Pulse or digital communications – Spread spectrum – Direct sequence
Reexamination Certificate
2000-11-20
2001-12-11
Ghebretinsae, Temesghen (Department: 2631)
Pulse or digital communications
Spread spectrum
Direct sequence
Reexamination Certificate
active
06330272
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to spread-spectrum communications, and more particularly to a multipath processor, variable bandwidth device, and power control system.
DESCRIPTION OF THE RELEVANT ART
Spread-spectrum modulation provides means for communicating in which a spread-spectrum signal occupies a bandwidth in excess of the minimum bandwidth necessary to send the same information. The band spread is accomplished by modulating an information-data signal with a chipping-sequence signal which is independent of an information-data signal. The information-data signal may come from a data device such as a computer, or an analog device which outputs an analog signal which has been digitized to an information-data signal, such as voice or video The chipping-sequence signal is generated by a chip-code where the time duration, T
c
, of each chip is substantially less than a data bit or data symbol. A synchronized reception of the information-data signal with the chipping-sequence signal at a receiver is used for despreading the spread-spectrum signal and subsequent recovery of data from the spread-spectrum signal.
Spread-spectrum modulation offers many advantages as a communications system for an office or urban environment. These advantages include reducing intentional and unintentional interference, combating multipath problems, and providing multiple access to a communications system shared by multiple users. Commercially, these applications include, but are not limited to, local area networks for computers and personal communications networks for telephone, as well as other data applications.
A cellular communications network, using spread-spectrum. modulation for communicating between a base station and a multiplicity of users, requires control of the power level of a particular mobile user station. Within a particular cell, a mobile station near the base station of the cell may be required to transmit with a power level less than that required when the mobile station is near an outer perimeter of the cell. This adjustment in power level is done to ensure a constant power level is received at the base station from each mobile station.
In a first geographical region, such as an urban environment, the cellular architecture may have small cells in which the respective base stations are close to each other, requiring a low power level from each mobile user. In a second geographical region, such as a rural environment, the cellular architecture may have large cells in which the respective bases stations are spread apart, requiring a relatively high power level from each mobile user. A mobile user who moves from the first geographical region to the second geographical region typically adjusts the power level of his transmitter in order to meet the requirements of a particular geographic region. If such adjustments were not made, a mobile user traveling from a sparsely populated region with larger cells, using the relatively higher power level with his spread-spectrum transmitter, to a densely populated region with many small cells may, without reducing the original power level of his spread-spectrum transmitter, cause undesirable interference within the smaller cell into which he has traveled and/or to adjacent cells. Also, if a mobile user moves behind a building and has his signal to the base station blocked by the building, then the mobile user's power level should be increased. These adjustments must be made quickly, with high dynamic range and in a manner to ensure an almost constant received power level with low root mean square error and peak deviations from the constant level.
Accordingly, there is a need to have a spread-spectrum system and method for automatically controlling a mobile user's spread-spectrum transmitter power level when operating in a cellular communications network.
SUMMARY OF THE INVENTION
A general object of the invention is high capacity communications, due to lower multipath fading and total equivalent bandwidth and data rate.
A second general object of the invention is a spread spectrum transmitter having variable and/or adjustable signal bandwidth capabilities.
Another general object of the invention is a system and method which results in maximization of user density within a cell domain while minimizing mobile user transmitted power.
A further object of the invention is to provide an apparatus and method which controls the power level of a mobile station so that the power level received at the base station of each cell is the same for each mobile station.
Another object of the invention is to provide a system and method for automatically and adaptively controlling the power level of a mobile user in a cellular communications network.
A further object of the invention is to provide a spread-spectrum system and method which allows operating a spread-spectrum transmitter in different geographic regions, wherein each geographic region has a multiplicity of cells, and wherein cells within a geographic region may have different size cells and transmitter power requirements.
In a multipath environment, a spread spectrum signal reflects from multiple surfaces, such as buildings, and is assumed to generate a multiplicity of spread-spectrum signals. The multiplicity of spread-spectrum signals typically appear in a plurality of groups of spread-spectrum signals, with each group of spread-spectrum signals having a plurality of spread-spectrum signals. The plurality of groups of spread-spectrum signals are a result of the spread-spectrum signal reflecting in a multipath environment.
A multipath processor for tracking a spread-spectrum signal arriving in a plurality of groups is provided. The multipath processor includes a first plurality of correlators, a second plurality of correlators, a first adder, a second adder, and a selector device or a combiner device. The first adder is coupled between the first plurality of correlators and the selector device or the combiner device. The second adder is coupled between the second plurality of correlators and the selector device or the combiner device.
The first plurality of correlators despreads a first plurality of spread-spectrum signals within a first group to generate a first plurality of despread signals. The first adder adds or combines the first plurality of despread signals to generate a first combined-despread signal.
The second plurality of correlators despreads a second plurality of spread-spectrum signals within a second group to generate a second plurality of despread signals. The second adder adds or combines the second plurality of despread signals to generate a second combined-despread signal.
The selector device selects either the first combined-despread signal or the second combined-despread signal. The selected combined-despread signal is outputted from the decision device as an output-despread signal. Alternatively, the combiner device may combine or add the first combined-despread signal with the second combined-despread signal to generate the output-despread signal.
The present invention also includes a variable-bandwidth spread-spectrum device for use with a spread-spectrum transmitter. The variable-bandwidth spread-spectrum device generates a spread-spectrum signal having a spread bandwidth. The variable-bandwidth spread-spectrum device uses a chipping-sequence signal having a chipping rate, with the chipping rate being less than the spread bandwidth.
The variable-bandwidth spread-spectrum device includes a chipping-sequence generator, spread-spectrum processing means, an impulse generator, and a filter. The spread-spectrum processing means is coupled to the chipping-sequence generator. The impulse generator is coupled to the spread-spectrum processing means. The filter is coupled to the impulse generator.
The chipping-sequence generator generates the chipping-sequence signal with the chipping rate. The spread-spectrum processing means processes a data signal with the chipping-sequence signal to generate a spread-data signal. The impulse generator, responsive to e
Ghebretinsae Temesghen
InterDigital Technology Corporation
Volpe and Koenig P.C.
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