A-MAC: Adaptive Medium Access Control for Next Generation Wireless Terminals
R96725018 陳品宏R96725044 曾有德
Mehmet C. Vuran, Member, IEEE, and Ian F. Akyildiz, Fellow, IEEESchool of Electrical and Computer Engineering, Georgia Institute of
TechnologyIEEE/ACM TRANSACTIONS ON NETWORKING, VOL. 15, NO. 3, JUNE 2007
2
Outline
I. Introduction
II. Related Work
III. The Virtual Cube Concept
IV. Network Modeling
V. A-MAC: Adaptive Medium Access Control
VI. Performance Evaluation
VII. Conclusion
3
I. Introduction
4
Next Generation Wireless Networks
Next Generation (NG) wireless networks are envisioned to provide high bandwidth to mobile users via bandwidth aggregation over heterogeneous wireless architectures
The various types of MAC protocols: TDMA, CDMA, WCDMA and CSMA/CA
QoS classes: Conversational, streaming, interactive and background Fig. 1. Next generation wireless networks.
5
Challenges
Heterogeneity in Access Schemes: Different access schemes in different wireless networks
Heterogeneity in Resource Allocation: No unified metric for comparison of the allocated resources
Heterogeneity in QoS Requirements: The MAC layer must efficiently evaluate the available resources in different networks to satisfy the QoS requirements
6
The Structure and The Components of A-MAC
Two-layer Adaptive Medium Access Control (A-MAC)
Access sub-layer: Specialized for accessing the network
Master sub-layer: Perform decision and scheduling requests for the most efficient network
A novel Virtual Cube concept is used to model the networks
Fig. 2. Main Components of A-MAC.
7
Main Object
Incompatibility among medium access and resource allocation techniques are melted into a unified medium access control framework, providing self-contained decision flexibility as well as capability to access various networks.
8
II. Related Works
9
Related Works
An Ad-hoc CEllular NETwork (ACENET) TCDMA protocol Hybrid TD/CDMA systems A multiple access protocol of cellular Internet and
satellite-based networks The proposed methods requires either a modification in
the existing infrastructure and base stations or a completely new architecture
Integration problems: Implementation costs, scalability and backward compatibility
Assumption
NG wireless terminals are capable of receiving signals from multiple network access points and transmitting signals to different access schemes simultaneously.
10
11
III. The Virtual Cube Concept
A. Resource-Space
B. Virtual Cube Structure
12
Resource-Space
Time Dimension: The time required to transfer information
Rate Dimension: The data rate of the network
Power Dimension:
The energy consumed
for transmitting information
through the network
13
Virtual Cube Structure
Three parameters: Cube Capacity (M bits/cube) Cube Power (P Watts/cube) Cube Duration (T sec/cube)
Two types of virtual cubes are used in the A-MAC: Virtual Information Cube
(VIC): The information sent through the network
Virtual Power Cube (VPC): The additional power needed to transmit M bits of information
Fig.3. Virtual cube model.
M
VIC
VPC
14
IV. Network Modeling
A. TDMA Modeling
B. CDMA Modeling
C. CSMA Modeling
D. Multi-Rate Networks
15
TDMA Modeling
A TDMA slot is characterized by slot duration and transmission rate
Each interface is characterized by an average energy per bit The number of virtual cubes that can be filled in three dimensions
of a resource bin:
Fig. 4. (a) TDMA and CDMA modeling.
(1)
16
CDMA Modeling
Direct Sequence-CDMA (DS-CDMA) each bit of duration is coded into a pseudo-noise code of chips of
duration the spreading gain the transmitted energy per bit is the bandwidth , is the data rate and is the transmitted signal
power
TDD CDMA the time is divided into radio frames, slots and sub-frames is determined by the length of the allocated slot
FDD CDMA is determined by the duration of the connection
17
CSMA Modeling
IEEE 802.11 It is impossible to deterministically calculate the
transmission time in CSMA based systems Using the last transmission information to model the
resource bin
Fig. 4. (b) CSMA Modeling.
