Abstract— in single-channel mode hence more amount of

Abstract— A mobile ad-hoc network (MANET) consists of a group of mobile nodes and
it enables communications between participating nodes without the burden of any
base stations. To increase the capacity of wireless
network, multiple transceivers can be used. Multiple transceivers increase the
cost of the equipment. So generally for data transmissions, a single
transceiver is used in each node. But single
transceiver is difficult to implement in multichannel environment. This problem
can be solved by Ad-hoc Multichannel Negotiation Protocol (AMNP). For improving
reliability, further Reliable Broadcast Algorithm (RBA) is introduced.
Simulation analysis in NS-2 based on the combination of AMNP – RBA   gives comparatively a better performance.

 

Keywords
— MANET, Multihop, MAC, Multichannel, AMNP and RBA.

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I.     
Introduction

      Nowadays there is tremendous increase in
usage of mobile laptops and PDA’s but we have only limited amount of radio
spectrum. Within the available radio spectrum we have to effectively
communicate between the nodes. Existing works have dedicated to using multiple
channels to increase the capacity of wireless communication by dividing the
radio spectrum into number of channels.

      Most of the mobile devices are equipped
with single transceivers and it operates in single-channel mode hence more
amount of bandwidth is wasted. To mitigate this problem, all mobile nodes have
to be equipped with multiple transceivers. 
Enhancement of the present MAC protocol can give better performance on
multichannel with single transceiver.

    
In 1 Jain proposes a CSMA based medium accesses
control protocol for multihop wireless network. In which channel selection is
based on signal to interference and noise ratio at the receiver. Although this
method increases the throughput up to 50% there is delay in performance due to
high packet transmission. In 2, Nasipuri propose a new CSMA protocol for ad-hoc
networks. In which the CSMA protocol divides the available bandwidth into
several channels and selects the channel randomly. It employs “soft channel
reservation” that gives preference to the channel
that was used for last successful transmission.

      In 14 Chen proposes a AMNP protocol
that reduces the collision and interruption probabilities, and it uses the same
frame format of IEEE 802.11 with some slight modifications but it lacks in reliable
broadcast transmission. In 15 Lou proposes RBA (Reliable broadcast
Transmission) with selected forward nodes to avoid broadcast storm and reduce
broadcast redundancy.

II.   Problem statement

A.   
Single
transceiver constraint

      In IEEE 802.11 DCF the MAC protocol is
designed for sharing a single channel between the nodes. Nowadays most of the
wireless devices are equipped with one
half-duplex transceiver to transmit or to receive data. The transceiver can
operate on multiple channels dynamically but it can either transmit or receive
data from one channel at a time. So a node cannot communicate with other nodes
when is communicating with another node in another channel concurrently. While
using multiple channels IEEE 802.11 DCF will not be suitable because it may
dynamically switch channels.

B.   
Multichannel
hidden terminal problem

The node which cannot hear the radio signal from the transmitter node
and may disturb the ongoing data transmission is called hidden terminal nodes.
Even though IEEE 802.11 provides RTSCTS handshaking signals, in multichannel
environment the nodes still may collide with each other.

C.Broadcast transmission problem

      Broadcasting
is an important activity in multi hop MANET. Broadcasting a message in single
channel is easy, because all the mobile nodes in a network use a single channel
so the message can be delivered.  But in
multichannel environment a node may miss the broadcast frame when is currently
transmitting or receiving data from other nodes.

III. Amnp –
RBA  implementation

      In IEEE 802.11 the sender and the receiver
should perform a four way handshaking mechanism: Request-to-send /clear-to-send
(RTS/CTS), data, and acknowledgment (ACK) when they have data to transmit in
the same channel.

   

 

Fig. 1 An illustration of AMNP, in which C0 represents the contention/reservation
channel and C1 and C2 represent the data channels. The identifier
BB represents the broadcast beacon, the BWT represents the broadcast waited
time and the CST is the channel switching/settling time, respectively.

 

 

Fig. 2 Frame format of MRTS, MCTS and CRI control frames

 

 

     
If mobile nodes equip with only one transceiver, some nodes will never
communicate with each other at the same time. As a result, few data frames will
be transmitted in the multichannel environment. If we assign mobile nodes to
access channels dynamically, a complicated and distributed channel scheduling
mechanism has to be provided for MANETs. It will be more difficult in the
MANET. 

      Instead of employing such complicated
scheme, AMNP allocates a dedicated contention or broadcast channel for all
mobile nodes to contend. The remaining channels are served as data channels
permanently. Fig 1 illustrates the channel usage of AMNP in which channels C1– Cn-1
represent data channels, and channel C0 serves as the dedicated
contention channel or broadcast channel. Since there is no stationary node for
supporting centralized multichannel control in MANETs, the distributed
negotiation protocol, which can provide ad hoc multichannel transmission, is
needed. To solve the above-mentioned problems, we employ the concept of IEEE
802.11 RTS/CTS handshaking mechanism to fulfill the multichannel negotiation
and transmission mechanism in multi-hop MANETs. We name the RTS/CTS mechanism
as MRTS/MCTS in the AMNP. Unlike IEEE 802.11 RTS/CTS mechanism, we need more
information to indicate the usage of other data channels.

