CN110710286A

CN110710286A - Transmission and reception of demodulation reference signals

Info

Publication number: CN110710286A
Application number: CN201780091530.3A
Authority: CN
Inventors: 辛雨; 伍一; 边峦剑
Original assignee: ZTE Corp
Current assignee: ZTE Corp
Priority date: 2017-07-28
Filing date: 2017-07-28
Publication date: 2020-01-17
Also published as: WO2019019173A1

Abstract

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

Description

Transmission and reception of demodulation reference signals

Technical Field

This document relates generally to wireless communications.

Background

Mobile telecommunications technology is bringing the world to an increasingly interconnected and networked society. 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 refined range of access requests and flexibility than existing wireless networks.

Disclosure of Invention

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.

In one exemplary aspect, a method of wireless communication 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 a subsequent transmission of the reference signal, communicating the second resource pattern for the subsequent transmission of the reference signal to one or more mobile stations, and transmitting the subsequent transmission of the reference signal using time-frequency resources corresponding to the second resource pattern.

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

In yet another exemplary aspect, a wireless communication base station is disclosed. The wireless communication base station includes a memory storing instructions for operation of the base station, and a processor in communication with the memory operable to execute the instructions to cause the base station to: 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 a subsequent transmission of a reference signal; communicating a second resource pattern for subsequent transmission of reference signals to one or more mobile stations; and transmitting a subsequent transmission of the reference signal using the time-frequency resources corresponding to the second resource pattern.

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: receiving an initial transmission of a reference signal using time-frequency resources corresponding to a first resource pattern; receiving information related to a second resource pattern representing time-frequency resources for subsequent reception of reference signals; and receiving subsequent receptions of the reference signal using the time-frequency resources corresponding to the second resource pattern.

In yet another exemplary aspect, the above-described methods are embodied in the form of processor-executable code and stored in a computer-readable program medium.

In yet another exemplary embodiment, an apparatus configured or operable to perform the above method is disclosed.

The above and other aspects and embodiments thereof are described in more detail in the accompanying drawings, the description and the claims.

Drawings

Fig. 1 shows an example of a base station communicating a resource pattern with DMRS signals to one or more mobile stations.

Fig. 2A-2C illustrate downlink DMRS patterns adopted by current Long Term Evolution (LTE) standards.

Fig. 3A-3G illustrate exemplary DMRS overhead reduction patterns.

Fig. 4 illustrates a block diagram for an exemplary wireless communication base station for transmitting a legacy DL DMRS pattern and a reduced DL DMRS pattern.

Fig. 5 illustrates an exemplary flow diagram for a base station using a resource pattern with a legacy and reduced DMRS signal.

Fig. 6 illustrates a block diagram of an exemplary wireless communication mobile station for receiving a legacy DL DMRS pattern and a reduced DL DMRS pattern.

Fig. 7 illustrates an exemplary flow diagram for a wireless communication mobile station using a resource pattern with a legacy and reduced DMRS signal.

Detailed Description

Radio spectrum shortage and demand for high data rate services have stimulated a need for improved 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 location of the reference signal. For example, in an Orthogonal Frequency Division Multiplexing (OFDM) -based transmission scheme, transmission resources are typically specified using time slots and subcarriers, forming a time-frequency grid of available transmission resources called resource elements. In such systems, the slots and subcarriers used for reference signal transmission are described using a resource pattern, which may be, for example, resource elements allocated to reference signals in a two-dimensional arrangement of resource elements known as Physical Resource Blocks (PRBs). A PRB is a unit of resource allocation available for transmission, which may repeat in the time dimension (slot) and frequency dimension (subcarrier).

In the current LTE specifications, three different Downlink (DL) demodulation reference signal (DMRS) patterns have been defined for a multiple-input multiple-output (MIMO) Transmission Mode (TM)9/10 for different transmission ranks. Depending on the transmission rank, one 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. Thus, in some embodiments, DMRS density may be reduced in, for example, wireless stationary link scenarios.

The disclosed techniques propose DMRS overhead reduction techniques, which may be used, for example, in scenarios with sufficiently high signal-to-noise ratio (SNR), such as small cell deployments. In some embodiments, the proposed reduced DMRS pattern may be applied to any similar stationary wireless link with a relatively high SNR. Some new low overhead DMRS patterns and supporting techniques are disclosed in this patent document. In some embodiments, the reduced DMRS pattern may be customized for LTE DL single user multiple input output (SU-MIMO) rank 3/4 in Transmission Mode (TM) 9/10. The reduced DMRS pattern provides some benefits. For example, the disclosed new DMRS patterns may reduce Resource Element (RE) overhead while maintaining performance at the same or similar level compared to legacy DMRS patterns. Therefore, LTE DL system efficiency can be improved by using the proposed DMRS pattern.

