Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W16/00—Network planning, e.g. coverage or traffic planning tools; Network deployment, e.g. resource partitioning or cells structures
  • H04W16/14—Spectrum sharing arrangements between different networks

Definitions

• the present invention relates to the field of communications technologies, and in particular, to a spectrum sensing method and system. Background technique
• the cognitive radio system In cognitive radio technology, it is generally assumed that the authorized system on a licensed frequency band works normally, and the cognitive radio system detects the spectrum usage of the authorized system; when the authorized system is found to be inoperative and the licensed frequency band is idle, the cognitive radio system uses This licensed band continues to detect the operating status of the licensed system in this band. Once the authorized system is found to resume operation, the cognitive radio system will exit the licensed band and transfer to the new licensed band to continue working.
• Spectrum Sensing discovers the idle spectrum by detecting wireless RF (radio frequency) signals; its Spectrum Analysis is measured by perceived results and wireless RF environment.
• Information analysis idle spectrum can be cognitive The line system provides communication capacity and the like; its Spectrum Decision determines the wireless parameters used by the cognitive radio system based on the perceived results and the analysis results.
• spectrum sensing is a prerequisite for the work of cognitive radio systems.
• the spectrum sensing problem is actually a binary detection problem.
• an authorization system such as a television system.
• the signal of the authorization system received at the spectrum sensing receiver is s( n ), the noise is v( n ), and the total received signal is x. ( n ) ;
• the authorization system is working, it is HI; suppose that if the authorization system does not work, it is H0; based on this, the received signals can be:
• an energy detection method may be used, that is, directly counting the energy of a signal received at a certain frequency point, and determining whether the frequency point is occupied according to the intensity of the energy; the process of energy detection is as follows: A total of N DTMB (Digital Television Multimedia Broadcasting) samples are captured in the window, and the energy check statistics obtained directly in the detection time window are: It should be noted that for a cognitive radio system operating in the broadcast television band, it is necessary to accurately detect whether there is a broadcast television signal at a certain frequency point, thereby judging the availability of the frequency point; for the DTMB system of the broadcast television frequency band, as shown in FIG.
• the basic unit of the data frame structure is a signal frame, and the signal frame is composed of a frame header and a frame body two-part time domain signal; the superframe is defined as a group of signal frames, the framing is defined as a set of superframes, and the top layer of the frame structure is a day frame.
• the signal structure is periodic and synchronized with natural time; the baseband symbol rate of the frame header and frame body signals is the same (7.56Msymbols/s); the frame header portion is composed of PN (pseudo-noise) sequence, and the frame header length can be There are three options; the frame header signal is modulated by the same 4QAM (Quadature Amplitude Modulation) of I and Q; the frame body part contains 36 symbols of system information and 3744 symbols of data, a total of 3780 symbols; The frame length is 500 ⁇ s (3780 X 1/7.56 ⁇ s).
• the frame sequence used in frame header mode is defined as a cyclically extended 8-bit m-sequence, which can be implemented by an LFSR (Linear Feedback Shift Register), which is "0" to +1 value and " ⁇ to -1 value”.
• LFSR Linear Feedback Shift Register
• the mapping is transformed into a non-returned binary symbol; the initial condition of the LFSR determines the phase of the generated PN sequence; there are 225 signal frames in a superframe; the frame header of each signal frame in each superframe uses a different phase
• the PN signal is used as the signal frame identifier.
• phase PN420 sequences can be generated, from sequence number 0 to sequence number 254; 225 PN420 sequences are selected in this standard, from sequence number 0 to sequence number 224; In order to minimize the correlation of adjacent serial numbers, the signal frame sequence sequence and the initial state of the LFSR are formed through computer optimization; the LFSR is reset to the initial phase of sequence number 0 at the beginning of each superframe.
• the frame header mode 2 is truncated by a 10th-order maximum-length pseudo-random binary sequence, and the length of the frame header signal is 595 symbols, which is the first 595 chips of the column of length 1023; the pseudo-random sequence generated by FIG. 2
• the first 595 chips, the "0" to +1 value and the "1" to -1 value map are transformed into non-returned binary symbols; there are 216 signal frames in one superframe; each signal in each superframe
• the frame header of the frame uses the same PN sequence.
