CN102064915B - Distributed differential space-time code transmission method suitable for fast fading channel - Google Patents

Abstract

The invention discloses a distributed differential space-time code (DDSTC) transmission method suitable for a fast fading channel. The thought of the method is to reduce the adverse effect caused by fast fading of the channel by reducing the frame length of DDSTC signals, therefore, the method is named as a reduced frame length-DDSTC transmission scheme, namely named as RFL-DDSTC (RFL, Reduced Frame Length) for short. In the method, the signals of the DDSTC in T symbol periods are merged in one symbol period for transmitting by adopting T orthogonal column vectors, so that the frame length of the DDSTC signals is greatly shortened, and the adverse effect caused by fast fading of the channel can be effectively reduced. Theoretical analysis and simulation results further verify that the RFL-DDSTC scheme proposed in the invention promotes the error code performance in the fast fading channel.

Description

A kind of distributed differential space-time coding transmission method of suitable fast fading channel

Technical field

Transmit diversity techniques, the particularly distributed differential space-time coding transmission method in a kind of fast fading channel when the invention belongs to a kind of distributed space in the cooperation communication system that adopts relaying.

Background technology

In recent years, the distributed differential space-time coding (DDSTC) in wireless relay network is owing to need not all to know that at via node and destination node place source node has obtained a lot of concerns to the channel information between via node and via node to the channel information between destination node.Surging along with people to the research interest of DDSTC, the various countries scholar has proposed multiple DDSTC transmission plan successively, as the DDSTC scheme based on Alamouti code, real orthogonal code, Sp (2) code, cyclic code, Cayley code and Clifford algebraic code etc.And up to now, supposed all in above-mentioned DDSTC scheme that wireless channel is obeyed slowly to change, and remain unchanged when sending two continuous DDSTC data blocks.Yet taken 2T symbol period according to each DDSTC data block of relay cooperative agreement, need to remain unchanged in 4T symbol period at above-mentioned this hypothesis lower channel.And this hypothesis is to be difficult to set up in fast fading channel, and therefore, worsening will appear in fast fading channel in the performance of DDSTC.

Summary of the invention

The impact that the DDSTC performance is brought in order to reduce the channel rapid fading has proposed a kind of new DDSTC transmission plan in the present invention.Be referred to as the distributed differential space-time coding transmission plan that reduces the signal frame length, referred to as RFL-DDSTC (RFL, Reduced Frame Length).This scheme utilizes T different orthogonal vectors that DDSTC is sent in Signal Compression to a symbol period in T symbol period, making the signal frame of DDSTC grow up reduces greatly, this new scheme thereby be referred to as the DDSTC that reduces frame length, i.e. RFL-DDSTC in the present invention.RFL-DDSTC reduces due to the signal frame length thereby can effectively reduce the impact that the channel rapid fading brings its performance, and, this thought that reduces the signal frame length of RFL-DDSTC goes in existing all DDSTC encoding schemes, as based on Sp (2) code, cyclic code is in the DDSTC scheme of Cayley code and Clifford algebraic code.Theory analysis and simulation result have further been verified the superior performance of RFL-DDSTC in fast fading channel that proposes in the present invention.

For achieving the above object, technical scheme of the present invention is achieved in that

Signal frame length at the via node place to DDSTC compresses with the orthogonal intersection sequence, carries out at first to received signal despreading in destination node, then the signal after despreading is carried out Differential Detection gets final product.Implementation process is divided into three steps particularly:

One, via node place's compression DDSTC signal frame length

Because the second step that sends each data block takies T symbol period, the frame length that is the transmitted signal of each relaying is T, in the RFL-DDSTC scheme, the Signal Compression that is T with frame length in T orthogonal vectors of each relaying place's employing is the short signal with unit frame length.It is 1 orthogonal vectors that T orthogonal vectors can adopt norm arbitrarily, elects it as T orthogonal intersection sequence.

For (τ-1) individual data block, suppose that the transmitted signal of the T at i relaying place * 1 dimension is

Wherein Be illustrated in the signal that (T+k) sends constantly, send like this

To take T symbol period.At each relaying place, at first adopt a spreading code Matrix C=[c ₁c ₂C _T] be compressed in the transmitted signal of T symbol period

Suppose the spreading code c of P * 1 dimension _k(k=1 ..., T) mutually orthogonal and norm is 1, namely satisfies

δ wherein _klExpression Kronecker delta function, c _kLength P be defined as its spreading gain.The compressed signal of the P that therefore, sends at i relaying place * 1 dimension is

$b_i^{(\mathrm{\τ}-1)}={\mathrm{Ct}}_i^{(\mathrm{\τ}-1)}=\underset{k=1}{\overset{T}{\mathrm{\Σ}}}{c}_k{t}_{\mathrm{ik}}^{(\mathrm{\τ}-1)}---\left(9\right)$

Obviously,

Only taken a symbol period, and

T spread spectrum code sequence c _k(k=1 ..., linear combination T), its weight coefficient is

The second step that sends like this (τ-1) individual data block will be completed within T+1 the moment, and corresponding channel gain is g _i(T+1), see channel status corresponding in accompanying drawing 2.Like this, the destination node place corresponding to the reception signal of (τ-1) individual data block is

$Y^{(\mathrm{\τ}-1)}=\underset{i=1}{\overset{R}{\mathrm{\Σ}}}{g}_i(T+1)b_i^{(\mathrm{\τ}-1)}+W^{(\mathrm{\τ}-1)}$

$=\underset{i=1}{\overset{R}{\mathrm{\Σ}}}{g}_i(T+1){\mathrm{Ct}}_i^{(\mathrm{\τ}-1)}+W^{(\mathrm{\τ}-1)}---\left(10\right)$

