This chapter considers the LTE uplink system performance in light of its different technology enablers and their respective practical constraints.
As introduced in Chapter 15, the LTE uplink multiple access employs a Single-Carrier Frequency Division Multiple Access (SC-FDMA) waveform, also known as DFT 1 -Spread OFDM (DFT-S-OFDM). This technology enables intra-cell orthogonality between the transmissions of different User Equipments (UEs) by means of a per-symbol Cyclic Prefix (CP), provided that each UE's transmissions are adequately time-aligned with its serving cell (see Figure 18.1). Intra-cell orthogonality is the main reason why a spectral efficiency two to three times higher than that of a WCDMA uplink can be achieved. The CP of the SC-FDMA waveform also facilitates the use of a simplified receiver structure with frequency-domain equalization in the eNodeB, which further improves uplink spectral efficiency.
The main drivers for the LTE uplink performance (many of which are generic to other FDM systems) are summarized in Table 18.1.
The discussion in this chapter includes a number of evaluations for typical LTE deployment scenarios, using a 10 MHz bandwidth, 20 dB building penetration loss and 3 km/h UE speed. Following the terminology used in 3GPP [1], we refer to the scenarios as Case 1 and Case 3 for inter-eNodeB distances of 500 m and 1732 m respectively.
18.2 Uplink Capacity
A wide range of factors affect the achievable uplink capacity. In this section we briefly discuss such aspects and explain their impact in the context of LTE. We then show some evaluations of the typical capacity of the LTE uplink.