Device-to-Device Communications in Unlicensed Spectrum: Problem Identification and Performance Maximization

The IEEE 802.11 standards for wireless local area networks define how the stations of an ad-hoc wireless network coordinate in order to share the medium efficiently. This work investigates the performance of such a network by considering the two different access mechanisms proposed in these standards. The IEEE 802.11 access mechanisms are based on the carrier sense multiple access with collision avoidance (CSMA/CA) protocol using a binary slotted exponential backoff mechanism. The basic CSMA/CA mechanism uses an acknowledgment message at the end of each transmitted packet, whereas the request to send/clear to send (RTS/CTS) CSMA/CA mechanism also uses a RTS/CTS message exchange before transmitting a packet. In this work, we analyze these two access mechanisms in terms of throughput and delay. Extensive numerical results are presented to highlight the characteristics of each access mechanism and to define the dependence of each mechanism on the backoff procedure parameters.

During the past few years the wireless technology market has experienced a tremendous growth. Users today expect to be able to communicate and access data anytime, anywhere, using almost any portable device. Infrared Data Association (IrDA) addressed the requirement for indoor multipoint wireless connectivity with the development of the advanced infrared (AIr) protocol stack utilizing the infrared spectrum. AIr medium access control (MAC) protocol employs a carrier sensing multiple access with collision avoidance (CSMA/CA) protocol in addition to a request to send/clear to send (RTS/CTS) packet exchange reservation scheme and a linear adjustment of the contention window (CW). This paper develops a new modelling approach to evaluate saturation performance of the AIr protocol based on conditional probability arguments rather than bi‐dimensional Markov chains. Moreover, we extend performance studies in former literature papers by providing an intuitive AIr packet delay analysis assuming error‐free transmissions and a fixed number of stations. Using OPNET simulation results, we validate our mathematical analysis and we show that the proposed model predicts AIr packet delay performance very accurately. Utilizing the derived mathematical analysis, we determine the significance of both link layer and physical parameters, such as burst size, minimum CW size value and minimum turnaround time on AIr packet delay performance. Finally, we propose suitable values for both backoff and protocol parameters that reduce average packet delay and, thus, maximize performance. Copyright © 2005 John Wiley & Sons, Ltd.

This paper presents a protocol-independent approach to reveal a new insight into the performance of carrier sense multiple access with collision avoidance (CSMA/CA) protocols: the family of CSMA/CA protocols, independent of implementation details, share the same optimal operation point where the maximum protocol capacity is achieved. The protocol- independent analysis is inspired by the concept of virtual time slot. At the timescale of virtual-slot, all the CSMA/CA protocols show the same behavior pattern and, therefore, a generic virtual- slot based S-G (VS S-G) analysis is developed to compute the optimal operation point. The accuracy of the VS S-G analysis is benchmarked against the precise protocol-specific analysis, in particular, for the 802.11 distributed coordination function (DCF) and the 802.15.4 contention access period (CAP). Furthermore, this paper discusses how to integrate the network-layer queueing analysis with the VS S-G analysis at the medium access control (MAC) layer to form a generic cross-layer framework for call- level network capacity analysis.

This paper presents a theoretical analysis of the maximum throughput of a wireless mesh backhaul network that is achievable over a practical carrier sense multiple access with collision avoidance (CSMA/CA) medium access control (MAC) protocol. We resort to the multicommodity flow (MCF) formulation augmented with the conflict-graph constraints, whereas we use a novel approach to take into account the collision overhead in the distributed CSMA/CA MAC. Such overhead due to random access has been ignored by existing MCF-based capacity studies, which assume impractical centralized scheduling and result in aggressive capacity planning, which is unachievable over the CSMA/CA MAC. This paper makes the following three main contributions: 1) we develop a generic method of integrating the CSMA/CA MAC analysis with the MCF formulation for optimal network capacity analysis, which readily generates an upper bound of the network throughput; 2) we define a new concept of CSMA/CA clique and theoretically study its relationship to a CSMA/CA area in terms of throughput; and 3) using the CSMA/CA clique as a tool, we derive a lower bound of the network throughput achievable over the CSMA/CA MAC by clique-based MCF formulation. NS-2 simulation results are presented to demonstrate the tightness of the upper and lower bounds that are newly developed, compared to those based on the MCF formulation assuming a slotted system and centralized scheduling.

