WO2022031245A1

WO2022031245A1 - A communication system with multiple-input single-output non-orthogonal multiple access (miso-noma) system and its communication method

Info

Publication number: WO2022031245A1
Application number: PCT/TR2021/050485
Authority: WO
Inventors: Jehad Mahmoud HAMAMREH; Muhammad Furqan ZIA
Original assignee: Antalya Bilim Universitesi Rektorlugu
Priority date: 2021-05-25
Filing date: 2021-05-25
Publication date: 2022-02-10

Abstract

The invention is a communication system and its method presenting a much simpler yet more efficient physical layer security (PLS) technique for achieving reliable and secure communication in the multiple-input single-output non-orthogonal multiple access (MISO-NOMA) systems.

Description

A COMMUNICATION SYSTEM WITH MULTIPLE-INPUT SINGLE-OUTPUT NON- ORTHOGONAL MULTIPLE ACCESS (MISO-NOMA) SYSTEM AND ITS COMMUNICATION METHOD

TECHNICAL FIELD

BACKGROUND

In the literature, several studies have focused on applying PLS to NOMA- based systems to improve their confidentiality against eavesdropping or illegitimate access by unintended devices.

Xiang et al. (Z. Xiang, W. Yang, G. Pan, Y. Cai, and Y. Song, “Physical layer security in cognitive radio inspired noma network,” IEEE Journal of Selected Topics in Signal Processing, vol. 13, no. 3, pp. 700-714, 2019) proposed a NOMA network with multiple primary and secondary users. This work focuses on PLS design in cognitive radio. In this technique, firstly, the primary and secondary users are paired following their channel gain, and afterwards, the signal is transmitted using powerdomain NOMA. This research suggests that by pairing the primary users with the most excellent gains or by minimizing the number of secondary users, the secrecy of data can be improved. Furthermore, Lv et al. (L.Lv, Z. Ding, Q. Ni, and J. Chen, “Secure miso-noma transmission with artificial noise,” IEEE Transactions on Vehicular Technology, vol. 67, no. 7, pp. 6700-6705, 2018), proposed new secrecy beamforming (SBF) technique by using artificial noise to secure private data of the two users within a NOMA network. This model is designed for MISO-NOMA systems such that only the eavesdropper receives a degraded version of the signals. Nevertheless, the proposed powerdomain technique still suffers from SINR degradation.

In addition, §ahin et al. (M. M. §ahin and H. Arslan, “Waveform-domain NOMA: The future of multiple access,” arXiv preprint arXiv:2003.05548, 2020 - arxiv.org) proposed a waveform-domain NOMA. This proposed model presents the idea for the utilization of multiple waveforms in the same resource element, where the most appropriate waveform is allocated to each user and then decoded at the receiver. Thus, this system suffers from the drawback that it requires additional processing at the receiver, resulting in high power consumption with enhanced complexity.

In “Z.Qin,Y. Liu, Z. Ding, Y. Gao, andM.EIkashlan, “Physicallayersecurityfor5gnon- orthogonal multiple access in large-scale networks,” 05 2016, pp. 1-6” authors analyzed the PLS efficiency of a downlink SISO-NOMA scenario for the first time in the literature. They developed a solution of devising the optimum power allocation strategy that enhances the secrecy sum-rate to the maximum against an external eavesdropper, given a particular constraint on each user’s QoS requirements in the network. It has been shown that the degree of confidentiality offered by NOMA is substantially higher than that provided by conventional OMA.

In “C. Zhong and Z. Zhang, “Non-orthogonal multiple access with cooperative full-duplex relaying,” IEEE Communications Letters, vol. PP, pp. 1-1 , 09 2016”, the authors proposed the secured transmission of a MISO-NOMA downlink case, where multiplexed users are divided into multiple categories, each consisting of a cellcentric, nearuser (NU) and a far-user (FU) cell-edge. The near user is considered an authorized user, while the far user is an internal eavesdropper. The authors analyzed the joint optimization of the beamforming system as well as the power allocation system, which enhances the near-user total sum secrecy rate to a certain level at the transmitter and target its rate requirements at the NU.

