WO2018063042A1

WO2018063042A1 - Method for demodulation reference signal allocation and signaling

Info

Publication number: WO2018063042A1
Application number: PCT/SE2016/050922
Authority: WO
Inventors: Karl Werner; Ning He; Andreas Cedergren; Robert Baldemair
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 2016-09-29
Filing date: 2016-09-29
Publication date: 2018-04-05

Abstract

The present disclosure relates to wireless communications and in particular to allocation and signalling of demodulation reference signals. In particular the proposed methods relates to methods for transmitting and receiving demodulation reference signals using dynamic reference signal patterns and to corresponding nodes and computer programs. The disclosure proposed a method, in a first wireless node of a communication system for transmitting a demodulation reference signal being associated with a transmission to a second wireless node, on at least one antenna port. The method comprises obtaining (S1) a rule, shared with the second wireless node, for demodulation reference signal pattern determination, and determining (S2), for at least one antenna port, one reference signal pattern, by applying the shared rule to one or more parameters that are available both in the first wireless node and in the second wireless node. The method further comprises transmitting (S4) the demodulation reference signal on the respective antenna ports in accordance with the determined demodulation reference signal pattern.

Description

METHOD FOR DEMODULATION REFERENCE SIGNAL ALLOCATION AND SIGNALING

TECHNICAL FIELD

The present disclosure relates to wireless communications and in particular to allocation and signalling of demodulation reference signals. In particular the proposed methods relate to methods for transmitting and receiving demodulation reference signals using dynamic reference signal patterns, and to corresponding nodes and computer programs.

BACKGROUND

3GPP Long Term Evolution, LTE, is the fourth-generation mobile communication technologies standard developed within the 3rd Generation Partnership Project, 3GPP, to improve the Universal Mobile Telecommunication System, UMTS, standard to cope with future requirements in terms of improved services such as higher data rates, improved efficiency, and lowered costs. In a typical cellular radio system, wireless devices or terminals also known as mobile stations and/or user equipment units, UEs, communicate via a radio access network, RAN, to one or more core networks. The Universal Terrestrial Radio Access Network, UTRAN, is the radio access network of a UMTS and Evolved UTRAN, E-UTRAN, is the radio access network of an LTE system. In a UTRAN and an E-UTRAN, a User Equipment, UE, is wirelessly connected to a Radio Base Station, RBS, commonly referred to as a NodeB, NB, in UMTS, and as an evolved NodeB, eNB or eNodeB, in LTE. An RBS is a general term for a radio network node capable of transmitting radio signals to a UE and receiving signals transmitted by a UE.

Specifications for the Evolved Packet System, EPS, have been completed within the 3GPP and this work continues in the coming 3GPP releases. The EPS comprises the Evolved Universal Terrestrial Radio Access Network, E-UTRAN, also known as the LTE radio access, and the Evolved Packet Core, EPC, also known as System Architecture Evolution, SAE, core network.

In LTE systems, known reference symbols are inserted into Orthogonal Frequency Division Multiplexing, OFDM, time-frequency grid at regular time- frequency positions, i.e. resource elements, RE. Using the knowledge about the reference signals, RS, a receiver of a user equipment or a radio base station can perform channel estimation for demodulation and other purposes, e.g. acquiring channel state information.

In the LTE specification (see e.g. the technical specification 3GPP TS 36.211 (V.13 2 .0), section 6.10), different types of reference signals are defined. In downlink, the transmitted reference signals, from the radio base station, include Cell specific Reference Signal, CRS, UE specific Reference Signals, UE-RS, Channel State Indicator Reference Signal, CSI-RS, Multicast/Broadcast Single Frequency Network, MBSFN, reference signals and positioning reference signals. Similarly, the reference signals transmitted in UL, i.e. from the user equipment, include UL DM-RS and Sounding Reference Signals, SRS. The corresponding defined procedures of RS sequence generation and mapping to REs form 'RS patterns'.

An RS pattern defines different parameters affecting a reference signal. One parameter is the overhead of the reference signal, i.e., the total number of resources, used by the RS pattern in a regular period and power offset of the reference signal related to the control or data signal. The RS pattern also defines mapping to REs in time domain, frequency domain and code domain, or cyclic shift as a special case of code, which includes the orthogonal cover code, OCC, structure, e.g., an OCC can extend in time domain, in frequency, or in both. The RS patters typically also define transmission modes and ranks. The mapping procedures are defined respectively for different transmission modes and ranks.

Thus, a RS pattern can be said to carry more information than merely a pattern (i.e. time-frequency grid). That is, a RS pattern can include the pattern (i.e. time-frequency grid) as well as the mapping method, the adopted transmission mode.

In LTE, the patterns of different types of reference signals are explicitly defined in the specification (see e.g. 3GPP TS 36.21 1 (V.l 1 .1 .0), section 6.10). The reference signals are generally designed to have a sufficiently high density and an optimized or good structure in both time and frequency domains to provide estimates for the entire time-frequency grid in the case of radio channels subject to high frequency and/or time selectivity. Generally, the design of RS patterns must take the most challenging channel characteristics into account and thus, high RS overhead and the associate structure design are typically required to guarantee proper demodulation under any channel condition. As an example, mapping of UE-specific reference signals, antenna port 5 (normal cyclic prefix), is illustrated in Figure 1.

Following LTE, the 5th generation mobile networks, 5G, is being developed. The expression 5G includes both an enhanced version of the present LTE standard and also a new radio standard, also called "new radio", NR. When referring to 5G in this disclosure, it refers mainly to NR. One task for 5G is to improve throughput, latency and capacity compared to LTE. This is achieved by increasing the sample rate and bandwidth per carrier. 5G also supports use of higher carrier frequencies i.e. above 5-10 GHz.

Similar to LTE, future communication systems like NR, are expected to depend on reference signals, RS, for demodulation of data (including both payload data and control data) information. The RS allow the receiver to characterize the radio channel in such a way that its effect on the modulation symbols may be predicted and therefore reversed. The reference signals are typically distributed in the time, frequency, code, and antenna domains according to a reference signal pattern.

The 5 generation mobile networks will be designed as a flexible system that may be deployed in many different scenarios. It is foreseen that such a system will support a number of at least partly new features and scenarios, which will put new requirements on the reference signal patterns. For example, reference signal patterns for the 5^th generation mobile networks will need to support flexible TTI duration, high Doppler and high delay spread as well as low Doppler and low delay spread scenarios, early decoding of data and extremely low Signal to Noise Ratio, SNR.

In the state of the art wireless communications systems like LTE, reference signal patterns are static or may only be changed on a slow time scale. For example, transmission mode selection in LTE may change reference pattern. If that approach is carried over to 5G a single reference signal pattern would need to support a wide range of requirements. However, designing one single reference signal pattern that can support the extreme points of all the above listed requirements would lead to a solution that is suboptimal at many working points. It may, for example, be very dense, which would create overly large overhead in some scenarios. Thus, this would not be a spectrally efficient solution. Hence it is likely that future communication systems will define multiple reference signal patterns.

This has also been observed in the international patent application PCT/SE2013/051155, which is titled "SELECT DM-RS PATTERN BASED ON CHANNEL CHARACTERISTICS" and published under WO2014126519 Al on 14.08.21. This patent application relates to a transmitting node, such as an eNodeB, that selects a demodulation reference signal, DM-RS, pattern from a plurality of DM-RS patterns based on current channel characteristics. The eNodeB may then explicitly inform the UE (e.g. by signaling a message to the UE) what RS pattern is used for transmission. However, such signaling might cause overhead and delay, which might be undesirable in certain scenarios.

Hence, given the requirements on reference signal patterns in future mobile communication systems, there is a need for new methods for demodulation reference signal allocation and signaling. SUMMARY

An object of the present disclosure is to provide methods and devices which seeks to mitigate, alleviate, or eliminate one or more of the above-identified deficiencies in the art and disadvantages singly or in any combination and allow for a flexible demodulation reference signal pattern design.

