A Survey of MAC Protocols in Ad Hoc Networks
Mingyu Wu, Ph. D student in Computer Science
The University of Texas at Dallas
Advisor: Dr. Andras Farago
This website is for private research purpose only. All the texts, graphs and
linked literatures are NOT for public sharing.
CONTENTS:
Introduction
Literature Reviews
Carrier Sense Medium Access (CSMA)
Medium Access Collision Avoidance (MACA/MACAW)
Floor Acquisition Multiple Access (FAMA/FAMA-NCS)
802.11/802.11e
Differentiated Distributed Coordination Function (DDCF)
Rate-Adaptive MAC (RBAR)
Infrastructure-Based MAC (MPC-MAC)
CDMA-Based MAC (CA-CDMA)
Dual Busy Tone Multiple Access (DBTMA)
Bidirectional Multi-channel MAC ((Bi-MCMAC)
Adaptive Clustering (AC-MAC)
Directional 802.11 (MAC-DA1/MAC-DA2)
Directional DBTMA (DBTMA-DA)
Comparison
Paper List with Abstracts
Paper List only
* Introduction
An mobile ad hoc network (MANET) is a wireless network temporarily and
spontaneously
created
infrastructure
or
by
central
mobile
control.
stations
without
Network
requiring
managements
any
and
communications are typically performed in a distributed manner. Though ad
hoc networks are treated with little difference in IEEE standards for wireless
networks as a whole, some unique features make ad hoc networks distinct
from other types of wireless networks such as wireless LANs.
The first peculiarity is infrastructureless, i.e. there is no pre-existing
hardware like base stations in traditional cellular networks or any
centralized mechanism managing the network. Ad hoc networks are usually
deployed in emergent and temporary situations such as accidents or public
gatherings, where mobile stations (MSs) may join the network at will, move
around, or become disconnected at any time. Global synchronization is hard
to achieve in such situations. And it is unrealistic to expect such a network
to be fully connected, in which case a MS can communicate directly with
every other nodes in the network via wireless channels. As a result, the
second important feature emerges - multihop communication. each node in
the network has to take the responsibility of relaying packets for its peers
and a packet may traverse multiple nodes before it reach the destination.
Two typical problems, namely hidden node and exposed node, come along
with multihop communication. We will discuss these two problems in
details in the next chapter. And, indeed, the major effort of research in this
are are focusing on how to solve these two problem.
Another major concern and interest of investigations in ad networks is
energy saving. Since ad networks solely consist of mobile stations which
also play the role of packets transmitters, if the battery of any single node
run out, it may jeopard the connectivity of entire network besides the fact
that the node itself stops being functional. Hence, the network should be
cleverly designed so that no battery energy would be wasted. Dynamically
adjusting transmission power according to the changing environment seems
to be a possible way to extend the battery life. The incorporation of
directional antennas to enhance signal transmission quality and lesson
inference could be another solution for the energy problem.
Because of the above-mentioned features, the state of ad hoc networks is far
less predictable than that of other networks and it is quite natural for
individual nodes to share the common wireless channels via distributed
mechanisms. Thus, how the medium access control (MAC) layer is designed
to allocate the communication resources efficiently and fairly of ad hoc
networks largely determines the network performance which can be
measured in term of throughput, transmission delay and fairness, etc. In the
following parts of the survey, we briefly introduce a variety of MAC
protocols that have been proposed for ad hoc networks and examine their
pros and cons.
* Literature Reviews
Carrier Sense Medium Access (CSMA)
Due to the lack of centralized control in ad hoc networks, researchers have
been mainly focused on contention based MAC protocols in this area.
Carrier Sense Medium Access (CSMA) is one of the earliest mechanisms
adopted for ad hoc networks. In CSMA, a transmitter will first sense the
wireless channel in the vicinity and refrain itself from transmission if the
channel is already in use. Various methods such as ALOHA [26] and
n-persistent algorithms [24] can used to determine how long the deferred
node should wait before the next attempt. CSMA introduces hidden node
and exposed node problems, which are mentioned earlier. In Fig. 1, we
assume each node can communicate with another node only if there is a link
(solid line) between them. When node A is sending a packet to B, C cannot
sense the ongoing signal as it is out of the communication range of A and
may try to send a packet to B as well. Then a collision will happen at node B.
This is being called hidden node problem, where a node out of the range of
the transmitter is potentially to cause collisions. On the other hand, as in Fig.
2, if node B is sending a packet to A, node C will sense the transmission
signal and refrain itself from sending anything to D even NO collision
would occur in such case. This is a typical exposed node problem, in which
case a node within the range of the transmitter may be unnecessarily
prohibited from accessing the medium and thus decrease the network
throughput.
Fig. 1: Hidden Node Problem with Physical Sensing (C hidden from A) - Collision
Fig. 2: Exposed Node Problem with Physical Sensing (C exposed from B) Inefficiency
Medium Access Collision Avoidance (MACA/MACAW)
To solve the problems with physical sensing, the mechanism of "virtual
sensing", or packet sensing by some researchers, has been proposed. The
virtual sensing mechanisms typically rely on the transmitter and receiver to
perform a handshake prior to the transmission of the data packet. More
specifically, The Medium Access Collision Avoidance (MACA) method
proposed by Karn [16] implements the handshake via a pair of
Request-To-Send (RTS) and Clear-To-Send (CTS) messages. When a node
wants to send data to another, it first sends a short RTS packet to the
destination. The receiver responds with a CTS packet. On receipt of the CTS,
the sender sends its queued data packet(s). All other nodes overhearing the
CTS message will defer themselves from sending out any packet until the
predicted transmission period, which is indicated in the CTS packet, is
passed. Any node that overhears the RTS signal but not CTS is ok to send
out packets in a certain time period as either the RTS/CTS handshake is not
completed or it is out of range of the receiver. MACAW [17] is an
enhancement
of
MACA
that
utilize
a
RTS-CTS-DS(Data
Sending)-Data-ACK message exchange and a new back-off algorithm.
Ideally,
such
RTS/CTS
message
exchanges
should
resolve
the
hidden/exposed node problems. However, as indicated by Haas and Deng,
new types of hidden/exposed node problems emerges when pure virtual
sensing protocols are used. Let us still explain the problems by examples. In
Fig. 3, after node A and exchange RTS/CTS messages, A begins to transmit
a data packet to B. At the same time, node D wants to send a data packet to
C and initiate a RTS/CTS handshake. Though C is allowed to receive to
receive the data packet from D since it doesn't conflict with the transmission
from A to B, C is NOT permitted to access the channel and answer D's RTS
message as it hears C's CTS message. There are two issues to be further
clarified with such problem. If we consider node B as a transmitter (of the
CTS message) and node C as another potential transmitter (of another CTS
message), this can still be called an exposed node problem (C is exposed to
B). But, in our opinion, it would be more appropriate to name it hidden node
problem since node A and D are the transmitters of the data packets and
node B and C are the receivers, in the conventional sense. We further
classify such case as an inefficiency problem which the network bandwidth
is underused, in contrast to the original hidden node problem where packet
collisions occur.
Similarly, another type of exposed node problem also occurs in case of pure
virtual sensing, as the example shown in Fig. 4. Here a data packet is
transiting from node B to A after the exchange of RTS/CTS. Now node C
sends a RTS to D and waits for a corresponding CTS, which may not be
received. The reason is, since the channel in the vicinity of node C is
occupied by B, a collision may happen at C when D sends back the CTS.
