CN111279775A

CN111279775A - Shared pilot signal

Info

Publication number: CN111279775A
Application number: CN201880052188.0A
Authority: CN
Inventors: 赛巴斯钦·华格纳; 欧麦尔·萨利姆; 布鲁诺·杰裘克斯
Original assignee: Jiekai Communications Shenzhen Co Ltd
Current assignee: Jiekai Communications Shenzhen Co Ltd
Priority date: 2017-08-11
Filing date: 2018-08-09
Publication date: 2020-06-12
Anticipated expiration: 2038-08-09
Also published as: GB201712917D0; GB2565352A; CN111279775B; WO2019029593A1

Abstract

The application discloses a method and a system for transmitting reference symbols in an OFDM transmission system, the reference symbols can be flexibly arranged in a mini-slot to improve the overhead allocated to the transmission of the reference symbols, and the reference symbols can be shared between a control part and a data part of the mini-slot.

Description

Shared pilot signal

Technical Field

The present application relates to a pilot signal in an Orthogonal Frequency Division Multiplexing (OFDM) transmission system, and more particularly, to a shared pilot signal.

Background

Wireless communication systems, such as Third Generation (3G) mobile telephone standards and technologies are well known, and such 3G standards and technologies have been developed by the Third Generation Partnership Project (3 GPP). The third generation of wireless communications has generally supported macrocell mobile telephone communications and communication systems and networks have evolved towards broadband and mobile systems.

The third generation partnership project has developed a so-called Long Term Evolution system (LTE), an Evolved universal mobile telecommunications system Terrestrial radio access Network (E-UTRAN), for a mobile access Network of one or more macro cells supported by base stations called enodebs or enbs (Evolved nodebs). Recently, LTE is further evolving towards so-called 5G or NR (new radio) systems, in which a base station called a gNB supports one or more macro cells.

NR proposes an Orthogonal Frequency Division Multiplexing (OFDM) transmission format for the radio link of the system. The OFDM system uses a plurality of subcarriers arranged at frequency intervals, each subcarrier is independently modulated, and a demodulation subcarrier set can recover a signal. Slots are used to define the transmission schedule, each slot comprising several OFDM symbols, NR having proposed that each slot comprises 7 or 14 OFDM symbols. Within each time slot, subcarriers or frequency resources may be used to carry one or more channels on the link. Further, each time slot may contain all uplink, downlink, or hybrid direction links.

To improve scheduling flexibility, NR also proposes mini-slots (TR 38.912) that may contain 1 — (slot length-1) OFDM symbols. Each mini-slot may start at any OFDM symbol within a single slot. The gNB allows scheduling of mini-slots on some pre-allocated resources, replacing existing scheduling decisions to meet the delay constraints of some delay-critical services. Some configurations may be limited to systems beyond 6GHz or to a minimized mini-slot length with 2 OFDM symbols. The gNB may schedule mini-slots through the same digital scheme as the slots or a different digital scheme.

The 5G provides a range of services including enhanced mobile broadband (eMBB) for high data rate transmission, high-reliability Low latency communications (URLLC) suitable for Low latency and high link reliability device requirements, and massive Machine Type of Communication (mtc) that supports a large number of Low power devices to achieve long lifetime requirements but is energy efficient.

TR 38.913 defines the delay as "the time required to successfully send an application layer data packet/message from a radio protocol layer 2/3 Service Data Unit (SDU) entry point to a radio protocol layer 2/3SDU exit point over the uplink and downlink radio interfaces". For URLLC, the user plane delay is targeted to Uplink (UL)0.5ms and Downlink (DL)0.5 ms.

TR 38.913 defines reliability as "reliability can be evaluated as the probability of successful transmission of X bytes at a certain channel quality (e.g., coverage margin) within a certain delay, which is the time it takes to transmit a small packet from the ingress point of a broadcast protocol layer 2/3SDU to the egress point of the broadcast protocol layer station interface 2/3 SDU". For URLLC, the user plane delay is 1ms, and the reliability requirement for a single transmission of a single packet is defined as 1 × 10^-532 bytes.

Many conventional radio systems use cell-specific pilot Reference Symbols (RS) to allow for consistent reception of data. In contrast, NR proposes to use a dedicated RS for each physical channel, instead of providing a cell-specific RS. In NR, RS sequence and density are defined as communication based on a slot.

