U.S. patent number RE37,820 [Application Number 09/864,469] was granted by the patent office on 2002-08-13 for arrangements of base transceiver stations of an area-covering network.
This patent grant is currently assigned to Littlefeet, Inc.. Invention is credited to Stefan Scheinert.
United States Patent |
RE37,820 |
Scheinert |
August 13, 2002 |
Arrangements of base transceiver stations of an area-covering
network
Abstract
An arrangement of an area covering, cellular radio communication
network having cell regions which can be. contiguously replicated
without interference. A central transceiver station is coupled to a
base station controller and has a plurality of decentral
transceiver stations surrounding and coupled to the central
transceiver station. Groups of adjacent decentral transceiver
stations are grouped in respective cell areas. All of the decentral
transceiver stations in each cell area are allocated the same
transmission frequencies, but the frequencies of each cell area are
different from the other cell areas in the cell region.
Inventors: |
Scheinert; Stefan (San Diego,
CA) |
Assignee: |
Littlefeet, Inc. (Poway,
CA)
|
Family
ID: |
27206524 |
Appl.
No.: |
09/864,469 |
Filed: |
May 24, 2001 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
493793 |
Jun 22, 1995 |
05787344 |
Jul 28, 1998 |
|
|
Foreign Application Priority Data
|
|
|
|
|
Jun 28, 1994 [DE] |
|
|
44 22 490 |
Jan 20, 1995 [DE] |
|
|
195 01 603 |
|
Current U.S.
Class: |
455/422.1;
455/446; 455/447; 455/449 |
Current CPC
Class: |
H04B
7/2609 (20130101); H04W 16/02 (20130101); H04W
16/12 (20130101); H04W 16/26 (20130101); H04W
16/24 (20130101) |
Current International
Class: |
H04B
7/26 (20060101); H04Q 7/36 (20060101); H04Q
007/20 () |
Field of
Search: |
;455/422,436,443,447,444,446,449,450,464,517,561,524,562,11.1,20 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
2659570 |
|
Jul 1978 |
|
DE |
|
2806178 |
|
Aug 1978 |
|
DE |
|
3211979 |
|
Mar 1982 |
|
DE |
|
3528974 |
|
Aug 1985 |
|
DE |
|
4141398 |
|
Dec 1991 |
|
DE |
|
0536864 |
|
Apr 1993 |
|
EP |
|
000568142 |
|
Nov 1993 |
|
EP |
|
0 622 918 |
|
Apr 1994 |
|
EP |
|
0 668 662 |
|
Aug 1994 |
|
EP |
|
0 693 834 |
|
Feb 1995 |
|
EP |
|
0 700 174 |
|
Aug 1995 |
|
EP |
|
0 736 982 |
|
Apr 1996 |
|
EP |
|
0177223 |
|
Jul 1989 |
|
JP |
|
WO 97/24818 |
|
Jul 1997 |
|
WO |
|
Primary Examiner: Cuchlinski, Jr.; William A
Assistant Examiner: Arthur; Gertrude
Attorney, Agent or Firm: Foster; Frank H. Kremblas, Foster,
Phillips & Pollick
Claims
I claim:
1. An arrangement of base transceiver stations in an area-covering
radio network comprising cell regions arranged continuously in
rows, each cell region comprising: (a) a central transceiver
station coupled to a base station controller; (b) a plurality of
decentral transceiver stations surrounding and coupled to the
central transceiver station; and (c) a plurality of cell areas,
each cell area operated at respectively different transmission
frequencies, each cell area being formed by a plurality of
adjacent, decentral transceiver stations to which the same
transmission frequencies are allocated.
2. An arrangement according to claim 1, wherein transmission power
of channel units for area coverage of the decentral transceiver
stations is lower than transmission power of a channel unit for
area coverage of a central cell.
3. An arrangement according to claim 1, wherein coupling of the
decentral transceiver stations to the respective central
transceiver station comprises a wireless point-to-point
connection.
4. An arrangement according to claim 3, wherein frequencies of the
point-to-point connections differ from the frequencies for the area
coverage of a central cell.
5. An arrangement according to claim 4, wherein the point-to-point
connections have a transmission power lower than transmission power
for the area coverage of the central cell.
6. An arrangement according to claim 1, wherein the central
transceiver station further comprises an aerial for area coverage
and a directional aerial or optical transmitter-receiver device for
the bidirectional data relay to a further base transceiver
station.
7. An arrangement according to claim 6, wherein the two aerials are
coupled together via two frequency-selective amplifiers connected
in antiparallel.
8. An arrangement according to claim 7 and further comprising a
frequency filter assembly and an amplifier connected in series, and
having a respective frequency converter inserted between them.
9. An arrangement according to claim 1 wherein the central
transceiver station has channel units for the area coverage and
additional channel units for bidirectional data relay to at lease
one additional central transceiver station, each additional channel
unit comprising: (a) a terminal assembly with two terminals on a
down-link side for separating signals according to the direction of
their transmission; (b) an encoder coupled to an output terminal at
the down-link side of the terminal assembly; (c) a first amplifier
receiving the output signal of the encoder; (d) a band filter
assembly with two terminals at an up-link side, receiving at one of
these terminals the output signal of the first amplifier, and with
one terminal for transmitting and receiving signals to/from an
aerial; (e) a second amplifier, which receives the signal output
from the second terminal at the up-link side of the band filter
assembly; and (f) a decoder at an output side of the second
amplifier, which is coupled to the second terminal at the down-link
side of the terminal assembly.
10. An arrangement according to claim 9, wherein the channel units
have transmission devices having a transmission power and the
transmission power of the transmission devices of the additional
channel units is lower than the transmission power of the
transmission device for area coverage.
11. An arrangement according to claim 9, wherein a transceiver
station further comprises at least one directional aerial and/or
optical transmitter-receiver and a time function element which is
started by a transmitter device and after the elapse of a time
interval actuates a receiver device.
12. An arrangement according to claim 9, wherein a transceiver
station has at least one selection switching circuit for selecting
an associated coupling aerial as a function of the reception field
strength of a signal relayed by a plurality of coupled base
transceiver stations.
13. A method of retrospectively condensing an existing
area-covering radio network comprising base transceiver stations
coupled via cable or radio link to base station controllers, the
method comprising arranging decentrally within the cell region of
each existing transceiver station a plurality of additional
transceiver stations so that they surround the existing transceiver
station of the respective cell region, the additional transceiver
stations being coupled to the existing transceiver station;
selecting the frequencies of the additional transceiver stations so
that a plurality of cell areas having respectively different
transmission frequencies are formed per cell region, and grouping a
plurality of adjacent, decentral transceiver stations into one cell
area by allocating to these the same transmission frequencies.
14. A method according to claim 13, wherein the original base
transceiver stations are located in the centre of each cell region,
and in addition to channel units for area coverage, further channel
units are provided for bidirectional data relay to at least one
further base transceiver station.
15. An arrangement of base transceiver stations of an area-covering
radio network having an area divided into a plurality of cell areas
each having a uniform transmission frequency, wherein respectively
abutting cell areas are operated at different transmission
frequencies, and wherein at least the cell areas which are operated
at certain transmission frequencies are each formed of a plurality
of cells, whose areas are covered by a respective base transceiver
station, each base transceiver station being allocated exclusively
to one cell area, the arrangement comprising: (a) a plurality of
base transceiver stations coupled to a base station controller via
an associated common connecting station; (b) common channel units
for all base transceiver stations of a cell area which are coupled
to the same connecting station for coupling to the base station
controller and disposed inside the associated connecting station;
(c) at each base transceiver station, an aerial for area coverage
of its associated cell and an additional aerial with a directional
characteristic oriented towards the associated connecting station;
and (d) a transmitting and a receiving branch connected in
antiparallel coupling both aerials of each transceiver station and
comprising at least a respective frequency converter and an
amplifier coupled to the output of each frequency converter.
