Showing papers on "Minimum-shift keying published in 2001"

Serially concatenated continuous phase modulation with iterative decoding

Abstract: Serially concatenated and interleaved continuous phase modulation (CPM) with iterative decoding is investigated. An a posteriori probability (APP) algorithm for CPM is developed based on the classic APP algorithm for channel codes. The system is analyzed through upper bounds on the average bit error probability. For coded and interleaved minimum shift keying, the weight spectrum is computed, resulting in a transfer function bound. This is cumbersome for a general CPM system; instead, only the most significant error events contributing to the weight spectrum are identified. Simulations show that, firstly, these events give a satisfactory view of system performance when equal outer codes are used, and secondly, that remarkably good performance can be obtained for some simple systems. Finally, power spectral densities and bandwidths are computed, allowing for a bandwidth/performanee comparison of different combinations.

Cyclic spectral analysis of continuous-phase modulated signals

Abstract: Continuous-phase modulated (CPM) signals play a prominent role in modern communication systems due to their desirable constant-modulus property and the ability to control their power and bandwidth efficiencies. Popular CPM signals include the classical minimum-shift keyed (MSK) signal, the LREC family of signals also known as continuous-phase frequency-shift-keyed (CPFSK) signals, and Gaussian MSK, which is used in state-of-the-art GSM and PCS mobile communication systems. CPM signals, like virtually all man-made communication signals, are known to exhibit cyclostationarity, which implies that their probabilistic parameters, such as mean, second moment, and higher order cumulants, are almost-periodic functions of time. A novel representation of CPM signals as a sum of PAM signals is presented for both integer and noninteger modulation index cases. Then, the Nth-order cyclostationarity properties of binary CPM signals are derived in terms of Nth-order temporal and spectral moment and cumulant functions. Moreover, the case of M-ary CPM signals is briefly addressed. The results are illustrated with simulations involving MSK, LREC, and GMSK signals.

A GMSK modulator using a /spl Delta//spl Sigma/ frequency discriminator-based synthesizer

Abstract: This paper describes a new transmitter architecture suitable for wideband GMSK modulation. The technique uses direct modulation of /spl Delta//spl Sigma/ frequency discriminator (/spl Delta//spl Sigma/FD)-based synthesizer to produce the modulated RF signal without any up-conversion. Digital equalization is used to extend the modulation data rate far beyond the synthesizer closed-loop BW. A prototype 1.9-GHz GSM transmitter was constructed consisting of a /spl Delta//spl Sigma/FD-based synthesizer and a digital transmit filter. The synthesizer consists of an 0.8-/spl mu/m BiCMOS /spl Delta//spl Sigma/FD chip, a digital signal processor FPGA, and an off-chip D/A converter, filter, and VCO. Measured results, using 271-kbit/s GSM modulation, demonstrate data rates well in excess of the 30-kHz synthesizer closed-loop BW are possible with digital equalization. Without modulation, the synthesizer exhibits a -76-dBc spurious noise level and a close-in phase noise of -74 dBc/Hz.

Cochannel interference reduction and path-diversity reception technique using CMA adaptive array antenna in digital land mobile communications

Abstract: This paper describes a cochannel interference (CCI) reduction and path-diversity reception technique using a constant modulus algorithm (CMA) adaptive array antenna in digital land mobile communications. In this technique, the incident signals are individually recovered by using a multistage constant modulus (CM) array that consists of a multistage cascade of signal recovering and canceling processes. The recovered signals are sorted into the desired signal and CCI signal, and then the desired signals are combined in order to obtain the path-diversity gain, Performance is evaluated for a Gaussian filtered minimum shift keying signal and /spl pi//4-shifted quadrature phase-shift keying signal. Each signal processing is carried out using block demodulation (e.g., CMA adaptive signal recovering process and signal canceling process). Computer simulation results show that CCI can be reduced efficiently for a high-bit-rate time-division multiple-access system for quasi-static and fading channel conditions and that the bit error rate (BER) performance is improved by combining the desired signals. The extent of the improvement in BER performance indicates the difference in diversity gain between maximal ratio combining and selective combining. This suggests that a CMA adaptive array antenna is equivalent to selective combining diversity reception.

Quadrature chaos shift keying

Abstract: In this paper we propose a multilevel version of the differential chaos shift keying (DCSK) scheme exhibiting the same bit error rate performance as DCSK but double data rate and spectral efficiency.

