Multi-rate Wireless Networks Research Articles

Theoretical and experimental study of performance anomaly in multi-rate IEEE802.11ac wireless networks

IEEE 802.11 wireless local area networks (WLANs) are shared networks, which use contention-based distributed coordination function (DCF) to share access to wireless medium among numerous wireless stations. The performance of the distributed coordination function mechanism mostly depends on the network load, number of wireless nodes and their data rates. The throughput unfairness, also known as performance anomaly is inherent in the very nature of mixed data rate Wi-Fi networks using the distributed coordination function. This unfairness exhibits itself through the fact that slow clients consume more airtime to transfer a given amount of data, leaving less airtime for fast clients. In this paper, we comprehensively examine the performance anomaly in multi-rate wireless networks using three approaches: experimental measurement, analytical modelling and simulation in Network Simulator v.3 (NS3). The results of our practical experiments benchmarking the throughput of a multi-rate 802.11ac wireless network clearly shows that even the recent wireless standards still suffer from airtime consumption unfairness. It was shown that even a single low-data rate station can decrease the throughput of high-data rate stations by 3–6 times. The simulation and analytical modelling confirm this finding with considerably high accuracy. Most of the theoretical models evaluating performance anomaly in Wi-Fi networks suggest that all stations get the same throughput independently of the used data rate. However, experimental and simulation results have demonstrated that despite a significant performance degradation high-speed stations still outperform stations with lower data rates once the difference between data rates becomes more significant. This is due to the better efficiency of the TCP protocol working over a fast wireless connection. It is also noteworthy that the throughput achieved by a station when it monopolistically uses the wireless media is considerably less than 50 % of its data rate due to significant overheads even in most recent Wi-Fi technologies. Mitigating performance anomaly in mixed-data rate WLANs requires a holistic approach that combines frame aggregation/fragmentation and adaption of data rates, contention window and other link-layer parameters.

Coded Caching in Multi-Rate Wireless Networks

Coded Caching in Multi-Rate Wireless Networks

A Responsible Airtime Approach for True Time-Based Fairness in Multi-Rate WiFi Networks

Airtime fairness, or time-based fairness, has been well recognized as a method to solve WiFi performance anomalies and provide a balance between fairness and spectrum efficiency in multi-rate wireless networks. However, the definition of airtime is vague and simplistic. In this paper, it is demonstrated that current airtime fair scheduling results in unfairness in reality because overheads are neglected or unfairly counted. We introduce a notion of responsible airtime, which covers not only the data transmission time, but also all overheads, even a TCP ACK segment in TCP traffic. An approach based on responsible airtime can provide true time-based fairness, but responsible airtime is too complicated to directly handle. A practical method is thus introduced for evaluating responsible airtime fairness indirectly via throughput measurement. The key element, throughput fair share, of a node, is based on the baseline property in time-based fairness. For each node, an achieving ratio of actual throughput to the throughput fair share is determined, and a new fairness index considering deficiency as well as equity is applied. To validate the feasibility of responsible airtime fairness, we have developed a simple responsible airtime fair scheduler in access points for download traffic. Extensive simulation experiments are conducted in various network and traffic environments using the ns3 simulator. The results show that true time-based fairness is achievable in practice.

Joint Throughput Optimization for Multichannel Multiradio Multirate Wireless Network with Network Coding

ABSTRACTNetwork coding has been proposed to increase network throughput by combining packets at intermediate nodes. In this paper, we propose a joint throughput optimization method for a multirate multichannel multiradio wireless network with network coding. We propose algorithms for congestion control, joint distributed rate control, and heuristic resource allocation to solve the utility maximization problem in the wireless network environment with network coding. To minimize performance degradation generated by packet loss, we propose a congestion control algorithm. Furthermore, we present a sophisticated resource allocation algorithm which finds a node for the worst traffic jam and selects a session that needs to be first transferred in the node. Then, the node is allocated with the channels and radios for the packets of the selected session. Furthermore, a rate selection method is presented to determine the rate of each node. The simulation results show that the proposed method achieves the optimal performance in a multirate multichannel multiradio wireless network.

