CN101325461B - Establishment and maintenance method of cognitive radio communication link based on rateless code - Google Patents

Abstract

The invention discloses a method for establishing and maintaining a cognitive radio communication link based on no rate code, which comprises a method for establishing a cognitive user transmitting end link, a method for maintaining the cognitive user transmitting end link, a method for establishing a cognitive user receiving end link and a method for maintaining the cognitive user receiving end link. The invention utilizes the characteristic that the non-rate code can self-adaptively cope with link deletion and data packet loss to establish and maintain the communication link, and fully utilizes the feedback response time slot required by the non-rate code, and the method does not need to have an additional common control channel between a master user and a slave user to carry out spectrogram exchange.

Description

Establishment and maintenance method of cognitive radio communication link based on rateless code

technical field

The invention relates to the field of wireless communication, and in particular to a method for initializing and establishing a communication link and maintaining a communication link at both sending and receiving ends of a cognitive user in a cognitive radio system.

Background technique

Spectrum sharing wireless communication is an inevitable trend and requirement of future wireless communication technology development. It can enable multiple heterogeneous communication systems with different systems or belonging to different operators to dynamically and opportunistically access the same shared frequency band, and realize the reliable and harmonious coexistence of spectrum licensed users and/or unlicensed users, thus effectively solving the problem of The urgent problem of the increasing scarcity of available wireless spectrum resources, while significantly improving the utilization efficiency of existing spectrum resources. Cognitive radio system is a technical means to realize spectrum sharing wireless communication.

Cognitive radio system is an intelligent spectrum sharing technology. It can realize spectrum reuse and improve spectrum utilization by sensing the spectrum environment, intelligently learning, and adjusting its transmission parameters in real time. In cognitive radio technology, designated user systems (also called primary users, Primary User) that have obtained spectrum authorization in advance have high priority to access the spectrum; while other unlicensed user systems (also called secondary users, Secondary User) Communication can only be done by opportunistically accessing the available spectrum without causing interference to the primary user. This requires the secondary user to have a certain "cognitive ability" by itself or with the help of other users (such as some relay and forwarding users), that is, to be able to continuously monitor the spectrum in real time to find available "spectrum holes" (i.e. Spectrum not occupied by primary users). A user with cognitive ability (which can be a secondary user or some relay users) is called a "cognitive user". Essentially, the cognitive radio system is to realize adaptive communication in an environment with limited interference in a multi-radio electromagnetic environment.

A prominent feature of cognitive radio is that the frequencies and bandwidths used by its links are not predetermined or fixed. Since there are no frequencies available in advance, their links must be established dynamically. Moreover, due to the influence of factors such as multipath and shadow fading in the wireless communication system, and the detection capability of the cognitive user itself has certain limitations, the channel state information obtained through spectrum sensing at both ends of the cognitive user includes interference status The information is not exactly the same, so that the available frequencies and bandwidths that are not completely consistent may be detected, so that the establishment of the communication link is usually difficult. FIG. 1 is a schematic diagram of spectrum sensing by a sending end and a receiving end of a cognitive user. Assuming that the system has 5 spectrum resources in total, they are labeled with numbers. Assume that the user sending end detects that the spectrum resources No. 1 and No. 3 have been occupied, and the available spectrum resources are No. 0, No. 2, and No. 4; while the user receiving end detects that No. 2 and No. For No. 0, No. 1 and No. 4.

Therefore, since the channel status information of the sending and receiving parties is not completely related and is not known to each other, if a communication link is to be established and maintained between the sending and receiving ends of the cognitive user, the sending and receiving ends must pass an appropriate "spectrum exchange". )” to know the interference distribution of the opposite end, not just its own location, to complete the link building process and start effective transmission. If the method of directly sensing or estimating the spectrum resources of the opposite end is adopted, not only the process is complicated, but additional dynamic interference may also be introduced. Therefore, when the sending end does not know the accurate state information of the channel, ARQ (Automatic Repeat Request) is often required to ensure reliable and effective transmission of information. In the traditional method, the sending end of the cognitive user generally adopts fixed code rate channel coding to protect the transmitted information, but since the spectrum resource used by the cognitive user may be occupied by the primary user at any time, the transmission channel of the cognitive user is not protected , the packet loss probability of the channel cannot be determined, that is, the instantaneous capacity of the channel is not fixed. Once the spectrum is blocked by the primary user and the channel capacity is smaller than the transmission code rate, the receiving end cannot guarantee correct decoding, resulting in communication failure. At this time, the receiving end needs to send feedback information to inform the sending end to adjust the transmission parameters and perform encoding and transmission again. Due to the different encoding methods, the previously received codes at the receiving end cannot be jointly decoded with the adjusted codes, resulting in the previous coded packets being almost unusable and discarded, resulting in a waste of information. If channel coding with a very low code rate is used to ensure the reliability of transmission as much as possible, the channel will also be wasted due to the transmission of too much redundant information, and even if a low code rate is used, this code rate cannot be guaranteed Reliable transmission must be possible in cognitive radio systems. In addition, some people propose a method of setting a common control channel to transmit spectrum sensing situation and feedback information among cognitive users, and it is assumed that the frequency spectrum of the common control channel is not interfered by the primary user. Although this method can ensure the reliable transmission of signals, it requires that the primary user cannot occupy the spectrum of the common control channel, which itself violates the principle that the activities of cognitive users in cognitive radio systems should not affect the primary user. Moreover, only a specific frequency is used for transmission, and the communication must be completed in a time-division manner, and the efficiency will not be too high.

