Spectral Efficiency

The media-based modulation (MBM) scheme is capable of providing high throughput, increasing spectrum efficiency, and enhancing bit error rate (BER) performance of communication systems. In this paper, an MBM employing radio frequency (RF) mirrors and golden code is investigated in a single-input multiple-output (GC-SIMO) application. The aim is to reduce complexity of the system, maximize linear relationships between RF mirrors and improve spectral efficiency of MBM to in order to obtain a high data rate with the use of less hardware. Orthogonal pairs of the super-symbol in the GC scheme’s encoder are employed, transmitted via different RF mirrors at different time slots in order to achieve the full data rate and high diversity. In the results having BER of 10−5 , the GC-SIMO, MBM exhibits better performance than GD-SIMO, with the gain of approximately 7 dB and 6.5 dB SNR for 4 b/s/Hz and 6 b/s/Hz, respectively. The derived theoretical average error probability of the proposed schem...

Sistemas de comunicações sem fio empregando duas ou mais antenas transmissoras e com uma ou mais antenas receptoras têm se destacado nos últimos anos. Existem várias razões para isto estar ocorrendo, entre elas: a demanda cada vez maior por alta taxa de dados, maior mobilidade do usuário, a busca por uma maior eficiência espectral e melhor qualidade de serviço (QoS -quality of service). A diversidade espacial proporcionada pelo uso de múltiplas antenas pode combater eficientemente desvanecimentos profundos provocados pelo canal de comunicação radiomóvel. A análise e descrição de canais MIMO (Multiple Input, Multiple Output) é bem mais complexa quando comparada a sistemas SISO (Single Input, Single Output), pois podemos ter NT (> 1) antenas transmissoras e NR (> 1) antenas receptoras, e no total teremos NTxNR canais. Neste artigo, focaremos a aplicação do processamento largamente linear (LL) em sistemas MISO (Multiple Input, Single Output) e MIMO, em especial na configuração proposta por Alamouti. Neste artigo apresentamos uma proposta de baixo custo computacional que usa o processamento LL em um sistema MIMO composto por duas antenas transmissoras e duas antenas receptoras. Os resultados de simulação confirmam a viabilidade da proposta.

Sistemas de comunicações sem fio empregando duas ou mais antenas transmissoras e com uma ou mais antenas receptoras têm se destacado nos últimos anos. Existem várias razões para isto estar ocorrendo, entre elas: a demanda cada vez maior por alta taxa de dados, maior mobilidade do usuário, a busca por uma maior eficiência espectral e melhor qualidade de serviço (QoS -quality of service). A diversidade espacial proporcionada pelo uso de múltiplas antenas pode combater eficientemente desvanecimentos profundos provocados pelo canal de comunicação radiomóvel. A análise e descrição de canais MIMO (Multiple Input, Multiple Output) é bem mais complexa quando comparada a sistemas SISO (Single Input, Single Output), pois podemos ter NT (> 1) antenas transmissoras e NR (> 1) antenas receptoras, e no total teremos NTxNR canais. Neste artigo, focaremos a aplicação do processamento largamente linear (LL) em sistemas MISO (Multiple Input, Single Output) e MIMO, em especial na configuração proposta por Alamouti. Neste artigo apresentamos uma proposta de baixo custo computacional que usa o processamento LL em um sistema MIMO composto por duas antenas transmissoras e duas antenas receptoras. Os resultados de simulação confirmam a viabilidade da proposta.

We present a simple alternative method for the compensation of quadrature imbalance in optical quadrature phase-shift-keying (QPSK) coherent systems. The method is based on the determination and the compensation of the phase mismatch by the introduction of a relevant signal-to-noise ratio metric. The principle is validated numerically and the algorithm is validated experimentally through bit-error-rate (BER) and error vector magnitude (EVM) measurements. A 20 Gb/s optical QPSK experiment reveals a good agreement of the proposed method with the Gram-Schmidt orthogonalization procedure (GSOP). Moreover, the robustness of both methods was verified with up to 30° phase misalignment by comparing the signal after phase imbalance compensation to that without compensation. A 10% reduction of EVM is achieved with our method for a high phase misalignment of 30 .

We report on the use of an InP/SOI hybrid photonic crystal nanocavity for the realization of a phase-preserving alloptical power limiter. This function is experimentally demonstrated with 20-Gbit/s NRZ-QPSK signals. Histogrambased measurements of the phase distributions indicate negligible variations of the phase noise while the amplitude fluctuations are suppressed, confirming the effectiveness of cavity switching for implementing the power-limiter function. Significant power penalty reduction is achieved, indicating a promising application for future photonic circuits.

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Absorber (SA). The 1 potential of the device to perform WDM regeneration is firstly demonstrated through the first pigtailed saturable absorber chip implemented with 8 independent fibres using a cost effective coupling technique. The cascadability and wavelength tunability assessment of this module associated to a power limiter fibre-based function has been experimentally demonstrated at 42.6 Gbit/s. Because this method of power limiting is not a suitable solution for all-optical multichannel 2R regeneration, a new SA structure allowing a power limiting function was proposed. We describe and characterize such a structure in this paper. This new SA opens the door to a complete passive all-optical 2R regeneration relying upon a single technology, as shown in this paper through the use of two SA: SA.0 for extinction ratio enhancement and SA.1 for power level equalization allowing receiver sensitivity (up to 3.5 dB) and Q factor (up to 1.4 dB) improvement for a RZ signal at 42.6 Gbit/s. The limitation of SA.1 when the regenerator must be cascaded a large number of times is also described, leading to the observation that SA.1 should be more suitable for phase encoded formats which are more spectrally efficient than OOK formats. A SA.1 used as a phase-preserving amplitude regenerator in a 42.6 Gbit/s RZ-DPSK transmission system is therefore assessed. A fibre launched power margin of 2 dB and a receiver sensitivity improvement of 5.5 dB are obtained. Finally, we use, for the first time an SA.1 as a phase-preserving amplitude regenerator of RZ DQPSK signals. The regenerator is assessed in a recirculating loop at 28 Gbaud. The system tolerance to nonlinear phase noise is enhanced by 3 dB and the distance improvement factor was 1.3 for a BER=10 -4 .

