KR20110071755A

KR20110071755A - Packet detection scheme using cross correlation and input signal power in mb-ofdm uwb system

Info

Publication number: KR20110071755A
Application number: KR1020090128403A
Authority: KR
Inventors: 김병학
Original assignee: 한국전자통신연구원
Priority date: 2009-12-21
Filing date: 2009-12-21
Publication date: 2011-06-29

Abstract

A method of finding valid packets in a digital receiver for transmitted data according to the MB-OFDM Multi-Band Orthogonal Frequency Division Multiplexing Ultra Wide Band (UWB) system standard is described. The present invention describes a packet detection method using a correlation between a received signal and a known preamble in a digital communication system using a predetermined preamble. The packet detector includes a complex cross correlator of a received signal and a known signal, calculates a moving average of the output of the complex correlator by sliding, and uses the average power of the input signal to change the amplitude of the receiver input signal. The present invention relates to an apparatus for increasing packet detection accuracy at a predetermined threshold by removing the dependency on the.

Description

Packet detection scheme using cross correlation and input signal power in MB-OFDM UWB system

The present invention relates to a packet detection method of the MB-OFDM UWB system, and more particularly, to improve the receiver packet detection performance in the variation of the input signal power and the signal-to-noise ratio of the MB-OFDM UWB system and the multipath fading channel environment. The present invention relates to a packet detection method of a MB-OFDM UWB system.

The present invention is derived from a study conducted as a part of the core technology development project of the IT new growth engine of the Ministry of Knowledge Economy and the Korea Institute for Industrial Technology Evaluation and Management (Task Management No .: 2009-S-013-01, Task Name: Wireless Video Area Network Construction) Development of intelligent Wix systems).

Multi-Band Orthogonal Frequency Division Multiplexing Ultra Wide Band (hereinafter referred to as MB-OFDM UWB) wireless communication technology uses a large amount of digital data through a wide spectrum frequency at low power in a short range. Next-generation high-speed data transmission technology for transmitting data. It is characterized by thousands of millions of low power pulses per second while using frequencies of GHz.

Compared to IEEE 802.11 and Bluetooth, which are two axes of existing wireless communication technology, it is far superior in speed and power consumption, so it is possible to connect personal computers, peripherals, and home appliances, which are located within a 10m distance from an office or home, to a high-speed wireless interface. Suitable for personal area network (PAN), it is emerging as a revolutionary wireless communication technology in the home appliance sector.

The UWB wireless communication system uses a single band method and a multi band method as a multiplexing method, especially when using a multi-band orthogonal frequency division multiplexing method (hereinafter referred to as MB-OFDM). Alternatively, an error occurs in the received signal due to the pulse noise due to the interference.

Therefore, it is efficient to determine whether the received signal is a valid signal without error and to process packet data only for the valid signal. To this end, a process of determining whether the signal is valid by analyzing only a preamble portion, which is a part thereof, without analyzing the data portion constituting the received signal at the packet detection apparatus of the receiver.

Conventionally, the cross correlation value of the signal received in this process was used as it is. That is, in the related art, the cross correlation value of the signal received by the preamble detector of the receiver is used as it is, but this method has an MB-OFDM environment in which a reception sampling error exists and a multipath fading channel exists. Causes a problem that the detection performance is degraded.

As such, missed detection when the receiver fails to detect one or more packets hinders the receiver's reliability and performance. Since the preamble detection apparatus of the conventional receiver uses the cross correlation value of the received signal as it is, packet detection performance is poor in various environments. Therefore, there is a need to improve the detection performance in the input signal power variation, the signal-to-noise ratio, and the multipath fading channel environment.

Accordingly, the present invention has been made to solve the above-described problem, MB-OFDM for effective packet detection in various environments by using the cross-correlation value of the received signal, the average value of the cross-correlation value and the received signal average power A packet detection method of a UWB system is presented.

To this end, the present invention takes a moving average of the cross-correlation values and reduces the factors that can cause the error of packet detection probability according to the input signal size, thereby effectively detecting the packet in various SNR and multipath fading channel environments. Design to work.

