Authors in  proposed a hybrid access protocol known, as contention time-division multiple access (C- TDMA). C-TDMA shows some features of contention- based (slotted-ALOHA) and reservation-based (PRMA) protocols. It has been recommended for use in the uplink of future European multimedia distribution systems. A simple Markov model is proposed to describe C-TDMA behavior. Their results in terms of throughput and delay under variable traffic conditions indicate that C-TDMA is able to grant optimum throughput/delay figures for typical multiuser systems. Moreover, for a digital speech scenario, a performance comparison with PRMA demon- strates that C-TDMA yields equivalent performance to PRMA in terms of number of users supported by the system with a limited packet dropping rate.
The reservation-basedTDMA protocols can be classified into two categories: fixed allocation and dynamic allocation. Fixed allocation protocols make slot assignments at the scale of the whole network. They do not have the conflict problem but are not suitable for networks with dynamically changing topologies. In contrast, dynamic allocation protocols, such as FPRP, HRMA, evolutionary-TDMA (E-TDMA), and DRAND, use distributed algorithms to assign slots by coordinating nearby nodes. FPRP is a fully-distributed protocol with a low probability of conflict. Using dynamic slot assignments, FPRP has many advantages, such as being scalable with the network size, suitable for changing topology, and insensitive to node mobility. These merits make FPRP a very promising MAC layer protocol for MANETs.
In Time-dynamic Multiple Access (TDMA) schemes, as a method to optimize resource utilization, each node is assigned a time slot to avoid collisions caused by contention. In , the author proposed a decentralized TDMA mechanism for adaptive control of data traffic. In , the authors proposed the TDMA-based “Distributed Packet Reservation Multiple Access” (D-PRMA) scheme, in which higher transmission priority is given to data and multimedia nodes than to general data nodes. However, the number of time slots allocated to the data and multimedia nodes in D-PRMA is determined from the total number of nodes, meaning that when the number of nodes increases, the system will not scale well.
In recent years, many energy-efficient MAC protocols have been proposed in literature which is classified into two main categories, contention-based and TDMA-based protocols. It has been widely recognized that contentionbased MAC protocols    are the most suitable for wireless sensor networks due to their self- organizing nature. On the other hand, TDMAbased MAC protocols  provide excellent trade-offs between energy savings and throughput performance. In these protocols, where nodes are assumed to be synchronized and accesses the communication channel by scheduling and reservation of time slots. Such protocols by nature preserve energy as they have duty cycle built-in and an inherent collision-free medium access. Their major problem consists in their high complexity due to non-trivial problem of synchronization in WSNs. Managing inter-cluster communication and interference is not an easy task, and the scalability is also not good when compared to contentionbased protocols.
The variety of studies conducted on different protocol suites and different protocol layers in 802.11 MANET environment proves that the built-in protocol functionalities have an positive impact on securing the mobile wireless environment while these methods are compared based on specific metrics for better evaluation  . The proposed method applied for preventing and mitigating IEEE 802.15.4 physical layer attacks, specifically the jamming attacks at the link layer rather than the physical layer . Due to limited resources and lack of centralized network architecture in WSN, the resources the two-tier hierarchical cluster based deployment model is selected. In such deployment model, a specific base station receives data from cluster head sensor nodes. The proposed method implements the modifications on randomly selected base stations where sensor nodes also be- have as base stations on the selected deployment model. The Request to Send/Clear To Send (RTS/CTS) mechanism is so called handshaking mechanism that prevent overhead problem and unnecessary use of “hello” discovery messages on the network . Since the cluster based deployment model is selected for this research, implementation of RTS/CTS mechanism would affect the overall throughput indeed which is used in different mechanisms by the researchers and its impact has proven . The role of CTS mechanism is to silence all wireless stations in its vicinity to avoid collisions and enables the sender of the RTS message to begin data transfer . Such mechanism prevents base stations to receive unexpected and huge amount of data from dif- ferent resources before authorization of handshaking process. Figure 8 illustrates the handshaking process be- tween two nodes and proposed CTS mitigates overhead and collision problem. While specific researchers pro- posed to solve and mitigate impact of jamming attacks on tactical networks and eliminate the collision at the data link layer , the jamming attack is investigated at the MAC layer of sensor networks that where collision occurs on “DATA” frames and results to degradation of overall network performance.