Again, the definitions of transmitter and receiver are associated with data
packet, not control packets (i.e., RTS/CTS). Please note that collisions occur
in such exposed node problem and the traditional problem with CSMA
incurs underutilization of the network bandwidth.
Fig. 3: Hidden Node Problem with Virtual Sensing (C hidden from A) - Inefficiency
Fig. 4: Exposed Node Problem with Virtual Sensing (C hidden from A) - Collision
Floor Acquisition Multiple Access (FAMA/FAMA-NCS)
By recognizing the problems existing in either pure physical or virtual
sensing mechanisms, Garica-Luna-Aceves and Fullmer propose the Floor
Acquisition Multiple Access protocol (FAMA/FAMA-NCS) [15], which
basically exploit both sensing techniques. In FAMA-NCS (FAMA
non-Persistent Carrier Sensing), the candidate sender needs to acquire the
privilege of using the "floor" (the channel) before it actually send out the
data packet. And the candidate sender initiate both physical (carrier) and
virtual sensing processes to compete for the common channel with its
neighbors. In case either the node detect ongoing signal in the channel or the
RTS/CTS process is not successful, it will back off from further
transmission. The lengths of RTS and CTS messages are carefully chosen so
that they will be in full effects. Specifically, the length of an RTS is longer
than the sum of maximum propagation delay, the transmit-to-receive
turn-around time and expected processing time. This is to ensure that the
RTS will reach any adjacent node before any node receive the complete
packet. Further, a CTS is longer than an RTS to guarantee a so-called
"CTS-Dominance", which means any neighboring node (of the CTS sender)
transmitting an RTS at the same time will at least hear part of the CTS and
defer itself. Thus, the dominating CTS acts as a busy-tone to protect the
following data packet transmission from collision.
However, as pointed out in [13], CTS-Dominance may lead to unexpected
adverse effect in the presence of RTS-collision. In any ad hoc network MAC
protocol, if nodes compete with each other by sending RTSs via a shared
channel, there is no way to prevent potential collision of multiple RTSs at a
same receiver. In FAMA/FAMA-NCS, if a node detects such RTS collisions,
the node may treat it as CTS dominance and refrain itself from accessing
the channel for the transmission time of the non-existing data packet. Since
the transmission time of data packets is usually much longer than control
packets, the channel resource is considerably wasted. The problem becomes
more severe as network load increases and RTS collisions happen more
frequently. The point is, even in the cases where RTS collisions are
inevitable, their impacts should not be falsely amplified. What is more,
FAMA-NCS is unable to completely address both the hidden node
inefficiency and exposed node collision problems explained earlier.
802.11/802.11e
The IEEE 802.11 MAC protocol [1] is another example of using both
physical sensing and RTS/CTS handshake mechanisms. 802.11 is actually
defined as the standard MAC and physical protocols for wireless LANs, not
specially designed for multihop ad hoc networks. The MAC sublayer
consists of two core functions: distributed coordination function (DCF) and
point coordination function (PCF).
DCF controls the medium accessing through the use of carrier sense
multiple access with collision avoidance (CSMA/CA) and a random backoff
time following a busy medium period. Carrier sense in CSMA/CA are
performed both through physical and virtual mechanisms. In addition to
RTS/CTS exchanges, all data packet receivers immediately sends back
positive acknowledgment (ACK packet) so that retransmission can be
scheduled by the sender if no ACK is received. The RTS and CTS packets
used in DCF contain a Duration/ID field defining the period of time that the
channel is to be reserved for the transmission of the actual data packet and
the ACK packet. All other nodes overhearing either the RTS or CTS or both
set the their virtual sense indicator, named as network allocation vector
(NAV) for the channel reservation period as specified in RTS/CTS.
Basically, a node can access the channel only if no signal is physically
detected and its NAV value becomes zero. RTS/CTS mechanism in 802.11
can also be used in the situations where multiple wireless networks utilizing
the same channel overlap, as the medium reservation mechanism works
across the network boundaries.
While DCF is designed for the asynchronous contention-based medium
access, the 802.11 MAC protocol also defines PCF which is based on DCF
and supports allocation-based medium access in the presence of an access
point (AP). An AP plays the role of a point coordinator and polls each
participating (called CF-pollable) nodes in a round robin fashion to grant
medium access on allocation basis. In 802.11, DCF and PCF are used
alternatively if the later is in effect. Obviously, PCF is basically considered
unsuitable for ad hoc networks because of the lack of centralized control in
such networks as discussed earlier. But the major advantage of PCF is that it
can guarantee maximum packet delay and thus provide quality-of-service in
a sense. For this reason, some researchers indeed try to modify the PCF
method to make it usable in ad hoc networks. We will talk about this later.
IEEE 802.11e [10], the recently proposed draft specification adding QoS
features to the existing 802.11 standard, provides two new MAC functions,
namely enhanced distribution coordination function (EDCF) and hybrid
coordination function (HCF). Basically, with these two new functions,
802.11e supports up to eight priority traffic classes (TC) so that
time-sensitive packets such as voice-over-ip packets will be able to acquire
better chance for transmission than other types of packets. Within a node,
each TC has an independent data packet queue. When a node is ready to
transmit and there are packets waiting in more than one queues, the transmit
opportunity (TXOP) is given to the TC queue with the highest priority. Also,
in HCF, the coordinator is able to issue a QoS polling to a particular node
that has time-sensitive data.
Though the 802.11 MAC layer protocol intends to address the hidden node
problem, it pays almost no effort in resolving the exposed node
problem. And both the hidden node inefficiency and exposed node
collision problems still exist in 802.11. Based on simulation results, Xu and
Saadawi [3] report that some serious instability and unfairness problems
occur when TCP in used on top of 802.11 in ad hoc networks. According to
their analysis, the problems are rooted in the fact that the 802.11 MAC
protocol does not address the hidden/exposed problems as expected and
some inappropriate parameter settings.
In spite of the problems mentioned above, the IEEE 802.11 standard has
rapidly gained its popularity because its simplicity and easy to implement. It
is actually now widely used in almost all test beds and simulations for the
research in ad hoc networks. Due to this fact, we feel that an MAC protocol
would be of more practical values if it is compatible with 802.11.
In [22], Xu, et al, give a mathematical derivation that, based on certain
assumptions, the interference range of a receiver is usually 1.78 times the
transmitter-receiver distance. Their simulation results also show that large
interference range deteriorates the performance of ad hoc networks as a
node that can not successfully receive a CTS packet is still able to cause
interference at the sender of the CTS. Based on such motivation, the authors
suggest a simple fix where a node can only reply to an RTS with a CTS if
the receiving power of the RTS is larger than a certain threshold, i.e., the
expected receiver is close enough to the transmitter to avoid perceivable
interference from other nodes.
Similar efforts to tune the 802.11 protocol for ad hoc networks can also be
found in [14, 23].
Differentiated Distributed Coordination Function (DDCF)
Bononi, et al, [9] propose a different modified version of DCF defined in
802.11 to support QoS. The objective of the proposed differentiated DCF
(DDCF) is to implement node differentiation based on distinct node roles,
which are assigned by the clustering method performed in an upper-layer.
