The Effect of Tandem Band and Amplitude Limiting on the E<inf>b</inf>/N<inf>o</inf>Performance of Minimum (Frequency) Shift Keying (MSK)

Abstract

Estimates Of distributions of ranfor high-speed digital computers. F~~~ 1964 to 1966 he was Phoenix, Ariz., where he was engaged in the development of switching dom variables for certain computer communications traffic n,," l o 7 n where he worked in the area of information processing in random model,!! Commun. Ass. Comput. Mach,, ~0 1 . 13, pp, 752-757, Absfracf-Minimum (frequency) shift keying (MSK) is a digital modulation technique which can be viewed either as frequency-shift keying (FSK) with peak frequency deviation precisely equal to f (1/4)RL where RL isthe link bit rate or as an offset-keyed quaternaryphase-shift-keyed modulation. In the absence of bandwidth or amplitude limiting between the modulator and the demodulator, the Eb/Niperformance of MSK is identical to that of coherently detected binary phase-shift keying (PSK). This paper briefly reviews and defines MSK. It then presents a system model in which a tandem assembly of a transmit band-limiting filter, a hard limiter, and a receive band-limiting filter are interposed between an ideal modulator and demodulator. This model is aimed at simulating actual links (such as spacecraft-to-ground links) i i~ which channel bandwidth (Bc) constraints are important, postmodu!ation filtering at RF is objectionable, and transmission through efficient transmitters which operate as amplitude limiters is a requirement.An analysis then derives the Eb/No degradation due to both bandwidth and amplitude limiting. Band limiting alone causes intersymbol interference on the data carried by each of the quadrature phasors but no interphasor crosstalk under the set of assumptions used. With amplitude limiting also present, an interphasor crosstalk mechanism exists. The average symbol distortion, symbol energy reduction, and noise reduction are derived for several periodic waveforms. For composite systems with 3-dB bandwidth (BL)-to-RL Electronics of the IEEE Communications Society for publication Paper approved by the Associate Editor for Communication without oral presentation. Manuscript Corporation, Princeton, N. J. 08540. The authors are with the Astro Electronics Division, RCA ratios of at least 0.6, the theoretical ,%/No degradation is less than 1 dB.Parametric experimental data are then reported on the ,postmodulation spectrum of a transmitter with band limiting plus subs& quent hard amplitude limiting. Data are also presented ,on the &/No degradation measured using tandem assemblies of a bandlimiting filter, an amplitude limiter, and a second band-limiting filter.The amplitude limiter substantially increa$es the level of the spectral side lobes beyond the main lobe. It was found that for all significant values of transmit bandpass filtering plus subsequent amplitude limiting, 99 percent of the transmitted energy is containedFurther, little Eb/No degradation (tenths of a decibel) was measured if BL was greater than 0.65 RL. A rapid degradation of &,/No occurred when BL = 0.55 RL. These data apply for the band-amplitude-band limited system model.The amplitude limiter...

Simulation of a Narrow Bandpass-Limited Satellite Channel

“…On the other hand, the phase of the elliptic filter is too nonlinear. These conclusions are generally either consistent with or corroborated by other simulated or experimental results obtained independently [3][4][5][6][7][8][9][10][11][12]. But a direct comparison of our data with that of the literature would be tenuous because of significant differences in the various approaches.…”

“…Since the bandpass limiter can be implemented with a solid-state device at UHF with much less severe AM to PM conversion problems that can plague TWT implementations at GHz frequencies [4,5,16], the ideal (hard-limiting) bandpass-limiting model is reasonable for our simulation.…”

“…We know of just three other investigations [4][5][6] that are closely related to our objective of communicating at high data rates with the model of Fig. 1.1. However, none of these efforts, which were experimental in nature, permitted both uplink and downlink noise sources simultaneously or included all the modulations we consider.…”

“…We are assuming without verification that AQPSK has the same spectrum as BPSK [28], and that SQPSK has the same spectrum as QPSK [5,29]. Both BPSK 2 and QPSK have the classical (sin r/r) spectrum with a zero-crossing bandwidth of exactly twice the symbol rate [30].…”

“…However, MSK generally has a much smaller fraction of out-of-band energy than QPSK [5 ] . The spectrum of CPQFSK is also quite compact because of the minimum signaling frequency separation for orthogonality and the phase continuity [31,32] .…”