White Paper
Improving TETRA ba station coverage
with revolutionary radio access solution
遨游宇宙
地欲解析
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Contents
Executive summary
3 Challenges when building the radio network
4 Coverage 4 Capacity 4 Quality
感谢信疫情
4 Other radio access issues
5 What can be done to improve TETRA coverage
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榴莲牛奶绕口令How the Nokia TB3 TETRA ba station solves the coverage problem 6 Nokia TB3 TETRA ba station capacity benefits 7 Conclusions
7 Terms and abbreviations 8
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Executive summary
TETRA networks usually have relatively few urs, making the cost of coverage per ur often substan-tial - typical networks are tho ud by the Public Safety organisations, which have tens of thousands, rather than millions of TETRA urs.
Yet, TETRA network coverage is expected every-where, at any time - a fire crew could easily find themlves in an unpopulated area, while a police officer would also expect indoor coverage in the bament of any downtown building.
At the same time, TETRA radio terminals are getting smaller and their radio performance is improving. Low power portable terminals clearly outnumber the high power mobile terminals and urs expect equally good coverage from both. High redundancy is also often a basic requirement – two radio carriers or heavy overlapping coverage is a minimum re-quirement. This also often solves capacity needs.
Unlike public cellular networks, building a TETRA network is typically driven by coverage, rather than capacity. Maximum coverage at minimum cost is particularly true when building TETRA networks. The new Nokia TB3 TETRA ba station is a solution that meets differing needs: •
A cost driven network rollout, where the obtai n-able coverage and quality of rvice is provided for the given number of ba station sites • A coverage driven network rollout, where the max imum coverage is provided by fewer sites.
有春的诗句
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Challenges when building the radio network
瓜子怎么种植Planning, implementing and main-taining the radio network are big challenges. The total cost of owner-ship must be t against the ne t-work’s technical perfor mance and the needs of the end-ur and so affordability and cost of rvice, combined with a high quality of rvice, are clear drivers for both the network owners and the end-urs.
In a TETRA network, ba station site rentals and transmission costs typically make up 80% of annual operating expenditure, which in turn forms 50-80 % of the total cost of ownership of the network, so it really does matter how the network is built.
There are veral factors in radio access that should be taken into account when planning and imple -menting the ne twork.
Coverage
TETRA network coverage is ex-pected everywhere, at any time: a fire crew could easily find the m-lves in an unpopulated area, while a police officer would also expect indoor coverage in the ba
ment of any downtown build-ing. One of the most important properties of the TETRA ne twork is therefore its radio coverage, which in turn is affected by variables such as the performance of TETRA termi-nal and ba station performance, antenna arrangements and the lo-cations of ba stations and urs. More coverage related issues are discusd on page 6.
Capacity
Most TETRA networks are not capac-ity driven, as urs number in the tens of thousands rather than mil-lions. Urs’ operational areas are well known and a typical ur pro-file differs from that of public cellu-lar urs – the network is for pro-fessional u and group calls and SDS/status messages dominate the communication. In normal opera-tion, the load on the ne twork is also rather evenly distri buted over the whole 24 hours and the demand for capacity is not as concentrated into busy hours as in public ne tworks. Particularly in rural areas, the need for high redundancy, such as re-dundant radio transceivers or over-lapping coverage, easily increas network capacity.
High capacity solutions that are widely ud in public cellular net-works, such as micro/pico cell solu-tions, are hardly ever required for TETRA networks. Often one (three traffic channels) or two carriers (7 traffic channels) are enough and four carriers (15 traffic channels) can also often fulfil the normal ca-pacity demand in denly popu-lated urban areas as well.
On the other hand, public safety networks often need to deal with sudden capacity demands, such as incidents where tens or even hun-dreds of urs and groups need the TETRA radio rvice in a very small geographical area.
Group calls combined with high cell density can create additional load on the network. Each ba station, rving members of the active talk group, rerves a traffic channel for the talk group and the more cells involved in a call the more channels are rerved.
Quality
Along with the coverage and capac-ity, the third technical dimension in radio network design is quality, with the target being to reach a good quality of rvice with a
minimum level of interference. The reference carrier to interference (C/I) ratio in TETRA system is 19 dB, with the principal source of inter-ference being the lack of freque n-cies – sometimes the available spec-trum ts challenges to network designers. Careful frequency plan-ning helps minimi this, but often it cannot fully solve interference problems.
The interference generated by other TETRA terminals, TETRA ba sta-tions and other possible noi
sources, such as ever-increasing man-made noi, can have a vere impact on the quality of rvice, often degrading the rvice area. Interference becomes a problem when the ratio between the rving signal and interfering signal be-comes too low. The probability of interference occurring increas when the terminal is working in an area with a weak rving signal strength, for example clo to a cell border or indoors. This is especially true in initial, often cost driven network design where the radio rvice is provided from the prede-fined number of ba station sites. Often this happens during the net-work start up pha where the cov-erage design is bas ed on mobile terminals rather than low power handheld terminals.
The interference may be experi-enced by the end-ur as effects that include reduced out - or indoor coverage for handhelds, lost calls and bad voice quality.
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Other
radio access issues
Site acquisition is today one of the most demanding tasks faced by the builder of radio networks as site location and its available infrastruc-ture have a great effect on the radio performance. Unfortunately, the final site lection does not always favour the radio performance and the best performing radio site may not be the one lected, due to fac-tors such as:
•
Overall site costs (rentals, masts, power systems, ante n-nas, transmission)带着梦想飞
• Usage of existing sites and in-frastructure
• Transmission availability •
Various regulations and per-missions t by authorities, city councils, landlords etc. Network planning and dimension-ing is often bad on the theoretical
calculations that takes into account only the radio performance issues - coverage, capacity, quality - and provides an excellent basis for ne t-work dimensioning. However, even during the initial dimensioning pha, the above 'real life factors' need to be taken into account.
What can be done to improve TETRA coverage
As mentioned above, radio cover-age is probably the most important property of the TETRA network. So what are the methods that can be ud to improve radio coverage? The most common methods are briefly introduced below. Higher antenna heights Higher transmit power • High power transmitters •
Transmit combining methods
Receiver nsitivity improv ements •
Improved Digital Signal Pro c-essing (DSP) algorithms • Diversity reception (uplink) • Space or polarisation diversity •
Diversity combiner techniques
Sectorising •
Virtual ctors (only uplink di-rection)
•
True ctorising (both down- and uplink)三合泥
Antenna solutions • Omnidirectional antennas • High gain panel antennas • High gain X-polarid antennas •
Mast Head Amplifiers
Radio repeaters (cell enhancers) •
For special indoor solutions
All the methods have their draw-backs as well - higher antenna heights are often difficult to
achieve, very high transmit power (e.g. > 100 Watts) in a ba station transmitter is not really a cost effec-tive solution, high transmit power in portable terminals means shorter battery times, doubling the antenna gain also means doubling the size of the antenna etc. Some improv e -ments commonly ud in public cellular networks, such as frequency hopping, are not specified for TETRA at all.
