CN101132266A - A Normalized Subcarrier Allocation Method Applicable to MC-CDMA System - Google Patents

Abstract

The invention provides a dynamic sub-carrier group allocation scheme based on user normalized priority, which is suitable for a multi-carrier code division multiple access (MC-CDMA) system. The basic principle of subcarrier group allocation is: the base station determines the initial normalized allocation priority according to the partial channel information fed back by each user, and iteratively updates it during the allocation process, and corresponds the user group to the subcarrier group in turn according to the priority. Compared with the traditional subcarrier group allocation scheme, the scheme provided by the present invention reduces the complexity of the algorithm while optimizing the transmission rate.

Description

A Normalized Subcarrier Allocation Method Applicable to MC-CDMA System

technical field

The invention belongs to the technical field of wireless communication, and relates to a carrier adaptive packet allocation scheme of packet multi-carrier code division multiple access technology in a downlink wireless communication link. Carrier dynamic iterative allocation scheme based on channel information.

Background technique

As a multiple access technology, code division multiple access (CDMA) has high spectrum utilization efficiency compared with traditional multiple access methods such as time division multiple access (TDMA) and frequency division multiple access (FDMA). Large capacity, strong anti-fading and interference capabilities, high-efficiency implementation, flexible access and other incomparable advantages. However, due to the existence of frequency-selective multipath fading channels, CDMA is easily affected by multi-user interference (MUI) and inter-symbol interference (ISI). Orthogonal Frequency Division Multiple Access (OFDMA), derived from Orthogonal Frequency Division Multiplexing (OFDM), can eliminate the impact of MUI. However, when OFDMA does not use error coding, it is difficult to obtain the diversity gain brought by multipath. Combining the above two technologies and utilizing the complementarity between CDMA and OFDMA, a multi-carrier code division multiple access (MC-CDMA) technology suitable for the downlink is constructed.

The combination of MC-CDMA technology and adaptive carrier grouping scheme produces adaptive grouping MC-CDMA system. Common subcarrier grouping schemes include continuous subcarrier grouping and equally spaced subcarrier grouping. Continuous subcarrier grouping, that is, according to the subcarrier sequence sequence, several adjacent subcarriers are grouped into one group, and the subcarrier sequence set of the carrier group is F _n =[f _(n-1)N+1 , f _{(n- 1) N} , . . . , f _nN ], where n=1, 2, . . . , N _g . Equally spaced subcarrier grouping, that is, selecting N subcarriers at equal frequency intervals to form a group, the subcarrier sequence set of the carrier group is _Fn = [ _Fn , _fNg+n , ..., f _{(N-1)Ng+ n} ], where n=1, 2, . . . , N _g . The subcarriers are grouped according to specific rules, and users using the same carrier group are distinguished by spreading code words without being interfered by other groups of users.

Contents of the invention

The carrier allocation scheme in the traditional multi-carrier code division multiple access (MC-CDMA) system needs to feed back the channel information of the user on all subcarriers, and according to the signal-to-noise ratio (SNR) of the user on each carrier or on each carrier group The equivalent signal-to-noise ratio for carrier allocation. Users need to feed back more channel information, which reduces the utilization efficiency of spectrum resources. Allocation is carried out according to the signal-to-noise ratio, without considering the impact of multiple access interference, which brings a certain capacity loss to the system. In order to suppress the impact of multiple access interference on the transmission rate and reduce the amount of information that users need to feed back, the present invention proposes an effective criterion for allocating subcarrier groups.

The subcarrier grouping method of the Adaptive Group Multicarrier Code Division Multiple Access (AG-MC-CDMA) system is as follows: assuming that the total number of subcarriers in the system is M, they are divided into N _g groups, and the number of subcarriers contained in each group is It is N=M/N _g . Here, the number of subcarriers M and the number of carrier groups N _g are design parameters, and M and N _g can be properly selected according to requirements. Each user selects a carrier group to transmit information bearing symbols. Each carrier group can accommodate up to N users. Different carrier groups are in different frequency bands, so users of different carrier groups can use the same spreading code. Since each group of carriers in MC-CDMA can accommodate multiple users, the allocation of carrier groups can be seen as the allocation of users from another perspective. The essence is to determine which carrier group a user uses, so it will not be distinguished below. Subcarrier allocation and user allocation concepts.