Basic principles of all-optical signal regeneration are presented, and main state-of-art techniques are reviewed. Optical fiber and semiconductor based devices are addressed, and some recently reported 2R and 3R signal regeneration experiments are discussed.

This paper presents the design, fabrication, and experimental validation of a compact 20port wideband Multiple-Input Multiple-Output (MIMO) antenna system tailored for nextgeneration 5G and emerging 6G indoor base-station applications. A key strength of the proposed design is its ability to accommodate 20 antenna elements within a compact footprint while maintaining stable isolation and strong MIMO performance. This is achieved through a uniquely engineered HIET-shaped monopole antenna element and a peripherally distributed 20-element layout that together enable exceptionally high port density while preserving wideband operation and low inter-element coupling-capabilities not achieved in prior sub-6-GHz MIMO designs. Realized on a compact 140 × 140 × 1.5 mm³ FR4 substrate, the proposed array achieves an impedance bandwidth of 3.6-8.2 GHz at-6 dB return loss (≈ VSWR 3:1), covering major 5G and prospective 6G bands including LTE Bands 43/46, NR Bands N77/N78/N79, U-NII bands for Wi-Fi 6/6E/7 and NR-U, portions of the upper C-band, and the lower X-band. Despite its dense configuration, the system maintains excellent isolation, achieving an envelope correlation coefficient (ECC) below 0.165 and a radiation efficiency of up to 85.4%. Simulated and measured S-parameters, radiation characteristics, and MIMO metrics show close agreement, validating the robustness of the design. Leveraging its high-port configuration, the proposed 20 × 20 MIMO system delivers an ergodic channel capacity of 97.7 bps/Hz at 20 dB SNR-significantly outperforming conventional low-port MIMO arrays. With its compact footprint, novel element structure, enhanced isolation mechanism, and superior channel capacity, the proposed antenna represents a distinct advancement in the development of space-efficient, high-capacity indoor 5G/6G base-station infrastructures.

Non-orthogonal multiple access (NOMA) scheme has gained remarkable consideration from researchers as it is a favorable technique for the future release of 5G and beyond. Recently proposed beamspace MIMO NOMA for mmWave communication has shown further improvement in its spectrum efficiency by employing beamforming with the aid of instantaneous channel state estimation. But, practically the downlink and the uplink channel state information (CSI) are not identical as the channel reciprocity is no more valid in the fast-varying environment of mmWave communication. Thus, this increases the transmission overhead due to pilot transmission in both uplink and downlink communication. To overcome this issue, we propose a semi-blind technique to design beamforming in downlink power-domain NOMA for mmWave communication which only requires statistical CSI. In the first step, the sum outage probability is derived by using the exact characterization of ratio of the indefinite quadratic form (IQF). In the second step, a heuristic approach with the aid of the interior point (IP) algorithm is developed to find the optimal solution for beam vectors by minimizing the derived sum outage probability. Moreover, a closed-form statistical beamforming solution is derived which is established on statistical signal-to-leakage-noise-ratio (SLNR) maximization. These two proposed methods are compared with the classical principle eigenvector-based solution. Monte Carlo simulations are used to validate the derived analytical expression of outage probability. The results of optimization demonstrate that the performance of both proposed beamforming is higher than the classical eigenvector-based solution. However, the heuristic-based beamforming algorithm via interiorpoint optimization is significantly better than the SLNR-based solution.

Spectrum usage due to an increasing number of mobile users using services like audio, video, and images is one of the challengings for wireless communication. Orthogonal Frequency Division Multiplexing (OFDM) is one of the promising techniques to increase spectral efficiency. However, the conventional OFDM using fast fourier transform (FFT) still has the drawback of reducing spectral efficiency. Discrete wavelet transforms (DWT) has been used as an alternative method replacing FFT to increase the spectral efficiency. This paper presents the fundamental of wavelets and their significance in wireless communication. A review of the literature has been done on how the DWT-OFDM performs better when compared to FFT-OFDM and on diversity technique such as transmit and receive diversity. The advantages of using diversity at both receiver and transmitter, i.e., Multiple inputs and multiple output systems and the overview of the technique is also considered. The flexibility, improve in the performance of BER, mitigate the interference DWT-OFDM with diversity at both transmitter and receiver provides emerging technology for future generation.

There are three types system can be modeled as MIMO channel [1]: a. point-to-point MIMO channel This type of MIMO system is a multiple antenna scenario, where both transmitter (TX) and receiver (RX) use several antennas with seperate modulation and demodulation for each antenna. We refer this type of channel as MIMO channel (Central transmitter and receiver). The uplink direction of any multiuser mobile communication system is an example of a MIMO system of this type. The joint receiver at the base station has to recover the individual users' signals. We will refer to this type of channel as the MIMO multiple access channel (Decentralized transmitters and central receiver). c. point-to-multipoint MIMO Channel The downlink direction of mobile multiuser communication systems is an example of what we call a MIMO broadcast channel (Central transmitter and decentralized receivers).

