DE102013224871A1 - Transmitter for use in multi-antenna wireless communication system for multi-shed input multi-shed output communication, has symbol generator to generate reference symbols and applying phase shifts to reference symbols respectively - Google Patents

Abstract

The transmitter has a reference symbol generator (706) to generate reference symbols for channel estimation. A reference symbol inserter (712) inserts the reference symbol into a stream of information symbols for transmission by an antenna at a symbol time period and frequency. Another reference symbol inserter inserts another reference symbol into stream of information symbols for transmission by the antenna at the symbol time period and frequency. The reference symbol generator applies phase shifts to reference symbols. An independent claim is also included for a receiver.

Description

Cross-reference to related applications

This application claims the benefit of US Provisional Patent Application No. 61 / 734,214, filed December 6, 2012, which is incorporated herein by reference.

Technical area

This application relates generally to a reference signal design, and more particularly to a reference signal design for multiple input multiple output (MIMO) communication.

background

Multiple-antenna techniques are used in communication systems to improve performance. These techniques are based on multiple antennas at the transmitter and / or receiver and can be grouped into three different categories: diversity, interference cancellation and spatial multiplexing. These three categories are often collectively referred to as MIMO communication, although not all of the multiple-antenna techniques that fall into these categories require at least two antennas at both the transmitter and the receiver.

To provide a specific example of a multi-antenna technique, it is known that a signal transmitted over a radio channel is damaged due to time dispersion. Time dispersion occurs when the transmitted signal propagates over the radio channel to a receiver via multiple independent fading paths with different delays. As in 1 is shown, such a channel, which may be subject to time dispersion ("time dispersive channel"), corresponds to a non-flat channel response 102 in the frequency domain.

In the case where the transmitted signal is a relative broadband carrier 104 is used, any symbol carried by the signal is transmitted over frequencies of the channel which may be subject to time dispersion, with both good quality (high signal strength) and poor quality (low signal strength). As a result, it is said that these symbols experience frequency diversity. On the other hand, in the case where the transmitted signal is a near-band relative carrier 106 such as those used in Orthogonal Frequency Division Multiplexing (OFDM) transmission, any symbol carried by the signal will experience comparatively low frequency diversity. As a result, the symbols may be limited to transmission over frequencies of the channel which may be subject to time dispersion with only poor quality (low signal strength), resulting in poor error rate performance at the receiver.

The multiple antenna technique of diversity can be used to improve performance in such a case. For example, in at least one application, diversity refers to the different fading experienced by signals transmitted by transmit antennas that are spatially separated. This diversity in fading can be exploited to provide artificial frequency diversity by transmitting the same narrow band carrier 106 with different relative delays from the multiple transmit antennas. It is important that the radio channel at the receiver must be estimated to use the artificially generated frequency diversity when the symbols passing through the narrowband carrier 106 be worn, decoded. Specifically, the receiver must estimate the radio channel and apply its inverse response to use the artificially generated frequency diversity, if symbols passing through the narrowband carrier 106 be worn, decoded.

Generally, many of the multiple-antenna techniques that fall within the aforementioned three categories (ie, diversity, interference cancellation, and spatial multiplexing) must perform channel estimation to improve performance. Depending on the specific multi-antenna technique implemented, channel estimation at the receiver and / or the transmitter may be required. A channel estimation is typically performed using a training-based method in which known symbols, called reference symbols or pilot symbols, are transmitted to a receiver to aid in estimating the channel. When there are multiple transmission antennas, the signal received by a reception antenna is a superposition of the signals transmitted from each of the transmission antennas. Thus, the reference symbols used by each of the plurality of transmission antennas are transmitted in a general manner so as not to interfere with each other to accurately estimate the channel.

2 illustrates three examples of reference signal patterns 200 which use different multiplexing techniques to prevent interference between reference symbols transmitted by multiple transmit antennas so that accurate channel estimation can be performed. The three exemplary reference signal patterns 200 Accordingly, a time division multiplexing (TDM) technique, a frequency division multiplexing (FDM) technique, and a code division multiplexing (CDM) technique are used.

