Cognitive assisted large scale terminal grant-free random access method

Abstract

This invention belongs to the field of wireless communication technology and discloses a cognitive-assisted method for large-scale unlicensed random access for terminals. First, active users perceive the uplink channel status, select the channel to be accessed based on the interference power level of each channel, and determine the uplink transmission power level. Then, active users randomly select a preamble sequence to spread their data, combining the preamble sequence and the spread data into a single signal frame, which is then transmitted to the base station through the selected channel at the selected power level. Finally, the base station uses sequential interference cancellation technology to separate signals of different power levels and recovers the transmission signal of the active user at each power level through preamble detection. Based on this, the contention result of active users is determined, and the random access performance is analyzed. This invention is applicable to large-scale user uplink burst transmission scenarios, effectively reducing large-scale unlicensed random access conflicts, increasing the probability of successful user access, and improving the throughput of the cellular network uplink channel.

Description

Technical Field

[0001] This invention belongs to the field of wireless communication technology, and specifically relates to a cognitive-assisted large-scale terminal unlicensed random access method. Background Technology

[0002] Massive Machine Type Communication (mMTC), one of the three major application scenarios of fifth-generation mobile communication systems, primarily involves deploying a massive number of machines and devices to access the network, enabling intelligent surveying, autonomous driving, smart healthcare, and other smart society applications. mMTC systems exhibit characteristics such as massive device access, small uplink data transmission, sporadic communication, and low terminal power consumption. These novel features present new challenges to wireless access technologies. For example, license-based random access suffers from high control signaling overhead and excessive transmission latency; limited spectrum resources cannot support orthogonal access by a massive number of terminals. Therefore, how to support efficient and low-overhead random access for mMTC terminals (users) with limited spectrum resources is one of the most critical issues that current wireless networks urgently need to address.

[0003] Unlicensed random access is one of the mainstream technologies supporting low-overhead access transmission for mMTC terminals. However, since the base station does not participate in access coordination and the terminal (user) is unaware of the network environment, the probability of user access collisions is relatively high. Currently, most research on unlicensed random access for mMTC terminals focuses on reducing access collisions. For example, document CN115499938A discloses an mMTC unlicensed random access method based on multiple power levels and multiple preambles. This method reduces user access collisions by transmitting multiple preambles to form a combined preamble and using multiple power levels to distinguish users. However, this scheme does not consider the advance awareness of the access environment, that is, the user is still unaware of the channel occupancy and interference situation before random access, and sending multiple preambles will consume additional transmission time and transmission power, as well as additional receive detection overhead. Summary of the Invention

[0004] To address the aforementioned technical challenges, this invention proposes a cognitively assisted method for unlicensed random access to large-scale terminals, applicable to scenarios involving bursty uplink transmissions from numerous machine-type terminals (users). This method combines unlicensed random access technology with cognitive radio technology. By empowering mMTC terminals (users) with spectrum awareness, it provides "eyes" for users' uplink random access, enabling active users to obtain current channel occupancy status before random access. This allows them to selectively avoid high-load channels and choose the channel with the lowest interference. Simultaneously, it differentiates users using multiple power levels and determines the uplink transmission power based on the interference power level of the selected channel to reduce random access collisions under a single preamble. This saves preamble time and power overhead, ultimately improving channel multiplexing efficiency and the probability of successful user access.

[0005] The cognitive-assisted large-scale terminal unauthorized random access method of the present invention comprises the following steps:

[0006] Step 1: Active users sense the uplink channel status within the sensing time slot, select the channel to be accessed based on the interference power level of different channels, and determine the uplink transmission power level; active users independently sense all N c The interference power levels of each uplink channel are analyzed, and those with interference power levels below a threshold are selected. Furthermore, the smallest channel is used as the uplink access channel, and a power level is selected from the power level set Q according to the power level selection criterion as the uplink transmission power level;

[0007] Step 2: Active users perform contention for access and data transmission within the transmission time slot; each active user randomly selects a preamble sequence from the preamble combination, uses the preamble sequence to spread the transmitted data, and combines the preamble sequence with the spread data into a signal frame, which is then transmitted to the base station through the selected channel at the selected power level.

[0008] Step 3: Active users receive access results from the base station during the feedback waiting time slot; the base station receives the uplink signal from the active user, uses sequential interference cancellation technology to detect the power level of the received signal, and then detects the preamble sequence carried on each power level through correlation calculation, thereby recovering the uplink transmission data of the active user and determining the user's access conflict situation, while feeding back the user access result.

[0009] It should be noted that the user refers to the terminal, and the active user refers to the active terminal that is waiting to access the transmission.

[0010] Furthermore, the active user access transmission time frame structure is as follows:

[0011] The time frame comprises three parts: a sensing time slot, a transmission time slot, and a feedback waiting time slot, wherein the length of the sensing time slot is τ and the length of the transmission time slot is T. d During the sensing time slot, active users use energy detection to sense the state of the uplink channel and obtain the interference power level of each channel. Based on the interference power level of each channel, they select the uplink access channel and the uplink transmission power level. During the transmission time slot, active users transmit preamble and data signals to the base station through the selected channel at the selected power level. During the feedback waiting time slot, active users wait for the access result feedback message from the base station.

