Patent Publication Number: US-2019181991-A1

Title: Granting Resources To A Wireless Device

Description:
TECHNICAL FIELD 
     Embodiments presented herein relate to a method, a network node, a, computer program, and a computer program product for granting resources to a wireless device. Embodiments presented herein further relate to a method, a wireless device, a, computer program, and a computer program product for receiving granting of resources from a network node. 
     BACKGROUND 
     In communications networks, there may be a challenge to obtain good performance and capacity for a given communications protocol, its parameters and the physical environment in which the communications network is deployed. 
     For example, one parameter in providing good performance and capacity for a given communications protocol in a communications network is packet data latency. Latency measurements can be performed in all stages of the communications network, for example when verifying a new software release or system component, and/or when deploying the communications network and when the communications network is in commercial operation. 
     Shorter latency than previous generations of 3GPP radio access technologies was one performance metric that guided the design of Long Term Evolution (LTE). LTE is also now recognized by the end-users to be a system that provides faster access to internet and lower packet latencies than previous generations of mobile radio technologies. 
     Packet latency is also a parameter that indirectly influences the throughput of the communications network. Traffic using the Hypertext Transfer Protocol (HTTP) and/or the Transmission Control Protocol (TCP) is currently one of the dominating application and transport layer protocol suite used on the Internet. The typical size of HTTP based transactions over the Internet is in the range of a few 10&#39;s of Kilo byte up to 1 Mega byte. In this size range, the TCP slow start period is a significant part of the total transport period of the packet stream. During TCP slow start the performance is packet latency limited. Hence, improved packet latency can potentially improve the average throughput, at least for this type of TCP based data transactions. 
     Radio resource efficiency could also be positively impacted by packet latency reductions. Lower packet data latency could increase the number of transmissions possible within a certain delay bound; hence higher Block Error Rate (BLER) targets could be used for the data transmissions freeing up radio resources potentially improving the capacity of the system. 
     The existing physical layer downlink control channels, Physical Downlink Control Channel (PDCCH) and enhanced PDCCH (ePDCCH), are used to carry Downlink Control Information (DCI) such as scheduling decisions for uplink (UL; from device to network) and downlink (DL; from network to device) and power control commands. Both PDCCH and ePDCCH are according to present communications networks transmitted once per 1 ms subframe. 
     3GPP TS 36.212 lists examples of different (DCI) formats for UL and DL resource assignments. UL scheduling grants use either DCI format 0 or DCI format 4. The latter was added in the 3rd Generation Partnership Project (3GPP) Release 10 (Rel-10) for supporting uplink spatial multiplexing 
     The existing way of operation, e.g. frame structure and control signalling, are designed for data allocations in subframes of a fixed length of 1 ms, which may vary only in allocated bandwidth. Specifically, the current DCIs define resource allocations within the entire subframe, and are only transmitted once per subframe. The existing way of operation does not indicate how scheduling of UL and DL data can be performed in short subframes, i.e., subframes shorter than 1 ms. 
     Hence, there is a need for efficient communications using short subframes. 
     SUMMARY 
     An object of embodiments herein is to provide mechanisms for communications using short subframe. 
     According to a first aspect there is presented a method for granting resources to a wireless device operating with a short Transmission Time Interval (sTTI). The method is performed by a network node. The method comprises transmitting, to the wireless device, a first control information message for a downlink channel. The method comprises transmitting, to the wireless device, a second control information message, wherein the second control information message is decodable based on a parameter of the first control information message, or based on signalled information. 
     According to a second aspect there is presented a network node for granting resources to a wireless device operating with an sTTI. The network node comprises processing circuitry. The processing circuitry is configured to cause the network node to transmit, to the wireless device, a first control information message for a downlink channel. The processing circuitry is configured to cause the network node to transmit, to the wireless device, a second control information message, wherein the second control information message is decodable based on a parameter of the first control information message, or based on signalled information. 
     According to a third aspect there is presented a network node for granting resources to a wireless device operating with an sTTI. The network node comprises processing circuitry and a computer program product. The computer program product stores instructions that, when executed by the processing circuitry, causes the network node to perform steps, or operations. The steps, or operations, cause the network node to transmit, to the wireless device, a first control information message for a downlink channel. The steps, or operations, cause the network node to transmit, to the wireless device, a second control information message, wherein the second control information message is decodable based on a parameter of the first control information message, or based on signalled information. 
     According to a fourth aspect there is presented a network node for granting resources to a wireless device operating with an sTTI. The network node comprises a transmit module configured to transmit, to the wireless device, a first control information message for a downlink channel. The network node comprises a transmit module configured to transmit, to the wireless device, a second control information message, wherein the second control information message is decodable based on a parameter of the first control information message, or based on signalled information. 
     According to a fifth aspect there is presented a computer program for granting resources to a wireless device operating with an sTTI, the computer program comprising computer program code which, when run on processing circuitry of a network node, causes the network node to perform a method according to the first aspect. 
     According to a sixth aspect there is presented a method for receiving granting of resources from a network node. The method is performed by a wireless device operating with an sTTI. The method comprises receiving a first control information message for a downlink channel from the network node. The method comprises decoding a second control information message received from the network node based on a parameter of the first control information message, or based on signalled information. 
