Project CHORIST

STATE OF THE ART

Most public safety organisations (police, fire brigades…) use either analogue or digital private communication networks, also known as Professional Mobile Radio (PMR) systems. These systems provide standard unit calls, but mainly group calls which allow several users to discuss in closed group, one user speaking and the others listening. Usually, a dispatcher located in a control room collaborates closely with field teams. Direct communications (i.e. without infrastructure) are a significant added value. All these services include powerful security features. Interfaces with public telephone networks are setup.

Figure 9: PMR mobile (TETRAPOL)

Data services today consist of sending SMS and very limited amounts of raw data.

Standards of the digital PMR world consist of TETRA, TETRAPOL and P25.

LONG TERM VISION

Description

Though technologies (radio interface and network protocols) for the future will differ drastically from the ones used today, end-user services will still be based on and be developed from today's services.

Services

On top of legacy services from narrowband PMR systems such as the unit calls, group calls and SMS, end users will be provided with new data services thanks to the available radio interface bandwidth

• real-time or off-line video streaming of recorded files by other field teams, or by video surveillance systems
• files transfer:
  • maps (topographic, city, buildings schematics…)
  • Digital cameras high-quality photos (for scene analysis, for facial identification…)
• aerial or satellite pictures
  • Fingerprints
  • Personal identification including criminal / terrorist intelligence
  • Car registration through plate number identification
  • Medical records
  • Hazardous materials
  • GIS data, showing static information (maps, roads, etc.) as well as dynamic ones (vehicle & people locations)
• Remote control of automatic devices (e.g. traffic signals or cameras)
• Email access
• Web browsing (intranet and internet) and many other applications not yet foreseen!

Figure 10: Mesh node

Protocols

PMR will benefit from both telecommunication technologies dedicated to professional applications and network technologies developed for the general public. The Internet Protocol (IPv6) suite (multicast, mobile IP, VoIP…) will have to be adapted to the PMR which differs from general public usage by higher security constraints, clustering, uploading instead of downloading, resource management, intensive use of wireless, mobility

Network protocols will be interoperable so that the same level of service is provided wherever someone is roaming; connection through public networks will be ensured in a seamless and transparent way to the user (such as satellite usage for long range deployment). Though some applications already exist in today's narrowband PMR networks, totally new applications which are both dedicated to public safety and making bandwidth-efficient have to be designed. To ensure interoperability between applications, standards will need to be developed which will define the protocols which allow these applications to communicate with each other, as well as the format of data structures maintained.

Radio interface

Modern digital communications technologies (QAM, OFDM), usually split into Wideband and Broadband services will be used to transmit information

Figure 11: TETRA TEDS base station

• Wideband: The TETRA Enhanced Data Service (TEDS) standard plans for enhancing existing TETRA PMR networks with a data rate between 30 and 150 kbit/s per channel. This allows most data services, except the real-time video streaming.
• Broadband: WiMAX and LTE (Long Term Evolution) technologies are competing to provide end users with 1-5 Mbit/s; WiFi has been discounted as it lacks adequate security and QoS management. These technologies can be used along with narrowband networks (overlay) or they can replace them to provide VoIP and data services. The mesh network technology promises to allow automatic radio coverage extensions inside buildings and in underground car parks.

Though promising, these technologies will need frequency spectrum allocation which is dedicated to public safety and this is far from being guaranteed at this time.

INNOVATION

• IP radio network allowing a huge set of video and data access applications for public safety field teams.
• Vehicular to pedestrian broadband cells.
• A self-forming inter-vehicular IPv6 mobile broadband wireless core network:
  • Two-tier, rapidly deployable and auto-configurable core network, where dynamically - allocated cluster-heads (CHs) allocate the radio resources (MAC/PHY) to the first tier.
  • Flexible routing decisions based on traffic identification.
  • Negotiated Quality of Service (QoS), naturally managed by using the Class of Service label fields.
  • Compatibility with security approaches (L3) as IP packets remain untouched inside the core network (e.g. with Virtual Private Networks -VPNs).
  • IPv6 unicast and multicast support.
• VoIP-distributed Group Call application taking advantage of the IP multicast features. Connection with legacy PMR network is done through a patch by Dispatch Operators.
• A vehicular-to-infrastructure WiMAX off-the-shelf long-range backhaul.

BENEFITS and IMPACTS

Wideband or broadband PMR systems will allow authorities to provide a more effective response during field operations: more information is accessed by field teams (pictures, maps, team deployment…) and by control rooms (to assess the situation and take more informed decisions). Moreover, rapidly deployable extensions will reduce the time and burden of deploying such networks inside buildings or following major disasters which have damaged the local PMR network.

High-level technology and access to more information will also bring have the drawbacks of information-overload, which will need to be managed.

Research, development and deployment of the radio networks, the associated mobile devices and the end-user applications will stimulate the sectors of industry and research that will also benefit from the enormous potential of data usage in PMR.

