Protecting Wi-Fi communication through spatial mapping matrix perturbation

Abstract

The perturbation of the spatial mapping matrix further protects Wi-Fi communication. In an embodiment, channel state information is obtained from a receiving device in the wireless network. A first set of beam steering vectors is derived based on the channel state information to guide radio signals to the receiving device. A second set of beam steering vectors is derived based on the channel state information to guide radio signals out of the receiving device. A perturbation matrix is ​​generated. The spatial mapping matrix is ​​formed by combining the first set of beam steering vectors and the second set of beam steering vectors with the perturbation matrix. Data symbols to be transmitted are pre-encoded into the receiving device using the spatial mapping matrix, and the data symbols are transmitted to the receiving device via the wireless network.

Description

Background Technology

[0001] Wi-Fi has become the preferred global standard for short-range data communication, found in homes, offices, and public places. Many locations offer free public Wi-Fi, and some cities offer free Wi-Fi hotspot access. New wireless standards are being rolled out to transmit increasingly more data over the air. However, by nature, all airborne communication technologies are more vulnerable to eavesdropping by intruders located near hotspots or remote nodes. Such intruders could be outside homes, near public areas of offices or nearby suites, or anywhere else suitable. This vulnerability can be mitigated by encrypting data transmitted over the air.

[0002] Key-based encryption techniques (WEP, WPA1, WPA2, etc.) work on the assumption that an eavesdropper will capture the transmitted data stream but will be unable to decrypt it. This assumption relies on the eavesdropper having limited time and processing resources, thus making it impossible for them to guess the security key. WPA2 uses a 64-bit hexadecimal numeric key. This assumption also relies on the eavesdropper not obtaining the key from any node through other clandestine means. While these are good assumptions, they are not foolproof, and encryption is not invincible. Other devices use simpler encryption techniques that exchange symmetric keys during the authentication phase. This technique is even less secure because the key exchange is easily sniffed, making the data vulnerable to attack. Summary of the Invention

[0003] In this embodiment, perturbation of the spatial mapping matrix further protects the wireless signals, such as Wi-Fi communications, described herein. In this embodiment, channel state information is obtained from a receiving device in a wireless network at the transmitting device. The channel state information is received via the wireless network. A first set of beam steering vectors is derived based on the channel state information to guide a first radio signal to the receiving device. A second set of beam steering vectors is derived based on the channel state information to guide a second radio signal out of the receiving device. In this embodiment, the second set of beam steering vectors is orthogonal to the first set of beam steering vectors. For example, a perturbation matrix is ​​generated in matrix form. The spatial mapping matrix is ​​formed by combining the first and second sets of beam steering vectors with the perturbation matrix. Data symbols to be transmitted are pre-encoded into the receiving device using the spatial mapping matrix, and the data symbols are transmitted to the receiving device via the wireless network.

[0004] In this embodiment, the channel state information includes a channel coefficient matrix. In this embodiment, deriving the first set of beam steering vectors and the second set of beam steering vectors includes applying singular value decomposition to the channel coefficient matrix.

[0005] The embodiments further include sending a channel state information request to the receiving device, and obtaining the channel state information includes receiving the channel state information as feedback in response to the channel state information request.

[0006] In one embodiment, the perturbation matrix is ​​configured to have a scalar selection factor chosen as zero or one for each perturbation matrix value. In another embodiment, the perturbation matrix is ​​configured to have a scalar power factor for each perturbation matrix value. In yet another embodiment, the perturbation matrix values ​​are random numbers in the range of zero to 2π.

[0007] The embodiment further includes modifying the perturbation matrix after precoding each data symbol in the data symbols, wherein the data symbols are a series of data symbols. The embodiment further includes: forming a second spatial mapping matrix by combining a first set of beam steering vectors and a second set of beam steering vectors with the second perturbation matrix; precoding the training symbols to be transmitted into the receiving device using the second spatial mapping matrix; and transmitting the precoded training symbols to the receiving device via a wireless network.

[0008] In this embodiment, the first perturbation matrix is ​​different from the second perturbation matrix. The embodiment further includes: generating noise symbols; forming a second spatial mapping matrix using a first set of beamdirection vectors and a second set of beamdirection vectors; precoding the noise symbols using the second set of beamdirection vectors; and transmitting the precoded noise symbols outside the receiving device. In this embodiment, precoding the noise symbols further includes selecting different beamdirection vectors from the second set of beamdirection vectors after precoding each noise symbol.

[0009] Some embodiments relate to a computer-readable medium having instructions stored thereon that, when executed by a computer, cause the computer to perform operations including: obtaining channel state information from a receiving device in a wireless network at a transmitting device, the channel state information being received via the wireless network; deriving a first set of beam-directing vectors based on the channel state information to direct a first radio signal to the receiving device; deriving a second set of beam-directing vectors based on the channel state information to direct a second radio signal away from the receiving device, wherein the second set of beam-directing vectors is orthogonal to the first set of beam-directing vectors; generating a perturbation matrix; forming a spatial mapping matrix by combining the first set of beam-directing vectors and the second set of beam-directing vectors with the perturbation matrix; precoding data symbols to be transmitted to the receiving device using the spatial mapping matrix; and transmitting the precoded data symbols to the receiving device via the wireless network.