[0012] Furthermore, in step 1, consider a single-cell mMTC system scenario:

[0013] The base station is equipped with M antennas, and N single-antenna active user terminals are evenly distributed in the cell. The length of a single burst of service data for each active user is v bits; the set of active user labels is... There are N in the system c Uplink random access is provided by K uplink frequency channels and K orthogonal preamble sequences of length J, where K ≤ J; the set of uplink channels is defined as follows. Preceding sequence set Where s k This represents the k-th leading sequence. Different leader sequences are orthogonal to each other and have an energy of 1, i.e. k≠p, both have Define the preceding matrix S = [s1, ..., s2] K ] T , SS H =I K S H I represents the Hermitian matrix of matrix S. K Represents a K-row, K-column identity matrix. Represent the complex field of row K and column J;

[0014] The uplink access channel selection method and the uplink transmit power level selection method are explained in detail below:

[0015] Step 1a: Define the set of user transmit power levels and divide the interference power level segments;

[0016] Let the set of uplink transmit power levels of active users be Q = {q1, ..., q}. L The set contains L power levels, where q l Indicates the l-th power level. I q The set of labels representing the transmit power level; corresponding to the transmit power level, the channel interference power level is also uniformly divided into L segments, let and Let these represent the start and end values ​​of the i-th segment, respectively, and define... in This indicates the interference power threshold of the accessible channel; Power level q in set Q i and q j Must satisfy q i <q j And the endpoint value of the i-th interference power level segment It is also less than the endpoint value of the j-th interference power level segment. Right now

[0017] Step 1b: Active users select the uplink access channel based on the interference power level;

[0018] Let there be active users n, n∈I a Perceive all N c The set of interference power levels for each uplink channel is in This indicates the level of interference power perceived by active user n on channel u; active user n from the point where the interference power threshold is met... The channel with the lowest current interference power level is selected from the available channels as the channel to be accessed, i.e., channel selection. As an uplink access channel;

[0019] If an active user perceives that the average interference power across all channels is higher than the interference power threshold... The active user re-attempted to connect after a one-frame delay;

[0020] Step 1c: Active users select uplink transmit power level;

[0021] Based on the uplink access channel selected in step 1b Query set Get active user n in the channel The perceived interference power level Determine the interference power level range in which it is located. but Belonging to the i-th segment, active user n selects the (L+1-i)-th power level q. L+1-i This serves as the transmit power level for its uplink access transmission.

[0022] Furthermore, the active user transmits preamble and data signals to the base station via a selected uplink channel at a selected transmit power level. The preamble and data transmission steps specifically include:

[0023] Step 2a-1: The active user randomly selects a leader sequence from the K leader sequences;

[0024] Let the leading index of active user n be c. n c n For any n ∈ {1, 2, ..., K}, the user's preceding selection vector is: Among them 1 [x] As an indicator function, 1 when the condition x is true. [x] =1, otherwise 1 [x] =0; therefore, the preamble sequence p sent by active user n is 0. n Represented as:

[0025]

[0026] Among them, S T This represents the transpose of the preceding matrix S; p n The transpose of , eye||p n || ２ =1.

[0027] Step 2a-2: Active users use the selected preamble sequence to spread their v-bit service data to generate a spreading sequence of length D = vJ;

[0028] Let v n = [d1, d2, ... d v ] represents the raw business data of active user n, using p n Data x after spreading n Represented as

[0029] x n = [x1, x2, ... x D ]=[d1p n d2p n , ...d v p n (2)

[0030] in, ||x n || 2 =1, D=vJ;

[0031] Steps 2a-3: Active users combine the preamble sequence and spread spectrum data into a signal frame and transmit the signal frame to the base station through the selected uplink channel at the selected power level.

[0032] Combining equations (1) and (2), an active user n transmits a frame signal z in the time domain. nfor:

[0033]

[0034] make This represents the channel selection vector of active user n, and a frame of signal F transmitted by active user n in the time-frequency two-dimensional space. n Represented as

[0035]

[0036] in, This represents the transmission signal of active user n on channel u;

[0037] Furthermore, the base station first performs power level detection on the received signal, specifically as follows:

[0038] Step 3a-1: The base station receives data from N. c The sum of signals in each uplink channel;

[0039] Consider an uplink channel from an active user to the base station that is a Rayleigh fading channel with additive white Gaussian noise. The channel characteristics remain constant and quasi-orthogonal within one frame. The signal G received by the base station in one frame is the sum of signals from N users, expressed as:

[0040]

[0041] Among them, F n =z n u n A single frame of signal representing active user n; N represents the distance from user n to base station M antennas. c Attenuation coefficient matrix of each uplink channel; N represents the relationship between user n and base station antenna m. c A vector of attenuation coefficients for each uplink channel, where Let represent the attenuation coefficient of the u-th uplink channel between user n and base station antenna m; N represents the additive white Gaussian noise matrix of the uplink channel. It follows a mean of 0 and a variance of σ. 2 I M Gaussian distribution, i.e., N~CN(0, σ) 2 I M ), where I is the average noise power. M Represents an M-dimensional identity matrix;

[0042] Step 3b-1: The base station performs bandpass filtering on the received uplink signal to obtain N. c The received signal of each uplink channel;

[0043] The base station receives a signal G that is a signal containing N c A broadband signal with multiple frequency bands; the received signal is processed by N... c Bandpass filtering yields N c The received signal of each uplink channel;

[0044] Let the received signal on the uplink channel u be G. u , u∈CH, is represented as

[0045]

[0046]

[0047] in, The power level received on channel u is q. l and signals, q l，n This indicates that active user n selects the l-th power level q. l ,l∈I q ; This represents the channel attenuation coefficient vector from active user n on channel u to the M antennas of the base station; Indicates the selected power level q on channel u l The collection of active users;

[0048] Step 3c-1: For the received signal G on each uplink channel u Sequential interference cancellation (SIC) technology is used to detect each power level signal in descending order of power level.

[0049] Assume the received signal G on channel u u The included power level signal satisfy: Calculate power level signal Signal-to-interference-to-noise ratio for:

[0050]

[0051] in, Indicates the selected power level q on channel u l A collection of active users Indicates the selected power level q on channel u j q j <q l The set of active users; N u，l and N u，j Representing the power level q on channel u respectively l and q jThe number of active users supported; σ 2 This indicates the channel noise power.

[0052] judge Is it greater than the detection threshold of the base station receiver? Right now Is it true or false?

[0053] If not, the power level q on channel u l q l-1 The signals carried on q1 cannot be detected, and the active user access at these power levels has failed.

[0054] If so, the base station uses SIC technology to detect power level signals in descending order of power level.