16. An arrangement according to claim 15, wherein the base
transceiver stations located at an edge of a cell area have a
smaller mutual distance than base transceiver stations located in
the interior of the cell area.
17. An arrangement according to claim 15, wherein base transceiver
stations located at an edge of a cell area have a lower
transmission power than base transceiver stations located in the
interior of the cell area.
18. An arrangement according to claim 15 wherein no individual cell
is allocated to the connecting stations.
19. An arrangement according to claim 15, wherein at least one
running time element is available in each of the connecting
stations, which is started by the transmitter of a channel unit and
after the elapse of its time interval actuates a receiver of the
respective channel unit.
20. An arrangement according to claim 15, wherein a time-lag device
with an adjustable time constant is connected at inputs and/or
outputs of the transmitting and receiving branches.
21. An arrangement according to claim 19, wherein the time interval
of the running time element in the connecting station corresponds
to the sum of twice the running time between the connecting station
and the most remote base transceiver station, twice the signal
running time through a base transceiver station with the time-lag
constant (T) set at the minimum, and a fixed, predetermined
reaction time.
Description
FIELD OF THE INVENTION
The invention relates to a plurality of arrangements of base
transceiver stations of an area-covering radio network and to a
method of operating such an arrangement.
The invention further comprises base transceiver stations adapted
to the new arrangements and a method of subsequently compressing an
existing continuous radio network.
DESCRIPTION OF RELATED ART
In order to operate radio telephones, in addition to the respective
mobile stations, an area-covering network of fixed transmission
stations is necessary in order to ensure interference-free radio
operation at any location within the area of coverage.
In order to permit a large number of mutually independent radio
participants to use their telephones simultaneously, the region of
coverage is divided into a plurality of individual cells, each
allocated with its own base transceiver station. By giving adjacent
zones different frequencies, it is possible to identify a
particular radio telephone with a respective base transceiver
station. If the radio telephone is set to a special frequency of
the current cells, radio communication is oriented to precisely one
fixed transmission station, from which the conversation is
forwarded to a base station controller. By the possibility of
allocating one and the same transmission frequency to a plurality
of zones which are relatively remote from one another, a very large
number of conversations can be transmitted simultaneously, using a
limited number of transmission frequencies.
If one ignores interference caused by topographical irregularities
etc., a radio network can be put together from a plurality of base
transceiver stations arranged in a specified structure, their
mutual distance being determined by the range afforded by the
transmission power. On the other hand, the spatial sequence of
different transmission frequencies is on the one hand such that
adjacent, base transceiver stations are allocated different
frequencies and furthermore a minimum distance is retained in base
transceiver stations using the same transmission frequencies in
order to eliminate reliably any interference.
From these peripheral conditions, certain structures arise which
can be linked together in lines to form a continuous grid. In
establishing the basic structure of such a radio network, the
following parameters need to be optimised:
On the one hand, the number of cells should be as large as possible
without increasing the number of base transceiver stations. With
the large number of cells, a large number of conversations can be
transmitted simultaneously. On the other hand, any conventional
base transceiver station requires a high level of investment, which
considerably increases the cost of the radio network. It has been
proposed in the prior art to provide at each base transceiver
station, instead of one non-directional aerial, three directional
aerials, each covering a transmission or reception angle of
approximately 1200, so that the number of cells can be tripled, but
such a modus operandi involves heavily increased aerial and
installation costs.
Furthermore, the participant capacity to be handled can be
increased if the number of channels per cell is increased. The more
channels there are available in one cell, the more participants can
telephone simultaneously from this cell. On the other hand,
however, the total number of frequencies should not be increased,
since the transmission frequencies available are limited by a
number of other data transmission systems. In order to achieve a
large number of channels per cell, the frequencies must be capable
of being repeated at the minimum possible distance from one
another. In order to meet this requirement, according to the prior
art a hexagonal grid is used, in which the base transceiver
stations are arranged in parallel columns, the transceiver stations
of adjacent columns being staggered relative to one another by half
a distance in the direction of the column. This gives the
associated cells a hexagonal shape, a large number of which are
joined together like honeycomb cells in order to form a continuous
network. In many applications, these basic areas are further
subdivided by the above-mentioned allocation of sectors to
different aerials. With the hexagonal structure, an elementary
system composed of seven base transceiver stations is put together,
each station requiring a different transmission frequency, since
each cell abuts six further cells.
Where such grid structures known from the prior art are used for
the base transceiver stations of an area-covering radio network,
the two above-mentioned optimisation criteria, in particular the
product of the radio cell area and the number of fixed stations
(which are cost-intensive due to being coupled to a base station
controller) and the ratio of the number of channels per cell to the
total number of transmission frequencies, cannot be varied.
Although the area per cell area can be reduced by reducing the
transmission power, which means simultaneously increasing the
number of fixed stations, because on the other hand the minimum
number of cells is specified by different transmission frequencies
(e.g. seven structure), the number of channels per cell can only be
increased by increasing the number of frequencies as a whole.
SUMMARY OF THE INVENTION
The problem of the invention arises from these disadvantages of
known arrangements of base transceiver stations of an areacovering
radio network, and consists in changing the basic structure of the
network in such a manner that, without increasing the number of
cost-intensive base transceiver stations coupled to a base station
controller, the number of cells per area is increased and/or
without increasing the total number of frequencies of the network,
the number of channels per cell can be increased.
To this end, the invention provides, in a first arrangement of base
transceiver stations of an area-covering radio network which are
coupled at least in part to base station controllers, that each
base transceiver station coupled to a base station controller is
surrounded by a plurality of further, decentral transceiver
stations which are coupled to the central transceiver station and
form one or more cell areas each having a different transmission
frequency. The advantage of this arrangement is that the area of
coverage of a base transceiver station coupled to a base station
controller is increased by the decentral transceiver stations
without increasing the transmission power of the central
transceiver station coupled to a base station controller. Since
cell areas having different transmission frequencies are coupled to
the decentral transceiver station, the number of cells per unit
area can be increased without having to raise the number of fixed
stations coupled to a base station controller. Since the decentral
transceiver stations are not coupled to a base station controller
but to a central transceiver station, they can be manufactured very
simply and cheaply, as will be explained more fully below. By a
favourable arrangement of the base stations and the decentral
transceiver station, the number of frequencies required for the
basic coverage (1 channel per cell) is reduced (e.g.
2.times.1+4.times.1), so that within an elementary base cell (of
approx. 9 times' the area of a single base transceiver station) it
is even possible to use all frequencies. Thus the number of
channels per unit area can be increased.
It has proved advantageous if the decentral cell area(s) as a whole
completely surround the central cell (s). This ensures on the one
hand an arrangement with an optimum coverage area, which may be
approximately four to ten times as large as the original or central
cell area. Thus the number of base stations coupled to a base
station controller is reduced by a corresponding factor. On the
other hand, the central cell area is completely surrounded by the
decentral cell areas, so that the transmission frequencies of the
central cell(s) can already be used in the adjacent transceiver
station coupled to a base station controller.
It has proved advantageous if the decentral cell areas have an
approximately annular or annular sector-shaped configuration
defined by approximately arc-shaped and/or polygonal border lines.
