Comparative Study of Hidden Node Problem and Solution Using Different Techniques and Protocols

Abstract— Hidden nodes in a wireless network refer to nodes that are out of range of other nodes or a collection of nodes. We will discuss a few problems introduced by the RTS/CTS mechanism of collision avoidance and focus on the virtual jamming problem, which allows a malicious node to effectively jam a large fragment of a wireless network at minimum expense of power. We have also discussed WiCCP (Wireless Central Coordinated Protocol) which is a protocol booster that also provides good solution to hidden nodes. Index Terms— Hidden Terminal Problem, CSMA, Hidden Terminal, Exposed Terminal, MACA
——————————  —————————— 1 HIDDEN TERMINAL PROBLEM IDDEN nodes are the nodes that are not in the range
of other nodes or a group of nodes. Take a physical star topology with an access point with many nodes surrounding it in a circular fashion: Each node is within communication range of the access point, but the nodes cannot communicate with each other as they do not have physical connection to each other. In a wireless network, it is possible that the node at the far edge of the access point’s range, known as r, can see the access point, but it is unlikely that the same node can see a node on the opposite end of the access point’s range, r2. These nodes are known as hidden. The problem is when nodes r and r2 start to send packets simultaneously to the access point. Since node r and r2 cannot sense the carrier, Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) does not work. To overcome this problem, handshaking is implemented in conjunction with the CSMA/CA scheme. The same problem exists in a MANET [2]. The hidden node problem can be observed easily in widespread (>50m radius) WLAN setups with many nodes that use directional antennas and have high upload. This is why IEEE 802.11 is suited for bridging the last mile, for broadband access, only to a very limited extent. Newer standards such as Wi-MAX assign time slots to individual stations, thus preventing multiple nodes from sending simultaneously and ensuring fairness, even in over- subscription scenarios [2].
IEEE 802.11 uses 802.11 RTS/CTS acknowledgment and handshake packets to partly overcome the hidden node problem. RTS/CTS is not a complete solution and may decrease throughput even further, but adaptive acknowledgments from the base station can help too.

Figure. 1 Hidden Node [3] 2 CARRIER SENSE MULTIPLE ACCESS (CSMA) In Carrier Sense Multiple Access: 1. If the channel is idle then transmit. 2. If the channel for communication is free then it is going to transmit without any precaution that there might be collision. 3. If the channel is busy, wait for a random time. 4. Waiting time is calculated using Truncated Binary Exponential Backoff (BEB) algorithm.

Fig. 2 Exposed Nodes [3]

H ————————————————  Viral V. Kapadia1 is with the Department of Computer Engineering, Birla Vishvakarma Mahavidyalaya, Vallabh Vidyanagar,, Gujarat, India.
 Sudarshan N. Patel2 is with the Department of Computer Engineering, A.D. Patel Institute of Technology, New Vallabh Vidyanagar, Gujarat, India.
 Rutvij H. Jhaveri3 is with the Department of Computer Engineering and Information Technology, Shri S’ad Vidya Mandal Institute of Technology, Bharuch, Gujarat, India.

JOURNAL OF COMPUTING, VOLUME 2, ISSUE 3, MARCH 2010, ISSN 2151-9617 HTTPS://SITES.GOOGLE.COM/SITE/JOURNALOFCOMPUTING/ 66 3 HIDDEN TERMINALS The notorious hidden node problem deals with a configuration of three nodes, like A, B, and C in Figure 1, whereby B is within the transmission range of A and C, while C is outside the range of A. In a situation like this, C will not be able to detect the ongoing transmission of A to B by carrier sensing and, consequently, it can inadvertently interfere with B’s reception of A’s packet [1]. The transmission range of a node A is defined as the area inside which other nodes are able to correctly receive A’s packets. On the other hand, the carrier sense range of A is the area encompassing those nodes whose transmission A can perceive (carrier sense) while not necessarily being able to receive the transmitted packets [1]. Generally, it is unreasonable to assume that the two areas are always the same, e.g., the carrier sense range can be twice the transmission range [7]. Suppose that every node in Figure 1 has the same transmission range (represented by a solid circle). Node C is out of the transmission range of node A and thus would appear as a hidden node to A. However, if the carrier sense range of C is larger than the transmission range of A (see the dashed circl

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