[0055] The power level signal detected at the output is The estimated value is denoted as

[0056] Furthermore, the base station performs preamble detection on the power level signal detected on each channel to recover active user data and determine the random access result;

[0057] The leader sequence detection method is specifically as follows:

[0058] Step 3a-2, extract each power level signal carried by each channel. The preamble and data signals of active users are separated from the data.

[0059] Will Decomposed into in, The power level q detected by the base station in channel u is... l The preamble signal, The power level q detected by the base station in channel u is... l Data signals; and They are represented as follows:

[0060]

[0061]

[0062] Step 3b-2: Receive the preamble signal Perform related operations with the preamble matrix S to obtain an estimate of the user's preamble selection vector, and then recover the user's preamble sequence;

[0063] Base station in channel u and power level q l Received and preamble signals Perform related operations with the preceding sequence matrix S, and denot the result as follows. Represented as:

[0064]

[0065] in, This represents the channel attenuation coefficient matrix from N active users on channel u to the base station; This represents N active users with respect to channel u and power level q. l The joint selection matrix; This represents a matrix of preamble sequences sent by N active users; Represents the leading matrix; This represents N active users at channel u and power level q. l The leading selection matrix on, This indicates that the active user n is in channel u and power level q. l The leading selection vector on; if The k-th element is 1, that is This indicates that active user n is using power level q on channel u. l The preamble sequence sent is s k ; This represents the noise matrix superimposed on the signals of N active users. and They have the same distribution;

[0066] Assuming the channel attenuation coefficient matrix Given that, compare it with Multiplying these values ​​yields the N active users at channel u and power level q. l Precedence selection matrix The estimated value for

[0067]

[0068] in, Representation matrix Hermitian matrix; rounded to the nearest whole number. Rounding down the elements yields an approximate estimate. This indicates that user n has channel u and power level q. l Preceding selection vector Approximate estimate;

[0069] Given that each active user selects only one preamble sequence to send, in the absence of access collisions, the matrix Each row has at most one element that is 1, and all other elements are 0; therefore, active user n operates at power level q on channel u. l The estimated preamble number of the transmitted sequence is:

[0070]

[0071] in, Representing vectors The kth element; here, This indicates that active user n is not using power level q on channel u. l A preamble signal is transmitted; correspondingly, active user n transmits a power level q on channel u. l Preamble sequence estimate sent for:

[0072]

[0073] Additional definition here It is an empty leader sequence;

[0074] For the received signal Traversing channel u and power level q l That is, to obtain all Given that each active user selects only one channel and one power level to perform random access, the preamble sequence p sent by active user n n The estimated value The calculation is as follows:

[0075]

[0076] Accordingly, the estimated value of the preamble matrix P sent by all N active users. The final test result was

[0077] Step 3c-2: Receive and process the data signals. Perform a test to restore active user data signals;

[0078] Base station in channel u and power level q l Received data signals Represented as

[0079]

[0080] in, This represents the spread spectrum data signal matrix transmitted by N active users;

[0081] Will With channel characteristic matrix Multiplying these values ​​yields the N active users at channel u and power level q.l Estimate of the spread spectrum signal matrix transmitted above for:

[0082]

[0083] Traversing channel u and power level q l Find all By summing these signals, we can obtain the signal sequences sent by N active users. The estimated value for:

[0084]

[0085] in, Indicates the signal sequence x sent by active user n. n The estimated value;

[0086] use right By performing de-expansion, the original business data of active users can be restored.

[0087] Furthermore, the user conflict detection method is as follows:

[0088] Two or more users that select the same channel, use the same power level, and the same preamble will experience an access conflict. In other words, users experiencing access conflicts are in the same set. and In, and its leading selection vector and same;

[0089] Step 3a-3: Obtain the set of active users carried by each power level on all channels;

[0090] Let channel u be at power level q l Set of active users sending preamble sequence The estimated value is The calculation is as follows:

[0091]

[0092] in, This indicates that the active user n is in channel u and power level q. l Preceding selection vector The estimated value; Representing vectors The 0-norm of a vector The number of non-zero elements; for the received and preamble signals. Traversing channel u and power level ql This will give you the set of active users across all channels.

[0093] Step 3b-3: Calculate the user pilot conflict pattern;

[0094] Define users n and n′ in channel u and power level q. l Pilot collision pattern e u，l (n, n′) is the user leader selection vector. and The product of, i.e.

[0095]

[0096] Given that base stations have difficulty obtaining accurate leading selection vectors for active users n and n′ and Only its estimated value can be obtained. and Therefore, in equation (20) and Substituting its estimated value, we obtain the pilot collision pattern e. u，l The estimated value of (n, n′) Right now

[0097]

[0098] If users n and n′ choose the same pilot sequence, e u，l (n, n′) = 1; otherwise, e u，l (n, n′) = 0;

[0099] Step 3c-3: Determine if there is a random access conflict among active users;

[0100] Based on equation (21), the following method for determining active user access conflicts is designed:

[0101]

[0102] 1) If e u，l (n, n′) = 1, active users n and n′ have an access conflict and both fail to access the system.

[0103] 2) If e u，l (n, n′) = 0, active users n and n′ did not experience any access conflicts and both successfully competed for access; traverse the entire user set. This will allow you to know the results of the access competition for all active users;

[0104] Step 3d-3: The base station will feed back the access results to active users;

[0105] For users who successfully connect, the base station sends a confirmation message to the user via a broadcast channel; for users who fail to connect, the base station sends a failure message to the user via a broadcast channel and notifies the user to try connecting again after a delay.

