Showing papers on "Spread spectrum published in 2008"

Spectrum Leasing to Cooperating Secondary Ad Hoc Networks

Abstract: The concept of cognitive radio (or secondary spectrum access) is currently under investigation as a promising paradigm to achieve efficient use of the frequency resource by allowing the coexistence of licensed (primary) and unlicensed (secondary) users in the same bandwidth. According to the property-rights model of cognitive radio, the primary terminals own a given bandwidth and may decide to lease it for a fraction of time to secondary nodes in exchange for appropriate remuneration. In this paper, we propose and analyze an implementation of this framework, whereby a primary link has the possibility to lease the owned spectrum to an ad hoc network of secondary nodes in exchange for cooperation in the form of distributed space-time coding. On one hand, the primary link attempts to maximize its quality of service in terms of either rate or probability of outage, accounting for the possible contribution from cooperation. On the other hand, nodes in the secondary ad hoc network compete among themselves for transmission within the leased time-slot following a distributed power control mechanism. The investigated model is conveniently cast in the framework of Stackelberg games. We consider both a baseline scenario with full channel state information and information-theoretic transmission strategies, and a more practical model with long-term channel state information and randomized distributed space-time coding. Analysis and numerical results show that spectrum leasing based on trading secondary spectrum access for cooperation is a promising framework for cognitive radio.

Joint Design and Separation Principle for Opportunistic Spectrum Access in the Presence of Sensing Errors

Abstract: Opportunistic spectrum access (OSA) that allows secondary users to independently search for and exploit instantaneous spectrum availability is considered. The design objective is to maximize the throughput of a secondary user while limiting the probability of colliding with primary users. Integrated in the joint design are three basic components: a spectrum sensor that identifies spectrum opportunities, a sensing strategy that determines which channels in the spectrum to sense, and an access strategy that decides whether to access based on potentially erroneous sensing outcomes. This joint design is formulated as a constrained partially observable Markov decision process (POMDP), and a separation principle is established. The separation principle reveals the optimality of myopic policies for the design of the spectrum sensor and the access strategy, leading to closed-form optimal solutions. Furthermore, it decouples the design of the sensing strategy from that of the spectrum sensor and the access strategy, and reduces the constrained POMDP to an unconstrained one. Numerical examples are provided to study the tradeoff between sensing time and transmission time, the interaction between the physical layer spectrum sensor and the MAC layer sensing and access strategies, and the robustness of the ensuing design to model mismatch.

Spread Spectrum Systems with Commercial Applications

Abstract: From the Publisher: The first spread spectrum challenge was answered by the original communicator to schedule a time for sending and receiving messages because of heavy "traffic" or the desire to avoid interception. Today, spread spectrum systems are a unique blend of analog and digital technology answering an ever increasing range of military, commercial, and consumer communications, data transmission, message privacy, signal hiding, and position location challenges. For nineteen years telecommunications, electrical, and electronics engineers looking for a thoroughly practical, self-contained guide to this important field have turned here. Now this new edition offers... Complete coverage of the latest commercial applications, including everything from direct sequence versus frequency hopping, operation below ambient noise level, error correction coding, near-far performance, linear signal requirements, and synchronization. A full CDMA guide that features discussion of the number of signals in a bandwidth, frequency division multiplex, time-division multiplex, code division multiple access, receiver sensitivity, multipath rejection, direct sequence, fading rate, and more. A new section on the testing and evaluation of spread spectrum systems, including techniques for monitoring sensitivity, selectivity, jamming margin, synch acquisition, loss of synchronization, S/N ratio versus interference level, process gain, cross correlation, transmitter measurements, and more. Three new appendices covering typical error correction coding integrated circuits; typical integrated circuit frequency synthesizers; and spread spectrum's effect on standard microwave communications links. Continuing the freedom from burdensome mathematical rigor and precedence that made the previous editions of this practical presentation of the technology so popular, the Third Edition is assured of its place as one of the most useful working references for a wide range of engineers.

