WO2019237476A1 - 一种基于独立性校验编码的ofdm信道训练鉴权方法 - Google Patents

一种基于独立性校验编码的ofdm信道训练鉴权方法 Download PDF

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WO2019237476A1
WO2019237476A1 PCT/CN2018/099051 CN2018099051W WO2019237476A1 WO 2019237476 A1 WO2019237476 A1 WO 2019237476A1 CN 2018099051 W CN2018099051 W CN 2018099051W WO 2019237476 A1 WO2019237476 A1 WO 2019237476A1
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pilot
subcarrier
codeword
attacker
receiver
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任品毅
徐东阳
王熠晨
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Xian Jiaotong University
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Xian Jiaotong University
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B17/00—Monitoring; Testing
    • H04B17/30—Monitoring; Testing of propagation channels
    • H04B17/391—Modelling the propagation channel
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/0202—Channel estimation
    • H04L25/0224—Channel estimation using sounding signals
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2602—Signal structure
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L63/00—Network architectures or network communication protocols for network security
    • H04L63/14—Network architectures or network communication protocols for network security for detecting or protecting against malicious traffic
    • H04L63/1441—Countermeasures against malicious traffic

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  • the present invention relates to the field of wireless communications, and in particular, to an OFDM channel training and authentication method based on independence check coding.
  • the current wireless communication technology is facing serious security risks. This kind of risk stems from the broadcast characteristics of wireless channels. It is specifically manifested by harmful signal sources that harm the communication links of other normal nodes.
  • the upper-level password encryption and decryption system can guarantee the security of the wireless communication environment to a certain extent, with the development of computer technology, the upper-level encryption system faces the risk of being deciphered, and the information of legitimate users is completely exposed to hostile targets. Based on this, the physical layer security mechanism has attracted widespread attention and research. Given that the OFDM system is currently the mainstream wireless communication system architecture and is widely used in practical wireless communication systems, attacks against this system have gradually become hot topics, and attacks Users can obtain the protocol and architecture characteristics of the system, causing serious threats to it.
  • pilots for channel estimation.
  • These pilot signals can be known by the attacker.
  • the attacker learns the frame synchronization information and pilot information of a legitimate transceiver, it can launch Pilot-aware attacks, during which the attacker interferes with the channel estimation between legitimate transceiver pairings by sending a specific pilot signal in synchronization with a legitimate user, paralyzing the system's next data transmission service.
  • pilot awareness attack is successfully implemented, it is difficult for a legitimate transceiver to obtain accurate legal link channel state information. Therefore, the key lies in how to design a pilot authentication mechanism to resist and weaken the influence of pilot awareness attacks on channel training in OFDM systems.
  • the purpose of the present invention is to provide an OFDM channel training and authentication method based on independence check coding to solve the above problems.
  • the present invention adopts the following technical solutions:
  • An OFDM channel training and authentication method based on independence check coding includes the following steps:
  • Step 1 Establish a system model; adopt random pilot mechanism, uplink transmitter uses random pilot for channel estimation, active attacker can adopt mixed attack mode; mixed attack mode includes channel training for partial frequency band interference legal channel, and full frequency band interference legality Channel training and keeping silent;
  • Step 2 By encoding the activation modes of each subcarrier, a code frequency domain is created, and an independence check coding criterion is constructed; considering 3 OFDM symbol times, energy detection is performed on a signal received on any single subcarrier. Configure a threshold to achieve accurate detection of the number of signals on each subcarrier. If there is a signal, the subcarrier is coded as 1, otherwise it is 0.
  • Step 3 construct an anti-attack channel training and authentication CTA protocol based on the independence check code ICC, including the representation, separation and identification of pilots;
  • Step 4. Optimize the bit rate to achieve the most stable channel estimation.
  • step 1 consider a pair of legitimate transceivers and a pilot-aware attacker, and two uplink communication links: uplink transmitter ⁇ receiver, pilot-aware attacker ⁇ receiver; the receiver has N T antennas, uplink transmitters and pilot-aware attackers are single antennas; in the frequency domain, each antenna of each uplink occupies N subcarriers simultaneously in each OFDM symbol.
