Random access scheduling for ambient IoT devices

Abstract

The present disclosure provides a method and system for energy- aware random access scheduling and resource allocation in wireless networks comprising ambient Internet of Things (IoT) devices. A paging signal is broadcast by a network entity, defining a time-frequency contention grid used by ultra-low power, battery-less devices to transmit random access messages via a slotted ALOHA protocol. Each message includes a unique device identifier, energy status, and message size. The network processes these messages to detect contention outcomes and allocates communication resources accordingly. Devices receiving acknowledgment (ACK) proceed with uplink transmission, while those receiving negative acknowledgment (NAK) reattempt access based on a probabilistic backoff scheme with a retry limit. The number of contention slots is dynamically optimized based on network load, latency goals, and energy constraints to minimize collisions and improve scalability. The invention enables efficient, fair, and low-power communication in dense IoT deployments, particularly within massive Machine-Type Communication (mMTC) scenarios in 5G and 6G networks.

Description

[0001] RANDOM ACCESS SCHEDULING FOR AMBIENT IOT DEVICES

[0002] Field of the Invention

[0003] The present disclosure relates to wireless communication systems, and more particularly, to random access scheduling and resource allocation techniques for densely deployed Ambient Internet of Things (IoT) devices in advanced 5G and next-generation 6G networks, particularly within the context of massive Machine-Type Communication (mMTC) scenarios.

[0004] Background of the Invention

[0005] Wireless communication systems are undergoing rapid evolution to support the increasing demand for massive connectivity. In next-generation networks such as Fifth Generation (5G) and future Sixth Generation (6G) systems, the infrastructure is expected to accommodate billions of connected devices. A significant portion of this connectivity growth arises from ultra-low-power and intermittently active devices used in massive Machine-Type Communication (mMTC) scenarios. These devices are typically constrained in terms of energy availability and communication capability, necessitating novel approaches for efficient and scalable network access.

[0006] Ambient Internet of Things (Ambient IoT) technology has emerged as a promising paradigm to support battery-less communication in such scenarios. Ambient IoT devices utilize backscatter communication techniques to transmit data by reflecting existing radio frequency (RF) signals and harvesting energy from them. This approach enables long-term deployment without requiring conventional batteries or active RF circuitry, thereby reducing cost and maintenance requirements. However, the absence of dedicated energy sources and conventional transceivers imposes significant limitations on communication management and access protocols, especially when large numbers of such devices attempt to access the network concurrently.

[0007] In dense network environments, the simultaneous access attempts by numerous Ambient IoT devices lead to high levels of contention for limited channel resources. Due to their energy-constrained nature, these devices are generally incapable of performing complex coordination procedures or supporting continuous connectivity. As a result, traditional medium access control (MAC) schemes such as ALOHA or Carrier Sense Multiple Access with Collision Avoidance (CSMA / CA) are either inefficient or impractical in such contexts. These methods often result in high collision rates, reduced throughput, increased latency, and unfair access distribution among devices with varying energy and timing characteristics.

[0008] Existing backscatter-based communication systems are generally designed for low-density environments and often employ single-tag interrogation, fixed polling schedules, or rigid slot allocations. Such techniques are not adaptable to the dynamic and bursty communication patterns characteristic of large-scale Ambient IoT deployments. Moreover, these systems typically lack mechanisms to ensure fairness, manage resource contention, or optimize throughput under variable load conditions. Consequently, the performance of current systems deteriorates significantly under high-density deployments, leading to inefficient spectrum utilization and unreliable service delivery.

[0009] Therefore, there exists a need for an access control and scheduling mechanism specifically designed for large-scale Ambient IoT networks operating under tight energy and timing constraints. Such a mechanism should provide scalable and energy-aware random access, mitigate contention-induced collisions, and ensure fair distribution of resources among heterogeneous devices. The system should minimize the computational and communication overhead at the device side, while enabling intelligent scheduling and dynamic resource allocation at the network side. These objectives are essential to achieve low-latency, high-throughput, and equitable communication in dense Ambient IoT environments.

[0010] Objective of the Invention

[0011] The principal objective of the present invention is to provide a method, system, and device architecture for intelligent and energy-aware random-access scheduling and resource allocation in wireless communication systems supporting ambient Internet of Things (IoT) devices. Another object of the invention is to support reliable and scalable communication between a network entity and a large population of ultra-low power or battery-less IoT devices in massive Machine Type Communication (mMTC) deployments using a contention-based protocol.

[0012] Another object of the invention is to dynamically optimize the number of contention time slots to reduce both per-device communication latency and overall network completion time, while managing collisions in slotted ALOHA-based access.

[0013] Another object is to incorporate device-level parameters such as harvested energy, retry count, and data size into the access scheduling and prioritization process, thereby enhancing efficiency and fairness.

[0014] Another object of the invention is to minimize repeated access collisions by adaptively adjusting contention resources based on observed network load and access success history.

[0015] Another object is to enable probabilistic reattempt mechanisms with bounded retry limits for devices receiving negative acknowledgment (NAK), thereby preventing persistent failures and supporting fairness among devices with different energy states.

[0016] A further object is to allow slot-frequency pair selection by devices through pseudorandom logic seeded by unique device identifiers, reducing access contention without requiring complex coordination or synchronization. A further object of the invention is to offer a lightweight and flexible scheduling framework that is compatible with ambient IoT hardware constraints and scalable to dense deployments in 5G advanced and 6G wireless systems.