Therefore, how to adaptively select an appropriate code rate for transmission to adapt to different channel parameters is a key problem faced by cognitive wireless communication links. The adaptive rate adaptation (Rate Adaption) capability of rateless codes (rateless codes) provides a new idea for solving this problem, which is the main motivation of the present invention.

The biggest difference between the rateless code and the traditional fixed code rate encoding method is that it does not set a fixed code rate at the sending end, and the sending end can continuously generate encoded packets in a certain way and send them out. The receiving end can try to decode according to the received encoded packets, and does not need to receive all the encoded packets. If the decoding fails, the receiver can receive some more encoded packets and continue to try to decode. No matter which packets are discarded by interference during transmission, the receiving end only needs to obtain a certain number of packets to complete the decoding, and this number is linear with the data packets to be sent. The receiver will repeat this process until the decoding is successful. At this time, the receiving end only needs to send a very simple feedback signal to inform the sending end that the decoding is successful, and then the sending end stops sending, thus completing the entire transmission process.

Utilizing the characteristic that the rateless code can deal with channel erasure excellently, when the two ends of the spectrum sharing wireless communication environment do not fully know the channel state of the other party, the sending packet is lost, or the signal of the main user is received due to the inaccurate spectrum sensing. When there is interference, the rateless code can always send coded packets continuously at different times or frequencies, and as long as the receiving end can receive enough coded packets at part of the time and frequency, it can always recover the data correctly, thus completing link establishment. Moreover, the use of rateless coding technology can make full use of the diversity gain between multiple spectrum resources, and more importantly, it can make full use of the characteristics of rateless codes that can adaptively approach the cognitive channel capacity to obtain huge coding gains, which is It cannot be obtained by the traditional method of using fixed rate coding.

Contents of the invention

The purpose of the present invention is to provide a reliable and efficient method for establishing and maintaining a communication link by using rateless codes at both sending and receiving ends of a cognitive user without using a common control channel in a cognitive radio system.

The method for establishing and maintaining a rateless code-based cognitive radio communication link of the present invention is characterized in that it includes a method for establishing a link at the sending end of a cognitive user, a method for maintaining a link at the sending end of a cognitive user, and a method for receiving a link at the receiving end of a cognitive user. The establishment method of the terminal link and the maintenance method of the receiving terminal link of the cognitive user. The feedback of type 1 described below indicates that the receiving terminal has successfully received data, and the feedback of type 2 indicates that the receiving terminal has detected that the primary user needs to occupy and is using Spectrum resource in , type 3 feedback indicates that the receiving end thinks the spectrum resource is available, and type 4 feedback indicates that the receiving end confirms that the new available spectrum resource is detected jointly with the transmitting end;

Assume: there are n spectrum resources in the entire cognitive system, which are marked with labels f=[f ₁ , f ₂ , ..., f _n ] respectively. When a certain cognitive user accesses, there are no other cognitive users. Knowing that users access in the same time slot,

The method for establishing a cognitive user sending end link includes the following steps:

1) The sending end senses all the n spectrum resources in the whole cognitive system, and obtains which spectrum resources are free and available, assuming that p available spectrum resources are detected, it is recorded as $f_t=[f_{t_1},{\mathrm{<figure-callout\; id="2"\; label="f\; t"\; filenames="H2008100637103E00011.png"\; state="\{\{state\}\}">f</figure-callout>}}_{t_{}},\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;,f_{t_p}],$ And 0≤p≤n; the transmitting end detects the available spectrum resources in real time, and updates f _t in real time when the available spectrum resources are found to be changed;

2) If the available spectrum resource f _t is an empty set, that is, all current spectrum resources are occupied, then proceed to step 1) re-sensing; if the available spectrum resource f _t is not an empty set, then proceed to step 3);

3) Coding and framing the user initialization system information m _s of the cognizant user according to the coding mode of the rateless code; use t _i to represent the coded frame, where i is the number of the coded frame, i=0, 1, 2,……;

个子信道进行发送；若imodp＝0，则编码帧就用第个子信道进行发送；4) The sending end makes each coded frame correspond to the available spectrum resource in the perceived current available spectrum resource _ft to transmit the coded frame, and each spectrum resource is regarded as a sub-channel; the specific mapping rule is: if imodp=k, and k≠0, then the coded frame uses the first

sub-channels for transmission; if imodp=0, the coded frame uses the first sub-channels to send;

5) The sending end continuously generates coded frames according to the coding rules of the rateless code until the receiving end informs it to stop sending, and at the same time monitors the feedback signal of the receiving end in the response time slot on the current available spectrum resource _ft , if it detects The feedback signal of type one then turns over to step 6); Otherwise, continue the process of step 5);

