Showing papers on "Continuous phase modulation published in 2002"

Postnonlinearity compensation with data-driven phase modulators in phase-shift keying transmission.

Abstract: A novel scheme for postnonlinearity compensation is proposed to reduce the phase jitter in phase-shift keying transmission. A phase modulator is used to modulate the phase of the data pulses in front of the receiver. The magnitude of the phase modulation is proportional to the detected pulse intensity, and the sign is opposite to that of the nonlinear phase shift caused by self-phase modulation. Thus, the nonlinear phase noise induced by amplitude fluctuation and self-phase modulation is partially compensated for. We show by numerical simulations that a differential phase-shift keying dispersion-managed soliton system at 10 Gbits/s with such postnonlinearity compensation can provide greater than 3 dB of improvement in ultralong-haul dense wavelength-division multiplexing transmissions.

Constant envelope multi-carrier modulation

Abstract: A constant envelope multi-carrier modulation scheme is proposed that combines DCT (discrete cosine transform) based multi-carrier modulation and continuous phase modulation (CPM) with the objective of producing a constant envelope waveform. Guard interval and frequency-domain equalization are used to remove ISI on frequency-selective multipath channels. Phase detection and correction is implemented with oversampling. On the AWGN channel, error probability performance is also given and compared with that of BPSK. Simulation results are presented on a multipath fading channel to compare its performance with that of OFDM.

Dual mode phone line networking modem utilizing conventional telephone wiring

Abstract: A networking modem capable of full duplex communication over a telephone line is adapted for use as a component of a computer system. The modem comprises a digital signal processor (DSP) capable of implementing a plurality of digital modulation and demodulation techniques, including pulse position modulation (PPM), quadrature phase shift keying (QPSK), and quadrature amplitude modulation (QAM). The DSP implements a digital phase locked loop (DPLL), including a carrier NCO and a carrier detector to synchronize local demodulation timing to an incoming carrier signal. Available processing options include spectral agility for optimizing channel capacity, symbol shaping to compensate for evolving channel conditions, and echo cancellation. The digital processing provides a flexible, adaptive, programmable, and backward compatible solution to eliminate various problems with prior art systems, including timing inaccuracies, incompatibility with standard modulation techniques, the half duplex limitation, and the susceptibility to noise that increases intersymbol interference and limits throughput.

Multiuser Serially Concatenated Continuous Phase Modulation

Abstract: A multiuser communication system using serially concatenated and randomly interleaved continuous phase modulation (SCCPM) over the additive white Gaussian noise (AWGN) channel is investigated. The users, which may be asynchronous, are allowed to have individual energy levels as well as carrier frequencies and phases. This model incorporates multiple-access signaling similar to direct-sequence code division multiple-access (DS-CDMA), trellis-coded multiple-access (TCMA), and frequency division multiple-access (FDMA) with arbitrary spectral overlap, as well as non-intentional co-channel or adjacent channel interference of the same signaling type. First, the system is analyzed through analytical upper bounds on the average bit error probability for a given user under maximum-likelihood (ML) detection, where the R> average is over the ensemble of systems over all sets of interleavers. It is shown that in a properly designed system, the bit error probability vanishes for infinite interleaver sizes and a sufficiently large channel signal-to-noise ratio (SNR), regardless of the signal correlation between the users. Thus, even with equal modulation, energy levels, and carrier frequencies and phases, the users can be detected adequately provided they employ random interleaving. The second part of the analysis concerns iterative decoding of multiuser SCCPM. A convergence analysis based on EXIT charts is presented, along with decoding threshold estimates. It is observed that in systems with no frequency offset, the performance of ML detection does not always carry over to iterative decoding. On the other hand, for many other systems excellent performance can be obtained both in terms of power efficiency (bit error rate as a function of SNR) and spectral efficiency (bandwidth). In particular, systems are demonstrated with performance within 1 dB of the average-power limited Shannon capacity at 1 bit/s/Hz, and within 2.3 dB at 2 bits/s/Hz.