This object is obtained by a method, in a first wireless node of a communication system for transmitting a demodulation reference signal being associated with a transmission to a second wireless node, on at least one antenna port. The method comprises obtaining a rule, shared with the second wireless node, for demodulation reference signal pattern determination, and determining, for at least one antenna port, one reference signal pattern, by applying the shared rule to one or more parameters that are available both in the first wireless node and in the second wireless node; wherein at least one of the one or more parameters is associated with the transmission to the second wireless node and wherein the demodulation reference signal pattern is for use in transmitting the demodulation reference signal. The method further comprises transmitting the demodulation reference signal on the respective antenna ports in accordance with the determined demodulation reference signal pattern. The proposed method allows for a flexible demodulation reference signal pattern design and allows adaptation to changing channel conditions and service requirements in an efficient way.

According to some aspects, the one or more parameters comprise at least one parameter required to receive and/or decode the transmission in the second wireless node. By using parameters that are anyhow needed to receive and/or decode the transmission, less extra signalling is required.

According to some aspects, the one or more parameters comprises at least one parameter indicative of channel characteristics of the transmission or of an associated reception. It has been shown that it might be efficient to adapt demodulation reference signal pattern based on channel characteristics of the transmission or of an associated reception. Hence, using parameters indicative of channel characteristics might be beneficial.

According to some aspects, the disclosure proposes a method in a second wireless node for receiving a demodulation reference signal, associated with a data transmission received from a first wireless node on one or more antenna ports. The method comprises obtaining a rule, shared with the first wireless node, for demodulation reference signal pattern determination, and determining, for each antenna port, one reference signal pattern, by applying the shared rule to one or more parameters that are available both in the second wireless node and in the first wireless node; wherein at least one of the one or more parameters is associated with the transmission to the second wireless node. The method further comprises receiving the demodulation reference signal, on the respective antenna ports, in accordance with the respective determined demodulation reference signal pattern. By determining the demodulation reference signal pattern (at least partly) based on parameters already known by the wireless node, extra signalling for this purpose is avoided. According to some aspects, the disclosure proposes a first wireless node comprising means adapted to obtain a rule, shared with the second wireless node, for demodulation reference signal pattern determination, determine, for at least one antenna port, one reference signal pattern, by applying the shared rule to one or more parameters that are available both in the first wireless node and in the second wireless node; wherein at least one of the one or more parameters is associated with the transmission to the second wireless node and wherein the demodulation reference signal pattern is for use in transmitting the demodulation reference signal, and transmit the demodulation reference signal on the respective antenna ports in accordance with the determined demodulation reference signal pattern.

According to some aspects, the disclosure proposes a second wireless node comprising means adapted to obtain a rule, shared with the first wireless node, for demodulation reference signal pattern determination, determine, for each antenna port, one reference signal pattern, by applying the shared rule to one or more parameters that are available both in the second wireless node and in the first wireless node; wherein at least one of the one or more parameters is associated with the transmission to the second wireless node, and receive the demodulation reference signal, on the respective antenna ports, in accordance with the respective determined demodulation reference signal pattern.

According to some aspects, the disclosure proposes a computer program comprising computer program code which, when executed in a wireless device, causes the wireless device to execute the methods described below and above.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing will be apparent from the following more particular description of the example embodiments, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the example embodiments.

Figure 1 illustrates an exemplary pattern of Downlink Reference Signal, DL-RS, for one antenna port;

Figure 2 shows an exemplary situation where the method of the disclosure can be performed;

Figure 3 illustrates reference signal patterns suitable in different situations;

Figure 4 illustrates on example of how which pattern, out of two, that gives the best performance depends on SNR working point;

Figure 5 is a flowchart illustrating method steps performed in a first wireless device according to the proposed technique;

Figure 6 is a flowchart illustrating method steps performed in a second wireless device according to the proposed technique; Figures 7a to 7f illustrates reference signal patterns suitable in different scenarios;

Figure 8a and 8b illustrates example node configurations of a first wireless device, according to some of the example embodiments; and

Figure 9a and 9b illustrates example node configurations of a second wireless device, according to some of the example embodiments.

DETAILED DESCRIPTION

Aspects of the present disclosure will be described more fully hereinafter with reference to the accompanying drawings. The apparatus and method/s disclosed herein can, however, be realized in many different forms and should not be construed as being limited to the aspects set forth herein. Like numbers in the drawings refer to like elements throughout.

The terminology used herein is for the purpose of describing particular aspects of the disclosure only, and it is not intended to limit the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

In this disclosure the term demodulation reference signal is used. A demodulation reference signal is a wireless device specific reference signal that a receiver uses to characterize the radio channel in connection with demodulation of data (including both payload data and control data). The demodulation reference signals are used both in uplink and in downlink and allows the receiver to characterize the radio channel in such a way that its effect on the modulation symbols may be predicted and therefore reversed. Examples of demodulation reference signals in LTE are the Demodulation Reference Signal, DM-RS, The reference signals are typically distributed in the time, frequency, code, and antenna domains according to a demodulation reference signal pattern. The demodulation reference signal pattern is in this disclosure sometimes merely referred to as a pattern.

An antenna port is generally used as a generic term for signal transmission under identical channel conditions. For each operating mode in the downlink direction for which an independent channel is assumed (e.g. SISO vs. M IMO), a separate logical antenna port is defined. Symbols that are transmitted via identical antenna ports are subject to the same channel conditions. In order to determine the characteristic channel for an antenna port, a UE must carry out separate channel estimation for each antenna port. Separate reference signals (pilot signals) that are suitable for estimating the respective channel are defined in the LTE standard for each antenna port. Future communication systems are assumed to operate in a similar way. This implies that the demodulation reference signal pattern is determined for each individual antenna port and may be different for different antenna ports.

As discussed in the background future communication systems are expected to operate in many different scenarios. With regards to demodulation reference signals, the different scenarios typically put different demands on the demodulation reference signals, in terms of how the energy of the reference signals is distributed in time within the system sub frames.

For example, if early decoding is required, the demodulation reference signal energy required to decode the transmission needs to be located "early" in the sub frame, as illustrated in the upper row of Figure 3.

However, if there instead is a high Doppler spread on the channel used for the transmission there need to be enough energy in each time instance where DMRS is transmitted, as the channel changes. Hence, the DM RS might need to be transmitted more often, as in the mid row of Figure 3. The bottom row shows energy distribution suitable in a case with both high Doppler, and early decoding.

The latter pattern would of course work in all three scenarios. However, the consequence would be a decrease in performance in comparison to the two upper cases, as the number of resources allocated to the demodulation reference signal would be higher than required. To further illustrate the benefit of using dynamic demodulation reference signal patterns, Figure 4 shows an example on how the "best" demodulation reference signal patterns to use may depend on SNR working point. By comparing "pract. ch. est." 42 with "dense RS, pract. ch. est." 41, it is visualized that for the low SNR region, denser demodulation reference signal patterns improves throughput. But in the high SNR region, throughput loss is observed due to the denser demodulation reference signal pattern that costs more in terms of overhead than the gain it can lead to. The dotted lines represent ideal channel estimation, and for those the "dense RS" is never beneficial as it only produces overhead.

This disclosure relates to how to indicate to a receiver and/or transmitter, which signal reference pattern is used, when dynamic signal reference patterns are used for demodulation reference signals associated with a transmission.

