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What do you expect from a Cellular service Provider

This paper discusses the review of a wireless network operation, limitations of the current network architecture, and a description of a new architecture that offers benefits such as backhaul cost reduction and increased availability. Conclusions and further research topics are also provided.

alfredalbert
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What do you expect from a Cellular service Provider

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  1. What do you expect from a Cellular service Provider - LOW SUBSCRIPTION FEE - HIGH QUALITY CONNECTION 1

  2. Outline • Review of the wireless network operation • Limitations of the current network architecture • Description of the new architecture and benefits • Backhaul cost reduction: Analysis and results • Increased availability: Analysis and results • Conclusions • Further research topics 2

  3. PacketNetwork A Simple Wireless Network Mobile Switching Center (MSC) Mobile Data Set Base Station Controller (BSC) PSTN MobileVoice Unit Packet Inter-Working Function Base Transceiver System (BTS) Challenge is to keep connection and not loose any data during handoff operation 3

  4. The Components • BTS • BTS consists of one or more transceivers placed at a single location. The BTS terminates the radio path on the network side. • BSC • Provides allocation and management of radio resources. • SDU: Selection and distribution unit. Also responsible for handoff coordination • MSC • Provides and controls mobile access to the PSTN. Interprets the dialed number, routes and switches call to destination number. Also manages mobile’s supplementary services. Maintains a register of visitors operating within the coverage area of the MSC’s connected BTSs. • PDSN: Packet data service node is basically a packet router. 4

  5. Current Wireless Network Architecture MSC PDSN TDM channels Packets BSC BSC (SDU) BSC (SDU) BSC (SDU) • - Backhaul cost is by $$$/mile • 10-100 miles between BTS and BSC • Voice or data use one DS0 channel at a time • BTSs are located in the tower • BSC and MSCs are located • in the central office 24xDs0 in T1 TDM channels BTS BTS BTS BTS BTS BTS 5

  6. Soft Handoff between two BTS Handoff: A handoff mechanism is needed to maintain connectivity as devices move, while minimizing disruptions to ongoing calls. This mechanism should exhibit low latency, incur little or no data loss, and scale to a large network.” Handoffs == ( Hard || Soft ) 6

  7. WR-B SDU SDU - - - - 2 2 SDU and soft handoff • 3 to 6 BTSs involved in soft handoff • SDU changeover due to weak signal • from primary BTS • BTS forwards even corrupted • radio frames to the SDU for selection WR-A BTS-2 SDU-1 SDU - - 1 BTS-1 BTS-3 7

  8. Problems with the current architecture • Duplicate traffic on the links: Frame selection is done at the BSC (One frame is generated for each soft handoff leg.) This results in duplicate traffic flow at the backhaul • No traffic aggregation: Each call is allocated DS0 capacity. Even when there is no activity on the call, the DS0 is reserved. At this rate, currently each BTS can support only around 20 calls per sector (normally 3 sectors per BTS). So, no traffic aggregation – does not utilize statistical multiplexing (results in inefficient backhaul link provisioning) • If six BTS, then more overhead: Seventy percent (70%) of wireless operators expenditure is on RAN. Around 30% expenses are backhaul cost. Only 15% of the BTS-BSC traffic is payload and rest is overhead. If six BTS are involved in the soft handoff then the overhead will be lot higher. • Carries dead payload: BTS forwards even error frames to BSC. Because the selection is done at the BSC. This means we are carrying dead payload to BSC. 8

  9. Problems with the current architecture (cont..) • Uneven utilization of links:For data services as well as voice, IP networks overlay on top of current wireless networks. This is very inefficient, not cost effective, and very difficult to deploy the new services. • Performance:Less propagation delay. Currently, for some of the BTS-BSC configurations, the links run 100 miles, it means several milliseconds of delay. This creates problem during soft handoff. • Availability:Less availability due to single point of failure (in terms of base stations, base station controllers and links connecting between them) 9

  10. Review • Simple wireless network operation • Different components in the network • Wireless network topology • Mobility and soft handoff • Problems with the existing architecture 10

  11. highway Rural Typical US city BTS Map 30x30 miles Urban 11

  12. BTS BTS BTS BTS BTS BTS 2G/3G RAN Network (Traditional) Interoffice distance (costs per mile) cost + Fixed Cost CO CO CO CO Channel Termination Cost Channel Termination Cost BSC MSC 12

  13. What configuration is best in terms of cost and availability • Cost Reduction: How and where to place wireless router in the RAN network with respect to network-level backhaul cost and availability. For example, existing WR can be part of GSR (high end router) ? How close it to BTS • Higher Availability: Distributed IP-RAN for backhaul cost savings and higher availability Variables in analysis • Different kinds of transport cost structures • Different types of links (T1/T3/Microwave etc.) • Different types of connectivity between BTS and wireless router • Number of carriers supported supported by BTS 13

