AN INTEGRATED ROUTING AND SCHEDULING APPROACH FOR PERSISTENT VEHICLE COMMUNICATION IN MOBILE WIMAX MESH NETWORKS

Transcription

1 AN INTEGRATED ROUTING AND SCHEDULING APPROACH FOR PERSISTENT VEHICLE COMMUNICATION IN MOBILE WIMAX MESH NETWORKS Rahul Amin and Kuang-Ching Wang Dept. of Electrical and Computer Engineering Clemson University Clemson, SC USA ABSTRACT The U.S. military has recently announced plans to evaluate the IEEE 82.16e Mobile WiMAX technology s potentials as a fast deployable solution for building a broadband tactical communication network. Specifically, the technology s provisions of mesh mode operation and terminal mobility allow a tactical network to be quickly deployed among mobile base stations and mobile battle units. The technology provides essential support for mesh connectivity and fast handover, while an overall deployment strategy and higher layer protocols remain to be established. This paper presents a practical network organization scheme and an integrated routing and link scheduling approach to enable persistent communication of fast moving ground vehicles over a mesh-mode Mobile WiMAX tactical backbone network. The solution exploits the mobile units mobility pattern and the Mobile WiMAX handover modes to optimize persistent communication with minimal disruption and signaling overheads. Simulations are conducted in ns-2 to assess the efficacy of the proposed methods. 1. INTRODUCTION The U.S. military has recently announced plans to evaluate commercial Mobile WiMAX solutions as a candidate technology for its next generation tactical networks [1]. Mobile WiMAX is based on the IEEE 82.16e-25 standard [2], which extends mobility support over the earlier IEEE standard that supports only fixed stations [3]. The two standards altogether offer a low-cost infrastructure solution [4] for long range, broadband (typically up to 3 miles non-line-ofsight, 6 miles line-of-sight, and 3 Mbps per 1 MHz channel [5]) mobile communications. A number of studies have examined the feasibility of adopting WiMAX and/or Mobile WiMAX for constructing a last-mile tactical network for the mobile warfighters. In [6], communications among base commands and nonmobile branch units using IEEE was studied. In [7], link-level performance assessments were done for communication between a moving vehicle and a single fixed base station using IEEE In [8], a solution for enabling mesh and ad hoc networking using the IEEE point-to-multipoint (PMP) mode was studied. In [9], operational needs of a last mile Parmesh Ramanathan Dept. of Electrical and Computer Engineering University of Wisconsin, Madison Madison, WI 5376 USA tactical network and the WiMAX standards potentials in meeting them were discussed. For warfighters on the move, of crucial need is sustained reliable communication with the commands over a tactical network infrastructure. This paper investigates the required network organization, message routing, and link layer scheduling methods for enabling persistent communication of fast moving vehicles over a Mobile WiMAX mesh network. The IEEE and 82.16e-25 standards together have provided the link layer functions needed to support persistent vehicle communication. Specifically, IEEE defines the mesh mode operation that allows construction of a wireless mesh of base stations (BS) to provide continuous coverage for subscriber stations (SS) over a large area, with only a few backhaulenabled BSs connected to the core command network via point-to-point communication links. In mesh mode, BSs maintain control and data connections of controllable bandwidth with neighboring BSs. IEEE 82.16e-25 provides the definition of a mobile station () and its network entry, scheduling, and BS handover procedures. The mobility extension was defined in the PMP mode but was not defined to interoperate with BSs in mesh mode. To enable persistent communication with a BS mesh, coordination of the two modes of operation with higher layer protocols must be defined. In this paper, a strategy is proposed to support persistent vehicle communication with a standardcompliant Mobile WiMAX mesh network. The tactical network operation involves a mesh of BSs deployed along potential paths that the s shall travel. Amidst a majority of mesh BSs, a few backhaul-enabled BSs are deployed. Each upon network entry instantiates network connections with the nearest base station, and the connections shall persist across subsequent BS handovers. The persistence is enabled at the link and network layer, respectively, by the Mobile WiMAX handover support and the proposed integrated routing and scheduling methods. The proposed routing and scheduling method exploits 1) the continuity of the wireless mesh infrastructure to enhance communication persistence and 2) the backhaul links to optimize end-to-end performance. Within the mesh, routes adapt to follow each wherever it moves. Once reaching the backhaul-enabled BSs, packets are routed with globally addressed routing protocols such as /7/$ IEEE 1 of 7

