1. Energy Consumption Perspective on Coded Cooperative Systems Liwen Yu and Andrej Stefanov

2. Motivation User cooperation represents and efficient approach of introducing diversity in both centralized and distributed wireless networks. For distributed networks such as multi-hop ad-hoc networks, cooperative communication can combine the following two advantages:  The power savings provided by multi-hopping;  The spatial diversity provided by the antennas of separate wireless mobile nodes.

3. Problem Formulation Objective:  Derive the transmission energy consumption for a coded cooperative system given a target frame error rate (FER) requirement.  Analyze the potential energy benefits cooperation bring to the wireless networks over direct transmission. Channel Model and User- cooperation System Model:

4. Approach  FER performance of a coded cooperative system can be expressed as:  The upper bound on the probability of confusing two code words c with e for the cooperative block fading channel is:  For a particular channel code in a quasi-static or block fading channel, the pair-wise error probability (PEP) of any error event as a function of the received SNR is parallel to the FER versus received SNR for medium to high SNR values.

5. Results  Utilizing offsets to relate the FER and PEP, a close form expression of the energy consumption for a coded cooperative system is obtained.  Only location information of cooperation users is needed for the estimation of energy consumption. It can be quickly implemented in energy-constrained wireless ad-hoc networks, where due to the limited power available or delay constraint, extensive computations are not desirable.

6. Results (cont’d)  The estimation agrees with the exact expressions and simulation results well. It is rather accurate, especially in medium to high SNR ranges.

7. Numerical Example: How to choose a “partner” to minimize the transmission energy ?  System setup: users in the network are only aware of location information of users that are within the routing circles; Rate ¼ (5 7 5 7) convolutional code is used; Channel power gain=1e-4; Noise spectral density N0=1.6e-20 W/Hz; Operating frequency=2.4 GHz;  Equivalence of the two metrics, 1) Min FER, 2) Min energy when choosing a “partner” to cooperate is shown.

8. Future Work Incorporate energy consumed by other parts of the circuitry besides the power amplifiers to the analysis of coded cooperative systems. Design energy-efficient cooperative routing protocol for ad-hoc wireless communication systems.