  • each The communication link samples L paths
  • the channel model is: Represents the impulse response of the channel between the uplink transmitter and the ith receiving antenna of the receiver, Represents the power delay spectrum of the first path; Represents the channel impulse response between the pilot-aware attacker and the receiver's i-th receiving antenna, and is independent of Represents the power delay spectrum of the l path.
  • the uplink transmitter uses a deterministic pilot, when a pilot-aware attack occurs, the attacker will transmit the same pilot signal at the same pilot point position as the legitimate transmitter, and the pilot signal is configured as follows:
  • the pilot signal of the uplink transmitter on the ith subcarrier is Among them, ⁇ B is the pilot transmit power, and ⁇ k represents the pilot phase corresponding to the k-th time slot;
  • the pilot signal of the pilot-aware attacker on the i-th subcarrier is Among them, ⁇ A is its pilot transmission power, Represents the pilot phase on the i-th subcarrier of the k-th OFDM symbol time.
  • the decoding criterion considering the mixed attack environment, the receiver can identify three types of results on the ith subcarrier i ⁇ [1, NB]: Case 1: The uplink transmitter and the attacker do not have Transmit signals; Case 2: Both the uplink transmitter and the attacker transmit signals; Case 3: An unknown node transmits signals; Case 3 further identifies the method by: differentially encoding the signals collected on adjacent subcarriers to get two For a codeword, two types of codewords are determined. If and only if the weight of the decoded codeword is consistent with the coding criterion, the codeword is determined to be the correct codeword.
  • the pilot representation stage the uplink transmitter and the attacker select a random pilot phase, and establish a one-to-one mapping of the pilot phase to the codeword based on the codebook.
  • the codeword is further Mapping to the subcarrier activation mode.
  • the specific principle is that if the value of the element of the codeword is equal to 1, the pilot signal is transmitted on the subcarrier, otherwise the subcarrier is placed in the idle state; both the uplink transmitter and the attacker generate their own Subcarrier activation mode, and synchronous transmission is maintained. Via the wireless environment, the superposition of signals on each subcarrier causes interference and is finally acquired by the receiver. Pilot separation stage: According to the observed subcarrier activation mode, the receiver controls each subcarrier.
  • the receiver can identify the specific attack type; get the uplink transmitter and attack under each attack type Codewords used by pilots; pilot identification stage: the receiver identifies the separated codewords by searching for the codewords in the codebook,
  • the recognition error probability can be defined as:
  • step 4 the instability of the channel estimation is measured, and the stability condition is defined as: coincident subcarriers are distributed at equal intervals and the number of coincident subcarriers satisfies s ⁇ L; the stability is measured and the index P s is defined:
  • C 2 (N, w, s * ) represents all possible two-to-two codeword combinations possible for the uplink transmitter and the attacker
  • w is the weight of the codeword
  • ⁇ (N, w, s * ) represents all possible codeword combinations that satisfy the CS condition
  • the probability of pilot identification error is:
  • the present invention has the following technical effects:
  • the invention utilizes the characteristics of random pilots to weaken pilot-aware attacks into a hybrid attack mode, and simultaneously establishes an independence check coding criterion according to the independent characteristics of the channels, so as to achieve the legal user pilot signals in the pilot interference environment by optimizing the codes Rate and its corresponding antenna, time slot, and subcarrier resource configuration, to further achieve stable and high-precision channel estimation.
  • Figure 1 is a system model diagram.
  • Figure 2 is a diagram of the proposed protocol framework.
  • Figure 3 is a compromise graph of safety and stability.
  • FIG. 4 is a diagram of pilot recognition error probability.
  • FIG. 5 is a graph of channel mean square error and legal pilot signal-to-noise ratio.
  • the system model diagram shown in Figure 1 considers a pair of legitimate transceivers and a pilot-aware attacker.
  • Two uplink communication links are uplink transmitter ⁇ receiver and pilot-aware attacker ⁇ receiver.
  • the receiver has N T antennas, transmitter and an uplink pilot perception attackers are single antenna.
  • each antenna of each uplink occupies N subcarriers simultaneously in each OFDM symbol.
  • each communication link samples L paths.
  • the channel model is: Represents the impulse response of the channel between the uplink transmitter and the ith receiving antenna of the receiver, Represents the power delay spectrum of the first path; Represents the channel impulse response between the pilot-aware attacker and the receiver's i-th receiving antenna, and is independent of Represents the power delay spectrum of the l path.
