CN101330712A - Method and apparatus for distributing sub carrier of multiple input/output-OFDM system - Google Patents

Abstract

The invention discloses a multiple input and output orthogonal frequency-division multiplexing system sub-carrier wave distribution method. In the method, sub-carrier waves are distributed through frequency division multiple access or space division multiple access according to the number of users; when the number of users is small, sub-carrier waves are distributed through the frequency division multiple access according to the channel capacity; when the number of users is large, the sub-carrier waves are distributed through the space division multiple access according to space subchannels. By adopting the multiple input and output orthogonal frequency-division multiplexing system sub-carrier wave distribution method, sub-carrier waves are distributed from the angles of channel capacity and space subchannels; and the defects of the prior art that sub-carrier waves are distributed just from the angle of a single criterion and other properties can not considered are overcome.

Description

Sub carrier of multiple input/output-OFDM system distribution method and device

Technical field

The present invention relates to the mobile communcations system subcarrier allocation, be particularly related to a kind of multi-user MIMO-OFDM (multiple input multiple output-Orthogonal Frequency DivisionMultiplexing that is used for, multi-input multi-output-orthogonal frequency division multiplexing) OFDM and FDMA (Frequency Division Multiple Access in the system, frequency division multiple access), the subcarrier self-adapting distribution method and the device that combine of SDMA (Space DivisionMultiple Access, space division multiple access).

Background technology

Changing environment when mobile radio channel is one, the signal to noise ratio of channel capacity and receiving terminal etc. all is a change at random.When adopting the fixing method of salary distribution, the variation that communication system just can't the adaptive channel situation.If in the MIMO-OFDM system, can make full use of the degree of freedom on space, time and the frequency dimension, can design the method for salary distribution more flexibly, make performance reach better.

In multi-user MIMO-OFDM system, because the randomness of different user present position, the channel fade condition that is experienced between most of users often independently.Sometime or on certain subcarrier, the certain user may be in the middle of the deep fading, be unsuitable in the channel data.And meanwhile, it is relatively good to have another part subscriber channel situation probably, so can obtain the benefit of multi-user diversity to greatest extent, satisfy the requirement of different user, the subcarrier allocation algorithm that proposition can be used in the multi-user MIMO-OFDM environment, thereby the improvement of obtained performance or the lifting of transmission rate in subcarrier is selected.

At present, research for the subcarrier allocation in the ofdm system is a focus, but it is less for multi-user MIMO-OFDM research, some carry out subcarrier allocation from single criterion method is just proposed, for example only from SNR (Signal to Noise Ratio, signal to noise ratio) ordering is considered, and SISO (Single Input Single Output, the single output of single input) does not compare and obviously improves.

Prior art is only carried out subcarrier allocation from single criterion can not take into account other performances, can cause the decline of overall system performance.

Summary of the invention

Technical problem to be solved by this invention is, a kind of multi-user's of being used for multiple input/output-OFDM sub-carrier wave distribution method is provided, distributes the problem that only causes systematic function to descend from certain criterion to overcome prior art ofdm system sub-carriers.

For achieving the above object, multi-user's sub carrier of multiple input/output-OFDM system distribution method provided by the invention is characterized in that carry out subcarrier allocation according to number of users how many corresponding employing frequency division multiple accesss or space division multiple access mode; When number of users more after a little while, adopt FDMA to carry out subcarrier allocation according to channel capacity; When number of users more for a long time, adopt the space division multiple access mode to carry out subcarrier allocation according to spatial sub-channel.

Said method is characterized in that, also comprises an initialization step, be used for beginning to distribute from first subcarrier, and all available subcarriers as a set.

Said method is characterized in that, comprises that also a subcarrier allocation finishes determining step, is used for judging whether the subcarrier of described set assigns; When next subcarrier to be allocated belongs to described set, be judged as subcarrier allocation and finish, otherwise proceed subcarrier allocation.

Said method is characterized in that, it is to give the user of momentary output value maximum thereon with a subcarrier allocation in the described set that described employing FDMA carries out subcarrier allocation according to channel capacity.