[0017] Summary of the Invention

[0018] This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

[0019] The present invention provides a method, system, and device for energy-aware and scalable random access scheduling in wireless networks supporting a large number of ultra-low power, battery-less ambient Internet of Things (IoT) devices. The invention is particularly well-suited for dense massive Machine-Type Communication (mMTC) scenarios in advanced 5G and emerging 6G networks.

[0020] In one aspect, a network entity, such as a base station or relay node, transmits a paging signal that defines a two-dimensional contention grid composed of multiple time domain slots and frequency subcarriers. Upon harvesting sufficient energy from an RF carrier signal, ambient loT devices decode this paging signal and initiate random access by selecting a slot-frequency pair and transmitting a random access message (Msg1) using a slotted ALOHA protocol. Each Msg1 includes a device-specific random identifier, an indication of energy status, and an optional data size indicator.

[0021] The system processes incoming access messages to determine successful contention and allocates uplink resources to a selected subset of devices. Scheduling responses include acknowledgment (ACK) for successful contenders and negative acknowledgment (NAK) for failed ones. Devices receiving a NAK apply a probabilistic backoff mechanism and are permitted to reattempt access within a bounded retry limit.

[0022] A key feature of the invention is the dynamic optimization of the number of contention slots, which is adjusted based on the number of active devices, average device delay, and overall access latency. This adaptive grid scaling reduces collision probability and access latency under varying network loads. The system may also incorporate feedback-driven contention control based on observed collision patterns. Additionally, devices employ pseudorandom selection logic seeded with device identifiers to reduce repeated slot collisions.

[0023] Further, the invention enables prioritization based on weighted factors such as energy level, message urgency, and historical access outcomes, ensuring fairness among heterogeneous devices. The proposed framework requires minimal device-side complexity and is designed to operate within the energy constraints of battery-less devices relying on RF energy harvesting. Through these mechanisms, the invention achieves robust, fair, and efficient random access, significantly improving network scalability and reliability in dense ambient IoT environments while remaining compatible with low-power and decentralized device architectures.

[0024] The foregoing general description of the illustrative embodiments and the following detailed description thereof are merely exemplary aspects of the teachings of this disclosure and are not restrictive.

[0025] Brief description of the drawings

[0026] The figures described below depict various aspects of the system and methods disclosed herein. It should be understood that each figure depicts an embodiment of a particular aspect of the disclosed system and methods, and that each of the figures is intended to accord with a possible embodiment thereof. Further, wherever possible, the following description refers to the reference numerals included in the following figures, in which features depicted in multiple figures are designated with consistent reference numerals.

[0027] Non-limiting and non-exhaustive examples are described with reference to the following figures.

[0028] Fig. 1 illustrates a wireless communication system for Ambient Internet of Things (IoT) devices (100), according to aspects of the present disclosure. Fig. 2 depicts the wireless communication system of Fig. 1 with multiple Ambient IoT devices (200), according to an embodiment.

[0029] Fig. 3 illustrates charging and communication between a reader and a device at every slot (300), according to aspects of the present disclosure.

[0030] Fig. 4 illustrates a flow diagram of communication from MsgO to Msg4 between reader and device (400), according to aspects of the present disclosure.

[0031] Fig. 5 depicts the structure of a MsgO signal transmitted by a reader in a wireless communication system, according to an embodiment Fig. 6 illustrates the structure of a Msg1 signal and time-frequency resource allocation for multiple devices, according to aspects of the present disclosure.

[0032] Fig. 7 depicts a flowchart for a slotted aloha-based multiaccess communication process, according to an embodiment.

[0033] Figure 8 illustrates a method (800) for performing energy-aware random access scheduling in a wireless communication system comprising a plurality of ultra-low power, battery-less ambient internet of Things (loT) devices, according to aspects of the present disclosure.

[0034] Figure 9 illustrates the system architecture (900) for an energy-aware wireless communication system designed to facilitate random access scheduling among a large number of ultra-low power, battery-less ambient Internet of Things (loT) devices, according to aspects of the present disclosure. Persons skilled in the art will appreciate that elements in the figures are illustrated for simplicity and clarity and may have not been drawn to scale. For example, the dimensions of some of the elements in the figure may be exaggerated relative to other elements to help to improve understanding of various exemplary embodiments of the present disclosure.

[0035] Throughout the drawings, it should be noted that like reference numbers are used to depict the same or similar elements, features, and structures.

[0036] Detailed Description of the Invention

[0037] The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of exemplary embodiments of the invention as defined by the claims and their equivalents. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary.

[0038] Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope and spirit of the invention. In addition, descriptions of well-known functions and constructions are omitted for clarity and conciseness.

[0039] The terms and words used in the following description and claims are not limited to the bibliographical meanings but are merely used by the inventor to enable a clear and consistent understanding of the invention. Accordingly, it should be apparent to those skilled in the art that the following description of exemplary embodiments of the present invention are provided for illustration purpose only and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.

[0040] It is to be understood that the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a component surface” includes reference to one or more of such surfaces.

