Resource allocation Managemen in wireless mesh (802.16) networks by mcgerald


									Routing & Scheduling Algorithm of IEEE 802.16 Mesh Backhaul Network for Radio Recourse Management (RRM)                          1

    Routing & Scheduling Algorithm of IEEE 802.16 Mesh Backhaul
           Network for Radio Recourse Management (RRM)
                                                        Konark kelaiya
                                             Department of Electrical Engineering
                                          Veermata Jeejabai Technical Institute (VJTI)
                                                  Matunga, Mumbai- 400019
                                               E- mail:

     ABSTRACT: The paper investigates the resource management issues in IEEE 802.16 mesh backhaul network. The
     aim is to exploit the multipath routing for efficient utilization of wireless radio resources, and thus provides spectral
     efficiency. The silent feature of scheduling algorithm is to allow dispatching data blocks dynamically, based on
     current buffer condition & route condition without a priori knowledge of traffic demand and thus useful for
     heterogeneous traffic load that is supported by IEEE 802.16 Netw ork which is a strong candidate in Wireless
     Networking aspects. The routing algorithm uses the application layer load demand information and PHY layer
     interference information.

     The routing algorithm designed on the basis to select route that provides least mean path interference from multiple
     hop and the scheduling algorithm designed to find maximum number of concurrent transmission that satisfies the
     Signal- to- interference plus noise ratio (SINR) constraints. The iterative allocation continues in both the algorithm
     until there is no unallocated capacity request.

     Keywords IEEE 802.16, Routing and Scheduling Algorithm, Spectral Utilization, SINR.

INTRODUCTION                                                           Radio resource management (RRM) is an important
                                                                    issue for broadband network operation. In 802.16 multihop

I  EEE 802.16 standard [1], also known as WiMax has
   been specifically designed to provide wireless last-mile
broadband access in the Metropolitan Area Network
                                                                    relay networks, RRM can be conducted through multihop
                                                                    route selection and time frame scheduling.
                                                                       To achieve better system performance and high spectral
(MAN), feasible alternative to DSL, T1 and Cable modem.             efficiency, route construction, route selection, and data
In order to provide the coverage and data rates envisioned,
                                                                    frame dispatching are coordinated.
even on uneven terrain, the use of multihop
Communication seems desirable. Hence WiMax supports a
Mesh mode in which unlike the traditional cellular systems,
the nodes can communicate without having a direct
connection with the base station.
   IEEE 802.16 technology is best known for its single hop
point to Multipoint (PMP) mode operation. However
recently IEEE 802.16 has introduced a multihop relay
extension of PMP mode.
   In the PMP mode, an SS directly connects to a BS
through a one-hop wireless connection. In mesh mode, an
SS can route traffic to the BS via multiple intermediate SSs
or transmit to another SS directly, as shown in Figure 1.
   In general, an IEEE 802.16 multihop relay network
consists of a node with backhaul connection toward the
outside network and several other nodes. The node with
backhaul connection is termed the mesh BS, while other              Fig. 1: An IEEE 802.16 mesh network: a new node joins the
nodes are termed mesh SSs. When a new node would like                                       network
to join in an existing active mesh, the new node, which is
termed the candidate node (CN), initiates the network entry         IEEE 802.16 MESH MODE OPERATION
process. In the existing active mesh network, a node termed
the sponsoring node (SN) sponsors and manages the                   In IEEE 802.16 Mesh mode, a Mesh base station (BS)
network entry process. After the network entry process              provides backhaul connectivity of the mesh network and
completes, the CN is attached to the SN.                            controls one or more subscriber stations (SS). When
176                                                                      Mobile and Pervasive Computing (CoMPC–2008)

centralized scheduling scheme is used, the Mesh BS is           destination node D. Figure 2 illustrates the routes for
responsible for collecting bandwidth request from               multiple hop relay network.
subscriber stations and for managing resource allocation.
   Mesh Network entry process involves following
messages shown in Table 1.