Said method is characterized in that, it is that the transmit antennas on the subcarrier in the described set is distributed to the user that can realize the speed maximum among all users that described employing space division multiple access mode is carried out subcarrier allocation according to spatial sub-channel.

For further realizing purpose of the present invention, the present invention also provides a kind of sub carrier of multiple input/output-OFDM system distributor, it is characterized in that, comprising:

The initial configuration module is used for beginning to distribute from first subcarrier, and all available subcarriers as a set;

The FDMA sub-carrier assignment module is used for carrying out subcarrier allocation according to channel capacity at number of users more after a little while;

Space division multiple access mode sub-carrier assignment module is used for carrying out subcarrier allocation according to spatial sub-channel more for a long time at number of users.

Further, the present invention also provides a kind of multiple input/output-OFDM system, comprises a subcarrier allocation device, it is characterized in that, described subcarrier allocation device comprises:

The initial configuration module is used for beginning to distribute from first subcarrier, and all available subcarriers as a set;

The FDMA sub-carrier assignment module is used for carrying out subcarrier allocation according to channel capacity at number of users more after a little while;

Space division multiple access mode sub-carrier assignment module is used for carrying out subcarrier allocation according to spatial sub-channel more for a long time at number of users.

Compared with prior art, the present invention carries out subcarrier allocation from the angle of channel capacity and spatial sub-channel, overcome prior art and only carried out subcarrier allocation from single criterion and can not take into account other performance defect, application of the present invention can make system's momentary output maximum, transmitting antenna speed maximum.

Description of drawings

Fig. 1 is an embodiment of the invention multi-user MIMO-OFDM system sub-carriers distribution method flow chart;

Fig. 2 is an embodiment of the invention multi-user MIMO-OFDM system block diagram.

Embodiment

Below in conjunction with the drawings and specific embodiments technical scheme of the present invention being described in detail, with purpose, effect and the technical scheme of further understanding the present invention, but is not the restriction that is used for claims protection range of the present invention.

The present invention carries out the subcarrier self-adapting distribution method that OFDM combines with FDMA, SDMA the multi-user MIMO-OFDM system from channel capacity, the availability of frequency spectrum, promptly know under the situation of certain form channel information at transmitting terminal, by reasonable adjustment, utilize various parameters and resource, allocative decision is complementary with channel as far as possible.

The sub-carrier wave distribution method that is used for multi-user MIMO-OFDM system provided by the invention comprises:

Initialization step is used for beginning to distribute from first subcarrier, and all available subcarriers as a set.

The subcarrier allocation step is used for adopting FDMA or SDMA mode to carry out subcarrier allocation according to number of users.Described subcarrier allocation step further comprises: adopt the FDMA mode to carry out the step of subcarrier allocation, be used for giving the user of momentary output value maximum thereon according to channel capacity with a subcarrier allocation of described set at number of users more after a little while; Adopt the SDMA mode to carry out the step of subcarrier allocation, being used for carrying out subcarrier allocation more for a long time according to spatial sub-channel at number of users is that the transmit antennas on the subcarrier of described set is distributed to the user that can realize the speed maximum among all users.

Subcarrier allocation finishes determining step, is used for judging whether the subcarrier of described set assigns.When next subcarrier to be allocated belongs to described set, be judged as subcarrier allocation and finish, otherwise described subcarrier allocation step is carried out in circulation.

If number of users is less, then adopt the FDMA mode, can be from the angle of channel capacity, carry out subcarrier allocation, suppose that at first transmitting terminal has the M transmit antennas, receiving terminal has N root reception antenna, according to the channel capacity formula of MIMO-OFDM system, obtain the situation that a variable characterizes each subscriber channel, thereby reduce the expense of feedback.Suppose that momentary output C can be expressed as:

$C^k=\frac{1}{N_c}\underset{m=1}{\overset{N_c}{\mathrm{\Σ}}}{C}_m^k$

$=\frac{1}{N_c}\underset{m=1}{\overset{N_c}{\mathrm{\Σ}}}{\log }_2\left(\det (I_N+\frac{E_S}{N_c{\mathrm{MN}}_0}{H}_m^k{\left(H_m^k\right)}^H)\right)$

