Physical structure and sequence design of midamble in OFDMA systems

• US 20100165954A1
• Filed: 12/30/2009
• Published: 07/01/2010
• Est. Priority Date: 12/31/2008
• Status: Active Grant

• Current Assignee: MediaTek, Inc.
• Original Assignee: MediaTek, Inc.
• Inventors: Liao, Pei-Kai, Lin, Chih-Yuan
• Granted Patent: US 8,811,300 B2
• Time in Patent Office: Days
• US Class Current: 370/335
• CPC Class Codes: H04J 11/005 of intercell interference
• CPC Class Codes: H04L 2025/03796 Location of reference signals
• CPC Class Codes: H04L 27/261 Details of reference signals
• CPC Class Codes: H04L 5/0007 the frequencies being orthogonal, e.g. OFDM(A), DMT
• CPC Class Codes: H04L 5/005 of common pilots, i.e. pilots destined for multiple users or terminals

Abstract

In wireless OFDMA systems, midamble is used to facilitate downlink (DL) channel estimation. Midamble signals are transmitted by a base station via a midamble channel allocated in a DL subframe. In a novel symbol-based midamble channel allocation scheme, a midamble channel is allocated in the first or the last OFDM symbol of multiple resource blocks of the subframe, while the remaining consecutive OFDM symbols are used for data transmission. The symbol-based midamble channel provides good coexistence between midamble signals and pilot signals without inducing additional limitation or complexity. Under a novel midamble channel and sequence arrangement, both code sequence and either time-domain or frequency-domain location degrees-of-freedom are considered such that the required number of midamble sequences is substantially smaller than the number of strong interferences. In addition, different midamble sequences are systematically generated based on a base sequence such that the receiving mobile station does not need to memorize all the different code sequences.

Claims

1. A method for providing a midamble channel in an IEEE 802.16m system, the method comprising:

allocating the midamble channel in a subframe having multiple resource blocks by a base station, wherein the resource blocks span over a two-dimensional radio resource region having an array of subcarriers along frequency domain and an array of OFDM symbols along time domain; and

transmitting midamble signals via the midamble channel such that the midamble signals occupy a single OFDM symbol within the subframe, wherein the midamble channel is allocated either in the first OFDM symbol or in the last OFDM symbol of the resource blocks of the subframe, and wherein the remaining consecutive OFDM symbols of the same resource blocks are used for data transmission.

2. The method of claim 1, wherein the resource blocks are six-symbol resource blocks, and wherein the remaining five consecutive symbols in each of the resource blocks are formed to be a five-symbol resource block for data transmission.

3. The method of claim 1, wherein the resource blocks are seven-symbol resource blocks, and wherein the remaining six consecutive symbols in each of the resource blocks are formed to be a six-symbol resource block for data transmission.

4. The method of claim 1, wherein pilot signals are mapped onto IEEE 802.16m predefined pilot patterns, and wherein the midamble signals do not collide with the pilot signals transmitted in the same resource blocks.

5. The method of claim 1, wherein Space Frequency Block Coding (SFBC) is applied in the same resource blocks for data transmission, and wherein the midamble signals do not limit the SFBC-based data transmissions.

6. The method of claim 1, wherein the midamble channel is shared among different transmit antennas of multiple base stations by at least one of code division multiplexing (CDM), frequency division multiplexing (FDM), and time division multiplexing (TDM).

7. The method of claim 1, wherein multiple midamble channels are allocated in multiple downlink subframes to provide multiple midamble opportunities for different transmit antennas of multiple base stations.

8. A base station in an OFDMA system, the base station comprising:

a midamble channel allocation module for allocating a midamble channel in a subframe having multiple resource blocks that span over a two-dimensional radio resource region having an array of subcarriers along frequency domain and an array of OFDM symbols along time domain; and

transmitting midamble signals via the midamble channel, wherein the midamble channel is allocated either in the first OFDM symbol or in the last OFDM symbol of the resource blocks of the subframe, and wherein the remaining consecutive OFDM symbols of the same resource blocks are used for data transmission.

9. The base station of claim 8, wherein the resource blocks are six-symbol resource blocks, and wherein the remaining five consecutive symbols in each of the resource blocks are formed to be a five-symbol resource block for data transmission.

10. The base station of claim 8, wherein the resource blocks are seven-symbol resource blocks, and wherein the remaining six consecutive symbols in each of the resource blocks are formed to be a six-symbol resource block for data transmission.

