CN100483979C - Subband adaptive Turbo code modulation method under fixed throughput in OFDM - Google Patents

Abstract

The invention is an in-OFDM fixed throughput bottom subband self-adapting Turbo coding modulating method, a subband-by-subband variable power self-adapting method which adopts continuous block distributing mode at a constant throughput and object miscoding rate, i.e. in an OFDM symbol, different subbands has a different transmitting power but each subcarrier wave in the same subband has the same transmitting power; at the same time, the invention also provides a symbol-by-symbol variable power self-adapting method, but each subcarrier wave in the same subband has the same transmitting power. Each self-adapting coding block includes N.M adjacent subcarrier waves in M adjacent OFDM symbols in time domain, where N is number of subcarrier wave in a subband and it adopts continuous speed Turbo coding modulation in each subband. By this method, it can save transmitting power, reduce feedback expense and is easy to implement.

Description

Sub-band adaptive Turbo coded modulation method under fixedly handling up among the OFDM

Technical field

The present invention relates to the adaptive coding modulation in the OFDM (OFDM).

Background technology

The OFDM technology is the mainstream technology that solves the high speed wireless data transmission at present.At present, the OFDM technology has been successfully applied among asymmetric user data loop (ADSL), digital video broadcasting (DVB) and wireless asynchronous transfer mode (WATM) system.To be the high-speed data that will transmit transmit with the subcarrier of many quadratures the principle of OFDM technology, and the data rate on each subcarrier is relatively low.Compare with common Frequency Division Multiplexing system, there is the higher availability of frequency spectrum in the quadrature crossover system that makes of OFDM sub-carriers.Among the OFDM whole signal bandwidth is divided into a plurality of very narrow sub-carrier band because each subcarrier bandwidth is less than the coherence bandwidth of channel, from but flat fading.Like this, compare with single-carrier system, it is many that the equilibrium among the OFDM will realize easily.

In order to improve the availability of frequency spectrum of wireless system, the high speed wireless data transmission requirement of fading channel adopts the transmission technology of self adaptation, high spectrum utilization.

The Turbo coded modulation is a kind of coding modulation technique of high spectrum utilization.The Turbo code of people such as Berrou proposition in 1993 is because the thought of its unique coding structure and iterative decoding makes it have the performance near the Shannon capacity theoretical value.Under certain coding structure and the decoding iterations, can be less than 1dB under white Gauss noise (AWGN) channel with the gap of the channel capacity limit.Afterwards, there are many people successively to propose several binary system Turbo codes and the method that high system chopping phase combines again, are called the Turbo coded modulation, be used for effectively improving the availability of frequency spectrum of system.1994, people such as S.L.Goff at first proposed the method for binary system Turbo code cascade gray mappings multi-system modulation.Then, Wachsmann has proposed a kind of with the method for Turbo code as multilevel coding (MLC) component code again.S.Benedetto has proposed the structure of parallel cascade Trellis-coded modulation (PCTCM), and P.Robertson has proposed the method for a kind of Ungerboeck of employing grid code as Turbo code component code and symbol interleaving.

In fading channel, with regular coding chopping phase ratio, adaptive modulation and coding (AMC) technology can effectively improve handling up of system and the error rate (BER) performance.Here so-calledly handle up that what refer to is exactly the availability of frequency spectrum of system, just unit spectral bandwidth information transmitted amount in the unit interval.The basic ideas of AMC technology are according in the adaptive variation transmitted power of the current characteristic of channel, symbol transmission speed, constellation size, code efficiency and the encoding mechanism one or more.Under the prerequisite of not sacrificing BER, some information that pass improve the availability of frequency spectrum more when channel condition is good, reduce throughput and guarantee certain BER requirement when bad channel conditions.Adaptive quadrature amplitude modulation(PAM) (AQAM) technology that Steele and Webb proposed in nineteen ninety-five can obtain to modulate than fixing QAM the performance gain of 5dB.And in rayleigh fading channel,, can obtain performance gain than the good 20dB of fixed modulation according to the modulation of model of reservoir with time-varying rate and change power.Then, Goldsmith has introduced Trellis-coded modulation (TCM) on the basis of Adaptive Modulation, is used for further improving the availability of frequency spectrum of system.In recent years, people study with combining of OFDM the AMC technology.Each subcarrier among the OFDM is become power adaptive modulation, not being all it and distributing different transmitted power and modulation system according to each subcarrier upper signal channel characteristic.Compare with fixed modulation, under identical throughput performance, can obtain sizable signal to noise ratio (snr) gain.Then, if introduced adaptive mesh coded modulation (ATCM), can also further improve the availability of frequency spectrum of system.But they are all supposed to make a start and know the characteristic of channel of each subcarrier fully, and in the closed-loop adaptation of reality, the adaptive information of making a start comes from the feedback of receiving end, therefore need very big feedback information by the subcarrier self adaptation in real system.In order to reduce the feedback overhead of system, Hanzo has proposed a kind of sub-band adaptive modulator approach based on fixed threshold.Wherein all subcarriers among the OFDM are divided into some subbands, adjacent plurality of sub carrier wave is called a subband on the frequency domain.In self adaptation, compare with the SNR thresholding under the various modulation systems according to the minimum SNR of subcarrier in each subband, each subband is chosen with a kind of modulation system.Like this, because same subband adopts identical modulation system, thereby can reduce receiving end greatly to the feedback information volume of making a start.But, only considered Adaptive Modulation in the sub-band adaptive of Hanzo, how sub-band adaptive is not modulated the effective ways that combine with adaptive coding and provide.