6) The sending end stops generating coded frames and immediately stops transmitting, and instead listens to the feedback signal of the receiving end in the response time slots on all currently available spectrum resources f _t , and transfers all the frequency spectrums that can receive type 3 feedback signals The resources are recorded separately, denoted as f _c , and all the spectrum resources in f _c are the available spectrum resources jointly recognized by the cognitive user sending end and the receiving end, thus completing the establishment of the cognitive user sending end link;

The method for maintaining the cognitive user sending end link includes the following steps:

1) After the communication link is established, the sending end uses the spectrum resources in _fc to encode and frame the information packet according to the coding method of the rateless code, and then transmits the information to be sent, while real-time monitoring of the entire recognition All spectrum resources in the known system are used for sensing, and wait for the feedback signal from the receiving end in the "acknowledgment time slot"; if it is found that the primary user needs to occupy the spectrum that is being transmitted for data, then go to step 2); if the confirmation is received If the user's feedback signal is known, then go to step 3); if new available spectrum resources are sensed, then go to step 5);

2) Release all the spectrum resources that the perceived primary user needs to occupy and no longer continue to occupy them, and use the remaining available spectrum resources to continue transmitting the data frames to be sent;

3) After confirming that the feedback signal from the cognitive user is received, immediately determine whether the type of the feedback signal is Type 1 or Type 2. If it is Type 1, it means that the data transmission has been completed, and the transmitter stops transmitting. If it is Type 2, then go to step 4);

4) Identify the spectrum through which the type 2 feedback is received, and immediately stop transmitting data on these spectrums, only use the remaining available spectrum resources, update the remaining available spectrum resources as f _c , and go to step 1 );

5) The transmitting end tries to receive the feedback from the receiving end in the "response time slot" on the newly perceived spectrum resource, if it is confirmed that the feedback from the receiving end is received on this frequency spectrum, then go to step 6); if the feedback is received If it is found that this spectrum is occupied by the primary user before the signal, then stop the activity on this spectrum and turn to step 1);

6) confirm that the feedback of the receiving end is feedback type three, then send confirmation information on these frequency spectra, and wait for further feedback from the receiving end; if the feedback of type four at the receiving end is obtained, record this frequency spectrum into f _c , and turn to step 1), Otherwise do not update f _c , go to step 1);

The method for establishing a link at the receiving end of a cognitive user includes the following steps:

1) The receiving end perceives all n spectrum resources in the entire cognitive system, and obtains which spectrum resources are free and available. Suppose that q available spectrum resources are detected, which are recorded as $f_r=[f_{r_1},{\mathrm{<figure-callout\; id="2"\; label="f\; r"\; filenames="H2008100637103E00011.png"\; state="\{\{state\}\}">f</figure-callout>}}_{r_{}},\&CenterDot;\&CenterDot;\&CenterDot;\&CenterDot;\&CenterDot;\&CenterDot;,f_{r_q}],$ And 0≤q≤n; the receiving end detects the available spectrum resources in real time, and updates f _r in real time when the available spectrum resources are found to be changed;

2) The receiving end tries to receive information on all the spectrums in f _r without knowing the spectrum sensing result f _t of the sending end. At this time, as long as the intersection of f _t and f _r is not empty, the receiving end can always be at The coding information of the transmitter is received on the intersection spectrum resources;

3) When the number of coded frames received reaches the number of coded frames marked by the user at the sending end, start decoding, and use the cyclic redundancy check (CRC) to determine whether the decoding is correct, and if it is correct, go to step 6 ); otherwise go to step 4);

4) continue to receive several encoding packets;

5) Try decoding again, if the decoding is successful, proceed to step 6); otherwise proceed to step 4);

6) After the decoding is completed, the receiving end records all the spectral resources that can receive the coded frame as f _c , f _c is the set of available spectral resources that the transmitting end and the receiving end perceive jointly, and the response of the spectral resources in f _c Send a feedback signal of type 1 on the time slot;

7) If the receiving end does not receive the coded frame from the sending end in the next 3 consecutive time slots, it will send two feedback signals of type 1 on the response time slots of all spectrum resources in f _c to notify the sending end end;

8) The receiving end learns the requirements of the sending end according to the initializing system information m _s of the sending end obtained through successful decoding, thus completing the establishment of the cognitive user receiving end link;

The method for maintaining the link at the receiving end of the cognitive user includes the following steps:

1) After the communication link is established, the receiving end uses the spectrum resource in _fc to receive the data frame transmitted by the transmitting end, while sensing all the spectrum resources in the entire cognitive system in real time, if the decoding is successful during this period , to restore all the information data to be sent by the transmitter, then go to step 2); if it is found that the primary user needs to occupy the frequency spectrum for data transmission when it is detected, then go to step 3); if new available spectrum resources are sensed , then go to step 4);

2) The receiving end sends a type 1 feedback on all _fc -marked spectrum resources in the "response time slot", telling the transmitting end to stop sending data immediately, thereby completing the entire data transmission;

3) Mark the perceived spectrum resources that the primary user needs to occupy as f _z , and send type 2 feedback in the "response slot" on these spectrums, and move the spectrum resources marked in f _z out of f _c , go to step 1);

4) Send several Type 3 feedbacks to the transmitter in the "response time slot" when new available spectrum resources are sensed, and try to receive the confirmation signal from the transmitter on these spectrums. If the confirmation signal from the transmitter is received, then Send type 4 feedback for further confirmation, and incorporate these new available spectrum resources into f _c , and go to step 1); if not received, go to step 1).

