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US 6,275,483 B1Granted
Fast and accurate identification of spread spectrum signals
AssigneeTexas Instruments Incorporated
InventorsAristides Papasakellariou, Yuan Kang Lee
Life of this patent
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AssigneeTexas Instruments Incorporated
InventorsAristides Papasakellariou, Yuan Kang Lee
Estimating the term…
In code division multiple access (CDMA) cellular-based communication systems in which a user station can demodulate multiple signals, not necessarily coming from the same base station, a method to rapidly identify at the user station spread spectrum code offsets at which actual signal paths exist. In such a system a plurality of base stations transmit data unmodulated pilot signals, wherein each of the pilot signals comprises a radio frequency signal modulated by a predetermined spread spectrum code at a predetermined rate. The base stations modulate their respective radio frequency signals with the same spread spectrum code but each of the base stations have a different, predetermined offset of the spread spectrum code from other of the base stations in a given vicinity, or, alternatively, the base stations modulate their respective radio frequency signals with different spread spectrum codes that are known by the user station. The method for the communications unit to identify the arrival time of each path from a specific base station by selecting specific code offsets with which to demodulate the signals of different paths originating from the specific base station, comprises the following steps. First, a radio frequency signal modulated by a predetermined spread spectrum code is received. The radio frequency signal is demodulated to produce a demodulated signal. A generated signal encoded with the spread spectrum code at a rate substantially the same as the predetermined rate is provided. A predetermined set of code offsets within which to search for the signals of different paths of the base stations is also provided. A new subset of code offsets is selected by a. processing the demodulated signal with the generated signal at a first predetermined offset of the set of code offsets to produce a decision value related to a degree of correlation between the demodulated signal and the generated signal, b. determining an SNR measurement at the predetermined offset using the decision value, c. repeating the steps of processing, and determining for the remaining the offsets in the set of code offsets for a predetermined number of iterations, and d. continuing further processing for a subset of code offsets which belong to the set of code offsets and which are of a predetermined number and have the largest SNR values. The step of selecting a new subset of code offsets is repeated for a predetermined number of iterations.
In a code division multiple access communications system in which a plurality of base stations transmit data unmodulated pilot signals, each of said pilot signals comprising a radio frequency signal modulated by a predetermined spread spectrum code at a predetermined rate, said base stations modulating their respective radio frequency signals with the same spread spectrum code but with each of said base stations having a different, predetermined or random offset of said spread spectrum code from other of said base stations in a given vicinity, or, alternatively, said base stations modulating their respective radio frequency signals with different spread spectrum codes that are known by a communications unit, and wherein a pilot signal from a base station may traverse multiple paths to said communications unit, a method for said communications unit to identify one of said pilot signals, comprising the steps of:
In a code division multiple access communications system in which base stations transmit pilot signals, said pilot signals comprising a radio frequency signal modulated by predetermined spread spectrum code(s) at a predetermined rate, said base stations modulating their respective radio frequency signals with the same spread spectrum code(s) but with each of said base stations having a different, predetermined offset of said spread spectrum code(s) from other of said base stations in a given vicinity, and a predetermined set of code offsets within which to search for said base stations, a method for a communications unit to identify base stations, comprising the steps of:
In a code division multiple access communications system in which base stations transmit pilot signals, said pilot signals comprising a radio frequency signal modulated by predetermined spread spectrum code(s) at a predetermined rate, said base stations modulating their respective radio frequency signals with the same spread spectrum code(s) but with each of said base stations having a different, predetermined offset of said spread spectrum code(s) from other of said base stations in a given vicinity, and a predetermined set of code offsets within which to search for said base stations, a method for a communications unit to identify base stations, comprising the steps of:
In a code division multiple access communications system in which base stations transmit pilot signals, said pilot signals comprising a radio frequency signal modulated by predetermined spread spectrum code(s) at a predetermined rate, said base stations modulating their respective radio frequency signals with the same spread spectrum code(s) but with each of said base stations having a different, predetermined offset of said spread spectrum code(s) from other of said base stations in a given vicinity, and within a predetermined set of code offsets within which to search for said base stations, a method for a communications unit to identify base stations, comprising the steps of:
In a code division multiple access communications system in which a plurality of base stations transmit data unmodulated pilot signals, each of said pilot signals comprising a radio frequency signal modulated by a predetermined spread spectrum code at a predetermined rate, said base stations modulating their respective radio frequency signals with the same spread spectrum code but with each of said base stations having a different, predetermined offset of said spread spectrum code from other of said base stations in a given vicinity, or, alternatively, said base stations modulating their respective radio frequency signals with different spread spectrum codes that are known by a communications unit, and wherein a pilot signal from a base station may traverse multiple paths to said communications unit, a method for said communications unit to identify one of said pilot signals, comprising the steps of:
In a code division multiple access communications system in which base stations transmit pilot signals, said pilot signals comprising a radio frequency signal modulated by predetermined spread spectrum code(s) at a predetermined rate, said base stations modulating their respective radio frequency signals with the same spread spectrum code(s) but with each of said base stations having a different, predetermined offset of said spread spectrum code(s) from other of said base stations in a given vicinity, and a predetermined set of code offsets within which to search for said base stations, a method for a communications unit to identify base stations, comprising the steps of:
In a code division multiple access communications system in which base stations transmit pilot signals, said pilot signals comprising a radio frequency signal modulated by predetermined spread spectrum code(s) at a predetermined rate, said base stations modulating their respective radio frequency signals with the same spread spectrum code(s) but with each of said base stations having a different, predetermined offset of said spread spectrum code(s) from other of said base stations in a given vicinity, and a predetermined set of code offsets within which to search for said base stations, a method for a communications unit to identify base stations, comprising the steps of:
In a code division multiple access communications system in which base stations transmit pilot signals, said pilot signals comprising a radio frequency signal modulated by predetermined spread spectrum code(s) at a predetermined rate, said base stations modulating their respective radio frequency signals with the same spread spectrum code(s) but with each of said base stations having a different, predetermined offset of said spread spectrum code(s) from other of said base stations in a given vicinity, and within a predetermined set of code offsets within which to search for said base stations, a method for a communications unit to identify base stations, comprising the steps of:
Dependencies are inferred from the claim text.