Abstract:
In certain circumstances, the uplink resources (e.g., overhead) used for transmission of the UL DM-RS may be excessive, consuming an unnecessary amount of the available uplink spectrum. While there is a balance between the number of DM-RS and the reliability of the shared data channel, reduction of the UL DM-RS overhead may enable the UE to increase the number of transmissions in a UL subframes. Various DM-RS reduction techniques discussed include reducing the number of UL DM-RS generally, per resource block, or per pairs of resource units, and accommodating transmission of uplink control channel information when UL DM-RS is reduced. Further disclosed techniques relate to adjusting the number of UCI in the uplink shared channel.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
       [0001]    This application claims the benefit of U.S. Provisional Application Ser. No. 61/971,465, entitled “SOME DETAILS FOR UL DM-RS OVERHEAD REDUCTION IN LTE” and filed on Mar. 27, 2014, which is expressly incorporated by reference herein in its entirety. 
     
    
     BACKGROUND 
       [0002]    1. Field 
         [0003]    The present disclosure relates generally to communication systems, and more particularly, to the application of UL DM-RS overhead reduction in LTE. 
         [0004]    2. Background 
         [0005]    Wireless communication systems are widely deployed to provide various telecommunication services such as telephony, video, data, messaging, and broadcasts. Typical wireless communication systems may employ multiple-access technologies capable of supporting communication with multiple users by sharing available system resources (e.g., bandwidth, transmit power). Examples of such multiple-access technologies include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, orthogonal frequency division multiple access (OFDMA) systems, single-carrier frequency division multiple access (SC-FDMA) systems, and time division synchronous code division multiple access (TD-SCDMA) systems. 
         [0006]    These multiple access technologies have been adopted in various telecommunication standards to provide a common protocol that enables different wireless devices to communicate on a municipal, national, regional, and even global level. An example of an emerging telecommunication standard is Long Term Evolution (LTE). LTE is a set of enhancements to the Universal Mobile Telecommunications System (UMTS) mobile standard promulgated by Third Generation Partnership Project (3GPP). LTE is designed to better support mobile broadband Internet access by improving spectral efficiency, lowering costs, improving services, making use of new spectrum, and better integrating with other open standards using OFDMA on the downlink (DL), SC-FDMA on the uplink (UL), and multiple-input multiple-output (MIMO) antenna technology. However, as the demand for mobile broadband access continues to increase, there exists a need for further improvements in LTE technology. Preferably, these improvements should be applicable to other multi-access technologies and the telecommunication standards that employ these technologies. In the LTE standard, the UL demodulation reference signal (DM-RS) transmitted by a UE in a UL subframe typically has a fixed overhead. For example, the UL DM-RS may be transmitted in fixed symbol positions for a cyclic prefix (CP) type. Moreover, the UE may also transmit uplink control information (UCI) to the base station in the UL subframe. 
       SUMMARY 
       [0007]    In certain circumstances, the uplink resources (e.g., overhead) used for transmission of the UL DM-RS may be excessive, consuming an unnecessary amount of the available uplink spectrum. While there is a balance between the number of DM-RS and the reliability of the shared data channel, reduction of the UL DM-RS overhead may enable the UE to increase the number of transmissions in a UL subframes. Various DM-RS reduction techniques discussed include reducing the number of UL DM-RS generally, per resource block, or per pairs of resource units, and accommodating transmission of uplink control channel information when UL DM-RS is reduced. Further disclosed techniques relate to adjusting the number of UCI in the uplink shared channel. 
         [0008]    Accordingly, in an aspect of the disclosure, a method, a computer program product, and an apparatus are provided. The apparatus may determine whether to apply a DM-RS overhead reduction scheme for an uplink subframe, identify a UCI transmission scheme for the uplink subframe based on whether the DM-RS overhead reduction scheme is applied, and transmit the UCI in the uplink subframe using the UCI transmission scheme. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a diagram illustrating an example of a network architecture. 
           [0010]      FIG. 2  is a diagram illustrating an example of an access network. 
           [0011]      FIG. 3  is a diagram illustrating an example of a DL frame structure in LTE. 
           [0012]      FIG. 4  is a diagram illustrating an example of an UL frame structure in LTE. 
           [0013]      FIG. 5  is a diagram illustrating an example of a radio protocol architecture for the user and control planes. 
           [0014]      FIG. 6  is a diagram illustrating an example of an evolved Node B and user equipment in an access network. 
           [0015]      FIG. 7  is a diagram illustrating a range expanded cellular region in a heterogeneous network. 
           [0016]      FIG. 8  is a diagram illustrating an UL subframe of a UE. 
           [0017]      FIG. 9  is a flow chart of a method of wireless communication. 
           [0018]      FIG. 10  is a conceptual data flow diagram illustrating the data flow between different modules/means/components in an exemplary apparatus. 
           [0019]      FIG. 11  is a diagram illustrating an example of a hardware implementation for an apparatus employing a processing system. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    The detailed description set forth below in connection with the appended drawings is intended as a description of various configurations and is not intended to represent the only configurations in which the concepts described herein may be practiced. The detailed description includes specific details for the purpose of providing a thorough understanding of various concepts. However, it will be apparent to those skilled in the art that these concepts may be practiced without these specific details. In some instances, well known structures and components are shown in block diagram form in order to avoid obscuring such concepts. 
         [0021]    Several aspects of telecommunication systems will now be presented with reference to various apparatus and methods. These apparatus and methods will be described in the following detailed description and illustrated in the accompanying drawings by various blocks, modules, components, circuits, steps, processes, algorithms, etc. (collectively referred to as “elements”). These elements may be implemented using electronic hardware, computer software, or any combination thereof. Whether such elements are implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. 
