Patent Application
20050047444
1. Field of the Invention
The present invention relates to TFI-OFDM transmission and reception systems and methods thereof for mitigating interference from adjacent piconets in multi-band orthogonal frequency division multiplexing for ultra wide band (UWB) transmissions.
2. Description of the Related Art
In a wireless communication environment utilizing a wide frequency band, such as the ultra wide band (UWB) 3.1˜10.6 GHz, the entire frequency band is divided into a single sub-band or a finite number of sub-bands. A continuous wave is not used in a time domain, of which signals exist in every time domain, but rather, a form of a wave packet is used, of which signals exist in a certain region of the time domain. In a single band system that uses a single frequency band, an impulse utilizing every frequency of the UWB is adopted for transmission and receiving signals. However, the single band system tends to be vulnerable to interference from other systems. To address his shortcoming, a multi-band system utilizes a plurality of sub-bands as the need arises to effectively cope with the interference. However, when using a RF circuit consisting of a single oscillator, the performance of the multi-band system may be seriously degraded since the energy finished from the multi-path fading channel reaches about 20% of the entire energy. To overcome this shortcoming, the Texas Instrument (TI) Co. suggested a time frequency interleaved-orthogonal frequency division multiplexing (TFI-OFDM) system for the transmission scheme.
Accordingly, there is a need to mitigate the effect of collisions resulting from adjacent simultaneously operating piconets (SOPs) in the convention TFI-OFDM system.
To address the above and other shortcomings, an aspect of the present invention is to provide a TFI-OFDM transmission system and method thereof for loading and transmitting different data in a positive and a negative frequency domain and applying a transmission scheme of time domain extension, and another aspect is to provide a corresponding TFI-OFDM reception system and method thereof.
To achieve the above aspects of the present invention, the TFI-OFDM transmission system includes a data generator generating data having a speed corresponding to transmission speed mode; a convolutional encoder convolutional-encoding the data; an interleaver bit-interleaving the encoded data; an OFDM modulator inputting a first data group into a positive frequency domain and a second data group into a negative frequency domain, executing an IFFT, and outputting OFDM symbols; a buffer temporarily storing the OFDM symbols in order to sequentially transmit the OFDM symbols in a time domain at least two times; and a frequency generator generating certain frequencies to transmit the OFDM symbols in a certain number of frequency bands corresponding to transmission channels.
Advantageously, the convolutional encoder has a ⅓ coding rate and outputs first, second, and third data groups which are respectively encoded in fir second, and third generators. The interleaver executes a tone-interleaving with respect to each of the first, second, and third data groups.
According to another aspect of the present invention, the TFI-OFDM transmission method includes (a) generating data having a rate corresponding to a transmission speed mode; (b) convolutional-encoding the data; (c) bit-interleaving the encoded data; (d) inputting a first data group into a positive frequency domain and a second data group into a negative frequency domain, executing an invert fast Fourier transform (IFFT), and outputting OFDM symbols; (e) sequentially transmitting the OFDM symbols in different frequency bands at least two times.
Advantageously, step (b) encodes at a ⅓ coding rate and outputs first, second, and third data groups. Step (c) executes a tone-interleaving to each of the first, second, and third data groups.
The TFI-OFDM reception system includes a receiver receiving OFDM symbols transmitted in a certain number of frequency bands corresponding to transmission channels, a collision detector determining collisions of at least two OFDM symbols by measuring the powers with respect to at least two OFDM symbols sequentially received and containing the same data, and a data detector detecting data to be processed based on collision information which is determined with respect to the at least two OFDM symbols by the collision detector.
The collision detector measures a first power and a second power with respect to first OFDM symbols and second OFDM symbols which are the same data sequentially received from a first frequency band and a second frequency band; measures a first average power and a second average power with respect to signals received from the first and second frequency bands; compares the first power and the first average power, compares the second power and the second average power, determines whether there are collisions in the first OFDM symbols and second OFDM symbols, and provides the information to the data detector.
According to yet another aspect of the present invention, the TFI-OFDM reception method includes (a) receiving OFDM symbols transmitted in a certain number of frequency bands corresponding to transmission channels; (b) determining collisions in at least two OFDM symbols by measuring the powers with respect to the at least two OFDM symbols sequentially received and containing the same data, and (c) detecting data to be processed from the at least two OFDM symbols based on the collision determination.
