JPWO2006043312A1 - Receiver and collision detection method - Google Patents

Abstract

A receiver for an ultra-wideband communication system using orthogonal frequency division multiplexing. In this receiver, the FFT unit (603) performs a Fourier transform on the received signal to generate a demodulated data symbol sequence. The power measurement unit (631) measures the total power of pilot subcarriers and guard subcarriers of the demodulated data symbol sequence, and sets a threshold value. The collision detection logic processing unit (633) determines that a collision has occurred in the symbol when the total power of the measured subcarriers is greater than the threshold, and determines that no collision has occurred in the symbol if the total power of the subcarrier is less than the threshold To do. The time despreading unit (604) performs time despreading on the demodulated data symbol sequence according to the determination result of the collision detection logic processing unit (633).

Description

  The present invention relates to a receiver and a collision detection method of an ultra wide band (UWB) communication system using orthogonal frequency division multiplexing (OFDM).

  In a communication system using a shared communication medium, it may be permitted to simultaneously transmit information to two or more users in a certain state. An MB-OFDM (Multiband Orthogonal Frequency Division Multiplexing) system specifies one or more time slots for frame transmission. These time slots are designated for information transmission from piconets in different frequency bands by a series of time-frequency codes.

  These time-frequency codes provide channelization for different piconets. Furthermore, different preamble patterns are used for different piconets. Although these time-frequency codes provide channelization, inter-symbol interference or collision of other adjacent piconets is not prevented.

  The frame is divided into two main parts, a PLCP (Physical Layer Convergence Protocol) header and a MAC frame body, each of which has a different purpose. Before the frame is sent, a preamble is added, which is later used for various purposes. In order to assist the reception algorithms for synchronization, carrier offset recovery, and channel estimation, a preamble is first received prior to the header. Following the preamble is a frame header portion that includes information such as the data rate of the MAC frame body, the frame payload length, and a seed identifier for the data scrambler. The next part following reception of the header is the frame payload. This is a communication entity, that is, a portion including data.

  A standard PLCP preamble consists of three different parts: a packet synchronization sequence, a frame synchronization sequence, and a channel estimation sequence. The packet synchronization sequence is generated by a time domain sequence of 21 consecutive periods. Each piconet uses a different time domain sequence. This part of the preamble part can be used for packet detection and acquisition, coarse carrier frequency estimation, and coarse symbol timing.

  Similarly, the frame synchronization sequence is generated by rotating a time domain sequence of three periods added continuously by 180 degrees. This part of the preamble part can be used to synchronize the reception algorithm in the preamble.

  The channel estimation sequence is generated by six periods of OFDM training symbols that are continuously added. This training symbol is obtained by passing the frequency domain sequence through an inverse fast Fourier transform (IFFT) process. This part of the preamble part can be used for channel frequency response estimation, fine carrier frequency estimation and fine symbol timing.

  The frame including the header and the MAC frame body undergoes several processes such as a data scrambler, a convolutional encoder, a puncturing unit, a bit interleaver, and finally a constellation mapper. The frame is then fed to an OFDM modulator where it is cut into symbols of a specific size, followed by the insertion of pilot and guard subcarriers. These symbols are IFFT transformed into time domain OFDM symbols.

  Each OFDM symbol is assigned one or two time slots depending on the time domain spreading factor according to the data rate. For example, when the time domain spreading factor is 2, the same information is spread into two symbols by the time domain spreading process. These two OFDM symbols are transmitted via different subbands, and frequency diversity is obtained. The time-frequency code described above is used to determine in which subband a symbol is transmitted.

  Since symbols are transmitted at random time intervals from different transmitters and piconets, symbol collisions can occur due to two or more symbols being transmitted simultaneously on the same subband. This situation occurs mainly when other piconets are in close proximity. If no OFDM symbol collision is detected, multiple symbols may interfere with each other, preventing reception of some or all of the symbols. Therefore, the received signal is a combination of overlapping symbols and becomes unreadable, so that the transmission information is referred to as lost.

Conventionally, there are many techniques for detecting data collisions. Patent Document 1 discloses a method and apparatus for detecting a collision of data packets using a pre-assigned transceiver code in a preamble. In this disclosure, the preamble of each transmitted packet is, for example, An initial pulse with an amplitude large enough to be detected even after attenuation and a pulse width twice the normal data pulse width, followed by transmission and reception of a predefined length specific to each transceiver And collision detection data having a device code. A collision is detected by determining whether a large initial pulse has a pulse width greater than the generated pulse width or if a subsequent large pulse occurs in the remainder of the packet.
US Pat. No. 4,885,743

  However, conventional data collision detection techniques are generally performed at the packet level, and not at the symbol level where each symbol has a fixed length. At the packet level, a packet can afford to have a preamble before its data portion. The preamble of those packets can include collision detection data that aids the collision detection process. On the other hand, the OFDM symbol does not have the space described above. Although the frame is preceded by a preamble, like other parts of the frame, this is cut into fixed size OFDM symbols, resulting in a stream of information carrying the OFDM symbols. Therefore, there is no preamble preceding the OFDM symbol or the like, and the collision detection method described in Patent Document 1 cannot be used at the symbol level.

  The present invention has been made in view of the above points, and at the symbol level, a receiver capable of detecting a collision with high accuracy and reducing errors without changing or adding resources in an existing system. It is another object of the present invention to provide a collision detection method.

  In order to solve such a problem, a collision detection method of the present invention is a collision detection method in an ultra-wideband communication system using orthogonal frequency division multiplexing, and includes a step of receiving a symbol, a pilot subcarrier from the received symbol, and A step of extracting guard subcarriers, a step of measuring power of the subcarriers, a step of setting a threshold value, and a collision occurs in the symbol when the total power of the measured subcarriers is larger than the threshold value And determining that no collision has occurred in the symbol when the threshold value is not reached.

  The collision detection method of the present invention is a collision detection method in an ultra-wideband communication system using orthogonal frequency division multiplexing, wherein a symbol is received, and a pilot subcarrier and a guard subcarrier are extracted from the received symbol. Dividing the subcarrier into two sets, conjugating a second set, calculating a correlation value between the first set and the conjugate of the second set, and the correlation value Is determined to be a collision with the symbol when it is larger than the threshold, and it is determined that a collision has not occurred with the symbol when the threshold is not reached.

  The collision detection method of the present invention is a collision detection method in an ultra-wideband communication system by frequency time spreading using orthogonal frequency division multiplexing, wherein a symbol is received, and a pilot subcarrier and guard are received from the received symbol. Extracting the subcarriers, dividing the subcarriers into two sets, performing conjugate transposition on the second set, and calculating a correlation value between the first set and the second set subjected to the conjugate transposition. And a step of determining that a collision has occurred in the symbol when the correlation value is greater than a threshold value, and a step of determining that a collision has not occurred in the symbol when the correlation value is less than the threshold value. Take the method.

  The receiver of the present invention is a receiver of an ultra-wide band system using orthogonal frequency division multiplexing, and performs FFT on a received signal to generate a demodulated data symbol sequence; A power measurement unit that measures the total power of pilot subcarriers and guard subcarriers in a data symbol sequence and sets a threshold value, and a collision occurs in the symbol when the measured total power of the subcarrier is larger than the threshold value A collision detection logic processing means for determining that no collision has occurred in the symbol when the threshold value is not satisfied, and the demodulated data symbol sequence according to the determination result of the collision detection logic processing means. And a time despreading means for performing time despreading.

