This paper investigates the outage probability in edge intelligence (EI)-enabled networks that support embodied agents, such as humanoid robotic assistants (HRAs) powered by foundation models (FMs), within indoor hotspot (InH) environments where base stations are typically mounted on walls or ceilings in corridors. The analysis considers both line-of-sight (LOS) and non-line-of-sight (NLOS) conditions in internet of things (IoT) environments. We propose a novel cache-aware inference offloading (CAIO) strategy that combines edge caching and cloud-based retrieval-augmented generation (RAG) to deliver timely and accurate FM inference. Closed-form expressions for outage probability are derived under Rayleigh fading for both CAIO and a cloud-only (CLD) benchmark. The system model incorporates realistic assumptions, including binomial point processes for user distribution and practical backhaul latency modeled using Gamma distributions. Unlike prior work that primarily addresses latency or energy efficiency, the present analysis explicitly considers FM inference accuracy and processing dynamics at both edge and cloud. Analytical and simulation results identify optimal BS inference accuracy, FM content popularity, and cache size under varying maximum RAG latency values to ensure reliable IoT operation, showing that CAIO consistently outperforms CLD across all scenarios for real-time FM inference for HRAs.

In this work, we investigate the use of reconfigurable intelligent surface (RIS) partitioning and transmit power allocation for terahertz (THz) enabled spectrum-sharing underlay device-to-device (D2D) communication, assuming that instantaneous channel state information (CSI) for co-channel interference (CCI) links is unavailable. We first derive closed-form expressions for the ergodic rate (ER) based on statistical CSI using the moment matching technique and Gaussian–Chebyshev quadrature approximation, while accounting for generalized fading and pointing errors. We then develop a low-complexity particle swarm optimization (PSO) algorithm based solution to jointly partition the RIS and allocate transmit powers, aiming to maximize the ER of the D2D user. Analytical findings are validated via extensive Monte Carlo simulations, which provide key system design insights and performance comparisons with both non-RIS systems and benchmark optimization schemes.

To efficiently implement Terahertz (THz) communications in the 6G era, ultra-massive multiple-input multiple-output (UM-MIMO) technique is considered essential. However, effective wideband THz UM-MIMO transmissions necessitate low-cost yet accurate channel estimation (CE) methods. In this article, we investigate the wideband THz UM-MIMO CE problem under hybrid near- and far-field propagation, molecular absorption, and multi-path reflection. The CE problem is reformulated into a compressed sensing (CS)-aided counterpart (CSCE), exploiting the inherent sparsity of THz UM-MIMO channels to reduce pilot overhead. Our key contributions are: 1) after analyzing the inefficiency of conventional Bayesian learning (BL)-based CSCE frameworks in solving this CE task, we propose a deep unfolding (DU)-aided BL (DUBL) CE algorithm, in which the unfolded expectation-maximization (EM) iteration is implemented through a carefully tailored deep neural network (DNN) architecture; 2) we design a staged offline training procedure equipped with a dedicated loss function to ensure efficient DUBL training; and 3) we conduct a detailed complexity analysis that explicitly quantifies the computational cost of each unrolled layer, thereby characterizing the online inference overhead of the proposed DUBL method. Simulation results demonstrate that the DUBL solution offers substantial THz UM-MIMO CE gains over representative baselines, while complexity comparison highlights its enhanced real-time inference.

In recent years, reconfigurable intelligent surfaces (RIS) have emerged as a promising technology for enhancing link reliability in wireless communication systems. This paper introduces a novel RIS-assisted terahertz (THz) communication system utilizing the spatial modulation (SM) technique. We derive the closed-form expressions for the probability density function (PDF) and moment generating function (MGF) of the SM-based RIS-assisted THz system over α-μ fading. Leveraging these derived channel statistics, we obtain an upper bound on the average bit error rate (BER) and a lower bound on the ergodic capacity to evaluate the performance of the proposed system. The asymptotic BER is analyzed to determine the system’s diversity gain. The numerical results validate the theoretical findings and provide valuable insights into the system’s performance. The analysis shows that the SM-based RIS-assisted THz system outperforms the existing traditional systems. Lastly, a trade-off between average BER performance and spectral efficiency is observed.

In this paper, we investigate a full-duplex underlay device-to-device (D2D) communication system, where multiple D2D pairs exchange information with the assistance of a single reconfigurable intelligent surface (RIS). We begin by deriving analytical expressions for the outage probability of the users, and subsequently for ergodic rate. The analysis is carried out over a generalized Nakagami-m fading channel and incorporates several practical impairments, including residual self-interference (RSI), hardware imperfections (HI), and co-channel interference (CCI) from both cellular and D2D users. Assuming only statistical channel state information (CSI) is available for the CCI links, we formulate a joint optimization problem for D2D transmit power allocation and RIS partitioning, with the objective of maximizing the ergodic sum rate of the network. This optimization problem is efficiently solved using the particle swarm optimization (PSO) algorithm. Simulation results validate the effectiveness of the proposed system, demonstrating superior performance over conventional half-duplex systems and highlighting the advantages of the proposed optimization framework compared to benchmark schemes.

To efficiently implement Terahertz (THz) communications in the 6G era, the ultra-massive multiple-input multipleoutput (UM-MIMO) technique is considered an essential building block. However, effective wideband THz UM-MIMO transmissions can never be achieved without pilot-inexpensive yet accurate channel estimation (CE) methods. In this article, we investigate the wideband THz UM-MIMO CE problem, accounting for the hybrid near- and far-field propagation characteristics, molecular absorption, and multi-path reflection. The CE problem is reformulated into a compressed sensing-aided counterpart, leveraging the inherent sparsity of THz UM-MIMO channels to reduce pilot overhead. We harness the power of model-driven deep learning and propose a deep unfolding (DU)-aided Bayesian learning (DUBL) CE algorithm. We tailor the structure of the deep neural network (DNN)-based unfolded expectation-maximization (EM) iteration, aiming to achieve efficient DUBL training performance. Simulation results demonstrate that the DUBL solution can offer substantial THz UM-MIMO CE gains over the considered representative benchmarks.

In this paper, the inference freshness of generative artificial intelligence (gen-AI) services in industrial Internet-of-Things (IIoT) networks is investigated. A freshness metric termed the peak age of inference (PAoIF) is proposed to quantify inference freshness by accounting for peak age of information and delays due to transmitting inference requests and results. A cache-aware offloading (CAO) strategy which employs multi-access edge computing in IIoT networks is also proposed for timely inference delivery. Leveraging novel closed-form expressions for PAoIF violation probability within the proposed CAO and benchmark strategies for IIoT, this study analyzes the impact of PAoIF violation age, gen-AI service request rate, and average transmission rate, on inference freshness. We identified scenarios where the proposed CAO strategy exhibits a lower PAoIF violation probability compared to the benchmark strategies under consideration. Furthermore, we show that PAoIF violation probability under the proposed CAO strategy is minimized via optimizing the average transmission rate in IIoT networks employing servers with limited computing resources. Therefore, the analysis shows that the proposed CAO strategy is a viable technique towards enabling inference freshness for gen-AI services in IIoT networks.

This paper explores a full-duplex underlay D2D communication system, where multiple D2D pairs exchange data with the help of a single RIS through RIS partitioning. Closed-form expressions for outage probability and ergodic rate are derived over generalized Nakagami-m fading, considering practical impairments such as residual self-interference, hardware imperfections, and co-channel interference (CCI). Assuming only statistical channel state information (CSI) availability for the CCI links, we formulate and solve a joint optimization problem for transmit power allocation and RIS partitioning using particle swarm optimization. Simulation results show significant performance gains over half-duplex systems and comparative benchmarks schemes.

This paper investigates the maximization of average energy efficiency (AEE) in MEC-enabled Industrial Internet of Things (IIoT) networks through a cache-based association strategy (CBAS). The system comprises autonomous mobile robots (AMRs), small-cell base stations (SBSs), and macro-cell base stations (MBSs) operating under line-of-sight obstructions, fading, and interference. To jointly optimize transmit power, SBS cache size, MBS cache size, and SBS intensity, parameters critical to CBAS efficiency, we propose a deep Q-network (DQN)-based approach that circumvents the computational burden of solving NP-hard formulations through exhaustive search. In addition to performance benchmarking, we enhance explainability by analyzing the learned state embeddings using t-SNE. Simulation results show that our approach achieves near-optimal AEE with significantly lower overhead, making it scalable and suitable for real-time IIoT deployments.

Minimizing the Age of Information (AoI) violation probability is essential for reliable and timely data delivery in MEC-enabled IIoT networks. This study proposes the Joint Caching and Power Control (JCPC) scheme, leveraging Deep Deterministic Policy Gradient (DDPG) to optimize caching decisions and power allocation under system-level AoI and power constraints. Simulations validate that JCPC outperforms baseline strategies, significantly reducing AoI violation probability and improving the efficiency of MEC-enabled IIoT networks.

Reconfigurable intelligent surfaces (RISs) hold great potential for addressing the challenges in terahertz (THz) communication. However, a single RIS cannot sufficiently overcome the high path loss of THz frequencies. This paper proposes a beam routing scheme for multi-RIS-assisted sixth-generation (6G) networks, employing a dynamic programming algorithm to optimize the propagation environment through multiple RISs for efficient multi-hop communication. A closed-form expression for ergodic capacity is derived. Simulation results demonstrate significant enhancements in throughput and reliability, highlighting the advantages of this approach over traditional methods and supporting the deployment of THz networks for future wireless applications.

This study explores a hybrid framework that merges terahertz (THz) and free space optics (FSO) technologies in a backhaul network. The combined FSO and THz systems leverage reconfigurable intelligent surfaces (RIS) and employ maximal ratio combining (MRC) at the receiver. Specifically, the closedform expressions for cumulative distribution function (CDF) of channel and signal-to-noise ratio (SNR) for RIS-assisted FSO and THz channels are derived by assuming the impediments such as atmospheric turbulence, fading, pointing errors, and pathloss. Using these statistics, outage probability, average symbol error rate (SER), and outage capacity are computed for the proposed RIS-assisted hybrid FSO/THz system. Numerical results compare the proposed hybrid FSO/THz system against various wireless systems, including RIS-assisted FSO, RIS-assisted THz, and hybrid FSO/THz systems without RIS.

This article investigates the Peak Age of Information (PAoI) violation probability of status update strategies in cache-enabled Industrial Internet of Things (IIoT) networks. Specifically, a PAoI characterization framework for PAoI violation probability analysis in cache-enabled IIoT networks is presented for status updates with and without a zero wait (ZW) policy. Furthermore, multicast-aware (MA) and hierarchical-aware (HA) status update strategies are also proposed for cache-enabled IIoT networks. Using newly derived PAoI cumulative distribution functions (CDFs) and a status update transmission delay probability density function (PDF), closed-form PAoI violation probability expressions are obtained for the MA and HA status update strategies. Extensive analysis shows that the ZW policy for status updates in cache-enabled IIoT networks can experience high PAoI violation probability when high transmission delay is encountered during the delivery of acknowledgement messages. Furthermore, the PAoI violation probability of the proposed MA and HA status update strategies are dependent upon the status update transmission delays, PAoI violation threshold, wireless link timeout threshold, and the popularity of wireless sensors (WSs). We show that the proposed MA and HA status update strategies exhibit lower PAoI violation probability over other benchmark strategies. Importantly, the proposed MA status update strategy with and without the ZW policy attains the lowest PAoI violation probability even in scenarios where status updates are requested from a large pool of WSs. Therefore, the analysis shows both the proposed MA and HA status update strategies as promising solutions toward the monitoring and control of mission-critical IIoT applications.

An important role played by industrial Internet of Things (IIoTs) networks is supporting the operations of autonomous mobile robots (AMRs) by leveraging multiple-access edge caching servers. At the same time, judicious content caching strategies are essential for minimizing content retrieval delays and the costs associated with updating caches. In this study, a novel multiagent reinforcement learning (MARL)-based cache update strategy termed multiagent cache update (MACU) is proposed. MACU leverages the multiagent deep deterministic policy gradient (MADDPG) framework and aims to optimize cache updates to reduce Age of Information (AoI), minimize events where AoI exceeds acceptable levels, and ensure that the costs associated with performing cache updates are kept low. Furthermore, to mitigate the computational complexity of training agents with MACU, the MACU with global critic (MACU-GC) variant is introduced, which diverges from traditional MADDPG by employing a singular global critic for enhanced training efficiency. Extensive numerical evaluations showcase the proposed strategies’ superiority over conventional deep reinforcement learning-based caching methods, achieving significant improvements in AoI costs, caching costs, and AoI violation costs, while effectively reducing content retrieval latency, enhancing hit rates, and optimizing AoI and link load metrics.