Step (b) includes (b-1) measuring a first power and a second power with respect to a first OFDM symbols and a second OFDM symbols which are the same data sequentially received from a first frequency band and a second frequency band; (b-2) measuring a first average power and a second average power with respect to each signal received from the first frequency band and second frequency band; and (b-3) comparing the first power and the first average power, comparing the second power and the second average power, determining whether there are collisions in the first OFDM symbols and second OFDM symbols, and providing the information to step (c).
These and/or other aspects and advantages of the present invention will be readily apparent and appreciated by describing in detail exemplary embodiments thereof with reference to the accompanying drawings, in which:
The present invention will now be described more fully with reference to the accompanying drawings, in which illustrative, non-limiting embodiments of the invention are shown. In the drawings, like reference numbers refer to like elements throughout
Prior to describing the exemplary embodiments of the present invention, it is assumed that a time frequency interleaved-orthogonal frequency division multiplexing (TFI-OFDM) system utilizes a ⅓ convolutional encoder, an applicable transmission speed mode is limited to 110 Mbps and 200 Mbps, and a transmission band has three frequency bands f1, f2, f3. It should be appreciated that the ⅓ convolutional encoder is exemplary for purposes of explanation and not limitation, as well as the transmission speed.
The data generator 310 generates binary data having a ratio corresponding to transmission speed modes, for example, 10 Mbps and 200 Mbps, which is defined in the system.
The convolutional encoder 320 convolutional-encodes an input data at a certain coding rate. For example, a 200 bit input data is output as 600 bit coded data at a ⅓ coding rate.
The interleaver 330 performs symbol interleaving and tone interleaving to the coded data.
The QPSK modulator 340 QPSK-modulates the input data For instance, if 200 bit data is input, the QPSK modulator 340 outputs 100 symbol data by mapping 2 bits into each symbol.
The OFDM modulator 350 modulates data of a frequency domain into OFDM symbols of a time domain using an invert fast Fourier transform (IFFT). According to an embodiment of the present invention, the OFDM modulator 350 outputs OFDM symbols in the form of a complex conjugate by inputting different data into the positive and negative frequency domains, respectively, and executing the IFFT. Hence, double the amount of data are transmitted as compared with the OFDM symbols of the time domain in the conventional TFI-OFDM transmission system.
The GI inserter 360 copies a certain interval of a rear part of the IFFT-executed OFDM symbols and inserts the certain interval into a front part of the OFDM symbol so as to maintain orthogonality of the OFDM symbols in multi-path channel conditions. The certain interval inserted into the front of the OFDM symbol is referred to as a guard interval (GP).
The D/A converter 370 converts a digital signal into an analog signal.
The buffer 380 temporarily stores the transmitted OFDM symbols and transmits the same OFDM symbols in the time domain sequentially more than two times, to thus extend the OFDM symbols into the time domain.
The frequency generator 390 generates frequencies corresponding to three frequency bands in accordance with a pre-set transmission channel pattern. Thus, the OFDM symbols, which are converted to the final analog signals, are up-converted sequentially into predetermined frequency bands.
Accordingly, in the TFI-OFDM transmission system according to an embodiment of the present invention, the OFDM symbols transmit double the data amount as compared with the conventional OFDM symbols, and the data are sequentially transmitted two times in the different frequency bands depending on the transmission channel.
The transmission system includes a convolutional encoder 321, an interleaver 331, a QPSK modulator 341, an OFDM modulator 351, a buffer 381, and a frequency generator 391.
The convolutional encoder 321 has a ⅓ coding rate and, accordingly, includes thee generator polynomials (hereinafter refer to as first, second, and third generators). The first, second, and third generators G1, G2 and G3 each output the encoded data. If 200-bit data is input, the first, second, and third generators G1, G2, and G3 each outputs 200-bit coded first, second, and third data groups, respectively.
The interleaver 331 omits the symbol interleaving and performs the tone interleaving alone with respect to the fist, second, and third data groups respectively output from the first, second, and third generators G1, G2, and G3 of the convolutional encoder 320.
The QPSK modulator 341 performs the QPSK modulation to the tone-interleaved first, second, and third data groups.
The OFDM modulator 351 modulates data of the frequency domain into OFDM symbols of the time domain through the IFFT. According to an alternate embodiment of the present invention, the OFDM modulator 351 inputs different data into the positive and the negative frequency domains, respectively, and executes the IFFT to the input data. The positive frequency domain is input with the first data group, and the negative frequency domain is input with the second data group. The IFFT-executed OFDM symbols correspond to the first and the second data groups.
