Cooperative Networks

 

Multiple antennas at the receiver and transmitter are often used to combat the effects of fading in wireless communication systems. However, implementing multiple antennas at the mobile stations is impractical for most wireless applications due to the limited size of the mobile unit.

There is an increasing trend in the development of communication systems that allow their users to communicate "anywhere and anytime" at high data rates. Wireless networks have the potential to offer this ubiquitous high-rate communication among mobile users. A wireless network is a collection of mobile terminals that are capable of transmitting and receiving information using wireless multiple access protocols. Because the terminals in the network are mobile, communication among the terminals suffers from time-varying fading, which frequently reduces the signal level making it difficult or sometimes impossible to recover the transmitted information. In order to combat fading in wireless networks a good idea is to allow cooperation among the terminals in the network.

We are studying a cooperative ARQ scheme that exploits space time diversity and cooperation between neighboring nodes. The proposed scheme can use simple RF hardware, and keeps all the complexity in the firmware that processes the packets.

Using simple approximation functions to the bit error rates for both cooperative ARQ and MRC, we show that cooperative ARQ achieves the same performance than other methods that exploit diversity at physical level. The price to pay is an increment on the number of elements/nodes needed to obtain the same performance.

The considerable saving in terms of transmission power that can be achieved with the studied scheme comes, however, with a decreased throughput, unless multilevel transmission is used. In fact, in this case cooperative ARQ can lead to an increased thoroughput. We identify the operational regions where different tradeoffs transmission power versus throughput can be achieved. Cooperative ARQ can thus adapt the parameter choice in order to operate in optimal conditions.
 

 

Publications

• J. Morillo, J. García, A. Pirez-Neira, "Collaborative ARQ in Energy-constrained Wireless Networks", Third ACM/SIGMOBILE Workshop on Foundation of Mobile Computing DIAL-M-POMC 2005, Cologne, Germany, September 2005.
• J. Morillo, J. García, A. Pirez-Neira, "Achieving full diversity order by means of a cooperative-ARQ protocol",Research Report UPC-DAC-RR-2005-57, Submitted for publication;
• J. García, "Addressing and Forwarding Schemes for Cooperative Wireless Networks", Research Report UPC-DAC-RR-XCSD-2005-8, Submitted for publication;
• Julian Morillo-Pozo, Jorge García-Vidal, Ana I. Pirez-Neira, "Diversity Order of Cooperative ARQ Schemes in Wireless Networks", Research Report UPC-DAC-RR-2006-4, Submitted for publication;