In this paper, the problem of energy-efficient uncrewed aerial vehicle (UAV)-assisted multi-access task offloading is investigated. In the studied system, several UAVs are deployed as edge servers to cooperatively aid task executions for several energy-limited computation-scarce terrestrial user equipments (UEs). An expected energy efficiency maximization problem is then formulated to jointly optimize UAV trajectories, UE local central processing unit (CPU) clock speeds, UAV-UE associations, time slot slicing, and UE offloading powers. This optimization is subject to practical constraints, including UAV mobility, local computing capabilities, mixed-integer UAV-UE pairing indicators, time slot division, UE transmit power, UAV computational capacities, and information causality. To tackle the multi-dimensional optimization problem under consideration, the duo-staggered perturbed actor-critic with modular networks (DSPAC-MN) solution in a multi-agent deep reinforcement learning (MADRL) setup, is proposed and tailored, after mapping the original problem into a stochastic (Markov) game. Time complexity and communication overhead are analyzed, while convergence performance is discussed. Compared to representative benchmarks, e.g., multi-agent deep deterministic policy gradient (MADDPG) and multi-agent twin-delayed DDPG (MATD3), the proposed DSPAC-MN is validated to be able to achieve the optimal performance of average energy efficiency, while ensuring 100% safe flights.

Channel estimation (CE) is a critical challenge in harnessing the potential of Terahertz (THz) ultra-massive multiple-input multiple-output (UM-MIMO) systems. Sparsity-exploiting compressed sensing (CS)-aided CE (CSCE) can enhance THz UM-MIMO CE performance with affordable pilot overhead. However, the near-field propagation region becomes significant in THz UM-MIMO networks due to the large array aperture and high carrier frequency, leading to a more profound coexistence of near- and far-field radiation patterns. This hybrid-field propagation characteristic renders existing CSCE frameworks ineffective due to the lack of an appropriate sparsifying matrix. In this work, we investigate the uplink THz UM-MIMO CE problem, by developing a practical THz UM-MIMO channel model that incorporates near- and far-field paths, molecular absorption, and reflection attenuation. We propose a dictionary learning (DL)-aided Bayesian THz CSCE solution to achieve accurate, robust and pilot-efficient CE, even in ill-posed scenarios. Specifically, we tailor a batch-delayed online DL (BD-ODL) algorithm to generate an appropriate dictionary for the hybrid-field THz UM-MIMO channel model. Furthermore, we propose a Bayesian learning (BL)-enabled CSCE framework to leverage THz sparsity and utilize the learnt dictionary. To establish a lower bound for the mean squared error (MSE), we derive the Bayesian Cramér-Rao bound (BCRB). We also conduct a complexity analysis to quantify the required computational resources. Numerical results show a significant improvement in normalized MSE (NMSE) performance compared to conventional CE and CSCE baselines, and demonstrate rapid convergence.

In this paper, the problem of energy-efficient unmanned aerial vehicle (UAV)-assisted computation offloading over the Terahertz (THz) spectrum is investigated. In the studied system, several UAVs are deployed as edge servers to aid task executions for multiple energy-limited computation-scarce terrestrial user equipments (UEs). Then, an expected energy efficiency maximization problem is formulated, aiming to jointly optimize UAVs’ trajectories, UEs’ local central processing unit (CPU) clock speeds, UAV-UE associations, time slot slicing, and UEs’ offloading powers. To tackle the considered multi-dimensional optimization problem, the duo-staggered perturbed actor-critic with modular networks (DSPAC-MN) solution in a multi-agent deep reinforcement learning (MADRL) setup, is proposed and tailored, after mapping the original problem into a stochastic (Markov) game. Compared to representative benchmarks in simulations, e.g., multi-agent deep deterministic policy gradient (MADDPG) and multi-agent twin-delayed DDPG (MATD3), the proposed DSPAC-MN can achieve the optimal performance of average energy efficiency, while ensuring 100% safe flights.

In the context of the Industrial Internet of Things (IIoT), multiple access edge computing (MEC) enables the provision of computational resources closer to users. The work presented in this paper explores a common IIoT application scenario wherein autonomous mobile robots (AMR) operate in a MEC-enabled network and depend on multimedia content stored at the MEC servers over the course of operation. The age of information (AoI) metric is used to measure the freshness of the cached content from the perspective of the AMR. At the same time, the energy cost associated with refreshing the cache files is simultaneously considered as well. This paper delves into achieving an optimal trade-off between minimizing the weighted AoI cost and the energy expended for cache refreshing. We address this problem by introducing a cache refreshing-deep deterministic policy gradient (CR-DDPG) algorithm, a model-free deep reinforcement learning method, to optimize both AoI and energy usage. Various simulation studies are conducted to evaluate the proposed CR-DDPG algorithm, and the results demonstrate that CR-DDPG consistently outperforms its baseline counterparts, rendering it a robust approach for cache-refreshing in dynamic IIoT environments.

Intelligent reflecting surface (IRS) technology is a promising solution for addressing the limitations of terahertz (THz) systems, including blockage effects and tremendous path loss. This paper investigates a novel IRS-assisted hybrid framework that seamlessly combines both THz and radio frequency (RF) technologies using a selection combining (SC) scheme, thereby enhancing system reliability. The study incorporates the deterministic and statistical properties of IRS in both RF and THz domains employing a sophisticated spatial scattering chan-nel model across generalized α - µ fading channels. Specifically, the exact closed-form expressions for the probability density function (PDF) and cumulative distribution function (CDF) of the output signal-to-noise ratio (SNR) are derived for both THz and RF links. From this, the outage probability and average symbol error rate (SER) are derived. Furthermore, asymptotic expressions are evaluated for outage and average SER, offering insights into diversity gain of the system. Simulation results reveal a significant enhancement in system performance and power savings for the proposed IRS-aided hybrid THz/RF system. These findings provide valuable insights into the practical implementation of IRS-assisted hybrid networks, contributing to the ongoing efforts for future wireless networks.

The mean peak age of information (PAoI) of computation offloading in multi-access edge computing (MEC) enabled industrial Internet-of-Things (IIoT) networks is investigated in this paper. Specifically, the mean PAoI and average energy consumption of energy-aware computation offloading (ECO) and cloud-only (CL) computation offloading are derived in closed-form. Numerical and simulation results show that the mean PAoI and average energy consumption of the ECO and CL strategies are dependent on the task generation rate and local computation capability experienced in the MEC-enabled IIoT networks. Specifically, the ECO strategy is shown to achieve lower mean PAoI even at high task generation rates in the MEC-enabled IIoT network. Furthermore, we show that the ECO strategy achieves lower average energy consumption than the CL strategy even when local computing capability in the MEC-enabled IIoT network is limited.

Intelligent reflecting surfaces (IRS) have emerged as a promising technology for addressing the inherent challenges associated with terahertz (THz) bands, thereby enhancing system performance and offering immense potential for future wireless systems. However, existing single and multi-IRS-aided wireless systems often overlook crucial IRS-related factors such as IRS unit-cell dimensions, IRS gain, and inter-IRS collaboration, potentially limiting system performance. To mitigate these limitations and to leverage the unique advantages of THz band, this study investigates a multi-IRS-empowered THz system, that incorporates design parameters such as, the transceiver antenna gains, operation frequency, link distances, molecular absorption losses, beam misalignment, transceiver hardware imperfections, and statistical characteristics of the THz channel. By utilizing a sophisticated channel model that integrates the joint effects of these parameters with IRS properties and inter-IRS collaboration, this study demonstrates a significant enhancement in system performance and power savings. Moreover, exact closed-form expression and asymptotic approximation for outage probability are derived to quantify the effects of the deterministic and statistical channel parameters. These findings provide valuable insights into the practical implementation of multi-IRS-assisted THz networks, contributing to the ongoing efforts to unlock the potential of THz band for future wireless applications.

This paper proposes an amplify-and-forward (AF)-based multihop THz backhaul communication integrated with an access THz link. The access link is assisted with an intel-ligent reflecting surfaces (IRS) with an aim to deal with the impediments in THz communication environment. The statistical analysis is presented by deriving the probability density function (PDF) and cumulative distribution function (CDF) of the in-stantaneous signal-to-noise ratio (SNR) for the proposed system. The combined effect of path loss, atmospheric attenuation, and generalized fading is considered for modelling the THz channel. Furthermore, with the aid of PDF and CDF statistics, we propose the exact expressions for outage probability and develop asymptotic analysis in high SNR regime. The simulations are presented to validate the exact analysis and to study various design aspects for the proposed system.

To minimize environmental impairments and channel fading in the THz band, this paper examines a multiple antenna-based THz communication system. The combined effects of path loss, molecular absorption, and statistical fading are considered for the THz system. A comprehensive correlation structure is utilized that uniquely determines the joint probability density function of the THz channel model. The considered correlation structure is a generalization of the correlation models based on hyper-power or power-correlation. The statistical characterizations of channel correlation for the combining schemes such as maximal ratio combining (MRC), selection combining (SC), and equal gain combining (EGC) are presented at the THz receiver. The asymptotic expressions are proposed for the outage probability for the mentioned diversity schemes. The obtained expressions are expressed in closed-form and are highly accurate in the high signal-to-noise ratio (SNR) region. From the analysis, diversity order and degradation due to correlation are determined. The obtained asymptotic expressions enable the easy estimation of the performance especially for more number of antennas, where Monte Carlo simulation takes a long time to execute. Additionally, presented results reveal the factors that can be utilized to optimize the system performance.

Terahertz (THz) wireless communication has emerged as a front-line technology for substantially improving the data rates for 6G networks. However, they suffer from tremendous path-attenuation that limits the communication distance. Intelligent reflecting surface (IRS) is an excellent cost-effective technology for enabling THz wireless systems. This article presents comprehensive analysis of an IRS-empowered THz system, incorporating a detailed channel model encompassing deterministic IRS channel gain, THz molecular absorption losses, and the characteristics of sum of double$\alpha -\mu $fading. The analysis considers IRS-specific parameters, such as unit-cell dimensions, gain, radiation pattern, and array factor, for accurate received signal power characterization. For statistical analysis, the probability density function, cumulative distribution function, and moments are characterized using programmable multivariate Fox’s H-functions. Using these derived statistical results, the exact closed-form solutions for outage probability, average bit error rate, and ergodic capacity are reported. Additionally, asymptotic approximations are presented for deeper insights. Finally, to validate the accuracy of analytical results, extensive Monte-Carlo simulations are conducted. Multiple results investigate various design aspects of the proposed system. The findings demonstrate that significant performance gains and power savings thereby making THz communication feasible and highly promising for future wireless networks.

This paper investigates a hybrid framework that combines free space optics (FSO) and terahertz (THz) technologies for a backhaul network. In this hybrid configuration, the FSO and THz systems are empowered by reconfigurable intelligent surface (RIS) and are combined at the receiver using either maximal ratio combining (MRC) or selection combining (SC). The performance of the RIS-assisted hybrid FSO/THz system is evaluated under multiple impairments for FSO and THz links. The exact closed-form expressions for probability density function (PDF), cumulative distribution function (CDF), and moment-generating function (MGF) of the output signal-to-noise ratio (SNR) of both RIS-assisted FSO and THz links are derived. Leveraging these SNR statistics, we compute the outage probability and the average symbol error rate (SER) of the proposed hybrid FSO/THz system with MRC and SC schemes. Additionally, this paper conducts an asymptotic analysis at high SNR levels, yielding asymptotic expressions for outage and average SER, which not only reduce computational complexity but also provide insights into the system’s diversity gain. In the numerical results, the performance of the proposed hybrid FSO/THz system is compared against other state-of-the-art wireless systems, including direct link FSO without RIS, RIS-aided FSO, and the hybrid FSO/THz systems without RIS using diversity combining techniques.

This paper investigates the energy efficiency of computation offloading strategies in multi-access edge computing-enabled (MEC-enabled) Internet-of-Vehicles (IoV) networks. First, the energy efficiency of computation offloading strategies in the MEC-enabled IoV network are derived in closed-form. Thereafter, a multi-agent deep reinforcement learning based (MADRL-based) energy efficiency maximization algorithm is proposed to enable computation offloading strategies to attain maximum energy efficiency in the MEC-enabled IoV network. It is shown through extensive analysis that the maximum attained energy efficiency hinges on the choice of task size and transmission timeout threshold, with a computation offloading strategy that jointly considers transmission and computation latencies outperforming existing strategies. It is also shown that the proposed MADRL-based energy efficiency maximization algorithm achieves near-optimal energy efficiency in the MEC-enabled IoV network, making it a promising solution towards achieving energy efficient MEC-enabled IoV networks.

