CN101814974B - Transmission method combined with network coding and channel decoding based on adaptive modulation - Google Patents

Abstract

The invention provides a transmission method combined with network coding and channel decoding based on adaptive modulation, which adaptively adjusts the modulation mode according to the actual channel condition and can improve the channel capacity as far as possible while maintaining lower bit error rate performance. The method comprises the following steps: two moving source nodes respectively carry out linear coding and modulation on the packets to be transmitted and the modulation mode is adaptively adjusted according to the channel condition; then the modulating signals are transmitted to a relay node; the relay node carries out modulating signal recognition on the received information from the two source nodes respectively and carries out corresponding soft demodulation according to the modulation mode information; after obtaining two-way demodulated soft decision information, the relay node carries out network coding, namely consolidating soft information, the consolidated soft information undergoes channel decoding to obtain target packets, and the relay node transmits the target packets by broadcasting; and the two source nodes receive the packets broadcast by the relay node and carry out decoding by virtue of the existing information, thus obtaining the opposite node information and completing information exchange.

Description

Based on the combined with network coding of Adaptive Modulation and the transmission method of channel decoding

Technical field

The present invention relates to the radio transmission technical field of coding Network Based and channel decoding.

Background technology

Network code is from broken information processing manner traditional the communication network in essence, and it has been a new research focus in the communication network research field.Network code mechanism is through allowing via node to the information that receives from the mulitpath forwarding of encoding; Receiving node carries out corresponding decoding to obtain raw information; Can realize the max-flow transmission of network in theory; And solve the transmission bottleneck problem of via node effectively, improving network throughput, improving load balancing, reducing transmission delay, saving node energy consumption, strengthening aspect such as network robustness and all demonstrate its superiority.The early stage research of network code only limits to the multicast transmission of cable network; Because the broadcast characteristic of wireless network self; Or perhaps wireless multicast advantage; Make the application of network code in wireless network bring new gain, comprise transmission rate, the throughput that improves wireless network and save energy etc.For the wireless network links transmission of making an uproar is arranged, network code should merge with the technology of the adverse effect of handling the wireless channel decline.

But become fading characteristic when having owing to mobile telecommunication channel, the effect that wireless signal receives multipath effect can produce serious amplitude fading and time delay expansion, causes performance of BER to worsen.A kind of method that overcomes amplitude fading is to increase transmitting power, adds surplus significantly; Another kind method is the Bit Transmission Rate that reduces in the wireless channel, and the reduction of Bit Transmission Rate can reduce the availability of frequency spectrum, has promptly reduced the capacity of system.In addition, because the budget of non-self-adapting system link must be satisfied the channel quality worst condition, thereby when channel quality was better, system just can not make full use of channel capacity, had caused the waste of frequency spectrum resource; And future mobile communications need develop the high speed data transfer business.

Therefore, in the prior art, under the continuous change condition of channel status, also do not have a kind ofly all reaching more excellent perfect wireless transmission scheme aspect power system capacity and the system's error performance two.

Summary of the invention

In view of this; In order to address the above problem; For this reason, the present invention proposes a kind of combined with network coding of Adaptive Modulation and the transmission method of channel decoding, the modulation system that source node adopts is adjusted according to the channel situation self adaptation; Can in the lower errored bit performance of maintenance, improve channel capacity as far as possible.

The objective of the invention is to realize like this:, comprise the steps: based on the combined with network coding of Adaptive Modulation and the transmission method of channel decoding

1) the first source node n ₁With the second source node n ₃Packet S to sending respectively ₁, S ₃Carry out uniform enconding and modulation, the scheme of modulation is adjusted according to the actual channel conditions self adaptation; Then modulation signal is sent to via node n ₂

2) via node n ₂The information from two source nodes to receiving is carried out Modulation Signals Recognition respectively, carries out corresponding soft demodulation respectively according to modulation system information then;

3) via node n ₂After obtaining the soft decision information after the two paths of signals demodulation, carry out network code, promptly merge soft information, the soft information via channel-decoding after merging is obtained the target data bag

And will

Its broadcasting;

4) two source nodes are received via node n ₂The packet S of broadcasting ₂, decipher promptly to obtain the other side's nodal information by existing information, accomplish information exchange.

Further, in the step 1), along with the increase of via node distance, the exponent number of the modulation system that source node adopts reduces, source node and via node are apart from approaching more, the order of modulation of employing is high more;

Further, in the step 1), in session cycle, the Packet Data Unit of one deck only adopts a kind of modulation system for a data flow of a source node;

Further, said modulation system is selected from a kind of in BPSK (two-phase PSK), QPSK (QPSK), 8PSK (eight phase phase shift keyings) or the 16QAM modulation systems such as (hexadecimal quadrature amplitude modulation(PAM)s).

