CN1463110A - Multiplexing method of combination of non-orthogonal partition and time division partition - Google Patents

Abstract

The multiplexing method combining non-orthogonal division and time division division belongs to the transmitting end of the downlink channel of wireless cellular communication. Under the support of hardware, in the same time slot, non-orthogonal The constellation overlapping method of code division realizes the non-orthogonal multiplexing used to transmit two sets of independent information at the same time, that is, the information of the bad user determines a cluster of constellation points in the nebula, and the information of the good user determines the nebula points in the nebula; however, Information between the above two users in the same time slot and other users in different time slots or in different groups is time-division multiplexed. The invention not only improves the throughput of the system but also reduces the complexity of realizing the multi-user non-orthogonal system.

Description

Multiplexing method combining non-orthogonal division and time division

technical field

The multiplexing method combining non-orthogonal division and time division division belongs to the field of wireless cellular communication downlink division multiplexing technology

Background technique

With the increasing demand of multimedia services, obtaining high throughput of wireless cellular system has become one of the research hotspots in the field of communication. In the traditional wireless cellular communication, the multiplexing method of orthogonal division is adopted to avoid the harmful effect of the interference between users on the system throughput, so as to realize the multi-user communication under a certain throughput.

Orthogonal division methods include time division multiplexing, frequency division multiplexing and orthogonal code division multiplexing. The main feature of time division multiplexing (Time-Division Multiplexing) is to use different time slots to transmit different signals. They do not overlap each other in time, but in the frequency domain the various signals are aliased together. Frequency-division multiplexing separates signals from various channels in the frequency domain, but aliases them together in the time domain. Code Division Multiple Access (CDMA) digital communication technology establishes orthogonal channels through unique code sequences, and the information of each user does not interfere with each other. However, this orthogonal division multiplexing method can only transmit one information sequence in a certain resource unit, and the throughput of the whole system is greatly limited.

The invention solves the limitation of the system throughput of the traditional orthogonal division method by adopting the non-orthogonal division multiplexing method in the wireless cellular system. The research on the broadcast channel capacity of the downlink channel confirms [References: Andrea Goldsmith, Capacity of broadcast fading channels with variable rate and power Global Telecommunications Conference, 1996.GLOBECOM'96.'Communications: The Key to Global Prosperity, 1996Page(s): 92 -96] The feasibility of this method, that is, under the same channel conditions, under the non-orthogonal segmentation method, the information of different users is interleaved with each other, and a larger system throughput can be obtained than the orthogonal segmentation.

However, there are still two problems when the non-orthogonal division multiplexing method is applied to the wireless cellular system. First, in the non-orthogonal division, the signals of different users are not orthogonal, that is, there are overlapping parts between them. In order to apply this segmentation method in the downlink channel and realize the multiplexing of information among different users, it is first necessary to ensure that each user can accurately obtain its own part of the information at the receiving end. The present invention utilizes the difference in receiving quality among users, and realizes this goal by designing overlapping constellations (see accompanying drawing 1), that is, different users transmit their own information.

The second problem is that in cellular communication, each cell has only one base station, that is, only one downlink channel, so this channel needs to transmit information of all users (generally more than two) in the cell at the same time, which is quite a problem. Complex process. Especially for non-orthogonal segmentation, the information between users overlaps with each other. Although constellation overlap can correctly obtain the required information for each user, when the number of users is greater than 2, this The implementation of the system will be very complex. In order to reduce the complexity of system realization, the present invention adopts a multiplexing method combining non-orthogonal and time division. This approach not only improves system throughput, but also avoids complex system design.

The invention adopts the constellation overlapping technology in the non-orthogonal division and combines it with the method of time division multiplexing, and improves the throughput of the wireless cellular system under the premise of ensuring that the complexity of system realization is low.

Contents of the invention

The present invention provides a new multiplexing method, a multiplexing method combining non-orthogonal and time division, the purpose of which is to realize a wireless cellular system larger than the existing multiplexing method without increasing bandwidth and power forward capacity. It is assumed that the base station knows the receiving quality of each user in the cell, that is, the receiving signal-to-noise ratio. Firstly, the users in the cell are divided into two categories (good users and poor users) according to the level of SNR. Then group them, and each group contains a good user and several bad users. Then, within a group, two user information with a certain difference in receiving quality are multiplexed together by non-orthogonal code division, and then the multiplexed information is multiplexed together by orthogonal time division.