Intelligent reflecting surfaces (IRS), a new paradigm for controlling the wireless propagation environment, is an excellent cost-effective technology for terahertz (THz) systems. In this paper, the performance of an IRS-assisted THz system, with N reflective elements, is systematically analyzed over the deterministic IRS channel gain, the THz path loss model, and the sum of independent and non-identically distributed (i.ni.d.) cascaded α−µ fading channels. The probability density function (PDF) and the cumulative distribution function (CDF) of the proposed system are statistically characterized in terms of programmable multi-variate Fox’s H function. Using derived statistical results, the closed-form solution for outage probability of THz-IRS system is reported along with its simple asymptotic expansions. The analytical results are validated using Monte-Carlo simulations. Results show that, sufficient signal-to-noise ratio (SNR) can be achieved with enough number of IRS antenna elements, making THz communication feasible.

The average energy efficiency of computation offloading in multi-access edge computing (MEC) enabled Internet-of-Vehicles (IoV) networks with wired backhaul links is investigated in this paper. Specifically, the cumulative distribution function (CDF) for computation delay over wired backhaul link is derived in closed-form. The average energy efficiency of computation offloading in MEC-enabled IoV networks with wired backhaul links is derived in closed-form, and is compared against non MEC-enabled IoV networks with wired backhaul links. Numerical and simulation results show that MEC-enabled IoV networks can attain at least 10 times higher energy efficiency than non MEC-enabled IoV networks. Furthermore, we show that energy efficiency can be maximized through the proper selection of task size and transmission deadline in the MEC-enabled IoV network.

In this work, we propose SVDNet, a novel deep learning (DL) architecture that utilizes singular value decomposition (SVD), for transmit power control in a multiuser multiple input multiple output (MU-MIMO) system. We propose a novel method of training SVDNet in a supervised manner for the power control task by using binary cross-entropy loss functions. SVDNet requires fewer computations than traditional power control algorithms such as weighted minimum mean squared error (WMMSE). Our simulation results show that the proposed SVDNet provides over a 50% increase in sum-rate performance as compared to similar supervised DL-based power control schemes while being significantly more computationally efficient than WMMSE.

To serve advanced use-cases in industrial internet of things (IIoT) setups, communication and computation over wireless networks have faced overlapping resource management challenges. Two crucial resources in this context are radio re-sources and computational resources. The problem to achieve the ultra-low latency for mission critical applications is motivating enterprises to invest in offloading capability of computation heavy tasks while retaining the bandwidth efficiency of edge nodes. This work proposes a novel multi-hop offloading framework powered by deep reinforcement learning to aid the edge nodes in making intelligent decisions on task offloading. The proposed method is benchmarked against existing state of the art techniques to measure task completion delay and algorithmic runtime.

Terahertz (THz) band offers large accessible bandwidth and spatially confined highly directed beams for the realization of secure and high data rate communication. In this work, the secrecy performance is investigated for a directional THz link, which suffers from high propagation loss and attenuation due to molecular absorption. The statistical characterization of the THz link is also considered for analyzing the system over precise channel model. A threat model is developed for the scenario where the main intended user and the eavesdropper (eve) are located in line-of-sight (LOS) with respect to the source. The performance analysis is carried out by deriving the probability of strictly positive secrecy capacity (SPSC) and the lower bounds of secrecy outage probability (SOP). The proposed theoretical expressions are validated using extensive Monte-Carlo simulations. The results demonstrate that limiting the broadcast range and tuning the frequency are powerful yet simple transmission protocols that can achieve the physical layer security in the THz bands.

A performance analysis of base station (BS) association strategies is conducted in this paper for an industrial fifth generation (5G) network comprising a mobile actuator operating in the presence of interference. Specifically, outage probability expressions are derived with a stochastic geometry framework for the random association (RA), strongest association (SA), closest association (CA), and closest with strongest association (CSA) strategies. An analysis reveals that the SA strategy exhibits the lowest outage probability at the expense of significantly higher overheads. In contrast, the CSA strategy has significantly less overheads and exhibited outage probability that is higher than the SA strategy but lower than the CA and RA strategies. Thus, the SA strategy is suitable for industrial use cases with very low outage probability requirements and high overhead tolerance while the CSA strategy can be adopted for industrial use cases with low overhead and higher outage probability requirements. It is also noted that the CSA strategy can be further improved by introducing more BS tiers.

In this paper, non-orthogonal multiple access (NOMA) is investigated as a potential solution to address spectrum scarcity in unmanned aerial vehicle (UAV) communications. In particular, the ergodic capacity of uplink (UL) NOMA is characterized within a stochastic geometry framework for a multi-UAV network comprising a ground station (GS) and multiple UAVs. Our analysis reveals that UL NOMA enables fairness, in terms of ergodic capacity, to be achieved in the multi-UAV network. When compared against conventional UL orthogonal multiple access (OMA), we show that the ergodic capacity and ergodic sum capacity is higher for the proposed UL NOMA transmissions. Thus, the proposed scheme enables higher throughput to be achieved in multi-UAV networks while simultaneously improving spectrum efficiency.

The present paper investigates the performance of a space shift keying (SSK)-based multiple-input single-output (MISO) hybrid free space optical (FSO)/radio frequency (RF) system. The proposed hybrid system considers an optical space shift keying (OSSK)-based FSO sub-system as a default transmission option with Nx1 apertures. The millimeter wave (MMW) RF link with M-ary pulse amplitude modulation (MPAM) signaling is utilized when FSO sub-system is in outage. A unified performance analysis is addressed and novel expressions for average bit error rate (BER) are obtained. Significant performance improvement is observed for the proposed system compared to the individual OSSK-based FSO sub-system. The theoretical analysis is verified by Monte-Carlo simulations.

In this paper, a decode-and-forward (DF)-relaying-based hybrid free space optical (FSO)/radio frequency (RF) system is proposed. The hybrid system incorporates DF-relayingbased FSO and RF sub-systems, where FSO sub-system transmits with higher priority and RF sub-system is used in case of FSO link failure. The exact and asymptotic expressions for outage probability and average symbol error rate (SER) are derived and diversity order is determined. To minimize the effect of pointing errors, the optimum transmit beam width and radius of receiver aperture are calculated. The obtained theoretical results are verified with the Monte-carlo simulations. The results show that the proposed system improves the performance compared to that of individual FSO and RF systems.

Free space optics (FSO) communication has garnered significant importance to provide gigabit capacity links owing to its unique features. However, its performance is limited by the adverse effects of transmission medium such as atmospheric turbulence induced fading, wind, etc. Therefore, it is wise to backup with reliable radio frequency (RF) links to improve the performance of FSO communication. The fusion of FSO and RF technologies is a suitable candidate for future satellite communication (SATCOM) systems. In this context, the present paper proposes a novel system model for High-Altitude Pseudo-Satellite (HAPS)-based relaying for downlink scenario utilizing both FSO and RF links. The performance of the proposed hybrid FSO/RF SATCOM system is investigated through average and asymptotic symbol error probability (SEP) analyses. Further, the obtained closed-form expressions for average SEP are validated using Monte-Carlo simulation results.

The impact of cellular interference on uplink unmanned aerial vehicle (UAV) communications is analyzed in this paper for a multi-UAV network. Specifically, the outage probability and finite signal-to-noise ratio (SNR) diversity gain of the multi-UAV network is characterized in the presence of interference from uplink UAVs and cellular base stations. We demonstrate that the operational altitude of the multi-UAV network determines the severity of cellular interference across low-to-high transmit power regimes. In particular, UAVs operating at higher altitudes are less affected by cellular interference, with higher finite SNR diversity gains and lower outage probability floors observed. Thus, interference mitigation techniques may have to be considered when multi-UAV networks are operating at low altitudes in areas with cellular networks.

In this paper, we demonstrate the necessity of robust cellular interference cancellation when co-locating uplink (UL) unmanned aerial vehicle (UAV) communications with cellular networks. Through a stochastic geometry based evaluation framework, we show through bit error rate (BER) and ergodic capacity analysis that multi-user interference (MUI) is the main limiting factor in UL UAV communications after cellular interference cancellation. It is also observed that high altitudes and weak residual cellular interference corresponds to lower BER. In contrast, low altitudes and weak residual cellular interference results in higher ergodic capacity. Hence, advanced interference cancellation techniques should be considered to suppress the presence of strong MUI in the multi-UAV network.

Spectrum sensing is an efficient way to determine the spectrum availabilities over the frequency range of interest, aiding in improving the spectrum utilization in the cognitive radio (CR) systems. Conventional Nyquist multiband sensing entails higher computational capability for sampling, quantization, and subsequent processing, lending the approach infeasible for applications with limited power budgets. In this brief, a power-efficient spectrum-sensing technique is proposed, which explores an accuracy-complexity tradeoff. The presented spectrum-sensing architecture is based on 1-bit quantization at the CR receiver and implements it in hardware by a resource- and power-efficient approach, using a finite-impulse-response (FIR) filter-bank channelizer. The proposed scheme allows the complex operators like multipliers and quantizers to be replaced by the inverter logic and high-speed comparators, reducing the hardware complexity and power consumption. We validate the proposed scheme on a field-programmable gate-array (FPGA) emulator for an aeronautical L-band digital aeronautical communication system (LDACS) application, and our results show that the proposed scheme achieves substantial resource reduction with at most 5% degradation in the detection accuracy in this case.

In this paper, we propose a switching scheme for a decode-and-forward (DF)-relaying-based hybrid free-space op-tics/radio frequency (FSO/RF) system. We consider two scenarios, a dual-hop (DH) scenario without direct link and a DH scenario with direct link using selection combining (SC) at the destination. The system switches between FSO and RF sub-systems based on the received SNR at the destination, where the FSO sub-system is given higher priority. The probability density function (PDF) of the FSO channel is in the form of Meijer G function and the derivation of the analytical expressions for a DH scenario involve multiple such Meijer G functions which are too complex to comprehend. Therefore, simpler asymptotic outage probability and the average symbol error rate (SER) expressions are derived for the FSO sub-system. The exact closed form expressions have been derived for the RF sub-system. The diversity order is determined using the asymptotic expressions.

Multiple spot beam and full frequency reuse based dual satellite systems are investigated in this work. Both satellites in the proposed DSS use precoding to mitigate intra satellite (inter spot beam) interference among its users. The inter satellite interference is mitigated through joint decoding at the receivers. To be specific, receivers in each spot beam utilize the structure of the strongest inter satellite interfering signal and treat the other inter satellite interfering signals as additive white Gaussian noise. The minimum sum-power needed to achieve a target data rate is evaluated using rank-relaxed semidefinite programming technique. The proposed technique is shown to achieve higher throughput than traditional interference ignorant decoder based protocol. The proposed protocol is also benchmarked against centralized precoding technique, where both satellites together act as a virtual single satellite and eliminate inter satellite and intra satellite interference through precoding. If the users associated with both satellites are co-located, then the proposed protocol is shown to outperform centralized precoding.

Continuous growth of air-traffic demands new technologies for future aeronautical communication systems. L-band Digital Aeronautical Communications System (LDACS) is considered as a potential candidate for the future air-to-ground links. Spectrum utilization efficiency of LDACS can be improved by enabling dynamic spectrum access (DSA) in the system. In this context, the present paper proposes a novel cyclostationary feature detection scheme based on the periodicity of the autocorrelation of LDACS signals for spectrum sensing, which is key requirement in DSA. A wideband spectrum sensing simulation model is developed to evaluate the detection performance of the proposed scheme. To improve the adaptability of the spectrum sensing unit to variable wide bandwidth, the proposed system uses interpolation and masking based filters that can extract individual LDACS channels from the wide-band signals. Results of simulation studies show that the proposed scheme provides better detection accuracy against the conventional cyclostationary feature detection scheme and energy detection scheme, while maintaining the false alarm rates to an acceptable level which balances the overall throughput of the system.

Cognitive dual satellite system, where primary and secondary satellites transmit data on multiple spot beams on the same sub-channel is investigated. To be specific, overlay mode of operation is proposed in which the secondary satellite acts as a relay for the primary satellite while simultaneously transmitting its data. Non-orthogonal multiple access (NOMA) precoding along with multi-resolution broadcasting is proposed for the secondary satellite. The NOMA precoder exploits the correlated channels and it can be used to transmit the data of both satellites for the users in each spot beam. The achievable data rates at both primary and secondary satellites are characterized. The overlay mode based cognitive dual satellite system is shown to achieve better sum-rate than the interweave mode based cognitive dual satellite system.