The outer cells areas together form a ring surrounding the central
cell (s), so that the inner border line of the decentral cell areas
ideally has the form of an arc. On the other side, in a cell region
according to the invention, adjoining the total of the central and
decentral cell areas of a central transceiver station coupled to a
base station controller is a plurality of identical cell regions
which duplicate the elementary cell region in the form of a square
or honeycomb-type grid so as to form a continuous network. The
external outlines of the cell areas are therefore formed from
approximately straight lines. Within the scope of the invention,
both a plurality of annular cell areas can be grouped around the
decentral cell(s) and/or due to the different frequency allocations
of individual decentral transceiver stations, annular-sector-shaped
cell areas can be created within a ring.
It is within the scope of the invention that the transmission power
of the channel units for the area coverage of the decentral base
transceiver stations is lower than the transmission power(s) of the
channel units for the area coverage of the central cell(s). Thus
the dimensions of the decentral transmission stations can be
reduced. The current requirement is low and can if necessary be
covered by a rechargeable battery. This gives rise to low
manufacturing and investment costs and fewer problems in the grant
of permission.
A practical further development of the invention involves combining
a large number of adjacent, decentral transceiver stations into one
cell area with identical frequencies. Provided that, for example, a
square grid is selected with identical cell regions, the decentral
cell areas have a severely distorted shape (corners of a square) so
that it is more favourable to cover these areas by means of a
plurality of decentral transceiver stations. In order not to
increase the number of necessary transmission frequencies, however,
it is recommended to allocate to adjacent decentral transceiver
stations the same frequencies and to join these transceiver
stations together to form a common cell area. Any running time
differences can be compensated.
It is within the scope of the invention to juxtapose a large number
of cell regions each formed from a respective central and a
plurality of decentral transceiver stations in order to form an
area-covering network with an approximately grid-type and/or
hexagonal structure. By means of such square and/or honeycombtype
grid structures, the terrain can be covered without leaving
gaps.
In an advantageous embodiment the transceiver stations within each
of the juxtaposed cell regions have relative positions which
approximately correspond geometrically. These correspondences are
ascribable to the identical base structure of each individual cell
region allocated to each transceiver station coupled to a base
transceiver station controller. In practice, the relative positions
will, albeit slightly, fluctuate within certain limits, on the one
hand due to variations in the terrain resulting in different ranges
for the transceiver stations, and on the other hand due to the
local conditions to be taken into account when choosing a site for
a decentral transceiver station demand a degree of flexibility in
planning.
It is within the scope of the invention that the frequencies of the
aerials for area coverage to transceiver stations of different cell
areas corresponding to one another due to their roughly
geometrically corresponding relative positions, are identical.
Since both the geometric base structure of a cell region and the
transmission frequencies of the individual cell areas are repeated,
not only the number of base transceiver stations coupled to a base
station controller but also the total number of transmission
frequencies can be limited to a minimum.
It has proved advantageous that the decentral part of a cell region
is divided into a plurality of, preferably four, cell areas with
different transmission frequencies, each cell area being allocated
an approximately constant central angle with respect to the central
transceiver station. In order to permit direct duplication of the
frequency of an elementary cell area, at least the outer ring of
the cell region needs to be divided into a plurality of roughly
annular-sector-shaped cell areas; so that when such cell areas are
juxtaposed, it never arises that two cell areas with identical
transmission frequencies abut one another. To this end, it is
recommended in the case of a square grid to divide the outer ring
into four cell areas, each with a central angle of approximately
90.degree., whereas in a honeycomb-type grid structure it is
practical to divide the outer ring into six cell areas of different
transmission frequencies, each cell area covering a central angle
of approximately 60.degree. with respect to the central transceiver
station coupled to a base station controller.
The invention further provides that the coupling of the decentral
transceiver stations to the respective central transceiver station
comprises a wireless point-to-point connection. Thus the laying of
cables is superfluous and the installation of a decentral
transceiver station can be carried out without great cost and the
initial outlay is thereby substantially reduced. The term
point-to-point connection is understood to include not only radio
link connections proper, but also connections in which the aerial
of the central transceiver station has only a low directional
characteristic, if any, in order to address, for example, a
plurality of aerials of decentral transceiver stations of a cell
area simultaneously.
Further advantages can be obtained if, for each point-to-point
connection to a decentral transceiver station, the central
transceiver station has its own, directional aerial and/or an
optical transmitter-receiver device. In this case, each decentral
transceiver station is coupled by means of its own radio link or
laser relay section to the central transceiver station.
In addition, an embodiment is conceivable in which a common aerial
for point-to-point connection to a plurality of decentral
transceiver stations is available at the central transceiver
station. This reduces the initial investment.
Furthermore, it is possible that the common aerial for connecting a
plurality of decentral transceiver stations is identical to the
aerial for the area coverage of the central cell. The combined use
of the area coverage aerial of the central cell(s) is the
arrangement involving the least extra cost.
If has proved advantageous if the frequencies of the point-to-point
connections differ from the frequencies of the area coverage of the
central cell(s). This prevents faults arising from interference
with the signal for the area coverage of the central cell(s).
It has proved practical if the transmission power of the
point-to-point connections is lower than the transmission power for
the area coverage of the central cell (s). If directional aerials
are used, together with high-quality receivers on the two
transceiver stations communicating with one another, the
transmission power can be reduced in order to eliminate faults due
to trapping. On the other hand, a reduction in the transmission
power in the case of transmission for example via the aerial for
the area coverage of the central cell(s) can be used to make
available to a mobile station, due to the different reception field
strength, a datum which can be referred to in selecting the signal
for the area coverage.
The invention can be developed further if the frequencies of the
point-to-point connections lie in a radio link frequency band or in
an optical frequency band. The choice of such transmission
frequencies is offered for technical reasons.
In addition, it is possible that the frequencies of the
point-to-point connections lie in the network operator frequency
range. It is thus possible to save on possible additional fees for
extra radio link frequencies.
If frequencies of the network operator frequency range are used,
the frequencies o the point-to-point connections my differ from the
frequencies for the area coverage to the respective decentral cell.
Thus acoustic feedback can be almost completely eliminated,
ensuring fault-free operation.
However, a type of coupling is conceivable in which the frequencies
of the point-to-point connections correspond to the frequencies for
the area coverage of the respective, decentral cell. However, in
this case it should be ensured that the directional aerial of the
decentral transceiver station for coupling to the central
transceiver station is spatially distant from all the aerials of
the same decentral transceiver station providing the area coverage
and/or is decoupled by further means in order to avoid interference
from acoustic feedback.
Often, it is not necessary to draw up a new radio network, but to
compress an already existing radio network in such a manner that,
due to the high number of transceiver stations, not only outdoor
operation of a mobile telephone, but also indoor operation is
possible. Here the problem arises of finding a suitable structure
in which if possible all the sites of existing base transceiver
stations can be reused, and investment in additional installations
at new sites will be kept as low as possible. In order to solve
this problem, the invention proposes a method of retrospectively
condensing an existing continuous radio network comprising base
transceiver stations, which are coupled to base station
controllers, wherein each existing transceiver station is
surrounded by a plurality of decentral transceiver stations which
are coupled to the central transceiver station and form one or more
cell areas surrounding the decentral cell(s) in the outer space
thereof, each cell area having a different transmission frequency.
Thus, without the cost associated with the installation of
conventional base transceiver stations coupled to a base station
controller, in the critical outer space of each central cell, a
reception field strength sufficient for indoor use can be achieved.
In this manner, it is easily possible to upgrade an already
existing continuous radio network by inserting decentral
transceiver stations to one of the arrangements according to the
invention described above for an area-covering radio network.
