16-ary Quadrature Amplitude Modulation Research Articles

Design of Orthogonal Pulse Waveforms With Tunable Frequency and Bandwidth for Carrier-Free THz Communications

Carrier-free pulse-based waveforms are desired in terahertz (THz) communications since pulse-based systems have simpler transceiver architectures than carrier-based systems. For such a pulse-based THz communication system, there still lacks pulse waveforms that can support high-order modulation and flexible multiple access. In this paper, a pulse-based waveform with continuously tunable center frequencies and bandwidths is designed for carrier-free THz communications. More specifically, a Gaussian pulse is utilized as the basic pulse, and then the weighted sum of its high-order derivatives is used to generate waveforms with tunable frequencies and bandwidths according to the probability density function of Rice distribution. Such a pulse-based waveform is called frequency and bandwidth continuously tunable (FBCT) pulse. By making the derivative orders of all weighted terms odd or even, a pair of orthogonal FBCT pulses can be generated. Based on the pair of orthogonal FBCT pulses, a basic pulse-based <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</i> -ary quadrature amplitude modulation (P <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</i> QAM) scheme can be readily achieved. Moreover, with frequency and bandwidth tunability, FBCT pulse can support pulse division multiple access (PDMA) with tunable bandwidth, through which frequencies with high molecular absorption loss can be avoided. Numerical results demonstrate that FBCT pulse is significantly effective and flexible in supporting carrier-free THz communications.

New Decision for QAM Based on SVM for Complex Impairments

In this paper, we propose a new decision method based on a support vector machine for quadrature amplitude modulation (QAM) to improve the bit error rate (BER) performance of QAM for arbitrary complex impairments when both modeled and unknown impairments exist simultaneously. To do this, we first propose an algorithm for assigning bit decision boundaries corresponding to each quadrant for <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</i> -ary QAM, considering the asymmetry of the QAM constellation caused by the impairments. Then, we determine the optimal decision boundaries by learning a linear classification model for each bit decision region from I and Q values of received QAM signals as two-dimensional support vectors. Finally, the decision rules for each bit are presented based on the obtained optimal decision boundaries, and the bit decisions are performed using the decision rules. Based on the above process, we can effectively demodulate QAM signals for arbitrary complex impairments without compensation processes. Through computer simulations, we show the proposed method outperforms conventional model-based compensation schemes in BER performance under the condition of complex impairments.

Energy Detection for M-QAM Signals

Accurate threshold setting for energy detector is important for example in dynamic spectrum access. This requires accurate statistical distribution models of the observed energy. In this paper, we consider energy detection (ED) for <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$M$ </tex-math></inline-formula> -ary quadrature amplitude modulation (QAM) signals. The derivation of the exact solution of the distribution model (ES) requires all combinations of QAM signals in the observed signals based on the brute-force search and it leads to a significant computational cost. For this issue, this paper proposes three statistical distribution models which assume <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$M=\infty $ </tex-math></inline-formula> to avoid the brute-force search. Due to the assumption of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$M$ </tex-math></inline-formula> , the proposed models are independent of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$M$ </tex-math></inline-formula> and can handle adaptive modulation where <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$M$ </tex-math></inline-formula> can be changed dynamically. In the numerical evaluations, we compare the three proposed models with the other typical approximation models under additive white Gaussian noise (AWGN) channel and Rayleigh fading channel. In addition, the proposed models are extended for more realistic scenario where imperfect synchronization is considered. The comprehensive numerical evaluations show that the first proposed model is most accurate among all considered models except ES but requires relatively high computational cost. The second proposed model where the observed energy is assumed to follow Gaussian distribution is the least complexity but can have reduced accuracy. The third proposed model based on skew-normal distribution can achieve comparable accuracy and less complexity compared to the first model.

