Keeping the mind up with IP technology - Part 2

Traditional land-mobile radio networks have not seen the scale of development and indeed opportunities experienced in other technologies. Radio-over-internet protocol (RoIP) will change that.

RoIP is essentially voice-over-IP with push-to-talk (PTT). This seemingly simple application has a profound impact on a radio network. Users no longer need to use a radio to communicate via the radio network.

Administrators can access any IP-enabled radio from basically anywhere. Operators can use existing, versatile and robust IP networks. RoIP is by nature interoperable; IP-enabled radios are simply nodes on a network, regardless of radio-format or frequency.

A basic RoIP channel connects a voice user to a remote IP-enabled radio via a packet-switched TCP/IP network. The remote radio in turn connects via its RF interface to a mobile user.

One RoIP interface unit (RIU) provides the RoIP interface between user and IP network, another between IP network and radio. Audio, PTT and squelch from the user are connected to the RIU at the local site and from the RIU at the remote site to the radio.

Once installed, IP addresses, codecs, etc are configured and signal levels adjusted, all from a central site. Now the user can make two-way voice calls to mobile radio users.

As with any other technology, RoIP has limitations. Yet they are straightforward and once understood give us the know-how we need to configure our RoIP channel. Analog signals are digitised and together with other user data organised in ‘data packets’ for transport - much like goods in a shipping container.

At the receiving end, packets are reassembled into a constant flow of user data and as needed converted back to analog. This is done by a coder/decoder (codec). Most codecs compress information to reduce bandwidth. Speech can tolerate compression, yet a sinusoid signal can be deformed beyond correct reproduction.

Figure 1: Principle functions of a RoIP channel.

Here, a ‘raw’ codec (no compression) is best used, yet this requires more bandwidth. The minimum bandwidth of a single voice channel is about 36 Kbps using minimum sampling rate and maximum compression (8 kHz/speex).

High-resolution and uncompressed audio requires up to 530 Kbps (32 kHz/raw16bit). If the IP network is congested, data packets can be ‘lost’. Here, TCP/IP is designed to retransmit packets which again can impact the correct reproduction of a time-continuous analog signal.

Obviously, a network needs more than one RoIP channel. These must be configured and maintained. Radio stations are often at remote sites and need to be monitored and controlled remotely. Network messages and parameters need to be read, sent or monitored. All this is done ideally from a central operations centre.

While radio networks are built on common technologies and standards, the organisations that use them have their own unique practices and structures. It is essential that we retain that competence and maximise long-term ROI.

A systems-thinking approach helps us meet these needs and balance costs and efficiency. The first and arguably most crucial step is to define a clear framework of requirements that discerns between necessity and features, priorities and benefits. We stipulate five core functions of a RoIP network:

• Transparent, efficient two-way speech - in all its networked forms;

• Transparent serial and parallel data transport and data configuration;

• Signalling and remote ‘calibration’ of signal paths;

• Dynamic networking of RoIP channels and users;

• Structured, comprehensive and efficient system administration.

Within this framework we then define the structure of the network, its elements and their capabilities. Rather than adapt an ‘off-the-shelf’ system or implement an (expensive) custom solution, we use a ‘best of both worlds’ approach: the bespoke deployment of standard modules.

• RoIP network elements encapsulate functions at the level they are executed at;

• The embedded capabilities are flexible and expendable;

• The system architecture supports the ‘evolution’ of new capabilities;

• The network is ‘upward’ compatible, allowing high-level functions and extension.

Figure 2: The RoIP channel with embedded functionality - system level.

Figure 3: The structured RoIP network.

This structured approach is not new. What is new is the technological means to do this efficiently: the ‘smart’ RoIP network element.

An RIU is by nature a ‘smart’ device. It already comes with its own microprocessor and DSP. It simply makes operational and economical sense to take full advantage of its inherent capabilities.

In a smart RoIP network, each RIU operates largely autonomously. Core functions are embedded within the element - two-way speech, data transport, control and configuration, signalling and tools.

Embedded client/server functions allow an RIU to be configured as a server supporting multiple client RIUs, eg, in group configuration.

This structured approach significantly simplifies system administration and furthers integration with operational control and systems. RIUs are managed as nodes on the IP network. Each RIU can be directly accessed via its embedded user interface (UI) using a simple web browser.

Higher-level systems and applications access the RIU and its functions via the IP network. Operations can readily add and extend functionality at the operations level, without having to adapt the RoIP network elements or their core functions.

Applications and interfaces can be added using simple building blocks (‘soft functions’) such as a ‘soft user terminal’ that provides the two-way voice interface on a PC, a ‘soft channel switch’ that allows a user to switch between allowed RoIP channels, a ‘group configuration’ module to manage groups of RIUs, or interfaces that link to standard applications.

Radios and their networks will continue to evolve as they have, but the underlying infrastructure will change. Our radio network will at least in part become like a computer network. Much of its implementation will be akin to deploying PCs, routers and gateways.

Standardisation of network elements will drive down costs, increase efficiency and reduce downtime, simplify ownership and further customisation. ‘Pre-integrated’ and ‘pre-configured’ sub-systems will be very easy to deploy and deliver excellent return on investment.

Traditionally, complex ‘one-off’ solutions will be more and more replaced by the bespoke and phased deployment of standardised modules and sub-systems.

RoIP will require us to change our mindset and yes, there will be a learning curve. In turn, RoIP will give us unprecedented capabilities and opportunities to develop, expand and enhance our radio network. Be it reduced costs, added features, more efficient control or enhanced interoperability, the possibilities are vast.