How LTE and 5G Are Enhancing PTT Performance & Coverage

Push-to-talk over cellular (PTT over cellular, also known as PoC or PTToC) is quickly becoming popular in the industrial operations, public safety, logistics, and field service sectors. With LTE (4G) and 5G networks coming of age, the capabilities, dependability, and range of PTT applications have transcended most of the constraints of old radio systems. This blog will discuss that LTE and 5G networks can improve the performance of PTT and coverage, the ways this is achieved through an architecture or protocol improvement, the tradeoffs in practice, and a preview.

Introduction to What Is PTT Over Cellular-A Brief Primer.

A PTT application (or push-to-talk application) applies a walkie-talkie type of half-duplex voice (and more multimedia) communication to devices, such as smartphones, tablets, rugged devices, by using mobile networks. Rather than an active radio system, PTT over cellular activates LTE/5G (and occasionally Wi-Fi) to transmit voice/data traffic.

The main features of the contemporary PTT applications:

• One touch voice: Press to talk, release to listen.
• Group and broadcast media.
• GPS, messaging, alert integration.
• Opportunity (occasionally) to legacy radios through gateways.

PTT over cellular will have significantly broader coverage (where it is available) than traditional two-way radios (because it does not require base station towers), lower capital requirement (because it requires no base station towers), and can support broader features (including multimedia, logging, etc.

But it is not a simple task to provide reliable and low latency voice communications over a cellular network that is packet switched. It is where LTE and 5G come in.

Key Enhancements LTE & 5G Bring to PTT

Here are the major ways in which LTE and 5G improve PTT performance and coverage:

1. Reduced latency and call setup.

The voice over packet networks had been characterized by delays in the establishment of calls and audio transfer in the previous networks. LTE and 5G, network backhaul, radio scheduling optimization, and voice-over-LTE (VoLTE) or voice over NR improvement ensure that round-trip delays are reduced, and the mouth to ear latency is minimal, allowing near-instantaneous talk.

In mission-critical PTT (TT standardized by 3GPP in Releases 13/14), there are strict KPIs based on call set-up times below some thresholds, and latency limits (e.g. target < 150-250 ms mouth-to-ear).

2. Network slicing and Quality of Service (QoS).

The 5G comes with network slicing and finer QoS control. Carriers have a chance to allocate the slices or virtual network partitions that have been optimized according to traffic on PTT (voice, group calls) such that PTT traffic is given priority even when the network is congested. This guarantees stable performanceAlso, LTE/5G provides differentiated QoS services (e.g. guaranteed bit rates, priority classes) that PTT applications can use.

3. Enhanced coverage through densification, handover, and multi-connectivity.

The smaller the cellular network (the more small cells, the more base stations), the smaller the coverage holes: this implies that PTT users are less likely to enter the dead- zone. Current equipment is also able to do handover more smoothly between cells and even between LTE and 5G layers.

In addition, methods such as LTE-WLAN Aggregation (LWA) can enable devices to connect to LTE and Wi-Fi at the same time to a single stream of data- increasing capacity and coverage in double-wireless areas.

4. Carrier diversity, redundancy, and failover.

A powerful PTT system based on LTE/5G is likely to have a redundant network path (e.g. multiple SIMs, multiple carriers) such that when one network becomes unavailable or congested, the traffic will be re-routed to another. This enhances coverage and reliability in hostile or emergency conditions.

5. Increased bandwidth to better features.

Though voice is used the most, LTE and 5G have higher data rates, which enable PTT applications to have multimedia capabilities: video push-to-talk, image or file sharing, maps, telemetry, and situational awareness. This makes an otherwise basic push-to-talk application an effective communications platform.

6. Local breakouts and edge computing

Delays caused by backhaul or long path routing are minimized by processing PTT traffic near the user (edge computing). In other implementations, the PTT servers or gateways are deployed locally (within the same region) so that voice traffic is not routed across global backbone unless needed, and responsiveness is enhanced.

Performance & Trade-offs: What the Data tells us.

To provide an idea of what is possible, a sample table of standard PTT performance improvements with LTE/5G (compared to older or overloaded networks) is shown below:

According to market research, the PoC (PTT over cellular) market is surging, and the implementation of LTE and 5G is mentioned as key drivers of growth. In reality, properly implemented PTT systems in LTE/5G can provide voice transmission latencies of less than 0.5 seconds, system availability of 99.999, call setup and voice latency of less than 300 ms in most implementations.