[0010] In some embodiments, deriving a set of beam steering vectors includes applying singular value decomposition to channel state information in the form of a channel coefficient matrix. In some embodiments, the perturbation matrix has a scalar selection factor chosen as zero or one for each perturbation matrix value and a scalar power factor for each perturbation matrix value.

[0011] Some embodiments relate to an apparatus comprising: a controller configured to obtain channel state information from a receiving device in a wireless network via a wireless network, derive a first set of beam steering vectors based on the channel state information to guide a first radio signal to the receiving device, derive a second set of beam steering vectors based on the channel state information to guide a second radio signal out of the receiving device, wherein the second set of beam steering vectors is orthogonal to the first set of beam steering vectors, generate a perturbation matrix, and form a spatial mapping matrix by combining the first set of beam steering vectors and the second set of beam steering vectors with the perturbation matrix; and a transceiver configured to precode data symbols to be transmitted into the receiving device using the spatial mapping matrix, and transmit the precoded data symbols to the receiving device via the wireless network.

[0012] In some embodiments, the controller is further configured to form a second spatial mapping matrix by combining a first set of beam steering vectors and a second set of beam steering vectors with a second perturbation matrix, and wherein the transceiver is further configured to use the second spatial mapping matrix to precode training symbols to be transmitted into the receiving device, and to transmit the precoded training symbols to the receiving device via a wireless network.

[0013] In some embodiments, the perturbation matrix has a scalar selection factor that is chosen to be zero or one for each perturbation matrix value.

[0014] In some embodiments, the controller is further configured to generate noise symbols and form a second spatial mapping matrix using a first set of beam steering vectors and a second set of beam steering vectors, wherein the transceiver is further configured to precode the noise symbols using the second spatial mapping matrix and transmit the precoded noise symbols outside the receiving device.

[0015] In some embodiments, precoding the noise symbols further includes selecting different beam steering vectors from a second set of beam steering vectors after precoding each noise symbol. Attached Figure Description

[0016] Figure 1 This is a simplified diagram of a wireless network with beamforming and eavesdroppers.

[0017] Figure 2 It is a signal diagram of the physical layer signals between the transmitting and receiving devices in a wireless network.

[0018] Figure 3This is a flowchart of a process used to enhance physical layer security when transmitting beam-directed wireless communications.

[0019] Figure 4 This is a diagram of wireless packets suitable for use in wireless networks.

[0020] Figure 5 This is a high-level block diagram of a wireless networking node.

[0021] Figure 6 This is a block diagram of the transmit chain of the transceiver module.

[0022] Throughout the description, similar reference numerals can be used to identify similar elements. Detailed Implementation

[0023] It will be readily understood that the components of the embodiments generally described herein and illustrated in the accompanying drawings can be arranged and designed in a wide variety of different configurations. Therefore, the more detailed descriptions of the various embodiments illustrated below are not intended to limit the scope of this disclosure, but merely to illustrate various embodiments. Although various aspects of the embodiments are presented in the drawings, the drawings are not necessarily drawn to scale unless specifically stated otherwise.

[0024] The invention may be implemented in other specific forms without departing from the spirit or essential characteristics thereof. The described embodiments should be considered in all respects as illustrative rather than restrictive. Therefore, the scope of the invention is indicated by the appended claims rather than by a detailed description thereof. All variations within the meaning and scope of the claims' equivalents are covered within the scope of the claims.

[0025] References to features, advantages, or similar language throughout this specification do not imply that all features and advantages achievable with this invention should be included in or in any single embodiment of the invention. Rather, language relating to features and advantages should be understood to mean that a particular feature, advantage, or characteristic described in connection with an embodiment is included in at least one embodiment of the invention. Therefore, discussions of features, advantages, and similar language throughout this specification may (but are not necessarily required to) refer to the same embodiment.

[0026] Furthermore, the features, advantages, and characteristics described in this invention can be combined in any suitable manner in one or more embodiments. Those skilled in the art will recognize that, in view of the description herein, this invention can be practiced without one or more specific features or advantages of a particular embodiment. In other instances, additional features and advantages that may not be present in all embodiments of the invention may be recognized in certain embodiments.

[0027] References to “an embodiment,” “embodiment,” or similar language throughout this specification mean that a particular feature, structure, or characteristic described in connection with the indicated embodiment is included in at least one embodiment of the invention. Therefore, the phrases “in one embodiment,” “in an embodiment,” and similar language throughout this specification may, but do not necessarily, refer to the same embodiment.

