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Statements

Subject Item
dbr:Carrier_interferometry
rdf:type
dbo:Organisation
rdfs:label
Carrier interferometry
rdfs:comment
Carrier Interferometry (CI) is a spread spectrum scheme designed to be used in an Orthogonal Frequency-Division Multiplexing (OFDM) communication system for multiplexing and multiple access, enabling the system to support multiple users at the same time over the same frequency band.
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n10:CI_Transceiver_copy.jpg
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dbc:Channel_access_methods
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13131203
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1049503768
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dbr:Fiber-optic_communication dbc:Channel_access_methods dbr:Spread_spectrum dbr:Spatial_multiplexing dbr:Distributed_antenna_system dbr:Equalization_(communications) dbr:Frequency-shift_keying dbr:Phased_array dbr:Mode-locking dbr:Hadamard_code dbr:Multi-carrier_code-division_multiple_access dbr:Multiple_access dbr:Discrete_Fourier_transform_(general) dbr:Direct-sequence_spread_spectrum dbr:Multiplexing dbr:MIMO dbr:Cyclic_delay_diversity dbr:Orthogonal_frequency-division_multiplexing dbr:Fast_Fourier_transform dbr:Subcarrier_multiplexing n19:CI_Transceiver_copy.jpg dbr:Spectral_interferometry dbr:Pseudonoise dbr:Crest_factor dbr:Orthogonality dbr:Software-defined_radio dbr:Fading
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dbo:abstract
Carrier Interferometry (CI) is a spread spectrum scheme designed to be used in an Orthogonal Frequency-Division Multiplexing (OFDM) communication system for multiplexing and multiple access, enabling the system to support multiple users at the same time over the same frequency band. Like MC-CDMA, CI-OFDM spreads each data symbol in the frequency domain. That is, each data symbol is carried over multiple OFDM subcarriers. But unlike MC-CDMA, which uses binary-phase Hadamard codes (code values of 0 or 180 degrees) or binary pseudonoise, CI codes are complex-valued orthogonal codes. In the simplest case, CI code values are coefficients of a discrete Fourier transform (DFT) matrix. Each row or column of the DFT matrix provides an orthogonal CI spreading code which spreads a data symbol. Spreading is achieved by multiplying a vector of data symbols by the DFT matrix to produce a vector of coded data symbols, then each coded data symbol is mapped to an OFDM subcarrier via an input bin of an inverse fast Fourier transform (IFFT). A block of contiguous subcarriers may be selected, or to achieve better frequency diversity, non-contiguous subcarriers distributed over a wide frequency band can be used. A guard interval, such as a cyclic prefix (CP), is added to the baseband CI-OFDM signal before the signal is processed by a radio front-end to convert it to an RF signal, which is then transmitted by an antenna. A significant advantage of CI-OFDM over other OFDM techniques is that CI spreading shapes the time-domain characteristics of the transmitted waveform. Thus, CI-OFDM signals have a much lower peak-to-average-power ratio (PAPR), or crest factor, compared to other types of OFDM. This greatly improves power efficiency and reduces the cost of power amplifiers used in the radio transmitter. A CI-OFDM receiver removes the cyclic prefix from a received CI-OFDM transmission and performs OFDM demodulation with a DFT (e.g., an FFT) typically used in OFDM receivers. The CI-spread symbol values are collected from their respective subcarriers in an inverse-mapping process and may be equalized to compensate for multipath fading or processed for spatial demultiplexing. The CI de-spreader performs an inverse-DFT on the spread symbols to recover the original data symbols. Since CI coding can shape the time-domain characteristics of the transmitted waveform, it can be used to synthesize various waveforms, such as direct-sequence spread spectrum and frequency shift key [4] signals. The advantage is that the receiver can select time-domain or frequency-domain equalization based on how much scattering occurs in the transmission channel. For rich scattering environments, frequency-domain equalization using FFTs requires less computation than conventional time-domain equalization and performs substantially better.
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dbr:Orthogonal_frequency-division_multiplexing
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dbr:CI
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dbr:Carrier_interferometry
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dbr:Carrier_interferometry
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dbr:Carrier_interferometry