Saturation Throughput Research Articles

Saturation Throughput Performance Analysis of a Medium Transparent MAC Protocol for 60 GHz Radio-Over-Fiber Networks

We demonstrate an analytical model for calculating the saturation throughput performance of a medium transparent medium access control (MAC) protocol in 60 GHz radio-over-fiber (RoF) networks. The proposed model incorporates effectively the medium transparent MAC mechanism, assuming a finite number of terminals and ideal channel conditions. It takes into account contention both at the optical and wireless layer, ensuring seamless and dynamic capacity allocation over both transmission media. This model enables extensive saturation throughput performance analysis for the medium transparent MAC and has been applied to 60 GHz RoF network scenarios considering variable numbers of available optical wavelengths, wireless nodes and serving antenna elements and for two different data rate values, namely 155 Mbps and 1 Gbps. Comparison between the model-based throughput results and respective simulation-based outcomes reveals that our model is extremely accurate in predicting the system throughput. Moreover, it confirms that the proposed medium transparent MAC protocol can effectively operate in high-speed 60 GHz RoF LAN environments.

Asynchronous Bypass Channels for Multi-Synchronous NoCs: A Router Microarchitecture, Topology, and Routing Algorithm

Network-on-chip (NoC) designs have emerged as a replacement for traditional shared-bus designs for on-chip communication. As with all current very large scale integration designs, however, reducing power consumption in NoCs is a critical challenge. One approach to reduce power consumption is to dynamically scale the voltage and frequency of each network node or groups of nodes (DVFS). Another approach is to replace the balanced clock tree with a globally-asynchronous, locally-synchronous (GALS) clocking scheme. In both DVFS and GALS designs, the chip as a whole is multi-synchronous. As the NoCs interconnecting those nodes must communicate across these clock domain boundaries, they tend to have high latencies as packets must be synchronized at the intermediate nodes. In this paper, we propose a novel router microarchitecture which offers superior performance with respect to typical synchronizing router designs for multi-synchronous networks. Our approach features asynchronous bypass channels which allow flit traversal of intermediate nodes within the network without the latching or synchronization overheads of typical designs. We also propose a new network topology and routing algorithm that leverage the advantages of the bypass channel offered by our router design. We present a detailed analysis of design decisions which affect the performance of the asynchronous bypass channel network. Our experiments show that our design improves the performance of a conventional synchronizing design with similar resources by up to 26% at low loads and increases saturation throughput by up to 50% for a uniform random traffic.

Throughput Analysis of Broadband Access in High Speed Railway

As the need for broadband access in high speed railway, it becomes necessary to understand the impact of mobility on traditional parameters of WLAN standards always working under stationary environment, such as throughput. In this paper, we provide the analysis of the impact of high speed in IEEE 802.11b PHY layer, and then propose the derivation of saturation throughput by applying 802.11b MAC schemes in TGC system. Our results show that WLAN standards have promising potential to be used in high speed environment.

Collaborative User Number Selection Based on Saturation Throughput and Sensing Performance

The number of collaborative users in a cognitive radio network is selected by maximizing the effective throughput of the cognitive radio network that considers both the spectrum-sensing performance and the saturation throughput performance. Numerical results show that the optimum number of collaborating users depends on the physical-layer techniques used, the physical channel conditions, and the upper-layer network parameters. These results give useful guidance on choosing the number of collaborative users involved in collaborative spectrum sensing.

Distributed MAC Protocol for Cognitive Radio Networks: Design, Analysis, and Optimization

In this paper, we investigate the joint optimal sensing and distributed Medium Access Control (MAC) protocol design problem for cognitive radio (CR) networks. We consider both scenarios with single and multiple channels. For each scenario, we design a synchronized MAC protocol for dynamic spectrum sharing among multiple secondary users (SUs), which incorporates spectrum sensing for protecting active primary users (PUs). We perform saturation throughput analysis for the corresponding proposed MAC protocols that explicitly capture the spectrum-sensing performance. Then, we find their optimal configuration by formulating throughput maximization problems subject to detection probability constraints for PUs. In particular, the optimal solution of the optimization problem returns the required sensing time for PUs' protection and optimal contention window to maximize the total throughput of the secondary network. Finally, numerical results are presented to illustrate developed theoretical findings in this paper and significant performance gains of the optimal sensing and protocol configuration.

