Preambles in OFDMA system
The present invention provides a preamble that is inserted into an OFDMA frame and has a common sequence for all the base stations participating in a transmission. The subscriber station performs fine synchronization using the common sequence on the common preamble, and the resulting peaks will provide the locations of candidate base stations. The base station specific search is then performed in the vicinities of those peaks by using base station specific pseudo-noise sequences. With this two stage cell search, the searching window is drastically reduced. The preamble is matched to known values by a respective receiver to decode the signals and permit multiple signals to be transferred from the transmitter to the receiver. The preamble may comprise two parts, Preamble- 1 and Preamble- 2 , which may be used in different systems, including multioutput, multi-input (MIMO) systems.
1. An integrated circuit in an orthogonal frequency division multiplexing access (OFDMA) system, comprising:
circuitry configured to receive at least one OFDMA frame, the at least one OFDMA frame having a first preamble and a second preamble, the first preamble having a common synchronization channel comprising common synchronization subcarriers, the common synchronization subcarriers carrying a common sequence, and the second preamble comprising a base station specific preamble, the first preamble further including other signaling information pertaining to the configuration of the second preamble; and
circuitry configured to perform synchronization based on the at least one OFDMA frame.
2. The integrated circuit of claim 1 , wherein the common sequence provides locations of candidate base stations and reduces a fine search window for the base station specific preamble.
3. The integrated circuit of claim 1 , wherein a length of the common sequence is scalable with a bandwidth of channel, thus providing the same synchronization performance for all bandwidth.
4. The integrated circuit of claim 1 , wherein the common sequence comprises pseudo-noise codes and results in a low peak-to-average power ratio (PAPR).
5. The integrated circuit of claim 1 , wherein the first preamble is located in a zone comprising a first dimension of subchannels and a second dimension of time division and multiplex OFDM symbols, the zone being defined by a subcarrier allocation method.
6. The integrated circuit of claim 1 , the second preamble is at a flexible location that is indicated by a preceding zone in the at least one OFDMA frame.
7. The integrated circuit of claim 1 , wherein the second preamble comprises cell-specific synchronization subcarriers.
8. The integrated circuit of claim 1 , wherein the other signaling information comprises either a number of antennas corresponding to the second preamble or information specifying whether an operation mode of the second preamble is for a partially utilized subchannel (PUSC) or a fully utilized subchannel (FUSC).
9. The integrated circuit of claim 1 , further comprising:
circuitry configured to downconvert a plurality of OFDM symbols to an intermediate or baseband frequency signal, wherein the plurality of OFDM symbols are included in the at least one OFDMA frame; and
circuitry configured to digitize the downconverted plurality of OFDM symbols into one or more digital streams.
10. A baseband processor in an orthogonal frequency division multiplexing access (OFDMA) system, configured to perform operations comprising:
constructing at least one OFDMA frame having a first preamble and a second preamble, the first preamble having a common synchronization channel comprising common synchronization subcarriers, the common synchronization subcarriers carrying a common sequence, and the second preamble comprising a base station specific preamble, the first preamble further including other signaling information pertaining to the configuration of the second preamble; and
encoding for transmission to a subscriber station the at least one OFDMA frame, wherein the at least one OFDMA frame is configured such that the subscriber station would be able to perform synchronization based on the at least one OFDMA frame.
11. The baseband processor of claim 10 , wherein a length of the common sequence is scalable with a bandwidth of channel, thus providing the same synchronization performance for all bandwidth.
12. The baseband processor of claim 10 , wherein the common sequence has a repeated time domain structure.
13. The baseband processor of claim 10 , wherein the common synchronization channel is separated by null-subcarriers.
14. The baseband processor of claim 10 , wherein the OFDMA systems is one of single-input single-output (SISO) system, multiple-input single output (MISO) system and a multiple-input multiple-output (MIMO) system.
15. The baseband processor of claim 10 , wherein the first preamble is at a flexible location that is indicated by a preceding zone in the at least one OFDMA frame.
16. The baseband processor of claim 10 , wherein the first preamble and the second preamble are located at a predefined location in the at least one OFDMA frame.
17. The baseband processor of claim 10 , wherein the one of the first preamble and the second preamble is located at the end of the at least one OFDMA frame.
18. The baseband processor of claim 10 , wherein the first preamble and the second preamble coexist with a legacy preamble.
19. The baseband processor of claim 10 , wherein the at least one OFDMA frame has a plurality of second preambles.
20. A subscriber station in an orthogonal frequency division multiplexing access (OFDMA) system comprising:
receive circuitry receiving at least one OFDMA frame, the at least one OFDMA frame having a first preamble and a second preamble, the first preamble having a common synchronization channel comprising common synchronization subcarriers, the common synchronization subcarriers carrying a common sequence, and the second preamble comprising a base station specific preamble, the first preamble further including other signaling information pertaining to the configuration of the second preamble; and
a subscriber station processor configured to perform synchronization based on the at least one OFDMA frame.