Int. J. Communications, Network and System Sciences, 2010, 3, 385-394
doi:10.4236/ijcns.2010.34049 blished Online April 2010 (http://www.SciRP.org/journal/ijcns/)
Pu
A Study on Scalable Video Coding for AMC with Mobile
Media-Based Multicast over WiMAX 802.16e
Tzu-Kai Cheng1, Feng-Ming Yang2, Jean-Lien C. Wu3
1Applied Research Center Taiwan Company, Telcordia Technologies, Inc., Taipei, Taiwan, China
2National Taiwan University of Science and Technology, Department of Electronic Engineering, Taipei, Taiwan, China
3Department of Computer and Communication Engineering, St. John’s University, Taipei, Taiwan, China
Received January 22, 2010; revised February 25, 2010; accepted March 21, 2010
Abstract
Adaptive Modulation and Coding (AMC), which is a technology used when channel condition changes, is
adapted in Mobile Worldwide Interoperability for Microwave Access (WiMAX). Scalable Video Coding
(SVC) is a video coding scheme used for different users with bandwidth level. SVC encodes a video into a
number of layers. Users receive different number of encoded layers based on their channel condition. In this
paper, Intermediate Control Server (ICS) is proposed to deal with the signaling between multimedia server
and BS. Both AMC and SVC are employed to enhance the user perceived video quality in the system.
Keywords: AMC, SVC, Server Signaling, 802.16e, Mobile WiMAX
1. Introduction
More television programs can be transmitted because
signals are compressed by compression technology in
digital television as compared to analog television [1,2].
For example, IPTV (Internet Protocol Television) is a
system where a digital television service is delivered by
Internet protocols over broadband network and contents
could be on-demand video or live streaming. On-demand
contents are already stored in the multimedia server after
being per-coded and compressed. The term “triple play”
means the service provider provides voice, data, and
video. The service containing triple play and mobile is
called “quadruple play”. In [3], a utility-based resource
allocation scheme, called U-LEM, for layer-encoded
multicast streaming service in fixed WiMAX networks is
proposed to discuss the time complexity. This work
proves this problem is NP-hard, and can run in polyno-
mial time.
In [4], the authors discussed the key success factors,
benefits, and associated challenges of introducing IPTV
into fixed WiMAX. A congestion control mechanism is
proposed in [5] which gave consideration to fairness and
system overhead applied in IEEE 802.16d broadband
wireless networks. In [6], the transmission performance
of the scalable video streaming services over Mobile
WiMAX system is investigated and the failure rate is
calculated in two scenarios. The less important layers are
transmitted using the second connection with lower pri-
ority as compared to the one connection scenario. A
mechanism called QoS-based Active Dropping to the
MAC layer is proposed in [7] to deal with the bandwidth
utilization. An equation between network loading and
dropping probability is investigated to show how to ad-
just between these two factors.
This paper is intended to enhance the user perceived
video quality by multicasting the videos encoded by
scalable video coding (SVC) over the Mobile WiMAX
[8]. The rest of the paper is organized as follows. Brief
introductions of works related to SVC over WiMAX are
in Section 2. In Section 3, the system model is described,
and there is a detailed description of the proposed
SVC+AMC quality enhancement scheme and the inter-
mediate control server (ICS) signaling. Simulation re-
sults are shown in Section 4 to stand for the proposed
scheme. Finally, this paper is concluded in Section 5.
2. Background
2.1. AMC (Adaptive Modulation and Coding)
WiMAX is expected to provide higher transmission rate
and wider transmission range and mobile WiMAX has
support for mobility. The value of signal-to-noise ratio
(SNR) varies according to the distance between mobile
station (MS) and BS. Modulation is changed according
to channel condition in AMC. When the channel condi-

T.-K. CHENG ET AL. 386
tion becomes worse, the more robust modulation is used.
Therefore, AMC can lead to improve system coverage
and capacity while maintaining high power and spectrum
efficiency. Table 1 shows the modulation and the re-
ceiver SNR [9].
2.2. SVC (Scalable Video Coding)
A video sequence is composed of a stream of individual
frames. The joint video team (JVT) develops the exten-
sion of H.264/AVC (Advanced Video Coding) SVC
which encodes a picture into one base layer and several
enhancement layers in general [10-12]. SVC has three
dimensions in spatial scalable, temporal scalable, and
quality scalable. Spatial scalable means the bit-stream
can provide different spatial resolutions. Temporal scal-
able means various frame rates are available. Quality
scalable, also called SNR scalable which means the vis-
ual quality is scalable. To achieve the scalability, the
base layer provides basic video quality with low bit rate
for user. Enhancement layer is used to refine the base
layer video quality. SVC can provide different video
quality for each level user by encoding an image into
several layers. The number of layers is not fixed, it is
decided in different applications when encoding. The
more the layer received, the better the perceived quality.
