Uplink Random Access Research Articles

An Uplink Random Access Scheme Based on ALOHA System Assisted by Gain Division Multiple Access

Gain division multiple access (GDMA) is a non-orthogonal multiple access (NOMA) technique for uplink communications. In GDMA, the receiver employs both the magnitudes and phases of channel gains associated to the users to separate users. In the power-domain NOMA, the receiver employs the power levels associated to users to separate users.We apply the GDMA concept together with orthogonal frequency division multiple access (OFDM) to combat the collision problem in the ALOHA system. Our goal is to minimize the complexity of the devices (users) required for coordination and to obtain high throughput simultaneously in the random access protocol. For the proposed unslotted OFDM-GDMA-ALOHA, each user randomly chooses a Zadoff-Chu (ZC) sequence as its preamble for the transmitted packet so that the receiver can simultaneously obtain the information for timing and the information for coarse channel estimation. Moreover, fine channel estimation is obtained by using a cluster-based method. Simulation for a coded unslotted OFDM-GDMA-ALOHA system with BPSK modulation demonstrates that the obtained throughput performance can be better than that obtained by the slotted ALOHA system without using GDMA.We also provide simulation for slotted OFDM-GDMA-ALOHA, which shows that very high throughput can be achieved if the synchronization of slots can be obtained.

System Throughput Maximization of Uplink NOMA Random Access Systems

Using wireless uplink non-orthogonal multiple access (NOMA), the throughput of an uplink random access system can be significantly improved. In this letter, assuming that each user only knows the channel response from itself to the base station, we study an uplink NOMA random access system which involves multiple power levels. For the signal decoding of a specific power level, we consider the effect of collisions happened at the lower and higher power levels. Our goal is to optimize the probability that a user selects a power level to transmit signals, in order to maximize the system throughput. We theoretically prove that the system throughput maximization problem is a convex problem and propose methods to find its optimal solution. Furthermore, we also prove that the optimal probability selecting the higher power level should be lower than or equal to that selecting the lower one. It is shown from simulation results that the proposed uplink NOMA system is more robust to the increase of users than a conventional orthogonal multiple access system.

Enabling Device‐to‐Device (D2D) Communication for the Next Generation WLAN

Device‐to‐device (D2D) communication technology is widely acknowledged as an emerging candidate to alleviate the wireless traffic explosion problem for the next generation wireless local area network (WLAN) IEEE 802.11ax. In this paper, we integrate D2D communication into IEEE 802.11ax for maximizing the spectrum efficiency. Due to the spectrum scarcity, the number of available resource units (RUs) is typically less than D2D pairs and stations (STAs), which makes the management of spectrum resources more complex. To tackle this issue, we design an efficient resource management algorithm for uplink random access and resource allocation in D2D‐enabled 802.11ax, which provides more channel access and resource reuse opportunities for STAs and D2D pairs. Specifically, we propose an enhanced back‐off mechanism and derive the optimal contention window (CW) by a theoretical model, which improves the uplink random access efficiency. To tackle the complex interference problem in RU scheduling phase, we develop an efficient and low‐complexity resource allocation algorithm based on the maximal independent set (MIS), which can schedule multiple D2D pairs to share the same RU with the specific STA. Simulation results demonstrate that the proposed algorithm significantly improves the network performance in terms of system throughput, collision rate, complete time, and channel utilization.

Application of 5G new radio for satellite links with low peak‐to‐average power ratios

SummaryThe aim of the paper is to consider feasibility of 5G new radio (NR) over satellite links also known as nonterrestrial networks (NTNs). Large propagation delay and Doppler frequency shift are challenges like is high peak‐to‐average power ratio (PAPR) of 5G NR signal because satellite systems would like to operate at very low‐power amplifier back‐off values. This paper provides a brief summary of progress made in initial synchronization and uplink random access process both in the literature and standardization. Furthermore, the paper explains what is the relationship between low PAPR and power amplifier back‐off and the density of reference symbols by showing that 2‐dB back‐off values can be attained using sufficient reference symbol density. Finally, open issues that need clarification are listed. Interestingly, all solutions to these problems do not mean changes in the standard but proper actions from vendors and operators.

Optimal Non-Uniform Deployments of LoRa Networks

LoRa wireless technology is an increasingly prominent solution for massive connectivity and the Internet of Things. Stochastic geometry and numerical analysis of LoRa networks usually consider uniform end-device deployments. Real deployments however will often be non-uniform, for example due to mobility. This letter mathematically investigates how non-uniform deployments affect network coverage and suggest optimal deployment strategies and uplink random access transmission schemes. We find that concave deployments of LoRa end-devices with a sub-linear spread of random access inter-transmission times provide optimal network coverage performance.

