CN108811143B - CTU (computer to utility) distribution method of uplink authorization-free SCMA (Single chip multiple Access) based on user activity - Google Patents
CTU (computer to utility) distribution method of uplink authorization-free SCMA (Single chip multiple Access) based on user activity Download PDFInfo
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Abstract
The invention discloses a CTU distribution method of an uplink authorization-free SCMA (Single chip multiple access) based on user activity, and relates to a CTU distribution method. The invention aims to solve the problems of high probability of CTU collision among users in the conventional CTU distribution and high calculation complexity. The process is as follows: firstly, the method comprises the following steps: in an authorization-free uplink SCMA system, calculating to obtain the average CTU collision probability corresponding to L CTUs of N _ length users in T' time slots, and simplifying the average CTU collision probability to obtain an NP-hard optimized expression; II, secondly, the method comprises the following steps: the user n is arranged according to the liveness W n Sorting from big to small and giving different priorities; n' represents a new set generated after the user set N is arranged from big to small according to the activity, and three: obtaining an optimal solution set; fourthly, the method comprises the following steps: and obtaining a user and CTU distribution relation matrix according to N, N' and the optimal solution set. The invention is used in the field of SCMA CTU distribution.
Description
Technical Field
The invention relates to a CTU distribution method in an uplink authorization-free SCMA.
Background
The enormous demand of wireless communication for massive access, low delay and high throughput makes the fifth generation mobile communication (5G) a hot topic of current research. The 5G can satisfy a higher quality of service (QoS) requirement, and satisfy a scenario of Internet of things (IoT).
However, as a key technology of a Long Term Evolution (LTE) system, an orthogonal multiple access (OFDMA) technology divides a frequency band into a plurality of mutually orthogonal subcarriers and distributes the subcarriers to different users, respectively, to achieve multiple access. Limited by the orthogonal division mode, the user gain of the OFDMA does not exceed 1, and the requirement of mass access cannot be met. Meanwhile, the transmission of the uplink LTE follows a request and scheduling mode, which also causes unavoidable delay. Therefore, SCMA is proposed as a new type of non-orthogonal multiple access technology based on a codebook form. The competition-based uplink SCMA transmission mode realizes multiple access through different code books allocated to different users. Because of the sparse codebook, a new dimension is introduced, and the SCMA receiver can decode the overlapped signal information, which also brings user gain that the conventional orthogonal multiple access technique does not have.
In an uplink unlicensed SCMA transmission system, a user communicates data by assigning each user to a CTU, which is a combination of time, frequency, codebook and pilot, before transmitting a message. The receiver detects the users by detecting the pilot sequences in each CTU and performs channel estimation. As long as no pilot collision occurs in the base station, the receiver can decode the information sequence by means of a Message Passing Algorithm (MPA). A traditional CTU allocation strategy adopts a modular division mode, the CTU allocation is completed according to the serial number of the user, and the information characteristics of the user such as activity, position and the like are not considered, so that the CTU collision probability among users in the existing CTU allocation is high, and the calculation complexity is high.
SCMA (sparse Code Multiple access) is sparse Code division Multiple access; the CTU (Contention Transmission Unit) is a contention Transmission unit.
Disclosure of Invention
The invention aims to solve the problems of high probability of CTU collision among users and high calculation complexity in the conventional CTU distribution, and provides a CTU distribution method of an uplink authorization-free SCMA (sparse code multiple access) based on user activity.
The CTU distribution method of the uplink authorization-free SCMA based on the user activity comprises the following specific processes:
the method comprises the following steps: in an authorization-free uplink SCMA system, calculating to obtain the average CTU collision probability corresponding to L CTUs of N _ length users in T' time slots, and simplifying the average CTU collision probability to obtain an NP-hard optimized expression;
step two: in an authorization-free uplink SCMA system, a user n is set according to an activity W n Sorting from big to small and giving different priorities; n — 1,2,. and N _ length;
the activity is high, and the priority is high;
n' represents the users in the user set N according to the activity W n The new set generated after the permutation from large to small, N' ═ nxtr,
wherein TR represents a mapping matrix from N to N'; the user set N comprises N _ length users; the set N 'includes N _ length' users;
step three: setting P co (m) represents CTU collision probability of the first m users in the set N' obtained in step two, and Δ P (m) ═ P co (m)-P co (m-1)]Representing CTU collision increment when the mth user is considered to be accessed into the authorization-free uplink SCMA system, carrying out iterative loop solution optimization on delta P (m) to obtain the optimal solution g each time m According to the optimal solution g at each time m Obtaining an optimal solution set G' ═ { G ═ G 1 ,…g m ,…,g N_length′ }；
Wherein m is 1, 2., N _ length'; p is co (m-1) representing the CTU collision probability of the first m-1 users in the set N' obtained in the step two;
step four: and obtaining a user and CTU distribution relation matrix G according to N, N 'and the optimal solution set G'.
