Chapter 14
Uplink Physical Layer Design
14.1 Introduction
While many of the requirements for the design of the LTE uplink physical layer and multiple-access scheme are similar to those of the downlink, the uplink also poses some unique challenges. Some of the desirable attributes for the LTE uplink include:
- Orthogonal uplink transmission by different User Equipment (UEs), to minimize intra-cell interference and maximize capacity;
- Flexibility to support a wide range of data rates, and to enable the data rate to be adapted to the Signal-to-Interference-plus-Noise Ratio (SINR);
- Sufficiently low Peak-to-Average Power Ratio (PAPR) (or Cubic Metric (CM) – see Section 21.3.3) of the transmitted waveform, to avoid excessive cost, size and power consumption of the UE Power Amplifier (PA);
- Ability to exploit the frequency diversity afforded by the wideband channel (up to 20 MHz), even when transmitting at low data rates;
- Support for frequency-selective scheduling;
- Support for advanced multiple-antenna techniques, to exploit spatial diversity and enhance uplink capacity.
The multiple-access scheme selected for the LTE uplink so as to fulfil these principle characteristics is Single Carrier-Frequency Division Multiple Access (SC-FDMA).
A major advantage of SC-FDMA over the Direct-Sequence Code Division Multiple Access (DS-CDMA) scheme used in UMTS is that it achieves intra-cell orthogonality even in frequency-selective channels. SC-FDMA avoids the high level ...