[0041] By the term “substantially” it is meant that the recited characteristic, parameter, or value need not be achieved exactly, but that deviations or variations, including for example, tolerances, measurement error, measurement accuracy limitations and other factors known to those of skill in the art, may occur in amounts that do not preclude the effect the characteristic is intended to provide.

[0042] Figures discussed below, and the various embodiments used to describe the principles of the present disclosure in this patent document are by way of illustration only and should not be construed in any way that would limit the scope of the disclosure. Those skilled in the art will understand that the principles of the present disclosure may be implemented in any suitably arranged system. The terms used to describe various embodiments are exemplary. It should be understood that these are provided to merely aid the understanding of the description, and that their use and definitions, in no way limit the scope of the invention. Terms first, second, and the like are used to differentiate between objects having the same terminology and are in no way intended to represent a chronological order, unless where explicitly stated otherwise. A set is defined as a non-empty set including at least one element.

[0043] The present disclosure relates to wireless communication systems supporting ambient Internet of Things (IoT) devices, with a focus on random access scheduling and resource allocation in dense, battery-less deployments. In particular, the invention addresses communication challenges in massive Machine Type Communication (mMTC) scenarios as expected in advanced 5G and emerging 6G networks. Ambient IoT devices are typically energy-constrained and rely on RF energy harvesting, making conventional random access mechanisms inefficient or inapplicable due to collision-prone behavior, latency, and lack of energy-awareness.

[0044] To address these limitations, the invention provides a system in which a network node, such as a base station or relay, transmits a paging signal that contains resource allocation parameters for slotted ALOHA-based random access. Ambient IoT devices harvest energy from a carrier wave (CW) signal transmitted by the network node, decode the paging signal, and randomly select a slot-frequency pair to transmit a Msg1 access request. Each message includes a unique random identifier and energy status. The base station uses this information to allocate dedicated communication resources and determine ACK / NAK feedback. Devices with NAK responses may retry based on probabilistic backoff and a retry limit. This framework supports energy-aware scheduling, minimizes collisions, and enables scalable communication among thousands of devices with minimal maintenance and power overhead.

[0045] Figure 1 illustrates an example wireless communication scenario involving a base station (BS) and a single battery-less ambient Internet of Things (IoT) device (100). In this configuration, the base station communicates with one device at a time, which is representative of a traditional or basic polling-based interaction model.

[0046] The base station first transmits a carrier wave (CW) signal, which is used by the ambient IoT device to harvest energy. Although traditionally used to carry modulated data, in this context, the carrier wave is unmodulated and serves solely as a power source for the battery-less device. This harvested energy powers the device’s internal circuitry and enables it to participate in communication without requiring a dedicated battery. After harvesting sufficient energy, the device waits for a paging signal from the base station. This paging signal contains resource allocation information, such as time and frequency slots for random access attempts.

[0047] Upon receiving the paging signal, the device transmits a random access message using a slotted ALOHA protocol. This message may include a random identifier, energy status, and data size indicator. The base station receives and evaluates this message to determine whether the device can be granted access. If successful, it allocates dedicated uplink resources for data transmission. This figure serves to illustrate the fundamental point-to-point operation between a network node and an energy-constrained ambient loT device, forming the basis for more advanced scheduling and multi-device coordination mechanisms described in subsequent embodiments.

[0048] Figure 2 illustrates a wireless communication system where a base station (BS) communicates with multiple ambient Internet of Things (IoT) devices simultaneously. Unlike the single-device polling scenario shown in Figure 1, this figure represents a scalable, energy-aware multi-device access mechanism suited for dense deployments of battery-less IoT devices.

[0049] In this system, the base station broadcasts a carrier wave (CW) signal to provide RF energy, enabling ambient IoT devices to harvest power for operation. After energy harvesting, the base station transmits a paging signal that contains contention resource configuration information, such as time and frequency domain slots. Each device interprets this information and randomly selects a time-frequency pair within a defined contention grid to initiate communication.

[0050] The devices transmit random access messages (Msg1) using a slotted ALOHA protocol, embedding a random identifier, energy status, and optional data size indicator. The base station collects these access requests, identifies contention outcomes (success or collision), and selects a subset of devices for further communication. Devices that are successfully decoded receive an ACK along with uplink resource allocations, while devices that collide or fail receive a NAK and reattempt communication using a probabilistic backoff strategy.

[0051] The approach shown in this figure supports high device density, reduced collisions, and fairness in resource scheduling. The base station dynamically adjusts the number of contention slots and manages feedback to ensure energy-efficient and reliable access for thousands of ultra-low-power ambient IoT devices. This multi-device access framework offers significant improvements in scalability and responsiveness for massive Machine-Type Communication (mMTC) scenarios.

[0052] Figure 3 represents a cyclic communication structure between a base station and multiple ambient IoT devices, where each slot is composed of an ordered sequence of messages: MsgO to Msg4. This figure also illustrates interleaving carrier wave (CW) transmissions and well-defined guard periods (TGapX) for synchronization and processing.

[0053] As described, each communication slot begins with a CW signal (R: CWTx) that allows ambient IoT devices to harvest the energy needed to operate. This is followed by the paging signal (MsgO) sent over the Physical Downlink Channel (PRDCH). MsgO includes contention resource configuration essentially telling devices how and when to access the network.