$=\underset{i=1}{\overset{R}{\mathrm{\&Sigma;}}}{g}_i(T+1)C\left(\sqrt{\frac{P_2}{{\mathrm{<figure-callout\; id="1"\; label="P"\; filenames="HDA0000038489670000011.png,HDA0000038489670000012.png"\; state="\{\{state\}\}">P</figure-callout>}}_1+1}}{A_{i}r}_i^{(\mathrm{\&tau;}-1)}\right)+W^{(\mathrm{\&tau;}-1)}$

Wherein

The reception signal of the T in i the relaying place first step * 1 dimension corresponding to (τ-1) individual data block, will

The substitution formula can get in (10)

$Y^{(\mathrm{\&tau;}-1)}=\sqrt{\frac{P_1{\mathrm{<figure-callout\; id="2T"\; label="P"\; filenames="HDA0000038489670000012.png"\; state="\{\{state\}\}">P</figure-callout>}}_2\mathrm{<figure-callout\; id="1"\; label="T\; P"\; filenames="HDA0000038489670000011.png,HDA0000038489670000012.png"\; state="\{\{state\}\}">T</figure-callout>}}{P_{}}}C{S}^{(\mathrm{\&tau;}-1)}{\tilde{H}}^{(\mathrm{\&tau;}-1)}+{\tilde{N}}^{(\mathrm{\&tau;}-1)}---\left(11\right)$

Wherein corresponding to the new channel vector of (τ-1) individual data block

Can be expressed as

Noise is

Equally, for the signal that will send from i relaying in τ data block

Still adopt the spreading code matrix to compress it.The signal that sends at i relaying of second step like this

Still only taken a symbol period, as shown in the channel status in accompanying drawing 2, corresponding channel gain is g _i(2T+2).Therefore, the reception signal corresponding to τ data block destination node place can be expressed as

$Y^{\left(\mathrm{\&tau;}\right)}=\sqrt{\frac{P_1{\mathrm{<figure-callout\; id="2T"\; label="P"\; filenames="HDA0000038489670000012.png"\; state="\{\{state\}\}">P</figure-callout>}}_2\mathrm{<figure-callout\; id="1"\; label="T\; P"\; filenames="HDA0000038489670000011.png,HDA0000038489670000012.png"\; state="\{\{state\}\}">T</figure-callout>}}{P_{}}}{\mathrm{CS}}^{\left(\mathrm{\&tau;}\right)}{\tilde{H}}^{\left(\mathrm{\&tau;}\right)}+{\tilde{N}}^{\left(\mathrm{\&tau;}\right)}=\sqrt{\frac{P_1{\mathrm{<figure-callout\; id="2T"\; label="P"\; filenames="HDA0000038489670000012.png"\; state="\{\{state\}\}">P</figure-callout>}}_2\mathrm{<figure-callout\; id="1"\; label="T\; P"\; filenames="HDA0000038489670000011.png,HDA0000038489670000012.png"\; state="\{\{state\}\}">T</figure-callout>}}{P_{}}}{\mathrm{CU}}^{\left(\mathrm{\&tau;}\right)}{S}^{(\mathrm{\&tau;}-1)}{\tilde{H}}^{\left(\mathrm{\&tau;}\right)}+{\tilde{N}}^{\left(\mathrm{\&tau;}\right)}---\left(12\right)$

Wherein channel vector is

Noise is ${\tilde{N}}^{\left(\mathrm{\&tau;}\right)}=\sqrt{\frac{P_2}{{\mathrm{<figure-callout\; id="1"\; label="P"\; filenames="HDA0000038489670000011.png,HDA0000038489670000012.png"\; state="\{\{state\}\}">P</figure-callout>}}_1+1}}\underset{i=1}{\overset{R}{\mathrm{\&Sigma;}}}{g}_i(2T+2){\mathrm{CA}}_i{v}_i^{\left(\mathrm{\&tau;}\right)}+W^{\left(\mathrm{\&tau;}\right)}.$

Two, destination node place's despreading receives signal

When destination node is carried out reception ﹠ disposal, at first receive signal Y to two ^(τ-1)And Y ^(τ)Use c _k(k=1 ..., T) carry out respectively despreading and process, obtain

$d_k^{(\mathrm{\&tau;}-1)}=c_k^H{Y}^{(\mathrm{\&tau;}-1)}=\underset{i=1}{\overset{R}{\mathrm{\&Sigma;}}}{g}_i(T+1)t_{\mathrm{ik}}^{(\mathrm{\&tau;}-1)}+c_k^H{W}^{(\mathrm{\&tau;}-1)}---\left(13\right)$

$d_k^{\left(\mathrm{\&tau;}\right)}=c_k^H{Y}^{\left(\mathrm{\&tau;}\right)}=\underset{i=1}{\overset{R}{\mathrm{\&Sigma;}}}{g}_i(2T+2)t_{\mathrm{ik}}^{\left(\mathrm{\&tau;}\right)}+c_k^H{W}^{\left(\mathrm{\&tau;}\right)}---\left(14\right)$

Subsequently, with Y ^(τ-1)And Y ^(τ)Signal after despreading is organized into respectively the vector of T * 1 dimension

With

With y ^(τ-1)And y ^(τ)Being write as matrix form can be expressed as

$y^{(\mathrm{\&tau;}-1)}=\sqrt{\frac{P_1{\mathrm{<figure-callout\; id="2T"\; label="P"\; filenames="HDA0000038489670000012.png"\; state="\{\{state\}\}">P</figure-callout>}}_2\mathrm{<figure-callout\; id="1"\; label="T\; P"\; filenames="HDA0000038489670000011.png,HDA0000038489670000012.png"\; state="\{\{state\}\}">T</figure-callout>}}{P_{}}}{S}^{(\mathrm{\&tau;}-1)}{\tilde{H}}^{(\mathrm{\&tau;}-1)}+Z^{(\mathrm{\&tau;}-1)}---\left(15\right)$

