Zhan Zhang

Bio: Zhan Zhang is an academic researcher from NTT DoCoMo. The author has contributed to research in topics: MIMO & Communication channel. The author has an hindex of 10, co-authored 86 publications receiving 484 citations.

DMRS Design and Channel Estimation for LTE-Advanced MIMO Uplink

Abstract: In 3GPP long term evolution (LTE) uplink, single transmit antenna is adopted due to its simplicity and acceptable performance. However, in order to satisfy the higher requirement of LTE-Advanced (LTE-A) on uplink spectrum efficiency, multi- ple transmit antennas must be supported in LTE-A uplink. At the same time, the backwards compatibility to LTE should be taken into considerations. Therefore, the demodulation reference signal (DMRS) as well as channel estimation have to be re-designed for LTE-A uplink to support multiple-input multiple-output (MIMO) transmission. In this paper, we propose the DMRS design for LTE-A MIMO uplink via frequency domain code division multiplexing (FD-CDM) with the maximum distance binding (MDB), which can minimize the interference among multiple transmit antennas. More importantly, it is backwards compatible to the DMRS in LTE uplink, i.e., few modifications to the current specifications are needed. Furthermore, the improved uplink channel estimation with dynamic channel impulse response reser- vation (DCIR 2 ) and frequency domain windowing/dewindowing

Method, system and transmitter for adaptive coordinated transmission in wireless communications

Abstract: Embodiments of the present invention include a method, system and transmitter for adaptive coordinated transmission in wireless communications. The method includes: determining more than one transmitter for performing coordinated transmission, configuring one of the more than one transmitter to be a serving transmitter with others of the more than one transmitter being cooperating transmitters, and determining more than one receiver; determining, by a cooperating transmitter, a cooperation mode according to measured signal parameters of the more than one receiver after receiving a cooperation request from the serving transmitter, and providing the cooperation mode to the serving transmitter; generating, by each of the more than one transmitter, a transmit signal corresponding to the more than one receiver according to the cooperation mode determined, and transmitting the transmit signal to each of the more than one receiver. The method, system and transmitter of the present invention increase spectrum efficiency for cell edge users as much as possible while having relatively low implementation complexity.

Multi-user MIMO transmission method in wireless communication system, base station and user terminal

Abstract: The invention discloses a multi-user multiple input multiple output (MU-MIMO) transmission method in a wireless communication system, a base station and a user terminal. The method comprises the following steps that: the base station receives detection pilot frequency SRS of N users to perform channel estimation and acquires downlink channel information according to the channel estimation result and channel reciprocity of the system, wherein N is more than 1; the base station performs quick response (QR) decomposition on the downlink channel information, acquires a multi-user beamforming (MU-BF) matrix P (i) of the ith user from a Q matrix acquired through decomposition, and acquires a downlink single-user beamforming (SU-BF) matrix V (i) of the ith user further, wherein i=1, ...,N; and the base station performs beamforming processing on transmitting data of the ith user according to the MU-BF matrix P (i) and the SU-BF matrix V (i). The method and equipment acquire beamforming matrixes for uplink and downlink MU-MIMO transmission by means of the channel reciprocity of the system and the QR decomposition, and the MU-MIMO transmission performance can be improved.

Multiple-input and multiple-output precoding method and apparatus for the method

Abstract: PROBLEM TO BE SOLVED: To provide an MIMO precoding method and an apparatus for the method. SOLUTION: In the method, an equivalent channel matrix is obtained using respective precoding matrixes in a prescribed code book and a channel state information matrix, the obtained equivalent channel matrix is decomposed to obtain a triangle matrix corresponding to the respective precoding matrixes, the precoding matrix corresponding to the triangle matrix for which the minimum value of the absolute value of diagonal elements is the largest is selected, and precoding is executed to signals to be transmitted after removing interference between streams using the precoding matrix. The precoding apparatus includes a precoding matrix selection module and a precoding module. Signal transmission quality in the MIMO system of a single user and multiple users can be effectively improved. COPYRIGHT: (C)2010,JPO&INPIT

Low-Complexity Enhanced DFT-based Channel Estimation for OFDM Systems with virtual Subcarriers

Abstract: Traditional discrete Fourier transform (DFT) based channel estimation will suffer from significant performance degradation due to the edge effect in practical orthogonal frequency division multiplexing (OFDM) systems with virtual subcarriers. In this paper, a novel enhanced DFT-based channel estimation method is proposed, which can effectively mitigate the edge effect caused by virtual subcarriers via edge value repetition in the frequency domain and zero insertion in the time domain, thus to improve the overall channel estimation performance for the usable subcarriers. Moreover, it does not need a priori statistical characteristics of the wireless channel and the complexity of channel estimation is not increased. Therefore, it is especially suitable for hardware implementation.

