WO2025136272A1

WO2025136272A1 - An on/off keying method in terahertz band

Info

Publication number: WO2025136272A1
Application number: PCT/TR2024/050379
Authority: WO
Inventors: Saira RAFIQUE; Abuu Bakari KIHERO; Huseyin Arslan
Original assignee: Istanbul Medipol Universitesi
Current assignee: Istanbul Medipol Universitesi
Priority date: 2023-12-20
Filing date: 2024-04-05
Publication date: 2025-06-26
Anticipated expiration: 2026-06-20

Abstract

The invention is related to an method of ON/OFF keying and communication in the terahertz (THz) band that adapt the pulse width of the transmitted signal by exploiting temporal broadening effect.

Description

AN ON/OFF KEYING METHOD IN TERAHERTZ BAND

Technical Field

The invention is related to a method of ON/OFF keying and communication in the terahertz (THz) band that adapt the pulse width of the transmitted signal by exploiting temporal broadening effect.

Prior Art

The next generation of wireless communication networks envisions to incorporate state-of-the- art applications such as autonomous vehicles, extended reality, and smart transportation systems that require high-rate communication and high-resolution sensing. THz band is expected to provide extremely high throughput (of the order of gigabits/sec) and millimeter-level sensing information due to its inherent wider bandwidth [1],

However, the high-rate communication and the immense sensing potential of these higher frequency bands is restricted by their challenging propagation mechanisms. Henceforth, the factors such as high attenuation losses including molecular absorption, TBE, reflection and scattering losses, limited coverage, and enhanced Doppler effect must be considered while designing or selecting the waveform for the THz band [2],

Owing to the limited coverage at higher frequencies, the use of multicarrier waveforms may not be a suitable option for such a short range. The multicarrier waveforms such as orthogonal frequency division multiplexing (OFDM) divides the given bandwidth into sub-channels, which increases the duration of transmission hence rendering it unsuitable for short distances. Additionally, multicarrier waveforms such as OFDM exhibit large peak-to-average-power-ratio (PAPR) compared to single carrier waveforms which requires power amplifiers (PAs) to operate at high peak power.

Furthermore, multicarrier waveforms lack robustness against the enhanced Doppler effect at the THz band. Henceforth, single carrier waveforms are better candidates to be opted in the THz band. For low complexity and short-range communication on-off keying (OOK) is the preferred data modulation scheme [3], OOK uses pulses of the femtosecond duration that span an ultra-wideband THz spectrum. OOK utilizes very short pulses to transmit a ”1” bit and no transmission for a ”0” bit. However, temporal broadening and the strict synchronization process limits the feasibility of pulse-based modulation scheme.

Molecular absorption and its relevant phenomenon i.e. TBE are considered detrimental for THz communication. The high pathloss due to scattering, reflection and molecular absorption losses incurred by the THz links put constraints on achieving the desired throughput, sensing resolution and coverage. However, these unique THz-specific propagation mechanisms can be exploited for the benefit of sensing, communication and, security. Nevertheless, some works in the literature focused on avoiding the frequency regions where the molecular absorption and TBE is significant to ensure reliable communication [4,7] given the fact that molecular absorption is frequency, distance and environment dependent. Additionally short distances were also preferred for THz communications that caused minimal TBE.

One of the studies [5] propose to exploit the fact that available transmission bandwidth shrinks with the distance. In a scenario with a single transmitter and multiple receivers at different distances, modulation order and symbol duration are adapted based on the location available bandwidth to ensure reliable communication.

In distance-adaptive absorption peak modulation [6], authors aim to enhance covertness by dynamically modulating the signal under molecular absorption peaks.

Another study [7] proposed that a self-interference cancellation (SIC) free receiver artificial noise scheme where TBE is exploited to enhance the effect of noise and corrupt the information signal at the eavesdroppers’ located at various distances.

As a result, all of the problem mentioned above has made it necessary to provide a novelty in the related field.

Brief Description and Objects of the Invention

The main object of the present invention is to prevent misdetection at the receiver in the terahertz (THz) band.