     According to a seventh aspect there is presented a wireless device for receiving granting of resources from a network node. The wireless device is configured for operating with an sTTI and comprises processing circuitry. The processing circuitry is configured to cause the wireless device to receive a first control information message for a downlink channel from the network node. The processing circuitry is configured to cause the wireless device to decode a second control information message received from the network node based on a parameter of the first control information message, or based on signalled information. 
     According to an eighth aspect there is presented a wireless device for receiving granting of resources from a network node. The wireless device is configured for operating with an sTTI and comprises processing circuitry and a computer program product. The computer program product stores instructions that, when executed by the processing circuitry, causes the wireless device to perform steps, or operations. The steps, or operations, cause the wireless device to receive a first control information message for a downlink channel from the network node. The steps, or operations, cause the wireless device to decode a second control information message received to from the network node based on a parameter of the first control information message, or based on signalled information. 
     According to a ninth aspect there is presented a wireless device for receiving granting of resources from a network node. The wireless device is configured for operating with an sTTI. The wireless device comprises a receive module configured receive a first control information message for a downlink channel from the network node. The wireless device comprises a decode module configured to decode a second control information message received from the network node based on a parameter of the first control information message, or based on signalled information. 
     According to a tenth aspect there is presented a computer program for receiving granting of resources from a network node, the computer program comprising computer program code which, when run on processing circuitry of a wireless device operating with an sTTI, causes the wireless device to perform a method according to the sixth aspect. 
     According to an eleventh aspect there is presented a computer program product comprising a computer program according to at least one of the fifth aspect and the tenth aspect and a computer readable storage medium on which the computer program is stored. The computer readable storage medium can be a non-transitory computer readable storage medium. 
     Advantageously these methods, these network nodes, these wireless devices, and these computer programs provide efficient communications using short subframes. 
     Advantageously this reduces the total number of blind decodes the wireless device needs to perform when in short TTI operation, and thereby limits the processing load in the wireless device. 
     It is to be noted that any feature of the first, second, third, fourth, fifth, sixth seventh, eight, ninth, tenth and eleventh aspects may be applied to any other aspect, wherever appropriate. Likewise, any advantage of the first aspect may equally apply to the second, third, fourth, fifth, sixth, seventh, eight, ninth, tenth, and/or eleventh aspect, respectively, and vice versa. Other objectives, features and advantages of the enclosed embodiments will be apparent from the following detailed disclosure, from the attached dependent claims as well as from the drawings. 
     Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to “a/an/the element, apparatus, component, means, step, etc.” are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, step, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The inventive concept is now described, by way of example, with reference to the accompanying drawings, in which: 
         FIG. 1  is a schematic diagram illustrating a communication network according to embodiments; 
         FIGS. 2, 3, 4, and 5  are flowcharts of methods according to embodiments; and 
         FIGS. 6, 7, and 8  are schematic illustrations of search spaces for DCI messages in short TTIs according to embodiments; 
         FIG. 9  is a schematic diagram showing functional units of a network node according to an embodiment; 
         FIG. 10  is a schematic diagram showing functional modules of a network node according to an embodiment; 
         FIG. 11  is a schematic diagram showing functional units of a wireless device according to an embodiment; 
         FIG. 12  is a schematic diagram showing functional modules of a wireless device according to an embodiment; and 
         FIG. 13  shows one example of a computer program product comprising computer readable means according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The inventive concept will now be described more fully hereinafter with reference to the accompanying drawings, in which certain embodiments of the inventive concept are shown. This inventive concept may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the inventive concept to those skilled in the art. Like numbers refer to like elements throughout the description. Any step or feature illustrated by dashed lines should be regarded as optional. 
       FIG. 1  is a schematic diagram illustrating a communications network  100  where embodiments presented herein can be applied. The communications network  100  comprises at least one network node  200 . The functionality of the network node  200  and how it interacts with other entities, nodes, and devices in the communications network  100  will be further disclosed below. 
     The communications network  100  further comprises at least one radio access network node  140 . The at least one radio access network node  140  is part of a radio access network  110  and operatively connected to a core network  120  which in turn is operatively connected to a service network  130 . The at least one radio access network node  140  provides network access in the radio access network  110 . A wireless device  300   a ,  300   b  served by the at least one radio access network node  140  is thereby enabled to access services and exchange data with the core network  120  and the service network  1300 . 
     Examples of wireless devices  300   a ,  300   b  include, but are not limited to, mobile stations, mobile phones, handsets, wireless local loop phones, user equipment (UE), smartphones, laptop computers, tablet computers, network equipped sensors, wireless modems, and Internet of Things devices. Examples of radio access network nodes  120  include, but are not limited to, radio base stations, base transceiver stations, NodeBs, evolved NodeBs, access points, and access nodes. As the skilled person understands, the communications network  100  may comprise a plurality of radio access network nodes  120 , each providing network access to a plurality of wireless devices  300   a ,  300   b . The herein disclosed embodiments are not limited to any particular number of network nodes  200 , radio access network nodes  120  or wireless devices  300   a ,  300   b.    
     The wireless device  300   a ,  300   b  accesses services and exchanges data with the core network  120  and the service network  130  by transmitting data in packets to the core network  120  and the service network  130  and by receiving data in packets from the core network  120  and the service network  130  via the radio access network node  140 . 
     Packet latency has above been identified as degrading network performance. One area to address when it comes to packet latency reductions is the reduction of transport time of data and control signalling, by addressing the length of a transmission time interval (TTI). In LTE release 8, a TTI corresponds to one subframe (SF) of length 1 millisecond. One such 1 ms TTI is constructed by using 14 OFDM or SC-FDMA symbols in the case of normal cyclic prefix and 12 OFDM or SC-FDMA symbols in the case of extended cyclic prefix. 