[0054] Devices that have harvested sufficient energy respond by transmitting Msg1 over the Physical Uplink Channel (PDRCH) using a slotted ALOHA protocol. This message contains a random device ID, energy status, and data size information. After Msg1 is received, the base station processes these messages and sends back Msg2 (again via PRDCH), indicating uplink scheduling assignments for devices that successfully contended. The base station or reader sends a PRDCH for Msg2 transmission corresponds to one or multiple A-loT Msg1 received from different devices.

[0055] The selected devices then transmit Msg3 (their actual data) over the PDRCH, and the base station concludes the slot with a transmission of Msg4 over the PRDCH — an ACK / NAK message. Msg4 can be configured either to acknowledge only successful Msg3s or to explicitly identify both successes and failures.

[0056] Between each stage, specific guard intervals (TGapA-TGapS) are shown in the figure. These allow:

[0057] • Time for devices to switch between RX and TX modes.

[0058] • Time for the base station to process incoming data and prepare the next response.

[0059] • Synchronization of time-sensitive events between nodes with strict energy constraints.

[0060] This highly structured process depicted in Figure 3 enables continuous operation of large-scale ambient IoT networks by coordinating device access, minimizing collisions, managing retry logic, and ensuring that energy-aware behavior is maintained throughout each communication cycle. Figure 4 illustrates a message timing diagram (400) depicting the detailed, slot-wise interaction between a reader (e.g., a base station or user equipment acting as a relay) and a battery-less Ambient IoT device. The figure represents a complete communication cycle involving energy transfer, device discovery, random access, scheduling, data exchange, and acknowledgment, all synchronized using well-defined time intervals.

[0061] At the start of the cycle, the reader transmits a Carrier Wave (CW) signal for a period denoted as Tew, enabling nearby Ambient IoT devices to harvest sufficient RF energy to power their basic operations such as synchronization, message decoding, and backscatter-based transmission.

[0062] Once the devices are energized, the reader sends a paging signal (MsgO) during the interval To, which includes synchronization information (e.g., frame markers, midambles) and resource allocation parameters. This signal is critical for clock recovery and for notifying devices to begin the random access process.

[0063] Following a guard interval TGapA, which accommodates processing and propagation delays, each energized device transmits a random access message (Msg1) during T1. Msg1 includes:

[0064] • A randomly generated temporary device identifier

[0065] • The energy status of the device

[0066] • An indicator of data size to be sent

[0067] The reader uses the received Msg1 transmissions to identify and schedule eligible devices. After another processing interval TGapB, the reader sends Msg2 during T2specifying uplink resource grants such as time slots and frequency subcarriers. The base station or reader sends a PRDCH for Msg2 transmission corresponds to one or multiple A-loT Msg1 received from different devices. This enables collision-free scheduling of subsequent transmissions.

[0068] A further pause, TGapC, gives the devices time to prepare their transmissions. Each selected device then sends Msg3 during T3, which contains the actual uplink data payload. Msg3 is constructed with error-checking and synchronization fields (e.g., CRC, line coding, preamble / postamble), and is aligned with OFDM slot boundaries when applicable.

[0069] Upon receipt of Msg3, the reader processes and decodes the data during TGapD, then sends Msg4 in the interval T4. Msg4 includes either:

[0070] • An ACK, confirming successful data receipt and instructing the device to terminate its operation for the current cycle, or

[0071] • A NAK, prompting the device to retry in a future slot following a probabilistic backoff strategy.

[0072] Following this, a second CW transmission for Tew is initiated. This ensures that:

[0073] 1. Devices that failed in the current cycle can recharge for future attempts.

[0074] 2. Newly activated devices or those needing more energy can join the next communication cycle. The TGapS period serves as a reset gap, it ensures all operations (including device sleep, retries, or energy harvesting) are settled before the start of the next cycle. This maintains clean temporal separation between two successive MsgO~Msg4 exchanges.

[0075] Each message in the sequence (MsgO to Msg4) includes:

[0076] • A preamble, carrying a start-of-frame indicator and synchronization pattern.

[0077] • A postamble, marking the end of the message and ensuring reliable framing.

[0078] Figure 5 presents the structure of MsgO, which is the initial paging and synchronization message transmitted by a base station (or reader) to one or more Ambient IoT devices in a wireless communication system. This message plays a critical role in initiating the random access communication cycle and is broadcast over the Physical Reader-to-Device Channel (PRDCH).

[0079] The MsgO frame begins with a Preamble, which serves as a synchronization sequence. This portion enables ambient IoT devices to detect the start of the frame, acquire timing, and align with the base station’s transmission. Accurate detection of this preamble is essential for the subsequent decoding of control and data content.

[0080] Following the preamble, the PRDCH section includes both control information and data. The control information (Layer 1) defines key physical layer parameters necessary for decoding the transmission and preparing devices for subsequent access. This control section may include:

[0081] • Modulation and coding schemes, such as On-Off Keying (OOK- 1 / OOK-4) for modulation, and Manchester, Pulse Interval Encoding (PIE), or Miller encoding for line coding.

[0082] • M value, indicating the number of chips per OFDM symbol.

[0083] • Msg0 size, defining the length of the Msg0 message.

[0084] • Receiving method, specifying whether devices should use coherent or non-coherent detection.

[0085] • Midamble overhead, if any, for channel estimation and synchronization assistance.

[0086] • Time, frequency, and phase accuracy requirements to ensure robust demodulation.