The arrangement of transceiver stations of an area-covering radio
network according to the invention requires special base
transceiver stations both for the central and for the decentral
transceiver stations. The central transceiver stations coupled to a
base station controller are distinguished by the fact that, in
addition to the channel units for the area coverage, further
channel units are available for the bidirectional data transfer to
at least one further base transceiver station. According to the
invention, the signals for the area coverage of the decentral cell
areas are generated or processed in the central transceiver
station, so that all the decentral transceiver stations need to do
is carry out amplification of the signals, in every case combined
with a frequency conversion. Therefore, for every channel of the
outer cell areas of the cell region, the respective central
transceiver station has its own channel unit. In this case each
channel unit consists preferably of a monitoring component, two
transmitting and receiving units oriented in anti-parallel, and a
filter assembly.
It is within the scope of the invention that the additional channel
units are connected to additional direction aerials and/or to
optical transmitter-receiver devices. In this embodiment, the
coupling of a decentral transceiver station takes the form of a
true, directional point-to-point connection.
In addition it is possible that the additional channel units are
connected to the aerial(s) for the area supply. If different
frequencies are used, the signals to be transmitted to the
decentral transceiver stations can also be transmitted or received
via the area coverage aerial(s) if the additional channel units are
connected to that aerial.
It has been found advantageous if the transmission power of the
transmitters of the additional channel units is lower than the
transmission amplitude of the transmitter for the area coverage.
This makes possible optimum separation due to the reduced reception
field strength, even if a frequency of the network operator
frequency band is used to couple the decentral transceiver
stations, so that the mobile station can distinguish the signal for
the area coverage clearly from the coupling signal for a decentral
transceiver station.
In an advantageous further embodiment of the invention, for one or
more of the additional direction aerials and/or optical
transmitter-receivers, a respective time function element is
provided, which is started by the additional transmitter and after
the elapse of its time constant actuates the additional receiver.
Due to the spatial distance of the decentral base transceiver
stations from the central transceiver station, a constant running
time corresponding to the distance between the central and
decentral transceiver station is added to the variable running
time, dependent on the site of the mobile station, of a signal
between the decentral transceiver station and the mobile station.
If a monitoring signal is consequently sent from the central
transceiver station via a decentral transceiver station to the
mobile station, a reply signal can reach the central transceiver
station at the earliest with a time-lag corresponding to twice the
value of the constant running time between the base transceiver
stations. This constant timelag can be taken into account by a time
function element whose time constant is approximately twice the
value of the constant running time between the central and
decentral transceiver station. If a plurality of decentral
transceiver stations is coupled via a signal aerial of the central
transceiver station, it is possible to use as a time constant of
the time function element a minimum or average value of the
different, but in each case constant, running times of the
individual decentral transceiver stations.
The invention is further characterised by one or more selection
circuits in order to select, as a function of the reception field
strength of a signal transmitted by a plurality of the coupled base
transceiver stations, the associated coupling aerial(s). If the
cells of a plurality of decentral transceiver stations are combined
into one cell area with common frequencies, the radio signal of a
mobile station will be received most strongly by the decentral
transceiver station in whose cell the mobile station is located at
that instant. Furthermore, however, a weakened signal is received
by the other transceiver stations of this cell area and is
transmitted to the central transceiver station. This selects, by
means of a selection switching circuit the transceiver station of
this cell area whose reception field is the strongest and then
transmits the signal directed at the mobile station solely to the
selected decentral transceiver station. Thus running time
differences between radio signals originating from different
decentral transceiver stations can be eliminated and the
transmission quality thereby improved. The same method can also be
applied to the central cell area. In this case, only the monitoring
channel is transmitted over all sectors of the central cell area,
but the speech channels are transmitted over only one sector, the
reception field strength of the individual sector aerials being
applied as a selection criterion.
It is within the scope of the invention to couple the additional
channel units to a base station controller. The outputs/inputs of
the additional channel units opposing the coupled decentral
transceiver stations according to the system are connected in
parallel in order to relay telephone conversations to conventional
channel units and are connected via a radio link connection and/or
via cable to a base station controller.
In the case of a transceiver station suitable for decentral
coupling, in addition to the aerial(s) for the area coverage, a
directional aerial or optical transmitter-receiver is available for
bidirectional data relay to a further base transceiver station.
This makes the costly, labour-intensive laying of a coupling cable
between the mutually remote case transceiver stations superfluous.
At least at the decentral transceiver stations, an aerial with a
directional characteristic should be used in order to keep the
transmission power for the coupling connection as low as possible
in order to avoid interference.
It has been found advantageous that the two aerials (groups of
aerials) are coupled together via two frequency-selective
amplifiers connected in antiparallel. According to the
bidirectional data transfer, amplification of the radio signals in
both directions is necessary. The two signal directions are usually
distinguished by the use of different frequencies, which is
effected by frequency-selective band filters connected upstream of
the amplifiers.
According to the invention, a respective frequency converter is
inserted between the frequency filter assembly and the amplifier
connected downstream. This embodiment makes possible the use of
different frequencies for the area coverage of the respective
decentral cells as well as for coupling to the central transceiver
station, whereby acoustic feedback and consequent faults are highly
reliably eliminated.
A transceiver station according to the invention for decentral
coupling further has a superordinate assembly for configuration,
initialisation and monitoring. This assembly should have all
simplify the service and therefore has no influence on the radio
signal to be relayed, apart from a purely monitoring function
during operation. This signal is solely amplified, and if necessary
its frequency is converted, by a decentral transceiver station, but
otherwise is transmitted in an unchanged form.
Highly advantageously, in order to supply power to a base
transceiver station of this type, for decentral coupling solar
cells can be used. Due to the low transmission power and the
minimum configuration of the electronic assemblies, the power
take-up of a base transceiver station of this type for decentral
coupling is several times smaller than the power take-up of
conventional base transceiver stations. If solar cells are used, a
transceiver station of this type is fully independent, so that
after installation at the site concerned, no connection to any
service lines is necessary. The installation of such a decentral
transceiver station is therefore extremely labour-saving.
It has been found advantageous if all assemblies, with the
exception of the aerial or possible solar cells, are housed in a
housing, which acts as a pedestal for the aerial(s) for the area
coverage and/or for the directional aerial. This pedestal has
preferably a very flat form with a base area of e.g. 1 square metre
and a height of approximately 20 cm. Due to the low number of
necessary assemblies, particularly in the region of the housing
edge, sufficient space still remains for receiving ballast elements
to increase the stability of the aerial(s).
In an advantageous further embodiment, the aerial(s) for the area
coverage are connected detachably via a plug-in mechanism to the
housing acting as a pedestal. In this case, after installation of
the pedestal-type housing at a favourable site, e.g. on the roof of
a block of flats, the area coverage aerial can be inserted into the
pedestal so that mechanical assembly is limited to only a few
manual operations. Then, all that remains each time is to connect
the aerial to an electricity supply.
Finally, according to the teaching of the invention, the
directional aerial is disposed on its own fixing device and is
connected via a connecting cable to the housing. In order to avoid
acoustic feedback, the directional aerial is installed at a site a
few metres away and to this end requires its own fixing device.
After this aerial has been connected to the electronic equipment,
all that remains to be done are adjustments.
In the arrangement described above, it may prove disadvantageous if
the base transceiver stations coupled to the base station
controller have their own cell which is surrounded by further cell
areas. This means that, in addition to the frequencies required for
the outer cell areas, further, different frequencies are required
for the central cells, so that although the above arrangement is an
improvement over the prior art, on the whole it is not the best
solution, it is therefore a particular concern of the invention, on
the basis of the above-mentioned arrangement, to permit a more
extensive reduction in the number of frequencies required without
restricting the advantages achieved with the first arrangement.
To this end, the invention proposes, in an arrangement of base
transceiver stations of a continuous radio network whose area is
divided into a large number of cell areas each with uniform
transmission frequencies, wherein mutually adjacent cell areas are
operated at different transmission frequencies, that at least the
cell areas which are operated at a specified transmission frequency
range are formed of a plurality of cells whose areas are covered by
a respective base transceiver station, each base transceiver
station being allocated to only one cell area.
