Showing papers on "Keying published in 2003"

Analysis of transmit-receive diversity in Rayleigh fading

Abstract: We analyze the error performance of a wireless communication system employing transmit-receive diversity in Rayleigh fading. By focusing on the complex Gaussian statistics of the independent and identically distributed entries of the channel matrix, we derive a formula for the characteristic function (c.f.) of the maximum output signal-to-noise ratio. We use this c.f. to obtain a closed-form expression of the symbol error probability (SEP) for coherent binary keying. The method is easily extended to obtain the SEP for the coherent reception of M-ary modulation schemes.

Comparison of return-to-zero differential phase-shift keying and ON-OFF keying in long-haul dispersion managed transmission

Abstract: Performance of return-to-zero (RZ) differential phase-shift keying (DPSK) in ultralong-haul dense wavelength-division-multiplexing (WDM) dispersion managed transmission is studied experimentally and compared with conventional ON-OFF keying (OOK) in a 10-Gb/s system. We show that, while OOK out-performs phase-shift keying in a low spectral efficiency WDM system, the performance of DPSK is comparable to OOK at 10-Gb/s transmission with a spectral efficiency of 0.2. Furthermore, RZ DPSK is advantageous in a high spectral efficiency (e.g., >0.4) system and our numerical simulation results show superior performance of DPSK at 10 Gb/s with 25-GHz channel separation.

Keyboard with reduced keying ambiguity

Abstract: When an array of proximity sensors is used as a keyboard, it can provide an ambiguous output if a user's finger overlaps several keys or if liquid is spilled on the keyboard This ambiguity is reduced by an iterative method that repeatedly measures a detected signal strength associated with each key, compares all the measured signal strengths to find a maximum, determines that the key having the maximum signal strength is the unique user-selected key and then suppresses or ignores signals from all other keys as long as the signal from the selected key remains above some nominal threshold value

A comparative study of DPSK and OOK WDM transmission over transoceanic distances and their performance degradations due to nonlinear phase noise

Abstract: We have compared experimentally the transmission performance of return-to-zero differential phase-shift keying (RZ-DPSK) with RZ-ON-OFF keying (OOK), nonreturn-to-zero differential phase-shift keying (NRZ-DPSK), and NRZ-OOK for 100/spl times/10-Gb/s transmission with a spectral efficiency of 0.22 b/s/Hz over transoceanic distances. The Q degradation of the RZ-DPSK after transmission over 9180 km was 3 dB greater than that of RZ-OOK. The experimental results clearly showed the major cause of degradation for DPSK is not cross-phase modulation but self-phase modulation. The calculated nonlinear phase noise, i.e., the Gordon-Mollenauer effect, agreed with the experimental results. A distributed-Raman-amplifier assisted erbium-doped-fiber-amplified transmission line acted well in reducing the nonlinear phase noise.

Depth keying

Abstract: We present a new solution to the known problem of video keying in a natural environment. We segment foreground objects from background objects using their relative distance from the camera, which makes it possible to do away with the use of color for keying. To do so, we developed and built a novel depth video camera, capable of producing RGB and D signals, where D stands for the distance to each pixel. The new RGBD camera enables the creation of a whole new gallery of effects and applications such as multi-layer background substitutions. This new modality makes the production of real time mixed reality video possible, as well as post- production manipulation of recorded video. We address the problem of color spill – in which the color of the foreground object is mixed, along its boundary, with the background color. This problem prevents an accurate separation of the foreground object from its background, and it is most visible when compositing the foreground objects to a new background. Most existing techniques are limited to the use of a constant background color. We offer a novel general approach to the problem with enabling the use of the natural background, based upon the D channel generated by the camera.

Rate-diversity tradeoff of space-time codes with fixed alphabet and optimal constructions for PSK modulation

Abstract: We show that for any (Q/spl times/M) space-time code S having a fixed, finite signal constellation, there is a tradeoff between the transmission rate R and the transmit diversity gain /spl nu/ achieved by the code. The tradeoff is characterized by R/spl les/Q-/spl nu/+1, where Q is the number of transmit antennas. When either binary phase-shift keying (BPSK) or quaternary phase-shift keying (QPSK) is used as the signal constellation, a systematic construction is presented to achieve the maximum possible rate for every possible value of transmit diversity gain.