In “Y. Zhang, H. Wang, Q. Yang, and Z. Ding, “Secrecy sum rate maximization in non-orthogonal multiple access,” pp. 930-933, 05 2016”, the drawback in the secrecy sum-rate maximization was investigated for a downlink MIMO-NOMA network. This network consists of a base station, multiple authorized users, and an external eavesdropper. The scenario considered by authors in “O.Maraqa, A.Rajasekaran, S.AI-Ahmadi, and S.Sait, “Asurveyofrate-optimalpowerdomain noma with enabling technologies of future wireless networks,” 08 2020.” is similar to that adopted in “C. Zhong and Z. Zhang, “Non-orthogonal multiple access with cooperative full-duplex relaying,” IEEE Communications Letters, vol. PP, pp. 1-1 , 09 2016” for the case of (i.e., MIMO-NOMA) networks. The authors also addressed the problem of internal (FU) that is eavesdropping the communication of nearby celledge users. According to the authors, this issue is solvable by designing an optimized, secure beamforming technique to enhance the secrecy rate subject to its maximum capacity for a certain transmit power level and target data rate. In “Y. Liu, Z. Qin, M. Elkashlan, Y. Gao, and L. Hanzo, “Enhancing the physical layer security of non- orthogonal multiple access in large-scale networks,” 01 2017”, PLS performance of NOMA in large-scale communication systems was analyzed using stochastic geometry, where scenarios for both single-antenna and multiantenna base stations are considered. In the scenario of a single antenna-aided base station, the secure area available around the base station is adopted to assist the multiplexed users’ judicious channel ordering. For the scenario of a multi-antenna-equipped base station, artificial noise is produced at the base station to enhance the secrecy of data further.

In “Z. Ding, Z. Zhao, M. Peng, and H. V. Poor, “On the spectral efficiency and security enhancements of noma assisted multicast-unicast streaming,” 11 2016”, the authors examined NOMA’s application with cases of mixed multicasting and unicasting transmission to increase the spectral efficiency and capability of the system to provide secrecy. The proposed design of joint beamforming and power allocation ensures unicasting, enhanced efficiency while maintaining the multicasting reliability. The authors in “B. He, A. Liu, N. Yang, and V. Lau, “On the design of secure non-orthogonal multiple access systems,” 12 2016” introduced a novel design of a secure NOMA network to protect the transmitted data from external eavesdroppers. In this work, ideal designs of data rates, the order of decoding and the power assigned to every user is studied. The secrecy loss probability is considered as the secrecy matrix. Firstly, secrecy loss and QoS are formulated. Afterward, a closed-form solution to this issue was developed. In addition, the issue of enhancing the secrecy rate among users to maximum (inspired by the requirement of providing fairness among the users) was also studied, subject to the limitations of certain secrecy loss and transmit power, where an iterative algorithm was proposed to eliminate this drawback.

In “T.-N. Tran and M. Voznak, “On secure system performance over SISO, MISO and MIMO-NOMA wireless networks equipped a multiple antenna based on tas protocol,” 12 2020”, the authors studied the secrecy efficiency of a downlink NOMA system with two users, which considers both SISO and MISO scenarios with different transmit antenna selection (TAS) techniques. Exact closed-form formulas for the probability of secrecy loss are obtained with suboptimal TAS and optimal TAS techniques and contrasted with the standard space-time transmission technique. A power allocation scheme is also proposed for all of the TAS techniques to achieve non-zero diversity order.

In “D. Xu, P. Ren, Q. Du, L. Sun, and Y. Wang, “Combat eavesdropping by full-duplex technology and signal transformation in non-orthogonal multiple access transmission,” pp. 1-6, 05 2017”, the authors recommended the properties of good eavesdropping- resilient techniques in the NOMA network. Although the conventional PLS techniques can resist the eavesdropping, there is a high probability of an internal eavesdropper to appear between the users in a NOMA network. Therefore, the authors summarized these properties in three rules that each NOMA network must follow to secure itself from eavesdropping:

(1 ) operation of successive interference cancellation (SIC) without the need for any extra processing.

(2) users should not be able to obtain each other’s information.

(3) the adopted technique is preferable to be independent of the spatial differences between channels due to high correlation.

In consideration of these rules, the authors introduced a new PLS technique. In this proposed technique, the original user’s information signals are converted into the signals to be transmitted using a specially designed angle conversion method, where the fundamentals of these variations are different for different users. A suitable system is also designed with fullduplex technology to ensure that users can learn their fundamentals safely. This technique helps provide a regular operation of SIC by allowing each user to gather the transmitted signals from other users. However, the original signals are challenging to determine from transmitted signals and can be obtained only by the corresponding authorized users.

