Implementation Issues A general block diagram of a multi-carrier transceiver employed in a cellular environment with a central base station (BS) and several terminal stations (TSs) in a point to multi-point topology is depicted in Figure 4-1. For the downlink, transmission occurs in the base station and reception in the terminal station and for the uplink, transmission occurs in the terminal station and reception in the base station. Although very similar in concept, note that in general the base station equipment handles more than one terminal station, hence, its architecture is more complex. The transmission operation starts with a stream of. | 4 Implementation Issues A general block diagram of a multi-carrier transceiver employed in a cellular environment with a central base station BS and several terminal stations TSs in a point to multi-point topology is depicted in Figure 4-1. For the downlink transmission occurs in the base station and reception in the terminal station and for the uplink transmission occurs in the terminal station and reception in the base station. Although very similar in concept note that in general the base station equipment handles more than one terminal station hence its architecture is more complex. The transmission operation starts with a stream of data symbols bits bytes or packets sent from a higher protocol layer . the medium access control MAC layer. These data symbols are channel encoded mapped into constellation symbols according to the designated symbol alphabet spread only in MC-SS and optionally interleaved. The modulated symbols and the corresponding reference pilot symbols are multiplexed to form a frame or a burst. The resulting symbols after framing or burst formatting are multiplexed and multi-carrier modulated by using OFDM and finally forwarded to the radio transmitter through a physical interface with digital-to-analog D A conversion. The reception operation starts with receiving an analog signal from the radio receiver. The analog-to-digital converter A D converts the analog signal to the digital domain. After multi-carrier demodulation IOFDM and deframing the extracted pilot symbols and reference symbols are used for channel estimation and synchronization. After optionally deinterleaving despreading only in the case of MC-SS and demapping the channel decoder corrects the channel errors to guarantee data integrity. Finally the received data symbols bits bytes or a packet are forwarded to the higher protocol layer for further processing. Although the heart of an orthogonal multi-carrier transmission is the FFT IFFT operation synchronization and channel .