Jamming-resistant Key Establishment using Uncoordinated Frequency Hopping

Abstract: We consider the following problem: how can two devices that do not share any secrets establish a shared secret key over a wireless radio channel in the presence of a communication jammer? An inherent challenge in solving this problem is that known anti-jamming techniques (e.g., frequency hopping or direct-sequence spread spectrum) which should support device communication during the key establishment require that the devices share a secret spreading key (or code) prior to the start of their communication. This requirement creates a circular dependency between antijamming spread-spectrum communication and key establishment, which has so far not been addressed. In this work, we propose an uncoordinated frequency hopping (UFH) scheme that breaks this dependency and enables key establishment in the presence of a communication jammer. We perform a detailed analysis of our UFH scheme and show its feasibility, both in terms of execution time and resource requirements.

Spread spectrum wireless resonant power delivery

Abstract: Wirelessly delivering electric power to a target device. Operation includes generating a spread spectrum sequence, generating spread spectrum alternating current power based upon the spread spectrum sequence, coupling the spread spectrum alternating current power to a transmitting element for wireless power transmission by a non-radiated magnetic field, dynamically tuning the wireless power transmission according to the spread spectrum sequence, and communicating the spread spectrum sequence to the target device. The spread spectrum sequence may include a frequency hopping sequence and/or a phase hopping sequence. Communicating the spread spectrum sequence to the target device may employ Radio Frequency (RF) communications and be used to exchange a target device identity, target device billing information, target device power receipt level(s), a target device battery charge state, a request for power delivery from the target device, and/or authentication information from the target device.

Synchronized MAC Protocol For Multi-Hop Cognitive Radio Networks

Abstract: Cognitive networks enable efficient sharing of the radio spectrum. Multi-hop cognitive network is a cooperative network in which cognitive users take help of their neighbors to forward data to the destination. Control signals used to enable cooperation communicate through a common control channel (CCC). Such usage introduces conditions like channel saturation which degrades the overall performance of the network. Thus, exchanging control information is a major challenge in cognitive radio networks. This paper proposes an alternative MAC protocol for multi-hop cognitive radio networks in which the use of a CCC is avoided. The scheme is applicable in heterogeneous environments where channels have different bandwidths and frequencies of operation. It inherently provides a solution to issues like CCC saturation problem, Denial of Service attacks (DoS) and multi-channel hidden problem. The proposed protocol is shown to provide better connectivity and higher throughput than a CCC based protocol, especially when the network is congested.

Sets of Optimal Frequency-Hopping Sequences

Abstract: In communication systems, frequency-hopping spread spectrum and direct-sequence spread spectrum are two main spread coding technologies. Frequency-hopping sequences are needed in FH-CDMA systems. In this correspondence, three algebraic constructions of sets of optimal frequency-hopping sequences are presented. The parameters of these sets of frequency-hopping sequences are new and flexible.

Distributed Spectrum Management Algorithms for Multiuser DSL Networks

Abstract: Modern digital subscriber line (DSL) networks suffer from crosstalk among different lines in the same cable bundle. This crosstalk can lead to a major performance degradation. By balancing the transmit power spectra, the impact of crosstalk can be minimized leading to spectacular performance gains. This is referred to as spectrum management. In this paper, a unifying perspective is presented on distributed spectrum management algorithms based on the Karush-Kuhn-Tucker (KKT) conditions. Furthermore, novel distributed algorithms are presented within the same KKT framework. The proposed distributed algorithms consist of local water-filling-like algorithms running in the individual modems, controlled by the spectrum management center. Extensive simulation results show that the proposed algorithms perform very well for several multi-user ADSL and VDSL scenarios.

Cognitive Radio Network setup without a Common Control Channel

Abstract: The concept of cognitive radio networks has introduced a new way of sharing the open spectrum flexibly and efficiently. However, there are several issues that hinder the deployment of such dynamic networks. The common control channel problem is one of such issue. Cognitive radio networks are designed by assuming the availability of a dedicated control channel. In this paper, we identify and discuss the network setup problem as a part of the common control channel problem. Probabilistic and deterministic ways to start the initial communication and setup a cognitive radio network without the need of having a common control channel in both centralized and multi-hop scenarios are suggested. Extensive MATLAB simulations validate the effectiveness of the algorithms.

