QUEUEING PRIORITY CHANNEL ASSIGNMENT STRATEGIES FOR PCS HAND-OFF AND INITIAL ACCESS

IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY,1994Yi-Bing Lin, Seshadri Mohan, and Anthony Noerpel

Speaker: R01922021 趙祈鈞

OUTLINE Introduction Related Works Analytic Models

Traffic ModelSystem Model

Simulation Conclusions

INTRODUCTION Personal Communication Service(PCS)

Cells and channelsProvides wireless access to PSTNHand-off, or Automatic Link Transfer(ALT)

PCS radio systemsDECT, CT-2 Plus (with signaling channel)WACS (directly on traffic channel)

INTRODUCTION ALT strategies

Portable-controlled DECT, WACS

Network-controlled CT-2 Plus

Portable-assisted

ALT-initial access channel assignment schemesNon-prioritized scheme (NPS) and Guard channel

INTRODUCTION ALT-initial access channel assignment

schemesFIFO //degradation interval

Measured-based priority scheme (MBPS) FIFO scheme with different queueing policy

RELATED WORKS Hong and Rappaport [10] //FIFO

Based on a special portable movement pattern by Poisson process

Tekinary and Jabbari [17] //FIFOTd normally distributed, Markov chain [9] says expo. dist. is more suitable for Markov

chainConsidered 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 paperNPS, FIFO and MBPS, 50/10 servers per cell

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:

TRAFFIC MODEL By Random Observer Property(ROP) of

Poisson

For K>=1,

TRAFFIC MODEL Use (1) and (2),

with Laplace transform

TRAFFIC MODEL

Let be an exponential distributionM/G/c => M/M/c ,so

Hand-off call arrival rate

TRAFFIC MODEL Pc: prob{call completed}

If If Obs. of Hong and Rappaport [10] not

generalPnc is more sensitive to Po than to Pf (X)From (10), ↑

ANALYTIC MODELS (SYSTEM) For NPS,

For FIFO t_d: expo.

Mean:

SYSTEM MODEL FOR NPS

t_co = min(t_c, t_m) //t_channel occupancy =min(t_call holding, t_remaining portable residual)

From the Erlang-B formulaFor lost systems (no queue)Total traffic load

Avg. arrival rate Avg. service rate

NPS:

SYSTEM MODEL FOR NPS

SYSTEM MODEL FOR FIFO FIFO t_q = min(t_d, t_m) //t_max queueing

= min(t_timeout, t_remaining portable

residual) A hand-off call is blocked if no channel is assigned before t_max queueing

density:

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

SYSTEM MODEL FOR FIFO Steady state probability for s(n)

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 queueSuppose the 1st call leaves the queue at t+tj

Ct needs to wait for j+1 calls before him.

SYSTEM MODEL FOR FIFO E[waiting time]

SIMULATION Discrete event simulation model

1st chooses aSimulates to obtain Po and PfUse (9) to compute new lambda_hRepeat until lambda_h converges

3 types of eventsARRIVAL

originating or hand-offCOMPLETION

Calls releasing channels (completes or portable moves)

WAIT

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)

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)

SIMULATION NPS vs. FIFO

c=10, 1/miu=3min 1/eta=10min 1/gamma=18s, 55s (c): Pr[f|nc]

FIFOBetter w/ small gammaPf↓ Pnc little↓because Po little↑

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