Methods and apparatus for random access in multi-carrier communication systems
First Claim
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1. In a wireless communication system, a method of establishing communication between a mobile and a base station using a ranging signal, the method comprising:
- modulating, in the mobile station, ranging signals on at least one ranging subchannel;
wherein the ranging subchannel includes multiple subcarrier blocks;
wherein subcarriers in each subcarrier block are contiguous in frequency;
wherein ranging subchannels associated with the base station employ predetermined block configurations; and
a sequence of all modulating signals in a ranging subchannel is a ranging sequence;
estimating by the mobile station, using a received downlink signal from the base station, a path loss between the base station and the mobile station;
setting a power level of the ranging signals by an open-loop power control, wherein the mobile station adds a negative offset to the open-loop power setting to begin sending the ranging signal and gradually increases power as a number of failures and retries increases;
detecting, by the base station, a presence of the ranging signal, a time delay, and the power level, wherein the detection process comprises;
applying Fast Fourier Transform (FFT) to a selected window of the ranging signal;
correlating, in the frequency-domain, stored ranging sequences with the ranging signal, wherein the correlation is performed segment-wise, and wherein each segment of the correlation is performed on the subcarrier block using a correlation result to detect and identify the ranging signal; and
correlating, in the time-domain, the identified ranging signal with a corresponding one of the stored ranging sequences, in a sliding-window fashion, to determine the time delay and power level of the ranging signal.
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Abstract
Methods and apparatus in a multi-carrier cellular wireless network (303, 304, 305, 320) with random access improve receiving reliability and reduce interference of uplink signals of a random access, while improving the detection performance of a base station receiver (310, 320) by employing specifically configured ranging signals.
25 Citations
20 Claims
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1. In a wireless communication system, a method of establishing communication between a mobile and a base station using a ranging signal, the method comprising:
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modulating, in the mobile station, ranging signals on at least one ranging subchannel; wherein the ranging subchannel includes multiple subcarrier blocks; wherein subcarriers in each subcarrier block are contiguous in frequency; wherein ranging subchannels associated with the base station employ predetermined block configurations; and a sequence of all modulating signals in a ranging subchannel is a ranging sequence; estimating by the mobile station, using a received downlink signal from the base station, a path loss between the base station and the mobile station; setting a power level of the ranging signals by an open-loop power control, wherein the mobile station adds a negative offset to the open-loop power setting to begin sending the ranging signal and gradually increases power as a number of failures and retries increases; detecting, by the base station, a presence of the ranging signal, a time delay, and the power level, wherein the detection process comprises; applying Fast Fourier Transform (FFT) to a selected window of the ranging signal; correlating, in the frequency-domain, stored ranging sequences with the ranging signal, wherein the correlation is performed segment-wise, and wherein each segment of the correlation is performed on the subcarrier block using a correlation result to detect and identify the ranging signal; and correlating, in the time-domain, the identified ranging signal with a corresponding one of the stored ranging sequences, in a sliding-window fashion, to determine the time delay and power level of the ranging signal. - View Dependent Claims (2, 3, 4)
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5. In a wireless communication system of cells, base stations, and mobile stations, a method of transmitting ranging signals by a mobile station to a base station for initiating a random access and establishing communication between the mobile station and the base station, wherein the base station uses the ranging signals to identify the mobile station, determine the mobile station'"'"'s signal power, and measure the mobile station'"'"'s time delay, the method comprising:
- constructing ranging subchannels;
wherein a ranging subchannel includes at least one block having a plurality of subcarriers; wherein the subcarriers in a block are contiguous in frequency; wherein power of a block is shaped by assigning different signal power levels to different subcarriers of the block; wherein a signal power towards both frequency boundaries of a subcarrier block is lower than a signal power of subcarriers towards the center of the block; and assigning specific block configurations to ranging subchannels for each cell; and transmitting binary or non-binary ranging signals over the ranging subchannels by modulating the plurality of subcarriers, wherein a sequence of modulating signals in a ranging subchannel is a ranging sequence, and wherein each ranging signal has low peak-to-average power ratio in the time domain. - View Dependent Claims (6, 7, 8, 9, 10)
- constructing ranging subchannels;
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11. In a network of base stations and remote stations, a remote station transmitter configured to transmit ranging signals for initiating communication with the base station, wherein the base station uses ranging signals to identify the remote station and determine at least one transmitter attribute, the transmitter comprising:
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a facility for constructing ranging subchannels; wherein a ranging subchannel comprises a plurality of subcarrier blocks; wherein the subcarriers of a block are contiguous in frequency; wherein different power levels are assigned to different subcarriers of the block; and
wherein a power level towards the high-end and low-end frequency boundaries of a subcarrier block is lower than a signal power of subcarriers towards the center of the block, or wherein a power level of the two subcarriers at both ends of a subcarrier block is zero;a modulator for modulating binary or non-binary ranging signals on the subcarriers of the ranging subchannels, wherein a sequence of modulating signals in a ranging subchannel is a ranging sequence; and wherein each ranging signal has low peak-to-average power ratio in the time domain. - View Dependent Claims (12, 13, 14, 15, 16)
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17. A communication system performing random access for establishing communication between two stations, the system comprising:
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at least one remote station estimating a path loss between itself and a base station by utilizing a received downlink signal from the base station, wherein the remote station sets power levels of a ranging signal by adding a negative offset to the power setting at the beginning of a signal transmission and gradually increases power as a function of a number of random access failures and retries; and at least one base station detecting a presence of each ranging signal, the ranging signal time delay, and the ranging signal power level, wherein; the base station performs hierarchical detection, in frequency domain and in time-domain, when the ranging signal is modulated on subcarriers of a ranging subchannel and the ranging subchannel is composed of blocks of contiguous subcarriers; and the detection process comprises; applying Fast Fourier Transform (FFT) to a selected window of a received signal; correlating, in the frequency-domain, the base-station-specific ranging sequences with a received signal; wherein the correlation is performed segment-wise; wherein each segment of the correlation is performed on a subcarrier block; and wherein the correlation result identifies a ranging signal; and correlating, in the time-domain, a full sequence of the identified ranging signal with the corresponding base-station-specific ranging sequence, in a sliding-window fashion, to find the ranging signal time-delay and power. - View Dependent Claims (18, 19, 20)
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Specification