(D-SEAD)

TECHNICAL FIELD

The invention proposes the integration of two recently developed novel techniques for future wireless systems; namely, a multi-dimensional OFDM modulation format termed as OFDM-SPM (Orthogonal Frequency Division Multiplexing with Subcarrier Power Modulation) with a recently developed multiple access communication technique termed as MU-AS-ST (Multi-User Auxiliary Signal Superposition Transmission) for doubling the spectral efficiency per area and per device through a specifically designed system model that integrates both designs yielding a more effective use of the scarce wireless spectrum.

PRIOR ART

At the top of the list of requirements for future wireless systems comes the spectral efficiency requirement where due to the emergence of the internet of things, the explosion in software and mobile devices, and due to many other technological advancements, such as extended reality (XR) services including augmented, mixed, and virtual reality (AR/MRA/R), haptics (tactile Internet), real-time gaming, telemedicine, brain computer interfaces, flying vehicles, and connected autonomous systems.

To serve this massive connection of devices and applications, many efforts have been devoted from both the part of wireless academia and wireless industry for developing spectrally-efficient techniques that are able to cope with the spectral efficiency challenge in the light of the scarcity of the spectrum allocated for wireless communication services and the data hunger per device where the number of installed apps per device is increasing day by day including apps of different kind serving various purposes in the life of their users such as bank account applications, social media apps, e-health applications, ...etc. In this regard, many techniques have been developed for serving the spectral efficiency demand of these massive connection of data-hungry devices, including but are not limited to the following set:

• Utilizing Millimeter wave (mm-wave) for increasing data rates by enabling the utilization of a larger portion of the frequency spectrum; however, whereas mm-wave transmission provides higher data rates, its deployment has been hindered by its propagation characteristics as mm-wave communications are highly sensitive to external variables like blockage and absorption and due to this it can only propagate for short distances,

• Utilizing cell densification, which is a rather conventional approach to improve the data rate in a given area in scenarios of high traffic demands; however, this approach incurs high costs of site rents and installation, requires time, and the effect of this is certainly only bounded to a certain area,

• Utilizing other Multiplexing techniques besides Orthogonal Frequency Division Multiplexing (OFDM) for improving the spectral efficiency collectively within the area they are utilized like Non-Orthogonal Multiple Access (NOMA) and Massive Multiple-Input-Multiple-Output (MIMO) techniques, however; o Utilizing these techniques, despite achieving gains in terms of spectral efficiency, also introduces specific drawbacks because such techniques are solely focused on improving the area spectral efficiency which corresponds to the number of users that can be served in an area rather than improving the spectral efficiency per device or user. o Utilizing these approaches result in increasing the processing latency, increasing the digital signal processing complexity of the transceiver design, and reducing the energy utilization efficiency,

• Utilizing In-band Full Duplex by allowing devices to transmit and receive on the same frequency at the same time; however, this design has the following dements: o Suffering from the self-interference problem, o Requiring a complex transceiver structure, and o Being incompatible with current wireless devices and standards.

• Utilizing multi-dimensional OFDM modulation formats which unlike the aforementioned ways that were mostly concentrated on increasing the total system data rate or throughput by enhancing the area spectral efficiency, opt to enhance the spectral efficiency per device/user by modifying and improving the OFDM waveform, which remains the backbone technology of current wireless standards (e.g., 4G-LTE, WiFi, WiGig, LiFi, DVB, etc.) as well as 5G systems.

In this category, many techniques have been developed where in each technique some enhancement in the spectral efficiency per device is attained through the manipulation of some parameter related to the OFDM waveform or the transmission medium, such as: o Utilizing the index of the transmitting antenna as an additional dimension for sending data where the indices of the active antennas are used an additional dimension for sending extra data bits as in the technique called Spatial Modulation OFDM (SM-OFDM), o Utilizing the Index of the active subcarriers in an OFDM block for conveying extra data bits as in:

■ SIM-OFDM (Subcarrier Index Modulation OFDM)

■ OFDM-IM (OFDM with Index Modulation), o Utilizing the number of the active subcarriers in the OFDM block for sending extra information as in OFDM-SNM (OFDM with Subcarrier Number Modulation) where the authors studied the use of the number of the active subcarriers, rather than the index, as a new dimension for sending more data bits, o Utilizing the gap between the active subcarriers in an OFDM block where the authors proposed a technique called OFDM-SGM (OFDM with Subcarrier Gap Modulation) where they study the gap between active subcarriers in an OFDM as an additional dimension for transmitting extra information bits.