THE PROTOTYPE

The development of the Module 3 prototype was conducted by THALES Communications, EURECOM, TKK (Helsinki University of Technology) and EADS Defence and Security.

2 prototypes were developed in parallel:

• a rapidly-deployable broadband ad-hoc mesh network (THALES Communications, EURECOM) with VoIP applications (EADS DS)
• a TEDS base station and modem (EADS DS)

In parallel, TKK has studied and experimented with local WiFi extensions of these networks; and EADS DS made studies on the use of WiMAX backhauls.

Broadband mesh technology constitutes the cornerstone for the construction of an ad-hoc, mobile core network, integrating two important capabilities: long-range coverage and QoS capabilities.

The rapidly deployable broadband ad-hoc mesh network

In order to build such an emergency broadband mesh network, a novel broadband air interface has been implemented. The MAC layer is label-oriented, where a label corresponds to a particular route within the mesh with negotiated QoS. Nodes in the mesh typically route traffic for several labels simultaneously. Moreover, the MAC layer is clustered, with dynamically-allocated cluster-heads (CHs) managing radio resources (MAC/PHY).

Figure 12: Broadband mesh MAC topology cluster

CHs are typically the best-connected nodes in a particular geographical area. In addition, the MAC layer provides distributed mechanisms for path discovery and maintenance. The mechanisms are based on MAC/PHY measurement reporting.

This broadband mesh network is complemented by a Label-Switching approach. The label-switching mesh interconnects with IP at the edges of the mesh network. Such an approach allows for flexible routing decisions, under the control of CHs. QoS is naturally managed by using the Class of Service field of labels. Labels are local to node and allow for local recovery decisions under the control of the Cluster Head. In effect, the label-switching approach is a set of techniques used to route packets at layer 2.5 (under IP layer) in a domain. IP packets entering a domain through an Edge router are assigned a label.

'Ingress Nodes' push labels according to QoS requirements while 'Egress Nodes' remove labels when exiting the MPLS domain. Labelled packets are switched by intermediate routers using the route defined by a list of labels. In MPLS, a specific protocol (LDP: Label Distribution Protocol) exists to assign labels locally in each router along the route. The LDP protocol is completely new: CHs play a central role in this respect. CHs will allocate the labels of each router residing in their cluster. Each mesh router services terminals on one interface and is connected to other routers on another interface. For the terminals it is acting as an In / Egress node; when relaying traffic, it is acting as a Label Switching Router (LSR).

This method allows for fast packet-switching based on QoS, traffic flow aggregation, and provides virtual paths between Ingress and Egress nodes. Moreover, this approach allows the communication system to be efficient in term of QoS management interoperability.

Figure 13: Video for field units

WiFi extensions

The wireless inter-vehicular backbone provided by the broadband ad-hoc mesh network is complemented by vehicle-to-pedestrian WiFi links. Mobile WiMAX would be more suitable, but this was not available at the time the tests took place.

No development on WiFi was made, although theoretical studies, laboratory experiments and field tests were conducted to check if that technology was suitable.

Simulations of pedestrians using voice and data (video) show that video quickly hampers voice transmission, as QoS is not managed. Requesting too many communications without quota causes voice transmission to be affected by collisions (leading to transmission errors), delay and jitter. The conclusion is that, though WiFi does not provide QoS management, applications will do so.

Tests showed that the H.264 video codec would be suitable to transmit streaming video on TEDS with a data-rate of 38 kbps. However, the image size is rather small and it is preferable to transmit a few high quality images than many of low quality.

VoIP

An application emulating standard PMR half-duplex group calls has been implemented. It works over IP, using the benefits of the multicast feature, allowing it to distribute IP packets only to those who are interested in them. Voice packets as well as most of the signalling are transmitted over RTP. For local coverage (say 30-50 nodes), the application works without infrastructure, i.e. in a peer-to-peer way: the nodes discover each other and users are able to participate in the groups which they have authority for. For large scale deployments, groups of 30-50 nodes can be aggregated, each being in contact with the other through proxy which implements SIP/RTP protocols derived from the ISSI used in the P25 standard.

One of these nodes was turned into a dispatcher position. It can be connected to a TETRAPOL dispatcher position (SADP) allowing it to connect a group communication in the IP world to a legacy group communication. The voice packets are translated between the two worlds; more important, speaker arbitration is done so that only one user is allowed to speak at any given time.

Figure 14: Satellite backhauling

TEDS

A preliminary version of the base station implementing the TEDS standard has been set up for laboratory and field tests. A test modem has also been added. Both implemented only limited features, so the performance levels achieved during the tests are far below what is expected for the product. WiFi extensions have been added to prove the interoperability of heterogeneous means.

Though the rapid deployment of a TEDS base station is possible, the main goal of TEDS is to augment the capabilities of today's narrowband TETRA infrastructure