It is very important to plan a public land mobile network, PLMN, on simulation software before performing the implementation on the ground. The design and implementation of a Base Station Network follows from the GSM network regulations document in the Request for Comments, RFCs. The mobile communication system on land is defined in cells and sectors as discussed further in the literature review. The GSM architecture for the PLMN has the base station subsystem which links to the mobile switching center. The base station transceivers are the first line connection to the user or mobile equipment. The BTS performs location updates and connects to the user equipment to ensure that the mobile user is connected to the cellular network. The PLMN uses microwaves and radio waves to transmit message signals over the atmosphere. The use of GSM technology allows for the voice connections, data connections, and short message services. there are mainly three service domains used in the GSM namely the bearer services, the telematic services and the supplementary services.
The GSM system has two frequency bands namely GSM 900 and GSM1800. The feasible frequencies and channel spacing of the two bands are:
Another advanced technology is the UMTS whose bandwidth is given as
When designing a PLMN, the design for the urban areas is different from that of the remote areas. In the urban regions, there are so many man-made structures which are referenced as the concrete jungle which must be taken into consideration as they are likely to cause a lot of interference and signal blocking, especially the skyscrapers. For the terrestrial communication using microwave electromagnetic signals, there propagation of a signal is modelled using a 2-ray model and Fresnel zones. When the earth is assumed to be flat, the 2-ray model is used to model a propagation channel where the receiver gets a signal using the direct path and the reflected ray.
Such that the path difference between the direct path and the reflected path is given as,
For the Fresnel zone design, seeks to avoid the destructive earth reflections which may not get the signals to the receiver end. The following estimates are considered when planning to set-up WiMAX and LTE PLMN networks in different areas,
|
Environment |
Path Loss Exponent, n |
|
Free Space |
2 |
|
Ideal Specular reflection |
4 |
|
Urban Cells |
2.7-3.5 |
|
Urban cells (shadowed) |
3-5 |
|
In building (line of sight) |
1.6 – 1.8 |
|
In building (obstructed path) |
4 -6 |
|
In factory (obstructed path) |
2-3 |
During the network planning, one is able to determine whether a network roll out in a given region is feasible or not depending on certain parameters under study. It is possible that during such a transmission, the message signals encounter some path losses while propagating. Some of the effects of atmospheric conditions on the message signal include the message signal scattering, reflection, diffraction, and fading. The impact is greater when the atmosphere is very humid or in rainy periods.
Coarse planning on terrestrial communication.
In the cell design, each base station is designed to implement the space division multiplex. Each base station covers a transmission area or cell and it is allocated a portion of the total channels available. Clusters are formed of the base stations close to each other using different frequencies.
Coverage planning – deals with the extent to which a base station will cover. In some clusters, there are fewer base stations with omni-coverage along very long distances. The timing advance for the adaptive frame synchronization is given as,
The design takes into consideration the frequency hopping in the efforts to utilize the frequency spectrum comprehensively. The base station antenna height is a key factor of consideration in the provision of services to minimize the interference,
It is important to determine the transmission and reception power based on the path losses of a signal. The received power is given as,
An increase in the cell size causes a loss of up to 12dB in signal energy for the transmitted message signals. As a result, the frequency re-use should be done at shorter distances. Another key loss is the free space propagation obtained from the Friis formula,
The loss the modelled with the expression,
The link budget enables the designer to tell the number of path losses per link that are possible when transmitting message signals over terrain. The Hata-Okamura model extends around the range of 2 GHz.
Cellular Network Design And Solution
Software planning tool used is the CelPlanner Suite; a product of CelPlan Technologies, Inc.
