Optimal Power Control Law for Equal-Rate DS-CDMA Networks Governed by a Successive Soft Interference Cancellation Scheme

Abstract

This paper studies the throughput maximization of a dense multiple access network of low-rate subscribers that share the same practical Forward Error Correction (FEC) code and modulation scheme, and transmit to a central node that implements a Successive Soft Interference Cancellation (soft SIC) strategy in order to mitigate Multiple Access Interference (MAI). In the user-asymptotic case, we make use of Variational Calculus (VC) tools to derive, in terms of the Packet Error Rate (PER) of the shared encoder and the Residual Energy (RE) from imperfect cancellation, the optimum energy profile that maximizes the network spectral efficiency, when a sum power constraint at the SIC input is enforced. Comparative performance analyses using a representative encoder are carried out. Simulation results show the benefit of the adopted soft SIC scheme in front of other SIC strategies, obtaining relevant throughput gains under high traffic loads.

Energy and Rate Allocation for Massive Multiple Access With Interference Cancelation

“…• For a variety of cases, we prove the existence of piecewise smooth allocation functions satisfying the stationary point equations of the spectral efficiency maximization problem. We fill the void in the existing literature [27]- [30], [33], [35]- [37] by considering several encoder sets with coding schemes achieving optimal first-and secondorder coding rates, and by exploring the best unbalance in terms of users' energy, rate, and reliability. Remarkably, we extend previous works by studying in-depth the threeway unbalance between the above magnitudes.…”

Joint Energy and Rate Allocation for Successive Interference Cancellation in the Finite Blocklength Regime

“…Spread spectrum modulation, appropriate at low peak-to-average transmission power ratios (PAPR), is adopted, using long spreading codes (their period far exceeding symbol duration) with common processing gain N . The aggregate signal (1) is first received by a transparent satellite: and roll-off factor , and ⌧ [k] ⇡ ⌧ a common userdelay under quasi-synchronous access [12], [13]. Directive antennas with line-of-sight transmission are assumed.…”

“…Specifically, an imperfect packet SIC policy [12] is considered (the non-persistent version of [17]), in which users are sequentially decoded, re-modulated (when successfully decoded) and canceled from the input signal. We reasonably assume, for system modeling, two characteristic curves known for each M i : (i) the PER curve of the decoding system; (ii) the associated average residual energy (RE) function modeling the accuracy of estimationcancellation [13]. Respectively, PER[ , R i ] and "( , R i ), both bivariate functions of the SINR and the encoder's rate R i .…”

“…Capacity-achieving encoders (unbounded packet length) were employed, for which a single SIC iteration suffices to decode all users. In [12], [13], specific hard/soft SIC policies were analyzed when all users adopted the same Work supported by project TEC2016-76409-C2-1-R (WINTER): Ministerio de Ciencia, Innovación y Universidades (Spanish administration), and the Catalan administration (AGAUR) under grants 2017 SGR 578 and FI-2018.…”

“…We have considered instead, for system optimization, a satellite scenario that consists of a massive user network operating with an on-board relay transponder and a SIC ground gateway for demodulation [12]. The network users adjust their transmitted power and select an appropriate finite blocklength encoder from the available set (instead of adopting a common encoder as in [12], [13]). Our main contribution is the corresponding joint optimization of the power control law, the per-user transmission rate and the SIC decoding order that maximize the system SE when the useful received power at the satellite is set to a fixed operating point.…”