Article

Survey on OFDMA based MAC protocols for the next generation WLAN

Authors:
To read the full-text of this research, you can request a copy directly from the authors.

Abstract

The physical (PHY) layer peak rate of the wireless local area network (WLAN) has been almost exponentially improved over the past 15 years since 1999. However, it is proved that the throughput is very low comparing to the PHY peak rate, and the media access control (MAC) efficiency is very low in the current WLANs specification, especially in dense deployment scenarios. Therefore, to achieve high MAC efficiency the IEEE Standards Association Standards Board (IEEE-SA) approves IEEE 802.11ax in March 2014, to draw up a brand new amendment for the next generation WLAN. One of the promising technologies to improve MAC efficiency is Orthogonal Frequency Division Multiple Access (OFDMA). In this paper, we firstly investigate the existing OFDMA based MAC protocols in the literature. Then, a framework of OFDMA based MAC protocol for the next generation WLAN is proposed. Finally, all of the existing OFDMA based MAC protocols listed in this paper are compared according to the proposed design issues. To the best of our knowledge this paper is the first survey focusing on OFDMA based MAC protocols for the next generation WLAN.

No full-text available

Request Full-text Paper PDF

To read the full-text of this research,
you can request a copy directly from the authors.

... In the past 20 years, wireless local area network (WLAN) has developed extremely rapidly and become a widely deployed wireless network based on IEEE 802.11 protocol [1][2][3][4][5][6]. WLAN is one of the most important bearer modes for wireless network services [1,7]. ...
... Half of network traffic in 2021 will be occupied by Wi-Fi [7]. In recent years, the human demand for mobile traffic has grown exponentially, which results in making the traditional WLANs unable to meet this expectation [4][5][6][7][8]. Therefore, both academia and industry are focusing on the next generation WLAN [1][2][3][4][5][6][7][8][9]. ...
... In recent years, the human demand for mobile traffic has grown exponentially, which results in making the traditional WLANs unable to meet this expectation [4][5][6][7][8]. Therefore, both academia and industry are focusing on the next generation WLAN [1][2][3][4][5][6][7][8][9]. ...
Article
Full-text available
The next generation wireless local area network (WLAN) needs to significantly improve the area throughput in high-dense deployment scenario. Orthogonal frequency division multiple access (OFDMA), considered as the key technology of the next generation WLAN, has been adopted by IEEE 802.11ax. However, most existing studies have one tricky problem: interference extension problem, i.e., the stations (STAs) placed at dispersive locations from one basic service set (BSS) access channel and transmit data simultaneously through OFDMA, thereby interfering a large area and suppressing the potential transmissions around this BSS. Unfortunately, high-dense deployment scenario exacerbates interference extension problem. This article proposes a spatial clustering group division-based OFDMA (SCGD-OFDMA) protocol, which enables the geographically close STAs to form spatial clustering groups, named SCGs. Each SCG has a leader STA and several member STAs. Each SCG’s leader STA contends for channel resources. After that, the leader STAs that successfully contending channel are scheduled by the access point one by one to trigger its member STAs to transmit uplink data by using OFDMA. Therefore, the geographical interference area is reduced and the area throughput is improved since the concurrent STAs in one SCG are located in limited area. This article theoretically analyzes the optimal SCG establishment, and throughput and area throughput of SCGD-OFDMA. Theoretical analysis is consistent with simulation results. The simulation results also show that when the number of STAs is 200 and all resource units are used for random access, SCGD-OFDMA outperforms IEEE 802.11ax and OMAX in area throughput by 56.13% and 190.97%, respectively.
... Knowing that SMA and DMA methods are two extensions of the EDCA function, they can severely degrade the use of wide channels at their turn, which is directly impacting the performances of VHT WLANs. Despite the persistence of EDCA unfairness in the history of WLANs, the research work in the literature confirms that EDCA remains the suitable function at MAC layer of future WLANs [8,9]. ...
... The ability to meet a suitable traffic differentiation between the different traffic classes raises up a relevant challenge at MAC layer of the current version of 802.11ac WLANs [9,14]. With the growing needs of multimedia and real-time applications, it results that the MAC layer requires upgrades, in order to achieve both VHT and QoS [13]. ...
... With the growing needs of multimedia and real-time applications, it results that the MAC layer requires upgrades, in order to achieve both VHT and QoS [13]. For this reason, the service differentiation of EDCA should be adapted to allow priority traffic classes (VO and VI) getting better QoS, while providing non-priority traffic classes (BE and BK) the opportunity of accessing the channel [9]. Knowing that the non-priority ACs suffer from starvation to accessing the channel under the EDCA function, the same problem also arises under SMA and DMA methods, since the latter are considered as extensions of the EDCA operation rules for enabling channel bonding. ...
Article
Using optimally wide channels in 802.11ac networks has been the topic of various research work. Nevertheless, the efficiency of both Static and Dynamic Multichannel Access methods (SMA and DMA) is a challenging issue, since they employ the Enhanced Distributed Channel Access (EDCA) to provide the Quality of Service (QoS). Indeed, EDCA enables QoS through service differentiation between priority (Voice and Video) and non-priority (Besteffort and Background) traffics. Consequently, the concept of priority may severely starve non-priority traffics from channel access, and lead to an unfair bandwidth allocation. In this paper, we highlight the starvation issue of non-priority traffics in 802.11ac networks. Thereby, we propose a Starvation avoidance DMA (SDMA) method by means of 80 and 160 MHz channel bonding. The individual throughput is measured for comparing SDMA and DMA methods. The obtained results show a significant improvement in throughput of non-priority traffics, while maintaining the throughput level of priority traffics.
... Currently, there are several valuable surveys focusing on the key technologies of IEEE 802.11ax from different perspectives [5][6][7][8][9][10][11]. Based on Draft 0.4, Afaqui et al. [12] Khorov et al. [7] analyze several potential technical characteristics of IEEE 802.11ax during the earlier stage. ...
... Deng and et al. [5,11] analyze the problems of legacy IEEE 802.11, and discuss the QoS requirements and the technical challenges faced by IEEE 802.11ax, and then propose a protocol framework for MU access and transmission. Our previous study [6] analyzes and investigates the MU-MAC protocol based on OFDMA, and proposes an efficient OFDMA based multiuser MAC protocol framework. ...