18
Multi-Rate Networks
Multi-code CDMA, e.g., IS-95-B and cdma2000
The number of virtual cubes in the rate dimension, ,of the CDMA frame model increases with the data rate
The power level, ,for a CDMA signal with a spreading gain , where is the power level of the fundamental spreading gain and is the fundamental spreading gain
Fig. 4. (c) Multi-code CDMA modeling.
19
Multi-Rate Networks (cont.)
Multi-channel communication, e.g., cellular networks and IEEE 802.11 standard
The number of virtual cubes in the rate dimension, , depends on many channel and transceiver dependent parameters such as the channel bandwidth, modulation and channel coding schemes
Fig. 4. (c) Multi-channel modeling.
20
V. A-MAC: Adaptive Medium Access Control
A. Decision
B. Scheduling
C. Adaptive Network Interfaces (ANIs)
21
The Structure and The Components of A-MAC
Fig. 2. Main Components of A-MAC.
SCHEDULING
3G GSMIEEE 802.11
DECISION
ADAPTIVE NETWORK INTERFACES
MASTER SUB-LAYER
ACCESS SUB-LAYER
NETWORK MODELS
22
Decision
A-MAC performs decision in each decision interval For a specific traffic flow , the decision block chooses the inte
rface such that the utility function
Aims to find the interface with maximum throughput capability for the minimum transmission power
(2)
23
Decision (cont.)
Constraints:
is the bandwidth share of the traffic in interface is the maximum power dissipation allowed for the decision inte
rval is the minimum required bandwidth in terms of VICs for the tra
ffic type in order to guarantee its QoS requirements is the set of active interfaces that are chosen by the decision block
(3)
(4)
24
Decision (cont.)
1) Single Type Traffic—Single Interface (STSI)
2) Single Type Traffic—Multiple Interfaces (STMI) If the (3) and (4) are met by one or more interfaces, the one that
maximizes (2) is chosen else…
the interfaces are sorted in a decreasing order of their utility functions
the constraint (4) becomes
A weight is associated with interface
(5)
(6)
25
Decision (cont.)
3) Multiple Type Traffic—Single Interface (MTSI) checks if the decision constraints hold for each traffic type each eligible traffic type is assigned a bandwidth share
such that checks if each flow satisfies (3) and (4)
the scheduler is informed of the bandwidth shares and MAC frame size of the interfaces
or the traffic type with the lowest priority is rejected and the bandwidth shares are updated
4) Multiple Type Traffic—Multiple Interfaces (MTMI)
26
Scheduling
In designing a scheduler, the requirements are considered:QoS GuaranteeChannel Dependent SchedulingDynamic BehaviorImplementation Complexity
Bin Sort Fair Queuing (BSFQ) schedulerFrame-based methoduses virtual time stamps to determine the scheduling orderBuilt-in buffer management component
BSFQ method
it
[ , + )it
NtNt
[ , + )
Fig. 1. Bin Sort Fair Queuing.27
virtual system clock
The output buffer is organized into N bins
Each bin is implicitly labeled with a virtual time interval and
each interval has length Δ
The current bin has the label
The i-th bin has the label
Δ
Packets from the current bin are transmitted, and updatesτ( t ) = t2
BSFQ method (cont.)
The output buffer is organized into N bins Each bin is implicitly labeled with a virtual time interval and
each interval has length Δ The current bin has the label
The ith bin has the labelOnly packets from the current bin are transmittedBin list is cyclic-list
The output link rate may change during the connection time due to wireless channel conditions
In order to prevent fluctuations in the bandwidth share of flows, the scheduler updates each bandwidth share in each decision interval
28
BSFQ method (cont.)
The jth packet of flow f is assigned with the virtual time stamp
is the arrival time of packet is the length of is the reserved data rate of f
29
BSFQ method (cont.)