Publication “A. Jaradat, J. Hamamreh, and H. Arslan, “Modulation options for OFDM-based waveforms: Classification, comparison, and future directions, ’’IEEE Access, vol. 7, pp. 17 263-17 278, 2019.” offers more details on this type of multidimensional modulation formats and compares them in terms of different performance metrics such as the bit error rate, the spectral efficiency, complexity of the design, and peak to average power ratio (PAPR). From the aforementioned techniques, it can be seen that the spectral efficiency problem is addressed only at one level, either at the area level or at the device level and thus, this patent presents a new technique where the enhancement of the spectral efficiency is provided both at the area level and at the device level where doubling the spectral efficiency per area and per device is achieved.

The proposed invention is termed as D-SEAD (Doubling the Spectral Efficiency per Area and per Device) and is based on the integration of two recently developed powerful techniques where a multiple access technique termed as MU- AS-ST (Multi-User Auxiliary Signal Superposition Transmission) which is proposed for solving the limitations and shortcomings of the current power domain NOMA (pd- NOMA) proposed for 5G systems is modulated using a recently developed multidimensional OFDM modulation format termed as OFDM-SPM (Orthogonal Frequency Division Multiplexing with Subcarrier Power Modulation) which explores the power of the subcarriers inside the OFDM waveform for doubling the spectral efficiency per device for future 6G systems.

In this invention, the multiple access design MU-AS-ST and the multidimensional OFDM design OFDM-SPM are integrated in a very specific way that ensures the gathering of many important benefits that are hard to be addressed simultaneously such as the doubling the spectral efficiency both per area and per device is, providing perfect secrecy against both internal and external eavesdroppers, achieving reliable communication and reduced design complexity especially at the receiver where all of the processing is carried at the transmitter and thus freeing the receiver from complex processing tasks, thus yielding energy efficiency.

For more information on the techniques which this design takes as a basis, the reader is referred to the following publications “Abewa, M., & Hamamreh, J. M. (2021 ). NC-OFDM-SPM: A Two-Dimensional Non-Coherent Modulation Scheme for Achieving the Coherent Performance of OFDM along with Sending an Additional Data-stream. RS Open Journal on Innovative Communication Technologies, 2(3). https://doi.org/10.46470/03d8ffbd.a97a5236”, and “Abewa, M., & Hamamreh, J. M. (2021 ). Multi-User Auxiliary Signal Superposition Transmission (MU-AS-ST) for Secure and Low-Complexity Multiple Access Communications. RS Open Journal on Innovative Communication Technologies, 2(4).

In the publication ‘M. M. §ahin and H. Arslan, "Waveform-Domain NOMA: The Future of Multiple Access," 2020 IEEE International Conference on Communications Workshops (ICC Workshops), 2020, pp. 1-6, doi: 10.1109/ICCWorkshops49005.2020.9145077.’ NOMA was modulated through index modulation yielding partial improvement in the data rate.

The proposed invention in this patent is different than the design presented in the above publication by the following points:

• Using the subcarrier power modulation instead of index modulation for the OFDM waveform which ensures doubling the spectral efficiency per user due the use of all the subcarriers for transmission unlike the index where only the active subcarriers are used,

• Using a different multiple access design which is not NOMA but an alternative of NOMA where the limitations of current NOMA are solved including security risks and design complexity issues.

• Having a simpler design due to the simple operations used in the design of D- SEAD especially at the receiver where for the power a simple thresholdbased detector is used and thus providing a much simpler detection process than the index modulation detector.

BRIEF DESCRIPTION OF THE INVENTION

At the top of the requirements that need to be addressed by the techniques developed for future wireless systems is the spectral efficiency requirement where:

• Enhancing the spectral efficiency per area is an urgent need where there is a massive interconnection of devices that are interconnected wirelessly and due to the scarcity of the spectrum allocated for wireless systems this interconnection can only be served through the use of techniques that serves many users at the same time such as multiple access designs where many users in the same coverage area can be served simultaneously through the same resources of frequency I time making the use of the scarce spectrum more efficient, • Increasing the data rate per device is also another type of spectral gain that needs to be considered due to the rising number of crucial software applications that serve various purposes in wireless devices such as mobile phones, computers, etc., and thus the enhancement in the spectral efficiency should not consider only the area level where many users can be served through the same set of resources but also focuses on enhancing the data rate at the device level to serve the need of these data-hungry devices that is increasing day per day.

