Full Duplex Media Access Control for
Wireless Multi-hop Networks
Kenta Tamaki∗ , Ari Raptino H.∗ , Yusuke Sugiyama∗ ,Masaki Bandai† , Shunsuke Saruwatari∗ and Takashi Watanabe∗∗ Shizuoka University, † Sophia University∗ Email: {tamaki, ari, sugiyama}@aurum.cs.inf.shizuoka.ac.jp, {saru, watanabe}@inf.shizuoka.ac.jp† Email: bandai@sophia.ac.jp

Abstract—Wireless full-duplexing enables a transmission anda reception on the same frequency channel at the same time,and has the potential to improve the end-to-end throughput of
wireless multi-hop networks. In the present paper, we propose amedia access control (MAC) protocol for wireless full-duplex andmulti-hop networks called Relay Full-Duplex MAC (RFD-MAC).
The RFD-MAC is an asynchronous full-duplex MAC protocol,
which consists of a primary transmission and a secondarytransmission. The RFD-MAC increases the full-duplex links byoverhearing frames, which include 1-bit information concerning
the existence of a successive frame, and selecting a secondarytransmission node using the gathered information. The gathered
information is also used to avoid a collision between the primaryand secondary transmission. Simulation results reveal that the
proposed RFD-MAC improves up to 68%, 49% and 56% of
end-to-end throughput compared to CSMA/CA, FD-MAC and
MFD-MAC, respectively.

I. I NTRODUCTION
For many years, wireless communication has been performed through half-duplexing because the signal received
from one’s own node is stronger than that received from another node. However, recent progress in several technologies,
such as analog circuits [1], digital circuits, and interference
cancellation [2]–[10], has made wireless full-duplexing possible [7]–[12].
The present paper focuses on the application of wirelessfull-duplexing to multi-hop networks [13]–[15]. Wireless fullduplexing has the potential to improve the end-to-end throughput of wireless multi-hop networks because a relay node cantransmit a frame while receiving another frame from anothernode. However, existing Full-Duplex Media Access Control(FD-MAC) protocols do not support multi-hop networks.
Although multi-hop networks can have relay full-duplexing
among three nodes, the existing FD-MAC supports only bidirectional full-duplexing between two nodes. Bidirectional fullduplexing and relay full-duplexing are described in detail in
Section II.
In view of this, the present paper proposes a full-duplex
media access control protocol for wireless full-duplex andmulti-hop networks called Relay Full-Duplex MAC (RFDMAC). RFD-MAC adds 1-bit information to each frame
header. This bit indicates whether the sender node of the frame
has a successive frame in its buffer. Each node overhears theframes, which includes the same information and determines
whether neighbor nodes have a successive frame. In using theinformation gathered for successive frames, each node selectsa full-duplex link, avoids collisions among other full-duplexing
nodes, and increases full-duplex opportunities. We evaluate
RFD-MAC through a computer simulation, and the evaluation
results reveal that RFD-MAC improves end-to-end throughput
compared to the Carrier Sense Multiple Access with Collision
Avoidance (CSMA/CA), FD-MAC [9] and MFD-MAC [16].
II. R ELATED R ESEARCH
Full-duplex communication enables transmission and reception on the same frequency channel at the same time [4], [5].
This particular characteristic of simultaneous communication
allows effective use of wireless resources in the time domain.
Half-duplex communication can only be used for conventional
radio because the transmitting signal is too strong to receive asignal from another node. However, the development of selfinterference cancellation has enabled full-duplex communication [2]–[5], [8], [9]. For example, received signals have beensuccessfully cancelled using FPGA on a WARP V2 platform[2]–[5], [10].
Wireless full-duplexing enables wireless multi-hop networks
to improve end-to-end throughput because each node canreceive a frame from a previous-hop node while transmitting
a frame to a next-hop node. In order to realize wireless fullduplex and multi-hop networks, there are two MAC protocol
issues to be addressed.
First, the MAC requires timing adjustment. Wireless fullduplexing must cancel self-interference in order to receive
a frame from another node. In order to maximize the performance of the self-interference cancellation, a sender node
must precisely estimate the signal strength of self-interference
and the received signal from another node. Precise estimation requires timing adjustment between uplink and downlink
transmission, which suppresses the fluctuation of the signal
strength. The FD-MAC has two candidate methods for timing
adjustment: synchronous [8] or asynchronous [9]. The present
paper uses the asynchronous method for timing adjustment. In
the asynchronous method, the destination node of the frame
starts to transmit a frame as a secondary transmission when
the header of the primary transmission includes the address ofthe destination node.
Second, the MAC must decide which node performs a
primary transmission or a secondary transmission. The existingAPA(a) Bidirectional
full-duplexing
Fig. 1.