Unmanned aerial vehicles (UAVs) are set to feature heavily in upcoming fifth generation (5G) networks. Yet, the adoption of multi-UAV networks means that spectrum scarcity in UAV communications is an issue in need of urgent solutions. Towards this end, downlink non-orthogonal multiple access (NOMA) is investigated in this paper for multi-UAV networks to improve spectrum utilization. Using the bivariate Rician shadowed fading model, closed-form expressions for the joint probability density function (PDF), marginal cumulative distribution functions (CDFs), and outage probability expressions are derived. Under a stochastic geometry framework for downlink NOMA at the UAVs, an outage probability analysis of the multi-UAV network is conducted, where it is shown that downlink NOMA attains lower outage probability than orthogonal multiple access (OMA). Furthermore, it is shown that NOMA is less susceptible to shadowing than OMA.

As unmanned aerial vehicles (UAVs) are expected to play a significant role in fifth generation (5G) networks, addressing spectrum scarcity in UAV communications remains a pressing issue. In this regard, the feasibility of full-duplex non-orthogonal multiple access (FD-NOMA) UAV communications to improve spectrum utilization is investigated in this paper. Specifically, closed-form outage probability expressions are presented for FD-NOMA, half-duplex non-orthogonal multiple access (HD-NOMA), and half-duplex orthogonal multiple access (HD-OMA) schemes over Rician shadowed fading channels. Extensive analysis revealed that the bottleneck of performance in FD-NOMA is at the downlink UAVs. Also, FD-NOMA exhibits lower outage probability at the ground station (GS) and downlink UAVs than HD-NOMA and HD-OMA under low transmit power regimes. At high transmit power regimes, FD-NOMA is limited by residual SI and inter-UAV interference at the downlink UAVs and FD-GS, respectively. The impact of shadowing is also shown to affect the reliability of FD-NOMA and HD-OMA at the downlink UAVs.

Blind reconstruction of channel coding parameters plays a significant role in non‐cooperative military and spectrum surveillance applications. Further, it also gives additional advantages in applications such as cognitive radio, adaptive modulation and coding, and so on. In this study, blind estimation algorithms are proposed to identify code dimension and codeword length parameters of low‐density parity‐check (LDPC) codes at the receiver over noisy or erroneous channel conditions assuming a non‐cooperative scenario. The proposed algorithms are validated using different test cases. Moreover, the accuracy of estimation of code dimension and codeword length parameters of LDPC codes using the proposed algorithms is also given for different M ‐ary phase‐shift keying schemes. From the simulation results, it is observed that the accuracy of estimation improves with decrease in code rate, codeword length, and modulation order.

A hybrid-duplex aeronautical communication system (HBD-ACS) consisting of a full-duplex-enabled ground station (GS) and two half-duplex (HD) air stations (ASs) is proposed as a direct solution to the spectrum crunch faced by the aviation industry. The closed-form outage probability and finite signal-to-noise ratio (SNR) diversity gain expressions in aeronautical communications over Rician fading channels are derived for a successive interference cancellation (SIC) detector. Similar expressions are also presented for an interference ignorant (II) detector and the HD-equivalent modes at GS and ASs. Through the outage and finite SNR diversity gain analysis conducted at the nodes, and system level, residual self-interference (SI) and inter-AS interference are found to be the primary limiting factors in the proposed HBD-ACS. Further investigations revealed that the II and SIC detectors in the proposed HBD-ACS are suitable for the weak and strong interference scenarios, respectively. When compared with the HD-ACS, the proposed HBD-ACS achieves a lower outage probability and higher diversity gains at higher multiplexing gains when operating at low SNRs. The finite SNR analysis also showed the possibility of the proposed HBD-ACS being able to attain interference-free diversity gains through proper management of the residual SI. Hence, the proposed HBD-ACS is more reliable and can provide a better throughput compared with the existing HD-ACS at low-to-moderate SNRs.

In this paper, we propose a switching scheme for a multiple-input-single-output (MISO) hybrid free-space op-tics/radio frequency (FSO/RF) system to switch the transmission between MISO FSO and RF sub-systems. We consider transmit aperture/antenna selection (TAS) scheme for selecting the best antenna/aperture among multiple transmit antennas/apertures. The proposed FSO sub-system transmits through its selected best link as long as the instantaneous signal-to-noise ratio (SNR) at the FSO receiver is greater than the threshold SNR. The system switches to the best link of the RF sub-system when the SNR falls below the threshold value. The outage probability and average symbol error rate (SER) of the proposed hybrid system is extensively analyzed and the results are validated using Monte-Carlo simulations. Asymptotic expressions are derived to obtain the diversity order of the proposed system. Finally, the performance of the MISO hybrid FSO/RF system is compared with the performance of a MISO FSO system to calculate the performance gain obtained using the proposed switching scheme.

Blind estimation of code and interleaver parameters plays a vital role in various applications such as non-cooperative systems, adaptive modulation and coding, signal intelligence, etc. The present paper proposes novel algorithms to jointly estimate code and interleaver parameters from Reed-Solomon (RS) coded and convolutionally interleaved data stream based on the rank ratio and non-zero-mean-ratio values for noiseless and noisy environments, respectively. Simulation results validating the proposed algorithms are given for various test cases and the accuracy of estimation of convolutional interleaver and RS code parameters is investigated for different values of interleaver width and modulation schemes. It is inferred that the accuracy of parameter estimation improves with decrease in modulation order and interleaver width of convolutional interleaver.

With the growing popularity of unmanned aerial vehicles (UAVs), spectrum management is a pressing issue, particularly for multi-UAV systems. To this end, a hybrid-duplex (HBD) UAV communication system (UCS) consisting of a full-duplex (FD) enabled ground station (GS), and legacy half-duplex (HD) UAVs is proposed in this paper. To model the fading and shadowing environment commonly encountered in UAV communications, a mix of Rician and Rician shadowed fading is assumed. In particular, novel power series approximations of the Rician shadowed fading power probability density function (PDF), and cumulative distribution function (CDF) are presented, along with closed-form outage probability expressions. Performance analysis shows that the proposed HBD-UCS exhibits lower outage probability than the HD-UCS when shadowing is encountered at low signal-to-noise ratios (SNRs). Also, inter-UAV interference has a stronger influence on outage probability decay at low SNR regimes, with lower inter-UAV interference corresponding to a sharper decline in outage probability.

Air traffic growth is expected to rise sharply in the near future, causing a swell in data communication demands on the congested aeronautical spectrum which cannot be met with existing aeronautical communication systems. To this end, a hybrid-duplex (HBD) aeronautical communications system consisting of a full-duplex (FD) enabled ground station, and legacy half-duplex (HD) air- stations is proposed as a direct solution to boost spectral efficiency. In particular, the system level outage probabilities and transmission power requirements of the proposed HBD and HD aeronautical communication systems are analyzed. Performance analysis shows that the proposed HBD system can attain better outage performance in the en route scenario. The proposed HBD system is also able to support an equivalent data rate as an HD system with lower transmit power and signal-to- interference-plus-noise-ratio (SINR) requirements and longer transmission range when inter-aircraft interference and residual self-interference is kept sufficiently low.

In this paper, we propose an adaptive filter based architecture for blind residual self-interference (SI) cancellation in a full-duplex (FD) multiple-input-multiple-output (MIMO) transceiver. Correspondingly, we present and compare the performances of three different SI cancellation algorithms employing adaptive filters based on the least mean squares (LMS), normalized LMS (NLMS) and recursive least squares (RLS) techniques. Simulation results obtained for a base-station in an FD MIMO multiple access/broadcast channel system show that the proposed RLS based SI cancellation algorithm offers the best performance in terms of convergence rate, bit-error-rate (BER) and signal-to-interference-plus-noise ratio (SINR). We also compare the usage of parallel adaptive filters at each receiver chain of an FD MIMO transceiver versus the usage of a single two-dimensional adaptive filter. It is observed that the usage of parallel adaptive filters offers relatively faster convergence, but at the cost of slightly inferior BER and SINR performance.

In this paper, we propose a novel switching scheme for hybrid free-space optical (FSO)/radio frequency (RF) system. The outage probability and average bit error rate (BER) expressions are derived for the proposed hybrid system considering decode-and-forward (DF) relaying dual-hop (DH) scenario with and without a direct link. For the scenario with direct link, selection combining (SC) scheme is assumed at the destination. Specifically, the system transmits over FSO channel as long as the instantaneous signal-to-noise ratio (SNR) at the FSO receiver is greater than the threshold SNR. If it falls below the threshold, then the system switches its transmission over millimeter wave (mmW) RF channel. Moreover, Gamma-Gamma and Nakagami-m distributions are used to characterize FSO and mmW RF links, respectively. The exact theoretical expressions are derived in closed-form and validated by Monte-carlo simulations for the proposed system. Finally, to confirm the efficiency of the proposed switching scheme, the performance of the hybrid FSO/RF system is compared with the performance of the FSO system.

Rise in wireless data traffics requires innovative interference management techniques to meet the demand. Transmit cooperation among multiple base stations has been proposed as a solution to this challenge and improve throughput. For base stations equipped with massive MIMO arrays, a proposed subspace encoding technique can decouple the joint multicell resource allocation problems into independent problems for each cell. The subspace encoding in the multicell environment is analytically equivalent to a reduction of degrees of freedom in a single cell broadcast channel. Hence, the resulting computational and conceptual simplicity can be exploited to arrive at the optimal resource allocation for maximum throughput.

Interference forwarding by a relay enhances the interference level and enables the cancellation of the interference. If the interfering source to relay link is not strong, then the relay can decode a part of the interference and forward it to the destination, and the destination can cancel only that part of the interference. It is known as partial decode-and-forward (PDF) and partial interference cancellation, respectively. In this work, even if the relay is clustered with the source, i.e., even if the interfering source to relay link is good, then the PDF protocol is shown to perform better than the complete decode-and-forward (CDF) protocol. To this end, closed-form expressions for the achievable diversity-multiplexing trade-off (DMT) with clustered full-duplex PDF relay and partial interference cancellation is derived. The benefits of the proposed protocol are demonstrated through numerical analysis. The impact of the multiplexing gain and interference level of the interfering signal on the DMT at the interference-limited receiver is also illustrated.

Blind reconstruction of code parameters plays a vital role in non-cooperative applications. It also provides additional advantages in applications such as adaptive modulation and coding, reconfigurable receivers, etc. In this paper, blind estimation algorithm is proposed to identify Reed-Solomon (RS) code parameters at the receiver over noisy channels. Simulation results validating the proposed algorithm are given for various test cases. Further, the accuracy of estimation of RS code parameters using the proposed algorithm is also evaluated for various M-ary quadrature amplitude modulation schemes. From the simulation results, it is observed that the accuracy of estimation improves with a decrease in code dimension and modulation order and the proposed algorithm outperforms other algorithms in the prior works.

To improve the error performance of digital storage and communication systems, forward error correcting (FEC) codes and interleaver play a significant role by counteracting random and burst errors, respectively. In most of the applications, accurate information about the type of FEC codes, coding and interleaving parameters are known at the receiver in order to successfully decode and de-interleave the message bits, respectively. However, in certain applications such as spectrum surveillance, adaptive modulation and coding (AMC)-based communication systems, cognitive radio, etc., all the coding and interleaving parameters need not be known at the receiver and blind/semiblind recognition of the same is mandatory. Therefore, in this paper, innovative algorithms for automatic recognition of type of FEC codes along with the parameter estimation of helical scan interleaver are proposed considering both erroneous and non-erroneous scenarios without any prior knowledge about the encoding scheme used in the transmitter. Note that the proposed algorithms will classify among block coded, convolutional coded, and uncoded data streams.

Traditional cellular systems have depended on coverage areas partitioned into disjoint cells where each user is served by a single base station, without any cooperation. To deal with the resulting inter-cell interference, this work combines the advantages of CoMP along with detection and broadcasting techniques with different channel output suitable for massive MIMO. Two novel interference management techniques, viz. Centralised Interference Cancellation (CIC) and Distributed Interference Cancellation (DIC) to optimise power allocation in a cooperative framework have been proposed. The schemes point out the trade off between achievable performance and computational complexity. Since large number of antennas require mathematical manipulation of big random matrices, a suboptimal two layer decoding method is proposed which combines selection diversity with least mean square filtering.

A two-user Z-channel with a full-duplex (FD) decode-and-forward (DF) relay, where one user is interference-limited while the other user is interference-free, is considered in this paper. The FD-DF relay can decode either a part of the interference or the entire interference. The former is called partial DF (PDF) protocol, and the latter is called complete DF (CDF) protocol. In the case of PDF protocol, the interference-limited user does partial interference cancellation. A closed-form expression for achievable diversity gain region (DGR) with the PDF protocol is presented. Furthermore, achievable DGR of the PDF protocol is optimized under the constraint that the interference-free receiver achieves optimal diversity gain. At low interference levels, the PDF protocol provides better DGR compared to both CDF protocol and direct transmission scheme. As the interference level increases, either the CDF protocol or the direct transmission scheme is shown to achieve better DGR compared to PDF protocol. The multiplexing gain regions where the PDF, CDF, and direct transmission schemes perform well are identified.