In this context, the invention proposes a new design that modulates a novel multiple access technique through a multi-dimensional OFDM modulation format for addressing the spectral efficiency need both at the area level and at the device level, where:

• Doubling the spectral efficiency per area is guaranteed through the use of the multiple access design termed as MU-AS-ST (Multi-User Auxiliary Signal Superposition transmission) which is a recent technique proposed as an alternative technique for power domain NOMA where the shortcomings and limitations of the NOMA technique such as security, receiver complexity and latency are solved through the use of specifically designed auxiliary signals transmitted with the superimposed users’ data,

• Doubling the spectral efficiency per device is ensured through the use of a recently developed multi-dimensional OFDM modulation format termed as Orthogonal Frequency Division Multiplexing with Subcarrier Power Modulation (OFDM-SPM) which explores the power of the subcarriers inside the OFDM waveform as an additional dimension for sending more information bits and since all of the subcarriers are manipulated for this purpose, OFDM-SPM was proven to double the data rate per device compared to conventional OFDM systems.

Table 1. General system model of the proposed design

The presented technique in this patent is termed as D-SEAD (Doubling the Spectral Efficiency per Area and per Device) where, due to its special design which integrates the cited techniques in a very specific way as shown in Table 1 and Figure 1 , achieves the combination of many benefits that are hardly met simultaneously, such as:

• Working in general scenarios, where unlike conventional NOMA where only users having different distance from the base station can be superimposed, this design works for the combination of any two users regardless of their distances from the base station,

• Ensuring perfect information secrecy against both external and internal eavesdropping,

• Ensuring reduced receiver complexity where, unlike conventional NOMA where successive cancellation at the receiver side leads to a complexity of the system, in this technique the specific design of the auxiliary signals solves this problem effectively making it a strong candidate for processing-restricted applications and low complexity application scenarios such as loT devices,

• Ensuring reduced transmission latency where this design is featured with its simple transceiver design, and since at the transmitter the design of the auxiliary signals employs diagonal matrices, this makes the computational cost lower, while at the receiver simply a conventional OFDM receiver is used and thus freeing the receiver from any complex processing. • Doubling the spectral efficiency per device where the exploration of the power of the subcarriers as an additional dimension in OFDM ensures doubling the data rate since all the subcarriers in an OFDM block are used. This is unlike the techniques which explore other dimensions such as the index of the subcarriers, the number of the active subcarriers, etc., where only partial enhancement of the data rate is reached (not doubling) since only the active subcarriers in the OFDM block are used for conveying more data bits.

• Offering very low-complex transceiver design where the detection of the bits transmitted through the manipulation of the power of the OFDM subcarriers is thresholding-based making it easier than other formats where complex detectors such as ML or LLR are used.

Through its very specific design, D-SEAD proposes a more efficient way of using the scarce wireless spectrum where the data rate is doubled both per area and per user.

LIST OF FIGURES

Figure 1. Transmitter of D-SEAD.

Figure 2. Receiver of D-SEAD.

Figure 3. Individual bit error rates of the proposed design.

Figure 4. Average bit error rates of the legitimate users and the illegitimate users.

Figure 5. Data rate results of the proposed design for the legitimate and eavesdropping nodes.

Figure 6. Peak to average power ratio (PAPR) results of D-SEAD compared to conventional OFDM.

Figure 7. The proposed design compared to conventional power domain NOMA through the BER performance metric.

Figure 8. General system model of MU-AS-ST.

Figure 9. Doubling the data rate per device using OFDM-SPM. DETAILED DESCRIPTION OF THE INVENTION

The invention is a novel design that proposes a more efficient way of using the scarce wireless spectrum where, through the use of a novel multiple access technique termed as MU-AS-ST which is modulated through a recently developed multi-dimensional OFDM modulation technique termed as OFDM-SPM, for doubling the spectral efficiency per area and per device is achieved.

Before explaining the design of the proposed technique, first a short discussion on the basis techniques MU-AS-ST and OFDM-SPM is carried out and then the specific design which arises from their integration and which is the subject of this patent application is discussed thoroughly in the subsequent sections.

