Cross-Layer Design for Combining Cooperative Diversity
with Truncated ARQ in Ad-hoc Wireless Networks
♣
Lin Dai and Khaled B. Letaief, Fellow, IEEE
Center for Wireless Information Technology
The Hong Kong University of Science & Technology
Clear Water Bay, HONG KONG
Email: eedailin@ust.hk
, eekhaled@ee.ust.hk
Abstract—We propose a cross-layer design which combines
truncated ARQ at the link layer and cooperative diversity at the
physical layer. In this scheme, both the source node and the relay
nodes utilize an orthogonal space-time block code for packet
retransmission. In contrast to the previous cooperative diversity
protocols, here cooperative diversity is invoked only if the
destination node receives an erroneous packet from the source
node. In addition, the relay nodes are not fixed and are selected
according to the channel conditions using CRC. It will be shown
that this combination of adaptive cooperative diversity and
truncated ARQ can greatly improve the system throughput
compared to the conventional truncated ARQ scheme and fixed
cooperative diversity protocols.
Keywords- Cooperative diversity, Truncated ARQ, Cross-layer
design, MIMO systems, Ad-hoc wireless network.
I. INTRODUCTION
The use of multiple antennas at both the transmitter and
receiver can bring significant capacity gains [1]. Unfortunately,
this could be impractical in an ad-hoc wireless network, due to
the size of the node or the mobile unit. In order to overcome
this limitation, a new form of spatial diversity, whereby
diversity gains are achieved via the cooperation of nodes, has
been proposed. The main idea behind this approach, which is
called cooperative diversity, is to use orthogonal relay
transmission to achieve diversity gain. In particular, each node
has one or several partners. The node and its partner(s) are
responsible for transmitting not only their own information, but
also the information of their partner(s). Therefore, a virtual
antenna array is obtained through the use of the relays’
antennas without complicated signal design or adding more
antennas at the nodes.
Sendonaris et al proposed the idea of cooperative diversity
and showed that node cooperation increases the sum-rate over
non-cooperative transmission for ergodic fading links [2-3].
Laneman et al further presented several cooperative protocols,
such as amplify-and-forward, decode-and-forward, selection
relaying and space-time-coded cooperation [4-5]. Other
important works include coded cooperation [6-7], cooperative
regions analysis [8], diversity-multiplexing tradeoff analysis on
cooperative protocols [9], and symbol error rate analysis for
Rayleigh-fading channels with K amplifying relays [10].
In most of the present cooperative protocols, no restrictions
are imposed on the selection of relays. Therefore, when the
channel between the source node and the relay node (s-r
channel) is poor, cooperative diversity may result in even
worse performance than the non-cooperative case due to severe
error propagation [4]. In [4], a selection relaying protocol with
2 nodes cooperation was proposed, where the relay forwards
the source node’s information only if the s-r channel fading
coefficient is above a given threshold. Obviously, such
selective protocol can achieve better performance than the
fixed ones. However, it is usually not trivial to select a suitable
threshold since it depends on the actual value of the channel
fading coefficients. A higher threshold will reduce the possible
performance gain while a lower one will allow more error
propagation which also degrades the performance.
ARQ protocol at the link layer is an effective means to
overcome the channel fading, where CRC is usually used for
error check and retransmissions are requested if the packet is
received erroneously [11-12]. In practice, the maximum
number of retransmissions is usually limited so as to minimize
the delay and buffer size and such variant ARQ is called
truncated ARQ protocol [11]. In this paper, we propose a novel
cross-layer design which combines truncated ARQ at the data
link layer and cooperative diversity at the physical layer. We
will show that through this combination, adaptive cooperative
diversity gain can be achieved without any specific threshold.
In this new scheme, Q idle nodes around the source node are
defined as relay candidates. These nodes also receive the
packet transmitted from the source node to the destination node
and check the CRC results. Only the ones who detect the
correct CRC are selected to be relays and involved in the
possible retransmission. Specifically, if the destination node
fails to detect the packet correctly, retransmission will start
where both the source node and the relays utilize a suitable
orthogonal space-time block code to retransmit this packet. It
can be seen that this new scheme is adaptive to the s-r channels
by virtue of the CRC bits instead of some specific threshold
and so no error propagation will be incurred by relaying. As a
result, this scheme, which is referred to as Selective
Cooperative diversity with ARQ (SCA), can be expected to
bring significant performance gain over the previous ARQ-
only or fixed cooperative diversity schemes. Another scheme
which combines truncated ARQ and fixed node cooperation is
also considered in this paper. This scheme, which is referred to
as Fixed Cooperative diversity with ARQ (FCA), is similar to
SCA, except that the relays are pre-assigned and are always
fixed during the whole transmission. Compared to SCA, FCA
♣ This work is supported in part by the Hong Kong Research Grant Council
under Grant No. HKUST6250/04E.
matter experts for publication in the IEEE GLOBECOM 2005 proceedings.This full text paper was peer reviewed at the direction of IEEE Communications Society subject
IEEE Globecom 2005 3175 0-7803-9415-1/05/$20.00 © 2005 IEEE
Authorized licensed use limited to: XIDIAN UNIVERSITY. Downloaded on July 05,2010 at 01:07:09 UTC from IEEE Xplore. Restrictions apply.
资源评论