的比值定义为等效归一SINR值δ_u ⁱ，用来确定用户分配优先级。在子载波组分配的过程中，经过多次迭代，每次迭代分配一个用户，如果每次被分配的用户都选择最大的δ_u ⁱ，那么所有用户全部被分配之后，系统在整个带宽内的传输速率也就接近最优。所以δ_u ⁱ大小近似反映了将第u个用户被分配到第i个子载波组对于总传输速率的重要性。本发明利用这一性质在每次迭代过程中根据δ_u ⁱ(u＝1，2，...，U_T，i＝1，2，...，N_g)来确定子载波分配的优先级。The principle of the new subcarrier group allocation scheme is as follows: According to the minimum mean square error criterion (MMSE) detection, the UE calculates and obtains its equivalent signal-to-interference-noise ratio (SINR) λ _u ⁱ in each carrier group, i=1, 2, . . . , N _g , u=1, 2, . . . , U _T , where U _T represents the number of activated users of the system. λ _u ⁱ reflects the channel condition of the user on the subcarrier group. The user feeds back its equivalent SINR information in each carrier group to the base station. According to the user's feedback information, the base station calculates the equivalent average SINR value of the i-th subcarrier group ${\stackrel{\‾}{\mathrm{\λ}}}_i=\sqrt[u_T]{(1+{\mathrm{\λ}}_i^1)(1+{\mathrm{\λ}}_i^2)\·\·\·(1+{\mathrm{\λ}}_i^{u_T})}.$ λ _u ⁱ and

The ratio of is defined as the equivalent normalized SINR value δ _u ⁱ , which is used to determine user allocation priority. In the process of subcarrier group allocation, after multiple iterations, each iteration allocates a user, if each allocated user selects the largest δ _u ⁱ , then after all users are allocated, the system’s performance in the entire bandwidth The transfer rate is also close to optimal. So the size of δ _u ⁱ approximately reflects the importance of allocating the u-th user to the i-th subcarrier group for the total transmission rate. The present invention uses this property to determine the priority of subcarrier allocation according to δ _u ⁱ (u=1, 2,..., U _T , i=1, 2,..., N _g ) in each iteration process class.

The subcarrier group allocation scheme provided by the present invention includes the following steps:

Consider a packet MC-CDMA system, the number of active users is U _T , the number of subcarriers is M, and the grouping method is adopted at equal intervals. Before implementing this solution, it is assumed that the length of the spread spectrum code used is N, and then the number of groups is N _g .

At the mobile station, the user calculates the equivalent signal-to-interference-noise ratio (SINR) of each subcarrier group according to the channel information, that is, ${\mathrm{\λ}}_u^i=\underset{\mathrm{no}=1}{\overset{N}{\mathrm{\Σ}}}{\mathrm{\Φ}}_{u,\mathrm{no}}^i/(N-\underset{\mathrm{no}=1}{\overset{N}{\mathrm{\Σ}}}{\mathrm{\Φ}}_{u,\mathrm{no}}^i),$ and return it to the base station. λ _u ⁱ represents the equivalent SINR of user u in the i-th subcarrier group, i=1, 2,..., N _g , u=1, 2,..., U _T , n represents the subcarrier in the carrier group number. in ${\mathrm{\Φ}}_{u,\mathrm{no}}^i={\left|h_{u,\mathrm{no}}^i\right|}^2/({\left|h_{u,\mathrm{no}}^i\right|}^2+{\mathrm{\σ}}^2),$ H _u,n ⁱ represents the channel fading coefficient of the u-th user on the n-th subcarrier in the i-th carrier group, and ^σ2 represents the noise variance.

After receiving part of the channel information returned by the mobile station, the base station calculates the user's equivalent average SINR according to the equivalent SINR, ${\stackrel{\‾}{\mathrm{\λ}}}_i=\sqrt[u_T]{(1+{\mathrm{\λ}}_i^1)(1+{\mathrm{\λ}}_i^2)\&Center\; Dot;\&Center\; Dot;\&Center\; Dot;(1+{\mathrm{\λ}}_i^{u_T})},$ Then calculate the user's equivalent normalized SINR value based on this, ${\mathrm{\δ}}_u^i=(1+{\mathrm{\λ}}_u^i)/{\stackrel{\‾}{\mathrm{\λ}}}_i,$ where i=1, 2, . . . , N _g , u=1, 2, . . . , U _T . Then do the iterative assignment.