The current stage of telecommunication technologies development is characterized by the rapid growth use of wireless technologies in access networks and the growth requirements for its quality. The bottleneck that significantly reduces the bandwidth of each subscriber connection is that the total bandwidth of the wireless local network is shared among its active members by the shared technology used. The access management sub-layer to the shared physical environment is responsible for this in the network architecture. The main method used at this sub-layer is the Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) scheme. This work is devoted to the analysis of CSMA/CA scheme and the development of an analytical model for its further study and use for the improvement of wireless local networks. The input data is a transition state diagram of a local area wireless network station in data transmission mode. According to the CSMA/CA scheme, stations cannot change their state after starting frame transmission until a confirmation frame of successful reception arrives from the addressee or until the time to wait for it expires. Considering this, it is proposed to use a simplified transition state diagram for the analysis. The operation of the station by the simplified transition state diagram is described using a system of differential equations. As a result of the solution of this system, expressions representing the probability of the station being in each of its states as a function of the intensities of the station’s transitions from each state to another are derived. The values of these intensities depend on both the outgoing traffic of the station and the traffic in the network. The resulting expressions can be used in further work on the analysis of the CSMA/CA scheme, as they make it possible to estimate the operation of the station at different ratios of the station’s output traffic and external traffic generated by other stations of the network. This can be used to develop an enhanced algorithm station operation of wireless local area networks by adapting the parameters of the CSMA/CA scheme to specific current loads of both the station and the network.

WBAN을 위한 MAC 프로토콜은 의료용 센서 노드의 가변적인 데이터를 효율적으로 처리하기 위해서 응급상황에서 발생하는 트래픽을 가장 높은 우선순위로 처리하는 CSMA/CA(: Carrier Sense Multiple Access with Collision Avoidance) 알고리즘을 수행하게 된다. 노드가 전송하는 응급 메시지는 충돌이 발생하게 되고 응급 메시지 재전송으로 인한 전송 지연이 발생할 수 있으며 재전송으로 인한 에너지 낭비를 가져올 수 있다. 본 논문에서는 이러한 문제점들을 개선하기 위해서 우선순위 큐잉을 적용한 CSMA/CA 알고리즘의 경우 MAC 명령어 프레임과 데이터 프레임의 우선순위를 정하여 서로 다른 백오프 파라미터를 적용하고 충돌로 인한 프레임 손실을 최소화하는 알고리즘을 제안하였다. 성능평가 결과 제안한 MAC 프로토콜을 사용했을 때가 IEEE 802.15.6을 사용했을때 보다 충돌 확률이 감소하여 패킷 전송 처리율이 증가하고 패킷 손실량이 감소함을 보였다. MAC protocol for WBAN performs CSMA/CA(:Carrier Sense Multiple Access with Collision Avoidance)algorithm that handles traffic which occurs in emergency with top priority in order to deal with variable data of sensor node for medicine. Emergency message that node sends undergoes collision and delay of transmission by retransmission of emergency message and waste of energy by retransmission. This paper suggests algorithm that minimizes loss of frame caused by collision and applies different backoff parameters by setting order of priority between MAC instruction frame and data frame in CSMA/CA algorithm case which applies order of priority queuing to improve aforementioned problem. According to performance evaluation, it has been found that using suggested MAC protocol showed lower collision probability, higher packet transmission processing ratio and lower packet loss compared with using IEEE 802.15.6.