A

B

C

D

R

(b) Relay full-duplexing
P

S

Bidirectional full-duplexing and relay full-duplexing

TABLE IC HARACTERISTIC OF VARIOUS MAC S
single-hop
multi-hopsynchronous[8][17]
asynchronous[9]
proposed MAC, [16], [18]R
Primary Transmission Area
Secondary Transmission Area

Fig. 2. Collision between a primary transmission and a secondary transmission

FD-MAC protocols [8], [9] are designed for the bidirectional
full-duplexing in Figure 1(a). Bidirectional full-duplexing has
only a bidirectional link such as AP and node A shown in
Figure 1(a). The wireless full-duplex and multi-hop network
can handle not only bidirectional full-duplexing but also relay
full-duplexing. A full-duplex situation, referred to as relay
full-duplexing, occurs for the case in which node B receives
a frame from node C while transmitting a frame to node
A in Figure 1(b). In order to make maximum use of bothbidirectional full-duplexing and relay full-duplexing, the MAC
protocol must properly select a secondary transmission node.
For example, in Figure 1(b), node B has two candidates fora secondary transmission node: nodes A and C. If the MAC
protocol selects a node that does not have a frame, then fullduplexing does not occur.
The MAC protocol must also take into account a collision
between a primary transmission and a secondary transmission.
Figure 2 illustrates a collision between a primary transmission
and a secondary transmission. In Figure 2, P denotes a primarytransmission node, and S denotes a secondary transmission
node. Moreover, R denotes the destination node of nodes P and
S. The solid line depicts the transmission range of the primarytransmission node, and the dotted line depicts the transmission
range of the secondary transmission node. Whenever a destination node of a primary transmission node is located within
the transmission range of a secondary transmission node, acollision occurs at the destination node.
We classify the existing full-duplexing MAC in Table I. As
mentioned previously, FD-MAC [8], [9] supports only singlehop networks. Multi-hop Full-Duplex MAC (MFD-MAC) applies wireless full-duplexing to a wireless multi-hop network[16]. The MFD-MAC selects the secondary transmission nodeby monitoring traffic on adjacent nodes. However, MFDMAC does not take into account collisions between primaryand secondary transmissions. [17], [18] propose full-duplexing
MAC protocols using directional antennas. For example, [17]achieved a throughput that was three times higher than that ofhalf-duplexing . However, the wireless full-duplexing devices
considered herein do not assume directional antennas. Instead,the present study assumes the same full-duplexing device asin [2], [3], [7]–[9], [12].
III. R ELAY F ULL -D UPLEX MAC
Based on the discussion in Section II, we propose theRelay Full-Duplex MAC (RFD-MAC) protocol, which en-