With respect to prior art; Method of the present invention is carried out self adaptation adjustment signal modulation rate according to actual channel condition; All make channel capacity reach the maximum systematic function that perhaps makes at any time and reach best relatively; Thereby make the mobile radio channel frequency band can obtain the higher availability of frequency spectrum crowded day by day today, thereby improve the bandwidth that the rate of information throughput improves transmission system effectively, can all reach gratifying degree aspect power system capacity and the system's error performance two.Method of the present invention is also used the co-design of network code and chnnel coding, can obtain more diversity gain.

Other advantages of the present invention, target; To in specification subsequently, set forth to a certain extent with characteristic; And to a certain extent,, perhaps can from practice of the present invention, obtain instruction based on being conspicuous to those skilled in the art to investigating of hereinafter.Target of the present invention and other advantages can be passed through following specification, claims, and the structure that is particularly pointed out in the accompanying drawing realizes and obtains.

Description of drawings

In order to make the object of the invention, technical scheme and advantage clearer, will combine accompanying drawing that the present invention is made further detailed description below:

Fig. 1 shows the system transmissions model based on the transmission method of the combined with network coding of Adaptive Modulation and channel decoding;

Fig. 2 shows the schematic flow sheet based on the transmission method of the combined with network coding of Adaptive Modulation and channel decoding;

Fig. 3 shows the example based on a selecting modulation mode of the transmission method of the combined with network coding of Adaptive Modulation and channel decoding.

Embodiment

Below will carry out detailed description to the preferred embodiments of the present invention with reference to accompanying drawing.

As shown in Figure 1, the system transmissions model for the transmission method of combined with network coding and the channel decoding based on Adaptive Modulation of the present invention comprises two moving source node n ₁, n ₃, and via node n ₂

1) source node n ₁With source node n ₃Packet S to sending respectively ₁, S ₃Carry out uniform enconding and modulation, the scheme of modulation is adjusted according to the actual channel conditions self adaptation; Then at first time slot, n ₁With S ₃Send to n ₂, at second time slot, n ₃With S ₃Send to n ₂

2) via node n ₂The information from two source nodes to receiving is carried out Modulation Signals Recognition respectively, carries out corresponding soft demodulation respectively according to modulation system information then;

3) via node n ₂After obtaining the soft decision information after the two paths of signals demodulation, carry out network code, promptly merge soft information, the soft information via channel-decoding after merging is obtained the target data bag

And it is broadcast to n at the 3rd time slot ₁And n ₃Broadcasting;

4) two source nodes are received via node n ₂The packet S of broadcasting ₂, decipher promptly to obtain the other side's nodal information by existing information, accomplish information exchange.

Be described in detail the implementing procedure of the transmission method of combined with network coding and the channel decoding based on Adaptive Modulation of the present invention below.As shown in Figure 2, S _i=[s _{I, 0}, s _{I, 1}..., s _{I, K-1}], i=1,3 expressions, two moving source node n ₁And n ₃The packet that sends.Suppose two packet S ₁And S ₃Identical length K is arranged, work as k=0,1 ... binary message bit s during K-1 _{I, k}{ 0,1} and independently of one another is with distributing for ∈.M _i=[m _{I, 0}, m _{I, 1}..., m _{I, N-1}], i=1,3 expression node ni places are through the set of the numeric code after the chnnel coding, m _{I, n}∈ 0,1}, then code check r=K/N.The n of this programme ₁And n ₃Adopt identical PCCC Turbo encoder.Γ representes the mapping function of Turbo encoder; Γ ^-1The mapping function of expression Turbo decoder, that is: Γ (S _i)=M _i, Γ ^-1(M _i)=S _i, i=1,3

From the coding after bit m _{I, n}To modulation symbol x _{I, n}Mapping table be shown: x _{I, n}=f _i(m _{I, n}).As shown in Figure 2, via node is that the pooling information of the soft information of two-way is decoded, and this just requires two source node n ₁And n ₃The channel encoder at place is identical and satisfy linear behavio(u)r:

Wherein,

Represent binary system XOR common in the network code algorithm: to m ₁, m ₃∈ M uses XOR and makes

Different with traditional approach is that after the chnnel coding, each source node selects the suitable modulating mode to send signal according to the actual channel situation.In this programme, the self adaptation adjustment at a slow speed of the modulation system basis of source node and the distance between the via node, promptly for a data flow of a source node in session cycle, the PDU of one deck (Packet Data Unit) only adopts a kind of modulation system.Design principle is to reduce option as far as possible, thereby simplifies the via node design.Source node is confirmed modulation scheme (BPSK, QPSK, 8PSK, 16QAM) according to MAC layer scheduler.

