In this paper, we study the random-access procedure for Ambient-IoT (A-IoT). Traditional approaches based on a slotted-ALOHA-like access over TDM/FDM resources suffer from sizable fraction of idled and/or collided resources, leading to reduced system throughput. To address this, we consider CDM of transmissions from multiple A-IoT devices, which enables detecting multiple A-IoT devices simultaneously in a TDM/FDM resource. CDM of A-IoT transmissions faces a number of challenges, including timing misalignment and loss of orthogonality, due to significantly higher sampling frequency offset (SFO) of low-complexity and low-power A-IoT devices, as compared to regular devices. We address these issues by adding a prefix or postfix to A-IoT transmissions and proposing a new multi-SFO hypotheses and successive interference cancellation (SIC) based reader processing. We show through simulations that CDM using the proposed approach is able to achieve significant gains in the system throughput over slotted-ALOHA-based schemes for A-IoT devices with high SFOs.

In this paper, we discuss UE power saving (PS) techniques for eXtended Reality (XR) applications in 5G NR system. XR traffic is characterized by pseudo periodic packet arrival, high bit rate, and low latency requirement. It is challenging to support such traffic in a small device form factor with limited battery size, e.g., head-mounted display (HMD) or XR glasses. Therefore, it is desired for 5G NR to support effective UE PS techniques. We first discuss a few PS techniques defined in 5G NR specifications Release 15 and 16. Then, we introduce new PS techniques that are evaluated via system level simulations with the UE power consumption model defined in a 3GPP. Evaluation results show that UE power consumption can be substantially reduced by the new PS techniques, up to 40%.

We present system-level evaluation results to characterize the performance of eXtended Reality (XR) applications over a 5G NR system. A split-rendering framework is assumed, where the XR device uses 5G to offload computation associated with rendering and encoding of video frames to an edge server. The XR traffic model includes rendered video frames on the downlink and user pose and control updates on the uplink. We present results for both sub-6 GHz (FR1) and millimeter-wave (FR2) bands. Additionally, we also discuss potential enhancements to further improve user experience for XR applications over 5G.

We investigate the benefits of channel-aware (opportunistic) scheduling of transmissions in ad hoc networks. The key challenge in optimizing the performance of such systems is finding a good compromise among three interdependent quantities: 1) the density of scheduled transmitters; 2) the quality of transmissions; and 3) the long term fairness among nodes. We propose two new channel-aware slotted CSMA protocols opportunistic CSMA and quantile-based CSMA (QT-CSMA) and develop new stochastic geometric models to quantify their performance in terms of spatial reuse and spatial fairness. When properly optimized, these protocols offer substantial improvements in performance relative to CSMA—particularly, when the density of nodes is moderate to high. In addition, we show that a simple version of QT-CSMA can achieve robust performance gains without requiring careful parameter optimization. The quantitative results in this paper suggest that channel-aware scheduling in ad hoc networks can provide substantial benefits which might far outweigh the associated implementation overheads.

We investigate the benefits of channel-aware (opportunistic) scheduling of transmissions in ad-hoc networks. The key challenge in optimizing the performance of such systems is finding a good compromise among three interdependent quantities, the density and channel quality of the scheduled transmitters, and the resulting interference at receivers. We propose two new channel-aware slotted CSMA protocols: opportunistic CSMA (O-CSMA) and quantile-based CSMA (QT-CSMA) and develop stochastic geometric models allowing us to quantify their performance in terms of spatial reuse and spatial fairness. When properly optimized these protocols offer substantial improvements in terms of both of these metrics relative to CSMA — particularly when the density of nodes is moderate to high. Moreover, we show that a simple version of QT-CSMA can achieve robust performance gains without requiring careful parameter optimization. The paper supports the case that the benefits associated with channel-aware scheduling in ad hoc networks, as in centralized base station scenarios, might far outweigh the associated overhead, and this can be done robustly using a QT-CSMA like protocol.

