Showing papers on "Phase-shift keying published in 1991"

System and method for generating signal waveforms in a CDMA cellular telephone system

Abstract: A system and method for communicating information signals using spread spectrum communication techniques. PN sequences are constructed that provide orthogonality between the users so that mutual interference will be reduced, allowing higher capacity and better link performance. With orthogonal PN codes, the cross-correlation is zero over a predetermined time interval, resulting in no interference between the orthogonal codes, provided only that the code time frames are time aligned with each other. In an exemplary embodiment, signals are communicated between a cell-site and mobile units using direct sequence spread spectrum communication signals. In the cell-to-mobile link, pilot, sync, paging and voice channels are defined. Information communicated on the cell-to-mobile link channels are, in general, encoded, interleaved, bi-phase shift key (BPSK) modulated with orthogonal covering of each BPSK symbol along with quadrature phase shift key (QPSK) spreading of the covered symbols. In the mobile-to-cell link, access and voice channels are defined. Information communicated on the mobile-to-cell link channels are, in general, encoded, interleaved, orthogonal signaling along with QPSK spreading.

An analysis of pilot symbol assisted modulation for Rayleigh fading channels (mobile radio)

Abstract: The author presents pilot-symbol-assisted modulation (PSAM) on a solid analytical basis, a feature missing from previous work. Closed-form expressions are presented for the bit error rate (BER) in binary-phase-shift-keying (BPSK) and in quadrature-phase-shift-keying (QPSK), for a tight upper bound on the symbol error rate in 16 quadrature-amplitude-modulation (16-QAM), and for the optimized receiver coefficients. The error rates obtained are lower than for differential detection for any combination of signal-to-noise ratio (SNR) and Doppler spread, and the performance is within 1 dB of a perfect reference system under slow-fading conditions and within 3 dB when the Doppler spread is 5% of the symbol rate. >

A new, simple and exact result for calculating the probability of error for two-dimensional signal constellations

Abstract: The author presents a simple integral expression for calculating the exact probability of a symbol error for an arbitrary array of signal points. The integrand contains only elementary functions and the range of integration is finite. The approach is introduced by applying it to M-ary phase shift keying (MPSK). The special case of M=2 gives novel and possibly useful expressions for calculating the Gaussian tail probability function and the related complementary error function. The approach is outlined for polygonal decision regions, and results are given for 16-point signal constellations. A method of obtaining, not exact, but even simpler and highly accurate expressions for symbol error probability when the latter is less than a few hundredths is presented. >

The land mobile satellite communication channel-recording, statistics, and channel model

Abstract: The communication channel between the MARECS satellite at 26 degrees W and a cruising van was measured and recorded in European areas exhibiting satellite elevations from 13 to 43 degrees . Different environments and mobile antennas were tested. The results of an extensive statistical evaluation include spectra of the fading amplitude; probability density, and distribution of the received signal power; and the percentage of time for fade and nonfade periods. Based on the physical phenomena of multipath fading and signal shadowing, an analog model of the land mobile satellite channel which can readily be used for software and hardware fading simulation is developed. The most important parameter of this model is the time-share of shadowing. The Rice factor which characterizes the channel during unshadowed periods, can vary from 3.9 to 18.1 dB. Block error probability density, error gap distribution, and block error probability are discussed. >

Effects of HPA-Nonlinearity on a 4-DPSK/OFDM-Signal for a Digital Sound Broadcasting System.

Abstract: Orthogonal Frequency Division Multiplexing (OFDM) in conjunction with a 4-DPSK modulation format has been proposed for the future digital audio broadcasting system (DAB), that should provide compact disk sound quality in portable, vehicular and fixed receivers. With properly chosen parameters, this system should be appropriate for both terrestrial and satellite transmission. In this paper the influence of the nonlinear distortions introduced by the high power amplifier (HPA) of the transmitter is examined. In particular, the degradation in power efficiency due to intermodulation effects and backoff operating, as well as spectral degradations are investigated.It is shown for three different kinds of limiting amplifier models, that even with an output backoff (OBO) in the region of 5-6 dB, the degradation of, e.g., a 512-carrier 4-DPSK/OFDM system relative to the linear case is below 1.7 dB, while the regenerated sidelobes of the transmitted spectrum are kept below -20 dB.