Distributed multichannel medium access control protocol without common control channel for single-hop cognitive radio networks

A novel distributed cognitive radio multichannel medium access protocol without common control channel was proposed. The protocol divided a transmission interval into two parts for exchanging control information and data, respectively. In addition to evaluating system saturation throughput of the proposed protocol, a three-dimensional multi channel Markov chain model to describe the sate of the cognitive users (CUs) in dynamic spectrum access was presented. The proposed analysis was applied to the packet transmission schemes employed by the basic, RTS/CTS access mechanism adopted in the normal IEEE 802.11. Analyzing the advantage of the two methods, a hybrid access mechanism was proposed to improve the system throughput. The simulation results show that the experiment results are close to the value computed by the model (less than 5%), and the proposed protocol significantly improves the performance of the system throughput by borrowing the licensed spectrum. By analyzing the dependence of throughput on system parameters, hybrid mechanism dynamically selecting access mechanism can maintain high throughput.

Adaptive channel allocation strategy for mobile ad hoc networks

Medium access control (MAC) protocol is essential since it is to address how to resolve potential contentions and collisions among wireless nodes and give them equal share of channel bandwidth. However, due to the existence of hidden/exposed terminal problem and partially connected network topology, IEEE 802.11 standard, the de facto and widely accepted wireless MAC protocol, does not function well in mobile ad hoc networks (MANETs) because it brings intensive collisions, unfair channel access, and quickly degraded system throughput in multi-hop environments, especially when the whole system is also dense and congested. One approach to alleviate this problem is to use multi-channel MAC protocol because these nodes can access the wireless channel simultaneously as long as they choose the different channels to transmit their packets. Nowadays, the modern wireless MAC protocols usually support multiple channels, where mobile nodes adapt their channels based on their channel selection strategies to transmit their own packets. In this paper, we put forth an adaptive channel allocation strategy for IEEE 802.11 based multi-channel MAC protocol in MANETs. An analytic model is also carried out to study the normalized saturation throughput of proposed scheme. In addition to theoretical analysis, simulations are conducted to evaluate the performance of the proposed scheme in congested multi-hop environments, and the results indicate that our adaptive channel allocation strategy did achieve far better performance than the legacy single channel IEEE 802.11 protocol without loss of simplicity.

Performance modeling of MPEG‐4 video streaming over IEEE 802.11 using distribution coordination function

AbstractDelivering video streaming over wireless Internet is becoming increasingly popular. However, most of the research studies focused on the modeling analysis of system performance such as saturation throughput and channel utilization. Perceived quality of video streaming cannot be assessed solely based on the results of analytical models. In this paper, we propose a model to assess the perceived quality of MPEG‐4 video streaming over IEEE 802.11 distribution coordination function (DCF)‐based wireless local area networks. The analysis of our proposed model considers not only effects of losses such as collision loss from channel access competition but also wireless loss caused by wireless interferences. Moreover, the impact of the loss of specific MPEG‐4 video frames is also taken into account in the performance analysis. The model was validated by comparing our performance results with results obtained from simulation and analytical models. The results show that our proposed model is able to predict the perceived quality of MPEG‐4 video streaming over DCF‐based WLAN more accurately than other models. Copyright © 2010 John Wiley & Sons, Ltd.

Nonpreemptive priority scheme for the S-MAC protocol in multimedia mobile sensor networks

S-MAC is a well-known medium access control (MAC) protocol designed for wireless sensor networks (WSNs). S-MAC uses a few novel techniques to reduce energy consumption and support self-configuration. Besides, S-MAC also achieves good scalability and collision avoidance by utilizing a combined scheduling and contention scheme. However, S-MAC does not have any priority scheme, making it unsuitable for multimedia applications and suffering from varying degree of starvation and fairness problems. In this paper, we propose a simple, efficient, but yet well-performing sliding contention window control mechanism to modify the S-MAC protocol such that priority can be supported along with the multimedia applications in multimedia mobile sensor networks. Furthermore, the proposed scheme could solve the starvation problem and alleviate the fairness problem. An analytic model is carried out to study the saturation throughput of proposed scheme. In addition, simulations were also conducted to analyze the proposed scheme and the results show that the proposed scheme is able to carry the prioritized traffic and mitigate the starvation and fairness problems.

Performance of IEEE 802.11 under Jamming

We study the performance of the IEEE 802.11 MAC protocol under a range of jammers that covers both channel-oblivious and channel-aware jamming. We consider two channel-oblivious jammers: a periodic jammer that jams deterministically at a specified rate, and a memoryless jammer whose interfering signals arrive according to a Poisson process. We also develop new models for channel-aware jamming, including a reactive jammer that only jams non-colliding transmissions and an omniscient jammer that optimally adjusts its strategy according to current states of the participating nodes. Our study comprises of a theoretical analysis of the saturation throughput of 802.11 under jamming, an extensive simulation study, and a testbed to conduct real world experimentation of jamming IEEE 802.11 using a software defined radio (GNU Radio combined with USRP boards). In our theoretical analysis, we use a discrete-time Markov chain analysis to derive formula for the saturation throughput of 802.11 under memoryless, reactive and omniscient jamming. One of our key results is a characterization of optimal omniscient jamming that establishes a lower bound on the saturation throughput of 802.11 under arbitrary jammer attacks. We validate the theoretical analysis by means of Qualnet simulations. Finally, we measure the real-world performance of periodic, memoryless and reactive jammers using our GNURadio/ USRP aided experimentation testbed.