         [0022]    By way of example, an element, or any portion of an element, or any combination of elements may be implemented with a “processing system” that includes one or more processors. Examples of processors include microprocessors, microcontrollers, digital signal processors (DSPs), field programmable gate arrays (FPGAs), programmable logic devices (PLDs), state machines, gated logic, discrete hardware circuits, and other suitable hardware configured to perform the various functionality described throughout this disclosure. One or more processors in the processing system may execute software. Software shall be construed broadly to mean instructions, instruction sets, code, code segments, program code, programs, subprograms, software modules, applications, software applications, software packages, routines, subroutines, objects, executables, threads of execution, procedures, functions, etc., whether referred to as software, firmware, middleware, microcode, hardware description language, or otherwise. 
         [0023]    Accordingly, in one or more exemplary embodiments, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on or encoded as one or more instructions or code on a computer-readable medium. Computer-readable media includes computer storage media. Storage media may be any available media that can be accessed by a computer. By way of example, and not limitation, such computer-readable media can comprise a random-access memory (RAM), a read-only memory (ROM), an electrically erasable programmable ROM (EEPROM), compact disk ROM (CD-ROM) or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to carry or store desired program code in the form of instructions or data structures and that can be accessed by a computer. Combinations of the above should also be included within the scope of computer-readable media. 
         [0024]      FIG. 1  is a diagram illustrating an LTE network architecture  100 . The LTE network architecture  100  may be referred to as an Evolved Packet System (EPS)  100 . The EPS  100  may include one or more user equipment (UE)  102 , an Evolved UMTS Terrestrial Radio Access Network (E-UTRAN)  104 , an Evolved Packet Core (EPC)  110 , and an Operator&#39;s Internet Protocol (IP) Services  122 . The EPS can interconnect with other access networks, but for simplicity those entities/interfaces are not shown. As shown, the EPS provides packet-switched services, however, as those skilled in the art will readily appreciate, the various concepts presented throughout this disclosure may be extended to networks providing circuit-switched services. 
         [0025]    The E-UTRAN includes the evolved Node B (eNB)  106  and other eNBs  108 , and may include a Multicast Coordination Entity (MCE)  128 . The eNB  106  provides user and control planes protocol terminations toward the UE  102 . The eNB  106  may be connected to the other eNBs  108  via a backhaul (e.g., an X2 interface). The MCE  128  allocates time/frequency radio resources for evolved Multimedia Broadcast Multicast Service (MBMS) (eMBMS), and determines the radio configuration (e.g., a modulation and coding scheme (MCS)) for the eMBMS. The MCE  128  may be a separate entity or part of the eNB  106 . The eNB  106  may also be referred to as a base station, a Node B, an access point, a base transceiver station, a radio base station, a radio transceiver, a transceiver function, a basic service set (BSS), an extended service set (ESS), or some other suitable terminology. The eNB  106  provides an access point to the EPC  110  for a UE  102 . Examples of UEs  102  include a cellular phone, a smart phone, a session initiation protocol (SIP) phone, a laptop, a personal digital assistant (PDA), a satellite radio, a global positioning system, a multimedia device, a video device, a digital audio player (e.g., MP3 player), a camera, a game console, a tablet, or any other similar functioning device. The UE  102  may also be referred to by those skilled in the art as a mobile station, a subscriber station, a mobile unit, a subscriber unit, a wireless unit, a remote unit, a mobile device, a wireless device, a wireless communications device, a remote device, a mobile subscriber station, an access terminal, a mobile terminal, a wireless terminal, a remote terminal, a handset, a user agent, a mobile client, a client, or some other suitable terminology. 
         [0026]    The eNB  106  is connected to the EPC  110 . The EPC  110  may include a Mobility Management Entity (MME)  112 , a Home Subscriber Server (HSS)  120 , other MMEs  114 , a Serving Gateway  116 , a Multimedia Broadcast Multicast Service (MBMS) Gateway  124 , a Broadcast Multicast Service Center (BM-SC)  126 , and a Packet Data Network (PDN) Gateway  118 . The MME  112  is the control node that processes the signaling between the UE  102  and the EPC  110 . Generally, the MME  112  provides bearer and connection management. All user IP packets are transferred through the Serving Gateway  116 , which itself is connected to the PDN Gateway  118 . The PDN Gateway  118  provides UE IP address allocation as well as other functions. The PDN Gateway  118  and the BM-SC  126  are connected to the IP Services  122 . The IP Services  122  may include the Internet, an intranet, an IP Multimedia Subsystem (IMS), a PS Streaming Service (PSS), and/or other IP services. The BM-SC  126  may provide functions for MBMS user service provisioning and delivery. The BM-SC  126  may serve as an entry point for content provider MBMS transmission, may be used to authorize and initiate MBMS Bearer Services within a PLMN, and may be used to schedule and deliver MBMS transmissions. The MBMS Gateway  124  may be used to distribute MBMS traffic to the eNBs (e.g.,  106 ,  108 ) belonging to a Multicast Broadcast Single Frequency Network (MBSFN) area broadcasting a particular service, and may be responsible for session management (start/stop) and for collecting eMBMS related charging information. 
         [0027]      FIG. 2  is a diagram illustrating an example of an access network  200  in an LTE network architecture. In this example, the access network  200  is divided into a number of cellular regions (cells)  202 . One or more lower power class eNBs  208  may have cellular regions  210  that overlap with one or more of the cells  202 . The lower power class eNB  208  may be a femto cell (e.g., home eNB (HeNB)), pico cell, micro cell, or remote radio head (RRH). The macro eNBs  204  are each assigned to a respective cell  202  and are configured to provide an access point to the EPC  110  for all the UEs  206  in the cells  202 . There is no centralized controller in this example of an access network  200 , but a centralized controller may be used in alternative configurations. The eNBs  204  are responsible for all radio related functions including radio bearer control, admission control, mobility control, scheduling, security, and connectivity to the serving gateway  116 . An eNB may support one or multiple (e.g., three) cells (also referred to as a sectors). The term “cell” can refer to the smallest coverage area of an eNB and/or an eNB subsystem serving are particular coverage area. Further, the terms “eNB,” “base station,” and “cell” may be used interchangeably herein. 