[0087] • Repetition parameters at the bit, chip, or frame level, used to enhance decoding reliability for energy-constrained devices.

[0088] The data portion of PRDCH carries higher-layer (L2) information, particularly resource configuration for Msg1, including time slot distribution, frequency domain resource availability, and other scheduling instructions needed by devices to perform slotted ALOHA-based access.

[0089] After PRDCH, padding may be used to adjust the total message length to a fixed frame size, ensuring consistency across transmissions. This is useful for alignment with OFDM symbol boundaries and framing in time-frequency resource grids. The message concludes with a Postamble, which signifies the end of the message. It may contain guard sequences or end-of-frame markers and ensures that devices can determine when MsgO has fully concluded.

[0090] Figure 6 illustrates the structure and operation of Msg1 transmission by Ambient IoT devices in response to the reception of MsgO from a reader or base station. This figure integrates both the physical frame format of Msg1 and the corresponding time-frequency contention grid used in slotted ALOHA-based random access scheduling.

[0091] At the top, the Msg1 frame is shown with its key components. It begins with a Preamble, which allows the reader to detect, synchronize, and align with the incoming signal from the device. Following the preamble is the Physical Device-to-Reader Channel (PORCH), which includes two major parts: (1) Control Information, such as modulation and coding schemes (e.g., OOK, BPSK, BFSK), chip duration, midamble overhead, time / frequency / phase accuracy, and number of repetitions; and (2) Data, which includes higher-layer fields such as the device’s random identifier, energy status, and the Msg3 payload size. A Postamble follows the PORCH to signal the end of the transmission, and optional Padding may be added to ensure frame alignment.

[0092] The lower part of Fig. 6 expands this view into a two-dimensional contention grid, where the horizontal axis represents time divided into multiple contention occasions (Occasion #1, #2,..., Occasion #X), each consists of multiple TDMA time slots Xt, and the vertical axis denotes the available subcarrier frequencies (Fsc#1, Fsc#2..., Fsc#). Each rectangular cell in this grid corresponds to a unique time-frequency resource slot. After receiving MsgO, each ambient loT device randomly selects one cell (i.e., one subcarrier in one occasion) from this grid to transmit Msg1, forming the basis of the slotted ALOHA access mechanism.

[0093] The frequency domain resources Y can be computed in two ways: 1. Using guard band percentage:

[0094]

[0095] Where:

[0096] * B: Total channel bandwidth (e.g., 1 MHz).

[0097] * G%: Percentage of bandwidth reserved as guard bands.

[0098] ® Btx_D2R : Bandwidth used by each device's transmission.

[0099] 2. Using subcarrier spacing:

[0100]

[0101] This formula more precisely aligns with NR subcarrier spacing:

[0102] ® No. of RBs: Resource blocks allocated to devices.

[0103] « 12: Each RB contains 12 subcarriers in NR.

[0104] ® SCS: Subcarrier Spacing (e.g., 15 kHz, 30 kHz).

[0105] « The first term finds the leftover bandwidth after subtracting allocated subcarrier space. * Dividing by 2 distributes the guard band evenly on both sides.

[0106] ® Subtracting SCS / 2 ensures subcarrier alignment at grid edges.

[0107] In the context of slotted ALOHA-based random access scheduling for Ambient loT networks, the number of available time domain resources — denoted by X plays a crucial role in determining both system performance and device-level energy efficiency. Each device randomly selects one of these X.Xt time slots to transmit its random access request (Msg1), and the value of X.Xt directly influences the probability of collision, access latency, and overall system throughput.

[0108] To achieve optimal performance, the system must determine the maximum value of TDMA time slots to transmit Msg1 in one access occasion, denoted by Xt*, considering the device implementation complexity, device power consumption, individual device latency and inventory latency. Thus, the total number of TDMA time slots in X access occasions to transmit Msg1 is X*Xt. The optimization objective is to minimize a cost function that accounts for both per-device communication delay and the overall duration required to complete access for all participating devices. This is mathematically expressed as:

[0109] Xt*=argminX [(N×LD)+L]

[0110] Where N is the number of devices attempting to transmit Msg1, LD is the average latency experienced by a single device, and L represents the total inventory or system-level completion time. The optimization is subject to several practical constraints. First, the total inventory latency L must lie within acceptable system-defined boundaries:

[0111] Lmin ≤ L ≤ Lmax

[0112] Second, the total communication duration for each device in a selected access occasion, given by the product Xt-LD, must not exceed the device's available energy budget ED. This considers the device power consumption and ensures that energy-constrained ambient devices can complete their transmission without exhausting their harvested energy:

[0113] Xt-I_D< ED

[0114] Finally, the optimization accounts for the probability of reattempts due to collisions in shared slots. The system must maintain the reattempt probability Pre attempt below a tolerable threshold pr:

[0115] Pre-attempt “ Pr

[0116] This comprehensive optimization ensures that the number of contention slots is neither too few leading to high collision rates and reattempts nor too many which would increase per-device latency and system idle time. The outcome is an energy-aware, latency-efficient, and scalable access strategy suitable for dense Ambient loT deployments operating under severe power and bandwidth constraints.