Article
Full-text available
High-dense deployment scenario is supposed to be the killer scenario of the future wireless networks. The next generation high efficiency wireless local area networks (WLANs) standard - IEEE 802.11ax, which will be released in the year 2019, directly faces to the high-dense deployment scenario. IEEE 802.11ax is one milestone of WLAN standardization. Thus, a series of media access control technologies are introduced in IEEE 802.11ax such as multi-user MAC (MU-MAC) enhancements, spatial reuse (SR) technology, and target wake-up time (TWT) based power saving mechanism. This paper comprehensively surveys the key technologies proposes a tutorial for IEEE 802.11ax. Some valuable insights are presented in this paper. To the best of our knowledge, this is the first work to directly investigate and analyze the latest stable version (Draft 4.0) of IEEE 802.11ax.
... Nowadays Wireless Local Area Network (WLAN) becomes an indispensable part of wireless network because of its low cost and easy scalability [1]. However, with the increasing Mao 1 design is one of the important means to support the QoS requirements of high priority traffic. ...
... Nowadays Wireless Local Area Network (WLAN) becomes an indispensable part of wireless network because of its low cost and easy scalability [1]. However, with the increasing Mao 1 design is one of the important means to support the QoS requirements of high priority traffic. ...
Article
Full-text available
With the increasing diversity of wireless services and explosive growth of traffic, Wireless Local Area Network (WLAN) has become the main carrier of wireless traffics. Therefore, how to ensure the quality of service (QoS) requirements of high priority traffics is one of the momentous targets of the next generation WLAN. The Orthogonal Frequency Division Multiple Access (OFDMA) has been introduced into the next generation WLAN as the key technology and has become an important feature. However, less attention is played to the QoS-guaranteed and fairness-guaranteed in the existing OFDMA-based Media Access Control (MAC) protocols. This article proposes a double random access QoS oriented OFDMA MAC protocol for the next generation WLAN, named DRA-OFDMA. What different from the existing work is that the idea of two phases for parallel OFDMA random access is introduced in the protocol. The traffic priorities are not distinguished in the first phase of the random access, thus fairness of traffic is ensured at some extent. Users, which are failed to be accessed in the first phase, with high priority are allowed to be accessed in the second phase on the remaining available sub-channels, thus the QoS for the high priority traffic is well guaranteed. The DRA-OFDMA MAC protocol proposed in this paper has good compatibility advantage. It can completely reuse available frame defined by 802.11ax standard. In addition, the Markov chain based theoretical analysis model for the proposed protocol is formulated and the corresponding network performance is also analyzed in our paper. Finally, the correctness of theoretical analysis model and performance analysis are verified by simulation. Simultaneously, the simulation results show that the throughput of DRA-OFDMA with high priority traffic is enhanced 22.05% and 89.6% than that of RA-OFDMA and OMAX respectively, and the fairness of low priority traffic is also well guaranteed.
... Besides that, a similar operation as in the multi-user MIMO case is expected, as there are almost the same challenges to solve. A survey of current OFDMA proposals for WLANs is presented in [60], showing also how the use of OFDMA is able to significantly improve the WLAN efficiency. ...
Preprint
Full-text available
new generation of Wireless Local Area Networks (WLANs) will make its appearance in the market in the forthcoming years based on the amendments to the IEEE 802.11 standards that have recently been approved or are under development. Examples of the most expected ones are IEEE 802.11aa (Robust Audio Video Transport Streaming), IEEE 802.11ac (Very-high throughput at < 6 GHz), IEEE 802.11af (TV White Spaces) and IEEE 802.11ah (Machine-to-Machine communications) specifications. The aim of this survey is to provide a comprehensive overview of these novel technical features and the related open technical challenges that will drive the future WLAN evolution. In contrast to other IEEE 802.11 surveys, this is a use case oriented study. Specifically, we first describe the three key scenarios in which next-generation WLANs will have to operate. We then review the most relevant amendments for each of these use cases focusing on the additional functionalities and the new technologies they include, such as multi-user MIMO techniques, groupcast communications, dynamic channel bonding, spectrum databases and channel sensing, enhanced power saving mechanisms and efficient small data transmissions. We also discuss the related work to highlight the key issues that must still be addressed. Finally, we review emerging trends that can influence the design of future WLANs, with special focus on software-defined MACs and the internet-working with cellular systems.
... Furthermore, the HE-WLAN and legacy WLAN (i.e., IEEE 802.11ac) are compared in [3]; and the insights of DL/UL orthogonal frequency division multiple access (OFDMA), dynamic clear channel assessment (CCA), and UL MU-MIMO concepts are also introduced. A survey on OFDMA-based medium access protocols and OFDMA-based concurrent MU medium access control algorithms for HE-WLAN are presented in [4]. The research results in [5] are for dynamic tuning the CCA which enhances spatial reusability for addressing OBSS congestion problems. ...
... Besides that, a similar operation as in the multi-user MIMO case is expected, as there are almost the same challenges to solve. A survey of current OFDMA proposals for WLANs is presented in [60], showing also how the use of OFDMA is able to significantly improve the WLAN efficiency. ...
... For more literatures on adopting OFDMA in WLAN, one can refer to our survey paper[9]. ...
Article
Full-text available
The IEEE 802.11ax, which was approved by the IEEE Standards Association (IEEE-SA) in March, 2014 as the next generation Wireless Local Area Network (WLAN) standard, has rigorous requirements in terms of high throughput and Quality of Service (QoS) support in the dense user scenario. To achieve high throughput by utilizing the wide bandwidth while decreasing the collision probability among stations, a Channel Bonding based QoS-aware Orthogonal Frequency Division Multiple Access (OFDMA) MAC protocol (CBQO) is proposed in this paper. Based on the combination of channel bonding and OFDMA, the capability of reducing collision probability in the dense user scenario is enhanced compared to the traditional OFDMA based MAC protocol, since the amount of subchannels is improved several times by the introduction of the channel bonding, and the wide channel provided by channel bonding are efficiently allocated among stations according to their QoS requirements, as the OFDMA provides a flexible and fine-grained management of the channel resource. Simulation results show that the proposed protocol outperforms the IEEE 802.11ac MAC protocol in terms of both throughput and delay of video traffic.
... As mentioned in Subsection III-B, while downlink multiuser channel access is adopted in the IEEE 802.11ac based on MU-MIMO, realizing uplink multiuser channel access is a more challenging task. Several MAC layer research issues need to be addressed for uplink multiuser channel access, including: a) how to initiate uplink multiuser transmissions (i.e., AP-initiated or STA-initiated) [120] [121], b) which STAs should be selected for multiuser transmission [122], c) how to transmit an ACK frame from the AP to each sending STA [123], and d) how to avoid the hidden terminal problem for each STA involved in uplink multiuser transmission, especially in OBSS scenarios [122]. Also, by employing IBFD communications at the PHY layer, the overlaying MAC scheme should account for the new types of transmission collisions introduced by pairwise and non-pairwise IBFD communications, as well as the ACK frame transmission and potential unfairness problems, as discussed in Subsection III-C. ...
