This paper presents a resilient framework for real-time, low-bitrate voice communication across heterogeneous wireless networks in emergency Search and Rescue (SAR) operations. The system supports IP-based voice transmission from high-bitrate Wi-Fi networks to constrained Long Range (LoRa™) and Direct Sequence Spread Spectrum (DSSS) links. A key innovation is an adaptive flow control mechanism that manages link asymmetry, achieving over 98% successful packet delivery. The design extends existing emergency satellite communication channels by enabling voice support without disrupting ongoing services, enhancing utilization of underused spectrum. Furthermore, the system is low-cost and rapidly deployable, offering a practical alternative to traditional solutions. Structured over-the-air and emulated testing demonstrate reliable sub-1 kbps voice transmission with consistent latency, jitter, and inter-arrival time across all links. These results highlight a viable upgrade path for legacy SAR systems operating in remote or infrastructure-degraded environments, as well as in areas where mainstream networks are rendered inoperative by disasters. • Novel IP protocol enables voice transmission over links below 1 kbps. • Codec 2 compresses voice to 700 bps while preserving intelligibility. • VoLB protocol supports voice across low-bitrate heterogeneous links. • Evaluated latency and jitter over Wi-Fi, CSS, and DSSS networks. • Achieves sub-0.8 s latency and jitter consistently below 0.05 s.

Next generation satellite systems are required to perform robust frame synchronisation in the presence of large frequency offsets at low carrier‐to‐noise ratios. Differential correlation‐based frame acquisition is an appealing choice for these systems as it provides adequate performance with reasonable complexity. However, the theoretical characterisation of the multi‐span differential correlation metric is still an open problem due to the fact that the correlation outputs with multiple delays are correlated. In this study, the authors derived novel closed‐form approximations for the distribution of the multi‐span differential correlation metric as well as the probabilities of miss‐detection and false alarm. The close agreement between the simulated and theoretical receiver operating curves validates the analysis. This analysis can be used to characterise the performance of multi‐span differential correlation‐based frame synchroniser in terms of the number of delays without running computationally extensive Monte Carlo simulations.

This paper is concerned with enhancing situation awareness messaging using multi-user detection (MUD) techniques. Situation awareness messaging involves sending short packets of situation update data. Low latency is an important requirement. This paper focuses on using satellite communications which have a substantial propagation delay. Random access systems without channel feedback information are particularly preferable for such situations. However, the main draw back of these systems is their low channel utilisation. In this paper, the capacity of a MUD-based random access system without a feedback channel is analysed. The results obtained showed substantial improvements when the system is employed with multi-user detectors. A large spread of received packet powers is typically expected in wide area mobile applications. In many implementations, a spread of powers inhibits receiver performance however when MUD is employed it becomes an enhancing factor.

The true Cramer-Rao lower bound (CRLB) is derived and evaluated for the estimation of carrier phase of Star 16-quadrature amplitude modulation (QAM) and can be simply applied to carrier frequency estimation. Different geometries are investigated by varying the ring ratio (RR). For signal-to-noise ratios (SNRs) between 6-15 dB, the CRLB with RR=3 is lower than that of Square 16-QAM. A modified phase estimator is presented, which closely follows the new CRLB. Investigation of symbol error performance in short packet length reveals Star 16-QAM to be superior to Square 16-QAM for SNR<13 dB, which is a reasonable operating range for a coded system. Although Square 16-QAM and Star RR=1.8 are optimum for a perfect receiver, when the effect of phase estimation is considered, we find Star RR=3 to be better for SNR below 10 dB.

In this paper, we present the true Cramer-Rao lower bounds (CRLBs) for the estimation of phase offset for common quadrature amplitude modulation (QAM), PSK, and PAM signals in AWGN channels. It is shown that the same analysis also applies to the QAM, FSK, and PAM CRLBs for frequency offset estimation. The ratio of the modulated to the unmodulated CRLBs is derived for all QAM, PSK, and PAM signals and calculated for specific cases of interest. This is useful to determine the limiting performance of synchronization circuits for coherent receivers without the need to simulate particular algorithms. The hounds are compared to the existing true CRLBs for an unmodulated carrier wave (CW), BPSK, and QPSK. We investigated new and existing QAM phase estimation algorithms in order to verify the new phase CRLB. This showed that new minimum distance estimator performs close to the QAM bound and provides a large improvement over the power law estimator at moderate to high signal-to-noise ratios.