  • the uplink transmitter uses a deterministic pilot, when a pilot-aware attack occurs, the attacker will transmit the same pilot signal at the same pilot point position as the legitimate transmitter, and the pilot signal is configured as follows:
  • the pilot signal of the uplink transmitter on the ith subcarrier is Among them, ⁇ B is the pilot transmit power, and ⁇ k represents the pilot phase corresponding to the k-th time slot; the pilot signal of the pilot-aware attacker on the i-th subcarrier is Among them, ⁇ A is its pilot transmission power, Represents the pilot phase on the i-th subcarrier of the k-th OFDM symbol time.
  • uplink transmitters use random pilots for channel estimation. At this time, active attackers can adopt a hybrid attack mode: 1. Use random pilots, and channel training on some bands interferes with legitimate channels; , Full-band interference with legal channel training; 3. Keep silent.
  • FIG. 1 shows the framework of the proposed protocol, including the following steps:
  • Step 2 Establish coding guidelines for independence check, which may include coding guidelines and decoding guidelines.
  • the receiver can recognize three types of results on the ith subcarrier i ⁇ [1, NB]: Case 1: The uplink transmitter and the attacker are not transmitting signals. Case 2: Both the uplink transmitter and the attacker transmit signals. Case 3: An unknown node (uplink transmitter or attacker) transmits a signal. Obviously, the receiver can recognize the behavior in the first two cases, but due to the ambiguity of the signal superposition on the subcarriers, case 3 needs to be further identified.
  • the specific method is to differentially encode the signals collected on adjacent subcarriers to Two types of codewords are determined. If and only if the weight of the decoded codeword is consistent with the coding criterion, the codeword is determined to be the correct codeword.
  • Step3 As shown in Figure 2, the pilot representation phase: the uplink transmitter and the attacker choose a random pilot phase, and according to the codebook of Step2, a one-to-one mapping of the pilot phase to the codeword is established. Under this mapping principle, The codeword is further mapped to the subcarrier activation mode. The specific principle is that if the element value of the codeword is equal to 1, the pilot signal is transmitted on the subcarrier, otherwise the subcarrier is placed in the idle state. Both the uplink transmitter and the attacker generate their own subcarrier activation modes and maintain synchronous transmission. Via the wireless environment, the superposition of the signals on each subcarrier causes interference and is finally acquired by the receiver.
  • Pilot separation stage According to the observed subcarrier activation mode, the receiver performs energy detection in Step 1 on each subcarrier to determine whether a signal exists on each subcarrier. Based on the result, a binary codeword vector is obtained. For the decoding criterion of Step 2, the receiver can: 1 identify the specific attack type; 2 obtain the codeword used by the uplink transmitter and the attacker under each attack type. Pilot identification stage: By searching for the codewords in the codebook, the receiver recognizes the separated codewords. In a mixed attack environment, the recognition error probability Pr can be defined as:
  • Step4 Consider 2 OFDM symbol times, labeled as k 0 and k 1 , and consider s subcarriers to overlap, then the signal model of the receiver can be expressed as:
  • the normalized mean square error of the channel is:
  • Step 5 In order to measure the instability of the channel estimation, the stability condition is defined as: coincident subcarriers are distributed at equal intervals and the number of coincident subcarriers satisfies s ⁇ L. To measure stability, define the index P s :
  • C 2 (N, w, s * ) represents all possible two-to-two codeword combinations possible for the uplink transmitter and the attacker
  • w is the weight of the codeword
  • ⁇ (N, w, s * ) represents all possible codeword combinations that satisfy the CS condition.
  • the probability of pilot identification error is:
  • FIG. 3 shows the improvement of the channel estimation accuracy of the present invention in a pilot-aware attack environment.
  • FIG. 4 shows the change of the probability of pilot identification error with the number of subcarriers N under the most stable channel estimation of the present invention.
  • FIG. 5 shows the change of the bit rate of the independence check coding proposed by the present invention under the most stable channel estimation with the number of subcarriers N.

