OFDMA is used on the downling, but since it presents a high Peak-to-average Power Ratio it is not possible to use it on the uplink. For instance, it would be possible to exploit the fact that user 1 might have a better radio link quality on some specific bandwidth area of the available bandwidth. This is useful for LTE since it makes possible to exploit frequency dependence scheduling. The main difference between an OFDM and an OFDMA (Orthogonal Frequency Division Multiple Access) system if the fact that in the OFDM the user are allocated on the time domain only while using an OFDMA system the user would be allocated by both time and frequency. On the receiving side of the OFDMA system we should expect an FFT operation that will them convert the symbol to the frequency domain again. This cyclic prefix in LTE has 5.2us on the first symbol, 4.7us for the rest of them and an extended cyclic prefix for larger cells. Before the transmission, however, a cyclic prefix is includes in the OFDM symbols in order to avoid intersymbol interference. Notice that a conversion from the frequency to the time domain was made when the IFFT was used. This operation produces OFDM symbols, which will be transmitted. Them they are used as input bands for an inverse fast Fourier transform operation. to focus on the - generally impressive - downlink speeds offered over mobile broadband, rather than the uplink. 5925 MHz to 6425 MHz is uplink band where as 3700 to 4200 MHz is downlink band. 6GHz band frequency is used for uplink and 4GHz frequency band is used for downlink in C band satellite communication operation. The chain to generate an OFDM signal starts by paralyzing the symbols that need to be transmitted, after they are modulated (in LTE the modulation can be QPSK, 16AQM, 64QAM). The direction from VSATs to sallite is known as uplink and the direction from satellite to VSATs is known as downlink. That improves robustness on the technology for mobile propagation conditions. Since the multiple subcarriers in OFDM are transmitted in parallel, it’s possible for each one to transmit with a lower symbol rate. 16 IEEE C802.16m-08/782, Fractional Frequency Reuse in Uplink, LG. Typically in OFDM systems we can have hundreds of subcarriers with a content spacing between them (15KHz on the LTE case). In this paper, interference mitigation schemes for LTE downlink networks are. The major difference in TDD and FDD is that in TDD system a single frequency is shared in time domain between Uplink and Downlink where as in FDD separate frequencies are used for Uplink and Downlink transmission. Each of this subcarriers can them be individually modulated. The Long Term Evolution (LTE, 4G ) standard defined by the 3GPP supports both FDD and TDD Duplex mode. In OFDM (Orthogonal Frequency Division Multiplexing) systems the original bandwidth is subdivided into multiple subcarriers.
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