$y^{\left(\mathrm{\&tau;}\right)}=\sqrt{\frac{P_1{\mathrm{<figure-callout\; id="2T"\; label="P"\; filenames="HDA0000038489670000012.png"\; state="\{\{state\}\}">P</figure-callout>}}_2\mathrm{<figure-callout\; id="1"\; label="T\; P"\; filenames="HDA0000038489670000011.png,HDA0000038489670000012.png"\; state="\{\{state\}\}">T</figure-callout>}}{P_{}}}{S}^{\left(\mathrm{\&tau;}\right)}{\tilde{H}}^{\left(\mathrm{\&tau;}\right)}+Z^{\left(\mathrm{\&tau;}\right)}---\left(16\right)$

Wherein Obviously, after despreading to received signal, the signal S that DDSTC is original ^(τ-1)And S ^(τ)Appear in formula (15) and (16).

Three, Differential Detection

Therefore, under the condition that following hypothesis is set up, can detect the DDSTC signal with the differential decoder in formula (5):

${\tilde{H}}^{(\mathrm{\&tau;}-1)}={\tilde{H}}^{\left(\mathrm{\&tau;}\right)}---\left(17\right)$

Above time interval between two channel gains be only (T+1) individual symbol period.Assumption when decoding with DDSTC (8) is compared, and the impact of assumption (17) performance in fast fading channel for DDSTC when new RFL-DDSTC scheme is decoded is less.Therefore, in fast fading channel, the frame length that reduces DDSTC can effectively improve its performance.

The technique effect that the present invention reaches is to be the signal of the signal unit of the being reduced to frame length of T with the original frame length of DDSTC, so can significantly reduce the adverse effect that fast fading channel brings DDSTC, thereby greatly improve the performance of DDSTC in fast fading channel.

Description of drawings

Fig. 1 is channel status corresponding when transmitting the DDSTC signal in fast fading channel;

Fig. 2 is channel status corresponding when transmitting the RFL-DDSTC signal in fast fading channel;

Fig. 3 is DDSTC and the error performance comparison diagram of RFL-DDSTC when R=2, and wherein abscissa is transmitting power P total in whole wireless relay network, and ordinate is error sign ratio;

Fig. 4 is DDSTC and the error performance comparison diagram of RFL-DDSTC when R=3, and wherein abscissa is transmitting power P total in whole wireless relay network, and ordinate is error sign ratio;

Fig. 5 is DDSTC and the error performance comparison diagram of RFL-DDSTC when R=4, and wherein abscissa is transmitting power P total in whole wireless relay network, and ordinate is error sign ratio;

Fig. 6 is DDSTC and the error performance comparison diagram of RFL-DDSTC when R=5, and wherein abscissa is transmitting power P total in whole wireless relay network, and ordinate is error sign ratio.

Below in conjunction with accompanying drawing, the present invention is described in further detail.

Embodiment

1) system model and distributed differential space-time coding scheme

Consider the cooperation communication system of an employing relaying, a source node is arranged in system, a destination node and R via node, intrasystem each node all arranges single antenna.Suppose from source node to the channel f i via node _iExpression is from i via node to the channel g destination node _iExpression.In cooperation communication system, transmitting T symbol need to complete in two steps: the time that each step takies is T symbol period.T symbol of transmission can be called is a data block, and therefore transmitting a data block will take 2T symbol period.When adopting distributed differential space-time coding (DDSTC) transmission in cooperation communication system, the system equation during τ data block of transmission be expressed from the next [2]

$X^{\left(\mathrm{\&tau;}\right)}=\sqrt{\frac{P_1{\mathrm{<figure-callout\; id="2T"\; label="P"\; filenames="HDA0000038489670000012.png"\; state="\{\{state\}\}">P</figure-callout>}}_2\mathrm{<figure-callout\; id="1"\; label="T\; P"\; filenames="HDA0000038489670000011.png,HDA0000038489670000012.png"\; state="\{\{state\}\}">T</figure-callout>}}{P_{}}}{S}^{\left(\mathrm{\&tau;}\right)}{H}^{\left(\mathrm{\&tau;}\right)}+W^{\left(\mathrm{\&tau;}\right)}---\left(1\right)$

P wherein ₁And P ₂Be respectively the average transmit power at source node when sending each data block and each via node place; The DDSTC matrix S of T * R dimension ^(τ)=[A ₁s ^(τ)A _Rs ^(τ)], A wherein _iThe T * T that is i via node place ties up unitary matrice, s ^(τ)=[s ₁S _T] ^TBe the signal vector when sending τ data block, it has normalized unit power, subscript () ^TTranspose of a matrix is got in expression; Corresponding R when sending τ data block * 1 dimension channel vector H ^(τ)Be defined as H ^(τ)=[f ₁g ₁F _Rg _R] ^TTotal noise

Wherein

And w ^(τ)Be respectively the first step at i via node place and the second step additive white Gaussian noise (AWGN) at the destination node place.

When sending τ data block, for transmission information U ^(τ)∈ U carries out differential coding to the signal of launching

s ^(τ)＝U ^(τ)s ^(τ-1) (2)

The information matrix U of T * T dimension wherein ^(τ)Be unitary matrice, and, U ^(τ)Matrix A with each via node place _iSatisfy following relation

A _iU ^(τ)＝U ^(τ)A _i (3)

Existing DDSTC scheme [2-4] is all supposed channel f _iAnd g _iRemain unchanged in two data blocks of transmitting continuously, i.e. H ^(τ)=H ^(τ-1), be updated to formula (2) and formula (3) in formula (1) this moment so and the reception signal X when uniting previous data block ^(τ-1), can obtain following difference equation

X ^(τ)＝U ^(τ)X ^(τ-1)+N ^(τ) (4)

Wherein the equivalence additive white Gaussian noise N ^(τ)=W ^(τ)-U ^(τ)W ^(τ-1). the reception signal X during for the middle adjacent two data blocks of formula (4) ^(τ)And X ^(τ-1), need not to know that channel condition information just can adopt following maximum likelihood decoding to sending information U ^(τ)Detect

${\hat{U}}^{\left(\mathrm{\&tau;}\right)}=\arg \underset{U^{\left(\mathrm{\&tau;}\right)}}{\min }\left|\right|X^{\left(\mathrm{\&tau;}\right)}-U^{\left(\mathrm{\&tau;}\right)}{X}^{(\mathrm{\&tau;}-1)}\left|\right|---\left(5\right)$

Wherein || || expression Frobenius norm.