On the bit error rate of lightwave systems with optical amplifiers

Abstract: The problem of evaluating the performances of communication systems with optical amplifiers and a wideband optical filter is addressed. Exact probability of error expressions for optical signals in presence of amplifier spontaneous noise and photodetector shot noise are given and compared with those predicted by Gaussian approximations for amplitude shift keying (ASK), frequency shift keying (FSK), or differential phase shift keying (DPSK) modulations, both for ideal photodetectors and for the case where shot noise is significant. >

Analysis of equal gain diversity on Nakagami fading channels

Abstract: An infinite series for the complementary probability distribution function (CDF) of the signal-to-noise ratio (SNR) at the output of L-branch equal-gain (EG) diversity combiners in Nakagami (1960) fading channels is derived. The bit error rate for a matched filter receiver is analyzed for the L-branch EG combiner and different fading parameters. Both coherent phase shift keying (CPSK) and differential coherent phase shift keying (DCPSK) are considered. The effects of gain unbalance between branches on the probability distribution of the SNR and on the bit error rates are investigated. Bit error rate results are also obtained for coherent and noncoherent reception of frequency shift keying (FSK). The effects of gain unbalances on FSK modulations are also investigated. Bit error rates for EG combining on Rayleigh fading channels are obtained for L>2. These results are presented as a special case of the more generalized Nakagami fading model. >

BER performance of QDPSK with postdetection diversity reception in mobile radio channels

Abstract: The bit-error-rate performance of Nyquist raised-cosine-filtered quaternary differential phase shift keying (RC-QDPSK) and pi /4-shift RC-QDPSK with postdetection diversity reception is theoretically analyzed for Rayleigh fading channels. A selection combiner, equal-gain combiner, and maximal-ratio combiner are considered for postdetection diversity reception. Diversity improvements on the average BER due to additive white Gaussian noise, cochannel interference, random FM noise, and delay spread of the multipath channel are calculated. Also analyzed is the combined effect of diversity reception and error control. The required E/sub b//N/sub 0/ and allowable RMS delay spread for achieving a certain BER and spectrum efficiency in cellular mobile systems are calculated when short BCH forward error correcting codes are used. The performance of automatic repeat request combined with time diversity reception is investigated. >

Dual diversity combining and equalization in digital cellular mobile radio

Abstract: The performance of digital data transmission over frequency-selective fading channels is investigated. For statistically independent diversity paths, estimates of average attainable error rates and outage probabilities as functions of system parameters are provided. The dependences among the important system parameters are exhibited graphically for several examples, including quaternary phase-shift keying (QPSK). In the optimized uncoded QPSK with 1.5 b/s/Hz, two orders of magnitude in outage probability can be gained by diversity reception. When one compares the uncoded average probability of error for the optimized mean squared error (MSE) systems one finds at most an order-of-magnitude difference among the different equalizers investigated except for the zero-forcing equalizer, whose performance is drastically inferior to the others. Again, dual diversity can provide two orders of magnitude improvement in the average error rate or in outage probability for the uncoded optimized systems. >

Spread spectrum communications system

Abstract: A spread spectrum communication system for direct sequence transmission of digital information having a modulation format which is particularly suitable for indoor communication within residential, office and industrial structures. The modulation format combines BPSK or MSK spreading with FM carrier modulation by data bits and a carrier frequency shift whose magnitude is related to both a chip rate and a spreading sequence length. The carrier, chip clock and data clock are all synchronous and the sequence length is an integral submultiple of the bit length. The system reduces the frequency error between the transmitter chip clock and the receiver chip clock to permit the elimination of a code phase tracking loop in the receiver to reduce the receiver complexity. The receiver has an extended dynamic range which makes possible the reception of very strong signal without an automatic gain control loop (AGC) as well as reducing the time needed for code phase acquisition. The transmission system is highly resistant to CW jamming and short distance multipath effects.

