Telecommunications – Transmitter and receiver at separate stations – Plural transmitters or receivers
Reexamination Certificate
2000-07-25
2002-05-14
Urban, Edward F. (Department: 2683)
Telecommunications
Transmitter and receiver at separate stations
Plural transmitters or receivers
C455S432300, C455S441000, C455S524000, C455S137000, C455S273000, C375S347000, C375S232000
Reexamination Certificate
active
06389295
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to communications systems and methods, in particular, to systems and methods for recovering information from signals generated in a communications medium.
BACKGROUND OF THE INVENTION
Radiotelephone systems are commonly employed to provide voice and data communications to a plurality of mobile units or subscribers. For example, analog cellular radiotelephone systems, such as designated AMPS, ETACS, NMT-450, and NMT-900, have been deployed successfully throughout the world. More recently, digital cellular radiotelephone 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.
As illustrated in
FIG. 1
, a conventional cellular communication system
20
includes one or more mobile terminals
10
which can communicate with one or more base stations
20
serving cells
30
. The base stations
20
are connected to a mobile telephone switching office (MTSO)
40
, which may in turn be connected to a public switched telephone network
50
. Although only two cells
20
are shown in
FIG. 1
, a typical cellular network may include hundreds of base stations, thousands of mobile terminals and more than one MTSO. Each cell will have allocated to it one or more dedicated control channels and one or more voice channels. Through this cellular infrastructure, a communication link may be effected between two mobile terminals
10
, or between a mobile terminal
10
and a landline telephone
60
, with a base station
20
typically functioning as a relay station for data and voice information.
Components of a radio communications channel connecting a mobile terminal
10
and abase station
20
which can affect communications between the terminal
10
and the base station
20
include the communications medium, i.e., the atmospheric signal path across which radio communications signals are transmitted, which may introduce fading and interference into the radio communications signals. The fading may include long-term fading due to variations in terrain along the signal propagation path, as well as short-term multipath fading due to reflections from features such as buildings which cause fluctuations in received signal strength and other distortions at a receiving station. Mobile terrestrial radiotelephone communications are particularly susceptible to short-term multipath fading because the signal pathways tend to be close to the ground. Other elements which may have an effect on communications include transmitting and receiving components commonly found in base stations and mobile terminals, such as transmitters, receivers and antennas.
Various signal estimation techniques are conventionally employed to deal with signal degradation on a channel, including diversity reception, signal coding, and specialized demodulation techniques which produce estimates of a channel transfer characteristic. Diversity reception techniques included spatial diversity reception using multiple spaced apart receiving antennas, and polarization diversity reception using multiple antennas designed to accept electromagnetic signals having particular polarizations. As signals from diverse paths typically exhibit uncorrelated fading, they may be combined in the receiver to provide a more accurate estimate of information from a received signal. Signal coding schemes typically employ redundancy to enhance the accuracy of an estimate produced from a received signal, while channel estimation techniques such as pilot tone or symbol assisted modulation and demodulation can provide improved knowledge of a transfer characteristic for the channel to aid in estimating information from a received signal.
Despite the theoretical advantages of these estimation techniques, they may provide less than optimal communication under various propagation conditions encountered in a typical cellular communications system. Diversity reception may not provide sufficient gain because of limitations on antenna size, orientation, and placement, and may be ineffective or unnecessary at particular speeds or other conditions. Coding schemes may entail an undesirable computational burden, while parameters used in estimating the channel may not be optimal for all mobile terminal speeds and under all delay spread conditions.
SUMMARY OF THE INVENTION
In light of the foregoing, it is an object of the present invention to provide communications apparatus and methods which can provide improved signal estimation.
It is another object of the present invention to provide cellular communications apparatus and methods which can provide more optimal signal estimation under differing conditions of delay spread and terminal speed.
These and other objects, features and advantages are provided according to the present invention by communications apparatus and methods in which information is recovered at one entity, e.g., a mobile terminal, from a signal generated in a communications medium by another entity, e.g., a cellular base station, by adaptively estimating the information from the signal based on a mobility characteristic which characterizes communications between the entities. The process can be bidirectional, i.e., adaptive estimation of received signal may be performed at either end of a communications channel. The mobility characteristic may characterize mobility properties of the entities which affect signal propagation between the entities, such as relative speeds of the entities with respect to one another, range between the entities, and the like. According to one embodiment, the mobility characteristic includes a cell type identifier which characterizes mobility of mobile terminals with respect to a base station, e.g., an identifier which identifies a cell served by the base station as a highway macrocell, an urban macrocell, a microcell or the like, and which bears a correlation to aggregate speed and range properties for terminals typically found within the cell. The cell type identifier may be broadcast to mobile terminals from the base station over, for example, a broadcast control channel, and the mobile terminals can adaptively estimate information from signals received from the base station based on the broadcast cell type identifier. For example, the mobile terminal may store various signal processing elements such as channel estimators, channel interpolation filters, channel trackers, and the like, as well as various parameters for such elements, and may apply these selected elements and parameters to a signal received from a base station based on a cell type identifier received from the station. Accordingly, more optimal signal estimation can be achieved by tailoring signal processing to the mobility characteristic.
In particular, according to the present invention, a communications system for communicating across a communications medium includes a first entity including means for generating a signal in the communications medium, the signal representing information, and a second entity including signal receiving means, responsive to the communications medium, for receiving a signal from the communications medium. The second also includes means for determining a mobility characteristic for communications between the first entity and the second entity, as well as adaptive estimating means, responsive to the signal receiving means, for adaptively estimating the information from the received signal based on the determined mobility characteristic.
According to one aspect of the present invention, the first entity further includes means for transmitting a mobility characteristic, and the means for determining a mobility characteristic includes means for receiving the transmitted mobility characteristic. The adaptive estimating means may include means for adaptively estimating the information based on the received mobility characteristic. The adaptive estimating means may include a number of
Ericsson Inc.
Myers Bigel & Sibley & Sajovec
Sobutka Philip J.
Urban Edward F.
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