The invention therefore dispenses completely with dividing an
elementary radio region into a central and a peripheral area. The
individual cell areas can therefor--e.g. as in a honeycomb with
hexagonal cells--be joined together directly without the
interposition of additional "central", cell areas which would have
to have different frequencies from all the surrounding cell areas.
It has turned out that ideally an arrangement can be achieved in
which only every three cell areas need different frequencies, which
are repeated periodically in the remaining cell areas, but not
those directly adjacent thereto.
By dividing the individual cell areas into a plurality of cells
which are covered by a respective base transceiver station, the
transmission power of the individual transceiver stations can be
further reduced, so that the range of the signals transmitted in a
cell area is significantly smaller than in conventional
arrangements, in which only a single radio station was provided in
such a cell area. Therefore, the common frequency distance, i.e.
the ratio of the reception field strength if a signal transmitted
in one cell area to the reception field strength of the signal
radiated at the same frequencies from the aerials of the closest
cell area, is significantly reduced and fault-free operation is
possible. In cell areas with only one central transmission aerial,
on the other hand, the interference is so great that its use
hitherto has only been practical if the frequencies were repeated,
not even in the next-but-one cell area, but at greater distances,
so that a large number of different transmission frequencies were
necessary. Thus elementary cell regions used in practice have at
least seven, but usually significantly more cell areas with
different respective transmission frequencies.
Finally, it is important that each base transceiver station is
allocated only one cell area. This makes it possible to install the
individual transceiver stations at the optimum site for one cell
area, so that the search for a site is generally unproblematic. In
particularly unfavourable cases, where it is not possible to
install the transceiver station at a desired site, by way of
compensation one or more extra transceiver stations can be inserted
in order to fill up any gaps in the radio network. It is also
possible at points with a particularly high level of traffic to
install extra transceiver stations in order thus to obtain a better
distance between common channels. In the prior art, this was only
possible at great cost with only one transceiver station per cell
area, since an extra transceiver station with its own transmission
frequencies was required, which necessitated a complete change in
the geometry of the network. In the present arrangement, however,
neither the transmission frequencies of the cell areas nor the
neighbourhood lists are changed.
In a preferred embodiment of the invention, in which the cell areas
have an approximately hexagonal shape and join together in lines to
form a continuous radio network with an approximately
honeycomb-shaped structure, optimum use of the transmission
frequencies can be achieved if these are divided into three bands
in all, each cell area being allocated transmission frequencies
from only one of these transmission frequency bands. Since the
frequencies available only have to be divided into three bands, on
the whole a very high number of frequencies is produced within a
cell area, so that a relatively large number of channels can be
used per cell area. Unlike the prior art, where in an elementary
region comprising twenty cell areas with different transmission
frequencies, for example, only approximately 5% maximum of the
total transmission frequencies available can be used, according to
the invention an increase in efficiency of 33% can be achieved.
An almost equally high level of efficiency can be achieved in a
radio network according to the invention if the cell areas have an
approximately rectangular shape and are joined together without
gaps into an approximately chessboard-type radio network, because
in this case the available transmission frequencies only have to be
divided into four bands in all, with transmission frequencies from
only one of these transmission frequency bands being allocated to
each cell area. Thus 25% efficiency can still be achieved.
Further advantages can be achieved if the base transceiver stations
located at the periphery of a cell area have a smaller mutual
distance than base transceiver stations located in the centre of
the cell area. Base transceiver stations whose cell is completely
surrounded by cells with the same frequency range and consequently
lie in the interior of a cell area have their transmission signal
amplified by the transmission of adjacent stations, so that their
range is increased without the need for greater transmission power.
Since this amplifying effect is not available in the peripheral
cells, because there cells border other channels at least in part,
either the transmission power must be increased, or if this is not
possible, the distance from the transceiver stations of the
adjacent cell area must be reduced in order that the reception
field strength does not fall below a minimum value in the border
region between the two cell areas.
The invention further proposes that the base transceiver stations
located at the edge of a cell area have a lower transmission power
than base transceiver stations located in the interior of the cell
area. The purpose of this measure is to minimise common channel
interference between the closest cell areas having the same
frequencies by operating the transceiver stations which are closest
to one another at the peripheries at a reduced transmission power.
Although the closest transceiver stations of two adjacent cell
areas therefore have to be moved closer together, this has no
adverse effects, since the cell areas are operated at different
frequencies.
The invention can be particularly advantageously improved if a
plurality of base transceiver stations are coupled via an allocated
central station to a base station controller. This makes it
possible to reduce the hardware costs in coupling the individual
transceiver stations, so that their number can be increased in an
economically practical manner.
By not giving the central stations effecting coupling to the base
station controller their own cells, it is possible to install these
central stations on sites selected solely by the criterion for a
favourable connection of the associated base transceiver stations.
This avoids the potential problem in the main application of having
to select the sites for the central radio station for their
favourable connection to the decentral transceiver stations on the
one hand, and for an optimum area coverage of the inner cell on the
other hand. The remaining single criterion can usually be met
without much difficulty. If all the conditions are simultaneously
favourably met, a base station and a central transceiver station
can be installed on the same site, permitting coupling via
cable.
Further advantages can be achieved if each central station is
allocated all the base transceiver stations of one or more cell
areas. This makes it possible to make available for all base
transceiver stations of a cell area common channel units for
coupling to the base station controller, which are disposed within
the associated central station. These channel units must
consequently only be available once for each cell area, in
particular in the associated central station. This permits a
reduction in hardware costs.
It has furthermore proved advantageous if in the central stations
at least one respective running time element is provided, which is
started by the transmitter of a channel unit and after the elapse
of its time constant actuates the receiver of the respective
channel unit.
It is also advantageous that each central station is coupled via a
point-to-point connection or an area-to-point connection to the
associated base transceiver stations. These may be bidirectional
radio connections, radio link connections with an omnidirectional
and a directional aerial, or optical connections by means of laser
beams or the like.
The invention can be further simplified if for all base transceiver
stations of a cell area one common aerial is available at the
central station. This may be an omnidirectional aerial for the cell
area within which the respective central station is installed,
whilst the aerial for connecting more remote cell areas can have a
directional characteristic, albeit covering a corresponding angle
of transmission in order to respond to all transceiver stations
within this cell area.
It is within the scope of the invention that the frequencies used
in the connection of the base transceiver stations to the
associated central station correspond to the frequencies for the
area coverage of the cell area concerned. In such a case, one base
transceiver station in particular provides amplification of the
signal, so that in a base transceiver station of this type the
connecting aerial and the aerial for area coverage can be coupled
together direct via amplifiers connected in antiparallel.
If on the other hand the connection frequencies of the base
transceiver stations differ from the frequencies for area coverage
of the cell areas concerned, and therefore the connection
frequencies lie respectively in a radio link band, then the base
transceiver stations must have in addition to the amplifiers
connected in antiparallel between the connecting aerial and the
area coverage aerial frequency converters connected upstream of the
amplifiers.
For both embodiments, a further development of the invention is
suitable in which, in one or both transmitting and receiving
branches connected in antiparallel a time-lag device with an
adjustable time constant is connected. In particular in cell areas
more remote from the associated central station effecting coupling
to a base station controller, the problem arises that the different
transceiver stations of this cell area may have different distances
from the associated connection station. Thus running time
differences can arise, which within the cell area would lead to
asynchronous transmission so that, for example, the desired
amplifying effect is not achieved. This adverse consequence is
counteracted by the invention in that, in the transceiver stations
sited closer to the connecting aerial, a greater time-lag is set
than in the more remote transceiver stations. Thus a signal is
still transmitted simultaneously from all transceiver stations of
this cell area.