A simple coherent GMSK demodulator

Abstract: We show that a symbol-by-symbol detector is the optimal MLSE demodulator for Gaussian minimum-shift keying (GMSK) (BT=0.3) on both AWGN and a class of weakly dispersive multipath fading channels. Furthermore, it is shown that, for the remaining weakly dispersive channels, a 2 state Viterbi equalizer is optimum. As an illustration of the importance of this result, a receiver is proposed which can reduce the power consumption of GSM handsets using conditional equalization, as more than 70% of the time the channel is considered to be weakly dispersive.

Analyzing spectral regrowth of QPSK and OQPSK signals

Abstract: A comparison is made between the spectral regrowth of quadrature phase shift keyed (QPSK) and offset QPSK (OQPSK) signals as they go through nonlinear amplifications. Contrary to existing approaches that assume the power amplifier input is Gaussian, our analysis is carried out without the Gaussian assumption, by using higher-order statistics. We show that it is possible to assess quantitatively whether and how much OQPSK is beneficial in reducing spectral regrowth. Simple closed form formulas are obtained when the pulse shape filter is time-limited. A particular measure of spectral broadening is also provided.

A multicarrier GMSK modulator

Abstract: A multicarrier Gaussian minimum shift keying (GMSK) modulator has been developed and implemented. The design contains four GMSK modulators, which generate GMSK modulated carriers at the specified center frequencies. Utilization of the redundancy in the stored waveforms reduces the size of the GMSK trajectory look-up table to less than one-quarter of the original size in the modulator. Conventionally, the power ramping and output power level controlling are performed in the analog domain. A novel digital ramp generator and output power level controller perform both the burst ramping and the dynamic power control in the digital domain. The power control is realized by scaling the ramp curve, which follows a raised cosine/sine curve. The four GMSK modulated signals are combined together in the digital domain. The digital multicarrier GMSK modulator is designed to fulfil the spectrum and phase error specifications of the GSM 900 and DCS 1800 base stations.

Turbo equalization for GMSK signaling over multipath channels based on the Gibbs sampler

Abstract: We consider the problem of Bayesian data restoration for Gaussian minimum shift keying (GMSK) signals over unknown multipath channels. As an alternative to the linear approximation method employed in the conventional finite impulse response (FIR) model, we develop a nonlinear signal model for this system. A Bayesian equalizer based on the Gibbs sampler, a Markov chain Monte Carlo (MCMC) procedure, is developed for estimating the a posteriori symbol probability in the GMSK system without explicit channel estimation. The basic idea of this technique is to generate ergodic random samples from the joint posterior distribution of all unknowns, and then to average the appropriate samples to obtain the estimates of the unknown quantities. Being soft-input soft-output in nature, the proposed Bayesian equalization technique is well suited for iterative processing in a coded system, which allows the Bayesian equalizer to successively refine its processing based on the information from the decoding stage, and vice versa.

Symbol timing recovery for GMSK modulation based on squaring algorithm

Abstract: A new all-digital symbol timing estimator for GMSK signals is proposed. It is based on the squaring algorithm and has a feedforward structure. Performance in AWGN channel is assessed by computer simulation, and is compared with the modified Cramer-Rao bound and other existing algorithms. The performance of the proposed estimator is shown to be close to that of the ML algorithm.

Automatic identification deivce and method for modulation system

Abstract: PROBLEM TO BE SOLVED: To realize a single identification device that identifies a modulation system of a received signal with unknown various communication item without previous provision of various known communication items with respect to a plurality of modulation systems. SOLUTION: The identification device is provided with an analog/digital modulation system identification circuit 1 that identifies a received signal as to whether the received signal adopts an analog modulation system, a linear digital modulation system or a nonlinear digital modulation system, an analog modulation system identification circuit 2 that identifies the received signal as to whether the received signal adopts an AM analog modulation system or an FM analog modulation system when the circuit 1 discriminates the analog modulation system, a linear modulation system identification circuit 3 that identifies the received signal as to whether the received signal adopts a BPSK, a QPSK, a π/4-shift QPSK, an 8-PSK, a multi-value M-ary, a PSK, a 16 QAM, in excess of an octal value, or a multi-value M-ary in excess of a rexadecimal value among linear digital modulation system when the circuit 1 discriminates the linear digital modulation system, and a nonlinear modulation system identification circuit 4 that identifies the received signal as to whether the received signal adopts an M-ary, an FSK, a 2-FSK, an MSK or a GMSK among a nonlinear digital modulation system when the circuit 1 discriminates the nonlinear digital modulation system.