      When two nodes communicate, first a node has to complete a MRTS/MCTS handshaking in the contention channel to
acquire the access right of the expected data channel if it has a packet to
transmit. The main purpose of the MRTS control frame is to inform its direct
receiver and neighbours the preselected data channel to indicate a virtual
carrier sensing delay named network allocation vector (NAV) this will prevent
the exposed and hidden node problems in the preselected channel. Likewise, the
MRTS also carries the newest status information of data channels to notify
other mobile nodes within its transmitting range for information updating.

      The frame format of MRTS is shown in Fig
2 where the frame control, receiver address, transmitter address and frame
check sequence fields are the same as the description in the IEEE 802.11
standard. In order to be compatible with the IEEE 802.11 standard, we use the
reserved value Type = 01 and Subtype = 0011 as indicated in the frame control
field to represent the MRTS control frame. The original duration field is
eliminated since the channel C0 is for contention and broadcast use only. Therefore
the NAV will not be used in C0 when contending for the channel access. The
additional fields selected channel (SC), channel usage indication (CUI) and the
nth used channel’s offset are described as follows. The SC field indicates
which channel that the sender prefers to transmit data with the receiver.

     The preferred channel (selected) is not
compulsory for the receiver depending on the availability of the channel on the
receiver’s side. The CUI field
length is one octet long and the content of CUI indicates the status of the
usage in each channel.  The bit will be
set to 0 if the corresponding data channel is not in use; the bit will be set
to 1, if the corresponding data channel is in use.

     
When a node has received a MRTS frame, it will compare the SC field of
the MRTS with its channel status and then check whether it can satisfy the
request. If the preselected channel is also available in receiver’s side, the
receiver will grant the transmission request and reply the MCTS frame back to the
sender immediately. Otherwise, the preselected channel cannot be granted to use
since the preselected data channel in receiver’s side is not free. The receiver
then reselects another available channel according to comparing with the status
of channel usage of the sender. The reselection rules are as follows:

 

1)  If the sender has another free
data channel and the channel is also available in receiver’s side. The receiver
will select the common available channel to receive data frames.

2)  If there is no available free
channel in the side of the sender or receiver now, the receiver will compare
all data channels of both sender and receiver and then select a common channel
which will be earliest released.

 

      Channel information from
both sides are taken in order to prevent the hidden node problem. After the
checking process, the receiver will reply a MCTS frame back to the sender to
make the final decision. The MCTS frame contains the current the usage status
of data channels.

      Taking Fig. 3 for example,
assuming there are 5 mobile nodes in the ad hoc network. Node c and d are the exposed terminal of node a and b, and node e is the hidden terminal of node b. Initially node e finishes its backoff count down and then sends an MRTS frame to
request the channel 1 for transmitting data. The receiver node d approves the request since the
channel 1 is also available in side of d.
After the negotiation of node d and e, node a finishes its backoff count down and sends an MRTS to node b to ask channel 1 for transmitting
data. Since channel 1 has been reserved by node d and e, the request
could not be accepted. Node b
compares channel statuses of node a
with node b and then selects an
available channel 2 in this example and sends MCTS back to node a. After receiving an MCTS from node b, node a is notified that channel 1 would not be accepted and the agreed
channel is channel 2. Node a will
resend an MRTS to refresh the reservation information (to node c in this example).

 

Fig. 3 Transmission of MRTS/MCTS frames to select a
channel

 

A.    Broadcast casting in AMNP

      The broadcast operation is an important activity in ad-hoc networks.
Broadcasting is done to achieve routing information exchanges, address
resolution protocol and message advertisement etc. Broadcasting can be done
easily when there is a single channel but in multichannel environment, a node may miss the broadcast frame when is currently transmitting or
receiving data from other nodes. Here a single transceiver constraint is chosen.
To solve this problem, AMNP uses a designated control frame named broadcast
beacon (BB) to announce to its neighbouring nodes of an upcoming broadcast
transmission.

 

 

 

Fig. 4 Frame format of Broadcast Beacon

 

      All nodes which received the BB will stay in the contention channel and
wait a broadcast waiting time (BWT) to receive this frame even though it
has made a successful reservation. All the scheduled reservations will be
delayed a SIFS + BWT + SIFS + broadcast frame length + SIFS period.

     Several problems remain by adopting this transmission of
the broadcast frame after a SIFS interval. The following four cases are
considered as shown in Fig 5, to describe the broadcast problems occurred in
the multichannel environment.

 

Case 1: After finishing the transmission where the
sender and the receiver will return to the contention channel during the time
period of the beginning of the BB and before the broadcast frame.

 

 

 

Fig. 5 Broadcast problems in Multichannel
environment

 

Case 2: When a new coming node, which may move in
from the outside of the sender’s transmission range or just power on in the
sender’s transmission range, arrives during the time period of the beginning of
the BB and before the broadcast frame.

 

Case 3: At a finished transmission where the
sender and the receiver will return to the contention channel in the broadcast
frame.

 

Case 4: At a finished transmission where the
sender and the receiver will return to the contention channel after the
broadcast frame.