Article
The emerging paradigm of the Internet of Everything, along with the increasing demand of Internet services everywhere, results in a remarkable and continuous growth of the global Internet traffic. As a cost-effective Internet access solution, WiFi networks currently generate a major portion of the global Internet traffic. Furthermore, the number of WiFi public hotspots worldwide is expected to increase by more than sevenfold by 2018. To face this huge increase in the number of densely deployed WiFi networks, and the massive amount of data to be supported by these networks in indoor and outdoor environments, it is necessary to improve the current WiFi standard and define specifications for high efficiency wireless local area networks (HEWs). This paper presents potential techniques that can be applied for HEWs, in order to achieve the required performance in dense HEW deployment scenarios, as expected in the near future. The HEW solutions under consideration includes physical layer techniques, medium access control layer strategies, spatial frequency reuse schemes, and power saving mechanisms. To accurately assess a newly proposed HEW scheme, we discuss suitable evaluation methodologies, by defining simulation scenarios that represent future HEW usage models, performance metrics that reflect HEW user experience, traffic models for dominant HEW applications, and channel models for indoor and outdoor HEW deployments. Finally, we highlight open issues for future HEW research and development.
... The main goal of this TG is improving the spectrum efficiency to enhance the system area throughput in high-density scenarios in terms of the number of APs and/or STAs. As argued by many researchers and standardization contributers [6][7][8], the current MAC protocols are very conservative when operating in dense environments. Because of this overprotecting behavior, the performance of the current high-density WLAN networks is degraded. ...
Article
Full-text available
To satisfy the increasing demand for wireless systems capacity, the industry is dramatically increasing the density of the deployed networks. Like other wireless technologies, Wi-Fi is following this trend, particularly because of its increasing popularity. In parallel, Wi-Fi is being deployed for new use cases that are atypically far from the context of its first introduction as an Ethernet network replacement. In fact, the conventional operation of Wi-Fi networks is not likely to be ready for these super dense environments and new challenging scenarios. For that reason, the high efficiency wireless local area network (HEW) study group (SG) was formed in May 2013 within the IEEE 802.11 working group (WG). The intents are to improve the “real world” Wi-Fi performance especially in dense deployments. In this context, this work proposes a new centralized solution to jointly adapt the transmission power and the physical carrier sensing based on artificial neural networks. The major intent of the proposed solution is to resolve the fairness issues while enhancing the spatial reuse in dense Wi-Fi environments. This work is the first to use artificial neural networks to improve spatial reuse in dense WLAN environments. For the evaluation of this proposal, the new designed algorithm is implemented in OPNET modeler. Relevant scenarios are simulated to assess the efficiency of the proposal in terms of addressing starvation issues caused by hidden and exposed node problems. The extensive simulations show that our learning-based solution is able to resolve the hidden and exposed node problems and improve the performance of high-density Wi-Fi deployments in terms of achieved throughput and fairness among contending nodes.
... 11 Wireless Local Area Networks (WLANs) become increasingly dense, which can hardly meet the demands of ever-increasing mobile users as well as large bandwidth applications [2], such as High-Definition (HD) video traffic. To improve the spectrum efficiency for the future high density deployment scenarios, IEEE Standards Association (IEEE-SA) established the High-Efficiency WLAN (HEW) Task Group [3], which is currently working on a new high area throughput amendment named IEEE 802.11ax for the Next Generation WLAN (NGW) [4][5][6]. Note that multiple frequency channels are expected to be available to enhance the system throughput, e.g., more than 400 MHz channel bandwidth are available in the 5 GHz frequency band [7]. ...
Article
Full-text available
Recently, explosive growth of bandwidth demands has motivated many technological revolutions in the Wireless Local Area Networks (WLANs) such as the IEEE 802.11ax task group, which is established to enhance the throughput performance for the Next Generation WLANs (NGW) under high dense deployment scenarios. However, on the one hand, it is known that the Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) has become a generally accepted access mechanism in the WLANs, which is shown to bring about serious collisions when the stations (STAs) are relatively crowded. In this case, the channel access efficiency is definitively decreased and thus some frequency channel resources are eventually wasted. On the other hand, due to the inherent fading effect of wireless channel, network throughput of the NGW (i.e., 802.11ax) is further degraded by the existence of Low-Rate-Links (LRLs), where the available data transmission rate is relatively low. To resolve the above two technical issues, a distributed multi-channel MAC protocol, called CRC-MMAC, is proposed for the NGW. In the proposed CRC-MMAC, the concept of reserved-cooperative-link (RCL) is proposed and initiated under multi-channel environment, to fully exploit the potential of both channel reservation and cooperative relay. Accordingly, collisions in the network are effectively decreased using channel reservation as well as the data transmission rate of LRLs is significantly improved with cooperative relay. Furthermore, an analysis of the upper bound of saturation throughput gain is derived, which is validated by extensive simulations. Compared with the ‘Baseline’ scheme, i.e., the existing Dynamic Channel Assignment (DCA) protocol [1] using TXOP (Transmission Opportunity), the experiments results show that the saturation throughput of CRC-MMAC exceeds about \(140\,\%\), and the average packet delay is decreased by nearly \(60\,\%\).
... It enables multi-user channel access and multi-user data transmission since different STAs could use different sub-channels simultaneously. The associated researchers [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] have proved that the introduction of OFDMA into 802.11 MAC protocol makes remarkable improvements for efficiency. ...
Article
Full-text available
Wireless local area networks (WLANs) are widely deployed for internet-centric data applications. It is predicted that by 2018, about two-thirds of the world's internet traffic will be video, and more than half of the traffic will be offloaded to Wi-Fi networks. Consequently, WLANs need major improvements in both throughput and efficiency. New technologies continue to be introduced for WLAN applications for this purpose. The IEEE 802.11ac standard is the currently implemented amendment by the IEEE 802.11 standard working group that promises data rates at gigabits per second. The main features of the IEEE 802.11ac standard are adopting increased bandwidth and higher order modulation than the previous standard, and multiple-input multiple-output (MIMO) and multi-user MIMO transmission modes. These features are designed to improve the user experience. In addition to technologies that enhance the efficiency of the WLAN, the IEEE 802.11ax standard is also investigating and evaluating advanced wireless technologies to utilize the existing spectrum more efficiently. These modern communications technologies are steadily advancing physical layer data rates in WLANs, although data throughput efficiency of the WLAN may degrade rapidly as the physical layer data rate increases. The fundamental reason for the degradation is that the current medium access control (MAC) protocol allocates the entire channel to one user as a single source due to equally distributed time domain contention resolution. The challenges and difficulties have already been identified for designing efficient MAC layer resource allocation (MAC-RA) schemes for the upcoming IEEE 802.11ax high-efficiency WLAN. However, there is no profound investigation outcome for this kind of efficient resource allocation. Therefore, in this paper, we conduct an extensive survey of the expected features and challenges for IEEE 802.11ax in the design of fair and efficient MAC-RA. The associated previous research work is summarized as to future directions. Moreover, the need for each directed scheme is highlighted.