Constellation overlapping is a technology to realize non-orthogonal multiplexing of two users in this scheme. It is a multi-resolution technology. Figure 1 shows an example of constellation overlapping. Information 1 and 2 in the figure are mutually independent information. After modulation, information 1 determines which constellation point the finally transmitted modulated signal is located in (points surrounded by dotted lines in FIG. 1 are referred to as being in the same nebula). And message 2 chooses the point of final emission in this nebula. Due to different noises, the constellations have different degrees of divergence, the reception quality is poor, the signal strength of users is small, and the noise is relatively large, so the divergence is more serious, and the constellation of information 2 can no longer be seen clearly, but information 1 can still be distinguished constellation, so those users with poor reception quality can receive the modulated information1. For users with good reception quality (high signal-to-noise ratio), the relative noise is relatively small, and the reception constellation divergence is relatively light. Not only can it distinguish which cluster is modulated, but also the points in the cluster, so it can first distinguish The information 1 transmitted by the currently received signal (demodulates the poor user information), and then demodulates the information (demodulates the current user information). If information 1 is the information we want to send to poor users, and information 2 is the information needed by users with good reception quality, so that both users can receive their own information according to their actual capabilities, thus avoiding time-sharing or frequency division transmission.

The present invention is characterized in that: at the transmitting end of the downlink channel of the wireless cellular communication system, under the support of hardware, in the same time slot, the constellation intersection of non-orthogonal code division is used between two users with very different signal-to-noise ratios. The iterative method realizes the non-orthogonal multiplexing used to transmit two sets of independent information at the same time, that is, the information of the poor user determines a cluster of constellation points in the nebula, and the information of the good user determines the nebula points in the nebula; however, the information of the same time slot Information between the above two users in different time slots or other users in different groups is time-division multiplexed. The group is grouping. In each group, the time slots occupied by each poor user are the same, and a good user is shared by each time slot, thereby realizing that there are two equal time slots in the grouping. users with very different signal-to-noise ratios, and the time slots occupied by each group are equal.

The method comprises the following steps in turn:

(1) Sort all users in a cell according to the known average received SNR, select (1/(N+1)) users with the largest SNR, and call these users good users, The remaining users become poor users, and the ratio of the number of good users to poor users is an integer N, that is, 1:N;

(2) Group these users into groups according to the ratio of 1:N. First, a good user with the highest SNR and N poor users with the highest SNR start to form a group; users are assigned;

(3) Divide the group into N time slots with the same time slot assigned to each poor user, and use constellation overlapping non-orthogonal multiplexing for the information of 1 bad user and 1 good user in each time slot Each signal point (x ₁ ) of a good user is superimposed on each signal point (x ₂ ) of a poor user, and the multiplexed signal x ₁₂ =x ₁ +x ₂ ;

(4) Between different groups and between time slots in a group, an orthogonal time division method is adopted.

On the premise that the transmitting end correctly grasps the channel conditions, this multiplexing method effectively utilizes the difference in signal-to-noise ratio between users, realizes the transmission of multiple user information in the same channel, and obtains better than the existing positive Cross-multiplexing method for greater system throughput.

Description of drawings

Figure 1 Constellation overlapping constellation diagram, in the figure a. represents the constellation diagram of the signal (x ₂ ) mapping of a poor user with a low SNR, b. represents the signal (x ₁ ) mapping of a good user with a high SNR The constellation diagram of c. indicates the constellation diagram of the signal x=x ₁ +x ₂ mapped after the signals of the two users are multiplexed

Figure 2 Schematic diagram of multiplexing from time division to the combination of non-orthogonal division and time division

Figure 3 Schematic diagram of the segmentation scheme between multiple groups

Fig. 4 block diagram of program flow of multiplexing method

Detailed ways

The multiplexing method combining non-orthogonal division and time division division utilizes the difference in receiving signal-to-noise ratio between different users, and effectively improves the system throughput. It is especially suitable for the downlink channel of wireless cellular communication, because in the cellular system, the signal-to-noise ratio of users in the same cell is very different due to the different distances from the base station and the influence of terrain. Assuming that the receiving signal-to-noise ratio of each user is known, the specific implementation steps for realizing the multiplexing method in a cell are as follows, and the flow chart is shown in Figure 4.

