Single Sideband

Description

Single Sideband (1SB) is a modulation and signal-processing technique that transmits only one of the two sidebands produced by amplitude modulation, thereby halving the occupied bandwidth compared to conventional double-sideband (DSB) transmission. In 3GPP Release 19, 1SB is studied within the framework of NR evolution, particularly in the context of study items documented in TS 38.191 (NR study on 7-24 GHz) and TS 38.769 (study on single sideband transmission for NR). The technique is attractive because it improves spectral efficiency, which is a critical resource in sub-7 GHz and centimetre-wave bands where operators must serve many users within limited spectrum.

From an architectural perspective, 1SB operates at the physical layer and interacts with the RF front-end, baseband processing, and the NR frame structure. A single-sideband signal can be generated using the Hilbert transform to produce an analytic signal, followed by complex mixing to shift the spectrum so that only the upper or lower sideband remains. On the receive side, coherent detection recovers the in-phase and quadrature components. Because one sideband is suppressed, the signal occupies roughly half the bandwidth of a DSB signal carrying the same information, or alternatively can carry the same information in the same bandwidth with additional redundancy for robustness.

In the 3GPP context, 1SB is being evaluated as a candidate waveform enhancement for NR, especially for uplink transmissions where power efficiency and spectral containment matter. The study considers coexistence with OFDM-based NR waveforms, impact on EVM and ACLR requirements, and compatibility with existing NR numerologies. Key components include the modulator/demodulator, the sideband filter, and the associated RF chain that must handle the asymmetric spectrum. The technique also has implications for carrier aggregation and bandwidth part (BWP) configuration, since the occupied bandwidth of a 1SB carrier differs from that of a conventional carrier.

The role of 1SB in the network is primarily to enhance spectral efficiency and to enable more flexible use of fragmented spectrum. It can be applied to specific channels or reference signals where bandwidth savings are beneficial, and it may complement other Rel-19 study areas such as enhanced MIMO and coverage enhancements. Because 1SB requires accurate phase and amplitude matching between I and Q branches, implementation complexity and RF impairments (IQ imbalance, phase noise) are important considerations in the study.

Overall, 1SB represents a physical-layer innovation that 3GPP is investigating to address spectrum scarcity and to improve the efficiency of NR transmissions. Its standardization status in Rel-19 is that of a study item, with specifications 38.191 and 38.769 providing the evaluation methodology and performance results that will inform potential normative work in future releases.

Purpose & Motivation

Single Sideband exists to solve the problem of spectrum scarcity in wireless communications. Conventional amplitude modulation and many double-sideband schemes waste half of their occupied bandwidth on a redundant sideband that carries the same information as the other. By suppressing one sideband, 1SB doubles spectral efficiency for a given information rate, or equivalently allows the same information to be transmitted in half the bandwidth. This is particularly valuable in 3GPP bands where spectrum is expensive and fragmented.

Historically, single-sideband modulation has been used in analogue radio and military HF communications for decades because of its bandwidth efficiency and power efficiency. However, its adoption in digital cellular systems was limited by the need for precise quadrature generation and coherent detection, which were costly in early digital hardware. With modern DSP capabilities, these barriers have diminished, prompting 3GPP to revisit 1SB in Rel-19 as a candidate for NR enhancements.

The motivation for studying 1SB in 3GPP is also driven by the need to support new services and denser deployments without additional spectrum. By improving the spectral efficiency of the physical layer, 1SB can help operators meet capacity demands in sub-7 GHz and millimetre-wave bands. The study in TS 38.769 evaluates whether 1SB can coexist with OFDM and whether its benefits outweigh the added complexity, providing a foundation for potential normative specification in later releases.