One solution would, as mentioned above, be to configure the wireless devices with a reference pattern using RRC (or other higher layer signaling). This would mitigate the issue described above, but would not enable fast change of reference signal pattern. A fast change would be one that potentially may happen on the time scales of a few subframes. However, fast change of reference signal pattern would be desirable as the radio conditions and service requirements may change rapidly, for example, when a wireless device is handed over to another network node, when urgent high priority traffic is scheduled, when wireless device speed changes drastically, or when the interference situation changes drastically. One option is then to indicate the used demodulation signal reference signal pattern in the Downlink Control Information, DCI. This solution is flexible, but with a large number of possible demodulation signal reference signal patterns it creates unnecessary overhead due to the extra signaling. Therefore, this disclosure proposes an alternative that allows for dynamic change of demodulation signal reference signal pattern to adapt to fast changing requirements of the transmission. The proposed solution is based on the observation that the optimal demodulation reference signal pattern for given situation is correlated with other parameters that are already known to the receiver. Relevant parameters for example reflect the channel characterization and/or service requirements. For example a particular modulation and coding scheme, MCS, is typically used when SNR is low. Hence, the use of this MCS is an indication of a low SNR. Thus, when this MCS is used a demodulation reference signal pattern suitable for a low SNR scenario is likely a good choice.

Hence, one core essence of the solution is to determine/signal reference signal pattern based on information that is already available at both the transmitter and the receiver (e.g. as they are needed for decoding), such as MCS and redundancy version, possibly combined with explicit signaling. Those parameters are also at least indirectly indicating the optimal demodulation reference signal pattern.

An example scenario where the proposed disclosure can be utilized is illustrated in Figure 2, which shows a wireless communication system, i.e., a cellular radio system, comprising a first wireless node, here a network node 20, and a second wireless node, here a wireless device 10. The network node 20 can be an access node or a base station (e.g. eNodeB in LTE) or any similar device/s configured to achieve the same functionalities. When the network node transmits data to the wireless device a corresponding downlink reference signal is also transmitted, which may be used by the wireless device to estimate a channel matrix H between the network node and the wireless device. Typically one matrix per group of subcarriers is estimated. The wireless communication system supports using dynamic reference signal patterns.

In this disclosure the first wireless node refers to the node transmitting the demodulation reference signal and its associated transmission and the second wireless node refers to the node receiving the demodulation reference signal and its associated transmission. Demodulation reference signals may be used both in uplink and downlink. Thus, the first wireless node is e.g. a wireless device and the second wireless node an access node, such as a base station, or the other way around. Examples of both alternatives will be given below.

In the example scenario, the network node 20 is about to transmit data to the wireless device 10. In accordance with the proposed solution the network node uses a rule, which is shared by the wireless device, in order to determine which reference signal pattern to use for enabling demodulation of the transmission. The rule involves parameters that are already available both in the network node and in the wireless device. If the rule results in only one admissible reference signal pattern, the wireless device can on its own figure out which reference signal pattern was used without any additional signaling, by using the same rule and the same parameters. In some scenarios the rule results in several admissible patterns, then some additional signaling is required. However, the amount of signaling might anyhow be reduced in comparison to using only signaling, as mentioned above.

Example operations in a first wireless node Figure 5 illustrates a method, performed in a first wireless node, for transmitting a demodulation reference signal being associated with a transmission to a second wireless node on at least one antenna port according to this disclosure. Hence, these are the steps that are performed in the transmitting device, which is either the network node (DL scenario) or the wireless device (UL scenario). The method is performed in a situation when the communication system supports several different demodulation reference signal patterns for use in connection with a transmission. Each reference signal pattern defines at least one of power offset, time resource, frequency resource and/or code to use for the demodulation reference signal.

The method comprises obtaining SI a rule, shared with the second wireless node, for demodulation reference signal pattern determination. The rule is e.g. a standardized table, which may be hardcoded or preprogrammed in the first wireless node. Then, the obtaining implies reading the rule from a memory or using a preprogrammed rule. According to some aspects the obtaining implies receiving the rule from another node. The predefined rule takes one or more parameters as input. These parameters are herein referred to as side information parameters. Side information parameters are parameters that are available both in the first wireless node and in the second wireless node. In other words, side information parameters are parameters that are needed in the first and/or second wireless nodes also for other purposes than for determining the demodulation reference signal pattern.

The method further comprises determining S2, for at least one antenna port, one reference signal pattern, by applying the shared rule to one or more parameters that are available both in the first wireless node and in the second wireless node. The determined demodulation reference signal pattern is for use in transmitting the demodulation reference signal. Stated differently, the first wireless node evaluates the rule in order to determine which demodulation reference signal pattern to use. In other words, the first wireless node comprises or has access to side information parameters. The predefined rule takes these parameters as input and outputs a list of admissible demodulation reference signal patterns. The side information parameters are e.g. parameters signalled on the control channel or also potentially semi-statically configured parameters.

Typically, one demodulation reference signal pattern is determined for each antenna port involved in the particular transmission. However, there may also be antenna ports not used for the data transmission. For those no pattern needs to be determined.

In one example implementation, at least one of the one or more parameters is associated with the transmission to the second wireless node. The transmission to the second wireless node is e.g. a transmission of data or a control signal transmission. According to some aspects, the one or more parameters comprises at least one of; a parameter related to the transmission itself, a parameter related to a control channel used in connection with the transmission, or a parameter related to a response to the transmission. In other words, the parameters might be radio parameters describing how the signal is transmitted. The parameter may also be related to the transmission of the demodulation reference signal itself. According to some aspects, the one or more parameters comprise at least one parameter required to receive and/or decode the transmission in the second wireless node. Examples of such parameters would be the modulation scheme or decoding rate. Those parameters are always already known by both transmitter and receiver.

According to some aspects, wherein the one or more parameters comprise at least one parameter indicative of channel characteristics of the transmission or of an associated reception. As described the background section it might be beneficial to adapt the pattern based on channel characteristics. This might be done implicitly by letting the rule take parameters indicative of channel characteristics as input.

The following are examples of side information parameters that the shared rule may take as input: 1) Redundancy version, rv, of the transmission - Redundancy is a usable parameter as in general denser demodulation reference signal patterns are needed for retransmissions.

2) Modulation and Coding Scheme, MCS - The MCS is correlated with (or at least indicative of) channel quality or condition. At higher SNR a less dense demodulation reference signal pattern is needed. Higher MCS are used at higher SNR. 3) Aggregation level (if the method is applied to the control channel) - Aggregation level is, similar as MCS, indicative of channel quality or conditions.

Subcarrier spacing of the scheduled numerology - Delay spread affects the demodulation reference signal pattern as for a given delay spread of the channel, the higher fraction of the subcarriers in a symbol with demodulation reference signal needs to be used for demodulation reference signal for increasing subcarrier spacing.

Transmission Time Interval, TTI, duration - TTI is a relevant parameter because if each TTI is self- contained w.r.t demodulation reference signal, then density needs to be higher for short TTIs.

The required time budget for decoding (as indicated by when an ACK/NACK is requested) - The reason is that if early decoding is required, enough demodulation reference signals to produce a good channel estimate must be available early on in the TTI.

7) Multiple Input Multiple Output, MIMO, order of the transmission - MIMO order may affect the choice demodulation reference signal pattern as more layers need to be assigned orthogonal demodulation reference signal. Also the effective data SIN and demodulation reference signal SINR is affected. 8) Physical Resource Block, PRB, bundling size - The rationale to use PRB bundling size is that if less frequency interpolation is possible, the demodulation reference signal pattern need to be denser.

9) MIMO mode - If reciprocity-based MIMO is used the channel might have hardened, i.e. became more flat and thus a lower demodulation reference signal density is sufficient.

10) Allocated bandwidth - Because with small allocated bandwidth, the demodulation reference signal pattern may need to be denser to achieve same processing gain.

In one example scenario, the rule and the side information parameters is enough to determine one demodulation reference signal pattern. Hence, according to some aspects, the shared rule identifies one (single and separate) admissible reference signal pattern for at least one antenna port. In this case no dedicated demodulation reference signal index need to be signaled. However, the predefined rule may itself be configurable (e.g. over Radio Resource Control, RRC, signaling) or may be static.

