CSI-based Precoding in Search Space Subsets

Abstract

Systems and methods for decoding transmissions are provided. In some embodiments, a method performed by a wireless device includes: determining a plurality of machine-type communication (MTC) physical downlink control channel (MPDCCH) transmission candidates to be monitored. For at least one candidate of the plurality of MPDCCH transmission candidates, the method includes: determining whether the candidate belongs to a first group of candidates or a second group of candidates. If the candidate belongs to the first group of candidates, the method includes: attempting to decode the MPDCCH transmission using a precoding scheme based on channel state information (CSI). If the candidate belongs to the second group of candidates, the method includes: attempting to decode the MPDCCH transmission using a predetermined precoding scheme. This enables more robust precoding techniques and can be regarded as a technique having a fallback solution for cases where CSI is lost or unreliable.

Description

[0001] Related Applications

[0002] This application claims the benefit of U.S. Provisional Patent Application Ser. No. 62 / 826,530, filed Mar. 29, 2019, and U.S. Provisional Patent Application Ser. No. 62 / 826,571, filed Mar. 29, 2019, the entire disclosures of which are hereby incorporated by reference. Technical Field

[0003] This disclosure relates to performing channel state information (CSI)-based precoding in a subset of a search space. Background Art

[0004] Recently, there has been a great deal of work in the Third Generation Partnership Project (3GPP) on technologies specifying coverage for machine-to-machine (M2M) and / or Internet of Things (IoT) related use cases. The latest work in 3GPP Releases 13, 14, and 15 includes enhancements to support machine type communication (MTC) with new user equipment (UE) categories (Cat-M1, Cat-M2), thus supporting reduced bandwidth of six physical resource blocks (PRBs) (up to 24 PRBs for Cat-M2) and narrowband IoT (NB-IoT) UEs providing a new radio interface (as well as UE categories Cat-NB1 and Cat-NB2).

[0005] The Long Term Evolution (LTE) enhancements introduced for MTC in 3GPP Releases 13, 14, and 15 are commonly referred to as "LTE-M", "LTE-MTC", or "eMTC" to denote support for bandwidth-constrained UEs and support for coverage enhancements and corresponding functionality associated with UE categories Cat-M1 and Cat-M2. In 3GPP standardization documents, devices compliant with this functionality are also referred to as bandwidth-reduced low complexity and / or coverage enhanced (BL / CE) UEs. This is to separate the discussion from NB-IoT (for which any version notation is used here), although the supported features are similar at a general level.

[0006] LTE-M (as well as NB-IoT) uses many of the basic functions and attributes of the LTE system. This includes basic physical layer attributes, which include the time / frequency grid, where each subcarrier and orthogonal frequency division multiplexing (OFDM) symbol corresponds to a resource element (RE). The grid can be divided in the frequency domain into resource blocks (RBs) consisting of 12 subcarriers, also denoted as physical resource blocks (PRBs), and in the time domain into time slots (usually consisting of 7 OFDM symbols) and subframes consisting of 2 time slots. In LTE, the duration of a time slot and a subframe is 0.5 ms and 1 ms, respectively. An RB or PRB is also used to denote a set of REs spanning 12 subcarriers and 7 OFDM symbols in a time slot, while a PRB pair is used to denote a set of REs spanning 12 subcarriers and 14 OFDM symbols in a subframe. An LTE UE needs to support reception and transmission over a bandwidth corresponding to up to 100 PRBs, while a Cat-M1 device should only support a bandwidth corresponding to 6 PRBs, which is denoted as narrowband (NB) in the 3GPP standard.

[0007] Some LTE physical channels and signals are reused for LTE-M with no or only minor changes to the physical layer attributes. For the downlink, this includes the primary synchronization signal and secondary synchronization signal (PSS / SSS) for data transmission, the cell-specific reference signal (CRS), the physical broadcast channel (PBCH), and the physical downlink shared channel (PDSCH). These physical channels and signals can be reused for LTE-M because they can be received within a bandwidth of only 6 PRBs. However, it is necessary to introduce other changes to accommodate the specific limitations and / or desired characteristics of communication using LTE-M devices. One such change involves the downlink control information (DCI), which is transmitted on the physical downlink control channel (PDCCH) in LTE. Since the PDCCH in LTE spans the entire system bandwidth transmitted from the base station (also known as eNodeB or eNB), it cannot be required that an LTE-M UE receive this PDCCH. Therefore, in Release 13, a new control channel, namely the MTC physical downlink control channel (MPDCCH), was introduced, which is mainly based on the enhanced physical downlink control channel (EPDCCH) defined in LTE Release 11.

[0008] Another desired feature in Release 13 is support for enhanced coverage for IoT devices. This is mainly achieved by introducing repetition of the physical channel by explicitly repeating the transmission of specific data or control packets in subsequent subframes, and / or by allowing the receiver to accumulate subsequent (conventional) transmissions of the channel and signals. The former includes control and data transmissions on the Machine-Type Communication (MTC) Physical Downlink Control Channel (MPDCCH) and PDSCH respectively, while the latter also includes signals that have been repeatedly transmitted in conventional LTE, such as PSS, SSS, and PBCH. By repeating the transmission and reception of the same packet, the LTE-M receiver can combine the information from these transmissions to obtain a sufficiently good cumulative signal-to-noise ratio (SNR) to successfully demodulate and decode the received packet even under poor coverage conditions. To distinguish LTE-M devices that require different amounts of coverage enhancement techniques, two different coverage enhancement modes are defined, namely CE mode A and CE mode B. Devices that do not require or only require little coverage enhancement are typically configured in CE mode A, while devices under poor coverage that require a larger amount of coverage enhancement (e.g., more repetition of the physical channel) are configured in CE mode B.

[0009] The LTE-M UE can be configured to monitor MPDCCH transmissions in 2, 4, or 6 PRB pairs adjacent in frequency. The eNB transmits a specific control message in one of a limited number of possible positions corresponding to a subset of resource elements within these configured PRB pairs. The LTE-M UE monitors MPDCCH candidates and attempts to blindly decode the MPDCCH candidates in a so-called search space (which includes a well-defined subset of these possible positions). There is a common search space (CSS) known to all (LTE-M) UEs, where common control messages are mainly transmitted, such as MPDCCH transmissions related to paging or random access. There is also a UE-specific search space (USS), which is used to schedule dedicated data transmissions in the downlink on the PDSCH or in the uplink on the Physical Uplink Shared Channel (PUSCH).

[0010] When a UE monitors MPDCCH in a specific search space, the UE does this by attempting to decode multiple MPDCCH candidates using one or more specific radio network temporary identifiers (RNTIs). The specific RNTI is associated with a bitmap that is used to scramble the cyclic redundancy check (CRC) of the MPDCCH candidates such that the UE can successfully decode the MPDCCH only when it applies the RNTI with which the MPDDCH was transmitted. There are different RNTIs for different purposes, and in this article, the dedicated RNTI will be mainly considered. Without limitation, it is assumed that the cell RNTI (C-RNTI) is used, where the C-RNTI is unique for each UE in the connected mode in the serving cell. A UE in the connected mode and configured in CE mode A needs to monitor MPDCCH candidates scrambled with the C-RNTI in both the UE-specific search space USS and the type 0 MPDCCH common search space (abbreviated as CSS-0 in this article for brevity).

[0011] In addition, MPDCCH candidates can include different numbers of resource elements to achieve different code rates. This is referred to as different aggregation levels (ALs), where the allowed set of ALs for MPDCCH is {1, 2, 4, 8, 16, 24}, where the aggregation level refers to the number of enhanced control channel elements (ECCEs) used for the MPDCCH candidate. Each ECCE is a set of resource elements (REs) corresponding to the number of REs contained in approximately 1 / 4 of a physical resource block (PRB), which means that the allowed ALs for MPDCCH candidates occupy REs corresponding to (approximately) {1 / 4, 1 / 2, 1, 2, 4, 6} PRB pairs.

[0012] Before attempting to decode an MPDCCH message, the LTE-M UE first receives a reference signal located in specific resource elements to estimate the propagation channel between the transmitting eNB and the UE. For MPDCCH transmission, the demodulation reference signal (DM-RS) is used, which will be described in more detail below.

[0013] The eNB can also use one of two different transmission modes (denoted as the local mode and the distributed mode respectively) to transmit MPDCCH messages. Briefly, the different modes refer to which resource elements (REs) are used for a specific MPDCCH candidate and how the data transmitted on these REs is related to the corresponding DM-RS. The local transmission uses the REs in as few PRB pairs as possible (i.e., only one PRB pair for aggregation levels up to 4), while the distributed transmission uses the REs in all the PRB pairs in which the UE is configured to monitor the MPDCCH. The relationship between the transmission mode and the use of DM-RS is further discussed below.

[0014] In a communication system, a reference signal or a pilot signal is transmitted to provide a phase reference that can be used by a receiver to synchronize the timing of transmissions and to adjust any frequency error between a transmitter and the receiver. In most communication systems, the reference signal is also used to provide a phase reference so that the receiver can estimate the propagation channel between the transmitter and the receiver in order to be able to demodulate and decode the transmitted data message. In a cellular system, the reference signal transmitted from a base station to a UE in a cell can be classified as a common reference signal or a dedicated reference signal. The common (usually referred to as cell-specific) reference signal is intended to be used by all UEs communicating with the cell and is typically broadcast with the same power in all directions within the cell, while the dedicated (usually referred to as user-specific) reference signal is intended to be received and used by only one user. Within this disclosure, LTE will be used as an exemplary cellular system, but the concepts provided herein apply to any communication system with different classes of reference signals, where attributes can be mapped to those described.

[0015] In LTE, there are different types of common reference signals, where the so-called cell-specific reference signal (CRS) is the most important type. It is transmitted in (almost) all subframes and is mainly used to support channel estimation for demodulating different physical control and data channels, but is also used, for example, to measure the signal strength and quality of its own cell and neighboring cells. In addition, there are two types of dedicated reference signals, namely, the so-called demodulation reference signals (DM-RS) for the physical downlink shared channel (PDSCH) and the enhanced physical downlink control channel (EPDCCH), respectively. The latter is also used as the demodulation reference signal for the MPDCCH.

[0016] Each type of reference signal can be transmitted from so-called antenna ports, which can be regarded as logical antennas. Each antenna port can then be mapped to one or more physical antennas. To support multi-antenna transmission schemes (such as transmit diversity and multiple-input multiple-output (MIMO)), each type of reference signal can be transmitted from multiple antenna ports. Each antenna port is mapped to a set of fixed resource elements (REs) in the orthogonal frequency division multiple access (OFDMA) physical layer time-frequency grid, and the reference symbols transmitted on each of these REs are defined in the standard.

[0017] In addition, several different transmission modes for data transmission on the PDSCH have been defined in LTE. In the first LTE release, the focus was on the transmission mode using the CRS for demodulation. Among other things, the UE uses the CRS symbols to perform the estimation of the propagation channel from each TX antenna port in the eNB to each RX antenna in the UE. The CRS is transmitted on antenna port p = 0, p ∈ {0, 1} or p ∈ {0, 1, 2, 3}, depending on whether 1, 2 or 4 antenna port transmissions are configured. To optimize the SNR of data transmission in the multi-antenna transmission scheme, the data symbols to be transmitted can be multiplied by a precoding vector or matrix. For TX diversity, the precoding vector typically aims to rotate the phase of the signals from the TX antennas so that the signals add constructively at the RX antennas in the UE, thus obtaining a beamforming gain. Similarly, the precoding matrix aims to maximize the spatial multiplexing gain of MIMO transmission. However, since the CRS symbols are common to all users in the cell, these symbols cannot be precoded for a specific user. Instead, the precoder for data transmission is signaled to the UE so that it can cancel the precoding when reconstructing the transmitted data symbols. The UE notifies the eNB of the preferred precoder selected from the codebook of possible precoders based on the measurement of the propagation channel.

[0018] When using user-specific reference signals (such as DM-RS), the eNB can perform phase rotation to improve the beamforming and spatial multiplexing gains on both the reference signal and the data symbols. This means that the UE can perform channel estimation and demodulate the data signal without knowing what precoder the eNB actually uses. In addition, the eNB is not limited to only using the precoders defined in the codebook and can also change the precoder in each subframe. This makes it possible, at least in theory, to adapt the transmission in a more flexible way to maximize the link-level performance, also in scenarios where the propagation channel changes rapidly. Nevertheless, the eNB may typically need some help from the UE measurements to know a good precoder selection, and the deficiencies in this process may degrade the overall performance.

[0019] As mentioned before, the user-specific reference signals can be used together with the specific transmission mode of the data channel PDSCH and with the enhanced physical control channel EPDCCH and the MTC physical control channel MPDCCH. The DM-RS for the PDSCH is transmitted on one or more of antenna ports p = 5, p = 7, p = 8 or p ∈ {7...14}. The DM-RS for the EPDCCH and MPDCCH is transmitted on one or more of p ∈ {107...110}.

[0020] As described above, for MPDCCH up to LTE Release 15, similar to other transport channels, the choice of the precoder is considered transparent to the UE. That is, the eNB selects the precoder without notifying the UE, although the UE can make some assumptions about, for example, how frequently the precoder can vary in time and / or frequency.

