Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1998-08-31
2003-03-18
Le, Thanh Cong (Department: 2684)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S067150, C455S561000
Reexamination Certificate
active
06535733
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of The Invention
This invention relates to wireless communications and, more particularly, to a measurement radio system in a wireless communications station for providing operating information to traffic radios.
2. Description of Related Art
FIG. 1
depicts a schematic diagram of a portion of a typical wireless telecommunications system, which provides wireless telecommunications service to a number of wireless terminals (e.g., wireless terminals
101
-
1
through
101
-
3
) that are situated within a geographic region. The heart of a typical wireless telecommunications system is a Mobile Switching Center (“MSC”)
120
, which might be known also as a Wireless Switching Center (“WSC”) or a Mobile Telephone Switching Office (“MTSO”). Typically, the Mobile Switching Center
120
is connected to a plurality of base stations (e.g., base stations
103
-
1
through
103
-
5
) that are dispersed throughout the geographic area serviced by the system and to the local and long-distance telephone offices (e.g., local-office
130
, local-office
138
and toll-office
140
). The Mobile Switching Center
120
is responsible for, among other things, establishing and maintaining calls between the wireless terminals and calls between a wireless terminal and a wireline terminal (e.g., wireline terminal
150
), which wireline terminal is connected to the Mobile Switching Center
120
via the local and/or long-distance networks.
The geographic area serviced by a wireless telecommunications system is divided into spatially distinct areas called “cells.” As depicted in
FIG. 1
, each cell is schematically represented by one hexagon in a honeycomb pattern; in practice, however, each cell has an irregular shape that depends on the topography of the terrain surrounding the cell. Typically, each cell contains a base station, which comprises the radios and antennas that the base station uses to communicate with the wireless terminals in that cell and also comprises the transmission equipment that the base station uses to communicate with Mobile Switching Center
120
. For example, when wireless terminal
101
-
1
desires to communicate with wireless terminal
101
-
2
, wireless terminal
101
-
1
transmits the desired information to base station
103
-
1
, which relays the information to Mobile Switching Center
120
. Upon receipt of the information, and with the knowledge that it is intended for wireless terminal
101
-
2
, Mobile Switching Center
120
then returns the information back to base station
103
-
1
, which relays the information, via radio, to wireless terminal
101
-
2
.
FIG. 2
depicts a block diagram of a first base station architecture in the prior art, which comprises one or more radios that are capable of transmitting outgoing signals via a transmit antenna (“TX”) and receiving incoming signals via a receive antenna (“Rx”). According to this architecture, there is only one transmit antenna per cell that transmits omni-directionally and only one receive antenna per cell that receives omni-directionally. Each radio in this architecture receives one incoming carrier signal via the receive antenna and demodulates that carrier signal into one or more baseband signals in accordance with the particular access scheme employed (e.g., frequency-division multiple access, time-division multiple access, code-division multiple-access, etc.). The incoming baseband signals are then transmitted to wireless switching center
120
. Analogously, outgoing baseband signals from wireless switching center
120
are modulated by the radio in accordance with the particular multiplexing scheme employed (e.g., frequency-division multiplexing, time-division multiplexing, code-division multiplexing, etc.) for transmission via the transmission antenna.
When wireless telecommunications system
100
is a terrestrial system, in contrast to a satellite-based system, the quality and availability of service is subject to the idiosyncrasies of the terrain surrounding the system. For example, when the topography of the terrain is hilly or mountainous, or when objects such as buildings or trees are present, a signal transmitted by a wireless terminal can be absorbed or reflected such that the signal quality is not uniform at the base station. As such, many independent paths result from the scattering and reflection of a signal between the many objects that lie between and around the mobile terminal and the base station. The scattering and reflection of the signal creates many different “copies” of the transmitted signal (“multipath signals”) arriving at the receive antenna of the base station with various amounts of delay, phase shift and attenuation. As a result, the signal received at the base station from the mobile unit is made up of the sum of many signals, each traveling over a separate path. Since these path lengths are not equal, the information carried over the radio link will experience a spread in delay as it travels between the base station and the mobile station. The amount of time dispersion between the earliest received copy of the transmitted signal and the latest arriving copy having a signal strength above a certain level is often referred to as delay spread. Delay spread can cause intersymbol interference (ISI). In addition to delay spread, the same multipath environment causes severe local variations in the received signal strength as the multipath signals are added constructively and destructively at the receive antenna of the base station. This phenomenon is widely known as multipath fading or fast fading or Rayleigh fading.
FIG. 3
depicts a block diagram of a second base station architecture in the prior art, which supports a technique known as N-way receive diversity to mitigate the effects of multipath fading. The base station architecture depicted in
FIG. 3
comprises one or more radios that are capable of transmitting outgoing signals via a single transmit antenna, as in the architecture of
FIG. 2
, but also comprises N spatially-separate receive antennas (“Rx
1
” through “RxN”). Because multipath fading is a localized phenomenon, it is highly unlikely that all of the spatially separated receive antennas will experience multipath fading at the same time. Therefore, if an incoming signal is weak at one receive antenna, it is likely to be satisfactory at one of the others. As is well-known in the prior art, a diversity combiner associated with the radios can combine N incoming signals, each from one of N receive antennas, using various techniques (e.g., selection diversity, equal gain combining diversity, maximum ratio combining diversity, etc.) to improve the reception of an incoming signal.
FIG. 4
depicts a block diagram of a third base station architecture in the prior art, which supports a technique for increasing the traffic capacity of the telecommunications system. This technique is known as “base station sectorization.” In accordance with base station sectorization, the cell serviced by a base station is subdivided into M tessellated pie-slices, each of which comprises a 360°/M sector whose focus is at the base station. The base station architecture in
FIG. 4
comprises M sets of radios and associated transmit and receive antennas, as shown, each of which operates independently of the others, except that the transmit and receive antennas associated with each sector are generally implemented so as to principally transmit into and receive from that sector.
The architecture in
FIG. 4
is, however, disadvantageous because it requires more radios than necessary to support a given traffic capacity, which unnecessarily increases the cost of the base station. The same average traffic capacity can be accommodated with fewer radios if they are pooled, as depicted in FIG.
5
.
FIG. 5
depicts a block diagram of a fourth base station architecture in the prior art, which supports receive diversity, sectorization, and radio pooling. The architecture comprises: a plurality of radios
501
-
1
through
501
-Z, sniffer radio
502
, switch matrix
503
, and M sets
Matusevich Alex
Murphy Myles Patrick
Seymour James Paul
Tsai Sheng-Jen
Tsamutalis Chris Constantine
Cong Le Thanh
Le Lana
Lucent Technologies - Inc.
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