Читать книгу Dynamic Spectrum Access Decisions - George F. Elmasry - Страница 73

1 Consider Figure 4.5, where we have the master DSA engine being able to establish flows with a TDMA based network through the TDMA waveform agent. Let us assume that the flow unit is defined as F bps, as shown in the figure below. The x axis is the time defined in unit T and the y axis is the flow defined in unit F. The curve defines the traffic demand between two peer nodes over the formed TDMA network. Let us assume the TDMA waveform DSA agent applies the following rules when creating flows (adding or subtracting flows):A flow can be added or subtracted every 0.5T time. The protocols necessitate that flows cannot be added or subtracted in a rate faster than 0.5T.If a fraction of F is needed, the entire flow F is added.If a flow is not needed, its resources are freed. Freeing resources cannot happen at a faster rate than 0.5T.Use the curve to draw the allocated flows versus time over the duration of this traffic demand.Can you find time periods when the allocated bps are less than the traffic demand and time periods when the allocated pbs are more than the traffic demand?State the reasons for encountering gaps between traffic demand and resources allocations.Would you design such a system with TOS bit marking of traffic flows? Why?

2 Consider a MANET with N + 1 nodes. One of these nodes is transmitting a DSA control traffic packet of size L bytes to all the other N nodes. The node under consideration can reach half of the network nodes through one over‐the‐air hop and the rest of the nodes through two over‐the‐air hops. Assume that we need spectrum allocation of 2 Hz per each transmitted bit.If we assume 100% reliability, how much over‐the‐air resources in Hz does it take for the control traffic DSA packet to reach every node in the network, assuming unicast transmission?Repeat (a) assuming broadcast transmission where every one‐hop‐away node that receives the packet will have to broadcast the packet in order to make sure it reaches the nodes that are two over‐the‐air hops away.Which method would you recommend for propagating DSA control traffic between nodes: unicast transmission or multicast transmission where the packet makes use of the multiple access capability of the waveform?

3 For the same MANET discussed in Problem 2 above, let us assume that the DSA control traffic packet is divided into smaller frames where over‐the‐air transmission is for one frame not the entire packet. Let us assume that the DSA control traffic packet is divided into 20 frames.Create a table that shows the probability of delivering the DSA control traffic packet with one transmission when the probability of delivering a frame is 1.0, 0.99, 0.98, 0.97, 0.96, and 0.95, respectively. Assume that losing frames are independent events and that you have to receive every frame in the packet to reconstruct the packet accurately. Make other appropriate approximations if needed.Let us consider the MANET case in problem 2 and consider the one over‐the‐air hop away and the two over‐the‐air hops away transmission cases. Let us consider the unicast transmission scenario. Create the same table as in part (a) if we have to use unicast and transmit the packet two over‐the‐air hops away to reach a node two over‐the‐air hops away from the transmitting node. Assume that packet segmentation to frames occurs with every over‐the‐air transmission.

4 Consider Figure 4.6 with a master routing engine, master DSA engine, waveform routing engine, and waveform DSA engine. What is your expectation of reactive routes stability when:master routing engine update time > waveform routing engine update time?master routing engine update time = waveform routing engine update time?master routing engine update time < waveform routing engine update time?