ables bidirectional full-duplexing and relay full-duplexing.
The RFD-MAC protocol is designed based on a synchronous
method [9], which is composed of a primary transmission anda secondary transmission. The RFD-MAC protocol enables
relay full-duplexing and avoids a collision between a primarytransmission and a secondary transmission.
RFD-MAC adds 1-bit information to each frame. The 1-bit
information indicates whether the node that sent the frame hasa successive frame. Whenever a node overhears a transmission
from its surrounding nodes, the node records the 1-bit information into a surrounding node table. The surrounding nodetable is described in detail in Section III-A. When a node starts
the primary transmission, the node also selects the secondarytransmission node and attaches the address of the secondarytransmission node. The selection algorithm is described indetail in Section III-B. The secondary transmission node,
which received the header of the primary transmission, starts
a secondary transmission.
A. Surrounding Node Table
RFD-MAC uses two types of frame: a primary transmission
frame and a secondary transmission frame. RFD-MAC uses
the same frame header format of IEEE 802.11. However, thefollowing two fields are used for different purpose: ‘Address
3’ and ‘More Data’. Figure 3 shows a IEEE 802.11 MAC
frame header [19]. The primary transmission node places thedesignated secondary transmission node address into ‘Address
3’. Both the primary transmission frame and the secondarytransmission frame use the ‘More Data’ field for the 1-bit
information related to a successive frame. In the ‘More Data’
field, 1 indicates that the source node of the frame has a
successive frame, and 0 indicates that the source node does
not have a successive frame.
Each node overhears primary transmission frames and secondary transmission frames from neighbor nodes and builds
a surrounding node table. Table II shows the surrounding
node table. The surrounding node table has the following
columns: Node Address, Has Frame, and Next Hop. The Node
Address column contains the source address of the overheard
frame. The Has Frame column contains the value in the ‘More
Data’ subfield in the overheard frame. The Next Hop column
contains 1 when the destination address of the overhead frame
is its own address and 0 when the destination address is some

2 bytes

2 bytes

6 bytes

6 bytes

6 bytes

6 bytes

2 bytes

Frame
Control

Duration/ID

Address1

Address2

Address
3

Sequence
Control

Address
4

2 bits2 bits4 bits

1 bit

1 bit

1 bit

1 bit

Subtype

To
DS

From
DS

More
Fragments

Retry

ProtocolVersionType

Fig. 3.

More Data = the source node of the frame has a
successive frame
1 bit
1 bit
1 bit
1 bit
Power
Mgt.

More
Data

WEP

Order

IEEE 802.11 header

other address.
In addition, each node updates the surrounding node table
when the node succeeds in transmitting a frame. If the recipient of the frame is not the final destination in the network
layer, the sender node of the frame updates the Has Frame
column of the corresponding recipient node to 1. The recipient
not being the final destination indicates that the recipient node
will hold the frame until the node transmits the frame.
B. Selection of a Secondary Transmission
As mentioned in Section II, whenever the destination nodeof a primary transmission (or the destination node of a secondary transmission) is located within the transmission range
of a secondary transmission (or the transmission range of a primary transmission), a collision occurs at the destination node.
In particular, a collision occurs when a primary transmission
node selects a secondary transmission node on another flow. In
order to avoid such collisions, the primary transmission node
selects a secondary transmission node from the same flow.
Generally speaking, a routing protocol in wireless multi-hop
networks selects a route with the least hop. The same flow
and the least hop ensure that the destinations of the primaryand secondary transmissions are different.
Figure 4 shows examples of collision and no collision
between nodes. In Figure 4, the solid line depicts the transmission range of the primary transmission node and the dotted line
depicts the transmission range of the secondary transmission
node. Figure 4(a) shows a collision between destination nodes
B and E. In Figure 4(a), node A, which is a primary transmission node, and node D, which is a secondary transmission
node, belong to different flows. Figure 4(b) shows the situationin which there is no collision between destination nodes B and
C. In Figure 4(b), node A, which is a primary transmission
node, and node B, which is a secondary transmission node,
belong to the same flow.
The primary transmission node uses the surrounding nodetable, which is described in Section III-A, for the selection of
a secondary node. The priority of the selection is as follows:
1) The next-hop node that has a frame2) The previous-hop node that has a frame3) The previous-hop node that does not have a frame4) The next-hop node that does not have a frame
TABLE IIE XAMPLE OF A S URROUNDING N ODE TABLE
Node Address
Has Frame Next Hop
A
1
1
C
1
0

