Showing papers on "Keying published in 2004"

A wideband frequency-shift keying wireless link for inductively powered biomedical implants

Abstract: A high data-rate frequency-shift keying (FSK) modulation protocol, a wideband inductive link, and three demodulator circuits have been developed with a data-rate-to-carrier-frequency ratio of up to 67%. The primary application of this novel FSK modulation/demodulation technique is to send data to inductively powered wireless biomedical implants at data rates in excess of 1 Mbps, using comparable carrier frequencies. This method can also be used in other applications such as radio-frequency identification tags and contactless smartcards by adding a back telemetry link. The inductive link utilizes a series-parallel inductive-capacitance tank combination on the transmitter side to provide more than 5 MHz of bandwidth. The demodulator circuits detect data bits by directly measuring the duration of each received FSK carrier cycle, as well as derive a constant frequency clock, which is used to sample the data bits. One of the demodulator circuits, digital FSK, occupies 0.29 mm/sup 2/ in the AMI 1.5-/spl mu/m, 2M/2P, standard CMOS process, and consumes 0.38 mW at 5 V. This circuit is simulated up to 4 Mbps, and experimentally tested up to 2.5 Mbps with a bit error rate of 10/sup -5/, while receiving a 5/10-MHz FSK carrier signal. It is also used in a wireless implantable neural microstimulation system.

Differential phase-shift keying for high spectral efficiency optical transmissions

Abstract: Differential phase-shift keying (DPSK) has attracted significant attentions in research and development during the last several years. An overview of DPSK for high spectral efficiency optical transmission is presented in this paper. The advantages of DPSK in terms of receiver sensitivity and tolerance to fiber nonlinearity will be discussed in detail. A simplified method for estimating the performance of phase-shift keying in numerical simulations is explained. Results of experimental and numerical investigations of several phase shift keying formats, including polarization division multiplexing and multilevel encoding, will be reviewed. Finally, methods for further enhancing performance of phase-shift keying in long-haul transmissions, specifically the compensation of nonlinear phase jitter, are presented.

MIKEY: Multimedia Internet KEYing

Abstract: This document describes a key management scheme that can be used for real-time applications (both for peer-to-peer communication and group communication) In particular, its use to support the Secure Real-time Transport Protocol is described in detail Security protocols for real-time multimedia applications have started to appear This has brought forward the need for a key management solution to support these protocols [STANDARDS-TRACK]

Optimal insertion of pilot symbols for transmissions over time-varying flat fading channels

Abstract: Two major training techniques for wireless channels are time-division multiplexed (TDM) training and superimposed training. For the TDM schemes with regular periodic placements (RPPs), the closed-form expression for the steady-state minimum mean square error (MMSE) of the channel estimate is obtained as a function of placement for Gauss-Markov flat fading channels. We then show that among all periodic placements, the single pilot RPP scheme (RPP-1) minimizes the maximum steady-state channel MMSE. For binary phase-shift keying (BPSK) and quadrature phase-shift keying (QPSK) signaling, we further show that the optimal placement that minimizes the maximum uncoded bit error rate (BER) is also RPP-1. We next compare the MMSE and BER performance under the superimposed training scheme with those under the optimal TDM scheme. It is shown that while the RPP-1 scheme performs better at high SNR and for slowly varying channels, the superimposed scheme outperforms RPP-1 in the other regimes. This demonstrates the potential for using superimposed training in relatively fast time-varying environments.

Method and apparatus for content protection in a secure content delivery system

Abstract: A system for secure delivery of on-demand content over broadband access networks utilizes a pair of servers and security mechanisms to prevent client processes from accessing and executing content without authorization. A plurality of encrypted titles are stored on a content server coupled to the network. An access server also coupled to the network contains the network addresses of the titles and various keying and authorization data necessary to decrypt and execute a title. A client application executing on a user's local computer system is required to retrieve the address, keying and authorization data from the access server before retrieving a title from the content server and enabling execution of the title on a user's local computer system.

Error probability minimizing pilots for OFDM with M-PSK modulation over Rayleigh-fading channels

Abstract: Orthogonal frequency division multiplexing (OFDM) with pilot symbol assisted channel estimation is a promising technique for high rate transmissions over wireless frequency-selective fading channels. In this paper, we analyze the symbol error rate (SER) performance of OFDM with M-ary phase-shift keying (M-PSK) modulation over Rayleigh-fading channels, in the presence of channel estimation errors. Both least-squares error (LSE) and minimum mean-square error (MMSE) channel estimators are considered. For prescribed power, our analysis not only yields exact SER formulas, but also quantifies the performance loss due to channel estimation errors. We also optimize the number of pilot symbols, the placement of pilot symbols, and the power allocation between pilot and information symbols, to minimize this loss, and thereby minimize SER. Simulations corroborate our SER performance analysis, and numerical results are presented to illustrate our optimal claims.

