I. System Overview

1.1 System Background

Very High Frequency (VHF) communication is the most critical voice‑based communication method in the maritime domain, widely employed for vessel traffic services (VTS), search and rescue operations, collision avoidance, port‑operations coordination, maritime administration, and the dissemination of safety information. Traditional VHF systems rely on dedicated shore‑based equipment and circuit‑switching to establish the communication network, but they suffer from significant drawbacks, including low bandwidth utilization, high operational and maintenance costs, and the inability to operate unmanned at remote shore stations.

With the maturation of IP networking technologies and the widespread adoption of VoIP (Voice over IP), integrating VoIP into maritime VHF communication systems has become an industry trend. Maritime VHF VoIP communication systems digitize VHF voice signals and transmit and switch them over IP networks, thereby enabling a transformative shift in VHF communications from traditional circuit switching to packet switching.

1.2 System Architecture

The maritime VHF VoIP communication system employs a pure IP, end-to-end radio transmission control architecture. The system’s overall architecture is composed of the following layers:

(1) Shore Station Equipment Level

Transceiver equipment deployed at each VHF base station is responsible for transmitting and receiving wireless signals in the VHF frequency band. The transceivers output analog audio signals, including received audio, transmitted audio, and PTT control signals.

(2) Signal Conversion Layer (Core)

Base station side: The analog audio from the VHF transceiver is connected via an audio cable to the ZMUX‑4102 VoIP multiplexing device. The ZMUX‑4102 digitizes and encodes the analog audio—supporting mainstream codecs such as G.711 and G.726—packages it into IP datagrams, and forwards it to the IP transport network.

On the control center side, a ZMUX‑4102 is deployed as well, performing the opposite function: it decodes voice data packets from the IP network back into analog audio signals and outputs them to the control center’s audio equipment—such as dispatch consoles, loudspeakers, and headset microphones—while simultaneously encoding the operator’s analog voice input into IP packets for transmission back to the base station. In this way, the two ends use the ZMUX‑4102 to achieve bidirectional conversion between analog and IP, enabling seamless integration between VHF analog radios and the IP network.

This device is compatible with conventional analog radio standards and supports multiple signaling protocols, including MDC1200, EIA Tone Remote, Selcal, and DTMF.

(3) IP Transport Network Layer

VoIP packets are transmitted between the ZMUX‑4102 at the base station and the ZMUX‑4102 at the control center over the IP transport network provided by the carrier. The transport network may be a dedicated line, an MPLS VPN, or the public Internet, and it supports the SIP protocol.

(4) Core Control Layer

Communication servers deployed at the VTS center or maritime command center are responsible for VoIP session management, call routing, channel allocation, and unified device management. The system supports redundant server configurations to ensure high availability.

(5) Operator Terminal Layer

Operators can initiate calls, monitor communications, and control remote VHF base stations using a PC or workstation running the radio‑operation terminal software. The terminal interface supports touchscreen operation and is compatible with a variety of display devices.

The architecture’s decentralized design eliminates the need for a centrally managed switching node; voice streams are transmitted directly between the two ends via the ZMUX‑4102, enabling flexible routing and low latency.

II. System Implementation

Network topology diagram of this system:

The implementation of this system follows a streamlined and efficient workflow, with particular emphasis on the deployment and connectivity of the ZMUX‑4102 equipment:

1. Base station installation: Install the ZMUX‑4102 in each VHF base station equipment room, connecting it via cables to the audio interface and the PTT control interface of the existing VHF transceivers.
2. Control Center Installation: Install the ZMUX‑4102 in the control center server room or next to the operator console, and connect its analog audio interfaces to the dispatch console, speakers, microphones, and other audio devices.
3. Network Configuration: Configure IP parameters for all ZMUX‑4102 units to ensure seamless intercommunication between base station‑side and central‑side equipment over the operator’s IP transport network.
4. System integration testing: Deploy the central server software and the operator terminal software, and configure the parameters for each channel. Conduct end-to-end voice call tests and DSC function tests to verify voice quality, latency, and other performance metrics.
5. Trial Operation and Delivery: The system is put into trial operation and, following completion of operator training, is officially delivered.

The entire implementation process makes full use of existing VHF base stations and the control center’s existing equipment, with the ZMUX‑4102 serving as the core conversion node to swiftly complete the VoIP upgrade.

III. Core Functions

3.1 Remote Voice Communication

Operation center personnel can establish a communication link with the transceivers at remote base stations via an IP network, thereby conducting VHF voice communications with vessels within the jurisdiction. The system supports distinguishing between duty channels and monitoring channels using the left and right audio channels.

3.2 Remote Device Control

It supports remote control of VHF radio station reception, transmission, and channel switching. Maritime regulatory personnel can easily perform remote operations on VHF base stations—such as remote broadcasting, remote frequency modulation, and remote power adjustment—simply by using an operator terminal.

3.3 Multi-Channel Management

The system supports the management and control of 2 to 12 VHF channels, allowing users to flexibly expand channel capacity. Operators can simultaneously manage and connect up to 12 radio channels.

