Liu Liu

Bio: Liu Liu is an academic researcher from NTT DoCoMo. The author has contributed to research in topics: Telecommunications link & User equipment. The author has an hindex of 15, co-authored 95 publications receiving 853 citations.

Radio base station, user terminal, radio communication system and radio communication method

Abstract: The present invention is designed to make it possible to adequately form the search space candidates to be used in the blind decoding of downlink control information when the radio resource region for downlink control channels is expanded. The radio base station of the present invention is a radio base station that transmits downlink control information for a user terminal by using an enhanced downlink control channel that is frequency-division-multiplexed with a downlink shared data channel, and has a configuring section that configures, for the user terminal, a plurality of resource sets that are each formed by including a plurality of resource blocks allocated to the enhanced downlink control channel, and a determining section that determines enhanced control channel elements to constitute a plurality of search space candidates such that the plurality of search space candidates of each resource set are all placed in different resource blocks.

Energy Source Aware Target Cell Selection and Coverage Optimization for Power Saving in Cellular Networks

Abstract: The spread of mobile connectivity is generating major social and economic benefits around the world, while along with the rapid growth of new telecommunication technologies like mobile broadband communication and M2M (Machine-to-Machine) networks, larger number of various base stations will be employed into the network, which will greatly increase the power expense and CO2 emission. In order to degrade the system power expense, variety of researches on new energy and novel transmission technology are put in agenda. In this paper, instead of reducing the absolute power expense, the research focuses on guiding more power consumption into green source energy, which implying that the UEs (User Equipment), especially the cell edge UEs, will have preferential access to the BSs (Base Station) with natural energy supply. To realize the tendentious connection, two detailed approaches are proposed, the HO (Hand Over) parameter tuning for target cell selection and power control for coverage optimization. The system evaluation shows that, by proper setting of parameters in HO and power control, both of the two approaches can achieve good balance between energy saving effect and system throughput impact.

Component Carrier Management for Carrier Aggregation in LTE-Advanced System

Abstract: This paper focuses on investigating appropriate management of Component Carriers(CCs) in carrier aggregation( CA) system, which is identified as one of the most distinct features of 4G systems including Long Term Evolution- Advanced (LTE-A). An LTE-A user equipment (UE) is allowed to concurrently utilize multiple carriers, which leads to scalable increase in user throughput. However, in certain circumstances, aggregating entire available carriers for a UE is not meaningful due to probably low channel quality or high traffic load in some of the CCs. Therefore, how to make good use of multiple carriers in real deployment scenarios is an important issue. Based on the analysis of resource allocation across multiple carriers in Layer-2, two CC management methods in Layer- 3 are proposed. The proposed method is shown by simulation results to be effective in providing comparable user throughput with lower implementation complexity, as compared to solely ingenious resource allocation.

Radio base station, user terminal and radio communication system

Abstract: A radio base station is disclosed to communicate with a user terminal that is capable of using a licensed band and an unlicensed band and has a control section that controls the transmission of downlink signals in the unlicensed band using LBT (Listen Before Talk), a selection section that selects the symbol to execute LBT, randomly, with equal probability, from a plurality of candidate symbols, and an acquiring section that acquires a measurement result, in which the received signal intensity in the LBT period is measured, wherein when the control section judges that the channel of the unlicensed band is in an idle state from the measurement result of received signal intensity, the control section executes control so that a beacon reference signal is transmitted in all of the candidate symbols that follow the symbol in which LBT was executed.

Beam axis detection and alignment for uniform circular array-based orbital angular momentum wireless communication

Abstract: Orbital angular momentum (OAM) provides a new dimension for multiplexing and consequently can improve the link capacity remarkably. In the scope of radio communication, uniform circular array (UCA) is usually used to generate OAM signals, where beam axis detection and alignment is a key factor that influences the detection of OAM signal and directly determines the capacity of OAM links. This study analyses the beam axis detection and alignment issues under the ideal (noiseless) condition. The authors first clarify the fact that for single-mode OAM transmission, the intensity of electric field in radial direction is characterised by the Bessel function of the first kind. Inspired by this property, they propose three practical methods for beam axis detection and alignment, that is, double parallelogram array method, double UCA method and single UCA method. Iterative translation and rotation strategy are applied to enhance the precision. Finally, the effectiveness of the proposed methods is justified by simulation.

User terminal, radio base station and radio communication method

Abstract: The present invention is designed to provide a user terminal, a radio base station and a radio communication method of novel structures that can achieve a good communication environment. A radio base station non-orthogonal-multiplexes downlink signals for a plurality of user terminals over a given radio resource, a user terminal having received the downlink signals for the plurality of user terminals decodes downlink signal for another user terminal, judges whether or not the downlink signal for the other user terminal has been successfully received, based on the decoding result of the downlink signal, reports a judgement result as to whether or not the downlink signal for the other user terminal has been successfully received and a judgement result as to whether or not a downlink signal for the user terminal has been successfully received, to the radio base station, and then the radio base station executes retransmission control of downlink signals based on reports from the user terminal.

Radio base station, user terminal, and radio communication method

Abstract: The present invention is designed to improve spectral efficiency in a radio communication system which can use non-orthogonal multiple access (NOMA). Steps are provided in which a radio base station configures one of a plurality of transmission mode including a first transmission mode, which groups a plurality of transmission methods including a transmission method to employ non-orthogonal multiple access (NOMA) and multiple-user multiple-input and multiple-output (MU-MIMO), and a second transmission mode, which groups a plurality of transmission methods including a transmission method to employ this NOMA and open-loop transmit diversity, and transmits a downlink signal for this user terminal based on the configured transmission mode.

User terminal, wireless base station, and wireless communication method

Abstract: In order that a user terminal properly identifies a connection cell in a radio communication system (LTE-U) for operating LTE in an unlicensed band, a user terminal for communicating with a radio base station in an unlicensed band is provided with a detection section that detects a synchronization signal transmitted from a radio base station using a dummy cell ID used in common among a plurality of radio base stations, an estimation section that performs channel estimation using a reference signal, and a reception processing section that performs reception processing of system information transmitted from a radio base station using a channel estimation result.

Terminal device, base station device, and communication method

Abstract: A first UL-DL configuration configured by using a common RRC message is set; an antenna port for one enhanced physical downlink control channel in a subframe is set based on whether or not the subframe is a predetermined special subframe in the first UL-DL configuration; and in a case where a second UL-DL configuration indicated by downlink control information which is transmitted on a physical downlink control channel is set, an antenna port for one enhanced physical downlink control channel in the subframe is set based on whether or not the subframe is the predetermined special subframe in the second UL-DL configuration.

User terminal and radio communication method

Abstract: The present invention is designed to enable adequate transmission power control when inter-base station CA is employed. When inter-base station CA is employed, radio base stations detect when a user terminal's transmission power reaches the maximum transmission power, and execute control to cancel this. For example, a user terminal has a transmission section that transmits an uplink physical channel to each component carrier, a power headroom generating section that generates power headroom, which is extra transmission power of the subject terminal, and a control section that, when the value of the power headroom becomes 0 or less, executes control so that the power headroom is triggered and reported to the radio base stations.