Two types of configurations are currently proposed for a single OFDM symbol with a Demodulation Reference Signal (DMRS). Fig. 1 shows a configuration type 1 in which two antenna ports are multiplexed in a frequency comb structure. Fig. 2 shows a configuration type 2 of a Frequency-Domain (FD) Orthogonal Cover Code (OCC) based on a neighboring Resource Element (RE), which can support up to 6 antenna ports.

In both configuration types, all resources of an OFDM symbol are used for DMRSs supporting at most antenna ports. For 2 antenna ports, configuration type 1 uses all resources and configuration type 2 uses 1/3 resources (which uses 2/3 resources for 4 antenna ports). This resource consumption may be appropriate when DMRS is used for a slot, but for a mini-slot that may be as short as 1 OFDM symbol, it occupies a significant portion of the resources. The overhead of the RS is very large based on the existing role of the RS in each physical channel.

By using OCC in the time domain,

configuration types

1 and 2 are defined to accommodate up to 8 and 12 antenna ports, respectively, over more than two symbols.

Fig. 3 shows a specific embodiment of DMRS overhead in a mini-slot. Mini-slot 1 includes 4 OFDM symbols, of which 2 OFDM symbols include a Physical Downlink Control Channel (PDCCH) carrying DMRS, and the other 2 OFDM symbols include data. The first data OFDM symbol further includes a DMRS of a PDSCH (Physical Downlink Shared Channel) data Channel in the mini-slot.

Mini-slot 2 includes two OFDM symbols, one for control information and one for data, each carrying a respective DMRS. In this mini-slot, DMRS does not use all resources in each OFDM symbol, and thus some resources may be provided for control information and data.

The first symbol in the mini-slot 302 includes control information carrying DMRS, and data on PDSCH, and the following two symbols include data carrying DMRS transmitted in the first symbol.

The embodiment of fig. 3 highlights the overhead that occurs when one DMRS is needed for each channel, and thus, an RS structure needs to be improved.

The present application is directed to solving at least some of the significant problems in the art.

Disclosure of Invention

This application presents some concepts in a simplified form that are further described below in the detailed description. This application is not intended to highlight essential or essential features of the claimed subject matter or to limit the scope of the claimed subject matter.

An embodiment of the present application provides a method for transmitting downlink data in a cellular communication system from a base station to a user equipment using an OFDM modulation format, the method including the steps of: defining a mini-slot comprising at least one control OFDM symbol and at least one data OFDM symbol, wherein DRMS is encoded on and shared between said control OFDM symbol and/or data OFDM symbol; transmitting the mini-slots from the base station to the user equipment.

The DRMS is encoded on one of the control OFDM symbols or one of the data OFDM symbols.

A portion of the DRMS is encoded on one of the control OFDM symbols and another portion of the DRMS is encoded on one of the data OFDM symbols.

Only one DRMS may be encoded on each subcarrier of the mini-slot.

The control information may occupy only a part of subcarriers of the at least one control OFDM symbol, and the remaining subcarriers of the at least one control OFDM symbol are used for carrying data.

The at least one control OFDM symbol occupies fewer frequency resources than the at least one data OFDM symbol, wherein DRMS of the frequency resources used by the at least one control OFDM symbol may be encoded on one control OFDM symbol, while DRMS of the frequency resources used only by the at least one data OFDM symbol is encoded on one data OFDM symbol.

The control OFDM symbol and the data OFDM symbol may be transmitted using the same at least one antenna port.

The mini-slots may be transmitted using multiple antenna ports.

Transmitting the at least one data OFDM symbol using more antenna ports than transmitting the at least one control OFDM symbol.

Transmitting the DRMS through all antenna ports used by the at least one data OFDM symbol, and transmitting the at least one control OFDM symbol through a part of the antenna ports.

The portion of the antenna ports may be a single port.

Additional antenna ports may be used in the at least one control OFDM symbol for more data OFDM symbols.

The single port may be a first port for transmitting the control OFDM symbol.

The transmission module of the data part of the at least one control OFDM symbol may be the same as the transmission module of the data OFDM symbol.

The DRMS may be a DRMS sequence.

The DMRS may comprise a double-sequence group, a first sequence of the double-sequence group spanning the at least one control OFDM symbol and a second sequence spanning the at least one data OFDM symbol of frequency resources not covered by the first sequence.

