Spread Spectrum Communication

Inter-vehicular communication (IVC) on highways is one of the major application areas of ad hoc networks that enable multi-hop data exchange and forwarding between cars and between car and stationary gateways. In an IVC scenario, some emergency situations on highways may require an immediate communication with police, hospitals, highway assistance booth or with other cars. These messages should be forwarded on a top priority basis to the destination for immediate attention. So it is evident that, in an IVC scenario, some message flows are to be treated as high priority messages in order to ensure a timely and reliable delivery. In this paper, we have proposed a prioritybased communication scheme, which essentially selects shortest path for a high priority flow and reserves a zone known as high priority zone, along this path. Other low priority flows are forced to avoid this zone and take a longer diverse route to forward their messages to allow a contention-free communication to high priority flows. In this context, the use of directional antenna, having smaller transmission beam-width and larger transmission range compared to omni-directinal antenna, helps to easily decouple interfering routes, and improves the overall utilization of the wireless medium through Space Division Multiple Access (SDMA).

Ultra-wideband (UWB) technology enables high-data-rate communications and centimeter-accurate indoor localization but suffers severe degradation in multipath fading channels due to dense multipath components, narrowband interference (NBI), and low signal-to-noise ratios (SNR). Conventional energy-based detection methods, including Rake receivers, fail under these conditions due to amplitude sensitivity. This paper introduces a phase congruency (PC)-based selective Rake (S-Rake) receiver that exploits phase alignment across frequencies rather than signal magnitude for robust feature detection. The proposed method computes PC metrics via Hilbert transforms and sub-band decomposition to identify phase-aligned multipath components, guiding S-Rake finger selection (4, 8, and 128 fingers) and time-of-arrival (TOA) estimation. Simulations using 6th-derivative Gaussian pulses over IEEE 802.15.3a CM4 channels (NLOS, 4-10 m) with AWGN and IEEE 802.11a interference (SIR=-30 dB to 0 dB) demonstrate that PC-based S-Rake achieves 4 dB SNR gain at BER=10⁻⁴ over conventional Rake under high interference. DS-UWB with PC outperforms TH-UWB by 3× lower BER at SIR=-30 dB. Increasing Rake fingers from 4 to 128 reduces BER by >40% and improves TOA accuracy by 62% (RMSE: 1.8 ns → 0.68 ns). PC maintains BER=10⁻³ at SIR=0 dB where conventional methods fail. Results establish PC as a transformative paradigm for interference-resilient UWB applications including IoT localization and 5G-coexistent communications.

Social media has become a place for communication and interaction. It is also a place for exchanging information and ideas. As a result of this exchange of information and ideas, digital communities have emerged, consisting of users who share similar interests. In this era, memes have become a practical means of communication. This is because memes provide a practical representation of life as it is. Memes are a form of entertaining communication, but they have now become a means of indirectly conveying stereotypes. Jomok memes are meme content that directly displays muscular, masculine black men in homoerotic poses. This occurs in a community called Sungut Lele. The purpose of this study is to analyse Jomok meme content as intersectionality content on social media. The research method used is qualitative research. The data collection techniques used are digital participatory observation, interviews, and document studies. The theory used is the theory of intersectionality proposed by Kimberle Crenshaw. The results of this study show that the Sungut Lele community practically uploads memes that have intersectionality visuals towards black people. Black people are visualised as muscular, erotic, and homosexual black men. This content constantly reinforces new stereotypes about black people, which causes discomfort to individuals. These findings show that memes are not only a means of communication that is full of entertainment, but also a means of indirectly conveying new stereotypes to the audience.

In this paper, we study the performance of optical code-division multiple access (CDMA) systems using various receivers structures. Two general classes of receivers based on required electronic bandwidth are studied. Optical orthogonal codes (OOCs) are utilized as signature sequences and the performance studied in this paper takes into account the effect of all major noise sources, i.e., quantum shot-noise, dark current noise, and Gaussian circuit noise. Furthermore, this paper introduces a generalized method of analyzing the performance of various optical CDMA receiver structures. Required mean number of photon count per chip time for reliable transmission of data bits for various receiver structures is investigated. Finally, the advantages and disadvantages of various receiver structures are discussed.