Bit error probabilities MDPSK over the nonselective Rayleigh fading channel with diversity reception

Abstract: Data transmission using M-ary differential phase shift keying (MDPSK) over the nonselective Rayleigh fading channel with diversity reception is considered. While previous studies on error probability mostly assume no fading fluctuation, the author considers, exclusively, the case in which the fading process fluctuates from one symbol interval to the next. Exact bit error probability results for 2, 4, and 8 DPSK as well as tight upper bounds are derived. Some applications of the results are discussed. >

Automatic adjustment of quadrature modulators

Abstract: A technique for the automatic correction of errors in RF quadrature modulators is described. The method uses a diode detector to provide amplitude feedback to guide the adaption of baseband circuits that correct for carrier leak, differential gain and phase mismatch errors.

Error performance of multiple symbol differential detection of PSK signals transmitted over correlated Rayleigh fading channels

Abstract: A study is made of the error performance of multiple-symbol differential detection of uncoded PSK (phase shift keying) signals transmitted over correlated flat Rayleigh fading channels. It is found that the optimal detector uses a decoding metric which is a quadratic form of Gaussian variates. By using the characteristic function/residue theorem approach, the authors are able to derive an exact expression for the pairwise error event probability for the optimal detector. Subsequently, it is found that multiple-symbol differential detection is a very effective strategy for eliminating the irreducible error floor commonly associated with conventional differential detection. It is also found that the error performances of these detectors are not very sensitive to the mismatch between the decoding metric and the channel fading statistics. >

Modems for emerging digital cellular-mobile radio system

Abstract: Digital modem techniques for emerging digital cellular telecommunications-mobile radio system applications are described and analyzed. In particular, theoretical performance, experimental results, principles of operation. and various architectures of pi /4-QPSK ( pi /4-shifted coherent or differential QPSK) modems for second-generation US digital cellular radio system applications are presented. The spectral/power efficiency and performance of the pi /4-QPSK modems (emerging American and Japanese digital cellular standards) are studied and briefly compared to GMSK (Gaussian minimum-shift keying) modems (proposed for European DECT and GSM cellular standards). Improved filtering strategies and digital pilot-aided (digital channel sounding) techniques are also considered for pi /4-QPSK and other digital modems. More spectrally efficient modem trends for future cellular mobile (land mobile) and satellite communication system applications are also highlighted. >

A new method for phase synchronization and automatic gain control of linearly modulated signals on frequency-flat fading channels

Abstract: An optimal phase synchronization and automatic gain control (AGC) scheme for coherent reception of linearly modulated signals on frequency-flat mobile fading channels is presented. The channel model and receiver performance are described. It is shown that using the technique allows the irreducible error floors (due to random FM) known from the noncoherent methods to be practically eliminated. Depending on the fastness of the fading, large power gains over the noncoherent methods are achieved. Unfavorable analog signal processing and/or the high bandwidth inefficiency of the FDM-pilot coherent methods are also avoided. >

Bit error rate performance of pi /4-DQPSK in a frequency-selective fast Rayleigh fading channel

Abstract: The bit error rate (BER) performance of pi /4-differential quadrature phase shift keying (DQPSK) modems in cellular mobile communication systems is derived and analyzed. The system is modeled as a frequency-selective fast Rayleigh fading channel corrupted by additive white Gaussian noise (AWGN) and co-channel interference (CCI). The probability density function of the phase difference between two consecutive symbols of M-ary differential phase shift keying (DPSK) signals is first derived. In M-ary DPSK systems, the information is completely contained in this phase difference. For pi /4-DQPSK, the BER is derived in a closed form and calculated directly. Numerical results show that for the 24 kBd (48 kb/s) pi /4-DQPSK operated at a carrier frequency of 850 MHz and C/I >