2 Mobile IP or ad hoc routing protocols. mobility events are signaled to the scheduling service to control migration of existing scheduling profiles to neighboring BSs, and to initiate adaptations in the global routing protocol. The rest of the paper is organized as follows. Section 2 reviews relevant backgrounds and previous studies of the WiMAX and Mobile WiMAX standards. Section 3 and 4 describe the proposed network model and integrated routing and scheduling solution. Simulation studies are presented in Section 5. The paper concludes in Section BACKGROUND AND RELATED WORK 2.1. WIMAX PMP AND MESH MODES The IEEE standard defines the mesh mode as an option beyond the default PMP mode [3]. The PMP mode allows SSs to communicate only through a BS. In mesh mode, SSs can communicate with any other SSs in range as well, allowing SSs to relay packets to or from other SSs. In mesh context, a backhaul-enabled node is a Mesh BS, and all other nodes (including s as later defined in IEEE 82.16e [2]) are Mesh SSs. Through contention-based procedures, all nodes establish framebased, contention-free schedules for data transmission. The schedules can be assigned by a Mesh BS for all dependent SSs using a centralized scheduling scheme (e.g., [1-12]), or be collaboratively determined by all nodes using a distributed scheduling scheme (e.g., [13]). PMP and mesh modes also have important differences in their supported duplex schemes and frame structures. PMP mode supports both time-division-duplex (TDD) and frequency-division-duplex (FDD) while mesh mode supports TDD only. In PMP mode frames are separated for uplink and downlink traffics; in mesh mode frames are separated for control and data traffics regardless of direction. In [8] and [14], efforts were made to realize the mesh mode frames under PMP mode operation. In both PMP and mesh modes, an SS must enter the network by connecting with a BS or, in mesh mode, with another SS following a network entry procedure that: 1) scans for and synchronizes to the node to be connected to, and then performs 2) ranging, 3) basic capabilities negotiation, 4) authorization, 5) registration, 6) IP address configuration, 7) time of day configuration, and 8) provisioned connections setup with the connected node. The two modes differ in exchanged messages during steps 1 to 3, while the remaining steps are done the same. The network entry procedure is closely relevant to the handover latency. As to be described in the following section, steps 1 and 2 are essential for a to restore basic communications with a new BS, while all other steps may be bypassed if BSs share existing states of the. Data is always transmitted contention-free on WiMAX links. Contention-free transmission opportunities are set up prior to data transmission in the form of connections. In PMP modes, five types of provisioned service connections of controlled bandwidth can be instantiated to provide different quality of service levels. The five service types are: Unsolicited Grant Service (UGS), Real-time Polling Service (rtps), Non-real-time Polling Service (nrtps), Best Effort (BE), and Extended real-time Polling Service (ertps). Aside from data channels, two or optionally three control channels are instantiated for each SS. In mesh mode, one mesh connection is created between any two neighboring nodes. Quality of service differentiation is on a packet by packet basis. Bandwidth of each mesh connection, as mentioned, is determined with a centralized or distributed scheduling scheme MOBILE WIMAX EXTENSION The IEEE 82.16e-25 standard specifies specific functions, primarily concerning handover across base stations. The handover functions are, however, defined for PMP mode only. In PMP mode, BSs can advertise a list of target BSs based on network topology, while each can also scan for neighboring BSs for