The design and development of sub-Terahertz (sub-THz) cellular systems entail the need for new channel models that can precisely predict channel characteristics beyond 100GHz in outdoor and dynamic environments. This work proposes a novel multiple-input and multiple-output (MIMO) channel model for cellular communication, developed within the framework of a class of spatio-temporal stochastic processes called ambit-process. The modeling methodology effectively captures the typicalities of sub-THz propagation like molecular absorption and scattering of the evolving multipaths while accounting for the propagation delay of electromagnetic waves across large array apertures deployed at the transmitter and the receiver. This allows for an accurate characterization of the spatial-wideband effect along with other relevant spatio-temporal attributes of the channel. Numerical simulations indicate a good level of agreement between the spectral efficiency and spatio-temporal correlation of the proposed model against a state-of-the-art stochastic Terahertz (THz) channel model and measurements reported in the literature.

The design and development of Terahertz (THz) and sub-Terahertz (sub-THz) communication systems entail the need for new channel models that can precisely predict channel attributes at such frequencies (≥100 GHz) in outdoor and dynamic environments. This work proposes a novel hybrid-stochastic ultra-wideband channel model for sub-THz bands, developed within the framework of a class of spatio-temporal stochastic processes called the ambit-process. The proposed model is capable of supporting bandwidths of upto 1 GHz. The spatio-temporal evolution of the ambit framework allows for a spatially consistent, reasonably accurate and tractable characterization of the fading statistics and multipath propagation of the cellular channels. We leverage a recently proposed convolution-based low-complexity algorithm with necessary modifications to study key features of the microcellular sub-THz channel like associated diffused reflection and scattering, molecular absorption, spatio-temporal correlations, and consistency between the time-evolving delay and Doppler of the multipaths. Simulation results on path loss, shadowing, delay spread, and channel correlations indicate that the ambit model accurately captures the typicalities of an urban microcellular sub-THz channel and agrees well with the measurement results reported in the literature.

To provide coverage to the network devices distributed all over the globe, non-terrestrial networks (NTNs) have been recognized to complement and extend the terrestrial network to remote areas. The Low Earth Orbit (LEO) NTNs face several unprecedented challenges over 5G-NR protocol due to high differential delay and Doppler shifts which drastically impacts the performance of NR-NTN users. In this work, we investigate the impact of large differential delay and Doppler shifts within a NTN cell on the 5G-NR resource allocation and medium access control (MAC) protocol. We then propose an uplink zone-based scheduling technique to address the high differential delay and Doppler shifts for LEO satellites for LEO satellite-based NTNs. Finally, we validate the performance of the proposed strategy by comparing it with the conventional 5G-NR protocol through numerical simulations over the recently developed Samsung’s NR-NTN System Level Simulator.

MultiSIM feature offers convenience to a user by providing connection to multiple operators for accessing different services through different SIMs with a User Equipment (UE). Generally, MultiSIM is deployed as a Dual Subscriber-Identity-Module (SIM) Dual Standby (DSDS) feature; sharing transceiver with secondary SIM (SIM-2), while primary SIM (SIM-I) is on an active data session with Operator-1. The sharing of transceiver (called tune away), causes inactivity on the Radio Link (RL) between UE and eNodeB (eNB) leading the Physical Channel Resource (PCR) wastage for Operator -1. Multi SIM Multi Standby (MSMS) feature is an enhancement over DSDS to scale up the usage with three or more SIMs with single transceiver. With MSMS deployment, PCR wastage will scale up as compared to DSDS, as it additionally introduces more challenges, like (a) increased number of tune away events due to more than two SIMs, (b) increase in tune away duration due to a cascading effect of simultaneous and back-to-back high priority procedures on secondary SIMs. MSMS will thus affect by increasing the backhaul retransmissions and buffering at Operator -1. To overcome the above challenges and to ensure MSMS is a reality soon, to the best of our knowledge for the first time, this paper proposes a new signaling via Non Access Stratum (NAS) layer, from UE to Evolved Packet Core (EPC) to indicate tune away when the duration of tune away spans several seconds. We propose to apply NAS signaling in a scenario specific manner to address tune away events. Through extensive simulation derived from mathematical modeling and measurements obtained from test bed with commercial UEs, the results reveal that for three SIMs in cascaded scenarios, with the proposed solution, the PCR wastage is reduced to only 7.9 % against 48.5% and eNB buffering reduced by 95% in comparison to the available literature for a practical deployment.

