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Mobile Phone Patent Abstract
A method for minimizing or eliminating external interference signals
in a CDMA mobile phone uses a memory for storing a plurality of
predetermined control voltage values, received signal strength indicator
(RSSI) data classified into various grades for each of the control
voltage values, reference value data classified into various grades
for each RSSI to meet a given signal receiving condition and control
voltage change data corresponding to the reference value data. The
method includes the steps of setting an initial control voltage
to control a damping device, receiving a communication signal, finding
one of the RSSI data grades where the RSSI of the received signal
belongs, finding one of the reference value data grades where the
received signal belongs, and evaluating the difference between the
normal signal and external interference signals based on the control
voltage, RSSI grade and reference value data grade. The control
voltage generator is controlled to reset the control voltage according
to the difference.
Mobile Phone Patent Claims
What is claimed is:
1. An apparatus for minimizing external interference signals in
a code division multiple access (CDMA) mobile phone, comprising:
a damping device for adjustably attenuating signals received from
an antenna;
a memory for storing information including a plurality of predetermined
control voltage values, received signal strength indicator (RSSI)
data classified into a plurality grades for each of said control
voltage values, reference value data classified into a plurality
of grades for each RSSI to meet a given signal receiving condition,
and control voltage change data corresponding to said reference
value data;
an RSSI detector for detecting the RSSI of a received signal;
a control voltage generator for generating the control voltage
to adjust attenuation levels of said damping device; and
a controller for evaluating the difference between the signals
received and external interference signals by analyzing said control
voltage and the detected RSSI based on the information stored in
said memory, and for adjusting said control voltage according to
said difference.
2. The apparatus as in claim 1, wherein said reference value data
is mean transmission energy rate per pseudo noise (PN) chip.
3. An apparatus as in claim 2, further comprising a transmission
energy rate detector for detecting said mean transmission energy
per PN chip, whereby said controller evaluates the difference between
said signals received and external interference signals based on
said control voltage, RSSI and mean transmission energy rate per
PN chip.
4. The apparatus as in claim 1, wherein said reference value data
is frame error rate (FER) data of a received signal.
5. The apparatus as in claim 4, further comprising a frame error
rate detector for detecting said FER, whereby said controller evaluates
the difference between said signals received and external interference
signals based on said control voltage, RSSI and FER.
6. In an apparatus for minimizing external interference signals
in a code division multiple access (CDMA) mobile phone with a low
noise amplifier connected to a damping device, which includes a
memory for storing a plurality of predetermined control voltage
values, received signal strength indicator (RSSI) data classified
into a plurality grades for each of said control voltage values,
reference value data classified into a plurality of grades for each
RSSI to meet a given signal receiving condition and control voltage
change data corresponding to said reference value data, a method
for eliminating said external interference signals comprising the
steps of:
(a) setting an initial control voltage to control said damping
device;
(b) receiving a communication signal;
(c) finding one of said RSSI data grades where the RSSI of said
received signal belongs;
(d) finding one of said reference value data grades where said
received signal belongs; and
(e) evaluating the difference between the communication signal
and said external interference signals based on said control voltage,
RSSI grade and reference value data grade, whereby said control
voltage generator is controlled to adjust said control voltage according
to said difference.
7. The method according to claim 6, further including in step (d),
if said RSSI does not belong to one of said RSSI grades, mean transmission
energy rate data is used as said reference value data; and
said step evaluating the difference is based on said control voltage
and said means transmission energy rate grade.
8. The method as in claim 6, including further steps of:
finding one of the grades of frame error rate (FER) data according
to a received signal in a forward communication channel if said
RSSI does not belong to one of said RSSI grades in step (d), said
reference value data being said FER data; and
evaluating the difference between the communication signal and
said external interference signals based on said control voltage
and said FER grade; and
adjusting said control voltage according to said difference; and
returning to said second step (b).
9. An apparatus for minimizing external interference signals in
a code division multiple access (CDMA) mobile phone with a low noise
amplifier connected to a damping device, comprising:
a memory for storing signal data representing a plurality of predetermined
control voltage values, received signal strength indicator (RSSI)
data classified into a plurality of grades for each of said control
voltage values, mean transmission energy rate data per pseudo noise
(PN) chip classified into a plurality of grades for each RSSI and
control voltage change data corresponding to said mean transmission
energy rate data;
an RSSI detector for detecting the RSSI of a received signal;
a transmission energy rate detector for detecting said mean transmission
energy per PN chip from said detected RSSI;
a control voltage generator for generating the control voltage
to control said damping device; and
a controller for evaluating the difference between the normal signal
and said external interference signals by appraising said control
voltage, the detected RSSI and the detected mean transmission energy
rate per PN based on the information stored in said memory, thereby
making said control voltage generator reset said control voltage
according to said difference.
