Unless otherwise indicated herein, the description in this section is not itself prior art to the claims and is not admitted to be prior art by inclusion in this section.
Cellular wireless networks typically include a number of base stations that radiate to define wireless coverage areas, such as cells and/or cell sectors, in which user equipment devices (UEs) (also known as wireless communication devices (WCDs)) such as cell phones, “smart” phones, tablet computers, tracking devices, embedded wireless modules, and other wirelessly equipped communication devices, can operate. Each base station is coupled to network infrastructure that provides connectivity with one or more transport networks, such as the public switched telephone network (PSTN) for voice communications and/or the Internet for voice and/or data communications.
In general, a wireless network operates in accordance with a particular air interface protocol or radio access technology, with communications from the base stations to UEs defining a downlink or forward link and communications from the UEs to the base stations defining an uplink or reverse link. Examples of existing air interface protocols include, without limitation, Orthogonal Frequency Division Multiple Access (OFDMA (e.g., Long Term Evolution (LTE) or Wireless Interoperability for Microwave Access (WiMAX)), Code Division Multiple Access (CDMA) (e.g., 1×RTT and 1×EV-DO), and Global System for Mobile Communications (GSM), among others.
Each air interface protocol has its own frame structure for transmissions on physical uplinks and downlinks. Each air interface protocol also defines its own procedures for allocating transmission resources within the uplink and downlink for transmitting and receiving control data (e.g., messaging sent between UEs and base stations for controlling access to the radio network) and user data (e.g., voice, voice over Internet Protocol (VoIP), email, Internet browsing, file downloads/uploads).
In LTE networks, for example, the downlink direction (from the base station to the UE) uses Orthogonal Frequency Division Multiple Access (OFDMA), which is a multi-carrier scheme based on Orthogonal Frequency Division Multiplexing (OFDM) whereby radio resources are allocated to multiple users. In operation, a downlink carrier's frequency bandwidth is split into many small 15 kHz subcarriers, and each individual subcarrier is modulated using, for example, QPSK (Quadrature Phase-Shift Keying), 16-QAM (Quadrature Amplitude Modulation), 64-QAM, or perhaps other digital modulation schemes.
In the uplink direction (from the UE to the base station), LTE uses a pre-coded version of OFDM known as Single Carrier Frequency Division Multiple Access (SC-FDMA), where data is spread across the subcarriers of multiple LTE resource blocks, which can then be modulated using, for example, QPSK, 16-QAM, 64-QAM, or perhaps other digital modulation schemes. By transforming the time domain symbols to the frequency domain with a discrete Fourier transform (DFT) before OFDM modulation, SC-FDMA creates a single-carrier waveform (i.e., the SC aspect of SC-FDMA) that is then frequency-shifted to the desired part of the frequency domain in the uplink (i.e., the FDMA aspect of SC-FDMA) for transmission by the UE to the base station.