The popular IEEE 802.11 wireless local area network (WLAN) is based on a carrier sense multiple access with collision avoidance (CSMA/CA), where a station listens to the medium before transmission in order to avoid collision. If there exist stations which can not hear each other, i.e., hidden stations, the potential collision probability increases, thus dramatically degrading the network throughput. The RTS/CTS (request-to-send/clear-to-send) frame exchange is a solution for the hidden station problem, but the RTS/CTS exchange itself consumes the network resources by transmitting the control frames. In order to maximize the network throughput, we need to use the RTS/CTS exchange adaptively only when hidden stations exist in the network. In this letter, a simple but very effective hidden station detection mechanism is proposed. Once a station detects the hidden stations via the proposed detection mechanism, it can trigger the usage of the RTS/CTS exchange. The simulation results demonstrate that the proposed mechanism can provide the maximum system throughput performance.

Performance Evaluation of Multiband CSMA/CA with RTS/CTS for M2M Communication with Finite Retransmission Strategy

Vehicular ad hoc networks (VANETs) enable higher safety, enhanced mobility management, and new infotainment services. Currently, the foreseen standard at the medium access control (MAC) layer for VANETs is IEEE 802.11p, which is based on carrier sense multiple access with collision avoidance (CSMA/CA). However, under heavy traffic conditions, CSMA/CA suffers from a high collision probability, particularly in the presence of hidden terminals. Furthermore, the adoption of the request-to-send/clear-to-send (RTS/CTS) mechanism is not effective when a high data rate is required. If high-throughput services are addressed, a new MAC protocol should, thus, be designed. To this aim, in this paper, we propose a new protocol, which is denoted as the orthogonal frequency-division multiple-access (OFDMA)-based MAC protocol for VANETs (OBV), and we compare it with other MAC protocols taken as benchmarks. To verify the feasibility and the performance of the proposed algorithm, we first propose an analytical model in a simplified scenario. Then, we develop exhaustive simulations in realistic scenarios, considering both urban and highway environments. Results show that OBV outperforms all reference protocols, even doubling their throughput under heavy-load network conditions.

The use of wireless access networks, particularly IEEE 802.11 wireless access networks, is an economical method for realizing a communication network between a core information network of a smart grid and a rural area network. This paper presents a novel analysis of the throughput performance of the IEEE 802.11 carrier sense multiple access with collision avoidance (CSMA/CA) protocol with a large propagation delay. The throughput analysis is performed by using a real model. A Markov chain model is used to analyze the throughput performance of the IEEE 802.11 CSMA/CA binary exponential backoff algorithm. The results of analysis and computer simulations show that the theoretical throughput is in good agreement with the throughput obtained from computer simulations under the propagation delay less than 20 µs. When the propagation delay is more than 20 µs, the throughput obtained from the simulation results becomes larger than the theoretical throughput because of short-term unfairness. The throughput degradation for a transmission rate of 6 Mb/s and a propagation delay of 40 µs is 16.8 %; this propagation delay corresponds to a transmission distance of 12 km.

The carrier-sensing multiple access with collision avoidance (CSMA/CA) protocol is the most well-known medium access control (MAC) protocol for wireless networks. Both the distributed coordination function (DCF) defined in IEEE 802.11 and the MAC layer defined in IEEE 802.15.4 are based on the CSMA/CA protocol. Nevertheless, these two standards have quite different carrier-sensing mechanisms. Different to continuous carrier sensing in DCF, an IEEE 802.15.4 node only senses the channel once just after a backoff. Sensing-once mechanism can reduce the computation loading on the CPU. However, it significantly increases the probability of failure transmission because a node is not fully aware of channel activity. This paper first proposes a software architecture integrating proper hardware features for designing a DCF-based MAC protocol and then successfully implements it on a low-power transceiver. In addition, this paper conducts experiments in a star topology network to compare the performance of the above DCF-MAC protocol with the IEEE 802.15.4 MAC protocol. Experimental results show that, without continuous sensing, the IEEE 802.15.4 network suffers a high transmission failure probability as the network size increases. Consequently, the proposed DCF-based MAC protocol outperforms the IEEE 802.15.4 MAC protocol in terms of packet loss probability and throughput.

