Orthogonal frequency-division multiplexing (OFDM) effectively mitigates intersymbol interference (ISI) caused by the delay spread of wireless channels. Therefore, it has been used in many wireless systems and adopted by various standards. In this paper, we present a comprehensive survey on OFDM for wireless communications. We address basic OFDM and related modulations, as well as techniques to improve the performance of OFDM for wireless communications, including channel estimation and signal detection, time- and frequency-offset estimation and correction, peak-to-average power ratio reduction, and multiple-input-multiple-output (MIMO) techniques. We also describe the applications of OFDM in current systems and standards.

OFDM and Its Wireless Applications: A Survey

A multiple-access MIMO WLAN system that employs MIMO, OFDM, and TDD. The system (1) uses a channel structure with a number of configurable transport channels, (2) supports multiple rates and transmission modes, which are configurable based on channel conditions and user terminal capabilities, (3) employs a pilot structure with several types of pilot (e.g., beacon, MIMO, steered reference, and carrier pilots) for different functions, (4) implements rate, timing, and power control loops for proper system operation, and (5) employs random access for system access by the user terminals, fast acknowledgment, and quick resource assignments. Calibration may be performed to account for differences in the frequency responses of transmit/receive chains at the access point and user terminals. The spatial processing may then be simplified by taking advantage of the reciprocal nature of the downlink and uplink and the calibration.

MIMO WLAN system

Techniques are described for efficiently estimating and compensating for the effects of a communication channel in a multi-carrier wireless communication system. The techniques exploit the fact that the transmitted symbols are drawn from a finite-alphabet to efficiently estimate the propagation channel for multi-carrier communication systems, such systems using OFDM modulation. A transmitter transmits data through a communication channel according to the modulation format. A receiver includes a demodulator to demodulate the data and an estimator to estimate the channel based on the demodulated data. The channel estimator applies a power-law operation to the demodulated data to identify the channel. The techniques can be used in both blind and semi-blind modes of channel estimation.

Channel estimation for wireless ofdm systems

A wireless telecommunication system comprises base stations for communicating with terminal devices. One or more base stations support a power boost operating mode in which a base station's available transmission power is concentrated in a subset of its available transmission resources to provide enhanced transmission powers as compared to transmission powers on these transmission resources when the base station is not operating in the power boost mode. A base station establishes an extent to which one or more base stations in the wireless telecommunications system support the power boost operating mode conveys an indication of this to a terminal device. The terminal device receives the indication and uses the corresponding information to control its acquisition of a base station of the wireless telecommunication system, for example by taking account of which base stations support power boosting and/or when power boosting is supported during a cell attach procedure.

Telecommunications apparatus and methods

Methods and apparatus in a fifth-generation wireless communications, including an example method, in a wireless device, that includes receiving a downlink signal comprising an uplink access configuration index, using the uplink access configuration index to identify an uplink access configuration from among a predetermined plurality of uplink access configurations, and transmitting to the wireless communications network according to the identified uplink access configuration. The example method further includes, in the same wireless device, receiving, in a first subframe, a first Orthogonal Frequency-Division Multiplexing (OFDM) transmission formatted according to a first numerology and receiving, in a second subframe, a second OFDM transmission formatted according to a second numerology, the second numerology differing from the first numerology. Variants of this method, corresponding apparatuses, and corresponding network-side methods and apparatuses are also disclosed.

Network architecture, methods, and devices for a wireless communications network

A method for communicating a plurality of data streams between a transmitting device with multiple transmit antennas and a receiving device, is disclosed. The method comprises determining a set of power weightings, efficiently quantizing the power weightings, and providing the set of power weightings the transmitting device. Another aspect of the invention comprises the transmitter implicitly signaling the number of data streams which the receiver should feedback information for through the amount of feedback requested. An additional aspect of the invention is a means of determining the best codebook weights by combining the maximum power and maximum capacity criteria.

Method and apparatus for closed loop data transmission

In a multiple-input, multiple-output (MIMO) communication system, a method and apparatus for multi-antenna transmission In accordance with the preferred embodiment of the present invention a reduced number of transmit weight matrices are fed back to the transmitter Each transmit weight matrix is then applied to a plurality of subcarriers Because each transmit weight matrix is applied to more than one subcarrier, the amount of weight matrixs being fed back to the transmitter is greatly reduced

Method and apparatus for multi-antenna transmission

A wireless communication terminal including a controller coupled to a wireless transceiver that receives a first control message on an anchor carrier, wherein the first control message includes a resource assignment for the anchor carrier. The transceiver is also configured to receive a second control message on the anchor carrier, the second control message associated with a set of component carriers, wherein the set of component carriers are distinct from the anchor carrier. The controller determines a resource assignment for at least one component carrier in the set of component carriers using both the first and the second control messages.

Resource allocation in wireless communication systems

A base station communicates a positioning reference signal (PRS) to wireless communication devices over a downlink in a wireless communication system by encoding a PRS into a first set of transmission resources, encoding other information into a second set of transmission resources, multiplexing the two sets of resources into a subframe such that the first set of resources is multiplexed into at least a portion of a first set of orthogonal frequency division multiplexed (OFDM) symbols based on an identifier associated with the base station and the second set of resources is multiplexed into a second set of OFDM symbols. Upon receiving the subframe, a wireless communication device determines which set of transmission resources contains the PRS based on the identifier associated with the base station that transmitted the subframe and processes the set of resources containing the PRS to estimate timing (e.g., time of arrival) information.

Method and apparatus for generating reference signals for accurate time-difference of arrival estimation

A wireless communication terminal including a transceiver coupled to a processor and corresponding methods are disclosed. The processor is configured to determine resource elements that carry data intended for the terminal from a set of allocated resource elements that carry data intended for the terminal excluding at least resource elements associated with a first set of one or more resource elements of a particular type that are shifted relative to a known reference signal pattern. The processor is also configured to decode the resource elements that carry the data intended for the terminal based on the resource elements that carry the data intended for the terminal.

Xiangyang Zhuang

Papers

Method and apparatus for closed loop data transmission

Method and apparatus for multi-antenna transmission

Resource allocation in wireless communication systems

Method and apparatus for generating reference signals for accurate time-difference of arrival estimation

Method of signaling particular types of resource elements in a wireless communication system