As most people know,
wireless network has been using direct communication between base station and the user terminal. But
recently, researchers around the world started research on relay networks.
In cooperative relay networks, several relay stations between transmitter and receiver work together to forward the signal transmitted from transmitter to receiver.
There are few things worth noted in Larsson's paper:
- The system model in his paper is MISO (Multiple Input Single Output) system.
- The system model is non-regenerative relay network, which means the system is amplify-and-forward. Amplify-and-forward means each relay stations will not decode the received signal from transmitter, they will just amplify the signal with some weight factor and forward it to the receiver. Another type of relay network is regenerative relay network which is characterized by decode-and-forward. In this type of network, each relay stations will decode the received signal first before forwarding it to the receiver. Although it removes the effect of noise from first hop, there's delay effect that needs to be handled.
- From his research, it is discovered that the optimal weight (the weight needed to achieve maximum signal-to-noise ratio (SNR)) on each relay stations depends on the link between relay stations-transmitter, and relay stations-receiver. Thus, reciprocal channels are assumed here.
- His research also shows that exploitation of large number of relays drastically enhance the effective SNR.