In this paper, we characterize the joint network capacity region (JNCR) for a licensed broadcast (primary) and ad hoc cognitive (secondary) network in a heterogeneous environment, including indoor and outdoor transmissions, under various spectrum (white space) detection techniques. Each technique delivers a different degree of RF-environment awareness - the more a device knows about its environment the larger the network capacity region. To quantify the gains, we develop a simple stochastic model capturing the interdependency amongst primary and secondary nodes and compare their joint capacity. Cognitive devices using the classical signal energy detection method are shown to perform poorly due to limitations on detecting primary transmitters in environments with indoor shadowing. This can be circumvented through direct use (e.g., database access) of location information on primary transmitters, or better yet, on that of primary receivers. The specific capacity trade-off between primary and secondary networks depends on white space detection techniques, resulting in JNCRs which range from complement convex to linear to (almost) convex. Our results show that, for example, the gain of positioning-assisted method over signal energy detection is 76% and the gain of receiver location-aware approach is 177% when the density of primary transmitters is 2 x 10^{-10}m^{-2}, the indoor shadowing level is -10dB, and the fraction of indoor nodes is 0.5. Furthermore we show that if cognitive devices have positioning information then the secondary network's capacity increases monotonically with increased indoor shadowing in the environment. These are the first analytical results quantifying, albeit for simple heterogeneous environmental model, the capacity gains one can expect when cognitive devices leverage additional information.

This paper considers the interplay between rate adaptation and inter-session network coding gains in wireless mesh or ad hoc networks. Inter-session network coding opportunities at relay nodes depend on packets being overheard by surrounding nodes ? The more packets nodes overhear, the more opportunities relays have to combine packets, resulting in a potential increase in network throughput. Thus, by adapting its transmission rate, a node can increase the range over which its packets are overheard, enabling additional opportunities for coding and increased overall throughput. This paper considers inter-session coding, restricted to a single relay (bottleneck) node, or star network topology. Even for such simple topologies the optimal joint rate adaptation and network coding policy is known to be NP-hard. Optimal rate vector selection is a combinatorial optimization problem, which is NP-hard, and finding optimal coding scheme turns out to be a clique partitioning problem which is also NP-hard. So, we provide heuristics to find a suboptimal rate vector and coding scheme. Additionally, we provide a linear programming formulation for network coding when only pairwise intersession coding is allowed. We evaluate the averaged throughput in two different scenarios, in which relays have different access opportunities, giving some intuition on the impact of rate adaptation in lightly and heavily loaded systems. The gains of joint rate adaptation and network coding are marginal when the relay has a higher access opportunity than other nodes, or when the MAC operates ideally it ranges from 9% to 19% as compared to a network without network coding and 4% over a network using regular network coding. While, when the relay has equal access opportunity as other source nodes, which is more typical of todays MAC protocols under heavy loads, the gain ranges from 40% to 62% as compared to the standard relaying case and is upto around 20% as compared to a network with regular pairwise network coding. This can further be increased to a gain of 40% to 120% by replacing pairwise coding with sub-optimal general network coding scheme.

We propose an analytical framework that optimizes the performance of various Hybrid Automatic Repeat reQuest (HARQ) schemes in wireless packet data systems. The optimization framework lends itself to maximizing the user throughput without assuming a specific HARQ scheme, a target packet error rate, and a mapping of signal-to-interference-noise ratios (SINR) into modulation and coding scheme (MCS) sets. Thus, a user selects an optimal amount of redundancy bits used for retransmissions, an optimal packet error rate, and an optimal SINR-MCS mapping such that the user throughput would be maximized. We show that there exists an optimal redundancy block size of incremental redundancy (IR) scheme when the number of retransmissions is limited, while as small as possible redundancy size is optimal when the number of retransmissions is unlimited. Our analytical results are verified through extensive simulations of the IEEE 802.16e system.

In this paper, a new slotted mode operation in a cdma2000 wireless system is proposed. The proposed operation is designed to support emerging services such as Push-To-Talk(PTT) that require low paging delay and low power consumption. The proposed operation tries to minimize the paging delay and maximize battery life while using the same amount energy as that of legacy reduced slot cycle mode with the assumption that the inter-arrival time of a PTT call follows an exponential distribution. In the performance analysis, it is shown that the average paging delay can be reduced or battery life can be reduced.