In this thesis, a mathematical model is derived for performance analysis of legacy IEEE 802.11 DCF MAC using markov chain. The performance of the proposed scheme is compared with that of the existing IEEE 802.11 DCF MAC.
Related Research Works
Therefore, devising a suitable relay station selection strategy in cooperative MAC design for wireless networks is not easy.
Motivation
If these lower speed stations are assisted by one of the relay stations in forwarding its data frame, the throughput gain of the system increases significantly. Moreover, if the lower rate station can increase their data transmission rate through cooperative MAC, they spend less time to send their data.
Objectives
Adversaries Related to Cooperative MAC Design
Therefore, a Cooperative MAC must invoke the trade-off between spatial reuse and reliability of signal transmission. Extra protocol overhead and overhearing of packet transmission can reduce the power effectiveness of wireless nodes.
Organization of Thesis
Chapter three highlights the details of legacy IEEE 802.11 DCF MAC and analysis of its throughput, end-to-end delay, and packet drop probability. Through analysis of various performance metrics of the proposed protocol is presented in this chapter.
Summary
An analytical model based on Markov chain and derivation of equations for throughput, end-to-end delay and packet drop probability are illustrated in this chapter. The fifth chapter shows the comparisons of various performance metrics between IEEE 802.11 DCF MAC and the proposed protocol.
Benefits of Cooperative Networking
- Higher Throughput and Lower Delay
- Higher Spatial Diversity
- Lower Power Consumption
- Lower Interference and Extended Coverage Region
- Network Condition Adaptability
A relay station for special cooperative data transmission can be dynamically selected under any of the above network conditions. I show in this thesis that new signaling methods must be incorporated to accommodate cooperative data transmission in the MAC layer of the data link layer.
Modeling the Wireless Channel
In most of the wireless data transmission takes place in passband of bandwidth around a center frequency. However, most of the processing, such as encoding/decoding, modulation/demodulation, synchronization, etc., is actually done at baseband.
Fading
- Large Scale Fading
- Power Decay with Distance and Shadowing
- Reflection from a Ground Plane
- Small Scale Fading
- Rayleigh Fading and Rician Fading
Small-scale fading is experienced as a result of the constructive and destructive interferences of the multiple signal paths between the transmitter and receiver. Rayleigh fading is a tractable model and is used in network system throughput analysis.
Diversity
- Time Diversity
- Frequency Diversity
- Space Diversity
- Cooperative Diversity
- Relaying Strategies
- Diversity Combining Techniques
- Relay Transmission Topology
This occurs on the spatial scale of the order of the carrier wavelength and is frequency dependent. If the receiver receives signals from multiple users, any of the diversity combining techniques such as equal gain combining, maximum ratio combining (MRC), switch combining and selection combining are used. Cooperative diversity is the technique of multiple antennas which improves the overall capacity of network systems.
If the direct data transfer is not successful, the relay node sends the overheard message from the source node to the destination via different paths. In this scheme, a relay station amplifies the received signal from the source and forwards the amplified version of the signal to the destination without determining the actual content of the signal. In this scheme, the relay first decodes the overheard signal from the source and before retransmitting it, the relay re-encodes the signal.
However, adaptive DF, where the source uses source-relay channel state information (CSI) or feedback from the relay to decide between retransmitting the message and allowing the relay to forward the message, achieves second-order diversity in the high signal. noise ratio (SNR) area. In this technique, the relay station compresses the overheard signal from the source station using any compression technique i.e. Wyner-Ziv encoding and forwards the compressed signal to the destination without decoding the signal. In the case of equal gain combinations, the receiver coherently summed up all versions of the received signals.
![Figure 2.2 shows the difference between DF and Compress and Forward (CF) [19].](https://thumb-ap.123doks.com/thumbv2/filepdfnet/10875269.0/37.918.206.814.289.711/figure-shows-difference-df-compress-forward-cf-19.webp)
Cooperation in Different Layers
Although relay transmission topology in cooperative diversity is dynamic, two main transmission topologies are usually studied. In this topology, signals are propagated through multiple relay paths in the same hop, the destination combines the received signals from multiple paths using combination techniques discussed in section 2.5.4.2. It provides power gain and diversity gain without installing multiple antennas in the relay nodes.
Although CDMA, TDMA, and FDMA use codes, timing, and frequency for cooperative diversity at the MAC layer, the main drawback of these diversity techniques is that cooperation is achieved at the cost of valuable resources, i.e., data rates, time, and bandwidth. generation. . To ensure cooperative diversity using CDMA, TDMA and FDMA, the complications in designing optimal methods are the increasing functions of the number of users in the network. Although sub-optimal solutions are also provided [21], it comes with additional overhead in the receiver structure, which is cost-inefficient in the design of inexpensive wireless devices.
In the latter case, transmitter selects relay nodes during the data transmission or data is transmitted simultaneously by both the transmitters and relay node, i.e. CDMAC [10]. Researchers are also devising methods for adapting cooperative routing techniques in the network layer of the OSI reference model. Control overhead in MAC layer collaboration can be reduced by adopting an efficient and effective relay station as well as the consumed power of the network system.
