Analysis of the priority stack random-access protocol in W-CDMA systems

In this paper, we discuss the random access procedures in legacy networks, long‐term evolution, LTE‐Advanced, and 5G networks. Random access is the first and incumbent step for connection establishment between base station/eNodeB/gNodeB and user equipment. Keeping in view its importance, there has been a regular thrive to improve the procedures of random access in communication networks. With the advent of new concepts such as machine‐type communication and Internet of Things, random access becomes extremely critical because huge number of devices try to connect to the network simultaneously. We present the evolution of random access process from legacy networks such as global system for mobile or wideband code division multiple access to 5G networks and beyond and their analysis. Simulations are performed in MATLAB to show various performance metrics such as access delay, total service time, and collision probability to demonstrate the pros and cons of one technique over another.

Various random access mechanisms, such as Aloha protocol and its corresponding variants have been widely studied as efficient methods to coordinate the medium access among competing users. But when two or more wireless users transmit packets at the same time over the same channel a collisions occur. When this happens, the received packets are discarded and retransmissions are required, which is a waste of power and bandwidth. In such a situation one of the most important objectives is to find techniques to improve these protocols to reduce the number of collisions or to avoid them. Several studies have contributed to this problem. In this paper, we propose a new approach named ZigZag decoding to enhance slotted Aloha mechanism by reducing the loss rate of packets colliding. We model the system by a Markov chain witch the number of backlogged packets is taken as the system state. We use a stochastic game to achieve our objective. We evaluate and compare the performances parameters of the proposed approach with those of slotted Aloha mechanism. All found results show that our approach is more efficient than the slotted Aloha mechanism.

The main aim of this paper is to contribute to the design of the signalling architecture for next-generation geo-satellite systems with on board processing functionality. We concentrate on the signalling channels, which are used by the satellite terminals for connection establishment. Two access methods are investigated: the dedicated and the random (Slotted Aloha) access. The dedicated access requires the introduction of a centralized scheduling technique in the network control centre. We study the system performance and demonstrate that the random access allows saving signalling bandwidth and maintaining high acceptance rate despite of collisions. This is achieved by harmonizing the random access with a centralised connection admission control algorithm and an intelligent scheduling of resource requests on board the satellite.

Orthogonal frequency-division multiple access (OFDMA) systems are considered promising candidates for implementing next-generation wireless communication systems. They provide multiple channels that can be accessed via random access schemes. However, traditional random access schemes could result in an excessive amount of access delay. To address this issue, we develop a fast retrial scheme that is based on slotted Aloha and exploits the structure of OFDMA. A salient feature of this scheme is that when collisions occur instead of retrials occuring randomly in time, they occur randomly in frequency, i.e., the scheme randomly selects the subchannels for retrial. To further achieve fast access, retrials are designed to follow the 1-persistent type, i.e., no exponential backoff. To achieve the maximum throughput, we limit the maximum number of allowed retrials according to the load condition. We also consider the issue of designing for an appropriate reuse factor for random access channels in order to overcome the intercell interference problem in OFDMA multicell environments. Our finding is that full sharing, i.e., a reuse factor of one, performs best for given random access channels. Through analysis and simulation, we confirm that our fast retrial algorithm has the advantage of high throughput and low access delay, and the full sharing policy for random access channels shows high throughput as well as low collision.

We perform a new analysis of the performance of the wideband code-division multiple access (W-CDMA) randomized slotted-offset random access channel (RAC) with Nakagami-m fading and compare it with that of a comparable randomized slotted-ALOHA-based RAC. Previously, it was shown that the W-CDMA RAC is fast, robust and simple to implement (see Esmailzadeh, R. and Gustafsson, M., Proc. 1997 IEEE ICUPC Conf, p.43-7, 1997). However, it was assumed that any random access packet arrival events involving multiple packets from cochannel mobile stations would result in lost packets. Closed-form equations are developed for the collision process of the arriving random access packets in slotted-offset and slotted-ALOHA RACs. An analysis is developed of the signal-to-interference-and-noise ratio of a packet involved in a multipacket DS-CDMA collision with a generalized Nakagami fading channel and diversity reception at the base station. A closed-form equation is developed for the bit error rate and packet throughput of the slotted-offset- and slotted-ALOHA-based RACs. The results of the analysis show that considerable improvement in the RAC performance can be achieved when multiple arrival collisions, on the same timeslot and with the same signature code, are partially resolved. The results also show the RAC's sensitivity to fading severity, packet E/sub b//N/sub 0/, spreading gain and number of base station receive selection diversity antennas. Compared to the randomized slotted-ALOHA designs, W-CDMA RAC performs as well in light fading conditions and slightly worse in severe fading conditions.

