CN109379174B - Grouping index OFDM communication method based on random sequence - Google Patents

Abstract

The invention belongs to the technical field of wireless communication, and particularly relates to a random sequence-based grouping index OFDM communication method. The principle of the random sequence-based packet index OFDM communication technology is that different random sequences are utilized to activate partial subcarriers in each carrier block in each OFDM symbol to transmit modulation symbols, and other subcarriers keep a silent state. The random sequence for controlling the activated sub-carriers of each OFDM symbol is determined by the index bits, and the randomness and the difference among the random sequences make the relationship between the index bits and the distribution of the activated carriers more complicated and make the information of the index bits more concealed. Compared with the grouping index OFDM communication technology, the invention introduces the PN sequence, greatly improves the anti-interception performance of the system without reducing the anti-interference performance of the system, and has application value in military and civil communication.

Description

Grouping index OFDM communication method based on random sequence

Technical Field

The invention belongs to the technical field of wireless communication, and particularly relates to a random sequence-based grouping index OFDM communication method.

Background

The communication technology is that an index modulation technology is combined with an OFDM technology, information bits are divided into G groups at a system transmitting end, the information bits are divided into two parts in each group, and one part is used as a signal modulation bit and is mapped into M-system constellation point symbols; one part is used as an index information bit, the activated part of subcarriers are selected from each group of subcarriers to transmit the constellation point symbols, and other subcarriers are set to be 0, so that the activation of the subcarriers is realized by utilizing a message-driven index mode. The prior art has the defects that a certain direct rule exists between the distribution of index bits and activated subcarriers, and the rule is single, lacks randomness and is easy to crack. In the communication process, if a communication enemy correctly detects the position of the activated carrier and simultaneously cracks the distribution rule of the index bit and the activated carrier, the index bit information is lost, so that the interception resistance of the SIM-OFDM system is poor. In present military and civil communication, the improvement of the anti-interception performance based on the prior art is very important, and the method has great development prospect in the future communication field.

Disclosure of Invention

Aiming at the problem of poor anti-interception performance of the existing SIM-OFDM communication technology, the invention provides an index OFDM communication method based on a random sequence, which can well improve the anti-interception performance of a system without reducing the anti-interference performance of the system.

A method for OFDM communication based on random sequence packet index, the method comprising the steps of:

step 1: determining system parameters, framing by a digital information source, determining the number of index bits and the number of modulation bits, and controlling the selection of a PN sequence by the index bits;

step 2: obtaining PN sequence bits according to the determined system parameters, selecting different subcarrier activation combinations according to different PN sequence bits, and determining a subcarrier activation combination according to the value of the PN sequence bits;

and step 3: according to the selected subcarrier activation combination, subcarrier index mapping and modulation are carried out, serial-parallel conversion is carried out, N-point IFFT operation is carried out, and CP is added;

and 4, step 4: according to the information source information sent after the steps 1 to 3, the information source information reaches a receiving end through a channel;

and 5: according to the signal received by the receiving end, removing CP from the signal, performing N-point FFT operation, and performing parallel-serial conversion;

step 6: and (5) according to the signal obtained after the processing in the step (5), carrying out signal detection and index inverse mapping, and outputting a bit.

The system parameters in step 1 include the total number N of subcarriers, the number G of subcarrier blocks, the number I of subcarriers in each subblock, the number k of activated subcarriers in each subblock, each activated subcarrier carrying a constellation point symbol, the modulation order M, framing by a digital information source, each frame having p₁+p₂G bits of information, where the front p₁Bits as index bits for controlling PN sequence selection, post p₂G bits as information modulation bits in G subcarrier blocks, M order modulation symbols generated from the information modulation bits, the number of modulation bits p₂Calculated from the following formula:

p₂＝k log₂M

the index bit controls the selection of the PN sequence, specifically expressed as: in the frame packet index OFDM, i.e. SIM-OFDM, information, a PN sequence generator can generate