Dynamic carrier system for parametric arrays

Abstract: A system configured to dynamically adjust the ultrasonic carrier level in a parametric array system in response to changing source signal input levels, and which employs a look-ahead delay strategy to enable optimal modulation of the carrier wave to eliminate constant ultrasonic carrier emission and reduce the ultrasonic carrier emission to what is actually needed to accommodate the db range of the source material, and at the same time, to also minimize noticeable distortion and sound artifacts of a high-power ultrasonic carrier, and/or distortion/artifacts arising from modulation of an ultrasonic carrier to reduce average power output; and thus it realizes advantages of carrier modulation based on source-signal level, while minimizing inherent drawbacks of carrier modulation.

Soft-output demodulator in space-time-coded continuous phase modulation

Abstract: Space-time coding has shown great promise for digital transmission in wireless communication links, especially when the channel response is known at the receiver. Space time coding combined with continuous phase modulation (CPM) can offer better tradeoffs in bandwidth and power efficiency. Because of the memory inherent in CPM, channel estimation is often harder than for linear modulations. We present an adaptive soft algorithm that performs joint channel estimation and data detection for space-time CPM systems. Properly designed pilot symbols are inserted at the very beginning to give good initial estimates of the channels. This soft receiver is further applied to the interleaved space-time CPM system to yield better performance with moderate complexity through iterative processing. Simulation results show that the receiver can often achieve near-coherent performance in quasistatic fading as well as in time-varying fading.

OFDM-CPM signals

Abstract: A class of orthogonal frequency division multiplexing–continuous phase modulation (OFDM-CPM) signals is introduced in which binary data sequence is mapped to complex symbols using the concept of correlated phase states of a CPM signal. Various types of signals are defined as a function of parameter h and pulse duration. An investigation of bit error rate and peak-to-average-power ratio performance of these signals is also presented.

Reduced complexity iterative demodulation and decoding of serial concatenated continuous phase modulation

Abstract: We present a structure for reduced complexity iterative demodulation and decoding of partial response continuous phase modulation (CPM) when serially concatenated with a convolutional code. The proposed receiver uses a single front-end filter and a 2 or 4 state trellis for decoding the inner CPM code. This can yield a significant savings, as the complexity of the optimal demodulator increases exponentially with the length of the CPM frequency pulse. Simulations show that for GMSK with BT = 1/6, the performance penalty for simplified iterative demodulation and decoding is less than 0.25 dB, compared to the receiver which performs optimal demodulation (which requires 32 filters and a 64 state inner trellis).

Apparatus and method for WGIO phase modulation

Abstract: An apparatus and method for WGIO phase modulation are described. In one embodiment, the method includes the receipt of a high-speed data stream, encoded according to an 8b/10b code. Once received, a symbol rate of the data stream is reduced by a predetermined amount. Finally, once the symbol rate is reduced, a square wave carrier is phase modulated, using the reduced data rate data stream to generate a WGIO signal having double side band spectrum distributed either side of the square wave carrier. Accordingly, in one embodiment, a 3GIO signal may be phase modulated in order to fall within a spectrum that is not currently occupied by a wireless protocol, including, for example, Wireless Local Area Network (WLAN), Wireless Wide Area Networks (WWAN), global positioning systems (GPS), or the like in order to prevent interference therebetween.

Detection of linear modulations in the presence of strong phase and frequency instabilities

Abstract: Noncoherent sequence detection algorithms, previously proposed by the authors, have a performance which approaches that of coherent detectors and are robust to phase and frequency instabilities. These schemes exhibit a negligible performance loss in the presence of a frequency offset, provided this offset does not exceed an order of 1% of the signaling frequency. For higher values, the performance rapidly degrades. In this paper, detection schemes are proposed, characterized by high robustness to frequency offsets and capable of tolerating offset values up to 10% of the signaling frequency. More generally, these detection schemes are very robust to rapidly varying phase and frequency instabilities. The general case of coded linear modulations is addressed, with explicit reference to M-ary phase shift keying and quadrature amplitude modulation.

