CN104009954A

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Info

Publication number: CN104009954A
Application number: CN201410266072.0A
Authority: CN
Inventors: 乔耀军; 周骥; 蔡浞; 纪越峰
Original assignee: Beijing University of Posts and Telecommunications
Current assignee: Beijing University of Posts and Telecommunications
Priority date: 2014-06-13
Filing date: 2014-06-13
Publication date: 2014-08-27

Abstract

本发明涉及一种利用快速哈特莱变换(FHT)实现Flip-OFDM的方法，属于光通信技术领域。由于快速哈特莱变换(FHT)是一种实变换，使用FHT实现多载波的复用和解复用，算法复杂度只有传统快速傅立叶变换的一半。本发明在一个符号周期内就能实现符号翻转操作，得到正符号，而传统方案中需要两个符号周期。本发明中CP添加和去除和延时等操作是传统方案的一半。因此本发明具有实现复杂度低的优点，适合对成本和实现复杂度要求高的系统，例如无源光网络，室内光无线通信和数据中心之间互联等系统。

The invention relates to a method for realizing Flip-OFDM by using Fast Hartley Transform (FHT), which belongs to the technical field of optical communication. Since the Fast Hartley Transform (FHT) is a real transform, using FHT to realize multiplexing and demultiplexing of multiple carriers, the algorithm complexity is only half of that of the traditional Fast Fourier Transform. The present invention can realize the sign inversion operation within one symbol period, and obtain the positive sign, while two symbol periods are required in the traditional solution. In the present invention, operations such as CP addition and removal and delay are half of the traditional solution. Therefore, the present invention has the advantage of low implementation complexity, and is suitable for systems with high requirements on cost and implementation complexity, such as passive optical network, indoor optical wireless communication, and interconnection between data centers.

Description

Translated fromChinese

快速哈特莱变换实现Flip-OFDM的方法Fast Hartley Transform Method to Realize Flip-OFDM

技术领域technical field

本发明属于高速光通信领域，特别涉及一种Flip-OFDM产生的方法。 The invention belongs to the field of high-speed optical communication, in particular to a method for generating Flip-OFDM. the

背景技术Background technique

随着Internet技术的发展以及各种视频等业务的蓬勃发展，光传输和接入系统的容量需求也在不断增长。为了满足光传输系统不断增长的容量需求，近年来，光OFDM(O-OFDM)技术开始被大量研究。O-OFDM技术具备高频谱效率，抗色散和偏振模色散能力强等优点。O-OFDM技术分为两大类：相干OFDM系统和强度调制-直接检测OFDM(IM/DD O-OFDM)系统。其中IM/DD O-OFDM系统结构简单且实现成本低，适用于对实现复杂度及成本要求高的系统，例如无源光网络，室内光无线通信和数据中心互联等系统。 With the development of Internet technology and the vigorous development of various video services, the capacity requirements of optical transmission and access systems are also increasing. In order to meet the ever-increasing capacity requirements of optical transmission systems, optical OFDM (O-OFDM) technology has been extensively studied in recent years. O-OFDM technology has the advantages of high spectral efficiency, strong ability to resist dispersion and polarization mode dispersion, etc. O-OFDM technology is divided into two categories: coherent OFDM system and intensity modulation-direct detection OFDM (IM/DD O-OFDM) system. Among them, the IM/DD O-OFDM system has a simple structure and low implementation cost, and is suitable for systems that require high implementation complexity and cost, such as passive optical networks, indoor optical wireless communications, and data center interconnection systems. the

应用于IM/DD系统的OFDM信号必须是正实数信号，因为光强只能大于零且不能携带相位信息。现在常见的IM/DD O-OFDM技术有直流偏置OFDM(DCO-OFDM)，非对称截断OFDM(ACO-OFDM)和翻转OFDM(Flip-OFDM)。其中DCO-OFDM系统中需要较大的直流偏置使双极性的信号变为正信号，导致功率效率较低。ACO-OFDM和Flip-OFDM由于不需要较大的直流偏置，具有功率效率高的优势而且更适用于自适应的光系统中。同时，Flip-OFDM和ACO-OFDM具有相同的频谱效率和误码性能，但是Flip-OFDM接收端的复杂度是ACO-OFDM的一半。因此Flip-OFDM更具优势。 The OFDM signal applied to the IM/DD system must be a positive real number signal, because the light intensity can only be greater than zero and cannot carry phase information. Common IM/DD O-OFDM technologies include DC offset OFDM (DCO-OFDM), asymmetric truncated OFDM (ACO-OFDM) and flipped OFDM (Flip-OFDM). Among them, the DCO-OFDM system requires a large DC bias to make the bipolar signal into a positive signal, resulting in low power efficiency. ACO-OFDM and Flip-OFDM have the advantages of high power efficiency and are more suitable for adaptive optical systems because they do not require a large DC bias. At the same time, Flip-OFDM and ACO-OFDM have the same spectral efficiency and bit error performance, but the complexity of the receiving end of Flip-OFDM is half of that of ACO-OFDM. Therefore, Flip-OFDM has more advantages. the

