KR20070048553A - Efficient spectrum sensing method and procedure in cognitive radio environment - Google Patents

Abstract

The present invention is characterized in that it consists of a sensing procedure at the time of terminal initialization and a sensing time at the Quiet Time. When the terminal initially attempts to access the base station, the detection process performs detection over the entire band to be detected. In order to reduce the detection time, the signal is first decoded to determine whether it is a radio recognition technology signal or not. If the signal of the base station to which the terminal can be connected, select it as a frequency that can communicate with the base station, and if it is not a signal of the radio recognition technology to determine whether the user's signal or the empty signal occupying the channel first Repeatedly characterized by a method for detecting the entire frequency band.

During Quiet Time, it is first determined whether the user is using the channel group currently being used by the wireless cognitive system, and after this process, the priority is made in the candidate frequency band which is not used by the wireless cognitive system but can be used later. Characterized by the process of determining whether or not to use the user.

Cognitive Radio, Spectrum Sensing, Terminal initialize, Quiet Time

Description

Efficient SPECTRUM SENSING METHOD AND PROCEDURE IN COGNITIVE RADIO ENVIRONMENT

1 illustrates a simplified function of a radio recognition technology.

2 is a diagram illustrating problems that may occur when using a wireless recognition technology.

3 is a block diagram showing a spectrum detection method and procedure according to the present invention

4 is a flowchart illustrating a spectrum sensing method and procedure according to the present invention.

The present invention provides a method for protecting a user's use of a corresponding frequency by paying and using a frequency fee in a cognitive radio that occupies and uses an empty frequency. It is about how to detect and find an empty frequency, and when using an empty frequency, first of all the procedure / method of detecting that the user is starting to use that frequency band.

Due to the rapidly evolving various forms of wireless communication technology, commercialization is limited as the frequency band saturates, and it is allocated to solve this problem especially in an environment where there is little room for using a low frequency band, but it is not actually used. Wireless cognitive technology has been proposed that can detect empty frequencies and share frequencies efficiently.

Therefore, the structure of the radio recognition technology has a characteristic of additionally having a frequency detection function and its operation technology in a general wireless communication system. Figure 1 is a simplified structure for this characteristic (101) is a block for converting a high frequency signal into a low band signal, (103) is the received signal processing portion in the baseband and (102), (104) This is an addition to the wireless communication system. The features of this block technology include empty frequency detection (physical layer), adaptive frequency allocation and use (physical layer, radio resource measurement and media access control layer), and the user's use of frequency. It can be classified as a function of emptying and moving to a different frequency band (radio resource measurement and media access control layer).

One of the advantages of this wireless recognition technology is that it is cheaper than the existing wireless communication service by using the radio frequency band at economical cost, and it is a wireless channel management, distribution, and interference detection technology for multiple channels in the future. It is likely to be used complementary to each other in conjunction with communication. For example, wireless cognitive technology is a good alternative to efficiently transmit high-speed data without causing frequency interference in shaded areas that occur in cellular environments or rural areas where cell sizes must be increased. However, the additional complexity to implement the radio recognition technology of the base station, the stability of the service caused by using only the empty frequency, etc. should be considered.

Among them, the function similar to detecting the empty frequency has been studied in many communication parts such as Radar, and the concept of many parts is established accordingly. However, if conventional signal sensing techniques detect the empty frequency or occupied signal in a given channel, the main purpose is to monitor the wide frequency band and find out which frequency band the system can use. Its main purpose is to find out if a user first appears on the frequency, which is a little different from conventional spectrum sensing.

Breaking down some of its features, as described above, it should support the ability to detect all frequency bands that a system can use, rather than one or two frequency bands. And when using this empty frequency band, first of all, the user needs to continuously monitor it during use in order not to interfere with the frequency occupied by the user. Due to this feature, if the frequency band to be detected increases, it is easy to secure multiple channels, but the development of an efficient system is needed because of the problem that time consumption increases during the overall spectrum detection process for securing multiple channels.

In addition, as illustrated in FIG. 2, if the user's area and the area of the wireless or system are adjacent to each other, the system base station 102 cannot detect the user signal. Under this situation, if the radio base station 102 occupies the channel used by the user 103 first, the downlink signal from the radio base system base station to the terminal may be used without interfering with the user, but uplink may be used. The signal first has the potential to interfere with the user. In order to prevent such a situation, in order to obtain a sufficiently reliable detection result, the presence or absence of a user in the entire coverage is first determined through a distributed sensing method that detects the same as the base station not only in the base station but also in all the terminals distributed in the coverage. The technique of the present invention is also required in a base station and a terminal because a method is required.