Performance analysis of direct-sequence spread-spectrum underwater acoustic communications with low signal-to-noise-ratio input signals.

Abstract: Direct-sequence spread-spectrum signals collected from the TREX04 experiment are analyzed to determine the bit-error-rate (BER) as a function of the input signal-to-noise ratio (SNR) for a single receiver. A total of 1160 packets of data are generated by adding ambient noise data collected at sea to the signal data (in postprocessing) to create signals with different input-SNR, some as low as -15 dB. Two methods are analyzed in detail, both using a time-updated channel impulse-response estimate as a (matched) filter to mitigate the multipath-induced interferences. The first method requires an independent estimate of the time-varying channel impulse-response function; the second method uses the channel impulse-response estimated from the previous symbol as the matched filter. The first method yields an average BER <10(-2) for input-SNR as low as -12 dB and the second method yields a similar performance for input-SNR as low as -8 dB. The measured BERs are modeled using the measured signal amplitude fluctuation statistics and processing gain obtained by de-spreading the received signal with the transmitted code sequence. Performance losses caused by imprecise symbol synchronization at low input-SNR, uncertainty in channel estimation, and signal fading are quantitatively modeled and compared with data.

Characterization and modelling of spectrum for dynamic spectrum access with spatial statistics and random fields

Abstract: There is need to develop better models and characterization methods for spectrum usage and radio environments of cognitive radios. Currently different theoretical and simulation based approaches towards enabling dynamic spectrum access would greatly benefit from the possibility to generate synthetic data for testing purposes. Such Radio Environment Maps must statistically exhibit the characteristics of realistic environments. Previous and on-going spectrum measurement campaigns are generating a vast amount of such data. In this paper we provide a partial answer to the spectrum modelling problem by showing how one can characterize and model spectrum maps with spatial statistics and random fields. We present the basic mathematical premises for building models and also through examples outline how one can generate useful statistics from real measurement data.

Array Antenna System and Spread Spectrum Beamformer Method

Abstract: A method for transmitting digital beamformed signals in a transmit array antenna apparatus utilizing a single transceiver with one power amplifier, one up-frequency converter and one digital-to-analog converter for said array transmit antenna apparatus comprising the steps of: generating a first set of direct-sequence spread spectrum codes; generating a plurality of weights, each weight being a beamforming amplitude and phase or delay for each element; generating a direct-sequence spread spectrum multiplexed signal containing such weights while using one of such first-set codes per element; converting such an multiplexed signal to a convenient radio frequency; amplifying and transmitting such a multiplexed radio frequency signal to the elements; generating a second set of direct-sequence spread spectrum codes; extracting a radio frequency signal with direction-bearing weight information at each element while using a subset of codes from the second set; generating a third set of direct-sequence spread spectrum codes at each element; transmitting a signal with array gain beamformed towards a specific direction while using a transmit array apparatus composed of spaced elements, such a transmit beamformed signal being a radio frequency signal, a direct-sequence spread spectrum radio frequency signal containing a subset of codes from the third set, or a sequence of radio frequency pulses that have short duration and high power.

Low probability of detection underwater acoustic communications using direct-sequence spread spectrum.

Abstract: Direct-sequence spread spectrum is used for underwater acoustic communications between nodes, at least one of which is moving. At-sea data show that the phase change due to source motion is significant: The differential phase between two adjacent symbols is often larger than the phase difference between symbols. This poses a challenge to phase-detection based receiver algorithms when the source or receiver is moving. A pair of energy detectors that are insensitive to the phase fluctuations is proposed, whose outputs are used to determine the relationship between adjacent symbols. Good performance is achieved for a signal-to-noise ratio (SNR) as low as -10 dB based on at-sea data. While the method can be applied to signaling using short code sequences, the focus in this paper is on long code sequences for the purpose of achieving a high processing gain (at the expense of a low data rate), so that communications can be carried out at a low input SNR to minimize the probability of detection (P(D)) by an interceptor. P(D) is calculated for a typical shallow water environment as a function of range for several source levels assuming a broadband energy detector with a known signal bandwidth.