This is different from 802.11e, which is to provide QoS on flow basis. The
authors assume their scheme is intended to for larger scale ad hoc networks
and certain virtual clustering method is available to determine different node
roles such as cluster heads and leaf nodes. In general, a node belonging to a
higher layer in the clustering structure will be given higher priority to access
the channel than a node in a lower layer. This is because a node in a higher
layer will take more responsibilities in administrating the network and
relaying packets between clusters, hence suffer heavier traffic load. The
differentiated channel accesses in DDCF is achieved by applying different
inter-frame space (IFS) and contention windows (CW) values, which are
parameters defined in 802.11 and used to synchronize channel accesses of
nodes.
One issue worth of mention is that the authors summarized four possible
ways to obtain differentiated priority support in the 802.11DCF protocol: "i)
the exploitation of variable IFS (like in PCF and EDCF), ii) variable CW
ranges for the selection of the backoff counter (related to the contention
control), iii) variable PBF (affecting the way the CW may increase after a
collision), and iv) the size of transmitted frames (because a channel capture
for long frames is a way to gain in throughput with respect to peer nodes
contending with short frames)." Our preliminary thought is that such
features may also be exploited in case we want to implement different
priorities for control and data packets to achieve objectives other than QoS,
e.g. implementing efficient busy tone schemes in single channel scenarios.
Rate-Adaptive MAC (RBAR)
Some researchers have investigated the effects of dynamically tuning some
parameters in 802.11 as well as general MAC protocols for ad hoc networks.
Holland, Vaidya and Bahl present a Received-Based AutoRate (RBAR)
protocol that adjusts the transmission rate according to latest channel
condition. In the scheme, the channel quality estimation and rate selection
are performed on the receiver side, because the authors believe the channel
quality experienced by the receiver actually determines whether a packet can
be successfully received. The channel quality estimation and rate selection
are carried out on a per-packet basis through modified RTS/CTS packets,
which contain the desired transmission rate and the size of the data packet
rather than the duration of the reservation. Other nodes hearing the
RTS/CTS packets calculate the reservation duration based on the provided
information. With such modifications, RBAR protocol can be incorporated
into 802.11.
According to the simulation results, RBAR improves the network
throughput over
previous
proposed
rate
adaptive protocols.
The
disadvantage of RBAR is computation overhead. Since the channel quality
sensing/estimation
is performed per packet, the overhead will be
considerable under heavy traffic and eventually leads to longer packet delay.
Infrastructure-Based MAC (MPC-MAC)
As mentioned earlier, the implementation of PCF function requires a central
coordinator and thus not applicable to ad hoc networks. But since PCF can
assist in providing QoS and priority access to time-sensitive traffic, You and
Hassanein propose a variation of the original PCF and apply it to ad hoc
networks. The proposed method, namely Mobile Point Coordinator (MPC),
allows an ad hoc network to create a virtual infrastructure on-the-fly by
selecting certain nodes as MPCs. The selected MPCs will function as the
point coordinators as specified in 802.11 PCF protocol. MPCs and the
cluster information are created and maintained dynamically by periodically
broadcasting "hello" messages. The infrastructure is maintained in such way
that a minimum distance between any two MPCs (i.e. cluster heads) will be
kept and each MPC will tend to coordinate as many nodes as possible.
Based on the MPC method, a new MAC protocol (MPC-MAC) for ad hoc
networks is presented. In MPC-MAC, DCF and PCF work in turn as
described in the 802.11 specifications. Basically, a free node, i.e., which has
not joined a cluster yet, call only transmit its data packets during the DCF
period. And only time-sensitive data packets from those that are coordinated
by MPCs can be transmitted during the PCF period. Hence, time-sensitive
packets have higher priority in transmission and QoS is guaranteed.
Despite the benefits gained by using MPCs, the protocol has following
disadvantages. First, additional messages and computation overhead are
required for maintaining clustering information. Smaller overhead may be
achieved by broadcasting "hello" messages less frequently. But the accuracy
of the cluster information will be impaired. What is more, as in any
cluster-based networks, the MPCs may become the bottleneck of the
network performance and single-node-failure scenario may occur.
Adaptive Clustering (AC-MAC)
The MPC-MAC protocol introduced above exploits the concept of
"clustering" in ad hoc networks. It doesn't specify which clustering
algorithm it uses or how effective the clustering mechanism is. Here let us
take a look at a specific clustering strategy for mobile, multihop, multimedia
(M3) wireless networks presented by Lin and Gerla [8]. According to the
authors, there are three major advantages of their CDMA-based adaptive
clustering strategy. First, channel resources are reused from cluster to cluster
i.e., two adjacent clusters are able to choose two different CDMA codes that
generate neglectable interference. Second, inside each cluster, channel
resources can be shared in an allocation-based manner. For example, as in
the MPC-MAC protocol, the polling-based PCF protocol may be
incorporated in ad hoc networks when clustering is available. Thus, QoS is
achieved is ad hoc networks. Finally, the clusters are independently (i.e., in
distributed manner) and dynamically maintained, and can be reconfigured
with minimum overhead as nodes get connected/disconnected or move.
The distributed clustering algorithm introduced in the paper will generate
non-overlapping, 2-hop-away clusters in an ad hoc network. The maximum
hop distance within a cluster is small so that synchronization inside the
cluster is feasible. The CDMA code assignment and channel access control
are performed as following. Each cluster is assigned a transmitting code
distinct from its neighbors for the intra-cluster communications. This means
there is no inter-cluster interference. And when an interconnecting node, a
node adjacent to any node in another cluster, is idle, it will randomly pick
and listen to one of the codes used by its neighbors. Within each cluster, all
the nodes are synchronized and the channel is shared using TDMA scheme.
Note that there is no central node needed as the cluster size is relatively
small and each node has the complete information of its cluster. The main
advantage of such TDMA scheme is there is no single-node-failure problem
as in the MPC-PCF protocol. But on the other hand, channel resource is
wasted when traffic load is low. And when the number of nodes in a cluster
grows, the minimum transmission delay also increases.
CDMA-Based MAC (CA-CDMA)
In [4], Muqattash and Krunz investigate the impact of the so-called near-far
problem in random access CDMA schemes, where nodes compete for
channel resources without admission control. The near-far problem occurs
when the CDMA codes used to a network are not perfectly orthogonal to
each other (non-zero correlated) due to the limited resources, and all
transmitters use the same transmission power. Under such conditions, the
signal from a transmitter closer to a receiver may cause the receiver unable
to correctly decode signals from a farther transmitter.
The two core ideas of the proposed protocol are splitted bandwidth (or say
multi-channel) and controlled access (CA). By splitted bandwidth, it means
the available bandwidth in a network is divided into two non-overlapping
channels: one used for transmitting control packets (i.e., RTS/CTS) and the
other for data packets. Therefore, the control and data packets won't
interfere with each other. For the controlled access part, a predetermined
interference margin is used as a threshold. In general, a node ready to
transmit first detects the condition of the channel in its vicinity and compute
out the maximum allowable power level that will not disturb any ongoing
transmission. Then the node sends out a RTS including the maximum
allowable power level. Upon receiving the RTS, the potential receiver also
detect the condition of the adjacent channel and calculate the allowed power
on the receiver side and the minimum power level required for the
successful receipt of the packet. If all required conditions satisfied, the
receiver will reply with a positive CTS with desired power level. Otherwise,
it sends back a negative CTS to prevent further retransmission of the RTS.
Thus, admission control is achieved and the upcoming transmission power is
dynamically adjusted according to the channel condition, in order to avoid
interfering with ongoing signals.