Under identical transmitting power, to compare with the regular coding modulation technique, the AMC technology can effectively improve the throughput performance of system.And,, adopt the AMC technology then can reach the purpose of effective reduction transmitting power such as speech business for the constant business of handling up of ask for something.

The purpose of this invention is to provide a kind of OFDM of being used for, constant target handle up and target BER restriction under, utilize sub-band adaptive Turbo coded modulation to reduce the method for the total transmitting power of system.That is to say,, reach the purpose of the total transmitting power of reduction system by being different transmitted bit number and the distribution of transmitted power in each subband among the OFDM.And so-called constant target is handled up and target BER restriction, requirement be that total transmitted bit number in each subband equals aims of systems and handles up, and receiving terminal BER is lower than target BER.Therefore, the problem to be solved in the present invention is exactly how to distribute the interior transmitting power of each subband and the problem of transmitted bit number.Transmitting power for allocation of subcarriers, such several method can be arranged: the one, each subcarrier transmitting power difference, two is that all subcarrier transmitting powers are identical in the subband, and the intersubband difference, three is that all subcarrier transmitting powers are identical in the OFDM symbol, and the intersymbol difference.By background knowledge as can be known, in the closed-loop adaptation of reality, the adaptive information of making a start comes from the feedback of receiving end, so the information of transmitted power is also from the feedback information of receiving end.For first kind of situation that each subcarrier transmitting power is different, just the adaptive situation of subcarrier one by one needs very big feedback information in real system, can't realize.And second kind and the required feedback information of the third power division are much smaller, and are easy to realize.Therefore we only consider these two kinds situations of distributing power.

Summary of the invention

The purpose of this invention is to provide fixedly handle up the code modulated method of sub-band adaptive Turbo under the requirement of a kind of OFDM of being used for, its target be constant handle up and target BER restriction under, the total transmitting power of optimization system.In the sub-band adaptive coded modulation, introduce the Turbo coded modulation of continuous speed among the present invention, be used for further reducing total transmitting power of system.Simultaneously, compare with pursuing subcarrier change power AMC, what we proposed becomes power and pursues feedback overhead and the implementation complexity that two kinds of subband adaptive approachs of symbol change power can also reduce system greatly by subband based on what fixedly handle up.

Main thought of the present invention is:

On adaptive structure, the coding that the subcarrier in the same subband on adjacent several OFDM symbol frequency domain on the time domain is united.Owing in the Turbo coded modulation, obtain the long encoding block of excellent performance need, and the number of sub carrier wave in each subband is limited in the simple OFDM symbol.And the time domain adjacent OFDM symbol characteristic of channel also has certain correlation, therefore in Adaptive Turbo coded modulation, in order to increase the length of Turbo encoding block, the coded modulation that we unite the subcarrier in the same subband on adjacent some OFDM symbol frequency domain.That is to say that adaptive coding piece comprises on the time domain NM adjacent sub-carrier in M the adjacent OFDM symbol, wherein N is a subcarrier number in subband on the frequency domain, referring to Fig. 1;

Adopt the Turbo code modulating method of continuous speed in each subband.The Turbo coded modulation itself is a kind of transmission technology of high spectrum utilization, adopts the Turbo coding modulation technique, can obtain very high coding gain, in handle up total transmitting power of down further reduction system of fixed target.And the Turbo coded modulation of so-called continuous speed, the characteristic of then having utilized the Turbo coding can punching continuously and repeat arbitrarily, the Turbo coding of realization random length encoding block.That is to say, can transmit the information of random length in each subband, thereby satisfied the requirement of system's arbitrary target throughput.