Dynamic Spectrum Allocation in Wireless Cognitive Sensor Networks: Improving Fairness and Energy Efficiency

Abstract: This paper considers the centralized spectrum allocations in resource-constrained wireless sensor networks with the following goals: (1) allocate spectrum as fairly as possible, (2) utilize spectrum resource maximally, (3) reflect the priority among sensor data, and (4) reduce spectrum handoff. The problem is formulated into a multi-objective problem, where we propose a new approach to solve it using modified game theory (MGT). In addition, cooperative game theory is adopted to obtain approximated solutions for MGT in reasonable time. The results obtained from numerical experiments show that the proposed algorithm allocates spectrum bands fairly with well observing each sensor's priority and nearly minimal spectrum handoffs.

CDMA-based RFID Systems in Dense Scenarios: Concepts and Challenges

Abstract: Radiofrequency identification (RFID) applications with large tag populations often require the fast identification of the tags present. Conventional RFID systems using framed ALOHA based medium access control algorithms waste bandwidth during the singulation process when tag replies collide on the shared wireless channel. In this paper, we investigate how code division multiplexing techniques can be used to decode tag replies in such collisions. Our analysis focusses on the choice of code set and detector for use in a spread spectrum RFID system. The paper also presents a method to estimate the number of tags in the range of such a spread spectrum RFID system.

Dynamic Jamming Mitigation for Wireless Broadcast Networks

Abstract: Wireless communications are inherently symmetric; that is, it takes an attacker the same amount of power to modulate a signal as it does for a legitimate node to modulate the same signal. As a result, wireless communications are often susceptible to the jamming attack in which the attacker injects a high level of noise into the system. Spread spectrum has long been used to resist jamming attacks in unicast environments, or when the jammer has less information than the other receivers. Recently, we proposed a scheme for broadcast jamming mitigation based on spread spectrum and a binary key tree and showed some improvements over a multiple-unicast system. In this paper, we extend our previous work in five ways. First, we provide a theoretical result that under our scheme, jammers can cause only a limited number of losses. Second, we develop a dynamic tree-remerging scheme that achieves higher power efficiency than previously proposed schemes, and scales to an arbitrary number of receivers without increasing the number of codes in use; in particular, we send each transmission on at most 2j + 1 codes, where j is the number of jammers. Third, we show that our scheme is close to optimal, demonstrating that under certain realistic restrictions, the system cannot escape jamming without using at least j +1 codes. Fourth, we provide a detailed analysis of false alarm rates, showing both experimental and theoretical results. Finally, we perform a more extensive analysis of our system using both a chip-accurate MATLAB simulation and a bit-accurate event-driven simulation in the ns-2 network simulator; these simulations demonstrate that our scheme approaches the best possible performance.

Carrier Frequency Offset Mitigation in Asynchronous Cooperative OFDM Transmissions

Abstract: Carrier frequency offset (CFO) mitigation is critical for orthogonal frequency-division multiplexing (OFDM)-based cooperative transmissions because even small CFO per transmitter may lead to severe performance loss, especially when the number of cooperative transmitters is large. In this paper, we show that cyclic prefix (CP) can be exploited to mitigate or even remove completely the CFO. The mitigation performance increases along with the CP length. In particular, long CP with length proportional to NI, where N is the fast Fourier transform (FFT) block length and I is the number of cooperative transmitters, can guarantee a complete CFO removal. While this comes with a reduction in bandwidth efficiency, the long CP in the proposed scheme is exploited to enhance transmission power efficiency in a way similar to spread-spectrum systems, and thus is different from conventional CP that degrades both bandwidth and power efficiency. An efficient CFO-mitigation algorithm is developed that has complexity at most O(NI 2), or even linear in N approximately in some cases. Implemented as a preprocessing procedure independently from cooperative encoding/decoding details, this algorithm makes the CFO problem effectively transparent to and thus has general applications in OFDM-based transmissions.