Cognitive radio (CR) has emerged as one of effective methods to enhance the utilization of existing radio spectrum. Main principle of CR is that secondary users (SUs) are allowed to use the spectrum unused by primary users (PUs) without interfering PU's transmissions. In this paper, PUs operate on a slot-by-slot basis and SUs try to exploit the slots unused by PUs. We propose OSA protocols in the single channel and we propose an opportunistic spectrum access (OSA) protocols in the multi-channel cognitive radio networks with one control channel and several licensed channels where a slot is divided into contention phase and transmission phase. A slot is divided into reporting phase, contention phase and transmission phase. The reporting phase plays a role of finding idle channels unused by PUs and the contention phase plays a role of selecting a SU who will send packets in the data transmission phase. One SU is selected by carrier sense multiple access / collision avoidance (CSMA/CA) with request to send / clear to send (RTS/CTS) mechanism on control channel and the SU is allowed to occupy all remaining part of all idle channels during the current slot. For mathematical analysis, first we deal with the single-channel case and we model the proposed OSA media access control (MAC) protocol by three-dimensional discrete time Markov chain (DTMC) whose one-step transition probability matrix has a special structure so as to apply the censored Markov chain method to obtain the steady state distribution. We obtain the throughput and the distribution of access delay. Next we deal with the multi-channel case and obtain the throughput and the distribution of access delay by using results of single-channel case. In numerical results, our mathematical analysis is verified by simulations and we give numerical results on throughput and access delay of the proposed MAC protocol. Finally, we find the maximum allowable number of SUs satisfying the requirements on throughput and access delay.

In this paper we present a two-dimensional medium access control (MAC) protocol. Orthogonal frequency division multiple access (OFDMA) can make multiple stations (STA) transmit simultaneously on different sub-channels. On the other hand, carrier sense multiple access with collision avoidance (CSMA/CA) could make different stations contend the available channel from the time domain to avoid collision with each other. We propose a two-dimensional MAC protocol based on OFDMA and CSMA/CA in broadband systems. With the new designed MAC protocol different stations will access the channel from the time-frequency domain without interference and collision. The combination of OFDMA with CSMA/CA will improve the system throughput with efficient MAC and decrease the collision probability. We design that different stations will contend the available time-frequency resources dynamically under fairness. The system throughput of the designed protocol is analyzed and simulation results are presented to show the performance under our designed protocol far better than the conventional CSMA/CA protocol.

A new flexible multiple access control (MAC) scheme embedding channelization in multi-band carrier sense multiple access / collision avoidance (CSMA/CA) systems is proposed to provide different priority classes among users, and its performance is investigated. In the proposed scheme, two priority classes of users, primary and secondary users, are considered; the classical CSMA/CA protocol is modified to multiband operation for secondary users, whereas channelization is provided for primary users to ensure the quality of service (QoS). The performance of the proposed MAC scheme is analyzed using a new multi-band CSMA/CA model based on a Markov chain capturing the primary user channel activity and the number of bands. The throughput of secondary users is obtained as a function of the primary user activity as well as other CSMA/CA parameters. It is shown that this mixed MAC scheme can guarantee the throughput of primary users certainly with minimal performance degradation to secondary users, especially when the number of available bands is large or the maximum contention window (CW) size for the CSMA/CA secondary users is small compared with the number of secondary users.

The effectiveness of wireless local area networks significantly depends on the method of access to the common physical environment. The main access method that is used today in wireless local area networks is carrier sense multiple access with collision avoidance (CSMA/CA), managing the efficient distribution of the common environment between active stations. In this paper, as a topic of research we consider the state transition diagram of a CSMA/CA - based network, and we describe it by a system of differential equations. Analytical expressions for the probabilities of being in one of the possible states of a network station are derived.KeywordsWireless local computer networkCarrier sense multiple access with collision avoidance (CSMA/CA)State transition diagram