[0106] Further analysis of active user access performance is as follows:

[0107] The random access probability is defined as the probability that an uplink signal sent by an active user is successfully decoded at the base station; let any active user n select channel u and power level q. l ,Right now The probability of this user's random access is analyzed from three aspects:

[0108] Steps 3a-4: Calculate the probability that an active user successfully acquires an access channel;

[0109] When an active user n perceives that the interference power level of at least one channel is below the interference power threshold, the user can obtain access to the channel; therefore, the probability P of an active user n successfully obtaining access to the channel is... ch The calculation is as follows:

[0110]

[0111] in, This indicates the level of interference perceived by active user n on channel u. Exceeding the interference power threshold The probability of;

[0112] Step 3b-4: Calculate the probability that the power level is correctly detected;

[0113] Let's assume that active user n successfully accesses channel u and selects power level q. l As the uplink transmit power; power level q on channel u l The probability that the active user signal carried can be correctly detected. The calculation is as follows:

[0114]

[0115] in, This represents the probability that the i-th power level on channel u can be correctly detected;

[0116] Step 3c-4: Calculate the probability that an active user will use a unique preamble on the selected channel and power level;

[0117] If channel u and power level q are selected l The number of users is N u，l User n in channel u and power level q l The probability of selecting a unique leader Calculated as

[0118]

[0119] Where K represents the number of orthogonal leader sequences;

[0120] Step 3d-4: Calculate the random access probability of active users;

[0121] Active user n selects channel u and power level q l Access probability Pr under certain conditions u，l The calculation is as follows:

[0122]

[0123] Equation (25) is applied to channel u and power level q. l The average probability of random access for active users is obtained as follows:

[0124]

[0125] in,

[0126] The beneficial effects of this invention are as follows: This invention comprehensively utilizes spectrum sensing results and interference power thresholds to optimize the random access channel for users, which can effectively reduce the probability of users having co-channel conflicts; by dynamically adjusting the uplink transmission power of users using spectrum sensing results, it can realize multi-user access transmission based on NOMA, thereby improving spectrum efficiency; This invention expands the time-frequency two-dimensional resource space of the existing two-step random access protocol into a time-frequency-power three-dimensional resource space, thereby effectively improving the probability of successful user access and increasing the throughput of the uplink channel of the cellular network. Attached Figure Description

[0127] Figure 1 This is a system model diagram in an embodiment of the present invention;

[0128] Figure 2 This is a diagram of the user's time frame structure in an embodiment of the present invention;

[0129] Figure 3 This is a schematic diagram of the access transmission protocol in an embodiment of the present invention;

[0130] Figure 4 This is a flowchart illustrating the implementation process of the method in this embodiment of the invention. Detailed Implementation

[0131] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0132] set up Figure 1 System scenario shown:

[0133] Consider a single-cell mMTC system scenario: the base station is equipped with M antennas, and N single-antenna terminals (users) are evenly distributed in the cell. The length of a single burst of service data for each user is v bits; the user identifier set is... There are N in the system c Uplink random access is provided by K uplink channels (channels) and K orthogonal preamble sequences of length J, where K ≤ J; the set of uplink channels is defined as follows. Preceding sequence set Where s k This represents the k-th leading sequence. Different leader sequences are orthogonal to each other and have an energy of 1, i.e. k≠p, both have Define the preceding matrix S = [s1, ..., s2] K ] T , SS H =I K S H I represents the Hermitian matrix of matrix S. K Represents a K-row, K-column identity matrix. Represents the complex field of row K and column J.

[0134] Considering that the terminal (user) uses an unlicensed random access protocol, design Figure 2 The user access transmission time frame structure shown is as follows:

[0135] The access transmission time frame consists of three parts: a sensing time slot, a transmission time slot, and a feedback waiting time slot. The length of the sensing time slot is τ, and the length of the transmission time slot is T. d During the sensing time slot, active users use the energy detection method to sense the state of the uplink channel and obtain the interference power level of each channel. Based on the interference power level of each channel, they select a random access channel and uplink transmission power level. During the transmission time slot, active users use a two-step unlicensed random access protocol to transmit preamble and data signals to the base station through the selected channel at the selected power level. During the feedback waiting time slot, active users wait for the base station's access result feedback message.

[0136] Combination Figure 1 System model, Figure 2 Time frame structure, Figure 3 Transmission protocol illustration and Figure 4 The specific implementation steps of this method for random access are described below:

[0137] Step 1: Within the sensing time slot, active users sense the channel status, select the channel to be accessed based on the interference power level of different channels, and determine the uplink transmit power level.

[0138] The specific steps for active users to select a channel to access are as follows:

[0139] Step 1a: Define the set of transmit power levels and divide the channel interference power level segments;

[0140] Let the set of uplink transmit power levels of active users be Q = {q1, ..., q}. L}, q l Indicates the l-th power level. Similarly, the channel interference power level is also uniformly divided into L segments, let and Let these represent the start and end values ​​of the i-th segment, respectively, and define... There's always q i <q j ,

[0141] Step 1b: Active users select the channel to be accessed based on the interference power level;

[0142] Let there be active users n, n∈I a Perceive all N c The interference power level of each uplink channel is in This indicates that terminal n senses the interference power level on channel u, and terminal n selects channel u. This serves as the uplink random access channel. If a user perceives that the interference power on all current channels is higher than the threshold, the user will retry access after a one-frame delay.

[0143] Step 1c: Active users select uplink transmit power level;

[0144] Based on the interference power level of the uplink access channel selected in step 1b Further determine the range of interference power levels in which it is located; let's assume Right now If the user belongs to the i-th segment, then user n selects the (L+1-i)-th power level q. L+1-i This serves as the transmit power level for its uplink access transmission.

[0145] Step 2: Within the transmission time slot, active users adopt... Figure 3 The two-step unlicensed random access protocol shown performs preamble and data transmission. This protocol is described below:

[0146] Step 2a, Random Access Transmission: An active user randomly selects a preamble sequence from the preamble set SC, uses the sequence to spread the data, and combines the preamble sequence and the spread data into a signal frame. The user signal frame is then transmitted to the base station through the selected channel at the selected power level.

[0147] Step 2b, Access Result Feedback: The base station receives the user's uplink signal and sequentially detects the power level and preamble signal. Based on this, it determines the user contention result and recovers the user data. Then, it feeds back the contention result to the user through the access response. User access conflict occurs when and only when two users access the same channel and the preamble sequence and transmission power level are the same.