在实现本发明的过程中，发明人发现现有的Flip-OFDM技术中至少存在以下问题： In the process of realizing the present invention, the inventor finds that there are at least the following problems in the existing Flip-OFDM technology:

1)现有的Flip-OFDM多采用快速傅里叶变换(Fast Fourier Transform-FFT)实现，由于FFT为复数运算，计算的复杂度较高。 1) The existing Flip-OFDM is mostly realized by Fast Fourier Transform (FFT). Since FFT is a complex operation, the computational complexity is high. the

2)现有的Flip-OFDM将一个符号周期扩展为两个符号周期，添加和去除CP，信道估计等操作需要进行两次，增加了实现的复杂度。 2) In the existing Flip-OFDM, one symbol period is extended to two symbol periods, operations such as adding and removing CPs, and channel estimation need to be performed twice, which increases the complexity of implementation. the

发明内容Contents of the invention

本发明提出了一种快速哈特莱变换(Fast Hartley Transform-FHT)实现Flip-OFDM的方法，应用于短距高速光通信。该方法在一个符号周期内实现翻转(Flip)，许多操作，例如添加和去除CP等，只需进行一次。而且FHT为实数运算，其算法复杂度是FFT的一半。因此相比传统的Flip-OFDM方案，本发明的复杂度降低一半。 The present invention proposes a Fast Hartley Transform-FHT method for realizing Flip-OFDM, which is applied to short-distance high-speed optical communication. This method implements Flip within one symbol period, and many operations, such as adding and removing CP, only need to be performed once. Moreover, FHT is a real number operation, and its algorithm complexity is half of that of FFT. Therefore, compared with the traditional Flip-OFDM scheme, the complexity of the present invention is reduced by half. the

附图说明Description of drawings

图1为改进型Flip-OFDM传输系统框图。 Fig. 1 is a block diagram of the improved Flip-OFDM transmission system. the

图2(a)为翻转(Flip)模块框图；图2(b)为解翻转(De-Flip)模块框图。 Figure 2(a) is a block diagram of the Flip module; Figure 2(b) is a block diagram of the De-Flip module. the

图3(a)为Flip模块前的OFDM符号；图3(b)为Flip模块后的Flip-OFDM符号。 Figure 3(a) is the OFDM symbol before the Flip module; Figure 3(b) is the Flip-OFDM symbol after the Flip module. the

图4为AWGN信道条件下，改进型和传统的Flip-OFDM系统的误码性能比较。 Fig. 4 shows the bit error performance comparison between the improved type and the traditional Flip-OFDM system under the AWGN channel condition. the

具体实施方式Detailed ways

图1为基于哈特莱变换的改进型Flip-OFDM原理框图，其中反哈特莱变换(Inverse-FHT)和哈特莱变换定义为： Figure 1 is a block diagram of the improved Flip-OFDM based on the Hartley transform, where the Inverse-Hartley transform (Inverse-FHT) and the Hartley transform are defined as:

${x x}_{n no} = = \frac{11}{N N} {Σ Σ}_{k k = = 00}^{N N - - 11} {X x}_{k k} cas cas ((\frac{22 πkn πkn}{N N})),, n no = = 0,1 0,1,, \cdot \cdot \cdot &Center Dot; \cdot &Center Dot;,, N N - - 11 - - - - - - ((11))$

${X x}_{k k} = = \frac{11}{N N} {Σ Σ}_{k k = = 00}^{N N - - 11} {x x}_{n no} cas cas ((\frac{22 πkn πkn}{N N})),, k k = = 0,1 0,1,, \cdot &Center Dot; \cdot &Center Dot; \cdot &Center Dot;,, N N - - 11 - - - - - - ((22))$

其中cas(.)＝cos(.)+sin(.).x为时域OFDM符号。X为频域数据信号。 Wherein cas(.)=cos(.)+sin(.).x is the time-domain OFDM symbol. X is a frequency domain data signal. the

显然，哈特莱变换为实数三角变换，因此如果实数星座用于子载波调制，生成的OFDM符号也是实的。如图一所示，数据序列首先进入实数星座映射模块101，生成的实数星座分配给偶载波，也就是奇载波置零。通过FHT模块102后，输出信号x是半波偶对称， Obviously, the Hartley transform is a real triangular transform, so if a real constellation is used for subcarrier modulation, the resulting OFDM symbols are also real. As shown in FIG. 1, the data sequence first enters the real number constellation mapping module 101, and the generated real number constellation is allocated to the even carrier, that is, the odd carrier is set to zero. After passing through the FHT module 102, the output signal x is half-wave evenly symmetrical,