Generation and transmission of millimeter-wave data-modulated optical signals using an optical injection phase-lock loop

Abstract: Generation and transmission of millimeter-wave data-modulated optical signals is presented using an optical injection phase-lock loop (OIPLL). Millimeter-wave signal generation is demonstrated with wide locking range, 30-GHz low phase noise level, -93 dBc/Hz, and a wide frequency tuning range, 4-60 GHz generation demonstrated using optical injection locking only, verified by using OIPLL in the 26-40 GHz range. The OIPLL is also used to transmit error-free 140-Mb/s amplitude shift keying and 68-Mb/s differential phase-shift keying (DPSK) modulated millimeter-wave signals over up to 65 km of uncompensated standard singlemode fiber. The DPSK system uses reference frequency modulation, eliminating the need for optical amplification.

Optical wireless communications: system model, capacity and coding

Abstract: This work is motivated by the need to understand the ultimate capacity of outdoor long-distance optical wireless communication with intensity modulation and direct detection. The channel under weak atmospheric turbulence is modeled as a stationary ergodic channel with lognormal intensity fading, where signals experience asymmetric statistics due to on-off keying signaling. Ergodic channel capacity with several different values of channel parameter /spl sigma/ and outage probabilities are computed to provide an information-theoretic view of the channel. Turbo codes matched to the channel are also investigated to shed insight into how much can be achieved with state-of-the-art coding schemes. It is shown that fixed rate turbo codes can perform close to the capacity when turbulence is weak, and that variable rate adaptive coding is necessary to bridge the gap when turbulence gets strong.

M-ary amplitude shift keying OFDM system

Abstract: Coherent M-ary amplitude-shift keying (MASK) is proposed for use in orthogonal frequency-division multiplexing (OFDM) systems. The frequency separation between subcarriers is only 1/2T instead of 1/T. With a slightly wider bandwidth, an /spl radic/M-ary ASK OFDM can achieve the same bit-error rate (BER) of M-ary quadrature amplitude modulation (QAM) OFDM and a better BER than that of M-ary phase-shift keying (MPSK) OFDM. The /spl radic/M-ary ASK OFDM has the same peak-to-average-power ratio as that of the M-ary QAM OFDM. The MASK OFDM can be implemented digitally and efficiently by fast cosine transform and demodulated by inverse fast cosine transform. Comparisons show that implementation complexity is reduced for additive white Gaussian noise channels with the use of the new scheme.

Impact of filtering on RZ-DPSK reception

Abstract: We discuss the influence of optical and electrical filtering on the performance of beat-noise limited balanced and single-ended direct detection of return-to-zero differential phase-shift keying (DPSK). Our simulations, supported by 40-Gb/s measurements, show that balanced DPSK detection outperforms both its single-ended equivalent and ON-OFF keying by /spl sim/2.7 dB, with higher gains at narrower optical filter bandwidths.

STOLAS: switching technologies for optically labeled signals

Abstract: GMPLS-based labeled optical burst switching (LOBS) networks are being considered as the next-generation optical Internet. GMPLS includes wavelength switching next to label and fiber (space) switching. We present a new concept of optically labeling bursts of packets suitable for LOBS networks supported by GMPLS. It is based on angle modulation, which enables control information to modulate the phase or frequency of the optical carrier, while payload data are transmitted via intensity modulation (IM). In particular, the optical label is orthogonally modulated, with respect to the payload, using either frequency shift keying or differential phase shift keying. We present a performance analysis of the modulation schemes by means of simulations where the influence of the payload IM extinction ratio and laser linewidth are investigated. In addition, the transmission performance of an IM/FSK combined modulated signal is experimentally validated at 10 Gb/s, demonstrating at the same time an FSK label swapping operation. Finally, a suitable optical label-controlled switch design is proposed that takes advantage of these novel labeling techniques, and efficiently combines widely tunable, fast switching lasers and SOA-MZI wavelength converters with an arrayed waveguide grating router.

Achievable information rate for outdoor free space optical communication with intensity modulation and direct detection

Abstract: This work investigates the achievable information rate with the state-of-the-art turbo coding and intensity modulation/direct detection for outdoor long-distance free-space optic (FSO) communications. The channel under weak atmospheric turbulence is modeled as a log-normal intensity fading channel where on-off keying makes it look asymmetric. While no effort is made to spectrally match the code to the asymmetry of the channel, the decoding strategy is optimally adjusted to match to the channel response. In addition to fixed rate turbo coding, a family of variable rate turbo codes are constructed and discussed. Shannon capacity is also briefly visited to denote the theoretic limit. It is shown that under low turbulence a single long turbo code is sufficient to get within 1 dB from the capacity, but when the turbulence gets strong, adaptive coding is necessary to close the gap. We expect these results to be useful for current and immediate future systems.