In “O. Abbasi and A. Ebrahimi, “Secrecy analysis of a NOMA system with full duplex and half duplex relay,” pp. 1-6, 05 2017”, the authors studied the PLS of NOMA using HDR and FDR, where along with two authorized users in a NOMA network, one eavesdropper is also present. It is presumed that a dedicated FDR or HDR assists the Far user. In “L. Lv, F. Zhou, J. Chen, and N. Al-Dhahir, “Secure cooperative communications with an untrusted relay: A NOMA-inspired jamming and relaying approach,” pp. 1-1 , 04 2019”, the issue of safe transmission in unauthorized relay networks has been investigated. In contrast to conventional orthogonal relaying, a modern, non-orthogonal relaying technique is proposed to optimize the secrecy rate. Specifically, the source and relay nodes are permitted to simultaneously transmit signals over non-orthogonal channels (which induces co-channel interference), and SIC is usually applied to the destination node to decode the corresponding signal. The authors also proposed two antenna selection scheme for transmitting the signals to further enhance the secrecy.

The authors proposed a novel PLS technique in “X. Chen, Z. Zhang, C. Zhong, D. W. K. Ng, and R. Jia, “Exploiting inter-user interference for secure massive non-orthogonal multiple access,” 02 2018”, for the 5G networks with huge connections, where several active eavesdroppers are present. NOMA is combined with non-orthogonal channel estimation (NOCE) to enhance the quality of signal only for the authorized user to establish secure communication. Moreover, the inter-user interference is harnessed without exploiting artificial noise, which helps confuse the eavesdroppers. The authors further suggest the boosting of transmit power during multiple access stage and channel estimation stage to control the inter-user interference for enhancing the secrecy of communication.

Therefore, the conventional solutions adopted by industry to provide secure communication in NOMA and other wireless technologies are based on cryptography, but they are not suitable for NOMA communication due to many reasons related to the extreme difficulties that would be encountered in key sharing, management and maintenance processes, especially for the scenarios that consists of massive number of loT devices. This would result in creating signaling overhead, delay and complexity, which are contrasting many of the loT requirements represented by simplicity, low complexity and power efficiency. These difficulties can be summarized in the following points:

• The key distribution and management processes for the legitimate parties are extremely difficult tasks, especially in large-scale, dense, and heterogeneous wireless networks, where a massive number of smart devices are simultaneously connected to the network, causing excessive complexity, high signaling overhead, and costly computational processes. Also, the management and control frames exchanged between communication entities are usually not very well protected.

• Longer key length results in more waste of resources, apart from the fact that implementing security methods with Shannon’s perfect secrecy is extremely hard to be practically carried out with today’s huge data volume. Particularly, for each message to be transmitted in perfect secrecy, it is required to use a secret key of length equal to that of the message itself and this key must be updated (i.e. , use a different key) with each new message.

• The fast developments and advances in computing power devices reveal the fact that current secret key-based techniques can be cracked, no matter how much mathematically complex they are, especially when quantum computing becomes a reality.

• Cryptography-based security methods add extra delay and complexity to the loT-based tactile communication applications such as autonomous driving, remote surgery operation, controlling unmanned aerial vehicles (UAVs), etc. These future applications require utmost secure communication with minimal latency.

• Given the extremely wide range of loT-based wireless applications including industrial, medical, commercial, governmental, and military related ones, designing practical security techniques is becoming an indispensable need for future xG systems.

BRIEF DESCRIPTION OF THE INVENTION

The future wireless communication systems demand much more enhanced security and reliability compared to currently deployed systems. In this invention, we present a much simpler yet more efficient physical layer security (PLS) technique for achieving reliable and secure communication in the multiple-input single-output non- orthogonal multiple access (MISO-NOMA) systems. This system can provide enhanced confidential communication and inter-user interference cancellation without using the successive interference cancellation (SIC) method.

The conventional power domain PD-NOMA was previously adopted under the name of multi-user superposition transmission (MUST) in release 13 of 3GPP but recently excluded from 3GPP-release 17 due to its performance degradation from the SIC at the receiver, which raises the chance of eavesdropping. After analyzing the drawbacks in conventional NOMA, we have invented a new kind of NOMA with more improved performance metrics.

