This paper investigates an over-the-air federated learning (OTA-FL) system that employs fluid antennas (FAs) at an access point. The system enhances learning performance by leveraging the additional degrees of freedom provided by antenna mobility. We analyze the convergence of the OTA-FL system and derive the optimality gap to illustrate the influence of FAs on learning performance. With these results, we formulate a nonconvex optimization problem to minimize the optimality gap by jointly optimizing the positions of the FAs, the beamforming vector, and the transmit power allocation at each user. To address the dynamic environment, we cast this optimization problem as a Markov decision process and propose the recurrent deterministic policy gradient (RDPG) algorithm. Finally, extensive simulations show that the FA-assisted OTA-FL system outperforms systems with fixed-position antennas and that the RDPG algorithm surpasses the existing methods.

This paper proposes an innovative approach to improve over-the-air federated learning (OTA-FL) systems by integrating fluid antennas (FAs) at the access point. By exploiting the mobility of FAs, we aim to increase the correlation among the users’ channels, thereby improving the learning performance. We analyze the performance of over-the-air computation and the convergence behavior of the OTA-FL system, highlighting the benefits of FAs. Since the learning performance improves as more devices participate in the FL aggregation, we formulate a non-convex optimization problem that maximizes the number of selected users by jointly optimizing FA positions and the beamforming vector, coupled with a user selection policy subject to a mean-squared error constraint. To address environmental dynamics, we describe the problem as a Markov decision process and develop a long short-term memory (LSTM)-based algorithm for efficient decision-making. Simulation results demonstrate that the proposed FA-assisted OTA-FL framework significantly outperforms conventional setups, achieving higher user selection rates and improved learning performance compared to existing benchmarks.

This paper investigates the performance of physical layer security (PLS) in wireless communication systems, where a reconfigurable intelligent surfaces (RIS) is deployed between the transmitter and legitimate receiver to enhance the communication security. The Fisher-Snedecor F distribution is adopted to model the underlying fading channels, owing to its accuracy, tractability and generality. On this basis, this paper evaluates the performance of the proposed system by deriving the average secrecy capacity (ASC) and the secrecy outage probability (SOP) under correlated Fisher-Snedecor F channel coefficients. Furthermore, the asymptotic behavior of the ASC and SOP in the high signal-to-noise ratio (SNR) regime is examined. Analyzing the correlated scenario is crucial as it provides a detailed understanding of how interdependencies among channel coefficients impact the system’s security and overall performance, offering valuable insights into real-world communication scenarios. Finally, this paper verifies the analytical results through numerical illustrations, and demonstrates the effectiveness of employing RIS.

System-on-chip (SoC) field programmable gate array (FPGA) devices are becoming increasingly prominent in a vast range of applications. The fusion of the FPGA’s unmatched parallel computing capacity and flexibility with a full-bore processing system makes these devices extremely powerful. With recent technological progress, SoC FPGA devices are implemented in increasingly complex systems where security and safety are often issues of concern. To cater to these concerns, these devices are commonly fit with encryption and authentication capabilities to ensure the confidentiality and authenticity of externally stored bitstreams, firmware, and bootloaders. However, while much effort is placed into securing these partitions when stored in external memory, little attention seems to be paid to the security of this data once it is decrypted for execution. This article investigates how vulnerable systems are to attacks that target decrypted data during execution. We demonstrate that data stored in external synchronous dynamic random access memory (SDRAM) can provide access to trusted and secured interfaces of SoC FPGA devices even with diligently applied security features.

Nonorthogonal multiple access (NOMA) has been viewed as a potential candidate for the upcoming generation of wireless communication systems. Comparing to traditional orthogonal multiple access (OMA), multiplexing users in the same time-frequency resource block can increase the number of served users and improve the efficiency of the systems in terms of spectral efficiency. Nevertheless, from a security viewpoint, when multiple users are utilizing the same time-frequency resource, there may be concerns regarding keeping information confidential. In this context, physical layer security (PLS) has been introduced as a supplement of protection to conventional encryption techniques by making use of the random nature of wireless transmission media for ensuring communication secrecy. The recent years have seen significant interests in PLS being applied to NOMA networks. Numerous scenarios have been investigated to assess the security of NOMA systems, including when active and passive eavesdroppers are present, as well as when these systems, are combined with relay and reconfigurable intelligent surfaces (RISs). Additionally, the security of the ambient backscatter (AmB)-NOMA systems are other issues that have lately drawn a lot of attention. In this article, a thorough analysis of the PLS-assisted NOMA systems research state-of-the-art is presented. In this regard, we begin by outlining the foundations of NOMA and PLS, respectively. Following that, we discuss the PLS performances for NOMA systems in four categories depending on the type of the eavesdropper, the existence of relay, RIS, and AmB systems in different conditions. Finally, a thorough explanation of the most recent PLS-assisted NOMA systems is given.

