Method and arrangement in a communications system
The object of the present invention is to provide a mechanism for a more efficient carrier search. The object is achieved by a method for sending a signal in a first node. The first node communicates with a second node via radio communication, which radio communication is performed by multi carrier transmission. The first node uses a carrier, being associated with a frequency range. The method comprises the step of transmitting an end-marker signal within or close to the frequency range. The end-marker signal is intended to be received and used by the second node for identifying the frequency range of the used carrier.
1. Method for sending a signal from a first node that communicates with a second node via multi-carrier radio communication using one or more carriers associated with a frequency range, the method comprising the steps of:
transmitting a first end-marker signal within or close to the frequency range during a preamble portion of a first frame, wherein the first end-marker signal indicates to a second node a lower end of the frequency range; and
transmitting a second end-marker signal within or close to the frequency range during the preamble portion of the first frame or a preamble portion of a second frame, wherein the second end-marker signal indicates to the second node an upper end of the frequency range, and wherein the second end-marker signal indicating the upper end of the frequency range comprises a different signal constellation from the first end-marker signal indicating the lower end of the frequency range.
2. Method according to claim 1 , wherein:
transmitting the first end-marker signal comprises transmitting the first end-marker signal at or close to the lower end of the frequency range; and
transmitting the second end-marker signal comprises transmitting the second end-marker signal at or close to the upper end of the frequency range.
3. Method according to claim 1 , wherein the first end-marker signal comprises one single end-marker signal and the second end-marker signal comprises three end-marker signals.
4. Method according to claim 1 , further comprising utilizing signal hopping by sending the first end-marker signal and the second end-marker signal at different subcarriers.
5. Method according to claim 1 , wherein a specific hopping pattern is used for end marker-signals of a specific carrier that is different from hopping patterns used for end-marker signals of other carriers.
6. Method according to claim 5 , wherein the first and second end-marker signals may use a predefined pseudo-random hopping sequence which associates the first end-marker signal with the second end-marker signal.
7. Method according to claim 1 , wherein transmitting at least one of the first end-marker signal and the second end-marker signal comprises transmitting a specific hopping pattern of the at least one end-marker signal, wherein the specific hopping pattern is associated with a specific operator and is different from hopping patterns used for end-marker signals of other operators.
8. Method according to claim 1 , wherein, different hopping patterns are used to distinguish between end marker-signals of macro and micro cells.
9. Method according to claim 1 , wherein the end-marker signals are transmitted at regular intervals.
10. An apparatus comprising a first node adapted to communicate with a second node via multi-carrier radio communication wherein the first node is adapted to use one or more carriers associated with a frequency range, the apparatus comprising a transmitter configured to:
transmit a first end-marker signal within or close to the frequency range during a preamble portion of a first frame, wherein the first end-marker signal indicates to a second node a lower end of the frequency range; and
transmit a second end-marker signal within or close to the frequency range during the preamble portion of the first frame or a preamble portion of a second frame, wherein the second end-marker signal indicates to the second node an upper end of the frequency range, and wherein the second end-marker indicating the upper end of the frequency range comprises a different signal constellation from the first end-marker indicating the lower end of the frequency range.
11. An apparatus according to claim 10 , wherein the first node is a base station, or a user terminal.
12. Method for managing a carrier search in a second node that communicates with a first node via multi-carrier radio communication using one or more carriers associated with a frequency range, the method comprising the steps of:
receiving a first end-marker signal within or close to the frequency range during a preamble portion of a first frame, wherein the first end-marker signal indicates to the second node a lower end of the frequency range; and
receiving a second end-marker signal within or close to the frequency range during the preamble portion of the first frame or a preamble portion of a second frame, wherein the second end-marker signal indicates to the second node an upper end of the frequency range, and wherein the second end-marker indicating the upper end of the frequency range comprises a different signal constellation from the first end-marker indicating the lower end of the frequency range.
13. Method according to claim 12 , wherein:
receiving the first end-marker signal comprises receiving the first end-marker signal at or close to the lower end of the frequency range; and
receiving the second end-marker signal comprises receiving the second end-marker signal at or close to the upper end of the frequency range.
14. Method according to claim 12 , wherein at least one of the first end-marker signal and the second end-marker signal is detected by scanning an entire frequency range of relevance by performing a set of broadband Discrete Fourier Transforms (DFTs).
15. Method according to claim 14 , wherein said scanning is performed by starting in a lower part of the relevant frequency range, and increasing a carrier frequency stepwise as soon as a DFT bandwidth is scanned and continuing until the entire frequency range of relevance is scanned.
16. Method according to claim 12 , wherein receiving the second end-marker signal comprises:
identifying that the received first end-marker signal indicates a lower end of a frequency band to be identified;
assuming a possible identified frequency range used, based on the end-marker signal candidate; and
verifying the assumption by listening to a broadcast signal transmitted by the first node.
17. An apparatus comprising a second node adapted to communicate with a first node via multi-carrier radio communication using one or more carriers associated with a frequency range, the apparatus comprising a receiver configured to:
receive a first end-marker signal within or close to the frequency range during a preamble portion of a first frame, wherein the first end-marker signal indicates a lower end of the frequency range; and
receive a second end-marker signal within or close to the frequency range during the preamble portion of the first frame or a preamble portion of a second frame, wherein the second end-marker signal indicates to the second node an upper end of the frequency range, and wherein the second end-marker indicating the upper end of the frequency range comprises a different signal constellation from the first end-marker indicating the lower end of the frequency range.
18. An apparatus according to claim 17 wherein the second node is a user terminal.