         [0028]    The modulation and multiple access scheme employed by the access network  200  may vary depending on the particular telecommunications standard being deployed. In LTE applications, OFDM is used on the DL and SC-FDMA is used on the UL to support both frequency division duplex (FDD) and time division duplex (TDD). As those skilled in the art will readily appreciate from the detailed description to follow, the various concepts presented herein are well suited for LTE applications. However, these concepts may be readily extended to other telecommunication standards employing other modulation and multiple access techniques. By way of example, these concepts may be extended to Evolution-Data Optimized (EV-DO) or Ultra Mobile Broadband (UMB). EV-DO and UMB are air interface standards promulgated by the 3rd Generation Partnership Project 2 (3GPP2) as part of the CDMA2000 family of standards and employs CDMA to provide broadband Internet access to mobile stations. These concepts may also be extended to Universal Terrestrial Radio Access (UTRA) employing Wideband-CDMA (W-CDMA) and other variants of CDMA, such as TD-SCDMA; Global System for Mobile Communications (GSM) employing TDMA; and Evolved UTRA (E-UTRA), IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, and Flash-OFDM employing OFDMA. UTRA, E-UTRA, UMTS, LTE and GSM are described in documents from the 3GPP organization. CDMA2000 and UMB are described in documents from the 3GPP2 organization. The actual wireless communication standard and the multiple access technology employed will depend on the specific application and the overall design constraints imposed on the system. 
         [0029]    The eNBs  204  may have multiple antennas supporting MIMO technology. The use of MIMO technology enables the eNBs  204  to exploit the spatial domain to support spatial multiplexing, beamforming, and transmit diversity. Spatial multiplexing may be used to transmit different streams of data simultaneously on the same frequency. The data streams may be transmitted to a single UE  206  to increase the data rate or to multiple UEs  206  to increase the overall system capacity. This is achieved by spatially precoding each data stream (i.e., applying a scaling of an amplitude and a phase) and then transmitting each spatially precoded stream through multiple transmit antennas on the DL. The spatially precoded data streams arrive at the UE(s)  206  with different spatial signatures, which enables each of the UE(s)  206  to recover the one or more data streams destined for that UE  206 . On the UL, each UE  206  transmits a spatially precoded data stream, which enables the eNB  204  to identify the source of each spatially precoded data stream. 
         [0030]    Spatial multiplexing is generally used when channel conditions are good. When channel conditions are less favorable, beamforming may be used to focus the transmission energy in one or more directions. This may be achieved by spatially precoding the data for transmission through multiple antennas. To achieve good coverage at the edges of the cell, a single stream beamforming transmission may be used in combination with transmit diversity. 
         [0031]    In the detailed description that follows, various aspects of an access network will be described with reference to a MIMO system supporting OFDM on the DL. OFDM is a spread-spectrum technique that modulates data over a number of subcarriers within an OFDM symbol. The subcarriers are spaced apart at precise frequencies. The spacing provides “orthogonality” that enables a receiver to recover the data from the subcarriers. In the time domain, a guard interval (e.g., cyclic prefix) may be added to each OFDM symbol to combat inter-OFDM-symbol interference. The UL may use SC-FDMA in the form of a DFT-spread OFDM signal to compensate for high peak-to-average power ratio (PAPR). 
         [0032]      FIG. 3  is a diagram  300  illustrating an example of a DL frame structure in LTE. A frame (10 ms) may be divided into 10 equally sized subframes. Each subframe may include two consecutive time slots. A resource grid may be used to represent two time slots, each time slot including a resource block. The resource grid is divided into multiple resource elements. In LTE, for a normal cyclic prefix, a resource block contains 12 consecutive subcarriers in the frequency domain and 7 consecutive OFDM symbols in the time domain, for a total of 84 resource elements. For an extended cyclic prefix, a resource block contains 12 consecutive subcarriers in the frequency domain and  6  consecutive OFDM symbols in the time domain, for a total of 72 resource elements. Some of the resource elements, indicated as R  302 ,  304 , include DL reference signals (DL-RS). The DL-RS include Cell-specific RS (CRS) (also sometimes called common RS)  302  and UE-specific RS (UE-RS)  304 . UE-RS  304  are transmitted only on the resource blocks upon which the corresponding physical DL shared channel (PDSCH) is mapped. The number of bits carried by each resource element depends on the modulation scheme. Thus, the more resource blocks that a UE receives and the higher the modulation scheme, the higher the data rate for the UE. 
         [0033]      FIG. 4  is a diagram  400  illustrating an example of an UL frame structure in LTE. The available resource blocks for the UL may be partitioned into a data section and a control section. The control section may be formed at the two edges of the system bandwidth and may have a configurable size. The resource blocks in the control section may be assigned to UEs for transmission of control information. The data section may include all resource blocks not included in the control section. The UL frame structure results in the data section including contiguous subcarriers, which may allow a single UE to be assigned all of the contiguous subcarriers in the data section. 
         [0034]    A UE may be assigned resource blocks  410   a,    410   b  in the control section to transmit control information to an eNB. The UE may also be assigned resource blocks  420   a,    420   b  in the data section to transmit data to the eNB. The UE may transmit control information in a physical UL control channel (PUCCH) on the assigned resource blocks in the control section. The UE may transmit only data or both data and control information in a physical UL shared channel (PUSCH) on the assigned resource blocks in the data section. A UL transmission may span both slots of a subframe and may hop across frequency. 
         [0035]    A set of resource blocks may be used to perform initial system access and achieve UL synchronization in a physical random access channel (PRACH)  430 . The PRACH  430  carries a random sequence and cannot carry any UL data/signaling. Each random access preamble occupies a bandwidth corresponding to six consecutive resource blocks. The starting frequency is specified by the network. That is, the transmission of the random access preamble is restricted to certain time and frequency resources. There is no frequency hopping for the PRACH. The PRACH attempt is carried in a single subframe (1 ms) or in a sequence of few contiguous subframes and a UE can make only a single PRACH attempt per frame (10 ms). 