In the present invention, in the establishment method of the cognitive user sending end link, the information packet is encoded and framed according to the encoding method of the rateless code, and the steps are as follows:

1) According to the initialization system information, set the length of the information m _s to be transmitted as L1, and divide m1 into small data packets, the length of each small data packet is k1, if L1 cannot be divisible by k1, the part of the last small data packet that is less than k1 long is filled with "0";

2) Use a cyclic redundancy check code to perform a cyclic redundancy check on each k1-long small data packet, and the length of each small data packet is correspondingly increased to k1+r1 according to the length r1 of the cyclic redundancy check code used bit;

个长度为k1+r1比特的小数据包送入无速率码的编码器进行编码，按照编码包的产生顺序将这些编码包记为C＝[c₀，c₁，c₂，…]，每一个编码包的下标表示此编码包在整个编码序列当中所处的位置，利用g个比特来表示编码包的下标；3) Will

A small data packet with a length of k1+r1 bits is sent to an encoder with no rate code for encoding, and these encoded packets are recorded as C=[c ₀ , c ₁ , c ₂ ,…] according to the order in which the encoded packets are generated, and each The subscript of a coding packet indicates the position of the coding packet in the entire coding sequence, and g bits are used to represent the subscript of the coding packet;

4) Send the subscript of each coded packet to a linear block code encoder with a code rate of 1/4 for coding, and generate data with a length of g×4 bits as a position mark, and place the position mark in each coded packet after;

5) A preamble sequence with a length of 64×4 is added before each coding packet to realize bit synchronization and channel estimation, and a 64-bit interval is added after each coding packet as a “response time slot”;

6) After the preamble sequence and before the data encoding packet, an initialization header sequence with a length of 64×4 bits is added. The content of the header sequence includes the user identification number of the transmitter and the target receiver, which is used for user identification and auxiliary realization of bit synchronization. Complete encoding and framing.

In the present invention, in the maintenance method of the cognitive user sending end link, the information packet is encoded and framed according to the encoding mode of the rateless code, and the steps are as follows:

个小数据包，每个小数据包长度为k2，若L2无法整除k2，则最后一个小数据包不足k2长的部分用“0”来填充；1) Assuming that the information to be transmitted is m and the length is L2, divide m into

small data packets, the length of each small data packet is k2, if L2 cannot be divisible by k2, the part of the last small data packet that is less than k2 is filled with "0";

2) Use a cyclic redundancy check code to perform a cyclic redundancy check on each k2-long small data packet, and the length of each small data packet is correspondingly increased to k2+r2 according to the length r2 of the cyclic redundancy check code used bit;

个长度为k2+r2比特的小数据包送入无速率码的编码器进行编码，按照编码包的产生顺序将这些编码包记为C＝[c₀，c₁，c₂，…]，每一个编码包的下标表示此编码包在整个编码序列当中所处的位置，利用g个比特来表示编码包的下标；3) Will

A small data packet with a length of k2+r2 bits is sent to an encoder with no rate code for encoding, and these encoded packets are recorded as C=[c ₀ , c ₁ , c ₂ ,…] according to the order in which the encoded packets are generated, and each The subscript of a coding packet indicates the position of the coding packet in the entire coding sequence, and g bits are used to represent the subscript of the coding packet;

4) Send the subscript of each encoded packet into a 1/4 code rate linear block code for encoding, and generate data with a length of g×4 bits as a position indicator, and place the position indicator after each encoded packet;

5) A preamble sequence with a length of 64×4 is added before each coding packet to realize bit synchronization and channel estimation, and a 64-bit interval is added after each coding packet as a “response slot”, Complete encoding and framing.

Advantages of the present invention:

The basic technical idea of the present invention is to use the characteristics of the rateless code to adaptively deal with link deletion and data packet loss to carry out the establishment and maintenance of the communication link, and make full use of the feedback response time slot required by the rateless code, so as not to An additional common control channel between master and slave users is required for "spectrum exchange".

Description of drawings

FIG. 1 is a schematic diagram of spectrum sensing by a transmitting end and a receiving end of a cognitive user;

Fig. 2 is a flow chart of the working method of the sending end of the cognitive user when establishing a communication link;

Fig. 3 is a schematic structural diagram of an encoded frame in the link establishment process;

Fig. 4 is a flow chart of the working method of the sending end of the cognitive user when maintaining the communication link;

Fig. 5 is a schematic structural diagram of an encoded frame in the link maintenance process;

Fig. 6 is a flow chart of the working method when the receiving end of the cognitive user establishes a communication link;

Fig. 7 is a flow chart of the working method when the receiving end of the cognitive user maintains the communication link;

Detailed ways

Further illustrate the present invention below in conjunction with accompanying drawing.