The invention has the beneficial effects that:
the invention introduces the complexity of a user as a reference factor of CTU distribution on the basis of an original modular division algorithm, re-deduces a formula of average CTU collision probability based on the complexity of the user, and the optimal solution based on the collision formula is a nonlinear mixed integer problem and is also an NP-hard problem. Compared with a violent solving method, the method greatly reduces the complexity of calculation while reducing the CTU collision probability among users.
The performance advantages and features of the invention compared to the original modulo division based allocation are embodied in:
1. the activity characteristic of the user is considered, and the collision probability, namely the packet loss rate, is greatly reduced in the scene of intensive access of the user.
2. The denser the users are, the larger the gap of the activity degrees is, and the more remarkable the performance improvement is.
3. Compared with a brute force solution problem, the method can obtain an optimal solution with extremely low complexity.
As can be seen from fig. 3a, with the algorithm proposed in the present invention, the packet loss rate is reduced by 17%, 20%, and 22% when the number of users is 24,30, and 36, respectively. In fig. 3b, when the number of users is 24 and the number of CTUs is 8, 10, and 12, packet loss rates are reduced by 23%, 19%, and 17%. Therefore, the algorithm provided by the invention has good packet loss rate performance; meanwhile, the more dense scenes of users can be known, the better the packet loss rate performance of the proposed algorithm is, which is very practical for the scenes of the internet of things with 5G mass access in the future.
Fig. 4 shows a graph comparing the complexity of the proposed algorithm with brute force solution when the number of users varies from 24 to 36. It can be seen from fig. 4 that the computational complexity can be reduced by 16 orders of magnitude when the number of users is 30.
Drawings
FIG. 1 is a schematic diagram of uplink unlicensed SCMA transmission according to the present invention, where ACK is an acknowledgement command;
FIG. 2 is a diagram of the relationship between the time-frequency resources, the codebook and the pilot frequency in the user and CTU of the present invention, C 1 Is a first codebook, C 2 Is a second codebook, C J Is the J-th codebook, P 1 For the first pilot sequence, P L+1 For the L +1 th pilot sequence, P L(J-1)+1 Is the L (J-1) +1 pilot sequence，P L For the Lth pilot sequence, P 2L For the 2L pilot sequence, P LJ Is the LJ-th pilot sequence, f is frequency, t is time, C is codebook, P is pilot sequence;
fig. 3a is a packet loss rate CDF graph corresponding to a CTU allocation algorithm based on user activity and a CTU allocation algorithm based on modulus under the condition that the number of CTUs is not changed, where CDF is cumulative probability density distribution; n is N _ length users;
fig. 3b is a graph of packet loss rate CDF corresponding to a CTU allocation algorithm based on user activity and a CTU allocation algorithm based on modular division under the condition that the number of users is not changed;
FIG. 4 is a comparison graph of the algorithm and the direct optimization solution complexity provided by the present invention.
Detailed Description
The first embodiment is as follows: the CTU allocation method of the uplink authorization-free SCMA based on the user activity of the embodiment specifically comprises the following processes:
therefore, in order to reduce the packet loss rate caused by CTU collision and further improve the sum rate of the whole uplink SCMA system, the invention introduces the activity of the user as an evaluation index to assist the base station to complete the distribution of CTU resources. The invention considers the following scenarios of the internet of things: the activity of each user is different and their activity is in a quasi-static state, i.e. the probability that each user is allowed access for a period of time is subject to an allocation regarding its activity. Meanwhile, the access probability of the user in a period of time can also be used for estimating the activity of the user in the next period of time. In addition, the invention deduces the expression of the CTU collision probability, and finds that the collision probability has close relation with the activity of the user and the distribution strategy of the CTU. In this case, a CTU optimization allocation strategy based on user activity is studied to reduce the collision probability and packet loss rate of CTUs and prove that the problem of packet loss rate optimization is an NP-hard problem. By utilizing the CTU distribution algorithm based on the user activity, the NP-hard problem is converted into a low-complexity solvable problem, and the optimization of the system packet loss rate is completed.
