Patent Publication Number: US-2013242780-A1

Title: Virtual gap patterns with multi-radio coexistence for protected measurements

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit under 35 U.S.C. §119(e) to U.S. Provisional Patent Application No. 61/612,181, entitled, VIRTUAL GAP PATTERNS WITH MULTI-RADIO COEXISTENCE FOR PROTECTED MEASUREMENTS, filed on Mar. 16, 2012, in the names of DAYAL, et al., the disclosure of which is expressly incorporated by reference herein in the entirety. The present application is also related to U.S. patent application Ser. No. 13/351,739, filed Jan. 17, 2012 and entitled “METHOD AND APPARATUS TO FACILITATE SUPPORT FOR MULTI-RADIO COEXISTENCE,” the disclosure of which is expressly incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
     1. Field 
     Aspects of the present disclosure relate generally to multi-radio techniques and, more specifically, to coexistence techniques for multi-radio devices. 
     2. Background 
     Wireless communication systems are widely deployed to provide various types of communication content such as voice, data, and so on. These systems may be multiple-access systems capable of supporting communication with multiple users by sharing the available system resources (e.g., bandwidth and transmit power). Examples of such multiple access systems include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, 3GPP Long Term Evolution (LTE) systems, and orthogonal frequency division multiple access (OFDMA) systems. 
     Generally, a wireless multiple-access communication system can simultaneously support communication for multiple wireless terminals. Each terminal communicates with one or more base stations via transmissions on the forward and reverse links. The forward link (or downlink) refers to the communication link from the base stations to the terminals, and the reverse link (or uplink) refers to the communication link from the terminals to the base stations. This communication link may be established via a single-in-single-out, multiple-in-single-out or a multiple-in-multiple out (MIMO) system. 
     Some conventional advanced devices include multiple radios for transmitting/receiving using different Radio Access Technologies (RATs). Examples of RATs include, e.g., Universal Mobile Telecommunications System (UMTS), Global System for Mobile Communications (GSM), cdma2000, WiMAX, WLAN (e.g., WiFi), Bluetooth, LTE, and the like. 
     An example mobile device includes an LTE User Equipment (UE), such as a fourth generation (4G) mobile phone. Such 4G phone may include various radios to provide a variety of functions for the user. For purposes of this example, the 4G phone includes an LTE radio for voice and data, an IEEE 802.11 (WiFi) radio, a Global Positioning System (GPS) radio, and a Bluetooth radio, where two of the above or all four may operate simultaneously. While the different radios provide useful functionalities for the phone, their inclusion in a single device gives rise to coexistence issues. Specifically, operation of one radio may in some cases interfere with operation of another radio through radiative, conductive, resource collision, and/or other interference mechanisms. Coexistence issues include such interference. 
     This is especially true for the LTE uplink channel, which is adjacent to the Industrial Scientific and Medical (ISM) band and may cause interference therewith. It is noted that Bluetooth and some Wireless LAN (WLAN) channels fall within the ISM band. In some instances, a Bluetooth error rate can become unacceptable when LTE is active in some channels of Band  7  or even Band  40  for some Bluetooth channel conditions. Even though there is no significant degradation to LTE, simultaneous operation with Bluetooth can result in disruption in voice services terminating in a Bluetooth headset. Such disruption may be unacceptable to the consumer. A similar issue exists when LTE transmissions interfere with GPS. Currently, there is no mechanism that can solve this issue since LTE by itself does not experience any degradation 
     With reference specifically to LTE, it is noted that a UE communicates with an evolved NodeB (eNB; e.g., a base station for a wireless communications network) to inform the eNB of interference seen by the UE on the downlink. Furthermore, the eNB may be able to estimate interference at the UE using a downlink error rate. In some instances, the eNB and the UE can cooperate to find a solution that reduces interference at the UE, even interference due to radios within the UE itself. However, in conventional LTE, the interference estimates regarding the downlink may not be adequate to comprehensively address interference. 
     In one instance, an LTE uplink signal interferes with a Bluetooth signal or WLAN signal. However, such interference is not reflected in the downlink measurement reports at the eNB. As a result, unilateral action on the part of the UE (e.g., moving the uplink signal to a different channel) may be thwarted by the eNB, which is not aware of the uplink coexistence issue and seeks to undo the unilateral action. For instance, even if the UE re-establishes the connection on a different frequency channel, the network can still handover the UE back to the original frequency channel that was corrupted by the in-device interference. This is a likely scenario because the desired signal strength on the corrupted channel may sometimes be higher than reflected in the measurement reports of the new channel based on Reference Signal Received Power (RSRP) to the eNB. Hence, a ping-pong effect of being transferred back and forth between the corrupted channel and the desired channel can happen if the eNB uses RSRP reports to make handover decisions. 
     Other unilateral action on the part of the UE, such as simply stopping uplink communications without coordination of the eNB may cause power loop malfunctions at the eNB. Additional issues that exist in conventional LTE include a general lack of ability on the part of the UE to suggest desired configurations as an alternative to configurations that have coexistence issues. For at least these reasons, uplink coexistence issues at the UE may remain unresolved for a long time period, degrading performance and efficiency for other radios of the UE. 
     SUMMARY 
     According to one aspect of the present disclosure, a method for wireless communication includes determining one or more potential virtual gap pattern configuration for a first radio access technology (RAT). The method may also include selecting one of the one or more potential gap pattern configuration based at least in part on protecting subframes which are used by the first RAT to perform clean signal reference measurements and/or based at least in part on performance of the second RAT. The method may also include quieting transmit activities of a second RAT during protected subframes of the first RAT in the determined one or more potential virtual gap pattern configuration. 
     According to another aspect of the present disclosure, an apparatus for wireless communication includes means for determining one or more potential virtual gap pattern configuration for a first radio access technology (RAT). The apparatus may also include means for selecting one of the one or more potential gap pattern configuration based at least in part on protecting subframes which are used by the first RAT to perform clean signal reference measurements and/or based at least in part on performance of the second RAT. The apparatus may also include means for quieting transmit activities of a second RAT during protected subframes of the first RAT in the determined one or more potential virtual gap pattern configuration. 
     According to one aspect of the present disclosure, a computer program product for wireless communication in a wireless network includes a computer readable medium having non-transitory program code recorded thereon. The program code includes program code to determine one or more potential virtual gap pattern configuration for a first radio access technology (RAT). The program code also includes program code to select one of the one or more potential gap pattern configuration based at least in part on protecting subframes which are used by the first RAT to perform clean signal reference measurements and/or based at least in part on performance of the second RAT. The program code also includes program code to quiet transmit activities of a second RAT during protected subframes of the first RAT in the determined one or more potential virtual gap pattern configuration. 
     According to one aspect of the present disclosure, an apparatus for wireless communication includes a memory and a processor(s) coupled to the memory. The processor(s) is configured to determine one or more potential virtual gap pattern configuration for a first radio access technology (RAT). The processor(s) is further configured to select one of the one or more potential gap pattern configuration based at least in part on protecting subframes which are used by the first RAT to perform clean signal reference measurements and/or based at least in part on performance of the second RAT. The processor(s) is further configured to quiet transmit activities of a second RAT during protected subframes of the first RAT in the determined one or more potential virtual gap pattern configuration. 
     Additional features and advantages of the disclosure will be described below. It should be appreciated by those skilled in the art that this disclosure may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present disclosure. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the teachings of the disclosure as set forth in the appended claims. The novel features, which are believed to be characteristic of the disclosure, 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 disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The features, nature, and advantages of the present disclosure will become more apparent from the detailed description set forth below when taken in conjunction with the drawings in which like reference characters identify correspondingly throughout. 
         FIG. 1  illustrates a multiple access wireless communication system according to one aspect. 
         FIG. 2  is a block diagram of a communication system according to one aspect. 
         FIG. 3  illustrates an exemplary frame structure in downlink Long Term Evolution (LTE) communications. 
         FIG. 4  is a block diagram conceptually illustrating an exemplary frame structure in uplink Long Term Evolution (LTE) communications. 
         FIG. 5  illustrates an example wireless communication environment. 
         FIG. 6  is a block diagram of an example design for a multi-radio wireless device. 
         FIG. 7  is graph showing respective potential collisions between seven example radios in a given decision period. 
         FIG. 8  is a diagram showing operation of an example Coexistence Manager (CxM) over time. 
         FIG. 9  is a block diagram illustrating adjacent frequency bands. 
         FIG. 10  is a block diagram of a system for providing support within a wireless communication environment for multi-radio coexistence management according to one aspect of the present disclosure. 
         FIG. 11  illustrates a virtual gap pattern method according to one aspect of the present disclosure. 
         FIG. 12  is a diagram illustrating an example of a hardware implementation for an apparatus employing a virtual gap pattern system. 
     