     According to embodiment disclosed herein the TTIs are shortened by introducing shortened subframes (below denoted short subframes). With a short TTI (below denoted sTTI), the subframes can be decided to have any duration in time and comprise resources on a number of OFDM or SC-FDMA symbols within a 1 ms subframe. As one example, the duration of a short subframe may be 0.5 ms, i.e., seven OFDM symbols or SC-FDMA symbols for the case with normal cyclic prefix. 
     As mentioned, one way to reduce latency is to reduce the transmission time interval (TTI), and instead of assigning resources with a time duration of 1 ms, there is then a need to assign resources with shorter duration such as a number of OFDM symbols or SC-FDMA symbols. This implies a need for device specific control signalling that enables indication of such short scheduling assignments. 
     Using scheduling with 1 ms TTIs, the wireless devices  300   a ,  300   b  are allocated frequency resources based on, e.g., bitmaps in DCI fields identifying used resource blocks. As the TTI length is shortened, this may lead to an increased signaling overhead if the allocation is specified several times per subframe. Having a grant only to a single wireless device  300   a ,  300   b  per such short TTI will limit the overhead. It might be further beneficial to share the frequency resources within a short TTI between several wireless device  300   a ,  300   b , while limiting the amount of control overhead. 
     In order for short TTIs to coexist with legacy LTE transmission, a short TTI frequency band can be defined on a subset of the available resource blocks. Within this short TTI frequency band, which can be either contiguous or spread out in frequency, transmission is performed using the shorter TTIs. Outside this short TTI frequency band, legacy LTE wireless devices can be scheduled with a 1 ms TTI length. 
     Since scheduling and control information is transmitted more often when using short TTIs, it can be beneficial to limit the amount of information transmitted on the fast time scale to keep the overhead at a reasonable level. Therefore, part of the control information may be transmitted on a slower timescale, and can also be directed to a group of wireless devices  300   a ,  300   b  using short TTI operation. Thus two new DCIs may be defined for short TTI transmission; a slow DCI that is valid for one full subframe (or more), and a device-specific fast DCI. In some aspects the slow DCI is sent less frequently than the fast DCI. 
     A wireless device  300   a ,  300   b  can be configured for short TTI operation by being assigned a group short TTI Radio Network Temporary Identifier (RNTI). The wireless device  300   a ,  300   b  could then searches the common search space (CSS) of the PDCCH for slow grants (comprising a slow Downlink Control Information (DCI) message) scrambled with the short TTI RNTI. This slow grant comprises the frequency allocation for a downlink (DL) and an uplink (UL) short TTI frequency band to be used for short TTI operation. After decoding such a slow grant the wireless device  300   a ,  300   b  is in short TTI operation and can extend its search space to an in-band control channel, also defined by the slow grant. 
     Within the short TTI band, an in-band control channel, in terms of a short PDCCH, is defined. This short PDCCH is used for fast grants (also referred to as fast DCI). To minimize the latency, the short PDCCH can be transmitted in every TTI, and typically on the first symbol of the TTI. The resources not occupied by control signaling can be assigned to short PDSCH data, to efficiently use frequency resources. As herein defined, the term short PDSCH and short PUSCH are used to denote the downlink and uplink physical shared channels with TTIs less than one sub-frame, respectively. Similarly, the term short PDCCH is used to denote downlink physical control channels with TTIs less than one sub-frame. 
     A DCI message is encoded onto a number of Control Channel Elements (CCEs) in the PDCCH region of the DL subframe. The wireless device  300   a ,  300   b  searches both in a CSS and a device-specific search space (hereinafter denoted USS; where U is short for UE as in User Equipment) in the PDCCH for different CCE aggregation levels (AL). The number PDCCH candidates of different sizes in LTE are given in Table 9.1.1-1 in 3GPP TS 36.213 v13.1.1. According to this table there are 22 PDCCH candidates to be monitored by the wireless device  300   a ,  300   b , and with 2 different DCI sizes defined for each transmission mode, there are a total of 44 possibilities that the wireless device  300   a ,  300   b  has to try with blind decoding. 
     In legacy LTE the wireless device  300   a ,  300   b  monitors a predefined USS for the PDCCH. With the introduction of a new in-band control channel (below denoted short PDCCH) the number of blind decoding attempts will increase for a wireless device  300   a ,  300   b  in short TTI operation. 
     It can then be desired to keep the number of blind decoding attempts in the short PDCCH to a low level. According to embodiments disclosed herein a reduced set of aggregation levels and/or starting positions are therefore used for the DCI messages in the short PDCCH. 
     The embodiments disclosed herein thus relate to mechanisms for granting resources to a wireless device  300   a  operating with an sTTI. In order to obtain such mechanisms there is provided a network node  200 , a method performed by the network node  200 , a computer program product comprising code, for example in the form of a computer program, that when run on processing circuitry of the network node  200 , causes the network node  200  to perform the method. 
     The embodiments disclosed herein further relate to mechanisms for receiving granting of resources from a network node  200 . In order to obtain such mechanisms there is further provided a wireless device  300   a ,  300   b  operating with an sTTI, a method performed by the wireless device  300   a ,  300   b , and a computer program product comprising code, for example in the form of a computer program, that when run on processing circuitry of the wireless device  300   a ,  300   b , causes the wireless device  300   a ,  300   b  to perform the method. 
       FIGS. 2 and 3  are flow charts illustrating embodiments of methods for granting resources to a wireless device  300   a  operating with an sTTI as performed by the network node  200 .  FIGS. 4 and 5  are flow charts illustrating embodiments of methods for receiving granting of resources from a network node  200  as performed by the wireless device  300   a ,  300   b  operating with an sTTI. The methods are advantageously provided as computer programs  1320   a ,  1320   b  (see below). 
     Reference is now made to  FIG. 2  illustrating a method for granting resources to a wireless device  300   a  operating with an sTTI as performed by the network node  200  according to an embodiment. 
     S 102 : The network node  200  transmits to the wireless device  300   a , a first control information message for a downlink channel. 
     S 104 : The network node  200  transmits, to the wireless device  300   a , a second control information message. The second control information message is, by the wireless device  300   a ,  300   b , decodable based on a parameter of the first control information message. The parameter indicates resources for operation with the sTTI. 
