In this paper, random interleaving multiplexing for random access scheme is proposed to further improve throughput and energy efficiency in satellite networks, which resort to the state-of-art physical layer techniques that can resolve multiple packet collisions. The bit and symbol level interleavers are randomly selected by active users from sets of interleavers, which are utilized to differentiate signals of different users sharing a subframe, and MAP detector can be employed to decode multiple superimposed packets. By further utilizing transmission diversity and interference cancellation technique, the proposed scheme can combine with Contention resolution diversity slotted ALOHA (CRDSA), called RIM-CRDSA protocols, and its an upper bound of throughput is derived. Simulation results show that the peak throughput of RIM-CRDSA can approach 2.0 bits/symbol, which largely outperform conventional random access protocols.

In this paper, we propose a new transmit power diversity scheme for contention resolution diversity slotted ALOHA (CRDSA) under total transmit power limitation in satellite networks. In the proposed scheme, the total transmit power of each device within a frame is considered to be the same, and allocated to multiple packet replicas, and the transmit power of each packet replica can be different, which enables the transmit power diversity. The threshold based capture model is employed at the gateway demodulator, and the recovery-error probability based on this model is derived. The threshold of capture and transmit powers of packet replicas are also jointly optimized to maximize the achievable sum rate (ASR) of CRDSA under total transmit power limitation. Simulation results show that the proposed scheme is more than 50% higher than the conventional one in terms of normalized ASR.

In this article, we propose an optimal irregular repetition slotted ALOHA (IRSA) under total transmit power constraint for random access (RA) in the Internet-of-Things (IoT)-oriented satellite networks, which is named as an optimal power-limited IRSA (PL-IRSA). In this proposal, the total transmit power for each satellite machine-type device (SMD) within a frame is considered to be the same and equally allocated into its multiple packet replicas. Due to a variant number of packet replicas, the transmit power of each packet replica for different SMDs may be different. The difference of transmit powers of packet replicas and path loss enhance the received power diversity, which is able to improve the throughput by using the capture effect. At the receiver side, we introduce a semi-analytical (SEA) model to approximate the physical-layer decoding and derive an asymptotic packet loss rate (PLR) based on this SEA model. From the derived results, an optimization problem is formulated and solved to find out the optimal degree distributions for different total transmit powers and code rates, which maximize the normalized system throughput. The simulation results demonstrate that the proposed optimal PL-IRSA can lead to significant performance improvement with respect to conventional ones.

In this paper, cooperative contention resolution diversity slotted ALOHA (CRDSA) with transmit power diversity is proposed for multi-satellite networks with partly overlapped coverage areas. The proposed scheme combines packet and power diversity transmission with efficient interference cancellation (IC) technique, which greatly improves the throughput. The packet loss ratio (PLR) of cooperative CRDSA with transmit power diversity is derived, and by using it as a fitness function, we formulate an optimization problem to find the optimized transmit power distribution, which further improves the throughput of cooperative CRDSA. Simulation results show that the cooperative CRDSA with optimized transmit power distribution remarkably outperforms the one with uniform transmit power distribution in terms of throughput.

An improved successive multiuser detection (SMUD) initial ranging (IR) algorithm with interference cancellation is presented for orthogonal frequency division multiple access systems followed by IEEE 802.16 m standard. The proposed method detects all the valid paths of IR subscriber stations, selects the path with the maximum signal‐to‐interference‐plus‐noise ratio, and estimates the parameters of the path by least‐square method. The estimated parameters are further processed by the parallel interference cancellation processing to improve their accuracy, and then the signal of the selected valid path is removed from the received signal in the successive interference cancellation (SIC) process. The proposed scheme can efficiently improve the parameter estimation accuracy of the selected valid path and reduce the residual multiple access interference in the SIC process. Simulation results show that the proposed method has a much better performance than the SMUD algorithm.

We propose a new SNR estimation method based on the preamble for OFDM systems in frequency selective channels. The OFDM training symbols in the preamble are equalized by the known data in frequency domain and employed to estimate the noise variance. The second order moments of the received symbols are used to estimate the signal plus noise power in the OFDM packets. The SNRs on the subchannels and the average SNR of the packets can all be estimated. Simulation results show that the proposed method is robust to frequency selectivity in wireless channels, and its performance is considerably improved compared with the available methods.