CN101827061A - Downstream link sub-carrier allocation and peak-to-mean suppression method of orthogonal frequency division multiplexing system - Google Patents

Abstract

The invention relates to a downlink subcarrier allocation and peak-to-average ratio suppression method of an orthogonal frequency division multiplexing system, belonging to the technical field of wireless communication. According to the upper limit of the downlink transmission power, the current downlink transmission link channel status of each user equipment, the service quality requirements of each transmission service, and the queuing status information of each service flow, combined with the peak-to-average ratio suppression of OFDM signals, the method can Subcarriers are adaptively allocated for each downlink transmission service, and no sideband information and extra power are required for transmission. The method can effectively suppress the peak-to-average ratio of the OFDM signal while allocating subcarriers reasonably, can realize the adaptive modulation of the OFDM downlink, and improve the spectrum efficiency of the system. The method is suitable for a wireless communication system in which the downlink transmission link is based on the OFDM multiple access mode.

Description

Downlink Subcarrier Allocation and Peak-to-Average Ratio Suppression Method for Orthogonal Frequency Division Multiplexing System

technical field

The invention relates to a downlink subcarrier allocation and peak-to-average ratio suppression method of an orthogonal frequency division multiplexing system, belonging to the technical field of wireless communication.

Background technique

Orthogonal Frequency Division Multiplexing (OFDM) technology has been used in digital TV broadcasting and high-speed wireless network, and it will be the core transmission technology of the next generation terrestrial wireless communication system. OFDM technology divides the entire transmission frequency band into multiple orthogonal sub-carriers, converts high-speed data signals into parallel low-speed sub-data streams, and modulates them for transmission on each sub-carrier. Orthogonal sub-carrier signals can be separated by using correlation technology at the receiving end, which can reduce the mutual interference between sub-carriers, thereby greatly improving the spectrum utilization of the system; at the same time, the signal bandwidth on each sub-carrier of OFDM is smaller than the correlation bandwidth of the channel , for each subcarrier can be regarded as flat fading, so that inter-symbol interference can be eliminated, making OFDM very effective against the influence of wireless channel multipath.

In the OFDM transmission system, due to the frequency selectivity and time-varying characteristics of the wireless channel, for a system in which all sub-channels use a fixed modulation scheme, the sub-channel with severe fading will have a large bit error rate, resulting in The bit error rate of the whole system is high, but the sub-channels with better channel quality are not fully utilized, thus reducing the spectrum utilization of the system. The current spectrum resources are increasingly tight, so the adaptive resource allocation for OFDM is of great significance.

At the same time, there is a very important defect in OFDM multi-carrier modulation: high peak-to-average ratio of transmission signals.

Existing methods often divide the above problem into two independent problems to solve. For subcarrier resource allocation, some literatures provide subcarrier resource allocation optimization methods with the goal of maximizing system throughput, and some literatures provide resource allocation methods with the optimization goal of minimizing system bit error rate performance. These methods To a certain extent, it embodies the idea of cross-layer design. Using cross-layer design to allocate OFDM subcarrier resources has become a research hotspot in the field of OFDM technology; and there are currently three types of methods for OFDM signal peak-to-average ratio. Distortion, coding, and signal scrambling. Signal pre-distortion methods mainly include limiting filter method, compression and expansion method, etc. This method is simple and easy, but it deteriorates the performance of the system bit error rate; , select the encoding pattern with small peak-to-average ratio for transmission. The main encoding methods include Gray complementary sequence, etc. This method is suitable for systems with a small number of subcarriers and stable performance. When the number of subcarriers is large, encoding and decoding are too complicated; signal scrambling methods Mainly, the information sequence is linearly transformed, and the sequence transformation form with a relatively low peak-average ratio is selected for transmission. Such methods mainly include partial sequence transmission method, selective sequence method, etc. The signal scrambling method does not lose the performance of the system bit error rate, but the calculation Complicated, requiring additional sideband information or power to be transmitted.

Contents of the invention

The purpose of the present invention is to propose a method for subcarrier allocation and peak-to-average ratio suppression in the downlink of an OFDM system, to adaptively allocate subcarrier resources for downlink transmission services, and to effectively suppress the peak-to-average ratio of OFDM symbols, And it does not need to transmit sideband information and extra power, and is suitable for a wireless communication system using OFDMA in the downlink.