Spectral efficiency of coded phase-shift keying for fiber-optic communication

Abstract: Several optical modulation and detection schemes are compared by computing their spectral efficiencies over additive white Gaussian noise channels. The bandwidth savings of differential quadrature phase-shift keying (D-QPSK) over both direct-detection on-off keying and differential binary phase-shift keying suggest that D-QPSK can improve the reach and efficiency of wavelength-division multiplexing systems. To test the theory, Reed-Solomon and low-density parity-check forward error correction codes are designed and evaluated. The codes generally behave as expected, except that for D-QPSK the gains are hampered by the differential detector. It is further shown that neither multiple-symbol differential detection nor decision-feedback detection is attractive when using strong codes.

An optical IM/FSK coding technique for the implementation of a label-controlled arrayed waveguide packet router

Abstract: In this paper, we present a new concept of optical packet/burst switching suitable for generalized multiprotocol label switched (GMPLS)-based optical networks. In such networks, optical labeled switched paths are being established in a similar way as label-switched paths in MPLS. We use a wavelength label as well as an orthogonally modulated label, with respect to the payload modulation format, and which is encoded using either frequency-shift keying (FSK) or differential phase-shift keying (DPSK). Wavelength is used for switching in the node, whereas the orthogonal label defines the label-switched path. We present both simulation and experimental results to assess transmission performance of the proposed combined modulation scheme. In addition, we propose a suitable optical node architecture that can take advantage of this stacked label concept. Toward this, we use widely tunable wavelength converters to efficiently route IM/FSK (or IM/DPSK) optically labeled packets in an arrayed-waveguide grating (AWG)-based node structure. We present performance simulation results in terms of packet loss ratio and internal block probability. Internal blocking is an inherent problem of AWG optical routers, and a specific wavelength assignment algorithm has been developed to minimize it. Finally, the feasibility of IM/FSK transmission is experimentally demonstrated over an 88-km single-mode fiber span, and novel aspects of FSK generation and detection techniques are presented.

Energy efficient source coding and modulation for wireless applications

Abstract: A simple and energy efficient source coded on/off keying modulation and near optimal error detection scheme for wireless applications is presented in this paper. Many low-power battery operated radio systems, especially for microsensor applications, has a need for saving power both at the system level and circuit level implementation. Our main objective in this paper is to come up with energy efficient coded modulation scheme that consumes comparatively less power both at system and circuit level. A simple on/off keying (OOK) digital modulation scheme is used for this purpose. The basic idea of minimum energy coding (ME-coding) for source with known statistics (probabilities of occurrence of symbols) is obtained from [A.C. Erin and H.H. Asada, Dec. 1999]. In ME-coding scheme, source bits are mapped to constant length codes (ME-codes) which has less number of high-bits in it. Since the OOK transmitter consumes energy only when transmitting a high bit, mapping to ME-codes reduces the total energy consumed in RF transmitter. In this paper, we have come up with ME-coding scheme for sources with unknown statistics and we further propose a new method of code-by-code detection that can detect and correct certain errors in the codeword received. The inferior performance of OOK when compared to other simple modulation schemes is overcome by ME-coding. A total of about 6 dB improvement in signal-to-noise ratio (SNR) per bit is observed when a 3-bit message symbol is mapped to a 7-bit ME-code. It also performs 3 dB better than a Hamming (7,4)-coded BPSK.

Method of determining training signal in OFDM, and apparatus and method for receiving OFDM signal using the training signal

Abstract: A method of determining a training signal so as to facilitate acquisition of symbol sync, frequency offset estimation, and channel estimation in an orthogonal frequency division multiplexing (OFDM) system, and an apparatus and method for receiving a baseband OFDM signal using the training signal are provided. The method of determining the training signal, which is transmitted from an OFDM transmitter to an OFDM receiver using N subcarriers in order to allow the OFDM receiver to perform symbol synchronization, frequency synchronization, and channel estimation in the OFDM system, includes determining a first training symbol by setting odd-numbered subcarriers to 0 in a frequency domain, obtaining even-numbered subcarriers using M-ary phase-shift keying (M-PSK), and performing differential modulation so that a change in the phase difference between remote two subcarriers is constant; and determining a second training symbol by setting even-numbered subcarriers to 0 in the frequency domain, obtaining odd-numbered subcarriers using M-PSK, and performing differential modulation so that a change in the phase difference between remote two subcarriers is constant. By performing all of symbol timing recovery, frequency offset estimation, and channel estimation using the training signal determined as described above, time taken for frequency offset estimation can be reduced, hardware complexity can be decreased, a frequency acquisition range can be expanded up to ½ of the entire bandwidth, and influence of a multi-path channel can be counterbalanced.