Group-Based Uplink OFDMA Random Access Algorithm for Next-Generation WLANs

The traditional wireless local area network(WLAN) standard, IEEE 802.11, adopts carrier sense multiple access/collision avoidance(CSMA/CA) mechanism to allow a single user to compete for channel access. The upcoming WLAN standard, IEEE 802.11ax, combines orthogonal frequency division multiple access(OFDMA) technology with random access, and use Uplink OFDMA Random Access(UORA) technology as uplink random access. Therefore, UORA which allow multiple users to access channel at the same time can improve the utilization of network resources. Although UORA technology in IEEE 802.11ax has the advantage of low signaling overhead, when the number of users of network is large, the increase of random access collisions will lead to the decrease of network throughput. Therefore, we propose a group-based UORA method. As a central scheduling node, Access Point(AP) divide Stations(STAs) and resources to groups and sets different GroupID for different groups. STAs can only access resources with the same GroupID randomly. The validity of group-based UORA method is verified by mathematical model analysis and simulation. The network throughput of our group-based UORA is higher than that of the original UORA in IEEE 802.11ax, so it has great practical significance.

Random Access Games With Cost of Waiting for Uplink NOMA Systems

In power domain non-orthogonal multiple access (NOMA) used for uplink random access (RA) systems, users need to control transmit power such that the received power at the base station can be one of the predetermined values. Thus, selecting one of the predetermined values incurs different transmission costs. Furthermore, users can often withdraw their (re)transmission, which involves a waiting (or regret) cost. This letter analyzes ${N}$ -user non-cooperative game of uplink NOMA RA systems, where waiting cost is taken into account. As results, we show the condition, under which a unique mixed-strategy Nash equilibrium (MNE) exists and its efficiency with respect to social welfare maximization (SWM).

Multichannel Uplink NOMA Random Access: Selection Diversity and Bistability

This letter investigates uplink random access (RA) systems based on power-domain non-orthogonal multiple access (NOMA) with multichannel. In NOMA RA systems, users transmit their packet with transmit power by inverting their channel gain, i.e., channel inversion, such that the received power of their packet at the base station (BS) can be one of the predefined values. While this facilitates the decoding process based on successive interference cancellation (SIC), it can incur excessive transmit power consumption upon low channel gains. To reduce transmit power (improve energy efficiency), this letter considers multichannel selection diversity, where users choose one channel whose channel gain is the maximum of all. We characterize the stability of multichannel NOMA RA systems with the cusp catastrophe and analyze diversity gain in terms of energy efficiency.

셀룰러 기반 무선 사물인터넷 네트워크에서의 역방향 랜덤접속 성공확률 근사화

랜덤접속은 LPWA(Low Power Wide Area)와 같은 무선 IoT(Internet-of-Things) 네트워크에서의 핵심접속 기술로 고려되고 있는 가운데, 본 논문은 셀룰러 기반의 무선 IoT 네트워크에서의 역방향 랜덤접속 성공확률의 근사화 방안을 제시한다. 수치 결과를 통해 제안된 근사화 방안은 원 성능을 잘 따르고 데이터 수집 장치의 밀도와 같은 핵심 네트워크 변수의 설계를 용이하게 함을 입증한다.

Exploiting capture and interference cancellation for uplink random multiple access in 5G millimeter-wave networks

The forthcoming 5G technology aims to provide massive device connectivity and ultra-high capacity with reduced latency and costs. These features will be enabled by increasing the density of the base stations, using millimeter-wave (mmWave) bands, massive multiple-input multiple-output systems, and non-orthogonal multiple access techniques. The ability to support a large number of terminals in a small area is in fact a great challenge to guarantee massive access. In this context, this paper proposes a new receiver model for the uplink of 5G mmWave cellular networks. The receiver, called Iterative Decoding and Interference Cancellation (IDIC), is based on the Slotted Aloha (SA) protocol and exploits the capture effect alongside the successive IC process to resolve packet collisions. A 5G propagation scenario, modeled according to recent mmWave channel measurements, is used to compare IDIC with the widely adopted Contention Resolution Diversity SA (CRDSA) scheme to show the performance gain of IDIC, when elements of practical relevance, like imperfect cancellation and receive power diversity, are considered. The impact of packet and power diversity is also investigated to derive the preferable uplink random access strategy that maximizes the system throughput according to the offered channel load.

Evolutionary Game Approach to Uplink NOMA Random Access Systems

This letter considers non-orthogonal multiple access (NOMA) as an uplink random access (RA) scheme. User equipments (UEs) in this RA system (re)transmit with some probability by selecting one of the target receive power levels. The packets received at the base station (BS) can be ordered with predetermined target power levels such that the BS can decode them using successive interference cancellation (SIC). We characterize this NOMA RA system using evolutionary game (EG) to show that the proportion of UEs of adopting a specific target power level upon retransmission is identified as evolutionary stable state (ESS).