[0021] However, there is a Release 16 work item, one of whose objectives is to improve MPDCCH performance. One of the factors that may have limited performance in earlier releases is the quality of channel estimation. One of the reasons for this is the fact that the UE cannot or can rarely make assumptions about the precoder being used. It has been concluded that, in addition to the DM-RS used for MPDCCH, channel estimation performance can be improved by using the CRS. To do this, the UE needs to know the exact relationship between the CRS and the DM-RS, that is, to know the precoder used by the eNB to transmit the MPDCCH and its associated DM-RS. Therefore, it is important that the eNB selects and changes the precoder in a deterministic manner that the UE also knows. This is addressed in an earlier patent application (International Application No. PCT / SE2015 / 050080) hereby incorporated by reference.

[0022] Precoder matrix selection can be based on several methods.

[0023] In one alternative, the network can simply use a constant precoder for the transmission of MPDCCH symbols. However, in this way, the transmission SNR can only be optimized for a limited set of channel realizations. Especially for local transmissions, in so-called closed-loop precoding, the network can select a specific precoder based on feedback of channel state information (CSI) from the UE in order to ensure that a precoder can be found that matches the current channel conditions.

[0024] In another alternative, the network can select and change the precoder independently of the channel. For example, based on an agreement reached at the 95th RAN1 meeting, the network can use some precoding cycles across time domain and / or frequency domain. Such cycles can be employed on a subset of the full codebook or precoder matrix defined in LTE Release 8. For MPDCCH, coverage is improved via repeated transmissions. Therefore, the precoder cycle allows the network to use different precoders to transmit the MPDCCH packet and its repetitions, which thus increases the chance of selecting a precoder that matches the current channel conditions more closely.

[0025] When using CSI-based precoding, the UE reports a preferred precoder according to a precoder matrix indicator (PMI). The UE determines the preferred PMI by estimating which one among a given set of precoders will result in the best reception performance for the transmission from the network node to the UE. The UE typically estimates a metric representing this performance and tries to find the PMI that optimizes this metric. An example of such a metric is the combined received SNR for different PMIs. Alternative metrics for the reception of downlink (DL) data channels include the estimated achievable data throughput selected for different PMIs. For the reception of DL control channels, the metric can be selected as the estimated block error rate (BLER) for a given transmission format of the control channel.

[0026] In a typical scenario, the network node configures the UE to send a periodic CSI report with the preferred PMI at a specified moment. Then, the network generally uses the reported PMI for subsequent DL transmissions until the next CSI report is received. In other scenarios, an aperiodic CSI report is used, in which case the network triggers the CSI report according to a specific DCI on, for example, the downlink control channel.

[0027] There are specific challenges currently. Therefore, improved systems and methods for CSI-based precoding are needed. Summary of the Invention

[0028] Systems and methods for decoding transmissions are provided. In some embodiments, a method performed by a wireless device includes: determining a plurality of machine-type communication MTC physical downlink control channel MPDCCH transmission candidates to be monitored. For at least one candidate among the plurality of MPDCCH transmission candidates, the method includes: determining whether the candidate belongs to a first group of candidates or a second group of candidates. The first group of candidates includes a first subset of a first search space, and the second group of candidates includes a combination of a second search space and a second subset of the first search space. The second subset is the complement of the first subset, the first search space includes a user equipment UE-specific search space, and the second search space includes a type 0 MPDCCH common search space. If the candidate belongs to the first group of candidates, the method includes: attempting to decode the MPDCCH transmission using a channel state information CSI-based precoding scheme. If the candidate belongs to the second group of candidates, the method includes: attempting to decode the MPDCCH transmission using a predetermined precoding scheme. This enables more robust precoding techniques and can be regarded as a technique with a fallback solution for cases where CSI is lost or unreliable.

[0029] In some embodiments, the predetermined precoding scheme is selected from the group consisting of: selecting the precoder based on a precoder cycle; and selecting a fixed precoder.

[0030] In some embodiments, determining whether the candidate belongs to the first group of candidates or the second group of candidates is based on the aggregation level (L) of the control channel candidate.

[0031] In some embodiments, determining whether the candidate belongs to the first group of candidates or the second group of candidates is based on one or more of the group consisting of: the aggregation level (L) of the control channel candidate; the index (m) identifying the control channel candidate within the search space for the aggregation level; the time repetition factor (R) of the control channel candidate; the sequential index (u) identifying the starting subframe of the control channel candidate for a given repetition factor; the time index identifying the time reference of the control channel candidate; the time index identifying the time reference of the search space; and the number of physical resource blocks for monitoring the control channel candidate within the search space.

[0032] In some embodiments, using a CSI-based precoding scheme includes: using a single precoding matrix that is to be used for all physical resource blocks used to transmit the control channel candidate.

[0033] In some embodiments, using a CSI-based precoding scheme includes: using multiple precoding matrices, each precoding matrix being to be used for a subset of the physical resource blocks used to transmit the control channel candidate. In some embodiments, when frequency hopping is used to transmit the control channel candidate, the subsets of the physical resource blocks belong to different narrowbands.

[0034] In some embodiments, frequency hopping between at least two different narrowbands is employed, and one precoding scheme is used in one of the narrowbands while a different precoding scheme is used in at least one other narrowband.

[0035] In some embodiments, using a predetermined precoding scheme includes: using multiple precoding matrices when the precoding technique is based on a precoder cycle. In some embodiments, the precoder used varies according to a predetermined time and / or frequency pattern.

[0036] In some embodiments, using a CSI-based precoding scheme includes: using a precoder based on channel state information transmitted by the wireless device. In some embodiments, the channel state information includes a precoding matrix indicator (PMI).

[0037] In some embodiments, the method further includes: using the determined precoder being used in a physical resource block (PRB) pair to obtain a channel estimate associated with an antenna port used for transmission in the PRB pair by performing channel estimation based on a combination of: a demodulation reference signal (DM-RS) located in the PRB pair, and at least one of a DM-RS located in one or more other PRB pairs and a cell-specific reference signal (CRS) located in any set of PRB pairs.

[0038] In some embodiments, the method further includes: using the determined precoder being used in a PRB pair to obtain a channel estimate associated with an antenna port used for transmission in another PRB pair by performing channel estimation based on a combination of: a DM-RS located in the PRB pair, and at least one of a DM-RS located in one or more other PRB pairs and a CRS located in any set of PRB pairs.

[0039] In some embodiments, the method further includes: using the determined precoder being used in a PRB pair to obtain a channel estimate associated with an antenna port used for transmission in the PRB pair by performing channel estimation based on a CRS located in any set of PRB pairs.

[0040] In some embodiments, the method further includes: using the obtained channel estimate associated with an antenna port used for transmission in one or more PRB pairs to demodulate information received in the PRB pair. In some embodiments, the information is associated with the MPDCCH or a physical downlink shared channel (PDSCH).

[0041] In some embodiments, a method for encoding transmissions performed by a base station includes: determining whether to encode an MPDCCH transmission to a wireless device using a CSI-based precoding scheme or a predetermined precoding scheme. If the CSI-based precoding scheme is used, the method includes: selecting a candidate for transmission from a first set of candidates, where the first set of candidates includes a first subset of a first search space that includes a UE-specific search space. If the predetermined precoding scheme is used, the method includes: selecting a candidate for transmission from a second set of candidates, where the second set of candidates includes a combination of a second search space and a second subset of the first search space, where the second subset is a complement of the first subset, and the second search space includes a type 0 MPDCCH common search space. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate several aspects of the present disclosure and, together with the description, serve to explain the principles of the present disclosure.

[0043] Figure 1 Shows an example of a cellular communication network according to some embodiments of the present disclosure;

[0044] Figure 2 Shows a method for decoding a transmission performed by a wireless device according to some embodiments of the present disclosure;

[0045] Figure 3 Shows a method for encoding a transmission performed by a base station according to some embodiments of the present disclosure;

[0046] Figures 4 - 6 Shows UE-specific search space (USS) candidates using different aggregation levels according to some embodiments of the present disclosure;

[0047] Figure 7 Shows a precoder for the transmission of an allocated physical resource block (PRB) pair for narrowband (NB) according to some embodiments of the present disclosure;

[0048] Figure 8 Shows an example where the maximum machine type communication (MTC) physical downlink control channel (MPDCCH) length is L and the MPDCCH start period is T according to some embodiments of the present disclosure;

[0049] Figure 9 Shows a hybrid precoding method according to some embodiments of the present disclosure;

[0050] Figure 10 Shows MPDCCH transmissions with different repetition factors according to some embodiments of the present disclosure;

[0051] Figure 11 Shows an exemplary resource element mapping according to some embodiments of the present disclosure;

[0052] Figure 12 Shows an example using a precoder matrix that defines the relationship between DMRS ports and CRS ports in a PRB pair according to some embodiments of the present disclosure;

[0053] Figure 13 Is a schematic block diagram of a radio access node according to some embodiments of the present disclosure;

[0054] Figure 14 Is a schematic block diagram showing a virtualized embodiment of a radio access node according to some embodiments of the present disclosure;

[0055] Figure 15 is a schematic block diagram of a radio access node according to some other embodiments of the present disclosure;

[0056] Figure 16 is a schematic block diagram of a UE according to some embodiments of the present disclosure;

[0057] Figure 17 is a schematic block diagram of a UE according to some other embodiments of the present disclosure;

[0058] Figure 18 illustrates a communication system including a telecommunication network such as a 3GPP-type cellular network according to some embodiments of the present disclosure;

[0059] Figure 19 illustrates a communication system including a host computer according to some embodiments of the present disclosure;

[0060] Figure 20 is a flowchart illustrating a method implemented in a communication system according to some embodiments of the present disclosure; and

[0061] Figures 21 - 23 is a flowchart illustrating a method implemented in a communication system according to some embodiments of the present disclosure. DETAILED DESCRIPTION

[0062] The embodiments set forth below represent information enabling those skilled in the art to practice the embodiments and illustrate the best mode of practicing the embodiments. When reading the following description with reference to the drawings, those skilled in the art will understand the concepts of the present disclosure and will recognize applications of these concepts not specifically mentioned herein. It should be understood that these concepts and applications fall within the scope of the present disclosure.

[0063] Radio Node: As used herein, a "radio node" is a radio access node or a wireless device.

[0064] Radio Access Node: As used herein, a "radio access node" or "radio network node" is any node in a radio access network of a cellular communication network for wirelessly transmitting and / or receiving signals. Some examples of radio access nodes include, but are not limited to, base stations (e.g., new radio (NR) base stations (gNBs) in a third generation partnership project (3GPP) fifth generation (5G) NR network or enhanced or evolved node Bs (eNBs) in a 3GPP long term evolution (LTE) network), high-power or macro base stations, low-power base stations (e.g., micro base stations, pico base stations, home eNBs, etc.), and relay nodes.

[0065] Core network node: As used herein, a "core network node" is any type of node in a core network. Some examples of core network nodes include, for example, a Mobility Management Entity (MME), a Packet Data Network Gateway (P-GW), a Service Capability Exposure Function (SCEF), etc.

[0066] Wireless device: As used herein, a "wireless device" is any type of device that accesses (i.e., is served by) a cellular communication network by wirelessly transmitting and / or receiving signals to / from a radio access node. Some examples of wireless devices include, but are not limited to, User Equipment (UE) and Machine-Type Communication (MTC) devices in a 3GPP network.

[0067] Network node: As used herein, a "network node" is any node that is part of either the radio access network or the core network of a cellular communication network / system.

[0068] Note that the description given herein focuses on 3GPP cellular communication systems and, therefore, 3GPP terms or terms similar to 3GPP terms are often used. However, the concepts disclosed herein are not limited to 3GPP systems.

[0069] Note that in the description herein, the term "cell" may be referred to; however, particularly with respect to 5G NR concepts, beams may be used instead of cells and, therefore, it is important to note that the concepts described herein apply equally to both cells and beams.

[0070] Figure 1FIG. 0 shows an example of a cellular communication network 100 in accordance with some embodiments of the present disclosure. In the embodiments described herein, the cellular communication network 100 is a 5G NR network. In this example, the cellular communication network 100 includes base stations 102-1 and 102-2, which are referred to as eNBs in LTE and gNBs in 5G NR, and which control corresponding macro cells 104-1 and 104-2. The base stations 102-1 and 102-2 are generally referred to herein collectively as base station 102 and individually as base station 102. Similarly, the macro cells 104-1 and 104-2 are generally referred to herein collectively as macro cell 104 and individually as macro cell 104. The cellular communication network 100 may also include a plurality of low power nodes 106-1 to 106-4, which control corresponding small cells 108-1 to 108-4. The low power nodes 106-1 to 106-4 may be small base stations (e.g., pico base stations or femto base stations) or remote radio heads (RRHs), etc. It is noted that although not shown, one or more of the small cells 108-1 to 108-4 may alternatively be provided by the base station 102. The low power nodes 106-1 to 106-4 are generally referred to herein collectively as low power node 106 and individually as low power node 106. Similarly, the small cells 108-1 to 108-4 are generally referred to herein collectively as small cell 108 and individually as small cell 108. The base stations 102 (and optionally the low power nodes 106) are connected to the core network 110.

[0071] The base stations 102 and the low power nodes 106 provide service to wireless devices 112-1 to 112-5 in the corresponding cells 104 and 108. The wireless devices 112-1 to 112-5 are generally referred to herein collectively as wireless device 112 and individually as wireless device 112. The wireless devices 112 are sometimes also referred to herein as UEs.