The present invention is to solve the above problems, an object of the present invention is to search a plurality of frequency bands to find a frequency band to communicate with an unknown base station, to find an empty frequency band to store information, and also to the base station In the case of communication with the user, first, it provides a technique for detecting whether the user starts using the corresponding frequency band, and re-examines the remaining empty frequency band to detect the presence of the user first.

In order to achieve the above, the present invention determines whether the frequency band is usable by the received downlink signal, detects and manages the usable frequency bands by the determination, and uses the detected usable frequency band. Communicates with the radio aware base station, periodically or aperiodically monitors whether a signal from a first user terminal or a first user base station is detected through a frequency band currently used, and performs the first user terminal or a first user base station. If a signal is detected, it first checks whether the available frequency band previously managed is used by the user, and first detects a frequency band not used by the user and detects a frequency band for resource use managed as a candidate channel. Suggest a method.

In order to achieve the object of the present invention, a frequency detection method / detection procedure in a wireless cognitive communication system according to the present invention is to find a base station to which the terminal can initially access for accessing a base station among several frequency channels. In this case, it is possible to find out the available channels and to determine whether the user uses the corresponding channel in the detection procedure for initializing the terminal and the channel used by the base station and the terminal during communication. In the case of a moveable candidate channel (Candidate Channel Set), it is characterized in that it consists of a channel detection procedure at the time of the first (Quite Time) to determine whether the user uses.

The detection procedure for initializing the terminal is characterized in that it consists of a procedure for determining whether the signal coming down from the current base station is an accessible signal and a procedure for determining whether the channel is available later even if it is not accessible. The channel detection procedure of Time) is characterized by consisting of a procedure of detecting channels currently used and a procedure of detecting a candidate channel.

Prior to describing a specific operation according to an embodiment of the present invention, terms to be used in the present invention are defined.

Where s represents an index indicating a sensing state (initialization, current channel detection, candidate channel detection, etc.), and i represents an index in a table (TK, TJ) of the selected channel. j represents a sensing state for terminal initialization, and J represents the total number of channels available in the radio recognition system. k denotes a detection state of a channel currently used in a wireless recognition system, K denotes a number of channels currently used in a wireless recognition system, l denotes a detection state of a candidate channel, and L denotes a number of candidate channels. N denotes the size of the FFT window and T denotes the number of FFT windows to average for each taking this FFT. TJ, TK, and TL each represent a table of all channel groups, a table of currently used channel groups, and a table of candidate channel groups.

In order to achieve the sensing procedure for initializing the terminal and the sensing procedure at the Quiet Time, the channel selector 30 will be described first. The initialization phase of the state index s for channel sensing is set by the user prior to using the present invention by selecting an index j or k that determines whether the terminal is initiating or sensing during Quiet Time. Accordingly, the channel selection step also selects one of TJ and TK, which are different tables, depending on whether the terminal is initiating or sensing at Quiet Time.

Initialize the channel index using the state index of channel detection (301), select a channel to match each state (302), tune the selected channel (303) and perform FFT operation on the received data r _p (t) of the selected channel. It is changed into a frequency domain signal through 304.

After the channel selection process is finished, whether the sensing procedure for initializing the terminal or the sensing time for the quiet time is selected according to the state index s (305). During this process, the FFT part is used continuously because it is common to other parts. After the FFT, the state transitions to each state according to the state index.

Hereinafter, in the case of a procedure for initializing a terminal, the state index s of the channel selector 30 becomes an index of j and an index p representing a channel number selects a channel in the table TJ (302).

In the terminal initialization procedure, the signal selected by the channel selector and decoded by the received signal in the frequency domain is decoded 401, and the decoded signal determines whether it is wireless or a base station used by the system (402). At this time, it can be detected using a specific signal of the radio recognition base station.

If it is a channel of a base station used by the radio recognition system, it is determined whether the signal is a base station to which the terminal is connected and communicating (403). If another radio recognition system is using the detected channel (404), it is detected as another base station. If the channel 405 of the base station that the terminal is being detected can be used, the terminal sets the information of the channel currently being detected.

If the channel is not in use by the wireless recognition system, the channel number is changed to determine whether the other channel is empty or not by calculating the amount of energy in the corresponding band. In this case, the sum of the statistical energy values in time is obtained in order to improve the detection probability of the incoming signal (501)-(506).

Statistically, the more temporal sum is obtained, the smaller the distribution of the calculated result is, and the more stable the amount of energy of the input signal can be calculated. This is compared with the threshold value through Equation 1 below (503).

At this time, the threshold value is first selected to be a value known to be unable to determine (decode) the signal among the user signals.

