This application is a 35 U.S.C. § 371 national phase filing of International Application No. PCT/SE2017/051122, filed Nov. 13, 2017, the content of which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

Embodiments described herein relate to methods and apparatus for transmitting and receiving control channel information. In particular, embodiments disclosed herein comprise obtaining a spatial relationship between a first wireless device and a second wireless device and controlling how control channel information is transmitted to the first wireless device and the second wireless device based on the spatial relationship.

BACKGROUND

Massive Multiple Input Multiple Output (MIMO) technology is a multi-user technology which may provide uniformly high quality of service to a plurality of wireless devices operating in high-mobility environments. Base stations may be provided with arrays of a large number of antennas, which may then be used to serve a plurality of wireless devices simultaneously by using spatial multiplexing.

The wireless devices may be informed about which radio resources have been allocated to them for the reception of payload data. This may be accomplished through the transmission of control channel information using a downlink control channel, for example, a Physical Downlink Control Channel (PDCCH). In order to obtain the control channel information, wireless devices may be configured to blindly search a predetermined search space of radio resources until the control channel information intended for the wireless device is found.

With existing solutions, the number of radio resources used for control channel information on a control channel, for example PDCCH, grows proportionally to the number of wireless devices being served by the base station. Hence, as the number of wireless devices increases, each wireless device may need to make a proportionally larger number of decoding attempts to find control channel information intended for that particular wireless device. This may result in excessive power consumption in wireless devices, particularly in circumstances where no control channel information is transmitted to the wireless device within a particular search space. Moreover, with the advent of new diverse 5G applications, for example applications for enhanced broadband access and/or for low-power communications, wireless devices may support different bandwidths and different numbers of decoding attempts per second.

SUMMARY

According to some embodiments there is provided a method, in a first wireless device, for obtaining first control channel information from a base station. The method comprises receiving an indication from the base station to operate in one of a first mode and a second mode; and operating in one of the first mode and the second mode based on the indication. In the first mode, the first wireless device is configured to attempt to decode one or more first predetermined search space entries in order to obtain the first control channel information, each first predetermined search space entry defining radio resources, wherein the first control channel information is to be transmitted on radio resources defined by one of the one or more first predetermined search space entries. In the second mode the first wireless device is configured to attempt to decode a plurality of second predetermined search space entries in order to obtain the first control channel information, each search space entry defining radio resources, and wherein the first control channel information is to be transmitted on radio resources defined by one of the plurality of second predetermined search space entries; wherein the number of first predetermined search space entries is less than the number of second predetermined search space entries.

According to some embodiments there is provided a method, in a base station, for transmitting first control channel information to a first wireless device and second control channel information to a second wireless device in a wireless communications network. The method comprises obtaining an indication of whether a spatial relationship between the first wireless device and the second wireless device meets a predetermined condition; and operating in one of a first mode and a second mode based on the indication. Operating in the first mode comprises transmitting the first control channel information and the second control channel information using common radio resources. Operating in the second mode comprises transmitting the first control channel information to the first wireless device and the second control channel information to the second wireless device using orthogonal radio resources.

According to some embodiments there is provided a communication system including a host computer comprising processing circuitry configured to provide user data; and a communication interface configured to forward the user data to a cellular network for transmission to a wireless device. The cellular network comprises a base station having a radio interface and processing circuitry, and the base station's processing circuitry is configured to perform any of the steps of as described in the method above.

According to some embodiments there is provided a first wireless device for obtaining control channel information from a base station. The first wireless device comprises an interface and processing circuitry configured to receive an indication from the base station to operate in one of a first mode and a second mode; and cause the first wireless device to operate in one of the first mode and the second mode based on the indication. In the first mode, the first wireless device is configured to attempt to decode one or more first predetermined search space entries in order to obtain the first control channel information, each search space entry defining radio resources, and wherein the first control channel information is to be transmitted on radio resources defined by one of the one or more first predetermined search space entries. In the second mode the first wireless device is configured to attempt to decode a plurality of second predetermined search space entries in order to obtain the first control channel information, each search space entry defining radio resources, and wherein the first control channel information is to be transmitted on radio resources defined by one of the plurality of second predetermined search space entries; wherein the number of first predetermined search space entries is less than the number of second predetermined search space entries.

According to some embodiments there is provided a communication system including a host computer comprising processing circuitry configured to provide user data; and a communication interface configured to forward user data to a cellular network for transmission to a wireless device. The wireless device comprises a radio interface and processing circuitry, and the wireless device's components are configured to perform any of the steps as described in the method above.

According to some embodiments there is provided a base station for transmitting first control channel information to a first wireless device and second control channel information to a second wireless device in a wireless communications network. The base station comprises an interface and processing circuitry configured to obtain an indication of whether a spatial relationship between the first wireless device and the second wireless device meets a predetermined condition; and cause the base station to operate in one of a first mode or a second mode based on the indication. In the first mode the base station is configured to transmit the first control channel information and the second control channel information using common radio resources. In the second mode the base station is configured to transmit first control channel information to the first wireless device and the second control channel information to the second wireless device using orthogonal radio resources.

According to some embodiments there is provided a computer program comprising instructions which, when executed on at least one processor, cause the at least one processor to carry out the method as described above.

According to some embodiments there is provided a computer program product comprising a computer-readable medium with the computer program as described above.