Address 3 = The designated secondarytransmission node address

RFD-MAC prioritizes the node that has a frame and belongs
to the same flow. There are two types of nodes in the same
flow: an upstream node and a downstream node. If both the
upstream node and the downstream node have a frame, thedownstream node has higher priority because frames jam theflow if the downstream node does not transmit any frames.
If neither the upstream node nor the downstream node havea frame, RFD-MAC prioritizes the upstream node because
the upstream node might have received a frame from a node
upstream of the upstream node. The surrounding node tablecannot know the reception from the upstream node of the
upstream node. If more than one candidate node has thesame priority, then RFD-MAC randomly selects among thecandidate nodes.
C. Example of Operation of RFD-MAC
Figure 5 shows the time sequence of RFD-MAC, and an
example of operation of RFD-MAC is as follows:
1) A node, that has a frame to transmit uses CSMA/CA toresolve the contention. The node that wins the contention
transmits a frame as a primary transmission. We define
this node as the primary transmission node.
2) The primary transmission node selects another node designated to transmit a frame as a secondary transmission
node. The selection algorithm is described in Section
III-B. We define the selected node as the secondarytransmission node.
3) The secondary transmission node starts if the secondarytransmission node has a frame. The other nodes set the
network allocation vector (NAV) and defer transmission.
4) Whenever the primary transmission node or the secondary transmission node finishes the transmission of
the frame before finishing the reception of the frame,
C

C

B
A

B

D

A

E

D
E

F

F

Primary Transmission Area
Secondary Transmission Area(a) Collision
Fig. 4.

Primary Transmission Area
Secondary Transmission Area(b) No Collision

Collision and no collision between nodes

A. Simulation Environment
We conduct a computer simulation to evaluate the RFDMAC. We compare the obtained end-to-end throughput andfull-duplexing ratio (FD ratio) with the following three MAC
protocols:
1) CSMA/CA
CSMA/CA is a contention-based MAC protocol. The
CSMA/CA is a baseline for performance without fullduplexing.
2) FD-MAC
FD-MAC [9] uses full-duplex communication. However,
FD-MAC is restricted to bidirectional full-duplexing. We
use FD-MAC as a baseline for comparing relay fullduplexing to bidirectional full-duplexing.
3) MFD-MAC
MFD-MAC [16] has a mechanism in which the primarynode specifies a secondary transmission node that is
likely to have a frame to transmit. Although this mechanism is designed to make maximum use of opportunities
for full-duplexing, it suffers from collisions among different flows, as mentioned in Section II. As a result of
these collisions, the collision ratio of the MFD-MAC
will be the largest among the MACs considered herein.
We used MFD-MAC as a baseline for performance evaluation without suppressing collisions between primaryand secondary transmissions.
4) RFD-MAC
RFD-MAC is the proposed MAC protocol as shownin Section III. RFD-MAC supports bidirectional fullduplexing and relay full-duplexing while avoiding collisions between primary and secondary transmissions.
The common simulation parameters are as follows. The
physical rate is 2 (Mbps). The radio range is 250 (m). The
frame size is 1,500 (bytes). The area size is 2,000 (m) × 2,000(m). The number of nodes is 100. The number of sourcedestination pairs (flows) is 3 or 7, and the simulation timeis 300 (s). The topology is a random network topology in
X SendReceive

Y

Send
Receive
Fig. 5.