         [0036]      FIG. 5  is a diagram  500  illustrating an example of a radio protocol architecture for the user and control planes in LTE. The radio protocol architecture for the UE and the eNB is shown with three layers: Layer 1, Layer 2, and Layer 3. Layer 1 (L1 layer) is the lowest layer and implements various physical layer signal processing functions. The L1 layer will be referred to herein as the physical layer  506 . Layer 2 (L2 layer)  508  is above the physical layer  506  and is responsible for the link between the UE and eNB over the physical layer  506 . 
         [0037]    In the user plane, the L2 layer  508  includes a media access control (MAC) sublayer  510 , a radio link control (RLC) sublayer  512 , and a packet data convergence protocol (PDCP)  514  sublayer, which are terminated at the eNB on the network side. Although not shown, the UE may have several upper layers above the L2 layer  508  including a network layer (e.g., IP layer) that is terminated at the PDN gateway  118  on the network side, and an application layer that is terminated at the other end of the connection (e.g., far end UE, server, etc.). 
         [0038]    The PDCP sublayer  514  provides multiplexing between different radio bearers and logical channels. The PDCP sublayer  514  also provides header compression for upper layer data packets to reduce radio transmission overhead, security by ciphering the data packets, and handover support for UEs between eNBs. The RLC sublayer  512  provides segmentation and reassembly of upper layer data packets, retransmission of lost data packets, and reordering of data packets to compensate for out-of-order reception due to hybrid automatic repeat request (HARQ). The MAC sublayer  510  provides multiplexing between logical and transport channels. The MAC sublayer  510  is also responsible for allocating the various radio resources (e.g., resource blocks) in one cell among the UEs. The MAC sublayer  510  is also responsible for HARQ operations. 
         [0039]    In the control plane, the radio protocol architecture for the UE and eNB is substantially the same for the physical layer  506  and the L2 layer  508  with the exception that there is no header compression function for the control plane. The control plane also includes a radio resource control (RRC) sublayer  516  in Layer 3 (L3 layer). The RRC sublayer  516  is responsible for obtaining radio resources (e.g., radio bearers) and for configuring the lower layers using RRC signaling between the eNB and the UE. 
         [0040]      FIG. 6  is a block diagram of an eNB  610  in communication with a UE  650  in an access network. In the DL, upper layer packets from the core network are provided to a controller/processor  675 . The controller/processor  675  implements the functionality of the L2 layer. In the DL, the controller/processor  675  provides header compression, ciphering, packet segmentation and reordering, multiplexing between logical and transport channels, and radio resource allocations to the UE  650  based on various priority metrics. The controller/processor  675  is also responsible for HARQ operations, retransmission of lost packets, and signaling to the UE  650 . 
         [0041]    The transmit (TX) processor  616  implements various signal processing functions for the L1 layer (i.e., physical layer). The signal processing functions include coding and interleaving to facilitate forward error correction (FEC) at the UE  650  and mapping to signal constellations based on various modulation schemes (e.g., binary phase-shift keying (BPSK), quadrature phase-shift keying (QPSK), M-phase-shift keying (M-PSK), M-quadrature amplitude modulation (M-QAM)). The coded and modulated symbols are then split into parallel streams. Each stream is then mapped to an OFDM subcarrier, multiplexed with a reference signal (e.g., pilot) in the time and/or frequency domain, and then combined together using an Inverse Fast Fourier Transform (IFFT) to produce a physical channel carrying a time domain OFDM symbol stream. The OFDM stream is spatially precoded to produce multiple spatial streams. Channel estimates from a channel estimator  674  may be used to determine the coding and modulation scheme, as well as for spatial processing. The channel estimate may be derived from a reference signal and/or channel condition feedback transmitted by the UE  650 . Each spatial stream may then be provided to a different antenna  620  via a separate transmitter  618 TX. Each transmitter  618 TX may modulate an RF carrier with a respective spatial stream for transmission. 
         [0042]    At the UE  650 , each receiver  654 RX receives a signal through its respective antenna  652 . Each receiver  654 RX recovers information modulated onto an RF carrier and provides the information to the receive (RX) processor  656 . The RX processor  656  implements various signal processing functions of the L1 layer. The RX processor  656  may perform spatial processing on the information to recover any spatial streams destined for the UE  650 . If multiple spatial streams are destined for the UE  650 , they may be combined by the RX processor  656  into a single OFDM symbol stream. The RX processor  656  then converts the OFDM symbol stream from the time-domain to the frequency domain using a Fast Fourier Transform (FFT). The frequency domain signal comprises a separate OFDM symbol stream for each subcarrier of the OFDM signal. The symbols on each subcarrier, and the reference signal, are recovered and demodulated by determining the most likely signal constellation points transmitted by the eNB  610 . These soft decisions may be based on channel estimates computed by the channel estimator  658 . The soft decisions are then decoded and deinterleaved to recover the data and control signals that were originally transmitted by the eNB  610  on the physical channel. The data and control signals are then provided to the controller/processor  659 . 
         [0043]    The controller/processor  659  implements the L2 layer. The controller/processor can be associated with a memory  660  that stores program codes and data. The memory  660  may be referred to as a computer-readable medium. In the UL, the controller/processor  659  provides demultiplexing between transport and logical channels, packet reassembly, deciphering, header decompression, control signal processing to recover upper layer packets from the core network. The upper layer packets are then provided to a data sink  662 , which represents all the protocol layers above the L2 layer. Various control signals may also be provided to the data sink  662  for L3 processing. The controller/processor  659  is also responsible for error detection using an acknowledgement (ACK) and/or negative acknowledgement (NACK) protocol to support HARQ operations. 
         [0044]    In the UL, a data source  667  is used to provide upper layer packets to the controller/processor  659 . The data source  667  represents all protocol layers above the L2 layer. Similar to the functionality described in connection with the DL transmission by the eNB  610 , the controller/processor  659  implements the L2 layer for the user plane and the control plane by providing header compression, ciphering, packet segmentation and reordering, and multiplexing between logical and transport channels based on radio resource allocations by the eNB  610 . The controller/processor  659  is also responsible for HARQ operations, retransmission of lost packets, and signaling to the eNB  610 . 