2.3. MAC CS Classification
The Medium Control Access (MAC) layer is to provide
an interface between the upper transport layers and the
PHY layer. The MAC layer receives packets, MAC Ser-
vice Data Units (MSDUs), from upper layers, and or-
ganizes them into MPDUs for transmission over the air.
The MAC layer of WiMAX, as shown in Figure 1, is
divided into three distinct sub-layers: Convergence
Sublayer (CS), Common Part Sublayer (CPS), and Secu-
rity Sublayer (SS). The MAC CS, which is the interface
between the MAC layer and layer 3 of the network, sup-
ports MSDU header suppression to reduce the higher
layer overheads on each packet and provides any trans-
formation or mapping of external network data through
CS Service Access Point (CS SAP) into MAC layer. The
MAC CPS performs all the packets operations including
fragmentation and concatenation of SDUs into MAC
PDUs, transmission of MAC PDUs, QoS control, and
ARQ. The MAC SS is responsible for encryption, au-
thorization, and keys exchange between BS and MS.
Besides the header suppression, MAC CS is also respon-
sible for classification. Classification is the process
which a MAC SDU is mapped onto a particular connec-
tion for transmission between two peers. The WiMAX
MAC layer is connection oriented. Before any data trans-
mission happens, BS and MS first establish a unidirec-
tional logical link, called a connection. Each connection
Table 1. The modulation and the receiver SNR.
ModulationCoding Rate Receiver SNR (dB)
BPSK 1/2 3.0
1/2 6.0
QPSK 3/4 8.5
1/2 11.5
16QAM 3/4 15.0
2/3 19.0
64QAM 3/4 21.0
Figure 1. The WiMAX MAC layer.

T.-K. CHENG ET AL. 387
is identified by a Connection InDentifier (CID), which is
16-bit long and serves as temporary and dynamic layer 2
addresses for data transmission and control plane traffic
over the particular link. MAC CS determines the appro-
priate CID based on not only the destination address but
also various other factors, e.g. source address and Ser-
vice Flow InDentifier (SFID). A service flow is a unidi-
rectional flow of packets with a particular set of QoS
parameters and is identified by a SFID. The BS is re-
sponsible for issuing the SFID and mapping it to unique
CIDs. The classification and the CID mapping from BS
to MS is revealed in Figure 2. CS specification is de-
fined in classification. The data from upper layer is clas-
sified and mapped to different to different SFID and CID.
CS specification is shown in Table 2.
2.4. Network Reference Model (NRM)
The WiMAX Forum defines itself as an industry-led
non-profit organization to promoting and certifying in-
teroperable WiMAX products and also determined a
network architecture which showed how a WiMAX net-
work connects with other networks [13,14]. The NRM
is a logical representation of the network architecture.
The NRM identifies key functional entities and reference
points between functional entities over which a network
interoperability framework is defined. The objective of
the NRM is to allow multiple implementation options for
a given functional entity, and achieve interoperability
among different functional entities. NRM structure is
represented in Figure 3.
Figure 2. Classification and the CID mapping from the BS to the MS.
Table 2. IEEE 802.16e CS specification.
Type Length Value Scope
[145/146].28 1
0: Reserved
1: Packet, IPv4
2: Packet, IPv6
3: Packet, IEEE 802.3/Ethernet
4: Packet, IEEE 802.1Q VLAN
5: Packet, IPv4 over IEEE 802.3/Ethernet
6: Packet, IPv6 over IEEE 802.3/Ethernet
7: Packet, IPv4 over IEEE 802.1Q VLAN
8: Packet, IPv6 over IEEE 802.1Q VLAN
9: ATM
10: Packet, IEEE 802.3/Etherneta with ROHC header compression
11: Packet, IEEE 802.3/Ethernetb with ECRTP header compression
12: Packet, IP2 with ROHC header compression
13: Packet, IP2 with ECRTP header compression
14-255: Reserved
DSx-
REQ
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T.-K. CHENG ET AL. 388
3. SVC+AMC Quality Enhancement and
ICS Signaling
3.1. System Model
When an MS requests a video, it sends the messages to
the BS, and the BS then forwards the request to the mul-
timedia server. When adapting SVC, which encodes a
frame into several layers, the multimedia server which
stores the videos performs the encoding procedure and
transmits the layers to the BS. For all MSs who are
watching the same video, the BS grouped them based on
their feedback channel condition. The group with better
channel condition gets more layers. On the contrary, the
group with worse channel condition gets fewer layers.
