Chapter 6

What does it mean for a wireless network to be operating in "infrastructure mode?" If the network is not in infrastructure mode, what mode of operation is it in, and what is the difference between that mode of operation and infrastructure mode?

What are the differences between the following types of wireless channel impairments: path loss, multipath propagation, interference from other sources?

For the two-sender, two-receiver example, give an example of two CDMA codes containing 1 and $-1$ values that do not allow the two receivers to extract the original transmitted bits from the two CDMA senders.

As a mobile node gets farther and farther away from a base station, what are two actions that a base station could take to ensure that the loss probability of a transmitted frame does not increase?

Suppose there are two ISPs providing WiFi access in a particular café, with each ISP operating its own AP and having its own IP address block. a. Further suppose that by accident, each ISP has configured its AP to operate over channel 11. Will the $802.11$ protocol completely break down in this situation? Discuss what happens when two stations, each associated with a different ISP, attempt to transmit at the same time. b. Now suppose that one AP operates over channel 1 and the other over channel 11 . How do your answers change?

Describe the role of the beacon frames in $802.11$.

Why are acknowledgments used in $802.11$ but not in wired Ethernet?

True or false: Ethernet and $802.11$ use the same frame structure.

Describe the format of the $802.15.1$ Bluetooth frame. You will have to do some reading outside of the text to find this information. Is there anything in the frame format that inherently limits the number of active nodes in an $802.15.1$ network to eight active nodes? Explain.

Consider the following idealized LTE scenario. The downstream channel (see Figure $6.20$ ) is slotted in time, across F frequencies. There are four nodes, $\mathrm{A},\mathrm{B},\mathrm{C}$, and $\mathrm{D}$, reachable from the base station at rates of $10\mathrm{Mbps}$, $5\mathrm{Mbps},2.5\mathrm{Mbps}$, and $1\mathrm{Mbps}$, respectively, on the downstream channel. These rates assume that the base station utilizes all time slots available on all F frequencies to send to just one station. The base station has an infinite amount of data to send to each of the nodes, and can send to any one of these four nodes using any of the F frequencies during any time slot in the downstream sub-frame. a. What is the maximum rate at which the base station can send to the nodes, assuming it can send to any node it chooses during each time slot? Is your solution fair? Explain and define what you mean by "fair." b. If there is a fairness requirement that each node must receive an equal amount of data during each one second interval, what is the average transmission rate by the base station (to all nodes) during the downstream sub-frame? Explain how you arrived at your answer. c. Suppose that the fairness criterion is that any node can receive at most twice as much data as any other node during the sub-frame. What is the average transmission rate by the base station (to all nodes) during the subframe? Explain how you arrived at your answer.