[0072] There are specific challenges currently. Although based on CSI precoding shows better performance than pre-defined precoding methods by knowing the channel conditions, due to some reliability issues, this method may be ineffective. For example, the CSI may be lost or misdecoded at the eNB side. If the UE has sent a preferred PMI, the UE generally expects the eNB to use that PMI in subsequent transmissions, but when the CSI report is not correctly received, the eNB does not know which precoding matrix indicator (PMI) the UE expects to use. In particular, when the reported PMI is intended for a downlink control channel (e.g., MPDCCH), there is currently no fallback solution. Therefore, improved systems and methods for CSI-based precoding are needed.

[0073] Systems and methods for decoding transmissions are provided.Figure 2 A method performed by a wireless device for decoding a transmission according to some embodiments of the present disclosure is shown. In some embodiments, the method includes determining a plurality of machine-type communication (MTC) physical downlink control channel (MPDCCH) transmission candidates to be monitored (step 200). For at least one candidate among the plurality of MPDCCH transmission candidates, the method includes determining whether the candidate belongs to a first group of candidates or a second group of candidates (step 202). The first group of candidates includes a first subset of a first search space, and the second group of candidates includes a combination of a second search space and a second subset of the first search space. The second subset is a complement of the first subset. The first search space includes a user equipment (UE)-specific search space, and the second search space includes a type 0 MPDCCH common search space. If the candidate belongs to the first group of candidates, the method includes attempting to decode the MPDCCH transmission using a channel state information (CSI)-based precoding scheme (step 204). If the candidate belongs to the second group of candidates, the method includes attempting to decode the MPDCCH transmission using a predetermined precoding scheme (step 206). This can allow for more robust precoding techniques and can be regarded as a technique with a fallback solution for cases where CSI is lost or unreliable.

[0074] Note that in this document, MPDCCH transmissions are sent from the network / base station to the wireless device.

[0075] Figure 3 A method performed by a base station for encoding a transmission according to some embodiments of the present disclosure is shown. In some embodiments, it is determined whether to encode an MPDCCH transmission to a wireless device using a CSI-based precoding scheme or a predetermined precoding scheme (step 300). If a CSI-based precoding scheme is used, the method includes selecting a candidate for transmission from a first group of candidates, where the first group of candidates includes a first subset of a first search space, and the first search space includes a UE-specific search space (step 302). If a predetermined precoding scheme is used, the method includes selecting a candidate for transmission from a second group of candidates, where the second group of candidates includes a combination of a second search space and a second subset of the first search space, where the second subset is a complement of the first subset, and the second search space includes a type 0 MPDCCH common search space (step 304). In some embodiments, for example, if CSI has not been received from the wireless device, or if the received CSI is considered unreliable by the base station, the base station may determine to use a predetermined precoding scheme. In some embodiments, for example, if the communication with the wireless device operates under poor coverage (where it is more likely to incorrectly determine the estimation of the preferred precoder), the CSI may be considered unreliable.

[0076] Some embodiments of the present disclosure divide the MPDCCH search space into two groups; one group G1 uses CSI-based precoding and one group G2 uses a predetermined precoding scheme. A typical example of a predetermined precoding scheme is to use a certain precoder cycle, where the precoder used changes according to a predetermined time and / or frequency pattern. This will be used as the default example of the predetermined precoding scheme to be used as a fallback in this description, but any other predetermined precoding scheme can be used instead of this scheme.

[0077] Since CSI-based precoding naturally involves unicast transmission from a base station to a UE, this scenario is specifically considered in the following description. However, this concept can be used in any scenario where CSI-based precoding makes sense. A UE in connected mode and configured in CE mode A needs to monitor MPDCCH candidates using the cell RNTI (C-RNTI) in both a UE-specific search space USS and a type 0 MPDCCH common search space (abbreviated herein as CSS-0 for brevity). These two search spaces are monitored within the same set of 2, 4, or 6 PRBs. Therefore, this case is the focus of the present disclosure.

[0078] In a first embodiment, CSI-based precoding is used for MPDCCH candidates transmitted in the UE-specific search space USS, while a precoder cycle is used for MPDCCH candidates transmitted in the type 0 MPDCCH common search space CSS-0.

[0079] A particular advantage of providing a fallback scheme is that it is likely to be able to maintain communication with the device even when CSI reports are not received correctly.

[0080] In one embodiment, after failing to receive a CSI report, MPDCCH candidates are further transmitted in CSS-0, where the MPDCCH contains a trigger for an aperiodic CSI report. In this way, the UE will get a second chance to provide a preferred PMI to the eNB, and then, upon successful detection, this PMI can be used for MPDCCH transmission in the USS thereafter until the next (periodic or aperiodic) CSI report is scheduled.

[0081] This first embodiment and its variations will now be described by discussing the properties of the MPDCCH search space.

[0082] The definition of the MPDCCH search space can be found in section 9.1.5 of 3GPP TS 36.213 v13.12.0, and some of the features relevant to this current disclosure are described herein. The UE-specific search space is defined according to the number of MPDCCH candidates to be monitored within a configured set of 2, 4, or 6 PRBs. Table 1 gives the number of candidates to be monitored for different aggregation levels when the UE is configured to monitor the MPDCCH in local mode and without any repetitions in CE mode A. In this case, it can be noted that the UE needs to monitor all possible candidates in the USS, since the number of candidates always matches the maximum possible candidates for the combination of aggregation level L and number of PRBs. For example, if the UE is configured to monitor MPDCCH candidates in 4 PRBs, there are a total of 8 + 4 + 2 + 1 = 15 candidates in the USS in each applicable subframe.

[0083] Table 1. Number of MPDCCH candidates in the USS in local mode without MPDCCH repetitions in CE mode A

[0084]

[0085] Compared to the USS, CSS-0 contains only candidates with the maximum aggregation level of the set of PRBs being monitored. Thus, CSS-0 candidates use aggregation level 8 or 16, depending on whether MPDCCH candidates are monitored within 2 or 4 PRBs, respectively. Since CSS-0 uses only the maximum aggregation level (corresponding to the lowest possible code rate), it can be expected to have a lower BLER performance compared to when using other aggregation levels, which makes it very suitable to be used as a fallback solution. This includes the cases addressed in this current disclosure, i.e., as a fallback solution when CSI-based precoding fails (e.g., due to missing CSI reports).

[0086] It can be noted that the USS and CSS-0 are constructed in a roughly similar manner, including the fact that the UE is required to monitor MPDCCH candidates using the maximum aggregation level in both search spaces. Furthermore, if the UE manages to detect an MPDCCH candidate using the C-RNTI for the maximum aggregation level, the UE cannot determine unambiguously whether the candidate was transmitted in the USS or in the CSS-0. However, when different precoding techniques are used in the two search spaces, the UE has a much higher probability of successfully decoding the MPDCCH when taking the precoder associated with the respective search space.

[0087] The first embodiment can be extended and varied in a number of ways. In one such embodiment, in addition to CSS-0, the MPDCCH candidates associated with the precoder cycle also include some candidates of the USS. The motivation for this is to allow the cycle to also be used for candidates with lower aggregation levels (i.e., higher code rates). This can be useful in situations where the network may assume that the radio propagation conditions are good enough such that the highest aggregation level can be avoided. This has the advantage that MPDCCHs for different UEs can be multiplexed within the same PRB, which is not possible when using CSS-0 since one MPDCCH using the maximum aggregation level occupies the entire PRB.

[0088] There are a number of ways in which this embodiment can be implemented by associating one or more USS candidates with the precoder cycle. Figure 4 and Figure 5 respectively show the use of USS candidates with different aggregation levels when MPDCCH monitoring is performed in 2 or 4 PRBs. Different MPDCCH candidates can be parameterized using the pair (L, m) N where m can take values between 0 and where is the number of candidates to be monitored for a specific aggregation level L and number of PRBs N, as given by Table 1. In a non-limiting example, MPDCCH candidates with even m in the USS can be associated with CSI-based precoding, while odd numbers can be associated with the precoder cycle. However, the partitioning of USS candidates between CSI-based precoding and the precoder cycle can be done in many other ways. In a typical embodiment, at least one candidate for each aggregation level in the USS (especially the candidate with the maximum aggregation level) remains associated with CSI-based precoding since, according to the first embodiment, the corresponding CSS-0 candidate has been assigned to the precoder cycle.

[0089] The search space examples used above refer to the case of a local transmission mode without MPDCCH repetition. If the UE is configured to monitor the MPDCCH in CE mode A with repetition, the number of candidates in the USS is given by Tables 2 and 3, where the former applies when the UE is configured to monitor the MPDCCH in two or four PRBs, and the latter applies when the UE is configured to monitor the MPDCCH in six PRBs. In addition to the aggregation level L, these tables also include a repetition factor R, which can take up to four different values, namely, r1 to r4. The network configures the maximum number of MPDCCH repetitions r max which can take any value {2, 4, 8,..., 256}. As a non-limiting example, if r max= 16, the values r1 to r4 take the values 2, 4, 8, and 16 respectively. More generally, r1 is equal to max(r max / 8, 1), and then the values of r2 (and possibly r3 and r4) are determined by doubling the previous value (until r max ).

[0090] Table 2. Number of MPDCCH candidates in the USS when the UE is configured to monitor MPDCCH in CE mode A with repetition and in 2 or 4 PRBs

[0091]

[0092] Table 3. Number of MPDCCH candidates in the USS when the UE is configured to monitor MPDCCH in CE mode A with repetition and in 6 (2 + 4) PRBs

[0093]

[0094] When monitoring MPDCCH within 2, 4, and 6 PRBs respectively, the MPDCCH candidates in the USS are shown in Figure 4 , Figure 5 and Figure 6 . The shaded boxes indicate examples of possible MPDCCH candidates at a specific time point. According to Table 2, when monitoring MPDCCH in 2 or 4 PRBs, all candidates are applicable to all possible repetition numbers. This is in contrast to the 6 PRB case shown in Figure 4 , where according to Table 3, some candidates are only applicable to some repetition values. Generally, the low aggregation levels monitored within the 2 PRB part of 6 PRBs are only applicable to the lower values of the configured repetition numbers. The intermediate aggregation levels are monitored within the 4 PRB part of 6 PRBs and are applicable to all repetition numbers except the highest one. The maximum aggregation level 24 is applicable to all repetition numbers.

[0095] Similar to the case without MPDCCH repetition, CSS-0 only contains candidates with the maximum aggregation level for the set of PRBs being monitored (but in this case, for all configured repetition numbers, i.e., generally from r max / 8 to r max ).

[0096] For how to adopt the embodiments discussed above in scenarios with MPDCCH repetition, multiple embodiments can be envisioned, including the embodiments described above for the case without repetition.

[0097] In some embodiments, USS candidates are partitioned considering the effective code rate of MPDCCH transmissions. The code rate of MPDCCH transmissions is substantially inversely proportional to L and R. The term "substantially" is used herein because the exact code rate may vary between subframes depending on the fact that the number of resource elements available for MPDCCH transmissions can vary. According to a first embodiment, CSS-0 is used for the precoder cycle, and since this includes candidates with the maximum aggregation level at all repetition levels, the USS can preferably be partitioned such that the corresponding combinations in the USS are associated with CSI-based precoding.

[0098] As an example, consider the case where MPDCCH is monitored in 4 PRBs and r max = 16. In this case, the UE needs to monitor MPDCCH candidates in the USS, where each of the 16 possible combinations is represented by a set L ∈ {2, 4, 8, 16} and R ∈ {2, 4, 8, 16}. Then, the highest code rate is represented by the lowest product of L and R, which is 4, and the lowest code rate is represented by the highest product 256. For all values between these maxima, there are multiple combinations of L and R that achieve the same code rate. Thus, in some embodiments, the combinations of L and R are partitioned such that for each effective code rate, some combinations are assigned to CSI-based precoding and other combinations are assigned to predetermined precoding.

[0099] There are multiple ways in which the above-described rate-based partitioning can be implemented. Assume in this description that L is represented by an index i L such that, for example Similarly, assume that R is represented by i R such that, for example Then, the constant code rate corresponding to the sum i L + i R is constant, as shown by the anti-diagonal entries in Table 4 below.

[0100] Table 4. The constant code rate corresponding to the sum i L + i R is constant

[0101]

[0102] In some embodiments, the partitioning into groups is based on whether one of the indices is odd or even. As a non-limiting example, if i L is even, CSI-based precoding is used; otherwise, the precoder cycle is used.

[0103] In other embodiments, the partitioning is performed such that the lower triangular part or the upper triangular part of the above table is associated with one of the precoding schemes. As a non - limiting example, CSI - based precoding is used for i L ≥i R combinations, and otherwise the precoder cycle is used. In other embodiments, other restrictions for associating combinations of indices with precoding techniques can be defined. In one such non - limiting example, CSI - based precoding is associated with the top row and the right - most column in the table, i.e., the condition (i R =1)|(i L =4).

[0104] The embodiments outlined above can be used even if there is no strict mathematical relationship between R and L and their corresponding indices. More generally, these embodiments and their variants can also be applied when the indices represent any increasing value order of R and L. This can apply, for example, to the case where aggregation level 24 is also used, which corresponds to when the UE is configured to monitor MPDCCH candidates in 6 PRBs according to Table 3 above. Then, there is no direct quantitative relationship between all combinations of indices and the corresponding code rates, although the qualitative relationship is maintained, and the above - described embodiments and their variants can still be used.

