Patent Application
20060083326
1. Field of the Invention
The present invention relates to a multi-band orthogonal frequency division multiplexing (OFDM), and more particularly, to an efficient symbol transmitting for an OFDM system which transmits symbols using a plurality of sub-bands.
2. Description of the Prior Art
An OFDM system transmits serially-incoming symbols by converting the symbols into parallel pattern of a predetermined size, and multiplexing the parallel symbols into subcarrier frequencies at orthogonal relation with each other.
A multi-band OFDM scheme transmits OFDM symbols, with hopping a plurality of frequency bands in the unit of symbols. One representative example can be found in a wireless communication system such as an Ultra Wideband (UWB) system. Accordingly, a multi-band OFDM scheme is used in association with a frequency hopping technology. A multi-band OFDM system, applied in the UWB, will be briefly described below. A multi-band OFDM system has a plurality of sub-bands of predetermined frequency bands. By transmitting the data (symbols) using the sub-bands, the multi-band OFDM system can transmit or receive a huge volume of data in unit time. Data security is guaranteed as the UWB system selects one of the sub-bands, and uses the selected sub-band according to predetermined rules.
The center frequency of three sub-bands of the first group is, respectively, 3432 MHz, 3960 MHz, and 4488 MHz. The center frequency of three sub-bands of the second group is, respectively, 5016 MHz, 5544 MHz, and 6072 MHz. The center frequency of three sub-bands of the third group is, respectively, 6600 MHz, 7128 MHz, and 7656 MHz. The center frequency of three sub-bands of the fourth group is, respectively, 8184 MHz, 8712 MHz, and 9240 MHz. The center frequency of the two sub-bands of the fifth groups is, respective, 9768 MHz and 10296 MHz.
The following Table 1 lists frequency bands being used in a multi-band OFDM system.
As shown in Table 1, a multi-band OFDM system transmits symbols, by using three sub-bands.
Hereinbelow, a multi-band OFDM system transmitting symbols using three sub-bands, will be described with reference to
Referring to
With reference to Table 1 and
Generally, when a symbol is received, the receiving end of a multi-band OFDM system first searches the first sub-band. In other words, the receiving end of the multi-band OFDM system acquires necessary information from the symbols of the first sub-band, and acquires necessary information from the symbols of the second and third sub-bands, using the acquired information from the symbols of the first sub-band.
Additionally, with reference to Table 1 and
The present invention provides a method for a multi-band OFDM system which at least twice transmits the same symbol, which enables a receiving end to receive symbols from a transmitting end without having an error.
According to an aspect of the present invention, there is provided a multi-band OFDM system, which includes a transmitting end which selects one among at least three symbols being repetitively transmitted at least two times, and transmits the selected symbol by using different wireless resources so that the selected symbol is not consecutively transmitted; and a receiving end which receives the symbols from the transmitting end.
The transmitting end transmits an n-th transmission symbol and an (n+1)th transmission symbol using the same wireless resource, and n is an even number which is equal or greater than 0. The wireless resource is a frequency band.
The transmitting end may select a lowest frequency among at least three frequency bands, and transmit the selected symbol a first time using a wireless resource having the selected frequency band. The wireless resource may consist of a first sub-band having a first frequency band, a second sub-band having a second frequency band, and a third sub-band having a third frequency band.
The above and/or other aspects of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings, in which:
Hereinafter, the present invention will be described in detail with reference to the drawings. The present invention proposes a method for transmitting the same symbol with using different sub-bands.
A symbol in a communication system can be divided into a preamble part and a payload part. The preamble contains brief information about symbol transmission, and the payload contains effective data which are transmitted from the transmitting end to a receiving end.
The PS sequence is used to detect symbols, estimate frequency (sub-band) for use, and acquire synchronization. Additionally, the PS sequence is used to calculate gains with respect to the received symbols. The FS sequence is used to detect a boundary of the frame, and distinguish the PS and CE sequences from the detected information. The CE sequence is used to perform channel estimation.
Table 2 below lists a method for transmitting payload according to the transmission rate of a multi-band OFDM system.
