03-01-2013, 04:55 PM
A Dual-Channel MAC Protocol for Mobile Ad Hoc
Networks
A Dual-Channel MAC Protocol.pdf (Size: 514.25 KB / Downloads: 26)
Abstract
—Recent studies have shown that the widely used
IEEE 802.11 MAC is considerably inefficient in multihop networks.
The inefficiency is due to the hidden terminal problem,
the exposed terminal problem, the receiver blocking problem,
and the intra-flow contention problem. These four problems
can lead to “explosion” of control packets and hence poor
throughput performance. To address these problems, we propose
a novel MAC protocol based upon the IEEE 802.11 MAC.
The unique features of the proposed MAC protocol are 1) a
system architecture with an out-of-band busy tone and two
communication channels, one for control frames and the other
for data frames, and 2) a message exchange procedure that
provides a comprehensive solution to all the aforementioned
four problems. Our studies show that the proposed scheme can
simultaneously overcome the four problems, greatly improve
spatial reuse, and eliminate the collisions of DATA packets.In
addition, the simulation results demonstrate that the new scheme
provides a more stable link layer with less control overheads
and much less routing failures and significantly improves the
throughput, as compared to the IEEE 802.11 MAC.
I. INTRODUCTION
The IEEE 802.11 MAC [1], a contention based medium
access protocol, has been successfully deployed in wireless
LANs and has also been implemented in many wireless
testbeds and simulation packages for wireless multihop networks.
However, the inefficiency of the 802.11 MAC in
multihop ad hoc networks has been widely recognized as a
serious problem. MAC layer contentions greatly affect the
performance of high layer protocols such as TCP and route
maintenance [2]–[4].
The source of the above problems comes mainly from the
MAC layer. The hidden terminals may introduce collisions
and the exposed terminals may lead to low efficiency [6]. In
addition to these two notorious problems, the receiver blocking
problem, i.e., the intended receiver does not respond the sender
with CTS or ACK due to the interference from other ongoing
transmissions, also deserves a serious attention. In fact, this
problem becomes more severe in the multihop environment
and result in inefficiency and starvation of some traffic flows
or nodes. Furthermore, for a multihop flow, the nodes along
the path have different degree of contention, which results in
severe collision and degraded throughput under heavy traffic
load. These problems will be detailed in Section II.
DUCHA: DUAL-CHANNEL MAC PROTOCOL
In this section, we present the new dual-channel MAC
protocol (DUCHA) for multi-hop mobile ad hoc networks.
The design is based upon CSMA/CA mechanism in the IEEE
802.11 MAC protocol.
A. Protocol Overview
To achieve the desired protocol behavior, we utilize dualchannel
for control packets and DATA packets, separately. RTS
and CTS are transmitted over control channel. Negative CTS
(NCTS) is used to solve the receiver blocking problem and is
also transmitted in the control channel. DATA is transmitted
over the data channel. An out-of-band receiver based busy
tone [7] [13] is used to solve the hidden terminal problem.
The ACK is not necessary here because our protocol can
guarantee that there is no collision for DATA packets. To deal
with wireless channel error, we introduce NACK signal which
is continuing busy tone signal when the receiver determines
that the received DATA packet is corrupted.
CONCLUSIONS
In this paper, we identified four problems that cause dramatic
performance degradation of the IEEE 802.11 MAC
in multihop ad hoc networks, namely, the hidden terminal
problem, the exposed terminal problem, the receiver blocking
problem, and the intra-flow contention problem. To mitigate
these problems, we proposed a new MAC protocol called
DUCHA. Our DUCHA protocol uses two channels: one for
control packets and the other for DATA packets; a busy tone
signal is used to solve the hidden terminal problem and
also used to transmit the NACK signal if necessary. Our
DUCHA protocol also uses NCTS to notify a sender that
its intended receiver is blocked and cannot receive DATA
packets; in contrast, the IEEE 802.11 MAC cannot distinguish
the receiver blocking from destination being unreachable.
Moreover, DUCHA is more friendly to the routing layer
since DUCHA can provide accurate next-hop information,
leading to reduction in the number of unnecessary rerouting
requests. Besides, DUCHA has the following nice features:
1) no collisions for DATA packets and NACK signal, 2)
much less control packets and discarded DATA packets, and
3) achieving much higher spatial reuse. More importantly,
DUCHA can simultaneously overcome the four problems that
cause inefficiency of the IEEE 802.11 MAC.