[0105] Some embodiments relate to the case when MPDCCH uses frequency hopping such that different sets of PRBs, which usually belong to different narrowbands, are used for MPDCCH transmission and monitoring at different times. The above - described embodiments for determining the precoding technique can also be used in this case. In the case of CSI - based reporting, depending on the reported CSI, the same or different precoders can be used for different narrowbands. However, there are some scenarios where new solutions can be used.

[0106] One such scenario is the case where valid CSI reporting is available in one of the narrowbands but not in the other, and only the network node is aware of this situation. For example, this can occur when the network detects valid CSI only for one of the narrowbands (even if the UE has been scheduled to transmit CSI for both narrowbands). Then, according to the previously described embodiments, the eNB will typically determine to use a fallback solution by selecting a search space (a part of the search space) associated with the precoder cycle.

[0107] Another scenario is where a valid CSI report is available in one of the narrowbands but not in the other, and both the UE and the network node are aware of this situation. For example, this may occur when CSI is reported only for one of the narrowbands, or when one of the CSI reports times out. In one embodiment related to this situation, a search space (a part of the search space) that is normally associated with CSI-based precoding is employed, but the CSI-based precoder is applied only to the narrowband with a valid CSI report, while the precoder is cyclically applied to the narrowband where no valid CSI report exists.

[0108] Some embodiments provided herein relate to different parameters, particularly parameters for determining what precoder technique to use for a certain MPDCCH candidate. This can, for example, involve how to partition the USS such that some candidates are associated with CSI-based precoding while other candidates are associated with cyclic precoding. These parameters can be defined from standard documents, or they can be configured by the network, for example, via broadcast system information or dedicated radio resource control (RRC) signaling.

[0109] Some embodiments provided herein relate to different parameters, particularly parameters for determining what precoder technique to use for a specific MPDCCH candidate. This relates to both the parameters that have been explicitly mentioned in the embodiments (such as A, B, k), and also to parameters that can be used in other ways to determine subgroups G1 and G2. These parameters can be defined from standard documents, or they can be configured by the network, for example, via broadcast system information or dedicated radio resource control (RRC) signaling.

[0110] Some embodiments propose a hybrid precoding technique that is a hybrid of CSI-based precoding and predefined precoding. By using this hybrid precoding, for situations where the CSI report is unreliable, decoded incorrectly, or lost, the predefined precoding can compensate for the performance degradation. The method is described for use within a wireless network, which is typically a cellular network that includes one or more network nodes (such as a base station, also denoted as a network node or eNB) and one or more wireless devices (also denoted as terminals or UEs). The embodiments disclosed herein can be applied to any node and device within a wireless network. The embodiments disclosed herein are described with reference to downlink transmissions (i.e., from the network node to the wireless device), but can also be applied to other scenarios.

[0111] In this hybrid precoding method, the precoding technique is selected based on the time / frequency location of the transmitted PRB. For simplicity of description, consider Figure 7A simple embodiment is shown, in which the precoder allocated for the PRB pair transmission of the NB is shown. In this example, the network node uses the precoder w defined by the periodic CSI after receiving the CSI report PMI to transmit the first A subframes. Then, for the transmission of subsequent subframes until the next CSI report is scheduled to be received, the eNB uses cyclic precoding as the predefined precoding technique. This embodiment can be summarized as:

[0112]

[0113] where N s and CSI p are the absolute subframe number and the period of the CSI report. The parameter A can be selected, for example, as:

[0114] · An absolute number

[0115] · A ratio of the CSI period (e.g., 75%)

[0116] Alternatively or additionally, A can be selected as a function of some other parameters. As an example, in one embodiment, A can be selected based on one or more of the following: the CSI period CSI of the periodic CSI report p , and the length L of the MPDCCH packet (including the number of repetitions).

[0117] A = f(CSI p , L).

[0118] In another embodiment, A can additionally or alternatively be based on the period T at which the MPDCCH transmission can start. Referring to Figure 8 , where the (maximum) MPDCCH length is L and the MPDCCH start period is T, A can be determined such that there is room for at least one MPDCCH transmission using cyclic precoding at the end of the CSI report period. For the case where the CSI report period and the MPDCCH period are aligned such that CSI p is an integer multiple of T, A can be selected as:

[0119] A = CSI p - kT

[0120] where k is a positive integer. In some embodiments, the MPDCCH start period is determined as the maximum MPDCCH length L multiplied by a constant G, in which case A can be expressed as:

[0121] A = CSI p - kGL

[0122] In the case where the MPDCCH start period and the CSI reporting period are not aligned, or in the case where there is an additional timing offset between the CSI reporting instance and the occurrence of the MPDCCH, the determination of A is adjusted accordingly to ensure that each type of precoding technique is used for at least one MPDCCH occasion. The timing offset can refer to, for example, the situation where there is a delay between the subframe in which the CSI reporting is scheduled and the first subframe in which the precoder according to the reported CSI is applied to the MPDCCH transmission.

[0123] In some embodiments, the number of MPDCCH occasions assigned to the precoder cycle itself can depend on the maximum MPDCCH length. For example, a large L is typically used for UEs in poor coverage, in which case it can also be assumed that the CSI reporting is less reliable. Therefore, increasing the use of fallback precoding techniques (e.g., precoder cycle) in these scenarios can be beneficial.

[0124] In another embodiment, the network node can use CSI-based precoding for the first B PRBs of the NB and cyclic precoding for the other PRBs. The precoder assigned for this embodiment is as Figure 9 shown.

[0125]

[0126] The parameter B can also depend on other parameters, similar to the description of parameter A above.

[0127] In a more general embodiment, the network node divides the subframes / PRBs transmitted within the time interval between two CSI reports into two subgroups G1 and G2; for the transmission of the first subgroup G1, the network node uses the precoder defined by the latest CSI report, and for the transmission of the second subgroup G2, the network node uses a predefined precoding method. This hybrid precoding technique for periodic CSI reporting can be summarized as:

[0128]

[0129] In some embodiments, the division into subgroups is made considering the different possible MPDCCH repetition factors being used. Figure 10 Four different repetition factors that can be used are shown, and the UE may need to receive one or more of these candidates non-overlapping in time. The parameter r max is the maximum number of repetitions of the subframes of the MPDCCH transmission that the UE is configured to receive. This typically corresponds to the parameter L used above. In addition, the UE may need to receive at r max / 2, r max / 4 and r maxRepetition is used to receive MPDCCH transmissions in / 8 subframes, starting from any timing indicated in Figure 10 As shown and similar to as described above, there may also be gaps between the possible starting points of MPDCCH candidates of length r max It can also be noted that the repetitions in the figure illustrate that the subframes used are contiguous in time, but there may also be gaps of one or more subframes within each MPDCCH transmission. These gaps can refer, for example, to subframes not used for any DL traffic to the LTE-M device, including uplink subframes in a time division duplex (TDD) deployment.

[0130] The division into subgroups G1 and G2 can be done between different MPDCCH candidates represented by the pair (R, m), where R is a specific repetition number between r max / 8 and r max and m is an order index identifying the moment at which the MPDCCH uses that specific repetition number. As a non-limiting example, the last timing of all repetitions except the maximum repetition number can belong to G2 which is used for precoder cycling, while the remaining timings belong to G1 which is used for CSI-based precoding. According to another example, CSI-based precoding is used for r max and r max / 4, while precoder cycling is used for r max / 2 and r max / 8. To allow the use of two precoding techniques for any repetition number, the association between MPDCCH candidates and subgroups can vary over time, for example, by switching the group association in an alternating manner. This objective can also be achieved by combining these types of embodiments with any previous embodiment or its variants. For example, the first division of MPDCCH candidates into subgroups is used for the first A subframes after the moment when a CSI report is scheduled, and the second division is used for the remaining subframes until a new CSI report is scheduled. The embodiments proposed herein can all be associated with multiple parameters that determine how to divide MPDCCH candidates into subgroups G1 and G2. These parameters can be used, for example, to determine which pairs (R, m) belong to which subgroup, and one example can be the parameter N R which represents the number of timings for a specific repetition number associated with one of the groups. Other parameters can define the switching pattern, such as the switching period T toggle etc.

[0131] Multiple other possible embodiments can be envisaged, and some of them are listed below. Different embodiments can be used alone or in combination with each other.

[0132] In one embodiment, subgroups G1 and G2 can be predefined and fixed, while in another embodiment, the elements of these subgroups can be chosen as a function of a number of other parameters.

[0133] In one embodiment, the predefined precoding can be considered as cyclic precoding, where the first precoder index is pseudo-randomly chosen as a function of the subframe / PRB index. This is addressed in an earlier patent application (U.S. Patent Application 62 / 806,253 filed on February 15, 2019) incorporated herein by reference. Generally, different precoding cyclic techniques can be used for different embodiments.

[0134] In another embodiment, constant precoding can be considered as predefined precoding.

[0135] In some embodiments, alternative parameterizations are used to indicate the time and frequency parameters that are incorporated into the function for selecting the precoding technique. In the time domain, the following non-limiting examples of such time indices can be used:

[0136] · The slot number n within a radio frame s ,

[0137] · The subframe number within a radio frame Or

[0138] · The cumulative slot or subframe number, e.g., where n f is the system frame number.

[0139] In an alternative embodiment, CSI-based precoding and predefined precoding can be selected based on a frequency index, such as the frequency index referring to:

[0140] · The PRB index within the system bandwidth,

[0141] · The PRB index within the narrowband where the MPDCCH is monitored, or

[0142] · The PRB index within a set of 2, 4, or 6 PRBs for which the MPDCCH candidates are monitored, or

[0143] · An index related to any other frequency granularity, such as a narrowband index or a subcarrier index.

[0144] In some embodiments, more than one type of index can be used to select the precoding method.

[0145] For the case of lost CSI, in one embodiment, the eNB can use the most recently received CSI report, while in another embodiment, the eNB can continue to use the predefined precoding technique until the eNB receives a new CSI report.

[0146] In one embodiment, a network node may divide the transmitted subframes / PRBs into N subgroups and use different precoding techniques for each subgroup that the UE also knows.

[0147] The above embodiments for determining a precoder for transmission in a wireless network may be used by network nodes in a wireless network, such as a base station or an eNB. More specifically, these embodiments may be used to determine what precoder to use for transmission from a network node to one or more UEs.

[0148] In one embodiment, the network node attempts to receive a CSI report from the UE. If the CSI report is successfully received, the network node determines the precoder to be used, as indicated by the PMI included in the CSI report. The network node also selects MPDCCH candidates belonging to subgroup G1 that is intended to be used for CSI-based precoding, and transmits the MPDCCH candidates using the precoder indicated by the PMI. If the CSI is not successfully received, the network node determines the precoder to be used based on a predefined precoding technique (e.g., precoder cycling). The network node also selects MPDCCH candidates belonging to subgroup G2 that is intended to be used for the predefined precoding technique, and transmits the MPDCCH candidates using the precoder determined based on the predefined precoding technique.

[0149] In a related embodiment, subgroup G1 includes a first search space and subgroup G2 includes a second search space.

[0150] In another related embodiment, subgroup G1 includes a first subset of the first search space, and subgroup G2 includes a combination of the second search space and a second subset of the first search space, where the second subset is the complement of the first subset.

[0151] In another related embodiment, the first search space includes a UE-specific search space and the second search space includes a type 0 MPDCCH common search space.

[0152] In a related embodiment, when it is determined that the CSI report is not successfully received, the eNB still selects MPDCCH candidates belonging to subgroup G1 that is intended to be used for CSI-based precoding, but uses the PMI according to the most recently correctly received CSI report. This embodiment may be particularly useful in scenarios where the eNB can assume that the channel for communication between the eNB and the UE changes slowly such that an older CSI report may still be valid. It may also be particularly useful in scenarios where subgroup G1 is applied to the CSI reporting period CSI pa larger initial portion, while G2 is only applied at the end. The network may attempt to communicate with the UE using the old precoder instead of waiting for the MPDCCH transmission until a predefined (fallback) technique is used. If the network does not receive an acknowledgment within a specific time T thres that the old precoder is useful for the MPDCCH transmission within a specific time T, the use of the old precoder can be aborted. This acknowledgment can refer, for example, to the eNB receiving HARQ feedback related to the DL PDSCH transmission scheduled via the MPDCCH, or receiving the UL PUSCH transmission scheduled via the MPDCCH. Time T thres can be expressed in any time unit, such as subframes, the number of MPDCCH transmission attempts, multiples of r max etc. According to the above embodiments, if the eNB does not receive such an acknowledgment, the eNB can continue by attempting MPDCCH candidates belonging to subgroup G2 that are intended to be used for the predefined precoding technique.

[0153] In one embodiment, the network node also uses the determined precoder to send DM-RS in the specific PRB pair.

[0154] In related embodiments, the network node also uses the determined precoder to send information associated with the physical channel in the PRB pair. In one such embodiment, the information is associated with the MTC physical control channel MPDCCH. In another embodiment, the information is associated with the physical downlink shared channel PDSCH.

[0155] All of the above embodiments for determining the precoder for transmission in a wireless system and network node have corresponding embodiments in the UE. Generally, in order for the UE to determine what precoder the network node uses in its transmission (CSI-based or predefined), the UE applies the same method as that used in the network node to determine the precoder used.