         [0045]    Channel estimates derived by a channel estimator  658  from a reference signal or feedback transmitted by the eNB  610  may be used by the TX processor  668  to select the appropriate coding and modulation schemes, and to facilitate spatial processing. The spatial streams generated by the TX processor  668  may be provided to different antenna  652  via separate transmitters  654 TX. Each transmitter  654 TX may modulate an RF carrier with a respective spatial stream for transmission. 
         [0046]    The UL transmission is processed at the eNB  610  in a manner similar to that described in connection with the receiver function at the UE  650 . Each receiver  618 RX receives a signal through its respective antenna  620 . Each receiver  618 RX recovers information modulated onto an RF carrier and provides the information to a RX processor  670 . The RX processor  670  may implement the L1 layer. 
         [0047]    The controller/processor  675  implements the L2 layer. The controller/processor  675  can be associated with a memory  676  that stores program codes and data. The memory  676  may be referred to as a computer-readable medium. In the UL, the control/processor  675  provides demultiplexing between transport and logical channels, packet reassembly, deciphering, header decompression, control signal processing to recover upper layer packets from the UE  650 . Upper layer packets from the controller/processor  675  may be provided to the core network. The controller/processor  675  is also responsible for error detection using an ACK and/or NACK protocol to support HARQ operations. 
         [0048]      FIG. 7  is a diagram  700  illustrating a range expanded cellular region in a heterogeneous network. A lower power class eNB such as the RRH  710   b  may have a range expanded cellular region  703  that is expanded from the cellular region  702  through enhanced inter-cell interference coordination between the RRH  710   b  and the macro eNB  710   a  and through interference cancellation performed by the UE  720 . In enhanced inter-cell interference coordination, the RRH  710   b  receives information from the macro eNB  710   a  regarding an interference condition of the UE  720 . The information allows the RRH  710   b  to serve the UE  720  in the range expanded cellular region  703  and to accept a handoff of the UE  720  from the macro eNB  710   a  as the UE  720  enters the range expanded cellular region  703 . 
         [0049]      FIG. 8  is a diagram illustrating a UL subframe  800  of a UE. In an aspect, as shown in  FIG. 8 , a UE may transmit a UL demodulation reference signal (DM-RS) to a base station in one or more symbols (e.g., symbols  802  and  804 ) of the UL subframe  800 . The UE may further transmit uplink control information (UCI) to the base station. For example, the UCI may include a scheduling request (SR), a channel quality indicator (CQI), a precoding matrix indicator (PMI), a precoding type indication (PTI), a rank indicator (RI), and/or an acknowledgment (ACK) or negative acknowledgement (NACK). In the LTE standard, the UL DM-RS typically has a fixed overhead. For example, as shown in  FIG. 8 , the UL DM-RS is transmitted in fixed symbol positions for a cyclic prefix (CP) type. In an aspect, the UCI may be piggybacked on PUSCH to maintain a single-carrier (SC) waveform (e.g., the UCI may be transmitted on PUSCH, instead of being transmitted on PUCCH in parallel with PUSCH) and avoid transmitting both PUCCH and PUSCH in the same slot. Piggybacking the UCI on PUSCH has the benefit of increasing the rate at which the UE can transmit UCI. However, those UCI transmitted on the PUSCH are susceptible to higher interference (e.g., more variable SINR or data collisions) and are generally transmitted at a lower transmit power relative to IoT. 
         [0050]    For example, for normal CP, the DM-RS is included in the middle of a time slot (e.g., the first time slot and the second time slot in  FIG. 8 ). In an aspect, as shown in  FIG. 8 , PUSCH data is rate matched around CQI/PMI/RI, but is punctured by ACK/NAK. For example, in the configuration of  FIG. 8 , an ACK/NAK may be transmitted in symbols adjacent to DM-RS, and RI may be transmitted in symbols adjacent to ACK/NAK. This positioning improves the likelihood that these symbols can be demodulated. 
         [0051]    The LTE standard (e.g., LTE Release  10 ) supports simultaneous PUCCH and PUSCH transmission by a UE in one subframe, where previously a UE could only transmit PUCCH or PUSCH in a given subframe. With simultaneous PUCCH and PUSCH transmission by a UE, the single-carrier (SC) waveform property may no longer be maintained. In an aspect, an eNB may semi-statically configure a UE to concurrently transmit (also referred to as parallel transmission) the PUCCH and PUSCH in one UL subframe. If a UL subframe is configured for parallel transmission of the PUCCH and PUSCH, and the scheduled UCI for that UL subframe includes ACK/NAK only or channel state information (CSI) only, the UE may transmit ACK/NAK or CSI on PUCCH, and UL data on PUSCH. However, if the UL subframe is configured for parallel transmission of the PUCCH and PUSCH, and the scheduled UCI includes both ACK/NAK and CSI, ACK/NAK is transmitted on PUCCH, while CSI and UL data are transmitted on PUSCH. In other words, CSI is piggybacked on PUSCH (i.e., transmitted on the PUSCH region, instead of in the PUCCH region). By this behavior, the transmission of ACK/NACK is prioritized over CSI for transmission in the PUCCH. 
         [0052]    Conventionally, UL DM-RS overhead may be fixed for all UL ranks For example, if the last symbol of a UL subframe is not configured for (potential) SRS transmissions, the UL DM-RS overhead for normal CP may be approximately two symbols (e.g., symbols  802  and  804  in  FIG. 8 ) of the  14  symbols in the UL subframe  800  (e.g., 2/14=14.3%). If the last symbol is configured for (potential) SRS transmissions, UL DM-RS overhead for normal CP may be approximately two symbols (e.g., symbols  802  and  804  in  FIG. 8 ) of 13 available symbols in the UL subframe (e.g., 2/13=15.4%). 
         [0053]    In an aspect, a UE may apply a UL DM-RS overhead reduction scheme for a UL subframe. For example, a UE served by a small cell may observe favorable channel conditions and may reduce the number of resources for transmission of DM-RS to improve UL efficiency. In one aspect, a UL DM-RS overhead reduction scheme applied by the UE may configure the subframe to include only one DM-RS symbol. For example, a symbol in the first slot of the UL subframe may be used for transmission of DM-RS  802 , while symbol  3   804  in the second slot of the UL subframe may be used for PUSCH data. 
