Busy Slots Research Articles

Delay-Guaranteed Admission Control for LAA Coexisting With WiFi

Licensed-assisted-access (LAA) is used to extend the LTE link into the unlicensed band. How to guarantee the quality-of-service (QoS) for LTE devices in the unlicensed band is a challenging problem due to the listen-before-talk contention access in 5-GHz unlicensed bands. In this letter, we quantitatively analyze the medium access control delay for tagged LAA eNBs and propose a delay-guaranteed admission control scheme. We consider the freezing time of busy slots caused by collision or successful transmission, and introduce the exponential backoff mechanism for delay analysis. Validated by simulation results, our method provides important insights into the system admission performance and fairness of access.

Throughput Analysis of LAA and Wi-Fi Coexistence Network With Asynchronous Channel Access

The licensed-assisted access (LAA) technology has been proposed as a promising solution to increase the network capability by extending the frequency bands for long term evolution networks. The performance evaluation of the LAA systems has been extensively studied in recent years. However, most existing works did not consider the fact that Wi-Fi stations and LAA equipments are typically not synchronized in such a heterogeneous network. They are not aligned in time domain because of different time-slot durations, channel access back off, and contention window sizes. Therefore, in this paper, we investigate the throughput performance of the LAA and Wi-Fi coexisting networks with asynchronous channel access. To deal with the asynchronism, we first introduce the concept of the heterogeneous network superframe based on the fact that the timing relation between LAA and Wi-Fi systems will be restored to a fixed pattern after a busy slot. Thereafter, we model the LAA and Wi-Fi channel access behaviors in superframes as 2-D Markov chains, respectively. Based on the Markov chains and the structure of the superframe, we analyze the throughput performance by fully considering the asynchronism of the heterogeneous channel access. The accuracy of our theoretical analysis is validated by numerical results. Meanwhile, we have also investigated the effects of the number of LAA equipments, Wi-Fi stations, and the maximum contention window size upon the system throughput.

A Mean Field Analysis of CSMA/CA Throughput

Due to the fact that Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) protocols are extensively used in commercial wireless networks, the analysis of this family of medium access control protocols has been a topic of great interest for the wireless networking community. In this paper, we present a mean field analysis for the throughput of a slotted CSMA/CA scheme in single-hop networks. The concept of mean field approximation originates in statistical mechanics and it is a widely used approximation method employed to address systems of many interacting particles that cannot be solved exactly. The idea is to simplify the treatment of a many-body system by describing the interaction of one particle with the other interacting particles by an average potential, the so-called mean field. In our analysis, the nodes of a wireless network constitute a set of interacting particles; the interaction of a certain node with the other nodes in the network is reduced to an averaged channel condition. We estimate the amount of busy slots and the network throughput with respect to the offered traffic. Our analysis is of a recursive form, in which at each step the amount of traffic is increased by a specific amount. Also, our model takes into accounts retransmissions of collided packets.

PLACE: Physical Layer Cardinality Estimation for Large-Scale RFID Systems

Estimating the number of RFID tags is a fundamental operation in RFID systems and has recently attracted wide attentions. Despite the subtleties in their designs, previous methods estimate the tag cardinality from the slot measurements, which distinguish idle and busy slots and based on that derive the cardinality following some probability models. In order to fundamentally improve the counting efficiency, in this paper we introduce PLACE, a physical layer based cardinality estimator. We show that it is possible to extract more information and infer integer states from the same slots in RFID communications. We propose a joint estimator that optimally combines multiple sub-estimators, each of which independently counts the number of tags with different inferred PHY states. Extensive experiments based on the GNURadio/USRP platform and the large-scale simulations demonstrate that PLACE achieves approximately 3 ~ 4× performance improvement over state-of-the-art cardinality estimation approaches.