Two-User NOMA Uplink Random Access Games

This letter considers the non-orthogonal multiple access technique for the uplink random access (RA) of 5G networks. Upon RA, users make use of the channel inversion , such that their received power at the base station (BS) can be one of two possible values. The BS can decode them with successive interference cancellation. This letter investigates this system by using two-user non-cooperative games and shows the achievable (expected) payoff region with mixed-strategy Nash equilibrium points and correlated equilibria.

Performance Analysis of NOMA Random Access

This letter applies non-orthogonal multiple access to uplink random access systems, where the transmit power from each user equipment (UE) is received at the base station as one of $L$ target (received) powers. More precisely, if a backlogged UE’s channel gain is greater than a threshold, it randomly aims at one of the target powers with channel inversion. Then, the BS decodes the received signals with successive interference cancellation. This letter investigates the performance of this system in terms of throughput, access delay, energy efficiency, and bistability.

Reliable M2M/IoT data delivery from FANETs via satellite

SummaryThe use of unmanned aerial vehicles (UAVs) is rising in several application fields. This work deals with the communication challenges in UAV swarms, or flying ad hoc network (FANET), when taking into account non–line‐of‐sight scenarios. The use of satellites is a necessity in such operating conditions; thus, this work provides architectural considerations and performance assessments when several (FANETs) share an uplink random access satellite channel, fed with M2M/IoT traffic generated from on‐board sensors, to be reliably delivered to a remote ground destination.

Measuring and Understanding RRC State Machine Optimization in Light of Recent Advancements

Broadband mobile networks utilize a radio resource control (RRC) state machine to allocate scarce radio resources. Current implementations introduce high latencies and cross-layer degradation. Recently, the RRC enhancements, continuous packet connectivity (CPC), and the enhanced forward access channel (Enhanced FACH), have emerged in UMTS. We measure the availability and performance of these enhancements on a network serving a market with a population in the millions. We demonstrate that these enhancements offer significant reductions in latency, mobile device energy consumption, and improved end user experience. We develop new over-the-air measurements that resolve existing limitations in measuring RRC parameters. We find CPC provides significant benefits with minimal resource costs, prompting us to rethink past optimization strategies. We examine the cross-layer performance of CPC and Enhanced FACH, concluding that CPC provides reductions in mobile device energy consumption for many applications. While the performance increase of HS-FACH is substantial, cross-layer performance is limited by the legacy uplink random access channel (RACH), and we conclude full support of Enhanced FACH is necessary to benefit most applications. Given that UMTS growth will exceed LTE for several more years and the greater worldwide deployment of UMTS, our quantitative results should be of great interest to network operators adding capacity to these networks. Finally, these results provide new insights for application developers wishing to optimize performance with these RRC enhancements.

Toward Massive, Ultrareliable, and Low-Latency Wireless Communication With Short Packets

Most of the recent advances in the design of high-speed wireless systems are based on information-theoretic principles that demonstrate how to efficiently transmit long data packets. However, the upcoming wireless systems, notably the fifth-generation (5G) system, will need to support novel traffic types that use short packets. For example, short packets represent the most common form of traffic generated by sensors and other devices involved in machine-to-machine (M2M) communications. Furthermore, there are emerging applications in which small packets are expected to carry critical information that should be received with low latency and ultrahigh reliability. Current wireless systems are not designed to support short-packet transmissions. For example, the design of current systems relies on the assumption that the metadata (control information) is of negligible size compared to the actual information payload. Hence, transmitting metadata using heuristic methods does not affect the overall system performance. However, when the packets are short, metadata may be of the same size as the payload, and the conventional methods to transmit it may be highly suboptimal. In this paper, we review recent advances in information theory, which provide the theoretical principles that govern the transmission of short packets. We then apply these principles to three exemplary scenarios (the two-way channel, the downlink broadcast channel, and the uplink random access channel), thereby illustrating how the transmission of control information can be optimized when the packets are short. The insights brought by these examples suggest that new principles are needed for the design of wireless protocols supporting short packets. These principles will have a direct impact on the system design.

