Telecommunications – Radiotelephone system – Security or fraud prevention
Reexamination Certificate
1997-10-24
2002-01-29
Chang, Vivian (Department: 2682)
Telecommunications
Radiotelephone system
Security or fraud prevention
C455S449000
Reexamination Certificate
active
06343213
ABSTRACT:
BACKGROUND OF THE INVENTION
A significant problem with mobile radio systems is the potentially harmful interference they may cause to other electronic equipment. As the use of mobile radios becomes more widespread, the occurrence of this interference will become more frequent. The problem is usually caused by the close proximity of the mobile radio transmitter to another piece of electronic equipment and the sensitivity of that equipment to extraneous signals.
There are two places where this problem is particularly dangerous, and perhaps life-threatening. These are in hospitals and in aircraft. As electronic control systems pervade other environments, however, the areas of danger will increase. Interference to automobile electronic braking systems, air bag actuators, or train system controls are examples of the areas where radio interference must be prevented to preserve the safety of operators and passengers.
Presently, the method used to prevent interference of this sort is simply to prohibit the use of mobile radios in sensitive areas. Passengers on aircraft are routinely told not to use their cellular phones. Doctors and staff are routinely told not to bring their cellular phones into some areas of the hospital. Unfortunately not everyone understands the danger and some operate their phones anyway. Some people use their cellular phones in aircraft, even some radio engineers who have said that because they know the aircraft radio frequencies are not the same as the cellular phone frequencies, there can be no interference and thus they are justified in using their mobile phone. They do not understand that interference between electronic systems may occur even when the systems operate in separate bands. Few people understand that even if they are not talking on the phone, if the phone is in “standby” mode, it may be still active and occasionally transmitting on the signalling channels and thus still a potential source of interference. As more and more people carry and use mobile phones, there will be more and more operation in areas where they are nominally prohibited.
As mobile radio systems are increasingly used for data communications, either through mobile radio systems or separate radio data services, many people will be operating these systems in prohibited areas not realizing that the warning not to operate their cellular phone also applies to their mobile radio fax modem or a data service. Many lap top computers with radio modems are operated on aircraft and there is a potential that these will be operated and interfere with the aircraft equipment.
SUMMARY OF THE INVENTION
Because it is impossible to prevent people operating their cellular phones (mobile radios) in sensitive areas, the present invention provides an arrangement whereby they can be operated safely in these areas, or the mobile radio can be signalled that it must not operate.
An effective means to limit the possibility of interference is to reduce the mobile radio transmit power. Several of the radio standards do provide low power modes of operation. If the mobile radio is commanded, via the signalling channels, to operate in the low power modes, their operation may be safe in some areas. Further, the signalling channels may also be used to broadcast (at low power) a message to the mobile handset which prohibits the handset from operation in areas where no level of mobile emissions can be tolerated. Thus the combination of low power operation and appropriate signalling commands can provide a means to protect sensitive areas from mobile radio interference.
The present invention operates in the following way:
(a) A base station with coverage in the sensitive area is installed and operated at a power level such as to be below the level of susceptibility of the sensitive equipment in the area.
(b) The base station providing coverage in the sensitive area sends signalling messages, using the signalling mechanisms in the air interface standard, instructing the mobile radios to operate in low power mode when they are within range. The low power level for the area is selected to be below the level of susceptibility for the sensitive equipment in the area.
(c) The mobile radio operation is controlled such that, before it makes any transmissions, it receives and interprets the local signalling channels and if any channel is broadcasting a “low power” command, it only responds to that signalling station and in low power mode. (This is required to prevent areas of overlapping coverage allowing a mobile to operate at high power in a sensitive area. The installation of the cell sites should be such that overlaps are minimized.)
(d) In some sensitive areas where it may be undesirable for the mobile equipment to operate, even at low power levels, the base station may broadcast an inhibiting signal which will instruct the mobile never to operate its transmitter. This inhibiting process may happen in three ways. In one case, where low levels of radio signals are possible, the base station may transmit a continuous inhibiting signal. In the second case, such as on an aircraft where the base station may operate while the aircraft is on the ground, but it may not be possible to operate the base station while in the air, the inhibit signal should deactivate all the mobiles in the area, and these mobiles should remain inactive until they receive an enabling signal from the same base station after the aircraft has landed and safe operation is possible again. In the third case, one or more base stations may be arranged in a protective ring around the sensitive region where all transmissions are prohibited. All mobiles passing through this ring would be signalled to inhibit their operation until they receive a corresponding enabling signal when they pass out of the sensitive area. To provide this on/off capability, two rings of coverage with the signalling could be used, one outer ring would provide an enabling signal to mobiles passing outwards, and the inner ring would disable mobiles passing inwards.
With this combination of low power operation and control by signalling messages the possibility of interference to equipment sensitive areas may be minimized.
SUSCEPTIBILITY LEVEL
The interference is usually simply related to the radiated power of the radio transmitter and the proximity to the sensitive equipment. For some systems, voluntary susceptibility standards are defined. For medical equipment, for example, this is nominally 3 volts per meter. This susceptibility level may be used to define the safe mobile radio power limit in proximity to the sensitive equipment. For the CT2
1
equipment (operating at 864 MHz), for example, the nominal operating power is +10 mW with a low power mode 16 dB below that. The minimum safe separation distance from the CT2 mobile radio and the sensitive electronic equipment may thus be calculated as approximately:
standard power
low power
susceptibility level
−4
dBm
−4
dBm
tx power
10
dBm
−6
dBm (low)
antenna gain
2
dB
2
dB
separation
.17
m
.028
m
The use of the low power mode thus reduces the separation distance between the mobile radio and the equipment from about 0.17 meter to about 0.028 meters (about an inch). Thus the CT2 radio, in the low power mode, would need to be on top of the sensitive equipment to begin to approach the susceptibility limit. It has been observed that Nortel (trademark) CT2 and similar radio systems operate in the low power mode a significant proportion of the time (about 40%). A similar low power level may be defined for other radio standards. The AMPS
2
, DECT
3
and the CDMA4
4
1 ETSI Standard 300-131/TIA Standard-661
2 TIA Standard IS54/IS136
3 ETSI Standard 300-175/TIA Standard-662
4 TIA Standard IS95 standards already include controlled power levels for the mobile handsets. If the low power modes of operation for the handsets can be assured through signalling mechanisms, safe operation may be possible in otherwise prohibited regions.
Manufacturers of mobile radio products are often asked how and if it is safe to operate them in sensit
Steer David
Teo Koon Hoo
Appiah Charles N.
Chang Vivian
Nortel Networks Limited
LandOfFree
Method to protect against interference from mobile radios does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method to protect against interference from mobile radios, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method to protect against interference from mobile radios will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2845955