In order to eliminate the running time problems just discussed, the
invention proposes that the time constant of a time function
element in the central station corresponds to the sum of twice the
running time between the central station and the most remote base
transceiver station, twice the signal running time through a base
transceiver station with the time-lag set at the minimum, and a
fixed, predetermined reaction time. Since in the arrangement
according to the invention the distances between a cell area and
the connection station allocated thereto may sometimes be
relatively great, the increased running time over this distance
must be allowed for by not actuating the receiver of a channel unit
until a significantly larger time constant has elapsed than in
known arrangements where the channel unit is located right in the
base transceiver station. The time constant according to the
invention must also take into account the running time
corresponding to the distance between the connecting and the
transceiver station, as well as the signal running time within the
base transceiver station.
Furthermore, the individual base transceiver stations of a cell
area must be synchronised by setting the time-lag of each of the
two time-lag devices of a base transceiver station to the
differential in the running time between the central station and
the most remote base transceiver station of the same cell area on
the one hand, minus the running time between the central station
and the respective base transceiver station on the other hand. By
dividing the time-lag up evenly between two time-lag devices, one
of which is connected in the transmitting branch and the other in
the receiving branch, it is achieved that both the area-covering
signal directed to a mobile statio is transmitted from all base
transceiver stations of the same cell area simultaneously, so that
the advantageous superposition effect is achieved. On the other
hand, the directional radio signal to the connection station is
transmitted from all participating basetransceiver stations
simultaneously, so that a signal accumulation is achieved and a
relatively high signal-to-noise ratio at least can be achieved.
A base transceiver station suitable for the radio network concept
according to the invention and which is provided with a connecting
aerial as well as an aerial for the area coverage--in which case
the aerials are coupled together via transmitting and receiving
branches consisting of a respective amplifier and if necessary a
frequency converter connected in antiparallel between the aerial
filters--is characterised in that a time-lag device with an
adjustable time constant is connected in the transmitting and/or
receiving branch. Thus a universally applicable transceiver station
is achieved, in which the time-lag corresponding to the different
distances from the connecting station can be individually set.
In order that both the area-covering radio signals transmitted from
the base transceiver stations of a cell area and the connecting
radio signals can be synchronised, the invention further proposes
that two time-lag devices with an adjustable time constant are
provided, one of which is connected in the transmitting and one in
the receiving circuit. By means of these two time-lag devices, the
different signal running time in a respective relay direction is
compensated.
It is within the scope of the invention that the two time-lag
devices are connected to the inputs and/or outputs of the
transmitting and receiving branches coupled to the connecting
aerial.
Particularly for the close vicinity of a connecting station, i.e.
the cell area in which the connecting station is installed, running
time compensation may be dispensable since in this case the running
time differences may be smaller. In this case, the time constant of
the time function element in the connecting station can also be
relatively small.
Independently of the presence of one of more time-lag devices in
the transmitting and receiving branch of a base transceiver
station, it has proved advantageous if in the receiving branch a
device for detecting the field strength of the signal received is
provided, which closes a switch incorporated in the transmitting
branch if a threshold value is exceeded. This measure makes it
possible to actuate in a predetermined manner only the transceiver
stations of a cell area in whose cell a mobile station is in fact
located, since only here is a radio contact required. By
disconnecting the remaining transceiver stations, the overall
transmission power being transmitted is reduced, so that common
channel interference with the closest cell area sharing the same
frequency is significantly reduced.
In this case it is practical if the threshold value is at or
slightly below the reception field strength corresponding to the
signal of a mobile station located at the periphery of the cell
concerned. Thus the field strength detector according to the
invention can reliably determine whether the mobile station
concerned is located inside its cell, thus ensuring a continuous
radio transmission. If a mobile station is located at the border
between two cells, it is recognised by both detectors of these
adjacent cells and both transceiver stations are actuated. Thus the
above-mentioned amplification effect is produced in this border
region, so that even in the case of such mobile tracking,
advantageous signal amplification is maintained.
It has been found advantageous if the switch is opened by the
reception field strength detector when the signal is below a
further threshold value. If this second threshold value is below
the first threshold value, a hysteresis is obtained which ensures
stable operation even at the periphery of a cell.
BRIEF DESCRIPTION OF THE DRAWINGS
Further features, details and advantages on the basis of the
invention will appear from the following description of a few
embodiments of the invention and from the drawing, in which:
FIG. 1 shows a cell having an approximately hexagonal basic
shape,
FIG. 2 another embodiment of a cell according to the invention
having an approximately square basic shape, supplemented along two
of its border lines by identical cells to form an area-covering
network.
FIG. 3 the radio network as in FIG. 2 on a different scale, in
which for the sake of clarity the decentral cells are not
shown,
FIG. 4 a block diagram of a central and of a decentral radio
station,
FIG. 5 a detail of the block diagram of a further embodiment of a
central transceiver station,
FIG. 6 a perspective diagram of a decentral transceiver
station,
FIG. 7 a detail of a radio network according to a further
embodiment of the invention,
FIG. 8 a detail of a radio network of another embodiment of the
invention,
FIG. 9 a cell at the periphery of a cell area,
FIG. 10a the signals transmitted from the connection statio of a
cell area plotted along the time axis,
FIG. 10b a diagram of the reply signals received by the same
connection station, corresponding to the diagram of FIG. 10a,
FIG. 11 a block diagram of a base transceiver station for an
arrangement according to the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 shows an elementary cell 1, a large number of which can be
joined together in lines to form an area-covering radio network
having an approximately honeycomb structure. In the centre of the
cell 1 is a base transceiver station 2, which is coupled via cable
or radio link to a base station controller (not shown). By means of
two directional aerials having a range 3, the central transceiver
station 2 serves the inner cells 4a and 4b. Within the cells 4a or
4b, a mobile station (not shown) communicates direct with the
central transceiver station 2.
In the case shown in FIG. 1, the central transceiver station 2 is
surrounded by decentral transceiver stations 5, each having an
identical range 6. In the arrangement shown in FIG. 1, the ranges 6
of the decentral radio stations 5 are approximately half as large
as the range of the central radio station 2, which is achieved by
suitable setting of the levels of transmission power. Thus the
ideally circular cells 7 of the decentral transceiver station 5 are
approximately half the radius of the central cell 4a, 4b. The
decentral transceiver stations 5 are so arranged that their cells 7
complement one another to form two rings concentrically surrounding
the central cell 4a, 4b.
In the decentral cells 7, communication with a mobile station via
different transmission frequencies from the inner zones 4a, 4b
takes place. However, according to a preferred embodiment of the
invention, not every decentral cell 7 has its own transmission
frequency. Rather, a plurality of adjacent transceiver stations 5
can be grouped into cell areas 8, whose border lines 9 in FIG. 1
are indicated by broken lines. The decentral transceiver stations 5
of the cells 7 allocated to the same cell area 8 communicate with
the mobile station at identical transmission frequencies. The cell
region 1 shown in FIG. 1 accordingly has two central and six
decentral cell areas 4a, 4b, 8, in which different transmission
frequencies are used in pairs. However, any number of cell regions
1 can be linked together in rows to form a honeycomb-shaped radio
network, in which the division of individual cell regions 1 into
cell areas 8 and the frequency allocations in the individual cell
areas 8 can be fully identical.
FIG. 2 shows a cell region 10 with a different basic structure.