${x x}_{n no + + N N / / 22} = = \frac{11}{N N} {Σ Σ}_{k k = = 00}^{\frac{N N}{22} - - 11} {X x}_{22 k k} cas cas ((22 π π * * 22 k k ((n no + + \frac{N N}{22})) / / N N)) = = \frac{11}{N N} {Σ Σ}_{k k = = 00}^{\frac{N N}{22} - - 11} {X x}_{22 k k} cas cas ((22 π π * * \frac{22 kn k n}{N N} + + 22 kπ kπ)) = = {x x}_{n no} - - - - - - ((33))$

因此，只需半个符号周期就可以携带整个OFDM符号的信息。FHT模块102的输出信号经过Flip模块103生成单极性信号。图2(a)为Flip模块103的结构：首先，我们通过符号剪裁模块201截取输入信号的前半个周期， Therefore, only half a symbol period can carry the information of the whole OFDM symbol. The output signal of the FHT module 102 passes through the Flip module 103 to generate a unipolar signal. Fig. 2 (a) is the structure of the Flip module 103: first, we intercept the first half cycle of the input signal by the symbol clipping module 201,

${y the y}_{k k} = = {x x}_{k k},, k k = = 0,1,2 0,1,2,, \cdot \cdot \cdot \cdot \cdot \cdot,, \frac{N N}{22} - - 11 - - - - - - ((44))$

然后我们通过极性分离模块202将y分解为， We then decompose y by polarity separation module 202 into,

${y the y}_{k k} = = {y the y}_{k k}^{+ +} + + {y the y}_{k k}^{- -} - - - - - - ((55))$

其中正数部分y⁺和负数部分y^-定义为， where the positive part y⁺ and the negative part^y- are defined as,

正数部分的传输位置不变，负数部分进行翻转后延时半个符号周期传输。最后两个部分通过符号复用模块203复用生成单极性符号The transmission position of the positive part remains unchanged, and the transmission of the negative part is delayed by half a symbol period after inversion. The last two parts are multiplexed by the symbol multiplexing module 203 to generate unipolar symbols

$\overset{&OverBar; &OverBar;}{x x} = = \{\begin{matrix} {y the y}_{k k}^{+ +} & 00 \leq \leq k k \leq \leq \frac{N N}{22} - - 11 \\ {y the y}_{k k - - \frac{N N}{22}}^{- -} & \frac{N N}{22} \leq \leq k k \leq \leq N N - - 11 \end{matrix} - - - - - - ((77))$

图3(a)所示，Flip模块103前符号为半波偶对称，图3(b)为Flip模块103后的正Flip-OFDM符号。 As shown in FIG. 3( a ), the symbols before the Flip module 103 are half-wave-even symmetrical, and FIG. 3( b ) shows the positive Flip-OFDM symbols after the Flip module 103 . the

在接收端，需要实现发射端的反操作，我们将详细介绍Flip模块103的反操作De-Flip模块104。如图2(b)所示，首先输入符号被符号分离模块204分为两个子符号，其中子符号1是前半个符号，子符号2是后半个符号。子符号1延时半个符号周期，子符号2进行极性翻转，然后通过符号相加模块205将两个子符号相加合并成一个符号，周期只有输入符号的一半。最后通过符号扩展模块206将这个符号延时扩展成半波偶对称的符号，周期与输入符号相同。经过FHT模块105和De-Mapper模块106最后恢复出发送数据序列。 At the receiving end, the inverse operation at the transmitting end needs to be implemented, and we will introduce the inverse operation De-Flip module 104 of the Flip module 103 in detail. As shown in FIG. 2( b ), first, the input symbol is divided into two sub-symbols by the symbol separation module 204, wherein sub-symbol 1 is the first half of the symbol, and sub-symbol 2 is the second half of the symbol. The sub-symbol 1 is delayed by half a symbol period, the polarity of the sub-symbol 2 is reversed, and then the two sub-symbols are added and combined into one symbol through the symbol addition module 205, and the period is only half of the input symbol. Finally, the symbol extension module 206 extends the delay of the symbol into half-wave even symmetrical symbols, and the period is the same as that of the input symbols. After the FHT module 105 and the De-Mapper module 106, the sent data sequence is finally restored. the