This article presents a critical literature review on the security aspects of field-programmable gate array (FPGA) devices. FPGA devices present unique challenges to cybersecurity through their reconfigurable nature. The article also pays special attention to emerging system-on-chip (SoC) FPGA devices that incorporate a hard processing system (HPS) on the same die as the FPGA logic. While this incorporation reduces the need for vulnerable external signals, the HPS in SoC FPGA devices adds a level of complexity that is not present for stand-alone FPGA devices. This added complexity necessarily hands over the task of securing the device to developers. Even with standard security features in place, the HPS might still have unhindered access to the FPGA logic. A single software flaw could open up a breach that might allow an attacker to extract the FPGA’s configuration data. A robust cybersecurity strategy is thus required for developers. As such, this work aims to provide the groundwork to build a solid threat-based cybersecurity design strategy that is specially adapted to SoC FPGA devices.

In this paper we present a likelihood ascent search (LAS) detector for massive multiple-input multiple-output (MIMO) systems with unknown channel state information (CSI). In contrast to previous works on LAS detection that assumed perfect CSI available at the receiver, our architecture takes into account the channel uncertainty and is based on the knowledge of the channel distribution information (CDI) at the receiver. The proposed LAS detector does not explicitly use the estimated channel matrix: it jointly processes the received training sequence and data symbols to estimate the transmitted data vectors. First, the maximum-likelihood (ML) detection metric is derived for the proposed LAS detector. Then, a low complexity implementation approach, suitable for large MIMO systems, is proposed. The performances of the proposed architecture are assessed and compared to those of conventional LAS detectors.

In massive multiple-input multiple-output (MIMO) systems, the channel hardens rapidly as the number of antennas grows. This means that the variance of the mutual information decreases rapidly relative to its mean. In this paper, we propose a likelihood ascent search (LAS) detector for massive MIMO systems that exploits the channel hardening behavior. In contrast to classical LAS receivers, the proposed channel hardening- exploiting LAS (CHE-LAS) does not require a matrix inversion. Therefore, the computational complexity of the proposed CHE-LAS is reduced compared to that of the conventional LAS algorithm. Moreover, simulation results show that the CHE-LAS detector achieves comparable performances as the LAS receiver.

The performance of coherent symbol detection in multiple-input multiple-output (MIMO) systems is tightly related to the channel knowledge at the receiver side. For MIMO detection, achieving near-optimal performance with a low computational complexity has been a topic of several recent researches. In this paper, we propose a robust detector for uncoded MIMO systems with imperfect CSI (ICSI). The proposed detector is based on the likelihood ascent search (LAS) algorithm which achieves near maximum likelihood (ML) performance with a reduced complexity. To take into account the channel estimation error, we propose to use a modified likelihood metric function. Moreover, to enhance the system performance, we suggest to perform the channel estimation and the data detection in an iterative manner. Simulation results show that the proposed scheme outperforms the conventional LAS detector.

Almost all existing channel estimation schemes, for multi-user multiple-input multiple-output (MU-MIMO) systems, were designed based on a fixed and known number of active users. However, in random access MU-MIMO systems, some users may be inactive and the estimation techniques designed with the assumption that all users are available may lead to performance losses. In this paper, we consider the popular least squares (LS) and linear minimum mean square error (LMMSE) estimations approaches. For such techniques, when the number of users varies, the channel estimation filter coefficients must be re-derived. The fundamental problem of interest here is to reduce the computational complexity of the LS and LMMSE channel estimation methods when some users are inactive. For each techniques, we propose an estimation approach with a low complexity and without performance loss. The proposed algorithms avoid the direct computation of matrix inverses required by the LS and LMMSE methods. Moreover, the mean square error (MSE) losses, due to the use of the LS and LMMSE estimator intended for the scenario without inactive users, are evaluated and compared with Monte-Carlo simulations results.

