Читать книгу Dynamic Spectrum Access Decisions - George F. Elmasry - Страница 45

1 Create a table of 11 entries that map dBm values to milliwatt values in the range of 1–50 mW. Use this table to create six approximate RSSI thresholds to express:Undetectable signalVery weak signalWeak signalGood signalVery good signalExcellent signal

2 State some of the dimensions you would want a spectrum sensor to consider in sensing a 5G commercial cellular signal.

3 Consider the case of M‐AM (M‐level amplitude modulation, where M is an even number) where the number of bits transmitted per symbol is (log2M). The transmitted signal is related to a data symbol xi ∈ {0, 1, …, M − 1} by si(t) = (2xi − M + 1) φ (t), where φ (t) is the common signal shape to all signals. This is essentially a one dimensional signal in space. Assume the net amplitude modulation is symmetric at each AM constellation point. Arrange the M constellation points on a straight line separated by a distance of d = 2a and answer the following:Draw the one‐dimensional signal space constellation for this case from s0 to sM − 1 symmetrically around the zero‐power point.Calculate the ideal signal energy for the inner six transmitted symbols in terms of a.Is simple energy detection ideal for this type of signal? Why?

4 Consider the 32‐QAM constellation case shown below. QAM signals are commonly used with microwave links. This is a two‐dimensional signal in space. In QAM, inner constellation points have four nearest neighbors, the edge points have three nearest neighbors, and the corner points have two nearest neighbors.Assuming signal spacing is d = 2a in each dimension, what are the various energies for the different points of the constellation?How many instantiations are there for each energy level?Is this type of signal a better candidate for energy detection than the one‐dimensional case in Problem 3? Why?What would you consider as another important metric in addition to energy detection when detecting microwave signals?

5 Comparing to AM and QAM, what do you think of the suitability of 4‐ary PSK and 8‐ary PSK signals for energy detection?