Fig. 3 has shown a simple case that adopts adaptive modulation scheme.System confirms modulation system according to CQI (channel quality information), and the feedback cycle of CQI can be adjusted according to the variation of environment.The big young pathbreaker of feedback overhead is as the important evidence of selecting the CQI feedback method.Physical layer submits to CQI to the MAC layer, and the method that generates CQI in physical layer inside exactly is the internal mechanism of physical layer.Utilize the scheme of adaptive modulation technology to confirm the suitable modulating mode, send information with higher rate to greatest extent according to current channel capacity demand.

X _iRepresent source node n _iPacket after place's modulation, it sends to via node n through channel ₂Y _iThe expression via node receive from node n _iPacket, Y _i=[y _{I, 0}, y _{I, 1}..., y _{I, N-1}], i=1,3.

Via node n ₂Receive Y _iAfter carry out Modulation Signals Recognition respectively and judge and receive the modulation system of signal at the source node place, just can carry out corresponding demodulation coding processing then.

What Turbo decoding was directed against in traditional joint network channel code scheme is the BPSK modulation system, and source node possibly adopt different modulation modes (comprising high order modulation) in this programme.If decipher the court verdict that input is imported hard demodulation at Turbo, its performance will sharply descend, so at n ₂The soft decision information that place's demodulation obtains is even more important.At this, we are the derivation that example is set forth soft decision information with 16QAM.

At moment k, the signaling point on the 16QAM planisphere with the real number on the complex plane to { A _k, B _kRepresent that it is by four bit { u _{K, i}, i=1,2,3,4 mappings obtain.Suppose symbols all in the planisphere, and the contained bit of all symbols, the probability of appearance equates.Use correlation reception, demodulator receives the in-phase branch and the quadrature branch Y of data _LkAnd Y _QkCan be expressed as: Y _Lk=a _kA _k+ I _k, Y _Qk=a _kB _k+ Q _k, a wherein _kBeing a Rayleigh stochastic variable under rayleigh fading channel, is 1 under the white Gaussian noise channel.I _kAnd Q _kBe that average is 0, variance is σ _N ²Gaussian noise, and they are separate.

By its likelihood logarithm ratio of bit calculation, i bit { u _{K, i}I=1,2,3,4 LLR is defined as:

$\mathrm{LLR}\left(u_{k,i}\right)=\log \frac{P(u_{k,i}=1|Y_{\mathrm{lm}},Y_{\mathrm{Qk}})}{P(u_{k,i}=0|Y_{\mathrm{lk}},Y_{\mathrm{Qk}})},i=\mathrm{1,2,3,4}$

Adopting the MAX-LOG-MAP algorithm, is that the distance of 0 constellation point and Y just can be in the hope of the soft decision information of this bit through asking from receiving distance that i nearest bit of signal Y is 1 constellation point and Y and i nearest bit.Obtain just having accomplished behind the soft decision information of four bits the soft decision demodulation of this symbol, promptly obtain the soft output of demodulator.Make V _i=[v _{I, 0}, v _{I, 1}... v _{I, N-1}], i=1,3 representatives receive signal Y _iSoft decision information.

Next step network code operation is the soft decision information V to the packet of two transmissions ₁And V ₃Merge (promptly by the bit XOR), can be expressed as:

$v_{2,n}=\mathrm{LLR}(m_{1,n}\⊕m_{3,n})=\ln \left(\frac{P(m_{1,n}\⊕m_{3,n}=0|y_{1,n},y_{3,n})}{P(m_{1,n}\⊕m_{3,n}=1|y_{1,n},y_{3,n})}\right)$

$=\ln \left(\frac{\exp \left(v_{1,n}\right)+\exp \left(v_{3,n}\right)}{1+\exp (v_{1,n}+v_{3,n})}\right)$

$=\mathrm{LLR}\left({\mathrm{<figure-callout\; id="2"\; label="m"\; filenames="HSA00000055409700011.png"\; state="\{\{state\}\}">m</figure-callout>}}_{2,n}\right)$

V ₁And V ₃The output signal V that merges (being network code) ₂The channel decoding just can access the target data bag