The prioritized random access mechanism has been researched in this paper. The current situation of large-scale node multiple access in the Internet of Things leaded to channel congestion and increased blocking rate. In M2M communication, there were a large number of nodes trying to RA. In this case, serious physical random access channel overload would occur, making it even difficult to access the network. Nodes spent a lot of time accessing the network, and even given resource management schemes could not guarantee acceptable end-to-end latency meet QoS guarantees. So, the traditional method has greater limitations in supporting different QoS in M2M communication, It would also have an unimaginable impact on the web, Therefore, it was necessary to propose a scheme to reduce the access delay while ensuring the success rate, The current priority-differentiated random access mechanism needed to consider how to match with the new features of M2M services. The reasonable random access scheme and efficiently manage the resource and allocated the channel were designed in the system where the traditional H2H service and the new M2M service coexist. The weights of different services were obtained by modeling and simulation. Therefore, by setting different threshold detecting preamble index matching service type and calling different back-off indexes to reduce the access collision, so as to optimize the random access mechanism. This study could make the node indicate its priority in the access process, and reduced the conflict and access delay. Under 5G communication technology, this solution would be widely used.

The traffic performance of integrated 3G wide-band code division multiple access (WCDMA) and GSM/GPRS network is evaluated. This type of network links two cellular radio systems which have different set of frequency bands and the same coverage size. The base station of 3G WCDMA is installed on an existing GSM/GPRS site. Dual-mode mobile terminals use handoff to establish calls on the better system. The soft handoff or inter-frequency hard handoff occurs when mobile terminals of 3G WCDMA or GSM/GPRS move between two adjacent cells, respectively. The inter-system hard handoffs are used between 3G WCDMA and GSM/GPRS systems. The data rate conversions between different systems, soft handoff region size, multiple data rate multimedia services, and the effect of the mobile terminal mobility on the user mean dwell time in each system are considered in the study. The simulation results demonstrate that a great traffic performance improvement on the complementary use of 3G WCDMA and GSM/GPRS cellular radio networks compared with the use of GSM/GPRS cellular radio networks. When high-data rate transmission is chosen for low-mobility subscribers, both the handoff failure probability, and carried traffic rates increase with the new call generation rate. However, both rates decrease conversely with the increasing new call generation rate as soon as the new call generation rate exceeds a critical value. This causes the integrated networks saturation. The higher mean speed for the mobile terminals produces lower new call blocking probabilities and total carried traffic. The new call blocking probabilities and total carried traffic increase with the size of the soft handoff region.

Slotted Aloha and carrier sensing multiple access (CSMA) are effective random access protocols, which can also be important elements of more advanced media access protocols. In this paper, we investigate slotted Aloha and CSMA protocols in a cognitive radio network, where primary users have higher priority than secondary users and secondary users need to monitor the channel to avoid interference to the primary users, it is thus proposed that slotted Aloha is used for primary users to access the channel and secondary users use slotted CSMA to sense the time slots of slotted Aloha and transmit their packets during idle time slots. A Rayleigh fading channel is considered and we derive the throughput of slotted Aloha and CSMA for the primary and secondary users.

The collection of physiological signals such as electrocardiogram, electroencephalogram, respiration, blood pressure, body accelerations etc. in a body area network is beneficial for revealing vital signs and investigating spontaneous physiological responses. However, the wire connection between the recording sites and the processing unit may disturb subject's daily activities. Up to now, several multi-users communication protocols such as IEEE 802.11, Bluetooth, etc. have been proposed for this purpose. In this paper we employed the slotted ALOHA for multi-users wireless data transmissions. The slotted ALOHA is so simple that it can be implemented by a 2.4-GHz RF transceiver (nRF2401, Nordic) incorporated on a 16-bit microcontroller (MSP430, Texas Instruments) for the consideration of low-power consumption. In this paper we proposed a modified slotted ALOHA for multi-biosignals transmission and built its simulation model using SIMULINK 2.0 to simulate and evaluate the performance of the proposed algorithm.

Throughput, delay, and stability for two slotted ALOHA packet radio systems are compared. One system is a slotted direct-sequence spread-spectrum multiple-access (DS/SSMA) network where each user employs a newly chosen random signature sequence for each bit in a transmitted packet. The other system is a multiple-channel slotted narrow-band ALOHA network where each packet is transmitted over a randomly selected channel. Accurate packet success probabilities for the code-division multiple-access (CDMA) system are computed using an improved Gaussian approximation technique which accounts for bit-to-bit error dependencies. Average throughput and delay results are obtained for the multiple-channel slotted ALOHA system and CDMA systems with block error correction. The first exit time (FET) is computed for both systems and used as a measure of the network stability. The CDMA system is shown to have better performance than the multiple-channel ALOHA system in all three areas.