     The first control information message transmitted in step S 102  can be regarded as a slow grant in a PDCCH. Such a slow grant could define a TTI frequency band for short TTI operation in the PDCCH. The slow grant can be transmitted on a rate equal to or slower than once each sub-frame. 
     The second control information message transmitted in step S 104  can be regarded as a fast grant. Such a fast grant can be user specific and be transmitted on a faster rate than once each sub-frame, for example once per TTI. At least two such grants can be provided in one (single) Orthogonal Frequency Division Multiplexing (OFDM) symbol in the short TTI frequency band and hence be transmitted to at least two wireless devices  300   a ,  300   b.    
     The term sTTI, or short TTI, is a TTI of a short subframe. The short subframe can have a shorter duration in time than 1 ms. The short TTI can be defined as being shorter than the interval between two consecutive PDCCH transmissions (as being transmitted once every 1 ms). To achieve latency reduction the networks node  200  can thus be configured to schedule data on short timeframes, such as at short TTI level. 
     Embodiments relating to further details of granting resources to a wireless device  300   a  will now be disclosed. 
     Reference is now made to  FIG. 3  illustrating methods for granting resources to a wireless device  300   a  operating with an sTTI as performed by the network node  200  according to further embodiments. It is assumed that steps S 102 , S 104  are performed as disclosed with reference to  FIG. 2  and a repeated description of these steps is therefore omitted. 
     According to some aspects the network node  200  signals to the wireless device  300   a  what resources to skip to find its own short PDSCH allocation. According to an embodiment the resources are CCE resources. The network node  200  could then be configured to provide the wireless device  300   a  with information regarding what CCEs within the TTI frequency band the wireless device can skip and hence be configured to perform step S 106 : 
     S 106 : The network node  200  provides information regarding what CCEs the wireless device  300   a  is to skip when attempting to decode the second control information message. This enables the wireless device  300   a  to skip some of the CCE that are configured for sTTI control signaling. The information could specify what CCEs within the TTI frequency band the wireless device  300   a  is to skip when attempting to decode the second control information message within the TTI frequency band. 
     Step S 106  can be performed after step S 104 . 
     Reference is now made to  FIG. 4  illustrating a method for receiving granting of resources from a network node  200  as performed by the wireless device  300   a ,  300   b  operating with an sTTI according to an embodiment. 
     As disclosed above, the network node  200  in step S 102  transmits, to the wireless device  300   a , a first control information message. It is assumed that the wireless device  300   a  receives this first control information message. Hence, the wireless device  300   a ,  300   b  is configured to perform step S 202 : 
     S 202 : The wireless device  300   a ,  300   b  receives a first control information message for a downlink channel from the network node  200 . 
     As disclosed above, the network node  200  in step S 104  transmits, to the wireless device  300   a , a second control information message. It is assumed that the wireless device  300   a  receives this second control information message. Hence, the wireless device  300   a ,  300   b  is configured to perform step S 206 : 
     S 206 : The wireless device  300   a ,  300   b  decodes the second control information message received from the network node  200  based on a parameter of the first control information message. As disclosed above, the parameter indicates resources for operation with the sTTI. 
     Reference is now made to  FIG. 5  illustrating methods for receiving granting of resources from a network node  200  as performed by the wireless device  300   a ,  300   b  operating with an sTTI according to further embodiments. It is assumed that steps S 202 , S 206  are performed as disclosed with reference to  FIG. 4  and a repeated description of these steps is therefore omitted. 
     As disclosed above, according to an embodiment the network node  200  in step S 106  provides information to the wireless device  300   a . Hence, according to an embodiment the wireless device  300   a ,  300   b  is configured to perform step S 204 : 
     S 204 : The wireless device  300   a ,  300   b  receives information regarding what CCE resources to skip when attempting to decode the second control information message. This enables the wireless device  300   a ,  300   b  to skip some of the CCEs that are configured for sTTI control signaling. The information could specify what CCEs within the TTI frequency band the wireless device  300   a ,  300   b  is to skip when attempting to decode the second control information message within the TTI frequency band. 
     Embodiments relating to further details of granting resources to a wireless device  300   a  as performed by the network node  200  and receiving granting of resources from a network node  200  as performed by the wireless device  300   a ,  300   b  will now be disclosed. 
     Embodiments applicable to both the methods performed by the network node  200  and the wireless device  300   a ,  300   b  will now be disclosed. 
     As disclosed above, the resources could be CCE resources. 
     According to an embodiment the first control information message is a slow grant in a PDCCH. The slow grant could define a TTI frequency band for operation with the sTTI. Further, the TTI frequency band could comprise the second control information message. The second control information message is then decodable by the wireless device  300   a ,  300   b  using less than all available candidate CCE resources within the TTI frequency band. 
     Further, the network node  200  could signal to the wireless device  300   a  the set of frequency resource blocks where to find the second control information message. Further, the network node  200  could signal to the wireless device  300   a  the set of frequency resource blocks and the number of time domain OFDM symbols where to find the second control information message. That is, according to an embodiment the parameter of the first control information message, or the signalled information, is a set of frequency resources or a set of time-frequency resources. 
     Further, the number of control channel candidates can be reduced and signalled in the first control information message. That is, according to an embodiment the parameter of the first control information message, or the signalled information, is a number of control channel candidates for at least one aggregation level. 
     Since the TTI frequency band is for short TTI operation the second control information message can be regarded as a fast Downlink Control Information (DCI) message being provided in a short PDCCH. The number of blind decoding attempts (in the short PDCCH) can be limited by the wireless device  300   a ,  300   b  using only a limited number of combinations of aggregation levels and/or starting positions of the DCI message. 