[0117] Figure 7 presents a flowchart (700) outlining a slotted ALOHA-based random access mechanism designed to enable Ambient loT devices to initiate communication with a base station by transmitting Msg1. This method supports low-power, asynchronous access in dense loT deployments, minimizing collisions and ensuring scalability and fairness in time-frequency resource allocation.

[0118] The process begins when the Ambient loT device has a pending transmission (Msg1) containing its random ID, message size, and energy status. Initially, a transmission attempt counter K is set to zero (K=0). This counter tracks the number of attempts the device makes to send Msg1 in a given access cycle and ensures it does not exceed the maximum number of retries (X. Xt), helping avoid excessive contention.

[0119] The device then monitors the network to determine if the next communication slot has started. This slotted approach ensures synchronization with the base station’s communication window and avoids out-of-bound transmissions. Once a new slot begins, the device proceeds by randomly selecting a subcarrier index f within the available subcarrier range [1, Y]. This subcarrier (Fsct) is used for frequency division multiplexing, allowing simultaneous transmissions from multiple devices with reduced interference.

[0120] After selecting a subcarrier, the device sends Msg1 on the chosen frequency. The frame transmission is followed by a wait period of T = 2 TP, where TP represents the propagation delay. This duration accounts for the round-trip time required for the message to reach the base station and for the base station to respond with an acknowledgment (ACK). Following the wait period, the device checks whether an ACK has been received. If it has, the device considers the access attempt successful, terminates the process, and proceeds to await further instructions (e.g., resource grants via Msg2). If no ACK is received, it indicates either a failed transmission or a collision with another device. In the event of no ACK, the retry counter K is incremented by one. The device then checks whether K has exceeded the maximum number of allowed attempts (X. Xt). if so, the device aborts the current access attempt and waits for the next paging opportunity (MsgO) before trying again. If K is still within the allowed retry window, the device proceeds to calculate a backoff time before the next attempt.

[0121] The backoff is determined by selecting a random number t in the range [1, X-K], and the device waits for a period T = t x T

[0122]

[0123] where T1_min is the minimum duration required to send Msg1. This randomized wait ensures that retries are distributed across time, reducing the chances of repeated collisions among devices competing for the same time slot Once the backoff period concludes, the device loops back to the slotchecking stage and repeats the process if required. This randomized slotted ALOHA mechanism effectively supports concurrent access attempts from a large number of ultra-low power Ambient loT devices, which may be operating under strict energy and timing constraints.

[0124] This random-access mechanism is tightly integrated with the broader Ambient loT system architecture. Devices rely on energy harvesting (e.g., via continuous wave signals from the base station or user equipment) and may determine whether to proceed with access based on their available energy level. If energy is insufficient, the device may enter a sleep mode until it has recharged, thus optimizing power consumption. Additionally, devices maintain essential identifiers such as device ID and message size in non-volatile memory (e.g., EEPROM) and use baseband logic units comprising decoders, encoders, and controllers to manage modulation, timing, and state transitions. The Msg1 frame is typically modulated by backscatter using schemes such as ASK, PSK, or FSK, depending on system parameters like data rate, power efficiency, and channel conditions.

[0125] In another embodiment, the slotted ALOHA-based random access procedure may be enhanced by incorporating energy-aware contention resolution strategies and device-class-based retry control. These improvements allow the system to dynamically adapt to varying network densities, device priorities, and power availability conditions.

[0126] Specifically, the maximum retry limit X may not be uniformly applied across all devices. Instead, it can be pre-configured or dynamically broadcast within the paging message (MsgO) based on device classification. For example, latency-sensitive or mission-critical devices may be allocated higher retry budgets than delay-tolerant or low-priority sensors. This flexible retry cap ensures Quality of Service (QoS) differentiation while avoiding unnecessary congestion. Additionally, the backoff window may be further optimized by considering the device’s residual energy level. Rather than selecting the backoff delay purely at random, the device may weight the backoff timer based on energy availability, such that highly charged devices choose shorter delays to expedite access, while low-energy devices defer to preserve power and avoid collisions. This energy-aware randomization improves network efficiency and fairness in environments with heterogeneous energy harvesting profiles.

[0127] Moreover, in this embodiment, the frequency selection mechanism can be enhanced using a pseudorandom function seeded with the device ID and retry index, which ensures consistent and non-overlapping frequency assignments across retries. This method significantly reduces the probability of persistent collisions caused by repeated random choices in dense deployments.

[0128] The system may also implement adaptive slot management, where the base station (or reader) monitors real-time Msg1 collision rates and dynamically adjusts the number of available time-frequency contention cells in future paging windows. For instance, if excessive collisions are detected during a cycle, the base station may increase the value of X or reallocate more subcarriers for the next round, thereby providing more opportunities for successful access.

[0129] In some cases, the ACK / NAK feedback (Msg4) may include collision diagnostics or recommended delay indices, enabling devices to reattempt access more intelligently. Such feedback helps mitigate backoff synchronization problems where multiple devices repeatedly choose similar retry times, leading to repeated contention.

[0130] Furthermore, the ambient loT device may include a lightweight contention controller implemented in baseband, which tracks retry attempts, computes optimal backoff times, and maintains a collision history across paging cycles. This controller ensures that the retry process is not only energy-aware but also statistically diversified, improving throughput and reducing retry redundancy in large-scale deployments.

[0131] This embodiment enhances the base procedure by providing a more robust, adaptive, and energy-optimized access framework, maintaining scalability and collision resilience even as the number of Ambient loT devices increases to thousands or tens of thousands.