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Abstract

一种基于独立性校验编码的OFDM信道训练鉴权方法，用以避免导频遭受的干扰、归零和欺骗风险。导频不仅仅被随机化并插入到子载波中，同时也被编码、对应为子载波激活模式(SAP)。这些经过编码的SAP虽然被恶意信号掩盖，却是可以被识别并解码成原始导频信号，并进一步被用于高精度的信道冲击响应(CIR)估计，成功解决导频攻击环境下的信道估计难题。本发明联合子载波编码和信道估计，通过优化码率和信道估计，实现了攻击环境下高安全性、高稳定性的无线信道训练鉴权。

Description

一种基于独立性校验编码的OFDM信道训练鉴权方法 技术领域
本发明涉及到无线通信领域，特别涉及一种基于独立性校验编码的OFDM信道训练鉴权方法。
背景技术
当前无线通信技术面临严重的安全风险，这种风险源于无线信道的广播特性，具体表现为有害信号源危害干扰其他正常节点的通信链路。虽然上层的密码加密解密体制可以在一定程度上保证无线通信环境的安全性，但是随着计算机技术的发展，上层的加密体制面临被破译的风险，合法用户的信息进而完全暴露于敌对目标。基于此，物理层安全机制引起了广泛的关注和研究，鉴于OFDM系统作为当前主流的无线通信系统架构并且被广泛应用于各个实际的无线通信系统中，针对该系统的攻击逐渐成为热点话题，攻击者可以获取该系统的协议和架构特征，对其造成严重的威胁。
研究物理层的信道训练协议。在OFDM系统中，信道训练的目的是利用公共已知的导频进行信道估计,这些导频信号可被攻击者获知，当攻击者获悉合法收发机的帧同步信息和导频信息后，可发动导频感知攻击，期间，该攻击者通过与某一合法用户同步地发送特定的导频信号，干扰合法收发机配对之间信道估计，瘫痪系统的下一步数据传输服务。而且，导频感知攻击一旦成功实施后，合法收发机很难再获取精确的合法链路信道状态信息。因此，关键在于如何设计导频鉴权机制来抵抗和削弱OFDM系统中的导频感知攻击对信道训练的影响。
发明内容
本发明的目的在于提供一种基于独立性校验编码的OFDM信道训练鉴权方法，以解决上述问题。
为实现上述目的，本发明采用以下技术方案：
一种基于独立性校验编码的OFDM信道训练鉴权方法，包括以下步骤：
步骤1，建立系统模型；采用随机导频机制，上行发射机采用随机导频进行信道估计，主动攻击者可采取混合攻击模式；混合攻击模式包括部分频带干扰合法信道的信道训练、全频带干扰合法信道训练和保持静默；
步骤2，通过对各个子载波激活模式的编码，创建了码频域，构建了独立性校验编码准则；考虑3个OFDM符号时间，对任意单个子载波上收到的信号进行能量检测，通过配置阈值，实现每个子载波上精准的信号个数检测，若存在信号，则该子载波被编码为1，反之则为0；根据得到的二进制编码，得到二元码字向量集合为：
Figure PCTCN2018099051-appb-000001
其中，L s表示码字的长度，s m表示第m个码字单元，；建立码频域为：
Figure PCTCN2018099051-appb-000002
其中b表示码字s对应频域的位置，N表示占用的子载波个数；最后得到一个N×C的二元码本C＝[c i,j]，码本中第i个码字定义为c i＝[c 1,i … c N,i] T；
构建独立性校验编码准则，包括编码准则和解码准则，用以抵抗混合攻击；
步骤3，构建基于独立性校验编码ICC的反攻击信道训练鉴权CTA协议，包括导频的表示，分离和识别；
步骤4，优化码率，实现最稳定信道估计。
进一步的，步骤1中，考虑一对合法收发机和一个导频感知攻击者，两个上行通信链路，分别为上行发射机→接收机，导频感知攻击者→接收机；接收机拥有N T根天线，上行发射机和导频感知攻击者均为单天线；频域上，每条上行链路的每根天线在每个OFDM符号内都同时占用N个子载波.时域上,每个通信链路均采样L条路径，信道模型为：
Figure PCTCN2018099051-appb-000003
代表上行发射机与接收机的第i根接收天线之间的信道冲激响应，
Figure PCTCN2018099051-appb-000004
代表第l条路径的功率时延谱；
Figure PCTCN2018099051-appb-000005
代表导频感知攻击者与接收机的第i根接收天线之间的信道冲激响应，并独立于
Figure PCTCN2018099051-appb-000006
代表第l条路径的功率时延谱。若上行发射机采用确定性导频，当导频感知攻击发生时，攻击者会在与合法发射机相同的导频点位置，发射相同的导频信号，导频信号 配置为：在第k个OFDM符号期间，上行发射机在第i个子载波上的的导频信号为