The establishment and maintenance method of the cognitive radio communication link based on the rateless code of the present invention includes the establishment method of the cognitive user sending end link, the maintenance method of the cognitive user sending end link and the cognitive user receiving end link The establishment method of the cognitive user and the maintenance method of the receiving end link of the cognitive user. The type 1 feedback described below indicates that the receiving end has successfully received data, and the type 2 feedback indicates that the receiving end has detected that the primary user needs to occupy the spectrum being used Resource, type 3 feedback indicates that the receiving end believes that the spectrum resource is available, and type 4 feedback indicates that the receiving end confirms that the new available spectrum resource has been detected jointly with the transmitting end;

Assume: there are 256 spectrum resources in the entire cognitive system, and all 256 spectrums are labeled from low to high according to their frequencies, and are respectively marked as [0, 1, ..., 255]. Each user in the cognitive radio system is assigned a unique user number with a length of b bits as a user identity mark, for example, if b=16, theoretically a maximum of 65536 users can be supported. Before the communication link is established, the transmitting and receiving ends of the cognitive user have no knowledge of the other party's spectrum sensing situation and the necessary information such as channel coding and modulation mapping methods to be used. Pass the necessary information to the other party. These information are called "initialization system information", denoted as m _s . When a certain cognitive user accesses, no other cognitive user accesses in the same time slot.

The establishment method (referring to Fig. 2) of cognitive user sending end link, comprises the following steps:

1) The sending end perceives all 256 spectrum resources in the entire cognitive system in real time, and obtains the cognitive result of the entire spectrum resources at the sending end, that is, which spectrum resources are idle and available at the current time. Assume that the cognitive sending end obtains p available spectrum resources through detection, and records the labels of these available spectrum resources, denoted as $f_t=[f_{t_1},{\mathrm{<figure-callout\; id="2"\; label="f\; t"\; filenames="H2008100637103E00011.png"\; state="\{\{state\}\}">f</figure-callout>}}_{t_{}},\&CenterDot;\&CenterDot;\&CenterDot;\&CenterDot;\&Center\; Dot;\&Center\; Dot;,f_{t_p}],$ 0≤p≤256; the transmitter senses all 256 spectrum resources in real time, and updates f _t in real time when it finds that the available spectrum resources change;

2) If the available spectrum resource f _t is an empty set, that is, all current spectrum resources are occupied, then proceed to step 1) re-sensing; if the available spectrum resource f _t is not an empty set, then proceed to step 3);

3) The initial system information m _s is coded and framed according to the encoding method of the rateless code, and the frame structure formed is shown in Figure 3 (the specific steps are introduced below); the coded frame is represented by t _i , where i is the number of the coded frame, i=0,1,2,...;

个子信道进行发送；若imodp＝0，则编码包就用第

个子信道进行发送；4) The sending end makes each coded frame correspond to the available spectrum resource in the currently available spectrum resource f _t that is perceived to transmit the coded frame, and each spectrum resource is regarded as a subchannel; the specific mapping rule is: if imodp=k, and k≠0, then the coded packet uses the first

sub-channel to send; if imodp=0, the coded packet will use the first

sub-channels to send;

5) The sending end continuously generates coded frames for transmission according to the coding rules of a certain rateless code (such as Raptor Code), and at the same time listens to the feedback signal of the receiving end in the response time slot on the currently available spectrum resource f _t , if detected Hear the feedback signal of type one and then turn to step 6); Otherwise, continue the process of step 5);

6) The sending end stops generating coded frames and immediately stops transmitting, and instead listens to the feedback signal of the receiving end in the response time slots on all currently available spectrum resources f _t , and transfers all the frequency spectrums that can receive type 3 feedback signals The resources are recorded separately, denoted as f _c , and all the spectrum resources in f _c are the available spectrum resources jointly recognized by the cognitive user sending end and the receiving end, thus completing the establishment of the cognitive user sending end link;

The above-mentioned initialization system information m _s is encoded and framed according to the coding method of the rateless code, and the length of the information m _s to be transmitted is assumed to be L1, and the information m _s is processed according to the following steps:

个长度为k1的小数据包；1) Divide m _s into several small data packets, each packet length is k1 bits, if L1 cannot be divisible by k1, then the part of the last small data packet that is less than k1 long is filled with "0", thus dividing

A small packet of length k1;

2) Carry out cyclic redundancy check for each small data packet with a length of k1, which is used for the decoder to judge whether the decoding is successful. In this example, the cyclic redundancy check code adopts CRC16, so that the length of each small data packet is k1+16 bits;

个长度为k1+16比特的小数据包送入某种无速率码(例如Raptor Code)的编码器进行编码，源源不断的产生长度同为k1+16比特的编码包C，按照编码包的产生顺序将这些编码包记为C＝[c₀，c₁，c₂，…]，每一个编码包的下标表示此编码包在整个编码序列当中所处的位置，利用16个比特来表示编码包的下标，则可以支持2¹⁶长的编码包；3) Put this

A small data packet with a length of k1+16 bits is sent to an encoder with a rateless code (such as Raptor Code) for encoding, and an encoded packet C with the same length as k1+16 bits is continuously generated, according to the generation of encoded packets These coding packets are recorded as C=[c ₀ , c ₁ , c ₂ ,…] in sequence, the subscript of each coding packet indicates the position of the coding packet in the entire coding sequence, and 16 bits are used to represent the coding The subscript of the package can support 2 ¹⁶ long encoding packages;