3.4 Internal Communication

Supports instant voice communication between operators via internal intercom.

3.5 Recording and Playback

The system is equipped with an automatic, continuous archiving function that indexes and records all voice and data, enabling rapid playback of the latest voice messages and phone calls directly on the operator’s terminal.

IV. System Advantages

4.1 Bidirectional Conversion, Smooth Upgrade

The ZMUX-4102 VoIP multiplexing device serves as the system’s central switching hub. It interfaces directly with the analog audio ports of existing VHF transceivers, enabling a seamless upgrade of traditional analog VHF base stations to IP‑based communication nodes without the need to replace or modify the existing analog radio equipment, thereby safeguarding users’ existing investments.

4.2 Expanding Communication Coverage

Traditional VHF communications are constrained by dedicated line transmission and base station deployment, resulting in limited coverage. By leveraging the wide-area reach of IP networks, VoIP systems have enabled a critical shift from unattended stations to remote operator‑assisted operation, significantly expanding the communication range of VHF systems.

4.3 Reducing Construction and Operating Costs

Compared with traditional VHF systems that rely on dedicated shore‑based equipment and circuit‑switching, the VoIP solution leverages existing, mature IP infrastructure for long‑distance transmission. By utilizing off‑the‑shelf IT hardware and standard network protocols, this approach significantly reduces both capital and operational costs.

4.4 Enhancing System Flexibility and Scalability

The system employs a modular design and an open architecture, making it easy to scale and upgrade according to evolving requirements. Channel capacity can be flexibly expanded through software licensing. The system can seamlessly integrate with other communication networks, vessel traffic management systems, or third-party platforms.

4.5 Enhancing Voice Quality and Management Standards

The system employs mainstream audio codec formats (such as G.711, G.726, and GSM) to ensure clear voice quality. Its digital voice‑management solution enables automatic call recording, storage, and remote playback, meeting the modern requirements for voice management in VHF communication systems.

4.6 Enhancing System Reliability

The system supports redundant configurations for the controller, power supply, links, and channels, ensuring high availability.

4.7 Achieving Unattended Operation

Remote shore stations can operate unattended, with staff at the control center able to perform all operations and monitoring of the remote VHF base stations. This shift not only reduces labor costs but also enhances working conditions for personnel at remote sites.

4.8 High compatibility

The ZMUX-4102 is compatible with traditional analog radio systems, enabling existing analog radio equipment to leverage mature IP infrastructure for long-distance transmission.

V. Future Extensions

5.1 Channel Capacity Expansion

The system supports the gradual expansion of channel capacity through the purchase of software licenses, allowing users to flexibly adjust system capacity in line with their business needs.

5.2 Multi-Site Network Expansion

The system can seamlessly integrate new VHF base stations into the existing IP network architecture. New sites require only the deployment of a VHF transceiver and a ZMUX‑4102 device to connect to the existing system, thereby extending VHF signal coverage across a broader maritime area.

5.3 Functional Module Extension

The system can integrate a variety of optional functional modules:

• Radio-based positioning (TDoA/RDF): Leveraging multi‑station time‑difference‑of‑arrival techniques to locate and visualize VHF signal sources.
• AIS Information Management: Integrates data from multiple AIS base stations to construct a unified traffic situational awareness map.
• Telephone module: Operators can directly dial mobile or landline phones from the console.
• Monitoring and Management System: Enables automated monitoring of all system components.

5.4 Intelligent Upgrade

The system can be deeply integrated with artificial intelligence technologies to deliver intelligent functions such as voice command recognition and text-to-speech broadcasting. For example, it can swiftly convert critical information into clear, intelligible speech, ensuring that emergency alerts are communicated to vessels at sea without delay.

5.5 Integration with the e-Navigation Framework

The system design complies with the relevant standards and recommendations of IALA (International Association of Lighthouse Authorities) and is interoperable with maritime services under the e‑Navigation framework.

5.6 Digital Voice Channel Expansion

With the advancement of VHF-band digitalization, the system can support four or more digital voice channels on each 25 kHz maritime VHF voice channel, further enhancing spectrum efficiency.

VI. Summary

The maritime VHF VoIP communication system is an innovative solution that brings modern VoIP technology into the realm of maritime VHF communications. Built on a pure IP architecture and centered around the ZMUX‑4102 VoIP multiplexing device, it efficiently converts the analog audio signals from VHF transceivers into IP packets, thereby achieving digitization, networking, and intelligent operation of VHF communications. This system effectively addresses the limitations of traditional VHF systems—such as high installation costs, limited coverage, elevated maintenance expenses, and the difficulty of staffing remote shore stations—while offering significant advantages in expanding communication reach, reducing operational costs, and enhancing management efficiency. Moreover, the system boasts excellent scalability, allowing for channel expansion, site capacity upgrades, and functional enhancements as business needs evolve, making it an ideal choice for meeting the modernization demands of maritime communications.