... A detailed survey of the most significant MU-MIMO-related solutions for WLANs is presented in [8]. Similarly, a short survey of the OFDMA-related works is presented in [9]. Other research works related to 802.11ax development focus on the performance of WLANs in dense scenarios, including: the evaluation of the dynamic sensitivity control mechanism [10], the use of BSS coloring [11], static and dynamic channel bonding [12], [13], channel access configuration [14], and more efficient but backward compatible alternatives to the legacy distributed coordination function [15], [16]. ...
Article
Full-text available
Next-generation 802.11ax WLANs will make extensive use of multi-user communications in both downlink (DL) and uplink (UL) directions to achieve high and efficient spectrum utilization in scenarios with many user stations per access point. It will become possible with the support of multi-user (MU) multiple input, multiple output (MIMO) and orthogonal frequency division multiple access (OFDMA) transmissions. In this paper, we first overview the novel characteristics introduced by IEEE 802.11ax to implement AP-initiated OFDMA and MU-MIMO transmissions in both downlink and uplink directions. Namely, we describe the changes made at the physical layer and at the medium access control layer to support OFDMA, the use of \emph{trigger frames} to schedule uplink multi-user transmissions, and the new \emph{multi-user RTS/CTS mechanism} to protect large multi-user transmissions from collisions. Then, in order to study the achievable throughput of an 802.11ax network, we use both mathematical analysis and simulations to numerically quantify the benefits of MU transmissions and the impact of 802.11ax overheads on the WLAN saturation throughput. Results show the advantages of MU transmissions in scenarios with many user stations, also providing some novel insights on the conditions in which 802.11ax WLANs are able to maximize their performance, such as the existence of an optimal number of active user stations in terms of throughput, or the need to provide strict prioritization to AP-initiated MU transmissions to avoid collisions with user stations.
... To improve the data rate for the next generation wireless networks, researchers inroduce several technologies such as orthogonal frequency division multiple access (OFDMA) [9,11], uplink multiuser multiple input multiple output (UL MU-MIMO) [7], non-orthogonal multiple access [4], massive MIMO [1], and full-duplex (FD) technology [5,12]. ...
Article
Full-text available
Continuously increasing the data rate in wireless networks is required to satisfy the ever-increasing service demands. Full-duplex (FD), a promising technology for wireless networks, is able to double the data rate theoretically. Although several researchers study the physical (PHY) and medium access control (MAC) protocols of FD technology, there are few study focusing on the multiuser MAC protocol design for the next generation wireless networks. In this paper, a power control (PC) based multiuser FD MAC protocol, named PC MU-FuPlex, is proposed. Moreover, the probability of establishing FD link is formulated specifically. The simulation results demonstrate that the proposed MAC protocol significantly improves the saturation throughput up to 200% compared to that without PC in higher modulation.
... In addition to these models, several papers exist in the literature since before the TGax was created in 2015. A detailed summary of these works is provided in [9]. Most of these works do not comply with the MU OFDMA model being considered in the TGax, and thus provide an incomplete understanding of the 802.11ax performance. ...
Conference Paper
Full-text available
IEEE 802.11ax is the upcoming standard of the IEEE 802.11 wireless local area networks (WLAN) family. Until its most recent standard, i.e. 802.11ac, the primary focus of the 802.11 Working Group has been to increase the overall through-put of the physical (PHY) layer using innovative mechanisms such as multiuser multiple input multiple output (MU-MIMO), higher order modulation and coding schemes etc. However, these PHY layer gains often fail to translate to high throughput at the medium access control (MAC) layer, particularly in dense deployment scenarios. To address this limitation, IEEE 802.11ax introduces new features, most notably the use of Orthogonal Frequency Division Multiple Access (OFDMA), thereby enabling concurrent MU transmissions. In this paper, we first provide an overview of the uplink MU OFDMA in IEEE 802.11ax. Second, we provide an analytical model for characterizing the performance of the 802.11ax MAC layer. We investigate the trade-off between providing high network throughput and supporting new users using a metric-namely, BSR delivery rate. Finally, we validate our analyses using extensive NS-3 simulations, and present the resulting findings.
... Another technology which is under consideration for improving MAC efficiency in the next WLAN generations is the Orthogonal Frequency Division Multiple Access (OFDMA). We refer to [22] for a recent review of OFDMAbased MAC protocols known in the literature; these protocols are compared according to a framework that includes specific design issues for next generation WLANs. ...
Article
Full-text available
The proliferation of wireless communications systems poses new challenges in terms of coexistence between heterogeneous devices operating within the same frequency bands. In fact, in case of high-density concentration of wireless devices, like indoor environments, the network performance is typically limited by the mutual interference among the devices themselves, such as for wireless local area networks (WLANs). In this paper, we analyze a protocol strategy for managing multiple access in wireless networks. A network of sensors colocated with the WLAN terminals forms a control layer for managing the medium access and scheduling resources in order to limit collisions and optimize the WLAN data traffic; this control layer is based on a low-power wideband technology characterized by interference robustness, like CDMA (code division multiple access) or UWB (ultra-wideband) for sensors. In this work, we perform an analytical and simulative performance study of the saturated throughput, showing numerical results for the UWB-IR (Impulse Radio) sensors case and highlighting the advantage that can be provided particularly in very high capacity systems, which constitute the necessary evolution of current WLAN versions.
... With OFDMA technology, the whole channel is divided into several sub-channels, and several subcarriers comprise one sub-channel. Thus, OFDMA enables multiuser channel access and multiuser data transmission since different nodes could use different sub-channels simultaneously [50]. Therefore, TDMA MAC protocols and OFDMA-based MAC protocols with fair subcarrier sharing (e.g. ...
Article
Full-text available
The authors consider the problem of multi-player evolutionary game with two strategies and an arbitrary number of players. A randomised probabilistic access model is considered where the users randomly select the strategies. The strategies are a selection between two radio access technologies to receive service from. For a fair resource allocation between a number of users, the payoff function of each player is considered to be inversely proportional to the number of players choosing a strategy. It is valid for the radio access technology selection problem where resources are divided fairly between the users. The necessary and sufficient conditions for the existence and uniqueness of a mixed Nash equilibrium point of the game is provided. In addition, it is proved that the mixed Nash equilibrium point of the game is globally asymptotically stable and also evolutionarily stable strategy.