There are three types system can be modeled as MIMO channel [1]: a. point-to-point MIMO channel This type of MIMO system is a multiple antenna scenario, where both transmitter (TX) and receiver (RX) use several antennas with seperate modulation and demodulation for each antenna. We refer this type of channel as MIMO channel (Central transmitter and receiver). The uplink direction of any multiuser mobile communication system is an example of a MIMO system of this type. The joint receiver at the base station has to recover the individual users' signals. We will refer to this type of channel as the MIMO multiple access channel (Decentralized transmitters and central receiver). c. point-to-multipoint MIMO Channel The downlink direction of mobile multiuser communication systems is an example of what we call a MIMO broadcast channel (Central transmitter and decentralized receivers).

This study proposes two approaches for improving the effectiveness of spatial modulation integrated into layer division multiplexing (SM-LDM) in broadcasting systems: biased-power allocation (Bi-PA) and shared antenna selection (SAS). Even though different data rates are employed in SM-LDM systems, Bi-PA enhances bit error rate (BER) fairness across layers. The ideal power ratios are adaptively determined by balancing signal-to-interference plus noise ratios with a preference for the lower layer (LL) that involves a higher modulation order. SAS alleviates the complexity of successive interference cancellation and enhances spectral and energy efficiencies. Both the LL and upper layer (UL) share the antenna selection decision and transmit using a single antenna. The UL carries a space shift keying signal while the entire power is allocated for the LL. We analyze the spectral efficiency for the SAS-based SM-LDM system with finite alphabet inputs. Numerical results demonstrate the advan...

This paper focuses in the analysis of 100% static and distributed inter-cell interference coordination techniques in the context of LTE networks. Several methods have been modeled and studied with the aim of deriving practical radio planning rules based on the joint effect of operational parameters and thresholds. The investigation places special emphasis on the efficiency vs. fairness tradeoff. Several metrics have been detected as interesting to allow not only the performance measurement from different point of view, but also to look at the effectiveness in the utilization of resources. Results show that similar levels of spectral efficiency can be achieved by means of a proper and accurate network tuning. On the other hand, interesting second order differences appear due to some inherent features of each approach. These can be exploited depending on the particular network operator needs.

This paper presents a joint study of several intercell interference coordination strategies considering both static and dynamic approaches, and with different adjustments in their basic parameters. A wide evaluation is presented with special emphasis on the efficiency vs. fairness tradeoff. Besides, additional performance metrics have been considered as enablers of a full understanding of the strengths and weaknesses of each method. Results show that, although spectral efficiency can achieve similar values with proper tuning, certain schemas outperform others in important parameters such as the effectiveness in the utilization of resources. Dynamic semi-centralized approaches appear as an attractive option with an acceptable level of adaptability, moderate complexity and good performance.

Motivated by the deployment of hybrid cooperative cognitive radio (HCCR) based relays in cellular environments, this paper proposes the hybrid cognitive Gaussian two-way relay channel (HCGTWRC) model. Recently, the combination of licensed and cognitive radios with cooperative systems has gained popularity. These combined techniques have the potential to outperform primary network and pure cognitive network by utilizing the complementary nature of licensed and cognitive radios. In the proposed HCGTWRC model, a relay jointly utilizes both the licensed as well as the unlicensed/cognitive radio resources (RRs). Unlike conventional two-way relay channel, in this proposed model, source uses licensed resources for transmission and relay forwards this information using cognitive RRs. These licensed and unlicensed resources are not affected by total resource constraints of source and relay. Here, unlicensed RRs are not only described by bandwidth and power but also by reliability/availability parameter because of its opportunistic nature. In this paper, the proposed HCGTWRC model is studied by taking information theoretic aspect. In this respect, firstly, upper and lower bounds of performance metrics such as capacity, spectral efficiency (SE), and energy efficiency (EE) are analytically derived for the proposed HCGTWRC model. Then the optimal resource (such as power and bandwidth) allocation is derived with respect to upper and lower bounds of each performance metrics. Further, the performance comparison of the proposed HCGTWRC model is presented with the existing one. Numerical results are also presented for the optimal resource allocation to validate the analytical ones.

We design a self-exploratory reinforcement learning (RL) framework, based on the Q-learning algorithm, that enables the base station (BS) to choose a suitable modulation and coding scheme (MCS) that maximizes the spectral efficiency while maintaining a low block error rate (BLER). In this framework, the BS chooses the MCS based on the channel quality indicator (CQI) reported by the user equipment (UE). A transmission is made with the chosen MCS and the results of this transmission are converted by the BS into rewards that the BS uses to learn the suitable mapping from CQI to MCS. Comparing with a conventional fixed look-up table and the outer loop link adaptation, the proposed framework achieves superior performance in terms of spectral efficiency and BLER.

In this search, an important methodology has been presented for communicated information rectification utilizing advanced channel windowing approach. The modern data communication technologies are ensured with numerous challenges because of their unpredictability and arrangement. Various digital transmission topologies in 4G can't fulfill the requirements in future arrangements, therefore, alternative multicarrier modulation (MCM) becoming the nominated approaches among all other data transmission techniques. Wherein prototype filter configuration is a fundamental system based on which the synthesis and analysis filters are derived. This paper presents a complete review on the ongoing advances of finite impulse response (FIR) filter plan procedures in MCM based correspondence frameworks. Initially, the essential issues are tried, taking into consideration the presentation of available data signal applicants and the FIR filter design concept. At that point the techniques for FIR filter configuration are summed up in subtleties and are center around the accompanying three group’s recurrence testing strategies, windowing based strategies and advancement-based techniques. At last, the exhibitions of different FIR structure strategies are assessed and measured by power spectral density (PSD) and bit error rate (BER), and variable MCM plots as well as their potential prototype filters are examined.