The PN sequence can be expressed as a PN sequence set

p₁The decimal number corresponding to the bit index bit is D, and the corresponding PN sequence is PN_D。

Selecting different subcarrier activation combinations according to the determined system parameters and different joint index bits in step 2 comprises: q is the number of bits required to select k subcarriers from the I subcarriers for activation, and

then there is 2^QThe combination of the activation of the subcarriers, the combination set of the g-th sub-block can be expressed as:

the corresponding PN sequence in a frame of SIM-OFDM information is represented as:

PN＝[u_1,1,u_1,2,…,u_1,Q,u_2,1,u_2,2,…,u_2,Q,…,u_G,1,u_G,2,…,u_G,Q]

wherein the PN sequence bit corresponding to the g sub-carrier block is [ u ]_g,1,u_g,2,…,u_g,Q]If the decimal number corresponding to the PN sequence bit is o, the activated combination of the sub-carriers corresponding to the sub-carrier block is

Wherein G is 1,2, …, G, beta_g,rE {0,1}, r 1,2, …, I, and

k values in the total are 1, I-k valuesIs 0, beta _g,r1 indicates that the subcarrier numbered r in the g-th subcarrier block is active, β_g,_r0 indicates that the subcarrier numbered r is in a silent state.

The invention has the beneficial effects that:

the grouping index OFDM communication technology based on the random sequence utilizes the index bit to control different random sequences to activate the subcarriers of each carrier block in each OFDM symbol, the randomness of the random sequences and the difference among the random sequences enable the relation between the index bit and the activated carrier distribution to be more complicated, namely the index bit information of the system is encrypted by the PN sequence, and the index bit information is enabled to be more concealed, so that the grouping index OFDM communication technology based on the random sequence has stronger anti-interception capability of the index bit information.

Drawings

Fig. 1 is a link diagram of a random sequence based packet index OFDM communication system.

Fig. 2 is a diagram of a transmitting end structure of the SIM-OFDM communication system.

Fig. 3 is a diagram of a transmitting end structure of a packet index OFDM communication system based on a random sequence.

Fig. 4 is an example of the relationship between the index bits, for example, I-4 and k-1, and the distribution of PN sequence bits and active subcarriers in the random sequence-based packet index OFDM communication system.

Fig. 5 is a diagram of a receiving end structure of a packet index OFDM communication system based on a random sequence.

Fig. 6 is a graph comparing the bit error rate of the random sequence based packet index OFDM system with that of the SIM-OFDM system in the gaussian channel.

Detailed Description

The invention is further described below with reference to the accompanying drawings.

The technical scheme of the invention is as follows:

the subcarriers of each carrier block in each OFDM symbol are activated by using different random sequences, the random sequence for controlling the activated subcarriers of each OFDM symbol is determined by index bits, and the randomness of the random sequences and the difference among the random sequences enable the relation between the index bits and the distribution of the activated carriers to be more complicated, and enable the information of the index bits to be more concealed. Dividing an information source bit into two parts at a system transmitting end, wherein one part is used as a signal modulation bit and is divided into constellation point symbols mapped into an M system; and one part is used as an index bit for selecting a random sequence from the random sequence set, and the activation of the subcarrier is realized by a random sequence driving mode.

The overall system link of the present invention is shown in fig. 1 and includes digitized source, subcarrier index mapping and modulation, serial-to-parallel conversion, IFFT, channel, FFT, parallel-to-serial conversion, and signal detection and demodulation.

Based on the grouping index OFDM modulation communication technology of the random sequence, partial subcarriers are activated to transmit modulation symbols in an index mode driven by the random sequence. The method is characterized by comprising the following steps:

step 1: by digital sources, each frame having p₁+p₂G bits of information; wherein the front p₁Bits as index bits for controlling PN sequence selection, post p₂G bits are used as information modulation bits in G subcarrier blocks, resulting in M-order modulation symbols.