  The receiver of the present invention is a receiver of an ultra-wide band system using orthogonal frequency division multiplexing, and performs FFT on a received signal to generate a demodulated data symbol sequence; Subcarrier detection means for dividing the data symbol string into two sets, conjugating the second set, and calculating a correlation value between the first set and the conjugate of the second set, and the correlation value A collision detection logic processing unit that determines that a collision has occurred in the symbol when greater than a threshold value, and determines that a collision has not occurred in the symbol when the threshold value is not satisfied, and a collision detection logic processing unit According to the determination result, a time despreading means for performing time despreading on the demodulated data symbol sequence is employed.

  The receiver of the present invention is a receiver for an ultra wide band system by frequency time spreading using orthogonal frequency division multiplexing, and performs FFT on the received signal to generate a demodulated data symbol sequence. Error measurement for dividing the demodulated data symbol sequence into two sets, performing conjugate transposition on the second set, and calculating a correlation value between the first set and the second set subjected to the conjugate transposition And a collision detection logic processing means for determining that a collision has occurred in the symbol when the correlation value is greater than a threshold, and determining that a collision has not occurred in the symbol when the correlation value is less than the threshold, and Frequency / time despreading means for performing frequency / time despreading on the demodulated data symbol sequence according to the determination result of the collision detection logic processing means A configuration that.

  According to the present invention, the total power of the subcarrier or the correlation value of the two sets of subcarriers is calculated, and at the symbol level by determining whether or not a collision has occurred by comparing the calculated result with a threshold value. Collisions with higher accuracy can be detected and errors can be reduced without changing or adding resources in existing systems.

The figure which shows the frame format of a MB-OFDM communication system The figure which shows the pilot subcarrier and guard subcarrier frequency allocation of an OFDM symbol The figure which shows the set of the values which define the pseudo random LFSR series pl Diagram defining time-frequency code The figure which shows the time-frequency map about the symbol transmission on three frequency bands using the time spreading factor 2. The block diagram which shows the structure of the receiver which concerns on Embodiment 1 of this invention. The flowchart which shows the threshold value setting method which concerns on Embodiment 1 of this invention. The flowchart which shows the collision detection method which concerns on Embodiment 1 of this invention. The block diagram which shows the structure of the receiver which concerns on Embodiment 2 of this invention. The flowchart which shows the collision detection method which concerns on Embodiment 2 of this invention. The block diagram which shows the structure of the receiver which concerns on Embodiment 3 of this invention. The figure explaining the process of adding two parts of the data symbol which concerns on Embodiment 3 of this invention The figure explaining the process of adding two parts of the data symbol which concerns on Embodiment 3 of this invention The flowchart which shows the collision detection method which concerns on Embodiment 3 of this invention.

  Before describing the present invention in detail, a brief description will be given of the MB-OFDM communication system and the situation on which the present invention was made. FIG. 1 is a diagram illustrating a frame format of a physical (PHY) frame. The physical frame of the MB-OFDM communication system includes a PLCP header 102, a pad bit 104, an optional bandwidth extension 106, a frame payload 108, an FCS (frame check sequence) 110, a tail bit 112, and a pad bit 114. The frame payload 108 and the FCS 110 constitute a MAC frame body.

  A physical frame begins with a PLCP preamble consisting of 30 OFDM symbol sequences. Following the PLCP preamble is a PLCP header, which is a series of bits specifying the data rate, payload length and scrambled identifier. The data rate conveys information about the modulation type, coding rate, and spreading factor used to transmit the MAC frame bodies 108, 110. The MAC header is also a part of the PLCP header 102. Following the PLCP header 102 is a frame payload 108, which is a series of bits that specify the source of the frame and includes a series of frame check sequences 110.

  Prior to OFDM modulation, the frame undergoes various processes such as data scrambling, convolutional coding, puncturing, bit interleaving and quaternary phase shift keying (QPSK) constellation mapping. The QPSK modulated multi-data stream is then divided into groups of 50 or 100 multi-subcarriers known as OFDM symbols.

  In each OFDM symbol, twelve subcarriers 210 are allocated to the pilot signal in order to make synchronization detection strong against frequency offset and phase noise. These pilot signals are put into subcarriers as shown in FIG. The pilot signal is BPSK modulated with a pseudo-random binary sequence generated using a linear feedback shift register (LFSR) to prevent generation of spectral lines.

The contribution by the pilot subcarrier to the kth OFDM symbol is given by P _n which is the inverse Fourier transform of the sequence, as shown in Equation (1) below. The positive / negative polarity of the pilot subcarrier is controlled by the following pseudo-random LFSR sequence pl as shown in FIG.

In each OFDM symbol, 10 subcarriers 220 are allocated to guard subcarriers or guard tones. The guard subcarrier is placed at the position shown in FIG. 2 in the subcarrier. The same linear feedback shift register (LFSR) sequence pl used to scramble the pilot subcarriers is used to generate modulation data for the guard subcarriers. The definition of the guard subcarrier symbol P _{n, k for} the _nth subcarrier of _{the kth} symbol is as shown in the following equation (2).

  Thereafter, the subcarrier is subjected to inverse Fourier transform in the time domain, and a prefix and a guard interval are added to the symbol. The time domain diffusion processing is performed with a diffusion rate of 2. The time domain spreading process consists of transmitting the same information with two symbols. These two OFDM symbols are transmitted over different subbands to obtain frequency diversity. Each device belongs to a piconet. In each of these piconets, transmission is performed using a time-frequency code, and the time-frequency allocation is as shown in FIG. If another device in another piconet is also transmitting and the piconet is in close proximity to each other, an intersymbol collision can occur as shown in FIG. This collision will corrupt the information in the symbol and affect the final bit error rate. In FIG. 5, the horizontal axis indicates time, F1, F2, and F3 indicate frequencies, and A and B indicate different symbols.

  The present invention has been made to overcome the above-mentioned problems of the prior art. An object of the present invention is to detect a collision and reduce errors without wasting resources caused by transmitting unnecessary control signals. The present invention uses existing resources in the system.

  The method of the present invention uses the power of the pilot and guard subcarriers of each OFDM symbol, and as a result, under various circumstances, including symbol collisions where the pilot carrier and guard carrier have similar ratios. The collision between two symbols can be detected.

(Embodiment 1)
FIG. 6 is a block diagram showing a configuration of the receiver according to Embodiment 1 of the present invention. Receiver 600 detects a collision in shared communication media using MB-OFDM technology. The receiver 600 includes a demodulator 670 and a collision detector 680 connected to the demodulator 670.

  The reception filter 601 of the demodulation unit 670 generates a baseband signal by filtering an input signal received from a shared communication medium (not shown). This filtering process removes unwanted spectral components from the sequence. The reception filter 601 is a root raised cosine filter. The GI removal unit 602 removes the prefix and guard interval from the baseband signal. A fast Fourier transform (FFT) unit 603 performs an FFT transform process on the output signal of the GI removal unit 602. The output of the FFT unit is an OFDM demodulated symbol sequence in the frequency domain, and includes information data that has been modulated according to a modulation scheme such as QPSK.

  The time despreading section 604 performs time despreading on the OFDM demodulated symbol sequence that is the output signal of the FFT section 603, and simply combines the same plurality of symbols that are time-spread into a single symbol. The time despreading unit 604 is connected to the collision detection unit 680, determines the symbol quality from the output signal of the collision detection unit 680, and performs despreading processing according to this signal.

