The rest of this dissertation is organized as follows: The greedy anti-void routing (GAR) proto-col and the associated proofs of correctness are described in Chapter 2. The three-dimensional greedy anti-void routing (3D-GAR) protocol and the corresponding proofs of correctness are provided in Chapter 3. Chapter 4 proposes the component-based routing platform (CRP) and the energy conserving multicast routing (ECMR) protocol. Chapter 5 shows the greedy fast-shift (GFS) block acknowledgement and the corresponding analytical models. The frame aggregation-based power-saving (FAPS) scheduling algorithm is introduced in Chapter 6.
Chapter 7 draws the conclusions of this dissertation.
Chapter 2
Greedy Anti-Void Routing Protocol
Chapter Overview
In the network layer unicast protocol design for achieving the green wireless access networks, a greedy anti-void routing (GAR) protocol is proposed in this chapter with the main theme of the wireless sensor network (WSN) since the WSN has stringent requirements on the energy saving issues. Exploiting the boundary finding technique for the unit disk graph (UDG), the proposed GAR protocol solves the void problem, i.e., the unreachability problem, incurred by the low-overhead green concept-based greedy forwarding (GF) algorithm associated with increased routing efficiency. The proposed rolling-ball UDG boundary traversal (RUT) is employed to completely guarantee the delivery of packets from the source to the destination node under the UDG settings. The boundary map (BM) and the indirect map searching (IMS) scheme are proposed as efficient algorithms for the realization of the RUT technique.
Moreover, the hop count reduction (HCR) scheme is utilized as a short-cutting technique to reduce the routing hops by listening to the neighbor’s traffic; while the intersection navigation (IN) mechanism is proposed to obtained the best rolling direction for boundary traversal with the adoption of shortest path criterion. In order to maintain the network requirement of the proposed RUT scheme under the non-UDG networks, the partial UDG construction (PUC) mechanism is proposed to transform the non-UDG into UDG settings for a portion of nodes that facilitate boundary traversal. These three schemes are incorporated within the GAR
protocol to further enhance the routing performance with reduced communication overhead.
The proofs of correctness for the GAR scheme are also given in this chapter. Comparing with the existing localized routing algorithms, the simulation results show that the proposed GAR-based protocols can provide better routing efficiency. These proposed GAR-GAR-based protocols can therefore be adopted as the unicast protocols in the green wireless access networks.
2.1 Introduction
A wireless sensor network (WSN) consists of sensor nodes (SNs) with wireless communication capabilities for specific sensing tasks. Due to the limited available resources, efficient design of localized multi-hop routing protocols [7] becomes a crucial subject within the WSNs. How to guarantee delivery of packets is considered an important issue for the localized routing algorithms. The well-known greedy forwarding (GF) algorithm [4] is considered a superior scheme with its low routing overheads. However, the void problem [5], which makes the GF technique unable to find its next closer hop to the destination, will cause the GF algorithm failing to guarantee the delivery of data packets.
Several routing algorithms are proposed to either resolve or reduce the void problem, which can be classified into based and graph-based schemes. In the non-graph-based algorithms [8–19], the intuitive schemes as proposed in [8] construct a two-hop neighbor table for implementing the GF algorithm. The network flooding mechanism is adopted within the GRA [9] and PSR [10] schemes while the void problem occurs. There also exist routing protocols that adopt the backtracking method at the occurrence of the network holes (such as GEDIR, [8], DFS [11], and SPEED [12]). The routing schemes as proposed by ARP [13]
and LFR [14] memorize the routing path after the void problem takes place. Moreover, other routing protocols (such as PAGER [15], NEAR [16], DUA [17], INF [18], and YAGR [19]) propagate and update the information of the observed void node in order to reduce the probability of encountering the void problem. By exploiting these routing algorithms, however, the void problem can only be either (i) partially alleviated or (ii) resolved with considerable routing overheads and significant converging time.
On the other hand, there are research works on the design of graph-based routing al-gorithms [5, 20–27] to deal with the void problem. Several routing schemes as surveyed in [20] adopt the planar graph [28] derived from the unit disk graph (UDG) as their network topologies, such as GPSR [5], GFG [21], Compass Routing II [22], AFR [23], GOAFR [24]
GOAFR+ [25], GOAFR++ [20], and GPVFR [26]. For conducting the above planar graph-based algorithms, the planarization technique is required to transform the underlying network graph into the planar graph. The Gabriel graph (GG) [29] and the relative neighborhood graph (RNG) [30] are the two commonly-used localized planarization techniques which aban-don some communication links from the UDG for achieving the planar graph. Nevertheless, the usage of the GG and RNG graphs has significant pitfalls due to the removal of critical communication links, leading to longer routing paths to the destination. As shown in Fig.
2.1, the nodes (NS, ND) are considered the transmission pair; while NV represents the node that the void problem occurs. The representative planar graph-based GPSR scheme can not forward the packets from NV to NA directly since both the GG and the RNG planarization rules abandon the communication link from NV to NA. Considering the GG planarization rule for example, the communication link from NV to NAis discarded since both NJ and NK are located within the forbidden region, which is defined as the smallest disk passing through both NV and NA. Therefore, based on the right-hand rule, the resulting path by adopting the GPSR protocol can be obtained as {NS, NV, NJ, NK, NA, NB, NX, NY, NZ, ND}. The two unnecessary forwarding nodes NJ and NK are observed as in Fig. 2.1.