The method finally comprises transmitting S4 the demodulation reference signal on the respective antenna ports in accordance with the determined demodulation reference signal pattern. Thereby the receiver can determine the used demodulation reference signal pattern (at least partly) based on side information known to both transmitter and receiver. According to some aspects, the one or more parameters comprise at least one parameter related to properties of the first or second wireless node. This might be e.g. parameters related to service requirements (such as User Equipment, UE, class). Rationale: certain services, e.g. Critical Machine Type Communications, C-MTC, have a different trade-off between reliability and spectral efficiency compared to MBB. Another example of parameters related to properties of the first or second wireless node is UE capabilities. Demodulation reference signal density may depend on wireless device processing capabilities. Hence, a low cost MTC device may not be able to (for example) perform advanced filtering (due to memory, processing, and synchronization constraints).

According to some aspects, the step of determining S2 the demodulation reference signal pattern comprises, selecting the demodulation reference signal pattern from a plurality of reference signal patterns having different amounts of energy allocated to reference signals in at least one multicarrier symbol of the protocol used for the transmission. In other words the density of the reference patters in at least one multicarrier symbol will be different for the different demodulation reference signal patterns. As mentioned, in some scenarios the shared rule sometimes identifies one single admissible reference signal pattern for each antenna port. However, in other example scenarios the rule results in several possible demodulation references signal patterns. In other words, according to some aspects, the determining S2 is based on a combination of the application of the rule and at least one other parameter. For example, the rule determines, based on side information parameter being within a predetermined range of values, a table of admissible reference signal patterns associated with the range. If the table comprises more than one admissible parameter other parameters are used to determine one of the admissible patterns to use. In other words, according to some aspects the determining S2 comprises identifying S21, using the shared rule, a set of admissible reference signal patterns for at least one antenna port. For example one table may be associated with MCS values below, say, 15, and one table may be associated for MCS values above 15. If the table comprises several patterns, the additional parameter is used to determine which pattern to use.

The same procedure could be applied to multiple side information parameters. For example one table maybe associated with rv 0 and MCS below, say 15, and another table may be associated with rv >0 and MCS above 15. A further table may be associated with rv 0 and MCS above 15.

If the first wireless node is the node deciding on the patterns, typically a base station or access node, the first wireless node selects one of the admissible demodulation reference signals based on other parameters. The first wireless node then selects (e.g. based on other parameters described in detail below) one of the patterns. Other parameters are e.g. extra parameters that are not known to the second wireless node. The selection step e.g. depends on computed processing gain of each pattern together with the one or more of the determination factors defined below.

Because the other parameters are typically not known by the second wireless node, the first wireless node indicates the selected demodulation reference signal pattern in a control channel (see parts on receiving the control channel below) in a way that is tied to parameters that the receiver determines in order to decode the data transmission. In other words, according to some aspects, the method comprises determining S23 one demodulation reference signal pattern from the set of admissible demodulation reference signal patterns to use for transmitting the demodulation reference signal from the respective antenna ports, based on at least one further parameter and transmitting S3 from the first wireless node control signalling indicating the determined demodulation reference signal pattern, from the set of admissible reference signal patterns, used when transmitting the demodulation reference signal.

On the other hand, it may be the second wireless node that decides which one of the admissible patterns to use. This would typically be the case for a demodulation reference signal transmitted in the uplink i.e. by ta first wireless node being a wireless device. In this case the common rule or formula would still be used but the extra indication would be sent from the second wireless node (typically a base station). Then at least one other parameter mentioned above would be an indication received from the second wireless node. In other words, then the method instead comprises receiving S22 from the second wireless node control signalling indicating one reference signal pattern, from a set of admissible reference signal patterns. In principle this would mean that the at least one further parameter (used for the determining S23) is obtained from the received control signalling. In other words, according to some aspects the method comprises determining one reference signal pattern from the set of admissible reference signal patterns to use, based on the control signalling.

In one example embodiment, each demodulation reference signal pattern is associated with a range of each of a set of associated side information parameters. For each side information parameter, all demodulation reference signal patterns with a range not including the parameter value are excluded. The final list of demodulation reference signal patterns contains all remaining demodulation reference signal patterns. The used demodulation signal reference signal pattern is efficiently conveyed to the receiver using Downlink Control Information, DCI, messages by using the observation that the optimal demodulation reference signal pattern for given situation is correlated with other parameters already known to the receiver. This reduces signaling load and still allows for the support of a large number of demodulation reference signal patterns.

Hence, either the first or the second wireless node (typically the base station) determines (or selects) which demodulation reference signal pattern to be used, from a set of admissible (or possible) reference signal patterns, based on the other parameters (also referred to as determination factors). Some examples will follow.

Transport format parameters. In general at high SNR, less dense reference signal patterns are required. Hence CQI reports or similar may be used to determine the required reference signal density. In systems using reciprocity, SNR may be determined in parts from reverse link measurements. It is also possible to base the demodulation reference signal pattern selection on scheduler decisions such as MCS.

Delay spread, Doppler numerology (subcarrier spacing). The minimum pilot density in frequency domain in Hz is proportional to channel coherence frequency (invers of channel delay spread, RMS DS). The minimum pilot density in time domain in seconds is proportional to channel coherence time (invers of channel Doppler spread). As an OFDM system allocates the resources in time and frequency grid, the minimum density in time and frequency is mapped to the time and frequency grids. For different numerology, in terms of subcarrier spacing, the demodulation reference signal pattern after the mapping will be different. Delay spread may be measured in the reverse link, signaled over the reverse link or be configured per network node (as it is related to the environment the node is placed in).

777 duration and constraints on early decoding. These are known parameters to the network. With a short TTI or when early decoding is desired, all reference signals needed to decode the TTI/the first part of the TTI needs to be present early on in the TTI.

Redundancy version. If the system operates with incremental redundancy, the accumulated energy of the data channel is effectively increased by each transmission, allowing successful decoding also at lower SNR. The same energy accumulation may typically not be done for the demodulation reference signal pattern due to limited buffer capabilities and limited coherence time of the channel. The demodulation reference signal density should therefore be increased for subsequent transmission, to match the increased received energy of the data. PRB bundling. If the receiver is restricted with respect to how large bandwidths interpolation for channel estimation may be done, for example in order to allow the network to make abrupt changes of precoder, then the processing gain in channel estimation may be lower. Thus a denser demodulation reference signal pattern may be needed.

Service requirements. Services with high reliability requirements (and less stringent spectral efficiency requirements) may use different demodulation reference signal patterns. A corresponding method, performed in a second wireless node, for receiving a demodulation reference signal, associated with a data transmission received from a first wireless node on one or more antenna ports, will now be described referring to Figure 6. Hence, the method is performed in a second wireless device receiving a transmission in accordance with the method described in connection with Figure 5. In short the method in the receiving node implies that the receiving node determines one or more of the side information parameters listed above (from the control channel or from static or semi statically configured parameters). Using a shared rule this set of parameters results in a list of admissible demodulation reference signal patterns. All the side information parameters (listed in connection with Figure 5) are known to the wireless device (as they are e.g. needed for decoding of the data channel). They are also known to the transmitter. Hence, no additional signaling is required to exchange these parameters.

The method comprises obtaining Sll a rule, shared with the first wireless node, for demodulation reference signal pattern determination and determining S13, for each antenna port, one reference signal pattern, by applying the shared rule to one or more parameters that are available both in the second wireless node and in the first wireless node. According to some aspects, the side information parameters are enough to determine demodulation reference signal pattern. In other words, the set of admissible patterns contains one single admissible pattern.

Typically, at least one of the one or more parameters is associated with the corresponding transmission. According to some aspects, the parameters comprise at least one parameter required to receive and/or decode the transmission in the second wireless node. As discussed above, parameters that are anyhow needed to receive or decode the transmission anyhow need to be present in the second wireless device. Hence, no additional signalling is needed.

