1 Optimal Power Allocation and AP Deployment in Green Wireless Cooperative Communications Xiaoxia Zhang Department of Electrical and Computer Engineering University of Waterloo

2 Outline Introduction System Model Power Allocation for a Single-User Link AP Deployment Conclusions and Future Work

Global Emission of CO 2 in Increased by 3% - Reaching an all-time high of 34 billion tonnes Figure 1. Global Emission of CO 2 in 2011 SAVE OUR ENVIRONMENT!!! Introduction 3

Eco-friendly renewable energy: solar, wind, tide, etc. Occupied 16.7 % of global energy in 2011 Figure 2. Renewable Energy Share of Global Final Energy Consumption, Sustainable Energy 4

In wireless communications - Up to 90% of power consumption in BSs - Energy cost is high and increasing Green wireless networks: network devices powered by sustainable energy - Example: Huawei Solar-powered base stations deployed over 1500 sites in over 30 countries and regions o Operation cost reduced over 60% o Carbon footprints reduced over 40% Figure 3. A Green Base Station Green Technology in Wireless Communications 5

Characteristics of Sustainable Energy - Variable or intermittent in its capacity - Highly dependent on the location and weather Fulfillment of users’ QoS demand is challenging. - Introduction of cooperative communication - More efficient green wireless network o Device deployment o Resource allocation Motivation 6

In a WLAN network where green APs are deployed, we would like to maximize the overall throughput by jointly allocating transmitting power and deploying the green APs, subject to the harvested energy constraint. Objective 7

8 Outline Introduction System Model Power Allocation for a Single-User Link AP Deployment Conclusions and Future Work

9 System Model A wireless local area network (WLAN) where a green AP is deployed. Nodes could communicate with each other in an ad hoc manner. Transmission links are separated by TDMA. AP can cooperate with the source nodes to transmit data to the destination. n links in total. Figure 4. A green wireless cooperative communication network.

10 System Model During each transmission period, only one source-destination pair (s i,d i ) exists. AP The AP functions as a relay node. - Two relaying protocols: Amplify-and-Forward Decode-and-Forward Easy to implementNoise cannot be eliminated Coding costNoise free need extra resources

11 Information theoretic achievable rate Achievable Rate for Single-User Relay Channel relay decoding rate destination decoding rate AWGN channel with path loss path loss exponent constant and identical for all links

12 Achievable Rate for Single-User Relay Channel Noise variances received at the relay and at the destination are the same value. Joint superposition encoding/decoding to maximize cooperation between source and relay. Generation of two codes. + relay decoding rate destination decoding rate

13 Problem Formulation Objective: maximize overall throughput under instant available power constraint. Links are scheduled by TDMA Power allocation on one link does not affect other links

14 Outline Introduction System Model Power Allocation for a Single-User Link AP Deployment Conclusions and Future Work

15 Objective: jointly determine, and to maximize the achievable rate. Power Allocation for a Single-User Link Note: optimum is achieved when destination decoding rate = relay decoding rate relay decoding rate destination decoding rate

16 Destination decoding rate is the bottleneck. Increase and reduce to balance. Coherent transmission. Synchronous Case relay decoding rate destination decoding rate Optimal power allocation is: Largest achievable rate is:

17 Relay decoding rate is the bottleneck. Source will set and. Independent transmission. Asynchronous Case Optimal power allocation is: Largest achievable rate is: relay decoding rate destination decoding rate

18 Outline Introduction System Model Power Allocation for a Single-User Link AP Deployment Conclusions and Future Work

19 Optimal power allocation and maximum rate depends on the location of AP. AP Deployment Direct transmission without help of relay can achieve highest rate. Relay closer to the source Synchronous case achieves higher rate Relay closer to the destination Asynchronous case achieves higher rate

20 Two local maximum Optimal AP Deployment for a Single Link Let, the two possible relay positions to maximize the throughput is the solutions to the following two equations:,,

21 Sustainable energy can only be exploited in some specific locations due to the availability and neighboring environment. Several candidate AP locations are considered. The optimal location can be decided based on the overall throughput which is calculated by Optimal AP Deployment

22 Simulation Results Figure 5. Rate comparison of three power allocation schemes when and. Synchronous Asynchronous

23 Simulation Results Figure 6. Achievable rate of a single user link with different AP locations.

24 Simulation Results Figure 7. The overall throughput by our proposed AP deployment metric and random deployment method. 100m×100m area 30 candidate locations

25 Outline Introduction System Model Power Allocation for a Single-User Link AP Deployment Conclusions and Future Work

26 Conclusions and Future Work  In this paper, a single-user channel achievable rate maximization problem is formulated and the optimal power allocation scheme is derived.  A throughput upper bound of each single-user channel is attained and the optimal AP deployment is provided.  In the future, we will consider the dynamic charging and discharging buffer in the AP.

27 Thanks!