The OFDM system downlink subcarrier allocation and peak-to-average ratio suppression method proposed by the present invention comprises the following steps:

(1) Construct the traffic channel transmission frame of the downlink of the OFDM system. The transmission frame includes a frame header, a control subframe and a service subframe. The frame header adopts a pseudo-random sequence, and the service subframe The frame adopts the block allocation method, and all the subcarriers of the downlink are divided into M consecutive subcarrier blocks, and the modulation mode of the subcarriers in each subcarrier block is the same;

(2) The modulation mode of the subcarriers in each subcarrier block is set as multi-ary quadrature amplitude modulation, and each subcarrier block is calculated and assigned to J users in different channel states in the current downlink transmission link For all user equipment in the device, the modulation method with the largest number of information bits carried by the subcarrier in the subcarrier block, the modulation method set B = {b _j (m)..., 1≤j≤J, 1≤m≤M }, where b _j (m) is the number of bits carried by each subcarrier in the subcarrier block, j represents the serial number of the user equipment in the current transmission link, and m represents the serial number of the subcarrier block;

(3) Retrieve the above set of modulation schemes, obtain the modulation scheme that maximizes the number of transmission bits of the jth user equipment, assign the subcarrier block corresponding to the modulation scheme to the jth user equipment, and finally obtain all subcarrier blocks initial allocation results;

(4) If the buffer length of the u-th transmission service belonging to the j-th user equipment is greater than the number of bits b _j (m) carried by the above subcarriers, it means that the current u-th transmission service has data to be transmitted. If it belongs to the j-th If the buffer length of the u-th transmission service of a user equipment is less than the number of bits b _j (m) carried by the above-mentioned subcarriers, it means that the current u-th transmission service has no data to be transmitted, and the services with data to be transmitted constitute a transmission service set O', assign weights to each transmission service in the transmission service set O according to the quality of service requirements of the transmission services, sort the transmission services in the transmission service set O' according to the size of the weights, and select from the sorted transmission service set In O", the first V transmission services are selected as the services that need to be transmitted in the current downlink transmission frame. The buffer length occupied by the V transmission services is the transmission rate requirement of the user equipment, where U is the maximum transmission rate that the user equipment can transmit. Number of services, 1≤u≤U;

(5) Judging the transmission rate requirements of the above step (4) according to the initial allocation results of the above step (3), if the transmission rate of the subcarrier block allocated to the jth user equipment is greater than the above-mentioned corresponding to the user equipment service transmission rate requirements, then reallocate the subcarrier blocks of the user equipment, and form a subcarrier block set W that needs to be reallocated, select a subcarrier block from the subcarrier block set W, and assign the selected subcarrier block Allocate to the jth user equipment, so that the transmission rate of the jth user equipment subcarrier block is greater than or equal to the above service transmission rate requirement, until the subcarrier block set W becomes an empty set or the subcarrier blocks of all user equipment are allocated;

(6) After the above distribution, the service set O' _j that needs to be transmitted by the jth user equipment is formed, and the services in the service set O' _j are sorted according to the service quality requirements of the transmission service, starting from the first service, if the service If the buffer length is greater than the number of bits carried by the current remaining subcarriers, the number of bits transmitted by the current service is the number of bits carried by the remaining subcarriers; The number is the service buffer length, and delete the transmission service less than the number of bits carried by the minimum subcarrier from _O'j , and allocate the number of bits carried by the remaining subcarriers to the transmission service with high service quality requirements;

(7) According to the order of the business in the above _O'j , number the transmission business of each user equipment in the J user equipments respectively, according to the number of bits of the business transmission allocated in the above step (6), the above-mentioned allocated The continuous subcarriers in the subcarrier block are allocated to each transmission service of the user equipment, and the starting position numbers of the subcarriers occupied by the current transmission services are recorded. After all the transmission services of the user equipment are allocated, the subcarrier allocation information is obtained , and calculate the peak-to-average ratio of the OFDM symbols of the current service subframe, if the current peak-to-average ratio is less than the set peak-to-average ratio threshold, the above-mentioned subcarrier allocation information is formed into a control subframe, and the control subframe is related to the service The subframes are composed of traffic channel transmission frames and sent; if the current peak-to-average ratio is greater than the set peak-to-average ratio threshold or less than the peak-to-average ratio of the OFDM symbols formed by the previous allocation, record the peak-to-average ratio, and according to The service number in _O'j rearranges the transmission services in _O'j , and records the subcarrier starting position numbers occupied by the current transmission services;

(8) According to the above rearrangement, repeat step (7) until the peak-to-average ratio of the OFDM symbol of the current service subframe is less than the set peak-to-average ratio threshold, or reaches the peak-to-average ratio after all business arrangements. ratio is the smallest, the subcarrier allocation adjustment is completed, and the traffic channel transmission frame is formed and sent.

Compared with the existing OFDM subcarrier allocation method and the peak-to-average ratio suppression method, the OFDM downlink subcarrier allocation and peak-to-average ratio suppression method proposed by the present invention have the following advantages:

1. Compared with the traditional subcarrier allocation, the method of the present invention can improve spectral efficiency and meet the quality of service requirements:

The present invention constructs the OFDM downlink transmission frame structure, puts the subcarrier allocation information in the control subframe and transmits it to the user equipment at the same time as the service subframe, and saves unnecessary control channels.

The present invention adopts the idea of cross-layer design, makes full use of the physical layer channel state information, transmission power information and application layer business service quality requirement information, dynamically allocates subcarriers for the current business transmission frame, and overcomes the static subcarrier allocation mode. The impact of quality requirements on the transmission performance of the system, while improving the spectral efficiency of the system.

The subcarrier allocation in the present invention adopts the combination of subcarrier block allocation and continuous subcarrier allocation in the subcarrier block, which improves the spectral efficiency of the system.