[0148] The preamble and data transmission steps are as follows:

[0149] Step 2a-1: The active user randomly selects a leader sequence from the K leader sequences;

[0150] Let user n select the leading index c. n c n If n ∈ {1, 2, ..., K}, then the user's preceding selection vector can be represented as: Among them 1 [x] As an indicator function, 1 when the condition x is true. [x] =1, otherwise 1 [x] =0; therefore, the leading sequence chosen by user n can be represented as

[0151]

[0152] Among them, S T This represents the transpose of the preceding matrix S; And ||p n || 2 =1;

[0153] Step 2a-2: Use the selected leader sequence p n Spread spectrum of v-bit service data to generate a spreading sequence of length D = vJ;

[0154] Let v n = [d1, d2, ... d v ] represents the business data of user n, using p n Data x after spreading n Represented as

[0155] x n = [x1, x2, ... x D ]=[d1p n d2p n , ...d v pn (2)

[0156] in, ||x n || ２ =1, D=vJ.

[0157] Steps 2a-3: Combine the preamble sequence and spread spectrum data into a single frame signal and transmit it through the selected uplink channel. At the selected power level Send signal frame zn to the base station;

[0158] Merge user preamble and service data, while also considering that user n selects an uplink power level of q. l，n We obtain a frame of signal z sent by user n in the time domain. n for

[0159]

[0160] make This represents the channel selection vector for user n, and a frame of signal F transmitted by user n in the time-frequency two-dimensional space. n It can be represented as

[0161]

[0162] in, This represents the transmitted signal of user n on channel u;

[0163] Step 3: Active users receive the access result from the base station during the feedback waiting time slot, as detailed below:

[0164] 1) The base station performs power level detection on the received signal;

[0165] Step 3a-1: The base station receives data from N. c The sum of signals in each uplink channel;

[0166] Consider an uplink channel from the user to the base station that is a Rayleigh fading channel with additive white Gaussian noise. The channel characteristics remain constant and quasi-orthogonal within one frame. The signal G received by the base station in one frame is the sum of signals from N users, expressed as:

[0167]

[0168] Among them, F n =z n u n This represents a frame of signal sent by user n; N represents the distance from user n to the base station (M antennas). cAttenuation coefficient matrix of each uplink channel; N represents the relationship between user n and base station antenna m. c A vector of attenuation coefficients for each uplink channel, where Let represent the attenuation coefficient of the u-th uplink channel between user n and base station antenna m; N represents the additive white Gaussian noise matrix of the uplink channel. It follows a mean of 0 and a variance of σ. 2 I M Gaussian distribution, i.e., N~CN(0, σ) 2 I M ), where I is the average noise power. M Represents an M-dimensional identity matrix;

[0169] Step 3b-1: The base station performs bandpass filtering on the received uplink signal to obtain N. c The received signal of each uplink channel;

[0170] The base station receives a signal G that is a signal containing N c A broadband signal with multiple frequency bands is subjected to N... c Bandpass filtering yields N c The received signal G of each uplink channel u , u∈CH;

[0171] Let the received signal on the uplink channel u be G. u , u∈CH, can be represented as

[0172]

[0173]

[0174] in, The power level received on channel u is q. l and signals, q l，n This indicates that user n selects the l-th power level q. l l∈{1, 2, ..., L}; This represents the channel attenuation coefficient vector from user n to the base station (M antennas) on channel u; Indicates the selected power level q on channel u l The user set;

[0175] Step 3c-1: Based on SIC technology, analyze the received signal G on each channel. u Perform power level detection.

[0176] Assume the received signal G on channel u u The included power level signal satisfy:

[0177] Calculate power level signal Signal-to-interference-to-noise ratio for

[0178]

[0179] in, Indicates the selected power level q on channel u l The user set, Indicates the selected power level q on channel u j (q j <q l The user set of N; u，l and N u，j Representing the power level q on channel u respectively l and q j The number of users it can support;

[0180] judge Is it greater than the detection threshold of the base station receiver? Right now Is it true or false?

[0181] If not, the power level q on channel u l All signals carried on ~q1 failed to be detected, and user access at these power levels failed;

[0182] If so, the base station uses SIC technology to detect the power level signals in descending order of power level.

[0183] The power level signal detected at the output is The estimated value is denoted as

[0184] 2) The base station performs preamble detection on the detected power level signal;

[0185] Step 3a-2, from the power level signal The preamble and data signals sent by the user terminal are decomposed from the data.

[0186] Will Decomposed into in, The power level q detected by the base station in channel u is... l The preamble signal, The power level q detected by the base station in channel u is... l The data signal. and They are respectively represented as

[0187]

[0188]

[0189] This assumes the system has a good timing synchronization mechanism, and the base station can easily extract power level signals by intercepting signal frame data. Remove the leader from the middle With data signals

[0190] Step 3b-2: Receive the preamble signal Perform related operations with the preamble matrix S to obtain an estimate of the user's preamble selection vector, and then recover the user's preamble sequence;

[0191] Base station in channel u and power level q l Received and preamble signals Perform related operations with the preceding sequence matrix S, and denot the result as follows. It is expressed as

[0192]

[0193] in, This represents the channel attenuation coefficient matrix for N users to the base station on channel u; This represents a matrix of preamble sequences sent by N users; This represents N users in channel u and power level q. l The leading selection matrix on, User n in channel u and power level q l The leading selection vector on; if User n uses power level q on channel u. l The preamble sequence sent is s k ; This represents the noise matrix superimposed on N user signals. and All follow a Gaussian distribution.

[0194] Assuming the channel attenuation coefficient matrix Given that, compare it with Multiply by this to obtain the channel u and power level q for N users. l Precedence selection matrix The estimated value for

[0195]

[0196] in, Representation matrix The Hermitian matrix. Rounding is used for... Rounding down the elements yields an approximate estimate. This indicates that user n has channel u and power level q. l Preceding selection vector Approximate estimate;

[0197] User n uses power level q on channel u. l The estimated preamble number of the transmitted sequence is:

[0198]

[0199] in, Representing vectors The k-th element. Here, This indicates that user n is not using power level q on channel u. l Send a preamble signal;

[0200] User n uses power level q on channel u. l Preamble sequence estimate sent for:

[0201]

[0202] Additional definition here It is an empty leader sequence;

[0203] Traversing channel u and power level q l User n sends a preamble sequence p n The estimated value It can be calculated as

[0204]

[0205] Accordingly, the estimated value of the preamble matrix P sent by all N users. The final test result was

[0206] Step 3c-2: Receive and process the data signals. Perform testing and restore user data signals;

[0207] Base station in channel u and power level q l Received data signals It can be represented as

[0208]

[0209] in, This represents the spread spectrum data signal matrix transmitted by N users.