Just fast keying: Key agreement in a hostile internet

Abstract: We describe Just Fast Keying (JFK), a new key-exchange protocol, primarily designed for use in the IP security architecture. It is simple, efficient, and secure; we sketch a proof of the latter property. JFK also has a number of novel engineering parameters that permit a variety of tradeoffs, most notably the ability to balance the need for perfect forward secrecy against susceptibility to denial-of-service attacks.

Digital Modulation Techniques

Abstract: First considers the three basic forms of digital modulation: amplitude-shift-keying, frequency-shift keying, and phase-shift keying Compares binary modulation systems, in terms of power efficiency and spectrum efficiency Explains the principle of quadrature modulation used with M-ary PSK Describes three modulation techniques that offer certain advantages for band-limited, nonlinear channels: offset quadrature phase-shift keying, QPSK, and minimum-shift keying Explains how the technique of quadrature partial response increases the bandwidth efficiency of OAM signaling Describes trellis coded modulation as a combination of convolutional coding and digital modulation, and show an example in detail Shows the principles behind orthogonal frequency-division multiplexing (OFDM) Compares digital modulation techniques in terms of error performance, complexity of implementation, and all bandwidth efficiency

An impulse radio asynchronous transceiver for high data rates

Abstract: The purpose of this paper is to provide an operative way of achieving high data rates for impulse radio (IR) transmission based systems. Since applications targeted for ultra wide band (UWB) are liable to be low-cost, we especially focus on simple transceiver design. To that effect, we present an original demodulation scheme adapted to a multi-band ON-OFF keying modulation. From the receiver point of view, we impose relaxed channel estimation constraints and derive suitable signal processing schemes and simple hardware architectures. Indeed, we only consider the benefit from a limited a priori channel knowledge: approximative delay spread and energy level. The associated optimum demodulation turns out to be a non-trivial energetic threshold comparison whose precise theoretical computation admits an analytical solution proving its feasibility. Numerical results are eventually performed for IEEE 802.15.3a channel models and FCC requirements; they obviously demonstrate the potential of these techniques.

All-optical regeneration of differential phase-shift keying signals based on phase-sensitive amplification.

Abstract: All-optical regeneration of differential phase-shift keying signals based on phase-sensitive amplification is described. Nearly ideal phase regeneration can be achieved in the undepleted-pump regime, and simultaneous amplitude and phase regeneration can be realized in the depleted-pump regime.

Keyed fibre optic connector

Abstract: A keying system for providing selective interconnection between a receptacle socket and a connector plug terminating an optic fibre, the connector plug adapted for insertion into the receptacle socket. The keying system comprises a raised boss configured to one of a plurality of predefined boss keying geometries and a cavity configured to one of a plurality of predefined cavity keying geometries. The boss is either in one of the receptacle socket or on a forward end of the connector plug and the cavity is formed in the other of the receptacle socket or the forward end of the connector plug. At least one of the predefined boss keying geometries matches at least one of the predefined cavity keying geometries. When the boss keying geometry matches the cavity keying geometry, the boss can be inserted into the cavity thereby interconnecting the connector plug with the receptacle socket. In this manner correct interconnections between connectors and other connectors or sockets can be insured thereby providing an enhanced level of security.

Equalization strategy for dual-polarization optical transport system

Abstract: A method is provided for an equalization strategy for compensating channel distortions in a dual-polarization optical transport system wherein the received signal includes a complex signal of a first transmitted polarization component and a complex signal of a second transmitted polarization component. In a first step, a blind self-recovery mode used a blind adaptation algorithm in calculating and modifying multiple complex equalizer transfer function coefficients to enable recovery of only the complex signal of the first transmitted polarization component. By recovering only a single polarization component in the first step the degenerate case of recovering only a single transmitted signal at both polarization component outputs of an equalizer is prevented. In a second step, equalization is performed in a training mode for calculating and modifying the multiple complex equalizer transfer function coefficients to enable recovery of the complex signals of the first and second transmitted polarization components. In a third step, equalization is performed in a data directed mode for continuing to calculate and modify the multiple complex equalizer transfer function coefficients to ensure continued recovery of the complex signals of the first and second transmitted polarization components. The method is suited for a digital signal processing implementation in a coherent receiver when a modulation scheme used on a transmitted signal is quadriphase-shift keying (QPSK). In other embodiments, the method can be used with modulation schemes such as binary PSK, M-ary PSK where M>4, or Quadrature Amplitude Modulation (QAM).