CoopGeo: A Beaconless Geographic Cross-Layer Protocol for Cooperative Wireless Ad Hoc Networks

Cooperative relaying has been proposed as a promising transmission technique that effectively creates spatial diversity through the cooperation among spatially distributed nodes. However, to achieve efficient communications while gaining full benefits from cooperation, more interactions at higher protocol layers, particularly the MAC (Medium Access Control) and network layers, are vitally required. This is ignored in most existing articles that mainly focus on physical (PHY)-layer relaying techniques. In this paper, we propose a novel cross-layer framework involving two levels of joint design---a MAC-network cross-layer design for forwarder selection (or termed routing) and a MAC-PHY for relay selection---over symbol-wise varying channels. Based on location knowledge and contention processes, the proposed cross-layer protocol, CoopGeo, aims at providing an efficient, distributed approach to select next hops and optimal relays along a communication path. Simulation results demonstrate that CoopGeo not only operates properly with varying densities of nodes, but performs significantly better than the existing protocol BOSS in terms of packet error rate, transmission error probability, and saturated throughput.

Performance analysis of distributed cluster-based MAC protocol for multiuser MIMO wireless networks

It is known that multiuser multiple-input multiple-output (MIMO) communication can enhance the performance of wireless networks. It can substantially increase the spectral efficiency of wireless networks by utilising multiuser interference rather than avoiding it. This paradigm shift has most impact on the medium access control (MAC) protocol because most existing MAC protocols are designed to reduce the interference. In this article, we propose a novel cluster-based carrier sense multiple access with collision avoidance (CB-CSMA/CA) scheme. The proposed scheme enables multiuser MIMO transmissions in wireless local area networks (WLANs) by utilising the multiuser interference cancellation capability of the physical layer. In this article we focus on the performance analysis of CB-CSMA/CA. We investigate saturation throughput applying optimum backoff parameters and in the presence of synchronisation errors. Furthermore, we study the impact of different clustering methods on non-saturation throughput. We show that CB-CSMA/CA improves throughput significantly compared to the CSMA/CA scheme used in the IEEE 802.11 system. It is a promising approach for a variety of network configurations including typical infrastructure WLANs as well as many other wireless cooperative networks.

3D Markov chain-based saturation throughput model of IEEE 802.11 EDCA

A new analytical model of enhanced distributed channel access (EDCA) which builds on an existing comprehensive model is presented. The model implements virtual collisions and combines the advantages of both accurate backoff countdown and accurate arbitration inter-frame space (AIFS) differentiation. The correctness of the model is evaluated by comparison with ns-2 simulations and two previous models. The comparison gives very good results.

Utilizing dynamic spectrum leasing for cognitive radios in 802.11-based wireless networks

Dynamic spectrum access (DSA) is proposed to deal with the growing shortage of available leased spectrum for wireless communication. We investigate a subset of DSA referred to as dynamic spectrum leasing (DSL). At its core, DSL allows spectrum lease holders and cognitive radios to cooperate in an effort to leverage spatial diversity to improve channel utilization for both parties. In this research, cognitive radios offer their services as an intermediate relay node in an effort to improve throughput of primary users utilizing a 802.11-based channel access mechanism. In return, the cognitive radio ‘piggy-backs’ some of its own data while acting as a relay. In this paper, a simple coordination scheme is introduced that allows a network of Secondary Users to coordinate with a primary user network’s access point. This scheme does not require any modification to the primary users’ 802.11-based protocol stack as our protocol is implemented only at the access point and the Secondary Users. Analytical insights into the overhead required for this coordination and the optimization of the overhead are presented. It is shown that, given sufficient relay channel conditions, forwarding packets through a secondary relay channel can be beneficial to both parties in terms of saturation throughput.

A new analytical model for the IEEE 802.15.4 CSMA-CA protocol

We give new analytical results for the performance of a wireless sensor network using the energy-conserving CSMA-CA MAC protocol of IEEE 802.15.4. We derive the throughput both under saturation and under a nonsaturation scenario in a star network involving periodic traffic, and validate the accuracy of our results using simulation for both acknowledgement and non-acknowledgement modes. Our analysis relies on the solution of a fixed point equation, and we prove the existence and uniqueness of the fixed point for the saturated case. The initial backoff window that maximizes saturation throughput is derived, and shown to be an approximately linear function of the number of active nodes. We also study the saturation model when the number of nodes tends to infinity, and obtain a simple expression for the asymptotic throughput.