Low-Complexity Frequency Offset Estimation for Probabilistically Shaped MQAM Coherent Optical Systems

Since the reduction of the proportion of high modulus constellation points with π/4 + <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i> π/2 ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i> = 0, 1, 2, 3) modulation phase in probabilistically shaped (PS)- <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</i> -ary quadrature amplitude modulation (MQAM) deteriorates the power spectrum peak of frequency offset from the 4th power signal, the conventional 4th power Fast Fourier Transform (FFT) algorithm is not suitable for PS-MQAM under moderate or strong shaping. In this paper a low-complexity multi-format frequency offset estimation (FOE) scheme is proposed, where the coarse estimation is based on extended quadrature phase shift keying (QPSK) partitioning and quasi-linear approximation in polar coordinates at the first stage, and the fine estimation in subsequent stage using Digital Amplification and 4th power FFT with Sparse Operation. The computational complexity is approximately reduced by 71% compared with radius directed (RD) 4th power FFT algorithm with the same mutual information (MI) performance under 2e-2 bit error rate (BER). Dual polarization (DP) PS-16/32/64QAM numerical simulations prove that the normalized mean square error (NMSE) of proposed FOE scheme is an order of magnitude lower than that of RD 4th power FFT algorithm. The higher FOE accuracy has been demonstrated experimentally in DP PS-16/32QAM systems.

An Analysis of the Error Rate Performance for Uplink Asynchronous Signal Detection in Non-Orthogonal Multiple Access

We investigate multiuser detection under uplink asynchronous scenario, where the triangular successive interference cancellation (T-SIC) detection scheme is exploited. As the existing analysis was conducted under some ideal assumptions for simplicity, the asynchronous scenario is analyzed under rigorous assumptions in this paper so that important insights are revealed for practical systems. Specifically, the average symbol error rate (SER) formulas are derived for a two-user system with arbitrary <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$M$ </tex-math></inline-formula> -ary quadrature amplitude modulation ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$M$ </tex-math></inline-formula> -QAM) over Rayleigh fading channels. These solutions are shown to have higher accuracies compared to the existing solutions. Furthermore, a novel iterative detection algorithm is proposed, i.e., the parallel T-SIC method, which is more efficient and effective compared to the iterative T-SIC method. Insightful discussion is conducted in terms of the potentials of the concerned iterative detection method. Simulation results show that the most significant improvement of the iterative detection reflects on the SER for the strongest user, and the reduction is always within 50% of the SER compared to the primary detection. The gains obtained by the iterative detection is negligible for higher order <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$M$ </tex-math></inline-formula> -QAM cases.

Performance analysis of space time coded generalized frequency division multiplexing system over generalized fading channels

AbstractDue to its low out‐of‐band emission and high spectral efficiency, the generalized frequency division multiplexing (GFDM) has been adopted as one of the most prominent waveform techniques for the 5G networks. To further combat the deep fading, the space time coding (STC) can be integrated with the GFDM system which provide high diversity gain that results into low symbol error rate at the receiver. In this article, a generalized model of space time coded GFDM system (STC‐GFDM) has been proposed. More precisely, a comprehensive analytical framework to compute the average symbol error rate (ASER) is introduced, which can be used for any MIMO configuration, code rate, and arbitrary fading channel. The proposed framework has wider applicability over generalized fading channels and having more accurate exact solution along with easy to evaluate approximate solution. Thus, the proposed framework extends the horizon of performance analysis of STC‐GFDM system over any fading scenario, that is not covered so far in the literature. In general, the closed from expressions of exact and approximate along with asymptotic ASER are derived for different fading channels using moment generating function (MGF) approach. Particularly, the ASER analysis has been performed analytically using derived expression over Rayleigh, TWDP, Nakagami‐q, and Nakagami‐m fading channels for ‐ary quadrature amplitude modulation (‐QAM). This analysis confirms that with the increase in transmit and receive antenna and decrease in modulation order, the ASER performance improves for all fading channels. Also, the improvement in ASER is observed as the power of specular components (ie, LOS paths) increases. Furthermore, these analytical results are validated using Monte‐Carlo simulation.

