Method and apparatus for controlling transceiver operations in a radio communications system to reduce same channel frequency interference

Transceiver frequency and power level are allocated in a radio communications system which includes a base station, a radio personal communications terminal, and a radio personal communications network, by using a smart card to store frequency and power level indicators. The stored indicators are used to set personal communications terminal-to-base station communications. The smart card may be removably coupled to the base station or the personal communications terminal. Since the smart cards are issued by the radio personal communications system carrier, appropriate frequencies and power levels can be assigned for base stations, to minimize same channel interference with the radio personal communications network.

FIELD OF THE INVENTION 
This invention relates to communications systems and more particularly to 
radio communications systems. 
BACKGROUND OF THE INVENTION 
Radio communication systems are increasingly being used for wireless mobile 
communications. An example of a radio communication system is a cellular 
phone system. The design and operation of an analog cellular phone system 
is described in an article entitled Advanced Mobile Phone Service by 
Blecher, IEEE Transactions on Vehicular Technology, Vol. VT29, No. 2, May, 
1980, pp. 238-244. The analog mobile cellular system is also referred to 
as the "AMPS" system. 
Recently, digital cellular phone systems have also been proposed and 
implemented using a Time-Division Multiple Access (TDMA) architecture. 
Standards have also been set by the Electronics Industries Association 
(EIA) and the Telecommunications Industries Association (TIA) for an 
American Digital Cellular (ADC) architecture which is a dual mode analog 
and digital system following EIA/TIA document IS-54B. Telephones which 
implement the IS-54B dual mode architecture are presently being marketed 
by the assignee of the present invention. 
Different standards have been promulgated for digital cellular phone 
systems in Europe. The European digital cellular system, also referred to 
as GSM, also uses a TDMA architecture. The GSM also uses a Subscriber 
Identification Module (SIM) which is removably coupled to a cellular phone 
in order to provide subscriber identification. The SIM is implemented 
using a "smart card", also referred to as a "chip card", which contains 
information such as a subscription number, telephone number and 
authentication codes in an embedded chip. The SIM can be exchanged between 
telephone units so that the user can insert the SIM into any compatible 
telephone. Cellular telephones using smart cards are also described in 
U.S. Pat. Nos. 5,091,942 to Dent; 5,134,717 to Soggard Rasumussen; and 
5,153,919 to Reeds, III et al. Citizens band (CB) radios are also known, 
which use removable crystals to set oscillator frequency. 
Proposals have recently been made to expand the cellular phone system into 
a radio personal communications system. The radio personal communications 
system provides mobile radio voice, digital, video and/or multimedia 
communications using radio personal communications terminals. Thus, any 
form of information may be sent and received. Radio personal 
communications terminals include a radio telephone, such as a cellular 
telephone, and may include other components for voice, digital, video 
and/or multimedia communications. 
A radio personal communication system includes at least one base station. A 
base station is a low power transceiver which communicates with a radio 
personal communications terminal such as a cellular telephone over a 
limited distance, such as tens of meters, and is also electrically 
connected to the conventional wire network. The base station allows the 
owner of a radio personal communications terminal to directly access the 
wire network without passing through the radio personal communications 
network, such as the cellular phone network, whose access rates are 
typically more costly. When located outside the range of the base station, 
the personal communications terminal automatically communicates with the 
radio personal communications network at the prevailing access rates. 
A major problem in implementing a radio personal communication system is 
the frequency overlap between the radio personal communications network 
(e.g., cellular phone network) and the base station. As understood by 
those having skill in the art, only a limited number of frequencies are 
available for radio communications. In the United States, cellular 
telephones have been allocated 832 30kHz wide channels. Within this 
spectrum, each regional provider can substantially allocate and use these 
frequencies as it sees fit. 
In a radio personal communications system, it is assumed that base station 
transmission will be in the same frequency spectrum as the radio personal 
communications network. Accordingly, the possibility of same channel 
interference arises when a base station is operating at the same channel 
as the network covering the same area. 
