A communication method for multiplexing users in terathertz band

Abstract

The invention is related to a method of allocating near users' signals in the guard durations of the far users' signals by exploiting the temporal broadening effect (TBE) in Terahertz bands, thereby improving system's spectral efficiency, sumrate, and facilitating massive multiple access in the network.

Description

[0001] A COMMUNICATION METHOD FOR MULTIPLEXING USERS IN TERATHERTZ BAND

[0002] Technical Field

[0003] The invention is related to a method of allocating near users’ signals in the guard durations of the far users’ signals by exploiting the temporal broadening effect (TBE) in Terahertz bands, thereby improving system’s spectral efficiency, sum rate, and facilitating massive multiple access in the network.

[0004] Prior Art networks. In each new generation of wireless technology several approaches are usually considered to meet the high demand of data rate. From 5G on, migration to higher frequency bands where there is ample spectrum that can be exploited to quench the incessant need of high data rate has been considered. In 5G, communication in millimeter wave (mmW) bands was introduced. For 6G and beyond, migration to Terahertz bands is being envisioned to be an appropriate solution for enhancing data rate even further.

[0005] However, the high data rate that can be potentially achieved in these high frequency bands cones with some propagation challenges / limitations that need to be addressed. In Terahertz channels, several exotic propagation characteristics have been observed that need to be taken into account during system design. One of the critical propagation hurdles in THz bands is the frequency- selective molecular absorption effect (MoA). Some of the frequencies in THz bands align with natural resonance frequencies of the atmospheric contents like Oxygen and water molecules. When excited at their resonance frequencies, these molecules absorb a significant amount of energy from the signal which consequently elevates the path loss at these particular frequencies. The MoA effect is a function of distance since the number of the absorbing molecules within the signal path increases with the transmitter (Tx)-receiver (Rx) separation distance. In time domain, MoA causes the THz channels to experience temporal dispersion. This dispersion is referred to as temporal broadening effect (TBE). Communication around the frequencies with MoA effect in THz band is generally avoided in most of the THz literature, mainly due to the MoA-induced high pathloss. The utilization of the THz spectral windows for communication has been considered instead, where the spectral windows refer to the range of MoA-free frequencies between any two consecutive MoA frequencies. Considering the distance-dependent nature of the MoA effect, the widths of the spectral windows reduce with Tx-Rx separation distance. Consequently, with relatively higher Tx-Rx separation, operating around or on the MoA frequencies become inevitable for some users. Operating around MoA frequencies imposes two critical challenges that require proper consideration during system design. First, the high pathloss problem that necessitates high transmission power in order to facilitate communication. This high gain beamforming approach can be user to address this challenge while preserving the system’s energy efficiency. The second challenge stem from the MoA-induced TBE which may lead to inter-symbol interference. To overcome this challenge, enough amount of guard duration needs to be inserted between consecutive symbol s / pulses to avoid the inter-symbol interference problem. However, the insertion of guard band lead to the system’s spectral efficiency loss, a problem that is yet to be addressed in this particular scenario.

[0006] In the literature, communication on the MoA frequencies is generally avoided, and the utilization of the spectral Windows, i.e., the range of MoA-free frequencies between and two consecutive MoA frequencies, is being considered. However, even in this case, the frequencies at the edge of the spectral window are prone to the high pathloss as they closer to the MoA frequencies. The natural solution here can be introducing guard band at the edges of the spectral window, which can degrade system spectral efficiency. Considering the fact that the MoA- induced pathloss is highly distance-dependent, a distance-aware bandwidth adaptive resource allocation technique is proposed in study of C. Han et. al. [1] to address this problem. Specifically, the technique assigns the spectrum resources at the edge of the spectral window to the near users and the resources at the middle of the spectral window to the users that are relatively far from the transmitter. Apparently, this technique does not consider the impact of the TBE on the signals of the users using the resources around the MoA frequencies.