In this paper, we study an electromagnetic optimization technique using Taguchi's method and apply it to circular antenna array (CAA) design. Taguchi's method was developed on the basis of the orthogonal array (OA) concept, which offers systematic and efficient characteristics. The newly proposed idea is the implementation of Taguchi optimization method for CAA of order 10, 16 and 24 respectively. The optimization procedure is then used to provide an optimum set of weights for different CAAs. Obtained results show that the desired radiation pattern with optimum sidelobe level (SLL) reduction is successfully achieved. Compared to traditional optimization techniques and well-known algorithms (Particle Swarm Optimization (PSO), Genetic Algorithm (GA), and Firefly Algorithm (FA)), Taguchi's method is easy to implement and efficient to reach the optimum solutions.

In this paper, we implement hybrid Woodward-Lawson Neural Networks and weighted Fourier method to synthesize antenna arrays. The neural networks (NN) is applied here to simplify the modeling of MIMO antenna arrays by assessing phases. The main problem is obviously to find optimal weights of the linear antenna array elements giving radiation pattern with minimum sidelobe level (SLL) and hence ameliorating the antenna array performance. To attain this purpose, an antenna array for reliable Multiple-Input Multiple-Output (MIMO) applications with frequency at 2.45 GHz is implemented. To validate the suggested method, many examples of uniformly excited array patterns with the main beam are put in the direction of the useful signal. The Woodward-Lawson Neural Networks synthesis method permits to find out interesting analytical equations for the synthesis of an antenna array and highlights the flexibility between the system parameters in input and those in output. The performance of this hybrid optimization underlines how well the system is suitable for a wireless communication and how it participates in reducing interference, as well.

The concepts of array processing and smart antenna give a promising solution to the significant increase of data rates in wireless transmission systems. In this paper, we deal with the problem of designing linear antenna arrays for specific radiation properties of MIMO applications based on Direction-Of-Arrival estimation and Taylor beamforming techniques. The objectives of this paper can be summarized as to minimize the maximum sidelobe level (SLL), combined the Taylor method and MUSIC (Multiple Signal Classification) algorithm. The performance of this hybrid optimization determines how well the system is convenient for a reliable wireless communication and interference reduction. This paper will discuss the application of MUSIC algorithm for linear array antenna (4, 8 and 16 antennas) in order to estimate the Direction-Of-Arrival of various angles of elevation and azimuth.

In this paper, we present a novel eavesdropping-resilient OFDM system through sorted subcarrier interleaving. The transmitter interleaves subcarriers in each OFDM signal according to its dynamic channel state information (CSI) to the legitimate receiver. More specifically, subcarriers are interleaved according to the sorted order of their instantaneous channel gains that are observed at the transmitter. Based on channel reciprocity, the legitimate receiver can derive the interleaving pattern initiated by the transmitter through its local channel estimate, and then de-interleave the received signals. In contrast, since spatially separated wireless channels in rich multipath environments are independent of each other, an eavesdropper at a third location cannot follow the dynamic subcarrier interleaving permutation, and thus fails to eavesdrop this transmission. Considering the imperfect reciprocity of noisy channel estimates at the legitimate terminals, only a subset of subcarriers in each OFDM signal is involved in the interleaving. A subcarrier selection algorithm is investigated to realize a trade-off between the eavesdropping resilience and transmission reliability. Theoretical analysis and Monte Carlo simulations have been provided to validate the proposed system. Compared with prior security enhancement schemes, the proposed approach requires only minor modifications to off-the-shelf systems and avoids additional resource consumption.

A novel physical layer authentication scheme is proposed in this paper by exploiting the time-varying carrier frequency offset (CFO) associated with each pair of wireless communications devices. In realistic scenarios, radio frequency oscillators in each transmitter-and-receiver pair always present device-dependent biases to the nominal oscillating frequency. The combination of these biases and mobility-induced Doppler shift, characterized as a time-varying CFO, can be used as a radiometric signature for wireless device authentication. In the proposed authentication scheme, the variable CFO values at different communication times are first estimated. Kalman filtering is then employed to predict the current value by tracking the past CFO variation, which is modeled as an autoregressive random process. To achieve the proposed authentication, the current CFO estimate is compared with the Kalman predicted CFO using hypothesis testing to determine whether the signal has followed a consistent CFO pattern. An adaptive CFO variation threshold is derived for device discrimination according to the signal-to-noise ratio and the Kalman prediction error. In addition, a software-defined radio (SDR) based prototype platform has been developed to validate the feasibility of using CFO for authentication. Simulation results further confirm the effectiveness of the proposed scheme in multipath fading channels.