inclusion in its own target BSs list. Each maintains up-to-date CINR (carrier-to-interference-andnoise ratio) from the serving BS as well as scanned neighboring BSs, based on which either an or a BS can initiate a handover process. Default handover procedure starts with either an sending a handover request to the serving BS or, vice versa, a BS sending a handover request to the. In either case, the decides the target BS to switch to, sends a handover indication message to the serving BS, and starts synchronizing with the target BS. The handover process can repeat the full network entry procedure, or be shortened to as little as two steps (synchronizing and ranging), provided the previous BS forwards all current connection states of the to the new BS. Two more fast handover options are specified: macrodiversity handover (MDHO) and fast base station switching (FBSS). With either option, the and the serving BS maintain a list of neighboring BSs called the Diversity Set. MDHO is essentially a soft-handover method, with all BSs in the Diversity Set transmitting the same message in the same frequency at the same time, while an receives all transmissions as one. Vice versa, all BSs in the set simultaneously receive messages transmitted by the. FBSS is a hard handover method. An communicates with only one BS at a time, while it can handover to any BS in the Diversity Set with even less effort than the fastest standard handover procedure. That is, an sends to the serving BS either a standard handover request message over the control connection or a predefined codeword over a pre-allocated fast-feedback channel, and then it can synchronize with the target BS. 2 of 7

3 The MDHO/FBSS options do have a downside by requiring all BSs to operate in the same frequency channel and transmit in synchronized time frames, rendering very limited network capacity and scheduling flexibility PHYSICAL LAYER The PMP mode can utilize one of three physical layers: orthogonal frequency-division multiplexing (OFDM), orthogonal frequency-division multiple access (OFDMA), and single carrier modulation. The mesh mode, on the other hand, is only supported by OFDM according to the standard. In [8] and [14], efforts were made to realize the OFDMA physical layer for supporting the mesh mode frame structure. Tactical Network Gateway Core Command Network Tactical Network : Mesh BS : Mesh SS Figure 1. The proposed network model 3. NETWORK MODEL The network model considered in this paper is illustrated in Figure 1. The network is built with a number of BSs deployed along pathways in a battlefield and is connected to the core network via a number of backhaul-enabled BSs (e.g., via satellite links). The BSs are configured in mesh mode, with the backhaul-enabled BSs being Mesh BSs, and all other BSs being Mesh SSs. Mobile battle units are fast moving vehicles traversing the pathways in either direction. To maintain persistent communication on the move, the vehicles are to be s communicating with and handing over across BSs along the path. The s and BSs, therefore, must be operated in the PMP mode to leverage the mobility support. To fulfill this model, each BS is equipped with dual radios, one operated in mesh mode and the other in PMP mode, while each is equipped with one PMP mode radio. The protocol architecture for the BSs and an is shown in Figure 2. Mesh BS Application Mobile IP home/foreign agents IP Mesh SS Transport (TCP, UDP) MAIGR MAIGR IP PMP Mesh LINK + PHY LINK + PHY PMP Mesh LINK + PHY LINK + PHY PMP LINK + PHY Figure 2. The proposed protocol architecture 3.1. BASE STATIONS All BSs, Mesh BSs and Mesh SSs, participate in mesh construction with their mesh mode radios. From a Mesh SS s perspective, its mesh radio provides a backhaul connection to the core network. The mesh connectivity is established upon deployment, and the mesh topology depends on the BS s positions and their transmit power. Bandwidth of each mesh connection is negotiated upon deployment. To avoid single points of failure, a distributed scheduling scheme is assumed to be used. The mesh routing agent on each BS mesh radio implements the proposed Mobility-Aware Intra-Gateway Routing (MAIGR) protocol. The Mesh BSs are gateways to the core command network, which is assumed to be a classical or ad hoc IP network, for which the Mesh BSs shall support its respective routing protocols. To support seamless IP mobility, Mobile IP is assumed to be