If a signal higher than the threshold is input, the channel is first determined to be a channel occupied by the user, and accordingly, information on the use of the empty channel is updated accordingly (505). On the contrary, if a signal lower than the threshold is input, the channel is determined to be an empty channel, and the channel information for the channel is updated (504).

After the detection of one channel is finished, it is determined whether all the channels have been detected (306). If the entire channel is not detected, the index of i is increased by one step (307) and the procedure described above is repeated.

The present invention generally does not first perform a procedure for determining whether a channel is empty or not, but first decodes a signal and detects a signal of a base station desired by the first. Thus, time for statistical stability when detecting a corresponding channel energy signal is determined. Delay is required, which has the advantage of reducing it.

The purpose of detecting Quiet Time is to find out if the user first appeared in the channel currently being used while communication is being performed. Quiet Time allows all wireless cognitive systems to stop transmitting and first detect if the user is in use, in order to ensure a more reliable detection result. If there is a procedure for canceling a signal transmitted from the base station, the idle time is unnecessary, and in this case, the present invention can be applied.

In addition to these priorities, first of all, if the user uses the channel, for the purpose of continuous and reliable transmission, the user may determine whether the user's channel is used for the extra empty frequencies, that is, the predetermined candidate channels. It is characterized by.

In the case of the above-described detection for initializing the terminal, the detection at the terminal is mainly performed, whereas the detection at the quiet time is performed at both the base station and the terminal.

Hereinafter, in the case of a detection process during Quiet Time, the state index s of the channel selector 30 becomes an index of k, and the index p representing the channel number indicates a channel in the currently used channel group TK. A choice is made (302).

In order to obtain a reliable result of the signal in the frequency domain selected and received by the channel selector 30, the process is performed through a zero mean calculation process as shown in Equation 2 below. This method uses a method of determining the presence or absence of a signal based on the type of the signal rather than the energy detection method described above.

는 채널의 FFT된 데이터를 나타내며

는 FFT된 데이터의 누적 평균값이 된다.In general, when a channel is used, a device such as a walkie talkie uses a small bandwidth, so when energy is detected using a wide bandwidth, such a signal is difficult to detect. So for this method

Represents the FFT data of the channel

Is the cumulative mean value of the FFT data.

The zero mean calculation process can obtain statistical stability by taking the average of signals over a period of time, thereby reducing the effect of reducing the effects of noise.

The signal affected by noise through averaging for a certain period of time determines if the first user who is present in the current band is using the current channel and what kind of first user is used. In addition, if the signal types are known in advance, each signal type can be detected using various signal processing techniques. Through this, it is possible to detect whether or not the priority user of the currently detected channel is used and update it. (604).

The signal thus determined determines whether the currently detected channel is a currently used channel or a case of detecting an extra channel (701), and if the channel is currently used, is this channel occupied (703)? Update the status information as to whether it is empty (704).

After updating the information, it is determined whether the detection of the currently used channel is completed (705). If the detection of the currently used channel is not completed, the index is updated (707) to continue the detection of the currently used channel. do.

If the detection of the current channel is completed, the channel group and state index for redundant channel detection are changed to the state index and channel group for the candidate channel group, and the detection is continued. At this time, the channel state index is 1 and the channel group is TL.

After changing the channel index to l, the same procedure as for the current channel described above is performed (601)-(604). If the detection of the candidate channel group is also completed, the detection procedure is completed (801) ~. (805).

As described above, the present invention is characterized in that each detection proceeds by dividing into two cases of the terminal initialization procedure and Quiet time as a detection procedure in a wireless recognition system, and use of a channel In the case of using the energy detection method to detect the signal, the procedure of calculating the average of the time axis to obtain a stable result value when detecting the energy for the channel by detecting the signal of the base station to which the terminal is connected through decoding in advance is simplified. It can save time.

Claims (2)

In the frequency detection method for the resource usage of the radio-cognitive terminal in a heterogeneous network in which the uplink signal acts as interference of the terminal located in the user base station in the radio-cognitive base station Determining whether the frequency band is usable by the received downlink signal; Detect and manage frequency bands usable by the determination; Perform communication with the radio aware base station using the detected available frequency band; Periodically or aperiodically monitoring whether a signal from a first user terminal or a first user base station is detected through a frequency band currently in use; If a signal of the preferred user terminal or preferred user base station is detected, checking whether the available frequency band previously managed is used by the preferred user; A frequency detection method of first detecting a frequency band not used by the user through the inspection and managing it as g complement channel. The method of claim 1, And determining whether it is a radio or a base station by decoding the downlink signal before detecting the usable frequency band.

Images