The DMRS may be non-user specific.

An embodiment of the present application further provides a method for receiving, at a user equipment, a downlink data transmission at a base station in a cellular communication system using an OFDM modulation format, the method including the steps of: receiving an OFDM signal comprising at least one mini-slot, the mini-slot comprising at least one control OFDM symbol and at least one data OFDM symbol, wherein at least one of the control OFDM symbol and data OFDM symbol receives a DMRS; decoding the mini-slot for the at least one control OFDM symbol and the at least one data OFDM symbol using the DMRS.

The DRMS may be encoded entirely on one of the control OFDM symbols or one of the data OFDM symbols.

A portion of the DRMS may be encoded on one of the control OFDM symbols and a portion of the DRMS may be encoded on one of the data OFDM symbols.

Only one DRMS may be encoded on each subcarrier of the mini-slot.

The at least one control OFDM symbol may occupy less frequency resources than the at least one data OFDM symbol, wherein DRMS of the frequency resources used by the at least one control OFDM symbol may be encoded on one control OFDM symbol, and DRMS of the frequency resources used only by the at least one data OFDM symbol is encoded on one data OFDM symbol.

The DMRS may be one DMRS sequence.

A non-transitory computer readable medium, the non-transitory computer readable medium may comprise: at least one of a hard disk, a compact disk Read-Only Memory (CD-ROM), an optical storage device, a magnetic storage device, a Read-Only Memory, a programmable Read-Only Memory, an erasable programmable Read-Only Memory, an electrically programmable Read-Only Memory (EPROM), an electrically erasable programmable Read-Only Memory, and a flash Memory.

Drawings

Further details, aspects and embodiments of the present application are described below, by way of example only, with reference to the accompanying drawings. Elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For ease of understanding, each figure includes a reference numeral.

Fig. 1 and 2 show examples of DMRSs for a plurality of ports.

FIG. 3 shows an example of a mini-slot.

Fig. 4 shows an example of a shared DMRS transmitted in a control portion.

Fig. 5 shows an example of mini-slots carrying partial DMRS transmissions in the control portion and the data portion.

Fig. 6 shows an example of DMRS transmitted in a data portion.

Detailed Description

Those skilled in the art will recognize and appreciate that the example details described herein are merely illustrative of some embodiments and that the inventive concepts set forth in the present application are applicable in a variety of alternative contexts.

The following application provides a method for improving spectral efficiency of DMRS transmission in a mini-slot by sharing the DMRS in a control channel and a data channel of the mini-slot.

The following will describe the environment of a cellular communication system that includes a land-based network component and remote User Equipment (UE), and more particularly to the wireless channel between a base station of a land-based network and user equipment. Transmissions from the base station to the user equipment are in the downlink direction and transmissions from the user equipment to the base station are in the uplink direction, and the base station may include or be connected to a gNB that performs network management and control functions.

Fig. 4 shows a schematic diagram of a shared DMRS in a mini-slot. Fig. 4(a) shows respective common control DMRS and data DMRS cases in a mini-slot of 3 OFDM symbol length. The first OFDM symbol carries the PDCCH of the mini-slot, and the DMRS of the control channel. The second OFDM symbol carries the mini-slot PDSCH data channel and DMRS. Therefore, as described above, DMRS overhead is large for transmission of a small amount of data.

In fig. 4(b), one DMRS transmission is shared between the control channel and the data channel, so that the first OFDM symbol includes the PDCCH, and the shared DMRS of the PDCCH and the subsequent PDCSH in the mini-slot. Therefore, DMRS overhead is reduced for the same mini-slot length. To allow both PDCCH and PDSCH to use the same DMRS, the channel is typically transmitted from the same antenna port.

Fig. 4(c) shows a configuration in which the PDCCH does not occupy the entire OFDM symbol, so that data can be multiplexed into the unused portion of the first OFDM symbol in the mini-slot, further increasing the data capacity. In this case, the shared DMRS sequence should span outside the control part, e.g., covering all frequency resources allocated to the mini-slot.

The particular arrangement of channels within each OFDM symbol is variable and depends on the particular configuration and channel usage of each system.

Fig. 5(a) shows a conventional embodiment in which the control portion (in the first OFDM symbol) uses fewer frequency resources (subcarriers) than the data portion of the mini-slot. Since DMRS is transmitted on respective subcarriers of the control portion and the data portion, system performance is not affected.