... Therefore, the standard organization of IEEE starts the standardization work for IEEE 802.11ax [3], 11ay [4] and 11be [5]. Among these standard, orthogonal frequency divisional multiplexing access (OFDMA) [6], multi user multiple input multiple output (MU-MIMO) and directional beamforming are key technologies to pursue high network throughput. To efficiently schedule multiple concurrently Existing works of [7][8][9][10][11][12][13][14][15][16][17] have investigated the concurrent transmission problem. ...
Article
Full-text available
Two conflict graph based concurrent transmission scheduling algorithms are proposed in this paper to efficiently solve the spatial TDMA (STDMA) scheduling problem for the next generation WLAN. Firstly, the STDMA scheduling problem for multiple timeslots is formulated as an multiple-step optimization problem. Secondly, a bi-weighted conflict graph is constructed to model the concurrent transmissions’ interference relationships, where the nodes denote the transmission request and the weights of the edges denote the interference level between any two transmission request nodes. If the interference between two transmission nodes is larger than the given interference threshold, then there are no edge between these two nodes. And only the acceptable interferences are modelled as the edges. Finally, a heuristic clique based algorithm (HCBA) and an optimal clique based algorithm (OCBA) are proposed, where HCBA assigns the transmission requests to the multiple timeslots one by one while OCBA assigns the transmission requests to the multiple timeslot once. The performance gap between the optimal one and the suboptimal one is evaluated. Simulation results show that HCBA not only has low complexity but also achieves similar performance comparing to OCBA.
... Considering that IEEE 802.11ax has introduced many new features of MAC layer technologies as well as PHY, we expect that it will become a new milestone in the evolution of the IEEE 802.11 standard. This is why, during recent years, both industrial and academia focus strongly on the standardization process and key technologies of IEEE 802.11ax [6][7][8][9][10]. Therefore, it is quite important to survey the key technologies of IEEE 802.11ax. ...
Article
Full-text available
With the ever-increasing demand for wireless traffic and quality of services (QoS), wireless local area networks (WLANs) have developed into one of the most dominant wireless networks that fully influence human life. As the most widely used WLANs standard, IEEE 802.11 will release the upcoming next generation WLANs standard amendment: IEEE 802.11ax. Thus, this article briefly surveys the key technologies of IEEE 802.11ax. Furthermore, performance requirements of IEEE 802.11ax are evaluated via a proposed systems and link-level integrated simulation platform (SLISP). Simulations results confirm that IEEE 802.11ax significantly improves the user experience in high-density deployment, while successfully achieves the average per user throughput requirement in project authorization request (PAR) of IEEE 802.11ax by four times compared to the legacy IEEE 802.11. To the best of our knowledge, this article is the first work to thoroughly and deeply evaluate the compliance of the performance requirements of IEEE 802.11ax.
... Radio Resource Management (RRM) which is the main element of OFDMA, is critical in achieving the required performance for higher system loads in which each of the main elements of Medium Access Control (MAC) and Physical (PHY) layers has to be managed accordingly [1]. In contrast to its counterpart, namely mobile WiMAX (IEEE802.16m), ...
Article
Full-text available
Packet scheduling is one of the key schemes used in Radio Resource Management (RRM) for Long Term Evolution (LTE) cellular network. It serves as the resource allocation for each time and frequency dimensions in LTE baseband processing. In previous research, a new scheduling algorithm was developed, namely the Modified-Proportional Fair (PF) scheduler that splits a single subframe into multiple time slots and allocates the resource block (RB) to the identified User Equipment (UE) in some chosen time slots and it is done continuously for each subframe depending on the instantaneous Channel Quality Indicator (CQI) feedback received from UEs. Results have shown that the Modified-PF scheduler produces the most outstanding overall performance in terms of spectral efficiency and throughput with comparable fairness as compared to other state-of-the-art schedulers, namely, Round Robin and Proportional Fair schedulers. However, the performance of the new scheduler is not analysed in UE mobility scenario. Hence, this research will determine the type of response by the scheduler towards different mobility condition by simulating the throughput and the spectral efficiency of the three schedulers for various UE velocities. It is observed that the Modified-PF again shows significant performance improvement for various mobility condition in terms of average UE throughput and average UE spectral efficiency in both single cell omnidirectional and tri-sector eNodeB. This shows that Modified-PF can be considered as one of the packet scheduling options for the LTE cellular network.
... UL and DL OFDMA was introduced by IEEE 802.11ax [46]. As shown in Fig. 4b, co-OFDMA refers to a master AP that successfully accesses the wireless channel coordinates with other APs called slave AP and allocates frequency resources among them. ...
Article
Full-text available
The IEEE 802.11ax for Wireless Local Area Network (WLAN), one of the most important wireless networks, will be released in 2020. In recent years, ultra-high definition video service and real-time applications attract increasing attention. Therefore, the next generation WLAN (beyond IEEE 802.11ax): IEEE 802.11be task group (TGbe) was formally established in 2019, which regards achieving extremely high throughput (EHT) as its core technical objective. This article investigates and analyzes the key technologies of IEEE 802.11be, and further provides our perspectives and insights on it. Specifically, this article gives a brief overview on IEEE 802.11be, including the target scenario and technical objective, key technologies overview, and the standardization process. After that, we further investigate, analyze and provide perspectives on the key technologies of IEEE 802.11be including multi-band operation, multi-AP coordination, enhanced link reliability, and latency & jitter guarantee. To the best of our knowledge, this is the first work to investigate, analyze and provide insights on IEEE 802.11be.
Chapter
Real-time applications (RTAs) are a major challenge for wireless networks. The traditional wireless local area network (WLAN) adopts Enhanced Distributed Channel Access (EDCA) in order to differentiate the quality of services (QoS) based on traffic priorities. However, for the high-dense scenario, the collisions frequently occur, thereby deteriorating both throughput and latency. The next generation WLAN standard: IEEE 802.11be aims to efficiently decrease the latency. Therefore, in this paper, we propose a soft channel in-band reservation protocol (SCRP). SCRP introduces channel reservation to alleviate channel collisions since the ongoing transmission piggybacking the predicted next transmission time. Moreover, a soft reservation canceling scheme is introduced to fully reuse the wireless resources. It means if the nodes who reserve the channel does not has packet to send at the reservation time, a low-overhead frame exchange may flexibly cancel the reservation and, in this case, other nodes can contend the channel resources. Simulation results show that SCRP significantly decreases the latency and improves the throughput of the entire network.