    
    
     DETAILED DESCRIPTION 
     Various aspects of the disclosure provide techniques to mitigate coexistence issues in multi-radio devices, where significant in-device coexistence problems can exist between, e.g., the LTE and Industrial Scientific and Medical (ISM) bands (e.g., for BT/WLAN). As explained above, some coexistence issues persist because an eNB is not aware of interference on the UE side that is experienced by other radios. According to one aspect, the UE declares a Radio Link Failure (RLF) and autonomously accesses a new channel or Radio Access Technology (RAT) if there is a coexistence issue on the present channel. The UE can declare a RLF in some examples for the following reasons: 1) UE reception is affected by interference due to coexistence, and 2) the UE transmitter is causing disruptive interference to another radio. The UE then sends a message indicating the coexistence issue to the eNB while reestablishing connection in the new channel or RAT. The eNB becomes aware of the coexistence issue by virtue of having received the message. 
     The techniques described herein can be used for various wireless communication networks such as Code Division Multiple Access (CDMA) networks, Time Division Multiple Access (TDMA) networks, Frequency Division Multiple Access (FDMA) networks, Orthogonal FDMA (OFDMA) networks, Single-Carrier FDMA (SC-FDMA) networks, etc. The terms “networks” and “systems” are often used interchangeably. A CDMA network can implement a radio technology such as Universal Terrestrial Radio Access (UTRA), cdma2000, etc. UTRA includes Wideband-CDMA (W-CDMA) and Low Chip Rate (LCR). cdma2000 covers IS-2000, IS-95 and IS-856 standards. A TDMA network can implement a radio technology such as Global System for Mobile Communications (GSM). An OFDMA network can implement a radio technology such as Evolved UTRA (E-UTRA), IEEE 802.11, IEEE 802.16, IEEE 802.20, Flash-OFDM®, etc. UTRA, E-UTRA, and GSM are part of Universal Mobile Telecommunication System (UMTS). Long Term Evolution (LTE) is an upcoming release of UMTS that uses E-UTRA. UTRA, E-UTRA, GSM, UMTS and LTE are described in documents from an organization named “3 rd  Generation Partnership Project” (3GPP). CDMA2000 is described in documents from an organization named “3 rd  Generation Partnership Project 2” (3GPP2). These various radio technologies and standards are known in the art. For clarity, certain aspects of the techniques are described below for LTE, and LTE terminology is used in portions of the description below. 
     Single carrier frequency division multiple access (SC-FDMA), which utilizes single carrier modulation and frequency domain equalization is a technique that can be utilized with various aspects described herein. SC-FDMA has similar performance and essentially the same overall complexity as those of an OFDMA system. SC-FDMA signal has lower peak-to-average power ratio (PAPR) because of its inherent single carrier structure. SC-FDMA has drawn great attention, especially in the uplink communications where lower PAPR greatly benefits the mobile terminal in terms of transmit power efficiency. It is currently a working assumption for an uplink multiple access scheme in 3GPP Long Term Evolution (LTE), or Evolved UTRA. 
     Referring to  FIG. 1 , a multiple access wireless communication system according to one aspect is illustrated. An evolved Node B  100  (eNB) includes a computer  115  that has processing resources and memory resources to manage the LTE communications by allocating resources and parameters, granting/denying requests from user equipment, and/or the like. The eNB  100  also has multiple antenna groups, one group including antenna  104  and antenna  106 , another group including antenna  108  and antenna  110 , and an additional group including antenna  112  and antenna  114 . In  FIG. 1 , only two antennas are shown for each antenna group, however, more or fewer antennas can be utilized for each antenna group. A User Equipment (UE)  116  (also referred to as an Access Terminal (AT)) is in communication with antennas  112  and  114 , while antennas  112  and  114  transmit information to the UE  116  over an uplink (UL)  188 . The UE  122  is in communication with antennas  106  and  108 , while antennas  106  and  108  transmit information to the UE  122  over a downlink (DL)  126  and receive information from the UE  122  over an uplink  124 . In a frequency division duplex (FDD) system, communication links  118 ,  120 ,  124  and  126  can use different frequencies for communication. For example, the downlink  120  can use a different frequency than used by the uplink  118 . 
     Each group of antennas and/or the area in which they are designed to communicate is often referred to as a sector of the eNB. In this aspect, respective antenna groups are designed to communicate to UEs in a sector of the areas covered by the eNB  100 . 
     In communication over the downlinks  120  and  126 , the transmitting antennas of the eNB  100  utilize beamforming to improve the signal-to-noise ratio of the uplinks for the different UEs  116  and  122 . Also, an eNB using beamforming to transmit to UEs scattered randomly through its coverage causes less interference to UEs in neighboring cells than a UE transmitting through a single antenna to all its UEs. 
     An eNB can be a fixed station used for communicating with the terminals and can also be referred to as an access point, base station, or some other terminology. A UE can also be called an access terminal, a wireless communication device, terminal, or some other terminology. 
       FIG. 2  is a block diagram of an aspect of a transmitter system  210  (also known as an eNB) and a receiver system  250  (also known as a UE) in a MIMO system  200 . In some instances, both a UE and an eNB each have a transceiver that includes a transmitter system and a receiver system. At the transmitter system  210 , traffic data for a number of data streams is provided from a data source  212  to a transmit (TX) data processor  214 . 
     A MIMO system employs multiple (N T ) transmit antennas and multiple (N R ) receive antennas for data transmission. A MIMO channel formed by the N T  transmit and N R  receive antennas may be decomposed into N S  independent channels, which are also referred to as spatial channels, wherein N S ≦min{N T , N R }. Each of the N S  independent channels corresponds to a dimension. The MIMO system can provide improved performance (e.g., higher throughput and/or greater reliability) if the additional dimensionalities created by the multiple transmit and receive antennas are utilized. 
     A MIMO system supports time division duplex (TDD) and frequency division duplex (FDD) systems. In a TDD system, the uplink and downlink transmissions are on the same frequency region so that the reciprocity principle allows the estimation of the downlink channel from the uplink channel. This enables the eNB to extract transmit beamforming gain on the downlink when multiple antennas are available at the eNB. 
     In an aspect, each data stream is transmitted over a respective transmit antenna. The TX data processor  214  formats, codes, and interleaves the traffic data for each data stream based on a particular coding scheme selected for that data stream to provide coded data. 