Fig. 1 shows a base station 120 communicating a resource pattern with

DMRS signals

140a, 140b to one or more

mobile stations

110a, 110 b. 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 Channel Quality Indications (CQIs) 130a, 130b to the base station. The CQI provides information about the quality of a communication channel between the base station and the mobile station to the base station. To support multi-layer demodulation, UE-specific DMRSs are defined in the current LTE specifications for TM 9/TM10 transmissions.

Fig. 2A-2C illustrate three different legacy DL DMRS patterns that have been defined for TM 9/10 at different transmission ranks according to the current LTE standard. Fig. 2A-2C include a resource pattern for each Physical Resource Block (PRB). As shown in fig. 2A, 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 referred to as a resource element. The 12 subcarriers include one resource block and the 7 OFDM symbols include one slot.

Fig. 2A shows DMRS pattern port 7/8 with orthogonal code OCC2 being used for transmission of DL SU-MIMO rank 1/2. In fig. 2A, DMRS signals are transmitted in 12 REs per PRB, and OCC2 is applied to two adjacent REs in the time domain so that port 7/8 can share the 12 REs. Thus, the DMRS overhead for rank 1/2 is 6 REs/PRBs/port.

Fig. 2B shows DMRS patterns using OCC2 for DL SU-MIMO rank 3/4 transmissions. The DMRS signal occupies 24 REs/PRB. Among the 24 REs, 12 REs are shared by port 7/8 using OCC2, and the other 12 REs are shared by port 9/10 using OCC 2. OCC2 will be applied to 2 adjacent REs in the time domain in the same way as for the rank 1/2DMRS pattern. The DMRS overhead for rank 3/4 may be found to be 6 REs/PRBs/port. Compared to the DMRS overhead of rank 1/2, as shown in fig. 2A, the DMRS overhead doubles for the rank 3/4 transmission shown in fig. 2B.

Fig. 2C shows DL SU-MIMO transmission of rank >4, where DMRS pattern using OCC4 is defined. DMRS signals are transmitted at 24 REs/PRB, and OCC4 is applied to 4 REs on a subcarrier spanning 2 slots. More specifically, port 7/8/11/13 shares 12 REs and port 9/10/12/14 shares another 12 REs. Thus, the DMRS overhead for rank >4 is 3 REs/PRB/port.

The DMRS patterns in fig. 2A-2C are designed for a general scenario. Specific scene (scene-specific) parameters such as SNR and moving speed have not been considered in DMRS pattern design. For these scenarios, like the small cell scenario, the wireless link between the eNB and the stationary UE may have the characteristics of high SNR, low frequency selectivity, and low time-selective fading. In such scenarios, the task difficulty of channel estimation is less, and DMRS overhead can be reduced while keeping channel estimation degradation to a minimum.

The benefit of DMRS overhead reduction is to take advantage of the possibility of allocating some of the REs forming the legacy DMRS pattern in TM 9/10 to, for example, PDSCH transmissions. These additional PDSCH REs may be used to increase throughput or improve block error rate performance. DMRS overhead reduction may be achieved by reducing DMRS density in the frequency domain, the time domain, or both the frequency and time domains.

As shown in fig. 2A-2C, the legacy DMRS overhead for rank 1/2 and rank 3/4 is 6 REs/PRBs/port, and the DMRS overhead for ranks greater than 4 is 3 REs/PRBs/port. In some embodiments, DMRS overhead reduction techniques may be applied to rank 3/4 transmissions. For example, some new low overhead DMRS patterns may be applied for LTE DL SU-MIMO rank 3/4 transmissions.

Fig. 3A-3B illustrate an exemplary DMRS overhead reduction pattern, where DMRS signals are transmitted at 8 REs/PRB and OCC4 may be applied to 4 REs on a subcarrier spanning two slots. The resource patterns in fig. 3A and 3B may allocate exactly two pairs of adjacent resource elements for reference signals per Physical Resource Block (PRB), where orthogonal codes may be applied to the adjacent resource elements. Each of the two adjacent resource elements in fig. 3A and 3B may be associated with any one of the

transmission ports

7, 8, 11 or 13. DMRS overhead for the DMRS patterns in fig. 3A and 3B is reduced by 66.7% compared to the legacy DL DMRS pattern in fig. 2B. Some differences between the patterns in fig. 3A and 3B are that the DMRS REs in fig. 3A have backward compatibility with mobile stations that may use the DMRS patterns in fig. 2A-2B. Unlike in fig. 3A, the DMRS REs in fig. 3B are uniformly distributed within a PRB. A benefit of having uniformly distributed DMRS REs is that it allows for improved channel estimation.