[0028] Many wireless transmitting devices use beamforming at the physical layer for a wide range of data communications. A beamforming system uses multiple antennas (often referred to as multiple antenna elements, or simply individual antennas) spaced at known distances to direct transmitted radio energy in one or more specific directions. The directed radio energy is called a beam. The beam is formed by controlling the phase of the radio signal at each antenna. In a dual-antenna system, two radio signals, each originating from a different antenna and emanating from a different location, are determined by the respective antenna positions and interfere with each other. In cases of constructive interference, the combined radio signal is stronger. In cases of destructive interference, the combined radio signal is weaker. More antennas and greater physical spacing increase the precision at which the formed beam can be oriented.

[0029] Figure 1 This is a simplified diagram of a wireless network. A transmitting device (TX) 102 directs a radio signal 110 to a receiving device (RX) 104. The transmitting device 102 and the receiving device 104 can be an access point (AP), router, station (STA), client, or any other node on the network. The terms "transmitting device" and "receiving device" refer to the functions shown. These functions can be reversed before or after transmission, such that the receiving device responds by transmitting back to the transmitting device. The transmitting device 102 has an antenna array 106 with two or more antenna elements to modulate the radio signal toward or away from the receiving device 104 as a modulating beam. As shown, one or more guiding radio signals 110 may be present to the receiving device 104, and one or more reflected radio signals 112 may be present to the receiving device. The reflected radio signals 112 may be reflected by a wall 116 or other vertical surface or by other environmental conditions. One or more of these beams are received at one or more antenna elements 108 of the receiving device 104.

[0030] The first eavesdropper 120 may be located near the receiving device 104 to additionally capture the guiding radio signal 110 or the reflected radio signal 112 of the receiving device 104. The first eavesdropper may be close enough to be within one of the beams or positioned to receive reflections of one or more beams. As described below, in some embodiments, the transmitting device 102 directs a noise beam 114 toward the first eavesdropper, which then blocks reception of either radio signal 110 or 112. The second eavesdropper 122 may be positioned away from the guiding radio signal 110 and the reflected radio signal 112 to capture other radio signals. The second eavesdropper may be outside the range of the noise radio signal 114 to allow the second eavesdropper to capture the reflected radio signal in the absence of noise.

[0031] The technique described in this paper makes data communication more difficult for eavesdroppers by reducing the strength of the data signal and increasing the amount of noise for them. This improves the security of the communication link. The technique described in this paper is not complex and can be accomplished primarily using the capabilities of existing Wi-Fi transmitters. For eavesdroppers, the data signal is significantly suppressed. The technique can be used in many different multi-antenna wireless devices, including Wi-Fi chips, and can be used in many different locations, including homes, conference rooms, airports, and vehicles.

[0032] The described technology can operate at the physical layer. Figure 2 This is a signal diagram of the physical layer signals between transmitting device 102 and receiving device 104. Transmitting device 102 obtains Channel State Information (CSI) from receiving device 104. In the diagram, receiving device 104 sends CSI message 212 to transmitting device 102. Depending on the protocol and implementation, CSI may be sent in response to a request, based on a periodic timer, in association with other data, or otherwise.

[0033] The transmitting device 102 uses CSI to form a 2^14 spatial mapping matrix. In some embodiments, two different spatial mapping matrices are formed. A first spatial mapping matrix is ​​applied to the training symbols, and a second spatial mapping matrix is ​​applied to the data. In some embodiments, the training field is a Long Training Field (LTF) or a Short Training Field (STF). This description is presented in the context of LTF; however, similar techniques and structures can be applied to other training configurations and structures. As used herein, data refers to the payload received by means of training. Therefore, data can be control, configuration or management information, routing information, status information, user data, or a combination of different types of information.

[0034] Transmitting device 102 transmits training signal 216 using a first spatial mapping matrix and data signal 218 using a second spatial mapping matrix. This introduces incoherence between the channel estimation based on training signal 216 and the actual channel of data signal 218, making it difficult for eavesdroppers 120, 122 to achieve equalization. The spatial mapping matrices are designed to allow channel equalization using only the training field for the intended user. In some embodiments, singular value decomposition is used in part to form the spatial mapping matrix, and many devices capable of beamforming already support this singular value decomposition. Therefore, the additional cost of the implementation is low. In some embodiments, transmitting device 102 also transmits noise signal 220 in a direction outside of receiving device 104 using another spatial mapping matrix. This signal may include eavesdropper 120.

[0035] In the embodiments, as described herein, an additional level of security is provided for wireless transmission. The described techniques and systems can be applied to any wireless communication interface that utilizes spatial extension. Security is further enhanced for systems with separate training and data by processing training and data in different ways.

[0036] Figure 3 This is a flowchart illustrating the process for enhancing physical layer security in beam-oriented wireless communication. To begin operation, transmitting device 102 obtains channel state information (e.g., an H matrix) from a client device, such as receiving device 104. The channel state information can be obtained implicitly or through feedback.

