Transmission and reception of demodulation reference signals

Abstract

Reducing reference signal overhead is an effective technique for improving the spectrum efficiency of wireless communications. In some embodiments, a base station may select between a traditional resource pattern for reference signals and a new resource pattern for reduced reference signals and transmit to a mobile station. The exemplary new resource pattern may reduce resource element overhead for reference signals.

Description

Technical Field

[0001] This document generally relates to wireless communications. Background Art

[0002] Mobile telecommunication technologies are moving the world towards an increasingly connected and networked society. Compared to existing wireless networks, next generation systems and wireless communication technologies will need to support a much wider range of use case characteristics and provide a more complex and sophisticated range of access requests and flexibility. Summary of the invention

[0003] This document relates to methods, systems, and devices for transmission and reception of reference signals, such as demodulation reference signals (DMRS), using flexible transmission resources.

[0004] In one exemplary aspect, a wireless communication method is disclosed. The wireless communication method includes transmitting an initial transmission of a reference signal using time-frequency resources corresponding to a first resource pattern, determining a second resource pattern representing time-frequency resources for subsequent transmissions of the reference signal, communicating the second resource pattern for subsequent transmissions of the reference signal to one or more mobile stations, and transmitting subsequent transmissions of the reference signal using the time-frequency resources corresponding to the second resource pattern.

[0005] In another exemplary aspect, a wireless communication method is disclosed. The wireless communication method includes: receiving, by a mobile station, an initial transmission of a reference signal using time-frequency resources corresponding to a first resource pattern; receiving, by the mobile station, information related to a second resource pattern indicating time-frequency resources for subsequent reception of the reference signal; and receiving, by the mobile station, subsequent reception of the reference signal using the time-frequency resources corresponding to the second resource pattern.

[0006] In yet another exemplary aspect, a wireless communication base station is disclosed. The wireless communication base station includes a memory storing instructions for base station operation, and a processor in communication with the memory, which is operable to execute the instructions to cause the base station to perform the following operations: transmit an initial transmission of a reference signal using time-frequency resources corresponding to a first resource pattern; determine a second resource pattern representing time-frequency resources for subsequent transmissions of the reference signal; communicate the second resource pattern for subsequent transmissions of the reference signal to one or more mobile stations; and transmit subsequent transmissions of the reference signal using the time-frequency resources corresponding to the second resource pattern.

[0007] In yet another exemplary aspect, a wireless communication mobile station is disclosed. The wireless communication mobile station includes a memory storing instructions for operation of the mobile station, and a processor in communication with the memory and operable to execute the instructions to cause the mobile station to: receive an initial transmission of a reference signal using time-frequency resources corresponding to a first resource pattern; receive information related to a second resource pattern indicating time-frequency resources for subsequent reception of the reference signal; and receive subsequent reception of the reference signal using the time-frequency resources corresponding to the second resource pattern.

[0008] In yet another exemplary aspect, the method described above is embodied in the form of processor-executable code and stored in a computer-readable program medium.

[0009] In yet another exemplary embodiment, a device configured or operable to perform the above method is disclosed.

[0010] The above and other aspects and their embodiments are described in more detail in the drawings, the description and the claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 An example of a base station communicating a resource pattern with a DMRS signal to one or more mobile stations is shown.

[0012] Figure 2A-2C A downlink DMRS pattern adopted by the current Long Term Evolution (LTE) standard is shown.

[0013] Figure 3A-3G An exemplary DMRS overhead reduction mode is shown.

[0014] Figure 4 A block diagram is shown for an exemplary wireless communication base station for transmitting a conventional DL DMRS pattern and a reduced DL DMRS pattern.

[0015] Figure 5 An exemplary flow diagram for a base station for using a resource mode with conventional and reduced DMRS signals is shown.

[0016] Figure 6 A block diagram of an exemplary wireless communication mobile station for receiving a conventional DL DMRS pattern and a reduced DL DMRS pattern is shown.

