Abstract-Although there has been a growing literature on cooperative diversity, the current literature is mainly limited to the Rayleigh fading channel model, which typically assumes a wireless communication scenario with a stationary base station antenna above rooftop level and a mobile station at street level. In this paper, we investigate cooperative diversity for intervehicular communication based on cascaded Nakagami fading. This channel model provides a realistic description of an intervehicular channel where two or more independent Nakagami fading processes are assumed to be generated by independent groups of scatterers around the two mobile terminals. We investigate the performance of amplify-and-forward relaying for an intervehicular cooperative scheme assisted by either a roadside access point or another vehicle that acts as a relay. Our diversity analysis reveals that the cooperative scheme is able to extract the full distributed spatial diversity. We further formulate a power-allocation problem for the considered scheme to optimize the power allocated to the broadcasting and relaying phases. Performance gains up to 3 dB are obtained through optimum power allocation, depending on the relay location.

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Reconfigurable intelligent surface (RIS)-based transmission technology offers a promising solution to enhance wireless communication performance cost-effectively through properly adjusting the parameters of a large number of passive reflecting elements. This letter proposes a cosine similarity theorem-based low-complexity algorithm for adapting the phase shifts of an RIS that assists a multiple-input multiple-output (MIMO) transmission system. A semi-analytical probabilistic approach is developed to derive the theoretical average bit error probability (ABEP) of the system. Furthermore, the validity of the theoretical analysis is supported through extensive computer simulations.Index Terms-Reconfigurable intelligent surfaces (RISs), multiple-input multiple-output (MIMO), cosine similarity theorem. I. INTRODUCTIONT HE fifth generation (5G) wireless communication technology promises an explosive growth on data rate, massive connectivity and latency performance. To achieve these goals, various transmission technologies have been developed in recent years. Massive multiple-input multiple-output (MIMO) and milimeter wave (mmWave) communication systems are considered as some of the prominent candidates among these technologies. On the other hand, to meet this challenge beyond 5G requirements, utilization of an increasing number of multi-antenna systems has raised strong concerns about the energy efficiency and hardware cost of large-scale MIMO systems.Recently, reconfigurable intelligent surface (RIS)-assisted communication technology has been considered as a promising solution to overcome the energy efficiency related issues of future wireless networks [1]-[3]. An RIS is a planar metasurface that consists of a number of low-cost passive reflecting elements, each of which smartly induces an independent phase shift to modify the propagation environment in more favorable way for the communication performance [4].The unprecedented potential of RISs on the signal quality of a communication system has led researchers to largely consider the RIS technology in various frontiers. In one of the early studies [3], the error performance of an RIS aided singleinput single-output (SISO) system is investigated through a Z. Yigit and Ibrahim Altunbas are with the

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We consider the design of convolutional codes and low-density parity-check (LDPC) codes with minimum-shift keying (MSK) when the receiver employs iterative decoding and demodulation. The main idea proposed is the design of coded schemes that are well matched to the iterative decoding algorithm being used rather than to hypothetical maximum-likelihood decoding. We first show that the design is crucially dependent on whether the continuous phase encoder (CPE) is realized in recursive form or in nonrecursive form. We then consider the design of convolutionally coded systems and low density parity check codes with MSK to obtain near-capacity performance. With convolutional codes, we show that it is possible to significantly improve the performance by using a mixture of recursive and nonrecursive realizations for the CPE. For low density parity check codes, we show that codes designed for binary phase shift keying are optimal for MSK only if the nonrecursive realization is used; for the recursive realization, we design new LDPC codes based on the concept of density evolution. We show that these codes outperform the best known codes for MSK and have lower decoding complexity.

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