Frequency overlap between the network and the base stations can be 
prevented if the network and base stations are allocated different bands 
of frequencies. However, such a hybrid system is not an efficient 
allocation of the frequency spectrum. Moreover, a hybrid personal 
communications terminal may be more expensive and complicated because 
additional circuitry may be required. Accordingly, in order to efficiently 
provide a radio personal communications system, it is desirable to provide 
base stations which operate in the same frequency bands as the radio 
personal communications networks, while avoiding same channel 
interference. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide an improved 
radio personal communications system and method. 
It is another object of the present invention to provide a radio personal 
communications system and method wherein same channel interference between 
the radio personal communications network, such as the cellular telephone 
network, and the base stations, are reduced. 
These and other objects are obtained, according to the present invention, 
by providing frequency indicating means, preferably a smart card, for 
storing therein an indicator of at least one radio transmission frequency. 
The radio personal communications terminal and/or base station is adapted 
for removably coupling the frequency indicating means thereto and for 
controlling the radio personal communications terminal and/or base station 
to operate at a frequency corresponding to a frequency which is stored in 
the smart card. Since the smart cards are issued by the radio personal 
communications system carriers, appropriate frequencies can be assigned 
for the base stations, to minimize same channel interference with the 
radio personal communications network. Moreover, by allowing radio 
personal communications system carriers to lease unused frequencies via 
smart cards, additional revenue may be generated from these frequencies. 
Preferably, according to the invention, the frequency indicating means 
(smart card) also stores therein a second indicator of at least one power 
level, and the radio personal communications terminal and/or base station 
operates at a frequency and power level corresponding to that which is 
stored in the smart card. The base station is preferably adapted for 
removably receiving the frequency and power level indicating means (smart 
card) and for controlling the transmission frequency and power of the base 
station to correspond to the stored frequency and power level. A stored 
frequency and power level are also preferably provided to the personal 
communications terminal which communicates with the base station, so that 
the terminal also transmits at a frequency and power level which is 
compatible with that of the base station. 
Alternatively, the frequency and power level indicating means (smart card) 
may be contained within the radio personal communications terminal. Then, 
when establishing contact with the base station, the terminal can set the 
frequency and power level of the base station and of the terminal based on 
a power level and frequency stored in the smart card. 
In a method according to the present invention, a base station for a radio 
telephone network is operated to reduce same channel interference with the 
radio telephone network by electrically connecting the base station to a 
wire telephone network and by receiving a frequency indicating signal, and 
also preferably a power level indicating signal, from a source external to 
the base station. The base station transceiver is then operated at a 
frequency, and preferably at a power level, corresponding to the received 
frequency and power level indicating signals. Preferably, the frequency 
and power level indicating signals are received by removably coupling a 
smart card, including a stored indication of at least one radio 
transmission frequency and power level, to the base station, and obtaining 
from the coupled smart card, signals representing the at least one radio 
transmission frequency and power level. The base station also preferably 
transmits a frequency and power level signal, based upon the stored 
indicators to a radio telephone with which it communicates, so that the 
radio telephone also can operate at a frequency and power level which is 
compatible with the base station. 
In an alternate method, the radio telephone is adapted for removably 
coupling a smart card thereto, where the smart card includes at least one 
stored indication of the radio transmission frequency and preferably a 
power level. The radio telephone transceiver is controlled to operate at a 
frequency and power level corresponding to the stored frequency and power 
level in the smart card. The radio telephone also transmits signals 
representing a radio transmission frequency and preferably a power level, 
to the base station, so that the base station can operate at this power 
level. 
The use of smart cards for storing frequency and power level indications 
allows the network operator to assign frequencies for base stations which 
minimize same channel interference with the radio network. The system 
carrier also can obtain additional revenue from unused frequencies within 
a network cell by leasing these frequencies for base station operation 
within the cell. An improved radio personal communications system and 
method is thereby provided.

DESCRIPTION OF PREFERRED EMBODIMENTS 
The present invention now will be described more fully hereinafter with 
reference to the accompanying drawings, in which preferred embodiments of 
the invention are shown. This invention may, however, be embodied in many 
different forms and should not be construed as limited to the embodiments 
set forth herein; rather, these embodiments are provided so that this 
disclosure will be thorough and complete, and will fully convey the scope 
of the invention to those skilled in the art. 