Another object of the invention is enhancing energy efficiency for the wireless communication in the terahertz (THz) band.

Another object of the invention reducing inter symbol interference for the wireless communication in the terahertz (THz) band. To achieve such goals, the present invention exploits THz-specific channel characteristic such as TBE to enhance the communication performance and energy efficiency of the THz communication systems. Molecular absorption is the major contributor of the pathloss for THz communication systems which causes the broadening of transmitted pulses at the receiver. In case of ON/OFF keying (OOK), if left uncompensated, TBE causes leakage of ON symbols into the OFF symbols which leads to misdetection at the receiver. By shrinking the transmitted bits, misdetection as a result of TBE can be avoided at the receiver. However, for the case of consecutive bits, only a single unshrinked pulse is transmitted and TBE is exploited to generate two consecutive bits at the receiver. Given the requirement of energy efficiency, this invention is a critical and much needed step in the THz systems. Additionally, transmitting extremely short duration pulses to avoid inter symbol interference (ISI) at the receiver which takes place as a consequence of TBE

Description of the Figures of the Invention

The figures and related descriptions necessary for the subject matter of the invention to be understood better are given below.

Figure la. Transmission scheme in the presence of alternating data bits 10101.

Figure lb. Transmission scheme in the presence of alternating data bits 1101.

Figure 1c. Transmission scheme in the presence of alternating data bits 111.

Figure Id. Transmission scheme in the presence of alternating data bits 1111.

Figure 2. A flowchart of the present method

Reference Numbers

The parts and components are given in the figures are referenced for the subject matter of the invention to be understood better.

100. ON pulse

110. Shrinked pulse

120. OFF pulse

130. Single bit received pulse

140. Two bit received pulse Detailed Description of the Invention

The invention is related to a method of ON/OFF keying (OOK) and communication in the terahertz (THz) band that adapt the pulse width of the transmitted signal by exploiting temporal broadening effect.

Figure 1 illustrates the proposed transmission scheme in the presence of random incoming information bits. The sub-figures following the arrows indicate data reception after experiencing TBE. In the THz channel, TBE occurs which is directly proportional to the distance between transmitter and receiver at a given frequency and environment. TBE demonstrates itself as the broadening of the transmitted signal/pulse in the time domain due to its interaction with the molecules present in the medium. The amount by which a pulse is broadened is defined by pulse broadening factor /3_br. In this invention, ON/OFF keying (OOK) is employed for the conventional ON pulse (110) or bit ‘ 1’ (prior to shrinking) and the OFF (110) pulse or ‘0’ (no transmission). At a given distance, /3_br is calculated by transmitting pilot pulses as follows or by using any mathematical formulas established in the literature such as [7].

After calculation of the maximum broadening, the transmitted-ON pulses (100) are shrinked in time such that the new shrinked pulse (110) duration is shorter than the original ON pulse (100). By doing so, when the shrinked pulse (110) broadens by TBE and transform the single bit received pulse (130) which will not leak into the OFF period or ‘0’ bit, rather it will occupy the time which was supposed to be occupied by ON pulse (100) without the TBE at the receiver. The amount of shrinking can be increased or decreased based on the TBE or /3_br.

Main requirement of the shrinking is to shrink ON-pulse in such a way that the broadened version of the same shrinked pulse (110) isn’t wider than original ON pulse (110) in time.

Fig la. indicates the transmission scheme in the presence of alternating data bits 10101. The ON bit ‘ 1’ of shrinked pulse (110) is shrinked in time, so that after broadening by TPE, the broadened version of the same shrinked pulse (110) does not leak into the OFF period and create misdetection. In the case of transmitting alternating bits 10101, three shrinked ON pulses (110) are sent with the OFF pulse (120) in between them. The OFF period remains constant throughout the proposed method. So ‘ 10’ is transmitted. Fig lb. illustrates the transmission scheme for 1101. It is worth mentioning here that the transmission of consecutive bits take advantage of TBE and enhances energy efficiency. Now to transmit 11, only a single ON bit ‘ 1’ of regular duration the ON pulse (100) is transmitted followed by the OFF pulse (120), given the known TBE between the transmitter and the receiver. A single ON bit will occupy time slots equal to two ON bits at the receiver after broadening to get two bit received pulse (140). Hence receiver will detect two ON bits because it detects the signal energy in two-bit durations. So ‘ I E is transmitted via only a single bit, which is unshrinked ON pulse (100). TBE is exploited to receive the two ON bits ‘ 11’. The remaining alternating bits ’OF are transmitted via OFF pulse (120) (the OFF period) followed by the shrinked pulse (110).