In this paper we study and analyze multiple-shift algorithms in the context of ultrawideband radio frame timehopping CDMA system (UWB-FTH-CDMA). In our analysis we consider major sources of noise, namely multiaccess interference and the additive white Gaussian noise. For multiaccess interference we consider a model in which mutual interference due to each user is based on frame asynchronous but half-chip synchronous. Since simple serial-search is a special case of the multiple-shift algorithm, we can analyze the advantage of multiple-shift algorithm. It is shown that multiple-shift algorithm is superior than simple serial-search algorithm in reducing the required average acquisition time by the square root of average acquisition time of the simple serial-search algorithm.

Populasi dari penelitian ini adalah masyarakat Kelurahan Titi Rante Pasar 1 Padang Bulan Medan sedangkan jumlah sampel adalah 100 responden yang diperoleh dari teknik penarikan Sampel. Sementara sampel ditentukan dengan dua cara yaitu purposive sampling yakni pernah membaca Harian Andalas yang dilanjutkan dengan accidental random sampling. Peneliti menemukan bahwa persepsi masyarakat masih sangat rendah tentang iklan produk/jasa Harian Andalas. Hanya sedikit responden yang mempersepsi Iklan Harian Andalas untuk menambah wawasan, menghibur diri atau mengusir rasa bosan. BAB I PENDAHULUAN 1.1 Latar Belakang Masalah Kemajuan teknologi berdampak pada konsumsi media massa yang semakin mudah. Hampir setiap hari, kita diterpa oleh tayangan iklan, baik itu di media elektronik (televisi, radio) maupun di media cetak (surat kabar, majalah, tabloid, dsb). Pertumbuhan media massa semakin beragam bentuknya dan mengarah pada spesialisasinya. Spesialisasi isi media tidak terjadi secara alamiah. Media massa berlombalomba untuk memenuhi kebutuhan pembacanya. Kebutuhan masyarakat akan informasi yang cepat saat ini, dimanfaatkan oleh berbagai media massa dalam perannya menyampaikan informasi, edukasi, opini, dan ilmu pengetahuan kepada para pembacanya. Pemenuhan kebutuhan khalayak tersebut, media massa umumnya selalu aktif dalam memproduksi informasi yang cepat, hangat dan orisinil. Pertumbuhan industri media mengarah ke situsai kompetisi yang semakin ketat, yang tidak diimbangi dengan kecepatan perluasan pasar yang ada. Iklan telah menjadi suatu sarana informasi bagi konsumen atau khalayak dalam upaya untuk memperoleh informasi tentang suatu produk atau jasa. Iklan juga telah banyak digunakan oleh banyak perusahaan sebagai sarana untuk memasarkan produk atau jasa yang ditawarkan kepada khalayak. Salah satu media iklan yang banyak kita jumpai dalam kehidupan sehari -hari adalah pada media cetak. Media ini terdiri dari lembaran dengan sejumlah kata-kata, gambar, atau foto, dalam tata warna dan halaman putih, dan fungsi utama media cetak adalah memberi informasi dan menghibur. Media cetak adalah suatu dokumen atas segala hal yang dikatakan orang lain dan rekaman peristiwa yang ditangkap oleh sang jurnalis dan diubah dalam bentuk kata-kata, gambar, foto, dan sebagainya. Iklan dalam media massa cetak, dijadikan produsen sebagai media pemasaran. Komunikasi pemasaran memegang peranan yang sangat penting bagi pemasar. Tanpa komunikasi, konsumen maupun masyarakat secara keseluruhan tidak akan mengetahui keberadaan produk di pasar. Simbiosis mutualisme antara produsen dengan media massa selalu terjadi. Produsen memerlukan media massa untuk memasarkan produknya, sementara media massa memerlukan pengiklan yang memasarkan produk untuk kelangsungan surat kabar. Mmedia cetak terbagi 4 varian yaitu surat kabar, majalah,tabloid, dan buletin. Surat kabar merupakan salah satu media penyampai pesan yang mempunyai daya jangkau luas dan massal. Surat kabar berfungsi sebagai penyampai berita kepada pembacanya. Setelah reformasi 1998, banyak sekali bermunculan media cetak yang dikategorikan sebagai surat kabar dan tabloid.

DVB-T technology has traditionally been used as an access network, providing digital TV programs along with IP based multimedia services to single end users. This paper presents an additional usage of DVB-T as a backbone for the interconnection of Local Area Networks, scattered all over the DVB-T coverage area.