      Table 1: Overview of Entry Process Messages

              Message Type               Acronym
       Mesh Network Configuration      MSH- NCFG
       Mesh network entry              MSH- NENT
       Mesh distributed Schedule       MSH- DSCH
       Mesh centralized schedule       MSH- CSCH
       Mesh centralized                MSH- CSCF

   Mesh Network Configuration (M S H-NCFG) and Mesh
Network Entry (MS H-NENT) messages are used for                          Fig. 2: Multiple Hop network construction
advertisement of the mesh network and for helping new
nodes to synchronize and to joining the mesh network.
                                                                   Accordingly here e  stablish multiple routes from A to D.
Active nodes within the mesh periodically advertise MSH-        The number shown next to a link is the normalized radio
NCFG messages with Network Descriptor, which outlines
                                                                resource required to transmit a fixed data block through the
the basic network configuration information such as BS ID
                                                                link them together.
number and the base channel currently used. A new node
that plans to join an active mesh network scans for active
networks and listens to M S H-NCFG message. The new
                                                                Route 1
node establishes coarse synchronization an d starts the         In the first route construction step, shown in Figure 3, the
network entry process based on the information given by         first route A-C-D is constructed and updates the bandwidth
MSH-NCFG. Among all possible neighbors that advertise           usage. Both residual radio resources of selected links and
MSH-NCFG, the joining node (which is called Candidate           interfered links are updated.
Node in the 802.16 Mesh mode terminology) selects a
potential Sponsoring Node t o connect to. A Mesh Network
Entry message (MSH-N ENT) with Net Entry Request
information is then sent by the Candidate Node to join the
   The other messages are for centralized scheduling. The
request and grant process uses the Mesh Centralized
Scheduling (M S H-CSCH) message type. A Subscriber
Station’s capacity requests are sent using the M S H-CSCH:
Request message to the Subscriber Station’s parent node.
After the Mesh BS determines the resource allocation
results, the MSH-CSCH: Grant is propagated along the
route from Mesh BS. To disseminate the link, node, and
scheduling tree configuration information to all participants
within the mesh network, the Mesh Centralized Scheduling
Configuration ( M S H-CSCF) message is broadcasted by
the Mesh BS and then re-broadcasted by intermediate                        Fig. 3: First Route through A – C – D
                                                                   Circle shows the interfering links.
BACKHAUL N/W                                                    Route 2
The objective of this section is to describe and analyze the    Another route chosen is A-E-F-G-D, however A – B – D
algorithm for routing. The algorithm is based on to create      initially looks a shorter route but it will cause more
maximum disjoints routes from the source node S to the          interference.
Routing & Scheduling Algorithm of IEEE 802.16 Mesh Backhaul Network for Radio Recourse Management (RRM)                    177

   In Figure 4, the second route is shown after these two          The route construction algorithm first adds the source
routes are constructed; the route selection algorithm deter-   node S, which is also the mesh BS, which serves as the
mines which route will be used for a given traffic flow.       gateway of the wireless mesh backbone. Until there are no
                                                               more resources to create a route, a route Γ D to destination
                                                               node D is computed in each route construction iteration,
                                                               and the wireless resource usage from the available wireless
                                                               resource is deducted. A directional link from node i to node
                                                               j is denoted as Lij with link rate rij . Radio resources are
                                                               calculated in normalized time. Residual radio resource
                                                               capacity is represented as tij , which is the normalized
                                                               residual usage time of link Lij . During a route construction
                                                               iteration, there are several node addition iterations (lines 8
                                                               through 22) that add one node to a routing tree in each
                                                               iteration. First, the tree γ is initialized and one node is
                                                               added each time to the tree γ and the set of already added
          Fig. 4: second route A – E – F – G – D               nodes In Route. The mesh BS node, which is the source
                                                               node S, is the first node to be added.
  The algorithm [2] shown as follow:                               Uγ(n) is the temporary radio resource usage along the
                                                               multihop route from S toward node n on γ. Since our
          Table 2: Route Construction algorithm                wireless mesh network model considers interference and
                                                               has different link rates at different wireless links, it is
                                                               difficult to directly measure radio resource usage in bits per
                                                               second across spatial locations. Calculating radio resources
                                                               in normalized time (tij and tij ) while considering interfered
                                                               links, and then converting to link capacity in bits per
                                                               second (Rij ) at different spatial locations.
                                                                   The criteria for route selection is to minimize radio
                                                               resource usage (in terms of normalized time) along the
                                                               multihop route. The notation Uγ(n) represents the multihop
                                                               radio resource cost from S to node n using routing tree γ.
                                                                   The notation > is used to indicate interference between
                                                               two links. Lij > L uv implies that link L ij interferes with link
                                                               Luv (when Luv is active, Lij cannot be active). We also
                                                               define Lij > Lij . The time of a bit transmitted over a link Lij
                                                               is 1/Rij. As Lij > Luv, L uv cannot be active during this 1/Rij
                                                               time duration. The wireless radio resource cost of
                                                               transmitting a bit over Lij is 1/Rij on Lij plus 1/Rij on the
                                                               interfered link Luv. At the beginning of the node addition
                                                               iteration, nodes already in the route examine the
                                                               neighboring nodes and pick a candidate child node with the
                                                               minimum one-hop transmission cost (lines 9 through 12).
                                                               The candidate child node, which has the minimum
                                                               multihop radio resource transmission cost, is added to the
                                                               routing tree. The multihop transmission cost values along
                                                               the route will be updated (lines 16 through 19). The node
                                                               addition iterations continue until Γ D, a route from S to D, is
                                                               derived. After new route _D is given, the cost at Luv for
                                                               transmitting one bit over route Γ D, tuv, is computed (lines
                                                               24 through 26). The ratios of available link resources and
                                                               transmission cost, fij , are calculated to determine the
                                                               bottleneck link, which is the link with the minimum fij
                                                               value. Then the maximum possible wireless resources Φ
                                                               along the route are allocated. After updating the available
                                                               resources and adding the current route Γ D to the set of
                                                               routes, the next available route is calculated.
178                                                                      Mobile and Pervasive Computing (CoMPC–2008)

