is a graphical representation of a modified method for downlink PDSCH packet transmission configured for cell range expansion in wireless communications. As illustrated in  FIG. 6A , for communications between eNode B  102  and UE  104 , which is within normal range  110 , eNode B  102  may transmit a PDSCH packet to UE  104 . If UE  104  can decode the PDSCH packet correctly, it will send back an ACK command. If UE  104  cannot decode the PDSCH packet correctly, it will send a NACK command to eNode B  102  for retransmission of the PDSCH packet. 
         [0032]    As shown in  FIG. 6B , UE  106 ,  108  may be configured to always transmit a NACK command in response to any new PDSCH packet transmission from eNode B  102 , because UE  106 ,  108  may not have time to decode the PDSCH packet by the time the UE  106 ,  108  is required to send an ACK/NACK response. In response to retransmission of the PDSCH packet, UE  106 ,  108  will send an ACK/NACK response based on the decoding results of the previous transmission of the same PDSCH packet. 
         [0033]    Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.

Technology Classification (CPC): 7