Fig. 3C-3G illustrate some exemplary DMRS overhead reduction patterns, where DMRS signals are transmitted at 4 REs/PRB for each of the five patterns, and OCC4 may be applied to the 4 REs. DMRS overhead for the five DMRS patterns in fig. 3C-3G is reduced by 83.3% compared to the conventional DLDMRS pattern in fig. 2B. The resource pattern in fig. 3C may allocate exactly two adjacent resource elements per Physical Resource Block (PRB) for the reference signal, where orthogonal codes may be applied to the adjacent resource elements. Two adjacent resource elements in fig. 3C may be associated with any one of the

transmission ports

7, 8, 11 or 13.

The resource patterns in fig. 3D and 3E include resource patterns 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 a second physical resource block to the reference signal, where the second physical resource block is adjacent to the first physical resource block. Thus, in some embodiments, the second physical resource block in fig. 3D and 3E does not allocate resource elements to the reference signal. For example, the second physical resource block in fig. 3D and 3E does not use or allocate any resource elements to the reference signal. A benefit of not using resource elements for reference signals is that these resource elements can be used for data transmission. Thus, more data may be transmitted from the base station to the mobile station in physical resource blocks. The orthogonal codes may be applied to adjacent resource elements of the first physical resource block. Each of the two adjacent resource elements in fig. 3D and 3E may be associated with any one of the

transmission ports

7, 8, 11 or 13.

The resource patterns in fig. 3F and 3G may allocate only two resource elements per Physical Resource Block (PRB) for the reference signal, where orthogonal codes may be applied to the two resource elements. Each of the two resource elements in fig. 3F and 3G is associated with any of the

ports

7, 8, 11 or 13.

One of the differences between the five patterns in fig. 3C-3G is the distribution of DMRS REs within a PRB. Depending on the channel conditions, the base station, such as an eNB, may select or determine the most appropriate mode. For example, the base station may determine frequency and time variations in a 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. The DMRS pattern in fig. 3C is more suitable for channels with relatively low variation in the frequency domain. In addition, the DMRS patterns in fig. 3D and 3E are more suitable for channels with lower variation in the time domain. The DMRS patterns in fig. 3F and 3G should be used for channels with variations in both the time domain and the frequency domain. The DMRS REs of the patterns in fig. 3D and 3F have backward compatibility with the legacy DMRS pattern, while the DMRS REs of the patterns in fig. 3E and 3G are uniformly distributed within a PRB.

In some embodiments, the DMRS overhead reduction mode as shown in fig. 3A-3G may be applied to other scenarios, e.g., for transmissions of rank 1/2 or rank greater than 4 in TM 9/10, if the base station or mobile station determines that the channel conditions are good.

Fig. 4 illustrates a block diagram of an exemplary wireless communication base station 400 for transmission of both legacy DL DMRS patterns and reduced DL DMRS patterns. The wireless communication base station includes a memory 405 that stores instructions for operation of the base station, and one or more processors 415 in communication with the memory 405 that are operable to execute the instructions to cause the base station to perform a number of exemplary operations.

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

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

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 a legacy DMRS pattern and a reduced DMRS pattern in the communication. Accordingly, the reference signal communication module 435 communicates information to the one or more mobile devices indicating a second resource pattern (such as one of the reduced DMRS patterns) for subsequent transmission of the reference signal.

The reference signal communication module 435 transmits a signal to the UE to inform the UE to switch for subsequent transmissions. In LTE, this can be implemented in two ways. The first signaling method is to use DCI so that DMRS patterns can be dynamically switched on a subframe basis. The main advantage of dynamic switching is that an appropriate DMRS pattern can be established quickly as channel conditions change. The large DCI overhead may be a penalty for this fast response. In some embodiments, the information indicating the reduced DMRS pattern may be communicated to the one or more mobile stations by transmitting the second resource pattern using Downlink Control Information (DCI).

