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Queueing Priority Channel Assignment Strategies for PCS Hand-Off and Initial Access

Queueing Priority Channel Assignment Strategies for PCS Hand-Off and Initial Access. IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY,1994 Yi-Bing Lin, Seshadri Mohan, and Anthony Noerpel. Speaker: R01922021 趙祈鈞. Outline. Introduction Related Works Analytic Models Traffic Model

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Queueing Priority Channel Assignment Strategies for PCS Hand-Off and Initial Access

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  1. QueueingPriority Channel Assignment Strategies for PCS Hand-Off and Initial Access IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY,1994 Yi-Bing Lin, Seshadri Mohan, and Anthony Noerpel Speaker: R01922021 趙祈鈞

  2. Outline • Introduction • Related Works • Analytic Models • Traffic Model • System Model • Simulation • Conclusions

  3. Introduction • Personal Communication Service(PCS) • Cells and channels • Provides wireless access to PSTN • Hand-off, or Automatic Link Transfer(ALT) • PCS radio systems • DECT, CT-2 Plus (with signaling channel) • WACS (directly on traffic channel)

  4. Introduction • ALT strategies • Portable-controlled • DECT, WACS • Network-controlled • CT-2 Plus • Portable-assisted • ALT-initial access channel assignment schemes • Non-prioritized scheme (NPS) and Guard channel

  5. Introduction • ALT-initial access channel assignment schemes • FIFO //degradation interval • Measured-based priority scheme (MBPS) • FIFO scheme with different queueing policy

  6. Related Works • Hong and Rappaport [10] //FIFO • Based on a special portable movement pattern by Poisson process • Tekinary and Jabbari [17] //FIFO • Td normally distributed, Markov chain • [9] says expo. dist. is more suitable for Markov chain • Considered the hand-off traffic as an indep. input (X) • Yoon and Kwan [19] • hand-off traffic as an indep. input (X) • M/M/C/K instead of timeout system • This paper • NPS, FIFO and MBPS, 50/10 servers per cell

  7. Analytic Models (Traffic) • A portable moves across K cell boundaries • Also # of hand-offs • Call holding time: tc (expo.) density: • Start at R0, visits K cells, tM_i: time in i-th cell • Time of R0 to 1: tm, density: • tMi is i.i.d., dist.: density: mean:

  8. TrafficModel • By Random Observer Property(ROP) of Poisson • For K>=1,

  9. Traffic Model • Use (1) and (2), • with Laplace transform

  10. Traffic Model • Let be an exponential distribution • M/G/c => M/M/c ,so • Hand-off call arrival rate

  11. Traffic Model • Pc: prob{call completed} • If • If • Obs. of Hong and Rappaport [10] not general • Pnc is more sensitive to Po than to Pf (X) • From (10), ↑

  12. Analytic Models(system) • For NPS, • For FIFO • t_d: expo. • Mean:

  13. System Model for nps • t_co = min(t_c, t_m) //t_channel occupancy = min(t_call holding, t_remaining portable residual)

  14. System Model for nps • From the Erlang-B formula • For lost systems (no queue) • Total traffic load • Avg. arrival rate • Avg. service rate • NPS:

  15. System Model for fifo • FIFO • t_q = min(t_d, t_m) //t_maxqueueing = min(t_timeout, t_remaining portable residual) • A hand-off call is blocked if no channel is assigned before t_maxqueueing • density:

  16. System Model for fifo • State s(n), n>=0 • n: # of busy channels • For 0<=n<c • S(n) has n busy channels, no HO in queue • For n=c+j>=c • All c channels busy, j HOs in queue, new calls dropped

  17. System Model for fifo • Steady state probability for s(n)

  18. System Model for fifo • Prob{originating call blocked} • Prob{hand-off call blocked} • Let a hand-off call Ct arrives at t in state s(n) • //n=c+j, so Ct will be in queue • Suppose the 1st call leaves the queue at t+tj • Ct needs to wait for j+1 calls before him.

  19. System Model for fifo • E[waiting time]

  20. Simulation • Discrete event simulation model • 1st chooses a • Simulates to obtain Po and Pf • Use (9) to compute new lambda_h • Repeat until lambda_h converges • 3 types of events • ARRIVAL • originating or hand-off • COMPLETION • Calls releasing channels (completes or portable moves) • WAIT

  21. Simulation • Sim_count: N • Record No, Nf • Initial, gen 1st • Max N: 800,000 • ARRIVAL • o or h: rand() • (13) Iter. ends • (10) e1:timeout(11)

  22. analysis vs. Simulation • Plot Pf, Po, Pnc and normalized E[waiting] • c=50, 1/miu=3min, 1/gamma=18s, 1/eta=30min • Compare with [17] • Pf and Po for MBPS always < that for FIFO (X)

  23. Simulation • NPS vs. FIFO • c=10, 1/miu=3min 1/eta=10min 1/gamma=18s, 55s • (c): Pr[f|nc] • FIFO • Better w/ small gamma • Pf↓ Pnc little↓ • because Po little↑

  24. Conclusions • Proposed analytic and simulation models to study ALT-initial access channel assignment schemes(NPS, FIFO, MBPS). • Major output measures: Po, Pf, Pnc • Vs. Hong and Rappaport [10] • Pnc is more sensitive to Po than to Pf (X general) • Indicated if mobility↑, impact of Pf on Pnc↑, of Po↓ • Vs. Tekinary and Jabbari [17] • MBPS provides lower Pf and Po (X) • Indicate that MBSP and FIFO roughly the same(Pf, Po) • FIFO significantly Pf↓, slightly Po↑ • Yield slightly better (smaller) Pnc //vs. NPS

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