     To send DL and UL grants, the network node  200  transmits DCI messages with different aggregation levels. For example, one DCI message can be encoded over 1, 2, 4, or 8 CCEs, where each CCE may span  36  resource elements. Depending on the supported number of simultaneously scheduled wireless devices  300   a ,  300   b , a different number of DCI messages need to be transmitted, and the number of blind decoding attempts will increase when there are many simultaneously served wireless devices  300   a ,  300   b.    
     According to one scenario, only one wireless device  300   a ,  300   b  is scheduled per TTI in the UL and only one wireless device  300   a ,  300   b  is scheduled per TTI in the DL. This then limits the number of DCI messages to two per TTI. According to other scenarios there are more than one UL and/or DL grant. 
       FIGS. 6, 7, and 8  are schematic illustrations of search spaces  600 ,  700 ,  800  for DCI messages in short TTIs (i)-(xxiv) according to embodiments. In  FIGS. 6, 7, and 8  regions shaded as regions  620 ,  720 ,  820  show possible positions for different aggregation levels of CCEs for each short TTI (i)-(xxiv). The regions shaded as regions  630 ,  730 ,  830  symbolize grants and/or DCI messages to one or more other wireless device  300   b . The regions shaded as regions  610 ,  710 ,  810  symbolize data. 
     In order to limit the amount of transmitted control information, the DCI messages can be placed consecutively, with the DL grant last, as shown in  FIG. 6 .  FIG. 6  schematically illustrates all combinations of search spaces for two grants. The regions shaded as region  620  show possible locations for aggregation levels of 1 to 4 CCEs. The wireless device receiving the DL grant can be configured to know that all resources after the grant belongs to it, since any possible UL grants (to that or to any other wireless device  300   a ,  300   b ) has been sent earlier. 
     In  FIG. 6 , the search space when having a maximum two DCI messages is shown. There are thus 12 different placements (the regions shaded as region  620 ) of the DCI message for the wireless device  300   a ,  300   b  to search for when attempting to decode the DCI message. 
     In order to limit the number of blind decoding attempts, the combination of aggregation levels can be restricted.  FIG. 7  schematically illustrates an example with search spaces only corresponding to two identical aggregation levels. Thus,  FIG. 7  represents an embodiment where the aggregation levels are restricted to be the same for both DCI messages  720 ,  7300 . In some examples, the messages are for different wireless devices. Thus, there are not so many positions to search for the fast DL and UL grants; 6 positions compared to the previous 12. 
     In another embodiment, the maximum aggregation level for the fast grants is less than or equal to the aggregation level of the received slow grant. 
     In yet another embodiment, the aggregation level is fixed for all fast DCI messages, where the fixed aggregation level is derived from the aggregation level of the slow DCI. One example is that the aggregation level of the fast DCI is always the same as the aggregation level used for the slow DCI. If the amount of payload (i.e. the number of control information bits) is significantly different between the slow DCI and the fast DCI, then a fixed larger, or lower, aggregation level is used for fast DCI as compared to the aggregation level for the slow DCI. 
     In another embodiment, a reduced set of aggregation levels used for fast DCI in a given subframe is signalled at the beginning of this subframe. Information indicating the set can be sent in a message common to all wireless devices  300   a ,  300   b  or be specific to a given wireless device  300   a ,  300   b . For instance, instead of aggregation levels 1, 2 and 4, the network node  200  can send information to restrict the possible aggregation levels to search for (e.g. to AL1 and AL2) in a given subframe. When having signalled this to the wireless devices  300   a ,  300   b  and received by the wireless device, the required number of tested combinations is reduced for the wireless devices  300   a ,  300   b.    
       FIG. 6  and  FIG. 7  illustrate scenarios where a first and a second fast DCI are transmitted in a short TTI. There could be also a higher number of fast DCIs sent in a short TTI using a similar arrangement as shown in  FIG. 6  or  FIG. 7 . In such scenarios, to detect (and decode) its fast DCI, a wireless device  300   a ,  300   b  needs to test all combinations of all possible aggregation levels for an increasing number of fast DCIs. For instance, the wireless device  300   a ,  300   b  can be configured to first assume to have the fast DCI in the first position and test all combinations of aggregation levels for the first fast DCI. If no combination leads to a correctly decoded fast DCI, the wireless device  300   a ,  300   b  can be configured to then assume to have the fast DCI in the second position and test all combinations of aggregation levels for the two first fast DCI. The wireless device  300   a ,  300   b  can be configured to continue to increase the number of tested fast DCI positions until one combination leads to a correctly decoded fast DCI. This procedure can represent a large amount of blind decoding attempts. In one embodiment, the network node  200  therefore signals to the wireless device  300   a ,  300   b  the position of the fast DCI intended to this wireless device  300   a ,  300   b . This information is sent in a device-specific message and helps reducing the number of blind decoding attempts as the wireless device  300   a ,  300   b  can directly test all combinations of aggregation levels for the correct number of fast DCIs. 
     The recent-most embodiment limits the number of blind decoding attempts, but restricts the aggregation level to be the same on both the UL and DL grants. This may be acceptable, for example, if both grants are targeting the same wireless device  300   a ,  300   b , and the amount of payload is somewhat similar in the UL and DL grants. This information that can be taken into account by the scheduler in the network node  200  when co-scheduling wireless devices  300   a ,  300   b  that require the same or similar aggregation levels. 
     If it is desired to schedule two or more wireless devices  300   a ,  300   b , one requiring aggregation level 1 (AL 1) and another one requiring aggregation level 4 (AL 4), both these wireless devices  300   a ,  300   b  may need to be scheduled with AL 4, which will increase the overhead. An alternative approach is therefore to fix the position of the DL grants, as shown in  FIG. 8 .  FIG. 8  schematically illustrates search spaces at fixed locations, without limitation of aggregation levels. The aggregation level of the UL grant is specified in a bit field in the fast DL grant. Regions shaded as region  840  in  FIG. 8  represent otherwise unknown extension of UL grant). Only 6 blind decoding attempts are necessary, but there is no restriction on the used aggregation level. In order for the wireless device  300   a ,  300   b  receiving the DL grant to know where to find the short PDSCH resources, the wireless device  300   a ,  300   b  needs to know the aggregation level of the UL grant. This can then be signalled, for example, according to Table 1. In some examples, the signalled information is within the DL fast DCI. For the case when multiple UL grants are allowed, Table 1 specifies the total number of CCEs the DL wireless device  300   a ,  300   b  is supposed to skip in order to find the short PDSCH resources (as a sum of the zero, one, or more UL grants). 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Indication of aggregation level of UL grant 
               