Other signaling methods are to introduce a new bit field in the RRC signaling. The eNB reconfigures the DMRS pattern through RRC signaling if deemed necessary, for example, when channel conditions become poor. With this semi-static handover method, the signaling overhead can be reduced significantly. Accordingly, in some embodiments, information indicating the reduced DMRS pattern may be communicated to one or more mobile stations by communicating the second resource pattern using a radio resource control message. In some embodiments, DMRS overhead reduction is used under wireless stationary links assuming small channel variations. In such embodiments, a semi-static DMRS pattern that switches through RRC signaling may be preferred.

The channel quality module 440 allows the base station to monitor the channel conditions. For example, as shown in fig. 1, a channel quality module 440 of a base station may receive Channel Quality Indication (CQI) values from one or more mobile stations using a receiver 420. Based on the CQI value, the channel quality module 440 may instruct the reference signal selection module 430 to select one of a legacy DMRS pattern or an exemplary reduced DMRS pattern. For example, when the CQI value indicates a modulation order that is a higher modulation order, such as 256QAM, 512QAM, or 1024QAM, or higher, channel quality module 440 may instruct reference signal selection module 430 to select or determine one of the example reduced DMRS patterns.

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

In a transferring operation 506, the base station transfers the second resource pattern for subsequent transmission of the reference signal to one or more mobile stations. For example, when the base station transmits 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 1024 QAM. Upon receiving the modulation order information, the mobile station knows that the 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.

In some embodiments, the transfer operation 506 may be performed prior to the initial transfer operation 502. For example, when the CQI transmitted by one of the mobile stations and received by the base station indicates a modulation order of 1024QAM, the transferring operation 506 may be performed before the initial transmitting operation 502, since the second resource pattern will be used after the initial transmission transmitting the reference signal according to the first resource pattern.

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

Fig. 6 illustrates a block diagram for an exemplary wireless communication mobile station 600 for receiving a legacy DL DMRS pattern and a reduced DL DMRS pattern. Wireless communication mobile station 600 includes a memory 605 that stores instructions for the operation of mobile station 600, and one or more processors 610 in communication with memory 605 and operable to execute the foregoing instructions to cause the mobile station to perform a number of exemplary operations.

For example, the reference signal receiving module 625 may receive the reference signal using the time-frequency resources corresponding to the resource pattern using the receiver 620. The reference signal receiving module can receive a reference signal transmitted by a base station using one of a legacy DMRS pattern (as described in fig. 2A-2C) or an exemplary reduced DMRS pattern (as described in fig. 3A-3G). For example, the reference signal receiving module 625 receives an initial transmission of a reference signal using time-frequency resources corresponding to the first resource pattern.

The reference signal communication module 630 uses the receiver 620 to receive information related to a resource pattern representing time-frequency resources used for initial or subsequent reception of reference signals. In some embodiments, after the initial transmission of the legacy DMRS pattern, the reference signal communication module 630 receives information from the base station that the base station may 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 the 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 the selection of the second resource mode by receiving information indicating the second resource mode from Downlink Control Information (DCI).

The channel quality module 635 provides information about the channel to the base station. For example, channel quality module 635 may transmit a Channel Quality Indication (CQI) value to a base station using transmitter 615. Based on the CQI value, the base station may determine to select one of a legacy DMRS pattern or an exemplary reduced DMRS pattern, and may communicate the selection of either mode to the mobile station.

In some cases, DMRS overhead reduction may result in a reduction in channel estimation accuracy. This may reduce system performance. Thus, the channel estimation module 640 may improve channel estimation in one of two ways. First, the channel estimation module 640 may improve channel estimation by using one of the exemplary reduced DMRS patterns (which uses more REs per PRB than one of the other exemplary reduced DMRS patterns for DMRS transmission). For example, by using the exemplary reduced DMRS pattern in fig. 3B, a UE may receive DMRS signals at 8 REs/PRB, which, although lower than the legacy DMRS pattern, is not lower than, for example, the reduced DMRS pattern in fig. 3G (only 2 REs/PRB is used for DMRS).