Evaluation of WiFi beacon transmissions for wireless based passive radar

Abstract: Wireless transmissions are a potentially powerful and widely available source of transmissions for passive radar detection. In this work we have carried out a detailed study on the use of IEEE 802.11 (WiFi) transmissions in a passive radar system. The WiFi transmission sequence has been found to be complex and dependent on the user environment but is dominated by direct sequence spread spectrum (DSSS) and orthogonal frequency division multiplexing (OFDM) signals. An ambiguity function analysis of the DSSS based WiFi beacon signal has been carried out followed by field measurements using a wireless based passive radar system. Range and Doppler characterization of this system is reported and compared with the theoretical predictions. Detection of moving human targets has been achieved for the first time using 802.11 transmissions. This work shows that this technique has considerable promise for a low cost and widely deployable detection and tracking system.

A 0.5-to-480MHz Self-Referenced CMOS Clock Generator with 90ppm Total Frequency Error and Spread-Spectrum Capability

Abstract: This work demonstrates a self-referenced CMOS LCO, or CMOS harmonic oscillator (CHO), that exhibits 90ppm total frequency error over process, bias and temperature, thus making it suitable for replacing XOs in many applications. Additionally, the clock generator can be configured to produce a number of different output frequencies, has 1/4 of the frequency error of the oscillator in [3] and includes a direct modulation technique enabling SSCG.

Opportunistic spectrum access using Fuzzy Logic for cognitive radio networks

Abstract: Recent studies and measurements have shown that, with the traditional spectrum access approach, the radio spectrum assigned to primary (licensed) users is vastly underutilized. While many spectrum methods have been proposed to use spectrum effectively, the opportunistic spectrum access has become the most viable approach to achieve near-optimal spectrum utilization by allowing secondary (unlicensed) users to sense and access available spectrum opportunistically. Opportunistic spectrum access approach is enabled by cognitive radios which are able to sense the unused spectrum and adapt their operating characteristics to the real-time environment. However, a naive spectrum access for secondary users can make spectrum utilization inefficient and increase interference to adjacent users. In this paper, we propose a novel approach using Fuzzy Logic System (FLS) to control the spectrum access. Three descriptors are used: spectrum utilization efficiency of the secondary user, its degree of mobility, and its distance to the primary user. The linguistic knowledge of spectrum access based on these three descriptors is obtained from a group of network experts. 27 fuzzy rules are set up based on this linguistic knowledge. The output of the FLS provide the possibility of accessing spectrum band for secondary users and the user with the greatest possibility will be assigned the available spectrum band.

Understanding and Improving the Spatial Reuse in Multihop Wireless Networks

Abstract: The importance of spatial reuse in wireless ad hoc networks has been long recognized as a key to improving the network capacity. In this paper, we show that 1) in the case that the achievable channel rate follows the Shannon capacity, spatial reuse depends only on the ratio of the transmit power to the carrier sense threshold and 2) in the case that only a set of discrete data rates are available, as a control knob for sustaining achievable data rates, tuning the transmit power provides more sophisticated rate control over tuning the carrier sense threshold, provided that there is a sufficient number of power levels available. Based on the findings, we then propose a decentralized power and rate control algorithm to enable each node to adjust, based on its signal interference level, its transmit power and data rate. The transmit power is so determined that the transmitter can sustain a high data rate while keeping the adverse interference effect on the other neighboring concurrent transmissions minimal. Simulation results have shown that compared to existing carrier sense threshold tuning algorithms, the proposed power and rate control algorithm yields higher network capacity.

Cognitive Radio Transmission Based on Direct Sequence MC-CDMA

Abstract: In this paper, we propose a cognitive cellular system based on DS MC-CDMA to coexist with a number of narrow-band legacy systems in the same frequency range. If the bandwidth and the frequency location of each narrow-band system are known to this cognitive MC-CDMA, it is possible to mitigate their interfering effect in the cognitive receivers by adaptive transmission. We will develop an algorithm for calculating the adaptive transmission parameters and show that it combats interference in the channel effectively.

