Over-the-air (OTA) phase synchronization for reciprocity-based coordinated multipoint (CoMP) joint transmission is disclosed. Phase synchronization reference signals (PSRS) are transmitted within a CoMP operation that can be used to determine the phase drifts of the transmit and receive chains of the base stations. These phase drifts can then be used to obtain a relative phase drift between the uplink and downlink channels. When estimating the uplink channel from the sounding reference signals (SRS), the relative phase drift may be applied to estimate the downlink channel as well. The OTA phase synchronization may be performed with a user equipment (UE)-assisted or inter-base station procedures.

A wireless cellular base station includes M antennas and one or more processing devices. For each antenna, the antenna transmits a calibration pilot symbol over the air and the other M1 antennas receive the calibration pilot symbol over the air. The processing devices select one of the M antennas as a reference antenna and for each antenna of the M antennas, the processing devices calculate channel reciprocity calibration coefficients of the antenna with respect to the reference antenna based on the received calibration pilot symbols.

Wireless communications systems and methods related to over-the-air uplink-downlink (UL-DL) reciprocity calibration. A central unit transmits downlink (DL) calibration reference signal (RS) and a calibration request. The central unit receives, in response to the calibration request, a first uplink (UL) calibration RS and a first DL channel estimate associated with a first transmission point (TP) and a first wireless communication device. The central unit transmits a DL coordinated multipoint (CoMP) joint transmission signal according to an uplink-downlink (UL-DL) reciprocity calibration. The UL-DL reciprocity calibration is based on at least a first UL channel estimate based on the first UL calibration RS, the first DL channel estimate, a second UL channel estimate associated with a second TP and the first wireless communication device, and a second DL channel estimate associated with the second TP and the first wireless communication device.

The data recovery from sub-carriers (DRSC) of a received OFDM signal, contributes a method and a circuit for utilizing parameters of OFDM sub-carriers comprised in the received OFDM signal or subspaces comprising the OFDM sub-carriers for recovering transmitted data symbols from the received OFDM signal affected by deterministic and random distortions introduced by a transmission link.

A wireless cellular base station includes M antennas and one or more processing devices. For each antenna, the antenna transmits a calibration pilot symbol over the air and the other M1 antennas receive the calibration pilot symbol over the air. The processing devices select one of the M antennas as a reference antenna and for each antenna of the M antennas, the processing devices calculate channel reciprocity calibration coefficients of the antenna with respect to the reference antenna based on the received calibration pilot symbols.

A wireless cellular base station (BS) transmitter transmits a downlink calibration pilot symbol. A receiver receives from a user equipment (UE) an uplink calibration pilot symbol and an effective downlink channel estimate transmitted by the UE. The effective downlink channel estimate is computed by the UE using the downlink calibration pilot symbol received from the BS. Processing devices compute an effective uplink channel estimate using the uplink calibration pilot symbol received from the UE and compute channel reciprocity calibration coefficients using the effective downlink channel estimate received from the UE and the effective uplink channel estimate computed by the BS. The BS includes multiple antennas, and the BS computes the channel reciprocity calibration coefficients for each antenna. Alternatively, the uplink channel estimate received by the BS is an inverted version of the effective downlink channel estimate, which the processing devices use for channel reciprocity compensation.

The present invention discloses a method and an apparatus for channel calibration among multiple RRUs, and pertains to the field of communications technologies. The method includes self-calibrating two RRUs to obtain two self-calibration coefficient, exchanging calibration sequences between the two RRUs through an air interface, returning, by one RRU, the calibration sequence received from another RRU to the another RRU in the air interface, and acquiring a calibration coefficient of the another RRU according to the calibration sequences and the self-calibration coefficients.

A first communication device receives a sounding packet that was transmitted by a second communication device over a communication channel, and performs a channel estimation on a subchannel block of the communication channel to determine steering matrix feedback information for the subchannel block. The subchannel block spans a contiguous partial bandwidth of the communication channel and does not span an entire bandwidth of the communication channel. The first communication device transmits a communication frame to the second communication device, the communication frame i) including the steering matrix feedback information for the subchannel block, and ii) not including steering matrix feedback information for the one or more other subchannel blocks of the communication channel.

This application presents an adaptive data recovery from distorted signals (ADRDS) of original data symbols from intervals or parameters of tone signals derived from a received OFDM signal, including responding to dynamic distortions introduced to the received OFDM signal by an OFDM transmission channel. Such ADRDS is implemented by converting back the derived intervals or parameters into original data symbols corresponding to distinctive sets of the intervals or parameters which the derived intervals or parameters belong to.

The data recovery from gradients (DRG) of sub-carriers of a received OFDM signal affected by deterministic and random distortions introduced by a transmission link, contributes a method and a system for utilizing gradients characterizing shapes of OFDM sub-carriers comprised in such OFDM signal for recovering data symbols transmitted originally.