2. Compared with the existing peak-to-average ratio suppression method, the method of the present invention does not lose system performance, and does not require additional transmission power and sideband information:

The existing signal distortion-like peak-to-average ratio suppression method is simple to implement, but it causes the loss of system performance; although the non-signal distortion-like peak-to-average ratio suppression method does not cause performance loss, it requires additional transmit power or sideband information. Cause waste of power resources or bandwidth resources. The invention combines peak-to-average ratio suppression with subcarrier allocation to adjust the subcarrier allocation mode of some services, and the method is simple and effective.

Subcarrier allocation information needs to be transmitted as control information in all adaptive subcarrier allocation systems. The present invention can achieve the purpose of peak-to-average ratio suppression by adjusting the subcarrier allocation positions of some services while meeting the system service quality requirements. , without wasting side information and extra power.

3. The present invention combines peak-to-average ratio suppression with subcarrier allocation, and has good adaptability:

The invention proposes an OFDM downlink subcarrier allocation method and a peak-to-average ratio suppression method, which are applicable to all wireless communication systems in which the downlink adopts OFDMA mode and can adapt to the time-varying characteristics of wireless channels.

Description of drawings

Fig. 1 is the block flow diagram of the inventive method;

Fig. 2 is a schematic diagram of an OFDM downlink service transmission frame in the method of the present invention;

Fig. 3 is a schematic diagram of the control subframe 1 of the service transmission frame in the method of the present invention;

Fig. 4 is a schematic diagram of the control subframe 2 of the service transmission frame in the method of the present invention;

Fig. 5 is the flowchart of adjusting the subcarrier allocation mode based on the principle of peak-to-average ratio suppression in the method of the present invention;

Fig. 6 is the comparative figure of the peak-to-average ratio suppression result of the method of the present invention and the partial sequence transmission method;

Fig. 7 is a comparison diagram of peak-to-average ratio suppression results when different peak-to-average ratio thresholds are used in the method of the present invention.

Detailed ways

The OFDM system downlink subcarrier allocation and peak-to-average ratio suppression method proposed by the present invention has a flow chart as shown in Figure 1, including the following steps:

(1) Construct the traffic channel transmission frame of the downlink of the OFDM system. The transmission frame includes a frame header, a control subframe and a service subframe. The frame header adopts a pseudo-random sequence, and the service subframe The frame adopts the block allocation method, and all the subcarriers of the downlink are divided into M consecutive subcarrier blocks, and the modulation mode of the subcarriers in each subcarrier block is the same;

(2) The modulation mode of the subcarriers in each subcarrier block is set as multi-ary quadrature amplitude modulation, and each subcarrier block is calculated and assigned to J users in different channel states in the current downlink transmission link For all user equipment in the device, the modulation method with the largest number of information bits carried by the subcarrier in the subcarrier block, the modulation method set B = {b _j (m)..., 1≤j≤J, 1≤m≤M }, where b _j (m) is the number of bits carried by each subcarrier in the subcarrier block, j represents the serial number of the user equipment in the current transmission link, and m represents the serial number of the subcarrier block;

(3) Retrieve the above set of modulation schemes, obtain the modulation scheme that maximizes the number of transmission bits of the jth user equipment, assign the subcarrier block corresponding to the modulation scheme to the jth user equipment, and finally obtain all subcarrier blocks initial allocation results;

(4) If the buffer length of the u-th transmission service belonging to the j-th user equipment is greater than the number of bits b _j (m) carried by the above subcarriers, it means that the current u-th transmission service has data to be transmitted. If it belongs to the j-th If the buffer length of the u-th transmission service of a user equipment is less than the number of bits b _j (m) carried by the above-mentioned subcarriers, it means that the current u-th transmission service has no data to be transmitted, and the services with data to be transmitted constitute a transmission service set O', assign weights to each transmission service in the transmission service set O' according to the quality of service requirements of the transmission services, sort the transmission services in the transmission service set O' according to the size of the weights, and select from the sorted transmission services Select the first V transmission services in the set O" as the services that need to be transmitted in the current downlink transmission frame, and the buffer length occupied by the V transmission services is the transmission rate requirement of the user equipment, where U is the transmission rate that the user equipment can transmit The maximum number of services, 1≤u≤U;

(5) Judging the transmission rate requirements of the above step (4) according to the initial allocation results of the above step (3), if the transmission rate of the subcarrier block allocated to the jth user equipment is greater than the above-mentioned corresponding to the user equipment service transmission rate requirements, then reallocate the subcarrier blocks of the user equipment, and form a subcarrier block set W that needs to be reallocated, select a subcarrier block from the subcarrier block set W, and assign the selected subcarrier block Allocate to the jth user equipment, so that the transmission rate of the jth user equipment subcarrier block is greater than or equal to the above service transmission rate requirement, until the subcarrier block set W becomes an empty set or the subcarrier blocks of all user equipment are allocated;

