Dear friends,

Next week we'll restart our network algorithms seminar.

New TIME and LOCATION are Wednesday 11:30-1pm in room 001, Handassa-Kitot Building, TAU.

As always, the NetAlgs seminar welcomes informal presentations of new

research results and work-in-progress pertaining to network algorithms

(broadly interpreted).

Mark your calendars: The first meeting will be held next week, 11:30,

Wednesday November 7th.

title: Ad hoc WiFi networks with low SNR

speaker: Guy Even (TAU)

time: 11:30, Wednesday November 7th

place: Room 001 (NOT 011!), Binyain Kitot Handassa

abstract:

The IEEE 802.11 standard (known as WiFi) is a carrier sense multiple

access with collision avoidance wireless network protocol. It was

designed as a distributed protocol to support local area networks

(LANs) with a star topology in which one access point serves multiple

clients. Ideally, neighboring LANs use nonoverlapping channels to

avoid interference.

The huge success of WiFi has lead to dense deployment of multiple

access points so that it is impossible to assign nonoverlapping

channels to neighboring LANs. In addition, proposals for utilizing

WiFi in ad hoc networks have been suggested and even incorporated in

standards. The topology of ad hoc networks is arbitrary and is not

limited to a union of disjoint stars.

We study the performance of WiFi with respect to low

signal-to-noise-ratio (SNR) links. There are many motivations for

considering  low SNR links especially in a mobile ad hoc setting.

First, decreasing the transmission power saves power and reduces

interference. Second, an ad hoc network may become disconnected if low

SNR links are not allowed. Third, the WiFi protocol does not have a

simple way to exclude links with low SNR if their packets are received

correctly.

In this talk I will present the following results:

1. A demonstration of the failure of the collision avoidance mechanism

in WiFi in ad hoc networks with low SNRs and long data packets.

2. A suggestion to fix this failure by introducing double

acknowledgment packets and increasing sensitivity to packet headers by

using matched filters.

3. A demonstration of the improvement in the performance of WiFi in ad

hoc networks with low SNRs and long data packets.

Joint work with: Ofer Amrani, Doron Aspir, Yaniv Fais, Moti Medina,

and Moni Shahar.