Infostations

1
Infostations

• Niraj Patel

2
Background

• An Infostation is a wireless information
  service, confined to a small
• geographical location with a limited coverage
  area. As users pass thorough the coverage area,
  the infostation deploys information to their PDA
  laptop computer. The process is automated and
  should not require any human interaction.
  Services an Infostation might provide
• -Restaurant listings
• -News
• -Synchronize Email
• -Local places of interest
• Developed at WINLAB in the early 90s,
  Infostation goals are to provide low cost, high
  bit rate, low power network connections to a
  restricted coverage area.

3
An Infostation System

• 1) Mobile devices,
• whose users would
• send and receive
• data to the Infostation.
• 2) The Infostation
• which consists of a
• Wireless access point
• that is hooked up to a
• PC that is connected
• to the internet.

4
Why Infostations?

• The problem with existing systems (Cellular) is
  they are primarily
• designed for voice. Because of this, they have
  to deliver service anywhere, and anytime. Also
  to deliver non voice services, high bit rates are
  necessary which would result in a high costing
  infrastructure.
• Advantages
• -Use of unlicensed bands, make it easy to deploy
  and make it cheaper
• -High Bandwidth (500MB/s)
• -No need for obsequies coverage

5
A Typical Scenario

• Consider an Infostation at an airport terminal,
  while in flight the user would have pre-written
  Emails on their PDA. They also decides that they
  would grab a bite to eat after landing. When
  they arrives at the terminal their PDA starts
  talking to the terminal infostation and sends out
  the emails. It also then retrieves local
  restaurant information. This all happens with
  automatically. They would have to do as little
  as possible.

6
Data Transmission (1-2)

• A cycle transmitted from the infostation.
• Index Includes information that clients can
  use and determine how or when to listen for
  each item, so they can conserve power by ignoring
  items they do not want.
• Requests After the index there is a pause.
  This allows clients to decide which items to
  listen to.
• Data The server transmits requested data items
• Feedback The client uploads data, or sends
  requests

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Data Transmission (2-2)

• Two ways the infostation broadcasts
• IP multicast The client joins the multicast
  group for the items it want but will receive
  unwanted data packets which it will later drop.
• Explicit Client Control In this method, the
  index includes information about when each item
  will be transmitted and the client goes into low
  power mode, waking up to receive the desired
  packets, then going back to sleep until its time
  to listen for the next index.
• In both cases, the client will listen when the
  Infostation sends out the new index in the next
  cycle.

8
Capacity in an InfostationOptimal Vs. Constant
power allocation

• The reasoning more power is used when the
  mobile device is near the Infostation to maximize
  capacity. This way power is saved to users from
  users who are further away and maximized to the
  optimal conditions.

9
Capacity in Infostations

• To optimize capacity in an Infostation, a
  different DPSK modulation schemes would be used
  at different SIRs . (DBPSK, DQPSK, 8-DPSK).

10
Capacity in Infostations

• The different Modulation Schemes have different
  SNRs mapped here with the SIR and Distance
• Depending on the SIR, a different modulation
  scheme is used.

11
Capacity in Infostations

• As quality improves, higher
• modulation schemes are used.
• Transfer rates vary from 0-24Mbps