• the PN sequence used in frame header mode 3 is defined as a cyclically extended 9P-m sequence, which can be implemented by an LFSR, which is transformed into a non-return-to-zero binary symbol by a "0" to +1 value and a mapping of " ⁇ to -1 value.”
• the initial condition determines the phase of the generated PN sequence, a total of 200 signal frames in a superframe, and the frame header of each signal frame in each superframe uses a PN signal of a different phase as a signal frame identifier; based on the LFSR
• 511 PN945 sequences of different phases can be generated, from sequence number 0 to sequence number 510; 200 PN945 sequences are selected from the standard, from sequence number 0 to sequence number 199; in addition, in order to minimize the correlation of adjacent sequence numbers,
• the computer optimizes the selection, the sequence of signal frame numbers formed and the initial state of the LFSR.
• the LFSR is reset to the initial phase of sequence number 0 at the beginning
• the spectrum sensing problem for broadcast television signals in cognitive radio systems requires high detection sensitivity (for example, a cognitive radio system operating in the broadcast television band needs to perceive a signal of -114 dBm), according to receiver characteristics.
• the spectrum sensing algorithm is required to satisfy the SNR (Signal to Noise Ratio) greater than -22 dB, and the authorized system signal is correctly detected with a detection probability greater than 0.9, and the false alarm probability is required to be less than 0.1; in addition, the spectrum sensing of the cognitive radio system is recognized
• the interference of the radio system ie, when detecting the current working frequency, whether there is an authorized system working, when the wireless RF signal receiving the cognitive radio system operating frequency is used for spectrum sensing, the RF of the cognitive radio system communication is also received. Signal), so the current spectrum sensing adopts the strategy of silent period sensing, that is, when the cognitive radio performs spectrum sensing, the cognitive radio system stops working and remains silent.
• the inventors have found that at least the following problems exist in the prior art: Since the cognitive radio system needs to remain silent in the spectrum sensing process, the cognitive radio system cannot perform normal communication during the spectrum sensing process, and wastes Radio resources; Further, for the energy detection algorithm, the detection performance is not high, and the sensitivity sensitivity requirement cannot be met, which requires a longer detection time overhead.
• energy detection is susceptible to interference from other wireless signals, such as adjacent channel leakage interference of TV or adjacent channel leakage interference of cognitive radio systems or interference from remote systems, etc., detection in such low SNR environments, energy The detection of the influence of noise uncertainty caused by factors such as temperature leads to the non-robustness of the detection.
• the detection performance of the DTMB system synchronization method is not high, and the time required to reach the sensitivity requirement is relatively large, which is not applicable to the spectrum sensing of the DTMB signal. Summary of the invention
• the embodiments of the present invention provide a spectrum sensing method and system to improve spectrum sensing performance and save time consumption of spectrum sensing.
• an embodiment of the present invention provides a spectrum sensing method, including: a cognitive radio system receiving a signal during one or more discrete silent periods, and processing the received signal to obtain a baseband signal;
• the cognitive radio system obtains a detection statistic based on the baseband signal, and according to the check The measured statistic determines the spectrum sensing result.
• the embodiment of the invention provides a spectrum sensing system, including:
• a first acquiring module configured to receive a signal during one or more discrete silent periods, and process the received signal to obtain a baseband signal
• a second acquiring module configured to obtain a detection statistic according to the baseband signal
• a determining module configured to determine a spectrum sensing result according to the detection statistic.
• the embodiment of the invention has at least the following advantages:
• the spectrum sensing method can obtain robust detection performance under a certain interference environment, and the detection performance is high; the spectrum sensing can be completed in a short time, thereby saving the detection time overhead; and being able to be discrete The spectrum sensing detection is completed in multiple silent periods, so that it is more flexible for various cognitive radio systems.
• FIG. 1 is a schematic structural diagram of a data frame of a DTMB system in the prior art
• FIG. 2 is a schematic diagram of three optional frame header modes and corresponding signal frame structures in the prior art
• FIG. 3 is a schematic diagram of a principle of a DTMB system synchronization method in the prior art
• FIG. 5 is a schematic block diagram of detecting by using a frame header in the first embodiment of the present invention.