We propose a novel transmission scheme for the parallel Gaussian broadcast channel with confidential messages (BCCM). In this model, The source node wishes to transmit a confidential message to each user over N independent sub-channels, where each sub-channel is degraded for one user than others. Our objective is to design a secure transmission technique that maximizes the sum secrecy rate under an average power constraint. The most common technique to tackle this problem in practice is orthogonal frequency division multiplexing (OFDM). Nevertheless, the OFDM-based BCCM suffers from excessive bandwidth utilization due to the sub-carrier orthogonality requirement. We propose a sparse non-orthogonal frequencydivision Multiplexing (SNOFDM) transmission scheme. In SNOFDM, sub-carriers are generated by first selecting a subset of orthogonal sub-channels to reduce spectral resources. Then, the selected sub-channels are multiplexed in time to generate non-orthogonal sub-carriers. This, in effect increases, the spectral efficiency compared to OFDM. To overcome the interference introduced due to the non-orthogonality of sub-carriers, the transmitter sends the sparsest representation of the transmitted codeword. Furthermore, we provide a sub-carrier selection and power control procedures to maximize the sum rate of SNOFDM according to CSI fed back from receivers to source node. Our numerical results show that SNOFDM offers better spectral efficiency and a higher secrecy rate compared to OFDM. We provide extensive simulation results to study the effects of transmission parameters of SNOFDM on the achievable secrecy rate. INDEX TERMS OFDM, SNOFDM, sparse signal processing, physical layer security, broadcast channel with confidential messages.

In this paper, we propose a spatial-temporal learning-based distributed routing framework for dynamic low Earth orbit (LEO) satellite networks, where graph attention networks (GAT) and long short-term memory (LSTM) are integrated within a deep Q-network (DQN)-based architecture to enable distributed and adaptive routing decisions based on local observations. The routing problem is formulated as a partially observable Markov decision process (POMDP) to address partial observability under dynamic topology and time-varying traffic. Simulation results show that the proposed method significantly outperforms conventional and learning-based routing schemes in terms of throughput, packet loss, queue length, and end-to-end delay, while achieving proactive congestion avoidance with up to 23.26% queue reduction. In addition, the proposed approach maintains low computational overhead with negligible carbon emissions, demonstrating its efficiency from a Green AI perspective.

In this paper, we propose a dueling double deep Q-network (DDQN)-based adaptive multi-objective handover framework for LEO satellite networks. The proposed method enables dynamic trade-off learning among throughput, blocking probability, and switching cost under time-varying network conditions. Simulation results demonstrate that the proposed approach consistently outperforms conventional baselines, achieving up to 10.3% throughput improvement and near-zero blocking under typical operating conditions.

In this paper, we propose a feedback-efficient hybrid precoding framework for wideband millimeter-wave (mmWave) multiple-input multiple-output orthogonal frequency-division multiplexing (MIMO-OFDM) systems. To mitigate the high cost of radio frequency (RF) chains and channel state information (CSI) feedback in large-scale antenna arrays, we first construct frequency-flat analog precoders by extracting dominant angle-of-arrival (AoA) and angle-of-departure (AoD) directions from sparse frequency-domain channels. For digital precoding, we design a quantized codebook using the Lloyd algorithm and develop a binary-search-based hierarchical interpolation algorithm that adaptively assigns codewords according to subcarrier correlation. The proposed method achieves sublinear feedback scaling by reducing the feedback overhead from O(K) to O(K/M +log M), where K is the number of subcarriers and M is the pilot spacing. Simulation results demonstrate that the proposed method achieves comparable or superior spectral efficiency and bit error rate (BER) performance to existing clustering and interpolation schemes, while significantly reducing computational complexity and exhibiting robustness under imperfect CSI.

An alternative code-division multiple-access (CDMA) scheme to spread spectrum (SS), called spread time (ST) is proposed for badlimited multiple-access channels. ST-CDMA can be considered the be-frequency dual of SS-CDMA. In ST-GDMA pslendsraodan (PN) sequences are assigned to each user, and the Fourier tcrursf@rm of the transmitted pulse for a given user is d&mined by modulating the phase of the desired transmitted spectnnn by the user's PN-skquence. The t"Btasd data for a parthdnr mer can be recoverad by sampling t8c output of a Plter matchd tcE tbe w " s pulse. ImplemenEwtloqs rare dascrilred in which wrface acoustic wave devices are used to perform the matched fislteL.ing or Fourier transformation. Averaged signal-to-intdremoe plus noise ratio (SIR) and spectral afldeacy are campuW fbr bo& asynchronous ST a d dCrect-seqnwe SS-CDMA systuns, assuming an arbitrary c h n d t r M e r fbnetion H(f), whicb is the same between all ppirS sf users. Tlhe resnlts are tlnt same for SS and ST providsd W t the magmnipude of the Fourier transform of the chip h p e in the SS system is the 88me 86 the nragnitwde of the Fader transform OP t4e ST pulse shape. The main advantag@ af tbe ST teehnlqus is the fled whick the transmitted spectrum can be sdwtwl. We dcrjlve the transmitted spectrum tbat maximizes the SIR subject to an average power constraint. ' Throughout this paper "transmitted spectrum" refers to the squared magnitude of the Fourier transform of the transmitted pulse.