Blind receivers for MSK signals transmitted through shallow water

Abstract: In this paper, blind receivers for minimum shift keying signals transmitted through shallow water are proposed. After having introduced the modulation scheme and its favorable properties, two different blind receiver structures are studied. The first processing step in both cases is explicit non-data-aided timing recovery, a task that has often been neglected in other work. Then, joint blind adaptive multichannel equalization and phase recovery is performed. The adaptive setting of the equalizer is attained by either the constant modulus algorithm or a decision-directed approach. Both structures have been tested with measured shallow water data gathered during the ROBLINKS 1999 sea trial. The obtained results suggest MSK as a useful modulation scheme for underwater communications and demonstrate that completely blind processing of the received signals is possible.

GCMAC-based predistortion for digital modulations

Abstract: The subject of this paper is the compensation for nonlinearities in digital communication systems by means of predistortion. In this work, we apply the generalized cerebellar model articulation controller (GCMAC) to simplify and accelerate the predistorter convergence. The range of analyzed predistorters includes: 1) a symbol-rate data predistorter that, for a given time span, achieves a similar level of compensation provided by present techniques, but with faster convergence; 2) a fractionally spaced data predistorter that controls, at the same time, the signal constellation and the transmitted spectrum; 3) a decision-feedback scheme that compensates for remote nonlinearities; and 4) a digital signal data predistorter. The performance of the proposed data and signal predistorters is evaluated using typical linear and nonlinear modulated transmitted signals such as QAM and GMSK.

On the design of LDPC codes for MSK

Abstract: We investigate serial concatenation of low-density parity check (LDPC) codes and minimum shift keying (MSK) with iterative decoding. We show that the design of LDPC codes is crucially dependent on the realization of the MSK modulator. For MSK modulators with nonrecursive continuous phase encoders (CPEs), optimal codes for BPSK are optimal, whereas for MSK modulators with recursive CPEs, the BPSK codes are not optimal. We show that for nonrecursive CPEs, iterative demodulation and decoding is not required even though the CPE has memory. However, iterative demodulation is essential for recursive CPEs. For recursive CPEs, we design LDPC codes using density evolution and differential evolution considering iterative demodulation and decoding. The resulting codes provide significantly improved performance over the existing codes.

Space shift keying modulation

Abstract: A space shift keying (SSK) modulation is disclosed. At the transmitter of a digital wireless communication with an antenna array, due to the fact that multipath fading will cause different responses for distinct array elements, different information signal bits (such as the “0” and “1” in binary shift keying) can be sent from different array elements to the receiver site. At the receiver site, the likelihood ratio test can be used to recognize the information signal bits transmitted from different array elements. The present signaling method for carrying information signal bits is a digital modulation method, which is known as space shift keying modulation.

An adaptive receiver based on software defined radio techniques

Abstract: We developed an identification algorithm that can distinguish twelve kinds of modulation modes using a blind process aimed at automatic identification of unknown modulated signals. We also developed an adaptive receiver, installed this algorithm, and we carried out an experiment to evaluate the receiver's ability. By the result of the validation experiment, for linear digital modulation modes with S/N /spl ges/ 3 dB, for GMSK of nonlinear digital modulation modes with S/N /spl ges/ 18 dB, and for the FM of analog modulation modes with S/N /spl ges/ 12 dB, we got a performance of identification probability of over 90 % respectively. Furthermore, based on the identification results, we evaluated the adaptive demodulation process by using the developed system and confirmed its effectiveness.

Code-division, minimum-shift-keying optical multiplexing

Abstract: Optical code-division multiplexing and demultiplexing (CDM) using orthogonal codes with minimum shift keying (MSK) waveforms allows more efficient use of the spectrum and greatly reduces cross-channel interference. Receiving multiple baseband data channels, a derivation mechanism converts the data signals into series of impulses. These impulses may be split into odd and even channels, each at half the original data rate, and transmitted to a plurality of Walsh filters configured to have an impulse response corresponding to one of a plurality of orthogonal MSK waveforms. Odd and even channels, encoded with MSK waveforms, may combine into an in-phase and quadrature channel, 90° out of phase. A laser output may be divided, phase shifted, and modulated with the in-phase and quadrature channels, which divisions are then combined into a single multiplexed output. Walsh filters may decode the incoming signal in order to reproduce the original baseband channels.