Performance degradation of phase-modulated systems due to nonlinear phase noise

Abstract: The error probability is calculated for phase-modulated systems with nonlinear phase noise. Using the assumption that the phase of amplifier noise and nonlinear phase noise are independent of each other, the error probability and penalty are calculated for both phase-shift keying (PSK) and differential phase-shift keying (DPSK) systems. The mean nonlinear phase shift must be less than about 1.00 and 0.63 rad for a penalty less than 1 dB for PSK and DPSK systems, respectively.

A GFSK demodulator for low-IF Bluetooth receiver

Abstract: An efficient mixed-mode Gaussian frequency-shift keying (GFSK) demodulator with a frequency offset cancellation circuit is presented. The structure is suitable for a low-IF Bluetooth receiver and can also be applied to other receivers involving continuous phase shift keying (CPSK) signals. The demodulator implementation is robust to tolerate process variations without requiring calibration. It can also track and cancel the time-varying local oscillator frequency offset between transmitter and receiver during the entire reception period. The chip was fabricated in CMOS 0.35-/spl mu/m digital process; it consumes 3 mA from a 3-V power supply and occupies 0.7 mm/sup 2/ of silicon area. A 16.2-dB input signal-to-noise ratio is obtained to achieve 0.1% bit-error rate as specified in Bluetooth specs. The co-channel interference rejection ratio is about 11 dB. Theoretical and experimental results are in good agreement.

Demodulators for a zero-IF Bluetooth receiver

Abstract: This paper presents low-complexity detectors for a zero-IF Bluetooth receiver based on a simple phase-domain analog-to-digital converter. Measurements and simulations prove that the detectors' sensitivity lies close to an ideal coherent Gaussian frequency-shift keying (GFSK) detector.

Spread spectrum techniques for indoor wireless IR communications

Abstract: Multipath dispersion and fluorescent light interference are two major problems in indoor wireless infrared communications systems. Multipath dispersion introduces intersymbol interference at data rates above 10 Mb/s, while fluorescent light induces severe narrowband interference to baseband modulation schemes commonly used such as OOK and PPM. This article reviews the research into the application of direct sequence spread spectrum techniques to ameliorate these key channel impairments without having to resort to complex signal Processing techniques. The inherent properties of a spreading sequence are exploited in order to combat the ISI and narrowband interference. In addition, to reducing the impact of these impairments, the DSSS modulation schemes have strived to be bandwidth-efficient and simple to implement. Three main DSSS waveform techniques have been developed and investigated. These are sequence inverse keying, complementary sequence inverse keying, and M-ary biorthogonal keying (MBOK). The operations of the three systems are explained; their performances were evaluated through simulations and experiments for a number of system parameters, including spreading sequence type and length. By comparison with OOK, our results show that SIK, CSIK, and MBOK are effective against multipath dispersion and fluorescent light interference because the penalties incurred on the DSSS schemes are between 0-7 dB, while the penalty on OOK in the same environment is more than 17 dB. The DSSS solution for IR wireless transmission demonstrates that a transmission waveform can be designed to remove the key channel impairments in a wireless IR system.

End-to-end protection of media stream encryption keys for voice-over-ip systems

Abstract: The present invention reduces the exposure of keying material to intermediary devices in a communication channel between first and second servers. In one embodiment(100), a second server receives a first half of media stream keys from a first server. The second server uses a Kerberos-based Application Request and tickets to communicate the second half of the media stream keys to the first server. Using this approach, the exposure of the media stream keys is reduced to only the servers.

Reconfigurable multilevel phase-shift keying encoder-decoder for all-optical networks

Abstract: We demonstrate the application of a uniform Bragg grating as a dynamically reconfigurable phase encoder-decoder for optical systems. Precise discrete phase modulation between chips is obtained simply by heating segments along the grating with fine resistive wires. Its reliability to generate and recognize various phase code sequences is demonstrated in a 16-chip 20-Gchip/s quaternary phase-shift keying coherent optical code-division multiple access experiment. The bit-error-rate response is also included to highlight its performance.

