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lecture24 - Lecture Outline (Week 13, lecture 2) Wireless...

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Lecture Outline (Week 13, lecture 2) Wireless Communications – 2 nd plus Generation (CDMA) Reading: Focus on these notes. Also read 10.3 for more details. 1. Problems with Frequency and Space Resource Allocation for Cellular Systems 1 st and 2 nd generation systems such as AMPS, TDMA and GSM rely on: Space division with frequency reuse (SDMA) Frequency division of allocated spectrum (FDMA) Time division within a frequency channel (TDMA) Tradeoff in how these resources are divided. N , the frequency reuse factor is often large (>10), reducing system capacity. Placement of base stations often is constrained. Cell shape is irregular. Density of users is often not uniform. Need to split cells when the number of users in a cell becomes large. Allocation of frequency to irregular cells is very complicated. Handoff of a call from one cell to another is abrupt and complicated 2. Motivation for Code Division Multiple Access (CDMA) Instead of assignment different frequency channels for cells, all cells use the same and entire frequency band for the system. Instead of dividing frequency into frequency channels for each phone call, all calls in all cells use the same entire frequency band for the system. Instead of dividing time into time slots, a phone call transmits continuously when the
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lecture24 - Lecture Outline (Week 13, lecture 2) Wireless...

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