[0210] Combine equation (16) with the channel characteristic matrix Multiplying these gives the values ​​of N users at channel u and power level q. l Estimate of the spread spectrum signal sequence transmitted above for

[0211]

[0212] Traversing channel u and power level q l Find all The signals are then summed to obtain the signal sequences sent by N users. The estimated value for

[0213]

[0214] in, This represents the signal sequence x sent by user n. n The estimated value;

[0215] use right By performing de-expansion, the user's original data information can be restored.

[0216] 3) The user access conflict detection algorithm is described below:

[0217] Step 3a-3: Detect the set of active users carried by each power level on each channel;

[0218] Let channel u be at power level q l Set of users sending preamble sequence The estimated value is Calculated as

[0219]

[0220] in, This indicates that user n has channel u and power level q. l Preceding selection vector The estimated value; Representing vectors The 0-norm;

[0221] For the received and preamble signals Traversing channel u and power level q l This will allow you to obtain the set of users on all channels.

[0222] Step 3b-3: Calculate the user pilot conflict pattern;

[0223] For each set Calculate the values ​​of any two users n and n′ in the channel u and power level q. l Pilot collision pattern e u，l (n, n′):

[0224]

[0225] Estimated value of pilot collision pattern Right now

[0226]

[0227] Step 3c-3: Determine if there is a user random access conflict;

[0228] Design the following method for determining user access conflicts:

[0229] If e u，l (n, n′) = 1, users n and n′ have an access conflict and both fail to access the system.

[0230] If e u，l (n, n′) = 0, users n and n′ did not conflict, and both successfully competed for access;

[0231] Traverse the entire user set This will give you the results of the access competition for all users.

[0232] Step 3c-4: The base station will feed back the access result to the user;

[0233] For users who successfully connect, the base station sends a "connection successful confirmation" message to the user via a broadcast channel; for users who fail to connect, the base station sends a "connection failed" message to the user via a broadcast channel and notifies them to try connecting again after a delay.

[0234] 4) The access performance analysis of the active users is as follows:

[0235] User n selects channel u and power level q l Access probability Pr under certain conditions u，l The calculation is as follows:

[0236]

[0237] in, Indicates the power level q on channel u l The probability that the carried signal can be correctly demodulated; This indicates that user n has channel u and power level q. l The probability of selecting a unique leader is calculated as follows:

[0238]

[0239]

[0240] For channel u and power level q l The average probability of a user successfully connecting is calculated as follows:

[0241]

[0242]

[0243] in, P ch This represents the probability that user n successfully obtains access to the channel.

[0244] The above description is merely a preferred embodiment of the present invention and is not intended to further limit the present invention. All equivalent changes made based on the description and drawings of the present invention are within the protection scope of the present invention.

Claims

1. A method for large-scale, unlicensed random access to terminals with cognitive assistance, characterized in that, The method steps are as follows: Step 1: Active users sense the uplink channel status within the sensing time slot, select the channel to be accessed based on the interference power level of different channels, and determine the uplink transmission power level; active users independently sense all N c The interference power levels of each uplink channel are analyzed, and those with interference power levels below a threshold are selected. Furthermore, the smallest channel is used as the uplink access channel, and a power level is selected from the power level set Q according to the power level selection criterion as the uplink transmission power level; Step 2: Active users perform contention for access and data transmission within the transmission time slot; each active user randomly selects a preamble sequence from the preamble combination, uses the preamble sequence to spread the transmitted data, and combines the preamble sequence with the spread data into a signal frame, which is then transmitted to the base station through the selected channel at the selected power level. Step 3: Active users receive the access result from the base station during the feedback waiting time slot; The base station receives the uplink signal from the active user, uses sequential interference cancellation technology to detect the power level of the received signal, and then detects the preamble sequence carried on each power level through correlation calculation, thereby recovering the uplink transmission data of the active user and determining the user's access conflict situation, while feeding back the user access result; In step 1, a single-cell mMTC system scenario is considered: The base station is equipped with M antennas, and N single-antenna active user terminals are evenly distributed in the cell. The length of a single burst of service data for each active user is v bits; the set of active user labels is... There are N in the system c Uplink random access is provided by K uplink frequency channels and K orthogonal preamble sequences of length J, where K ≤ J; the set of uplink channels is defined as follows. Preceding sequence set Where s k This represents the k-th leading sequence. Different leader sequences are orthogonal to each other and have an energy of 1, i.e. All Define the leading matrix SS H =I K S H I represents the Hermitian matrix of matrix S. K Represents a K-row, K-column identity matrix. Represent the complex field of row K and column J; The uplink access channel selection method and the uplink transmit power level selection method are explained in detail below: Step 1a: Define the set of user transmit power levels and divide the interference power level segments; Let the set of uplink transmit power levels of active users be Q = {q1, ..., q} L The set contains L power levels, where q l Indicates the l-th power level. I q The set of labels representing the transmit power level; corresponding to the transmit power level, the channel interference power level is also uniformly divided into L segments, let and Let these represent the start and end values ​​of the i-th segment, respectively, and define... in This indicates the interference power threshold of the accessible channel; Power level q in set Q i and q j Must satisfy q i j And the endpoint value of the i-th interference power level segment It is also less than the endpoint value of the j-th interference power level segment. Right now ​ Step 1b: Active users select the uplink access channel based on the interference power level; Let there be active users n, n∈I a Perceive all N c The set of interference power levels for each uplink channel is in This indicates the level of interference power perceived by active user n on channel u; Active users n from satisfying the interference power threshold, i.e. The channel with the lowest current interference power level is selected from the available channels as the channel to be accessed, i.e., channel selection. As an uplink access channel; If an active user perceives that the average interference power across all channels is higher than the interference power threshold... The active user re-attempted to connect after a one-frame delay; Step 1c: Active users select uplink transmit power level; Based on the uplink access channel selected in step 1b Query set Get active user n in the channel The perceived interference power level Determine the interference power level range in which it is located. but Belonging to the i-th segment, active user n selects the (L+1-i)-th power level q. L+1-i This serves as the transmit power level for its uplink access transmission.

