What are OFDMA channels?
OFDMA stands for orthogonal frequency division multiplexing access. It is an extension of OFDM. The difference is that OFDMA is multi-user where OFDM is single-user. It has 3x higher throughput than single-user OFDM for short packets of data or multiple endpoints.
How many sub channels will be required for OFDM?
Each OFDM channel consists of 128 to 2048 sub-carriers and can occupy bandwidths from 1.25 MHz to 20 MHz. In addition, each of these sub-carriers is modulated using BPSK, QPSK, 16-QAM, or 64-QAM modulation, depending on the requirements of the physical channel.
What is the channel spacing used for OFDM subcarriers?
312.5 kHz
OFDM and subcarriers allow Wi-Fi to be more fault tolerant and carry data more reliably. Older Wi-Fi standards, such as 802.11ab/g/n/ac, use 64 subcarriers. Each Wi-Fi channel is 20 MHz. Therefore, each subcarrier is spaced 312.5 kHz apart.
What are upstream OFDMA channels?
OFDMA is used in the upstream by cable modems transmitting data to the CMTS. OFDMA is a time- and frequency-shared medium, meaning the CMTS schedules time and frequency slots to the modems allowing the modems to time share the same frequency and transmit their data on OFDMA subcarriers on the upstream.
What is a channel estimation?
Channel Estimation is the process of finding correlation between the array of complex numbers on the left and the array of complex numbers on the right. The detailed method of the estimation can very depending on the implementation.
What are orthogonal channels?
Two radio-frequency channels in which the emissions have orthogonal polarizations . Simply,we can say that Two transmissions are orthogonal if they have no influence on one another. This can be achieved in four domains: time, space, frequency and code. All channels can be considered as orthogonal channels.
Why IFFT is used in OFDM transmitter?
The OFDM signal is generated by implementing the Inverse Fast Fourier Transform (IFFT) at the transmitter which is used to convert frequency domain to time domain and Fast Fourier Transform (FFT) which is used to convert time domain to frequency domain at the receiver side is implemented.
What is a downstream OFDM channel?
OFDM is used in the downstream and is a common channel shared by all compatible cable modems. OFDMA is used in the upstream by cable modems transmitting data to the CMTS.
What is docsis OFDM?
Version 3.1 of DOCSIS specifications, an international telecommunications standard for cable TV systems, introduces downstream Orthogonal Frequency Division Multiplexing (OFDM) channels, which are highly flexible in terms of frequency, bandwidth, modulation type, and active spectrum.
Why do we do channel estimation?
Channel estimation plays an important role in a communication receiver. In order to mitigate hostile channel effects on the received signal, precise channel estimation is required to provide information for further processing of the received signal. Channel estimators can be categorized as non-data-aided or data-aided.
What is meant by channel estimation?
Why is channel estimation necessary?
What is orthogonality in OFDM?
What is orthogonal frequency-division multiplexing (OFDM)? Orthogonal frequency-division multiplexing is a method of data transmission where a single information stream is split among several closely spaced narrowband subchannel frequencies instead of a single Wideband channel frequency.