Assuming that the total number of subcarriers is N, all subcarriers are divided into G sub-blocks, each sub-block has I ═ N/G subcarriers, k subcarriers are activated in each sub-block, each activated subcarrier carries one symbol, then p₂＝k log₂The M, k subcarriers carry k constellation point symbols.

Step 2: the PN sequence driven index technology selects different subcarrier activation combinations according to different PN sequence bits, and determines one subcarrier activation combination through the value of the PN sequence bits.

And step 3: mapping and modulating the subcarrier index, carrying out serial-parallel conversion, carrying out N-point IFFT operation, and adding CP.

And 4, step 4: and (4) sending the information source information after the steps 1-3, and reaching a receiving end through a channel.

And 5: and removing the CP, performing N-point FFT operation, and performing parallel-serial conversion.

Step 6: and the signal detection and the index are inversely mapped, and bits are output.

The index bit described in step 1 controls the selection of the PN sequence, which may be specifically expressed as:

in each frame of SIM-OFDM information, the index bit number is p₁Bit, PN sequence generator can generate 2p1 kinds of PN sequences, and the PN sequence set can be expressed as

Let p be₁The decimal number corresponding to the bit index bit is D, and the corresponding PN sequence is PN_D。

The PN sequence driven indexing technique in step 2 can be specifically expressed as:

assuming that Q is the number of bits required to select k subcarriers from the I subcarriers for activation, there is 2^QThe sub-carriers activate the combination, and the combination set of the g sub-block can be expressed as

If the corresponding PN sequence in a certain frame of SIM-OFDM information is expressed as

PN＝[u_1,1,u_1,2,…,u_1,Q,u_2,1,u_2,2,…,u_2,Q,…,u_G,1,u_G,2,…,u_G,Q]

Wherein the PN sequence bit corresponding to the g sub-carrier block is [ u ]_g,1,u_g,2,…,u_g,Q]If the decimal number corresponding to the PN sequence bit is o, the activated combination of the sub-carriers corresponding to the sub-carrier block is

Wherein G is 1,2, …, G, beta_g,rE {0,1}, r 1,2, …, I, and

k values of 1, I-k values of 0, beta_g,_r1 indicates that the subcarrier numbered r in the g-th subcarrier block is active, β_g,_r0 represents a numberThe sub-carriers of r are in a silent state.

A grouping index OFDM communication technology based on random sequence activates part of sub-carriers to transmit modulation symbols by an index mode driven by the random sequence. The method comprises the following steps:

step 1: by digital sources, each frame having p₁+p₂G bits of information; wherein the front p₁Bits as index bits for controlling PN sequence selection, post p₂G bits are used as information modulation bits in G subcarrier blocks to generate M-order modulation symbols;

step 2: the PN sequence driven index technology selects different subcarrier activation combinations according to different PN sequence bits, and determines a subcarrier activation combination through the value of the PN sequence bits;

and step 3: mapping and modulating subcarrier indexes, performing serial-parallel conversion, performing N-point IFFT operation, and adding a CP (program control protocol);

and 4, step 4: the information source information is sent after the step 1-3 and reaches a receiving end through a channel;

and 5: removing the CP, performing N-point FFT operation, and performing parallel-serial conversion;

step 6: and the signal detection and the index are inversely mapped, and bits are output.