Using a TDM technique, reference symbols are each transmitted from a transmit antenna over the same frequency. An example of a reference signal pattern 202 Using a TDM technique is in the above 2 shown for two transmit antennas. During a first symbol time period t1, the upper transmission antenna transmits a reference symbol over frequency f2, while the lower transmission antenna transmits nothing over the frequency f2. During a second symbol time period t2, the lower transmit antenna transmits a reference symbol over frequency f2, while the lower transmit antenna transmits nothing over frequency f2. Because the reference symbols are respectively transmitted one by one from the two transmitting antennas via the frequency f2, the reference signals in the time domain are orthogonal to each other and do not interfere with each other.

Using an FDM technique, reference symbols are transmitted simultaneously by transmit antennas but over different frequencies. An example of a reference signal pattern 204 using an FDM technique is in the middle of 2 shown for two transmit antennas. During a symbol time period t1, however, the upper transmit antenna transmits a reference symbol over frequency f3 but nothing about frequency f2, while the lower transmit antenna transmits a reference symbol over frequency f2 but nothing about frequency f3. Because the reference symbols are respectively transmitted through the two transmit antennas over different frequencies during the same symbol time period t1, the reference symbols are orthogonal to each other in the frequency domain and do not interfere with each other.

Finally, using a CDM technique, reference symbols are transmitted from transmit antennas over the same frequency and at the same symbol time periods using mutually different orthogonal cover codes. An example of a reference signal pattern 206 that uses a CDM technique is below in 2 shown for two transmit antennas. During a first symbol time period t1 and a second symbol time period t2, both the upper and lower transmit antennas transmit two reference symbols (one per symbol time period) above the frequency f2. The upper transmission antenna accordingly applies the coverage code +1, +1 (in 2 referred to as coverage code 1) to the two reference symbols that it transmits, and the lower transmission antenna accordingly applies the coverage code +1, -1 (in 2 referred to as coverage code 2) to the two reference symbols that it transmits. Because the coverage codes 1 and 2 are mutually orthogonal, the two reference symbols transmitted by each antenna can be separated from each other, assuming that the channel is fixed substantially over the symbol time periods t1 and t2.

Standardized wireless communication systems, such as 3GPP Long Term Evolution (LTE), use predefined reference signal patterns to support channel estimation. These patterns typically use a combination of TDM, FDM and possibly CDM to define a certain number of reference signals (that is, signals consisting of one or more reference symbols) that can each be transmitted through different transmitting antennas without being mutually connected to one another Disrupt receiving antenna. Often, when using the three techniques of TDM, FDM, and CDM alone, the predefined reference signal patterns of these standard wireless communication systems can not be extended to define many (if any) additional reference signals without using additional resource elements (where a resource element of the resource available carrier / sound over a symbol period). Use of additional resource elements is disadvantageous because these resource elements can no longer be used to carry information symbols and their addition to an existing reference signal pattern can cause backward compatibility problems with older devices operating within those systems.

However, new versions of the standardized wireless communication systems are expected to continue to increase the number of transmit antennas used to perform multiple antenna techniques, thus creating a corresponding need to expand their predefined reference signal patterns to define other reference signals that do not annoy each other to perform a channel estimation. For example, it is expected that the new versions of the 3GPP LTE wireless standards (version 12 and following), for example, support 16, 32, 64 or more transmitting antennas at a base station for performing multi-antenna techniques, or what is termed massive MIMO, given the large number of antennas to be used. It is also possible that in a new version a user terminal (UE) or terminal will support multiple transmit antennas.

Short description of the drawings / figures

The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate the embodiments of the present disclosure, and together with the description serve to explain the principles of the embodiments and to enable one skilled in the art to utilize the embodiments.