We propose a novel backoff mechanism, in which the history of packet lost is taken into account for Contention Window size optimization. The packet lost involves packet collision and channel error.In this study, we utilize two parameters x and y, that are used to update CW value. We check the channel and if the packet lost rate is increased because of channel error or collision, we increase the CW size for decreasing the packet lost and when the packet lost rate of the channel is decreased we decrease the CW size slowly for increasing the throughput. The CS (Channel State) is three elements array that is updated upon each transmission trial, i.e. each time the station transmits the packet successfully and receives the acknowledgement (ACK for data and CTS for RTS packets) or when the packet becomes collide because of channel error or collision. When we store the new channel state, the oldest channel state in the CS array is removed and the remaining stored states are shifted to the left.
There are a lot of resource constraints for these Sensors, and energy must be conserved in order to function properly when needed. The most energy consuming task or operation in sensor networks is when they coordinate among themselves i.e communication or data transmission. Most the research is focused on the design of low power electronic devices so that the energy consumption the sensors should be minimized. In order to overcome the limitations in the hardware, further efficiency can be achieved through the design of energy efficient communication protocols. To ensure the successful operations of the network one of the most important techniques is Medium Access Control (MAC). MAC protocol tries to avoid collisions from interfering nodes, which is considered as one of the main function of these protocols. Most of the energy is wasted during the idle listening period by the classical IEEE 802.11MAC protocol for wireless local area network. One of the ways to prolong the life time of the network is to design energy efficient
Studies in multiple accesses have been limited to basic networks incorporating several transmitters with one destination. As such, it definitely does not present the self- organizing wireless sensor networks known to have several dynamic pairs of transmitters and receivers. To create extension of MAC operation for multi-destination networks, researchers explored the problem of contention- based access that relate to wireless networks using two fixed receivers and employed conflict algorithms to determine bounds on maximum stable throughout (Nguyen, Katz, Noble, and Satyanarayanan, 1996). The Group time-division multiple access (TDMA) algorithm was employed as a time-division mechanism in a network with two destinations for the purpose of separating groups of nodes containing packets of data destined for different locations. Transmission scheduling idea is not new even though how it is used in this context. Depending on traffic need, each group is allocated time. Analysis of TDMA was undertaken with focus on throughput properties and best time allocation was ascertained as a function of loads offered independent of any underlying multiple access protocols in each group of users. The same analysis can be undertaken in multi-destination networks with arbitrary topology (Ali et al ., 2006). The assumption with a fixed pair of transmitter and receiver is that it contrasts the dynamic and independent design of sensor networks where all nodes are able to transmit and receive packets of data as source-destination pairs for the purpose of relaying the same (Maheshwari, Gupta, and Das, 2006). Assuming that only one transceiver for each node exists; simultaneous packet transmission and reception by any node within a network must be ruled out. This calls for the need to create a mechanism that activates nodes to function as transmitters or receivers (Demirkol, Ersoy, and Alagoz, 2006). The need to create such a mechanism cannot be avoided. This is because the problem of achieving best channel access schedule for multi-hop networks and network partitioning into activation sets is NP-complete and requires practical solutions (Tang and Garcia-Luna- Aceves, 1999). We introduce in this paper these issues based on limited knowledge of network connectivity map to partition nodes into disjoint transmitter-receiver sets. Instead of creating problem-free schedules like in link scheduling, we may consider a room for multiple transmissions for each receiver and rely on one MAC protocol to resolve any problems that may not be avoided.