Obviously, the proposed scheme is considerably complicated in terms of
both hardware and software. First, it requires parallel CDMA circuits to
simultaneously monitor the data and control packets. And the channel
condition detection and power level estimation are perform on per-packet
basis, which may incur perceivable overhead.
Dual Busy Tone Multiple Access (DBTMA)
In the previous section, we have seen an example of splitting the whole
bandwidth into multiple channels in ad hoc networks. Here we discuss
another multi-channel scheme - Dual Busy Tone Multiple Access (DBTMA)
protocol proposed by Hass and Deng [13]. The major motivation and
argument for the authors to adopt the multi-channel strategy is, as we
present earlier, either using physical or virtual sensing or the combination of
these two sensing methods via single channel cannot completely resolve the
hidden node and exposed node problems.
Hass and Deng borrowed the basic idea of busy tone from the
Received-Initiated Bust-Tone Multiple Access scheme [18], where the data
packet receiver broadcasts a out-of-band busy tone during the process of
transmission. The busy tone serves two roles. First, it takes the same
function as CTS to acknowledge the RTS from the data packet sender.
Second, it prevents nearby nodes from interfering with current transmission.
In addition to the receive busy tone, DBTMA also uses a transmit busy tone,
which a transmitter will send out through the transmission of its RTS packet.
Thus, the RTS will have better opportunity to be successfully received by
the intended receiver. Note that the possibility of the collision of two RTS
packet still exists, though it has been reduced by using the transmit busy
tone. The simulation results presented in the paper show significant
improvement in terms of network throughput over previous proposed
schemes. But the problems of DBTMA is it requires more complicated
hardware than what is required by 802.11 to implement the two out-of-band
busy tones. Also, the authors assume the bandwidth allocated to the two
busy tones are neglectable, which is not necessarily true under heavy traffic
conditions. Finally, it is quite difficult to make this scheme compatible with
802.11 without major modifications, in terms of both hardware and
software.
Bidirectional Multi-channel MAC (Bi-MCMAC)
Kuang and Williamson [12] also point out that RTS/CTS fails to solve the
hidden node problem completely. Their solution, namely Bidirectional
Multi--channel MAC (Bi-MCMAC) protocol, is to divide the bandwidth
into one control channel and several data channels. The scheme is called
bidirectional because the data packet receiver may send its own outgoing
data packet to the sender after the receipt of the first packet. More
specifically, the scheme uses the RTS-CTS-Data-ACK handshake. After
receiving the first data packet, if the receiver has an outbound packet for the
same sender, it will send out the data packet directly and piggyback the
acknowledge information. Otherwise, the receiver sends back a normal
ACK packet. The purpose of doing so is to save the handshake procedure
for the second data packet and hence enhance the throughput.
To utilize the multiple data channels, the formats of RTS/CTS packets have
to be modified to specify which data channel is to be used. The NAV field
also has to be modified so that other nodes will be able to record the
reservation information for each channel. When a node has a data packet
ready, it sends out a modified RTS to the intended receiver with a list of free
channels available on the sender side. Upon the receipt of the RTS, the
receiver checks its own list of available free channels and compare it with
the list coming with the RTS. If there is at least one common channel from
both lists, the receiver pick one such channel and send back a CTS with
necessary information. Note that the free channel information is not
guaranteed to be valid due to the constant change of the environment. To
increase the opportunity of successful selection of the free channel, a
heuristic strategy is used: the receiver always tends to select the channel
used in the last successful transmission, given this channel is available.
Otherwise, the receiver simply picks the lowest-numbered channel.
Splitting one data channel into multiple channels is an interesting topic and
more research than what is presented in this paper can be done to investigate
the impact of such strategy on the network performance.
Directional 802.11 (MAC-DA1/MAC-DA2)
In [2], Huang and Shen summarize various MAC protocols for ad hoc
networks using omnidirectional and directional antennas, and compare the
differences between these two groups. The omnidirectional MAC protocols
listed in the paper include 802.11, MACA/MACAW, FAMA, and DBTMA,
while the directional category includes the corresponding directional
versions of the four protocols [2, 19, 20]. The directional antenna model
assumed in the paper is as following.
"Each node is equipped with a directional antenna consisting of N antenna
elements which are deployed into non-overlapping fixed sectors each
spanning an angle of 36O/N degrees. When being transmitted, a signal will
be propagated in exactly one or all of the sectors, which corresponds to
unicast and broadcast, respectively. Signals will be sensed in all sectors and
the antenna is capable of recognizing the sector with the maximum gain.
When receiving, exactly one sector, which usually is the one chosen by the
sensing process, will collect the signals."
Based on the simulation results, the authors argue that using directional
antennas is able to eliminate the hidden node and exposed node problems
and increase the spatial reuse of channel reuse. But in our opinions, it is still
not clear if any new type of problem would occur in the presence of
directional antennas. There are some interesting topics subject to
investigation. For example, how the way directional antennas being utilized
will obtain optimal network performance. And how directional antennas can
be exploit in multi-channel protocols, etc. Sundaresan and Sivakumar [11]
systematically introduce three types of smart antennas, which are switched
beam, fully adaptive array, and MIMO links, respectively, and present an
unified MAC protocol for ad hoc networks equipped with these antennas.
Their work may provide some fundamental ideas for future research in this
area.
Directional DBTMA (DBTMA-DA)
idden/
This is the directional antenna version [2] of the DBTMA protocol. It is
covered in the previous section.
* Comparison
Additional
Single/ multi 802.11
Flat/ Cluster omnidirectional/
Hardware
xposed nodes channel
compatible
structure
Pros
C
directional antenna
Requirement
mainly) Hidden Single
No
Flat
Omni
No
Simplicity
H
Single
No
Flat
Omni
No
Simplicity
Ex
xposed
Single
Need
modifications
Flat
Omni
No
Solves hidden node problem.
Fa
oth
Single
Yes
Flat
Omni
No
mainly)
xposed
Simplicity; Easy to implement; H
Prevalent in reality. QoS support. Pr
oth
Single
Yes
Cluster
Omni
No
oth
Single
Yes
Flat
Omni
No
oth
one
oth
one
QoS support.
Sa
Rate adaptive; Improve throughput
Co
over 802.11.
Single
Yes
Flat
Omni
No
Implement PCF in
networks; QoS support.
ad
hoc Bo
fa
Efficient and robust clustering
C
Need
Single
Cluster
Omni
Yes
algorithm;
No
cluster
head
un
modifications
needed.
Access
control
based
on
the
Co
Need
Multi
estimation of channel condition;
Flat
Omni
Yes
modifications
O
No
contention
between
ch
data/control packets.
Need
Multi
Solve both hidden and exposed Re
Flat
modifications
Omni
Yes
node problems; Best performance ha
oth
one
one
among omni MAC protocols; No m
contention between data/control w
packets.
ch
Improve throughput over 802.11;
Need
Multi
Re
Flat
Omni
Yes
No
contention
between
modifications
Ex
data/control packets.
Solve both hidden and exposed
Need
Single
Flat
Directional
Yes
node problems; Increase channel Re
modifications
spatial reuse.
Solve both hidden and exposed
Need
Multi
Flat
Directional
Yes
node problems; Increase channel Re
modifications
spatial reuse.