1 Figure 4 illustrates examples of both a relative broadband carrier and a relative narrowband carrier that are transmitted over a channel that may be subject to time dispersion.

2 Figure 3 illustrates three examples of reference signal patterns that use different multiplexing techniques to reduce interference between multiple transmit antennas.

3 FIG. 10 illustrates a multi-antenna communication system according to embodiments of the present disclosure. FIG.

4 FIG. 12 illustrates a reference signal pattern using a Phase Division Multiplexing (PDM) technique according to embodiments of the present disclosure. FIG.

5 represents a predefined reference signal pattern.

6 FIG. 12 illustrates a transmitter with 16 transmit antennas grouped into clusters in accordance with embodiments of the present disclosure.

7 illustrates a portion of a multiple antenna transmitter according to embodiments of the present disclosure.

8th illustrates a portion of a receiver according to embodiments of the present disclosure.

9 illustrates different antenna cluster patterns according to embodiments of the present disclosure.

The embodiments of the present disclosure will be described with reference to the attached drawings. The drawing in which an element appears for the first time is usually indicated by the left numeral in the corresponding reference numeral.

Detailed description

In the following description, numerous specific details are set forth in order to provide a thorough understanding of the embodiments of the present disclosure. However, it will be apparent to those skilled in the art that the embodiments including structures, systems and methods may be practiced without the specific details. The description and illustration herein are the common means used by those skilled in the art to convey the substance of their work to others skilled in the art. In other instances, well-known methods, procedures, components, and circuits are not described in detail to avoid unnecessary confusion of aspects of the disclosure.

References in the specification to "one embodiment," "an exemplary embodiment," etc., indicate that this described embodiment may have a particular feature, structure, or characteristic, but each embodiment does not necessarily encompass the particular feature, structure, and characteristic. In addition, such terms do not necessarily refer to the same embodiment. Further, when describing a particular feature, structure, or characteristic in connection with one embodiment, it is within the skill of those in the art to effect such feature, structure, or characteristics in conjunction with other embodiments, whether explicitly described or not.

1. Overview

The present disclosure is directed to a system and method for extending a reference signal pattern for defining additional reference signals using Phase Division Multiplexing (PDM) technique. In one embodiment, the reference signal pattern is a predefined reference signal pattern in a wireless communication standard and is extended, for example, to support massive MIMO communication. These and other features of the present disclosure will be described below.

It is noted that each "transmit antenna" referred to below is considered to correspond to a single antenna port. It is further noted that when it is said below that channel estimation is performed, channel state information may possibly be obtained instead.

2. Reference Signal Pattern Design Using Phase Split Multiplexing (PDM)

3 Fig. 10 illustrates an example of a multiple-antenna wireless communication system 300 which may be used to describe a reference signal pattern design using PDM. As in 3 The multi-antenna wireless communication system is shown in FIG 300 a transmitter 302 with M transmit antennas 306 and a receiver 304 with at least one receiving antenna 308 , The transmitting antennas 306 transmit information to the receiving antenna 308 over one or more carrier frequencies using a multiple antenna technique. In order to perform the multiple antenna technology better, the channel 310 between the transmitting antennas 306 and the receiving antenna 308 to be appreciated. At a carrier frequency f, the channel 310 in the frequency domain are represented by: H (f) = [h ₁ (f) h ₂ (f) ... h _M (f)] (1) Assuming that the individual channel elements h ₁ -h _M are flat across the bandwidth of the carrier at the frequency f.

To estimate H (f), a reference signal pattern defining M reference signals can be designed using a phase division multiplexing (PDM) technique. Using a PDM technique, each of the M reference signals is from a different one of the transmit antennas 306 transmitted over (at least) M resource elements. The (at least) M resource elements associated with each reference signal correspond to each other such that the M reference signals, when transmitted, overlap in time and frequency. Generally, the PDM technique prevents interference between the M reference signals (or at least allows them to be separated at the receiver) by applying a different phase shift to each reference signal over the M resource elements. Once this through the receiving antenna 308 can be received, the receiver 304 use the M reference signals to estimate H (f) or some portion of H (f).