Our novel algorithm combines the benefit of pre-coder matrices with simultaneous transmission using antenna diversity to provide simple, reliable, and secure communication without complex processing at the receivers in downlink scenarios. The effectiveness of the proposed algorithm is verified and proven by extensive analysis and numerical simulations.

LIST OF FIGURES

Figure 1. Basic block diagram of proposed new NOMA with signal precoding using spatial diversity-based system (i.e., simultaneous transmission from two antennas enabled by MISO)

Figure2. Bit Error rate (BER) versus SNR performance for the proposed algorithm

Figure 3. Throughput versus SNR performance for the proposed algorithm

Figure 4. Comparison of peak to average power ratio (PAPR) performances of the conventional OFDM and proposed algorithm

DETAILED DESCRIPTION OF THE INVENTION

The system design of the sections that build up our invention are explained separately below.

THE TRANSMITTER DESIGN

The transmitter in our proposed system comprises a two-user two-antenna multicarrier down-link authorized transmitter (Tx) that aims to communicate with two single antenna authorized users in the presence of a passive single antenna eavesdropper as can be seen in Fig. 1 .

Our MISO system employs spatial diversity enabled by transmitting the same composite signal (i.e., two user signals) simultaneously from two antennas. Furthermore, it is considered that the transmitter has no information regarding the channel of a passive eavesdropper.

CHANNEL MODEL

The channel between transmitter (Tx) and any random user -slowly varies multi-path Rayleigh fading with the exponentially decaying function that we presume is known at the transmitter. Also, channel reciprocity property is adopted, where channel sounding techniques have the potential to be implemented to estimate the channel from the transmitter (Tx) to the receiver using the channel from the receiver to transmitter in time division duplexing (TDD) method. The communication system employs a simultaneous transmission of two user signals from two antennas. The authorized transmitter is responsible for the security of communication within the users so that the external eavesdropper cannot receive the user’s signal information, nor the users get each other’s data.

THE RECEIVER DESIGN

The receiver consists of user-1 , user-2, and external eavesdropper. Both the users decode their authorized precoded data, which helps in keeping the data entirely secret. While eavesdropper trying to intercept and access the data from user- 1 and user-2 receives the degraded version of signals.

The algorithm is designed to meet the need for secure, low latency, and low computational power at the receiver. In our invention, we superimpose the data sequence of two users along side pre-coder matrices and transmit them simultaneously from two antennas. However, it should ensure that this simultaneous transmission occurs in different channels and not on the same channel. It allows us to devise a set of intelligent pre-coder that can prevent external eavesdropping and internal eavesdropping. Besides, compared to a single-user channel-based security algorithm, the transmission of two users signals from two antennas create more difficulty for the eavesdropper. Therefore, the pre-coders used in the invention are a function of multiple authorized user channels. However, in the case of single-user channels, pre-coder is a function of single user channel only. The simultaneous transmission role facilitates authorized users' ability to decode the intended information while making it more difficult for unauthorized users to decipher the signal being transmitted.

Besides, in conventional NOMA, there is only one transmission used with successive interference cancellation (SIC) at the authorized receiver. But in our proposed technique, SIC is not required. We transmit the signal simultaneously from two antennas, which results in an automatic interference cancellation because of the specially designed precoding matrices.

In our invention, we ensure reliability and security through joint PHY and MAC mechanisms. In particular, NOMA inspired pre-coded superposition coding, together with cross-layer principles of simultaneous transmission with antenna diversity, is implemented. It made communication more secure and reliable for downlink scenarios without requiring any additional computational processing at the receiver.

We consider two users, and each user consists of one antenna, i.e. , a total of two antennas at the transmitter, as shown in Fig. 1. The total number of carriers in one OFDM block for each user at the receiver is ^Nf. In this way, the frequency response for the OFDM symbol for user-1 and user-2 can be represented asxi = [xo xi XNn] 2 C^[Nf^1] and X2 = [xo xi XNA ] 2 C^[Nf^1].Note thatykm2c^[Nf^1],Hkm2c^[Nf^Nf^]andzkm2c^[Nf¹ 'present the received signal, the channel's frequency response, and AWGN that is experienced between kth user and mth antenna of transmitter.

