Cognitive relay-sharing by using hierarchical modulation under interference constraints

Dynamic interference‐limited relay sharing in cognitive radio networks by using hierarchical modulation

“…In fact, using higher order modulation for the PU only makes the SU's BER formulas more complicated in our case, and does not affect the contribution of the paper which is to demonstrate how beneficial the existence of a cognitive relay might be both to assist the SU which is restricted by transmitting power and the PU which is influenced by the spectrum sharing. Meanwhile, calculating the BER for any general hierarchical QAM constellation is straightforward based on the results in [32], and the discussion made in Appendix A of [21].…”

“…Moreover since the relay uses DF technique, we consider the effect of sources-relay links (ST → R and PT → R), by setting a threshold for SNR at the relay [8][9][10], and make the scenario more practical in comparison to the work done in [21] this way. All cases and subcases mentioned in this section are summerised in Table 1.…”

“…In [20], we applied this modulation technique to a cooperative system with two data sources and a relay utilising this method in order to transmit both sources' information data to the destination simultaneously. In [21], we utilised HM in radio cognitive context in order to improve secondary user's (SU's) performance and compensate the degradation of primary users' (PUs') performance and even improve it by allowing the existing relay to send information data of both PU and SU. In addition, in [22] we considered a scenario in which the information sender has two types of data with two different levels of priority; i.e.…”

“…Therefore, most of the time the SU transmits data with low power via direct link only (without relay) which leads to low QoS for the SU and low utilisation of the relay channel. In [21], we expand our work, [20], to the case that the two users are not in the same level of priority in the network and apply HM into a relay-based CR network in which the relay is shared with both PU and SU.…”

“…Major contributions: In the sequel of our work in [21], this paper is concerned with a cooperative system with HM for unequal protection of the transmitting data in a CR network (existence of a PU and an SU) when the same frequency band is used by both the PU and the SU under interference limitation (underlay spectrum sharing). The main contributions in this paper are:…”