According to some aspects, the parameters comprises at least one of; a parameter related to the transmission itself, a parameters related to a control channel used in connection with the transmission, or a parameter related to a response to the transmission. According to some aspects, the parameters comprises at least one parameter related to properties of the first or second wireless node, see above. The method further comprises receiving S14 the demodulation reference signal, on the respective antenna ports, in accordance with the respective determined demodulation reference signal pattern. In other words, when the second wireless device knows when (e.g. which physical resources) and how the demodulation reference signal is transmitted, it can receive it accordingly. As mentioned above, sometimes the shared rule identifies one single admissible reference signal pattern per antenna port. Thus, the shared rule alone enables the second wireless node to identify the pattern.

Alternatively, the rule identifies a plurality of admissible patterns. Then an extra indication of which demodulation reference signal pattern is used, is also signalled on a control channel. This indication is used together with the side information for determining the demodulation reference signal pattern. The parameter could be in the form of a dedicated demodulation reference signal pattern index that is signaled between the first and second wireless nodes. The index e.g. points at one pattern in a table of admissible patterns.

There are then different scenarios regarding how the indication is signalled e.g. for uplink and downlink demodulation reference signals. In a first example embodiment the first wireless node is both the node tranmsitting the demodulation reference signal and the node determining the pattern, e.g. a base station. The second wireless node is then typically a wireless device. The base station will in connection with the transmission send an indication (e.g. a table index) indicating one of the plurality of admissible patterns to use for the transmission. Then the method in a second wireless node comprises receiving S12 from the wireless first wireless node control signalling indicating one reference signal pattern from a set of admissible reference signal patterns for at least one antenna port. Consequently, the determining S13 comprises identifying S131, using the shared rule, the set of admissible reference signal patterns for at least one antenna port and determining S132 the demodulation reference signal pattern, from the set of admissible reference signal patterns, based on the control signalling. For example, the receiver extracts an index from the control message and uses the index to determine the used demodulation reference signal patterns. This would typically be the case for a demodulation reference signal transmitted in the downlink.

Alternatively, if the second wireless node is the node deciding on the demodulation reference signal pattern, then the second wireless device will using control signalling (e.g. in connection with a scheduling assignment) provide an indication (e.g. an index), that should be used by the first wireless device (e.g. a wireless device), together with the shared rule, to decide which demodulation reference pattern to use. The rest of the procedure would be similar to when the index was determined and signaled by the first wireless node. This would typically be the case for a demodulation reference signal transmitted in the uplink. Example demodulation reference signal patterns

As discussed above, the 5th generation mobile networks will be designed as a flexible system that may be deployed in many different scenarios. It is foreseen that such a system will support a number of at least partly new features and scenarios, which will put new requirements on the demodulation reference signal patterns.

Figures 7a through to Figure 7f show examples on how the pattern may be adopted to different scenarios and different side information parameters. The purpose of the methods described above is that there is a benefit in having multiple patterns and in allowing dynamic adaptation/change of pattern. These examples show how the different side information parameters may be used to achieve this.

The future communications systems are expected to support a plurality of system numerologies (defined as the OFDM configuration in terms of sub-carrier spacing, symbol duration, cyclic prefix, resource block size, etc.). The different numerologies might put different demands on the demodulation reference signal pattern. For example, with the same delay spread, the RS pattern of numerology 2 will need to be denser in frequency (as measured in subcarrier bandwidths) compared to numerology 1, if numerology 2 has larger subcarrier spacing than numerology 1. On the other hand, for the same Doppler spread, numerology 2 may have sparser RS in time (as measured in OFDM symbol duration) compared to numerology 1.

Future systems typically also need to support operation under high Doppler and high delay spread, as well as in low Doppler, low delay spread scenarios. Doppler spread is a measure of the spectral broadening caused by the time rate of change of the mobile radio channel, and is defined as the range of frequencies over which the received Doppler spectrum is essentially non-zero. In telecommunications, the delay spread is a measure of the multipath richness of a communications channel. If Doppler or delay spread is high, there typically need to be enough demodulation reference signal symbols (in terms of energy) at the different points in time, as the channel is expected to vary in time. However, is Doppler and delay spread is low, it might be enough to have demodulation reference signal symbols in only one symbol.

Another important parameter is SNR. Future systems must be able to support communication at extremely low Signal to Noise Ratio, SNR, (for example in certain M-MTC scenarios) as well as communication at extremely high SNR (for example if 5G is deployed as wireless backhaul in Line Of Sight, LOS, scenarios), or in certain indoor scenarios.

A first example of two different scenarios is illustrated in Figure 7a. In the left image of Figure 7a, a pattern comprising very few demodulation reference signal symbols in one symbol is used. This is possible when the delay spread is low and SN is high and numerology 1 is used. However, if numerology 2 is used, a pattern having a higher density might be required, see right image of Figure 7a. The reason might be that numerology 2 has a higher subcarrier spacing and the same RS density in absolute frequency will translate to a higher density as measured in subcarriers.

In Figure 7b it is illustrated how the demodulation reference pattern might be adopted to the SNR level. At High SNR, a demodulation reference signal pattern with low energy is generally enough to be able to decode a transmission, see left image of Figure 7b. However, when SNR is low, then accurate channel estimation is more important. Hence, a demodulation reference signal pattern with more energy is required.

A further example is illustrated in Figure 7c. In this Scenario Doppler is High. When Doppler is high, the reference symbols need to be spread out over time, even if the SNR is high, as the channel varies over time.

The future communications systems are also expected to support early decoding of data, when latency requirements dictate it. Hence, it might be required to decode one symbol before the end of the TTI, which implies that the demodulation reference signal symbols need to be scheduled early within the system TTIs, as shown in Figure 7d. More specifically enough demodulation reference signal symbols to receive and decode the data need to be scheduled early in the TTIs. Hence, in the example of Figure 7e, the pattern to the left is not enough, as SNR is low. Therefore, a pattern with high demodulation reference signal energy early in the TTI is required, see left image of Figure 7e.

A further parameter that has an impact on choice of demodulation reference pattern is Transmission Time Interval, TTI, duration. Future systems are expected to support flexible TTI. TTI refers to the duration of a transmission on the radio link. 5G systems are expected to support both very short and very long TTIs in one system. Hence, the patterns might need to be adapted to the TTI of a particular transmission, which is illustrated in Figure 5f.

5G is also expected to support very large antenna arrays with UE specific beamforming, different means for Channel State Indication, CSI, acquisition, including reciprocity based solutions and feedback based solutions, convergence between uplink-, sidelink-, and downlink- transmissions, transmission at a wide range of data rates, including varying bandwidths, modulation schemes, MIMO orders, and code rates, very reliable transmissions, high spectral efficiency and self-contained (w.r.t demodulation reference signal pattern) sub frames. Example Node Configurations

Turning now to Figure 8a, which is a schematic diagram that illustrates some modules of an example embodiment of a first wireless node being configured for system for transmitting a demodulation reference signal being associated with a transmission to a second wireless node, on at least one antenna port. The first wireless node 20 is either a base station, such as an eNodeB in LTE, configured to transmit a downlink demodulation reference signal, or a wireless device configured to transmit an uplink demodulation reference signal. The first wireless node is configured to implement all aspects of the methods described in relation to Figure 5.

The first wireless node 20 comprises a radio communication interface (COM) 21 configured for communication with a second wireless node. The radio communication interface 21 may be adapted to communicate over one or several radio access technologies. If several technologies are supported, the node typically comprises several communication interfaces, e.g. one WLAN or Bluetooth communication interface and one cellular communication interface.

As shown in Figure 8a, the first wireless node 20 according to some aspects comprises a network communication interface (NW COM) 24. This is relevant when the first wireless node is a network node or access point. The network communication interface 24 is configured for communication with other first wireless nodes e.g. in a core network. This communication is often wired e.g. using fiber. However, it may as well be wireless.