[0037] In some embodiments, the transmitting device 102 uses the H matrix to derive at operation 304 a first set of one or more orthogonal beam steering vectors (e.g., v1, v2, ..., v...) that have significant power in the direction of the client. k And at operation 306, a second set of orthogonal beam steering vectors with very little or no power in the direction of the client are derived (e.g., n1, n2...n...). r For example, singular value decomposition (SVD) can be used to compute both the first set of beam steering vectors and the second set of beam steering vectors.

[0038] The transmitting device then targets the training symbol Q at operation 312. LTF Form a spatial mapping matrix, and at operation 314 target the data symbol Q. DATA Different second spatial mapping matrices are formed. The sum of the products of one beam steering vector matrix, the perturbation matrix, and another beam steering vector matrix can be used to calculate the spatial mapping matrix. Two different perturbation matrices can be generated, one for training symbol A. LTF And another one for data symbol A DATAIn some embodiments, training symbols and data symbols are treated the same, and there exists only one spatial mapping matrix Q and one perturbation matrix A. This simplified approach still provides significant protection against most eavesdroppers. The perturbation matrix can be generated using elements suitable for different implementations. In some embodiments, each element includes a random or pseudo-random number θ with a value between 0 and 2π. i,j A selection factor ξ having values ​​selected from the set {0,1} i,j And the power scaling factor p used for power control.

[0039] The transmitting device 102 then uses the training space mapping matrix Q at operation 316. LTF The LTF symbol sequence is pre-encoded (i.e., pre-multiplied) and the data space mapping matrix Q is used. DATA The data symbol sequence is pre-coded. Then, at operation 318, the pre-coded training symbols and data symbols representing the training signal 216 and the data signal 218 are transmitted from the antenna array 106 of the transmitting device 102.

[0040] The impact on eavesdroppers 120 and 122 is twofold: firstly, the data sequence has a very low received signal strength, and secondly, if the noise is transmitted as noise signal 220 on the second set of beam steering vectors, the noise sequence has a much higher received signal strength. Secondly, generating different perturbation matrices for training and data can suppress eavesdroppers because the channel coefficients received on the LTF are not suitable for equalizing the data.

[0041] Consider in more detail Figure 3 The operation of this method allows us to understand the development of a new spatial mapping matrix, which in some embodiments begins with the transmitting device obtaining the CSI from the receiving device. In some embodiments, this is referred to as the H matrix. The H matrix can be obtained implicitly or through feedback. Although embodiments are described in the context of the H matrix, the CSI can be received in any of a variety of other formats. The CSI describes the current state of the wireless channel between the transmitter and receiver. The H matrix is ​​a channel coefficient matrix that includes the attenuation and phase shift experienced by each spatial stream at each receive antenna in each subcarrier, such as OFDM (Orthogonal Frequency Division Multiplexing) subcarriers in the IEEE 802.11n specification. In IEEE 802.11n, the receiver generates the CSI by analyzing the received packets using a training sequence in the packet header.

[0042] The CSI between the transmitting and receiving devices can alternatively take many other forms. In the example below, the dimension of the H matrix is ​​N. RX ×N TX , where N RX N is the number of antennas in the receiving device, and N TXN represents the number of antennas in the transmitting device. SS It is the amount of spatial stream sent from the transmitting device to the receiving device.

[0043] The transmitting device 102 then uses the H matrix to derive one or more orthogonal vectors (e.g., v1, v2... v) that have significant power in the direction of, for example, the client of the receiving device 104. k And derive a second set of orthogonal vectors (e.g., n1, n2...n) that do not have significant power in the direction of the receiving device 104. r In this embodiment, the second set of vectors is also orthogonal to the first set of vectors. For example, singular value decomposition (SVD) can be used to compute the two sets of vectors.

[0044] An example of using SVD is selecting a set N from the first set. SS Vectors, and through V = [v1, v2, ..., v NSS ) represents the matrix formed by these column vectors, and is defined by N = [n1, n2, ..., nn]. r The matrix consisting of the second set of vectors is represented as column vectors, where N consists of all vectors in the null space of H, and therefore r = N. Tx -N Rx .exist Figure 3 In this context, this refers to operation 308, which selects a vector from the first set of beam steering vectors to become a column vector of the first matrix, and operation 310, which selects a vector from the second set of beam steering vectors to become a column vector of the second matrix.

[0045] The singular value decomposition (SVD) of matrix H is given by H = LΛR H , where L and R are unitary matrices (called the left singular vector matrix and the right singular vector matrix, respectively), and R H This represents the Hermitian transpose of matrix R. This decomposition of the channel coefficient matrix H can be obtained using signal processing algorithms.