     The coded data for each data stream can be multiplexed with pilot data using OFDM techniques. The pilot data is a known data pattern processed in a known manner and can be used at the receiver system to estimate the channel response. The multiplexed pilot and coded data for each data stream is then modulated (e.g., symbol mapped) based on a particular modulation scheme (e.g., BPSK, QPSK, M-PSK, or M-QAM) selected for that data stream to provide modulation symbols. The data rate, coding, and modulation for each data stream can be determined by instructions performed by a processor  230  operating with a memory  232 . 
     The modulation symbols for respective data streams are then provided to a TX MIMO processor  220 , which can further process the modulation symbols (e.g., for OFDM). The TX MIMO processor  220  then provides N T  modulation symbol streams to N T  transmitters (TMTR)  222   a  through  222   t . In certain aspects, the TX MIMO processor  220  applies beamforming weights to the symbols of the data streams and to the antenna from which the symbol is being transmitted. 
     Each transmitter  222  receives and processes a respective symbol stream to provide one or more analog signals, and further conditions (e.g., amplifies, filters, and upconverts) the analog signals to provide a modulated signal suitable for transmission over the MIMO channel. N T  modulated signals from the transmitters  222   a  through  222   t  are then transmitted from N T  antennas  224   a  through  224   t , respectively. 
     At a receiver system  250 , the transmitted modulated signals are received by N R  antennas  252   a  through  252   r  and the received signal from each antenna  252  is provided to a respective receiver (RCVR)  254   a  through  254   r . Each receiver  254  conditions (e.g., filters, amplifies, and downconverts) a respective received signal, digitizes the conditioned signal to provide samples, and further processes the samples to provide a corresponding “received” symbol stream. 
     An RX data processor  260  then receives and processes the N R  received symbol streams from N R  receivers  254  based on a particular receiver processing technique to provide N R  “detected” symbol streams. The RX data processor  260  then demodulates, deinterleaves, and decodes each detected symbol stream to recover the traffic data for the data stream. The processing by the RX data processor  260  is complementary to the processing performed by the TX MIMO processor  220  and the TX data processor  214  at the transmitter system  210 . 
     A processor  270  (operating with a memory  272 ) periodically determines which pre-coding matrix to use (discussed below). The processor  270  formulates an uplink message having a matrix index portion and a rank value portion. 
     The uplink message can include various types of information regarding the communication link and/or the received data stream. The uplink message is then processed by a TX data processor  238 , which also receives traffic data for a number of data streams from a data source  236 , modulated by a modulator  280 , conditioned by transmitters  254   a  through  254   r , and transmitted back to the transmitter system  210 . 
     At the transmitter system  210 , the modulated signals from the receiver system  250  are received by antennas  224 , conditioned by receivers  222 , demodulated by a demodulator  240 , and processed by an RX data processor  242  to extract the uplink message transmitted by the receiver system  250 . The processor  230  then determines which pre-coding matrix to use for determining the beamforming weights, then processes the extracted message. 
       FIG. 3  is a block diagram conceptually illustrating an exemplary frame structure in downlink Long Term Evolution (LTE) communications. The transmission timeline for the downlink may be partitioned into units of radio frames. Each radio frame may have a predetermined duration (e.g., 10 milliseconds (ms)) and may be partitioned into 10 subframes with indices of 0 through 9. Each subframe may include two slots. Each radio frame may thus include 20 slots with indices of 0 through 19. Each slot may include L symbol periods, e.g., 7 symbol periods for a normal cyclic prefix (as shown in  FIG. 3 ) or 6 symbol periods for an extended cyclic prefix. The 2L symbol periods in each subframe may be assigned indices of 0 through 2L−1. The available time frequency resources may be partitioned into resource blocks. Each resource block may cover N subcarriers (e.g., 12 subcarriers) in one slot. 
     In LTE, an eNB may send a Primary Synchronization Signal (PSS) and a Secondary Synchronization Signal (SSS) for each cell in the eNB. The PSS and SSS may be sent in symbol periods 6 and 5, respectively, in each of subframes  0  and  5  of each radio frame with the normal cyclic prefix, as shown in  FIG. 3 . The synchronization signals may be used by UEs for cell detection and acquisition. The eNB may send a Physical Broadcast Channel (PBCH) in symbol periods 0 to 3 in slot  1  of subframe  0 . The PBCH may carry certain system information. 
     The eNB may send a Cell-specific Reference Signal (CRS) for each cell in the eNB. The CRS may be sent in symbols 0, 1, and 4 of each slot in case of the normal cyclic prefix, and in symbols 0, 1, and 3 of each slot in case of the extended cyclic prefix. The CRS may be used by UEs for coherent demodulation of physical channels, timing and frequency tracking, Radio Link Monitoring (RLM), Reference Signal Received Power (RSRP), and Reference Signal Received Quality (RSRQ) measurements, etc. 
     The eNB may send a Physical Control Format Indicator Channel (PCFICH) in the first symbol period of each subframe, as seen in  FIG. 3 . The PCFICH may convey the number of symbol periods (M) used for control channels, where M may be equal to 1, 2 or 3 and may change from subframe to subframe. M may also be equal to 4 for a small system bandwidth, e.g., with less than 10 resource blocks. In the example shown in  FIG. 3 , M=3. The eNB may send a Physical HARQ Indicator Channel (PHICH) and a Physical Downlink Control Channel (PDCCH) in the first M symbol periods of each subframe. The PDCCH and PHICH are also included in the first three symbol periods in the example shown in  FIG. 3 . The PHICH may carry information to support Hybrid Automatic Repeat Request (HARQ). The PDCCH may carry information on resource allocation for UEs and control information for downlink channels. The eNB may send a Physical Downlink Shared Channel (PDSCH) in the remaining symbol periods of each subframe. The PDSCH may carry data for UEs scheduled for data transmission on the downlink. The various signals and channels in LTE are described in 3GPP TS 36.211, entitled “Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Channels and Modulation,” which is publicly available. 
     The eNB may send the PSS, SSS and PBCH in the center 1.08 MHz of the system bandwidth used by the eNB. The eNB may send the PCFICH and PHICH across the entire system bandwidth in each symbol period in which these channels are sent. The eNB may send the PDCCH to groups of UEs in certain portions of the system bandwidth. The eNB may send the PDSCH to specific UEs in specific portions of the system bandwidth. The eNB may send the PSS, SSS, PBCH, PCFICH and PHICH in a broadcast manner to all UEs, may send the PDCCH in a unicast manner to specific UEs, and may also send the PDSCH in a unicast manner to specific UEs. 