First unequal error protection (UEP) proposals date back to the 1960's (Masnick and Wolf; 1967), but now with the introduction of scalable video, UEP develops to a key concept for the transport of multimedia data. The paper presents an overview of some new approaches realizing UEP properties in physical transport, especially multicarrier modulation, or with LDPC and Turbo codes. For multicarrier modulation, UEP bit-loading together with hierarchical modulation is described allowing for an arbitrary number of classes, arbitrary SNR margins between the classes, and arbitrary number of bits per class. In Turbo coding, pruning, as a counterpart of puncturing is presented for flexible bit-rate adaptations, including tables with optimized pruning patterns. Bit- and/or check-irregular LDPC codes may be designed to provide UEP to its code bits. However, irregular degree distributions alone do not ensure UEP, and other necessary properties of the parity-check matrix for providing UEP are...

his feature topic is a continuation of our November 2014 feature topic on the Future of Wi-Fi. In this second part of the feature topic, five papers selected from a pool of high-quality submissions are introduced. We hope our readers will find these articles useful for understanding recent developments and for inspiring their own work. Our feature topic begins with an article entitled "802.11 WLAN: History and New Enabling MIMO Techniques for Next Generation Standards," by Kim and Lee. It examines the IEEE 802.11 standard that defines wireless local area networks (WLAN). A detailed technical overview of the WLAN system and recent developments focusing on multiple-input multiple-output (MIMO) technologies are also presented. The next article, entitled "Emerging Technologies for WLAN" by Jones and Sampath, reviews a few key features of the published IEEE 802.11ac-2013 amendment, and potential emerging technologies being considered in a few amendments that are under development, including IEEE 802.11ah, IEEE 802.11ai, and IEEE 802.11ax. Further, the authors present channel measurement and prototype performance data to demonstrate the gains of MIMO and MU-MIMO, which are two important features of IEEE 802.11ac, in an indoor environment. The third article of this feature topic focuses on Wi-Fi based indoor positioning, which has recently attracted increasing attention from both academia and industry. Yang and Shao illustrate in their article "WiFi-Based Indoor Positioning" their proposed approach and compare its performance with a few existing mechanisms in terms of cost, complexity, and system performance. The last two articles continue to cover another very popular topic from Part I of our feature topic: the interworking of Wi-Fi and cellular systems. The first article is contributed by Zhang et al. and is entitled "Coexistence of Wi-Fi and Heterogeneous Small Cell Network Sharing Unlicensed Spectrum." The authors examine the potentials and challenges associated with coexisting Wi-Fi systems and heterogeneous cellular networks sharing the unlicensed spectrum. The authors also present a network architecture that can be applied in small cells to exploit unlicensed spectrum used by Wi-Fi systems. In the second article, "Enhanced Capacity & Coverage by Wi-Fi LTE Integration," Ling et al. discuss a few solutions that integrate Wi-Fi with LTE access networks, in order to enable Wi-Fi networks to serve more users with higher throughput demands and as an effective traffic offload solution for cellular operators, all coming with the benefits of using the unlicensed spectrum.

Spectrum and infrastructure sharing among multiple mobile network operators is a vital solution to substantially and sustainably improves cost and network efficiency. However, such approach may face several challenges, such as the imposed restrictions on the independence of operators, the complexity of spectrum management policies and the mutual interference issues among operators. Therefore, in this study, we propose a flexible hybrid spectrum access strategy, namely, hybrid millimetre wave (mmWave) spectrum slicing-sharing access (HMSSSA), to optimise the coverage probability via distributing the spectrum in a hybrid manner. Accordingly, the interference problem can be addressed, and the coverage probability can be improved. In the proposed strategy, the spectrum splits into three different classes: (i) exclusive right assigned to all of the operators, (ii) semi-pooled among all the operators and (iii) fully pooled (shared) as open access among all the operators with the ultra-flexibility feature. Adaptive hybrid multi-state mmWave cell selection (AHMMC-S) scheme is adopted to optimally associate a typical user to the mmWave base station (mBS) that offers high signal-to-interference plus noise ratio. Numerical results demonstrate that our proposed strategy reduces the outage probability significantly, provides a degree of freedom to the subscribers to optimally select mBS with high signal quality and maintains an acceptable level of mBS densification.

This paper presents a detailed performance analysis of 5G N71 deployment in a live network environment, focusing on its impact on coverage enhancement, uplink performance, and overall network efficiency. Unlike mid-band 5G layers such as N78 and N40, which primarily address capacity requirements, the low-band N71 spectrum is deployed to improve coverage, particularly in indoor and cell-edge scenarios. The study was conducted across multiple sites using a 2×2 MIMO configuration, and performance evaluation was carried out using OSS-based key performance indicators (KPIs), drive test measurements, and user-experienced data including Ookla speed tests. The results indicate that N71 significantly improves coverage, with better signal propagation and deeper indoor penetration compared to higher frequency bands. In addition, uplink performance shows noticeable enhancement due to lower path loss and full-duplex operation, outperforming N40 and N78 in several scenarios. Traffic distribution analysis highlights the role of N71 in extending 5G service to areas previously dominated by LTE, thereby improving overall network accessibility. Despite limitations in carrier aggregation support and device compatibility, the deployment demonstrates stable network performance with no adverse impact on key KPIs. Overall, the findings confirm that N71 is an effective and scalable solution for enhancing 5G coverage and improving uplink performance in real-world network deployments.

We present a geometry-first formulation of quantum transport in two-boundary wave systems and develop a unifying obstruction framework separating negotiable mismatch from irreducible nodal constraints. Using a power-family density interpolating between initial and final boundary conditions, we show that the log-transport defect admits an exact decomposition into geometric, reweighting, and boundary-localized terms. We prove that at the self-dual point this defect reduces to a purely geometric obstruction, and we identify Cantor-gap obstruction as the fundamental mechanism underlying hard transport failure in interference-dominated and aperiodic geometries. The framework is representation-independent, analytically controlled, and numerically testable, and it situates transport obstruction alongside universality structures familiar from quantum chaos, quasicrystals, and singular-continuous spectra.