supported. Each Mesh BS implements Mobile IP home agent and foreign agent services, and a dynamic host configuration protocol (DHCP) service for assigned addresses upon their entry. Each BS has a distinct range of IP addresses to allocate to s, while each retains its assigned address throughout the network; the address times out only after long durations of inactivity (no messages destined for an or no periodic presence indications sent from an ) MOBILE STATIONS s communicate through a BS in range using their PMP radios. Upon network entry, each acquires three control connections and one data connection with the initial BS. The specifies one among the five provisioned services and the desired bandwidth for its data connection. All connections, once instantiated, will persist across handovers until the s request to terminate them. Each address, once assigned, also persists until the exits the network and the address timeouts unrefreshed. Transport protocol connections (TCP, UDP) are maintained persistently across handovers with their retained IP addresses, the BS full-state handover support, and the proposed MAIGR protocol. 3 of 7

4 4. ROUTING AND SCHEDULING FOR FAST 4.1. ROUTING Message routing is accomplished in two separate domains. Exterior to the Mesh BSs is the IP-based core network. Routing in the exterior domain is done with IP routing with seamless mobility protocols such as Mobile IP. IP and Mobile IP routing protocols are deployed as is at the Mesh BSs. Interior to the Mesh BSs is the intragateway mesh domain. Routing in the mesh domain is based on the MAIGR protocol in separate intra-gateway routing zones. An intra-gateway routing zone is defined with respect to each Mesh BS, enclosing the Mesh BS and all Mesh SSs that declare the Mesh BS as their gateway. Typically but not necessarily, a Mesh SS declares a closest Mesh BS to be its gateway. Originally defined in [15], Mobile IP utilizes home agents to assign home addresses to s and foreign agents to assign care-of addresses for s entering a new network. A home agent is the default gateway for an s home network where it has acquired its home address. The home agent always caches the most recent incoming packets for an in a limited-size buffer. Once an enters a new network, it registers with a foreign agent, who assigns to the a care-of address and notifies to its home agent of the care-of address. Once informed, the home agent starts tunneling cached packets and new packets for the towards the care-of address. Optionally, the home agent may notify Mobile-IP-enabled senders to redirect their future packets to the care-of address directly. Assured of seamless mobility, the continues using its home address for sending and receiving IP packets via the foreign agent as its default gateway. For the proposed network, Mobile IP is deployed by having each Mesh BS host the home agent and foreign agent services. Hence, an acquires its home address with the Mesh BS of the first connected intra-gateway routing zone. Then, it registers with a new foreign agent whenever entering a new routing zone. Re-association with a new foreign agent represents an opportunity of route optimization via a closest backhaul link, since it usually results in a shorter and more reliable route to a communication endpoint in the core network. The frequency of such re-association is determined by the choice of routing zone sizes. The signaling latency of such re-associations, to be shown shortly in the following, is masked by the MAIGR protocol and has minimal effects to the communication continuity. In the case of scarce backhaul bandwidth, the Mesh BS foreign agents can selectively bypass the re-association procedure, and the communication will persist transparently. Within each intra-gateway routing zone, each BS executes the MAIGR protocol to: 1) route packets from a towards the zone s Mesh BS, and 2) route packets from a mesh or backhaul link towards a. The protocol maintains the following: (1) Next hop towards closest Mesh BS: Upon deployment and periodically, Mesh BSs send a flooding message with a forwarding hop count updated by all relaying Mesh SSs. The message ends at another Mesh BS or a specified maximum hop count. Each Mesh SS records the next hop towards the least hop-distance Mesh BS. (2) Next hop towards an, at the serving BS: At the current serving BS of an, the next hop is the connection identifier (CID) of the s data