图4中比较了本发明和传统Flip-OFDM在AWGN信道条件下的误码性能。由于本发明采用FHT而传统的方案采用FFT，如果产生实数的OFDM信号，传统方案需要使用厄米特共轭，有一半的子载波不传递有用信息，而本发明不需要厄米特共轭。因此如果L为传统方案调制信号的星座图阶数，为了得到相同的传输速率，本发明调制信号的星座图阶数为图4所示，相同速率条件下，本发明和传统Flip-OFDM的BER VS.Eb/NO曲线是基本吻合的，也就是说本发明和传统Flip-OFDM有相同误码性能。 Figure 4 compares the bit error performance of the present invention and the traditional Flip-OFDM under the AWGN channel condition. Since the present invention adopts FHT while the traditional scheme adopts FFT, if a real OFDM signal is generated, the traditional scheme needs to use Hermitian conjugation, and half of the subcarriers do not transmit useful information, but the present invention does not require Hermitian conjugation. Therefore if L is the constellation diagram order of the traditional scheme modulation signal, in order to obtain the same transmission rate, the constellation diagram order of the modulation signal of the present invention is As shown in Fig. 4, under the same rate condition, the BER VS.Eb/NO curves of the present invention and the traditional Flip-OFDM are basically consistent, that is to say, the present invention has the same bit error performance as the traditional Flip-OFDM.

该发明主要技术优势： The main technical advantages of the invention:

1.在一个符号周期内实现Flip-OFDM，使CP添加和去除，信道估计，延时等操作都减半； 1. Realize Flip-OFDM in one symbol period, so that CP addition and removal, channel estimation, delay and other operations are all halved;

2.使用FHT算法实现OFDM，相比FFT算法，复杂度降低一半。 2. Using the FHT algorithm to implement OFDM, compared with the FFT algorithm, the complexity is reduced by half. the

上面对本发明“快速哈特莱变换实现Flip-OFDM的方法”进行了详细的说明，但本发明的具体实现形式并不局限于此。该实施的说明只是用于帮助理解本发明的方法及其核心思想；同时，对于本领域的一般技术人员，依据本发明的思想，在具体实施方式及应用范围上均会有改变之处，综上所述，本说明书内容不应理解为对本发明的限制。在不背离本发明所述方法的精神和权利要求范围的情况下对它进行的各种显而易见的改变都在本发明的保护范围之内。 The "method for realizing Flip-OFDM by fast Hartley transform" of the present invention has been described in detail above, but the specific implementation form of the present invention is not limited thereto. The description of this implementation is only used to help understand the method of the present invention and its core idea; at the same time, for those of ordinary skill in the art, according to the idea of the present invention, there will be changes in the specific implementation and scope of application. As mentioned above, the contents of this specification should not be construed as limiting the present invention. Various obvious changes made to it without departing from the spirit of the method described in the present invention and the scope of the claims are within the protection scope of the present invention. the

Claims

1. quick hartley transform (FHT) is realized a method of Flip-OFDM, comprises the realization of Flip-OFDM transmitting terminal and receiving terminal.It is characterized in that,

Described Flip-OFDM transmitting terminal comprises: the mapping of real number constellation point, and FHT, Flip module, parallel serial conversion, adds Cyclic Prefix, digital-to-analogue conversion and low pass filter;

Described Flip-OFDM receiving terminal comprises: low pass filter, analog-to-digital conversion, removes Cyclic Prefix, parallel serial conversion, channel estimating, De-Flip, FHT, crucial point constellation demapping.

2. quick hartley transform according to claim 1 is realized the method for Flip-OFDM, it is characterized in that,

The real number constellation point mapping block of described Flip-OFDM transmitting terminal, for binary data sequence being mapped as to real number constellation symbol, and gives even carrier wave by the allocation of symbols generating, strange carrier wave zero setting.This distribution symbol is through the FHT module of described Flip-OFDM transmitting terminal, and output symbol has half-wave even symmetry character.

3. quick hartley transform according to claim 1 is realized the method for Flip-OFDM, it is characterized in that,

The Flip module of described Flip-OFDM transmitting terminal, for the turning operation of input signal, obtains positive real number signal.Flip module mainly comprises:

Symbol is cut out module, for input half-wave even symmetry symbol is cut out, and half period symbol before only retaining;

Polarity separation module, for input signal is carried out to polarity separation, extracts positive part and the negative part of signal;

Symbol Multiplexing module, for input signal is carried out to time-domain multiplexed, obtains the symbol of complete cycle;

The De-Flip module of described Flip-OFDM receiving terminal, for the solution turning operation of input signal, realizes the anti-operation of described transmitting terminal Flip module.De-Flip module mainly comprises:

Symbol division module, separates incoming symbol, and front half symbol period is as a subsymbol, and rear half symbol period is as another subsymbol;

Symbol summation module, is added two symbols of input;

Sign extended module, carries out incoming symbol time delay expansion and becomes the symbol of half-wave even symmetry.