10. An apparatus for minimizing external interference signals in
a code division multiple access (CDMA) mobile phone with a low noise
amplifier connected to a damping device, comprising:
a memory for storing signal data representing a plurality of predetermined
control voltage values, received signal strength indicator (RSSI)
data classified into a plurality of grades for each of said control
voltage values, frame error rate (FER) data according to a received
signal in a forward communication channel classified into a plurality
of grades for each RSSI and control voltage change data corresponding
to said FER data;
an RSSI detector for detecting the RSSI of a received signal;
a frame error rate detector for detecting said FER;
a control voltage generator for generating the control voltage
to control said damping device; and
a controller for evaluating the difference between the received
signal and said external interference signals by processing said
control voltage, the detected RSSI and the detected FER based on
the signal data stored in said memory, thereby making said control
voltage generator reset said control voltage according to said difference.
Mobile Phone Patent Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a code division multiple access
(CDMA) mobile phone in a digital communication system, and more
particularly a circuit for minimizing or eliminating external interference
signals in such a mobile phone.
2. Description of the Related Art
Generally, mobile phone or cellular communication systems employ
multiple access communication techniques such as CDMA or Advanced
Mobile Phone Service (AMPS). Typically, digital systems employ CDMA
and frequency modulation is used in AMPS. CDMA may be used in dual
mode to allow reception of an analog signal. Namely, it may be used
not only in CDMA mode but also in AMPS mode. In such usage, when
digital signals are communicated, there often occur analog interfering
signals to cut a call signal or cause erroneous reception of the
digital signals. This error is called intermodulation distortion
(IMD), which affects a CDMA mobile phone near an AMPS radio station.
A strong external interference signal overloads the low noise amplifier
of the CDMA phone so that the IMD component severely interferes
with the CDMA frequency band, causing it to be off-line. Following
is a specific description of the influence of such interference
signals.
The received interference signals pass through the low noise amplifier
to produce second and third order harmonics Eo, which may be expressed
by Eq. 1.
If there are generated dual tones with the same amplitude and different
frequencies, the dual tones are expressed by Eq. 2.
Substituting Ei of equation 2 in equation 1: ##EQU1##
As expressed by Eq. 3, two signals with different frequencies F1
and F2 are amplified to generate non-linear components in the form
of the products obtained by multiplying the mixed forms of the second
and third orders. The second order mixing is 2F1, 2F2, F1+F2 and
F1-F2. Such signals of the mixed component occur outside the narrow
band of most systems, and therefore are negligible. The third order
mixing is 2F1+F2, 2F1-F2, 2F2-F1 and 2F2+F1, whose signals are IMDs
occurring in the pass band of most systems.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an apparatus
for minimizing or eliminating external interference signals generated
from AMPS stations in a CDMA mobile phone to prevent communication
errors such as cutting of a call within the area affected by the
AMPS station, and method therefor.
According to the present invention, a device and a method are disclosed
for eliminating or minimizing external interference signals in a
CDMA mobile phone. The device includes a low noise amplifier connected
to damping device and a memory for storing information representing
a plurality of predetermined control voltage values, received signal
strength indicator (RSSI) data classified into various grades for
each of the control voltage values, reference value data classified
into various grades for each RSSI to meet a given signal receiving
condition and control voltage change data corresponding to the reference
value data. The method comprises the steps of setting an initial
control voltage to control the damping device, receiving a communication
signal, finding one of the RSSI data grades where the RSSI of the
received signal belongs, finding one of the reference value data
grades where the received signal belongs, and evaluating the difference
between the received signal and external interference signals based
on the control voltage, RSSI grade and reference value data grade.
The control voltage generator is controlled to adjust the control
voltage according to the difference.
In one aspect of the present invention, the reference value data
may be mean transmission energy rate per chip or frame error rate
(FER) data according to the second service option in the forward
communication channel.