2) problem that occurs in fast fading channel of distributed differential space-time coding

Above-mentioned formula is based on the hypothesis of the slow conversion of channel to the decoding of DDSTC in (5), thereby H is arranged ^(τ)=H ^(τ-1)Yet in the communication environment of reality, present the rapid fading characteristic because the relative motion meeting between mobile subscriber and base station causes channel, this makes channel obey the hypothesis that changes slowly and no longer sets up.In cooperation communication system, be in often the user of mobile status due to destination node, so the channel g between supposing in the present invention from the via node to the destination node _iBe fast fading channel, and the channel from the source node to the via node is the quasistatic slow fading channel.Like this, at t ₁The channel gain g of the moment from i via node to destination node _i(t ₁) can adopt following fast fading channel model [5]

g _i(t ₁)＝α(t ₁-t ₂)g _i(t ₂)+n _i(t ₁) (6)

N wherein _i(t ₁) be another independently multiple Gaussian noise of zero-mean, its variance is

At t ₁The moment and t ₂Channel gain is constantly obeyed Jakes decline model, and both coefficient correlations are

$\mathrm{\&alpha;}(t_1-t_2)=E\left[g_i\left(t_1\right)g_i^{*}\left(t_2\right)\right]=J_0\left(2\mathrm{\&pi;}{f}_d(t_1-t_2)T_s\right)---\left(7\right)$

J wherein ₀() is first kind zero Bessel function, f _dBe maximum doppler frequency, T _sBe symbol period.

In cooperation communication system, need 2T mark space owing to sending each data block, for (τ-1) and the DDSTC of τ data block that send, the state of corresponding channel gain is as shown in Figure 1 in fast fading channel.Can find out from accompanying drawing 1, for two data blocks of continuous transmission, channel g _iVariable condition from g _i(T+1) change to g _i(4T), between them, the maximum time interval is (3T-1) individual symbol period.Yet under the hypothesis of the slow fading channel in document [2-4], the difference equation that obtain in formula (4) must satisfy following constraints

g _i(T+1)＝g _i(T+1+t)，t＝1，2，…，3T-1 (8)

Obviously, be to be difficult to guarantee at fast fading channel following formula (8), therefore, deterioration has appearred in the performance of DDSTC in fast fading channel.

3) the DDSTC scheme (RFL-DDSTC) that reduces frame length that proposes

Propose a kind of new method in the present invention and improved the performance of DDSTC in fast fading channel, its basic thought is that the frame length that reduces DDSTC is resisted the impact that fast fading channel brings, therefore claim that this new differential coding scheme is the DDSTC that reduces frame length, referred to as RFL-DDSTC.

Because the second step that sends each data block takies T symbol period, the frame length that is the transmitted signal of each relaying is T, in the RFL-DDSTC scheme, the Signal Compression that is T with frame length in T orthogonal vectors of each relaying place's employing is the short signal with unit frame length.It is 1 orthogonal vectors that T orthogonal vectors can adopt norm arbitrarily, it can be elected as T orthogonal intersection sequence.

For (τ-1) individual data block, suppose that the transmitted signal of the T at i relaying place * 1 dimension is

Wherein

Be illustrated in the signal that (T+k) sends constantly, send like this To take T symbol period.At each relaying place, at first adopt a spreading code Matrix C=[c ₁c ₂C _T] be compressed in the transmitted signal of T symbol period

Suppose the spreading code c of P * 1 dimension _k(k=1 ..., T) mutually orthogonal and norm is 1, namely satisfies

δ wherein _klExpression Kronecker delta function, c _kLength P be defined as its spreading gain.The compressed signal of the P that therefore, sends at i relaying place * 1 dimension is

$b_i^{(\mathrm{\&tau;}-1)}={\mathrm{Ct}}_i^{(\mathrm{\&tau;}-1)}=\underset{k=1}{\overset{T}{\mathrm{\&Sigma;}}}{c}_k{t}_{\mathrm{ik}}^{(\mathrm{\&tau;}-1)}---\left(9\right)$

Obviously, Only taken a symbol period, and

T spread spectrum code sequence c _k(k=1 ..., linear combination T), its weight coefficient is

The second step that sends like this (τ-1) individual data block will be completed within T+1 the moment, and corresponding channel gain is g _i(T+1), see shown in channel status in accompanying drawing 2.Like this, destination node corresponding to the reception signal of (τ-1) individual data block is

$Y^{(\mathrm{\&tau;}-1)}=\underset{i=1}{\overset{R}{\mathrm{\&Sigma;}}}{g}_i(T+1)b_i^{(\mathrm{\&tau;}-1)}+W^{(\mathrm{\&tau;}-1)}$

$=\underset{i=1}{\overset{R}{\mathrm{\&Sigma;}}}{g}_i(T+1){\mathrm{Ct}}_i^{(\mathrm{\&tau;}-1)}+W^{(\mathrm{\&tau;}-1)}---\left(10\right)$