A throughput-oriented reliable multicast in multi-rate wireless networks

A throughput-oriented reliable multicast in multi-rate wireless networks

Joint Routing and Channel Assignment in Multi-rate Wireless Mesh Networks

Joint Routing and Channel Assignment in Multi-rate Wireless Mesh Networks

Distributed Joint Rate Control, Resource Allocation, and Congestion Control for Throughput Optimization in Multirate Multiradio Multichannel Wireless Network with Intersession/Intrasession Network Coding

Wireless multihop networks are increasingly used because of their low cost and easy deployment. However, there are still many restrictions that degrade performance. Network coding has been proposed to improve the throughput of a wireless network through the characteristics of overhearing and broadcast. In this paper, we model the network utility maximization problem using a combined intrasession and intersession network coding method to improve the network utility in multiradio, multichannel, and multirate wireless network. And we propose a network throughput optimization scheme with a rate control, resource allocation and congestion control algorithm. We formulate an optimal framework reflecting wireless network environment. Also, we propose a rate selection scheme to choose the transmission rate on each node. We evaluate the proposed algorithms by simulation. The performance evaluation results show that the proposed scheme can improve throughput for network by utility optimization in a multiradio, multichannel, and multirate wireless network.

A Novel Approach for Performance Analysis of Multi-Rate Relay Networks

In a multi-rate data WLAN, the data rate is a function of the distance from the access point (AP). To extend the coverage of the AP to cover a target terminal outside the AP coverage area, relay nodes are deployed between the AP and the target terminal. Therefore, for a given relationship between the throughput and the distance, and a given distance between the access point and the target receiver, there is a minimum number of nodes that provides the maximum throughput to the target receiver. It is always desirable to optimize the deployment from various aspects. These aspects are application-dependent and they range from energy conservation in sensor networks to throughput and coverage maximization in data networks. This paper presents a novel approach to determine the optimal bounds for the Medium Access Control (MAC) throughput at the target receiver in a multi-hop multi-rate wireless data network. We use the principles of linear programming and a model for the physical layer (PHY) throughput-distance relationship to determine the optimal performance bounds for the MAC throughput of a target terminal as a function of distance from the AP and the number of hops. We determine the performance bounds for two scenarios. The first scenario assumes all network nodes are visible to each other. The second scenario assumes each node is only visible to it neighbors. Additionally, we determine the physical locations for the relays to reach the optimal MAC throughput for a target terminal located at a specific distance from the AP

A Throughput-oriented Reliable Multicast in Multi-rate Wireless Networks

As low transmission delays can meet the requirements of many applications, high-throughput is the request of various others. Therefore, with consideration of the multi-user diversity (MUD) and the wireless broadcast advantage (WBA) features, we deal with the problem of maximising the multicast throughput. Hence, we introduce two new rate-aware multicast metrics: EMTH and XMTH. EMTH helps to choose the transmission rates that estimate the best multicast throughput expected. XMTH can reach extreme throughput values if the high computational needs are satisfied. Both metrics carry out a rate adaptation process and take into consideration the link reliabilities. They can be used to choose multi-rate multicast schemes and to decide reliable multicast paths. Results show that the proposed metrics give the best system performance in terms of throughput. They confirm that, using EMTH and XMTH, it is possible to trade-off a very good throughput improvement for an insignificant delay increase.

Does Network Coding Combined With Interference Cancellation Bring Any Gain to a Wireless Network?

We investigate the achievable performance gain that network coding (NC) when combined with successive interference cancellation (SIC) brings to a multihop wireless network. While SIC enables concurrent receptions from multiple transmitters, NC reduces the transmission time-slot overhead, and each of these techniques has shown independently great benefits in improving the network performance. We present a cross-layer formulation for the joint routing and scheduling problem in a wireless network with NC (with opportunistic listening) and SIC capabilities. We use the realistic signal-to-interference-plus-noise ratio (SINR) interference model. To solve this combinatorially complex nonlinear problem, we decompose it (using column generation) to two linear subproblems--namely opportunistic NC aware routing and scheduling subproblems. Our scheduling subproblem consists of activating noninterfering NC components, rather than links, which do not interfere with each other and will be used to route the traffic. We further extend our design to consider a multi-rate multihop wireless network with interference cancellation capabilities. We use numerical evaluation to present the achieved performance gain and compare our work to three other models: a base model with no NC and SIC, a model with only NC, and a model with only SIC capabilities. The numerical results show that our proposed method (both with and without variable transmission rate selection) achieves performance gains that range between moderate and significant for the various considered scenarios. Such improvements are attributed to the joint capabilities of SIC and NC in effectively controlling the interference and improving the spatial reuse.

Interference Aware Multipath Routing in Multi-rate Wireless Sensor Networks

In wireless sensor networks, sensor nodes have a short transmission range and data is transferred from source to destination node using the multi-hop transmission. Sensor nodes are powered by battery and the link qualities are different, and the routing protocol in the wireless sensor network is one of the important technical issues. Multipath routing was proposed to reduce the data congestion and increase data throughput. In the multipath routing, however, each path can be interfered by the other path, and it can aggravate network performance. In this paper, we propose the multipath routing scheme for multi-rate wireless sensor networks. The multipath routing selects transmission paths to minimize transmission delay and path interference.

