Multiplex communications – Communication over free space – Combining or distributing information via code word channels...
Reexamination Certificate
1998-03-02
2001-03-13
Olms, Douglas (Department: 2661)
Multiplex communications
Communication over free space
Combining or distributing information via code word channels...
C370S345000
Reexamination Certificate
active
06201801
ABSTRACT:
FIELD OF INVENTION
The present invention relates generally to communications systems and, more specifically, to a cellular radio communications system.
BACKGROUND OF THE INVENTION
Cellular communications systems are commonly employed to provide voice and data communications to a plurality of mobile units or subscribers. Analog cellular systems, such as designated AMPS, ETACS, NMT-450, and NMT-900, have been deployed successfully throughout the world. More recently, digital cellular systems such as designated IS-54B in North America and the pan-European GSM system have been introduced. These systems, and others, are described, for example, in the book titled
Cellular Radio Systems
by Balston, et al., published by Artech House, Norwood, Mass., 1993.
Frequency reuse is commonly employed in cellular technology wherein groups of frequencies are allocated for use in regions of limited geographic coverage known as cells. Cells containing equivalent groups of frequencies are geographically separated to allow mobile units in different cells to simultaneously use the same frequency without interfering with each other. By so doing many thousands of subscribers may be served by a system of only several hundred frequencies.
In the United States, for example, Federal authorities have allocated to cellular communications a block of the UHF frequency spectrum further subdivided into pairs of narrow frequency bands called channels. Channel pairing results from the frequency duplex arrangement wherein the transmit and receive frequencies in each pair are offset by 45 MHz. At present there are 832, 30-KHz wide, radio channels allocated to cellular mobile communications in the United States. To address the capacity limitations of this analog system a digital transmission standard has been provided, designated IS-54B, wherein these frequency channels are further subdivided into 3 time slots.
As illustrated in
FIG. 1
, a cellular communication system
20
as in the prior art includes one or more mobile stations or units
21
, one or more base stations
23
and a mobile telephone switching office (MTSO)
25
. Although only three cells
36
are shown in
FIG. 1
, a typical cellular network may comprise hundreds of base stations, thousands of mobile stations and more than one MTSO. Each cell will have allocated to it one or more dedicated control channels and one or more voice channels. A typical cell may have, for example, one control channel, and
21
voice/data, or traffic, channels. The control channel is a dedicated channel used for transmitting cell identification and paging information. The traffic channels carry the voice and data information.
The MTSO
25
is the central coordinating element of the overall cellular network
20
. It typically includes a cellular processor
28
, a cellular switch
29
and also provides the interface to the public switched telephone network (PSTN)
30
. Through the cellular network
20
, a duplex radio communication link
32
may be effected between two mobile stations
21
or, between a mobile station
21
and a landline telephone user
33
. The function of the base station
23
is commonly to handle the radio communication with the mobile station
21
. In this capacity, the base station
23
functions chiefly as a relay station for data and voice signals. The base station
23
also supervises the quality of the link
32
and monitors the received signal strength from the mobile station
21
.
A typical base station
23
as in the prior art is schematically illustrated in
FIG. 2
which shows, as an example, the functional components of model number RBS 882 manufactured by Ericsson Telecom AB, Stockholm, Sweden for the CMS 8800 cellular mobile telephone system. A full description of this analog cellular network is provided in publication number EN/LZT 101 908 R2B, published by Ericsson Telecom AB.
A now common sight along many highways, the base station
23
includes a control unit
34
and an antenna tower
35
. The control unit
34
comprises the base station electronics and is usually positioned within a ruggedized enclosure at, or near, the base of the tower. Within this enclosure are the radio control group
37
, or RCG, an exchange radio interface (ERI)
38
and a primary power supply
41
for converting electric power from the AC grid to power the individual components within the base station
23
, and a backup power supply
42
.
The ERI
38
provides signals between the MTSO
25
and the base station
23
. The ERI
38
receives data from the RCG
37
and transfers it to the MTSO
25
on a dedicated MTS0-BS link
45
. In the reverse direction, the ERI
38
receives data from the MTSO
25
and sends it the RCG
37
for subsequent transmission to a mobile station
21
.
The radio control group
37
includes the electronic equipment necessary to effect radio communications. A functional block diagram of an RCG
37
as in the prior art is shown in FIG.
3
. The configuration shown illustrates one control channel transmit/receive module (TRM)
51
, a number of voice channel TRMs
52
, and one signal strength receiver
53
, as is a typical configuration required to serve one cell or sector of a cell. Each TRM
51
,
52
includes a respective transmitter
54
, receiver
55
and control unit
57
. The TRMs
51
,
52
are not typically frequency agile and operate instead on only one predetermined channel. Control signals from the ERI
38
are received by the individual control units
57
. Voice and data traffic signals are routed over a separate interface to the ERI
38
.
Each individual transmitter
54
for control and voice is connected to a transmit combiner
58
. The transmit combiner combines all of the input signals onto a single output coupled through a coaxial cable
62
to the transmit antenna
63
. Through the use of the combiner
58
, up to 16 transmitters
54
can typically be connected to a common transmit antenna
63
. The combiner
58
is used because there is often a premium for space on the masts and towers used to support the antennas. In an extreme case, one mast may be required to support over 100 radio channels.
On the receive side, each of two receive antennas
65
is coupled to a respective receive combiner
66
A,
66
B where the signals received are separated according to frequency and passed on to the individual receivers
55
in each of the TRMs
51
,
52
. The two receive antennas
65
are typically spaced 3 to 5 meters apart on the tower so that they may receive signals with uncorrelated fading patterns to thereby provide space diversity reception. There are many conventional techniques for both pre-detection and post-detection diversity which are described, for example, in Chapter 10 of the book entitled “
Mobile Communications Engineering
”, by William C. Y. Lee, published by McGraw-Hill, 1992.
One visible feature of a typical base station
23
is the antenna tower
35
. In order to achieve a reasonable coverage area, the antennas
63
,
65
are desirably mounted at some distance above the ground. Referring now additionally to the prior art schematic plan view illustration of
FIG. 4A
, in rural areas the towers
35
are commonly located at the center of a cell
36
thereby providing omni-directional coverage. In an omni-directional cell, the control channel(s) and the active voice channel(s) are broadcast in all areas of the cell—usually from a single antenna. Where base stations
23
are more densely located, a sectorized antenna system may be employed as in the prior art, and shown by the schematic diagram of FIG.
4
B. Sectorization requires directional antennas
70
having, for example, a 120 degree radiation pattern as illustrated in FIG.
4
B. Each sector
71
is itself a cell having its own control channel(s) and traffic channel(s). Note that “channel” may refer to a specific carrier frequency in an analog system or to a specific carrier/slot combination in a hybrid TDMA/FDMA system, such as IS-54 and GSM.
FIG. 5A
illustrates a typical antenna system as in the prior art and as discussed above.
FIG. 5B
illustrates two typ
Ericsson Inc.
Myers Bigel & Sibley & Sajovec
Olms Douglas
Sam Phirin
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