   

     
In case1 the nodes will receive the broadcast frame because it stays
connected in contention channel after the transmission so it receives the
broadcast frame. In case 2 it is not sure the nodes will receive the broadcast
frame depending upon the physical response time and ready time.

     Case 3 and case 4 will definitely miss the
broadcast frame, to solve this problem we prefer reliable broadcast algorithm.

 

B.
 Reliable broadcast Algorithm

In reliable
broadcast algorithm it requires only selected forward nodes among the 1-hop neighbours
to send ACKs to confirm their receipt of the packet. Forward nodes are selected
in such a way that all senders’ 2-hop neighbour nodes are covered. Moreover, no
ACK is needed for non-forward 1-hop neighbours, each of which is covered by at
least two forward neighbours, one by the sender itself and one by one of the
selected forward nodes. The sender waits for the ACKs from all of its forward
nodes. If not all ACKs are received, it will resend the packet until the
maximum times of retry is reached. If the sender fails to receive all ACKs from
the forward nodes, it assumes that the non-replied forward nodes are out of its
range and chooses other nodes to take their roles as forward nodes.

The forward nodes
are selected based on the following greedy algorithm:

In the sample
network shown in Figure 6, N(1)={1,2,3,4, 6}
and N2(1) ={1,2,3,4,5,6,7}. When
using the FNSSP, sender node 1 selects nodes 2, 3 and 4 as its forward nodes.
Node 3 is selected because there is no node in N(1) to cover it.

 

Algorithm: Forward Node Set Selection Process (FNSSP)

Step 1: The forward node set F is initialized to be empty.

Step 2: Add in F the node that covers the largest number of 2-    hop neighbours that are not yet covered by
current F. A tie is broken by node ID.

Step 3: Repeat step 2 until all 2-hop neighbours are covered.

Fig 6 A sample
network where the sender 1 uses the FNSSP to select its

forward nodes.

 

IV. Simulation results

      The network is varied from 54 to 108 nodes. The mobility model uses the random
waypoint model in a rectangular field. Here each mobile node starts its
journey from a random location to a random destination with a randomly chosen
speed (uniformly distributed between 0–94 m/s).

 

TABLE I

SIMULATION
CONFIGURATION PARAMETERS

 

 
Simulation Parameters

 
Value

Simulation
Area

300m*300m

Transmission
range

100 m

Transmission
rate

2 Mb/sec

SIFS

10µs

DIFS

50µs

MRTS frame length

variable 160 bits

MCTS frame length

112 bits

ACK frame length

112 bits

MAC header length

34 octets

broadcast frame
length

128 octets

 

     
In all simulation analysis, one contention channel and 11 data channels
are considered. Simulation area is 300m x 300m, transmission range is about
100m and transmission rate is about 2Mb/sec.

     
In Fig 7 When 54 nodes are considered AMNP performs better than IEEE
802.11. When frame arrival rate increases to 20, a significant amount of
increase of throughput can be noted.

 

Fig. 7 Comparison of Throughput derived by
IEEE 802.11 and AMNP

When
108 nodes are considered AMNP performs better than IEEE 802.11. When frame
arrival rate increases to 20, a considerable amount of increase of throughput
can be noted when compared to IEEE 802.11.

Fig. 8 Comparison of Throughput derived by
IEEE 802.11 and AMNP

          MAC delay is the sum of MAC operations including back-off countdown,
channel negotiation and transmission delay.

   

 

Fig. 9 Comparison of Mac delay derived by
IEEE 802.11 and AMNP

Fig. 10 Comparison of Mac delay derived by
IEEE 802.11 and AMNP

     

      The Fig. 9 and Fig. 10 show comparative
delay analysis for IEEE 802.11 and AMNP protocol with 54,108 nodes. It is seen
that AMNP protocol has lower MAC delay compared to IEEE 802.11 protocol.

 

 

Fig. 11 Comparison of Mac delay derived by
RBA and AMNP-RBA

                End – to – End delay is the total delay in the network; AMNP-RBA has
higher delay because it is sum of back-off countdown, channel negotiation,
transmission delay and the delay in broadcasting.

Broadcast delivery ratio is the ratio of the nodes
that received the broadcast packets to the number of the network. AMNP-RBA has
lesser BDR compared to RBA because it is used in multichannel environment.

 

 

Fig. 12 Comparison of Broadcast delivery ratio derived by RBA and    AMNP-RBA

V.    Conclusion

          The multi-hop MANET transmission capacity
can be improved by adopting parallel multichannel access schemes. AMNP protocol
addresses the problems like multichannel hidden terminal problem and the
multichannel broadcast problem. This is due to those mobile nodes that cannot
listen to all channels simultaneously. The proposed new MRTS and MCTS
handshaking message conquers the multichannel hidden terminal problem.  The BB control frame to conquer the
multichannel broadcast problem. The performance analysis shows that there is an
encouraging result. The parameters are compared for 802.11 and AMNP. It is
concluded that the combination of AMNP – RBA gives a reliable broadcast
transmission. Because in AMNP case 3 and case 4 are assumed for reliable
transfer.

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