A user equipment (UE) with Dual Subscriber-identity-module (SIM) Dual Standby (DSDS) feature can connect to two network operators, such as, each SIM is associated with one operator and with one Protocol Software Stack (PSS) while both the SIMs share same Radio Frequency Integrated Circuit (RFIC). UE schedules SIM-1 to communicate with Operator-1 and at the same time SIM-2 remains standby and vice versa. The ongoing data session with Operator-1, through SIM-1 is interrupted while the UE's RFIC tunes away to attend a higher priority signaling through SIM-2 to Operator-2. This tune away procedure of RFIC results in allocated Physical Channel Resource (PCR) wastage at Operator-1 for SIM-1 during the tune away period. After the end of tune away at SIM-1, it further more suffers from low PCR allocation from Operator-1, because of no response from SIM-1 during tune away period. To overcome the above challenges, to the best of our knowledge, for first time this paper proposed Signaling indication from UE to network for RFIC tune away event to reduce network PCR wastage. This signaling is done by: (a) Radio Resource Control (RRC) layer (b) Medium Access Control (MAC) layer (c) Layer 1 (L1). Each of the above-mentioned signaling has particular level of latency and reliability. We propose to apply above-mentioned signaling in scenario specific manner to address all possible tune away events. Through extensive simulation derived from mathematical modelling and measurements obtained from test bed with commercial DSDS UEs, the results reveal an improvement in overall PCR utilization for an operator and increase in UE admission by up to 30% in comparison with current DSDS solutions.

Augmented reality (AR), virtual reality (VR), health and payments are fueling the next wave of cellular connected smart devices leading to increased number of user equipment (UE) per person. This trend of multiple devices per user and his frequent needs to transfer on going session(s) from one smart device to another opens up several challenges for cellular technology, like: (a) managing separate operator subscription for each UE, (b) supporting low latency for session transfer, and (c) supporting seamless change of smart device after session transfer. In literature, session transfers one at a time from a source UE (S_UE) to a target UE (T_UE) using Session Initiation Protocol (SIP), with high latency of the order of several seconds per session and significant power consumption on every T_UE. We present a Session Cloning Protocol (SCP), which to the best of our knowledge is novel and first of its kind to provide low latency and low power consumption for session transfer between smart devices. SCP proposes using a peer-to-peer (P2P) link to share the required connectivity parameters from S_UE to a proximate T_UE. SCP contributes the following: (a) Session transfer from S_UE to T_UE when T_UE was offline at beginning of session transfer initiation, and S_UE was in connected state with one or more sessions. (b) State and parameter transfer from S_UE to T_UE, when T_UE was offline and S_UE was either in idle or out of coverage states, and (c) Upgrading/Downgrading of Quality of Service (QoS) of the transferred session(s) at T_UE when its capability is higher/lower than S_UE respectively. The simulation reveals that SCP reduces the latency of session transfer by over 90%, and energy consumption by over 99% as compared to SIP based session transfer.

Global mobile traffic pattern is recently experiencing a paradigm shift largely influenced by the exponentially growing social networking services. These services are uniquely characterized by bandwidth-intensive asynchronously accessed multiple-object based popular contents. Traditional mobile networks have not been designed to cater to these new requirements. Consequently, in 5G networks there is a need to bring in novel architectural enhancements directed towards efficient network performance in terms of service delivery. Previous works in literature have proposed edge node caching based approaches. However, the treatment is not pragmatic as it is not linked opportunistically with contents and delivery methods diversity. In this paper, first we present a service-level multi-connectivity approach that leverages the combined potential of multicast and unicast in disseminating contents/sub-contents. Further, we extend the approach to build a unified service delivery framework while incorporating proximal Device-to-Device (D2D) clusters and relay systems. We propose a bandwidth resource effective method of initial spreading of cache-able contents via multicast delivery and provide an algorithm for selecting caching devices directed to maximize the coverage of contents along with optimizing resource cost and latency performance for the network. We show with simulation results the proposed system brings significant performance gains over previous approaches for both synchronous and asynchronous contents.