MESH BS SCHEDULING                                              ∆ = ∆ + dk. After completion of iterative steps on all
                                                                conflict pairs, minimum ∆ resolves all possible interference
The mesh BS, which acts as a gateway, is the coordinator        between P0 and P1 .
of radio resource allocation by scheduling and dispatching
data blocks.                                                                 Table 3: Algorithm to compute ∆
   T he objective of scheduler design based on to maximize
overall data throughput. For this here have presented a
route interference resolving by computing data dispatching
delay between two routes. Figure 5 illustrates the
dispatching of data blocks.

        Fig. 5: Interference between multiple routes

   All links in the paths have the same transmission rates
and data blocks are a fixed size. Let T denote the time to
completely transmit a single block over a link. The current     RESULT
block is sent along path P1, and the second block is sent
along path P2. In the multihop mesh, the block delivery is
sequenced as the following transmission events in P1: GW
? 1, 1 ? 4, 4 ? AP1, each taking T units of time. As can
be seen, the event mesh BS ? 2 can only take place at the
same time as the event 4 ? AP1. The mesh BS has to wait
∆ = 2T units to send on P2 after it has finished dispatching
data for AP1 on link GW ? 1. As can be noted for the same
figure, ∆ = T if the second block is sent along path P3.
Without this waiting, there will be a collision at the
receiver side leading to a decrease in the throughput. Next
present the algorithm to find for any two paths in the mesh
network. Based on finding, the propose pipeline    d
scheduling in dispatching data blocks from the mesh BS
has been described.
   ∆ is computed with iteratrative steps. The scheduling of
P0 is fixed and the scheduling of P1 is delayed to avoid
interfer ence. The initial value of ∆ is set to zero. When an
active conflict pair is found, we compute the necessary
delay value dk to resolve the conflict of ?k, and then update                Fig. 6: Throughput vs. no of nodes
Routing & Scheduling Algorithm of IEEE 802.16 Mesh Backhaul Network for Radio Recourse Management (RRM)                179

CONCLUSION                                                      [2] Wei, H.Y. and Ganguly, S., Design of 802.16 WiMAX-
                                                                    Based Radio Access Network, 17 thIEEE International
With this scheme an efficient route is constructed with a           Symposium on Personal, Indoor and Mobile Radio
time slot scheduling increases the overall normalized               Communications IEEE, Washington, DC, 2006.
throughput of network.                                          [3] Harish Shetiya and Vinod Sharma, Algorithms for Routing
                                                                    and Centralized Scheduling to Provide QoS in IEEE 802.16
REFERENCES                                                          Mesh Networks, WMuNeP’05, October 13, 2005, Montreal,
                                                                    Quebec, Canada.
[1] IEEE, IEEE Standard for Local and Metropolitan Area
    Networks—Part 16: Air Interface for Fixed Broadband         [4] Wei, H.Y., Ganguly, S. , Izmailov, R. and Haas, Z.
    Wireless Access systems—Amendment 2: Medium Access              Interference- Aware IEEE 802.16 WiMax Mesh Networks,
    Control Modifications and Additional Physical Layer             61st IEEE Vehicular Technology Conference, IEEE,
    Specifications for 2–11 GHz, Standard 802.16a-2003, IEEE,       Washington, DC, 2005.
    Washington, DC, 2003

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