The uplink authorization-free SCMA system model is as follows:
suppose that there are N users, L CTUs, J codebooks, and K subcarriers in an uplink SCMA system. And there is a correspondence: n ≧ J > K, the information received in the base station can be expressed as:
where y ═ y 1 y 2 ... y K ] T Is the information received in the sub-carriers; x is the number of n ＝[x n1 x n2 ... x nK ] T Is a UE n The information sent; f. of n ＝[f n1 f n2 ... f nK ] T The corresponding relation between the user and the subcarrier can also be understood as codebook information; h is n ＝[h n1 h n2 ... h nK ] T Is a user UE n The channel state parameter of (a); n-CN (0,1) is Additive White Gaussian Noise (AWGN).
A transmission diagram of an uplink unlicensed SCMA is shown in fig. 1. Unlike the request-based scheduling mode of transmission, when a user wants to access, it transmits information in a follow-up and go (arrival and go) manner. I.e. neither a transmission request nor an access grant feedback from the base station to the user is required. For the uplink SCMA system, the codebook in the CTU corresponds to f in equation (1) n The pilot sequence in the CTU is used to assist in estimating the channel information h n . Therefore, before the user sends information, the uplink unlicensed SCMA system allocates CTUs to the user. And finally, after blind detection, the base station feeds back an ACK to the user to confirm transmission.
Each CTU has its unique pilot sequence but may share one and the same SCMA codebook. The pilot sequence can help the receiver estimate the channel information. User information aliased to each other on one subcarrier can be demodulated at the cost of less than 0.5dB performance loss as long as they are assigned different CTUs. This loss of performance is quite acceptable for a real system. So in general in an uplink SCMA system, multiple users may share one CTU, and multiple CTUs may share one pilot sequence, but each CTU has its own pilot sequence. The relation between users and time-frequency resources, codebooks and pilots in CTUs is shown in fig. 2.
However, if users select the same CTU, they share the same pilot sequence to estimate their respective channel information. The receiver cannot decode the user information and this process is called pilot collision or CTU collision.
Assuming that there are N users in an uplink SCMA system, where N users are in an active state, the probability of CTU collision is:
the average arrival rate λ of users is defined as the number of users expected to need to transmit data per Transmission Time Interval (TTI), and can be expressed as,
wherein W n Is the activity of the user UEn, the probability of n active users being subjected to a Poisson distribution
P n ＝e -λ (λ) n /n！ (10)
The packet loss rate is defined as the probability of the first transmission failure of a user to the base station. Its upper bound can be expressed as:
the distribution relationship between the user and the CTU plays a decisive role in packet loss rate. An optimized allocation can effectively reduce the collision probability of the CTUs, thereby reducing the error rate. Let g be nl (0,1) denotes the secondThe distribution relationship between n users and the l CTU, if g nl 1 means that the nth user is allocated the lth CTU, whereas g nl 0 means no pairing, and g n ＝[g n1 g n2 ... g nL ] T An allocation relation vector, g, representing the nth user l ＝[g 1l g 2l ... g Nl ] T Is the assignment of the ith CTU. As can be seen from the above, one user can be allocated to only one CTU, but one CTU may correspond to a plurality of users. Therefore, the following constraints can be obtained:
on the premise of having a mapping relationship, the average CTU collision probability corresponding to L CTUs of N users in T time slots can be obtained:
wherein W n (t) represents the probability of access of the nth user in the tth time slot. From equation (13), it can be known that the collision probability of the pilot is closely related to the activity of the user and the allocation relationship of the CTU. The mapping relationship between users and CTUs in the original CTU allocation algorithm based on the modular division is as follows:
CTU_index＝UE_index mod CTU_num
(14)
that is to say:
this allocation strategy of CTUs ignores the liveness characteristics of the user. So in the following, how to achieve the purpose of minimizing CTU collision probability by allocating CTU resources using the activity information of the user is discussed. Let N and L be used to represent the user and the set of CTUs, respectively. The optimization formula can be expressed as:
min P co
the optimized solution is an N × L matrix G representing the entire assignment correspondence of N users to L CTUs. The optimization problem is a nonlinear mixed integer problem, which is an NP-hard problem, that is, the problem has extremely high complexity, and it is impossible for the base station to directly solve and redistribute.