4 Fig. 16 illustrates a specific example of such a reference signal pattern 400 which is designed using a PDM technique to estimate H (f) at the carrier frequency f1 in accordance with embodiments of the present disclosure. As shown, the transmit antennas transmit 306 while M symbol time periods t1-tM (which need not be consecutive) each have a different reference signal consisting of M reference symbols across the carrier frequency f1. More specifically, the transmitting antenna transmits 306-1 a reference signal consisting of reference symbols RS ₁₁ , RS ₁₂ , ..., RS _1M , via the carrier frequency f1, transmits the transmitting antenna 306-2 a reference signal consisting of reference symbols RS ₂₁ , RS ₂₂ , ..., RS _2M , via the carrier frequency f1, etc.

It should be noted that the single carrier frequency f1 is used for exemplary purposes and that in other embodiments corresponding ones of the M reference symbols making up each of the reference signals may be transmitted over other carrier frequencies to further estimate H (f) at these other carrier frequencies. For example, the second reference symbol of each reference signal RS ₁₂ , RS ₂₂ , ..., RS _{M2 may be} transmitted over the carrier frequency f2 to further estimate H (f) at the carrier frequency f2. It should also be noted that in the case where two or more carrier frequencies are used, corresponding ones of the M reference symbols each making up the reference signals may be transmitted at the same symbol time period but over the different two or more carrier frequencies. For example, the second reference symbol RS _22, ..., RS can _M2 of each reference signal RS _12, on the Carrier frequency f2 at the same symbol time period t1 as the first reference symbol of each reference signal RS1 ₁₁ , RS ₂₁ , ..., RS _{M1 are} transmitted.

wobei der Exponent T eine Transponierte bezeichnet, N die Anzahl von Frequenzbereichträgern (oder Unterträgern) ist, die durch jede der Sendeantennen 306 übertragen werden, f der Index des Trägers ist, über den die Referenzsymbole übertragen werden, i der Index der Symbolzeitperiode ist, die der Phasenverschiebung entspricht, und τ_1i, ..., τ_Mi unterschiedliche zyklische Zeitverzögerungen bezeichnen, die entsprechend auf die verschiedenen Sendeantennen 306 angewendet werden. Weil wir den Kanal 310 nur unter Verwendung der bestimmten Trägerfrequenz f1 in dem vorstehenden Beispiel schätzen, kann der Einfachheit halber C(f)_i als C_i geschrieben werden.To prevent the reference signals from interfering with each other, each of the M reference symbols transmitted over the same symbol time period and frequency is multiplied by a different corresponding phase shift. These phase shifts are given by:

where the exponent T denotes a transposed, N is the number of frequency distributors (or subcarriers) passing through each of the transmit antennas 306 f is the index of the carrier over which the reference symbols are transmitted, i is the index of the symbol time period corresponding to the phase shift, and τ _1i , ..., τ _Mi denote different cyclic time delays corresponding to the different transmit antennas 306 be applied. Because we have the channel 310 only using the determined carrier frequency f1 in the above example, C (f) _{i may} be written as C _{i for} the sake of simplicity.

In response to transmitting the above-described reference symbols, the receiving antenna becomes 308 M receive reference symbols during corresponding symbol time periods via the carrier frequency f1. The first reference symbol received will correspond to the superimposition of the reference symbols RS ₁₁ , RS ₂₁ , ..., RS _M1, respectively, by the transmit antennas 306 have been transmitted during the first symbol time period t1, the second received reference symbol will correspond to the superimposition of the reference symbols RS ₁₂ , RS ₂₂ , ..., RS _M2 corresponding to the transmit antennas 306 during the second symbol time period t2, etc.