  The constellation demapper 605 demodulates the symbols output from the time despreading unit 604 according to a predetermined modulation method such as QPSK. This demodulation process generates a soft decision signal.

  The collision detection unit 680 detects a collision in the OFDM demodulated symbol sequence output from the FFT unit 603. As shown in FIG. 6, the collision detection unit 680 includes a power measurement unit 631, a comparison unit 632, and a collision detection logic processing unit 633.

  The power measurement unit 631 extracts specific pilot subcarriers and guard subcarriers from the OFDM demodulated symbol sequence output from the FFT unit 603. There are 12 pilot subcarriers 210 and 10 guard subcarriers 220 in one OFDM symbol. The positions of these pilot and guard subcarriers are defined in advance and are known to the transmitter and receiver (see FIG. 2). The power measurement unit 631 measures the total power of the extracted pilot subcarriers and guard subcarriers using a technique involving squaring and summation or averaging. Such techniques are well known to those skilled in the relevant art. Hereinafter, the total power of the measured subcarriers is defined as P (i) (i is the number of OFDM symbols). The power measuring unit 631 calculates the threshold T by taking the average of the total power P of subcarriers for N (N is 2 or more) OFDM symbols. For example, {T = [(P (1) + P (2) +... + P (N)) / N]}. This process will be described in more detail later with reference to FIG.

  After setting threshold T, power measuring section 631 measures the power of pilot subcarriers and guard subcarriers of OFDM symbols received subsequently.

  The power measurement unit 631 generates a signal indicating the threshold T and a power indication signal indicating the total power of the pilot subcarrier and the guard subcarrier, and outputs these to the comparison unit 632.

  The comparison unit 632 compares the power indication signal with the threshold T, generates a signal indicating the comparison result, and outputs the signal to the collision detection logic processing unit 633. Comparing unit 632 outputs a signal representing a defective symbol when the power indication signal is greater than threshold value T, and outputs a signal representing a good symbol otherwise.

  The collision detection logic processing unit 633 refers to the value of the output signal of the comparison unit 632 and generates a result signal indicating the status determination of the symbol. That is, the result signal indicates whether the symbol is a good symbol or a bad symbol.

  The components of the demodulator can be realized by various techniques that will be obvious to those skilled in the related art. These components can be realized by electronic circuits and / or digital processing techniques.

  FIG. 7 is a flowchart showing calculation and setting of the threshold value. Such a method begins at step 701 where an OFDM symbol is obtained from a signal received via a shared communication medium such as a wireless channel.

  In step 702, a template for pilot and guard subcarriers is generated using the saved pilot and guard subcarrier positions 720. In step 704, pilot and guard subcarriers are extracted using this template.

  In step 706, power measurement is performed on the extracted pilot subcarriers and guard subcarriers. In order to obtain a better estimate of the threshold, the threshold is calculated for N received OFDM symbols. In step 708, if the number of received OFDM symbols is less than N, the flow returns to step 701, and if not, the process proceeds to step 710.

  In step 710, the average subcarrier power of N OFDM symbols is calculated. This average is set as a threshold in step 712.

  By obtaining this threshold value, the collision detection process can proceed to collision detection for subsequent received OFDM symbols by using this threshold value.

  FIG. 8 is a flowchart showing a collision detection method. The method begins at step 801 where an OFDM symbol is received.

  In step 802, a template for pilot and guard subcarriers is generated using the saved pilot and guard subcarrier positions 820. In step 804, pilot subcarriers and guard subcarriers are extracted using this template.

  In step 806, power measurement is performed on the pilot and guard subcarriers extracted in step 804. In step 807, the total power of this subcarrier is compared with the threshold shown in FIG. 7. If the total power is higher than the threshold, the process proceeds to step 810. If not, go to Step 811.

  In step 810, it is determined that the symbol is a good symbol that does not collide with other symbols. In this step, the collision detection logic processing unit 633 generates a result signal indicating that the symbol status determination is good. On the other hand, in step 811, the symbol is determined as a defective symbol, in other words, a symbol having a collision. In this step, the collision detection logic processing unit 633 generates a result signal indicating that the symbol status determination is bad or collision. The result signal is used to determine time despreading and to select good / bad symbols.

  Note that these symbols may be weighted before the processing of the time despreading unit 604. The symbol weighting process can be realized by various techniques that will be obvious to those skilled in the related art.

  According to the present embodiment, by determining whether or not a collision has occurred by comparing the total power of the subcarrier and the threshold, at the symbol level, without changing or adding resources in the existing system, It is possible to detect collisions with higher accuracy and reduce errors.

(Embodiment 2)
FIG. 9 is a block diagram showing a configuration of a receiver according to Embodiment 2 of the present invention. In the receiver 900 shown in FIG. 9, the same components as those in the receiver 600 shown in FIG.

  The receiver 900 illustrated in FIG. 9 employs a configuration in which the power measurement unit 631 is deleted and a subcarrier detection unit 931 is added, compared to the receiver 600 illustrated in FIG. Further, the operation of the comparison unit 932 of the receiver 900 is different from that of the comparison unit 632 of the receiver 600.

  The subcarrier detection unit 931 processes the OFDM demodulated symbol output from the FFT unit 603 and extracts a specific subcarrier. The detection process is performed by generating a mask of specific positions of subcarriers and sampling these subcarriers. For example, in the MB-OFDM communication system, there are 12 pilot subcarriers 210 and 10 guard subcarriers 220. By using this mask, subcarriers can be sampled and stored in a buffer. These samples are further divided into two sets. These two sets of subcarrier samples go through a process of determining symbol quality. Through this process, the subcarrier detector 931 provides information for enabling accurate detection of a collision in the input signal. This process will be described in detail later with reference to FIG. Subcarrier detection section 931 generates a subcarrier mismatch indication signal indicating the result of pilot and guard subcarrier detection, and outputs the generated signal to comparison section 932.

  Comparing section 932 compares the subcarrier mismatch indication signal with threshold T1, and generates a signal indicating the comparison result. Comparator 932 outputs a signal representing a corrupted symbol to collision detection logic processor 633 if the subcarrier mismatch indication signal does not satisfy threshold T1, and if the subcarrier mismatch indication signal satisfies threshold T1. A signal representing a good symbol is output to the collision detection logic processing unit 633.

  FIG. 10 is a flowchart showing a collision detection method. The method begins at step 1001 where an OFDM symbol is received.

  In step 1003, the pilot and guard subcarriers are sampled using the saved pilot and guard subcarrier positions 1020. In step 1005, the subcarrier samples are evenly divided into two different sets of complex numbers. The original values of the pilot subcarrier and the guard subcarrier are mapped to specific positions in the modulator on the transmission side. These values are uniquely defined, and the first 11 subcarrier samples are conjugates of the next 11 subcarrier samples. After step 1005, in step 1007, a second set of subcarrier samples is conjugated, correlated with the first set, and correlator output power is obtained. In step 1009, the power of the correlator output is compared with a threshold value T1. If the result is higher than the threshold T1, the flow proceeds to Step 1011. Otherwise, go to step 1013.

  In step 1011, it is determined that the symbol is a good symbol that does not collide with other symbols. In this step, the collision detection logic processing unit 633 generates a result signal indicating that the symbol status determination is good. On the other hand, in step 1013, the symbol is determined as a defective symbol, in other words, a symbol having a collision. In this step, the collision detection logic processing unit 633 generates a result signal indicating that the symbol status determination is bad or collision. The result signal is used to determine time despreading and to select good / bad symbols.