The first wireless node 20 comprises a controller, CTL, or a processing circuitry 22 that may be constituted by any suitable Central Processing Unit, CPU, microcontroller, Digital Signal Processor, DSP, etc. capable of executing computer program code. The computer program may be stored in a memory, MEM 23. The memory 23 can be any combination of a Read And write Memory, RAM, and a Read Only Memory, ROM. The memory 23 may also comprise persistent storage, which, for example, can be any single one or combination of magnetic memory, optical memory, or solid state memory or even remotely mounted memory. According to some aspects, the disclosure relates to a computer program comprising computer program code which, when executed, causes a first wireless node to execute the methods described above. According to some aspects the disclosure pertains to a computer program product or a computer readable medium holding said computer program. The processing circuitry 22 is configured to cause the first wireless node 20 to obtain a rule, shared with the second wireless node, for demodulation reference signal pattern determination, determine for at least one antenna port, one reference signal pattern, by applying the shared rule to one or more parameters that are available both in the first wireless node and in the second wireless node; wherein at least one of the one or more parameters is associated with the transmission to the second wireless node and wherein the demodulation reference signal pattern is for use in transmitting the demodulation reference signal, and transmit the demodulation reference signal on the respective antenna ports in accordance with the determined demodulation reference signal pattern. According to some aspects, the one or more parameters comprise at least one parameter required to receive and/or decode the transmission in the second wireless node.

According to some aspects, the one or more parameters comprises at least one of; a parameter related to the transmission itself, a parameter related to a control channel used in connection with the transmission, or a parameter related to a response to the transmission. According to some aspects, the transmission is a transmission of data or a control signal transmission.

According to some aspects, the one or more parameters comprise at least one parameter indicative of channel characteristics of the transmission or of an associated reception.

According to some aspects, the one or more parameters comprise at least one parameter related to properties of the first or second wireless node. According to some aspects, the determined demodulation reference signal pattern is one demodulation reference signal pattern from a plurality of reference signal patterns having different amounts of energy allocated to reference signals in at least one multicarrier symbol of the protocol used for the transmission.

According to some aspects, wherein the shared rule identifies one admissible demodulation reference signal pattern for at least one antenna port.

According to some aspects, wherein the first wireless node is adapted to determine the demodulation reference signal pattern, based on a combination of the application of the rule and at least one other parameter.

According to some aspects, the first wireless node is adapted to determine the demodulation reference signal pattern by identifying, using the shared rule, a set of admissible reference signal patterns for at least one antenna port, and determining one reference signal pattern from the set of admissible reference signal patterns to use for transmitting the demodulation reference signal from the respective antenna ports, based on at least one further parameter. Then the first wireless node is adapted to transmit, to the second wireless node, control signaling indicating the determined demodulation reference signal pattern, from the set of admissible reference signal patterns, used when transmitting the demodulation reference signal.

According to some aspects, the determined demodulation reference signal pattern defines at least one of power offset, time resource, frequency resource and/or code to use for the demodulation reference signal.

According to some aspects the processing circuitry 22 or the first wireless node 20 comprises modules configured to perform the methods described above. The modules are illustrated in Figure 8b. The modules are implemented in hardware or in software or in a combination thereof. The modules are according to one aspect implemented as a computer program stored in a memory 23 which run on the processing circuitry 22.

According to some aspects the first wireless node 20 or the processing circuitry 22 comprises an obtainer 221 configured to obtain a rule, shared with the second wireless node, for demodulation reference signal pattern determination,

According to some aspects the first wireless node 20 or the processing circuitry 22 comprises a determiner 222 configured to determine, for at least one antenna port, one reference signal pattern, by applying the shared rule to one or more parameters that are available both in the first wireless node and in the second wireless node; wherein at least one of the one or more parameters is associated with the transmission to the second wireless node and wherein the demodulation reference signal pattern is for use in transmitting the demodulation reference signal, According to some aspects the first wireless node 20 or the processing circuitry 22 comprises a first transmitter module 223 configured to transmit from the first wireless node control signalling indicating the determined demodulation reference signal pattern, from the set of admissible reference signal patterns, used when transmitting the demodulation reference signal.

According to some aspects the first wireless node 20 or the processing circuitry 22 comprises a second transmitter module 224 configured to transmit the demodulation reference signal on the respective antenna ports in accordance with the determined demodulation reference signal pattern. Figure 9a illustrates an example of a second wireless node 10, which incorporates some of the example embodiments discussed above. Figure 9a discloses a second wireless node 10 being configured for receiving a demodulation reference signal, associated with a data transmission received from a first wireless node on one or more antenna ports. The second wireless node 10 is either a base station, such as an eNodeB in LTE, configured to receive an uplink demodulation reference signal, or a wireless device configured to receive a downlink demodulation reference signal. The second wireless node 10 is configured to implement all aspects of the methods described in relation to Figure 6.

As shown in Figure 9a, the second wireless node 10 comprises a radio communication interface or radio circuitry 11 configured to receive and transmit any form of communications or control signals within a network. It should be appreciated that the radio circuitry 11 is according to some aspects comprised as any number of transceiving, receiving, and/or transmitting units or circuitry. It should further be appreciated that the radio circuitry 11 can e.g. be in the form of any input/output communications port known in the art. The radio circuitry 11 e.g. comprises F circuitry and baseband processing circuitry (not shown). As shown in Figure 9a, the second wireless node 10 according to some aspects comprises a network communication interface (NW COM) 14. This is relevant when the second wireless node is a network node or access point. The network communication interface 14 is configured for communication with other first wireless nodes e.g. in a core network. This communication is often wired e.g. using fiber. However, it may as well be wireless. The second wireless node 10 according to some aspects further comprises at least one memory unit or circuitry 13 that is in communication with the radio circuitry 11. The memory 13 can e.g. be configured to store received or transmitted data and/or executable program instructions. The memory 13 is e.g. configured to store any form of contextual data. The memory 13 can e.g. be any suitable type of computer readable memory and can e.g. be of volatile and/or non-volatile type The second wireless node 10 further comprises processing circuitry 12 which configured to cause the second wireless node to obtain a rule, shared with the first wireless node, for demodulation reference signal pattern determination, to determine, for each antenna port, one reference signal pattern, by applying the shared rule to one or more parameters that are available both in the second wireless node and in the first wireless node; wherein at least one of the one or more parameters is associated with the transmission to the second wireless node, and to receive the demodulation reference signal, on the respective antenna ports, in accordance with the respective determined demodulation reference signal pattern. The processing circuitry 12 is e.g. any suitable type of computation unit, e.g. a microprocessor, Digital Signal Processor, DSP, Field Programmable Gate Array, FPGA, or Application Specific Integrated Circuit, ASIC, or any other form of circuitry. It should be appreciated that the processing circuitry need not be provided as a single unit but is according to some aspects provided as any number of units or circuitry. The controller, CTL, or processing circuitry 12 is e.g. constituted by any suitable type of computation unit, e.g. a microprocessor, Central Processing Unit, CPU, microcontroller, Digital Signal Processor, DSP, Field Programmable Gate Array, FPGA, or Application Specific Integrated Circuit, ASIC, or any other form of circuitry capable of executing computer program code. The computer program is e.g. stored in a memory, M EM, 13. The memory 13 can be any combination of a Read And write Memory, RAM, and a Read Only Memory, ROM. The memory 13 in some situations also comprise persistent storage, which, for example, can be any single one or combination of magnetic memory, optical memory, or solid state memory or even remotely mounted memory. It should be appreciated that the processing circuitry need not be provided as a single unit but is according to some aspects provided as any number of units or circuitry. According to some aspects, the disclosure relates to a computer program comprising computer program code which, when executed, causes a second wireless node to execute the methods described above and below.

According to some aspects, the parameters comprise at least one parameter required to receive and/or decode the transmission in the second wireless node.

According to some aspects, the parameters comprises at least one of; a parameter related to the transmission itself, a parameters related to a control channel used in connection with the transmission, or a parameter related to a response to the transmission.

According to some aspects, the parameters comprise at least one parameter related to properties of the first or second wireless node.

