Aimed at inspiring researchers and practitioners, this paper presents comprehensive and multidimensional discussions of the potential and benefits of integrating power line and wireless communication systems to enhance data communication in both indoor and outdoor environments. By systematically examining the strengths and weaknesses of power line and wireless communication systems, we first elucidate the rationale behind their integration—hybrid communication systems. Then we categorize these hybrid communication systems and provide an in-depth analysis of each category, considering technical, chronological, industrial, and standardization aspects. Moreover, we discuss strategies for designing hybrid communication devices. Next, a qualitative assessment of hybrid communication systems follows, offering guidance for advancing their use, while a concise summary of key lessons imparts valuable insights for future endeavors. Lastly, the paper identifies a range of pertinent topics for further exploration and, consequently, advancing hybrid communication systems for smart grid, Internet of Things, and Industry 4.0 or 5.0 applications.

This paper investigates the degradation caused by interference resulting from cyclic prefix violation and symbol timing offset in narrowband power line communication systems. In this sense, it presents a unified formulation from which Hermitian symmetric orthogonal frequency division multiplexing (HS-OFDM), orthogonal chirp division multiplexing (OCDM), single-carrier cyclic prefix (SCCP), and orthogonal time–frequency division multiplexing (OTFDM) can be easily derived. The paper then provides closed-form expressions for quantifying the aforementioned interference in the presence of a frequency domain equalizer. The numerical analyses exhibit the performances of these schemes under various data communication conditions, such as the availability of channel state information, the presence or absence of interference, modeling of additive noise as a white or colored Gaussian random process, frequency domain equalizer type, and the use of bit and power allocation techniques. The closed-form expressions and performance analyses regarding achievable data rate and bit error probability provide guidance for dealing with distinct constraints in narrowband power line communication (PLC) systems using the HS-OFDM, OCDM, SCCP, or OTFDM scheme. Lastly, the unified formulation and results obtained motivate the design of multi-scheme transceivers.

This paper introduces a multicarrier communication technique termed orthogonal chirp-frequency division multiplexing (OCFDM). It relies on a unitary transform named discrete modular chirp transform. The proposed OCFDM amalgamates characteristics from the orthogonal frequency division multiplexing (OFDM) and orthogonal chirp division multiplexing (OCDM), partitioning the frequency spectrum into distinct subbands and populating each of them with orthogonal chirps. By deriving the reconstructed signal at the receiver, the paper shows that the normalized signal-to-noise ratio exhibits changes across subbands, allowing the use of resource allocation, for instance, for power allocation or bit-loading. Moreover, it is shown that the OCFDM introduces an additional degree of freedom through its tile geometries, allowing it to be configured to perform in between OFDM and OCDM and, consequently, to offer novel and balanced trade-offs among symbol error rate, data rate, and robustness to interference. Numerical analyses illustrate those trade-offs and confirm the versatility and efficacy of the OCFDM.

This paper introduces a novel transform, called modular chirp transform (MCT), and its corresponding multicarrier communication scheme, named orthogonal chirp-frequency division multiplexing (OCFDM). This chirp spread spectrum (CSS)-based scheme has some useful properties that enable multiple access and resource allocation mechanisms; this contrasts with well-known CSS-based schemes, such as long-range (LoRa) and orthogonal chirp division multiplexing (OCDM), that lack such properties. The feasibility of the proposed scheme for enabling resource allocation and multiple access in CSS-based multicarrier schemes is shown through numerical analyses of the normalized signal-to-noise ratio at the receiver and the transmitted signal's spectrogram.

This letter revisits orthogonal chirp-division multiplexing (OCDM) for baseband data communication systems, usually employed in wireline communication. We demonstrate that an existing formulation for generating real-valued chirp sequences shows limited temporal spreading. In the sequel, we introduce the hermitian-symmetric (HS)-OCDM technique, which correctly spreads chirp sequences, thereby improving performance. Numerical simulations show that the proposal offers enhanced robustness against cyclic prefix length violations and synchronization impairments granted to the spreading of the chirp signals in the whole symbol duration.

This paper introduces the orthogonal chirp-frequency-division multiple access (OCFDMA), a technique based on orthogonal chirp-frequency-division multiplexing that partitions the frequency band into independent chirp-based subchannels, referred to as voices. By leveraging the block-circulant property of the discrete modular chirp transform, OCFDMA assigns each user one or more voices to achieve orthogonal, interference-free, multiple-access transmissions, thereby enabling per-user processing and reducing transceiver complexity. User-oriented geometries are developed to allow flexible trade-offs between bit-error rate (BER) and data rate by adjusting the number and size of voices. Per-voice linear models are derived, and both minimum-variance unbiased and minimum mean-squared-error channel estimators are presented, along with optimal pilot designs. The proposed technique is compared with state-of-the-art chirp-based multiple-access techniques, such as orthogonal chirp-division multiple access (OCDMA), as well as orthogonal frequency-division multiple access (OFDMA)-related techniques widely adopted in current wireless standards. Numerical experiments show that OCFDMA achieves superior peruser BER, strong robustness to cyclic-prefix-length violation and carrier-frequency offset, competitive data rates, and a peak-to-average power ratio comparable to OFDMA for both downlink and uplink connections.