[0156] In one embodiment, the UE determines multiple MPDCCH candidates to be monitored in multiple search spaces using a user-specific RNTI. For each candidate, the UE determines whether the candidate belongs to subgroup G1 intended to be used for CSI-based precoding or subgroup G2 intended to be used for a predefined precoding technique (such as precoder cycling). This determination is based on what search space the candidate belongs to and / or a certain candidate characterization that identifies which subset of the search space the candidate belongs to, where the subset is associated with one of the precoding techniques.

[0157] In a related embodiment, subgroup G1 includes a first search space and subgroup G2 includes a second search space.

[0158] In another related embodiment, subgroup G1 includes a first subset of a first search space, and subgroup G2 includes a combination of a second search space and a second subset of the first search space, where the second subset is the complement of the first subset.

[0159] In another related embodiment, the first search space includes a UE-specific search space, and the second search space includes a type 0 MPDCCH common search space.

[0160] In one embodiment, the UE also uses the determined precoder being used in a PRB pair to obtain a channel estimate associated with the antenna port used for transmission in the PRB pair by performing channel estimation based on a combination of: DM-RS located in the PRB pair, and at least one of DM-RS located in one or more other PRB pairs and CRS located in any set of PRB pairs.

[0161] In a related embodiment, the UE uses the determined precoder being used in a PRB pair to obtain a channel estimate associated with the antenna port used for transmission in another PRB pair by performing channel estimation based on a combination of: DM-RS located in the PRB pair, and at least one of DM-RS located in one or more other PRB pairs and CRS located in any set of PRB pairs.

[0162] In another related embodiment, the UE uses the determined precoder being used in a PRB pair to obtain a channel estimate associated with the antenna port used for transmission in the PRB pair by performing channel estimation based on CRS located in any set of PRB pairs.

[0163] Similar to the description of the network node embodiment, the UE receives MPDCCH candidates and determines whether an MPDCCH candidate belongs to subgroup G1 or G2 based on one or more indices representing the time and / or frequency position of the PRB pair.

[0164] Figure 11 Exemplary positions of resource elements carrying CRS using antenna ports 0 to 3 within a PRB are shown, denoted as C0, C1, C2, and C3 respectively. Similarly, exemplary positions of resource elements carrying DM-RS using antenna ports 107 and 109 are shown, denoted as D107 and D109 respectively. Figure 12 An example is also shown when the precoder matrix w1 is used to define the relationship between DM-RS ports 107 and 109 and CRS ports 0 - 3 within a PRB. The above embodiments for performing channel estimation based on a combination of different reference signals will now be briefly discussed with reference to these figures.

[0165] ReferenceFigure 11 and Figure 12 , the channel estimates of DM-RS antenna ports 107 and 109 within a PRB can be derived based on CRS ports 0 to 3 in a variety of different ways.

[0166] In a first channel estimation embodiment, first, channel estimation for each antenna port is performed separately for all antenna ports 0, 1, 2, 3, 107, and 109 (or generally a subset thereof) using any channel estimation technique known in the prior art. The basic principle of this technique is that the (complex) value representing the received signal associated with the resource element containing the reference signal is divided by the known (complex) value of the symbol transmitted on that resource element to form the raw channel estimate of the resource element. Due to noise and interference, each such raw channel estimate will have a specific channel estimation error. Then, interpolation and other filtering techniques can be used to combine multiple resource elements associated with the same antenna port within a PRB to obtain the filtered channel estimate of any resource element within the PRB. Some of these techniques are called MMSE channel estimation, which aims to minimize the mean square error of the channel estimate. Once the channel estimates for all antenna ports have been obtained separately, these channel estimates can be combined to obtain an improved channel estimate for the DM-RS port. Assume that for a specific resource element, the channel estimates obtained separately for each port are represented as and for CRS ports 0 - 3 respectively, and as and for DM-RS ports 107 and 109 respectively. Additionally, assume that these channel estimates are collected into vectors and respectively. Then, when using the precoder matrix w1, the improved channel estimate of the DM-RS port can be derived, for example, according to the following formula:

[0167]

[0168] where α DM-RS and α CRS are parameters that can be selected as non-limiting examples, and the goal is to minimize the mean square error of the combined channel estimate. The optimal selection of these parameters can depend separately on the expected channel estimation errors of the DM-RS and CRS-based channel estimates. These channel estimation errors can in turn depend on the number of resource elements available for different types of channel estimation, as well as any known possible power differences between the eNB transmitting the DM-RS and CRS ports. Additionally, for different resource elements, the optimal parameter selection can be different because, for example, it can be expected that the channel estimation error of a specific antenna port is smaller in resource elements closer to the location where the reference signal is transmitted than in resource elements farther away.

[0169] In a second channel estimation embodiment, given a precoder and a known possible power difference, the channel estimation of the DM-RS port is obtained by first estimating the channel of the CRS port, and the resource elements transmitting the reference symbols of the DM-RS port are also used in this process. Thus, the channel estimation of the CRS port will have a lower channel estimation compared to when only the resource elements for which the CRS is transmitted are used. Once the CRS-based estimation is obtained, the channel estimation of the DM-RS port can be obtained by multiplying with the precoder matrix used in the PRB pair.

[0170] Various other variations and alternatives of the above channel estimation algorithms can be envisioned. The present disclosure is not limited to a specific channel estimation algorithm for combining CRS and DM-RS ports.

[0171] In some embodiments, the UE also uses the obtained channel estimation associated with the antenna ports used for transmission in one or more PRB pairs to demodulate the information received in the PRB pair. In one such embodiment, the information is associated with the MTC physical control channel MPDCCH. In another embodiment, the information is associated with the physical downlink shared channel PDSCH.

[0172] In the above description, the precoder determination and its use for associating DM-RS with CRS are mainly described with respect to the MPDCCH applied in the LTE system. However, the present disclosure is not limited to this case, but when using a DM-RS-based transmission mode, it can also be applied to establishing the relationship between the dedicated demodulation reference signal and the common reference signal for the data channel PDSCH or other channels in LTE or other radio access technologies. Similarly, the present disclosure can be applied to a more general case where no common reference signal is necessarily transmitted, but the precoder represents the relationship between the DM-RS and a set of virtual and / or physical antenna ports at the transmitter. In this case, each precoder itself may not necessarily be useful to the receiver, but when using a set of multiple precoders, the receiver can use the information of the multiple precoders to perform combined channel estimation on multiple resource blocks where multiple precoders are being used.

[0173] Some embodiments of the present disclosure can also be generalized to other communication scenarios not limited by the above description. One such example is sidelink or peer-to-peer communication between two UEs. Another example is uplink communication where the UE is the transmitter and the base station is the receiver. It can be noted that the embodiments of the present disclosure can be applied to the transmitter, but not necessarily to the corresponding receiver.

[0174] Figure 13Schematic block diagram of a radio access node 1300 according to some embodiments of the present disclosure. The radio access node 1300 may be, for example, base station 102 or 106. As shown, the radio access node 1300 includes a control system 1302, which includes one or more processors 1304 (e.g., a central processing unit (CPU), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), etc.), a memory 1306, and a network interface 1308. The one or more processors 1304 are also referred to herein as processing circuitry. Additionally, the radio access node 1300 includes one or more radio units 1310, each radio unit including one or more transmitters 1312 and one or more receivers 1314 coupled to one or more antennas 1316. The radio unit 1310 may be referred to as radio interface circuitry or a part of the radio interface circuitry. In some embodiments, the radio unit 1310 is external to the control system 1302 and is connected to the control system 1302 via, for example, a wired connection (e.g., an optical cable). However, in some other embodiments, the radio unit 1310 and possibly the antennas 1316 are integrated with the control system 1302. The one or more processors 1304 operate to provide one or more functions of the radio access node 1300 as described herein. In some embodiments, these functions are implemented by software stored, for example, in the memory 1306 and executed by the one or more processors 1304.

[0175] Figure 14 Schematic block diagram showing a virtualized embodiment of a radio access node 1300 according to some embodiments of the present disclosure. This discussion equally applies to other types of network nodes. Additionally, other types of network nodes may have a similar virtualized architecture.

[0176] As used herein, a "virtualized" radio access node is an implementation of radio access node 1300, where at least a portion of the functionality of radio access node 1300 is implemented as virtual components (e.g., via virtual machines executed on physical processing nodes in a network). As shown, in this example, radio access node 1300 includes a control system 1302, which includes one or more processors 1304 (e.g., CPU, ASIC, FPGA, etc.), a memory 1306, a network interface 1308, and one or more radio units 1310, each radio unit 1310 including one or more transmitters 1312 and one or more receivers 1314 coupled to one or more antennas 1316, as described above. Control system 1302 is connected to radio units 1310 via, for example, an optical cable. Control system 1302 is connected to one or more processing nodes 1400 via network interface 1308, and one or more processing nodes 1400 are coupled to network 1402 or are included as part of network 1402. Each processing node 1400 includes one or more processors 1404 (e.g., CPU, ASIC, FPGA, etc.), a memory 1406, and a network interface 1408.

[0177] In this example, the functionality 1410 of radio access node 1300 described herein is implemented at one or more of the processing nodes 1400 or is distributed across control system 1302 and one or more processing nodes 1400 in any desired manner. In some particular embodiments, some or all of the functionality 1410 of radio access node 1300 described herein is implemented as virtual components executed by one or more virtual machines implemented in a virtual environment hosted by processing nodes 1400. As would be understood by one of ordinary skill in the art, additional signaling or communication between processing nodes 1400 and control system 1302 is used in order to perform at least some of the desired functionality 1410. Note that in certain embodiments, control system 1302 may not be included, in which case radio units 1310 communicate directly with processing nodes 1400 via an appropriate network interface.

[0178] In some embodiments, a computer program is provided that includes instructions that, when executed by at least one processor, cause the at least one processor to perform the functionality of radio access node 1300 or a node (e.g., processing node 1400) that implements one or more of the functionality 1410 of radio access node 1300 in a virtual environment according to any of the embodiments described herein. In some embodiments, a carrier is provided that includes the above computer program product. The carrier is one of an electrical signal, an optical signal, a radio signal, or a computer-readable storage medium (e.g., a non-transitory computer-readable medium such as a memory).

[0179] Figure 15 is a schematic block diagram of a radio access node 1300 according to some other embodiments of the present disclosure. The radio access node 1300 includes one or more modules 1500, each implemented in software. The modules 1500 provide the functions of the radio access node 1300 described herein. This discussion equally applies to Figure 14 the processing node 1400, where the modules 1500 may be implemented at one of the processing nodes 1400 or distributed across multiple processing nodes 1400 and / or distributed across the processing nodes 1400 and the control system 1302.

[0180] Figure 16 is a schematic block diagram of a UE 1600 according to some embodiments of the present disclosure. As shown, the UE 1600 includes one or more processors 1602 (e.g., CPU, ASIC, FPGA, etc.), a memory 1604, and one or more transceivers 1606, each transceiver including one or more transmitters 1608 and one or more receivers 1610 coupled to one or more antennas 1612. The transceiver 1606 includes radio front-end circuitry connected to the antenna 1612, which is configured to condition signals transmitted between the antenna 1612 and the processor 1602, as would be understood by a person of ordinary skill in the art. The processor 1602 is also referred to herein as processing circuitry. The transceiver 1606 is also referred to herein as radio circuitry. In some embodiments, the functions of the UE 1600 described above may be implemented in whole or in part by software, such as stored in the memory 1604 and executed by the processor 1602. Note that the UE 1600 may include additional components not shown in Figure 16 e.g., one or more user interface components (e.g., input / output interfaces including a display, buttons, touchscreens, microphones, speakers, and / or the like and / or any other components for allowing information to be input into the UE 1600 and / or allowing information to be output from the UE 1600), a power supply (e.g., a battery and associated power circuitry), etc.

[0181] In some embodiments, a computer program including instructions is provided, which when executed by at least one processor causes the at least one processor to perform the functions of the UE 1600 according to any of the embodiments described herein. In some embodiments, a carrier including the above computer program product is provided. The carrier is one of an electrical signal, an optical signal, a radio signal, or a computer-readable storage medium (e.g., a non-transitory computer-readable medium such as a memory).

[0182] Figure 17FIG. 0 is a schematic block diagram of a UE 1600 according to some other embodiments of the present disclosure. The UE 1600 includes one or more modules 1700, each implemented in software. The modules 1700 provide the functionality of the UE 1600 described herein.

[0183] Reference Figure 18 , according to one embodiment, a communication system includes a telecommunication network 1800 such as a 3GPP-type cellular network, which includes an access network 1802 such as a RAN and a core network 1804. The access network 1802 includes a plurality of base stations 1806A, 1806B, 1806C (e.g., NB, eNB, gNB) or other types of wireless access points (APs), each defining a corresponding coverage area 1808A, 1808B, 1808C. Each base station 1806A, 1806B, 1806C can be connected to the core network 1804 through a wired or wireless connection 1810. A first UE 1812 located in the coverage area 1808C is configured to be wirelessly connected to or paged by the corresponding base station 1806C. A second UE 1814 in the coverage area 1808A can be wirelessly connected to the corresponding base station 1806A. Although multiple UEs 1812, 1814 are shown in this example, the disclosed embodiments are equally applicable to the case where there is a single UE in the coverage area or a single UE is connected to the corresponding base station 1806.

