Technique for setting cell coverage

An apparatus for setting cell coverage for a radio communication system, includes: first and second portable devices; base station equipment having a switch which loops back a signal from the first portable device to the second portable device in a zig mode; a mode setter for setting the zig mode, the mode setter being located in one of either the first or second portable devices or the base station equipment; and a detector for detecting a received electric field strength from the signal looped back from the first portable device to the second portable device.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a technique for setting cell coverage in a 
radio communication system and, more particularly, to a technique for 
setting an optimal cell coverage, reflecting the characteristics of a base 
station intended to be actually established and a user's demands for the 
talking quality. 
2. Description of the Related Art 
A cell coverage determines the number of base stations to be established 
(this is relative to the establishment cost), and the talking quality. If 
a cell coverage is smaller, the number of base stations increases. If the 
cell coverage is larger, the number of base stations decreases but the 
talking quality is deteriorated. Therefore, it is very important to 
optimally set a cell coverage in designing a cell for a cellular or 
multi-cellular radio private exchange. 
To decide the cell coverage, it is a general procedure to establish a 
signal generator at a place where a base station is intended to be 
established so that the signal generator generates a signal of a band 
which is used by the base station equipment. Then, the strength of the 
signal is measured by moving a signal analyzer. The measured signal is 
then regarded as a Received Signal Strength Indicator (hereinafter, 
referred to as the RSSI). Therefore, a cell coverage is determined, 
depending upon where the RSSI of a magnitude that enables talking is 
detected. 
However, the characteristics of the base station equipment to be 
established and used cannot be considered at all if the cell coverage is 
determined in such a way. That is, the transmission power of the base 
station equipment can be considered, but the reception characteristics of 
the base station equipment or the transmission power and reception 
characteristics of the portable device cannot be considered. Therefore, in 
case that cells are designed and base stations are established in this 
way, there may show many differences from the case of actual operation. 
In other words, the best way to set a cell coverage that overcomes such 
problems is to set the cell coverage after the user tries a call with a 
system actually established. But setting a cell coverage is a factor which 
determines the number of base stations, and influences the maintenance of 
the talking quality. Therefore, it is unfeasible to set a cell coverage 
after establishing base stations. 
The following patents each disclose features in common with the present 
invention but do not teach or suggest the technique for setting an optimal 
cell coverage of the present invention. 
U.S. Pat. No. 5,375,123 to Andersson et al., entitled Allocation Of 
Channels Using Interference Estimation, U.S. Pat. No. 5,561,841 to Markus, 
entitled Method And Apparatus For Planning A Cellular Radio Network By 
Creating A Model On A Digital Map Adding Properties And Optimizing 
Parameters, Based On Statistical Simulation Results, U.S. Pat. No. 
5,561,839 to Osterberg et al, entitled Method And Arrangement In Mobile 
Telecommunications Networks To Provide For Improved Cell Planning, U.S. 
Pat. No. 5,521,958 to Selig et al, entitled Telecommunications Test System 
Including A Test And Trouble Shooting Expert System, U.S. Pat. No. 
5,465,390 to Cohen, entitled Method For Laying Out The Infrastructure Of A 
Cellular Communications Network, U.S. Pat. No. 5,448,616 to Kaewell Jr. et 
al., entitled Integrated Bit Error Rate Test Function In Analog Channel 
Unit Of digital Cellular Network, U.S. Pat. No. 5,031,204 to McKernan, 
entitled Interactive Diagnostic System For Cellular Telephones, and U.S. 
Pat. No. 4,860,281 to Finley et al., entitled Individual Subchannel 
Loophack In The PCM Interfaces Of A Digital Telephone Exchange With 
Control Of The Outbound Path. 
SUMMARY OF THE INVENTION 
Accordingly, an object of the present invention is to provide an optimal 
technique which can minimize the differences from the case of actual 
operation, making up a most similar environment to the case of actual call 
when a base station is installed. 
To accomplish the object of the present invention, there is provided a 
device for setting cell coverage for a radio communication system, 
comprising: first and second portable devices; base station equipment 
having a switch which loops back a signal from the first portable device 
to the second portable device in a zig mode; a mode setter for setting the 
zig mode, the mode setter being located in the first or second portable 
devices or in the base station equipment; and a detector for detecting a 
received electric field strength from the signal looped back to the second 
portable device. 