Interference forwarding in a Z-channel makes interference stronger, which in turn enables usage of simple detectors like successive interference canceler (SIC) at interference-limited destination. In this work, the following protocols with SIC at the interference-limited destination are investigated: direct transmission (SICDirect), half-duplex decode-and-forward (SICDF), and half-duplex amplify-and-forward (SICAF) protocols. The achievable diversity orders of these protocols using M-PAM and M-QAM modulation are obtained. Moreover, minimum required exponential orders of the average received signal powers at the relay and interference-limited destination to restore full diversity are presented. The SICAFand SICDFprotocols are shown to achieve the same diversity order as that of the orthogonal transmission scheme while achieving better spectral efficiency than the orthogonal transmission. Closed-form expressions for the achievable diversity gain regions (DGRs) with the SICDirect, SICDF, and SICAFprotocols are derived. Selective decode-and-forward with SIC (SICSDF) is also considered. The multiplexing gain regions and the interference levels where the SICAFand SICSDFprotocols achieve better DGR than the SICDirectprotocol are obtained.

The next-generation heterogeneous networks are expected to offer higher data-rate and better QoS to the customers by leveraging smaller cells like femtocells and making use of orthogonal frequency division multiple access (OFDMA). However, uncoordinated dense deployment of femtocells in a macrocell network pose unique challenges involving cross-tier interference and resource management which may lead to significant performance degradation in the system. As part of addressing these challenges, this paper proposes a Cross- Polarized Complementary Frequency Allocation (CPCFA) strategy which exploits frequency and polarization diversity to mitigate interference in two-tier femto-macro networks. This strategy combines the benefits of reverse frequency allocation (RFA) and orthogonal polarized transmission which is analyzed as a potential solution for maximizing spectral efficiency and minimizing interference in heterogeneous networks. The results of analytic and simulation studies prove that CPCFA increases the scope for an easily implementable, remarkable opportunity in the context of two-tier femto-macro network that can substantially increase the system capacity, area of interference-free femtocell exclusive region as well as the coverage probability without additional network complexities.

In the present work, the diversity multiplexing tradeoff (DMT) for a decode-and-forward relay assisted two-user Z-channel with Nakagami-m fading is studied. In a two-user Z-channel, only one user is interference-limited while the other user is interference-free. Two transmission schemes, namely, common message only (CMO) and rate splitting (RS) schemes, are studied. In the CMO scheme, the interfering source uses single-user (SU) codes, and the interference-limited destination cancels the total interference. In the RS scheme, the interfering source uses multi-user (MU) codes, and the interference-limited user does partial interference cancellation. Closed-form expressions for the achievable DMTs with both the schemes are presented. The RS and the CMO schemes are shown to provide better DMT at the moderate and higher levels of interference, respectively.

The present paper focuses on the interference management in a two-user Z-channel where one user is interference-limited while the other user is interference-free. The achievable diversity gain region (DGR) with interference forwarding by a full-duplex decode-and-forward (FD-DF) relay and successive interference cancellation (SIC) at the interference-limited destination is studied. The achievable DGR of the FD-DF relay is compared with that of the direct transmission scheme. The impact of the phase-noise in the self-interference cancellation circuit of the full-duplex relay and the impact of the number of blocks in the superposition block Markov (SPBM) encoding on the achievable DGR are studied. The direct transmission scheme with joint decoding at the interference-limited receiver is shown to perform well at the lower multiplexing gain region (MGR). If the multiplexing gain of the interference is high, then the interference forwarding by the DF relay does not help, and the direct transmission scheme with interference ignorant detection at the interference-limited receiver achieves better DGR. The FD-DF relay is shown to provide better DGR at only the moderate MGR.

Multihop cooperative communication is emerging as a key concept to extend the coverage area of the network and potentially increase the capacity. The spectral efficiency of such networks can be improved by adapting the transmission to time-varying channel conditions, referred to as incremental relaying. Although such incremental relaying concepts are progressively being studied, many challenges, such as erroneous transmissions by intermediate nodes and end-to-end delay of the network, limit its practical use due to lack of an efficient implementation. This paper proposes an efficient multihop incremental relaying technique. In this method, erroneous relay forwarding is mitigated, and the overhead for coordination among nodes is reduced by exploiting the implicit feedback channel available due to the broadcast nature of wireless transmissions. The proposed scheme fully leverages the benefit of overhearing and eliminates the additional feedback slots required for validation. Further, it ensures reliable forwarding of information, which optimizes the throughput of multihop networks. Thorough analysis of the proposed scheme is performed under different deployment environments, and the theoretical analyses presented in this paper are supported with results from extensive simulation studies.

Rateless code properties ideally suit multi-node transmissions and have been extensively employed in multihop delay tolerant networks (DTNs). However conventional multihop networks, where the transmission proceeds from one-hop to the next, may lead to starvation of some nodes with good channel conditions. In such instances, the overall latency can be alleviated by cooperation among the forwarding nodes. This paper analytically quantifies the latency of both conventional and cooperative rateless coded delay tolerant multihop networks by deriving the exact closed form equations for the channel usage. These are verified and supported with results from extensive simulation studies.

Duality relations among achievable QoS parameters help us transform the problems in the broadcast channel to convex problems in multiple access channels. But a multiple access channel being considered as dual of a broadcast channel must exploit the additional freedom of power allocation traditionally considered only in a broadcast channel. This work proposes a novel algorithm for optimising the sum-capacity of a multiple access channel under sum power constraint where the users are coupled by individual power usage as well as interference. Optimal resource allocation has a certain distributed feature which can be exploited to formulate the algorithm. Power allocation problem for an arbitrary number of users is solved by dealing with only two users at a time. The algorithm gives insights about how the decoding priority affects achievable rates of different users which have been used for further characterisation of a rate region boundary. Simulation results have been presented in the end to support the theoretical arguments.

Wireless small cell networks and device-to-device (D2D) communications are seen as two major features of next-generation wireless networks. In this paper, a novel approach for enabling D2D communication underlaid on a wireless small cell network is proposed. Unlike existing works which focus on network performance analysis given a chosen communication mode, in this paper, the strategic selection of a desired wireless communication mode between pairs of users is studied. On the one hand, communication using the small cells can provide reliable transmission but is limited by interference and backhaul constraints. On the other hand, D2D communication can provide high capacity due to devices' proximity but is limited by increased interference. To capture these properties, the problem is modeled as a noncooperative game in which pairs of communicating users can strategically decide on whether to communicate with one another via the small cell infrastructure or via direct D2D communication. In this proposed game, each device selects its preferred communication mode while optimizing a utility function that captures the various involved tradeoffs between communication performance and associated costs. For solving this game, a distributed best response-based approach is proposed using which the users can reach a Nash equilibrium. Simulation results show that the resulting network at the equilibrium is composed of a mixture of D2D and small cell communication links. The results also show that the proposed approach yields a significant improvement in terms of the average utility per communicating pair when compared with the cases in which the users communicate via only the small cells or via only D2D.

This study addresses the problem of spectrum trading in a cognitive radio network with multiple primary users (PUs) competing to sell spectrum to a secondary user (SU). The spectrum trading process is modelled using a ‘Cournot game model’ of competition by which the PUs set the size of spectrum to sell. In this study, the spectrum requirements for the PUs’ services are not fixed but time varying, and the spectrum trading process is carried out before the realisation of these values. If the spectrum retained for a PU after selling is less than the spectrum requirement for the PU's service, a cost must be charged to the PU. The Nash equilibrium (NE) for a static game when the PUs have complete knowledge on the utility functions of other PUs is studied first. A dynamic game, in which the players adaptively change their strategies to reach the NE, is discussed subsequently. Finally, the trading problem is extended to a scenario which involves multiple SUs.

ABSTRACT The invention of cognitive radio (CR) concept aims to overcome the spectral scarcity issues of emerging radio systems by exploiting under‐utilization of licensed spectrum. Determining how to allocate unused frequency bands among CR is one of the most important problems in CR networks. Because different CRs may have different quality‐of‐service requirements, they may have different objectives. In voice communication, high‐speed transmission is the most important factor; hence, voice radios always try to maximize their transmission rate. However, in data communication, the most important factor is the bit error rate. The data radios always try to maximize their signal‐to‐interference‐plus‐noise ratio (SINR). In this paper, two non‐cooperative games named interference minimization game and capacity maximization game, which reflect the target of data radios and voice radios, respectively, are proposed. From the simulations, after these games are applied, the average SINRs of all players at each channel are improved. The average SINR of players in each channel after applying the capacity maximization game is smaller than that after applying the interference minimization game. However, in comparison with that after applying the interference minimization game, the average capacity of players after applying capacity maximization approach is larger. Copyright © 2012 John Wiley & Sons, Ltd.

Multihop cooperative communication is emerging as a key concept to extend the coverage area and potentially increase the capacity of wireless networks. With multiple hops, processing at the forwarding nodes is a major source of error propagation. In this context, a novel spectrally efficient transmission scheme with error protection for such networks is proposed in this paper. The proposed scheme retains the spatial diversity and enhances the bandwidth efficiency by integrating incremental redundancy concepts into such cooperative multihop systems. The guard against error propagation and the overhead for coordination among multiple nodes in such networks is mitigated by the implicit feedback channel available due to broadcast nature of wireless transmissions. The proposed scheme fully leverages the benefit of overhearing and eliminates the additional feedback slots required for validation. Further, it ensures reliable forwarding of information which optimizes the throughput of multihop networks. Theoretical framework is also developed for the proposed system and supported with results from extensive simulation studies.

Interference issues arising from spectrum reuse in femto-macro networks can result in significant performance degradation in the system. As part of addressing these challenges, this paper proposes cross-polarized data transmission as a potential solution for permitting interference free spectrum reuse in cellular systems. Different from prior art techniques, the paper evaluates a scenario where femtocell network makes use of right hand circular polarization (RHCP) and macrocell network makes use of left hand circular polarization (LHCP) for data transmission so as to aid co-channel allocation. The polarizations being orthogonal to each other due to their sense of rotation ensure isolation between the networks and hence enable both of them to efficiently reuse the same spectral resources simultaneously in the same location. Analytical and simulation results prove that this technology opens the scope for an easily implementable, remarkable opportunity in the context of two-tier femto-macro network that will increase system capacity, spectral efficiency and the probability of successful transmission.

Rateless codes have been found to be particularly attractive for decode and forward based relaying strategy in delay tolerant multihop networks. The latency performance of such networks is dependent on the worst links that results in the starvation of subsequent nodes with good channel conditions. The total delay suffered by such networks can be constrained by limiting the number of rateless coded transmissions, especially for applications with critical latency requirements. However, the performance of rateless codes deteriorates in such circumstances due to the lack of sufficient mutual information for successfully recovering the entire source packets. The fraction of source packets that can be recovered will depend on the encoded packets received across the transmission channel. This paper investigates the degradation in the performance of such rateless coded networks by deriving the average packet recovery rate. In order to improve the reliability in such delay constrained networks, a novel spectrally efficient transmission scheme for reliable multihop data transfer is proposed. The proposed scheme exploits the broadcast nature of wireless transmissions, which provides an inherent implicit feedback channel, to ensure the reliable delivery of information packets to the nodes in the network. Rather than allocating dedicated channels to feedback the packet recovery information, the implicit feedback channel determines such information which enhances the spectral efficiency. Further, the optimum number of packets recoverable within the specified delay constraint to reduce the reprocessing of lost packets across hops is analytically analysed in this paper.

Existing localization approaches developed using acoustic vector sensor (AVS) signals normally assume that the sources are static and the number of sources is known. In this paper, a novel approach is developed to estimate the 2-D direction of arrival (DOA) of an unknown and time-varying number of acoustic sources using a single AVS. A random finite set (RFS) is employed to characterize the randomness of the state process, i.e., the dynamics of source motion and the number of active sources. Also the measurement processes are modeled by RFS since we allow the AVS report undesired events by sending an empty set other than received signals under regular cases. We further employ particle filtering to approximate the posterior DOA distributions. The performance of the proposed approach is demonstrated by simulated experiments.

Cooperation among nodes is proposed as an effective means of combating fading and for enhancing system's overall capacity and coverage. The robustness of rateless codes makes them particularly attractive for such networks. Yet, the decoding aspects of rateless codes are discarded in most of the traditional distributed networks. In this paper, the intermediate packet decodability of rateless codes is exploited to reduce the number of packets being processed at the relay nodes. This is achieved by harnessing the back channel (from destination to relays) for feedback. The relay transmissions and processing are thereby confined to assist the receiver in decoding the remaining information. It is shown both analytically and through simulation studies that such a scheme achieves significant savings in computation complexity, memory usage and overall energy consumption.

