Method and apparatus for allocating channels in an orthogonal frequency division multiple access system

• US 20050197132A1
• Filed: 03/04/2005
• Published: 09/08/2005
• Est. Priority Date: 03/05/2004
• Status: Active Grant

• Current Assignee: Samsung Electronics Co. Ltd.
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: Yoon, Soon-Young, Maeng, Seung-Joo, Lee, Jae-Hyok, Jang, Ji-Ho, Jeon, Jae-Ho, Oh, Jeong-Tae
• Granted Patent: US 7,636,571 B2
• Time in Patent Office: Days
• US Class Current: 455/450
• CPC Class Codes: H04L 5/0062 Avoidance of ingress interference, e.g. ham radio channels
• CPC Class Codes: H04L 5/0073 Allocation arrangements that take into account other cell interferences for intercell interference mitigation or co-ordination in orthogonal multiplex systems H04J11/005
• CPC Class Codes: H04L 5/0094 Indication of how sub-channels of the path are allocated
• CPC Class Codes: H04W 24/00 Supervisory, monitoring or testing arrangements
• CPC Class Codes: H04W 28/26 Resource reservation
• CPC Class Codes: H04W 36/0072 of resource information of target access point
• CPC Class Codes: H04W 36/18 for allowing seamless reselection, e.g. soft reselection
• CPC Class Codes: H04W 72/0453 Resources in frequency domain, e.g. a carrier in FDMA
• CPC Class Codes: H04W 72/21 in the uplink direction of a wireless link, i.e. towards the network
• CPC Class Codes: H04W 72/23 in the downlink direction of a wireless link, i.e. towards a terminal

Abstract

A method for allocating a frequency to a subscriber station (SS) in handover operation in an Orthogonal Frequency Division Multiple Access (OFDMA) system. In the method, the SS checks safety channel frequencies for a target base station (BS), generates a safety channel frequency request message for requesting allocation of the checked safety channel frequencies, and transmits the safety channel frequency request message. Upon receiving the safety channel frequency request message from the SS, a serving BS allocates frequencies for a requested channel, and transmits an allocation message with the frequency allocation information to the SS. The serving BS transmits a channel allocation request message to the target BS according to the frequency allocation information. Upon receiving the channel allocation request message, the target BS allocates the safety channel frequencies to the SS.

Claims

1. A method for allocating a frequency to a subscriber station (SS) in handover operation in an Orthogonal Frequency Division Multiple Access (OFDMA) system, the method comprising the steps of:

searching, by the SS, safety channel frequencies for a target base station (BS), generating a safety channel frequency request message for requesting allocation of the checked safety channel frequencies, and transmitting the safety channel frequency request message;

upon receiving the safety channel frequency request message from the SS, allocating, by a serving BS, frequencies for a requested channel, and transmitting an allocation message with the frequency allocation information to the SS;

transmitting, by the serving BS, a channel allocation request message to the target BS according to the frequency allocation information; and

upon receiving the channel allocation request message, allocating, by the target BS, the safety channel frequencies to the SS.

2. The method of claim 1, wherein the target BS allocates safety channel frequencies for a safety channel according to the channel allocation request message received from the serving BS, generates a channel allocation response message, and transmits the channel allocation response message to the serving BS.

3. The method of claim 1, further comprising the steps of:

upon receiving the channel allocation request message from the serving BS, determining by the target BS whether the requested channel is allocable; and

if the requested channel is allocable, generating, by the target BS, an affirmative channel allocation response message, transmitting the affirmative channel allocation response message to the serving BS, and allocating the safety channel frequencies to the SS in a next frame.

4. The method of claim 1, wherein the SS checks the safety channel frequencies for the target BS using a signal-to-noise ratio (SNR) of a preamble.

5. The method of claim 1, wherein the SS checks the safety channel frequencies for the target BS using information previously received from the serving BS.

6. A method for performing handover in a subscriber station (SS) of a system which uses an Orthogonal Frequency Division Multiple Access (OFDMA) scheme and allocates a predetermined number of frequencies among orthogonal frequencies as safety channel frequencies, the method comprising the steps of:

checking safety channel frequencies for a target base station (BS);

generating a safety channel frequency request message for requesting allocation of the checked safety channel frequencies, and transmitting the safety channel frequency request message; and

upon receiving a channel allocation message from the serving BS, performing handover through a channel allocated in a next frame.