[0046] The following provides an example where N TX =4 and N TX =2, and receive H with the following value:

[0047]

[0048] Then, it can be verified that:

[0049]

[0050]

[0051]

[0052] As an example, consider the following two cases to show the application of SVD as \(H = L\Lambda R\). H :

[0053] Case 1: Assume that only one stream is to be transmitted. Thus, \(N_{ss}=1\). The first column of the \(R\) matrix can be chosen as \(V\). In this case,

[0054]

[0055] Case 2: Assume that two streams are to be transmitted. Thus, \(N_{ss}=2\). The first two columns of the \(R\) matrix can be chosen as \(V\). In this case,

[0056]

[0057] It should be noted that at the intended receiving device, the stream transmitted along the first column of the \(R\) matrix is received with the highest power. In particular,

[0058]

[0059] that is, the unit signal transmitted along the vector \(v_1\) is received with a power of \(3.9267\) 2 which is exactly the square of the first singular value.

[0060] Similarly, it can be verified for the unit signal transmitted along the second vector of \(R\), that is,

[0061]

[0062] is received with a power of \(1.7459\) 2 which is the square of the second singular value.

[0063] On the same basis, the signals transmitted along the third and fourth vectors of \(R\) are received with a power of 0 (since the corresponding singular values are 0). The third and fourth vectors of the \(R\) matrix span the null space of \(H\). Thus, in this case, the dimension of the null space of \(H\) is 2. In general, for a \(P\times Q\) matrix \(H\) of rank \(P\) (where \(P < Q\)), it can be shown that the dimension of the null space of \(H\) is \(Q - P\).

[0064] In summary, for an \(N\) Rx \(\times N\) Tx matrix \(H\) (where \(N\) Rx \(< N\) Tx ), the dimension of the right singular vector matrix is \(N\) Tx \(\times N\) Tx , where the first \(N\) Rx vectors will correspond to non - zero singular values and will be used to construct the \(V\) matrix, and the remaining \(N\) Tx \(- N\) RxEach vector corresponds to a zero singular value and will be used to construct an N matrix.

[0065] Using matrices V and N, a spatial spread matrix Q can be formed by combining the V and N matrices with a perturbation matrix A. V and N represent the characteristics of the wireless channel between the transmitter and receiver. As described above, in some embodiments, these characteristics are generated based on measurements of training data taken by the receiving device. These characteristics of the wireless channel will be the same for both training and data symbols, since the training symbols are designed for receiving data symbols. In some embodiments, the spatial spread matrix Q is the same for both training and data symbols. This can be achieved by using the same perturbation matrix A for both training and data symbols.

[0066] In other embodiments, two different perturbation matrices are generated, namely A for the training symbols. LTF and A for data symbols DATA This is to form two different spatial expansion matrices. At operation 312, the first spatial expansion matrix Q is formed for the training symbols. LTF Furthermore, at operation 314, a second spatial extension matrix QDATA is formed for the data symbols. In some embodiments, Q... LTF =V + N × A LTF And Q Data =V + N × A Data A LTF and A Data This is a perturbation matrix. Perturbation matrices can be generated in any of a variety of different ways. In some embodiments, they are random matrices of the following form:

[0067]

[0068] Where θ i,j It is a random number (or pseudo-random number) between 0 and 2π. These are numbers selected from the set {0,1} used to select rows of the aforementioned matrix. These factors allow for flexible selection of any number of columns in matrix N. p is a scalar used to scale all values ​​for power control. This scalar p can be used to control the relative power transmitted in the signal V and the interference N components.

[0069] LTF symbol random number θ i,j This may differ from the random numbers used for the data. Furthermore, those random numbers applied to the data can be changed sign-by-sign. This provides an additional layer of security. These random numbers can be generated in any of a variety of different ways. In some embodiments, a pseudo-random number θ for both the LTF and the data can be generated using, for example, an LFSR (Linear Feedback Shift Register). i,j .

[0070] factor The LTF and data may be different or the same, and may change symbol by symbol or remain unchanged, depending on the specific implementation.

[0071] The dimensions of the above matrices can be as follows:

[0072]

[0073] Pre-encoding of training and data symbols is performed at operation 316 using the appropriate spatial expansion matrix. Pre-encoding can take any of several different forms. Using current hardware and processes, this is achieved by interpolating the LTF sequence with the spatial expansion matrix Q of the training sequence. LTF Multiplication is used to pre-encode the symbols. Similarly, the data sequence is multiplied by the spatial expansion matrix Q of the data sequence. Data Multiply.

[0074] The precoded symbols can then be transmitted from the transmitting device via a wireless network at operation 318. Symbols precoded with the V component are directed to the receiving device. Symbols precoded with the N component are directed outside the receiving device. In many cases, the symbols precoded with the N component will be the strongest signal that the eavesdropper will receive.