Interference forwarding in an interference channel makes the interference stronger which in turn enables the usage of simple detectors like the successive interference canceler (SIC) at the destinations. In this paper, detect and forward (DF), amplify and forward (AF) based interference forwarding protocols (also called as AF-SIC and DF-SIC protocols) are analyzed. Symbol error rate (SER) performance of the SIC, AF-SIC and DF-SIC protocols using M-PAM modulation is studied. Also the relay channel gains required to restore full diversity for the AF-SIC and the DF-SIC protocols are obtained. Impact of the relay power and relay location on the SER performance is also studied. The proposed protocols are proved to provide the same SER performance as the orthogonal transmission scheme while improving the spectral efficiency.

Femtocell, also known as home base station is one of the promising cost-effective technologies that ensure a steady increase in system capacity, improvement in service quality and a better data rate for users mainly in the indoor environment. However massive rollout of femtocells cause severe interference to the existing macrocell network and drive users into outage. Moreover, though femtocells can provide improved home coverage and capacity for indoor users, many a times, these femtocells are under-utilised when they do not serve any voice or data request. In this paper a novel idea to extend the coverage of femtocells beyond the home environment through multiple hops is proposed. The idea is to exploit the under-utilised femtocells to serve the high data rate requests of many outdoor user equipments and reduce the probability of their outage. This will not only extend the coverage of femtocell and relax the burden on the macrocell base station, but also helps in reducing the interference to the co-existing macrocell network, because of reduced transmission power and path loss, achieved through relaying.

The general problem addressed in this paper is tracking the 2-D direction of arrival (DOA) of an acoustic source signal by using a single acoustic vector sensor (AVS). A Bayesian framework and its particle filtering implementation are introduced to adapt to the underwater ambient noise environment, in which both the interference and background noise exist. Several innovations are explored here: 1) a particle filtering based acoustic source tracking algorithm for AVS is developed; and 2) by using a multi-modality likelihood model to model the source detection and false alarm separately, the algorithm is able to alleviate the effect due to noise and interference. Particularly, by employing additional acoustic information, the proposed approach is able to track the 2-D DOA by using a single AVS. The performance of proposed approach is fully investigated under different simulated ambient noisy environments. Experiment results show that the proposed algorithm outperforms the traditional Capon beamforming approach and is able to lock on the 2-D DOA of the source even in a very challenging environment.

Femtocell, also known as home base station is one of the promising technologies that ensure a steady increase in system capacity, improvement in service quality and a better data rate for users mainly in the indoor environment. Even though femtocells can provide improved home coverage and capacity for indoor users, many a times, these femtocells are under-utilized when they do not serve any voice or data request. In this paper a novel idea to extend the coverage of femtocells beyond the home environment through multihops is proposed. The idea is to exploit the under-utilized femtocells to serve the high data rate requests of many outdoor UEs. This will not only extend the coverage of femtocell but also relax the burden on the macro cell base station, improve the cell capacity and ensure power efficiency.

When a message is forwarded through a network, a node will have multiple opportunities to reliably receive the message and cooperate in transmission. However, the transmit power of each node in a network is limited and so is the transmission range. Therefore, multihop transmission is a potential technique to deliver the data over large distances. Rateless code properties ideally suit decode and forward based relaying strategies as it improves the outage and bandwidth efficiency. In decode and forward based multihop networks, the messages are decoded and relayed over sequential point-to-point communication links. In a conventional multihop network, the intermediate nodes will have to wait indefinitely to correctly decode the information. To quantify the impact of this unknown waiting time, this paper analyses the performance of a multihop network with strict delay constraints. The average packet loss for such a network is obtained as a function of the total delay. By optimizing the total delay based on the performance across each links, the average packet loss can be minimized.

Cooperation among nodes in a network provides spatial diversity as well as it enhances the system's overall capacity and coverage. However the benefits provided by such systems depends on the level of cooperation (based on the relay information quality) and on the coordination among nodes. One way of achieving proper coordination is through the use of feedback channels. An implicit feedback channel available during relaying has been determined to minimize the feedback among cooperating nodes. In addition, it improves the reliability of information decoding at the destination by mitigating erroneous relay transmissions. The present paper studies the outage analysis of a cooperative transmission scheme assisted by the implicit feedback channel. The analysis is performed in a delay constrained network employing rateless codes. Further, a performance improvement of the order of 2.5 dB is observed for such networks.

A novel number theoretic transform called Inverse Gray Robust Symmetrical Number System (IGRSNS) is proposed for error control coding in this paper. IGRSNS is obtained by modifying Robust Symmetrical Number System (RSNS) that was proposed earlier, using Inverse Gray code property. Due to ambiguities present in each residue, RSNS has a short dynamic range (DR) compared to that in other number systems. The short DR of RSNS enables it to be effectively used for error detection without the addition of any redundant modulus as in Redundant Residue Number System. Although RSNS has a large redundant range, its detection ability is not optimal due to the Gray code property associated with it. In an attempt to overcome this limitation, we have proposed Inverse Gray coding to be combined with RSNS in increasing its effectiveness in error detection. The resulting IGRSNS thus inherits properties of both RSNS and Gray code. Analysis and simulations show that IGRSNS has a near-optimal error detection ability. The potential of IGRSNS for error correction is also investigated. Further, a novel error correction algorithm using one redundant modulus is proposed. Simulations show that the proposed algorithm performs well under all cases of single bit errors.

In this paper, a preprocessing architecture for folding Analog-to-Digital converter (ADC) based on a new number system called Robust Folding Number System (RFNS) is presented. The RFNS is developed from robust symmetrical number system (RSNS) that was proposed by Pace et al. The enhanced Dynamic Range (DR) of RFNS due to the introduction of the folding bit results in higher ADC resolution. The Symmetrical Residues (SRs) that are obtained in the intermediate step during processing of analog signals are converted to equivalent residues by simple mapping. This results in a conversion architecture that is less complex compared to that proposed in.

In wireless networks, designing transmission schemes adapting to time varying channel conditions is key to achieve better spectral efficiency. The design of such schemes for multi-hop wireless networks requires coordination among nodes in the network, which is achieved through feedback between nodes. Spectral efficiency can be improved for such networks by designing transmission schemes with limited feedback. Incremental code relaying (ICR) with implicit feedback proposed previously is one that mitigates the use of feedback link. In this paper, location-aware ICR with power allocation is proposed that dynamically makes the routing decisions based on the link that offers the maximum capacity. Theoretical upper bounds for bit-error rate (BER) is derived and is verified by the simulation results, yielding further insight to the proposed scheme.

Selective decode and forward (SDF) based cooperative relaying protocol can provide full diversity. But SDF protocol requires bandwidth consuming cyclic redundancy check (CRC) bits to prevent error propagation from the relay. Link adaptive regenerative relaying (LAR) scheme avoids the need for CRC bits to reduce the error propagation from relay and can provide full diversity. But in the conventional LAR based schemes, relay will always participate in the cooperation irrespective of the quality of the source to destination link. This results in a spectral efficiency of 0.5 symbols per channel use (SPCU) only. To improve the transmission rate, the present paper proposes selective link adaptive regenerative relaying (SLAR) scheme, where the relay will make use of the source to destination channel information to decide whether to cooperate or not. It is proved that the proposed scheme can achieve the full diversity order. The spectral efficiency and power efficiency of the protocol are considerably improved compared to the conventional LAR scheme.

In this paper, an incremental redundancy based cooperative coding scheme for wireless networks is proposed. User cooperation is an effective way of mitigating fading where one user cooperates with another user in transmitting its information, thereby providing spatial diversity. Wireless transmissions are broadcast by nature and this provides a new dimension to the system in terms of an implicit feedback channel from the relay to the source. To exploit the implicit feedback channel a novel incremental redundancy based transmission scheme called incremental code relaying with implicit feedback (ICRIF) is proposed. This scheme enhances the reliability of information transmitted by the relay and thereby improving the throughput at the destination. By employing a powerful code such as low-density parity-check (LDPC) code, the benefit of the proposed scheme is clearly established. The simplified error probability for correct reception of the proposed scheme is derived with respect to direct transmissions and transmissions assisted by the relay.

The paper analyzes power spectral density (PSD) of orthogonal pulse-based signals for time hopping ultra wideband (TH-UWB) systems. Our extensive studies show that the PSD of these signals not only depends on the time dithering code and the modulation schemes, but also on the energy spectral density (ESD) of orthogonal pulses. The different order orthogonal pulses provide different ESD which changes the shape of continuous spectral component with symbols. We show that orthogonal pulse-based signals reduce the dynamic range of amplitude of discrete spectral components. Further, we reduce the dynamic range by adopting longer TH code over orthogonal pulse-based signals. As a result, UWB system performance improves with average transmitted power. The theoretical analysis of PSD of orthogonal pulse-based TH-UWB signal is provided in details and verified through simulation results.

The cognitive radio allows spectrum sharing between licensed users (primary users) and many unlicensed users (secondary users). The secondary users are only allowed to use a licensed spectrum in the absence of its rightful owner. Thus, the ability to accurately sense the presence of the rightful owners is highly essential. In this paper, a novel cooperative spectrum sensing (CSS) approach to efficiently sense a wideband spectrum is introduced. This paper addresses two specific issues in CSS. The first issue is on dynamic detection of primary user's bands. A dynamic band clustering (DBC) algorithm that uses K-means clustering technique is proposed in this paper. The proposed algorithm reduces the number of erroneous narrow sub-bands resulting from spurious noise. This in turn minimizes the number of sub-bands to be detected and hence the overall sensing time. The second issue is on combining the local decisions made by different secondary users. A novel dynamic weighting decision fusion algorithm is also proposed in this paper. Based on extensive simulation studies, the proposed fusion algorithm is shown to be superior to conventional decision fusion techniques.

Layered space-time block spread CDMA (LST BSCDMA) has been previously proposed as an alternative to conventional CDMA systems for high-rate mobile communications. This paper proposes two approaches to obtain channel state information (CSI) for LST BS-CDMA system. The basic approach suffers from high computational complexity and poor performance in systems with high order of transmitter diversity due to inter-layer interference (ILI). The second approach reduces computation complexity and eliminates ILI, making it suitable for systems with higher order of transmitter diversity. The detailed simulation studies show that the highly accurate CSI obtained using the improved technique leads to considerable superior performance.

In this paper, two distributed transmission schemes, namely Distributed Transmitter Maximal Ratio Combining (D-TxMRC) and Distributed Space Time Block Coding (D-STBC) are analysed. The array and diversity gain inherent to the underlying Multiple Input Multiple Output (MIMO) technique are studied, both under independent and correlated fading scenario. It is shown that D-TxMRC is capable of achieving high array gain at the expense of complexity, while only limited array gain is attained using D-STBC scheme. As far as diversity gain is concerned, both schemes achieve full diversity in the order of total number of cooperating nodes under independent fading. The overall performance of the schemes under random network scenario is analysed using average outage probability as a performance metric. The averaging encompasses channel variation as well as network dependent parameters. Effects of different network parameters towards system performance are also analysed. Finally, the performance of cooperative schemes in a more practical network with regular node placements are also studied.

In this paper, a new architecture to compute 1-D Discrete Wavelet Transform (DWT) based on Folding Number System (FNS) is introduced. Numbers for FNS are extracted directly from analog input without any forward converter like in the Residue Number System (RNS) based DWT. The large Dynamic Range makes the FNS DWT more efficient than those implemented using RNS systems. The proposed 1D DWT architecture makes use of the relation between the coefficients of the low-pass and high-pass decomposition filters for orthogonal wavelets families to compute the transform with minimum numbers of modular multipliers. These multipliers are based on pipelined Look-Up Tables (LUT). A 6-tap Daubechies analysis filter bank is synthesized at a structural level using VHDL. FLEX10K devices of Altera are used in the simulation of DWT using binary arithmetic, RNS and FNS to evaluate its performance. Simulations show a significant throughput improvement is achieved in the proposed FNS DWT architecture when {2k- 1.2k,2k+ 1} moduli set is used.

In this paper, a low complexity antenna selection scheme for multi-antenna broadcast systems is developed. Using sum-rate capacity maximisation as the selection criteria, the proposed scheme exploits the duality principle of broadcast and multiple access channel in order to reduce the computational complexity. The performance of the proposed scheme under i.i.d. Rayleigh fading channel is then evaluated via Monte Carlo simulation under different system parameters, and its performance is compared to the full complexity brute force scheme. It is demonstrated that the scheme is able to achieve most of the gain available in the system with a considerably lower complexity.