            
           
           
               
               
            
               
                 Bit field 
                 Meaning 
               
               
                   
               
               
                 00 
                 No UL grant 
               
               
                 01 
                 UL grant with AL 1 
               
               
                 10 
                 UL grant with AL 2 
               
               
                 11 
                 UL grant with AL 4 
               
               
                   
               
            
           
         
       
     
     A summary of the above disclosed embodiments will now be presented. These embodiment apply equally well to the network node  200  as the wireless device  300   a ,  300   b.    
     According to some of the above disclosed embodiments the second control information message is a fast DCI message. 
     According to some of the above disclosed embodiments there are limited combinations of aggregation levels for the fast DCI message. That is, according to an embodiment the available CCE resources are defined by aggregation levels of CCEs. 
     According to some of the above disclosed embodiments there are limited combinations of starting positions for the fast DCI message. That is, according to an embodiment the available CCE resources are defined by starting positions of CCEs within the TTI frequency band. 
     According to some of the above disclosed embodiments a candidate CCE resource is defined by a combination of aggregation level and starting position. That is, according to an embodiment each of the available candidate CCE resources is defined by a unique combination of an aggregation level of CCEs and starting position of CCEs within the TTI frequency band. 
     According to some of the above disclosed embodiments all fast DCI messages are of the same aggregation level. That is, according to an embodiment the second control information message has a fixed aggregation level of CCEs. 
     According to some of the above disclosed embodiments all aggregation levels of the fast DCI are less or equal to the aggregation level of received slow DCI (slow grant). That is, according to an embodiment the DCI message has an aggregation level of CCEs not larger than the aggregation level (of CCEs) of the first control information. The wireless device  300   a ,  300   b  could determine the AL of the fast grant based on the AL of the slow grant, the AL of the fast grant being e.g. equal or less than the AL of the slow grant. 
     According to some of the above disclosed embodiments all aggregation levels of the fast DCI are equal to the aggregation level of the received slow DCI (slow grant). That is, according to an embodiment the second control information message has an aggregation level of CCEs equal to the aggregation level (of CCEs) of the first control information. 
     According to some of the above disclosed embodiments the DCI message is a fast grant. That is, according to an embodiment the second control information message is a fast grant. 
     According to some of the above disclosed embodiments there is at maximum one DL fast grant. That is, according to an embodiment the second control information message comprises at most one downlink grant. 
     According to some of the above disclosed embodiments there is at maximum one UL fast grant and one DL fast grant. That is, according to an embodiment the second control information message comprises at most one uplink grant and one downlink grant. 
     According to some of the above disclosed embodiments the starting positions of the candidates are fixed. That is, according to an embodiment the second control information message has a fixed or predetermined set of available starting positions within the TTI frequency band. In this respect the starting positions of the candidates could be hardcoded, or otherwise stored in or obtained by, the wireless device  300   a ,  300   b  or provided to the wireless device  300   a ,  300   b  from the network node  200 . 
     In some examples a slow grant may be considered as a control message comprising information of a frequency band for short TTI operation of the wireless device. In some examples, the slow grant may be considered as a control message in a CSS, and/or the fast grant may be considered as control message in a USS. In some examples, a slow grant may be considered as control message transmitted once per subframe, and/or a fast grant may be considered as a control message type which is transmitted (or uses a time resources which allows transmission) a plurality of times per subframe (e.g. once per wireless device  300   a ,  300   b  in sTTI operation served by a cell). 
     The wireless device  300   a ,  300   b  determines information about a second control information message, in order to allow improved decoding (i.e. searching through candidates) of the second control information message. For example, the wireless device determines a parameter of the first control information message. In some examples, the determining is obtained from a decoding of the first control information message. In some aspects, the wireless device  300   a ,  300   b  decodes the first control information message, stores a value of the parameter used for successful decoding (e.g. the AL), and retrieves the value from the storage, and uses the value to decode the second control information message (e.g. decoding only for the stored AL). The determined information reduces the number of blind decodes needed. Thus, less than all possible candidate CCEs need to be considered. 
     In some examples, the wireless device  300   a ,  300   b  determines the information from an earlier control information message, i.e. first control information message. In some examples, the information is signalled to the wireless device  300   a ,  300   b , e.g. from the network node  200 . In further examples, the information is fixed or predetermined, and for example, may be obtained by the wireless device  300   a ,  300   b  from a storage medium. In some aspects, processing circuitry  310  of the wireless device  300   a ,  300   b  obtains the information from a storage medium  330  (see description of  FIG. 11  below) of the wireless device  300   a ,  300   b.    