         [0054]    In another aspect, a UL DM-RS overhead reduction scheme applied by the UE may allow for frequency-domain DM-RS reduction. In such aspect, DM-RS may not be present in all resource elements and/or resource blocks. For example, DM-RS may be present in one of every N adjacent resource elements, or DM-RS may be present in one of every N resource blocks (e.g., where N can be an integer value of 2, 3, 4). 
         [0055]    In another aspect, a UL DM-RS overhead reduction scheme applied by the UE may enable time-division multiplexing (TDM) such that DM-RS and UL data are transmitted in one symbol. In other words, a symbol may be partitioned into two or more sub-symbols. One sub-symbol may carry DM-RS, and another sub-symbol may carry UL data. In such aspect, a guard period/CP may be included between the DM-RS and the UL data. That is, the original DM-RS symbol may be configured to have three sequential time portions, such that a first time portion includes a CP and the DM-RS, a second time portion serves as a guard period, and a third time portion includes a CP and PUSCH data. This aspect differs from the use of short block DM-RS in that the DM-RS and CP may be positioned in the center symbol of the slot, and may be preceded or followed by a data sub-symbol and CP. Furthermore, the DM-RS may be shorter than a short block DM-RS. 
         [0056]    When a UE applies a UL DM-RS overhead reduction scheme for a UL subframe, the UE may select an appropriate scheme for transmitting UCI in the same UL subframe. In one aspect, the UE may enable concurrent transmission of the PUCCH and PUSCH in the UL subframe when a UL DM-RS overhead reduction scheme is applied in order to provide sufficient performance for UCI. In such aspect, ACK/NAK may be transmitted on PUCCH. RI may be transmitted on either PUCCH or PUSCH. CQI/PMI may be transmitted on PUCCH or PUSCH. It should be noted that CSI may be periodic CSI or aperiodic CSI. In an aspect, periodic CSI and aperiodic CSI may be handled in a similar or different manner. For example, the UE may transmit periodic CSI on PUCCH and may transmit aperiodic CSI on PUSCH. Furthermore, the periodic CSI and aperiodic CSI may or may not be transmitted in different subframes. 
         [0057]    In another aspect, the UE may apply a separate configuration offset associated with a UL DM-RS overhead reduction scheme for transmission of UCI in the UL subframe. The configured offset corresponds to the number of REs used for UCI piggybacked on PUSCH. A larger offset value implies that a larger number of REs allocated to UCI on PUSCH and consequently, fewer number of REs remaining for UL data on PUSCH. For example, when the UE piggybacks UCI on PUSCH, the number of REs occupied by UCI may depend on PUSCH parameters and a semi-statically configured offset (β), e.g., configured by RRC. In an aspect, the offset may be separately configured for ACK/NAK, RI, and/or CQI/PMI. That is, ACK/NAK, RI, or CQI/PMI may each be associated with a different offset value. 
         [0058]    In an aspect, if the UE applies a DM-RS overhead reduction scheme to a UL subframe only for some PUSCH transmissions (e.g., UL DM-RS overhead reduction scheme is enabled but not applied for SPS transmissions), the UE may apply one of two separate offset configurations. For example, the UE may apply a first offset (β) when the UE does not apply a UL DM-RS overhead reduction scheme to a UL subframe and may apply a second offset (β′) when a UL DM-RS overhead reduction scheme is applied to a UL subframe. By using different offsets, UCI piggybacked on PUSCH can still achieve appropriate performance target for both the case when there is no DM-RS reduction and the case when there is DM-RS reduction. In an aspect, the second offset (β′) may be configured to be the first offset (β) adjusted by a delta value (e.g., β′=β+delta value). 
         [0059]    In an aspect, the possible values for β′ for a particular UCI type (e.g., ACK/NAK, RI, or CQI/PMI) may be the same as the values for β (where β and β′ may each be either a single value for all UCI types or a set of values corresponding to different or combinations of UCI types). Alternatively, the possible values for β′ maybe different from the values for β (e.g., the β′ may have an increased range of values with respect to β). A UE may determine whether to apply β or β′ for a particular UL subframe based on whether or not the UE is to apply a UL DM-RS overhead reduction scheme for the UL subframe. 
         [0060]    In an aspect, ACK/NAK may be included in both slots (e.g., the first and second time slots of a UL subframe) when a UL DM-RS overhead reduction scheme is not applied by the UE for a UL subframe. However, a different offset (e.g., β′) may be applied by the UE when a UL DM-RS overhead reduction scheme is applied by the UE for a UL subframe to overcome potential performance differences due to the reduced DM-RS overhead (e.g., as compared with the regular DM-RS overhead case). 
         [0061]    In an aspect, the UE may determine that for transmission of at least some UCI (or all UCL), the at least some UCI is mapped to resource elements in one of the two time slots of the UL subframe based on the presence and location of the DM-RS. As an example, at least one ACK/NAK piggybacked on PUSCH may be included in a time slot where DM-RS is present. For example, if UL DM-RS is included in the first time slot but not the second time slot, the UE may include an ACK/NAK in the first time slot. In such example, the UE may not include an ACK/NAK in the second time slot since no DM-RS is included in the second time slot. In an aspect, the number of symbols for ACK/NAK may remain  2  symbols, adjacent to the symbol that includes DM-RS. Alternatively, the UE may include ACK/NACK in more than two symbols of the subframe. For example, in addition to symbol  2  and symbol  4  of the first time slot, the UE may further include ACK/NACK in symbol  0  and symbol  6  of the first time slot, such that a total of four symbols are used for transmission of ACK/NAK in only the first time slot of the UL subframe. 