     A number of resource elements may be available in each symbol period. Each resource element may cover one subcarrier in one symbol period and may be used to send one modulation symbol, which may be a real or complex value. Resource elements not used for a reference signal in each symbol period may be arranged into resource element groups (REGs). Each REG may include four resource elements in one symbol period. The PCFICH may occupy four REGs, which may be spaced approximately equally across frequency, in symbol period 0. The PHICH may occupy three REGs, which may be spread across frequency, in one or more configurable symbol periods. For example, the three REGs for the PHICH may all belong in symbol period 0 or may be spread in symbol periods 0, 1 and 2. The PDCCH may occupy 9, 18, 32 or 64 REGs, which may be selected from the available REGs, in the first M symbol periods. Only certain combinations of REGs may be allowed for the PDCCH. 
     A UE may know the specific REGs used for the PHICH and the PCFICH. The UE may search different combinations of REGs for the PDCCH. The number of combinations to search is typically less than the number of allowed combinations for the PDCCH. An eNB may send the PDCCH to the UE in any of the combinations that the UE will search. 
       FIG. 4  is a block diagram conceptually illustrating an exemplary frame structure in uplink Long Term Evolution (LTE) communications. The available Resource Blocks (RBs) for the uplink 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 design in  FIG. 4  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. 
     A UE may be assigned resource blocks in the control section to transmit control information to an eNB. The UE may also be assigned resource blocks in the data section to transmit data to the eNodeB. The UE may transmit control information in a Physical Uplink 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 Uplink Shared Channel (PUSCH) on the assigned resource blocks in the data section. An uplink transmission may span both slots of a subframe and may hop across frequency as shown in  FIG. 4 . 
     The PSS, SSS, CRS, PBCH, PUCCH and PUSCH in LTE are described in 3GPP TS 36.211, entitled “Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Channels and Modulation,” which is publicly available. 
     In an aspect, described herein are systems and methods for providing support within a wireless communication environment, such as a 3GPP LTE environment or the like, to facilitate multi-radio coexistence solutions. 
     Referring now to  FIG. 5 , illustrated is an example wireless communication environment  500  in which various aspects described herein can function. The wireless communication environment  500  can include a wireless device  510 , which can be capable of communicating with multiple communication systems. These systems can include, for example, one or more cellular systems  520  and/or  530 , one or more WLAN systems  540  and/or  550 , one or more wireless personal area network (WPAN) systems  560 , one or more broadcast systems  570 , one or more satellite positioning systems  580 , other systems not shown in  FIG. 5 , or any combination thereof. It should be appreciated that in the following description the terms “network” and “system” are often used interchangeably. 
     The cellular systems  520  and  530  can each be a CDMA, TDMA, FDMA, OFDMA, Single Carrier FDMA (SC-FDMA), or other suitable system. A CDMA system can implement a radio technology such as Universal Terrestrial Radio Access (UTRA), cdma2000, etc. UTRA includes Wideband CDMA (WCDMA) and other variants of CDMA. Moreover, cdma2000 covers IS-2000 (CDMA2000 1X), IS-95 and IS-856 (HRPD) standards. A TDMA system can implement a radio technology such as Global System for Mobile Communications (GSM), Digital Advanced Mobile Phone System (D-AMPS), etc. An OFDMA system can implement a radio technology such as Evolved UTRA (E-UTRA), Ultra Mobile Broadband (UMB), IEEE 802.16 (WiMAX), IEEE 802.20, Flash-OFDM®, etc. UTRA and E-UTRA are part of Universal Mobile Telecommunication System (UMTS). 3GPP Long Term Evolution (LTE) and LTE-Advanced (LTE-A) are new releases of UMTS that use E-UTRA. UTRA, E-UTRA, UMTS, LTE, LTE-A and GSM are described in documents from an organization named “3 rd  Generation Partnership Project” (3GPP). cdma2000 and UMB are described in documents from an organization named “3 rd  Generation Partnership Project 2” (3GPP2). In an aspect, the cellular system  520  can include a number of base stations  522 , which can support bi-directional communication for wireless devices within their coverage. Similarly, the cellular system  530  can include a number of base stations  532  that can support bi-directional communication for wireless devices within their coverage. 
     WLAN systems  540  and  550  can respectively implement radio technologies such as IEEE 802.11 (WiFi), Hiperlan, etc. The WLAN system  540  can include one or more access points  542  that can support bi-directional communication. Similarly, the WLAN system  550  can include one or more access points  552  that can support bi-directional communication. The WPAN system  560  can implement a radio technology such as Bluetooth (BT), IEEE 802.15, etc. Further, the WPAN system  560  can support bi-directional communication for various devices such as wireless device  510 , a headset  562 , a computer  564 , a mouse  566 , or the like. 
     The broadcast system  570  can be a television (TV) broadcast system, a frequency modulation (FM) broadcast system, a digital broadcast system, etc. A digital broadcast system can implement a radio technology such as MediaFLO™, Digital Video Broadcasting for Handhelds (DVB-H), Integrated Services Digital Broadcasting for Terrestrial Television Broadcasting (ISDB-T), or the like. Further, the broadcast system  570  can include one or more broadcast stations  572  that can support one-way communication. 
     The satellite positioning system  580  can be the United States Global Positioning System (GPS), the European Galileo system, the Russian GLONASS system, the Quasi-Zenith Satellite System (QZSS) over Japan, the Indian Regional Navigational Satellite System (IRNSS) over India, the Beidou system over China, and/or any other suitable system. Further, the satellite positioning system  580  can include a number of satellites  582  that transmit signals for position determination. 
     In an aspect, the wireless device  510  can be stationary or mobile and can also be referred to as a user equipment (UE), a mobile station, a mobile equipment, a terminal, an access terminal, a subscriber unit, a station, etc. The wireless device  510  can be cellular phone, a personal digital assistance (PDA), a wireless modem, a handheld device, a laptop computer, a cordless phone, a wireless local loop (WLL) station, etc. In addition, a wireless device  510  can engage in two-way communication with the cellular system  520  and/or  530 , the WLAN system  540  and/or  550 , devices with the WPAN system  560 , and/or any other suitable systems(s) and/or devices(s). The wireless device  510  can additionally or alternatively receive signals from the broadcast system  570  and/or satellite positioning system  580 . In general, it can be appreciated that the wireless device  510  can communicate with any number of systems at any given moment. Also, the wireless device  510  may experience coexistence issues among various ones of its constituent radio devices that operate at the same time. Accordingly, device  510  includes a coexistence manager (CxM, not shown) that has a functional module to detect and mitigate coexistence issues, as explained further below. 