Packet detection method of the MB-OFDM UWB system according to an embodiment of the present invention for achieving the above object comprises the steps of: obtaining a cross-correlation value of the received signal and the preamble code value; Obtaining energy of the received signal; Obtaining a mean value of the cross-correlation values and an average value of the energy of the received signal; And determining whether a valid packet is detected by using the average value of the cross-correlation value and the average value of the energy of the received signal.

According to the present invention, by detecting a packet by using the average value of the cross-correlation value and the cross-correlation value of the received signal and the received signal average power, the cross-correlation of the signal received by the preamble detection apparatus of the conventional receiver (cross correlation) is used to improve the problems such as reception sampling error, deterioration in detection performance in a multipath fading channel environment, packet detection performance deteriorates according to the input signal power.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. The following description and the annexed drawings are provided to aid the overall understanding of the present invention, and detailed descriptions of well-known functions and configurations that may unnecessarily obscure the subject matter of the present invention will be omitted.

The systems disclosed in the present invention are generally systems for signal acquisition in a wireless communication system and are not limited to one system that illustrates a packet detection system for detecting packets in a received signal. In the description, a general MB-OFDM UWB system will be described. However, in the present invention, a configuration of a general MB-OFDM UWB system and a packet detector will be different.

1 is a block diagram illustrating the configuration of a transceiver for a typical MB-OFDM UWB system.

Referring to FIG. 1, an MB-OFDM UWB (Multi-Band Orthogonal Frequency Division Multiplexing Ultra Wide Band) system is illustrated. The receiver of the MB-OFDM UWB system can classify the RF modules 1 and 2, the AD converter 3, the packet detector 4, and the packet processor 5. The received MB-OFDM UWB signal is filtered and amplified by the RF modules 1 and 2 and transferred to the AD converter 3, which converts the amplified signal into a digital signal. The packet detector 4 determines whether the converted digital signal is a valid packet without noise or error and detects the valid packet. A detailed method for determining whether a valid packet is described later. The detected valid packet is received by the packet processor 5 through data processing such as fast Fourier transform, deinterleaving, viterbi decoding, descrambling, and the like. Will decode. Since such MB-OFDM UWB system can be easily understood from known technology, detailed description thereof will be omitted.

2 is a diagram illustrating a structure to which a packet detection method is applied according to an embodiment of the present invention.

The packet detector 4 shown in FIG. 1, that is, the packet detector shown in FIG. 2, has an energy calculator (energy calculator including MAF) 20, a cross correlator 30, and a power calculator (MAF calculator). 40), magnitude normalizer 50, correlator (correlator including MAF) 60, energy value controller 70, detector 80. Here, MAF means a moving avergae filter, which is well known and thus a detailed description thereof will be omitted. Reference numeral 10 denotes a preamble code value, and reference numeral 11 denotes a received signal. The cross correlator 30 calculates a cross correlation value between the received signal and the preamble code value 10 known to the receiver according to the MB-OFDM UWB scheme. The detector 80 detects valid packets according to the packet detection method according to the present invention. Unexplained configurations are described below.

Hereinafter, a packet detection method according to the present invention will be described in more detail with reference to the above-described configuration and the following equation.

First, the received signal 11 input to the cross correlator 30 included in the packet detector 4 may be referred to as Rx_in (k) and may be represented by Equation (1).

Here, the transmission signal p (k) can be represented by the following signal sequence.

Here, P _TFCn means preamble according to the n-th TFC. And,

Indicates a channel. The received Rx_in (k) is input to the cross correlator 30 of the packet detector 3, and this is expressed by the following equation (2).

It is necessary to calculate the energy of the received signal 11 according to the detection algorithm of the packet detector 3. That is, the energy calculator 20 performs the calculation as shown in Equation (3) below for this calculation.

Rx_in (k) and the above received signal (11)

The output of cross correlator 30 is denoted by C_temp (k). At this time, the energy of the received signal 11 is expressed as P_temp (k). These values are small or large depending on the average power of the packet detector input signal.

