Channel Allocation for GPRS

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Channel Allocation for GPRS

• From IEEE Tran. Veh. Technol., Vol. 50, no. 2,
  2001.
• Author P. Lin and Y.-B. Lin
• CSIE, NTU CSIE, NCTU

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Outline

• Introduction
• GPRS architecture
• Packet data logical channel
• Channel allocation schemes
• System model
• Analysis results
• Simulation method
• Performance
• Conclusion

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Introduction

• GPRS shares GSM frequency bands with telephone
  and circuit-switched data traffic
• GPRS uses the same TDMA/ FDMA structure as that
  of GSM to form physical channels
• Allocation of channel for GPRS is flexible where
  one to eight channels can be allocated to a user
  or one channel can be shared by several users

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GPRS architecture
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Packet data logical channel

• Packet data traffic channel (PDTCH)
• Employed for transferring of user data
• Packet broadcast control channel (PBCCH)
• Broadcast control
• Packet common control channel (PCCCH)
• The packet random access channel (PRACH)
• The packet paging channel (PPCH)
• The packet access grant channel (PAGCH)
• The packet notification channel (PNCH)
• Packet dedicated control channels
• The packet associated control channel (PACCH)
• The packet timing advance control channel (PTCCH)

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Packet data logical channel (contd)
Group Name Direction Function
PTC PDTCH Downlink and uplink Data
PBCCH PBCCH Downlink Broadcast
PCCCH PRACH Uplink Random access
PCCCH PPCH Downlink Paging
PCCCH PAGCH Downlink Access grant
PCCCH PNCH Downlink Multicast
PDCH PTCCH Downlink and uplink Timing advance
PDCH PACCH Downlink and uplink Associated control
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Dynamic allocation uplink data transfer
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Dynamic allocation downlink data transfer
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Channel allocation schemes

• Fixed Resource Allocation (FRA)
• For a data request of K channels, the BS
  assigns exact K
• channels to GPRS packet request
• Dynamic Resource Allocation (DRA)
• For a data request of K channels, DRA
  allocates at most K
• channels to the request
• Fixed Resource Allocation with Queue Capability
  (FRAQ)
• FRAQ_N a queue for the new calls only
• FRAQ_H a queue for the handoff calls only
• FRAQ_NH a queue for both new and handoff
  calls
• Dynamic Resource Allocation with Queue
  Capability (DRAQ)
• DRAQ_N similar to FRAQ_N
• DRAQ_H similar to FRAQ_H
• DRAQ_NH similar to FRAQ_NH

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System model

• A GPRS data request specifies K channels for
  transmission
• The GSM voice call arrival and GPRS packet
  requests to a cell form Poisson streams with
  rates and , respectively
• The voice call holding time and packet
  transmission time are exponentially distributed
  with mean times and ,
  respectively

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The timimg diagram
the residence time of voice user at a cell j,
which are independent and identically
distributed random variables with a general
function with mean
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voice handoff call arrival rate to a cell
the new call blocking probability for the GSM
dropping/ blocking probability for the GPRS
GSM voice user mobility rate
probability that a GSM voice call is not
completed (either blocked or forced to
terminate)
the GSM voice call traffic load
the GPRS packet call traffic load
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Analytic model for FRA
(1)
where
(2)
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Analytic model for FRA (contd)
(3)
state space
stationary probability
(4)
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Analytic model for FRA (contd)
where
(5)
(6)
(7)
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The iterative algorithm for FRA

• Step 1 Select an initial value for
• Step 2
• Step 3 Compute and using (2) and
  (4)-(7)
• Step 4 Compute using (1)
• Step 5 If then go
  to step 2. Otherwise
• ,go to step 6. Note that is
  a predefined threshold
• say
• Step 6 The values for , and
  converge. Compute
• from (3)

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Analytic model for DRA
Lets consider the case when K3
The state transition for DRA
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Analytic model for DRA (contd)
The balance equations for the Markov process are
expressed
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Analytic model for DRA (contd)
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Analytic model for FRAQ
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Analytic model for FRAQ (contd)
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Analytic model for FRAQ (contd)
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Simulation method

• We consider a 6x6 wrapped mesh cell structure
• The model follows the discrete event simulation
  approach

6X6 wrapped mesh cell structure
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Performance of FRA ( )

• Performance of GPRS data rate increase as K
  increase
• Effects of packet size in Fig. 6(b)
• Effect of voice call arrival in Fig. 6(c)
• Effect of voice user mobility in Fig. 6(d)
• voice user mobility has no apparent effect on
  

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Performance of FRA ( )

• Effect of packet size in Fig. 7(b)
• Effect of voice call arrival in Fig. 7(c)
• packet request have less chance to served
  as K
• increases, and decreases as K
  increases
• Effect of voice user mobility in Fig. 7(d)
• high mobility, handoffs are more likely to
  occur in a voice call,thus for high
  mobility is larger

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Comparison for the FRA and DRA algorithms

• Performance of
• DRA algorithms (with or without queueing)
  always outperform FRA (with or without queueing)
• Performance of
• the DRAQ_NH outperforms other algorithms

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Effect of the variations of the distribution for
input parameters
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The average number of channels assigned to packet
transmission
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The average waiting time for the accepted voice
call request
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Conclusion

• The dynamic allocation effectively increases the
  GPRS packet acceptance rate and queueing
  mechanisms significantly reduce the voice call
  incompletion probability