Fig 1c. demonstrates the transmission mechanism of three consecutive ON pulses 111. Like Fig. lb for ‘ 11’ is transmitted via ON pulse (100) and OFF pulse (120), i.e. a regular unshrinked- ON pulse (110) followed by an OFF pulse (120) to incorporate broadening effect. And the last ON bit ‘ 1’ is transmitted by shrinked pulse (110).

As you can see from both Fig. 1c and Id, the shrinking applies two consecutive pulses to be transmitted to the receiver side. After first two consecutive pulses, the same principal is applied next two consecutive pulses. However, the last pulse isn’t consecutive with any pulse and if it is ON pulse (100), it is always shrinked.

Fig Id. represents the proposed transmission scheme for 1111. To transmit ‘ 11’, ON pulse (100) and OFF pulse (120) are transmitted which leads to the reception of two bit received pulse (140) i.e. presence of energy in two symbol/bit durations.

Referring to the Fig. 2; first of all, distance between the receiver and the transmitter is calculated or determined. It is assumed that the location coordinates of Tx (x y_±l

and Rx (x₂, y₂, z₂) are known in the three-dimentional space. Hence distance between the receiver and the transmitter can be calculated via d = j(x₂ — x_x)² + (y₂ — y- ² + (z₂ — z-^².

After that, temporal broadening factor /3_br is calculated. TBE is a phenomenon that happens as a consequence of molecular absorption which depends on three factors i.e. frequency, distance, and environment. For a fixed frequency and environment, the temporal broadening factor /3_br directly relates with the distance between the receiver and the transmitter and it can be calculated mathematically as done in [7], or through the THz channel estimation by transmitting pilot pulses of duration T_TX which is width of the pulse at transmitter side in time. After passing through the channel, let the T_Rxbe the duration of received pulse in time. Hence the broadening factor can be defined as,

Pbr ⁼ T_RX /T_TX

Determining both the distance and temporal broadening factor enables the calculation of the shrinking factor. The distance dependent pulse broadening factor /3_br causes misdetection at the receiver. Hence this effect is compensated at the transmitter through pulse shrinking. The greater the value of (3_br, the more shrinking of the pulse is required. For instance, let TBE expands the T_TX twice, hence to avoid ISI, T_TX should be set half of the orginal pulse duration. For a broadening factor (3_br, the duration of the shrinked pulse is defined as T_{shrinked tx}

Pbr for the avoidance of misdetection at receiver.

Due to the growing demand for increasing data throughput as well as high-sensing resolution, the migration towards terahertz frequency bands has become inevitable. Currently, international standardization organizations such as 3GPP and IEEE 802.15 are actively focusing on the THz band. Therefore, the proposed invention lies in the scope of these organizations. The propagation mechanisms of THz band are exploited to improve energy efficiency and BER performance of the THz communication systems. Besides, many throughput and latency critical use-cases such as immersive extended reality, smart cities, intemet-of-things (loT), connected vehicular technologies (vehi cl e-to- vehicle (V2V), vehicle-to-infrastructure, vehicle-to-everything (V2X)), autonomous vehicles, telemedicine, and high-definition holographic communication can benefit from the proposed invention.

REFERENCES

[1] Chaccour, Christina, et al. "Seven defining features of terahertz (THz) wireless systems: A fellowship of communication and sensing." IEEE Communications Surveys & Tutorials 24.2 (2022): 967-993.