The index of the bin used to store packet is equal to:
If = 0 then is stored in the current bin.If < N then is stored in the -th bin following the
current bin.If > N then the packet is discarded.
30
31
Adaptive Network Interfaces (ANIs)
1) Network Structure Awareness gathering information about the underlying network structures achieved in different wireless systems, i.e., GSM, UMTS, cdma2000,
and WLAN
2) Network Modeling ANIs model or update the network MAC structure (resource bin) and
inform the master sub-layer
3) Access and Communication An ANI performs access to the network if it is selected for a transmissi
on by the master sub-layer The communication with the AP is performed according to the network
specific procedures
32
VI. Performance Evaluation
A. Traffic Models
B. Network Models
C. Simulation Results
33
Traffic Models
Modeling based on a three-step Morkov model.
Modeling based on a three-step Morkov model.
Exponential distribution and statistically independent
Exponential distribution and statistically independentExponential distributionExponential distribution
The stations generate IP packets with length of 260 bits in every 20 seconds
The stations generate IP packets with length of 260 bits in every 20 secondsExponential distributionExponential distribution
Modeling with a multi-state model.
Modeling with a multi-state model.
Exponential distributionExponential distributionThe bit rate in each state is determined independently using a truncated exponential distribution
The bit rate in each state is determined independently using a truncated exponential distribution
The length of each packet is geometrically distributed and independent of each other
The length of each packet is geometrically distributed and independent of each other
34
Network Models
35
Simulation Results
In a 200 m × 200 m grid, nodes are placed with uniform distribution
Adaptive Node refer to the node equipped with A-MAC Analyze the performance of A-MAC with different number of
nodes and different percentage of traffic distribution in the heterogeneous network structure
Each simulation lasts 230 s and the results are average of 5 trials for each 5 random topologies
Two sets of simulations: Fixed Topology and Dynamic Topology
36
Fixed Topology
All nodes are stationary
The adaptive node is assumed to be in the coverage area of three of the network structures
The traffic type distribution (Voice, ABR, CBR, VBR) is chosen as (65%, 15%, 10%, 10%)
, and denote the percentage of nodes in TDMA, CDMA and WLAN networks
37
Fixed Topology (cont.)
Fig. 5. Average throughput of voice traffic with = (a) (10%, 10%, 80%), (b) (50%, 30%, 20%) .
38
Fixed Topology (cont.)
Fig. 5. Average throughput of CBR traffic with = (c) (10%, 10%, 80%), (d) (50%, 30%, 20%) .
39
Fixed Topology (cont.)
Fig. 6. Average throughput of best-effort traffic with = (a) (10%, 10%, 80%), (b) (50%, 30%, 20%).
40
Dynamic Topology
100 mobile nodes
The adaptive node roams through TDMA to the CDMA network, passing through the coverage area of WLAN APs
The simulation lasts 230 s
Averaging the throughput for intervals of 5
Fig. 7. Sample topology used in the mobility simulations. ●: TDMA BS; : ◆CDMA BS; ■: WLAN AP.
41
Dynamic Topology (cont.)
Fig. 8. (a) Throughput of voice traffic in dynamic topology.
42
Dynamic Topology (cont.)
Fig. 8. (b) Throughput of CBR traffic in dynamic topology.
43
Dynamic Topology (cont.)
Fig. 8. (c) Throughput of VBR traffic in dynamic topology.
44
Dynamic Topology (cont.)
Fig. 8. (d) Throughput of ABR traffic in dynamic topology.
45
VII. Conclusion
46
Conclusion
Adaptive medium access control (A-MAC) for NG wireless terminals Novel virtual cube model Network modeling QoS-based decision QoS-based scheduling
The first effort on designing a MAC protocol that achieves adaptation to multiple network structures with QoS aware procedures
Doesn’t require any modifications to the existing network structures
A cost function can be incorporated into the network modeling framework as a fourth dimension in the virtual cube concept such that the decision is performed accordingly
Thanks for your listening.