Image Processing Reference
In-Depth Information
Fig. 8.3 Time variations of
the signal to noise ratio
(SNR) for the direct and the
relay paths
Cooperative relaying has been investigated to improve the spectral-efficiency
(SE) of the wireless system. The application of cooperative relaying in wireless
systems can be traced back to the groundbreaking work of Cover and El Gamal [
25
]
on the information-theoretic characterization of the relay channel. The work builds
upon the three-node (one source node, one destination node and one relay node)
channel model first introduced by Van der Meulen [
26
] and examines its channel
capacity for the case where the channel is contaminated by additive white Gaussian
noise (AWGN). Recent works on this subject are mainly focused on taking advan-
tage of the underlying spatial diversity introduced by the relay node(s) to combat
channel fading and improve the reliability of the system [
27
-
37
]. The spatial
diversity has also been exploited to improve the spectral efficiency of the wireless
channel through distributed space-time multiplexing techniques [
38
,
39
]. One
possibility of cooperative relaying is that mobile terminals can share their antennas
and form a virtual multiple-input-multiple-output (MIMO) channel to take advan-
tage of the provided spatial diversity. In contrast to the transmit diversity or the
receive diversity, this form of spatial diversity is referred to as
cooperative diversity
.
Laneman et al. [
27
] developed different cooperative fixed relaying schemes such as
Amplify-and-Forward (AF) and Decode-and-Forward (DF), selection relaying
and incremental relaying, and examined their performance in terms of the outage
probability. Unlike this work where the authors constrained the relay node to operate
in the half duplex mode, employing TDMA scheme, Sendonaris et al. [
29
,
30
]studied
the cooperation of mobile users when both users have data to transmit and address
practical implementation issues within a CDMA framework.
Cooperative communication can also be adopted in cellular systems to improve
the system efficiency. The resulting network from the integration of multihop
communication with cellular system is referred to as a Multihop Cellular Network
(MCN) or a Hybrid Ad-hoc Network (HANET) [
40
-
42
]. There has been consider-
able interest from both the standardization bodies and the academia in MCNs.
Opportunity Driven Multiple Access (ODMA) [
43
] is a multihop relaying protocol,
proposed by the 3rd Generation Partnership Project (3GPP) to be applied to