1. Divide all users in a cell into good and bad categories according to the receiving quality (that is, the level of the average signal-to-noise ratio), and the ratio of the number of users in the two categories is N. (N is an integer). The received information of these users in the same cell is sent by the same base station, and the information will be transmitted through the same channel. Specifically, all users are sorted according to the average receiving SNR, and then the (1/(N+1)) users with the largest SNR are selected. We will make these users good users, and the rest Users become bad users, so the ratio of good users to bad users is 1:N

2. Divide these users into groups. First, start with the good user with the highest SNR, find out the N with the highest SNR from the bad users, and form a group with this good user. Then find the one with the highest SNR among the remaining users, and form a group with the one with the highest SNR among the remaining poor users. And so on, until all users are assigned.

3. In our method, this group of time is divided into N time periods, each time period is τ, and the information of 1 bad user and 1 good user in each time period is non-orthogonal Multiplexing (constellation overlap), each signal point (x ₁ ) of a good user is superimposed on each signal point (x ₂ ) of a bad user. The multiplexed signal x ₁₂ =x ₁ +x ₂ . [References: Alexander Seeger, Broadcast Communication on fading channel using hierarchical coded modulation, Global Telecommunications Conference, 2000.GLOBECOM′00.IEEE, Volume: 1, 2000 Page(s): 92-97 vol.1] is actually composed of The information of the user with poor quality determines which nebula the signal is located in (see Figure 1), x ₁ is the center of this nebula, and the other information x ₂ selects a constellation point in this nebula.

4. Each time period in each group is independent. In this way, each poor user in the group will occupy a time period of size τ, while the information of good users is transmitted throughout N·τ, as shown in Figure 2. Figure 2 describes how users within a group are multiplexed, and makes a comparison with the traditional time division multiplexing method. The left side of the arrow in Figure 2 indicates that the information of different users is transmitted by the method of time division division, and each square represents a time slot, and it can be seen that each user occupies a time slot respectively. The right side of the arrow describes our multiplexing method that combines non-orthogonal division and time division division. There are 3 time slots in total, and users 2, 3, and 4 are in the first, second, and third time slots respectively. The respective information is transmitted, and there is user 1's information in each time slot; and user 1's information is taken together with another user in this time slot in a non-orthogonal division method in each time slot.

5. Between different groups, the method of orthogonal time division is still adopted. Considering fairness, each group gets the same resource, that is, the same time slot.

It can be seen that this multiplexing method not only utilizes the difference in signal-to-noise ratio between different users, realizes non-orthogonal multiplexing between two users, and improves the system throughput. At the same time, orthogonal time-division multiplexing is adopted between groups and between different time slots within a group, which avoids the complexity of implementing a non-orthogonal system for multiple users. The flowchart is shown in Figure 4.

The following will illustrate how such a multiplexing method should be implemented:

The transmission of the downlink channel requires the information of multiple users to be sent. Suppose there are 6 users in the cell (respectively called users 1, 2, 3, 4, 5, and 6), and the signal-to-noise ratios of these users are 2dB and 3dB respectively. , 5dB, 5dB, 14dB, 15dB. As mentioned above in the description of the method, users in the system are divided into two types according to the level of the received signal-to-noise ratio, good users and poor users, and the ratio of the numbers is 1:2. Then the good users are the users (user 5, user 6) whose signal-to-noise ratio is 14dB and 15dB, and the rest of the users are poor users. After grouping according to step 2, user 1, user 2 and user 5 are divided into one group, and user 3, user 4 and user 6 form the second group. Each group will get 1/2 of the transmission time of the system and divide the system time The information of each group occupies a time slot each time and is transmitted alternately.

The following describes in detail how the user information of the second group is sent:

1) The information of each user first undergoes error correction coding (using Turbo code, that is, parallel concatenated convolutional code), and then the information of user 3 and user 4 is modulated by QPSK (quaternary phase shift keying), and user 6 The information is 16QAM (hexadecimal quadrature amplitude modulation) modulation

2) Dividing this group of occupied time slots into two parts of the same size, one part of the time slots transmits the information of user 3 and user 6, while the other part transmits the information of user 4 and user 6. That is to say, the information of user 3 and user 4 is only transmitted in a certain part of the time, while user 6 will be able to transmit information in the time slots occupied by this group.

