NYMAN On the advantage of multi-hop extensions to IEEE infrastructure mode Sathya Narayanan Panasonic Pei Liu Shivendra Panwar Polytechnic University

NYMAN Overview We study the effect of using multi-hopping Instead of reducing the transmission rate of nodes use multi-hop (two-hop) transmissions at highest rate (11 Mbps). The SIR (Signal-To-Interference Ratio) experienced by nodes when the transmission power is reduced at edge nodes to reach an intermediate node, rather than the access point directly. This improves the throughput of nodes at the edge of the network. Important note: Advantages discussed from both forwarding nodes and source nodes perspective.

NYMAN IEEE MAC Infrastructure mode and ad hoc mode DCF Operation Multiple rates 11 Mbps, 5.5. Mbps, 2 Mbps, 1 Mbps Single hop MAC

NYMAN Advantages of multi-hop extension Studying the effect of multi-hop extensions w.r.t The network throughput in a multi-rate network The SIR experienced by edge nodes Initial study demonstrates possible improvements in both area Result in next few slides …

NYMAN Simulation 24 nodes – AP in the middle Manual rate selection High speed nodes at 11 Mbps Low speed nodes at 1 Mbps Increase the number of slow nodes to study impact on throughput

NYMAN Average Throughput per node drops for all nodes when slower nodes are introduced in the network

NYMAN Total useful throughput of the network increases when multi-hop (two) is used maintaining higher data rate at all nodes

NYMAN Forwarding node Increase in total throughput is not an incentive for the forwarding node to participate in multi-hop scheme. What is the effect on the throughput experienced by forwarding node? Assumption: Each forwarding node only has to support one slow node

NYMAN Current MAC: The available throughput at the forwarding node is equally shared with the slow node. Opportunistic MAC: The total available throughput of the network is equally shared among all nodes

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NYMAN A B A C A C B C A B B C B A d i i i Rayleigh fading model

NYMAN Simulation C Program Calculate interference at each point in the cell from proximal cells at the same channel Each point represented by polar co- ordinates R = 1:100:1 Theta = 1:360:1

NYMAN b

NYMAN Downstream Coverage

NYMAN Downstream coverage with reduced transmission power at edge node

NYMAN Upstream coverage

NYMAN Upstream coverage using multi-hop and reduced transmission power

NYMAN Review comments Simple answer to most of the comments: Work in progress ;)

NYMAN Reviewer 1: Not clear on: 1. how the network topology would impact the results and in general the effects of multi-hop extensions. 2. What is the performance v.s. cost tradeoffs of the proposed solution. 3. how would things change if each forwarding node can be responsible for more than one slower node. Would there still be enough benefits for the forwarding nodes? 4. Results are based on analysis/simulation. Any verification using experiment done or planned in the future? How would that be done?

NYMAN Reviewer 1: Some response Not clear on: 1. how the network topology would impact the results and in general the effects of multi-hop extensions. 2. What is the performance v.s. cost tradeoffs of the proposed solution. 3. how would things change if each forwarding node can be responsible for more than one slower node. Would there still be enough benefits for the forwarding nodes? Response: That was a simplifying assumption. As long as the forwarding node shares only a part of its available bandwidth it will have the benefits. If more than one slow node use the same forwarding node, the slow nodes could probably loose their benefit. 4. Results are based on analysis/simulation. Any verification using experiment done or planned in the future? How would that be done?

NYMAN Reviewer 1: Some response Not clear on: 1. how the network topology would impact the results and in general the effects of multi-hop extensions. 2. What is the performance v.s. cost tradeoffs of the proposed solution. 3. how would things change if each forwarding node can be responsible for more than one slower node. Would there still be enough benefits for the forwarding nodes? 4. Results are based on analysis/simulation. Any verification using experiment done or planned in the future? How would that be done? Answer: More open questions left in the simulation/analysis area (some raised here). Plan is to address those questions first. No plan for experimental study right now.

NYMAN Reviewer 2: The capacity and coverage improvement of multi-hop networks has been well documented. The paper presents a opnet simulation of systems in a multi-hop system. 1. The problem with multi-hop systems however are additional delays and additional collisions. 2. Instead of restricting themselves to just throughput and coverage benefit analysis, the authors should also discuss the added multi-hop delays and scalability issues to make their message more powerful.

NYMAN Reviewer 2: Some response The capacity and coverage improvement of multi-hop networks has been well documented. The paper presents a OPNET simulation of systems in a multi-hop system. Answer: We don’t know of any coverage improvement work in a cellular, 3 frequency band environment. Our contribution is in demonstrating incentive for forwarding nodes participation. 1. The problem with multi-hop systems however are additional delays and additional collisions. 2. Instead of restricting themselves to just throughput and coverage benefit analysis, the authors should also discuss the added multi-hop delays and scalability issues to make their message more powerful.

NYMAN Reviewer 2: Some response The capacity and coverage improvement of multi-hop networks has been well documented. The paper presents a opnet simulation of systems in a multi-hop system. 1. The problem with multi-hop systems however are additional delays and additional collisions. Answer: Actually the delay should go down because of the higher transmission rates maintained in a two hop situation. Additional collisions is possible only when transmission power reduction is used – we need study the effect of proposed reduction factors on the carrier- sense threshold. 2. Instead of restricting themselves to just throughput and coverage benefit analysis, the authors should also discuss the added multi-hop delays and scalability issues to make their message more powerful.