This paper proposes a distributed energy-harvesting random access protocol called harvest-or-access by applying slotted ALOHA to wireless powered communication networks (WPCNs). From the fact that there are a considerable number of idle slots during which any nodes do not attempt transmission in slotted ALOHA, the idle slots are made available for wireless energy transfer (WET). If any random access (RA) slot is recognized as an idle slot, the hybrid access point (HAP) opportunistically performs the WET in this slot. The wireless devices (WDs) can harvest energy for every idle slot and attempt random access by using this harvested energy. An asymptotic throughput analysis in a high signal-to-noise ratio (SNR) environment with a sufficient number of accessing WDs shows that there is an optimal number of RA slots allocated to maximize throughput and this optimal number of RA slots depends only on the average of the minimum SNRs of the WDs without knowledge of full channel state information. Monte Carlo simulation results further show that the proposed harvest-or-access protocol outperforms the conventional harvest-then-transmit-based random access protocols especially when the number of WDs is large.

Click to increase image sizeClick to decrease image size Additional informationNotes on contributorsK GiridharK Giridhar received the BSc (Applied Sciences) degree from PSG College of Technology, Coimbatore, in 1985, and the ME degree in Electrical Communication Engineering from Indian Institute of Science, Bangalore, in 1989, and the PhD degree in Electrical and Computer Engineering from University of California, Santa Barbara, CA, in 1993.He has also worked for a year each, as a Member of Research Staff at Bharat Electronics, Bangalore, and as a Research Affiliate in Electrical Engineering at Stanford University, California. In 1994, he joined the Indian Institute of Technology, Madras, and currently, is an Associate Professor of Electrical Engineering.His present research interests are in the areas of noncoherent and multiuser detection, space-time processing, adaptive estimation, and various transceiver algorithms for 3G and 4G wireless systems. He is involved in telecommunication product development activity based on the DECT Wireless in Local Loop system developed by HTM. He has also been a visiting faculty at Sri Sathya Sai Institute of Higher Learning, Prasanthi Nilayam, Andhra Pradesh, and at Stanford University, California.B SrikrishnaB Srikrishna received the BTech degree in electronics and communication engineering from the Indian Institute of Technology, Madras, India in 1996 and the MS and PhD degrees in electrical and computer engineering from Rice University, Houston, TX, USA in 1998 and 2001 respectively. He worked as a Senior Engineer at Qualcomm, Inc., Campbell, CA, USA from June 2001 to March 2003 on wideband code-division multiple access (WCDMA) modem design. Since May 2003, he is at the Indian Institute of Technology, Madras, as Assistant Professor in the Department of Electrical Engineering. His current research interests include high-speed wireless packet data systems, adaptive modulation and coding for wireless systems, cellular network optimization, multiple access communications and information theory.

Chapter 6 - WCDMA Overview

Future Internet of Things deployments generate a multitude of new challenges and opportunities. While 5G networks promise massive throughput rates with ultra low delays, many verticals in the areas of Industry 4.0, Smart City, or Smart Agriculture only transmit tiny amounts of data and instead demand high energy efficiency. This is addressed by access technologies like Low Power Wide Area Networks being complementary to high performance 5G networks. Especially Long Range Wide Area Network (LoRaWAN) promises transmissions across long distances with low energy requirements with the drawback of unreliable transmission due to potential message collisions through random channel access. For that reason, a broad parameter study simulation for LoRaWAN channel access with slotted Aloha is presented for real world scenarios and influences like clock drifts or cross traffic. The key impact factors of this channel access approach are studied with focus on the collision probability in various scenarios and simulation results are compared to the current state of the art. The contribution of this work are guidelines for parameter settings in a LoRaWAN with slotted Aloha channel access and performance comparisons for different settings. This information is crucial to scale and operate future LoRaWANs.

Enabling machine-type communication (MTC) over large scale cellular networks is a promising solution to handling the emerging MTC traffic. To enable a massive number of machines to connect to the base station, random access mechanisms and data aggregation have been largely studied separately in the literature. In this paper, we use stochastic geometry to investigate MTC over cellular with access class barring enhanced random access and data aggregation. We present an approximate yet accurate and tractable analytical framework for characterizing the MTC performance in terms of the machine type device (MTD) success probability, average number of successful MTDs and probability of successful preamble utilization. We validate the proposed model by comparison with simulations. Our results show that while the provision of more resources for the relaying phase benefits MTC, the provision of more preambles in the random access is not always beneficial to MTC. Thus, system parameters need to be chosen carefully to benefit the MTC traffic.