CN109286992B - Time slot competition access transmitting and receiving method based on multi-power and time diversity - Google Patents
Time slot competition access transmitting and receiving method based on multi-power and time diversity Download PDFInfo
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Abstract
The invention discloses a time slot competition access sending and receiving method based on multi-power and time diversity, which mainly comprises the following steps: firstly, randomly selecting a plurality of time slots at a sending end to send signals, and sending signals with different power levels at different time slots; firstly demodulating the signals which do not collide at a receiving end, then reconstructing the signals according to the demodulation information, eliminating interference on other time slots distributed by the signals by using a serial interference elimination method, and then re-demodulating the signals which do not collide after the interference elimination, thereby iterating until all the signals are correctly demodulated or no signals which do not collide exist. The method is suitable for a competitive access channel communication system, and can remarkably improve the capacity of an access channel by methods such as power classification, time domain repetition and the like under the condition of limited time and frequency resources.
Description
Technical Field
The invention relates to the technical field of wireless communication, in particular to a time slot competition access transmitting and receiving method based on multi-power and time diversity.
Background
In modern communication systems, Random Access (RA) is an indispensable Access method. In the random access system, a plurality of users transmit on demand at any time on the same channel in a competitive mode. For each user, the user transmits in the shared contention access channel as long as there is data to transmit. If a plurality of users send data to the same receiving device at the same time, signal collision can be caused, and message packet loss can be caused. In the traditional communication, the random access mode is mainly applied to the interaction of signaling such as a network access request, a resource allocation request, network access state information maintenance and the like sent by a user to a base station; in the modern communication scene mainly based on data service, random access no longer exists in the transmission of signaling, and random access can be directly used for sending data in some special scenes; in the field of Internet of things (IoT) and Machine to Machine communication (M2M), state information of a plurality of objects is sent to an information acquisition device through random access in a wireless transmission manner, and the information acquisition device is connected with a network, so that object-object communication is completed. The existing random access system mainly comprises an access system based on competitive access (ALOHA) or time slot competitive access, wherein the ALOHA is pure random access, and a user can send a data packet at any time as long as the user has a data transmission requirement; the slotted ALOHA increases the slot synchronization on the basis of the ALOHA, so that a user can not transmit data at any time and can only select to transmit data at the beginning of one slot, and the maximum throughput rate of a competitive channel can be doubled by the slot synchronization.
Therefore, the invention provides a time slot competition access transmitting and receiving method based on multi-power and time diversity, which aims to solve the problems in the prior art.
Disclosure of Invention
The invention aims to provide a time slot competition access transmitting and receiving method based on multi-power and time diversity, which can obviously improve the capacity of an access channel by methods such as power classification, time domain repetition and the like under the condition of limited time and frequency resources.
The time slot competition access system comprises a system containing NslotsContention access superframe of one time slot, for each burst signal, MpowerA power class, each power class having a transmission power of
Wherein M ispower1,2, … is an integer greater than 0.
For a packet from user i, first, N is randomly selected in a super framereplicaEach time slot having a time slot number of
The data packets sent in each time slot are referred to as duplicates of the data packets from user i. Each replica is at random at a given time slot
To select power for transmission. The information that user i needs to send includes the bits of replica indication flag
Significant information bits
And check bits
Wherein the time slot indication flag bit
Indicating the slot positions of all copies of the packet
When the data packet is correctly received, it can be based on
Judging the time slot of the replica; significant information bits
Including valid data to be transmitted; check bits
All information is checked and used by a receiving end to judge whether the information is received correctly, and the information bits are checked by using redundancy cyclic check (CRC) under normal conditions.
And carrying out error correction coding on the data packet, wherein the error correction channel coding comprises LDPC, turbo, polarization code and the like.
M is to be(i)The symbols after channel coding are
The information symbol finally transmitted is
Wherein
The training sequence of the data packet is used for signal capture at the receiving end.