Fixedly handle up and limit the adaptive algorithm of following varitron band transmitted power with target BER.So-called varitron band transmitted power refers in an OFDM symbol, and the transmitted power on each subband is different, but the sub-carrier power in the same subband is identical.Becoming in the power adaptive by subband, concerning each subband, receiving end need be fed back two numerical value to being made a start, and represents the transmitted power and the transmitted bit number of this subband respectively like this.Become power with subcarrier one by one and compare, its feedback overhead will reduce greatly.By in the sub-band adaptive, take continuous block-distributing algorithm, concrete grammar is such: before Bit Allocation in Discrete, the transmitting power that each subband distributed is 0.At first general objective is handled up, just all subbands total bit number that need transmit is divided into some bit blocks, supposes to be expressed as B ₀..., B _K-1, N subband is expressed as S ₀..., S _N-1The target of Fen Peiing is exactly each bit block to be assigned in the suitable subband transmit at last, and the transmitting power sum minimum on all required under target BER subbands.Allocation bit piece B at first ₀, for each subband, transmit a bit block must increase certain transmitting power more, could satisfy the requirement of receiving terminal target BER.And because the characteristic of channel difference in each subband among the OFDM, even transmit identical bit number, the required minimum emissive power of each subband is also inequality.By calculating subband S ₀..., S _N-1Transmitted bit piece B ₀, satisfying under the receiving terminal BER, the minimum emissive power of required increase is determined B ₀Ownership.Promptly be in all subbands of hypothesis, S _jInterior transmission B ₀The transmitting power minimum of required increase is then with B ₀Be assigned to subband S _jInterior transmission.B ₀Assigning, next is B ₁, distribute all bit blocks successively.Certainly, its last distribution result has multiple situation, might transmit a plurality of bit blocks in certain subband, also might also not pass by a bit block.Compare with the bit number of distribution similar number in all subbands, according to the characteristic of channel in each subband, for distributing the transmitted bit of suitable different numbers in the different subbands, can be under the prerequisite that guarantees receiving terminal target BER, the transmitting power that the system that effectively reduces is total.The front is when determining the ownership of each bit block, need the relatively required transmitting power size of different sub-band transmission same bits piece, just to calculate transmission certain-length bit in each subband, and can reach target BER at receiving terminal, the problem of required transmitting power.For the Turbo coded modulation, we can't provide the definite expression formula of an error rate BER and signal to noise ratio snr relation at present, that is to say badly according to the characteristic of channel in the subband and transmitting power, calculate to receive BER accurately.At this, we adopt the inverted criterion of channel, estimate reaching the required transmitted power of target BER.So-called channel is inverted criterion, and the transmitted power and the characteristic of channel are inversely proportional in other words, thereby keeps receiving the constant of SNR.Adopt channel to be inverted under the criterion, since under the receiving terminal target BER required constant reception SNR as can be known, such as determining that the characteristic of channel is also known by software emulation, then according to transmitted power and these characteristics of characteristic of channel inverse ratio, can be in the hope of required transmitted power.By in the sub-band adaptive, we require the transmitted power in the subband constant, and therefore, we will be inverted the average back of transmitted power of each subcarrier that criterion calculates as transmitted power unified in this subband by channel in each subband at last.In the subband transmitted power on average down, target BER satisfied is based on following three facts.The one, the correlation of the characteristic of channel is very strong in the subband; The 2nd, the Turbo coded modulation itself has very strong diversity ability; The 3rd, under the certain situation of total transmitting power, the channel capacity under the mean allocation transmitted power will be higher than by the channel capacity under the channel inversion criterion.By in the sub-band adaptive, each subband need feed back a transmission power value and a transmitted bit length numerical value.In order further to reduce feedback information volume, it is also conceivable that the algorithm of following negate transmitted power.

Constant handling up, the negate transmitted power adaptive algorithm under the target BER.Interior each subcarrier transmitted power of OFDM symbol this moment equates transmitted power difference between the different OFDM symbols.During the negate transmitted power, only need performance number of feedback in each symbol, compare, further reduced the system feedback expense with the varitron band transmitted power of front.In the negate transmitted power self adaptation, determine transmitted power total in the symbol, determine separately transmitted bit number according to the characteristic of channel in each subband again according to handle up requirement and the characteristic of channel of system.