$=\underset{i=1}{\overset{R}{\mathrm{\&Sigma;}}}{g}_i(T+1)C\left(\sqrt{\frac{P_2}{{\mathrm{<figure-callout\; id="1"\; label="P"\; filenames="HDA0000038489670000011.png,HDA0000038489670000012.png"\; state="\{\{state\}\}">P</figure-callout>}}_1+1}}{A}_i{r}_i^{(\mathrm{\&tau;}-1)}\right)+W^{(\mathrm{\&tau;}-1)}$

Wherein

The reception signal of the T in i the relaying place first step * 1 dimension corresponding to (τ-1) individual data block, will The substitution formula can get in (10)

$Y^{(\mathrm{\&tau;}-1)}=\sqrt{\frac{P_1{\mathrm{<figure-callout\; id="2T"\; label="P"\; filenames="HDA0000038489670000012.png"\; state="\{\{state\}\}">P</figure-callout>}}_2\mathrm{<figure-callout\; id="1"\; label="T\; P"\; filenames="HDA0000038489670000011.png,HDA0000038489670000012.png"\; state="\{\{state\}\}">T</figure-callout>}}{P_{}}}C{S}^{(\mathrm{\&tau;}-1)}{\tilde{H}}^{(\mathrm{\&tau;}-1)}+{\tilde{N}}^{(\mathrm{\&tau;}-1)}---\left(11\right)$

Wherein corresponding to the new channel vector of (τ-1) individual data block

Can be expressed as

Noise is

Equally, for the signal that will send from i relaying in τ data block

Still adopt the spreading code matrix to compress it.The signal that sends at i relaying of second step like this

Still only taken a symbol period, as shown in Figure 2, corresponding channel gain is g _i(2T+2).Therefore, the reception signal corresponding to τ data block destination node can be expressed as

$Y^{\left(\mathrm{\&tau;}\right)}=\sqrt{\frac{P_1{\mathrm{<figure-callout\; id="2T"\; label="P"\; filenames="HDA0000038489670000012.png"\; state="\{\{state\}\}">P</figure-callout>}}_2\mathrm{<figure-callout\; id="1"\; label="T\; P"\; filenames="HDA0000038489670000011.png,HDA0000038489670000012.png"\; state="\{\{state\}\}">T</figure-callout>}}{P_{}}}{\mathrm{CS}}^{\left(\mathrm{\&tau;}\right)}{\tilde{H}}^{\left(\mathrm{\&tau;}\right)}+{\tilde{N}}^{\left(\mathrm{\&tau;}\right)}=\sqrt{\frac{P_1{\mathrm{<figure-callout\; id="2T"\; label="P"\; filenames="HDA0000038489670000012.png"\; state="\{\{state\}\}">P</figure-callout>}}_2\mathrm{<figure-callout\; id="1"\; label="T\; P"\; filenames="HDA0000038489670000011.png,HDA0000038489670000012.png"\; state="\{\{state\}\}">T</figure-callout>}}{P_{}}}{\mathrm{CU}}^{\left(\mathrm{\&tau;}\right)}{S}^{(\mathrm{\&tau;}-1)}{\tilde{H}}^{\left(\mathrm{\&tau;}\right)}+{\tilde{N}}^{\left(\mathrm{\&tau;}\right)}---\left(12\right)$

Wherein channel vector is

Noise is ${\tilde{N}}^{\left(\mathrm{\&tau;}\right)}=\sqrt{\frac{P_2}{{\mathrm{<figure-callout\; id="1"\; label="P"\; filenames="HDA0000038489670000011.png,HDA0000038489670000012.png"\; state="\{\{state\}\}">P</figure-callout>}}_1+1}}\underset{i=1}{\overset{R}{\mathrm{\&Sigma;}}}{g}_i(2T+2){\mathrm{CA}}_i{v}_i^{\left(\mathrm{\&tau;}\right)}+W^{\left(\mathrm{\&tau;}\right)}.$

When the destination node place processes, at first receive signal Y to two ^(τ-1)And Y ^(τ)Use c _k(k=1 ..., T) carry out respectively despreading and process, obtain

$d_k^{(\mathrm{\&tau;}-1)}=c_k^H{Y}^{(\mathrm{\&tau;}-1)}=\underset{i=1}{\overset{R}{\mathrm{\&Sigma;}}}{g}_i(T+1)t_{\mathrm{ik}}^{(\mathrm{\&tau;}-1)}+c_k^H{W}^{(\mathrm{\&tau;}-1)}---\left(13\right)$

$d_k^{\left(\mathrm{\&tau;}\right)}=c_k^H{Y}^{\left(\mathrm{\&tau;}\right)}=\underset{i=1}{\overset{R}{\mathrm{\&Sigma;}}}{g}_i(2T+2)t_{\mathrm{ik}}^{\left(\mathrm{\&tau;}\right)}+c_k^H{W}^{\left(\mathrm{\&tau;}\right)}---\left(14\right)$

Subsequently, with Y ^(τ-1)And Y ^(τ)Signal after despreading is organized into respectively the vector of T * 1 dimension

With

With y ^(τ-1)And y ^(τ)Being write as matrix form can be expressed as

$y^{(\mathrm{\&tau;}-1)}=\sqrt{\frac{P_1{\mathrm{<figure-callout\; id="2T"\; label="P"\; filenames="HDA0000038489670000012.png"\; state="\{\{state\}\}">P</figure-callout>}}_2\mathrm{<figure-callout\; id="1"\; label="T\; P"\; filenames="HDA0000038489670000011.png,HDA0000038489670000012.png"\; state="\{\{state\}\}">T</figure-callout>}}{P_{}}}{S}^{(\mathrm{\&tau;}-1)}{\tilde{H}}^{(\mathrm{\&tau;}-1)}+Z^{(\mathrm{\&tau;}-1)}---\left(15\right)$