2. The method for large-scale unauthorized random access to terminals with cognitive assistance according to claim 1, characterized in that, The specific structure of the active user access transmission time frame is as follows: The time frame comprises three parts: a sensing time slot, a transmission time slot, and a feedback waiting time slot, wherein the length of the sensing time slot is τ and the length of the transmission time slot is T. d During the sensing time slot, active users use the energy detection method to sense the status of the uplink channel and obtain the interference power level of each channel. Based on the interference power level of each channel, they select the uplink access channel and the uplink transmit power level. During the transmission time slot, active users transmit preamble and data signals to the base station through the selected channel at the selected power level. During the feedback waiting time slot, active users wait for access result feedback messages from the base station.

3. The method for large-scale unlicensed random access to terminals with cognitive assistance according to claim 1, characterized in that, Active users transmit preamble and data signals to the base station via a selected uplink channel at a selected transmit power level. The preamble and data transmission steps are as follows: Step 2a-1: The active user randomly selects a leader sequence from the K leader sequences; Let the leading index of active user n be c. n c n Given n ∈ {1,2,…,K} and n ∈ {1,2,…,N}, the user's leading selection vector is: Among them 1 [x] As an indicator function, 1 when the condition x is true. [x] =1, otherwise 1 [x] =0; therefore, the preamble sequence p sent by active user n is 0. n Represented as: Among them, S T This represents the transpose of the preceding matrix S; p n The transpose of , And ||p n || 2 =1, Step 2a-2: Active users use the selected preamble sequence to spread their v-bit service data to generate a spreading sequence of length D = vJ; Let v n =[d1,d2,...d v [This refers to] the raw business data of active user n, using p n Data x after spreading n Represented as x n =[x1,x2,...x D ]=[d1p n ,d2p n ,...d v p n ] (2) in, ||x n || 2 =1, D=vJ; Steps 2a-3: Active users combine the preamble sequence and spread spectrum data into a signal frame and transmit the signal frame to the base station through the selected uplink channel at the selected power level. Combining equations (1) and (2), an active user n transmits a frame signal z in the time domain. n for: make This represents the channel selection vector of active user n, and a frame of signal F transmitted by active user n in the time-frequency two-dimensional space. n Represented as in, This represents the transmission signal of active user n on channel u; 4. The cognitive-assisted large-scale terminal unauthorized random access method according to claim 3, characterized in that, The base station first performs power level detection on the received signal, specifically as follows: Step 3a-1: The base station receives data from N. c The sum of signals in each uplink channel; Consider an uplink channel from an active user to the base station that is a Rayleigh fading channel with additive white Gaussian noise. The channel characteristics remain constant and quasi-orthogonal within one frame. The signal G received by the base station in one frame is the sum of signals from N users, expressed as: Among them, F n =z n u n A single frame of signal representing active user n; N represents the distance from user n to base station M antennas. c Attenuation coefficient matrix of each uplink channel; N represents the relationship between user n and base station antenna m. c A vector of attenuation coefficients for each uplink channel, where Let represent the attenuation coefficient of the u-th uplink channel between user n and base station antenna m; N represents the additive white Gaussian noise matrix of the uplink channel. It follows a mean of 0 and a variance of σ. 2 I M The Gaussian distribution, i.e., N~CN(0,σ) 2 I M ), where I is the average noise power. M Represents an M-dimensional identity matrix; Step 3b-1: The base station performs bandpass filtering on the received uplink signal to obtain N. c The received signal of each uplink channel; The base station receives a signal G that is a signal containing N c A broadband signal with multiple frequency bands; the received signal is processed by N... c Bandpass filtering yields N c The received signal of each uplink channel; Let the received signal on the uplink channel u be G. u , u∈CH, is represented as in, The power level received on channel u is q. l and signals, q l,n This indicates that active user n selects the l-th power level q. l ,l∈I q ; This represents the channel attenuation coefficient vector from active user n on channel u to the M antennas of the base station; Indicates the selected power level q on channel u l The collection of active users; Step 3c-1: For the received signal G on each uplink channel u Sequential interference cancellation (SIC) technology is used to detect each power level signal in descending order of power level. Assume the received signal G on channel u u The included power level signal satisfy: Calculate power level signal Signal-to-interference-to-noise ratio for: in, Indicates the selected power level q on channel u l A collection of active users Indicates the selected power level q on channel u j q j l The set of active users; N u,l and N u,j Representing the power level q on channel u respectively l and q j The number of active users supported; σ 2 Indicates channel noise power.​ judge Is it greater than the detection threshold of the base station receiver? Right now Is it true or false? If not, the power level q on channel u l ,q l-1 The signals carried on q1 cannot be detected, and the active user access at these power levels has failed. If so, the base station uses SIC technology to detect power level signals in descending order of power level. The power level signal detected at the output is The estimated value is denoted as 5. The cognitive-assisted large-scale terminal unauthorized random access method according to claim 4, characterized in that, The base station further performs preamble detection on the power level signal detected on each channel to recover active user data and determine the random access result; The leader sequence detection method is specifically as follows: Step 3a-2, extract each power level signal carried by each channel. The preamble and data signals of active users are separated from the data. Will Decomposed into in, The power level q detected by the base station in channel u is... l The preamble signal, The power level q detected by the base station in channel u is... l Data signals; and They are represented as follows: Step 3b-2: Receive the preamble signal Perform related operations with the preamble matrix S to obtain an estimate of the user's preamble selection vector, and then recover the user's preamble sequence; Base station in channel u and power level q l Received and preamble signals Perform related operations with the preceding sequence matrix S, and denot the result as follows. Represented as: in, This represents the channel attenuation coefficient matrix from N active users on channel u to the base station; This represents N active users with respect to channel u and power level q. l The joint selection matrix; This represents a matrix of preamble sequences sent by N active users; Represents the leading matrix; This represents N active users at channel u and power level q. l The leading selection matrix on, This indicates that the active user n is in channel u and power level q. l The leading selection vector on; if The k-th element is 1, that is This indicates that active user n is using power level q on channel u. l The preamble sequence sent is s k ; This represents the noise matrix superimposed on the signals of N active users. and They have the same distribution; Assuming the channel attenuation coefficient matrix Given that, compare it with Multiplying these values ​​yields the N active users at channel u and power level q. l Precedence selection matrix The estimated value for in, Representation matrix Hermitian matrix; rounded to the nearest whole number. Rounding down the elements yields an approximate estimate. This indicates that user n has channel u and power level q. l Preceding selection vector Approximate estimate; Given that each active user selects only one preamble sequence to send, in the absence of access collisions, the matrix Each row has at most one element that is 1, and all other elements are 0; therefore, active user n operates at power level q on channel u. l The estimated preamble number of the transmitted sequence is: in, Representing vectors The kth element; here, This indicates that active user n is not using power level q on channel u. l A preamble signal is transmitted; correspondingly, active user n transmits a power level q on channel u. l Preamble sequence estimate sent for: Additional definition here It is an empty leader sequence; For the received signal Traversing channel u and power level q l That is, to obtain all Given that each active user selects only one channel and one power level to perform random access, the preamble sequence p sent by active user n n The estimated value The calculation is as follows: Accordingly, the estimated value of the preamble matrix P sent by all N active users. The final test result was Step 3c-2: Receive and process the data signals. Perform a test to restore active user data signals; Base station in channel u and power level q l Received data signals Represented as in, This represents the spread spectrum data signal matrix transmitted by N active users; Will With channel characteristic matrix Multiplying these values ​​yields the N active users at channel u and power level q. l Estimate of the spread spectrum signal matrix transmitted above for: Traversing channel u and power level q l Find all By summing these signals, we can obtain the signal sequences sent by N active users. The estimated value for: in, Indicates the signal sequence x sent by active user n. n The estimated value; use right By performing de-expansion, the original business data of active users can be restored.

