Cooperative Network
▶ Introduction
 

Interference and signal loss due to distance and fading severely reduce the data delivery performance of wireless networks. Cooperative technology can optimize the packet losses due to the effect of interference and fading. Thus cooperative transmission significantly increases network performance by providing alternate paths when a defined link fails. Cooperative communications also increase reliability and transmission rates and optimize transmission power.

In traditional cooperative transmissions, the sender transmits the data packet to the receiver in the first phase (first time-slot), and neighbors overhear the signal. This overheard signal is then retransmitted by single or multiple neighbors in the second phase (second time slot). Thus, multiple copies of the data packet may be received at the receiver. The receiver applies the maximum ratio combining (MRC) technique before decoding the packet, which is the core technology for cooperative communications. A neighbor who retransmits the overheard signal is called a relay or helper. Cooperative communication exploits the wireless broadcast advantage by using neighbor nodes as relays. Two-hop cooperation has some additional benefits over traditional cooperation. In two-hop cooperative transmission, sender transmits a data packet to a relay in the first phase, and a neighbor overhears the data packet. Subsequently, the relay retransmits the data packet to the receiver in the second phase. Receiver does not need to apply the MRC technique in two-hop cooperation.

Fig. 1. Cooperative transmission

Usually, single relay is used in any traditional cooperative communication. However, More than one relay can transmit in a single time-slot or in different time-slot. Nowadays, back-up relay can be used for further increasing the reliability, where the back-up relay transmits the data packet in case of the transmission failure of first relay. Cooperative transmission is applied in wireless or ad hoc wireless networks. Nowadays, cooperative transmission is becoming popularity in cognitive radio, smart grid, body area network and vehicular communication for reliable transmissions.

The major challenges for cooperative communications are (i) the relay selection process and (ii) the relay transmission process as they take additional time. Both the processes also enlarge the transmission region beyond the expected transmission region of sender and receiver. The enlarged transmission region may causes of (i) collisions for the hidden terminal problem and (ii) bandwidth wastage for the exposed terminal problem. Collisions and bandwidth wastage degrade the throughput and overall network performance below what is expected. Thus, one should take care of these challenging issues for designing wireless cooperative networks in order to obtain expected benefits.


▶ Research Issues

 


▶ References

 
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  6. Zhang, Y. Zhang, and Y. Fang, “A coverage inference protocol for wireless sensor networks,” IEEE Trans. Mobile Comput., vol. 9, no. 6, pp. 850?864, 2010.


▶ Achievements

 
  1. Muhammad Shoaib Siddiqui, Syed Obaid Amin, and Choong Seon Hong, "Hop-by-hop Traceback in Wireless Sensor Networks", IEEE Communication Letters, Vol. 16, No.2, pp.242-245, February 2012