$y^{\left(\mathrm{\&tau;}\right)}=\sqrt{\frac{P_1{\mathrm{<figure-callout\; id="2T"\; label="P"\; filenames="HDA0000038489670000012.png"\; state="\{\{state\}\}">P</figure-callout>}}_2\mathrm{<figure-callout\; id="1"\; label="T\; P"\; filenames="HDA0000038489670000011.png,HDA0000038489670000012.png"\; state="\{\{state\}\}">T</figure-callout>}}{P_{}}}{S}^{\left(\mathrm{\&tau;}\right)}{\tilde{H}}^{\left(\mathrm{\&tau;}\right)}+Z^{\left(\mathrm{\&tau;}\right)}---\left(16\right)$

Wherein Obviously, after despreading to received signal, the signal S that DDSTC is original ^(τ-1)And S ^(τ)Appear in formula (15) and (16).Therefore, under the condition that following hypothesis is set up, can detect the DDSTC signal with the differential decoder in formula (5):

${\tilde{H}}^{(\mathrm{\&tau;}-1)}={\tilde{H}}^{\left(\mathrm{\&tau;}\right)}---\left(17\right)$

Above time interval between two channel gains be only (T+1) individual symbol period.Hypothesis when decoding with DDSTC (8) is compared, and the impact of hypothesis (17) performance in fast fading channel for DDSTC when new RFL-DDSTC scheme is decoded is less.Therefore, in fast fading channel, the frame length that reduces DDSTC can effectively improve its performance.

4) performance evaluation

In order to estimate the performance of DDSTC in fast fading channel, suppose for k of the second step of (τ-1) and τ data block constantly, the signal that i relaying sends is respectively

With

Like this, corresponding these two constantly the reception signal at destination node place be respectively

$x_k^{(\mathrm{\&tau;}-1)}=\underset{i=1}{\overset{R}{\mathrm{\&Sigma;}}}{g}_i(T+k)t_{\mathrm{ik}}^{(\mathrm{\&tau;}-1)}+w_k^{(\mathrm{\&tau;}-1)}---\left(18\right)$

$x_k^{\left(\mathrm{\&tau;}\right)}=\underset{i=1}{\overset{R}{\mathrm{\&Sigma;}}}{g}_i(3T+k)t_{\mathrm{ik}}^{\left(\mathrm{\&tau;}\right)}+w_k^{\left(\mathrm{\&tau;}\right)}---\left(19\right)$

According to the fast fading channel model in formula (6), channel gain g _i(3T+k) (k=1 ..., T) can be expressed as

g _i(3T+k)＝α(2T)g _i(T+k)+n _i(3T+k) (20)

N wherein _iBe (3T+k) another independently multiple Gaussian noise of zero-mean, its variance is

Formula (20) is updated in formula (19), can gets

$x_k^{\left(\text{\&tau;}\right)}=\mathrm{\&alpha;}\left(2T\right)\underset{i=1}{\overset{R}{\mathrm{\&Sigma;}}}{g}_i(T+k)t_{\mathrm{ik}}^{\left(\mathrm{\&tau;}\right)}+\underset{i=1}{\overset{R}{\mathrm{\&Sigma;}}}{n}_i(3T+k)t_{\mathrm{ik}}^{\left(\mathrm{\&tau;}\right)}+w_k^{\left(\mathrm{\&tau;}\right)}---\left(21\right)$

Therefore, the equivalent signal-to-noise ratio of system is

${\mathrm{SNR}}_{\mathrm{DDSTC}}=\frac{{\mathrm{<figure-callout\; id="2"\; label="RP"\; filenames="HDA0000038489670000011.png,HDA0000038489670000012.png"\; state="\{\{state\}\}">RP</figure-callout>}}_2{\mathrm{\&alpha;}}^2\left(2T\right)}{{\mathrm{RP}}_2[1-{\mathrm{\&alpha;}}^2\left(2T\right)]+\frac{{\mathrm{RP}}_2}{{\mathrm{<figure-callout\; id="1"\; label="P"\; filenames="HDA0000038489670000011.png,HDA0000038489670000012.png"\; state="\{\{state\}\}">P</figure-callout>}}_1+1}+1}---\left(22\right)$

Due to

Wherein P is transmitted power total in whole network, further has

${\mathrm{SNR}}_{\mathrm{DDSTC}}=\frac{{\mathrm{\&alpha;}}^2\left(2T\right)}{[1-{\mathrm{\&alpha;}}^2\left(2T\right)]+\frac{4+4/P}{P+2}}---\left(23\right)$

For formula (23), when P → ∞,

This shows, " floor effect " will appear in DDSTC its performance curve when transmitted power is higher in fast fading channel.

Can analyze in the same way the performance of RFL-DDSTC scheme in fast fading channel that proposes in the present invention.Can draw when P → ∞,

With SNR _DDSTCCompare, clearly new RFL-DDSTC scheme has reduced " floor effect " significantly.And along with the increase of frame length T, the lifting of this performance can be more obvious.

5) simulation result

This section provides simulation result and estimates DDSTC and the performance of RFL-DDSTC in fast fading channel.In all analogous diagram, transverse axis represents the total transmitting power P in whole network, and the longitudinal axis represents error sign ratio.In all emulation, information symbol adopts the QPSK modulation, and spread spectrum code sequence employing spreading gain is 64 Hadamard spreading code, and the system carrier frequency is f _c=2GHz, message transmission rate is r=120kbit/s, the translational speed of destination node is respectively V ₁=150km/h and V ₂=250km/h.