• FIG. 6 is a schematic block diagram of detecting by using multiple frame headers in Embodiment 1 of the present invention.
• FIG. 7 is a schematic structural diagram of a spectrum sensing system according to Embodiment 3 of the present invention. detailed description
• Embodiment 1 of the present invention provides a spectrum sensing method for implementing in a cognitive radio system.
• Spectrum sensing as shown in Figure 4, the method includes the following steps:
• Step 401 A cognitive radio system (such as a spectrum sensing module of a cognitive radio system) receives signals during one or more discrete silent periods, and processes the received signals to obtain a baseband signal.
• a cognitive radio system such as a spectrum sensing module of a cognitive radio system
• one or more discrete silent periods are specifically one or more GPs of the TD-LTE system. (protected time slot); or, is one or more discrete TD-LTE silent subframes.
• Step 402 The cognitive radio system obtains a detection statistic according to the baseband signal, and determines a spectrum sensing result according to the detection metric.
• the cognitive radio system obtains detection statistics according to the baseband signal, including: the cognitive radio system filters the baseband signal through the filter, and performs modulo processing on the filtered result; the cognitive radio system selects the modulo processing The maximum value in the subsequent results is calculated as the average of the results after the modulo processing; the cognitive radio system obtains the detection statistic based on the maximum value and the average value.
• the cognitive radio system filters the baseband signal through the filter, including: the cognitive radio system performs zero-padding processing on the baseband signal, and filters the baseband signal after the zero-padding process by the filter; wherein, the zero-padding The number is determined by the filter length.
• the signal is a signal having a frame header plus frame body (or a known sequence plus data sequence) structure, and may be a signal having multiple frame header (known sequence) modes, and the signal includes But not limited to digital TV multimedia broadcast DTMB signals.
• the subsequent description uses the signal as a DTMB signal as an example, and will not be described again for other types of signals.
• the baseband signal is the DTMB baseband signal
• the DTMB signal corresponds to the frame header mode PN420, the frame header mode PN595, and the frame header mode PN945.
• the frame header is In mode PN420
• the frame header length N is 420
• the signal frame length M is 4200.
• the frame header mode PN595 the frame header length N is 595
• the signal frame length M is 4375
• the frame header mode PN945 the frame header length is N.
• the signal frame length M is 4725.
• the cognitive radio system can obtain a DTMB baseband signal x ( n ) whose signal is at a symbol rate of 7.56 MHz; and the DTMB baseband signal can pass the received signal (a signal received during one or more discrete silent periods) The sampling filtering is obtained. In the embodiment of the present invention, how to process the received signal to obtain the DTMB baseband signal is not described.
• the cognitive radio system may be one or more GPs of the TD-LTE system for one or more discrete silent periods (one or more discrete silent periods for the TD-LTE system) Or, the reception of the DTMB signal is completed in one or more discrete TD-LTE silence subframes, and the DTMB baseband signal is obtained.
• Sufficient DTMB signals are captured for detection during a discrete silent period.
• the detection process includes: The cognitive radio system (or its spectrum sensing module) processes the received signal to obtain the DTMB baseband signal; passes the DTMB baseband signal through 3 filters.
• the tap coefficients of the three filters are respectively a function of the entire frame header sequence or a partial frame header sequence; the three filter output results are subjected to modulo processing; for each filter output modulo result, the largest one is selected.
• the decision threshold is a function of the target false alarm probability, DTMB frame length, filter length
• the result of the logic false or the first identifier such as 0
• the authorization system is not working at this time, no DTMB signal
• the logical result or the second identifier such as 1).
• Work, there is DTMB signal logically or merge the three judgment results to get the final judgment result.
• the detection process includes: a process based on a discrete silent period, cognitive radio system (or its spectrum) Perceptual module) repeatedly performs processing in a discrete silent period during K discrete silent periods (ie, the cognitive radio system processes the received signal to obtain the DTMB baseband signal; passes the DTMB baseband signal through 3 filters, 3 filters
• the tap coefficients of the device are respectively a function of the entire frame header sequence or a partial frame header sequence; the three filter output results are subjected to modulo processing; for each filter output modulo result, the maximum value thereof is selected, and the average is calculated.