The method comprises the following steps: in an authorization-free uplink SCMA system, calculating to obtain the average CTU collision probability corresponding to L CTUs of N _ length users in T' time slots, and simplifying the average CTU collision probability to obtain an NP-hard optimized expression;
step two: in an authorization-free uplink SCMA system, a user n is set according to an activity W n Sorting from big to small and giving different priorities; n — 1,2,. and N _ length;
the activity is high, and the priority is high;
n' represents the users in the user set N according to the activity W n The new set generated after the permutation from large to small, N' ═ nxtr,
wherein TR represents a mapping matrix from N to N'; the user set N comprises N _ length users; the set N 'includes N _ length' users;
step three: setting P co (m) denotes CTU collision probability of the first m users in the set N' obtained in step two, and Δ P (m) ═ P co (m)-P co (m-1)]Representing CTU collision increment when the mth user is considered to be accessed to the unlicensed uplink SCMA system, and carrying out iterative loop solution optimization on delta P (m) to obtain optimal solution g each time m According to the optimal solution g at each time m Obtaining an optimal solution set G' ═ { G ═ G 1 ,…g m ,…,g N_length′ }；
Wherein m is 1, 2., N _ length'; p co (m-1) representing the CTU collision probability of the first m-1 users in the set N' obtained in the step two;
step four: and obtaining a user and CTU distribution relation matrix G according to N, N 'and the optimal solution set G'.
And step two, step three and step four are further optimization of the NP-hard optimization formula of the step one, and G obtained in the step four is the optimization result of the NP-hard optimization formula of the step one.
The second embodiment is as follows: the first difference between the present embodiment and the specific embodiment is: in the first step, in an authorization-free uplink SCMA system, calculating to obtain the average CTU collision probability corresponding to L CTUs of N _ length users in T' time slots, and simplifying the average CTU collision probability to obtain an NP-hard optimized formula; the specific process is as follows:
wherein the content of the first and second substances,
g nl {0,1} represents the assignment of the nth user to the lth CTU, if g nl 1 means that the nth user is assigned to the lth CTU, whereas g nl 0 means that the nth user and the lth CTU are not paired;
g n ＝[g n1 g n2 ... g nL ] T an allocation relation vector representing the nth user; t is transposition;
g l ＝[g 1l g 2l ... g N_lengthl ] T an allocation relation vector representing the ith CTU;
W n (t) the activity is used for representing the probability of accessing the nth user in the tth time slot; n ≠ N, g, N ═ 1,2 n′l The {0,1} represents the allocation relationship between the nth' user and the lth CTU;
W n' (t) the activity is used for representing the probability of accessing the nth user in the tth time slot; t is time;
the formula (1) is simplified
Wherein, W n The activity of the nth user; e (W) n (t)) is to obtain W n (t) desire;
and the NP-hard optimized formula at this time is obtained:
min P co
Other steps and parameters are the same as those in the first embodiment.
The third concrete implementation mode: the present embodiment differs from the first or second embodiment in that: setting P in the third step co (m) denotes CTU collision probability of the first m users in the set N' obtained in step two, and Δ P (m) ═ P co (m)-P co (m-1)]Representing CTU collision increment when the mth user is considered to be accessed into the authorization-free uplink SCMA system, carrying out iterative loop solution optimization on delta P (m) to obtain the optimal solution g each time m According to the optimal solution g at each time m Obtaining an optimal solution set G' ═ { G ═ G 1 ,…g m ,…,g N_length′ }; the specific process is as follows:
when the number m of the access users is less than or equal to L, the CTU allocation is not required to be completed through optimized calculation at the moment, and the method is as follows
Allocating different CTUs to each user;
mod is the remainder;
when the number of access users m > L, the CTU collision increment occurring when the mth user is considered to access the authorization-free uplink SCMA system is expressed as:
wherein, g ml The assignment relationship between the mth access user and the lth CTU is expressed as {0,1}, if g ml 1, it means that the mth user is allocated to the lth CTU; otherwise if g ml If the number is 0, the mth access user and the lth CTU are not paired;
W m representing the activity of the mth user; p co (l, m-1) represents the probability of collision of the l-th CTU in the (m-1) -th iteration;
by storing the collision value obtained from the last iteration as known information, the amount of optimization calculation can be greatly reduced at the cost of a small amount of space complexity.
