Compare wireless multiple access techniques: FDMA/TDMA/CDMA and OFDMA. 1. (2 points) NMT-900 is a first generation cellular systems that operates in the 900 MHz band. It is uses analog FM modulation to transmit voice signals. The system uses FDMA to support multiple voice calls. The uplink spectrum is 890 MHz - 915 MHz and the downlink spectrum is 935 MHz - 960 MHz. The bandwidth required for each voice call is 12.5 kHz. A. What is the duplexing scheme of this system? B. How many simultaneous calls can be supported in this system? 2. (3 points) GSM is a second generation cellular systems that operates in the 900 MHz band with 25 MHz in the downlink and 25 MHz in the uplink. It is uses digital GMSK modulation to transmit digitized voice and data on a single 200 kHz carrier. The system uses 8-slot TDMA to carry multiple voice calls on the same carrier. Each time slots (also called "bursts") 15 is equal toms which amounts to 114 data bits (excluding overhead bits). A multi-frame is defined as a group of 26 consecutive 8-slot TDMA frames. Two TDMA frames are reserved for control and signaling, leaving 24 frames for data. A. A traffic channel is defined as the repetitive occurrence of one time slot, repeated every multi-frame. Calculate the bit rate each traffic channel. B. How many full-duplex carriers in this system? C. What is the duplexing scheme of this system? 3. (5 points) Suppose we have two CDMA users A and B. User A uses this spreading sequence (1,1,1,-1,-1,1,-1) and user B uses this sequence (1,-1,-1,-1,1,1,-1). Also, suppose the base station receives the following signal which is spread using DSSS from all active users in the cell (1,1,3,1,-1,-1,-1; 1,-3,-1,1,3,-1,-1). a) How many data bits are represented by the received DSSS signal? b) Decode the data bits that were transmitted by user A. c) Decode the data bits that were transmitted by user B.