Copyright 1999, S.D. Personick. All Rights Reserved. Telecommunications Networking II Lectures Cellular and PCS Systems

Copyright 1999, S.D. Personick. All Rights Reserved. What’s the Problem We Are Trying to Solve? To Network Radio Port

Copyright 1999, S.D. Personick. All Rights Reserved. Engineering Objectives Low cost, small size, light weight, long battery lifetime-- in handheld appliances Maximize utilization of valuable spectrum: - number of simultaneous users per unit volume of space - diversity of applications supported Minimize base-station costs High customer-perceived quality of service

Copyright 1999, S.D. Personick. All Rights Reserved. Review of Frequency Division Multiplexing 800MHz825 MHz Channel: e.g., 5kHz Sub-band e.g., 5 MHz

Copyright 1999, S.D. Personick. All Rights Reserved. Review of Frequency Division Multiplexing Available Total Bandwidth = B (toward radio port) Number of simultaneous mobile users = N Allocation per mobile user = B/N Time available for communication = T # of bits per second that can be transmitted per Hz of bandwidth = C (bits/sec-Hz) Total # of bits transmitted = N x (B/N) x T x C = BTC

Copyright 1999, S.D. Personick. All Rights Reserved. Time x Bandwidth Resource: FDM 0 B T B x T x C

Copyright 1999, S.D. Personick. All Rights Reserved. What determines C? Examples: Early digital radio systems: C= 1 bit per second per Hz Early modems: 1200 bits per second in a 3 kHz band Modern digital radio systems: C= 4-6 bps per Hz Latest modems: 56 kbps in a 3 kHz band = 19 bps per Hz Cable modems: 20 Mbps in a 6 Mhz band = 3.5 bps per Hz

Copyright 1999, S.D. Personick. All Rights Reserved. Review of Time Division Multiplexing Available time = T N mobile users Divide T into N time slots of duration T/N Available bandwidth = B (toward the radio port) Each mobile user can send B x C (bits per second per Hz) x T/N bits Total bits sent = B x C x (T/N) x N = BTC

Copyright 1999, S.D. Personick. All Rights Reserved. Review of Time Division Multiplexing (cont’d) Coordinating in the upstream direction (toward the radio port/cell site): -Need a timing reference transmitted by the radio port -Need “guard bands” to allow for timing errors -Each upstream transmission requires accommodation and synchronization at the radio port

Copyright 1999, S.D. Personick. All Rights Reserved. Upstream Communication Three packets in three time slots arriving at a radio port Time

Copyright 1999, S.D. Personick. All Rights Reserved. Buffering Delay (example) Voice Coder Voice input 16 kbps, continuous Buffer Memory 160 kbps, 1 millisecond bursts, each followed by 9 milliseconds of no output Buffer stores 10 ms of voice coder output (160 bits)

Copyright 1999, S.D. Personick. All Rights Reserved. Time x Bandwidth Resource 0 B T

Copyright 1999, S.D. Personick. All Rights Reserved. Time x Bandwidth Resource: FDM 0 B T B x T x C

Copyright 1999, S.D. Personick. All Rights Reserved. Time x Bandwidth Resource TDM 0 B T B x T x C

Copyright 1999, S.D. Personick. All Rights Reserved. Time Division Multiplexing 800MHz825 MHz Shared TDM Channel: e.g., 32 kHz Sub-band e.g., 5 MHz

Copyright 1999, S.D. Personick. All Rights Reserved. Time x Bandwidth Resource Frequency Hopping 0 B T B x T x C

Copyright 1999, S.D. Personick. All Rights Reserved. Time x Bandwidth Resource Uncordinated Frequency Hopping 0 B T B x T x C x  where:  = [m/n][1-(1/n)]**m-1 n=# channels m=# users  ~[m/n]e**-(m/n)

Copyright 1999, S.D. Personick. All Rights Reserved. Code Division Multiple Access S(t) = +/- 1 T (seconds H(t) = +/- 1 “chip” sequence: S(t)

Copyright 1999, S.D. Personick. All Rights Reserved. Let I=the Integral of [S(t) x H(t)]dt, over T I = T, if S(t) = H(t) I= (A-B) T, where A= # matches, and B= number of mismatches, if H(t) is not equal to S(t) Objective: Pick chip sequences which are ~ “orthogonal”, I.e., I<<T when two different chip sequences are cross-correlated

Copyright 1999, S.D. Personick. All Rights Reserved. Engineering Objectives Low cost, small size, light weight, long battery lifetime-- in handheld appliances Maximize utilization of valuable spectrum: - number of simultaneous users per unit volume of space - diversity of applications supported Minimize base-station costs High customer-perceived quality of service

Copyright 1999, S.D. Personick. All Rights Reserved. Low Cost, Light Weight, Long Battery Lifetime Simplify the handset: move complexity to the radio port/radio port controller/network -handsets communicate with the base station(s), not directly with each other Low power transmitters in the handsets: relatively large, carefully designed antennas at the radio ports (radio port antennas become directional); small cells

Copyright 1999, S.D. Personick. All Rights Reserved. Maximize Utilization of Valuable Spectrum: Frequency Re-use B/x vs [(B/3) x 27]/x where B=Total bandwidth x = channel bandwidth

Copyright 1999, S.D. Personick. All Rights Reserved. Maximize Utilization of Valuable Spectrum Increase Frequency Reuse Systems that support multiple applications (not just voice)

Copyright 1999, S.D. Personick. All Rights Reserved. Wireless is More Than Wireless Wireless radio ports, radio port controllers, and the global network must be interconnected by a suitable communications fabric, which is often comprised of wires (T1), fiber, or coaxial facilities Wireless facilities require network management and service management functionality, implemented in complex software

Copyright 1999, S.D. Personick. All Rights Reserved. The Underlying “Wireless” Communication Fabric Mux Radio Port Radio Port Controller Unit To Network

Copyright 1999, S.D. Personick. All Rights Reserved. Network and Service Management (example) Radio Port Controller Unit Radio Port Mux To Network Setup Request Authorization request/response

Copyright 1999, S.D. Personick. All Rights Reserved. Call Setup 800MHz825 MHz Access Channels Dedicated Control & Paging Channels

Copyright 1999, S.D. Personick. All Rights Reserved. Network and Service Management (example #2) Radio Port Controller Unit Radio Port Mux To Network Handoff coordination

Copyright 1999, S.D. Personick. All Rights Reserved. Middleware for Wireless Access Accommodate the limited, varying, and discontinuous connectivity of wireless appliances Accommodate the limited processing and display/user interface capabilities of some types of wireless appliances Support the preferences of nomadic users Do all of the above in a way that is transparent to users and the networks to which they are connected

Copyright 1999, S.D. Personick. All Rights Reserved. Cellular Generations First generation cellular -optimized for voice and vehicular use -analog; supports data (modems, overlays) Second generation cellular - digital: -GSM (TDM), CDMA -Optimized by voice, supports data Third Generation Cellular: “IMT 2000”