4) Send each 16-bit information representing the subscript of the encoded packet into a 1/4 code rate linear block code encoder for encoding protection, that is, use 64 bits to represent the position information of the encoded packet, and convert the 64-bit The encoding packet location information is placed after each encoding packet;

5) A preamble sequence of length 64×4 is added before each coding packet to realize bit synchronization and channel estimation, and a 64-bit gap protection is added after each coding packet. The gap protection can also be used as "response slot";

6) After the preamble sequence and before the data encoding packet, an initialization header sequence with a length of 64×4 bits is added, and its content includes the user identification number of the transmitter and the target receiver, which is used for user identification and auxiliary realization of bit synchronization. The composed frame structure is shown in Fig. 3 .

The maintenance method (referring to Fig. 4) of cognitive user sending end link, comprises the following steps:

1) After the communication link is established, the sending end uses the spectrum resource in _fc to encode the information packet and frame the information to be sent according to the coding method of the rateless code. The frame structure formed is shown in Figure 5 (The specific steps are described below), and then transmit, while sensing all the spectrum resources in the entire cognitive system in real time, and waiting for the feedback signal from the receiving end in the "response time slot"; if it is found that the primary user starts activities, it needs to occupy For the frequency spectrum in which data is being transmitted, proceed to step 2); if a feedback signal from a cognitive user is received, proceed to step 3); if new available spectrum resources are sensed, proceed to step 5);

2) Release all the spectrum resources that the perceived primary user needs to occupy and no longer continue to occupy them, and use the remaining available spectrum resources to continue to transmit the data frames to be sent;

3) After confirming that the feedback signal from the cognitive user is received, immediately determine whether the type of the feedback signal is Type 1 or Type 2. If it is Type 1, it means that the data transmission has been completed, and the transmitter stops transmitting. If it is Type 2, then go to step 4);

4) According to the frequency of the received signal, distinguish which spectrums the type 2 feedback is received through, and immediately stop transmitting data on these spectrums, and only use the remaining available spectrum resources, and update the remaining available spectrum resources as f _c , go to step 1);

5) The transmitting end tries to receive the feedback from the receiving end in the "response time slot" on the newly perceived spectrum resource, if it is confirmed that the feedback from the receiving end is received on this frequency spectrum, then go to step 6); if the feedback is received If it is found that this spectrum is occupied by the primary user before the signal, then stop the activity on this spectrum and turn to step 1);

6) Confirm that the feedback from the receiving end is Feedback Type 3, which means that the receiving end also believes that this spectrum resource is available, and then sends a fixed confirmation message on these spectrums, for example, sending a message consisting of 16 "1110" with a length of 64 1-bit binary data, waiting for further feedback from the receiving end; if a type 4 feedback from the receiving end is obtained, further confirmation is completed, record this spectrum into f _c , and go to step 1); otherwise, do not update f _c and go to step 1) .

The information packet is encoded and framed according to the encoding method of the rateless code, and the length of the information m to be transmitted is assumed to be L2, and the information m is processed according to the following steps:

1) Divide m into several small data packets, each of which has a length of k2 bits. If L2 cannot divide k2, the part of the last small data packet that is less than k2 long is filled with "0", thus dividing A small packet of length k2;

2) Carry out a cyclic redundancy check for each k2 long small data packet, which is used by the decoder to judge whether the decoding is successful. In this example, the cyclic redundancy check code still uses CRC16, so that the length of each small data packet is k2+16 bits;

个长度为k2+16比特的小数据包送入某种无速率码(例如Raptor Code)的编码器进行编码，源源不断的产生长度同为k2+16比特的编码包C，按照编码包的产生顺序将这些编码包记为C＝[c₀，c₁，c₂，…]，每一个编码包的下标表示此编码包在整个编码序列当中所处的位置，利用16个比特来表示编码包的下标，则可以支持2¹⁶长的编码包；3) Put this

A small data packet with a length of k2+16 bits is sent to an encoder with a rateless code (such as Raptor Code) for encoding, and an encoded packet C with the same length as k2+16 bits is continuously generated, according to the generation of encoded packets These coding packets are recorded as C=[c ₀ , c ₁ , c ₂ ,…] in sequence, the subscript of each coding packet indicates the position of the coding packet in the entire coding sequence, and 16 bits are used to represent the coding The subscript of the package can support 2 ¹⁶ long encoding packages;

4) Send each 16-bit information representing the subscript of the encoded packet into a 1/4 code rate linear block code encoder for encoding protection, that is, use 64 bits to represent the position information of the encoded packet, and convert the 64-bit The encoding packet location information is placed after each encoding packet;

5) A preamble sequence of length 64×4 is added before each coding packet to realize bit synchronization and channel estimation, and a 64-bit gap protection is added after each coding packet. The gap protection can also be used as "Response slot". The composed frame structure is shown in Fig. 5 .