Noncoherent detection for trellis-coded MPSK

Abstract: This letter shows several methods for improving the decoding of noncoherent trellis-coded M-ary phase-shift keying. We propose two new metrics for the basic decision-feedback algorithm. These metrics are derived based on the idea of reducing the effect of incorrect amplitude of the reference signal. We also propose a new decoding algorithm that uses a simple way to estimate the metric of the future sequence.

Single-carrier-frequency transmitter of GSM base station

Abstract: A single-carrier transmitter of GSM base station is composed of a GMSK signal modulation part consisting of FPGA, DUC, CPU, DAC and LPF, and upper mixing, filtering and amplifying part, and antenna. Said DUC consists of internal controller, shaping filter, digital frequency modulator, gain controller, interpolation filter, NCO2 unit, and orthogonal frequency mixer. SAid FPGA is composed of address latch and decoder, address, data and writing signal selector, test signal generator and differential encoder. It can eliminate the DC error and unbalanced amplitude and phase between I and Q, improve spectral quality, and increase system performance.

Feedforward joint phase and timing estimation for MSK—type signals

Abstract: Novel non data—aided (NDA) algorithms are proposed for joint estimation of timing and carrier phase in MSK—type modulations. They are based on maximum likelihood methods and have a feedforward structure which is suitable to fully digital implementation. Performance with MSK and Gaussian MSK. (GMSK) is assessed by computer simulations and compared with that of other existing estimation schemes.

Time-of-arrival estimation for E-OTD location in GERAN

Abstract: In this paper, the problem of time-of-arrival (TOA) estimation for E-OTD location in a GSM/EDGE Radio Access Network (GERAN) is described. To increase the number of available bursts for TOA estimation (and therefore increase the accuracy), the mobile can use bursts from all time slots. However, this requires that the TOA estimation algorithm is able to handle GMSK and 8PSK bursts without a-priori knowledge about the modulation scheme. In this paper, the mutual effect of different modulation formats on the TOA estimation performance for E-OTD location is investigated. A TOA estimation algorithm is described, which does not require a blind detection of the modulation scheme.

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 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 64 filters and a 64 state inner trellis).

A multicarrier GMSK modulator for base station

Abstract: In conventional base station solutions, transmitted carriers are combined after power amplifiers (PAs). This paper describes an architecture in which four GMSK modulated signals are combined in the digital domain. This saves a large number of analog components, many of which require production tuning. Consequently, an expensive and tedious part of manufacturing is eliminated. The proposed multicarrier GMSK modulator does not use an analog I/Q modulator. Therefore the difficulties of adjusting the dc offset, the phasing and the amplitude levels between the in-phase and quadrature phase signal paths are avoided.

Demodulation of CPFSK and GMSK Signals Using Digital Signal Processing DPLL with Sequence Estimator

Abstract: SUMMARY Phase locked loops (PLL's) are well known as a threshold extension demodulator for analogue FM signals. This capability may lead to the low bit error rate demodulation for digital FM signals. A PLL has also its native frequency tracking ability and is suited to the demodulation of the signals having large Doppler shifts, for example signals from Low Earth Orbit (LEO) satellites. In this paper, we study the demodulation scheme of Continuous Phase FSK (CPFSK) and Gaussian filtered MSK (GMSK) signals using a Digital Signal Processing type Digital PLL (DSP DPLL). First we propose a DSP DPLL completely equivalent to an Analog PLL (APLL). Next we adopt the sequence estimation scheme to compensate the Inter-Symbol Interference (ISI) associated with the finite loop bandwidth of the DSP DPLL. Through computer simulations it is clarified that the proposed DSP DPLL with sequence estimator can achieve better BER performance compared with the conventional Limiter Discriminator (LD) detection on the AWGN channel. We have also shown that the DSP DPLL with sequence estimator has excellent BER characteristics on Rician fading channels having actual large Doppler shifts.