The present invention will now be described more specifically with
reference to the drawings attached only by way of example.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram for illustrating a partial structure
of a CDMA mobile phone according to a first embodiment of the present
invention;
FIG. 2 is a graph for illustrating the RSSI of a received signal
versus decibel;
FIG. 3 is a graph for illustrating Ec/Io versus the received level
of a signal;
FIG. 4 is a graph for illustrating attenuation versus control voltage;
FIGS. 5A and 5B illustrate a flow chart for eliminating external
interference signals according to the first embodiment of the present
invention;
FIG. 6 is a block diagram for illustrating a partial structure
of a CDMA mobile phone according to a second embodiment of the present
invention;
FIG. 7 is a graph for illustrating FER versus the received level
of a signal; and
FIGS. 8A and 8B illustrate a flow chart for eliminating external
interference signals according to the second embodiment of the present
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
In the attached drawings, same reference numerals are used to represent
parts serving same functions and detailed descriptions for parts
not essential to describe the inventive concept are omitted.
In the first illustrative embodiment of the invention, two factors
are considered to detect IMD signals. The first is RSSI and the
second is the pilot channel, sink channel, paging channel and mean
transmission energy rate per PN chip (hereinafter referred to as
Ec/Io). The RSSI is to consider natural losses of the signal power
during transmission from the transmitter to the receiver. The natural
losses are path loss or free space attenuation, absorption, fading
free space attenuation, atmospheric absorption, etc.
In the second illustrative embodiment of the invention, the two
factors used to detect IMD signals are the RSSI and the FER. The
service option is the standard for the loop-back service option
of a terminal. FER is represented by percentage %, calculated in
"1-(properly received frames/all received frames)". The
following equations 4 to 9 are expressions for the signal power
transmitted from the transmitter to the receiver, and provide the
RSSI and Ec/Io or FER to eliminate the external interference signals
from an AMPS station. The power density of a receiving antenna may
be expressed by Eq. 4.
Wherein "Pt" represents the level of a signal generated
by the transmitter, and "d" the distance between the transmitter
and the receiver. The power PAr received by the receiving antenna
may be expressed by Eq. 5.
Wherein Aea represents effective area and varies in proportion
to the antenna gain and .lambda./4.pi.. The antenna gain G may be
expressed by Eq. 6.
Wherein .eta. represents efficiency, and the power PAr received
by the receiving antenna may be expressed by Eq. 7.
Wherein Aea/G is c.sup.2 /4.pi.f.sup.2, the unit of "d"
is kilometer, and the unit of "f" megahertz, and the gain
of a signal transmitted from the transmitter to the receiver may
be expressed by Eq. 8.
The free space loss may be expressed in decibels by Eq. 9.
Referring to FIG. 1, the CDMA phone comprises an antenna 11 for
receiving a CDMA signal, a damping device 12 for attenuating the
received signal to a given level, low noise amplifier 13 for amplifying
the received signal to a prescribed level with reducing noises,
control voltage generator 17 for generating a control voltage Vt
to control the damping device 12, RSSI detector 15 for detecting
the RSSI of the received signal, Ec/Io detector 16 for detecting
the Ec/Io from the RSSI detector 15, and controller 14 for controlling
the control voltage generator 17 to generate the control voltage
determined according to the RSSI and Ec/Io.
The RSSI is divided into weak, medium and strong level, as shown
in FIG. 2. The weak level is 82 to 86 with a received level of 0
to -100 dBm, which represents the total received signal to be weak.
The medium level is 87 to 96 with a received level of -100 dBm to
-90 dBm, which represents the total received signal to be medium.
The strong level is over 97 with a received level of over -90 d/dBm,
which represents the total received signal to be strong enough to
enable communication without error. Accordingly, the received level
is in proportion to the RSSI so that the RSSI increases with the
level of a CDMA signal received through the antenna 11.
As shown in FIG. 3, Ec/Io is divided into zero, remaining, first
change and second change modes. When Ec/Io is in the range of 0-1,
the mean transmission energy rate per PN chip is at a maximum. When
Ec/Io is in the range of 2-10, the mean transmission energy rate
per PN chip is at medium level, representing remaining mode without
any control. When Ec/Io is in the range of 11-12, the mean transmission
energy rate per PN chip has a low value, representing the first
change mode to need a controlled increase of the rate. Being essentially
the same with the first change mode, the second change mode represents
Ec/Io to exceed 13, which means an increase of the instantaneous
speed by doubling the control condition. Accordingly, the received
level is inversely proportional to Ec/Io.