The index bit described in step 1 controls the selection of the PN sequence, which may be specifically expressed as:

in each frame of SIM-OFDM information, the index bit number is p₁Bit, PN sequence generator generation

The PN sequence can be expressed as a PN sequence set

Let p be₁The decimal number corresponding to the bit index bit is D, and the corresponding PN sequence is PN_D。

The PN sequence driven indexing technique in step 2 can be specifically expressed as:

for a system with N subcarriers, there are N/G subcarriers in each subcarrier block,assuming that Q is the number of bits required to select k subcarriers from the I subcarriers for activation, there is 2^QThe sub-carriers activate the combination, and the combination set of the g sub-block can be expressed as

If the corresponding PN sequence in some frame index OFDM information is expressed as

PN＝[u_1,1,u_1,2,…,u_1,Q,u_2,1,u_2,2,…,u_2,Q,…,u_G,1,u_G,2,…,u_G,Q]

Wherein the PN sequence bit corresponding to the g sub-carrier block is [ u ]_g,1,u_g,2,…,u_g,Q]If the decimal number corresponding to the PN sequence bit is o, the activated combination of the sub-carriers corresponding to the sub-carrier block is

Wherein G is 1,2, …, G, beta_g,rE {0,1}, r 1,2, …, I, and

k values of 1, I-k values of 0, beta _g,r1 indicates that the subcarrier numbered r in the g-th subcarrier block is active, β_g,r0 indicates that the subcarrier numbered r is in a silent state.

Fig. 2 is a block diagram of a transmitting end of a SIM-OFDM communication system, such as the block diagram of the transmitting end of the OFDM communication system based on random sequence shown in fig. 3, where the transmitting end mainly includes the following steps:

step 1: parameters of the system are determined. The method comprises the total number N of subcarriers, the grouping number G of subcarriers, the number I of subcarriers in each group, the number k of activated subcarriers in each group, the modulation order M and the index bit number p₁. Framing by a digitized source, each frame having p ═ p₁+p₂G bit information bits, according to p₁Determining the number of PN sequences according to the formula

And p₂＝k log₂M calculates the needed PN sequence bit number and modulation bit number in each subcarrier block.

Step 2: the PN sequence driven index technology selects different subcarrier activation combinations according to different PN sequence bits, and determines one subcarrier activation combination through the value of the PN sequence bits. As shown in fig. 4, when 8 different PN sequences are set, and the relationship between the index bits, the PN sequence bits, and the active subcarrier distribution is exemplified by I ═ 4, and k ═ 1, the rule between the PN sequence bits and the active subcarrier distribution is the same as the rule between the index bits and the active subcarrier distribution in the SIM-OFDM system, and there is a certain rule between the selection of different PN sequences and the index bits, so that the relationship between the index bit information and the active carrier distribution is more complicated.

Q is the number of bits required to select k subcarriers from the I subcarriers for activation, then there are 2^QThe sub-carriers activate the combination, and the combination set of the g sub-block can be expressed as

If the corresponding PN sequence in a certain frame of SIM-OFDM information is expressed as

PN＝[u_1,1,u_1,2,…,u_1,Q,u_2,1,u_2,2,…,u_2,Q,…,u_G,1,u_G,2,…,u_G,Q]

Wherein the PN sequence bit corresponding to the g sub-carrier block is [ u ]_g,1,u_g,2,…,u_g,Q]If the decimal number corresponding to the PN sequence bit is o, the activated combination of the sub-carriers corresponding to the sub-carrier block is

Wherein G is 1,2, …, G, beta_g,rE {0,1}, r 1,2, …, I, and

k values of 1, I-k values of 0, beta _g,r1 indicates that the subcarrier numbered r in the g-th subcarrier block is active, β_g,r0 indicates that the subcarrier numbered r is in a silent state.

M-order modulation mapping is carried out on modulation bits to k constellation symbols s_g＝{s_g,1,s_g,2,…,s_g,kAnd after sub-carrier information mapping, the transmission signal of each sub-carrier block may be denoted as X_g＝[x_g,1,x_g,2,…,x_g,I]^TG is 1,2, …, G, wherein

j-1, …, I, r-1, 2, …, k, i.e., X_gThere are k constellation point symbols mapped by modulation information bits.

The system transmit signal may be expressed as:

and step 3: mapping and modulating the subcarrier index, carrying out serial-parallel conversion, carrying out N-point IFFT operation, and adding CP.