[0017] Figure 7 An exemplary flow diagram for a wireless communication mobile station for using a resource mode with conventional and reduced DMRS signals is shown. DETAILED DESCRIPTION

[0018] The shortage of radio spectrum and the demand for high data rate services have stimulated the demand for improving spectral efficiency. Reducing reference signal overhead is an effective technique for improving the spectral efficiency of wireless communications. In a typical communication system, the receiver has a priori knowledge of the time-frequency position of the reference signal. For example, in a transmission scheme based on orthogonal frequency division multiplexing (OFDM), time slots and subcarriers are usually used to specify transmission resources, thereby forming a time-frequency grid of available transmission resources called resource elements. In such a system, a resource pattern is used to describe the time slots and subcarriers used for reference signal transmission, which can be, for example, resource elements allocated to reference signals in a two-dimensional arrangement of resource elements called physical resource blocks (PRBs). PRBs are units of resource allocation available for transmission, which can be repeated in the time dimension (time slot) and the frequency dimension (subcarrier).

[0019] In the current LTE specification, three different downlink (DL) demodulation reference signal (DMRS) patterns have been defined for multiple-input multiple-output (MIMO) transmission mode (TM) 9 / 10 for different transmission ranks. Depending on the transmission rank, a DMRS pattern will be selected for user equipment (UE) or mobile station specific reference signal transmission. These three DMRS patterns are designed for general radio links and are not optimal for certain scenarios, such as for wireless stationary links in small cell scenarios. Therefore, in some embodiments, the DMRS density can be reduced in, for example, wireless stationary link scenarios.

[0020] The disclosed technology proposes a DMRS overhead reduction technique, which can be used, for example, in scenarios with a sufficiently high signal-to-noise ratio (SNR), such as small cell deployments. In some embodiments, the proposed reduced DMRS pattern can be applied to any similar stable wireless link with a relatively high SNR. Some new low-overhead DMRS patterns and supporting technologies are disclosed in this patent document. In some embodiments, a reduced DMRS pattern can be customized for LTE DL single user multiple input and output (SU-MIMO) rank 3 / 4 in transmission mode (TM) 9 / 10. The reduced DMRS pattern provides some benefits. For example, compared with the traditional DMRS pattern, the disclosed new DMRS pattern can reduce resource element (RE) overhead while keeping performance at the same or similar level. Therefore, LTE DL system efficiency can be improved by using the proposed DMRS pattern.

[0021] Figure 1The base station 120 is shown delivering a resource pattern with DMRS signals 140a, 140b to one or more mobile stations 110a, 110b. One or more mobile stations 110a, 110b may also send channel-related information to the base station. For example, the mobile stations 110a, 110b may send a channel quality indication (CQI) 130a, 130b to the base station. The CQI provides information about the quality of the communication channel between the base station and the mobile station to the base station. In order to support multi-layer demodulation, UE-specific DMRS is defined for TM 9 / TM10 transmission in the current LTE specification.

[0022] Figure 2A-2C Three different legacy DL DMRS patterns that have been defined for TM 9 / 10 at different transmission ranks according to the current LTE standard are shown. Figure 2A-2C Includes the resource pattern used for each physical resource block (PRB). Figure 2A As shown in , a PRB includes 12 subcarriers along the y-axis and 7 OFDM symbols along the x-axis. Each intersection of an OFDM symbol and a subcarrier is called a resource element. The 12 subcarriers comprise a resource block and the 7 OFDM symbols comprise a time slot.

[0023] Figure 2A It is shown that DMRS pattern ports 7 / 8 with orthogonal code OCC 2 are used for DL ​​SU-MIMO rank 1 / 2 transmission. Figure 2A In , DMRS signals are transmitted in 12 REs per PRB, and OCC2 is applied to two adjacent REs in the time domain so that ports 7 / 8 can share these 12 REs. Therefore, the DMRS overhead for rank 1 / 2 is 6 REs / PRB / port.

[0024] Figure 2B DMRS pattern using OCC2 for DL ​​SU-MIMO rank 3 / 4 transmission is shown. The DMRS signal occupies 24 REs / PRBs. Of these 24 REs, 12 REs are shared by ports 7 / 8 using OCC2, and the other 12 REs are shared by ports 9 / 10 using OCC2. In the same way as the rank 1 / 2 DMRS pattern, OCC2 is applied to 2 adjacent REs in the time domain. It can be found that the DMRS overhead for rank 3 / 4 is 6 REs / PRBs / port. Compared to the DMRS overhead for rank 1 / 2, as Figure 2A As shown in Figure 2B For the rank 3 / 4 transmission shown in , the DMRS overhead is doubled.