* Paper List with Abstracts
1. IEEE, ANSI/IEEE std 802.11, 1999 Edition (R2003), Part 11: Wireless LAN
Medium Access Control (MAC) and Physical Layer (PHY) Specifications
<Full Text>
2. Zhuochuan Huang and Chien-Chung Shen, "A comparison study of
omnidirectional and directional MAC protocols for ad hoc networks", IEEE Global
Telecommunications Conference, Vol. 1 , pp. 57 - 61, Nov. 2002
<Abstract> Traditional MAC protocols used in ad hoc networks employ
omnidirectional antennas. Directional antennas have emerged as an alternative due to
their capability of spatial reuse, low probability of detection, robustness to jamming,
and other beneficial features. We conducted a comparison study of existing
directional and omnidirectional MAC protocols by contrasting their features and
evaluating their performance under various network load and topology. Specifically
we presented rationale for the better performance of some directional antenna based
MAC protocols by using the metric of effective spatial reuse, which is also evidenced
by the simulation study.
<Full Text>
3. Shugong Xu and Tarek Saadawi, "Does the IEEE 802.11 MAC protocol work well
in multihop wireless ad hoc networks?", IEEE Communications Magazine, Vol.
39, No. 6, pp. 130 - 137, June 2001
<Abstract> The IEEE 802.11 MAC protocol is the standard for wireless LANs; it is
widely used in testbeds and simulations for wireless multihop ad hoc networks.
However, this protocol was not designed for multihop networks. Although it can
support some ad hoc network architecture, it is not intended to support the wireless
mobile ad hoc network, in which multihop connectivity is one of the most prominent
features. In this article we focus on the following question: can the IEEE 802.11 MAC
protocol function well in multihop networks? By presenting several serious problems
encountered in an IEEE 802.11-based multihop network and revealing the in-depth
cause of these problems, we conclude that the current version of this wireless LAN
protocol does not function well in multihop ad hoc networks. We thus doubt whether
the WaveLAN-based system is workable as a mobile ad hoc testbed.
<Full Text>
4. Alaa Muqattash and Marwan Krunz, "CDMA-based MAC protocol for wireless ad
hoc networks", Proceedings of the 4th ACM international symposium on Mobile ad
hoc networking & computing, pp. 153 - 164, June 2003
<Abstract> We propose a CDMA-based power controlled medium access protocol for
mobile ad hoc networks (MANETs). Unlike previously proposed protocols, ours
accounts for the multiple access interference (MAI), thereby addressing the notorious
near-far problem that undermines the throughput performance in MANETs.
Channel-gain information obtained from overheard RTS and CTS packets over an
out-of-band control channel is used to dynamically bound the transmission power of
mobile terminals in the vicinity of a receiver. By properly estimating the required
transmission power for data packets,
the proposed protocol
allows for
interference-limited simultaneous transmissions to take place in the neighborhood of a
receiving terminal. Simulation results indicate that compared to the IEEE 802.11
approach, the proposed protocol achieves a significant increase in network throughput
at no additional cost in energy consumption.
<Full Text>
5. Gavin Holland, Nitin Vaidya, and Paramvir Bahl, "A rate-adaptive MAC protocol
for multi-Hop wireless networks", Proceedings of the 7th annual international
conference on Mobile computing and networking, pp. 236 - 251, July 2001
<Abstract> Wireless local area networks (W-LANs) have become increasingly
popular due to the recent availability of affordable devices that are capable of
communicating at high data rates. These high rates are possible, in part, through new
modulation schemes that are optimized for the channel conditions bringing about a
dramatic increase in bandwidth efficiency. Since the choice of which modulation
scheme to use depends on the current state of the transmission channel, newer
wireless devices often support multiple modulation schemes, and hence multiple
datarates, with mechanisms to switch between them Users are given the option to
either select an operational datarate manually or to let the device automatically choose
the appropriate modulation scheme (data rate) to match the prevailing conditions.
Automatic rate selection protocols have been studied for cellular networks but there
have been relatively few proposals for W-LANs. In this paper we present a rate
adaptive MAC protocol called the Receiver-Based AutoRate (RBAR) protocol. The
novelty of RBAR is that its rate adaptation mechanism is in the receiver instead of in
the sender. This is in contrast to existing schemes in devices like the WaveLAN II
[15]. We show that RBAR is better because it results in a more efficient channel
quality estimation which is then reflected in a higher overall throughput Our protocol
is based on the RTS/CTS mechanism and consequently it can be incorporated into
many medium access control protocols including the widely popular IEEE 802.11
protocol. Simulation results of an implementation of RBAR inside IEEE 802.11 show
that RBAR performs consistently well.
<Full Text>
6. Ruben Merz, Jean-Yves Le Boudec, Jorg Widmer, and Bozidar Radunovic, "A
rate-adaptive MAC protocol for low-power ultra-wide band ad-hoc networks", 3rd
International Conference on AD-HOC Networks and Wireless (Ad-Hoc Now), pp.
306 - 311, July 2004
<Abstract> Recent theoretical results show that it is optimal to allow interfering
sources to transmit simultaneously, as long as they are outside a well-defined
exclusion region around a destination, and to adapt the rate to interference. In contrast,
interference from inside the exclusion region needs to be controlled. Based on these
theoretical findings, we design a fully distributed rate-adaptive MAC protocol for
ultra-wide band (UWB) where sources constantly adapt their channel code (and thus
their rate) to the level of interference experienced at the destination. To mitigate the
interference of sources inside the exclusion region, we propose a specific
demodulation scheme that cancels most of the interfering energy. Through simulation
we show that we achieve a significant increase in network throughput compared to
traditional MAC proposals.
<Full Text>
7. Tiantong You and Hossam Hassanein, "Infrastructure-based MAC in wireless
mobile ad-hoc networks", 27th Annual IEEE Conference on Local Computer
Networks, pp. 821 - 830, November 2002
<Abstract> In this paper, an efficient and on-the fly infrastructure is created using our
proposed mobile point coordinator (MPC) protocol. Based on this protocol, we also
develop an efficient MAC protocol, namely MPC-MAC. Our MAC protocol extends
the IEEE 802.11 standard for use in multihop wireless ad-hoc networks implementing
both the DCF and PCF modes of operation. The goal, and also the challenge, is to
achieve QoS delivery and priority access for real-time traffic in ad hoc wireless
environments while maintaining backward compatibility with the IEEE 802.11
standard. The performance of MPC-MAC is compared to the IEEE 802.11
DCF-based MAC without MPC. Simulation experiments show that in all cases the use
of PCF benefits real-time packets by decreasing the average delay and the discard
ratio. However, this may come at the expense of increasing the average delay for
non-real-time data. On the other hand, the discard ratio for both real-time and
non-real-time packets improves with the use of PCF. Therefore, our MPC-MAC
outperforms the standard DCF IEEE 802.11 MAC protocol in multi-hop ad-hoc
environments.
<Full Text>
8. Chunhung Richard Lin and Mario Gerla, "Adaptive clustering for mobile wireless
networks", IEEE Journal on Selected Areas in Communications, Vol. 15, No. 7, pp.
1265 - 1275, September 1997
<Abstract> This paper describes a self-organizing, multihop, mobile radio network
which relies on a code-division access scheme for multimedia support. In the
proposed network architecture, nodes are organized into nonoverlapping clusters. The
clusters are independently controlled, and are dynamically reconfigured as the nodes
move. This network architecture has three main advantages. First, it provides spatial
reuse of the bandwidth due to node clustering. Second, bandwidth can be shared or
reserved in a controlled fashion in each cluster. Finally, the cluster algorithm is robust
in the face of topological changes caused by node motion, node failure, and node
insertion/removal. Simulation shows that this architecture provides an efficient, stable
infrastructure for the integration of different types of traffic in a dynamic radio
network.