Adjacent channel interference susceptibility of serial concatenated continuous phase modulation

Abstract: Iterative decoding of a serially concatenated outer convolutional code and an inner continuous phase modulation (CPM) separated by a random interleaver is examined. This scheme, which is known to produce a high coding gain, is examined for various CPMs such as MSK, LRC, GMSK and TFM. CPM signals are constant envelope signals with very high bandwidth efficiency, providing good immunity to adjacent channel interference (ACI). The susceptibility of the serial concatenated system to ACI is examined. Simulations show that this configuration can tolerate much stronger ACI than previous CPM schemes, including those detected with the Viterbi algorithm.

On the feasibility of blind equalization for EDGE systems

Abstract: The main goal of this paper is to find whether or not blind equalization can be used in EDGE (enhanced data rate for GSM evolution) systems in the perspective of increasing the data rate. An EDGE system uses 8-PSK modulation as well as the binary GMSK modulation defined for GSM. The main problem is that GMSK modulation is nonlinear, but most blind equalization techniques are derived for linear modulation. Linear approximation of the real GMSK signal has to be performed in order to apply blind equalization. It is of interest to determine if the input sequence resulting from linearisation and the derotation in the receiver is white, which is a key assumption in many blind equalization algorithms. We show that the whiteness property is preserved. We make a comparison among three blind algorithms: two fractionally spaced and one based on baud-rate HOS. The simulation results indicate that blind equalization performs well and the algorithms have potential as a feasible solution to channel tracking in EDGE systems.

Frequency error measurement in GMSK signals in a multipath propagation environment

Abstract: The paper presents an efficient method for evaluating the carrier frequency in GMSK communication systems. This method operates in a nonintrusive way. It utilizes the learning vector quantisation neural network based demodulator for reconstructing the transmitted phases. From these and the expected phases is estimated the carrier frequency error. The method is able to operate both in static and multipath propagation cases and it does not require a high frequency sampling rate because the base-band signal is processed. In order to apply the method two procedures, PSP (Procedure for Static Propagation) and PMP (Procedure for Multipath Propagation), are set-up. Tests performed on GMSK signals show that the method is quite attractive, fast and more accurate if compared with other approaches.

M-CPM with MRC diversity in Rician-, Hoyt-, and Nakagami-fading channels

Abstract: An equation is derived for the bit error probability (BEP) of M-ary continuous phase modulation (CPM) with differential phase detection (DPD) and maximal ratio combining (MRC) in various fading channels. As an example, the BEP of Gaussian minimum shift keying with B/sub g/T=0.5 is computed. In the case of a Rician channel, the Doppler frequency shift is also taken into account. As an example, the BEP of M-ary continuous phase frequency shift keying with M=2, 4, 8 and f/sub Dm/T=0.04 is computed.

Disk-like recording medium, disk drive device, and disk manufacturing device and method

Abstract: PROBLEM TO BE SOLVED: To efficiently include the information of an address, etc., in the wobble component, and moreover improve the S/N when the information included in the wobble component is reproduced. SOLUTION: In an optical disk, address information modulated by an MSK (minimum shift keying) modulation method and address information modulated by a method for modulation by adding an even-order harmonic signal to a sine-wave carrier signal and changing the polarity of the harmonic signal in response to the sign of data to be modulated, are recorded on the wobble. COPYRIGHT: (C)2003,JPO

Automatic frequency control of GMSK time-dispersive channels

Abstract: A GMSK modulated signal has a voice/data signal minimum shift key (MSK) modulated in time slots of the carrier signal. A mixing signal is used to demodulate at least part of the voice/data signal from the carrier signal for each time slot. A plurality of amplitude and phases of the demodulated voice/data signal are converted into a plurality of received quadrature data. The received quadrature data is processed to determine a frequency slope error value, a binary cyclical redundancy check (CRC) value, an average signal-to-noise ratio (SNR) value, a received signal strength indicator (RSSI) value, and a sequence of digital bits forming at least part of the voice/data signal. The frequency slope error value is weighted with a first weighting value or a second weighting value when the binary CRC value is in its first binary state or its second binary state, respectively, to produce a weighted frequency slope error value. The first weighting value includes the combination of the SNR value and the RSSI value and the second weighting value zeroes the frequency slope error value. An average weighted frequency slope error value is determined for a plurality of time slots of the carrier signal. An average weight value is determined from the first weighting value and/or the second weighting value for the plurality of time slots. For each time slot, the average weighted frequency slope error value and the average weight value are combined to obtain an unweighted frequency error value. The unweighted frequency error value is utilized to adjust a frequency of the mixing signal to obtain frequency synchronization and frame synchronization with the GMSK modulated signal.