The invention discloses a time slot competition access sending method based on multi-power and time diversity, which comprises the following steps:
step 1: packing the data packet to be transmitted, randomly selecting a plurality of time slots in an ALOHA superframe for the data packet, wherein the data packet transmitted in each time slot is called a copy of the data packet;
step 2: adding pointer information of sending time slot in the data packet replica in the step 1, so that a receiving end can find the time slot number of the replica after demodulating the data packet;
and step 3: adding cyclic check to the replica in the step 2 for judging whether the signal is correctly received at a receiving end;
and 4, step 4: modulating and coding the replica of step 3 and giving the replica at each given power level
Distributing power at medium random;
and 5: and (4) enabling the replica after modulation and coding in the step (4) to access the channel on the basis of competition in the next superframe until the start time of the next superframe is finished.
Preferably, the pointer information of the timeslot in step 2 is a timeslot indicator flag bit
The ping-pong storage processing is that a receiving end at least comprises a memory with the capacity of two superframes, and received signals are stored in an RAM after being subjected to down-conversion, A/D conversion and down-sampling. And receiving and storing the signal of the current superframe, and simultaneously performing signal processing on the signal stored in the last superframe. The storage processing method is called ping-pong storage processing.
Power dominance is the power dominance of a packet if no other packet is transmitted in a given time slot at a power level greater than or equal to the transmit power of the packet.
The clean packet is a packet that is called a clean packet when only one packet exists in a time slot and does not collide with other packets, or when one packet collides with a plurality of packets in a time slot but the power of the packet is dominant so that the packet can be demodulated and decoded correctly.
A collision packet is a packet transmitted in a given time slot, and is called a collision packet when the packet cannot be demodulated correctly due to signal collision caused by transmission of a plurality of other packets in the same time slot.
The invention discloses a time slot competition access receiving method based on multi-power and time diversity, which comprises the following steps:
step 1: performing ping-pong storage processing on the received signals, and processing the received signals of the previous superframe while receiving the signals of the current superframe;
step 2: detecting a data packet in a current superframe through the correlation operation of a local training sequence and a received signal, and if a pure packet exists in a captured time slot, performing demodulation decoding and cyclic check; if no clean packet exists in the current superframe, jumping to the step 6;
and step 3: if the clean signal cycle check in the step 2 is successful, indicating a mark bit according to a replica in the clean packet demodulation information
Finding out the time slot where the pure packet complex product is located, and realizing the reconstruction of the replica by recoding and remodulating the replica signal;
and 4, step 4: using the reconstructed replica signal in the replica time slot as interference, reconstructing the signal by using a linear least square algorithm, eliminating serial interference, and storing the signal after the interference elimination into a memory again;
and 5: returning to the step 2 after all the current pure packets passing the verification are subjected to interference elimination, and starting the next iteration;
step 6: and finishing the iteration and returning to the step 1 to wait for the next superframe to be processed after the next superframe is received.
Preferably, said step 4 uses a linear least squares algorithm, wherein a least mean square error (LMS) filter is used as an M-th order finite impulse response (Fir) filter, and the following variables are defined:
w (n) is the coefficient of a least mean square error (LMS) filter, and is an M-dimensional vector, the initial value is the default receiving filter coefficient, and the coefficient is updated along with the self-adaption of an iterative algorithm;
x (n) is the input sampling signal of the least mean square error (LMS) filter, the waveform of the coding signal remodulated for the replica signal in the step 3 is s (n), and the signal s (n) is corrected according to the frequency offset and phase offset of the signal to obtain the input waveform of the filter:
wherein, wcThe digital frequency offset of the current jump signal is phi, the initial phase of the current jump signal is phi, and the vector of the input signal is defined as:
x(n)＝[x(n-M+1),x(n-M+2)，…x(n)]T；
d (n) is the expected sampling signal of the least mean square error (LMS) filter, and the received signal in the replica time slot is sampled to be used as the expected signal d (n) of the LMS filter;
y (n) is the output signal of the least mean square error (LMS) filter, and y (n) is the reconstructed signal corrected by the LMS filter;
and e (n) is the output error signal of the least mean square error (LMS) filter, which is used as the signal after interference elimination for next user to demodulate.
Preferably, the step 4 further comprises the steps of:
step 4-1: initializing parameters: n is 0, w (0) is 0;
step 4-2: calculating an output signal of said least mean square error (LMS) filter using current said filter coefficients w (n) and current input data x (n): y (n) ═ wH(n)x(n)；
Step 4-3: calculating an output error signal of the filter at the current time: e (n) ═ d (n) -y (n);
step 4-4: adaptively updating filter coefficients:
w(n+1)＝w(n)+2μx(n)e(n)；
and 4-5: and (4) processing the next sampling point, wherein n is n +1, and returning to the step 4-2 until the processing of all the signal sampling points in one time slot is finished.