According to some aspects, wherein the shared rule identifies one admissible reference signal pattern per antenna port.

According to some aspects, the second wireless node is adapted to receive from the wireless first wireless node control signalling indicating one reference signal pattern from a set of admissible reference signal patterns for at least one antenna port. Then, the second wireless node is adapted to determine the one reference signal pattern per antenna port by first identifying, using the shared rule, the set of admissible reference signal patterns for at least one antenna port, and then determining the demodulation reference signal pattern, from the set of admissible reference signal patterns, based on the received control signalling.

According to some aspects, wherein the determined demodulation reference signal pattern defines at least one of time resource, frequency resource and/or code used when for transmitting the demodulation reference signal. According to some aspects the second wireless node 10 or the processing circuitry 12 comprises modules configured to perform the methods described above. The modules are implemented in hardware or in software or in a combination thereof. The modules are illustrated in Figure 9b. The modules are according to one aspect implemented as a computer program stored in a memory 13 which run on the processing circuitry 12. According to some aspects the second wireless node 10 or the processing circuitry 12 comprises an obtainer 121 configured to obtain a rule, shared with the first wireless node, for demodulation reference signal pattern determination.

According to some aspects the second wireless node 10 or the processing circuitry 12 comprises a first receiver module 122 configured to receive from the wireless first wireless node control signalling indicating one reference signal pattern from a set of admissible reference signal patterns for at least one antenna port.

According to some aspects the second wireless node 10 or the processing circuitry 12 comprises a determiner 123 configured to determine, for each antenna port, one reference signal pattern, by applying the shared rule to one or more parameters that are available both in the second wireless node and in the first wireless node; wherein at least one of the one or more parameters is associated with the transmission to the second wireless node.

According to some aspects the second wireless node 10 or the processing circuitry 12 comprises a second receiver module 124 configured to receive the demodulation reference signal, on the respective antenna ports, in accordance with the respective determined demodulation reference signal pattern.

Aspects of the disclosure are described with reference to the drawings, e.g., block diagrams and/or flowcharts. It is understood that several entities in the drawings, e.g., blocks of the block diagrams, and also combinations of entities in the drawings, can be implemented by computer program instructions, which instructions can be stored in a computer-readable memory, and also loaded onto a computer or other programmable data processing apparatus. Such computer program instructions can be provided to a processor of a general purpose computer, a special purpose computer and/or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer and/or other programmable data processing apparatus, create means for implementing the functions/acts specified in the block diagrams and/or flowchart block or blocks. In some implementations and according to some aspects of the disclosure, the functions or steps noted in the blocks can occur out of the order noted in the operational illustrations. For example, two blocks shown in succession can in fact be executed substantially concurrently or the blocks can sometimes be executed in the reverse order, depending upon the functionality/acts involved. Also, the functions or steps noted in the blocks can according to some aspects of the disclosure be executed continuously in a loop.

In the drawings and specification, there have been disclosed exemplary aspects of the disclosure. However, many variations and modifications can be made to these aspects without substantially departing from the principles of the present disclosure. Thus, the disclosure should be regarded as illustrative rather than restrictive, and not as being limited to the particular aspects discussed above. Accordingly, although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation.

The description of the example embodiments provided herein have been presented for purposes of illustration. The description is not intended to be exhaustive or to limit example embodiments to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of various alternatives to the provided embodiments. The examples discussed herein were chosen and described in order to explain the principles and the nature of various example embodiments and its practical application to enable one skilled in the art to utilize the example embodiments in various manners and with various modifications as are suited to the particular use contemplated. The features of the embodiments described herein may be combined in all possible combinations of methods, apparatus, modules, systems, and computer program products. It should be appreciated that the example embodiments presented herein may be practiced in any combination with each other.

A "wireless device" as the term may be used herein, is to be broadly interpreted to include a radiotelephone having ability for Internet/intranet access, web browser, organizer, calendar, a camera (e.g., video and/or still image camera), a sound recorder (e.g., a microphone), and/or Global Positioning System, GPS, receiver; a Personal Communications System, PCS, user equipment that according to some aspects combine a cellular radiotelephone with data processing; a Personal Digital Assistant, PDA, that can include a radiotelephone or wireless communication system; a laptop; a camera (e.g., video and/or still image camera) having communication ability; and any other computation or communication device capable of transceiving, such as a personal computer, a home entertainment system, a television, etc. It should be noted that the word "comprising" does not necessarily exclude the presence of other elements or steps than those listed and the words "a" or "an" preceding an element do not exclude the presence of a plurality of such elements. It should further be noted that any reference signs do not limit the scope of the claims, that the example embodiments may be implemented at least in part by means of both hardware and software, and that several "means", "units" or "devices" may be represented by the same item of hardware.

The various example embodiments described herein are described in the general context of method steps or processes, which may be implemented in one aspect by a computer program product, embodied in a computer-readable medium, including computer-executable instructions, such as program code, executed by computers in networked environments. A 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 (DVD), etc. Generally, program modules may include routines, programs, objects, components, data structures, etc. that performs 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.

Claims

1. A method in a first wireless node of a communication system for transmitting a demodulation reference signal being associated with a transmission to a second wireless node, on at least one antenna port, the method comprising:

- obtaining (SI) a rule, shared with the second wireless node, for demodulation reference signal pattern determination,

- determining (S2), for at least one antenna port, one reference signal pattern, by applying the shared rule to one or more parameters that are available both in the first wireless node and in the second wireless node; wherein at least one of the one or more parameters is associated with the transmission to the second wireless node and wherein the demodulation reference signal pattern is for use in transmitting the demodulation reference signal,

- transmitting (S4) the demodulation reference signal on the respective antenna ports in accordance with the determined demodulation reference signal pattern.

2. The method of claim 1, wherein the one or more parameters comprises at least one parameter required to receive and/or decode the transmission in the second wireless node.

3. The method of claim 1 or 2, wherein the one or more parameters comprises at least one of; a parameter related to the transmission itself, a parameter related to a control channel used in connection with the transmission, or a parameter related to a response to the transmission.

4. The method of any of the preceding claims, wherein the transmission is a transmission of data or a control signal transmission.

5. The method of any of the preceding claims, wherein the one or more parameters comprises at least one parameter indicative of channel characteristics of the transmission or of an associated reception.

6. The method of any of the preceding claims, wherein the one or more parameters comprises at least one parameter related to properties of the first or second wireless node.

7. The method of any of the preceding claims, the determining (S2) comprises selecting the demodulation reference signal pattern from a plurality of reference signal patterns having different amounts of energy allocated to reference signals in at least one multicarrier symbol of the protocol used for the transmission.

8. The method of any of the preceding claims, wherein the shared rule identifies one admissible reference signal pattern for at least one antenna port.

9. The method of any of the preceding claims, wherein the determining (S2) is based on a combination of the application of the rule and at least one other parameter.

10. The method of any of the preceding claims 1-9, wherein the determining (S2) comprises: identifying (S21), using the shared rule, a set of admissible reference signal patterns for at least one antenna port, determining (S23) one reference signal pattern from the set of admissible reference signal patterns to use for transmitting the demodulation reference signal from the respective antenna ports, based on at least one further parameter.

11. The method of claim 10, wherein the method comprises: receiving (S22) from the second wireless node control signalling indicating a demodulation reference signal pattern, from the set of admissible reference signal patterns, to be used by the first wireless node when transmitting the demodulation reference signal, wherein the at least one further parameter is obtained from the received control signalling.

12. The method of claim 10, wherein the method comprises: transmitting (S3) from the first wireless node control signalling indicating the determined demodulation reference signal pattern, from the set of admissible reference signal patterns, used when transmitting the demodulation reference signal.

13. The method of any of the preceding claims, wherein the determined demodulation reference signal pattern defines at least one of power offset, time resource, frequency resource and/or code to use for the demodulation reference signal.