connection. The routing table is updated during network entry or handover. (3) Next hop towards an, at a non-serving BS: At any non-serving BS, the next hop is either a mesh link CID or unknown. In non-trivial cases, the must be associated with another BS, which need not be in the same routing zone. A BS acquires knowledge of next hop towards the when the enters the network and/or when it hands over to a different BS by: when receiving from a neighboring BS a forwarded packet sent by an unknown, record the BS as next hop to the. when notified of a handover of a currently associated, record the target BS as next hop to the. (4) Next hop towards an exterior network: For Mesh SSs, next hop towards an exterior network is always its Mesh BS. For Mesh BSs, next hop towards an exterior network is a pointer to its IP routing agent. Upon an s initial network entry, it sends out a DHCP request to the closest BS for acquiring its home address. The request is forwarded towards the Mesh BS (home agent) by potentially multiple Mesh SSs, who will all have acquired the next hop towards the. Upon each handover, a handover indication message indicating the target BS is sent to the serving BS. The network layer is informed of the handover with the target BS address for updating the next hop to the. Note that the target BS can belong to a routing zone different from that of the serving BS. When an moves into a new routing zone, its incoming packets are delivered uninterrupted over the mesh from the previous routing zone. Until the time the new zone s foreign agent establishes re-association with the home agent and starts receiving packets via the new zone s backhaul link, the packets continue to be delivered over the mesh and the transition is transparent to the. While it may potentially cause out-of-order arrivals from the mesh and 4 of 7

5 backhaul links, it assures that no packets are dropped due to no route to the at any time SCHEDULING For dual-radio BSs and single-radio s deployed as in Figure 1, scheduling is done for the mesh and PMP radios independently. All mesh radios are configured in the same frequency channel to maximize mesh connectivity. Coordinated distributed scheduling as defined in [3] is assumed, such that the mesh radios are each allocated contention-free slots in the control subframe to request and respond to bandwidth change requests. For mesh links, bandwidth in terms of bytes per frame is the only schedulable entity, which is assumed to be assigned with a dynamic bandwidth allocation scheme as [12], or a static algorithm that assigns even bandwidth share to all contending links. Each PMP radio is configured in a frequency channel different from that of the mesh radios. If FBSS fast handover is supported, all PMP radios are configured with the same frequency channel and synchronized frames. If the standard handover procedure is supported, each BS is assigned a frequency channel different from its neighboring BS s; an scans and synchronizes to the closest BS s frequency initially, and switches to the target BS s frequency during handover. For scheduling, each requests for a desired bandwidth upon initial entry. If granted, the same bandwidth persists across handovers as long as bandwidth is available. Dynamic service changes according to the provisioned service definitions and admission control methods, when applicable, are handled by each BS via distributed scheduling messages. 5. SIMULATION STUDIES 5.1. SIMULATOR SETUP The proposed solutions were implemented as extensions to the network simulator ns-2 and the NIST IEEE extension ( release) [16]. The NIST extension models the IEEE PMP mode with a single static bandwidth allocation scheme, and the IEEE 82.16e-25 standard handover. All BSs and s are simulated using the NIST node model. Extensions were made for simulating mesh mode operation and BS-supported handover. Table 1 lists the key simulation parameters. Based on the protocol architecture shown in Figure 2, for each node, a routing agent is implemented to model the MAIGR protocol, Mobile IP, and the Mesh BS gateway functions. Mesh links are assumed to have contentionfree schedules assigned within each BS s two-hop neighborhood and hence are modeled using a wired connection with 19 Mbps per link bandwidth and 3 ms link propagation latency. The links are NIST PMP connections. Accounting for the uplink and downlink TDD ratio and the scheduling overheads, the effective