     Turning next to  FIG. 6 , a block diagram is provided that illustrates an example design for a multi-radio wireless device  600  and may be used as an implementation of the radio  510  of  FIG. 5 . As  FIG. 6  illustrates, the wireless device  600  can include N radios  620   a  through  620   n , which can be coupled to N antennas  610   a  through  610   n , respectively, where N can be any integer value. It should be appreciated, however, that respective radios  620  can be coupled to any number of antennas  610  and that multiple radios  620  can also share a given antenna  610 . 
     In general, a radio  620  can be a unit that radiates or emits energy in an electromagnetic spectrum, receives energy in an electromagnetic spectrum, or generates energy that propagates via conductive means. By way of example, a radio  620  can be a unit that transmits a signal to a system or a device or a unit that receives signals from a system or device. Accordingly, it can be appreciated that a radio  620  can be utilized to support wireless communication. In another example, a radio  620  can also be a unit (e.g., a screen on a computer, a circuit board, etc.) that emits noise, which can impact the performance of other radios. Accordingly, it can be further appreciated that a radio  620  can also be a unit that emits noise and interference without supporting wireless communication. 
     In an aspect, respective radios  620  can support communication with one or more systems. Multiple radios  620  can additionally or alternatively be used for a given system, e.g., to transmit or receive on different frequency bands (e.g., cellular and PCS bands). 
     In another aspect, a digital processor  630  can be coupled to radios  620   a  through  620   n  and can perform various functions, such as processing for data being transmitted or received via the radios  620 . The processing for each radio  620  can be dependent on the radio technology supported by that radio and can include encryption, encoding, modulation, etc., for a transmitter; demodulation, decoding, decryption, etc., for a receiver, or the like. In one example, the digital processor  630  can include a coexistence manager (CxM)  640  that can control operation of the radios  620  in order to improve the performance of the wireless device  600  as generally described herein. The coexistence manager  640  can have access to a database  644 , which can store information used to control the operation of the radios  620 . As explained further below, the coexistence manager  640  can be adapted for a variety of techniques to decrease interference between the radios. In one example, the coexistence manager  640  requests a measurement gap pattern or DRX cycle that allows an ISM radio to communicate during periods of LTE inactivity. 
     For simplicity, digital processor  630  is shown in  FIG. 6  as a single processor. However, it should be appreciated that the digital processor  630  can include any number of processors, controllers, memories, etc. In one example, a controller/processor  650  can direct the operation of various units within the wireless device  600 . Additionally or alternatively, a memory  652  can store program codes and data for the wireless device  600 . The digital processor  630 , controller/processor  650 , and memory  652  can be implemented on one or more integrated circuits (ICs), application specific integrated circuits (ASICs), etc. By way of specific, non-limiting example, the digital processor  630  can be implemented on a Mobile Station Modem (MSM) ASIC. 
     In an aspect, the coexistence manager  640  can manage operation of respective radios  620  utilized by wireless device  600  in order to avoid interference and/or other performance degradation associated with collisions between respective radios  620 . coexistence manager  640  may perform one or more processes, such as those illustrated in  FIG. 11 . By way of further illustration, a graph  700  in  FIG. 7  represents respective potential collisions between seven example radios in a given decision period. In the example shown in graph  700 , the seven radios include a WLAN transmitter (Tw), an LTE transmitter (Tl), an FM transmitter (Tf), a GSM/WCDMA transmitter (Tc/Tw), an LTE receiver (Rl), a Bluetooth receiver (Rb), and a GPS receiver (Rg). The four transmitters are represented by four nodes on the left side of the graph  700 . The four receivers are represented by three nodes on the right side of the graph  700 . 
     A potential collision between a transmitter and a receiver is represented on the graph  700  by a branch connecting the node for the transmitter and the node for the receiver. Accordingly, in the example shown in the graph  700 , collisions may exist between (1) the WLAN transmitter (Tw) and the Bluetooth receiver (Rb); (2) the LTE transmitter (Tl) and the Bluetooth receiver (Rb); (3) the WLAN transmitter (Tw) and the LTE receiver (Rl); (4) the FM transmitter (Tf) and the GPS receiver (Rg); (5) a WLAN transmitter (Tw), a GSM/WCDMA transmitter (Tc/Tw), and a GPS receiver (Rg). 
     In one aspect, an example coexistence manager  640  can operate in time in a manner such as that shown by diagram  800  in  FIG. 8 . As diagram  800  illustrates, a timeline for coexistence manager operation can be divided into Decision Units (DUs), which can be any suitable uniform or non-uniform length (e.g., 100 μs) where notifications are processed, and a response phase (e.g., 20 μs) where commands are provided to various radios  620  and/or other operations are performed based on actions taken in the evaluation phase. In one example, the timeline shown in the diagram  800  can have a latency parameter defined by a worst case operation of the timeline, e.g., the timing of a response in the case that a notification is obtained from a given radio immediately following termination of the notification phase in a given DU. 
     As shown in  FIG. 9 , Long Term Evolution (LTE) in band  7  (for frequency division duplex (FDD) uplink), band  40  (for time division duplex (TDD) communication), and band  38  (for TDD downlink) is adjacent to the 2.4 GHz Industrial Scientific and Medical (ISM) band used by Bluetooth (BT) and Wireless Local Area Network (WLAN) technologies. Frequency planning for these bands is such that there is limited or no guard band permitting traditional filtering solutions to avoid interference at adjacent frequencies. For example, a 20 MHz guard band exists between ISM and band  7 , but no guard band exists between ISM and band  40 . 
     To be compliant with appropriate standards, communication devices operating over a particular band are to be operable over the entire specified frequency range. For example, in order to be LTE compliant, a mobile station/user equipment should be able to communicate across the entirety of both band  40  (2300-2400 MHz) and band  7  (2500-2570 MHz) as defined by the 3rd Generation Partnership Project (3GPP). Without a sufficient guard band, devices employ filters that overlap into other bands causing band interference. Because band  40  filters are 100 MHz wide to cover the entire band, the rollover from those filters crosses over into the ISM band causing interference. Similarly, ISM devices that use the entirety of the ISM band (e.g., from 2401 through approximately 2480 MHz) will employ filters that rollover into the neighboring band  40  and band  7  and may cause interference. 