Fig. 5(b) illustrates a transmission system that avoids DMRS repetition. The shared DMRS of the control portion is transmitted in the first OFDM symbol on the corresponding subcarrier. In the first data OFDM symbol, the DMRS is transmitted on subcarriers outside of the control portion of the mini-slot, and the DMRS is not transmitted on subcarriers used by the control portion of the mini-slot. The subcarriers common to the control portion and the data portion depend on the shared DMRS placed in the first OFDM symbol within the control region of the mini-slot. Therefore, these DMRSs from the control portion are used to decode the corresponding subcarriers in the entire mini-slot. The additional frequency subcarriers allocated to the mini-slot data will require a dedicated DMRS to demodulate the data on these frequency carriers. These data are the first data symbol in which DMRS is placed on an additional subcarrier not belonging to the control region, and the second symbol of the mini-slot.

In the above disclosed embodiments, the DMRS is transmitted in the first symbol of each channel, and when the DMRS is idle at the beginning of each channel transmission, the delay may be minimized. However, DMRS may be transmitted in different OFDM symbols in a mini-slot.

In general, when the DMRS is transmitted in the first symbol, a user equipment may receive the DMRS and decode the PDCCH. The PDCCH contains the allocation details of the data frequency carriers to allow decoding of the data OFDM symbols. If DMRS is transmitted only in data symbols, the user equipment must decode the received signals in different orders and restrict the use of subcarriers in the control part and the data part, and particularly all subcarriers used by PDCCH in mini-slots must be used for PDSCH in mini-slot OFDM symbols. The user equipment therefore receives the shared DMRS on all relevant subcarriers to decode the PDCCH and then the PDSCH. The PDSCH may use more subcarriers if all PDCH subcarriers are included.

Fig. 6(a) shows a conventional embodiment in which the control (PDCCH) and data (PDSCH) portions of a mini-slot carry DMRS in the first relevant OFDM symbol.

Fig. 6(b) shows the same mini-slot, both the control part and the data part of which use the same frequency resources. The DMRS is transmitted only in the first OFDM symbol of the data portion, and the shared DMRS is used to demodulate control information first and then data. Once the user equipment receives the DMRS, both the control portion and the data portion may be decoded.

In fig. 6(c), only a portion of the subcarriers used by the data are used for the control portion of the mini-slot, and the data use the remaining portion of the mini-slot. As shown in fig. 6(c), DMRS is transmitted between all data subcarriers, and thus, a user equipment can decode a control portion and a data portion of a mini-slot. The shared DMRS in the first symbol of data will be allocated to the frequency carrier configured and used by the control region, and the additional spectrum carrier used by the data will be provided with a dedicated DMRS.

In order to share the DMRS between the control OFDM symbol and the data OFDM symbol, these symbols must all be transmitted through the same antenna port.

In the case where a plurality of antenna ports are used for data transmission, the antenna ports used by the control section may be the same group as the antenna ports used when data is transmitted, or may be only a part of the antenna ports used when data is transmitted. The control section may select a specific port, such as the first port. The shared DMRSs for all antenna ports used for data may be embedded in a control region or a data region, thereby facilitating demodulation of control information and data information through the shared pilots. Another technique may be to embed the shared pilot in the control region or data region of a common antenna port (used for transmission of control information and data), and the additional antenna port used for data transmission may have a dedicated DMRS in the data region.

If the precoding vector is optimized for multi-layer data transmission, this precoding vector may not be optimal for single port control transmission. One compensation scheme is to apply a power offset in the control region, and the other is to make a precoding design choice to select the first precoding vector to optimize multi-layer data and single-layer control information transmission. In the first scheme, if the control area has some REs (resource elements) beyond or inside the CORESET, these REs can be used for data multiplexing. In this scheme, although the control information may be transmitted through a single antenna port or through single antenna transmit diversity, the data REs in the data region or the data REs multiplexed in the control region may be transmitted through multi-antenna port transmission.

The mini-slot data may be further multiplexed in the control region by the following mechanism. If data is transmitted through N ports, DMRSs of the N antenna ports are transmitted in a control part or a data part. In a Control part without a CORESET (Control-resource set) or Control Channel Element (CCE), the gNB multiplexes data transmitted by the multiple antenna ports.

