A method, comprising: receiving a customer data transmission request for a data stream to be transmitted, the customer data transmission request comprising customer criteria including a bandwidth of the data stream to be transmitted; determining, whether any spectrum-related criteria, including a minimum bandwidth block size and/or a requirement for contiguous bandwidth blocks, satisfies the customer data transmission request, identifying a set of available spectral fragments, each of the available spectral fragments being defined by a respective bandwidth size, at least two of the available spectral fragments being separated by an allocated spectral region, at least two of the available spectral fragments having different bandwidth sizes; allocating at least two of the available spectral fragments for the data stream, based on the customer criteria of the customer data transmission request and the spectrum-related criteria satisfying the customer data transmission request, to provide a set of allocated spectral fragments for the data stream at least two of the allocated spectral fragments being separated by an allocated spectral region, at least two of the allocated spectral fragments having different bandwidth sizes; dividing the data stream into a set of output sub-streams, the output sub-streams associated with a respective ones of the allocated spectral fragments and having respective data rates compatible with the respective bandwidth sizes of the respective allocated spectral fragment; modulating the output sub-streams to provide respective modulated signals adapted for transmission via the respective allocated spectral fragments, each of the output sub-streams being modulated by respective modulators according to a unique or a common modulation technique; and upconverting the modulated signals onto the respective allocated spectral fragments, wherein each modulator is optimized according to a specific type of traffic and/or specific channel conditions associated with its corresponding spectral fragment. receiving a customer data transmission request for a data stream to be transmitted, the customer data transmission request comprising customer criteria including a bandwidth of the data stream to be transmitted; determining, whether any spectrum-related criteria, including a minimum bandwidth block size and/or a requirement for contiguous bandwidth blocks, satisfies the customer data transmission request, identifying a set of available spectral fragments, each of the available spectral fragments being defined by a respective bandwidth size, at least two of the available spectral fragments being separated by an allocated spectral region, at least two of the available spectral fragments having different bandwidth sizes; allocating at least two of the available spectral fragments for the data stream, based on the customer criteria of the customer data transmission request and the spectrum-related criteria satisfying the customer data transmission request, to provide a set of allocated spectral fragments for the data stream at least two of the allocated spectral fragments being separated by an allocated spectral region, at least two of the allocated spectral fragments having different bandwidth sizes; dividing the data stream into a set of output sub-streams, the output sub-streams associated with a respective ones of the allocated spectral fragments and having respective data rates compatible with the respective bandwidth sizes of the respective allocated spectral fragment; modulating the output sub-streams to provide respective modulated signals adapted for transmission via the respective allocated spectral fragments, each of the output sub-streams being modulated by respective modulators according to a unique or a common modulation technique; and upconverting the modulated signals onto the respective allocated spectral fragments, wherein each modulator is optimized according to a specific type of traffic and/or specific channel conditions associated with its corresponding spectral fragment.