A- MU-AS-ST (Multi-User Auxiliary Signal Superposition Transmission)

The Multi-User Auxiliary Signal Superposition Transmission (MU-AS-ST) is a novel technique proposed as an alternative for power domain NOMA which was proposed for 5G systems and was considered a study item from release 13 till release 16 of 3GPP under the name MUST (Multi-User Superposition Transmission); however, it was eliminated from the work items in release 17 due to some limitations and shortcomings. The limitations of conventional power domain NOMA can be summarized as follows:

• Working only in scenarios where the superimposed users must have different distances from the base station where in the transmission a far user and a near user are combined while if the users have the same distance from the base station NOMA fails.

• Increasing the complexity of the design through the use of successive interference cancellation (SIC) which is performed by the near user to eliminate the dominating signal of the far user and decoding its own signal.

• Having significant interference at the far user where the signal of the near user is not cancelled but treated as noise.

• Having security issues at the near user due to SIC and at the far user due to the non-cancellation of the near user’s signal, and also there is a need for securing this design against external eavesdropping activities taking into account the broadcast nature of the wireless channels and the sensitivity of the data in this era such as bank account details and transactions, private messages and documents, etc.

Through specifically designed auxiliary signals superimposed with the users transmitted data which is transmitted from different antenna sources and combined at the receiver, MU-AS-ST is able to solve the limitations and shortcomings of power domain NOMA and offers the following contribution points:

• Working in general scenarios where, unlike conventional NOMA where only users having different distance from the base station can be super-imposed, this design works for the combination of any two users regardless of their distances from the base station,

• Ensuring perfect information secrecy against both external and internal eavesdropping,

• Ensuring reduced receiver complexity where, unlike conventional NOMA where successive cancellation at the receiver side leads to a complexity of the system. In this technique the specific design of the auxiliary signals solves this problem effectively making it a strong candidate for processing-restricted applications and low complexity applications such as loT devices,

• Ensuring reduced transmission latency where this design is featured with its simple transceiver design and since at the transmitter the design of the auxiliary signals employs diagonal matrices, this makes the computational cost lower, while at the receiver simply a conventional OFDM receiver is used and thus freeing the receiver from any complex processing.

The system model for the proposed design in this invention is presented in Figure 8, and the publication “Abewa, M., & Hamamreh, J. M. (2021 ). Multi-User Auxiliary Signal Superposition Transmission (MU-AS-ST) for Secure and Low- Complexity Multiple Access Communications. RS Open Journal on Innovative Communication Technologies, 2(4). offers more details on MU-AS-ST including a detailed study of the system model proposed for solving the limitations of current conventional NOMA design through the use of auxiliary signal superposition transmission and offers a theoretical derivation of the bit error rate of the proposed design and the signal to interference plus noise ratio (SINR) which measures the quality of the communication link in both MU-AS-ST and PD-NOMA where it was shown that MU-AS-ST surpasses conventional power domain NOMA.

B- OFDM-SPM

The Orthogonal Frequency Division Multiplexing with Subcarrier Power Modulation (OFDM-SPM) is a multi-dimensional OFDM technique that was proposed for doubling the spectral efficiency per device for future 6G systems through the manipulation of the power of the transmitting subcarriers in the OFDM waveform where through this exploration half of the incoming data is modulated through a classical modulation technique such BPSK I QAM and the other half is modulated through subcarrier power modulator block which, depending on the incoming binary bit, sets the data to a high (H) or low (L) value that is chosen such that the error rate is the minimum possible.

As shown from the system model for OFDM-SPM with BPSK presented in Figure 9, it can be seen that, for sending the same number of data bits, OFDM-SPM needs half the subcarriers required by conventional OFDM for performing this transmission and due to this OFDM-SPM has two power modes including the power saving mode where, for transmitting the same number of bits using conventional OFDM, OFDM-SPM uses only half of the subcarriers that OFDM would require and there is also the power reassignment mode where for enhancing the reliability of the OFDM-SPM scheme, the saved power is reassigned to the transmit subcarriers as expressed by the equation below: where E _b is the energy per bit, and the high and low levels in the reassignment mode are chosen based on this this equation such that the minimum error rate of the scheme is achieved.