<Full Text>
9. Luciano Bononi, Luca Budriesi, Danilo Blasi, Vincenzo Cacace, Luca Casone,
Salvatore Rotolo, "A differentiated distributed coordination function MAC protocol
for cluster-based wireless ad hoc networks", Proceedings of the 1st ACM
international workshop on performance evaluation of wireless ad hoc, sensor, and
ubiquitous networks, pp. 77 - 86, 2004
<Abstract> Wireless Mobile Ad Hoc Networks (MANETs) have been defined as
infrastructure-less networks, including mobile and fixed nodes relying on peer-to-peer
protocols and management. To support more reliable communications, efficient
network management and high resources' utilization, distributed clustering protocols
have been considered as a solution to introduce some kind of hierarchy in MANETs
by means of dynamic and adaptive virtual infrastructures. In clustering schemes, the
different node-roles, and respective management tasks, could take advantage by
Medium Access Control (MAC) protocols able to differentiate distributed nodes'
accesses. To cope with the system dynamics, the MAC itself is required to exploit
existing clustering schemes, and to be adaptive to load and clustering variations, with
no static access schemes. In this paper we propose and analyze a possible solution for
the mutual support of distributed MAC and clustering schemes, named Differentiated
Distributed Coordination Function (DDCF). The DDCF scheme is based on the IEEE
802.11 DCF access scheme, and inspired to the IEEE 802.11e design. Unlike
IEEE802.11e, whose focus is to support Quality of Service (QoS) on the prioritized
frame-flows basis, the focus of the DDCF is to implement nodes differentiation based
on the node roles, which have been assigned by the upper-layer clustering scheme.
Extensive, still preliminary, performance evaluation shown that the proposed DDCF
access scheme can adaptively exploit the roles of cluster nodes, to support
heterogeneous and differentiated MAC access needs.
<Full Text>
10. Yunli Chen, Qing-An Zeng and Dharma P. Agrawal, "Performance evaluation
for IEEE 802.11e enhanced distributed coordination function", Wireless
Communications and Mobile Computing, Vol. 4, pp. 639–653, 2004
<Abstract> The IEEE 802.11e working group aims to enhance the current 802.11
medium access control (MAC) to support integrated data and voice (or video)
communications. Till now, a draft of the IEEE 802.11e enhanced distributed
coordination function (EDCF) has been proposed. In the literature, there is very
limited analysis about EDCF since it is a new protocol, and most related work are
only confined to simulation or saturation state. In this paper, we evaluate the
performance of EDCF by dividing the traffic into two groups, namely real-time
packets and non-realtime packets, and use an analytical model to quantify the
performance of both IFS priority and contention window (CW) priority in the EDCF.
In our analysis, we assume that the traffic arrival is a Poisson process. We provide a
queue model for EDCF. Since there are multiple stations contending for one channel
in the system, the queue model for EDCF cannot be a regular M/G/1 model. We
redefine the service time and the waiting time so that we can still use M/G/1 model in
the analysis. To validate the accuracy of our analytical results, we have done
extensive simulations and we observed that EDCF does provide service differentiation
between different traffic categories. But due to the inherent contention characteristic
of carrier sense multiple access with collision avoidance (CSMA/CA) MAC protocol,
the delay cannot be guaranteed, even for the highest priority traffic. A lot more work
needs to be done for the MAC protocol to effectively support service differentiation in
the future.
<Full Text>
11. Karthikeyan Sundaresan, Raghupathy Sivakumar, "A unified MAC layer
framework for ad-hoc networks with smart antennas", Proceedings of the 5th ACM
international symposium on Mobile ad hoc networking and computing, pp. 244 - 255,
2004
<Abstract> Smart antennas represent a broad variety of antennas that differ in their
performance and transceiver complexity. The superior capabilities of smart antennas,
however, can be leveraged only through appropriately designed higher layer network
protocols, including at the medium access control (MAC) layer. Although several
related works have considered such tailored protocols, they do so in the context of
specific antenna technologies. In this paper, we explore the possibility for a unified
approach to medium access control in ad-hoc networks with smart antennas. We first
present a unified representation of the PHY layer capabilities of the different types of
smart antennas, and their relevance to MAC layer design. We then define a unified
MAC problem formulation, and derive unified MAC algorithms from the formulation.
Finally, using the algorithms developed, we investigate the relative performance
trade-offs of the different technologies under varying network conditions.
<Full Text>
12. Tianbo Kuang, Carey Williamson, "A bidirectional multi-channel MAC protocol
for improving TCP performance on multihop wireless ad hoc networks",
Proceedings of the 7th ACM international symposium on Modeling, analysis and
simulation of wireless and mobile systems, pp. 301 - 310, 2004
<Abstract> In ad hoc networks, the hidden- and the exposed-terminal problems can
severely reduce the network capacity on the MAC layer. To address these problems,
the ready-to-send and clear-to-send (RTS/CTS) dialogue has been proposed in the
literature. However, MAC schemes using only the RTS/CTS dialogue cannot
completely solve the hidden and the exposed terminal problems, as pure "packet
sensing" MAC schemes are not safe even in fully connected networks. We propose a
new MAC protocol, termed the dual busy tone multiple access (DBTMA) scheme.
The operation of the DBTMA protocol is based on the RTS packet and two
narrow-bandwidth, out-of-band busy tones. With the use of the RTS packet and the
receive busy tone, which is set up by the receiver, our scheme completely solves the
hidden- and the exposed-terminal problems. The busy tone, which is set up by the
transmitter, provides protection for the RTS packets, increasing the probability of
successful RTS reception and, consequently, increasing the throughput. This paper
outlines the operation rules of the DBTMA scheme and analyzes its performance.
Simulation results are also provided to support the analytical results. It is concluded
that the DBTMA protocol is superior to other schemes that rely on the RTS/CTS
dialogue on a single channel or to those that rely on a single busy tone. As a point of
reference, the DBTMA scheme out-performs FAMA-NCS by 20-40% in our
simulations using the network topologies borrowed from the FAMA-NCS paper. In an
ad hoc network with a large coverage area, DBTMA achieves performance gain of
140% over FAMA-NCS and performance gain of 20% over RI-BTMA.
<Full Text>
13. Zygmunt J. Haas, Jing Deng, "Dual busy tone multiple access (DBTMA)-a
multiple access control scheme for ad hoc networks", IEEE Transactions on
Communications, June 2002,Vol. 50, No. 6, pp. 975 - 985
<Abstract> The TCP protocol often suffers from performance problems in
conventional single-channel multihop wireless ad hoc networks. The problems arise
from hidden node and exposed node issues, which can lead to channel contention in
the forward direction between TCP DATA packets that are part of the same TCP flow
control window, as well as contention between TCP DATA and TCP ACK packets
flowing in opposite directions. In this paper, we propose and evaluate a novel
bidirectional multi-channel MAC protocol designed to improve TCP performance
over a multihop wireless network. The protocol uses multiple transmission channels at
the physical layer to reduce TCP DATA-DATA contention, and bidirectional
RTS/CTS channel reservations to reduce TCP DATA-ACK collisions. With four
channels, simulation results for static multihop networks show TCP throughput gains
of 50% to 180%, compared to a conventional IEEE 802.11 MAC protocol. Fairness is
also improved with our protocol, since contention is confined to a short handshake
period on the control channel.