  14. Cost Model • Commercial BTS network topology. BTS are connected to BSC using the chain of Central Offices. • Real ILEC cost structure is assumed for the T1 leased lines from urban and rural areas to the BSC. • 20-30 Node network in urban area and 10 BTS in rural areas. • Soft hand factor of 2.0: How many BTS are in soft handoff • 1.5 T1 per BTS per carrier • BTS Network Regions: I) Dense Urban, ii) Urban iii) Suburban iv) Rural • Cost models • Channel termination costs • Interoffice fixed costs • Per mile costs: Transport cost changes according to distance and the type of transport (T1/T3/OC3) 14

  15. Configurations Four BTS network configuration are considered: • Traditional BTS-BSC network (Config-1, fully star, call it “Traditional”) • One Wireless Router supporting multiple BTSs (10-30). For example, existing WR can be part of GSR (high end router) ? How close it to BTS (Config-2, call it “star”) • Meshed Wireless Routers (Config-3, one wireless router per BTS, full mesh within the central office region. Call this “WR”) • Meshed Wireless Routers (WR) and each WR connected to multiple Gateway Routers for higher availability (Config-4, with connection to all the nearby high end routers. Call this “WR-HA”) 15

  16. BTS BTS BTS BTS BTS BTS 2G/3G RAN Network (Traditional) Interoffice distance (costs per mile) cost + Fixed Cost CO CO CO CO Channel Termination Cost Channel Termination Cost BSC MSC - Around 150 BTS per BSC 16

  17. BTS BTS BTS BTS BTS BTS BTS BTS BTS BTS BTS BTS WR supporting multiple BTSs (Star Topology) WR WR CO CO WR-BTS links WR-BTS links WR supports multiple BTS (10-20). Selection and distribution is done in the WR. WR collocated with CO 17

  18. GR Gateway Router GR Gateway Router Each packet Contains several radio frames. WR WR WR WR WR WR WR WR WR WR WR WR WR WR Radio frames Embedded in IP packets WR WR WR WR Solution: Distributed Control Wireless Router is an IP router with RF termination. Functions include BTS, SDU, power control, and handoff control Gateway Router is a IP router connected to the internet core 18

  19. Solution (cont.) GR-GR links GR Gateway Router GR Gateway Router Transit traffic management is handled by IP routing, QoS WR-GR links WR/BTS WR/BTS • Radio frame routing • using IP routing • Radio neighbors exchange • resource info. using IP • routing protocols • Mobility is handled through • IP signaling protocols • Radio resource management • is handled by IP traffic • management • WR assumes SDU function WR/BTS WR/BTS WR/BTS WR/BTS WR/BTS WR WR/BTS WR WR-WR Links WR-WR Links 19

  20. Solution (cont.) • Distributed SDU. Distributed bearer and control • Radio Routing Protocol: IP routing merged with Radio frame routing for soft handoff and mobility. Wireless extensions of OSPF with radio neighbors. • Radio Discovery Protocol: Discovering Radio Neighbors • Radio Resource Management: IP traffic management merged/enhanced with Radio Traffic Management. Radio Power Control integrated and aligned with IP QoS • RSVP extensions for Radio: IP resource management merged/enhanced with Radio Resource Management. For example, Radio Resource Management and soft hand off signaled with RSVP. • IP transport in Radio Access Network Disruptive Technology 20

  21. Benefits • Cost Reduction: Efficient use of backhaul links and aggregation. Only 15% of the BTS-BSC traffic is payload and rest is overhead. Around 30% expenses are backhaul cost.Objective is to reduce the backhaul traffic and small number of high speed backhaul links. • Scalability: • Separation of call processing and bearer paths • Distributed SDU and Distributed Control • Ability to provide coverage and capacity during peak hours • Redundancy and Availability: Due to meshed architecture, network is robust and works around the failures. 21

  22. Benefits (continued) • Marriage of IP and wireless protocols: Seamless operation of IP-Network-Layer with Radio Control. • Reuse already deployed routers in the Central Offices. • New wireless services:Automatic Reconfiguration of Radio Access Network. Expand cell attributes to provide more capacity • Performance:Less propagation delay. Currently, for some of the BTS-BSC configurations, the links run 100 miles, it means several milliseconds of delay. This creates problem during soft handoff. Due to short lengths between base stations, the delay will be negligible. 22

