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DVB-H Systems and Receivers
Published in Borko Furht, Syed Ahson, Handbook of Mobile Broadcasting, 2008
F. Boronat, R. Llorente, J. Lloret, D. Vicente
The DVB-H standard allows the building of hierarchical networks. In ETSI 102 377,26 a hierarchical network to either support a progressive quality-of-service (QoS) degradation or allow multiformat-multidevice transmissions is proposed. In hierarchical modulation, the possible digital states of the constellation (i.e., the number of states in a QAM) are interpreted differently than in the nonhierarchical case. Several data streams are available for transmission. The one defined by the number of the quadrant in which the state is located is named the first stream, and the one defined by the location of the state within its quadrant is named the second stream. The hierarchical modulation allows the transmission of two streams, having different bit rates and performance, in the same RF channel. The sum of the bit rates of the two streams is equal to the bit rate of a nonhierarchical stream using the same modulation.
Adaptive clustering with continuous phase modulation in NOMA systems
Published in International Journal of Electronics, 2022
Guowei Lei, Wenqing Ni, Wenliang Liao, Sunqing Su
As shown in Figure 2, PSK modulation is focused on two cases: hierarchical modulation (Kaneko et al., 2015) and phase rotation modulation (Chang & Fukawa, 2018). In (a), the two-layer hierarchical modulation is defined: the symbol for the first user is modulated across I component (shown as white circle), i.e. BPSK (±1). Then, the symbol for the second user is modulated across Q component with the centre of −1 and +1 respectively (shown as dark black and grey black). However, the combination is just nominal QPSK or 4QAM because of the sequential symbols. Actually, the Gray labelling in Shieh et al., (2016) can be considered as a special case of hierarchical modulation. In (b), the phase rotation is defined: the symbol for the first user is modulated across I component (shown as dark black circle), i.e. BPSK (±1). The symbol for the second user is modulated with rotated phase exp(jπ/2) of the symbol for the first user. The two modes of modulation can bring two merits: one is clear that the symbols can be decoded without SIC. The other is about the scenario where two or more users have the similar distances to BS. It may not be a good choice to exploit the difference of power allocation for them. There are many state-of-arts dealing with this scenario, in which several weak or strong users are combined together or exploiting user pairing in downlink NOMA system. We would like to leave this subject to next section on adaptive clustering of users.