Here also, a central transceiver station 2 is surrounded by
decentral transceiver stations 5 in an approximate ring, but
instead of a hexagonal basic shape, the cell region 10 has an
approximately square basic shape. To form an area-covering radio
network 11, a plurality of square cell regions 10 are joined
together in rows to form a rectangular grid network. As can be seen
from FIG. 2, in this case the cells 7 of the individual decentral
transceiver stations 5 join up to form a homogeneously closed radio
network 11.
FIG. 3 shows a larger detail of the radio network 11 in which the
individual cells 7 are no longer indicated, but only the cell areas
12-17, within which constant transmission frequencies are used. As
is known, none of these cell areas 12-17 borders another cell area
12-17 having an identical frequency. In this embodiment, the cell
area of the central transceiver stations 2 is divided into two
cells 12, 13 having different transmission frequencies by means of
two directional 180.degree. aerials, in order to achieve a longer
range 3 of the central cell area 4. Thus six different cell areas
12-17 arranged in pairs having different transmission frequencies
are achieved.
As can be seen from FIG. 2, the area of the cells 4a, 4b of the
cost-intensive transceiver stations 2 coupled to a base station
controller corresponds roughly to a ninth of the total area.
Consequently, the number of these cost-intensive transceiver
stations can be reduced to approximately a ninth, which brings the
extra cost of the very simple, decentral transceiver stations below
the break-even point. Furthermore, the total number of cell areas
arranged in pairs of two different frequencies with six in all is
significantly smaller than in conventional grid structures, where
the hexagonal cell regions of one transceiver station is divided
into three sectors by the use of directional 120.degree.-aerials,
so that in all twelve (four-structure with 3 sectors each) to
twenty-one (seven-structure with 3 sectors each) cell areas
arranged in pairs with two different transmission frequencies are
formed.
FIG. 4 shows a block diagram for a central transceiver station 2
and as an exceptional case only one decentral transceiver station
5. At the upper left-hand corner of FIG. 4, a base station
controller 18 is shown which is connected for example to a mobile
exchange.
The base station controller 18 communicates via a radio link
connection 20 to the central transceiver station 2. In this
transceiver station 2 is an interface component 21, which splits
the signal received from the radio link aerial 22 into individual
transmission channels 23 to 26.
To each transmission channel 23-26, a respective channel unit 27 to
30 is connected.
Each channel unit 27-30 comprises a terminal assembly 31, which
separates the channel 23-26 concerned according to the direction of
transmission and accordingly has two terminals 32, 33 on the
down-link side. The terminal 32, which makes available the signals
arriving from the base station controller 18 is connected to an
encoder 34, whose output signal 35 is fed via an amplifier 30 to a
band filter assembly 37, whence the signal leaves the channel unit
27 and is passed to a combiner 38 in order to be combined with the
output signals of other channel units 28 and transmitted to an
aerial 39 for area coverage of the central cell area.
Via an air interface 40, this transmission signal passes to the
aerial 41 of a mobile station 42, for example in the form of a
mobile telephone. The reply signal of the mobile station 42 is
transmitted in the reverse direction via the air interface 40 to
the receiving device 39 of the central transceiver station 2, where
it is allocated to the respective channel unit 27, 28 via the
combiner 38.
In the band filter assembly 37, the reception signal 43, which has
a different frequency from the transmission signal 35, is separated
therefrom and sent to the input of an amplifier 44. This is
connected on the output side to a decoder 45, in which the signal
received is processed and sent via the terminal 33 to the terminal
assembly 31 of the respective transmission channel 23, 24. Via the
interface component 21, the radio link connection 20, the base
station controller 18 and the mobile exchange 19, the reply signal
is fed into the conventional telephone network. Apart from the
division into smaller sectors, the central cell area 4a, 4b is
served in much the same way as conventional transmission
devices.
In contrast to these, in the central transceiver station 2
according to the invention, further channel units 29, 30 are
provided, which are connected to corresponding relay channels 25,
26 of the interface component 21. These channel units are no
different in their basic equipment from conventional channel units
27, 28, but have different transmitting and receiving frequencies.
They are coupled on the output side to a transmitter-receiver 47
via a combiner 46.
In contrast to the transmitter-receiver 39 for the central cell 4,
in this case however an aerial 47 with a strongly directional
character is used, so that the air interface 48 takes the form of a
true radio link connection, in which case the transmitter-receiver
49 of the decentral transceiver station 5 on the up-link side has a
corresponding, directional aerial.
The aerial 49 is connected to a band filter assembly 50, which by
means of the different frequencies distinguishes the signal 51
arriving from the central transceiver station 2 from the signal 52
directed towards the central transceiver station 2. The
transmission signal 51 is fed to a frequency converter 53, whose
output frequency 54 corresponds to the transmission frequency of
the respective cell area 8. The transmission signal having the
frequency 54 is then amplified in an amplifier 55 to a transmission
power which ensures the necessary range 6, and is transmitted via a
band filter component 56 on the output side and a
transmitter-receiver 57 connected in series. Via the air interface
58, this transmission signal passes to the aerial 59 of a mobile
station 60 which is located within the cell 7 of this decentral
transceiver station 5.
The reply signal of this mobile station 60 is picked up by the
receiver device 57 and separated from the amplified transmission
signal 54 by the band filter assembly 56. Then it is transformed by
a further frequency converter 61 into a frequency range 62 which is
used for the radio link connection 48. After amplification by the
amplifier 63, this signal 52 is sent via the input-side band filter
50 to the radio link aerial 49. The signal 48 transmitted therefrom
is received by the complementary radio link aerial 47 of the
central transceiver station 2 and is allocated from there in the
combiner 46 to the corresponding channel unit 29, where apart from
other transmission frequencies it is processed just like the signal
40 received from the aerial 39 in the inner cell 4. The reply
signal passes via the interface component 21, the radio link
connection 20 and the base station controller 18 into the telephone
network.
In addition to this standard variant, in the channel units 29, 30
communicating with a decentral transceiver station 5 a time
function element can be incorporated, which is started by the
decoder 34 and after expiry of the time interval set actuates the
encoder 45 in order to compensate the constant running times on the
radio link section 48.
If a plurality of decentral cells 7 are grouped into one cell area
8, all the transceiver stations 5 thus grouped can be addressed via
a common aerial 47 of the central transceiver station 2. In
addition, however, it is possible to provide for each of the
decentral transceiver stations 5 its own directional aerial 47, 64
(cf. FIG. 5). In order to transmit a plurality of channels 25, 26,
each of these directional aerials 47, 64 must have its own combiner
or coupler 46, 65 connected upstream.
In order to avoid interference, selection switching circuits (not
shown in FIG. 5) are integrated into the extra channel units 29,
30, which selection switching circuits compare the signal
amplitudes ascribable to different reception field strengths on the
down-link-side inputs 66, 67, which are allocated to different
radio link aerials 47, 64 and thus to different transceiver
stations 5, and in down-link transmission select only the
transmission aerial 47, 64 in which the highest reception field
strength was registered. Thus although a plurality of cells 7 are
combined into a common cell area 8, only that transceiver station 5
is ever actuated in whose cell 7 the mobile station 60 is located
at that moment. Thus the heterodyning of several signals of the
same frequency on the air interface 58 is avoided.
A constructive configuration of a decentral transceiver station 5
is shown in FIG. 6. A flat housing 68 with a base area of
approximately 1 square metre and height of approximately 20 cm has
approximately centrally on its upper face 69 a plug-in device 70
for a transmission mast 71, on which two transmitting and receiving
aerials 57 are located, each having a directional characteristic of
180.degree.. This aerials 57 are oriented in opposite directions,
so that together they cover a cell 7 with an approximately circular
circumference. In order to reduce interference, the aerials 57 can
be inclined at a slight angle so as to converge at the bottom. The
connection of the aerials 57 to the housing 68 is effected by means
of cables (not shown).