In each iteration, the maximum value is selected from the U _T N _g δ _u ⁱ as the basis for deciding that the u-th user is assigned to the i-th subcarrier group.

During the allocation process, δ _u ⁱ is updated iteratively. When a user is allocated, the equivalent normalized SINR value on all subcarrier groups is set to zero, that is, the user no longer participates in subsequent allocation. When the number of users that can be accommodated by a certain subcarrier group reaches the maximum, the equivalent normalized SINR value of all users on it is zero, that is, this subcarrier group does not participate in subsequent allocation. At the same time, the impact on the equivalent average SINR value of the allocated user and full user subcarrier groups is removed, and the equivalent average SINR value of the carrier group and the equivalent normalized SINR value of the user are iteratively calculated to allocate the next user.

The advantage of the adaptive sub-carrier group allocation proposed by the present invention is: through the normalized allocation priority, the order of allocation is determined, and the allocation priority can be continuously updated during the allocation process, providing more accurate allocation As a result, not only the transmission rate of the system is increased, but also the computational complexity is reduced.

Description of drawings

FIG. 1 shows a system block diagram of an MC-CDMA transmitting end that performs subcarrier allocation according to partial channel information.

Fig. 2 shows the system block diagram of the user receiving end of the MC-CDMA system.

FIG. 3 shows the overall flow of system allocation calculation in the present invention.

Fig. 4 shows the flow of calculating the equivalent normalized SINR value δ _u ⁱ at the base station, (i=1, 2, ..., N _g , u = 1, 2, ..., U _T ).

Fig. 5 shows the flow of calculating the equivalent SINR value λ _u ⁱ by the UE, (i=l, 2, ..., N _g , u = l, 2, ..., U _T ).

FIG. 6 shows the flow of updating A, # and δ _u ⁱ at the base station (i=1, 2, ..., N _g , u = 1, 2, ..., U _T ).

Table 1 shows the specific parameters used by the system in the simulation.

Fig. 7 shows the performance comparison between the present invention and the RCG algorithm and the random algorithm when the total number of users is 32.

Fig. 8 shows the performance comparison between the present invention and the RCG algorithm and the random algorithm when the total number of users is 64.

Fig. 9 shows the performance comparison between the present invention and the RCG algorithm and the random algorithm when the total number of users is 128.

Detailed ways

The invention will be described in detail below through the accompanying drawings and embodiments.

FIG. 1 shows a system block diagram of an MC-CDMA transmitter that allocates subcarrier groups according to returned partial channel information. Assume that the number of active users in the system is U _T , and the total number of subcarriers is M. The base station knows part of the channel information returned by the mobile station, and calculates the equivalent normalized SINR value δ _u ⁱ . The length of the spreading code is set to N, and the number of subcarrier groups is N _g =M/N.

The base station implements equal power allocation to all users, and maximizes the total transmission rate of the system by optimizing the selection of user subcarrier groups. Right now:

$\mathrm{<span\; class="notranslate">\; C</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; max</span>}\underset{\mathrm{<span\; class="notranslate">\; i</span>}}{\overset{{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; g</span>}}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}\underset{\mathrm{<span\; class="notranslate">\; u</span>}}{\overset{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}\mathrm{<span\; class="notranslate">\; B</span>}{\mathrm{<span\; class="notranslate">\; log</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; u</span>}}^{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; )</span>$

U _i is the number of users actually accommodated by the i-th subcarrier group, B is the subcarrier bandwidth, and λ _u ⁱ is the equivalent SINR of user u on subcarrier group i.

Fig. 2 shows the system block diagram of the user receiving end of the MC-CDMA system. The user feeds back its equivalent SINR on all subcarrier groups to the base station to participate in subcarrier group allocation. For the signal transmitted by the base station, the user terminal detects and restores user data.