Totally blind channel estimation for OFDM on fast varying mobile radio channels

Abstract: A new blind channel estimation scheme for orthogonal frequency division multiplexing systems is proposed based on the maximum likelihood principle. By avoiding the use of second- and higher-order statistics, a very fast convergence rate is achieved. A novel approach is also proposed for resolving the phase ambiguity of the blind channel estimate without the need for any reference symbols. The approach combines different modulation schemes on adjacent subcarriers, such as 3-phase shift keying (PSK) and quarternary PSK (QPSK), to resolve phase ambiguity. Simulations were performed for mobile radio environments with high Doppler frequencies and short-to-medium delay spreads. The achieved performance is comparable to that of pilot-based channel estimation for the case of QPSK-modulation.

Sparse channel estimation with zero tap detection

Abstract: Algorithms for the estimation of a channel whose impulse response is characterized by a large number of negligible tap coefficients are developed and compared. Exploiting this sparsity, the estimation problem is transformed into an equivalent on-off keying detection problem, whose solution gives an indication on the position of the zero taps. The proposed schemes are compared to the standard least squares estimate via simulations in terms of mean square error and bit error rate. A scheme based on sphere decoding appears to give the best performance while maintaining moderate complexity.

An orthogonal space-time coded CPM system with fast decoding for two transmit antennas

Abstract: Trellis-coded space-time (TC-ST) coding for continuous-phase modulation (TC-ST-CPM) was recently proposed by Zhang and Fitz. In this paper, we propose an orthogonal space-time coding for CPM (OST-CPM) systems and two transmit antennas. In the proposed OST-CPM, signals from two transmit antennas at any time t are orthogonal while both of them have continuous phases. Similar to Alamouti's OST coding for phase-shift keying (PSK) and quadrature amplitude modulation (QAM) systems, the newly proposed OST-CPM has a fast decoding algorithm.

Multichannel equalization by decision-directed passive phase conjugation: experimental results

Abstract: An adaptive technique for underwater acoustic communication using passive phase conjugation (PPC) is developed. Multipath channel-parameter identification is accomplished by decision-directed model building and finite-window block-updated least squares computed by LSQR (an iterative linear systems solver). The resulting channel estimates are then used by the PPC processor to generate decisions for use in the next processing block. This architecture effectively accomplishes array equalization with low computation cost in shallow-water environments that exhibit rapidly fluctuating multipath scattering. The performance on shallow-water acoustic communications channels is demonstrated at ranges of 0.9-4.6 km under windy surface conditions and shipping noise, using measured wide-band telemetry data with binary phase-shift keying signaling. The algorithm is evaluated with sparse receiver apertures using subsets of a 14-element array.

WDM transmission at 6-Tbit/s capacity over transatlantic distance, using 42.7-Gb/s differential phase-shift keying without pulse carver

Abstract: We report the transmission of a record 6 Tbit/s capacity over 6,120 km distance, involving channels modulated at 42.7 Gb/s bit-rate with differential phase-shift keying (DPSK). The performance is found similar to DPSK with subsequent pulse carving, namely RZ-DPSK.

A spectrally clean transmitting system for solid-state phased-array radars

Abstract: Navy radar operations are being curtailed in a littoral environment. This is due to two factors: the encroachment of cell phone systems into the naval radar bands; in-band interference from other radars. The spectral width of most pulsed radars is significantly wider than necessary with present modulation schemes. Most radars utilize some form of constant envelope pulse with phase or frequency modulation. This causes the spectrum to broaden to several times the information bandwidth. If both the amplitude and phase of the transmitted signal are allowed to change, a significantly narrower bandwidth can be achieved. The paper presents a method to create waveforms with instantaneous bandwidths of 20 MHz confined within -100 dB. The theoretical spectral results of three popular phase modulation schemes (phase shift keying, minimum phase shift keying and derivative phase shift keying) are compared with the spectrally clean results. In addition, the Chireix out-phasing method is presented as an alternative to generating amplitude and phase modulated waveforms. The Chireix method provides a way of improving the efficiency compared to the conventional class A power amplifier. Preliminary results are shown for a spectrally clean waveform.