With the ever-increasing bandwidth demands of services and applications, wireless media becomes more and more congested. In view of the facts that multiple orthogonal bands are already available (e.g., three orthogonal channels in 2.4 GHz and 12 channels in 5 GHz band) , high throughput can be achieved by establishing parallel transmissions over multiple frequency channels , . Since several wireless standards such as IEEE 802.11n  and 802.11ac  have been proposed to enhance the network performance under the multi-channel condition. However, due to the inflexibility of channel utilization, and the requirement of simultaneously sensing on all-channels per node, performance of the multi- channel system is thus restricted. In order to maximize the utilization of multiple available spectrum resources, the design of multi-channel medium access control (McMAC) protocol to coordinate multiple channel access becomes a widely studied research topic , particularly in the next generation wireless networks , where more devices are deployed densely under the limited spectrum resources condition.
deployed. Sensor nodes are constrained in its resources like memory, power, size, processing, and bandwidth. WSN has a varied and large number of applications in almost all fields of human life interactions. These applications have heterogeneous data to be sensed and transmitted with different QoS requirements. As some human life-saving applications require a infalliable and timely end to end delivery, the resource-constrained nature of WSN poses challenges to guarantee the required reliable, definitive and timely delivery of such application . For reliable and timely delivery; resources need to be managed optimally along the path from the node until the data reaches the base station. The energy of each sensor node is constrained since it is battery operated and hence it needs to be optimally utilized so that end to end communication of critical data could be achieved reliably and within time. This can be accomplished by managing the resources efficiently and fairly by reserving the required resources along the path to the destination. Also, the efficiency of resource management and end-to-end QoS can be augmented by designing appropriate resource reservation mechanisms. Resource reservation in WSN is a demanding and challenging task as there is no prior information about event occurrences in future, reservations must be preserved in a confined environment and data may need to be transmitted periodically. Integrated Services is one such approach that aids to satisfy the needs of QoS-demanding applications. Applications convey their QoS requirements to the network efficiently and robustly by means of RSVP. RSVP is the main component of the Integrated Services of Internet which provides best-effort and real-time service. RSVP for traditional networks is a network control protocol specified in RFC 2205. RSVP does not provide any network service; it communicates the end-to- end system requirements to the network permitting the receiver to appeal an end-to-end QoS for its data flows and reserving needed resources at routers along the path in real- time applications. All nodes in the data path must be RSVP compliance for an assured QoS. Resource reservation challenges of WSN are inherited from traditional wireless networks, such as time-varying channels and unreliable links along with characteristics of WSNs, such as severe resource constraints and harsh environmental conditions. These Resource Reservation challenges for WSNs are discussed below:Resource constraints: WSNs are limited in resources such as bandwidth, memory, energy and processing capability.
Advanced Medium Access Control (A-MAC) is a TDMA-based MAC protocol developed for low rate and reliable data transportation with the view of prolonging the network lifetime, adapted from LMAC protocol. Compared to conventional TDMA-based protocols, which depend on central node manager to allocate the time slot for nodes within the cluster, our protocol uses distributed technique where node selects its own time slot by collecting its neighborhood information. The protocol uses the supplied en- ergy efficiently by applying a scheduled power down mode when there is no data transmission activity. The protocol is structured into several frames, where each frame consists of several time slots. As shown in Fig. 3 below, each node transmits a beacon message at the beginning of its time slot, which is used for two purposes; as synchronization signal and neighbor information exchanges. By us- ing this message, the controlled node informs which of its neighboring nodes will be participating in the next data session. The intended nodes need to stay in listening mode in order to be able to receive the intended packet, while other nodes turn to power down mode until the end of current time slot.