Referring now to FIGS. 1A and 1B, conceptual diagrams of a radio personal 
communications system are shown. As shown in FIG. 1A, radio personal 
communications system 100 includes at least one radio personal 
communications network 102, such as a cellular telephone cell, for 
transmitting and receiving messages in a network range indicated by 104, 
via cell antenna 106. Network 102 also interfaces with the wired network 
108. It will be understood by those having skill in the art that a radio 
personal communication system 100 typically includes many radio personal 
communication networks, or cells, 102 to cover a large area. 
Still referring to FIG. 1A, system 100 also includes a base station 110. 
Base station 110 includes a low power transceiver for transmitting and 
receiving via base station antenna 112, over a limited base station range 
114, typically on the order of tens of meters. Thus, a base station may be 
used for transmission and receipt of radio personal communications in a 
home or office. Base station 110 also is electrically connected to the 
wire network 108. 
Still referring to FIG. 1A, a radio personal communications terminal 120 is 
shown for radio communications with both base station 110 and network 102 
via antenna 122. Radio personal communications terminal includes a radio 
telephone such as a cellular phone. Radio personal communications terminal 
120 may also include, for example, a full computer keyboard and display, a 
scanner, and full graphics and multimedia capabilities. 
As illustrated in FIG. 1A, when terminal 120 is in the range 114 of the 
base station 110, a radio link 124 therebetween is automatically 
established. As shown in FIG. 1B, when the terminal 120 is outside the 
range 114 of the base station 110, but within the range 104 of the network 
102, a new radio link 126 is automatically established with the network 
102. Thus, when the user is relatively close to the base station 110 (i.e. 
within the home or office), wireless communications take place with the 
base station so that the radio personal communications network 102, with 
its higher rate structure, is bypassed. When the user is relatively far 
from the base station 110, communications take place with the network 102. 
It will be understood by those having skill in the art that a complete 
radio personal communications system 100 will typically include many base 
stations 110, terminals 120 and radio networks (cells) 102. It will be 
understood by those having skill in the art that conventional 
communications and handoff protocols may be used with the present 
invention, and need not be described further herein. For purposes of this 
description, it will be assumed that the spectrum allocation is the IS-54B 
cellular phone spectrum allocation which is illustrated in Table 1 below. 
TABLE 1 
______________________________________ 
Boundary Transmitter Center 
Bandwidth Number of 
Channel Frequency (MHz) 
System (MHz) Channels Number MOBILE BASE 
______________________________________ 
Not Used 1 (824.010) 
(869.010) 
A" 1 33 991 824.040 
869.040 
1023 825.000 
870.000 
A 10 333 1 825.030 
870.030 
333 834.990 
879.990 
B 10 333 334 835.020 
880.020 
666 844.980 
889.980 
A' 1.5 50 667 845.010 
890.010 
716 846.480 
891.480 
B' 1.5 83 717 846.510 
891.510 
799 848.970 
893.970 
______________________________________ 
Transmitter 
Channel Number 
Center Frequency (MHz) 
______________________________________ 
MOBILE 1 .ltoreq. N .ltoreq. 799 
0.030 N + 825.000 
990 .ltoreq. N .ltoreq. 1023 
0.030 (N-1023) + 825.000 
BASE 1 .ltoreq. N .ltoreq. 799 
0.030 N + 870.000 
990 .ltoreq. N .ltoreq. 1023 
0.030 (N-1023) + 870.000 
______________________________________ 
In the radio personal communication system 100 described in FIGS. 1A and 
1B, it is important to avoid same channel interference between base 
station 110 and network 102. According to the invention, the operator of 
network 102, which has been assigned the use of the frequency spectrum in 
the region by a regulatory authority, is allowed to assign frequencies and 
preferably power levels, of base station 110. The network operator can 
assign frequencies and preferably power levels to base station 110 to 
minimize same channel interference and to maximize revenue from the 
assigned frequency spectrum. Frequency indicating means, in the form of a 
smart card, removable memory module or other token, is removably coupled 
to the base station 110 or personal communications terminal 120 to provide 
frequency information, and also preferably power level information, which 
governs terminal-to-base station communications. 
