What do you expect from a Cellular service Provider

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What do you expect from a Cellular service
Provider

• - LOW SUBSCRIPTION FEE
• - HIGH QUALITY CONNECTION

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

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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
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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 mobiles
  supplementary services. Maintains a register of
  visitors operating within the coverage area of
  the MSCs connected BTSs.
• PDSN Packet data service node is basically a
  packet router.

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
 
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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 )
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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
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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.

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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)

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Review

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

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highway
Typical US city BTS Map 30x30 miles
Rural
Urban
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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

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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

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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)

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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)

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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
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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
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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
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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
WR/BTS
WR
WR/BTS
WR-WR Links
WR-WR Links
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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
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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.

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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.

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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
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WR collocated with BTS with HA (WR-HA)
GR Gateway Router
Central Office
WR-GR links
WR/BTS
WR/BTS
WR/BTS
WR
WR/BTS
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.
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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

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Cost ComparisonsUrban (30 node network)

Star (10 BTS per WR)
No. of Carriers (increased bandwidth at BTS,
1carrier requires 2 Mpbs)
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Cost ComparisonRural (around 10 nodes)

No. of Carriers (increased bandwidth at BTS,
1carrier requires 2 Mpbs)
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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.

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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.)

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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.

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Availability Model (example)
Calculate MTBF and MTTR of all the components in
each element
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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.
Link Avail .99 .999 .9999 .99999
Traditional (Hours) 174 17.77 2.01 0.438
WR-HA (Minutes) 5.25 5.25 5.25 5.25
BTS Availability 0.99999 GR Availability 0.99999
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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.
Link Avail .99 .999 .9999 .99999
Traditional (Hours) 174 17.77 2.01 0.438
WR-HA (Minutes) 5.85 5.78 5.78 5.78
Assumptions BTS Availability 0.99999 GR
Availability 0.99
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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 GRs 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.

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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).