3) Assuming that user 3 obtains signal x ₃ after modulation, let the modulated signal and the modulated signal x ₆ of the good user (user 6) in this group realize non-orthogonal multiplexing through constellation overlapping, that is, each good user A signal point is superimposed on each signal point of the poor user respectively. The multiplexed signal x _3,6 =x ₃ +x ₆ .

4) The information x ₄ of the same user 4 is also superimposed with the information of user 6 to obtain x _4,6

5) The signals x _3,6 and x _4,6 obtained after constellation overlap are time-division multiplexed, that is, they are alternately transmitted at different time periods.

In this way, we have realized the transmission of all user information in the second group. Similarly, in another time slot, another group of information is transmitted similarly to this group. In this way, the transmission of all user information is realized in the same channel, as shown in FIG. 3 . It can be seen that in Figure 3, users are divided into two layers. Users on the upper layer (users 5 and 6) are so-called good users, while users on the lower layer (users 1, 2, 3, 4) are poor users. . Each poor user occupies a time slot, which is represented by a small square, and in this time slot, there will be a good user's information and its non-orthogonal division multiplexing and then it will be transmitted together. For example, user 1 occupies the first time slot, and user 5's information will also be transmitted in this time slot. Similarly, the information of user 5 will also be transmitted in the time slot occupied by user 2.

The present invention can be realized by computer software, and can also be realized by programmable logic device FPGA.

The multiplexing method utilizes the difference in signal-to-noise ratio between different users, realizes non-orthogonal multiplexing between two users, and improves system throughput. For example, in a white Gaussian additive noise downlink channel with two users, if the signal-to-noise ratios of the two users are 5dB and 15dB respectively, after using this multiplexing method, the data rate of the two users is similar to that of the time-division system Ratio, respectively increased by 38% and 20%. At the same time, due to the use of orthogonal time-division multiplexing between groups and between different time slots within a group, the complexity of implementing a non-orthogonal system for multiple users is avoided.

Claims (3)

1. the nonopiate multiplexing method of cutting apart combination with the time-division of cutting apart, contain time-multiplexed step, it is characterized in that: at the transmitting terminal of radio honeycomb communication system down channel, under hardware supports, in same time slot, the constellation crossover method of utilizing non-orthogonal codes to divide between the very big user of two signal to noise ratio difference realizes in order to transmit the nonopiate multiplexing of two groups of independent information simultaneously, i.e. cluster constellation point in poor user's the information decision nebula, and the nebula point in good user's the information decision nebula; But the information between other users that above-mentioned two users in the same time slot are interior with different time slots or different groups are interior is time-multiplexed.

2. the nonopiate multiplexing method of cutting apart combination with the time-division of cutting apart according to claim 1, it is characterized in that: described group is promptly divided into groups, in each grouping, the shared time slot of each difference user is identical, a good user then is that each time slot is public, thereby exist the user that two signal to noise ratios differ greatly in each impartial time slot of having realized dividing into groups, and the shared time slot of each grouping equates.

3. the nonopiate multiplexing method of cutting apart combination with the time-division of cutting apart according to claim 1 and 2, it is characterized in that: described method contains following steps successively:

(1) the size ordering of all users in the sub-district according to known average received signal to noise ratio, select (1/ (N+1)) the individual user of signal to noise ratio maximum, these users have been called the user, remaining user becomes poor user, good user is an Integer N with difference user's number ratio, promptly 1: N;

(2) these user grouping, in 1: the ratio grouping of N, at first form one group since a highest good user and N the highest poor user of signal to noise ratio of signal to noise ratio; Remaining user handles like this, all is assigned with up to all users;

(3) the identical time slot of assigning to each difference user is divided into N time period to grouping, has 1 poor user and 1 good user's information to adopt the nonopiate multiplexing of constellation crossover formula, each signaling point (x of good user in each time period ₁) all be superimposed on respectively poor user each signaling point (x ₂) on, the signal x after the multiple connection ₁₂=x ₁+ x ₂

(4) between different group and the group, between each time slot in the grouping, adopt the quadrature time division way.

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