(6) After the above distribution, the service set O' _j that needs to be transmitted by the jth user equipment is formed, and the services in the service set O' _j are sorted according to the service quality requirements of the transmission service, starting from the first service, if the service If the buffer length is greater than the number of bits carried by the current remaining subcarriers, the number of bits transmitted by the current service is the number of bits carried by the remaining subcarriers; The number is the service buffer length, and delete the transmission service less than the number of bits carried by the minimum subcarrier from _O'j , and allocate the number of bits carried by the remaining subcarriers to the transmission service with high service quality requirements;

(7) According to the order of the business in the above _O'j , number the transmission business of each user equipment in the J user equipments respectively, according to the number of bits of the business transmission allocated in the above step (6), the above-mentioned allocated The continuous subcarriers in the subcarrier block are allocated to each transmission service of the user equipment, and the starting position numbers of the subcarriers occupied by the current transmission services are recorded. After all the transmission services of the user equipment are allocated, the subcarrier allocation information is obtained , and calculate the peak-to-average ratio of the OFDM symbols of the current service subframe, if the current peak-to-average ratio is less than the set peak-to-average ratio threshold, the above-mentioned subcarrier allocation information is formed into a control subframe, and the control subframe is related to the service The subframes are composed of traffic channel transmission frames and sent; if the current peak-to-average ratio is greater than the set peak-to-average ratio threshold or less than the peak-to-average ratio of the OFDM symbols formed by the previous allocation, record the peak-to-average ratio, and according to The service number in _O'j rearranges the transmission services in _O'j , and records the subcarrier starting position numbers occupied by the current transmission services;

(8) According to the above rearrangement, repeat step (7) until the peak-to-average ratio of the OFDM symbol of the current service subframe is less than the set peak-to-average ratio threshold, or reaches the peak-to-average ratio after all business arrangements. ratio is the smallest, the subcarrier allocation adjustment is completed, and the traffic channel transmission frame is formed and sent.

The embodiment of the method of the present invention is described in detail below in conjunction with accompanying drawing, comprises the following steps:

(1) According to the OFDM downlink service transmission frame structure, as shown in Figures 2, 3, and 4, set the downlink baseband Nyquist sampling frequency as f _b , and control the total number of subcarriers contained in OFDM symbols in subframes 1 and 2 is N _c , the control subframes 1 and 2 adopt BPSK modulation; the total number of subcarriers contained in the OFDM symbol in the service subframe is N _d , where N _d =LN _c , L=4 ^p (p is a positive integer, designed by the system Personnel setting), the business subframe only contains one OFDM symbol, and its subcarrier allocation information and subcarrier modulation information are determined by control subframes 1 and 2.

The control subframe 1 carries the relevant parameter information of M (determined by the number of subcarriers in the control subframe and the number of subcarriers in the service subframe) subcarrier blocks, where the relevant parameters of the mth subcarrier block are represented by {m, C(m), b (m)} indicates that m is the number of the subcarrier block, each subcarrier block contains s subcarriers, C(m) is the number of the user equipment owning the subcarrier block, and b(m) is each subcarrier block of the subcarrier block The carrier carries the number of bits. Each downlink service adopts the continuous subcarrier allocation method, and the control subframe 2 carries the subcarrier allocation information of each transmission service, and {G(u), N(u)} represents the subcarrier allocation information of the uth service , G(u) is the serial number of the service, and N(u) is the position of the subcarrier at which the service terminates. Each service subframe OFDM symbol contains V services.

V＝floor(2N _c /(Q+log ₂ (LN _c )))(1)

(2) Determine all the alternative modulation modes of the subcarrier block, assign the same transmit power p to each downlink service subcarrier, and assume that when the mth subcarrier block is allocated to the jth user equipment, each subcarrier can carry b _j (m) bits, then the number of bits that can be carried by the subcarrier with the best channel condition is b _{j, max} (m), that is

Where: H _j (n) is the downlink channel impulse response of the nth subcarrier; BER _req is the bit error rate requirement of the current user equipment after signal detection; σ ² _j is the average power of channel noise. For the mth subcarrier block, let b _j (m) = b _{j, max} (m), then the average bit error rate of the subcarrier block

${\mathrm{<span\; class="notranslate">\; BER</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}}{\overset{\mathrm{<span\; class="notranslate">\; ms</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; \{</span>\frac{\mathrm{<span\; class="notranslate">\; 3</span>}\mathrm{<span\; class="notranslate">\; p</span>}{<span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; |</span>}^{\mathrm{<span\; class="notranslate">\; 2</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">\; 2</span>}}^{{\mathrm{<span\; class="notranslate">\; b</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; \&sigma;</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; \}</span><span\; class="notranslate">\; /</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

If BER _j,m >BER _req , then b _j (m)=b _j (m)-1, continue to execute formula (3) until the average bit error rate meets the requirement.

All alternative modulation modes when the subcarrier blocks are allocated to different user equipments are calculated according to the above method.