Referring to FIG. 4, there is no attention when the control voltage
Vt is zero. The damping device control signal is divided in N equal
values according to the characteristics of the damping device 12
in order to effectively attenuate all the signals received by the
antenna 11. The external interference signals cause the RSSI to
increase and thus Ec/Io also. Hence, decreasing of the RSSI means
corresponding decrease of the external interference signals or the
original signal. Table 1 shows control voltages Vt.
TABLE 1 ______________________________________ Control Vt (V) Class
Code Value ______________________________________ 0 0 000 1.23 A
101 1.64 B 132 2.23 C 183 3.1 MAX 250 ______________________________________
In this case, the control voltage Vt represents average value.
According to Table 1, the relation between the RSSI and the Ec/Io
varies with Vt, which is illustrated in Table 2. The values of Table
2 may be stored into a memory associated with controller 14. The
memory may be externally or internally mounted in controller 14.
TABLE 2 ______________________________________ Vt RSSI Ec/Io Voltage
Set Mode ______________________________________ 0 Weak 0-2 Remaining
3-10 Remaining 11-12 Remaining 13- Remaining Medium 0-2 Remaining
3-10 Remaining 11-12 A 13- A Strong 0-2 Remaining 3-10 Remaining
11-12 A 13- B A Weak 0-2 0 3-10 Remaining 11-12 0 13- 0 Medium 0-2
0 3-10 Remaining 11-12 B 13- C Strong 0-2 0 3-10 Remaining 11-12
B 13- C B Weak 0-2 0 3-10 Remaining 11-12 A 13- 0 Medium 0-2 0 3-10
Remaining 11-12 C 13- C Strong 0-2 0 3-10 Remaining 11-12 C 13-
C C Weak 0-2 0 3-10 Remaining 11-12 B 13- 0 Medium 0-2 0 3-10 Remaining
11-12 MAX 13- MAX Strong 0-2 A 3-10 Remaining 11-12 MAX 13- MAX
MAX Weak 0-2 A 3-10 Remaining 11-12 C 13- B Medium 0-2 A 3-10 Remaining
11-12 C 13- B Strong 0-2 B 3-10 Remaining 11-12 Remaining 13- Remaining
______________________________________
Referring to FIG. 4 and Table 2, when the control voltage Vt is
changed from B state with strong RSSI and Ec/Io of 10-11 to C state,
the attenuation level should be raised. In this case, since the
level of the original signal is low and RSSI is high, it is interpreted
that external interferences exist and therefore, the control voltage
is changed to C state to increase the attenuation. The time and
level for such controlling may be suitably set through field test.
Preferably, when Ec/Io is in changing mode, the change is made only
after detecting three times and a RSSI bar reflects the differences
of the ideal and the voltage control to eliminate the external interference,
that is, the offset value is added to or subtracted from the RSSI
bar for each control voltage. The same offset value should be applied
to the transmission open loop power control.
FIGS. 5A and 5B describe a process for eliminating the external
interference signals according to the first illustrative embodiment
of the present invention. In step 5q, the controller 14 sets the
damping device control voltage through control voltage generator
17. Detecting a signal received by the antenna 11 in step 5a, it
is checked to which one of the RSSI grades-weak, medium and strong-the
received signal belongs in steps 5b-5d. If the RSSI grade is weak,
the steps of 5i-5l are carried out. If the RSSI grade is medium,
the steps of 5e-5h are carried out as shown in FIG. 5B. If the RSSI
is strong, the process is returned to step 5a for processing the
next received signal because it does not need the attenuation control.
The steps 5i-5l are to check to which one of the Ec/Io grades the
received signal belongs, e. g. zero, remaining, first change and
second change. In steps 6e-6h, the difference between the original
signal and the external interference signals is detected based on
the damping device control voltage, RSSI and Ec/Io. The damping
control voltage is set by performing the attenuation control according
to the difference. Thereafter, it is returned to step 5a for processing
the next received signal. The steps 5e-5h and 6a-6d as shown in
FIG. 5B are executed in the same way.
If the RSSI is not determined to belong to any one of the three
grades, it is checked through the steps of 5m-5p to which one of
the Ec/Io grades the signal received by the antenna 11 belongs as
previously described. The difference between the original signal
and the external interference signals is detected based on the damping
device control voltage and Ec/Io, so that the damping control voltage
is set by performing the attenuation control according to the difference.
Thereafter, it is returned to step 5a for processing the next received
signal.