An additional multiplexing can also be obtained on the resource units carrying the control information. The first data antenna port is used for transmitting control information and the remaining antenna ports (spatial layers other than the first layer) are used for transmitting data. If multiple antenna transmission modules are agreed to be used from a fixed subset, the user equipment may find some interference from the control information, or the user equipment may not know that the antenna port is in use, but the user equipment may attempt to demodulate the reference symbols from the fixed subset. By comparing the estimated channel powers at different transmission modules (different antenna ports), the user equipment can identify the active transmission module.

In one example, a conventional mini-slot may be 10 PRBs (physical resource blocks) for 2 OFDM symbols, where the first symbol is used for control and the second symbol is used for data. If the RS density of the control region is 1/3 (single antenna configuration 2), there are 40 RSs and 80 REs of control information in 10 × 12 — 120 REs, and 40 RSs and 80 data REs in the data part using configuration type 2(1/3RS), so there are 80+80 — 160 REs available for control and data as a whole.

If the transmission of DMRS and the use of shared pilots in the control portion have the same RS density, 40 RSs and 80 control information RSs are available in the control portion. In the data portion, the entire OFDM symbol is available and 120 REs are provided. Therefore, the mini-slot with the shared DMRS provides 200 REs compared to 160 REs provided by the conventional method without loss of channel estimation quality.

In another example, a mini-slot is configured to: the control information is transmitted using a single antenna port and the data portion is transmitted through two antenna ports. The splitting of the DMRS and control information resource elements by control symbols for the respective DMRSs of the control and data parts is the same as in the previous embodiment. If the data part uses 2 antenna ports for the same resource (10 PRBs ═ 120 REs), the DMRS part in the data region occupies the same number of resource elements as the DMRS configuring one or two antenna ports in type 2. However, 80 data REs effectively become 80 × 2 ═ 160 REs. Therefore, when both have dedicated DMRSs, all available control REs and data REs are 80+ 160-240.

For a shared DMRS scenario where DMRSs for two ports are embedded in a control region and control information is transmitted through one of the antenna ports, the control portion resource usage remains unchanged (40 RSs and 80 REs), but all resource elements in the data portion are now available for two port usage information data, providing 240 REs, providing a total of 320 REs for control and data compared to 240 in the conventional case.

Therefore, the proposed DMRS sharing structure reduces the expected overhead.

NR intends to support multi-user (MU) MIMO of PDCCH. Reference symbols may be shared between control and data for the purpose of overhead reduction discussed above. The control portion of the mini-slot may embed reference symbols so that the user equipment can estimate its channel and intent to decode the control information, and then each user's data transmission can be accomplished by using their antenna port that receives the reference symbols and the respective control information.

The reference sequences may be orthogonal or non-orthogonal for each User scheduled in a MU-MIMO (Multi-User Multiple-Input Multiple-Output) system. The reference sequence of each user may be a function of a Radio Network Temporary Identity (RNTI), or may be notified to the relevant user in advance through higher layer (MAC or RRC) signaling. Each scheduled user equipment considers itself to be the only one scheduled on the physical resource, so that the reference symbols (sequences) appear to be transmitted to the user equipment from a single antenna port for control and data transmission.

In one embodiment, the orthogonal sequence may be a length of Zadoff-Chu sequence with different cyclic shifts that are orthogonal to each other. If PN sequences are used, they are not perfectly orthogonal but have good auto-and cross-correlation properties. While a user may perform channel estimation and demodulation on the control information, another technique is to use orthogonal cover codes in time, frequency, or time-frequency for the reference symbols of different users. With respect to the density of the reference sequence, it may follow any configuration, such as configuration type 1 or configuration type 2 or variants of these configurations.

As described below, MIMO operations may be through multiplexing techniques similar to LTE TM5(MU-MIMO) or through multi-layer beamforming similar to LTE TM7 when transmitting to two users simultaneously using dual-layer beamforming on the same time-frequency resources.

The "transmitted" users can be scheduled for single layer and single port transmission and they do not need to know the presence of other users to decode the data. One way to improve demodulation performance is to communicate to these users some restriction information by which the users can apply some interference suppression or cancellation strategy.

While it is generally accepted that the typical use of mini-slots is for a single user, the standard does not limit the use of mini-slots to a single user, and therefore, the network is free to schedule multiple users in a single mini-slot, for which a single user is scheduled, the DMRS should be user-specific.

