Opportunistic Spectrum Sharing Based on OFDM With Index Modulation

Qiang Li, Miaowen Wen, Shuping Dang, Ertugrul Basar, H. Vincent Poor, Fangjiong Chen
2019 IEEE Transactions on Wireless Communications  
In this paper, a novel opportunistic spectrum sharing scheme, based on orthogonal frequency division multiplexing with index modulation (OFDM-IM), is proposed for cognitive radio (CR) networks. In the considered OFDM-IM based CR (OFDM-IM-CR) model, the primary transmitter (PT) communicates with the primary receiver with the aid of an amplifiedand-forward (AF) relay by transmitting OFDM-IM signals. Meanwhile, the secondary transmitter (ST) passively senses the spectrum and transmits its own
more » ... mation over those inactive subcarriers of the primary network to the secondary receiver if the signal-to-noise ratio of the PT→ST link is above a predefined threshold; otherwise, the ST stays in silent mode. Two different types of maximum-likelihood (ML) detectors are designed for the primary network, based on the knowledge of either the estimated channel state information or the statistical channel information of the secondary network. A complexity-reducing method, which is applicable to both types and achieves near optimal performance, is further proposed. To evaluate the performance, a tight upper bound on the bit error rate (BER) is derived, assuming the first type of ML detection. Simulation results corroborate the analysis and show that OFDM-IM-CR has the potential of outperforming OFDM-CR and OFDM-IM-AF in terms of BER with higher spectral efficiency. of OFDM-based CR (OFDM-CR) networks, ranging from resource allocation to spectrum monitoring, have received considerable research attention [11]-[15]. Recently, a promising variant of OFDM has been proposed by applying the concept of index modulation (IM) [16] . The rationale behind IM is to utilize the index(es) of some building blocks of a communication system to transmit extra information [17]- [21] . To be more specific, in OFDM with IM (OFDM-IM), only a subset of all available subcarriers are activated to carry ordinarily modulated M -ary symbols and the resulting subcarrier activation patterns (SAPs) implicitly convey additional information bits that are known as IM bits. By deactivating partial subcarriers, some transmit power can be saved, which can be used in return for the transmission of M -ary modulation symbols. The transmission of IM bits consumes no power and has stronger protection than that of ordinary modulation bits [22] . Therefore, OFDM-IM achieves better error performance than its OFDM counterpart. Moreover, OFDM-IM enjoys the flexibility in system configuration and provides a good trade-off between the spectral efficiency and the system performance by adjusting the number of active subcarriers. To extend the wireless coverage, relay-aided OFDM-IM is proposed. In [23], adaptive mapping schemes between IM bits and SAPs are presented for dual-hop OFDM-IM DF relaying networks. To enhance the system reliability, in [24]-[26], multiple relays with relay selection are employed for dual-hop OFDM-IM. In contrast to the dual-hop schemes in [23]-[26], multi-hop DF relaying is developed for OFDM-IM in [27], further enlarging the communication coverage. In view of two information-carrying units, the potential of OFDM-IM is investigated in overlay OFDM-based CR networks, where the PU transmits classical OFDM signals, and the SU employs OFDM-IM to forward the PU's information via M -ary symbols and convey its own information through SAPs [28] . However, how to explore the opportunity to access the idle spectrum when the PU employs OFDM-IM for information transmission, is still an open topic. In particular, since partial subcarriers in OFDM-IM are inherently inactive (spectrum holes), they can potentially be used by SUs for improving the spectral efficiency. Against the background, in this paper, we propose a novel OFDM-IM-based CR (OFDM-IM-CR) model for spectrum sharing to improve spectrum utilization. The contributions of this paper are summarized as follows. • In OFDM-IM-CR, the PU relies on dual-hop OFDM-IM AF (OFDM-IM-AF) relaying for priority transmission and the SU exploits spectrum holes of the primary network for opportunistic communications. Specifically, in the first phase, the primary transmitter (PT) broadcasts OFDM-IM signals to an AF relay and the secondary transmitter (ST). Upon receiving this signal, the ST measures the signal-to-noise ratio (SNR) and performs spectrum sensing. In the second phase, the relay amplifies and forwards the received signal to the primary receiver (PR). Meanwhile, if the SNR of the PT→ST link is above a predefined threshold, the ST transmits its own information on those inactive subcarriers of the primary network to the secondary receiver (SR); otherwise, the
doi:10.1109/twc.2019.2943159 fatcat:rpuyzhz5ibbtjetkgumhdlbrt4