Assuming that H does not change significantly over the symbol time periods t1 to tM, and (for simplicity) that there is no noise and no interference, each of the M reference symbols, by the receiving antenna 308 is received in the frequency domain represented by the following: y _i = HC _i p _i , i = {1, ..., M} (3) where p _{i is} the reference signal on the RE in the time symbol t1. If C _i at the receiver 304 for all i, then from equation (3) there are M equations and M unknowns (that is, M individual channel elements h ₁ -h _M of H at f1). Thus, the receiver 304 Estimate H at f1 using, for example, the following zero-forcing function: H = y _i P * / iC _i * (C _i x C _i *) ^-1 , i = {1, ..., M} (4)

It should be noted that the zero-forcing function in equation (4) represents only one function for estimating H and that other methods of estimating H are possible, as recognized by those skilled in the art. It should further be noted that the receiver of C _i for all i by receiving information about the particular cyclic time delays τ _1i , ..., τ _Mi from the transmitter 302 can learn via a control channel, higher layer signaling, predefined sets, or through some other means.

3. Extend reference signal patterns using PDM

The system and method of the present disclosure is configured to use the PDM technique described above to expand a reference signal pattern to define additional reference signals, thereby supporting channel estimation for a larger number of transmit antennas. The reference signal pattern may be, for example, a predefined reference signal pattern in a wireless communication standard and may be extended to support, for example, massive MIMO communication.

To provide an example, the reference signal pattern becomes 500 considered that in 5 is shown. This reference signal pattern 500 corresponds to a predefined reference signal pattern in the 3GPP LTE wireless communication standard defining eight different reference signals, each referred to as a downlink demodulation reference signal. The reference signal pattern 500 used a frequency / time / code division multiplexing technique to prevent interference between the eight different reference signals it defines. In particular, the eight different reference signals are frequency-multiplexed into two groups of four reference signals, as by the resource block pair diagram 502-1 and 502-2 (which respectively represent resource elements over the same 14 symbol time periods and 12 subcarrier frequencies). More specifically, reference signals 1-4 are assigned to one group and are transmitted over frequencies f1, f6 and f11, and reference signals 5-8 are assigned to the other group and are transmitted over frequencies f2, f7 and f12. Because reference signals 1-4 are transmitted over different frequencies as reference signals 5-8, the two groups of reference signals do not interfere with each other.

All 12 reference symbols included in the resource block pair diagram 502-1 are transmitted for each of the four reference signals 1-4, and all 12 reference symbols included in the resource block pair diagram 502-2 are transmitted are transmitted for each of the four reference signals 5-8. An interference between the 12 overlapping reference symbols in each of the resource block pairs 502 is accomplished by applying four mutually orthogonal coverage codes (which are described below in FIG 5 are shown) prevented. More specifically, a different one of the four mutually orthogonal coverage codes is applied to: (1) the four reference symbols transmitted by each reference signal 1-4 over frequency f1; (2) the four reference symbols transmitted by each reference signal 1-4 over frequency f6; and (3) the four reference symbols transmitted by each reference signal 1-4 over frequency f11. Similarly, a different one of the four mutually orthogonal coverage codes is applied to: (1) the four reference symbols transmitted by each reference signal 5-8 over frequency f2; (2) the four reference symbols transmitted by each reference signal 5-8 over frequency f7; and (3) the four reference symbols transmitted by each reference signal 5-8 over frequency f12.

The system and method of the present disclosure may include the reference signal pattern 500 to define additional reference signals so that channel estimation can be performed for more than the currently supported eight transmit antennas. Specifically, for more than eight transmit antennas, the transmit antennas may be grouped into clusters of one or more antennas such that the number of clusters is less than or equal to the number of individual reference signals represented by the reference signal pattern 500 be defined, or eight in this case. Thus, for example, it is assumed that it is desirable to provide a channel estimate for 12 transmit antennas using the eight individual reference signals provided by the reference signal pattern 500 are defined to support. For example, in one embodiment, two clusters of three transmit antennas and six clusters of one transmit antenna may be formed such that the total number of clusters is equal to eight. In another embodiment, four clusters may be formed with three transmit antennas. 6 represents another example 600 in which 16 transmit antennas at a transmitter 602 in eight clusters 604 be grouped by two transmitting antennas.