The high and low levels are found through an exhaustive process of trial and error, according to equation (1) where, for a value of H, the corresponding value of L is found as:

And through this process, for the power reassignment mode which is the mode used in the design proposed in this patent, the value for H and L were found as: (H, L) = (1.918, 0.5668). Comparing the proposed OFDM-SPM with conventional OFDM, OFDM-SPM has shown to offer a significant advantage over conventional OFDM in terms of spectral efficiency where OFDM-SPM is superior to conventional OFDM as it offers the following merits:

• Doubling the spectral efficiency of the system using only one sinusoidal carrier unlike conventional modulation schemes (e.g., QPSK, M-QAM, M-PSK) that have to use two orthogonal carriers (sine and cosine) to improve spectral efficiency. And from another standpoint, OFDM-SPM combined with binary phase-shift keying (BPSK) symbol modulation can transfer as much data as conventional OFDM with BPSK using only half the number of subcarriers that conventional OFDM requires.

• Reducing the transmission delay as the number of subcarriers used by OFDM-SPM is half the number of those used in conventional OFDM, OFDM- SPM with BPSK also reduces the transmission delay for the same amount of throughput, since a fewer number of subcarriers translates to fewer resources in the time domain as well.

• Reducing complexity as it can use half of the IFFT size that OFDM would require for achieving the same throughput, and also, the OFDM-SPM detection process is another source of reducing complexity because it uses simple threshold-based detectors unlike those schemes that depend on using maximum likelihood detectors which involve high complexity, especially for large mapping tables.

• Offering in the option of reducing the transmission power by half while maintaining the spectral gain, at the expense of some degradation in the BER or reallocating the saved power for an improvement in the system BER.

The above contributions are for the OFDM-SPM using a binary coherent modulation such as BPSK and targets processing-restricted applications such as the loT; however, OFDM-SPM was also studied with higher order modulations such as QAM where it was shown that its performance does not degrade when the modulation order increases.

OFDM-SPM was also used for solving the classical trade-off between coherent and non-coherent modulation where a non-coherent version of OFDM-SPM using DPSK was developed and was shown to achieve the performance of a coherent system such as OFDM-BPSK and thus it combines the benefit of simple receiver design found through the use of a non-coherent structure such as DPSK and attains good performance as guaranteed by the coherent modulation, as detailed in the publication “Abewa, M., & Hamamreh, J. M. (2021 ). NC-OFDM-SPM: A Two- Dimensional Non-Coherent Modulation Scheme for Achieving the Coherent Performance of OFDM along with Sending an Additional Data-stream. RS Open Journal on Innovative Communication Technologies, 2(3).

For more details on OFDM-SPM, the reader is referred to the website of the laboratory where the publications and FAQs related to this novel technique (OFDM SPM) are found at the following link: https://sites.qooqle.com/view/wislab/research- topics/faq-about-ofdm-spm

C- PROPOSED DESIGN (D-SEAD)

1. Transmitter Design of D-SEAD

As shown in the transmitter design in Figure 1 , the method for the data processing passes through the following steps;

• Modulating the incoming binary data of two different users UE ₁ and UE ₂ using binary phase shift keying (BPSK), resulting in the BPSK vectors b ₁ and b ₂ for users UE ₁ and UE ₂ , respectively,

• Modulating the incoming binary data of UE ₁ and UE ₂ through a subcarrier power modulator (SPM) where, according to the incoming bit, the power of the transmit subcarrier is set to high or low if the incoming bit is T or ‘O’, respectively, resulting in the power vectors p ₁ and p ₂ for users UE ₁ and UE ₂ , respectively,

• Forming the joint stream for each user where for UE ₁ the vector = p ₁ x b ₁ embeds both the BPSK and the power modulation dimensions and similarly for UE ₂ the vector x ₂ = p ₂ x b ₂ represents the joint stream that is going to be transmitted for user UE ₂ ,

• Superimposing the joint streams x ₁ and x ₂ , resulting in the vector

• Adding specifically designed auxiliary signals on top of the superimposed data and thus the resulting signal can be expressed asu ₁ • Performing conventional OFDM operations to signals u ₁ and u ₂ such as taking the Inverse Fast Fourier Transform (IFFT), Adding the cyclic prefix (CP) and converting the signal from digital to analog.

• Transmitting each of the signals from a separate antenna where the signal u ₁ is sent from antenna A ₁ and the signal u ₂ is sent from the antenna A ₂ .

2. Receiver Design of D-SEAD

The receiver of the proposed design is shown in Figure 2, where the below steps are followed for the method of detecting the transmitted data;

• Performing the analog to digital conversion,

• Removing the cyclic prefix,

• Taking the Fast Fourier Transform (FFT),

• Performing equalization to remove the channel effect by dividing the received samples by the effective channel for each legitimate user,

• Demodulating the individual streams for each user, as shown in Figure 2, where: o Demodulating the Power stream for each user is threshold-based where the power of the received samples is compared to a predefined threshold set as the midpoint between the high and low power levels. o Demodulating the BPSK bits for each user is done through a conventional BPSK demodulator.

