Multiplex communications – Wide area network – Packet switching
Patent
1995-02-17
1996-10-29
Olms, Douglas W.
Multiplex communications
Wide area network
Packet switching
370 50, 370 951, 375200, 375202, 375206, 379 58, 379 59, 455 331, H04J 1300
Patent
active
055703526
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to cellular network systems with mobile stations communicating with base stations using frequency-hopping, and having an enhanced effect of interference diversity. The cellular-network systems according to the invention may conform to the GSM system known per se, for instance.
New requirements arise when mobile phone services are offered in urban population centres: the system is supposed to have a large capacity, base station equipment should be small-sized because of the very limited possibilities of providing equipment rooms in urban areas, and the system should operate on low radio power levels to make small-sized subscriber's units possible. Moreover, the system is expected to cover also the interiors of buildings, and to offer a good coverage in spite of the fact that it is difficult to predict the radio coverage of antennas to be positioned at low elevations. In addition to the above, the system is supposed to offer easier frequency planning of a radio network than before. Such cellular networks are built of so-called short-range microcells.
To build a mobile phone network in an environment as described above is a task very different from realizing a classic cellular network. While the primary object of a cellular network is to minimize the number of base station sites by increasing the range of the cells to the technical maximum and by installing the maximum number of transceiver units permitted by the frequency band of the network on each base station site, the primary object of microcellular networks is to achieve low radio powers and small installation units suitable for outdoor deployment.
However, conventional cellular technique (cell splitting) does not meet the requirements of a microcellular network. This is due to the fact that with the cell radius decreasing and the radio coverage at the same time becoming more difficult to predict than before (because antennas are positioned below roof-tops to restrict the cell size) either the overlapping of the cells increases or the coverage of the system is compromised (depending on a shadowing caused by buildings or natural obstacles in each direction). An increasing degree of overlapping of the cells makes it necessary to widen the reuse pattern, which eliminates at least part of the additional capacity supposed to be obtained by means of cell splitting.
SUMMARY OF THE INVENTION
The object of the present invention is thus to provide a digital TDMA/FDMA (Time Division Multiple Access/Frequency Division Multiple Access) cellular network system, e.g. a TDMA/FDMA cellular system according to the GSM system, in order to comply with the above requirements for a microcellular network. This is achieved by means of a cellular network system according to the present invention.
The basic idea of the invention is to give up classic cell planning, according to which a part (particular frequencies) of a frequency band available is allocated to each cell, and to utilize instead (within the scope of the restrictions placed by the other properties of the system) substantially the full available frequency band in as many cells as possible, preferably in all cells of the system.
The difference between the idea of the invention and that of the prior art may be described more accurately as follows. Conventional cell planning tries to find the densest reuse pattern, by means of which a limited available frequency band can be effectively utilized (the denser the reuse pattern, the greater the capacity). This takes place in such a way that the number (K) of the coverage areas (cells or sectors) of a reuse pattern is first derived from the minimum required for C/I (carrier-to-interference ratio) of the system the (GSM system requires 9 dB, for instance). The available frequency band is then divided evenly among the coverage areas. The basis for the present invention is a very different idea: cell planning is simplified by choosing the number (K) of the coverage areas of the reuse pattern to equal with the number of avai
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Hom Shick
Nokia Telecommunications Oy
Olms Douglas W.
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