     In-device coexistence problems can exist with respect to a UE between resources such as, for example, LTE and ISM bands (e.g., for Bluetooth/WLAN). In current LTE implementations, any interference issues to LTE are reflected in the downlink measurements (e.g., Reference Signal Received Quality (RSRQ) metrics, etc.) reported by a UE and/or the downlink error rate which the eNB can use to make inter-frequency or inter-RAT handoff decisions to, e.g., move LTE to a channel or RAT with no coexistence issues. However, it can be appreciated that these existing techniques will not work if, for example, the LTE uplink is causing interference to Bluetooth/WLAN but the LTE downlink does not see any interference from Bluetooth/WLAN. More particularly, even if the UE autonomously moves itself to another channel on the uplink, the eNB can in some cases handover the UE back to the problematic channel for load balancing purposes. In any case, it can be appreciated that existing techniques do not facilitate use of the bandwidth of the problematic channel in the most efficient way. 
     Turning now to  FIG. 10 , a block diagram of a system  1000  for providing support within a wireless communication environment for multi-radio coexistence management is illustrated. In an aspect, the system  1000  can include one or more UEs  1010  and/or eNBs  1040 , which can engage in uplink and/or downlink communications, and/or any other suitable communication with each other and/or any other entities in the system  1000 . In one example, the UE  1010  and/or eNB  1040  can be operable to communicate using a variety resources, including frequency channels and sub-bands, some of which can potentially be colliding with other radio resources (e.g., a broadband radio such as an LTE modem). Thus, the UE  1010  can utilize various techniques for managing coexistence between multiple radios utilized by the UE  1010 , as generally described herein. 
     To mitigate at least the above shortcomings, the UE  1010  can utilize respective features described herein and illustrated by the system  1000  to facilitate support for multi-radio coexistence within the UE  1010 . For example, a virtual gap determination module  1012  and a virtual implementation determination  1014  may be provided. The various modules  1012 - 1014  may, in some examples, be implemented as part of a coexistence manager such as the coexistence manager  640  of  FIG. 6 . The various modules  1012 - 1014  and others may be configured to implement the embodiments discussed herein. 
     Virtual Gap Patterns with Multi-Radio Coexistence for Protected Measurements 
     Various aspects of the disclosure provide techniques to mitigate coexistence issues in multi-radio devices, where significant in-device coexistence problems can exist between, e.g., the LTE and Industrial Scientific and Medical (ISM) bands (e.g., for BT/WLAN). In one aspect of the disclosure, a UE determines one or more potential virtual gap pattern configurations for a first radio access technology (RAT). The UE also selects one of the one or more potential gap pattern configurations based at least in part on protecting subframes which are used by the first RAT to perform clean signal reference measurements and/or based at least in part on performance of the second RAT. Further, the UE quiets transmit activities of a second RAT during protected subframes of the first RAT in the determined one or more potential virtual gap pattern configurations. 
     In some current gap patterns, radio access technologies (RATs), e.g., Bluetooth and LTE follow some gap pattern. In the current gap pattern, both RATs may be shut down or quieted for a period of time. For example, the LTE radio as well as the Bluetooth radio are quieted for a period of time. Further, current gap patterns may be HARQ compliant gap patterns that ensure that uplink, downlink and ACK/NAK communications are received during a HARQ compliant gap. 
     Offered is a virtual gap pattern implementation to mitigate coexistence issues in multi-radio devices. In an in-device coexistence (IDC) of Long Term Evolution (LTE) with Bluetooth (BT) voice, some LTE downlink (DL) subframes may be protected from Bluetooth interference to ensure proper measurements of the LTE signal. Such measurements may include reference signal received power (RSRP), reference signal received quality (RSRQ), or other measurements. In the virtual gap pattern implementation, the UE may protect LTE subframes from Bluetooth interference prior to the detection of coexistence problems. During these protected LTE subframes, Bluetooth (or other radios) may be quieted or otherwise configured to prevent interference to LTE operation. This creates a virtual gap pattern, rather than an actual gap pattern (which would involve turning off aggressor radios or disabling victim radio reception) to manage coexistence. 
     In one aspect of the disclosure, a virtual gap pattern may be implemented in conjunction with heterogeneous network (HetNet). In this aspect, a set of LTE downlink subframes may also be identified by the base station/eNB for making restricted measurements, by the UE, in certain subframes in the HetNet. The UE may confirm that such subframes do not overlap with Bluetooth. 
     The virtual gap pattern may also be implemented with multimedia broadcast single frequency network (MBSFN) subframes, which may be configured by the base station/eNB. Typically, the UE does not implement measurements, e.g., RSRP and RSRQ measurements, on these MBSFN subframes. When the MBSFN subframes are configured, the virtual gap pattern may be implemented such that a subset of downlink subframes may autonomously be identified by the user equipment (UE) to be used for measurements if other subframes are not desirable for measurements such as multimedia broadcast single frequency network (MBSFN) subframes. 
     To ensure that the Bluetooth transmissions do not overlap with some subframes of LTE, the UE selects those subframes, which are protected from Bluetooth overlap according to the virtual gap pattern where all the LTE subframes are being used by the eNodeB. LTE downlink subframes may be protected even before a coexistence problem is detected at UE and indicated to the eNB. For instance, coexistence problems may not occur when Bluetooth is not in operation, during low power levels or other implementations that are free of coexistence problems. The Bluetooth radio may transmit whenever there are free downlink LTE subframes that are not affected by Bluetooth. The UE may not communicate the configuration to the eNodeB, thus preventing the eNodeB from adjusting its grants based on the virtual gap pattern. 