14. A method in a second wireless node for receiving a demodulation reference signal, associated with a data transmission received from a first wireless node on one or more antenna ports, the method comprising: obtaining (Sll) a rule, shared with the first wireless node, for demodulation reference signal pattern determination, determining (S13), for each antenna port, one reference signal pattern, by applying the shared rule to one or more parameters that are available both in the second wireless node and in the first wireless node; wherein at least one of the one or more parameters is associated with the transmission to the second wireless node, and - receiving (S14) the demodulation reference signal, on the respective antenna ports, in accordance with the respective determined demodulation reference signal pattern.

15. The method of claim 14, wherein the parameters comprises at least one parameter required to receive and/or decode the transmission in the second wireless node.

16. The method of claim 14 or 15, wherein the parameters comprises at least one of; a parameter related to the transmission itself, a parameters related to a control channel used in connection with the transmission, or a parameter related to a response to the transmission.

17. The method of any of claims 14 to 16, wherein the parameters comprises at least one parameter related to properties of the first or second wireless node.

18. The method of any of claims 14 to 17, wherein the shared rule identifies one admissible reference signal pattern per antenna port.

19. The method of any of claims 14 to 18, comprising: receiving (S12) from the wireless first wireless node control signalling indicating one reference signal pattern from a set of admissible reference signal patterns for at least one antenna port, and wherein the determining (S13) comprises: identifying (S131), using the shared rule, the set of admissible reference signal patterns for at least one antenna port, determining (S132) the demodulation reference signal pattern, from the set of admissible reference signal patterns, based on the control signalling. 20. The method of any of claims 12 to 17, wherein the determined demodulation reference signal pattern defines at least one of time resource, frequency resource and/or code used when for transmitting the demodulation reference signal.

21. A first wireless node in a cellular communication network configured for system for transmitting a demodulation reference signal being associated with a transmission to a second wireless node, on at least one antenna port, the first wireless node comprising processing circuitry and memory, said memory comprising instructions executable by said processor whereby said network node is operable to: obtain a rule, shared with the second wireless node, for demodulation reference signal pattern determination, determine, for at least one antenna port, one reference signal pattern, by applying the shared rule to one or more parameters that are available both in the first wireless node and in the second wireless node; wherein at least one of the one or more parameters is associated with the transmission to the second wireless node and wherein the demodulation reference signal pattern is for use in transmitting the demodulation reference signal, and transmit the demodulation reference signal on the respective antenna ports in accordance with the determined demodulation reference signal pattern. A first wireless node (10) configured for system for transmitting a demodulation reference signal being associated with a transmission to a second wireless node, on at least one antenna port, the first wireless node (10) comprising means adapted to: obtain a rule, shared with the second wireless node, for demodulation reference signal pattern determination, determine, for at least one antenna port, one reference signal pattern, by applying the shared rule to one or more parameters that are available both in the first wireless node and in the second wireless node; wherein at least one of the one or more parameters is associated with the transmission to the second wireless node and wherein the demodulation reference signal pattern is for use in transmitting the demodulation reference signal, and transmit the demodulation reference signal on the respective antenna ports in accordance with the determined demodulation reference signal pattern. The first wireless node of claim 22, wherein the one or more parameters comprises at least one parameter required to receive and/or decode the transmission in the second wireless node. The first wireless node of claim 22 or 23, wherein the one or more parameters comprises at least one of; a parameter related to the transmission itself, a parameter related to a control channel used in connection with the transmission, or a parameter related to a response to the transmission.

25. The first wireless node of any of claims 22 to 24, wherein the transmission is a transmission of data or a control signal transmission.

26. The first wireless node of any of claims 22 to 25, wherein the one or more parameters comprises at least one parameter indicative of channel characteristics of the transmission or of an associated reception.

27. The first wireless node of any of claims 22 to 26, wherein the one or more parameters comprises at least one parameter related to properties of the first or second wireless node.

28. The first wireless node of any of claims 22 to 27, wherein the determined demodulation reference signal pattern is one demodulation reference signal pattern from a plurality of reference signal patterns having different amounts of energy allocated to reference signals in at least one multicarrier symbol of the protocol used for the transmission.

29. The first wireless node of any of claims 22 to 28, wherein the shared rule identifies one admissible demodulation reference signal pattern for at least one antenna port.

30. The first wireless node of any of claims 22 to 29, wherein the first wireless node is adapted to determine the demodulation reference signal pattern, based on a combination of the application of the rule and at least one other parameter.

31. The first wireless node of any of claims 22 to 30, wherein the first wireless node is a base station.

32. The first wireless node of any of claims 22 to 31, wherein the first wireless node is adapted to determine the demodulation reference signal pattern by identifying, using the shared rule, a set of admissible reference signal patterns for at least one antenna port and determining one reference signal pattern from the set of admissible reference signal patterns to use for transmitting the demodulation reference signal from the respective antenna ports, based on at least one further parameter.

33. The first wireless node of any of claims 22 to 32, wherein the determined demodulation reference signal pattern defines at least one of power offset, time resource, frequency resource and/or code to use for the demodulation reference signal.

34. A second wireless node in a cellular communication network configured for receiving a demodulation reference signal, associated with a data transmission received from a first wireless node on one or more antenna ports, the first wireless node comprising processing circuitry and memory, said memory comprising instructions executable by said processor whereby said network node is operable to: obtain a rule, shared with the first wireless node, for demodulation reference signal pattern determination, - determine , for each antenna port, one reference signal pattern, by applying the shared rule to one or more parameters that are available both in the second wireless node and in the first wireless node; wherein at least one of the one or more parameters is associated with the transmission to the second wireless node, and receive the demodulation reference signal, on the respective antenna ports, in accordance with the respective determined demodulation reference signal pattern.

35. A second wireless node (10) configured for receiving a demodulation reference signal, associated with a data transmission received from a first wireless node on one or more antenna ports, the second wireless node (10) comprising means adapted to: obtain a rule, shared with the first wireless node, for demodulation reference signal pattern determination, determine, for each antenna port, one reference signal pattern, by applying the shared rule to one or more parameters that are available both in the second wireless node and in the first wireless node; wherein at least one of the one or more parameters is associated with the transmission to the second wireless node, and - receive the demodulation reference signal, on the respective antenna ports, in accordance with the respective determined demodulation reference signal pattern.

36. The second wireless node of claim 35, wherein the parameters comprises at least one parameter required to receive and/or decode the transmission in the second wireless node.

37. The second wireless node of claim 35 or 36, wherein the parameters comprises at least one of; a parameter related to the transmission itself, a parameters related to a control channel used in connection with the transmission, or a parameter related to a response to the transmission.

38. The second wireless node of at least one of claims 35 to 37, wherein the parameters comprises at least one parameter related to properties of the first or second wireless node.

39. The second wireless node of at least one of claims 35 to 38, wherein the shared rule identifies one admissible reference signal pattern per antenna port.

40. The second wireless node of at least one of claims 35 to 39, wherein the second wireless node is adapted to receive from the wireless first wireless node control signalling indicating one reference signal pattern from a set of admissible reference signal patterns for at least one antenna port, and wherein the second wireless node is adapted to determine (S13) the one reference signal pattern per antenna port by identifying (S131), using the shared rule, the set of admissible reference signal patterns for at least one antenna port, and determining (S132) the demodulation reference signal pattern, from the set of admissible reference signal patterns, based on the control signalling.

41. The second wireless node of at least one of claims 35 to 40, wherein the determined demodulation reference signal pattern defines at least one of time resource, frequency resource and/or code used when for transmitting the demodulation reference signal.

42. A computer program comprising computer program code which, when executed by at least one processor of a network node, causes the network node to carry out the methods according to any of the claims 1-13.

43. A computer program comprising computer program code which, when executed by at least one processor of a wireless device, causes the wireless device (10) to carry out the method according to any of the claims 14-20.

44. A carrier containing the computer program of claims 40 or 41, wherein the carrier is one of an electronic signal, optical signal, radio signal, or computer readable storage medium.