• the value is obtained by obtaining the three detection statistics by the maximum value; the three detection statistics are respectively determined, and the decision threshold is the target false alarm probability, the DTMB frame length, the filter length, and the number of discrete silent periods K. Function) to get 3K decisions (logical false or first identifier, or logically true or The second identifier); logically or merging the above 3K judgment results to obtain a final judgment result.
• 3K decisions logical false or first identifier, or logically true or The second identifier
• logically or merging the above 3K judgment results to obtain a final judgment result.
• the detection process includes: The cognitive radio system (or its spectrum sensing module) receives signals during a discrete silent period , processing the received signal to obtain a DTMB baseband signal;
• the DTMB baseband signal is passed through a filter to obtain a filtering result of each segment of the signal, and the tap coefficient of the filter is a function of a frame header sequence of the frame header mode ⁇ 420 at initialization or a partial frame header sequence of the frame header mode ⁇ 420 at initialization;
• the filtering result is subjected to modulo processing; marking the segment filtering and taking the position of the maximum value of the modulo result, and combining the filtering results corresponding to the maximum value positions, and modulating the combined result to obtain a value a; Summing and modulo, obtaining the value b; obtaining the detection statistic by a/b; determining the detection statistic and the decision threshold (the decision threshold is the target false alarm probability, the DTMB frame length, the filter length, and the number of silent periods K) a function, obtaining a logical false or first identified decision result, or a logically true or second identified decision result; repeating the above steps twice, the filter tap coefficients are respectively initialized frame headers during two repeated executions
• Case 1 the block diagram shown in Figure 5, which uses a frame header for detection, that is, enough DTMB signals are captured for detection during a discrete silent period.
• the cognitive radio system obtains the detection statistic according to the baseband signal further includes: Step 1.
• the cognitive radio system arbitrarily intercepts the DTMB of the M symbol length
• the cognitive radio system fills the signal ⁇ ( ⁇ ) to zero to obtain the signal u( n ), and the number of zeros is filtered according to The length of the device is determined.
• Step 3 The cognitive radio system filters the signal u (n) through three filters, and the filtered output is:
• the cognitive radio system performs the following modulo processing on the filtered output (ie, each sample result):
• the cognitive radio system determines the spectrum sensing result according to the detection statistic, including:
• the electrical system performs the following judgment by using three detection statistic and a decision threshold:
• ⁇ Represents logical false or first identification (0), at which point the authorization system is considered to be not working, no DTMB signal;
• D i represents logical truth or second identification (1), at which point the authorized system is working, there is a DTMB signal;
• the decision threshold is determined according to the target false alarm probability, M value, and L value.
• Step 7 The cognitive radio system combines the decision result D ( ", D ( , ⁇ logically OR (or) to obtain the final decision result 1 ⁇ 01 ⁇ 1 ⁇ ), ⁇ 1 , 2 , 3 , and based on the decision result D determines the spectrum perception result.
• Case 2 In this case, multiple frame headers are used for detection, and detection is performed by an OR combining method.
• the cognitive radio system obtains the detection statistic according to the baseband signal, and further includes: Step 1.
• the cognitive radio system obtains the same length of the K segment in the DTMB baseband signal x ( n ) corresponding to the plurality of discrete silent periods.
• Step 2 The cognitive radio system processes each DTMB of the K-segment DTMB baseband signal according to the processing of the DTMB baseband signal x ( n ) corresponding to a discrete silent period (ie, step 1 - step 5 of the case).
• the baseband signals are processed separately to obtain corresponding 3*K detection statistics.
• Step 4 The cognitive radio system logically logically 3*K decision results D(W , D( 2'k ), D( 3'k )
• the cognitive radio system obtains the detection statistic according to the baseband signal, and further includes: Step 1.
• the cognitive radio system obtains the same length of the K segment in the DTMB baseband signal x ( n ) corresponding to the plurality of discrete silent periods.
• Step 2 The cognitive radio system fills the intercepted DTMB baseband signal x W ( n ) to obtain a signal.
• the number of zeros is determined by the length of the filter.