In the case where the above-mentioned value is large, it does not matter much, but in the case where the value is small, the probability of error is increased in the packet detection algorithm due to the uncertainty on the channel.

Therefore, it is necessary to normalize to have a constant value regardless of the size of C_temp (k) and P_temp (k). That is, normalization is performed in the size normalizer 50, which uses Equation (4) and Equation (5), and the output of the normalized value is expressed as C_norm, P_norm = P_in.

here,

Preamble 1 ~ 10 (

Is a signal string representing the symbol of.

Thereafter, the general packet algorithm determines packet detection when the following equation (6) is satisfied. Where W is the detection weighting factor.

C_in (k)> P_temp (k) * W

However, in the present invention, the signal C (k) having passed through the moving average filter of length MA_F_L (Ex: 4) for C_in (k) is obtained as in Equation (7) below. That is, the signal C (k) passing through the moving average filter of length MA_F_L (Ex: 4) for C_in (k) in the correlator 60 is obtained as shown in Equation (7) below.

The signal passing through the moving average filte of length MA_CAF_L (Ex: 128) with respect to C_in (k) is obtained by using Equation (8) below. That is, the signal passing through the moving average filter of length MA_CAF_L (Ex: 128) for C_in (k) in the energy value controller 70 obtains C_A as shown in Equation (8) below.

Subsequently, the packet detection algorithm of the present invention determines packet detection when the following equation (9) is given. Where K is the detection weighting factor. That is, the detector 80 performs a packet detection algorithm to detect the packet.

C (k)> C_A (k) * K

In addition, the UWB demodulator should be operated on signals that are input at very low transmit power. In general, a variable gain amplifier (VGA) existing in the RF stage is set such that an initial value approaches a maximum value. Therefore, when the transmitter and the receiver are in close proximity, the signal input to the packet detector is often generated due to saturation.

Figure 3a is a diagram illustrating the packet detection parameters at 20dB large signal input, SNR -1dB, Figure 3b is a diagram illustrating the packet detection parameters at 20dB large signal input, SNR 19dB, Figure 3c is a diagram of 20dB large signal input, SNR A diagram illustrating a packet detection parameter at 39 dB. 3A is a case where SNR is -1db in a fading channel, FIG. 3B is a case where SNR is 19db in a fading channel, and FIG. 3C is a case where SNR is 39db in a fading channel.

If a signal 20dB larger than the Auto Gain Control is correctly input (when the transmitter and the receiver are close to each other), C_in (k) (blue) and C_A (k) as shown in the three graphs shown in FIG. * K (red)

Here, three graphs shown in FIG. 3 illustrate cases where the SNRs of the fading channel are -1, 19, and 39 dB, respectively. At this time, even if the signal with a high SNR is 20dB larger than the input signal expected, the noise is increased by 20dB, the signal can be seen that the phenomenon of saturation occurs. Thus, it can be seen that the ratio between the peak point and the non-peak point in the blue signal shown in FIG. 3 is not large.

In addition, when the SNR is low, it can be seen that C_in (k) (blue) and C_A (k) * K (red) have almost close values at the point where C_in (k) is the peak. In this case, the probability of miss detection of a packet increases. In order to solve this problem, the moving avergae filter (MAF) for the input signal power can be corrected as shown below. That is, the power calculator 40 may perform the correction according to Equation 10 below to correct the K value.

If the value of Equation (10) is greater than a certain level, the value is changed as C_A (k) = C_A (k) * weight, and the detector 80 performs packet detection according to Equation (9) described above.

4A is a diagram illustrating packet detection parameters at 20dB small signal input, SNR -1dB, and FIG. 4B is a diagram illustrating packet detection parameters at 20dB small signal input, SNR 19dB.

If the value of "Equation (10) described above with reference to FIG. 4 is greater than a specific level, C_A (k) = C_A (k) * weight is changed, and the detector 80 according to the above Equation (9). Packet detection. For example,

If (purple) is greater than 1024, it changes to equation (11) to perform packet detection. That is, the energy value controller 70 changes the equation (11), and the detector 80 detects the packet accordingly.