Performance Analysis for Downlink NOMA Over $\alpha$-$\mu$ Generalized Fading Channels

This work presents a performance analysis for downlink non-orthogonal multiple accesses (DL-NOMA) systems where the channel gains follow the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\alpha$</tex-math></inline-formula> - <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula> fading distribution. Specifically, closed-form expressions are derived for DL-NOMA in terms of the outage probability (OP), bit error rate (BER), and ergodic capacity (EC). The OP analysis considers two main scenarios, the first is when the individual user's rate is required to satisfy a certain quality of service (QoS), while the second is when the individual user's NOMA rate is less than that of the conventional orthogonal multiple access (OMA) rate. Moreover, the derived BER performance is generalized for the case of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$M$</tex-math></inline-formula> -ary quadrature amplitude modulation (MQAM). The results demonstrate the interplay between the system performance, the power allocation coefficients, target data rates, and the channel fading parameters. Moreover, the OP results reveal that NOMA users with OMA data rate experience higher outage compared to NOMA with fixed target data rate. The accuracy of the derived expressions is validated using extensive Monte Carlo simulation.

Information rates in Kerr nonlinearity limited optical fiber communication systems.

Achievable information rates of optical communication systems are inherently limited by nonlinear distortions due to the Kerr effect occurred in optical fibres. These nonlinear impairments become more significant for communication systems with larger transmission bandwidths, closer channel spacing and higher-order modulation formats. In this paper, the efficacy of nonlinearity compensation techniques, including both digital back-propagation and optical phase conjugation, for enhancing achievable information rates in lumped EDFA- and distributed Raman-amplified fully-loaded C -band systems is investigated considering practical transceiver limitations. The performance of multiple modulation formats, such as dual-polarisation quadrature phase shift keying (DP-QPSK), dual-polarisation 16 -ary quadrature amplitude modulation (DP-16QAM), DP-64QAM and DP-256QAM, has been studied in C -band systems with different transmission distances. It is found that the capabilities of both nonlinearity compensation techniques for enhancing achievable information rates strongly depend on signal modulation formats as well as target transmission distances.

Reconfigurable Intelligent Surface-Aided Single-Input Single-Output K-Complex Symbol Golden Codeword-Based Modulation

Small reconfigurable intelligent surfaces (RISs) have greater potential for flexibility and ubiquity compared to large RISs. In the literature, the theoretical average bit error probability (ABEP) of a phase-adjustable element access-point-based RIS (AP-RIS) is derived by exploiting the central-limit theorem for large surface size. Hence, the analysis does not hold for small surface sizes. In this paper, we first formulate a simple closed-form expression for the ABEP of a phase-adjustable element AP-RIS with $M$ -ary quadrature amplitude modulation ( $M$ QAM). Compared to the results available in literature, this expression is valid even for small RISs. Second, we investigate AP-RIS-aided single-input single-output $K$ -complex symbol Golden codeword-based modulation, which encodes/transmits $K~M$ QAM symbols in each of $K$ consecutive independently faded time slots. The encoding ensures that each symbol experiences $K$ different fadings, hence resulting in a $K$ -fold increase in diversity order, while the AP-RIS maximizes the received signal-to-noise ratio (SNR) in each slot and yields significant SNR gains with increasing size. An increase in $K$ yields significant SNR gains for small RISs. A theoretical bound on the ABEP is formulated and validated by simulation. Finally, a detector based on sorted symbol set sphere decoding is devised.

Nonlinearity Tolerant LUT-Based Probabilistic Shaping for Extended-Reach Single-Span Links

We propose Huffman-coded sphere shaping (HCSS) as a method for probabilistic constellation shaping which provides improved tolerance to fiber nonlinearities in single-span links. An implementation of this algorithm based on look-up-tables (LUTs) allows for low-complexity, multiplier-free shaping. The advantage of short-length shaping for mitigating fiber nonlinear impairments is experimentally demonstrated for a system employing dual–polarization 64–ary quadrature amplitude modulation (DP-64QAM) at 56 GBd and operating over 210 km of standard single-mode fiber (SSMF). A gain in achievable information rate (AIR) of 0.4 bits/4D-symbol compared with uniform signaling is measured, corresponding to a 100% improvement in shaping gain compared with ideal Maxwell–Boltzmann (MB) shaping. The combinatorial mapping and demapping algorithms can be implemented with integer addition and comparison operations only, utilizing an LUT with 100 kbit size.