<Full Text>
14. Jing Deng, Ben Liang, Pramod K. Varshney, "Tuning the Carrier Sensing Range
of IEEE 802.11 MAC", Global Telecommunications Conference, December 2004,
Vol. 5,pp. 2987 - 2991
<Abstract> We investigate the effects of the carrier sensing range of the IEEE 802.11
Multiple Access Control (MAC) scheme in this paper. Contrary to a simple and
inaccurate cut-off circular collision model that is commonly used, we employ a more
accurate collision model to realistically simulate MAC schemes in ad hoc networks.
We argue that the carrier sensing range is a tunable parameter that can significantly
affect the MAC performance in multihop ad hoc networks. An optimal carrier sensing
range should balance the trade-off between the amount of spatial frequency reuse and
the possibility of packet collisions. A reward formulation for the optimization of the
carrier sensing range is presented. Extensive simulation results are provided to
substantiate our study.
<Full Text>
15. J. J. Garcia-Luna-Aceves, Chane L. Fullmer, "Floor acquisition multiple access
(FAMA) in single-channel wireless networks", Mobile Networks and Applications,
October 1999, Vol. 4, No. 3, pp. 157 - 174
<Abstract> The FAMA-NCS protocol is introduced for wireless LANs and ad-hoc
networks that are based on a single channel and asynchronous transmissions (i.e., no
time slotting). FAMA-NCS (for floor acquisition multiple access with non-persistent
carrier sensing) guarantees that a single sender is able to send data packets free of
collisions to a given receiver at any given time. FAMA-NCS is based on a three-way
handshake between sender and receiver in which the sender uses non-persistent
carrier sensing to transmit a request-to-send (RTS) and the receiver sends a
clear-to-send (CTS) that lasts much longer than the RTS to serve as a “busy tone” that
forces all hidden nodes to back off long enough to allow a collision-free data packet
to arrive at the receiver. It is shown that carrier sensing is needed to support
collision-free transmissions in the presence of hidden terminals when nodes transmit
RTSs asynchronously. The throughput of FAMA-NCS is analyzed for single-channel
networks with and without hidden terminals; the analysis shows that FAMA-NCS
performs better than ALOHA, CSMA, and all prior proposals based on collision
avoidance dialogues (e.g., MACA, MACAW, and IEEE 802.11 DFWMAC) in the
presence of hidden terminals. Simulation experiments are used to confirm the
analytical results.
<Full Text>
16. Phil Karn, "MACA - A new channel access method for packet radio",
ARRL/CRRL Amateur Radio 9th computer Networking Conference, 1990, pp. 134 140
<Abstract> The existing Carrier Sense Multiple Access (CSMA) method widely used
in amateur packet radio on shared simplex packet radio channels frequently suffers
from the well-known "hidden terminal problem" and the less well known but related
problem of the "exposed terminal." This paper proposes a new scheme, Multiple
Access with Collision Avoidance (MACA), that could greatly relieve these problems.
MACA can also be easily extended to provide automatic transmitter power control.
This could increase the carrying capacity of a channel substantially.
<Full Text>
17. Vaduvur Bharghavan, Alan Demers, Scott Shenker, Lixia Zhang, "MACAW: a
media access protocol for wireless LAN's", Proceedings of the conference on
Communications architectures, protocols and applications, 1994, pp. 210 - 225
<Abstract> In recent years, a wide variety of mobile computing devices has emerged,
including portables, palmtops, and personal digital assistants. Providing adequate
network connectivity for these devices will require a new generation of wireless LAN
technology. In this paper we study media access protocols for a single channel
wireless LAN being developed at Xerox Corporation's Palo Alto Research Center. We
start with the MACA media access protocol first proposed by Karn [9] and later
refined by Biba [3] which uses an RTS-CTS-DATA packet exchange and binary
exponential back-off. Using packet-level simulations, we examine various
performance and design issues in such protocols. Our analysis leads to a new protocol,
MACAW, which uses an RTS-CTS-DS-DATA-ACK message exchange and includes
a significantly different backoff algorithm.
<Full Text>
18. Cheng-shong Wu and Victor O.K. Li, "Receiver-initiated busy-tone multiple
access in packet radio networks", Proceedings of the ACM workshop on Frontiers in
computer communications technology, 1987, pp. 336 - 342
<Abstract> The ALOHA and Carrier Sense Multiple Access (CSMA) protocols have
been proposed for packet radio networks (PRN). However, CSMA/CD which gives
superior performance and has been successful applied in local area networks cannot
be readily applied in PRN since the locally generated signals will overwhelm a remote
transmission, rendering it impossible to tell whether a collision has occurred or not. In
addition, CSMA and CSMA/CD suffer from the “hidden node” problem in a multihop
PRN. In this paper, we develop the Receiver-Initiated Busy-Tone Multiple Access
Protocol to resolve these difficulties. Both fully connected and multihop networks are
studied. The busy tone serves as an acknowledgement and prevents conflicting
transmissions from other nodes, including “hidden nodes”.
<Full Text>
19. Young-Bae KO, Vinaychandra Shankarkumar, and Nitin H. Vaidya, "Medium
access control protocols using directional antennas in ad hoc networks", Mobile
Networks and Applications, IEEE INFOCOM, 2000, Vol. 1, pp. 13 - 21
<Abstract> Using directional antennas can be beneficial for wireless ad hoc networks
consisting of a collection of wireless hosts. To best utilize directional antennas, a
suitable medium access control (MAC) protocol must be designed. Current MAC
protocols, such as the IEEE 802.11 standard, do not benefit when using directional
antennas, because these protocols have been designed for omnidirectional antennas. In
this paper, we attempt to design new MAC protocols suitable for ad hoc networks
based on directional antennas.
<Full Text>
20. A. Nasipuri, S. Ye, J. You, and R. E. Hiromoto, "A MAC Protocol for Mobile Ad
Hoc Networks Using Directional Antennas", Wireless Communications and
Networking Conference, Vol. 3, 2000, pp. 1214 - 1219
<Abstract> We propose a medium access control (MAC) protocol for an ad hoc
network of mobile wireless terminals that are equipped with multiple directional
antennas. Use of directional antennas in ad hoc networks can largely reduce the radio
interference, thereby improving the packet throughput. However, the main problem of
using directional antennas in such networks is due to the dynamic nature of the
network caused by frequent node movements. This gives rise to problems such as
locating and tracking during random channel access. The MAC protocol presented in
this paper proposes a solution to these problems without the help of additional
hardware. Results obtained from detailed computer simulations demonstrate the
performance improvement obtained with the proposed scheme.
<Full Text>
21. Zhuochuan Huang, Chien-Chung Shen, Chavalit Srisathapornphat, and Chaiporn
Jaikaeo, "A busy-tone based directional MAC protocol for ad hoc networks", IEEE
MILCOM, 2002, Vol. 2, pp. 1233 - 1238
<Abstract> In mobile wireless ad hoc networking environments, such as the future
combat system (FCS), the shared wireless communication medium is an inherently
limited resource and is collision prone. In this paper, we propose to adapt the dual
busy tone multiple access (DBTMA) protocol for use with directional antennas, which
further increases effective channel capacity. In contrast to other directional antenna
based MAC protocols, our protocol, termed DBTMA/DA, is capable of reserving
channel capacity in finer grain without relying on extra locationing support. A
simulation study is performed to demonstrate the better network performance of
DBTMA/DA over DBTMA and the IEEE 802.11a MAC protocols.