Information security is becoming a critical challenge in wireless communications due to the open nature of wireless channels and the transparency of standardized transmission schemes. Among the various wireless security techniques, user authentication is one essential measure to identify legitimate users and protect the integrity of transmissions. In this paper, a novel physical layer authentication scheme is proposed to enhance the communication security by exploiting the unique characteristics of oscillator in each communication device. In realistic scenarios, radio frequency (RF) oscillators in each transmitter and receiver pair always present some bias to the nominal carrier frequency due to manufacturing limitations and operating conditions. This bias is characterized by a device-dependent carrier frequency offset (CFO), which can be used to identify a specific wireless transmitter. In the proposed authentication scheme, the CFO at different time of the received signal is first estimated. It is then examined by a hypothesis testing to determine whether the signal has the consistent CFO for authentication purpose. Adaptive thresholds of CFO variation are derived for user discrimination based on the received signal-to-noise ratio (SNR). Simulation results further confirm the effectiveness of the proposed scheme in multipath fading environments.

Distributed video coding paradigm aims at transferring the major part of the processing computation effort from the encoder to the decoder. Motion interpolation is done at the decoder to generate side information (SI) through motion compensated temporal interpolation (MCTI). SI is considered as a noisy version of the original data: channel control coding schemes, such as turbo coding, are used to eliminate the errors (SI inaccuracies). The video data is turbo encoded and the parity bits are sent to the decoder. The systematic bits, however, are discarded since the decoder already disposes of SI that can be used for the channel likelihood ratio calculations. However, when the MCTI generation of SI is highly corrupted, the channel likelihood ratios based on the SI are inefficient and even misleading. A number of parity bits number exceeding the original data length may then be required, thus leading to an undesirable expansion effect. In this paper, we propose a method to detect adaptively the situations where the SI is of lower quality. Then puncturing matrices, enabling systematic bits, are used to help computing reliable channel likelihood ratios. An improvement up to 0.5 dB is reported for PSNRs vs bit rate performances.

An iterative design method for Orthogonal Frequency Division Multiplexing (OFDM) system parameter estimation and synchronization under a blind scenario for cognitive radio systems is proposed in this paper. A novel envelope spectrumbased arbitrary oversampling ratio estimator is presented first, based on which the algorithms are then developed to provide the identification of other OFDM parameters (number of subcarriers, cyclic prefix (CP) length). Carrier frequency offset (CFO) and timing offset are estimated for the purpose of synchronization with the help of the identified parameters. An iterative scheme is employed to increase the estimation accuracy. To validate the proposed design, the performance is evaluated under an experimental propagation environment and the results show that the proposed design is capable of adapting blind parameter estimation and synchronization for cognitive radio with improved performances.

To ensure proper operations of primary users and a fair spectrum sharing among the secondary users, spectrum sensing and user identification at cognitive radio (CR) have to be achieved with high accuracy under low signal- to-noise ratio (SNR). Motivated by the unavailability of perfect synchronization and prior noise knowledge at the CR sensing device, a robust sensing and user identification technique using noise insensitive threshold under low SNR is proposed in this paper for signals from precoded cyclic prefix Orthogonal Frequency Division Multiplexing (PCP-OFDM) system, which is proposed recently to provide a fast-adapting CR communication platform using a PCP enabled signaling link for dynamic system interaction. The proposed spectrum sensing and user identification are achieved with time domain cyclic correlations based on the inherent PCP feature in the received signals. Different users are distinguished in the sensing process with their unique PCPs. The impact of unknown noise statistics on the sensing threshold determination is removed with the proposed correlation ratio metric. The effect of unknown timing offset is also mitigated with the cyclic correlations. Numerical results are provided to verify the analysis and evaluate the performance of the proposed algorithm.