Chapter
With the rapid development of wireless local area network (WLAN) and the proliferation of intelligent terminals, the current WLAN protocol is no longer able to meet the needs of users. Therefore, the next generation WLAN: IEEE 802.11ax has emerged to meet the growing demand for user traffic. Orthogonal Frequency Division Multiple Access (OFDMA), which enables simultaneous transmission of data by different User Equipment (UEs), is considered to be one of the key technologies of IEEE 802.11ax. In order to achieve high throughput rates and low access latency to ensure quality of service (QoS), IEEE 802.11ax supports two uplink access modes: scheduling access and random access. However, how to adaptively and efficiently switch these two access mechanisms in the process of real-time operation of the system, and effectively reduce the drawbacks caused by these two mechanisms is a thorny problem. This paper proposes an evaluation mechanism of network traffic load based on OFDMA-MAC protocol, and its performance is verified by simulation. The simulation results show that the traffic load assessment mechanism effectively improves the network throughput and quality of service (QoS), and also adapts to the dynamic changes in network traffic.
Conference Paper
To provide better QoS guarantee for the next generation WLAN, IEEE 802.11ax task group is founded in March 2014. As a promising technology to accommodate multiple nodes concurrent transmissions in dense deployment scenario, orthogonal frequency division multiple access (OFDMA) will be adopted in IEEE 802.11ax with great possibility. In this paper, an OFDMA based multiple access protocol with QoS guarantee is proposed for the next generation WLAN. Firstly, a redundant access mechanism is given to increase the access success probability of the video traffic where the video stations can concurrently send multiple RTS packets in multiple subchannels. Secondly, a priority based resource allocation scheme is presented to let AP allocate more resources to the video stations. Simulation results show that our protocol outperforms the existing OFDMA based multiple access for IEEE 802.11ax (OMAX) protocol in terms of delay and delay jitter of video traffic in dense deployment scenario.
Conference Paper
Most recently, an enhancement amendment named IEEE 802.11ax is proposed by the High-Efficiency WLAN (HEW) Task Group for the Next Generation WLAN (NGW), with a focus on improving spectrum efficiency as well as area throughput. However, collisions among stations (STAs) and Low-Rate-Links (LRLs) severely degrade the network performance, which have become a great matter of concern. In this paper, a channel reservation based multi-channel MAC protocol with serial cooperation is proposed for the next generation WLAN, called CRSC-MMAC, to explore the capabilities of both cooperative relay and channel reservation. In particular, with cooperative relay available, a LRL is divided into two wireless links that sequentially occur on the same data channel with higher data rate. Besides, by using multi-step channel reservation, multiple cooperative transmission opportunities can be reserved in advance with only one successful handshake on the control channel, and thus collisions are effectively alleviated. Extensive simulations are deployed using ns-2 simulator, simulation results show that saturation throughput of the proposed CRSC-MMAC protocol is nearly two times of that of the ‘Baseline’ scheme, and average packet delay of CRSC-MMAC is decreased by nearly 33%.
Conference Paper
In wireless networks, the capability of sensing the received power variation on wireless channel is named as channel sensing capability (CSC). However, as wireless networks become increasingly dense, it decreases the reliability of multiuser transmission if only CSC is simply used for indicating channel state. Thus, in this paper, a novel conception named as neighbor channel sensing capability (NCSC) is proposed to describe the capability of nodes for sensing the channel state of their neighbor nodes. We prove that the consistency of NCSC, defined as the variable of the difference of the received power of two neighboring nodes, obeys a Gaussian distribution when the location of all transmitting nodes obeys a homogeneous Poisson point process. Moreover, we derive the mean and variance of the consistency of NCSC, and give the expression of NCSC to accurately describe the capability of sensing the channel state of neighbor nodes. The simulation results show that NCSC can efficiently indicate and validate our analysis model and derivation.
Chapter
Narrow-Band Internet of Things (NB-IoT) is 3GPPs cellular technology designed for Low-Power Wide Area Network (LPWN) and it is a promising approach that NB-IoT combines with NOMA which is designed for accommodating more devices in the 5G era. Previous works mainly focus on uplink channel resource allocation to achieve connectivity maximization in NB-IoT with NOMA; however, few articles consider NB-IoT downside issues and downlink resource allocation problem to achieve maximum system throughput has not been studied in NB-IoT with NOMA. Thus, in this paper to provide a reliable and seamless service for NB-IoT users (NUs) and maximizing network downlink throughput, we propose a resource allocation algorithm for joint equipment QoS requirements and resource allocation fairness. In this scheme, we design algorithm to implement the mapping between NUs and subchannels for suboptimal system throughput. Then we convert the power allocation problem of the NUs on the same subchannel into a DC problem and we design algorithm to solve it to get suboptimal solution. Numerical results show that the proposed scheme achieves a better performance compared with exiting schemes in terms of the system throughput.
Article
Full-text available
The next generation Wireless Local Area Network (WLAN) IEEE 802.11be regards Extremely High Throughput (EHT) as its core technology goal, among which multi-band capability and AP cooperation technology are regarded as its key technologies. However, the existing research on Orthogonal Frequency Division Multiple Access (OFDMA) protocol does not consider the multi-band capability and AP collaboration technology of IEEE 802.11be, so the improvement of system performance is limited and does not meet the EHT requirement. Especially when the nodes in overlapping coverage area have a large number of traffic, it is more important to improve the throughput of nodes in overlapping coverage area. In order to improve the throughput of nodes in overlapping coverage area, this paper proposes a spatial clustering group OFDMA protocol associated with multiple Basic Service Sets (BSSs). The protocol allows nodes in overlapping coverage area to be associated with multiple BSSs at the same time by using multi-band capability, that is, multi-association; Using AP collaboration technology allows nodes to perform parallel backoff with channels on multiple BSSs to improve access efficiency. Nodes in the overlapping coverage area are associated with the channels of multiple BSSs for parallel backoff. Node completed backoff and successfully accessed triggers a spatial clustering group (SCG) with close to its spatial location. OFDMA mode is used by SCG to access and transmit, thus increasing the access opportunities of nodes within overlapping coverage, thereby improving the throughput. The simulation results show that using the SCG-OFDMA protocol proposed in this paper associated with two BSSs, its throughput of nodes within overlapping coverage can achieve 353.41% higher than the IEEE 802.11ax protocol and 558.33% higher than the OMAX protocol respectively.