Extending the Effective Throughput of NoCs With Distributed Shared-Buffer Routers

Router microarchitecture plays a central role in the performance of networks-on-chip (NoCs). Buffers are needed in routers to house incoming flits that cannot be immediately forwarded due to contention. This buffering can be done at the inputs or the outputs of a router, corresponding to an input-buffered router (IBR) or an output-buffered router (OBR). OBRs are attractive because they can sustain higher throughputs and have lower queuing delays under high loads than IBRs. However, a direct implementation of an OBR requires a router speedup equal to the number of ports, making such a design prohibitive under aggressive clocking needs and limited power budgets of most NoC applications. In this paper, a new router design based on a distributed shared-buffer (DSB) architecture is proposed that aims to practically emulate an OBR. The proposed architecture introduces innovations to address the unique constraints of NoCs, including efficient pipelining and novel flow control. Practical DSB configurations are also presented with reduced power overheads while exhibiting negligible performance degradation. Compared to a state-of-the-art pipelined IBR, the proposed DSB router achieves up to 19% higher throughput on synthetic traffic and reduces packet latency on average by 61% when running SPLASH-2 benchmarks with high contention. On average, the saturation throughput of DSB routers is within 7% of the theoretically ideal saturation throughput under the synthetic workloads evaluated.

A cooperative-ARQ protocol with frame combining

This article presents a low coordination overhead cooperative Automatic Repeat reQuest (ARQ) scheme with an integrated frame combiner, which exploits space diversity and cooperation between neighbouring nodes. A comparison between cooperation with and without frame combiner is also performed. In channels with a strong Line of Sight (LOS) component and low Signal-to-Noise ratio (SNR), the efficiency of the proposed protocol is many times higher than for other ARQ schemes. For non-LOS scenarios, the cooperative ARQ without frame combiner achieves the best efficiency results, and the overhead introduced by the frame combiner mechanism leads to results that can be even below the classical ARQ mechanism. In AWGN channels, the saturation throughput of the proposed scheme integrated into a IEEE 802.11 DCF based MAC is also studied. When the number of active stations is high, the cooperative ARQ without frame combiner shows to be the best option, while for light network loads, the presented scheme performs better.

The performances study of IEEE 802.11e to support QoS in channel error environment

ABSTRACTOne of the most important functions in IEEE 802.11e is enhanced distributed coordination function (EDCF). EDCF is an enhanced version of IEEE 802.11 distributed coordination function (DCF) which provides a priority scheme by differentiating the inter‐frame space and the initial window size. We proposed a modified Markov chain model to study the EDCF priority scheme. We have theoretically analyzed the saturation throughput and delay by using the modified Markov chain model in non‐ideal channel scenario. We also have compared it with the Markov chain model that exists under ideal channel scenario. Simulations are also conducted to validate analytical results. Our study shows that the modified model under ideal channel scenario is better than that in channel error scenario. Copyright © 2011 John Wiley & Sons, Ltd.

Spare node cooperative method for IEEE 802.11 networks

Most of the existing cooperation methods select relay node(s) mainly based on the channel state information, but do not consider whether the selected relay nodes work or not. If the selected relays are invalidated, the performance of cooperative communication will deteriorate. To resolve the above problem, this paper investigates cooperative communication in IEEE 802.11 networks, and proposes a novel Spare Cooperative Method (SCM). SCM chooses a spare cooperation node to enhance the reliability of communication, and uses an enhanced handshaking mechanism to coordinate the access of source nodes and cooperation nodes to the wireless channel. The performance of SCM is comprehensively analyzed in terms of outage probability and saturated throughput. The analysis shows that SCM improves the performance of IEEE 802.11.

Throughput analysis and bandwidth allocation for IEEE 802.11 WLAN with hidden terminals

Motivated by observations from real world wireless local area network (WLAN) deployments, we develop in this paper a novel analytical model to characterize the saturation throughput of an IEEE 802.11-based access point (AP) and stations under the influence of hidden terminals. Unlike existing models, our model can accommodate different numbers of hidden nodes without increasing the model complexity. Given any number of hidden nodes, only four constraints are needed to describe the interaction between stations and the AP with the consideration of both uplink and downlink traffic. Simulation evaluation shows that our model predicts network performance accurately over a wide range of network sizes and indicates the existence of a throughput starvation problem. To address this problem, based on our model, we formulate a bandwidth allocation problem to optimize the network throughput and fairness under some predefined requirements by systematically tuning the AP and stations contention windows. Simulation results show that the starvation problem is resolved with our approach, and the target throughput is met.