Security Enhancement via Antenna Selection in MIMOME Channels With Discrete Inputs

Transmit antenna selection (TAS) is an emerging technology in physical layer security. To provide new insights into the achievable secrecy performance of TAS in practical communication systems, this paper investigates the average secrecy rate (ASR) and secrecy outage probability (SOP) under practical modulation schemes in TAS aided multiple-input multiple-output multiple-antenna eavesdropper (MIMOME) wiretap channels over Rayleigh fading. Particularly, this research concentrates more on the square $M$ -ary quadrature amplitude modulation ( $M$ -QAM). Furthermore, in the considered MIMOME channel, a single antenna is selected to transmit the secret message, and selection combining (SC) or maximal-ratio combining (MRC) is utilized at the legitimate receiver and the eavesdropper. Based on this system model, novel expressions for the ASR and SOP are formulated to characterize the secrecy performance of the finite-alphabet driven MIMOME channel. Besides exact analysis, an asymptotic analysis is performed using the considered performance metrics in high signal-to-noise ratio (SNR) regime. Theoretical analyses suggest that the asymptotic ASR and SOP converge to finite constants in high SNR regime due to the discrete constellation constraint, and we find that the asymptotic behaviour of discrete inputs differs from that of Gaussian inputs. Furthermore, we derive concise expressions to characterize the rate of convergence (ROC) of the ASR and SOP, respectively. To unveil more system design insights, we discuss the relationship between the ROC and several important system parameters such as the antenna number and the modulation order.

Phase and Frequency Recovery Algorithms for Probabilistically Shaped Transmission

In additive white Gaussian noise (AWGN) channels, probabilistic shaping (PS) approaches the information-theoretical capacity using typical square $M$ -ary quadrature amplitude modulation ( $M$ -QAM) constellations with nonuniform a priori probabilities. However, shaped constellations may have a detrimental impact on the chain of digital signal processing algorithms of typical coherent receivers, reducing or even eliminating the expected shaping gains. In this article, we evaluate carrier phase recovery (CPR) and carrier frequency recovery (CFR) algorithms for probabilistically shaped transmission. The results are obtained by offline processing of experimental data with laser imperfections and additive noise loading. We investigate an existing two-stage CPR, where the first stage is based on pilots with 3.1% overhead, and the second stage uses the blind phase search (BPS) algorithm. We show that the BPS stage is severely impaired by PS at moderate and low SNRs. These impairments can be partially compensated using extremely long noise rejection windows, which may be undesirable from a computational complexity standpoint. Conversely, using only the pilot-based stage exhibits penalties at high SNRs, as phase noise dominates over additive noise. In order to obtain a suitable performance over the full range of SNRs, we propose to detune the PS factor (with respect to the AWGN-optimized value) to optimize the BPS stage. In scenarios with relatively low phase noise and low modulation orders, we show that an equivalent performance can be obtained without shaping factor detuning by operating with the two-stage approach at high SNRs and switching off the BPS stage at moderate and low SNRs. We also show that typical blind CFR based on the 4 $^{th}$ power algorithm is severely affected by PS at moderate block lengths, but its expected performance can be recovered using very long block lengths. Alternatively, a pilot-based algorithm with 3.1% overhead (employing the same pilots used for the first stage of the two-stage CPR algorithm) achieves a suitable performance in all the investigated scenarios.