[0007] Communication on or around MoA frequencies has also been leveraged for physical layer security in number of studies of W. Gao et al. [2] [3], In study of distance-adaptive absorption peak modulation [2], the distance dependent MoA is exploited to enhance covertness for beyond the desired user’s distance. This is achieved through a proper optimization of the transmission power and selection of the MoApeak frequency with respect to the desired user’s distance from the transmitter. With such optimization, the transmitted signal undergoes excessive attenuation beyond the desired distance thereby providing an inherent covertness against eavesdroppers and jammers. Similarly, study of DNN-Powered SIC-Free Receiver [3] exploits the MoA- induced TBE to secure communication against an attacker that may be located between the transmitter and the desired user, a scenario where the approach in study of distance-adaptive absorption peak modulation [2] does not guarantee the secrecy. In this case, a deep neural network (DNN)-based self-interference cancellation (SlC)-free receiver artificial noise (AN) assisted mechanism is proposed to address the in-beam security challenge, by considering randomly distributed eavesdroppers in THz communications. By exploiting the different temporal broadening effects of the AN signal at distinct distances, the SIC can be saved with a proper signal detection design rather than using conventional high-complexity cancellation techniques.

[0008] In the current literature, the problem of the spectral efficiency loss due to the necessary guard durations required to mitigate TBE in THz band is not yet addressed. Apart from the spectral efficiency loss, large guard durations also elongate the time used to serve one user which in turn increases the waiting time for other users.

[0009] As a result, all of the problem mentioned above has made it necessary to provide a novelty in the related field.

[0010] Brief Description and Objects of the Invention

[0011] The main object of the present invention is to enhance spectral efficiency by reduces the spectral loss due to TBE in the THz communication operating on or near to the MoA peak frequencies.

[0012] Another object of the invention is to facilitate massive user multiplexing in wireless networks operating in THz band as more users can simultaneously share the same frequency bands while remaining orthogonal with other.

[0013] Another object of the invention is to enhances networks sum rate and reduces users waiting delay / latency by intelligently allowing some near users to access the network simultaneously through the necessary guard durations of the relatively far users.

[0014] To achieve such objects, the invention proposes that allocating the guard duration of a far receiver to the near receivers which are closer to the transmitter than the far receiver. The invention defines the signal need to be allocated. The signals of far receiver and the near receiver is configured to prevent interference by overlapping each other in time domain due to TBE. So, the duration, starting time of the signal are chosen according to prevent such an overlapping. This property suggests that this guard duration can be used to transmit signal of some users that are at shorter distance compared to that of the originally targeted user without creating any interference problem. Clearly, this approach allows the system to serve more users by using guard durations of other users, thereby reclaiming the spectral efficiency that could be lost due to the insertion of the guard durations in the first place.

[0015] Furthermore, the power of the signals is optimized in the transmitter with respect to the attenuation caused by MoA.

[0016] Description of the Figures of the Invention

[0017] The figures and related descriptions necessary for the subject matter of the invention to be understood better are given below.

[0018] Figure 1. A schematic view of the transmitter and the far and the near user devices that shows distance among them.

[0019] Figure 2. A schematic presentation of signals for the far and the near user devices in time domain.

[0020] Figure 3. A schematic presentation of signals of Figure 2 at the near user device.

[0021] Figure 4. A schematic presentation of signals of Figure 2 at the far user device.

[0022] Reference Numbers

[0023] The parts and components are given in the figures are referenced for the subject matter of the invention to be understood better.

[0024] 110. Transmitter

[0025] 120. Near receiver

[0026] 130. Far receiver

[0027] 140. First distance

[0028] 150. Second distance

[0029] 210. Far receiver signal 215. Near receiver signal

[0030] 220a. Transmission power of far signal

[0031] 220b. Attenuated transmission power of far signal at near receiver

[0032] 220c. Attenuated transmission power of far signal at far receiver

[0033] 225a. Transmission power of near signal

[0034] 225b. Attenuated transmission power of near signal at near receiver

[0035] 225c. Attenuated transmission power of near signal at far receiver

[0036] 230a. Duration of far receiver’s signal

[0037] 230b. Broadened duration of far receiver’s signal at near receiver

[0038] 230c. Broadened duration of far receiver’s signal at far receiver

[0039] 235a. Duration of near receiver’s signal

[0040] 240. Noise level at near receiver

[0041] 245a. Guard duration

[0042] 245b. Clean guard duration between signals

[0043] 250. Noise level at far receiver

[0044] 255. Starting time

[0045] Detailed Description of the Invention

[0046] The invention is related to a method of allocating near users’ signals in the guard durations of the far users’ signals by exploiting the temporal broadening effect (TBE) in Terahertz bands, thereby improving system’s spectral efficiency, sum rate, and facilitating massive multiple access in the network.