Second, to overcome possible performance degradation due to DMRS overhead reduction, in an exemplary embodiment, the channel estimation module 640 can use Decision Directed (DD) channel estimation methods to utilize information on non-pilot symbols. The DD channel estimation module 640 may use the DD channel estimates 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 amounts to increasing the density of DMRS signals and thus improving the quality of the channel estimation. In some embodiments, the channel estimation module 640 determines that the mobile station has successfully demodulated data in a first PRB including a legacy DMRS signal using time-frequency resources corresponding to a first resource pattern. Subsequently, when the mobile station receives a second PRB having a reduced DMRS signal using time-frequency resources corresponding to a second resource pattern, the channel estimation module 640 may estimate the channel by using data symbols from resource elements of a first Physical Resource Block (PRB) including a legacy DMRS signal corresponding to the first resource pattern. Accordingly, the data symbols of the first PRB may be used as the DMRS for the second PRB.

Fig. 7 illustrates an exemplary flow diagram for operations performed by a wireless communication mobile station to use a resource pattern with legacy and reduced DMRS signals. 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 related to a second resource pattern representing time-frequency resources for a subsequent transmission of a reference signal. At receive subsequent transmission operation 706, the mobile station receives subsequent receptions of the reference signal using the time-frequency resources corresponding to the second resource pattern.

The term "exemplary" is used to refer to an "… … example" and does not indicate an ideal or preferred embodiment unless otherwise indicated.

Some of the embodiments described herein are described in the general context of methods or processes, which may be implemented in one embodiment by a computer program product, embodied in a computer-readable medium, including computer-executable instructions, such as program code, executed by computers in network environments. The computer-readable medium may include removable and non-removable storage devices including, but not limited to, Read Only Memory (ROM), Random Access Memory (RAM), Compact Discs (CDs), Digital Versatile Discs (DVDs), and the like. Thus, a computer-readable medium may include a non-transitory storage medium. Generally, program modules may include routines, programs, objects, components, data structures, etc. that perform particular tasks or implement particular abstract data types. Computer-executable instructions, associated data structures, and program modules represent examples of program code for executing steps of the methods disclosed herein. The particular sequence of such executable instructions or associated data structures represents examples of corresponding acts for implementing the functions described in such steps or processes.

Some of the disclosed embodiments may be implemented as devices or modules using hardware circuitry, software, or a combination thereof. For example, a hardware circuit implementation may include discrete analog and/or digital components, e.g., integrated as part of a printed circuit board. Alternatively, or in addition, the disclosed components or modules may be implemented as Application Specific Integrated Circuits (ASICs) and/or Field Programmable Gate Array (FPGA) devices. Some embodiments may additionally or alternatively include a Digital Signal Processor (DSP), which is a special-purpose microprocessor having a configuration that optimizes the operational needs of digital signal processing associated with the disclosed functionality of this application. Similarly, various components or sub-components within each module may be implemented in software, hardware, or firmware. Connectivity between modules and/or components within modules may be provided using any of the connectivity methods and media known in the art, including but not limited to communications over the internet, wired or wireless networks using suitable protocols.

While this document contains many specifics, these should not be construed as limitations on the scope of the claimed invention or of what may be claimed, but rather as descriptions of features specific to particular embodiments. Certain features that are described in this document in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable subcombination. Furthermore, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination. Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results.

Only a few embodiments and examples have been described and other embodiments, modifications, and variations may be made based on what is described and illustrated in this disclosure.

Claims

1. A method of wireless communication, comprising:

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 a subsequent transmission of the reference signal;

communicating a second resource pattern for a subsequent transmission of the reference signal to one or more mobile stations; and

transmitting a subsequent transmission of the reference signal using time-frequency resources corresponding to the second resource pattern.

2. The method of claim 1, wherein the communicating step comprises transmitting the information indicating the second resource pattern using a Radio Resource Control (RRC) message.

3. The method of claim 1, wherein the communicating step comprises transmitting information indicating the second resource mode using Downlink Control Information (DCI).

4. The method of claim 1, wherein the determining step is performed in accordance with a received Channel Quality Indication (CQI) value.

5. The method of claim 4, wherein the Channel Quality Indication (CQI) value indicates a modulation order of any one of 256 Quadrature Amplitude Modulation (QAM), 512QAM, and 1024 QAM.

6. The method of claim 1, wherein the first resource pattern is a legacy demodulation reference signal (DMRS) pattern defined for a multiple-input multiple-output (MIMO) transmission mode in a legacy communication network.

7. The method of claim 1, wherein the second resource pattern comprises two pairs of adjacent resource elements per Physical Resource Block (PRB) for the reference signal, the method further comprising applying an orthogonal code to the adjacent resource elements.

8. The method of claim 7, wherein the two pairs of neighboring resource elements per PRB are exactly two pairs of neighboring resource elements per PRB for the reference signal.