PAPR reduction of OFDM signals using multiamplitude CPM

Abstract: A major drawback with an orthogonal frequency division multiplexing (OFDM) system is its high peak-to-average-power ratio (PAPR). Here, the use of multiamplitude continuous phase modulation (CPM) signals for reducing PAPR is proposed and investigated. In this method, two signal points represent the same information and the one that minimises PAPR is chosen. The concept of partial transmit sequences (PTS) is used to select the best signal points. It is shown through simulations that the proposed scheme reduces the PAPR of 128-carrier OFDM-CPM signals by >4 dB.

Discrimination of the amplitude modulation rate

Abstract: This study examines the amplitude modulation rate discrimination for sinusoidal and noise carriers. It was shown that the discrimination of AM rates is a monotonically growing function of modulation rate. Higher values of the discrimination thresholds were observed for a narrowband carrier. It appears that in the case of a narrowband noise carrier, the spectral range of the noise envelope is similar to that of the modulation rates of the signal (up to 120 Hz). It results in a masking in the modulation rate domain and in a much higher threshold growth than that observed for a wideband noise carrier or a sinusoidal carrier. The results are consistent with the idea of the so-called second stage of filtering acting on the envelope of the acoustic signal. This hypothesis postulates the existence of a so-called modulation filter bank, (MFB), responsible for the frequency selectivity observed in the amplitude modulation rate domain. The existence of the MFB suggests that a certain form of the spectral analysis of any acoustic signal envelope may be performed in the auditory system after initial filtering in the auditory filter bank. A model of the modulation rate discrimination based either on the classical concept of the excitation patterns or on the modulation excitation patterns has not accounted for our experimental data. According to both the models, an increase in the frequency discrimination threshold versus modulation rate should be slower than that measured in the experiment.

Detection of OFDM-CPM signals over multipath channels

Abstract: A class of orthogonal frequency division multiplexing-continuous phase modulation (OFDM-CPM) signals is introduced in which binary data sequence is mapped to complex symbols using the concept of correlated phase states of a CPM signal. Canonical optimum and suboptimum multiple-symbol-observation OFDM-CPM receivers are derived. Multipath channel with AWGN is assumed. The receivers are analyzed for bit-error-rate (BER) performance in terms of highand low-SNR bounds. These bounds are illustrated as a function of parameter h, time delay and attenuation level. It is shown through numerical computation that the OFDM-CPM system outperforms a similar OFDM-PSK system in a two-ray multipath model. Moreover, an OFDM-CPM system gives the best error performance when the parameter h is 0.5 with an observation interval of 2.

Measurement of the modulation efficiency of an optical phase modulator using a self-homodyne receiver

Abstract: The authors describe a self-homodyne technique to measure the modulation efficiency of an optical phase modulator. The phase modulator is driven by a sine wave and the baseband spectrum is measured and analyzed. Combinations of the ratio of harmonics are used to estimate V/sub /spl pi// of a commercially available modulator with a resolution of 0.8%. The method offers simplicity because it uses a single laser, does not require sensitive optical adjustments, and lends itself to the measurement of V/sub /spl pi// as a function of modulation frequency and optical carrier wavelength.

Coded continuous phase modulation with low-complexity noncoherent reception

Abstract: Coded continuous phase modulation based on a feedback-free modulator with noncoherent detection is discussed. Low-complexity receiver processing is achieved by using only two or three linear filters for demodulation and applying noncoherent sequence estimation with reduced-state Viterbi decoding and simple branch metric calculation. Overall, the proposed noncoherent receiver provides significant advantages over previously presented approaches.