Clustering has been proven to be a promising approach for mimicking the operation of the fixed infrastructure and managing the resources in multi-hop networks. In order to achieve good performance, the formation and maintenance procedure of clusters should operate with minimum overhead, allowing mobile nodes to join and leave without perturbing the membership of the cluster and preserving current cluster structure as much as possible. In this paper, we propose a Flexible Weight Based Clustering Algorithm (FWCA) in Mobile Ad hoc Networks. The goals are yielding low number of clusters, maintaining stable clusters, minimizing the number of invocations for the algorithm and maximizing lifetime of mobile nodes in the system. Through simulations we have compared the performance of our algorithm with that of WCA in terms of the number of clusters formed, number of re-affiliations, number of states transitions on each clusterhead and number of clusterheads changes. The results demonstrate the superior performance of the proposed algorithm.

The process of communication jamming can be modeled as a two-person zero-sum noncooperative dynamic game played between a communicator (a transmitter-receiver pair) and a jammer. We consider a one-way time-slotted packet radio communication link in the presence of a jammer, where the data rate is fixed and 1) in each slot, the communicator and jammer choose their respective power levels in a random fashion from a zero and a positive value; 2) both players are subject to temporal energy constraints which account for protection of the communicating and jamming transmitters from overheating. The payoff function is the time average of the mean payoff per slot. The game is solved for certain ranges of the players' transmitter parameters. Structures of steady-state solutions to the game are also investigated. The general behavior of the players' strategies and payoff increment is found to depend on a parameter related to the payoff matrix, which we call the payoff parameter, and the transmitters' parameters. When the payoff parameter is lower than a threshold, the optimal steady-state strategies are mixed and the payoff increment constant over time, whereas when it is greater than the threshold, the strategies are pure, and the payoff increment exhibits oscillatory behavior.

Proper channel selection is essential to exploit the benefits of multi-channel systems by distributing conflicting transmissions across non-interfering channels. Critical to channel selection is the channel quality metric. We propose a busy time ratio (BI'R) metric that captures channel contention and user traffic load under a variety of network dynamics. We also propose a distributed collaborative sensing scheme to reduce sensing overhead and energy consumptions. The proposed algorithms can be implemented using conventional 802.11 hardware with single radio interface. The proposed metric can be integrated with routing and channel selection. Experimental results show that the proposed scheme significantly outperforms the existing channel selection methods.

In this paper, we present an analytical model as well as a practical mechanism to detect denial of service (DoS) attacks on secondary users in dynamic spectrum access (DSA) networks. In particular, we analyze primary user emulation attacks (PUEA) in cognitive radio networks without using any location information and therefore can do away with any dedicated sensor network. To the best of our knowledge, there are no studies available that detect PUEA using analytical models. We present an analysis using Fenton's approximation and Wald's sequential probability ratio test (WSPRT) to detect PUEA. Simulation results demonstrate that it is possible to keep the probability of missing the primary below a desired threshold while at the same time keeping the probability of successful PUEA low.

The paper presents theoretical and experimental investigations of the spectra of fractal comb-structured signals for different values of their coefficient of generation, as well as analyzes autocorrelation characteristics and phase portraits depending on the coefficient of generation. It is established that signal base increases with increasing fractal order and with decreasing coefficient of generation.

Nonlinear distortion of the radio-over-fiber (ROF) link and, multipath dispersion of the wireless link are the two major factors that limit the performance of a fiber based wireless system. This is especially true when the radio frequency is only a few GHz. The fact that both of these impairing factors are generally unknown, makes any equalization effort very difficult. In this paper, an algorithm that estimates both the nonlinear transfer function of the ROF link plus the impulse response of the wireless channel is described. Correlation properties of pseudo noise (PN) sequences are used for this estimation. This eases the implementation because, PN sequences are widely used in spread spectrum systems and their properties are well understood. An efficient, Vandermonde matrix approach is used to separate the Volterra kernels of the fiber-wireless channel which, eliminates the computation of higher order correlation functions.