[2] D. Serghiou, M. Khalily, T. W. C. Brown and R. Tafazolli, "Terahertz Channel Propagation Phenomena, Measurement Techniques and Modeling for 6G Wireless Communication Applications: A Survey, Open Challenges and Future Research Directions," in IEEE Communications Surveys & Tutorials, vol. 24, no. 4, pp. 1957-1996, Fourthquarter 2022, doi: 10.1109/COMST.2022.3205505.

[3] S. Tarboush, H. Sarieddeen, M. -S. Alouini and T. Y. Al-Naffouri, "Single- Versus

Multicarrier Terahertz -Band Communications: A Comparative Study," in IEEE Open Journal of the Communications Society, vol. 3, pp. 1466-1486, 2022, doi:

10.1109/OJCOMS.2022.3201038.

[4] W. Gao, Y. Chen, C. Han and Z. Chen, "Distance-Adaptive Absorption-Peak Hopping (DA- APH) Modulation for Terahertz Covert Communications," 2019 IEEE Global Communications Conference (GLOBECOM), Waikoloa, HI, USA, 2019, pp. 1-6, doi: 10.1109/GLOBECOM38437.2019.9013380.

[5] Z. Hossain and J. M. Jornet, “Hierarchical bandwidth modulation for ultra-broadband terahertz communications,” in ICC 2019-2019 IEEE International Conference on Communications (ICC). IEEE, 2019, pp.1-7.

[6] W. Gao, Y. Chen, C. Han and Z. Chen, "Distance-Adaptive Absorption Peak Modulation (DA-APM) for Terahertz Covert Communications," in IEEE Transactions on Wireless Communications, vol. 20, no. 3, pp. 2064-2077, March 2021, doi: 10.1109/TWC.2020.3038902.

[7] Gao, Weijun, Chong Han, and Zhi Chen. "DNN-powered SIC-free receiver artificial noise aided terahertz secure communications with randomly distributed eavesdroppers." IEEE Transactions on Wireless Communications 21.1 (2021): 563-576.

Claims

1. A computer implemented ON/OFF keying method for wireless communication between a transmitter and receiver in terahertz band, characterized by

Determining a temporal broadening factor broadens the pulses of keying which are ON pulses (100) or OFF pulses (120), during the transmission between the transmitter and the receiver and the shrinking factor which is the rate for shrinking width of the ON pulse (100) in time at the transmitter,

Determining at least two consecutive pulses to be transmitted to the receiver side, Shrinking first pulse if the first pulse to be received by the receiver is the ON pulse (100) and the second pulse to be received by the receiver is the OFF pulse (120) and sending only one pulse, if the first pulse to be received by the receiver the ON pulse (100) and the second pulse to be received by the receiver is the ON pulse (100).

2. A method according to Claim 1, characterized by shrinking the third consecutive pulse if it is the ON pulse (100) and is the last pulse to be received by the receiver.

3. A method according to Claim 1, characterized by calculating the distance between the transmitter and the receiver and using the distance to calculate the temporal broadening factor.

4. A method according to Claim 1, characterized by calculating the temporal broadening factor by formula of

Pbr = T_RX /T_TX wherein

P_br is temporal broadening factor, T_Rx is width of the pulse at receiver side and T_TX is width of the pulse at transmitter side.

5. A method according to Claim 1, characterized by shrinked width of the ON pulse (100) at the transmitter size is defined by formula of wherein

P_br is temporal broadening factor, T_{shrinked tx} is shrinked width of the ON pulse (100) and T_TX is width of the pulse at transmitter side.

6. A signal transmitting method for wireless communication between a transmitter and receiver in terahertz band characterized by modulating the signal before transmitting by the ON/OFF keying method of any preceding claims. 7. A data processing device comprising means for carrying out the steps of the method of

Claim 6.

8. A computer program comprising instructions which, when the program is executed by a data processing device, cause the data processing device to carry out the steps of the method of Claim 6.

9. A computer-readable medium comprising instructions which, when executed by a computer, cause the computer to carry out the steps of the method of Claim 6.