Amplifiers – With semiconductor amplifying device – Including plural amplifier channels
Reexamination Certificate
2000-06-05
2002-07-16
Mottola, Steven J. (Department: 2817)
Amplifiers
With semiconductor amplifying device
Including plural amplifier channels
C330S298000
Reexamination Certificate
active
06420935
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present system and method pertains to communication systems and methods of the types used in communication networks and distribution services. More particularly the present invention relates to radio frequency (RF) transmission systems having modular architectures that accept an input signal(s), amplifies the signal(s) using modular components, and transmits the amplified signal(s) via radio waves to at least one receiver.
2. Discussion of the Background
By their very nature wireless technologies do not require the same investment in infrastructure that originally motivated the United States (U.S.) to permit local telephone companies and cable operators to create “wired” service monopolies. However, in order to compete with “wired” technologies, wireless technologies have a number of unique obstacles that must be overcome. These obstacles include distributing radio waves to areas located in valleys, blocked by mountains, buildings, etc. as well as maintaining a network of high powered transmitters used to reliably broadcast the radio waves to service areas.
Multi-channel multi-point distribution service (MMDS) is generally referred to as “wireless cable,” and is one of the wireless service industries that faces the inherent obstacles associated with wireless technologies. Although this document refers to MMDS and wireless cable synonymously, the following other channels of wireless cable when appropriate will be described individually: multi-point distribution service (MDS); Instructional Television Fixed Service (ITFS); and private operational fixed service (OFS).
One of the obstacles facing MMDS service providers is “blocking”. In order to further illustrate blocking,
FIG. 1
shows a conventional MMDS system where blocking is not a problem. A main transmitter
1
is capable of directly transmitting an analog signal to a receiver
2
without any intervening structures blocking the transmitted signal. When blocking does not occur, the receiver
2
couples the transmitted signal through an antenna
3
and to a home-unit
4
. Once in the home-unit, a receiver
5
receives the signal and passes it to a set top
6
which descrambles and tunes the signal. A television
7
then displays a video image that was carried by the signal.
FIG. 2
illustrates a scenario where blocking is a problem. A MMDS signal
8
is blocked by an obstruction (e.g., a hill)
9
so that the receiver
2
cannot receive the MMDS signal. It is estimated that blocking reduces a service area of an MMDS service provider from a theoretical value of 100% to 40%.
FIG. 3
illustrates a conventional approach developed by the MMDS industry to counter the effects of blocking and improve the service area. A booster
10
is strategically placed such that it can receive the MMDS signal from the main transmitter
1
and rebroadcast the MMDS signal to the receiver
2
. Thus, the booster
10
can improve service area coverage because the booster
10
can cover areas that are outside of a line-of-sight of the main transmitter
1
.
There are generally two types of MMDS boosters
10
used to improve service are coverage. A first type of MMDS booster is a single channel booster which receives 1 of 33 different MMDS channels (actually carriers which are capable of holding multiple audio/video programs) broadcast from the main transmitter
1
, and amplifies and transmits that selected single channel to a receiver
2
. Because the single channel boosters only process one channel, they do not provide service for the remaining 32 channels. A second type of MMDS booster is a broadband booster, which amplifies all of the channels (typically 33) transmitted from the main transmitter
1
and rebroadcasts the channels to the receiver
2
. The broadband boosters require power amplifiers having greater power than those of the single channel boosters because the broadband boosters must amplify up to 33 MMDS channels while single channel boosters amplify only one channel.
As a practical matter, boosters
10
(single channel and broadband boosters) are expensive because they contain a single-unit power amplifier as well as supporting electronics. The expense of the boosters
10
is further escalated by the operational need to have two power amplifiers, or more often, a back-up booster system
10
in order to improve booster reliability. When only redundant power amplifiers are used, one amplifier serves as the operational amplifier and the other is used as a spare. However, aside from the high expense, the use of two single-unit amplifiers is not optimum because if one of the amplifiers fails, service to the service area will cease until the back-up amplifier can be brought on-line. Similarly, when two booster systems
10
are used to improve reliability, the back-up booster system
10
will not begin to broadcast until the operational booster system
10
fails. A gap in service to the service area will exist during the period when the operational booster system
10
fails and the back-up booster system
10
is brought on-line.
Co-channel interference is a second obstacle facing the MMDS industry and limits the effectiveness of current MMDS boosters. Co-channel interference occurs when a stray signal (say from a neighboring one of the boosters
10
) interferes with an intended signal by acting as a coherent noise source. Co-channel interference has been particularly problematic with analog MMDS signals, preventing the boosters
10
from being placed close to one another for fear their respective signals would cause co-channel interference. However, with digital MMDS signals, digital signal processing techniques have been developed that effectively combat co-channel interference so more boosters
10
may be used to cover greater percentages of the MMDS service area.
Even though more of the MMDS boosters
10
may be used in a given service area, the single-unit amplifier architecture of the MMDS boosters
10
(single channel and broadband boosters) is problematic in that when the single unit amplifier fails, service from that MMDS booster
10
is interrupted until a spare amplifier can be brought on-line. Similarly, when a back-up booster
10
is used, service is interrupted until the back-up booster
10
is brought on line. Thus, the MMDS boosters
10
do not degrade gracefully, but rather, fail with little notice, making the MMDS boosters
10
difficult to maintain. When individual ones of the boosters
10
fail, other neighboring boosters are not equipped to increase their transmission powers in order to compensate for the failed booster
10
. While some MMDS boosters
10
are equipped to communicate with a network manager, the communication is generally “reactive”, in that the failed booster
10
reports its failure, but is incapable of reconfiguring itself in order to restore service.
FIG. 4
illustrates an exemplary conventional broadband MMDS booster
10
which may or may not be supported by a back-up booster
10
(not shown). MMDS signals received through a receive antenna
11
are passed through a low noise amplifier
12
, where they amplified. From the LNA
12
, the RF signals are passed through a power amplifier assembly
13
, which includes a single-unit amplifier, where the RF signals are amplified and passed to a conventional antenna coupler
17
. The antenna coupler
17
couples the output signal from the PA assembly
13
and passes the signal to the transmit antenna
18
. The amplifier unit
14
is typically powered by a system power supply
15
that distributes low voltage direct current (DC) voltage to all of the components of the booster
10
. A control head
16
, which is placed in a separate housing than either the power supply
15
, the PA assembly
13
, or a coupler
17
, provides system control functions such as turning on and off the PA assembly.
The amplifier unit
14
is a single-unit amplifier and is not simultaneously operated with one or more of the power-amplifiers for several reasons. First, conventional combining networks for combining output powers from
Correa Paulo
Harris Clifford
Ungvarsky Carl
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