On the design of multiuser codebooks for uplink SCMA systems

Sparse code multiple access (SCMA) is a promising uplink multiple access technique that can achieve superior spectral efficiency, provided that multidimensional codebooks are carefully designed. In this letter, we investigate the multiuser codebook design for SCMA systems over Rayleigh fading channels. The criterion of the proposed design is derived from the cutoff rate analysis of the equivalent multiple-input multiple-output system. Furthermore, new codebooks with signal-space diversity are suggested, while simulations show that this criterion is efficient in developing codebooks with substantial performance improvement, compared with the existing ones

The Antiquity of the Avesta

Paper read before the Bombay Branch of the Royal Asiatic Society, read 26th June 1896. Dr. Gerson Da Cunha in the Chair

Multiplexing eMBB and URLLC in wireless powered communication networks: a deep reinforcement learning-based approach

This paper investigates the multiplexing of enhanced mobile broadband (eMBB) and ultra-reliable low-latency communications (URLLC) services in a wireless powered communication network, where a hybrid access point coordinates the wireless energy transfer (WET) to users and receives information from them. The preemptive puncturing is adopted to multiplex URLLC traffic onto eMBB transmission. Apart from the energy used for wireless information transmission (WIT), the rest energy in user’s battery is reserved to avoid insufficient energy for future WIT. The problem is formulated to jointly allocate subcarriers, time, and energy to maximize the uplink eMBB sum rate under the constraints of URLLC latency, radio frequency to direct current (RF/DC) sensitivity, user’s battery capacity, and subcarriers availability. We propose a deep reinforcement learning-based approach named mixed deep deterministic policy gradient (Mixed-DDPG), which decomposes the optimization problem into a discrete subproblem for subcarriers allocation and a continuous subproblem for time and energy allocation, and solves them alternately. Numerical results show that the proposed algorithm achieves a higher eMBB sum rate than the existing schemes

User-centred design of flexible hypermedia for a mobile guide: Reflections on the hyperaudio experience

A user-centred design approach involves end-users from the very beginning. Considering users at the early stages compels designers to think in terms of utility and usability and helps develop the system on what is actually needed. This paper discusses the case of HyperAudio, a context-sensitive adaptive and mobile guide to museums developed in the late 90s. User requirements were collected via a survey to understand visitors’ profiles and visit styles in Natural Science museums. The knowledge acquired supported the specification of system requirements, helping defining user model, data structure and adaptive behaviour of the system. User requirements guided the design decisions on what could be implemented by using simple adaptable triggers and what instead needed more sophisticated adaptive techniques, a fundamental choice when all the computation must be done on a PDA. Graphical and interactive environments for developing and testing complex adaptive systems are discussed as a further step towards an iterative design that considers the user interaction a central point. The paper discusses how such an environment allows designers and developers to experiment with different system’s behaviours and to widely test it under realistic conditions by simulation of the actual context evolving over time. The understanding gained in HyperAudio is then considered in the perspective of the developments that followed that first experience: our findings seem still valid despite the passed time

XR-RF Imaging Enabled by Software-Defined Metasurfaces and Machine Learning: Foundational Vision, Technologies and Challenges

We present a new approach to Extended Reality (XR), denoted as iCOPYWAVES, which seeks to offer naturally low-latency operation and cost-effectiveness, overcoming the critical scalability issues faced by existing solutions. iCOPYWAVES is enabled by emerging PWEs, a recently proposed technology in wireless communications. Empowered by intelligent (meta)surfaces, PWEs transform the wave propagation phenomenon into a software-defined process. We leverage PWEs to i) create, and then ii) selectively copy the scattered RF wavefront of an object from one location in space to another, where a machine learning module, accelerated by FPGAs, translates it to visual input for an XR headset using PWEdriven, RF imaging principles (XR-RF). This makes for an XR system whose operation is bounded in the physical layer and, hence, has the prospects for minimal end-to-end latency. Over large distances, RF-to-fiber/fiber-to-RF is employed to provide intermediate connectivity. The paper provides a tutorial on the iCOPYWAVES system architecture and workflow. A proof-of-concept implementation via simulations is provided, demonstrating the reconstruction of challenging objects in iCOPYWAVES produced computer graphics