Of the present invention by subband change power adaptive Turbo coded modulation method, N subcarrier in the same subband on adjacent M on the time domain the OFDM symbol frequency domain carried out combined coding, and in each subband, adopt the Turbo coded modulation of continuous speed, it is characterized in that: this code modulating method be a kind of constant handle up and target error rate BER restriction under, that takes the continuous blocks method of salary distribution becomes power adaptive Turbo code modulating method by subband, the described subband change power that pursues is meant in an OFDM symbol, transmitted power difference on the different sub-band, but the transmitted power of each subcarrier in the same subband is identical, when usefulness had the structure operation of Turbo coded modulation now, described method was carried out successively according to the following steps:

(1) set following parameter:

N _c: total number of sub-carriers,

N _b: sub-band sum,

R _b: mean allocation is target throughput on each subcarrier, is called for short the target average throughput, then N _cR _bBe total target throughput,

BER _Target: target BER,

S _j: transmitted power on each subcarrier in j the subband, it all is identical to all subcarriers in the same subband,

b _j: in j the subband, the existing throughput that obtains after each the distribution on each subcarrier is a variable,

H _{J, k}: in j the subband, the channel frequency domain response on k subcarrier,

S _BER(b): in awgn channel, send under b the bit, required minimum received power when satisfying receiving terminal BER and requiring supposes that noise power is given,

Δ b: when taking the continuous blocks method of salary distribution, be assigned to the granularity of handling up on each subcarrier at every turn, promptly except that the length of last allocation bit piece at every turn number institute value divided by subcarrier in each subband, the average throughput that increases on each subcarrier in also promptly except that last, at every turn distributing

b _Max: the maximum throughput under the restriction of actual coding modulation parameter on each subcarrier,

Adaptive target is, average after, be finally allocated to that the throughput on each subcarrier equals target average throughput R in each subband _b, promptly $\frac{1}{N_b}\underset{j=1}{\overset{N_b}{\mathrm{\Σ}}}{b}_j=R_b,$ And error rate BER≤BERtarget;

(2) initialization

B when initial _j=0, S _j=0, j=1..N _b

(3) all bits that will transmit on all subbands are carried out piecemeal, be expressed as B respectively ₀..., B _K-1Piece, every contained bit number is Δ bN except that last _c/ N _b, the length of last bit block is that total length is divided by Δ bN _c/ N _bRemainder, the average throughput of Δ b wherein, N for increasing on each subcarrier to each subband the time except that last each bit block of distribution _c/ N _bBe the number of sub carrier wave in each subband;

(4) for B ₀..., B _K-1The piece bit set is for any one B _i, need from all N subband, find out one and guarantee under the receiving target BER transmission B _iThe subband of the transmitted power minimum of required increase also promptly will be obtained the transmitted power Δ S of the required increase of each subband transmitted bit piece successively according to following formula _i:

$\begin{array}{cc}{\mathrm{\ΔS}}_j=\underset{k=1}{\overset{\mathrm{Nc}/N_b}{\mathrm{\Σ}}}\frac{S_{\mathrm{BER}}(b_j+\mathrm{\Δb}\′)-S_{\mathrm{BER}}\left(b_j\right)}{{\left|H_{j,k}\right|}^2}& j\∈J\end{array}$

Wherein, $\mathrm{\Δb}\′=\min \{\mathrm{\Δb},N_b\·R_b-\underset{j=1}{\overset{N_b}{\mathrm{\Σ}}}{b}_j\},$

In the Δ b ' calculating distribution of bit block newly next time, be assigned to the average throughput numerical value on each subcarrier,

Xiang Weifen mixes after the bit block, can be for the residue throughput of this sub-distribution;

Simultaneously, also will satisfy following constraint: the maximum throughput on each subcarrier is b _Max, the set that participates in the subband of Δ b ' distribution like this is: J={j|b _j≤ b _Max-Δ b ' }, wherein, b _MaxBe the maximum throughput that distributes on each subcarrier, it is subjected to the restriction of actual modulated parameter;

Participating in bit block B again _iAmong the sets of subbands J that distributes, guaranteeing under the receiving target BER, finding out a transmission B _iThe subband j that required increase transmitted power is minimum ^*, that is:

$j^{*}=\arg \underset{\∀j\∈J}{\min }\mathrm{\Δ}{S}_j$

Then this bit block B _iBe assigned to j in the subband ^*Subband j is upgraded in transmission simultaneously ^*Throughput on interior each subcarrier $b_{j^{*}}=b_j+\mathrm{\Δb}\′;$

(5) judge whether all bit blocks that will transmit assign, judge to assign just to be equivalent to and distribute the back to judge $\frac{1}{N_b}\underset{j=1}{\overset{N_b}{\mathrm{\Σ}}}{b}_j=R_b$ Whether set up,, then forward step (4) to, carry out next bit block and distribute if equation is false; If equation is set up, then all bit and power division finish, { b _jBe the numerical value of always handling up on each subcarrier in j the subband that final distribution obtains;

The transmitting power of each subcarrier is

$S_j=\frac{N_b}{N_c}\underset{k=1}{\overset{\mathrm{Nc}/N_b}{\mathrm{\Σ}}}\frac{S_{\mathrm{BER}}\left(b_j\right)}{{\left|H_{j,k}\right|}^2}$ j＝1..N _b。

L-G simulation test shows: it has saved transmitting power, has also promptly obtained snr gain, can satisfy the needs that all types of target is handled up simultaneously, and greatly reduce the feedback overhead and the implementation complexity of system.

Description of drawings:

Fig. 1: combined coding piece schematic diagram.

Fig. 2: the Turbo coded modulation structure that the present invention uses.

Fig. 3: the program flow chart of the method for the invention.

Embodiment

Our thinking based on continuous blocks distribution, varitron band transmitting power is such: at first, the transmitted bit number and the transmitted power of distributing on each subband are all 0.At first all bits that will transmit on all subbands are carried out piecemeal, the length of each bit block of front is Δ bN _c/ N _b, the average throughput that increases on the subcarrier when meaning is promptly distributed each bit block is equal to the granularity Δ b that handles up, N _c/ N _bRefer to the number of sub carrier wave in each subband.Owing to want the total length of transmitted bit to differ surely by Δ bN _c/ N _bDivide exactly, so the length of last bit block is that total length is divided by Δ bN _c/ N _bRemainder.Certainly, if aliquot, the length of last bit block should be Δ bN _c/ N _bSelecting suitable subband for each bit block and transmit one by one then, and calculate required transmitting power.Begin in each the distribution, will judge also whether bit block to be allocated has arrived last piece, and how much its length is.In addition, because each subcarrier also has a maximum throughput b _MaxRestriction, so distribute beginning, also to judge the distribution that has which subband can not participate in this bit block each, transmit because if at last this bit block is assigned in these subbands, the throughput on each subcarrier has just exceeded b _MaxRestriction, bring can not realize in practice.After determining the length of the bit block of participating in the distribution and can participating in the scope of subband of this sub-distribution, be to utilize the inverted criterion of channel to calculate these subbands will transmit this bit block with that, under the requirement of receiving terminal target BER, the transmitting power of required increase separately.Choose the subband of required increase transmitting power minimum then, and bit block is assigned in this subband transmits.Finish in each the distribution, will judge once all whether all bit blocks assign, also are $\frac{1}{N_b}\underset{j=1}{\overset{N_b}{\mathrm{\Σ}}}{b}_j=R_b$ Whether set up.If set up, then all distribute end, otherwise carry out the distribution of next bit block.All distribute finish after, can calculate according to final bit allocation result and requiredly in each final subband satisfy the transmitting power numerical value of receiving terminal target BER under requiring.

Provided in the present patent application fixedly handle up and target BER restriction under two kinds of adaptive algorithms: the adaptive algorithm of varitron band transmitted power and the adaptive algorithm of negate transmitted power.Two kinds of algorithms can satisfy the different requirements of system to self adaptation complexity and feedback overhead respectively.

The Turbo coded modulation structure of using in this method is seen Fig. 2.In coded modulation, front end is the binary system Turbo encoder of a standard, encoder output information position

And check digit

Then with its output through punching and interweave after carry out multi-system modulation again, the multi-system symbol adopts gray mappings.The conventional letter number of constellation points is M=2 ^m, the bit sequence before k modulates constantly is { u _{K, i}, i=1...m, modulation symbol is output as { A _k, B _k.At receiving terminal, numerical symbol { X is recovered in butt joint earlier _k, Y _kCarry out demodulation, and calculate the likelihood ratio of each transmitted bit, adopt the decoding algorithm of binary system Turbo code to decipher again.