Performance of an RCPC-coded OFDM-based digital audio broadcasting (DAB) system

Abstract: A system proposal for DAB is investigated. The kernel is orthogonal frequency division multiplexing (OFDM) with 4-DPSK (differential phase shift keying) modulation, rectangular pulse-shaping, and a guard interval to reject multipath distortions. Emphasis is on the use of source-adapted channel coding with rate-compatible punctured convolutional (RCPC) codes. Based on analytical and simulated BER (bit error rate) curves for several propagation conditions and on preliminary source significance information (SSI), a static code design with unequal error protection (UEP) is presented that also takes auxiliary data services into account. The gain due to UEP is on the order of 8dB in signal power or 25% in bandwidth. >

Symmetric 3 x 3 coupler-based demodulator for fiber optic interferometric sensors

Abstract: A method for demodulation of fiber optic interferometric sensors that utilizes a 3 x 3 coupler is described. The passive demodulation scheme does not require carrier (phase) modulation. The demodulation scheme relies on the three outputs of a 3 x 3 coupler and uses all three of its phase modulated output signals to recreate the stimulus inducing the original optical phase modulation. The demodulator scale factor (volts/radian) is stable against fluctuations in both fringe visibility and average received power. Upon initial implementation of the scheme, a dynamic range of 116 dB was obtained (at 600 Hz in a 1 Hz bandwidth with maximum THD at 4%). The minimum detectable signal at 600 Hz was 220 μrad/√Hz and the maximum tolerable signal was 140 radians. Both the maximum tolerable signal and the minimum detectable signal (noise floor) was observed to increase with decreasing frequency. Thus, depending on the frequency, the demodulation scheme is capable of detecting phase signals less than a milliradian to in excess of kiloradians.

Bit error probability for coherent M-ary PSK systems

Abstract: A simple technique for evaluating the bit-error probability of coherent M-ary phase-shift keying (PSK) with any bit-mapping is proposed. Closed-form expressions are given in terms of error functions for half- and quadrant-plane probabilities in the decision space, avoiding the numerical evaluation of complicated integrals that occurs in the direct method. Bit error probability expressions for M-ary PSK with Gray, natural binary, and folded binary bit-mappings are derived. >

Differential quadrature phase shift keying encoder for subcarrier systems

Abstract: This invention features a differential QPSK digital communications apparatus and method, suitable for optical communications systems, where a pair of synchronous binary input data streams S 0 (t) and S 1 (t) are encoded into a pair of encoded binary data streams d 0 (t) and d 1 (t) which QPSK modulate the phase φ(t) of a carrier signal. An encoder features time delay circuits for delaying d 0 (t) and d 1 (t) by a period T to produce d 0 (t-T) and d 1 (t-T) respectively. A logic circuit produces d 0 (t) and d 1 (t) from S 0 (t), S 1 (t), d 0 (t-T) and d 1 (t-T) according to logical relationships. A microwave subcarrier is modulated by a microwave QPSK subcarrier modulator. The microwave QPSK subcarrier modulator includes an in-phase and quadrature subcarrier signal source, a mixer for mixing the in-phase subcarrier with d 0 (t), a second mixer for mixing the quadrature subcarrier with d 1 (t), and a combiner circuit for combining the two mixer outputs to produce a QPSK modulated microwave subcarrier signal. An optical modulator modulates the QPSK modulated microwave subcarrier signal onto an optical carrier signal, an optical detector detects the modulated subcarrier from the optical carrier signal to produce a detected subcarrier signal, and a QPSK demodulator recovers S 0 (t) and S 1 (t) from the detected subcarrier signal.