Pertanian global saat ini berada di persimpangan jalan yang kritis. Di satu sisi, kebutuhan untuk meningkatkan produktivitas pangan demi memenuhi kebutuhan populasi manusia yang terus bertumbuh menjadi prioritas utama. Di sisi lain, cara-cara konvensional yang digunakan untuk mencapai target tersebut telah membawa konsekuensi ekologis yang berat. Penggunaan input kimia yang intensif selama lebih dari setengah abad terakhir telah menyebabkan fenomena yang dikenal sebagai "kelelahan tanah" (soil fatigue). Tanah bukan lagi dianggap sebagai organisme hidup yang dinamis, melainkan sekadar media fisik tempat tanaman berdiri yang terus-menerus dipaksa untuk berproduksi melalui suntikan pupuk sintetis

The aim of the present paper is to increase the reliability of a Kalman filter-based DS-SS receiver by considering in the state space models the multipath coefficients and associated delays. The objective being to operate at very low SNRs in shallow water (to achieve furtive transmissions) and with the need of a limited computational cost, the implementation relies on the Unscented Kalman Filter, which is known to be more robust than the popular Extended Kalman Filter. The proposed receiver schemes are discussed and compared using experimental data.

Computationally inexpensive algorithm for detecting of dispersed transients has been developed using Cumulative Sums (CUSUM) scheme for detecting abrupt changes in statistical characteristics of the signal. The efficiency of the algorithm is demonstrated on pulsar PSR J0835–4510.

The lack of available spectrum for wireless communications is a threat to the successful deployment of applications designed for intelligent transportation systems (ITSs). The ITS services should be available to a high number of road users and have a fast response time. The interworking between radio access networks is one way to increase spectrum availability. In particular, the joint operation of the dedicated short-range communication (DSRC) technology and TV white spaces (TVWS) has been proposed to increase the dissemination distance for safety messages in vehicular networking. However, previous works have often assumed that the only restriction on the opportunistic access of TVWS is the presence of a TV transmitter (i.e., the primary user). Other secondary users, such as the popular White-Fi networks to be deployed in TV bands, are omitted from the analysis of opportunistic channel access over TVWS. This is despite several proposals in the literature that use secondary networks...

Summary In this paper, we discuss security problems, with a focus on collaborative attacks, in the Worldwide Interoperability for Microwave Access (WiMAX) scenario. The WiMAX protocol suite, which includes but is not limited to DOCSIS, DES, and AES, consists of a large number of protocols. We present briefly the WiMAX standard and its vulnerabilities. We pinpoint the problems with individual protocols in the WiMAX protocol suite, and discuss collaborative attacks on WiMAX systems. We present several typical WiMAX attack scenarios, including: bringing a large number of attackers to increase their computation power and break WiMAX protocols; assembling a sufficient number of attackers to influence the decision-making of core machines, which includes routing attacks and Sybil attacks; and exploiting implementations that do not conform to the WiMAX specification completely, causing interoperability problems among various protocols, including the ones in typical WiMAX/WiFi/LAN deployment...

Among all the techniques combining multi-carrier modulation and spread spectrum, the multi-carrier code division multiple access (MC-CDMA) system is by far the most widely studied. In this paper, we present the performance of the MC-CDMA system associated with key single-user detection techniques. We are interested in problems related to identification and equalization of mobile radio channels, using the kernel method in Hilbert space with a reproducing kernel, and a linear adaptive algorithm, for MC-CDMA systems. In this context, we tested the efficiency of these algorithms, considering practical frequency selective fading channels, called broadband radio access network (BRAN), standardized for MC-CDMA systems. As far as the equalization problem encountered after channel identification is concerned, we use the orthogonality restoration combination (ORC) and the minimum mean square error (MMSE) equalizer techniques to correct the distortion of the channel. Simulation results demonstrate that the kernel algorithm is efficient for practical channels.

In this paper we study the availability of TV white spaces in Europe. Specifically, we focus on the 470-790 MHz UHF band, which will predominantly remain in use for TV broadcasting after the analog-to-digital switchover and the assignment of the 800 MHz band to licensed services have been completed. The expected number of unused, available TV channels in any location of the eleven countries we studied is 56% when we adopt the statistical channel model of the ITU-R. Similarly, a person residing in these countries can expect to enjoy 49% unused TV channels. If, in addition, restrictions apply to the use of adjacent TV channels, these numbers reduce to 25% and 18%, respectively. These figures are significantly smaller than those recently reported for the United States. We also study how these results change when we use the Longley-Rice irregular terrain model instead. We show that while the overall expected availability of white spaces is essentially the same, the local variability of the available spectrum shows significant changes. This underlines the importance of using appropriate system models before making far-reaching conclusions.