• the cognitive radio system marks m corresponding to the maximum value of the modulo result corresponding to each k by:
• Step 6 The cognitive radio system combines the matched filtered output results corresponding to the m values of the above markers by the following manner, and performs modulo processing on the combined results:
• Step 7 The cognitive radio system averages the matched filtering result of the k-segment signal by the following method, and performs modulo processing on the averaged result:
• Step 8 The cognitive radio system takes the maximum value of step 6 (that is, the result of modulo processing the combined result) and the average value of step 7 (that is, after modulo processing the result after averaging) The result is divided by the following test statistic: mean P]
• Mean P mean p Further, the cognitive radio system determines the spectrum sensing result based on the detection statistic, including: Step 9. The cognitive radio system performs the detection statistic (ie, the three detection statistic in step 8) and the decision threshold. The following judgment:
• D ⁇ represents logical false or first identification (0), at this time, it is considered that the authorization system is not working, no DTMB signal; D i" represents logical truth or second identification (1) At this time, it is considered that the authorization system is working, there is a DTMB signal; for the decision threshold, and the decision threshold is determined according to the target false alarm probability, K value, M value, and L value.
• the foregoing spectrum sensing detection method may be completed in other discrete silent periods, or may be completed in a continuous silent period for a long time; in addition, it may be completed in the GP of TD-LTE, and the specific implementation is implemented.
• the method is that the spectrum sensing module keeps synchronization with the TD-LTE system and receives the DTMB signal in the GP of the TD-LTE. If a single GP is used for the detection, the usage is used. In the detection method of one, if multiple GPs are used for detection, the detection methods of cases two and three are used.
• the spectrum sensing of current cognitive radio faces the problem of detecting weak signals, requiring high detection performance of the algorithm, and requiring the sensing algorithm to quickly detect the authorized system signal, requiring less detection time overhead; in addition, spectrum sensing may be authorized
• the interference of the system and even the cognitive radio system requires the perceptual algorithm to have a relatively high robustness.
• the spectrum sensing algorithm is energy detection, but the energy detection is difficult to meet the requirements of detection performance and detection time overhead, and may be affected by other interferences, thereby causing a serious decline in detection performance; and the synchronous detection method of the broadcast television system Not fully suitable for spectrum sensing of cognitive radio systems.
• the embodiment of the present invention provides a spectrum sensing method for a DTMB signal, which effectively detects a DTMB signal by detecting a DTMB frame header signal; the method can obtain a higher relative energy detection algorithm. Detecting performance to achieve weak signal detection requirements; and the method can effectively combat the influence of wireless environment interference and system noise level changes on spectrum sensing, thereby greatly improving the robustness of the cognitive system and obtaining robustness under certain interference environments.
• the detection performance is high, and the detection performance is high; the method is applicable not only to the spectrum sensing during the continuous long-term silent period, but also to the sensing of multiple discrete short-time silent periods, and the spectrum sensing can be completed in a short time. Thereby, the time overhead of detection is saved; and the spectrum sensing detection can be completed in a plurality of discrete silent periods, thereby being more flexible and applicable to various cognitive radio systems.
• Embodiment 2 of the present invention provides a spectrum sensing method, which is assumed that TD-LTE has a cognitive radio function, that is, a TD-LTE base station has a cognitive module to discover available DTMB broadcast system idle frequency bands,
• the special subframe configuration of TD-LTE is configured as 0, and the spectrum sensing process includes:
• Step 1 The spectrum sensing module on the TD-LTE base station side maintains downlink synchronization with the TD-LTE base station;
• Step 2 The spectrum sensing module receives the DTMB signal of a certain frequency point in the GP of the TD-LTE;
• Step 3 Spectrum sensing module pair The received signal is filtered and sampled to obtain a symbol rate of
• S PN42 2 0° 0W , SpN595 (') , SpN945 (') are the initial frame header sequences of the three frame header modes respectively; Step 5 ⁇ for each sample result of the filter output:
• D Representing "0”, D i stands for " ⁇ ; for the decision threshold, the decision threshold is determined according to the target false alarm probability (0.1), ⁇ value, L value;
• Step 8 Perform the above steps 2 - 7 in 5 consecutive TD-LTE GPs to obtain 15 decision results 1 ⁇ ', ⁇ 1 , 2 , 3 ; 1 ⁇ 1 ,..., 5 ;
• the embodiment of the present invention further provides a spectrum sensing system (which may specifically be a cognitive radio system, or a spectrum sensing module in a cognitive radio system), as shown in FIG.
