Can cooperation reduce the average transmitted power per participating user?

The answer is (in general) affirmative: For a given target bit error rate (BER), cooperation reduces the average transmitted power per user when partners are appropriately selected. The more cooperating users are available and the larger the propagation exponent, the larger the reduction on transmitted power per user. This conclusion is drawn from a preliminary study which considers a community of users located randomly along a straight line. The users communicate with a Base Station (BS) located at the end of this line, and the transmission is subject to path loss. The communication is established either directly (Direct Mode), or via another member of the community (Relaying Mode). We show that the total power needed to achieve a certain BER at the BS is on average lower for the Relaying Mode than for the Direct Mode, even without exploiting any receive diversity benefit. There exist cases, however, where the Relaying Mode is not beneficial. This is true for environments with a propagation exponent smaller than two (δ <; 2). For δ = 2, the Relaying Mode performs identical to the Direct Mode.