Question:
(a) Suppose that you are a communication engineer and you have to construct a mobile telephone network with bandwidth W = 4.2 MHz in each link. The data rate is R = 10 kb/s. You have the following alternatives:
i) A system based on TDMA with parameters
• Frequency reuse factor 1/7
• Each link divided into radio channels of 200 kHz
• Ten users per channel
ii) A system based on DS CDMA with parameters
• Frequency reuse factor 1
• Voice activity gain γv = 2.5
• No antenna sectorization
• The required signal-to-noise ratio Eb/I0 = 6 dB
• Other-cell relative interference factor f = 0.6
What alternative would you choose?
(b) You want to distribute the total transmission rate D among 10 users.
(i) How is this done in FDMA, a TDMA and a CDMA system?
(ii) How long should the parameters transmission rate DT, bandwidth BT and signal to noise ratio S/N be selected for each user and why?
(c)
(i) How does the near/far effect influence TDMA systems?
(ii) What happens in CDMA systems?
(iii) What are countermeasures in TDMA systems, what about CDMA systems?
(d)
(i) What is the main physical reason for the failure of many MAC schemes known from wired networks?
(ii) What is done in wired networks to avoid this effect?
(e) Which of the MAC schemes can give hard guarantees related to bandwidth and access delay?