[0025] Figure 2CDL SU-MIMO transmission for rank>4 is shown, where a DMRS pattern using OCC4 is defined. The DMRS signal is transmitted with 24 REs / PRBs, and OCC4 is applied to 4 REs on a subcarrier across 2 slots. More specifically, ports 7 / 8 / 11 / 13 share 12 REs, and ports 9 / 10 / 12 / 14 share another 12 REs. Therefore, the DMRS overhead for rank>4 is 3 REs / PRBs / port.

[0026] Figure 2A-2C The DMRS patterns in are designed for general scenarios. Scenario-specific parameters such as SNR and mobile speed have not been considered in the DMRS pattern design. For these scenarios, similar to the small cell scenario, the radio link between the eNB and the stationary UE can have the characteristics of high SNR, low frequency selectivity and low time selective fading. In such scenarios, the task of channel estimation is less difficult, and the DMRS overhead can be reduced while keeping the channel estimation degradation to a minimum.

[0027] The benefit of DMRS overhead reduction is to utilize the possibility of allocating some of the REs that form the traditional DMRS pattern in TM 9 / 10 to, for example, PDSCH transmission. These additional PDSCH REs can be used to increase throughput or improve block error rate performance. DMRS overhead reduction can be achieved by reducing the DMRS density in the frequency domain, the time domain, or both the frequency domain and the time domain.

[0028] As in Figure 2A-2C As shown in , the traditional DMRS overhead for rank 1 / 2 and rank 3 / 4 is 6 RE / PRB / port, and the DMRS overhead for ranks greater than 4 is 3 RE / PRB / port. In some embodiments, DMRS overhead reduction techniques can be applied to rank 3 / 4 transmissions. For example, some new low-overhead DMRS patterns can be applied to LTE DL SU-MIMO rank 3 / 4 transmissions.

[0029] Figure 3A-3B An exemplary DMRS overhead reduction mode is shown, where a DMRS signal is transmitted in 8 REs / PRBs, and OCC4 may be applied to 4 REs on a subcarrier spanning two slots. Figure 3A and Figure 3B The resource pattern in may allocate exactly two pairs of adjacent resource elements per physical resource block (PRB) for reference signals, where orthogonal codes may be applied to the adjacent resource elements. Figure 3A and Figure 3B Each of the two adjacent resource elements in may be associated with any one of transmission ports 7, 8, 11 or 13. Figure 2BThe traditional DL DMRS mode in Figure 3A and Figure 3B The DMRS overhead of the DMRS mode in is reduced by 66.7%. Figure 3A and Figure 3B Some of the differences between the modes are Figure 3A The DMRS RE in the DMRS RE has backward compatibility with mobile stations, which can use Figure 2A-2B DMRS mode in. Figure 3A The difference in Figure 3B The DMRS REs in are uniformly distributed within the PRB. The benefit of having uniformly distributed DMRS REs is that it allows for improved channel estimation.

[0030] Figure 3C-3G Some exemplary DMRS overhead reduction modes are shown, where for each of the five modes, the DMRS signal is transmitted with 4 REs / PRBs, and OCC4 can be applied to 4 REs. Figure 2B The traditional DLDMRS mode in Figure 3C-3G The DMRS overhead of the five DMRS patterns in is reduced by 83.3%. Figure 3C The resource pattern in may allocate exactly two adjacent resource elements per physical resource block (PRB) for a reference signal, where orthogonal codes may be applied to the adjacent resource elements. Figure 3C Two adjacent resource elements in may be associated with any one of transmission ports 7, 8, 11 or 13.