         [0062]    In an aspect, the UE may apply the previously described scheme for transmission of ACK/NACK in a similar manner for the transmission of RI in the UL subframe. For example, when a DM-RS resource overhead reduction scheme is applied by the UE that places the DM-RS in the first time slot, the UE may include RI in two symbols within the first time slot of the UL subframe, and not the second time slot. In an aspect, the UE may apply the previously described scheme for transmission of ACK/NACK in a similar manner for the transmission of CQI/PMI. For example, the UE may include CQI/PMI in the first time slot of the UL subframe, and not the second time slot. In other aspects, however, the UE may include CQI/PMI in both first and second time slots of the UL subframe. 
         [0063]    In an aspect, the number of resource elements to be used for transmission of UCI on PUSCH when the UE applies a DM-RS overhead reduction scheme for a UL subframe may be based on PUSCH parameters and an offset value. For example, such offset value may be separately configured from an offset value applied by the UE for transmission of UCI when the UE does not apply a UL DM-RS overhead reduction scheme. If the UE transmits UCI only in one slot of a UL subframe, this implies that the computed resource elements are only mapped to one slot (instead of two slots). 
         [0064]    In an aspect, a UE may determine that a UL DM-RS overhead reduction scheme should not be applied for a UL subframe when one or more conditions exist. For example, one such condition may include transmission of a PUSCH associated with a random access response grant (e.g., for contention-based random access procedure) in the UL subframe. For a non-contention based random access procedure, the UE may apply either a regular or reduced UL DM-RS overhead. Another such condition may include application of semi-persistent scheduling (SPS) to the PUSCH in the UL subframe, since it may be preferable to have regular UL DM-RS due to lack of fast rate adaptation. Another such condition may include transmission of A-CSI only on the PUSCH in the UL subframe. For example, when A-CSI only transmission on PUSCH is triggered, regular DM-RS may be applied by the UE for the UL subframe. Another such condition may include PUSCH transmissions in the UL subframe scheduled by downlink control information (DCI) format 0 at least when DCI format 0 is received from the common search space, in order to provide necessary fallback operation. In an aspect, DCI format 0 in the UE-specific search space may still be associated with a UL DM-RS overhead reduction scheme. Another such condition may include transmission of a PUSCH of rank 3 or above in the UL subframe. For example, the UE may always use regular DM-RS for transmission of a PUSCH of rank 3 or above. 
         [0065]      FIG. 9  is a flow chart  900  of a method of wireless communication. The method may be performed by a UE. It should be understood that the steps indicated with dashed lines in  FIG. 9  represent optional steps. 
         [0066]    At step  902 , the UE receives an indication of a DM-RS overhead reduction scheme for a UL subframe, e.g., via an RRC configuration, a MAC indication, or a dynamic indication via a control channel. 
         [0067]    At step  904 , the UE receives an indication of a DM-RS scheme without overhead reduction for a second UL subframe. 
         [0068]    At step  906 , the UE determines whether to apply a DM-RS overhead reduction scheme for the UL subframe. In an aspect, the UE may determine to apply the DM-RS overhead reduction scheme based on the indication received in step  902 . If the UE determines to apply a DM-RS overhead reduction scheme for the UL subframe ( 906 ), then the UE proceeds to step  908 . Otherwise, if the UE determines not to apply the DM-RS overhead reduction scheme for the UL subframe ( 906 ), then the UE proceeds to step  912   
         [0069]    At step  908 , the UE may identify a UCI transmission scheme for the UL subframe. In an aspect, the identified UCI transmission scheme may include concurrent transmission of a PUCCH and a PUSCH in the UL subframe when the DM-RS overhead reduction scheme is applied, where one or more portions of the UCI are transmitted in the PUCCH or PUSCH or both. For example, the UCI may include at least one of a CQI, a PMI, a scheduling request (SR), an ACK, a NACK, a precoding type indicator (PTI), or an RI. In another aspect, the identified UCI transmission scheme may include allocating resources in the UL subframe for UCI transmission based on a configuration offset associated with the DM-RS overhead reduction scheme. For example, the resources allocated for UCI transmission in the UL subframe may include resources carrying a PUSCH. In another aspect, the UCI transmission scheme may include allocating resources in the second UL subframe for UCI transmission based on a configuration offset associated with the DM-RS scheme without overhead reduction. 
         [0070]    At step  910 , the UE may transmit the UCI in the UL subframe using the identified UCI transmission scheme. 
         [0071]    At step  912 , the UE may apply a UCI transmission scheme associated with no DM-RS overhead reduction. For example, the UE may determine not to apply the DM-RS overhead reduction scheme when transmitting a PUSCH associated with certain UCI, contention based communications, or transmission conditions is present. For example, the UE may determine not to apply the DM-RS overhead reduction scheme when transmitting a random access response grant in the UL subframe, SPS is applied to the PUSCH in the UL subframe, A-CSI only is triggered to transmit on the PUSCH in the UL subframe, PUSCH transmissions in the UL subframe are scheduled by DCI format 0, a PUSCH of rank 3 or above is transmitted in the UL subframe, or a combination thereof. 
         [0072]    At step  914 , the UE may transmit the UCI in the UL subframe using the UCI transmission scheme associated with no DM-RS overhead reduction. 
         [0073]      FIG. 10  is a conceptual data flow diagram  1000  illustrating the data flow between different modules/means/components in an exemplary apparatus  1002 . The apparatus may be a UE. The receiving module  1004  receives an indication of a DM-RS overhead reduction scheme for an uplink subframe or an indication of a DM-RS scheme without overhead reduction for a second uplink subframe. For example, the receiving module  1004  may receive DM-RS scheme indication  1032  from base station  1050 , which may indicate a DM-RS overhead reduction scheme for an uplink subframe or a DM-RS scheme without overhead reduction for a second uplink subframe. The DM-RS overhead reduction scheme determining module  1006  determines whether to apply a DM-RS overhead reduction scheme for an uplink subframe. For example, the DM-RS overhead reduction scheme determining module  1006  may receive an indication  1016  of a DM-RS overhead reduction scheme for an uplink subframe and/or an indication  1018  of a DM-RS scheme without overhead reduction for a second uplink subframe. The DM-RS overhead reduction scheme determining module  1006  then determines whether to apply a DM-RS overhead reduction scheme based on indication  1016  and/or  1018 . The DM-RS overhead reduction scheme determining module  1006  provides a signal  1020  indicating that the DM-RS overhead reduction scheme should be applied or provides a signal  1026  indicating that a UCI transmission scheme associated with no DM-RS overhead reduction should be applied. The UCI transmission scheme identifying module  1008  identifies a UCI transmission scheme for the uplink subframe based on whether the DM-RS overhead reduction scheme is applied. For example, the UCI transmission scheme identifying module  1008  may receive the signal  1020  indicating that the DM-RS overhead reduction scheme should be applied and may identify a UCI transmission scheme for the uplink subframe. The UCI transmission scheme identifying module  1008  may provide the identified UCI transmission scheme  1022  to the UCI transmission module  1010 . The UCI transmission module  1010  transmits, via the transmission module  1014 , the UCI  1024  in the uplink subframe using the UCI transmission scheme. For example, the UCI is transmitted to the base station  1050  using uplink signal  1030 . 