  According to the present embodiment, the subcarrier is divided into two sets, the second set is conjugated, the correlation value between the first set and the second set conjugate is calculated, and the correlation value and By detecting whether or not a collision has occurred by comparing with a threshold value, it is possible to detect a collision with higher accuracy and reduce errors without changing or adding resources in an existing system at the symbol level. be able to.

(Embodiment 3)
FIG. 11 is a block diagram showing a configuration of a receiver according to Embodiment 3 of the present invention. Note that in the receiver 1100 illustrated in FIG. 11, the same components as those in the receiver 600 illustrated in FIG. 6 of Embodiment 1 are denoted by the same reference numerals, and description thereof is omitted.

  Compared with the receiver 600 shown in FIG. 6, the receiver 1100 shown in FIG. 11 deletes the time despreading unit 604 and the power measurement unit 631, subcarrier extractor 1101, frequency / time despreading unit 1102, and A configuration in which an error measurement unit 1131 is added is adopted. Further, the operation of the comparison unit 1132 of the receiver 1100 is different from that of the comparison unit 632 of the receiver 600.

  The subcarrier extractor 1101 extracts pilot subcarriers and guard subcarriers included in the received data symbol with reference to predetermined positions.

  Since the symbol of the output signal of the subcarrier extractor 1101 has conjugate symmetry, the frequency / time despreading section 1102 performs conjugate transposition processing on the second part of the symbol, and the same symbol Combine with the first part of. The joining process can be performed using two-part averaging or by weighting. The output signal of the subcarrier extractor 1101 is time-spread, and the frequency / time despreading section 1102 simply combines the same plurality of symbols that have been time-spread into a single symbol. The frequency / time despreading unit 1102 is connected to the collision detection unit 680, determines the symbol quality from the output signal of the collision detection unit 680, and performs despreading processing according to this signal.

  Error measurement section 1131 receives the OFDM demodulated data symbol output from subcarrier extractor 1101, and separates this data symbol into two different parts.

  When the QPSK-modulated multi-data stream is divided into 50 multi-subcarrier groups 402, frequency domain spreading processing as shown in FIG. 12A is performed. The 50 subcarriers 1204 precede the subcarrier 1206 obtained by conjugate transposition of them and form a conjugate symmetrical input of 100 subcarriers (subcarrier 1202 + subcarrier 1208) prior to IFFT processing.

  The subcarriers of data symbols can be sampled and stored in a buffer or register. FIG. 12B shows a process for retrieving two different portions of a data symbol. The extraction process is the reverse process of FIG. In order to extract the same data 1252 of the first part, it is necessary to perform conjugate transposition processing on the second part 1253 of the data symbol. The first part 1254 to be processed is placed in the data register 1256 and the second part 1255 is placed in the reference pattern register 1257.

  The error measurement unit 1131 determines the correlation coefficient of the data stream by comparing the data sample stored in the data register 1256 with the data sample stored in the reference pattern register 1257. Error measurement section 1131 generates an error indication signal indicating a correlation coefficient and outputs the error indication signal to comparison section 1132.

  The comparison unit 1132 compares the error indication signal with the threshold value T2, and generates a signal indicating the comparison result. Comparator 1132 outputs a signal representing a corrupted symbol to collision detection logic processor 633 if the error indication signal does not satisfy threshold value T2, and represents a good symbol if the error indication signal satisfies threshold value T2. The signal is output to the collision detection logic processing unit 633. The threshold value T2 determines the detection possibility and the false alarm rate. If the threshold value T2 is low, the possibility of detection increases, but the possibility of a false alarm also increases. Most communication systems need to be tolerant of some errors due to noise and multipath. Therefore, an appropriate threshold must be chosen so that a good balance is maintained between detection and the possibility of false alarms.

  FIG. 13 is a flowchart showing a collision detection method. The method begins at step 1301 where an OFDM symbol is received.

  In step 1302, the received symbols are sampled and both parts of the data symbols are extracted.

  In step 1304, the data symbol subcarrier samples are averaged into two different complex parts. In step 1306, conjugate transpose is performed on the second portion of the data symbol subcarrier sample. Conjugation processing of the second part of the data symbol has already been described with reference to FIG. The two portions 1254 and 1255 are arranged in the data register 1256 and the reference pattern register 1257.

  In step 1308, data correlation values are generated from the received data symbol subcarrier samples. This step involves correlating the data in the two registers. The data in the data register 1256 is compared with the data stored in the reference pattern register 1257. In step 1310, the number of matches and the correlation coefficient are generated and stored in the correlation array.

  In step 1312, the correlation coefficient is compared with a predetermined threshold T2. If the result is higher than the threshold T2, the flow proceeds to step 1313. Otherwise, go to step 1315.

  In step 1313, it is determined that the symbol is a good symbol that does not collide with other symbols. In this step, the collision detection logic processing unit 633 generates a result signal indicating that the symbol status determination is good. On the other hand, in step 1315, the symbol is determined as a defective symbol, in other words, a symbol having a collision. In this step, the collision detection logic processing unit 633 generates a result signal indicating that the symbol status determination is bad or collision. The result signal is used to determine time despreading and to select good / bad symbols.

  According to the present embodiment, the subcarriers are divided into two sets, conjugate transposition is performed on the second set, and a correlation value between the first set and the second set conjugate-translated is calculated. By detecting whether or not a collision has occurred by comparing the correlation value with a threshold value, it is possible to detect a collision with higher accuracy without changing or adding resources in the existing system at the symbol level. Errors can be reduced.

  Although the above description is considered as a preferred embodiment of the present invention, the present invention is not limited to the disclosed embodiment, and can be realized in various forms and embodiments.

  The present invention is suitable for use in a receiver of an ultra-wideband communication system using orthogonal frequency division multiplexing.

  The present invention relates to a receiver and a collision detection method of an ultra wide band (UWB) communication system using orthogonal frequency division multiplexing (OFDM).

  In a communication system using a shared communication medium, it may be permitted to simultaneously transmit information to two or more users in a certain state. An MB-OFDM (Multiband Orthogonal Frequency Division Multiplexing) system specifies one or more time slots for frame transmission. These time slots are designated for information transmission from piconets in different frequency bands by a series of time-frequency codes.

  These time-frequency codes provide channelization for different piconets. Furthermore, different preamble patterns are used for different piconets. Although these time-frequency codes provide channelization, inter-symbol interference or collision of other adjacent piconets is not prevented.

  The frame is divided into two main parts, a PLCP (Physical Layer Convergence Protocol) header and a MAC frame body, each of which has a different purpose. Before the frame is sent, a preamble is added, which is later used for various purposes. In order to assist the reception algorithms for synchronization, carrier offset recovery, and channel estimation, a preamble is first received prior to the header. Following the preamble is a frame header portion that includes information such as the data rate of the MAC frame body, the frame payload length, and a seed identifier for the data scrambler. The next part following reception of the header is the frame payload. This is a communication entity, that is, a portion including data.

  A standard PLCP preamble consists of three different parts: a packet synchronization sequence, a frame synchronization sequence, and a channel estimation sequence. The packet synchronization sequence is generated by a time domain sequence of 21 consecutive periods. Each piconet uses a different time domain sequence. This part of the preamble part can be used for packet detection and acquisition, coarse carrier frequency estimation, and coarse symbol timing.