Fig. 3 has provided respectively in Fig. 6 in the wireless relay network that (is abbreviated as " FF ch " in figure) under fast fading channel and has adopted respectively distributed difference Alamouti code and cyclic code to be respectively R=2 at the relaying number, 3,4 and the performance curve of 5 o'clock, its signal frame length is T=R.In order to compare, give DDSTC (is abbreviated as " QS ch ") in figure under the quasistatic slow fading channel performance in figure.Simulation result shows, serious floor effect has appearred in the error performance of DDSTC in fast fading channel, and along with the increase of the translational speed of signal frame length T and destination node, floor effect is further serious.The performance of RFL-DDSTC obviously is better than DDSTC, and when transmitting power was low, the performance of RFL-DDSTC was comparatively near the performance of DDSTC in the quasistatic slow fading channel.Further, equal the number R of via node due to the signal frame length T of DDSTC, can see in from Fig. 3 to Fig. 6, increase along with R, the performance of DDSTC further worsens, the performance advantage of RFL-DDSTC is more obvious, and above-mentioned simulation result has been verified the conclusion that draws in the performance evaluation well.

A kind of new distributed differential space-time coding transmission plan---RFL-DDSTC that is suitable under fast fading channel has been proposed in the present invention.This scheme makes the frame length of DDSTC signal greatly shorten, thereby can effectively reduce the impact that fast fading channel brings by adopting T quadrature column vector that the signal of DDSTC in T symbol period merged in a symbol period.Theory analysis and simulation result have verified that further the lifting to error performance of RFL-DDSTC scheme in fast fading channel that proposes in the present invention (see accompanying drawing 3～Fig. 6).

Claims (1)

1. the distributed differential space-time coding transmission method of a suitable fast fading channel, is characterized in that, is divided into the three following steps:

One, the via node compaction profile formula differential space-time coding DDSTC of place signal frame length

In distributed differential space-time coding DDSTC, the second step that sends each data block takies T symbol period, the frame length that is the transmitted signal of each relaying is T, and in reducing the distributed differential space-time coding RFL-DDSTC of signal frame length, the Signal Compression that T orthogonal vectors of each relaying place's employing are T with frame length is the short signal with unit frame length, it is 1 orthogonal vectors that T orthogonal vectors adopt norm arbitrarily, elects it as T orthogonal intersection sequence

For (τ-1) individual data block, suppose that the transmitted signal of the T at i relaying place * 1 dimension is $t_i^{(\mathrm{\&tau;}-1)}={\left[\begin{array}{cccc}{t}_{i1}^{(\mathrm{\&tau;}-1)}& t_{i2}^{(\mathrm{\&tau;}-1)}& ...& t_{\mathrm{iT}}^{(\mathrm{\&tau;}-1)}\end{array}\right]}^T,$ Be illustrated in the signal that (T+k) sends constantly, send like this To take T symbol period, at each relaying place, at first adopt a spreading code Matrix C=[c ₁c ₂C _T] be compressed in the transmitted signal of T symbol period

(k=1 ..., T), suppose the spreading code c of P * 1 dimension _k(k=1 ..., T) mutually orthogonal and norm is 1, namely satisfies

δ wherein _klExpression Kronecker delta function, c _kLength P be defined as its spreading gain, therefore, the compressed signal of the P that sends at i relaying place * 1 dimension is

$b_i^{(\mathrm{\&tau;}-1)}={\mathrm{Ct}}_i^{(\mathrm{\&tau;}-1)}=\underset{k=1}{\overset{T}{\mathrm{\&Sigma;}}}{c}_k{t}_{\mathrm{ik}}^{(\mathrm{\&tau;}-1)}---\left(9\right)$

Obviously,

Only taken a symbol period, and T spread spectrum code sequence c _k(k=1 ..., linear combination T), its weight coefficient is

The second step that sends like this (τ-1) individual data block will be completed within T+1 the moment, and corresponding channel gain is g _i(T+1), like this, destination node corresponding to the reception signal of (τ-1) individual data block is

$Y^{(\mathrm{\&tau;}-1)}=\underset{i=1}{\overset{R}{\mathrm{\&Sigma;}}}{g}_i(T+1)b_i^{(\mathrm{\&tau;}-1)}+W^{(\mathrm{\&tau;}-1)}$

$=\underset{i=1}{\overset{R}{\mathrm{\&Sigma;}}}{g}_i(T+1){\mathrm{Ct}}_i^{(\mathrm{\&tau;}-1)}+W^{(\mathrm{\&tau;}-1)}---\left(10\right)$

$=\underset{i=1}{\overset{R}{\mathrm{\&Sigma;}}}{g}_i(T+1)C\left(\sqrt{\frac{P_2}{P_1+1}}{A}_i{r}_i^{(\mathrm{\&tau;}-1)}\right)+W^{(\mathrm{\&tau;}-1)}$

Wherein, P ₁And P ₂Be respectively the average transmit power at source node when sending each data block and each via node place; A _iThe T * T that is i via node place ties up unitary matrice;

The reception signal of the T in i the relaying place first step * 1 dimension corresponding to (τ-1) individual data block, will

The substitution formula can get in (10)

$Y^{(\mathrm{\&tau;}-1)}=\sqrt{\frac{P_1{P}_{2}T}{P_1+1}}C{S}^{(\mathrm{\&tau;}-1)}{\tilde{H}}^{(\mathrm{\&tau;}-1)}+{\tilde{N}}^{(\mathrm{\&tau;}-1)}---\left(11\right)$

Wherein corresponding to the new channel vector of (τ-1) individual data block

Can be expressed as ${\tilde{H}}^{(\mathrm{\&tau;}-1)}={\left[\begin{array}{cccc}{f}_1{g}_1(T+1)& f_2{g}_2(T+1)& ...& f_R{g}_R(T+1)\end{array}\right]}^T,$ Noise is ${\tilde{N}}^{(\mathrm{\&tau;}-1)}=\sqrt{\frac{P_2}{P_1+1}}\underset{i=1}{\overset{R}{\mathrm{\&Sigma;}}}{g}_i(T+1){\mathrm{CA}}_i{v}_i^{(\mathrm{\&tau;}-1)}+W^{(\mathrm{\&tau;}-1)};$