6. The method for large-scale unlicensed random access to terminals with cognitive assistance according to claim 5, characterized in that, The specific method for detecting user conflicts is as follows: Two or more users that select the same channel, use the same power level, and the same preamble will experience an access conflict. In other words, users experiencing access conflicts are in the same set. and In, and its leading selection vector and same; Step 3a-3: Obtain the set of active users carried by each power level on all channels; Let channel u be at power level q l Set of active users sending preamble sequence The estimated value is The calculation is as follows: in, This indicates that the active user n is in channel u and power level q. l Preceding selection vector The estimated value; Representing vectors The 0-norm of a vector The number of non-zero elements; for the received and preamble signals. Traversing channel u and power level q l This will give you the set of active users across all channels. Step 3b-3: Calculate the user pilot conflict pattern; Define users n, n′ in channel u and power level q l Pilot collision pattern e u,l (n,n′) is the user leader selection vector. and The product of, i.e. Given that base stations have difficulty obtaining accurate pre-selection vectors for active users n and n′ and Only its estimated value can be obtained. and Therefore, in equation (20) and Substituting its estimated value, we obtain the pilot collision pattern e. u,l The estimated value of (n,n′) Right now If users n and n′ select the same pilot sequence, e u,l (n,n′)=1; otherwise, e u,l (n,n′)=0; Step 3c-3: Determine if there is a random access conflict among active users; Based on equation (21), the following method for determining active user access conflicts is designed: 1) If e u,l (n,n′)=1, active users n and n′ have an access conflict and both fail to access the system. 2) If e u,l (n,n′)=0, active users n,n ′ No access conflict occurred; both successfully competed for access. The entire user set was then traversed. This will allow you to know the results of the access competition for all active users; Step 3d-3: The base station will feed back the access results to active users; For users who successfully connect, the base station sends a confirmation message to the user via a broadcast channel; for users who fail to connect, the base station sends a failure message to the user via a broadcast channel and notifies the user to try connecting again after a delay.

7. The method for large-scale unlicensed random access to terminals with cognitive assistance according to claim 6, characterized in that, The access performance analysis of active users is as follows: The random access probability is defined as the probability that an uplink signal sent by an active user is successfully decoded at the base station; let any active user n select channel u and power level q. l ,Right now The probability of this user's random access is analyzed from three aspects: Steps 3a-4: Calculate the probability that an active user successfully acquires an access channel; When an active user n perceives that the interference power level of at least one channel is lower than the interference power threshold, the user is able to obtain access to the channel; Therefore, the probability P of an active user n successfully acquiring an access channel is... ch The calculation is as follows: in, This indicates the level of interference perceived by active user n on channel u. Exceeding the interference power threshold The probability of; Step 3b-4: Calculate the probability that the power level is correctly detected; Let's assume that active user n successfully accesses channel u and selects power level q. l As the uplink transmit power; power level q on channel u l The probability that the active user signal carried can be correctly detected. The calculation is as follows: in, This represents the probability that the i-th power level on channel u can be correctly detected; Step 3c-4: Calculate the probability that an active user will use a unique preamble on the selected channel and power level; If channel u and power level q are selected l The number of users is N u,l User n in channel u and power level q l The probability of selecting a unique leader Calculated as Where K represents the number of orthogonal leader sequences; Step 3d-4: Calculate the random access probability of active users; Active user n selects channel u and power level q l Access probability Pr under certain conditions u,l The calculation is as follows: Equation (25) is applied to channel u and power level q. l The average probability of random access for active users is obtained as follows: in,

Images