The system parameters are:
The mobile terminal is given as,
The mobile environment is presented as,
Site Surveys Site surveys are performed for all proposed site locations. The following must be checked for each site:
In addition, the radio environment must be checked to ensure that there is no other radio equipment on site that causes problems. Radio measurements are performed to adjust the parameters used in the planning tool to reality i.e. adjustments are made to meet the specific site climate and terrain requirements. For instance, parameters used in a cold climate will differ from those used in a tropical climate. Drive tests are done using a test transmitter mounted on a vehicle, and signal strength is measured while driving around the site area. The results from these measurements can then be compared to the values the planning tool produces when simulating the same type of transmitter. The planning parameters can then be adjusted to match the actual measurements.
As highlighted at the inception of the literature review, the GSM operates on two frequency bands and the UMTS has one broadband which accommodates the frequencies at a channel spacing of 200kHz. One key factor in determining the channels in a frequency band is obtaining the Absolute Radio Frequency Channel Number. The ARFCN is given as,
The key factor in utilizing the channels efficiently is through the frequency reuse. The frequency spectrum is limited and it is not possible to have everyone access all the frequencies they need to use, hence, the need for frequency reuse techniques in a cellular network. The concept is deployed such that different geographical regions especially those apart from each other or in different sectors can use the same frequency without encountering interference. The key focus in frequency reuse is the maximum utilization of the frequency spectrum and the user capacity. The frequency reuse plan yields clustering of cells. Clusters are attributed to the number of cells that are contained within a given cluster and as a result, the distance from one cluster to another can be used to determine proper frequency reuse.
The radius of the cluster is given by,
Grade of service is 2 percent. The tele traffic load is expected in terms of 36 local service areas. The traffic loads for the total area are given as,
As discussed earlier in the path loss model, the cellular network can be tested over different morphology and terrain types such as water, low vegetation, medium vegetation, dense vegetation, suburban area, urban area, dense urban area, commercial industrial transport, urban recreational, freeway for country side and the urban area, and the forest environment. Using the Celplanner software,
When performing radio planning, the designer aims at improving the performance of an existing network, providing high spectrum efficiency for the economic benefits of the service provider with little or no interferences, and large cluster sizes. Decreasing a cell size while designing the network may increase the user capacity, the number of handovers per call, as well as increase the complexity of the location updates for subscribers within a given cell. A decrease in the cell sizes is the plan for most networks to ensure that the system is operating in the best mode for a given region considering that number of users in a given region to maximize user capacity on BSS resources. The following table has details used in the design of cells within regions on the basis of user capacity:
|
Cell sizes |
Distances (metric units) |
|
Macro-cellular |
1-30 km |
|
Micro-cellular |
200-2000 m |
|
Pico-cellular |
4-200 m |
References
[1] Dharma P. Agrawal, and Qing-An Zeng, “Introduction to Wireless and Mobile Systems”3rd Ed., 2011.
[2] Agbinya, J.I and Masihpour M., “Planning of WiMAX and LTE Networks”, in Planning and Optimisation of 3G and 4G Wireless Networks (ed. Agbinya, JI.); ISBN:978-87-92329-24-0; River Publishers, Denmark, 2009.
[3] Agbinya,JI “Design Consideration of Mohots and Wireless Chain Networks”, Wireless Personal Communication”, © Springer 2006, Vol. 40.
[4] Parsons, J. D., “The Mobile Radio Channel”, Second Edition, John Wiley & Sons Ltd, 2000
[5] T.S. Rappport, Wireless Communication, 2nd Ed, 2009, Prentic Hall.
[6] Lee, William C. Y., “Mobile Cellular Telecommunications: Analog and Digital Systems”, second Edition, McGraw-Hill, Inc.
[7] CelPlanner User Guide, CelPlanner Manuals
[8] CelPlan Technologies, Inc. website www.celplan.com
[9] ETSI ETR 364, Digital cellular telecommunications system; Radio network planning aspects (GSM 03.30 version 5.0.0)
[10] Mohsin Murtaza and Assoc. Prof Johnson I Agbinya lecture, laboratory and PBL notes
[11] Hamad-Ameen, Cell Planning in GSM Mobile, WSEAS Transaction on Communications https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.214.5918&rep=rep1&type=pdfa
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