FIG. 2 illustrates a frequency and power level indicating means according 
to the invention. As shown, frequency and power level indicating means 200 
is preferably a smart card 202, also referred to as a "chip card", or 
other token, which includes memory means 208 for storing therein 
indications of at least one radio transmission frequency 204 and at least 
one power level 206. Memory 208 is preferably an electrically erasable 
programmable read only memory (EEPROM), which operates under control of a 
controller 210. A plurality of smart card electrical contacts 212a-212n, 
only three of which are illustrated in FIG. 2, allow communication of the 
frequency and power level indicators 204, 206 external to the smart card 
202. It will be understood by those having skill in the art that memory 
208 may also contain other information 214, for example identification 
information such as subscription number, telephone number and 
authentication codes, and/or other preprogrammed telephone numbers. A 
smart card is currently used in the European digital cellular system (GSM) 
for purposes of subscriber identification. The GSM smart card is referred 
to as a Subscriber Identification Module (SIM) and is described in 
International Standards ISO 7816-1, -2, and -3. 
FIG. 3 illustrates a block diagram of a preferred embodiment of the present 
invention, in which a base station 110 includes means for removably 
coupling the frequency and power level indicating means 200 thereto. FIG. 
3 illustrates a recess 302 for removably coupling the frequency and power 
level indicating means 200 to base station 110. However, other removable 
coupling arrangements may be provided. Contacts 212a-212n electrically 
contact corresponding base station contacts 304a-304n for obtaining 
signals representing the frequency and power level indications 204, 206 
from smart card 202. It will be understood that electromagnetic, optical 
or other means may also be used to obtain the signals from the removably 
coupled smart card 202. 
According to the invention, base station 110 uses the obtained frequency 
and power level 204, 206, respectively, to govern operation of base 
station 110. Frequency and power level signals are also preferably used to 
control operation of the radio personal communications terminal 120 as 
will be described below. As will also be described below the terminal 120 
may be controlled to operate at the same frequency and power level as base 
station 110. Alternatively, a different frequency and power level may be 
provided. If a different frequency or power level is used, smart card 202 
may store multiple frequencies 204 and power levels 206. Alternatively, 
the base station 110 or terminal 120 may determine the second frequency 
and power level from a single stored indication in smart card 202. The 
base station 110 is preferably configured so that it will not operate 
without a frequency and power level indicating means 200 coupled thereto. 
Thus, the network operator can receive revenue from the use of the 
frequency, and simultaneously prevent radio communications between base 
station 110 and terminal 120 from interfering with the cellular network. 
Referring again to FIG. 3, the remaining circuitry of base station 110 will 
now be described. The design of the remaining circuitry of base station 
110 is well known to those having skill in the art, and need not be 
described in detail. Microprocessor 360, for example a Zilog Z80 
microcontroller, controls the base station 110. Radio transceiver 310 
provides two-way communications with the terminal 120 and network 102 via 
antenna 112. Signals received by antenna 112 are down converted by the 
radio transceiver 310, and provided to a demodulator 315. The demodulator 
produces a bit stream, i.e. a sequence of binary data representing the 
received data. The bit stream is then provided to the receive digital 
signal processor (DSP) 355, where it is converted to an analog audio 
signal according to methods well known to those having skill in the art. 
The resultant analog signal is transferred to the subscriber loop 
interface circuit 345. Loop interface circuit 345 is a commonly used 
circuit which provides the interface to the wired network 108, also 
referred to as the Public Switched Telephone Network (PSTN). PSTN 108 is 
the regular "wire line" telephone system supplied by, for example, the 
regional Bell Operating Companies, and may use copper wire, optical fiber 
or other stationary transmission channels. 
Still referring to FIG. 3, receive DSP 355 is controlled by microprocessor 
360. Microprocessor 360 provides timing signals and instructions. 
Operating instructions for the receive DSP 355 are typically contained in 
electrically erasable programmable read-only memory (EEPROM) 330. Flash 
ROM 335 typically contains instructions for the microprocessor 360 itself. 