C_A (k) = C_A (k) * 0.75

In addition,

If (purple) is larger than 512 and smaller than 1024, packet detection can be performed by changing to the following equation (12). That is, the energy value controller 70 changes to Equation 12, and the detector 80 detects the packet accordingly.

C_A (k) = C_A (k) * 0.875

5 is a diagram illustrating an example of a packet detection process according to the present invention. Here, the respective constituent functions of FIG. 2 described above will be described according to the displayed flowchart.

As shown in FIG. 5, the packet detection method according to the embodiment of the present invention receives a received signal (S10).

Subsequently, the received Rx_in (k) is input to the cross correlator 30 of the packet detector 3 and is represented by Equation (2) (S12). The energy of the received signal 11 is calculated in accordance with the detection algorithm of the packet detector 3.

At this time, the energy of the received signal 11 is expressed as P_temp (k). These values are small or large depending on the average power of the packet detector input signal. In the case where the above-mentioned value is large, it does not matter much, but in the case where the value is small, the probability of error is increased in the packet detection algorithm due to the uncertainty on the channel.

Thus, normalization is performed to have a constant value regardless of the sizes of C_temp (k) and P_temp (k) (S13). That is, normalization is performed in the size normalizer 50, which uses Equation (4) and Equation (5), and the output of the normalized value is expressed as C_norm, P_norm = P_in.

Subsequently, a signal C (k) passing through a moving average filter of length MA_F_L (Ex: 4) with respect to C_in (k) is obtained as in Equation (7) below (S14). That is, the signal C (k) passing through the moving average filter of the length MA_F_L (Ex: 4) with respect to C_in (k) in the correlator 60 is obtained as shown in Equation (7).

Subsequently, when the packet detection algorithm of the present invention is equal to the above expression (9), it determines packet detection. Where K is the detection weighting factor. That is, the detector 80 performs a packet detection algorithm to detect a packet (S15 to S27).

In this case, when the SNR of the received signal is low, the probability of miss detection of a packet increases. In order to solve this problem, the moving avergae filter (MAF) for the input signal power is performed as in Equation (10) above to correct the K value (S30 to S34).

In summary, in the present invention, when the first packet detection is completed, the flag_cnt is changed from 0 to 1 and the packet detection is performed after 160 to 175 samples for TFC3, 4, 5, 6, and 7 as shown in the above equations. In case of TFC1,2, packet detection is confirmed after 490 ~ 505 samples, and in case of TFC8,9,10, packet detection is checked after 325 ~ 340 samples.

In the case of TFC1, 2, 5, 6, 7, if packet detection is not performed after 160 to 175 samples, packet detection is initialized (cnt_limit = 0, flag_cnt = 0) as shown in FIG. Function reduces the probability of false alarms. Therefore, the number of preambles for packet detection is two for TFC3, 4, 5, 6, and 7, four for TFC1 and 2, and three for TFC8, 9 and 10.

cnt_limit is a value that counts the number of input samples after the first packet detection is performed, and flag_cnt is the number of consecutive packet detections that occur. According to an embodiment, the ranges of values 160 to 175, 490 to 505, and 325 to 340 may be adjusted, the input variables S10 to S12 of the upper left of FIG. 5 may be changed, and the power calculator output S31 of the upper right. The variable of the P calculation method using ˜S37) can also be changed.

6 is a diagram illustrating a packet detection error rate (PDER) in the fading channel (CM1) when a 20dB signal is large, Figure 7 is a packet detection error rate (PDER) in the fading channel (CM1) when a signal 20dB large is input. 8 is a diagram illustrating a packet detection error rate (PDER) in the fading channel (CM1) when a small signal 20dB input, Figure 9 is a diagram showing a packet detection error rate (PDER) in the fading channel (CM1) when a small signal 20dB is input, It is a figure which shows the packet detection error rate PDER.

As shown in Figure 6, it can be seen that the performance of the invention is improved. It can be seen that the packet detection error probability suggested by the present invention is smaller than other methods according to K (threshold).