Furthermore, the planar graph-based schemes, e.g., the GPSR and GOAFR++ algorithms, will in general lose their properties of guaranteed packet delivery due to the unexpected net-work partition within the non-UDG netnet-works. The reason is also attributed to the situations that critical communication links are removed by adopting the GG and RNG planarization techniques. In order to resolve the network partition problem, a cross-link detection pro-tocol (CLDP) is therefore suggested in [31] for planarization of the underlying non-UDG networks. However, for the purposes of both detecting the cross links and planarizing the underlying network, the CLDP planarization will introduce excessive control overhead since all communication links are required to be probed and frequently traversed. Moreover, the
sV
Figure 2.1: The example routing paths constructed by using the proposed GAR protocol and the conventional schemes under the existence of the void problem.
problems of multiple cross links and concurrent probing can further enlarge the total number of communication overhead within the CLDP technique.
Due to the drawbacks of link removal from the planar graph-based algorithms, the adop-tion of UDG without planarizaadop-tion for the modeling of underlying network is suggested. A representative UDG-based routing scheme, i.e., the BOUNDHOLE algorithm [27], forwards the packets around the network holes by identifying the locations of the holes. However, due to the occurrence of routing loop, the delivery of packets can not be guaranteed in the BOUNDHOLE scheme even if a route exists from the source to the destination node. For example, as shown in Fig. 2.1, it is assumed that the node NX is located within the transmis-sion range of NB; while it is considered out of the transmission ranges of nodes NA and NE. Based on the minimal sweeping angle criterion within the BOUNDHOLE algorithm, NA will choose NE as its next hop node since the counter-clockwise sweeping from NV to NE (hinged at NA) is smaller comparing with that from NV to NB. Therefore, the missing communication link from NB to NX can be observed, and the resulting path by adopting the BOUNDHOLE
scheme becomes {NS, NV, NA, NE, NF, NG, NH, NV}. It is observed that the undeliverable routing path from the source node NSis constructed even with un-partitioned network topol-ogy. Moreover, two cases of edge intersections within the BOUNDHOLE algorithm [27] result in high routing overhead in order to identify the network holes.
In this chapter, a greedy anti-void routing (GAR) protocol is proposed to guarantee packet delivery with increased routing efficiency by completely resolving the void problem based on the UDG setting. The GAR protocol is designed to be a combination of both the conventional GF algorithm and the proposed rolling-ball UDG boundary traversal (RUT) scheme. The GF scheme is executed by the GAR algorithm without the occurrence of void problem; while the RUT scheme is served as the remedy for resolving the void problem, leading to the assurance for packet delivery. Moreover, the correctness of the proposed GAR protocol is validated via the given proofs. The implementation and computational complexities of the GAR protocol are also explained, including that for the proposed boundary map (BM) and the indirect map searching (IMS) algorithm for the BM construction.
Furthermore, the associated three additional enhanced mechanisms are also exploited, in-cluding the hop count reduction (HCR), the intersection navigation (IN), and the partial UDG construction (PUC) schemes. The HCR scheme is a short-cutting technique that acquires in-formation by listening to one-hop neighbor’s packet forwarding; while the other short-cutting method as proposed in [32] requires information from two-hop neighbors which can result in excessive control packet exchanges. With the occurrence of void node, the IN mechanism determines its rolling direction based on the criterion of smallest hop counts for boundary traversal. Similar to the CLDP method [31], the IN scheme acquires information over mul-tiple hops in order to process its algorithm. However, it is required for the CLDP technique to traverse all the communication links in the networks; while the IN scheme only exploits a small portion of network links for conducting the boundary traversal. Moreover, in order to meet the network requirement for the RUT scheme under non-UDG network, the PUC mechanism is utilized to transform the non-UDG into the UDG setting for the nodes that are adopted for boundary traversal.
By adopting these three enhanced schemes, both the routing efficiency and the
communi-cation overhead of the original GAR algorithm can further be improved. The performance of the proposed GAR protocol and the version with the enhanced mechanisms (denoted as the GAR-E algorithm) is evaluated via simulations under both the UDG network for ideal case and the non-UDG setting for realistic scenario. The simulation results show that the GAR-based schemes can both guarantee the delivery of data packets and pertain better routing performance under the UDG network. On the other hand, comparing with the other existing schemes, feasible routing performance with reduced communication overhead can be provided by the GAR-based algorithms within the non-UDG network environment.
The remainder of this chapter is organized as follows. Section 2.2 describes the network model and the problem statement. The proposed GAR protocol is explained in Section 2.3;
while Section 2.4 provides the practical realization of the GAR algorithm. Section 2.5 exploits the three enhanced mechanisms, including the hop count reduction (HCR), the intersection navigation (IN), and the partial UDG construction (PUC) mechanisms. The performance of the GAR-based protocols is evaluated and compared in Section 2.6. Section 2.7 summarizes this chapter.