One case is to schedule multiple users on orthogonal time-frequency resources, thus excluding MU-MIMO or multi-layer beamforming for multiple users on the same resource. For these mini-slots of multiple users, the shared DMRS can only be achieved if the users transmit through the same antenna port and include a port for transmitting control information. In this case, DMRS sharing between control and data for these users may be achieved by using a common (mini-slot user-common) DMRS (a kind of LTE cell-specific reference symbol).

Various methods of sharing DMRS between control and data of mini-slots are presented, including single-port and multi-port transmissions, and scheduling of single or multiple users in mini-slots.

Sharing may be achieved using a single sequence spanning mini-slot time-frequency resources.

In the alternative, two sequences can be used in addition to the control frequency carrier, including one control DMRS sequence spanning the control region frequency carrier and one data DMRS sequence spanning the remaining frequency resources of the scheduled mini-slot data.

The advantages of using a single sequence are: the detection and channel estimation performance of DMRS may be better, which is advantageous in case of multi-port transmission to a single user or multiple users. All the discussions in the previous section apply equally to the case where the DMRS is a single sequence.

Using two different DMRS sequences, one for the control DMRS and the other for the data DMRS, may limit the mini-slot usage for single-antenna port transmissions. To overcome this limitation, DMRSs of additional ports may be added in the control region. These additional DMRSs in the control region may follow the DMRS configuration of data or may be multiplexed on the same resources as the DMRSs of the control region. By selecting different cyclic shifts, DMRSs for additional data ports may be placed in the control region in an orthogonal manner using Zadoff-chu (zc) sequences. For PN sequences used for DMRS, multiplexing on the same resource will result in a decrease in correlation performance.

The above discloses primarily a kind of pre-loaded data DMRS (DMRS that occupies one or two symbols at the beginning of data in a mini-slot) on each frequency resource in the mini-slot. However, for a long mini-slot, the mini-slot may require more DMRS, e.g., in a high doppler scenario.

Although not shown in detail, any device or apparatus forming part of a network may comprise at least a processor, a memory unit, and a communication interface configured to perform any of the methods mentioned in the present disclosure. Various aspects and concepts are further described below.

The signal processing functions in the embodiments of the present application, in particular the signal processing functions of the gNB and the user equipment, may be implemented using computer systems or architectures well known to those skilled in the art. For a given application or environment, a computer system, such as a desktop, laptop or notebook computer, handheld computing device (PDA, cell phone, palmtop, etc.), mainframe, server, client, or any other type of special or general purpose computing device may be used. The computer system may include one or more processors, which may be implemented using a general-purpose or special-purpose processing engine such as, for example, a microprocessor, microcontroller or other control module.

The computer system may also include a main memory, such as a Random Access Memory (RAM) or other dynamic memory, for storing information and instructions to be executed by the processor. Such main memory may also be used for storing temporary variables or other intermediate information during execution of instructions to be executed by the processor. Likewise, the computer system may include a Read Only Memory (ROM) or other static storage device for storing static information and instructions for the processor.

The computer system may also include an information storage system that may include, for example, a media drive and a removable storage interface. The media drive may include a drive or other structure to support fixed or removable storage media, such as a hard disk drive, a floppy disk drive, a magnetic tape drive, an optical disk drive, a Compact Disk (CD), a Digital Video Drive (DVD) read-write drive (R or RW), or other removable or fixed media drive. The storage media may include, for example, a hard disk, floppy disk, magnetic tape, optical disk, CD, DVD, or other fixed or removable medium that is read by and written to by a media drive. The storage media may include a computer-readable storage medium having stored thereon particular computer software or data.

In alternative embodiments, the information storage system may include other similar components for allowing computer programs or other instructions or data to be loaded into the computer system. These components may include, for example, removable storage units and interfaces, such as program cartridges and cartridge interfaces, removable memory (e.g., flash memory or other removable memory modules) and memory slots, and other removable storage units and interfaces that allow software and data to be transferred from the removable storage unit to the computer system.

The computer system may also include a communications interface operable to allow software and data to be transferred between the computer system and external devices. The communication interface may include a modem, a network interface (e.g., an ethernet or other NIC network card), a communication port (e.g., a Universal Serial Bus (USB) port), a PCMCIA (Personal Computer memory card International Association) slot and card, etc. Software and data are transferred via the communication interface in the form of signals, which may be electronic, electromagnetic, optical or other signals capable of being received by the communication interface medium.