FIG. 3 shows the overall flow of system allocation calculation in the present invention, which is used for subcarrier group allocation in FIG. 1 . The process starts from step 301 and enters into initialization step 302 . The specific operation process is as follows: For i=1, 2, ..., N _g , define the vector A _i to store the serial number of the user obtained from the i-th subcarrier component, and define #A _i as the number of elements in A _i number. The initialization process sets A _i =, #A _i =0.

Thereafter, enter step 303, for the ith subcarrier group, calculate the equivalent normalized SINR value δ _u ⁱ is the comparison basis for the uth user to be allocated to the ith subcarrier group, where i=1, 2,..., N _g , u=1, 2, . . . , U _T .

In step 304, start to enter the loop flow, and set the initial value u=1 of the counting variable.

In step 305, select the maximum value from δ _u ⁱ values (i=1, 2, ..., N _g , u = 1, 2, ..., U _T ), and obtain its sequence number u and i, Assign α and β respectively.

In step 306, following the result of the previous step, user α is assigned to the β carrier group.

In step 307, the values of A _i , #A _i and δ _u ⁱ are updated, where i=1, 2, . . . , N _g , u=1, 2, . . . , U _T .

In step 308, the count variable is incremented by one unit of measure, ie u=u+1.

In step 309, the counting variable is judged at this step, and if _u≤UT is true, then return to step 305, otherwise, enter step 310, and end the process.

Fig. 4 shows the flow of calculating the equivalent normalized SINR value δ _u ⁱ at the base station, (i=1, 2, ..., N _g , u = 1, 2, ..., U _T ).

The calculation process starts from step 401 and enters step 402 to calculate the equivalent SINR values of all users in each carrier group, that is, λ _u ⁱ , (i=1, 2, ..., N _g , u = 1, 2, ... , U _T ). Its specific calculation process will be shown in Figure 5.

In step 403, the initialization vector $B=1_{1\&times;u_T},$ $C=1_{1\&times;N_g}$ Represent unallocated users and sub-carrier groups that are not full of users, and #B and #C are defined to represent the number of elements in B and C, respectively. .

In step 404 update vectors B, C are received from FIG. 6 .

In step 405, the vector B' and C' are detected and assigned after the start of the allocation process for the following calculations, where B' is the sequence number set of non-1 elements of vector B, and C' is the sequence number set of non-1 elements of vector C.

In step 406, the counting variables i=1, i _c =C'(i) are initialized.

In step 407, calculate the average equivalent SINR of each subcarrier group, that is, the geometric mean of the equivalent SINR of all users

${\stackrel{<span\; class="notranslate">\; \&OverBar;</span>}{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}}_{{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}}<span\; class="notranslate">\; =</span>\sqrt[{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; T</span>}}]{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}}^{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}}^{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; T</span>}}}<span\; class="notranslate">\; )</span>}$

In step 408, the count variables u=1, u _b =B'(u) are initialized.

In step 409, calculate ${\mathrm{\&delta;}}_{u_b}^{i_c}=(1+{\mathrm{\&lambda;}}_{u_b}^{i_c})/{\stackrel{\&OverBar;}{\mathrm{\&lambda;}}}_{i_c},$ That is, the ratio of the user's equivalent SINR in a certain group to the average equivalent SINR.

In step 410, the count variable is incremented by one unit of measure, ie _uc = B'(u+1).

In step 411, judge the counting variable, if the counting variable is less than or equal to #B' (the number of unassigned users), then return to step 409 to continue the process, otherwise enter step 412.

In step 412, the count variable is incremented by one unit of measure, i _c =C'(i+1).

In step 413, judge the counting variable, if the counting variable is less than or equal to #C (the number of unallocated subcarrier groups), then return to step 407 to continue the process, otherwise enter step 414 and end.

Fig. 5 shows the process of calculating the equivalent SINR value λ _u ⁱ at the user end, (i=1, 2, ..., N _g , u = 1, 2, ..., U _T ), this process is in each mobile station.

From step 501, go to step 502, and initialize i=1 for the counting variable.