Chapter
The next generation wireless local area network (WLAN) needs to significantly promote the area throughput in high dense scenario. OFDMA, considered as the key technology of next generation WLAN, has been adopted by IEEE 802.11ax. However, the existing studies on the OFDMA protocol have the interference extensions problem, i.e. multiple users are located in the dispersive area, and then the geographical interference area is expanded. In this paper, a spatial clustering group based OFDMA multiple access scheme (SCG-OFDMA) is proposed. SCG-OFDMA enables the users in close area to form spatial clustering groups dynamically, then the users in the spatial clustering group access channel and transmit data by OFDMA. It reduces the geographical interference area, and enhances the area throughput. Simulation results show that the area throughput of SCG-OFDMA is higher than OMAX and DCF by 20\(\%\) and 36\(\%\) respectively.
Conference Paper
Wireless Local Area Networks (WLANs) are becoming an essential form of communication in our life, and they have known a strong history of development. The current IEEE 802.11ac technology aims at achieving a Very High Throughput (VHT), by utilizing wider channels 80 and 160 MHz. The wide channels are obtained by bonding adjacent 20 MHz sub-channels. This is why, Static and Dynamic Multichannel Access (SMA and DMA) methods are proposed for controlling such multichannel transmissions. SMA and DMA guarantee the requirements of Quality of Service (QoS) for VHT WLANs, by following the existing 802.11e Enhanced Distributed Channel Access (EDCA). However, EDCA still suffers from the starvation among low priority ACs. Although several enhancements have been proposed since the emergence of the starvation issue, none of the proposed research works have addressed the critical state of low priority ACs BestEffort (BE) and BacKground (BK) under wide channels. In this paper, we propose to enhance the DMA method, in order to improve the multichannel access efficience and hence increase the throughputs of BK and BE. The obtained simulation results demonstrate the contribution of the Starvation resolution within the DMA method (SDMA) for increasing the throughputs of low priority ACs while maintaining the throughputs of high priority ACs.
Book
Full-text available
Since my Ph.D., I have been studying and working for the use of Reinforcement Learning techniques for MAC Layer resource allocation schemes in WLANs (Wi-Fi). In this book, I compile a few of my contributions related to this effort. I proposed to replace probabilistic channel access mechanisms with more intelligent and optimized mechanisms based on Reinforcement Learning techniques. Recently, I have started working on the use of Federated Reinforcement Learning to improve how Future Wi-Fi networks share and use the spectrum. This book starts by highlighting the issues and challenges faced by probabilistic MAC layer resource allocation mechanisms. Initially, it proposes to replace the state-of-the-art mechanism with a self-scrutinized channel observation-based channel access mechanism. Later, with the use of the Reinforcement Learning technique (Q learning), it proposes an intelligent Q learning-based Resource Allocation (iQRA) mechanism for Wi-Fi networks. In the end, a Federated Reinforcement Learning-based iQRA framework is proposed to enhance the share and use of the spectrum.
Chapter
In order to improve the network performance in the high dense multi-BSSs, the next generation WLAN: IEEE 802.11ax introduces spatial reuse (SR) technology to improve the spectrum utilization, manage the multi-BSSs interferences and increase the possibility of simultaneous transmissions. This paper firstly introduces the SR technologies of IEEE 802.11ax in detail. After that, to fully verify the performance, we build a system & link level integrated simulation platform for IEEE 802.11ax and achieve the SR. Finally, we evaluate the performance of the SR through the built simulation platform, the simulation results clearly indicate that the network throughput is improved by 34.3\(\%\) in uplink scenarios. To the best of our knowledge, this is the first work to introduce and evaluate the SR technologies for IEEE 802.11ax.
Article
Full-text available
The next generation wireless local area network (WLAN) needs to significantly improve the area throughput in high dense scenario. Orthogonal Frequency Division Multiple Access (OFDMA),considered as the key technology of next generation WLAN,has been adopted by next generation WLAN communication standard. However,the existing studies on the OFDMA protocol have the interference extensions problem,i.e. multiple users are located in the dispersive area,and then the geographical interference area is enlarged. In this paper,a spatial clustering group based OFDMA multiple access protocol (SCG-OFDMA) is proposed. SCG-OFDMA enables the users in close area to form spatial clustering groups dynamically,then the users in the spatial clustering group access channel and transmit data by OFDMA. It reduces the geographical interference area,and enhances the area throughput. The theoretical analysis of SCG-OFDMA is also carried out. The simulation results of SCG-OFDMA are in agreement with the theoretical analysis. Simulation results show that the area throughput of SCG-OFDMA is higher than existing OFDMA protocol and distributing coordination function by 15.98% and 31.26% respectively. It provides a reference to design media access control protocol of the next generation WLAN. © 2018, Editorial Board of Journal of Northwestern Polytechnical University. All right reserved.
Conference Paper
Full-text available
To enhance the throughput of wireless local area networks (WLANs) while satisfying the quality of service (QoS) requirements, this paper proposes a novel DCF-based multi-user MAC protocol employing orthogonal frequency division multiple access (OFDMA) scheme. In the proposed protocol, an access point (AP) acts as a master to organize all the stations within the basic service set (BSS) and reserves the radio resource by the conventional distributed coordination function (DCF). In the resource reservation period, the AP performs a flexible access control utilizing the fine-grained resource block and the opportunistic scheduling based on the QoS requirements and the channel condition of each station. With the objective to increase the spectrum efficiency as well as to satisfy the QoS requirements, this paper also proposes a dynamic resource allocation algorithm. Numerical results confirm that the proposed multi-user MAC protocol ensures the QoS requirement with a high probability and enhances the throughput performance.
Conference Paper
Recently, IEEE 802 started a task group to investigate and deliver next generation WLAN technologies for the scenarios of dense networks with a large number of stations and access point. The proposal is specified as the IEEE 802.11ax amendment. Due to the significant network capacity increase achieved by 802.11ax, the term high-efficiency WLAN (HEW) is also used in reference to this new amendment. This paper summarizes the IEEE 802.11ax standardization activities in progress and presents an overview of the most important features proposed in the 802.11ax amendment. Expected features and challenges for 802.11ax in the design of physical layer (PHY) and media access control sub-layer (MAC), toward a new era of wireless LANs, are also discussed.
Conference Paper
The IEEE 802.11 specification for Wireless Local Area Networks (WLANs) supports 20 MHz channels utilizing bandwidths up to 160 MHz. However, the support of devices simultaneously transmitting over different, non-overlapping channels, is not specifically addressed. Recently, there has been interest in developing a 802.11 specification for Carrier Grade Wi-Fi which has led to the requirement for solutions with efficient frequency resource utilization that are not currently supported. In this paper we propose a Medium Access Control (MAC) method, called Multi-User Parallel Channel Access (MU/PCA) that enables simultaneous transmission to multiple devices of various bandwidths, while maintaining backward compatibility with 802.11. We present analytical and simulation results demonstrating the throughput gains that can be achieved using the proposed MU/PCA scheme as compared to the current Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA) scheme that is used in 802.11.
