We provide extensive numerical results for both problems for medium-size mesh networks using an iterated optimal search technique. Via numerical and simulation results, we show that: 1) joint design provides a significant throughput gain over a default configuration in slotted-ALOHA-based wireless networks; and 2) the throughput gain obtained by the simple network coding is significant, especially at low transmission power. We also propose simple heuristics to configure slotted-ALOHA-based wireless mesh networks. These heuristics are extensively evaluated via simulation and found to be very efficient.

1.2 INTRODUCTION:

Although the worldwide success of the Internet is partly due to the simplicity and robustness of its layered network architecture, this architecture, developed for wired networks, is not efficient for multi hop wireless networks. Cross-layer approaches have been proposed to enhance the adaptability and performance of these networks by jointly tuning the parameters of different layers.

One of the critical performance metrics in multi hop wireless networks is throughput. It is highly dependent on the configuration of routing, medium access, and physical-layer parameters and on their interactions; In the case of a (conflict-free) scheduled network. Configuring a wireless network based on random access is much more difficult, and one might be tempted to simply use a so-called default configuration comprised, for example in the case of slotted ALOHA, of a minimum-hop routing and equal attempt probability. While one would expect that joint configuration of routing, medium access, and physical-layer parameters of a random access network can provide better performance than the default configuration, there is no clear indication so far on how much improvement can be achieved by joint design and how to jointly configure the parameters.

In a single-channel wireless network, during a transmission, the interference seen by a receiver is the additive interference from all the other simultaneous transmissions. As a consequence, it is essential to use a proper interference model when configuring the wireless network. The physical interference model based on signal-to-interference-plus-noise ratio (SINR) is the more realistic interference model for wireless networks. Simpler interference models such as primary interference model, protocol model, and capture threshold model can provide misleading insights about the optimal configuration of routing, medium access control (MAC), and physical-layer parameters as well as throughput improvements by joint design.

The throughput optimization problem of any network is a link-rate constrained optimization problem. For popular but complex MAC protocols such as the IEEE 802.11-based carrier-sense multiple access with collision avoidance (CSMA/CA) MAC, modeling the effective link rate in terms of network parameters under a realistic interference model is an open research issue in the context of multi hop wireless networks. The fundamental random access protocol, slotted ALOHA, was first proposed in 1970 by Abramson. It has contention characteristics similar to CSMA/CA in a WLAN. Due to its simplicity of operation and analytical formulation, the protocol is often considered for understanding the contention in heavy loaded random access networks. In this paper, we first study the optimal joint configuration of routing, access probability, and transmission rate parameters in slotted ALOHA fixed wireless networks to maximize the minimum throughput of the flows under an interference model based on SINR. The critical assumption to perform this study is that the channel gains are quasi time-invariant. Try this The objective is to provide insights on throughput gains obtained by optimized configurations over a default configuration. Note that, from this point onward, we use the term MAC in a narrow sense since we focus on a very specific MAC protocol.

Network coding has emerged as a promising technique both in wire line and wireless networks to improve throughput performance. Wireless networks suffer from interference due to the inherent broadcast nature of the wireless medium. Network coding is an important method that turns this apparent broadcast limitation into an advantage for better throughput performance. Network coding has been used in many contexts in wireless networks, including: 1) end-to-end multicasting; 2) end-to-end unicasting; 3) at the link layer; and 4) physical-layer transmission. The existing works in 1), 2), and 4) are mainly theoretical. Link-layer network coding is studied theoretically in for unicast applications, and COPE bridges the gap between theory and practice and provides an operational protocol for general unicast traffic. Due to the simplicity and practicality of link-layer network coding, this technique has attracted a lot of attention from the wireless research community.

In a wireless network, (link-layer) network coding opportunities significantly depend on the routing, MAC, and physical-layer parameters and the interactions among the three layers. It is expected that network coding opportunities as well as throughput performance can be improved significantly by joint configuration of routing, MAC, and physical-layer parameters. However, how to jointly configure the network parameters when network coding is enabled is unknown.

In a second part, we study the optimal joint configuration of routing, access probability, and transmission rate parameters in slotted ALOHA wireless networks with network coding to maximize the minimum throughput of the flows. We restrict ourselves to simple link-layer network coding without any opportunistic listening as it is too complex to analyze link-layer network coding with opportunistic listening for a wireless network and optimize the network parameters under a realistic interference model.

The contributions are as follows.

• We model the effective link rate for slotted ALOHA systems under an SINR-based physical interference model using the concept of a conflict-free set of nodes. These link rate models are found to be very complex and are not a convex function of their parameters.

• We formulate the joint routing, access probability, and rate allocation problem to determine the weighted max-min throughputs of the flows and the optimal configuration of routing, access probability, and transmission rate parameters in slotted-ALOHA-based wireless networks. This problem is also extended to joint routing, access probability, network coding, and rate allocation problem. These problems turn out to be very large nonlinear and non convex optimization problems. They are valid for any fixed wireless multi hop network with quasi time-invariant channel gains.

