Prefixing of OFDM symbols to support variable subframe length

A method in an orthogonal frequency division multiplexing, OFDM, first radio node, the method comprising:

• transmitting, in a first mode of operation with a first subcarrier spacing f1 or in a second mode of operation with a second subcarrier spacing f2, a sequence of prefixed OFDM symbols;
• wherein the sequence of prefixed OFDM symbols is aligned with a predefined repeating radio frame, which is common to both the first and second modes of operation;
• wherein the first and second subcarrier spacings are related by an integer factor, f1/f2=1/p, with p≠1 integer;
• wherein in a repeating interval of 0.5 ms duration in the first or second mode of operation, an initial prefixed OFDM symbol has a longer prefix than any remaining prefixed OFDM symbol(s) in the repeating interval, and the remaining prefixed OFDM symbols in the repeating interval have prefixes of the same length, wherein a difference in duration between the initial prefixed OFDM symbol and any of the remaining prefixed OFDM symbol(s) in the repeating interval is 16 Ts, wherein Ts=1/(2048×15000) seconds;
• and
• wherein the beginning of a prefixed OFDM symbol according to the first mode of operation is aligned with the beginning of a sequence of an integer number of prefixed OFDM symbols according to the second mode of operation, and the end of said prefixed OFDM symbol according to the first mode of operation is aligned with the end of said sequence of an integer number of prefixed OFDM symbols according to the second mode of operation.

A second radio node configured for orthogonal frequency division multiplexing, OFDM, comprising:

• a receiver;
• a transmitter;
• and
• a processing circuitry operatively connected to the transmitter and receiver, the processing circuitry being configured to cause the receiver to:
• receive, in a first mode of operation with a first subcarrier spacing f1 or in a second mode of operation with a second subcarrier spacing f2, a sequence of prefixed OFDM symbols from a first radio node;
• wherein transmission of the received sequence of prefixed OFDM symbols is assumed to have been aligned with a predefined repeating radio frame, which is common to both the first and second modes of operation;
• wherein the first and second subcarrier spacings are related by an integer factor, f1/f2=1/p, with p≠1 integer;
• wherein in a repeating interval of 0.5 ms duration in the first or second mode of operation, an initial prefixed OFDM symbol has a longer prefix than any remaining prefixed OFDM symbol(s) in the repeating interval, and the remaining prefixed OFDM symbols in the repeating interval have prefixes of the same length, wherein a difference in duration between the initial prefixed OFDM symbol and any of the remaining prefixed OFDM symbol(s) in the repeating interval is 16 Ts, wherein Ts=1/(2048×15000) seconds;
• and
• wherein the beginning of a prefixed OFDM symbol according to the first mode of operation is aligned with the beginning of a sequence of an integer number of prefixed OFDM symbols according to the second mode of operation, and the end of said prefixed OFDM symbol according to the first mode of operation is aligned with the end of said sequence of an integer number of prefixed OFDM symbols according to the second mode of operation.

A method in an orthogonal frequency division multiplexing, OFDM, second radio node, the method comprising:

• receiving, in a first mode of operation with a first subcarrier spacing f1 or in a second mode of operation with a second subcarrier spacing f2, a sequence of prefixed OFDM symbols from a first radio node;
• wherein transmission of the received sequence of prefixed OFDM symbols is assumed to have been aligned with a predefined repeating radio frame, which is common to both the first and second modes of operation;
• wherein the first and second subcarrier spacings are related by an integer factor, f1/f2=1/p, with p≠1 integer;
• wherein in a repeating interval of 0.5 ms duration in the first or second mode of operation, an initial prefixed OFDM symbol has a longer prefix than any remaining prefixed OFDM symbol(s) in the repeating interval, and the remaining prefixed OFDM symbols in the repeating interval have prefixes of the same length, wherein a difference in duration between the initial prefixed OFDM symbol and any of the remaining prefixed OFDM symbol(s) in the repeating interval is 16 Ts, wherein Ts=1/(2048×15000) seconds;
• and
• wherein the beginning of a prefixed OFDM symbol according to the first mode of operation is aligned with the beginning of a sequence of an integer number of prefixed OFDM symbols according to the second mode of operation, and the end of said prefixed OFDM symbol according to the first mode of operation is aligned with the end of said sequence of an integer number of prefixed OFDM symbols according to the second mode of operation.