[0047] Referring to Figure 1; the system that carried out the method of present invention comprises a transmitter (110) and a far receiver (130) and at least one near receiver (120) and each of them single or multiple antenna systems. The system may comprise multiple near receiver (120). The distance between the transmitter (110) and the near receiver (120) is defined as a first distance (140) and the distance between the far receiver (130) and the transmitter (110) is defined as second distance (150). The second distance (150) is always longer than the first distance (140). Even if there is a multiple near receiver (120), all the first distances (140) still shorter than the first distance (140).

[0048] The transmitter (110) communicates with the far receiver (130) and near receiver (120) on or close to the MoA peak frequency such that the far receiver signal (210), which is signal to be transmitted to far receiver (130), from the transmitter (110) is expected to be received by the far receiver (130). The aim is to leverage the distance-dependent property of TB and exploit the guard duration GDfar(245a) allocated for the far receiver (130) to transmit the signal of the near receiver (120).

[0049] Referring to the Fig. 2; First of all, a channel estimation is performed to find the amount of broadening that the signal undergoes at the desired near receiver (120) and far receiver (130). Since the MoA phenomenon and its associated TBE are functions of operational frequency, distance, and the propagation environment, the broadening factors pnearand >farfor the the near receiver (120) and the far receiver (130) need to be estimated first.

[0050] At a given distance, / 3bris calculated by transmitting pilot pulses with pulse duration TTXfrom the transmitter (110) to the receivers as follows or by using any mathematical formulas established in the literature such as [3], Let TRXnearand TRXfarbe durations of the pilot pulses received by the near receiver (120) and the far receiver (130), respectively.

[0051] Alternatively, considering the reciprocity nature of the TBE, pnearand >farcan also be estimated by sending the pilot pulses with pulse duration TTXfrom the LTEs (120) and (130) to the TP (110). Simlarly, TRXnearand TRXfarare the durations of the pilot pulses received by the TP (110) from the near LTE (120) and the far LTE (130), respectively. Consequenly, the broadening factors are calculated as

[0052] Additionally / 3brcan also be calculated by using any mathematical formulas established in the literature such as [3],

[0053] After that, the guard duration GDfar(245a) is calculated. The guard duration (245a) is required to mitigate inter symbol interference (1ST) due to TBE in far receivers’ signal / pulses (210): GDfar= (fifar— 1) x TTXfarwhere TTXfar(230) is the pulse duration of the far receiver signal (210).

[0054] The guard duration GDfar(245a) is checked that if it is big enough to accommodate the near receiver signal (215), which is signal to be transmitted to near receiver (120), with TTXnear, which is duration of near receiver’s signal (235a). It is possible to multiplex near receiver signal (215) in the guard duration (245a) of the far receiver signal (210) if pnear> pfar / 2, given that the GDfaris calculated as in above. If the seleceted near receiver signal (215) does not satisfy the mention condition, another near UE whose pnearsatisfy the condition can be selected.

[0055] Referring to Fig. 3; The main aim here is to allocate the guard duration (245a) of the far receiver signal (210) for the near receiver signal (215) wherein after broadening of the far receiver signal (210) and the near receiving signal (215) at the near receiver (120), the both receiver signals doesn’t interfere in time domain. Since both of the far receiver signal (210) and the near receiver signal (215) broaden due to the TBE and thus these signals must be designed considering the broadening effect. Specifically, the width of the far receiver signal (210) and the near receiver signal (215) is designed in such a way that they do not interfere with each other at least at the near receiver (130) because of broadening effect.

[0056] For this, tfi nearwhich is the starting time (255) for the near receiver signal (215) is calculated. Transmission time (250) of the near receiver signal (215) with respect to the far receiver signal (210) is calculated as tRXnear= TTXfarx pnear.

[0057] After that, TTXnearwhich is the allowable pulse duration of near receiver signal (235a) of the near receiver signal (215) is calculated to not to interfere with the far receiver signal (210) at the near receiver distance dnearwhich is the first distance (140) due to TBE:

[0058] Referring to Fig. 4; The present invention also proposes solution for power requirements. MoA mediums causes power losses for the transmitted signal. So the signal needs to be optimized before transmitted to meet requirement of the far receiver (130) and the near receiver (120).

[0059] For optimizing far receiver signal (210), Prxfarwhich is the transmit power of far signal (220a) for the far receiver signal (210) such that it arrives at the far receiver (130) with sufficient power PRXfarwhich is attenuated transmission power of far signal at far receiver (220c) that is above Pnoisefarwhich is the noise level of far receiver (250) at the far receiver (130), such as satisfying the signal-to-noise ratio requirement for detection.