     In some examples, the first and second control information message may be of the same type, e.g. both being slow DCIs or both being fast DCIs. In some examples, the first and second control information messages are of different type; slow one being a DCI and the other being a fast DCI. In some examples, one or both control information messages are messages each containing only part of the control information for a wireless device  300   a ,  300   b  in a subframe. 
     In some examples, the first control information message is a higher layer configuration message, such as a radio resource control (RRC) message. 
     The information may indicate one or more of an aggregation level, a starting position of the second control information message, or a set of one or more aggregation level or a starting position. 
       FIG. 9  schematically illustrates, in terms of a number of functional units, the components of a network node  200  according to an embodiment. Processing circuitry  210  is provided using any combination of one or more of a suitable central processing unit (CPU), multiprocessor, microcontroller, digital signal processor (DSP), etc., capable of executing software instructions stored in a computer program product  1310   a  (as in  FIG. 13 ), e.g. in the form of a storage medium  230 . The processing circuitry  210  may further be provided as at least one application specific integrated circuit (ASIC), or field programmable gate array (FPGA). 
     Particularly, the processing circuitry  210  is configured to cause the network node  200  to perform a set of operations, or steps, S 102 -S 106 , as disclosed above. For example, the storage medium  230  may store the set of operations, and the processing circuitry  210  may be configured to retrieve the set of operations from the storage medium  230  to cause the network node  200  to perform the set of operations. The set of operations may be provided as a set of executable instructions. Thus the processing circuitry  210  is thereby arranged to execute methods as herein disclosed. 
     The storage medium  230  may also comprise persistent storage, which, for example, can be any single one or combination of magnetic memory, optical memory, solid state memory or even remotely mounted memory. 
     The network node  200  may further comprise a communications interface  220  for communications at least with a wireless device  300   a ,  300   b . As such the communications interface  220  may comprise one or more transmitters and receivers, comprising analogue and digital components and a suitable number of antennas for wireless communications and ports for wireline communications. 
     The processing circuitry  210  controls the general operation of the network node  200  e.g. by sending data and control signals to the communications interface  220  and the storage medium  230 , by receiving data and reports from the communications interface  220 , and by retrieving data and instructions from the storage medium  230 . Other components, as well as the related functionality, of the network node  200  are omitted in order not to obscure the concepts presented herein. 
       FIG. 10  schematically illustrates, in terms of a number of functional modules, the components of a network node  200  according to an embodiment. The network node  200  of  FIG. 10  comprises a number of functional modules; an transmit module  210   a  configured to perform step S 102 , and a transmit module  210   b  configured to perform step S 104 . The network node  200  of  FIG. 10  may further comprise a number of optional functional modules, such as a provide module  210   c  configured to perform step S 106 . In general terms, each functional module  210   a - 210   c  may be implemented in hardware or in software. Preferably, one or more or all functional modules  210   a - 210   c  may be implemented by the processing circuitry  210 , possibly in cooperation with functional units  220  and/or  230 . The processing circuitry  210  may thus be arranged to from the storage medium  230  fetch instructions as provided by a functional module  210   a - 210   c  and to execute these instructions, thereby performing any steps of the network node  200  as disclosed herein. 
     The network node  200  may be provided as a standalone device or as a part of at least one further device. For example, the network node  200  may be provided in a node of the radio access network  110  or in a node of the core network  120 . For example, the network node  200 , or at least its functionality, could be implemented in a radio base station, a base transceiver station, a NodeBs, an evolved NodeBs, an access points, or an access node. Alternatively, functionality of the network node  200  may be distributed between at least two devices, or nodes. These at least two nodes, or devices, may either be part of the same network part (such as the radio access network  110  or the core network  120 ) or may be spread between at least two such network devices, parts, or nodes. In general terms, instructions that are required to be performed in real time may be performed in one or more device, or node, in the radio access network  110 . 
     Thus, a first portion of the instructions performed by the network node  200  may be executed in a first device, and a second portion of the of the instructions performed by the network node  200  may be executed in a second device; the herein disclosed embodiments are not limited to any particular number of devices on which the instructions performed by the network node  200  may be executed. Hence, the methods according to the herein disclosed embodiments are suitable to be performed by a network node  200  residing in a cloud computational environment. Therefore, although a single processing circuitry  210  is illustrated in  FIG. 9  the processing circuitry  210  may be distributed among a plurality of devices, or nodes. The same applies to the functional modules  210   a - 210   c  of  FIG. 10  and the computer program  1320   a  of  FIG. 13  (see below). 
       FIG. 11  schematically illustrates, in terms of a number of functional units, the components of a wireless device  300   a ,  300   b  according to an embodiment. Processing circuitry  310  is provided using any combination of one or more of a suitable central processing unit (CPU), multiprocessor, microcontroller, digital signal processor (DSP), etc., capable of executing software instructions stored in a computer program product  1310   b  (as in  FIG. 13 ), e.g. in the form of a storage medium  330 . The processing circuitry  310  may further be provided as at least one application specific integrated circuit (ASIC), or field programmable gate array (FPGA). 