Optimum and suboptimum receivers for M-ary CPM signals based upon the Laurent representation

Abstract: This paper involves a method for reduced complexity demodulation of continuous phase modulated (CPM) signals, which is based upon the extended Laurent representation of the nonlinear CPM modulation as a sum of time-offset pulse amplitude modulations. For signaling schemes with a long memory we derive a reduced complexity maximum-likelihood (ML) detector by approximating the CPM signal with a set of optimized pulses. The implementation is done for the non-binary case and for partial response CPM systems. It is demonstrated that, in the context of sequence detection, a remarkable receiver complexity reduction is possible using this method. The performance criteria used in the paper is symbol error probability and comparisons are made with other algorithms.

Techniques for acquiring and tracking MIL-STD-181B signals

Abstract: The paper examines the use of spectral estimation and maximum likelihood estimation techniques in acquiring and tracking current MIL-STD-188-181B UHF SATCOM waveforms Digital signal processing (DSP)-based algorithms are presented that can acquire and track the carrier phase, carrier frequency offset, and symbol timing for the dual-h quaternary continuous phase modulated (CPM) waveforms The algorithms are derived mathematically first, then using computer simulations Performance is presented for various modulation rates, channel conditions, and different signal-to-noise ratio (SNR) levels Several methods are then proposed to enhance the performance of these algorithms without requiring additional computational resources The algorithms are easily configurable for different modulations and data rates, thus making them suitable for implementation in next generation software-defined UHF tactical radios

DFSE equalization of dual-h CPM over UHF MILSATCOM channels

Abstract: To meet the demand for higher data rate MIL-STD-188-181B has added a set of dual-h continuous phase modulation (CPM) waveforms that nearly double the available data rates without requiring additional transmit power. Unfortunately, rates greater than 56 kbit/s are constrained by severe intersymbol interference (ISI) induced by narrow satellite crystal filters. In this paper, we study the application of decision feedback sequence estimation (DFSE) in order to equalize a 64 kbit/s dual-h quaternary full response CPM waveform transmitted over a representative 25 kHz UHF MILSATCOM channel. The performance is evaluated by Monte-Carlo simulation. Results show DFSE equalization offers an effective and computationally manageable approach to higher data rates using legacy waveforms.

A comparison of adaptively equalized pcm/fm, soqpsk, and multi-h cpm in a multipath channel

Abstract: It is widely recognized that telemetry channels, particularly airborne channels, are afflicted by multipath propagation effects. It has also been shown that adaptive equalization can be highly effective in mitigating these effects. However, numerous other factors influence the behavior of adaptive equalization, and the type of modulation employed is certainly one of these factors. This is particularly true on modulations which exhibit different operating bandwidths. In this paper, we will examine the effect multipath and adaptive equalization for three modulation techniques which are either already in use, or have been proposed, for airborne telemetry.

Orthogonal space-time coding for CPM system with fast decoding

Abstract: Trellis-coded space-time (TC-ST) coding for continuous phase modulation (TC-ST-CPM) was recently studied by X. Zhang and M.P. Fitz (see Proc. 38th Annual Allerton Conf. on Commun. Control and Computing, 2000). Similar to TC-ST for PSK and QAM systems, it has good performance but its decoding complexity may be high. We propose an orthogonal space-time coding for CPM (OST-CPM) systems. Similar to S. Alamouti's OST coding for PSK and QAM systems (see IEEE J. Select. Areas Commun., vol.16, no.8, p.1451-8, 1998), the newly proposed OST-CPM has a fast decoding algorithm.

Turbo-detected coded continuous-phase modulation for military UHF satellite communications

Abstract: The joint iterative demodulation and decoding of coded continuous-phase modulation (CPM) has been shown to offer near-optimal performance for constant envelope signalling in additive white Gaussian noise. An in-depth trade study of the parameters for such a system is used to derive the optimal waveform parameters for a variety of channels. In particular, the optimal parameters are selected for the military 25-kHz UHF follow-on (UFO) satellite communications (SATCOM) channel. A set of four waveforms are defined for that application that provide a range of power-efficient and bandwidth-efficient solutions, with data rates from 56 kbps to 80 kbps. Each operates within the typical link margins available for UHF SATCOM and meets typical (MIL-STD-188-181B) adjacent channel interference specifications. The implementation of a prototype modem using commercial off-the-shelf (COTS) hardware is described.

