Dr Mahyar Shirvanimoghaddam

IEEE In this paper, we consider a massive grant-free nonorthogonal multiple access (GF-NOMA) scheme where devices have strict latency requirements and no retransmission opportunities are available. Each device chooses a pilot sequence from a predetermined set as its signature and transmits its selected pilot and data simultaneously. A collision occurs when two or more devices choose the same pilot sequence. Existing GF-NOMA schemes assume that a collision of at least one pair of users entails a collision for all simultaneously transmitting users, which is suboptimal in terms of individual outage and system throughput. For that, we propose a novel framework where collisions are treated as interference to the remaining received signals. With the aid of Poisson Point Processes and Ordered Statistics, we derive simplified expressions that can well approximate the outage probability and throughput of the system for both successive joint decoding (SJD) and successive interference cancellation (SIC). Numerical results verify the accuracy of our analytical expressions. For low data rate transmissions, results show that the performance of SIC is close to that of SJD in terms of outage probability, for packet arrival rates up to 10 packets per slot. However, SJD can achieve almost double the throughput of SIC and is, thus, far more superior.

IEEE Fifth-generation cellular mobile networks are expected to support mission critical URLLC services in addition to enhanced mobile broadband applications. This article first introduces three emerging mission critical applications of URLLC and identifies their requirements on end-to-end latency and reliability. We then investigate the various sources of end-to-end delay of current wireless networks by taking 4G LTE as an example. Then we propose and evaluate several techniques to reduce the end-to-end latency from the perspectives of error control coding, signal processing, and radio resource management. We also briefly discuss other network design approaches with the potential for further latency reduction.

© 2015 IEEE. This letter proposes a novel nonlinear constellation mapping (NLCM) scheme for the rate compatible modulation (RCM) approach in low-To-moderate signal to noise ratios (SNRs). In NLCM, each RCM coded symbol is mapped to a complexvalued amplitude phase shift keying (APSK) constellation point. Moreover, we provide a novelmethod of designing code degree and weight set for a wide SNR range. The proposed NLCM is developed to increase the throughput and decrease the peak to average power ratio (PAPR) at the same time. Both analysis and simulation results show that the NLCM scheme outperforms the original RCM in terms of throughput and PAPR.