Two-Stage Multiple Access for Many Devices of Unique Identifications over Frequency-Selective Fading Channels

In this paper, we consider sparse index multiple access for uplink random access in a wireless system of a number of devices when a fraction of them are active. This multiple access scheme is suitable for the case that an access point (AP) needs not only to receive data symbols, but also to identify active devices when there are a number of devices with unique identification sequences (the number of devices can be easily more than a million) with low signaling/control overhead. We propose a two-stage transmission scheme for random access and derive computationally efficient methods to estimate the channel state information (CSI) of active devices over frequency-selective fading channels in the first stage and to perform joint active device identification and data detection in the second stage using a well-known sparse signal estimation method in compressive sensing. Simulation results demonstrate that the proposed approach can successfully estimate the CSI of active devices under reasonable conditions and identify the unique identification sequences or vectors of active devices with a high probability. For example, when 6 out of 64 devices become active, the AP can identify all six devices (using estimated CSI) with a probability higher than ${1- 10^{-2}}$ over frequency-selective fading channels.

Utility-Optimal Random Access for Wireless Multimedia Networks

In this letter, we consider the uplink random access problem in a wireless multimedia network (WMN) with audio, video, and best effort applications. Since these multimedia applications have different quality-of-service (QoS) requirements, we model their utilities with concave, step, and quasi-concave functions. We assume that the access point performs admission control and assigns transmission probabilities to the users for random access, based on solving a non-convex network utility maximization problem. We propose a novel enumeration algorithm to obtain the global optimal solution by solving a number of computationally tractable convex optimization problems. We characterize the total number of iterations of the algorithm analytically. Simulation results show that our proposed algorithm achieves a higher average network aggregate utility than a carrier sense multiple access (CSMA) scheme implemented in a slotted time system.

4세대 이동통신시스템을 위한 우선순위 기반 지능적 상향링크 랜덤 접속 방법 및 표준화

4세대 이동통신시스템에서는 사용자가 이용하는 서비스 종류 및 가입한 요금제, 서비스 이용 형태 등에 따라서 각 사용자에게 서로 다른 품질의 서비스를 제공하는 것이 매우 중요하다. 본 논문에서는 단말이 상향링크 자원 요청을 위해서 수행하는 random access 과정을 개선하여 각 사용자 별 서비스 품질 차별화를 도모하였다. 구체적으로 bandwidth request 채널의 구조를 primary 영역과 secondary 영역으로 구분하였고 각 영역을 이용하여 random access를 수행할 수 있는 사용자의 등급을 영역 별로 제한하였다. 이러한 제안 기술을 이용하면 서로 다른 등급의 사용자 사이에 발생하는 불필요한 random access 경쟁을 방지할 수 있기 때문에 전체적인 사용자의 random access 성공 확률을 유지하면서 primary 영역을 이용하여 random access를 시도하는 사용자의 성공 확률을 증가시킬 수 있다. 제안 기술은 2010년 3월 IEEE 802.16 Session #66 회의에서 발표되었고 제안 기술의 개념 및 필요한 메시지가 802. 16m 표준에 채택되는 성과를 거두었다. Fourth-generation (4G) cellular communication systems must provide different quality-of-service (QoS) to users according to the service type, membership class, and usage case of each user. For the purpose of user's QoS differentiation, we propose an enhanced uplink random access scheme for bandwidth request. More specifically, we divide a bandwidth request channel into two parts: One is a primary region and the other is a secondary region. Then, each region has a unique minimum access class that allows only specific users to perform random access through that region. By doing so, we can reduce collision probability and increase the success probability of bandwidth request. From the perspective of standardization, we presented this scheme in the IEEE 802.16m Session #66 held on March 2010. As a result, the concept of the proposed scheme and required messages were defined in the 802.16m standard.

Joint collision resolution and transmit‐power adjustment for Aloha‐type random access

ABSTRACTWe consider uplink random access for which slotted Aloha has usually been employed with unknown channel conditions. Upon failure of a transmission attempt, a user cannot tell whether the failure was caused by collision with other simultaneously transmitting users or by his use of insufficient transmit power. If a transmission attempt failed due to collision which could have been resolved by retransmission, increasing transmit power would just waste power and, moreover, reduce the other users' chance of successful access. To handle this lack of information on the cause of failure, we propose a novel Cause‐of‐Failure resolution, where the transmit power is increased after a given number of consecutive unsuccessful access attempts when the probability that a given failure is caused by collision becomes sufficiently low. To exploit the thus‐obtained transmit power for the next random access attempt, we also determine the Cause‐of‐Success based on the number of consecutive successful attempts, i.e., whether to (probabilistically) decrease or maintain the current transmit power. This way, users can adjust their transmit power for random access, which we call Auto Power Fallback (APF), considered as an advanced version of the power ramping algorithm. We evaluate APF by modeling analysis and numerical computation based on the slotted Aloha, showing that APF determines a suitable transmit power for uplink random accesses while achieving good performance. Copyright © 2011 John Wiley & Sons, Ltd.