chapter2.3【荐】.ppt

2006 Computer Networks 2.6 The Mobile Telephone System Huge Market.. History First-Generation Mobile Phones: Analog Voice Second-Generation Mobile Phones: Digital Voice Third-Generation Mobile Phones:Digital Voice and Data Applications Technology Evolution Advanced Mobile Phone System (a) Frequencies are not reused in adjacent cells. (b) To add more users, smaller cells can be used. Frequency Reuse in FDMA A portion of the GSM framing structure. AMPS View Handoff Soft handoff, phone is acquired by the new BS before the previous one signs off. Hard handoff, old BS drops the phone before the new one acquires it. AMPS Channel Categories The 832 channels are divided into four categories: Control (base to mobile) to manage the system Paging (base to mobile) to alert users to calls for them Access (bidirectional) for call setup and channel assignment Data (bidirectional) for voice, fax, or data 2.6.2 PCS: D-AMPS Digital Advanced Mobile Phone System (a) A D-AMPS channel with three users. (b) A D-AMPS channel with six users. GSMGlobal System for Mobile Communications GSM uses 124 frequency channels, each of which uses an eight-slot TDM system GSM (2) A portion of the GSM framing structure. CDMA : everybody talking at once, each pair in a different language. TDMA FDMA CDMA – Coding Mechanism 1, Each station has its own unique chip sequence; 2, Orthogonal chip sequences by Walsh codes: normalized inner product of any two distinct chip sequences, S and T (written as S?T), is 0. (a) Binary chip sequences for four stations (b) Bipolar chip sequences (c) Six examples of transmissions (d) Recovery of station C’s signal Third-Generation Mobile Phones:Digital Voice and Data Basic services an IMT-2000 network should provide High-quality voice transmission Messaging (replace e-mail, fax, SMS, chat, etc.) Multimedia (music, videos, films, TV, etc.) Internet access (web surfing, w/multimedia.) International Mobile Telecommunications Y