For another aspect of the present invention, there is provided a device for 
setting cell coverage for a radio communication system equipped with base 
station equipment and first and second portable devices, the device 
comprising: a mode setter for setting a zig mode, the mode setter being 
located in the first or second portable devices or in the base station 
equipment; and a switch which loops back a call signal input from the 
first portable device to the second portable device in a zig mode.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
A preferred embodiment of the present invention is described below in 
detail with reference to the attached drawings. 
In the following description, many specified things, such as specific 
circuit elements are shown. However, it is obvious to anyone who has 
common knowledge in this field of art that the present invention can be 
put in operation without these specific elements and they are provided 
only to promote the general understanding of the invention. In describing 
the present invention, a detailed explanation has been omitted if the 
relevant well known function or a detailed description of the composition 
could obscure the point of the present invention. 
FIG. 1 is a diagram of a radio communication system, assuming that it is 
actually constructed and composed of private exchange 11, controller 12, a 
plurality of base station equipment 13a-13n, and a plurality of portable 
devices 14a-14n. 
According to the composition, in case of originating a call, the devices 
are connected in the sequence: portable device--base station 
equipment--controller--private exchange--office exchange (not shown). In 
case of receiving a call, they are connected in the sequence: office 
exchange--private exchange--controller--base station equipment--portable 
device. 
To make a call to the portable device existing within a cell, they are 
connected in the sequence: the first portable device--base station 
equipment--controller--private exchange controller--base station 
equipment--the second portable device. 
The above description is an explanation, assuming a case of an actual call 
in a previously constructed system to promote the understanding of the 
present invention. The present invention makes it possible to set an 
optimal cell coverage by making up such an environment most similarly. 
That is, the signal transmitted in the sequence: the first portable 
device--base station equipment--the second portable device. For this, a 
switch which loops back a signal from the first portable device to the 
second portable device is added to the base station equipment. 
FIG. 2 is a schematic diagram of base station equipment according to an 
embodiment of the present invention. A switch 82 is added to the general 
composition. Memory 71 includes not only a program which controls its own 
operation of base station equipment but also a program which sets an 
optimal cell coverage according to the present invention. Controller 73 
controls the overall operation to set an optimal cell coverage based on 
the above mentioned program. 
FIG. 3 is a diagram of showing the connections between switch 82, CT-2/CAI 
(Cordless Telephone Second Generation/Common Air Interface) baseband 
circuit 72 and S interface 74, and also showing PCM (Pulse Code 
Modulation) to each one, input or output ports Tx1, Rx1, Tx2, Rx2, for 
convenience taking CT-2/CAI baseband circuit having the first and second 
basebands respectively corresponding to the first and second portable 
devices. 
Reference code K is a signal generated from the controller to control the 
operation of the switch 82 according to a normal mode or zig mode. 
When a normal mode is selected, contact al is connected to contact a2, and 
contact b1 is connected to contact b3, so that the signal of the first 
portable device is transmitted to a private exchange through the S 
interface 74 via a controller. In case of the second portable device, 
contact b2 is connected to contact a2, and contact a3 is connected to 
contact b3. 
When a user selects the zig mode for setting a cell coverage, contact a1 is 
connected to contact a3, and contact b1 is connected to contact b2 so that 
the signal of the first portable device is looped back to the second 
portable device. For this, using a portable device which has the zig mode 
selection key or a console of the base station equipment, a user sets the 
zig mode. In the base station equipment, the first portable device is 
placed in a virtual talking condition through the same procedure as in the 
case where a private exchange and controller are provided. As for the 
second portable device, the same procedure is taken as for the first 
portable device. The signal of the first portable device is looped back to 
the second portable device. In doing so, the effect of talking can be as 
if transmitted in the sequence: the first portable device--base station 
equipment--controller--private exchange--controller--base station 
equipment--the second portable device. In such a condition, if a cell 
coverage in which actual speech is possible is set while moving the 
location of the portable device, an optimal cell coverage can be set. 
As described above, the present invention provides the advantage of setting 
a cell coverage after trying a virtual speech, connecting the two portable 
devices only through base station equipment, even though the whole system 
has not been constructed. That is, it has an advantage in that it can 
fully reflect not only the characteristics of the base station to be 
established but also the user's demand for the talking quality, thus 
minimizing the differences from the case of the actual operation. 
It should be understood that the present invention is not limited to the 
particular embodiment disclosed herein as the best mode contemplated for 
carrying out the present invention, but rather that the present invention 
is not limited to the specific embodiments described in this specification 
except as defined in the appended claims.