We proposed a precoded in-band pilots design for OFDM signal (PIP-OFDM) in [1]. With a special design, user identification in cognitive network is easily achieved by demodulating unknown information on identification pilot subcarriers embedded in the transmitted PIP-OFDM signal. In this paper, we discuss synchronization issues of PIP-OFDM system. Different from conventional OFDM system, synchronization in PIP-OFDM system is realized at low SNR. Benefit from the redundant information on pilots, performance of synchronization in PIP-OFDM system is greatly improved by processing multiple OFDM symbols. Coarse timing and frequency synchronization are briefly introduced using cyclic prefix correlation and pilots' energy correlation in frequency domain. Fine timing and frequency synchronization are realized with modified maximum likelihood estimator based on phase shift estimation in frequency and new method using the similar principle, respectively. System performance is evaluated by theoretical formulation and computer simulations in terms of mean square error. Results show that synchronization algorithms in this paper work effectively at low SNR from -5dB to 5dB.

In the last few years distributed video coding (DVC) has become a new paradigm for video compression where the encoding process needs to be simple. DVC allows for the development of new applications where the computational complexity and the amount of memory inside the video encoder are limited. In this paper, we introduce a new data representation and coding method for DVC systems. The proposed method consists of an adaptive binary representation based on the maximum difference between the source picture and the side information. This adaptive representation provides a reduction of bitrate without any loss of information, while maintaining the low complexity of the encoder. Experimental results show a significant increase in performance over conventional DVC methods.

Spectrum sensing and signal identification at low SNR, where synchronization and demodulation are not achievable, have emerged as two of the most critical challenges in cognitive radio network. A precoded in-band pilots design for OFDM signal (PIP-OFDM) is proposed in this paper to simplify the spectrum sensing and signal identification for dynamic spectrum sharing. The actual design of pilot signal in this OFDM system contains two groups of pilot tones, i.e. uniform pilot tones and identification pilot tones. Combining the two groups of pilot tones embedded in the OFDM signal, the spectrum sensing based on detecting the energy on pilot tones achieves an exceptionally good performance. In addition, the unique identification pilot code design for each transmitter in this network makes the signal identification easy and reliable. Theoretical analysis and simulation show that this design works well in spectrum sensing and signal identification at low SNR.

An adaptive Orthogonal Frequency Division Multiplexing (OFDM) system, with a preceded cyclic prefix (PCP), was proposed earlier to address the recent need of robust and flexible transmission technique in cognitive radio (CR) communications [1]. Identification of PCP-OFDM signals is therefore of great importance for the design of fair spectrum sharing mechanism, particularly at very low signal-to-noise ratio (SNR)when synchronization is not achievable. The preceded cyclic prefix, multiplexed with the data-carrying OFDM signals, provides one unique and recognizable feature of PCP-OFDM signals. In this paper, a robust PCP-OFDM signal identification technique is proposed under very low SNR in the presence of unknown timing and carrier frequency offset (CFO). Robust performance with very low false alarm probability and short sensing time was achieved under various channel conditions including Rician, Rayleigh and the additive white Gaussian noise (AWGN) channels.

In this paper we study the performance of source matching technique for an optical code division multiple access (OCDMA) system in the presence of source coherence effects and square law detection process. We use a binary-asymmetric channel (BAC) model for an OCDMA system employing an all-optical passive correlator receiver. Source coherence effects lead to relative-intensity-noise (RIN) and phase-induced-intensity-noise (PIIN), which are included in our analysis. Previous studies only considered multiple access interference (MAI) noise, resulting in a Z-channel (where errors only occur for the transmission of data bit zero) model, and neglected RIN and PIIN. The presence of RIN and PIIN leads to errors occurring for both transmitted data bits one and zero, thus a BAC model. We show that source matching gain depends on the normalized source coherence time, defined as the ratio of the optical source coherence time to the bit duration. Our analysis shows that, while MAI limited analysis predicts that increasing the number of users increases the source matching gain, when taking into account RIN and PIIN, source matching gain is both bit rate and source type dependent, and tends to zero for very high numbers of users.

Channel estimation and equalization techniques are crucial for the ubiquitous wireless communication systems. Conventional receivers for most wireless standards preset the channel length to the maximal expected duration of the channel impulse response for the adopted channel estimation and equalization algorithms. The excessive channel length often significantly increases the implementational complexity of the wireless receivers and leads to the redundant information which would induce the additional estimation errors. Moreover, such a scheme does not allow the dynamic memory allocation for variable channel lengths. This could further increase the power consumption and reduce the battery life of a mobile device. The knowledge of the actual channel length would, in principle, help the system designers decrease the complexity of the channel estimators using maximum likelihood (ML) and minimum-mean-square-error (MMSE) algorithms. In this paper, we address this important channel length estimation problem and propose a novel algorithm to estimate the channel length without the need of pilots or training sequence. In addition, we provide the analysis on the effectiveness of the proposed non-pilot-aided channel length estimator through Monte Carlo simulations.