[0132] Figure 8 illustrates a method (800) for implementing energy-aware random access scheduling in a wireless network populated by ultra-low power, battery-less Ambient Internet of Things (loT) devices. This method is designed to address the challenges of collision avoidance, energy limitations, and scalability in dense loT environments through a structured, probabilistic slotted ALOHA framework.

[0133] The process begins at step 805, where the network node or base station broadcasts a paging signal. This signal includes a contention grid that defines available time slots (X) and frequency subcarriers (Y), together forming unique contention cells. Each device in the network receives this grid and uses it as the basis for initiating random access attempts. This gridbased division of resources supports time-frequency multiplexing and helps manage contention among numerous devices.

[0134] At step 810, each device randomly selects a time slot and frequency subcarrier from the received contention grid. This selection is entirely decentralized, allowing devices to operate asynchronously and autonomously without coordination overhead. This randomization ensures fairness and spreads traffic across the grid to lower the probability of collisions. The device also performs a local energy check to determine if its harvested energy exceeds a minimum threshold, ensuring that only capable devices proceed with transmission — thereby conserving network and device resources.

[0135] In step 815, the selected device constructs and transmits a random access message (Msg1). This message contains key metadata including a randomized device identifier, energy status, and optionally a data size indicator. These parameters are essential for the network to decide which devices to schedule for further communication. Devices may use backscatter modulation such as OOK, BPSK, or BFSK, tailored for energyefficient operation.

[0136] Following transmission, the device waits for feedback in step 820, where it checks for the reception of an ACK (Acknowledgment) from the network. If the ACK is received, the device considers the access successful and exits the loop. If no ACK is received, the device assumes a failure™- potentially due to a collision and proceeds to step 825 to process a NAK (Negative Acknowledgment) and reassess its current energy level.

[0137] At step 830, the device evaluates whether it has reached the retry limit (e.g., a maximum number Z of allowed attempts). This retry limit is either preconfigured or dynamically assigned based on the device’s class or priority. If the limit is exceeded, the device aborts the current transmission cycle and waits for the next paging opportunity. Otherwise, it advances to step 835, where it applies a probabilistic backoff strategy — choosing a random wait time based on the remaining number of slots — to reattempt access. This approach distributes retries and helps avoid synchronized recollisions.

[0138] In step 840, the device waits for the start of the next slot, after which it loops back to reselect contention parameters and reinitiate access if permitted. This cyclical structure ensures ongoing communication while preserving energy and network stability.

[0139] This method also incorporates dynamic slot optimization, wherein the number of contention slots can be increased or decreased based on factors such as observed collision rates, network load, and historical access patterns. Additionally, devices with low historical success may be prioritized in future contention rounds to promote fairness. Devices can also be filtered out of contention if their energy levels fall below the operational threshold, ensuring that limited resources are not wasted. Moreover, slot-frequency pairs that consistently lead to collisions can be suppressed or deprioritized in future windows, allowing the system to adaptively improve channel utilization. The final scheduling decisions may be influenced by a weighted score that considers the device’s energy, data priority, and prior success, ensuring that critical transmissions are favored under congestion.

[0140] Figure 9 illustrates the system architecture (900) for an energy-aware wireless communication system designed to facilitate random access scheduling among a large number of ultra-low power, battery-less ambient Internet of Things (IoT) devices. This system is comprised of two primary components: a network node 905 and an ambient loT device 935, each equipped with specialized modules that work in coordination to support slotted ALOHA-based access while accounting for device energy levels, contention outcomes, and dynamic network conditions.

[0141] The network node 905 is equipped with a scheduler 910, which is configured to broadcast a paging signal that contains a two-dimensional contention grid. This grid defines multiple time slots and subcarriers, allowing devices to randomly select a unique contention cell for initiating access. Alongside the scheduler, a transmitter 915 is used to disseminate the paging messages and subsequent responses, including acknowledgments (ACKs) or negative acknowledgments (NAKs). These responses may be bundled into a shared downlink message for multiple devices to conserve bandwidth and reduce latency. A receiver 920 in the network node is responsible for collecting incoming Msg1 frames transmitted by ambient loT devices. These frames include vital information such as a device’s random identifier, energy status, and potentially data size or priority tags. The processor 925 evaluates these received messages, detects any contention or collisions, and determines which transmissions were successful. The processor may also apply filtering logic to exclude devices that fall below an energy threshold to avoid unnecessary use of access slots. Supporting this decision-making, a controller 930 dynamically adjusts system parameters, including the number of contention slots and the allowable retry limit for devices. This enables the network node to respond to fluctuating load and contention conditions, ensuring efficient slot usage and fairness among devices with varying historical access success.

[0142] Complementing the network node is the ambient loT device 935, designed for minimal power consumption and autonomous operation. It includes an energy harvester 940 that captures energy from carrier wave (CW) signals transmitted by the network node. This harvested energy powers the device’s internal modules without requiring a battery. Once powered, the receiver 945 decodes the paging signal and identifies its assigned contention opportunities. A logic unit 950 processes this information and uses a pseudorandom function often seeded with the device’s ID to select a time slot and frequency subcarrier. It constructs Msg1 with relevant fields, including device ID, energy status, data size, and optionally a priority indicator used by the network for contention resolution.