[0031] Figure 3D and Figure 3E The resource pattern in includes a resource pattern corresponding to exactly two pairs of adjacent resource elements in the first physical resource block for reference signals. The resource pattern may not allocate any resource element of the second physical resource block for reference signals, where the second physical resource block is adjacent to the first physical resource block. Therefore, in some embodiments, Figure 3D and Figure 3E The second physical resource block in has no resource elements allocated to the reference signal. Figure 3D and Figure 3E The second physical resource block in the physical resource block does not use or allocate any resource elements for reference signals. The benefit of not using resource elements for reference signals is that these resource elements can be used for data transmission. Therefore, more data can be transmitted from the base station to the mobile station in the physical resource block. Orthogonal codes can be applied to adjacent resource elements of the first physical resource block. Figure 3D and Figure 3E Each of two adjacent resource elements in may be associated with any one of transmission ports 7, 8, 11 or 13.

[0032] Figure 3F and Figure 3G The resource pattern in may allocate only two resource elements per physical resource block (PRB) for a reference signal, where orthogonal codes may be applied to the two resource elements. Figure 3F and Figure 3G Each of the two resource elements in is associated with any one of ports 7, 8, 11 or 13.

[0033] exist Figure 3C-3G One of the differences between the five modes is the distribution of DMRS REs within the PRB. Depending on the channel conditions, a base station such as an eNB can select or determine the most appropriate mode. For example, the base station can determine the frequency and time variations in the channel between the mobile station and the base station by receiving any one of a sounding reference signal (SRS) or a channel quality indication (CQI) from the mobile station. Figure 3C The DMRS pattern in is more suitable for channels with relatively low variations in the frequency domain. Figure 3D and Figure 3E The DMRS pattern in is more suitable for channels with lower variations in the time domain. For channels with variations in both the time domain and the frequency domain, Figure 3F and Figure 3G DMRS mode in. Figure 3D and Figure 3F The DMRS RE of the pattern in has backward compatibility with the traditional DMRS pattern, and Figure 3E and Figure 3G The DMRS REs in the pattern are evenly distributed within the PRB.

[0034] In some embodiments, if the base station or mobile station determines that the channel condition is good, then Figure 3A-3G The DMRS overhead reduction pattern shown in can be applied to other scenarios, for example, for transmission of rank 1 / 2 or rank greater than 4 in TM 9 / 10.

[0035] Figure 4 A block diagram of an exemplary wireless communication base station 400 is shown for transmission for both conventional DL DMRS patterns and reduced DL DMRS patterns. The wireless communication base station includes a memory 405 storing instructions for base station operation, and one or more processors 415 in communication with the memory 405 operable to execute the instructions to cause the base station to perform a number of exemplary operations.

[0036] For example, the reference signal generation module 425 may generate a reference signal, such as a DMRS, using a time-frequency resource corresponding to a resource pattern. The reference signal generation module 425 may generate an initial transmission of a DMRS for a first resource pattern, which may be Figure 2A-2CThe reference signal generation module 425 may also generate a subsequent transmission of a DMRS for a second resource pattern, which may be as described in Figure 3A-3G The transmitter 415 of the base station transmits the initial transmission and subsequent transmissions of the reference signal using the time-frequency resources corresponding to the selected or determined resource pattern.

[0037] The reference signal selection module 430 selects or determines a resource pattern representing a time-frequency resource for reference signal transmission. The reference signal selection module 430 may select between a first resource pattern corresponding to a legacy pattern and a second resource pattern corresponding to one of the exemplary reduced DMRS patterns. For example, the eNB may select and notify the UE which DMRS pattern will be used.

[0038] The reference signal communication module 435 may communicate information indicating the reduced DMRS pattern to one or more mobile stations. For example, if channel conditions change, the eNB may switch between the legacy DMRS pattern and the reduced DMRS pattern in communication. Thus, the reference signal communication module 435 communicates information indicating a second resource pattern (such as one of the reduced DMRS patterns) for subsequent transmission of a reference signal to one or more mobile devices.

[0039] The reference signal communication module 435 transmits a signal to the UE to notify the UE to switch for subsequent transmission. In LTE, this can be implemented in two ways. The first signaling method is to use DCI so that the DMRS mode can be dynamically switched on a subframe basis. The main advantage of dynamic switching is that the appropriate DMRS mode can be quickly established as channel conditions change. Large DCI overhead may be the price paid for this rapid response. In some embodiments, information indicating a reduced DMRS mode can be delivered to one or more mobile stations by transmitting a second resource mode using downlink control information (DCI).