Successive interference cancellation (SIC) is fundamentally the important detection technique of power-domain non-orthogonal multiple access (pNOMA) in 5G and currently under intense research in beyond 5G (B5G) networks. However, it faces challenges in terms of error propagation, computational efficiency and scalability. Resonance based aiding algorithm techniques such as Woods–Saxon Stochastic Resonance (WSSR) and Classical Stochastic Resonance (CSR) based were proposed to aid the SIC to improve weak signal detection. This paper presents a comparative study using time and space complexity analysis of WSSR-assisted SIC (WSSR-SIC) and CSR-based SIC (CSR-SIC) as base line using Big O. We evaluate both the time and space complexities under realistic channel conditions. Simulation results demonstrate that CSR-SIC produces better latency of 0.35ms, good for uRLLC requirement. Equally, WSSR-SIC achieves superior weak signal detection presents better link reliability for rescuing weaker users (where system reliability trumps minimal latency; 0.85 ms, still < 1 ms 5G latency requirement). The findings highlight WSSR-SIC as a promising detection scheme for mMTC and eMBB to support next-generation NOMA systems for massive connectivity requirements of internet-of-thing (IoT) and internet-of-everything (IoET).

This paper investigates low-complexity approaches to small-cell base-station (SBS) design, suitable for future 5G millimeter-wave (mmWave) indoor deployments. Using large-scale antenna systems and high-bandwidth spectrum, such SBS can theoretically achieve the anticipated future data bandwidth demand of 10 000 fold in the next 20 years. We look to exploit small cell distances to simplify SBS design, particularly considering dense indoor installations. We compare theoretical results, based on a link budget analysis, with the system simulation of a densely deployed indoor network using appropriate mmWave channel propagation conditions. The frequency diverse bands of 28 and 72 GHz of the mmWave spectrum are assumed in the analysis. We investigate the performance of low-complexity approaches using a minimal number of antennas at the base station and the user equipment. Using the appropriate power consumption models and the state-of-the-art sub-component power usage, we determine the total power consumption and the energy efficiency of such systems. With mmWave being typified nonline-of-sight communication, we further investigate and propose the use of direct sequence spread spectrum as a means to overcome this, and discuss the use of multipath detection and combining as a suitable mechanism to maximize link reliability.

Faster-than-Nyquist (FTN) signaling appears as an attractive method to improve spectral efficiency at the price of an increased complexity at the receiver. The receiver generally implements a turbo-equalization/detection scheme to benefit from all the promises of the FTN signaling. However, this is not the only limitation we have to deal with. Indeed, compressing in the time domain impact the emitted signal and it usually results in an increase of the envelope fluctuations. This leads to an inherent multi-objectives trade-off between performance, targeted spectral efficiency and limited Peak to Average Power Ratio (PAPR). The last aspect is crucial when considering a satellite communication link due to non-linear amplification effects that can occur on-board the satellite. Usually, FTN studies focus on spectral efficiency increase for a fixed modulation order, trying to trade-off between performance and PAPR properties. In this paper, we show that, for a given asymptotic spectral efficiency, we can compress low order modulations to increase the spectral efficiency of these schemes while controlling the PAPR increase to achieve a better PAPR than the non compressed scheme with a higher modulation order. Thus, for the same asymptotic spectral efficiency, we can achieve 1 dB gain in terms of PAPR and 2 dB gain in Bit Error Rate (BER) performances for a coded 8-PSK FTN system compared to a coded 16-APSK. For the same BER performances, the asymptotic spectral efficiency gain obtained in linear context is over 20 %, higher when nonlinearities are taken into account.

Faster-than-Nyquist (FTN) signaling appears as an attractive method to improve spectral efficiency at the price of an increased complexity at the receiver. The receiver generally implements a turbo-equalization/detection scheme to benefit from all the promises of the FTN signaling. However, this is not the only limitation we have to deal with. Indeed, compressing in the time domain impact the emitted signal and it usually results in an increase of the envelope fluctuations. This leads to an inherent multi-objectives trade-off between performance, targeted spectral efficiency and limited Peak to Average Power Ratio (PAPR). The last aspect is crucial when considering a satellite communication link due to non-linear amplification effects that can occur on-board the satellite. Usually, FTN studies focus on spectral efficiency increase for a fixed modulation order, trying to trade-off between performance and PAPR properties. In this paper, we show that, for a given asymptotic spectral efficiency, we can compress low order modulations to increase the spectral efficiency of these schemes while controlling the PAPR increase to achieve a better PAPR than the non compressed scheme with a higher modulation order. Thus, for the same asymptotic spectral efficiency, we can achieve 1 dB gain in terms of PAPR and 2 dB gain in Bit Error Rate (BER) performances for a coded 8-PSK FTN system compared to a coded 16-APSK. For the same BER performances, the asymptotic spectral efficiency gain obtained in linear context is over 20 %, higher when nonlinearities are taken into account.

This paper presents a comparison of different instances of advanced iterative receivers for the non linear satellite channel. A comparison of the performance and complexity of each of the selected receivers is drawn. It is shown that the frequency domain implementation of the linear equalizer achieves good performance complexity trade-off. The cost to pay for the frequency domain processing is the addition of a Cyclic Prefix (CP) to ensure the blocks orthogonality. The consequence is a channel dependent spectral efficiency loss. We thus investigate on the efficiency gain related to the CP omission for frequency domain equalizers for different block sizes and show that for large block sizes, the equalizer's performance is not much sacrificed.