However, network quality, backhaul capacity, server architecture (centralized vs distributed) and the status of the PTT app optimization (e.g. codec, buffering, jitter control) are critical to the actual performance.

Challenges & Considerations

Although LTE/5G open numerous possibilities, they still have a number of challenges:

• Network Congestion PTT traffic can continue to contend with other data traffic in highly demanded regions unless it is prioritized through both QoS and slicing.
• Coverage Inefficiencies: Cellular coverage can be low or non-existent in very remote or rural locations and hybrid systems or radio back up can still be required.
• Interoperability: The PTT over cellular is not integrated with legacy radio systems (e.g. LMR, TETRA, P25) without the need of gateways (RoIP).
• Cost & CapEx/OpEx: Edge server deployment, or redundant infrastructure deployment, may have cost; initial investment is not yet a trivial matter in some organizations.
• Security & Encryption: Traffic in PTT should be encrypted with strong encryption, authentication, and a secure design of servers in order to deal with sensitive communications.
• Standardization: Although MCPTT is a 3GPP standard, numerous PTT applications are now proprietary or over-the-top (OTT). OTT PTT does not necessarily ensure real-time or interoperability.

Best Practices for Maximizing PTT Over LTE/5G Performance

In order to maximize LTE/5G PTT applications, remember:

• Adopt MCPTT-compatible solutions or platforms with high KPIs.
• Install regional or distributed PTT servers to minimize latency (edge or local breakout).
• Enabling QoS / priority traffic / using carriers which enable network slicing.
• Redundancy Use redundant SIMs / multi-carrier fallback in mission environments.
• Connect to legacy radio infrastructures through RoIP gateways.
• Measure performance (latency, packet loss, jitter) and dynamically change capacity.
• Maximize in-app codecs and buffering to reduce delay.
• Add failure or offline backup features in case of a loss of connection.

Future Directions & Innovations

• AI / Voice analytics: Voice recognition, Smart routing, network adaptation.
• Stricter IoT / sensor integration: PTT apps might be able to be directly connected to IoT devices (in the near future) to provide automatic warnings or data-driven communication.
• Beyond 5G / 6G: Sub-ms guaranteed ultra-low-latency networks will even blur the radio / cellular boundary.
• intent-driven orchestration: In the next-gen network, intent-based orchestration dynamically assigns resources to PTT flows according to the priorities.
• Private LTE / 5G networks: A business can create their own internal cellular network with inherent PTT services to ensure high reliability and low latency internal communication.

Conclusion

The LTE and 5G networks are changing the capabilities of push-to-talk technology. These mobile networks allow PTT to be reliable and flexible- even in the mission-critical environment by providing lower latency, QoS prioritization, network slicing, redundancy, and sufficient bandwidth to support multimedia. The challenges still exist but with proper design (edge architecture, fallback, interoperability) the full potential of PTT over cellular can be achieved.

StackIOT has a strong, scalable, and secure PTT platform that fits organizations that want to create a solution specifically adapted to your domain. StackIOT provides performance and reliability-based cellular PTT solutions designed to deliver business quality to your enterprise- FTB- learn more at StackIOT.

FAQs

1. What is PTT over cellular?

PTT over cellular refers to the process of providing push-to-talk voice (and more often data) communication over LTE/5G networks, so that walkie-talkie style communication is possible on cellular networks without having radio facilities.

2. What is the difference between a push-to-talk application and a voice call?

A PTT application is instant half-duplex voice: when a button is pressed, you speak and when it is released, you listen and there is little setup delay. It is mission communication oriented as opposed to normal phone calls.

3. Is LTE / 5G truly going to make the PTT reliable everywhere?

It goes a long way in terms of minimizing latency, allowing control over QoS, providing a dense coverage, and redundancy. However in extremely remote places where cellular coverage is unavailable, fallback radio or hybrid solutions are still possible.

4. What is MCPTT?

The 3GPP standard (Releases 13/14) that stipulates the services of PTT over LTE/5G with stringent KPIs, inter-operability, group management, QoS, and resilience capabilities is MCPTT (Mission Critical Push-to-Talk).

5. Is it possible to have PTT applications to work with legacy radio (LMR, P25)?

Yes. Interoperability is frequently provided through Radio over IP (RoIP) gateways providing the ability to seamlessly communicate between users of the PTT app and users of traditional radios.