In step 503, calculate ${\mathrm{\&Phi;}}_{u,\mathrm{no}}^i={\left|h_{u,\mathrm{no}}^i\right|}^2/({\left|h_{u,\mathrm{no}}^i\right|}^2+{\mathrm{\&sigma;}}^2).$

In step 504, the equivalent SINR value of the user on the subcarrier group is calculated:

${\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; u</span>}}^{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; \&Phi;</span>}}_{\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; no</span>}}^{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; /</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\underset{\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; \&Phi;</span>}}_{\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; no</span>}}^{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; )</span>$

In step 505, the count variable is incremented by one unit of measure, i=i+1.

In step 506, judge the counting variable, if the counting variable is less than or equal to N _g , return to step 503 to continue the calculation process, otherwise enter step 507 to end the process.

Fig. 6 shows the flow of updating A, #A and δ _u ⁱ (i=1, 2, ..., N _g , u=1, 2, ..., U _T ). Enter step 602 from step 601 to update A _β and #A _β . The specific process is as follows: when user α is determined to be allocated to the β subcarrier group, put the sequence number of α into A _β , and update A _β Add 1 to the number of elements in , that is, #A _β =#A _β +1.

In step 603, a count variable i=1 is initialized.

In step 604, after user α is allocated to the subcarrier group, δ _α ⁱ is set to 0, where i=1, 2, . . . , N _g , and this user does not participate in subsequent allocation.

In step 605, the counting variable is judged, and when i=β is true, go to step 606, otherwise go to step 608.

In step 606, the count variable is judged, and when #A _β =N is true, enter step 607, otherwise, enter step 608.

In step 607, when the number of users accommodated by the β-th subcarrier group reaches the maximum number of users it can accommodate, set δ _u ^β to 0, where u=1, 2, ..., U _T , this carrier group does not Then participate in the subsequent distribution.

In step 608, the count variable is incremented by one unit of measure, i=i+1.

In step 609, in the vectors B and C, the elements corresponding to the allocated users and the full subcarrier groups are set to 0, indicating that the elements have been allocated and no longer participate in the calculation in the update calculation.

In step 610, judge the counting variable, if i≤N _g return to step 604 to continue the update process, otherwise enter step 611 to end.

performance analysis

Figures 7 to 9 show performance comparisons between the present invention and the traditional RCG allocation algorithm and random allocation algorithm in the group MC-CDMA scheme under the condition of 6-path channel. RCG is a well-known subcarrier allocation algorithm, which is suitable for packet MC-CDMA schemes through corresponding improvements, and its performance is close to optimal, while its complexity is relatively low. The random allocation algorithm is to randomly allocate carrier groups to users. The allocation is simple, but the performance is also limited. Since the optimal algorithm is difficult to realize, RCG, random algorithm and the algorithm of the present invention are used for performance simulation comparison.

Table 1 gives the specific parameters involved in the simulation system, such as bandwidth, carrier frequency, number of users, number of subcarriers, length of spreading code, and so on. For simplicity and fairness, equal power distribution is used in the simulation.

Figures 7-9 show the performance simulation diagrams of 32, 64, and 128 users respectively, the abscissa indicates the transmission signal-to-noise ratio, and the ordinate indicates the total transmission rate of the system. It can be seen from the simulation diagram that the performance of the algorithm of the present invention is obviously better than that of the random algorithm, and also better than that of the RCG algorithm.

Complexity Analysis

Here, a brief complexity analysis of the algorithm proposed by the present invention is carried out:

分配过程中更新δ_u ⁱ并确定用户优先级的复杂度近似为

当系统子载波数较大时N_g＞logU_T，算法的复杂度近似为

可以看出，算法中初始化和更新部分的复杂度在一个数量级，虽然算法进行迭代的分配方案，迭代部分看似复杂，其实并没有引进大量的复杂度，因此本发明的计算复杂度约为

即本发明的复杂度与用户数和子载波组数的乘积呈线性关系。The complexity of the initial calculation of δ _u ⁱ , (i=, 2, ..., N _g u = 1, 2, ..., U _T ) is approximately

The complexity of updating δ _u ⁱ and determining user priority during the allocation process is approximately

When the number of sub-carriers in the system is large, N _g > log U _T , the complexity of the algorithm is approximately

It can be seen that the complexity of the initialization and update part of the algorithm is an order of magnitude. Although the iterative distribution scheme of the algorithm seems complicated, it does not introduce a lot of complexity. Therefore, the computational complexity of the present invention is about

That is, the complexity of the present invention has a linear relationship with the product of the number of users and the number of subcarrier groups.