• We solve the optimization problems numerically for several mesh1 network scenarios with a single transmission rate at all nodes by using an iterated optimal search (IOS) technique, i.e., we study the optimal joint configuration of routing and access probability parameters in single-rate systems. Via numerical and simulation results, we show that the performance gains obtained by jointly optimizing the configuration of access probability and routing parameters over a default configuration comprising equal access probability at each node and a minimum-hop routing are very significant in slotted ALOHA systems. Specifically, we find gains on the order of 80%–300%. We also show that: 1) a significant amount of throughput improvement can be achieved by optimizing only the access probability parameters; whereas 2) a small amount of throughput improvement is achieved by optimizing only the routing parameters. Furthermore, the performance gain obtained by jointly optimizing routing, access probability, and network coding over a joint design without network coding Go Here (i.e., the gain obtained for enabling the simple network coding) is significant, especially at low transmission power. At higher transmission power, network coding becomes less attractive because there are more and more single-hop paths to the gateway. We also find that the typical rate imbalance between downlink and uplink flows in wireless mesh networks surprisingly plays a role in favor of network coding due to retransmissions.

• Due to their computational complexity, the optimization problems are intractable for large networks. For large single-rate wireless mesh networks, we propose simple heuristics to configure the routing and access probability parameters. We show via simulation that the max-min throughputs obtained by the heuristics are significantly higher than the max-min throughputs obtained by default designs and compare well to the optimal max-min throughputs.

• We solve the joint problems for multi rate systems by our IOS technique and compare the throughput performance of multi rate and single-rate systems. We find that by using two rates, there are some (limited) throughput improvements only for powers at which the network would not be connected if using the highest rate only.

In this paper, we study a simple MAC protocol and a simple network coding scheme to keep the formulation tractable. Our objectives are to provide insights on: 1) the interaction of routing, access probability, network coding, and transmission rate; 2) the throughput gains obtained by a joint design over a default design; and 3) throughput gains obtained by simple network coding.

1.3 LITRATURE SURVEY

JOINT CONFIGURATION OF ROUTING AND MEDIUM ACCESS PARAMETERS IN WIRELESS NETWORKS

PUBLICATION: M. F. Uddin, C. Rosenberg, W. Zhuang, andA.Girard, in Proc. IEEE GLOBECOM, Dec. 2009, pp. 1–8.

We study cross-layer design in random-access-based fixed wireless multihop networks under a physical interference model. Due to the complexity of the problem, we consider a simple slotted ALOHA medium access control (MAC) protocol for link-layer operation. We formulate a joint routing, access probability, and rate allocation optimization problem to determine the optimal max-min throughput of the flows and the optimal configuration of the routing, access probability, and transmission rate parameters in a slotted ALOHA system. We then also adapt this problem to include an XOR-like network coding without opportunistic listening. Both problems are complex nonlinear and nonconvex. We provide extensive numerical results for both problems for medium-size mesh networks using an iterated optimal search technique. Via numerical and simulation results, we show that: 1) joint design provides a significant throughput gain over a default configuration in slotted-ALOHA-based wireless networks; and 2) the throughput gain obtained by the simple network coding is significant, especially at low transmission power. We also propose simple heuristics to configure slotted-ALOHA-based wireless mesh networks. These heuristics are extensively evaluated via simulation and found to be very efficient.

ENGINEERING WIRELESS MESH NETWORKS:JOINT SCHEDULING, ROUTING, POWER CONTROL AND RATE ADAPTATION

PUBLICATION: J. Luo, C. Rosenberg, and A. Girard, IEEE/ACM Trans. Netw., vol. 8, no. 5, pp. 1387–1400, Oct. 2010.

We present a number of significant engineering insights on what makes a good configuration for medium- to large-size wireless mesh networks (WMNs) when the objective function is to maximize the minimum throughput among all flows. For this, we first develop efficient and exact computational tools using column generation with greedy pricing that allow us to compute exact solutions for networks significantly larger than what has been possible so far. We also develop very fast approximations that compute nearly optimal solutions for even larger cases. Finally, we adapt our tools to the case of proportional fairness and show that the engineering insights are very similar.

MAC-LAYER PROACTIVE MIXING FOR NETWORK CODING IN MULTI-HOP WIRELESS NETWORKS

PUBLICATION: J. Zhang, Y. P. Chen, and I. Marsic, Comput. Netw., vol. 54, no. 2, pp. 196–207, Feb. 2010.

We present BEND, a MAC layer solution to practical network coding in multi-hop wireless networks. It is the first exploration of the broadcasting nature of wireless channels to proactively capture more coding opportunities. In BEND, any node can code and forward a packet even when the node is not the intended MAC receiver of the packet, if the node believes that in doing so it can lead the packet to its ultimate destination. Essentially, BEND considers the union of all interface queue contents at the nodes within a neighborhood, i.e. a “neighborhood coding repository”, whereas traditional mixing methods only process “individual coding repositories” at separate nodes.