$=\frac{1}{N_c}\underset{m=1}{\overset{N_c}{\mathrm{\Σ}}}\underset{i=1}{\overset{n}{\mathrm{\Σ}}}{\log }_2(1+\frac{E_S}{N_c{\mathrm{MN}}_0}{\mathrm{\λ}}^{m,i})$

Wherein, C _m ^kBe the momentary output on k user's m the subcarrier, E _SBe the gross energy of OFDM symbols transmitted on all antennas, and n=min (M, N), λ _{M, i} ^kRepresent matrix H _m ^k(H _m ^k) ^HI characteristic value.

$C_m^k=\underset{i=1}{\overset{n}{\mathrm{\Σ}}}\log 2(1+\frac{E_S}{N_c{\mathrm{MN}}_0}{\mathrm{\λ}}_{m,i}^k)$

$\≤n\log 2(1+\frac{E_S}{N_c{\mathrm{MN}}_0}\frac{1}{n}\underset{i=1}{\overset{n}{\mathrm{\Σ}}}{\mathrm{\λ}}_{m,i}^k)$

$=n\log 2(1+\frac{E_S}{N_c{\mathrm{MN}}_0}\frac{1}{n}\mathrm{tr}\left(H_m^k{\left(H_m^k\right)}^H\right))$

Here, the mark of tr () representing matrix, design object is the momentary output maximization that makes multi-user MIMO-OFDM system, this target can equivalence be to give the user of capacity maximum thereon with each subcarrier allocation, that is to say,

$\underset{k=[\mathrm{1,2},..,K]}{\arg \max }\left(n\log 2(1+\frac{E_S}{N_c{\mathrm{MN}}_0}\frac{1}{n}\mathrm{tr}\left(H_m^k{\left(H_m^k\right)}^H\right))\right)$

As can be seen from the above equation, the mimo channel matrix trace is one and can effectively characterizes the tolerance that maximum can realize transmission rate on each subcarrier.According to this conclusion, it is as follows to draw the subcarrier allocation criterion:

For making multi-user MIMO-OFDM system get the momentary output maximum, can give tr (H thereon with m subcarrier allocation _m ^k(H _m ^k) ^H)) k maximum user of value.

If number of users is more, then adopt the SDMA mode, can be from the angle of spatial sub-channel, the above-mentioned result who obtains is that supposition is only given a user with a subcarrier allocation.In fact, in space multiplexing system, because the existence of many antennas can be decomposed into each subcarrier a series of independently spatial sub-channels.Therefore, can be by being that unit distributes independently with the antenna between a plurality of users, thus realize that a plurality of users share same subcarrier.Maximum accessible speed can be expressed as on the i transmit antennas of subcarrier m

$C_{m,i}^k=\log 2(1+\frac{E_S}{N_c{\mathrm{MN}}_0}\frac{1}{{\left({\left(H_{m,i}^k\right)}^H{H}_{m,i}^k\right)}^{-1}})$

As can be seen from the above equation, ((H _{M, i} ^k) ^HH _{M, i} ^k) ^-1Can reflect the maximum speed that can realize well, so the i transmit antennas on m the subcarrier can be distributed to ((H among all users _{M, i} ^k) ^HH _{M, i} ^k) ^-1K the user that value is minimum.

Fig. 1 is the sub-carrier wave distribution method flow chart in the embodiment of the invention multi-user MIMO-OFDM system, has shown the concrete subcarrier allocation process of this method among the figure.With reference to figure 1, the present embodiment sub-carrier wave distribution method comprises:

Step S100: finish initialization procedure, begin to distribute from first subcarrier, and all available subcarriers as a set, even m=1, set A=1,2 ..., N _c, wherein m represents m subcarrier, A represents the set of all subcarriers, N _cExpression available subcarrier number;

Step S200:, then seek and satisfy if number of users is less $\mathrm{\α}=\underset{k=[\mathrm{1,2},...,K]}{\arg \max }\left(\mathrm{tr}\left(H_m^k{\left(H_m^k\right)}^H\right)\right),$ That is to say and give tr (H m subcarrier allocation _m ^k(H _m ^k) ^H)) k maximum user of value; If number of users is more, then seeks and satisfy $\mathrm{\β}=\underset{k=[\mathrm{1,2},...,K]}{\arg \min }\left({\left({\left(H_{m,i}^k\right)}^H{H}_{m,i}^k\right)}^{-1}\right),$ I transmit antennas on m the subcarrier is distributed to ((H _{M, i} ^k) ^HH _{M, i} ^k) ^-1K the user that value is minimum;

Step S300: prepare the next son carrier wave is distributed, promptly upgrade m and A, m=m+1, A=A-{m};

Step S400: if subcarrier does not distribute end, promptly m ∈ A then turns back to step S200, if subcarrier has distributed end, promptly $m\∉A,$ Then finish the subcarrier allocation process.

Fig. 2 is the multi-user MIMO-OFDM system block diagram, shown among the figure that each user need give transmitting terminal the channel matrix feedback that receiving terminal estimates, transmitting terminal carries out subcarrier allocation according to criterion, is mapped on the transmitting antenna through processing such as spatial reuse, IFFT conversion afterwards and launches.

With reference to figure 1, multi-user MIMO-OFDM system comprises that one uses the subcarrier allocation device 10 of above-mentioned sub-carrier wave distribution method, this subcarrier allocation device 10 comprises: initial configuration module 101, be used for beginning to distribute from first subcarrier, and all available subcarriers as a set; FDMA mode sub-carrier assignment module 102 is used for carrying out subcarrier allocation according to channel capacity at number of users more after a little while; SDMA mode sub-carrier assignment module 103 is used for carrying out subcarrier allocation according to spatial sub-channel more for a long time at number of users.

Though the present invention discloses as above with a preferred embodiment; right its is not in order to limit the present invention; under the situation that does not deviate from spirit of the present invention and essence thereof; those of ordinary skill in the art work as can make various corresponding changes and distortion according to the present invention, but these corresponding changes and distortion all should belong to the protection range of the appended claim of the present invention.

Claims (12)

1, a kind of sub carrier of multiple input/output-OFDM system distribution method is characterized in that, carries out subcarrier allocation according to number of users how many corresponding employing frequency division multiple accesss or space division multiple access mode; When number of users more after a little while, adopt FDMA to carry out subcarrier allocation according to channel capacity; When number of users more for a long time, adopt the space division multiple access mode to carry out subcarrier allocation according to spatial sub-channel.

2, method according to claim 1 is characterized in that, also comprises an initialization step, be used for beginning to distribute from first subcarrier, and all available subcarriers as a set.

3, method according to claim 2 is characterized in that, comprises that also a subcarrier allocation finishes determining step, is used for judging whether the subcarrier of described set assigns; When next subcarrier to be allocated belongs to described set, be judged as subcarrier allocation and finish, otherwise proceed subcarrier allocation.

4, method according to claim 1 is characterized in that, it is to give the user of momentary output value maximum thereon with a subcarrier allocation in the described set that described employing FDMA carries out subcarrier allocation according to channel capacity.

5, method according to claim 1, it is characterized in that it is that the transmit antennas on the subcarrier in the described set is distributed to the user that can realize the speed maximum among all users that described employing space division multiple access mode is carried out subcarrier allocation according to spatial sub-channel.

6, method according to claim 1 is characterized in that, described channel capacity is by representing with following formula:

$C^k=\frac{1}{N_c}\underset{m=1}{\overset{N_c}{\mathrm{\Σ}}}{C}_m^k$

$=\frac{1}{N_c}\underset{m=1}{\overset{N_c}{\mathrm{\Σ}}}{\log }_2\left(\det (I_N+\frac{E_S}{N_c{\mathrm{MN}}_0}{H}_m^k{\left(H_m^k\right)}^H)\right),$

$=\frac{1}{N_c}\underset{m=1}{\overset{N_c}{\mathrm{\Σ}}}\underset{i=1}{\overset{n}{\mathrm{\Σ}}}{\log }_2(1+\frac{E_S}{N_c{\mathrm{MN}}_0}{\mathrm{\λ}}_{m,i}^k)$

Wherein, M is the transmitting terminal number of transmit antennas,

N is a receiving terminal reception antenna number,

N _CBe the available subcarrier number,

C _m ^kBe the momentary output on k user's m the subcarrier,

E _SBe the gross energy of OFDM symbols transmitted on all antennas,

n＝min(M，N)，

λ _{M, i} ^kRepresent matrix H _m ^k(H _m ^k) ^HI characteristic value.

7, method according to claim 6 is characterized in that, the momentary output C on described k user's m the subcarrier _m ^kObtain by following formula:

$C_m^k=\underset{i=1}{\overset{n}{\mathrm{\Σ}}}\log 2(1+\frac{E_S}{N_c{\mathrm{MN}}_0}{\mathrm{\λ}}_{m,j}^k)$

$\≤n\log 2(1+\frac{E_S}{N_c{\mathrm{MN}}_0}\frac{1}{n}\underset{i=1}{\overset{n}{\mathrm{\Σ}}}{\mathrm{\λ}}_{m,i}^k),$

$=n\log 2(1+\frac{E_S}{N_c{\mathrm{MN}}_0}\frac{1}{n}\mathrm{tr}\left(H_m^k{\left(H_m^k\right)}^H\right))$

Wherein, the mark of tr () representing matrix, its design object is the momentary output maximization that makes multi-user's multiple input/output-OFDM system.

8, according to claim 4,6 or 7 described methods, it is characterized in that the maximum of described momentary output is weighed with following formula:

$\underset{k=[\mathrm{1,2},...,K]}{\arg \max }\left(n\log 2(1+\frac{E_S}{N_c{\mathrm{MN}}_0}\frac{1}{n}\mathrm{tr}\left(H_m^k{\left(H_m^k\right)}^H\right))\right),$

Wherein, tr (H _m ^k(H _m ^k) ^H)) when value is maximum, described momentary output maximum.

9, method according to claim 5 is characterized in that, described maximum can realize that speed obtains according to following formula:

$C_{m,i}^k=\log 2(1+\frac{E_S}{N_c{\mathrm{MN}}_0}\frac{1}{{\left({\left(H_{m,i}^k\right)}^H{H}_{m,i}^k\right)}^{-1}}),$

Wherein, C _{M, i} ^kBe that m the maximum on the i transmit antennas on the subcarrier can realize speed;

M is the transmitting terminal number of transmit antennas,

N is a receiving terminal reception antenna number,

N _CBe the available subcarrier number,

E _SIt is the gross energy of OFDM symbols transmitted on all antennas.

10, method according to claim 9 is characterized in that, described maximum can realize that speed weighs with following formula: $\underset{k=[\mathrm{1,2},...,K]}{\arg \min }\left({\left({\left(H_{m,i}^k\right)}^H{H}_{m,i}^k\right)}^{-1}\right),$ Wherein, ((H _{M, i} ^k) ^HH _{M, i} ^k) ^-1Value hour, the described speed maximum that realizes.

11, a kind of sub carrier of multiple input/output-OFDM system distributor is characterized in that, comprising:

The initial configuration module is used for beginning to distribute from first subcarrier, and all available subcarriers as a set;

The FDMA sub-carrier assignment module is used for carrying out subcarrier allocation according to channel capacity at number of users more after a little while;

Space division multiple access mode sub-carrier assignment module is used for carrying out subcarrier allocation according to spatial sub-channel more for a long time at number of users.

12, a kind of multiple input/output-OFDM system comprises a subcarrier allocation device, it is characterized in that, described subcarrier allocation device comprises:

The initial configuration module is used for beginning to distribute from first subcarrier, and all available subcarriers as a set;

The FDMA sub-carrier assignment module is used for carrying out subcarrier allocation according to channel capacity at number of users more after a little while;

Space division multiple access mode sub-carrier assignment module is used for carrying out subcarrier allocation according to spatial sub-channel more for a long time at number of users.

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