LDPC coded modulation with unequal protection

Multiple modulation modes and coding rates are often used in wireless communication systems to satisfy different QoS requirements. The starting point of this paper is the observation that the error probabilities of different bits in modulation are different. At the same time, different coding rates can also provide different protection capabilities. Furthermore, in hierarchical modulation, modulation factor alpha is introduced to provide flexible bit protections. In this paper, we study the effect of modulation factor and propose a scheme of LDPC coded modulation with unequal or equal protection for different code streams at the bit level. This scheme not only can provide different protection strategies for requirements of diverse users and purposes, but also can achieve additional transmission rates without increasing hardware complexity. Moreover, by choosing an appropriate factor of modulation, different bits with different LDPC rates can reduce or eliminate the SNR-gap to achieve equal protection.