However, the BS can not distinguish the layer ID re-
ceived from the multimedia server. In order to solve this
problem, an Intermediate Control Server (ICS) is newly
added in the system, see Figure 4. A WiMAX network is
served by an ICS. After executing the videos in the mul-
timedia server, the ICS forwards the SVC-encoded layers
to BS.
Figure 3. Network reference model.
Figure 4. The proposed system model with a newly added ICS.

T.-K. CHENG ET AL. 389
In our proposed scheme, SVC is implemented to en-
code a frame into three layers. Layer 0 is meant to be the
base layer, which contains the most important informa-
tion. Layer 1 and layer 2 belong to the enhancement lay-
er, which carries less information as compared to layer 0.
In order to assure the video quality perceived by user
within worse channel condition, layer 0 is encoded to
carry 50% information of the original frame. After re-
ceiving and decoding layer 1 with layer 0, the containing
information is refined to 75%. Users with best channel
condition get all three layers, the frame which is decoded
by combining layer 0, layer 1, and layer 2 is the same as
the original transmitted frame. The retrieval frames are
shown in Figure 5.
3.2. The ICS Signaling
The multimedia server encodes the video into three lay-
ers in the application layer. All layers are packetized and
added different protocol headers from the upper layer to
lower layer, the BS could not distinguish the layer ID.
An ICS is used to solve this problem. An ICS is indi-
vidually set between multimedia server and the BS for
flexibility and extensibility of many applications pro-
vided by different operators in the future. The major task
of ICS is to re-packetize the packets received from mul-
timedia server so that the BS recognizes the layer IDs.
The proposed system model with network layers is
shown in Figure 6.
When the ICS receives the SVC-encoded layer packet,
it decodes the packet in the application layer and gets the
layer ID information. While transmitting to the BS, the
ICS re-packages the SVC-encoded frame by adding the
layer ID information in the reserved filed of each net-
work protocol header. The Network Abstraction Layer
(NAL) unit [15], shown in Figure 7, defines the interface
between the encoded video data itself and the possible
transport layers or storage formats. Each NAL unit re-
gardless of its type is encapsulated in the RTP/UDP/IP
packet. The encapsulation of NAL unit is shown in Ta-
ble 3. Three bits in NAL unit are used to indicate the
layer ID.
When the packet transmits by RTP (Real-time Trans-
port Protocol), there are seven bits in the payload type
filed [16]. The RTP header format is presented in Figure
8. The reserved values in payload type, which is dis-
played in Table 4, are 72 to 76 [17]. We use three values,
72, 73, and 74, to indicate the layer ID. In UDP (User
Datagram Protocol) header format which is shown in
Figure 9, there are 8-bit protocol numbers [18]. Part of
the assigned protocol numbers is presented in Table 5,
the values 72-76 and 80-254 are unassigned [19], and
three values, 72, 73, and 74, are used to denote the layer
ID. Continuing transmitting to lower layer, the IPv4 (Int-
ernet Protocol version 4) header is displayed in Figure
10 [20]. 2-bit reserved field could be used to show the
layer ID. ‘00’ denotes layer 0, ‘01’ denotes layer1, and
‘10’ denotes layer2 separately. In this way, MAC layer
can clearly distinguish what the received layer ID is.
Figure 5. The retrieval frame of SVC.
Figure 6. The proposed system model with network layers.
Table 3. The encapsulation of NAL unit in RTP/UDP/IP
header.
IP headerUDP
header
RTP
header
NAL unit
header NAL unit payload
H.264 Standard Header byte H.264 Standard Header Extension byte
0 Nal_ref
_idc Nal_unit_type Lyaer ID Temporal
Layer ID
Quality
Level
1 bit 2 bit 5 bit 3 bit 3 bit 2 bit
Figure 7. NAL unit header format.
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T.-K. CHENG ET AL. 390
Figure 8. RTP header format.
Figure 9. UDP header format.
Figure 10. IPv4 header format.
Table 4. Partial RTP payload type.
PT Encoding Name Media Type Clock Rate (Hz)
34 H.263 V 90,000
35-71 Unassigned ?