With the transmission rate ranging from 53.3 Mbps to 200 Mbps, a multi-band OFDM system uses a quadrature phase shift keying (QPSK), while the system uses a dual carrier modulation (DCM) with respect to the transmission rate ranging from 320 Mbps to 480 Mbps.
Additionally, when the transmission rate ranges from 53.3 Mbps to 200 Mbps, a multi-band OFDM system has a Time Spreading Factor (TSF) of 2. In other words, when the transmission rate ranges from 53.3 Mbps to 200 Mbps, a transmitting end of a multi-band OFDM system twice transmits one symbol at predetermined time interval.
Compared to the conventional example, the present invention proposes to transmit repetitive transmission symbols over different frequency bands, without shifting frequency hopping pattern. In one example, symbol 1 may be transmitted from the first and sixth points, instead of being consecutively transmitted from the first and second points. More specifically, a transmitting end may transmit symbol 1 from the first and sixth points, transmit symbol 2 from the second and third points, and transmit symbol 3 from the fourth and fifth points.
By doing as the above, symbol 1 is transmitted over the first and third sub-bands, symbol 2 is transmitted over the first and second sub-bands, and symbol 3 is transmitted over the second and third sub bands. As the transmitting end sends out symbols 1 to 3 in the way described above, a multi-band OFDM system can have not only time diversity, but also frequency diversity.
An alternative method to transmit three symbols using TFC No. 3 will now be described below.
The transmitting end transmits symbol 1 from first and sixth points, transmits symbol 2 from fourth and fifth points, and transmits symbol 3 from second and third points. Accordingly, symbol 1 is transmitted over the first and third sub-bands, symbol 2 is transmitted over the second and third sub-bands, and symbol 3 is transmitted over the first and second sub-bands.
Symbol 1 of the first group is transmitted from the first and sixth points, symbol 2 is transmitted from the second and third points, and symbol 3 is transmitted from the fourth and fifth points. Symbol 4 of the second group is transmitted from the seventh and twelfth points, symbol 5 is transmitted from the eighth and ninth points, and symbol 6 is transmitted from the tenth and eleventh points.
Accordingly, symbol 1 is transmitted over the first and second sub-bands, symbol 2 is transmitted over the first and third sub-bands, and symbol 3 is transmitted over the third and second sub-bands. Symbol 4 is transmitted over the first and second sub-bands, symbol 5 is transmitted over the first and third sub-bands, and symbol 6 is transmitted over the third and second sub-bands.
By transmitting symbol 1 using different sub-bands as shown in
An alternative method of transmitting three symbols using TFC No. 4, will now be described below.
A transmitting end transmits symbol 1 from first and sixth points, transmits symbol 2 from fourth and fifth points, and transmits symbol 3 from second and third points. Accordingly, symbol 1 is transmitted over the first and second sub-bands, symbol 2 is transmitted over the third and second sub-bands, and symbol 3 is transmitted over the first and third sub-bands.
The transmitting end includes a symbol-based interleaver which keeps symbols for transmission in a predetermined order in time domain so that the symbols can be transmitted by using TFC No. 3 or TFC No. 4. More specifically, the transmitting end is provided with the symbol-based interleaver to transmit the consecutively received symbols 1 to 3 in the way as explained with reference to
Referring to
The receiving end includes a symbol-based deinterleaver to reverse interleave at the symbol-based interleaver 600 of the transmitting end.
As described above, by transmitting symbol containing the same information with using at least different wireless resources, the receiving end can safely receive the data through an intact wireless resource, when an error occurs from one of the wireless resources. Additionally, because the symbols are not consecutively transmitted using the same wireless resource, time for processing received symbols is guaranteed.
The above description is illustrative and not restrictive. Many variations of the invention will become apparent to those of skill in the art upon review of this disclosure. The scope of the invention should, therefore, be determined not with reference to the above description, but instead should be determined with reference to the appended claims along with their full scope of equivalents.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2005-35386 | Apr 2005 | KR | national |
This application claims priority from U.S. Provisional Application No. 60/618,592 filed on Oct. 15, 2004 in the United States Patent and Trademark Office, and Korean Patent Application No. 2005-35386 filed on Feb. 17, 2005 in the Korean Intellectual Property Office, the entire contents of which are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 60618592 | Oct 2004 | US |