In this application, the terms "computer program product," "computer-readable medium," and the like may be used generally to refer to tangible media, such as memory, storage devices, or storage units. These and other forms of computer-readable media may store one or more instructions for use by a processor, including a computer system, to cause the processor to perform specified operations. Such instructions, generally referred to as "computer program code" (which may be grouped in the form of computer programs or other groupings), may be executed to enable the computer system to perform functions of embodiments of the present application. It is noted that the code may directly cause the processor to perform specified operations, may be compiled to perform the specified operations, and/or may be combined with other software, hardware, and/or firmware elements (e.g., libraries of functions that perform standard functions) to perform the specified operations.

The non-transitory computer readable medium may include: at least one of a hard disk, a CD-ROM, an optical storage device, a magnetic storage device, a Read-Only Memory, a Programmable Read-Only Memory, an Erasable Programmable Read-Only Memory (EPROM), an electrically Erasable Programmable Read-Only Memory, and a flash Memory.

In embodiments where the elements are implemented using software, the software may be stored in a computer-readable medium and loaded into the computer system using, for example, a removable storage drive. When a processor in the computer system executes the control module (in this embodiment, software instructions or executable computer program code), the processor performs the functions of the present application as described herein.

Furthermore, the present concepts may be applied to any circuit that performs signal processing functions using network elements. Further, for example, a semiconductor manufacturer may employ the inventive concept in the design of a stand-alone device, such as a microcontroller of a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), and/or any other subsystem component.

It will be appreciated that for clarity the above description has described embodiments of the application with reference to a single processing logic, but that the concepts of the application may equally well be implemented by a plurality of different functional units and processors providing signal processing functions, and that references to specific functional units are therefore only to be seen as references to suitable ways of providing the described functionality, rather than indications of strict logical or physical structure or organization.

Aspects of the present application may be implemented in any suitable form including hardware, software, firmware or any combination of these. The present application may optionally be implemented, at least in part, as computer software or configurable modular components, such as FPGA devices, running on one or more data processors and/or digital signal processors. Thus, the elements and components of an embodiment of the application may be physically, functionally and logically implemented in any suitable way. Indeed the functionality may be implemented in a single unit, in a plurality of units or as part of other functional units.

While the present application has been described in connection with certain embodiments, it is not intended to be limited to the specific form set forth herein, but on the contrary, it is intended to be limited only by the appended claims. Furthermore, although a particular described feature may appear to relate to particular embodiments, one of ordinary skill in the art would recognize that various features described in the embodiments may be combined in accordance with the application. In the claims, the word "comprising" does not exclude the presence of other elements or steps.

Furthermore, although individually listed, a plurality of means, elements or method steps may be implemented by e.g. a single unit or processor. Furthermore, although individual features may be included in different claims, these may possibly advantageously be combined, and the inclusion in different claims does not imply that a combination of features is not feasible and/or advantageous. Likewise, the inclusion of a feature in a single claim does not imply a limitation to the claim, but rather indicates that the feature is equally applicable to other claims as appropriate.

Furthermore, the order of features in the claims does not imply any specific order in which the features must be performed, in particular the order of individual steps in a method claim does not imply that the steps must be performed in this order, but rather the steps may be performed in any suitable order. Furthermore, singular references do not exclude a plurality, and thus, references to "a", "an", "the", etc. do not exclude a plurality.

While the present application has been described in connection with certain embodiments, it is not intended to be limited to the specific form set forth herein, but on the contrary, it is intended to be limited only by the appended claims. Furthermore, although a particular described feature may appear to relate to particular embodiments, one of ordinary skill in the art would recognize that various features described in the embodiments may be combined in accordance with the application. In the claims, the word "comprising" or "comprises" does not exclude the presence of other elements.

Claims

1. A method for transmitting downlink data in a cellular communication system from a base station to a user equipment using an orthogonal frequency division multiplexing, OFDM, modulation format, the method comprising:

defining a mini-slot comprising at least one control OFDM symbol and at least one data OFDM symbol, wherein demodulation reference signals DRMS are encoded on and shared between said control OFDM symbol and/or data OFDM symbol;

transmitting the mini-slots from the base station to the user equipment.