72-76 Reserved N/A N/A
77-95 Unassigned ?
96-127 Dynamic ?
Table 5. Partial UDP protocol number.
Decimal Octal Protocol Numbers
69 105 SIMP monitoring
70 106 SIMP polling
71 107 SIMP packet core/U
72-76 110-114 Unassigned
77 115 Backroom SIMP polling
78 116 Backroom SIMP monitoring
79 117 SIMP message generators
80-254 120-376 Unassigned
255 377 Reserved
3.3. The SVC+AMC Quality Enhancement
Scheme
In the SVC+AMC quality enhancement scheme, the BS
multicasts different layers using different modulations
based on different connections. The mapping of the layer
to Connection IDentifiers (CIDs) is decided by the clas-
sification rule in the MAC CS specification defined in
the IEEE 802.16e standard. Three reserved value 14-255
are used to indicate the layer IDs which are “Packet,
IPv4 over 802.3/Ethernet ECRTP compression SVC-enc-
oded layer 0”, “Packet, IPv4 over 802.3/Ethernet ECRTP
compression SVC-encoded layer 1”, and “Packet, IPv4
over 802.3/Ethernet ECRTP compression SVC- encoded
layer 2”. Based on the CS classification rule, the layers
are easily mapped to different CIDs. In the 802.16e
OFDMA DL-MAP_IE format, there are 8-bit CIDs as-
signed for this Information Element (IE). Three values in
the unassigned CIDs are chosen to indicate these three
connections.
The SVC+AMC quality enhancement scheme groups
MSs who are receiving the same channel into three
groups according to their fast-feedback channel condi-
tion to the BS. The fast-feedback CQICH information is
allocated in the uplink subframe in OFDMA frame.
These MSs who subscribe the same video are all in
group 0 to receive layer 0. If there are some with better
channel condition, they are grouped into group 1 to re-

T.-K. CHENG ET AL. 391
ceive layer 1, so they are in group 0 and group 1 at the
same time. For those MSs with the best channel condi-
tion, they are grouped into group 2 to receive layer 2,
therefore, they are in group 0, 1, and 2. While transmit-
ting, the BS multicasts layer 0 to group 0 using QPSK
through CID 0, multicasts layer 1 to group 1 using
16QAM through CID 1, and multicasts layer 2 to group 2
using 64QAM through CID 2. For this reason, users with
better channel condition could enjoy better perceived
video quality.
4. Simulation
4.1. Simulation Parameters
The fundamental simulation parameters [21-23] are sho-
wn in Table 6. Network congestion is considered in the
system. Assume packet loss rates in the channel are
0.30%, 0.24%, and 0.21% while using QPSK, 16QAM,
and 64QAM respectively.
PSNR (Peak Signal-to-Noise Ratio) is a conventional
assessment method used to assess the quality of the re-
constructed images. PSNR is used to compare the simi-
larity between the original frame and the retrieval frame.
Each pixel in the retrieval frame is compared with each
related pixel in the original frame. The equation of PSNR
is shown in following. In general, when the value of
PSNR reaches 30dB, it means the difference between
original frame and retrieval frame is hardly recognized
by human eyes.
2
10
( 255)
PSNR10 logdB
MSE
 (1)
  
2
11
1
MSE, ,
()
wh
ij
ij ij
wh 




(2)
4.2. Simulation Results
Simulation results are used to show the SVC+AMC
quality enhancement scheme improves the user per-
ceived video quality effectively. There are three methods
considered in two scenarios. The first method, referred as
Normal scheme, transmits the original video to MSs us-
ing 16QAM without applying SVC and AMC. The sec-
ond method, referred as the AMC scheme, transmits the
original video which is not encoded by SVC to MSs ac-
cording to their channel condition. MSs in worse channel
condition receive the video using QPSK. The BS multi-
casts the video to MSs in normal channel condition using
16QAM and multicasts to MSs with better channel con-
dition using 64QAM. The last one is the SVC+AMC
quality enhancement scheme proposed in this paper. In
SVC+AMC, the BS transmits the SVC-encoded layers to
all MSs using QPSK, to MSs with normal channel condi-
tion using 16QAM, and to MSs in better channel condi-
tion using 64QAM.
We setup two different scenarios and use two videos
to simulate. Scenario1 has 20 MSs which are investi-
gated to the PSNR rate on Mobile WiMAX system.