7. The method of claim 6, wherein the SS checks the safety channel frequencies for the target BS using a signal-to-noise ratio (SNR) of a preamble.

8. The method of claim 6, wherein the SS checks the safety channel frequencies for the target BS using information previously received from the serving BS.

9. A method for controlling handover of a subscriber station (SS) in a serving base station (BS) of a system including the serving BS in communication with the SS and a target BS during handover of the SS, the BSs using an Orthogonal Frequency Division Multiple Access (OFDMA) scheme, the system allocating a predetermined number of frequencies among orthogonal frequencies as safety channel frequencies, the method comprising the steps of:

upon receiving a safety channel frequency request message from the SS, allocating channel resources for the target BS included in the safety channel frequency request message, to the SS in a next frame; and

generating a message for requesting the target BS to allocate a safety channel to the SS, and transmitting the message to the target BS.

10. The method of claim 9, further comprising the step of releasing a channel allocated to the SS and allocating a new channel to the SS, if the SS ends the handover and enters coverage of the serving BS.

11. The method of claim 10, further comprising the step of informing the target BS of the end of handover of the SS.

12. The method of claim 9, further comprising the step of releasing a channel allocated to the SS, if the SS ends the handover.

13. The method of claim 12, further comprising the step of informing the target BS of the end of the handover of the SS.

14. The method of claim 9, further comprising the step of releasing a safety channel allocated to the SS, if the SS ends a call during the handover.

15. The method of claim 14, further comprising the step of informing the target BS of the end of the handover of the SS.

16. A subscriber station (SS) apparatus for performing handover in a system including a serving base station (BS) in communication with the SS, and a target BS during handover of the SS, the BSs using an Orthogonal Frequency Division Multiple Access (OFDMA) scheme, the system allocating a predetermined number of frequencies among orthogonal frequencies as safety channel frequencies, the apparatus comprising:

a signal-to-noise ratio (SNR) measurer for measuring SNRs of signals received from the serving BS and the target BS;

a controller for determining a when to perform a handover and for selecting safety channel frequencies for the target BS depending on the SNRs measured by the SNR measurer, and generating a channel allocation request message for requesting allocating of safety channels for the target BS in a next frame when the handover is necessary;

a data transmission processor for encoding and modulating the channel allocation request message generated by the controller; and

a radio frequency (RF) unit for transmitting an output signal of the data transmission processor using the OFDMA scheme.

17. The SS apparatus of claim 16, wherein upon receiving a channel allocation message from the serving BS, the controller performs communication through the allocated channels by controlling the RF unit.

18. A system for providing handover of a subscriber station (SS), the system including a serving base station (BS) in communication with the SS, and a target BS during handover of the SS, the BSs using an Orthogonal Frequency Division Multiple Access (OFDMA) scheme, the system comprising:

the SS for checking safety channel frequencies for the target BS during handover, generating a safety channel frequency request message for requesting allocation of the checked safety channel frequencies, transmitting the safety channel frequency request message to the serving BS, and upon receiving a channel allocation message from the serving BS, performing handover using a channel allocated in the channel allocation message from a next frame;

the serving BS for, upon receiving the safety channel frequency request message from the SS, generating a channel allocation request message for requesting the target BS to allocate a safety channel to the SS, transmitting the channel allocation request message to the target BS, and upon receiving a channel allocation response message from the target BS, selecting frequencies to be allocated to the SS according to the received message, allocating the selected frequencies to the SS, generating channel allocation information using the allocated frequencies, and transmitting the channel allocation information to the SS; and

the target BS for, upon receiving the channel allocation request message from the serving BS, determining whether the requested channel is allocable, generating a channel allocation response message using the determination result, transmitting the channel allocation response message to the serving BS, and if the requested channel is allocable, allocating the requested channel to the SS.

19. The system of claim 18, wherein if the SS is not required to use the safety channel, the serving BS and the target BS transition from a safety channel mode to a normal channel mode.

20. The system of claim 18, wherein the BSs change frequencies set for safety channels at a predetermined time.