(3) Initially allocate subcarrier blocks according to the principle of maximizing the transmission rate, let _Aj be the set of subcarrier blocks allocated to the jth user equipment, which is initialized to be empty. According to the principle of maximizing the total transmission rate of the downlink, the subcarrier blocks are initially allocated. Search for the modulation scheme with the largest number of transmitted bits for the mth subcarrier block, that is,

${\mathrm{<span\; class="notranslate">\; j</span>}}^{<span\; class="notranslate">\; *</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="arg\; max"\; filenames="HSA00000066040800013.png,HSA00000066040800021.png"\; state="\{\{state\}\}">arg</figure-callout></span><figure-callout\; id="1"\; label="arg\; max"\; filenames="HSA00000066040800013.png,HSA00000066040800021.png"\; state="\{\{state\}\}">\; </figure-callout>}\underset{}{\mathrm{<span\; class="notranslate">\; </span>}}\underset{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; \&le;</span>\mathrm{<span\; class="notranslate">\; j</span>}<span\; class="notranslate">\; \&le;</span>\mathrm{<span\; class="notranslate">\; J</span>}}{\mathrm{<span\; class="notranslate">max</span>}}<span\; class="notranslate">\; \{</span>{\mathrm{<span\; class="notranslate">\; b</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \}</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$

Then there are: $A_{j^{*}}=A_{j^{*}}\&cup;\left\{m\right\}---\left(5\right)$

Equations (4) and (5) are repeatedly executed for all subcarrier blocks to obtain the initial subcarrier block allocation results. However, the allocation at this time does not take into account the QoS requirements of the transmission service.

(4) Calculate the transmission rate requirement of the current transmission service, so that the occupied length of the FIFO cache currently storing the uth transmission service (belonging to the jth user equipment) is B(u), if it satisfies

$\mathrm{<span\; class="notranslate">\; B</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&Greater\; Equal;</span>\underset{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; \&le;</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; \&le;</span>\mathrm{<span\; class="notranslate">\; m</span>}}{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="min"\; filenames="HSA00000066040800013.png,HSA00000066040800021.png"\; state="\{\{state\}\}">min</figure-callout></span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; b</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 6</span>}<span\; class="notranslate">\; )</span>$

It is considered that the current u-th service has data to be transmitted, otherwise the service has no data transmission. The business that satisfies this condition at the current moment constitutes a business set O', and the number of business in O' is U'.

If U'>V, it is necessary to filter out V services to be transmitted. Assign different weights α to each service in the service set O', then there is T _req (u)=a(u)B _d (u), sort the U' services according to T _req , and select the first V services, And remove other business from O'. Assume that the system contains four types of services, namely CBR service, rtVBR service, nrtVBR service and UBR service. Here, O' is classified according to the purpose user equipment and service type to obtain the service set O' _{CBR, j} , O' _{rtVBR , j} , O' _{nrtBR, j} , and O' _{UBR, j} . Then the transmission rate requirements for each type of business are:

$\mathrm{<span\; class="notranslate">\; CBR</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; j</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}_{\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; \&Element;</span>{\mathrm{<span\; class="notranslate">\; o</span>}}_{\mathrm{<span\; class="notranslate">\; CBR</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; j</span>}}^{<span\; class="notranslate">\; /</span>}}\mathrm{<span\; class="notranslate">\; B</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ,</span>$

$\mathrm{<span\; class="notranslate">\; rtVBR</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; j</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}_{\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; \&Element;</span>{\mathrm{<span\; class="notranslate">\; o</span>}}_{\mathrm{<span\; class="notranslate">\; rtVBR</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; j</span>}}^{<span\; class="notranslate">\; /</span>}}\mathrm{<span\; class="notranslate">\; B</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ,</span>$

$\mathrm{<span\; class="notranslate">\; wxya</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; j</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}_{\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; \&Element;</span>{\mathrm{<span\; class="notranslate">\; o</span>}}_{\mathrm{<span\; class="notranslate">\; wxya</span>}}^{<span\; class="notranslate">\; /</span>}}\mathrm{<span\; class="notranslate">\; B</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ,</span>$

$\mathrm{<span\; class="notranslate">\; UBR</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; j</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}_{\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; \&Element;</span>{\mathrm{<span\; class="notranslate">\; o</span>}}_{\mathrm{<span\; class="notranslate">\; UBR</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; j</span>}}^{<span\; class="notranslate">\; /</span>}}\mathrm{<span\; class="notranslate">\; B</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; .</span>$

(5) Optimize and adjust subcarrier block allocation according to service transmission rate requirements. The purpose of adjusting the initial allocation of subcarrier block is to meet the QoS requirements of various services as much as possible. First adjust according to CBR(j).