The establishment method (referring to Fig. 6) of cognitive user receiving end link, comprises the following steps:

1) The receiving end perceives all 256 spectrum resources in the entire cognitive system in real time, and obtains the cognitive result of the entire spectrum resources at the receiving end, that is, which spectrum resources are idle and available. Assuming that q available spectrum resources are detected, it is recorded as $f_r=[f_{r_1},{\mathrm{<figure-callout\; id="2"\; label="f\; r"\; filenames="H2008100637103E00011.png"\; state="\{\{state\}\}">f</figure-callout>}}_{r_{}},\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;,f_{r_q}],$ And 0≤q≤256;

2) The receiving end tries to receive information on all the spectrums in f _r without knowing the spectrum sensing result f _t of the sending end. At this time, as long as the intersection of f _t and f _r is not empty, the receiving end can always be at The coding information of the transmitter is received on the intersection spectrum resources;

3) When the number of coded frames received reaches the number of coded frames marked by the user at the sending end, decoding begins. In this example, CRC16 is used to determine whether the decoding is correct. If it is correct, proceed to step 6); otherwise, proceed to step 4);

4) Continue to receive several encoded frames, for example, continue to receive 2 frames;

5) Try decoding again, if the decoding is successful, proceed to step 6); otherwise proceed to step 4);

6) After the decoding is completed, the receiving end records all the spectral resources that can receive the coded frame as f _c , f _c is the set of available spectral resources that the transmitting end and the receiving end perceive jointly, and the response of the spectral resources in f _c Send a feedback signal of type 1 on the time slot;

7) If the receiving end does not receive the coded frame from the sending end in the next 3 consecutive time slots, it will send two feedback signals of type 1 on the response time slots of all spectrum resources in f _c to notify the sending end end;

8) The receiving end learns the requirements of the sending end according to the initializing system information m _s of the sending end obtained through successful decoding, thus completing the establishment of the cognitive user receiving end link;

The maintenance method (referring to Fig. 7) of cognitive user receiving terminal link, comprises the following steps:

1) After the communication link is established, the receiving end uses the spectrum resource in _fc to receive the data frame transmitted by the transmitting end, while sensing all the spectrum resources in the entire cognitive system in real time, if the decoding is successful during this period , and successfully recover all the information data to be sent by the transmitter, then go to step 2); if it is found that the primary user starts activities and needs to occupy the spectrum that is being transmitted, then go to step 3); if a new available spectrum is sensed resources, go to step 4);

2) The receiving end sends a type 1 feedback on all _fc -marked spectrum resources in the "response time slot", telling the transmitting end to stop sending data immediately, thereby completing the entire data transmission;

3) Mark the perceived spectrum resources that the primary user needs to occupy as f _z , and send type 2 feedback in the "response slot" on these spectrums, and move the spectrum resources marked in f _z out of f _c , go to step 1);

4) Send several Type 3 feedbacks to the transmitter in the "response time slot" when new available spectrum resources are sensed, and try to receive the confirmation signal from the transmitter on these spectrums. If the confirmation signal from the transmitter is received, then Send type 4 feedback for further confirmation, and incorporate these new available spectrum resources into f _c , and go to step 1); if not received, go to step 1).

Four types of feedback are used in the whole process, namely type 1, type 2, type 3 and type 4, so in theory, two bits of data can be used to distinguish these four types of feedback, for example, "01" means type 1, "10 "Indicates type two, "11" indicates type three, and "00" indicates type four. However, considering the possibility of data interference during wireless channel transmission, 6-bit data is used here to indicate a feedback type: "010101" indicates type 1, "101010" indicates type 2, "111111" indicates type 3, "000000 "Indicates type four, and these data are protected by channel coding with one-sixth code rate. Finally, a 12-bit "feedback frame header" sequence is added before the coded and protected data to form a 48-bit feedback data frame.

Claims (2)

1. based on the foundation and the maintaining method of the cognition radio communication link of no-rate codes, it is characterized in that comprising the method for building up of cognitive user transmitting terminal link and the method for building up of cognitive user receiving terminal link, the feedback of the type one of the following stated represents that receiving terminal has successfully received data, and the feedback of type three represents that receiving terminal thinks that this frequency spectrum resource can use;

If: whole frequency spectrum resources has n in the whole cognitive system, uses label f=[f respectively ₁, f ₂... ..., f _n] come mark, when a certain cognitive user inserts, there are not other cognitive user to insert at identical time slot,

The method for building up of cognitive user transmitting terminal link may further comprise the steps:

1) transmitting terminal carries out perception to whole n frequency spectrum resources in the whole cognitive system, and it is idle available obtaining which frequency spectrum resource, establishes and detects p usable spectrum resource, and it is designated as

And 0≤p≤n; The detection usable spectrum resource that transmitting terminal is real-time when finding that the usable spectrum resource changes, is upgraded f in real time _t

2) if usable spectrum resource f _tBe empty set, promptly current all frequency spectrum resources are all occupied, then change the step 1) perception again of cognitive user transmitting terminal link establishing method over to; If usable spectrum resource f _tNot empty set, then change the step 3) of cognitive user transmitting terminal link establishing method over to;

3) with user's initialization system information m of cognitive user _sCoded system according to no-rate codes is encoded and framing to packets of information; Use t _iThe presentation code frame, wherein i is the numbering of coded frame, i=0,1,2,