Particularly, fixedly handle up and target BER restriction down the adaptive algorithm of varitron band transmitted power comprise following step, see Fig. 3:

When 1) initial, the throughput b that distributes in each subband _j=0, transmitting power S _j=0, j=1..N _b, N wherein _bBe sub-band sum.

2) calculate next time in the distribution of bit block newly, be assigned to the average throughput numerical value Δ b ' on each subcarrier.Δ b ' chooses the smaller value of handling up granularity and distributing residue to handle up

$\mathrm{\Δb}\′=\min \{\mathrm{\Δb},N_b\·R_b-\underset{j=1}{\overset{N_b}{\mathrm{\Σ}}}{b}_j\}$

3) because the maximum throughput that distributes on each subcarrier is subjected to the restriction of actual modulated parameter, then use J={j|b _j≤ b _Max-Δ b ' } expression can also participate in down the set of subband of sub-distribution.Calculate each subband subcarrier then and increasing progressively the Δ required transmitting power that increases progressively of b ' time of handling up

$\begin{array}{cc}{\mathrm{\ΔS}}_j=\underset{k=1}{\overset{\mathrm{Nc}/N_b}{\mathrm{\Σ}}}\frac{S_{\mathrm{BER}}(b_j+\mathrm{\Δb}\′)-S_{\mathrm{BER}}\left(b_j\right)}{{\left|H_{j,k}\right|}^2}& j\∈J\end{array}$

4) $j^{*}=\arg \underset{\∀j\∈J}{\min }\mathrm{\Δ}{S}_j,$ Be illustrated among the sets of subbands J that participates in the distribution, guaranteeing under the receiving terminal target BER subband j ^*The transmitting power of the required increase of interior this bit block of transmission is minimum, then this bit block is assigned to subband j ^*Interior transmission.Upgrade subband j then ^*Throughput numerical value on each interior subcarrier

$b_{j^{*}}=b_j+\mathrm{\Δb}\′.$

5) judge whether all bits that will transmit assign, i.e. equation $\frac{1}{N_b}\underset{j=1}{\overset{N_b}{\mathrm{\Σ}}}{b}_j=R_b$ Whether set up.If equation is false, then forward 2 to), carry out the distribution of next bit block; If equation is set up, then all bit and power division finish.{ b _jBeing the numerical value of handling up on each subcarrier in final j the subband that distributes, the transmitting power of each subcarrier wherein is

$S_j=\frac{N_b}{N_c}\underset{k=1}{\overset{\mathrm{Nc}/N_b}{\mathrm{\Σ}}}\frac{S_{\mathrm{BER}}\left(b_j\right)}{{\left|H_{j,k}\right|}^2}$ j＝1..N _b

So far, whole Bit Allocation in Discrete finish.

In addition, limit the adaptive algorithm of following negate transmitted power with target BER, be divided into following step for fixedly handling up:

1) at first, supposing that the transmitted power of each subcarrier is in this OFDM symbol is S.Then total transmitting power is N in subband _bUnder the S, the received power that adopts channel inversion criterion to calculate is:

${\hat{S}}_j=\frac{S}{\frac{N_b}{N_c}\underset{k=1}{\overset{N_c/N_b}{\mathrm{\Σ}}}\frac{1}{{\left|H_{j,k}\right|}^2}}$ j＝1..N _b

2) thus, the average throughput in the whole symbol is

$\frac{1}{N_b}\underset{j=1}{\overset{N_b}{\mathrm{\Σ}}}{b}_j=\frac{1}{N_b}\underset{j=1}{\overset{N_b}{\mathrm{\Σ}}}{S}_{\mathrm{BER}}^{-1}\left({\hat{S}}_j\right)$

Wherein,

Be S _BERThe inverse function of (), it is illustrated among the AWGN, adopts the Turbo coded modulation under target BER, and received power is given maximum throughput regularly.

3) adjust transmitted power S until $\frac{1}{N_b}\underset{j=1}{\overset{N_b}{\mathrm{\Σ}}}{b}_j=R_b$ Formula is set up.The S of last gained is the transmitting power on each subcarrier in this OFDM symbol, b _jIt is the throughput of transmissions that distributes on each subcarrier in j the subband.

Now illustrate as follows:

Following result is from emulation of the computer software, and computer operating system is windows2000, and simulation software adopts matlab.