[0184] The telecommunication network 1800 is itself connected to a host computer 1816, which can be embodied in the hardware and / or software of a stand-alone server, a cloud-implemented server, a distributed server, or as processing resources in a server farm. The host computer 1816 can be under the ownership or control of a service provider, or can be operated by or on behalf of a service provider. The connections 1818 and 1820 between the telecommunication network 1800 and the host computer 1816 can extend directly from the core network 1804 to the host computer 1816, or can be via an optional intermediate network 1822. The intermediate network 1822 can be one of a public, private, or managed network, or a combination of more than one of them; the intermediate network 1822 (if any) can be a backbone network or the Internet; in particular, the intermediate network 1822 can include two or more sub-networks (not shown).

[0185] Overall, Figure 18The communication system enables connectivity between the connected UEs 1812, 1814 and the host computer 1816. This connectivity can be described as an over-the-top (OTT) connection 1824. The host computer 1816 and the connected UEs 1812, 1814 are configured to transfer data and / or signaling via the OTT connection 1824 using the access network 1802, the core network 1804, any intermediate network 1822, and possibly other infrastructure (not shown) as intermediaries. The OTT connection 1824 can be transparent because the participating communication devices through which the OTT connection 1824 passes are unaware of the routing of the uplink and downlink communications. For example, the base station 1806 may not be notified or need not be notified of the past routing of the incoming downlink communication of data to be forwarded (e.g., handed over) from the host computer 1816 to the connected UE 1812. Similarly, the base station 1806 need not know the future routing of the outgoing uplink communication from the UE 1812 to the host computer 1816.

[0186] According to one embodiment, an example implementation of the UE, base station, and host computer discussed in the previous paragraphs will now be described with reference to Figure 19 In the communication system 1900, the host computer 1902 includes hardware 1904, and the hardware 1904 includes a communication interface 1906 configured to establish and maintain a wired or wireless connection to interfaces of different communication devices of the communication system 1900. The host computer 1902 further includes a processing circuit 1908, and the processing circuit 1908 may have storage and / or processing capabilities. In particular, the processing circuit 1908 may include one or more programmable processors, ASICs, FPGAs, or a combination of these items (not shown) suitable for executing instructions. The host computer 1902 further includes software 1910, and the software 1910 is stored in or accessible by the host computer 1902 and executable by the processing circuit 1908. The software 1910 includes a host application 1912. The host application 1912 is operable to provide services to remote users such as the UE 1914 connected via the OTT connection 1916 terminating at the UE 1914 and the host computer 1902. When providing services to remote users, the host application 1912 may provide user data transmitted using the OTT connection 1916.

[0187] The communication system 1900 further includes a base station 1918 provided in the telecommunication system, and the base station 1918 includes hardware 1920 enabling it to communicate with the host computer 1902 and the UE 1914. The hardware 1920 may include a communication interface 1922 for establishing and maintaining a wired or wireless connection to interfaces of different communication devices of the communication system 1900, and for establishing and maintaining a connection with the coverage area served by the base station 1918 ( Figure 19The radio interface 1924 of at least the radio connection 1926 of the UE 1914 (not shown in [figure number]). The communication interface 1922 may be configured to facilitate the connection 1928 with the host computer 1902. The connection 1928 may be direct, or the connection 1928 may be through the core network of the telecommunication system ( Figure 19 not shown in [figure number]) and / or through one or more intermediate networks external to the telecommunication system. In the illustrated embodiment, the hardware 1920 of the base station 1918 further includes a processing circuit 1930, which may include one or more programmable processors, ASICs, FPGAs, or a combination of these items (not shown) suitable for executing instructions. The base station 1918 also has software 1932 stored internally or accessible via an external connection.

[0188] The communication system 1900 also includes the aforementioned UE 1914. The hardware 1934 of the UE 1914 may include a radio interface 1936, which is configured to establish and maintain a radio connection 1926 with a base station in the coverage area where the UE 1914 is currently located. The hardware 1934 of the UE 1914 further includes a processing circuit 1938, which may include one or more programmable processors, ASICs, FPGAs, or a combination of these items (not shown) suitable for executing instructions. The UE 1914 also includes software 1940, which is stored in the UE 1914 or accessible by the UE 1914 and executable by the processing circuit 1938. The software 1940 includes a client application 1942. The client application 1942 is operable to provide services to a human or non-human user via the UE 1914 with the support of the host computer 1902. In the host computer 1902, the executing host application 1912 may communicate with the executing client application 1942 via the OTT connection 1916 terminating at the UE 1914 and the host computer 1902. When providing services to the user, the client application 1942 may receive request data from the host application 1912 and provide user data in response to the request data. The OTT connection 1916 may transmit both the request data and the user data. The client application 1942 may interact with the user to generate user-provided user data.

[0189] Note that Figure 19 the illustrated host computer 1902, base station 1918, and UE 1914 may be similar or identical to Figure 18 one of the host computers 1816, base stations 1806A, 1806B, 1806C, and one of the UEs 1812, 1814, respectively. That is, the internal working principles of these entities may be as Figure 19 shown, and independently, the surrounding network topology may be Figure 18 the surrounding network topology of [figure number].

[0190] In Figure 19 it, the OTT connection 1916 has been abstractly drawn to show the communication between the host computer 1902 and the UE 1914 via the base station 1918, without explicitly referring to any intermediate devices and the exact routing of messages via these devices. The network infrastructure can determine the routing, and the network infrastructure can be configured to hide the routing from the UE 1914 or from the service provider operating the host computer 1902 or both. When the OTT connection 1916 is active, the network infrastructure can further make a decision according to which the network infrastructure dynamically changes the routing (e.g., based on load balancing considerations or reconfiguration of the network).

[0191] The wireless connection 1926 between the UE 1914 and the base station 1918 is in accordance with the teachings of the embodiments described throughout this disclosure. One or more of the various embodiments improve the performance of the OTT services provided to the UE 1914 using the OTT connection 1916, where the wireless connection 1926 forms the final segment. More precisely, the teachings of these embodiments are capable of improving, for example, data rate, latency, power consumption, etc., thus providing benefits such as reduced user waiting time, relaxed file size limitations, better responsiveness, extended battery life, extended operating range.

[0192] A measurement process may be provided for purposes of monitoring data rate, latency, and other factors that are improved in one or more embodiments. In response to changes in the measurement results, there may also be optional network functions for reconfiguring the OTT connection 1916 between the host computer 1902 and the UE 1914. The measurement process and / or network functions for reconfiguring the OTT connection 1916 may be implemented in the software 1910 and hardware 1904 of the host computer 1902 or in the software 1940 and hardware 1934 of the UE 1914 or in both. In some embodiments, sensors (not shown) may be deployed in or associated with communication devices through which the OTT connection 1916 passes; the sensors may participate in the measurement process by providing values of the monitored quantities exemplified above or providing values of other physical quantities from which the software 1910, 1940 may calculate or estimate the monitored quantities. Reconfiguration of the OTT connection 1916 may include message format, retransmission settings, preferred routing, etc. The reconfiguration need not affect the base station 1918 and may be unknown or imperceptible to the base station 1918. Such processes and functions may be known and practiced in the art. In a particular embodiment, the measurement may involve proprietary UE signaling that facilitates measurement by the host computer 1902 of throughput, propagation time, latency, etc. The measurement may be implemented because the software 1910 and 1940 cause messages, particularly empty messages or "dummy" messages, to be sent using the OTT connection 1916 during their monitoring of propagation time, errors, etc.

[0193] Figure 20 is a flowchart showing a method implemented in a communication system according to one embodiment. The communication system includes a host computer, a base station, and a UE, which may be those host computers, base stations, and UEs referred to Figure 18 and 19 described. For simplicity of the present disclosure, only the reference to Figure 20 is included in this section. In step 2000, the host computer provides user data. In sub-step 2002 (which may be optional) of step 2000, the host computer provides user data by executing a host application. In step 2004, the host computer initiates a transmission carrying the user data to the UE. In step 2006 (which may be optional), according to the teachings of the embodiments described throughout the present disclosure, the base station sends the user data carried in the transmission initiated by the host computer to the UE. In step 2008 (which may also be optional), the UE executes a client application associated with the host application executed by the host computer.

[0194] Figure 21 is a flowchart showing a method implemented in a communication system according to one embodiment. The communication system includes a host computer, a base station, and a UE, which may be those host computers, base stations, and UEs referred to Figure 18 and19 The host computers, base stations, and UEs described. To simplify the present disclosure, only the Figure 21 accompanying drawings references are included in this section. In step 2100 of the method, the host computer provides user data. In an optional sub-step (not shown), the host computer provides user data by executing a host application. In step 2102, the host computer initiates a transmission carrying the user data to the UE. According to the teachings of the embodiments described throughout the present disclosure, this transmission may be via a base station. In step 2104 (which may be optional), the UE receives the user data carried in the transmission.

[0195] Figure 22 is a flowchart showing a method implemented in a communication system according to an embodiment. The communication system includes a host computer, a base station, and a UE, which may be the Figure 18 and 19 host computers, base stations, and UEs described. To simplify the present disclosure, only the Figure 22 accompanying drawings references are included in this section. In step 2200 (which may be optional), the UE receives input data provided by the host computer. Additionally or alternatively, in step 2202, the UE provides user data. In sub-step 2204 of step 2200 (which may be optional), the UE provides user data by executing a client application. In sub-step 2206 of step 2202 (which may be optional), the UE executes a client application that provides user data in response to the received input data provided by the host computer. When providing user data, the executed client application may further consider user input received from the user. Regardless of the specific manner of providing user data, the UE initiates a transmission of the user data to the host computer in sub-step 2208 (which may be optional). In step 2210 of the method, according to the teachings of the embodiments described throughout the present disclosure, the host computer receives the user data sent from the UE.

[0196] Figure 23 is a flowchart showing a method implemented in a communication system according to an embodiment. The communication system includes a host computer, a base station, and a UE, which may be the Figure 18 and 19 host computers, base stations, and UEs described. To simplify the present disclosure, only the Figure 23 accompanying drawings references are included in this section. In step 2300 (which may be optional), according to the teachings of the embodiments described throughout the present disclosure, the base station receives user data from the UE. In step 2302 (which may be optional), the base station initiates a transmission of the received user data to the host computer. In step 2304 (which may be optional), the host computer receives the user data carried in the transmission initiated by the base station.

[0197] Any suitable steps, methods, features, functions, or benefits disclosed herein may be performed by one or more functional units or modules of one or more virtual devices. Each virtual device may include a plurality of these functional units. These functional units may be implemented via a processing circuit, which may include one or more microprocessors or microcontrollers and other digital hardware that may include a digital signal processor (DSP), dedicated digital logic, etc. The processing circuit may be configured to execute program code stored in a memory, which may include one or several types of memories, such as read-only memory (ROM), random access memory (RAM), cache memory, flash memory devices, optical storage devices, etc. The program code stored in the memory includes program instructions for executing one or more telecommunication and / or data communication protocols and instructions for executing one or more techniques described herein. In some implementations, the processing circuit may be used to cause the corresponding functional units to perform corresponding functions according to one or more embodiments of the present disclosure.

[0198] Although the processes in the figures may show a specific order of operations performed by specific embodiments of the present disclosure, it should be understood that such an order is exemplary (e.g., alternative embodiments may perform the operations in a different order, combine specific operations, overlap specific operations, etc.).

[0199] Embodiment

[0200] Embodiments of Group A

[0201] 1. A method for decoding a transmission performed by a wireless device, the method comprising:

[0202] - Determining a plurality of transmission candidates to be monitored;

[0203] - For one or more of the plurality of transmission candidates, determining whether the candidate belongs to a first group of candidates or a second group of candidates;

[0204] - If the candidate belongs to the first group of candidates, attempting to decode the transmission using a CSI-based precoding scheme; and

[0205] - If the candidate belongs to the second group of candidates, attempting to decode the transmission using a predetermined precoding scheme.

[0206] 2. The method according to embodiment 1, wherein the transmission is an MPDCCH transmission.

[0207] 3. The method according to any one of Embodiments 1 to 2, wherein determining whether a candidate belongs to the first group of candidates or the second group of candidates includes: determining based on at least one of the time or frequency position of the associated resource block.

[0208] 4. The method according to any one of Embodiments 1 to 3, wherein the precoding technique is determined based on at least one of the following: a time index representing the time position of a resource block counted in time units, and a frequency index representing the frequency position of a resource block counted in frequency units.

[0209] 5. The method according to any one of Embodiments 1 to 4, wherein the time unit corresponds to a subframe.

[0210] 6. The method according to any one of Embodiments 1 to 5, wherein the frequency unit corresponds to the frequency range of a resource block.

[0211] 7. The method according to any one of Embodiments 1 to 6, wherein a threshold for using the precoding technique is determined based on a plurality of other parameters.

[0212] 8. The method according to any one of Embodiments 1 to 7, wherein cycling on a set of precoders is regarded as predefined precoding.

[0213] 9. The method according to any one of Embodiments 1 to 8, wherein an index of a first precoder is generated based on at least one of the following: a time index representing the time position of a resource block, and a frequency index representing the frequency position of a resource block.

[0214] 10. The method according to any one of Embodiments 1 to 9, wherein a fixed precoder can be used as predefined precoding.

[0215] 11. The method according to any one of Embodiments 1 to 10, wherein the frequency unit corresponds to the frequency range of a resource block.

[0216] 12. The method according to any one of Embodiments 1 to 11, wherein the precoding technique is selected from the group including: selecting a precoder based on CSI sent from a wireless device; selecting a precoder based on precoder cycling; and selecting a fixed precoder.