<Full Text>
22. Kaixin Xu, Mario Ger1a, and Sang Bae, "How effective is the IEEE 802.11
RTS/CTS handshake in ad hoc networks", IEEE Global Telecommunications
Conference, 2002, Vol. 1, pp. 72 - 76
<Abstract> IEEE 802.11 MAC mainly relies on two techniques to combat
interference: physical carrier sensing and RTS/CTS handshake (also known as
"virtual carrier sensing"). Ideally, the RTS/CTS handshake can eliminate most
interference. However, the effectiveness of RTS/CTS handshake is based on the
assumption that hidden nodes are within transmission range of receivers. In this paper,
we prove using analytic models that in ad hoc networks, such an assumption cannot
hold due to the fact that power needed for interrupting a packet reception is much
lower than that of delivering a packet successfully. Thus, the "virtual carrier sensing"
implemented by RTS/CTS handshake cannot prevent all interference. Physical carrier
sensing can complement this in some degree. However, since interference happens at
receivers, while physical carrier sensing is detecting transmitters (the same problem
causing the hidden terminal situation), physical carrier sensing cannot help much,
unless a very large carrier sensing range is adopted, which is limited by the antenna
sensitivity. We investigate how effective is the RTS/CTS handshake in terms of
reducing interference. We show that in some situations, the interference range is much
larger than transmission range, where RTS/CTS cannot function well. Then, a simple
MAC layer scheme is proposed to solve this problem. Simulation results verify that
our scheme can help IEEE 802.11 resolve most interference caused by large
interference range.
<Full Text>
23. Huei-Jiun Ju, Izhak Rubin, and Yen-Cheng Kuan, "An adaptive RTS/CTS control
mechanism for IEEE 802.11 MAC protocol", IEEE Vehicular Technology
Conference, 2003, Vol. 2, pp. 1469 - 1473
<Abstract> In this paper, we study the impact of using or disengaging the RTS/CTS
dialogue in IEEE 802.11 DCF MAC protocol under the fact that carrier sensing,
transmission and interference ranges are distinctively different. The resulting
throughput performance features of a linear topology network configuration are
demonstrated when applying constant bit rate (CBR) UDP as well as TCP type traffic
flows. Based on these results, we propose a new RTS/CTS control mechanism. Under
our scheme, a terminal node decides dynamically and individually whether to use a
RTS/CTS dialogue for the transmission of its current data packet. We show that this
new mechanism yields distinctive performance improvements.
<Full Text>
24. Fouad A. Tobagi, Leonard Kleinrock, "Packet Switching in Radio Channels:
Part I--Carrier Sense Multiple-Access Modes and Their Throughput-Delay
Characteristics", IEEE Transactions on Communications, 1975, Vol. 23, No. 12, pp.
1400 - 1416
<Abstract> Radio communication is considered as a method for providing remote
terminal access to computers. Digital byte streams from each terminal are partitioned
into packets (blocks) and transmitted in a burst mode over a shared radio channel.
When many terminals operate in this fashion, transmissions may conflict with and
destroy each other. A means for controlling this is for the terminal to sense the
presence of other transmissions; this leads to a new method for multiplexing in a
packet radio environment: carrier sense multiple access (CSMA). Two protocols are
described for CSMA and their throughput-delay characteristics are given. These
results show the large advantage CSMA provides as compared to the random ALOHA
access modes.
<Full Text>
25. Fouad A. Tobagi, Leonard Kleinrock, "Packet Switching in Radio Channels:
Part II--The Hidden Terminal Problem in Carrier Sense Multiple-Access and the
Busy-Tone Solution", IEEE Transactions on Communications, 1975, Vol. 23, No. 12,
pp. 1417 - 1433
<Abstract> We consider a population of terminals communicating with a central
station over a packet-switched multiple-access radio channel. The performance of
carrier sense multiple access (CSMA) [1] used as a method for multiplexing these
terminals is highly dependent on the ability of each terminal to sense the carrier of
any other transmission on the channel. Many situations exist in which some terminals
are "hidden" from each other (either because they are out-of-sight or out-of-range). In
this paper we show that the existence of hidden terminals significantly degrades the
performance of CSMA. Furthermore, we introduce and analyze the busy-tone
multiple-access (BTMA) mode as a natural extension of CSMA to eliminate the
hidden-terminal problem. Numerical results giving the bandwidth utilization and
packet delays are shown, illustrating that BTMA with hidden terminals performs
almost as well as CSMA without hidden terminals.
<Full Text>
26. N. Abramson, “The ALOHA System-Another alternative for computer
communications”, 1970 Fall Joint Comput. Conf., AFIPS Press, 1970, vol. 37, pp.
281-285.
Paper List only
1. IEEE, ANSI/IEEE std 802.11, 1999 Edition (R2003), Part 11: Wireless LAN
Medium Access Control (MAC) and Physical Layer (PHY) Specifications
2. Zhuochuan Huang and Chien-Chung Shen, "A comparison study of
omnidirectional and directional MAC protocols for ad hoc networks", IEEE Global
Telecommunications Conference, Vol. 1 , pp. 57 - 61, Nov. 2002
3. Shugong Xu and Tarek Saadawi, "Does the IEEE 802.11 MAC protocol work well
in multihop wireless ad hoc networks?", IEEE Communications Magazine, Vol.
39, No. 6, pp. 130 - 137, June 2001
4. Alaa Muqattash and Marwan Krunz, "CDMA-based MAC protocol for wireless ad
hoc networks", Proceedings of the 4th ACM international symposium on Mobile ad
hoc networking & computing, pp. 153 - 164, June 2003
5. Gavin Holland, Nitin Vaidya, and Paramvir Bahl, "A rate-adaptive MAC protocol
for multi-Hop wireless networks", Proceedings of the 7th annual international
conference on Mobile computing and networking, pp. 236 - 251, July 2001
6. Ruben Merz, Jean-Yves Le Boudec, Jorg Widmer, and Bozidar Radunovic, "A
rate-adaptive MAC protocol for low-power ultra-wide band ad-hoc networks", 3rd
International Conference on AD-HOC Networks and Wireless (Ad-Hoc Now), pp.
306 - 311, July 2004
7. Tiantong You and Hossam Hassanein, "Infrastructure-based MAC in wireless
mobile ad-hoc networks", 27th Annual IEEE Conference on Local Computer
Networks, pp. 821 - 830, November 2002
8. Chunhung Richard Lin and Mario Gerla, "Adaptive clustering for mobile wireless
networks", IEEE Journal on Selected Areas in Communications, Vol. 15, No. 7, pp.
1265 - 1275, September 1997
9. Luciano Bononi, Luca Budriesi, Danilo Blasi, Vincenzo Cacace, Luca Casone,
Salvatore Rotolo, "A differentiated distributed coordination function MAC protocol
for cluster-based wireless ad hoc networks", Proceedings of the 1st ACM
international workshop on performance evaluation of wireless ad hoc, sensor, and
ubiquitous networks, pp. 77 - 86, 2004
10. Yunli Chen, Qing-An Zeng and Dharma P. Agrawal, "Performance evaluation
for IEEE 802.11e enhanced distributed coordination function", Wireless
Communications and Mobile Computing, Vol. 4, pp. 639–653, 2004
11. Karthikeyan Sundaresan, Raghupathy Sivakumar, "A unified MAC layer
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