The time slot competition access sending and receiving method based on the multi-power and time diversity can solve the internal interference of the system caused by signal collision in a competition access channel and improve the throughput rate of the access channel. The method is suitable for a competitive access channel communication system, and the capacity of the access channel can be obviously improved by methods such as power classification, time domain repetition and the like under the condition of limited time and frequency resources.
Drawings
Fig. 1 is a flow chart illustrating a method for transmitting timeslot Aloha based on multiple power and time diversity.
Fig. 2 is a flow chart of a time slot Aloha receiving method based on iterative successive interference cancellation.
Fig. 3 is a schematic diagram of the distribution of multiple power diversity time slot Aloha received signals in time slots.
Detailed Description
In order to make the implementation objects, technical solutions and advantages of the present invention clearer, the technical solutions in the implementation examples of the present invention will be described in more detail below with reference to the accompanying drawings in the implementation examples of the present invention. In the drawings, the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described are a part of the embodiments of the present invention, and not all embodiments. The embodiments described below with reference to the accompanying drawings are exemplary and intended to be illustrative of the present invention and are not to be construed as limiting the present invention. All other embodiments obtained by those skilled in the art without any creative effort based on the embodiments of the present invention belong to the protection scope of the present invention.
As shown in fig. 1, in the signaling method, a plurality of slots are randomly selected for each packet, a slot indicator is added on the basis of valid information, and a check bit is added. And all information including effective information, a time slot indication mark and a check bit is used as a coding block to carry out channel coding, the obtained coded information is modulated and upconverted after a training sequence is added, and the information is transmitted in the next superframe according to the randomly selected time slot and the randomly selected power.
Assuming that the time slots and powers of the respective user signals are as shown in fig. 3, there are 3 replicas for each user's data packet, and the user randomly selects 3 time slots in the super frame to transmit the replica signals. For each burst signal there is MpowerUnder the condition that the two power intervals are large enough, when a large signal collides with one or more small signals, the signal-to-interference-and-noise ratio (SINR) of the large signal is larger than the decoding threshold of the signal. According to this characteristic, when a large signal collides with a small signal, the large signal can be regarded as a clean packet. For the received signal shown in fig. 3, the processing at the receiving end is as follows
Step 1: ping-pong storing the received signal samples of the two superframes;
step 2: searching a pure packet, wherein the pure packet is a data packet of the user 4 in the time slot 2 and a data packet of the user 5 in the time slot 7 in the first iteration;
and step 3: original information is obtained according to the demodulation and decoding of the two pure packets, and signals of the user 4 in the time slots 4 and 5 and signals of the user 5 in the time slots 3 and 4 are reconstructed;
and 4, step 4: the signal reconstructed in step 3 is used as interference to perform interference cancellation on the mixed signals of the time slots 2, 3, 4, 5 and 7. And storing the residual signal after the interference elimination into a Random Access Memory (RAM);
and 5: in the second iteration, since all signals of the users 4 and 5 have been eliminated, the copy of the user 1 in the time slot 2, the copy of the user 2 in the time slot 5 and the copy of the user 3 in the time slot 7 are both changed into clean packets from collision packets, and can be demodulated and decoded for them;
step 6: interference elimination is carried out on the copies of the users 1,2 and 3, and residual signals are stored in an RAM;
and 7: and (4) the pure packet does not exist in the superframe, and the iteration is finished.
In the engineering implementation, the implementation method is as shown in fig. 2, in step 1, the signal is stored in the local RAM, the clean packet existing in the received signal is searched first to perform signal demodulation and channel decoding, when the check code judges that the check is correct, the channel coding and modulation are performed on the demodulated information again, and the interference of the known signal is eliminated and written back to the local RAM through the serial interference elimination module. This is iterated until no clean packets can be found in the received signal that can be correctly demodulated.
According to the slotted ALOHA transmission example shown in fig. 3, after the slotted ALOHA reception method based on iterative successive interference cancellation described herein, the data packets of all users in the superframe can be correctly demodulated.
