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Cooperative relaying for a system that consists of different configurations of a collocated and uniform linear antenna is analyzed. The amplify-and-forward relaying (AF) and selection combining (S-AF) schemes based on maximal ratio combining (MRC) method for single- and multi-relay are investigated. In this study, the bit-error-rate (BER) expression for collocated and uniform linear antenna in cooperative communication system over flat Rayleigh fading channel is derived. The result for 3-element collocated antennas (tripole) shows improvement in performance over dual-polarized antennas. Also increasing number of tripole antenna does not add improvement.

Relay systems have been widely investigated in wireless communications as a way to overcome deep fading and therefore enhance signal quality in multi-path fading channels. In relaying network we have a two-hop link where the signal is transmitted in the first hop from a source to a relay node and in the second hop the signal at the relay node is retransmitted to the destination. At the same time, the source will transmit another copy of the signal directly to the destination. Therefore, the signal is transmitted from the source directly and via a relay node, so, the destination will receive the transmitted signal from two links referred as source-relay-destination and source-destination link. Now the signal received at the relay is forwarded to the destination by implementing two schemes known as amplify forward (AF) and decode forward (DF) [

Since future wireless system trends require wireless terminals small in size, the advantage of using multiple antennas at a relay node will be limited by the space separation between antennas and thus correlation of wireless terminals will affect the system performance. In this paper the study of cooperative communication is applied for collocated antennas known as “vector antenna” (VA) implemented at a relay node over independent and identically distributed Rayleigh fading channels. Vector antenna can independently detect or excite all six EM field components enabling the communication system to access additional signaling dimensions, which may enhance performance in the same way as antenna arrays [

The organization of this paper is as follows: in Section 2 the system model is introduced for VA and ULA in a relay network and the output SNR is analyzed. In Section 3 the BER analysis for AF and S-AF schemes is presented. Finally, simulation of the system presented is compared with theoretical values of the equation derived.

BPSK modulation is considered for a relay communication network that consists of two-hop channel as shown in

For a single vector antenna at the receiver side of relay node, each arriving multipath component is a two- dimensional vector

can be written as

where

Multi-relays system with vector antenna and ULA

we write

If the multipath component is reflected or scattered by an object in the far field, then the signal can be approx- imated as a plane wave at the receiver and suppose that the multipath component arrives at the sensor from the direction

nonconductive, homogeneous, and isotropic medium, the received signal can be modeled by [

where

The

where

with relay system notation, we can write the received signal from source to relay to be

where

where each of

where

where

The noise

The output SNR at destination can be re-written as

where

To simplify the analysis, the noise is ignore at the relay gain. The output SNR of MRC at relay for tripoleatenna is exponentially distributed and follows the Gamma distribution with probability density function pdf given by

where

Now using the results in [

where

Assuming independent of

where

For S-AF only the best relay which contributes most to received SNR is chosen for re-transmission. The received SNR can be expressed as

The received SNR for S-AF can be written as

where

in [

where

in

can be written as

In this section, simulation and theoretical results of cooperative communication for AF and S-AF schemes presented. We assume that the multipath components of the received signals are uniformly distributed on a sphere

where the azimuth angle

probability density function

and the polarizations

(i.e.

mitted power for all participate scheme on each relay is

transmitted power

In

BER for tripole antenna with multi-relays

BER simulation for tripole antenna at single and mul- ti-relays

a relay did not add gain in diversity to the relay system while multi-relay network with single triple antenna would give us significant improvement.

In

The study of cooperative communication for collocated antennas setting employed at relay node and ULA at source and destination is investigated. Two schemes of relaying network known as AF and S-AF are presented and closed form BER for tripole antennas is derived. The theoretical and simulation results are compared for one- and multi-relay network. Results shows that tripole antenna outperformed the dual antenna case and the 6-

BER simulation for 2, 3 and 6 collocated antennas at single relay

BER Simulation for selective vs AF for tripole and relay

element vector antenna can add more gain in low SNR region over tripole case. Also increasing number of tripole antenna showing no gain is attained while increasing number of relays will enhance the receiver performance and achieve higher gain.