Signal modulation using guard band determination for improved frequency spectrum efficiency

An apparatus for signal modulation, comprising:

• a determination unit, configured to determine at least one guard band between at least two continuous available sub-bands among multiple available sub-bands that can be used by a communication entity and are discrete;
• and
• a modulation unit, configured to:
• use the at least one guard band in signal modulation for the communication entity;
• reserve a reserved band in the size of a guard bandwidth at one of the two ends of the at least two continuous available sub-bands, the guard bandwidth being the bandwidth of the guard band;
• use a remaining part except for the reversed band of the at least two continuous available sub-bands in the signal modulation to generate a modulated signal;
• and
• perform frequency shift on the modulated signal in a direction towards said one of the two ends, so as to generate spare bands at the two ends of the at least two continuous available sub-bands, respectively, wherein a sum of the bandwidths of the spare bands at the two ends is equal to the guard bandwidth.