Conference Paper
In Orthogonal Frequency Division Multiple Access (OFDMA), there are multiple sub-channels which enable multiple stations to transmit concurrently on different sub-channels. The stations can obtain the channel information of all the sub-channels at each time instant. Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) allows different stations to randomly contend for the available subchannels from the time domain to avoid collision with each other. This gives a resource in time and frequency domain. In this paper, we present a Concurrent OFDMA-based CSMA/CA (C-OFDMA) MAC protocol for Next Generation Wireless Local Area Network where all the stations that transmit successful Request-To-Send (RTS) packet in the contention phase send their traffic concurrently to the Access Point (AP). The proposed C-OFDMA protocol is compared with existing IEEE 802.11 DCF, IEEE 802.11 RTS/CTS, and Hybrid-OFDMA MAC protocols and simulation results show that it provides improved throughput for crowded WLAN systems.
Article
With the increase of the number of Wireless Local Area Network devices (laptop PC, PDA, cellphones and set-top boxes) multi-user communication get a great interest for future versions of IEEE 802.11 standard. However, current CSMA/CA WLAN protocols do not support multiple transmissions on the same time frequency resource. This hinders these systems from taking a potential increase of the available throughput in dense deployments. In this contribution we propose a new RTS/CTS mechanism destined for WLAN SDMA/OFDMA access. We provide a capacity based analytical framework to assess the performance of these PHY layer techniques from MAC perspective in a multi-user context. Taking into account the MAC overhead it is shown that SDMA provides a substantial gain for multi-user throughput.
Article
In this paper, we present a multi-channel carrier sense multiple access with collision avoidance (CSMA/CA) protocol for orthogonal frequency division multiple access (OFDMA) systems. The CSMA/CA system in conventional single-channel operation has the advantage of not requiring the signaling for bandwidth request and allocation over the scheduled access system but it sacrifices system efficiency significantly. We overcome the system efficiency limitation by exploiting the OFDMA system features that multiple stations can transmit simultaneously on different sub-channels, and the stations can obtain the channel information of all the sub-channels at each time instant. The OFDMA-based multi-channel CSMA/CA protocol is designed to enable the stations to contend with each other for channel access both in time and frequency domains through a two-dimensional backoff scheme. The protocol takes a generalized form of the conventional single-channel CSMA/CA protocol: It allows to segment the channel bandwidth into multiple narrow-band random access channels and adjust the transmission probability according to the multi-channel activity in a flexible manner. For throughput analysis, we devise a multi-channel p-persistent CSMA protocol that can emulate the multi-channel CSMA/CA protocol and then analyze its saturated throughput. The simulation and analysis results reveal that the proposed system performs far better than the single-channel CSMA/CA system while using the same total bandwidth and even close to the scheduled access system. Further, we examine how stringent time synchronization is required among the constituent stations in implementing of the OFDMA-based multi-channel CSMA/CA system.
Conference Paper
Existing medium access control (MAC) schemes for wireless local area networks (WLAN) have been shown to lack scalability in crowded networks, and efficiency in supporting heterogeneous traffic types. These issues are mostly due to the use of random multiple access techniques in the MAC layer. The design of these techniques is highly linked to the choice of the underlying physical (PHY) layer technology. The advent of new PHY schemes that are based on orthogonal frequency division multiple access (OFDMA) provides new opportunities for devising more efficient MAC protocols. We propose a new adaptive MAC design based on OFDMA technology. The design uses OFDMA to reduce collision during transmission request phases, and makes channel access more predictable. To improve efficiency, we combine the OFDMA access with a carrier sense multiple access (CSMA) scheme. Data transmission opportunities are assigned through an access point that can schedule traffic streams in both time and frequency (subchannels) domains. We demonstrate the effectiveness of the proposed MAC and compare it to existing mechanisms through simulation experiments and by deriving an analytical model for the operation of the MAC in saturation mode.
Conference Paper
Random access is critical to OFDMA wireless networks. However, due to special features of an OFDMA system, how to carry out random access in an efficient manner is still an open issue for OFDMA wireless networks. In this paper, a new random access protocol is proposed for OFDMA wireless networks. It is distinguished by a novel mechanism called concurrent multi-channel carrier sense multiple access (CM-CSMA/CA). Simulation results show that the new random access protocol is highly efficient in uplink access and also significantly outperforms existing random access protocols for OFDMA wireless networks.
Article
In this letter, we present an opportunistic multichannel CSMA protocol for OFDMA systems in frequency-selective fading channel. In order to opportunistically exploit the frequency selectivity, an OFDM-based single-channel CSMA protocol can employ water-filling power allocation as it allows a single station to utilize the whole frequency bandwidth at each time instant. In contrast, the proposed OFDMA-based multichannel CSMA protocol achieves the multi-user diversity gain by arranging multiple stations to transmit on their favorable sub-channels simultaneously. The proposed protocol is designed as an opportunistic version of the original multi-channel CSMA protocol, which was proposed in our previous work, and adopts a channel-adaptive backoff (or transmission probability control) algorithm, enabling each station to attempt data transmission on its high-SNR sub-channel with a high probability. The opportunistic multi-channel CSMA turns out to improve the total data rate significantly over the opportunistic single-channel CSMA, and to achieve almost full multi-user diversity gain despite the distributed operation.
Article
In WLAN systems, the difference in propagation delay among stations (STAs) can exceed the predefined cyclic prefix length, leading to multiple access interference (MAI). To solve this MAI problem, it is necessary to use a longer cyclic prefix length for orthogonality between different subchannels; however, this sacrifices system efficiency due to the cyclic prefix overhead. In this paper, we propose a group contention-based OFDMA to solve the MAI problem with an adequate cyclic prefix length and support a larger number of STAs. The STAs within the cyclic prefix duration that are synchronized to an access point (AP), are included in the same contending group and compete with other STAs of the group in transmitting packets. The proposed scheme allows for the adoption of an adequate cyclic prefix length without MAI, and is able to reduce the cyclic prefix overhead. In addition, since no packet errors are induced by MAI in any of the STAs, the STAs can transmit simultaneously without redundant short interframe spaces (SIFSs) and other control packets. Through analysis and simulation, we show that for a large number of STAs, the proposed scheme achieves higher throughput than 802.11 protocols and a conventional CSMA combined with OFDMA.