Referring to FIG. 6, the illustrative second embodiment according
to the present invention, the CDMA phone includes an FER detector
18 instead of the Ec/Io detector as shown in FIG. 1. The FER detector
18 detects FER from the RSSI, and the controller 14 controls the
control voltage generator 17 to generate the control voltage determined
according to the RSSI and FER.
Referring to FIG. 7, the FER is divided into zero, remaining, first
change and second change modes. When the FER is 0%, the transmitted
frame is received with best quality. When the FER is 0-2%, the transmitted
frame is received with medium quality, representing remaining mode
without any control. When the FER is 2-10%, the transmitted frame
is received with low quality, representing the first change mode
to need a controlled increase of the rate. Being essentially the
same with the first change mode, the second change mode represents
the FER to exceed 10%, which means an increase of the instantaneous
speed by doubling the control condition. In conclusion, the received
level is inversely proportional to FER.
As shown in the previous embodiment employing Ec/Io, the RSSI and
FER increase with the external interference signals. According to
Table 1, the relation between the RSSI and the FER varies with Vt,
which is illustrated in Table 3.
TABLE 3 ______________________________________ FER Vt RSSI (%)
Voltage Set Mode ______________________________________ 0 Weak 0
Remaining 0-2 Remaining 2-10 Remaining 10- Remaining Medium 0 Remaining
0-2 Remaining 2-10 A 10- A Strong 0 Remaining 0-2 Remaining 2-10
A 10- B A Weak 0 0 0-2 Remaining 2-10 0 10- 0 Medium 0 0 0-2 Remaining
2-10 B 10- C Strong 0 0 0-2 Remaining 2-10 B 10- C B Weak 0 0 0-2
Remaining 2-10 A 10- 0 Medium 0 0 0-2 Remaining 2-10 C 10- C Strong
0 0 0-2 Remaining 2-10 C 10- C C Weak 0 0 0-2 Remaining 2-10 B 10-
0 Medium 0 0 0-2 Remaining 2-10 MAX 10- MAX Strong 0 A 0-2 Remaining
2-10 MAX 10- MAX MAX Weak 0 A 0-2 Remaining 2-10 C 10- B Medium
0 A 0-2 Remaining 2-10 C 10- B Strong 0 B 0-2 Remaining 2-10 Remaining
10- Remaining ______________________________________
Referring to FIG. 4 and Table 3, when the control voltage Vt is
changed from B state to C state with strong RSSI and FER of 2-10%,
the attenuation level should be raised. Namely, since the level
of the original signal is low with high RSSI, it is interpreted
that external interference signals exist and therefore, the control
voltage is changed to C state to increase the attenuation.
Describing the process for eliminating the external interference
signals according to the second embodiment in reference to FIGS.
8A and 8B, in step 8q, the controller 14 sets the damping device
control voltage. Detecting a signal received by the antenna 11 in
step 8a, it is checked to which one of the RSSI grades-weak, medium
and strong-the received signal belongs in steps 8b-8d. If the RSSI
grade is weak, the steps of 8i-8l are carried out. If the RSSI grade
is medium, the steps of 8e-8h are carried out as shown in FIG. 8B.
If the RSSI is strong, it is returned to step 8a for processing
the next received signal because it does not need the attenuation
control.
The steps 8i-8l are to check to which one of the FER grades the
received signal belongs, e. g. zero, remaining, FER first change
and second change. In steps 9e-9h, the difference between the original
signal and the external interference signals is detected based on
the damping device control voltage, RSSI and FER, and the damping
control voltage is set by performing the attenuation control according
to the difference. Thereafter, it is returned to step 8a for processing
the next received signal. The steps 8e-8h and 9a-9d as shown in
FIG. 8B are executed in the same way.
If the RSSI is not determined to belong to any one of the three
grades, it is checked through the steps of 8m-8p to which one of
the FER grades the signal received by the antenna 11 belongs as
previously described. The difference between the original signal
and the external interference signals is detected based on the damping
device control voltage and FER, that the damping control voltage
is set by performing the attenuation control according to the difference.
Thereafter, it is returned to step 8a for processing the next received
signal.
Although the present invention has been described with reference
to the specific embodiments together with accompanying drawings,
it will be readily appreciated by those skilled in this art that
various modifications may be made without departing from the gist
of the present invention.
Thus, the inventive CDMA phone eliminates the external interference
signals generated from an AMPS station to receive only CDMA signals,
so that communication errors are prevented even in the area of the
AMPS station. |