Transmitted Signal from Antenna-1 and Antenna-2

The design of pre-coded matrices for our invention’s algorithm is explained in extensive detail in the preceding discussion. The following equation indicates the superimposed pre-coded transmitted signal from antenna-1.: U1 = Ml aXl + M2aX2 (1 )

Similarly, the data, along with the precoding matrices, are superimposed and transmitted from antenna-2. The equation can be given as:

U2= Ml bXl + M2bX2 (2) where data vectors for user-1 and user-2 are xiand X2in the frequency domain, the overall power is equal between the two users, whereas the pre-coder matrices are Mia, M2a, M and M2b. These pre-coders will ensure that users 1 and user 2 will receive reliable signals that are also secure against eavesdropping by internal and external hackers. We will briefly explain how the signal at user-1 , user-2, and eavesdropper is affected. Afterward, the pre-coding matrices will be explained in depth.

Signal Received at User-1

The signal received from the transmission via antenna-1 in the frequency domain at user-1 can be written as: Yu = H11 U1 + Z11 (3) where Hu and zn are the channel's frequency response and AWGN between user-1 and antenna-1 .

Similarly, the transmitted signal via antenna-2 to user-1 is:

Y12 = H12U2+ Z12 (4) where, H^ and zi2 are the channels' frequency response and AWGN between user-1 and antenna-2.

The composite signal received at user-1 from simultaneous transmission through antenna-1 and antenna-2 can be given as: yi = yn + yi2 (5) where, yn and yi2 are the signal received at user-1 from simultaneous transmission through antenna-1 and antenna-2. The combined signal can be shown as follows after placing the values of ynand yi2. yi = H11 U1 + zn + H12U2 + Z12 (6)

We substitute the ui and U2values from (1 ) and (2) and simplify them, yi = Hn (MlaXl + M2aX2) + Z11 + Hl2(Ml bXl + M2bX2) + Z12 (7) yi = (Hu Mla + Hl2Mlb)Xl + (Hn M2a+ Hl2M2b)X2 + Z11 + Z12 (8)

In (8), the first term is the desired term for user-1 and the second term is unwanted term for it. Pre-coder matrices ensure that both the unwanted term and the channel effects are removed from user-1 and canceled.

Signal Received at User-2

Similar to user-1 , the expression for the composite signal received at user-2 from the simultaneous transmission via antenna-1 and antenna-2 can be given as: y2= y2i + y22 (9)

The signal received from the transmission via antenna-1 in the frequency domain at user-2 can be given as: y2i = H21 U1 + Z21 (10) where H21 and Z21 are the channels' frequency response and AWGN between user-2 and antenna-1 .

Similarly, the signal that is received at user-2 from transmission using antenna-2 is given as: y22 = H22U2 + Z22 (11 ) where H22 and Z22 are the channels' frequency response and AWGN between user-2 and antenna-2.

After substituting y2i and y22, the composite signal is given as: y2 = H21 U1 + Z21 + H22U2 + Z22 (12)

Substituting the values of ui and U2from (1 ) and (2) and simplifying, we get: y2 = H2l (MlaXl + M2aX2) + Z21 + H22(Ml bXl + M2bX2) + Z22 (13) y2 = (H2lMla + H22Mlb)Xl + (H2l M2a + H22M2b)X2 + Z21 + Z22 (14)

In (14), the first term is the desired term for user-2 and the second term is unwanted. Pre-coder matrices ensure that both the unwanted term and the channel effects are removed from user-1 and canceled.

Signal Received at Eavesdropper

The composite signal received by eavesdropper due to simultaneous transmission through antenna-1 and antenna-2 can be given as: ys = ysi + y32 (15)

The received signal in the frequency domain at the eavesdropper from transmission through antenna-1 can be given as: ysi = H31U1 + Z31 (16) where H31 and Z31 are the channels' frequency response and AWGN between eavesdropper and antenna-1.

Similarly, the signal that is received at eavesdropper from transmission using antenna-2 is given as: y32 = H32U2 + Z32 (17) where Hs-iand zsiare the channels' frequency response and AWGN between eavesdropper and antenna-2.

Substituting the values ysi and y32, the composite signal can be presented as: ys = H31 U1 + Z31 + H32U2 + Z32 (18)

Substituting the values of uiand U2 from (1 ) and (2) and simplifying, we get: y3 = H3l (MlaXl + M2aX2) + Z31 + H32(Ml bXl + M2bX2) + Z32 (19) y3 = (Hsi Mla + H32Mlb)Xl + (H3l M2a+ H32M2b)X2 + Z31 + Z32 (20)

The eavesdropper would like to receive user-1 and user-2 information. Therefore, both the first and second terms in (20) are the desired terms for it.