Comparison of modulation formats for 42.7-gb/s single-channel transmission through 1980 km of SSMF

Abstract: We experimentally compare nonreturn-to-zero and return-to-zero on-off keying with a number of recently proposed modulation formats for 1980-km 42.7-Gb/s single-channel transmission over standard single-mode fiber. Substantial performance improvements are obtained with the new formats.

Wide-band RF receiver using the "five-port" technology

Abstract: Many experiments have been proposed in order to demonstrate that the "five-port" system performs a homodyne demodulation . The large bandwith of a five-port circuit is its main advantage. However, this kind of system must be calibrated for each frequency in order to carry out the inphase and quadrature demodulation. The subject of this paper is to show a new calibration method. This technique uses the training sequence received at each received burst of data to calibrate the five-port system. A method to synchronize the receiver with the training sequence of each burst is presented. We also study the effect of adjacent channels and cochannel interferer on the calibration. Results on quaternary phase-shift keying demodulation are presented.

Wireless internet access system and method

Abstract: A wireless Internet access system and method supports the transmission and reception of multiple types of traffic between mobile subscriber units and existing networks. A frame structure is used that can support the transmission of multiple types of traffic and adapt to changes in the traffic types needed and the amount of data for a particular traffic type. In addition, data transmission is performed using orthogonal frequency division multiplexing and differential phase shift keying to avoid intersymbol interference. Receiving units in the mobile subscriber units and existing networks include antenna arrays to provide a multipath transmission.

Keying methods and apparatus for inkjet print cartridges and inkjet printers

Abstract: An inkjet printer and inkjet print cartridge are each especially configured for inter-engaging with one another via a plurality of keying features of the cartridge and keying structures of the printer such that loading of a foreign print cartridge into the printer is either not possible or results in the printer being inoperative. Thus, only print cartridges particularly configured and intended to be used in the printer will fit into the printer and enable its operation.

10-Gb/s RZ-DPSK transmitter using a saturated SOA as a power booster and limiting amplifier

Abstract: The performance of a semiconductor optical amplifier (SOA) in the deep saturation regime is studied for single-channel return-to-zero (RZ) and nonreturn-to-zero differential phase-shift keying (DPSK) and on-off keying signals at 10 Gb/s. It is found that saturated SOAs can be used as power boosters and limiting amplifiers for RZ-DPSK transmitters with almost no compromise of performance.

Cascaded all-optical wavelength conversion for RZ-DPSK signal based on four-wave mixing in semiconductor optical amplifier

Abstract: We have demonstrated ten-stage cascaded wavelength conversion together with 800-km transmission for 10-Gb/s return-to-zero differential phase-shift keying (RZ-DPSK) format using four-wave mixing (FWM) in semiconductor optical amplifiers. To the best of our knowledge, this is the first experiment reported on cascade wavelength conversion for RZ-DPSK format, which cannot be realized by methods based on cross-gain modulation and cross-phase modulation using a semiconductor optical amplifier. Compared with wavelength conversion using FWM for conventional on-off keying format, the signal-to-pump ratio for RZ-DPSK format can be increased to higher level to achieve better performance.

Maximal-ratio combining architectures and performance with channel estimation based on a training sequence

Abstract: Maximum-ratio combining (MRC) is a simple and effective combining scheme for adaptive antenna arrays to combat noise, fading, and to a certain degree, cochannel interference. However, it requires estimation of the spatial signature (i.e., the channel gain and phase at each antenna element) of the desired signal across the array. Assuming that this estimate is obtained by correlation using a known training sequence of K symbols embedded in the useful signal, we proceed to develop a fully analytical assessment of the impact of estimation error on the output signal-to-noise ratio (SNR) of the array. The originality of the approach revolves around the derivation of the distribution of the normalized SNR, that is the real SNR normalized to the ideal (i.e., perfect estimation) SNR. The end result is a set of distributions which can potentially reduce or in certain cases eliminate the need for simulation to determine certain design parameters such as array size, training sequence length, etc. These are then applied to find closed-form expressions for the outage probability and the error probability in differential phase-shift keying and quarternary phase-shift keying after training in uncorrelated Rayleigh fading.