9. The method of claim 1, wherein the second resource pattern comprises two adjacent resource elements per Physical Resource Block (PRB) for the reference signal, the method further comprising applying orthogonal codes to the two adjacent resource elements.

10. The method of claim 9, wherein the two neighboring resource elements per PRB are exactly two neighboring resource elements per PRB for the reference signal.

11. The method of claim 1, wherein:

the second resource pattern comprises 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.

12. The method of claim 11, wherein the first PRB has two pairs of neighboring resource elements for the reference signal for which the first PRB has exactly two pairs of neighboring resource elements.

13. The method of claim 11, wherein:

the second resource pattern includes a second Physical Resource Block (PRB) adjacent to the first physical resource block, and

the second PRB does not allocate resource elements to the reference signal.

14. The method of claim 1, wherein the second resource pattern comprises only two resource elements per Physical Resource Block (PRB) for the reference signal, wherein an orthogonal code is applied to the two resource elements.

15. The method of claim 7, 9, 11 or 14, wherein the allocated resource element is associated with any of transmission ports 7, 8, 11 or 13.

16. The method of claim 1, wherein the reference signal is a demodulation reference signal (DMRS) for use by a receiving device for channel estimation.

17. A method of wireless communication, comprising:

receiving, by the mobile station, an initial transmission of a reference signal using a time-frequency resource corresponding to the first resource pattern;

receiving, by the mobile station, information related to a second resource pattern representing time-frequency resources for subsequent reception of the reference signal; and

receiving, by the mobile station, subsequent receptions of the reference signal using time-frequency resources corresponding to the second resource pattern.

18. The method of claim 17, wherein the information related to the second resource pattern is received as a function of a mobile station transmitting a Channel Quality Indication (CQI) value.

19. The method of claim 18, wherein the Channel Quality Indication (CQI) value indicates a modulation order of any one of 256 Quadrature Amplitude Modulation (QAM), 512QAM, and 1024 QAM.

20. The method of claim 17, wherein receiving information related to selection of the second resource pattern comprises receiving information indicating the second resource pattern from a Radio Resource Control (RRC) message.

21. The method of claim 17, wherein receiving information related to selection of the second resource mode comprises receiving information indicating the second resource mode from Downlink Control Information (DCI).

22. The method of claim 17, wherein the first resource pattern is a legacy demodulation reference signal (DMRS) pattern defined for a multiple-input multiple-output (MIMO) transmission mode in a legacy communication network.

23. The method of claim 17, wherein the second resource pattern comprises two pairs of adjacent resource elements per Physical Resource Block (PRB) for the reference signal, an orthogonal code being applied to the adjacent resource elements.

24. The method of claim 23, wherein the two pairs of neighboring resource elements per PRB are exactly two pairs of neighboring resource elements per PRB for the reference signal.

25. The method of claim 17, wherein the second resource pattern comprises two adjacent resource elements per Physical Resource Block (PRB) for the reference signal, an orthogonal code being applied to the two adjacent resource elements.

26. The method of claim 25, wherein the two neighboring resource elements per PRB are exactly two neighboring resource elements per PRB for the reference signal.

27. The method of claim 17, wherein:

orthogonal codes are applied to adjacent resource elements in the first physical resource block.

28. The method of claim 27, wherein the first PRB has two pairs of neighboring resource elements for which the first PRB happens to have two pairs of neighboring resource elements for the reference signal.

29. The method of claim 27, wherein:

the second PRB does not allocate resource elements to the reference signal.

30. The method of claim 17, wherein the second resource pattern comprises only two resource elements per Physical Resource Block (PRB) for the reference signal, wherein an orthogonal code is applied to the two resource elements.

31. The method of claim 23, 25, 27 or 30, wherein the allocated resource element is associated with any of transmission ports 7, 8, 11 or 13.

32. The method of claim 17, wherein the reference signal is a demodulation reference signal (DMRS) for use by a receiving device for channel estimation.

33. The method of claim 17, further comprising:

performing channel estimation using the received reference signals for the second resource pattern.

34. The method of claim 17, further comprising:

decision directed channel estimation is performed using data symbols of resource elements from a first physical resource block.

35. 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 of claims 1 to 16.

36. A computer readable program storage medium having code stored thereon, which when executed by a processor causes the processor to implement the method of any one of claims 1 to 16.

37. 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 of claims 17 to 34.

38. A computer readable program storage medium having code stored thereon, which when executed by a processor causes the processor to implement the method of any of claims 17 to 34.