While the current generation of peer-to-peer networks share predominantly static files, future peer-to-peer networks will support sharing of files that are modified frequently by their users. In this paper, we present techniques to maintain temporal consistency of replicated files in a peer-to-peer network. We consider the Gnutella P2P network and present techniques for maintaining consistency in Gnutella even when peers containing replicated files dynamically join and leave the network. An experimental evaluation of our techniques shows that: (i) a hybrid approach based on push and pull achieves high fidelity in highly dynamic P2P networks and (ii) the run-time overheads of our techniques are small, making them a practical choice for P2P networks.

While the current generation of peer-to-peer networks share predominantly static files, future peer-to-peer networks will support sharing of files that are modified frequently by their users. In this paper, we present techniques to maintain temporal consistency of replicated files in a peer-to-peer network. We consider the Gnutella P2P network and present techniques for maintaining consistency in Gnutella even when peers containing replicated files dynamically join and leave the network. An experimental evaluation of our techniques shows that: (i) a hybrid approach based on push and pull achieves high fidelity in highly dynamic P2P networks and (ii) the run-time overheads of our techniques are small, making them a practical choice for P2P networks.

Time of arrival (TOA) based localization extracts the positions from the signal delay between senders and receivers in a network and puts high requirements on synchronization, in particular synchronization on the line-of-sight (LOS) signal. We propose an ultrasound based system with pure LOS synchronization and data transmission for sender identification. We use two carriers with 38 respectively 40 kHz in a baseband OFDM scheme and by comparison of the phase shift of both carriers we estimate with the Cramér-Rao lower bound a distance error between sender and receiver of 0.047 mm for a transmission range of 20 m. We transmit 8 bit in 1.5 ms where no intersymbol interferences are expected in most practical scenarios for robust localization.

We introduce a set theoretic framework for quantization index modulation (QIM) watermarking and illustrate its potency by designing a semi-fragile watermark that is both visually adaptive and tolerant to compression. We determine the watermarked image to satisfy the multiple constraints of watermark detectability, imperceptibility and robustness to compression using the method of projections onto convex sets (POCS). Mark embedding is performed through implicit quantization of statistical features, specifically the mean, of randomly selected pixel locations from the image. This is accomplished by defining a detectability constraint set that imposes the quantization constraint. We present experimental results demonstrating the efficacy of the technique in the presence of JPEG compression.

The paper presents a dynamic subchannel assignment algorithm based on orthogonal frequency division multiple access technology operating in the time division duplexing and a new cross-layer design based on a proposed routing protocol jointed with the MAC protocol. The proposed dynamic sub-channel assignment algorithm provides a new interference avoidance mechanism which solves several drawbacks of existing radio resource allocation techniques in wireless networks using OFDMA/TDD, such as the hidden node and exposed node problems, mobility, and cochannels interference in frequency (CCI). Besides, in wireless networks, when a route is established, the radio resource allocation problems may decrease the end to end performance proportionally with the length of each route. The contention at MAC layer may cause the routing protocol at network layer to respond by finding new routes and routing table updates. The proposed routing protocol is jointed with the MAC protocol based on dynamic su...

An open ITS platform combining interactive satellite services with other communication channels is being developed and evaluated in field trials within the SafeTRIP project [1]. Prototyping and in-field validation of a novel waveform for messaging return channel over satellite for land mobile is an important objective of the project. The overall system architecture has recently been standardized by ETSI under the name of S-MIM (S-band Mobile Interactive Multimedia). The messaging protocol, described in the Part 3 of the standard, is based on the Enhanced Spread Spectrum Aloha (E-SSA). Its main asset resides in the low power required at the transmitter, which will allow the reuse of off-the-shelf power amplifiers and low-cost omnidirectional antennas. This paper will present a comprehensive summary of previous E-SSA performance analysis from simulations and the first field trials results using the E-SSA waveform. The presented results have been derived from static and mobile field trials carried out in Germany with fully functional E-SSA modulator and demodulator prototypes and the EUTELSAT10A satellite. Results for the static and mobile performance of the E-SSA demonstrator with an omni-directional antenna under Line-ofsight (LOS) conditions are presented. The measured Packet Error Rates of transmissions via satellite at different terminal power levels confirm the theoretical link budget calculations for single and multiple simultaneously transmitting terminals. The degradation due to fading effects of the transmission channel under mobile conditions has been measured during the trials to approx. 3 dB. The resulting overall required transmitter power in the multi-user scenario of the trials setup has been only -3 dBW to reach a high QoS under mobile conditions. This value confirms the suitability of the E-SSA waveform for interactive mobile services for the mass market.