Cooperation in wireless communications is an attractive means to gain spectral efficiency or diversity. Typically, cooperation is studied at the level of an individual end-to-end link. On the other hand, the primary goal of the the protocol proposed herein is not the improvement of individual link quality, but rather to improve global resource utilization throughout the network in the context of a distributed base station system. A simple Alamouti-type cooperative protocol for mobiles with half-duplex air interfaces is presented. The effect of cooperation on the overall network in terms of resource availability, connection capacity, and offered quality of service is studied via emulation of an agent-system organizing the distributed base station model. Despite the limitations of the simplistic cooperation protocol used, it is shown that cooperation yields improved performance through synergistic effects at the system level.

A new multicarrier system, termed multi-symbol encapsulated orthogonal frequency division multiplexing (MSE-OFDM), was proposed earlier, in which one cyclic prefix (CP) is used for multiple OFDM symbols. The motivation of MSE-OFDM is to address the disadvantages of OFDM system, i.e., the sensitivity to carrier frequency offset and high peak to average power ratio at the same time. In this paper, we propose a new time slicing technique by replacing the cyclic prefix with preceded pseudo random sequence for MSE-OFDM system. With the proposed time slicing technique, multiple multimedia data streams with dynamic data rates can be easily multiplexed. In addition, this system overcomes the high sensitivity to frequency offset inherited with OFDMA system and can be used for both uplink and downlink for mobile multimedia communications with variable data rates. The proposed time slicing system also enables the power saving for mobile receivers, through which the batter life can be substantially extended.

Traditional cellular communication schemes are based on one to one wireless links. In a distributed base station (DBS) scheme, more then one station can relay the same mobile. This paper studies the impact of channel interference on the behavior of an agent system which manages the multiple connections at the DBS. It is shown that DBS can provide an important gain in diversity, accommodating more mobiles with a given QoS despite interference, provided that some mild conditions on network topology are met. It is also established that the agent system is both stable and efficient.

In this paper, we propose new techniques for CDMA/MIMO systems that employ multiple spreading codes. Rather than assigning each transmit antenna a different spreading waveform, the data to be transmitted on a given signaling interval determines which spreading waveforms will be used by each transmit antenna. Compared to a more conventional approach, which employs fixed spreading waveforms for each transmit antenna, our approach provides bit error rate performance improvement at moderate and high Eb/No.

This paper describes a FPGA implementation of an elliptic curve cryptosystem. Such systems are becoming increasingly popular as they provide the highest strength per bit of any cryptosystem commonly used today. The cryptosystem was built exploiting the wNAF representation of the private key as well as parallelism through the arithmetic units

This paper introduces a simple method to provide soft-macro diversity through distributed low-complexity base stations communicating to a central node to achieve a macrodiversity gain using maximal ratio combining. Having shown that this is feasible, a distributed resource allocation protocol is proposed based on agent processes exploiting minimal information on the state of the mobiles. This protocol proves to be adaptive, scalable and stable

In this paper, a simple product expression is found for the DPSK bit error rate of distributed base station systems affected by Rician fading. In this context, the received signals' fading envelopes are Rician, uncorrelated among themselves, and in general have different variances and K factors. It is assumed that maximal-ratio diversity combining is applied. This bit error rate expression is extended to cover QAM modulation via approximation. Furthermore, a new product form of the probability density function (PDF) for a sum of non-central chi-square variates with different variances is derived, since it constitutes a necessary step in our analysis

Performance of a new position location system using the transmitter identification (TxID) RF watermark in the digital TV (DTV) signals is analyzed in this paper. Compared to the Global Positioning System (GPS), DTV signals are received from transmitters at relatively short distances, while the broadcast transmitters operate at levels up to a few megawatts of effective radiated power (ERP), which makes the new position location system very robust even inside buildings. Practical receiver implementation issues including non-ideal correlation function and frequency synchronization are analyzed and discussed. New algorithms of removing the bandlimitation effect and frequency synchronization are proposed. Performances of the proposed techniques are evaluated through analysis and Monte Carlo simulations. Possible ways to improve the accuracy of the new position location system are discussed.

