System Planning

The text below mainly provides a checklist of items and tasks that need to be understood and catered for when starting a TETRA network project.

Differences between PMR and cellular network planning
As most mobile network planners today are experts in cellular network design, it may be useful to highlight the main points that make PMR system planning different to that of main stream cellular network planning, the points being:
      – PMR uses group calls with only one channel per group, but several sites in one call
      – Supports both semi-duplex and full duplex calls
      – Average call duration is much shorter
      – Calls can have multiple levels of priority
      – Radio resources are queued if not free immediately
      – Traffic from and to dispatch stations and command systems
      – Data applications like AVL may represent significant load 
      – Radio network dimensioning is mostly coverage driven 
      – Cell handovers are initiated by the terminal

The above differences are reflected to several differences in the details of the planning process, even if the basic laws of nature like radio wave propagation characteristics remain the same. Thus it is not self-evident that cellular network planning experts would produce high quality PMR network plans without some further education. 

Network planning process flow
Mobile network planning can be roughly grouped into four main groups of task that partly interact with each other:
      – Site planning & acquisition
      – Radio network planning
      – Transmission planning
      – Core network planning

In addition to the tasks related to planning the network itself, equally important is the role played by tasks that can be called “operational planning” of the system and its usage. These aspects are dealt with in another section titled “Numbering”. The relationship between the various network planning phases can be described with the following diagram that shows how sites, radio coverage and transmission are interrelated.

  Site planning
& acquisition

–> 

 Radio network
planning

 –>

 Transmission
planning 

 –>

  Core network
planning

 | <——–

 —-

 —-feedback

 

 

 

 

 | <——–

 —-

 —————–

 —-

 feedback

 

 

The planning phase can be further expanded to lists of planning tasks as follows

  Site planning
& acquisition

 

 Radio network
planning

 

 Transmission
planning 

 

  Core network
planning

 

 

 

 

 

 

 

Equipment rooms
Antenna locations
Power supply 
Feeders and antennas 
Transmission

 

Coverage planning 
Capacity dimensioning
Frequency planning
Radio parameter planning

 

Transmission
topology
Redundancy 
Signalling capacity 
Voice/data payload capacity

 

Traffic capacity
Processing capacity
Delay performance
Application & CC interfaces
Numbering plan
Routing plans
System parameters

Planning challenges
Radio network planning as such requires significant effort. The practical planning of a project is often combined with radio site planning, which requires site visits that consume time. Experience and competence naturally reduce the time needed, but the effort needed is typically said to be in the range one to two sites per working week.

Mistakes made in radio network planning could be expensive to correct afterwards, and thus the use of professional staff and tools  – such as accurate digital maps – for planning is of prime importance.  Typically the expertise and tools can be sought from:
      – In-house experts (if available)
      – Professional consulting companies
      – Manufacturers’ design teams (if considered appropriate)

The main PMR specific areas in radio network design are a couple of aspects in the capacity planning. First, group call traffic for each site must be calculated separately based on the number of active groups present at each site and the traffic per group. This capacity must then be added to the capacity needed for individual calls. Secondly, systems applying queuing should be dimensioned using the so-called Erlang C formula instead of the Erlang B formula (even though in cases when call set-up time requirements are strict, the queuing time target must be set short and the difference between Erlang B & C becomes minor). Also, intense use of data applications may need special attention in capacity planning.

Time is often limited in radio network planning and therefore the option of using leased sites versus building green field sites should be carefully considered taking into account both the total cost and timetable impact. Also, the build permits and other environmental issues may have a surprisingly large impact on the overall timetable.

In core network planning the main PMR specific issues relate to control room/dispatching interfaces and the concepts of fleet or VPN for user organisations that need to be supported, especially in a shared network having multiple separate user organisations who require both privacy and the possibility to cooperate when needed. These operational planning concepts are discussed in more detail in the Numbering section.