Joint Spectrum and Power Allocation for Inter-Cell Spectrum Sharing in Cognitive Radio Networks

Abstract: Cognitive radio (CR) networking achieves high utilization of the scarce spectrum resources without causing any performance degradation to the licensed users. Since the spectrum availability varies over time and space, the infrastructure-based CR networks are required to have a dynamic inter-cell spectrum sharing capability. This allows fair resource allocation as well as capacity maximization and avoids the starvation problems seen in the classical spectrum sharing approaches. In this paper, a joint spectrum and power allocation framework is proposed that addresses these concerns by (i) opportunistically negotiating additional spectrum based on the licensed user activity (exclusive allocation), and (ii) having a share of reserved spectrum for each cell (common use sharing). Our algorithm accounts for the maximum cell capacity, minimizes the interference caused to neighboring cells, and protects the licensed users through a sophisticated power allocation method. Simulation results reveal that the proposed inter-cell spectrum sharing framework achieves better fairness and higher network capacity than the conventional spectrum sharing methods.

A design of energy detector in cognitive radio under noise uncertainty

Abstract: Cognitive radio is proposed as an approach to solve the conflict between the spectrum congestion and under-utilization. Energy detector is the detector most widely used in cognitive radio system due to its generality and low complexity. In this paper, the performance of energy detector under noise uncertainty is studied. The discrete form and continuous form of the noise uncertainty model are proposed. The average detection performances of the energy detector are analyzed under various types of noise uncertainty models, based on which a design of energy detector is put forward. Selecting different statistic decision thresholds will result in different detection performance. According to a prior knowledge about the noise variance distribution, a proper threshold can be selected to improve the detection performance as much as possible under the existence of noise uncertainty.

The Impact of Adjacent Channel Interference in Multi-Radio Systems using IEEE 802.11

Abstract: A promising approach for improving the capacity of Wireless Mesh Networks is by making use of multiple non-overlapping RF channels. Multi-channel protocols have the advantage that several devices can transmit in parallel within a collision domain on distinct channels. When using IEEE 802.11b/g/a most protocol designers assume 3 and 12 non-overlapping channels, respectively. However, this simplified assumption does not hold. We present results from measurements that show that the number of available non-interfering channels depends on the antenna separation, PHY modulation, RF band, traffic pattern and whether single- or multi-radio systems are used. The problem is caused by adjacent channel interference (ACI) where nearby transmitters "bleed over" to other frequencies and either cause spurious carrier sensing or frame corruption. For nearby transceivers, as in the factory defaults of multi-radio devices, this results in at most two non- interfering channels, one within 2.4 GHz and the other within the 5 GHz band. Only if the distance between the antennas is increased, non-interfering channels within the bands themselves become available. Moreover, our comparison of single- and multi- radio systems allows us to isolate ACI from board crosstalk and radiation leakage of which only the multi-radio systems seem to suffer. Finally, we show how a packet-level simulator can be improved to realistically incorporate ACI. With the help of this simulator more confident statements about the performance of various multi-channel protocols can be made.

