Channel Characteristics and Frequency Multiplexing
In the previous chapter, Section 1.6 identifies the figures of merit for uplink transmission techniques in cellular systems as high spectral efficiency, high throughput, low delay, and long battery life in portable devices. The challenge of radio system design is to optimize these figures of merit in the presence of impairments in communication channels. In order to increase spectral efficiency and achieve increasingly high transmission rates, successive generations of cellular systems have moved to signals with higher and higher bandwidth. As indicated in Table 1.3, the technologies developed by 3GPP for long term cellular evolution (LTE) will use signals with bandwidths as high as 20 MHz.
To set the stage for the presentation of the SC-FDMA system under consideration by 3GPP in the remainder of this book, this chapter provides background information on radio signal propagation. It then describes two approaches to frequency-domain signal processing in the transmission of individual signals: orthogonal frequency division multiplexing (OFDM) and single carrier transmission with frequency-domain equalization (SC/FDE).
2.2 Radio Channel Characteristics
Radio signal propagation in cellular systems is the subject of a huge body of theoretical and experimental research and a thorough exposition of important issues would fill a volume larger than this book. The purpose of the following paragraphs is to describe briefly ...