data

data

busytone
offset
data
data

ACK
ACK

B. Throughput vs. Sending Rate
We evaluated the end-to-end throughput by varying thesending rate. The aggregate end-to-end throughput versus thesending rate is shown in Figure 6(a) (♯ of flows = 3) and 6(b)(♯ of flows = 7). The vertical and horizontal axes denote thethroughput and traffic generation rate, respectively.
In Figure 6, the proposed RFD-MAC achieves the highest
throughput overall. Compared with the CSMA/CA, FD-MAC
and MFD-MAC, RFD-MAC improves up to 68%, 49% and
56% of end-to-end throughput, respectively. The reasons forthis are as follows. Unlike CSMA/CA, RFD-MAC uses fullduplexing. FD-MAC supports only bidirectional full-duplexing
whereas RFD-MAC supports both bidirectional and relay fullduplexing. The RFD-MAC suppresses collisions between primary and secondary transmissions by selecting the secondarytransmission node from the same flow, whereas MFD-MAC
does not take into account such collisions.
C. Full-duplexing Ratio vs. Sending Rate
In order to verify that RFD-MAC increases full-duplexing
opportunities, we evaluated the full-duplexing ratio by varying
the sending rate. Figure 7(a) (♯ of flows = 3) and 7(b) (♯ offlows = 7) show the aggregate full-duplex ratio versus thesending rate. The vertical and horizontal axes denote the fullduplex ratio and the traffic generation rate, respectively.
The full-duplex ratio of the proposed RFD-MAC is thehighest overall. Compared with the FD-MAC and MFD-MAC,
End-to-End Throughput (Mbps)

IV. P ERFORMANCE E VALUATION

which the nodes are randomly distributed inside the area. The
number of simulation trials is 10. We use Dynamic Source
Routing (DSR) [20] as the routing protocol.

0.25
0.2

0.15
CSMA/CA
FD-MACMFD-MAC
RFD-MAC (Proposed)

0.1

0.05
0
0

0.4

1.2

1.6

2

2.4

(a) ♯ of flows = 3
0.25
0.2

0.15
CSMA/CA
FD-MACMFD-MAC
RFD-MAC (Proposed)

0.1

0.05

ACK
ACK

0.8

Sending Rate [Mbps]
End-to-End Throughput (Mbps)

the node transmits a busytone until the reception ends.
The busytone ensures that surrounding nodes do not start
the next transmission until the current transmission has
finished.
5) The primary and secondary transmission nodes exchange
ACK frames at the same time with full-duplexing afterending the primary and secondary transmissions.

0
0

0.4

0.8

1.2

1.6

2

Sending Rate [Mbps](b) ♯ of flows = 7

RFD-MAC time sequenceFig. 6.

End-to-end Throughput

2.4

0.6
0.5
FD Ratio

0.4
0.3

CSMA/CA
FD-MACMFD-MAC
RFD-MAC (Proposed)

0.2
0.1
0
0

0.4

0.8

1.2

1.6

2

2.4

Sending Rate [Mbps](a) ♯ of flows = 3
0.6
0.5
FD Ratio

0.4
0.3

CSMA/CA
FD-MACMFD-MAC
RFD-MAC (Proposed)

0.2
0.1
0
0

0.4

0.8

1.2

1.6

2

2.4

Sending Rate [Mbps](b) ♯ of flows = 7
Fig. 7.

Full-duplex ratio

RFD-MAC improves up to 815% and 22% of full-duplex ratio,
respectively. The reasons for this are as follows. CSMA/CA isa half-duplex protocol, which results in a full-duplex ratio of
0. FD-MAC supports only bidirectional full-duplexing. RFDMAC supports both bidirectional and relay full-duplexing andyields a higher full-duplex ratio than FD-MAC. The MFDMAC improves full-duplexing opportunities by monitoring
the adjacent nodes traffic, although the mechanism is not as
effective as the information exchange of the RFD-MAC withrespect to finding full-duplexing opportunities. In addition, thefull duplex ratio of RFD-MAC does not depend on the traffic.
In Figure 7, RFD-MAC achieves a high full-duplex ratio when
the sending rate is low, although other MACs achieve a low
full-duplex ratio.
V. C ONCLUSION
In the present paper, we proposed a full-duplex MAC
protocol for the RFD-MAC multi-hop network. We evaluatedthe proposed RFD-MAC through a computer simulation. The
evaluation results reveal that the proposed RFD-MAC achieves
a higher throughput than CSMA/CA, FD-MAC, or MFDMAC.
ACKNOWLEDGEMENT
This research was partially supported by the Scientific
Research (A), (MEXT Grant: 24240009).
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