  Similarly, the frame synchronization sequence is generated by rotating a time domain sequence of three periods added continuously by 180 degrees. This part of the preamble part can be used to synchronize the reception algorithm in the preamble.

  The channel estimation sequence is generated by six periods of OFDM training symbols that are continuously added. This training symbol is obtained by passing the frequency domain sequence through an inverse fast Fourier transform (IFFT) process. This part of the preamble part can be used for channel frequency response estimation, fine carrier frequency estimation and fine symbol timing.

The frame including the header and the MAC frame body undergoes several processes such as a data scrambler, a convolutional encoder, a puncturing unit, a bit interleaver, and finally a constellation mapper. The frame is then fed to an OFDM modulator where it is cut into symbols of a specific size, followed by the insertion of pilot and guard subcarriers. These symbols are IFFT transformed into time domain OFDM symbols.

  Each OFDM symbol is assigned one or two time slots depending on the time domain spreading factor according to the data rate. For example, when the time domain spreading factor is 2, the same information is spread into two symbols by the time domain spreading process. These two OFDM symbols are transmitted via different subbands, and frequency diversity is obtained. The time-frequency code described above is used to determine in which subband a symbol is transmitted.

  Since symbols are transmitted at random time intervals from different transmitters and piconets, symbol collisions can occur due to two or more symbols being transmitted simultaneously on the same subband. This situation occurs mainly when other piconets are in close proximity. If no OFDM symbol collision is detected, multiple symbols may interfere with each other, preventing reception of some or all of the symbols. Therefore, the received signal is a combination of overlapping symbols and becomes unreadable, so that the transmission information is referred to as lost.

Conventionally, there are many techniques for detecting data collisions. Patent Document 1 discloses a method and apparatus for detecting a collision of data packets using a pre-assigned transceiver code in a preamble. In this disclosure, the preamble of each transmitted packet is, for example, An initial pulse with an amplitude large enough to be detected even after attenuation and a pulse width twice the normal data pulse width, followed by transmission and reception of a predefined length specific to each transceiver And collision detection data having a device code. A collision is detected by determining whether a large initial pulse has a pulse width greater than the generated pulse width or if a subsequent large pulse occurs in the remainder of the packet.
U.S. Pat. No. 4,885,743

  However, conventional data collision detection techniques are generally performed at the packet level, and not at the symbol level where each symbol has a fixed length. At the packet level, a packet can afford to have a preamble before its data portion. The preamble of those packets can include collision detection data that aids the collision detection process. On the other hand, the OFDM symbol does not have the space described above. Although the frame is preceded by a preamble, like other parts of the frame, this is cut into fixed size OFDM symbols, resulting in a stream of information carrying the OFDM symbols. Therefore, there is no preamble preceding the OFDM symbol or the like, and the collision detection method described in Patent Document 1 cannot be used at the symbol level.

  The present invention has been made in view of the above points, and at the symbol level, a receiver capable of detecting a collision with high accuracy and reducing errors without changing or adding resources in an existing system. It is another object of the present invention to provide a collision detection method.

In order to solve such a problem, a collision detection method of the present invention is a collision detection method in an ultra-wideband communication system using orthogonal frequency division multiplexing, and includes a step of receiving a symbol, a pilot subcarrier from the received symbol, and A step of extracting guard subcarriers, a step of measuring power of the subcarriers, a step of setting a threshold value, and a collision occurs in the symbol when the total power of the measured subcarriers is larger than the threshold value And determining that no collision has occurred in the symbol when the threshold value is not reached.

  The collision detection method of the present invention is a collision detection method in an ultra-wideband communication system using orthogonal frequency division multiplexing, wherein a symbol is received, and a pilot subcarrier and a guard subcarrier are extracted from the received symbol. Dividing the subcarrier into two sets, conjugating a second set, calculating a correlation value between the first set and the conjugate of the second set, and the correlation value Is determined to be a collision with the symbol when it is larger than the threshold, and it is determined that a collision has not occurred with the symbol when the threshold is not reached.

  The collision detection method of the present invention is a collision detection method in an ultra-wideband communication system by frequency time spreading using orthogonal frequency division multiplexing, wherein a symbol is received, and a pilot subcarrier and guard are received from the received symbol. Extracting the subcarriers, dividing the subcarriers into two sets, performing conjugate transposition on the second set, and calculating a correlation value between the first set and the second set subjected to the conjugate transposition. And a step of determining that a collision has occurred in the symbol when the correlation value is greater than a threshold value, and a step of determining that a collision has not occurred in the symbol when the correlation value is less than the threshold value. Take the method.

  The receiver of the present invention is a receiver of an ultra-wide band system using orthogonal frequency division multiplexing, and performs FFT on a received signal to generate a demodulated data symbol sequence; A power measurement unit that measures the total power of pilot subcarriers and guard subcarriers in a data symbol sequence and sets a threshold value, and a collision occurs in the symbol when the measured total power of the subcarrier is larger than the threshold value A collision detection logic processing means for determining that no collision has occurred in the symbol when the threshold value is not satisfied, and the demodulated data symbol sequence according to the determination result of the collision detection logic processing means. And a time despreading means for performing time despreading.

  The receiver of the present invention is a receiver of an ultra-wide band system using orthogonal frequency division multiplexing, and performs FFT on a received signal to generate a demodulated data symbol sequence; Subcarrier detection means for dividing the data symbol string into two sets, conjugating the second set, and calculating a correlation value between the first set and the conjugate of the second set, and the correlation value A collision detection logic processing unit that determines that a collision has occurred in the symbol when greater than a threshold value, and determines that a collision has not occurred in the symbol when the threshold value is not satisfied, and a collision detection logic processing unit According to the determination result, a time despreading means for performing time despreading on the demodulated data symbol sequence is employed.

  The receiver of the present invention is a receiver for an ultra wide band system by frequency time spreading using orthogonal frequency division multiplexing, and performs FFT on the received signal to generate a demodulated data symbol sequence. Error measurement for dividing the demodulated data symbol sequence into two sets, performing conjugate transposition on the second set, and calculating a correlation value between the first set and the second set subjected to the conjugate transposition And a collision detection logic processing means for determining that a collision has occurred in the symbol when the correlation value is greater than a threshold, and determining that a collision has not occurred in the symbol when the correlation value is less than the threshold, and Frequency / time despreading means for performing frequency / time despreading on the demodulated data symbol sequence according to the determination result of the collision detection logic processing means A configuration that.

  According to the present invention, the total power of the subcarrier or the correlation value of the two sets of subcarriers is calculated, and at the symbol level by determining whether or not a collision has occurred by comparing the calculated result with a threshold value. Collisions with higher accuracy can be detected and errors can be reduced without changing or adding resources in existing systems.

  Before describing the present invention in detail, a brief description will be given of the MB-OFDM communication system and the situation on which the present invention was made. FIG. 1 is a diagram illustrating a frame format of a physical (PHY) frame. The physical frame of the MB-OFDM communication system includes a PLCP header 102, a pad bit 104, an optional bandwidth extension 106, a frame payload 108, an FCS (frame check sequence) 110, a tail bit 112, and a pad bit 114. The frame payload 108 and the FCS 110 constitute a MAC frame body.