Receive Antenna Selection Under Discrete Inputs: Approximation and Applications

To analyze the achievable performance of antenna selection (AS) in practical multi-antenna systems, this paper studies the receive antenna selection (RAS) in single-input multiple-output (AS-SIMO) systems under discrete inputs. We first propose an approximate expression to evaluate the instantaneous mutual information (MI) of $M$ -ary quadrature amplitude modulation ( $M$ -QAM) signaling over additive white Gaussian noise (AWGN) channels. Then, by exploiting this approximate formula, we develop a closed-form formula for the ergodic MI in AS-SIMO systems with $M$ -QAM signaling. Additionally, we also analyze the asymptotic MI for a large number of receive antennas $N_{\mathrm{r}}$ . This asymptotic analysis suggests that the scaling rate of the MI with $N_{\mathrm{r}}$ becomes zero rate in contrast to the double logarithmic rate under Gaussian inputs. Besides, our result is also extended to discuss the mutual information of multiple-input multiple-output (MIMO) systems having discrete inputs with receive antenna selection, and an upper bound for the MI is derived. Finally, the derived result is applied to analyze several performance measures of the discrete inputs driven AS-SIMO systems. Specifically, it is first used to discuss the relationship between the ergodic MI and the number of active antennas. Our investigation shows that this relationship follows Pareto principle, i.e., 80% of the MI of full-antenna selection can be achieved via 20% of the total antennas. Then, our proposed approximation is employed to analytically study the effective MI which takes channel estimation (CE) into consideration, indicating that CE is a main limit of large-scale systems. Moreover, the energy efficiency (EE) is explored on the basis of our results, and we find there exists an optimal number of active antennas to maximize the energy efficiency. In addition to theoretical derivations, all the analytical results are validated by numerical simulations.

Approximating Ergodic Mutual Information for Mixture Gamma Fading Channels With Discrete Inputs

To evaluate the performance of wireless multi-path channels with discrete inputs, this letter investigates the ergodic mutual information (EMI) of a generalized fading type named mixture gamma distribution (MGD) under $M$ -ary quadrature amplitude modulation ( $M$ -QAM) signaling. An accurate closed-form expression for the EMI is developed to approximate the exact value. The MGD fading can be specialized into several regularly used fading cases including Rayleigh fading, Nakagami- $m$ fading, $\eta -\mu $ fading, $\kappa -\mu $ fading, and ${\mathcal {K}}_{G}$ fading, and then the corresponding closed-form EMI formulas are separately derived to measure these fadings. Compared with the Gaussian source signals based research on MGD fading, this work sheds light on the performance with discrete inputs instead of Gaussian inputs, thereby being more practical. This study can be regarded as a unified tool to evaluate the EMI with discrete inputs over arbitrary wireless channels.

Threshold Based Signal Detection and the Average Symbol Error Probability for Downlink NOMA Systems With M-ary QAM

Non-orthogonal multiple access (NOMA) is a technique which allows multiple users to share the same radio access resources. However, there exist interferences among these users in the NOMA system. These interferences need to be taken into account in the signal detection and error performance analysis. In the downlink NOMA system, the far user detects its signal by treating the near user's signal as interference, while the near user employs successive interference cancellation (SIC) to detect its signal. Based on the conventional signal detection, it is not straightforward to derive the error performance for both the far user and near user. By analyzing the constellation relationships between the far user's signal and superposition coded (SC) signal, and the near user's signal and SC signal, in this article, a simple threshold based detection algorithm is proposed to detect both the far user's signal and near user's signal. Furthermore, by aid of the constellation relationships, in this article, simple expressions of the average symbol error probability (ASEP) with squared M -ary quadrature amplitude modulation for both the far user and near user are easily derived in Rayleigh fading channels. Simulation results validate the derived theoretical ASEP results.

Modulation-Based Simultaneous Wireless Information and Power Transfer

Due to the rapid growth of IoT and other connected devices, developing battery-less and/or self-sustainable devices to enable green communication is crucial. This letter presents a practical simultaneous wireless information and power transfer (SWIPT) scheme based on an $M$ -ary quadrature-amplitude modulation (QAM) modulation based technique ( ${MS} $ ). The proposed scheme employs hybrid constellation shaping system (HCS) to improve the spectral efficiency. We compare ${MS} $ with the traditional power splitting scheme based SWIPT ( ${PS} $ ) technique. We demonstrate that our proposed scheme outperforms ${PS} $ in terms of the error rate performance. ${MS} $ scheme is mainly focused on improving the reliability of low powered IoT sensors and it offers better achievable information rate at operating SNR region as compared to that of ${PS} $ . Those improvements come at the expense of a slight reduction in the maximum achievable spectral efficiency.