MAC layer and Existing Protocols
- Issues in Designing a MAC layer protocol
- Bandwidth Efficiency
- Quality of Service (QoS)
- Synchronization
- Error Prone Shared Broadcast Channel
- Mobility of Nodes
- Multiple Access Techniques in MAC layer
- Classifications of Multiple Access Protocols
- Time Division Multiple Access (TDMA)
- Frequency Division Multiple Access (FDMA)
- Code Division Multiple Access (CDMA)
- Space Division Multiple Access (SDMA)
- Classifications of CSMA/CA based MAC protocols
- Contention Based Protocols
- Contention Based Protocols with Reservation Mechanisms
- Contention Based Protocol with Scheduling Mechanisms
Access to the shared media should be controlled in such a way that wireless nodes receive a fair share of the available bandwidth. Bandwidth efficiency can be defined as the ratio of the bandwidth used for actual data transmission to the total available bandwidth. A MAC protocol design must take this mobility factor into account so that the performance of the wireless network system is not significantly affected by node mobility.
Several multiple access techniques have been developed to control the access of wireless nodes to the medium. Many formal protocols have been designed to control multiple access of the shared medium in a multipoint environment. In Time Division Multiple Access, all wireless stations share the time channel bandwidth.
Each station must know the start of a slot and the location of the slot. A satellite can reuse the same frequency to cover many different regions of the earth's surface. The bandwidth for a particular data transfer session must be known by the neighbors of the communicating pair.
Summary
- IEEE 802.11 RTS-CTS Access Mechanism
- Hidden Station Problem
- Exposed Station Problem
- Analysis of IEEE 802.11 DCF MAC using Markov Model
- Description of the Model
- Saturated Throughput Analysis
- Average Frame Delay Analysis
- Packet Drop Probability
- Summary
In order to mitigate collisions within the collision domain, each wireless station using IEEE 802.11 DCF follows a random binary exponential off (BEB) algorithm. To solve the previous problem, IEEE 802.11 DCF used RTS and CTS control frames. Therefore, the collision time is minimized for a long data frame, which was imminent in the IEEE 802.11 DCF basic access mechanism.
IEEE 802.11 DCF MAC makes perfect use of the conflict window size which is doubled every time a collision occurs during a frame transmission. According to IEEE 802.11 DCF, the size of the contention window is doubled each time a collision occurs until a maximum size is reached. Stations do not reach full transmission capacity due to the overhead used in the RTS-CTS access mechanism of IEEE 802.11 DCF MAC.
The above analysis shows that if the number of wireless stations is limited to less than 10, the probability of the packet being dropped due to collision is negligible in IEEE 802.11 DCF MAC. Throughput, end-to-end frame delay, packet drop probability and collision probability of IEEE 802.11 DCF MAC protocol are analyzed mathematically. Variations of different performance metrics of IEEE 802.11 DCF MAC versus the number of wireless stations and different frame sizes are shown graphically.
- Cooperation Initiation
- Relay Station Selection and CoopTable Maintenance
- Data Transmission using a Relay
- Analytical Modeling and Performance Evaluation
- Throughput Analysis without Mobility
- Throughput Analysis for Error Prone Environment
- Throughput Analysis with Mobility
- Throughput Analysis over Rayleigh Fading Channel
- Average Frame Delay Analysis
- Summary
In IEEE 802.11 DCF MAC, if a data frame is received by a station, it first examines the destination address (DA) field of the received frame. If the frame is not intended for the station, the station discards the frame by setting its own NAV (Network Allocation Vector) to the value of the duration field tagged inside the received packet header. It also shows the supported maximum data rate for the two hop links relative to the geographic position of an auxiliary station.
This section presents a mathematical analysis of the proposed cooperative MAC to evaluate its performance. Let denote the probability that the auxiliary station is located within the common geographic region between the transmitter and the receiver, where the transmission range of the sender and receivers are at the data rate to the auxiliary station. In the case of cooperation, let it be the time required to transmit the frame from the source station to the destination station using the relay station.
Two modes are determined by the receiver by evaluating a certain threshold value of the received signal power level. If part of the frame falls into the fading state, the frame is received in error. The throughput of the proposed protocol is derived in error prone channel and flat fading Rayleigh channel.
Recommendation for Future Works
To effectively and efficiently exploit the benefits of cooperative data transmission of the physical layers at the upper layer of the OSI reference model, protocols applicable to those layers must be designed. Therefore, it requires cross-layer protocols at each upper layer of the OSI reference model. Interference from external sources or other transmission channels can affect accurate average power measurements.
Therefore, a security mechanism must be developed such that intermediate relay nodes cannot interfere with the privacy and integrity metrics of the transmitted frames. In the future, comprehensive comparisons of both the simulation and analytical models of the proposed cooperative MAC protocol will be explored. 10] Moh, S., Yu, C., "A cooperative diversity-based robust mac protocol in wireless ad hoc networks", IEEE Transactions on parallel and distribution systems, vol.
11] Zhou, T., Sharif, H., Hempel, M., Mahasukhon, P., Wang, W., and Ma, T., "A novel adaptive distributed cooperative relaying mac protocol for vehicular networks", IEEE Journal on selected areas in communications, vol. Simplified processing for high spectral efficiency wireless communications using multi-element arrays”, IEEE Journal on Selected Areas in Communications, vol. 18] Alamouti, S., “A simple transmit diversity scheme for wireless communications”, IEEE Journal on Selected Areas in Communications, vol.