A directional transmitting and receiving aerial 49 for the air
interface 48 to a central transmission station 2 is mounted on a
post erected at a distance and is connected to the housing 68 via a
cable 73. Due to the low transmission power of the aerials 49, 57
and the minimal configuration of the electronics components within
the transmission station 5, the current supply can be ensured by
means of solar cells disposed on the upper face 69 of the housing
68.
FIG. 7 shows a detail of a radio network 101. It shows a large
number of cell area 102, which join one another continuously so
that an individual cell area assumes the approximately hexagonal
shape of an individual honeycomb cell 103. Each cell area 102 can
be circumscribed by a circle of radius 140.
Mutually abutting cell areas 102 have different frequencies. Thus
for example the cell area 102 characterised by A can be operated in
a first transmission frequency range, the cell areas 102 referenced
B are operated in a second transmission frequency range, and the
cell areas 102 referenced C are operated at a third transmission
frequency range. As can be seen, accordingly three transmission
frequency ranges A, B and C are sufficient to create a radio
network 101 with continuously abutting cell areas 102, in which
adjacent cell areas 102 are allocated different transmission
frequency ranges A, B or C.
In the embodiment shown in FIG. 7, each cell area 102 is divided
into seven cells 104 in all, although this is not obligatory. The
cells 104 have to be arranged within a cell area 102 not according
to a predetermined geometric grid, but are arranged in a row in
such a manner that continuous coverage of the entire cell area 102
is ensured. It is also possible to create relatively large cell
areas 102 in which a central cell 104 is surrounded not by a single
ring of approximately six peripheral cells 104, but for example of
two such rings, so that on the whole approximately nineteen cells
104 per cell area 102 are formed.
Due to the grouping together of a plurality of cells 104 into cell
areas 102 having uniform transmission frequencies A; B; C; the
mutual interference even in the case of transceiver stations 105
lying in different cell areas but operating at the same
transmission frequency, e.g. B, and having the minimum distance
107, is so slight that interference-free operation of the radio
network is ensured. This is because the spacing of such transceiver
stations 105 which are particularly sensitive to common channel
operation corresponds at least approximately to the radius 140 of a
cell area 102, whilst the radius 106 of a cell 104 on the contrary
can be reduced to almost any size by increasing the number of
transceiver stations 105 per cell area 102.
All the transceiver stations 105 of a cell area 102 are coupled via
a common connecting station 108 to a base station controller not
shown. In order to reduce the cost of hardware, a plurality of cell
areas 102 are associated with the same connecting station 108.
Although preferably an approximately hexagonal structure 109 of the
cell areas 102 respectively coupled to a common station 108 is
again preferred, this is not obligatory. Furthermore, the potential
sites 110 for the connecting stations 108 can be varied within the
shaded area, for example, without changing the hexagonal structure
109.
In the detail from a radio network 111 shown in FIG. 8, the cell
areas 112 have an approximately rectangular structure 113. It is
not important how the cells 114 are arranged within these cell
areas 112; but again, a hexagonal structure similar to the one in
FIG. 7 is an option. In this case also the transceiver stations 115
are located respectively in the centre of a cell 114; the range 116
corresponds to the radius of these cells 114. The minimum distance
117 between two transceiver stations 115 composed of different cell
areas but with the same transmission frequency range is slightly
larger than one edge of the rectangle 113. However, this distance
117 is entirely adequate to ensure interference-free radio
operation due to the small ranges 116. In this case also, a
plurality of cell areas 112 are coupled via a common connecting
station 118 to a base station controller not shown.
In this case, for example, four cell areas 112 can be allocated to
one connecting station 108, so that their field of influence in
each case has an approximately rectangular shape 119. The site 120
of the connecting station 118 can be moved to virtually anywhere
within the area of this rectangle 119 or even beyond that area if
coupling is effected via an aerial with a strongly directional
characteristic, although obviously the region in the centre of the
rectangle 119 is preferred, because from there the minimum running
time of the connecting signal to all transceiver stations 115 is
achieved.
FIG. 9 shows a detail of a cell 104 on an enlarged scale, which is
located on the hexagonal edge 103 of its cell area 102. Within its
cell area 102, the adjacent transceiver stations 105 transmit the
same radio signal, so that in the peripheral region 121 between two
such adjacent transceiver stations 5 a signal accumulation and
therefore effective enlargement of the range 106 by approximately
150% for example to a radius 141 is obtained.
Since the distance 123 between two adjacent transceiver stations
105 composed of different cell areas 102, 102' must be smaller than
twice the normal radius 106 of a cell 104, but the distance 122
between adjacent transceiver stations 105 within the same cell area
102 must be smaller than twice the radius 141 of a cell 104
enlarged by the signal accumulation, the distance 122 between two
transceiver stations 105 of the same cell area 102 can be larger
than the distance 123 to a transceiver station 105 in the adjacent
cell area 102', which is operated at a different transmission
frequency range.
In FIGS. 10a, 10b the transceiver station 124 transmitted from a
connecting station 108, 118 is plotted on the time axis 125, as is
the signal 126 received from the same connecting statio 108, 118.
It can be seen from FIG. 10a that the signals transmitted are
divided according to different communication channels into
individual time blocks 127a, 127b etc. The corresponding reply
signals of the base transceiver stations 105, 115 being addressed
are divided according to the same channel division into the time
blocks 128a, 128b etc.
At the end of a transmitted signal block 127a, in the respective
connecting station 118 a time function element with the time
constant 129 is started and after expiry of this time constant 129
the receiving device of the respective channel unit is actuated in
order to receive the reply signal 128a of this channel. The time
constant 129 comprises on the one hand the time 130, which
corresponds to the waiting time set in conventional transceiver
stations and takes into account particularly the reaction time of a
mobile station, and on the other hand an extra time interval 131,
which takes into account in particular twice the signal running
time between the respective connection station 108, 118 and the
base transceiver station 105, 115 furthest therefrom but coupled
thereto.
This ensures that the most remote base transceiver station 105, 115
has sufficient time 129 to receive the signal block 127a, to relay
it, to receive the reply signal from the mobile station and to send
the reply signal back as a signal block 128a to the connecting
station 108, 118.
FIG. 11 shows a block diagram of a base transceiver station
105.
This shows the aerial 132 for area coverage of the associated cell
104, via which communication with a mobile station 133 located in
this cell 104 takes place. On the other side an additional aerial
134 is provided which has a characteristic oriented towards the
connecting station 108. Since the radio link connection 134 in the
example shown lies in the radio link band, frequency conversion
within the transceiver station is necessary. This assembly
therefore has almost the same structure as the decentral
transceiver station shown in FIG. 4 and referenced 5.
In contrast to this decentral transceiver station 5, in the present
case both in the transmission branch 135 and in the receiving
branch 136 of the base transceiver station 105, a respective
additional time-lag device 137, 138 is connected. The time
constants T of the time-lag devices 137, 138 are adjustable in a
range corresponding approximately to the additional time interval
131 of the respective connecting station 108.
Since the time constants T of the time-lay devices 137, 138 of the
transceiver station 105 most remote from the connecting station 108
are set at zero, but in the closest transceiver station 105 on the
other hand are set at approximately half the time interval 131, it
can be ensured that the signal received by the connecting station
108 is transmitted simultaneously by all transceiver stations 105
of the same cell area 102, so that the desired signal accumulation
is obtained in the peripheral region 121. The signal transmitted as
a reply by the mobile station 133 can also, if received by a
plurality of transceiver stations 105, be transmitted synchronously
via the directional aerials 134 to the connecting station 108.
* * * * *