在最不理想的信道状态情况下，其复杂度为

也就是说RCG算法的复杂度在

之间浮动。As a reference, we introduce the classic algorithm RCG algorithm in the OFDMA system to compare the complexity. For the sake of fairness, we make some changes to the RCG algorithm so that it can be used in the grouping subcarrier system. We know that the complexity of the RCG algorithm is mainly determined by the state of the channel, and its complexity can be roughly analyzed from two extreme situations. In the case of the most ideal channel state, its complexity is

In the case of the least ideal channel state, its complexity is

That is to say, the complexity of the RCG algorithm is

floating between.

本发明降低了实施中的计算复杂度。In practical systems, the maximum complexity of an algorithm is often one of the important factors that determine its feasibility. In the actual MC-CDMA system, using a shorter intra-group spreading code length is more conducive to the implementation of multi-user detection, so the maximum complexity relative to the RCG algorithm is

The invention reduces the computational complexity in implementation.

Table 1

Simulation parameters Comments (units) bandwidth 1.25 (MHz) carrier frequency 2(G Hz) Number of subcarriers (M) 128 Duration of one OFDM symbol 107.7 (microseconds) guard interval 5.13 (microseconds) Maximum multi-frequency shift 83.1(Hz) Number of users ( _UT ) 32, 64, 128 Spreading code length (N) 32 Expected bit error rate at the receiver ^10-4 Mobile station moving speed 44(km/h)

Claims (6)

1. A dynamic sub-carrier group distribution scheme suitable for multi-carrier CDMA (MC-CDMA) system is characterized in that a base station firstly determines the initial normalized distribution priority of users according to partial channel information fed back by the users, distributes the users with the highest priority to corresponding carrier groups, and then gradually and iteratively updates the normalized distribution priority to the users in the distribution process, wherein each iteration process corresponds to one user to the distributed carrier groups.

2. The partial channel information fed back from the user to the base station as claimed in claim 1, wherein: the user does not need to return all channel information of the base station, and only returns the equivalent signal-to-noise ratio (SINR), namely lambda, of the user in each subcarrier group _u ⁱ Wherein i =1,2,. Cndot., N _g ，u＝1，2，...，U _T . Here N _g Indicating the number of sub-carrier packets, U _T Indicating the number of system active users.

3. The user equivalent SINR value according to claim 2 is calculated by:

wherein

Here, N denotes the spreading code length, H _u，n ⁱ Represents the channel fading coefficient, sigma, of the u-th user on the n-th carrier of the i-th sub-carrier group ² Representing the noise variance.

4. The normalized allocation priority based subcarrier group allocation scheme according to claim 1, wherein the allocation steps are as follows:

base station calculates user equivalent normalized SINR value delta _u ⁱ I.e. the normalized allocation priority;

from delta _u ⁱ Selecting the maximum value from the values, and numbering the user and the subcarrier group corresponding to the maximum value (respectively marked as alpha and beta);

corresponding the alpha user to beta sub-carrier group;

updating delta _u ⁱ And repeating the above steps until all the active users are corresponding to the corresponding subcarrier groups.

5. The user equivalent normalized SINR value of claim 4 calculated as follows: firstly, calculating equivalent average SINR value of carrier group

Calculating an equivalent normalized SINR value according to the equivalent SINR value

6. Update δ according to claim 4 _u ⁱ The method of (2), characterized by: when the alpha user is allocated, order

I.e. the alpha-th user is no longer involved in the subsequent allocation. When the number of users accommodated by the beta sub-carrier groups reaches the full users, the order is given

I.e. the beta group is no longer involved in the subsequent allocation. Meanwhile, the influence of the distributed users and the sub-carrier groups on the calculation of the equivalent average SINR value of the carrier group is removed, and the equivalent average SINR value of the carrier group and the equivalent normalized SINR value of the users are calculated in an iterative mode.

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