Apparatuses and methods for detecting a group delay in a communication system

1. A transceiver for a radio base station of a wideband communication system, wherein said transceiver is configured to detect a group delay for performing calibration and comprises a transmission part that includes a circuit that is configured to:

split an available system bandwidth into multiple, J, groups of contiguous subcarriers, each group of contiguous subcarriers representing a subband of the available bandwidth;

generate, for each subband, a constant amplitude zero auto correlation (CAZAC) calibration sequence having a predefined length, M, the CAZAC calibration sequence being generated in the time domain;

convert each CAZAC calibration sequence into frequency domain by using an M-point fast fourier transformation (FFT) operation where M further represents the number of contiguous subcarriers for each subband;

map each converted CAZAC calibration sequence into a dedicated subband;

superimpose the mapped CAZAC calibration sequences to form a CAZAC calibration signal which is further transformed from the frequency domain into the time domain using an N-point inverse FFT (IFFT) operation, where N is a length of a symbol;

append the transformed CAZAC calibration signal with a cyclic prefix (CP) to form a resulting CAZAC calibration signal; and

upconvert the resulting CAZAC calibration signal to a carrier frequency prior to transmitting the upconverted resulting CAZAC calibration signal, said transmitted resulting CAZAC calibration signal passing through a radio frequency (RF) chain, which induces different group delays in subbands before reaching a receiver part of the transceiver.

2. The transceiver of claim 1 , wherein each CAZAC calibration sequence is given by:

x i [n ]=exp( j 2π( N zc −1) t ( t +1)/ N zc ,

where n is an index of a length of a respective CAZAC calibration sequence, i is an index of a dedicated subband, N Zc is a prime number and t is a sequence root.

3. The transceiver of claim 2 , wherein the frequency domain of each converted CAZAC calibration sequence is given by:

X

i

⁡

(

k

)

=

∑

k

=

0

k

=

N

zc

-

1

⁢

x

i

⁡

[

n

]

⁢

exp

⁡

(

-

j2π

⁢

⁢

nk

/

N

)

,

where k=0, 1, 2, (N−1), and n=0, 1, 2, . . . ,(N−1), and where N is larger than the length of a calibration CAZAC sequence.

4. The transceiver of claim 1 , wherein the RF chain through which the upconverted resulting CAZAC calibration signal passes includes a digital upconverter (DUC), and a digital-to-analog converter (DAC).

5. The transceiver of claim 1 , wherein said transceiver further comprises a receiver part comprising a circuit that is configured to:

receive the transmitted resulting CAZAC calibration signal generated by the transmitter part and downconvert the transmitted resulting CAZAC calibration signal as received into a baseband CAZAC calibration signal;

remove a cyclic prefix (CP) of the baseband CAZAC calibration signal and transform the baseband CAZAC calibration signal from the time domain to the frequency domain using an N-point FFT operation, where N is a length of a symbol;

extract from the transformed CAZAC calibration signal, CAZAC calibration sequences of a predefined length M and map each extracted CAZAC calibration sequence into a dedicated subband of the available bandwidth;

determine, for each mapped CAZAC calibration sequence, a recovered CAZAC calibration sequence by multiplying a predefined conjugated frequency response of the mapped CAZAC calibration sequence with the corresponding mapped CAZAC calibration sequence;

convert each recovered CAZAC calibration sequence into the time domain using an IFFT operation, the IFFT having a predefined number of points T; and

jointly estimate, for each converted recovered CAZAC calibration sequence, a group delay by selecting a maximum amplitude value of the converted recovered CAZAC calibration sequence and determining a corresponding time index where the maximum amplitude value occurs.

6. The transceiver of claim 5 , wherein the circuit in the receiver part is further configured to determine a resulting group delay by adding the group delays of all converted recovered CAZAC calibration sequences.

7. The transceiver of claim 5 , wherein zeros are padded to each converted CAZAC calibration sequence in positions of the converted CAZAC calibration sequence corresponding to T−M, so as to achieve accuracy when estimating the group delay of each converted recovered CAZAC calibration sequence.

8. The transceiver of claim 5 , wherein the symbol length N used for the FFT operation is larger than the length of each recovered CAZAC calibration sequence and also larger than T.

9. The transceiver of claim 5 , wherein each recovered CAZAC calibration sequence is given by

C i ( k )= R i ( k )×[ p i ( k )]*, k= 0, 1, . . . , ( M −1)

where i denotes an group index, R i (k) corresponds to a mapped CAZAC calibration sequence, and [P i (k)]* corresponds to a predefined conjugated frequency response of the mapped CAZAC calibration sequence.

10. The transceiver of claim 9 , wherein an estimate of the group delay of a recovered CAZAC calibration sequence is given by:

{circumflex over (Γ)} i =T−τ i

where T is chosen larger than M and τ i is the time index where the maximum amplitude value

11. The transceiver of claim 10 , wherein the circuit is further configured to determine, for each recovered CAZAC calibration sequence, an amplitude attenuation given by

{circumflex over (β)} i =max i /[M* ( M/T )].

12. A method for performing in a transceiver of a radio base station configured for use in a wideband communication system, said method enabling detection of a group delay for performing calibration and the method comprising in a transmit part of the transceiver:

splitting an available system bandwidth into multiple, J, groups of contiguous subcarriers, each group of contiguous subcarriers representing a subband of the available bandwidth;

generating in time domain, for each subband of the available bandwidth, a CAZAC calibration sequence having a predefined length, M;

converting each CAZAC calibration sequence into frequency domain by using a M-points FFT operation where M further represents the number of contiguous subcarriers for each subband;

mapping each converted CAZAC calibration sequence into a dedicated subband;

superimposing the mapped CAZAC calibration sequences to form a CAZAC calibration signal which is further transformed from frequency domain into time domain using an N-points IFFT operation, where N is a length of a symbol;

appending the transformed CAZAC calibration signal with a cyclic prefix, CP, to form a resulting CAZAC calibration signal;

upconverting the resulting CAZAC calibration signal to a carrier frequency prior to transmitting the upconverted resulting CAZAC calibration signal, said transmitted resulting CAZAC calibration signal passing through a radio frequency (RF) chain, which induces different group delays in subbands before reaching a receiver part of the transceiver.

13. The method of claim 12 , further comprising in a receiver part of the transceiver:

receiving from the transmission part the transmitted resulting CAZAC calibration signal generated by the transmission part, and downconverting the transmitted resulting CAZAC calibration signal as received into a baseband CAZAC calibration signal;

removing a cyclic prefix, CP, of the baseband CAZAC calibration signal and transforming the baseband CAZAC calibration signal from time domain to frequency domain using a N-points FFT operation, the FFT, where N is a length of a symbol;

extracting from the transformed CAZAC calibration signal, CAZAC calibration sequences of a predefined length M and mapping each extracted CAZAC calibration sequence of length M into a dedicated subband of the available bandwidth;

determining for each mapped CAZAC calibration sequence, a recovered CAZAC calibration sequence by multiplying a predefined conjugated frequency response of the mapped CAZAC calibration sequence with the corresponding mapped CAZAC calibration sequence;

converting each recovered CAZAC calibration sequence into time domain using an IFFT, operation, the IFFT having a predefined number of points T;

jointly estimating, for each converted recovered CAZAC calibration sequence, a group delay by selecting a maximum amplitude value of the converted recovered CAZAC calibration sequence and determining a corresponding time index where the maximum amplitude value occurs.