• the system includes:
• a first acquisition block 11 for receiving a signal during one or more discrete silent periods, and processing the received signal to obtain a baseband signal
• a second obtaining module 12 configured to obtain a detection statistic according to the baseband signal
• the determining module 13 is configured to determine a spectrum sensing result according to the detection statistic.
• the second obtaining module 12 is specifically configured to filter the baseband signal by using a filter, and perform modulo processing on the filtered result; select a maximum value in the result of the modulo processing, and calculate and take An average of the results after the modulo processing; and obtaining a detection statistic based on the maximum value and the average value.
• the second obtaining module 12 is further configured to perform zero-padding processing on the baseband signal, and perform filtering processing on the baseband signal after zero-padding processing by using the filter; wherein, the number of zero-padding is performed by the filter The length is determined.
• the signal is a signal having a frame header plus frame structure, and the signal includes a digital television multimedia broadcast DTMB signal.
• the baseband signal is the DTMB baseband signal x ( n ), and DTMB
• the signal corresponds to a frame header mode PN420, a frame header mode PN595, and a frame header mode PN945.
• the second obtaining module 12 is further configured to arbitrarily intercept M in a DTMB baseband signal x ( n ) corresponding to a discrete silent period.
• the filter is filtered and the filtered output is:
• the determining module 13 is further configured to: determine, by using the detection statistic and the threshold:
• the decision result 15 , D , D is obtained, where W represents a logical false or first identifier, represents a logical truth or a second identifier, is a decision threshold, and the decision threshold is determined according to a target false alarm probability, an M value, and an L value. ;
• the second obtaining module 12 is further configured to obtain a DTMB baseband signal x( k ), 3 ⁇ 4 0, . 1 of the same length of the K segment in the DTMB baseband signal x ( n ) corresponding to the plurality of discrete silent periods.
• each DTMB baseband signal in the K-segment DTMB baseband signal is processed separately to obtain a corresponding 3*K detection statistics;
• the baseband signal is a DTMB baseband signal x ( n )
• the DTMB signal corresponds to a frame header mode PN420, a frame header Mode PN595, frame header mode PN945;
• the second obtaining module 12 is further configured to obtain a DTMB baseband signal x( k ), 3 ⁇ 4 0, . 1 of the same length of the K segment in the DTMB baseband signal x ( n ) corresponding to the plurality of discrete silent periods. (, and each segment of the signal length is M; the DTMB baseband signal x(k )( n ) is padded to obtain the signal u(k )( n ), and the signal is 1 ⁇
• the three filters are filtered and the filtered output is:
• the matching filtering results of the k-segment signals are averaged as follows, and the averaging results are subjected to modulo processing:
• the result of the modulo processing on the combined result is divided by the result of the modulo processing on the averaging result, and the following detection statistic is obtained: mean, mean, mean, the determination module 13, further Used to pass the detection statistic and the decision threshold as follows
• the tap coefficients of the filter are a function of the entire frame header sequence or a partial frame header sequence, and the tap coefficients of the filter are specifically:
• the one or more discrete silent periods are specifically one or more guard slots GP of the TD-LTE system; or, for one or more discrete TD-LTE silent subframe.
• the modules of the device of the present invention may be integrated into one or may be deployed separately.
• the above modules can be combined into one module, or they can be further split into multiple sub-modules.
• the present invention can be implemented by means of software plus a necessary general hardware platform, and of course, can also be through hardware, but in many cases, the former is a better implementation. the way.
• the technical solution of the present invention which is essential or contributes to the prior art, may be embodied in the form of a software product stored in a storage medium, including a plurality of instructions for making a A computer device (which may be a personal computer, server, or network device, etc.) performs the methods described in various embodiments of the present invention.
• modules in the apparatus in the embodiments may be distributed in the apparatus of the embodiment according to the embodiment, or may be correspondingly changed in one or more apparatuses different from the embodiment.
• the modules of the above embodiments may be combined into one module, or may be further split into a plurality of sub-modules.

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