For the mth iteration, Δ p (m) optimization is simplified to:
minΔP(m)
optimized result g m ＝[g m1 g m2 ... g mL ] T Representing CTU assignment relation vectors for the mth user in the new set N';
judging whether m is equal to N _ length', if yes, executing step four; and if not, the step three is executed again until m is equal to N _ length'.
CTU collisions may be considered from another perspective, which may also be understood as one CTU being assigned to multiple accessed users. Therefore, for the ith CTU in the L set, compared with the result obtained in (5), there is no lower collision probability obtained by other user allocation modes on the premise that the collision rate of other CTUs is not increased, so that the result obtained by the dynamic planning can meet the condition of the Pareto optimal solution.
Other steps and parameters are the same as those in the first or second embodiment.
The fourth concrete implementation mode: the difference between this embodiment and one of the first to third embodiments is: in the fourth step, a user and CTU distribution relation matrix G is obtained according to N, N 'and the optimal solution set G'; the specific process is as follows:
other steps and parameters are the same as those in one of the first to third embodiments.
The summary of the proposed uplink SCMA CTU allocation strategy based on user activity is shown in algorithm 1: .
The following examples were used to demonstrate the beneficial effects of the present invention:
the first embodiment is as follows:
the simulation scenario of the figure is that 4 mutually orthogonal subcarriers, 6 codebooks and 12 CTUs are provided. The activity of the user is known a priori to the base station. The channel conditions are ideal channel estimates, i.e. the receiver of the base station can demodulate the user information as long as the users are assigned to different CTUs. The cumulative probability density distribution (CDF) of packet loss ratios corresponding to the CTU allocation algorithm based on user liveness and the CTU allocation algorithm based on modular division, which are proposed by us, is shown in fig. 3a and 3 b. Fig. 4 shows a comparison graph of algorithm complexity and brute force solution when the number of users varies from 24 to 36.
The following points can be seen from the simulation result:
1. in fig. 3a, in the case that the number of CTUs is 12, a light-colored star line represents a packet loss rate CDF map of a previous CTU allocation algorithm based on modular division, and a dark-colored square line represents a packet loss rate CDF map of a proposed CTU allocation algorithm based on user activity; the solid line indicates the case where the number of users is 24, the broken line indicates the case where the number of users is 30, and the dotted line indicates the case where the number of users is 36. As can be seen from the images, with the proposed algorithm, the packet loss rates are reduced by 17%, 20%, and 22% for the number of users 24,30, and 36, respectively. This is because the proposed algorithm takes into account the liveness information of the users, providing more CTU resources for more active users, thereby reducing the collision probability. Similarly, in fig. 3b, when the number of users is 24 and the number of CTUs is 8, 10, and 12, the packet loss rate decreases by 23%, 19%, and 17%. Therefore, it can be seen that the proposed algorithm has very good packet loss rate performance; meanwhile, the more dense scenes of users can be known, the better the packet loss rate performance of the proposed algorithm is, which is very practical for the scenes of the internet of things with 5G mass access in the future.
2. Fig. 4 shows a graph comparing the complexity of the proposed algorithm with brute force solution when the number of users varies from 24 to 36. It can be seen from fig. 4 that the computational complexity can be reduced by 16 orders of magnitude when the number of users is 30. This is because the algorithm stores and applies the local optima obtained from each iteration to the next calculation by means of the idea of dynamic programming.
The present invention is capable of other embodiments and its several details are capable of modifications in various obvious respects, all without departing from the spirit and scope of the present invention.