[0040] Another signaling method is to introduce a new bit field in the RRC signaling. If it is deemed necessary, for example when the channel conditions deteriorate, the eNB reconfigures the DMRS mode through RRC signaling. Using this semi-static switching method, the signaling overhead can be greatly reduced. Therefore, in some embodiments, the information indicating the reduced DMRS mode can be delivered to one or more mobile stations by transmitting the second resource mode using a radio resource control message. In some embodiments, the DMRS overhead reduction is used under a wireless stable link assuming small channel changes. In such an embodiment, a semi-static DMRS mode switched by RRC signaling may be preferred.

[0041] Channel quality module 440 allows the base station to monitor channel conditions. Figure 1 As shown, the channel quality module 440 of the base station can use the receiver 420 to receive a channel quality indication (CQI) value from one or more mobile stations. Based on the CQI value, the channel quality module 440 can instruct the reference signal selection module 430 to select one of the traditional DMRS mode or the exemplary reduced DMRS mode. For example, when the CQI value indicates that the modulation order is a higher modulation order, such as 256QAM, 512QAM, or 1024QAM, or higher, the channel quality module 440 can instruct the reference signal selection module 430 to select or determine one of the exemplary reduced DMRS modes.

[0042] Figure 5 An exemplary flow chart of operations performed by a base station to use resource patterns with traditional and reduced DMRS signals is shown. At an initial transmission operation 502, the base station transmits an initial transmission of a reference signal using time-frequency resources corresponding to a first resource pattern. The first resource pattern may be a traditional resource pattern that is known a priori to the receiver. At a determination operation 504, the base station selects or determines a second resource pattern representing time-frequency resources for subsequent transmissions of the reference signal. In some embodiments, the determination operation 504 may be performed prior to the initial transmission operation 502. For example, prior to transmitting the initial transmission of the reference signal, the base station may select or determine a second resource pattern (such as one of the reduced DMRS patterns) representing time-frequency resources for subsequent transmissions of the reference signal. Alternatively or additionally, the determination operation 504 may be performed after the initial transmission operation 502 based on the operating conditions of the current wireless channel.

[0043] In a communicating operation 506, the base station communicates the second resource pattern for subsequent transmission of the reference signal to one or more mobile stations. For example, when the base station sends the DCI to the mobile device as part of the communicating operation 506, the DCI may include a CQI indicating a modulation order of either 256QAM or 1024QAM. Upon receiving the modulation order information, the mobile station knows that a second resource pattern (such as one of the reduced DMRS patterns) will be used after the initial transmission of the reference signal according to the first resource pattern.

[0044] In some embodiments, the transfer operation 506 may be performed before the initial transmission operation 502. For example, when the CQI sent by one of the mobile stations and received by the base station indicates that the modulation order is 1024QAM, the transfer operation 506 may be performed before the initial transmission operation 502 because the second resource pattern will be used after the initial transmission of the reference signal according to the first resource pattern.

[0045] At subsequent transmission operation 508, the base station transmits subsequent transmissions of the reference signal to one or more mobile devices using time-frequency resources corresponding to the second resource pattern.

[0046] Figure 6 A block diagram is shown for an exemplary wireless communication mobile station 600 for receiving a conventional DL DMRS pattern and a reduced DL DMRS pattern. The wireless communication mobile station 600 includes a memory 605 storing instructions for operation of the mobile station 600, and one or more processors 610 in communication with the memory 605 and operable to execute the aforementioned instructions to cause the mobile station to perform a plurality of exemplary operations.

[0047] For example, the reference signal receiving module 625 may use the receiver 620 to receive the reference signal using the time-frequency resources corresponding to the resource pattern. The reference signal receiving module may receive the reference signal received by the base station using the traditional DMRS pattern (such as Figure 2A-2C ) or one of the exemplary reduced DMRS patterns (such as Figure 3A-3G For example, the reference signal receiving module 625 uses the time-frequency resources corresponding to the first resource mode to receive the initial transmission of the reference signal.