There is only one connection between the multimedia
server and the BS, all layer-encoded videos are transmit-
ted via this connection. The ICS forwards the SVC-en-
coded layers to the BS. Scenario2 is basically the same
as Scenario1 except the channel conditions of MSs.
In Scenario1 of the first video, 20% of MSs are in
worse channel condition, 40% of MSs are in normal
channel condition, and 40% of MSs are in better channel
condition. Therefore, there are 20 MSs in group 0, 16
MSs in group 1, and 8 MSs in group 2. The above-men-
tioned three methods are employed to simulate the sce-
nario. Figure 11 shows the simulation results. The aver-
age values of PSNR in normal, AMC, and SVC+AMC
scheme are 26.22, 27.58, and 32.18, separately. The
AMC scheme is compared to the normal scheme first.
The average value of PSNR in the AMC scheme is just a
little higher than the normal scheme. While in the normal
scheme, all MSs receive the non-encoded video using
16QAM. In normal scheme, the average PSNR in the
system becomes lower because 20% of MSs receive the
video in an unsuitable modulation and coding scheme
and 40% of MSs with better channel condition should
deserve better video quality. In the AMC scheme, all
MSs receive the full video in a suitable packet loss rate
according to their channel condition. Packet loss rate
becomes smaller while transmitting to MSs with better
channel condition using 64QAM. Packet loss occurs
more often in MSs with worse channel condition because
of the more robust modulation and coding scheme. For
that reason, PSNR is only a little better in the AMC
scheme than in normal scheme. The SVC+AMC scheme,
which receives the SVC-encoded video based on their
channel condition, gets the highest average PSNR. MSs
in worse channel condition receive layer 0 using QPSK
resulting in less packet loss, but the perceived quality is
still embraceable. Two layers are transmitted to MSs
Table 6. Fundamental simulation parameters.
Parameter Value
Channel Bandwidth 10 MHz
Size of FFT 1024
Number of Sub-channels 30
OFDMA Symbol Time 102.9 μs
Frame Duration 5 ms
Modulation Scheme QPSK, 16QAM, 64QAM
Mobility Model Random Waypoint
Number of MSs 20
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T.-K. CHENG ET AL. 392
who are in normal channel condition using 16QAM also
cause less packet loss. The result of better channel condi-
tion MSs in SVC+AMC is the same to the AMC scheme,
because the retrieval frame is the same as the non-en-
coded one.
In Scenario2 of the first video, 80% of MSs are in
worse channel condition, 10% of MSs are in normal
channel condition, and 10% of MSs are in better channel
condition. Therefore, there are 20 MSs in group 0, 4 MSs
in group 1, and 2 MSs in group 2. The average values of
PSNR in three schemes are 16.15, 18.60, and 28.37. The
simulation results of Scenario2 employed with these three
methods is shown in Figure 12. The reason why the
PSNR in the AMC scheme is higher than that in the
normal scheme, and the SVC+AMC scheme gets the best
quality is the same as Scenario1.
However, the variation between the two scenarios is
obvious. In Scenario1, PSNR ranges from 26.22 to 32.18,
but PSNR ranges from 16.15 to 28.37 in Scenario2. Each
MS in better channel condition whether the percentage is
10% or 40% receives almost the same level of the video
quality. But PSNR is influenced more because 80% of
MSs with worse channel condition. Once the packet loss
rate gets higher, the value of PSNR becomes lower. The-
refore, the proposed SVC + AMC scheme enhances the
user perceived video quality better in the situation that
the percentage of worse channel condition is larger in the
system.
0.00
5.00
10.00
15.00
20.00
25.00
30.00
35.00
40.00
45.00
1163146617691106 121 136151166181 196211 226 241256
Fram e
PSNR (dB)
Normal
AMC
AMC+SVC
Figure 11. 20% worse channel condition MSs, 40% normal channel condition MSs, and 40% better channel condition MSs in
normal, AMC, and SVC + AMC methods in the first video.
0.00
5.00
10.00
15.00
20.00
25.00
30.00
35.00
1163146617691106121136 151 166181 196211 226 241256
Frame
PSNR (dB)
Normal
AMC
AMC+SVC
Figure 12. 80% worse channel condition MSs, 10% normal channel condition MSs, and 10% better channel condition MSs in
normal, AMC, and SVC + AMC methods in the first video.