[0060] The transmit power PT nearwhich is transmission power of near signal (225a) for the near receiver signal (215) is also optimized such that it arrives at the near UE (120) with sufficient power PRrthat is above PVoise which is the noise level at near receiver (240) to satisfies the signal-to-noise requirement for detection, while it arrives at the far receiver (130) with the power PRXfar, which is attenuated transmission power of near signal at far receiver (225c), below Pnoisefarwhich is the noise level of the far receiver (250) so that it does not degrade the detection performsance of the far receiver signal (210).

[0061] The invention can work with any wireless networks operating on Terahertz frequencies where an access point, base station, transmission point, serves with multiple users. The said network can be a communication network, wireless sensing network, or both, as in the case of integrated sensing and communication (ISAC) network. The proposed technique is also applicable to the scenarios where massive multiple access is necessary as in the case of the Internet-of-Things (loT) and massive Machine Type Communication (mMTC) related use cases in 5G and Beyond wireless networks.

[0062] REFERENCES

[0063] [1] C. Han and I. F. Akyildiz, "Distance-aware multi-carrier (DAMC) modulation in Terahertz Band communication," 2014 IEEE International Conference on Communications (ICC), Sydney, NSW, Australia, 2014, pp. 5461-5467, doi: 10.1109 / ICC.2014.6884190. [2] W. Gao, Y. Chen, C. Han, and Z. Chen, “Distance-adaptive absorption peak modulation

[0064] (DA-APM) for terahertz covert communications,” IEEE Trans. Wireless Commun., vol. 20, no. 3, pp. 2064-2077, Mar. 2021.

[0065] [3] W. Gao, C. Han, and Z. Chen, “DNN-Powered SIC-Free Receiver Artificial Noise Aided Terahertz Secure Communications With Randomly Distributed Eavesdroppers,” IEEE Trans. Wireless Commun., 2021.

Claims

CLAIMS1. A computer implemented wireless communication method in terahertz band for a transmitter (110) and a far receiver (130) and at least one near receiver (120) wherein distance between the transmitter (110) and the near receiver (120) is lower than distance between the far receiver (130) and the transmitter (110), characterized by Determining guard duration (245a) for the far receiver (130) to mitigate inter symbol interference due to temporal broadening effect and broadening factors of the far receiver signal (210) and the near receiving signal (215),Allocating the guard duration (245a) of the far receiver signal (210) for the near receiver signal (215) wherein after broadening of the far receiver signal (210) and the near receiving signal (215) at the near receiver (120), the both receiver signals doesn’t interfere in time domain.

2. A method according to Claim 1, characterized by allocating the guard duration (245a) for multiple the near receiver signal (215).

3. A method according to Claim 1, characterized by allocating the guard duration (245a) for two near receiver signals (215) if the broadening factors of the near receiver (120) is bigger than half of the broadening factors of the far receiver (130).

4. A method according to Claim 1, characterized by calculating starting time (255) of the near receiver signal (215) with respect to duration of the near receiver signal (215) at the near receiver (120) in such a way that the both receiver signal doesn’t interfere in time domain.

5. A method according to Claim 1 or 4, characterized by calculating duration of the near receiver signal (110) at the transmitter (110) wherein after broadening of the far receiver signal (210) and the near receiving signal (215) at the near receiver (120), the both receiver signal doesn’t interfere in time domain.

6. A method according to Claim 1, characterized by determining an acceptable noise level of the far receiver (130) and the calculating transmission power of the far receiver signal(210) at transmitter (110) in a such way that the far receiver signal (210) at the far receiver (130) is still above the acceptable noise level of the far receiver (130).

7. A method according to Claim 1 or 7, characterized by determining an acceptable noise level of the near receiver (120) and the calculating transmission power of the near receiver signal (215) at transmitter (110) in a such way that the near receiver signal (215) at the near receiver (120) is still above the acceptable noise level of the near receiver (120).

8. A method according to Claim 1 or 7, characterized by determining an acceptable noise level of the far receiver (130) and the calculating transmission power of the near receiver signal (215) at transmitter (110) in a such way that the near receiver signal (215) at the far receiver (130) is below or equal to the acceptable noise level of the far receiver (130).

9. A data processing device comprising means for carrying out the steps of the method of Claim 1 to 8.

10. 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 1 to 8.

11. 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 1 to 8.

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