The Service Process and Modeling of Radio Channel in Multi-rate Wireless Networks

The Service Process and Modeling of Radio Channel in Multi-rate Wireless Networks

Auction-based Bandwidth Management with Network Coding and Cooperative Communication in Wireless Networks

In this paper, we propose a generalized Vickrey-Clarke-Groves auction mechanism for bandwidth management with network coding techniques. In our bandwidth auction, we utilize network coding and cooperative network coding in single-rate wireless networks and multi-rate wireless networks, respectively. Network coding techniques are used to reduce the number of wireless transmissions. Social surplus is maximized by deriving the optimization problem so as to efficiently allocate the bandwidth. We evaluate the performance of our proposed auctions with simulation. In numerical examples, we show the effectiveness of bandwidth auction mechanism. Then, we investigate the effectiveness of network coding in single-rate wireless networks and the effectiveness of cooperative network coding in multi-rate wireless networks.

Joint Routing and Scheduling in WMNs with Variable-Width Spectrum Allocation

This paper addresses, in the context of wireless network design, the problem of optimally partitioning the spectrum into a set of nonoverlapping channels with nonuniform spectrum widths. While narrower bands split the total available spectrum into more nonoverlapping channels allowing more parallel concurrent transmissions, wider spectrum bands yield links with larger transport capacity. Thus, we model the combinatorially complex problem of joint routing, link scheduling, and variable-width channel allocation in both single and multirate multihop wireless networks as a mixed integer linear program, and present a solution framework using the column generation decomposition approach. Given the nature and complexity of the resulting dual subproblem, we propose heuristic methods for partitioning the spectrum and allocating resources to each active links, and hence obtain solutions for larger network instances. We present several numerical results and engineering insights suggesting both spectrum width and transmission rates as effective tunable knobs for combatting interference and promoting spatial reuse and thus achieving superior performance in multihop settings.

Partial Bit Strings Pruning Channel Assignment in Multi-Rate Multi-Channel Wireless Networks

IEEE 802.11 based wireless networks are extensively used in mesh, ad hoc, and sensor networks due to less expense and easier deployment. IEEE 802.11a/b/g standard supports multi-rate and multi-channel settings to facilitate network transmissions. Many researchers focus on maximizing network throughput and propose channel assignment algorithms in IEEE based multi-rate multi-channel (M2) wireless networks. Less works are devoted to the study of network capacity in M2 wireless networks. In our observation, static channel assignment algorithms for maximizing network throughput may limit network capacity, and the improvement on network capacity comes mainly from higher data rate communication links. Therefore, we model the optimization problem and derive the optimization formula in detail. Subsequently, we propose an efficient channel assignment algorithm, Partial Bit Strings Pruning (PBSP) channel assignment to maximize network capacity. The results of associated simulations show that the performance of our PBSP channel assignment algorithm is superior to the algorithm based on the well-know minimum-interference approach.

Quality-Differentiated Video Multicast in Multirate Wireless Networks

Adaptation of modulation and transmission bit-rates for video multicast in a multirate wireless network is a challenging problem because of network dynamics, variable video bit-rates, and heterogeneous clients who may expect differentiated video qualities. Prior work on the leader-based schemes selects the transmission bit-rate that provides reliable transmission for the node that experiences the worst channel condition. However, this may penalize other nodes that can achieve a higher throughput by receiving at a higher rate. In this work, we investigate a rate-adaptive video multicast scheme that can provide heterogeneous clients differentiated visual qualities matching their channel conditions. We first propose a rate scheduling model that selects the optimal transmission bit-rate for each video frame to maximize the total visual quality for a multicast group subject to the minimum-visual-quality-guaranteed constraint. We then present a practical and easy-to-implement protocol, called QDM, which constructs a cluster-based structure to characterize node heterogeneity and adapts the transmission bit-rate to network dynamics based on video quality perceived by the representative cluster heads. Since QDM selects the rate by a sample-based technique, it is suitable for real-time streaming even without any preprocess. We show that QDM can adapt to network dynamics and variable video-bit rates efficiently, and produce a gain of 2-5 dB in terms of the average video quality as compared to the leader-based approach.

