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Outline

Outline. Wireless introduction Wireless cellular (GSM, CDMA, UMTS, WiMAX) Wireless LANs, MAC layer Wireless Ad hoc networks routing: proactive routing, on-demand routing, scalable routing, geo-routing multicast TCP QoS, adaptive voice/video apps Sensor networks. BS. BS. BS.

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Outline

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  1. Outline Wireless introduction Wireless cellular (GSM, CDMA, UMTS, WiMAX) Wireless LANs, MAC layer Wireless Ad hoc networks routing: proactive routing, on-demand routing, scalable routing, geo-routing multicast TCP QoS, adaptive voice/video apps Sensor networks

  2. BS BS BS Backbone Network BS BS BS Cellular Concept • Geographical separation • Capacity (frequency) reuse • Backbone connectivity

  3. HLR (home location register) – information MSC (mobile switching center) VLR (visitor location register) – information BS (base station) - modulation, antenna Organization of Cellular Networks

  4. Handoff • Handoff: Transfer of a mobile from one cell to another • Each base station constantly monitors the received power from each mobile • When power drops below given threshold, base station asks neighbor station (with stronger received power) to pick up the mobile, on a new channel • The handoff process takes about 300 ms

  5. To register and make a phone call • When phone is switched on , it scans a preprogrammed list of 21 control channels, to find the most powerful signal • It transmits its ID number on it to the MSC which • informs the local HLR • adds it to VLR and informs the home MSC which informs the HLR • registration is done every 15 min • To make a call, user transmits dest Ph # on random access channel; MSC will assign a data channel • At the same time MSC pages the destination cell for the other party (idle phone listens on all page ch.)

  6. How does a call get to the mobile ? • Suppose (310) 643 - 1111 is roaming in the (408) area code • Cell phone registers with the (408) MSC, which adds it to (408) VLR and informs the (310) HLR of the location of the cell phone • A call comes in for (310) 643 – 1111. Then (310) MSC queries its HLR, and directs the call to the (408) MSC • The (408) MSC forwards the call to the mobile

  7. Cellular Wireless Network Evolution • First Generation: Analog voice • AMPS: Advance Mobile Phone Systems • Residential cordless phones • FDMA • Second Generation: Digital voice • GSM: European Digital Cellular - TDMA • IS-54/136: North American - TDMA • IS-95: CDMA (Qualcomm) • DECT: Digital European Cordless Telephone

  8. Cellular Evolution (cont) • Third Generation: Packet data • will combine the functions of: cellular, cordless, wireless LANs, paging etc. • will support multimedia services (data, voice, video, image) • Requirements • 384 Kbps for full area coverage • 2 Mbps for local area coverage • variable bit rate • packet traffic support • flexibility (eg, multiple, multimedia streams on a single connection)

  9. Cellular Evolution (cont) • Third Generation: Packet data • 2.5 G • GPRS (for GSM) (General Packet Radio Service ) • EDGE (for GSM) (Enhanced Data rates for Global Evolution) • 1xRTT (for CDMA) • 3G (W-digital CDMA) • IMT-2000/UMTS (International Mobile Telecommunications) (Universal Mobile Transport Service) • CDMA 2000, WCDMA, TD-CDMA, TD-SCDMA • 3+G, 4G systems • OFDM, Software radio, Array antennas • WiMAX

  10. Access techniques for mobile communications FDMA (TACS) P F TDMA (GSM, DECT) ATDMA (UMTS) T P F CDMA (UMTS) T P F P - Power T - Time F - Frequency T

  11. Spread Spectrum

  12. CDMA (Code Division Multiple Access) • unique “code” assigned to each user; i.e., code set partitioning • all users share same frequency, but each user has own “chipping” sequence (i.e., code) to encode data • Note: chipping rate >> data rate (eg, 64 chips per data bit) • encoded signal = (original data bit) X (chipping sequence) • decoding:inner-product of encoded signal and chipping sequence • allows multiple users to “coexist” and transmit simultaneously with minimal interference (if codes are “orthogonal”)

  13. CDMA Encode/Decode

  14. CDMA: two-sender interference

  15. . m inner-product S T = = 0 1 SSi.Ti m i=1 . S S = 1 C = (1,1,1,1) 4,1 C = (1,1) 2,1 C = (1,1,-1,-1) 4,2 = (1,-1,1,-1) C 4,3 = (1,-1) C 2,2 C = (1,-1,-1,1) 4,4 Orthogonal Variable Spreading Factor