Figure PCTCN2018099051-appb-000007
其中,ρ B为其导频发射功率，φ k表示第k个时隙对应的导频相位；导频感知攻击者在第i个子载波上的的导频信号为
Figure PCTCN2018099051-appb-000008
其中，ρ A为其导频发射功率，
Figure PCTCN2018099051-appb-000009
表示第k个OFDM符号时间第i个子载波上的导频相位。
进一步的，步骤2中，编码准则：对于一个N×C的二元码本C＝[c i,j],当且仅当，对于码本矩阵内任意两个列向量集合
Figure PCTCN2018099051-appb-000010
最少存在s个行向量集合
Figure PCTCN2018099051-appb-000011
使得，
Figure PCTCN2018099051-appb-000012
成立。
进一步的，步骤2中，解码准则：考虑到混合攻击环境，接收机可以在第i个子载波i∈[1，NB]上识别出三种类型的结果：情况1：上行发射机和攻击者没有传输信号；情况2：上行发射机和攻击者都传输信号；情况3：一个未知节点传输信号；情况3进一步识别的方法为：对相邻子载波上收集到的信号进行差分编码，得到两种码字，对两种码字进行判定，当且仅当解码出来的码字权重与编码准则一致，判决该码字为正确的码字。
进一步的，步骤3中，导频表示阶段：上行发射机和攻击者选择随机导频相位，根据码本，建立导频相位到码字的一对一映射，在该映射原理下，码字进一步映射为子载波激活模式，具体原理是，如果码字的元素数值等于1，则导频信号该子载波上发送，否则该子载波被置于空闲状态；上行发射机和攻击者都产生各自的子载波激活模式，并且保持同步传输，经由无线环境，各个子载波上信号的叠加产生干扰，最终被接收机获取；导频分离阶段：根据观察到的子载波激活模式，接收机对各个子载波进行能量检测，判断每一个子载波上是否存在信号，根据结果，得到一个二元码字向量,借助于解码准则，接收机能够识别具体的攻击类型；得到每个攻击类型下上行发射机和攻击者使用的码字；导频识别阶段:通过搜索码本中的码字，接收机识别分离出的码字，在混合攻击环境下，识别错误概率可定义为：
Figure PCTCN2018099051-appb-000013
进一步的，步骤4中，衡量信道估计的不稳定性，定义稳定性条件为：重合的子载波 等间隔分布并且重合的子载波个数满足s≥L；衡量稳定性，定义指标P s：
Figure PCTCN2018099051-appb-000014
其中C 2(N,w,s *)表示上行发射机和攻击者所有可能的两两码字组合可能，w为码字权重，
Figure PCTCN2018099051-appb-000015
κ(N,w,s *)表示满足CS条件的所有可能码字组合；建立一个优化问题，目标是最大化
Figure PCTCN2018099051-appb-000016
约束条件为：
Figure PCTCN2018099051-appb-000017
通过解决这个优化条件，得到最稳定信道估计下的码率表达式为：
Figure PCTCN2018099051-appb-000018
其中，
Figure PCTCN2018099051-appb-000019
导频识别错误概率为：
Figure PCTCN2018099051-appb-000020
与现有技术相比，本发明有以下技术效果：
本发明利用随机导频的特性来弱化导频感知攻击为混合攻击模式，同时根据信道的独立特性建立独立性校验编码准则，来实现导频干扰环境下合法用户导频信号的，通过优化码率及其对应的天线、时隙和子载波资源配置，进一步实现稳定而又高精度的信道估计。
附图说明
图1是系统模型图。
图2是所提协议框架图。
图3是安全性与稳定性的折衷曲线图。
图4是导频识别错误概率图。
图5是信道均方误差与合法导频信噪比曲线图。
具体实施方式
以下结合附图对本发明进一步说明：
图1给出的系统模型图，考虑一对合法收发机和一个导频感知攻击者，两个上行通信链路，分别为上行发射机→接收机，导频感知攻击者→接收机。接收机拥有N T根天线，上行发射机和导频感知攻击者均为单天线。频域上，每条上行链路的每根天线在每个OFDM符号内都同时占用N个子载波.时域上,每个通信链路均采样L条路径，信道模型为：
Figure PCTCN2018099051-appb-000021
代表上行发射机与接收机的第i根接收天线之间的信道冲激响应，