[0075] Figure 4 This is a diagram of a wireless packet 410 that can be transmitted via a wireless network in an 802.11n communication system. Although the example is presented in the context of 802.11n, the same principles, techniques, and structures can be applied to other wireless networking and communication standards, including 802.11n / ac / ax / be, Bluetooth, cellular, and other types of wireless networks and communications. Packets may have more or fewer fields to support traditional or new operating modes. The order of fields can also be modified to suit different implementations. The techniques and structures described herein can also be applied to other packet structures not shown herein. The packet begins with a traditional short training field (L-STF) 402. This field includes training symbols that can be received and demodulated by traditional devices. Other devices can also train this field. Following L-STF 402 is a first high-throughput long training field (HT-LTF1) 404. This field can be used to train high-throughput data. A high-throughput signal field (HT-SIG) 406 follows the first HT-LTF1, followed by an additional HT-LTF 408. Then comes the data field 408. Data fields can contain service data, user data, padding bits, tail bits, and any other data to be sent from the transmitter to the receiving device.

[0076] As described above, the same spatial mapping matrix can be used to precode each field of the radio packet 410, or different spatial mapping matrices from the data fields can be used to precode the training fields. Different spatial mapping matrices can be formed by combining beamdirection vectors with different perturbation matrices. To direct the radio signal to the receiving device, the same set of beamdirection vectors can be used to form two vectors. In embodiments using two different spatial mapping matrices, it is sufficient to apply the first spatial mapping matrix to either the LTF field HT-LTF1 404 or HT-LTF 408. In some embodiments, all training fields, including HT-SIG 406, are precoded using one or more spatial mapping matrices, and the data fields are precoded using different spatial mapping matrices.

[0077] In addition to the perturbation matrix used when precoding training and data into the receiving device, noise symbols can be generated and transmitted over a wireless network to outside the receiving device. The noise signal can be random, pseudo-random, or based on another pattern that is difficult to filter out from radio signals. Beamdirection can be applied to the noise by precoding the noise symbols using a spatial mapping matrix formed using beamdirection vectors. The spatial mapping matrix can be formed with or without a perturbation matrix. The perturbation matrix used for training or data, or different perturbation matrices, can be used.

[0078] The security added to the physical layer by the perturbation matrix does not require any modification to the receiving device. The receiving device can transmit CSI according to relevant wireless standards such as 802.11n or cellular standards. The receiving device then receives training symbols and trains these symbols to allow them to receive data symbols. However, accurately receiving data symbols is very difficult for an eavesdropper.

[0079] As an example, for a receiving device, consider N Tx =4,N Rx =2,N SS The above case is equal to 2. For LTF, the net received channel coefficient matrix is...

[0080]

[0081]

[0082] Here, r i It is a column of a unitary matrix, and therefore when i ≠ j, and

[0083] Similarly, the data vector Q Data x Data Received as

[0084]

[0085] Therefore, the channel estimation matrix It can be used to equalize the received data vectors

[0086] On the other hand, the channel coefficient matrix at the eavesdropper's location can be decomposed into... But now, R ev The matrix does not match the V and N matrices used for precoding the LTF and data. Therefore, V will not maximize signal reception at the eavesdropper's receiver, and H... eav N≠0

[0087] Therefore H eav Q LTF =H eav V+H eav N×A LTF ≠H eav V+H eav N×A Data =H eav Q Data Equation 13

[0088] Therefore, eavesdroppers cannot use the channel coefficients received on the LTF to accurately equalize the data.

[0089] In some embodiments, noise can be transmitted along the columns of the N matrix. As an example, this can be accomplished using the following additional matrix as a spatial expansion matrix during both the training field transmission and data transmission:

[0090] in This is a matrix formed by selecting any number of columns from matrix N. Since there is no data to be sent, any desired number and combination of columns can be used. When there is other traffic on the wireless network, fewer columns can be used to reduce overall system noise.

[0091] In this example, the following vectors are transmitted during the transmission of LTF symbols and data symbols, respectively:

[0092] LTF: Q×[x] LTF ,n 1,L ,…,n m,L ] T Equation 14

[0093] Data: Q×[x Data ,n 1,D ,…,n m,D ] T Equation 15

[0094] Where m is The number of columns in the matrix. 1,L ,…,n m,L These are noise samples transmitted during the LTF period, and n 1,D ,…,n m,D These are noise samples transmitted during data transmission. These noise samples can be drawn from any distribution and then appropriately scaled to maintain the same transmit power level between LTF symbols and data symbols.

[0095] When transmitting noise, the expected LTF symbol received by the user can be represented as:

[0096]

[0097] (because )

[0098] This can be compared to the previous setup, in which the symbols expected to be received by the user during the LTF could be represented as:

[0099]

[0100] (Because HN=0)

[0101] As a result, the received LTF symbols were the same in both settings.

[0102] On the other hand, for the eavesdropper, under the new settings, the symbols received during the LTF period can be represented as:

[0103]

[0104] Under the previous settings, this meant

[0105] H ev Q LTF x LTF =HVx LTF +HNA LTF x LTF Equation 19

[0106] Part 1 (i.e., HVx) LTF The result is the same in both settings. Additionally, and NA LTF x LTF Both produce vectors in the column space of matrix N. Therefore, by appropriately choosing A... LTF It can make and HNA LTF x LTF Statistically similar.

