1. QoS Routing and Scheduling in TDMA based Wireless Mesh Backhaul Networks Chi-Yao Hong, Ai-Chun Pang,and Jean-Lien C. Wu IEEE Wireless Communications and Networking Conference, 2007. WCNC 2007. Mei-zhen Chen

2. Outline  Introduction  Motivation  The Proposed Mechanism  Performance Evaluation  Conclusions

3. Introduction (WMBNs) wired connections wireless connections wired/wireless connections (MR)

4. Introduction (cont.)   Authors present an integrated mechanism for real- time applications over TDMA-based WMBNs,and propose QoS-aware routing and scheduling algorithms under the integrated mechanism.   The algorithms can work with any type of network topologies, and the link capacity and interference are taken into account to guarantee QoS.

5. Motivation   An appropriate routing algorithm needs to find one or more feasible routes for each pair interference signal-to-interference-and-noise ratio (SINR) Selected routed paths a linear-programming optimization technique The routes shall not be restricted by a particular topology The actual traffic demand of an MR varies as depending on application needs of its serving clients a dynamic routing strategy

6. The Proposed Mechanism -assumptions (1/4)   Consider a single-channel single-transceiver MAC.   There is only one gateway in the network.   Packet loss is assumed to be neglected.   The TDD (time division duplexing) mode is chosen here for uplink and downlink transmissions.   the traffic demand of an MR v, D[v]

7. The Proposed Mechanism -assumptions (2/4)   The IEEE 802.16 standard provides multiple transmission rates by applying different modulation schemes and coding rates.   The receiver minimum input level sensitivity, R SS The receiver signal-to-noise ratio (SNR) The number of OFDM subcarriers The number of allocated subchannels The sampling frequency in MHz BW is the channel bandwidth and η is a constant sampling factor.

8. The Proposed Mechanism -assumptions (3/4)  On the other hand, R SS is also given by where EIRP is the effective isotropically-radiated power Gt(dBi) : transmitter antenna gain. Gr(dBi) : receiver antenna gain. SLt : transmitter loss SLr : receiver loss. TxPower(dBW) : the transmission power. LM(dB) : the link margin. PL(dB): the transmission path loss.

9. The Proposed Mechanism -assumptions (4/4)   The MRs in WMBNs are assumed to be stationary and communicate without obstructions, the fading effects are negligible.   Adopt two-ray ground reflection model as our path loss model.

10. The Proposed Mechanism -flowchart gateway

11. The Proposed Mechanism -routing algorithm (1/4)   Authors slightly modify the Dijkstra’s algorithm to find a path from the gateway to a particular MR. the weights of wireless links could be changed as the alteration of network flows. the modified algorithm terminates immediately after the path from the gateway to the target MR is discovered

12. The Proposed Mechanism -routing algorithm (2/4)   A mesh network is modeled as an undirected graph G = (V,E) V : MRs E : wireless links   E[G] : set of the wireless links.   R[i, j] : the bit rate of link (i, j) derived.   B[i, j] : the available bandwidth of link (i, j).   D[v] : the traffic demand of router v.   I[v] : the granted bandwidth of router v. (initially set by 0)   U[G] : a subset of the nodes whose demands have not been satisfied.   P[G] : a subset of the wireless links along the selected path.

13. The Proposed Mechanism -routing algorithm (3/4) W[i, j] : the occupancy ratio of a link (i, j). S[m, n] : the subtracted bandwidth quantity of link (m, n) interfered by link (i, j).

14. The Proposed Mechanism -routing algorithm (4/4)   to maximize the achievable traffic demand of router v, D’[v]

15. The Proposed Mechanism -scheduling algorithm   F[i, j] : whether the demand of link (i, j) is already scheduled in the current schedule period   S[i, j] : whether link (i, j) is interfered by any other active links

16. The Proposed Mechanism -scheduling algorithm (cont.) Q[G]: the subset of the links whose demands are satisfied. extract non- blocking links

17. Performance Evaluation (1/5)  20MRs are randomly distributed  25 × 25 km 2 area  A gateway is placed in the center of the area   The packet overheads conform to the RTP, UDP, IP and IEEE 802.16 packet formats.   The event-driven simulation is implemented by C++ programs.

18. Performance Evaluation (2/5)

19. Performance Evaluation (3/5)

20. Performance Evaluation (4/5)

21. Performance Evaluation (5/5) the mean traffic demand: 150Kbps

22. Conclusions   Authors considered the QoS problem for routing and scheduling in TDMA-based WMBNs.   Authors proposed an integrated routing and scheduling mechanism to provides QoS guarantees.   A linear programming optimization was devised to solve the amount of non-collision bandwidth.