2. The method of claim 1, wherein the DRMS are each encoded on one of the control OFDM symbols.

3. The method of claim 1, wherein the DRMS are each encoded on one of the data OFDM symbols

4. The method of claim 1, wherein a portion of the DRMS is encoded on one of the control OFDM symbols and another portion of the DRMS is encoded on one of the data OFDM symbols.

5. The method of claim 1, wherein only one DRMS is encoded on each subcarrier of the mini-slot.

6. The method according to claims 1-5, wherein control information occupies only a part of the sub-carriers of the at least one control OFDM symbol, and the remaining sub-carriers of the at least one control OFDM symbol are used for carrying data.

7. The method of claim 1, wherein the at least one control OFDM symbol occupies fewer frequency resources than the at least one data OFDM symbol, wherein the DRMS of the frequency resources used by the at least one control OFDM symbol is encoded on one control OFDM symbol, and wherein the DRMS of the frequency resources used only by the at least one data OFDM symbol is encoded on one data OFDM symbol.

8. The method according to any of claims 1-7, wherein the control OFDM symbol and data OFDM symbol are transmitted using the same at least one antenna port.

9. The method according to any of claims 1-7, wherein said mini-slots are transmitted using multiple antenna ports.

10. The method of claim 9, wherein more antenna ports are used for transmitting the at least one data OFDM symbol than for transmitting the at least one control OFDM symbol.

11. The method of claim 10, wherein the DRMS is transmitted through all antenna ports used by the at least one data OFDM symbol, and wherein the at least one control OFDM symbol is transmitted through a portion of the antenna ports.

12. The method of claim 10, wherein the portion of the antenna ports is a single port.

13. The method of claim 12, wherein additional antenna ports are used in the at least one control OFDM symbol for more data OFDM symbols.

14. The method of claim 12, wherein the single port is a first port for transmitting the control OFDM symbol.

15. The method of claim 6, wherein the transmission module for the data portion of the at least one control OFDM symbol is the same as the transmission module for the data OFDM symbol.

16. The method of any of claims 1-15, wherein the DRMS is a DRMS sequence.

17. The method of any of claims 1-15, wherein the DMRS comprises a set of double sequences, a first sequence of the set of double sequences spanning the at least one control OFDM symbol and a second sequence spanning the at least one data OFDM symbol of frequency resources not covered by the first sequence.

18. The method of claim 1, wherein the DMRS is non-user specific.

19. A method of receiving at a user equipment a downlink data transmission of a base station in a cellular communication system using an orthogonal frequency division multiplexing, OFDM, modulation format, the method comprising:

receiving an OFDM signal comprising at least one mini-slot, said mini-slot comprising at least one control OFDM symbol and at least one data OFDM symbol, wherein at least one of said control OFDM symbol and data OFDM symbol receives a demodulation reference signal, DMRS;

decoding the mini-slot for the at least one control OFDM symbol and the at least one data OFDM symbol using the DMRS.

20. The method of claim 19, wherein the DRMS is encoded entirely on one of the control OFDM symbols.

21. The method of claim 19, wherein the DRMS is encoded entirely on one of the data OFDM symbols.

22. The method of claim 19, wherein a portion of the DRMS is encoded on one of the control OFDM symbols and a portion of the DRMS is encoded on one of the data OFDM symbols.

23. The method of any of claims 19-22, wherein only one DRMS is encoded on each subcarrier of the mini-slot.

24. The method according to any of claims 19-23, wherein control information occupies only a part of the subcarriers of the at least one control OFDM symbol, and the remaining subcarriers of the at least one control OFDM symbol are used for carrying data.

25. The method of any of claims 19-24, wherein the at least one control OFDM symbol occupies fewer frequency resources than the at least one data OFDM symbol, wherein DRMS of the frequency resources used by the at least one control OFDM symbol is encoded on one control OFDM symbol and DRMS of the frequency resources used only by the at least one data OFDM symbol is encoded on one data OFDM symbol.

26. The method of any one of claims 19-25, wherein the DMRS is a DMRS sequence.

27. The method of any of claims 19-25, wherein the DMRS comprises a set of double-sequences, a first sequence of the set of double-sequences spanning the at least one control OFDM symbol and a second sequence spanning the at least one data OFDM symbol of frequency resources not covered by the first sequence.