Infostations Niraj Patel Background An Infostation is a

Infostations Niraj Patel

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 90’s, Infostation goals are to provide low cost, high bit rate, low power network connections to a restricted coverage area.

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.

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 (500 MB/s) -No need for obsequies coverage

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.

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

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.

Capacity in an Infostation Optimal 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.

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

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.

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