Optimally near-far resistant multiuser detection in differentially coherent synchronous channels

Abstract: The noncoherent demodulation of differentially phase-shift keyed signals transmitted simultaneously via a synchronous code-division multiple-access (CDMA) channel is studied under the assumption of white Gaussian background noise. A class of noncoherent linear detectors is defined with the objective of obtaining the optimal one. The performance criterion considered is near-far resistance that denotes worst-case multiuser asymptotic efficiency over near-far environments. It is shown that the optimal linear detector is a noncoherent decorrelating detector. The commonality between the properties of the decorrelating detectors for coherent and noncoherent channels is established. In particular, it is shown that no other differential phase-shift keying (DPSK), multiuser detector achieves a higher near-far resistance than does the noncoherent decorrelator. >

Multi-h phase-coded modulation

Abstract: An overview of some recent results for multi-h phase-coded modulation (MHPM) schemes is provided. These schemes offer power and bandwidth efficiency where time-varying modulation indices are used. Following a brief description of the structure of MHPM, its fundamental properties (e.g., minimum Euclidean distance and power spectra) are described. Decoding and demodulation of MHPM also are discussed. and some results on synchronization are summarized. MHPM combined with convolutional codes, asymmetric modulation indices, or nonuniform mapping are investigated. >

Bisdn compatible modem codec for digital information communication system

Abstract: A modem/codec is designed for a digital signal transmission system using a single satellite transponder. The system is capable of transmitting data of a rate of 155.52 Mbps, and is thus compatible with the BISDN rate. A codec of rate 13/15 is used, and an octal phase shift keying modem is also used. In this way, the digital signal transmission system is capable of receiving data at a rate of 155.52 Mbps over a single INTELSAT V/VA transponder with a usable bandwidth of 72 MHz.

A new 4-state 8PSK TCM scheme for fast fading, shadowed mobile radio channels

Abstract: The design of a 4-state, rate-2/3, 8PSK trellis-coded modulation (TCM) code, based on the design criteria for fading channels, is presented. To evaluate and compare the performance of this code with the other 4-state 8PSK TCM schemes presented in the literature, computer simulation is performed for a shadowed Rician fading channel. The simulation results show the superiority of the scheme for bit-error probabilities of 10/sup -3/ or less. This makes the code a suitable choice for both speech and data transmission over mobile fading channels. >

Digital discriminator for pulse shaped π/4 shifted differentially encoded quadrature phase shift keying

Abstract: A digital radio receiver for synchronization of radiowave transmissions for digital and analog FM signals in TDMA systems such as cellular telephones uses a tangent type discriminator that minimizes the bit error rate. The digital discriminator employs A/D converter circuit that samples a received intermediate frequency (IF) signal, a sorter circuit that produces a predetermined number of samples to be used in the decoding, a sample and phase adjustment circuit that allows for a carrier phase adjustment and sample timing adjustment, a divider circuit that eliminates the need for a conventional limiter by causing a ratio of amplitudes to be processed instead of absolute signal amplitudes, an inverse tangent circuit that creates a decoded phase angle from the ratio, a delay circuit and a summer circuit that create a differential signal, a modulo-2π correction circuit that corrects for wrap-around errors about the real axis, an integrate and dump filter for summing up all phase angles pertaining to a single symbol, and a four-phase decoder circuit to decode the signal into a pair of bits. An adjustment circuit minimizes phase error between a reference sequence of symbols and the decoded symbols by simultaneously adjusting the sample timing and carrier phase adjustments. The digital discriminator also can decode conventional analog FM radio broadcasts by deactivating the IDF, the adjustment circuit, and SPA circuit, and bypassing the four-phase decoder.