Design of Pre-coders

Now, we design the Mia, M , M2a and M2b pre-coder matrices that will be superimposed with the modulated signal to provide secure information to the authorized users, ensuring safe communication from the internal and external eavesdroppers the composite received signal from simultaneous transmission via the antenna 1 and antenna 2. The pre-coder design is inspired by several interesting works in the literature. The design procedure of Mia and M is discussed below:

We take measures to isolate the impact of the channel at user-1 , therefore we consider equation 8 and equate its first term with identity matrix as can be seen in equation 21 , HuMia + Hi2Mib=l (21 )

As both users cause interference. Now, we will remove this interference by equating the first term of (14) with zero. The new equation formed is given below:

H2lMla + H₂₂Mlb=0 (22)

In order to find the values of pre-coders Mia and M , we will solve equations (21 ) and (22) simultaneously,

Mla= H22(H22H12 + H22H12)-¹ (23)

Mlb= - H22(H22Hl2 + H22H12)'¹ (24)

To design M2a and M2b, we will first recall the earlier steps used in designingM-ia and M . To remove the channel's effect at user-2, the second term in equation (14) can be set equal to identity matrix and can be written as: H₂iM₂a + H₂₂M2b= I (25)

For canceling the interference caused by user 2 on user 1 . We consider equation 8 and equate its second term to 0.

HnM_2a + Hi₂M2b=0 (26)

In order to find the values of pre-coders M2a and M2b we will solve (21 ) and (22) simultaneously,

M2a= H12(H12H21 + H11 H22)-¹ (27)

M_2b = - H11 (H12H21 + H11 H22)-¹ (28)

In the simultaneous transmission, the pre-coder matrices Mia, M , M2a and M2b are superimposed with the data to provide reliable and secure transmission against internal and external eavesdroppers. The pre-coder matrices are provided in equations (23), (24), (27) and (28).

Mathematical signal-to-interference-plus-noise ratio (SINR) analysis for the proposed algorithm

For the case of an eavesdropper, it is observed from the equation (20) that the eavesdropper is interested in eavesdropping the data of both user-1 and user-2. The signal to interference noise ratio (SINR) at eavesdropper for eavesdropping the information intended for user-1 is given as:

where, o2 31 and 0232 are the variances of noise power corresponding toHsizsiand H32Z32, respectively. Similarly, the SINR at eavesdropper for eavesdropping the information intended for user-2 is given as:

It is clear from equations 29 and 30 that there is a severe performance degradation at eavesdropper when it tries to eavesdrop the information intended for either user because of interference terms (inter-user interference) in the denominators of these equations. Moreover, the terms Hu, H12, H2iand H22 are unknown to the eavesdropper, making eavesdropping more challenging.

Below a step-by-step explanation of our invention's algorithm is given in the consideration of a multi-user OFDM communication system with two users:

Firstly, the data sequence of two users is passed through a modulator and then converted from serial to parallel, so it becomes a column vector.

The pre-coder matrices are devised where four different channel-dependent intelligent pre-coder matrices are superimposed with these data vectors.

The mixture of the data vector and pre-coder matrices is transmitted simultaneously from two antennas to the receiver of both user 1 and user 2, easily decrypted at the authorized users.

The simultaneous transmission of data from two antennas with superimposed pre-coder matrices helps in automatic interference cancellation. It eliminates the need for successive interference cancellation (SIC), which minimizes the computational complexity at the authorized receiver and increases the complexity for the eavesdropper.

Many existing communication security problems can be solved with this invented NOMA scheme such as, the problem of external and internal eavesdropping, complexity problems, and high-power consumption issues, also it provides improved PAPR performance. Advantages of Our New Invented NOMA Scheme:

• The proposed scheme can provide security against external Eve because the pre-coders are dependent on the channels of the legitimate nodes.

• The proposed scheme can also provide security against internal Eve by ensuring that there will be no leakage of information among users.

• Due to the diagonal channel matrices, the inverse operation is simple. Hence, pre-coder matrices can be designed by simple computation.

• In our proposed scheme, there is no need of successive interference cancellation (SIC) at the receiver because we transmit the signal simultaneously from two antennas at one time and there is an automatic interference cancellation due to the specially designed pre-coding matrices. Hence, it can support applications with processing limited receiver (loT-based application).