  A physical frame begins with a PLCP preamble consisting of 30 OFDM symbol sequences. Following the PLCP preamble is a PLCP header, which is a series of bits specifying the data rate, payload length and scrambled identifier. The data rate conveys information about the modulation type, coding rate, and spreading factor used to transmit the MAC frame bodies 108, 110. The MAC header is also a part of the PLCP header 102. Following the PLCP header 102 is a frame payload 108, which is a series of bits that specify the source of the frame and includes a series of frame check sequences 110.

  Prior to OFDM modulation, the frame undergoes various processes such as data scrambling, convolutional coding, puncturing, bit interleaving and quaternary phase shift keying (QPSK) constellation mapping. The QPSK modulated multi-data stream is then divided into groups of 50 or 100 multi-subcarriers known as OFDM symbols.

  In each OFDM symbol, twelve subcarriers 210 are allocated to the pilot signal in order to make synchronization detection strong against frequency offset and phase noise. These pilot signals are put into subcarriers as shown in FIG. The pilot signal is BPSK modulated with a pseudo-random binary sequence generated using a linear feedback shift register (LFSR) to prevent generation of spectral lines.

The contribution of pilot subcarriers to the kth OFDM symbol is given by P _n which is the inverse Fourier transform of the sequence, as shown in Equation (1) below. The positive / negative polarity of the pilot subcarrier is controlled by the following pseudo-random LFSR sequence pl as shown in FIG.

In each OFDM symbol, 10 subcarriers 220 are allocated to guard subcarriers or guard tones. The guard subcarrier is placed at the position shown in FIG. 2 in the subcarrier. The same linear feedback shift register (LFSR) sequence pl used to scramble the pilot subcarriers is used to generate modulation data for the guard subcarriers. The definition of the guard subcarrier symbol P _{n, k for} the _nth subcarrier of _{the kth} symbol is as shown in the following equation (2).

  Thereafter, the subcarrier is subjected to inverse Fourier transform in the time domain, and a prefix and a guard interval are added to the symbol. The time domain diffusion processing is performed with a diffusion rate of 2. The time domain spreading process consists of transmitting the same information with two symbols. These two OFDM symbols are transmitted over different subbands to obtain frequency diversity. Each device belongs to a piconet. In each of these piconets, transmission is performed using a time-frequency code, and the time-frequency allocation is as shown in FIG. If another device in another piconet is also transmitting and the piconet is in close proximity to each other, an intersymbol collision can occur as shown in FIG. This collision will corrupt the information in the symbol and affect the final bit error rate. In FIG. 5, the horizontal axis indicates time, F1, F2, and F3 indicate frequencies, and A and B indicate different symbols.

The present invention has been made to overcome the above-mentioned problems of the prior art. An object of the present invention is to detect a collision and reduce errors without wasting resources caused by transmitting unnecessary control signals. The present invention uses existing resources in the system.

  The method of the present invention uses the power of the pilot and guard subcarriers of each OFDM symbol, and as a result, under various circumstances, including symbol collisions where the pilot carrier and guard carrier have similar ratios. The collision between two symbols can be detected.

(Embodiment 1)
FIG. 6 is a block diagram showing a configuration of the receiver according to Embodiment 1 of the present invention. Receiver 600 detects a collision in shared communication media using MB-OFDM technology. The receiver 600 includes a demodulator 670 and a collision detector 680 connected to the demodulator 670.

  The reception filter 601 of the demodulation unit 670 generates a baseband signal by filtering an input signal received from a shared communication medium (not shown). This filtering process removes unwanted spectral components from the sequence. The reception filter 601 is a root raised cosine filter. The GI removal unit 602 removes the prefix and guard interval from the baseband signal. A fast Fourier transform (FFT) unit 603 performs an FFT transform process on the output signal of the GI removal unit 602. The output of the FFT unit is an OFDM demodulated symbol sequence in the frequency domain, and includes information data that has been modulated according to a modulation scheme such as QPSK.

  The time despreading section 604 performs time despreading on the OFDM demodulated symbol sequence that is the output signal of the FFT section 603, and simply combines the same plurality of symbols that are time-spread into a single symbol. The time despreading unit 604 is connected to the collision detection unit 680, determines the symbol quality from the output signal of the collision detection unit 680, and performs despreading processing according to this signal.

  The constellation demapper 605 demodulates the symbols output from the time despreading unit 604 according to a predetermined modulation method such as QPSK. This demodulation process generates a soft decision signal.

  The collision detection unit 680 detects a collision in the OFDM demodulated symbol sequence output from the FFT unit 603. As shown in FIG. 6, the collision detection unit 680 includes a power measurement unit 631, a comparison unit 632, and a collision detection logic processing unit 633.

The power measurement unit 631 extracts specific pilot subcarriers and guard subcarriers from the OFDM demodulated symbol sequence output from the FFT unit 603. There are 12 pilot subcarriers 210 and 10 guard subcarriers 220 in one OFDM symbol. The positions of these pilot and guard subcarriers are defined in advance and are known to the transmitter and receiver (see FIG. 2). The power measurement unit 631 measures the total power of the extracted pilot subcarriers and guard subcarriers using a technique involving squaring and summation or averaging. Such techniques are well known to those skilled in the relevant art. Hereinafter, the total power of the measured subcarriers is expressed as P (i)
Where i is the number of OFDM symbols. The power measuring unit 631 calculates the threshold T by taking the average of the total power P of subcarriers for N (N is 2 or more) OFDM symbols. For example, {T = [(P (1) + P (2) +... + P (N)) / N]}. This process will be described in more detail later with reference to FIG.

After setting threshold T, power measuring section 631 measures the power of pilot subcarriers and guard subcarriers of OFDM symbols received subsequently.

  The power measurement unit 631 generates a signal indicating the threshold T and a power indication signal indicating the total power of the pilot subcarrier and the guard subcarrier, and outputs these to the comparison unit 632.

  The comparison unit 632 compares the power indication signal with the threshold T, generates a signal indicating the comparison result, and outputs the signal to the collision detection logic processing unit 633. Comparing unit 632 outputs a signal representing a defective symbol when the power indication signal is greater than threshold value T, and outputs a signal representing a good symbol otherwise.

  The collision detection logic processing unit 633 refers to the value of the output signal of the comparison unit 632 and generates a result signal indicating the status determination of the symbol. That is, the result signal indicates whether the symbol is a good symbol or a bad symbol.

  The components of the demodulator can be realized by various techniques that will be obvious to those skilled in the related art. These components can be realized by electronic circuits and / or digital processing techniques.

  FIG. 7 is a flowchart showing calculation and setting of the threshold value. Such a method begins at step 701 where an OFDM symbol is obtained from a signal received via a shared communication medium such as a wireless channel.

  In step 702, a template for pilot and guard subcarriers is generated using the saved pilot and guard subcarrier positions 720. In step 704, pilot and guard subcarriers are extracted using this template.

  In step 706, power measurement is performed on the extracted pilot subcarriers and guard subcarriers. In order to obtain a better estimate of the threshold, the threshold is calculated for N received OFDM symbols. In step 708, if the number of received OFDM symbols is less than N, the flow returns to step 701, and if not, the process proceeds to step 710.

  In step 710, the average subcarrier power of N OFDM symbols is calculated. This average is set as a threshold in step 712.

  By obtaining this threshold value, the collision detection process can proceed to collision detection for subsequent received OFDM symbols by using this threshold value.

  FIG. 8 is a flowchart showing a collision detection method. The method begins at step 801 where an OFDM symbol is received.