Subsequently, a GI is inserted into the OFDM symbols and the OFDM symbols are converted to an analog signal.
The buffer 381 temporarily stores the OFDM symbols to extend the OFDM symbols into the time domain. Hence, the same OFDM symbols are sequentially transmitted in the time domain at least two times. The frequency generator 391 generates frequencies corresponding to the three frequency bands f1, f2, f3 in accordance with the predetermined transmission channel pattern
The final analog-converted OFDM symbols are sequentially up-converted two times to a certain frequency band. For example, if the transmission channel is {f1, f2, f3 f1, f2, f3}, the final analog-converted OFDM symbols are transmitted once in the frequency domain f1 at the time T0, temporarily stored in the buffer 380, and transmitted once again in the frequency domain f2 at the next time T1.
The above descriptions are made with respect to the 110 Mbps and 200 Mbps modes. As for a 55 Mbps mode, the OFDM modulator 350 or 351 utilizes a different data input scheme. Specifically, a half (½) of the positive frequency domain is input with actual first data, and the remaining half (½) of the positive frequency domain is input with the same data which is the copy of the actual first data. Similarly, a half (½) of the negative frequency domain is input with actual second data, and the remaining half (½) of the negative frequency domain is input with the copy of the actual second data. These loaded data are IFFT-executed and output as the OFDM symbols having double the data amount as compared with the conventional OFDM symbols of the 55 Mbps. Next, the OFDM symbols are data-processed and transmitted in the time domain two times as mentioned above. Consequently, the same data transmission rate is obtained as in the 55 Mbps mode. As for a 480 Mbps mode, the conventional transmission scheme is applied.
As shown in
Referring now to
The transmission scheme extended to the time domain according to an embodiment of the present invention, transits the same OFDM symbol two times along the time axis so that the collided OFDM symbols A1, B1, A3, and B3 are re-transmitted in other frequency bands at the previous time interval or at the next time interval. As a result, even if an OFDM symbol has collided and is lost, other OFDM symbols are losslessly transmitted since the same OFDM symbols are transmitted two times so that the adjacent SOP performance is definitely enhanced.
If the transmission system of
Consequently, effects are equivalent to the {fraction (1/2)} convolutional encoding so that a {fraction (1/2)} rate of error correction capability is maintained though a {fraction (1/2)} rate convolutional decoding at a reception side.
In the transmission channel CH#1={f1, f2, f3, f1, f2, f3, . . . } of
In the transmission channel CH#2={f1, f3, f2, f1, f3, f2, . . . } of
In the transmission channel CH#3={f1, f1, f2, f2, f3, . . . } of
In the transmission channel CH#4={f1, f1, f3, f3, f2, f2, . . . } of
In the light of the foregoing, the TFI-OFDM transmission system according to an embodiment of the present invention transmits the different data loaded in the positive and negative frequency domains, respectively, and transmits the OFDM symbols extended into the time domain As a result, the data transmission rate becomes the same as the conventional TFI-OFDM transmission scheme and the effects of the collision due to interfering signals from the adjacent SOP is mitigated
The receiver 810 down-converts a certain number of frequency bands into predetermined transmission channel patterns.
The synchronization and channel estimation part 820 detects a sync signal through cross-correlation between preambles by scanning a specific frequency band of the certain number of the frequency bands. A channel is estimated by using two reference OFDM symbols per one frequency band. For example, for the transmission channel pattern {f1, f2, f3, f1, f2, f3 . . . }, OFDM symbols transmitted in the underlined identical frequency band f, are present at three OFDM-symbol intervals on the time axis. Thus, a phase difference results from a phase offset, timing offset, and frequency offset between two OFDM symbols transmitted in a single frequency band Accordingly, channels are estimated using the phase difference of two OFDM symbols.
The collision detector 830 determines collisions of OFDM symbols that are transmitted in the multi-path channel conditions. The algorithm for the collision determination can vary. According to an embodiment of the present invention, the collisions are detected by measuring the powers of the received symbols. The steps for the collision determination will follow with reference to
The OFDM demodulator 840 outputs data of the frequency domain from the OFDM symbols of the time domain that are input with the same specification as in the transmitting end by using the fast Fourier transform (FFT).