In an ideal Software Radio, digitization of the received signal occurs immediately after receive antenna to enable channelization to be performed in the discrete time domain. However, this vision is still far from reality due to limitations of current analog to digital converter performance. In this paper, a novel number system called the Folding Number System (FNS) is proposed for use in Software Radio. We implement sample rate conversion immediately after the receive antenna using this number system thus providing an efficient solution to the above problem. By decomposing the input analog signal into separate channels in parallel, symmetrical residues are obtained with reduced number of comparators. These residues together with the folding information are processed in parallel in the FNS domain. The FNS has the same computational complexity as that in Residue Number System but the need for the intermediate steps such conversion of the analog data into binary and subsequently into residues is absent.

In this paper, the application of rate-compatible punctured convolutional (RCPC) code into coded cooperation relay system is studied. As opposed to conventional coded cooperation systems, RCPC is attractive for its better spectral efficiency. In addition, the broadcast nature of relay transmission provides a new dimension to the system in the form of implicit feedback channel from relay to source. This allows the source node to justify the quality of information bits at relay node and react accordingly by taking over relay's role to transmit the additional parity. At the destination, selection code combining is then performed, which provides a diversity benefit to the underlying RCPC code. The performance of the proposed scheme in terms of the number of correctly decoded bits (goodput), bit error probability, and the required number of slots for message transmission are then analysed. Extension to the case where there are multiple relays to assist the transmission is also discussed.

In this paper, antenna selection algorithm for multiuser downlink systems where each terminal is equipped with multiple antennas is proposed. As opposed to point to point systems, the broadcast nature of the transmission complicates the selection process as the selection criteria must take into consideration performances of all users collectively. Moreover, computational complexity required needs to be kept as low as possible for practical reason. Exploiting duality between broadcast and multiple access channel, the proposed scheme provides a heuristic approach to selection process in order to maximise the sum-rate capacity of the system, and it is shown that a close to optimal performance can be attained at a considerably lower complexity.

A block-spreading code division multiple access (BS-CDMA) system is proposed for broadband uplink transmission, giving rise to a significantly improved multiuser performance without using complex multiuser detection techniques. This is because the code orthogonality is easily maintained when channel variation across the consecutive blocks, in a block-by-block high-speed transmission, is negligible. The proposed system uses frequency domain equalisation at the receiver to combat multipath interference efficiently over frequency selective fading channels. We propose despreading before equalisation, which reduces the frequency domain process to symbol-wise operation. A cell-specific scrambling code is employed to suppress other-cell interference for uplink transmission in a multicell system. Our analytical and simulation studies show that the proposed BS-CDMA system has superior multiuser performance over the conventional direct sequence CDMA and cyclic prefix CDMA systems for uplink transmission.

This paper presents a novel robust number theoretic transform called inverse gray robust symmetrical number system (IGRSNS) and proposes its application for CDMA systems. The transceiver structure for three moduli IGRSNS-CDMA with one redundant modulus is proposed. The proposed system is simulated for different values of moduli sets under various channel conditions. Simulation results show that the BER performance of IGRSNS-CDMA outperforms that of RNS-CDMA under all circumstances.

This paper analyses the effect of relay node and the importance of power allocation scheme in cooperative relay networks. It is shown that adding relay node alone is not sufficient to improve system performance. Under a simplest scenario where relay node adopts decode and forward relaying, direct transmission may perform better under certain cases with equal total power constraints. Furthermore, in practical scenario when source node has to transmit its message to relay node before cooperatively transmitting it to destination, the existence of relay node may even degrade system performance. By adopting the right relaying technique and proper power allocation scheme, it is shown that cooperative relay transmission can be made strictly better than direct transmission.

The paper describes information theoretic capacity of orthogonal pulse based modulation schemes for time hopping ultra wideband (TH-UWB) systems over a multiple access and multipath fading channel. Orthogonal pulse based modulation schemes such as pulse shape modulation (PSM), biorthogonal PSM (BPSM) and a combination of orthogonal pulse position modulation (OPPM) and BPSM have been proposed for reducing inter symbol interference (ISI) and multiple access interference (MAI) as well as for improving system performance. System capacity of TH-UWB systems can be increased by employing these modulations for higher level modulation schemes. The capacity of OPPM-BPSM outperforms PSM and BPSM schemes over a multipath fading channel. The complete mathematical analysis and theoretical simulation results are provided in detail.

A CDMA scheme employing block processing (BS-CDMA) had been proposed earlier as an effective multiple access scheme that is robust against multiuser interference (MUI) during uplink transmission where conventional CDMA schemes fail due to orthogonality destruction. However, residual MUI arises in BS-CDMA and its degradation impact becomes severe when high mobility users are present. Two interference cancellation techniques are proposed in this paper that utilizes the users' mobility condition to determine the detection ordering sequence. Based on extensive simulation studies, results show that the proposed techniques perform well in the presence of high number of users with high mobility.

This paper studies two MIMO architectures for single-carrier CDMA system employing block spreading, namely Layered Space-Time Block Spread CDMA (LST BS-CDMA) and Space-Time Coded Block Spread CDMA (STC BS-CDMA). It is shown that under low mobility conditions, the proposed systems are virtually free from Multiple User Interference (MUI) and the block processing technique used leads to considerable reduction in the overall processing complexity. Extensive simulation was performed to study the impact of the spreading factor and Doppler frequency on the proposed systems. A new parameter called channel coherence ratio (CCR) is introduced as a key parameter in determining the performance of MIMO BS-CDMA.

This paper proposes a novel method for constructing ultra wide band (UWB) pulses based on a linear combination of Gaussian pulses. These pulses while meeting FCC power spectral density (PSD) mask requirements insure negligible interference with narrow band (NB) systems using flexible interference avoidance property they possess. Improved performance is achieved when errors due to imperfect synchronization exist between the transmitter and receiver (timing jitter). The coefficients of pulses designed can be generated using simple delay elements and amplifiers. The performance of these pulses in multipath channel such as channel model 1 (CM1) with timing jitter is evaluated by simulation and is found to be better than that of other designs.

This paper describes a combined modulation scheme for time hopping ultra wideband (TH-UWB) radio systems based on biphase shift keying (BPSK), orthogonal pulse position modulation (OPPM) and pulse shape modulation (BPSM). A set of M = 2ksymbols are constructed by using L = 22lorthogonal pulse positions and N = 22k-l-1biorthogonal pulses, where k and l are nonnegative integers such that 0 ≤ l ≤ k - 1. The selection of number of pulse positions and pulses depend on the system performance and the availability of orthogonal pulses with estimable auto-correlation properties. The proposed scheme achieves higher data rate by introducing more number of orthogonal pulses in the same pulse repetition interval. It also reduces the system complexity by half by introducing antipodal version of orthogonal pulses. The proposed transmission scheme is analyzed through computer simulations in the presence of multipath channel.

This paper describes a combined modulation scheme for time hopping ultra wideband (TH-UWB) radio systems using on-off keying (OOK) and pulse shape modulation (PSM). For this scheme, a set of orthogonal pulses is used to represent bits in a symbol. These orthogonal pulses are transmitted simultaneously in the same time slot resulting in a composite pulse. By assigning different subset of orthogonal pulses for each user, multi-user interference can be reduced considerably. The proposed transmission scheme can achieve higher data rate by using fewer pulses and can use fewer number of receiver correlators than those used in PSM. Due to the presence of OOK, the proposed scheme requires minimum energy and is applicable for energy constrained UWB systems. The bit-error-rate (BER) performance of the proposed transmission scheme is analyzed both mathematically and through computer simulations in additive white Gaussian noise (AWGN) channel and modified IEEE 802.15.3a S-V UWB multipath channel model. The present paper also compares the proposed scheme with existing PSM and its combined modulation schemes.

This paper evaluates the performance of distributed space time coding in generic ad-hoc network scenario. The condition where multiple nodes (confined within a certain geographical area) wanting to exchange information to one another is considered. Effect of different system parameters such as total number of nodes, path loss exponent, node density, and error threshold, toward overall system performance are analysed.

The present paper proposes a new relaying scheme called successive dirty paper coding. Theoretical achievable rate of the scheme is derived and its performance is compared to other existing relaying schemes in terms of their outage probability. It is shown via numerical studies and supported by simulation analysis that the proposed scheme is able to achieve higher bandwidth efficiency by reusing relay slots to transmit new messages. An improvement of up to M-fold, where M is the average number of relay stages in every transmission, compared to traditional non-cooperative relaying is observed.

Peak to average power ratio (PAPR) is one of the key parameters for efficient power amplification in multicarrier systems. Practical implementation difficulties and the performance constraints are two major limiting factors for many of the methods suggested for PAPR reduction. It is in this context, this paper suggests a simplified approach for PAPR reduction of multicarrier CDMA systems based on efficient coding of optimal binary phase sequences. Using this method, the side information related to phase values for PAPR reduction are spread using dedicated spread code and add with other user data before transmitting through channel. The overheads required for the proposed method is very minimal and the system performance is robust against channel estimation errors.

This paper presents sub optimal method to perform antenna selection in MIMO-OFDM systems. This method allows reduction in the complexity by exploiting inter-subcarrier correlation or through disjoint selection of transmit and receive antennas. Their performances and complexities are then analysed and contrasted with respect to conventional brute force method.

This paper describes a combined modulation scheme for time hopping ultra wideband (TH-UWB) radio systems based on orthogonal pulse position modulation (OPPM) and bi-orthogonal pulse shape modulation (BPSM). A set of M=2ksymbols are constructed by using L = 2lorthogonal pulse positions and N = 2k-l-1biorthogonal pulses, where k > 1 and l are nonnegative integers such that 0 les l les k-1. The selection of the number of pulse positions and pulses depends on the system performance and the availability of orthogonal pulses with estimable auto-correlation properties. This scheme allows an increase in the number of bits per symbol and consequently, reduces the duration of the pulse repetition interval which is obtain by increasing the number of orthogonal pulses. The proposed scheme achieves higher data rate by using a large number of orthogonal pulses in the same pulse repetition interval. It also reduces the system complexity by half by introducing antipodal version of orthogonal pulses. The proposed transmission scheme is analyzed through computer simulations in a multipath channel using two sets of orthogonal pulses.

Space-time coded block spread CDMA (STC BS-CDMA) was previously proposed to enhance the advantages offered by CDMA system with block processing. However, STC BS-CDMA suffers from long decoding delay and large single block transmission time which makes it unsuitable for communication systems delivering delay-critical applications and poor performance in systems with high mobility conditions. This paper proposes space-frequency coded BS-CDMA (SFC BS-CDMA) which performs space-frequency coding instead of space-time encoding. This reduces the decoding delay significantly and transmission time of a single block, making it an attractive alternative in delay-critical communication systems. This paper also compares the two MIMO BS-CDMA systems and provides extensive simulation results.

A joint transmit and receive antenna selection technique for MIMO-OFDM is presented. By appropriately ordering and tabulating the minimum channel sub-matrix's sub-stream signal to noise ratio in all subcarriers, an optimal antenna subset can be obtained. This procedure can be simplified further by analysing the inter-subcarrier correlation and by exploiting group selection methods. Complexity analyses on the proposed algorithm are presented, and performance improvements achievable are demonstrated through simulation studies.

In this paper, a novel receive antenna subset selection technique is proposed for multiple input multiple output spatial multiplexing (MIMO-SM) systems with linear minimum mean square error (MMSE) receivers in the presence of unknown co-channel interference. This antenna selection technique is directly implemented based on training sample sequence by utilizing backward greedy algorithm (BGA) under the least squares (LS) criterion. In the case of practical implementation. Diagonal loading (DL) technique is incorporated into the selection process to insure robustness of antenna selection given limited training sample support. Simulation results show that the proposed antenna selection technique is able to retain the diversity order of a full complexity system in the presence of unknown multiple access interference (MAI)

In this paper, tap selection based Minimum Mean Square Error (MMSE) equalization technique is discussed for Ultra Wideband (UWB) systems in the presence of Inter Symbol Interference (ISI) and Multiple Access Interference (MAI). A novel tap selection technique based on Matching Pursuit (MP) algorithm is proposed. Given finite training sample support, Diagonal Loading (DL) technique is incorporated into MP algorithm to insure the robustness of tap selection. Moreover, a fast heuristic MP based tap selection technique is developed to facilitate the tradeoff between equalization performance and computational complexity. Simulation results show that the proposed tap selection based equalizer outperforms the RAKE receiver and the conventional MMSE equalizer significantly given the same amount of training symbols.

In this paper, a novel receive antenna selection technique is proposed for Multiple Input Multiple Output (MIMO) spatial multiplexing systems with linear receivers in the presence of unknown interference. This antenna selection technique is directly implemented based on training sample sequence under the Least Squares (LS) criterion. Simulation results show that the proposed antenna selection technique is able to retain the diversity benefit of full complexity system in the presence of unknown Multiple Access Interference (MAI), without the need for explicit channel estimation. In addition, practical implementation with manageable complexity is made possible by extending the fast Backward Greedy Algorithm (BGA) into the proposed antenna selection algorithm.