After the transmit antennas are grouped into clusters, each antenna cluster may be assigned to transmit a different one of the individual reference signals defined by the reference signal 00. For example, it is assumed that it is desirable to use the reference signal pattern 500 to use a channel estimate for the in 6 shown 16 transmit antennas, which in eight clusters 604 are grouped by two transmitting tins. In this case, each cluster can 604 be assigned to a single and different of the eight reference signals by the original reference signal pattern 500 are defined to be transmitted.

To prevent the reference signals passing through each antenna within one of the clusters 604 may interfere with one another, the PDM technique described in Section 2 above may be used. Specifically, different phase shifts described in Section 2 can be applied to the different reference signals transmitted by each antenna within a cluster to prevent the reference signals from interfering with each other. A receiver with knowledge of the phase shifts used for each cluster can then estimate the full (or, if desired, partial) channel for all of the transmit antennas in the clusters using the reference signal once received.

To further describe this functionality 7 a section 700 the transmitter 602 who in 6 is shown, including two sub-transmitter chains 702 and 704 , a reference symbol generator 706 , a precoder 708 according to embodiments of the present disclosure. In one embodiment, the section is 700 the transmitter 602 implemented in a base station (or "Evolved Node B").

As in 7 The two sub-transmitter chains are shown 702 and 704 each with the two transmit antennas of cluster 604-1 coupled. Each sub-tag chain 702 and 704 transmits a series of parallel information symbol data streams 728 and 730 which can be coded to perform a multiple antenna technique. The parallel information symbol data streams 728 and 730 are respectively modulated onto different subcarriers and as a series of time domain symbols 736 and 738 by subcarrier modulators 714 and 718 outputting an inverse fast Fourier transform in the case of OFDM transmission and outputting OFDM symbols. Cyclic prefix adders 720 and 722 then optionally add cyclic prefixes to the time domain samples 736 and 738 before this through boost converter 724 and 726 up through the two transmit antennas of the cluster 604-1 be transmitted.

For example, it is assumed that clusters 604-1 the transmission reference signal 1, by the reference signal pattern 500 in 5 is defined, can be the reference symbol generator 706 the reference symbols 744 for reference signal 1 generate. A reference symbol inserter 712 and 714 (for example, multiplexer) can then use the reference symbols 744 into each of the parallel information symbol data streams 728 and 730 for transmission at the same particular symbol time periods and frequencies determined by the reference signal pattern 500 are defined. To a disturbance between the reference symbols 744 passing through each of the two transmit antennas in the cluster 604-1 can be transmitted, therefore, the precoder 708 can be used to implement the PDM technique described in Section 2 above. Specifically, the precoder 708 can be used to different phase shifts, as described above in Section 2, to the reference symbols 744 apply through each of the two transmit antennas in the cluster 604-1 to be transmitted, as well as the reference symbols 744 apply to different frequencies through each of the two transmit antennas in the cluster 604-1 to be transferred. The precoded reference symbols passing through each antenna in the cluster 604-1 are to be transferred accordingly 746 and 748 designated.

For example, consider a reference symbol represented by the reference symbol generator 706 for transmission through each of the two transmit antennas in the cluster 604-1 was generated at the same symbol time period and frequency. Before the reference symbol passes through each of the two transmit antennas in the cluster 604-1 is transmitted, the precoder 708 as part of the PDM technique, apply different corresponding phase shifts to the reference symbol before passing through each of the two transmit antennas in the cluster 604-1 is transmitted. More specifically, a first phase shift may be applied to the reference symbol from one of the transmit antennas in the cluster 604-1 and a second phase shift other than the first may be applied to the reference symbol from the other of the transmit antennas in the cluster 604-1 is transmitted. These phase shifts can be generated according to equation (2) described above in section 2.