  23. GR Gateway Router GR Gateway Router Central Office Central Office WR-GR links WR-GR links WR/BTS WR/BTS WR/BTS WR/BTS WR/BTS WR/BTS WR/BTS WR/BTS WR WR WR-WR Links WR-WR Links WR collocated with BTS (WR) GR-GR links * WR-GR link (primarily) used for backhauling selected traffic to the destination * WR-WR link (primarily) is used for selection and distribution traffic between two wireless routers. * GR-GR links are links between two IP routers. These routers do not distinguish between wireless and wireline traffic 23

  24. WR collocated with BTS with HA (WR-HA) GR Gateway Router Central Office WR/BTS WR/BTS WR/BTS WR/BTS WR WR-WR Links GR Gateway Router Central Office WR-GR links WR/BTS WR/BTS WR/BTS WR/BTS WR WR-WR Links GR is collocated in the the closest CO Connectivity to two (atleast) GRs is established for higher availability. The second GR is collocated in the neighboring Central office. 24

  25. data data stream stream voice voice Overhead Overhead stream stream / stream / stream Overhead Overhead Segment. Segment. / stream / stream multiplexer multiplexer packetizer packetizer D t D t scheduler Overhead / container Traffic Models • Traffic Mix • 100% voice + 0% data • 100% data, 14.4K, 64K and 144Kbps • 80 % voice + 20% data, 14.4K, 64K and 144Kbps • 20 % voice + 80% data, 14.4K, 64K and 144Kbps 25

  26. 800000 700000 600000 WR (one per BTS) 500000 WR with HA Traditional 400000 300000 200000 100000 0 1 3 5 7 9 11 Cost Comparisons—Urban (30 node network) $$$$$ Star (10 BTS per WR) No. of Carriers (increased bandwidth at BTS, 1carrier requires ~~2 Mpbs) 26

  27. Cost Comparison—Rural (around 10 nodes) $$$$ No. of Carriers (increased bandwidth at BTS, 1carrier requires ~~2 Mpbs) 27

  28. Why less cost ?? • Backhaul cost reduced with WR mesh architecture. Customer saves $$$$ (per mile backhaul cost) • Why is the backhaul much less with WR? What is new with WR? • Frame Selection is done at the WR. No duplicate traffic after the selection is done • The aggregation of voice and data traffic from multiple WRs enables better Statistical multiplexing and reduces the backhaul requirement. This also enables customer to use less costly T3 and saves them more $$$$ • Flexible and more reliable traffic routing. 28

  29. Review and Conclusions • Statistical multiplexing and compression techniques are not accounted in the results described. If counted, more savings are realized • Cost savings for one carrier are not much but substantial for multiple carriers. • Star at the near-by-CO with a high speed (e.g., DS3/OC3) uplink is the optimum but without higher availability. • Mesh is ideal for higher availability and cost savings • All the WR cases win over traditional deployment • Ongoing work: Different kinds of transport cost structures and different types of links (T1/T3/Microwave etc.) 29

  30. CO CO CO CO WR WR WR BSC WR WR MSC WR WR BTS BTS BTS BTS BTS BTS WR WR Service Availability • Single point of failure at BTS • Single point of failure at BSC • No rerouting around congested nodes • possible. • Rerouting around failed links/nodes • Rerouting around congested links/nodes • Wireless router is also IP router hence no • need to deploy full mesh • If BTS fails, neighboring resources can be • used to complete the calls. 30

  31. Line Card Backplane Line card WR Control Processor WR WR WR Tower Control Processor WR WR WR WR GR SW SW GR Availability Model (example) Calculate MTBF and MTTR of all the components in each element 31

  32. Annual Down Time Comparison Link availability is varied from 0.99 to 0.99999 and downtime is computed For traditional and WR-HA network topologies. BTS Availability: 0.99999 GR Availability: 0.99999 32

  33. Annual Down Time Comparison Link availability is varied from 0.99 to 0.99999 and downtime is computed For traditional (2G/3G) and WR-HA network topologies. Assumptions: BTS Availability: 0.99999 GR Availability: 0.99 33

  34. RESULTS • In conventional case, when a link fails, the call level reliability is low because the call is not redirected without dropping. However, in mesh architecture, the call can still be maintained and the rerouting takes place at the frame/packet level. • Though GR’s availability is only 0.99, the overall service downtime is not impacted due to the fact that there are multiple paths from BTS to another GR. 34

  35. Review and Conclusions • Distributed RAN architecture saves backhaul cost (less than half of the cost of existing architecture ) • Distributed RAN architecture supports 99.999% service-level availability compared to conventional network. In fact, full mesh is not required for realizing the 99.999% availability. Even partial mesh can achieve this level of availability • Distributed architecture increases the complexity of control and requires working prototype for understanding the new protocols. • Disruptive technology: Required new protocols design and approval from vendor and hence may take long time to get to the field (this is weakness in this architecture). 35

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