Let R _j be the transmission rate that can be achieved by all subcarrier blocks initially assigned to the jth user equipment, R _j ^/ is the downlink service transmission rate requirement for the jth user equipment, and its initial value is:

${\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; \&Element;</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}}}\mathrm{<span\; class="notranslate">\; the\; s</span>}{\mathrm{<span\; class="notranslate">\; b</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ,</span>$

${\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}}^{<span\; class="notranslate">\; /</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; CBR</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; j</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; .</span>$

则集合A_j中子载波块可以进行重新分配。为了保证每次子载波块重新调整分配导致总传输速率的减少量最小，令e_j(m)为归一化传输速率减少量，由下式表示：Let W be the set of all subcarrier blocks that may need to be reallocated, for the jth user equipment if there is

Then the subcarrier blocks in the set A _j can be reallocated. In order to ensure that each subcarrier block re-adjustment allocation leads to the smallest reduction in the total transmission rate, let e _j (m) be the normalized transmission rate reduction, expressed by the following formula:

_ej (m)=(b(m) _-bj (m))/b(m), m∈W.(7)

则j＝j+1，继续执行；在满足

且W不为空集的情况下，计算选取W中使得e_j(m)最小的子载波块标号m(m当前属于第j^＊个用户设备)，若第j^＊个用户设备减掉子载波块m后能够达到的传输速率小于其业务传输速率要求，则子载波块m不能重新分配，从W中剔除m；否则子载波块重新分配给当前用户设备，更新针对第j和j^＊用户设备此时子载波块分配集合以及所分配子载波块能达到的传输速率。只要满足或W成为空集，则针对第j个用户设备的子载波块分配调整结束。继续对第j+1个用户设备执行同样的调整过程，直到所有用户设备子载波块分配调整完毕。According to CBR(j), the process of adjusting subcarrier block allocation starts from J=1, if any

Then j=j+1, continue to execute;

And when W is not an empty set, calculate and select the subcarrier block label m that makes e _j (m) the smallest in W (m currently belongs to the ^jth user equipment), if the ^jth user equipment subtracts the subcarrier If the transmission rate that can be achieved after block m is less than the service transmission rate requirement, then the subcarrier block m cannot be redistributed, and m is removed from W; otherwise, the subcarrier block is reassigned to the current user equipment, and the update is for the jth and j ^* user equipment At this time, the subcarrier block allocation set and the transmission rate that the allocated subcarrier blocks can achieve. as long as you are satisfied or W becomes an empty set, then the subcarrier block allocation adjustment for the jth user equipment ends. Continue to perform the same adjustment process on the j+1th user equipment until all user equipment subcarrier block allocations are adjusted.

The above process is to adjust subcarrier block allocation according to CBR(j), and use the same method to sequentially adjust subcarrier block allocation according to rtVBR(j), nrtVBR(j) and UBR(j). This method can ensure that more and more user equipments meet the service transmission rate requirement, and the total service transmission rate reduction of the downlink is minimal.

(6) Calculate the number of bits required to be transmitted by each service in the current frame. After the subcarrier block allocation is adjusted, the subcarrier block set of the jth user equipment is A _j , and the service set that the user equipment needs to transmit is denoted by _O'j . The services in O' _j are sorted according to the size of T _req (u), and T _req (u) reflects the QoS requirements of the services.

Let B ^/ (u) be the number of bits to be transmitted for each service. For all subcarrier blocks in set A _j and all services in set O' _j , if ∑B(u)<∑sb _j (m), then each service B ^/ (u) is equal to its FIFO buffer length B( u). If ∑B(u)＞∑sb _j (m) is satisfied, then

For each service B ^/ (u), remove all services smaller than the minimum word carrier transmission capacity min(b _j (m)) from O' _j . At this time, the transmission capacity of the remaining subcarriers is allocated to services with a large T _req (u). This not only embodies the principle of fair distribution, but also takes into account the QoS requirements of the business.

(7) Based on the principle of optimizing PAPR to allocate subcarriers for each service, the peak-to-average ratio of OFDM symbols in the downlink service subframe can be expressed as

$\mathrm{<span\; class="notranslate">\; PAPR</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 10</span>}\mathrm{<span\; class="notranslate">\; lg</span>}<span\; class="notranslate">\; (</span><span\; class="notranslate">\; (</span>\underset{\mathrm{<span\; class="notranslate">\; t</span>}}{\mathrm{<span\; class="notranslate">\; max</span>}}<span\; class="notranslate">\; \{</span>{<span\; class="notranslate">\; |</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; |</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \}</span><span\; class="notranslate">\; )</span><span\; class="notranslate">\; /</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; mean</span>}<span\; class="notranslate">\; \{</span>{<span\; class="notranslate">\; |</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; |</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \}</span><span\; class="notranslate">\; )</span><span\; class="notranslate">\; )</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 9</span>}<span\; class="notranslate">\; )</span>$

Where x(t) is a time-domain expression of OFDM symbols in a service subframe.

For the jth user equipment, mark all subcarriers included in the subcarrier block in A _j with temporary subcarrier position numbers, and establish a mapping table η _j corresponding to the actual position numbers. The services in O' _j are sorted according to B ^/ (u) from large to small, and marked with temporary service numbers, and a mapping table ψ _j corresponding to the actual service numbers is established. Let PAPR _th be the threshold value that can guarantee the working efficiency of the high power amplifier. In practice, PAPR _th can be obtained according to the characteristics of the amplifier and the empirical value of the peak-to-average ratio of OFDM symbols. In the subcarrier allocation process, the subcarrier position number occupied by each service in the subcarrier block allocated by the user equipment is adjusted according to the threshold value, so as to achieve the purpose of suppressing PAPR.