Linear models and capacity bounds for continuous phase modulation

Abstract: We derive upper bounds on the capacity of an additive Gaussian noise channel with continuous phase modulation (CPM). We propose an MMSE approximation to Laurent's (1986) linear decomposition using an arbitrary number of filtered, linearly modulated pulses. Using this linear modulation structure, we derive capacity bounds for both white and colored noise channels with CPM modulation by showing the system is equivalent to a multiple access channel (MAC) with intersymbol interference (ISI). The rate sum capacity of this cooperative MAC is used for the upper bound. Numerical results are presented for a channel using CPM with both white and colored noise. The bounds show a significant gap between a channel using CPM and a channel with unconstrained modulation.

Digital data embedding/detection apparatus based on periodic phase shift

Abstract: When a music signal undergoes sinusoidal phase modulation using a second-order all-pass filter, if the period of modulation is equal to or lower than several hundreds Hz, that modulation is not perceived by a human being. Watermark information is embedded using this phase modulation as a carrier, thus implementing digital watermarking. On the detector, since a model of the all-pass filter used in phase modulation is known, the filter is estimated by ARMA model parameter estimation, and the dynamic characteristics of phase modulation are estimated from its temporal change.

A soft output GMSK demodulator using a 4-filter MLSE for small BT product

Abstract: We consider GMSK for use in frequency division multiple access (FDMA) satellite communication systems where only limited system bandwidth is available. The demodulator employs maximum likelihood sequence estimation (MLSE) of the GMSK signal using a simplified Viterbi processor. For the case of GMSK having a time-bandwidth product of BT=1/4, a two matched filter approximation gives very good performance, while, for BT=1/6, a two filter approximation is very similar to a four filter approximation. For a convolutional code with rate 1/2 and constraint length 7, simulation shows that soft output Viterbi algorithm (SOVA) decoding using a four-filter demodulator for BT=1/6 and BT=1/8, results in a performance improvement of 2.1 dB and 2.3 dB, respectively, in signal-to-noise ratio (SNR), compared to hard decision Viterbi algorithm (HOVA) decoding, at a bit error probability (BEP) of 10/sup -5/. When compared to a BPSK system that employs a similar soft decision decoder, the BEP power penalty for these schemes is 2.3 dB and 4.1 dB respectively. The spectral efficiency, relative the 95% RF power containment bandwidth, is 1.88 bits per sec per Hz (bps/Hz) and 2.1 bps/Hz of bandwidth for BT=1/6 and 1/8 GMSK respectively, and only 0.35 bps/Hz for BPSK. As ratios, the spectral efficiency improvement factor is 5.37 and 6.0 respectively.

Performance of turbo coded continuous phase modulation in fading channels

Abstract: Fading channels impose an intrinsic parametric uncertainty as a threat to reliable communications In the case perfect channel information is present, optimal maximum a posteriori (MAP) algorithms were investigated in the literature This paper focuses on the case of unknown channel information We propose a MAP algorithm which takes the parametric uncertainty of the fading phenomenon into account by marginalizing the related probability distributions over the fading levels The algorithm is applied to a serially concatenated system that employs continuous phase modulation as the inner code and a turbo code as the outer code

Inherent limitations in data-aided time synchronization of continuous phase-modulation signals over time-selective fading channels

Abstract: Time synchronization of continuous phase modulation (CPM) signals over time selective, Rayleigh fading channels is considered. The Cramer-Rao lower bound (CRLB) for this problem is studied for data-aided (DA) synchronization (i.e., known symbol sequence transmission) over a time-selective Rayleigh fading (i.e., Gaussian multiplicative noise) channel. Exact expressions for the bound are derived as well as simplified, approximate forms that enable derivation of a number of properties that describe the bound's dependence on key parameters such as signal-to-noise ratio (SNR), channel correlation, sampling rate, sequence length, and sequence choice. Comparison with the well-known slow fading (i.e., constant) channel bound is emphasized. Further simplifications are obtained for the special case of minimum phase keying (MSK), wherein it is shown how the bound may be used as a sequence design tool to optimize synchronization performance.

