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ECE 5221 Personal Communication Systems

ECE 5221 Personal Communication Systems. Prepared by: Dr . Ivica Kostanic Lecture 20: Traffic planning (4). Spring 2011. Outline . Blocked calls delayed – Erlang C Traffic estimation in cellular networks.

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ECE 5221 Personal Communication Systems

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  1. ECE 5221 Personal Communication Systems Prepared by: Dr. Ivica Kostanic Lecture 20: Traffic planning (4) Spring 2011

  2. Outline • Blocked calls delayed – Erlang C • Traffic estimation in cellular networks Important note: Slides present summary of the results. Detailed derivations are given in notes.

  3. M/M/C systems do not reject service requests If the resources are not available the request is placed in the queue Queue is assumed infinite GOS is inadequate measure of QoS Some examples dispatch voice low end packet data services (SMS, MMS, e-mail, …) Relevant QoS parameters in lossless systems Probability of service delay Average delay for all requests Average delay for the requests placed in the queue 90% delay percentile Average number of requests in the queue Probability of a delay that exceeds a given threshold QoS in lossless systems of M/M/C type

  4. Trunking model for lossless systems - Erlang C State diagram of M/M/C system • Erlang C assumptions • Call arrival process is Poisson • Service time is exponentially distributed • There are C identical servers (channels) • The queue is infinite • Common QoS parameter in M/M/C systems are • delay probability • average delay • number of users in the queue Probability of delay Erlang C delay formula Offered traffic Server utilization

  5. Erlang C - performance curves Erlang C family of curves • Erlang C formula can be given in a form of • family of curves • table (Appendix)

  6. Erlang C - Summary of performance parameters Alternative notation Probability of delay exceeding T1 H – average call holding time

  7. Erlang C - examples Example. Consider a cell site supporting MMS service. Assume that the messages are exponentially distributed with average length of 2 Meg. The cell site provides two channels that have transfer rate of 200kbps. If there are 125 requests per hour estimate probability of • Request being delayed • Request being delayed by more than 10 sec Answers: • Call holding time: 10 sec • Average service rate: 0.1 request/sec • Birth rate: 0.034 requests/sec • Offered traffic: 0.034 E • Average resource utilization: 0.17 • Probability of delay: 0.04940 ~ 5% • Probability of delay exceeding 10 sec: 0.009 ~ 1%

  8. We need to estimate Geographical distribution of users Traffic volume generated per user Geographical distribution may be estimated using Population density Average family income Land use (clutter) Road usage, etc. Traffic volume may be estimated using Estimate of call holding time (CHT) Estimate of number of calls within the busy hour Once the system is operational traffic data is available from switch reports Future offered traffic is estimated through the traffic trending process Estimation of offered traffic

  9. Estimate user distribution using following GIS and market data Average population density Land use with four morphological classifications (Dense Urban, Urban, Suburban and Rural) Road use map with four types of roads (Interstates, Highways, Major roads and Secondary roads) Total population in the market and penetration rate Step 1: Convert all GIS data to relative traffic demand grids Step 2: Eliminate all GIS data outside of market boundary Step 3: Determine the total number of users within the boundary Estimation of user distribution - example Example of relative weights for the road types Interstates : 10 Highways : 5 Major roads : 3 Second. roads : 1 Example of relative weights for the land use types Dense urban : 10 Urban : 5 Suburban : 3 Rural : 1

  10. Step 4: Use the following “grid algebra” equation Estimation of user distribution - example where Fraction of users within their residence area Fraction of user distributed through “clutter” Population density relative demand grid Land use demand grid Fraction of users on the roads Total population Penetration rate Roaming factor

  11. Estimation of call holding time (CHT) Part of CTIA semiannual report Average CHT for local calls: 2.27 min (136.2) Average CHT for roaming calls: 3.32min (199.2 sec)

  12. Estimation of number of calls in busy hour • Average plan (Summer 2011, in FL) • 45 dollars per month • 450 peak time minutes (from 8:00 AM to 8:00 PM) • Average number of phone calls during week day • Assuming that 15% of usage within busy hour - user makes 1.2 calls • Traffic per subscriber Note: Homework 5 assigned

  13. Appendix – Erlang C table

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