11. The base station of claim 8, wherein the midamble channel is shared among different transmit antennas of multiple base stations by at least one of code division multiplexing (CDM), frequency division multiplexing (FDM), and time division multiplexing (TDM).

12. The base station of claim 8, wherein multiple midamble channels are allocated in multiple downlink subframes to provide multiple midamble opportunities for different transmit antennas of multiple base stations.

13. A method, comprising:

allocating a midamble channel in a downlink subframe by a base station, wherein the base station and a number of dominant neighboring base stations are located within an OFDMA system;

mapping a midamble sequence onto the midamble channel, wherein the midamble sequence is generated based on a predefined base midamble sequence; and

transmitting a plurality of midamble signals associated with the mapped midamble sequence, wherein the midamble channel and the midamble sequence are arranged such that the plurality of midamble signals do not interfere with other midamble signals associated with other midamble sequences transmitted by the dominant neighboring base stations.

14. The method of claim 13, wherein the midamble sequence is generated by cyclic shifting the base midamble sequence, and wherein the shifting rule is based on a Cell_ID of the base station.

15. The method of claim 13, wherein the midamble sequence is generated by separation-and-combination (SC) operation on the base midamble sequence, and wherein the SC rule is based on a Cell_ID of the base station.

16. The method of claim 13, wherein the midamble sequence is generated by pseudo-randomly interleaving the base midamble sequence, and wherein the interleaving rule is based on a Cell_ID of the base station.

17. The method of claim 13, wherein a second midamble sequence is mapped onto a second midamble channel and transmitted by one of the dominant neighboring base stations, and wherein the midamble channel and the second midamble channel are allocated in the same downlink subframe location with either an overlapping subcarrier set or non-overlapping subcarrier sets.

18. The method of claim 13, wherein the same midamble sequence is mapped onto a second midamble channel and transmitted by one of the dominant neighboring base stations, and wherein the midamble channel and the second midamble channel are allocated either in different downlink subframe locations or in non-overlapping subcarrier sets in the same downlink subframe location.

19. A base station located in an OFDMA system having a number of dominant neighboring base stations, the base station comprising:

a midamble channel allocation module for allocating a midamble channel in a downlink subframe;

a midamble sequence generator for generating a midamble sequence and mapping the midamble sequence onto the midamble channel, wherein the midamble sequence is generated based on a predefined base midamble sequence; and

a transmitter that transmits a plurality of midamble signals associated with the mapped midamble sequence, wherein the midamble channel and the midamble sequence are arranged such that the plurality of midamble signals do not interfere with other midamble signals associated other midamble sequences transmitted by the dominant neighboring base stations.

20. The base station of claim 19, wherein the midamble sequence is generated by cyclic shifting the base midamble sequence, and wherein the shifting rule is based on a Cell_ID of the base station.

21. The base station of claim 19, wherein the midamble sequence is generated by separation-and-combination (SC) operation on the base midamble sequence, and wherein the SC rule is based on a Cell_ID of the base station.

22. The base station of claim 19, wherein the midamble sequence is generated by pseudo-randomly interleaving the base midamble sequence, and wherein the interleaving rule is based on a Cell_ID of the base station.

23. The base station of claim 19, wherein a second midamble sequence is mapped onto a second midamble channel and transmitted by one of the dominant neighboring base stations, and wherein the midamble channel and the second midamble channel are allocated in the same downlink subframe location with either an overlapping subcarrier set or non-overlapping subcarrier sets.

24. The base station of claim 19, wherein the same midamble sequence is mapped onto a second midamble channel and transmitted by one of the dominant neighboring base stations, and wherein the midamble channel and the second midamble channel are allocated either in different downlink subframe locations or in non-overlapping subcarrier sets in the same downlink subframe location.

25. A method, comprising:

decoding synchronization channel (SCH) information broadcasted by a base station and thereby obtaining a Cell_ID of the base station in a wireless OFDMA system;

obtaining a midamble code sequence based on the Cell_ID of the base station;

receiving midamble signals transmitted via an allocated midamble channel by the base station; and

performing channel estimation by matching the received midamble signals using the obtained midamble code sequence.

26. The method of claim 25, wherein the midamble channel is allocated in the first or the last OFDM symbol in a downlink subframe.

27. The method of claim 25, wherein the midamble code sequence is obtained by cyclic shifting a base code sequence, and wherein the shifting rule is based on the Cell_ID of the base station.