Assessment of linear modulation techniques and their application to personal radio communications systems

A number of simple two-level linear modulation schemes are described and characterised. It is shown that, through proper choice of filter parameters, linear modulations can be designed to achieve full compatibility with standard receiver architectures, but with better all-round performance than constant envelope techniques. In particular, the schemes presented are designed to be interchangeable with standard constant envelope techniques (GMSK with various B_b T products), maintaining full compatibility with the appropriate non-coherent LD and coherent detection techniques, but yielding improved spectral characteristics and cochannel performance. As an example, it is shown that for systems requiring preservation of the possibility of simple 2-level LD detection, one of the schemes (ESFM) can effectively provide an extra degree of freedom in system design, leading to capacity gains. These techniques therefore deserve consideration as possible alternatives to standard modulation methods, such as GMSK