These instructions are uploaded into the microprocessor 360 during 
initialization. SRAM 325 is a static random access memory which is 
typically used by the DSP 355 and the microprocessor 360 as a scratch pad 
memory for temporary storage of information. Power management and 
distribution circuits 340 are also connected to microprocessor 360. 
To transmit, signals received from wire network 108 are coupled to the 
transmit DSP 320 by a loop interface circuit 345. The transmit DSP 320 
digitizes the analog signal and converts it into a bit stream which is 
then passed onto the modulator 305. The transmit circuits basically 
perform complementary functions to those already described for the receive 
circuits. 
FIG. 4 illustrates a schematic block diagram of a radio transceiver 310 of 
FIG. 3. As shown, transceiver 310 includes circuitry for both the 
reception and transmission of the radio frequency signals. Signals 
received by the antenna 112 are directed to the receive circuits by the 
duplexer 401. The duplexer is a filter with two separate bandpass 
responses: one for passing signals in the receive band and another for 
passing signals in the transmit band. In the ADC architecture, described 
above, the receive and transmit frequencies are separated by 45 mHz. The 
duplexer 401 allows simultaneous transmission and reception of signals. 
After passing through the duplexer 401, received signals are amplified by a 
low noise radio frequency (RF) amplifier 402. This amplifier provides just 
enough gain to overcome the expected losses in the front end circuitry. 
After amplification, unwanted components of the signal are filtered out by 
the receive filter 403. After filtering, the signal is mixed down to a 
first intermediate frequency (IF) by mixing it in mixer 404 with a second 
signal generated by the channel synthesizer 415 and filtered by Local 
Oscillator (LO) filter 414. The first IF signal is then amplified by 
amplifier 405 and unwanted mixing products are removed by IF filter 406. 
After filtering, the first IF is mixed in mixer 407 to yet another lower 
frequency or second IF signal, using a signal provided by local oscillator 
synthesizer 416. The second IF signal is then filtered by two filters 408 
and 410, and amplified by multistage amplifiers 409 and 411 to obtain an 
IF signal 412 and a radio signal strength indication (RSSI) signal 413. 
Thereafter, it undergoes a process of detection, for example, as described 
in U.S. Pat. No. 5,048,059 to Dent, the disclosure of which is 
incorporated herein by reference. 
In order to transmit, a datastream 419 is generated by the transmit DSP 320 
(FIG. 3). In ADC architecture, the datastream is organized as bursts for 
time division multiplexing with other users. Reference oscillator 418 
generates a precise frequency which is used as a stable reference for the 
RF circuits. The output of oscillator 418 is passed through a multiplier 
421 where it experiences a sixfold increase in frequency. This frequency 
is then passed into a quadrature network 422 which produces two signals of 
equal amplitude which have a quadrature phase relationship, i.e. they are 
offset by 90.degree.. These quadrature signals, along with the datastream 
419, are combined in the modulator 423 to create a modulated signal, as 
described in an article entitled I and Q Modulators for Cellular 
Communications Systems, D. E. Norton et al., Microwave Journal, Vol. 34, 
No. 10, October 1991, pp. 63-79. The modulated signal is passed to a mixer 
424 which translates the signal to radio frequency. The exact radio 
frequency is determined by the local oscillator signal provided by the 
channel synthesizer 415. The radio frequency signal is passed through a 
variable gain controlled amplifier 425. The gain of this amplifier, which 
is controlled by means of a voltage on transmit power control line 420, 
determines the eventual output power, since the linear power amplifier 427 
has fixed gain. Filtering is performed by transmit filter 426. 
According to the invention, a frequency indicator 204 stored in smart card 
202 is converted to a synthesizer command and applied to line 417 to 
produce the requisite transmit and receive frequency. A power level 
indicator 206 stored in smart card 202 is converted to a transmit power 
control signal and applied to line 420 to control the transmit power. The 
conversions are preferably performed by microprocessor 360 using 
conventional techniques. Operations performed to set the frequency and 
power level will be described below in connection with FIG. 6. 
