An Architecture for High Data Rate Very Low Frequency Communication

Abstract

The very low frequency (VLF) band of 3 kHz to 30 kHz is used for strategic long range communication from shore to ship, in particular, near-surface submarines. The navies of various countries place a lot of importance to the use of VLF band for broadcasting information to submarines. It is thus a simplex mode of communication. The allocated bandwidth is typically limited to the order of 200 Hz. Because of the limited bandwidth, the message source is only text or data and not voice. Classically, frequency shift keying (FSK) and minimum shift keying (MSK) have been used as the modulation techniques for VLF communication with data rates of 50-200 bps. In this paper, authors report the design of an architecture for high data rate VLF communication between 400-800 bps. The key elements of the high data rate communication system are Gaussian minimum shift keying (GMSK) modulation and low delay parity check (LDPC) channel coding. The architecture is completely non-data aided. Thus, carrier phase synchronization, timing recovery, and LDPC frame synchronization algorithms use properties of the signal rather than preamble or header data to perform the respective tasks. The block level description of the communication transmitter and receiver is given in Fig. 1. The transmitter encodes the non-return to zero (NRZ) source data using LDPC codes. The coded data is modulated using GMSK and is transmitted. The output of the source block is assumed to be source encoded. The receiver chain begins with a pass-band analog antenna filter which limits the signal and noise in the band of the signal. The signal enhancement block filters the signal to reduce the atmospheric radio noise (ARN) component. The output is passed through an IF filter with a bandwidth

CPFSK Signal Detection in White and Bursty Impulsive Noises

“…Examples are atmospheric noise in low-frequency communications, ambient noise in shallow underwater channels and impulsive noise in powerline communications, etc. [1]- [4]. This kind of noise The associate editor coordinating the review of this manuscript and approving it for publication was Mohammad S. Khan.…”

“…is referred to as impulsive noise, and commonly modeled by a heavy-tailed distribution. As a typical heavy-tailed distribution, symmetric α-stable (SαS) distribution has received considerable attention from the research community [1]- [8].…”

“…As a typical scenario, SαS noise is dominant for very low frequency and low frequency (VLF/LF) communication system [1]. Because it has constant envelope and high spectrum efficiency, minimum shift keying (MSK) modulation has been widely used in VLF/LF communication system [1]. The detection algorithm of MSK signal in white SαS noise has been investigated in our previous work [19].…”