WCDMA Packet Scheduling survey

1
WCDMA Packet Scheduling survey

• ReporterTsang-Yuan Tsai
• Date2005/05/14

2
Outline

• Introduction
• WCDMA(Wideband Code Division Multiple Access)
  Packet scheduling categories
• Fair Throughput scheduling
• C/I (Carrier over Interference ratio) scheduling
• Fair Time scheduling
• Conclusion
• Comment

3
Types of CDMA
4
WCDMA scheduling category

• Fair throughput scheduling
• To give all users the same throughput independent
  of where they are. So the lower C/I (Carrier
  Interference ratio) user (bad quality) need get
  more resources thaan users with a high C/I in
  order to get the same
• throughput.
• Fair time scheduling
• Allocated the same amount of power to the
  different users and schedules them the same
  amount of of time, ie. all users get the same
  amount of time.
• C/I (Carrier Interference ratio) scheduling
• A good C/I have high priority than packets with a
  lower C/I. The C/I provides maximum system
  capacity at the expense of fairness. All power is
  allocated to UE1 until its buffer is empty. First
  then UE2 is being served.

5
Example of the different scheduling
Fair Throughput
Fair Time
C/I scheduling
6
Outline

• Introduction
• WCDMA Packet scheduling scheme
• Fair Throughput scheduling
• C/I (Carrier over Interference ratio) scheduling
• Conclusion
• Comment

7
Dynamic Bandwidth Allocation with Fair Scheduling
for WCDMA Systems(1/6)

• Architecture

8
Dynamic Bandwidth Allocation with Fair Scheduling
for WCDMA Systems(2/6)
9
Dynamic Bandwidth Allocation with Fair Scheduling
for WCDMA Systems(3/6)

• Scheme
• IfBi (k) 0 , thenSi (k) 0
• IfBi (k) gt 0, thenSi (k) g i T where
• is the minimum rate guaranteed to user I
• If SiBi (k) lt CT then
• Si (k) g i T (CT - SiBi (k) ) F i / SjFj
• where C is the maximal amount of service that
  can be provided by the network

10
Dynamic Bandwidth Allocation with Fair Scheduling
for WCDMA Systems(4/6)

• Example
• F1F2 F3122
• T10ms, C 2Mbps CT20000bits
• Q1(tk) 1500 bits,Q2(tk) 1500 bits,
• Q3(tk) 0 bit
• r1 (k) 500kbps ,r2(k) 1000kbps ,
• r3(k) 0 kbps
• Setp 1B1(k) 1500 500k10/1000 6500 bits gt
  0
• B2(k) 1500 1000k10/1000 11500
  bits gt 0
• B3(k) 0 010/1000 0

11
Dynamic Bandwidth Allocation with Fair Scheduling
for WCDMA Systems(5/6)

• Step 2
• BecauseB1(k) gt0 ,B2(k) gt0 andB3(k) 0
• g 1 1 2Mbps/(122) 0.4Mbps
• g 2 2 2Mbps/(122) 0.8Mbps
• gt S1(k) g 1T (CT - SiBi (k) ) F i /
  SjFj
• 0.4M 10/1000 (20000-12000)1/(12)
• 6666 bits
• S2(k) g 2T (CT - SiBi (k) ) F i /
  SjFj
• 13333 bits

12
Dynamic Bandwidth Allocation with Fair Scheduling
for WCDMA Systems(6/6)

• Step 3
• C1 (k) S1(k) / T 6600 bits/ 10ms 666.6kbps
• C2(k) S2(k) / T 13333 bits/ 10ms 1333.3kbps

13
Outline

• Introduction
• WCDMA Packet scheduling scheme
• Fair Throughput scheduling
• C/I (Carrier over Interference ratio) scheduling
• Conclusion
• Comment

14
Best Channel First

• C/IThe difference between the power of the
  carrier and the power of the interference
• Scheme Quality good first selecting The
  highest C/I value ms to be selected first )

15
Fair Power-Efficient Channel-Dependent
Scheduling for CDMA Packet Network(1/6)

• Architecture

16
Fair Power-Efficient Channel-Dependent
Scheduling for CDMA Packet Network(2/6)

• Scheme
• Assuming no power control is used and the
  transmitted power for each Ms is fixed
• Higher received power can be interpreted as a
  better channel condition
• Normalized received power and the highest one is
  chossed

17
Fair Power-Efficient Channel-Dependent
Scheduling for CDMA Packet Network(3/6)

• Let the received power pi,t for Msi at any time t
  be described by the random variable Xi,t with an
  average µi,t and variance si,t2
• Normalized received power Yi,t
• The scheduler will select the packet to transmit
  to the MS with maximum received power

18
Fair Power-Efficient Channel-Dependent
Scheduling for CDMA Packet Network(4/6)

• The real received power Vi,t by reversing the
  translation and normalization
• The expected gain gi for Msi (real)
• The expected gain gi for the Rayleigh fading
  channel (Theorem)

Where m is the active Ms number
19
Fair Power-Efficient Channel-Dependent
Scheduling for CDMA Packet Network(5/6)

• Scheduling probability Qi for mobile station i
• Coefficient of variation (cov) the smaller gt
  more fair

where is the mean of Qi for i 1 to m

• -Average queueing delay
• expected gain with the theorem expected gain of
• the rayleigh fading channel

20
Fair Power-Efficient Channel-Dependent
Scheduling for CDMA Packet Network(6/6)

• Example

21
Conclusion

• Related fair time scheduling is not found
• The no of the conference papers much more than
  the no of the journal papers

22
Comment(1/3)
Delay Jitter is the important metric measure in
the Real-Time traffic.And the Real-Time traffic
packet length is fixed and small. So if we give a
fixed time slice to service, we can get the fixed
delay in all delay variables.(the same delay
jitter)
23
Comment(2/3)

• WCDMA resources are allocated by Spreading Factor
  (SF) parameter. The SF sturcture
• is called Orthogonal Variable Spreading
  Factor (OVSF) as the following and the values
• are 4, 8, 16, 32,,512
• Rate Fixed Chip Rate / SF , So the ratio
  between the different SF is 1 2 4 8

24
Comment(3/3)

• Provide three user allocated by SF1, SF2 and SF
  4
• then the rate ratio 4 2 1
• Schedued by 1214121 sequence and the fixed time
  slice, So
• SF1 user 4 time slices (fixed delay)
• SF2 user 2 time slices
• SF4 user 1 time slices