[0048] The reference signal communication module 630 uses the receiver 620 to receive information related to a resource pattern representing a time-frequency resource for initial or subsequent reception of a reference signal. In some embodiments, after an initial transmission of a conventional DMRS pattern, the reference signal communication module 630 receives information from a base station that the base station can transmit a reduced DMRS pattern for subsequent reception of the reference signal. In some embodiments, the reference signal communication module 630 receives information related to selection of the second resource pattern by receiving information indicating the second resource pattern from a radio resource control (RRC) message. In some embodiments, the reference signal communication module 630 receives information related to selection of the second resource pattern by receiving information indicating the second resource pattern from downlink control information (DCI).

[0049] The channel quality module 635 provides information about the channel to the base station. For example, the channel quality module 635 can transmit a channel quality indication (CQI) value to the base station using the transmitter 615. Based on the CQI value, the base station can determine to select one of the traditional DMRS mode or the exemplary reduced DMRS mode, and can communicate the selection of either mode to the mobile station.

[0050] In some cases, the DMRS overhead reduction may result in a reduction in channel estimation accuracy. This may degrade system performance. Therefore, the channel estimation module 640 may use one of two approaches to improve channel estimation. First, the channel estimation module 640 may improve channel estimation by using one of the exemplary reduced DMRS patterns (for DMRS transmission, the pattern uses more REs per PRB than one of the other exemplary reduced DMRS patterns). For example, by using Figure 3B In the exemplary reduced DMRS mode in , the UE can receive the DMRS signal with 8 RE / PRBs, which is lower than the traditional DMRS mode, but not lower than, for example Figure 3G The reduced DMRS mode in (only 2 RE / PRBs are used for DMRS).

[0051] Second, in order to overcome the possible performance degradation caused by the reduction of DMRS overhead, in an exemplary embodiment, the channel estimation module 640 can use a decision-directed (DD) channel estimation method to utilize information on non-pilot symbols. The channel estimation module 640 can use DD channel estimation to reliably process detected data symbols such as pilot symbols and use them for channel estimation. The benefit of using DD channel estimation is that it is equivalent to increasing the density of DMRS signals and thus improving the quality of channel estimation. In some embodiments, the channel estimation module 640 determines that the mobile station has data that is successfully demodulated in the first PRB, and the first PRB includes a traditional DMRS signal using a time-frequency resource corresponding to the first resource pattern. Subsequently, when the mobile station receives a second PRB, the second PRB has a reduced DMRS signal using a time-frequency resource corresponding to the second resource pattern, and the channel estimation module 640 can estimate the channel by using data symbols of resource elements from a first physical resource block (PRB), and the first physical resource block (PRB) includes a traditional DMRS signal corresponding to the first resource pattern. Therefore, the data symbol of the first PRB can be used as a DMRS for the second PRB.

[0052] Figure 7 An exemplary flow chart for operations performed by a wireless communication mobile station to use resource patterns with conventional and reduced DMRS signals is shown. At receive initial transmission operation 702, the mobile station receives an initial transmission of a reference signal using time-frequency resources corresponding to a first resource pattern. At receive information operation 704, the mobile station receives information associated with a second resource pattern indicating time-frequency resources for subsequent transmissions of reference signals. At receive subsequent transmission operation 706, the mobile station receives subsequent receptions of reference signals using time-frequency resources corresponding to the second resource pattern.

[0053] The term "exemplary" is used to mean "an example of" and not to denote an ideal or preferred embodiment unless otherwise stated.

[0054] Some of the embodiments described herein are described in the general context of a method or process, which in one embodiment can be implemented by a computer program product embodied in a computer-readable medium, the computer program product including computer-executable instructions, such as program code executed by a computer in a network environment. Computer-readable media may include removable and non-removable storage devices, including but not limited to read-only memory (ROM), random access memory (RAM), compact disk (CD), digital versatile disk (DVD), etc. Therefore, computer-readable media may include non-transitory storage media. Typically, program modules may include routines, programs, objects, components, data structures, etc. that perform specific tasks or implement specific abstract data types. Instructions executable by a computer or processor, related data structures, and program modules represent examples of program codes for executing the steps of the method disclosed herein. Such a specific sequence of executable instructions or related data structures represents an example of corresponding actions for implementing the functions described in such steps or processes.