bandwidth is Mbps uplink and Mbps downlink shared by all s associated with a base station SIMULATED SCENARIOS AND RESULTS The simulated network model is illustrated in Figure 3, consisting of three consecutive routing zones, each having seven base stations: one Mesh BS at the center and three Mesh SSs on each side. Three mobility patterns were studied: 1) a convoy of 7 vehicles in constant 4 m intervals moving in the forward direction at a common speed of 288 km/hr (8 m/sec), 2) two convoys of 3 vehicles in 4 m intervals moving in opposite directions at 288 km/hr speed, and 3) one convoy of 7 vehicles in 4 m intervals moving in the forward direction at 288 km/hr for 25 seconds, after which the entire convoy turned to move in the opposite direction. In each experiment, each vehicle instantiates a TCP connection to the sink node on the core network. Uplink ( sink) and downlink (sink ) TCP traffic was studied in two separate experiments. The mobility patterns were artificial for exercising the protocol functionalities. Routing Zone (S: Mesh SS, B: Mesh BS) 1 km S S S B S S S Internet Sink Tactical Net Gateway Zone 1 Zone 2 Zone 3 Figure 3. Simulated network model Table 1. Simulated IEEE and TCP parameters Parameter Value Frequency Bandwidth 5 MHz Frame Duration.4 seconds Scan Duration 5 frames (.2 seconds) Scan Iterations 2 Modulation OFDM_64QAM_3_4 Scheduler Round Robin Distance between 2 BSs 1 km Per backhaul link rate/latency 1 Mbps/3msec BS coverage Range 8 m Uplink-to-Downlink Ratio 4:1 TCP Variant TCP Reno Max TCP Window Size 32 5 of 7

6 Figure 4. Uplink per- throughput in scenario Figure 6. Uplink per- throughput in scenario Figure 5. Downlink per- throughput for scenario 2 All WiMAX parameters adhered to the default values in the NIST extension [16] if not specified otherwise. Figures 4 and 5 show the uplink and downlink TCP throughput for an in the first mobility scenario, while Figures 6 and 7 show the same for the second scenario. The third scenario had throughput similar to that of the first scenario and hence its throughput figures are not included here. With the programmed speed, each undergoes a handover every 12.5 second. From the four figures, it was consistently observed that a dip in throughput accompanied each handover operation. Each dip was found to be due to one (in scenario 1) or three closely located (in scenario 2) TCP timeout events. The duration of the dip was assessed by the time between the last TCP acknowledgement (ACK) arrival at the sender before a timeout and the first ACK arrival after a timeout, denoted as the inactive time. In scenario 1, the average inactive time was.6 seconds for uplink and 1.7 seconds for downlink connections; in scenario 2, the average inactive time was.2 seconds for uplink and 1.1 seconds for downlink connections. The periodic TCP timeout was confirmed to be due to the scanning and handover procedures. With the standard handover procedure simulated, each monitors the signal-to-noise ratio of its received packet; when the ratio is lower than the link-going-down-factor (1.8), it requests Figure 7. Downlink per- throughput in scenario 2 with the current BS for two.2 second scanning periods for locating a target BS. During scanning periods packet transmissions in both ways are halted. The two scanning periods are interleaved with a.2 second pausing, during which normal packet transmissions can proceed. After the second scanning period, packet transmissions resume for another 2 frames (.8 seconds), after which the starts the handover procedure. During the handover, normal packet transmissions are halted until the acquires a new data connection with the target BS. Take the uplink experiment in scenario 1 for example, TCP connections were able to tolerate the halt during the first scanning period without loss, but the TCP timeout timer duration (3.2 second in the scenario) could not sustain the halt due to the second scanning period and the closely following handover. In the second scenario, with less s sharing the bandwidth, the TCP round trip time and hence the timeout timer duration (.4 second) is even lower, causing one timeout for each scanning and handover period. It was noted that the MAIGR protocol updates the routing information at the time the handover procedure initiates; as soon as the handover procedure was completed, the routing tables were already updated and incurred no further delays. The overall throughput is also shown in each figure. In all scenarios, the aggregate uplink TCP throughput of 6 of 7

