Telecommunications – Transmitter and receiver at same station – Radiotelephone equipment detail
Reexamination Certificate
1999-08-23
2004-10-05
Gesesse, Tilahun (Department: 2684)
Telecommunications
Transmitter and receiver at same station
Radiotelephone equipment detail
C455S550100, C455S500000
Reexamination Certificate
active
06801788
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to wireless communication systems and, more particularly, to base station transceiver subsystems used in a Code Division Multiple Access (CDMA) network or other digital and analog telecommunication systems.
2. Description of Related Art
FIG. 1
(prior art) is a block-flow diagram which graphically represents a wireless communication system. From
FIG. 1
it is seen that a basic wireless communication system comprises a mobile station
10
, a base station
20
, a reverse link
30
, which represents the electromagnetic wave communication link transmitted from mobile station
10
to base station
20
, and a forward link
40
which represents the electromagnetic wave communication link transmitted from base station
20
to mobile station
10
.
FIG. 2
(prior art) shows a cell grid and cell sites. In a wireless communication system based on the general cellular principle, a service area
49
is divided geographically, into a number of small areas
50
,
52
,
54
,
56
called “cells.” In each cell there is a cell site
58
,
60
,
62
,
64
where radio equipment known as a Base Station Transceiver Subsystem (BTS) is installed. Multiple cell layouts such as macro cells, micro cells, and Pico cells can be provided within a particular geographical area to effect hierarchical coverage (where macro cells provide the largest coverage and Pico cells the smallest). Pico cells may be used to provide coverage,inside buildings, to cover a special area (campus, stadium, airport and shopping mall), to temporarily cover for special events or areas hit by natural disasters, to cover outlying remote locations, to supplement macro or mini cells with hole-filling, or to enhance the capacity of hot spots.
FIG. 3
(prior art) is a block diagram of a wireless system network connected to a land line Public Switched Telephone Network (PSTN)
68
. As shown in
FIG. 3
, a BTS
66
provides a link to mobile subscribers or (mobile stations)
10
. Each BTS
66
typically may include two or more antennas
67
, which may be omni antennas or directional antennas. Omni antenna configurations provide 360° of coverage, whereas directional antennas provide less than 360° of coverage across an area known as a sector. For example, there may be two, three or more sectors in a typical directional configuration such that each sector of a two sector configuration generally provides 180° of coverage and each sector of a three sector configuration generally provides 120° of coverage, etc. For satisfactory reception and transmission, each sector typically requires at least two antennas for diversity reception.
Continuing with the description of
FIG. 3
, each BTS
66
is coupled to a Base Station Controller (BSC)
70
(multiple BTSs
66
may be coupled to a single BSC
70
). Likewise, each BSC
70
is coupled to a Mobile Switching Center (MSC)
72
and the MSC
72
is in turn coupled to a PSTN
68
.
FIG. 4
(prior art) is a functional block diagram of a BTS. As shown in
FIG. 4
, a conventional BTS
66
typically comprises four major functional blocks for each sector of coverage: an RF front-end
74
, a plurality of transceivers
76
, a plurality of modem processors
78
, and a controller
80
. Controller
80
interfaces with a BSC
70
over a T1 or E1 line
81
, and the RF front-end
74
is connected to the antennas
67
which are typically mounted at the top of a tower or pole
82
as represented in
FIG. 5
(prior art), where
FIG. 5
illustrates an outdoor and ground based BTS coupled to a tower topped mounted antenna.
In a typical system, the four major functional blocks of the BTS
66
, shown in
FIG. 4
, are contained in one physical cabinet or housing which is in close proximity to a pole (or tower)
82
at ground level. Long coaxial cables
84
are then run to the top of the pole
82
where the antennas
67
are mounted. The cable length typically varies from 50 to 200 feet, depending on various installation scenarios. Cables of these lengths suffer from undesirable power losses. Accordingly, thick coaxial cable diameters of approximately ¾ to 1½ inches are used to minimize the cable power loss, which is typically about 2 to 4 dB. Minimizing these power losses is important because such losses in the cables degrade the receiver sensitivity and reduce transmission power.
FIG. 5
depicts a prior art BTS unit
66
connected via a long length of cable
84
to an antenna
67
at the top of a supporting structure
82
.
FIG. 6
(prior art) is a block diagram of yet another known BTS architecture where a tower top mounted RF front-end module consists of a Low Noise Amp (LNA) and a Power Amp (PA)
74
(hereinafter LNA/PA unit
74
). The cable power loss in this architecture is not as critical as in the previous mentioned architecture because the power loss can be made up with additional amplification. However, there is still a need to use rather thick cables due to the signals between the LNA/PA unit
74
and the transceiver
76
in the BTS
66
are high frequency/radio-frequency (RF) signals. Other problems are associated with transmitted RF signals between the LNA/PA unit
74
and the BTS
66
, such as power losses, system noise, and mechanical clutter. Furthermore additional complex circuitry either or both in the RF front-end module and the transceiver may be required to automatically compensate for the wide range of cable losses that arise in different installation scenarios due to varying cable lengths. Such problems get more severe as the operating RF Frequencies are allocated in the increasingly higher frequency bands. This is the case for personal communications systems.
In other words, as the length of a cable
84
increases, or as the frequency transmitted through a cable
84
increases, power losses between the LNA/PA unit
74
and the BTS
66
increase. Thus, the long cables
84
used to connect the LNA/PA unit
74
to the BTSs
66
(often in excess of 150 feet, sometimes even exceeding 300 feet) introduce large power losses. For example, a 100 W power amplifier in a base station transceiver unit transmits only 50 W of power at the antenna when there is a 3 dB loss in the cable. Power losses in the cable work against reception as well, reducing the ability of the receiver to detect received signals. Also, with Personal Communication Systems (PCS) operating at high frequencies, the power loss in the cable
84
running between the LNA/PA unit
74
and the transceiver
76
in the BTS
66
increases. Thus, RF cable losses incurred on both the transmit and receive paths result in poorer than desired transmission efficiency and lower than desired receiver sensitivity, making the use of relatively thick (high conductance) coaxial cables necessary to minimize loss.
Generally, in a wireless environment, wherein radio frequencies are transmitted through air, interferences are inevitable. That is, unless a transmitting antenna is directly in the line-of-site of the receiving antenna and no obstacles, such as trees, buildings, rock formations, water towers, etc., are in the way, then reflections will cause fading and multipath signals. In order to minimize the effects of fading and multipath, diversity receivers can be used increase the carrier-to-noise ratio (and/or Eb/No. A diversity receiver requires its own antenna. Thus, for each transmission frequency two antennas are used on the receiving side. One antenna is a transmit/receive antenna and the second antenna is used for a diversity receiver which is utilized to overcome some of the fading and multi-path problems.
In some cell sites, where the communication capacity is high, there is a need to transmit more than one RF carrier signal. The transmission of multiple RF carriers per sector requires a corresponding number of transmit antennas per sector. Additional receiving antennas are also required especially if diversity receivers are utilized in the system. Increasing the number of antennas creates an “eye-sore” for the public and is not desirable.
A conventio
Brady Bruce F.
Chien Mark C.
Csapo John S.
Johnson Mitchell
Rapp Robert A.
Gesesse Tilahun
Samsung Electronics Co,. Ltd.
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