Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1996-07-02
2003-06-17
Le, Thanh Cong (Department: 2684)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S234100, C455S235100
Reexamination Certificate
active
06580905
ABSTRACT:
BACKGROUND
The present invention is directed to a system and method for controlling the level of signals output from remote antenna units to transmission media in a distributed antenna network. More particularly, the present invention reduces the gain of a remote antenna unit when its output signal level is determined to be greater than the maximum output level which may be received by the transmission media. Accordingly, received signals that are stronger than the maximum output level may be transmitted across the transmission media without saturating the system.
As personal communication services (PCS) evolve as the next generation of cellular telephone technology, systems and techniques for simply and efficiently transmitting and receiving communication signals are being investigated. One known system is a distributed antenna network (which is also referred to as a multicast network) which provides coverage over substantial areas by a plurality of remote antenna units. An example of a distributed antenna network is illustrated in
FIG. 1
where an individual transceiver
10
is connected to a plurality of cells
20
1
, . . .
20
n
by transmission media
30
which transports radio signals between the transceiver unit
10
and the cells
20
1
. . .
20
n
. Each of the cells
20
1
, . . .
20
n
include remote antenna units
21
1
, . . .
21
n
. The remote antenna units
21
1
, . . .
21
n
may be connected to the transmission media
30
by frequency converting circuitry
22
1
, . . .
22
n
for certain applications.
Various infrastructures are being developed and modifications of existing infrastructures are of great interest as alternatives for PCS because they are fully capable of providing high quality signals at lower costs than traditional cellular infrastructures. For example, CATV infrastructures have been modified for use in PCS. Such modifications include the CATV infrastructures using a hybrid fiber/coax (HFC) cable infrastructure to increase capacity and improve service quality. Although it is theoretically possible for any CATV infrastructure to support PCS with the proper modifications, the HFC cable infrastructure offers an attractive option as an economical alternative to wireless providers seeking to avoid the high cost of network construction.
FIG. 2
illustrates the basic components of a CATV infrastructure used to support PCS. In
FIG. 2
, base station equipments
50
1
and
50
2
are connected to a public network such as a public switched telephone network. Remote antenna signal processors (RASPs)
52
1
and
52
2
connect the base station equipments
50
1
and
50
2
to a fiber equipment
54
. The fiber equipment
54
is connected to a fiber node
58
by fiber optic cable
56
and the fiber node
58
is connected to remote antenna driver (RAD) nodes
62
1
and
62
2
by two-way coaxial cable
60
. The RAD nodes
62
1
and
62
2
each include a group of RADs
64
1
and
64
2
and
66
1
and
66
2
respectively connected to antennas
68
1
,
68
2
,
70
1
, and
70
2
. This CATV infrastructure converts radio frequency signals into CATV frequency signals usable in the existing CATV infrastructure and converts CATV frequency signals back into radio frequency signals for broadcast. More specifically, the RASPs
52
1
and
52
2
convert the radio frequency signals from the base station equipments
50
1
and
50
2
and then send the converted signals in the downlink path toward the appropriate fiber node
58
and onto the coaxial cable
60
.
The RADs
64
1
,
64
2
,
66
1
and
66
2
are connected to the coaxial cable
60
for converting CATV frequency signals into assigned radio frequency signals. Radio frequency signals may be received by the RADs
64
1
,
64
2
,
66
1
and
66
2
which convert these signals into signals of frequencies suitable for transmission in the uplink path of the CATV infrastructure. Thereafter, the RASPs
52
1
and
52
2
convert the upstream CATV frequency signals back into radio frequency signals for processing by the base station equipments
50
1
and
50
2
. This CATV infrastructure also may accommodate equipment for multiple modulation schemes, such as time division multiple access (TDMA), code division multiple access (CDMA) and frequency division multiple access (FDMA).
Radio telephony systems may utilize this CATV infrastructure by operating on available portions of the radio frequency spectrum over fiber optic and coaxial cables which are widely available in urban areas so that such systems may be installed to take advantage of this existing infrastructure. The large installed base of fiber optic and coaxial cables used by CATV operators may thereby be effectively exploited at a minimal cost by this infrastructure which distributes the signals to the appropriate antenna locations. To efficiently provide RF coverage in new cellular and PCS communication systems, it is becoming increasingly common to use distributed antenna systems. In distributed antenna systems, it is often necessary to transmit RF signals covering a wide range of amplitudes across transmission media with a limited and more narrow range of amplitudes for the signals. Conventional automatic gain control (AGC) techniques for controlling the gain are insufficient in allowing the wide range of signals to be fully transmitted over the transmission media of a limited dynamic range. In conventional AGC techniques, even though stronger signals, which exceed the maximum signal level for the transmission media, from sources relatively near the remote antenna units are limited to be below the maximum signal level for transmission across the transmission media, weak signals from sources relatively far away from the remote antenna units are undesirably reduced below the noise floor and effectively cut off. The conventional techniques do not adequately control gain so that strong signals do not saturate the system and weak signals are not unnecessarily reduced below the noise floor.
SUMMARY
One object of the present invention therefore is to provide a system and method for controlling the level of signals transmitted from remote antenna units over transmission media in a distributed antenna network so that signals covering a wide range of amplitudes may be transmitted over transmission media having a more narrow range of amplitudes for transmitting signals.
Another object of the present invention is to provide a system and method for comparing a predetermined reference level with the level of signals received by each remote antenna unit in a distributed antenna network, and controlling the gain of the respective remote antenna units based upon this comparison to prevent strong signals from saturating the system.
According to one embodiment of the present invention, the foregoing and other objects are attained in a system and method for controlling the gain of signals transported over transmission media in a distributed antenna network. The system comprises a plurality of remote antenna units where each remote antenna unit includes a signal level comparator for comparing the level of the signals received by the respective antenna unit with a predetermined reference level, and a gain controller for reducing the gain of the remote antenna unit when the signal level comparator determines that the level of the received signal exceeds said predetermined reference level. As a result, the signal levels output from the remote antenna units are prevented from exceeding a maximum signal level so that strong signals do not saturate the system.
In a further embodiment of the present invention, the predetermined reference level is set to correspond with the maximum level for transmitting signals over the transmission media. Thereby, the level of the signals output over the transmission media are prevented from saturating the system without being unduly restricted.
In a still further embodiment of the present invention, the signal level comparator generates an error signal when the received signal exceeds the predetermined reference level which is used for reducing the gain in proportio
Morelen Steven
Naidu Arun
Cong Le Thanh
Ericsson Inc.
Myers Bigel & Sibley & Sajovec
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