Minimum-shift-keyed Research Articles

Performance evaluation of externally modulated optical minimum shift keyed data

We evaluate the performance of the externally modulated optical minimum shift keying (MSK) signal. The tolerance against fiber dispersion, linear crosstalk, self phase modulation (SPM), and stimulated Brillouin scattering (SBS) threshold for MSK is studied and compared with that of 50% duty cycle return-to-zero differential phase shift keying (RZ-DPSK) and 50% duty cycle RZ on-off-keying (RZ-OOK), via both experiment and simulation. Simulation results show that the MSK signal has the widest tolerance against SPM and the smallest linear crosstalk among these formats. Experimental results agree with the simulation on negative penalty against SPM tolerance and show widest tolerance against dispersion tolerance for MSK. The measured SBS threshold of both MSK and RZ-DPSK is more than 10 dB higher than that of an RZ-OOK system.

Cyclic spectral analysis of continuous-phase modulated signals

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.

Limiter discriminator-detected GMSK with FM and GMSK interference in a land mobile channel

This paper addresses Gaussian minimum-shift keyed (GMSK) receiver performance analysis for limiter discriminator detection with cochannel interference resulting from a combined cellular voice and packet radio network. A specific example is cellular digital packet data (CDPD), which shares spectrum with cellular voice users; thus, the CDPD receiver will see both narrow-band frequency modulation (NBFM) voice and GMSK data interference. Previous studies investigated the performance of a GMSK receiver with a single GMSK interferer and multipath delay. In this paper, we extend earlier work to multiple Rayleigh fading (Doppler spread) interferers having NBFM (f/sub dm/=12 kHz) analog modulation and/or GMSK modulation. Probability of bit-error expressions are derived for the frequency modulation (FM) and GMSK interferer cases assuming medium-to-high signal-to-noise ratio regions. For scenarios of from one to six NBFM interferers, having the same total power, a corresponding Gaussian approximation is within 1.5 dB. Simulation results are also presented for various combinations of FM and GMSK interference. FM interference is only slightly worse than GMSK interference. Delay spread representing an urban scenario resulted in only a slight increase in the error floor.

Spectrally efficient MSK scheme for SCPC communicationsystems

A spectrally efficient scheme is described, for SCPC (single channel per carrier) communication systems, in which slightly modified MSK (minimum shift keyed) channels can be allowed to overlap spectrally, with a channel spacing equal to half the individual channel bit rate, without causing any crosschannel interference.

Simulation of co-channel interference in coexisting cellular TDMA networks

Uplink co-channel interference (CCI) between minimum-shift-keyed (MSK) time-division multiple access (TDMA) data packets generated by transmitters distributed uniformly over a circular area has been simulated in software, taking distance-dependent attenuation, log-normal shadowing, and multipath fading into account. The radio-link model and analytical derivation of bit error probability versus signal-to-interference ratio of a link with a single interferer are presented. The computer model is used to extend the bit error rate analysis to the case of multiple cochannel interferers. Numerical bit error rate (BER) results obtained from simulations of mutually interfering TDMA packet transmissions are compared with known theoretical results for the MSK channel under additive white Gaussian noise (AWGN) only. Possible improvements and future applications of the model to the problem of resource sharing between coexisting networks are suggested. >

Serial MSK spread-spectrum multiple-access communications

A serial minimum-shift-keyed (MSK) direct-sequence spread-spectrum multiple-access (DS/SSMA) communication system is described and analyzed to obtain the signal-to-noise ratio. The single-channel system generates the same transmitted signals as a corresponding parallel MSK/DS/SSMA system. Hence, the transmitted signals have a constant envelope and desirable spectral properties. However, hardware is required for only one channel, and the multiple-access capability of the system compares favorably with a standard binary DS/SSMA system.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A surface transverse wave-based MSK system

A minimum-shift-keyed (MSK) system using one 1-GHz surface-transverse-wave (STW) resonator in the transmitter and two identical STW resonators in the receiver is described. It is shown to operate with data rates of over 100 kb/s and consume 150 mW. The system has a very high sensitivity and is tolerant to additive noise. Since the signal is never up- or down-converted. this system eliminates high power consumption. The system should find applications in cellular radios and in industrial communications.

Error correction/masking for digital voice transmission over the land mobile satellite system

The development of a 2400-b/s speech digitizer which provides an acceptable level of intelligibility and quality over land mobile satellite channels is described. Performance tests over simulated channels in the UHF band (800 MHz) are presented. The voice digitizer is a linear prediction (LPC) vocoder which uses a channel error correction and concealment procedure tailored to error statistics for a minimum-shift keyed (MSK) downlink to a moving vehicle. The error-handling technique is based on perceptual criteria and utilizes the parametric nature of LPC representation of speech. A single-error-correcting, single-burst-detecting (28, 20) fire code is shown to be the best choice for the application. The intelligibility of the vocoder is measured and compared to the standard LPC-10 algorithm. The major remaining sources of speech quality degradation due to channel errors are determined and ranked.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Serial MSK-Type Detection of Partial Response Continuous Phase Modulation

