Methods, processing device, computer programs, computer program products, and antenna apparatus for calibration of antenna apparatus

The method (20) as claimed in any of the preceding claims, wherein estimating (23) the fine delay and initial phase for the receive chains (51, . . . , 5n) comprises:

• switching the receive chain (51) of one of the two or more transceiver chains (41) into a receive calibration mode,
• transmitting, by the reference calibration antenna (11), a calibration pilot signal,
• receiving synchronously, by the receive chains (51, . . . , 5n), the calibration pilot signal transmitted from the reference calibration antenna (11),
• estimating (23) a fine delay and initial phase for all receive chains (51, . . . , 5n) of the transceiver chains (41, . . . , 4n) simultaneously based on their phase-frequency characteristics.

The method (20) as claimed in any of the preceding claims, wherein the estimating (23) of fine delay and initial phase for the transmit chains (61, . . . , 6n) comprises:

• switching, by means of the antenna calibration control unit (10), the transmit chain (61, . . . , 6n) of one of the two or more transceiver chains (41, . . . , 4n) into a transmit calibration mode,
• transmitting, by the transmit chains (61, . . . , 6n), a calibration pilot signal on a respective specified sub-carrier,
• receiving, by the reference calibration antenna (11), calibration pilot signals transmitted from the transmit chains (61, . . . , 6n), and
• estimating the fine delay and initial phase for the transmit chains (61, . . . , 6n) based on their phase-frequency characteristics.

The method (20) as claimed in any of the preceding claims, wherein an amplitude calibration based on the amplitude-frequency characteristics of the respective transceiver chains (41, . . . , 4n) comprises:

• transforming a received signal ra(t) into frequency domain and extracting valid sub-carriers ra(k) of a specified antenna a, wherein system bandwidth is divided into N1 sub-bands wherein each sub-band comprises M1 sub-carriers and each sub-band has, among its M1 sub-carriers, N sub-carriers mapped pilot signal from respective n transceiver chains (41, . . . 4n) and wherein the remaining M1−N sub-carriers are reserved for noise estimation,
• performing a channel estimation Ha(k) in frequency domain for the specified antenna a based on a least square error criterion, in accordance with:
• for mean power Paverage,a and noise power Pnoise,a for antenna a,
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• transforming Ha(k) into time-domain ha(n), thus obtaining ha(n) after noise removal,
• ha(n)=IDFT(Ha(k))
• ha′(n)=ha(n), when ha(n)>Tthreshold*Pnoise,
• wherein Tthreshold is a threshold for valid signal selection from the received signal,
• calculating amplitude compensation coefficient Acomp,a′ in accordance with
• Acomp,a′=ha′(n)/√{square root over (Paverage,a)}
• performing a Discrete Fourier Transform, DFT, equivalent to time-domain interpolation, for obtaining an amplitude compensation coefficient Acomp,a(k) for the system bandwidth as:
• Acomp,a(k)=DFT([Acomp,a′,zeros(1,1200−sizeof(Acomp,a′))],k=1, 2, . . . , 1200

A processing device (30) for calibration of an antenna apparatus (1), the antenna apparatus (1) comprising an antenna array (7) and two or more transceiver chains (41, . . . , 4n), each transceiver chain (41, . . . , 4n) comprising a receive chain (51, . . . , 5n) and a transmit chain (61, . . . , 6n) and an antenna element (71, . . . , 7n), wherein one transceiver chain (41) of the at least two transceiver chains (41, . . . , 4n) further comprises an antenna calibration control unit (10) and a reference calibration antenna (11), wherein the antenna calibration control unit (10) is arranged to switch the transceiver chain (41) between a calibration mode and a operation mode, wherein the processing device (30) is arranged to:

• estimate, by means of a coarse receive delay unit (31) and a coarse transmit delay unit (32), a coarse receive delays for the receive chains (51, . . . , 5n) and coarse transmit delays for the transmit chains (61, . . . , 6n), respectively,
• adjust, by a first timing unit (33), a timing of the receive chains (51, . . . , 5n) based on the estimated coarse receive delays so that the receive chains (51, . . . , 5n) align with the maximum coarse receive delay difference and adjusting a timing of the transmit chains (61, . . . , 6n) based on the estimated coarse transmit delays so that the transmit chains (61, . . . , 6n) align with the maximum coarse transmit delay difference,
• estimate, by a fine delay and initial phase unit (34), a fine delay and initial phase for the receive chains (51, . . . , 5n) and the transmit chains (61, . . . , 6n) based on their phase-frequency characteristics,
• adjust, by a second timing unit (35), an intermediate frequency timing of the antenna apparatus (1) based on the estimated fine delay,
• compensate, by a first compensating unit (36), initial phase and residual delay at base band frequency-domain signal,
• estimate, by an estimation unit (37), amplitude-frequency characteristics of the transceiver chains (41, . . . , 4n), and
• compensate, by a second compensating unit (38), the estimated amplitude-frequency characteristics at base band frequency-domain signal.

A computer program (42) for a processing device (30) for calibration of an antenna apparatus (1), the antenna apparatus (1) comprising an antenna array (7) and two or more transceiver chains (41, . . . , 4n), each transceiver chain (41, . . . , 4n) comprising a receive chain (51, . . . , 5n) and a transmit chain (61, . . . , 6n) and an antenna element (71, . . . , 7n), wherein one transceiver chain (41) of the at least two transceiver chains (41, . . . , 4n) further comprises an antenna calibration control unit (10) and a reference calibration antenna (11), wherein the antenna calibration control unit (10) is arranged to switch the transceiver chain (40 between a calibration mode and a operation mode, the computer program (42) comprising computer program code, which, when run on the processing device (30), causes the processing device (30) to perform the steps of:

• estimating coarse receive delays for the receive chains (51, . . . , 5n) and coarse transmit delays for the transmit chains (61, . . . , 6n),
• adjusting a timing of the receive chains (51, . . . , 5n) based on the estimated coarse receive delays so that the receive chains (51, . . . , 5n) align with the maximum coarse receive delay difference and adjusting a timing of the transmit chains (61, . . . 6n) based on the estimated coarse transmit delays so that the transmit chains (61, . . . , 6n) align with the maximum coarse transmit delay difference,
• estimating a fine delay and initial phase for the receive chains (51, . . . , 5n) and the transmit chains (61, . . . , 6n) based on their phase-frequency characteristics,
• adjusting (24) an intermediate frequency timing of the antenna apparatus (1) based on the estimated fine delay,
• compensating initial phase and residual delay at base band frequency-domain signal,
• estimating amplitude-frequency characteristics of the transceiver chains (41, . . . , 4n), and
• compensating the estimated amplitude-frequency characteristics at base band frequency-domain signal.