Distributed Turbo Coding and Cooperative Transmission Scheme for Wireless Networks
A generalised distributed turbo coding (DTC) scheme for a general relay network with an arbitrary number of relays. Simulation results show that the proposed DTC scheme considerably outperforms the distributed coding with amplify and forward protocol (DC-AAF) and approaches the perfect DTC scheme and the capacity of wireless relay networks at a high signal to noise ratio (SNR).
Signals transmitted over a wireless channel can suffer from time varying fading and decoding errors that result in transmission errors. A common method of dealing with these transmission errors is for the relay to request a particular signal to be re-transmitted. One drawback to this method is that it cannot be used where there is no ability to request re-transmission. The other major drawback is that it can also result in significant delays in transmissions particularly in high signal to noise ratio environments. Delays are not acceptable in certain applications, such as two way voice communications, and this invention provides a solution.
A novel distributed turbo coding (DTC) scheme for a general wireless network with an arbitrary number of relays. For each transmission, based on the decoding results at relays, all relays are divided into two groups, which are called a decode and forward (DAF) relay group and an amplify and forward (AAF) relay group. All relays, which can correctly decode the signals transmitted from the source, are included in the DAF relay group and the rest of relays, which fail to make a correct decoding, are included in the AAF relay group. All the relays in the AAF relay group amplify the received signals from the source and forward it to the destination, while the relays in the DAF relay group decode the received signals, interleave, re-encode the interleaved symbols and forward them to the destination. All signals forwarded from the relays in the AAF relay group are combined together with the received signal transmitted from the source into one signal at destination and the signals from the DAF relay group are combined together into another signal. After combination, the overall codeword consists of the combined coded information symbols transmitted from the relays in the AAF relay group and the combined coded interleaved information symbols transmitted from the relays in the DAF relay group. These two signals form a generalised distributed turbo coding and an iterative decoding is then performed between these two signals.
Simulation results show that the proposed DTC scheme considerably outperforms the distributed coding with amplify and forward protocol (DC-AAF) and effectively overcomes the effect of error propagation due to imperfect decoding at relays. It also approaches the perfect DTC scheme and the capacity of wireless relay networks at a high signal to noise ratio (SNR).
For improving the performance of wireless ad-hoc networks, mesh networks, IEEE 802.15.4 (ZigBee systems) and increasing celluar coverage and improving the quality of service in cooperative wireless networks, such as 3G, WLAN and WiMax systems. The invention can significantly improve the performance of relayed transmission, thus providing power savings and capacity increases in these systems compared to other existing relaying protocols.