Telecommunications – Carrier wave repeater or relay system – Portable or mobile repeater
Reexamination Certificate
2001-05-29
2004-08-03
Trost, William (Department: 2683)
Telecommunications
Carrier wave repeater or relay system
Portable or mobile repeater
C455S003020, C455S003050, C455S127100, C455S129000, C455S522000
Reexamination Certificate
active
06771930
ABSTRACT:
FIELD OF INVENTION
The present invention relates generally to a system and method for uplink power control and detection in a communication system.
BACKGROUND OF THE INVENTION
Communication systems, such as satellite communication systems, typically include one or more control loops for power transmission.
FIG. 1
illustrates, in block format, a typical power detect and control scheme for a satellite communication system. System
100
includes an indoor unit (IDU)
102
which provides signals to an outdoor unit (ODU)
104
over a cable
103
. Generally, IDU
102
is configured to control the level of the RF (radio frequency) signal to be transmitted to a satellite. For example, by increasing or decreasing the signals provided to ODU
104
, IDU
102
can vary the output power of the RF signal transmitted to the satellite.
Collectively, IDU
102
, ODU
104
, and cable
103
are generally termed “ground station”. The ground station may be located on, for example, a stationary structure (e.g., building) or a moving structure (e.g., vehicle) such that communication with the satellite is permissible. In many applications, the IDU is located near or within a computer, e.g., a card that fits inside the computer processor or a box in proximity to the computer. The cable or multiple cables interconnect the IDU with the ODU, which may be located outside, e.g., on the roof of a building or a vehicle. Another ground station, generally illustrated in
FIG. 1
as a dish antenna, provides similar functionality for the opposite end of the communication link in order to connect the user of ground station
100
to a telecommunications or computer network.
As is often the case in wireless transmission, obstructions, e.g., clouds, rain, structures, and the like, can decrease the transmission reception of the RF signal received at the satellite, i.e., the signal-to-noise (SNR) of the RF signal decreases. The satellite may transmit a signal back to the ground station indicating that the RF signal received at the satellite is too weak, for example, the strength (i.e., power level) of the received signal is too low for optimum detection. In response, the ground station typically has two options; reduce the data bit rate (which is generally undesirable) by either a method of bandwidth reduction or increased error correction coding, or increase the RF signal strength. To increase the RF signal strength, the IDU increases the signal power to the ODU, thereby increasing the RF signal strength transmitted to the satellite.
ODU
104
includes a power amplifier (not shown) to increase or boost the RF signal in preparation for transmission to the satellite. Power amplifiers are often characterized by the maximum power capability of the device. For instance, as increasing RF power is supplied to an amplification device, the output power of the device increases accordingly, until a “saturation level” of the device is reached. At saturation, or the maximum RF power capability, the amplifier output no longer behaves linearly to an increase in power, regardless of the amount of input power. When in saturation the RF waveform is “clipped” and the maximum amount of energy is contained in the primary signal. As the input power is further increased, the excess signal energy creates additional signal distortion and signal harmonics.
Signal harmonics can mix together to form a spectrum image of the primary signal in an adjacent communication channel. The adjacent channel interference caused by the power amplifier distortion begins to decrease the SNR of the signals from other users in adjacent transmission channels. To compensate for the lower SNR, the IDU of those users, operating in adjacent channels, typically increase the power to the ODU. Increasing the power continues to increase the harmonics and in turn decrease the SNR; thus the cycle continues. In addition to causing disruptive interference, governing regulatory bodies such as the FCC generally place limits on the acceptable levels of adjacent channel interference.
To reduce the interference caused by harmonics, it is desirable to control the level of power supplied to the ODU. When the input signal is amplified by about 1 dB (decibel) less than the small signal gain, it is commonly called the 1 dB compression point (P1 dB). As the input signal to the amplifier is increased past P1 dB, the output signal is no longer in a linear relationship with the input signal and a rapid decrease in gain is experienced; thereby causing signal harmonics. It is desirable to detect and limit the amount of power to a component, such as a power amplifier, to approximately P1 dB of the component to avoid creating signal harmonics which can adversely affect signal transmission.
Referring to
FIG. 2
, a ground station
200
of a prior art uplink power detect and control system is illustrated. Ground station
200
includes an IDU
202
, an ODU
204
, and signal transfer means
203
. Signal transfer means
203
includes, for example, one or more cables suitable for signal transmission between IDU
202
and ODU
204
, e.g., industry standard RG-6 type cable (coax) such as Belden 9114.
Generally, IDU
202
includes a modem
210
to receive and transmit IF (intermediate frequency) signals to ODU
204
and a DC (direct current) power supply
212
to transmit DC power to ODU
204
. A typical modem
210
has a demodulator
214
, a modulator
216
, an automatic gain control
218
, and an automatic level control
220
. Demodulator
214
converts the received IF signals into digital data which can be coupled to a computer or other digital appliance via a serial or parallel digital interface. Automatic gain control
218
is used to adjust the input IF signal level up or down to provide an approximately constant signal level to demodulator
214
. Modulator
216
converts digital data from the serial or parallel digital interface to an IF signal. Automatic level control
220
is used to increase or decrease the output signal level provided to the ODU based on link conditions (e.g., weather, temperature, interference, etc.).
Generally, ODU
204
includes a receiver
222
, an antenna
224
, a transmitter and power amplifier
226
, an RF power detector
228
, and interface circuitry
230
. The receiver
222
comprises a low noise amplifier to amplify the input RF signal from the antenna and a down conversion mixer to convert the RF signal to an IF signal. Additionally, receiver
222
may contain one or more RF, IF or local oscillator (LO) amplifiers as well. Antenna
224
may be any antenna suitable for receiving and transmitting the proper frequencies; such as a dish, dipole, phased array, or any other suitable antenna. Transmitter
226
receives the IF signal from IDU
202
. A signal mixer (not shown) within transmitter
226
generates an RF signal from the received IF and DC signals. Transmitter
226
also comprises a power amplifier, e.g., a high power amplifier (HPA), which boosts the RF signal in preparation for transmission to the satellite.
Inclusion of RF power detector
228
is one prior art technique for detecting and limiting the power to transmitter
226
by means of the automatic level control
220
for reducing the effects of signal interference. RF power detector
228
(also called a “forward power detector”) generally includes a coupler, detector diode, comparator, and signal transmission means (e.g., interface circuitry
230
) for transmitting signals back to IDU
202
.
In operation, RF power detector
228
samples the output signal from the power amplifier (prior to antenna transmission) and sends the signal back to the IDU. Interface circuitry
230
is required in order to use automatic level control
220
. An additional signal transfer means
203
, e.g., an additional cable or multiplexing circuitry, is required to transmit the output RF signal from ODU
204
to IDU
202
(generally illustrated in
FIG. 2
as “Forward Power Telemetry”). Using the sampled power output at the ODU, the IDU can gauge how much more power station
200
can transmit without causing the amplifier to
Snell & Wilmer L.L.P.
Trost William
U.S. Monolithics, L.L.C.
Zewdu Meless
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