4) transmitting terminal is with each coded frame and the current usable spectrum resource f that perceives _tIn the usable spectrum resource do the emission that correspondence is carried out coded frame, each frequency spectrum resource is all regarded a subchannel as; Concrete mapping ruler is: if imodp=k, and k ≠ 0, then coded frame is just with the

Individual subchannel sends; If imod p=0, then coded frame is just with the Individual subchannel sends;

5) transmitting terminal produces coded frame endlessly according to the coding rule of no-rate codes and informs that up to receiving terminal it stops to send, simultaneously at current usable spectrum resource f _tOn reply the feedback signal of intercepting receiving terminal in the time slot, if listen to the step 6) that the feedback signal of type one then changes cognitive user transmitting terminal link establishing method over to; Otherwise, the process of the step 5) of continuation cognitive user transmitting terminal link establishing method;

6) transmitting terminal stops to continue to produce coded frame and stopping emission immediately, then at all current usable spectrum resource f _tOn reply the feedback signal of intercepting receiving terminal in the time slot, and all frequency spectrum resources that can receive the feedback signal of type three are noted down separately, be designated as f _c, f _cIn all frequency spectrum resources be exactly cognitive user transmitting terminal and receiving terminal the usable spectrum resource of common approval, thereby finished the foundation of cognitive user transmitting terminal link;

The method for building up of cognitive user receiving terminal link may further comprise the steps:

1) receiving terminal carries out perception to whole n frequency spectrum resources in the whole cognitive system, and it is idle available obtaining which frequency spectrum resource, establishes and detects q usable spectrum resource, and it is designated as

And 0≤q≤n; The detection usable spectrum resource that receiving terminal is real-time when finding that the usable spectrum resource changes, is upgraded f in real time _r

2) receiving terminal is being attempted at t _rIn all frequency spectrums on carry out message pick-up, the frequency spectrum perception that need not to know transmitting terminal is f as a result _t, at this moment, as long as f _tWith f _rCommon factor be not empty, then receiving terminal always can receive the coded message of transmitting terminal certainly on it occurs simultaneously frequency spectrum resource;

3) when the coded frame quantity that receives reaches the quantity of coded frame of user's beacon information of transmitting terminal, begin to decipher, and utilize cyclic redundancy check (CRC) to judge whether that decoding is correct, if correctly, change the step 6) of cognitive user receiving terminal link establishing method over to; Otherwise change the step 4) of cognitive user receiving terminal link establishing method over to;

4) continue to receive several encoded packets;

5) if trial and error decoding again successfully decoded, changes the step 6) of cognitive user receiving terminal link establishing method over to; Otherwise change the step 4) of cognitive user receiving terminal link establishing method over to;

6) decoding finishes, but receiving terminal is designated as f with the frequency spectrum resource of all received code frames _c, f _cBe the set of the usable spectrum resource that transmitting terminal and receiving terminal perceived jointly, and at f _cThe feedback signal of replying transmission types one on the time slot of intermediate frequency spectrum resource;

7) if receiving terminal is not all received the coded frame of transmitting terminal in continuous 3 time slots next, then at f _cIn all frequency spectrum resource reply the feedback signal that sends twice type one on the time slot, be used for notifying transmitting terminal;

8) the transmitting terminal initialization system information m that obtains according to decoding success of receiving terminal _s, learn the requirement of transmitting terminal, thereby finished the foundation of cognitive user receiving terminal link.

2. the foundation and the maintaining method of the cognition radio communication link based on no-rate codes according to claim 1, it is characterized in that the coded system according to no-rate codes in the method for building up of cognitive user transmitting terminal link encodes and framing to packets of information, its step is as follows:

1), establishes the information m that will transmit according to initialization system information _sLength be L1, m1 is divided into " L1/k1] individual small data packets, each small data packets length is k1, if L1 can't divide exactly k1, then the long part of the not enough k1 of last small data packets is filled with " 0 ";

2) utilize cyclic redundancy check (CRC) code to carry out cyclic redundancy check (CRC) to the long small data packets of each k1, each small data packets length is increased to the k1+r1 bit accordingly according to the length r1 of the cyclic redundancy check (CRC) code that adopts;

3) will

Individual length is that the encoder that the small data packets of k1+r1 bit is sent into no-rate codes is encoded, and according to the generation order of encoded packets these encoded packets is designated as C=[c ₀, c ₁, c ₂... ], the subscript of each encoded packets is represented this encoded packets residing position in the middle of entire coded sequence, utilizes g bit to come the subscript of presentation code bag;

4) the linear block codes encoder of the subscript of each encoded packets being sent into one 1/4 code check is encoded, generation length be the data of g * 4 bits as location mark, and location mark is placed on after each encoded packets;

5) adding length before each encoded packets is that 64 * 4 targeting sequencing is used for realizing bit synchronization and channel estimating, and adds the interval of 64 bits after each encoded packets, as " replying time slot ";

6) after targeting sequencing, also will add the initialization preamble sequence that length is 64 * 4 bits before the digital coding bag, the preamble sequence content comprises the customer identification number of transmitter and target receiver, be used for User Recognition and the auxiliary bit synchronization that realizes, finish coding and framing.

Images