Figure PCTCN2018099051-appb-000022
代表第l条路径的功率时延谱；
Figure PCTCN2018099051-appb-000023
代表导频感知攻击者与接收机的第i根接收天线之间的信道冲激响应，并独立于
Figure PCTCN2018099051-appb-000024
代表第l条路径的功率时延谱。若上行发射机采用确定性导频，当导频感知攻击发生时，攻击者会在与合法发射机相同的导频点位置，发射相同的导频信号，导频信号配置为：在第k个OFDM符号期间，上行发射机在第i个子载波上的的导频信号为
Figure PCTCN2018099051-appb-000025
其中,ρ B为其导频发射功率，φ k表示第k个时隙对应的导频相位；导频感知攻击者在第i个子载波上的的导频信号为
Figure PCTCN2018099051-appb-000026
其中，ρ A为其导频发射功率，
Figure PCTCN2018099051-appb-000027
表示第k个OFDM符号时间第i个子载波上的导频相位。为了防止导频污染，上行发射机采用随机导频进行信道估计，此时，主动攻击者可采取混合攻击模式：1.采用随机导频，部分频带干扰合法信道的信道训练；2采用随机导频，全频带干扰合法信道训练；3.保持静默。
图2给出了所提协议的框架图，包括如下步骤：
Step 1:考虑3个OFDM符号时间，对任意单个子载波上收到的信号进行能量检测，通过配置阈值，实现每个子载波上精准的信号个数检测，若存在信号，则该子载波被编码为1，反之则为0。根据得到的二进制编码，得到二元码字向量集合为：
Figure PCTCN2018099051-appb-000028
其中，L s表示码字的长度，s m表示第m个码字单元，；建立码频域为：
Figure PCTCN2018099051-appb-000029
其中b表示码字s对应频域的位置，N表 示占用的子载波个数；最后得到一个N×C的二元码本C＝[c i,j]，码本中第i个码字定义为c i＝[c 1,i … c N,i] T；
Step 2:构建独立性检验编码准则，具体可包括编码准则和解码准则。
编码准则：对于一个N×C的二元码本C＝[c i,j],当且仅当，对于码本矩阵内任意两个列向量集合
Figure PCTCN2018099051-appb-000030
最少存在s个行向量集合
Figure PCTCN2018099051-appb-000031
使得，
Figure PCTCN2018099051-appb-000032
成立。
解码准则：
考虑到混合攻击环境，接收机可以在第i个子载波i∈[1，NB]上识别出三种类型的结果：情况1：上行发射机和攻击者没有传输信号。情况2：上行发射机和攻击者都传输信号。情况3：一个未知节点(上行发射机或者攻击者)传输信号。显然，接收机可以识别前两种情况下的行为，但由于子载波上信号叠加的模糊性，情况3需要进一步识别，具体方法为，对相邻子载波上收集到的信号进行差分编码，得到两种码字，对两种码字进行判定，当且仅当解码出来的码字权重与编码准则一致，判决该码字为正确的码字。
Step3:如图2所示，导频表示阶段：上行发射机和攻击者选择随机导频相位，根据Step2的码本，建立导频相位到码字的一对一映射，在该映射原理下，码字进一步映射为子载波激活模式，具体原理是，如果码字的元素数值等于1，则导频信号该子载波上发送，否则该子载波被置于空闲状态。上行发射机和攻击者都产生各自的子载波激活模式，并且保持同步传输，经由无线环境，各个子载波上信号的叠加产生干扰，最终被接收机获取。导频分离阶段：根据观察到的子载波激活模式，接收机对各个子载波进行Step1采用的能量检测，判断每一个子载波上是否存在信号，根据结果，得到一个二元码字向量,借助于Step2的解码准则，接收机可：1识别具体的攻击类型；2得到每个攻击类型下上行发射机和攻击者使用的码字。导频识别阶段:通过搜索码本中的码字，接收机识别分离出的码字，在混合攻击环境下，识别错误概率P r可定义为：
Figure PCTCN2018099051-appb-000033
Step4:考虑2个OFDM符号时间，标记为k 0和k 1,并且考虑s个子载波重叠,则，接收机的信号模型可表示为：
Y L＝X LH L+N L
其中，X L是一个2×2导频信号矩阵，等于X L＝[x L,1 x L,2]，其中 x L,1＝[x B[k 0] x B[k 1]] T,x L,2＝[x A[k 0] x A[k 1]] T，H L是一个2×N Ts矩阵，等于
