Hyperbolic frequency modulation for multiple users in underwater acoustic communications

Abstract

Nonlinear frequency-modulated signals have been effectively applied in multiple-user communication schemes. In this paper, we propose to implement a multiple-user communication scheme using hyperbolic frequency-modulated (HFM) signals for underwater acoustic communications. We derive constraints on the HFM parameters to optimally reduce multiple access interference (MAI) at the transmission side. Additional constraints on the frequency-modulation (FM) rate reduce the underwater channel effects of multipath and scaling. The proposed signaling scheme is compared to an HFM-based code-division multiple-access (HFM-CDMA) scheme to demonstrate improved error performance. MOTIVATION AND RELATION TO PRIOR WORKUnderwater acoustic (UWA) communications methods, such as orthogonal frequency-division multiplexing (OFDM) and code-division multiple access (CDMA), have been widelyused for multiple users [1][2][3][4]. As the UWA communications channel is highly time-varying, it can cause undesirable distortions, such as multipath and Doppler scaling, under certain conditions [5][6][7]. Existing UWA communications schemes do not fully exploit matching the UWA channel characteristics to signaling schemes and often have to compensate for that at the receiver. In [1], the distorted OFDM signal due to Doppler is compensated at the receiver using resampling, and any remaining Doppler is removed using inter-carrier interference reduction techniques. A multiple resampling OFDM receiver front-end is designed in [2] such that each resampling branch deals with a different Doppler factor. Adaptive multi-user detection techniques are applied in [3], but their assumed UWA channel model does not include multiple Doppler paths at the receiver. A spread spectrum hyperbolic frequency modulation scheme in [8] can potentially match the UWA channel but only assumes one Doppler scale path and does not compensate for multiple time delay paths that can distort any potential scale diversity. In [9], we design an HFM scheme to match the This work is funded by the National Science Foundation grant NSF-ECCS 1102357.UWA communications channel. The HFM scheme is integrated with the use of a discrete time-scale canonical model, which represents the received signal from a wideband channel as a linear superposition of discrete time shifts and Doppler scalings of the transmitted signal, weighted by the wideband spreading function (WSF) [10]. We demonstrate an inherent joint multipath-scale diversity using this scheme, and we combine it with direct sequence CDMA for use in multi-user UWA communications. The different users are distinguished by a unique pseudo-noise (PN) sequence [9]. As we demonstrate, the scheme can successfully resolve information bits at the receiver side, but the performance degrades as the number of users increases.A nonlinear frequency-modulated signaling scheme is developed in [11] by deriving constraints on the nonlinear phase function of the transmit signal to achieve orthogonality; the scheme, combined with frequency-hopping CDMA, is use...

JLHS: A Joint Linear Frequency Modulation and Hyperbolic Frequency Modulation Approach for Speed Measurement

“…The construction of a new family of frequency hopping codes called hyperbolic frequency hop codes was given, and it was shown that the hyperbolic frequency hop codes possessed nearly ideal characteristics for use in both types of system. Zhou et al [21] derived constraints on the HFM parameters to optimally reduce Multiple Access Interference (MAI) at the transmission side. Additional constraints on the frequency-modulation rate reduced the underwater channel effects of multipath and scaling.…”

Multi‐user underwater acoustic communication using binary phase‐coded hyperbolic frequency‐modulated signals

“…In addition, multi‐user HFM is also studied in the UWA channel. Multi‐user communication for the UWA channel in [12] is accomplished by using an HFM signal and to reduce MAI different FM rates are used, but the surge in the number of users results in BER degradation, and up to four users can be catered. Recently, the researchers in [13] implemented hyperbolic chirp using pseudo‐random (PN) codes for different users, and orthogonality was maintained using three methods which include Gram–Schmidt iteration, insertion, and multiplication methods, respectively, while at the receiver simple matched filter was used.…”

Impact of MAC Delay on AUV Localization: Underwater Localization Based on Hyperbolic Frequency Modulation Signal

“…Owing to the high-temporal correlation, the multiple HFM signals which arrive at the receiver at the same time can be separated using a bank of matched filter. In other words, the different ANs are able to transmit their packet simultaneously without collision [ 8 , 9 ]. Accordingly, the localization performance can be decoupled from the MAC delay.…”