Transmission and reception of a random access preamble signal

1. A preamble receiver configured to receive radio signals comprising a preamble sequence, the preamble receiver comprising:

at least one antenna element and corresponding radio unit configured to receive a radio signal;

at least one analog to digital converter configured to perform analog to digital conversion of the received radio signal;

at least one Fast Fourier Transform (FFT) circuit configured to determine a FFT of the analog to digital converted signal;

at least one detector configured to detect the preamble sequence based on the determined FFT;

wherein the preamble sequence comprises a concatenation in time of a plurality of short sequences, wherein each such short sequence has a same time duration as an orthogonal frequency-division multiplexing (OFDM) symbol used for carrying data traffic in a radio access network of the preamble receiver, wherein a size of the FFT used for detecting the preamble signal is the same size as one used for detecting an OFDM symbol carrying data traffic in the radio access network.

2. The preamble receiver of claim 1 , wherein the preamble receiver is configured to use one FFT hardware resource and FFT configuration both for detecting OFDM symbols carrying data and for detecting preamble sequences.

3. The preamble receiver of claim 1 , further comprising a preamble detector circuit configured to:

determine a plurality of FFTs from a plurality of FFT windows; and

non-coherently combine the determined FFTs into a combined received preamble signal.

4. The preamble receiver of claim 1 , further comprising a preamble detector circuit configured to:

determine a plurality of FFTs from a plurality of FFT windows; and

coherently combine the determined FFTs into a combined received preamble signal.

5. The preamble receiver of claim 1 , wherein the preamble sequence is used for any of: initial access, handover, request for scheduling, and resynchronization.

6. The preamble receiver of claim 1 :

wherein the preamble receiver is configured for beamforming;

wherein beamforming weights are configured to change between FFT windows such that a number of spatial directions for which preamble detection is done is increased.

7. The preamble receiver of claim 6 :

wherein the preamble receiver comprises hardware support for more than one simultaneous analog beamforming configuration;

wherein the preamble receiver is configured for switching at a first switching rate between spatial directions with one beamforming configuration, and for switching at a second switching rate between spatial directions with another beamforming configuration, the first rate being different from the second rate.

8. The preamble receiver of claim 6 , wherein a single inverse FFT is applied per beam direction and polarization.

9. The preamble receiver of claim 6 , wherein the preamble receiver is configured to perform simultaneous beam-forming and matched filtering by a comprised joint filter.

10. A method, performed in a preamble receiver, for receiving a radio signal and detecting a preamble sequence comprised in the radio signal, the method comprising:

receiving a radio signal comprising a preamble signal constructed from a plurality of short sequences via at least one antenna element and radio unit, the short sequence having a same time duration as an Orthogonal Frequency-Division Multiplexing (OFDM) symbol used for carrying data traffic in a radio access network of the preamble transmitter;

performing analog to digital conversion of the radio signal by an Analog-to-Digital Converter comprised in the preamble receiver;

determining a Fast Fourier Transform (FFT) of the analog to digital converted signal, wherein a size of the FFT used for detecting the preamble signal is the same size as for detecting an OFDM symbol used for carrying data traffic in the radio access network;

detecting the preamble sequence based on the determined FFT.

11. The method of claim 10 , wherein the determining an FFT comprises determining an FFT using a single configuration for detecting OFDM symbols carrying data and for detecting preamble sequences.

12. The method of claim 10 , wherein the detecting comprises:

determining a plurality of FFTs from a plurality of FFT windows; and

non-coherently combining the FFT results into a combined received preamble signal.

13. The method of claim 10 , wherein the detecting comprises:

determining a plurality of FFTs from a plurality of FFT windows; and coherently combining the FFT results into a combined received preamble signal.

14. A computer program product stored in a non-transitory computer readable medium for controlling a preamble receiver to receive a radio signal and detect a preamble sequence comprised in the radio signal, the computer program product comprising software instructions which, when run on processing circuitry of the preamble receiver, causes the preamble receiver to:

receive a radio signal comprising a preamble signal constructed from a plurality of short sequences via at least one antenna element and radio unit, the short sequence having a same time duration as an Orthogonal Frequency-Division Multiplexing (OFDM) symbol used for carrying data traffic in a radio access network of the preamble transmitter;

perform analog to digital conversion of the radio signal by an Analog-to-Digital Converter comprised in the preamble receiver;

determine a Fast Fourier Transform (FFT) of the analog to digital converted signal, wherein a size of the FFT used for detecting the preamble signal is the same size as for detecting an OFDM symbol used for carrying data traffic in the radio access network;

detect the preamble sequence based on the determined FFT.