[0107] Although the above expression describes the received training symbols, the received data symbols will be similarly affected.

[0108] In yet another embodiment, n can be randomly drawn from the set {+1, -1}. 1,L ,…,n m,L And randomly select n from the constellations in the data 1,D ,…,n m,D This generates noise. Compared to generating deterministic values, this implementation reduces complexity while automatically ensuring power balance between LTF symbols and data symbols.

[0109] In another embodiment, different spatial expansion matrices can be used for LTF symbols and data symbols, for example: and in and It can contain different subsets of the columns of an N matrix. This provides greater diversity in the null space where noise is directed to potential eavesdroppers.

[0110] In another embodiment, This can be symbolically changed by selecting different subsets of the columns of matrix N. This provides even more diversity in the null space. Additionally, it is possible to target... and Choose the same or different number of columns among the data symbols.

[0111] Figure 5 This is a high-level block diagram of a wireless networking node 500, such as a Wi-Fi AP or STA, or any other node in a hub-based wireless network or peer-to-peer wireless network utilizing beamforming. The networking node 500 can operate as a transmitting and receiving device as described above. It can also be configured to connect to external devices, such as data routers, computers, terminals, and edge devices. A transceiver module 502, including a transmit and receive chain with suitable radio frequency components, is coupled to an antenna array using two or more antenna elements 504, 506. The transceiver module transmits and receives data via the antennas to connect to other nodes on the wireless network. The transceiver module is coupled to a microcontroller (MCU) 508 or optionally to another controller or processor of a wired interface 510.

[0112] The wired interface can connect to controllers, peripherals, and other nodes on a wired network to communicate using Ethernet, USB (Universal Serial Bus), and any additional or other wired communication interfaces. The wired interface can be configured to connect to one or more remote computers, remote sensors and / or controllers, detection devices, handheld devices, multifunction devices (MFDs), speakers, mobile devices, tablets, mobile phones, smartphones, or other such devices. Remote computers can also be personal computers (PCs), servers, routers, network PCs, RFID-enabled devices, peer-to-peer devices, or other public network nodes. Communication connections can include LANs, WANs, Bluetooth networks, or other networks.

[0113] The MCU 508 includes a processing core, memory, data buffers, and data storage devices. The MCU 508 is coupled to various interfaces and resources, which may be coupled internally to the MCU or via an external bus 518, as shown, or a combination of both. These interfaces and resources may include a user interface 512, which may be wired or wireless, a general-purpose input / output interface 514, and a data storage device 516 for configuring registers, user data, and other data. Resources may also include an instruction storage device 520, which may be integrated with or separate from the data storage device 516. The data 516 and instruction storage device 520 may include various transient and non-transient computer-readable media, such as volatile memory, non-volatile memory, removable storage devices, and non-removable storage devices. This storage device may take the form of, for example, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM) and electrically erasable programmable read-only memory (EEPROM), flash memory or other memory technologies, high-density disk read-only memory (CDROM), digital versatile optical disc (DVD) or other optical disc storage devices, magnetic tape cassettes, magnetic tapes, disk storage devices or other magnetic storage devices, or any other medium capable of storing computer-readable instructions and data.

[0114] The instruction storage device 520 includes computer-readable instructions for use by the MCU or other processing resources of the networking node 500, such as program code in an application module, and may include or represent software routines, software subroutines, software objects, etc., applicable to the operations described herein. These instructions may include computer code, such as networking code, protocol code, beacon code, authentication code, and router code.

[0115] Specifically, the instructions may include beam-directing code 522 to derive a beam-directing vector using channel state information and other data, and to combine the beam-directing vector with other information to form a spatial mapping matrix for use by transceiver module 502. The instructions may also include perturbation matrix code 524 for generating a perturbation matrix and noise generation code 526 for generating elements of the perturbation matrix and for generating symbols to be transmitted outside the receiving device, as well as for other purposes.

[0116] Figure 6 This is a block diagram of the transmit chain 600 of transceiver module 502. Transceiver module 502 also has a receive chain that performs similar operations in reverse order. Transmit chain 600 includes encoder 602 to receive training symbols, data symbols, and noise symbols from MCU 508 or another source, and to encode these symbols using forward error correction codes such as Reed-Solomon codes or parity-check codes. Encoder is coupled to interleaver 604. Interleaver is coupled to space mapping module 606 to pre-encode the interleaved symbols using a space mapping matrix. Space mapping module 606 is coupled to insertion module 608 to insert pilot symbols and other symbols. Insertion module 608 is coupled to inverse fast Fourier transform (IFFT) 610 to transform the symbols into the time domain. IFFT 610 is coupled to cyclic prefix insertion module 612 to insert guard intervals and other structures. Cyclic prefix insertion module is coupled to RF module 614 for RF modulation and amplification, which is coupled to antenna array 616. The transmission chain may include other or additional components to suit a particular wireless transmission format, including scramblers for transposing, inverting, or encoding messages, and convolutional encoders for Viterbi or other error correction codes. These bits can be punctured and mapped to any of a variety of other phase-shift or frequency-shift paradigms.