It should be noted that other predefined reference signal patterns may be extended in the 3GPP LTE standard as described above. For example, the predefined reference signal patterns defining cell specific reference signals (CRS) and channel state information reference signals (CSI-RS) may be extended as described above. It is further noted that the predefined reference signal patterns (CSI-RS, for example) can be extended to specifically support elevation beamforming. Finally, it should be noted that the precoder 708 in the reference symbol generator 706 may be included.

Referring now to 8th becomes a partial receiver chain 800 according to embodiments of the present invention. The partial receiver chain 800 includes a receiving antenna 802 , a down-converter 804 , a cyclic prefix remover 806 , a subcarrier demodulator 808 , a reference symbol remover 810 and a channel estimator 812 , In one embodiment, the sub-receiver chain is 800 implemented in a terminal or user terminal (for example, a mobile phone, laptop, tablet, etc.).

Generally, the sub-receiver chain 800 used to send the signals (including the reference signals) through the antennas in the cluster 604-1 , this in 7 is shown to be transmitted, and to remove the reference symbols from the received signal for channel estimation. Specifically, the down-converter 804 a signal through the receiving antenna 802 down to time domain symbols 818 regain. The CP remover 806 then can do any cyclic prefix of the time domain symbols 818 remove time-domain symbols 820 which are free from cyclic prefixes. The time domain symbols 820 which are free of cyclic prefixes can then be read by the subcarrier demodulator 808 demodulated, which can perform a fast Fourier transform in the case of OFDM transmission to parallel data streams of information and reference symbols 822 regain. The reference symbol remover 810 can then use the reference symbols 824 included in the parallel data streams of information and reference symbols 822 are included and remove them from the channel estimator 812 provide. The channel estimator 812 can then have a knowledge of the phase shifts that are due to the different reference symbols generated by the transmitter 602 be used as part of the PDM technique to at least partially perform a channel estimation.

Referring now to 9 are different antenna cluster patterns 900 according to embodiments of the present disclosure. These antenna cluster patterns 900 may be used to select which antennas are used at a transmitter to form different clusters for expanding a reference signal pattern, as described above.

For example, assuming a rectangular array of antennas at the transmitter, four different types of antenna cluster patterns may be used 902 . 904 . 906 and 908 can be used to select which antennas form different clusters at the transmitter. The first antenna cluster pattern 902 uses a diagonal pattern in which antennas belonging to clusters are selected over different diagonal lines of antennas in the rectangular field. The second antenna cluster pattern 904 uses a horizontal pattern in which antennas belonging to clusters are selected over different horizontal lines of antennas in the rectangular field. The third antenna pattern 906 uses a vertical pattern in which antennas belonging to clusters are selected over different vertical lines of antennas in the rectangular array. Finally, the fourth antenna pattern uses 908 a checkerboard pattern, as in 9 shown. Assuming a linear array of antennas at the transmitter, an antenna pattern may still be used 910 using a striped pattern that in 9 is shown, continue to be used.

It should be noted that the antenna cluster patterns 900 in conjunction with other antenna cluster patterns, other numbers of antennas (e.g., other than 16) at the transmitter, and clusters with non-uniform sizes and sizes other than four antennas per cluster.

4. Conclusion

The present disclosure has been described by means of functional building blocks that illustrate the implementation of specific functions and relationships of these. The boundaries of these functional building blocks have been arbitrarily defined herein for the sake of simplicity. Other limits may be defined as long as the specific functions and relationships are adequately performed by them.

The present disclosure relates to a system and method for expanding a reference signal pattern to define additional reference signals using a Phase Division Multiplexing (PDM) technique. The reference signal pattern may be a predefined reference signal pattern in a wireless communication standard and may be extended to support massive MIMO communication.