  In step 802, a template for pilot and guard subcarriers is generated using the saved pilot and guard subcarrier positions 820. In step 804, pilot subcarriers and guard subcarriers are extracted using this template.

In step 806, power measurement is performed on the pilot and guard subcarriers extracted in step 804. In step 807, the total power of this subcarrier is compared with the threshold shown in FIG. 7. If the total power is higher than the threshold, the process proceeds to step 810. If not, go to Step 811.

  In step 810, it is determined that the symbol is a good symbol that does not collide with other symbols. In this step, the collision detection logic processing unit 633 generates a result signal indicating that the symbol status determination is good. On the other hand, in step 811, the symbol is determined as a defective symbol, in other words, a symbol having a collision. In this step, the collision detection logic processing unit 633 generates a result signal indicating that the symbol status determination is bad or collision. The result signal is used to determine time despreading and to select good / bad symbols.

  Note that these symbols may be weighted before the processing of the time despreading unit 604. The symbol weighting process can be realized by various techniques that will be obvious to those skilled in the related art.

  According to the present embodiment, by determining whether or not a collision has occurred by comparing the total power of the subcarrier and the threshold, at the symbol level, without changing or adding resources in the existing system, It is possible to detect collisions with higher accuracy and reduce errors.

(Embodiment 2)
FIG. 9 is a block diagram showing a configuration of a receiver according to Embodiment 2 of the present invention. In the receiver 900 shown in FIG. 9, the same components as those in the receiver 600 shown in FIG.

  The receiver 900 illustrated in FIG. 9 employs a configuration in which the power measurement unit 631 is deleted and a subcarrier detection unit 931 is added, compared to the receiver 600 illustrated in FIG. Further, the operation of the comparison unit 932 of the receiver 900 is different from that of the comparison unit 632 of the receiver 600.

  The subcarrier detection unit 931 processes the OFDM demodulated symbol output from the FFT unit 603 and extracts a specific subcarrier. The detection process is performed by generating a mask of specific positions of subcarriers and sampling these subcarriers. For example, in the MB-OFDM communication system, there are 12 pilot subcarriers 210 and 10 guard subcarriers 220. By using this mask, subcarriers can be sampled and stored in a buffer. These samples are further divided into two sets. These two sets of subcarrier samples go through a process of determining symbol quality. Through this process, the subcarrier detector 931 provides information for enabling accurate detection of a collision in the input signal. This process will be described in detail later with reference to FIG. Subcarrier detection section 931 generates a subcarrier mismatch indication signal indicating the result of pilot and guard subcarrier detection, and outputs the generated signal to comparison section 932.

  Comparing section 932 compares the subcarrier mismatch indication signal with threshold T1, and generates a signal indicating the comparison result. Comparator 932 outputs a signal representing a corrupted symbol to collision detection logic processor 633 if the subcarrier mismatch indication signal does not satisfy threshold T1, and if the subcarrier mismatch indication signal satisfies threshold T1. A signal representing a good symbol is output to the collision detection logic processing unit 633.

  FIG. 10 is a flowchart showing a collision detection method. The method begins at step 1001 where an OFDM symbol is received.

  In step 1003, the pilot and guard subcarriers are sampled using the saved pilot and guard subcarrier positions 1020. In step 1005, the subcarrier samples are evenly divided into two different sets of complex numbers. The original values of the pilot subcarrier and the guard subcarrier are mapped to specific positions in the modulator on the transmission side. These values are uniquely defined, and the first 11 subcarrier samples are conjugates of the next 11 subcarrier samples. After step 1005, in step 1007, a second set of subcarrier samples is conjugated, correlated with the first set, and correlator output power is obtained. In step 1009, the power of the correlator output is compared with a threshold value T1. If the result is higher than the threshold T1, the flow proceeds to Step 1011. Otherwise, go to step 1013.

  In step 1011, it is determined that the symbol is a good symbol that does not collide with other symbols. In this step, the collision detection logic processing unit 633 generates a result signal indicating that the symbol status determination is good. On the other hand, in step 1013, the symbol is determined as a defective symbol, in other words, a symbol having a collision. In this step, the collision detection logic processing unit 633 generates a result signal indicating that the symbol status determination is bad or collision. The result signal is used to determine time despreading and to select good / bad symbols.

  According to the present embodiment, the subcarrier is divided into two sets, the second set is conjugated, the correlation value between the first set and the second set conjugate is calculated, and the correlation value and By detecting whether or not a collision has occurred by comparing with a threshold value, it is possible to detect a collision with higher accuracy and reduce errors without changing or adding resources in an existing system at the symbol level. be able to.

(Embodiment 3)
FIG. 11 is a block diagram showing a configuration of a receiver according to Embodiment 3 of the present invention. Note that in the receiver 1100 illustrated in FIG. 11, the same components as those in the receiver 600 illustrated in FIG. 6 of Embodiment 1 are denoted by the same reference numerals, and description thereof is omitted.

  Compared with the receiver 600 shown in FIG. 6, the receiver 1100 shown in FIG. 11 deletes the time despreading unit 604 and the power measurement unit 631, subcarrier extractor 1101, frequency / time despreading unit 1102, and A configuration in which an error measurement unit 1131 is added is adopted. Further, the operation of the comparison unit 1132 of the receiver 1100 is different from that of the comparison unit 632 of the receiver 600.

  The subcarrier extractor 1101 extracts pilot subcarriers and guard subcarriers included in the received data symbol with reference to predetermined positions.

  Since the symbol of the output signal of the subcarrier extractor 1101 has conjugate symmetry, the frequency / time despreading section 1102 performs conjugate transposition processing on the second part of the symbol, and the same symbol Combine with the first part of. The joining process can be performed using two-part averaging or by weighting. The output signal of the subcarrier extractor 1101 is time-spread, and the frequency / time despreading section 1102 simply combines the same plurality of symbols that have been time-spread into a single symbol. The frequency / time despreading unit 1102 is connected to the collision detection unit 680, determines the symbol quality from the output signal of the collision detection unit 680, and performs despreading processing according to this signal.

Error measurement section 1131 receives the OFDM demodulated data symbol output from subcarrier extractor 1101, and separates this data symbol into two different parts.

  When the QPSK-modulated multi-data stream is divided into 50 multi-subcarrier groups 402, frequency domain spreading processing as shown in FIG. 12A is performed. The 50 subcarriers 1204 precede the subcarrier 1206 obtained by conjugate transposition of them and form a conjugate symmetrical input of 100 subcarriers (subcarrier 1202 + subcarrier 1208) prior to IFFT processing.

  The subcarriers of data symbols can be sampled and stored in a buffer or register. FIG. 12B shows a process for retrieving two different portions of a data symbol. The extraction process is the reverse process of FIG. In order to extract the same data 1252 of the first part, it is necessary to perform conjugate transposition processing on the second part 1253 of the data symbol. The first part 1254 to be processed is placed in the data register 1256 and the second part 1255 is placed in the reference pattern register 1257.

  The error measurement unit 1131 determines the correlation coefficient of the data stream by comparing the data sample stored in the data register 1256 with the data sample stored in the reference pattern register 1257. Error measurement section 1131 generates an error indication signal indicating a correlation coefficient and outputs the error indication signal to comparison section 1132.