[0117] Although the operations of the methods herein are shown and described in a specific order, the order of operations for each method may be changed so that certain operations can be performed in reverse order, or that certain operations can be performed at least partially concurrently with other operations. In another embodiment, instructions or sub-operations of different operations may be implemented intermittently and / or alternately.

[0118] It should also be noted that at least some of the operations of the methods described herein can be implemented using software instructions stored on a computer-usable storage medium for execution by a computer. As an example, embodiments of a computer program product include a computer-usable storage medium for storing a computer-readable program.

[0119] The computer-usable or computer-readable storage medium may be an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system (or device or apparatus). Examples of non-transient computer-usable and computer-readable storage media include semiconductor or solid-state memory, magnetic tape, removable computer disks, random access memory (RAM), read-only memory (ROM), hard disks, and optical discs. Current examples of optical discs include high-density disks with read-only memory (CD-ROM), high-density disks with read / write capability (CD-R / W), and digital video optical discs (DVDs).

[0120] Alternatively, embodiments of the present invention can be implemented entirely in hardware or in implementations that include both hardware and software elements. In software-based embodiments, the software may include, but is not limited to, firmware, resident software, microcode, etc.

[0121] While specific embodiments of the invention have been described and illustrated, the invention is not limited to the specific form or arrangement of the components thus described and illustrated. The scope of the invention will be defined by the appended claims and their equivalents.

Claims

1. A communication method, characterized in that, include: Channel state information is obtained at the transmitting device from a receiving device in the wireless network, the channel state information being received through the wireless network; Based on the channel state information, a first set of beam steering vectors is derived to guide the first radio signal to the receiving device; Based on the channel state information, a second set of beam steering vectors is derived to guide the second radio signal outside the receiving device, wherein the second set of beam steering vectors is orthogonal to the first set of beam steering vectors; Generate the perturbation matrix; A spatial mapping matrix is ​​formed by combining the first set of beam steering vectors and the second set of beam steering vectors with the disturbance matrix; The spatial mapping matrix is ​​used to pre-encode the data symbols to be transmitted into the receiving device; as well as The pre-encoded data symbols are sent to the receiving device via the wireless network.

2. The method according to claim 1, characterized in that, The channel state information includes the channel coefficient matrix.

3. The method according to claim 2, characterized in that, Derivation of a set of beam steering vectors involves applying singular value decomposition to the channel coefficient matrix.

4. The method according to claim 1, characterized in that, Additionally, it includes sending a channel state information request to the receiving device, and obtaining the channel state information includes receiving the channel state information as feedback in response to the channel state information request.

5. The method according to claim 1, characterized in that, The perturbation matrix is ​​configured to have a scalar selection factor that is chosen to be zero or one for each perturbation matrix value.

6. The method according to claim 1, characterized in that, The perturbation matrix is ​​configured to have a scalar power factor for each perturbation matrix value.

7. The method according to claim 1, characterized in that, The perturbation matrix value is a random number in the range of zero to 2π.

8. The method according to claim 1, characterized in that, The data symbols are a series of data symbols, and the method further includes changing the perturbation matrix value after precoding each data symbol in the series of data symbols.

9. A computer-readable medium having instructions stored thereon, characterized in that, When executed by a computer, the instructions cause the computer to perform operations including the following: Channel state information is obtained at the transmitting device from a receiving device in the wireless network, the channel state information being received through the wireless network; Based on the channel state information, a first set of beam steering vectors is derived to guide the first radio signal to the receiving device; Based on the channel state information, a second set of beam steering vectors is derived to guide the second radio signal outside the receiving device, wherein the second set of beam steering vectors is orthogonal to the first set of beam steering vectors; Generate the perturbation matrix; A spatial mapping matrix is ​​formed by combining the first set of beam steering vectors and the second set of beam steering vectors with the disturbance matrix; The spatial mapping matrix is ​​used to pre-encode the data symbols to be transmitted into the receiving device; as well as The pre-encoded data symbols are sent to the receiving device via the wireless network.

10. A communication device, characterized in that, include: A controller is configured to obtain channel state information from a receiving device in the wireless network via the wireless network, derive a first set of beam steering vectors based on the channel state information to guide a first radio signal to the receiving device, and derive a second set of beam steering vectors based on the channel state information to guide a second radio signal out of the receiving device, wherein the second set of beam steering vectors is orthogonal to the first set of beam steering vectors, generates a perturbation matrix, and forms a spatial mapping matrix by combining the first set of beam steering vectors and the second set of beam steering vectors with the perturbation matrix; as well as A transceiver is used to precode data symbols to be transmitted into the receiving device using the space mapping matrix, and to transmit the precoded data symbols to the receiving device via the wireless network.

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