     In the virtual gap pattern, LTE, for example, is always transmitting according to some aspects of the present disclosure. LTE radio continues to transmit or receive, while restrictions, such as quieting transmission or reception may be imposed on the transmission and/or reception of the Bluetooth radio. By only restricting the Bluetooth radio communication, the virtual gap pattern ensures that some LTE downlink subframes and/or uplink subframes are always free of interference from Bluetooth radio communications. Further, the virtual gap pattern is not subject to HARQ constraints so long as some downlink subframes are available to LTE where there is no Bluetooth transmission. Furthermore, the virtual gap pattern does not incorporate multiplexing between two RATs because only one of the RATs (e.g., LTE) continuously transmit or receive without being quieted or shut down. However, Bluetooth communication is subject to interference when the Bluetooth communication overlaps an LTE uplink subframe. 
     One example of a virtual gap pattern includes a pattern where all LTE subframes are occupied but certain downlink subframes are protected. The eNB may be unaware of the virtual gap pattern. As a result, the eNB may schedule grants in any subframe whether or not, the subframes overlap with Bluetooth transmission. All LTE uplink subframes are presumed to be occupied, because the eNB is unaware of coexistence problems at the UE. This presumption results in an error on Bluetooth if Bluetooth attempts to receive in a slot overlapping with LTE uplink subframes, when there is a coexistence problem. 
     Certain LTE downlink subframes may be protected periodically. For example, one LTE downlink subframe is protected every 10 ms (for example, subframe  0 ), resulting in denial of Bluetooth transmit/uplink attempts during the protected LTE downlink subframe. These protected LTE downlink subframes may be used by LTE to make intra-frequency measurements. Thus, Bluetooth transmission is denied every time at subframe  0  every 10 ms. The other LTE downlink subframes are virtual gaps, which means that LTE may continue to schedule communications in those subframes and Bluetooth may transmit/uplink during those subframes, even though Bluetooth may interfere with the LTE downlink operation. 
     In the virtual gap pattern implementation, the LTE RAT is not creating real gaps (such as gap patterns imposed by an eNodeB) on either uplink or downlink because LTE RAT is always transmitting and/or receiving. Instead, the virtual gap pattern allows for Bluetooth communication in some LTE subframes without impacting the performance of Bluetooth communication even when Bluetooth is not allowed to transmit on some downlink subframes. Although these gaps are not real gaps because LTE still scheduling on these subframes, the virtual gaps from a Bluetooth perspective are gaps on the LTE time line because Bluetooth can communicate during the virtual gaps. In this case, the Bluetooth communication may or may not interfere with the LTE subframe. The LTE subframes, which do not overlap with Bluetooth, may be used for signal measurement. LTE subframes which do overlap with Bluetooth subframes may be used by a UE to determine if there are potential coexistence issues between LTE downlink and Bluetooth uplink for purposes of triggering some other coexistence management. 
     Virtual gaps may be configured into different modifications. The virtual gap pattern may allow all LTE uplink and downlink subframes including HARQ feedback used by LTE or always available to LTE. Thus, with respect to the virtual gap pattern, HARQ constraint is irrelevant. 
     All possible virtual gap patterns that use one or more downlink subframes may be considered. For example, LTE time division duplex (TDD) may be specified as configuration 1 including six downlink subframes and four uplink subframes. While the four uplink subframes may be assigned to LTE, the remaining six downlink subframes may be assigned to Bluetooth and LTE according to different possible virtual gap patterns. 
     A weight metric may be assigned to the possible virtual gap patterns based on the desired performance of potential virtual gap pattern as related to desired performance by LTE and/or Bluetooth. A specified virtual gap pattern of the potential virtual gap patterns may be specified based on a search procedure in conjunction with the modifications. In one aspect of the disclosure, the weight metric may be set to 0 (indicating an undesired pattern) in any pattern where LTE uplink subframe is not used. The weight metric may also be set to zero when any LTE uplink subframes are in the virtual gap (alternatively, these patterns may be removed from the list of potential patterns). In addition, the weight metric may be set to zero when any vitual gap pattern that has no overlap with restricted measurement subframes (if configured), potentially leaves such subframes unprotected. Restricted measurements for some network implementations, such as a heterogeneous network configuration, are configured such that the virtual gap pattern implementation applies some overlap with the restricted measurement subframes. In this case, at least one of the restricted measurement subframes is included in the protected LTE downlink subframes. Otherwise, the weight metric is set to zero. The search procedure may be repeated to determine an improved or optimized virtual gap pattern in accordance with the modifications. The determination may be based on an offset between LTE and Bluetooth. 
     If there is an implementation constraint, such as only measuring the same set of subframes periodically (for example, every 20 ms), then the virtual gap pattern implementation may account for the implementation constraint. For example, the UE may make use of restricted measurements functionality on these subframes. Thus, the virtual gap pattern approach ensures that a set of LTE downlink subframes is available at a certain periodicity. For example, when there are restricted measurements for use in HetNet, the restricted measurements are periodic with a period of 20 ms. 
     The alternate option of allowing Bluetooth to transmit anytime and relying on clean subframes (i.e., the LTE downlink subframes that do not overlap with Bluetooth) for measurement may not be desired due to the inability to guarantee the availability of clean subframes periodically because of Bluetooth link errors, overlap patterns and the like. As noted, the virtual gap pattern may be used even if a coexistence problem is not indicated to the eNB. The virtual gap pattern may not be imposed by the eNB but rather may be used autonomously by the UE for measurement protection purposes. 
     In order to search for an acceptable virtual gap pattern, one aspect may only consider a metric of Bluetooth transmit packet error rate (PER). Based on the metric, Bluetooth transmission may be prevented to protect some LTE downlink subframes. The Bluetooth receptions may be free of interference and free of coexistence issues. The UE may incorporate a potential coexistence interference assessment to determine whether Bluetooth reception is affected by LTE uplink. 
     In some aspects of the disclosure, virtual gaps may be configured based on an LTE time division duplex (TDD) configuration. Table 1 below illustrates LTE TDD configurations and corresponding virtual gap patterns, where U represents uplink, D represents downlink, and S represents special subframes, and where the protected LTE subframes are indicated bold letters while the unbolded letters represent virtual gaps. For example, in the following LTE TDD configurations 1, 2, 4, 5 where Bluetooth operating in slave mode, one or more LTE downlink subframes may be protected every 10 ms while ensuring that both Bluetooth transmission and reception have no/minimum error. A same virtual gap can be used for all Bluetooth offsets. 
     