For understanding the reception mechanism better, the following sections analyze the received signal at each user end including legitimate and eavesdropping nodes.

- Received signal at UE1

The transmitted signalsu ₁ and u ₂ are received simultaneously at this user node and thus the received signal, written in the frequency domain, can be expressed as follows by summing the signals coming from antenna A ₁ and antenna A ₂ : where is the additive white gaussian noise, and are, respectively, the channels between the receiving user equipment and antenna and antenna

- Receiver signal at UE2

Similarly, the received signal at the second user can be expressed by the following equations: where is the additive white gaussian noise, and are, respectively, the channels between the receiving user equipment and antenna A _± and antenna

- Design of the auxiliary signals

The auxiliary signals are designed such that the interference that the users create to each other is eliminated and such that legitimate user device receives its own signal and thus eliminating the risks of internal eavesdropping in the case of the presence of an untrusted legitimate user among the superimposed users.

For user 1 , by looking at the received signal in equation (6), it can be seen that the first term of this equation (i.e., is the desired term with respect to this user while the other terms can be set to zero to ensure that this user receives only its own data, yielding the following equation:

Similarly, for user 2, by looking at equation (9), the only desired term with respect to while the other terms correspond to interference and noise and thus, for this user to receive only its own data, the following equation can be written:

By solving (10) and (11 ) together, the values of the auxiliary signals that guarantee full inter-user interference cancellation are found as follows:

When the above values for r ₁ and r ₂ are used then, then the received signals at UE _lt UE ₂ expressed by equation (6) and (9) can be written, respectively, as follows:

Then, as shown in the receiver of MU-AS-ST, when the equalization by the effective channels in (16), (17) is done, the transmitted joint data stream is recovered as follows:

And, since equation (18) and (19) can be written as follows:

For the first user UE ₁ , Equation (20) is the input to both the subcarrier power demodulator block and the BPSK demodulator block where the subcarrier power demodulator detects the power vector p ₁ and the BPSK demodulator detects the BPSK vector bi from the incoming joint stream also UE ₂ detects its originally transmitted data b ₁ , p ₁ in the same manner as user UE ₁ .

- Received Signal at the external eavesdropper

The eavesdropper user equipment UE _X receives the broadcasted signals from antenna A ₁ and antenna A ₂ and, as such, the received signal at the eavesdropper device can be written as follows: where, n _x is the additive white gaussian noise, and H _X1 , H _X2 are, respectively, the channels between the receiving user equipment and antenna A ₁ and antenna A ₂ . Unlike the legitimate users, this received signal does not contain the data of only one user but the data of both users and more than that, it is very extremely challenging to be decoded due to the many unknowns that this received signal in (23) contains with respect to an external eavesdropping device and thus this makes from this design a robust design against external eavesdropping activities.

To show the complexity of this received signal, y _UEx can be written it as follows where are replaced by their values which are, together with the channels are all unknowns to this external receiving node.

The signal in (23) can be written as follows:

D- Performance Demonstration

The performance of the proposed design was quantified in terms of many metrics such as the bit error rate, spectral efficiency I throughput (in bits/s/Hz), and peak to average power ratio (PAPR) simulated in the MATLAB simulation environment using the simulation parameters that are specified in Table 1 .

Table 2. simulation parameters

The generated performance results for the proposed design can be seen from the attached figures, which include the following results: • Displaying the bit error rates of both the legitimate nodes UE ₁ and UE ₂ as shown in Figure 3, where three types of bit error rates are displayed, including: o Bit error rates for the BPSK stream which evaluates the amount of error encountered in the detection of the BPSK bits which is an operation performed by the BPSK demodulator block as shown in Figure 2., o Bit error rates for the power Stream for each user which corresponds to the bit error rate encountered during the detection of the power modulated bits and this is done through the SPM Demodulator block represented in Figure 2., o Average bit error rate for each user which corresponds to the overall reliability performance for the user and is the average between the above two types, the BPSK error rate and the power error rate.