  The comparison unit 1132 compares the error indication signal with the threshold value T2, and generates a signal indicating the comparison result. Comparator 1132 outputs a signal representing a corrupted symbol to collision detection logic processor 633 if the error indication signal does not satisfy threshold value T2, and represents a good symbol if the error indication signal satisfies threshold value T2. The signal is output to the collision detection logic processing unit 633. The threshold value T2 determines the detection possibility and the false alarm rate. If the threshold value T2 is low, the possibility of detection increases, but the possibility of a false alarm also increases. Most communication systems need to be tolerant of some errors due to noise and multipath. Therefore, an appropriate threshold must be chosen so that a good balance is maintained between detection and the possibility of false alarms.

  FIG. 13 is a flowchart showing a collision detection method. The method begins at step 1301 where an OFDM symbol is received.

  In step 1302, the received symbols are sampled and both parts of the data symbols are extracted.

  In step 1304, the data symbol subcarrier samples are averaged into two different complex parts. In step 1306, conjugate transpose is performed on the second portion of the data symbol subcarrier sample. Conjugation processing of the second part of the data symbol has already been described with reference to FIG. The two portions 1254 and 1255 are arranged in the data register 1256 and the reference pattern register 1257.

  In step 1308, data correlation values are generated from the received data symbol subcarrier samples. This step involves correlating the data in the two registers. The data in the data register 1256 is compared with the data stored in the reference pattern register 1257. In step 1310, the number of matches and the correlation coefficient are generated and stored in the correlation array.

  In step 1312, the correlation coefficient is compared with a predetermined threshold T2. If the result is higher than the threshold T2, the flow proceeds to step 1313. Otherwise, go to step 1315.

  In step 1313, it is determined that the symbol is a good symbol that does not collide with other symbols. In this step, the collision detection logic processing unit 633 generates a result signal indicating that the symbol status determination is good. On the other hand, in step 1315, the symbol is determined as a defective symbol, in other words, a symbol having a collision. In this step, the collision detection logic processing unit 633 generates a result signal indicating that the symbol status determination is bad or collision. The result signal is used to determine time despreading and to select good / bad symbols.

  According to the present embodiment, the subcarriers are divided into two sets, conjugate transposition is performed on the second set, and a correlation value between the first set and the second set conjugate-translated is calculated. By detecting whether or not a collision has occurred by comparing the correlation value with a threshold value, it is possible to detect a collision with higher accuracy without changing or adding resources in the existing system at the symbol level. Errors can be reduced.

  Although the above description is considered as a preferred embodiment of the present invention, the present invention is not limited to the disclosed embodiment, and can be realized in various forms and embodiments.

  The present invention is suitable for use in a receiver of an ultra-wideband communication system using orthogonal frequency division multiplexing.

The figure which shows the frame format of a MB-OFDM communication system The figure which shows the pilot subcarrier and guard subcarrier frequency allocation of an OFDM symbol Diagram showing a set of values defining a pseudo-random LFSR sequence pl Diagram defining time-frequency code The figure which shows the time-frequency map about the symbol transmission on three frequency bands using the time spreading factor 2. The block diagram which shows the structure of the receiver which concerns on Embodiment 1 of this invention. The flowchart which shows the threshold value setting method which concerns on Embodiment 1 of this invention. The flowchart which shows the collision detection method which concerns on Embodiment 1 of this invention. The block diagram which shows the structure of the receiver which concerns on Embodiment 2 of this invention. The flowchart which shows the collision detection method which concerns on Embodiment 2 of this invention. The block diagram which shows the structure of the receiver which concerns on Embodiment 3 of this invention. The figure explaining the process of adding two parts of the data symbol which concerns on Embodiment 3 of this invention The figure explaining the process of adding two parts of the data symbol which concerns on Embodiment 3 of this invention The flowchart which shows the collision detection method which concerns on Embodiment 3 of this invention.

Claims (8)

A collision detection method in an ultra-wideband communication system using orthogonal frequency division multiplexing,
(A) receiving a symbol;
(B) extracting a pilot subcarrier and a guard subcarrier from the received symbol;
(C) measuring the power of the subcarrier;
(D) setting a threshold;
(E) A step of determining that a collision has occurred in the symbol when the total power of the measured subcarriers is greater than the threshold, and determining that a collision has not occurred in the symbol when the total power of the subcarriers is less than the threshold. And. The collision detection method according to claim 1, wherein step (d) calculates the threshold value by taking an average of total power of subcarriers of N OFDM symbols (N is an integer of 2 or more) received in the past. . A collision detection method in an ultra-wideband communication system using orthogonal frequency division multiplexing,
(A) receiving a symbol;
(B) extracting a pilot subcarrier and a guard subcarrier from the received symbol;
(C) dividing the subcarrier into two sets, conjugating a second set, and calculating a correlation value between the first set and the conjugate of the second set;
(D) determining that a collision has occurred in the symbol when the correlation value is greater than a threshold value, and determining that a collision has not occurred in the symbol when the correlation value is less than the threshold value. A collision detection method in an ultra-wideband communication system by frequency time spreading using orthogonal frequency division multiplexing,
(A) receiving a symbol;
(B) extracting a pilot subcarrier and a guard subcarrier from the received symbol;
(C) dividing the subcarrier into two sets, performing conjugate transposition on a second set, and calculating a correlation value between the first set and the second set subjected to the conjugate transposition,
(D) determining that a collision has occurred in the symbol when the correlation value is greater than a threshold value, and determining that a collision has not occurred in the symbol when the correlation value is less than the threshold value. A receiver for an ultra-wideband system using orthogonal frequency division multiplexing,
FFT means for performing a Fourier transform on the received signal to generate a demodulated data symbol sequence;
Power measurement means for measuring the total power of pilot subcarriers and guard subcarriers of the demodulated data symbol sequence and setting a threshold;
A collision detection logic process for determining that a collision has occurred in the symbol when the total power of the measured subcarriers is greater than the threshold, and determining that a collision has not occurred in the symbol when the total power of the subcarrier is less than the threshold. Means,
Time despreading means for performing time despreading on the demodulated data symbol sequence according to the determination result of the collision detection logic processing means. The receiver according to claim 5, wherein the power measurement unit calculates the threshold value by taking an average of total power of subcarriers of N (N is an integer of 2 or more) OFDM symbols received in the past. A receiver for an ultra-wideband system using orthogonal frequency division multiplexing,
FFT means for performing a Fourier transform on the received signal to generate a demodulated data symbol sequence;
Subcarrier detection means for dividing the demodulated data symbol sequence into two sets, conjugating a second set, and calculating a correlation value between the first set and the conjugate of the second set;
Collision detection logic processing means for determining that a collision has occurred in the symbol when the correlation value is greater than a threshold, and determining that a collision has not occurred in the symbol when the correlation value is less than the threshold;
Time despreading means for performing time despreading on the demodulated data symbol sequence according to the determination result of the collision detection logic processing means. A receiver for an ultra wide band system using frequency time spreading using orthogonal frequency division multiplexing,
FFT means for performing a Fourier transform on the received signal to generate a demodulated data symbol sequence;
An error measuring unit that divides the demodulated data symbol sequence into two sets, performs conjugate transposition on a second set, and calculates a correlation value between the first set and the second set subjected to the conjugate transposition; ,
Collision detection logic processing means for determining that a collision has occurred in the symbol when the correlation value is greater than a threshold, and determining that a collision has not occurred in the symbol when the correlation value is less than the threshold;
Frequency / time despreading means for performing frequency / time despreading on the demodulated data symbol sequence according to the determination result of the collision detection logic processing means.

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