       
         
           
               
               
             
               
                   
               
               
                 TDD Config 
                 Virtual gap pattern 
               
               
                   
               
             
            
               
                 1 
                 DS UUD DS UUD   
               
               
                 2 
                 DS UDD DS UDD   
               
               
                 4 
                 DS UUDD DD DD   
               
               
                 5 
                 DS UDD DD DD D 
               
               
                   
               
            
           
         
       
     
     In other LTE TDD Configurations, which may include three consecutive uplink subframes, some offsets may lead to Bluetooth receive error. A coexistence trigger may allow the UE to compensate for these offsets. For the remaining offsets, virtual gaps may be found to ensure proper Bluetooth operation. 
       FIG. 11  illustrates a virtual gap pattern method according to one aspect of the present disclosure. As shown in  FIG. 11 , the method includes determining at least one potential virtual gap pattern configuration for a first radio access technology (RAT), as shown in block  1102 , and selecting one of the at least one potential gap pattern configuration based at least in part on protecting subframes which are used by the first RAT to perform clean signal reference measurements and/or based at least in part on performance of the second RAT, as shown in block  1104 . The method also includes quieting transmit activities of a second RAT during protected subframes of the first RAT in the determined potential virtual gap pattern configuration, as shown in block  1106 . 
       FIG. 12  is a diagram illustrating an example of a hardware implementation for an apparatus  1200  employing a virtual gap pattern system  1214 . The apparatus  1200  may include a determining module  1202 , a selecting module  1204  and a quieting module  1206 . The virtual gap pattern system  1214  may be implemented with a bus architecture, represented generally by the bus  1224 . The bus  1224  may include any number of interconnecting buses and bridges depending on the specific application of the virtual gap pattern system  1214  and the overall design constraints. The bus  1224  links together various circuits including one or more processors and/or hardware modules, represented by the processor  1230 , the determining module  1202 , the selecting module  1204  and the quieting module  1206 , and the computer-readable medium  1232 . The bus  1224  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. 
     The apparatus includes a virtual gap pattern system  1214  coupled to a transceiver  1222 . The transceiver  1222  is coupled to one or more antennas  1220 . The transceiver  1222  provides a means for communicating with various other apparatus over a transmission medium. The virtual gap pattern system  1214  includes a processor  1230  coupled to a computer-readable medium  1232 . The processor  1230  is responsible for general processing, including the execution of software stored on the computer-readable medium  1232 . The software, when executed by the processor  1230 , causes the virtual gap pattern system  1214  to perform the various functions described above for any particular apparatus. The computer-readable medium  1232  may also be used for storing data that is manipulated by the processor  1230  when executing software. The virtual gap pattern system  1214  further includes the determining module  1202  for determining at least one potential virtual gap pattern configuration for a first radio access technology (RAT). The virtual gap pattern system  1214  may also include the selecting module  1204  for selecting one of the at least one potential gap pattern configuration based at least in part on protecting subframes which are used by the first RAT to perform clean signal reference measurements and/or based at least in part on performance of the second RAT. The virtual gap pattern system  1214  further includes the quieting module  1206  for quieting transmit activities of a second RAT during protected subframes of the first RAT in the determined potential virtual gap pattern configuration. The modules may be software modules running in the processor  1230 , resident/stored in the computer readable medium  1232 , one or more hardware modules coupled to the processor  1230 , or some combination thereof. The virtual gap pattern system  1214  may be a component of the eNodeB  110  and may include the memory  442  and/or at least one of the TX MIMO processor  430 , transmit processor  420 , the receive processor  438 , and the controller/processor  440 . The virtual gap pattern system  1214  may be a component of the UE  120  and may include the memory  660  and/or at least one of the TX MIMO processor  466 , transmit processor  464 , the receive processor  458 , and the controller/processor  480 . 
     In one configuration, the apparatus  1200  for wireless communication includes means for determining, means for selecting and means for quieting. The aforementioned means may be one or more of the aforementioned modules of the apparatus  1000  and/or the virtual gap pattern system  1214  of the apparatus  1200  configured to perform the functions recited by the aforementioned means. As described above, the virtual gap pattern system  1214  may include the determining module  1202 , the selecting module  1204 , the quieting module  1206 , TX MIMO processor  220 , transmit processor  230 , the receive processor  270 , and the controller/processor  1230 . As such, in one configuration, the aforementioned means may be the determining module  1202 , the selecting module  1204 , the quieting module  1206 , the virtual gap determination module  1012 , the virtual gap implementation module  1014 , the digital processor  630 , TX MIMO processor  220 , transmit processor  230 , the receive processor  270 , and the controller/processor  1230  configured to perform the functions recited by the aforementioned means. 
     The examples above describe aspects implemented in an LTE system. However, the scope of the disclosure is not so limited. Various aspects may be adapted for use with other communication systems, such as those that employ any of a variety of communication protocols including, but not limited to, CDMA systems, TDMA systems, FDMA systems, and OFDMA systems. 
     It is understood that the specific order or hierarchy of steps in the processes disclosed is an example of exemplary approaches. Based upon design preferences, it is understood that the specific order or hierarchy of steps in the processes may be rearranged while remaining within the scope of the present disclosure. 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. 
     Those of skill in the art would understand that information and signals may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof. 
     Those of skill would further appreciate that the various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the aspects disclosed herein may be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present disclosure. 
     The various illustrative logical blocks, modules, and circuits described in connection with the aspects disclosed herein may be implemented or performed with a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration. 
     The steps of a method or algorithm described in connection with the aspects disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. An exemplary storage medium is coupled to the processor such the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor. The processor and the storage medium may reside in an ASIC. The ASIC may reside in a user terminal. In the alternative, the processor and the storage medium may reside as discrete components in a user terminal. 
     The previous description of the disclosed aspects is provided to enable any person skilled in the art to make or use the present disclosure. 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 without departing from the spirit or scope of the disclosure. Thus, the present disclosure is not intended to be limited to the aspects shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.