• Displaying a more detailed Bit error rate graph in Figure 4, in which the following is represented: o Displaying the average error rate I overall error rate for the legitimate users as explained above, o Displaying the BER rates for several eavesdropping scenarios that were simulated including:

■ Displaying the BER for the internal eavesdropping case which corresponds to the case where one of the two legitimate superimposed users tries to listen to the data of the other user be it the power data or the BPSK data and as can be seen the results, this trial results in a very poor performance which reflects the perfect internal security which is achieved in this design due to the use of the auxiliary signals.

■ Displaying the BER results for the case where an external eavesdropping device UE _X is trying to listen to the data of the legitimate users and as can be seen from the simulation results the external eavesdropper is unable to decode any kind of data related to the legitimate users and this is due to the complexity and the hard combinations that are involved in the received signal as shown in the design of the auxiliary signals where this external user receives a signal that is a specific complex combination of many unknowns to this external device and thus degrading its performance resulting in external security of the proposed scheme.

• Displaying the performance of the proposed design in terms of spectral efficiency as shown in Figure 5, where the individual data rates corresponding to the BPSK stream and the power stream are displayed per user along with the average overall data rate for each user where it can be seen that the data rate is doubled per device, and also the overall spectral efficiency I throughput of the design is displayed where it can be seen that 4 bits/s/Hz is achieved corresponding to doubling the spectral efficiency per area and per device where two users are superimposed through the multiple access scheme and the data rate is doubled for each user as well.

• Displaying the peak to average power ratio (PAPR) which is a crucial metric to be measured for any design that is based on OFDM as it is known that OFDM has higher peaks which are undesired at the input of the power amplifier and thus the PAPR of D-SEAD was studied and was shown not to add any degradation to conventional OFDM as shown in Figure 6 where a slightly better performance is achieved compared to a conventional OFDM system.

E- Comparison to the state-of-the art

As explained in the brief description and shown in the details of the transmission and reception operations above, the proposed design is a novel integration of OFDM-SPM and MU-AS-ST for doubling the spectral efficiency of future wireless systems per area and per device while guaranteeing a low-complex receiver and reliable transmission mechanism.

Due to this integration, D-SEAD is a design that is characterized by the following set of merits and advantages compared to the state-of the art:

• Having a low-complex transceiver where most of the processing is carried at the transmitting base station and thus freeing the receiver from any complex processing tasks where, compared to conventional OFDM, the only difference lies in the use of the subcarrier power modulator block which detects the power bits and which is a thresholding-based detector and thus it is less complex than some of the techniques which explore an extra dimension for data transmission such as OFDM with Subcarrier Number Modulation (OFDM- SNM), OFDM with Index Modulation (OFDM-IM), Subcarrier Index Modulation OFDM (SIM-OFDM) which usually employ either a maximum likelihood (ML) detector for optimum performance, or a log likelihood ratio (LLR) detector for reduced complexity.

• Making faster computational operations at the transmitter due to using diagonal matrices in the design of the auxiliary signals, this is with the simple modulation process that OFDM-SPM guarantees where a conventional BPSK modulator is used along with the power block modulator which sets the data to specifically chosen high and low power levels,

• Guaranteeing easier integration with the available wireless technologies because all the design is based on OFDM which is already studied enough and supported with different platforms and is compatible with current wireless devices and standards.

• Working in general scenarios where, unlike conventional NOMA where only the users having different distance from the base station can be superimposed, this design works for the combination of any two users regardless of their distances from the base station,

• Ensuring perfect interference cancellation between the superimposed users due to the use of the auxiliary signals,

• Ensuring perfect information secrecy against both external and internal eavesdropping due to the special design of the auxiliary signals,

• Ensuring reduced transmission latency where this design is featured with its simple transceiver design, and since at the transmitter the design of the auxiliary signals employs diagonal matrices, this makes the computational cost lower, while at the receiver simply a conventional OFDM receiver is used and thus freeing the receiver from any complex processing.,

• Doubling the spectral efficiency per area and per device, where in this design the scenario for two users was considered as shown in the simulations results attached.,

• Achieving good transmission reliability as shown in the bit error rate graphs.

• Achieving slightly better PAPR performance than conventional OFDM, without the use of any PAPR reduction technique. As shown in the simulation results in Figure 7, the proposed design was compared to the conventional power domain NOMA design which is the scheme that gained most interest from the part of the wireless literature during the 5G era, and for all of the simulated power reallocation scenarios for the far and the near user in NOMA, D-SEAD reaches better reliability performance, this is while being characterized with the points that are mentioned above.