Claims (4)
1. The CTU distribution method of the uplink authorization-free SCMA based on the user activity is characterized in that: the method comprises the following specific processes:
the method comprises the following steps: in an authorization-free uplink SCMA system, calculating to obtain the average CTU collision probability corresponding to L CTUs of N _ length users in T' time slots, and simplifying the average CTU collision probability to obtain an NP-hard optimized expression;
step two: in an authorization-free uplink SCMA system, a user n is set according to an activity W n Sorting from big to small and giving different priorities; n — 1,2,. and N _ length;
the activity is high, and the priority is high;
n' represents the users in the user set N according to the activity W n The new set generated after the permutation from large to small, N' ═ nxtr,
wherein TR represents a mapping matrix from N to N'; the user set N comprises N _ length users; the set N 'includes N _ length' users;
step three: setting P co (m) represents CTU collision probability of the first m users in the set N' obtained in step two, and Δ P (m) ═ P co (m)-P co (m-1)]Representing CTU collision increment when the mth user is considered to be accessed into the authorization-free uplink SCMA system, carrying out iterative loop solution optimization on delta P (m) to obtain the optimal solution g each time m According to the optimal solution g of each time m Obtaining an optimal solution set G' ═ { G ═ G 1 ,...g m ,...,g N_length′ }；
Wherein m is 1, 2., N _ length'; p co (m-1) representing the CTU collision probability of the first m-1 users in the set N' obtained in the step two;
step four: and obtaining a user and CTU distribution relation matrix G according to N, N 'and the optimal solution set G'.
2. The method for allocating CTUs of an uplink unlicensed SCMA based on user activity as claimed in claim 1, wherein: in the first step, in an authorization-free uplink SCMA system, calculating to obtain the average CTU collision probability corresponding to L CTUs of N _ length users in T' time slots, and simplifying the average CTU collision probability to obtain an NP-hard optimized formula; the specific process is as follows:
wherein the content of the first and second substances,
g nl {0,1} represents the assignment of the nth user to the lth CTU, if g nl 1 means that the nth user is assigned to the lth CTU, whereas g nl 0 means that the nth user and the lth CTU are not paired;
g n ＝[g n1 g n2 ...g nL ] T an allocation relation vector representing the nth user; t is transposition;
g l ＝[g 1l g 2l ...g N_lengthl ] T an allocation relation vector representing the ith CTU;
W n (t) the activity is used for representing the probability of accessing the nth user in the tth time slot; n ≠ N, g, N ═ 1,2 n′l The {0,1} represents the allocation relationship between the nth' user and the lth CTU;
W n' (t) the activity is used for representing the probability of accessing the nth user in the tth time slot; t is time;
the formula (1) is simplified
Wherein, W n The activity of the nth user; e (W) n (t)) is to obtain W n (t) expectation;
and the NP-hard optimized formula at this time is obtained:
min P co
3. the method for CTU distribution of an uplink unlicensed SCMA based on user activity as claimed in claim 2, wherein: setting P in the third step co (m) represents CTU collision probability of the first m users in the set N' obtained in step two, and Δ P (m) ═ P co (m)-P co (m-1)]Representing CTU collision increment when the mth user is considered to be accessed into the authorization-free uplink SCMA system, carrying out iterative loop solution optimization on delta P (m) to obtain the optimal solution g each time m According to the optimal solution g at each time m Obtaining an optimal solution set G' ═ { G ═ G 1 ,...g m ,...,g N_length′ }; the specific process is as follows:
m is 0, when the number of access users m is less than or equal to L
Allocating different CTUs to each user;
when the number of access users m > L, the CTU collision increment occurring when the mth user is considered to access the authorization-free uplink SCMA system is expressed as:
wherein, g ml The assignment relationship between the mth access user and the lth CTU is expressed as {0,1}, if g ml 1, it means that the mth user is allocated to the lth CTU; otherwise if g ml If the number is 0, the mth access user and the lth CTU are not paired;
W m representing the activity of the mth user; p co (l, m-1) represents the probability of collision of the l-th CTU in the (m-1) -th iteration;
for the mth iteration, Δ p (m) optimization is simplified to:
minΔP(m)
optimized result g m ＝[g m1 g m2 ...g mL ] T Representing the CTU assignment relationship vector for the mth user in the new set N';
judging whether m is equal to N _ length', if yes, executing step four; and if not, the step three is executed again until m is equal to N _ length'.
4. The method for CTU distribution of an uplink unlicensed SCMA based on user activity as claimed in claim 3, wherein: in the fourth step, a user and CTU distribution relation matrix G is obtained according to N, N 'and the optimal solution set G'; the specific process is as follows:
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| CN107113826A (en) * | 2015-01-27 | 2017-08-29 | 华为技术有限公司 | Transmission system and method for exempting from authorized uplink transmission plan |
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| WO2017016425A1 (en) * | 2015-07-27 | 2017-02-02 | Huawei Technologies Co., Ltd. | Link adaptation in grant-free multiple access systems |
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