Design of Asymptotically Optimal Improper Constellations With Hexagonal Packing

This paper addresses the problem of designing asymptotically optimal improper constellations with a given circularity coefficient (correlation coefficient between the constellation and its complex conjugate). The designed constellations are optimal in the sense that, at high signal-to-noise-ratio (SNR) and for a large number of symbols, yield the lowest probability of error under an average power constraint for additive white Gaussian noise channels. As the number of symbols grows, the optimal constellation is the intersection of the hexagonal lattice with an ellipse whose eccentricity determines the circularity coefficient. Based on this asymptotic result, we propose an algorithm to design finite improper constellations. The proposed constellations provide significant SNR gains with respect to previous improper designs, which were generated through a widely linear transformation of a standard $M$ -ary quadrature amplitude modulation constellation. As an application example, we study the use of these improper constellations by a secondary user in an underlay cognitive radio network.

Average Symbol Error Rate Analysis for Non-Orthogonal Multiple Access With $M$ -Ary QAM Signals in Rayleigh Fading Channels

This letter investigates a symbol error rate (SER) performance of the downlink non-orthogonal multiple access (NOMA) scheme with symbol-level successive interference cancellation (SIC). Exact and closed-form expressions for average SERs of individual users are derived under Rayleigh fading channels considering imperfect SIC when the square quadrature amplitude modulation (QAM) symbols of two users are superposed and transmitted using NOMA. In addition, a power allocation criterion of NOMA is provided for the design of feasible QAM constellations when the modulation orders of two users are given.

Reduced Complexity Detection Schemes for Golden Code Systems

The Golden code has full-rate and full-diversity. However, its applications are limited because of the very high detection complexity. The complexity of sphere decoding depends on the size of signal set, $M^{2}$ , and the depth of search. Meanwhile, the complexity of fast essentially maximum likelihood (ML) detection is still $\mathcal {O}(M^{2})$ for $M$ -ary quadrature amplitude modulation ( $M$ QAM). In this paper, we propose two reduced complexity detection schemes, fast essentially ML with detection subset and sphere decoding with detection subset. Two theoretical bounds on the average bit error probability for the Golden code with $M$ QAM are also formulated in this paper. Simulation results demonstrate that both the fast essentially ML with detection subset and sphere decoding with detection subset agree well with the formulated theoretical bounds and can achieve the error performance of the conventional fast essentially ML detector and sphere decoding.

Modulation Mode Detection and Classification for In Vivo Nano-Scale Communication Systems Operating in Terahertz Band.

This paper initiates the efforts to design an intelligent/cognitive nano receiver operating in terahertz band. Specifically, we investigate two essential ingredients of an intelligent nano receiver-modulation mode detection (to differentiate between pulse-based modulation and carrier-based modulation) and modulation classification (to identify the exact modulation scheme in use). To implement modulation mode detection, we construct a binary hypothesis test in nano-receiver's passband and provide closed-form expressions for the two error probabilities. As for modulation classification, we aim to represent the received signal of interest by a Gaussian mixture model (GMM). This necessitates the explicit estimation of the THz channel impulse response and its subsequent compensation (via deconvolution). We then learn the GMM parameters via expectation-maximization algorithm. We then do Gaussian approximation of each mixture density to compute symmetric Kullback-Leibler divergence in order to differentiate between various modulation schemes (i.e., M -ary phase shift keying and M -ary quadrature amplitude modulation). The simulation results on mode detection indicate that there exists a unique Pareto-optimal point (for both SNR and the decision threshold), where both error probabilities are minimized. The main takeaway message by the simulation results on modulation classification is that for a pre-specified probability of correct classification, higher SNR is required to correctly identify a higher order modulation scheme. On a broader note, this paper should trigger the interest of the community in the design of intelligent/cognitive nano receivers (capable of performing various intelligent tasks, e.g., modulation prediction, and so on).