7 all s was approximately 45~55 percent of the available bandwidth, while the aggregate downlink TCP throughput was about 85~98 percent of the bandwidth. In Figure 6 and 7, the throughput was seen to be halved in the middle of the run. This was during the time two convoys met at the same base station. The BS scheduler grants each vehicle whatever bandwidth it requests for in a round-robin fashion and resulted in equal sharing. Bandwidth sharing in these scenarios has been observed to be fair. Overall, it was concluded that TCP throughput was affected mostly due to the required scanning and handover latencies, while routing latencies were effectively masked by the MAIGR protocol. TCP throughput degrades primarily due to timeouts. Additional simulations were conducted over scenarios with paths of higher latencies and delaybandwidth products. The timeout occurrences reduced due to the corresponding higher TCP timeout durations. TCP throughput dips remained to be seen due to out-oforder ACK arrivals halving the TCP sending window, but it recovered quickly due to the duplicate ACK arrivals LIMITATIONS AND FUTURE WORK The simulation model is still under continued development. The current model has made simplified assumptions of the mesh link transmission characteristics (error-free and full-duplex). It was also assumed that all s had uniform bandwidth demands and mobility patterns, with which grant conflict effects across handovers were not modeled. The different provisioned service types intended to support different traffic types at different quality of service levels have not been considered either. The mobility patterns and network scales remain to be extended for further studies. 6. CONCLUSIONS The paper proposes a deployment strategy for Mobile WiMAX mesh networks and an integrated routing and scheduling approach to support fast moving vehicles persistent connection to the tactical communication network. The solution exploits the connected nature of a wireless mesh network to minimize communication interruption during handovers. The Mobile IP and MAIGR protocols together realize seamless mobile transport connections. The solutions were assessed using the ns-2 simulator with extensions of the dual-radio mesh network architecture and the integrated routing protocols over an IEEE PMP model. REFERENCE [1] Army-technology.com, US Army s CERDEC to Evaluate WiBro, news/ news1298.html, accessed in May 27. [2] IEEE, IEEE Std 82.16r-25 and IEEE Std /Cor1-25, getieee82/82.16.html, access in May 27. [3] IEEE, IEEE Std , org/getieee82/82.16.html, access in May 27. [4] Nortel Networks, News Release: Nortel Demonstrates Commitment to Leadership in 4G Mobile Broadband, Oct. 1, 26. [5] Agilent Technologies, News Release: Understanding WiMAX, index.html, Feb. 1, 26. [6] K. Wongthavarawat and A. Ganz, IEEE Based Last Mile Broadband Wireless Military Networks with Quality of Service Support, in IEEE MILCOM, Vol. 2, pp , 23. [7] B. K. Hartzog and T. X. Brown, Wimax Potential Commercial Off-The-Shelf Solution for Tactical Mobile Mesh Communications, in IEEE MILCOM, pp.1-7, 26. [8] M. Sherman, K. M. Mcneill, K. Conner, P. Khuu, and T. Mcnevin, A PMP-Friendly MANET Networking Approach for WiMAX/IEEE 82.16, in IEEE MILCOM, pp.1-7, 26. [9] B. Bennett and P. Hemmings, Operational Considerations of Deploying Wimax Technology as a Last-Mile Tactical Communication System, in IEEE MILCOM, pp.1-7, 26. [1] H. Wei, S. Ganguly, R. Izmailov, and Z. Haas, Interference-Aware IEEE WiMax Mesh Networks, in IEEE VTC, Vol.5, pp , 25 [11] C. Schwingenschlogl, V. Dastis, P.S. Mogre, M. Hollick, and R. Steinmetz, Performance Analysis of the Real-time Capabilities of Coordinated Centralized Scheduling in Mesh Mode, in IEEE VTC, Vol.3, pp , 26. [12] M. S. Kuran, B. Yilmaz, F. Alagoz, and T. Tugcu, Quality of Service in Mesh Mode IEEE Networks, in SoftCOM, pp , 26. [13] M. Cao, W. Ma, Q. Xhang, and X. Wang, Analysis of IEEE Mesh Mode Scheduler Performance, IEEE Transactions on Wireless Communications, Vol.6, No.4, pp , 27. [14] Y. Lebrun, F. Horlin, A. Bourdoux, and L. Van der Perre, Feasibility Study of the Mesh Extension for the IEEE 82.16e Communication System, in IEEE VTC, pp.93-96, 26. [15] IETF, RFC 22 IP Mobility Support, C. Perkins Ed., [16] NIST, Seamless and Security Project: Software Tools, accessed in May of 7