[0143] The backscatter transmitter 955 is responsible for sending Msg1 using low-power modulation techniques such as On-Off Keying (OOK), Binary Phase Shift Keying (BPSK), or Binary Frequency Shift Keying (BFSK), as appropriate. This ensures minimal energy expenditure during communication. Finally, a retry controller 960 governs the reattempt behavior of the device. It listens for NAKs or lack of ACKs and, if within the retry limit, enables probabilistic reattempts in future contention slots. The retry controller also ensures that devices exceeding the maximum number of retries enter a low-power sleep mode, conserving energy until the next paging signal is received.

[0144] Together, the elements in Figure 9 form a complete system capable of supporting the claims related to energy-aware scheduling, optimized contention resolution, and intelligent device behavior in large-scale ambient loT networks. The architecture supports dynamic adaptation and fairness while maintaining the energy constraints essential for battery-less operation.

[0145] A number of implementations have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the disclosure. Accordingly, other implementations are within the scope of the following claims.

Claims

We Claim:

1. A method for performing energy-aware random access scheduling in a wireless network comprising a plurality of ultra-low power, battery-less ambient Internet of Things (loT) devices, the method comprising:transmitting a paging signal including information about available time and frequency domain contention resources;enabling each device to randomly select a time slot and frequency subcarrier from a contention grid and transmit a random access message using a slotted ALOHA protocol;receiving the random access messages, each including a device identifier, energy status, and data size indicator;evaluating contention outcomes and selecting a subset of devices for uplink scheduling based on energy level and contention success;transmitting a scheduling response including an acknowledgment (ACK) for successful transmissions and a negative acknowledgment (NAK) for failed transmissions; andenabling devices receiving NAKs to probabilistically reattempt access in future slots up to a retry limit;Wherein the maximum number of time slots allocated for transmitting the random access message (Msg1) during a single access occasion is determined based on at least one of: the total number of ambient loT devices in the network, an implementation complexity of the devices, a power consumption constraint associated with the devices, an individualdevice latency requirement, and an overall inventory completion time, such that a combined metric comprising communication delay and access collision probability is minimized.

2. The method as claimed in claim 1, wherein the contention grid comprises X time slots and Y frequency subcarriers, each forming a unique contention cell.

3. The method as claimed in claim 1, wherein the network suppresses, reuse of slot-frequency pairs that experienced repeated contention failures in previous access windows.

4. The method as claimed in claim 1, wherein the retry attempt of a device is governed by a backoff strategy based on the retry index and number of remaining slots.

5. The method as claimed in claim 1, wherein each device performs an energy check prior to access and transmits Msg1 only if its harvested energy exceeds a minimum threshold.

6. The method as claimed in claim 1, wherein devices with lower historical access success are prioritized for resource allocation in future contention cycles.

7. The method as claimed in claim 1, wherein the base station monitors collision rates and adjusts the number of available contention slots in subsequent windows to reduce repeated Msg1 collisions.

8. The method as claimed in claim 1, wherein device selection for uplink scheduling is prioritized based on a weighted score combining energy level, message size, and past access success.

9. The method as claimed in claim 1, wherein the base station or reader sends a PRDCH for Msg2 transmission corresponds to one or multiple A-loT Msg1 received from different devices.

10. A wireless communication system for random access scheduling with a plurality of ambient loT devices, the system comprising:a scheduler configured to transmit a paging signal defining a two-dimensional contention grid of time slots and subcarriers;a receiver configured to collect random access messages, each including a random device identifier and energy status;a processing unit configured to evaluate slot collisions and select eligible devices based on contention outcomes and energy availability; a transmitter configured to send ACK / NAK responses and resource allocations; anda controller configured to dynamically adjust contention parameters including slot count and retry limit based on current network load and collision feedback.

11. The system as claimed in claim 10, wherein the ACK / NAK response is embedded in a shared downlink message addressed to multiple devices.

12. The system as claimed in claim 10, wherein the processing unit filters out devices with energy levels below a threshold from contention to prevent wasted slot occupancy.

13. The system as claimed in claim 10, wherein the controller adjusts the number of contention slots based on predicted device load derived from past access attempts.

14. An ambient Internet of Things (loT) device comprising:an energy harvester configured to extract energy from a received carrier wave (CW) signal;a receiver configured to decode paging messages including contention slot information;a logic unit configured to select a random time slot and subcarrier and construct a Msg1 frame including a device ID, energy status, and data size;a backscatter transmitter configured to transmit the Msg1 frame using On-Off Keying (OOK), BPSK, or BFSK modulation; anda retry controller configured to reattempt transmission based on NAK reception and retry count.

15. The device as claimed in claim 14, wherein the retry controller limits the number of reattempts to a maximum value Z and disables further transmissions until a subsequent paging message is received, wherein Z is either preconfigured or dynamically determined based on the device class or assigned priority level.

16. The device as claimed in claim 14, wherein the retry controller transitions the device into a low-power sleep state after exceeding the maximum number of retries.

17. The device as claimed in claim 14, wherein the logic unit uses a pseudorandom function seeded with device ID to select slot-frequency pairs for contention.

18. The device as claimed in claim 14, wherein the random access message further includes a priority tag used by the network to resolve contention among simultaneous Msg1 transmissions.

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