Cyclic Block Filtered Multitone Modulation: Design and Performance Analysis

Nowadays, high data rate communication demand is growing. Thus, several communication technologies, both wireless and wireline, have adopted Filter Bank Modulation (FBM) at the physical layer. In a general FBM scheme, the high data rate stream is converted into a series of several parallel low data rate streams. These streams are modulated with a series of carrier signals. In frequency domain, the available bandwidth is partitioned in disjointed sub-channels. If the sub-channel number is sufficiently high, the sub-channel frequency response is quasi-flat and the equalizer can be simplified. Furthermore, FBM schemes have low complexity digital implementation and bit loading could be used to minimize the transmission power. In this thesis, a FBM transceiver is presented. The idea is to obtain good sub-channel frequency confinement as it is done by the family of exponentially modulated filter banks that is typically referred to as Filtered Multitone (FMT) modulation. However, differently from conventional FMT, the linear convolutions are replaced with circular convolutions. Since transmission occurs in blocks, the scheme is referred to as Cylic Block Filtered Multitone Modulation (CB-FMT). This thesis focuses on the principles, design, implementation and performances analysis of CB-FMT. In particular, it is shown that an efficient realization of both the transmitter and the receiver is possible in the frequency domain (FD), and it is based on the concatenation of an inner Discrete Fourier Transform (DFT) and a bank of outer DFTs. Such an implementation suggests a simple sub-channel FD equalizer. The overall required implementation complexity is lower than in FMT. Furthermore, the orthogonal filter bank design is simplified. The sub-channel frequency confinement in CB-FMT yields compact power spectrum and lower peak-to-average power ratio than in Orthogonal Frequency Division Multiplexing (OFDM). Then, the orthogonal prototype pulse design problem is considered. The orthogonality conditions are derived in time domain and frequency domain. These conditions are translated in matrix form and pulse coefficients are parameterized with hyper-spherical coordinates, a non-linear combination of trigonometric functions. The mathematical analysis shows that exists an infinite number of solutions. Next, the orthogonality is discussed in presence of a transmission medium. In general, the channel could destroy the orthogonality. Finally, optimal orthogonal pulses are designed to maximize the in-band-toout- band energy ratio and the achievable rate in time-variant channel scenario. These optimal pulses improve the performance of the baseline root-raisedcosine pulse. Furthermore, the equalization task is discussed. Equalizers are necessary to restore the orthogonality when an equivalent filter is inserted between the transmitter and the receiver. This filter could represent the transmission medium, a real interpolation filter or the hardware non-ideality. We discuss several equalizers, both for time-invariant and time-variant channels. A cyclic prefix (CP) can be added to the transmitted signal. We show that when the CP length is greater than the channel impulse response length, perfect reconstruction (PR) is possible. For time-invariant channels, a simple 1-tap equalizer is sufficient to restore the orthogonality. We show that in the time-variant scenario, the 1-tap equalizer is not sufficient to restore the orthogonality. Several equalizers are proposed for the time-variant case. Finally, performances in real application scenarios are evaluated. We start from Power Line Communications. For in-home high data rate communications, broadband PLC (BB-PLC) is used. BB-PLC generally operates in the band 2-30 MHz. Transmission above 30 MHz is possible, but the electromagnetic compatibility (EMC) limits are more stringent than the limits in the band below 30 MHz. In the 2-30 MHz range there are several sub-bands dedicated to other communication systems, e.g. to amateur radio. A spectrum notching mask has to be fulfilled by the power spectral density (PSD) of the transmitted signal to grant coexistence. For command and control applications, narrowband PLC (NB-PLC) is used. NB-PLC operates in portions of the 3-500 kHz spectrum and it has to obey certain spectral masks for EMC and coexistence issues, similarly to BB-PLC. Although OFDM allows simple spectrum management by switching on-off the sub-channels, its poor sub-channel frequency selectivity translates into a poor spectrum usage. An agile use of the spectrum and higher spectral efficiency can be obtained with filter bank modulation. In particular, we investigate the use of CB-FMT modulation and compare it to pulse-shaped OFDM (PS-OFDM) deployed in the G3-PLC and IEEE P1901.2 standards for NB-PLC. For BB-PLC, we compare CB-FMT with the HomePlug standard. The comparison shows that higher spectral efficiency and improved spectrum management can be achieved with CB-FMT. For the wireless scenario, the land mobile radio systems are considered. The transmitted signal propagates through a multipath channel. This propagation model is caused by several natural and man-made obstacles that introduce reflections, diffraction and scattering. Time-invariant and time-variant scenarios are considered. The FD equalization allows the exploitation of the transmission medium time and frequency diversity; thus, it potentially yields lower symbol error rate and higher achievable rate in time-variant frequency-selective fading.