If in the absence of error of transmission, the purpose information packet can be expressed as:

${\mathrm{<figure-callout\; id="2"\; label="S"\; filenames="HSA00000055409700011.png"\; state="\{\{state\}\}">S</figure-callout>}}_2={\mathrm{\&Gamma;}}^{-1}\left(V_3\right)={\mathrm{\&Gamma;}}^{-1}(V_1\&CirclePlus;V_3)={\mathrm{\&Gamma;}}^{-1}(M_1\&CirclePlus;M_3)$

$={\mathrm{\&Gamma;}}^{-1}(\mathrm{\&Gamma;}\left(S_1\right)\&CirclePlus;\mathrm{\&Gamma;}\left(S_3\right))$

$={\mathrm{\&Gamma;}}^{-1}\left(\mathrm{\&Gamma;}(S_1\&CirclePlus;S_3)\right)$

$=S_1\&CirclePlus;S_3$

Can find out soft decision information V ₁And V ₃Through merging (being network code) afterwards, output signal V ₂Get into Turbo decoder (SISO iterative decoding) and just can access the target data bag

When the Turbo code decoding algorithm of traditional scheme was derived, mostly the modulation system of use was BPSK or QPSK.To the soft demodulation of high-order, must do approximate to the LLR of input Turbo code decoder.What the LLR of input can be similar to thinks Gaussian distributed, and its condition PDF is:

$p\left(Y_k\right|u_k)=\frac{1}{\sqrt{2\mathrm{\&pi;}{\mathrm{\&sigma;}}^2}}\exp \{-\frac{{(Y_k-u_{k}m)}^2}{2{\mathrm{\&sigma;}}^2}\}$

Wherein m and σ ²Be absolute value and the variance of LLR, can use statistic:

$m=\frac{1}{N}\underset{k=1}{\overset{N}{\mathrm{\&Sigma;}}}\left|z_k\right|,{\mathrm{\&sigma;}}^2=\frac{1}{N}\underset{k=1}{\overset{N}{\mathrm{\&Sigma;}}}\left|z_k\right|-{\mathrm{<figure-callout\; id="2"\; label="m"\; filenames="HSA00000055409700011.png"\; state="\{\{state\}\}">m</figure-callout>}}^2$ Replace.

Decoder output is the target data bag $S_{}$ ${}_2=(S_1\&CirclePlus;S_3).$

Because xor operation has following character:

Receiving node is received the S of via node broadcasting ₂, decipher (XOR) by existing information, can obtain the other side's nodal information, accomplish information exchange.

The above is merely the preferred embodiments of the present invention, is not limited to the present invention, and obviously, those skilled in the art can carry out various changes and modification and not break away from the spirit and scope of the present invention the present invention.Like this, belong within the scope of claim of the present invention and equivalent technologies thereof if of the present invention these are revised with modification, then the present invention also is intended to comprise these changes and modification interior.

Claims (3)

1. based on the combined with network coding of Adaptive Modulation and the transmission method of channel decoding, it is characterized in that: comprise the steps:

1) the first source node (n ₁) and the second source node (n ₃) the packet S to sending respectively ₁, S ₃Carry out uniform enconding and modulation, modulation system is adjusted according to actual channel situation self adaptation; Then modulation signal is sent to via node (n ₂);

2) via node (n ₂) information from two source nodes that receives is carried out Modulation Signals Recognition respectively, carry out corresponding soft demodulation respectively according to modulation system information then;

3) via node (n ₂) obtain the soft decision information after the two paths of signals demodulation after, carry out network code, promptly merge soft information, the soft information via channel-decoding after merging is obtained the target data bag

And with its broadcasting;

4) two source nodes are received via node (n ₂) broadcasting packet S ₂, decipher promptly to obtain the other side's nodal information by existing information, accomplish information exchange;

In the step 1), along with the increase of via node distance, the exponent number of the modulation system that source node adopts reduces, source node and via node are apart from approaching more, the order of modulation of employing is high more.

2. as claimed in claim 1 based on the combined with network coding of Adaptive Modulation and the transmission method of channel decoding; It is characterized in that: in the step 1); In session cycle, the Packet Data Unit of one deck only adopts a kind of modulation system for a data flow of a source node.

3. as claimed in claim 2 based on the combined with network coding of Adaptive Modulation and the transmission method of channel decoding, it is characterized in that: said modulation system is selected from a kind of of following modulation system: two-phase PSK, QPSK, eight phase phase shift keyings or hexadecimal quadrature amplitude modulation(PAM).

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