Identifying and coordinating joint impact of spatial reuse and multi-rate capability on wireless ad-hoc networks

In this paper, we derive an analytical model to evaluate the effect of jointly tuning the carrier sense threshold and employing multiple data rates on the network capacity in wireless ad-hoc networks. In order to capture the effect of the carrier sense threshold, the proposed model characterizes the channel states within the carrier sense range of an individual transmitter. Multi-rate capability for transmission is incorporated in identifying the channel states observed by a node. Towards maximizing the per-node throughput derived from the analytical model, a control reference and its optimal operating range is then identified. Based on the findings we propose a reference based channel access scheme, working in run-time and distributed fashion. Under the proposed scheme, each node measures the number of idle slots between two consecutive busy slots on-line and tunes the contention window size so as to ensure the measured control reference located within its optimal operation range. At the same time each node performs the selection of the data rate and the corresponding carrier sense threshold dealing with the current channel and network dynamics. Simulation results show that the proposed scheme achieves a performance improvement of up to 81 % in terms of per-node throughput over conventional 802.11 DCF algorithm.

An Efficient Link Polling Policy by Pattern Matching for Bluetooth Piconets

Bluetooth has a master-slave configuration, called a piconet. Unspecified in the Bluetooth standard, the link polling policy adopted by a master may significantly influence the bandwidth utilization of a piconet. Several works have dedicated to this issue by A. Capone et al. (2001), I. Chakrabory et al. (2001), A. Das et al. (2001), M. Kalia et al. (1999) and M. Kalia et al. (2000). However, none of them addresses the asymmetry of traffics between masters and slaves, and the different data packet types provided by Bluetooth are not fully exploited. In this paper, we propose an efficient pattern matching polling (PMP) policy for data link scheduling that properly resolves these deficiencies. A polling pattern is a sequence of Bluetooth packets of different type combinations (e.g., DHf/DH3/DH5/DMf/DM3/DM5) to be exchanged by a master-slave pair that can properly reflect the traffic ratio (i.e., asymmetry) of the pair. By judiciously selecting a proper polling pattern together with polling times for the link, the precious wireless bandwidth can be better utilized. The ultimate goal is to reduce the unfilled, or even null, payloads in each busy slot. In addition, an overflow mechanism is included to handle unpredictable traffic dynamics. Extensive simulations are presented to justify the capability of PMP in handling regular as well as bursty traffics.

Counter Rotating Slotted Ring: A New Architecture for Ring MANs

In this paper, we describe and analyze a new architecture for ring Metropolitan Area Networks (MANs): Counter Rotating Slotted Ring (CRSR). CRSR consists of two unidirectional rings shared among the network stations. Both the rings have erasure nodes appropriately placed between each or several stations. The transmission time is slotted. Each slot has some control bits and one of the control bit indicates if the slot is busy or not. An empty slot can be marked as busy and used for transmitting data. Once a busy slot reaches its destination, the data is read and the slot is marked as “read”. The erasure nodes identify the “read” slots and erase the data from these slots so that the slots can be reused. This process reduces the traffic intensity, which in turn results in less bandwidth requirements for transporting the same amount of information. The performance of CRSR is evaluated by using mathematical and simulation techniques. Several interesting results are presented in this paper in comparison with DQDB.

An algorithm for slot reuse in DQDB networks with erasure nodes

Abstract The Distributed Queue Dual Bus (DQDB) protocol, which has been specified by the IEEE 802.6 as the Metropolitan Area Network (MAN) standard, has the performance limiting feature in which busy slots must continue to propagate downstream, even if they have already been read. We address the issue of slot reuse in DQDB. We introduce and evaluate the performance of a new erasure node algorithm. The algorithm effectively balances the slot reuse and request cancellation functions by buffering the request stream and only passing those requests that have not been satisfied by erased slots. We show that our algorithm possesses a number of desirable features which makes it superior to existing algorithms.

Effective erasure node algorithm for slot reuse in DQDB

The distributed queue dual bus (DQDB) protocol, which has been specified by the IEEE 802.6 as the metropolitan area networks (MANs) standard, has an undesirable feature in that already received (i.e. read) busy slots continue to propagate downstream unnecessarily. The use of special nodes, known as erasure nodes, allows conversion of read slots to empty, so that downstream nodes may reuse these slots. This should result in an increase of the total throughput of the network. The authors introduce and evaluate the performance of an erasure node algorithm. The algorithm keeps track of past activities on both buses to effectively balance the slot erasure and the request cancellation functions. It is shown that this algorithm possesses a number of features which make it superior to existing algorithms.