T.-K. CHENG ET AL. 393
Three methods are also considered with two scenarios
in the second video. The simulation results are shown
separately in Figure 13 and Figure 14. In Scenario1 of
the second video, 20% worse channel condition MSs,
40% normal channel condition MSs, and 40% better
channel condition MSs in normal, AMC, and SVC+
AMC methods. Therefore the average values of PSNR in
three schemes are 26.90, 28.30, and 33.76. In Scenario2
of the second video, 80% worse channel condition MSs,
10% normal channel condition MSs, and 10% better
channel condition MSs in normal, AMC, and SVC +
AMC methods. Therefore the average values of PSNR
ranges are 15.91, 18.42, and 29.19. The reason why the
SVC + AMC scheme performs better than the other two
schemes is the same when simulating in the first video in
despite Scenario1 or Scenario2, and the reason why
Scenario1 performs better than Scenario2 is also the
same for the first video.
In summary, no matter how the percentage of the MSs
in worse, normal, and better channel condition changes,
the proposed SVC + AMC scheme can further enhance
the user perceived video quality. When a full video
adapts AMC without SVC, the video quality is almost
the same as the normal scheme. According to the simula-
tion results, SVC + AMC improves the user perceived
video quality well, it improves more significantly when
there are more users with worse channel condition.
0.00
5.00
10.00
15.00
20.00
25.00
30.00
35.00
40.00
45.00
50.00
1163146617691106 121 136 151 166181 196 211 226 241256
Frame
PSNR (dB)
Normal
AMC
AMC+SVC
Figure 13. 20% worse channel condition MSs, 40% normal channel condition MSs, and 40% better channel condition MSs in
normal, AMC, and SVC + AMC methods in the second video.
0.00
5.00
10.00
15.00
20.00
25.00
30.00
35.00
40.00
1163146617691106 121136151166181 196211 226 241 256
Frame
PSNR (dB)
Norma l
AMC
AMC+SVC
Figure 14. 80% worse channel condition MSs, 10% normal channel condition MSs, and 10% better channel condition MSs in
normal, AMC, and SVC + AMC methods in the second video.
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T.-K. CHENG ET AL. 394
5. Conclusions
We proposed an effective video quality enhancement
approach applied on mobile media-based multicast over
WiMAX. A signaling mechanism is designed between
the multimedia server and the BS. The channel condition
varies when MSs move. The BS multicasts different
number of layers to MSs within different channel condi-
tion using different modulation and coding scheme. MSs
with worse channel condition receive fewer layers by
more robust modulation and coding scheme. The signal
mechanism between the multimedia server and the BS is
performed by an ICS between the multimedia server and
the BS. The main task of ICS is to decode the SVC-en-
coded layers from multimedia server and re-package the
packet with layer ID information in different protocol
headers. The mapping of the layer and CID is discussed
and performed in the MAC CS specification.
Simulation results show that the proposed SVC to-
gether with AMC can indeed effectively improve the
user perceived video quality, even when there are many
users with bad channel condition. The ICS signaling re-
solves the problem that the BS can not distinguish the
layer ID received from the multimedia server.
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[11] “Joint Draft 5: Scalable Video Coding,” ITU-T and ISO/
IEC JTC1, JVT-R201, January 2006.
[12] “Joint Scalable Video Model JSVM-5,” ITU-T and ISO/
IEC JTC1, JVT-R202, January 2006.
[13] “Network Working Group Stage 2 Specification, Release
1.1,” Published by WiMAX Forum, September 2007.
[14] “Network Working Group Stage 3 Specification, Release
1.1,” Published by WiMAX Forum, September 2007.
[15] “RFC 3984 on RTP Payload Format for H.264 Video,”
February 2005.
[16] “RFC 3550 on RTP: A Transport Protocol for Real-Time
Applications,” July 2003.
[17] “RFC 3551 on RTP Profile for Audio and Video Confer-
ences with Minimal Control,” July 2003.
[18] “RFC 768 on User Datagram Protocol,” August 1980.
[19] “RFC 762 on Assigned Numbers,” January 1980.
[20] “RFC on Internet Protocol,” September 1981.
[21] “Multi-Hop Relay System Evaluation Methodology (Cha-
nnel Model and Performance Metric),” IEEE 802.16j-06/
013r3, February 2007.
[22] “Mobile WiMAX－Part 1: A Technical Overview and
Per- formance Evaluation,” Published by WiMAX Forum,
August 2006.
[23] L. H. Wan, W. C. Ma and Z. H. Guo, “A Crosslayer
Packet Scheduling and Subchannel Allocation Scheme in
802.16e OFDMA System,” In Proceedings of IEEE
WCNC, March 2007, pp. 1865-1870.