Direct carrier modulation for wireless digital communications using an improved microwave-photonic vector modulator (MPVM) approach

Abstract: This paper presents a demonstration of direct carrier modulation via the use of an improved microwave/photonic vector modulator (MPVM). This modulation approach is suitable for direct digital modulation of microwave and millimeter-wave signals and allows for tuning of the carrier frequency over wide bandwidths and dynamic reconfiguration of the modulation format. An all-optical control approach is used to achieve faster data rates and better carrier tunability than previously reported work in this area. Specifically, experimental results showing direct QPSK and 16 QAM modulation of carrier frequencies between 1.0 and 2.0 GHz with data rates to 8 Mbs are presented.

System and method for obtaining accurate symbol rate and carrier phase, frequency, and timing acquisition for minimum shift keyed waveform

Abstract: The present invention relates generally to communication systems, both wired and wireless, employing a continuous phase modulation (“CPM”) waveform with a minimum shift keying (“MSK”) preamble. The present inventive system and method uses information from contiguous Fourier Transforms taken on contiguous data blocks to determine baud rate, phase, frequency offset, and bit timing of the CPM waveform or can be used to determine the frequency of continuous wave waveform. More particularly, the inventive system and method is applicable to the military satellite communications UHF frequency band for deciding whether a signal of interest is.

Spectrally Efficient Continuous Phase Modulation

Abstract: Spectrally efficient continuous phase modulation (CPM) systems and generalizations of CPM for wireless links are considered. Continuous phase modulation defines constant envelope phase codes, which are advantageous when using non-linear amplifiers. The channel is an additive white Gaussian noise (AWGN) channel and the spectrum requirement is a mask, which puts stringent requirements on the spectral main lobe and the spectral side lobes. The thesis covers complexity and power efficiency of spectrally efficient coded modulation systems with zero or a small envelope variation. Reduced state sequence detection and approximate metrics are used to simplify the maximum likelihood sequence detector. Modulation system parameters are numerically optimized in order to probe the full potential of the systems and we build an empirical model for the optimum parameters of CPM based on numerical results. The optimized schemes also improve the sensitivity for a detector based on reduced state sequence detection. We study serially concatenated convolutionally encoded CPM for spectrally efficient systems, and we generalize multi-level CPM to a system called multi-pulse continuous phase modulation (mpCPM). We show that convolutional encoding does not improve the system, but mpCPM can gain up to 0.7 dB over CPM. We also illustrate that mpCPM can provide unequal error protection. Then, we develop a modulation system called constrained envelope continuous phase modulation (ceCPM) , which exhibit a small controlled envelope variation. We show design examples where the performance gain for ceCPM over CPM is up to 2.5 dB.

Carrier recovery apparatus for digital QAM receivers

Abstract: A carrier recovery apparatus for digital Quadrature Amplitude Modulation (QAM) receivers is disclosed. The carrier recovery apparatus includes a phase detector, a lock controller, a frequency locker and a phase loop filter, and provide phase/frequency error information for a numerically controlled oscillator (NCO) to generate recovered carrier frequency. The phase detector detects the symbol energy information and the phase error information of the extracted symbols from the I/Q extractor. The lock controller monitors the symbol energy from the phase detector, separates the extracted symbols into two groups: valid and non-valid, and outputs the control flag of valid symbols into both the frequency locker and the phase loop filter. To achieve a wide range acquisition and a good tracking performance, the lock controller controls the operation of the frequency locker and the phase loop filter in three operations. The detected frequency offset from the frequency locker and the phase offset detected from the phase loop filter are both fed into the NCO to recover the carrier offset.