Method and arrangement in a telecommunication system

A device for use in a communication system, the device comprising:

• a transmitter configured to generate and transmit a random access transmission to a receiver in order to access the communication system, the random access transmission comprising a preamble followed by a message block followed by a guard period, wherein:
• the preamble includes a first cyclic prefix;
• the message block includes a second cyclic prefix that is shorter than the first cyclic prefix, the second cyclic prefix having a length that is at least equal to a maximum delay spread of a channel between the device and the receiver;
• and
• a length of the guard period is at least a maximum round-trip time for signals between the device and the receiver.

A method of operating a receiver in a communication system, the method comprising:

• receiving from a user equipment a random access transmission including a preamble followed by a message block followed by a guard period, wherein:
• the preamble includes a first cyclic prefix;
• the message block includes a second cyclic prefix that is shorter than the first cyclic prefix, the second cyclic prefix having a length that is at least equal to a maximum delay spread of a channel between the user equipment and the receiver;
• and
• a length of the guard period is at least a maximum round-trip time for signals between the user equipment and the receiver;
• processing the random access transmission in the frequency domain by the steps of:
• applying a Fourier transform to a portion of the received random access transmission;
• calculating a conjugate complex Fourier transform of each of a plurality of preambles in a set of possible preambles, and multiplying each of the calculated Fourier transformed preambles by the result of the applying step;
• calculating an inverse Fourier transform of each result from the multiplying step;
• comparing the results of the calculating an inverse Fourier transform step with a threshold to determine which of the preambles was used in the random access transmission;
• and
• decoding the message block after timing synchronisation has been established using the preamble.

A receiver in a communication system comprising:

• a processor;
• and a memory coupled to the processor;
• wherein the processor is configured to process in the frequency domain a random access transmission received from a user equipment, the random access transmission including a preamble followed by a message block followed by a guard period, wherein:
• the preamble includes a first cyclic prefix;
• the message block includes a second cyclic prefix that is shorter than the first cyclic prefix, the second cyclic prefix having a length that is at least equal to a maximum delay spread of a channel between the user equipment and the receiver;
• and
• a length of the guard period is at least a maximum round-trip time for signals between the user equipment and the receiver;
• said processor being configured to:
• apply a Fourier transform to a portion of the received random access transmission;
• calculate a conjugate complex Fourier transform of each of a plurality of preambles in a set of possible preambles, and multiplying each of the calculated Fourier transformed preambles by the result of the applying step;
• calculate an inverse Fourier transform of each result from the multiplying step;
• compare the results of the calculating an inverse Fourier transform step with a threshold to determine which of the preambles was used in the random access transmission;
• and
• decode the message block after timing synchronisation has been established using the preamble.