  16. CDMA (Code Division Multiple Access): IS-95 QUALCOMM, San Diego • Based on DS spread spectrum • Two frequency bands (1.23 Mhz), one for forward channel (cell-site to subscriber) and one for reverse channel (sub to cell-site) • CDMA allows reuse of same spectrum over all cells. Net capacity improvement: • 4 to 6 over digital TDMA (eg. GSM) • 20 over analog FM/FDMA (AMPS)

  17. CDMA (cont’d) • One of 64 PS (Pseudo Random) codes assigned to subscriber at call set up time • RAKE receiver (to overcome multi path-fading) • Pilot tone inserted in forward link for: • power control • coherent reference • Speech activity detection • Voice compression to 8 kbps (16 kbps with FEC) • IS-95: 20 wideband channels, BW=1.25 MHz

  18. Traffic-Driven Power Saving in Operational 3G Cellular Networks ACM Mobicom 2011 Las Vegas, Nevada, USA Chunyi Peng1, Suk-Bok Lee1, Songwu Lu1, Haiyun Luo∗, Hewu Li2 1University of California, Los Angeles 2Tsinghua University

  19. Surging Energy Consumption in 2G/3G 0.5% of world-wide electricity by cellular networks in 2008 [Fettweis] ~124Twh in 2011 (expected) [ABI] CO2 emission, comparable to ¼ by cars Operation cost, e.g., $1.5B by China Mobile in 2009 Rising energy consumption at 16-20%/year Moore’s law: 2x power every 4~5 years by 2030 [Fettweis]: G. Fettweis and E. Zimmermann, ICT energy consumption-trends and challenges, WPMC’08. [ABI]: ABI Research. Mobile networks go green–minimizing power consumption and leveraging renewable energy, 2008. Mobicom 2011 C Peng (UCLA) 19

  20. Energy Consumption in Cellular Networks 10kw X 10K = 0.1GW 0.1w X 5B = 0.5GW 1~3kw X 4M = 8GW <10% (~1%) Mobile Terminals >90% (~99%) Cellular Infrastructure ~80% by BSes The key to green 3G is on BS network Source: Nokia Siemens Networks (NSN) Mobicom 2011 C Peng (UCLA) 20

  21. Case Study in a Regional 3G Network Current Power (Kw) Ideal Load: (#link in 15min) Power-load curve in a big city with 177 BSes (3G UMTS) Non-energy-proportionality (Non-EP) to traffic load Mobicom 2011 C Peng (UCLA) 21

  22. Root Cause for Energy Inefficiency Traffic is highly dynamic Fluctuate over time Be uneven at BSes Low usage at night Large energy overhead at light traffic => non-EP. Turn off BS completely to save more energy! Mobicom 2011 C Peng (UCLA) 23

  23. Solution I: Building Virtual Grids Divide into BS virtual grids BSes within a grid cover each other Decouple coverage constraint Location-dependent capacity meets location-dep. traffic Virtual BS Grids turn on/off BSes s.t. cap >= load ✗ ✗ ✗ ✗ ✗ ✗ ✔ ✔ ri + d(i,j) < Ri rj + d(i,j) < Rj ✔ ✔ ✗ i ✗ ✗ j ✗ Mobicom 2011 C Peng (UCLA) 24

  24. Recall the Case Study Current GreenBS Ideal Power-load curve in a big city with 177 BSes (3G UMTS) Mobicom 2011 C Peng (UCLA) 25

  25. C-RAN, Cloud Radio Access Network: Cloud Paradigm for Wireless Networks 中国移动通信公司

  26. Cell Site Map • Dense Cell improve Coverage • Each site includes signal access and processing High Energy Consumption, Low Resource Efficiency, Traffic unbalance.

  27. C-RAN: Cloud Paradigm for Wireless Networks • 通过结合集中化的基带处理、高速的光传输网络和分布式的远端无线模块，形成绿色清洁、集中化处理、协作化无线电、云计算化的无线接入网构架

  28. C-RAN: Cloud Paradigm for Wireless Networks • C-RAN breaks down the base station into two parts • Baseband Unit (BBU) – a digital unit the implements the MAC phy and Antenna array system (AAS) • Remote Radio Head (RRH) that obtains the digital signals, coverts digital signals to analog, amplifies the power and sends the actual transmission. • RRH typically connect using fiber with BU • RRH can support multiple cellular technology (GSM, 3G, LTE ) eliminating the need for multiple antennas. • BBUs are centralized and provides services on the cloud

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