Prefixing of OFDM symbols to support variable subframe length

1. A first radio node configured for orthogonal frequency division multiplexing, OFDM, comprising:

a receiver;

a transmitter;

a processing circuitry operatively connected to the transmitter and receiver, the processing circuitry being configured to:

transmit a sequence of prefixed OFDM symbols 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;

wherein the first and second subcarrier spacings are related by a non-unit integer factor, f1/f2=p or f1/f2=1/p, with p≠1 integer;

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, or with an integer multiple of the predefined repeating radio frame;

wherein, in a repeating interval in the first and 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; and

wherein boundaries of one prefixed OFDM symbol according to the first mode of operation are aligned with boundaries of two or more of the prefixed OFDM symbols according to the second mode of operation.

2. The first radio node of claim 1 , wherein a total duration of one prefixed OFDM symbol transmitted in the first mode of operation is equal to a total duration of an integer number of prefixed OFDM symbols transmitted in the second mode of operation.

3. The first radio node of claim 1 , wherein the repeating interval is 0.5 ms.

4. The first radio node of claim 1 , wherein the beginnings and ends of the prefixed OFDM symbols transmitted in the first mode of operation are aligned, with respect to the predefined repeating radio frame or a multiple of the predefined repeating radio frame, with the beginning and end of a sequence of an integer number of prefixed OFDM symbols transmitted in the second mode of operation.

5. The first radio node of claim 1 , wherein the beginnings and ends of the prefixed OFDM symbols transmitted in the first mode of operation are aligned with the beginning and end of a sequence of an integer number of prefixed OFDM symbols transmitted in the second mode of operation.

6. The first radio node of claim 1 , wherein alignment of boundaries occurs at least as often as the predefined repeating radio frame repeats.

7. The first radio node of claim 1 , wherein the processing circuitry is further configured to assign prefixes of such lengths as to make a total duration of a first integer number N 1 of prefixed OFDM symbol transmitted in the first mode of operation equal to a total duration of a second integer number N 2 of prefixed OFDM symbols transmitted in the second mode of operation.

8. The first radio node of claim 1 , wherein, with respect to the predefined repeating radio frame, a not-frame-initial boundary of a symbol transmitted in the first mode of operation is aligned with a not-frame-initial boundary of a symbol transmitted in the second mode of operation.

9. The first radio node of claim 1 , wherein the first and second subcarrier spacings are related by a power of two, f1/f2=2 q or f1/f2=2 −q , with q≥1 integer.

10. The first radio node of claim 1 , wherein, in a repeating interval in both the first mode of operation and the second mode of operation, an initial prefixed OFDM symbol in the sequence of prefixed OFDM symbols has a longer prefix than any remaining prefixed OFDM symbol(s) in the repeating interval, and the remaining prefixed OFDM symbols have prefixes of the same length.

11. 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, or with an integer multiple of the predefined repeating radio frame;

wherein the first and second subcarrier spacings are related by an integer factor, f1/f2=p or f1/f2=1/p, with p≠1 integer;

wherein in a repeating interval in the first and 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; and

wherein boundaries of one prefixed OFDM symbol according to the first mode of operation are aligned with boundaries of two or more of the prefixed OFDM symbols according to the second mode of operation.

12. 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:

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, or with an integer multiple of the predefined repeating radio frame;

wherein the first and second subcarrier spacings are related by an integer factor, f1/f2=p or f1/f2=1/p, with p≠1 integer;

wherein in a repeating interval in the first and 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; and

wherein boundaries of one prefixed OFDM symbol according to the first mode of operation are aligned with boundaries of two or more of the prefixed OFDM symbols according to the second mode of operation.

13. 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, or with an integer multiple of the predefined repeating radio frame;

wherein the first and second subcarrier spacings are related by an integer factor, f1/f2=p or f1/f2=1/p, with p≠1 integer;

wherein in a repeating interval in the first and 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; and

wherein boundaries of one prefixed OFDM symbol according to the first mode of operation are aligned with boundaries of two or more of the prefixed OFDM symbols according to the second mode of operation.