[0217] 13. The method according to any one of Embodiments 1 to 12, wherein when using frequency hopping to transmit control channel candidates, a subset of physical resource blocks belongs to different narrowbands.

[0218] 14. The method according to any one of embodiments 1 to 13, wherein frequency hopping is employed between at least two different narrow bands, and a precoding technique is used in one of the narrow bands, while a different precoding technique is used in at least one other narrow band.

[0219] 15. The method according to any one of embodiments 1 to 14, wherein when the precoding technique is based on a precoder cycle, the precoding matrix set includes a plurality of precoding matrices.

[0220] 16. The method according to any one of embodiments 1 to 15, wherein the channel state information includes a precoding matrix indicator PMI.

[0221] 17. The method according to any one of embodiments 1 to 16, further comprising:

[0222] - Using the determined precoder being used in the PRB pair for obtaining a channel estimate associated with the antenna port used for transmission in the PRB pair by performing channel estimation based on a combination of: DM-RS located in the PRB pair, and at least one of DM-RS located in one or more other PRB pairs and CRS located in any set of PRB pairs.

[0223] 18. The method according to any one of embodiments 1 to 17, further comprising:

[0224] - Using the determined precoder being used in the PRB pair for obtaining a channel estimate associated with the antenna port used for transmission in another PRB pair by performing channel estimation based on a combination of: DM-RS located in the PRB pair, and at least one of DM-RS located in one or more other PRB pairs and CRS located in any set of PRB pairs.

[0225] 19. The method according to any one of embodiments 1 to 18, further comprising:

[0226] - Using the determined precoder being used in the PRB pair for obtaining a channel estimate associated with the antenna port used for transmission in the PRB pair by performing channel estimation based on CRS located in any set of PRB pairs.

[0227] 20. The method according to any one of embodiments 1 to 19, further comprising:

[0228] - Using the obtained channel estimate associated with the antenna port used for transmission in one or more PRB pairs to demodulate the information received in the PRB pair.

[0229] 21. The method according to embodiment 20, wherein the information is associated with the MTC physical control channel MPDCCH or the physical downlink shared channel PDSCH.

[0230] 22. The method according to any one of embodiments 1 to 21, wherein the predetermined precoding scheme will be to use a certain precoder cycle, wherein the precoder used varies according to a predetermined time and / or frequency pattern.

[0231] 23. The method according to any one of the foregoing embodiments, further comprising:

[0232] - providing user data; and

[0233] - forwarding the user data to the host computer via transmission to the base station.

[0234] Embodiments of Group B

[0235] 24. A method for encoding a transmission performed by a base station, the method comprising:

[0236] - determining whether to encode the transmission to the wireless device using a CSI-based precoding scheme or a predetermined precoding scheme;

[0237] - if using a CSI-based precoding scheme, selecting a candidate for transmission from a first set of candidates;

[0238] - if using a predetermined precoding scheme, selecting a candidate for transmission from a second set of candidates.

[0239] 25. The method according to embodiment 24, wherein the transmission is an MPDCCH transmission.

[0240] 26. The method according to any one of embodiments 24 to 25, wherein determining whether a candidate belongs to the first set of candidates or the second set of candidates includes: determining based on at least one of the time or frequency position of the associated resource block.

[0241] 27. The method according to any one of embodiments 24 to 26, wherein the precoding technique is determined based on at least one of: a time index representing the time position of the resource block counted in time units, and a frequency index representing the frequency position of the resource block counted in frequency units.

[0242] 28. The method according to any one of embodiments 24 to 26, wherein the time unit corresponds to a subframe.

[0243] 29. The method according to any one of embodiments 24 to 28, wherein the frequency unit corresponds to the frequency range of the resource block.

[0244] 30. The method according to any one of embodiments 24 to 29, wherein a threshold for using precoding techniques is determined based on a plurality of other parameters.

[0245] 31. The method according to any one of embodiments 24 to 30, wherein cycling over a set of precoders is considered as predefined precoding.

[0246] 32. The method according to any one of embodiments 24 to 31, wherein an index of a first precoder is generated based on at least one of the following: a time index indicating a time position of a resource block, and a frequency index indicating a frequency position of a resource block.

[0247] 33. The method according to any one of embodiments 24 to 32, wherein a fixed precoder can be used as predefined precoding.

[0248] 34. The method according to any one of embodiments 24 to 33, wherein a frequency unit corresponds to a frequency range of a resource block.

[0249] 35. The method according to any one of embodiments 24 to 34, wherein the precoding technique is selected from the group comprising: selecting a precoder based on CSI transmitted from a wireless device; selecting a precoder based on precoder cycling; and selecting a fixed precoder.

[0250] 36. The method according to any one of embodiments 24 to 35, wherein when frequency hopping is used to transmit control channel candidates, a subset of physical resource blocks belongs to different narrowbands.

[0251] 37. The method according to any one of embodiments 24 to 36, wherein frequency hopping between at least two different narrowbands is employed, and one precoding technique is used in one narrowband while a different precoding technique is used in at least one other narrowband.

[0252] 38. The method according to any one of embodiments 24 to 37, wherein when the precoding technique is based on precoder cycling, the set of precoding matrices includes a plurality of precoding matrices.

[0253] 39. The method according to any one of embodiments 24 to 38, wherein the channel state information includes a precoding matrix indicator PMI.

[0254] 40. The method according to any one of embodiments 24 to 39, wherein a predefined precoding scheme will be to use a certain precoder cycling, wherein the precoder used varies according to a predefined time and / or frequency pattern.

[0255] 41. The method according to any one of the foregoing embodiments further comprises:

[0256] - obtaining user data; and

[0257] - forwarding the user data to a host computer or a wireless device.

[0258] Embodiments of Group C

[0259] 42. A wireless device for decoding a transmission, the wireless device comprising:

[0260] - a processing circuit configured to perform any of the steps of any one of Group A embodiments;

[0261] and

[0262] - a power supply circuit configured to supply power to the wireless device.

[0263] 43. A base station for encoding a transmission, the base station comprising:

[0264] - a processing circuit configured to perform any of the steps of any one of Group B embodiments;

[0265] and

[0266] - a power supply circuit configured to supply power to the base station.

[0267] 44. A user equipment UE for decoding a transmission, the UE comprising:

[0268] - an antenna configured to transmit and receive wireless signals;

[0269] - a radio front-end circuit connected to the antenna and the processing circuit and configured to condition signals transmitted between the antenna and the processing circuit;

[0270] - a processing circuit configured to perform any of the steps of any one of Group A embodiments;

[0271] - an input interface connected to the processing circuit and configured to allow information to be input into the UE for processing by the processing circuit;

[0272] - an output interface connected to the processing circuit and configured to output from the UE information that has been processed by the processing circuit; and

[0273] - a battery connected to the processing circuit and configured to supply power to the UE.

[0274] 45. A communication system comprising a host computer, the host computer comprising:

[0275] - A processing circuit configured to provide user data; and

[0276] - A communication interface configured to forward user data to a cellular network for transmission to a user equipment UE;

[0277] - Wherein the cellular network includes a base station having a radio interface and a processing circuit, and the processing circuit of the base station is configured to perform any of the steps of any one of Group B embodiments.

[0278] 46. The communication system according to the previous embodiment, further comprising: a base station.

[0279] 47. The communication system according to the previous two embodiments, further comprising: a UE, wherein the UE is configured to communicate with the base station.

[0280] 48. The communication system according to the previous three embodiments, wherein:

[0281] - The processing circuit of the host computer is configured to execute a host application to provide user data;

[0282] And

[0283] - The UE includes a processing circuit configured to execute a client application associated with the host application.

[0284] 49. A method implemented in a communication system including a host computer, a base station, and a user equipment UE, the method comprising:

[0285] - At the host computer, providing user data; and

[0286] - At the host computer, initiating a transmission carrying user data to the UE via a cellular network including the base station, wherein the base station performs any of the steps of any one of Group B embodiments.

[0287] 50. The method according to the previous embodiment, further comprising: at the base station, sending the user data.

[0288] 51. The method according to the previous two embodiments, wherein the user data is provided at the host computer by executing a host application, and the method further comprises: at the UE, executing a client application associated with the host application.

[0289] 52. A user equipment UE configured to communicate with a base station, the UE including a radio interface and a processing circuit, the processing circuit being configured to perform the method according to the previous three embodiments.

[0290] 53. A communication system including a host computer, the host computer comprising:

[0291] - A processing circuit configured to provide user data; and

[0292] - A communication interface configured to forward user data to a cellular network for transmission to a user equipment UE;

[0293] - wherein the UE includes a radio interface and a processing circuit, and the components of the UE are configured to perform any of the steps of any one of Group A embodiments.

[0294] 54. The communication system according to the previous embodiment, wherein the cellular network further includes a base station configured to communicate with the UE.

[0295] 55. The communication system according to the previous two embodiments, wherein:

[0296] - The processing circuit of the host computer is configured to execute a host application to provide user data;

[0297] and

[0298] - The processing circuit of the UE is configured to execute a client application associated with the host application.

[0299] 56. A method implemented in a communication system including a host computer, a base station, and a user equipment UE, the method comprising:

[0300] - At the host computer, providing user data; and

[0301] - At the host computer, initiating a transmission carrying user data to the UE via a cellular network including a base station, wherein the UE performs any of the steps of any one of Group A embodiments.

[0302] 57. The method according to the previous embodiment, further comprising: at the UE, receiving user data from the base station.

[0303] 58. A communication system including a host computer, the host computer including:

[0304] - A communication interface configured to receive user data sourced from a transmission from a user equipment UE to a base station;

[0305] - wherein the UE includes a radio interface and a processing circuit, and the processing circuit of the UE is configured to perform any of the steps of any one of Group A embodiments.

[0306] 59. The communication system according to the previous embodiment, further comprising: a UE.

[0307] 60. The communication system according to the previous two embodiments further comprises: a base station, wherein the base station comprises a radio interface configured to communicate with the UE and a communication interface configured to forward user data carried by a transmission from the UE to the base station to the host computer.

[0308] 61. The communication system according to the previous three embodiments, wherein:

[0309] - The processing circuitry of the host computer is configured to execute a host application; and

[0310] - The processing circuitry of the UE is configured to execute a client application associated with the host application so as to provide user data.

[0311] 62. The communication system according to the previous four embodiments, wherein:

[0312] - The processing circuitry of the host computer is configured to execute a host application so as to provide request data;

[0313] And

[0314] - The processing circuitry of the UE is configured to execute a client application associated with the host application so as to provide user data in response to the request data.

[0315] 63. A method implemented in a communication system comprising a host computer, a base station and a user equipment UE, the method comprising:

[0316] - At the host computer, receiving user data sent from the UE to the base station, wherein the UE executes any step of any one of the Group A embodiments.

[0317] 64. The method according to the previous embodiment further comprises: at the UE, providing user data to the base station.

[0318] 65. The method according to the previous two embodiments further comprises:

[0319] - At the UE, executing a client application so as to provide user data to be sent; and

[0320] - At the host computer, executing a host application associated with the client application.

[0321] 66. The method according to the previous three embodiments further comprises:

[0322] - At the UE, executing a client application; and

[0323] - At the UE, receiving input data to the client application, the input data being provided at the host computer by executing a host application associated with the client application;

[0324] - Among them, the user data to be sent is provided by the client application in response to the input data.

[0325] 67. A communication system including a host computer, the host computer including a communication interface configured to receive user data sourced from a transmission from a user equipment UE to a base station, wherein the base station includes a radio interface and a processing circuit, and the processing circuit of the base station is configured to perform any step of any one of the Group B embodiments.

[0326] 68. The communication system according to the previous embodiment, further comprising: a base station.

[0327] 69. The communication system according to the previous two embodiments, further comprising: a UE, wherein the UE is configured to communicate with the base station.

[0328] 70. The communication system according to the previous three embodiments, wherein:

[0329] - The processing circuit of the host computer is configured to execute a host application; and

[0330] - The UE is configured to execute a client application associated with the host application, thereby providing user data to be received by the host computer.

[0331] 71. A method implemented in a communication system including a host computer, a base station, and a user equipment UE, the method comprising:

[0332] - At the host computer, receiving user data sourced from a transmission that the base station has received from the UE, wherein the UE performs any step of any one of the Group A embodiments.

[0333] 72. The method according to the previous embodiment, further comprising: at the base station, receiving user data from the UE.

[0334] 73. The method according to the previous two embodiments, further comprising: at the base station, initiating transmission of the received user data to the host computer.

[0335] At least some of the following abbreviations may be used in the present disclosure. If there is an inconsistency between the abbreviations, the usage above shall be preferred. If listed multiple times below, the first listing shall be preferred over subsequent listings.

