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Wireless local loop

This note describes how ATDI software can be used across current Wireless Local Loop technologies including DECT and PMP to design, optimise and roll out networks employing technologies such as TDMA, CDMA, FDMA and mixed time and frequency domain transmission systems. The methods and sub-tools within systems such as ICS telecom nG have come from our work with various customers. The following general modelling methods have application in fixed radio access/wireless local loop and are included in ATDI planning tools.

General WLL Planning Methods

The following general modelling methods have application in WLL networks and are included in ATDI planning tools. Please refer to the technologies section on microwave links for details of tools for transmission bearer planning.

• The ability to compute the coverage of ground area from a given transmitter type and specification to a given receiver type and specification.
• The ability to compute the degree of interference suffered by both subscribers (down link) and base stations (up link) from all on the same or adjacent channels.
• The degree of resilience built into a system allowing the network to be optimised for overlap, traffic demand or critical coverage.
• The ability to link the planning tools via a network to develop the system using a number of planners each with privilege to change their own zone yet compute the effects of those adjacent.
• The ability to link the planning tools via an Open Database Connectivity protocol to external database such as Oracle and MS Access allowing the sharing of engineering data across a multi-discipline project team.
• The counting of subscriber population covered under a transmitter footprint with the addition of an irregular polygon limit.
• The counting of area under a transmitter footprint but showing the results over a variety of different urbanisation categories including urban and suburban areas with the addition of an irregular polygon limit.

Specific WLL Planning Methods

The design and subsequently the roll out of fixed radio access/wireless local loop networks are very unique. Initially the design can progress as if the subscriber population is mobile and using an omnidirectional antenna. At this point the exact location of the subscriber is unknown. Very soon into the project, the marketers in the team are able to input the likely locations of subscribers from the voters roll or from chamber of commerce data yet the base stations to which each would look for service is still not set. Once the network commences deployment, subscribers will be promoted from potential to actual with real parent base stations and real antenna pointing. ICS telecom nG mirrors this concept in allowing a three stage transition from a theoretical to a practical network.

The coverage calculated can be filtered to only display on specific ground use types such as suburban or urban or industrial areas. This then allows the planner to focus on the desired target market for the service. Similarly, interference calculations over rural or open areas away from that target market can be ignored or reduced in significance. This can be taken a stage further with the introduction of a specific ground use layer representing the service requirements. Instances where this has been used includes the mapping of roof lines on a clutter file thereby allowing filtering of all locations not at roof level.

ICS telecom nG can be set to calculate field strength or signal level into a specific antenna only where there is a defined Fresnel Zone clear of obstructions. This is particularly relevant for systems in the region 3.5 GHz to 10 GHz and can be applied further in the MVDS and bandwidth on demand services at 35-40 GHz. For such high frequency systems no path between base station and subscriber is of interest unless obstruction free.

Once subscriber locations are known, they can be introduced into the planning tool via a subscriber database. At this stage they are simply locations but once each subscriber is parented to a base station this can be noted on the database and the predicted signal level to each reported to installation teams. Each subscriber is described by a directional antenna pointed toward the parent. The objective in the intermediate stage in planning is to parent the orphan subscribers whilst deploying a minimum of base stations.

The computation of traffic capacity of a network will of course be dependant on the number of subscribers served by a given base station. In the early stages this might be by best server. The planning task in hand requires that the engineer parents the subscribers and he can do this in ICS telecom nG by directing the traffic analysis sweeping certain subscribers up within a series of irregular polygons. Once parented, the work proceeds using the traffic demand noted in the subscriber database and directed into base station parents.

The traffic generated per subscriber is variable allowing for different subscriber terminal equipment serving differing numbers of actual users. Subscribers and their callsign or telephone number can be shown on screen at any time.

Relevant ATDI Software tools:

ICS telecom nG
for all general fixed link network planning in the bands 1.5GHz to 55GHz.

ICS map server
for the creation and manipulation of high definition terrain and buildings data allowing planning to go ahead anywhere in the world

Point to point  l  Point to multipoint  l  Mobile  l  Spectrum management  l  Electronic warfare  
Broadcast  l  WiMAX