• Mixture of channel-based pre-coded signals of two users that are transmitted simultaneously from two antennas is more challenging to eavesdrop compared to channel adaptive secure transmission based on a single user.

SIMULATION RESULTS FOR OUR INVENTION’S ALGORITHM

We have evaluated the performance for superimposed pre-coder matrices with simultaneous transmission using antenna diversity for two users’ signals. The simulation of bit error rate (BER), throughput, and PAPR used as performance metrics proves the effectiveness of our proposed technique.

• Bit Error Rate (BER) Analysis: Figure 2 compares the bit error rate (BER) versus signal to noise ratio (SNR) plots for the invention. It is evident from figure 2 that the user-1 (Bob1 ) and user-2 (Bob2) performances are similar. However, there is a considerable difference between authorized users' BER performances and those of eavesdroppers. The labels E-Eve-1 and E-Eve-2 represents external eavesdropper, and similarly, l-Eve-1 and l-Eve-2 represents the internal eavesdropper attempting to eavesdrop the signal. The degraded performance shown by both the eavesdroppers proves the efficiency of our invention’s algorithm. The results of the BER analysis demonstrate that the proposed scheme provides efficient performance for the communications.

• Throughput Analysis: Figure 3 represents the throughput plots for the basic of our invention, multiple input single output (MISO) system. Through experiments, we have observed that the number of transmitted packets in our system is equal to the number of time slots, enhancing the joint throughput of authorized users. As can be seen from Fig. 3, the individual throughput performances of user-1 (Bob-1 ) and user- 2 (Bob-2) employing our invention’s algorithm are similar to each other. The excellent throughput performance of the authorized user's signals and the deterioration of external and internal eavesdropper's signals proves our algorithm's robustness.

It is essential to consider that although eavesdroppers' throughput performance is not zero, it is still possible to provide quality of service (QoS) based security. QoSbased security refers to the protection provided considering the requirements of various communication networks such as (voice, video, etc.). Further, it is observed that different communication networks have different QoS requirements for effective communication. Therefore, to enhance a specific network's security, we degrade the performance of eavesdropper below the requirements of QoS for that network.

• Peak to Average Power Ratio (PAPR) Analysis: Figure 4 depicts a comparison of the peak to average power ratio (PAPR) performances of the conventional OFDM and OFDM with our invention’s algorithm for user-1 (Bob-1) and user-2 (Bob-2). It can be observed in Fig. 4 that the proposed method's PAPR performance outperforms the conventional method at high SNR values. The developed scheme gets improved PAPR because the precoder matrices, when designed at the transmitter, change the signal's distribution from being gaussian to something less random than gaussian and close to uniform. Therefore, it resolves one of the significant challenges faced by OFDM systems by reducing the PAPR, which results in improved spectral and energy efficiency.

Overall, as can be seen from the above-detailed analysis, the proposed invention can be a good solution for providing secure communication, especially for the low processing loT-based devices.

Claims

CLAIMS A communication system with multiple-input single-output non-orthogonal multiple access (MISO-NOMA) system that employs spatial diversity, characterized by comprising;

- two-user two-antenna multi-carrier down-link authorized transmitter (Tx) to communicate with two single antenna authorized users by sending data sequences in the presence of a passive single antenna eavesdropper, and wherein the data sequences of two users are superimposed along side different pre-coder matrices and transmitted simultaneously from two antennas (two different channels),

- a channel between transmitter (Tx) and any random user that slowly varies multi-path Rayleigh fading with the exponentially decaying function, and wherein channel reciprocity property is adopted, where channel sounding techniques have the potential to be implemented to estimate the channel from the transmitter (Tx) to the receiver using the channel from the receiver to transmitter in time division duplexing (TDD) method. The communication device of claim 1 characterized by wherein the pre-coders are four different channel-dependent and a function of multiple authorized user channels. A method of a communication system with multiple-input single-output non- orthogonal multiple access (MISO-NOMA) system characterized by comprising the steps below;

- the data sequence of two users is passed through a modulator and then converted from serial to parallel, to become a column vector,

- the pre-coder matrices are devised where four different channeldependent intelligent pre-coder matrices are superimposed with these data vectors,

- the mixture of the data vector and pre-coder matrices is transmitted simultaneously from two antennas to the receiver of both user 1 and user 2, which are easy to decrypt at the authorized users due to automatic interference cancellation which require very low computational processing.