Wireless communication systems are quickly evolving to fulfil the increasing need for higher spectral efficiency, lower latency, and seamless connectivity. Although the conventional multiple-input multiple-output (MIMO) architecture improves reliability and throughput, it still faces high hardware complexity, spectral inefficiency, and interference issues in dense environments. Existing solutions, such as double-sided microstrip patch antennas or 8×8 MIMO arrays, yield moderate improvements but are not flexible enough for next-generation networks. To overcome these limitations, this paper puts forward a slot-based distributed generalized spatial modulation (DGS-MIMO) framework, which integrates dynamic antenna subset activation and adaptive sub-band allocation. In this way, the number of radio frequency (RF) chains is reduced, power consumption is lower, and spectral utilization is improved. Experimental validation shows excellent impedance matching (return loss up to-36.29 dB), high gain (6.98 dB), high radiation efficiency, and low signal reflection (voltage standing wave ratio (VSWR) as low as approximately 1.03). These results prove the robustness and efficiency of the proposed system in comparison with conventional designs. Besides the performance enhancement, the framework has great potential to be applied in real-world 5G/6G applications, especially in internet of things (IoT) deployments and vehicular communication scenarios where scalability, energy efficiency, and reliability are important.

In this paper, we propose a training-based channel estimation scheme for large non-orthogonal space-time block coded (STBC) MIMO systems. The proposed scheme employs a block transmission strategy where an N t × Nt pilot matrix is sent (for training purposes) followed by several N t × Nt square data STBC matrices, where N t is the number of transmit antennas. At the receiver, we iterate between channel estimation (using an MMSE estimator) and detection (using a low-complexity likelihood ascent search (LAS) detector) till convergence or for a fixed number of iterations. Our simulation results show that excellent bit error rate and nearness-to-capacity performance are achieved by the proposed scheme at low complexities. The fact that we could show such good results for large STBCs (e.g., 16×16 STBC from cyclic division algebras) operating at spectral efficiencies in excess of 20 bps/Hz (even after accounting for the overheads meant for pilot-based channel estimation and turbo coding) establishes the effectiveness of the proposed scheme.

We consider the impact of transceiver power consumption on the energy efficiency (EE) of the Zero Forcing (ZF) detector in the uplink of massive MIMO systems, where a base station (BS) with M antennas communicates coherently with K single antenna user terminals (UTs). We consider the problem of maximizing the EE with respect to (M, K) for a fixed sum spectral efficiency. Through analysis we study the impact of system parameters on the optimal EE. System parameters consists of the average channel gain to the users and the power consumption parameters (PCPs) (e.g., power consumed by each RF antenna/receiver at BS). When the average user channel gain is high or else the BS/UT design is power inefficient, our analysis reveals that it is optimal to have a few BS antennas and a single user, i.e., non-massive MIMO regime. Similarly, when the channel gain is small or else the BS/UT design is power efficient, it is optimal of have a larger (M, K), i.e., massive MIMO regime. Tight analytical bounds on the optimal EE are proposed for both these regimes. The impact of the system parameters on the optimal EE is studied and several interesting insights are drawn.

Recently, we reported a low-complexity likelihood ascent search (LAS) detection algorithm for large MIMO systems with several tens of antennas that can achieve high spectral efficiencies of the order of tens to hundreds of bpsIHz. Through simulations, we showed that this algorithm achieves increasingly near SISO AWGN performance for increasing number of antennas in i.i.d. Rayleigh fading. However, no bit error performance analysis of the algorithm was reported. In this paper, we extend our work on this low-complexity large MIMO detector in two directions: i) We report an asymptotic bit error probability analysis of the LAS algorithm in the large system limit, where N" N r ~00 keeping Nt = Nr, where Nt, and NT are the number of transmit and receive antennas, respectively. Specifically, we prove that the error performance of the LAS detector for V-BLAST with 4-QAM in i.i.d. Rayleigh fading converges to that of the maximum-likelihood (ML) detector as Nt ~N r -e, x keeping Nt = NT. ii) We present simulated BER and nearness to capacity results for V-BLAST as well as high-rate non-orthogonal STBC from Division Algebras (DA), in a more realistic spatially correlated MIMO channel model. Our simulation results show that a) at an uncoded BER of 10-3, the performance of the LAS detector in decoding 16 x 16 STBC from DA with N, =Nr =16 and 16-QAM degrades in spatially correlated fading by about 7 dB compared to that in i.i.d. fading, and b) with a rate-3/4 outer turbo code and 48 bps/Hz spectral efficiency, the performance degrades by about 6 dB at a coded BER of 10-4. Our results further show that providing asymmetry in number of antennas such that N r > Nt keeping the total receiver array length same as that for N r = Nt, the detector is able to pick up the extra receive diversity thereby significantly improving the BER performance.

Non-orthogonal space-time block codes (STBC) from cyclic division algebras (CDA) having large dimensions are attractive because they can simultaneously achieve both high spectral efficiencies (same spectral efficiency as in V-BLAST for a given number of transmit antennas) as well as full transmit diversity. Decoding of non-orthogonal STBCs with hundreds of dimensions has been a challenge. In this paper, we present a probabilistic data association (PDA) based algorithm for decoding non-orthogonal STBCs with large dimensions. Our simulation results show that the proposed PDA-based algorithm achieves near SISO AWGN uncoded BER as well as near-capacity coded BER (within about 5 dB of the theoretical capacity) for large non-orthogonal STBCs from CDA. We study the effect of spatial correlation on the BER, and show that the performance loss due to spatial correlation can be alleviated by providing more receive spatial dimensions. We report good BER performance when a training-based iterative decoding/channel estimation is used (instead of assuming perfect channel knowledge) in channels with large coherence times. A comparison of the performances of the PDA algorithm and the likelihood ascent search (LAS) algorithm (reported in our recent work) is also presented.