Laser linewidth requirements and improvements for coherent optical beam forming networks in satellites

Abstract: A coherent optical beam forming network using phase-locked semiconductor lasers as sources is presented. For this scheme the spectral purity of the intermediate frequency derived from mixing the signals from two semiconductor lasers is considered. The relationship between the linewidths of the lasers in a satellite transmitter and the phase error at the detector of a microwave differential quaternary phase-shift keying earth station receiver is analyzed. The demands placed on the linewidths from the point of view of phase stability requirements are calculated using quaternary phase-shift keying modulation at data rates of 33 and 131 Mb/s. It is shown that a substantial improvement in performance can be achieved when phase locking the two lasers to each other is feasible. >

Transmission limitations of CPFSK coherent lightwave systems due to stimulated Brillouin scattering in optical fiber

Abstract: Transmission limitations imposed by stimulated Brillouin scattering (SBS) are investigated for repeaterless coherent lightwave systems, particularly for continuous phase-shift keying (CPFSK). The effects of SBS on the modulated signals in optical fibers are studied for CPFSK, amplitude shift keying (ASK), and phase shift keying (PSK). A generalized model based on the maximum power spectrum density (PSD) in the modulated signals is proposed for SBS analysis. This model is useful to estimate the Brillouin gain and its threshold to determine the optical power limitation of the fiber for any modulated signal with non-negligible linewidth. It is clarified theoretically that the Brillouin gain with CPFSK approaches that with ASK and PSK at higher bit rates if the modulation index is 1 and 0.65, respectively. The dependency of Brillouin gain on bit rate and linewidth of a laser diode transmitter are evaluated. SBS induced by CPFSK modulated signals was measured to clarify the modulation condition dependences and to verify the model. >

Tangental type differential detector for pulse shaped pi/4 shifted differentially encoded quadrature phase shift keying

Abstract: A digital radio receiver for synchronization of radiowave transmissions for digital and analog FM signals in TDMA systems such as cellular telephones uses a tangent type differential detector that minimizes the bit error rate. The differential detector employs an A/D converter circuit that samples a received signal, a sorter circuit that selects a predetermined number of samples to be used in the decoding, a sample and phase adjustment circuit that allows for a carrier phase adjustment and sample timing adjustment, a divider circuit that eliminates the need for a conventional limiter by causing a ratio of amplitudes to be processed instead of absolute signal amplitudes, an inverse tangent circuit creates a decoded phase angle from the ratio, a delay circuit and a summer circuit that create a differential signal, a modulo-2π correction circuit that corrects for wrap-around errors about the real axis, and a four-phase decoder circuit to decode the signal into a pair of bits. An adjustment circuit minimizes phase error between a reference sequence of symbols and the decoded symbols by simultaneously adjusting the sample timing and carrier phase adjustments. The differential detector can be modified to decode conventional analog FM radio broadcasts by processing more samples per symbol, deactivating the adjustment circuit, and the SPA circuit, and bypassing the four-phase decoder.

Chromatic dispersion limitations for FSK and DPSK systems with direct detection receivers

Abstract: Chromatic dispersion limitations for frequency-shift keying (FSK) and differential phase-shift keying (DPSK) systems using narrow-linewidth lasers and direct-detection receivers are discussed. The limitations are found to depend strongly on the receiver configuration. The receiver must include an optical frequency discriminator, such as a Mach-Zehnder interferometer, and either a balanced photodetector pair or a single photodetector at the interferometer output. For transmission at 1550 nm over 1310-nm optimized single-mode fiber, the distance for 1-dB eye closure penalty at 10 Gb/s ranges from 20 to 70 km, depending on the modulation format and the receiver configuration. >

Equivocation in nonlinear digital carrier synchronizers

Abstract: The nonlinear (nondecision-aided) digital phase estimator provides rapid phase estimation of an M-ary phase-shift-keyed modulated carrier. This carrier synchronization technique exhibits an anomaly, dubbed equivocation, which can degrade performance. A statistical description of equivocation, a jump in the reference phase trajectory of approximately=2 pi /M rad in a carrier synchronization technique, for the simple case of negligible frequency offset and additive white Gaussian noise is derived. Equivocation is shown to significantly degrade the bit error probability performance even in this benign channel. Since the algorithm as proposed is unsuitable for general use, a modified nonlinear (nondecision-aided) equivocation-free phase estimator is presented. The results of a simulation of this modified architecture developed to demonstrate the improved performance are presented. >