Optical fiber-based distributed antenna systems, components, and related methods for calibration thereof

Abstract: Optical fiber-based wireless systems and related components and methods are disclosed. The systems support radio frequency (RF) communications with clients over optical fiber, including Radio-over-Fiber (RoF) communications. The systems may be provided as part of an indoor distributed antenna system (IDAS) to provide wireless communication services to clients inside a building or other facility. The communications can be distributed between a head end unit (HEU) that receives carrier signals from one or more service or carrier providers and converts the signals to RoF signals for distribution over optical fibers to end points, which may be remote antenna units (RAUs). In one embodiment, calibration of communication downlinks and communication uplinks is performed to compensate for signal strength losses in the system.

System for and method of configuring distributed antenna communications system

Abstract: A distributed antenna system comprises a plurality of antennas and a multi-port hub. The multi-port hub comprises an interface to a telecommunications network and a plurality of transceivers. The multi-port hub is configured to operate in a first mode ('normal' mode) in which the multi-port hub receives a downlink communications signal via the interface and distributes the downlink communications signal to the plurality of antennas using a selected downlink transmission frequency within a downlink frequency range and in which the multi-port hub receives uplink communications signals from the plurality of antennas at a selected uplink receive frequency. The multi-port hub is also configured to operate in a second mode ('listening' mode) in which the multi-port hub receives communications signals from the plurality of antennas at one or more frequencies within the downlink frequency range. The transmission frequency for the first mode ('normal' mode) may be selected based on field strength of the signals received in the second mode ('listening' mode).

Mobile communication method, mobile station, and radio base station

Abstract: In a mobile communication method according to the present invention, a mobile station (UE) transmits uplink data to a radio base station by using an uplink radio resource assigned to the mobile station by predetermined scheduling information, in a predetermined cycle. The method includes the steps: (A) notifying, to the mobile station (UE), the predetermined cycle and information on the uplink radio resource; (B) notifying, to the mobile station (UE), the predetermined scheduling information; and (C) transmitting uplink data in the predetermined cycle by using the uplink radio resource assigned by the predetermined scheduling information, the transmission starting at a certain point determined on the basis of the received predetermined scheduling information. In the step (C), the predetermined scheduling information is discarded, when the information on the uplink radio resource and information notified by the predetermined scheduling information are inconsistent with each other.

Systems, methods, and devices for increasing radio frequency (RF) power in distributed antenna systems

Abstract: A system, and related methods and devices, is disclosed for increasing an output power of a frequency band in a distributed antenna system that includes at least one RXU module that is operatively coupled to at least one RAU module. A first group of the plurality of channels within a first frequency band may be allocated to the RAU module, and a second group of the plurality of the channels within the first frequency band may be allocated to the RXU module. The at least one RAU module may be configured to receive RF signals from the first group of the plurality of channels being used in the first frequency band, and the at least one RXU module may be configured to receive RF signals from the second group of the plurality of channels being used in the first frequency band. In this manner, the amount of composite power per channel is increased.

Optical fiber-based distributed antenna systems, components, and related methods for monitoring and configuring thereof

Abstract: Optical fiber-based wireless systems and related components and methods are disclosed. The systems support radio frequency (RF) communications with clients over optical fiber, including Radio-over-Fiber (RoF) communications. The systems may be provided as part of an indoor distributed antenna system (IDAS) to provide wireless communication services to clients inside a building or other facility. The communications can be distributed between a head end unit (HEU) that receives carrier signals from one or more service or carrier providers and converts the signals to RoF signals for distribution over optical fibers to end points, which may be remote antenna units (RAUs). A microprocessor-based control system or systems may also be employed. The control systems may include one or more microprocessors or microcontrollers in one or more of the components of the system that execute software instructions to control the various components and provide various features for the optical fiber-based distributed antenna systems.