The system receiving end mainly comprises the following steps:

and 4, step 4: and (4) sending the information source information after the steps 1-3, and reaching a receiving end through a channel.

And 5: and removing the CP, performing N-point FFT operation, and performing parallel-serial conversion.

Step 6: and the signal detection and the index are inversely mapped, and bits are output.

The method comprises the steps of judging activated subcarriers by an energy amplifier at a system receiving end, determining subcarrier activation combination, demodulating PN sequence bits according to index inverse mapping, carrying out maximum correlation demodulation on the demodulated PN sequence bits, finding out corresponding PN sequences, and then pushing out index bits of the system. The receiving end principle is shown in fig. 5.

As shown in fig. 6, under the gaussian channel, the error rate performance of the present invention is slightly better than or substantially the same as that of the SIM-OFDM system, the simulation parameters are I-4, k-1, and the PN sequence number is 8, and this simulation result proves that the interference resistance performance of the present invention is not inferior to that of the SIM-OFDM system.

The invention introduces PN sequence based on SIM-OFDM, which improves the anti-interception performance of the system without reducing the anti-interference performance of the system, and has application value in military and civil communication.

Claims (1)

1. A method for OFDM communication based on random sequence packet index, comprising the steps of:

step 1: determining system parameters, framing by a digital information source, determining the number of index bits and the number of modulation bits, and controlling the selection of a PN sequence by the index bits;

the system parameters comprise the total number N of subcarriers, the number G of subcarrier blocks, the number I of subcarriers in each subblock, the number k of activated subcarriers in each subblock, each activated subcarrier carries a constellation point symbol, the modulation order M is framed by a digital information source, and each frame has p₁+p₂G bits of information, where the front p₁Bits as index bits for controlling PN sequence selection, post p₂G bits as information modulation bits in G subcarrier blocks, M order modulation symbols generated from the information modulation bits, the number of modulation bits p₂Calculated from the following formula:

p₂＝k log₂ M

the index bit controls the selection of the PN sequence, specifically expressed as: in the frame packet index OFDM, i.e. SIM-OFDM, information, a PN sequence generator can generate

A PN sequence, a set of PN sequences being represented as

p₁The decimal number corresponding to the bit index bit is D, and the corresponding PN sequence is PN_D；

Step 2: obtaining PN sequence bits according to the determined system parameters, and selecting different subcarrier activation combinations according to different PN sequence bits;

q is the number of bits required to select k subcarriers from the I subcarriers for activation, and

then there is 2^QEach sub-carrier activates a combination, and the combination set of the g sub-block is expressed as:

the corresponding PN sequence in a frame of SIM-OFDM information is represented as:

PN＝[u_1,1,u_1,2,…,u_1,Q,u_2,1,u_2,2,…,u_2,Q,…,u_G,1,u_G,2,…,u_G,Q]

wherein the PN sequence bit corresponding to the g sub-carrier block is [ u ]_g,1,u_g,2,…,u_g,Q]If the decimal number corresponding to the PN sequence bit is o, the activated combination of the sub-carriers corresponding to the sub-carrier block is

Wherein G is 1,2, …, G, beta_g,rE {0,1}, r 1,2, …, I, and

k values of 1, I-k values of 0, beta_g,r1 indicates that the subcarrier numbered r in the g-th subcarrier block is active, β_g,r0 indicates that the subcarrier numbered r is in a silent state;

and step 3: according to the selected subcarrier activation combination, subcarrier index mapping and modulation are carried out, serial-parallel conversion is carried out, N-point IFFT operation is carried out, and CP is added;

and 4, step 4: according to the information source information sent after the steps 1 to 3, the information source information reaches a receiving end through a channel;

and 5: according to the signal received by the receiving end, removing CP from the signal, performing N-point FFT operation, and performing parallel-serial conversion;

step 6: and (5) according to the signal obtained after the processing in the step (5), carrying out signal detection and index inverse mapping, and outputting a bit.

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