This paper presents performance evaluation of antenna selection capability proposed in IEEE 802.16e (Amendment of IEEE 802.16-2004 standard for combined Fixed and Mobile Broadband Wireless Access operation in licensed band), under 2048 points orthogonal frequency division multiple access (OFDMA) mode of operation. It is shown that channel condition plays significant role on the amount of gain achievable by the scheme. Modification to the selection method is proposed and additional gain achieved is demonstrated. Measurements under different signal to noise ratio (SNR) values for different channel models are analysed. Results of the experimental studies are then summarised

This paper proposes three different channel estimation techniques for layered space-time block spread CDMA (LST BS-CDMA) systems, using different pilot patterns. The first technique applies the normal channel estimation method for VBLAST systems on each subcarrier. The second technique constructs time-domain sequences that give a set of nulls at predefined frequency and interpolates those nulled tones to obtain the full frequency response of the channel. The third technique improves on the second technique and eliminates the need for knowledge of the channel delay spread. The LST BS-CDMA system is simulated and its performance is compared when the three different channel estimation technique is used

In this paper, diagonally loaded linear Minimum Mean Square Error (MMSE) equalization technique is proposed for Ultra Wideband (UWB) multipath channel in the presence of Inter Symbol Interference (ISI) and Multiple Access Interference (MAI). In the case of practical implementation under limited training sample support, the optimal solution for linear least squares problems is the Minimum Norm (MN) solution. But it suffers from performance degradation when the sample covariance matrices are ill-conditioned. Diagonal Loading (DL) technique is incorporated into MN solution and shown to achieve significant performance improvement when the amount of training symbols is comparable with the number of taps utilized by the equalizer. Moreover, a rank-reduced Multistage Wiener Filter (MWF) with DL is proposed for UWB multipath channel equalization which requires large number of taps. It is shown to converge to the MN solution with much reduced computational complexity.

This paper proposes an over-sampling multi-channel equalizer per sub-band for multi-band ultra-wideband (UWB) system and compares its performance with conventional RAKE receiver when operating in practical UWB channel models. Three transmission modes have been considered, and inter-symbol interference (ISI) is found to be inherent to certain transmission modes due to the large UWB channel delay spreads. Through detailed analytical and simulation studies, the proposed over-sampled minimum mean square error (MMSE) equalizer is shown to be able to handle ISI under any channel conditions or transmission modes, with an acceptable BER. In addition, the rich multipath diversity of the UWB channels is harnessed by the over-sampling scheme, for output SNR improvement. Over-sampling is done in the expense of an increase in system complexity

This paper proposes a space-time coding architecture for single-carrier block spread CDMA systems. The proposed scheme employs a novel block spreading and despreading operation, which lead to significant reduction in the receiver complexity. The performance of the system is enhanced through space-time coding transmission. Extensive simulation studies are carried out and the performance of the proposed system is compared against conventional CDMA systems.

In this paper, a symbol relocated (SR) scheme has been proposed for variable spreading factor orthogonal frequency code division multiplexing (VSF-OFCDM) systems to achieve frequency diversity during retransmission. The performance has been evaluated for two combining schemes of hybrid auto repeat request (ARQ) namely chase combining and incremental redundancy. The results show that the proposed SR scheme achieves significant improvement in terms of system throughput over the conventional schemes. This effect is more significant for chase combining because the rotated mechanism is more effective when the same packet is transmitted during the retransmission. It is also found that SR scheme is not sensitive to Doppler frequency variation, which makes SR scheme an attractive candidate for fast fading channels. Further investigations also suggest the suitability of the SR scheme for smaller spreading factors (in frequency domain) and larger coding rates.

Ultra-wideband (UWB) technology is one of the promising solutions for short-range indoor wireless communication applications. UWB systems spread the transmitted signal power over an extremely large frequency band, and the power spectral density of the signal is very low. Due to the wide bandwidth of the transmitted signal, UWB signal energy will spread over the frequency bands allocated to other radio systems. In order to evaluate the effects of UWB system to narrowband systems (such as IEEE802.11a wireless LAN) in its overlay band, it is important to understand and quantify the power spectral density (PSD) of UWB signal. In this paper, a detailed analysis on the PSD of direct sequence coded UWB (DS-UWB) signal is presented. The theoretical and simulation results reveal that the interfering DS-UWB power can be reduced by regulating UWB chip rate, pulse shape, pulse width and scrambling codes in the frequencies of victim narrowband systems.

A novel chip level interleaving (CLI) scheme is proposed for multicarrier code division multiple access (MC-CDMA) system by reordering the chip sequences to achieve frequency diversity and randomization effect in frequency domain. The performance has been evaluated and simulation results show that the proposed CLI scheme increases system capacity significantly compared to the conventional schemes. By using block spread chip interleaving structure, the interleaver structure for the proposed CLI scheme is very simple to implement and has less delay latency. Moreover, the performance comparisons of various frequency domain interleaving schemes, namely bit level interleaving (BLI), symbol level interleaving (SLI) and the proposed CLI for MC-CDMA systems have been subsequently investigated by taking into consideration of complexity. The effects of different interleaving schemes under various scenarios such as outdoor (large delay spread) and indoor (small delay spread) environments have been evaluated and a switching mode has been discussed to choose the optimum interleaving scheme under different scenarios to maximize the system throughput.

This paper presents an advanced architecture for residue number system (RNS)-based code-division multiple-access (CDMA) system for high-rate data transmission by combining RNS representation, phase shift keying/quadrature amplitude modulation (PSK/QAM) and orthogonal modulation. The residues obtained from a fixed number of bits are again divided into spread code index and data symbol for modulation. The modulated data symbol is spread using the indexed orthogonal codes and transmitted through a communication channel. The proposed system uses a lower number of orthogonal codes than conventional RNS-based CDMA and the performance is comparable. The computational complexity of the proposed system is compared against alternative schemes such as M-ary CDMA and conventional RNS-based CDMA. The modified system is simulated extensively for different channel conditions and the results are discussed.

This paper proposes a unified two-dimensional maximum-likelihood multipath channel estimator for both multicarrier and single-carrier CDMA systems with cyclic prefix. The conditions for the optimal training sequence and the lower bound for the performance of this estimator are obtained by solving an optimisation problem. Optimal and sub-optimal training sequences are designed from several classes of sequences with ideal autocorrelation and cross correlation properties. Furthermore, the complexity of this channel estimator is reduced considerably by applying the optimal training sequence. The simulation results demonstrate that this channel estimator combined with optimal or sub-optimal sequence can give near single-user channel estimation performance even for fully loaded systems.

One of the distinguishing features of impulse radio or ultra-wideband (UWB) systems is by their broad bandwidth. The resulting power spectral density of UWB systems can become very small due to the very large bandwidth. With such low radiated power, it is important to design a receiver that maximises the signal-to-noise ratio (SNR). Conventionally, this is achieved by a pulse matched filter. Due to the high data rate of UWB, pulse matching may not be feasible. Therefore, a template matching approach is employed instead. A local-oscillator (LO) based UWB receiver scheme is presented, derived from the conventional down-converter for narrowband systems. Instead of carrier modulation, the LO in the proposed receiver is for sub-optimal template matching with the received signals, matched in time but not in amplitude. This sub-optimal matched template is made possible by certain properties of the received UWB signals. The output is then low-pass filtered, and sampled. The selection of suitable low pass filters (LPF) and sampling rate for maximum energy collection with favourable correlation properties is investigated in this paper.

This paper proposes a multiband multicarrier CDMA system with a simplified receiver structure for downlink transmission. An adaptive algorithm is proposed for allocating multiple subbands for users based on their channel gain and usage. The band allocation algorithm together with adaptive modulation can considerably increase the system capacity. A simplified receiver structure intended to reduce the complexity of channel equalizer-despreader structure of conventional multicarrier CDMA system is also proposed. The combined system is extensively simulated for different channel parameters and the results are discussed.

This paper shows how a unified model can he used to describe the signal received in frequency domain over a multiple-antenna, frequency-selective, multipath fading channel for multicarrier CDMA and single carrier CDMA systems with cyclic prefix. This realization validates the abstraction of these CDMA problems into a mathematical model which can be used for practical problems such as channel estimation and data detection. Moreover, the optimal multiuser detection problem based on the maximal-likelihood criteria for this unified model is addressed as a combinatorial optimization problem. A sequential quadratic programming approach is proposed to approximate this problem, which corresponds to a near-optimal software-defined decision-feedback multiuser receiver for both single-carrier and multicarrier CDMA systems. An efficient gradient projection algorithm is applied for data detection in the proposed receiver. The simulation results show that this scheme can reach near single-user performance even for fully-loaded systems and outperform conventional soft-interference cancellation methods.

A dynamic subcarrier allocation algorithm is developed and studied in order to improve the capacity of a multi-user OFDM system in the downlink environment. The proposed algorithm uses a decentralized approach and considers the instantaneous channel response of each user in parallel. In order to reduce the complexity of the system, the available subcarriers are divided into a number of partitions and the algorithm attempts to allocate the partition with the highest average channel gain to each user. However, situations may arise whereby two or more users attempt to select the same partition. As such, an important aspect of the algorithm is to resolve such conflicts. Based on the above allocation plan, adaptive modulation is employed for each user on the allocated partitions. The results obtained show that the proposed dynamic allocation scheme outperforms a static allocation scheme in terms of a lower BER and a higher system capacity for the same SNR. In addition, it is possible to obtain performance improvements at the expense of an increase in the system complexity by dividing the subcarriers into a larger number of partitions.

In this paper we suggest a new single carrier cyclic prefix assisted multiple access scheme for the asynchronous broadband CDMA system in uplink. Frequency domain equalization is applied instead of conventional RAKE combining or time domain equalization. A new serial type multistage interference cancellation in frequency domain is proposed to cancel the multiple access interference while keeping low computational complexity. We also investigated the effects of interference rejection weight control for this multistage interference cancellation. Another hybrid system combining the successive interference cancellation and parallel interference cancellation is also proposed, which can reach the similar performance of the serial type while reducing the processing delay greatly.

This paper presents an advanced architecture for a residue number system (RNS) based CDMA system for high-rate data transmission by combining RNS representation, PSK/QAM modulation and orthogonal modulation. The proposed system uses a lesser spreading factor than RNS based CDMA and the performance is comparable. The modified system is simulated extensively for different channel conditions and found that it can be used for faster data transmission without affecting the system performance.

This paper is concerned with a new method to enhance the bandwidth efficiency of an MC-CDMA system by using a residue number based representation for information symbols. The residues are mapped into a set of orthogonal sequences and are transmitted in parallel. To increase the data rate further, a modified residue representation scheme is used with significantly lesser number of orthogonal sequences. A multicarrier modulation scheme is used for both transmission and reception of residue channels. The issues involved in the design of an enhanced RNS based MC-CDMA architecture is discussed and the performance of the system is evaluated in a frequency selective Rayleigh fading channel via extensive simulations.

This paper presents a new method to improve bandwidth efficiency of RNS based CDMA system by combining RNS representation, PSK/QAM modulation and orthogonal modulation. Using the proposed method significantly reduces the computational complexity of the receiver unit and significantly increases the data transmission rate. The modified system is simulated extensively for different channel conditions and found that it can be used for faster data transmission without affecting the system performance.

This paper explores the use of redundant residue number systems to incorporate incremental redundancy in a communication system. By exploiting this property further, one can design an appropriate coding scheme for transmission at the currently experienced SNR level. A link adaptation procedure and an adaptive decoding method is presented for the efficient implementation of the system. The proposed system is extensively simulated with parameters suitable for wireless local area network (WLAN) standards and the results are discussed.

Establishing synchronization with locally generated spread code is one of the most important tasks in DS-CDMA systems for effective and reliable communications. A three-step procedure is proposed in this paper for fast code synchronization and subsequent path delay estimation for a single base station based system in a multipath environment. The synchronization procedure starts from the slot synchronization and then frame synchronization with the help of long code masked symbol. The path delays are estimated from the power delay profile computed from the instantaneous signal power of pilot symbols. The average power delay profile is used as the threshold. This three-step procedure is extensively simulated for different power delay profiles and the results are discussed.

High data rates in wireless radio environments are becoming common. Current system designs are inadequate to meet the speed requirements that are anticipated in the newer services. The computational complexities in the subsystems increase in direct proportion. We propose alternative multiply accumulate units for the pulse shaping filters that use a new representation for their coefficients. Consequently, these new structures are fast, efficient and consume less power. The filters proposed take into account constraints, such as, intersymbol interference, response characteristics etc. in their design methodology.