Referring now to FIG. 5, according to another embodiment of the invention, 
frequency and power level indicating means 200 can also be used in radio 
personal communications terminal 120 to control the frequency and power 
level thereof and/or to control the frequency and power level of base 
station 110 by radio transmission. The design of terminal 120 is similar 
to that of base station 110 (FIG. 3) except that a loop interface circuit 
345 is not present. When terminal 120 is a cellular phone, it includes a 
keypad 502, a display 504, a speaker 506, and a microphone 508. In order 
to provide a radio personal communications terminal for receipt and 
transmission of audio, video and data and/or multimedia signals, keypad 
502 may be a full scale personal computer keyboard and display 504 may be 
a large graphics display. A scanner 510 may also be provided as may other 
devices 512 such as disk drives and modems. Apart from the use of smart 
card 200 for setting power levels and frequencies, the design of terminal 
120 is well known to those having skill in the art and need not be 
described herein. 
Referring now to FIG. 6, operations for controlling frequency and power 
level of a personal communications terminal and/or a base station, based 
upon stored frequency and power level information from a smart card, 
according to the invention, will now be displayed. It will be understood 
that other operations may be used. 
Operations begin when power is applied to terminal 120 at Block 602. Upon 
application of power, the terminal 120 scans a set of control channels 
which are allocated to base stations 110, and determines if a signal level 
above threshold has been detected, at Block 606. It will be understood 
that each base station 110 is typically allocated only one of the set of 
control channels. If a signal level above threshold has been detected, 
then terminal 120 is within the range 114 of base station 110. If a signal 
level above threshold was not detected, then the terminal 120 is not 
within the range of base station 110 and communications are initiated with 
network 102 at Block 608, using conventional techniques. 
Referring again to Block 606, if a base station control channel signal 
above threshold is detected, the terminal 120 locks onto the strongest 
signal at Block 610. Once locked on, terminal 120 performs a registration 
at Block 612. Similar to cellular phone systems, this registration 
information occurs at a predetermined power level and a predetermined 
frequency which depends upon the control channel which has been locked. 
During the registration process, the base station 110 instructs the 
terminal 120 to tune to another frequency, to which the base station opens 
a channel and transmits at a defined power level. This can be the same 
frequency and power level which is determined by the frequency and power 
level indicators, or can be a different frequency and power level. Once 
the transfer has been completed, the base station drops the control 
channel frequency to prevent another user from attempting to use the same 
base station. 
According to the invention, the stored frequency and power level indicators 
are obtained from the smart card 202 which is preferably removably coupled 
to the base station 110, but which may also be removably coupled to the 
terminal 120. At Block 616, the obtained frequency and power levels are 
converted to signals which are used to set the synthesizer 415 and 
amplifier 425 for the unit which is removably coupled to the smart card. 
Signals representing a frequency and power level (the same frequency/power 
level or different frequency/power level) are then transmitted to the 
other unit, which does not contain the smart card, at Block 618. That unit 
uses the received frequency and power level signals to set its synthesizer 
and amplifier at Block 620. Communications then take place between the 
base station 110 and terminal 120 at the frequencies and power levels 
which were set in the earlier operations, at Block 622. 
It will be understood by those having skill in the art that a separate 
voice channel frequency and power level may be stored in the smart card 
202 for the base station 110 and terminal 120. The power levels may be 
different for the base station and the terminal if, for example, the base 
station has a larger antenna or a more sensitive receiver. It is also 
contemplated that the frequencies will be different since the terminal and 
base station would not typically transmit or receive on the same 
frequencies in a duplex transceiver. Alternatively, a single frequency and 
power level may be stored and a second frequency and power level may be 
determined from the single frequency and power level. 
Accordingly, the network provider can use a frequency and power level 
indicating means such as a smart card, to allocate frequencies and power 
levels of base station-to-terminal communications. By allocating the 
frequency and power level of base station-to-terminal communications, same 
frequency interference within a network cell is reduced and the network 
provider obtains additional revenue from the licensed frequency spectrum 
for the base station. 
In the drawings and specification, there have been disclosed typical 
preferred embodiments of the invention and, although specific terms are 
employed, they are used in a generic and descriptive sense only and not 
for purposes of limitation, the scope of the invention being set forth in 
the following claims.