     Particularly, the processing circuitry  310  is configured to cause the wireless device  300   a ,  300   b  to perform a set of operations, or steps, S 202 -S 208 , as disclosed above. For example, the storage medium  330  may store the set of operations, and the processing circuitry  310  may be configured to retrieve the set of operations from the storage medium  330  to cause the wireless device  300   a ,  300   b  to perform the set of operations. The set of operations may be provided as a set of executable instructions. Thus the processing circuitry  310  is thereby arranged to execute methods as herein disclosed. 
     The storage medium  330  may also comprise persistent storage, which, for example, can be any single one or combination of magnetic memory, optical memory, solid state memory or even remotely mounted memory. 
     The wireless device  300   a ,  300   b  may further comprise a communications interface  320  for communications at least with a network node  200 . As such the communications interface  320  may comprise one or more transmitters and receivers, comprising analogue and digital components and a suitable number of antennas for wireless communications and ports for wireline communications. 
     The processing circuitry  310  controls the general operation of the wireless device  300   a ,  300   b  e.g. by sending data and control signals to the communications interface  320  and the storage medium  330 , by receiving data and reports from the communications interface  320 , and by retrieving data and instructions from the storage medium  330 . Other components, as well as the related functionality, of the wireless device  300   a ,  300   b  are omitted in order not to obscure the concepts presented herein. 
       FIG. 12  schematically illustrates, in terms of a number of functional modules, the components of a wireless device  300   a ,  300   b  according to an embodiment. The wireless device  300   a ,  300   b  of  FIG. 12  comprises a number of functional modules; a receive module  310   a  configured to perform step S 102 , and a decode module  310   c  configured to perform step S 206 . The wireless device  300   a ,  300   b  of  FIG. 12  may further comprises a number of optional functional modules, such a receive module  310   b  configured to perform step S 204 . In general terms, each functional module  310   a - 310   c  may be implemented in hardware or in software. Preferably, one or more or all functional modules  310   a - 310   c  may be implemented by the processing circuitry  310 , possibly in cooperation with functional units  320  and/or  330 . 
     The processing circuitry  310  may thus be arranged to from the storage medium  330  fetch instructions as provided by a functional module  310   a - 310   c  and to execute these instructions, thereby performing any steps of the wireless device  300   a ,  300   b  as disclosed herein. 
       FIG. 13  shows one example of a computer program product  1310   a ,  1310   b  comprising computer readable means  1330 . On this computer readable means  1330 , a computer program  1320   a  can be stored, which computer program  1320   a  can cause the processing circuitry  210  and thereto operatively coupled entities and devices, such as the communications interface  220  and the storage medium  230 , to execute methods according to embodiments described herein. The computer program  1320   a  and/or computer program product  1310   a  may thus provide means for performing any steps of the network node  200  as herein disclosed. On this computer readable means  1330 , a computer program  1320   b  can be stored, which computer program  1320   b  can cause the processing circuitry  310  and thereto operatively coupled entities and devices, such as the communications interface  320  and the storage medium  330 , to execute methods according to embodiments described herein. The computer program  1320   b  and/or computer program product  1310   b  may thus provide means for performing any steps of the wireless device  300   a ,  300   b  as herein disclosed. 
     In the example of  FIG. 13 , the computer program product  1310   a ,  13100   b  is illustrated as an optical disc, such as a CD (compact disc) or a DVD (digital versatile disc) or a Blu-Ray disc. The computer program product  1310   a ,  1310   b  could also be embodied as a memory, such as a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM), or an electrically erasable programmable read-only memory (EEPROM) and more particularly as a non-volatile storage medium of a device in an external memory such as a USB (Universal Serial Bus) memory or a Flash memory, such as a compact Flash memory. Thus, while the computer program  1320   a ,  1320   b  is here schematically shown as a track on the depicted optical disk, the computer program  1320   a ,  1320   b  can be stored in any way which is suitable for the computer program product  1310   a ,  1310   b.    
     An LTE subframe lasting 1 ms contains 14 OFDM symbols for normal CP. A New Radio (5G), NR, subframe may have a fixed duration of 1 ms and may therefore contain a different number of OFDM symbols for different subcarrier spacings. An LTE slot corresponds to 7 OFDM symbols for normal CP. An NR slot corresponds to 7 or 14 OFDM symbols; at 15 kHz subcarrier spacing, a slot with 7 OFDM symbols occupies 0.5 ms. Concerning NR terminology, reference is made to 3GPP TR 38.802 v14.0.0 and later versions. 
     Aspects of the disclosure may be applicable to either LTE or NR radio communications. References to a short TTI may alternatively be considered as a mini-slot, according to NR terminology. The mini-slot may have a length of 1 symbol, 2 symbols, 3 or more symbols, or a length of between 1 symbol and a NR slot length minus 1 symbol. The short TTI may have a length of 1 symbol, 2 symbols, 3 or more symbols, an LTE slot length (7 symbols) or a length of between 1 symbol and a LTE subframe length minus 1 symbol. The short TTI, or mini-slot may be considered as having a length less than 1 ms or less than 0.5 ms. 
     The inventive concept has mainly been described above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the inventive concept, as defined by the appended claims.