Suppose that ofdm system channel width is 10MHz, be divided into 1024 subcarriers.A time slot comprises 8 OFDM symbols on the time domain, and length is 1ms.Channel adopts M.1225 vehicle-mounted channel model A, and its six footpaths maximum delay is about 2.5 μ s.Target BER is 10 ^-4The sub-band adaptive frequency domain is divided into 16 subbands, and the sub-carrier number in each subband is 1024/16=64.The symbolic number M=8 of time domain combined coding is referring to Fig. 1.Comprising sub-carrier number in such encoding block is 512.The Turbo coded modulation adopts the minimum a kind of universal architecture of current complexity, i.e. the structure of binary system Turbo code and multi-system chopping phase cascade is referring to Fig. 2.Component recursive system convolution (RSC) multinomial of Turbo code is (13,11), and different efficient Turbo codes are evenly punchinged by 1/3 code check position and got.4 iteration, maximum a posteriori probability (MAP) algorithm are adopted in decoding.Modulation system is chosen two kinds, is respectively 8PSK and 64QAM.Each granularity Δ b that handles up that distributes is chosen for 1bit/s/Hz in the adaptive algorithm.

By software emulation as seen, with respect to fixing Turbo coded modulation, adopt the adaptive technique of the varitron band transmitted power in the present patent application can obtain very big SNR gain.At target BER is 10 ^-4Down, target throughput is respectively 1,2 and during 3bits/s/Hz, adopt fixedly that the required SNR of Turbo coded modulation is respectively 13.5dB, 18.5dB and 23dB, required SNR is respectively 6dB, 11.5dB and 16dB under the adaptive technique of this varitron band transmitted power and adopt.Comparatively speaking, new method has been saved transmitting power, and the SNR gain that brings is about 7.5dB, 7dB and 7dB respectively.In addition, if adopt the adaptive technique of the negate transmitted power in the present patent application, the above SNR gain of 5dB is also arranged.

Coded modulation in the present patent application has adopted the minimum a kind of general Turbo coded modulation structure of present complexity, and its structure as shown in Figure 2.In its coded modulation, front end is the binary system Turbo encoder of a standard, encoder output information position

And check digit

Then with its output through punching and interweave after carry out multi-system modulation again, the multi-system symbol adopts gray mappings.The conventional letter number of constellation points is M=2 ^m, the bit sequence before k modulates constantly is { u _{K, i}, i=1...m, modulation symbol is output as { A _k, B _k.At receiving terminal, numerical symbol { X is recovered in butt joint earlier _k, Y _kCarry out demodulation, and calculate the likelihood ratio of each transmitted bit, adopt the decoding algorithm of binary system Turbo code to decipher again.

This shows that the present invention has the following advantages:

1) can obtain the gain of bigger SNR. Employing approaches the Turbo coded modulation of channel capacity, so that can obtain More excellent self adaptation throughput performance.

2) can satisfy the requirement that all types of target is handled up. Adopted the coding method based on continuous speed, so that the distribution of bit more Add flexibly.

Can reduce the system feedback expense. Two kinds of methods that become power that propose among the present invention, a kind of is that subband becomes power one by one, a kind of That symbol becomes power one by one. These two kinds of methods are compared with the self adaptation that becomes power by subcarrier, can greatly reduce the feedback of system Expense and implementation complexity.

Claims (1)

1.OFDM in the down sub-band adaptive Turbo coded modulation method of fixedly handling up, N subcarrier in the same subband on adjacent M on the time domain the OFDM symbol frequency domain carried out combined coding, and in each subband, adopt the Turbo coded modulation of continuous speed, it is characterized in that: this code modulating method be a kind of constant handle up and target error rate BER restriction under, that takes the continuous blocks method of salary distribution becomes power adaptive Turbo code modulating method by subband, the described subband change power that pursues is meant in an OFDM symbol, transmitted power difference on the different sub-band, but the transmitted power of each subcarrier in the same subband is identical, when usefulness had the structure operation of Turbo coded modulation now, described method was carried out successively according to the following steps:

(1) set following parameter:

N _c: total number of sub-carriers,

N _b: sub-band sum,

R _b: mean allocation is target throughput on each subcarrier, is called for short the target average throughput, then N _cR _bBe total target throughput,