         [0074]    The apparatus may include additional modules that perform each of the blocks of the algorithm in the aforementioned flow chart of  FIG. 9 . As such, each block in the aforementioned flow charts of  FIG. 9  may be performed by a module and the apparatus may include one or more of those modules. The modules may be one or more hardware components specifically configured to carry out the stated processes/algorithm, implemented by a processor configured to perform the stated processes/algorithm, stored within a computer-readable medium for implementation by a processor, or some combination thereof. 
         [0075]      FIG. 11  is a diagram  1100  illustrating an example of a hardware implementation for an apparatus  1002 ′ employing a processing system  1114 . The processing system  1114  may be implemented with a bus architecture, represented generally by the bus  1124 . The bus  1124  may include any number of interconnecting buses and bridges depending on the specific application of the processing system  1114  and the overall design constraints. The bus  1124  links together various circuits including one or more processors and/or hardware modules, represented by the processor  1104 , the modules  1004 ,  1006 ,  1008 ,  1010 , and  1014 , and the computer-readable medium/memory  1106 . The bus  1124  may also link various other circuits such as timing sources, peripherals, voltage regulators, and power management circuits, which are well known in the art, and therefore, will not be described any further. 
         [0076]    The processing system  1114  may be coupled to a transceiver  1110 . The transceiver  1110  is coupled to one or more antennas  1120 . The transceiver  1110  provides a means for communicating with various other apparatus over a transmission medium. The transceiver  1110  receives a signal from the one or more antennas  1120 , extracts information from the received signal, and provides the extracted information to the processing system  1114 , specifically the reception module  1004 . In addition, the transceiver  1110  receives information from the processing system  1114 , specifically the transmission module  1014 , and based on the received information, generates a signal to be applied to the one or more antennas  1120 . The processing system  1114  includes a processor  1104  coupled to a computer-readable medium/memory  1106 . The processor  1104  is responsible for general processing, including the execution of software stored on the computer-readable medium/memory  1106 . The software, when executed by the processor  1104 , causes the processing system  1114  to perform the various functions described supra for any particular apparatus. The computer-readable medium/memory  1106  may also be used for storing data that is manipulated by the processor  1104  when executing software. The processing system further includes at least one of the modules  1004 ,  1006 ,  1008 ,  1010 , and  1014 . The modules may be software modules running in the processor  1104 , resident/stored in the computer readable medium/memory  1106 , one or more hardware modules coupled to the processor  1104 , or some combination thereof. The processing system  1114  may be a component of the UE  650  and may include the memory  660  and/or at least one of the TX processor  668 , the RX processor  656 , and the controller/processor  659 . 
         [0077]    In one configuration, the apparatus  1002 / 1002 ′ for wireless communication includes means for means for determining whether to apply a DM-RS overhead reduction scheme for an uplink subframe, means for identifying a UCI transmission scheme for the uplink subframe based on whether the DM-RS overhead reduction scheme is applied, means for transmitting the UCI in the uplink subframe using the UCI transmission scheme, means for receiving an indication of the DM-RS overhead reduction scheme, where the determination is based on the indication of the DM-RS overhead reduction scheme, and means for receiving an indication of the DM-RS scheme without overhead reduction for a second uplink subframe. 
         [0078]    The aforementioned means may be one or more of the aforementioned modules of the apparatus  1002  and/or the processing system  1114  of the apparatus  1002 ′ configured to perform the functions recited by the aforementioned means. As described supra, the processing system  1114  may include the TX Processor  668 , the RX Processor  656 , and the controller/processor  659 . As such, in one configuration, the aforementioned means may be the TX Processor  668 , the RX Processor  656 , and the controller/processor  659  configured to perform the functions recited by the aforementioned means. 
         [0079]    It is understood that the specific order or hierarchy of steps in the processes/flow charts disclosed is an illustration of exemplary approaches. Based upon design preferences, it is understood that the specific order or hierarchy of steps in the processes/flow charts may be rearranged. Further, some steps may be combined or omitted. The accompanying method claims present elements of the various steps in a sample order, and are not meant to be limited to the specific order or hierarchy presented. 
         [0080]    The previous description is provided to enable any person skilled in the art to practice the various aspects described herein. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects. Thus, the claims are not intended to be limited to the aspects shown herein, but is to be accorded the full scope consistent with the language claims, wherein reference to an element in the singular is not intended to mean “one and only one” unless specifically so stated, but rather “one or more.” The word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any aspect described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other aspects.” Unless specifically stated otherwise, the term “some” refers to one or more. Combinations such as “at least one of A, B, or C,” “at least one of A, B, and C,” and “A, B, C, or any combination thereof” include any combination of A, B, and/or C, and may include multiples of A, multiples of B, or multiples of C. Specifically, combinations such as “at least one of A, B, or C,” “at least one of A, B, and C,” and “A, B, C, or any combination thereof” may be A only, B only, C only, A and B, A and C, B and C, or A and B and C, where any such combinations may contain one or more member or members of A, B, or C. All structural and functional equivalents to the elements of the various aspects described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. No claim element is to be construed as a means plus function unless the element is expressly recited using the phrase “means for.”