Iterative carrier phase recovery suited to turbo-coded systems

Abstract: This paper examines the problem of carrier phase recovery in turbo-coded systems. We introduce a new concept of "a priori probability aided phase estimation", where the extrinsic information (log-likelihood ratio) obtained from turbo decoder is used to aid an iterative phase estimation process, which is based on a maximum-likelihood strategy. The phase estimator operates jointly with the turbo decoding rather than separately prior to the decoder as in traditional approaches. This technique provides reliable phase estimation with variance of estimation errors approaching the Cramer-Rao bound at very low signal-to-noise ratio and allows robust decoding with a wide range of phase errors. This paper addresses its application in turbo-coded binary phase-shift keying and quaternary phase-shift keying systems over the additive white Gaussian noise channel. The bit-error-rate performance is investigated and shows that the performance of this technique is very close to the optimally synchronised system and significantly outperforms the traditional non-data-aided method without using additional pilot symbols.

On the Q factor inaccuracy in the performance analysis of optical direct-detection DPSK systems

Abstract: In this letter, we analyze the validity of the use of the Q parameter evaluation in the study of the bit-error-rate (BER) performance of direct-detection differential phase-shift keying optical systems. We show that the inaccuracy of the estimate of the BER based on the Q factor can be very large.

Virtual studio system

Abstract: A method of providing a visual representation of a scene to a participant in a studio is provided, wherein the studio is arranged to be viewed by a camera to provide a camera image and has at least a portion of a background object arranged to be keyed out of the camera image by a keying process. The method includes obtaining an estimate of the viewpoint of the participant; rendering an image of the scene based on the viewpoint of the participant; and projecting at least a portion of the rendered image onto the background object to provide a projected image portion visible to the participant. The projected image portion is projected so as to be keyed out of the camera image by the keying process.

Blind and semiblind detections of OFDM signals in fading channels

Abstract: This paper considers the problem of blind joint channel estimation and data detection for orthogonal frequency-division multiplexing (OFDM) systems in a fading environment. Employing a regression model for a time-varying channel, we convert the problem into one that finds the data sequence x whose associated least-squares (LS) channel estimate z(x) is closest to the space of some regression curves (surfaces). We apply the branch-and-bound principle to solve the nonlinear integer programming problem associated with finding the curve that fits a subchannel in the LS sense. A recursive formula for fast metric update is obtained by exploiting the intrinsic characteristic of our objective function. The impacts of reordering the data sequence and selective detection are addressed. By employing a preferred order along with a selective detection method, we greatly reduce the detector complexity while giving up little performance loss. Both the complete and the reduced-complexity algorithms can be used for blind and semiblind detections of OFDM signals in a subchannel-by-subchannel manner. To further reduce the complexity and exploit the frequency-domain channel correlation, we suggest a two-stage approach that detects a few selected positions in some subchannels first, and then, treating the detected symbols as pilots, determines the remaining symbols within a properly chosen time-frequency block by a two-dimensional model-based pilot-assisted algorithm. The proposed methods do not require the information of the channel statistics like signal-to-noise ratio or channel correlation function. Performance of differential modulations like differential quaternary phase-shift keying and STAR 16-ary quadrature amplitude modulation are provided. Both blind and semiblind schemes yield satisfactory performance.

Low complexity indoor wireless data links using chirp spread spectrum

Abstract: This dissertation proposes the use of Chirp Spread Spectrum (CSS) modulation for the transfer of high-speed (>10 megabits per second) data in the indoor wireless environment. CSS utilizes the properties of chirp signals to combat the effects of multipath fading. The major advantage CSS has over other spectrum spreading techniques is its analog-only implementation. Two main methods for deploying CSS are described: Binary Orthogonal Keying (BOK), in which chirp signals with different characteristics represent different data symbols, and Direct Modulation (DM), where data is modulated using a conventional non-coherent modulation scheme, and then has its bandwidth spread by the chirp signal. Performance equations for the Gaussian channel are derived for both systems. Several other key system design parameters are identified and explored, including chirp windowing, occupied bandwidth, and quasi-RAKE filter configuration. Computer simulations and prototype measurements show close agreement with the developed theory. Raw bit error rates less than 10−5 at 20 megabits per second are achieved, with a bandwidth of 200 MHz in non line of sight wireless channels over 10 m with less than 2 milli-Watts of transmit power. Techniques for designing SAW chirp filters with both linear and nonlinear time-frequency responses are described, and measurements of a prototype SAW device are presented. Novel methods for enhancing the throughput of a binary CSS system are presented which increase the number of bits per symbol of the modulation CSS signal. Computer simulations show that data rates of 50 megabits per second are achievable for a single channel system using this method.