Can LoRa Transmit Audio?

LoRa technology can indeed transmit audio signals. Here is a detailed analysis:

1. LoRa Wireless Audio Module: The LoRa wireless audio module WS8302DLS supports the transmission of voice signals through I2S digital audio or analog audio interfaces, and supports PTT function and configuration of audio encoding rate.
2. VLoRa Voice Transmission Solution: VLoRa uses the Codec 2 encoder and decoder to convert low-bitrate voice signals into digital format, suitable for emergency communication on a single LoRa channel.
3. Low-cost and Secure Long-distance Communication System: This system uses LoRa technology for voice signal transmission, achieves long-distance communication through spread spectrum modulation, and uses voice encoding technology to reduce the overall data rate of voice signals to below 7.5 kbps, making it very suitable for voice transmission.
4. Voice Over LoRa™ System: Researchers have developed a Voice-over LoRa system for voice communication in emergency services, which includes a WiFi-to-LoRa gateway and a LoRa-to-satellite gateway, demonstrating the application of LoRa in voice transmission.
5. LoRa Digital Voice Module: The LoRa digital voice module supports full-duplex, multi-party conversation, and reserves priority bits, suitable for real-time audio applications.

LoRa technology can transmit audio signals and has been practically applied and verified in multiple application scenarios.

I. Application of VLoRa Technology in Emergency Communication

The application cases of VLoRa technology in emergency communication mainly include the following aspects:

1. Backup plan for emergency communication system: VLoRa system is designed as an adaptive backup system for emergency communication in areas where satellite signals cannot cover or other communication systems are unreliable, non-existent, or failed. This system can provide voice transmission services when needed, ensuring smooth communication in the event of a disaster.
2. Rescue Messenger System based on LoRa: BitStream-The Rescue Messenger is a LoRa-based solution designed to help emergency rescue personnel communicate effectively with trapped people. This system not only provides customized messages and GPS location information, but can also be integrated into mobile devices to enhance functionality, reducing loss of life and property in natural disasters.
3. High-reliability and High-efficiency Emergency Recovery Technology: The National Institute of Information and Communications Technology (NICT) has built a test environment that uses a hybrid of LoRa and LTE technologies to achieve emergency recovery of the optical control network. Through time-division access control and non-IP/LPWA mesh network, this technology successfully solves problems such as network overload and packet loss, achieving rapid emergency response.

II. Low Data Rate Optimization for Long-distance Voice Transmission with LoRa Technology?

In order to achieve low data rate optimization for long-distance voice transmission with LoRa technology, the following methods can be used:

1. Voice encoding technology: By analyzing and synthesizing the speech signal using a linear predictive coding (LPC) model, the speech signal is decomposed into voiced frames and unvoiced frames, and they are optimized separately to reduce the data rate. For example, the speech signal is decomposed into main frames and sub-frames, the sub-frame with the highest energy is selected, and pulse coding and quantization are used to represent these sub-frames. This method can reduce the data rate to below 7.5 kbps, which is suitable for the data transmission capacity of LoRa modules.
2. Encryption and decryption methods: To ensure message privacy and prevent unauthorized access, an encryption and decryption method has been developed. The generated output bits are divided into packets of 128 bits and encrypted using XOR operation. The receiving party uses the same key for decryption to restore the original message.
3. Chirp Spread Spectrum (CSS) technology: CSS technology uses linear frequency modulation pulse coding to achieve maximum sound quality for long-distance communication. The CSS system has excellent range and data rate scalability, low power consumption, and low latency, making it particularly suitable for long-distance communication.
4. Low Data Rate Optimization (LDRO) function: When the transmission time of a single symbol exceeds 16 milliseconds, the LDRO bit must be enabled to enhance the robustness of LoRa connections under low rate conditions.

III. Architecture and Working Principle of Voice Over LoRa™ System

The Voice Over LoRa™ system is a system that uses LoRa technology for voice transmission and is mainly used for low-bitrate voice communication scenarios such as emergency services. Its architecture and working principle are as follows:

1. Initialization process: The start of the voice stream is triggered by an initialization packet, which contains information about the payload size of 3 bytes and the sequence number of 0. In addition, it specifies the encoder (such as G.711, Codec 2, or G.729) used to encode the audio data.
2. Data transmission: Voice data is transmitted through a series of data packets called Stream Datapackets. Each data packet only contains the encoded audio data as the payload.
3. Termination process: When the voice stream ends, a Stream Termination Packet is sent to release the playback resources.
4. Application layer processing: At the application layer, Python is responsible for voice processing tasks. Use the Pyaudio library to access the audio platform and compress the audio to the Codec 2 module. The compressed data is packed in real time and sent to the Arduino through a serial link, and then transmitted to the LoRa physical layer.
5. Receiver processing: At the receiver, data is transmitted from the Arduino to the application and decoded and buffered by Pyaudio for playback. The bit rate is managed by the selected encoder, and the total amount of generated data depends on the recording duration.
6. Protocol testing and performance evaluation: Researchers have written some applications to repeat the VLoRa protocol under controlled conditions. These applications allow the specification of the encoder and packet size for automated data collection. They analyzed the research results on the physical layer performance of LoRa in the past and found that the generated throughput is sufficient to support the target Codec 2 bit rate (700 bits/second).
7. Delay issue and solution: Because Codec 2 generates data at a fixed rate (700 bits/second), when the transmission rate exceeds this capacity, the data cannot be transmitted immediately. Smaller data packets need to be queued, resulting in higher latency. To solve this problem, a buffer can be created on the sending or receiving end to synchronize the data generation process with the transmission rate. Although this method can stabilize the voice stream, it will increase latency.

The Voice Over LoRa™ system achieves low-bitrate voice communication by utilizing the low-power and wide-area characteristics of LoRa technology.

IV. Specific Implementation Methods for Full-duplex and Multi-party Communication Functions Supported by LoRa Digital Voice Module

The specific implementation methods for full-duplex and multi-party communication functions supported by the LoRa digital voice module mainly depend on broadband spread spectrum technology and full-duplex communication technology. According to the LoRa digital voice module, it uses broadband spread spectrum technology, which means that it can simultaneously transmit and receive on the same channel, thereby achieving full-duplex communication. Users only need to connect a microphone, voice amplifier, and antenna to form a complete intercom, indicating that the module’s full-duplex function is implemented through hardware interfaces.

Furthermore, the Backscatter Multiple Access (BSMA) scheme is mentioned, which is a solution to achieve full-duplex communication in LoRa networks. The BSMA scheme uses LoRa characteristics such as preview code collision and narrowband characteristics to reduce data packet conflicts. It achieves over 100 dB signal suppression ratio through antenna isolation, analog cancellation, and digital cancellation technology, far exceeding traditional methods. The BSMA scheme is not only applicable to LoRa, but also to any protocol that supports device-side channel awareness, indicating that the full-duplex and multi-party communication functions of the LoRa digital voice module can be implemented on the gateway through the BSMA scheme without modifying existing terminal devices.