Hop Optimization and Relay Node Selection in Multi-hop Wireless Ad- hoc Networks Xiaohua (Edward) Li Department of Electrical and Computer Engineering State University of New York at Binghamton

1.Introduction Multi-hop transmission – – Benefits: Make network flexible, Create larger network Save energy of source node – – Deficits: Increase system complexity Extra interference among relay nodes

1.Introduction (cont' ) Our objective – – Analyze mutual interference & cooperation – – Derive node SINR – – Develop efficient & scalable ways to optimize path capacity

2.System Model Consider H-hop relaying in wireless network with J+1 nodes Each node has transmission power p Node i receives signal power pd ij -α from node j d ij : distance between node i and j α ： path-loss exponent

2.System Model: slotted transmission protocol Slot #012…..k Node 0Tx Pk 0Tx Pk 1Tx Pk 2…..Tx Pk k….. Node 1 Rx Pk 0 Tx Pk 0 Rx Pk 1 Tx Pk 1 Rx Pk 2 Tx Pk k-1 Rx Pk k : Node j…..Tx Pk k-j Rx Pk k-j+1 ….. :

2.System Model: received signal of node i d ij : distance between node i and j α ： path-loss exponent u(k): signal at time k v j (k): noise N: power of noise

3. SINR Analysis and Optimization Slot #…..k-1k….. : Node j-1Tx Pk k-j Rx Pk k-j+1 ….. Node j….. Rx Pk k-j Tx Pk k-j Rx Pk k-j+1 Node j+1 : Simplify the received signal Signal known by Node j

3. SINR Analysis and Optimization (cont’) SINR of node j at time k SINR of node j at time k-1 Notice: here we track the same packet u(k-j+1)

3. SINR Analysis and Optimization (cont’) For the detection of u(k-j+1) Apply maximal ratio combing (MRC) to find the maximum SINR of y j (k)

3. SINR Analysis and Optimization (cont’) Calculate the overall SINR with MRC Notice: This SINR is for a node j in an H-hop when detecting packets

3. SINR Analysis and Optimization (cont’) Calculate path capacity Like a water pipe, the capacity is limited by the minimum tunnel Network-wide optimization for optimal relaying path

4. Hop optimization and node selection First term of s j is the dominating one (when l =0) Formulate the problem to a max-min scheme

4. Hop optimization and node selection (cont’) With some approximation, the complex min-max optimization can be simplified to a simple equation solving: – –Find d 0 from – –Find other d j from:

4. Hop optimization and node selection (cont’) Apply previous method and locate the points M nodes are closed to these points Select nodes closest to the calculated points

5. Simulations

5. Simulations (cont’)

6. Conclusion An efficiency way to optimize multi- hop wireless networks in hop node selection – Efficient and scalable for large networks – Consider node cooperation and competition