[0055] Some of the disclosed embodiments may be implemented as devices or modules using hardware circuits, software, or a combination thereof. For example, a hardware circuit implementation may include discrete analog and / or digital components, which are, for example, integrated as a part of a printed circuit board. Alternatively, or additionally, the disclosed components or modules may be implemented as application specific integrated circuits (ASICs) and / or field programmable gate arrays (FPGAs) devices. Some embodiments may additionally or alternatively include a digital signal processor (DSP), which is a dedicated microprocessor with a structure that optimizes the operation of digital signal processing related to the disclosed functions of this application. Similarly, multiple components or subcomponents within each module may be implemented in software, hardware, or firmware. The communication between the modules and / or the components within the modules may be provided using any one of the communication methods and media known in the prior art, which include, but are not limited to, communicating on the Internet, wired, or wireless networks using suitable protocols.

[0056] Although this document contains many details, these should not be interpreted as limitations on the scope of the claimed invention or the claimed invention, but rather as descriptions of features peculiar to a particular embodiment. Certain features described in this document with a single embodiment as the background may also be implemented in a combined form in a single embodiment. On the contrary, the individual features described with a single embodiment as the background may also be implemented separately in multiple embodiments or in any suitable sub-combination. In addition, although the above-mentioned features may be described as acting in the form of certain combinations, and even initially claimed as such, one or more features in the claimed combination may be removed from the combination in some cases, and the claimed combination may be for a sub-combination or a deformation of a sub-combination. Similarly, although operations are depicted in a particular order in the figure, this should not be understood as requiring such operations to be performed in the particular order shown or in a sequential order, or to perform all illustrated operations, to achieve the desired result.

[0057] Only a few implementations and examples are described, and other implementations, improvements, and variations may be made based on what is described and illustrated in this disclosure.

Claims

1. A wireless communication method, comprising: transmitting an initial transmission of a reference signal using a time-frequency resource corresponding to a first resource pattern, wherein the first resource pattern is a conventional demodulation reference signal (DMRS) pattern defined for a multiple-input multiple-output (MIMO) transmission mode in a conventional communication network; determining a second resource pattern representing time-frequency resources for subsequent transmission of the reference signal, wherein the determining step is performed based on a received channel quality indication CQI value, and wherein the second resource pattern is a reduced DMRS pattern; communicating a second resource pattern for subsequent transmission of the reference signal to one or more mobile stations; and Subsequent transmissions of the reference signal are transmitted using time-frequency resources corresponding to the second resource pattern.

2. The method according to claim 1, wherein: The step of delivering includes transmitting information indicating the second resource mode using a radio resource control, RRC, message.

3. The method according to claim 1, wherein: The transmitting step includes transmitting information indicating the second resource mode using downlink control information DCI.

4. The method according to claim 1, wherein: The CQI value indicates a modulation order of any one of 256-quadrature amplitude modulation QAM, 512QAM, and 1024QAM.

5. The method according to claim 1, wherein: The second resource pattern includes two pairs of adjacent resource elements per physical resource block (PRB) for the reference signal, and the method further includes applying orthogonal codes to the adjacent resource elements.

6. The method according to claim 5, wherein: The two pairs of adjacent resource elements for each PRB means that each PRB has exactly two pairs of adjacent resource elements for the reference signal.

7. The method according to claim 1, wherein: The second resource pattern includes two adjacent resource elements per physical resource block (PRB) for the reference signal, and the method further includes applying an orthogonal code to the two adjacent resource elements.

8. The method according to claim 7, wherein: Each PRB has two adjacent resource elements. Each PRB has exactly two adjacent resource elements for the reference signal.

9. The method according to claim 1, wherein: The second resource pattern includes a first physical resource block PRB having two pairs of adjacent resource elements for the reference signal, and The method also includes applying orthogonal codes to adjacent resource elements in the first physical resource block.

10. The method according to claim 9, wherein: The first PRB having two pairs of adjacent resource elements means that the first PRB has exactly two pairs of adjacent resource elements for the reference signal.

11. The method according to claim 9, wherein: The second resource pattern comprises a second physical resource block (PRB) adjacent to the first physical resource block, and The second PRB has no resource element allocated to the reference signal.