Wise MAC  uses an equivalent preamble technique for message transmission however reduces energy consumption by having nodes bear in mind sampling offsets of neighbors. Nodes utilize this data in selecting optimum time for beginning preamble transmission, effectively reducing the length of preamble transmission and thus saving energy. ZMAC  may be a hybrid TDMA/CSMA-basedprotocol. Nodes have their appointed slots that they use once they have knowledge to send. Nodes will even utilize alternative nodes' slots, if free, by victimisation prioritized back-offs. Nodes use back-offs before making an attempt to use any slots even their own. However, back-offs for own slots area unit shorter then for others' that ensures that nodes get their own slots once they would like it. μ-MAC  tries to realize energy potency by high sleep ratios. Application- level information is employed for flow specification. The operation of μ- MAC alternates between rivalry amount and contention-free amount. Throughout rivalry amount, topology discovery and sub-channel formatting is performed. In topology discovery, each node gets to know about their two-hop neighbor that is important for collision- free transmission. A sub-channel may be a collection of connected time slots within the contention-free period. There’s one general-traffic sub-channel carrying interest from base station or routing setup information, and variety of detector-report sub channels carrying reports from sensor nodes. DEE-MAC  is TDMA-based and organizes nodes in clusters. It divides time into session with every session consisting of a rivalry amount and a transmission amount. Nodes send their interest to the
3) Distributed Energy-Aware MAC Protocol: The distributed energy -aware MAC (DE - MAC)  protocol is a TDMAbased MAC protocol for addressing the energy management problem in WSNs. The DE-MAC protocol exploits the inherent features of TDMA to avoid energy waste caused by collision and control overhead, and employs a periodical listening and sleeping mechanism to avoid idle listening and overhearing. Unlike some existing MAC protocols that treat all nodes equally with respect to energy conservation, DE-MAC treats those critical nodes (i.e., with lower energy) differently by using them less frequently to achieve load balancing among all nodes. A group of neighbor nodes periodically perform a local election process based on their energy levels to elect the worst-off node(s) as the winner(s) and let the winner(s) sleep more than its (or their) neighbor nodes. The protocol initially assigns the same number of transmission slots to each node in a TDMA frame. A node can independently decide to initiate an election if its current energy level is below a threshold value. Once an election is initiated, each node sends its energy level to all of its neighbors, which is included to its regularly scheduled transmission packet during its scheduled timeslot. To receive the energy level information from other nodes, all nodes listen to all transmitted packets. There are no sleeping nodes when other nodes are transmitting. This is to enable the integration of leader-election with regular TDMA transmission and thus save bandwidth. At the end of the election process, the node with the minimum energy level is elected as a winner. Once one or more winners are elected, all the losers reduce the number of their timeslots by a constant factor (e.g., two) and the winners have timeslots twice the number of the losers.
Several variations of TDMA are also proposed for low- energy WSN. At the best, they can provide energy-e ﬃ cient, fair, and collision-free channel access. Low-Energy Adaptive Clustering Hierarchy (LEACH)  protocol uses TDMA with clustered network topology. LEACH utilizes a single base station, with which all cluster heads employ only direct communications. Intercluster interferences are managed by CDMA. In large networks, the energy e ﬃ ciency of cluster heads is limited due to the direct communication with a base station. However, cluster members operate quite energy eﬃciently. For increasing network lifetime, LEACH proposes to compress data in cluster heads and to rotate of cluster heads. A drawback is that LEACH does not support dynamically changing network size. In addition, the assumption that all nodes can reach the base station with the maximum transmission power level strictly limits the coverage area and operation environment. These problems are addressed in Power Aware Clustered TDMA (PACT)  protocol. PACT is a variation of LEACH, which performs data relaying between clusters by intercluster gateway nodes, similar to . Disadvantages of PACT are relatively high control tra ﬃ c overhead and idle listening in larger networks. Relatively complex data slot scheduling algorithm performs well in static networks, but lacks support for dynamic network.