FIG. 6 illustrates the above-mentioned equations (10-12) and the upper right side of FIG. 5 with and without applying the above, and the packet error probability in the general packet detection method. Here, the x-axis of FIG. 6 means K (threshold) of Equation (9). 6 denotes a packet detection scheme proposed by the present invention, C does not apply the above-described equations (10 to 12), and G denotes a general packet detection method algorithm. Moreover, 19 dB or 39 dB represents SNR.

6 and 7 illustrate a packet detection error probability (PDER) for a signal input 20 dB larger than a receiver expected input signal. 6A and 6B are diagrams under the same conditions, and FIG. 6B is an enlarged view of the probability axis of FIG. 6A in a section of 0 to 0.1. 7A and 7B are diagrams under the same conditions, and FIG. 7B is an enlarged view of the probability axis of FIG. 7A in a section of 0 to 0.1. In FIG. 6 and FIG. 7, the frequency error for the simulation was 80 kHz.

8 and 9 illustrate a packet detection error probability PDER for an input signal 20 dB smaller than a receiver expected input signal (where the performance of P_ and C_ in FIGS. 8 and 9 are the same).

As described above, the present invention has described a method for finding a valid packet from a digital receiver for data transmitted according to the MB-OFDM Multi-Band Orthogonal Frequency Division Multiplexing Ultra Wide Band (UWB) system standard. In other words, a packet detection method using a correlation between a received signal and a known preamble in a digital communication system using a predetermined preamble is proposed. The packet detector includes a complex cross correlator of a received signal and a known signal, calculates a moving average of the output of the complex correlator by sliding, and uses the average power of the input signal to change the amplitude of the receiver input signal. By eliminating the dependency on the B, it increases the packet detection accuracy at a predetermined threshold.

As described above, the packet is detected using the average value of the cross correlation value, the cross correlation value of the received signal, and the received signal average power, so that the signal received by the preamble detection apparatus of the conventional receiver is correlated. (cross correlation) is used to improve the problems such as reception sampling error, deterioration in detection performance in a multipath fading channel environment, packet detection performance deteriorates according to the input signal power.

Although the preferred embodiments of the present invention have been shown and described above, the present invention is not limited to the specific embodiments described above, and the present invention may be commonly used in the art without departing from the gist of the present invention as claimed in the claims. Various modifications can be made by those skilled in the art, and these modifications should not be individually understood from the technical spirit or the scope of the present invention.

1 is a block diagram showing the configuration of a transceiver for a typical MB-OFDM UWB system;

3A is a diagram illustrating packet detection parameters at 20 dB large signal input, SNR -1 dB.

3B is a diagram illustrating packet detection parameters at 20 dB greater signal input, SNR 19 dB.

3C is a diagram illustrating packet detection parameters at 20 dB greater signal input, SNR 39 dB.

4A is a diagram illustrating packet detection parameters at 20 dB small signal input, SNR -1 dB.

4b illustrates a packet detection parameter at 20 dB small signal input, SNR 19 dB.

5 illustrates an example of a packet detection procedure according to the present invention.

6 is a diagram illustrating a packet detection error rate (PDER) in a fading channel (CM1) when a signal having a large 20dB is input.

FIG. 7 is a diagram illustrating a packet detection error rate (PDER) in a fading channel (CM1) when a signal of 20 dB greater is input.

8 is a diagram illustrating a packet detection error rate (PDER) in the fading channel (CM1) when a small signal of 20dB is input.

9 is a diagram illustrating a packet detection error rate (PDER) in the fading channel (CM1) when a small signal of 20dB is input.

* Description of the symbols for the main parts of the drawings *

4: packet detector 20: energy calculator

30: cross correlator 40: power calculator

50: size normalizer 60: correlator

70: energy value controller 80: detector

Claims

As a packet detection method of an MB-OFDM UWB system,

Obtaining a cross-correlation value between the received signal and the preamble code value;

Obtaining energy of the received signal;

Obtaining an average value of the cross-correlation value and an energy value of the received signal; And

And detecting the packet by determining whether the packet is valid using the average value of the cross-correlation value and the average value of energy of the received signal.