Adaptive Relaying Method Selection for Multi-Rate Wireless Networks with Network Coding

To maximize the throughput of multi-rate wireless networks, in this letter, we propose a scheme to adaptively select the relaying method among analog network coding (ANC), conventional network coding (CNC), no relaying (i.e. direct transmission without relaying), and plain routing. We first discuss the achievable data rates with different relaying methods under specific channel conditions, and then propose an algorithm with polynomial-time complexity that provides a sub-optimal solution to the relaying method selection problem. Simulation results show that the proposed scheme can effectively improve the network throughput compared with existing schemes, and its performance is near to the optimal performance. The results in this letter also provide some insights for the design of routing protocols in the future.

An integrated routing and rate adaptation framework for multi-rate multi-hop wireless networks

In this paper, we propose a new integrated framework for joint routing and rate adaptation in multi-rate multi-hop wireless networks. Unlike many previous efforts, our framework considers several factors that affect end-to-end performance. Among these factors, the framework takes into account the effect of the relative positions of the links on a path when choosing the rates of operation and the importance of avoiding congested areas. The key element of our framework is a new comprehensive path metric that we call ETM (for expected transmission cost in multi-rate wireless networks). We analytically derive the ETM metric. We show that the ETM metric can be used to determine the best end-to-end path with a greedy routing approach. We also show that the metric can be used to dynamically select the best transmission rate for each link on the path via a dynamic programming approach. We implement the ETM-framework on an indoor wireless mesh network and compare its performance with that of frameworks based on the popular ETT and the recently proposed ETOP metrics. Our experiments demonstrate that the ETM-framework can yield throughput improvements of up to 253 and 368 % as compared with the ETT and ETOP frameworks.

EARC: Enhanced Adaptation of Link Rate and Contention Window for IEEE 802.11 Multi-Rate Wireless Networks

IEEE 802.11 wireless network supports multiple link rates at the physical layer. Each link rate is associated with a certain required Signal-to-Interference-and-Noise Ratio (SINR) threshold for successfully decoding received packets. On transmission failures, the 802.11 DCF performs a binary exponential backoff mechanism to discourage channel access attempts, hoping to reduce congestion. When traditional link adaptation is applied, both rate reduction and binary backoff represent double penalties for this wireless link, which may cause overly conservative transmission attempts. On the other hand, once transmission succeeds, 802.11 DCF resets the backoff contention window to the minimum value to encourage channel access attempts. At the same time, traditional link adaptation may also decide to increase the data rate, which leads to overly aggressive transmission attempts. We observe this improper interaction of link rate and backoff mechanism that harms the 802.11 system performance, due to separate consideration of those two parameters. In this paper, we propose to jointly adapt the rate and backoff parameters. Specifically, an Enhanced Adaptation of link Rate and Contention window, abbreviated as EARC, is devised. EARC is a closed-loop (receiver-assisted) link rate adaptation protocol that jointly considers the backoff mechanism. With only one extra byte carried by the DATA packet, EARC incurs little controlling overhead despite its receiver-assisted nature. Moreover, since SINR information commonly utilized by receiver-assisted protocols is not precisely supported in real devices, we introduce a rate selection reference (RSR) table empirically derived by constantly monitoring the environmental energy level and reception behavior. The RSR table then guides the receiver to select the best sustainable rate for the transmitter. Simulation results demonstrate the RSR table is a practical option for making the rate decision, and the proposed EARC approach is effective in maintaining high system throughput, compared to other link adaptation algorithms.

An interference avoidance MAC protocol design in mobile ad hoc networks

The multi-rate IEEE 802.11 DCF MAC protocol can transmit control signals at a basic transmission rate and data signals at various transmission rates. When the transmission rates of the control signals and the data signals differ, the transmission range of the lower transmission rate is larger than the transmission range of the higher transmission rate. Since a lower transmission rate increases the transmission range, it also increases the nodes in the Network Allocation Vector (NAV) status and decreases the network throughput. However, if a neighbor receiving the control signal of the ongoing communication pair communicates with another node, it may occur signal interference. This study proposes a Space Overlapping MAC (SO-MAC) protocol to increase the communication pairs and avoid interferences in single radio for multi-rate wireless network. The SO-MAC protocol uses a channel division mechanism to avoid interference between the data and control signals. This study also proposes a bandwidth allocation strategy for the sub-channels to maximize the utilization of the bandwidth of the divided sub-channels. To solve the interference between the data signals, SO-MAC allows a neighbor of the sender and the receiver to use the received signal strength to determine whether it can send or receive the data signal to increase the communication pairs. Simulation results show that, compared to the IEEE 802.11 DCF protocol and DCA protocol, the proposed SO-MAC protocol with the bandwidth allocation strategy can increase the communication pairs, achieve better throughput, reduce the number of handshake failures, and decrease the delay of transmitting a packet.