For all user equipments, according to the order of the temporary numbering of the current business in O _j ^/ , assign the corresponding number of sub-carriers to each business continuously, record the starting position number of the sub-carriers currently occupied by each business, according to the modulation of the sub-carriers in A _j The standard information and the number of service transmission bits in O' _j modulate each service to form a service OFDM symbol, and calculate the PAPR of the current OFDM symbol according to formula (7). If PAPR≤PAPR _th is satisfied, the current subcarrier allocation information is formed into a control subcarrier Frame OFDM symbols are framed with service OFDM symbols for transmission; if PAPR _k >PAPR _th , subcarrier allocation must be adjusted.

The process of adjusting the subcarrier allocation mode based on the principle of peak-to-average ratio suppression is shown in Figure 5. The adjustment process is performed on the subcarrier position numbers occupied by services in the allocated subcarrier blocks in each user equipment. The service sets of different user equipments may include different numbers of services. In order to reduce the amount of calculation, more than 4 services can be classified as 4 services, and only 1 service does not need to be adjusted. In this way, there are at most 24 service arrangements for a user equipment, and each arrangement corresponds to a service occupying a different subcarrier position number, that is to say, a maximum of 23 adjustments can be made. When adjusting for the jth user equipment, the subcarrier allocation method of other user equipment services remains unchanged, calculate the PAPR value of the current OFDM symbol every time an arrangement is changed, stop the adjustment if it reaches the threshold, and record the current subcarrier allocation result ; If the threshold cannot be reached, record the allocation result that reduces the PAPR, and continue to change the arrangement mode to adjust until the threshold is reached, or all the arrangement modes of all user equipments are adjusted to obtain the smallest possible peak-to-average ratio.

The following is a simulation example of the method of the present invention. The OFDM symbol in the downlink traffic channel control subframe has 1024 subcarriers, the symbol duration is 25.6 μs, the duration of the cyclic prefix is 3.2 μs, and L=16. Assume that there are 4 user equipments in the downlink of the current spot beam, and the channels of each user equipment are Rice channels, the Rice factors are 40, 44, 45 and 46 respectively, the signal-to-noise ratio is 15dB, and the bit error rate after subcarrier signal detection is The requirement is 5×10 ^-4 . Each user equipment (UT) has four services being transmitted respectively, and the service settings are shown in Table 1.

Table 1 Service transmission rate requirements setting

After the determination of the alternative modulation mode of each subcarrier block and the initial allocation of subcarrier blocks, the transmission rate B _j (1≤j≤4) that can be achieved by different types of transmission services belonging to each user equipment is calculated. At this time, the downlink The total transfer rate is B. After the subcarrier allocation is adjusted according to the transmission rate requirements of different types of transmission services of each user equipment, the transmission rate that can be achieved by different types of transmission services belonging to each user equipment is B _j ^/ (1≤j≤4), and the downlink The total transmission rate of the link is B ^/ . It can be seen from Table 2 that the initial subcarrier block allocation results can meet the different types of service transmission rate requirements of each user equipment after being adjusted according to the service transmission rate requirements.

Table 2 Service transmission rate after subcarrier block adjustment and allocation (Mbs ^-1 )

After allocating subcarriers to each service, the peak-to-average ratio suppression performance obtained by adjusting the subcarrier position number occupied by each user equipment service is simulated, and the complementary cumulative distribution function (CCDF, complementary cumulative distribution function) curve is used to describe it. After allocating subcarriers to each service, we simulated the peak-to-average ratio suppression after adjusting the position of the subcarrier occupied by the service of each user equipment.

In Figure 6, papr-origin represents the cumulative probability distribution CDF of peak-to-average ratio before adjustment, papr-adjust represents the cumulative probability distribution CDF of peak-to-average ratio after adjustment, and papr-pts represents the peak-to-average ratio after suppression using the partial transmission sequence method The cumulative probability distribution CDF of the peak-to-average ratio. At this time, the sequence block in the PTS method corresponds to the subcarrier block that each user equipment can allocate. It can be seen that the probability papr-adjust of PAPR less than 9.2dB is much larger than papr-pts, which means that the peak-to-average ratio of more OFDM symbols has been effectively suppressed; when the cumulative probability reaches 10e-4, papr-adjust is more than papr The PAPR that -pts can achieve is about 0.4dB.

The original PAPR curve in Figure 7 shows the peak-to-average ratio of OFDM symbols without joint optimization of the subcarrier allocation method, and the subcarrier allocation when the PAPR _th is 10.5dB, 9.0dB, 7.5dB and 0dB And the peak-average joint optimization results, it can be seen that the performance of these four cases has been greatly improved compared with the original PAPR. When the PAPR _th is 0dB, it means that each OFDM symbol must be jointly optimized. The peak-to-average ratio performance at this time is the best performance that the proposed method can achieve. It can be seen that when the PAPR _th is 7.5dB, it is close to the peak-to-average ratio suppression best performance. The probability that the peak-to-average ratio of the four curves is less than 10.5dB can reach or exceed 99.9%. As the value of PAPR _th becomes smaller, the peak-to-average ratio suppression performance that can be achieved by joint optimization is better, because only the OFDM symbols exceeding PAPR _th are processed by joint optimization.