The phase compensator 850 compensates the phase of the received signal by utilizing a combination of a reference-based method and a decision-directed method.
The equalizer 860 removes multi-paths of the received signal by generally using a ONE-TAP equalizer according to the OFDM transmission characteristics.
The data detector 870 detects only data to be received and processed based on the determination of the collision detector 830. Preferably, but not necessarily, the data detector 870 detects data which correspond to non-collided OFDM symbols of the same OFDM symbols received twice.
The deinterleaver 880 deinterleaves the detected data of the data detector 870 in the reverse order of interleaving at the transmitting end
The first OFDM symbols twitted in the frequency bands f1 and f2 are received in sequence.
The collision detector 830 measures a power R1 of the first OFDM symbols (hereafter refer to as a ‘first power’) transmitted in the current frequency band f1 and a power R2 of the first OFDM symbols (hereinafter refer to as a ‘second power’) transmitted in the next frequency band f2. Next, an average power TH1 is calculated with respect to the OFDM symbols previously transmitted in the frequency band f, (hereinafter referred to as a ‘first average power’), and an average power TH2 is calculated with respect to the OFDM symbols previously transmitted in the frequency band f2 (hereinafter refer to as a ‘second average power) at step S911.
The first power R1 is compared with the first average power TH1, and the second power R2 is compared with the second average power TH2 at step S913. If the first power R1 is less than the sum of the first average power TH1 and a margin m1 and the second power R2 is less than the sum of the second average power TH2 and a margin m2, then there are no collisions in the first OFDM symbols transmitted in the frequency band f1 and the first OFDM symbols transmitted in the frequency band f2 (step S915). Hence, the data detector 870 detects the data using both of the first OFDM symbols Knitted in the frequency bands f1 and f2 at step S917.
If the first power R1 is greater than the sum of the first average power TH1 and the margin m1 and the second power R2 is less than the sum of the second average power TH2 and the margin m2 at step S921, then the first OFDM symbols transmitted in the frequency band f, have collisions (step S923). Accordingly, the data detector 870 detects data by use of the first OFDM symbols transmitted in the frequency band f2 at step S925.
If the first power R1 is less than the sum of the first average power TH1 and the margin m1 and the second power R2 is greater than the sum of the second average power TH2 and the margin m2 at step S931, then the first OFDM symbols transmitted in the frequency band f2 have collisions (step S933). Accordingly, the data detector 870 detects data by use of the first OFDM symbols transmitted in the frequency band f1 at step S935.
If the first power R1 is greater than the sum of the first average power TH1 and the margin m1 and the second power R2 is greater than the sum of the second average power TH2 and the margin m2 at step S931, then there are collisions in both of the first OFDM symbols transmitted in the frequency band f, and the first OFDM symbols transmitted in the frequency band f2 (step S941). Accordingly, the data detector 870 detects data using both of the first OFDM symbols transmitted in the frequency bands ft and f2. Alternatively, the data detector 870 may not use both of the first OFDM symbols (step S942).
Referring back to
As described, the collision detection is executed with respect to the same OFDM symbols received in sequence.
In the light of the foregoing, the reception performance is enhanced by selectively using the non-collided (OFDM symbolic in the multi-piconet environment for the data reception.
The TFI-OFDM transmission system according to an embodiment of the present invention OFDM-modulates the different data in the positive and negative frequency domains and transmits the modulated OFDM symbols in the time domain at least two times, to thus mitigate the collisions resulting from the adjacent SOPs in the multi-piconet environment
The TFI-OFDM reception system according to an embodiment of the present invention selectively utilities the non-collided OFDM symbols for data reception in the multi-piconet environment
While the embodiments of the present invention have been described with reference to exemplary embodiments thereof, additional variations and modifications of the embodiments may occur to those skilled in the art once they learn of the basic inventive concepts. Therefore, it is intended that the appended claims shall be construed to include both the above embodiments and all such variations and modifications that fall within the spirit and scope of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2004-21276 | Mar 2004 | KR | national |
This application claims the benefit of U.S. Provisional Application No. 60/486,414, filed on Jul. 14, 2003 in the United States Patent and Trademark Office, and Korean Patent Application No. 2004-21276, filed on Mar. 29, 2004 in the Korean Patent Office, the disclosures of which are incorporated herein by reference in their entirety.
| Number | Date | Country | |
|---|---|---|---|
| 60486414 | Jul 2003 | US |
