Wireless packet scheduling in an integrated CDMA system using channel status information

1
Wireless packet scheduling in an integrated CDMA
system using channel status information

• AuthorSeung Sik Choi and Dong Ho Cho
• SourceComputer Communications, Volume 27,
  Number 9, June 2004, Pages 890-897
• Reporter Tsang-Yuan Tsai
• Date2005/1/15

2
Outline

• Introduction
• System Model with channel status
• Implementation issues
• Virtual time implementation
• Credit table implementation
• Weighted Fair Queueing with State control (WFQS)
• Simulation Results
• Conclusions

3
Outline

• Introduction
• System Model with channel status
• Implementation issues
• Virtual time implementation
• Credit table implementation
• Weighted Fair Queueing with State control (WFQS)
• Simulation Results
• Conclusions

4
CDMA system Characteristics

• Interference limited
• Different Bit Error Rate (BER) values for
  multimedia services
• Multiple sessions can be served simultaneously
  using different pseudonoise (PN) codes.

5
Types of CDMA
6
Throughput maximization strategy

• Delay-sensitive voice users are allocated first,
  and then residual resources are allocated to data
  users.
• Nv is the no of voices users and Nd is the no of
  data users. N Nv Nd

7
Outline

• Introduction
• System Model with channel status
• Implementation issues
• Virtual time implementation
• Credit table implementation
• Weighted Fair Queueing with State control (WFQS)
• Simulation Results
• Conclusions

8
Base station scheduler

• Virtual Packet Generator
• makes virtual packet according to the size of
  frame and rate requirement
• Power Resource Allocation Find valid spreading
  codes and determined power index

9
Channel state model using a two-state Markov
chain (1/3)
The steady-state probability Pe that a frame
error occurs can be given by
10
Outline

• Introduction
• System Model with channel status
• Implementation issues
• Virtual time implementation
• Credit table implementation
• Weighted Fair Queueing with State control (WFQS)
• Simulation Results
• Conclusions

11
Virtual time implement (1/3)

• The virtual time v(t) is defined
• Consider the kth virtual packet of a given
  session i with a length of Lki bits. Suppose that
  this virtual packet arrives at time aki, is
  serviced at time ski, and is ended at dki. Then,
  the virtual finishing time can be obtained by

where max(Fik-1, v(aki)) Fik-1 means no
backlog max(Fik-1i, v(aik)) Fik-1
means backlog
12
Virtual time implement (2/3)

• Provided
• two sessions (blue,red)
• service rate 400bps is the same in the blue and
  red sessions
• Packet length 100bytes 800bits

9
2
1
9
1
F1blue 800/400 1 3 F1red 800/400 3 5
13
Virtual time implement (3/3)
9
2
1
9
1
2
F2blue 800/400 3 5 F2red 800/400 6 8
14
Outline

• Introduction
• System Model with channel status
• Implementation issues
• Virtual time implementation
• Credit table implementation
• Weighted Fair Queueing with State control (WFQS)
• Simulation Results
• Conclusions

15
Credit table (1/2)

• Let Ci(tn) be the credit value of the ith user in
  the time tn
• where Sdi(tn,tn-1) is power resource of
  data session i
• during (tn,tn-1 and Fi is service shared
  for ith user

16
Credit table (2/2)

• Let Vi(tn) be the normalized credit value in the
  nth frame
• where nf is the number of frames during the call.
• The lowest Vi(n) value user is allocated first.

17
Example Assumption initial value

• Three users user 1, user2 and user3
• Service share F12R, F2R and F3R
• where R is the data length (bit/frame) to be
  transmitted in a frame with 128 spreading gain.
• Data rate Chip rate (fixed) / Spreading gain

18
Example - User burst traffic
19
Example Credit table initial
20
Example Frame1

• User1
• C1(1) 0 2R/2R 1
• V1(1) 1/1 1

21
Example Frame2

• User3( V3(1) is the lowest )
• C3(2) 0 R/R 1
• V3(2) 1/1 1
• User1
• C1(2) 1 R/2R 3/2
• V1(2) (3/2)/2 3/4

22
Example Frame3

• User2( V2(2) is the lowest )
• C2(3) 0 R/R 1
• V2(3) 1/1 1
• User1(V1(2) lt V3(2)
• C1(3) 3/2 R/2R 2
• V1(3) 2/3

23
Example Frame4

• User3( V3(3) is the lowest )
• C3(4) 1 R/R 2
• V3(4) 2/3
• User1(V1(3) lt V2(3)
• C1(4) 3/2 R/2R 2
• V1(4) 2/3

24
Example Frame5

• User2( V2(4) is the lowest )
• C2(5) 1 R/R 2
• V2(5) 2/3
• User1(V1(4) lt V2(4)
• C1(5) 5/2 R/2R 3
• V1(5) 3/5
• Until frame 5,
• user 1,2 and 3 transmit 6R,
• 2R, and 2R

25
Outline

• Introduction
• System Model with channel status
• Implementation issues
• Virtual time implementation
• Credit table implementation
• Weighted Fair Queueing with State control (WFQS)
• Simulation Results
• Conclusions

26
Weighted Fair Queueing with State control (1/2)
Radio resource enough ?
Based on two- state Markov chain
27
Weighted Fair Queueing with State control (2/2)
Fik small first
Credit table
28
Outline

• Introduction
• System Model with channel status
• Implementation issues
• Virtual time implementation
• Credit table implementation
• Weighted Fair Queueing with State control (WFQS)
• Simulation Results
• Conclusions

29
Simulation assumption

• Voice source packets MMPP (Markov Modulated
  Poisson Process)
• Data source packets Poisson process
• Frame size 20msec
• Transmission rate of data user 8kbps to 64kbps
• Burst error p 0.95 and q varies from 0.5 to
  0.7
• Average length of the bad state
• 44 ms in q 0.5
• 66 ms in q 0.7

30
Delay in bad state channel consideration (1/2)

• Delay of each data user when a bad state channel
  is given to
• data mobile 4 (Nv16)

31
Throughput in bad state channel consideration
(2/2)

• Throughput of each data user when a bad state
  channel is
• given to data mobile 4 (Nv16)

32
Simulation Result (1/2)
Delay of data users vs number of voice users (p
0.98)
33
Simulation Result (2/2)
Throughput of data users vs number of voice users
(p 0.98)
34
Conclusions

• Weighted fair queueing for data service in a
  voice/data integrated CDMA
• Throughput can be increased compared with a
  conventional WFQ scheme
• In reliable network the WFQS will get better
  effective.