Finally, it should be pointed out that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art will understand that: the technical solutions described in the foregoing embodiments can be modified, or some technical features can be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solution depart from the spirit and scope of the technical solution of the embodiments of the present invention.
Claims (2)
1. A time slot competition access sending and receiving method based on multi-power and time diversity obviously improves the capacity of an access channel by a power classification and time domain repetition method under the condition of limited time and frequency resources, and is characterized in that: the time slot competition access receiving method comprises the following steps:
step 1: packing the data packet to be transmitted, randomly selecting a plurality of time slots in a competitive access superframe for the data packet, wherein the data packet transmitted in each time slot is called a replica of the data packet;
step 2: adding pointer information of sending time slot in the data packet replica in the step 1, so that a receiving end can find the time slot number of the replica after demodulating the data packet; the pointer information of the time slot is a time slot indication mark bit
And step 3: adding cyclic check to the replica in the step 2 for judging whether the signal is correctly received at a receiving end;
and 4, step 4: modulating and coding the replica of step 3 and giving the replica at each given power level
Distributing power at medium random;
and 5: placing the replica modulated and coded in the step 4 in the next superframe based on the competition access channel until the starting time of the next superframe is finished;
step 6: performing ping-pong storage processing on the received signals, and processing the received signals of the previous superframe while receiving the signals of the current superframe;
and 7: detecting a data packet in a current superframe through the correlation operation of a local training sequence and a received signal, and if a pure packet exists in a captured time slot, performing demodulation decoding and cyclic check; if no clean packet exists in the current superframe, jumping to step 11;
and 8: if the signal cycle check of the clean packet is successful in the step 7, indicating a mark bit according to the replica in the clean packet demodulation information
Finding out the time slot where the pure packet complex product is located, and realizing the reconstruction of the replica by recoding and remodulating the replica signal;
and step 9: using the reconstructed replica signal in the replica time slot as interference, reconstructing the signal by using a linear least square algorithm, eliminating serial interference, and storing the signal after the interference elimination into a memory again; the method utilizes a linear least square algorithm, wherein a minimum mean square error filter is used as an M-order finite impulse response filter, and the following variables are defined:
w (n) is a minimum mean square error filter coefficient and an M-dimensional vector, an initial value is a default receiving filter coefficient, and the coefficient is updated adaptively along with an iterative algorithm;
x (n) is a minimum mean square error filter input sampling signal, the waveform of the coding signal remodulated on the replica signal in the step 8 is s (n), and the signal s (n) is corrected according to the frequency offset and the phase offset of the signal to obtain the input waveform of the filter:
wherein, wcThe digital frequency offset of the current jump signal is phi, the initial phase of the current jump signal is phi, and the vector of the input signal is defined as:
x(n)＝[x(n-M+1),x(n-M+2)，…x(n)]T；
d (n) is the expected sampling signal of the minimum mean square error filter, and the received signal in the replica time slot is sampled to be used as the expected signal d (n) of the LMS filter;
y (n) is the output signal of the minimum mean square error filter, and y (n) is the reconstructed signal corrected by the LMS filter;
e (n) is the output error signal of the minimum mean square error filter, which is used as the signal after the interference elimination for the next user to demodulate;
step 10: after all the checked clean packets are subjected to interference elimination, returning to the step 7, and starting the next iteration;
step 11: and finishing the iteration and returning to the step 6 to wait for the next superframe to be processed after the next superframe is received.
2. The slot contention access transmission and reception method based on multi-power and time diversity according to claim 1, wherein: the step 9 further comprises the steps of:
step 9-1: initializing parameters: n is 0, w (0) is 0;
step 9-2: calculating an output signal of the minimum mean square error filter using the current filter coefficients w (n) and the current input data x (n): y (n) ═ wH(n)x(n)；
Step 9-3: calculating an output error signal of the filter at the current time: e (n) ═ d (n) -y (n);
step 9-4: adaptively updating filter coefficients:
w(n+1)＝w(n)+2μx(n)e(n)；
step 9-5: and (4) processing the next sampling point, wherein n is n +1, and returning to the step 4-2 until the processing of all the signal sampling points in one time slot is finished.
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