Claims (1)

1. an OFDM system downlink subcarrier allocation and peak-to-average ratio suppression method, is characterized in that, the method comprises the following steps: (1) Construct the traffic channel transmission frame of the downlink of the OFDM system. The transmission frame includes a frame header, a control subframe and a service subframe. The frame header adopts a pseudo-random sequence, and the service subframe The frame adopts the block allocation method, and all the subcarriers of the downlink are divided into M consecutive subcarrier blocks, and the modulation mode of the subcarriers in each subcarrier block is the same; (2) The modulation mode of the subcarriers in each subcarrier block is set as multi-ary quadrature amplitude modulation, and each subcarrier block is calculated and assigned to J users in different channel states in the current downlink transmission link For all user equipment in the device, the modulation method with the largest number of information bits carried by the subcarrier in the subcarrier block, the modulation method set B = {b _j (m)..., 1≤j≤J, 1≤m≤M }, where b _j (m) is the number of bits carried by each subcarrier in the subcarrier block, j represents the serial number of the user equipment in the current transmission link, and m represents the serial number of the subcarrier block; (3) Retrieve the above set of modulation schemes, obtain the modulation scheme that maximizes the number of transmission bits of the jth user equipment, assign the subcarrier block corresponding to the modulation scheme to the jth user equipment, and finally obtain all subcarrier blocks initial allocation results; (4) If the buffer length of the u-th transmission service belonging to the j-th user equipment is greater than the number of bits b _j (m) carried by the above subcarriers, it means that the current u-th transmission service has data to be transmitted. If it belongs to the j-th If the buffer length of the u-th transmission service of a user equipment is less than the number of bits b _j (m) carried by the above-mentioned subcarriers, it means that the current u-th transmission service has no data to be transmitted, and the services with data to be transmitted constitute a transmission service set O, assign weights to each transmission service in the transmission service set O' according to the quality of service requirements of the transmission services, sort the transmission services in the transmission service set O according to the size of the weights, and select from the sorted transmission service set O Select the first V transmission services as the services that need to be transmitted in the current downlink transmission frame, and the buffer length occupied by the V transmission services is the transmission rate requirement of the user equipment, where U is the maximum number of services that the user equipment can transmit , 1≤u≤U; (5) Judging the transmission rate requirements of the above step (4) according to the initial allocation results of the above step (3), if the transmission rate of the subcarrier block allocated to the jth user equipment is greater than the above-mentioned corresponding to the user equipment service transmission rate requirements, then reallocate the subcarrier blocks of the user equipment, and form a subcarrier block set W that needs to be reallocated, select a subcarrier block from the subcarrier block set W, and assign the selected subcarrier block Allocate to the jth user equipment, so that the transmission rate of the jth user equipment subcarrier block is greater than or equal to the above service transmission rate requirement, until the subcarrier block set W becomes an empty set or the subcarrier blocks of all user equipment are allocated; (6) After the above distribution, the service set O' _j that needs to be transmitted by the jth user equipment is formed, and the services in the service set O' _j are sorted according to the service quality requirements of the transmission service, starting from the first service, if the service If the buffer length is greater than the number of bits carried by the current remaining subcarriers, the number of bits transmitted by the current service is the number of bits carried by the remaining subcarriers; The number is the service buffer length, and delete the transmission service less than the number of bits carried by the minimum subcarrier from _O'j , and allocate the number of bits carried by the remaining subcarriers to the transmission service with high service quality requirements; (7) According to the order of the business in the above _O'j , number the transmission business of each user equipment in the J user equipments respectively, according to the number of bits of the business transmission allocated in the above step (6), the above-mentioned allocated The continuous subcarriers in the subcarrier block are allocated to each transmission service of the user equipment, and the starting position numbers of the subcarriers occupied by the current transmission services are recorded. After all the transmission services of the user equipment are allocated, the subcarrier allocation information is obtained , and calculate the peak-to-average ratio of the OFDM symbols of the current service subframe, if the current peak-to-average ratio is less than the set peak-to-average ratio threshold, the above-mentioned subcarrier allocation information is formed into a control subframe, and the control subframe is related to the service The subframes are composed of traffic channel transmission frames and sent; if the current peak-to-average ratio is greater than the set peak-to-average ratio threshold or less than the peak-to-average ratio of the OFDM symbols formed by the previous allocation, record the peak-to-average ratio, and according to The service number in _O'j rearranges the transmission services in _O'j , and records the subcarrier starting position numbers occupied by the current transmission services; (8) According to the above rearrangement, repeat step (7) until the peak-to-average ratio of the OFDM symbol of the current service subframe is less than the set peak-to-average ratio threshold, or reaches the peak-to-average ratio after all business arrangements. ratio is the smallest, the subcarrier allocation adjustment is completed, and the traffic channel transmission frame is formed and sent.

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