Multiple-bit differential detection of offset QPSK

Abstract: Analogous to multiple-symbol differential detection of quadrature phase-shift keying (QPSK), a multiple-bit differential detection scheme is described for offset QPSK that also exhibits continuous improvement in performance with increasing observation interval. Being derived from maximum-likelihood considerations together with the representation of differentially encoded offset QPSK as a continuous phase modulation, the proposed scheme is purported to be the most power-efficient scheme for such a modulation and detection method.

Performance of Manchester-coded payload in an optical FSK labeling scheme

Abstract: The modulation crosstalk between combined frequency-shift keying (FSK) and intensity modulation (IM) in an optical label-switching network is analyzed both theoretically and experimentally. A comparison between the performance of nonreturn-to-zero (NRZ) and Manchester-coded payload is made. It is shown that Manchester coding of the payload helps to suppress the crosstalk introduced into the optical FSK label, thus achieving better network performance than NRZ coding.

Upgraded Optical Communication System with Increased Transmission Capacity and Method

Abstract: A method for upgrading a wavelength division multiplex (WDM) optical communication system includes replacing an installed transmitter operable to transmit a data stream at a defined bit rate with a return-to-zero M-ary phased shift keying (RZ-mPSK) transmitter operable to transmit the data stream at the defined bit rate and at least one other data stream at the defined bit rate together in an RZ-mPSK signal having a combined bit rate at least double the defined bit rate and a symbol rate equal to the defined bit rate. An installed receiver operable to receive the data stream at the defined bit rate is replaced with an RZ-mPSK receiver operable to recover the data stream at the defined bit rate and the at least one other data stream at the defined bit rate from the RZ-mPSK signal.

Mobile communication device having rotating keypad assembly

Abstract: A mobile communication device comprises a housing having a keypad assembly including one or more arrangements of keys for keying information into the mobile communication device. The keypad assembly may rotate within the housing either about an axis generally perpendicular to the face of the keypad assembly or about an axis generally parallel to the face of the keypad assembly for presenting different arrangements of keys to the user of the mobile communication device.

Encoding device and method and decoding device and method

Abstract: An encoding device in a data transmission/reception system includes a first convolutional encoder that encodes an outer code, an interleaver that permutes input data, a second convolutional encoder that encodes an inner code, and a muti-level modulation mapping circuit that performs signal-point mapping based on eight-phase shift keying. When the encoding device uses the second convolutional encoder having two or more memories, the first convolutional encoder uses, as the outer code, a code with a minimum output distance greater than the maximum input distance at which the minimum-distance inner code is generated.

System and method for optical transmission

Abstract: A system and method for generating multilevel coded optical signals for optical transmission are disclosed. The method comprises driving modulators with synchronous data signals having the same data rate to generate a multilevel optical signal using differential phase shift keying and amplitude shift keying modulation.

M-ary orthagonal coded communications method and system

Abstract: A transmitter (910) encodes and a receiver (920) decodes a signal using M-ary bi orthogonal keying. The transmitter (910) receives a stream of data bits and breaks a number of data bits off the stream to form a bit sequence. The transmitter (910) then chooses a code that corresponds to the bit sequence, and transmits the chosen code. The receiver (920) receives the code and correlates it with all possible codes to generate a plurality of correlation values. It then compares these correlation values to determine which code was sent, and therefore what the received bit sequence is. The codes are mutually orthogonal, and prefereable include a plurality of code words and an equal number of code word inverses. The code may be scrambled by multiplying it with a pseudo-random sequence at the transmitter, and descrambled by multiplying it by the same pseudo-random sequence at the receiver.

A fully digital frequency shift keying demodulator chip for wireless biomedical implants

Abstract: A fully digital frequency shift keying (D-FSK) data transfer protocol and demodulator circuit has been developed with the data-rate to carrier-frequency ratio of up to 67%. Its primary application is in the magnetically coupled wireless systems such as biomedical implants and RFID-tags with high data rates above 1 Mbps. The demodulator circuit extracts the serial data bit stream and a constant-frequency clock from an FSK carrier signal in the 4/spl sim/20 MHz range, which can power the wireless system as well. The circuit occupies 0.29 mm/sup 2/ in the AMI 1.5 /spl mu/m 2M/2P standard CMOS process and has a simulated data-rate of up to 2 Mbps and a measured rate of 200 Kbps while consuming less than 0.4 mW.