[0336] · 3GPP Third Generation Partnership Project

[0337] · 4G Fourth Generation

[0338] · 5G Fifth Generation

[0339] · AL Aggregation Level

[0340] ·AN Access Network

[0341] ·AP Access Point

[0342] ·ASIC Application Specific Integrated Circuit

[0343] ·AUSF Authentication Server Function

[0344] ·BCCH Broadcast Control Channel

[0345] ·BCH Broadcast Channel

[0346] ·BLER Block Error Rate

[0347] ·BS Base Station

[0348] ·CCCH Common Control Channel

[0349] ·CE Coverage Enhancement

[0350] ·CPU Central Processing Unit

[0351] ·CRC Cyclic Redundancy Check

[0352] ·C-RNTI Cell Radio Network Temporary Identifier

[0353] ·CRS Cell-Specific Reference Signal

[0354] ·CSI Channel State Information

[0355] ·CSI-RS Channel State Information Reference Signal

[0356] ·CSS Common Search Space

[0357] ·DCI Downlink Control Information

[0358] ·DL Downlink

[0359] ·DM Demodulation

[0360] ·DMRS Demodulation Reference Signal

[0361] ·DN Data Network

[0362] ·DSP Digital Signal Processor

[0363] ·ECCE Enhanced Control Channel Element

[0364] ·eMTC Enhanced Machine-Type Communication

[0365] ·eNB Enhanced or Evolved Node B

[0366] ·ePDCCH Enhanced Physical Downlink Control Channel

[0367] ·Field Programmable Gate Array (FPGA)

[0368] ·Gigahertz (GHz)

[0369] ·New Radio Base Station (gNB)

[0370] ·Hybrid Automatic Repeat reQuest (HARQ)

[0371] ·Internet of Things (IoT)

[0372] ·Internet Protocol (IP)

[0373] ·Long Term Evolution (LTE)

[0374] ·Machine-to-Machine (M2M)

[0375] ·Multiple-Input Multiple-Output (MIMO)

[0376] ·Mobility Management Entity (MME)

[0377] ·Minimum Mean Square Error (MMSE)

[0378] ·Machine-Type Communication Physical Downlink Control Channel (MPDCCH)

[0379] ·Machine-Type Communication (MTC)

[0380] ·NarrowBand Internet of Things (NB-IoT)

[0381] ·New Radio (NR)

[0382] ·Orthogonal Frequency Division Multiplexing (OFDM)

[0383] ·Orthogonal Frequency Division Multiple Access (OFDMA)

[0384] ·Over The Top (OTT)

[0385] ·Physical Broadcast Channel (PBCH)

[0386] ·Physical Downlink Control Channel (PDCCH)

[0387] ·Physical Downlink Shared Channel (PDSCH)

[0388] ·Packet Data Network Gateway (P-GW)

[0389] ·Precoder Matrix Indicator (PMI)

[0390] ·Physical Resource Block (PRB)

[0391] ·Primary Synchronization Signal (PSS)

[0392] ·Physical Uplink Control Channel (PUCCH)

[0393] · Physical Uplink Shared Channel (PUSCH)

[0394] · Random Access Memory (RAM)

[0395] · Radio Access Network (RAN)

[0396] · Radio Access Technology (RAT)

[0397] · Resource Block (RB)

[0398] · Resource Element (RE)

[0399] · Radio Frequency (RF)

[0400] · Radio Network Temporary Identifier (RNTI)

[0401] · Read-Only Memory (ROM)

[0402] · Radio Resource Control (RRC)

[0403] · Remote Radio Head (RRH)

[0404] · Radio Resource Management (RRM)

[0405] · Remote Radio Unit (RRU)

[0406] · Reference Signal (RS)

[0407] · Round-Trip Time (RTT)

[0408] · Receiver (RX)

[0409] · Service Capability Exposure Function (SCEF)

[0410] · Serving Gateway (S-GW)

[0411] · Signal-to-Noise Ratio (SNR)

[0412] · Secondary Synchronization Signal (SSS)

[0413] · Transmitter (TX)

[0414] · User Equipment (UE)

[0415] · Uplink (UL)

[0416] · Universal Serial Bus (USB)

[0417] · UE-Specific Search Space (USS)

[0418] Those skilled in the art will recognize improvements and modifications to the embodiments of the present disclosure. All such improvements and modifications are considered to be within the scope of the concepts disclosed herein.

Claims

1. A method for decoding a transmission performed by a wireless device, the method comprising: Determining (200) a plurality of machine type communication MTC physical downlink control channel MPDCCH transmission candidates to be monitored; For an MPDCCH transmission candidate among the plurality of MPDCCH transmission candidates, determining (202) whether the MPDCCH transmission candidate belongs to a first group of candidates or a second group of candidates, wherein the first group of candidates includes a first subset of a first search space, and the second group of candidates includes a combination of a second search space and a second subset of the first search space, wherein the second subset is a complement of the first subset, the first search space includes a user equipment UE specific search space, and the second search space includes a type 0 MPDCCH common search space; If the MPDCCH transmission candidate belongs to the first group of candidates, attempting (204) to decode the MPDCCH transmission using a precoding scheme based on channel state information CSI; and If the MPDCCH transmission candidate belongs to the second group of candidates, attempting (206) to decode the MPDCCH transmission using a predetermined precoding scheme.

2. The method according to claim 1, wherein, The predetermined precoding scheme is selected from the group consisting of: Selecting a precoder based on a precoder cycle; and Selecting a fixed precoder.

3. The method according to any one of claims 1 to 2, wherein Determining whether the MPDCCH transmission candidate belongs to the first group of candidates or the second group of candidates is based on the aggregation level (L) of the MPDCCH transmission candidate.

4. The method according to any one of claims 1 to 2, wherein Determining whether the MPDCCH transmission candidate belongs to the first group of candidates or the second group of candidates is based on one or more of the group consisting of: The aggregation level (L) of the MPDCCH transmission candidate; The index (m) identifying the MPDCCH transmission candidate within the search space for the aggregation level; The time repetition factor (R) of the MPDCCH transmission candidate; The sequential index (u) identifying the starting subframe of the MPDCCH transmission candidate for a given repetition factor; The time index identifying the time reference of the MPDCCH transmission candidate; The time index identifying the time reference of the search space; And The number of physical resource blocks for monitoring MPDCCH transmission candidates within the search space.

5. The method according to any one of claims 1 to 2, wherein Using a CSI-based precoding scheme includes: using a single precoding matrix, the single precoding matrix to be used for all physical resource blocks used to transmit the MPDCCH transmission candidate.

6. The method according to any one of claims 1 to 2, wherein Using a CSI-based precoding scheme includes: using a plurality of precoding matrices, each precoding matrix to be used for a subset of the physical resource blocks used to transmit the MPDCCH transmission candidate.

7. The method according to claim 6, wherein, When the MPDCCH transmission candidate is transmitted using frequency hopping, the subset of the physical resource blocks belongs to different narrowbands.

8. The method according to any one of claims 1 to 2, wherein Frequency hopping between at least two different narrowbands is employed, and one precoding scheme is used in one of the narrowbands while a different precoding scheme is used in at least one other narrowband.

9. The method according to any one of claims 1 to 2, wherein Using a predetermined precoding scheme includes: when the precoding technique is based on a precoder cycle, using multiple precoding matrices.

10. The method according to any one of claims 1 to 2, wherein, Using a CSI-based precoding scheme includes: using a precoder based on the channel state information transmitted by the wireless device.

11. The method according to claim 10, wherein The channel state information includes a precoding matrix indicator PMI.

12. The method according to any one of claims 1 to 2, further comprising: Using the determined precoder being used in a physical resource block PRB pair for obtaining a channel estimate associated with an antenna port used for transmission in the PRB pair by performing channel estimation based on a combination of: a demodulation reference signal DM-RS located in the PRB pair, and at least one of a DM-RS located in one or more other PRB pairs and a cell-specific reference signal CRS located in any set of PRB pairs.

13. The method according to any one of claims 1 to 2, further comprising: Using the determined precoder being used in a PRB pair for obtaining a channel estimate associated with an antenna port used for transmission in another PRB pair by performing channel estimation based on a combination of: a DM-RS located in the PRB pair, and at least one of a DM-RS located in one or more other PRB pairs and a CRS located in any set of PRB pairs.

14. The method according to any one of claims 1 to 2, further comprising: Using the determined precoder being used in a PRB pair for obtaining a channel estimate associated with an antenna port used for transmission in the PRB pair by performing channel estimation based on a CRS located in any set of PRB pairs.

15. The method according to claim 12, further comprising: Using the obtained channel estimate associated with an antenna port used for transmission in one or more PRB pairs to demodulate information received in the PRB pair.

16. The method according to claim 12, further comprising: Using the obtained channel estimate associated with an antenna port used for transmission in one or more PRB pairs to demodulate information received in the PRB pair, wherein the information is associated with the MPDCCH or a physical downlink shared channel PDSCH.

17. A method for encoding a transmission performed by a base station, the method comprising: Determining (300) whether to encode a machine type communication MTC physical downlink control channel MPDCCH transmission to a wireless device using a CSI-based precoding scheme or a predetermined precoding scheme; If using the CSI-based precoding scheme, selecting (302) an MPDCCH transmission candidate from a first set of candidates, wherein the first set of candidates includes a first subset of a first search space, and the first search space includes a user equipment UE-specific search space; If the predetermined precoding scheme is used, an MPDCCH transmission candidate is selected (304) from a second set of candidates, where the second set of candidates includes a combination of a second search space and a second subset of the first search space, where the second subset is the complement of the first subset, and the second search space includes a type 0 MPDCCH common search space.

18. The method according to claim 17, further comprising: Determining to encode transmissions to the wireless device using the predetermined precoding scheme if CSI has not been received from the wireless device or if CSI received from the wireless device is considered unreliable.

19. The method according to any one of claims 17 to 18, wherein The predetermined precoding scheme is selected from a group including: Selecting a precoder based on a precoder cycle; and Selecting a fixed precoder.

20. The method according to any one of claims 17 to 18, wherein, Determining whether to encode the MPDCCH transmission to the wireless device using a CSI-based precoding scheme or a predetermined precoding scheme is based on the aggregation level (L) of the MPDCCH transmission candidate.

21. The method according to any one of claims 17 to 18, wherein Determining whether to encode the MPDCCH transmission to the wireless device using a CSI-based precoding scheme or a predetermined precoding scheme is based on one or more of a group including: The aggregation level (L) of the MPDCCH transmission candidate; The index (m) identifying the MPDCCH transmission candidate for the aggregation level within the search space; The time repetition factor (R) of the MPDCCH transmission candidate; The sequential index (u) identifying the starting subframe of the MPDCCH transmission candidate for a given repetition factor; The time index identifying the time reference of the MPDCCH transmission candidate; The time index identifying the time reference of the search space; And The number of physical resource blocks for monitoring MPDCCH transmission candidates within the search space.

22. The method according to any one of claims 17 to 18, wherein Using a CSI-based precoding scheme includes: using a single precoding matrix, where the single precoding matrix is to be used for all physical resource blocks used to transmit the MPDCCH transmission candidate.

23. The method according to any one of claims 17 to 18, wherein Using a CSI-based precoding scheme includes: using multiple precoding matrices, where each precoding matrix is to be used for a subset of the physical resource blocks used to transmit the MPDCCH transmission candidate.

24. The method according to claim 23, wherein When the MPDCCH transmission candidate is transmitted using frequency hopping, the subset of the physical resource blocks belongs to different narrowbands.

25. The method according to any one of claims 17 to 18, wherein Frequency hopping between at least two different narrowbands is employed, and one precoding scheme is used in one of the narrowbands while a different precoding scheme is used in at least one other narrowband.

26. The method according to any one of claims 17 to 18, wherein Using a predetermined precoding scheme includes: using multiple precoding matrices when the precoding technique is based on a precoder cycle.

27. The method according to any one of claims 17 to 18, wherein Using a CSI-based precoding scheme includes: using a precoder based on channel state information transmitted by the wireless device.

28. The method according to claim 25, wherein, The CSI includes a precoding matrix indicator (PMI).

29. A wireless device (1600) for decoding transmissions, the wireless device (1600) comprising: One or more processors (1602); and a memory (1604) including instructions to cause the wireless device (1600) to: determine a plurality of machine-type communication (MTC) physical downlink control channel (MPDCCH) transmission candidates to be monitored; for an MPDCCH transmission candidate among the plurality of MPDCCH transmission candidates, determine whether the MPDCCH transmission candidate belongs to a first group of candidates or a second group of candidates, wherein the first group of candidates includes a first subset of a first search space, the second group of candidates includes a combination of a second search space and a second subset of the first search space, wherein the second subset is a complement of the first subset, the first search space includes a user equipment (UE)-specific search space, and the second search space includes a type 0 MPDCCH common search space; if the MPDCCH transmission candidate belongs to the first group of candidates, attempt to decode the MPDCCH transmission using a precoding scheme based on channel state information (CSI); and if the MPDCCH transmission candidate belongs to the second group of candidates, attempt to decode the MPDCCH transmission using a predetermined precoding scheme.

30. The wireless device (1600) according to claim 29, wherein, The instructions further cause the wireless device (1600) to perform the method according to any one of claims 2 to 16.

31. A base station (1300) for encoding a transmission, the base station (1300) including: one or more processors (1304); and a memory (1306) including instructions to cause the base station (1300) to: determine whether to encode a machine-type communication (MTC) physical downlink control channel (MPDCCH) transmission to a wireless device using a precoding scheme based on channel state information (CSI) or a predetermined precoding scheme; if using the CSI-based precoding scheme, select an MPDCCH transmission candidate from a first group of candidates, wherein the first group of candidates includes a first subset of a first search space, and the first search space includes a UE-specific search space; if using the predetermined precoding scheme, select an MPDCCH transmission candidate from a second group of candidates, wherein the second group of candidates includes a combination of a second search space and a second subset of the first search space, wherein the second subset is a complement of the first subset, and the second search space includes a type 0 MPDCCH common search space.

32. The base station (1300) according to claim 31, wherein, The instructions further cause the base station (1300) to perform the method according to any one of claims 18 to 28.

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