A DISTRIBUTED CSMA ALGORITHM FOR THROUGHPUT AND UTILITY MAXIMIZATION IN WIRELESS NETWORKS

PUBLICATION: L. Jiang and J. Walrand, IEEE/ACM Trans. Netw., vol. 18, no. 3, pp. 960–972, Jun. 2010.

In multihop wireless networks, designing distributed scheduling algorithms to achieve the maximal throughput is a challenging problem because of the complex interference constraints among different links. Traditional maximal-weight scheduling (MWS), although throughput-optimal, is difficult to implement in distributed networks. On the other hand, a distributed greedy protocol similar to IEEE 802.11 does not guarantee the maximal throughput. In this paper, we introduce an adaptive carrier sense multiple access (CSMA) scheduling algorithm that can achieve the maximal throughput distributively. Some of the major advantages of the algorithm are that it applies to a very general interference model and that it is simple, distributed, and asynchronous. Furthermore, the algorithm is combined with congestion control to achieve the optimal utility and fairness of competing flows. Simulations verify the effectiveness of the algorithm. Also, the adaptive CSMA scheduling is a modular MAC-layer algorithm that can be combined with various protocols in the transport layer and network layer. Finally, the paper explores some implementation issues in the setting of 802.11 networks.

CHAPTER 2

2.0 SYSTEM ANALYSIS

2.1 EXISTING SYSTEM:

In a single-channel wireless network, during a transmission, the interference seen by a receiver is the additive interference from all the other simultaneous transmissions. As a consequence, it is essential to use a proper interference model when configuring the wireless network. The physical interference model based on signal-to-interference-plus-noise ratio (SINR) is the more realistic interference model for wireless networks. Simpler interference models such as primary interference model, protocol model, and capture threshold model can provide misleading insights about the optimal configuration of routing, medium access control (MAC), and physical-layer parameters as well as throughput improvements by joint design

2.1.1 DISADVANTAGES:

The throughput optimization problem of any network is a link-rate constrained optimization problem
Due to its simplicity of operation and analytical formulation, the protocol is often considered for understanding the contention in heavy loaded random access networks.

2.2 PROPOSED SYSTEM:

In this paper, we first study the optimal joint configuration of routing, access probability, and transmission rate parameters in slotted ALOHA fixed wireless networks to maximize the minimum throughput of the flows under an interference model based on SINR.In this paper, we study a simple MAC protocol and a simple network coding scheme to keep the formulation tractable. Our objectives are to provide insights on: 1) the interaction of routing, access probability, network coding, and transmission rate; 2) the throughput gains obtained by a joint design over a default design; and 3) throughput gains obtained by simple network coding.

The contributions are as follows.

2.2.1 ADVANTAGES:

We solve the joint problems for multirate systems by our IOS technique and compare the throughput performance of multirate and single-rate systems.
Due to their computational complexity, the optimization problems are intractable for large networks. For large single-rate wireless mesh networks, we propose simple heuristics to configure the routing and access probability parameters.
we show that the performance gains obtained by jointly optimizing the configuration of access probability and routing parameters over a default configuration comprising equal access probability at each node and a minimum-hop routing are very significant in slotted ALOHA systems. Specifically, we find gains on the order of 80%–300%.

2.3 HARDWARE & SOFTWARE REQUIREMENTS:

2.3.1 HARDWARE REQUIREMENT:

v Processor – Pentium –IV

Speed – 1.1 GHz
- RAM – 256 MB (min)
- Hard Disk – 20 GB
- Floppy Drive – 1.44 MB
- Key Board – Standard Windows Keyboard
- Mouse – Two or Three Button Mouse
- Monitor – SVGA

2.3.2 SOFTWARE REQUIREMENTS:

Operating System : Windows XP
Front End : Microsoft Visual Studio .NET 2008
Document : MS-Office 2007

blem, we consider a simple slotted ALOHA medium access control (MAC) protocol for link-layer operation. We formulate a joint routing, access probability, and rate allocation optimization problem to determine the optimal max-min throughput of the flows and the optimal configuration of the routing, access probability, and transmission rate parameters in a slotted ALOHA system. We then also adapt this problem to include an XOR-like network coding without opportunistic listening. Both problems are complex nonlinear and nonconvex. We provide extensive numerical results for both problems for medium-size mesh networks using an iterated optimal search technique. Via numerical and simulation results, we show that: 1) joint design provides a significant throughput gain over a default configuration in slotted-ALOHA-based wireless networks; and 2) the throughput gain obtained by the simple network coding is significant, especially at low transmission power. We also propose simple heuristics to configure slotted-ALOHA-based wireless mesh networks. These heuristics are extensively evaluated via simulation and found to be very efficient.

Joint Routing and Medium Access Control in Fixed Random Access Wireless Multihop Networks

2.3 HARDWARE & SOFTWARE REQUIREMENTS:

v Processor – Pentium –IV

2.3.2 SOFTWARE REQUIREMENTS: