Download On the Integration of MPEG-4 streams Pulled Out of High

“Multiplexing Live Video
Streams & Voice with Data over
a High Capacity Packet
Switched Wireless Network”
Spyros Psychis, Polychronis Koutsakis and Michael Paterakis
Electronics & Computer Engrg. Dept.
&
Telecommunication Systems Institute
Technical University of Crete
Chania, Greece
1
Introduction
• Wireless Networks: currently allow users
to experience services that until now only
the wire-line networks provided.
• The main concern remains: how to
extend the broadband frontier to the end
user given the constraints of the wireless
media.
2
Introduction (cont.)
• Well designed MAC protocols are
needed in order to:
– Maximize system’s capacity
– Integrate the different classes of
traffic
– Satisfy the diverse and sometimes
contradictory QoS requirements of
each traffic class
3
Concept
• Within the cell, spatially dispersed MTs share a
radio channel that connects them to a fixed
base station or a wireless hotspot.
• Base station allocates the channel resources,
delivers scheduling and feedback information
and serves as an interface to the MSC, which
provides access to the fixed network
infrastructure and the Internet.
4
Channel Structure
Frame
Information
R1 R2 …. Rn
I
I
I
….
I
I
I
I
1st Minislot 2nd Minislot
• Uplink channel time is divided into time
The request intervals consist of slots,
frames of equal length.
which are subdivided into two mini-slots,
and each mini-slot accommodates exactly
• one,
Eachfixed
frame
consists
of a request
length,
request
packet.interval
and an information interval.
5
Channel Structure (cont.)
• The size of the request interval per channel frame
is variable. The number of the request slots varies
depending on the number of video terminals that
“live” in the system.
• Frame duration is selected such that an active
Voice Terminal generates a new voice packet (of
ATM size) at the beginning of each channel frame
• Only Voice and Data Terms use the request
intervals in order to transmit their request to the
BS.
– Voice Terms are given priority to request
transmissions
– When all Voice request have been transmitted the
Data request transmission follows
6
Voice Traffic
• We assume that the Voice Terminals (VTs)
are equipped with Voice Activity
Detectors (VAD). The output of the VAD is
modeled by a two-state discrete time
Markov chain.
• VTs only require channel access during
talkspurt. (when in talkspurt, they
generate traffic @ 32 Kbps).
• The upper delay limit that a voice packet
can suffer is assumed equal to 40 ms.
• Maximum Pdrop=0,01
7
Data Traffic
• Data traffic model is based on statistics
collected on email usage from a University and
Research Network.
• The pdf for the length of the data msgs was
found to be well approximated by the Cauchy
(0.8,1) distribution.
• The msg inter-arrival time distribution is
exponential.
• An upper bound on the average data msg delay
equal to 2 secs is assumed (tolerable delay for
email msg transmission).
8
Video Terminals
• Video Terminals are streaming actual MPEG4 streams (steady cam) encoded @ 25 fps
(one Video Frame every 40 ms).
• The mean bit rate is 400 Kbps, the peak
rate is 2 Mbps, and the standard deviation
of the bit rate is equal to 434 Kbps.
• Maximum transmission delay for Video
Packets is assumed to be equal to 40 ms.
• Maximum Pdrop = 0,0001
9
BS Scheduling and Terminal Actions
(Video)
• The video terminals envoy their slot requests to
the BS by transmitting them within the header of
the first packet of their current video frame.
• The BS allocates channel resources at the end of
the corresponding request interval.
– Video terminals have the highest priority in acquiring
the slots they demand.
– If a full allocation is possible, the BS then proceeds to
the allocation.
– Otherwise, the BS grants to the video users as many of
the slots they requested as possible (partial allocation).
10
BS scheduling and Terminal Actions
(Voice)
• Voice terminals, which have successfully
transmitted their request packets to the BS,
do not acquire all the available (after the
servicing of video terminals) information
slots in the frame.
• BS allocates a slot to each requesting voice
terminal with a probability p*. When there
are no video terminals in the system, p* is
set equal to 1.
11
BS scheduling and Terminal actions
(Data)
• Data Terminals follow the same allocation
procedure with Voice Terminals after the
Voice contention period is over.
• They can receive only one information slot
per channel frame and can keep it just as
long as they have data packets to transmit.
• We do not use preemption of data
reservations but still voice users are given
priority both in slots and in allocation
policy..
12
Performance Evaluation Simulations
• Channel Rate = 20 Mbps
• Initially the system was simulated under all
possible video loads from 0 to 22 streams with no
active Data Terminals in order to specify the
boundaries where the number of R-slots must
change.
• Each run simulated one hour of actual network
activity (300005 channel frames).
• These simulation runs helped us choose the value
of p* (which turns out that must be equal to 0.1 in
order to get close to optimal results for all the
examined cases of video load).
13
Estimation Runs
Voice - Video capacity
100
1400
90
1200
80
70
60
800
50
600
40
30
400
Throughput %
Voice Terminals
1000
20
200
10
0
0
0
1
2
3
4
•Rslots= 30
•Rslots= 25
5
6
7
8
9 10 11 12 13 14 15 16 17 18 19 20 21 22
Video Terminals
•Rslots= 20
•Rslots= 12
•Rslots= 5
•Throughput
14
Simulation
nd
(2
Set)
• During the second set of experiments we
simulated the system under Voice and Data traffic
only (Rslots=30).
• We tried to accommodate as many Voice Terminals
as possible under the constraint that the data
throughput should match the data load value
(steady state stable operation).
• Crude theoretical estimation of the voice
capacity:
[(Total number of information slots – estimated data
throughput) / probability of talkspurt]
15
Simulation Results
nd
(2
Set)
λ
Voice Terms Capacity
(Theoretical)
Voice Terms
Difference
Capacity
0.25
1212
1212
0
0.5
1165
1135
-30
0.75
1118
1078
-40
1
1071
1030
-41
1.25
1024
985
-39
1.5
978
938
-40
1.75
930
890
-40
2
883
845
-38
16
Simulation
rd
(3
Set)
During the third set of experiments we simulated the
system under certain mixtures of Voice, Video and Data
traffic.
R-Slots
λ
5
12
12
20
20
25
25
25
25
30
0.5
0.5
1.5
0.5
1.5
0.5
1.5
0.5
1.5
1.5
Video Terms Voice Terms
20
15
15
10
10
5
5
1
1
0
0
288
94
496
298
780
586
971
771
938
Average Throughput
(%)
51.24
61.85
61.40
66.44
65.69
76.75
76.30
82.27
81.37
91.72
17
Conclusions and Contributions of
this Work
• The goal was to design efficient MAC scheduling
mechanisms in order to satisfy the diverse
nature of the traffic types that the network
must accommodate and the contradictory QoS
requirements of each traffic type.
• Simulation results show that the proposed
mechanism achieves high aggregate channel
throughput in all cases of traffic load, while
preserving the Quality of Service (QoS)
requirements of each traffic type.
18
Ideas for Future Work
• The evaluation of the proposed mechanisms
when used over a wireless error prone channel.
• Investigating the case in which different media
encoding techniques together with less strict
QoS requirements for the time sensitive traffic
are used.
• Incorporating the proposed mechanisms in a
wider system framework (MAC and BS
scheduling schemes together with a content
placement scheme throughout the wireless and
wireline network).
19