Partial response continuous phase modulation (CPM) schemes have a high spectrum utilization and also a high immunity to nonlinear distortion, since they have a constant envelope. Schemes with high power efficiency can also be designed when they are coherently detected with a Viterbi detector. These schemes are sometimes complex, however. In this paper two minimum-shift-keyed (MSK)type receivers are studied. The MSK-type receiver can be implemented as a serial receiver and as a parallel receiver. Both receivers are useful for binary modulation schemes with modulation index <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">h = 1/2</tex> . Only coherent detection of signals transmitted over an additive white Gaussian noise channel is considered. The serial receiver can be implemented with only two filters and simple decision logic. The decisions are made serially in one decision eye pattern. Two types of receiver filters are considered. Error probability results are presented for the receiver, both with and without phase and timing errors present in the receiver. It is shown that, assuming perfect phase and time synchronization, the serial and parallel receivers have equal performances. The advantages of the serial receiver over the parallel receiver are the same for partial response continuous phase modulation as for classical MSK; i.e., both in implementation aspects and in the reduced sensitivity to phase errors.

Minimum-shift keyed modem implementations for high data rates

IGITAL communications links capable of conveying data at hundreds of megabits per second (Mb/s) are becoming increasingly important in various applications. An example is the use of time division multiple access (TDMA) transmission through a satellite relay wherein several data channels are routed through single uplink and downlink paths (antenna beams). Separation of the channels from each other is accomplished through interleaving and deinterleaving in time, with possible rerouting taking place in the satellite. When carrying traffic from large metropolitan areas, the required data rates can exceed 100 Mb/s. One such implementation, currently under study by NASA,' involves data transmission at rates of up to 550 Mb/s. Such applications require the use of modulation schemes that use the available bandwidth efficiently. Furthermore, because power is at a premium on board a satellite, the utmost in power efficiency is desired of the chosen modulation scheme. This implies the use of a constant-envelope modulation scheme since amplifiers, such as traveling wavetube amplifiers, are most efficient when operated near saturation. Three popular constant-envelope modulation schemes for efficient transmission of digital data are quadriphase-shift keying (QPSK), offset (or staggered) quadriphase-shift keying (OQPSK), and minimum-shift keying (MSK). Two excellent recent articles [1,2] in IEEE Communications Magazine have discussed their general properties and attributes as well as those of other modulation schemes with constant (or nearly constant) envelopes. Other recent papers [3-61 have presented analytical results and computer

Conversion and Matched Filter Approximations for Serial Minimum-Shift Keyed Modulation

Serial minimum-shift keyed (MSK) modulation, a technique for generating and detecting MSK using series filtering, is ideally suited for high data rate applications provided the required conversion and matched filters can be closely approximated. Lowpass implementations of these filters as parallel inphase- and quadrature-mixer structures are characterized in this paper in terms of signal-to-noise ratio (SNR) degradation from ideal and envelope deviation. Several hardware implementation techniques utilizing microwave devices or lumped elements are presented. Optimization of parameter values results in realizations whose SNR degradation is less than 0.5 dB at error probabilities of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> .

Calculation of error probability for MSK and OQPSK systems operating in a fading multipath environment

A technique is given for determining the error-rate performance of a class of digital communication systems operating with fading multipath interference. The approach uses a truncated series to represent the fading process and takes into account the effects of intersymbol interference caused by linear filtering in the receiver or channel. Application of the method to the cases of minimum shift keyed (MSK) and offset quadriphase shift key (OQPSK) systems reveals a slight performance advantage for MSK.

An Application of Saw Convolves to High Bandwidth Spread Spectrum Communications

A spread spectrum communications subsystem that is based on the separated medium acoustoelectric convolver is described. The subsystem generates minimum-shift-keyed (MSK) waveforms with the aid of SAW filters and performs differential-phase-shift-keyed (DPSK) data demodulation with acoustoelectric convolvers. The convolver provides a BT product of 2200 with a 3-dB bandwidth of 100 MHz. The signals processed by the subsystem have a BT product of 1100. In this paper, the subsystem, the generation of MSK waveforms, and the use of acoustoelectric convolvers are described. Important subsystem performance characteristics, including dynamic range (/spl cong/50 dB), contribution to implementation loss (/spl cong/1 dB), DPSK demodulation, and distortion levels are illustrated and discussed.

An MSK Approach to Offset QASK

This paper demonstrates that an offset quadrature amplitude-shift-keyed (OQASK) signal can be represented as an ncomponent version of a minimum-shift-keyed (MSK) signal. For example, the signal set obtained by summing two MSK signals which are 6 dB different in power and are formed by continuous phase, frequency modulating the same oscillator with two independent binary antipodal data streams, is spectrally equivalent to an OQASK signal set composed of 16 signals in which the symbol pulse is a half-cycle sinusoid rather, than the conventional rectangular form. Such generalizations as the above allow for potentially simpler implementation of spectrally shaped OQASK.