Starting with IOS version 12.0, time -based access lists allow an administrator to base security policies on the time of day and day of the week. This is a powerful tool, which allows the administrator to enable policies such as limiting the download of Web-based music or the playing of games over the internal network to after normal business hours. The end result is that the system users can play music and games when network response times are not an issue. This can be important from a political viewpoint, because a lot of users think that the administrators and security administrators prevent them from having fun, even when it does not affect any company goal. Additional benefits can be realized by using time-based access lists in the areas of dial-on-demand routing, policy-based routing, and queuing. These are all beyond the scope of this book, but are still useful in the daily administration of a network.
acquire throughputs as high as 600Mbps. This paper provides a brief background on MIMO systems including the system model, capacity analysis, and channel models. Focus is then given to spatial diversity, specifically to space time block codes (STBC). We discuss Alamouti STBC as well as other orthogonal STBC for 3 and 4 transmit antennas and finally show simulation results and analysis. II. MULTIPLE ACCESS TECHNIQUES: Multiple access schemes are used to allow many simultaneous users to use the same fixed bandwidth radio spectrum. In any radio system, the bandwidth, which is allocated to it, is always limited. For mobile phone systems the total bandwidth is typically 50 MHz, which is split in half to provide the forward and reverse links of the system. Sharing of the spectrum is required in order increase the user capacity of any wireless network. FDMA, TDMA and CDMA are the three major methods of sharing the available bandwidth to multiple users in wireless system. There are many extensions, and hybrid techniques for these methods, such as OFDM, and hybrid TDMA and FDMA systems. However, an understanding of the three major methods is required for understanding of any extensions to these methods.
Our simulation is based on open source simulator on Linux. TDMA model is simulating using open source simulator (NS- 2). NS-2 makes available significant support for simulation of OSI and TCP/IP model protocols. We investigated a performance evaluation to compare the loss rate and packet dropped. Binary Exponential Backoff Algorithm (BEBA) is executing which regulate the CW size dynamically in reply to collision probability. Embedded an algorithm in the IEEE 802.11g DCF. TDMA technique by allocated a unique time slots for every station.
As the number of sensors that are able to transmit in a single timestep decreases (which is associated with the increase in network size), the establishment of transmission priority is necessary. This dissertation discusses a method for prioritizing wireless data that is used in place of a transmission scheduling scheme. This priority based transmission scheme will allocate bandwidth dynamically, as opposed to using a static schedule, to ensure successful transmission of highly important data. If it is not necessary to transmit data to maintain observability (e.g., sensor readings or state estimation has not changed between timesteps), it would not be feasible to transmit data from a particular, or multiple units. Therefore, if units could prioritize their own data based on importance, then bandwidth would be more available, or the control system could be made to run at a faster speed. Large wireless networks, even with prioritized transmissions, run into the risk of data collision without a TDMA communication protocol. When there is a high demand for units to allocate a small transmission window, communication media are considered highly saturated/contented. Contention exists when two or more wireless units may wish to communicate at the same time. In the event that units do communicate at the same instant, carrier sense multiple access with collision detection or avoidance (CSMA-CD or -CA) techniques may be used to predict and prevent multiple contended units’ data from colliding and becoming lost or misreported. In Chapter 5, a modified CSMA-CA approach is explored that strategically prioritizes data transmissions from the most useful sensors in a contended medium. The method defined in Chapter 5 relies heavily on a dynamic measurement fusion approach programmed within each wireless sensor. Both Chapters 4 and 5 of this dissertation are shown to lead to the development of wireless control algorithms that can handle different combinations of sensor data while providing accurate state estimates, which are shown to improve control performance.
The current data network that enables us to communicate with our family and friends is based on the Internet Protocol (IP) technology. This network that is known as the Internet was initially meant for communication between researchers for the development of their research work . As such the Internet is specifically limited in scope to provide the functions necessary to deliver packets from a source to a destination over an interconnected system. There is no service guarantee in the Internet. There are also no mechanisms to augment end-to-end data reliability, flow control, sequencing or other services commonly found in host-to-host protocol .