Figure PCTCN2018099051-appb-000034
其中,N T表示发射天线个数,
Figure PCTCN2018099051-appb-000035
Figure PCTCN2018099051-appb-000036
F L,s是s×L维DFT矩阵。N L是2×N Ts维矩阵，满足
Figure PCTCN2018099051-appb-000037
1×s维向量
Figure PCTCN2018099051-appb-000038
表示第i根天线第k个OFDM符号时间内的噪声矢量。根据此模型，得到子载波信道估计为：
Figure PCTCN2018099051-appb-000039
信道归一化均方误差为：
Figure PCTCN2018099051-appb-000040
Step5:为了衡量信道估计的不稳定性，定义稳定性条件为：重合的子载波等间隔分布并且重合的子载波个数满足s≥L。为了衡量稳定性，定义指标P s：
Figure PCTCN2018099051-appb-000041
其中C 2(N,w,s *)表示上行发射机和攻击者所有可能的两两码字组合可能，w为码字权重，
Figure PCTCN2018099051-appb-000042
κ(N,w,s *)表示满足CS条件的所有可能码字组合。建立一个优化问题，目标是最大化
Figure PCTCN2018099051-appb-000043
约束条件为：
Figure PCTCN2018099051-appb-000044
通过解决这个优化条件，得到最稳定信道估计下的码率表达式为：
Figure PCTCN2018099051-appb-000045
其中，
Figure PCTCN2018099051-appb-000046
导频识别错误概率为：
Figure PCTCN2018099051-appb-000047
本发明的仿真验证分别表示为图3，图4和图5。图3表示了此发明在导频感知攻击环境下对信道估计精度的提高。图4表明了本发明在最稳定信道估计下导频识别错误概率随子载波个数N的变化情况。图5表示了本发明在最稳定信道估计下所提独立性校验编码的码率随着子载波个数N的变化情况。

Claims (6)

  1. 一种基于独立性校验编码的OFDM信道训练鉴权方法，其特征在于，包括以下步骤：
    步骤1，建立系统模型；采用随机导频机制，上行发射机采用随机导频进行信道估计，主动攻击者采取混合攻击模式；混合攻击模式包括部分频带干扰合法信道的信道训练、全频带干扰合法信道训练和保持静默；
    步骤2，通过对各个子载波激活模式的编码，创建了码频域，构建了独立性校验编码准则；考虑3个OFDM符号时间，对任意单个子载波上收到的信号进行能量检测，通过配置阈值，实现每个子载波上精准的信号个数检测，若存在信号，则该子载波被编码为1，反之则为0；根据得到的二进制编码，得到二元码字向量集合为：
    Figure PCTCN2018099051-appb-100001
    其中，L s表示码字的长度，s m表示第m个码字单元，；建立码频域为：
    Figure PCTCN2018099051-appb-100002
    其中b表示码字s对应频域的位置，N表示占用的子载波个数；最后得到一个N×C的二元码本C＝[c i,j]，码本中第i个码字定义为c i＝[c 1,i…c N,i] T；
    构建独立性校验编码准则，包括编码准则和解码准则，用以抵抗混合攻击；
    步骤3，构建基于独立性校验编码ICC的反攻击信道训练鉴权CTA协议，包括导频的表示，分离和识别；
    步骤4，优化码率，实现最稳定信道估计。
  2. 根据权利要求1所述的一种基于独立性校验编码的OFDM信道训练鉴权方法，其特征在于，步骤1中，考虑一对合法收发机和一个导频感知攻击者，两个上行通信链路，分别为上行发射机→接收机，导频感知攻击者→接收机；接收机拥有NT根天线，上行发射机和导频感知攻击者均为单天线；频域上，每条上行链路的每根天线在每个OFDM符号内都同时占用N个子载波.时域上,每个通信链路均采样L条路径，信道模型为：
    Figure PCTCN2018099051-appb-100003
    代表上行发射机与接收机的第i根接收天线之间的信道冲激响应，
    Figure PCTCN2018099051-appb-100004
    代表第l条路径的功率时延谱；
    Figure PCTCN2018099051-appb-100005