BER _Target: target BER,

S _j: transmitted power on each subcarrier in j the subband, it all is identical to all subcarriers in the same subband,

b _j: in j the subband, the existing throughput that obtains after each the distribution on each subcarrier is a variable,

H _{J, k}: in j the subband, the channel frequency domain response on k subcarrier,

S _BER(b): in awgn channel, send under b the bit, required minimum received power when satisfying receiving terminal BER and requiring supposes that noise power is given,

Δ b: when taking the continuous blocks method of salary distribution, be assigned to the granularity of handling up on each subcarrier at every turn, promptly remove last

The length of outer each allocation bit piece is divided by the number institute value of subcarrier in each subband, and is also promptly every except that last

The average throughput that increases on each subcarrier in the sub-distribution,

b _Max: the maximum throughput under the restriction of actual coding modulation parameter on each subcarrier,

Adaptive target is, average after, be finally allocated to that the throughput on each subcarrier equals target average throughput R in each subband _b, promptly $\frac{1}{N_b}\underset{j=1}{\overset{N_b}{\mathrm{\Σ}}}{b}_j=R_b,$ And error rate BER≤BERtarget;

(2) initialization

B when initial _j=0, S _j=0, j=1..N _b

(3) all bits that will transmit on all subbands are carried out piecemeal, be expressed as B respectively ₀..., B _K-1Piece, every contained bit number is Δ bN except that last _c/ N _b, the length of last bit block is that total length is divided by Δ bN _c/ N _bRemainder, the average throughput of Δ b wherein, N for increasing on each subcarrier to each subband the time except that last each bit block of distribution _c/ N _bBe the number of sub carrier wave in each subband;

(4) for B ₀..., B _K-1The piece bit set is for any one B _i, need from all N subband, find out one and guarantee under the receiving target BER transmission B _iThe subband of the transmitted power minimum of required increase also promptly will be obtained the transmitted power Δ S of the required increase of each subband transmitted bit piece successively according to following formula _i:

$\begin{array}{cc}{\mathrm{\ΔS}}_j=\underset{k=1}{\overset{\mathrm{Nc}/N_b}{\mathrm{\Σ}}}\frac{S_{\mathrm{BER}}(b_j+\mathrm{\Δb}\′)-S_{\mathrm{BER}}\left(b_j\right)}{{\left|H_{j,k}\right|}^2}& j\∈J\end{array}$

Wherein, $\mathrm{\Δb}\′=\min \{\mathrm{\Δb},N_b\·R_b-\underset{j=1}{\overset{N_b}{\mathrm{\Σ}}}{b}_j\},$

In the Δ b ' calculating distribution of bit block newly next time, be assigned to the average throughput numerical value on each subcarrier,

Xiang Weifen mixes after the bit block, can be for the residue throughput of this sub-distribution;

Simultaneously, also will satisfy following constraint: the maximum throughput on each subcarrier is b _Max, the set that participates in the subband of Δ b ' distribution like this is: J={j|b _j≤ b _Max-Δ b ' }, wherein, b _MaxBe the maximum throughput that distributes on each subcarrier, it is subjected to the restriction of actual modulated parameter;

Participating in bit block B again _iAmong the sets of subbands J that distributes, guaranteeing under the receiving target BER, finding out a transmission B _iThe subband j that required increase transmitted power is minimum ^*, that is:

$j^{*}=\arg \underset{\∀j\∈J}{\min }\mathrm{\Δ}{S}_j$

Then this bit block B _iBe assigned to j in the subband ^*Subband j is upgraded in transmission simultaneously ^*Throughput on interior each subcarrier , $b_{j^{*}}=b_j+\mathrm{\Δb}\′;$

(5) judge whether all bit blocks that will transmit assign, judge to assign just to be equivalent to and distribute the back to judge $\frac{1}{N_b}\underset{j=1}{\overset{N_b}{\mathrm{\Σ}}}{b}_j=R_b$ Whether set up,, then forward step (4) to, carry out next bit block and distribute if equation is false; If equation is set up, then all bit and power division finish, { b _jBe the numerical value of always handling up on each subcarrier in j the subband that final distribution obtains;

The transmitting power of each subcarrier is

$\begin{array}{cc}{S}_j=\frac{N_b}{N_c}\underset{k=1}{\overset{\mathrm{Nc}/N_b}{\mathrm{\Σ}}}\frac{S_{\mathrm{BER}}\left(b_j\right)}{{\left|H_{j,k}\right|}^2}& j=1..N_b.\end{array}$

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