In this paper, we present a low-complexity algorithm for detection in high-rate, non-orthogonal space-time block coded (STBC) large-multiple-input multiple-output (MIMO) systems that achieve high spectral efficiencies of the order of tens of bps/Hz. We also present a training-based iterative detection/channel estimation scheme for such large STBC MIMO systems. Our simulation results show that excellent bit error rate and nearness-to-capacity performance are achieved by the proposed multistage likelihood ascent search ( -LAS) detector in conjunction with the proposed iterative detection/channel estimation scheme at low complexities. The fact that we could show such good results for large STBCs like 16 16 and 32 32 STBCs from Cyclic Division Algebras (CDA) operating at spectral efficiencies in excess of 20 bps/Hz (even after accounting for the overheads meant for pilot based training for channel estimation and turbo coding) establishes the effectiveness of the proposed detector and channel estimator. We decode perfect codes of large dimensions using the proposed detector. With the feasibility of such a low-complexity detection/channel estimation scheme, large-MIMO systems with tens of antennas operating at several tens of bps/Hz spectral efficiencies can become practical, enabling interesting high data rate wireless applications.

In our recent work, we reported an exhaustive study on the simulated bit error rate (BER) performance of a low-complexity likelihood ascent search (LAS) algorithm for detection in large multiple-input multiple-output (MIMO) systems with large number of antennas that achieve high spectral efficiencies. Though the algorithm was shown to achieve increasingly closer to near maximum-likelihood (ML) performance through simulations, no BER analysis was reported. Here, we extend our work on LAS and report an asymptotic BER analysis of the LAS algorithm in the large system limit, where N t , N r → ∞ with N t = N r , where N t and N r are the number of transmit and receive antennas. We prove that the error performance of the LAS detector in V-BLAST with 4-QAM in i.i.d. Rayleigh fading converges to that of the ML detector as N t , N r → ∞.

We consider large MIMO systems, where by 'large' we mean number of transmit and receive antennas of the order of tens to hundreds. Such large MIMO systems will be of immense interest because of the very high spectral efficiencies possible in such systems. We present a low-complexity detector which achieves uncoded near-exponential diversity performance for hundreds of antennas in V-BLAST (i.e., achieves near SISO AWGN performance in a large MIMO fading environment) with an average per-bit complexity of just O(NtNr), where Nt and Nr denote the number of transmit and receive antennas, respectively. With an outer turbo code, the proposed detector achieves good coded bit error performance as well. For example, in a 600 transmit and 600 receive antennas V-BLAST system with a high spectral efficiency of 200 bps/Hz (using BPSK and rate-1/3 turbo code), our simulation results show that the proposed detector performs close to within about 4.6 dB of the theoretical capacity. We also adopt the proposed detector for the low-complexity decoding of high-rate non-orthogonal spacetime block codes (STBC) from division algebras (DA). We have decoded the 16 × 16 full-rate STBC from DA using the proposed detector and show that it performs close to within about 5.5 dB of the capacity using 4-QAM and rate-3/4 turbo code at a spectral efficiency of 24 bps/Hz. The practical feasibility of the proposed high-performance low-complexity detector could trigger wide interest in the implementation of large MIMO systems.

Millimeter wave (mmWave) system tends to have a large number of antenna elements to compensate for the high channel path loss. The immense number of BS antennas incurs high system costs, power, and interconnect bandwidth. To circumvent these obstacles, two-step hybrid precoding algorithms that enable the use of fewer RF chains have been proposed. However, the precoding schemes already in place are either too complex or not performing well enough. In this study, an equivalent channel hybrid precoding was proposed. The part from the transmitter RF chain to the receiver RF chain is regarded as equivalent channel. By reducing the dimension of channel matrix to the level of RF link number, baseband pre-coder is simply calculated from decomposing the equivalent channel matrix H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">equ</sub> , which greatly reduces the complexity. Based on this novel precoding approach and convolutional neural netwo...

Millimeter wave (mmWave) system tends to have a large number of antenna elements to compensate for the high channel path loss. The immense number of BS antennas incurs high system costs, power, and interconnect bandwidth. To circumvent these obstacles, two-step hybrid precoding algorithms that enable the use of fewer RF chains have been proposed. However, the precoding schemes already in place are either too complex or not performing well enough. In this study, an equivalent channel hybrid precoding was proposed. The part from the transmitter RF chain to the receiver RF chain is regarded as equivalent channel. By reducing the dimension of channel matrix to the level of RF link number, baseband pre-coder is simply calculated from decomposing the equivalent channel matrix H equ , which greatly reduces the complexity. Based on this novel precoding approach and convolutional neural network (CNN), a novel combiner neural network architecture was also proposed, which can be trained to learn how to optimize the combiner for maximizing the spectral efficiency with hardware limitation and imperfect CSI. Simulation results show that the proposed approaches achieve significant performance improvement. INDEX TERMS mmWave, MIMO, hybrid precoding, deep learning, CNN.

The energy efficiency in telecommunication networks is gaining more relevance as the Internet traffic is growing. The introduction of OFDM and dynamic operation opens new horizons in the operation of optical networks, improving the network flexibility and its efficiency. In this paper, we compare the performance in terms of energy efficiency of a flexible-grid OFDM-based solution with a fixed-grid WDM network in a dynamic scenario with time-varying connections. We highlight the benefits that the bandwidth elasticity and the flexibility of selecting different modulation formats can offer compared to the rigidity of the conventional networks.