    代表导频感知攻击者与接收机的第i根接收天线之间的信道冲激响应，并独立于
    Figure PCTCN2018099051-appb-100006
    代表第l条路径的功率时延谱；若上行发射机采用确定性导频，当导频感知攻击 发生时，攻击者会在与合法发射机相同的导频点位置，发射相同的导频信号，导频信号配置为：在第k个OFDM符号期间，上行发射机在第i个子载波上的导频信号为
    Figure PCTCN2018099051-appb-100007
    其中,ρ B为其导频发射功率，φ k表示第k个时隙对应的导频相位；导频感知攻击者在第i个子载波上的的导频信号为
    Figure PCTCN2018099051-appb-100008
    其中，ρ A为其导频发射功率，
    Figure PCTCN2018099051-appb-100009
    表示第k个OFDM符号时间第i个子载波上的导频相位。
  3. 根据权利要求1所述的一种基于独立性校验编码的OFDM信道训练鉴权方法，其特征在于，步骤2中，编码准则：对于一个N×C的二元码本C＝[c i,j],当且仅当，对于码本矩阵内任意两个列向量集合
    Figure PCTCN2018099051-appb-100010
    最少存在s个行向量集合
    Figure PCTCN2018099051-appb-100011
    使得，
    Figure PCTCN2018099051-appb-100012
    c i,j＝1成立。
  4. 根据权利要求1所述的一种基于独立性校验编码的OFDM信道训练鉴权方法，其特征在于，步骤2中，解码准则：考虑到混合攻击环境，接收机在第i个子载波i∈[1,N]上识别出三种类型的结果：情况1：上行发射机和攻击者没有传输信号；情况2：上行发射机和攻击者都传输信号；情况3：一个未知节点传输信号；情况3进一步识别的方法为：对相邻子载波上收集到的信号进行差分编码，得到两种码字，对两种码字进行判定，当且仅当解码出来的码字权重与编码准则一致，判决该码字为正确的码字。
  5. 根据权利要求1所述的一种基于独立性校验编码的OFDM信道训练鉴权方法，其特征在于，步骤3中，导频表示阶段：上行发射机和攻击者选择随机导频相位，根据码本，建立导频相位到码字的一对一映射，在该映射原理下，码字进一步映射为子载波激活模式，具体原理是，如果码字的元素数值等于1，则导频信号该子载波上发送，否则该子载波被置于空闲状态；上行发射机和攻击者都产生各自的子载波激活模式，并且保持同步传输，经由无线环境，各个子载波上信号的叠加产生干扰，最终被接收机获取；导频分离阶段：根据观察到的子载波激活模式，接收机对各个子载波进行能量检测，判断每一个子载波上是否存在信号，根据结果，得到一个二元码字向量,借助于解码准则，接收机能够识别具体的攻击类型；得到每个攻击类型下上行发射机和攻击者使用的码字；导频识别阶段:通过搜索码本中的码字，接收机识别分离出的码字，在混合攻击环境下，识别错误 概率P r定义为：
    Figure PCTCN2018099051-appb-100013
  6. 根据权利要求1所述的一种基于独立性校验编码的OFDM信道训练鉴权方法，其特征在于，步骤4中，衡量信道估计的不稳定性，定义稳定性条件为：重合的子载波等间隔分布并且重合的子载波个数满足s≥L；衡量稳定性，定义指标P s：
    Figure PCTCN2018099051-appb-100014
    其中C 2(N,w,s *)表示上行发射机和攻击者所有可能的两两码字组合可能，w为码字权重，
    Figure PCTCN2018099051-appb-100015
    κ(N,w,s *)表示满足CS条件的所有可能码字组合；建立一个优化问题，目标是最大化
    Figure PCTCN2018099051-appb-100016
    约束条件为：
    Figure PCTCN2018099051-appb-100017
    通过解决这个优化条件，得到最稳定信道估计下的码率表达式为：
    Figure PCTCN2018099051-appb-100018
    其中，
    Figure PCTCN2018099051-appb-100019
    导频识别错误概率P r为：
    Figure PCTCN2018099051-appb-100020
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