Performance of wireless local area networks (WLANs) over fiber systems is investigated under multipath fading for different graded index fiber profiles and optical system imperfections. The effect of OFDM cyclic prefix to the multimode fiber dispersion is investigated for the first time. Comparison of the WLAN over fiber systems operating at 5 GHz and 60 GHz is presented. External modulators, namely Mach Zehnder external modulators, are employed in the system architecture. Wireless and optical impairments are attacked together and solved in a collaborative and efficient manner

A new multicarrier system, termed multi-symbol encapsulated orthogonal frequency division multiplexing (MSE-OFDM), was proposed, in which one cyclic prefix (CP) is used for multiple OFDM symbols. The motivations for this new OFDM system are either to reduce the redundancy caused by the CP or to increase the system robustness to frequency offset, depending on the two different proposed implementations for the MSE-OFDM systems. The corresponding frequency offset and channel estimation algorithms are investigated. Possible ways to reduce the complexity of the joint maximum likelihood (ML) estimator, including the approximation of the joint ML estimator and FFT pruning, are discussed. The performance of the proposed estimators is also analyzed and verified through numerical simulations.

A new multi-symbol encapsulated orthogonal frequency division multiplexing (MSE-OFDM) system is proposed, in which one cyclic prefix (CP) is used for a frame of multiple OFDM symbols. A system level comparison between a conventional OFDM and the proposed MSE-OFDM system is presented in this study. Two different realizations of the MSE-OFDM, i.e., CP-reduced and FFT size-reduced MSE-OFDM systems, are investigated for different system requirement. An analysis on the bandwidth efficiency, impact of synchronization errors on the system performance and peak to average power ratio (PAPR) of these systems is presented. Comparisons are made on two different assumptions, i.e., either keeping the symbol size of the MSE-OFDM (i.e., number of the subcarriers) unchanged to increase the bandwidth efficiency, or keeping the bandwidth efficiency unchanged (ratio between CP and useful data transmission time) for system robustness to synchronization errors and a lower peak-to-average power ratio. In the first case for CP-reduced MSE-OFDM, bandwidth efficiency is improved due to a reduced number of CPs inserted between OFDM symbols. For the latter case of FFT size-reduced MSE-OFDM, robustness to synchronization errors is improved considerably due to the smaller number of subcarriers. The proposed system is of particular interest for fixed wireless systems and digital subscriber loops (DSL). Large frame size can be used in these applications, due to the static nature of the channel conditions. Implementation complexity of the MSE-OFDM system is also discussed.

A method for computing the average bit-error probability of binary differential phase-shift keying (DPSK) and frequency shift-keying (FSK) signals transmitted over Nakagami asymptotically slow fading channels with postdetection diversity reception is presented to extend previously published results. The previously published results apply only for maximum ratio combining, i.e., with predetection combining, where phase coherency is necessary. The results for postdetection combining are derived with the explicit expressions for the most practical cases of independent channels and particular cases of correlated channels.

Presents predetection and postdetection combining schemes for selection diversity reception with multiple antennas for MM-wave indoor radio channels. For those combining schemes, a reduction in complexity is achieved by limiting the number of combined signals to small values and by increasing the number of received signals. Bit error rate (BER) performance of binary phase shift keying (BPSK) with predetection combining of selected signals (CSS) and BER performance of differential BPSK with postdetection CSS are analyzed for slow fading and Rayleigh-distributed envelope statistics. Predetection maximal ratio combining of signals that comes from a single group or several groups of diversity channels as well as postdetection combining of received signals for groups of channels are considered. In comparing predetection combining with groups (PCG) and predetection combining of the best signals (PCB), we observe that the required SNR for achieving a certain BER is approximatively the same (with PCG having a slight advantage of 0.5 dB) for a given number, N, of diversity channels and L combined signals. Furthermore. PCG is equivalent to PCB for L=N since both techniques then correspond to conventional predetection maximal ratio combining (MRC), PCG and PCB are also equivalent when L=1 as both schemes then correspond to conventional selection combining. A small degradation of approximately 2 dB in the required SNR is observed when postdetection diversity reception with groups (PDG) is used instead of PCG. For L=N, PDG reduces to post detection MRC. The PDG technique is considered more suitable than PCB or PCG for MM-indoor wireless systems.