12. The method according to claim 1, wherein: The second resource pattern comprises only two resource elements per physical resource block (PRB) for the reference signal, wherein orthogonal codes are applied to the two resource elements.

13. The method of claim 5, 7, 9 or 12, wherein: The allocated resource elements are associated with any one of transmission ports 7 , 8 , 11 or 13 .

14. The method according to claim 1, wherein: The reference signal is a demodulation reference signal DMRS used by a receiving device for channel estimation.

15. A wireless communication method, comprising: Receiving, by a mobile station, an initial transmission of a reference signal using a time-frequency resource corresponding to a first resource pattern, wherein the first resource pattern is a conventional demodulation reference signal DMRS pattern defined for a multiple-input multiple-output MIMO transmission mode in a conventional communication network; receiving, by the mobile station, information related to a second resource pattern representing time-frequency resources for subsequent reception of the reference signal, wherein the information related to the second resource pattern is received based on a channel quality indication CQI value transmitted by the mobile station, and wherein the second resource pattern is a reduced DMRS pattern; and Subsequent receptions of the reference signal are received by the mobile station using time-frequency resources corresponding to the second resource pattern.

16. The method according to claim 15, wherein: The CQI value indicates a modulation order of any one of 256-quadrature amplitude modulation QAM, 512QAM, and 1024QAM.

17. The method according to claim 15, wherein: Receiving information related to selection of the second resource pattern includes receiving information indicating the second resource pattern from a radio resource control (RRC) message.

18. The method according to claim 15, wherein: Receiving information related to selection of the second resource mode includes receiving information indicating the second resource mode from downlink control information DCI.

19. The method according to claim 15, wherein: The second resource pattern includes two pairs of adjacent resource elements per physical resource block (PRB) for the reference signal, and orthogonal codes are applied to the adjacent resource elements.

20. The method according to claim 19, wherein: The two pairs of adjacent resource elements for each PRB means that each PRB has exactly two pairs of adjacent resource elements for the reference signal.

21. The method according to claim 15, wherein: The second resource pattern includes two adjacent resource elements per physical resource block (PRB) for the reference signal, and orthogonal codes are applied to the two adjacent resource elements.

22. The method according to claim 21, wherein: Each PRB has two adjacent resource elements. Each PRB has exactly two adjacent resource elements for the reference signal.

23. The method of claim 15, wherein: The second resource pattern includes a first physical resource block PRB having two pairs of adjacent resource elements for the reference signal, and Orthogonal codes are applied to adjacent resource elements in the first physical resource block.

24. The method according to claim 23, wherein: The first PRB having two pairs of adjacent resource elements means that the first PRB has exactly two pairs of adjacent resource elements for the reference signal.

25. The method of claim 23, wherein: The second resource pattern comprises a second physical resource block (PRB) adjacent to the first physical resource block, and The second PRB has no resource element allocated to the reference signal.

26. The method of claim 15, wherein: The second resource pattern comprises only two resource elements per physical resource block (PRB) for the reference signal, wherein orthogonal codes are applied to the two resource elements.

27. The method of claim 19, 21, 23 or 26, wherein: The allocated resource elements are associated with any one of transmission ports 7 , 8 , 11 or 13 .

28. The method of claim 15, wherein: The reference signal is a demodulation reference signal DMRS used by a receiving device for channel estimation.

29. The method of claim 15, further comprising: Channel estimation is performed using the received reference signal of the second resource pattern.

30. The method of claim 15, further comprising: Decision directed channel estimation is performed using data symbols from resource elements of a first physical resource block.

31. An apparatus for wireless communication, comprising a memory and a processor, wherein: The processor reads the code from the memory and implements the method of any one of claims 1 to 14.

32. A computer-readable program storage medium storing codes which, when executed by a processor, cause the processor to implement the method of any one of claims 1 to 14.

33. An apparatus for wireless communication, comprising a memory and a processor, wherein: The processor reads code from the memory and implements the method of any one of claims 15 to 30.

34. A computer-readable program storage medium storing codes which, when executed by a processor, cause the processor to implement the method of any one of claims 15 to 30.

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