Claims (19)

Transmitter, with: a reference symbol generator configured to generate a first reference symbol and a second reference symbol for channel estimation; a first reference symbol inserter configured to insert the first reference symbol into a first data stream of information symbols for transmission through a first antenna at a symbol time period and frequency; and a second reference symbol inserter configured to insert the second reference symbol into a second data stream of information symbols for transmission through a second antenna at the symbol time period and frequency; wherein the reference symbol generator, as part of a phase division multiplexing technique, applies a first phase shift to the first reference symbol and a second phase shift to the second reference symbol. The transmitter of claim 1, wherein the first antenna and the second antenna are grouped into a cluster as part of the phase division multiplexing technique. The transmitter of claim 1, wherein the reference symbol generator further applies a portion of an orthogonal coverage code to the first reference symbol and the second reference symbol as part of a code division multiplexing technique. The transmitter of claim 4, wherein the first reference symbol and the second reference symbol are part of a demodulation reference signal. The transmitter of claim 1, wherein the first reference symbol and the second reference symbol are frequency-multiplexed with a third reference symbol transmitted by a third antenna at the symbol time period. The transmitter of claim 1, wherein the first reference symbol is transmitted by the first antenna in a first orthogonal frequency division multiplexing symbol, and the second reference symbol is transmitted by the second antenna in a second orthogonal frequency division multiplexing symbol. A transmitter according to claim 1, wherein the first phase shift equals

is, and the second phase shift equal

where f is the frequency over which the first and second reference symbols are transmitted, N is a number of frequency domain _carriers , i is a symbol time period _index , and τ _0i and τ _{1i are} different cyclic shift _values . The transmitter of claim 1, wherein the first data stream of information symbols and the second data stream of information symbols are coded to perform a multi-antenna technique using the first antenna and the second antenna. A transmitter according to claim 1, wherein the multiple antenna technique is diversity, interference suppression or spatial multiplexing. Transmitter, with: a reference symbol generator configured to generate a first reference symbol and a second reference symbol, both of which form part of a reference signal for channel estimation; a first reference symbol inserter configured to insert the first reference symbol into a first data stream of information symbols for transmission through a first antenna at a symbol time period and frequency; and a second reference symbol inserter configured to insert the second reference symbol into a second data stream of information symbols for transmission through a second antenna at the symbol time period and frequency; wherein the reference symbol generator, as part of a phase division multiplexing technique, applies a first phase shift to the first reference symbol and a second phase shift to the second reference symbol to expand a predefined reference signal. A transmitter according to claim 10, wherein the first antenna and the second antenna are grouped into a cluster as part of the phase division multiplexing technique. The transmitter of claim 10, wherein the reference symbol generator further applies a portion of an orthogonal coverage code to the first reference symbol and the second reference symbol as part of a code division multiplexing technique. The transmitter of claim 12, wherein the first reference symbol and the second reference symbol are a part of a reference signal for channel estimation by only one receiver. The transmitter of claim 10, wherein the first reference symbol and the second reference symbol are frequency-multiplexed with a third reference symbol transmitted by a third antenna at the symbol time period. Receiver, with: a reference symbol remover configured to remove from a data stream of information symbols a received reference symbol that is a superposition of at least a first and a second reference symbol transmitted from different antennas; and a channel estimator configured to use the received reference symbol to estimate a channel, wherein different phase shifts have been applied to the first reference symbol and the second reference symbol as part of a phase division multiplexing technique. The receiver of claim 15, wherein the channel estimator further uses the different applied phase shifts to estimate the channel. A receiver according to claim 15, wherein the received reference symbol is a part of a received orthogonal frequency division multiplexing symbol. The receiver of claim 15, wherein the data stream of information symbols is encoded to perform a multi-antenna technique. A receiver according to claim 18, wherein the multi-antenna technique is diversity, interference suppression or spatial multiplexing.

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