Robust Modulation Methods and Smart Antennas in Wireless Communications

Abstract: 1. In Pursuit of Bandwidth Efficiencies for Wireless Terrestrial and Satellite Communications. Introduction. 2. Bandwidth-Efficient Modulation Techniques. Introduction. Bandwidth and Power Efficiency Plane. Conclusions. References. 3. Higher Order Modulation Methods. Introduction. Signal State Space Diagrams. Performance Representations. Conclusions. Glossary of Terms. References. 4. Dynamics of Linear and Continuous Phase Modulation Methods in Digital Communications. Introduction. Linear Modulation. Continuous Phase Modulation. Phase Trellises in CPM. GMSK Modulation. Tamed Frequency Modulation (TFM). Signal Orthogonality. Conclusions. References. 5. Error Control Coding. Introduction. Code Families. Code Performance. Block Coding. Convolutional Encoding. Concatenated Coding. Interleaving. Coding Break-through. Conclusions. References. 6. Trellis Coded Modulation (Codulation). Introduction. The Theory. Attributes of Trellis Coded Modulation. Practical Systems. Performance Degraders. Conclusions. Glossary of Terms. References. 7. Spread Spectrum Communication Systems. Introduction. Spread Spectrum Techniques. Code Generation. Codes for Spread Spectrum Multiplexing. Spread Spectrum Interference Analysis. The Multipath Phenomenon. Purely Random or Pseudo-Random- What's the Difference? Conclusions. Glossary of Terms. References. 8. Terrestrial-based Wireless Communications. Introduction. Frequency Bands of Operation. Interference Analysis. Increasing Capacity. Cellular Standards. Personal Communications Service. Conclusions. References. 9. The Butler Matrix. Introduction. Planar Array Beams. Multiple Volumetric Beams. Butler Array Application. Conclusions. References. 10. Sidelobe Cancellers in Smart Antenna Applications. Introduction. Single Interferer Sidelobe Canceller. Multiple Interferers. Conclusions. References. 11. A Look at Switched-Beam Smart Antennas. Introduction. Trunking Efficiency. Smart Antennas. Configurations. Conclusions. References. 12. Deterministic Signals, Random Noise, and Coherent Noise (Pseudo) Combining in an Array Antenna. Introduction. Coherent Signals. Coherent Noise. An Adaptive Array in a Quiescent Signal Field. 13. Adaptive Arrays in Cellular Communications. Introduction. The Theory. Simulation Results. Conclusions. References. 14. Summary Smart Antennas in Cellular Communications. Introduction. Adaptive Array Genre. Where Are Smart Antennas Going? Conclusions. A. Gaussian Low-Pass Filter. B. Scattering Matrix of the Quadrature Hybrid. C. Example of Trunking and Erlang Tables. D. Glossary of Terms. Index. The Author.

Performance of chirp spread spectrum in wireless communication systems

Abstract: This paper analyzes the structure and modem scheme of chirp-BOK system. In additive white Gaussian noise channel, an approach of studying the performance of chirp-BOK is presented and the BER-SNR result is evidently improved compared with traditional BOK. Furthermore, the BER of multi-user chirp-BOK system is discussed.

Multi-Path Propagation Measurements for Vehicular Networks at 5.9 GHz

Abstract: Broadband sounding of the vehicle-to-vehicle channel is reported in suburban, rural, and highway environments. A direct sequence spread spectrum waveform based on zero correlation zone sequences was used with an instantaneous bandwidth of about 40 MHz. Cumulative distribution functions are presented for the maximum excess delay, RMS delay spread, and coherence bandwidth using a threshold of 15 dB below the peak. The highway environment showed the largest median RMS delay spread (about 110 ns), the largest median maximum excess delay (about 600 ns) and the smallest median 90% coherence bandwidth (about 900 kHz). In general, the distributions of these quantities for the suburban environment were narrower than those for the rural and highway environments. This is interpreted in terms of the more restricted range of distances to scattering objects in the suburban environment.

Chaotic Communications, their applications and advantages over traditional methods of communication

Abstract: The discovery of randomness in apparently predictable physical systems have evolved into a new science, the science of chaos. Chaotic systems are unstable and aperiodic, making them naturally harder to identify and to predict. Recently, many researchers have been looking at ways to utilize the characteristics of chaos in communication systems and have actually achieved quite remarkable results. This field of communication is called chaotic communication. Chaotic communication signals are spread spectrum signals, which utilize large bandwidth and have low power spectrum density. In traditional communication systems, the analogue sample functions sent through the channel are weight sums of sinusoid waveforms and are linear. However, in chaotic communication systems, the samples are segments of chaotic waveforms and are nonlinear. This nonlinear, unstable and aperiodic characteristic of chaotic communication has numerous features that make it attractive for communication use. It has wideband characteristic, it is resistant against multi-path fading and it offers a cheaper solution to traditional spread spectrum systems. In chaotic communications, the digital information to be transmitted is placed directly onto a wide-band chaotic signal. This paper provides an overview of chaotic communication, chaotic modulation schemes such as: chaos shift keying (CSK), differential chaos shift keying (DSK), additive chaos modulation (ACM) and multiplicative chaos modulation (MCM). Synchronized chaotic systems and direct chaotic communication are also described in this paper.