Equally, for the signal that will send from i relaying in τ data block

Still adopt the spreading code matrix to compress it, the signal that sends at i relaying of second step like this

Still only taken a symbol period, corresponding channel gain is g _i(2T+2), therefore, can be expressed as corresponding to the reception signal of τ data block destination node

$Y^{\left(\mathrm{\&tau;}\right)}=\sqrt{\frac{P_1{P}_{2}T}{P_1+1}}{\mathrm{CS}}^{\left(\mathrm{\&tau;}\right)}{\tilde{H}}^{\left(\mathrm{\&tau;}\right)}+{\tilde{N}}^{\left(\mathrm{\&tau;}\right)}=\sqrt{\frac{P_1{P}_{2}T}{P_1+1}}{\mathrm{CU}}^{\left(\mathrm{\&tau;}\right)}{S}^{(\mathrm{\&tau;}-1)}{\tilde{H}}^{\left(\mathrm{\&tau;}\right)}+{\tilde{N}}^{\left(\mathrm{\&tau;}\right)}---\left(12\right)$

Wherein channel vector is ${\tilde{H}}^{\left(\mathrm{\&tau;}\right)}={\left[\begin{array}{cccc}{f}_1{g}_1(2T+2)& f_2{g}_2(2T+2)& ...& f_R{g}_R(2T+2)\end{array}\right]}^T,$ Noise is ${\tilde{N}}^{\left(\mathrm{\&tau;}\right)}=\sqrt{\frac{P_2}{P_1+1}}\underset{i=1}{\overset{R}{\mathrm{\&Sigma;}}}{g}_i(2T+2){\mathrm{CA}}_i{v}_i^{\left(\mathrm{\&tau;}\right)}+W^{\left(\mathrm{\&tau;}\right)};$

Two, destination node place's despreading receives signal

When destination node is carried out reception ﹠ disposal, at first receive signal Y to two ^(τ-1)And Y ^(τ)Use c _k(k=1 ..., T) carry out respectively despreading and process, obtain

$d_k^{(\mathrm{\&tau;}-1)}=c_k^H{Y}^{(\mathrm{\&tau;}-1)}=\underset{i=1}{\overset{R}{\mathrm{\&Sigma;}}}{g}_i(T+1)t_{\mathrm{ik}}^{(\mathrm{\&tau;}-1)}+c_k^H{w}^{(\mathrm{\&tau;}-1)}---\left(13\right)$

$d_k^{\left(\mathrm{\&tau;}\right)}=c_k^H{Y}^{\left(\mathrm{\&tau;}\right)}=\underset{i=1}{\overset{R}{\mathrm{\&Sigma;}}}{g}_i(2T+2)t_{\mathrm{ik}}^{\left(\mathrm{\&tau;}\right)}+c_k^H{W}^{\left(\mathrm{\&tau;}\right)}---\left(14\right)$

Subsequently, with Y ^(τ-1)And Y ^(τ)Signal after despreading is organized into respectively the vector of T * 1 dimension $y^{(\mathrm{\&tau;}-1)}:={\left[\begin{array}{cccc}{d}_2^{(\mathrm{\&tau;}-1)}& d_2^{(\mathrm{\&tau;}-1)}& ...& d_T^{(\mathrm{\&tau;}-1)}\end{array}\right]}^T$ With $y^{\left(\mathrm{\&tau;}\right)}:={\left[\begin{array}{cccc}{d}_2^{\left(\mathrm{\&tau;}\right)}& d_2^{\left(\mathrm{\&tau;}\right)}& ...& d_T^{\left(\mathrm{\&tau;}\right)}\end{array}\right]}^T,$ With y ^(τ-1)And y ^(τ)Being write as matrix form can be expressed as

$y^{(\mathrm{\&tau;}-1)}=\sqrt{\frac{P_1{P}_{2}T}{P_1+1}}{S}^{(\mathrm{\&tau;}-1)}{\tilde{H}}^{(\mathrm{\&tau;}-1)}+Z^{(\mathrm{\&tau;}-1)}---\left(15\right)$

$y^{\left(\mathrm{\&tau;}\right)}=\sqrt{\frac{P_1{P}_{2}T}{P_1+1}}{S}^{\left(\mathrm{\&tau;}\right)}{\tilde{H}}^{\left(\mathrm{\&tau;}\right)}+Z^{\left(\mathrm{\&tau;}\right)}---\left(16\right)$

Wherein ${\text{Z}}^{\left(\mathrm{\&tau;}\right)}{=\left[\begin{array}{cccc}{c}_1^H{W}^{\left(\mathrm{\&tau;}\right)}& c_2^H{W}^{\left(\mathrm{\&tau;}\right)}& ...& c_T^H{W}^{\left(\mathrm{\&tau;}\right)}\end{array}\right]}^T,$ Obviously, after despreading to received signal, the signal S that DDSTC is original ^(τ-1)And S ^(τ)Appear in formula (15) and (16);

Three, Differential Detection

In hypothesis

Under the condition of setting up, use ${\hat{U}}^{\left(\mathrm{\&tau;}\right)}=\arg \underset{U^{\left(\mathrm{\&tau;}\right)}}{\min }\left|\right|X^{\left(\mathrm{\&tau;}\right)}-U^{\left(\mathrm{\&tau;}\right)}{X}^{(\mathrm{\&tau;}-1)}\left|\right|$ Differential decoder comes detection signal U ^(τ), the time interval between top two channel gains is only (T+1) individual symbol period at this moment, the hypothesis g when decoding with DDSTC _i(T+1)=g _i(T+1+t), t=1,2 ..., 3T-1 compares, and the impact of hypothesis (17) performance in fast fading channel for DDSTC when reducing the distributed differential space-time coding RFL-DDSTC decoding of signal frame length is less.

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